A highly reversible, low-strain Mg-ion insertion anode material for rechargeable Mg-ion batteries

Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li4Ti5O12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g−1. This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries. Yu-Guo Guo at the Institute of Chemistry, Chinese Academy of Sciences and colleagues from China and the USA have developed a new battery material based on magnesium ions. Rechargeable lithium-ion batteries are ubiquitous in modern electronic devices. To increase the storage capacity of rechargeable batteries even further, however, the number of electrical charges per ion must be increased. This can be achieved by replacing lithium ions, which have one free electron, with a magnesium ion, which has two. The researchers discovered that Li4Ti5O12 is particularly suitable as a battery electrode for magnesium ions as it easily allows their storage between the crystal layers of the material. They also verified that these ions can be easily moved in and out of the crystal during charging and use of the battery, enhancing the prospects for practical magnesium-ion batteries. Spinel Li4Ti5O12 nanoparticle has been demonstrated as an Mg-ion insertion anode material with ‘zero-strain’ characteristics (only ∼0.8% volume change) during Mg-ion insertion/extraction cycles, and a remarkable capacity retention capability of >95% after 500 cycles.