【作者】 陈红；

【导师】 陈岗；

【作者基本信息】 吉林大学 ， 材料物理与化学， 2011， 博士

【摘要】 二次电池作为一种可循环使用的高效洁净新能源,是综合缓解能源、资源和环境问题的一种重要技术途径。在强大的社会发展需求推动下,新型锂离子电池的研究和开发一直是近年来国际上一系列重大科技发展计划的热点。基于新构思、新材料和新技术的新型锂离子电池不断涌现,锂离子电池正向着高能量、高功率、长寿命、绿色环保等方向发展。锂离子电池电极材料不仅仅具有优秀的电化学性能,由于特殊的几何构型和多重的离子价态更是展现出丰富的物理现象和思想。本论文中,我们系统地研究了几类锂离子电池电极材料,详尽的探讨了材料的合成条件、晶体结构与磁学、电化学性质。并对材料表现出来的新奇的磁性现象和电化学性能给出了科学的解释。(1)单斜结构Li0.33MnO2被认为是一种新型的3V电池正极材料,但是对其电化学过程中结构演化等一些基础问题的研究尚不明朗。本章中我们通过低温固相烧结法制备了Li0.33MnO2,并通过测量循环伏安曲线、阻抗谱及原位XRD、XAS和Raman谱发现材料在低电压区间下具有更好的容量保持率。而高电压区间下迅速的容量损失主要是由于材料表面形成了较厚的尖晶石层。在Li+离子插入后,Li0.33MnO2转变为尖晶石相得LiMnO2。此外Li0.33MnO2材料的直流磁化率曲线和磁化率倒数曲线都印证了存在两个磁转变过程。定量分析交流磁化率峰位对于频率的依赖性关系发现随着温度的降低Li0.33MnO2 (?)将经历从顺磁态到原子尺度自旋玻璃态、再到团簇自旋玻璃态的转变。(2)NiO具有立方的NaCl结构,作为负极材料理论电容量可达718mAh.g-1,由于其具有较高的可逆比容和低廉的价格,所以NiO被认为是一种具有广阔应用前景的锂二次电池负极材料。NiO也是一种典型的P型半导体,低温呈现反铁磁,奈尔转变温度为523K。本章中我们通过熔盐法制备了Li离子掺杂的Li0.29Ni0.71O材料,并探讨了离子掺杂对于体系电化学和磁学性质的调制行为。直流磁化率研究发现掺杂后Li0.29Ni0.71O表现出重入自旋玻璃态行为,从亚铁磁到自旋玻璃态的转变,可能的产生原因在于掺杂诱导体系出现多重相互竞争的交换相互作用。Li离子的掺杂后对于电化学性能的提升并未表现出我们所期待的效果,其首次循环就出现的不可逆的Li20是引起材料容量降低的主要原因。(3)层状结构的Li(Nix,Mnl-x-y,Coy)O2材料中+4价的Mn离子不存在Jahn-Teller效应,抑制了充放电过程中Mn离子变价所能引起的结构相变。Co3+离子在体系中不存在电化学活性,主要起到稳定结构的作用。而Ni离子承载着电化学变价的作用,在锂离子插入和脱出的过程中由+2价变为+3价。在充放电过程中各种离子“各司其职”使该材料展现出良好的电化学性能。但是这个接近于完美的结构中离子之间的无序是制约其电化学性能的一个主要因素。我们通过溶胶-凝胶法制备了442三元掺杂材料并研究材料的磁性行为。研究发现材料在低温呈现团簇自旋玻璃态,这与Chernova等人通过固相法制备的材料表现的原子尺度自旋玻璃态具有明显的差别。我们认为这种差别来源于过渡金属层间的离子无序分布诱导团簇行为的出现。(4)富锂Li[Li(l/3-x/3)Mn(2/3-2x/3Nix]O2体系在最近几年内因为其高比容量和良好的循环性能,吸引了广泛的关注。但是对于该系列材料磁性的研究却相对较少。富锂材料一方面具有六方层状结构,过渡金属层为失措的三角点阵；另一方面富锂材料一定程度上又可以看成是有六方层状结构的LiMO2和单斜结构Li2MnO3形成的固溶体,在层状结构中引入了无序。这也就提供我们一个难得的机会去探讨几何失措与无序分布在材料磁性表象上的竞争作用。我们通过溶胶-凝胶法制备了富锂的材料Li[Li0.2Mn0.4Ni0.4]O2,研究材料在低温呈现类自旋玻璃态行为。计算体系的自旋失措因子F=7.8小于几何失措效应起效果所需要的最低标准10。我们认定在该类富锂材料中类自旋玻璃态产生的原因为过渡金属层间的离子无序分布。更多还原

