The life span of high-energy cells (3.5 Ah, 18 650, LiNi_0.88Co_0.11Al_0.01O₂ (NCA)|C/Si, cell type A) is investigated as a function of depth of discharges (DoD, between 20 and 100%) and cycling rates (between 1C and C/5). The most relevant degradation mechanism for this cell type is the cycling-induced fracturing of active material. This mechanical degradation of the anode is particularly damaging for the cell life span because it generates chain reactions, i.e., solid electrolyte interphase (SEI) formation. The impedance analysis indicates that electrolyte shortage occurs at the end of life (when the capacity loss exceeds 20%) of all cells, regardless of their cycling protocols. It is revealed that electrochemical activation of the Li_0.75Si phase at around 3.0 V causes enormous mechanical stress. Therefore, all of the cells discharged down to 2.65 V show poor lifetime, regardless of their cycling rates and DoDs. The lifetime could be significantly prolonged by cycling the cells above 3.1 V. The scanning electron microscopy (SEM)–energy-dispersive spectrometry (EDX) reveals that some graphite particles are coated by the dense agglomeration of Si particles. The large volume changes of Si might also induce mechanical stress onto the topmost layer of graphite particles underneath the Si coatings, in addition to the mechanical degradation of the Si particle itself.

中文翻译：

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管理高能 LiNi0.88Co0.11Al0.01O2|C-Si 锂离子电池的寿命

高能电池的寿命（3.5 Ah，18 650，LiNi _0.88 Co _0.11 Al _0.01 O ₂ (NCA)|C/Si，电池类型A) 被研究为放电深度（DoD，介于 20% 和 100% 之间）和循环速率（介于 1C 和 C/5 之间）的函数。这种电池类型最相关的降解机制是活性材料的循环诱导断裂。阳极的这种机械退化对电池寿命特别有害，因为它会产生链式反应，即固体电解质中间相 (SEI) 的形成。阻抗分析表明，无论循环协议如何，所有电池在寿命结束时（当容量损失超过 20% 时）都会发生电解质短缺。结果表明，Li _{0.75 的}电化学活化大约 3.0 V 的 Si 相会导致巨大的机械应力。因此，所有放电至 2.65 V 的电池都显示出较差的使用寿命，无论其循环速率和 DoD 是多少。通过将电池循环到 3.1 V 以上，寿命可以显着延长。 扫描电子显微镜 (SEM) - 能量色散光谱 (EDX) 显示一些石墨颗粒被 Si 颗粒的致密团聚包覆。除了 Si 颗粒本身的机械降解外，Si 的大体积变化还可能在 Si 涂层下方的石墨颗粒最顶层上引起机械应力。