How much Li is needed for anode in Li metal battery?

In Li metal batteries, it is commonly accepted that battery life is affected by the quantity of Li. A lower N/P ratio typically signifies more stringent conditions and leads to shorter lifespans due to continuous Li consumption. However, this consumption is entangled with other evolving factors, such as solid electrolyte interphase (SEI) buildup and electrolyte usage. These competing factors dictate battery failure, yet a universal guideline for optimal Li anode quantity remains elusive. Using Li|| nickel‑cobalt‑manganese (NCM811) in ester-based electrolyte as an example, we tracked the cycling dependent evolution of the original Li metal anode of varying thicknesses and the corresponding developed SEI, alongside the electrochemical evolution. We discovered that the continuous consumption of fresh Li, which predominates at the initial cycling process, is finite. This consumption ceases when either the fresh Li is depleted or the electrolyte becomes inadequate to wet the Li/SEI interface. This marks a critical turning point, triggering rapid capacity decline due to the unavailability of fresh Li. Additionally, we identified a direct correlation between the consumption of fresh Li and SEI growth. These findings advance the understanding of failure mechanisms in Li metal batteries and guide strategies for long-term cycling stability.