Abstract: Provided is a new 5 V class spinel exhibiting an operating potential of 4.5 V or higher (5 V class) with respect to the Li metal reference potential, having an excellent discharge capacity retention ratio at high temperatures, for example 45° C. Suggested is a spinel type lithium-manganese-nickel-containing composite oxide containing a crystalline phase in which a portion of Mn sites in LiMn2O4-? are substituted with Li; another metal element M1, wherein M1 represents a metal element including at least one of Ni, Co and Fe and another metal element M2, wherein M2 represents a metal element including at least one of Mg, Ti, Al, Ba, Cr and Nb, and the spinel type lithium-manganese-nickel-containing composite oxide comprising a composite oxide phase containing Ni, Mn and B.

Abstract: Provided is a new 5 V class spinel exhibiting an operating potential of 4.5 V or higher (5 V class) with respect to the Li metal reference potential, having an excellent discharge capacity retention ratio at high temperatures (for example, 45° C.). Suggested is a spinel type lithium-manganese-nickel-containing composite oxide containing a crystalline phase in which a portion of Mn sites in LiMn2O4-? are substituted with Li; another metal element M1 including Ni (here, the M1 represents a metal element including at least one of Ni, Co and Fe), and another metal element M2 (here, the M2 represents a metal element including at least one of Mg, Ti, Al, Ba, Cr and Nb), and the spinel type lithium-manganese-nickel-containing composite oxide comprising a composite oxide phase containing Ni, Mn and B.