The carrier alternation from Li atoms to Li vacancies leads to interface instability in solid-state lithium alloy anodes.

In the pursuit of energy-dense all-solid-state lithium batteries (ASSBs), Li-rich Mn-based oxide (LRMO) cathodes provide an exciting path forward with unexpectedly high capacity, low cost, and excellent processibility. However, the cause for LRMO|solid electrolyte interfacial degradation remains a mystery, hindering the application of LRMO-based ASSBs. Here, we first reveal that the surface oxygen instability of LRMO is the driving force for interfacial degradation, which severely blocks the interfacial Li-ion transport and triggers fast battery failure. By replacing the charge compensation of surface oxygen with sulfite, the overoxidation and interfacial degradation can be effectively prevented, therefore achieving a high specific capacity (~248 mAh g ⁻¹ , 1.1 mAh cm ⁻² ; ~225 mAh g ⁻¹ , 2.9 mAh cm ⁻² ) and excellent long-term cycling stability of >300 cycles with 81.2% capacity retention at room temperature. These findings emphasize the importance of irreversible anion reactions in interfacial failure and provide fresh insights into constructing stable interfaces in LRMO-based ASSBs.

The fundamental understanding of the elusive evolution behavior of the buried solid-solid interfaces is the major barrier to exploring solid-state electrochemical devices. Here, we uncover the interfacial void evolution principles in solid-state batteries, build a solid-state void nucleation and growth model, and make an analogy with the bubble formation in liquid phases. In solid-state lithium metal batteries, the lithium stripping–induced interfacial void formation determines the morphological instabilities that result in battery failure. The void-induced contact loss processes are quantified in a phase diagram under wide current densities ranging from 1.0 to 10.0 milliamperes per square centimeter by rational electrochemistry calculations. The in situ–visualized morphological evolutions reveal the microscopic features of void defects under different stripping circumstances. The electrochemical-morphological relationship helps to elucidate the current density– and areal capacity–dependent void nucleation and growth mechanisms, which affords fresh insights on understanding and designing solid-solid interfaces for advanced solid-state batteries.

Lithium–sulfur (Li–S) battery is identified as one of the most promising next‐generation energy storage systems due to its ultra‐high theoretical energy density up to 2600 Wh kg⁻¹. However, Li metal anode suffers from dramatic volume change during cycling, continuous corrosion by polysulfide electrolyte, and dendrite formation, rendering limited cycling lifespan. Considering Li metal anode as a double‐edged sword that contributes to ultrahigh energy density as well as limited cycling lifespan, it is necessary to evaluate Li‐based alloy as anode materials to substitute Li metal for high‐performance Li–S batteries. In this contribution, the authors systematically evaluate the potential and feasibility of using Li metal or Li‐based alloys to construct Li–S batteries with an actual energy density of 500 Wh kg⁻¹. A quantitative analysis method is proposed by evaluating the required amount of electrolyte for a targeted energy density. Based on a three‐level (ideal material level, practical electrode level, and pouch cell level) analysis, highly lithiated lithium–magnesium (Li–Mg) alloy is capable to achieve 500 Wh kg⁻¹ Li–S batteries besides Li metal. Accordingly, research on Li–Mg and other Li‐based alloys are reviewed to inspire a promising pathway to realize high‐energy‐density and long‐cycling Li–S batteries.