Semi-solid alkali metal electrodes enabling high critical current densities in solid electrolyte batteries

Abstract

The need for higher energy density rechargeable batteries has generated interest in alkali metal electrodes paired with solid electrolytes. However, metal penetration and electrolyte fracture at low current densities have emerged as fundamental barriers. Here, we show that for pure metals in the Li-Na-K system, the critical current densities scale inversely to mechanical deformation resistance. Furthermore, we demonstrate two electrode architectures in which the presence of a liquid phase enables high current densities while preserving the shape retention and packaging advantages of solid electrodes. First, biphasic Na-K alloys show K + critical current densities (with K-β″-Al2O3 electrolyte) that exceed 15 mA⋅cm -2 . Second, introducing a wetting interfacial film of Na-K liquid between Li metal and Li6.75La3Zr1.75Ta0.25O12 (LLZTO) solid electrolyte doubles the critical current density and permits cycling at areal capacities exceeding 3.5 mAh⋅cm -2 . These design approaches hold promise for overcoming electro-chemo-mechanical stability issues that have heretofore limited performance of solid-state metal batteries.

From High‐ to Low‐Temperature: The Revival of Sodium‐Beta Alumina for Sodium Solid‐State Batteries

“…This is in line with findings from Park et al. They showed that pure alkali metals have CCDs that scale inversely to their yield stress [136] . The stress exponent value of sodium suggests that the rate‐controlling mechanism is dislocation climb, which was also proposed for lithium [134] .…”

“…The plastic properties with a yield strength between 0.19 MPa and 0.28 MPa at a strain rate of 10 −3 s −1 may explain the rate capabilities of sodium as the negative electrode [135] . The yield strength is 0.41 MPa, when it is taken as one‐third the hardness for ductile metals [136] . The soft nature of sodium assists in maintaining a uniform deposit morphology and interface contact.…”

Suppressing void formation in all-solid-state batteries: the role of interfacial adhesion on alkali metal vacancy transport

“…The use of metallic ≥ alloys in the liquid state, as recently demonstrated for a Li/LLZO system containing a thin liquid Na-K alloy layer, is another promising avenue to achieve both good adhesion and fast Li transport. 42 The strong interaction between alkali metals and metallic substrates is also an important consideration for the selection of current collectors, particularly for alkali metal free designs, in which alkali metal is directly deposited from the SSE onto the current collector (CC). 86 The simple bond breaking model presented in the current study could be further extended to understand the preference for void formation at the Li/SSE versus Li/CC interfaces.…”

“…41 Void formation at the Li/LLZO interface was also recently shown to be suppressed by the introduction of a thin liquid Na-K alloy layer. 42 It should also be highlighted that metal vacancy assisted void formation is not unique to all-solid-state batteries and is a common phenomenon observed other fields including radiation induced voids in bimetallic composites 43 and cavity formation during oxide film growth 44,45 .…”

Linking the Defects to the Formation and Growth of Li Dendrite in All‐Solid‐State Batteries

“…Significant efforts have been devoted to promoting the critical current density (CCD) during Li deposition/dissolution, that is, the maximum working current density of a SE to avoid metal filament penetration. However, practical application shows that the exploitation of present interface design strategies, such as introducing artificial or sacrificial interlayers, [ 9–11 ] enhancing electrode kinetics, [ 12,13 ] and blocking electron mobility, [ 14 ] are far from satisfactory. There are still large gaps between present CCDs and practical requirements (4 mA cm −2 or even higher).…”