Progress in the research of aqueous sodium ion batteries
Aqueous sodium ion batteries have the dual advantages of abundant sodium resource reserves and intrinsically safe aqueous electrolytes, and are regarded as an ideal large-scale static energy storage technology. Previously, researchers have made some explorations on aqueous sodium ion battery systems (Nature Communications 2015, 6, 6401; Advanced Energy Materials 2015, 5, 1501005; Advanced Energy Materials 2017, 7, 1701189). At present, aqueous sodium ion batteries are mainly restricted by the narrow voltage window (less than 2 V) of aqueous electrolytes, which further limits the improvement of key electrochemical performance indicators such as output voltage, energy density and cycle life of aqueous sodium ion batteries. Voltage window aqueous electrolyte is the key core technology to realize high performance aqueous sodium ion battery.
Recently, Jiang Liwei, a Ph.D. candidate in the E01 group of the Clean Energy Key Laboratory of the Institute of Physics of the Chinese Academy of Sciences / National Research Center for Condensed Matter Physics in Beijing, under the guidance of researcher Hu Yongsheng and associate researcher Suo Limin, adopted (TEAOTF) salt and sodium trifluoromethanesulfonate (NaOTF) salt are dissolved in water together, a new type of ultra-high salt concentration Water-in-Salt electrolyte containing inert cations (9 m NaOTF + 22 m TEAOTF )(figure 1). This electrolyte not only can achieve a wide voltage window (~ 3.3 V), but also can effectively inhibit the dissolution of electrode materials in the circulation process (Figure 2), and because of the large TEA + cation radius (calculated value is 3.6 Angstroms) The positive and negative electrode materials will be embedded, avoiding the common cation co-intercalation problem of mixed cation electrolytes (Figure 2). In addition, Raman spectroscopy and nuclear magnetic resonance spectroscopy show that the interaction between TEA + and OTF- anions and cations in this new ultra-high salt concentration electrolyte is very weak, which makes it have a relatively low viscosity even at an ultra-high salt concentration of 31 m And higher conductivity (Figure 3 and Figure 4). Molecular dynamics simulations further revealed that the coordination of anions and cations in the two solutions is different: Na + ions coordinate with one oxygen atom in OTF-, and TEA + ions coordinate with two oxygen atoms in OTF- (Figure 4). The Na1.88Mn (Fe (CN) 6) 0.97 · 1.35H2O (NaMnHCF) // NaTiOPO4 full battery assembled using this electrolyte exhibited excellent electrical performance in both low-rate (0.25C) and high-rate conditions (1C) Chemical properties (0.25C, 200 weeks, 90% retention rate; 1C, 800 weeks, 76% retention rate) (Figure 5).
The results of this study were published recently in Advanced Materials (Advanced Materials, 2019, DOI: 10.1002 / adma.201904427). The article is titled High-Voltage Aqueous Na-Ion Battery Enabled by Inert-Cation-Assisted Water-in-Salt Electrolyte .
Relevant work received the National Outstanding Youth Science Fund (51725206), the National Natural Science Foundation of China (51672275, 51421002, 51872322), the National Key Research and Development Program (2016YFB0901500), the Class A Strategic Leading Science and Technology Project of the Chinese Academy of Sciences (XDA21070500), and the Beijing Municipal Science and Technology Commission Z181100004718008) and the support of the Yangtze River Delta Research Center, Institute of Physics, Chinese Academy of Sciences.
Figure 1 Design idea of ​​9 m NaOTF + 22 m TEAOTF Water-in-Salt electrolyte
Figure 2 The effect of 9 m NaOTF + 22 m TEAOTF electrolyte on the performance of positive and negative electrodes
Fig. 3 9 m NaOTF + 22 m TEAOTF electrolyte viscosity and conductivity and molecular dynamics simulation results of sodium ion fast channel
Fig.4 Raman spectrum, nuclear magnetic resonance and molecular dynamics simulation of NaOTF aqueous solution, TEAOTF aqueous solution and 9 m NaOTF + 22 m TEAOTF electrolyte
Figure 5 The electrochemical performance of NaMnHCF // NaTiOPO4 full battery and its comparison with the reported performance of aqueous sodium ion battery
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