Date Published: January 28, 2019
Publisher: John Wiley and Sons Inc.
Author(s): Chao Chen, Tingting Yu, Meng Yang, Xiangyu Zhao, Xiaodong Shen.
The chloride ion battery has been developed as one of the alternative battery chemistries beyond lithium ion, toward abundant material resources and high energy density. Its application, however, is limited by the dissolution of electrode materials and side reactions in the liquid electrolyte. Herein, a solid polymer electrolyte allowing chloride ion transfer and consisting of poly(ethylene oxide) as the polymer matrix, tributylmethylammonium chloride as the chloride salt, and succinonitrile as the solid plasticizer is reported. The as‐prepared polymer electrolyte shows conductivities of 10−5–10−4 S cm−1 in the temperature range of 298–343 K. When it is assembled with the iron oxychloride/lithium electrode system, reversible electrochemical redox reactions of FeOCl/FeO at the cathode side and Li/LiCl at the anode side are realized, demonstrating the first all‐solid‐state rechargeable chloride ion battery.
With the increasing shortage of fossil energy and the pollution of the environment, the development of sustainable clean energy and its harvest, conversion, storage, and usage have been focused.1, 2, 3 Rechargeable batteries have been considered as one of the typical energy storage technologies for different applications in portable electronics, mobile instruments, and stationary grid‐scale stations.4 Besides the commercial batteries such as lead‐acid batteries,5 Ni‐MH batteries,6 and lithium ion batteries,7 various alternative battery chemistries based on cation (Na+, K+, Mg2+, Ca2+, Zn2+, Al3+),8, 9, 10, 11, 12, 13 anion (F−, Cl−, O2−),14, 15, 16, 17, 18 or dual ion (Li+/TFSI−, AlCl4−/Al3+, Ca2+/PF6−, Li+/Mg2+; TFSI = bis(trifluoromethylsulfonyl)imide) transfer have been increasingly studied.19, 20, 21, 22 With regard to anion battery systems, the chloride ion battery (CIB) is intriguing owing to that the nontoxic and abundant chloride‐containing materials for both electrode and electrolyte are available worldwide.23 Moreover, the CIB shows a variety of potential electrochemical couples with high theoretical volumetric energy density up to 2500 Wh l−1, which is higher than those of conventional lithium ion batteries.24
Figure1a shows the X‐ray diffraction (XRD) patterns of the pure PEO, succinonitrile (SN) and tributylmethylammonium chloride (TBMACl), binary SPE films of PEO‐TBMACl and SN‐TBMACl, and ternary PEO‐TBMACl‐SN SPE films. The pure PEO sample has diffraction peaks that are identical to those previously reported,44 indicating its monoclinic crystalline structure. The pure SN sample shows a plastic crystal structure with both amorphous and crystalline phases, as reported in literature.45, 46 The crystalline species exhibits two sharp characteristic peaks at 20.0° and 28.0° corresponding to (110) and (200) lattice planes, respectively. The TBMACl salt possesses a crystalline structure with dozens of diffraction peaks. The broad background centered at about 20.0° was ascribed to the use of amorphous 3M tape for preventing the chloride salt from moisture absorption during the testing. When the TBMACl was mixed with SN in a 1:3 mass ratio, the diffraction peaks of each component almost disappeared, and instead, an evident amorphous structure was formed, indicating the strong chemical interaction between TBMACl and SN due to the high polarity of SN. For the binary PEO‐TBMACl system, the TBMACl can be fully dissolved in the PEO matrix when the mass ratio of PEO and TBMACl is above 1:1, as confirmed by the disappearance of the TBMACl diffraction peaks. Excess TBMACl would be separated from the PEO matrix as the mass ratio decreases to 1:2 (PEO1‐TBMACl2). The addition of SN in the binary PEO‐TBMACl system contributes to a further decrease in crystallinity, as indicated by the evidently weakened and broadened diffraction peaks.
In summary, we developed the first all‐solid‐state rechargeable chloride ion battery by employing a ternary solid polymer electrolyte, which is composed of a PEO polymer matrix, a quaternary ammonium chloride salt, and a solid SN plasticizer. The as‐prepared SPE shows conductivities of 10−5–10−4 S cm−1 in the temperature range of 298–343 K and a high electrochemical stability with the anodic potential of more than 4.2 V versus Li. The chemical interactions, as confirmed by XRD, DSC, and FTIR characterizations, among components of the SPE contributed to the dissociation of the chloride salt and thus bring about the notable increase of the conductivity, resulting in the evident increase of the reversible capacity of the ASS‐RCIB. The electrochemical reaction mechanism of the ASS‐RCIB using the SPE is based on the chloride ion shuttle via the redox reactions of FeOCl/FeO at the cathode side and Li/LiCl at the anode side, as validated by XRD, TEM, XPS and electrochemical measurements.
PEO with an average molecular weight of 300 000 g mol−1, SN (99%), anhydrous acetonitrile (99.8% and packaged under argon), and anhydrous NMP (99.5% and packaged under argon) were purchased from Alfa Aesar. TBMACl (99%) was obtained from Lanzhou Institute of Chemical Physics. PEO and TBMACl were vacuum dried at 313 and 353 K for 48 h before use, respectively. The SPE films were prepared by a solution casting method. For the binary PEO‐TBMACl series, the PEO and TBMACl with a mass ratio range from 5:1 to 1:2 were used. The optimized PEO‐TBMACl composition with a mass ratio of 1:1 was selected to prepare the ternary PEO‐TBMACl‐SN series. The PEO and TBMACl were dissolved in ACN, followed by the addition of different amounts of SN. The mixture was stirred for 48 h at 450 rpm to obtain a homogeneous viscous solution, which was casted onto Teflon plate and allowed to evaporate the ACN solvent in a nitrogen‐filled box for 48 h. Afterward, the samples were dried under vacuum at 323 K for 48 h and stored in an argon‐filled glove box. The schematic illustration for preparation of the SPE films is shown in Scheme S1 in the Supporting Information. The synthesis of the FeOCl cathode material was performed by a thermal decomposition of FeCl3·6H2O at 493 K for 1 h. Then, the product was thoroughly washed with acetone, followed by an overnight drying under vacuum at 333 K.
The authors declare no conflict of interest.