【作者】 江剑兵；

【导师】 胡国荣；

【作者基本信息】 中南大学 ， 电化学工程， 2014， 博士

【摘要】 摘要：能源危机、环境污染、全球变暖等一系列问题严重威胁到人类的生存和发展。为解决以上问题,各国政府纷纷投入大量人力物力开发利用电动汽车。锂离子电池具有体积小、电压高、容量大、寿命长、自放电小、无记忆效应和绿色环保等优点而成为车载动力的首选。磷酸铁锂和锰酸锂作为最可能应用于动力电池的正极材料。然而在我国磷酸铁锂热火朝天的几年里,世界各大主流汽车厂商电动汽车电池正极材料逐步向以日韩为代表的锰系正极材料转移。但是日本以及韩国对动力LiMn2O4正极材料进行封锁,在技术上进行保密,因此,研究开发出性能优越的尖晶石LiMn2O4具有非常重要的现实意义。本文从前驱体入手,提出采用控制结晶一步氧化法制备球形四氧化三锰前驱体,然后联合高温固相法制备球形锰酸锂,并从资源综合利用角度出发,采用液相法进行掺杂改性研究。论述了控制结晶法合成前驱体的理论基础。根据同时平衡原理和质量守恒定律推导,绘制出Mn-NH3-SO42--H2O的φ-pH图,并对晶粒形成和长大机理进行理论分析,为制备形貌单一、粒径分布均匀的球形四氧化三锰前驱体提供理论基础。系统研究了控制结晶一步氧化法制备球形四氧化三锰工艺。研究了反应温度、反应时间、搅拌速度、MnS04摩尔浓度、氨水浓度、氨锰摩尔比、硫酸锰加料速度对前驱体物理化学指标的影响,研究结果表明,在反应温度为70℃、搅拌速度为500r·min-1、反应时间为12h、硫酸锰浓度为1.25mol·L-1、氨水浓度为2mol·L-1、NH3/Mn摩尔比为2.4、硫酸锰加料速度为600mL·h-1。制备的Mn304纯度高达99.74%,粒度分布较好,平均粒径为11.201μm,振实密度达到2.28g·cm-3。拉曼光谱分析表明所有Raman峰与尖晶石Mn304的特征峰完全吻合。系统研究了高温固相法制备球形锰酸锂。研究结果表明最佳烧结工艺为500℃、650℃预烧6h后升温至800℃烧结10h,此条件下合成的LiMn204材料颗粒球形度较好、结晶完善、电化学性能较好,常温0.1C首次放电比容量高达125.5mAh·g-1,1C首次放电比容量为119.9mAh·g-1,循环300次后容量保持率为87.66%,高温(55℃)1C首次放电比容量为114.9mAh·g-1,循环200次后容量保持率为86.24%。LiMn2O4电极循环伏安结果发现两对氧化还原峰,与LiMn204电极的充放电曲线的特征平台表现一致。研究了联合控制结晶一步氧化高温固相法制备球形掺镁锰酸锂。研究发现控制NH3/Mn摩尔比,可以得到Mg含量可控、振实密度较大的球形掺Mg的Mn304前驱体。XRD结果显示经过高温固相反应,Mg取代部分Mn成功进入尖晶石LiMn204晶格。镁掺杂改善了锰酸锂的循环性能,当前驱体中镁含量约为1.5%时,得到的LiMn2-xMgxO4电化学性能最好,常温1C首次放电比容量为113.1mAh·g-1,循环300次后容量保持106.4mAh·g-1；高温1C首次放电比容量为121.4mAh·g-1,循环300次后容量保持99.3mAh·g-1。循环性能基本能满足动力电池要求。为进一步改善锰酸锂的循环性能、降低原料成本、提高资源综合回收利用,采用液相法分别对锰酸锂进行了Ni、Co单一和Ni、Co复合掺杂。XRD结果表明,Ni、Co成功取代部分Mn进入尖晶石LiMn204晶格,减小了材料的晶格常数。钻掺杂锰酸锂具有较高的放电比容量和较好的循环性能,当前驱体中钴含量为8%时,材料1C首次放电比容量为117.3mAh-g-1,循环200周后容量保持率为95.82%；镍掺杂有效改善了LiMn204的循环性能,但是材料的比容量较低；Ni、Co复合掺杂LiMn204具有较高的比容量和较好的循环性能,当前驱体中Ni、Co的百分含量分别为1%左右时,制备的LiMn204常温和高温1C首次放电比容量分别为112.8和118.2mAh-g-1,常温500次循环后容量保持率为97.52%,高温300次循环后容量保持率为90.52%,所有物理化学指标都达到动力电池要求。XPS分析结果表明,Ni、Co复合掺杂提高了锰的平均价态,Ni、Co复合掺杂样品中Mn、Ni、Co的价态分别为+4、+2、+3价。最后对球形锰酸锂及Ni、Co复合掺杂锰酸锂进行中试。中试结果表明锰酸锂具有较好的常温电化学性能,1C首次放电比容量为115.8mAh·g1,循环500次后容量保持率为89.29%；Ni、Co复合掺杂锰酸锂具有优越的电化学性能,常温和高温1C首次放电比容量分别为112.8和111.2mAh-g-1,500次循环后容量保持率分别为91.22%和83.81%。成本分析认为该工艺具有非常好的经济效益。更多还原

