Research On Anode And Anode Sodium Additive For Na-Ion Batteries

Lithium-ion batteries（LIBs）have conquered the portable electronics market and the electric vehicles due to their high energy density and long cycle life since its commercialization.However,lithium resources in the earth’s crust are limited and unevenly distributed.At the same time,the demand for lithium resources in secondary battery-related industries is huge,which makes the production cost of LIBs increase year by year.Sodium-ion batteries（SIBs）that have attracted much attention are highly similar to LIBs in terms of working principle,battery composition,production process,and production equipment.Sodium resources are abundant and widely distributed in the crust,so the production cost of SIBs is relatively low,especially suitable for large-scale energy storage equipment.The matching degree of cathode and anode materials of SIBs determines the performance of the battery to a large extent.The initial coulombic efficiency of the cathode material of the SIBs with mature technology is about 98%,but the initial coulombic efficiency of the anode material is low,which limits the performance of the cathode material.Based on these,this research was carried out on the anode and sodium supplement materials of SIBs.In this paper,an O3-phase layered oxide Na Fe_0.5Ti_0.5O₂was designed and prepared.Only 0.06 Na⁺is embedded in the structure during the first discharge process,but the reversible specific capacity is about 90 m Ah/g in the subsequent charge and discharge process.The capacity retention rate is above 89%after 650cycles at 1 C rate and is about 80%after 270 cycles at a high rate of 10 C,exhibiting excellent cycle stability and rate performance.The limited amount of Na⁺embedded during the first discharge process makes it cannot be used as anode materials for SIBs.According to its special electrochemical properties,Na Fe_0.5Ti_0.5O₂is applied as a sodium additive in anode for full cell.The full cell with sodium supplement has higher energy density and better cycle stability.Due to the fact that Na Fe_0.5Ti_0.5O₂can not only provide additional sodium ions but also participates in the charge and discharge process.Na Fe_0.5Ti_0.5O₂is unstable in air,and the anode materials that can be used with it are limited,so it is difficult to achieve industrialization.Therefore,developing carbon-based anode materials with high capacity and high initial coulombic efficiency is more meaningful.Asphalt is a by-product of petroleum refining,which has the characteristics of low cost,wide source of goods,high carbon content,and few impurities.However,asphalt is prone to form a graphitization structure at high temperatures,and its sodium storage performance is poor.In this paper,the pre-oxidation treatment is carried out to improve the degree of disorder after carbonization,and the as-prepared amorphous carbon has a high specific capacity and initial coulombic efficiency,which are 229.6 m Ah/g and 84.1%.The effects of pre-oxidation temperature and carbonization temperature on the performances of amorphous carbon were explored.To further understand the impact of carbonization temperature on the properties of amorphous carbon materials,the pine nutshell was pre-oxidized and carbonized at different temperatures.By comparing the XRD diffraction patterns of the experimental materials and fitting their Raman spectra,it is found that with the increase of carbonization temperature,the interlayer spacing of the materials decreases,and the degree of disorder decreases.At the same time,the reversible specific capacity and the initial coulombic efficiency are improved.Thus,the variation law of the internal microstructure of the material during high-temperature carbonization is revealed.