基于VO2的金属相变设计和制备动力锂离子电池电极材料

Lithium ion batteries exhibit a lot of advantages such as the high voltage and high specific energy density, leading to the wide application prospect in electric vehicles, aerospace devices and other large equipments. However, until now, high-power lithium ion batteries commonly suffer from the high current density and high internal resistance during the charge and discharge processes at high current rates, which easily cause the local overheating and rapid capacity decay. To solve these problems, a new concept is proposed to design electrode materials for high-power lithium-ion batteries based on the unique metallic transition of VO2. Herein, it is expected that VO2 and foreign doped VO2 nanosheets or nanoribbons can be controllably fabricated by using graphene oxide as growing nucleus. And the ohmic polarization resistance of the electrode material can be dramatically reduced by harnessing the the metallic transition of VO2, and at the same time the charge-transfer resistance and lithium solid-state diffusion time can be largely reduced on the basis of the ultrathin feature of VO2. Thus, the electric conductivity and high-rate performances of the electrode materials can be significantly improved. We will further explore the structure change of VO2 and doped VO2 during the charge-discharge processes after their metallic transition, and make clear the relationship between temperature, phase transformation and lithium storage, as well as their lithium storage mechanisms. Moreover, we will systematically investigate the influence of foreign doping type and doping amount on the electrochemical performances and kinetics at different temperatures, and find the key factors affecting their properties for lithium storage. This can lay a foundation for the design, fabrication and practical application of high-power lithium ion batteries used in electric vehicles and aerospace devices under specific environment.

锂离子电池具有电压高、比能量大等优点，在电动汽车、航空航天器等大型设备上具有广阔的应用前景。但目前动力锂离子电池在高倍率充放电时存在电流大、内阻高，易造成电池局部温度过高和容量衰减快等问题。为此，本课题提出基于VO2的金属相变特性设计适用于动力锂离子电池电极材料的新思路。以期以氧化石墨烯为生长点，实现超薄VO2和掺杂VO2纳米片或纳米带的可控制备，利用其金属相变降低电极材料的欧姆极化电阻，结合其超薄特性降低电荷传递电阻和锂离子固相扩散时间，从而提高电池材料的导电性和高倍率性能。探索VO2和掺杂VO2相变后充放电过程中材料结构的变化，明晰温度、相变和储锂三者之间的关系以及储锂机理。并系统研究掺杂元素和掺杂量对VO2材料不同温度电化学性能和动力学的影响，探明影响此类材料储锂性能的关键因素，为适用于电动车和特定环境航空航天器用动力锂离子电池电极材料的设计、制备和实际应用奠定基础。

锂离子电池具有工作电压高、比能量大等优点，在电动汽车、航空航天器等大型设备上具有广阔的应用前景。但目前动力锂离子电池在高倍率充放电时存在电流大、内阻高，易造成电池局部温度过高和容量衰减快等问题。为此，本课题提出基于VO2等钒基材料的特性，构筑适用于动力锂离子电池电极材料的新思路，利用材料相变、元素掺杂和复合等措施降低电极材料的欧姆极化电阻，电荷传递电阻和锂离子固相扩散时间，从而提高电池材料的导电性和高倍率性能。主要研究内容如下：1) VO2/石墨烯复合电极：通过调节氧化石墨烯的超声时间和水热过程中的容积率，获得二氧化钒与石墨烯紧密结合的具有较高充放电容量电极材料；同时采用微波合成法快速（5-30 min）制备具有三维网络结构的VOx/石墨烯电池正极，此电极为锂离子提供更多嵌入空间及更好的热力学嵌锂位置。2）高导电性氮化钒/石墨烯三维凝胶电极：通过GO和NH4VO3的水热以及后续的在氨气气氛下的热处理制备石墨烯-氮化钒量子点三维凝胶复合物，提供了一种有效构建2D-0D的方法，提供锂离子和电子的快速传输通道。3)钨掺杂VO2：通过水热法制备钨掺杂VO2(B)三维网络正极材料，由于钨的掺杂极大的降低了VO2的金属相变温度，有利于电子的快速传导，获得倍率性能优异的锂离子电池正极材料。在完成本课题设定目标后，近一步研究多价离子在钒化合物中储存和传输机制，具体如下：4) VO2(B)纳米纤维储锌机理研究：通过原位X射线衍射和各种电化学表征，证明了VO2(B)纳米纤维是一种新的在独特隧道中的插层赝电容和超快锌离子储存的动力学行为。VO2(B)纳米纤维表现出高可逆性容量357 mAh g-1，出色的倍率性能和高能量和功率密度。5) VOxNy储锌机理研究：通过首次充电电化学活化反应，岩盐结构氮化钒（氮氧化钒）的高价氮离子（N3-）被低价氧（O2-）离子取代，产生具有大量空位/缺陷的阴离子无序岩盐结构的正极材料；此无序岩盐结构的VOxNy表现出高可逆容量，出色的倍率性能（9.6×104 W kg-1，600 C）和长的循环寿命。