Electrochemical Characterization of LiCoO­2 Composite Particles by Single Particle Measurement

Active materials for rechargeable lithium-ion batteries are generally coated with polymer binder and conductive carbon on a current collector and evaluated as a porous composite electrode. However, the use of composite electrode makes it difficult to understand the intrinsic electrochemical properties of active material since the electrode structural factors such as porosity and thickness are included in the electrochemical response of composite electrode. In order to prevent such misunderstanding, single particle measurement is one of useful tools. In the case of single particle measurement, a micro current collector is used to establish electrical connection to an active material particle. Thus, the structural factors of composite electrode can be neglected, resulting in precise understanding the intrinsic electrochemical properties of active materials. In this study, LiCoO₂ was focused and its electrochemical properties, particularly the cycleability at high temperatures was investigated by single particle measurement. Furthermore, the cluster particle of LiCoO₂ composite electrode was also evaluated in order to investigate the effects of PVdF binder and conductive carbon on the cycleability of LiCoO₂. As shown in Figure 1, the rate capability of cluster particle was low compared with LiCoO₂ single particle, namely the discharge capacity was decreased at high discharge rates. This difference is expected to be due to the blocking effect of PVdF binder on Li⁺ diffusion to LiCoO₂ particle from an electrolyte solution. In contrast, the capacity retention in charge-discharge cycle test (Figure 2) was significantly improved in the cluster particle. This result suggests that LiCoO₂ is stabilized by PVdF binder and conductive carbon.