摘要
当今能源和环境问题日渐突出,同时随着科技的迅猛发展对电池的性能提出了更高的要求。LiFePO4作为新一代的锂离子电池正极材料,因其结构稳定、来源广泛、价格低廉、安全性能好、对环境无污染、理论容量高等优点而成为目前各国的研究热点。电子电导率低和锂离子扩散速率慢是影响LiFePO4性能的主要因素,本文采取新的碳源和高价金属阳离子掺杂等手段对LiFePO4进行了微波合成与改性,得到了具有优异电化学性能的LiFePO4复合正极材料。利用XRD、SEM和TEM等测试方法对正极材料的相组成和微观形貌进行了分析,组装扣式电池后,采用恒流充放电技术测试其电化学性能。
以柠檬酸为碳源合成的LiFePO4/C正极材料,当添加10wt%柠檬酸时材料的电化学性能最好,在0.1C倍率下首次放电比容量最高,达到141.63mAh·g-1,10次循环后比容量保持在134.33 mAh·g-1,仅损失5.16%;在0.3C和1C倍率下的首次放电比容量分别为116.54mAh·g-1和87.21mAh·g-1,循环性能较好。
以PAM为碳源合成的LiFePO4/C正极材料,当添加5wt%PAM时在0.1C倍率下的首次放电比容量最高,为150.22mAh·g-1,循环10次后放电比容量为104.71mAh·g-1,容量衰减较多。在0.3C和1C倍率下的首次放电比容量分别为95.15mAh·g-1和57.21mAh·g-1,其高倍率放电容量和循环性能都不是很好。以TiO2为金属离子添加物合成了LiFePO4/Ti4+正极材料,当掺杂1%Ti4+时样品的性能最佳,在0.1C倍率下的首次放电比容量为123.08 mAh·g-1,第10次循环的放电比容量为116.63mAh·g-1;在0.3C和1C倍率下的首次放电比容量分别为97.92mAh·g-1和59.38mAh·g-1,循环性能良好。
合成了LiFePO4/(C+Ti4+)复合正极材料,以添加5%柠檬酸和掺杂1%Ti4+的样品的电化学性能最好,在0.1C下的首次放电比容量为138.52 mAh·g-1,循环10次后放电比容量为129.42mAh·g-1;在0.3C和1C倍率下的首次放电比容量分别为114.95mAh·g-1和102.39mAh·g-1,循环性能稳定。
Higherandhigherrequirements forlithium ionbatteries areput forwardwiththequick developments of science and technology and due to the serious problems ofenergyand environment. LiFePO4 is becoming the hot issue as a cathode material forlithium ion batteries because of its stabilization, abundance, cheapness, security,environmental friendlyness and high theoretical capacity. However, its low electronconductivity and low lithium ion diffusion rate are the major obstacles affecting thepropertiesofLiFePO4.Theaimsofthepresentworkaretoincorporatethenewsourceof carbon and to dope with higher valence of ion to improve the electrochemicalproperties of LiFePO4. LiFePO4/C, LiFePO4/Ti4+ and LiFePO4/(C+Ti4+) compositecathode materials were synthesized using microwave heating. The microstructure andmorphologies of these composites were investigated by XRD, SEM and TEM. Thelithium ion batteries were assembled in an Ar-filled glove box. The electrochemicalperformanceswereevaluatedbygalvanostaticcharge-discharge.
Carbon-coated LiFePO4 composite was synthesized using citric acid as carbonsource. The material with 10wt% carbon exhibited the best electrochemicalperformance. Its initial charge specific capacity is 141.63 mAh·g-1 at 0.1C. Thecapacitymaintained to be 134.33 mAh·g-1 after 10 cycles, with the capacityloss ratiobeing 5.16%. The initial charge specific capacity is 116.54 mAh·g-1 and 87.21mAh·g-1 at 0.3C and 1C, respectively. And the cycling behavior of the material isgoodundertheseconditions.
LiFePO4/C composite using PAM as carbon source delivered a high initialspecific discharge capacityof 150.22 mAh·g-1 with 5wt% PAM at 0.1C. The capacitymaintained to be 104.71mAh·g-1 after 10 cycles. The capacityloss ratio is larger thanthat with citric acid as carbon source. The initial charge specific capacity is 95.15mAh·g-1 and 57.21 mAh·g-1 at 0.3C and 1C, and the cycling behavior of the materialisnotsogood.
LiFePO4/Ti4+ composite showed a high initial specific discharge capacity of123.08 mAh·g-1 with 1mol% Ti4+ at 0.1C. The capacity maintained to be 116.63mAh·g-1 after 10 cycles. The initial charge specific capacity is 97.92 mAh·g-1 and59.38 mAh·g-1 at 0.3C and 1C, respectively, and the cycling behavior of the material isquitepoor.
