Chromium nitride as a stable cathode current collector for all-solid-state thin film Li-ion batteries

Abstract

The development of highly oxidation resistant current collectors which are inert against lithium at elevated temperatures (>600 °C) and high potentials (3–5 V vs. Li⁺/Li) is required for the realization of high voltage, thin film, all-solid-state Li-ion batteries. This is due to the method of building such batteries using layer by layer deposition, requiring the first layer to remain stable during all subsequent processing steps. A new cathode current collector based on Cr₂N thin films and prepared by reactive pulsed DC sputtering at 300 °C is reported here. By varying the nitrogen partial pressure in the reactor several Cr_xN thin film alloys are prepared and their microstructural and electrical properties are characterized. We demonstrate that the alloy with an estimated composition of Cr_2.1N exhibits a relatively low sheet resistance of 2.6 Ω sq⁻¹ for a ∼500 nm film, high oxidation resistance and no reaction with lithium up to 600 °C. Furthermore, we observed electrochemical stability in the potential range 3–5 V vs. Li⁺/Li. Finally, as a proof of concept the electrochemical behavior of cells using Cr_2.1N thin films as a current collector for the high voltage cathode LiMn_1.5Ni_0.5O₄ is presented.