摘要
锂离子电池被认为是在空间和时间上可以存储和转换电能的比较理想的装置,生产和生活中对其需求不断增长,对能量密度,尺寸适应性,安全性能的要求也越来越高。使用聚合物电解质可以提高电池的能量密度和形状适应性,避免液态锂离子电池的漏液问题,提高电池的安全性。
本论文利用复合相分离原理,使用水做非溶剂的同时,又作为产生微孔的引发剂,制备出各种具有连通微孔结构的聚偏氟乙烯-六氟丙稀共聚物微孔膜,并以此为基体进行凝胶化,获得了聚合物电解质。使用扫描电镜、孔隙率分析、拉伸强度测试研究了微孔膜的孔结构和力学性质,利用X射线粉末衍射和差示量热扫描研究了聚合物膜的结晶组成和非晶化程度。微孔膜吸取电解液凝胶化后,获得聚合物电解质。采用交流阻抗研究了聚合物电解质的离子电导率,稳态电流和交流阻抗法研究了其锂离子迁移数,以及电压线性扫描研究了其电化学稳定性。将获得的聚合物电解质组装成锂二次电池,研究了电池在不同荷电状态的阻抗及电池在充放电循环中阻抗的变化,并与使用液态电解液和金属锂或人造石墨负极的电池进行了对比。最后对组装的锂二次电池的充放电循环性能、倍率放电能力、运输安全中的耐受热冲击能力、滥用时候的抗过充电能力、处在电池组模拟环境中被强制放电时的安全性能表现进行了研究。
使用复合相分离的方法可以制备出具有恒定微孔分布和适当结晶度的微孔膜,其孔结构和孔隙率范围适合做作为凝胶电解质的基体使用。微孔膜在具有良好强度的同时,吸取电解液凝胶化后所得聚合物电解质获得了达1.76×10~(-3)Scm~(-1)的室温锂离子电导率和低至5.75 kJ mol~(-1)的离子传输表观活化能。所组装锂二次电池的电解质本体阻抗大于同等液态金属锂电池和锂离子电池,但是界面阻抗和电池总阻抗小于同等液态电池。特别是在充放电循环过程中,界面和电极反应阻抗的增加也明显小于液态电池,这让所得聚合物锂二次电池获得了更好的循环性能。但是其倍率放电能力低于同等液态锂二次电池。其在运输中的热冲击和过充电、强制放电滥用情况下的安全性能不弱于或者优于液态锂离子电池。
通过这种方法来制备聚合物电解质可以减少有机溶剂的使用和污染,免去了已有工艺中除去有机溶剂的步骤和成本,可以在利用现有锂离子电池技术和设备的基础上,以较低的成本完成聚合物锂二次电池的升级。
Lithium ion batteries are among the category of the most competitive and widely used energy storage and conversion devices.However,safety issue of lithium ion batteries is still a challenge due to the possibility of leakage of liquid electrolyte. Gel polymer electrolytes can prevent the leakage without ruining the performance of the batteries evidently,owing to the depressed fluidness and sufficient ion transfer ability.
In this paper,a series of polymer electrolytes with interconnected pores based on poly(vinylidene difluoride-co-hexafluoropropylene)[P(VDF-HFP)]copolymer was prepared by a simple phase separation process using water as both non-solvent and pore inducer.The prepared porous membrane was characterized by SEM,XRD and DSC.With a narrow pore size distribution and low crystallinity,the resulting polymer electrolytes show a high ionic conductivity up to 1.76×10~(-3) S cm~(-1) at room temperature and exhibit low apparent activation energy of 5.75 kJ mol~(-1) for the transportation of ions.The bulk electrolyte impedances of the assembled Li [P(VDF-HFP)[LiFePO_4 polymer batteries are higher than those of batteries with liquid electrolyte,such as Li |PE| LiFePO_4 and C |PE| LiFePO_4,while the interfacial impedance and the overall impedance of selected Li |P(VDF-HFP)| LiFePO_4 batteries are lower than those of liquid ones.What is more,in the charging-discharging circling, the overall impedances of the selected Li |P(VDF-HFP)| LiFePO_4 batteries increase slower than those of the liquid ones,resulting the polymer batteries a better cycling performance.However,the rate discharging capability of the polymer lithium secondary batteries is still a little worse than that of the liquid ones.The safety performance of the assembled polymer batteries was examined on the items of thermal shock simulation during transmission,overcharging and forced discharging under abuse.The results are not worse,sometimes better,than the liquid ones.
This method for polymer electrolyte preparation could reduce the use of organic solvent as well as the pollution it causes,is free from solvent removing step and its cost,making it much easier to upgrade to polymer lithium secondary battery with the technology and equipment we have got on liquid lithium ion batteries.
引文
[1]吴宇平,戴晓兵,马军旗,程预江.锂离子电池-应用与实践[M].北京:化学工业出版社,2004:3-4.
[2]李国欣.新型化学电源技术概论[M].上海:上海科学技术出版社,2007.
