【作者】 王茹英；

【导师】 杨文胜；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2012， 博士

【摘要】 锂离子电池因为其能量密度大、使用寿命长和无记忆效应等特点，是目前应用最广泛的二次电池。正极和负极材料是决定锂离子电池性能最关键的电极材料，目前商品化的正极材料和负极材料分别是LiCoO₂和中间相碳微球（MCMB），存在成本高、倍率性能差、安全性能低下等问题，严重阻碍了锂离子电池在动力电池和储能方面的进一步发展，因此开发成本低、寿命长、倍率性能好和安全性能高的锂离子电池正、负极材料，来满足3G网络、电动汽车以及风能和太阳能储能的要求是十分重要的。为了提高锂离子电池的综合性能，本论文采用碳改性钛酸锂负极材料提高其常温和高温循环寿命以及倍率性能，采用价格低廉的钴镍锰三元材料代替钴酸锂，采用表面包覆镍酸锂提高层状正极材料的常温和高温循环寿命及倍率性能等。具体研究内容如下：1、采用高温固相合成方法，制备了Li₄Ti₅O₁₂负极材料，合成产物具有立方尖晶石结构。系统研究了锂钛金属元素比例、二次煅烧温度对材料的结构和电化学性能的影响。当Li/Ti物质的量比为1.05、二次煅烧温度为800oC时合成的材料具有最佳的电化学性能。2、以蔗糖和/或KS-6作为碳源，采用高温固相法制备了Li₄Ti₅O₁₂/C复合材料。系统研究了不同碳源对Li₄Ti₅O₁₂的结构、形貌、循环寿命和倍率性能的影响。蔗糖分解碳包覆在Li₄Ti₅O₁₂表面，KS-6分布在Li₄Ti₅O₁₂颗粒之间，碳改性并没有改变Li₄Ti₅O₁₂主体的尖晶石结构，不同的碳源对Li₄Ti₅O₁₂/C复合材料的综合性能具有不同的影响，与只添加蔗糖或KS-6的Li₄Ti₅O₁₂/C复合材料相比较，二者协同作用的Li₄Ti₅O₁₂/C复合材料（LTO-1）具有最佳的综合性能。Li₄Ti₅O₁₂/C复合材料（LTO-1）0.2C首次充放电比容量分别为170.5和152.5mAh·g^-1，1C比容量为149.9mAh·g^-1，经过1000周循环后其放电比容量为145.3mAh·g^-1，1000周的容量保持率高达96.9%，远高于纯Li₄Ti₅O₁₂的73.8%，而且该材料和锰酸锂组装的全电池可以通过3C-20V过充、短路和穿钉等安全性测试。3、以蔗糖和VGCF作为碳源，采用高温固相法制备了Li₄Ti₅O₁₂/C复合材料。蔗糖分解碳包覆在Li₄Ti₅O₁₂表面，VGCF具有较大的长径比和良好的导电性能，能够增加颗粒之间的导电性。初始添加蔗糖1%+0.5%VGCF的Li₄Ti₅O₁₂/C复合材料（LTO-b），在高温55oC下，其1C放电比容量为157.5mAh·g^-1，100周的容量保持率为97.8%，表现出了良好的高温循环稳定性。由该材料和锰酸锂组装的（LTO-b）/LiMn₂O₄全电池，在0.1-3V和1-3V的电压区间循环寿命几乎无差别，而且，该电池在55oC储存150天后的容量恢复率为99.8%，和初始容量几乎一致，表现出良好的耐过放性能和优良的高温存储性能。4、以共沉淀法得到的[Ni_3/8Co_1/8Mn_4/8]CO₃和LiOH·H₂O混合均匀，高温煅烧得到价格低廉的Li_1+x[Ni_3/8Co_1/8Mn_4/8]O₂正极材料，研究比较了Li/[Ni_3/8Co_1/8Mn_4/8]物质的量比对其结构、组成、形貌、和电化学性能的影响。Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂材料具有最佳的电化学性能，常温下，在2.75-4.2V电压区间，其300次循环的容量保持率为95.7%，55oC高温下，在2.75-4.2V和2.75-4.5V电压区间，其比容量为150.3和189.3mAh·g^-1，100次循环后的容量保持率分别为90.6%和88.2%，而且MCMB/Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂电池可以通过3C-5V过充实验和短路实验。和LiCoO₂相比较，Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂材料在2.75-4.5V电压区间具有更高的放电比容量及更好的高温循环稳定性，更佳的倍率性能和耐过充性能，而且价格只有LiCoO₂的一半左右。5、在恒pH值下将钴铝层状双羟基复合金属氧化物（CoAl-LDH）均匀包覆于球状Ni（OH）₂表面，与LiOH·H₂O混合均匀后，经高温煅烧得到钴铝酸锂包覆镍酸锂0.08LiCo_0.75Al_0.25O₂-0.92LiNiO₂正极材料。电化学测试表明，0.08LiCo_0.75Al_0.25O₂-0.92LiNiO₂正极比容量高、具有良好的倍率性能和循环寿命，其0.1C、0.5C和3C的放电比容量分别为211.0、195.6和161.0mAh g^-1，0.5C30次循环后容量保持率为93.2%，明显优于LiNiO₂和钴酸锂包覆镍酸锂0.08LiCoO₂-0.92LiNiO₂正极材料。更多还原

