【作者】 张政；

【导师】 黄英；

【作者基本信息】 西北工业大学 ， 材料学， 2022， 博士

【摘要】 可充电的锂离子电池由于其能量密度高而成为研究热点。但是,由于对高能量密度的便携式电子产品和电动车的需求越来越大,常规的锂离子电池已经很难适应新一代高能量储能系统的需求。锂金属是最有前途的负极材料,它的优势在于其高理论比容量(3860 mA h g^-1)和极低电位（-3.040 V vs标准氢电极）。但由于常规液体电解质中锂金属的热力学不稳定,在锂沉积/剥离过程中产生的锂枝晶会穿过隔膜,造成电池的短路,从而引起火灾、爆炸等安全问题。因此,设计高能量密度和高安全性的锂离子电池仍然存在严峻的挑战。传统液体电解质虽然具有较高的电导率和较好的界面润湿性,但其安全性能差。为了解决上述问题,固态电解质是一种很好的替代方法,它可以从根本上解决电解液泄漏问题,使其安全性得到极大改善。在目前大量的固态电解质中,复合固态电解质因其综合性能优异而被认为是有希望的候选者。然而,复合固态电解质实际应用到固态锂金属电池中还需解决以下问题,包括低的离子电导率、电化学稳定性差以及在固态锂金属电池存在固-固界面接触性差的问题。基于上述问题,本文通过不同的策略改性聚环氧乙烷（PEO）聚合物基体制备复合固态电解质,研究了复合固态电解质在固态锂金属电池中的应用。论文的主要研究内容如下:（1）由Li_1.5Al_0.5Ti_1.5（PO₄）₃（LATP）陶瓷颗粒和PEO聚合物基体制备复合固态电解质。系统研究了LATP和复合固态电解质的结构、形貌和电化学性能结果显示,复合电解质离子电导率可达1.00×10^-4 S·cm^-1,锂离子迁移数为0.37,电化学窗口可达5.2 V。采用LiFePO₄作为正极的固态锂金属电池,在100次循环后,其可逆容量达到136.0 mA h g^-1,并具有优异的倍率性能。此外,锂对称电池可稳定运行1800 h。（2）研究了一种固定阴离子的复合固态电解质以保护锂金属阳极。复合固态电解质是由Li_6.7La₃Zr_1.7Ta_0.3O₁₂陶瓷填料、PEO和双三氟甲烷磺酸亚酰胺锂组成。复合固态电解质的电化学性能结果显示,其离子电导率可达1.7×10^-4 S·cm^-1,电化学稳定性窗可达5.4 V,锂离子迁移数为0.5。此外,陶瓷颗粒的均匀分布提高了复合固态电解质的热稳定性、机械强度和界面相容性。由于陶瓷颗粒的加入,电解质体系中的阴离子被固定,从而使锂金属均匀分布,抑制了锂枝晶的生长。采用LiFePO₄作为正极的固态锂金属电池,在200次循环后,其可逆容量达到139.4 mA h g^-1,并具有优异的倍率性能。（3）提出利用液体电解质的优点与固态电解质的刚性相结合的策略,制备了一种基于金属有机框架（MOFs）的独特纳米多孔结构,其中将液态电解质浸入MOFs材料的框架中以获得功能填料。当这些填料添加到PEO基体中时,复合固态电解质获得了优异的电化学性能,其离子电导率为1.47×10^-4 S cm^-1,,电化学窗口可达5.2 V和锂离子迁移数为0.47。此外,复合固态电解质获得了更好的界面相容性。采用LiFePO₄作为正极的固态锂金属电池,在200次循环后,其可逆容量达到135.4 mA h g^-1。（4）提出采用中空MOFs与离子液体相结合的策略获得多功能填料。研制了一种含离子液体的中空多孔纳米笼新型多功能填料。当这些填料分散在PEO聚合物基体中使复合固态电解质的电化学性能得到了提高(离子电导率1.91×10^-4 S cm^-1、电化学稳定窗口5.2 V和锂离子迁移数0.5)。此外,该复合固态电解质对锂金属的界面稳定性高达1600 h。即使在室温下,采用LiFePO₄作为正极的固态锂金属电池,在50次循环后,其可逆容量达到135.4 mA h g^-1。（5）为解决不可控的锂枝晶生长和不良的固-固界面接触,通过设计三维结构的复合固态电解质来解决此问题,该电解质由均匀分散在PEO聚合物基体中的聚丙烯腈纤维/陶瓷网络增强,构成三维电解质以形成连续传导路径。这种连续的框架不仅加快了锂离子的快速迁移,而且促进了锂金属均匀沉积,有效地抑制了锂枝晶的生长。复合固态电解质具有1.76×10^-4 S cm^-1的高离子电导率,5.2 V的宽电化学稳定窗口和0.53的高锂离子转移数。得益于结构优势,复合固态电解质在锂对称电池中稳定运行4000 h。采用LiFePO₄作为正极的固态锂金属电池,在1000次循环后,其可逆容量达到120.7 mA h g^-1。即使在室温下,电池仍可以稳定运行。此外,复合固态电解质在高压正极中表现出稳定的循环性能（6）为以更简单的方式来获得三维复合固态电解质,通过将PEO聚合物基体填充到3D玻璃纤维布框架中制备了三维复合固态电解质。这种独特的三维电解质具有坚固的网络结构,可保证玻璃纤维布均匀分布在PEO基体中。结果显示,复合固态电解质的物理和电化学性能均高于PEO电解质。凭借这些优势,锂对称电池在2000 h循环期间表现出稳定的循环性能。采用LiCoO₂和LiFePO₄作为正极的固态锂金属电池分别可以获得128.3 mA h g^-1和155.2 mA h g^-1的比容量（100次循环）。更多还原

【Abstract】 Rechargeable lithium-ion batteries are developed have become a research hotspot due to their high energy density.However,due to the increasing demand for high-energy-density portable electronic products and electric vehicles,conventional lithium-ion batteries have been difficult to adapt to the needs of a new generation of high-energy energy storage systems.Lithium metal is the most promising anode,and its advantages lie in its high theoretical specific capacity(3860 mA h g^-1)and extremely low potential（-3.040 V vs.standard hydrogen electrode）.However,due to the thermodynamic instability of lithium metal in conventional liquid electrolytes,lithium dendrites generated during the lithium plating/stripping process can pass through the separator and cause a short circuit in the battery,resulting in safety problems such as fire and explosion.Therefore,there are still serious challenges in designing lithium-ion batteries with high