【作者】 刘云建；

【导师】 李新海； 郭华军； 王志兴；

【作者基本信息】 中南大学 ， 电化学工程， 2009， 博士

【摘要】 本文在综合评述了锂离子动力电池的研究现状的基础上,系统地研究了锰酸锂和磷酸铁锂电池动力电池的制作与性能,通过对锂离子电池正极、负极和电解液等关键材料进行表征和分析,研究和改进锰酸锂电池的电化学性能、储存性能和安全性能及机理,研究了磷酸铁锂电池的制作和性能及作用机理。系统地比较研究了几种不同LiMn₂O₄、负极和电解液样品的结构与性能。最后选取了合适的LiMn₂O₄,石墨以及电解液作为锰酸锂电池的关键材料。电极容量比分别为1.33、1.19和1.08的锰酸锂电池中LiMn₂O₄放电比容量分别为101,105和107mAh/g。170次循环容量保持率分别为87.3,85.4和84.1%。在电池正极组分中添加2%的Li₂CO₃,MgO和LiF,LiMn₂O₄的放电比容量分别为106.1,107.2和107.5mAh/g。100次循环容量保持率分别为90.8、91.8和93%。LiF的含量为2%时效果最佳。当正极极片面密度为2.5 g/dm²,导电剂含量为3%时,20C放电容量为1C放电容量的94.1%。1C充5C放100次循环容量保持率为92%。配置EC:EMC:E=2:7:1,lmol/L LiPF₆的低温功能电解液,研究发现在-40℃下,以0.2和1C放电,分别放出常温容量的81.1和63.4%。锰酸锂电池半荷电储存一个月后容量恢复率为96.3%,100次循环容量保持率达到94.1%。通过XRD、SEM、TEM和XPS研究表明,储存后MnO₂、R-CO₃Li、Li₂CO₃、LiF和Li_xPF_y等共同组成正极表面钝化膜,LiMn₂O₄晶格发生氧缺陷现象。储存前后LiMn₂O₄电极峰电流分别为0.55和0.36mA,电极和电解液界面的吸附双电层阻抗分别为20.28和53.3 1Ω。LiMn₂O₄的交换电流密度为0.69和1.01mA/cm²。负极SEI膜增厚并变致密,阻抗由183.1增大到310Ω。储存后电解液中LiPF₆发生了一定程度的分解,溶剂被氧化生成小分子物质。电极表面极化、正极材料中Mn溶解以及氧缺陷、SEI膜增厚所消耗的活性锂、电解液的分解和氧化是导致储存后锰酸锂电池储存后容量衰减的主要原因。高温储存研究发现锰酸锂电池在第一天内容量损失最大,此后每天损失的容量逐步减少。锰酸锂电池的循环稳定性的改善程度随着储存时间的延长而增加。随着储存时间的增加,正极表面钝化膜不断增厚,LiMn₂O₄晶格不断发生收缩并变稳定,颗粒/电解液界面积减小,电极氧化性减弱,从而导致容量衰减变慢。放电态和满电态下储存锰酸锂电池容量恢复率分别为99.2%和93.5%。满电态下储存的锰酸锂电池循环稳定性改善最大。荷电态对储存后容量衰减的影响主要是由Mn溶解量的不同以及储存后正极表面极化不同而引起的。随着荷电态的增加,Mn⁴⁺可能先被还原成Mn³⁺,进而发生歧化反应生成Mn²⁺,从而导致容量衰减增大。正极表面钝化膜将LiMn₂O₄材料与电解液分隔开;LiMn₂O₄的晶格收缩,稳定性增强;负极SEI不断地增厚和变致密可能是储存后锰酸锂电池的循环稳定性改善的原因。在锰酸锂正极中添加LiF,半荷电储存后电池的容量恢复率从96.3%提高到98%。研究表明LiF能够有效地抑制Mn的溶解并且降低储存后正极表面的阻抗。锰酸锂电池（347080-16Ah）在热冲击、穿刺、短路安全测试下未爆炸。3C/10V过充测试电池发生爆炸,电池表面最高温度达到290℃。爆炸后粉末的主要成分为C、MnO和Li₂CO₃。当电压达到5.0V,正极材料表面出现了大量的裂缝。裂缝的出现导致过充后期电压和温度急剧上升直至爆炸。采用Al₂O₃包覆的LiMn₂O₄制作锰酸锂电池,经过3C/10V过充后不爆炸、不起火。研究比较了3种不同LiFePO₄的结构与性能。研究了碳纳米管（CNT）对磷酸铁锂电池性能的影响。添加CNT后,1C/0.1C的放电比容量比值由原来的92.1提高到96.3%,0.1C的放电容量都为124mAh/g;磷酸铁锂电极的电荷反应阻抗由173.1Ω减小为36.88Ω,极化减小,电池200次循环容量保持率由原来的93.7提高到96.6%。采用PVDF和LA133为粘结剂的LiFePO₄的1/3C放电比容量分别为124和120mAh/g。200次循环容量保持率分别为96.3%和93.2%。采用两种LiFePO₄复配体系,制作347080磷酸铁锂动力电池。10C/1C的放电容量比值为95.9%,3C充电10C放40次循环容量保持率为96.9%。磷酸铁锂电池在热冲击、过充、穿刺、短路等滥用条件下均未发生爆炸起火现象。更多还原

