新型尖晶石结构锂离子电池材料的研究与应用

【作者】 颜群轩；

【导师】 王志兴；

【作者基本信息】 中南大学 ， 电化学工程， 2009， 硕士

【摘要】 尖晶石型的锂离子电池正极材料LiNi_0.5Mn_1.5O₄具有4.7V的高电压放电平台,充放电比容量高,表现出了优良的电化学性能,逐渐成为当今正极材料研究的一个热点。本论文采用复合碳酸盐共沉淀法制备出了比容量高、循环性能优良的尖晶石型LiNi_0.5Mn_1.5O₄,并研究了Mg、Fe、Al掺杂对其物理性能、晶体结构及电化学性能的影响。尖晶石型的Li₄Ti₅O₁₂是一种零应变锂离子电池负极材料,具有优良的结构稳定性和安全性能。Li₄Ti₅O₁₂理论比容量为175mAh·g^-1并且集中在平台区域；循环性能好,有很好的充放电平台。本论文采用溶胶-凝胶法合成了Li₄Ti₅O₁₂并对其物理性能和电化学性能进行了研究。采用液相共沉淀法制备镍锰复合碳酸盐前驱体,650℃焙烧后生成的镍锰复合氧化物与Li₂CO₃混合,在空气中于750℃-900℃下焙烧10h,600℃退火10h得到LiNi_0.5Mn_1.5O₄。采用XRD,SEM和恒电流充放电测试等对样品进行了表征。SEM结果表明:合成温度对LiNi_0.5Mn_1.5O₄的表面形貌及粒径有较大影响;XRD结果表明:合成的样品均为纯的立方尖晶石结构。电化学测试结果表明,800℃合成的样品在室温下具有较好的电化学性能:0.1C、1C、2C、4C首次放电容量分别130.24mAh·g^-1、129.47mAh·g^-1、115.5mAh·g^-1、108.05mAh·g^-1,且大倍率下具有较好的循环性能。分别采用Mg、Fe、Al掺杂,研究了掺杂量对LiM_xNi_0.5-xMn_1.5O₄性能的影响。SEM表明Mg、Fe、Al掺杂对材料的表面形貌有很大影响;XRD表明当Mg、Fe、Al达到一定量时晶体结构发生变化。电化学测试结果表明Mg、Fe掺杂使得电化学性能变差,Al能过改善电化学性能,LiAl_0.05Ni_0.45Mn_1.5O₄在1C的倍率下充电,10C倍率下放电,循环测试表明其具有非常好的大电流特性。本文还研究了一种制备锂离子电池负极材料的Li₄Ti₅O₁₂新工艺。以醋酸锂和钛酸丁酯为原料,异丙醇为溶剂,采用溶胶-凝胶法制备前驱体,再通过一定的热处理后制备了锂离子电池负极材料Li₄Ti₅O₁₂。采用XRD、SEM及电化学性能测试等分析手段考察了不同热处理温度对产品性能的影响。结果发现,经过850℃热处理24h后得到的产品粒径分布均匀、结晶度好;并且表现出较好的电化学性能,在1-2.5V之间充放电,0.1C、1.0C和2.0C首次放电比容量分别达到158.5mAh·g^-1、137.8mAh·g^-1、124.3mAh·g^-1,并且大电流充放电时具有较好的循环性能。研究表明该方法是适合制备高活性的Li₄Ti₅O₁₂工艺方法。本文还利用LiAl_0.05Ni_0.45Mn_1.5O₄为正极,Li₄Ti₅O₁₂为负极组装成全电池进行研究,在2.0-3.5V范围内充放电,LiAl_0.05Ni_0.45Mn_1.5O₄/Li₄Ti₅O₁₂全电池在3.1V左右有一个放电平台。更多还原

【Abstract】 As the cathode material of lithium ion batteries, cubic spinel LiNi_0.5Mn_1.5O₄ shows excellent electrochemical performance, such as high discharge plateau at 4.7V and high energy density, and it is emerging as an active research topic. In this paper, the spinel LiNi_0.5Mn_1.5O₄ with high energy density and excellent cycle performance were synthesized by coprecipitation composite carbonate process methods. The effects of synthesizing conditions on the physical properties and electrochemical performances of LiNi_0.5Mn_1.5O₄ were investigated. Spinel Li₄Ti₅O₁₂, an attractive negative electrode regarded as a "zero strain" material with better safety and excellent structure stability, has been studied extensively . Its theoretical specific capacity is 175mAh·g^-1. The sample also exhibit excellent cycle performance and plateau voltage.In this paper, the spinel Li₄Ti₅O₁₂ was synthesized by Sol-Gel method. The effects of synthesizing conditions on the physical properties and electrochemical performances of Li₄Ti₅O₁₂ were investigated.The LiNi_0.5Mn_1.5O₄ spinel has been prepared by a composite carbonate process, and the effects of calcination temperature on the physical properties and electrochemical performance of the samples have been investigated. The results of XRD and scanning electron microscopy （SEM） showed that as calcination temperature increases , the grain sizes of the samples is obviously increase. It was found that the samples calcined at 800℃present good electrochemical performance. Between 3.5-4.9V versus Li, it delivered 130.24mAh·g^-1, 129.47mAh·g^-1, 115.5 mAh·g^-1, 108.05mAh·g^-1 at 0.1C, 1C, 2C, 4C rates respectively. And it showed good cycle performance under high current density .The effect of doping elements and doping amount into LiMxNi_0.5-xMn_1.5O₄（x: Mg, Fe, Al） on its electrochemical properites was studied. The SEM analysis indicates that the particles Surface Morphology have great affected by the doping elements. Further more, XRD characterization of the products revealed that the when the doping element reaching certain content the crystal structure of the compound was changed. Electrochemical measurements showed that the doping Of Mg and Al can not improve the electrochemical. But Al doping can improve the electrochemical. In addition, high-rate test indicated that the LiAl_0.05Ni_0.45Mn_1.5O₄ powers has excellent electrochemical performance when charged and discharge at 1C and 10C, respectively.A novel technique was developed to prepare Li₄Ti₅O₁₂ anode material for lithium secondary batteries in this paper. The precursor was prepared by sol-gel method using terbutyl titanate, lithium acetate and isopropanol as starting materials. Then the precursor was calcined for 24 hours in air to obtain Li₄Ti₅O₁₂. The influence of temperature on performance of product was studied. The investigation of XRD, SEM and the determination of the eldctromical properties show that the Li₄Ti₅O₁₂ powers prepared by this method are narrowly distributed, well crystallized. The Li₄Ti₅O₁₂ powers also have excellent electrochemical performance.Between 1.0-2.5V versus Li, it delivered 158.5mAh·g^-1, 137.8mAh·g^-1 and 124.3mAh·g^-1 at 0.1C, 1.0Cand 2.0C respectively. And it showed good cycle performance under high current density. Study shows that this method is appropriate for preparing Li₄Ti₅O₁₂ with high electrochemical performance. The LiAl_0.05Ni_0.45Mn_1.5O₄/Li₄Ti₅O₁₂ full cell system was investigated also. The LiAl_0.05Ni_0.45Mn_1.5O₄/Li₄Ti₅O₁₂ cell system charge and discharge between 2.0V to 3.5V. And it show a voltage plateau at 3.1V.更多还原