Abstract: A lithium secondary battery comprises a negative electrode having lithium as an active material, a positive electrode comprising a boron-containing lithium-manganese composite oxide as an active material and a nonaqueous electrolyte comprising a solute and a solvent, the boron-containing lithium-manganese composite oxide having an atomic ratio between B and Mn (B/Mn) of 0.01 to 0.20 and an average valence of manganese before charge-discharge of at least 3.80, and the solvent being a mixed solvent containing 5 to 50% by volume of a butylene carbonate. This battery is highly reliable, since the positive electrode active material minimally decomposes and hence the internal resistance minimally increases, even when the battery is continuously charged at a high voltage by mistake.

Abstract: A nonaqueous electrolyte battery has a positive electrode, a negative electrode and separator laminate rolled into a spiral electrode unit contained in an external case filled with nonaqueous electrolyte. Battery voltage is between 3.5 V and 5.0 V when charged. A positive electrode supporting member material and the external case are both aluminum. The positive Electrode supporting member is exposed for at least a portion of the outermost winding of the spiral electrode unit, and this exposed supporting member contacts the inner surface of the external case to make an electrical connection.