Nanostructured Si−C Composites As High‐Capacity Anode Material For All‐Solid‐State Lithium‐Ion Batteries**

Abstract Silicon carbon void structures (Si−C) are attractive anode materials for lithium‐ion batteries to cope with the volume changes of silicon during cycling. In this study, Si−C with varying Si contents (28–37 %) are evaluated in all‐solid‐state batteries (ASSBs) for the first time. The carbon matrix enables enhanced performance and lifetime of the Si−C composites compared to bare silicon nanoparticles in half‐cells even at high loadings of up to 7.4 mAh cm −2 . In full cells with nickel‐rich NCM (LiNi 0.9 Co 0.05 Mn 0.05 O 2 , 210 mAh g −1 ), kinetic limitations in the anode lead to a lowered voltage plateau compared to NCM half‐cells. The solid electrolyte (Li 6 PS 5 Cl, 3 mS cm −1 ) does not penetrate the Si−C void structure resulting in less side reactions and higher initial coulombic efficiency compared to a liquid electrolyte (72.7 % vs. 31.0 %). Investigating the influence of balancing of full cells using 3‐electrode ASSB cells revealed a higher delithiation of the cathode as a result of the higher cut‐off voltage of the anode at high n/p ratios. During galvanostatic cycling, full cells with either a low or rather high overbalancing of the anode showed the highest capacity retention of up to 87.7 % after 50 cycles.