Understanding and regulation of stress-induced structural evolution in silicon anodes for high-energy-density batteries

Silicon (Si)-based electrodes are widely regarded as a promising anode option for next-generation high-energy batteries. Although the substantial volume expansion during charge/discharge cycles is recognized as a primary cause of Si-based anode failure, the correlation between material volume changes, electrode-scale electrochemical-mechanical behavior, and electrochemical performance remains unclear. This poses a significant obstacle to the design of high-performance Si-based anodes. Herein, by combining operando detection of spatial stress in pouch cells (8 × 8 cm) with materials characterization, we elucidate the dependence of electrochemical performance on the inner stress-driven structural evolution of Si-based anodes, where large, uneven stress/strain dominates their mechanical degradation, compromising electrochemical reversibility. Significantly, we unveil that, beyond the basic function of Li compensation, prelithiation redirects the stress-induced structural evolution of the electrode from pore and crack formation to a void-filling-dominated process, effectively mitigating volume changes and reaction inhomogeneity. With ~25% prelithiation degree of the anode, LiCoO₂||Si/C pouch cells, featuring an anode specific capacity of ~1300 mAh g^-1 and areal capacity of ~2.3 mAh cm^-2, deliver a remarkable reduction in anode porosity of 14.4% during the initial charge, in contrast to a 5.4% increase in the unprelithiated counterpart. Synchronously, electrode swelling diminishes from over 153% to below 18%. Harnessing this favorable electrochemical-mechanical behavior, the pouch cell delivers a 27.1% improvement in capacity retention after 200 cycles at 0.5 C, outside of a 90.4% increase in cumulative discharge capacity.