Reassessing the Quantity of Lithium in Metal Batteries: The Less Is More Philosophy from Metal-Free to Metal Anode

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Lithium metal-free batteries (LMFBs, often called anode-free batteries), characterized by the absence of pre-loaded lithium metal or host materials at the anode, have emerged as a focal point in battery research due to their theoretically highest energy density.[1] However, LMFBs face significant challenges: their practical energy density and cycle performance are severely limited by lithium inventory loss during initial charging and the limited reversibility of lithium plating/stripping during battery cycles.[2] We reassess the impact of lithium metal quantity at the anode on battery performance.[3] By incorporating a minimal amount of lithium, lean lithium metal batteries (LLMBs) slightly compromise energy density (the 'less') but, as demonstrated in Figure 1, achieve higher practical energy densities and longer lifespans than LMFBs (the 'more') with an N/P ratio of 0.2, an average lithium Coulombic efficiency of 99.9%, and considering an initial capacity loss of 5%. This makes LLMBs a pragmatic choice even under lenient technical conditions. It is important to note that this discussion does not endorse one over the other; LMFBs and LLMBs inherently share many similarities and overlapping technologies, such as benefits derived from advanced electrolytes and protocol management. Moreover, LMFBs offer manufacturing advantages by avoiding strict measures required for handling fragile lithium metal, presenting distinct benefits. Additionally, performance metrics derived from LLMBs are invaluable for guiding future LMFB evaluations. Certain LMFB enhancements, like the creation of artificial SEI layers or the use of 3D current collectors, might inadvertently increase battery weight and size, negating the foundational purpose of LMFBs. In such scenarios, the energy density and battery performance of LLMBs, under comparable conditions, can serve as benchmarks to assess the tangible impact of such interventions on LMFBs, ultimately aiming to genuinely elevate battery efficacy. References [1] S. Nanda, A. Gupta, A. Manthiram, Adv. Energy Mater. 11 (2021) 2000804. [2] C. Heubner, S. Maletti, H. Auer, J. Hüttl, K. Voigt, O. Lohrberg, K. Nikolowski, M. Partsch, A. Michaelis, Adv. Funct. Mater. 31 (2021) 2106608. [3] D. Wang, J. Qiu, N. Inui, R. Hagiwara, J. Hwang, K. Matsumoto, ACS Energy Lett. 8 (2023) 5248.

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