The development of rechargeable batteries with high‐energy density is critical for future decarbonization of transportation. Anode‐free Li‐ion batteries, using a bare current collector at the anode side without any excess of Li, provide the highest volumetric energy density (>1500 Wh L⁻¹) among all possible cell configurations. Furthermore, elimination of the anode material coating reduces material consumption and greatly simplifies cell production, which in turn lowers costs. Although significant progress has been made recently by the application of modified current collectors, optimized cycling parameters and improved liquid electrolytes, insufficient efficiencies, and dendritic growth during lithium plating lead to poor cycle life of typically less than 100 cycles as well as safety issues. Alternatively, very recent studies have demonstrated anode‐free solid‐state batteries that combine the benefits of high energy anode‐free cell configuration and solid‐state systems with high safety, exceeding 1000 cycles. This review provides an overview of recent developments toward anode‐free solid‐state batteries and highlights the current issues and challenges in this nascent field. It is concluded that, although major challenges remain at the present, the lessons learned in the fields of liquid electrolytes and solid‐state lithium metal batteries can accelerate the development of anode‐free solid‐state batteries of practical relevance.

Zero‐excess Li metal batteries (ZELMBs), in which a Li‐anode is formed in situ during charging, have received much attention in recent years. ZELMBs bear great potential to increase energy density and facilitate battery production, thereby reducing cost as well as material and energy consumption. Practical application of ZELMBs has so far been limited by challenges related to the non‐uniform deposition behavior of Li, leading to inadequate performance and safety concerns. To address these issues, promising approaches have been developed in recent years, including modifications of the current collector, electrolyte, and cycling protocols. While these approaches improve the long‐term stability of ZELMB, they also reduce the energy density by introducing inactive materials into the cell. Herein, critical design criteria for the various optimization approaches in ZELMB research are established. Nominal volumetric and gravimetric energy densities are determined based on the degree of modification. Thresholds are determined for each of the strategies at which the energy density gain of ZELMB vanishes compared to other cell configurations. These findings are compared to literature results to provide guidance for the further development of ZELMB.

Li-In electrodes are widely applied as counter electrodes in fundamental research on Li-metal all-solid-state batteries. It is commonly assumed that the Li-In anode is not rate limiting, i.e. the measurement results are expected to be representative of the investigated electrode of interest. However, this assumption is rarely verified, and some counterexamples were recently demonstrated in literature. Herein, we fabricate Li-In anodes in three different ways and systematically evaluate the electrochemical properties in two- and three-electrode half-cells. The most common method of pressing Li and In metal sheets together during cell assembly resulted in poor homogeneity and low rate performance, which may result in data misinterpretation when applied for investigations on cathodic phenomena. The formation of a Li-poor region on the separator side of the anode is identified as a major kinetic bottleneck. An alternative fabrication of a Li-In powder anode resulted in no kinetic benefits. In contrast, preparing a composite from Li-In powder and sulfide electrolyte powder alleviated the kinetic limitation, resulted in superior rate performance, and minimized the impedance. The results emphasize the need to fabricate optimized Li-In anodes to ensure suitability as a counter electrode in solid-state cells.