Interface Design of Solid–Liquid Hybrid Electrodes for High‐Energy‐Density Flexible Lithium‐Ion Batteries

The silicon microparticles (SiMPs) offer a promising solution for high-energy-density lithium-ion battery systems. However, the inevitable volume expansion (>300%) of SiMPs during alloying often leads to particle breakage, interface rupture, and electrode separation, resulting in rapid capacity decay. Herein, an effective strategy is proposed for designing a novel solid-liquid hybrid electrode (Si@EGaSn) for high-energy-density flexible lithium-ion batteries. The Si@EGaSn electrode has a liquid-phase top layer containing SiMPs and a solid-phase copper gallium alloy bottom layer. The top layer can not only electrically connect the fractured SiMPs, but also form a stable solid electrolyte interface during alloying processes. The bottom layer can firmly adhere the electrodes to the current collector. Consequently, the optimal Si@EGaSn electrode delivers a highly reversible capacity of 767.1 mAh g^-1 at 0.5 A g^-1 and a high capacity retention of >99% during 200 cycles. After loading the electrode into metallic textiles, the assembled high-voltage pouch cell of NCM811//Si@EGaSn shows a high areal capacity of 3.2 mAh cm^-2, high volumetric energy density of 500 Wh L^-1 and negligible capacity decay during 3000 flexing cycles at a small bending radius of 4.0 mm. This work provides a new electrode design approach to achieve high-energy-density flexible lithium-ion batteries.