关键词： Solid polymer electrolyte   Theoretical calculation   Functional groups   In-situ interfacial modification   All-solid-state lithium battery  

摘要： Solid polymer electrolytes (SPEs) have great potential to solve the safety issue of lithium batteries, nevertheless, the design of SPE with well comprehensive performance has always been a formidable challenge. As we know, in the polymer different groups have different functions, and there are complex interactions between them. Hence, the roles of various functional groups in electrolytes is too complex to be clearly understood, which restricts the structural design of SPE by experience. Herein, theoretical calculations are conducted in designing polymer electrolyte with dual functional groups of ethylene carbonate (EC) and ethyoxyl (EO) group, revealing the interaction between lithium ions and different groups as well as the lithium ions migration mechanism. Designed SPE demonstrates high conductivity of 1.84 x 10(-4) S cm(-1) (30 degrees C), and wide electrochemical window of 4.75 V. Combining with in-situ interface modification technology, the SPE not only prolongs solid-state LiFePO4 (LFP)/Li battery cycle life to 600 cycles (110 mA h g(-1) retained), but also shows potential application in high energy density LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode and Si anode batteries. In this work, theoretical calculation is demonstrated to be a high effective method for constructing the functional groups of polymer electrolyte matrix.

关键词： Solid lithium battery   Solid polymer electrolyte   Free-standing polymer electrolyte   Room-temperature solid battery  

摘要： This study reports a networked solid polymer electrolyte (N-SPE) containing no solvent, ionic liquid, oligomer, or semisolid additives for lithium-ion batteries (LIBs). The N-SPE comprises a lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt as well as a polymer framework constructed using cage-like polyhedral oligomeric silses-quioxane (POSS) and serving as hubs to network poly(ethylene oxide-co-polypropylene oxide) (P(EO-co-PO)) chains. The networking prevents polymer chain twisting that hinders ion transport. Raman analysis indicates that the POSS hubs improve the dissociation of LiTFSI and localize TFSI- anions. The N-SPE exhibits a low glass transition temperature of -43 degrees C, a high 25 degrees C ionic conductivity of 1.1 x 10(-4) S cm(-1), and a small activation energy of 3.5 kJ mol(-1) for ion conduction. The localization of TFSI- results in a high lithium transference number of 0.62, which is determined to be beneficial to Li+ transport. By incorporating the N-SPE into the LiFePO4 cathode and using a free-standing N-SPE membrane, this study assembles a Li vertical bar N-SPE vertical bar LiFePO4 battery, which delivers a high capacity of 160 mAh g(-1) at 25 degrees C and exhibits excellent charge-discharge cycling stability. The free-standing feature of the N-SPE makes roll-to-roll assembly of LIBs readily scalable for industrial applications.

关键词： Solid-state batteries   Lithium batteries   Polymer electrolyte   Room temperature   Electrolyte/electrode interface  

摘要： Safe and efficient utilization of electrochemical energy is of prime importance for e-mobility and sustainable development of the current society. Solid state batteries (SSBs) have emerged as one of the most promising solutions to address aforementioned challenges due to the replacement of conventional liquid electrolytes with inherently safer solid electrolytes. Polymer electrolyte (PE)-based SSBs have better processability and flexibility than inorganic electrolyte-based ones;however, the room temperature (RT) operation of the PE-based SSBs remains as one of the most critical issues. Herein, a nanofiber-reinforced polymer electrolyte (NRPE) comprising of poly(vinylidene fluoride) fibers along with a high molecular weight though flowable polymer matrix is proposed as an innovative electrolyte for SSBs. These NRPEs are self-standing, highly conductive, and stable against Li metal (Li degrees) electrode, endowing the Li degrees parallel to LiFePO4 cells with good performances at operational temperatures down to RT. The outstanding physicochemical and electrochemical properties of NRPEs make them as appealing candidates for attaining high-performance SSBs.

