LITHIUM MANGANESE COMPOSITE OXIDE, SECONDARY BATTERY, ELECTRONIC DEVICE, AND METHOD FOR FORMING LAYER
To increase the volume density or weight density of lithium ions that can be received and released in and from a positive electrode active material to achieve high capacity and high energy density of a secondary battery. A lithium manganese composite oxide represented by LixMnyMzOw that includes a region belonging to a space group C2/c and is covered with a carbon-containing layer is used as the positive electrode active material. The element M is an element other than lithium and manganese. The lithium manganese composite oxide has high structural stability and high capacity.
The present invention relates to an object, a method, or a manufacturing method. The present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a storage device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a structure of a secondary battery and a method for manufacturing the secondary battery. In particular, one embodiment of the present invention relates to a positive electrode active material of a lithium-ion secondary battery.
BACKGROUND ARTExamples of the secondary battery include a nickel-metal hydride battery, a lead-acid battery, and a lithium-ion secondary battery.
Such secondary batteries are used as power sources in portable information terminals typified by mobile phones. In particular, lithium-ion secondary batteries have been actively developed because the capacity thereof can be increased and the size thereof can be reduced.
As examples of positive electrode active materials of a lithium-ion secondary battery, phosphate compounds each having an olivine structure and containing lithium (Li) and iron (Fe), manganese (Mn), cobalt (Co), or nickel (Ni), such as lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), and lithium nickel phosphate (LiNiPO4), which are disclosed in Patent Document 1, are known.
In addition, as described in Non-Patent Document 1, a method for evaluating the valence of metal in a metal oxide, and the like by electron energy loss spectroscopy (EELS) is known.
REFERENCE
- [Patent Document 1] Japanese Published Patent Application No. H11-25983
- [Non-Patent Document 1] Z. L. Wang et. al, “EELS analysis of cation valence states and oxygen vacancies in magnetic oxides”, Micron, 2000, vol. 31, pp. 571-580
- [Non-Patent Document 2] H. Tan et. al, “Oxidation state and chemical shift investigation in transition metal oxides by EELS”, Ultramicroscopy, 2012, vol. 116, pp. 24-33
An object is to increase the volume density or weight density of lithium ions that can be received and released in and from a positive electrode active material to achieve high capacity and high energy density of a secondary battery.
Another object is to provide a positive electrode active material that can be manufactured at low cost.
Furthermore, high ionic conductivity and high electrical conductivity are required as the properties of a positive electrode active material of a lithium-ion secondary battery. Thus, another object is to provide a positive electrode active material having high ionic conductivity and high electrical conductivity.
Another object is to provide an electrode having high electrical conductivity. Another object is to provide an electrode having low resistance.
Another object is to provide a method for manufacturing an electrode having high electrical conductivity. Another object is to provide a method for manufacturing a positive electrode active material having high electrical conductivity of a lithium-ion secondary battery.
Another object is to provide a novel material. Another object is to provide a novel positive electrode active material. Another object is to provide a novel battery. Another object is to provide a novel lithium-ion secondary battery. Note that the descriptions of these objects do not disturb the existence of other objects.
In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.
One embodiment of the present invention is a lithium manganese composite oxide represented by LixMnyMzOw that includes a region belonging to a space group C2/c and is coated with a carbon-containing layer. Here, the element M is an element other than lithium and manganese. In the above structure, a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26≦(y+z)/w<0.5 are satisfied is preferably included. Furthermore, in the above structure, the carbon-containing layer preferably includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm. Moreover, the element M is preferably nickel.
Another embodiment of the present invention is a lithium manganese composite oxide represented by LixMnyMzOw that includes a region coated with a carbon-containing layer and in which the ratio of the integral intensity of L3 peak to the integral intensity of L2 peak of manganese that is obtained by EELS (L3/L2) is greater than or equal to 1.4 and less than or equal to 2.3. Here, the element M is an element other than lithium and manganese. In the above structure, a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26≦(y+z)/w<0.5 are satisfied is preferably included. Furthermore, in the above structure, the carbon-containing layer preferably includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm. Moreover, the element M is preferably nickel.
Another embodiment of the present invention is a lithium manganese composite oxide represented by LixMnyMzOw that includes a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26 (y+z)/w<0.5 are satisfied and a region coated with a carbon-containing layer with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm. Here, the element M is an element other than lithium and manganese. The element M is preferably nickel.
Another embodiment of the present invention is a method for forming a carbon-containing layer on the surface of a lithium manganese composite oxide represented by LixMnyMzOw by forming a layer containing graphene oxide on the surface of the lithium manganese composite oxide and then reducing the graphene oxide. Here, the element M is an element other than lithium and manganese.
A positive electrode active material that can be manufactured at low cost can be provided.
The volume density or weight density of lithium ions that can be received and released in and from a positive electrode active material can be increased to achieve high capacity and high energy density of a secondary battery.
A secondary battery having excellent cycle characteristics can be fabricated.
A positive electrode active material having high ionic conductivity and high electrical conductivity can be provided.
High capacity and high energy density of a positive electrode of a lithium-ion secondary battery can be achieved.
High capacity and high energy density of a lithium-ion secondary battery can be achieved.
A novel material can be provided. A novel positive electrode active material can be provided. A novel battery can be provided. A novel lithium-ion secondary battery can be provided.
Note that the description of these effects does not disturb the existence of other effects. One embodiment of the present invention does not have to achieve all the objects listed above. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.
In the accompanying drawings:
FIGS. 11A1 to 11B2 illustrate examples of power storage devices;
Embodiments and examples of the present invention will be described below in detail with reference to the drawings. However, the present invention is not limited to the description below, and it is easily understood by those skilled in the art that modes and details disclosed herein can be modified in various ways. Furthermore, the present invention is not construed as being limited to the description of the embodiments and examples.
Embodiment 1 Synthesizing Lithium Manganese Composite OxideA method for manufacturing a lithium manganese composite oxide represented by LixMnyMzOw will be described in detail below. Here, the element M is preferably silicon, phosphorus, or a metal element other than lithium and manganese. Furthermore, it is preferable that 0≦x/(y+z)<2, y>0, z>0, and 0.26≦(y+z)/w<0.5 be satisfied. Here, the lithium manganese composite oxide is an oxide containing at least lithium and manganese. The lithium manganese composite oxide may contain another metal, or an element such as silicon or phosphorus.
Although an example where Ni is used as the element M is described in this embodiment, a similar effect can be obtained even when silicon, phosphorus, or a metal element other than lithium and manganese is used.
