Synergistic coupling of a self-defense redox mediator and anti-superoxide disproportionator in lithium-oxygen batteries for high stability

https://doi.org/10.1016/j.cej.2022.139878Get rights and content

Highlights

  • Cobalt iodide acts as a self-defense redox mediator for Li-O2 batteries.

  • Propagermanium is a neutralizing agent with anti-superoxide disproportionation.

  • Propagermanium restrains parasitic reaction in battery chemistry.

  • Propagermanium enhances the durability of CoI2–self-defense redox mediator.

  • The combination of propagermanium and CoI2 reduces overpotential and extends cycle life.

Abstract

In this study, a detailed analysis of the characteristics of lithium–oxygen batteries (LOBs) combined with cobalt iodide as a self-defense redox mediator is conducted, and their synergistic effect with propagermanium as an anti-superoxide disproportionator is explored. Cobalt iodide acts as a self-defense redox mediator for the electrodes and nonaqueous electrolytes. The Li anode is coated with Co metal by cobalt cations to prevent the growth of dendrites and passivation layers, while the iodide anions lower the overpotential, acting as a typical redox mediator. However, as the number of cycles increased, the iodide anions become oxidized and its function as a redox mediator is inhibited. To prevent this degradation, as an effective anti-superoxide disproportionator, propagermanium is proposed as a means of effectively inhibiting the parasitic reaction in LOBs. Consequently, the simultaneous use of a self-defensive redox mediator and anti-superoxide disproportionator yielded LOBs with a low discharge–charge overpotential (0.48 V) and long-term cycling performance (300 cycles).

Introduction

Lithium–oxygen batteries (LOBs) store and use energy by reversibly adsorbing/desorbing oxygen species. Regarding the discharging and charging processes in LOBs, oxygen reduction/evolution reactions (ORR/OER) lead to the formation and decomposition of Li2O2 through the solvation of superoxide intermediates (e.g., radical dotO2, radical dotOH, 1O2, LiO2, and Li2-xO2) [1], [2], [3], [4], [5], [6]. Parasitic reactions occur when solvated superoxide intermediates attack organic solvents or Li salts instead of participating in the ORR/OER, failing to generate Li2O2 and O2. In addition, solvated superoxide intermediates can oxidatively degrade the Li-anode and the O2 cathode.

One of the major challenges faced by LOBs is the inability to decompose gaseous O2 and solid Li2O2 effectively without side reactions during the reversible discharging–charging processes. Hence, the search for efficient solid catalysts focuses on reducing the overpotential and improving electrical energy efficiency [7], [8]. In recent years, beyond searching for solid catalysts for highly efficient ORR/OER activity, a new approach is to introduce soluble redox mediators (RMs) into nonaqueous electrolytes. The use of RMs, such as lithium iodide (LiI), 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ), anthraquinone (AQ), and 2,2,6,6-tetramethylpiperidin-1-yl (TEMPO), to efficiently consume the generated solvated superoxide intermediates is an excellent solution [9], [10], [11], [12], [13], [14], [15], [16]. Moreover, Bi-CoPc as a redox mediator promotes the decomposition of discharge products at low charge potential [17]. Soluble RMs are rapidly oxidized during the charging (OER) process, leading to the fast decomposition of Li2O2 created in the previous discharge process [18]. However, because the O2 cathode and Li anode share the same electrolyte solution in the cell, soluble RMs have undesirable effects, such as promoting harmful redox shuttling and crossover reactions [15].

