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

钠离子电池(NIB)以显著较低的成本提供了锂离子电池的替代方案，有可能实现可持续的大规模可再生能源存储。然而，众所周知，NiB阴极在重复循环过程中会经历巨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离子和氧化还原非活性离子组合的层状钠过渡金属氧化物阴极可以表现出更好的稳定性和循环性，尽管这种稳定的机制还不是很清楚。为了合理地设计出能量密度更高、使用寿命更长的镍离子电池正极，需要在多个尺度上对正极结构进行控制：长程晶体结构、金属的纳米局域有序结构、电子结构和界面结构都起着决定性的作用。本项目旨在通过原子替代来控制纳米级、电子结构和界面结构来设计改进的钠离子电池正极。“未被取代的”(单一金属)和“被取代的”(混合金属)层状NiB阴极将被制备、电化学测试，并使用一系列对纳米尺度敏感的强大的表征技术进行研究：固态核磁共振、同步加速器X射线衍射和PDF、原位SQUID磁测量和扫描电化学显微镜。在此基础上，提出并合成了进一步优化的阴极材料。

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.