First, starting materials Li2CO3, MnCO3, and NiO are weighed.
In this embodiment, the ratio of the materials is adjusted to form a lithium manganese composite oxide having a layered rock-salt structure and a spinel structure in each particle.
When the ratio of Li2CO3 to MnCO3 and NiO is 1:0.7:0.3, Li2Mn0.7Ni0.3O3 is formed. Thus, it is important to change this ratio.
In this embodiment, Li2CO3, MnCO3, and NiO are weighed such that the ratio of Li2CO3 to MnCO3 and NiO is 0.84:0.8062:0.318. Note that the ratio is represented as a molar ratio. Acetone is added to the powder of these materials, and then, they are mixed in a ball mill to prepare mixed powder.
After that, heating is performed to volatilize acetone, so that a mixed material is obtained.
Then, the mixed material is put into a melting pot, and is fired at a temperature in the range from 800° C. to 1100° C. in the air for 5 to 20 hours inclusive to synthesize a novel material.
Subsequently, grinding is performed to separate the sintered particles. For the grinding, acetone is added and then mixing is performed in a ball mill.
After the grinding, heating is performed to volatilize acetone, and then, vacuum drying is performed, so that a powdery lithium manganese composite oxide is obtained.
In this embodiment, Li2CO3, MnCO3, and NiO are used as starting materials; however, materials are not particularly limited thereto and any other material may be used as long as a lithium manganese composite oxide having a spinel structure on part of the surface of each particle with a layered rock-salt structure can be formed.
- [Coating with Carbon-Containing Layer]
The obtained lithium manganese composite oxide is coated with a carbon-containing layer. Here, graphene oxide is used as an example of a coating material.
Note that graphene in this specification refers to single-layer graphene or multilayer graphene including two or more and a hundred or less layers. Single-layer graphene refers to a one-atom-thick sheet of carbon molecules. Graphene oxide refers to a compound formed by oxidation of such graphene. When graphene oxide is reduced to form a carbon material, oxygen contained in the graphene oxide is not entirely released and partly remains in the carbon material. In the case where the carbon material formed by reducing the graphene oxide contains oxygen, the proportion of the oxygen measured by XPS is higher than or equal to 2% and lower than or equal to 20%, preferably higher than or equal to 3% and lower than or equal to 15% of the total of the proportions of elements detected by XPS.
Graphene oxide can be formed by various synthesis methods such as a Hummers method, a modified Hummers method, and oxidation of graphite.
For example, in a Hummers method, graphite such as flake graphite is oxidized to give graphite oxide. The obtained graphite oxide is graphite that is oxidized in places and thus to which a functional group such as a carbonyl group, a carboxyl group, or a hydroxyl group is bonded. In the graphite oxide, the crystallinity of the graphite is lost and the distance between layers is increased. Therefore, graphene oxide can be easily obtained by separation of the layers from each other by ultrasonic treatment or the like.
The length of one side (also referred to as a flake size) of the graphene oxide is greater than or equal to 50 nm and less than or equal to 100 μm, preferably greater than or equal to 800 nm and less than or equal to 20 μm.
Next, a method for covering the lithium manganese composite oxide with graphene oxide will be described. Graphene oxide and water are put in a mixer to form an aqueous dispersion of graphene oxide. Then, the lithium manganese composite oxide is put in the aqueous dispersion and the mixture is kneaded. Here, kneading refers to mixing in a highly viscous state. The kneading can separate aggregation of lithium manganese composite oxide powder, uniformly dispersing the lithium manganese composite oxide and the graphene oxide.
The obtained mixture is dried under reduced pressure in a bell jar and then ground in a mortar, so that the lithium manganese composite oxide covered with graphene oxide is obtained.
[Reducing Graphene Oxide]Then, the graphene oxide covering the surface of the lithium manganese composite oxide is reduced. The reducing the graphene oxide may be performed by heat treatment or by causing a reaction in a solvent containing a reducing agent. Here, the reduction is performed by causing a reaction in a solvent containing a reducing agent.
Examples of the reducing agent include ascorbic acid, hydrazine, dimethyl hydrazine, hydroquinone, sodium boron hydride (NaBH4), tetra butyl ammonium bromide (TBAB), LiAlH4, ethylene glycol, polyethylene glycol, N,N-diethylhydroxylamine, and a derivative thereof.
A polar solvent can be used as the solvent. Any material can be used for the polar solvent as long as it can dissolve the reducing agent. Examples of the material of the polar solvent include water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and a mixed solution of any two or more of the above.
Then, the solution is filtered by suction filtration or the like.
After that, washing and drying are performed. The drying is preferably performed in a reduced pressure (vacuum) atmosphere or a reduction atmosphere. This drying step is preferably performed at, for example, 50° C. to 200° C. inclusive in vacuum for 1 hour to 48 hours inclusive. The drying allows evaporation, volatilization, or removal of the polar solvent and moisture.
Note that heating can facilitate the reduction reaction. After drying following the chemical reduction, heating may further be performed.
Through the above steps, the graphene oxide is reduced, so that the carbon-containing layer can be formed on the surface of the lithium manganese composite oxide. Note that it is possible that oxygen in the graphene oxide is not necessarily entirely released and partly remains in the carbon-containing layer. When the carbon-containing layer contains oxygen, the proportion of the oxygen measured by XPS is higher than or equal to 2% and lower than or equal to 20%, preferably higher than or equal to 3% and lower than or equal to 15% of the total of the proportions of elements detected by XPS.
The thickness of the carbon-containing layer formed on the surface of the lithium manganese composite oxide is preferably greater than or equal to 1 nm and less than or equal to 10 nm.
Embodiment 2In this embodiment, the structure of a storage battery including a positive electrode active material manufactured by the manufacturing method described in Embodiment 1 will be described with reference to
In a coin-type storage battery 300, a positive electrode can 301 doubling as a positive electrode terminal and a negative electrode can 302 doubling as a negative electrode terminal are insulated from each other and sealed by a gasket 303 made of polypropylene or the like. A positive electrode 304 includes a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector 305. The positive electrode active material layer 306 may further include a binder for increasing adhesion of positive electrode active materials, a conductive additive for increasing the conductivity of the positive electrode active material layer, and the like in addition to the active materials. As the conductive additive, a material that has a large specific surface area is preferably used; for example, acetylene black (AB) can be used. Alternatively, a carbon material such as a carbon nanotube, graphene, or fullerene can be used.