energy density and high safety.Although traditional liquid electrolytes have high electrical conductivity and good interfacial wettability,their safety performance is poor.In order to solve the above problems,solid-state electrolyte is a good alternative method,which can fundamentally solve the problem of electrolyte leakage and greatly improve its safety.Among the current large number of solid-state electrolytes,composite solid-state electrolytes are considered as promising candidates due to their excellent comprehensive properties.However,the practical application of composite solid-state electrolytes to solid-state lithium metal batteries still needs to solve the following problems,including low ionic conductivity,poor electrochemical stability,and poor solid-solid interfacial contact in solid-state lithium metal batteries.Based on the above problems,in this paper,composite solid-state electrolytes were prepared by modifying polyethylene oxide（PEO）polymer matrix by different strategies,and the application of composite solid electrolytes in solid lithium metal batteries was studied.The main research contents of the paper are as follows:（1）A composite solid electrolyte was prepared from Li_1.5Al_0.5Ti_1.5（PO₄）₃（LATP）ceramic particles and PEO polymer matrix.The structures,morphologies,and electrochemical properties of LATP and composite solid-state electrolyte were systematically investigated.The results show that the ionic conductivity of the composite electrolyte can reache 1.00×10^-4 S·cm^-1,the lithium ion transference number is 0.37,and the electrochemical window can reach 5.2 V.The solid-state lithium metal battery using LiFePO₄ as cathode achieves a reversible capacity of 136.0 mA h g^-1 after100 cycles and exhibits excellent rate capability.（2）An anion-immobilized composite solid-state electrolyte was investigated to protect lithium metal anodes.The composite solid-state electrolyte is composed of Li_6.7La₃Zr_1.7Ta_0.3O₁₂ ceramic fillers,PEO,and bistrifluoromethanesulfonimide lithium salt.The electrochemical performance results of the composite solid-state electrolyte show that its ionic conductivity can reach 1.7×10^-4 S·cm^-1,the electrochemical stability window can reach 5.4 V,and the lithium ion transference number is 0.5.In addition,the uniform distribution of ceramic particles improves the thermal stability,mechanical strength,and interfacial compatibility of composite solid-state electrolyte.Due to the addition of ceramic particles,the anions in the electrolyte system are fixed,so that the lithium metal is uniformly distributed and the growth of lithium dendrites is suppressed.The solid-state lithium metal battery using LiFePO₄ as the cathode achieves a reversible capacity of 139.4 mA h g^-1 after 200 cycles,and exhibits excellent rate performance.