| 摘要: | 近年來，矽為倍受矚目的材料，因為矽負極高出於傳統石墨負極約十倍的理論電容量，但於充放電過程中，其高體積變化率很高以及不斷生成的SEI使矽材料粉末化，造成矽負極電池壽命不佳。本研究將探索一種新型的矽材料表面修飾方法，使用具可呼吸性網狀光聚合物保護矽負極材料期望可克服前述難題並將此技術應用於高能鋰離子電池。
本研究第一部分，將光聚合物(Bismaleimide, BMI)單體溶於溶劑中並吸附至矽粉末表面，再以光照聚合出具分歧網狀的結構，使其均勻包覆於矽負極材料。在充放電過程中，具彈性和呼吸性的保護層固定了因體積變化產生的破碎材料、避免矽材料與電解液直接接觸，並且形成較好、較薄的SEI層，經100迴圈充放電後，其SEI電阻值較小。這三種功能對於抑制活性材料溶解和保持矽負極電池的循環壽命，都具有關鍵性的貢獻，使材料還能夠在0.2C速率下300迴圈充放電後保有約830 mAh/g-Si。
第二部分，使用較短鏈的光聚合物單體(N,N′-1,3-Phenylene bismaleimide, HVA)，作單聚合或與BMI共聚合反應，產生緊密程度不同於BMI的結構，藉交流阻抗分析與循環壽命測試，發現較緊密的包覆層，較不利於鋰離子的傳導，使得介面電阻提升，進而造成放電電容降低。
在光聚合物包覆層穩定負極基礎上, 本研究進一步探討具二維結構的石墨烯奈米帶(Graphene nanoribbon)，作為新型導電添加劑，有效地增加電極材料導電度，達到電池電性表現提升的目標。
;Silicon Anode is considered as the most critical component for advanced lithium battery since it promises higher theoretical capacity over conventional graphite anode. However, Si suffers from huge volume variation and continuous formation of SEI layer during repeated lithiation/delithiation process, resulted in pulverization that quickly deteriorated the cyclic performance of lithium battery.
In the first part of this study, the monomer (Bismaleimide, BMI) of photo-polymer was dissolved in the solvent, adsorbed onto the surface of the silicon powder, and then polymerized with light illumination to form a breathable network-like structure that encapsulated the silicon anode material. During the charging and discharging process, the elastic and breathable protective layer retained the anode materials, avoided direct contact with the electrrolyte and formed a better and thinner SEI layer with less SEI resistance after 100 cycles. These functions are critical factors that contributes to the enhancement of cycle life of silicon based anode batteries. The Si@3p-BMI anode displayed highly stable capacity of ~830 mAh/g-Si up to 300 cycles under 0.2C charge rate.
In the second part of the study, a shorter chain monomer of photo-polymer (N,N′-1,3-Phenylene bismaleimide, HVA), for homopolymerization or copolymerization with BMI to produce coating layer with different tightness in structure. The influence of different photo-polymer coatings on the electrical properties of the cells was discussed. In AC impedance test and cycle life test, the tighter coated layer hindered ability of lithium ions transport, enhancing the interface resistance and reduced discharge capacitance.
On the basis of the stable anode of the photo-polymer coating layer, this study explores further the use of two-dimensional structure graphene nanoribbons (GRs), as a new type of conductive additives, which shows increased electronic conductivity and improved the electrical performance of the battery. |
