Disordered rocksalt cathode materials for Na-ion Batteries

用于钠离子电池的无序岩盐阴极材料迫切需要开发比锂离子电池更便宜且更可持续的可充电电池。Na离子提供了一种有吸引力的替代方案，但由于缺乏合适的高能量Na离子阴极材料，该技术在性能，特别是能量密度方面低于Li离子。关键的挑战与Na+离子大于Li+的事实有关。Na+的尺寸增加诱导了主体结构的变化，当离子被去除和重新插入时，这种变化比Li+严重得多，导致循环过程中的降解。当合成层状过渡金属氧化物主体时，对可以引入到层状过渡金属氧化物主体中的Na+的量也有限制，因为它们太大而不能被取代到过渡金属层中的位点中。这意味着最好的阴极通常只利用可能的Na+离子的一小部分，从而限制了能量密度。该项目旨在研究基于无序岩盐晶体结构的新型Na离子阴极，最近发现了几种非常有前途的锂离子类似物。这种结构的无序性质允许放松对Na含量的限制，从而释放了合成“富Na”组合物的可能性，该组合物具有实现比当前最先进阴极更高能量密度的潜力。无序岩盐结构也已被证明在充电-放电反应期间比在层状相中表现出不太明显的结构变化，从而允许在更宽的组成范围内稳定循环。为了制备这些相，将采用一系列合成方法，包括机械化学球磨、原位电化学制备和离子交换。为了了解循环过程中发生的化学和结构变化，将采用一系列先进的表征技术，包括衍射，电子显微镜和光谱学。钻石光源和ISIS中子和μ子源沿着其他国际研究设施也将作为这项研究的一部分，以深入了解这些材料的结构和电子特性。具体的博士论文目标是：1）基于地球丰富元素识别、合成和鉴定新的Na离子无序岩盐组合物，2）定义无序岩盐相的合成可行性的极限，3）发展对这些材料在Na离子电池中充电和放电期间的化学和结构稳定性的全面理解，4）与Faradion合作，识别和优化有前景的商业化候选项目。该项目福尔斯EPSRC能源存储，电化学科学和能源应用材料研究领域。该项目由英国非水钠离子电池技术公司Faradion提供部分资金。这是一个与Faradion Ltd.合作的为期3.5年的EPSRC DTP-CASE学生奖学金。

Disordered rocksalt cathode materials for Na-ion BatteriesThere is a pressing need to develop rechargeable batteries that are cheaper and more sustainable than the Li-ion battery. Na-ion offers an attractive alternative, but this technology falls short of Li-ion on performance, particularly energy density, due to a lack of suitable high energy Na-ion cathode materials. The key challenges are related to the fact that Na+ ions are larger than Li+. The increased size of Na+ induces changes in the host structure that are much more severe than Li+ when the ions are removed and reinserted, leading to degradation over cycling. There is also a limit to the amount of Na+ that can be incorporated into layered transition metal oxide hosts when they are synthesised, as they are too large to be substituted into sites in the transition metal layers. This means that the best cathodes typically only utilise a fraction of the Na+ ions that may be possible, thus restricting the energy density.This project aims to investigate a new class of Na-ion cathodes based on the disordered rocksalt crystal structure, following the recent discovery of several highly promising Li-ion analogues. The disordered nature of this structure permits the constraints on Na content to be relaxed, unlocking the possibility of synthesising "Na-rich" compositions with the potential to achieve higher energy densities than current state-of-the-art cathodes. The disordered rocksalt structure has also been shown to exhibit much less pronounced structural change during the charge-discharge reaction than in layered phases, allowing stable cycling over much wider compositional ranges. To make these phases, a range of synthetic approaches will be employed including mechanochemical ball-milling, in-situ electrochemical preparation and ion exchange. To understand the chemical and structural changes taking place during cycling, a range of advanced characterisation techniques will be employed, including diffraction, electron microscopy and spectroscopy. Diamond Light Source and ISIS neutron and muon source along with other international research facilities will also be used as part of this research to provide insight into the structural and electronic properties of these materials. The specific PhD thesis aims are: 1) to identify, synthesise and characterise new Na-ion disordered rocksalt compositions based on earth abundant elements, 2) to define the limits of synthetic viability of disordered rocksalt phases, 3) to develop a comprehensive understanding of the chemical and structural stability of these materials during charge and discharge in Na-ion cells, 4) to identify and optimise promising candidates for commercialisation in partnership with Faradion.This project falls within the EPSRC Energy Storage, Electrochemical Sciences and Materials for Energy applications research areas. It is part-funded by Faradion, the UK-based non-aqueous sodium-ion cell technology company.This is a 3.5-year EPSRC DTP-CASE studentship in association with Faradion Ltd.