固态锂金属电池兼具高热稳定性、高化学稳定性和高能量密度，是下一代储能电池的重要发展方向之一。NASICON型Li_1.3Al_0.3Ti_1.7(PO₄)₃（LATP）具有环境稳定性优异、离子导电性良好、原材料经济等优势，作为氧化物固态电解质应用成为固态锂金属电池领域的研究热点。然而，LATP固态电解质的离子电导率相较于传统液态电解液偏低问题，以及LATP与锂金属的化学势不匹配问题，限制了LATP基固态锂金属电池的发展与应用。

      本论文基于正交试验，结合现代表征技术与机器学习算法，多维度剖析了固相法制备LATP固态电解质中各工艺参数对离子电导率的影响规律，以及工艺参数间的耦合关系，实现了较低烧结温度下高离子电导率LATP基固态电解质的可控制备。进一步地，本论文设计了基于液态电解液的LATP基固态电解质/锂电极复合界面层，结合理论计算，研究了该复合界面层对锂电极稳定性的促进作用，探讨了在复合界面层引入高浓度锂盐PEO基聚合物取代电解液后电池的循环稳定性和工作温度，制备了具有优异电化学性能的LATP基固态锂金属电池。具体研究内容如下：

      （1）基于正交试验设计与分析，构建了表征测试数据集，通过对电解质材料的物相、结构和电化学性能的系统研究，揭示了LATP固态电解质制备工艺参数中原料组合、粉体煅烧温度和块体烧结温度对离子电导率的影响规律，解析了工艺参数间的耦合关系。结合机器学习，建立了工艺参数与离子电导率的关联数学模型，提炼出制备高离子电导率LATP的关键要素。研究表明，原料组合主要决定了电解质块体的物相种类；而煅烧温度对电解质块体相组成和组织结构的影响均有限；烧结温度则与电解质块体的结构致密度呈强关联性，能够显著影响LATP的离子电导率。工艺参数对离子电导率提升的影响权重为，烧结温度>原料>煅烧温度。以Li₂CO₃、NH₄H₂PO₄、Al₂O₃和Ti(OH)₄为原料，在700~900 ℃煅烧和950 ℃烧结的条件下，制备的LATP固态电解质块体具有无锂离子绝缘相以及结构致密的特征，展现出较高的离子电导率（0.289~0.339 mS cm^-1）。

      （2）采用三种含Ti化合物（TiO₂、Ti(OH)₄和C₁₆H₃₆O₄Ti）作为LATP的制备原料，研究了Ti源对LATP微观结构、相组成、烧结行为以及锂离子传输机制的影响。以优选Ti源为策略，实现了可低温致密化LATP的低成本制备，有效缓解了高温烧结引起的元素挥发等问题。使用C₁₆H₃₆O₄Ti作为Ti源制备的LATP，可以在750 ℃较低温度烧结，获得超过90%的致密度以及0.67 mS cm^-1的室温离子电导率。晶体-非晶复合NASICON型主相，与低含量（<5 wt%）LiTiOPO₄第二相的协同作用，有利于LATP晶粒在较低温度下融合，形成致密、均匀而且连续的组织结构，为锂离子迁移提供均匀化的传输网络；这是LATP固态电解质能够在低温烧结，并且展现高离子电导率的内在机理。通过在LATP中掺杂B元素影响电解质材料中P元素含量，间接调控LiTiOPO₄第二相的比例，实现了对烧结体结构与锂离子传输性能的进一步优化。制备的B掺杂型Li_1.3Al_0.23B_0.07Ti_1.7(PO₄)₃（LABTP）在750 ℃烧结后的致密度达到了98%，室温离子电导率可达0.92 mS cm^-1。

