Study On The Failure Mechanism And Improvement Strategy Of Molybdenum Disulfide-Based Anode Materials In Lithium-Ion Batteries

The development of safe and efficient lithium-ion batteries(LIBs)batteries is an important way to solve the environmental and energy crisis in China.Also,it's the only way to realize the rational allocation of power resources and industrial upgrading.Transition metal chalcogenides(TMCs),such as MoS₂,hold conversion-pseudocapacitance synergistic lithiation properties,and the layered structure can buffer the volume vibration during charge/discharge process,showing excellent blueprint as anode materials in LIBs.However,poor cycling stability is the primary problem to be solved.In general,it's convinced that conductivity and volume expansion issues are the root causes for the short lifespan.Lacking of in-depth mechanism study,many novel optimization strategies generated limited effects.TMCs films prepared by magnetron sputtering occupy the advantages of uniform growth,high repeatability and high purity,which provides great convenience to study the MoS₂ failure issue.Herein,MoS₂ film prepared via magnetron sputtering was the main research object,and a variety of ex-situ tests were performed.By adjusting the growth structure of MoS₂ and observing the structural evolution of the active material during long-term cycling,the corrosion failure mechanism on the Cu foil and the structural evolution failure mechanism on the sulfur-resistant current collectors were revealed,providing a theoretical basis for the performance optimization of MoS₂.Based on the above-mentioned failure mechanisms,we studied the modification strategy and obtained some beneficial results and conclusions.The main research results were as follows:MoS₂ with different porosity were prepared on Ti foils.The electrochemical performance showed that MP-MoS₂(middle porosity-MoS₂)sample held the best rate and cyclic charge/discharge performances.After 300 cycles,the charge-discharge capacity reached up to 1136 m Ah/g and 1157 m Ah/g,respectively,with the coulombic efficiency of 98.19%.The same parameters were used to verify the conclusion on stainless steel(SS)foils.The results showed that MP-MoS₂ on SS foils was also the best experimental group.Therefore,sputtering power of 100 W,reaction time of 1 h and deposition chamber temperature of 400°C were the optimal parameters for MoS₂'preparation.MP-MoS₂ prepared on Ni foils with these parameter could also maintain stable cycling and nice charge/discharge capacity.Cu/TMCs samples were prepared to study the severe capacity decay issue.The novel corrosion failure mechanism between sulfur and Cu towards TMCs was revealed.Taking lithium-ion battery and MoS₂ as the example,massive Cu₂S nanoparticles were spontaneously generated by consuming Cu in the current collector and S element generated by the delithiation of MoS₂(or saying Li₂S),which destroyed the structural integrity and stability of MoS₂-Li₂S-S system,especially increased the interface resistance,leading to the capacity decrease of ca.200 m Ah/g within 50 cycles.By introducing a Ti protective layer between Cu and MoS₂ film,the rapid decay phenomenon could be effectively eliminated with stable operation over 300 cycles.MP-MoS₂ film was prepared on different sulfur-resistance substrates.The self recovery phenomenon of charge-discharge capacity of MoS₂ anode on Ni,Ti and SS current collectors was closely related to the size change of Mo nanoparticles.In the first300 cycles,Mo atoms spontaneously aggregated and grew up,which affected the migration and capacitive adsorption of Li⁺,resulting in a sharp decrease in capacity.Then Mo was oxidized to Mo_xS_y and Mo_xS_y was lithiated to form Mo/Li₂S,which gradually pulverized rough Mo particles into small particles and made the capacity performance recover significantly.Therefore,for the modification and optimization of MoS₂,more attention should be paid to limit the aggregation and growth of Mo.Al₂O₃ films with different thickness were deposited on the Ni/MoS₂ surface.The results showed that the contact angle,microarea roughness and electrochemical impedance initially decreased and then increased with the increased of the amount of Al₂O₃ deposition.The sample deposited at 100 W for 1 h at 400°C revealed the best performance,and conveyed a charge discharge capacity of over 0.50 m Ah/cm~2 after800 cycles,and the agglomeration growth of Mo particles was significantly inhibited.Benefit from a large number of pores on the surface,the MoS₂-Al₂O₃ sample prepared at room temperature with the optimized preparation parameters of 100 W sputtering for1 h also showed excellent charge-discharge capacity and cycle stability in 800 cycles.