MXene materials are a class of two-dimensional transition metal carbides, nitrides or carbon-nitrogen compounds with important application prospects in the fields of energy, optics, biology, sensing, and electromagnetic shielding. Recently, studies have shown that two-dimensional MXene materials prepared by Lewis acid molten salt etching have excellent electrochemical lithium-storage performance, and surface functional groups have a great influence on lithium storage performance. Therefore, this paper systematically studies the effect of heat treatment on the functional group of Ti3C2Tx (T is Br, O functional group) and the electrochemical lithium storage performance. The structural stability and functional group desorption behavior of Ti3C2Tx MXene at different heat treatment temperatures are analyzed, and the electrochemical properties of MXene treated at different temperatures are compared to clarify the role of different functional groups in the lithium storage process. The research results show that heat treatment can desorb the Br functional group, thereby improving the lithium storage performance; when the heat treatment temperature is greater than 300 ℃, the O functional group on the surface may react with Ti3C2Tx MXene to generate TiO2 and contribute additional lithium storage capacity, but when the heat treatment temperature is 900 ℃, the structure of Ti3C2Tx MXene is destroyed, and the lithium storage capacity is greatly reduced. Therefore, heattreating the Ti3C2Tx MXene sample at 700 ℃ can obtain the highest lithium storage capacity, reaching 241.9 mAh·g-1, which is a 32.2% increase in capacity compared with the untreated Ti3C2Tx MXene.