微波裂解离子液体法包覆磷酸铁锂碳膜的界面性质调控研究

A carbon film coated lithium-ion battery electrode materials is an important, widespread concerned issue to improve the performance of lithium-ion batteries. Carbon film coated by pyrolysis of ionic liquid is a cracking study recently. By screening an appropriate ionic liquid and selecting the appropriate pyrolysis method, we can obtain the carbon film with specific properties of the particle surface in this project. Wherein, the interface properties regulation of the particles/carbon film is a fundamental scientific problem. Ionic liquid and its cleavage intermediates have microwave dielectric natures and microwave-aided heating gradual change. Using LiFePO4 particles as the test sample, carbon film coated LiFePO4 was prepared by microwave pyrolysis of ionic liquid. Through LiFePO4/C interface structure, we will investigate some problems (for example, the diffusion of the substance, reaction, composition, thickness, amorphous/crystalline and morphology) existed in the LiFePO4/C interface and its both sides. The relation between interface properties and charge-discharge characteristics of electrode material will be revealed. The research of the project has a great significance to reveal the interface structure and the performances control law in the microwave pyrolysis of ionic liquid process. The research results are also have reference values to perfect a novel technology for electrode material coated conductive carbon film by microwave pyrolysis of ionic liquid method.

锂离子电池电极材料的碳膜包覆是一个长期以来提高锂离子电池性能的广为关注的重要课题。用离子液体裂解包覆碳膜是最近的一个研究热点。通过筛选适当的离子液体，选择恰当的裂解方法，获得颗粒表面特定性能的碳膜。其中颗粒/碳膜的界面性质调控是关键科学问题。本项目提出利用离子液体及其裂解中间产物的微波介电性质和吸波加热的渐变性，以磷酸铁锂颗粒为试验样本，采用微波裂解离子液体法包覆碳膜。以颗粒/碳膜界面结构为关注点，探讨界面及其两侧物质的扩散、反应、成分、厚度、非晶/晶态、形貌等问题，揭示界面性质与电极材料充放电性能之间的关联。本项目的研究对揭示高温微波裂解离子液体工艺对界面结构和性质调控的规律具有重要意义，对完善一种微波裂解离子液体包覆电极材料的导电碳膜新技术具有参考价值。

本项目利用离子液体及其裂解中间产物的微波介电性质和吸波加热的渐变性，采用微波裂解离子液体法在磷酸铁锂颗粒表面包覆碳膜。研究了微波辐照下磷酸铁锂的合成、微波辐照下不同类型离子液体的裂解机理、微波辐照对碳材料的结构和表面官能团的影响规律、微波裂解离子液体在磷酸铁锂颗粒表面包覆碳膜的工艺探索以及碳包覆磷酸铁锂材料的电化学性能优化等。结果表明：(1)微波辐照不影响磷酸铁锂晶体结构，但对其形貌和粒度有显著影响。(2)离子液体在微波场中吸收微波后迅速升温，逐步缩聚、脱除小分子形成富碳中间产物，接着裂解成N、S、N-S掺杂的碳。(3)微波辐照有利于增加碳材料表面缺陷，提高碳材料表面吡啶氮和吡咯氮的含量，同时改善碳材料表面官能团分布，从而提高碳材料的储锂活性点。(4)以离子液体[BMIm]N(CN)2、EMImNTf2 、[VEIm]NTf2等为碳源均能在磷酸铁锂颗粒表面获得致密、均匀的纳米级碳膜，由于离子液体优异的的润湿性能，使得碳膜紧密结合在磷酸铁锂颗粒表面，提高了磷酸铁锂的电子电导率和离子电导率；碳膜抑制了磷酸铁锂颗粒的生长，从而降低了锂离子迁移路径；碳膜还降低了磷酸铁锂的电荷转移电阻，从而提升了磷酸铁锂颗粒的倍率性能。总之，微波裂解离子液体在磷酸铁锂颗粒表面包覆碳膜有利于改善其电化学性能，该工艺具备工业化应用的潜力。项目资助发表SCI收录论文20篇。申请专利8项，其中授权专利4项，转让3项。培养研究生6名。项目投入经费50万元，支出45万元，结余5万元。结余经费用于本项目研究后续支出。