Ionic Liquid Enabled High-Energy-Density Solid-State Lithium Batteries with High-Areal-Capacity Cathode and...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid-state lithium batteries (SSLBs) promise higher energy density and safety than conventional lithium-ion batteries.
• Key challenges include thick electrolytes, low ionic conductivity, and high interfacial resistance, limiting practical application.
• Composite solid electrolytes (CSEs) offer a potential solution by combining different materials to overcome these limitations.

Purpose of the Study:

• To develop a thin and highly conductive composite solid electrolyte (CSE) for SSLBs.
• To reduce the interfacial resistance between the electrolyte and electrodes.
• To fabricate and evaluate a high-energy-density SSLB using the developed CSE and a thick composite cathode.

Main Methods:

• Fabrication of an 18 µm-thick CSE using a polyethylene scaffold, garnet-type Li$_{6.25}$La$_{3}$Zr$_{2}$Ga$_{0.25}$O$_{12}$ (LLZGO) oxide, and an ionic liquid (IL) additive within a polymer matrix.
• Integration of LLZGO and N-propyl-N-methylpyrrolidinium bis(trifluorosulfonyl)imide (PMP-TFSI) IL into a LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_{2}$ (NCM-811) cathode.
• Electrochemical characterization of the CSE, including ionic conductivity measurements, and testing of assembled LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_{2}$ (NCM-811)||CSE||Li and composite cathode||CSE||Li cells.

Main Results:

• Achieved a CSE ionic conductivity of 8.6 × 10$^{-4}$ S cm$^{-1}$ at 30 °C, with the IL enhancing Li$^{+}$ conduction and reducing interfacial resistance.
• Demonstrated remarkable charge-discharge performance in a LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_{2}$ (NCM-811)||CSE||Li cell.
• Developed a high-mass-loading NCM-811 cathode (≈20 mg cm$^{-2}$) and achieved an areal capacity of ≈4 mAh cm$^{-2}$ in a composite cathode||CSE||Li cell.
• Projected an energy density of ≈420 Wh kg$^{-1}$ for the resulting anode-free pouch cell.

Conclusions:

• The developed scaffold-supported CSE with IL additive significantly enhances Li$^{+}$ transport and reduces interfacial resistance in SSLBs.
• The integration of LLZGO and IL into a thick NCM-811 cathode enables high areal capacity and contributes to high energy density.
• This study presents a scalable strategy for fabricating high-performance, high-energy-density oxide-based SSLBs.