关键词： 固态电池   聚合物电解质   功能基元   锂金属   离子电导率  

摘要： 相对于液体电解质有机溶剂渗漏、易燃等缺陷,以及无机固态电解质制备工艺复杂、界面相容性和力学性能差等弊端,聚合物电解质具有无液体渗漏、力学性能及界面相容性良好、形状尺寸可调节和制备工艺简单等优点,更适用于高能量密度固态锂电池。然而,目前已报道的聚合物电解质综合性能难以满足高能量密度固态锂电池需求,依然存在诸多问题,如离子电导率和离子迁移数较低、电化学窗口窄等,这些问题尚待深入研究解决。本论文工作重点是开发具有高离子电导率、宽电化学窗口、对电极材料具有良好界面相容性的新型聚合物电解质,为聚合物电解质在固态锂电池的实际应用提供理论基础和实验支持。（1）设计制备了由柔性聚乙二醇（PEG）和刚性六亚甲基二异氰酸酯三聚体（HDI）功能基元构成的嵌段聚合物电解质（BC-SPE）。HDI由六甲撑和极性基团异氰酸酯基组成,分子链属性为刚性链段,具有良好机械强度和热稳定性。PEG主链由聚环氧乙烷非极性基团组成,分子链属性为柔性链段,醚键能与Li+发生络合-解络合,是Li+传输的主要运动路径。通过改变PEG和HDI功能基元比例R(R=9（）)9（）)),可调控BC-SPE聚合物电解质的综合性能。随着R值的增加,BC-SPE的拉伸强度、邵氏硬度、电化学窗口和界面阻抗都会降低,离子电导率会增加。当R为1.87时,离子电导率为5.7?10-4 S cm-1（55℃）、电化学窗口>4.65 V,与磷酸铁锂组装成固态锂电池,在1 C倍率下可稳定循环100圈,放电比容量保持率为86%,库伦效率接近99%。根据固态电池实际需求可通过改变R值来调控BC-SPE聚合物电解质性能。（2）设计制备了具有聚环氧丙烷和硅氧烷特性的硅烷封端聚环氧丙烷聚合物电解质（MS-SPE）。硅烷封端聚环氧丙烷预聚体（MS）主链含有大量醚键,可以为锂离子的传输提供运动路径;封端基团为甲氧基硅烷,可以降低聚合物结晶性,提高无定型区域外,还可以发生脱水缩合反应,形成三维网状结构,提高聚合物电解质的力学性能和热稳定性。MS-SPE的室温离子电导率为3.6?10-4 S cm-1、离子迁移数为0.65、电化学稳定窗口>5 V,相比于聚环氧乙烷显著提高。MS-SPE与磷酸铁锂组装成固态锂电池,室温3 C倍率下循环650圈后容量没有衰减,库伦效率接近99.7%。MS-SPE制备工艺简单、机械性能好、易批量生产并有助于消除电池内部的短路隐患,提高锂电池的安全性。（3）设计制备了聚碳酸乙烯亚乙酯宽温聚合物电解质（PVEC-SPE）。PVEC-SPE结构中极性基团[-O-（C=O）-O-]可以促进锂盐电离,羰基（C=O）可以与Li+发生络合-解络合作用,构筑Li+传输路径。通过设计小分子低聚物和大分子高聚物复合结构,实现了微量小分子低聚物提高PVEC-SPE与电极材料界面相容性,而大分子高聚物提高PVEC-SPE的热稳定性和力学性能目的。优化后PVEC-SPE在室温和零下15℃的离子电导率分别为2.1?10-3 S cm-1和2.28?10-4 S cm-1。通过VEC原位聚合与磷酸铁锂正极材料形成低阻抗界面,组装成的固态锂电池可在室温和低温下工作,室温下1 C倍率循环100圈后容量为在140 m A h g-1,容量保持率为99%。原位聚合制备PVEC-SPE固态锂电池,制备方法简单易行,无污染,得到的电解质膜结构均匀,适用于不同尺寸和形状的能量器件。

