检索问题
研究固态电池中界面反应、锂枝晶和接触损失时，常用哪些原位和非原位表征方法？请比较 EIS、XPS、SEM/TEM、cryo-TEM、ToF-SIMS、Raman、X-ray/中子成像等方法能回答的问题、适用场景、局限性和代表文献。要求能指导实验设计。
固态电池（ASSBs）因其高能量密度和增强的安全性，被认为是下一代电池技术的重要发展方向。然而，界面反应、锂枝晶形成以及接触损失是限制其大规模应用的关键挑战。为了深入理解这些问题并指导实验设计，研究人员广泛采用各种原位（in situ）和非原位（ex situ）表征技术来探测电池内部的微观结构、化学组成和电化学行为。以下将详细比较电化学阻抗谱（EIS）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）/透射电子显微镜（TEM）、冷冻透射电子显微镜（cryo-TEM）、飞行时间二次离子质谱（ToF-SIMS）、拉曼光谱（Raman）以及X射线/中子成像等方法，探讨它们在研究固态电池界面反应、锂枝晶和接触损失方面的能力、适用场景、局限性及代表性文献。
1. 电化学阻抗谱 (Electrochemical Impedance Spectroscopy, EIS)
- 能回答的问题: EIS是一种强大的电化学技术，用于研究电极/电解质界面的电荷传输动力学和阻抗特性。它可以提供关于界面电荷转移电阻、固体电解质界面（SEI）膜形成与演变、离子传输路径以及界面稳定性等信息。通过拟合等效电路模型，可以区分不同电化学过程的贡献，例如锂离子穿过SEI膜、电荷转移反应以及固态电解质/SEI界面的电阻。
- 适用场景: EIS特别适用于评估界面稳定性和动力学，尤其是在不同操作条件（如温度、电压、循环次数）下界面阻抗的变化。在半固态电池中，EIS已被用于深入理解复杂的电化学过程，发现除了Li+穿透SEI膜和电荷转移外，SE/SEI界面也存在额外电阻。这种方法对于研究新材料的界面兼容性、优化电池设计和预测电池寿命具有重要意义。例如，研究发现LiPON/LiCr0.05Ni0.45Mn1.5O4-δ界面的巨大电荷转移电阻导致5V级全固态电池性能不佳，通过介电BaTiO3纳米颗粒修饰界面可显著降低阻抗并提高倍率性能。
- 局限性: EIS的解析依赖于等效电路模型的选择和拟合，不同的模型可能导致不同的解释。此外，EIS是一种宏观技术，难以提供界面反应的微观形貌和化学信息。在复杂的多组分界面中，准确分离不同过程的阻抗贡献可能具有挑战性。
- 代表文献:
- Naguib等人使用EIS研究了液态电解质和石榴石固态电解质（LLZO）界面的反应，发现形成了自发反应层，其中包含富锂相和中间的Li-La-Zr氧化物。
- Yada等人利用交流阻抗分析揭示了5V级全固态电池中LiPON/LiCr0.05Ni0.45Mn1.5O4-δ界面的巨大电荷转移电阻（RLiPON/LNM > 107 Ω cm2），并通过BaTiO3纳米颗粒的介电修饰将其降低了四个数量级，从而显著改善了电池的倍率性能。
- Feng等人通过EIS研究了NCM523基半固态锂离子电池的界面动力学，揭示了Li+穿透SEI膜和电荷转移之外的额外电化学过程，并归因于SE/SEI界面的电阻。
2. X射线光电子能谱 (X-ray Photoelectron Spectroscopy, XPS)
- 能回答的问题: XPS是一种表面敏感的元素和化学态分析技术，可以提供材料表面几纳米深度的元素组成、化学键合状态和相对含量信息。在固态电池研究中，XPS常用于分析界面处的化学反应产物、SEI层的组成和结构，以及电极材料在循环过程中表面的化学变化。
- 适用场景: XPS特别适用于分析固态电解质和电极之间的界面反应产物，例如LiPON/LiCoO2界面在制造过程中的温度升高会导致LiPON网络结构改变和Co还原，从而增加界面阻抗。还可以用于研究SEI膜的形成和演变，以及其对离子传输和电池性能的影响。此外，结合深度刻蚀（depth profiling），XPS可以提供界面反应层的深度分布信息。例如，在NMC622和LLZO固态电解质的界面，XPS可以检测到在高温或高充电电压下形成的Ni2+和Co2+等还原态过渡金属物种。
- 局限性: XPS是一种非原位技术，需要将样品从电池中取出并进行制备，这可能会导致样品暴露在空气中而发生变化，从而引入伪影。它也只提供表面信息，对于深层或埋藏界面的分析能力有限，除非结合深度刻蚀。
- 代表文献:
- Iida等人使用XPS详细表征了LiPON/LiCoO2界面，揭示了制造过程中的温度升高导致LiPON网络结构变化和LiCoO2层中Co的还原，这导致了界面阻抗的增加。
- Kim等人使用XPS检测了NMC622阴极与LLZO固态电解质界面在高温（80 °C）和高电压（4.3 V）循环后形成的还原态过渡金属物种（Ni2+, Co2+），这些产物导致容量损失和电池效率降低。
- Naguib等人通过XPS深度分析，揭示了液态电解质与LLZO固态电解质界面形成了包含富锂相（如Li2CO3）和中间Li-La-Zr氧化物的自发反应层。
3. 扫描电子显微镜 (Scanning Electron Microscopy, SEM) / 透射电子显微镜 (Transmission Electron Microscopy, TEM)
- 能回答的问题: SEM和TEM是强大的形貌和结构表征技术。
- SEM 提供材料表面的高分辨率二维图像，可用于观察电极材料的颗粒形貌、尺寸分布、裂纹形成、枝晶生长以及界面处的形貌变化。结合能量色散X射线光谱（EDS），SEM还可以进行元素分布分析。
- TEM 提供更高的分辨率，可以观察材料的晶体结构、缺陷、纳米尺度的界面结构、SEI层的形貌和组成，以及枝晶的内部结构。高角环形暗场扫描透射电子显微镜（HAADF-STEM）结合EDS或电子能量损失谱（EELS）可以提供纳米尺度的元素映射和化学键合信息。
- 适用场景:
- SEM 常用于观察电池循环前后电极表面形貌的变化，例如锂金属负极上的枝晶生长，以及电极/电解质界面处的接触损失和裂纹形成。在硫化物基固态电池的有机复合正极中，SEM结合纳米压痕可以建立全面的化学-力学映射，将杨氏模量和硬度与锂分布联系起来。聚焦离子束扫描电子显微镜（FIB-SEM）可以进行三维重构，提供埋藏界面的形貌信息。
- TEM 适用于更精细的界面结构分析，例如研究SEI层的纳米结构、组成，以及锂枝晶的生长机制。它可以揭示电极颗粒内部的结构变化，如锂化/脱锂引起的相变和应力诱导的缺陷。
- 局限性: SEM和TEM都是非原位技术，样品制备可能非常复杂，尤其是对于对空气和电子束敏感的固态电池材料。样品制备过程也可能引入伪影。TEM的样品通常需要非常薄（几十到几百纳米），难以代表整个电池的宏观行为。
- 代表文献:
- Kim等人通过聚焦离子束扫描电子显微镜（FIB-SEM）观察了NMC622|LLZO界面在循环后出现的晶间裂纹和分层，这些机械失效导致容量降低和效率下降。
- Ai等人结合ToF-SIMS和SEM纳米压痕测量，对硫化物基固态电池的有机复合正极进行了化学-力学行为的系统定量研究，建立了杨氏模量、硬度和锂分布之间的关系。
- Hao等人综述了冷冻透射电子显微镜（cryo-TEM）和冷冻聚焦离子束（cryo-FIB）等先进电子显微镜技术在分析功能隔膜结构-电池电化学性能关系方面的应用。
- Huo等人结合结构和化学表征与理论模拟，通过SEM揭示了硅负极在固态电池中的化学-力学失效机制，包括SEI生长导致的电阻增加和脱锂过程中的微观空洞形成。
4. 冷冻透射电子显微镜 (Cryo-TEM)
- 能回答的问题: Cryo-TEM是一种在低温下对样品进行成像的TEM技术，可以有效减少电子束辐射损伤和样品污染，从而在接近自然状态下观察软物质、液体电解质中的SEI层以及锂枝晶的纳米结构和组成。它可以提供高分辨率的界面结构和化学信息，特别是对锂金属负极与电解质形成的脆弱且对电子束敏感的SEI膜和枝晶形态非常有利。