A negative electrode 307 includes a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector 308. The negative electrode active material layer 309 may further include a binder for increasing adhesion of negative electrode active materials, a conductive additive for increasing the conductivity of the negative electrode active material layer, and the like in addition to the negative electrode active materials. A separator 310 and an electrolyte (not illustrated) are provided between the positive electrode active material layer 306 and the negative electrode active material layer 309.
A material with which lithium can be dissolved and precipitated or a material into and from which lithium ions can be inserted and extracted can be used for the negative electrode active materials used for the negative electrode active material layer 309; for example, a lithium metal, a carbon-based material, and an alloy-based material can be used. The lithium metal is preferable because of its low redox potential (3.045 V lower than that of a standard hydrogen electrode) and high specific capacity per unit weight and per unit volume (3860 mAh/g and 2062 mAh/cm3).
Examples of the carbon-based material include graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), a carbon nanotube, graphene, carbon black, and the like.
Examples of the graphite include artificial graphite such as meso-carbon microbeads (MCMB), coke-based artificial graphite, or pitch-based artificial graphite and natural graphite such as spherical natural graphite.
Graphite has a low potential substantially equal to that of a lithium metal (e.g., lower than or equal to 0.3 V vs. Li/Li+) when lithium ions are intercalated into the graphite (while a lithium-graphite intercalation compound is formed). For this reason, a lithium-ion secondary battery can have a high operating voltage. In addition, graphite is preferable because of its advantages such as relatively high capacity per unit volume, small volume expansion, low cost, and safety greater than that of a lithium metal.
For the negative electrode active materials, an alloy-based material which enables charge-discharge reactions by an alloying reaction and a dealloying reaction with lithium metal can be used. In the case where carrier ions are lithium ions, a material containing at least one of Ga, Al, Si, Ge, Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, and the like can be used for example. Such elements have higher capacity than carbon. In particular, silicon has a significantly high theoretical capacity of 4200 mAh/g. For this reason, silicon is preferably used for the negative electrode active materials. Examples of the alloy-based material using such elements include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, and the like. Here, SiO refers to a film in which the silicon content is higher than that in SiO2.
Alternatively, for the negative electrode active materials, an oxide such as titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O12), lithium-graphite intercalation compound (LixC6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.
Still alternatively, for the negative electrode active materials, Li3-xMxN (M=Co, Ni, or Cu) with a Li3N structure, which is a nitride containing lithium and a transition metal, can be used. For example, Li2.6Co0.4N3 is preferable because of high charge and discharge capacity (900 mAh/g and 1890 mAh/cm3).
A nitride containing lithium and a transition metal is preferably used, in which case lithium ions are contained in the negative electrode active materials and thus the negative electrode active materials can be used in combination with a material for a positive electrode active material which does not contain lithium ions, such as V2O5 or Cr3O8. In the case of using a material containing lithium ions as a positive electrode active material, the nitride containing lithium and a transition metal can be used for the negative electrode active material by extracting the lithium ions contained in the positive electrode active material in advance.
Alternatively, a material which causes a conversion reaction can be used for the negative electrode active materials; for example, a transition metal oxide which does not cause an alloy reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used. Other examples of the material which causes a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, sulfides such as CoS0.89, NiS, and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.
The current collectors 305 and 308 can each be formed using a highly conductive material which is not alloyed with a carrier ion of lithium among other elements, such as a metal typified by stainless steel, gold, platinum, zinc, iron, nickel, copper, aluminum, titanium, and tantalum or an alloy thereof. Alternatively, an aluminum alloy to which an element which improves heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, is added can be used. Still alternatively, a metal element which forms silicide by reacting with silicon can be used. Examples of the metal element which forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like. The current collectors can each have a foil-like shape, a plate-like shape (sheet-like shape), a net-like shape, a cylindrical shape, a coil shape, a punching-metal shape, an expanded-metal shape, or the like as appropriate. The current collectors each preferably have a thickness of 5 μm to 30 μm inclusive.
The positive electrode active materials described in Embodiment 1 can be used for the positive electrode active material layer 306.
As the separator 310, an insulator such as cellulose (paper), polyethylene, and polypropylene with pores can be used.
As an electrolyte of an electrolytic solution, a material which contains carrier ions is used. Typical examples of the electrolyte are lithium salts such as LiPF6, LiClO4, LiAsF6, LiBF4, LiCF3SO3, Li(CF3SO2)2N, and Li(C2F5SO2)2N. One of these electrolytes may be used alone, or two or more of them may be used in an appropriate combination and in an appropriate ratio.
Note that when carrier ions are alkali metal ions other than lithium ions, alkaline-earth metal ions, beryllium ions, or magnesium ions, instead of lithium in the above lithium salts, an alkali metal (e.g., sodium and potassium), an alkaline-earth metal (e.g., calcium, strontium, barium, beryllium, and magnesium) may be used for the supporting electrolyte.
As a solvent of the electrolytic solution, a material with the carrier ion mobility is used. As the solvent of the electrolytic solution, an aprotic organic solvent is preferably used. Typical examples of aprotic organic solvents include ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, and the like, and one or more of these materials can be used. When a gelled high-molecular material is used as the solvent of the electrolytic solution, safety against liquid leakage and the like is improved. Furthermore, the storage battery can be thinner and more lightweight. Typical examples of gelled high-molecular materials include a silicone gel, an acrylic gel, an acrylonitrile gel, polyethylene oxide, polypropylene oxide, a fluorine-based polymer, and the like. Alternatively, the use of one or more kinds of ionic liquids (room temperature molten salts) which have features of non-flammability and non-volatility as a solvent of the electrolytic solution can prevent the storage battery from exploding or catching fire even when the storage battery internally shorts out or the internal temperature increases owing to overcharging and others.
Instead of the electrolytic solution, a solid electrolyte including an inorganic material such as a sulfide-based inorganic material or an oxide-based inorganic material, or a solid electrolyte including a macromolecular material such as a polyethylene oxide (PEO)-based macromolecular material may alternatively be used. When the solid electrolyte is used, a separator and a spacer are not necessary. Furthermore, the battery can be entirely solidified; therefore, there is no possibility of liquid leakage and thus the safety of the battery is dramatically increased.
For the positive electrode can 301 and the negative electrode can 302, a metal having a corrosion-resistant property to an electrolytic solution, such as nickel, aluminum, or titanium, an alloy of such a metal, or an alloy of such a metal and another metal (e.g., stainless steel or the like) can be used. Alternatively, the positive electrode can 301 and the negative electrode can 302 are preferably coated with nickel, aluminum, or the like in order to prevent corrosion due to the electrolytic solution. The positive electrode can 301 and the negative electrode can 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.
