Preparation Of Alloy/Three-Dimensional Porous Carbon Composites And Their Application In Sodium-Ion Batteries

The growing number of people worldwide has led to the continuous use of fossil fuels,which has led to problems such as environmental pollution.Therefore,there is an urgent need to use renewable energy to fill the energy gap.Clean energy such as wind,hydro and tidal energy can be utilized instead of non renewable energy,but they are subject to geographical or climatic influences.Therefore,it is necessary to develop energy storage equipment with low cost,high safety and environment-friendly to overcome the limitations of these conditions.In recent years,lithium-ion batteries(LIBs)have been widely used in large energy storage equipment because of their high energy density,high average output voltage(about 3.6V)and wide operating temperature range.However,lithium resources are scarce and unevenly distributed,so sodium-ion batteries(SIBs)have been considered as one of the most promising alternatives to LIBs due to their abundant resources and similar reaction mechanism with LIBs.Since the Na⁺radius is larger than the Li⁺radius,some of the traditional anode materials of LIBs are unsuitable as the anode materials of SIBs.Therefore,it is necessary to find the anode of SIBs with high capacity and long service life in order to further promote the commercialization of SIBs.In this paper,nano-alloy particles are wrapped in three-dimensional porous carbon to ensure the stability of electrode structure and effectively inhibit the volume expansion of alloy particles,so as to improve the electrochemical properties of composite electrode materials.The following is the main research work during the postgraduate period:(1)Nano SbZn alloy particles encapsulated in 3D porous carbon(SbZn@3DPCs)were synthesized using the KCl template method combined with freeze-drying and high-temperature annealing.The Zn in the composite has good toughness,which is helpful to suppress the huge volume expansion of metal Sb during the electrochemical reaction and prevent the pulverization of the electrode.At the same time,the three-dimensional porous amorphous carbon tightly wraps the alloy particles,which not only inhibits the volume expansion of the alloy particles and prevents their agglomeration,but also improves the conductivity and cycle stability of the electrode.Therefore,SbZn@3DPCs exhibit excellent cycling stability and rate capability,which has a capacity of 296.2 m Ah g^-1 at 0.1 A g^-1 after 200 cycles.Zn as an inactive material shows no capacity,so the actual capacity provided by Sb was calculated to be 618 m Ah g^-1,which reached 93%of the theoretical capacity.Moreover,the electrode shows a capacity of 200.2 m Ah g^-1 at 5 A g^-1 and after 1000 cycles,which has good cycling stability.The composite electrode also has good rate performance(capacity of 224 m Ah g^-1 at a current of 10 A g^-1).(2)The preparation method is the same as that of the previous experiment,alloy composite electrodes in eutectic composition(Sn_0.43Bi_0.57@3DPCs,where the Sn:Bi mass ratio was 43:57)were prepared by using SnBi alloy in combination with porous carbon.Eutectic alloys can achieve smaller particle size.On the one hand,the reduction of particle size can inhibit volume expansion.On the other hand,it also shortens the transmission path of Na⁺.In addition,the grain size of eutectic alloy is also small,which makes it have more dislocations and defects,thus providing more active sites for electrochemical reaction.The addition of 3D porous carbon also prevents the volume expansion and improves the conductivity of the electrode.Therefore,Sn_0.43Bi_0.57@3DPCs display excellent electrochemical performance,which have a capacity of 258.6 m Ah g^-1 after 100 cycles at 0.1 A g^-1 and 156 m Ah g^-1 after 1000cycles at 1 A g^-1.It also has a good rate performance(114 m Ah g^-1 at 10 A g^-1).