Study On Low-cost And High-performance Oxide Secondary Battery Oxide Electrode Materials

The research of conventional secondary battery electrodes mainly focuses on single-phase structure materials.However,with the rapid development in the areas of electric vehicles and energy storage,the existing materials are insufficient to meet the demands of increasing energy density.In recent years,composite-structure materials with high energy density have been widely studied.However,almost all the composite-structure materials are revealed by structural characterization after the preparation of materials,rarely to the initial design from the point of composite-structure.In addition,there are still great challenges on how to further control phase structure proportion to eventually control the electrochemical performance and how to understand electrochemical reaction mechanism of composite structure materials.In this study,the composite-structure materials are deeply study from three aspects:design of composite-structure,structural regulation and electrochemical reaction mechanism.First,the in-situ high-temperature X-ray diffraction?in-situ HRXRD?was conducted to analyze the reaction process of Na_2/3Ni_1/3-xFe_xTi_2/3O₂?NNFT?material.The generation and evolution process of composite-structure materials have been explored and the triphase composite electrode material A?P2??B?T1???1-A-B??T2?,?0?A?1,0?B?1?was obtained,which provides guidance for the synthesis of composite-structure materials.Based on the guidance of composite-structure design research,another series of composite-structure electrode materials of Na_2/3Co_1/3-xMn_xTi_2/3O₂?NCMT?and Na_x Li_2-xTiSiO₅?NLTS?were designed and fabricated.The regulation of different phase structure proportion in the composite structural materials can be relarized by changing the components with different ratios,and the relationship between the phase structure proportion and electrochemical performances has been studied.The experimental results show that NNFT material has good rate performance and cycling stability when the ratio of P2,T1 and T2 is 46:21:33.For the composite-structure materials designed on the basis of manganese based material,they can reduce the proportion of layered structure,indirectly reducing the flake material for improveing material circulation performance.For NLTS?x=0.5?,two-phase compositions of Na_x Li_2-xTiSiO₅ and Na_xLi_2-xTiSiO₅was prepared.They show a reversable capacity about 305 mAh/g for the first discharge,which is slightly higer than the single-phase structure.Meanwhile,Na_0.5Li_1.5TiSiO₄ material with partially substituted by lithium with sodium ion still has a low working voltage,which is beneficial to improve the energy density of lithium ion battery.Moreover,the low cost of Na element that introduced can not only reduce material cost but also improve electrochemical performance.Finally,the structural transformation and electrochemical reaction mechanism have been analyzed using in-situ electrochemical X-ray diffraction?in-situ EXRD?.The corresponding relationship between the insertion/extraction mechanism of composite-structure material and the phenomenon of multi-stage in charge/discharge curves have been explored.It has been found that the Na⁺inserts into the T1structure firstly and then into the P2 structure.And the Na⁺ions can be reversibly inserts/extracts form T1 and P2 strutures in the following charge/discharge process.By studying the relationship between structure regulation and performance,and exploring the reaction mechanism,the electrochemical properties of composite structure are improved.