Cooperation between Active Material, Polymeric Binder and Conductive Carbon Additive in Lithium Ion Battery Cathode Honghe Zheng,* ,†,‡ Ruizhi Yang, † Gao Liu, ‡ Xiangyun Song, ‡ and Vincent S. Battaglia ‡ † School of Energy, Soochow University, Suzhou, Jiangsu 215006, China ‡ Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, California 94720, United States 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 Li- Ni 0.8 Co 0.15 Al 0.05 O 2 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. 1. INTRODUCTION Electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) call for high energy density at moderate/high power levels. To meet the aggressive requirements of lithium batteries for EV and PHEV purposes, much effort has been made in the research and development of high-energy electrode materials. Because of the cathode-limited property of lithium ion cells, new cathode materials of high potential and high capacity have been highlighted for many years; however, less attention is paid to the engineering approaches of the cathode laminate; for instance, the optimization of electrode compositions, structure, porosity, and so on. 1-4 Typically, a lithium ion battery cathode is a composite consisting of agglomerated primary particles of active intercalation compounds (called secondary particles) and inactive materials coated and calendered onto Al current collectors. The inactive materials are referred to as polymeric binder and conductive additive(s). The active material acts as the lithium reservoir in the electrode, the binder plays the role of binding the active materials and the conductive additive together and adherent to the current collector, and the conductive additive contributes to an increase in the electronic conductivity of the laminate. Cooperation between the different components contributes to an electrochemical property enhancement of the electrode by placing the electrode particles closer together and making the laminate more conductive. However, it should be noted that the role of each component is also restrained by the others. 5,6 For example, the electronic conductivity resulting from a carbon additive can be brought down by the presence of a more nonconductive binder and oxide active material, and the close contact between active material particles with the help of a binder can be spoiled by the appearance of more nanocarbon additive, etc. From this point of view, the optimization of electrode compositions is crucial for fabrication of high-quality electrodes for EV or PHEV purposes. Although there are some reports in the literature regarding the effects of electrode composition on electrochemical performance, the results obtained are always very specific. Many fundamental scientific issues relating to the cooperation among different cathode elements remains a matter of conjecture. Comprehensive understanding of how the cooper- ation among electrode elements affects the physical and electrochemical properties of the laminate is of great significance for designing high-quality electrodes to meet the requirements of EVs and PHEVs. The current work systematically demonstrates the physical and electrochemical properties of a LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode laminate as a function of the electrode compositions. LiNi 0.8 Co 0.15 Al 0.05 O 2 was chosen as the cathode material Received: September 1, 2011 Revised: January 17, 2012 Published: January 23, 2012 Article pubs.acs.org/JPCC © 2012 American Chemical Society 4875 dx.doi.org/10.1021/jp208428w | J. Phys. Chem. C 2012, 116, 4875-4882