原位合金化策略反应机理及协同效应原理的基础研究

Potassium-ion batteries have a substantial potential market and scientific value because of the abundant and low-cost potassium resources. Currently, the anode material research focuses on the low-cost and conductive carbon materials, but the compact density is low while the energy density is not high. Sn, Sb, and Bi can form alloys with potassium to provide a high capacity. However, the volume change during charging and discharging is huge, resulting in a low stability. Alloys are attractive in lithium and sodium ion batteries due to the synergistic effect between elements. However, the alloy prepared by the conventional ball milling method has a large size and a poor uniformity of elemental distribution, and does not solve the problem of instability. The in situ alloying strategy can produce alloy nanoparticles with a small size and uniform elemental distribution, forming a strong synergistic effect between atoms to solve the instability. Therefore, to deeply understand the strategy, this project will 1) adopt the first principles and theoretically calculate the bonding, crystal structure, and kinetic characteristics during the formation and potassium storage of (Bi, Sb) nanoparticles in this strategy; 2) characterize the dynamic evolution of bonding, crystal structure, elemental distribution, and valence state during charge and discharge in real-time by in situ XRD, in situ Raman, and TEM, together with elemental and valence analysis; 3) determine the formation mechanism of alloy nanoparticles and resolve the principle of the strong synergistic effect between atoms by combining the results from calculation, material characterization, and electrochemical methods.

因为丰富而低成本的钾资源，钾离子电池具有很大的潜在市场和科学研究价值。目前其负极材料研究集中在价格低、导电性好的碳材料，但其压实密度较小、能量密度偏低。Sn、Sb、Bi可与钾形成合金，提供高容量。但充放电过程体积变化大、稳定性低。由于协同效应，合金在锂和钠离子电池中得到了关注。但传统球磨法制备的合金尺寸大、元素分布均匀性欠佳，没有解决钾电池负极的不稳定性。然而，原位合金化策略可以产生尺寸小、元素分布均匀的纳米合金颗粒，形成原子间的强协同效应来解决这个问题。因此，为了深入认知该策略，本项目将1）采用第一性原理，理论计算此策略中(Bi,Sb)纳米合金形成及储钾过程中原子成键、晶体结构变化及动力学特征；2）通过原位XRD、原位Raman、TEM及元素和价态分析，实时表征充放电时原子成键、晶相、元素分布和价态的动态演变；3）结合电化学方法，探明原位合金化策略的反应机理，揭示强协同效应的原理。

针对原位合金化策略反应机理及储钾协同效应原理尚不清晰等瓶颈问题，本项目采用原位X射线粉末衍射、透射电镜及元素和价态分析等实验方法，结合电化学手段以及理论计算，探究了同时含有铋、锑元素的前驱体氯氧化铋锑和磷酸铋锑通过原位合金化策略产生铋锑合金的反应机理和储钾机制，及铋锑元素通过协同效应高效储钾的原理。本项目实现了对电化学嵌/脱钾过程中氯氧化铋锑和磷酸铋锑相转变过程的精准表征，阐明了氯氧化铋锑和磷酸铋锑组分、结构、形成铋锑合金的反应机制和演变规律，揭示了原位合金化策略形成铋锑合金并储钾的反应机理及其影响其储钾特性的内在作用机制。相关研究成果构建了原位合金化策略储钾的理论基础，为设计高性能合金化型钾离子电池负极材料和发展钾离子电池提供了重要的理论指导和实验借鉴。