电位调制联合多效界面构筑多电子传输钒基氧代氟磷酸族高能量大功率室温可充钠电池正极材料研究

Under the increasing global energy crisis and worldwide environmental pollution, room-temperature rechargeable sodium battery is an excellent candidate for large-scale energy storage with its resource abundance and good performance, which can be extensively used in intermittent clean energy storage and smart grid development. Nax(VOyPO4)2F3-2y (0≤x≤4,0≤y≤1), denominated by us, is a series of emerging family polyanion materials with broad constituents. Based on multi-electron redox reactions during sodium (de)insertion, this family materials have a large theoretical capacity (243 mA h g-1), a high average potential (~4.0 V vs. Na+/Na) and high thermal stability thanks also to the inductive effect of the anion groups. They are therefore considered as a class of promising high safety high energy cathode materials for sodium batteries. However, only about 60% of the theoretical capacity could be practically obtained at present, due to the high redox potential of V4+/5+ (exceeding the decomposition potential of electrolyte) and the precipitous drop of Na+ diffusivity near the insertion/extraction limit (x≤1), which now becomes the key bottleneck problem hindering the research and development of this family materials..We have recently designed and synthesized a new Nax(VOyPO4)2F3-2y by an original potential tuning method, and have successfully realized 2.91 e transfer generating a reversible capacity of 177 mA h g-1, the highest so far in literature to our knowledge. In this project, we are going to further develop this potential tuning method based on systematic fundamental study to safely release higher capacities thus higher energy, and to improve the overall electrochemical performance of the oxyfluorophosphate family combining with multi-functional interface technology..The crystallographic structure evolution of Nax(VOyPO4)2F3-2y family along with composition and temperature will be first fully identified, so as to establish their structure-performance relationship under a uniform space group, especially to thoroughly explore the influence of potential modulation and interface structure on their crystal structure and electrochemical performance. Potential tuning is then proposed to effectively adjust the reaction potential of V4+/5+, efficiently improve the sodium diffusivity at extreme Na+ level (x≤1) and availably increase the practical multi-electron-based capacity. On the other hand, multi-functional interfaces are introduced to enhance the electric conductivity of the family materials and to improve their stability with electrolyte. Finally, the two technologies are synchronized and integrated to rationally design and reliably fabricate high safety, high energy, high power, long lifetime and low cost Nax(VOyPO4)2F3-2y cathodes for sodium batteries..Combining In-situ and Ex-situ characterization, supported with structural and electrochemical analysis, the underlying fundamental issues on energy storage mechanism, mass transportation, subtle structure change, interface effect, electric property, electrode thermodynamics and kinetics during charge/discharge will be comprehensively investigated. The effect and modification of potential tuning and multi-functional interfaces will be illustrated from multiple dimensions and multiple scales. With a fruitful technical and theoretical system, the achievements of this project are expected to enrich the “novel design - simple synthesis - structural property - advanced performance” theory and technique systems of battery materials, to promote the industrial application of multi-electron transfer vanadium-based oxyfluorophosphate family materials, and to expedite the development of room-temperature rechargeable sodium batteries as well as that of large-scale energy storage.

室温储能钠电池研究具有重要的理论和应用价值。项目选择组分宽广、理论容量大、平均电位高、热力学稳定的Nax(VOyPO4)2F3-2y (0≤x≤4,0≤y≤1)作为正极解决方案。针对系列材料实际容量小(60% ca.)和电导率低的问题，从制约其发展的多电子传输反应核心瓶颈入手。系统研究系列材料的结构演化规律，在统一空间晶系下建立其本征结构性能关系，揭示电位调制和界面构效对结构性能之影响。进而利用电位调制技术有效调控V4+/5+电位、突破Na+深度可逆嵌脱、提升Na+极限扩散速率以获得高容量，采用多效界面改善材料电导及其与电解液的稳定性。科学设计、综合集成，高效构筑高安全、高能量、大功率、长寿命、宽工况、低成本的实用电池材料。多维度、多尺度分析其深度嵌脱钠的储能机理、物质输运、结构性能和电极热、动力学过程，建立相关技术理论体系，促进钒基氧代氟磷酸族材料的生产应用，助推钠电池及储能产业发展。

钒基氧代氟磷酸族系列材料Nax(VOyPO4)2F3-2y (0≤x≤4, 0≤y≤1)具有热力学稳定、理论容量大、理论电位高、嵌脱钠体积变化小等特点，是一类非常有前景的钠电池正极材料。研究和制备高安全、高性能、低成本的Nax(VOyPO4)2F3-2y对于开发先进室温可充钠电池具有重要的理论和技术价值，对于促进大规模能源存储发展和应用具有重要的战略和现实意义。.本项目针对系列家族材料实际容量小、电导率低和倍率、循环性能不好等问题，从系列材料充放电过程中的多电子氧化还原反应入手，研究电位调制与多效界面技术和理论，开发兼具高安全、高容量、高电压、大功率、长寿命的Nax(VOyPO4)2F3-2y。在优化固相制备工艺的基础上，系统研究了家族材料从VPO4到(VO)2P2O7、Na4P2O7、Na3V2(PO4)3、Na3V2(PO4)2F3、Na3V2O2(PO4)2F、Na4(VOPO4)2F等一系列Nax(VOyPO4)2F3-2y (0≤x≤4, 0≤y≤1)的结构性能演化过程与规律，揭示了制备方法、化学组分、晶相结构和电池性能之间的构效关系。进而设计开发了F调控、O调控、Na调控和缺陷调控等电位调制方法，有效调控了系列材料充放电过程中V2+/3+、V3+/4+、V4+/5+等多电子反应电位，突破了Na+深度可逆嵌脱及其扩散和迁移速率。同时，采用无定形碳、碳纳米管、石墨烯、氧化物、磷酸盐等复合材料构筑多效表界面结构，大幅改善了系列材料的导电能力及其与电解液的相容性和稳定性。最后，联合电位调制与多效界面，科学设计、综合集成，高效构筑了高安全、高性能、实用化的Nax(VOyPO4)2F3-2y，探究了其储能机理、电位调制和界面作用机制、电荷传输和电极热、动力学过程，建立了电位调制和多效界面设计制备高性能系列材料的技术和理论基础。.此外，进一步丰富和发展电位调制与多效界面技术理论，在锂电池LiVPO4F正极材料、Li2MnSiO4正极材料、三元正极及其前驱体材料、锰氧化物负极材料和超级电容器微纳电极材料等其它能源材料与器件中，逐步验证、研究和拓展了本项目相关技术与理论的普适性和实用性，获得了显著的结构调控和电化学改性效果，研发了锂电池和超级电容器的一系列高性能关键材料，超额完成了项目的研究内容和研究目标，在能源材料和能量存储领域具有重要的科学意义、技术价值和应用前景。

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