Fast cycling of lithium metal in solid-state batteries by constriction-susceptible anode materials.

Interface reaction between lithium (Li) and materials at the anode is not well understood in an all-solid environment. This paper unveils a new phenomenon of constriction susceptibility for materials at such an interface, the utilization of which helps facilitate the design of an active three-dimensional scaffold to host rapid plating and stripping of a significant amount of a thick Li metal layer. Here we focus on the well-known anode material silicon (Si) to demonstrate that, rather than strong Li-Si alloying at the conventional solid-liquid interface, the lithiation reaction of micrometre-sized Si can be significantly constricted at the solid-solid interface so that it occurs only at thin surface sites of Si particles due to a reaction-induced, diffusion-limiting process. The dynamic interaction between surface lithiation and Li plating of a family of anode materials, as predicted by our constrained ensemble computational approach and represented by Si, silver (Ag) and alloys of magnesium (Mg), can thus more homogeneously distribute current densities for the rapid cycling of Li metal at high areal capacity, which is important in regard to solid-state battery application.

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.

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

Li dendrite penetration, and associated microcrack propagation, at high current densities is one main challenge to the stable cycling of solid-state batteries. The interfacial decomposition reaction between Li dendrite and a solid electrolyte was recently used to suppress Li dendrite penetration through a novel effect of "dynamic stability". Here we use a two-parameter space to classify electrolytes and propose that the effect may require the electrolyte to occupy a certain region in the space, with the principle of delicately balancing the two property metrics of a sufficient decomposition energy with the Li metal and a low critical mechanical modulus. Furthermore, in our computational prediction prepared using a combination of high-throughput computation and machine learning, we show that the positions of electrolytes in such a space can be controlled by the chemical composition of the electrolyte; the compositions can also be attained by experimental synthesis using core-shell microstructures. The designed electrolytes following this principle further demonstrate stable long cycling from 10 000 to 20 000 cycles at high current densities of 8.6-30 mA/cm2 in solid-state batteries, while in contrast the control electrolyte with a nonideal position in the two-parameter space showed a capacity decay that was faster by at least an order of magnitude due to Li dendrite penetration.

A dynamic stability design strategy for lithium metal solid state batteries.

A solid-state electrolyte is expected to suppress lithium (Li) dendrite penetration with high mechanical strength1-4. However, in practice it still remains challenging to realise a lithium metal anode for batteries, because micrometre- or submicrometre-sized cracks in ceramic pellets can frequently be generated during battery assembly or long-time cycling3,5. Once cracks form, lithium dendrite penetration is inevitable6,7. Here we describe a solid-state battery design with a hierarchy of interface stabilities (to lithium metal responses), to achieve an ultrahigh current density with no lithium dendrite penetration. Our multilayer design has the structure of a less-stable electrolyte sandwiched between more-stable solid electrolytes, which prevents any lithium dendrite growth through well localized decompositions in the less stable electrolyte layer. A mechanism analogous to the expansion screw effect is proposed, whereby any cracks are filled by dynamically generated decompositions that are also well constrained, probably by the 'anchoring' effect the decompositions induce. The cycling performance of the lithium metal anode paired with a LiNi0.8Mn0.1Co0.1O2 cathode is very stable, with an 82 per cent capacity retention after 10,000 cycles at a 20C rate (8.6 milliamps per centimetre squared) and 81.3 per cent capacity retention after 2,000 cycles at a 1.5C rate (0.64 milliamps per centimetre squared). Our design also enables a specific power of 110.6 kilowatts per kilogram and specific energy up to 631.1 watt hours per kilogram at the micrometre-sized cathode material level.

Strain-Stabilized Ceramic-Sulfide Electrolytes.

Ceramic-sulfide solid electrolytes are a promising material system for enabling solid-state batteries. However, one challenge that remains is the discrepancy in the reported electrochemical stability. Recent work has suggested that it may be due to the sensitivity of ceramic sulfides to mechanically induced stability. Small changes in ceramic-sulfide microstructure, for example, have been shown to cause substantial differences in the electrochemical stability. In this work, a rigorous theoretical framework is constructed to enable the simulation of such mechanically induced stability for a generalized constraint mechanism. It is shown that the susceptibility for voltage widening in ceramic sulfides can be significantly influenced by the choice of different decay morphology models. This results in a less intrusive microstructure requirement for improved stability, which stems from the tendency of sulfides to decay via inclusions rather than homogeneously. This predicted decay morphology is experimentally confirmed. Li10 GeP2 S12 is stabilized by a thin amorphous shell, which prior models predict is too thin for stabilization. The generality of this framework is discussed in light of stabilization methods beyond microstructure, such as on the battery cell level. The relation of our picture to the observed lithium metal formation in ceramic sulfides is also discussed.

Advanced sulfide solid electrolyte by core-shell structural design.

Solid electrolyte is critical to next-generation solid-state lithium-ion batteries with high energy density and improved safety. Sulfide solid electrolytes show some unique properties, such as the high ionic conductivity and low mechanical stiffness. Here we show that the electrochemical stability window of sulfide electrolytes can be improved by controlling synthesis parameters and the consequent core-shell microstructural compositions. This results in a stability window of 0.7-3.1 V and quasi-stability window of up to 5 V for Li-Si-P-S sulfide electrolytes with high Si composition in the shell, a window much larger than the previously predicted one of 1.7-2.1 V. Theoretical and computational work explains this improved voltage window in terms of volume constriction, which resists the decomposition accompanying expansion of the solid electrolyte. It is shown that in the limiting case of a core-shell morphology that imposes a constant volume constraint on the electrolyte, the stability window can be further opened up. Advanced strategies to design the next-generation sulfide solid electrolytes are also discussed based on our understanding.