【Abstract】 Lithium-ion secondary battery, as a new recycling and clean energy, is a kind of important technical method to solve energy, resource and environment problems. With the strong request of social development, the research and development of new lithium-ion battery have attached much attention. New lithium-ion battery has been developed greatly based on the new thoughts, new material and new technology and tending to high energy, high power, long life and environmental protection. The electrode materials not only show good electrochemical properties, also display abundant physical phenomena and thoughts due to the special crystal structure and multi-valence sates.In this thesis, we explored some typical kinds of electrode materials and studied their synthesis processes, lattice structure, magnetic properties and electrochemical properties. We also offered our perspective on their novel and abundant magnetic phenomena.(1) Monoclinic Li0.33Mn02 has been studied as a good 3V cathode material, but the structural transition during electrochemical cycling is still uncertainty. In this chapter, we prepare Li0.33MnO2 and find the material show good capacity retention in low voltage and the surface of Li0.33MnO2 will change into a spinel layer in high voltage by study the CV, impedance, in situ XRD, XAS and Raman. Furthermore, Li0.33MnO2 shows two magnetic transitions due to dc and ac susceptibility data. The quantitative studies on relation between ac peaks and frequencies shows Li0.33MnO2 display the transition from paramagnetism into atomic-scale spin glass, then into cluster spin glass with the decreasing of temperature.(2) Cubic NiO has a high theoretical capacity of 718 mAh g-1 as a negative material and is considered a promising negative materials because of the high capacity and low price. NiO is a typical P-type semiconductor and antiferromagnetism with Neel temperature 523 K. We synthesize Lio.29Ni0.71O by molten salt method and discuss the effect of nonmagnetic Li+ ion doping on the electrochemical and magnetic properties. Dc susceptibility shows a reentrant spin glass behavior from ferrimagnetism to spin glass in Lio.29Ni0.71O. The possible reason may lie in the multi-competitive exchange interactions when Li+ ions are introduced into NiO lattice. Li0.29Ni0.71O does not show better electrochemical properties in comparison with that of NiO which may originate from the irreversible Li2O in the fist cycling.(3) In layered Li(Nix,Mnl-x-y,Coy)O2 material, the structural phase transition during the charge/discharge process will be suppresed because Mn4+ ions shows non-Jahn-Teller effect. Co3+ ions does not have electrochemical properties and Ni2+ ions will change the valence from+2 into+3 in the electrochemical cycles. One of the major problems to restrict electrochemical properties is the disordered arrangements of transitions ions in the transition-metal layers. In this chapter, we firstly synthesizes the 442 materials, and then studies and discusses the magnetic behaviors. Our research results shows 442 material shows cluster spin glass behavior, which is quite different from the atomic spin glass in Chernova’s reports. Such difference may come from the scale of disordered cluster due to the different preparation process.(4) Lithium-rich Li[Li(l/3-x/3)Mn(2/3-2x/3)Nix]O2 system has attracted much attentions in recent years due to the high specific capacity and good cycling. But the magnetic studies on this materials are lack comparatively. Such type of lithium-rich materials has rhombohedral layered structure with triangle lattice in the transition-metal layers. On the other hand this material can be considered to be the solid solution of LiMnO2 and Li2MnO3. This provide us a possibility and chance to discuss the effect of geometrical frustration and disorder on the formation of spin glass. We find Li[Li0.2Mn0.4Ni0.4]O2 show a spin-glass-like behavior. Calculated spin-frustration parameter F=7.8 is far below the standard parameter 10 which geometrical frustration works. So we can conclude that the origin of spin glass in Li[Li0.2Mn0.4Ni0.4]O2 is disorder arrangements of transition metal oxides rather than geometrical frustrartion.更多还原