Rechargeable Mg/Li hybrid ion batteries with Mg²⁺/Li⁺ double-salt electrolytes and safe Mg anodes are a viable option for large-scale energy storage. Nevertheless, achieving the desired reasonable electrochemical performance remains a great challenge due to the capacity limitations of conventional Li-intercalation cathodes. To mitigate this limitation, the 3D oxygenated MXene Ti₃C₂@CoS₂/FeS₂ (denoted as o-Ti₃C₂@CoS₂, o-Ti₃C₂@FeS₂) with both dual-storage mechanism and multidimensional structure to achieve the desirable storage capacity is engineered. Benefiting from the formation of special structure and interfacial chemical bonds Ti–O–Co/Ti–O–Fe, as well as the electronegative o-Ti₃C₂ weaken the Co–S/Fe–S bonds, the o-Ti₃C₂@CoS₂ cathode exhibits superior capacity up to 425 mAh g⁻¹ at 100 mA g⁻¹ and overwhelming advantageous ultra-long life over 2,400 cycles at 500 mA g⁻¹. Simultaneously, the o-Ti₃C₂@FeS₂ also displays a high-rate capability, outstanding cycling stability, and fast diffusion kinetics. Furthermore, the conversion reaction of Mg²⁺/Li⁺ co-intercalation and the charge storage mechanism during cycling are thoroughly clarified by systematic ex-situ characterizations and theoretical computations. This study reveals the influence of MXene electrode structure on the importance of electrochemical performance and provides guidance for the future design of high-performance MXene materials for energy storage applications.

Magnesium (Mg) batteries (MBs), as post-lithium-ion batteries, have received great attention in recent years due to their advantages of high energy density, low cost, and safety insurance. However, the formation of passivation layers on the surface of Mg metal anode and the poor compatibility between Mg metal and conventional electrolytes during charge-discharge cycles seriously affect the performance of MBs. The great possibility of generating Mg dendrites has also caused controversy among researchers. Moreover, the regulation of Mg deposition and the enhancement of battery cycle stability is largely limited by interfacial stability between Mg metal anode and electrolyte. In this review, recent advances in interfacial science and engineering of MBs are summarized and discussed. Special attention is given to interfacial chemistry including passivation layer formation, incompatibilities, ion transport, and dendrite growth. Strategies for building stable electrode/interfaces, such as anode designing and electrolyte modification, construction of artificial solid electrolyte interphase (SEI) layers, and development of solid-state electrolytes to improve interfacial contacts and inhibit Mg dendrite and passivation layer formation, are reviewed. Innovative approaches, representative examples, and challenges in developing high-performance anodes are described in detail. Based on the review of these strategies, reference is provided for future research to improve the performance of MBs, especially in terms of interface and anode design.

Domain boundaries are regarded as the effective active sites for electrochemical energy storage materials due to defects enrichment therein. However, layered double hydroxides (LDHs) tend to grow into single crystalline nano sheets due to their unique two-dimentional (2D) lattice structure. Previously, much efforts were made on the designing hierarchical structure to provide more exposed electroactive sites as well as accelerate the mass transfer. Herein, we demonstrate a strategy to introduce low angle grain boundary (LAGB) in the flakes of Ni/Co layered double hydroxides (NiCo-LDHs). These defect-rich nano flakes were self-assembled into hydrangea-like spheres that further constructed hollow cage structure. Both the formation of hierarchical structure and grain boundaries are interpreted with the synergistic effect of Ni²⁺/Co²⁺ ratio in an “etching-growth” process. The domain boundary defect also results in the preferential formation of oxygen vacancy (Vo). Additionally, density functional theory (DFT) calculation reveals that Co substitution is a critical factor for the formation of adjacent lattice defects, which contributes to the formation of domains boundary. The fabricated battery-type Faradaic NiCo-LDH-2 electrode material exhibits significantly enhanced specific capacitance of 899 C·g⁻¹ at a current density of 1 A·g⁻¹. NiCo-LDH-2//AC asymmetric capacitor shows a maximum energy density of 101.1 Wh·kg⁻¹ at the power density of 1.5 kW·kg⁻¹.

While argyrodite sulfides are getting more and more attention as highly promising solid-state electrolytes (SSEs) for solid batteries, they also suffer from the typical sulfide setbacks such as poor electrochemical compatibility with Li anode and high-voltage cathodes and serious sensitivity to humid air, which hinders their practical applications. Herein, we have devised an effective strategy to overcome these challenging shortcomings through modification of chalcogen chemistry under the guidance of theoretical modeling. The resultant Li_6.25PS₄O_1.25Cl_0.75 delivered excellent electrochemical compatibility with both pure Li anode and high-voltage LiCoO₂ cathode, without compromising the superb ionic conductivity of the pristine sulfide. Furthermore, the current SSE also exhibited highly improved stability to oxygen and humidity, with further advantage being more insulating to electrons. The remarkably enhanced compatibility with electrodes is attributed to in situ formation of helpful electrolyte–electrode interphases. The formation of in situ anode–electrolyte interphase (AEI) enabled stable Li plating/stripping in the Li|Li_6.25PS₄O_1.25Cl_0.75|Li symmetric cells at a high current density up to 1 mA cm⁻² over 200 h and 2 mA cm⁻² for another 100 h. The in situ amorphous nano-film cathode–electrolyte interphase (CEI) facilitated protection of the SSE from decomposition at elevated voltage. Consequently, the synergistic effect of AEI and CEI helped the LiCoO₂|Li_6.25PS₄O_1.25Cl_0.75|Li full-battery cell to achieve markedly better cycling stability than that using the pristine Li₆PS₅Cl as SSE, at a high area loading of the active cathode material (4 mg cm⁻²) in type-2032 coin cells. This work is to add a desirable SSE in the argyrodite sulfide family, so that high-performance solid battery cells could be fabricated without the usual need of strict control of the ambient atmosphere.