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, 尖晶石LiMn2O4相对于广泛用于小型电器方面的LiCoO2有着明显的优势, 但是尖晶石LiMn2O4较差的循环性能以及高温性能成为制约其商业化发展的最大障碍.
尖晶石LiMn2O4的容量衰退机理大致可以分为两个方面: 1) 在充电/放电过程中, 随着Li的脱出和嵌入, Mn3+产生Jahn-Teller效应影响[3]; 2) Mn在电解液中的溶解(尤其是高温溶解)造成电池容量损失更为严重[4]. 也有一种观点认为在锂的脱嵌过程中存在单相-两相-单相的变化过程(0.4
杂离子为锂离子, 合成方法采用二次固相反应焙烧法. 锂掺杂可以在很宽范围内形成固溶体, 以保证产品良好的均匀性与单一相结构, 同时可以抑制Jahn-Teller效应[10], 改善循环性能. 1 实验 1.1 富锂尖晶石Li1+xMn2-xO4的合成 将Li2CO3和MnO2粉末按照组成Li1+xMn2-x-O4(x=0, 0.02, 0.04, 0.06, 0.08, 0.10)的化学计...+xMn2-xO4循环性能的影响 Fig.7 Effect of doped amount x on cycleability of Li1+xMn2-xO4 从容量衰减率与锰平均化合价的关系(图7(b))可以看出, 容量衰减基本上随着锰平均化合价的增大而减小. 由于Mn3+(d4)是一个有较强Jahn-Teller效应的离子, 在一定条件下尖晶石结构中的Mn3+-O6八面体发生变形, 而Mn3+配位体的......
. They reported spin state transition at 220 K for PrCoO3. The spin state is expected to show considerable lattice distortion because of the strong Jahn-Teller nature of t2g5eg1 configuration. Raman... mode is observed. This increase in peak position of Raman mode may be due to spin state transition caused by the Jahn-Teller distortions. To further analyze Raman spectra, all the modes of Raman spectra......
performance 锂离子电池具有高比容量,高比能量等优点,是便携式设备以及电动汽车等的理想电源.而尖晶石LiMn2O4正极材料以其无毒,廉价,锰储量大等优点,引起人们越来越多的关注[1-4].尖晶石LiMn2O4正极材料的研究始于20世纪80年代,该材料为立方晶系,空间群为Fd3m,由于LiMn2O4在循环过程中产生Jahn-Teller效应,材料由立方晶系向四方晶系转变,这种转变将造成约6%的体积变化,从...结合能为1573 kJ/mol,比Mn-O键强,Al3+的掺入能提高锰酸锂材料的热稳定性；而且Al3+离子半径为0.535 ,比Mn3+(0.65 )稍小,Al3+的成功取代Mn3+,会使尖晶石的晶格发生收缩,在一定程度上抑制Jahn-Teller效应[20, 23],因此,少量掺入铝可以使尖晶石LiAlxMn2-xO4的循环性能得到一定改善. 图3 不同铝掺杂量的锰酸锂的SEM像......
and tetragonal symmetry, causing a Jahn-Teller effect in the lattice, and leading to a serious capacity fading with cycling[2]. Therefore, most of the studies on spinel LiMn2O4 were concerning... stoichiometry of the samples based on charge balance. Obviously, the average Mn valences of the Li-rich samples are higher than 3.5, which is the critical of Jahn-Teller effect. The increase......
in the 4 V region[12-14]. From a structural point of view, when the oxidation state of Mn falls below 3.5, the Jahn-Teller distortion occurs and consequently deteriorates the rechargeability of spinel... of the Jahn-Teller effect of Mn3+ in Li2Mn2O4 for 450 ℃ sample, a slight distortion from cubic to tetragonal unit cell is also observed from the cell parameters (a=8.146 ?, c=8.480 ?, c/a=1.04) calculated from......
has Jahn-Teller effect, which can cause the capacity to decay very fast during charge and discharge [9], and the dissolution of Mn can cause further deterioration of cycling properties at high... of the lithium ion and reduce diffusion rate of the lithium ion, which increases the density of the lithium ion on the particle surface of LiMn2O4, aggravates Jahn-Teller effect and accelerates capacity fading......
可以看出,LiMn2O4的大电流放电性能不如掺钴后的性能,而且随着钴含量的提高,高倍率放电能力有增强的趋势. 图5所示为LiCoxMn2-xO4 的容量与循环次数的关系.可以看出,纯LiMn2O4经50次循环后容量损失率很高,达到31%；Co掺杂后电池的容量保持率提高.造成纯尖晶石LiMn2O4容量衰减快的主要原因之一是在充放电过程中存在Jahn-Teller效应,其来自于LiMn2O4中的Mn3+周围正八面体晶体场发生的畸 变[11].掺钴后提高了电池的循环性能的主要原因是Co3+离子取代了其中部分的Mn3+,降低了Jahn-Teller效应造成的影响,使立方晶体结构在循环过程得以保持[8].已有研究结果表明,掺钴后还可以减少锰的溶解[12]. 图5 LiCoxMn2-xO4的循环寿命曲线 Fig.5 Cycling......
with the accuracy of 0.025 eV/nm. The Monkhorst-Pack k-points 5×5×6 were assigned to define the accuracy of the sampling[13]. No observed Jahn-Teller effect is found in the doped λ-MnO2 as Mn is expected to appear with formal valence of +4. Consequently, the Jahn-Teller effect is not taken into account in this case[13-14]. 2.2 Geometric structure and calculation models The spinel λ-MnO2 belongs......
instability caused by Jahn-Teller effect and dissolution of manganese into electrolyte during the charge-discharge cycle [9,10]. To date, a variety of doping and coating techniques have been explored to control...+ shrinks the lattice and improves the stability of the structure [20,21]. Meanwhile, the decrease of Mn3+ is beneficial to the suppression of Jahn-Teller distortion and improvement of the cycleability......
