关键词： solid-state electrolytes   space-charge models   Li-ion batteries   polymer-ceramic electrolyte   molecular dynamics   solid-solid interface   GSHMC  

摘要： Unlocking the full potential of solid-state electrolytes (SSEs) is key to enabling safer and more-energy dense technologies than today's Li-ion batteries. In particular, composite materials comprising a conductive, flexible polymer matrix embedding ceramic filler particles are emerging as a good strategy to provide the combination of conductivity and mechanical and chemical stability demanded from SSEs. However, the electrochemical activity of these materials strongly depends on their polymer/ceramic interfacial Li-ion dynamics at the molecular scale, whose fundamental understanding remains elusive. While this interface has been explored for non-conductive ceramic fillers, atomistic modeling of interfaces involving a potentially more promising conductive ceramic filler is still lacking. We address this shortfall by employing molecular dynamics and enhanced Monte Carlo techniques to gain unprecedented insights into the interfacial Li-ion dynamics in a composite polymer-ceramic electrolyte, which integrates polyethylene oxide plus LiN(CF3SO2)(2) lithium imide salt (LiTFSI), and Li-ion conductive cubic Li7La3Zr2O12 (LLZO) inclusions. Our simulations automatically produce the interfacial Li-ion distribution assumed in space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and experimental measurements of tensile strength and ionic conductivity, we are able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold. Our results pave the way for the computational modeling of other conductive filler/polymer combinations and the rational design of composite SSEs.

关键词： all‐   solid‐   state lithium batteries   composite polymer electrolytes   exfoliation   layered double hydroxide   room temperature  

摘要： Solid electrolytes are the most promising substitutes for liquid electrolytes to construct high-safety and high-energy-density energy storage devices. Nevertheless, the poor lithium ion mobility and ionic conductivity at room temperature (RT) have seriously hindered their practical usage. Herein, single-layer layered-double-hydroxide nanosheets (SLN) reinforced poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composite polymer electrolyte is designed, which delivers an exceptionally high ionic conductivity of 2.2 x 10(-4) S cm(-1) (25 degrees C), superior Li+ transfer number (approximate to 0.78) and wide electrochemical window (approximate to 4.9 V) with a low SLN loading (approximate to 1 wt%). The Li symmetric cells demonstrate ultra-long lifespan stable cycling over approximate to 900 h at 0.1 mA cm(-2), RT. Moreover, the all-solid-state Li|LiFePO4 cells can run stably with a high capacity retention of 98.6% over 190 cycles at 0.1 C, RT. Moreover, using LiCoO2/LiNi0.8Co0.1Mn0.1O2, the all-solid-state lithium metal batteries also demonstrate excellent cycling at RT. Density functional theory calculations are performed to elucidate the working mechanism of SLN in the polymer matrix. This is the first report of all-solid-state lithium batteries working at RT with PVDF-HFP based solid electrolyte, providing a novel strategy and significant step toward cost-effective and scalable solid electrolytes for practical usage at RT.

关键词： Lithium battery   Solid-state electrolyte   Composite   Oxygen vacancy   Lithium ion   Ion transport  

摘要： Perovskite Li-3x La2/3-x TiO3 (LLTO) nanofibers have been heat-treated in the hydrogen-containing atmosphere and then incorporated with the poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a composite electrolyte. Hydrogen treatment has created oxygen vacancies in the LLTO nanofibers, which has reduced the activation energy of Li ion transport along intra-grains and inter-grains, leading to an improvement in the ion conductivity of LLTO nanofibers. Hydrogen treatment of the LLTO nanofibers has also enhanced the chemical interaction between the LLTO nanofibers and the polymer matrix in the composite electrolyte, and favored the Li ion transport at the nanofiber/polymer interface, improving the ion conductivity of the composite electrolyte to 3.4 x 10(-4) S/cm at room temperature. As a result, the Li|composite-electrolyte|Li half-cell exhibits good stability during lithium plating/stripping cycling at room temperature, showing an overpotential of -91 mV at a constant current density of 0.5 mA/cm(2). The full-cell battery with the composite electrolyte, lithium metal anode and lithium iron phosphate cathode shows excellent rate capacity and cycling performance.

