Understanding Electrode-Electrolyte Interfaces for Next-Generation Batteries

电池的生产能力将在未来几十年内大幅增长，这是由于可再生（但间歇性）发电的预计扩张，即将禁止柴油和汽油发动机，这将推动电动汽车制造的快速增长，以及分散式电网的渗透，以及许多其他影响。为了满足这种存储需求，需要开发新一代电池，这些电池在可持续性、性能和安全特性方面都要优于当前的电池技术。用玻璃态、陶瓷态和其他多晶相的新型固体电解质（SE）替代传统的液体电解质（LE），已显示出满足这些要求的前景。潜在的SE已经证明了诸如超级电容器量级的循环稳定性、高室温离子电导率、宽电化学窗口以及由于它们在空气中的热力学稳定性而在电池结构受损（例如，当电动汽车碰撞时）下改进的安全性的特性。尽管有这些优点，但将SE结合到可操作的全固态电池（ASSB）中提出了要减轻的无数限制。例如，在LE由于高度的电极润湿而实现快速界面动力学的情况下，SE-电极界面由于高电阻而引起速率限制，从而抑制离子传输。这种高电阻被认为是由于晶格失配、界面接触不良、离子缺陷空间电荷层和界面形成而产生的。因此，在众多挑战中，这些复杂的挑战使得寻找合适的SE材料成为一项非常重要的任务。为了充分优化这些候选材料作为电解质，需要全面了解界面和体离子动力学。然而，由于界面和传输机制的掩埋性质，离子迁移率的直接观察是困难的，因此对于高性能SSB设计至关重要的完整动态图像仍然难以捉摸。在这方面，本项目旨在阐明负责改善离子导电性的结构基序;将材料合成和表征的结果与密度泛函理论（DFT）计算和从头算分子动力学（AIMD）模拟的结果仔细结合。具有许多有希望的候选SE的材料家族是硫化物，其中硫化物阴离子的极化性为离子迁移提供了低的静电势垒，例如，Li 10 GeP 2S 12（LGPS）和Li 6PS 5Cl显示出室温离子电导率约为，并且超过，许多有机的。最近对锂-硼-硫型系统的研究表明，它比LGPS具有更好的离子电导率和电化学稳定性，本研究项目将开始在该系列中。不同的合成方法和组成掺杂对结构和所得的导电性的候选SE的影响将探索使用X射线和中子粉末衍射与多核固态NMR光谱的组合。预计DFT和AIMD计算将有助于阐明此类系统中的离子迁移机制，并为未来高性能SE材料和界面的潜在优化路线提供有价值的见解。

The production capacity of batteries is set to rise drastically within the coming decades, precipitated by the projected expansion in renewable (yet intermittent) power generation, the upcoming bans on diesel and petrol engines that are driving a rapid increase in electric car manufacture, and the permeation of decentralised power networks, among many other influences. The scale of resource extraction required to furnish such storage needs necessitates the development of a new generation of batteries with improvements in sustainability, performance, and safety characteristics over current battery technologies.The substitution of conventional liquid electrolytes (LEs) with novel solid electrolytes (SEs) in glassy, ceramic, and other polycrystalline phases has shown promise in addressing these requirements. Potential SEs have demonstrated characteristics such as cycling stabilities on the order of supercapacitors, high room temperature ionic conductivities, wide electrochemical windows, and improved safety under compromisation of cell structure (when electric cars crash, for example) due to their thermodynamic stability in air. Despite these advantages, the incorporation of SEs into operational, all-solid-state batteries (ASSBs) presents a myriad of constraints to be mitigated. For example, where LEs enable fast interfacial kinetics due to a high degree of electrode wetting, SE-electrode interfaces induce a rate-limitation due to high resistance, thereby inhibiting ion transport. This high resistance is considered to originate owing to crystal lattice mismatch, poor interfacial contact, ion-deficient space-charge layers, and interphase formation. Hence, such complex challenges, amongst many others, make finding suitable SE materials a highly non-trivial task.To fully optimise these candidate materials as electrolytes, a comprehensive understanding of the interfacial and bulk ion dynamics is needed. However, owing to the buried nature of interfaces and transport mechanisms, the direct observation of ion mobility is difficult and the complete dynamic picture, which is crucial to the design of high-performance SSBs, therefore remains elusive. In this vein, this project aims to elucidate the structural motifs responsible for improved ionic conductivity; carefully combining results from materials synthesis and characterisation with those from density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations.One family of materials hosting many promising candidate SEs are sulphides, where the polarisability of the sulphide anion provides a low electrostatic barrier to ion migration, with, for example, Li10GeP2S12 (LGPS) and Li6PS5Cl showing room temperature ionic conductivities on the order of, and surpassing, many organic LEs. Recent work on lithium-boron-sulphur-type systems suggest better ionic conductivities and electrochemical stabilities than LGPS, and it is within this family where this research project will begin. The effects of different synthetic methods and compositional doping on structure and the resulting conductivity of candidate SEs will be explored using a combination of X-ray and neutron powder diffraction with multinuclear solid-state NMR spectroscopy. It is anticipated that DFT and AIMD calculations will assist in elucidating ion mobility mechanisms in such systems, and provide valuable insights into potential optimisation routes for future high-performance SE materials and interfaces.