Silicon-Hydroborate Composite Electrodes with High Interfacial Stability for NMC811/Silicon Solid-State Batteries

Abstract

Hydroborate solid electrolytes are compatible with high-voltage LiNi_0.8 Mn_0.1 Co_0.1O₂ (NMC811) positive electrodes, but their integration with high-capacity negative electrodes at industry-relevant areal capacities remains a challenge. Herein, we demonstrate a zero-lithium-excess NMC811 hydroborate solid-state battery achieving a high areal capacity of 3 mAh cm^-2 at room temperature, enabled by a 3D silicon composite negative electrode. The Li₃(CB₁₁H₁₂)₂(CB₉H₁₀) electrolyte is kinetically sufficiently stable to keep resistance growth low at ~0.3 Ω cm² h^-0.5 in contact with lithiated nanosized silicon particles and carbon fibers in 3D composite electrodes, resulting in high cycling stability. While 2D silicon electrodes require impractically high stack pressure of 50 MPa to avoid contact loss upon delithiation, we demonstrate that silicon-hydroborate 3D composite electrodes can be operated under moderate stack pressures of 8 MPa. Our findings demonstrate the feasibility of silicon-based hydroborate solid-state batteries with industry-relevant areal capacity operated under moderate stack pressure.