插层结构调控对双层V2O5储钠性能的影响及机理研究

Bilayered V2O5 has been recognized as promising cathode materials for energy storage sodium-ion batteries, as it offers the essential advantage of very high theoretical capacity (250 mAh/g). However, due to the relatively larger radius of Na+, the diffusion of Na+ in bilayered V2O5 is very slow and the layer structure is easy to collapse, resulting in the fast capacity fading. These issues seriously hamper the practical application of bilayered V2O5 in sodium ion batteries. The purpose of this subject is to improve the sodium storage performance of bilayered V2O5 by the strategy of interlayer structure design: (1) optimizing the diffusion path of Na+ in bilayered V2O5 by tuning the interlayer water content; (2) improving the stability of layer structure of V2O5 by pre-intercalation of multivalent metal cations; (3) Increasing the interlayer space and improving the conductivity of bilayered V2O5 by intercalating conductiing polymers within the interlayer space; (4) Further improve the sodium storage performance by constructing multivalent metal cation/conducting polymer multi-components intercalation layer with synergic activity. Combining first-principles calculations, the effect and mechanism of different interlayer structures on the sodium storage performance of bilayered V2O5 will be analyzed. The investigations of this project will promote not only the further understanding of the mechanism of electrochemical reaction of V2O5 in theoretical aspect, but also the performance improvement and wide application in practical aspect. Meanwhile, this project may also provide a positive reference for the applications of V2O5 in the other relative fields, such as Mg-ion batteries, Al-ion batteries, and sensors.

双层V2O5具有250 mAh/g的高理论比容量，是一种理想的储能型钠离子正极材料。但因Na+半径较大，在V2O5层间的扩散阻力大，循环过程中V2O5层状结构容易坍塌进而导致材料失去活性，这是目前制约双层V2O5实际应用发展的关键问题。针对以上问题，本项目采用插层结构调控改善双层V2O5储钠性能：(1)调控插层水分子优化Na+的扩散通道；(2)在层间预嵌高价金属离子提高其层状结构稳定性；(3)在层间插入导电高分子拓宽材料的层间距并提高其导电性；(4)构筑高价金属离子/导电高分子复合插层的V2O5，利用二者的协同效应进一步提升材料的储钠性能。结合第一性原理计算分析不同插层结构对材料储钠性能的影响规律和内在机理。项目研究对深入理解双层V2O5嵌/脱Na+反应机理，促进其性能提升和实际应用具有重要的理论和实际意义。同时对V2O5在Mg2+电池、Al3+电池、传感器等领域中的应用也具有积极借鉴意义。

双层V2O5具有250mAh/g的高理论比容量，是一种很有应用前景的钠离子电池正极材料。但因Na+半径较大，在V2O5层间的扩散阻力大，循环过程中V2O5层状结构容易坍塌进而导致材料失去活性，这严重制约了双层V2O5正极材料的实际应用和发展。该项目通过插层结构调控(层间水分子调控、预嵌金属阳离子、预嵌导电高分子)改善双层V2O5的储钠动力学、层状结构稳定性和循环性能。取得的重要结果主要如下：(1) 研究了层间水分子含量对双层V2O5结构和储钠行为的影响及机理，发现过多的层间水会阻碍Na+的快速扩散，而过少的层间水分子不利于双层V2O5相结构稳定性。经过200℃热处理后的双层V2O5具有相对最佳的储钠性能，在100mA/g电流密度下经过100次循环后其可逆比容量保持在96.9mAh/g。(2) 制备了不同金属阳离子预嵌双层V2O5材料，发现金属阳离子预嵌对材料微观形貌、层间距和V4+含量等都有影响，其中Y3+预嵌可有效提高材料的循环稳定性，Zn2+预嵌可显著改善材料的倍率性能。预嵌金属阳离子(M)与V2O5板层中的O原子以及层间H2O中的O形成的[MO6]八面体柱撑结构是改善材料层状结构稳定性的关键。(3) 研究了有机分子PEG预嵌对双层V2O5结构和储钠行为的影响及机理，发现有机分子预嵌拓宽了材料的层间距，引入了更多的低价V4+，进而有效提高了材料的Na+扩散系数(提高1个数量级)、循环性能和倍率性能。(4) 通过单体聚合法制备了导电高分子/金属阳离子复合插层双层V2O5材料，发现PPy/Fe3+复合插层可改善材料的循环性能，提高材料的放电电压，尤其是可极大地提高材料的大电流充放电性能。例如在1000mA/g电流密度下，PPy/Fe3+复合插层双层V2O5的可逆比容量保持在54.8mAh/g，而纯双层V2O5的可逆比容量仅为4.9mAh/g。项目研究对深入理解双层V2O5嵌/脱Na+反应行为及机理，尤其是如何从插层调控角度改善双层V2O5的储钠性能具有重要的理论和实际意义。同时，对双层V2O5材料在Mg2+电池、Zn2+电池和Li+电池等领域中的应用也具有积极借鉴意义。