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.

Li_xCoO₂ and Li_xNiO₂ (0.5 < x < 1) are used as prototype cathode materials in lithium ion batteries. Both systems show degradation and fatigue when used as cathode material during electrochemical cycling. In order to analyze the change of the structure and the electronic structure of Li_xCoO₂ and Li_xNiO₂ as a function of Li content x in detail, we have performed X-ray diffraction studies, photoelectron spectroscopy (PES) investigations and band structure calculations for a series of compounds Li_x(Co,Ni)O₂ (0 < x⩽ 1). The calculated density of states (DOS) are weighted by theoretical photoionization cross sections and compared with the DOS gained from the PES experiments. Consistently, the experimental and calculated DOS show a broadening of the Co/Ni 3d states upon lithium de-intercalation. The change of the shape of the experimental PES curves with decreasing lithium concentration can be interpreted from the calculated partial DOS as an increasing energetic overlap of the Co/Ni 3d and O 2p states and a change in the orbital overlap of Co/Ni and O wave functions.

Increasing the fast charging capabilities and the driving range of electric vehicles are major goals in Li‐ion battery research to accelerate mass market adoption and reduce greenhouse gas emissions. This requires a fundamental understanding of the performance limiting factors to enable a knowledge‐based optimization of materials, electrode design and cell architectures. Herein, electrochemical fundamentals and recent insights concerning rate performance limitations of Li‐ion batteries at the electrode level are reviewed and discussed from charge and mass transport perspectives. The application of straightforward analytical and semi‐empirical models is highlighted in view of understanding specific performance limiting factors of electrodes for Li‐ion batteries based on experimental investigations. The summarized insights are discussed regarding promising improvement strategies to approach the practical limits of liquid electrolyte‐based Li‐ion batteries.

The stability of the valence state of the 3d transition metal ions and the stoichiometry of LiMO₂ (M = Co, Ni, Mn) layered oxides at the surface–electrolyte interface plays a crucial role in energy storage applications. The surface oxidation/reduction of the cations caused by the contact of the solids to air or to the electrolyte results in the blocking of the Li-transport through the interface that leads to the fast batteries deterioration. The influence of the end-of-charge voltage on the chemical composition and the oxidation state of 3d transition metal ions, as well as the stability of the solid–electrolyte interface formed during the electrochemical Li-deintercalation/intercalation of the LiCoO₂ and Li(Ni,Mn,Co)O₂, have been investigated by X-ray photoelectron spectroscopy. While the chemical composition of the solid–electrolyte interface is similar for both layered oxide surfaces, the electrochemical cycling to some critical voltage values leads to the disappearance of the interface. By the analysis of the shape of the 2p and 3s photoelectron emissions we show that the formation of the solid–electrolyte interface layer correlates with the partial reduction of the trivalent Co ions at the electrolyte–LiCoO₂ interface and the amount of the Co²⁺ ions is increased as the solid–electrolyte interface vanishes. In contrast, the Mn⁴⁺, Co³⁺ and Ni²⁺ ions of the Li(Ni,Mn,Co)O₂ are stable at the interface under the electrochemical cycling to higher end-of-charge voltage. A correlation between deterioration of the LiCoO₂ and Li(Ni,Mn,Co)O₂ batteries and the change of electronic structure at the surface/interface after the electrochemical cycling has been found. The dissolution of the solid–electrolyte interface layer might be the reason for the fast deterioration of the Li-ion batteries.