为了深入解析锂离子电池电极材料的电化学性能，以更加有效地进行化学改性，本论文以电化学阻抗技术（EIS）为主要手段，研究了以钴酸锂、锰酸锂和天然石墨等为代表的电极材料在电极反应中的动力学过程，探析了各种材料电极过程的主要控制因素，并对其改性提出了方向性建议。研究表明，钴酸锂正极材料的界面和电荷转移通道主要形成于首次循环中，此后其界面阻抗、电荷转移电阻和离子扩散特性趋于稳定。LiCo1/3Ni1/3Mn1/3O2和钴酸锂具有一样的晶格类型，界面阻抗是其电化学阻抗的主要构成因素，同时发现该材料具有比钴酸锂更好的本征电子导电性。但是，其界面稳定性、高倍率工作性能及电化学反应速度都还有待于进一步改善。实验证明，SnO2改性后的尖晶石型LiMn2O4循环性能显著提高的原因是通过包覆减小了电极的界面阻抗和电荷转移电阻，通过掺杂提高了LiMn2O4的结构稳定性，抑制了Mn2+的溶解。对硫化聚丙烯腈新型正极材料在首次循环过程中阻抗的测试结果显示，首次循环后复合正极材料的导电性大大提高，锂离子嵌入/脱出的可逆性也趋于稳定。作者引入导电高分子掺杂的质子酸理论对该材料的储锂机理进行解释，即首先嵌入到“H洞位”上的锂离子为复合正极提供电子，从而提高了材料的导电性能。同时，嵌入到“H洞位”的锂离子很难脱出，是该正极材料首次不可逆容量的主要根源。界面阻抗是天然石墨负极材料电化学反应过程中的速控因素。本论文研究发现，通过氧化提纯和包覆改性，能够减小天然石墨负极的界面电阻，同时提高其导电性能，从而使其循环性能得到了显著的提高。
In order to provide further insight into the electrochemical properties of electrode materials used for lithium-ion batteries, the electrochemical impedance of electrode materials, including LiCoO2, LiCo1/3Ni1/3Mn1/3O2, LiMn2O4 and natural graphite, during cycling has been investigated. This is of great importance to carry out the research concerning modification of the electrode materials. Moreover, the control step of the electrochemical reactions was analyzed based on the electrochemical impedance spectroscopy (EIS) analysis. The results showed that both the interface and the charge-transfer-channel of LiCoO2 cathode were mainly formed during the first charge/discharge cycle. The resistance of interface and the charge transfer resistance of LiCoO2 cathode changed little during subsequent charge/discharge cycles. For LiCo1/3Ni1/3Mn1/3O2, the resistance of interface was the control step in the first cycle. Despite the fact that LiCo1/3Ni1/3Mn1/3O2 material exhibited higher conductivity than LiCoO2 material, much better performance remained to be achieved in terms of the stability of the electrode interface. Moreover, the rate performance of LiCo1/3Ni1/3Mn1/3O2 material should be improved.Spinel LiMn2O4 is regarded as one of the most promising cathode materials for lithium ion batteries. It has such advantages as low price, high safety and environment-friendly. However, its general application and mass production are inhibited by the problems of lower specific capacity and worse cycling performance. Research on the electrochemical properties of this material was conducted in present work by the method of EIS. And then, SnO2 was employed as additive to improve the performance of pristine spinel LiMn2O4. The results showed that both the impedance of interface and the charge transfer resistance were decreased by addition of SnO2. Consequently, the SnO2-modified sample with 2% SnO2 exhibited higher specific capacity and better capacity retention than pristine LiMn2O4.The electrochemical characteristics of the sulfurized PAN during the first charge/discharge cycle were investigated. The results showed that the conductivity of the sulfurized PAN cathode increased rapidly after the initial cycle. At the same time, the reversibility of the electrochemical reaction increased initially (in the early stage), and then kept stable in subsequent cycles. The mechanism of lithium storage with respect to sulfurized PAN was proposed according to the proton-acid-mechanism. The lithium ions adsorbed on the “H” site were difficult to disengage during the first cycle, resulting in the increase of conductivity and the non-reversible capacity. The natural graphite is regarded as one of the most promising anode materials for lithium ion batteries. However, its universal application is hindered by the poor cycling performance, which is associated with the increasing impedance of interface. The modification improved the cycling performance of natural graphite as a consequence of the decrease of interface impedance and the increase of conductivity.
