Fast-Charging Capability Limits of Electric Vehicle Battery Chemistries

The fast cycling capability of Li-ion batteries is a key performance indicator for a range of applications including electric vehicles (EVs), in which systems must deliver/accept high currents while avoiding excessive degradation. We evaluate four leading EV battery chemistries in this context, encompassing cathodes focused on design-to-performance, LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811), and design-to-cost, LiMn 0.6 Fe 0.4 PO 4 (LMFP), alongside current state-of-the-art (graphite and graphite @ SiO x composite) and next-generation (high SiO x ) anodes. These chemistries are adopted as model systems to examine three common test protocols for evaluating fast cycling, specifically tuned to fast charge, fast discharge, or both. The capacity, degradation induced, and operational state-of-charge range were highly dependent on selected testing protocols. Significant loss of lithium inventory (LLI) was observed under fast-charging conditions, associated with lithium plating, observed via monitoring of anode potential in three-electrode cells, differential voltage analysis, and visual inspection of electrodes postmortem. LMFP cells induced a greater level of Li plating than NMC, reaching negative anode potentials in the early stages of fast charging. While the SiO x anode performed relatively well at high rates, it suffered a greater degree of degradation, including both LLI and impedance increase associated with excess SEI growth. This study provides a basis for battery material design and charging protocols tuned for fast cycling.