- 适用场景: Cryo-TEM特别适用于研究锂金属负极界面处的SEI形成机制和枝晶生长过程，因为这些物质对电子束非常敏感。例如，在电子漏斗介导的阴离子限制策略中，cryo-TEM断层扫描和ToF-SIMS映射揭示了富含LiF的裂纹状界面相，能够实现无枝晶锂沉积。通过冷冻技术，可以捕获瞬态的界面结构，避免传统TEM样品制备过程中可能引起的结构和化学变化。
- 局限性: 样品制备仍然复杂且耗时，需要专业的冷冻和转移设备。图像解析和数据分析也需要专业知识。作为非原位技术，仍然不能实时观察动态变化。
- 代表文献:
- Chen等人通过cryo-TEM断层扫描和ToF-SIMS映射，揭示了电子漏斗介导的阴离子限制策略在固态电池中形成的富含LiF的裂纹状界面相，该界面相能够实现超过11,000小时的无枝晶锂沉积。
- Hao等人强调了cryo-TEM在分析功能隔膜和人工SEI/CEI层结构与电池电化学性能之间关系中的作用，特别是在稳定固态电解质方面。
5. 飞行时间二次离子质谱 (Time-of-Flight Secondary Ion Mass Spectrometry, ToF-SIMS)
- 能回答的问题: ToF-SIMS是一种表面敏感的质谱成像技术，能够提供极高的表面化学灵敏度和横向空间分辨率（纳米到微米级）。它可以识别和映射材料表面和浅层（几纳米）的元素、分子和同位素分布，特别适用于探测界面处的微量化学组分和反应产物。
- 适用场景: ToF-SIMS在固态电池中常用于研究电极/电解质界面的化学组成和分布，例如检测界面处的锂、氧、氮、磷等元素以及有机或无机副产物。它可以提供锂离子传输路径、SEI层组成以及枝晶形成过程中化学物种分布的详细信息。结合深度刻蚀，可以获得界面反应产物的深度分布图，从而揭示界面层的多层结构。例如，在LiPON/LiCoO2界面研究中，ToF-SIMS用于揭示界面处的化学物种和化学组成，发现Co的还原可能是界面阻抗增加的原因。在硫化物基固态电池中，ToF-SIMS可以与纳米压痕结合，对复合正极的化学-力学行为进行定量映射，关联杨氏模量、硬度与锂分布。
- 局限性: ToF-SIMS是表面敏感的，对于深埋界面的分析需要深度刻蚀，这可能会对样品造成损伤。定量分析较为困难，且质谱数据的解释需要专业知识。同样，它也是非原位技术。
- 代表文献:
- Iida等人使用ToF-SIMS详细表征了LiPON/LiCoO2界面，提供了关于化学物种和化学组成的信息，并指出Co还原导致界面阻抗增加。
- Chen等人通过ToF-SIMS映射，结合cryo-TEM断层扫描，揭示了电子漏斗介导的阴离子限制策略在固态电池中形成的富含LiF的界面相，有助于抑制枝晶生长。
- Ai等人通过结合ToF-SIMS和SEM纳米压痕，对硫化物基固态电池的有机复合正极进行了高空间分辨率的化学-力学映射研究，连接了杨氏模量、硬度与锂分布。
6. 拉曼光谱 (Raman Spectroscopy)
- 能回答的问题: 拉曼光谱是一种无损的振动光谱技术，可以提供材料的分子结构、晶格振动和化学键合信息。在固态电池中，它可以用于识别电极和电解质材料的相变、副反应产物的形成、SEI层的组成以及锂枝晶的化学性质。
- 适用场景: 拉曼光谱可以用于原位研究电化学循环过程中电极材料的结构演变，例如石墨负极的锂化/脱锂过程，以及SEI层的形成和变化。在研究混合离子-电子导体（MIEC）中间层中的锂动力学时，原位拉曼光谱可以揭示石墨中间层中锂的插层-挤出行为和Li0/Li+的分布变化。该技术对于识别不同固态电解质、电极材料和界面产物的特征峰非常有用。
- 局限性: 拉曼信号可能较弱，且容易受到荧光背景的干扰。空间分辨率有限（通常微米级），难以对纳米尺度的异质性进行详细分析。光谱的解释需要丰富的经验和参考数据库。
- 代表文献:
- Cao等人利用原位中子成像和拉曼光谱研究了全固态锂金属电池中石墨中间层的锂动力学。研究揭示了在电池组装过程中，插层-挤出主导的机械化学反应将石墨转化为Li-石墨中间层，该中间层由SE、Li0和稀释的石墨插层化合物组成。在充电过程中，Li+优先在Li-石墨|SE界面沉积，进一步电镀会导致Li0枝晶形成，引发短路和Li0从负极向正极的逆向迁移。
7. X射线成像 (X-ray Imaging)
- 能回答的问题: X射线成像（包括X射线计算机断层扫描，X-ray CT）是一种无损的三维（3D）结构成像技术，可以揭示电池内部的宏观和微观结构，包括电极颗粒、空隙、裂纹、界面接触和枝晶的分布。
- 适用场景:
- X射线CT 适用于观察电池在循环过程中的内部结构演变，例如电极体积变化、裂纹扩展、界面脱层、锂枝晶的形成和生长路径。通过原位或延时X射线CT，可以追踪材料制造或组件在役行为和降解过程中的结构演变。它可以帮助研究界面接触损失的机制，例如硅负极在脱锂过程中微观空洞的形成，这会导致界面机械应力增加。
- 原位X射线吸收谱 (XAS) 结合CT可以提供化学态和结构信息，用于研究电极材料的氧化还原反应和局部结构变化。
- 局限性: X射线对轻元素（如锂）的对比度相对较低，可能需要同步辐射光源才能获得足够高的分辨率和对比度。辐射损伤是需要考虑的问题，尤其是在长时间原位实验中。
- 代表文献:
- Kim等人使用原位X射线吸收光谱（XAS）研究了NMC622阴极与LLZO固态电解质界面附近的区域，发现高温或高电压下会形成还原态过渡金属物种。
- Liu等人综述了X射线技术在研究锂电池结构稳定性、动态特性、化学环境变化和形态演变方面的应用，强调其在揭示不均匀反应、锂金属镀层和SEI稳定化方面的潜力。
- Zhang等人综述了包括X射线断层扫描在内的先进成像技术在揭示ASSBs界面不稳定性、枝晶生长和化学-机械降解方面的进展和挑战。
- Huo等人结合结构和化学表征与理论模拟，通过X射线CT等手段揭示了硅负极在固态电池中的化学-力学失效机制。
8. 中子成像 (Neutron Imaging)
- 能回答的问题: 中子成像是一种独特的无损原位成像技术，特别擅长于可视化轻元素（如锂）的分布和动态变化，因为它对轻元素的散射截面远大于X射线。它可以提供电池内部锂浓度、反应机制和传输限制的动态信息。
- 适用场景: 中子成像在研究锂离子电池，特别是全固态锂电池中锂的分布、迁移和枝晶生长方面具有显著优势。它可以原位观察锂金属负极上的锂沉积/剥离过程，追踪锂枝晶的形成和演变，以及锂在固态电解质和电极中的传输路径。例如，在研究混合离子-电子导体（MIEC）中间层中的锂动力学时，原位中子成像揭示了锂在石墨中间层中的行为，包括组装过程中的机械化学反应和充电过程中Li+的优先沉积位置。
- 局限性: 中子成像需要大型中子源设施，可及性较低。空间分辨率通常不如电子显微镜，但高于X射线成像对轻元素的灵敏度。
- 代表文献:
- Cao等人强调了中子成像作为一种无损原位方法，用于可视化全固态锂电池的潜力，并比较了其与其他原位可视化策略的优点，特别是在锂浓度动态、反应机制和传输限制方面的应用。
- Cao等人通过原位中子成像和拉曼光谱研究了全固态锂金属电池中石墨中间层的锂动力学，揭示了锂在中间层的行为，包括机械化学反应和Li+的优先沉积。
- Zhang等人强调了中子成像在可视化ASSBs内部微观结构和化学变化方面的关键作用，特别是在揭示锂负极、复合正极和固态电解质中的失效行为方面。
实验设计指导
在设计固态电池界面反应、锂枝晶和接触损失的研究实验时，需要根据具体的研究问题和关注尺度，选择和组合不同的表征技术：
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确定研究问题和尺度：
- 宏观性能下降（容量衰减、功率衰减）：从EIS开始，结合充放电曲线，可以初步评估电池性能的整体下降和阻抗变化。
- 界面化学反应和产物：XPS和ToF-SIMS是首选，尤其是在表面和浅层，可以确定化学物种和分布。如果需要深度信息，可结合深度刻蚀。
