Plasma-enhanced atomic layer deposition of vanadium phosphate as a lithium-ion battery electrode material

Abstract

Vanadium phosphate films were deposited by a new process consisting of sequential exposures to trimethyl phosphate (TMP) plasma, O 2 plasma, and either vanadium oxytriisopropoxide [VTIP, OV(O-i-Pr) 3 ] or tetrakisethylmethylamido vanadium [TEMAV, V(NEtMe) 4 ] as the vanadium precursor. At a substrate temperature of 300 C, the decomposition behavior of these precursors could not be neglected; while VTIP decomposed and thus yielded a plasma-enhanced chemical vapor deposition process, the author found that the decomposition of the TEMAV precursor was inhibited by the preceding TMP plasma/O 2 plasma exposures. The TEMAV process showed linear growth, saturating behavior, and yielded uniform and smooth films; as such, it was regarded as a plasma-enhanced atomic layer deposition process. The resulting films had an elastic recoil detection-measured stoichiometry of V 1.1 PO 4.3 with 3% hydrogen and no detectable carbon contamination. They could be electrochemically lithiated and showed desirable properties as lithiumion battery electrodes in the potential region between 1.4 and 3.6 V versus Li þ /Li, including low capacity fading and an excellent rate capability. In a wider potential region, they showed a remarkably high capacity (equivalent to three lithium ions per vanadium atom), at the expense of reduced cyclability. V

Plasma-enhanced atomic layer deposition of nickel and cobalt phosphate for lithium ion batteries

“…Both materials exhibit a good coulombic efficiency with a decent, but not ideal, cycle life (where approximately 89% of the capacity is retained after 50 cycles for both phosphates). The capacity retention is slightly worse compared to other metal phosphates deposited through a similar ALD process, 22,23,25 which is thought to originate from the nature of the electrochemical reactions. While the previously reported metal phosphates relied on intercalation-type reactions, the conversion or alloying reactions that might take place in the nickel and cobalt phosphate could lead to a slightly less stable cycle life.…”

“…In this work, an initial attempt towards researching ALD of nickel phosphate will be made based on earlier work by Dobbelaere et al 21 In this work, aluminium phosphate was deposited through a plasma-enhanced ALD process (PE-ALD), combining trimethylphosphate plasma (TMP*, with the star denoting the plasma state) with oxygen plasma and trimethylaluminum (TMA). However, it was quickly found that by changing the metal precursor, other metal phosphates such as titanium, 22 vanadium, 23 zinc, 24 iron 25 and cobalt phosphates 26 could be deposited as well. For the deposition of nickel phosphate in this work, the metal-organic precursor of choice became nickelocene, inspired by our earlier work on PE-ALD of cobalt phosphate and as this precursor has already proven to be successful towards PE-ALD of nickel oxide.…”

Mechanistic studies of atomic layer deposition on oxidation catalysts – AlOx and POx deposition

“…For example, T. Dobbelaere et al developed an ALD process for vanadium phosphate on flat substrates involving O 2 plasma. 1 In fact, plasma has the drawback of surface recombination and might not be suitable for ALD on powders, especially in fixed bed geometry or with porous powders. 27,28 Therefore, surface modification of existing bulk catalysts is in some cases the only option to obtain the desired surface layer.…”

Atomic Layer Deposition of Nitrogen-Doped Al Phosphate Coatings for Li-Ion Battery Applications

“…5 times higher than for typical ALD. By changing the metal precursor at the end of each cycle, the approach could be extended to titanium 16 , vanadium 25 , zinc 26 , iron 17 and cobalt phosphate 27 .…”