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Cite this: RSC Adv., 2021, 11, 37150

Surface coating of a LiNixCoyAl1xyO2 (x > 0.85)
cathode with Li3PO4 for applying a water-based
hybrid polymer binder during Li-ion battery
preparation†
Tatsuya Watanabe,a Tamae Yokokawa,a Mitsuru Yamada,a Shoudai Kurosumi,bShinsaku Ugawa,b Hojin Lee,b Yuta Irii,c Fumihiko Maki,c Takao Gunji, a Jianfei Wu
and Futoshi Matsumoto *ad

To produce water-stable Ni-rich lithium nickel cobalt aluminum oxides (LiNixCoyAl1xyO2, x > 0.85, NCAs),
the formation of trilithium phosphate (Li3PO4)-coated layers on the NCA surfaces was attempted throughthe use of a surface reaction in a mixture of ethanol and water and a post-heat treatment at 350 and 400  C.
Received 24th August 2021
Accepted 20th October 2021

Based on the results of X-ray photoelectron spectroscopy (XPS), the coated layers consisted of nickel
phosphate (Ni3(PO4)2) and Li3PO4. The coated NCA surface could have suﬃcient water stability tomaintain the cathode performance in a water slurry for 1 day. In addition, the coated layers formed on

DOI: 10.1039/d1ra06409f

the NCA surfaces did not block Li+-ion transfer through the Ni3(PO4)2/Li3PO4-coating layers andrsc.li/rsc-advancesenhanced the high-rate discharge performance.

1

Introduction

Lithium-ion batteries (LIBs) have spread to our daily life as
power sources of mobile devices1,2 and are helping to establish
the world of electrically driven vehicles.3,4 LIBs are chemical
devices in which chemical energy converts to electrical energy inthe discharging process and electrical energy converts tochemical energy in the charging process.5,6 The chemicals bear
the energy conversion in the LIB. Chemicals such as anodes,
cathodes, electrolytes, solvents, binders, and conductive additives have been designed for them to not only exhibit maximum
performance but also to not cause trouble for other chemicals.7–9 Usually, electrolytes, solvents, binders, conductive
additives and so on have also been modied for anode andcathode materials to exhibit maximum performance.10,11 Moreover, recently, in anode and cathode materials, their composition and surface had to be modied to increase the battery
performance and to decrease the cost of LIBs.12–14 For example,
coating the cathode surface was attempted to prepare a cathodea

Department of Materials and Life Chemistry, Kanagawa University, 3-27-1,
Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686, Japan. E-mail:fmatsumoto@kanagawa-u.ac.jpbc

JSR Corporation, 100 Kawajiri-cho, Yokkaichi, Mie 510-8552, Japan

Nihon Kagaku Sangyo Co., Ltd., 1-28-13 Nakane, Soka, Saitama 340-0005, Japand

Qingdao Industrial Energy Storage Research Institute, Qingdao Institute of Bioenergy
and Bioprocess Technology, Chinese Academy of Sciences, No. 189, Songling Road,
266101 Qingdao, China† Electronic supplementary
10.1039/d1ra06409f

information

37150 | RSC Adv., 2021, 11, 37150–37161(ESI)

available.

See

DOI:

with a water-based slurry.15,16 Aqueous processes for the fabrication of anode and cathode electrodes in LIBs with watersoluble and aqueous polymers, i.e., water-based polymers,
have attracted much attention as binders to establish environmentally compatible fabrication processes for LIBs and to
reduce the price of LIBs.17,18 In the conventional slurry process,poly(vinylidene diuoride) (PVdF) polymer binder, active
materials and conductive additives are dissolved in N-methylpyrrolidone (NMP) solvent, which is listed as a carcinogenic
chemical with reproductive toxicity and should be collectedwithout atmospheric emission.19 Then, the slurry is cast on
current collectors, and nally, the solvent is evaporated ina vacuum drying process to form an active material layer on thecurrent collector. The cathode materials dissolved increasingly
less in water and the charging/discharging cycle performance
was degraded when the surface was in contact with water.
Ni-rich lithium nickel cobalt aluminum oxide (LiNixCoyAl1xyO2, NCA) cathode materials, which are responsible forthe energy storage capability of Panasonic cylindrical 18650
cells, exhibit a higher reversible capacity (>190 mA h g1) andare regarded as an attractive cathode material due to theiroutstanding electrochemical performance, thermal stability
and environmentally friendly features.20–22 However, NCAs still
have several problems, such as severe capacity fading during thecharge–discharge process and thermal runaway attributed tostructural instability.23,24 In addition, there are serious problems
with the dissolution of the surface of NCAs and the lithium ion/
proton (Li+/H+) exchange reaction from/into NCAs caused bycontacting the NCA surfaces with water and then a drastic drop

