LiNi0.5Co0.5O2 layered material could be a possible cathode material for advanced lithium-ion batteries in applications such as medical devices. The material was prepared by the co-precipitation method, which leads to a highly stoichiometric and homogeneous powder with a desirable particle size. It has shown reasonable cycling stability at a C/2 rate up to 100 cycles, and is expected to be much more stable at lower rates and capable of providing the needed capacity. We also showed that the use of lithium fluoroalkyl-phosphate Li[PF3(C2F5)(3)] salt-based electrolyte significantly improves the calendar life of the battery. Aging tests have been performed under severe conditions (storage at 50 degreesC and 4.1 V) clearly show a huge capacity loss for the conventional cathode LiNi0.8Co0.2O2 while LiNi0.5Co0.5O2 electrode exhibits a limited capacity fading. Finally, because it has less nickel content, differential scanning calorimetry (DSC) measurements confirm that LiNi0.5Co0.5O2 is much safe than the LiNi0.8Co0.2O2 cathode. (C) 2003 Elsevier Science B.V. All rights reserved.