Determining the Role of Ion Transport Throughput in Solid‐State Lithium Batteries

Solid-state lithium metal batteries (SSLMBs) are promising candidates for high-energy-density energy storage devices. However, there still lacks an evaluation criterion to estimate real research status and compare overall performance of the developed SSLMBs. Herein, we propose a comprehensive descriptor, Li⁺ transport throughput ( φ L i + φ _ L i⁺ ), to estimate actual conditions and output performance of the SSLMBs. The φ L i + φ _ L i⁺ is defined as molar number of Li⁺ passing through unit area of electrode/electrolyte interface in an hour (mol m⁻² h⁻¹ ) during cycling of battery, which is a quantizable value after taking complex aspects including cycle rate, electrode areal capacity and polarization into account. On this basis, we evaluate the φ L i + φ _ L i⁺ of liquid, quasi-solid-state and solid-state batteries, and highlight three key aspects to achieve high value of φ L i + φ _ L i⁺ via building highly efficient cross-phase, cross-gap and cross-interface ion transport in the solid-state battery systems. We believe that the new concept of φ L i + φ _ L i⁺ provides milestone guidelines towards large-scale commercialization of SSLMBs.