PEO-Li21Si5 as a pre-lithiation and structural protection layer for lithium-ion batteries

Abstract

The Li₂₁Si₅ alloy is a promising pre-lithiation material for lithium-ion batteries (LIBs). However, its instability in atmospheric environments and polar solutions limits its applications, particularly in the field of water-based anodes. Herein, a PEO-Li₂₁Si₅ coating strategy was proposed to efficiently replenish lithium and stabilize the electrode structure for LIBs. Polyethylene oxide (PEO) was added to Li₂₁Si₅ to create a PEO-Li₂₁Si₅ pre-lithiation layer, which was coated on the surface of the Si@C anode. HRTEM and XPS tests indicated that the PEO (weakly polar) would react with the interface of the Li₂₁Si₅ to build a stable passivation layer, allowing lithium ions inside the Li₂₁Si₅ to be released during the first cycle, which in turn improved the ICE of the LIBs. Moreover, PEO-Li₂₁Si₅ was able to coat the Si@C particles due to the wettability of the electrolyte to PEO. And it would suppress the displacement caused by the cyclic expansion of the Si, achieving the stability of the electrode structure. This strategy achieved an initial coulombic efficiency (ICE) of over 100% with stable and long-lasting cycles.