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.

Sodium (Na) metal batteries (SMBs) using Na anode are potential “beyond lithium” electrochemical technology for future energy storage applications. However, uncontrollable Na dendrite growth has plagued the application of SMBs. Understanding Na deposition mechanisms, particularly the early stage of Na deposition kinetics, is critical to enable the SMBs. In this context, we conducted in situ observations of the early stage of electrochemical Na deposition. We revealed an important electrochemical Ostwald ripening (EOR) phenomenon which dictated the early stage of Na deposition. Namely, small Na nanocrystals were nucleated randomly, which then grew. During growth, smaller Na nanocrystals were contained by bigger ones via EOR. We observed two types of EOR with one involving only electrochemical reaction driven by electrochemical potential difference between bigger and smaller nanocrystals; while the other being dominated by mass transport governed by surface energy minimization. The results provide new understanding to the Na deposition mechanism, which may be useful for the development of SMB for energy storage applications.

Rechargeable lithium-carbon dioxide (Li-CO₂) batteries have attracted much attention due to their high theoretical energy densities and capture of CO₂. However, the electrochemical reaction mechanisms of rechargeable Li-CO₂ batteries, particularly the decomposition mechanisms of the discharge product Li₂CO₃ are still unclear, impeding their practical applications. Exploring electrochemistry of Li₂CO₃ is critical for improving the performance of Li-CO₂ batteries. Herein, in-situ environmental transmission electron microscopy (ETEM) technique was used to study electrochemistry of Li₂CO₃ in Li-CO₂ batteries during discharge and charge processes. During discharge, Li₂CO₃ was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes (CNTs) and Ag nanowires (Ag NWs), but it was hard to decompose during charging at room temperature. To promote the decomposition of Li₂CO₃, the charge reactions were conducted at high temperatures, during which Li₂CO₃ was decomposed to lithium with release of gases. Density functional theory (DFT) calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li₂CO₃. This study not only provides a fundamental understanding to the high temperature Li-CO₂ nanobatteries, but also offers a valid technique, i.e., discharging/charging at high temperatures, to improve the cyclability of Li-CO₂ batteries for energy storage applications.