Cooperation between Active Material, Polymeric Binder and Conductive Carbon Additive in Lithium Ion Battery Cathode

Abstract

A lithium ion battery electrode is a composite of active material, polymeric binder, and conductive carbon additive(s). Cooperation among the different components plays a subtle and important role in determining the physical and electrochemical properties of the electrode. In this study, the physical and electrochemical properties of a LiNi0.8Co0.15Al0.05O2 cathode were investigated as a function of the electrode compositions. The electrode conductivity, porosity, specific capacity, first Coulombic efficiency, and rate capability were found significantly affected by the polyvinylidene difluoride (PVDF)-to-acetylene black (AB) ratio and the total inactive material amount. The electronic conductivity of the laminate does not so much decide the rate performance of the electrode as it is generally believed. The rate capability of the electrode is enhanced by an increase in the total inactive material content at a PVDF/AB ratio of 5:4, whereas it is deteriorated by increasing the total inactive material content at PVDF/AB ratios of 5:1 and 5:2. At a PVDF/AB ratio of 5:3, the rate performance is not considerably affected by the inactive material content. The result is explained by the competition between the ion-blocking effect of PVDF binder and the electronic conducting effect of the AB additive. A long-term cycling experiment shows the mechanical integrity of the laminate is important for the durability of the composite electrode.