A Stretchable and Safe Polymer Electrolyte with a Protecting‐Layer Strategy for Solid‐State Lithium Metal Batteries

Abstract

An elastic and safe electrolyte is demanded for flexible batteries. Herein, a stretchable solid electrolyte comprised of crosslinked elastic polymer matrix, poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP), and flameproof triethyl phosphate (TEP) is fabricated, which exhibits ultrahigh elongation of 450%, nonflammability and ionic conductivity above 1 mS cm−1. In addition, in order to improve the interface compatibility between the electrolyte and Li anode and stabilize the solid‐electrolyte interphase (SEI), a protecting layer containing poly(ethylene oxide) (PEO) is designed to effectively prevent the anode from reacting with TEP and optimize the chemical composition in SEI, leading to a tougher and more stable SEI on the anode. The LiFePO4/Li cells employing this double‐layer electrolyte exhibit an 85.0% capacity retention after 300 cycles at 1 C. Moreover, a flexible battery based on this solid electrolyte is fabricated, which can work in stretched, folded, and twisted conditions. This design of a stretchable double‐layer solid electrolyte provides a new concept for safe and flexible solid‐state batteries.

Long-chain fluorocarbon-driven hybrid solid polymer electrolyte for lithium metal batteries

“…1–3 Nevertheless, due to the potential safety hazards and low theoretical energy densities of conventional lithium-ion batteries consisting of flammable liquid electrolyte (LE) and graphite anodes, researchers have begun to pursue superior alternatives. 4–6 Combining a non-volatile and non-inflammable solid electrolyte with Li metal anodes that have high capacity and low electrochemical potential provides a feasible solution. 5,6 As a substitute for LEs, Li + -conducting solid electrolytes form a critical component of solid-state lithium metal batteries (SLMBs) and require several alternative properties, such as subduing Li dendrite growth, high mechanical flexibility, and durable electrochemical and thermal stability.…”

“…4–6 Combining a non-volatile and non-inflammable solid electrolyte with Li metal anodes that have high capacity and low electrochemical potential provides a feasible solution. 5,6 As a substitute for LEs, Li + -conducting solid electrolytes form a critical component of solid-state lithium metal batteries (SLMBs) and require several alternative properties, such as subduing Li dendrite growth, high mechanical flexibility, and durable electrochemical and thermal stability. 5,7,8 Among the different solid electrolyte categories, inorganic electrolytes tend to show high ion conductivity and tough mechanical strength.…”

“…5,6 As a substitute for LEs, Li + -conducting solid electrolytes form a critical component of solid-state lithium metal batteries (SLMBs) and require several alternative properties, such as subduing Li dendrite growth, high mechanical flexibility, and durable electrochemical and thermal stability. 5,7,8 Among the different solid electrolyte categories, inorganic electrolytes tend to show high ion conductivity and tough mechanical strength. However, the rigid interface between the electrode and an inorganic electrolyte cannot buffer the volume change during the charging and discharging process, which causes large dynamic interface impedance, and the uneven deposition of lithium ions on the Li metal interface may cause destructive lithium dendrites to grow along the grain boundaries.…”

Double-Layer Solid Composite Electrolytes Enabling Improved Room-Temperature Cycling Performance for High-Voltage Lithium Metal Batteries

“…Generally, SSEs include solid inorganic electrolytes (SIEs), solid polymer electrolytes (SPEs), and solid composite electrolytes (SCEs) . SIEs have attracted attention mainly because of their high ionic conductivity and large moduli for lithium dendrite inhibition, but their inherent mechanical brittleness and high interface impedance leads to severely limited utilization. − Compared with SIEs, SPEs are known for the easier processing, higher mechanical flexibility, and better interfacial compatibility, while they always show a low ionic conductivity at 25 °C (<10 –4 S cm –1 ), which is hard to meet the normal operation of room-temperature batteries. ,, As a solution to the issues, SCEs constructed through compounding inorganic fillers with SPEs are considered to be the most promising candidate for safe electrolytes on account of the combined advanced features of SIEs and SPEs, such as acceptable ionic conductivity, good interface contact with electrodes, improved mechanical strength to realize lithium dendrite inhibition, and so on. − Unfortunately, a monocomponent polymer matrix for SCEs is still powerless to satisfy the increasingly diversified demands.…”

“…32,33 The promising efforts to overcome such incompatibility between a wide electrochemical window and good interface stability focuses on constructing multilayer SCEs with Janus characteristics. 21,23,28,30,33 Herein, novel double-layer SCEs consisting of an antioxidative PVDF-based layer facing the cathode and a lithium metal-friendly (PEO+PVDF)-based layer against the anode, are proposed for room-temperature high-voltage LMBs. Specially, the bipolymer feature of the (PEO+PVDF)-based layer therein not only endows the electrolytes with excellent lithium affinity but also avoids the PEO-introduced mechanical softness with the help of the mechanical support of PVDF polymers.…”