Preparation And Electrochemical Properties Of Tin Phosphide-based Composites

The shortage of fossil energy has led people to pay attention to energy storage technology.It is urgent to develop new energy storage devices with sustainable development and environmental protection.As a representative of secondary batteries,lithium-ion batteries occupy a dominant position in the market,and have been widely used in mobile phones,computers,electric vehicles and other equipment.However,lithium-ion batteries have the scarcity of lithium resources,large safety hazards,and high cost,which limits their use in large-scale production facilities.Sodium is a new type of secondary battery that is rich in natural resources,low in cost,and has similar physical and chemical properties to lithium.As a material that can be used as a negative electrode for sodium ion batteries,tin phosphide(Sn4P3)has a theoretical specific capacity of up to 1132 mAh/g and a volume specific capacity of up to 6650 mAh/cm3.The two active elements Sn and P can participate in the sodium-storage reaction together,and Sn and P can produce synergistic effects.However,when Sn4P3 is applied to a sodium negative electrode material,there are many problems such as volume expansion,cycle performance degradation,and high irreversible capacity.With the purpose of enhancing the Na-storage performance of Sn4P3,three kinds of SnO2/carbon-based composites with different structures were used as precursors,and three kinds of electrochemical properties of Sn4P3/carbon nanocomposites were prepared by low temperature solid-phase phosphating:(1)Sn02/graphene nanocomposite with a good spatial network structure was prepared by a simple chemical reduction method.Then,a solid phase phosphating method is used to obtain a Sn4P3/GA nanocomposite.By comparing the performance of different content of graphene composites,it was finally determined that the Sn4P3-GA nanocomposites with a graphene content of 24.6%exhibited an ultra-high cyclic specific capacity,and the specific capacity was still 657 mAh/g after 100 cycles at 0.1 A/g(2)The SnO2 hollow spheres with a particle size of about 300 nm were prepared by hydrothermal method,then carbonized by dopamine coating to obtain a hollow carbon-coated SnO2.And hollow Sn4P3@C was prepared by simple low-temperature solid phase phosphating.When the current density increasing from 0.2 A/g to 10 A/g,the reversible capacity is 555 mAh/g to 93 mAh/g.After 200 cycles at 0.2 A/g,the specific capacity is still 372 mAh/g with a coulomb efficiency closing to 100%.(3)Core-shell Sn4P3@C was obtained by solid phase phosphating with conformal core-shell SnO2@C as precursor.The unique spatial structure of the material allows enough space to accommodate the large volume changes during the charging and discharging.The carbon shell with a thickness of 30 nm not only enhanced the electron transmission rate,but also protected the internal Sn4P3 microsphere from damage.Uniform SEI film is formed on the surface of carbon shell during charge-discharge process,which is more beneficial to maintain the structural integrity.At 0.2 A/g,the specific capacity is still 420 mAh/g after 300 cycles.And the rate performance of Sn4P3@C is excellent,which the maximum charge and discharge current can reach 20 A/g,and the structure is not damaged.Thanks to the special hollow core shell structure,the stable capacities of 205 and 103 mAh/g for the Sn4P3@C composite electrode can be achieved after 4000 cycles at 2 and 5 A/g,respectively.