电动汽车用磷酸铁锂动力电池的制作及性能测试_英文_概要

1、ISSN 1674-8484CN 11-5904/U汽车安全与节能学报,2011年,第2卷第1期J Automotive Safety and Energy, 2011, Vol. 2 No. 1Manufacture and Performanee Tests of Lithium Iron PhosphateBatteries Used as Electric Vehicle PowerZHANG Guoqi ng, ZHANG Lei, RAO Zho nghao, LI Yong(Faculty of Materials and En ergy, Guan gdo ng Uni ver

2、sity of Tech no logy,Gua ngzhou 510006, ChinaAbstract: Owi ng to the outsta nding electrochemical performa nee, the LiFePO 4 power batteries could be used on electric vehicles and hybrid electric vehicles. A ki nd of LiFePO 4 power batteries, Cyli ndrical 26650, was manu factured fromcommercialized

3、LiFePO 4, graphite and electrolyte. To get batteries with good high- curre nt performa nee, the optimal content of con ductive age nt was studied and determ ined at 8% of mass fraction. The electrochemical properties of the batteries were investigated. The batteries had high dischargi ng voltage pla

4、tform and capacity eve n at high discharge current. When discharged at 30 C current, they could give out 91.1% of rated capacity. Moreover, they could be fast charged to 80% of rated capacity in ten minutes. The capacity retention rate after 2 000 cycles at 1 C current was 79.9%. Discharge tests at

5、- 20 °C and 45 °C also showed impressive performa nee. The battery voltage, resista nee and capacty varied little after vibration test. Through the safety tests of nail, no in ? ammati on or explosi on occurred.Key words: hybrid and electric vehicles; power batteries; lithium iron phosphat

6、e; lithium ion batteries;电动汽车用磷酸铁锂动力电池的制作及性能测试张国庆、张磊、饶忠浩、李雍(广东工业大学 材料与能源学院，广州510006,中国摘要：磷酸铁锂电池的优异性能使其可以应用在电动汽车和混合动力汽车上。用市售磷酸铁锂、石墨和电解液制作了圆柱型26650磷酸铁锂动力电池。为改善电池的大电流性能，研究了正极导电剂的最佳质量分数为 8%。研究了所制备的动力电 池的充放电性能。电池在高倍率下放电仍有较高的电压平台和放电容量。30 C (96A放电时,可放出额定容量的91.1%。电池大电流充电性能较好,5C (16 A充电10 min左右,可充入额定容量的80%。1

7、 C充放电循环2 000次,仍能保持额定容量的 79.9%。高低温下电池放电性能良好。电池经过振动测试，内阻、电压和容量变化很小。针刺实验中没有发生起火和爆炸，电池温度峰值为94.7 C。关键词：混合动力 汽车/电动汽车；动力电池；磷酸铁锂；锂离子电池中图分类号：TQ 152收稿日期 / Received : 2010-12-13基金项目 / Supported by : The Research Cooperati on Project of Guangdong Province and the Mi nistry of Educati on 广东省教育 部产学研结合项目（2008B0905

8、00013第一作者/ First author :张国庆（1963-,男（汉，河 北教授。E-mail: 第二作者 / Seco nd author :张磊,E- mail :rockyzha In troduct ionWith the dema nd for more power to satisfy the rapidly grow ingautomotive markets, focus is being directed at the lithium ion batteries, which have en ergy den sities exceedi ng 130 Whkg -1

9、and cycle life of more than 1 000 cycles. However, compared with traditional markets like laptops and cellular phon es, new applicati ons have much higher en ergy and power requirements. In these applications, where safety is of paramount importanee,10/1368 7169 ZHANG Guoqing, et al:Ma nu facture an

10、d performa nee tests of lithium iron phosphate batteries used as electric vehicle powerthe use of LiCoO2 and its derivatives raises serious concerns for developers because of in here nt thermal in stability. These in here nt safety limitatio ns have un til now preve nted lithium ion batteries from e

11、n teri ng the large applicati ons such as electric and hybrid electric vehicles.Comparatively, ir on-based oliv ine phosphate has bee n the focus of research1. LiFePO4 has high theoretical capacity of 170 mAhg-1 and an average voltage of about3.5 V vs. Li+/Li. Due to the low cost, environmental beni

12、gnity, excellent structural stability, lo ng cycli ng life and high reversible capacity, lithium iron phosphate has bee n recog ni zed as a promisi ng can didate material for cathode of lithium ion batteries2. However,the poor con ductivity, result ing from the low electr onic con ductivity of the L

