Synthesis And Energy Storage Properties Of Transition Metal-Sn/C Composite

Sodium ion batteries have abundant reserves and can be widely used in large-scale energy storage systems.It's urgent to find appropriate anode materials for sodium ion batteries.Transition metal(Co,Ni and Fe)-Snalloy negative electrodes has become attractive anodes for sodium ion batteries because of abundant resources and large theoretical capacity.The addition of transition metals(Co,Ni and Fe)can effectively alleviate the volume expansion of Sn,and the combination of transition metals(Co,Ni and Fe)-Snalloy with carbon can also improve the electrochemical performance of transition metals-Snalloy.Thus,this paper studies the synthesis and energy storage properties of transition metal-Sn/C composite.The main research contents are listed on below:(1)SnO₂-CoSn₂/C heterojunction nanocomposites were synthesized by hydrothermal method.It shows excellent cycle performance and rate capacity as anode for SIBs.It delivers an initial specific capacity of 573 m Ah g^-1 at a current density of 50 m A g^-1.After 100 cycles,the capacity retention is 80%with the specific capacity of 456 m Ah g^-1.The reversible capacities of 586,551,501,441,370,276 and 200 m Ah g^-1are respectively obtained at the rate from 0.1C to 10C.When the rate returns to 0.1C,it can deiliver the specific capacity of541 m Ah g^-1.The outstanding electrochemical performance of SnO₂-CoSn₂/C anode is attributed to the interface effect of SnO₂-CoSn₂ heterojunction,which can accelerate the Na⁺diffusion and charge transfer.SnO₂-CoSn₂/C can provide up to 273 m Ah g^-1 reversible capacity as the anode material for potassium ion batteries.(2)Ni-Sn@C-1h nanowire composite was synthesized by two steps method of electrospinning technique and low temperature sintering.Ni-Snnanocrystals coated by carbon nanowires can effectively restrain the volume expansion,showing great cycling stability.The initial charge capacity of Ni-Sn@C-1h anode is 258 m Ah g^-1 at a rate of 0.1C.After 100 cycles,it can still deliver a reversible capacity of 246 m Ah g^-1 with a capacity retention of 95%.Even at a large rate of 1C,it shows the highest capacity of 215 m Ah g^-1and the specific capacity of 200 m Ah g^-1 is still hold with a capacity retention of 93%.(3)Fe-Sn/C porous composite was synthesized by MOFs template method and subsequent calcination.Firstly,Fe-MOFs metal organic framework was synthesized,then mixed with SnCl₂ uniformly.Finanlly,the mixture was calcined in inert atmosphere to obtain Fe-Sn/C porous composite.As the anode material for SIBs,it shows 286 m Ah g^-1 reversible capacity at the rate of 0.1C.At the rate of 0.5C,it can provide the initial charge capacity of143 m Ah g^-1.The poor electrochemical performance of Fe-Sn/C electrodes is due to the constant formation of thick SEI film on the broken surface of materials during the sodiation/desodiation process.