金属锂负极的枝晶抑制技术及其可充性研究

Lithium (Li) metal is considered as one of the most attractive anode material for the high energy rechargeable batteries, due to its extremely high theoretical specific capacity (3860 mAh/g), and the lowest negative reduction potential (−3.045 V vs. SHE). However, several seemingly insurmountable barriers, including dendritic Li growth and limited Columbic efficiency during repeated Li deposition/stripping processes, have prevented their practical applications. Herein, we propose to develop dendrite suppression techniques and solve the poor cycling stability of Li-metal anode. This research project is oriented to develop novel electrolyte systems, via screening highly stable ether solvents, highly dissociated organic Li salts, and high concentration electrolytes, so as to get a deep insight into the effect of electrolyte composition and solution chemistry structure on Li deposition behavior; explore suitable interfacial modification methods, including SEI formation additive and in-situ polymer coating, so as to promote the interfacial stability of Li metal anode with a rigid and flexible SEI layer, and then enable long-term and stable cycling of lithium metal anode with high Coulombic efficiency at high current densities. Furthermore, practical applications of lithium metal anode in rechargeable Li batteries, such as Li-V2O5 and Li-S cells, could be anticipated by integrating these novel electrolyte systems and functional additives with suitable cathode materials. These researches are expected to pave the way for the modification and utilization of lithium metal anode，and provide some knowledge and technical support for the development of next generation high energy Li metal batteries.

金属锂具有极高的比能量(3860mAh/g)和最负的电极电势(-3.045Vvs. SHE)，是极具竞争力的电池负极材料。然而，锂金属在充放电过程中易产生枝晶，导致电池性能急速衰减，并引起安全性隐患，阻碍了其商业化应用。针对锂负极存在的枝晶生长和循环寿命低下等科学难题，本项目提出开发与锂负极兼容的新型电解液体系，通过筛选高稳定性醚类溶剂、高解离度有机电解质锂盐和高浓度电解液，理清溶液组成及化学结构对锂沉积行为的影响；同时探索电极界面修饰技术，采用SEI成膜添加剂、聚合物表面包覆等方法，构建高机械强度和高结构柔韧性的电化学反应界面，进而实现金属锂无枝晶、高效率、长寿命循环。在此基础上，优选高性能正极材料，如多电子钒氧化物V2O5、高容量S电极等，构建具有应用前景的高能可充锂金属电池。通过本项目的实施，可为锂负极改性研究提供解决对策，进而为发展下一代高比能化学电源新体系提供技术支持和知识积累。

金属锂负极具有极高的理论比容量(3860 mAh g−1)，最负的电极电势(−3.040 V vs SHE)，被视为下一代高比能电池的理想负极材料。然而，锂枝晶的不可控生长及循环稳定性低下等问题严重阻碍了锂金属电池的实际应用。针对锂负极存在的枝晶生长和可充性难题，本项目开展了四个方面的研究探索工作：其一，筛选了一种硫酸二甲酯DMS作为SEI成膜添加剂，选择性构建富含Li2S、Li2O等无机相SEI膜。与传统的烷基碳酸锂LiROCO2基有机SEI相比，无机相SEI膜具有更优异的机械强度，因此能维持沉积过程中界面结构的稳定，抑制锂枝晶的突出生长。其二，开发了一种亲锂性Ag/Au异质金属表面修饰法，诱导锂的均匀成核。该Ag/Au纳米修饰层可与锂形成合金降低锂的成核势垒，并为锂成核提供均匀而丰富的活性位点，诱导锂均匀沉积为球状和紧密排列的柱状，从而实现锂负极无枝晶可逆电沉积。其三，通过在金属锂表面构建纳米多孔异质Cu修饰层，系统解决锂电沉积反应的均匀性问题。该纳米多孔Cu修饰层的互穿导电网络产生电场屏蔽效应，均一化电极表面电场分布；多孔电极结构缩短离子扩散路径，均一化液相传质流量；纳米颗粒提供丰富的电化学界面，均一化界面成核及反应动力学；从而首次实现理想的平面状致密锂沉积。其四，通过将介孔结构的SiO2纳米微球与柔性PVDF聚合物复合，制备了兼具高离子电导、高机械强度和高电化学稳定性的复合人工SEI膜，成功地实现了>4.5 V级高电压锂金属电池的长寿命稳定循环。无机SiO2纳米粒子的加入，提高了聚合物膜的机械强度；丰富的介孔结构利于储存电解液，提供快速的锂离子传输通道；聚合物主体能够作为一道屏障，显著减少界面副反应；从而维持高容量及长循环过程中界面SEI膜的结构稳定性。以上工作为系统解决锂的枝晶生长、库伦效率低下及循环寿命差等问题提供了一些可行性方案，有望促进锂金属电池的研究和规模应用。