- 形貌结构变化（枝晶、裂纹、空隙）：SEM/FIB-SEM提供微米尺度的二维和三维形貌信息。对于纳米尺度的枝晶和SEI层，TEM和Cryo-TEM是必不可少的。
- 轻元素（Li）动态：中子成像具有独特优势，可以原位追踪Li的分布和迁移，尤其适用于锂金属负极电池。
- 电极材料晶体/分子结构变化：拉曼光谱可以提供分子和晶体结构信息，用于识别相变和反应产物。X射线衍射（XRD，此处未详细讨论但常用）也很有用。
- 整体三维结构和缺陷：X射线CT可以无损地揭示电池内部的宏观三维结构、缺陷和密度变化。
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原位与非原位结合：
- 原位技术（如原位EIS、原位拉曼、原位中子成像、原位XAS/CT）对于捕捉动态过程至关重要，如SEI形成、枝晶生长和界面应力演变。它们能避免非原位样品制备带来的伪影，提供最真实的反应机制信息。然而，原位实验设计通常更复杂，对电池封装和测试条件有严格要求。
- 非原位技术（如XPS、ToF-SIMS、SEM、TEM、Cryo-TEM）在提供高空间分辨率和高化学灵敏度的详细信息方面不可替代。在原位观察到宏观变化后，通常需要非原位分析来深入解析其微观机制和化学组成。为减少非原位分析中的伪影，应采用惰性气氛下样品转移和制备技术（如冷冻FIB），特别是对于空气敏感的样品。
-
多技术联用：
- 没有单一技术可以全面解决所有问题。通常需要结合多种互补技术来获得全面的理解。例如，EIS提供宏观动力学信息，XPS和ToF-SIMS提供界面化学组成，SEM/TEM提供形貌和微观结构，中子成像提供锂分布和动态。
- 例如，Iida等人结合ToF-SIMS、XPS、UPS/LEIPS对LiPON/LiCoO2界面进行详细表征，从而获得了化学物种、化学组成、化学状态和能带图信息，并推断Co还原导致界面阻抗增加。这种综合性方法能够从不同角度揭示界面问题的本质。
- Chen等人结合cryo-TEM断层扫描和ToF-SIMS映射，揭示了电子漏斗介导的阴离子限制策略在固态电池中形成的富含LiF的裂纹状界面相，从而解释了其优异的无枝晶锂沉积性能。
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考虑环境因素：
- 温度和电压： 界面反应和机械稳定性对操作温度和充电电压非常敏感。例如，NMC622与LLZO的电化学不稳定性在高温（80 °C）和高电压（4.3 V）下更显著，导致还原态过渡金属物种的形成和机械失效。实验设计时应覆盖实际操作条件范围。
- 应力与应变： 固态电池中的应力与应变，尤其是在电极/电解质界面处，是引起失效的关键因素。结合力学测试（如纳米压痕，与SEM/ToF-SIMS结合）和有限元模拟，可以深入理解化学-力学耦合失效机制。
- 中间层设计： 引入中间层是解决界面不兼容性的一种策略。研究中间层中Li的动力学和作用机制至关重要，此时原位中子成像和拉曼光谱等技术尤为适用。
通过上述方法的综合运用和实验设计的精心考量，可以更全面、深入地理解固态电池中的界面反应、锂枝晶和接触损失等复杂问题，为开发高性能、长寿命的下一代固态电池提供关键指导。
References
1Characterization of cathode-electrolyte interface in all-solid-state batteries using TOF-SIMS, XPS, and UPS/LEIPSOpenAlex
Shin‐ichi Iida, Masahiro Terashima, K. Mamiya, et al.
In recent years, all-solid-state batteries (ASSBs) have been attracting attention as the next generation batteries for electric vehicles, energy storage systems, etc. Despite the growing interest, there are still many challenges faced in the commercial use of ASSBs. One of the biggest issues is the internal resistance, especially generated at the interface between solid electrolyte and electrode. The internal resistance at the interface limits the charge-discharge cycling performances. In order to solve this issue, it is necessary to examine the chemical and physical interactions at the interface. In this study, we have performed a detailed characterization of a LiPON/LiCoO2 interface using time-of-flight secondary ion mass spectrometry, x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy inverse photoelectron spectroscopy to obtain information on chemical species, chemical compositions, chemical states, and energy band diagrams. These powerful techniques have revealed that an interlayer between LiPON and LiCoO2 was formed due to the temperature rise during the manufacturing process. The temperature rise caused a change of the LiPON network structure and stimulated Co reduction in the LiCoO2 layer near the interface. Energy band diagram analysis suggests that the electron diffusion from LiPON to LiCoO2 may have triggered the reduction of Co. We concluded that the chemical changes that occur at the interface caused an increase in interfacial impedance. Preventing the chemical reduction of Co would be a key to minimize the internal resistance. In this article, the detailed chemical interactions between the LiPON and LiCoO2 layers will be discussed.
2Lithium ion battery degradation: what you need to knowOpenAlex
Jacqueline Edge, Simon E. J. O’Kane, Ryan Prosser, et al.
