锂电池氧化物固体电解质“冷烧结”(< 350 ℃)的原子尺度机理研究

Despite being one of the most popular and extensively studied solid electrolytes for all-solid-state Li batteries, oxide solid electrolytes have been continuously plagued by its overly high sintering temperature (> 1000 ℃), where the severe Li loss makes it difficult to precisely control the composition. Fortunately, “Cold Sintering Process” (CSP), a novel technique developed in 2016, may provide a fundamental solution. Based on the hydrothermal dissolution-precipitation process at particle surfaces, it could lower the sintering temperature from over 1000 ℃ to at least 350 ℃, while maintaining a similar density. Nevertheless, currently CSP cannot be effectively applied to solid electrolytes yet: it relies on quite a few experimental parameters, but the present mechanistic understanding is too limited to efficiently guide their optimization. Aiming at filling such a gap, this project will establish the structure-processing-property relationship for the CSP of oxide solid electrolytes from the most fundamental level, i.e. the atomic scale, using the aberration-corrected electron microscopy as the primary investigation tool, so that all-solid-state Li batteries can effectively, rapidly benefit from the newly emerged CSP technique. The principles obtained here may address the long-standing controllability and repeatability issues for the sintering of oxide solid electrolytes, significantly improving the efficiency in both basic research and materials design.

尽管作为全固态锂电池研究中最热门的几类固体电解质之一而广受关注，氧化物固体电解质因烧结温度过高（> 1000 ℃），长期受制备时锂挥发、成分难以精确控制的困扰。2016年研发的“冷烧结”技术有望从根本上解决这个问题。利用颗粒表面在水热条件下的溶解-沉积，该技术可在350 ℃以下达到传统烧结方法上千度热处理所获得的密度。但是，目前“冷烧结”还无法被有效应用于固体电解质：这一技术受诸多实验参数影响，而目前其机理尚不明确，无法有效指导工艺优化。本项目旨在填补这一空白，用球差校正电镜为主的研究方法，从最本质的原子尺度揭示氧化物固体电解质“冷烧结”的工艺-结构-性能关联，以确保该新生的先进技术被高效、迅速的应用于全固态电池领域。研究成果有望解决氧化物固体电解质烧结可控性低、可重复性差这一顽疾，极大的提升基础研究和新材料研发的效率。

氧化物固态电解质对于实现安全、高能量密度的全固态锂电池具有独特优势。但是，此类材料通常需要经过1000 °C以上高温烧结才能充分致密化，从而具备有意义的离子电导率，而在此高温下不可避免的锂元素挥发将使最终成分难于控制，为规模化生产制造了瓶颈。为了克服这一挑战，本项目探索了以“冷烧结”这一新技术实现低温烧结固态电解质的可能性。在具备原子尺度分辨率的球差校正透射电镜观测所主导的机理研究的指导下，本项目成功的在低至200 °C的温度下对原本需要在1100 °C以上才能充分致密化的氧化物固态电解质陶瓷进行了烧结，达到了和传统高温烧结所制得的陶瓷相当的离子电导率和致密度。与此同时，本项目在使用球差校正透射电镜进行研究的过程中，还在固态电解质的离子传输机理、锂枝晶生长的微观起源等重要科学问题的探索上取得了进展。相关成果发表在Nature Materials、Nature Communications、Matter等高影响力期刊上。