Solid‐State Prealkylation of Electrode Architectures (SPEAR): Direct Control of Prelithiation Levels in Silicon Anodes and Electrochemical Cycling

ABSTRACT The Solid‐state Prealkylation of Electrode ARchitectures (SPEAR) is different than traditional electrochemical prealkylation processes. Through SPEAR, alkylation is driven by solid‐state diffusion without the simultaneous SEI formation concomitant with polarization. We investigate the prelithiation of 80 wt. % Si‐based anodes to varying amounts (up to Li _1.38 Si) to understand the trade‐off between improved Li capacity and expansion‐induced stress. Through dilatometry, we found that solid‐state lithiation led to filling of the electrode pores through silicon expansion. This swelling changed the SEI formation process and accessibility of the silicon compared to an electrochemically lithiated electrode. Indeed, optimal prelithiation to Li _0.82 Si increases the initial C/3 cycling capacity post‐SEI formation up to 43%, consistent with deeper Si activation through the electrode bulk. Prelithiation and cycling cells prelithiated beyond Li _0.82 Si results in a state of charge (SOC) close to 100% which facilitates parasitic degradation mechanisms and volume expansion of the Si electrode. The results demonstrate a pathway to modify silicon activation/SEI formation to enable high‐energy electrodes.