Preparation Of Tin Phosphide/Expanded Graphite Composite Material And Study On Electrochemical Performance

High-performance secondary batteries represented by lithium ion batteries and sodium ion batteries have attracted widespread attention in recent years,among them,the energy density of lithium-ion batteries with graphite as the negative electrode needs to be improved,at the same time,the limited reserves of lithium resources are difficult to support the development of lithium-ion batteries in the future.Because of the similar working principles and abundant reserves,sodium ion batteries are one of the better secondary batteries to replace lithium ion batteries.At this stage,both are facing the problem of low energy density,so the development of high-capacity negative electrode materials are urgent.Tin phosphide?Sn₄P₃?has a large mass specific capacity?1230m Ah/g?,a very large volume specific capacity?6650 m Ah/cm³?,and a low voltage platform,so it has the great development potential.However,the conductivity of tin phosphide is not good and there is a large volume expansion in the process of charging and discharging.In this regard,we prepared tin phosphide by gas phase phosphating and solvothermal,then used expanded graphite with better conductivity as a modified material,and prepared tin phosphide/expanded graphite composite material by mechanical ball milling.The structure,morphology,and sodium/lithium storage properties of tin and phosphide/expanded graphite composites were characterized and tested.The research contents of this article are as follows:?1?Tin phosphide was prepared by gas phase phosphating,its phase were characterized,and its sodium/lithium storage performance was tested.The results show that the phenomenon of agglomeration of tin phosphide prepared by gas phase phosphating is more serious.When used as a negative electrode of sodium ion battery,at 0.1 C rate,the first discharge specific capacity is 798.4 m Ah/g,and the discharge specific capacity is 175.5 m Ah/g after 100 cycles;when it used as a negative electrode of lithium ion battery,at 0.1 C rate,the first discharge specific capacity is 1292.3 m Ah/g,after 50 cycles,the discharge specific capacity is 319.5 m Ah/g,showing lower cycle stability.?2?For the problem of poor conductivity of tin phosphide and serious volume expansion,we used expanded graphite with high conductivity and large specific surface area as the modified material,and prepared the tin phosphide/expanded graphite composite material by planetary ball milling and in-situ phosphating.The electrochemical test results show that the composite material prepared by the planetary ball milling has better performance.When used as a negative electrode of sodium ion battery,the discharge specific capacity reaches 402.2 m Ah/g after 100 cycles at 0.1 C,which is an increase of 229%compared with tin phosphide,The discharge specific capacity is 103.7 m Ah/g after 500 cycles at 1 C rate;as the negative electrode of lithium ion battery,the discharge specific capacity is 777.3 m Ah/g after 50 cycles at 0.1 C rate,which has a higher discharge specific capacity and cycle stability?3?Solvent-thermal was used to synthesize tin phosphide with better crystallinity,combined with mechanical ball milling to prepare tin phosphide/expanded graphite composite material.When the mass ratio of tin phosphide to expanded graphite was 5:1,the composite material showed the better electrochemical performance.As a negative electrode of sodium ion battery,the discharge specific capacity is 510.8 m Ah/g after 50cycles at 0.1 C rate,the discharge specific capacity is 319.5 m Ah/g after 100 cycles at1 C rate,and the discharge specific capacity after 1000 cycles is 166.8 m Ah/g.The structural characterization and electrochemical test results show that the prepared composite material has higher first-cycle Coulomb efficiency,discharge specific capacity and cycle stability.