Controlling bulk and surface reactions in high-performance sodium ion battery cathodes

钠离子电池（NIB）以显著更低的成本提供了锂离子电池的替代品，有可能实现可持续的大规模可再生能源存储。然而，已知NIB阴极在重复循环期间经历大的结构相变和副反应，导致快速降解。有趣的是，已经观察到，具有氧化还原活性和氧化还原非活性离子的组合为特征的组成的层状钠过渡金属氧化物阴极可以显示出改善的稳定性和可循环性，尽管这种稳定化的机制还没有很好地理解。为了合理设计具有更高能量密度和更长使用寿命的最佳NIB阴极，需要在多个尺度上控制阴极结构：金属的长程晶体结构、纳米尺度局域有序、电子结构和界面结构都起着决定性的作用，本项目试图通过原子替代来控制纳米尺度、电子结构、和界面结构。“未取代的”（单一金属）和“取代的”（混合金属）层状NIB阴极将被制备，电化学测试，并使用在纳米级敏感的表征技术的强大集合进行研究：固态NMR，同步加速器XRD和PDF，原位SQUID磁力测定和扫描电化学显微镜。基于这些结果，将提出和合成进一步优化的阴极。

Sodium-ion batteries (NIBs) provide an alternative to lithium-ion batteries at a significantly lower cost, potentially enabling sustainable large-scale storage of renewable energy. However, NIB cathodes are known to undergo large structural phase transitions and side reactions during repeated cycling, leading to rapid degradation. Interestingly, it has been observed that layered sodium transition metal oxide cathodes with compositions featuring a combination of redox-active and redox-inactive ions can show improved stability and cyclability, although the mechanisms of this stabilisation are not well understood. In order to rationally design optimal NIB cathodes with higher energy densities and longer service lifetimes, control of cathode structure at multiple scales are needed: the long-range crystallographic structure, nanoscale local ordering of metals, electronic structure, and interfacial structure all play decisive roles.This project seeks to design improved sodium ion battery cathodes by using atomic substitution to control the nanoscale, electronic, and interfacial structures. "Unsubstituted" (single metal) and "substituted" (mixed metal) layered NIB cathodes will be prepared, electrochemically tested, and studied using a powerful collection of characterisation techniques sensitive at the nanoscale: solid-state NMR, synchrotron XRD and PDF, in situ SQUID magnetometry and scanning electrochemical microscopy. Based on these results, further optimised cathodes will be proposed and synthesised.