[3]郭丙焜,徐徽,王先友,肖立新.锂离子电池[M].长沙:中南大学出版社,2002:12-13.
[4]郭炳焜,李新海,杨松青.化学电源-电池原理及制造技术[M].长沙:中南工业大学出版社,2000.
[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,2002:6.
[6]植谷庆雄,聚合物锂电池[M],Tokyo:CMC,1999:68
[7]吴宇平,张汉平,吴锋,李朝晖.聚合物锂离子电池[M].北京:化学工业出版社,2007.
[8]郑洪河.锂离子电池电解质[M].北京:化学工业出版社,2007
[9]李朝晖.聚偏氟乙烯-六氟丙烯基微孔复合聚合物电解质的电化学性能研究[D].湘潭:湘潭大学,2004.
[10]Fenton D.E.,ParkeI J.M.,Wright P.V.,Complexes of alkaline metal ions with poly(ethylene oxide)[J].Polymer,1973,14:589-591.
[11]Armand M B,Chabagno J M,DuclotM.Seeond International Meeting on Solid Eleetrolytes[C],St.Andrews.Scotland,SePtember,1978.
[12]Gadjourova,Z.;Martin y Marero,D.;Andersen,K.H.;Andreev,Y.G.;Bruce,P.G.,Structures of the Polymer Electrolyte Complexes PEO6:LiXF6(X=P,Sb),Determined from Neutron Powder Diffraction Data,Chem.Mater.[J],2001,13(4):1282-1285.
[13]Mao,G.;Saboungi,M.-L.;Price,D.L.;Armand,M.;Mezei,F.;Pouget,S.,-Relaxation in PEO-LiTFSI Polymer Electrolytes,Macromolecules[J],2002:35(2):415-419.
[14]Martin-Litas,I.;Andreev,Y.G.;Bruce,P.G.,Ab Initio Structure Solution of the Polymer Electrolyte Poly(ethylene oxide)3:LiAsF6,Chem.Mater.[J],2002,14(5):2166-2170.
[15]Borodin,O.;Smith,G.D.;Douglas,R.,Force Field Development and MD Simulations of Poly(ethylene oxide)/LiBF4 Polymer Electrolytes,J.Phys.Chem. B.[J],2003,107(28):6824-6837.
[16]Appetecchi G.B.,Zane D.,and Scrosati B.,PEO-Based Electrolyte Membranes Based on LiBC_4O_8 Salt,J.Electrochem.Soc.[J],2004,151(9):A1369-1374.
[17]Zhou,Z.B.and Matsumoto H.,Lithium-doped,organic ionic plastic crystal electrolytes exhibiting high ambient-temperature conductivities.Electrochemistry Communications[J],2007.9(5):p.1017-1022.
[18]Zhang,C.H.,Andreev Y.G.,and Bruce P.G.,Crystalline small-molecule electrolytes.Angewandte Chemic-International Edition[J],,2007.46(16):p.2848-2850.
[19]Zhang,C.H.,et al.,Raising the conductivity of crystalline polymer electrolytes by aliovalent doping.Journal of the American Chemical Society[J],,2005.127(51):p.18305-18308.
[20]Christie,A.M.,et al.,Increasing the conductivity of crystalline polymer electrolytes.Nature[J],,2005.433(7021):p.50-53.
[21]MacFarlane,D.R.,Huang J.H.,and Forsyth M.,Lithium-doped plastic crystal electrolytes exhibiting fast ion conduction for secondary batteries.Nature[J],,1999.402(6763):p.792-794.
[22]张汉平.锂离子电池的研制及凝胶聚合物电解质的研究[D].上海:复旦大学,2007.
[23]Cheng,L.P.,et al.,PVDF membrane formation by diffusion-induced phase separation-morphology prediction based on phase behavior and mass transfer modeling.Journal of Polymer Science Part B-Polymer Physics[J],1999.37(16):p.2079-2092.
[24]Magistris A.,Mustarelli P.,Parazzoli F.,Quartarone E.,Piaggio P.and Bottino A.,Structure,porosity and conductivity of PVdF films for polymer electrolytes,Journal of Power Sources[J],2001,97-98:657-660.
[25]Dar-Jong Lin,Cheng-Liang Chang,Fane-Ming Huang and Liao-Ping Cheng,Effect of salt additive on the formation of microporous poly(vinylidene fluoride)membranes by phase inversion from LiClO_4/Water/DMF/PVDF system,Polymer[J],2003,44(2):413-422.
[26]Tarascon,J.M.,et al.,Performance of Bellcore's plastic rechargeable Li-ion batteries.Solid State Ionics[J],1996.86-88(Part 1):p.49-54.
[27]庞东旭,吕少丽,魏秀珍,朱宝库,徐又一.凝固浴温度与相转化聚醚砜中空纤 维膜的结构与性能[J].中国组织工程研究与临床康复,2008,(27).
[28]左丹英,曾友国,徐又一.浸没凝胶相转化制备聚合物膜的孔结构及其形成机理[J].高分子通报,2008,(4).
