A one (single) particle measurement was employed to estimate electrochemical parameters of active materials for lithium ion batteries in order to design porous electrodes and cells. A micro electrode was used as a current collector for LiCoO 2 and graphite particles. In the cases of materials with large expansion and shrinkage during discharge and charge process, a tweezers-type current collector was developed and applied to the measurement. Si particle as an anode material for post lithium ion batteries was measured by using a tweezers-type current collector to stabilize a contact between active material and current collector. Successfully, the tweezers-type current collector provided a stable contact to the active material particle. The electrochemical parameters for various active materials were obtained from the one (single) particle measurement. Based on these parameters, the porous electrode and lithium ion cell can be designed.

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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.