锂离子电池硅基材料结构设计与制备研究

发布时间：2019-02-13 05:54

【摘要】：硅作为锂离子电池负极材料的理论比能量高达4200mAh/g，但是在嵌锂过程中其体积会发生急剧膨胀，造成循环性能差、SEI膜不断破裂修复等诸多问题，从而限制商业化。为真正克服硅膨胀的难题，必须通过巧妙的结构设计，形成微纳混合结构，同时颗粒内部预留一定空体积以容纳硅的体积膨胀。本文先从刻蚀制备多孔硅着手，为后期材料制备打基础；然后设计并制备了类石榴结构和中空多孔核壳结构硅基材料。通过XRD、SEM、BET等手段表征了材料的结构特征，同时采用恒流充放电和交流阻抗评价其电化学性能。 采用Ag/HF-H2O2体系刻蚀硅能成功制备出多孔硅，然而其循环性能依然很差；采用Ag/HF-H2O2体系刻蚀SiO，，溶剂为水/乙醇(1:1)且HF浓度为5mol/L时刻蚀效果较好；采用Cu/HF-H2O2体系和Cu/HF-Fe3+体系刻蚀硅均只能在硅表面刻蚀出浅孔。NaOH刻蚀歧化SiO制备出的多孔材料，首次可逆容量为793mAh/g，30次循环容量保持率为72.9%。 通过歧化、刻蚀、碳包覆的技术路线制备类石榴结构硅基材料，并研究了各步骤的工艺条件及对性能的影响。研究发现，为确保SiO发生歧化，温度至少得升至900℃；HF刻蚀歧化SiO可以制备出相互交联的多孔结构。同时，详尽研究了物料装载量、乙炔气体流速、包覆温度与时间对乙炔气相碳包覆的的影响。 以聚苯胺为碳源制备中空多孔核壳结构硅基材料，并进一步优化了结构参数。研究发现，碳壳增厚和空体积增大均利于循环性能提高。将20%石墨与HF-mSiO@C材料混合后可将100次容量保持率提升至95.2%。通过选用蔗糖为碳源，可将制备步骤简化为球磨、歧化+碳化、刻蚀。制备出的HF-mSiO@C材料首次可逆容量为1067mAh/g，首次库伦效率为60.1%，140次循环容量保持率为86.4%，平均库伦效率为99.5%。预嵌锂30min的HF-mSiO@C材料，首次库伦效率达到80.0%，150次循环容量保持率达到88.8%。通过更长时间的预嵌锂，可使首次库伦效率超过100%。 通过测试循环前后极片的横截面，证实了中空多孔核壳结构可有效缓解硅的体积膨胀。研究了电极最终失效的主要原因，研究发现，空体积无法完全容纳硅的体积膨胀，致使碳壳被撑破，最终造成硅核与碳壳完全分离，硅核失去电接触而失效。
[Abstract]:The theoretical specific energy of silicon as a cathode material for lithium ion batteries is as high as 4200mAh/ g, but its volume will expand rapidly in the process of lithium intercalation, resulting in poor cycling performance, continuous rupture and repair of SEI films, and so on, thus limiting commercialization. In order to overcome the problem of silicon expansion, the micro-nano mixed structure must be formed by ingenious structural design, and a certain void volume is reserved in the grain to accommodate the volume expansion of silicon. In this paper, we first prepare porous silicon by etching, and then design and prepare pomegranate like structure and hollow porous core shell structure silicon based materials. The structure of the material was characterized by XRD,SEM,BET, and its electrochemical performance was evaluated by constant current charge-discharge and AC impedance. Porous silicon can be prepared successfully by etching silicon with Ag/HF-H2O2 system, but its cycling performance is still very poor, and the etching effect of SiO, solvent is water / ethanol (1:1) and HF concentration is 5mol/L when using Ag/HF-H2O2 system. Both Cu/HF-H2O2 system and Cu/HF-Fe3 system can only etch shallow pores on the surface of silicon. The first reversible capacity of porous material prepared by NaOH etching of SiO is 793mAh/ g ~ (-1) and the retention rate of 30 cycles is 72.9%. The silicon-based pomegranate structure materials were prepared by the technological route of disproportionation, etching and carbon coating, and the technological conditions of each step and their effects on the properties were studied. It is found that the temperature must rise to 900 鈩

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