Anode-free lithium metal batteries are the most promising candidate to outperform lithium metal batteries due to higher energy density and reduced safety hazards with the absence of metallic lithium anode during initial cell fabrication. In general, researchers report capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of anode-free lithium metal batteries. However, evaluating the behavior of batteries from limited aspects may easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, we present an integrated protocol combining different types of cell configuration to determine various sources of irreversible coulombic efficiency in anode-free lithium metal cells. The decrypted information from the protocol provides an insightful understanding of the behaviors of LMBs and AFLMBs, which promotes their development for practical applications.

A cell with doped LPS – Li1.5Al0.33Sc0.17Ge1.5(PO4)3 shows improved conductivity and a capacity retention of 83.6% for more than 80 cycles.

It is essential to decouple the interfacial reactions taking place at the anode and cathode in rechargeable batteries. However, due to the reactive nature of Li, it is challenging to use Li‐metal batteries (LMBs) protocol to decouple the interfacial reactions. The by‐products from the anode or cathode become mixed in Li/NMC111 cells, which make decoupling interfacial reactions difficult. Here, reactions at electrodes are successfully decoupled and demystified using a protocol combining anode‐free LMB (AFLMB) with online electrochemical mass spectroscopy. LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) and EC/ethyl methyl carbonate (1:1 v/v%) electrolytes are used to compare interfacial reactions in Li/NMC111 and Cu/NMC111 cells. In Cu/NMC111, the evolution of CO2, CO, and C2H4 gases at the initial stage of first charging is due to interfacial reactions at Cu surface due to solid–electrolyte‐interphase formation. However, the evolution of CO2 and CO gases at high voltage in the entire cycles is associated with chemical and/or electrochemical electrolyte oxidation at the cathode. This work paves a new concept to decouple interfacial reactions at electrodes for developing electrochemically stable electrolytes to improve the performance with the long‐cycling life of AFLMBs and LMBs.

Anode-free lithium metal batteries (AFLMBs) have been extensively studied due to their intrinsic high energy and safety without a metallic Li anode in cell design. Yet, the dendrite and dead-Li buildup continuously consumes the active Li upon cycling, leading to the poor lifespan of AFLMBs. Here, we introduce lithium oxalate into the cathode as an electrode additive providing a Li reservoir to extend the lifespan of AFLMBs. The AFLMB using 20% lithium oxalate and a LiNi0.3Co0.3Mn0.3O2 composite cathode exhibits >80 and 40% capacity retention after 50 and 100 cycles, respectively, outperforming the poor cycle life of fewer than 20 cycles obtained from the cell using a pure LiNi0.3Co0.3Mn0.3O2 cathode. Surprisingly, the average Coulombic efficiency of AFLMBs is found to improve as the amount of lithium oxalate increases in the composite cathode. This abnormal phenomenon could be attributed to the as-formed carbon dioxide after the first activation cycle forming a Li2CO3-rich solid–electrolyte interphase and improving the Li deposition and stripping efficiency. The findings in this work provide a new strategy to delay the capacity roll-over of AFLMBs from an electrode engineering perspective, which can be coupled with other approaches such as functional electrolytes synergistically to further improve the cycle life of AFLMBs for practical application.

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