# Universal Chemomechanical Design Rules for Solid-Ion Conductors to Prevent Dendrite Formation in Lithium Metal Batteries

## TL;DR

This paper introduces a universal chemomechanical framework for designing solid-ion conductors that can suppress dendrite formation in lithium metal batteries by either pressure-driven or density-driven mechanisms, with a focus on novel soft, low molar volume SICs.

## Contribution

It establishes a universal chemomechanical paradigm to design SICs that can either block dendrites or suppress them through density control, revealing a new regime with soft, low molar volume materials.

## Key findings

- SICs can be tailored for pressure-driven or density-driven dendrite suppression.
- Soft SICs with low molar volume effectively promote uniform lithium plating.
- Cell cycle-life is extended using these SICs with high-voltage cathodes.

## Abstract

Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. While high shear modulus solid-ion conductors (SICs) have been prioritized to resolve pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SICs mechanical properties and partial molar volume of Li+ relative to those of the lithium anode on plating outcomes. Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly soft, as is typical of polymer electrolytes, but feature atypically low Li+ partial molar volume, more reminiscent of hard ceramics. Li plating mediated by these SICs is uniform, as revealed using synchrotron hard x-ray microtomography. As a result, cell cycle-life is extended, even when assembled with thin Li anodes and high-voltage NMC-622 cathodes, where 20 percent of the Li inventory is reversibly cycled.

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Source: https://tomesphere.com/paper/1901.04910