To improve energy density and cycle life when a carbon material and a composite material are used as a negative electrode by operating the negative electrode in a specific range of current density by setting its capacity higher than a logical capacity of the negative material and lower than a capacity of lithium metal.
Operating current density of a negative electrode is set 0.4-8.0 mA/cm2. For example, in the case of using a negative electrode mixture containing a mixture of highly purified natural graphite with furnace black and a binding agent, discharge capacity hardly decreases after a given cycle test at a defined charge capacity. Thickness of the negative electrode and negative electrode mixture layer is 0.1-100 μm, the thickness ratio of the negative electrode to a positive electrode mixture layer is 1/10-1/2, and density of the negative electrode mixture layer is 0.5-8.0 g/cm3. An active material used for the positive electrode is LiXO2 or LiX2O4 (where, X is a transition metal such as Co, Ni, Mn or the like, or part of it is replaced by Al or alkaline earth metal such as Mg). An electrolyte layer holding electrolyte and electrolytic solution in polymer such as ethylene oxide is suitable.
KANEDA JUNYA
HONBOU HIDETOSHI
MURANAKA TADASHI
