Decoupling Interfacial Reactions at Anode and Cathode by Combining Online Electrochemical Mass Spectroscopy with Anode‐Free Li‐Metal Battery

Abstract

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.

Challenges, Strategies, and Prospects of the Anode‐Free Lithium Metal Batteries

“…[17] In this regard, optimization of the Li-ion utilization degree is the key enabler to the advancement of the AF-LMB configuration. [18] Obviously, the interfacial electrochemical behavior between the substrate and the electrolyte plays a decisive role, and corresponding alleviating strategies and mechanism elucidation are highly required for system optimizations. [19] For conventional LIBs, the N/P ratios of the areal capacities are maintained as 1À1.1, as the host anode needs to accommodate the equivalent amount of Li þ that migrated from the cathode counterpart.…”

“…[ 17 ] In this regard, optimization of the Li‐ion utilization degree is the key enabler to the advancement of the AF‐LMB configuration. [ 18 ] Obviously, the interfacial electrochemical behavior between the substrate and the electrolyte plays a decisive role, and corresponding alleviating strategies and mechanism elucidation are highly required for system optimizations. [ 19 ]…”

A Powerful Protocol Based on Anode-Free Cells Combined with Various Analytical Techniques

“…However, above 4.38 V in the first, second, and third cycle, the evolution of CO and CO 2 together with O 2 releasing is due to both electrochemical and/or chemical interfacial reaction on the surface of the cathode (Figure 4c). 3 The schemes of decupled and compared the interfacial reactions in both NMC||Cu and Li-metal batteries in the presence of carbonate-based electrolyte have been illustrated in Figures 4d and 4e. In general, the anode-free protocol combined with GC-Mass capable of decoupling the interfacial reactions at anode and cathode surface opens a new way to provide a better understanding of electrolyte decomposition at cathode and anode surface, particularly when the metal anode is reactive.…”

“…Mater. 2021 , 31, 2006951 . Report of successful decoupling of the electrolyte decomposition reaction at both the anode and cathode surface using a protocol integrating anode-free cells with in situ GC-MS for the first time. Huang, C.-J.…”

“…29−31 Interestingly, an anode-free cell complementary with various analytical methods is a powerful protocol for decoupling interfacial and quantifying irreversible phenomena. 3,4 Figure 1 demonstrates that various protocols, including Li||Li, Li||Cu, cathode||Li, and cathode||Cu anode-free cells, provide different information in terms of their chemistries for diagnosing and understanding the failure mechanism of batteries. Among them, the Li||Li symmetric cell is well-suited to investigate internal short circuit (ISC), critical current density phenomenon, and SEI polarization on Li surface.…”