The expansion of lithium-ion batteries from consumer electronics to larger-scale transport and energy storage applications has made understanding the many mechanisms responsible for battery degradation increasingly important. The literature in this complex topic has grown considerably; this perspective aims to distil current knowledge into a succinct form, as a reference and a guide to understanding battery degradation. Unlike other reviews, this work emphasises the coupling between the different mechanisms and the different physical and chemical approaches used to trigger, identify and monitor various mechanisms, as well as the various computational models that attempt to simulate these interactions. Degradation is separated into three levels: the actual mechanisms themselves, the observable consequences at cell level called modes and the operational effects such as capacity or power fade. Five principal and thirteen secondary mechanisms were found that are generally considered to be the cause of degradation during normal operation, which all give rise to five observable modes. A flowchart illustrates the different feedback loops that couple the various forms of degradation, whilst a table is presented to highlight the experimental conditions that are most likely to trigger specific degradation mechanisms. Together, they provide a powerful guide to designing experiments or models for investigating battery degradation.
3Electron-funnel mediated anion confinement enables ultra-reversible interphases in solid-state batteriesOpenAlex
Yi Chen, Ji Qian, Ke Wang, et al.
Solid-state lithium metal batteries face challenges from irreversible interfacial degradation and sluggish ion transport. We propose an electron-funnel-mediated anion confinement strategy via atomic-level electronic field engineering. Incorporating electron-withdrawing –NO 2 groups into Zr-based frameworks induces a 0.38 eV upward d-band center shift, generating a quantum-confined electrostatic gradient that polarizes TFSI - anions. This reduces TFSI - decomposition energy barrier (ΔG: −0.35 → −1.22 eV), selectively promoting LiF nucleation while suppressing side reactions. Concurrently, Zr 4+ -PEO Lewis interactions disrupt polymer crystallinity, enhancing ionic conductivity and Li + transference number. Cryo-TEM tomography and TOF-SIMS mapping reveal a fractal LiF-rich interphase enabling dendrite-free lithium plating for >11,000 h with polarization <40 mV. LiFePO 4 full cells achieve 86.3% capacity retention after 400 cycles at 1C (1.3 mAh cm −2 ). This work establishes anion confinement as a universal framework synchronizing ion transport and interfacial durability, advancing practical solid-state batteries with exceptional longevity. • Electron-funnel engineering tailors anion dynamics via quantum-confined electrostatic gradients. • Zr 4+ -PEO interactions reduce crystallinity, boosting ionic conductivity. • LiF-rich interphase suppresses dendrites and ensures ultra-stable lithium cycling. • Universal framework synchronizes ion transport and interfacial durability in solid-state batteries.
4In operando neutron imaging characterizations of all-solid-state batteriesOpenAlex
Daxian Cao, Yuxuan Zhang, Tongtai Ji, et al.
Abstract The surge in electric vehicle demand has propagated the extensive application of lithium-ion batteries (LIBs) in recent years. Gaining significant traction due to their promising high-energy density and elevated safety over traditional LIBs, all-solid-state Li batteries (ASLBs) have nonetheless been faced with hurdles relating to battery performance. These include concerns with interfacial compatibility, structural stability, Li dendrite inhibition, and large-scale manufacturing. To tackle these issues, it is necessary to employ advanced characterization methods to comprehend the intrinsic mechanisms within ASLBs. In this article, we advocate for the use of neutron imaging as a nondestructive approach for the operando visualization of ASLBs. We draw comparisons with other operando visualization strategies, underline the benefits of neutron imaging, and discuss its potential applicability in the scrutiny of all-solid-state Li metal batteries and all-solid-state Li-sulfur batteries. Neutron imaging provides valuable insights into the dynamics of Li concentration, reaction mechanisms, and transport constraints in ASLBs. These insights are pivotal in contributing to the evolution of high-performance all-solid-state batteries. Graphical abstract This article discusses the application of neutron imaging for operando characterization of all-solid-state batteries. It compares neutron imaging to other techniques and highlights its advantages in visualizing light elements such as lithium. It also covers recent progress in using neutron imaging to investigate reaction mechanisms, lithium dynamics, and failure modes in all-solid-state lithium metal and lithium sulfur batteries. It also analyzes the future outlook for neutron imaging as a powerful nondestructive tool to gain insights into interfacial phenomena in all-solid-state batteries.
5Electro-Chemo-Mechanical Evolution at the Garnet Solid Electrolyte–Cathode InterfaceOpenAlex
Young-Gyu Kim, Subhash Chandra, Iradwikanari Waluyo, et al.
Solid-state batteries promise higher energy density and improved safety compared with lithium-ion batteries. However, electro-chemomechanical instabilities at the solid electrolyte interface with the cathode and the anode hinder their large scale implementation. Here, we focus on resolving electro-chemo-mechanical instability mechanisms and their onset conditions between a state-of-the-art cathode, LiNi0.6Mn0.2Co0.2O2 (NMC622), and the garnet Li7La3Zr2O12 (LLZO) solid electrolyte. We used thin-film NMC622 on LLZO pellets to place the interfacial region within the detection depth of the X-ray characterization techniques. The experimental probes of the near-interface region included in operando X-ray absorption spectroscopy and ex situ focused ion beam scanning electron microscopy. Electrochemical degradation was not observable during cycling at room temperature with 4.3 V versus Li/Li+ charge voltage cutoff, or with stepwise potentiostatic hold up to 4.1 V versus Li/Li+. In contrast, secondary phases including reduced transition metal species (Ni2+, Co2+) were found after cycling up to 4.3 V versus Li/Li+ at 80 °C and during potentiostatic hold at 4.3 V versus Li/Li+ (Ni2+). Intergranular cracks between NMC622 grains and delamination at the NMC622|LLZO interface occurred readily after the first charge. These interface reaction products and mechanical failure lowered the capacity and cell efficiency due to partial loss of the NMC622 phase, partial loss of contact at the interface, and a higher polarization resistance. Electrochemical instability between delithiated NMC622 and LLZO could be mitigated by using a low charge voltage cutoff or cycling at lower temperature. Ways to engineer the mechanical properties to avoid crack deflection and delamination at the interface are also discussed for enhancing mechanical stability.
6High-Spatial-Resolution Quantitative Chemomechanical Mapping of Organic Composite Cathodes for Sulfide-Based Solid-State BatteriesOpenAlex
Qing Ai, Zhaoyang Chen, Boyu Zhang, et al.
Understanding the chemomechanical behaviors of electrodes, particularly at electrode/electrolyte interfaces, is critical for improving the performance of all-solid-state batteries. However, due to the instability of electrolyte materials under ambient conditions, such characterizations are challenging, particularly for sulfide-based all-solid-state batteries. Herein, by combining time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) and in-SEM nanoindentation measurements, a systematic quantitative investigation of the chemomechanical behaviors of pyrene-4,5,9,10-tetraone (PTO)/Li6PS5Cl composite cathodes is carried out. Chemical and quantitative mechanical information on the composite cathode was collected with high spatial resolution after developing and implementing an air-free characterization protocol. By directly connecting the Young’s modulus and hardness with the Li distribution in the composite cathode, a comprehensive chemomechanical mapping of the PTO/Li6PS5Cl composite cathode has been established. This work improves our knowledge of the critical chemomechanical phenomena that occur at the cathode/electrolyte interfaces in all-solid-state batteries.
7Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery ResearchOpenAlex
Dongqing Liu, Zulipiya Shadike, Ruoqian Lin, et al.
