Atomic Layer Deposition of LiCoO2 Thin-Film Electrodes for All-Solid-State Li-Ion Micro-Batteries

Abstract

One of the remaining challenges in the field of portable electronics is the miniaturization of lithium-ion batteries. To prepare all-solid-state batteries with a sufficient high storage capacity it is vital to prepare high quality thin films for battery stacks on 3D-structured substrates. A remote plasma atomic layer deposition (ALD) process has therefore been developed for LiCoO2 which can serve as a cathode material. A combination of CoCp2 as cobalt precursor, LiOtBu as lithium precursor and O2 plasma as oxidant source was used to create super-cycles to deposit LiCoO2 from Co3O4 and Li2CO3 cycles. The thin films were deposited at a temperature of 325°C and showed linear growth with a rate of 0.06 nm/cycle. After annealing the samples at 700°C for 6 minutes high temperature phase LiCoO2 was obtained, as was demonstrated by XRD and Raman spectroscopy. A new procedure was proposed to obtain the composition of all three chemical elements in the LiCoO2 films. Elastic Backscattering Spectroscopy (EBS) measurements turned out to be very convenient and reliable to obtain the quantities of all chemical elements, including lithium. Moreover, the ALD-deposited LiCoO2 thin film electrodes were electrochemically characterized, revealing good electrochemical performance. To the best of our knowledge this paper provides the first evidence that electrochemically active LiCoO2 can be deposited by ALD.