鋰電池三元系正極材料之添加劑製備及電池性能探討

Electrochemical characterizations of organic surface-modified LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

趙信豪(Sin-Hao Jhao)

指導教授 ： 諸柏仁

國立中央大學/理學院/化學系/碩士(2012年)

摘要

安全性為鋰離子電池中最受注目的議題。先前的研究指出，正極材料在高溫下容易釋氧，且氧會與電解液作用產生燃燒，造成危險性；因此，若有一機制能抓取釋出的氧或阻斷燃燒反應，則可增加鋰離子電池安全性。
　　本系統使用自由基捕捉劑巴比妥酸(BTA)的衍生物-1,3DBTA，與雙馬來醯亞胺(BMI)及其衍生物(C4BMI, PMI, Si(MI)3)共聚形成樹枝狀寡聚物(dendrimeric oligomers)，應用於三元系正極材料中；其主要目的是想藉由1,3DBTA來抓取正極材料因高溫釋出的氧及阻斷燃燒反應以達到安全目的。
　　本研究所合成之添加劑，具有高分子的纏繞特性，可有效且緻密地包覆正極材料，藉由表面形成之鈍化膜穩定正極材料，並避免活性粒子表面的過渡金屬與電解質直接接觸。相對的此披覆正極表面的樹枝狀寡聚物，會導致鋰離子傳輸速率下降與鈍化膜界面阻抗上升。由熱差式掃描分析儀(DSC)可觀察到添加劑能有效地抑制正極材料在高溫時的放熱量；且在循環壽命方面，含o-BMI與o-C4BMI之樣品的表現較好，第50圈電容量保留值分別為95.20%與97.54%。
　　本研究證實以自由基捕捉劑對正極材料進行表面修飾能改善鋰離子電池之安全性，同時也增進電池循環壽命能力。相較於一般阻燃劑添加於電解液中，雖然可以提升電解液的耐燃性來增加整體的安全性，但卻大幅度犧牲電池電容量；相比之下，本研究提高正極材料熱穩定性與增進循環壽命能力，但在電性表現上功率密度只略為犧牲。

關鍵字

鋰離子電池 ； 添加劑 ； 安全

並列摘要

Safety is the most sought-after property in Lithium battery. This research shows battery safety can be improved with the addition of functional additive to the cathode materials. In this research, barbituric acid (BTA) and its derivatives, 1,3DBTA(1,3-Dimethylbarbituric acid) which are well-known free radicals scavenger are first mixed with different organic copolymer (BMI, C4BMI, Si(MI)3, PMI) to form dendrimeric oligomers before compounded with various cathode materials which included LiCoO2, LiNiO2 and LiNi1/3Co1/3Mn1/3O2. LiCoO2 is the most widely used cathode material in present commercial lithium ion batteries.
SEM measurements confirmed the coating on the electrode materials is highly homogeneous, with part of the additive ingredient attached to PVdF binder. After formation with three repeating cycle, The SEI morphology was found to be smoother than pristine. Nitrogen mapping by EDS shows the dendrimeric additive is homogeneously spread out on the cathode materials surface which indicated the organic additives were adsorbed on the surface of LiNi1/3Co1/3Mn1/3O2. At 0.2C-rate and 6C-rate, the electrochemical performances of cathode containing additives were about 150 mAh/g and 105 mAh/g, respectively. Due to the additive effects, the lithium ion transfer rate are all decreased, and the SEI interface impedance rose. The delay of exothermic temperature and reduction of exothermic reaction heat release by more than 50% as derived from differential scanning thermal analyzer (DSC) suggested these additives effectively inhibits the reaction heat during oxygen release when temperature reached above 250℃ to 320℃. In cycle-life performance, oligomer with o-BMI and o-C4BMI retained 95.20% and 97.54% capacity at 50cycle under 0.2C-rate, but the pristine without any additive modification showed a capacity retention of 87% under the same condition.
Although the additives affect battery’s power density, carefully balancing the component composition, it is found the battery performance and security features can both be enhanced. Compared with other safety technology which uses flame retardants to reduce electrolyte flammability, temperature control is not satisfactory, and the charge capacity usually suffers greatly. In contrast, present approach improves both thermal stability and cycle life without much cost of the charge capacity.

並列關鍵字

Lithium-ion battery ； BTA ； Safety

參考文獻

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