An official website of the United States government
Abstract It remains a challenge to design aqueous electrolytes to secure the complete reversibility of zinc metal anodes. The concentrated water‐in‐salt electrolytes, e.g., 30 m ZnCl2, are promising candidates to address the challenges of the Zn metal anode. However, the pure 30 m ZnCl2electrolyte fails to deliver a smooth surface morphology and a practically relevant Coulombic efficiency. Herein, it is reported that a small concentration of vanillin, 5 mg mLwater−1, added to 30 m ZnCl2transforms the reversibility of Zn metal anode by eliminating dendrites, lowering the Hammett acidity, and forming an effective solid electrolyte interphase. The presence of vanillin in the electrolyte enables the Zn metal anode to exhibit a high Coulombic efficiency of 99.34% at a low current density of 0.2 mA cm−2, at which the impacts of the hydrogen evolution reaction are allowed to play out. Using this new electrolyte, a full cell Zn metal battery with an anode/cathode capacity (N/P) ratio of 2:1 demonstrates no capacity fading over 800 cycles.
more »
« less
Electrolyte Interphases in Aqueous Batteries
Abstract The narrow electrochemical stability window of water poses a challenge to the development of aqueous electrolytes. In contrast to non‐aqueous electrolytes, the products of water electrolysis do not contribute to the formation of a passivation layer on electrodes. As a result, aqueous electrolytes require the reactions of additional components, such as additives and co‐solvents, to facilitate the formation of the desired solid electrolyte interphase (SEI) on the anode and cathode electrolyte interphase (CEI) on the cathode. This review highlights the fundamental principles and recent advancements in generating electrolyte interphases in aqueous batteries.
more »
« less
- Award ID(s):
- 2038381
- PAR ID:
- 10468884
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 2
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Aqueous Li-ion batteries (ALIBs) are an important class of battery chemistries owing to the intrinsic non-flammability of aqueous electrolytes. However, water is detrimental to most cathode materials and could result in rapid cell failure. Identifying the degradation mechanisms and evaluating the pros and cons of different cathode materials are crucial to guide the materials selection and maximize their electrochemical performance in ALIBs. In this study, we investigate the stability of LiFePO4(LFP), LiMn2O4(LMO) and LiNi0.8Mn0.1Co0.1O2(NMC) cathodes, without protective coating, in three different aqueous electrolytes, i.e., salt-in-water, water-in-salt, and molecular crowding electrolytes. The latter two are the widely reported “water-deficient electrolytes.” LFP cycled in the molecular crowding electrolyte exhibits the best cycle life in both symmetric and full cells owing to the stable crystal structure. Mn dissolution and surface reduction accelerate the capacity decay of LMO in water-rich electrolyte. On the other hand, the bulk structural collapse leads to the degradation of NMC cathodes. LMO demonstrates better full-cell performance than NMC in water-deficient aqueous electrolytes. LFP is shown to be more promising than LMO and NMC for long-cycle-life ALIB full cells, especially in the molecular crowding electrolyte. However, none of the aqueous electrolytes studied here provide enough battery performance that can compete with conventional non-aqueous electrolytes. This work reveals the degradation mechanisms of olivine, spinel, and layered cathodes in different aqueous electrolytes and yields insights into improving electrode materials and electrolytes for ALIBs.more » « less
-
Despite extensive research efforts in developing aqueous rechargeable zinc metal batteries (RZMBs) as high-energy-density alternatives to both lithium ion and lithium metal batteries, the commercial prospects for RZMBs are still obfuscated by fundamental scientific questions. In particular, the electrode–electrolyte interphase properties and behaviors are still intensely debated topics in this field. In this review, we provide a comprehensive and thorough overview of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) in aqueous RZMBs, with an emphasis on the formation mechanisms and characteristics of the SEI and CEI. We then summarize state-of-the-art techniques for characterizing the SEI/CEI to reveal the intrinsic correlation between the functionalities of the interphases and the electrochemical performances. Finally, future directions are proposed, including studies on aqueous SEI/CEI evolution as a function of pH and temperature, as well as SEI/CEI studies for high-energy-density and long-lifetime RZMBs.more » « less
-
The role of the cathode–electrolyte interphase (CEI) on battery performance has been historically overlooked due to the anodic stability of carbonate-based electrolytes used in Li-ion batteries. Yet, over the past few decades, degradation in device lifetime has been attributed to cathode surface reactivity, ion transport at the cathode/electrolyte interface, and structural transformations that occur at the cathode surface. In this review, we highlight recent progress in analytical techniques that have facilitated these insights and elucidated not only the CEI composition but also the spatial distribution of electrolyte decomposition products in the CEI as well as cathode-driven reactions that occur during battery operation. With a deeper understanding of the CEI and the processes that lead to its formation, these advanced characterization tools can unlock routes to mitigate impedance rise, particle cracking, transition metal dissolution, and electrolyte consumption, ultimately enabling longer lasting, safer batteries.more » « less
-
Abstract Interphase layers that form at contact points between the solid electrolyte (SE) and cathode active material in solid‐state lithium‐ion batteries (SS‐LIBs) increase cell impedance, but the mechanisms for this interphase formation are poorly understood. Here, we demonstrate a simple workflow to study cathode–electrolyte interphase (CEI) formation using 4D‐scanning transmission electron microscopy (4D‐STEM) that does not require SS‐LIB assembly. We show benefits of MoCl5:EtOH as a chemical delithiating agent, and prepare chemically delithiated cathode LiNi0.6Co0.2Mn0.2O2(NMC) powder in contact with Li10GeP2S12(LGPS) SE powder as a SS‐LIB CEI surrogate. We map the composition and structure of the CEI layers using 4D‐STEM, energy dispersive X‐ray spectroscopy (EDS), and electron pair distribution function analysis (ePDF). EDS indicates O migration from NMC into LGPS. ePDF analysis indicates sulfate and phosphate formation localized on the surface of LGPS, as well as Li2O formation within the LGPS phase, and self‐decomposition of NMC. These results are consistent with an electrochemical self‐discharge mechanism for interphase formation arising from coupled redox reactions of sulfur oxidation in LGPS and transition metal reduction in NMC. This suggests that coatings which stop anion transport but allow Li+and e−transport may prevent interphase formation and reduce impedance in SS‐LIBs.more » « less