关键词： 聚合物固体电解质   固态锂电池   离子电导率   空间电荷层理论   界面电阻   原位聚合   Li6.25Ga0.25La3Zr2O12  

摘要： 近年来,锂离子电池成功地应用于动力汽车和消费电子等领域。然而,传统的锂离子电池主要使用的是有机液态电解质,不可避免地带来电解质的泄露、燃烧等安全风险。另外,使用石墨负极的传统锂离子电池的能量密度已经达到了其理论极限值,无法满足目前的储能需求。由于具有优秀的安全性,用固体电解质替代液体电解质有望彻底解决锂离子电池的安全问题。更重要的是,固态电池可以使用锂金属作为负极,以获得更高的能量密度。相比于陶瓷固体电解质,聚合物固体电解质具有机械柔性、易成膜、成本低以及更好的界面接触等优点。然而,聚合物固体电解质的离子电导率较低,电化学稳定性差。这些缺点限制了在固态电池的应用。为解决上述问题,我们开展了以下研究工作:(1)复合固体电解质的离子导电机理:将Li6.25Ga0.25La3Zr2O12(LLZO)纳米颗粒分散在聚氧化乙烯(PEO)中,制备了聚合物型PEO-LLZO复合固体电解质。PEO-LLZO复合固体电解质在30℃的电导率为7.2×10-5 S/cm,比PEO的电导率高约4个数量级。复合固体电解质电导率的提高主要与PEO/LLZO界面处的空间电荷层有关。根据TEM观察,空间电荷层的宽度约为3 nm。利用相场理论计算了缺陷在空间电荷层的浓度和分布,并揭示了空间电荷层的形成过程。进一步,我们构建了随机电阻模型,并利用蒙特-卡罗方法模拟了复合固体电解质中锂离子的传导;结果表明,复合固体电解质电导率的提高是由于渗流效应,连续的空间电荷层为锂离子传输提供了快速路径。(2)三维LLZO网络(3D-LLZO)复合固体电解质:制备了具有连续锂离子传输通道的3D-LLZO网络的复合固体电解质。其中,3D-LLZO是采用以聚氨酯泡沫为模板的有机泡沫浸渍法制备。由于具有连续交联的渗流通道,3D复合固体电解质在30℃时的离子电导率为1.2×10-4 S/cm,相比LLZO纳米颗粒复合固体电解质增加了 1倍。3D复合固体电解质离子电导的增加验证了空间电荷层理论的正确性。此外,3D复合固体电解质的迁移数、热稳定性、机械强度以及电化学稳定性也具有较大的提升。Li/3D复合固体电解质/Li对称电池可稳定循环超过360小时而不发生短路。此外,LiFePO4/3D复合固体电解质/Li全固态电池在0.5 C展示了优异的稳定循环性以及高放电比容量。(3)三维LLZO纳米纤维复合固体电解质:使用LLZO纳米纤维填料进一步优化了复合固体电解质的离子电导率。LLZO纳米纤维是通过静电纺丝制备而成,LLZO纳米纤维的直径约为120 nm。LLZO纳米纤维复合固体电解质的室温离子电导率为3.2×10-4S/cm,约为LLZO纳米颗粒复合固体电解质的4倍,并且复合固体电解质的电化学窗口达到4.8 V。Li/纳米纤维复合固体电解质/Li对称电池在0.45 mA/cm2电流密度下可稳定循环超过1500圈(1000 h),表现出了超强的抑制锂枝晶的能力。使用PEO-LiTF SI-LLZO替代PVDF作为粘结剂,设计了一种集成化的界面结构的全固态电池,优化了正极/电解质之间的界面接触,有效地降低了界面电阻。因此,LiFePO4/纳米纤维复合电解质/Li全固态电池在0.5 C的倍率下可以稳定循环800次,且放电比容量相对于最大值保持率高达90.4%。(4)原位聚合的复合固体电解质:利用液体电解质的聚合反应制备了一种新型的复合固体电解质。聚合的复合电解质(PCEs)在室温下的电化学稳定窗口可达6.5 V。此外,PCEs在30℃下的离子电导率为1.8×10-4 S/cm,锂离子迁移数为0.58。Li/PCEs/Li对称电池在0.5 mA/cm2下能稳定循环超过1000 h,与锂负极具有极好的相容性且有效地抑制了枝晶的生长。采用原位聚合方法,PCEs与正/负极均能保持共形的界面接触,固态电池的界面电阻约降低了一半。当PCEs 与 LiNi0.6Co0.2Mn0.2O2(NCM622)和 LiNi0.85Co0.05Al0.1O2(NCA)等高电压正极和Li负极相搭配时,固态电池表现了优异的电池性能:包括高比容量、库伦效率和较长的室温循环寿命。(5)原位聚合的准固体电解质:采用原位聚合策略,在电化学电池中原位引发液体电解质的聚合反应,制备了一种具有交联结构的准固体电解质。因此,准固体电解质与所有电极之间建立了超共形的界面接触,固态电池的界面电阻大幅度降低。此外,准固体电解质在室温离子电导率高达4.3×10-3 S/cm,Li+迁移数为0.55,电化学稳定窗口为5.2 V。在电池循环过程中,锂负极表面原位形成的富LiF的固体电解质中间相(SEI)层,有效地阻止了枝晶生长和锂负极的粉化。因此,NCA-Li、NCM622-Li固态锂金属电池可以实现在较大电流密度下充-放电,并能获得高的放电比容量和长的

