【作者】 余鼎；

【导师】 赖琼钰；

【作者基本信息】 四川大学 ， 无机化学， 2003， 硕士

【摘要】 LiMn₂O₄具有尖晶石结构，理论容量达148mAh.g^-1，其制备工艺简单，价格低廉，是一种很有前景的锂离子电池正极材料；目前阻碍其商业化的主要困难是循环性能特别是高于55℃的循环性能差，容量发生较大衰减。 提出并采用了碳酸盐湿法合成尖晶石LiMn₂O₄，具有操作简便，成本低廉，合成时间较短等特点。所得的材料结晶性能较好，组装的电池首次放电容量可以达到111mAh.g^-1，电化学性能较优。 LiMn₂O₄中的Mn为Mn[Ⅲ]和Mn[Ⅳ]的混合价态，真正在电化学反应过程中起作用的是Mn[Ⅲ]离子，因此有必要测定Mn[Ⅲ]离子在尖晶石LiMn₂O₄中的浓度。尖晶石LiMn₂O₄可完全溶解于4mol·L^-1 H₄P₂O₇+4mol／L H₂SO₄的混合酸中，通过双波长光度法可同时准确测定其中的Mn[Ⅲ]和Mn[Ⅳ]离子的浓度。此法用于LiMn₂O₄中锰测定尚未见报导。 尖晶石LiMn₂O₄容量衰减可能的机理包括尖晶石结构的LiMn₂O₄发生Jahn-Teller畸变效应，造成在[MnO₆]结构单元c轴方向的2个Mn-O键被拉长了，因而键的强度也相应减弱，使整个结构单元的稳定性减弱；以及LiMn₂O₄电极在电解液中溶解等。选用了Co、Ni、Cr等金属元素进行掺杂以抑制LiMn₂O₄尖晶石的Jahn-Teller畸变，结果表明掺镍样品LiMn_1.95Ni_0.05O₄有最佳的充放电容量及循环性能，第3次放电容量达到了120mAh.g^-1。首次采用了Li₄SiO₄、Li₃PO₄并采用了LiCoO₂对LiMn₂O₄尖晶石材料进行了包覆，结果表明P包覆LiMn₂O₄电极与Co包覆LiMn₂O₄电极的循环性能及充放电容量均较优。更多还原

【Abstract】 LiMrn2O4 spinel, which theoretic cycle capacity is 148 mAh.g-1, is considered as the most promising cathode materials for Lithium Ion battery for its highlights of low cost, easily prepared and environment free. However, the serious capacity fading upon cycling especially at surroundings over 55# hampered its immediately commercial application.The stoichiometric LiMn2O4 spinel was prepared by carbonate wet method using Li2CO3, Mn(CH3COO)2-4H20 and CO2 as raw materials. The products were measured by TG/DTA, XRD, IR. The results Showed that the sample calcined at 800 # for 10h was well crystallized monophase product, and its initial cycling capacity can reach 111 mAh.g-1.The value of Mn in LiMn2O4 spinel is mixed value of Mn[III] and Mn[IV], it is Mn[III] that reacts in electrochemical process. LiMn204 spinel can fully resolve in 4 mol-L-1 H4P2O7+4mol/L H2S04 mixture, based on the Lambert-Beer law, we put forward a new method to determine the contents of Mn[III] and Mn[IV] in LiMn2O4 spinel simultaneously by spectrophotometric analysis with pyrophosphoric acid.There are two possible theory of capacity fading of LiMn204 spinel. The two Mn-O bonds of [MnO6] unit along the c-axis in LiMn204 spinel are prolonged because of Jahn-Teller distortion, resulting in the weaken of Mn-O bonds and structural break of LiMn2O4 spinel. The doping of LiMn2O4 spinel with elements of Co, Ni,Cr et al can restrain the Jahn-Teller distortion and improve the stability of material. In our experiment, the Ni-doped sample LiMn1.95Ni0.05O4 exhibited theexcellent capacity of 120mAh.g-1 in the third cycle. The other major reason of capacity fading of LiMn2O4 spinel is the Mn dissolution into electrolyte. By surface coated with Li4SiO4, Li2PO4 and LiCoO2, the Mn dissolution of LiMn2O4 spinel can be effectively suppressed, exhibited improved capability.更多还原