【作者】 赵萱；

【导师】 刘韩星；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2010， 博士

【摘要】 锂离子电池作为清洁高效的能源已经广泛应用于照相机、手机、笔记本电脑等便携式移动设备,并逐渐应用于电动汽车。一直以来,昂贵的价格制约着锂离子电池大规模车用化的发展。降低锂离子电池成本的关键是研究开发价格低廉的新材料以及采用简单易行的低成本制备方法。新材料的开发到最终应用往往需要数十年的时间,而制备工艺的优化通常能应用于多种材料的合成。熔盐合成法是一种工艺简单的制备多元复合氧化物的方法,目前已经应用于个别电池材料的研究,但研究熔盐种类有限,缺乏系统性。本论文选择了层状结构材料Li(Ni0.5Mn0.5)O2、Li(Ni0.2Mn0.2Co0.6)O2和尖晶石结构LiMn2O4作为研究对象,系统研究了熔盐种类以及反应条件在熔盐法合成中对这些材料结构、形貌和电化学性能的影响。探索了熔盐法在合成层状和尖晶石状结构材料时,熔盐的选择规律。在对Li(Ni0.5M0.5)O2材料的研究中,发现LiCl熔盐易造成最终产物的缺锂。LiNO3和Li2CO3作为熔盐均能合成出Li(Ni0.5Mn0.5)O2层状材料。LiNO3作为熔盐制备的材料循环稳定性好,其放电比容量大于Li2CO3熔盐制备的材料,但Li2CO3熔盐制备的材料放电比容量随循环有增大的趋势。将LiNO3和Li2CO3按不同比例组合所得熔盐对制备的Li(Ni0.5Mn0.5)O2形貌影响很大。当用0.9LiNO3-0.05Li2CO3作熔盐时,Li(Ni0.5Mn0.5)O2颗粒尺寸均匀,表面光滑,在恒流模式下充放电,放电比容量为150 mAh g-1,恒流恒压模式下为200 mAh g-1。0.9LiNO3-0.05Li2CO3和0.38LiOH-0.62LiNO3均能作为熔盐制备Li(Ni0.2Mn0.2Co0.6)O2材料,但因为熔盐熔点不同,材料颗粒形貌不同,且放电比容量均不高。高温下的二次热处理能有效提高材料的放电比容量,以0.38LiOH-0.62LiNO3为熔盐,经二次处理过的Li(Ni0.2Mn0.2Co0.6)O2材料放电比容量达150 mAh g-1此外,氯化物和硫酸盐实验证明不适合制备层状Li(Ni0.2Mn0.2Co0.6)O2材料。氯化物在制备尖晶石结构材料时优势明显。0.5NaCl-0.5KCl和0.6LiCl-0.4KCl都能制备出LiMn2O4材料。以0.5NaCl-0.5KCl作为熔盐制备的LiMn2O4材料具有一次纳米颗粒团聚成二次微米颗粒的形貌。具有该形貌的LiMn2O4,能达到124 mAh g-1的放电比容量,且循环性能优异。最后,在上述材料的研究基础上,本论文总结了熔盐法合成锂离子电池正极材料的熔盐选择规律以及制备工艺影响。用熔盐法制备的锂离子电池材料均具有较好的循环性能。除氯化物和硫酸盐外,其它含锂单组分盐或者复合熔盐均能用于制备层状结构材料。熔盐的熔点对合成材料的形貌影响很大,进而影响材料的电化学性能。氯化物可优先选为制备尖晶石结构材料所用熔盐。熔盐法合成在高温(800℃左右)加热5-6小时就能制备出结构、形貌和电化学性能良好的电池材料。更多还原

【Abstract】 Lithium-ion battery as a clean and efficient energy storage device has been widely used in cameras, mobile phones, notebook computers and other portable mobile devices. Lithium-ion battery also gradually finds application in electric vehicle, but its high price considerably restricts its viability as vehicule power source. The key methods to reduce the cost of lithium-ion battery rely on the new low cost materials and low cost preparation processes. On one hand, development of new materials often requires decades to reach commercial product and research on a selected material has often prove to be very specific. On the other hand, optimization of preparation technique has more impact as the same preparation route can be readily applied to synthesize a variety of materials.Molten salt synthesis method is a simple process for preparing multiple complex oxides. Despite those key advantages, molten salt technique has not been studied in a complete and systematic way. This thesis uses molten salt method to synthesize layered structure material Li(Ni0.5Mn0.5)O2, Li (Ni0.2Mn0.2Co0.6)O2, and spinel structure LiMn2O4. The effects of the molten salts and reaction conditions on the structure, morphology, and electrochemical properties have been systematically investigated. One of the aims of the present thesis is to outline general rules when choosing molten salts in synthesis of layered and spinel structure mateirals.Li(Ni0.5Mn0.5)O2 materials can not be synthesized from LiCl molten salt, since this synthesis route could easily lead to lack of lithium in the final product. Alternative salts to synthesize Li(Ni0.5Mn0.5)O2 layered materials include LiNO3 and Li2CO3. The material made by LiN03 molten salt shows good cycling stability and its discharge capacity is greater than material made by Li2CO3 molten salt. However, the material prepared with Li2CO3 molten salt shows an increasing discharge capacity with cycling. To tentatively use advantages of both materials, combination of LiNO3 and Li2CO3 in different proportions also can be used as molten salt, which have different effect on the morphology of Li(Ni0.5Mn0.5)O2. When 0.9LiNO3-0.05Li2CO3 is used as molten salt, the Li(Ni0.5Mn0.5)O2 has a homogeneous particle size distribution. The discharge capacity is 150 mAh g-1 in CC mode, and 200 mAh g-1 in CCCV mode.0.9LiNO3-0.05Li2CO3 and 0.38LiOH-0.62LiNO3 molten salt combination both can be used to synthesize Li(Ni0.2Mn0.2Co0.6)O2 materials. Because of the different melting point of the molten salts, the materials have different morphology. Both materials have low discharge capacity. Additionnal high temperature heat treatment can improve the discharge capacity of the material synthesized using 0.38LiOH-0.62LiNO3 as molten salt. The discharge capacity of Li(Ni0.2Mn0.2Co0.6)O2 can reach 150 mAh g-1 after two heat treatments. Other salts such as chloride and sulfate have proved not to be suitable for preparation of layered Li(Ni0.2Mn0.2Co0.6)O2 materials.Chloride is good at preparation of spinel materials.0.5NaCl-0.5KCl and 0.6LiCl-0.4KCl both can be used to synthesize LiMn2O4 materials. Morphology of LiMn2O4 prepared using 0.5NaCl-0.5KCl as molten salt has aggregated spherical particles in the nanosized range. The resulting discharge capacity is 124 mAh g-1 with excellent cycling performance.Finally, on the basis of the above-mentioned materials, the thesis summarizes molten salt selection rules and the preparation parameters for the molten salt synthesis of lithium-ion battery cathode material. Except for chloride and sulfate, other lithium containing salts or combinations can be used for the preparation of layered materials. Chloride molten salt is useful to prepare spinel structure material. Molten salt synthesis at around 800℃for 5-6 hours is enough to obtain battery materials with good morphology and electrochemical properties. Paremeters of salts such as melting point affects the morphology and thereby affects the electrochemical performance. Therefore choice of the salts combination as well as the synthesis parameters has proved to be critical to the cycling performance.更多还原