由共沉澱法合成低碳含量之磷酸鋰亞錳於高速率鋰離子二次電池正極材料之應用

Co-precipitation synthesis of low carbon-coated LiMn0.6V0.4PO4 as high-rate cathode materials for lithium ion battery

馬維侖(Wei-Lun Ma)

指導教授 ： 陳玉惠

中原大學/理學院/化學研究所/碩士(2015年)

https://doi.org/10.6840/cycu201500615

摘要

本實驗主要利用共沉澱法合成一系列添加聚乙烯吡咯烷酮作為碳源之磷酸鋰亞錳(LiMn0.6V0.4PO4/C)正極材料，其具有低碳含量1.73 - 7.57 wt%。從XRD圖譜中，所製得樣品符合標準品磷酸鋰亞錳(JCPDS#33-0803)之橄欖石結構，並從晶格體積變小( 297.7 Å3 )之現象，證實釩離子成功摻雜入結構。SEM觀察可得到最小粒子約20 nm，且合成磷酸鋰亞錳樣品具有良好碳包覆形貌，進一步從比表面積與粒徑之分析，發現隨著碳含量增加，其粒徑大小隨之降低，提升了比表面積以及總孔體積，同時也與SEM之結果相符。然而，碳包覆能有效改善磷酸鋰亞錳樣品之導電性( 10-10 S cm-1 → 3.7 × 10-7 S cm-1 )，並在循環伏安圖中(CV)，能明顯觀察出有4組氧化還原峰。在0.1 C定電流充放電下，碳含量為5.11 wt% 之LMVP/C-5具有最高電容量160.0 mAh g-1，相較於無碳包覆之LMVP，提升76 % 電容量，並在充放電50次後，仍保有145.1 mAh g-1，其電荷保持率90 %。再以0.1、0.5、1.0、2.0與5.0 C之不同充放電速率進行倍率放電測試，分別可得電容量139.1、97、80、70與69 mAh g-1，與其他文獻相比，LMVP/C-5具有良好倍率放電能力。最後，從EIS測試可得，所製得磷酸鋰亞錳樣品皆具有較佳鋰離子擴散能力(1.0 × 10-16 cm2 s-1 → 2.15× 10-12 cm2 s-1)以及較低電荷轉移阻抗( Rct)。

關鍵字

磷酸鋰亞錳 ； 鋰離子二次電池 ； 共沉澱

並列摘要

In this study, a series of the carbon-coated LiMn0.6V0.4PO4/C cathode materials ( LMVP/C ) with low carbon contents (1.73 - 7.57 wt.%) are successfully synthesized with various amount of polyvinylpyrrolidone (PVP) as an extra carbon source by the co-precipitation method. The XRD analysis indicates that compared to that of pure LMP (303.2 Å3), a smaller lattice volume (297.7 Å3) is obtained for the LMVP/C with 5.11 wt.% carbon content (LMVP/C-5), implying a decrease of lattice in LMVP/C-5 due to the Jahn-Teller effect. The discharge capacity of the LMVP/C-5 electrode in voltage range of 2 - 4.5 V at 0.1, 0.5, 1.0, 2.0 and 5.0 C rate are 139.1, 97, 80, 70 and 69 mAh g-1, respectively. Besides, after 50 cycles the capacity retains 145.1 mAh g-1 at 0.1 C, keeping good capacity retention. The EIS analysis exhibits that LMVP/C-5 not only has much lower charge transfer resistance ( 229.5 Ω ) than LMVP ( 488.0 Ω ) but also has fifteen times higher Li+ diffusion coefficient ( 2.74 × 10-13 cm2 s-1 ) than LMVP ( 1.77 × 10-14 cm2 s-1 ), indicating a significant improvement in the migration of the Li ions at the electrode/electrolyte interface. This study shows that LMVP/C-5 is a promising high-rate cathode material for use in high power lithium ion battery.

並列關鍵字

Co-precipitation ； lithium ion battery ； LiMnPO4

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