Rechargeable lithium metal batteries (LMBs) have attracted wide attention for future electric vehicles and next‐generation energy storage because of their exceptionally high specific energy density. Recently, the development of electrode materials for LMBs has been extensively discussed and reviewed in the literature, but there have been very few reports that systematically review the status and progress of electrolytes for such applications. Actually, the viability of practical LMBs critically depends on the development of suitable liquid electrolytes due to the high reactivity of Li metals toward most solvents. This paper provides a systematic summary of the background and recent advances of the electrolytes for LMBs with an emphasis on the thermodynamic and kinetic stabilities at the interfaces. In addition, the emerging advanced characterization techniques for understanding the electrolyte–electrode interfaces are surveyed. Finally, a perspective for future directions is provided.

Lithium metal is an ideal electrode material for future rechargeable lithium metal batteries. However, the widespread deployment of metallic lithium anode is significantly hindered by its dendritic growth and low Coulombic efficiency, especially in ester solvents. Herein, by rationally manipulating the electrolyte solvation structure with a high donor number solvent, enhancement of the solubility of lithium nitrate in an ester‐based electrolyte is successfully demonstrated, which enables high‐voltage lithium metal batteries. Remarkably, the electrolyte with a high concentration of LiNO3 additive presents an excellent Coulombic efficiency up to 98.8 % during stable galvanostatic lithium plating/stripping cycles. A full‐cell lithium metal battery with a lithium nickel manganese cobalt oxide cathode exhibits a stable cycling performance showing limited capacity decay. This approach provides an effective electrolyte manipulation strategy to develop high‐voltage lithium metal batteries.

Calcium‐metal batteries (CMBs) provide a promising option for high‐energy and cost‐effective energy‐storage technology beyond the current state‐of‐the‐art lithium‐ion batteries. Nevertheless, the development of room‐temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium‐metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium‐metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium‐metal anode, accompanied by a very stable long‐term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs.

The surface morphology of Li metal anode significantly dictates the stability and safety of Li metal batteries. The key parameters for morphological control and causes for dendritic growth of Li anode are still not clear. Although the plating kinetics is generally believed to be associated with Li growth habits, the detailed models are still not well defined. In this work, the temperature effect on the stability and efficiency of Li anode is systematically investigated in a variety of electrolyte composition for Li metal batteries. A dendrite‐free growth mechanism is observed, and a high Coulombic efficiency up to ≈99.4% in Li||Cu cells is achieved by tuning the deposition behaviors at elevated temperatures. The results provide insights into the Li dendrite growth mechanism and general principle for developing stable Li anode.

ion batteries (LIBs), which significantly hinders the technology adoption rate. The energy density of SIBs is greatly limited by the anode material, [10] for example, the conventional anode, hard carbon, can only provide a specific capacity of ≈250 mAh g −1 . Sodium metal is an ideal alternative of the anode materials for SIBs due to its relatively high theoretical specific capacity (1166 mAh g −1 ) and low redox potential (−2.71 V vs the standard hydrogen electrode). [11][12][13][14][15] Typical sodium metal batteries, such as sodium-sulfur and sodium-oxygen batteries, have ultrahigh theoretical energy densities of 1274 and 1605 Wh kg −1 , respectively, which are 10 times higher than that of the SIBs (120 Wh kg −1 ). [16][17][18][19][20][21][22][23] Applications of Li metal anode have been hindered by the scarcity and uneven distribution of Li resource. Benefiting from the wide distribution of Na resource, it is possible to design high power, high energy density and low-cost sodium-based batteries by "enhanced cathode materials," [24] "electrolyte design" [25] and sodium metal anode protection.Although the sodium metal anode holds promising potential for providing high energy density, its practical applications are encountered with several essential challenges, such as dendritic growth and side reactions, thus leading to serious safety issues and short battery life. To overcome these problems, tremendous efforts have been devoted to suppressing the sodium dendrite growth and enhancing the Coulombic efficiency (CE) of sodium metal anode. A variety of strategies have been proposed to improve the reversibility and cycling stability, including the utilization of 3D current collectors, manipulation of artificial solid-electrolyte interphase (SEI) and development of stable electrolyte solvation structure. For example, the 3D metal skeletons, [26,27] carbon-based materials, [28][29][30][31][32] and pillared Mxene [33] have been used as current collectors for sodium metal anode, which successfully change the sodium plating/stripping behaviors and achieve better cycling performances by reducing the local current densities at the electrode surface. However, the direct consequences for using 3D current collectors include the introduction of voids and additional weight of inactive materials and the sacrifice of the first cycle CE caused by increased anode surface area. The utilization of artificial SEI is another common strategy to physically suppress the Na dendrite and increase the CE of sodium anode. [34][35][36][37][38][39] Nevertheless, it is still challenging to design suitable artificial SEI because of the large size of the Sodium metal batteries have attracted rapidly rising attention due to their low cost and high energy densities. However, the instability and low efficiency of metallic sodium anodes pose significant concerns for their practical applications. Here a highly stable sodium metal anode enabled by an etherbased electrolyte is reported, which exhibits a long-term stable cycling up to 400 cycles and achie...

