Ion transport in solid electrolyte interphases

固体电解质界面中的离子传输

• 批准号: 2887685
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2887685
• 关键词: Ion; transport; solid; electrolyte; interphases

Lithium Metal Batteries (LMBs), with lithium metal as the anode, have recently garnered significant interest as a higher energy density alternative to conventional lithium-ion batteries (LIBs) for high-end electric vehicles and novel applications, including electric flight. However, the successful commercialisation of LMBs will require batteries with high specific energies (above 500 Wh/kg) at a low cost of US $100/kWh. Additionally, batteries must retain 80-90% of their capacity over 1000 cycles, necessitating a coulombic efficiency (CE) of over 99.99%. Achieving these targets also demands the implementation of high-energy cathodes and the development of novel electrolytes compatible with both electrodes. Liquid electrolytes are ideal, as they ensure good electrode contact and compatibility with existing manufacturing routes established for LIBs.Nevertheless, lithium metal anodes operate outside of the electrochemical stability window of any electrolyte, leading to spontaneous electrolyte reduction when the electrochemical potential of the anode exceeds the lowest unoccupied molecular orbital (LUMO) of the electrolyte. Kinetic stability is achieved through the formation of a surface layer composed of insoluble reaction products, first named the solid electrolyte interphase (SEI) by Peled in 1979.Currently, the cycle life of LMBs is limited by inhomogeneous lithium plating/stripping, which exposes additional lithium to the electrolyte and results in 'active' lithium loss due to the formation of SEI and electrochemically isolated 'dead' lithium. This reduces the CE, requiring the use of excess lithium in the form of lithium foil to extend cycle life to practical values, thus reducing specific energy. This non-uniform lithium plating and stripping behavior is influenced by the fundamental properties of the liquid electrolyte and metallic lithium. Electrolyte transport and thermodynamic properties govern the development of salt concentration gradients and overpotentials during cell operation. In extreme cases, the electrolyte can be entirely depleted of salt at the anode surface during charge, leading to the nucleation of fractal lithium dendrites and associated safety concerns. Recent studies have also shown that charge-transfer kinetics influence deposition morphology, with fast interfacial charge-transfer observed to positively correlate with CE. Additionally, the microstructure and anisotropic nanomechanical properties of lithium metal affect cycling behaviour. In fact, inhomogeneous stripping is influenced by crystallographic texture, and more uniform deposition morphologies are achieved under applied stack pressures.However, the degradation phenomena observed in LMBs cannot be fully described by the properties of lithium and the electrolyte alone. Ultimately, it is the SEI that controls cycling performance by regulating lithium morphology and 'dead' lithium formation. This demands a better understanding of the properties of the SEI and their influence on cycling performance, enabling the rational design of SEIs to guide future electrolyte development.This project aims to first examine the nanostructure of the SEI through surface/interfacial characterisation techniques, including atomic force microscopy, x-ray photoelectron spectroscopy, electron microscopy, and electrochemical impedance spectroscopy. Knowledge of SEI nanostructure alone is inadequate to predict cell performance, as it is not yet understood how SEI properties are affected by its structure and composition. Therefore, the second objective of the project is to investigate the structure-property relationships to facilitate rational SEI design and guide future electrolyte development.This project falls within the EPSRC Energy research area. The goal of this theme is for the UK to meet its environmental and energy targets.

以锂金属为阳极的锂金属电池（LMB）作为传统锂离子电池（LIB）的更高能量密度替代品，最近引起了人们的极大兴趣，适用于高端电动汽车和电动飞行等新型应用。然而，LMB的成功商业化将需要具有高比能量（500 Wh/kg以上）且成本低至100美元/kWh的电池。此外，电池在 1000 次循环后必须保持 80-90% 的容量，因此库仑效率 (CE) 必须超过 99.99%。实现这些目标还需要采用高能阴极并开发与两种电极兼容的新型电解质。液体电解质是理想的选择，因为它们可确保良好的电极接触以及与为锂离子电池建立的现有制造路线的兼容性。然而，锂金属阳极在任何电解质的电化学稳定性窗口之外运行，当阳极的电化学电位超过时，会导致电解质自发还原。电解质的最低未占分子轨道（LUMO）。动力学稳定性是通过形成由不溶性反应产物组成的表面层来实现的，Peled 于 1979 年首次将其命名为固体电解质界面 (SEI)。目前，LMB 的循环寿命受到不均匀的锂沉积/剥离的限制，这会暴露额外的锂离子。锂进入电解质，并由于 SEI 的形成和电化学隔离的“死”锂而导致“活性”锂损失。这降低了CE，需要使用锂箔形式的过量锂来将循环寿命延长至实用值，从而降低比能量。这种不均匀的锂沉积和剥离行为受到液体电解质和金属锂的基本性质的影响。电解质传输和热力学特性控制着电池运行期间盐浓度梯度和超电势的发展。在极端情况下，充电过程中电解质可能会完全耗尽阳极表面的盐，导致分形锂枝晶的成核和相关的安全问题。最近的研究还表明，电荷转移动力学影响沉积形态，观察到快速界面电荷转移与 CE 呈正相关。此外，锂金属的微观结构和各向异性纳米力学特性影响循环行为。事实上，不均匀剥离受到晶体结构的影响，并且在施加的堆压力下实现了更均匀的沉积形态。然而，在LMB中观察到的降解现象不能仅通过锂和电解质的性质来完全描述。最终，SEI 通过调节锂形态和“死”锂形成来控制循环性能。这就需要更好地了解SEI的特性及其对循环性能的影响，从而能够合理设计SEI以指导未来电解质的开发。该项目旨在首先通过表面/界面表征技术（包括原子表征技术）检查SEI的纳米结构。力显微镜、X射线光电子能谱、电子显微镜和电化学阻抗谱。仅对 SEI 纳米结构的了解不足以预测电池性能，因为尚不清楚 SEI 性能如何受到其结构和组成的影响。因此，该项目的第二个目标是研究结构-性能关系，以促进合理的SEI设计并指导未来电解质的开发。该项目属于EPSRC能源研究领域。该主题的目标是让英国实现其环境和能源目标。