锂离子电池正极材料球形磷酸亚铁锂的研究
摘要
橄榄石型LiFePO_4理论比容量高、价格低廉、环境友好、循环性能优良、安全性能突出,被认为是最具开发和应用潜力的新一代锂离子电池正极材料。由于LiFePO_4的电子导电率低和锂离子扩散速度慢,导致初始容量损失和倍率放电性能差;又因其堆积密度低,导致体积能量密度小。这两点影响了LiFePO_4材料的实用化。
本文以制备球形LiFePO_4为研究目的,对其合成与改性做了详细研究。采用液相沉淀-高温煅烧法合成球形LiFePO_4,研究了合成条件对前躯体NH_4FePO_4·H_2O、产物LiFePO_4结构、形貌及电化学性能的影响,通过X射线衍射(X-Ray Diffraction)分析了合成前躯体及产物的结构晶型,扫描电镜(Scanning Electron Microscope)观察了材料的形貌,恒流充放电测试研究了合成材料的比容量和循环性能,用循环伏安(Cyclic Voltammogram)和电化学阻抗谱(Electrochemical Impedance Spectroscope)简单分析了材料的电化学反应机理。
研究结果表明,采用FeSO_4·7H_2O、H3PO4和NH3·H_2O为原料合成的前躯体为NH_4FePO_4·H_2O,其晶体结构与目标产物LiFePO_4的晶体结构具有相似性,在高温固相反应之前就达到“结构预置”的效果,反应过程中晶体结构变化较小,反应易于进行。掺碳对振实密度有很大影响,随着含碳量的增加,振实密度逐渐减小,掺碳5 mass%的LiFePO_4/C振实密度为1.28 g·cm~(-3)。采用氟化锂为锂源,蔗糖为碳源,碳含量10 mass%,550℃烧结12 h制备的LiFePO_4材料放电容量保持在120 mAh·g~(-1) (0.1 C)左右。镍掺杂材料放电容量保持在110 mAh·g~(-1) (0.1 C)左右,通过镍掺杂,材料的比容量和循环性能并没有得到有效改善。对LiFePO_4进行掺碳处理后Rct变小,交换电流密度j°变大,加速了Li~+的脱嵌,电极反应速率增大,有利于电化学反应的进行,从而提高材料在实际充放电过程中的容量。
Olivine-type LiFePO_4 is considered as the most promising candidate for the next generation cathode materials of lithium ion batteries because it has high theoretical specific capacity, is cheap and environmentally friendly, also has good cycling characteristics and excellent safety. However, it’s poor electronic conductivity, which leads to initial capacity loss and poor rate capability. And it’s low pile density, which leads to low volumetric specific capacity. That prevent LiFePO_4 to be put into commercially used.
In this work, we aim at preparing spherical LiFePO_4. Used liquid deposit-high temperature sinter method to synthesis spherical LiFePO_4. Researched the influence of synthesis condition to NH_4FePO_4·H_2O precursor and LiFePO_4 product in structure, pattern and electrochemical performance. In addition, X-Ray Diffraction (XRD) was used to analyze the crystal structure of precursor and product, Scanning Electron Microscope (SEM) was used to observe the superficial morphology, charge-discharge test was used to study the specific capacity and cyclic properties, Cyclic Voltammogram (CV) and Electrochemical Impedance Spectroscope (EIS) was used to discuss the electrochemical reactive mechanism.
The results of the study show that use FeSO_4·7H_2O, H3PO4 and NH3·H_2O as materials to prepare NH_4FePO_4·H_2O precursor, the structure of the precursor and LiFePO_4 are similarity, it is an effect of“structure preset”before sinter. Carbon doping can influence the tap density greatly, with the increase of carbon content the tap density decrease. The tap density is 1.28 g·cm~(-3), when doped with 5 mass% carbon content. Using LiF as lithium source, sucrose as carbon source, carbon content is 10 mass%, 550℃sinter for 12 h to prepare LiFePO_4, the sample has a discharge specific capacity of 120 mAh·g~(-1) (0.1 C). The discharge specific capacity of nickel doping sample is about 110 mAh·g~(-1) (0.1 C), the discharge specific capacity and the cycle performance aren’t change efficiently by nickel doping. After carbon doping, Rct decrease, j°increase, it accelerates the extraction of Li~+, so the electrode reaction speed is accelerated, it is advantage to the electrochemical reaction, also enhance the real capacity.
