二维金属氧化物纳米片/MXene超晶格的设计与储能性能研究

Metal oxides (MO) are recognized as an important class of anode materials for lithium/sodium secondary batteries because of their high theoretical specific capacity. However, a great challenge lies in their low conductivity and large volume change during charge-discharge process. In this study, we propound new MO/transition metal carbide (MXene) composites with a superlattice structure composed of alternately stacked unilamellar MO and MXene nanosheets through the interface control and electrostatic assembly. In these MO/MXene composites, MO nanosheets provide a large number of active sites; highly conductive MXene nanosheets significantly improve the electrical conductivity; the MO/MXene interfaces modified by the surfactant buffer the volume change and promote the ion transport; the unique superlattice structure prevents the aggregation of the nanosheets. Therefore, the MO/MXene superlattice materials are expected to exhibit high reversible specific capacity, excellent cycle performance and rate performance. Here, we are going to precisely regulate the charge distribution on the surface of the MXene nanosheets by the surfactant. Based on a hypothesized area-matching model using the in-plane unit cell area of both nanosheets, the mixing ratio is calculated to obtain the superlattice via face-to-face restacking. The MO/MXene superlattice materials is fabricated via solution-phase electrostatic assembly between negatively charged MO nanosheets and positively charged MXene nanosheets. The influence of the preparation process on the superlattice structure is studied to achieve the controllable preparation. The electrochemical performances for Li and Na storage of the MO/MXene superlattice materials are investigated for clarifying the structure-activity relationship and the energy storage mechanism. We believe this study will open up new horizons for the development of high-capacity, long-cycle life and good-rate performance anode materials for lithium/sodium secondary batteries.

金属氧化物(MO)是一类具有高理论比容量的锂/钠二次电池负极材料，提高电导率、缓解充放电过程中的体积变化是其亟待解决的问题。本项目提出基于界面调控和静电自组装，设计具有二维-二维单层交替堆叠超晶格结构的MO/过渡金属碳化物(MXene)复合材料的新思路。MO纳米片提供大量活性位点，高导电性的MXene纳米片显著提高电导率，表面活性剂修饰的界面缓冲体积变化并促进离子传输，超晶格结构防止纳米片团聚。因此，MO/MXene超晶格有望展现出高可逆比容量、优异的循环性能和倍率性能。本项目拟以表面活性剂精确调控MXene片层表面电荷分布，结合区域匹配模型计算，通过液相静电自组装制备MO/MXene超晶格复合材料；研究制备工艺对复合材料结构的影响，实现可控制备；研究MO/MXene超晶格的储锂/钠性能，分析构效关系，揭示储能机制，为发展新型高比容、长寿命、高倍率的锂/钠二次电池电极材料提供有益的认识。

金属氧化物是一类具有高理论比容量的锂/钠二次电池负极材料，提高电导率、缓解充放电过程中的体积变化是其亟待解决的问题。本项目采用无机盐模板法、二维过渡金属碳化物（MXene）转化法制备了多种二维金属氧化物纳米片材料；采用刻蚀剥离法制备了具有单层或少层结构的二维MXene纳米片；探索了静电自组装、混合-抽滤法等多种二维-二维交替堆叠结构的金属氧化物/MXene复合材料的制备策略，制备了一系列具有高比容量、优异的倍率性能和循环性能的二维-二维金属氧化物/MXene复合材料，并对其进行了系统的表征，研究了制备参数工艺对复合材料的形貌结构的影响，实现了其可控制备。.将制备的金属氧化物/MXene复合材料通过传统混浆-涂覆法和真空抽膜法两种方法制备成电极测试其电化学行为与性能，其中真空抽膜法制备的工作电极具有柔性自支撑的特性。MXene抑制了金属氧化物的团聚和充放电过程中的体积膨胀，且有利于电子和离子的快速传输；金属氧化物暴露出大量的活性位点，有效防止了MXene的自堆叠；二维-二维结构使复合材料具有优异的结构稳定性。因此，制备的金属氧化物/MXene复合材料表现出了高比容量、稳定的循环性能和优异的倍率性能。.结合理论分析与实验测试结果，分析了二维-二维金属氧化物/MXene复合材料在锂离子电池中的储能机制。构建了锂在二维-二维金属氧化物/MXene异质界面上的吸附/迁移的理论模型，阐明了MXene对异质界面处电子和离子的快速传输的促进作用，揭示了金属氧化物与MXene两种组分的协同效应及其对复合材料电化学性能的影响。为发展新型高比容、长寿命、高倍率的锂/钠二次电池电极材料提供了有益的认识。.