High-capacity alloy anode materials for Li-ion batteries have long been held back by limited cyclability caused by the large volume changes during lithium insertion and removal. Hollow and yolk-shell nanostructures have been used to increase the cycling stability by providing an inner void space to accommodate volume changes and a mechanically and dimensionally stable outer surface. These materials, however, require complex synthesis procedures. Here, using in situ transmission electron microscopy, we show that sufficiently small antimony nanocrystals spontaneously form uniform voids on the removal of lithium, which are then reversibly filled and vacated during cycling. This behaviour is found to arise from a resilient native oxide layer that allows for an initial expansion during lithiation but mechanically prevents shrinkage as antimony forms voids during delithiation. We developed a chemomechanical model that explains these observations, and we demonstrate that this behaviour is size dependent. Thus, antimony naturally evolves to form optimal nanostructures for alloy anodes, as we show through electrochemical experiments in a half-cell configuration in which 15-nm antimony nanocrystals have a consistently higher Coulombic efficiency than larger nanoparticles.

锂离子电池的高容量合金负极材料长期以来一直受到循环能力的限制，这种循环能力是由于锂插入和取出过程中体积的巨大变化而引起的。中空和卵黄壳纳米结构已用于通过提供内部空隙空间以适应体积变化以及机械和尺寸稳定的外表面来提高循环稳定性。但是，这些材料需要复杂的合成程序。在这里，使用原位透射电子显微镜，我们显示足够小的锑纳米晶体在去除锂时自发地形成均匀的空隙，然后在循环过程中可逆地填充和排出空隙。发现此行为是由于弹性天然氧化物层引起的，该氧化物层在锂化期间允许初始膨胀，但由于锑在脱锂期间形成空隙而在机械上防止收缩。我们开发了一种化学机械模型来解释这些观察结果，并且我们证明了这种行为与尺寸有关。因此，正如我们在半电池配置中通过电化学实验所显示的那样，锑自然演化为合金阳极形成最佳的纳米结构，其中15nm锑纳米晶体始终比较大的纳米颗粒具有更高的库仑效率。