| With the rapid development of human society,the consumption of energy is increasing.Traditional natural energy resources such as oil and coal,due to non-renewable,environmental pollution,etc.,have not been well adapted to the needs of sustainable development.Lithium-ion batteries have been widely used in all aspects of society due to their advantages of high energy density,environmental protection,and sustainable development.Electrode materials are the key to battery performance.Therefore,it is particularly important to develop electrode materials with high energy density,low price,and environmental protection.At present,commercialized graphitic carbon is used as the mainstream anode material because of its low price and good cycle stability.However,its theoretical capacity is low(372 mAh/g),which limits its further development.Therefore,there is a need to develop high-energy density negative electrode materials.Tin-based materials have high specific capacity(Sn and SnO2 are 994 and 1494 mAh/g,respectively),and are one of the candidate materials for the next generation of anode materials.However,in the process of charging and discharging tin-based materials,the structure is easy to collapse and the material is crushed,so the cycle performance is poor.Therefore,it is necessary to modify the tin-based negative electrode material.Many scholars have used carbon/graphene coating,nano-design,metal/non-metal ion doping and other methods to modify tin-based anode materials to slow down the volume expansion during charging and discharging,thereby stabilizing the structure and improving electrochemical performance.Based on the research of a large number of scholars on tin-based anode materials for lithium-ion batteries,this paper studies mesoporous carbon coated nano-Sn,fluorine-doped porous carbon modified SnO2,metal W-doped carbon nanosheets coated SnO2,metal oxide MoO2 combined with SnO2,the three-phase composite of TiN,SnO2 and carbon nanosheets,and their microstructure,phase structure and electrochemical properties.Sodium alginate was used as a chelating agent to adsorb metal Sn2+ ions and as a carbon source,and mesoporous carbon-coated nano-Sn was prepared by gel sol and reduction method.Through material characterization and electrochemical performance testing,the results show that the nanometer Sn and mesoporous carbon package Coating can effectively reduce the stress of the material in the process of inserting and releasing lithium and alleviate the volume expansion.The mesoporous carbon-coated nano-Sn composite material was charged and discharged 550 times at a current density of 1 A/g,and the capacity still reached 1116 mAh/g.It has a capacity of 406 mAh/g at a high current of 5 A/g and a current density of 10 cycles,showing very good high-current charging and discharging performance.Since the coating of mesoporous carbon plays a role in slowing down volume expansion and stabilizing the structure of the composite material,excellent cycle stability can be obtained.In addition,the nano-Sn embedded in carbon shortens the transmission distance between electrons and ions,increases the transmission rate of ions and the transfer speed of electrons,and thus obtains excellent high-current charging and discharging performance.NaCl was used as a template,and a fluorine-doped porous carbon modified SnO2 composite material was prepared by wet ball milling and high-temperature pyrolysis.Through material characterization and electrochemical performance testing,the results show that the fluorine-doped porous carbon modified SnO2 composite material can effectively suppress volume expansion and show good electrochemical performance.The fluorine-doped porous carbon modified SnO2 composite material has a capacity of 820 mAh/g after 100 cycles of charge and discharge at a current density of 0.2 A/g;800 cycles of charge and discharge at a current density of 2 A/g,and the capacity remains at 820 mAh/g.Because fluorine is doped in carbon and SnO2,on the one hand,F-has strong electronegativity,it can improve the ability of adsorbing lithium ions and increase the capacity of the material;on the other hand,due to fluorine doping,stable F-Sn and F-C bonds are formed.Therefore,the structure of the material can be stabilized,and the volume expansion of the composite material during charging and discharging can be suppressed.Tungsten-doped carbon nanosheets coated SnO2 composite materials synthesized by hydrothermal and dry grinding methods,through material characterization and electrochemical performance testing,the results show that tungsten-doped carbon nanosheets coated with SnO2 can improve the first coulombic efficiency and stabilize the structure,and obtain excellent electrochemical performance.The tungsten-doped carbon nanosheet-coated SnO2 composite material was charged and discharged 500 times at a current density of 0.2 A/g,and the available capacity was 820 mAh/g and the first-time coulombic efficiency was 76.2%.In flake graphite,W doping can not only prevent the aggregation of tin in the Sn/Li2O compound and enhance the reversible conversion reaction,but also improve the electronic conductivity.On the other hand,SnO2 nanoparticles can not only shorten the diffusion path of ions,but also provide more active sites to store lithium ions.In order to stabilize the structure of SnO2,the metal oxide MoO2 was introduced,and the MoO2-SnO2-C three-phase composite material was prepared by high-energy ball milling.Through material characterization and electrochemical performance testing,the results show that MoO2 can inhibit the agglomeration of SnO2 and is stable structure,thus obtaining excellent electrochemical performance.The MoO2-SnO2-C three-phase composite material is charged and discharged 300 times at a current density of 0.2 A/g,and can obtain a capacity of 1210 mAh/g and a first coulombic efficiency of 73.45%;charge and discharge at a current density of 1.0 A/g after 1000 cycles,the achievable capacity is 630 mAh/g;the discharge specific capacity is 688 mAh/g at a rate of 5.0 A/g.The metal oxide MoO2 can inhibit the coarsening of Sn during the charging and discharging process,and can improve the reversible reaction,and promote the conversion of Sn/Li2O to SnO2,because it improves the first coulombic efficiency.On the other hand,nano-sized SnO2 can increase the diffusion rate of lithium ions and the transfer rate of electrons,thereby obtaining excellent rate performance.At the same time,the ultra-thin carbon graphite sheet framework protects the material structure,relieves volume expansion,and fixes nano-MoO2 and SnO2 particles,thereby improving the stability of electrochemical cycles.High-energy ball milling is used to synthesize TiN/SnO2@C composite material,through material characterization and electrochemical performance testing,the results show that TiN has the effect of enhancing conductivity and stabilizing the structure of SnO2,thus obtaining excellent electrochemical performance.TiN/SnO2@C composite material can obtain a capacity of 837 mAh/g at a current density of 0.2 A/g for 100 cycles of charge and discharge;at a current density of 1.0 A/g,a capacity of 987 mAh can be obtained/g capacity;the discharge specific capacity is 467 mAh/g at a rate of 5.0 A/g.Because TiN has enhanced electronic conductivity,and at the same time,through the structure of a strong and stable Ti-N-0 stable material,it inhibits the volume expansion of SnO2 during charge and discharge,and improves the electrochemical performance of the composite material. |
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