Comparison of Electrode Processing and Electrochemical Performance of LiNi0.6Mn0.2Co0.2O2 and LiFePO4 Based Electrodes for Stationary Energy Storage Applications

摘要

Three factors are considered key for the large-scale application of lithium ion batteries (LIBs) in stationary energy storage systems: long cycle life, low costs, and safety properties. LIB cathodes, like LiNixMnyCozO2 (NMC, x+y+z=1) are commonly considered as suitable active material for the positive electrodes of stationary energy storage systems, as they have a lower cost/kWh ratio compared to safer LiFePO4 (LFP) based cathodes on battery pack level. The lower charge and discharge rates of LIBs in home storage application provides new possibilities for the processing of high energy electrodes by decreasing the ratio of inactive components like conductive agent and binder without any loss of the electrochemical performance of LIBs. In this study, we present new processing strategies for a successful integration of LiNi0.6Mn0.2Co0.2O2 (NMC622) and LFP as positive active material for high energy LIBs. The focus is on the evaluation of the active/inactive material ratio for precise and upscalable processing of the electrode paste. The energy density of the positive electrodes can be improved by the limitation of the conductive agent and binder content as well as the increase of areal capacity. Nevertheless, the adhesion of the composite electrode on the current collector, the calendering process and the electrochemical performance depend strongly on the dry film thickness and the electrode composition. Here, we investigate the influence of different conductive agent contents and areal electrode capacities on its adhesive and conductive properties of the composite electrode on the current collector. The electrochemical rate performance of the NMC622 and LFP based electrodes as well as the long-term cycling stability and the aging behavior versus graphite based anodes are investigated. Based on the results, we propose an optimized electrode paste recipe and the corresponding processing conditions for the application of the different positive electrodes in high energy LIBs.