硅氧化物负极材料的氧含量调控及储锂机理研究

Silicon suboxides (SiOx，0<x<2) are known as high specific capacity and superior cycle stability, which are expected to the most promising anodes for advanced Li-ion batteries. Optimal SiOx anode would be achieved after making a technical breakthrough to prepare SiOx with various oxygen contents and thorough understanding about the lithium storage mechanism. Because SiOx anodes exhibit distinct lithium transportation behaviors, which are strongly depended on oxygen content. In this project, we initially propose a facile approach to prepare SiOx with various oxygen contents in control. Firstly, siloxene is synthesized by chemical exfoliation of commercial CaSi2 in dilute HCl aqueous solution. Then, as-prepared siloxene is further oxidized by H2O or O2. Various oxidized siloxenes perform heat treating to obtain SiOx anodes with different oxygen content. The oxygen content shows a strong relationship with siloxene oxidation conditions. Furthermore, We apply FTIR and Raman spectra to investigate the evolution of siloxene structure, combined simulation results of reaction thermodynamics and kinetics. We expect to elucidate the oxygen-controllable mechanism during the preparation of SiOx. Subsequently, charging/discharge testing, CV, EIS and GITT are employed to characterize the electrochemical performances of SiOx anodes. In addition, We apply the in-situ TEM and operando solid state NMR to in-depth investigate the relationship among components, microstructure, and lithium transportation behaviors of silicon suboxides at realistic cycling conditions, which are highly challenging. The results will provide insight into the evolution process of electrochemical-lithiated products, which are highly relevant to the electrochemical performance of SiOx. We promise to give an unambiguous concept about the lithium storage mechanism of SiOx. According to our research, we aim to afford high performance SiOx anodes with reversible capacity of 1000 mAh/g and superior cyclic stability. Meanwhile, the project will give a suggestive idea to develop commercial available SiOx anodes.

硅氧化物（SiOx，0<x<2）作为锂离子电池负极材料，可逆容量较高，循环稳定性较好，具有商业化前景。但不同氧含量SiOx电化学锂化行为存在显著差异且存在制备技术壁垒。因此SiOx制备技术的突破和储锂机理的解析，有望获得最佳电化学性能的SiOx负极材料。本项目拟建立不同氧含量SiOx的可控制备方法，采用盐酸体系化学剥离CaSi2制备硅氧烯，通过控制硅氧烯的氧化程度实现对硅氧化物中氧含量的可控调节。利用红外和Raman光谱等表征技术，研究硅氧烯氧化产物演变过程，结合理论计算的硅氧烯氧化反应热力学和动力学结果，揭示硅氧化物氧含量可控调节机理。通过电化学测试，结合原位透射电镜和原位固体核磁等表征技术，研究SiOx的电化学性能和锂化过程的物相演变，阐明SiOx储锂机理。通过本项目的研究，预期优选出比容量达1000mAh/g且循环稳定的新型SiOx负极材料，为开发商用硅氧化物负极材料提供新思路。

硅氧化物（SiOx，0<x<2）作为锂离子电池负极材料，具有可逆比容量较高、循环稳定性较好等优势，在高比能锂离子电池中具有重要应用前景。SiOx的电化学嵌脱锂行为与其组成（即氧含量）有直接关系，但SiOx含氧量的精确调控一直是该领域的难题，同时SiOx负极材料还存在首次库伦效率低、长循环稳定性有待提升等问题。针对上述问题，本项目开展了不同氧含量SiOx的可控制备方法探索，研究了氧含量调控的反应机制及不同氧含量SiOx负极材料的脱嵌锂电化学行为，同时研究了提升SiOx负极材料首效与循环稳定性的材料改性方法。通过对化学剥离CaSi2制备的硅氧烯在水或一定湿度的空气中进行氧化处理，制备得到了氧含量精确可调（x值1-2范围内）的SiOx材料，并通过先进的表征技术与理论计算，揭示了氧化过程的反应机制和影响SiOx中氧含量的关键因素，同时通过对不同氧含量SiOx负极材料电化学行为的深入对比研究，确定了最优的氧化程度，阐明了SiOx锂化过程的物相演变和储锂机制，及材料表面与体相结构对其电化学性能的影响机制。进一步发展了金属Sn复合改性（将不可逆Li2O相转化为电化学可逆物相）和Mg2Si固相反应（预先将部分SiOx转化为硅酸镁，同时补偿部分活性硅）两种创新方法，可将SiOx负极材料的首次库伦效率从不足70%提高至80%以上。此外，利用具有优异导电性和柔性薄片结构的石墨烯对SiOx进行复合改性，设计制备出兼具长寿命与高容量的石墨烯复合氧化亚硅负极材料，并揭示了石墨烯通过机械作用抑制SiOx颗粒膨胀和维持复合颗粒结构稳定性的作用机制，应用该复合负极材料的大容量软包电池在比能量超过350 Wh/kg的同时仍能够维持500圈后的稳定循环，该材料技术也成功实现了成果转化。本项目的研究结果为硅氧化物负极材料的可控制备提供了新的思路，深化了对其储能机制的科学认知水平，并为创制满足高比能锂离子电池应用需求的新一代硅基负极材料提供了科学指导。