Preparation And Electrochemical Properties Of Silicon-2D Transition Metal Carbide Composites

As a negative electrode material of lithium-ion batteries（LIBs）with great development prospect,silicon has high theoretical capacity,suitable lithium storage potential,abundant reserves and environmental friendliness.However,silicon can undergo drastic volume changes during charging and discharging,which may lead to structural collapse of the active material or stripping away from the collector fluid,resulting in rapid capacity decay and limiting its application in lithium-ion batteries.A lot of progress has been made in the research of silicon-based negative electrode materials by nanomaterials and composite.However,the structural design and interface control of silicon nanocomposites need further investigation.On the basis of previous studies,this paper designs different silicon/Ti₃C₂T_x MXene composites for nano-silicon and micron silicon precursors by focusing on silicon-based negative electrode materials and combining with the two-dimensional metal carbide materials（MXene,represented by Ti₃C₂T_x）,which are widely concerned at present.By modifying the interface of silicon materials and adjusting the structure and proportion of MXene surface groups,the interface properties of silicon/MXene composites were regulated,and the preparation,synergism and electrochemical properties of silicon/MXene composites were studied.The main research contents of this paper are as follows:（1）NH₂-Si/MXene composite was constructed by electrostatic self-assembly method and the effect of porous MXene matrix on the electrochemical performance of composite electrode was discussed.NH₂-Si（nanoparticle）modified with negative surface charge can self-assemble with MXene with positive surface charge through electrostatic interaction to form porous composite structure.MXene nanoparticle closely loads the silicon nanoparticle and effectively buffers the volume change during charge and discharge process to maintain a stable electrode structure.The open holes and the high conductivity of MXene improve the carrier transport efficiency in the electrode materials,so the NH₂-Si/MXene composites have a higher reversible discharge specific capacity(1203.3 m A h g^-1)after 100 cycles.（2）Three-dimensional multistage aerogel P-Si@MXene@GO composite was constructed by spray drying method and liquid nitrogen freeze-drying method.The porous structure can provide space for the volume expansion of silicon during the lithium process.MXene nanoparticle is completely coated on the surface of porous silicon particles through spray drying,which can improve the electronic conductivity and cooperate to construct a stable solid electrolyte interface film.The graphene oxide sheets bearing P-Si@MXene interweave to form a three-dimensional porous aerogel structure.The multi-stage structure frame can further enhance the cyclic stability and electronic transport capacity of the composite electrode,so that the composite electrode material has a high long-term cyclic stability(discharge capacity of 713.49 m A h g^-1after 100 cycles).（3）By regulating the surface structure of MXene,the influence of MXene surface groups on the composite interface with silicon-based materials and the electrochemical performance were studied.The surface properties of MXene can be regulated by changing the heat treatment conditions,such as controlling the types and proportions of-O,-OH,-F,-Cl and other groups,and comparing the effects of various surface groups on the preparation process of Si/MXene composite electrode,as well as their effects on the interface properties and electrochemical properties.Among them,MXene heat-treated at 300°C in air for 1 hour carries more oxygen-containing groups,improves the stability of the composite interface due to the presence of Ti-O bonds,and has the highest first coulomb efficiency（92.09%）.