锂离子蓄电池正极材料LiMn_2O_4高温容量衰减解析

收稿日期:2001204218

作者简介:陈彦彬(1969—

),男,河南省人,高级工程师,博士,主要研究方向为化学电源与电极材料、电镀及电解质溶液化学。

Biography :CHEN Yan 2bin (1969—

),male ,senior engineer ,Ph D.锂离子蓄电池正极材料LiMn 2O 4高温容量衰减解析

陈彦彬,　刘庆国

(北京科技大学固体电解质研究室,北京100083)

摘要:有关锂离子蓄电池正极材料LiMn 2O 4的衰减机理的认识目前尚存在争议。通过对LiMn 2O 4高温循环数据的解析,比较了两个电位平台容量衰减的相对速度。结果表明,放电过程中高电位平台容量的衰减速度快于低电位平台,而充电过程中低电位平台的衰减速度更快。循环过程中极化增大所导致的电位平台间的容量转移决定了两平台容量的相对衰减速度,极化增大与钝化膜的增厚、电解质的积累性氧化所引起的电导率下降有关。另外电解质的氧化也呈加速趋势,加快了高电位平台放电容量的衰减速度。几种掺杂材料在循环过程中容量衰减的相对速度与极化增加的相对快慢完全吻合,进一步印证了容量衰减与材料溶解、结构变化、钝化膜增厚之间的对应关系。关键词:锂离子蓄电池;LiMn 2O 4尖晶石;容量;电解质;自放电

中图分类号:TM 912.9 文献标识码:A 文章编号:10022087X (2002)0120005204

Analysis of the capacity fading of LiMn 2O 4a s cathode material for

Li 2ion batterie s at high temperature

CHEN Yan 2bin ,L IU Qing 2guo

(L aboratory of Soli d Elect rolyte ,Beiji ng U niversity of Science and Technology ,Beiji ng 100083,Chi na )

Abstract :The dispute of capacity 2fading mechanism for spinel LiMn 2O 4as the cathode material used in Li 2ion battery is still remaining.The fading rates at each voltage plateau were compared by analyzing the cycling data of the spinel LiMn 2O 4.The results show that the capacity 2fading rate at the upper voltage plateau is more rapid 2ly than that at the lower voltage plateau during discharge.However ,the fading rate at the upper voltage plateau is slower than that at the lower voltage plateau in charging process.The relative fading rate is lied on the capaci 2ty shift between the two voltage plateaus ,which is caused by the polarization increasing during cycling process.The polarization increasing is related to the passivated 2film thickening and the conductivity decreasing due to the accumulative oxidation of electrolyte.In addition ,the fading rate of discharge capacity at the upper voltage plateau is also increased by the accelerating trend of electrolyte oxidation.The related capacity 2fading rate of se 2veral doped materials during cycling process is in accordance with the related rate of polarization increasing.Thus ,the corresponding relations among the capacity fading ,the material dissolving ,the structure modifying and the passivated 2film thickening are confirmed.

K ey w ords :Li 2ion batteries ;spinel LiMn 2O 4;capacity ;electrolyte ;self 2discharge

目前以LiCoO 2为正极材料的锂离子蓄电池以其比能量高、循环寿命长的优点在便携式电器中得到成功应用,但由于钴资源有限、价格昂贵,正极材料的成本占电池总成本的1/3以上,因此其大规模应用受到限制。而LiMn 2O 4以其电化学性能良好、价格低、资源丰富等优势而具有很好的应用前景。然而,该材料也面临着期待解决的技术难题,那就是高温性能问

题。

LiMn 2O 4的高温容量衰减现象已受到材料工作者和锂电池界的普遍关注,有关衰减机理方面的研究也有不少文献报道,其主要原因包括[1～10]:锰的溶解、结构的变化、活性粉体的断裂、钝化膜的形成、Jahn 2Teller 效应、电解液的氧化等。但各研究者的结果及观点尚不一致。首先就两个电位平台衰减速度的相对快慢存在分歧。Xia 等人[6]报道,无论在高温还是室

温下,高电位平台(4.15V )的容量衰减在材料的整个衰减中起

主导作用,原因是循环过程中该区不稳定的两相结构逐渐变成稳定的单相结构;而Robertson [7]和Huang [8]等人则报道,容量

衰减主要发生在低电位平台(4.05V ),其原因是三价锰的含量较高,溶解速度也相应较快。其次,Thackery [11]及Liu [12]等报