Comparing Na- and Li-ion diffusion in isostructural disordered rocksalt battery materials - muon

Na-ion and Li-ion batteries are central to the Net Zero agenda, enabling vehicle electrification. However, new battery cathode materials are required which can store charge more densely and enable faster ion diffusion to increase driving range and reduce charging times. We are investigating a new class of cathode materials known as disordered rocksalts, which deliver some of the highest reported energy densities and fast-charging capability despite their intrinsically disordered structure. While theoretical mechanisms to explain the fast ion diffusion in disordered rocksalts have been proposed, this important property has never been investigated experimentally in these new cathode materials. Here, we propose to employ muon spectroscopy to directly measure Na+ and Li+ ion diffusion in two archetypal, isotstructural disordered rocksalts, Li2MnO2F and Na2MnO2F. In combination with polarised neutron QENS, for which we have applied to LET in parallel with this proposal, we will investigate ion diffusion over a range of lengthscales and temperatures and compare how fast Li and Na ions can diffuse through the rocksalt structure. This will reveal new experimental insight into how these materials are able to exhibit fast charging capability and high energy densities as cathode materials for rechargeable batteries.

钠离子电池与锂离子电池是净零排放议程的核心支撑技术，可为机动车电气化提供关键赋能。然而，当前亟需研发新型电池正极材料，这类材料需具备更高的电荷存储密度与更快的离子扩散速率，以提升电动汽车续航里程并缩短充电时长。我们目前正研究一类新型正极材料，即无序岩盐（disordered rocksalts）；尽管其本征结构呈无序状态，但该类材料已被报道具备最高的能量密度之一与优异的快充能力。尽管学界已提出用于解释无序岩盐中快速离子扩散的理论机制，但这类新型正极材料的这一重要特性尚未得到实验验证。本研究拟采用μ子光谱学（muon spectroscopy），直接测量两种典型同构无序岩盐材料——Li2MnO2F与Na2MnO2F中的钠离子与锂离子扩散行为。本研究将结合极化中子准弹性中子散射（polarised neutron QENS）技术——我们已同步向LET谱仪提交了相关申请——在一系列长度尺度与温度条件下开展离子扩散研究，并对比锂离子与钠离子在岩盐结构中的扩散速率差异。本研究将为理解这类材料作为可充电电池正极材料时实现快充能力与高能量密度的内在机制提供全新的实验认知。