Capacity and cycle performance of a lithium-ion polymer battery using commercially available LiNiCoO₂

Commercially available lithium-nickel-cobalt oxide (LiNi_0.82Co_0.18O₂) issued a high-capacity cathode material in the fabrication of a bi-cell type of lithium-ion polymer battery (LIPB) following the Bellcore scheme. The capacity and cycle performance of the battery is evaluated. An ethylene carbonate (EC)-based electrolyte mixed with dimethyl carbonate (DMC) or ethyl methyl carbonate (EMC) is employed as a means to increase the utilization of cathode active material. LiNi_0.82Co_0.18O₂ displays a higher initial discharge capacity (∼180 mAh g^-1) than conventional LiCoO₂. As a result, both capacity and cycle performance are improved when using an EMC-containing electrolyte solution. In particular, the high-rate capability is enhanced, e.g. the discharge capacity at the 2C rate reaches about 70% of that at the 0.2C rate. All the improved performance characteristics are probably due to the EMC-containing electrolyte solution causing a trans-esterification reaction associated with an equilibrium mixture of EMC, DMC and diethyl carbonate (DEC).