A Two-Parameter Space to Tune Solid Electrolytes for Lithium Dendrite Constriction

A scalable Li-Al-Cl stratified structure for stable all-solid-state lithium metal batteries

Sulfides are promising electrolyte materials for all-solid-state Li metal batteries due to their high ionic conductivity and machinability. However, compatibility issues at the negative electrode/sulfide electrolyte interface hinder their practical implementation. Despite previous studies have proposed considerable strategies to improve the negative electrode/sulfide electrolyte interfacial stability, industrial-scale engineering solutions remain elusive. Here, we introduce a scalable Li-Al-Cl stratified structure, formed through the strain-activated separating behavior of thermodynamically unfavorable Li/Li9Al4 and Li/LiCl interfaces, to stabilize the negative electrode/sulfide electrolyte interface. In the Li-Al-Cl stratified structure, Li9Al4 and LiCl are enriched at the surface to serve as a robust solid electrolyte interphase and are diluted in bulk by Li metal to construct a skeleton. Enabled by its unique structural characteristic, the Li-Al-Cl stratified structure significantly enhances the stability of negative electrode/sulfide electrolyte interface. This work reports a strain-activated phase separation phenomenon and proposes a practical pathway for negative electrode/sulfide electrolyte interface engineering.

Fast Kinetics Design for Solid-State Battery Device

Fast kinetics of solid-state batteries at the device level is not adequately explored to achieve fast charging and discharging. In this work, a leap forward is achieved for fast kinetics in full cells with high cathode loading and areal capacity. This kinetic improvement is achieved by designing a hierarchical structure of electrode composites. In the cathode, the authors' design enables high areal capacities above 3 mAh cm-2 to be stably cycled at high current densities of ≈13-40 mA cm-2, yielding a C-rate from 5 to 10 C. In the anode, the authors' design breaks the common rule of the negative correlation between critical C-rate and the discharge voltage that is observed in most other anodes. The overall design enables the fast cycling of such batteries for over 4000 cycles at room temperature and 5 C charge-rate. The design principles unveiled by this work help to understand critical kinetic processes in battery devices that limit the fast cycling at high cathode loading and speed up the design of high-performance solid-state batteries.

Anharmonic Cation-Anion Coupling Dynamics Assisted Lithium-Ion Diffusion in Sulfide Solid Electrolytes

Sulfide-based lithium superionic conductors often show higher Li-ion conductivity than other types of electrolyte materials. This work unveils a unique Li-ion conductive behavior in these materials through the perspective of anharmonic coupling assisted Li-ion diffusion. Li hopping events can happen simultaneously with various types of lattice dynamics, while only a statistically important synchronization of motions may indicate coupling. This method enables a direct evaluation of the coupling strength between these motions, which more fundamentally decides if a specific type of lattice motion is really anharmonically coupled to the Li hopping event and whether the coupling can facilitate the Li diffusion. By a new ab initio computational approach, this work unveils a unique phenomenon in prototype sulfide electrolytes in comparison with typical halide ones, that Li-ion conduction can be boosted by the anharmonic coupling of low-frequency Li phonon modes with high-frequency anion stretching or flexing phonon modes, rather than the low-frequency rotational modes. The coupling pushes Li ions toward the diffusion channels for reduced diffusion barriers. The result from the lower temperature range (≈0-300 K) of simulation can also be more relevant to the application of solid-state batteries.

Effect of Solvents on a Li10GeP2S12-Based Composite Electrolyte via Solution Method for Solid-State Battery Applications

Using a solution approach to process composite electrolytes for solid-state battery applications is a viable strategy for lowering the thickness of electrolyte layers and boosting the cell energy density. To fully utilize the super ionic conductivity of sulfides, more research about their solvent and binder compatibility is needed. Herein, the allowable solvent polarity is discovered through systematically pairing the solid electrolyte Li₁₀GeP₂S₁₂ (LGPS) with eight types of aprotic solvents. To further consider the influence of oxygen and moisture solvation that is important to practical manufacturing scenario, we also design experiments to flow dry air and N₂, or further mixed with water vapor, through these solvents to unveil their detrimental effects. Finally, a low polar solvent, dimethyl carbonate (DMC), and a previously unfavored commercial polymer, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), are chosen to fabricate a ∼40 μm thick LGPS-based composite electrolyte, giving 2 mS·cm^-1 conductivity. It cycles between lithium/graphite composite electrodes at 0.5 mA·cm^-2 for over 450 h with a capacity of 0.5 mAh·cm^-2 and can withstand a 10-fold current surge.