The negative electrode 307, the positive electrode 304, and the separator 310 are immersed in the electrolytic solution. Then, as illustrated in
Here, a current flow in charging a battery will be described with reference to
Two terminals in
Next, an example of a cylindrical storage battery will be described with reference to
Although the positive electrode 604 and the negative electrode 606 can be formed in a manner similar to that of the positive electrode and the negative electrode of the coin-type storage battery described above, the difference lies in that, since the positive electrode and the negative electrode of the cylindrical storage battery are wound, active materials are formed on both sides of the current collectors. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be formed using a metal material such as aluminum. The positive electrode terminal 603 and the negative electrode terminal 607 are resistance-welded to a safety valve mechanism 612 and the bottom of the battery can 602, respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 through a positive temperature coefficient (PTC) element 611. The safety valve mechanism 612 cuts off electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611, which serves as a thermally sensitive resistor whose resistance increases as temperature rises, limits the amount of current by increasing the resistance, in order to prevent abnormal heat generation. Note that barium titanate (BaTiO3)-based semiconductor ceramic can be used for the PTC element.
[Laminated Storage Battery]Next, an example of a laminated storage battery will be described with reference to
A laminated storage battery 500 illustrated in
In the laminated storage battery 500 illustrated in
As the exterior body 509 in the laminated storage battery 500, for example, a laminate film having a three-layer structure in which a highly flexible metal thin film of aluminum, stainless steel, copper, nickel, or the like is provided over a film formed of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film of a polyamide-based resin, a polyester-based resin, or the like is provided as the outer surface of the exterior body over the metal thin film can be used.
The example in
Here, an example of a method for fabricating the laminated storage battery whose external view is illustrated in
First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked.
After that, the negative electrode 506, the separator 507, and the positive electrode 503 are placed over the exterior body 509.
Subsequently, the exterior body 509 is folded along a dashed line as illustrated in
Next, the electrolytic solution 508 is introduced into the exterior body 509 from the inlet of the exterior body 509. The electrolytic solution 508 is preferably introduced in a reduced pressure atmosphere or in an inert gas atmosphere. Lastly, the inlet is bonded. In the above manner, the laminated storage battery 500 can be fabricated.
Note that in this embodiment, the coin-type storage battery, the laminated storage battery, and the cylindrical storage battery are given as examples of the storage battery; however, any of storage batteries with a variety of shapes, such as a sealed storage battery and a square-type storage battery, can be used. Furthermore, a structure in which a plurality of positive electrodes, a plurality of negative electrodes, and a plurality of separators are stacked or wound may be employed.
For each of the positive electrodes of the storage batteries 300, 500, and 600, which are described in this embodiment, the positive electrode active material layer of one embodiment of the present invention can be used. Thus, the discharge capacity of the storage batteries 300, 500, and 600 can be increased.
In addition, a flexible power storage device can be incorporated along a curved inside/outside wall surface of a house or a building or a curved interior/exterior surface of a car.
Structural examples of power storage devices (storage batteries) will be described with reference to
The circuit board 900 includes terminals 911 and a circuit 912. The terminals 911 are connected to the terminals 951 and 952, the antennas 914 and 915, and the circuit 912. Note that a plurality of terminals 911 serving as a control signal input terminal, a power supply terminal, and the like may be provided.
The circuit 912 may be provided on the rear surface of the circuit board 900. The shape of each of the antennas 914 and 915 is not limited to a coil shape and may be a linear shape or a plate shape. Further, a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic-field antenna, or a dielectric antenna may be used. Alternatively, the antenna 914 or the antenna 915 may be a flat-plate conductor. The flat-plate conductor can serve as one of conductors for electric field coupling. That is, the antenna 914 or the antenna 915 can serve as one of two conductors of a capacitor. Thus, electric power can be transmitted and received not only by an electromagnetic field or a magnetic field but also by an electric field.
The line width of the antenna 914 is preferably larger than that of the antenna 915. This makes it possible to increase the amount of electric power received by the antenna 914.
The power storage device includes a layer 916 between the storage battery 913 and the antennas 914 and 915. The layer 916 may have a function of preventing an adverse effect on an electromagnetic field by the storage battery 913. As the layer 916, for example, a magnetic body can be used.
Note that the structure of the power storage device is not limited to that shown in
For example, as shown in FIGS. 11A1 and 11A2, two opposite surfaces of the storage battery 913 in
As illustrated in FIG. 11A1, the antenna 914 is provided on one of the opposite surfaces of the storage battery 913 with the layer 916 interposed therebetween, and as illustrated in FIG. 11A2, the antenna 915 is provided on the other of the opposite surfaces of the storage battery 913 with a layer 917 interposed therebetween. The layer 917 may have a function of preventing an adverse effect on an electromagnetic field by the storage battery 913. As the layer 917, for example, a magnetic body can be used.
With the above structure, both of the antennas 914 and 915 can be increased in size.
Alternatively, as illustrated in FIGS. 11B1 and 11B2, two opposite surfaces of the storage battery 913 in
As illustrated in FIG. 11B1, the antenna 914 is provided on one of the opposite surfaces of the storage battery 913 with the layer 916 interposed therebetween, and as illustrated in FIG. 11B2, an antenna 918 is provided on the other of the opposite surfaces of the storage battery 913 with the layer 917 interposed therebetween. The antenna 918 has a function of communicating data with an external device, for example. An antenna with a shape that can be applied to the antennas 914 and 915, for example, can be used as the antenna 918. As a system for communication using the antenna 918 between the power storage device and another device, a response method that can be used between the power storage device and another device, such as NFC, can be employed.
Alternatively, as illustrated in
The display device 920 can display, for example, an image showing whether charge is being carried out, an image showing the amount of stored power, or the like. As the display device 920, electronic paper, a liquid crystal display device, an electroluminescent (EL) display device, or the like can be used. For example, the use of electronic paper can reduce power consumption of the display device 920.
Alternatively, as illustrated in
The sensor 921 has a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, electric current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays. With the sensor 921, for example, data on an environment (e.g., temperature) where the power storage device is placed can be determined and stored in a memory inside the circuit 912.
