晶格杂化-纳微结构协同调控强化钒基负极材料电化学储锂机理研究

Transition metal oxides (TMOs) represent promising anode candidates for rechargeable lithium-ion batteries (LIBs) due to their high theoretical capacity and cost effectiveness. However, challenges still exist for the electrochemical performance of TMOs with respect of their obvious volume expansion, intrinsically poor electron/ionic conductivity and the sluggish kinetics during the electrode electrochemical process. These drawbacks result in low capacity retention, poor rate performance and insufficient cycle lifespan, thus constituting the major obstacles on TMOs application. In order to solve these problem, the crystal of vanadium oxide and polyethylene glycol is hybridized into vanadyl ethylene glycolate (VEG), which allows for both high Li-ion solid diffusion and high theoretical capacity. Meanwhile, VEG/graphene nanocomposite of typical morphology is synthesized through nanostructure regulation. In virtue of crystal and nanostructure manipulation, the aim of synergistically intensifying the volume accommodation, electron/ionic transfer and electrochemical reactivity is achieved, and the corresponding structure-effect relationship is investigated as well as the manipulation principle. This project will provide novel procedure on promoting the electron/ion diffusion of conversion-type anode and support the design theory of the development on large capacity anode materials.

过渡金属氧化物具有理论容量高、成本低廉等优势，是理想的大容量锂二次电池负极材料。但是，过渡金属氧化物负极存在体积膨胀显著、电子离子本征电导率低、电极电化学过程本征动力学差等缺陷，造成容量保持率、倍率性能和循环寿命差等问题。本课题利用凝胶固态电解质的高导锂特性，对钒氧化物进行有机-无机晶格杂化，通过解析晶格杂化匹配性、杂化分子导锂特性与储锂机理，构建兼具高导锂、高容量特性的乙二醇氧钒杂化分子，大幅改善电极体相的离子电导率。课题同时运用纳微结构调控手段,构建乙二醇氧钒/石墨烯纳米复合结构，揭示乙二醇氧钒/石墨烯纳米复合结构的构效关系及调控机制。通过晶格杂化结构调控和三维结构调控，实现复合负极材料的抗膨胀性能、电子离子传输性能、电极电化学反应活性的同步强化。通过解析晶格杂化-纳微结构协同调控强化钒基负极材料电化学储锂机理，构建强化转换型负极材料传质传荷的新策略，为大容量负极材料设计提供科学依据。

过渡金属氧化物具有理论比容量高、成本低廉等优势，是理想的大容量锂二次电池负极材料。但是，过渡金属氧化物负极存在体积膨胀显著、电子离子本征电导率低、电极电化学过程本征动力学差等缺陷，造成容量保持率、倍率性能和循环寿命差等问题。受凝胶固态电解质（如聚乙二醇）的高导锂特性的启发，本课题采用混合溶解热合成方法，运用晶格杂化、纳微结构复合手段，构建出乙二醇氧钒/石墨烯（VEG/rGO）复合负极材料，大幅提高材料的高倍率、长循环储锂性能。制备的纯VEG负极在电流密度为100 mA g-1，可提供高达864 mA h g-1的比容量，近400周循环，容量保持率达到98%。倍率性能表明：当电流密度从100增加到8000 mA g-1时，容量保持高达64%。实验证实：当石墨烯含量为40 （wt）%时，VEG能均匀的生长在二维石墨烯片表面，VEG/rGO具有接近1000 mA h g-1的比容量。通过解析晶格杂化匹配性、杂化分子导锂特性、构效关系与储锂机理，同步强化，实现复合负极材料的高抗膨胀性能、电子离子高传输性能、电极电化学高反应活性。通过储锂机制的深入解析，实验发现了可逆的欠电位锂沉积行为，并提出金属锂/锂离子混合储锂过程，为有机金属化合物负极材料设计提供科学依据。