The cathode material in a lithium (Li) battery determines the system cost, energy density, and thermal stability. In anode-free batteries, the cathode also serves as the source of Li for electrodeposition, thus impacting the reversibility of plating and stripping. Here, we show that the reason LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes deliver lower Coulombic efficiencies than LiFePO₄ (LFP) is the formation of tortuous Li deposits, acidic species in the electrolyte, and accumulation of “dead” Li⁰. Batteries containing an LFP cathode generate dense Li deposits that can be reversibly stripped, but Li is lost to the solid electrolyte interphase (SEI) and corrosion according to operando ⁷Li NMR, which seemingly “revives” dead Li⁰. X-ray photoelectron spectroscopy (XPS) and in situ ¹⁹F/¹H NMR indicate that these differences arise because upper cutoff voltage alters electrolyte decomposition, where low-voltage LFP cells prevent anodic decomposition, ultimately mitigating the formation of protic species that proliferate upon charging NMC811.

锂 (Li) 电池中的正极材料决定了系统成本、能量密度和热稳定性。在无阳极电池中，阴极还充当电沉积的锂源，从而影响电镀和剥离的可逆性。在这里，我们展示了 LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811) 阴极库仑效率低于 LiFePO 的原因 < b4>（LFP）是曲折的锂沉积物、电解质中的酸性物质以及“死”锂 ⁰ 的积累的形成。含有 LFP 正极的电池会产生密集的锂沉积物，可以可逆地剥离，但根据操作 ⁷ Li NMR，Li 会损失到固体电解质界面 (SEI) 和腐蚀中，这似乎“复活”了死亡的 Li < b7> 。 X 射线光电子能谱 (XPS) 和原位 ¹⁹ F/ ¹ H NMR 表明，这些差异的出现是因为上限截止电压改变了电解质分解，而低电压 LFP 电池阻止阳极氧化分解，最终减少在 NMC811 充电时增殖的质子物质的形成。