Boosting the energy density of sulfide-based all-solid-state batteries at low temperatures by charging to high voltages up to 6 V

Sulfide electrolyte-based all-solid-state batteries (ASSBs) are potential next generation energy storage technology due to the high ionic conductivity of sulfide electrolytes and potentially improved energy density and safety. However, the performance of ASSBs at/below subzero temperatures has not been explored systematically. Herein, low temperature (LT) performance of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)|Li_9.54Si_1.74P_1.44S_11.7Cl_0.3 (LiSPSCl)|Li₄Ti₅O₁₂ (LTO) ASSBs was investigated. By charging the ASSB to 6 V at −40 °C, a capacity of 100.7 mAh∙g⁻¹ at 20 mA∙g⁻¹ was achieved, which is much higher than that charged to 4.3 V (4.6 mAh∙g⁻¹) at −40 °C. Moreover, atomic resolution microscopy revealed that the NCM811 remained almost intact even after being charged to 6 V. In contrast, NCM811 was entirely destructed when charged to 6 V at room temperature. The sharp difference arises from the large internal charge transfer resistance at LT which requires high voltage to overcome. Nevertheless, such high voltage is not harmful to the active material but beneficial to extracting most energy out of the ASSBs at LT. We also demonstrated that thinner electrolyte is favorable for LT operation of ASSBs due to the reduced ion transfer distance. This work provides new strategies to boost the capacity and energy density of sulfide-based ASSBs at LT for dedicated LT applications.