Sodium and Potassium Superconcentrated Aqueous Electrolytes for 2 V-Class Aqueous Batteries

When and Where

Nov 30, 2022
11:15am - 11:30am

Hynes, Level 3, Ballroom C

Presenter

Tomooki Hosaka

Ayumi Noda

Kento Chiguchi

Rie Takahashi

Kei Kubota

Shinichi Komaba

Co-Author(s)

Tomooki Hosaka¹,Ayumi Noda¹,Kento Chiguchi¹,Rie Takahashi¹,Kei Kubota¹,Shinichi Komaba¹

Tokyo University of Science¹

Abstract

Tomooki Hosaka¹,Ayumi Noda¹,Kento Chiguchi¹,Rie Takahashi¹,Kei Kubota¹,Shinichi Komaba¹

Tokyo University of Science¹

Recently, superconcentrated aqueous electrolytes have attracted significant attention because of their wide potential window compared with conventional aqueous solutions. According to the literature, 21 mol kg-1 LiN(SO2CF3)2 (LiTFSA)/H2O and 27.8 mol kg-1 Li(TFSA)0.7[N(SO2C2F5)2 (BETA)]0.3/H2O electrolytes show potential window of ~2 V and ~3.5 V, respectively.1, 2 As well as the Li electrolytes, superconcentrated aqueous Na and K electrolytes have been recently studied. In general, aqueous Na and K solutions show higher ionic conductivity than Li counterparts because of their weak Lewis acidity, i.e. weak interaction between the cations and solvents/anions, and consequent small Stokes radii of Na+ and K+ ions.3 Moreover, these cations with weak Lewis acidity stabilize N(SO2F)2− (FSA−) anion in highly concentrated aqueous solutions.4, 5 In order to prepare superconcentrated solutions, both anionic mixing and cationic mixing are effective because larger entropy increase from the solid mixtures to the liquid mixtures at the eutectic mixture makes the liquid phase more stable. Based on the dual cation and dual anion strategy, we recently reported superconcentrated electrolytes of 33 mol kg−1 Na0.45K0.55FSA/H2O 6 and 55 mol kg−1 K(FSA)0.6(OTf)0.4/H2O electrolytes, 7 showing the wide potential windows of close to 3 V. In this presentation, we present electrochemical performance and charge-discharge mechanism of aqueous Na- and K-ion batteries using the superconcentrated solutions. Using the Na0.45K0.55FSA electrolyte, we designed Na/K dual-ion batteries with K2Mn[Fe(CN)6] (KMnHCF) positive electrode material and the NASICON-type polyanionic compounds, NaTi2(PO4)3 (NTP) or Na3V2(PO4)3 (NVP), as negative electrode materials. The NTP||K2Mn[Fe(CN)6] cell shows reversible charge-discharge curves with mainly two discharge voltage plateaus located at 1.7 V and 1.3 V and excellent capacity retention. Furthermore, the NVP||K2Mn[Fe(CN)6] cell demonstrated a 2 V-class operation. In the 55 mol kg−1 K(FSA)0.6(OTf)0.4 electrolyte, we evaluated K2Mn0.5Fe0.5[Fe(CN)6] (KMnFeHCF) positive and PTCDI negative electrodes, which have been utilized for aqueous K-ion batteries using with 22 mol kg-1 KOTf electrolyte.8 Both positive and negative electrodes achieved highly reversible charge-discharge for 200 cycles. The cycle performances were much better than either 31 mol kg−1 KFSA or 20 mol kg−1 KOTf electrolytes. Similar to the half cell, the full cell of PTCDI |55 mol kg−1 K(FSA)0.6(OTf)0.4| K2Fe0.5Mn0.5[Fe(CN)6] delivered highly reversible charge-discharge curves for 200 cycles, achieving capacity retention of 96 %. We will discuss the impact of mixed anions and cations on the electrode reaction, including mobile ionic species and the surface layer of the electrode in the presentation. References: 1. L. Suo, K. Xu et al., Science, 2015, 350, 938-943. 2. Y. Yamada, A. Yamada et al., Nat. Energy, 2016, 1, 16129. 3. T. Hosaka, S. Komaba et al., Chem. Rev., 2020, 120, 6358–6466. 4. D. Reber, C. Battaglia et al., Electrochim. Acta, 2019, 321, 134644. 5. S. Ko, Y. Yamada and A. Yamada, Electrochem. Commun., 2020, 116, 106764. 6. T. Hosaka, S. Komaba et al., ACS Appl. Mater. Interfaces, 2022,14, 20, 23507. 7. R. Takahashi, T. Hosaka, S. Komaba, ECSJ Spring Meet., 2020, 3I19. 8. L. Jiang, Y.-S. Hu et al., Nat. Energy, 2019, 4, 495.