Zaifa Wang

Air sensitivity remains a substantial barrier to the commercialization of sodium (Na)-layered oxides (NLOs). This problem has puzzled the community for decades because of the complexity of interactions between air components and their impact on both bulk and surfaces of NLOs. We show here that water vapor plays a pivotal role in initiating destructive acid and oxidative degradations of NLOs only when coupled with carbon dioxide or oxygen, respectively. Quantification analysis revealed that reducing the defined cation competition coefficient (η), which integrates the effects of ionic potential and sodium content, and increasing the particle size can enhance the resistance to acid attack, whereas using high-potential redox couples can eliminate oxidative degradation. These findings elucidate the underlying air deterioration mechanisms and rationalize the design of air-stable NLOs.

The two biggest promises of solid-state lithium (Li) metal batteries (SSLMBs) are the suppression of Li dendrites by solid-state electrolyte (SSE) and the realization of a high-energy-density Li anode. However, LMBs have not met their expectations due to Li dendrite growth causing short-circuiting. In fact, Li dendrites grow even more easily in SSE than in liquid electrolyte, but the reason for this remains unclear. Here we report in situ transmission electron microscopy observations of Li dendrite penetration through SSE and “dead” Li formation dynamics in SSLMBs. We show direct evidence that large electrochemomechanical stress generates cracks in the SSE and drives Li through the SSE directly. We revealed that fresh Li nucleation sites emerged in every discharge cycle, creating new “dead” Li in the following charging cycle and becoming the dominant Coulombic efficiency decay mechanism in SSLMBs. These results indicate that engineering flaw size and reducing electronic conductivity in SSEs are essential to improve the performance of SSLMBs.

Lithium–indium (Li-In) alloys are important anode materials for sulfide-based all-solid-state batteries (ASSBs), but how different Li concentrations in the alloy anodes impact the electrochemical performance of ASSBs remains unexplored. This paper systematically investigates the impact that different Li concentrations in Li-In anodes have on the performance of ASSBs. We show that In with 1 ​wt% Li (LiIn-1) exhibits the best performance for ASSBs among all the tested Li-In anodes. In essence, LiIn-1 not only provides sufficient Li to compensate for first-cycle capacity loss in the anode but also facilitates the formation of a LiIn alloy phase that has the best charge transfer kinetics among all the LixIn alloy phases. The ASSB with a LiIn-1 anode and a LiNi0.8Mn0.1Co0.1O2 cathode reached 3400 cycles at an initial capacity of 125 mAh/g. Remarkably, ASSBs with a high cathode active material (CAM) loading of 36 ​mg/cm2 delivered a high areal capacity of 4.05 mAh/cm2 at high current density (4.8 ​mA/cm2), with a capacity retention of 92% after 740 cycles. At an ultra-high CAM loading of 55.3 ​mg/cm2, the ASSB achieved a stable areal capacity of 8.4 mAh/cm2 at current density of 1.7 ​mA/cm2. These results bring us one step closer to the practical application of ASSBs.