Zhang et al. presented an InI3 self-defense redox mediator (SDRM) to address this problem [19]. During the charging process, In3+ on the Li anode is electrochemically reduced to form a more stable In film layer that can protect against attack by iodide redox-shuttle/crossover reactions or superoxide intermediates. In addition, the electrochemically deposited In layer can reduce dendritic growth on the surface of the Li anode [20]. According to the above principle, iodide-based SDRM is designed to suppress the parasitic shuttle effect in LOBs [21], [22], but the available metal iodides are limited because of the presence of a dense protective film on the Li surface that impedes charge transfer and degrades cycling performance. In addition, the excess solvated superoxide (radical dotO2) form the intermediates by nucleophilic attack toward electrolyte during repeated discharge–charge cycling. Furthermore, an oxidized I3/I2 redox couple that decomposes the parasitic LiOH or carboxylates produced as byproducts is formed. However, LiOH and carboxylates refuse decomposition and remain in irreversible forms, and the catalysis of I3/I2 redox couple induces a high overpotential and further promotes nucleophilic attack [11], [12], [13], [21]. Therefore, SDRMs require a scavenging system to eliminate harmful superoxide species and prevent redox-shuttle/crossover reactions. According to previous study, the anti-superoxide disproportionation reaction of organogermanium (OG) could prevent parasitic solvated superoxide intermediates reactions during LOB operations [23].

Herein, the anti-superoxide disproportionation activity of OG in preventing parasitic reactions caused by solvated superoxide intermediates in LOBs containing SDRM was studied. The reaction of OG was found to lead to high durability of the cobalt iodide (CoI2)–SDRM using chemical and electrochemical methods. CoI2–SDRM promoted a low discharge–charge overpotential (0.48 V), and the anti-superoxide disproportionation activity of OG promoted long-term cycling performance (300 cycles).

Section snippets

Characterization of cobalt iodide self-defense redox mediator

Fig. 1a shows the discharge–charge profiles for the bare LOB cell with 0.1 M CoI2, and the discharge–charge profiles for the LOB cell with 0.1 M CoI2 are provided for comparison in Fig. 1b. After 5 cycles, the LOB cell containing CoI2 shows a significant reduction in discharge–charge voltage gap by 0.6 V compared with the bare LOB cell, confirming that CoI2 acted as an RM in LOB cells. Fig. 1c shows the surfaces of the Li anodes before and after 5 cycles in the LOB cell containing CoI2. The Li

Conclusion

The simultaneous application of propagermanium−ASD and CoI2−SDRM in LOB can restrain parasitic reactions, such as redox-shuttle/crossover reactions and superoxide-related nucleophilic attacks, resulting in high efficiency with low overpotential and stable and long-term cycling. The positive role of the synergistic coupling of propagermanium−ASD and CoI2−SDRM is threefold: (i) propagermanium−ASD delays the oxidation of the I−/I3 redox couple in the nonaqueous electrolyte, (ii) during the

Synthesis of propagermanium powder and anti-superoxide disproportionator@carbon cloth

Ge-132 (0.15 g, Sigma Aldrich, 99 %) was dissolved in 10 mL of distilled water with 1 mL isopropyl alcohol. To synthesize propagermanium powder, the prepared solution was frozen overnight at −5 °C in a refrigerator and subsequently dried for 24 h in a freeze-dryer. In the case of ASD CC, carbon cloth (W0S1002, CeTech) was immersed in the solution prepared as above and manufactured in the same manner as above [23]. The morphology and phase evolution of the samples were investigated using FESEM

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (2022R1A2C3003319 and 2022R1A2C4002372), South Korea, the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2018M3D1A1058744), South Korea. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of

References (34)

  • M. Balaish et al.

    A critical review on lithium-air battery electrolytes

    Phys. Chem. Chem. Phys.

    (2014)
  • B.D. Adams et al.

    Towards a stable organic electrolyte for the lithium oxygen battery

    Adv. Energy. Mater.

    (2015)
  • M. Balaish et al.

    A critical review on functionalization of air-cathodes for nonaqueous Li-O2 batteries

    Adv. Funct. Mater.

    (2020)
  • X. Lin et al.

    The application of carbon materials in nonaqueous Na-O2 batteries

    CarbonEnergy

    (2019)
  • A. Liu et al.

    Recent progress in MXene-based materials for metal-air batteries: potential high-performance electrodes

    Electrochem. Energy Rev.

    (2022)
  • T. Liu et al.

    Cycling Li-O2 batteries via LiOH formation and decomposition

    Science

    (2015)
  • H.-D. Lim et al.

    Superior rechargeability and efficiency of lithium-oxygen batteries: hierarchical air electrode architecture combined with a soluble catalyst

    Angew. Chem. Int. Ed.

    (2014)
  • Cited by (3)

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