電動汽車用磷酸鐵鋰動力電池的制作及性能測試_英文_

1、ISSN 1674-8484CN 11-5904/U汽車安全與節(jié)能學(xué)報(bào), 2011年, 第2卷 第1期J Automotive Safety and Energy, 2011, Vol. 2 No. 110/1368 71Manufacture and Performance Tests of Lithium Iron PhosphateBatteries Used as Electric Vehicle PowerZHANG Guoqing, ZHANG Lei, RAO Zhonghao, LI Yong(Faculty of Materials and Energy, Guangdong

2、 University of Technology, Guangzhou 510006, China)Abstract: Owing to the outstanding electrochemical performance, the LiFePO4 power batteries could be used on electricvehicles and hybrid electric vehicles. A kind of LiFePO4 power batteries, Cylindrical 26650, was manufactured fromcommercialized LiF

3、ePO4, graphite and electrolyte. To get batteries with good high-current performance, the optimal contentof conductive agent was studied and determined at 8% of mass fraction. The electrochemical properties of the batteries wereinvestigated. The batteries had high discharging voltage platform and cap

4、acity even at high discharge current. When dischargedat 30 C current, they could give out 91.1% of rated capacity. Moreover, they could be fast charged to 80% of rated capacity inten minutes. The capacity retention rate after 2 000 cycles at 1 C current was 79.9%. Discharge tests at -20 and 45 alsos

5、howed impressive performance. The battery voltage, resistance and capacity varied little after vibration test. Through the safetytests of nail, no in ammation or explosion occurred.Key words: hybrid and electric vehicles; power batteries; lithium iron phosphate; lithium ion batteries;電動汽車用磷酸鐵鋰動力電池的制

6、作及性能測試張國慶、張 磊、饒忠浩、李 雍( 廣東工業(yè)大學(xué) 材料與能源學(xué)院,廣州 510006, 中國 )摘 要： 磷酸鐵鋰電池的優(yōu)異性能使其可以應(yīng)用在電動汽車和混合動力汽車上。用市售磷酸鐵鋰、石墨和電解液制作了圓柱型26650磷酸鐵鋰動力電池。為改善電池的大電流性能，研究了正極導(dǎo)電劑的最佳質(zhì)量分?jǐn)?shù)為8%。研究了所制備的動力電池的充放電性能。電池在高倍率下放電仍有較高的電壓平臺和放電容量。30 C（96 A）放電時(shí)，可放出額定容量的91.1%。電池大電流充電性能較好，5C（16 A）充電 10 min 左右，可充入額定容量的80%。1 C充放電循環(huán) 2 000次，仍能保持額定容量的79.9%。

7、高低溫下電池放電性能良好。電池經(jīng)過振動測試，內(nèi)阻、電壓和容量變化很小。針刺實(shí)驗(yàn)中沒有發(fā)生起火和爆炸，電池溫度峰值為 94.7 。關(guān)鍵詞： 混合動力汽車/電動汽車；動力電池；磷酸鐵鋰; 鋰離子電池中圖分類號： TQ 152IntroductionWith the demand for more power to satisfy the rapidly growingautomotive markets, focus is being directed at the lithium ionbatteries, which have energy densities exceeding 130 Wh

8、·kg-1 and cycle life of more than 1 000 cycles. However, compared with traditional markets like laptops and cellular phones, new applications have much higher energy and power requirements. In these applications, where safety is of paramount importance,收稿日期/ Received： 2010-12-13基金項(xiàng)目/ Supported

9、by： The Research Cooperation Project of Guangdong Province and the Ministry of Education /廣東省教育部產(chǎn)學(xué)研結(jié)合項(xiàng)目 (2008B090500013)ZHANG Guoqing, et al: Manufacture and performance tests of lithium iron phosphate batteries used as electric vehicle powerthe use of LiCoO2 and its derivatives raises serious conce

10、rns for developers because of inherent thermal instability. These inherent safety limitations have until now prevented lithium ion batteries from entering the large applications such as electric and hybrid electric vehicles.Comparatively, iron-based olivine phosphate has been the focus of research1.

11、 LiFePO4 has high theoretical capacity of 170 mAh·g-1 and an average voltage of about 3.5 V vs. Li+/Li. Due to the low cost, environmental benignity, excellent structural stability, long cycling life and high reversible capacity, lithium iron phosphate has been recognized as a promising candida

12、te material for cathode of lithium ion batteries2. However, the poor conductivity, resulting from the low electronic conductivity of the LiFePO4, has posed a bottleneck forcommercial applications3. Therefore, researches of LiFePO4 materials and batteries mainly focus on enhancing their high-current

13、performance4-5. In this paper, effect of conductive agent content was studied to get batteries with good high-current performance as well as acceptable capacity sacrifice, and their charge-discharge performance was investigated.69capacities of the batteries decreased as the increase of the Super P c

14、ontent. Low resistance could result in good high-current performance, but the capacity is also important. When the mass fraction of Super P is above 8%, the resistance decline is not obvious any more, but the capacity decrease didnt slow down. To get batteries with good high-current performance as w

15、ell as acceptable capacity, the mass fraction of the conductive agent was determined at 8%.2.2 High-Current Discharge PerformanceOne cell was charged at a current of 1 C (3.2 A), thendischarged 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 wer

16、e 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. Voltage-capacity curves were shown in Figure 2. Every curve had quite flat platform, and only when approaching the end-voltage of

17、discharge, these curves began to decline. Voltage platform varied from 3.23 V to 2.65 V when discharge rate changed from 0.5 C to 30 C. Both capacity andvoltage performed excellently.1 ExperimentsCylindrical 26650 LiFePO4 power batteries were manufactured. Lithium iron phosphate, or graphite, was mi

