Cylindrical Graphite/LiFeP04 Commercial Batteries Cycled at High Current Densities Study by Post Mortem Analysis

摘要

Lithium ion battery technology is today playing a key role in the development of high power and energy densities devices. To boost the quality of this technology, it is vital to gain a deeper understanding of the causes leading to the battery end of life and loose of performance. In fact, Li-ion battery manufacturers have to deal most of all with problems concerning the cells aging in order to ensure long-term reliability and safety. In this context, determination of degradation mechanisms and their correlation with cell performances is essential for the production of a new cell concept that can meet targeted lifetimes [1-3]. An evaluation of performances of Graphite/LiFeP04 commercial cylindrical batteries at high discharge current (6C) is discussed in this study. The combination of many temperature, charging C-rate and end-of-charge voltage are very important to define and understand the aging mechanism in cycled Li-ion cells. A study on the degradation mechanisms of the battery is realised by post-mortem analysis in order to identify the main degradation mechanisms following a well-defined protocol [4]. Systematic degradation mechanisms are evaluated by microstructural (SEM) and crystallographic (XRD) analyses. Elemental analysis of the electrode composition was determined by EDS and ICP techniques. The electrochemical performances of selected areas of the harvested electrodes were determined by galvanostatic testing in half-cell configuration and electrochemical impedance spectroscopy. The cell state of Health (SOH) evolution was evaluated with the capacity and the internal resistance, as a function of Full Equivalent Cycles (FEC). These results were combined with non-destructive cell electrochemical measurements to provide a global view of the main degradation processes.