13、iFePO4, has posed a bottle neck for commercial applicatio ns3. Therefore, researches of LiFePO4 materials and batteries mainly focus on enhancing their high-current performance4-5. In this paper, effect of con ductive age nt content was studied to get batteries with good high- curre nt performa nee

14、as well as acceptable capacity sacrifice, and their charge-discharge performa nee was in vestigated.1 Experime ntsCyli ndrical 26650 LiFePO4 power batteries were manu factured. Lithium iron phosphate, or graphite, was mixed togetherwith super P, Polyvinylidene Fluoride (PVDF and N-Methyl Pyrrolidone

15、 (NMP in proporti on, and the n stirred to obta in homoge neous slurry. The slurry was the n coated on aluminum or copper foil. After fully dried, the electrode sheet was rolled to appropriate thick ness, and the n sliced to adequate small size. Positive, n egative electrode sheet and separator were

16、 stacked and coiled into battery core. The battery core was put into the battery shell and the positive, negative electrodes were weld with the battery cap and the shell respectively. Electrolyte (1 mol/L LiPF6, EC+DEC+DMC, 1:1:1 was then in fused into the battery shell. The battery was then mounted

17、 by the battery cap and sealed. At last, the batteries were activated with particular charg in g-discharg ing method.To optimize their properties, batteries with differe nt weight ratio of the con ductive age nt (super P in cathode were manu factured. After the optimizati on, battery properties such

18、 as high-curre nt chargi ng-discharg ing performa nee, high and low temperature performa nee, cycle life, vibrati on en durability and security, were tested.2 Results2.1 Effect of Co nductive Age nt ContentTo get batteries with good high-curre nt performa nee, the optimal content of con ductive age

19、nt in cathode was studied6. Batteries were fabricated in which Super P contents (mass fractio n, w were 4%, 6%, 8% and 10% in cathode respectively. (Bi nder contents were the same as the con ductive age nt Resista nces and capacities of these batteries were show nin Figure 1. It indicated that both

20、the resistances and the capacities of the batteries decreased as the in crease of the Super P content. Low resista nee could result in good high-curre nt performa nee, but the capacity is also importa nt. When the mass fractio n of Super P is above 8%, the resista nee decli ne is not obvious any mor

21、e, but the capacity decrease didn ' t slow down. To get batteries with gooeldugtent performanee as well as acceptable capacity, the mass fracti on of the eon ductive age nt was determ ined at 8%.2.2 High-Curre nt Discharge Performa neeOne cell was charged at a current of 1 C (3.2 A, then dischar

22、ged at different rates of 0.5, 1,2, 4, 10, 30 C (1.6, 3.2, 6.4, 12.8, 32, 96 A. The discharge capacities were 3.243,3.168, 3.157., 3.130, 3.115, 2.955 Ah, respectively. Capacities at 1,2, 4, 10, and 30 C reached 97.6%, 97.2%, 96.4%, 95.9%, and 91.1% of the capacity at 0.5 C. Voltagecapacity curves w

23、ere shown in Figure 2. Every curve had quite flat platform, and only whe n approachi ng the en d-voltage of discharge, these curves bega n to decli ne. Voltage platform varied from 3.23 V to 2.65 V whe n discharge rate chan ged from 0.5 C to 30 C. Both capacity andvoltage performed excelle ntly.Fig.

24、 1 Resistances and Capacities of the Batteries Fig. 2 Voltage-Capacity Curves ofDischarge at Differe ntCurre nts70J Automotive Safety and En ergy 2011, Vol. 2 No. 12.3 High-Curre nt Charge Performa neeWhe n using fuel vehicles, people are used to the convenience of fast refueli ng.Whe n electric veh

25、icles took the place, they n eed to be charged quickly sometimes. This requires electric vehicle batteries could be fast charged at high currents. One fully- discharged cell was charged to 3.65 V with a con sta nt curre nt of 5 C. The voltagecapacity curve was shown inFigure 3. The charge capacity w

26、as 2.676 Ah, that' s 82.0%of the battery ' s 1 C discharge capacity. The process only took 10 min. That means the cells had high-curre nt and fast charge capability.2.4 Discharge Performa nee at High & LowTemperatureElectric vehicles are used outdoors; the ambie nt temperature varies fro

