Synthesis Of Two-dimensional Ti₃C₂T_x MXene Materials And Their Application In Lithium Metal Anode

Lithium metal is a very promising anode material due to the high theoretical capacity up to 3860mAh/g.However,the practical application of lithium metal batteries is suffered from the uncontrolled lithium dendrite growth and formation of dead lithium,which result to low cycle efficiency and serious safety issues.This study aims to design a series of two-dimensional Ti₃C₂T_x MXene materials as new lithium metal anode host materials to solve the uncontrolled lithium dendrite growth and the formation of dead lithium,thereby improving its cycle life and coulombic efficiency.The research work mainly includes the following two aspects:?1?Titanium carbide?Ti₃C₂T_x?MXene material with accordion-like shape was prepared by etching titanium aluminum carbide with hydrofluoric acid.Then,porous Ti₃C₂T_x MXene material with low fluorine content was obtained after further hydrothermally treatment in an alkali solution.It's revealed that porous Ti₃C₂T_x MXene material display much improved electrochemical properties when it was used as lithium metal anode host materials.At a current density of 1 mA/cm² and a charge and discharge capacity of 1mAh/cm²,the high Coulomb efficiency of 97.3%can be maintained for 200cycles.Furthermore,both the nucleation overpotential and the polarization difference are lowered for low-fluorine porous Ti₃C₂T_x.It's suggested that the pore formation can increase the specific surface area of the titanium carbide,thereby reducing the effective local current density,and finally inhibiting the growth of the lithium dendrites.At the same time,the holes created provide enough space for lithium to deposit.In addition,the hydroxyl group of the substituted fluorine group has a good hydrophilicity,which not only provides nucleation sites,but also reduces the effective local current density.The hydroxyl group is also capable of inducing initial nucleation and subsequent growth of lithium,leading to preferentially nucleate on the titanium carbide substrate rather than the random outer layer.?2?In this study,lithium fluoride and concentrated hydrochloric acid solution with low corrosion was used to prepare accordion-like titanium carbide material,and the delaminated titanium carbide was obtained through further intercalating and ultrasonic processing.This material was used as a negative electrode for a lithium metal battery,demonstrating good electrochemical performance.At a current density of 1 mA/cm²and a charge and discharge capacity of 1mAh/cm²,the Coulomb efficiency can be maintained for 150 cycles.It should be notable that delaminated titanium carbide exhibits superior electrochemical performance after electrochemical pretreatment,and the Coulomb efficiency of 95%can be maintained for 250 cycles.These can be attributed to the delamination which can increase the specific surface area of titanium carbide,thereby reducing the effective local current density and ultimately inhibiting the growth of lithium dendrites.In addition,the pretreatment will form a certain SEI layer on the surface of the titanium carbide.The formed SEI layer not only can fix the surface of the titanium carbide,but also can isolate the contact between the electrolyte and the metal lithium,and reduce the consumption of the electrolyte.Pretreatment also leaves a portion of metallic lithium,and the residual metallic lithium acts as a support structure for limiting volumetric variations.At the same time,the residual metal lithium provides an active site for lithium growth and reduces the effective local current density and nucleation overpotential.This is conducive to stable lithium deposition and supplementing the consumed metal lithium,leading to longer life of the lithium metal battery.