The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.
8Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal–Sulfur and Selenium BatteriesOpenAlex
Hongchang Hao, Tanya Hutter, Brad Boyce, et al.
Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal–sulfur batteries remain challenged by several factors, including polysulfides’ (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li–S and the emerging Na–S and K–S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li–S are relatively mature, less progress has been made with Na–S and K–S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal–selenium and the metal–selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal–sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li–S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure–battery electrochemical performance interrelations. Throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.
9Li Dynamics in Mixed Ionic-Electronic Conducting Interlayer of All-Solid-State Li-metal BatteriesOpenAlex
Daxian Cao, Yuxuan Zhang, Tongtai Ji, et al.
Lithium–metal (Li0) anodes potentially enable all-solid-state batteries with high energy density. However, it shows incompatibility with sulfide solid-state electrolytes (SEs). One strategy is introducing an interlayer, generally made of a mixed ionic-electronic conductor (MIEC). Yet, how Li behaves within MIEC remains unknown. Herein, we investigated the Li dynamics in a graphite interlayer, a typical MIEC, by using operando neutron imaging and Raman spectroscopy. This study revealed that intercalation-extrusion-dominated mechanochemical reactions during cell assembly transform the graphite into a Li-graphite interlayer consisting of SE, Li0, and graphite-intercalation compounds. During charging, Li+ preferentially deposited at the Li-graphite|SE interface. Upon further plating, Li0-dendrites formed, inducing short circuits and the reverse migration of Li0. Modeling indicates the interface has the lowest nucleation barrier, governing lithium transport paths. Our study elucidates intricate mechano-chemo-electrochemical processes in mixed conducting interlayers. The behavior of Li+ and Li0 in the interlayer is governed by multiple competing factors.
10Solid-state batteries: The critical role of mechanicsOpenAlex
Sergiy Kalnaus, Nancy J. Dudney, Andrew S. Westover, et al.
Solid-state batteries with lithium metal anodes have the potential for higher energy density, longer lifetime, wider operating temperature, and increased safety. Although the bulk of the research has focused on improving transport kinetics and electrochemical stability of the materials and interfaces, there are also critical challenges that require investigation of the mechanics of materials. In batteries with solid-solid interfaces, mechanical contacts, and the development of stresses during operation of the solid-state batteries, become as critical as the electrochemical stability to keep steady charge transfer at these interfaces. This review will focus on stress and strain that result from normal and extended battery cycling and the associated mechanisms for stress relief, some of which lead to failure of these batteries.
11Interfacial Reactions and Performance of Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub>-Stabilized Li–Sulfur Hybrid CellOpenAlex
Michael Naguib, Asma Sharafi, Ethan C. Self, et al.
Herein, we report on the characterization of a Li–S hybrid cell containing a garnet solid electrolyte (Li7La3Zr2O12, LLZO) and conventional liquid electrolyte. While the liquid electrolyte provided ionically conductive pathways throughout the porous cathode, the LLZO acted as a physical barrier to protect the Li metal anode and prevent polysulfide shuttling during battery operation. This hybrid cell exhibited an initial capacity of 1000 mAh/g(S) and high Coulombic efficiency (>99%). The interface between the liquid electrolyte and LLZO was studied using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS). These results indicate that a spontaneous interfacial reaction layer formed between the LLZO and liquid electrolyte. XPS depth profiling experiments indicate that this layer consisted of Li-enriched phases near the surface (e.g., Li2CO3) and intermediate Li–La–Zr oxides in subsurface regions. The reaction layer extended well beyond the LLZO surface, and bulk pristine LLZO was not observed even at the deepest sputtering depths used in this study (∼90 nm). Overall, these results highlight that developing stable electrode/electrolyte interfaces is critical for solid-state batteries and their hybrids.
12Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion BatteriesOpenAlex
Tianyu Li, Xiao‐Zi Yuan, Lei Zhang, et al.
Abstract The demand for lithium-ion batteries (LIBs) with high mass-specific capacities, high rate capabilities and long-term cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNi x Mn y Co 1− x − y O 2 , $$x \geqslant 0.5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>x</mml:mi><mml:mo>⩾</mml:mo><mml:mn>0.5</mml:mn></mml:mrow></mml:math> ) cathodes and graphite (Li x C 6 ) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid electrolyte interfaces are also reviewed, and trade-offs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions. Graphic Abstract The demand for lithium-ion batteries (LIBs) with high mass specific capacities, high rate capabilities and longterm cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNi x Mn y Co 1− x − y O 2 , x ≥ 0.5) cathodes and graphite (Li x C 6 ) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid-electrolyte interfaces (SEIs) are also reviewed and tradeoffs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.
13Visualizing the Future: Recent Progress and Challenges on Advanced Imaging Characterization for All-Solid-State BatteriesOpenAlex
Xia Zhang, Markus Osenberg, Ralf Ziesche, et al.
All-solid-state batteries (ASSBs) offer high safety and energy density, but their degradation and failure mechanisms remain poorly understood due to the buried interfaces within solid-state electrodes and electrolytes. Local probing methods are crucial for addressing key challenges such as interfacial instabilities, dendrite growth, and chemo-mechanical degradation. State-of-the-art imaging techniques provide critical insights into morphological, structural, and compositional evolution of the ubiquitous interfaces in ASSBs. This review highlights recent progress in cutting-edge visualization techniques, including neutron imaging, X-ray tomography, focused ion beam scanning electron microscopy, and cryogenic electron microscopy, which reveal microstructural and chemical changes in ASSBs at scales from the atomic to the macroscopic level. We particularly focus on the elusive failure behaviors at lithium anodes, composite cathodes, solid-state electrolytes, and beyond. Additionally, we discuss the strengths and limitations of each technique, aiming to enhance the understanding of ASSB operation and degradation mechanisms to advance the development of high-energy-density, high-safety ASSBs.
14Chemo-mechanical failure mechanisms of the silicon anode in solid-state batteriesOpenAlex
Hanyu Huo, Ming Jiang, Yang Bai, et al.
Abstract Silicon is a promising anode material due to its high theoretical specific capacity, low lithiation potential and low lithium dendrite risk. Yet, the electrochemical performance of silicon anodes in solid-state batteries is still poor (for example, low actual specific capacity and fast capacity decay), hindering practical applications. Here the chemo-mechanical failure mechanisms of composite Si/Li 6 PS 5 Cl and solid-electrolyte-free silicon anodes are revealed by combining structural and chemical characterizations with theoretical simulations. The growth of the solid electrolyte interphase at the Si|Li 6 PS 5 Cl interface causes severe resistance increase in composite anodes, explaining their fast capacity decay. Solid-electrolyte-free silicon anodes show sufficient ionic and electronic conductivities, enabling a high specific capacity. However, microscale void formation during delithiation causes larger mechanical stress at the two-dimensional interfaces of these anodes than in composite anodes. Understanding these chemo-mechanical failure mechanisms of different anode architectures and the role of interphase formation helps to provide guidelines for the design of improved electrode materials.
15Dielectric Modification of 5V‐Class Cathodes for High‐Voltage All‐Solid‐State Lithium BatteriesOpenAlex
Chihiro Yada, Akihiro Ohmori, Kazuto Ide, et al.
