Promise and Perspectives of Garnet-Based Anode-Free Solid-State Batteries

Abstract

With the rapid advancement of energy storage technologies, lithium-ion batteries (LIBs) based on graphite anodes and liquid organic electrolytes have achieved remarkable progress. Nevertheless, the limited specific capacity of graphite anodes and the safety concerns associated with organic electrolytes hinder further enhancement of LIBs. In pursuit of higher energy density and improved safety, solid-state Li metal batteries (SSLMBs) have drawn significant attention. Furthermore, anode-free solid-state batteries (AFSSBs), as a particularly promising innovation in the field of energy storage, have gained increasing interest in recent years. With increasing research investment and continuous technological optimization, AFSSBs hold great potential for widespread applications including electric vehicles, grid energy storage, and beyond.

Central to AFSSBs, solid-state electrolytes (SSEs) are crucial for achieving high energy density and performance. Among the various SSEs, garnet-type oxide SSEs stand out as one of the most promising systems due to their favorable thermodynamic stability with Li metal anodes, excellent ionic conductivity (∼10^–3 S cm^–1), and wide electrochemical window (>6 V). However, poor solid–solid interface contact and the growth of Li dendrite have led to sluggish interfacial ion and electron transfer kinetics, thereby impeding the commercialization of garnet-based AFSSBs. Although previous reviews have highlighted interfacial challenges and summarized corresponding mitigation strategies, specific case studies remain scarce and a comprehensive understanding of interfacial dynamics in garnet-based AFSSBs has not yet been established.

In this Account, we critically evaluate the unique advantages of garnet-based AFSSBs, including their enhanced energy density and improved safety, compared to conventional battery technologies. Additionally, we summarize current understanding primarily from the perspective of interfacial dynamics, covering Li nucleation and growth mechanisms, interfacial evolution at the garnet/current collector interface during Li deposition, and dendrite growth behaviors, aiming to provide deeper insights into interfacial dynamics. Building upon this, we summarize the major interfacial challenges in garnet-based AFSSBs that significantly hinder the interfacial ion and electron transport. In order to enhance the interfacial charge transfer kinetics, we discuss critical parameters, including the properties of the garnet electrolyte and current collector as well as the interfacial wettability at the Li/garnet and Li/current collector interface. Furthermore, we present an overview of our innovative strategy designed to improve interfacial contact and Li-ion transport between the garnet electrolyte and current collector. Finally, we summarize the progress and provide an outlook for garnet-based AFSSBs, exploring their future improvements and development directions toward practical applications. We believe this Account offers an insightful analysis of recent advancements in garnet-based AFSSBs, contributing significantly to the global energy transition toward sustainable energy solutions.