Doping Modification Of Tin-based Anode Materials For Li-ion Batteries And Its Electrochemical Properties

In today's society,people's demand for electronic equipment is increasing,and the normal operation of electronic equipment is inseparable from lithium-ion batteries.At the same time,lithium-ion batteries are used in aviation equipment and electric vehicles because of their relatively high energy density,small size,little pollution to the environment.However,the battery capacity is not large enough and the life is not long enough,which has always been the main reason for limiting the application of lithium-ion batteries.The battery capacity is determined by the electrode material,so finding an electrode material that is environmentally friendly,has high energy density and is safe has become a hot research topic.At present,graphite is the main negative electrode material in batteries,which is highly conductive,relatively stable,and has abundant reserves in nature.However,its theoretical capacity is too low,only 372 m Ah g^-1,which limits its use in many scenarios.The theoretical capacity of tin-based oxide materials(SnO₂ is 1494 m Ah g^-1)is very high,which is more than 4 times that of graphite,and has good research value as a negative electrode material.However,during the charging and discharging process,the tin-based oxide material has a serious problem(volume expansion reaches 300%),which will cause the material to fall off the electrode and puncture the diaphragm,resulting in a short circuit of the battery,which can no longer perform the charging and discharging function.Therefore,scholars have done a lot of research on the modification of tin-based oxide materials,including carbon/graphene coating of materials,doping of metal/non-metal oxides,and making materials into nano-scale particles.The volume change can be controlled to maintain a complete electrode structure,so that the battery can have good electrochemical performance.In this thesis,on the basis of summarizing previous researches,Co₃O₄ metal oxide particles doped carbon nanosheets coated SnO₂;Mxene material,SnO₂ and carbon nanosheets were composited;NaCl was used as template,Na-doped porous carbon modified SnO₂ as negative electrode battery performance when material.First,a new SnO₂-Co₃O₄-C composite was successfully synthesized by hydrothermal method and two-step ball milling method.After XRD,XPS,SEM,TEM and other tests,it was found that SnO₂ and Co₃O₄ nanoparticles were evenly embedded on the graphite nanosheets.Since carbon nanosheets can inhibit the coarsening and expansion of SnO₂ during lithium intercalation/delithiation,and Co₃O₄ can provide more active sites for Li⁺,this structure can improve the reversible capacity and life of the battery.Through electrochemical tests,it was found the capacity could reach 842 m Ah g^-1 after 300 cycles at a current of 0.2 Ag^-1.When the current is 1 Ag^-1,the capacity can reach 596.1 m Ah g^-1 after 980 cycles.At the same time,the material also has excellent rate performance,with a capacity of 337 m Ah g^-1at 5 Ag^-1.The SnO₂-Ti₂C-C composite was synthesized by heat treatment and high-energy ball milling by using Ti2C,an Mxene material,which can greatly improve the lithium ion migration rate.After XRD,XPS,SEM,TEM,electrochemical properties and other tests.The capacity of the composite is 1036.87 m Ah g-1(after 200 cycles)when the current is 0.2 Ag^-1,and 763.18 m Ah g^-1(after 500 cycles)when the current rises to 2.0 Ag^-1.At the large current density of 5 Ag^-1,the capacity is 447.58 m Ah g^-1.Since Ti₂C enhances the movement rate of Li⁺,it also prevents Sn from agglomerating in the Sn/Li₂ composite.At the same time,the graphite nanosheets inhibit the volume expansion of SnO₂,so that the battery exhibits excellent cycle performance and rate performance.A novel SnO₂@C-Na composite was successfully prepared by high-temperature calcination and wet milling using NaCl as a template.The composites were tested by XRD,XPS,SEM,TEM and electrochemical properties.When the current is 0.2 Ag^-1,the capacity is1045 m Ah g^-1(after 300 cycles),and when the current density is increased to 1 Ag^-1,the capacity is 918 m Ah g^-1(after 980 cycles).When the current is 5A g^-1,the capacity is 502 m Ah g^-1.Because NaCl as a template successfully makes the material exhibit a porous structure,this structure allows more free movement of lithium ions and improves the stability and cycle performance of the material.At the same time,the doping of Na element enhances the intrinsic conductivity of the material and improves the polarization phenomenon of the material under high current.Therefore,the battery has the high-rate capacity.