      （3）在锂金属电极和LABTP电解质表面分别修饰人工SEI层（Li_xSn-LiF）和LiF涂层，以及在固态电解质/电极界面区域引入薄层液态电解液，构筑复合界面层，增强固态电解质/锂电极界面处锂均匀沉积和锂枝晶抑制能力，提高界面结构稳定性。人工SEI层能够有效增大锂离子传输通量，调控锂电极表面的锂沉积形态。LiF涂层充当了物理接触与电子传输的“双功能”阻绝层，不仅能够抑制锂枝晶穿刺，也可以防止锂在电解质内形核。二者界面区域的电解液增强了刚性电解质与电极间的润湿性，显著降低了界面阻抗。基于复合界面层的LABTP半固态锂金属对称电池在室温、0.5 mA cm^-2和40 ℃、1.0 mA cm^-2的条件下能够分别工作超过800 h和400 h。基于复合界面层的LABTP半固态锂金属全电池在室温、2C条件下经过1100圈充放电循环后的容量保持率为89.6%，在40 ℃、5C条件下经过300圈充放电循环后的容量保持率仍有92.9%。

      （4）将高浓度锂盐载体[Li(G3)₁]TFSI引入聚氧化乙烯（PEO）基聚合物，制备了凝胶类高浓度锂盐PEO基聚合物界面层（PPI）。分子动力学模拟等研究结果揭示了G3对LiTFSI的强解离作用，以及引入[Li(G3)₁]TFSI能够有效提高聚合物体系中锂离子的浓度与扩散系数。组分优化后PPI的热稳定性较优，室温离子电导率为0.94 mS cm^-1，对锂电极与磷酸铁锂电极均展现良好的适配性。基于优化后PPI修饰LABTP基电解质/电极界面，制备的准固态锂金属全电池具有优异的循环稳定性和宽温工作特性。电池在室温、2C条件下经过1000圈充放电循环后的容量保持率可以达到95.7%；在0 ℃、0.5C和80 ℃、5C条件下分别能够稳定循环300圈和600圈，容量保持率分别为94.6%和95.6%。

    With high thermal stability, chemical stability, and energy density, solid-state lithium metal batteries are considered a huge advancement in next-generation energy storage technologies. Among various oxide solid electrolytes for lithium metal batteries, NASICON-type Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) has garnered considerable interest due to its environmental stability, high ionic conductivity, and cost effectiveness. However, the lower ionic conductivity of LATP solid-state electrolytes compared to traditional liquid electrolytes, as well as the mismatch in chemical potential between LATP and lithium metal, have limited the development and application of LATP-based solid-state lithium batteries.

    In this work, the effects of various process parameters on the ionic conductivity of LATP, as well as the interaction among these parameters, during the solid-state preparation of LATP were analyzed multidimensionally via orthogonal experiments and combining modern characterization techniques with machine learning algorithms. The preparation method for LATP-based solid electrolytes, which can be sintered at low temperatures and can achieve high ionic conductivity, was investigated. Furthermore, the LATP/Li composite interlayer based on a liquid electrolyte was introduced and its stability with a lithium metal anode was studied via experiments and theoretical calculations. Moreover, high-concentration polyoxyethylene (PEO)-based polymer-interphase (PPI) layer was introduced in the composite interlayer instead of the liquid electrolyte. The cycling stability and working temperature of the PPI modified LATP-based batteries were investigated, and the LATP-based solid-state lithium metal battery with excellent electrochemical performance was prepared. The main contents of this thesis are detailed as follows:

    (1) Based on the orthogonal experimental design and analysis, a characterization test dataset was constructed. Moreover, through a systematic investigation of the LATP material’s phase, structure and electrochemical properties, the effects of source, calcination temperature, and sintering temperature of LATP pellets on the ionic conductivity were studied and the interaction among the abovementioned parameters was analyzed. Combined with machine learning, a mathematical model of the association between process parameters and ionic conductivity was established and the key elements for the preparation of high-ionic-conductivity LATP were refined. It was demonstrated that the source mainly affect the phase composition of the electrolyte pellet, while the calcination temperature exerts a limited effect on both the phase composition and structure of the electrolyte pellet. The sintering temperature substantially affects the density of the solid electrolyte pellet, influencing its ionic conductivity the most. The order of importance of process parameters on the enhancement of ionic conductivity is sintering temperature > source > calcination temperature. The LATP prepared from Li₂CO₃, NH₄H₂PO₄, Al₂O₃, and Ti(OH)₄ as source was calcined at 700~900 ℃ and sintered at 950 ℃, without lithium-ion insulating phases and exhibte the dense structure, which owned high ionic conductivity (0.289~0.339 mS cm^-1).

