Study On Silicate Cathode Materials For Lithium (Sodium) Ion Batteries Based On First Principles

The excessive use of fossil fuels and increasingly serious environmental pollution drive people to develop green new energy,and the rational use and distribution of new energy drives people to seek more efficient energy storage system.As the biggest dark horse of energy storage system,lithium?sodium?ion battery has attracted much attention.The choice of electrode materials is very important to the performance of battery,so the research of electrode materials has been focused since the day of the battery.Recently,researchers have found that silicate-like polyanionic cathode materials have stable cell structure,and can achieve two moles of lithium?sodium?ions per unit formula in the electrochemical cycle,reaching a high theoretical specific capacity.In this paper,the properties of silicate anode materials are studied by means of vasp software package.Based on the approximate solution of schrodinger equation,the wave function in a stable state can be obtained only by inputting the basic elements of the constituent substances,and the corresponding physical and chemical properties can be deduced.Therefore,in the process of approximate processing,different functional methods for the same system will also produce different qualitative analysis results,especially for the strongly correlated system which is greatly affected by the electronic interaction.In this paper,we first use of GGA,GGA+U,GGA+SP,GGA+U+SP four approximate calculation the Li₂FeSiO₄ material crystal structure and electronic properties,electrochemical properties,compared with previous experimental results and found the qualitative prediction results of non-magnetic structure Li₂FeSiO₄ far,with the experimental results and GGA+U+SP approximate method can accurately predict Li₂FeSiO₄ structural features as well as electronic,electrochemistry,mechanical and thermodynamic performance.Besides,magnetic and off-site correction will lead to opposite changes in structure and mechanical properties of Li₂FeSiO₄ materials.Then,based on the above approximation method,the structural properties,electronic properties,electrochemical properties,mechanical properties and thermodynamic properties of Na₂MSiO₄?M=Fe,Mn,Co,Ni?are discussed.The first-order deintercalation voltage platform of Na₂FeSiO₄ material was found to be low.Na₂MnSiO₄ material has poor cycling stability.Na₂CoSiO₄ material has general electronic conductivity.Na₂NiSiO₄ material is greatly affected by temperature.These four materials are not the best choice to be used as cathode materials alone,so we can learn from previous experience to improve their comprehensive properties by appropriate element doping.