关键词： 复合电解质   聚氧化乙烯   金属-有机框架材料   锂金属电池  

摘要： 固态聚合物电解质具有柔韧性好和易于加工的优势,可制备各种形状的固态锂电池,杜绝漏液问题。但固态聚合物电解质存在离子电导率低以及对锂金属负极不稳定等问题。本研究以纳米金属-有机框架材料UiO-66为聚合物电解质的填料,用于改善电解质的性能。UiO-66与聚氧化乙烯(poly(ethylene oxide),PEO)链上醚基的氧原子的配位作用以及与锂盐中阴离子的相互作用,可显著提高聚合物电解质的离子电导率(25℃,3.0×10^(-5)S/cm;60℃,5.8×10^(-4)S/cm),并将锂离子迁移数提高至0.36,电化学窗口拓宽至4.9V。此外,制备的PEO基固态电解质对金属锂具有良好的稳定性,对称电池在60℃、0.15mA·cm^(-2)电流密度下可稳定循环1000h,锂电池的电化学性能得到显著改善。

关键词： Hybrid solid polymer electrolyte   Lithiated nanosheets   Li+ conducting highways   Mechanical stability   All-solid-state lithium metal battery  

摘要： Solid-state electrolyte is a key component of high-energy-density and security all-solid-state lithium metal battery. However, the present solid polymer electrolyte (SPE) often suffers from the trade-off between ionic conductivity and mechanical stability. To this end, lithiated polydopamine-modified graphene oxide nanosheets (LiDGO) are fabricated, and incorporated into the representative poly(ethylene oxide) (PEO) matrix to prepare hybrid solid polymer electrolyte (HSPE). Despite the decreased crystallinity of PEO, the intrinsic advantage of organic-inorganic hybridization affords PEO-based HSPE highly improved mechanical stability. The tensile strength and elongation at break of HSPE are, respectively, 237% and 133% higher than those of blank PEO. The constructed long-range conduction pathways with locally concentrated Li+ at PEO-LiDGO interfaces impart HSPE highly enhanced ionic conductivity. The ionic conductivity reaches 3.4 x 10(-5 )S cm(-1) at 30 degrees C, 10 times higher than that of blank PEO. These then bring excellent battery performances. The assembled battery achieves a discharge capacity of similar to 156 mAh g(-1) after 200 cycles with ultra-high capacity retention of 98.7%. The strategy of utilizing lithiated nanosheets to address the trade-off between ionic conductivity and mechanical stability of SPE may pave the way for the development of high performance all-solid-state lithium metal batteries.

关键词： Solid-state electrolytes   LLTO nanofibers   Gradient design   Composite polymer electrolytes   Multilayered structure   Li metal batteries  

摘要： Solid-state composite polymer electrolytes (CPEs) are promising for solving the safety problem of lithium metal batteries. However, the CPEs with comparable thickness (10 mu m), improved ion conductivities and excellent mechanical strength are great challenges. In the present study, ultrathin (9.6 mu m), flexible, mechanically strong, and sandwiched structure solid-state electrolytes (SSEs) are fabricated by a tape casting process, involving the 75 wt % LLTO/PVDF-CPE (LLTO-75) layer designed as intermediate layer sandwiched by two 15 wt % LLTO/PVDF-CPE (LLTO-15) layers. The LLTO-15 is a soft, stable layer on upper and lower sides that could create excellent interfacial contact with electrodes, and LLTO-75 possesses physical rigidity that could inhibit the Li dendrites growth. The balancing between the excellent interfacial contact of LLTO-15 and the inhibition of lithium dendrites growth of LLTO-75 gives sandwiched SSE a high ionic conductivity (4.7 x 10(-4) S cm(-1)) at room temperature, an excellent mechanical strength (7.2 MPa), and uniform Li plating/stripping. When coupled with LiFePO4 and Li metal, the battery assembled with sandwiched SSE maintains 91.7% of its capacity and 99.7% of the Coulombic efficiency, after 1000 cycles. Our study suggests that the proposed sandwiched structure SSE is one of the alternatives for high performance solid-state LMBs.