关键词： 固态聚合物电解质   壳聚糖   聚环氧乙烷   离子电导率   电化学性能  

摘要： 相比于传统的有机电解液，固态聚合物电解质具有较高的安全性能，电化学稳定性，然而，固态聚合物电解质具有较低的离子电导率成为目前仍需要亟待解决的问题。聚环氧乙烷(PEO)作为聚合物电解质基体，由于PEO分子中存在醚氧基基团能够与锂离子络合，已经被广泛的研究。然而，PEO具有较好的结晶性，使得制备得到的聚合电解质具有较低的离子电导率。因此，采用与聚合物共混，加入增塑剂等方法破坏聚合物的结晶结构增加无定形态，从而提高固态聚合物电解质的离子电导率。　　壳聚糖分子中存在氨基和醚氧基基团，能够与锂离子络合，促进锂盐的解离。因此，本论文研究壳聚糖为基体的聚合物电解质。并采用溶剂挥发的方法，将不同质量分数的聚环氧乙烷(PEO)与壳聚糖溶液共混，并在室温下将混合溶液倒入聚四氟乙烯的模具中成膜，制备得到壳聚糖/PEO基聚合物电解质。通过对加入不同质量分数下的聚合物电解质进行XRD，机械性能，热稳定性性能以及离子电导率等测试，加入质量分数为33%的PEO制备得到的壳聚糖/PEO基聚合物电解质，由于壳聚糖与PEO分子间氢键的相互作用使得该质量分数下的聚合物电解质具有较高的机械性能和热稳定性能，并具有较多的无定形形态，其离子电导率达到6.8E-04Scm?1，电化学电压窗口达到~5V，锂离子迁移数为0.74。　　将33%质量分数下的PEO制备的壳聚糖/PEO基聚合物电解质组装成电池，正极为LiFePO4，负极为锂片，在室温下测试，采用0.1C的电流密度经过130圈充放电循环，其比容量达到120mAhg-1，其库伦效率达到90%以上。此外，将该聚合物电解质制备成软包电池，在压力和弯曲下，仍能点亮LED灯，说明该聚合物电解质具有较好的柔性。　　进一步研究了不同质量分数的纳米二氧化硅加入，制备得到的壳聚糖/PEO/SiO2基聚合物电解质，其离子电导率，机械性能，热稳定性以及电化学性能的影响。由于SiO2与聚合物之间的路易斯酸碱作用提高了聚合物电解质的机械性能以及热稳定性能，并且二氧化硅有利的酸性表面与锂盐中的阴离子相互作用，促进了锂盐的分解，为锂离子的迁移提供的路径。当加入质量分数为4%的纳米二氧化硅，制备得到的壳聚糖/PEO/SiO2基聚合物电解质具有较高的离子电导率，较好的机械性能，较高的锂离子迁移数以及较宽的电化学电压窗口。其离子电导率达到5.8E-04Scm-1，锂离子迁移数达到0.7，电化学电压窗口达到~5.3V。　　将质量分数为4%的纳米二氧化硅下制备得到的壳聚糖/PEO/SiO2基聚合物电解质组装成纽扣电池，在室温下，采用0.2C的电流密度，经过300圈循环充放电，其比容量达到100mAhg-1，其库伦效率达到95%以上。此外，将该聚合物电解质制作成软包电池，将其裁剪后，电压读数并未发生较大的变化，并且剪切后仍能点亮LED灯，说明加入无机纳米SiO2提高了聚合物电解质的电化学性能以及安全性能。因此，本论文制备壳聚糖基聚合物电解质为制备高能量密度的固态电池提供了参考。

