Interfacial Engineering of Magnesiophilic Coordination Layer Stabilizes Mg Metal Anode.

Rechargeable magnesium batteries (RMBs) are seriously plagued by the direct exposure of the Mg anode to the electrolyte components, leading to spontaneous and electrochemical side reactions and interfacial passivation. Herein, a benign coordination layer is constructed at the Mg/electrolyte interface where aniline with a strong magnesiophilic amine group and high stability to Mg is chosen as representative, which has higher adsorption energy than DME (1,2-dimethoxyethane) and trace water. This Mg coordination environment mitigates side reactions, forming a non-passivating interface consisting of aniline and much fewer by-products after several cycles. Therefore, the Mg symmetrical cell operates with a low overpotential and uniform Mg0 deposition. This interfacial coordination can also be adopted for Mg anode protection in various electrolyte cases of Mg(TFSI)2 electrolyte systems.

Defect Engineering: Can it Mitigate Strong Coulomb Effect of Mg2+ in Cathode Materials for Rechargeable Magnesium Batteries?

Rechargeable magnesium batteries (RMBs) have been considered a promising "post lithium-ion battery" system to meet the rapidly increasing demand of the emerging electric vehicle and grid energy storage market. However, the sluggish diffusion kinetics of bivalent Mg2+ in the host material, related to the strong Coulomb effect between Mg2+ and host anion lattices, hinders their further development toward practical applications. Defect engineering, regarded as an effective strategy to break through the slow migration puzzle, has been validated in various cathode materials for RMBs. In this review, we first thoroughly understand the intrinsic mechanism of Mg2+ diffusion in cathode materials, from which the key factors affecting ion diffusion are further presented. Then, the positive effects of purposely introduced defects, including vacancy and doping, and the corresponding strategies for introducing various defects are discussed. The applications of defect engineering in cathode materials for RMBs with advanced electrochemical properties are also summarized. Finally, the existing challenges and future perspectives of defect engineering in cathode materials for the overall high-performance RMBs are described.

Solvation Sheath Engineering by Multivalent Cations Enabling Multifunctional SEI for Fast-Charging Lithium-Metal Batteries.

With the pursuit of high energy and power density, the fast-charging capability of lithium-metal batteries has progressively been the primary focus of attention. To prevent the formation of lithium dendrites during fast charging, the ideal solid electrolyte interphase should be capable of concurrent fast Li+ transport and uniform nucleation sites; however, its construction in a facile manner remains a challenge. Here, as Al3+ has a higher charge and Al metal is lithiophilic, we tuned the Li+ solvation structure by introducing LiNO3 and aluminum ethoxide together, resulting in the dissolution of LiNO3 and the simultaneous generation of fast ionic conductor and lithiophilic sites. Consequently, our approach facilitated the deposition of lithium metal in a uniform and chunky way, even at a high current density. As a result, the Coulombic efficiency of the Li||Cu cell increased to over 99%. Moreover, the Li||LiFePO4 full cell demonstrated significantly enhanced cycling performance with a remarkable capacity retention of 94.5% at 4 C, far superior to the 46.1% capacity retention observed with the base electrolyte.