本文以制备球形LiFePO_4为研究目的,对其合成与改性做了详细研究。采用液相沉淀-高温煅烧法合成球形LiFePO_4,研究了合成条件对前躯体NH_4FePO_4·H_2O、产物LiFePO_4结构、形貌及电化学性能的影响,通过X射线衍射(X-Ray Diffraction)分析了合成前躯体及产物的结构晶型,扫描电镜(Scanning Electron Microscope)观察了材料的形貌,恒流充放电测试研究了合成材料的比容量和循环性能,用循环伏安(Cyclic Voltammogram)和电化学阻抗谱(Electrochemical Impedance Spectroscope)简单分析了材料的电化学反应机理。
研究结果表明,采用FeSO_4·7H_2O、H3PO4和NH3·H_2O为原料合成的前躯体为NH_4FePO_4·H_2O,其晶体结构与目标产物LiFePO_4的晶体结构具有相似性,在高温固相反应之前就达到“结构预置”的效果,反应过程中晶体结构变化较小,反应易于进行。掺碳对振实密度有很大影响,随着含碳量的增加,振实密度逐渐减小,掺碳5 mass%的LiFePO_4/C振实密度为1.28 g·cm~(-3)。采用氟化锂为锂源,蔗糖为碳源,碳含量10 mass%,550℃烧结12 h制备的LiFePO_4材料放电容量保持在120 mAh·g~(-1) (0.1 C)左右。镍掺杂材料放电容量保持在110 mAh·g~(-1) (0.1 C)左右,通过镍掺杂,材料的比容量和循环性能并没有得到有效改善。对LiFePO_4进行掺碳处理后Rct变小,交换电流密度j°变大,加速了Li~+的脱嵌,电极反应速率增大,有利于电化学反应的进行,从而提高材料在实际充放电过程中的容量。
Olivine-type LiFePO_4 is considered as the most promising candidate for the next generation cathode materials of lithium ion batteries because it has high theoretical specific capacity, is cheap and environmentally friendly, also has good cycling characteristics and excellent safety. However, it’s poor electronic conductivity, which leads to initial capacity loss and poor rate capability. And it’s low pile density, which leads to low volumetric specific capacity. That prevent LiFePO_4 to be put into commercially used.
In this work, we aim at preparing spherical LiFePO_4. Used liquid deposit-high temperature sinter method to synthesis spherical LiFePO_4. Researched the influence of synthesis condition to NH_4FePO_4·H_2O precursor and LiFePO_4 product in structure, pattern and electrochemical performance. In addition, X-Ray Diffraction (XRD) was used to analyze the crystal structure of precursor and product, Scanning Electron Microscope (SEM) was used to observe the superficial morphology, charge-discharge test was used to study the specific capacity and cyclic properties, Cyclic Voltammogram (CV) and Electrochemical Impedance Spectroscope (EIS) was used to discuss the electrochemical reactive mechanism.
The results of the study show that use FeSO_4·7H_2O, H3PO4 and NH3·H_2O as materials to prepare NH_4FePO_4·H_2O precursor, the structure of the precursor and LiFePO_4 are similarity, it is an effect of“structure preset”before sinter. Carbon doping can influence the tap density greatly, with the increase of carbon content the tap density decrease. The tap density is 1.28 g·cm~(-3), when doped with 5 mass% carbon content. Using LiF as lithium source, sucrose as carbon source, carbon content is 10 mass%, 550℃sinter for 12 h to prepare LiFePO_4, the sample has a discharge specific capacity of 120 mAh·g~(-1) (0.1 C). The discharge specific capacity of nickel doping sample is about 110 mAh·g~(-1) (0.1 C), the discharge specific capacity and the cycle performance aren’t change efficiently by nickel doping. After carbon doping, Rct decrease, j°increase, it accelerates the extraction of Li~+, so the electrode reaction speed is accelerated, it is advantage to the electrochemical reaction, also enhance the real capacity.