[29]操建华,李继定,鲁胜,林阳政,陈翠仙.干燥方式对相转化法制备PVDF微孔膜性能的影响[J].天津工业大学学报,2008,(4).
[30]左丹英,徐又一,曾秋霞,龚玉洁.浸没沉淀相转化法制备结晶性聚合物微孔膜的研究进展[J].化学通报,2008,(5).
[31]吕少丽,朱宝库,徐又一.凝固浴温度对相转化聚醚砜中空纤维膜结构与性能的影响[J].膜科学与技术,2006,(5).
[32]魏永明,杨晓天,许振良.相转化法聚合物/溶剂/非溶剂铸膜体系的热力学计算[J].南京工业大学学报(自然科学版),2005,(2).
[33]杨振生,李凭力,常贺英,王世昌.扩散致相转化法制备结晶性聚合物多孔膜[J].高分子通报,2005,(3).
[34]武利顺,孙俊芬,王庆瑞.相转化膜孔形成机理的研究进展[J].膜科学与技术,2007,(3).
[35]李朝晖,张汉平,张鹏,吴宇平,.偏氟乙烯-六氟丙烯共聚物基微孔-凝胶聚合物电解质的研究进展[J].高分子通报,2007,(7).
[36]李婷婷,舒红英,徐佩.电纺纳米纤维的研究及应用[J].江西化工,2008,(3).
[37]马海红,史铁钧,宋秋生.电纺法制备聚合物纳米纤维的研究进展[J].高分子通报,2008,(9).
[38]周明阳.电纺法制备纳米纤维及其应用研究[J].化工时刊,2007,(6).
[39]肖文军,伍伯林,谭松庭.电纺聚合物纳米纤维研究进展[J].材料导报,2007,(2).
[40]马礼敦.高等结构分析[M].上海:复旦大学出版社,2001.
[41]何曼君,陈维孝,董西侠,高分子物理[M].上海:复旦大学出版,2000:199.
[42]舒余德,陈白珍.冶金电化学研究方法[M].长沙:中南工业大学出版社,1990.
[43]Bord A.J.,Faulkner L.R.电化学方法[M].北京:化学工业出版社,1986
[44]曹楚南,张鉴清.电化学阻抗谱导论[M].北京:科学出版社,2002:20-24
[45]柳厚田,徐品弟译.电化学中的仪器方法[M].上海:复旦大学出版社,1992.
[46]藤岛昭,相泽益男,井上撤著,陈震,姚建年译,电化学测定方法[M].北京:北京大学出版社,1995.
[47]李荻,电化学原理[M].北京:北京航空航天大学出版社,1999.
[48]查全性.电极过程动力学导论(第三版)[M].北京:科学出版社,2002.
[49]National Institute of Standards and Technology.NIST Chemistry WebBook[EB/OL].:NIST Standard Reference Database Number 69,http://webbook.nist.gov/chemistry,2008-01-10
[50]Cheng,L.P.,Effect of temperature on the formation of microporous PVDF membranes by precipitation from 1-octanol/DMF/PVDF and water/DMF/PVDF systems.Macromolecules[J],1999.32(20):p.6668-6674.
[51]Arora,P.and Zhang Z.,Battery Separators.Chem.Rev.[J],2004.104(10):p.4419-4462.
[52]Rosenberg Y.,et al.,The sol/gel contribution to the behavior of γ-irradiated poly(vinylidene fluoride),J.Applied Polymer Science.[J],1991,43:533
[53]Macdonald J.R.,Simplified Impedance/Frequency-Response Results for Intrinsically Conducting Solids and Liquids,J.Chem.Phys.[J],1974,61:3977-3996
[54]Groce F.,Gerace F.,Dautzemberg G.,et al.Appetecchi and B.Scrosati,Synthesis and characterization of highly conducting gel electrolytes,Eletrochimica Acta[J],1994,39(14):2187-2194
[55]Marc Doyle,and John Newman,Analysis of transference number measurements based on the potentiostatic polarization of solid polymer electrolytes,J.Electrochem.Soc.[J],1995,142(10):3465-3468
[56]Yuria Saito,Hiroshi Kataoka,Tetsuo Sakai and Shigehito Deki,Conduction properties of lithium gel electrolytes investigated by impedance spectroscopy and pulsed-field gradient NMR with electric field,Electrochimica Acta[J],2001,46(10-11):1747-1751
[57]Poul Ravn Sφrensen,and Torben Jacobsen,Conductivity,charge transfer and transport number-an ac-investigation of the polymer electrolyte LiSCN-poly(ethyleneoxide),Eletrochimica Acta[J],1982,27(12):1671-1798
[58]Evans J.,C.Vincent A.,and Bruce P.G.,Electrochemical measurement of transference numbers in polymer electrolytes,Polymer[J],1987,28:2324-2328
[59]Bruce,RG.and C.A.Vincent,Steady-state current flow in solid binary electrolyte cells.Journal of Electroanalytical Chemistry[J],1987.225(1-2):p.1-17.