    (2) Three Ti sources (TiO₂, Ti(OH)_4, and C₁₆H₃₆O₄Ti) were used as the raw materials for preparing LATP, and the effects of Ti source on the microstructure, phase composition, sintering behavior and lithium-ion transport mechanism of LATP were investigated. The preferred Ti source strategy was used to realize the low-cost preparation of low-temperature dense LATP, which effectively alleviated elemental volatilization caused by high-temperature sintering. The results show that with C₁₆H₃₆O₄Ti as the Ti source, LATP pellets can be sintered at 750 °C with a relative density of more than 90% and their ionic conductivity at room temperature can reach 0.67 mS cm^-1. The hybrid crystalline–amorphous phase structure with a low ratio (<5 wt%) of LiTiOPO₄ can synergistically facilitate grain fusion and promote structural densification under low-temperature sintering. The sintered LATP pellet exhibits an interconnected structure, providing a uniform lithium-ion transport network. This is the intrinsic mechanism that enables LATP solid electrolytes to sinter at low temperature and exhibit high ionic conductivity. Moreover, the doped boron in LATP affects the P element content, indirectly modulating the ratio of LiTiOPO₄ and promoting structural homogenization. Thus, B doping can further improve the density and ionic conductivity. The density of the B-doped Li_1.3Al_0.23B_0.07Ti_1.7(PO₄)₃ (LABTP) can reach 98% when sintered at 750 °C, and its ionic conductivity can reach 0.92 mS cm^-1.

    (3) The composite interlayer comprised an artificial SEI layer (Li_xSn-LiF) modified on the lithium metal surface, a LiF coating layer modified on LABTP, and the liquid electrolyte in the electrolyte-electrode interface region, which promoted uniform deposition of lithium and inhibited growth of lithium dendrites, formed a stable electrolyte-lithium electrode interface. The artificial SEI layer can effectively enhance the transport flux of lithium ions and modify the morphology of lithium deposition on the lithium anode surface. As a physical and electronic "dual-function" barrier layer, the LiF layer can effectively prevent lithium dendrite puncturing and lithium nucleation within the electrolyte. The liquid electrolyte enhances the wettability between the rigid electrolyte and electrode, which significantly reduces the interface impedance. The lithium symmetric batteries with modified LABTP can function for more than 800 h at room temperature with 0.5 mA cm^-2 and for 400 h at 40 °C with 1.0 mA cm^-2. The batteries prepared using modified LABTP as the solid electrolyte exhibit a capacity retention ratio of 89.6% after over 1100 cycles at room temperature with 2C and 92.9% after 300 cycles at 40 °C with 5C.

    (4) The gel-like high-concentration PPI layer was synthesized by introducing a high-concentration lithium carrier [Li(G3)₁]TFSI into the PEO-based polymer. MD simulations reveal that G3 can strongly dissociate LiTFSI. Moreover, [Li(G3)1]TFSI can considerably and effectively increase the concentration and diffusion coefficient of lithium ions in the polymer system. The optimized PPI demonstrates excellent thermal stability, an ionic conductivity of 0.94 mS cm^-1 at room temperature, and exhibits excellent suitability for lithium electrodes and lithium iron phosphate electrodes. A quasi-solid-state batteries prepared via PPI modification exhibits a capacity retention rate of 95.7% after 1000 cycles at room temperature and 2C. Moreover, it exhibits a capacity retention ratio of 94.6% and 95.6% after 300 cycles at 0 °C with 0.5C and 600 cycles at 80 °C with 5C, respectively.