Furthermore, structural examples of the storage battery 913 will be described with reference to
The storage battery 913 illustrated in
Note that as illustrated in
For the housing 930a, an insulating material such as an organic resin can be used. In particular, when a material such as an organic resin is used for the side on which an antenna is formed, blocking of an electric field by the storage battery 913 can be prevented. When an electric field is not significantly blocked by the housing 930a, an antenna such as the antennas 914 and 915 may be provided inside the housing 930a. For the housing 930b, a metal material can be used, for example.
The negative electrode 931 is connected to the terminal 911 in
Next, examples where a storage battery is used in a vehicle will be described. The use of storage batteries in vehicles enables production of next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).
The power storage device can also supply electric power to an instrument panel included in the automobile 8100, such as a speedometer or a tachometer. Furthermore, the power storage device can supply electric power to a semiconductor device included in the automobile 8100, such as a navigation system.
Furthermore, although not illustrated, the vehicle may include a power receiving device so that it can be charged by being supplied with electric power from an above-ground power transmitting device in a contactless manner. In the case of the contactless power feeding system, by fitting a power transmitting device in a road or an exterior wall, charging can be performed not only when the electric vehicle is stopped but also when driven. In addition, the contactless power feeding system may be utilized to perform transmission and reception of electric power between vehicles. Furthermore, a solar cell may be provided in the exterior of the automobile to charge the power storage device when the automobile stops or moves. To supply electric power in such a contactless manner, an electromagnetic induction method or a magnetic resonance method can be used.
According to one embodiment of the present invention, the power storage device can have improved cycle characteristics and reliability. Furthermore, according to one embodiment of the present invention, the power storage device itself can be made more compact and lightweight as a result of improved characteristics of the power storage device. The compact and lightweight power storage device contributes to a reduction in the weight of a vehicle, and thus increases the driving distance. Furthermore, the power storage device included in the vehicle can be used as a power source for supplying electric power to products other than the vehicle. In such a case, the use of a commercial power source can be avoided at peak time of electric power demand.
This embodiment can be implemented in combination with any of the other embodiments as appropriate.
Example 1In this example, a lithium manganese composite oxide coated with a carbon-containing layer was formed by the method described in Embodiment 1, and discharge capacity was measured.
(Synthesizing Lithium Manganese Composite Oxide)Starting materials Li2CO3, MnCO3, and NiO were weighed such that the molar ratio of Li2CO3 to MnCO3 and NiO was 0.84:0.8062:0.318. Next, acetone was added to the powder of these materials, and then, they were mixed in a ball mill to prepare mixed powder.
After that, heating was performed to volatilize acetone, so that a mixed material was obtained.
Then, the mixed material was put in a melting pot, and was fired at 1000° C. in the air for 10 hours to synthesize a novel material. The flow rate of the air gas was 10 L/min.
Subsequently, grinding was performed to separate the sintered particles. For the grinding, acetone was added and then mixing was performed in a ball mill.
After the grinding, heating was performed to volatilize the acetone, so that a lithium manganese composite oxide containing nickel was formed. The sample obtained here is referred to as Sample X.
(Coating with Carbon-Containing Layer)
Then, a process for covering the obtained lithium manganese composite oxide with a carbon-containing layer will be described. Here, the process for coating the lithium manganese composite oxide with a carbon-containing layer that is described in this example includes Step 1 of covering with graphene oxide and Step 2 of reducing the graphene oxide.
(Step 1: Covering with Graphene Oxide)
First, covering with graphene oxide (Step 1) will be described. Graphene oxide (0.0303 g) and water (1.05 g) were mixed in a mixer to form an aqueous dispersion of graphene oxide. In first mixing, one third of the total amount of water was used, another one third of the total amount of water was added in second mixing, and the other one third of the total amount of water was added in third mixing. Five-minute mixing was performed at 2000 rpm three times.
Then, the lithium manganese composite oxide obtained by the synthesis (Sample X, 3 g) was put in the formed aqueous dispersion, and the mixture was kneaded in a mixer at 2000 rpm six times. Time for one mixing was 5 minutes.
The obtained mixture was dried under reduced pressure in a bell jar at 50° C. and then ground in an alumina mortar, so that the lithium manganese composite oxide covered with graphene oxide was obtained.
(Step 2: Reducing Graphene Oxide)Next, reducing the graphene oxide (Step 2) will be described. The graphene oxide covering the surface of the lithium manganese composite oxide was reduced. Ascorbic acid was used as a reducing agent, and 80 vol % ethanol solution was used as a solvent. Ascorbic acid (13.5 g) and lithium hydroxide (3.12 g) were put in 1 L of 80 vol % ethanol solution to form a reducing solution. The obtained lithium manganese composite oxide powder was put in the solution and reduction was performed at 60° C. for 3 hours.
Then, the obtained solution was filtrated by suction filtration. For the filtration, filter paper with a particle retention capability of 1 μm was used. Then, washing and drying were performed. The drying was performed at 50° C. under reduced pressure. After the drying, the obtained powder was ground in a mortar. After that, drying was performed at 170° C. under reduced pressure for 10 hours.
The powder obtained through Steps 1 and 2 is referred to as Sample A.
Comparative Example Process Using GlucoseNext, in a comparative example, the lithium manganese composite oxide obtained by synthesis (Sample X) was coated with carbon with the use of glucose.
Glucose was weighed so that glucose with respect to the obtained lithium manganese composite oxide (Sample X) was 11 weight %. Next, acetone was added to the powder of these materials, and then, they were mixed in a ball mill. After that, heating was performed to volatilize acetone, so that a mixed material was obtained.
Then, the mixed material was put in a melting pot and fired at 600° C. in a nitrogen atmosphere for 10 hours. The flow rate of nitrogen was 5 L/min. The obtained powder is referred to as Comparative Sample B.
(Evaluation by X-Ray Diffraction)To evaluate the coating state of the carbon-containing layer, the resistivities of the particles Sample A and Sample X (before coated) were measured using a powder resistivity measurement system (MCP-PD51 by Mitsubishi Chemical Analytech Co., Ltd.).
An electrode was fabricated using Sample A as a positive electrode active material. Sample A was mixed with acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVDF) as a resin, and N-methyl-2-pyrrolidone (NMP) as a polar solvent to form slurry. The weight ratio of Sample A to the PVDF and the AB was 90:5:5. Then, the slurry was applied to a current collector and dried. Note that a surface of the current collector was treated with an undercoat in advance.
The electrode obtained here is referred to as Electrode A. In addition, an electrode using Li2MnO3 was fabricated as a comparative electrode. Li2MnO3 was formed using Li2CO3 and MnCO3 (the molar ratio of Li2CO3 to MnCO3=1:1) as materials. The materials were mixed under the conditions of firing temperature and firing time that are described as those for the synthesis method of the lithium manganese composite oxide. The fabricated electrode is referred to as Comparative Electrode C.
