Inorganic Ultra-Rich Solid Composite Electrolytes for High-Voltage Solid-State Batteries

Abstract

Solid-state batteries (SSB), in which flammable organic liquid electrolytes are replaced by inherently safer solid electrolytes (SEs), are considered to be the evolution of current Li-ion battery technology toward greater safety and higher energy density. Among the various SEs, the PEO-LiTFSI system has been the most studied due to its low cost and ease of processing. However, the relatively low oxidation stability of PEO-LiTFSI at about 4.0 V vs. Li/Li+ does not allow the use of high-voltage cathode active materials, which limits the available energy density [1]. We propose that a high content of Li-ion conductive ceramic in the PEO-LiTFSI matrix increases oxidation stability, allowing stable cell cycling with Ni-rich NMC cathode at higher voltages. This class of inorganic ultra-rich composite SEs has attracted much interest recently [2, 3].In this work, we present a self-standing, dense, flexible (Fig.1a), and thermally stable (Fig.1b) composite solid electrolyte (INURSE 30) that has an ultra-high content of Li-ion conductive LLZO (90 wt%, as confirmed by TGA in Fig. 1b)in the PEO-LiTFSI matrix. The ionic conductivity of INURSE 30 is 1.4x10-5 S/cm at 60ºC. The INURSE 30 electrolyte shows long-term cycling stability of more than 2000 h at a current density of 0.01 mA/cm2 in symmetric cells with Li electrodes. In addition, the high-voltage stability of INURSE 30 was demonstrated in solid-state cells with a composite solid-state cathode containing 75 wt% NMC622 and a Li metal anode. The Li/INURSE 30/NMC622 coin cell shows good coulombic efficiency and capacity retention, as shown in Fig.1c. K.V. acknowledges the financial support from Fundacíon CIDETEC and DESTINY PhD programme which received funding from the European Union's Horizon2020 research and innovation programme under the Marie Skłodowska-Curie Actions COFUND - Grant Agreement No: 945357.