关键词： poly(ethylene glycol) grafted polymer-like quantum dot   poly(ethylene oxide)   Hybrid polymer electrolyte   Ion-conductive network   All-solid-state lithium battery  

摘要： Solid-state polymer electrolytes (SPEs) show great potential owing to inherent flexibility and safety but limited by the low ionic conductivity. Herein, poly (ethylene glycol) grafted polymer-like quantum dots (PPQDs) with average diameter of similar to 2.5 nm and abundant conduction groups are synthesized as nanofillers for hybrid polymer electrolytes. The functionalization of poly (ethylene glycol) provides abundant Li+ transfer sites and meanwhile enhances the compatibility between PPQDs and poly (ethylene oxide) (PEO). Accordingly, these PPQDs uniformly disperse and form rich networks with PEO chains to effectively reduce the crystallinity of PEO and promote the dissociation of lithium salts, different from large-size or inorganic fillers. Consequently, efficient ion-conductive networks are constructed by PPQDs and PEO for vertical Li+ conduction: 5.53 x 10(-5) S cm(-1) at 30 degrees C, 16 times higher than that of PEO electrolyte. Furthermore, the hydrogen-bonding interactions at PPQD-PEO interfaces afford excellent stability and flexibility to electrolytes. And superior cycling performance of similar to 146 mAh g(-1) after 150 cycles at 1.0C with capacity decay of 0.046% per cycle is therefore achieved. Compared with traditional fillers, PPQDs with inherent advantages, i.e., molecular-level size and designable groups, endow hybrid electrolytes with dramatically enhanced ion conduction and stability, manifesting great potential for all-solid-state lithium batteries.

关键词： 聚合物固态电解质   微相分离   锂金属电池   嵌段构型  

摘要： 在对具有高能量密度和长寿命的能量存储和转换系统迫切需要情势的推动下,高安全性、绿色化、实用性二次能源产业方兴未艾。具有高安全系数、高电化学性能及高机械性能的固态聚合物电解质正逐渐取代传统液态电池。本文主要基于固态电池能源系统存在机械性能差、电化学性能不理想缺陷对单体PEGMA-CH3、1-乙烯基咪唑离子液体的聚合设计了两种不同的方案路线,从而获得性能卓越的固态电解质且实现其在实用储能设备的广泛应用。具体研究工作如下:（1）将PEGMA及良好化学性质的咪唑基聚合离子液体自由基聚合（ATRP）,接支引入PEO框架,成功制备了具备自修复特性及含二元嵌段结构电解质固态膜PEO@BPIL和PEO@RPIL。新型电解质具有更多的无定形结构和更高的聚合物链段迁移混合动力。除了降低PEO的结晶度外,醚键和咪唑阳离子的协同作用有利于提供连续的快速锂离子传输通道,使锂离子传输数高达0.63。优异的电化学窗口和离子电导率可以达到5.0 V（***+/Li）和2.2×10-4 S·cm-1（60℃）。组装的锂金属电池在0.2 C下具有160 m Ah·g-1的高放电容量。超长稳定的极化循环测试图进一步阐明了聚合离子液体和咪唑电化学特性出色的协同作用和高水平的锂枝晶防御能力,使PEO@PPIL-3-SPE成为界面性能杰出的固态聚合物电解质。（2）以改性后的大分子刷状结构溴化纤维素为引发剂,对单体PEGMA-CH3、离子液体1-乙烯基咪唑进行嵌段式聚合,支链上大量醚键和离子液体的引入,使电解质的性能结果量级化上升,所测的锂离子迁移数(t Li+)最高为0.32,电化学窗口已超越5.0 V vs Li/Li+（60℃）。这归因于聚合物中的刷状结构有利于形成更多的且分布均匀离子通道,减小离子迁移阻力。且单体PEGMA-CH3和咪唑型离子液体（IL）上就有大量带电基团和醚键,有利于解离锂盐。上述的特性使得基于CB-PEGMA@IL-SPE所装的Li Fe PO4/Li电池表现出优异的长循环能力（超过150次循环）和良好的速率容量。刷状柔性优良的CB-PEGMA@IL-SPE为制备可穿戴高新电子设备提供了可行性的渠道。

