Compromise between energy density and stability: Proper capacity balancing enables high-performance solid-state batteries

Controlling electro-chemo-mechanical effects remains a key challenge in advancing the development of solid-state batteries (SSBs) with layered Ni-rich cathode and sulfide solid electrolyte. While surface coatings suppress parasitic side reactions, mechanical failure can still be severe, and there is a relative lack of effective strategies to counteract it. To improve the integrity of the cathode, herein we propose a capacity balancing approach with Li 4 Ti 5 O 12 (LTO) as a model anode in thiophosphate-based SSBs. By leveraging the tip-shaped lithiation tail of LTO with a low negative-to-positive balancing (LB), this strategy enables a reduced upper cut-off potential of the LiNi 0.85 Co 0.10 Mn 0.05 O 2 (NCM85) cathode used, thereby mitigating mechanical stress/strain induced by the H2-H3 phase transition. As polarization increases during cycling, the potential is gradually increased, compensating for the loss of capacity without external voltage adjustment. Three-electrode measurements validate the proposed mechanism across several C-rates and corroborate this self-regulating process. Unlike high negative-to-positive balancing (HB), the LB configuration achieves improved structural integrity, reduced charge-transfer resistance, and prolonged cycle life, retaining 80% capacity after about 1300 cycles at 1C, compared to 400 cycles in HB. Overall, this work offers a simple, yet effective strategy for extending the longevity of cathodes for the development of high-performance SSBs.