Non-uniform cycling of Li metal batteries: Impacts to life and performance

Advances in cell design have improved lithium-metal battery (LMB) cycle life, but few studies assess performance under discharge profiles representative of real-world use. These profiles, which are often overlooked due to the complexity and risk of misinterpretation, can hinder accurate analysis or even prevent publication. Realistic discharge profiles include high currents during acceleration, current reversal during regenerative braking, and low steady currents at cruising speed. This work examines LMB performance using localized high-concentration electrolytes (LHCEs) under dynamic cycling, focusing on acceleration and regeneration pulses. These profiles bridge practical usage and controlled conditions for reproducible trends. Single-layer pouch cells are tested with LHCEs of lithium bis(fluorosulfonyl)imide (LiFSI), 1,2-dimethoxyethane (DME), with either 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) or bis(2,2,2-trifluoroethyl) ether (BTFE). The inclusion of pulsing dramatically alters the failure of the cells and increases cell-to-cell variability. Increasing the ionic conductivity and electrolyte volume decreases cell-to-cell performance variability. Cells with LHCE-BTFE exhibit more consistent cycling capacity behavior and fewer performance metric fluctuations, such as a rise of polarization or peak cell pressure, under non-uniform cycling compared to LHCE-TTE. These findings suggest that rapid transition from benchtop testing to real-world deployment for LMBs will require the inclusion of more realistic cycling conditions.