(Measuring Discharge Capacity) Half cells were fabricated using Electrode A and Comparative Electrode C.
For the cells, the coin cell described in Embodiment 2 was used. Lithium was used for counter electrodes of the half cells. An electrolytic solution was formed by dissolving LiPF6 as a salt in a mixed solution containing ethylene carbonate and diethyl carbonate, which are aprotic organic solvents, at a volume ratio of 1:1. As a separator, polypropylene (PP) was used.
Furthermore, the capacity of Electrode A was increased as the number of charge and discharge cycles increased.
In this example, the cycle characteristics of the half cell using Electrode A, which was fabricated in Example 1, were evaluated.
Charge and discharge cycles of the half cell using Electrode A, which was fabricated in Example 1, were continued even after the ninth cycle, and changes in discharge capacity were evaluated.
In addition, Electrode X was fabricated using Sample X formed in Example 1. The compounding ratio of Sample X to PVDF and AB used for Electrode X is based on that for Electrode A. A half cell was fabricated using Electrode X, and was charged and then discharged. A counter electrode, an electrolytic solution, a separator, and the like that were used for the half cell were the same as those of the half cell fabricated using Electrode A in Example 1. Charging and discharging were performed under the conditions for charging and discharging the half cell fabricated using Electrode A in Example 1. Charge and discharge cycles of the half cell fabricated using Electrode X were performed in a manner similar to that of charge and discharge cycles of the half cell fabricated using Electrode A, and the changes in discharge capacity were evaluated.
The initial discharge capacities of both the half cells were as high as 260 mAh/g or more. The capacity of the half cell using Electrode A was increased from the initial capacity, and the maximum capacity was 285.7 mAh/g. The discharge capacity after 40 cycles was 267.0 mAh/g, which is 93% of the maximum capacity. The use of Sample A obtained by forming a covering layer and performing reduction enabled achievement of more excellent cycle characteristics than those when Sample X was used.
Example 3In this example, TEM analysis results of electrodes fabricated using the lithium manganese composite oxide of one embodiment of the present invention will be described.
Half cells were fabricated using Electrode A described in Example 1. For the cells, the coin cell described in Embodiment 2 was used. Lithium was used for counter electrodes of the half cells. An electrolytic solution was formed by dissolving LiPF6 as a salt in a mixed solution containing ethylene carbonate and diethyl carbonate, which are aprotic organic solvents, at a volume ratio of 1:1. As a separator, polypropylene (PP) was used.
Half Cell A-1, Half Cell A-2, and Half Cell A-3 were each fabricated using Electrode A. Half Cell A-1 was neither charged nor discharged. Half Cell A-2 was only charged.
In addition, Half Cell X-3 was fabricated using Electrode X fabricated in Example 2, and it was charged and then discharged. The conditions for charging and discharging were similar to those for Half Cell A-3.
Next, Half Cells A-1 to A-3 and Half Cell X-3 were disassembled in an inert atmosphere to take out the electrodes. Electrodes A taken out from Half Cells A-1, A-2, and A-3 are referred to as Electrodes A-1, A-2, and A-3, respectively. Electrode X taken out from Half Cell X-3 is referred to as Electrode X-3.
Then, the electrodes were sliced using a focused ion beam system (FIB).
[TEM Observation]The sliced Electrodes A-1 to A-3 were observed with a TEM (H-9000NAR manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 200 kV.
As can be seen in each of
Next, portions indicated by points 1 to 7 in
In all the cases of Electrodes A-1 to A-3, the spectra of the point 6 and the point 7 have stronger peaks of the K-edges of C and weaker peaks of Mn, O, Ni, and the like than those of the points 1 to 5. The point 6 presumably corresponds to the coating film of the particle. The spectrum of the point 6 has a strong peak of C, which suggests that reduced graphene oxide is the main component of the coating film. The spectrum of the point 7 also has a strong peak of C, which implies that reduced graphene oxide exists between the particles.
Next, consideration will be given focusing attention on the L3 edges and the L2 edges of Mn. Table 1 shows the ratio of the L3 edge to the L2 edge (L3/L2) of each of the points 1 to 7 in
Here, the L3/L2 ratio obtained by EELS depends on the way to remove background noise. The measurement data described in this example was obtained by removing background noise mainly using a Hartree-Slater cross section.
According to
For example, the L3/L2 ratios of manganese inside the particle in Electrode A-3 are 1.9 at the measurement point (point 5) 3 nm from the surface of the particle, and 2.0 at the measurement point (point 2) 122 nm from the surface of the particle. Thus, the distribution of the L3/L2 ratios of manganese inside the particle is narrow. This implies that the distribution of the valences of manganese inside the particle is also narrow.
The average value of the L3/L2 ratios of manganese at the five points in Table 1 is 1.80, the average value of the L3/L2 ratios of manganese at the five points in Table 2 is 1.81, and the average value of the L3/L2 ratios of manganese at the five points in Table 3 is 1.90. These suggest that the valence of manganese is close to 4 in all the electrodes. Here, the L3/L2 ratio of manganese of the lithium manganese composite oxide of one embodiment of the present invention that is obtained by TEM-EELS analysis is preferably greater than or equal to 1.3 and less than 2.5, more preferably greater than or equal to 1.4 and less than or equal to 2.3, still more preferably greater than or equal to 1.5 and less than or equal to 2.2, particularly preferably greater than or equal to 1.6 and less than or equal to 2.1.
As described in Example 2, the half cell using Electrode A has excellent cycle characteristics. Sample A obtained through covering with graphene oxide (Step 1) and reducing the graphene oxide (Step 2) described in Example 1 may be a more stable particle with a narrow distribution of the valences inside the particle.
[TEM-EDX Analysis]Next,
Tables 4 to 6 show the results of quantitative analysis performed focusing attention on Mn, Ni, and O. Here, the results calculated assuming that the sum of the proportions of atomicities of Mn, Ni, and O is 100% are shown in Tables 4 to 6. Note that the sum of the proportions of atomicities of Mn, Ni, and O might have a margin of error of approximately 0.1% from 100% because the values are rounded to unit.
From Tables 4 to 6, the values {(Mn+Ni)/O} are each calculated by dividing the sum of the proportions of atomicities of Mn and Ni by the proportion of atomicity of O. The average value of {(Mn+Ni)/O} of the five measurement points in Table 4 is 0.41. The average value of {(Mn+Ni)/O} of the five measurement points in Table 5 is 0.47. The average value of {(Mn+Ni)/O} of the five measurement points in Table 6 is 0.44.