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RSC Advancesin the charging/discharging capacities.25–29 For NCAs to avoid
water contact, various surface coatings of NCAs were
proposed15,30,31 as well as the addition of acid and buﬀer
chemicals to keep the pH in aqueous slurry.32–34 Trilithium
phosphate (Li3PO4) coating on NCAs to give waterproof properties to the surface of NCAs has been attracted.35,36 The Li3PO4
surface layer is also applied to conventional LIBs in whichcathodes are prepared with a conventional solvent process witha PVdF binder and NMP solvent to hinder side reactions
between the cathode and the organic electrolyte and oxygen
release from the cathode surface, resulting in the improvementof cathode performance and thermal stability.37–40 Li3PO4 haschemical and thermal stability and exhibits intrinsic Li+
conductivity with stable P]O bonds.37–40 Wet coating of Li3PO4
is a simple method by adding phosphate ion (PO43) ions toa reaction solution in which NCA particles are dispersed. On the
NCA surface, PO43 ions react with lithium hydroxide (LiOH)
and lithium carbonate (Li2CO3) residues formed on the NCA
surface, and then Li3PO4 is formed on the NCA surfaces. As
mentioned above, there are several reports that Li3PO4coated NCA has waterproof properties and that NCA cathodes
prepared with aqueous processes exhibit more stable cathode
performance than those prepared with conventional organic
solvent processes.35,36 However, we cannot think that Li3PO4coated NCA has water-proof properties enough to apply
Li3PO4-coated NCA to commercially available LIB production
because the results were obtained with cathodes preparedwith fresh slurry and Li3PO4-coated NCA was not exposed fora long time. When slurry solutions of electrode active materials are used, once prepared, typically for one day at least in
the production line of commercially available LIBs. Therefore, the slurry that was stored for a long time should be used
to prepare the cathodes for performance testing of Li3PO4coated NCA.
Additionally, in this study, a Li3PO4 coating on NCA particle
surfaces was examined because of the simple wetting process of
the Li3PO4 layer and the suitable property of Li3PO4 as
a protective layer. In contrast to other research, a mixture ofwater and ethanol was used as a solvent for the coating process.
Giﬃn et al. used ethanol as the solvent for the coatingprocess.35,36 We think that they considered the employment of
ethanol solvent in the coating process to lower the acidity of
H3PO4 and inhibit the dissolution of Li and nickel (Ni) ionsfrom the NCA particle surfaces. However, we think that thereaction of eqn (1) hardly occurs in ethanol solvent.
3LiOH + H3PO4 / Li3PO4 + 3H2O

(1)

To accelerate the reaction of eqn (1), water might be needed.
Therefore, we used a mixture of water and ethanol as a solvent
for the coating process. Although the results are not shown inthis paper, we examined the ratio of water/ethanol for thecoating solvent and the concentration of phosphoric acid
(H3PO4) as a source of PO43 ions added to the coating solution.
In addition, the Li3PO4-coated NCA cathodes were preparedwith aqueous slurries stored for 1 and 24 h aer the preparationof the slurries. Li3PO4 is water-soluble. Therefore, the Li3PO4© 2021 The Author(s). Published by the Royal Society of Chemistrylayer formed on the NCA surface will be dissolved from the NCA
surface to aqueous slurry during the storage of the slurries. To
overcome this problem, the Li3PO4-coated NCA samples were
thermally treated (heat-treated) at temperatures from 200 to
450  C to form water-insoluble layers in the reaction between
the coated Li3PO4 and the NCA surface.

