Lou Pengtao, Bi Zhuanfang, Wang Xinru, Shang Guangyi
School of Physics, Beihang University, Beijing 100191, People's Republic of China.
Langmuir. 2024 Aug 20;40(33):17740-17746. doi: 10.1021/acs.langmuir.4c02130. Epub 2024 Aug 8.
Mechanical damage of LiMnO active material caused by volume change, phase transition, and lithium diffusion-induced stress is the main degradation mechanism in lithium-ion batteries. Young's modulus is a key parameter of mechanical property, and its variation with lithium content or state of charge (SOC) at the nanoscale is an important issue because such variation may have influences on the stress level and lithium-ion transport. In this study, we successfully developed bimodal atomic force microscopy (bimodal AFM) and related approaches to carry out surface topography imaging and Young's modulus mapping of LiMnO nanosized particles. It was validated that the size of particles decreased with decreasing SOC due to delithiation during the charging cycle. The variation in Young's modulus with SOC was quantitatively determined using the silicon material as a reference, and the trend of the variation is consistent with the reported results of molecular dynamics simulation. Furthermore, spatially nonuniform distribution of Young's modulus on the nanosized particle surface was found even upon completion of charging. This phenomenon could be attributed to the coexistence of two phases during the charging process. Our experimental study reveals the correlation between Young's modulus of LiMnO and SOC at the nanosized particle level, and we believe that the bimodal AFM will be widely used in the nanocharacterization of the electrode materials because lithium content- or SOC-dependent mechanical properties are common in battery electrode materials.
由体积变化、相变以及锂扩散诱导应力引起的LiMnO活性材料的机械损伤是锂离子电池中的主要降解机制。杨氏模量是力学性能的一个关键参数，其在纳米尺度下随锂含量或充电状态（SOC）的变化是一个重要问题，因为这种变化可能会对应力水平和锂离子传输产生影响。在本研究中，我们成功开发了双峰原子力显微镜（双峰AFM）及相关方法，以对LiMnO纳米颗粒进行表面形貌成像和杨氏模量映射。结果证实，在充电循环过程中，由于脱锂，颗粒尺寸随着SOC的降低而减小。以硅材料为参考，定量测定了杨氏模量随SOC的变化，其变化趋势与已报道的分子动力学模拟结果一致。此外，即使在充电完成后，也发现纳米颗粒表面的杨氏模量存在空间不均匀分布。这种现象可归因于充电过程中两相的共存。我们的实验研究揭示了纳米颗粒水平上LiMnO的杨氏模量与SOC之间的相关性，并且我们认为双峰AFM将在电极材料的纳米表征中得到广泛应用，因为依赖于锂含量或SOC的力学性能在电池电极材料中很常见。