【Abstract】 The development of Li-ion power batteries are reviewed in detail. The fabrication and properties of LiMn₂O₄ and LiFePO₄ batteries are studied in this paper.The electrochemical,storage and safety performance and mechanism are studied and improved through cathode,anode and electrolyte studying.The fabrication,performance and mechanism of LiFePO4 battery are studied.Several LiMn₂O₄ cathode,anode and electrolyte samples are compared for battery fabrication.Conformable LiMn₂O₄,artifical graphite and electrolyte sample are chosen for power batteries fabrication.The cell balances are designed as 1.33,1.19 and 1.08, respectively.The capacities of LiMn₂O₄ are 101,105 and 107mAh/g,and the capacity retention ratios are 87.3,85.4 and 84.1%after 170 cycles, respectively.2wt%Li₂CO₃,MgO and LiF is added in the cathode, respectively.The capacities of LiMn₂O₄ batteries are 106.1,107.2 and 107.5mAh/g,and the capacity retention ratio after 100 cycles are 90.8, 91.8 and 93%,respectively.The electrochemical performance is best when content of additive LiF is 2 wt%.It is found that the discharge capacity at 20C rate is equivalent with 94.1%at 1C rate when the area density is 2.5g/dm² and conductive is 3wt%.The capacity retention ratio is 92%with 1C charged and 5C discharged after 100 cycles.The content of electrolyte salt is EC:EMC:E=2:7:1,1.0mol/L LiPF₆.The results show that the discharge capacity at 0.2C and 1C at -40℃are and 81.1%and 63.4%of that at room temperature,respectively.The ratio of capacity recovery of LiMn₂O₄ battery after storage at room temperature for a month is 96.3%.The capacity retention ratio is 94.1%after 100 cycles.The XRD,SEM,TEM and XPS results show that the film covered on the cathode is composed by MnO₂,R-CO₃Li,Li₂CO₃, Li_xPF_y and LiF after storage.And oxygen deficiency in the LiMn₂O₄ electrode is detected.The migration resistance of LiMn₂O₄/electrolyte is increased from 20.28 to 53.31Ωafter storage.And the exchange current is increased from 0.69 to 1.01mA/cm² after storage.AC impedance for anode result shows that the SEI film is incrassated and compacted,and the impedance is increased from 183.1 to 310Ω.FTIR results show that LiPF₆ decomposes at a certain degree after storage.And the solvent in the electrolyte is oxided to small molecular weight substance.The polarization of electrode,Mn dissolution and Oxygen deficiency in the LiMn₂O₄,decomposition and oxygenation of electrolyte,Li⁺ consuming during the incrassated and compacted SEI film is the reason of capacity fading during storage.The capacity lost in the first day is maximal during the high temperature storage.The capacity lost in every day is decreased with the time extending.The improvement of cycling performance of battery after storage is increased with time extending.The capacity loss is slow because of thickness of film covered on the cathode increasing,shrinked and strengthened of LiMn₂O₄ structure,decreasing area of particle/electrolyte,weakened oxygen of electrode.The ratio of capacity recovery of LiMn₂O₄ battery at discharge state is highest,99.2%;and that is 93.5%at charged state.The improvement of cycling performance after charged storage is best.The difference of capacity fading of LiMn₂O₄ battery with different charge state is because of different Mn dissolution and polarization of electrode.Mn⁴⁺ may be deoxidized to Mn³⁺ first,and then reacts with H⁺ to create Mn²⁺ with charged increased.The cycling performance is improved because of the the film covered on the cathode,strengthened spinel structure and the improved SEI on the anode.The capacity recovery of LiMn₂O₄ battery with half charged is increased from 96.3 to 98%after storage with LiF added in the cathode. The results show that the LiF restrain the dissolution of Mn and the polarization of cathode after storage.The LiMn₂O₄ battery（347080-16Ah） is tested by heat concussion, puncture,short circuit and overcharge.The LiMn₂O₄ battery shows good safety performance and doesn’t explode.But the battery blast after 3C/10V overcharge.The maximal temperature of battery surface arrives at 290℃after blast.The carbon,MnO,and Li₂CO₃ are observed in the exploded powders.Cracks in the cathode electrode particles are detected with the voltage increased to 5.0V.Cracks may be the reason of voltage and temperature increasing rapidly and blast.The battery is fabricated with Al₂O₃ coated LiMn₂O₄ and doesn’t explode after 3C/10V overcharge.Three LiFePO₄ samples are compared for battery fabrication.Effect of carbon nanotube on the electrochemical performance of C-LiFePO₄/graphite battery is studied.The capacity ratio of 0.1C/1C is increased from 92.1 to 96.3%with CNT added,but the capacities discharge at 0.1C are 124mAh/g.Cyclic voltammograms and AC impedance results show that charge transfer resistance is decreased from 173.1 to 36.88Ωwith CNT added,and the polarization of electrode is decreased.And the capacity retention ratio is increased from 93.7 to 96.6%after 200 cycles.The first discharge capacity of LiFePO₄ battery with LA133 and PVDF-binder is 120 and 124 mAh/g discharged at 1/3C, respectively.The capacity retention ratios are 96.3 and 93.2%.347080 size LiFePO₄ power battery is fabricated with two LiFePO₄ sample mixed according to their characteristic.The capacity ratio of 1C/10C is 95.9%, and the capacity retention ratio is 96.9%after 40 cycles with 3C charged and 10 discharged.The battery doesn’t explode under heat concussion, puncture,short circuit and overcharge.更多还原