【作者】 张微；

【导师】 邓伯华；

【作者基本信息】 武汉理工大学 ， 应用化学， 2009， 硕士

【摘要】 由于Co价格昂贵,且有一定毒性,人们一直试图寻找目前广泛商品化的锂离子电池正极材料LiCoO₂的替代材料。其中LiNi_xCo_1-2xMn_xO₂系列材料相对于LiCoO₂材料成本更低,且有望得到更好的性能,早已成为国内外的研究热点。本文采用碳酸盐共沉淀法成功合成了球形LiNi_1/3Co_1/3Mn_1/3O₂正极材料,同时采用TG-DTA、ICP、XRD、SEM、模拟电池测试等多种测试手段对该体系的制备与结构、形貌、性能做了系统的研究。综合考察了预处理方式和高温处理方式对材料的影响,优化了合成工艺。实验表明:控制溶液pH值在7.4-7.6,沉淀剂与金属盐溶液浓度比为1.2～1.5,反应温度为50℃得到球形前体,氧化、掺Li后850℃下煅烧15h得到的材料有很好的电化学性能。2.5-4.5V,0.05C放电时,材料比容量可达191.5mAh/g;2C放电仍有169.2mAh/g;0.1C循环30圈,保持率为97.2%。对LiNi_1/3Co_1/3Mn_1/3O₂材料掺Li改性发现适量增加Li含量能显著提高材料循环性能,Li_1.1Ni_1/3Co_1/3Mn_1/3O₂材料综合性能最佳。在LiNi_1/3Co_1/3Mn_1/3O₂材料的基础上,进一步降低Co含量,得到LiNi_0.4Co_0.2Mn_0.4O₂和LiNi_0.45Co_0.1Mn_0.45O₂材料,降低了成本,循环性能也有所提高。LiNi_0.45Co_0.1Mn_0.45O₂材料循环性能优异,但比容量不高,倍率性能差。LiNi_0.4Co_0.2Mn_0.4O₂材料具有优异的电性能:比容量可达193.3 mAh/g;2C放电比容量为170.6 mAh/g;0.1C循环30圈容量保持率为93.0%。作为比较,用氢氧根法合成出了LiNi_1/3Co_1/3Mn_1/3O₂材料,经优化比较得出该体系在前体制备时控制pH在10.5,高温处理时煅烧温度选择950℃时材料性能最好。本实验未使用氨水等络合剂,合成出的材料为块状粒子。用两种共沉淀法合成出的LiNi_1/3Co_1/3Mn_1/3O₂材料均有较高的比容量和较好的循环性能,但用碳酸盐法合成出的材料倍率性能更好。更多还原

【Abstract】 People have been trying to find the alternate materials for commercial LiCoO₂ because of the cost and toxicity of Co.The materials of LiNi_xCO_1-2xMn_xO₂ series have been the hot point at home and abroad for a long time as it’s cheaper than LiCoO₂ but may acquire better performance.A series of spherical cathode material—LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by carbonate co-precipitation method and then examined by TG-DTA、ICP、XRD、SEM etc.in this thesis.The synthetic process was optimized after a comprehensive inspection of the effect of the pretreatment and thermal treatment.The experiment results showed that the best synthetic process was as follows:pH=7.4-7.6,the concentration ratio of the precipitator to the metal salt solution was 1.5,reaction temperature was 50℃,the calcination temperature and holding time were 850℃and 15h,respectively.For the best sample of LiNi_1/3CO_1/3Mn_1/3O₂,the discharge capacity could reach 191.5mAh/g in the voltage range of 2.5-4.5V and at 0.05C;the capacity of 169.2mAh/g could be retained at 2C;cycled at 0.1C for 30 cycles,the retention rate could reach 97.2%.The results showed that increasing the Li content could improve the cycle performance significantly.Li_1.1Ni_1/3Co_1/3Mn_1/3O₂ showed the best performance.On the base of LiNi_1/3Co_1/3Mn_1/3O₂ material,the Co content was reduced to synthesize LiNi_0.4Co_0.2Mn_0.4O₂ and LiNi_0.45Co_0.1Mn_0.45O₂ which had lower cost but better cycle performance.The LiNi_0.45Co_0.1Mn_0.45O₂ had excellent cycle performance but low capacity,poor high-rate capability.The electrochemistry performance of LiNi_0.4Co_0.2Mn_0.4O₂ was very well:the discharge capacity could reach 193.3mAh/g; the capacity was 170.6mAh/g when discharged at 2C;cycled at 0.1C for 30 cycles, the retention rate was 93.0%.For comparison,LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by hydroxyl co-precipitation method.The materials had the best performance when controlled pH=10.5 and the calcination temperature at 950℃.The surface topography of the materials were lumpish as NH₃·H₂O and other complexing agents hadn’t been used.The capacity and cycle performance of LiNi_1/3Co_1/3Mn_1/3O₂ synthesized by the two different co-precipitation methods were both very well,but the high-rate dischargeability of the materials prepared by carbonate co-precipitation method were much better.更多还原