A “5V-class” all-solid-state lithium battery (Li/Li3.2PO3.8N0.2/LiCr0.05Ni0.45Mn1.5O4-δ) demonstrates an improved rate capability when its electrolyte/cathode interface is modified by dielectric BaTiO3 nanoparticles. Such “dielectric modification” is supposed to be able to resolve a Li+-deficient layer at the interface, which has limited the charge-transfer reactions rates. There is an urgent demand to popularize high-energy and high-power rechargeable batteries with no safety concerns for automobile applications; “5V-class” all-solid-state lithium batteries are one of the solutions. Here we demonstrate that the charge-transfer reaction rate can be enhanced by four orders of magnitude at solid electrolyte (LiPON)/5V-class cathode (LiCr0.05Ni0.45Mn1.5O4-δ) interface when the electric potential distribution at the interface is designed by dielectric BaTiO3 nanoparticles (BTNs). The resultant BTN-modified Li/LiPON/LiCr0.05Ni0.45Mn1.5O4-δ battery demonstrated an improved rate capability with discharge capacity of 100 mA h g−1 at 8C rate. The ever-increasing demand for electric vehicles (EVs) is aspiring for next-generation rechargeable batteries with higher energy densities. Because the energy density of a battery (W h L−1) is defined as the product of its capacity (A h L−1) and voltage (V), the increase in its voltage is a conclusive approach to improve its energy density. The operating voltage of a battery is determined by the difference in electrode potentials between cathodes and anodes, both of which principally need to be within the potential stability windows of electrolytes in order to avoid their electrochemical decomposition over prolonged charge/discharge cycles. Therefore, high-voltage batteries cannot be realized without electrolytes with wide potential stability windows. In fact, looking back on the history of rechargeable batteries from the standpoint of their operating voltage, Ni-Cd and Ni-MH batteries1 are classified as the “first-generation” because their voltages are limited as small as 1.2 V, mainly due to the narrow potential stability windows of aqueous-based electrolytes. Indeed Ni-MH batteries have yielded great commercial success as power sources for hybrid vehicles (HVs) since the release of the Prius in 1997, but their limited energy density has restricted their application for pure EVs that require more energy than HVs. The low energy densities of Ni-MH batteries was overcome by the “second-generation” lithium-ion batteries operating at ca. 4 V range using 4V-class cathodes such as LiCoO2,2, 3 LiMn2O4,4 Li(Ni, Co, Al)O2,5 or Li(Ni, Co, Mn)O2.6 Their high-voltage is owed mainly to the wide potential stability windows of non-aqueous solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), etc.,7 in liquid electrolytes.8 Although such 4V-class lithium-ion batteries are now going to be dominantly used as power sources for EVs, a strong demand to improve their driving range is awaiting the realization of the “third-generation” batteries operating at ca. 5 V range. To date, several kinds of 5V-class cathodes,9 such as LiNi0.5Mn1.5O4-δ,10 Cr-doped LiNi0.5Mn1.5O4,11 LiCoPO4,12 Li2CoPO4F,13 LiNiPO4,14, 15 Li2NiPO4F,16, 17 LiNiVO4,18, 19 etc. have been reported. However, when they are used with conventional liquid-based electrolytes, they face problems in terms of durability and cycle stability because they give rise to strong oxidation atmospheres against the electrolytes and decompose them.20 Although the kinetics of such side-reactions can be slowed down by techniques like surface coating on cathode materials,21 concentration-gradient cathodes,22 and additives into the electrolyte,23, 24 etc., it should not be possible to suppress the side-reactions completely as long as liquid-based electrolytes are used. Such an underlying problem in the 5V-class batteries led us to utilize inorganic solid electrolytes8 that generally possess wider electrochemical potential windows compared to conventional liquid-based electrolytes. The resultant 5V-class all-solid-state lithium batteries are expected to ensure not only better durability, but also improved safety because of the non-flammable properties of the solid electrolytes.25, 26 As an example of an inorganic solid electrolyte, in this work we used a lithium-oxynitride phosphate glass, Li3.2PO3.8N0.2 (LiPON), that is reported to be stable up to 5.5 V (vs. Li/Li+).27 The LiPON was combined with 5V-class LiCr0.05Ni0.45Mn1.5O4-δ (LNM) cathodes11 with spinel structure whose charge/discharge capacities are predominantly given at around 4.8 V (vs. Li/Li+) using the Ni2+ ⇌ Ni4+ redox couple as well as small capacities at around 4.0 V (vs. Li/Li+) using the Mn3+ ⇌ Mn4+ redox couple. The as-prepared 5V-class Li/LiPON/LNM battery, however, exhibited no charge/discharge reactions at all at potentials between 3.0 and 5.3 V in potential sweep measurements carried out at 0.1 mV s−1. A.c. impedance analysis revealed that its poor electrochemical performance was attributed to the huge charge transfer resistance at the LiPON/LNM interface (RLiPON/LNM > 107 Ω cm2) measured at 4.7 V where reversible charge/discharge reactions should have occurred. Such a poor performance in the 5V-class battery was unexpected to the authors because we have previously observed reasonable charge/discharge reactions in 4V-class all-solid-state batteries (Li/LiPON/LiCoO228 and Li/LiPON/LiMn2O429). One of the possible causes to yield the huge RLiPON/LNM in the 5V-class Li/LiPON/LNM battery is the large electric field at the interface (ELiPON/LNM) generated by the large electric potential difference between the two materials (φLNM – φLiPON). Therefore, with a view to reduce the large ELiPON/LNM, we attempted to modify the LiPON/LNM interface by dielectric materials of BaTiO3, and studied how the RLiPON/LNM was influenced by the modification. BaTiO3 nanoparticles (BTNs) with 10 or 100 nm in diameters were modified at the LiPON/LNM interfaces. It is known that the dielectric constants of BTNs strongly depend on their particle sizes: their dielectric constants are reported to be ca. 2 × 102 and ca. 3 × 103, respectively.30 Figure 1a illustrates a thin-film battery studied in this work. BTNs (d = 10 nm) were deposited on LNM cathodes by spin-coating of precursor liquids containing BTNs in 2-methoxy ethanol solvent (JGC C&C). The amount of BTNs modified at the interface was controlled by regulating the solid-content concentrations of BTNs in the precursors in the range from 0.0016 to 8 wt%. After drying the solvent, we deposited LiPON on the BTN-modified LNM thin film and annealed it at 498 K, and finally deposited the Li anode on the top. Later on, a “x wt% battery” denotes a BTN-modified Li/LiPON/LNM battery whose LiPON/LNM interface was modified using BTN-dispersion liquid with x wt% solid content concentration. Meanwhile, in order to study the size effect of the BTNs on the battery performances, BTNs (d = 100 nm) were also dispersed on LNM cathodes by means of electrospray deposition, in which the precursor liquids contained BTNs (d = 100 nm) in 2-methoxy ethanol solvent. The amount of BTNs (d = 100 nm) modified at the interface was controlled by regulating the deposition time at 15, 60, and 120 min. A series of potential sweep curves of BTN (d = 10 nm)-modified Li/LiPON/LNM batteries (0.0016 ≤ x ≤ 8) are summarized in Figure 1b. No redox reactions were observed in the “8 wt% battery” whose LiPON/LNM interface was completely covered by the BTNs, which is because the BTNs behaved as an insulating layer for charge-transfer reactions. In contrast, the batteries whose LiPON/LNM interfaces were partially covered by the BTNs (0.0016, 0.008, 0.16, and 0.8 wt% batteries) exhibited charge/discharge reactions depending on the amount of the BTNs. The most active charge/discharge reaction was observed in the case of the “0.008 wt% battery” where each BTN was distributed at intervals of ca. 30–50 nm according to the FE-SEM image shown in Figure 1b; the coverage ratio of the BTNs was estimated as 24% by comparing the intensities of Ba and Ni in X-ray photoelectron spectroscopy (XPS). It is noteworthy that no capacity degradation was observed in the optimal “0.008 wt% battery” after 100 charge/discharge cycles at 2C rate between 3.5–4.9 V, see Figure 2. The remarkable cycle stability is owed not only to the electrochemical stability of the LiPON at the high voltage, but also its elastic property that can adapt the volume change in the LNM cathode after continuous charge/discharge cycles. We also examined the size effect of the BTNs on the battery performances. Figure 3a represents a series of Nyquist plots of BTN (d = 100 nm)-modified Li/LiPON/LNM batteries. The semicircles in Figure 3a correspond to charge-transfer resistances at the LiPON/LNM interfaces (RLiPON/LNM) measured at 4.7 V. The RLiPON/LNM decreased as the amount of BTNs (d = 100 nm) increased. The optimal RLiPON/LNM of 2 × 103 Ω cm2 was recorded in a battery where BTNs (d = 100 nm) were deposited on the LNM cathode by the electrospray deposition for 120 min. The optimal RLiPON/LNM was about 4 orders of magnitude smaller than that in the unmodified battery (RLiPON/LNM > 1 × 107 Ω cm2). As seen in the FE-SEM images in Figure 3a, the optimal battery possesses BTNs (d = 100 nm) at intervals of every 1–2 μm, which is greater than 30-50 nm in the case of BTNs (d = 10 nm) as has been proved in Figure 1. This result suggests that the optimal interval of BTNs should depend on their dielectric constants; that is, BTNs (d = 100 nm) are supposed to have a more significant effect in reducing RLiPON/LNM because they possess ca. 15-times larger dielectric constant than BTNs (d = 10 nm). Figure 3b represents a rate capability of the BTN (d = 100 nm)-modified Li/LiPON/LNM battery in comparison with that of an unmodified battery. When the BTN (d = 100 nm)-modified battery was discharged at 8C rate, it retained 84% of its discharge capacity of 120 mA h g−1 recorded at 0.25C rate. It should be also noted that no capacity degradation was observed over 20 charge/discharge cycles in the BTN-modified battery. In contrast, the unmodified battery showed only 45 mA h g−1 at 0.25C rate. Hereafter we discuss the effect of BTNs on improving the charge transfer rates at the LiPON/LNM interface. In general, 5V-class batteries possess larger electric field at their electrolyte/cathode interfaces than 4V-class batteries due to the large potential difference between the two materials. Such a large interfacial electric field in the 5V-class battery (ELiPON/LNM) becomes a driving force to extract a lot of lithium ions from LiPON to LNM at open-circuit conditions, as illustrated in Figure 4a. As a result, Li+-deficient layers should be developed at the LiPON-side of the interface, which in turn behave as a resistive layer for charge-transfer reactions. Such a phenomenon was previously discussed by Takada and co-workers31-35 based on the space-charge theory.36 In contrast, when dielectric BTNs are modified at the LiPON/LNM interfaces, as illustrated in Figure 4b, electric dipoles in the BTNs should be arranged in such a way to reduce the large ELiPON/LNM: their negative charges will face the positive charges in the LNM cathode, whereas their positive charges will face the other side. As a result, as indicated by the dashed gray arrows in Figure 4b, lithium ions originally located behind the BTNs are expected to migrate toward the vicinities of the LNM/LiPON/BTN triple-phase-boundaries so as to maintain local charge neutralities. Such a rearrangement of the Li+ distribution will yield “Li+ pathways” for charge transfer reactions as indicated by double-headed arrows in Figure 4b, where the Li+ concentration in LiPON is approximately equal to that in the stoichiometric Li3.2PO3.8N0.2. Such “Li+ pathways” are supposed to spread concentrically away from the centers of BTNs, the radii of which should depend on their sizes (i.e., dielectric constants): it would appear that the BTNs (d = 10 nm) and BTNs (d = 100 nm) yield “Li+ pathways” concentrically with radii of ca. several tens of nanometers and ca. 1–2 μm, respectively, according to the experimental results in Figure 1 and 3. In contrast, when TiO2 (d = 100 nm) nanoparticles were modified at LiPON/LNM interfaces as a comparison experiment, the battery showed no charge/discharge reaction at all (Figure S1 in the Supporting information), because TiO2 (d = 100 nm) possess only ca. 1/30 smaller dielectric constants than that of the BTNs (d = 100 nm). It is expected that the role of dielectric properties in reducing RLiPON/LNM will be clarified in more detail using advanced analytical techniques like electron holography (EH)-equipped transmission electron microscopy (TEM)37 that can analyze electric potential distributions at around electrode/electrolyte interfaces, together with the aid of modelling studies on electric potential distribution and the Li+ concentration profile around the interface. In summary, we have studied the impact of electric potential distributions at electrolyte/cathode interfaces on charge-transfer reactions in 5V-class all-solid-state batteries. It was revealed that an as-prepared 5V-class Li/LiPON/LNM battery had huge charge-transfer resistance (RLiPON/LNM > 1 × 107 Ω cm2), which would be due to the greatly developed Li+-deficient layers at the LiPON-side of the interface that were caused by the large electric potential difference (φLNM – φLiPON). The large RLiPON/LNM could be reduced down to 2 × 103 Ω cm2 by designing the electric potential distribution around the interface using dielectric materials of BTNs. Such “dielectric modification” induces rearrangement of the Li+ distribution at the interface, and eventually yields “Li+ pathways” for charge-transfer reactions. It should be noted that the volume fraction of the modified BTNs is only ca. 0.04% compared to the total volume of the battery; therefore the “dielectric modification” addressed in this work does not lose energy density of batteries. Nevertheless, the charge-transfer reaction rate could be enhanced by 4 orders of magnitude. It is concluded that dielectric materials (e.g., BaTiO3) can be used as modifying agents at electrolyte/cathode interfaces in 5V-class all-solid-state lithium batteries with a view to increasing their power densities without losing their energy densities. Preparation of a BTN-modified Li/LiPON/LNM Battery: A crystalline LNM thin film (60 nm in thickness) was deposited on a Pt-coated glassy carbon substrate (973 K) by pulsed laser deposition (PLD) with light source of a fourth-harmonic neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (266 nm; LOTIS TII LS-2137/4-BBO) with fixed energy fluence (1.4 J cm−2) and fixed repetition frequency (10 Hz). The oxygen partial pressure inside the chamber was 27 Pa. BTNs (d = 100 nm) were dispersed on the LNM film by electrospray deposition (PDS-D, HAMAMATSU Nano Technology Inc.), where precursor liquids contained BTNs (d = 100 nm) dispersed in 2-methoxy ethanol solvent with solid content concentration of 0.08 wt%. The diameter of the nozzle was 24 μm and the distance between the nozzle and substrate was 20 mm. The applied voltage between the nozzle and the substrate was 1450 V. Meanwhile, BTNs (d = 10 nm) were dispersed on LNM films by spin-coating, as described in the main text. Then LiPON thin films (2.5 μm in thickness) were deposited on the BTN-dispersed LNM thin films by RF magnetron sputtering as reported elsewhere.27 The resultant LiPON/LNM laminate was annealed at 498 K in air. Finally, a lithium anode (1.0 μm in thickness) was deposited on the LiPON film by vacuum evaporation. The geometric electrode area of the battery was 0.20 cm2. Electrochemical Characterization of the Batteries: The batteries were characterized by the potential sweep method (0.1 mV s−1) in the range of 3.0–5.3 V, galvanostatic charge/discharge tests between 3.5–4.9 V at 0.25, 1, 2, 4, 8 C rate, as well as a.c. impedance spectroscopy at 4.7 V in the frequency of 500 kHz to 0.1 Hz with amplitude of 10 mV. 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16Lithium Metal Anodes with Nonaqueous ElectrolytesOpenAlex
Ji‐Guang Zhang, Wu Xu, Jie Xiao, et al.