18、xed together with super P, Polyvinylidene Fluoride (PVDF) and N-Methyl Pyrrolidone (NMP) in proportion, and then stirred to obtain homogeneous slurry. The slurry was then coated on aluminum or copper foil. After fully dried, the electrode sheet was rolled to appropriate thickness, and then sliced to

19、 adequate small size. Positive, negative electrode sheet and separator were 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

20、:1:1) was then infused into the battery shell. The battery was then mounted by the battery cap and sealed. At last, the batteries were activated with particular charging-discharging method.To optimize their properties, batteries with different weight ratio of the conductive agent (super P) in cathod

21、e weremanufactured. After the optimization, battery properties such as high-current charging-discharging performance, high and low temperature performance, cycle life, vibration endurability and security, were tested.Fig. 1 Resistances and Capacities of the Batteries2 Results2.1 Effect of Conductive

22、 Agent ContentTo get batteries with good high-current performance, the optimal content of conductive agent in cathode was studied6. Batteries were fabricated in which Super P contents (massfraction, w) were 4%, 6%, 8% and 10% in cathode respectively. (Binder contents were the same as the conductive

23、agent) Resistances and capacities of these batteries were shown in Figure 1. It indicated that both the resistances and theFig. 2 Voltage-Capacity Curves of Discharge at DifferentCurrents70J Automotive Safety and Energy 2011, Vol. 2 No. 12.3 High-Current Charge PerformanceWhen using fuel vehicles, p

24、eople are used to the convenience of fast refueling. When electric vehicles took the place, they need 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 constant current of 5 C. The

25、voltage-capacity curve was shown in Figure 3. The charge capacity was 2.676 Ah, thats 82.0% of the batterys 1 C discharge capacity. The process only took 10 min. That means the cells had high-current and fast charge capability.2.4 Discharge Performance at High & LowTemperatureElectric vehicles a

26、re used outdoors; the ambient temperature varies from summer to winter. That demands the batteries can work both at high and low temperature. One battery was charged at room temperature, and then discharged at 25, 45 and 20 respectively. When discharged at 45 and 20 , the battery was placed at that

27、temperature for not less than 6 h. The voltage-capacity curves were shown in Figure 4. Discharge capacities at 25, 45 and 20 were 3.223, 3.231 and 2.773 Ah, respectively. The discharge capacity at 45 was a little higher than that at room temperature. The batteries could work at 20 , and discharge ca

28、pacities only declined by 14.0%.Fig. 3 Voltage-Capacity Curve of Charge at 5 C Current2.5 Cycle LifeLong operational life of electric vehicle batteries is important, because it means less maintenance costs and more competitiveness against fuel vehicles. The cycle life of batteries we made was tested

29、. The charging and discharging currents were both 1 C. As shown in Figure 5, after 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 excellent cycle performance and long oper

30、ational life.Fig. 4 Voltage-Capacity Curves of Discharge at DifferentTemperature2.6 Vibration EndurabilityWhen travelling on road, electric vehicles were in the status of irregular vibration. As the power source for electric vehicles, the batteries must have sufficient vibration endurance. 50batteri

31、es were investigated in a simulation vibration test. In the vibration parameters, the constant acceleration is 30 m/s2; the scan frequency range is 3035 Hz; the vibration time is 2 h. The resistances, voltages and capacities of the batteries were tested both before and after the vibration. Changes o

32、f these properties were shown in Figure 6.As figured in the graphs, the resistance-risings did not exceed 0.4 m; the voltage-droppings were no more than 20 mV; and the capacity retention rates were above 96.8%. After one cycle of discharge and charge, capacities of all batteries recovered to above 9

33、8%. Changes of these properties were all in acceptableranges.Fig. 5 Cycling Curve at 1 C Current2.7 SecurityConsidering the application on electric vehicles, security of the batteries was of paramount importance7-8. Extreme damage to the batteries was simulated by piercing a nail through the battery

34、 horizontally. The voltage and temperature were inspected through the process and shown in Figure 7. The voltage of the battery dropped to zero immediately whenthe battery was nailed. Meanwhile, the surface temperatureZHANG Guoqing, et al: Manufacture and performance tests of lithium iron phosphate

35、batteries used as electric vehicle power71of the battery rose to the peak of 94.7 in a few seconds. Then the flame retardant in electrodes worked to enlarge the resistance of the battery, so the temperature started to decrease. No inflammation or explosion occurred through the whole process, so the

36、security of the batteries is satisfying.3 ConclusionLiFePO4 power batteries are considered to be the most competitive candidate for electric vehicles power source. Increasing content of conductive agent can improve the high-current performance of the batteries but lower the capacity. In our manufact

37、ure procedure, mass fraction of 8% of super P brought good high-current performance with acceptable capacity sacrifice. The cylindrical 26650 LiFePO4 powerbatteries we manufactured could output 91.1% of rated capacity at highest 30 C discharge current, simultaneously had a high voltage platform of 2

38、.65 V, and therefore could supplied strong power for electric vehicles. They could be fast charged to 80% of rated capacity in ten minutes at 5 C charging current, which saved charging time by far. After 2 000 cycles at discharging current of 1 C, the capacity retention rate was 79.9%; the working l

39、ife was gratifying. High and low temperature, vibration conditions were common to vehicles, and the simulating tests performed impressively. Even damaged extremely, the batteries did not explode or burn. Due to their extraordinary electrochemical and safety performance, the LiFePO4 power batteries c

40、ould be used on electric vehicles and hybrid electric vehicles.(a) ResistanceChange(b) Voltage ChangeReferences1 Padhi A K, Nanivndaswamy K S, Goodenough J B. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries J. J Electrochemical Society, 1997, 144 (4): 1188-1194.2 Padhi A K, Nanivndaswamy K S, Masquelier C, et al. Effect of