Cathode–electrolyte interphase (CEI) formation between the cathode and the electrolyte is a critical factor that determines the stability of lithium-ion batteries (LiBs). The CEI layer consists of various by-products (e.g., LiF, Li₂CO₃, ROLi, and ROCO₂Li (R: alkyl group)) decomposed from redox reactions between the cathode and the electrolyte, which can lead to dramatic capacity fading and stability issues. Herein, we empirically identify the energy level band bending of a Ni-rich NMC cathode (i.e., Li(Ni_0.5Mn_0.3Co_0.2)O₂) with the visual evidence of Li⁺ transfer from the electrode to the CEI layer (adsorbate). Negatively charged elements tend to be present at the close surface of the cathode, while the positively charged Li⁺ migrates from the cathode to the CEI layer. Hence, a downward band bending could be depicted based on the work function and the energy level difference between the Fermi level (E_F) and the valence band maximum (E_VBM). Energy level alignment itself is likely to be the key process that leads to the active formation of unstable CEI layers on charge–discharge.

中文翻译：

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了解锂离子电池具有能级能带弯曲的阴极-电解质界面 (CEI) 层的主动形成

阴极和电解质之间的阴极-电解质界面（CEI）形成是决定锂离子电池（LiBs）稳定性的关键因素。CEI 层由阴极和电解质之间的氧化还原反应分解的各种副产物（例如LiF、Li ₂ CO ₃、ROLi 和 ROCO ₂ Li（R：烷基））组成，这会导致显着的容量衰减和稳定性问题。^{在此，我们通过 Li +}的视觉证据凭经验确定了富镍 NMC 阴极（即Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ ）的能级能带弯曲从电极转移到 CEI 层（吸附物）。带负电的元素倾向于出现在正极的近表面，而带正电的 Li ⁺从正极迁移到 CEI 层。因此，可以根据功函数和费米能级 (EF) 与价带最大值 (E VBM) 之间的能级差来描述_向下的能带_弯曲。能级对齐本身可能是导致在充放电过程中主动形成不稳定 CEI 层的关键过程。