Li+ crosstalk-driven calendar aging in Si/C composite anodes

Abstract

To meet the demand for high-energy density, lithium-ion batteries (LIBs) with silicon/graphite (Si/C) composite anodes are capturing an increasing share of the market. Contrary to the common belief of low self-discharge, we demonstrate that LIBs with anodes containing 15 wt% Si retain only 77.7% of their capacity after 24 h of storage at room temperature. We quantitatively analyse the impact of Si addition on calendar aging, emphasizing the critical role of Li⁺ crosstalk during storage through a synergy of cross-scale characterizations and multidimensional simulations. Si induces severe side reactions, leading to significant Li loss and potential jump. To balance inter-particle potentials, graphite is compelled to transfer Li⁺ to Si, resulting in additional capacity loss. Theoretical calculations indicate that modifying the Li⁺ crosstalk pathway can suppress self-discharge, for instance, by increasing the Li diffusion coefficient (D_Li⁺) of active materials. To validate this approach, the Si@C material with a higher D_Li⁺ is synthesized, and the improved batteries with anodes containing 15 wt% Si@C retain 93.0% of their capacity after 24 h of storage. This work uncovers the underlying impact of Li⁺ crosstalk on calendar aging, offering new perspectives and guidance for investigating degradation mechanisms in other composite electrode systems.