Robert Frederick Smith School of Chemical and Biomolecular Engineering and ‡Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14853, United States.
Acc Chem Res. 2018 Jan 16;51(1):80-88. doi: 10.1021/acs.accounts.7b00484. Epub 2017 Dec 11.
Stable electrochemical interphases play a critical role in regulating transport of mass and charge in all electrochemical energy storage (EES) systems. In state-of-the-art rechargeable lithium ion batteries, they are rarely formed by design but instead spontaneously emerge from electrochemical degradation of electrolyte and electrode components. High-energy secondary batteries that utilize reactive metal anodes (e.g., Li, Na, Si, Sn, Al) to store large amounts of charge by alloying and/or electrodeposition reactions introduce fundamental challenges that require rational design in order to stabilize the interphases. Chemical instability of the electrodes in contact with electrolytes, morphological instability of the metal-electrolyte interface upon plating and stripping, and hydrodynamic-instability-induced electroconvection of the electrolyte at high currents are all known to cause metal electrode-electrolyte interfaces to continuously evolve in morphology, uniformity, and composition. Additionally, metal anodes undergo large changes in volume during lithiation and delithiation, which means that even in the rare cases where spontaneously formed solid electrode-electrolyte interphases (SEIs) are in thermodynamic equilibrium with the electrode, the SEI is under dynamic strain, which inevitably leads to cracking and/or rupture during extended battery cycling. There is an urgent need for interphases that are able to overcome each of these sources of instability with minimal losses of electrolyte and electrode components. Complementary chemical synthesis strategies are likewise urgently needed to create self-limited and mechanically durable SEIs that are able to flex and shrink to accommodate volume change. These needs are acute for practically relevant cells that cannot utilize large excesses of anode and electrolyte as employed in proof-of-concept-type experiments reported in the scientific literature. This disconnect between practical needs and research practices makes it difficult to translate promising literature results, underscoring the importance of research designed to reveal principles for good interphase design. This Account considers the fundamental processes involved in interphase formation, stability, and failure and on that basis identifies design principles, synthesis procedures, and characterization methods for enabling stable metal anode-electrolyte interfaces for EES. We first review results from experimental, continuum theoretical, and computational analyses of interfacial transport to identify fundamental connections between the composition of the SEI at metal-electrolyte interfaces and stability. Design principles and tools for creating stable artificial solid-electrolyte interphases (ASEIs) based on polymers, ionic liquids, ceramics, nanoparticles, salts, and their combinations are subsequently discussed. Interphases composed of a second electrochemically active material that stores charge by different processes from the underlying metal electrode emerge as particularly attractive routes toward so-called hybrid electrodes that enable facile scale-up of ASEI designs for commercially relevant EES.
稳定的电化学界面在调节所有电化学储能(EES)系统中的质量和电荷输运方面起着关键作用。在最先进的可充电锂离子电池中,它们很少是通过设计形成的,而是自发地从电解质和电极组件的电化学降解中出现的。利用反应性金属阳极(例如 Li、Na、Si、Sn、Al)通过合金化和/或电沉积反应来储存大量电荷的高能二次电池带来了根本性的挑战,需要进行合理的设计以稳定界面。与电解质接触的电极的化学不稳定性、电镀和剥离时金属-电解质界面的形态不稳定性以及高电流下引起的流体动力不稳定的电解质电对流,都会导致金属电极-电解质界面在形态、均匀性和组成方面不断演变。此外,金属阳极在嵌锂和脱锂过程中体积会发生较大变化,这意味着即使在自发形成的固-固电极-电解质界面(SEI)与电极处于热力学平衡的极少数情况下,SEI 也处于动态应变状态,这不可避免地会导致在延长的电池循环过程中出现开裂和/或破裂。因此,迫切需要能够克服这些不稳定性源而又最小化电解质和电极组件损失的界面。同样迫切需要互补的化学合成策略来创建自限制且机械耐用的 SEI,使其能够灵活收缩以适应体积变化。对于实际相关的电池来说,这些需求是紧迫的,因为这些电池不能像科学文献中报道的概念验证型实验那样利用大量的阳极和电解质。这种实际需求与研究实践之间的脱节使得很难将有前景的文献结果转化为实际应用,这凸显了设计用于揭示良好界面设计原则的研究的重要性。本综述考虑了界面形成、稳定性和失效的基本过程,并在此基础上确定了用于 EES 的稳定金属阳极-电解质界面的设计原则、合成程序和表征方法。我们首先回顾了界面传输的实验、连续体理论和计算分析的结果,以确定金属-电解质界面处 SEI 的组成与稳定性之间的基本联系。随后讨论了基于聚合物、离子液体、陶瓷、纳米粒子、盐及其组合的稳定人工固态电解质界面(ASEI)的设计原则和工具。由通过与底层金属电极不同的过程存储电荷的第二种电化学活性材料组成的界面作为特别有吸引力的途径出现,可实现所谓的混合电极,从而便于大规模应用适用于商业相关 EES 的 ASEI 设计。