2 Experimental
LiNiaCobAl1abO2 (a > 0.85) particle sample (NCA, cat. # NC-02,
Nihon Kagaku Sangyo Co., Ltd., Japan) was used as an NCA
cathode material for Li3PO4 coating. Particles with D50% ¼ 14mm were used without any purication. Surface coating with
Li3PO4 was conducted using a wet method, as shown in Fig. S1.†
Four grams of NCA particles was dispersed in ethanol (10 g)with a magnetic stirrer at 25  C for 2 min. Then, 0.05 M H3PO4
aqueous solution (2.4 mL) was dropped to the NCA-dispersed
ethanol solution for 10 min. Aer dropping the H3PO4 solution, the mixture of water, ethanol and NCA particles was stirred
at 25  C for 30 min. Aer ltration of the resulting NCA particle,
the particles were dried up at 130  C for 1 h and then sintered at
200–450  C for 2 h in an argon (Ar) or air atmosphere to form thecoating layer on the NCA particle surface. The coated NCA
particles were characterized with scanning electron microscopy(SEM), powder X-ray diﬀraction (pXRD), X-ray photoelectron
spectroscopy (XPS) and scanning transmission electron
microscopy-X-ray energy-dispersive spectrometry (STEM-EDX).
Their equipment and measurement conditions are describedin the experimental section of ESI.† For the water stability test of
the coated NCA particles, 1 g of coated particles was dispersed
in 5 mL of water for 1 h. Aer 1 h, the coated NCA particles weredried at 130  C for 1 h, and their surfaces were observed with
SEM to conrm the water stability of the coated NCA particles.
The methods for cathode preparation and cathode performance testing with coated and pristine NCA are also describedin the experimental section of ESI.† Cathodes were preparedwith coated and pristine NCA in the water process with aqueousslurry in which NCA, water-based hybrid polymer binder
TRD202A (JSR, Japan), carboxymethyl cellulose (CMC) andconductive additive (acetylene black (AB)) were dispersed inwater. The prepared aqueous slurries were le for 1 and 24 h
before casting on aluminum (Al) current collector foil toconrm the stability of NCA against water. The pH of the slurries was measured with a pH meter at 30, 60 and 90 min aer
slurry preparation. The concentration of Ni ions in slurries,
which were dissolved from NCA surfaces to the slurry solutions,
was analyzed with inductively coupled plasma-mass spectrometry (ICP-MS, Agilent, 7700 spectrometer).
In charging/discharging cycle and C-rate performance testsof coated NCA cathodes, constant-current/constant-voltage(CC–CV) mode was applied to NCA cathodes. The cutoﬀ
voltage and charge/discharge current density were 2.5–4.25 V(vs. Li/Li+) and 0.1–5 C, respectively. The pristine NCA cathodeprepared with PVdF binder exhibited a discharge capacity of
200 mA h g1. In the calculation of the discharge capacity
retention, 200 mA h g1 was considered an indicator of 100%
capacity retention.

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3 Results and discussion
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3.1

Characterization of coated NCA cathode materials

Fig. 1 shows the SEM images of (a) pristine NCA particles, (b–g)
coated NCA particles without (b) and with (c–h) heat treatment
at (c) 200, (d) 250, (e) 300, (f) 350, (g) 400 and (h) 450  C under (A)Ar and (B) air atmospheres. Usually, the heat treatment under
Ar atmosphere is applied to the samples to form coated layer of
Li3PO4 having high degree of crystallinity. In this study, the heat
treatment under air atmosphere was examined because
compounds other than Li3PO4 should be produce and thecompounds protect eﬃciently the surface of NCA particles. The
surfaces (b–h) of NCA particles on which the Li3PO4 moiety iscovered are rougher than those of uncoated NCA (a). Moreover, thesurface of coated NCA particles (c–h) aer heat treatment becamerougher than that of coated NCA particles (b) without heat treatment due to an increase in the degree of crystallinity of Li3PO4 byheat treatment. The diﬀerence in the surface morphology between
the coated NCA particles heat-treated under Ar and air cannot be
observed from the SEM images in Fig. 1.