Example 4In this example, the relation between the conditions for reduction of graphene oxide and the characteristics of a storage battery of one embodiment of the present invention will be described.
(Synthesis of Lithium Manganese Composite Oxides)First, Samples 101 to 117 were prepared. Starting materials Li2CO3, MnCO3, and NiO were weighed such that the molar ratio of Li2CO3 to MnCO3 and NiO was 0.84:0.8062:0.318. Next, acetone or ethanol was added to the powder of these materials, and then, they were mixed in a ball mill or a bead mill to prepare mixed powder. Note that acetone and the ball mill were used in the cases of forming Samples 109 to 111, and ethanol and the bead mill were used in the cases of forming the other samples.
After that, heating was performed to volatilize acetone or ethanol, so that a mixed material was obtained (in the cases of forming all the samples).
Then, the mixed material was put in a melting pot, and was fired at 1000° C. in the air for 10 hours to synthesize a novel material (in the cases of forming all the samples). The flow rate of the air gas was 10 L/min.
Subsequently, grinding was performed to separate the sintered particles. For the grinding, acetone or ethanol was added and then mixing was performed in a ball mill or a bead mill. Note that acetone and the ball mill were used in the cases of forming Samples 109 to 111, and ethanol and the bead mill were used in the cases of forming the other samples.
After the grinding, heating was performed to volatilize acetone or ethanol, so that a lithium manganese composite oxide containing nickel was formed (in the cases of forming all the samples). Then, heat treatment was performed at 600° C. for 3 hours in the cases of forming Samples 104 and 109 to 111; at 900° C. for 3 hours in the case of forming Sample 117; and at 800° C. for 3 hours in the cases of forming Samples 101 to 103, 105, and 112 to 116. Note that heat treatment was not performed in the cases of forming Samples 106 to 108.
(Coating with Carbon-Containing Layer)
Then, the obtained lithium manganese composite oxide was coated with a carbon-containing layer. Here, a process for covering the lithium manganese composite oxide with a carbon-containing layer that is described in this example includes Step 1 of covering with graphene oxide and Step 2 of reducing the graphene oxide.
(Step 1: Covering with Graphene Oxide)
First, covering with graphene oxide (Step 1) will be described. Two kinds of solutions GO1 and GO2 were prepared. In GO1, the concentration of graphene oxide in water is 1 wt %. In GO2, the concentration of graphene oxide in water is 2 wt %. The lithium manganese composite oxides for forming Samples 108 to 111 were each mixed with the solution GO1 in a mixer, and the lithium manganese composite oxides for forming the other samples were each mixed with the solution GO2 in a mixer.
The obtained mixture was dried under reduced pressure in a bell jar at 50° C. and then ground in an alumina mortar.
(Step 2: Reducing Graphene Oxide)Next, reducing the graphene oxide (Step 2) will be described. The graphene oxide of each of the obtained samples was reduced. First, a reducing solution was prepared. Ascorbic acid as a reducing agent and lithium hydroxide were used as solutes, and a 80 vol % ethanol solution was used as a solvent. The molar amount of lithium hydroxide was equal to that of ascorbic acid.
Eleven kinds of solutions with the following different weight ratios of ascorbic acid to the lithium manganese composite oxide the were prepared: 0.75 wt %, 1.6 wt %, 2.43 wt %, 2.7 wt %, 3.38 wt %, 8.44 wt %, 16.88 wt %, 28.13 wt %, 33.75 wt %, 67.5 wt %, and 135 wt %. The samples were put in the seven kinds of solutions according to the combinations shown in Table 7, and reduction was performed at 60° C. for 3 hours.
Then, the obtained solution was filtrated by suction filtration. For the filtration, filter paper with a particle retention capability of 1 μm was used. Then, washing and drying were performed. The drying was performed at 50° C. under reduced pressure. After the drying, the obtained powder was ground in a mortar. After that, drying was performed at 170° C. under reduced pressure for 10 hours.
Through the above steps, Samples 101 to 117 were obtained.
(Fabricating Electrodes)Next, electrodes were fabricated using Samples 101 to 117 as positive electrode active materials. Each sample was mixed with acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVDF) as a resin, and N-methyl-2-pyrrolidone (NMP) as a polar solvent to form slurry. The weight ratio of each sample to the PVDF and the AB was 90:5:5. Then, the slurry was applied to a current collector and dried. Note that a surface of the current collector was treated with an undercoat in advance.
(Measuring Discharge Capacities)Half cells were fabricated using the obtained electrodes. For the cells, the coin cell described in Embodiment 2 was used. Lithium was used for counter electrodes of the half cells. An electrolytic solution was formed by dissolving LiPF6 as a salt in a mixed solution containing ethylene carbonate and diethyl carbonate, which are aprotic organic solvents, at a volume ratio of 1:1. As a separator, polypropylene (PP) was used.
As shown in
Next, the Rietveld analysis was performed using the obtained X-ray diffraction spectra.
(Rietveld Analysis)The crystal data of the lithium manganese composite oxide can be acquired by the Rietveld analysis. As analysis software, TOPAS (DIFFRACplus TOPAS Version 3) manufactured by Bruker AXS is used. On the assumption that the obtained lithium manganese composite oxide includes the first crystal phase and the second crystal phase, the Rietveld analysis was performed on the basis of the X-ray diffraction measurement. The proportions of the first crystal phase and the second crystal phase, the lattice constants of the first and second crystal phases, and each site occupancy of atoms were calculated under the conditions where the initial first crystal phase is Li2MnO3 with a layered rock-salt structure that belongs to the space group C12/m1 and the initial second crystal phase is LiNi0.5Mn1.5O4 with a spinel structure that belongs to the space group Fd-3m.
Here, the lithium manganese composite oxide analyzed in this example contains lithium, manganese, nickel, and nickel as metals; however, it is difficult to distinguish manganese from nickel because a difference between the X-ray scattering capabilities of manganese and nickel is little. Thus, the occupancies of a 4g site, a 2b site, a 2c site, and a 4h site of a layered rock-salt structure of the first crystal phase were calculated as the sum of the occupancies of manganese and nickel.
