锂离子无机固体电解质Li3xLa2/3-xTiO3和Li7La3Zr2O12电性能提高的研究

In recent years, all-solid-state lithium ion batteries are attracting more attention owing to high power density and high safety. As an important part of the battery, the inorganic solid state electrolytes become hot and significant issues because of their advantages over the molten and aqueous electrolytes, such as high safety, good capacity retention. Among them, a lot of attention was paid to LLTO (Li3xLa2/3-xTiO3) and LLZO (Li7La3Zr2O12), presenting a promising application potential in all-solid-state lithium batteries..In this project, LLTO and LLZO would be prepared via sol-gel route and solid reaction method. The relationships between the lattice structure, microstructure and transport properties would be studied in LLTO and compared with that in the LLZO ceramics by using XRD,SEM, XPS, ICP and impedance spectrum. The conduction mechanics and behavior in these two different ceramics would be summarized on the basis of the lattice structure and the grain boundary structure, demonstrating the conduction essence and building the principle for improving the ionic conductivity in the inorganic solid state electrolytes. Thereafter, the grain boundary structure would be designed and controlled through adding the proper second phase into LLTO, thus enhancing the ionic conductivity. Meanwhile, the ionic conductivity would be increased by doped elements properly. Finally, all-solid-state battery would be fabricated and examined using the improved inorganic solid state electrolytes. The project will solve the safety problems, and promote the application of the inorganic solid state electrolytes in all-solid-state batteries. The project plays a key role in the commercial development of all-solid-state lithium batteries.

该项目利用固相反应法和溶胶凝胶法等工艺制备出在锂离子电池中非常具有潜在应用价值的LLTO（Li3xLa2/3-xTiO3）和LLZO（Li7La3Zr2O12）无机固体电解质。利用XRD、SEM、XPS、ICP和电化学工作站等实验手段表征分析其晶体结构、微观结构与电性能之间的关系，从晶体结构、晶界结构和离子传导机制的角度总结出LLTO和LLZO的导电规律，找到两者导电机理存在差异的原因，从而获得能够有效提高无机固体电解质电导率的理论基础。在此基础上，引入合适的第二相进行包覆型复合，设计和调控晶界结构，进而提高电导率；利用合适的元素原子对LLTO掺杂改性，以达到提高电导率的目的；最后利用优化后的电解质组装三明治结构的全固态锂电池，测试评价其电化学性能。该研究项目对解决当前锂电池普遍存在的安全隐患、提高锂电池安全性和促进锂电池产业进步具有重要的实践意义和科学意义。

锂离子二次电池由于其显著的优越性和潜在的应用价值，在各种新能源中备受瞩目。当前商用锂离子电池的电解质主要采用电解液或有机聚合物，安全隐患（爆炸、起火和漏液等事故）较大，采用无机固体电解质可有效解决此问题，该类电解质具有广泛的应用前景，成为当前锂电池行业的一个研究热点。.本项目围绕LLTO（Li3xLa2/3-xTiO3）和LLZO（Li7La3Zr2O12）制备工艺、晶体结构、微观结构、锂离子浓度、锂离子电导性能以及它们之间的关系展开研究。.(1)采用复阻抗谱方法研究了Li0.5La0.5TiO3 (LLTO) - Li3PO4复合电解质的电导率。利用XRD、SEM和相对致密度等实验手段研究了第二相Li3PO4在LLTO基体上的分散复合。发现，该第二相的加入降低了锂离子电导率，尽管非晶态的Li3PO4使得LLTO的致密性变好，揭示了锂离子电导率的变化主要和LLTO晶体结构、晶界处的微观形貌和锂离子浓度有关。.(2)确定了LLZO的形成机理。结果表明：当不使用保护粉时，在680-720℃反应形成四方LLZO；随着温度升高，锂挥发加剧，四方LLZO逐渐分解为La2Zr2O7。当使用保护粉时，四方LLZO在1100℃仍可稳定存在，并在高温下转变为立方LLZO。为弥补高温烧结过程中的锂元素挥发，因而采用了保护粉方式烧结。当烧结温度约为1230℃时，获得了较致密的立方LLZO陶瓷，其室温电导率约为3.5910-4S·cm-1。.在LLTO电解质基体中复合多种形式的LLZO成分，制备了LLTO基复合电解质。作为添加物的LLZO成分在热处理过程中发生了分解，分解产物参与了LLTO基体晶界处发生的Li、Zr、La、Ti和O五种元素之间的复杂协同效应，提高了晶界区域载流子浓度和空位浓度，通过空间电荷层效应提高基体的晶界电导率和总电导率。复合5wt%LLZO的样品室温总电导率达到了最高，超过了纯相LLTO样品总电导率的2倍。.(3)在锆元素位置掺杂Ta元素，可起到稳定立方结构和提高电导率的作用。表明，经过1150℃烧结制备Ta掺杂LLZO的电导率比未掺杂样品提高了约一个数量级。.(4)通过制作LLZO全固态半电池，发现，LLZO与商用电极材料钴酸锂或富锂锰酸锂之间均具有良好的电化学稳定性。.该研究项目对解决当前锂电池普遍存在的安全隐患、提高锂电池安全和促进锂电池产业进步具有重要意义。