【Abstract】 Lithium-ion batteries are the most widely used secondary batteriescurrently because of their large energy density, long cycle life and nomemory effect and so on. The cathode and anode materials are the mostcritical materials; LiCoO₂and MCMB are the two curretlycommercialized materials. However, the high cost, low rate capacity andpoor safety performance seriously hampered the further development oflithium-ion battery in a large-scale power. It is an urgent need to developlow-cost, long-life, good rate capacity and good safety materials to meetthe demand of3G network, the wind and solar energy storage, electricvehicles and other application. This thesis focused on studyingLi₄Ti₅O₁₂/C composite anode materials, cheap LiNixCoyMn1-x-yO₂cathode material and LiCo_0.75Al_0.25O₂coated LiNiO₂cathode materialinstead of LiCoO₂to improve the cycle life, rate capability and safety ofLi-ion batteries at room temperature and high temperature. Theconclusions have been summarized as following:1. Spinel Li₄Ti₅O₁₂have been synthesized via a solid state reactionwith TiO₂-anatase and Li2CO3as the starting materials. The effects ofLi/Ti molar ratio and the calcinaton temperature on the morphology， structure and electrochemical performance have been investigated. Itwas found that the best Li/Ti molar ratio is1.05and the best secondarycalcining temperature is800oC.2. Li₄Ti₅O₁₂/C composites have been synthesized via a solid statereaction with TiO₂-anatase, Li2CO3and different carbon sources, such asconductive graphite KS-6and sucrose, as the starting materials. It wasfound that the carbon layer from sucrose was homogeneously coated onthe Li₄Ti₅O₁₂surface and the KS-6was embedded among the Li₄Ti₅O₁₂particles as a conductive bridge without affecting the major spinelstructure of Li₄Ti₅O₁₂. Moreover, it was demonstrated that the sucroseand KS-6played different roles in improving the electrochemicalproperties of Li₄Ti₅O₁₂/C composite. Compared with samples preparedby solely KS-6or sucrose as the carbon source, the Li₄Ti₅O₁₂/Ccomposite （LTO-1） with KS-6and sucrose as carbon sources togetherrevealed the optimal electrochemical performance. It showed a highinitial specific capacity of152.5mAh·g^-1at0.2C and an excellentcycling performance with96.8%capacity retention after1000cycles at25oC at1C. Furthermore, the （LTO-1）/LiMn2O4full batterydemonstrated a good cycling performance at55oC and could pass the5C-20V overcharge test, external short-circuit and nail-puncture test.3. Li₄Ti₅O₁₂/C composites have been synthesized via a solid statereaction with TiO₂-anatase, Li2CO3, sucrose and VGCF as the starting material. VGCF has a larger length-diameter ratio than KS-6and goodconductive properties. The Li₄Ti₅O₁₂/C composite （LTO-b） with1%sucrose and0.5%VGCF showed good cycling performance at25and55oC. It showed an initial capacity of157.5mAh·g^-1at1C and anexcellent cycling performance with97.8%capacity retention after100cycles at55oC. Moreover, the （LTO-b）/LiMn2O4full batteries havesimilar cycling performance at0.1-3V and1-3V, which shows goodanti-redischarge properties. In addition, the capacity recovery ratio of（LTO-b）/LiMn2O4full batteries are99.8%（to the initial capacity） after150days at55oC, which shows excellent storage performance.4. Li_1+x[Ni_3/8Co_1/8Mn_4/8]O₂cathode materials have been prepared bycalcination of LiOH·H2O and [Ni_3/8Co_1/8Mn_4/8]CO3under O₂atmosphere.The structure and morphology have been studied, and theelectrochemical behavior and safe characteristic have been tested by14500R-type MCMB/Li_1+x[Ni_3/8Co_1/8Mn_4/8]O₂batteries. The capacityretention ratio of Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂is95.7%after300cycles in2.75-4.2V at25oC. At55oC, in2.75-4.2V and2.75-4.5V, thedischarge specific capacities are150.3mAh·g^-1and189.3mAh·g^-1, withthe capacity retention ratios are90.6%and88.2%after100cycles,respectively. The MCMB/Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂batteries can pass the3C-5V overcharge test and short-circus experiment. Compared withLiCoO₂，the Li_1.11[Ni_3/8Co_1/8Mn_4/8]O₂material has higher capacity and better cycling performance in2.75-4.5V at55oC, with better rate andanti-recharged property, and with an about50%price of LiCoO2.5. CoAl-LDH or Co（OH）₂coated spherical Ni（OH）₂precursorswere obtained via a coprecipitation method at a constant pH. After theprecursors and LiOH H2O were mixed, the mixtures were annealed athigh temperature in O2atmosphere, and then the0.08LiCo_0.75Al_0.25O₂-0.92LiNiO₂,0.08LiCoO2-0.92LiNiO2and LiNiO2cathode materials were synthesized. Effects of the coating layer werealso studied. The results showed that the0.08LiCo_0.75Al_0.25O₂-0.92LiNiO2material owned the best rate andcycle-life. The0.1C,0.5C and3C discharging capacities were211.0mAh g^-1,195.6mAh·g^-1and161.0mAh g^-1respectively, and thecapacity retention ratio after30cycles at0.5C was93.2%. Theseresults were much better than both pure LiNiO2and0.08LiCoO2-0.92LiNiO2.更多还原