Atomic Layer Deposition of LiCoO₂Thin-Film Electrodes for All-Solid-State Li-Ion Micro-Batteries

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 LiCoO 2 which can serve as a cathode material. A combination of CoCp 2 as cobalt precursor, LiO t Bu as lithium precursor and O 2 plasma as oxidant source was used to create super-cycles to deposit LiCoO 2 from Co 3 O 4 and Li 2 CO 3 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 LiCoO 2 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 LiCoO 2 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 LiCoO 2 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 LiCoO 2 can be deposited by ALD.