【Abstract】 Abstract:The serious problems such as energy crisis,environmental pollution,global warming have already threatened the human living and its development. To solve the problems above, governments have invested a lot of manpower and material resources in the development and utilization of electric cars. As the Li-ion battery has many advantages, such as high working-voltage, large capacity, long circle-life and non memory effect, it becomes the first choice of novel power battery. Both of LiFePO4and LiMn2O4were most likely to be used on power battery. When we studied on LiFePO4, manganese lithium ion battery cathode material was mostly produced in Korea and Japan. So it is significant to study LiMn2O4in that Korea and Japan block material and technology secrecy. This paper reports on the synthesis of spherical Mn3O4particles by a controlled crystallization oxidization method and the preparation spherical LiMn2O4material by a solid-state reaction. At the same time, in order to realize comprehensive utilization of resources, LiMn2O4was modified by liquid-phase doping method.Theoretical basis for controlled crystallization oxidization method synthesis of Mn3O4precursor was discussed。According to the principle of simultaneity balance and mass conservation, the cp-pH diagram of Mn-NH3-SO42--H2O was drawn. The crystal formation and growth mechanism was also discussed, which provided the theoretical foundation for synthesis of Mn3O4precursor with homo-morphology and uniform particle size distribution.The progress of controlled crystallization oxidization method for preparing Mn3O4precursor was studied systematically. The effect of reaction temperature,reaction time,stirring rate,molarity of MnSO4,molarity of NH3·H2O,molar ratio of NH3/Mn、feeding velocity of MnSO4on the physical chemical properties of Mn3O4were studied. The results show that under the condition of1.25mol·L-1MnSO4,2mol·L NH3·H2O,molar ratio of NH3/Mn2.4,feed MnSO4at600mL·h-1、stirring at500r·min-1,react for12h at70℃, the purity,tap density and mean grain size of Mn3O4precursor are99.74%,2.28g-cm-j and11.20μm, respectively. According to the Raman result, all of the characteristic peaks match exactly with spinel Mn3O4.The progress of solid-state reaction at high temperature for prepare spherical LiMn2O4was studied systematically. The results show the optimum technical parameters as follows:the presintering temperature are500℃and650℃, the sintering temperature is800℃and the sintering is10h. The results of electrochemical performance tests show that the first discharge specific capacity of LiMn2O4obtained under optimum conditions can reach125.5mAh·g-1at0.1C and119.9mAh·g-1at1C, the capacity retention ratio after300cycles is87.66%at room temperature, the first discharge specific capacity is114.9mAh·g-1at1C, the capacity retention ratio after200cycles is86.24%at55℃. The CV spectrums indicated LiMn2O4cathode have two obvious redox peaks, which coincides with the charge and discharge curves of LiMn2O4.The progress of preparing Mg-doping lithium manganese oxide by uniting controlled crystallization oxidization and solid-state reaction has been studied. The results show that the content of Mg in Mg-doping spherical Mn3O4precursor that with large tap density can been controlled by adjusting molar ratio of NH3/Mn. XRD indicate that magnesium ionsentered into the lattice of LiMn2O4substituting some Mn. Mg doping improves the cycle performance of LiMn2O4. The electrochemical properties of LiMn2-xMgxO4which prepared from Mg-doping spherical Mn3O4in which the content of Mg in Mn3O4is about1.5%is the best. When it charges and discharges at148mA·g-1, the first discharge specific capacity of LiMn2-xMgxO4is113.1mAh·g-1at room temperature and121.4mAh·g-1at high temperature, after300cycles, the discharge, cycle performance can meet the standards of power battery.In order to further improve the cycle performance of LiMn2O4,cutting the raw material cost and comprehensive recovery of resource, LiMn2-xNixO4,LiMn2-xCoxO4and LiMn2-x-yNixCoyO4have been prepared by liquid-phase method. XRD indicate that Ni,Co ions substitute some Mn entered into the lattice of LiMn2O4that caused reduction of lattice constants. Co-doping lithium manganese oxide shows high discharge specific capacity and good performance. The first discharge specific capacity of LiMn2-xCoxO4which was prepared from Co-doping spherical Mn3O4in which the content of Co in Mn3O4is about8%is117.3mAh·g-1at1C, after200cycles, capacity retention ratio is95.82%; Ni-doping improve the cycle performance of lithium manganese oxide but its discharge specific capacity is too low; Ni,Co co-doping lithium manganese oxide shows high discharge specific capacity and good performance, LiMn2-xCox04prepared from the precursor in which both of Ni and Co content are1%shows the best electrochemical properties. When it charges and discharges at148mA·g-1, its initial discharge specific capacity is112.8mAh·g-1and its capacity retention ratio after500cycles is97.52%at room temperature; its initial discharge specific capacity is118.2mAh·g-1and its capacity retention ratio after300cycles is90.52%at high temperature. All of its physical and chemical indexes can meet the standards of power battery. The results of XPS show that valence state of Mn,Ni,Co in LiMn2-xCoxO4is+4,+2,+3, respectively.Finally, A pilot plant scale test of preparing spherical LiMn2O4and LiMn2-xCoxO4was carried out in a3mj reactor. The LiMn2O4prepared in pilot plant scale test shows good electrochemistry properties at room temperature. Its initial discharge specific capacity is115.8mAh·g-1and its capacity retention ratio after500cycles is89.29%; LiMn2-xCoxO4shows superior electrochemistry properties, its initial discharge specific capacity of is112.8mAh·g-1at room temperature and11.2mAh·g-1at high temperature, after500cycles, its capacity retention ratio is91.22%at room temperature and83.81%at high temperature. Cost analyses indicate that this progress shows good economic prospects.更多还原