ZnO基纳米复合材料高首效储锂的机制及其在锂离子电池中的应用研究

As one of the most important next-generation electrode materials with high specific energy and diverse Li-ion storage mechanisms, ZnO in nano-dimensions exhibits poor cyclibility due to crystal coarsening, exfoliation, and other accompanying side effects during lithiation/delithiation processes; meanwhile abundant solid electrolyte inter-phases (SEIs) are readily formed around the nano-sized ZnO, leading to a lower initial coulombic efficiency (ICE) and poor utilization in lithium ion batteries. In order to realize the efficient application of ZnO in lithium ion batteries with lower cost and avoid many tedious procedures related to prelithiation, the project will try to fabricate a series of novel ZnO nanohybrids by a new fast vaporization-solidification method; those nanohybrids should not only exhibit excellent cycling performance, and also show high initial coulombic efficiencies (ICEs). In those novel ZnO nanohybrids, we will realize both goals of the adjustable dimensions of crystal size and the tunable surface/interfaces modifications with organic functional groups through altering the precursor organic species, evaporation temperature, reaction duration, and the annealing processes. On the one hand, we will try to achieve rational insights into the formation, evolutions, and mechanisms of the microstructures and organic species in various ZnO nanohybrids, and their influences on ICE, cyclibility, and other electrochemical properties; on the other hand, the differences of lithiation processes and microstructure evolutions between ZnO nanohybrids with high ICEs and commercial counterparts will be thoroughly analyzed and discussed to obtain the reasons why ICEs of those novel ZnO nanohybrids had been improved, deepen our insights into the challenging issues why SEIs were formed, and provide universal strategies for designing other anode materials with superior cycling performance and high ICEs.

纳米ZnO作为新一代高能、多机制储锂的重要电极材料之一，易于发生颗粒粗化、脱落等现象，循环能力差；同时纳米ZnO表面易于形成大量固态电解液相（SEI）, 导致其首次库伦效率较低，限制了其锂电池应用。为了实现ZnO低成本，高效应用，避免繁琐的预锂化过程，本项目拟借助快速蒸发-急速固化法，合成一系列既具有优良循环能力，又具有较高首次库伦效率的ZnO纳米复合材料；通过改变前驱物类别、蒸发温度、反应时间，以及退火过程等参数实现ZnO纳米颗粒尺寸可调和表面有机可控修饰。一方面，分析不同微结构的ZnO纳米复合材料，研究微结构及其功能化演变的过程和机制，及其对首次库伦效率、循环稳定性等的影响；另一方面，对比高库伦首效ZnO纳米复合材料与传统商业材料锂化过程和微结构衍变过程的差异，深入研究首次库伦效率获得改善的原因，加深对SEI成因等难点问题的认识，为设计其它高库伦首效的高性能负极材料提供普适性方法。

项目针对ZnO基过渡金属氧化物等在储锂负极应用中存在首次库伦效率低、容量退化快等问题，提出其表面原位形成亚埃级厚的有机表/界面层，巧妙地避开材料表面吸附的亲氧、羟氧等自由基与电解液的相互作用，遏制了SEI的大量形成；而且原位形成的有机界面层还有助于保证ZnO颗粒小、彼此分立，在后期电化学过程中能有效遏制晶粒粗化过程。基于该ZnO纳米复合材料的储锂负极，首次库伦效率可高达91.4%，储锂过程中ZnO完全转化可逆，经过1400多次循环，容量持有率仍保持95%，示例型的扣式全电池中，初始锂利用率高达85.4%。此外，项目还拓展了锰基过渡金属氧化物的致密储锂应用；针对传统阳离子存储能量密度不够高，项目还提出了阴-阳离子接力存储模式，并实现了其在锂、钠、钾、钙等金属电池领域的验证。结果表明：借助阴阳离子的交替、接力存储，器件的储能密度能得到大幅度提升。总之，项目实现了预期ZnO基过渡金属氧化物的高首效储锂，发表了Adv Mater、Adv Energy Mater等该领域的重要论文11篇，被引三百余次，参加相关领域的学术会议2人次，培养博士生1名，超额完成项目预期目标，取得了相对良好的效果。