Single Particle Measurement of Single Crystal LiCoO2 and Wire-Shaped LiCoO2

Abstract

Lithium-ion batteries (LIBs) with high gravimetric and volumetric energy density are very important key devices to encourage the popularization of an environmental friendly energy system, which is consisted of solar cells, wind power generations, smart grid, and batteries. LiCoO2 is widely used as the active material for the positive electrode. Many researchers have reported the dynamics of crystal structure change accompanied with the lithium insertion and extraction1. In commercial Li-ion battery, the positive electrode is composite electrode which is composed of polycrystalline LiCoO2 powder, binders and conductive agents. It is difficult to obtain the intrinsic property of LiCoO2 from the composite electrode. LiCoO2 thin film electrode is widely used as the model electrode in order to discuss the mechanism of charge and discharge reaction. However, the thin film electrode is not appropriate for commercial batteries. In this study, the single crystal LiCoO2 powders and wire-shape LiCoO2 particles which are accumulated one-dimensionally by single crystal LiCoO2 are synthesized by a flux method in order to discuss the Li transfer phenomenon in LiCoO2 crystal by using a single particle measurement technique. Figure 1 shows the SEM images of single crystal and wire-shaped LiCoO2. The single particle measurement technique is very powerful to measure the intrinsic electrochemical properties of the active material with 5~30 μm size, because it can eliminate the effect of binders and conductive agents. The schematic diagram of the single particle measurement system is demonstrated in Fig.2. This technique has revealed that LiCoO2, LiMn2O4 and LiFePO4 particles have very good rate characteristics2-4. This study focuses on the effect of morphological and crystalline variations of LiCoO2 to the electrochemical characteristics. References 1) T. Ohzuku, and A. Ueda, J. Electrochem. Soc., 141, 2972 (1994)2) K. Dokko, N. Nakata, K. Kanamura, J. Power Sources 189, 783 (2009)3) T. Saito, H. Munakata, K. Kanamura, J. Soc. Inorg. Mater., Jpn., 18, 201 (2011)4) H. Munakata, B. Takemura, T. Saito, K. Kanamura, J. Power Sources 217, 444 (2012)