Two-dimensional transition metal dichalcogenides (TMDCs) have attracted much attention due to their unique "sandwich" structure. As a typical two-dimensional layered transition metal sulfide, MoS₂ has a layered structure composed of S-Mo-S triple layers with covalent bonds. The atoms in MoS₂ layer are combined by covalent bonds, while the interaction between layers depends on the van der Waals forces. This special S—Mo—S layered structure is conductive to the rapid diffusion of lithium ions, and the intercalation of lithium ions between layers during a charging and discharging process does not affect the volume change. However, MoS₂ has some problems such as poor conductivity and easy decomposition of the structure, severely hindering the development of MoS₂ electrode materials. This paper was to composite a liquid metal (LM) with MoS₂ materials. Among them, LM has an excellent ion and electron conductivity, which can improve the conductivity of MoS₂. The moderate interlayer distance of MoS₂ can restrict LM droplets within the framework, thereby allowing LM to better exert its self-healing properties for the preparation of negative electrode materials with self-healing capabilities.

400 mg of LM was firstly added into 50 mL of N, N-Dimethylformamide (DMF), and then a certain amount of phosphomolybdic acid was added into the LM and DMF under ultrasound. Also, the required thiourea and catalyst NaBH₄ were mixed in a beaker in a molar Mo∶S ratio of 1.0∶2.6. Afterwards, the two solutions were transferred to a polytetrafluoroethylene liner and reacted at 200 ℃ for 24 h. The resulting reaction solutions were washed with deionized water, N, N-Dimethylformamide, and anhydrous ethanol, respectively. Finally, the washed materials were dried in a vacuum drying oven at 70 ℃ for 12 h to obtain the final reaction product. The prepared active material was mixed with acetylene carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8∶1∶1. The material was fully ground in a ball mill in the presence of an appropriate amount of solvent N-Methyl-2-pyrrolidone (NMP) to obtain a uniformly mixed slurry. The slurry was evenly coated on a copper foil and dried in a vacuum at 70 ℃ for 12 h. The dried material was cut into 12 mm discs with a slicer as a battery negative electrode, and it was assembled into a CR2016 button battery in a glove box filled with argon. Among them, the metal lithium sheet was a counter electrode, the polypropylene porous membrane (Celgard2400) was a separator, the electrolyte solute was 1 mol·L^-1 LiPF₆, the solvent was a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of 1∶1∶1, and the foam nickel was a gasket.

The results show that the liquid metal effectively combines with MoS₂ via electrostatic adsorption and coordination bonds to form a stable composite structure. In addition, the composite material has a higher deformability and a chemical stability, promoting the repair of the crack surface of the electrode material, reducing the internal redox reaction, and improving the cycle stability of the lithium-ion battery. When a mass ratio of LM∶MoS₂ is 2∶1, the composite material shows the optimum performance. At a current density of 0.1 A·g^-1, after 100 cycles, the specific capacity of the composite material is stable at 656.1 mA·h·g^-1, the capacity retention rate reaches 74.3%, effectively improving the cycle stability of the electrode material.

A lithium-ion battery negative electrode material LM@MoS₂ with self-healing characteristics was prepared by a hydrothermal method. The cracks generated in the electrode during the charging and discharging process were repaired via utilizing the fluidity and high surface tension of liquid metal, effectively improving the cycle life of the electrode material. The optimum cycle stability of the electrode was obtained at a mass ratio of LM∶MoS₂ of 2∶1. The LM@MoS₂ prepared could reduce the internal redox reaction of the battery, thereby improving the electrochemical performance of the battery in the process of repeated insertion and extraction of lithium ions, reducing mechanical fractures, and improving the electrochemical performance of the battery.