基于聚合物刷诱导的金属锂负极的电沉积行为及枝晶抑制机理研究

Metal lithium is a highly potential anode material due to its high theoretical specific capacity is about 10 times than that of graphite. However, security risks caused by uncontrollable dendrite growth seriously hinder the application of lithium anode. To suppress dendrite formation induced by the uneven Li-ion transfer, we propose in this project to introduce controllable polymer brush with lithophilic functional groups and nano-structure into the copper foil through surface initiated polymerization way. Here we put forward the research for consideration that the surface modifying is beneficial for the uniform deposition. Densely and uniformly distributed lithiophilic sites from the functional groups, limited nucleus size by nano-brushes and excellent interfacial wettability which together guide the initial nucleation layer with smooth and uniform morphology, suppress lithium dendrite growth at the nucleating stages and lead to a dendrite-free electrodeposition lithium anode. The relationship between the surface modification by polymer brush, morphologies of lithium deposition and electrochemical performances of the anode would be established in this study. Meanwhile, efforts will also be devoted to develop versatile fabrication technologies to control the morphology and structure of the dendrite-free lithium anode. In addition, it would be of fundamental importance to understand the mechanism of how the polymer brush influence the suppression of dendrite, and the process of nucleation and growth of deposition layer by means of the in-situ techniques and simulation calculations. The outcomes from this research project will provide new ideas and theoretical guidance for designing, synthesizing and application of high-performance dendrite-free lithium metal anode.

锂金属的理论比容量约为石墨的十倍，是一种极具潜力的高性能负极材料，但由于不可控的枝晶生长所带来的安全隐患严重制约其实际应用。项目针对因离子传质及分布不均而导致的锂枝晶生长问题，从调控沉积基体表界面性质的角度出发，创新性地通过表面引发聚合技术对平面铜集流体接枝含亲锂官能团且纳米结构可控的聚合物刷，分别利用其亲锂官能团形成均匀致密的形核位点，纳米刷型结构均化离子传质并控制晶核尺寸过度长大，以及优良的界面润湿性协同促使锂的均匀形核，诱导形成均匀平整的电沉积锂负极，抑制枝晶生成。项目拟通过对聚合物刷化学性质及物理结构的优化调控，建立无枝晶电沉积锂负极的控制关键及设计原理。结合电化学原位表征与模拟计算，明确聚合物刷对于抑制枝晶形核生长的作用机制，建立均匀无枝晶电沉积锂负极的形核生长模型，揭示聚合物刷-沉积锂形貌-电化学性能之间的本质关联，为无枝晶锂负极材料的设计合成与集成应用提供新的思路和科学依据。

金属锂负极具有超高的理论容量（3860 mA h g-1）和最低的电化学电位（-3.04 V vs.标准氢电极），在高能量密度二次电池体系中具有广阔的应用潜力，但其不可控枝晶生长带来的安全隐患成为限制金属锂二次电池发展的瓶颈。因此，研究金属锂的电结晶行为，实现其电结晶过程的有效调控，从而抑制锂枝晶生长成为金属锂电极应用的关键问题。基于此，项目研究了电沉积基底与锂离子的静电交互作用对锂电极电结晶形核行为的影响机制。团队首次将聚（N-异丙基丙烯酰胺）（PNIPAM）聚合物刷引入锂电结晶过程，揭示了PNIPAM 聚合物刷与锂离子的静电相互作用对锂电结晶形核行为与沉积形态演变的影响机制。结果表明：PNIPAM 聚合物刷上的酰胺氧亲锂官能团可诱导锂在基底表面的初始成核位置均匀分布，增加成核的可能性，并使离子分布均匀。密度泛函理论计算揭示了锂离子与酰胺氧之间存在强烈的静电交互作用，以及电沉积锂原子可在PNIPAM 聚合物刷接枝铜基体上实现均匀分布。此外，聚合物刷独特的三维纳米结构的空间限域作用，可从锂电结晶的成核阶段诱导其非枝晶化形核生长。所得平面柱状锂负极在20 mA cm-2 的超高电流密度下显示出优异的循环稳定性，电池可以连续运行超过1050 h。在以磷酸铁锂（LiFePO4）为正极的全电池中也表现出优异的循环稳定性（500 次循环后放电容量仍保持在120mAh g-1）和倍率性能（5 C：85 mAh g-1）。基于此，本项目提出的从晶体形成的初始“萌芽”阶段调控离子电沉积的调控方法，可为金属锂电结晶非枝晶化形核生长提供新的思路。