Atomic layer deposition (ALD) is an excellent tool for realisation of uniform coating of cathode materials on highly 3D-nanostructured microbatteries. We have developed an ALD-process for deposition of iron phosphate, FePO 4 , as a cathode material and characterised its electrochemical properties towards a lithium metal anode. Thin films were deposited between 196 and 376 C using the precursor pairs: trimethyl phosphate (TMP, Me 3 PO 4) with both H 2 O and ozone (O 3) as an oxygen source, and Fe(thd) 3 (Hthd ¼ 2,2,6,6-tetramethyl-3,5-heptanedionate) with O 3. The as-deposited films are amorphous and crystallize to trigonal FePO 4 after heat treatment in air at 600 C. The amorphous FePO 4 films were characterised electrochemically proving exceptional cyclability and capacities almost reaching the 100% theoretical value (178 mA h g À1) for 1 hour charge-discharge rates.

Atomic layer deposition (ALD) technique is a thin film deposition method that provides highly conformal films on 3D structured supports, including powder materials. The technique relies on sequential self-limiting gas-to-surface reactions which enable control of thin film depositions even down to the atomic level on complex surface geometries. Even if ALD technique has been used in the semiconductor industry in production scale for several years now, there are rather few reports on ALD of battery materials. However, the recent development in processes for lithium containing films clearly opens up new possibilities. Promising applications of ALD include 3D structured all-solid-state batteries and surface modification of electrode powders. The present paper presents an overview of the present status in application of ALD in the field of lithium ion batteries.