目前在電池產業中，LiCoO2為最廣泛使用的陰極材料，為了提高電池實際應用時的電容量，則必須將充電上限截止電位提高至更高的電位，但是充電上限截止電位提高造成晶體結構不穩定和電解質大量地分解，導致電池循環性能快速地下降，並且衍生出電池安全性的潛在風險，除此之外，形成於陰極表面的鈍化膜不僅阻礙鋰離子的傳遞，並且造成電池內部阻抗持續地上升。 改良LiCoO2於高電位時電化學性能的方法有許多種，常見的改良方法為將陰極材料表面塗佈金屬氧化物或是金屬磷酸化合物，以塗佈層作為保護層改善晶體結構穩定性並且避免活性材料與電解質直接接觸。 本研究中，首先使用機械熱處理法以TiO2對LiCoO2陰極材料進行表面改質，再將有機物修飾於陰極材料表面，以表面塗佈的TiO2改善陰極材料的結構穩定性，以表面修飾的有機物避免活性粒子表面的過渡金屬與電解質直接接觸，抑制特定形成鈍化膜的反應；本研究中於陰極材料表面修飾之有機物不僅具有相當佳的電化學穩定性，而且改質後的陰極材料釋放氧氣時的反應焓降低37 ~ 41 %、鈍化膜的分解溫度提高20 ~ 22°C、電池內部的介面阻抗明顯地下降。 本研究確證以TiO2對LiCoO2進行表面修飾，具有穩定晶體結構、增加電池循環穩定性和改善電池熱穩定性等優點；而於修飾TiO2之LiCoO2表面再修飾有機物時，不但可強化上述性能，並且可抑制陰極表面形成鈍化膜，降低電池內部的介面阻抗。 In order to obtain a higher capacity from LiCoO2, it must be charged to higher potential but this leads to a rapid capacity loss thought to be caused by side reactions with the electrolyte at high potentials as well as structural instability. The chemical and electrochemical side reactions occurs at the electrode/electrolyte interface, which formation surface layer on the electrode. The surface layer create a barrier for Li+ ions during electrochemical charge/discharge cycling. This barrier increases cell impedance and decreases cycling efficiency of the battery. Many efforts have been paid to improve the electrochemical performance of LiCoO2 at high voltages. An effective strategy is to coat the surface of the materials with various metal oxides and metal phosphates. The surface coating itself acts as a protective layer not only to prevent a direct contact of the active core material with the electrolyte solution, but also improves the structural stability. In this study, a mechano-thermal process is employed to form coating of TiO2 on LiCoO2 surface which is subsequently functionalized with long chain poly-ether or polyether oligomer. TiO2 coating on the surface to improves the crystal structure stability. And the organic compounds modified on the surface to prevent a direct contact of the transitional metal on the cathode surface with the electrolyte solution. The organic compounds displayed fair electrochemical stability even if the potential is elevated to 4.5V. The organic modification altered cathode surface properties which inhibits specific reaction to form surface layer. The reaction enthalpy of oxygen release from LixCoO2 is reduce 37~41 %, and surface layer decompose temperature elevate 20 ~ 22°C. From these results, we conclude that TiO2 coating on LiCoO2 particles surface suppress capacity fading, stabilize crystal structure, elevate upper cut-off potential and improve battery thermal stability. Subsequent functionalization with poly-ether or polyether oligomer not only strengthens the above-mentioned performance, it hinders the formation of passivation layer, and prevents the continual increase of internal resistance during long term operation.