High-energy rechargeable lithium (Li) metal batteries (LMBs) with Li metal anode (LMA) were first developed in the 1970s, but their practical applications have been hindered by the safety and low-efficiency concerns related to LMA. Recently, a worldwide effort on LMA-based rechargeable LMBs has been revived to replace graphite-based, Li-ion batteries because of the much higher energy density that can be achieved with LMBs. This review focuses on the recent progress on the stabilization of LMA with nonaqueous electrolytes and reveals the fundamental mechanisms behind this improved stability. Various strategies that can enhance the stability of LMA in practical conditions and perspectives on the future development of LMA are also discussed. These strategies include the use of novel electrolytes such as superconcentrated electrolytes, localized high-concentration electrolytes, and highly fluorinated electrolytes, surface coatings that can form a solid electrolyte interphase with a high interfacial energy and self-healing capabilities, development of "anode-free" Li batteries to minimize the interaction between LMA and electrolyte, approaches to enable operation of LMA in practical conditions, etc. Combination of these strategies ultimately will lead us closer to the large-scale application of LMBs which often is called the "Holy Grail" of energy storage systems.
17Insights into interfacial effect and local lithium-ion transport in polycrystalline cathodes of solid-state batteriesOpenAlex
Shuaifeng Lou, Qianwen Liu, Fang Zhang, et al.
Interfacial issues commonly exist in solid-state batteries, and the microstructural complexity combines with the chemical heterogeneity to govern the local interfacial chemistry. The conventional wisdom suggests that "point-to-point" ion diffusion at the interface determines the ion transport kinetics. Here, we show that solid-solid ion transport kinetics are not only impacted by the physical interfacial contact but are also closely associated with the interior local environments within polycrystalline particles. In spite of the initial discrete interfacial contact, solid-state batteries may still display homogeneous lithium-ion transportation owing to the chemical potential force to achieve an ionic-electronic equilibrium. Nevertheless, once the interior local environment within secondary particle is disrupted upon cycling, it triggers charge distribution from homogeneity to heterogeneity and leads to fast capacity fading. Our work highlights the importance of interior local environment within polycrystalline particles for electrochemical reactions in solid-state batteries and provides crucial insights into underlying mechanism in interfacial transport.
18Interfacial Dynamics Study of NCM523-Based Semi-Solid-State Lithium-Ion Batteries by Electrochemical Impedance SpectroscopyOpenAlex
Zhenhua Feng, Xiangyun Qiu, Xin Chen, et al.
The use of solid electrolytes (SE) in solid-state batteries holds the promise of achieving higher energy densities and enhancing safety. However, current solid-state batteries face significant interface impedance issues, mainly dealing with the effect of the evolution of the solid–solid interface on ion transport. Semi-solid-state batteries (SSB), containing a small amount of liquid electrolyte, serve as appropriate transitional products in the development process of solid-state batteries. More importantly, the clarity of the relevant interface dynamics can provide theoretical guidance for the subsequent all-solid-state batteries. Therefore, this paper investigates SSB through Electrochemical Impedance Spectroscopy (EIS), primarily employing a combination of theoretical modeling, simulation predictions, and experimental analyses to elucidate the complex electrochemical processes within these batteries. Based on detailed exploration of the complex electrochemical processes within SSB, we have discovered additional electrochemical processes beyond Li+ penetration through the solid-electrolyte interphase (SEI) film and charge transfer. We attribute the additional electrochemical reaction processes to the resistance present at the SE/SEI interface of SSB on account of numerical analysis and interface characterization. Furthermore, this interface resistance exhibits a trend of initial decrease followed by continuous increase, elucidating the attribution and numerical variations of various impedance components within the EIS. The application of EIS techniques to analyze ion transport processes in SSB serves as a suitable transition toward achieving all-solid-state batteries as well as provides guidance for subsequent interface optimization of solid-state batteries and propels their transition from laboratory experimentation to commercialization.
19X-ray computed tomographyOpenAlex
Philip J. Withers, Charles A. Bouman, Simone Carmignato, et al.
X-ray computed tomography (CT) can reveal the internal details of objects in three dimensions non-destructively. In this Primer, we outline the basic principles of CT and describe the ways in which a CT scan can be acquired using X-ray tubes and synchrotron sources, including the different possible contrast modes that can be exploited. We explain the process of computationally reconstructing three-dimensional (3D) images from 2D radiographs and how to segment the 3D images for subsequent visualization and quantification. Whereas CT is widely used in medical and heavy industrial contexts at relatively low resolutions, here we focus on the application of higher resolution X-ray CT across science and engineering. We consider the application of X-ray CT to study subjects across the materials, metrology and manufacturing, engineering, food, biological, geological and palaeontological sciences. We examine how CT can be used to follow the structural evolution of materials in three dimensions in real time or in a time-lapse manner, for example to follow materials manufacturing or the in-service behaviour and degradation of manufactured components. Finally, we consider the potential for radiation damage and common sources of imaging artefacts, discuss reproducibility issues and consider future advances and opportunities. This Primer on X-ray computed tomography explores the different experimental configurations for three-dimensional data acquisition as well as the fundamentals of three-dimensional data reconstruction, segmentation and analysis with examples across the physical and life sciences.
20Revealing Li dynamics in mixed ionic-electronic conducting interlayer of all-solid-state batteriesOpenAlex
Daxian Cao, Yuxuan Zhang, Kenneth S. Burch, et al.
Lithium-metal (Li0) anode is considered the holy grail of all-solid-state batteries owing to their exceedingly high energy density; in practice, their stability remains unsatisfactory because of the incompatibility between Li0 and solid-state electrolytes (SEs). One strategy is introducing an interlayer, which often consists of the mixed ionic-electronic conductor (MIEC), to stabilize the Li0. However, how Li ions (Li+) transport within MIEC remains unknown. Herein, we investigate the Li, including Li0 and Li+, dynamics in a graphite interlayer, a typical MIEC, using operando neutron imaging and Raman spectroscopy. Our study reveals the Li evolution during mechano-chemistry and mechano-electrochemistry reactions. During cell assembly, intercalation–extrusion-dominated mechano-chemical reactions transform the graphite into a Li-graphite interlayer consisting of SE, Li0, and diluted graphite-intercalation compounds. During battery operation, dictated by the lowest nucleation energy, Li0 plating preferentially occurred at the Li-graphite|SE interface and then transferred into the Li-graphite interlayer without intercalation. Upon further plating, Li0-dendrites formed, inducing short circuits and reverse immigration of Li0 from the anode to the cathode during charging. Continuum modeling was conducted to explain the Li dynamics. We concluded that with the MIEC interlayer, a lowest nucleation barrier at the Li0 side is necessary to drive the Li+ to transport across MIEC and preferentially deposit onto the Li0.