Realizing rechargeable magnesium batteries (RMBs) requires cathode materials, into and from which Mg cations can be inserted and extracted near room temperature. Oxide materials are advantageous due to their high electrode potential. However, activating oxide cathodes near room temperature is challenging due to the sluggish Mg diffusion in oxides, which is attributed to the inherently strong affinity between Mg and other constituent elements. Herein, we show that an amorphous oxide cathode containing Ti and Mo enables reversible Mg insertion/extraction near room temperature (60 °C). Li extraction from Li₂Ti_1/3Mo_2/3O₃ induces a phase transformation from a layered rock-salt structure into a composite of a major amorphous oxide with a minor disordered rock-salt oxide. This amorphous oxide yields a reversible capacity of up to ∼160 mAh g^–1 at a current density of 5 mA g^–1. Multimodal analyses reveal that the major amorphous phase accommodates Mg by means of the redox reaction of the constituent Mo^4+/6+. This amorphous phase can be further classified into Mg-poor and Mg-rich amorphous phases, whose phase fractions change during charging and discharging, i.e., the two-phase reaction between the distinct amorphous phases. The large free volume introduced by delithiation, i.e., the remnants of the Li vacancies, in the amorphous structure is considered to flatten the energy landscape for Mg hopping, facilitating Mg diffusion and eventually enabling operation at a relatively low temperature of 60 °C. The present study provides a new opportunity for utilizing amorphous phases for designing novel cathode materials for RMBs.

中文翻译：

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利用脱锂诱导无定形氧化物作为可充电镁电池的阴极

实现可充电镁电池（RMB）需要阴极材料，镁阳离子可以在接近室温的温度下插入和脱出。氧化物材料由于其高电极电势而具有优势。然而，由于镁在氧化物中的扩散缓慢，在室温附近激活氧化物阴极具有挑战性，这归因于镁和其他组成元素之间固有的强亲和力。在此，我们表明，含有 Ti 和 Mo 的非晶氧化物阴极能够在室温（60 °C）附近实现可逆的 Mg 插入/脱出。从Li ₂ Ti _1/3 Mo _2/3 O ₃中提取Li引起从层状岩盐结构到主要无定形氧化物与次要无序岩盐氧化物的复合物的相变。这种非晶氧化物在电流密度为 5 mA g ^{–1时产生高达 ∼160 mAh g –1}的可逆容量。多峰分析表明，主要非晶相通过成分Mo ^4+/6+的氧化还原反应容纳Mg 。该非晶相可进一步分为贫镁非晶相和富镁非晶相，其相分数在充电和放电过程中发生变化，即不同非晶相之间的两相反应。脱锂引入的大自由体积，即非晶结构中锂空位的残余物，被认为可以使镁跳跃的能量景观变得平坦，促进镁扩散并最终能够在 60 °C 的相对较低温度下运行。本研究为利用非晶相设计新型人民币正极材料提供了新的机会。