Electrochemical Insights into the Capacity Fade of Micron-Sized Silicon Anodes in Li-Ion Batteries and a Mitigation Strategy

The practical deployment of Si anodes in Li-ion batteries is hindered by rapid capacity fade, commonly attributed to large volume changes and associated structural degradation. However, this study identifies the primary degradation mechanism as the formation and accumulation of electrochemically inactive, Li-rich LiaSi alloys, which irreversibly consume active Si and lithium inventory. To mitigate this, a Si–SiOₓ hybrid electrode design is proposed, leveraging a spontaneous internal redox reaction driven by galvanic coupling between phases. In this configuration, the Li-rich LiaSi in the Si phase functions as the negative electrode, while the Li-lean LibSi in the SiOₓ phase acts as the positive electrode. This local galvanic interaction drives the reaction: LiaSi (negative) + LibSi (positive) → Lia−δSi + Lib+δSi, thereby reactivating inactive Li–Si alloys. Electrochemical evaluation of hybrid electrodes with varying Si/SiOₓ weight ratios reveals that a 1:2 ratio optimally balances overall capacity and capacity retention. In full cells with LiNi₀.₈Co₀.₁Mn₀.₁O₂ cathodes, the 1:2 Si–SiOₓ hybrid cell retains 62% of its 5th cycle capacity after 200 cycles at 0.5 C, compared to only 15% for Si-only anodes. This work elucidates a previously unrecognized degradation mechanism and introduces an internal redox strategy to enhance the long-term cycling stability of Si-based anodes.