LiFePO4/(C+Ti4+) composite using citric acid and TiO2 delivered a high initialspecific discharge capacity of 138.52 mAh·g-1 with 5wt% citric acid and 1mol% Ti4+at 0.1C. The capacity maintained to be 129.42 mAh·g-1 after 10 cycles. The initialcharge specific capacity is 114.95 mAh·g-1 and 102.39 mAh·g-1 at 0.3C and 1C, andthecyclingbehaviorofthematerialisverygood.
引文
[1]雷永泉,万群,石永康.新能源材料[M].天津:天津大学出版社,2000:1-143.
[2] Nagaura T, Tozawak K. Lithium ion rechargeable battery [J]. Prog. Batts. Sol. Cells,1990,9:209-210.
[3]陈立泉.电动车锂离子电池的材料问题[J].中国工程科学,2002,4(11):32-36.
[4]赵健,杨维芝,赵佳明.锂离子电池的应用开发[J].电池工业,2000,5(1):31-36.
[5]吴宇平,万春荣,姜长印.锂离子二次电池[M].北京:化学工业出版社,2002:12.
[6] JacekLipkowski,PhilipNRoss.Theelectrochemistrvofnovelmaterials [M].NewYork:VCHPublisherInc,1994:116-117.
[7]刘建睿,王猛,尹大川,等.锂离子蓄电池正极材料锂钒氧化物研究进展[J].电源技术,2001,25(3):308-311.
[8] Miura K, Yamada A, Tanaka M. Electric states of spinel LixMn2O4as a cathode of therechargeablebattery[J].ElectrochimicaActa,1996,41:249-256.
[9]周恒辉,慈云祥,刘昌炎.锂离子电池电极材料研究进展[J].化学进展, 1998, 10(1):85-94.
[10]郭炳昆,徐辉,王先友,等.锂离子电池[M].长沙:中南大学出版社, 2002: 17-38,145-156.
[11]Padhi A K, Nanjundaswamy K S, Goodenough J B. Phospho-olivines as PositiveElectrode Materials for Rechargeable Lithium Batteries [J]. Journal of TheElectrochemicalSociety,1997,144(4):1188-1194.
[12]Streltsov A, Belokneva L, Tsirelson G, et al. Multipole Analysis of the Electron DensityofTriphyliteLiFePO4usingX-rayDifferactionData[J].ActaCryst,1993,49:147-153.
[13]Andersson A S, Thomas J O. The source of fist-cycle capacity loss in LiFePO4 [J].JournalofPowerSources,2001,97-98:498-502.
[14]Yamada A, Chung S C, Hinokuma K. Optimized LiFePO4 for Lithium Battery Cathodes[J].JElectrochemSoc,2001,148(3):224-229.
[15]PadhiAK,NanjundaswamyKS,MasquelierC,etal.EffectofstructureontheFe3+/Fe2+redoxcoupleinironphosphates[J].JElectrochemSoc,1997,144(5):1609-1613.
[16]Andersson A S. Lithium extraction/insertion in LiFePO4: an X-ray diffraction andMossbauerspectroscopystudy[J].SolidStateIonices,2000,130(1/20):41-52.
[17]Park K S, Son J T, Chung H T, et al. Synthesis of LiFePO4 by copreicpitation andmicrowaveheating[J].Electrochemistrycommunications,2003,5:829-842.
[18]Baghurst D R, Chippindale A M, Mingos D M P. Microwave syntheses forsuperconductingceramics[J].Nature[J].1988,332(6162):311.
[19]MingosDMP,BaghurstDR,Br.Ceram.Trans[J].1992,91:124-127.
[20]Yan H W, Huang X J, Chen L Q. Microwave synthesis of LiMn2O4cathode material [J].JPowerSources,1999,81-82:647-650.
[21]Masashi Higuchi, Keiichi Katayama, Yasuo Azuma. Synthesis of LiFePO4 cathodematerialbymicrowaveprocessing[J].JPowerSources,2003,119-121:258-261.
[22]Song M S, Kang Y M, Kim J H. Simple and fast synthesis of LiFePO4-C composite forlithium rechargeable batteries by ball-milling and microwave heating [J]. Journal ofPowerSources,2007,166:260-265.
[23]Takahashi M, Tobishima S, Takei K, et al. Characterization of LiFePO4 as the cathodematerialforrechargeablelithiumbatteries[J].SolidStateIonics,2002,148:283.
[24]Yanmada A, Hosoya M, Chung S C. Olivine-type cathodes achievements and problems[J].JPowerSources,2003,119-121:232.
[25]Ravet N, Chouinard Y, Magnan J F, et a1. Electroactivity of natural and synthetictriphylite[J].JPowerSources,2001,97-98:503-507.
[26]李发喜,仇卫华,胡环宇,等.微波合成锂离子电池正极复合材料LiFePO4/C电化学性能[J].北京科技大学学报,2005,27(1):86.
