Understanding Crystal and Electronic Structure of Battery Electrode Materials Using In Situ, Variable-Temperature SQUID Magnetometry

Designing the next generation of high-performance rechargeable batteries will require a detailed understanding of the electrode materials. In particular, the changes in crystal structure and electronic structure experienced by the electrodes during charge and discharge directly control the voltage, capacity, and reversibility of the cell. Therefore, there has been great interest in the development of new tools to efficiently characterize these processes<i>. </i>Here, we demonstrate a new <i>in situ</i> variable-temperature SQUID magnetometry probe for electrochemical cells, allowing for the quantitative monitoring of electrode reduction/oxidation in a functioning battery. This probe can be used to continuously measure the room-temperature magnetic moment of a charging and discharging battery cell as the metal oxidation states (and therefore number of unpaired electrons) changes and can also be used to obtain full variable-temperature magnetic data down to 2K at discrete points of charge without battery disassembly. This technique provides quantitative measurements of transition metal reduction/oxidation while also revealing electronic structure transitions including charge ordering and insulator-metal transitions. We employ <i>in situ</i> SQUID magnetometry alongside <i>in situ </i>high-resolution synchrotron diffraction (beamline I11, Diamond Light Source) to understand the simultaneous evolution of crystal and electronic structure in Nickel-rich battery electrodes, revealing bulk irreversibility in the first charge cycle. Furthermore, we introduce new open software tools that make it easier to process, interactively visualize, and automatically analyze the large sets of data produced by these <i>in situ</i> techniques.