关键词： PVC基聚合物电解质   LATP无机电解质   界面   全固态锂电池  

摘要： 随着便携式电子产品与新能源汽车的广泛应用,人们对锂离子电池的研究也日益深入。其中,全固态锂电池由于其高安全性和高能量密度而备受关注。然而,由固体电解质与电极接触引起的界面问题成为阻碍固态锂电池发展的主要因素。针对界面问题,本论文从聚碳酸亚乙烯酯(PVC)聚合物电解质和Li1.3Al0.3Ti1.7(PO4)3(LATP)无机固体电解质出发,展开了深入研究。首先,通过添加磷酸三甲酯(TMP)增塑剂,改善了 PVC聚合物电解质/锂金属负极之间的界面接触,有效抑制了锂枝晶的生长。其次,在LATP无机固体电解质与正负电极间原位引入PVC+TEGDME(四甘醇二甲醚)聚合物,改善了无机固体电解质与电极之间的界面接触,大大降低了界面电阻,同时有效阻止了 LATP被Li电极还原。具体的研究内容如下:(1)在纤维素膜的支撑下,以VC为单体、TMP为增塑剂,通过原位聚合方法制备得到PVC-TMP固体电解质。实验探究了不同含量TMP对电解质的影响。随着TMP含量的增加,离子电导率逐渐增大,电化学稳定窗口和锂离子迁移数呈现先增大后减小的趋势。TMP的引入降低了PVC的聚合度,加快了 PVC链段的运动,且TMP有利于锂盐的解离。当加入10 wt%TMP时,电解质的离子电导率为2.54×10-5 S cm-1(50℃)。另外,TMP的存在增加了 PVC的柔韧性,改善了 PVC与锂负极的接触。基于PVC-TMP聚合物电解质的固态锂电池在50℃下的初始阻抗仅为118Ω。Li/PVC-TMP/Li 电池在 50℃、0.05 mA cm-2 下在 1000 h 内表现出稳定的循环。LiFePO4/PVC-TMP/Li电池在0.5 C下循环150圈后的容量保持率为79.7%。(2)以商业化的LATP粉末为原料,将其压制成LATP陶瓷片,进而烧结。首先,对LATP陶瓷片的烧结温度和时间进行了探究。结果表明,烧结温度和时间分别为850℃、2 h时,得到LATP陶瓷片晶粒适中,晶界较少,且没有杂质相。其次,在LATP电解质与电极间原位引入PVC+TEGDME聚合物电解质。与纯LATP基固态锂电池相比,被修饰后的LATP基固态锂电池在50℃下的初始阻抗从5925Ω降低至286Ω。Li/LATP-PVC+TEGDME/Li 电池在 50 ℃、0.09 mA cm-2 下在 350 h 内表现出稳定的循环,极化电压仅为0.0035 V。LiFePO4/LATP-PVC+TEGDME/Li电池在0.5 C下100圈后仍有94%的容量。此外,在50℃下,NCM811/LATP-PVC+TEGDME/Li电池在0.1 C下的平均放电比容量为181.4 mAh g-1。

