锂离子电池正极材料尖晶石锰酸锂的制备与改性研究

【作者】 马尚德；

【导师】 秦毅红； 张云河；

【作者基本信息】 中南大学 ， 电化学工程， 2007， 硕士

【摘要】 尖晶石型LiMn₂O₄具有工作电压高、安全性能好、生产成本低、对环境友好等特点，是21世纪最具有发展前景的锂离子电池正极材料之一。但尖晶石型LiMn₂O₄的理论比容量较低，电化学循环性能较差阻碍着其规模化应用。为寻找提高尖晶石型LiMn₂O₄的体积比能量和抑制容量衰减的有效方法，本文进行了高密度锰氧化物的制备、尖晶石型LiMn₂O₄的制备、掺杂对尖晶石型LiMn₂O₄的影响和Li⁺离子脱／嵌过程探索等研究工作。以电解锰粉为原料，采取低温焙烧-机械活化-高温焙烧的工艺制备高密度锰氧化物。考查了焙烧温度、焙烧时间和升温速率对物化性能和微观形貌的影响。结果表明：低温过程是锰的氧化过程，高温过程是锰氧化物的晶化过程。优化的热处理制度为：低温焙烧温度为700℃，保温7h，高温焙烧温度为1050℃，保温时间为7h。高密度锰氧化物为Mn₃O₄和Mn₂O₃的混合物，D₅₀≈4.0μm时粉体的振实密度为2.70g·cm^-3。以高密度锰氧化物为前驱体，以Li₂CO₃为锂源，采用机械活化和固相烧结相结合的二段烧结法制备了尖晶石LiMn₂O₄。研究了烧结温度、烧结时间和配锂量对尖晶石结构、微观形貌和电化学性能的影响，结果表明：烧结温度对尖晶石结构、微观形貌和电化学性能有显著影响。烧结时间对尖晶石结构、微观形貌和电化学性能影响较小。配锂量对微观形貌影响小，对电化学性能影响大。缺锂型锂锰氧化物电化学循环性能差，富锂型锂锰氧化物电化学循环性能好，尖晶石锰酸锂的首次放电比容量的最大值出现在配锂量x（Li_xMn₂O₄）＝1.0附近，其中Li_1.015Mn₂O₄的首次放电比容量最高，为111.25mAh·g^-1（0.1C，4.2V，vs．C、），循环30周期容量保持率为95.03％。分别以CO₃O₄、NiO、TiO₂和ZrO₂为掺杂体，制备了掺杂锂锰氧化物Li_1.015Mn_2-xM_xO₄（M＝Co、Ni、Ti、Zr）。考查了掺杂离子、掺杂量对锂锰氧化物结构、微观形貌和电化学性能的影响，结果表明：掺杂改善了锂锰氧化物体系中阳离子混排程度，而未明显改变尖晶石结构。Ni掺杂改善了颗粒微观形貌，Co、Zr掺杂细化了微观颗粒。Ti掺杂提高了首次放电比容量。随着掺杂量的增大，首次放电比容量降低，电化学循环稳定性增强，掺杂有效抑制了电化学容量衰减。采用交流阻抗技术对尖晶石型LiMn₂O₄脱／嵌锂过程进行了探索，结果表明：掺杂提高了交换电流密度，稳定了尖晶石结构，也对锂离子扩散系数有影响。更多还原

【Abstract】 Spinel LiMn₂O₄ is one of the most promising cathode materials of 21st century because of high working voltage, excellent security, low manufacture cost, and environment friendly. But large-scale application is restricted because of low theoretical specific capacity and poor electrochemical performance. This dissertation emphasized on searching for resultful methods to improve bulk specific energy density and to restrain capacity fading. And the article mainly included preparation of high density manganese oxide, preparation of spinel LiMn₂O₄, doping effects on spinel LiMn₂O₄ and discussion about Li deintercalation/intercalation process.High tap density manganese oxide was prepared through low temperature sintering-mechanical activation-high temperature sintering route with electrolytic manganese powder as raw material. The effects of sintering temperature, dwelling time and calefactive velocity on physical-chemistry property of manganese oxide were studied, and showed that the low temperature sintering process is the oxidation of Mn, and the high temperature sintering process actually the crystallization process of manganese oxide prepared in low temperature sintering. And heat treatment system is as follows: low sintering temperature is 700℃and dwelling time is 7h, high temperature sintering 1050℃, respectively, and dwelling time is 7h. X-ray-diffraction spectra indicated that the manganese oxides were the mixture of Mn₃O₄ and Mn₂O₃, and its tap density is 2.70g·cm^-3(D₅₀≈4.0μm).LiMn₂O₄ was prepared with high tap density manganese oxides we as precursor and Li₂CO₃ as Li sources through the mechanical activation-high temperature solid state route. Effect of sintering temperature, sintering time and x（Li_xMn₂O₄） on spinel structure, morphology and electrochemical property, and the result showed that Sintering temperature affected Spinel structure, morphology and electrochemical property evidently. Sintering time affected spinel structure, morphology and electrochemical property slightly. Electrochemical property was affected by X（Li_xMn₂O₄） remarkably, Li-rich spinel LiMn₂O₄ exhibited good capacity retention, and Li-poor spinel LiMn₂O₄ showed poor capacity retention. And the initial discharge specific capacity of Li_1.015Mn₂O₄ is 111.25mAh·g^-1（0.1C, 4.2V, vs.C） and is the maximum among the different Li/Mn molar ratio, and has a high capacity retention of 95.03% after 30 cycles.Lithium manganese oxides of Li_1.015Mn_2-xM_xO₄（M=Co、Ni、Ti、Zr） were prepared with Co₃O₄、NiO、TiO₂、ZrO₂ as dopant. Effects on structure, morphology and electrochemical property were investigated, and the results indicated that Li_1.015Mn_2-xM_xO₄（M=Co、Ni、Ti、Zr; x≤0.1） exhibited a cubic pure spinel structure, except Li_1.015Mn_1.9Zr_0.1O₄. Cations order was optimized. With the increasing of dopant content, initial specific capacity deceased and electrochemical performance was enhanced. Initial specific capacity deceased unnotably when x≤0.01 but notably when x＞0.1. Particle sizes became smaller and tap density decreased in a way with the import of substituted ionic.Li deintercalation/intercalation process from spinel LiMn₂O₄ was studied by AC impedance measurement. It was found that the exchange current density and structure stability were enhanced through doping, and diffusion coefficient of Li⁺ was also affected by doping.更多还原