27、m summer to win ter. That dema nds the batteries can work both at high and low temperature. One battery was charged at room temperature, and the n discharged at 25, 45 and -20 respectively. When discharged at 45C and -20 °C , the battery was placed at that temperature for not less than 6 h. The

28、 voltage-capacity curves were shown in Figure 4. Discharge capacities at 25, 45 and -2C were 3.223, 3.231 and 2.773 Ah, respectively. The discharge capacity at 45C was a little higher than that at room temperature. The batteries could work at -20 C , and discharge capacities only declined by 14.0%.2

29、.5 Cycle LifeLong operati on al life of electric vehicle batteries is importa nt, because it means less maintenance costs and more competitive ness aga inst fuel vehicles. The cycle life of batteries we made was tested. The charg ing and dischargi ng curre nts were both 1 C. As shown in Figure 5, af

30、ter 2 000 cycles, the battery capacity dropped from 3.257 Ah to 2.601 Ah, and capacity fading rate was 20.1%. Average fading rate per cycle was only 0.01%. Hence the batteries had excelle nt cycle performa nce and long operati on al life.2.6 Vibrati on En durabilityWhen travelling on road, electric

31、vehicles were in the status of irregular vibration.As the power source for electric vehicles, the batteries must have sufficie nt vibrati on en dura nce. 50batteries were investigated in a simulation vibration test. In the vibration parameters, the constant acceleration is 30 m/s 2; the scan frequen

32、cy range is 30-35 Hz; the vibration time is 2 h. The resistances, voltages and capacities of the batteries were tested both before and after the vibration. Changes of these properties were shown in Figure 6.As figured in the graphs, the resistance-sings did not exceed 0.4 mQ ; the voltagedropp ings

33、were no more tha n 20 mV; and the capacity rete nti on rates were above 96.8%. After one cycle of discharge and charge, capacities of all batteries recovered to above 98%. Chan ges of these properties were all in acceptableran ges.Fig. 3 Voltage-Capacity Curve of Charge at 5 C CurrentFig. 5 Cycling

34、Curve at 1 C CurrentFig. 4 Voltage-Capacity Curves of Discharge at Differe ntTemperature2.7 SecurityCon sideri ng the applicati on on electric vehicles, security of the batteries was of param ount importa nee 7-8. Extreme damage to the batteries was simulated by pierci ng a n ail through the battery

35、 horiz on tally. The voltage and temperature were in spected through the process and show n in Figure 7. The voltage of the battery dropped to zero immediately whe nthe battery was n ailed. Mea nwhile, the surface temperature71ZHANG Guoqing, et al: Manu facture and performa nee tests of lithium iron

36、 phosphate batteries used as electric vehicle power Figure 6 Properties Change ThroughVibration TestFig. 7Voltage and Temperature Change Curve of Nail Test(a Resista neeChangeof the battery rose to the peak of 94.7C in a few see on ds. The n the flame retarda nt in electrodes worked to enl arge the

37、resista nee of the battery, so the temperature started to decrease. No in flammati on or explosi on occurred through the whole process, so the security of the batteries is satisfy ing.3 Con clusi onLiFePO4 power batteries are con sidered to be the most competitive can didate for electric vehicles &#

38、39; power source. In creas ing content of con ductive age nt can improve the high-curre nt performa nee of the batteries but lower the capacity .In our manu facture procedure, mass fract ion of 8% of super P brought good high-curre nt performa nee with acceptable capacity sacrifice. The cyli ndrical

39、 26650 LiFePO 4 powerbatteries we manu factured could output 91.1% of rated capacity at highest 30 C discharge curre nt, simulta neously had a high voltage platform of 2.65 V, and thereforecould supplied strong power for electric vehicles. They could be fast charged to 80% of rated capacity in ten m

40、inutes at 5 C charging current, which saved charging time by far. After 2 000 cycles at dischargi ng curre nt of 1 C, the capacity rete nti on rate was 79.9%; the working life was gratifying. High and low temperature, vibration conditions were com mon to vehicles, and the simulati ng tests performed

41、 impressively. Eve n damaged extremely, the batteries did not explode or burn. Due to their extraordinary electrochemical and safety performa nee, the LiFePO4 power batteries could be used on electric vehicles and hybrid electric vehicles.Refere nces1 Padhi A K, Nanivndaswamy K S, Goodenough J B. Phospho-olivines as positive-electrode materials for rechargeable lithiumbatteries J. J Elec