Electrochemical Lithiation/Delithiation of ZnO in 3D-Structured Electrodes: Elucidating the Mechanism and the Solid Electrolyte Interphase Formation

Abstract

Conversion/alloy active materials, such as ZnO, are one of the most promising candidates to replace graphite anodes in lithium-ion batteries. Besides a high specific capacity (q ZnO = 987 mAh g–1), ZnO offers a high lithium-ion diffusion and fast reaction kinetics, leading to a high-rate capability, which is required for the intended fast charging of battery electric vehicles. However, lithium-ion storage in ZnO is accompanied by the formation of lithium-rich solid electrolyte interphase (SEI) layers, immense volume expansion, and a large voltage hysteresis. Nonetheless, ZnO is appealing as an anode material for lithium-ion batteries and is investigated intensively. Surprisingly, the conclusions reported on the reaction mechanism are contradictory and the formation and composition of the SEI are addressed in only a few works. In this work, we investigate lithiation, delithiation, and SEI formation with ZnO in ether-based electrolytes for the first time reported in the literature. The combination of operando and ex situ experiments (cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction, coupled gas chromatography and mass spectrometry, differential electrochemical mass spectrometry, and scanning electron microscopy) clarifies the misunderstanding of the reaction mechanism. We evidence that the conversion and alloy reaction take place simultaneously inside the bulk of the electrode. Furthermore, we show that a two-layered SEI is formed on the surface. The SEI is decomposed reversibly upon cycling. In the end, we address the issue of the volume expansion and associated capacity fading by incorporating ZnO into a mesoporous carbon network. This approach reduces the capacity fading and yields cells with a specific capacity of above 500 mAh g–1 after 150 cycles.

Solid–Electrolyte Interphase of Molecular Crowding Electrolytes

“…A stable SEI is critical not only for lithium insertion electrode materials but also for other conversion/alloy active materials such as NiO and ZnO, which are promising candidates to achieve a higher energy density of batteries. − We compare our work with conversion/alloy electrodes using LiTFSI in ether solvent (e.g., diglyme or tetraglyme, which has the same structure of −CH 2 CH 2 O– as PEG does). It is revealed by an operando study that a SEI with a LiF inner layer and organic-component outer layer also forms on the ZnO electrode, and dynamic SEI formation and decomposition occur during cycling . The reported work is consistent with our result, and we believe that designing a robust SEI with a denser LiF inner layer is a key to achieve more sustainable and high-energy battery systems.…”

MXene/ZnO flexible freestanding film as a dendrite-free support in lithium metal batteries

“…Compared to the initial discharge, the weakened peak intensity of ZnO suggests the reaction of Li and partial ZnO, and the fully discharged product of lithium-zinc alloys can suppress the formation of lithium dendrites. [60][61][62][63][64] The presence of ZnO suggests that a considerably large number of ZnO NPs are stable aer long-term cycling. The reason should be that the reaction of Li ions with ZnO NPs wrapped inside MXene lm is difficult, as Li ions need to go through a long travel path composed of 2D layers of MXene.…”

Nonlinear Electrochemical Analysis: Worth the Effort to Reveal New Insights into Energy Materials

“…[ 5 ] In many cases, results from different techniques need to be combined to obtain sound conclusions. [ 6,7 ]…”

“…[5] In many cases, results from different techniques need to be combined to obtain sound conclusions. [6,7] The terminology for the aforementioned methods shifted during the last decade and is not always consistent throughout the literature. Nowadays, the general understanding is as follows: An operando experiment means a characterization experiment in an electrochemical cell (e.g., battery, fuel cell, electrolyzer) under current flow, with either the potential or the current controlled.…”