A Single‐Ion Conducting Borate Network Polymer as a Viable Quasi‐Solid Electrolyte for Lithium Metal Batteries

• Published in: Advanced materials (Weinheim) 2020-03, Vol.32 (10), p.e1905771-n/a
• Main Authors: Shin, Dong‐Myeong, Bachman, Jonathan E., Taylor, Mercedes K., Kamcev, Jovan, Park, Jesse G., Ziebel, Michael E., Velasquez, Ever, Jarenwattananon, Nanette N., Sethi, Gurmukh K., Cui, Yi, Long, Jeffrey R.
• Format: Article
• Language: English
• Subjects: borate network polymers; Electrochemical analysis; Electrode materials; Electrolytes; Energy storage; Flame retardants; Lithium; lithium metal batteries; Lithium-ion batteries; Molten salt electrolytes; Polymers; Safety; Selectivity; single‐ion conducting polymers; Solid electrolytes; Storage batteries; Thermal conductivity; Thermal stability
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201905771

Lithium‐ion batteries have remained a state‐of‐the‐art electrochemical energy storage technology for decades now, but their energy densities are limited by electrode materials and conventional liquid electrolytes can pose significant safety concerns. Lithium metal batteries featuring Li metal anodes, solid polymer electrolytes, and high‐voltage cathodes represent promising candidates for next‐generation devices exhibiting improved power and safety, but such solid polymer electrolytes generally do not exhibit the required excellent electrochemical properties and thermal stability in tandem. Here, an interpenetrating network polymer with weakly coordinating anion nodes that functions as a high‐performing single‐ion conducting electrolyte in the presence of minimal plasticizer, with a wide electrochemical stability window, a high room‐temperature conductivity of 1.5 × 10−4 S cm−1, and exceptional selectivity for Li‐ion conduction (tLi+ = 0.95) is reported. Importantly, this material is also flame retardant and highly stable in contact with lithium metal. Significantly, a lithium metal battery prototype containing this quasi‐solid electrolyte is shown to outperform a conventional battery featuring a polymer electrolyte. An anionic porous aromatic framework consists of immobile weakly coordinating borate anions, which facilitate sole Li+ mobility, connected through butenediol linkers, which enable post‐synthetic crosslinking. The framework exhibits remarkable Li+ ion selectivity and room‐temperature conductivity, flame retardancy, and stability toward Li metal and high‐potential cathode materials. This material endows outstanding power performance and cycling stability in a battery prototype.