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MXenes are a class of two-dimensional inorganic materials comprising transition-metal carbides, nitrides, or carbonitrides of several atomic layers thick. Their general formula is (Mn+1XnTx), where M is a transition metal, such as Ti, n is the number of atomic layers, X is carbon and/or nitrogen, and Tx is the functional group introduced in the reaction process, such as OH, H, or F. They are obtained from the MAX precursor (Mn+1AXn, where A is a group of 13 or 14 elements, such as Al and Si). In 2011, Gogotsi, Barsoum, et al. first reported the synthesis of Ti3C2Tx by selective etching of the Al layer using a Ti3AlC2 MAX phase precursor impregnated with HF solution. The advantageous properties of MXenes, such as large specific surface area, fast charge–discharge performance, and small volume change, have made them attractive for lithium-ion battery anode materials, as first reported by the group Simon and Gogotsi in 2012. Since then, much attention has been paid to MXenes. Researchers hope to use MXenes for lithium-ion battery anode materials with high capacity, high safety, and improved energy density and battery life. However, a multilayer MXene material will collapse or accumulate during the preparation process, resulting in a large reduction in the contact area, thus reducing the electron and ion transport capacity of the MXene material perpendicular to the layer structure. Hence, MXenes are usually combined with other materials to improve the obtained structure, expand the layer spacing, and help enhance their electrochemical properties. This paper reviews the approaches to improving the electrochemical properties of MXenes by doping with transition-metal oxides, transition-metal sulfides, and silicon, as well as the scheme to achieve a stable and dendrite-free metal anode by using MXenes and high-capacity anode materials. Last, future challenges faced by MXenes as anode materials for lithium-ion batteries are analyzed and prospected. |