Table 8 shows the crystal data of Li2MnO3 with a layered rock-salt structure (C12/m1) that is used for the Rietveld analysis. The lattice constants a, b, c, and β were 4.9555 [Å], 8.5906 [Å], 5.0284 [Å], and 109.07°, respectively. Table 9 shows the crystal data of LiMn2O4 with a spinel structure (Fd-3m). The lattice constant a was 8.1700 [Å]. Here, B denotes a temperature factor called the Debye-Waller factor.
Here, assume that the occupancies of the 4g site, the 2b site, the 2c site, the 4h site, a 4i site, and a 8i site in Element X are A(X)4g, A(X)2b, A(X)2c, A(X)4h, A(X)4i, and A(X)8i, respectively. For example, when the occupancy at the 4g site is expressed as the sum of the occupancies of manganese and nickel, it is expressed by A(Mn+Ni)4g.
In starting Rietveld analysis of the layered rock-salt structure in Table 8, the lattice constants in Table 8 and the occupancies shown in Condition 1 in Table 10 were input as the initial values. In starting Rietveld analysis of the spinel structure in Table 9, the lattice constants in Table 9 and the occupancies shown in Condition 3 in Table 11 were input as the initial values. In the Rietveld analysis, fitting was performed such that Condition 2 in Table 10 and Condition 4 in Table 11 were satisfied. Note that the coordinates might be changed from the initial coordinates by the fitting; however, the change does not greatly affect the symmetry.
The Rietveld analysis was performed on Samples 101 to 111. Table 12 shows Rwp, Rp, Rexp, GOF, and the proportions of the first and second crystal phases. Table 13 shows the lattice constants of the first and second crystal phases and the oxygen occupancies at the 4i site of the first crystal phase.
Here, Rwp is obtained by dividing the sum of residual squares by the sum total of the observed intensity, and Rp is a difference between the observed intensity and the theoretical diffraction intensity. Rexp is the expected value of Rwp, which is the statistically estimated minimum Rwp. In addition, GOF, which stands for “good of fitness”, is obtained by dividing Rwp by Rexp and is preferably close to 1.
As shown in Table 12, the proportion of the second crystal phase with a spinel structure was greater than 10% when the concentration of ascorbic acid is high, for example, 33. 75 wt % or more in reduction. It is suggested that reduction treatment might reduce part of the lithium manganese composite oxide as well as graphene oxide and the part might have a spinel structure.
The theoretical capacity of the spinel structure is known to be as low as 147 mAh/g. Therefore, an increase in the proportion of the spinel structure implies a decrease in the capacity of the obtained sample.
EXPLANATION OF REFERENCE101: covering layer, 300: storage battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 400: storage battery, 402: positive electrode, 404: negative electrode, 500: storage battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolytic solution, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 600: storage battery, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 610: gasket, 611: PTC element, 612: safety valve mechanism, 900: circuit board, 910: label, 911: terminal, 912: circuit, 913: storage battery, 914: antenna, 915: antenna, 916: layer, 917: layer, 918: antenna, 919: terminal, 920: display device, 921: sensor, 922: terminal, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 932: positive electrode, 933: separator, 951: terminal, 952: terminal, 7100: portable display device, 7101: housing, 7102: display portion, 7103: operation button, 7104: power storage device, 7400: mobile phone, 7401: housing, 7402: display portion, 7403: operation button, 7404: external connection port, 7405: speaker, 7406: michrophone, 7407: power storage device, 8021: charging apparatus, 8022: cable, 8100: automobile, 8101: headlight
This application is based on Japanese Patent Application serial no. 2013-209366 filed with Japan Patent Office on Oct. 4, 2013, the entire contents of which are hereby incorporated by reference.
Claims
1. A lithium manganese composite oxide represented by LixMnyMzOw comprising:
- a region belonging to a space group C2/c,
- wherein element M is an element other than lithium and manganese, and
- wherein the lithium manganese composite oxide is covered with a carbon-containing layer.
2. The lithium manganese composite oxide according to claim 1, further comprising: a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26 (y+z)/w<0.5 are satisfied.
3. The lithium manganese composite oxide according to claim 1,
- wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm.
4. A lithium manganese composite oxide represented by LixMnyMzOw comprising:
- a region belonging to a space group C2/c,
- wherein element M is an element other than lithium and manganese,
- wherein a ratio of the integral intensity of L3 peak to the integral intensity of L2 peak of manganese that is obtained by electron energy loss spectroscopy (L3/L2) is greater than or equal to 1.4 and less than or equal to 2.3, and
- wherein the lithium manganese composite oxide is covered with a carbon-containing layer.
5. The lithium manganese composite oxide according to claim 4, further comprising:
- a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26 (y+z)/w<0.5 are satisfied.
6. The lithium manganese composite oxide according to claim 4, wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm.
7. A lithium manganese composite oxide represented by LixMnyMzOw comprising:
- a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26≦(y+z)/w<0.5 are satisfied,
- wherein the element M is an element other than lithium and manganese,
- wherein the lithium manganese composite oxide includes a region covered with a carbon-containing layer, and
- wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm.
8. The lithium manganese composite oxide according to claim 1, wherein the element M is nickel.
9. The lithium manganese composite oxide according to claim 4, wherein the element M is nickel.
10. The lithium manganese composite oxide according to claim 7, wherein the element M is nickel.
11. A lithium-ion secondary battery comprising:
- the lithium manganese composite oxide according to claim 1 as a positive electrode active material.
12. A lithium-ion secondary battery comprising:
- the lithium manganese composite oxide according to claim 4 as a positive electrode active material.
13. A lithium-ion secondary battery comprising:
- the lithium manganese composite oxide according to claim 7 as a positive electrode active material.
14. An electronic device comprising:
- the lithium-ion secondary battery according to claim 9.
15. A method for forming a carbon-containing layer on a surface of a lithium manganese composite oxide represented by LixMnyMzOw, comprising:
- forming a layer containing graphene oxide on a surface of the lithium manganese composite oxide; and
- reducing the graphene oxide,
- wherein the element M is an element other than lithium and manganese.
Type: Application
Filed: Sep 26, 2014
Publication Date: Apr 9, 2015
Inventors: Tatsuya IKENUMA (Atsugi), Shuhei YOSHITOMI (Ayase), Takahiro KAWAKAMI (Atsugi), Yumiko YONEDA (Former family: SAITO) (Isehara), Yohei MOMMA (Isehara)
Application Number: 14/497,386
International Classification: H01M 4/36 (20060101); H01M 4/131 (20060101); H01M 4/1391 (20060101); H01M 4/587 (20060101); H01M 4/04 (20060101); H01M 10/0525 (20060101); H01M 4/505 (20060101);
