Effect of Post-Heating Treatment of Ultrasonically Sprayed and Pyrolysed LiMn2O4 Powders on the Performance of Secondary Battery

以超音波霧化熱分解法製得鋰錳氧粉末之後續熱處理對二次電池效能的影響

鄧宗憲(Tsung-Hsien Teng) ； 楊木榮(Mu-Rong Yang)

《臺北科技大學學報》 41卷2期 (2008/12) Pp. 51-61

https://doi.org/10.29768/JNTUT.200812.0004

摘要

本研究利用硝酸鋰和硝酸錳水溶液所配置的起始質，成功地藉由超音波霧化熱分解法來合成純相且粉末型態為球狀的鋰錳氧奈米結晶粉末之鋰離子二次電池正極材料，探討後續熱處理對LiMn2O4粉末的物理化學性質的影響效應。經由X光繞射圖譜和X光吸收光譜學等分析，我們可以發現，在X光粉末繞射之結果，顯示後續熱處理時間的增加，不但能有效提升粉末的結晶性，同時可使得粉末中錳三價離子的比率增加，因此粉末的晶格常數亦隨著熱處理時間的增加而變大，並且稍微地改變了粉末的化學成分。而錳三價離子的比率增加能提升電池的初始電容量，當LiMn2O4粉末在800℃熱分解及800℃ 4小時的熱處理條件下，可得到最佳的初始電容量(129mAhg^(-1))，並且經由30個循環伏安測試後，依然維持121mAhg^(-1)的放電電容量。在粉末的微細結構分析方面，經歸一處理後的X光吸收近端邊緣結構分析圖譜中，若改變熱處理的時間，能提高圖譜中峰形的強度，並且峰形將往高能量的位置偏移，指出粉末的錳離子的平均價數隨熱處理時間增加而變小。另外，在X光吸收精細結構分析圖譜中，顯示出Mn-O的鍵長進一步地隨熱處理時間的增加而增加。樣品結構之無序化(disorder)程度σ(Debye-Waller factor)的變化亦隨著熱處理的時間增加而增加，唯有在熱分解800℃，及800℃ 4小時的熱處理條件下的樣品σ値是最小的，顯示其結構趨向有序(order)，指出具有最佳的結構對稱性，而其亦呈現最佳的電化學性質。由結果顯示，證實了藉由超音波霧化熱分解法和後續熱處理的製程方式下，可成功地製備LiMn2O4粉末。並且後續熱處理是改善經由超音波霧化熱分解法所製得的粉末的電化學特性的一個有效的方法。

關鍵字

尖晶石鋰錳氧氧化物 ； 超音波霧化熱分解法 ； 後續熱處理 ； X光吸收光譜學

並列摘要

The LiMn2O4 spinel oxides have been successfully synthesized with ultrasonic spray pyrolysis method from an aqueous mixing solution of lithium nitrate and manganese nitrate. The effects of post heat treatment on the physicochemical properties of the LiMn2O4 powders have been carefully examined by means of X-ray diffraction spectra, titration of manganese valence and X-ray absorption spectroscopy. The results indicated that the post heat activation would influence the microstructure and crystallization of the pyrolysed particles. This profile variation in the potential plateau is considered to be caused by an increase in the amount of active Mn(superscript 3+). The more amount of active Mn(superscript 3+), the flatter and longer the plateau is. This result is in agreement with the variation trend of lattice parameters which increase with increasing the heat treatment time. The capacity loss increases with increasing the heat treatment time. From the fitting results of X-ray absorption spectra, the (Mn-O) and (Mn-Mn) bond distances are found to become larger as the heat-treatment time is prolonged. The cell with 4-hour heat-treatment powder as cathode gives best electrochemical performance and exhibited an initial highest capacity of 129mAhg^(-1). The capacity after 30 cycles can still reaches to 121mAhg^(-1). Among the parameters of the valence change, lattice constant and Debye-Waller factor discussed in the study, the short range ordering (Debye-Waller factor, σ) is most critical to the electrochemical performance of the cell. In other words, the Debye-Waller factor can be used as an important index to evaluate the quality of the LiMn2O4 powder as cathode materials in lithium ion secondary cell. The post heat treatment is an effective way to improve the ultrasonically spray-pyrolysed powders in terms of the electrochemical characteristics.

並列關鍵字

Li-Mn-O spinel ； ultrasonic spray pyrolysis ； post heat-treatment ； X-ray absorption spectroscopy