（3）A strategy to exploit the advantages of liquid electrolytes combined with the rigidity of solid electrolytes is proposed to fabricate a unique nanoporous structure based on metal-organic frameworks（MOFs）,in which liquid electrolytes are immersed into the MOF materials to obtain functionalities filler.When these fillers are added to the PEO matrix,the composite solid-state electrolyte achieved excellent electrochemical performance with an ionic conductivity 1.47×10^-4 S cm^-1,an electrochemical window up to 5.2 V and a lithium ion transference number of 0.47.In addition,the composite solid-state electrolyte obtained better interfacial compatibility.The solid-state lithium metal battery using LiFePO₄ as the cathode achieves a reversible capacity of 135.4 mA h g^-1 after 100 cycles.（4）A strategy of combining hollow MOFs with ionic liquids is proposed to obtain multifunctional fillers.A novel multifunctional filler with hollow porous nanocages containing ionic liquids was developed.When these fillers were dispersed in the PEO polymer matrix,the electrochemical performance of the composite solid electrolyte was improved(ionic conductivity 1.91×10^-4 S cm^-1,electrochemical stability window of 5.2V and lithium ion transference number of 0.5.In addition,the interfacial stability of the composite solid-state electrolyte towards Li metal is as high as 1600 h.Even at room temperature,the solid-state lithium metal battery using LiFePO₄ as the cathode achieves a reversible capacity of 128.2 mA h g^-1 after 50 cycles.（5）To address the uncontrollable Li dendrite growth and poor solid-solid interfacial contact,this problem was addressed by designing three-dimensionally composite solid-state electrolyte composed of polyacrylonitrile uniformly dispersed in a PEO polymer matrix.The fiber/ceramic network is reinforced to form a three-dimensional electrolyte to form a continuous conduction path.This continuous framework not only accelerates the rapid migration of Li ions,but also promotes the uniform deposition of lithium metal,effectively suppressing the lithium dendrite growth.The composite solid-state electrolyte exhibits a high ionic conductivity of1.76×10^-4 S cm^-1,a wide electrochemical stability window of 5.2 V,and a high lithium ion transference number of 0.53.Benefiting from the structural advantages,the composite solid-state electrolyte can operate stably for 4000 h in lithium symmetric batteries.The solid-state lithium metal battery using LiFePO₄ as the cathode achieves a reversible capacity of 120.7 mA h g^-1 after 1000 cycles.The battery operates stably even at room temperature.In addition,the composite solid-state electrolyte exhibits stable cycling performance in high-voltage cathodes.（6）To obtain a 3D composite solid electrolyte in a simpler way,a 3D composite solid electrolyte was prepared by filling the PEO polymer matrix into a 3D glass fiber cloth frame.This unique three-dimensional electrolyte has a robust network structure that ensures uniform distribution of the glass fiber cloth in the PEO matrix.The results show that the physical and electrochemical properties of the composite solid-state electrolyte are higher than that of the PEO electrolyte.With these advantages,the lithium symmetric battery exhibits stable cycling performance during 2000 h cycling.Solid-state lithium metal batteries using LiCoO₂and LiFePO₄ cathodes can achieve specific capacities of 128.3 mA h g^-1 and 155.2 mA h g^-1（100 cycles）,respectively.更多还原