Transition metal sulfides hold promising potentials as Li‐free conversion‐type cathode materials for high energy density lithium metal batteries. However, the practical deployment of these materials is hampered by their poor rate capability and short cycling life. In this work, the authors take the advantage of hollow structure of CuS nanoboxes to accommodate the volume expansion and facilitate the ion diffusion during discharge–charge processes. As a result, the hollow CuS nanoboxes achieve excellent rate performance (≈371 mAh g−1 at 20 C) and ultra‐long cycle life (>1000 cycles). The structure and valence evolution of the CuS nanobox cathode are identified by scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. Furthermore, the lithium storage mechanism is revealed by galvanostatic intermittent titration technique and operando Raman spectroscopy for the initial charge–discharge process and the following reversible processes. These results suggest that the hollow CuS nanobox material is a promising candidate as a low‐cost Li‐free cathode material for high‐rate and long‐life lithium metal batteries.

Lithium (Li) metal is regarded as the ultimate anode for next-generation Li-ion batteries due to its highest specific capacity and lowest electrochemical potential. However, the Li metal anode has limitations, including virtually infinite volume change, nonuniform Li deposition, and an unstable electrode-electrolyte interface, which lead to rapid capacity degradation and poor cycling stability, significantly hindering its practical application. To address these issues, intensive efforts have been devoted toward accommodating and guiding Li deposition as well as stabilizing the interface using various carbon materials, which have demonstrated excellent effectiveness, benefiting from their vast variety and excellent tunability of the structure-property relationship. This review is intended as a guide through the fundamental Carbon Energy.

In recent years, due to its great promise in boosting the energy density of lithium batteries for future energy storage, research on the Li metal anode, as an alternative to the graphite anode in Li‐ion batteries, has gained significant momentum. However, the practical use of Li metal anodes has been plagued by unstable Li (re)deposition and poor cyclability. Although tremendous efforts have been devoted to the stabilization of Li metal anodes, the mechanisms of electrochemical (re‐)deposition/dissolution of Li and solid‐electrolyte‐interphase (SEI) formation remain elusive. This article highlights the recent mechanistic understandings and observations of Li deposition/dissolution and SEI formation achieved from advanced characterization techniques and simulation methods, and discusses major limitations and open questions in these processes. In particular, the authors provide their perspectives on advanced and emerging/potential methods for obtaining new insights into these questions. In addition, they give an outlook into cutting‐edge interdisciplinary research topics for Li metal anodes. It pushes beyond the current knowledge and is expected to accelerate development toward a more in‐depth and comprehensive understanding, in order to guide future research on Li metal anodes toward practical application.