关键词： 锂离子电池   原位电化学聚合   聚甲基丙烯酸三氟乙酯   高压三元NCM811   界面工程  

摘要： 锂离子电池（LIBs）因其高能量密度、长循环寿命、低自放电和长储存寿命而广泛应用于便携式电子产品、电动汽车、电网存储、空间探索和国防等领域。然而,其低安全性和能量密度瓶颈仍是阻碍其发展和应用的巨大挑战。作为新一代锂离子电池技术,固态电池中固态电解质的应用不仅避免了传统有机电解液的易燃易泄露的问题,而且可以有效抑制锂枝晶的生长,使得锂金属负极的应用成为可能。因此,高电压固态锂金属电池被认为是下一代兼具安全性和高能量密度的动力电池体系。但是,在高比能固态锂金属电池的开发中,高电压正极与固态电解质之间的固-固界面问题限制了电池的性能。正极-电解质界面层（Cathode Electrolyte Interphase,CEI）构筑技术,是目前正极界面工程中最具应用前景的工艺之一。传统界面缓冲层构筑技术中,以叠层法最为常见。但由于电解质材料制备过程的独立性,组装过程的二次接触会导致界面阻抗的增大,原位聚合法的出现解决了这一问题,然而,在现有以热、光、辐射作为引发条件的原位聚合技术中,引发剂的添加增加了界面组分的复杂性,将导致副反应的发生。为解决以上问题,本文提出了原位电化学聚合法构筑耐高电压缓冲层的界面修饰技术,本方法无需使用引发剂,在电池内部引发聚合反应实现缓冲层的原位构筑,为高比能固态锂金属安全电池的开发提供了设计思路。本文的主要研究内容包括:1、以基于高镍三元正极LiNi0.8Co0.1Mn0.1O2（NCM811）/聚氧化乙烯（PEO）基电解质/Li的固态电池的正极界面为研究对象,通过原位电化学聚合构筑了耐高电压的聚甲基丙烯酸三氟乙酯基凝胶正极界面缓冲层（Gel-PTFEMA）。对电池的电化学性能进行测试与表征,并初步探讨了界面优化机理。研究发现,凝胶聚甲基丙烯酸三氟乙酯（Gel-PTFEMA）缓冲层的引入,有利于减小正极-电解质的界面阻抗,提升离子电导率。室温下经改性的Gel-PTFEMA-PEO电解质的离子电导率在室温下可达0.65×10-4 S cm-1,60℃下可达3.91×10-4 S cm-1。同时,Gel-PTFEMA具有良好抗氧化能力,使PEO基的固态电解质的电化学窗口拓宽至5.0 V,提高了电池在高电压下的循环稳定性。经界面优化的NCM811-Li电池在60℃,0.1C条件下,首圈放电容量达到212.6 m A h g-1,50次充放电循环后,容量保持率为74.0%。2、为了进一步降低电池的整体安全隐患,本文进一步通过电化学本体聚合,在不添加溶剂和电解液的条件下,在NCM811/PEO/Li电池的正极界面处原位构筑了聚甲基丙烯酸三氟乙酯（PTFEMA）全固态缓冲层。结果表明,无溶剂参与、且以电化学引发的本体聚法同样能形成连续的耐高电压离子导电网络,为锂离子提供有效传输通道。PTFEMA-PEO电解质的离子电导率在室温下为1.02×10-4 S cm-1,60℃下为4.72×10-4 S cm-1,电化学窗口被拓宽至5.1V。NCM811/PTFEMA-PEO/Li电池在高电压下优异的循环稳定性。在0.1C,60℃下首次放电容量达到179.8 m A h g-1,50次充放电循环后,容量保持率66.6%。这说明PTFEMA全固态界面层的构筑有效地改善了高电压正极和全固态PEO电解质之间的界面稳定性。本文从电化学溶液聚合和电化学本体聚合两种方法,在NCM811/PEO/Li电池体系中原位构筑了耐高电压的聚合物界面缓冲层,降低界面阻抗的同时还提高了高电压下正极材料的结构稳定性,为高比能固态锂电池中正极界面优化提供了新的设计思路。另一方面,在电池制备过程中加入液态单体,通过电化学引发原位构筑聚合物界面层,该方法工艺简单、成本低,可以与传统电池制造工艺相匹配,是一种具有商业应用潜力的界面构筑方法。