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Polymer–ceramic composite electrolytes are major contenders for applications in commercial Li-metal solid-state batteries. However, the cycling performance and energy density of such batteries are ...

Alucones are one of the best-known films in the Molecular Layer Deposition (MLD) field. In this work, we prove that alucone/Al2O3 nanolaminate synthesis can be successfully performed by alternating alucone MLD growth with static O2 plasma exposures. Upon plasma treatment, only the top part of the alucone is densified into Al2O3, while the rest of the film remains relatively unaltered. X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) depth profiling show that the process yields a bilayer structure, which remains stable in air. Fourier-transform infrared spectroscopy (FTIR) measurements show that Al2O3 features are generated after plasma treatment, while the original alucone features remain, confirming that plasma treatment results in a bilayer structure. Also, an intermediate carboxylate is created in the interface. Calculations of Al atom density during plasma exposure point towards a partial loss of Al atoms during plasma treatment, in addition to the removal of the glycerol backbone. The effect of different process parameters has been studied. Densification at the highest temperature possible (200 °C) has the best alucone preservation without hindering its thermal stability. In addition, operating at the lowest plasma power is found the most beneficial for the film, but there is a threshold that must be surpassed to achieve successful densification. About 70% of the original alucone film thickness can be expected to remain after densification, but thicker films may result in more diffuse interfaces. Additionally, this process has also been successfully performed in multilayers, showing real potential for encapsulation applications.

The industrial development of Li metal solid state batteries will be boosted not only by providing highly Li+ conductive electrolyte materials, but also by demonstrating their technical viability in the actual device. For the first time, the electrochemical performances of two different electrolytes, a pure Li7La3Zr2O12 ceramic and a polymer–ceramic composite, are compared in a solid state battery with a Li metal anode and a LiFePO4 cathode. No liquid or gel additive was added to improve the interfacial contacts. The technological viability of these two systems was assessed under realistic cycling conditions with a competitive cathode loading of 1 mA h cm−2. Here, we show promising performances for both electrolytes at 70 °C under slow cycling rates; however, the composite stands out under fast cycling rates due to enhanced interfacial contacts. The energy density of the two systems is compared to the electric vehicle industry targets providing clear specifications for future system development.