本研究目的在於提升鋰離子電池其能量密度及輸出功率，使其更能因應行動裝置及動力型鋰離子電池高能量密度及高功率的需求。本研究使用溶膠凝膠法(Sol-gel synthesis)自行製備之磷酸鋰錳 (LiMnPO4)作為陰極材料，磷酸鋰錳(4.0 V)擁有比同系列磷酸鋰鐵(3.4 V)更高的放電電位，預期應擁有比磷酸鋰鐵更好的性能表現。但因磷酸鋰錳電子導電度及鋰離子導電度比磷酸鋰鐵更差，且在進行充放電時，錳離子因其氧化還原會受到楊-泰勒效應(Jahn-Teller effect)影響，導致電容量縮短循環壽命。為改善此缺點，本研究分別以不同比例少量的鐵離子及銪離子進行摻雜，將之取代於錳離子位置上，期望能解決材料缺點並改善電性表現。實驗結果顯示，以溶膠凝膠法合成之未摻雜磷酸鋰錳，在0.01C放電速率下電容量為 40mAh/g，在經過鐵摻雜後電容量、電池阻抗及循環壽命皆有明顯的提升；尤其是6%鐵摻雜磷酸鋰錳與未摻雜之磷酸鋰錳相比，可提升50%左右的電容量，並仍能維持4.0V的工作電位。充放電曲線並未顯示兩段式工作平台，表示鐵摻雜成功的均勻混合在磷酸鋰錳之中，沒有產生嚴重的磷酸鋰鐵分相。而銪摻雜磷酸鋰錳僅添加了0.33%，便在電容量及電池阻抗之表現有所改善；其在0.01C放電速率下，也可提升電容量至60mAh/g，僅用微量摻雜便可達到與6%鐵摻雜相同的電容量表現。 In order to meet the demand of higher energy density and higher power for modern portable electronics and for automobile applications, efforts are devoted to the development of lithium battery with higher energy and power density. This work use LiMnPO4 as cathode material, which was synthesized by Sol-gel synthesis. LiMnPO4 has higher working potential (4.0V) than LiFePO4, and is expected to deliver better electrical performance than LiFePO4. However, due to poorer electron conductivity, slower lithium ion intercalation rate, and the fact that Jahn-Teller effect in MnPO4 octahedral affects Mn ion during charging (reduction) and discharging (oxidation) cycling, LiMnPO4 shows lower capacity and cycle life than LiFePO4. To circumvent these defects, we proposed to dope the cathode material with small amount of Fe ion and Eu ion respectively in LiMnPO4 . The results shows pristine LiMnPO4 prepared by sol-gel method has a discharging capacity of 40 mAh/g at 0.01C, but the discharging capacity, battery impedance, and cycle life are all substantially improved after doping with small amount of Fe. In the most pronounced case with 6wt% doping, an increase of 50% discharging capacity is observed compared to that in pristine sample, and maintains a high working potential at 4.0V. The absence of two-steps working plateau suggested that Fe ion was distributed homogeneously in LiMnPO4 , preclude the formation of LiFePO4 phase. In the case of Eu doping, a pronounced improvement in discharging capacity and battery impedance was found with only 0.33% Eu addition in LiMnPO4. At 0.01 C charge rate this sample yield 60 mAh/g of discharging capacity which is equal to that achieved by 6% of Fe doping.
