"Water-in-salt" polymer electrolyte for Li-ion batteries

• Published in: Energy & environmental science Vol. 13; no. 9; pp. 2878 - 2887
• Main Authors: Zhang, Jiaxun, Cui, Chunyu, Wang, Peng-Fei, Li, Qin, Chen, Long, Han, Fudong, Jin, Ting, Liu, Sufu, Choudhary, Hema, Raghavan, Srinivasa R, Eidson, Nico, von Cresce, Arthur, Ma, Lin, Uddin, Jasim, Addison, Dan, Yang, Chongyin, Wang, Chunsheng
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 16.09.2020; Royal Society of Chemistry (RSC)
• Subjects: Addition polymerization; Anodes; Anodic coatings; Aqueous electrolytes; Batteries; Bipolar cells; Crosslinking; Electrochemistry; Electrodes; Electrolytes; Flux density; Hydrogels; Lithium; Lithium fluoride; Lithium manganese oxides; Lithium-ion batteries; Polymers; Product safety; Rechargeable batteries; Salts; Separators; Solid state; Stability; Ultraviolet radiation; Wearable technology
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d0ee01510e

Recent success in extending the electrochemical stability window of aqueous electrolytes to 3.0 V by using 21 mol kg -1 "water-in-salt" (WiS) has raised a high expectation for developing safe aqueous Li-ion batteries. However, the most compatible Li 4 Ti 5 O 12 anodes still cannot use WiS electrolyte due to the cathodic limit (1.9 V vs. Li/Li + ). Herein, a UV-curable hydrophilic polymer is introduced to further extend the cathodic limit of WiS electrolytes and replace the separator. In addition, a localized strongly basic solid polymer electrolyte (SPE) layer is coated on the anode to promote the formation of an LiF-rich SEI. The synthetic impacts of UV-crosslinking and local alkaline SPE on the anodes extend the electrochemical stability window of the solid-state aqueous polymer electrolyte to ∼3.86 V even at a reduced salt concentration of 12 mol kg −1 . It enables a separator-free LiMn 2 O 4 //Li 4 Ti 5 O 12 aqueous full cell with a practical capacity ratio (P/N = 1.14) of the cathode and anode to deliver a steady energy density of 151 W h kg −1 at 0.5C with an initial Coulombic efficiency of 90.50% and cycled for over 600 cycles with an average Coulombic efficiency of 99.97%, which has never been reported before for an aqueous LiMn 2 O 4 //Li 4 Ti 5 O 12 full cell. This flexible and long-duration aqueous Li-ion battery with hydrogel WiSE can be widely used as a power source in wearable devices and electrical transportations where both energy density and battery safety are of high priority. An ultra-thick LTO electrode with UV-curable polymer electrolyte as the binder is demonstrated as a solid state battery electrode. And a high-voltage (7.4 V) solid-state bipolar cell is assembled with a solid-state UV-curable polymer as the electrolyte. An extended electrochemical stability window of 3.86 V is achieved at 12 mol kg −1 aqueous polymer electrolyte enabled 3 V full cells with an unprecedented high initial CE of 90.50% and average CE of 99.97%.