“Water-in-Salt” electrolyte enabled LiMn2O4/TiS2 Lithium-ion batteries
Graphical abstract
Introduction
The traditional lithium-ion (Li-ion) batteries have been widely used as high energy density power sources for various portable devices. However, the safety concern due to the use of the flammable organic electrolyte solvents has raised much attention in recent years [1], [2], [3]. Replacement of organic electrolytes by aqueous electrolytes can allow for intrinsically safe batteries [4], [5], [6]. However, the low energy density induced by the narrow thermodynamic stability window of water hinders their future widespread applications [7], [8]. Recently, the thermodynamic stability window of water has been significantly extended from 1.5 V to 3.0 V (1.9–4.9 V vs. Li/Li+) through increasing the salt concentration, which enables more suitable electrode materials and more choices for current collectors in the aqueous battery system [9], [10], [11], [12], [13], [14], [15], [16], [17].
Among all the electrode materials used in traditional Li-ion batteries, titanium disulfide (TiS2) is a well-known intercalation cathode material for the Li-ion battery with a lithium intercalation/deintercalation potential at 2.1 V vs. Li/Li+ [18], [19], which sits well inside of the stability window of the “Water-in-Salt” (WIS) electrolyte. In addition, the TiS2 also shows a high theoretical specific capacity of 240 mAh g− 1, excellent cycling stability, and high electronic/ionic conductivity, making it an attractive anode for the aqueous Li-ion battery (ALIB) in the WIS electrolyte [20], [21], [22]. To the best of our knowledge, TiS2 has never been explored in aqueous electrolytes. It is because the operation potential of TiS2 is lower than that of the hydrogen evolution (2.6 V vs. Li/Li+) in the traditional, neutral aqueous electrolytes.
In this work, we investigated the electrochemical performance of TiS2 anode in the WIS electrolyte (21 mol LiTFSI in 1 kg H2O, 21 m). The expanded stability window and substantial reduction of water chemical activity not only enable the reversible electrochemical reaction between TiS2 and Li+ but also significantly suppress the irreversible parasitic reaction [9], [12]. The LiMn2O4/TiS2 full cell using commercial LiMn2O4 as cathode and “Water-in-Salt” as electrolyte shows one of the best electrochemical performances of ALIBs reported to date.
Section snippets
Material
Lithium bis(trifluoromethane sulfonyl)imide (LiN(SO2CF3)2, LiTFSI) (> 98%) and lithium nitrate (LiNO3) were purchased from Tokyo Chemical Industry and Sigma-Aldrich, respectively. The aqueous “Water-in-Salt” electrolyte was prepared by dissolving 21 mol LiTFSI in 1 kg deionized H2O (21 m LiTFSI electrolyte). The salt-in-water control electrolytes were made by dissolving 1 m LiNO3 and 1 m LiTFSI in deionized H2O, respectively. The anode material TiS2 (Sigma-Aldrich) and cathode material LiMn2O4 (MTI
Results and discussion
The XRD in Fig. 1a reveals that the as-received TiS2 material has a pure layered crystal structure (JCPDS-15-0853). Additionally, the SEM images of pristine TiS2 powder in Fig. 1b show that the as-received sample has an irregular shape and its particle size ranged from a few to dozens of micrometers.
Electrochemical stability windows of the different electrolytes were measured in a three-electrode cell using linear sweep voltammetry with SS grid as both working and counter electrodes and the
Conclusion
In summary, we demonstrated that the TiS2 electrode material in liquid organic electrolyte Li-ion batteries can be utilized as an anode in WIS electrolyte Li-ion batteries. Paired with a LiMn2O4 cathode, the LiMn2O4/TiS2 full cell delivered a high discharge voltage of 1.7 V and energy density of 78 Wh kg− 1. These results reveal a promising future for exploring more anode materials for the intrinsically safe aqueous batteries. Furthermore, this work also raises the possibility of using metal
Conflict of interest
The authors declare no conflict of interests.
Acknowledgments
The authors acknowledge the financial support of DOE ARPA-E (DEAR0000389) and the technical support of the NanoCenter at the University of Maryland. Wei Sun was supported by a fellowship from China Scholarship Council (201506150044).
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