关键词： 固态锂电池   聚合物电解质   界面   失效机制   表征技术  

摘要： 固态聚合物锂电池具有高能量密度和高安全性的优点,有望解决新能源汽车的续航里程焦虑和安全问题。但是,现有的固态聚合物锂电池存在容量衰减快、过充、产气、内短路、日历失效等电池失效问题。而且,由于聚合物电解质不耐辐照,其较强的界面黏附性使得电极/电解质界面难以剥离,导致缺乏合适的表征技术深入研究固态聚合物锂电池的失效机制,这极大的限制了科学家对电池失效机制的深入理解,制约了电池失效解决方案的发展。因此,本文从锂枝晶生长、正极结构演变与机械失效、界面微结构演变和界面反应、聚合物电解质结构变化的角度出发,回顾了固态聚合物锂电池失效机制及其表征技术的研究进展,阐述了固态聚合物锂电池失效机制的研究思路。

关键词： Polyethylene oxides  

摘要： Covalently networked polymers offer desirable non-crystallinity and mechanical strength for solid polymer electrolytes (SPEs), but the chemically active cross-links involved in their construction could deteriorate the compatibility with high-energy cathode materials that are electrophilic and/or in the charged state. Herein we reveal a strong dependence of cyclability of such cathodes on the reactivity of covalently networked SPEs and demonstrate a polymer design that renders these SPEs chemically inert. We designed and synthesized two hybrid networks, both with polyethylene oxide as the cation conducting component and polyhedral oligomeric silsesquioxane as the branch point, but respectively use alkylamino and chemically inert triazole groups as cross-links. All-solid-state cells using the alkylamino-containing SPE underwent rapid degradation while cells using triazole SPEs showed stable cycling.

关键词： Crosslinking   Solid polymer electrolyte   Electrochemical stability window   Integration method   All-solid-state lithium battery  

摘要： A new crosslinked copolymer electrolyte is prepared with a simply method. The optimal electrolyte presents a maximum conductivity of 1.15 x 10(-4) S cm(-1) at 60 degrees C. Especially, this new electrolyte presents an outstanding electrochemical stability not only for a wide electrochemical window (0-5.1 V) but also for a long-term compatibility with the Li metal. Due to electrochemical stability, LiMn0.2 Fe0.8PO4 is selected as cathode material cycling between 3 V and 4.25 V. Moreover, a convenient integration method is used in this work to enhance the interfacial contact between cathode and electrolyte. Finally, the all-solid-state battery LiMn0.2 Fe0.8PO4/Li shows a maximum capacity of 161.1 mAh g(-1) and an excellent capacity retention ratio of 94.5% after 100 cycles. This new crosslinked polymer electrolyte may provide useful insights for introducing high voltage cathode material rather than LiFePO4 only into solid polymer electrolytes system.

关键词： Solid-state electrolyte   Hybrid electrolyte   Lithium batteries   Vertically-aligned structure   Li dendrite  

摘要： All-solid-state lithium batteries (ASSLBs) assembled with solid polymer electrolytes (SPEs) have been regarded as promising next-generation rechargeable batteries with improved safety and high energy densities. However, the Li dendrites and poor Li+ transport greatly inhibit their practical applications when coupled with relatively high loading cathodes. Herein, we combine a glass fiber (GF)-reinforced composite polymer electrolyte based on poly(ethylene oxide) (labeled as PEO@GF) to suppress Li dendrite growth with a freeze-casted vertically-aligned (VL) electrode to facilitate Li+ transport in the high loading cathode. Benefiting from the enhanced mechanical strength and uniformed Li deposition enabled by the implanted GF, the Li-Li symmetric cells exhibit significantly improved cycling stability up to 2000 h (0.2 mA cm(-2), 0.2 mAh cm(-2)) and 1000 h (0.42 mA cm(-2), 0.4 mAh cm(-2)), which are over one order of magnitude longer than those of the pure PEO electrolyte. Furthermore, VL-LiFePO4 (LFP) cathode divides the thick electrode into numerous vertically-aligned "thin electrodes", which significantly decreases the Li+ transport distance and enables the Li vertical bar PEO@GF vertical bar VL-LFP cell with a high LFP loading of 10.5 mg cm(-2) to deliver a high areal capacity of 1.52 mAh cm(-2). The rational structure design of both electrolyte and electrode offers an opportunity for developing high-performance ASSLBs with high active material loadings.