Study On Synergistic Improvement Of The Performance Of Stannic Oxide-based Anode By Carbon Cloth And Metal-organic Framework

Due to its high theoretical specific capacity(782 mAhg^-1),fast diffusion rate of lithiumion and low risk of lithium metal precipitation,SnO₂ is expected to become one of the cathode materials to replace graphite and realize industrial preparation.However,during the embedding and stripping reaction of Li⁺,the volume expansion of SnO₂ will be about 3 times larger than its own volume,which will lead to the breakage,falling off or even unusable of the electrode active material.In addition,the low conductivity of SnO₂ itself leads to poor cycling charging-discharging capacity and rate performance,which inhibits its practical production and application.In this paper,the urgent problems in the practical application of SnO₂ electrode materials will be studied.Combining carbon cloth（CC）with porous Metal-Organic Framework（MOF）and tin dioxide（SnO₂）nanoparticles,and synergistic effect between them would use to inhibit the volume expansion of SnO₂ nanoparticles,improve their electrical conductivity and increase capacity.The details are as follows:（1）Hydrothermal method was developed to prepare SnO₂ nanoparticles of differentsizes with Sn Cl₄·5H₂O as raw material at different reaction temperatures.The SnO₂ nanoparticles prepared at different reaction temperatures were characterized by XRD.It is found that the grain size of SnO₂ prepared at 160℃is the smallest,and it has good cycling stability and Li⁺transport ability.（2）Co-MOF was grown on CC,and the morphology of the metal-organic frameworkwas controlled by changing the annealing temperature,and it was characterized by SEM.The electrochemical properties of MOF-structured composites（SnO₂/C@CC）at different annealing temperatures were tested.It is found that the nanosheets derived from the metal-organic framework annealed at 500℃have the largest size and the most uniform distribution,and the comparative study shows that it has excellent rate and charge-discharge cycle ability.（3）The annealed SnO₂/C@CC at 500℃was compared with the composite material（SnO₂@CC）where the SnO₂ nanoparticles were directly grown on CC.It was found that the introduction of a metal-organic framework effectively inhibited the volume expansion of SnO₂nanoparticles and significantly improved the electrochemical performance.The results indicate that the initial discharge capacity of SnO₂/C@CC can reach 1717 mAhg^-1,the current density is 3A g^-1,and the capacity is stable at 1000 mAhg^-1 after 500 cycles,which is higher than the theoretical specific capacity.When the current is 5 A g^-1,the electrode material stably displays a capacity of 600 mAhg^-1 after the same cycles.And its structure remains stable and consistent before and after charging-discharging.The excellent electrochemical performance of SnO₂/C@CC electrode materials is due to the synergistic effect of SnO₂ nanoparticles with suitable size,stable porous carbon framework derived from Co-MOF and CC.The porous carbon skeleton can effectively alleviate the volume change of SnO₂ nanoparticles in the charge-discharge reaction process and improve the lithium embedding space,and enhance the Li⁺transport capacity.The addition of CC can not only provide enough sites for the growth of active substances,but also enhance the conductivity of electrode materials and reduce the capacity loss of the battery.