[27]Huang H, Yin S C, Nazar L F. Approaching theoretical capacity of LiFePO4 at roomtemperature[J].ElectrochemSolidStateLetter,2001,4(10):170.
[28]Hoon-TaekChung, Soo-Kwan Jang. Effects of nano-carbon webs on the electrochemicalpropertiesinLiFePO4/Ccomposite[J].SolidStateCommun,2004,131(8):549.
[29]张宝,罗文斌,等. LiFePO4/C锂离子电池正极材料的电化学性能研究[J].中国有色金属学报,2005,15(2):300.
[30]Chen Z H, Dahn J R. Reducing carbon in LiFePO4/C composite electrodes to maximizespecific energy, volumetric energy and tap density [J]. Electrochem Soc, 2002, 149(9):1184.
[31]Pier Paolo Prosini, Daniela Zane, Mauro Pasquali. Improved electrochemicalperformanceofaLiFePO4basedcompositecathode [J].ElectrochemActa,2001,46(23):3517.
[32]杨书廷,赵娜红,尹艳红,等. PAM软模板法合成LiFePO4/C纳米共生物[J].电池,2005,35(4):263-265.
[33]F Corce, A D Epifanio, J Hassoun, et al. A novel concept for the synthesis of animproved LiFePO4 lithium battery cathode [J]. Electrochem Solid-State Letter, 2002,5(3):47.
[34]罗文斌,李新海,张宝,等.锂离子蓄电池正极材料LiFePO4的合成研究[J].研究与设计,2004,28(12):750.
[35]Park K S, Son J T, Chung H T, et al. Surface modification by silver coating forimprovingelectrochemical properties of LiFePO4 [J].Solid State Commun, 2004, 129(5):311.
[36]ChungSY, BlokingJ T, Chiang YM, et al. Electronicallyconductive phosphor-olivinesaslithiumstorageelectrodes[J].NatureMater,2002,2:123-128.
[37]倪江锋,周恒辉,陈继涛.金属氧化物掺杂改善LiFePO4电化学性能[J].无机化学学报,2005,21(4):476.
[38]刘恒,孙红刚,周大利,等.改进的固相法制备磷酸铁锂电池材料[J].四川大学学报,2004,36(4):74-77.
[39]文衍宣,郑绵平,童张法,等.掺杂元素对锂离子电池正极材料LiFePO4的影响[J].无机盐工业,2005,37(4):12-14.
[40]唐致远,高飞,薛建军,等.锂离子电池正极材料LiFePO4的制备及电化学性能研究[J].天津大学学报,2007,40(4):468-472.
[41]Singhal A, Skandan G, Amatucci G, et al. Nanostructured electrodes for next generationrechargeableelectrochemicaldevices[J].JPowerSources,2003,129(1):38.
[42]Prosini P P, Carewska M, Scaccia S, et al. Long-term cyclability of nanostructuredLiFePO4[J].ElectrochimActa,2003,48(28):4205.
[43]Barker J, Saidi M Y, Swoyer J L, et al. Lithiumiron (II) Phospho-olivines Prepared by aNovel Carbothermal Reduction Method [J]. Electrochem Solid-State Letter, 2003, 6(3):53.
[44]庄大高,赵新兵,谢健,等.碳包覆镍掺杂LiFePO4正极材料的合成与电化学性能[J].稀有金属材料与工程,2007,36(1):149-152.
[45]钟参云,曲涛,田彦文.锂离子电池正极材料LiFePO4的研究进展[J].稀有金属与硬质合金,2005,33(2):39-41.
[46]郑明森.锂离子电池阴极界面特性及其电极过程动力学[D].厦门:厦门大学,2006.
[47]A J巴德, L R福克纳, (谷林瑛,宋诗哲,许淳淳译).电化学测定方法原理及应用[M].北京:化学工业出版社,1988.
[48]崔妍.微波合成锂离子电池正极材料LiFePO4的研究[D].天津:天津大学,2007.
[49]Robert Dominko, Miran Gaberscek, Jernej Drofenik, et al. ANovel Coating Technologyfor Preparation of Cathodes in Li-Ion Batteries [J]. Electrochemical and Solid-StateLetters,2001,4(11):187-190.
[50]李冀辉,黎梅,张志宏,等.常用化学反应速查手册[M].河北:河北科学出版社,1995,408-412.
[51]谭忠印,马金,王琛,等.原子力显微镜对聚丙烯酞胺凝胶分形结构的研究[J].中国科学B辑,1999,29(2):97-100.
[52]刘业翔,胡国荣,禹筱元.锂离子电池研究与开发的新进展[J].电池, 2002, 32(5):269-273.
[53]Shlyakhtina O A, Sun H C, Young S Y. Characterization of nanocrystalline HT-LiCoO2cathodematerialsforlithiumionbatteries[J].ElectrochimicaActa,2004,50:511-516.