引文
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2 R. J. Brodd, K. R. Bullock, R. A. Leising et al. Batteries, 1977 to 2002. J. Electrochem Soc. 2004, 151(3): K1~K11
3 S. Bruno. Recent Advances in Lithium Ion Battery Materials. Electrochim. Acta, 2000, 45(8): 2461~2466
4 B. H. Deng, H. Nakamura, M. Yoshio. Comparison and Improvement of the High Rate Performance of Different Types of LiMn_2O_4 Spinels. J. Power Sources. 2005, 14l(1): 116~121
5 M. Winter, J. O. Besenhard, M. E. Spahr et al. Insertion Electrode Materials for Rechargeable Lithium Batteries. Adv. Mater. 1998, 10(10): 725~763
6 A. K. Padhi, K. S. Nanjundawamy, J. B. Goodenough. Phospho-olivine as Positive Electrode Materials for Rechargeable Lithium Batteries. J. Electrochem Soc. 1997, 144(4): 1188~1194
7 M. Thackeray. Lithium-ion Batteries-an Unexpected Conductor. Nat. Mater. 2002, 1(2): 81~82
8卢俊彪,唐子龙,张中泰等.镁离子掺杂对LiFePO_4/C材料电池性能的影响.物理化学学报. 2005, 21(3): 319~323
9 H. Huang, S. C. Yin, L. F. Nazar. Approaching Theoretical Capacity of LiFePO_4 at Room Temperature at High Rates. J. Electrochem. Solid State Lett. 2001, 4(10): A170~A172
10 F. Croce, A. D. Epifanio, J. Hassoun et al. A Novel Concept for the Synthesis of an Improved LiFePO_4 Lithium Battery Cathode. J. Electrochem. Solid Lett. 2002, 5(3): A47~A50
11 S. Y. Chung, J. T. Blocking, Y. M. Chiang. Electronically Conductive Phospho-olivines as Lithium Storage Electrodes. Nat. Mater. 2002, 1(2): 123~128
12吕鸣样,黄长保,宋玉谨.化学电源.天津:天津大学出版社. 1992: 306~307
13汪继强.锂离子蓄电池技术发展及市场前景.电源技术. 1996, 26(4): 147~151
14陈立泉.锂离子正极材料的研究发展.电池. 2002, 32(6): 6~8
15赖琼钰.化学研究与运用.电化学. 1998, 10(1): 22~25
16吴宇平,方世壁,刘昌炎等.锂离子电池正极材料氧化钴锂的进展.电源技术. 1997, 21(5): 208~209
17赵健,杨维芝,赵佳明.锂离子电池的应用开发.电池工业. 2000, 5(1): 31~36
18安平,其鲁.锂离子二次电池的应用和发展.北京大学学报. 2006, 42(SI): 1~7
19 M. Wakihara. Recent Developments in Lithium Ion Batteries. Mat. Sci. Eng. R. 2001, 33(4): 109~134
20 P. G. Bruce, A. R. Armstrong, R. L. Gitzendanner et al. New Intercalation Compounds for Lithium Batteries: Layered LiMnO_2. J. Mater. Chem. 1999, 9(1): 193~198
21庄大高.锂离子电池正极材料LiFePO_4的合成及电化学性能研究.浙江大学博士论文. 2006: 9~10
22 K. Mizushima, P. C. Jones, P. J. Wiseman et a1. LixCoO_2(0
24 J. Akimoto, Y. Gotoh, Y. Oosawa. Synthesis and Structure Refinement of LiCoO_2 Single Crystals. J. Solid State Chem. 1998, 141(1): 298~302
25吴宇平,万春荣,姜长印.喷雾干燥法制备LiCoO_2超细粉.无机化学学报. 1999, 14(4): 657~661
26 Y. X. Li, C. R. Wan, Y. P. Wu et al. Synthesis and Characterization of Ultrafine LiCoO_2 Powders by a Spray-drying Method. J. Power Sources. 2000, 85(2): 294~298
27 L. Cheng, W. C. Liu. Reaction Mechanism and Kinetics Analysis of Lithium Nickel Oxide during Solid-state Reaction. J. Mater. Chem. 2000, 10(6): 1403~1407
28 P. Barboux, J. M. Tarascon, F. K. Shokoohi. The Use of Acetates As Precursors for the Low-temperature Synthesis of LiMn_2O_4 and LiCoO_2 Intercalation Compounds. J. Solid State Chem. 1991, 94(1): 185~196
29 J. Schoonman, H. L. Tuller, E. M. Kelder. Defect Chemical Aspects of Lithium-ion Battery Cathode. J. Power Sources. 1999, 81-82: 44~88
30 R. Kanno, H. Kubo, Y. Kawamoto et al. Phase Relationship and Lithium Deintercalaton in Lithium Nickel Oxides. J. Solid State Chem. 1994, 110(2): 216~225
31 L. Hernan, J. Morales, L. Sanchez et al. Use of Li-M-Mn-O [M=Co, Cr, Ti] Spinels Prepared by a Sol-gel Method as Cathodes in High-voltage Lithium Batteries. Solid State Ionics. 1999, 118(3-4): 179~185
32 M. Okada, Y. S. Lee, M. Yoshio. Cycle Characterization of LiM_xMn_(2-x)O_4 (M=Co, Ni) Materials for Lithium Secondary Battery at Wide Voltage Region. J. Power Sources. 2000, 90(2): 196~200
33 K. Rissouli, K. Benkhouja, B. Ramos et al. Electrical Conductivity in Lithium Orthophosphates. Mater. Sci. Eng. B. 2003, 98(3): A185~A189
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