ISSN 1070-4272, Russian Journal of Applied Chemistry, 2016, Vol. 89, No. 5, pp. 697í702. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © Yu.V. Shmatok, N.I. Globa, S.A. Kirillov, 2016, published in Zhurnal Prikladnoi Khimii, 2016, Vol. 89, No. 5, pp. 560í565.
INORGANIC SYNTHESIS AND INDUSTRIAL
Characteristics of Co
Synthesized by the Microwave Method
with the Use of Citrate Precursors
Yu. V. Shmatok, N. I. Globa, and S. A. Kirillov
Joint Department of Electrochemical Energy Systems,
National Academy of Sciences of Ukraine, blvd. Akademika Vernadskogo 38a, Kiev, 03680 Ukraine
Received May 18, 2016
Abstract—Synthesis of Co
powders by the microwave method from citrate precursors is described. The struc-
tural, surface, and thermogravimetric characteristics of the resulting powders were studied depending on the cobalt
ions and citric acid ratio. The speciﬁ c capacity of the samples was determined to be from 665 to 831 mA h g
after 100 cycles at a current density of 0.5C.
Oxides of transition metals (titanium, cobalt, molyb-
denum, nickel, iron, etc.) are among the most effective
anode materials for lithium-ion batteries (LIBs) [1, 2]. To
the advantages of these oxides belongs the high speciﬁ c
capacity, which is within the range 300–1200 mA h g
at a substantial reversibility under cycling conditions.
Cobalt oxide Co
is characterized as an anode
material for LIBs by a high speciﬁ c capacity (890 mA h g
and a discharge voltage of about 1 V [1–3]. The processes
reduction-oxidation in solutions based on
aprotic solvents have been rather well studied [1, 4] and
occur in accordance with the overall reaction that can be
3Co + 4Li
A topical task is to improve the stability of the
speciﬁ c capacity of Co
under cycling and operation
at high discharge rates. It is known [2, 5] that the speciﬁ c
characteristics of Co
can be improved by controlling
its structure, dispersity, and morphology, which is, in
turn, provided by synthesis conditions. A promising
way is to use nanosized Co
whose synthesis was
described in [4–9]. Such methods as template and sol-
gel synthesis, spray-pyrolysis, and co-precipitation
have been used for this purpose. These methods make it
possible to obtain various nanostructured Co
in the form of nanoparticles, nanocubes, nanoﬁ bers,
nanotubes, nanoplates, etc., which positively affects the
electrochemical characteristics of oxides.
Recently, considerable interest is aroused by synthesis
of a number of electrode materials, including those of the
nanosized type, by microwave (MW) irradiation .
This method differs from the conventional techniques
in that it can provide a uniform heating of the internal
volume of a sample and signiﬁ cantly reduce the duration
of thermal processes leading to an increase in the size of
particles and in their agglomeration [10–12].
It was suggested to obtain Co
with particle sizes
in the range from several tens to hundreds of nanometers
by MW synthesis [13–18]. However, data on their
electrochemical tests have been insufﬁ ciently reported.
The use of citrate precursors has become rather
popular for synthesis of simple and complex oxides,
including electrode materials with controllable dispersity
[19–22]. The properties of the oxides being synthesized
are determined by a number of factors, including the
pyrolysis temperature, ratio between metal and citric acid
ions, nature of the metal salt anion, and pH of the medium.
In the general case, synthesis with citrate precursors is
performed in several successive stages, which include the
evaporation of the working solution until a polymeric gel