Study On Doping Modification And Electrochemical Performance Of Layered Transition Metal Oxide Sodium Ion Battery

With the consumption of fossil fuels and the development of new energy technologies,the integration and storage of intermittent renewable energy in the grid system has become increasingly important.Among various energy storage technologies,secondary batteries are favored due to their high flexibility,high energy conversion efficiency,and ease of maintenance.Lithium-ion batteries are the most mature secondary batteries with the best performance in all aspects.However,lithium is unevenly distributed in the earth’s crust and its content is small,the cost of lithium-ion batteries is getting higher and higher as the current development of portable electronic equipment and new energy vehicles consumption of lithium resources.Thus,lithium-ion batteries is not suitable for large-scale energy storage.As an element of the same main group of lithium,sodium has similar physical and chemical properties to lithium,but it is more widely distributed in the earth’s crust and has more abundant reserves compared to lithium which lead to the lower price.Sodium-ion batteries are currently the most promising alternative to lithium-ion batteries to become the main force of large-scale energy storage grids.In the current research on sodium ion battery materials,layered transition metal oxide materials have high energy density and rich composition can be adjusted.They have received wide attention from researchers.However,the phase transition process during charge and discharge is complicated,and large volume changes cause material poor cycles performance etc.At present,transition metal elements are mainly used for material modification,and rare earth metals are widely used in various aspects,but there are few reports on electrode materials.Therefore,this article uses rare earth metal lanthanum as part of the doping,and the materials obtained under different preparation conditions After testing,the optimal preparation conditions of the cathode material were selected,and then a more in-depth study was carried out on the materials under this condition.The main contents are as follows:(1)The material is prepared by high-temperature solid-phase sintering method,and three groups of lanthanum-doped materials are obtained by adjusting the sintering temperature(900℃,950℃,1000 ℃),which are respectively denoted as NLO-900,NLO-950 and NLO-1000.The materials are respectively P2/O3 mixed phase and pure P2 phase in structure.At a current density of 0.1 C(10mA g-1),NLO-900,NLO-950,and NLO-1000 have specific discharge capacities of 142.4 mAh g-1,139.4 mAh g-1 and 151 mAh g-1,respectively.NLO-1000 still has a specific capacity of 88mAh g-1 at a current density of 5C(500mA g-1),and when it is restored to 0.1C,the specific capacity recovers to 148.8mAh g-1,which is 98.54%of the initial value.High specific capacity and rate performance.(2)By adjusting the addition amount of sodium carbonate(0%,5%,10%,15%)for the secondary calcination,4 groups of materials were prepared,denoted as A0,A5,A10,and A15,where A0 to A10 are in line with P2.The type is the same,and the charge and discharge curve of A15 is a typical O3 type.The discharge specific capacities at a current density of 0.1 C are 145.6 mAh g-1,145.7 mAh g-1,164.8 mAh g-1 and 107.5 mAh g-1,respectively.Among them,the material with the addition of 10%sodium carbonate has high specific capacity and better rate performance without changing the phase.(3)The electrochemical analysis and structural study of the lanthanum-doped material obtained under the optimization of the preliminary preparation conditions were carried out.Its initial specific capacity is 122.5 mAh g-1 and 108.1 mAh g-1 at 1C and 2C,and.the capacity retention rate after 100 cycles is 74%and 81.31%,respectively.The material still has a capacity retention rate of 63%,69.3%and 93.9%after 200 cycles at 5C,10C and 20C respectively.The kinetic calculation of GITT and EIS shows that the sodium ion diffusivity of the lanthanum-doped material is 4.275×10-12 cm2 s-1 and the surface activation energy of 37.97KJ mol-1.The phase change process of the electrode material was observed by in-situ XRD during the charge and discharge process.It was found that the doped material was a P2-OP4 phase transition,which effectively suppressed the irreversible phase transition caused by the traditional P2-O2 type and improved the structural stability.