Long‐cycling and High‐voltage Solid State Lithium Metal Batteries Enabled by Fluorinated and Crosslinked Polyether Electrolytes

Abstract

Solid‐state lithium metal batteries (LMBs), constructed through the in‐situ fabrication of polymer electrolytes, are considered a critical strategy for the next‐generation battery systems with high energy density and enhanced safety. However, the constrained oxidation stability of polymers, such as the extensively utilized polyethers, limits their applications in high‐voltage batteries and further energy density improvements. Herein, an in‐situ fabricated fluorinated and crosslinked polyether‐based gel polymer electrolyte, FGPE, is presented, exhibiting a high oxidation potential (5.1 V). The fluorinated polyether significantly improves compatibility with both lithium metal and high‐voltage cathode, attributed to the electron‐withdrawing ‐CF3 group and the generated LiF‐rich electrolyte/electrode interphase. Consequently, the solid‐state Li||LiNi0.6Co0.2Mn0.2O2 batteries employing FGPE demonstrate exceptional cycling performances of 1000 cycles with 78% retention, representing one of the best results ever reported for polymer electrolytes. Moreover, FGPE enables batteries to operate at 4.7 V, realizing the highest operating voltage of polyether‐based batteries to date. Notably, our designed in‐situ FGPE provides the solid‐state batteries with exceptional cycling stability even at practical conditions, including high cathode loading (21 mg cm‐2) and industry‐level 18650‐type cylindrical cells (1.3 Ah, 500 cycles). This work provides critical insights into the development of oxidation‐stable polymer electrolytes and the advancement of practical high‐voltage LMBs.

Preparation of Main-Chain Fluorinated Alternating Polymer by START Polymerization for All-Solid-State Electrolytes

“…Fluorinated materials help to form SEI on the electrode/electrolyte interface, , and it is a passivation layer to prevent further chemical reactions between the electrode and electrolyte. , Besides, fluorine has perfect thermal and electrochemical stability, excellent dielectric properties, low surface energy, and high electronegativity, so fluorinated materials have become a good choice in battery components as additives and binders . Moreover, fluorinated polymers are also crucial to the performance of batteries in terms of ion transport, electrochemical stability, cycle stability, etc. − Some studies have shown that the ion conductivity after fluorination at room temperature was significantly improved, and the Coulomb efficiency (CE) and cycle stability were also greatly improved. − Chen et al , synthesized two kinds of fluorinated alternating polymer electrolytes: main-chain and side-chain fluorinated. It was found that the side-chain fluorinated polymers were easier to cleave; the voltage window, specific capacity, and cycle stability were also inferior to those of main-chain type.…”

Coupling of Ethylene-Oxide-Based Polymeric Network Structure and Counterion Chemistry to Ionic Conductivity and Ion Selectivity

“…8−10 Wen et al 9 designed a single-lithium-ionconducting network based on crosslinked PEO to achieve good performance in a solid-state battery. Recently, Zhu et al 10 used fluorinated crosslinked polyether electrolytes to further widen the chemical stability range of the polyether. A deeper understanding of ion transport in polymer networks may enable the design of mechanically robust polymer electrolytes with enhanced ionic conductivity as well as selective ion transport (important for separation processes).…”

“…One approach to realize such systems with both good mechanical and transport properties is to utilize polymers that contain both soft (for ion transport) and hard (for strong mechanical strength) segments . Another approach is to add crosslinks, as polymer networks are generally mechanically more robust than their linear polymer counterpart as long as the crosslinks do not impede transport. , Such a crosslinking approach has shown potential for solid-state battery applications. − Wen et al designed a single-lithium-ion-conducting network based on crosslinked PEO to achieve good performance in a solid-state battery. Recently, Zhu et al .…”

“…Another approach is to add crosslinks, as polymer networks are generally mechanically more robust than their linear polymer counterpart as long as the crosslinks do not impede transport. , Such a crosslinking approach has shown potential for solid-state battery applications. − Wen et al designed a single-lithium-ion-conducting network based on crosslinked PEO to achieve good performance in a solid-state battery. Recently, Zhu et al . used fluorinated crosslinked polyether electrolytes to further widen the chemical stability range of the polyether.…”