Probing the chemical degradation of cathode material interfaces in Li-ion Batteries

为了使未来几代锂离子电池应用于电动汽车，需要对其寿命和功率密度进行重大改进。实现长电池寿命的最重要方面之一是正极材料（正极）的稳定性。在许多充放电循环或在极端温度下操作时，这些材料表面会发生不良副反应，如电解质分解，过渡金属溶解和气体释放。目前观察这些电极-电解质界面的技术必须在电池拆卸后进行，因为访问这些隐藏界面的主要挑战。然而，这种方法是不可靠的，因为电池接口通常是高度反应性的，并且在拆卸和转移到测量系统期间容易发生变化。本项目旨在研究锂离子电池在运行过程中阴极（正极）和电解质界面发生的变化。这将利用结合薄膜的新型电化学电池，通过薄膜可以进行硬x射线光电子能谱（HaXPES）和x射线吸收光谱（XAS）。它还将使用一个专门设计的室，用于在真空环境中组装和拆卸电池，该室可以直接连接到表面敏感的表征工具。这些方法将用于揭示发生的可逆和不可逆反应，例如表面层的形成，过渡金属的溶解以及随后将这些物质镀到阳极（负极）上。将研究与应用相关的电池材料，以获得有关其界面稳定性的新见解，这种理解将为阴极材料的设计和循环协议提供信息，以帮助延长锂离子电池的寿命。使用新的表征工具也将有助于展示这些工具可以为电池研究界提供的能力。该项目与庄信万丰有关，将与庄信万丰技术中心的电池材料和先进表面表征小组合作。现场和操作x射线测量将在钻石光源和其他国际同步加速器设施进行。该项目属于EPSRC能源存储和物理科学研究领域，将使用先进的表征技术来研究电池材料中的化学变化。

For future generations of lithium ion batteries to be implemented in electric vehicles, significant improvements in their lifetime and power densities are required. One of the most important aspects in achieving a long battery lifetime is the stability of the cathode materials (positive electrode). Over many charge-discharge cycles or when operated under extreme temperatures, undesirable side reactions occur at the surface of these materials such as electrolyte decomposition, transition metal dissolution and gas evolution. Current techniques to look at these electrode-electrolyte interfaces must be performed after the battery has been disassembled, due to the major challenge of accessing such buried interfaces. However, such approaches are unreliable as battery interfaces are usually highly reactive and liable to change during disassembly and transfer to the measurement system. This project aims to investigate the changes occurring at interfaces between the cathode (positive electrode) and electrolyte in Li-ion batteries during operation. This will make use of novel electrochemical cells that incorporate thin membranes through which hard X-ray photoelectron spectroscopy (HaXPES) and X-ray Absorption Spectroscopy (XAS) can be performed. It will also use a specially designed chamber for assembling and disassembling batteries in a vacuum environment that can be directly connected to surface-sensitive characterisation tools. These approaches will be used to reveal the reversible and irreversible reactions occurring, such as the formation of surface layers, transition metal dissolution and the subsequent plating of these species onto the anode (negative electrode). Application-relevant battery materials will be studied to obtain novel insights about their interfacial stability, and this understanding will inform the design of cathode materials and cycling protocols to help extend the life of Li-ion batteries. The use of new characterisation tools will also help demonstrate the capabilities these can provide to the battery research community. This project is linked with Johnson Matthey and will involve work with both the Battery Materials and Advanced Surface Characterisation Groups at Johnson Matthey's Technology Centre. In situ and operando X-ray measurements will be performed at Diamond Light Source and other international synchrotron facilities. This project falls within the EPSRC research areas of Energy Storage and Physical Sciences, where advanced characterisation techniques will be used to study chemical changes occuring in battery materials.