摘要

在锂离子电池中，一氧化硅(SiO)负极材料具有较高的理论比容量，低的电压平台以及比硅(Si)低的体积膨胀率，被认为是最具商业化潜力的负极材料。但是，SiO仍存在两大重要问题：第一是在首次嵌锂过程中，SiO会形成大量的不可逆产物，造成首次库伦效率低；第二是在循环过程中，体积膨胀引起的循环性能衰减。因此本论文制定两条实验思路，首先采用SiO与TiH₂复合的方法，对SiO的循环性能进行改进。其中对SiO-TiH₂复合材料的复合工艺进行了优化，研究了热处理温度与复合比例对SiO-TiH₂复合材料的电化学性能的影响；其次利用锂蒸气对SiO进行预锂化，并探究了预锂化顺序、粒度、预锂化温度和预锂化时间对预锂化SiO的电化学性能的影响；最后，在预锂化SiO的基础上为进一步提升其电化学性能，利用磷酸盐对预锂化SiO的表面进行除碱，探索不同磷酸盐改性对预锂化SiO电化学性能的影响。

首先将SiO与TiH₂球磨混合，惰性气体保护下高温热处理，制备得到SiO-TiH₂复合负极材料。研究了热处理温度和复合比例两个因素对SiO-TiH₂复合材料电化学性能的影响。结果表明，TiH₂的复合可以有效提高SiO的循环性能，800℃复合SiO-TiH₂的100次循环容量保持率最高，达到82.3%，剩余比容量在682.2 mAh/g；此外，TiH₂可以夺走SiO中的氧，有效提高复合材料的首次库伦效率，其中1000℃处理的复合材料首效最高可达77.5%。选取SiO:TiH₂质量比为3:1、4:1和5:1三个复合比例进行研究，结果表明，质量比为4:1的SiO-TiH₂复合材料电化学性能最佳，首次库伦效率为74.4%，100次循环后的容量保持率也有53.6%，剩余比容量在555.2 mAh/g。

其次，为提高SiO负极材料的首效，采用锂蒸气预锂化的方法来改善SiO的首次库伦效率。从预锂化/碳包覆顺序、SiO原料粒度、预锂化温度和预锂化时间等因素对预锂化工艺进行优化，探究其电化学性能。结果表明：先包碳再进行预锂化处理的SiO的首次库仑效率最佳(74.6%)，相比未预锂化SiO，首次库伦效率提升了17.4%，并在此基础上，对粒度、预锂化温度和时间进行进一步优化，并最终选出在700℃预锂化3 h的1 μm SiO具有最佳的首次库伦效率，达到76.2%。

最后，为解决SiO预锂化后碱性过强的问题，采用磷酸二氢铵和磷酸二氢锂以及磷酸分别对预锂化SiO进行除碱改性处理。实验表明：减少表面残存碱可有效提高预锂化SiO的首次库伦效率，对比三种磷酸盐的改性结果，磷酸二氢铵的改性效果最佳，SiO的首次库伦效率可以提升到85%，接近日本信越同类产品的水平(89%)。

Silicon monoxide (SiO) is considered to be the most promising anode material for lithium-ion batteries because of its high theoretical specific capacity, low voltage plateau and lower volume expansion rate than silicon (Si). However, SiO still has two major problems: the first is the formation of a large number of irreversible products during the first lithium intercalation process, resulting in low initial Coulombic efficiency; the second is the degradation of cycle performance caused by volume expansion during the cycle process. Therefore, two experimental ideas are formulated in this paper. Firstly, the method of compositing SiO and TiH₂ was used to improve the cycle performance of SiO. The composite process of SiO-TiH₂ composites was optimized, and the effects of heat treatment temperature and composite ratio on the electrochemical properties of SiO-TiH₂ composites were studied. Secondly, SiO was pre-lithiated by lithium vapor, and the effects of pre-lithiation sequence, particle size, pre-lithiation temperature and pre-lithiation time on the electrochemical properties of pre-lithiated SiO were explored; Finally, in order to further improve the electrochemical performance of pre-lithiated SiO, phosphate was used to remove the alkali on the surface of pre-lithiated SiO, and the effects of different phosphate modifications on the electrochemical performance of pre-lithated SiO were explored.

Firstly, SiO and TiH₂ were ball-milled and mixed, and were subjected to high-temperature heat treatment under the protection of inert gas to prepare the SiO-TiH₂ composite anode material. The effects of heat treatment temperature and composite ratio on the electrochemical properties of SiO-TiH₂ composites were investigated. The results show that the composite of TiH₂ can effectively improve the cycling performance of SiO. The composite of SiO-TiH₂ at 800℃ has the highest capacity retention of 82.3% after 100 cycles, and the residual specific capacity is 682.2 mAh/g; In addition, TiH₂ can take away the oxygen in SiO and effectively improve the initial Coulombic efficiency of the composites, and the first coulombic efficiency of the composites treated at 1000℃ can reach up to 77. 5%. When the mass ratio of SiO:TiH₂ is 3:1, 4:1 and 5:1, the electrochemical performance of the composite is the best with the initial coulombic efficiency of 74.4% and the capacity retention rate of 53.6% after 100 cycles. The residual specific capacity is 555.2 mAh/g.

Secondly, in order to improve the first efficiency of SiO anode material, the method of lithium vapor pre-lithiation is used to improve the first coulombic efficiency of SiO anode material. The pre-lithiation process was optimized from the factors of pre-lithiation/carbon coating order, SiO raw material particle size, pre-lithiation temperature and pre-lithiation time, and its electrochemical performance was explored. The results show that the SiO coated with carbon before pre-lithiation has the best initial Coulombic efficiency (74.6%), which is 17.4% higher than that of SiO without pre-lithiation. On this basis, the particle size, pre-lithiation temperature and time are further optimized. And finally, 1 μm SiO pre-lithiated at 700℃ for 3 h was selected to have the best initial coulombic efficiency of 76.2%.

Finally, in order to solve the problem that the alkalinity of pre-lithiated SiO is too strong, ammonium dihydrogen phosphate, lithium dihydrogen phosphate and phosphoric acid are used to remove the alkalinity of pre-lithiated SiO. The results show that the reduction of residual alkali on the surface can effectively improve the initial Coulombic efficiency of pre-lithiated SiO. Compared with the results of three kinds of phosphate modification, ammonium dihydrogen phosphate has the best modification effect, and the initial Coulombic efficiency of SiO can be improved to 85%, which is close to the level of similar products in Japan Shin-Etsu (89%).

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