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

Abstract

The development of solid-state electrolytes (SSEs) for high energy density lithium metal batteries (LMBs) usually needs to take into account of the interfacial compatibility against lithium metal and the electrolyte stability suitable for a high-potential cathode. In this study, through a facile two-step coating process, novel double-layer solid composite electrolytes (SCEs) with Janus characteristics are customized for the high-voltage LMBs with improved room-temperature cycling performance. Among which, high-voltage resistant poly­(vinylidene fluoride) (PVDF) is adopted here for the construction of an electrolyte layer facing the cathode, while the other layer against the lithium anode is composed of the polymer matrix of poly­(ethylene oxide) (PEO) blended with PVDF to obtain a lithium metal-friendly interface. With the further incorporation of Laponite clay, the PVDF/(PEO+PVDF)-L SCEs not only exhibit improved mechanical properties, but also achieve a highly increased ionic conductivity (5.2 × 10–4 S cm–1) and lithium ion migration number (0.471) at room temperature. The assembled NCM523|PVDF/­(PEO+PVDF)-L SCEs|Li cells thus are able to deliver the initial discharge capacity of 153.9 mAh g–1 with 80.8% capacity retention after 200 cycles at 0.3 C. Such easily manufactured double-layer SCEs capable of operating steadily at room temperature provide a competitive electrolyte option for high-voltage solid-state LMBs.

Challenges of polymer electrolyte with wide electrochemical window for high energy solid‐state lithium batteries

“…Therefore, these electrolytes are often used to prepare the GPEs. 75 Zou et al prepared PVDF-PEO organic composite electrolyte through blending, with ionic conductivity up to 5.2 Â 10 À5 S cm À1 at room temperature and ESW up to 4.4 V. 76 The capacity retention rate of NCM523/PVDF/ PVDF-PEO/Li battery with NCM523 high voltage positive electrode was more than 80.0% after 200 cycles. The bilayer structure improved the oxidation resistance and cycling stability of the electrolyte (Figure 7A(i-iii)).…”

“…Reproduced with permission. 76 Copyright 2021, American Chemical Society. Compared with PVDF side, the surface of (PEO + PVDF) + L side doped with PEO becomes smooth, which is beneficial to improve the contact between electrode and electrolyte and reduce the interfacial impedance.…”

“…And the comparison of (ii) ionic conductivity and (iii) ESW of PVDF‐based SPEs with different components. Reproduced with permission 76 . Copyright 2021, American Chemical Society.…”

Recent Advances and Future Perspectives of PVDF-Based Composite Polymer Electrolytes for Lithium Metal Batteries: A Review

“…(h) Cycling performance plots of the solid-state LMBs at 25 °C. (g and h) Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…PVDF coblended polymers can often bring unexpected effects in the suppression of lithium dendrites. Zhang et al prepared bilayer CPEs (PVDF/(PEO+PVDF)-L) for high-pressure LMBs using a two-step coating method . The PVDF/(PEO+PVDF)-L CPE has both good mechanical character and in the case of Laponite clay introduction improved conductivity of Li + (5.2 mS cm –1 ) (Figure g) and 0.471 of t Li + at normal temperature, and the battery assembled with NCM523 high-voltage cathode can be stable for 200 cycles (Figure h), which drives the commercialization of high-voltage LMBs forward.…”