Preparation And Sodium Storage Properties Of Graphene/black Phosphorene Composites

At present,lithium-ion batteries(LIBs)play a major role in the field of energy storage.However,due to the scarcity,the large-scale development of its industry faces various restrictions.Sodium-ion batteries(SIBs)have ushered in great development opportunities to LIBs due to the rich sodium resources and low cost.However,the current development of SIBs is limited by their lower energy density and the key to improving the energy density of SIBs lies in the development of electrode materials with high specific capacity.Black phosphorus(BP)has aroused grand attention because of its high theoretical capacity up to 2596 m Ah/g.Additionally,the volume expansion that is involved in the sodiation of BP,which can leads to the pulverization of BP and dispersion in electrolyte,which results in rapid capacity fading.At present,the main way to solve this problem is to nanosized BP and composite with high conductivity materials.In addition,the preparation of BP-based composites in previous report still has the problems of complicated process,low yield and high cost.To address these issues,the graphene/black phosphorene composites(G/BP)was prepared by combining BP with C in one-step method.On this basis,the sodium storage performance of the G/BP was further optimized by polyaniline(PANI)coating.Detailed research contents are as follows:(1)Using cheap red phosphorus as raw material,the influence of reaction temperature and time on the conversion rate of red phosphorus in the solvothermal process were explored.Then,the graphene was added as a carbon carrier,and BP was grown in situ on the G by solvothermal method to obtain composites in one step.The effect of adding graphene obtained at different centrifugal speeds and different contents in composites on its sodium storage performance were explored.Results indicate that BP prepared under the optimal conditions which delivers the initial discharge specific capacity of 460 m Ah/g in 100 m A/g,the reversible capacity can be omitted,the 1stcycle charge and discharge capacities of G/BP-1 are 687 and 1401 m Ah/g respectively.Compared with BP,the performance of composites is improved,which can be attributed to the P-C bond formed in-situ growth process of BP between with G.It?s not only enhance the ionic and electronic conductivity of the G/BP,but also relieve the huge volume expansion of BP during insertion/extraction of sodium.(2)Using BP with high crystallinity and C as raw materials,the G/BP was directly prepared by high-pressure homogenization method.The influence of the size and composition ratio of the G/BP on the sodium storage performance were explored.The results show that when the mass ratio of BP to C is 1.5:1,the prepared G/BP exhibited best electrochemical performance.The 1st-cycle charge and discharge capacities of G/BP with optimal preparation condition are 1038 and 1758 m Ah/g,respectively.Reversible specific capacity of composites is improved can be attributed to the high crystallinity of BP and the P-C bond formed in composites,which can not only accelerate electron transfer but also enhance the structural stability of the composites.(3)The G/BP prepared by high-pressure homogenization was modified with PANI by in-situ polymerization method.The coating time and the amount of aniline monomer were controlled to change the coating amount of PANI to prepare a series of PANI@G/BP.The electrochemical performance test shows that the coating amount of polyaniline has a greater impact on the electrochemical performance of the PANI@G/BP.The cycle performance of PANI@G/BP-2 with optimal coating is significantly better than that of the uncoated G/BP.The initial discharge and charge capacities of the PANI@G/BP-2 are 1755 and 1102 m Ah/g at 100 m A/g,respectively.The 1st-cycle coulombic efficiency is 62.8%.The reversible specific capacity is 568 m Ah/g after 10 cycles,and the capacity retention rate is 51.5%.In addition,the cyclic performance of PANI@G/BP-2 is improved significantly compared with G/BP,and the reversible specific capacity is increased by 169 m Ah/g.Combining the above electrochemical data and previous literatures,it?s indicated that the PANI coating can prevent the side reaction between BP and electrolyte,improve the reaction degree of BP and alleviate the volume expansion of BP,thereby increase the sodium storage performance of PANI@G/BP.