Paper
The coated layers formed on the NCA particle that was heattreated at 400  C under air were observed with TEM (Fig. 2) andTEM-EDX (Fig. 3). Before the heat treatment, the coated layer
was thick, and its thickness was 50–100 nm (Fig. 2(a)). The
coated layer shrunk aer the heat-treatment. In the case of heat
treatment under an Ar atmosphere, the thickness of the coatedlayer became 20–30 nm. Under an air atmosphere in the heat
treatment, the coated layer shrank more, and its thickness was
10–20 nm. From the TEM-EDX images of the coated layers aerheat treatment (Fig. 3), it was conrmed that the NCA surfaces
were covered uniformly with the coated layers containing
phosphorus atoms. The thickness of the coated layers aer heat
treatment decreased with the increase in temperature for heat
treatment, resulting in a higher density of the coated layer withan increase in the temperature of heat treatment. The decreasein the thickness of the coated layers aer the heat treatment
under Ar and air might be due to shrinkage, resulting in an
increase in the density of the coated layer, or decomposition of
the coated layer for the decomposition products to y from thecoated layer along Ar and air ows. In addition, when compared

SEM images of (a) pristine NCA and (b–h) coated NCA samples. (b) Coated NCA samples without heat treatment, (c–h) coated NCA withheat treatment. Temperature of heat treatment: (c) 200, (d) 250, (e) 300, (f) 350, (g) 400 and (h) 450  C. Atmosphere for heat-treatment: (A) Ar
and (B) air.
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Fig. 2

RSC Advances

TEM images of coated NCA (a) without heat treatment and with heat treatment at 400  C in (b) Ar and (c) air atmospheres.

between EDX images of Ni and Co, Ni atoms distribute more
widely than Co. Fig. S2† shows TG-DTA charts of (a) coated NCA,(b) Li3PO4 powder and (c) pristine NCA under air. The chart of(a) coated NCA exhibited a large decrease in weight at temperatures from 150 to 300  C. (b) Li3PO4 powder also exhibiteda large decrease in weight at 150–300  C, although water
desorption from the Li3PO4 powder might occur at temperatures lower than 150  C. On the other hand, (c) pristine NAC did
not exhibit any large change in weight at temperatures up to400  C. It could be conrmed that some kind of compounds
took leave from the coated layers during the heat treatment ofcoated NCA samples. The condensation reaction of PO43 ionson NCA surfaces can be considered the reason for the decrease
in weight during the TG-DTA experiments.
XPS spectra of the coated NCA samples were obtained todetermine the composition of the coated layers. Fig. 4 shows
atomic percentages in sample surfaces (a–h). In Fig. 4, thepercentages of oxygen (O), Ni, Li and phosphorus (P) on the NCA

surfaces are shown representatively. Other elements containedon the NCA surface were cobalt, aluminum and carbon. The
origin of carbon might be Li2CO3 formed on the NCA surface.
Pristine NCA particle surfaces are covered with the Li2CO3 layer
because Li2CO3 was formed by reacting the LiOH residue on
pristine NCA with carbon dioxide (CO2) gas under air in theinterval of experiments. When compared with pristine NCA, thepercentage of nickel on the coated NCAs is higher. The
percentages of Li and P decreased in the coated NCAs. The Ni
percentages gradually increased with increasing heat treatment
temperature. The O and P elements were almost constant. The
XPS spectra (Fig. 5) of P in the coated NCA surfaces are characteristic. The XPS spectra for 2p of the coated NCAs shied tolower binding energy with the increase in heat-treatment
temperature. In the case of heat treatment under an air atmosphere, the XPS peak shi for 2p can be observed even at 200  C.
The 2p peak for Li3PO4 can be observed at 133.2 eV, as shown in
Fig. 5.41 The 2p peak at approximately 130 eV can be assigned toFig. 3 STEM-EELS mapping of Ni, Co and P elements and their mixed mapping of coated NCA with heat treatment at 400  C in (A) Ar and (B) air
atmospheres.

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Fig. 4 Atomic percentage on the surface of samples evaluated with XPS. (a) Pristine NCA and (b–h) coated NCA samples. (b) Li3PO4-coated NCA
samples without heat treatment, (c–h) coated NCA with heat treatment. Temperature of heat treatment: (c) 200, (d) 250, (e) 300, (f) 350, (g) 400
and (h) 450  C. Atmosphere for heat-treatment: (A) Ar and (B) air. : oxygen, : nickel, : lithium, : phosphorus.

one for nickel phosphate (Ni3(PO4)2).42 The heat treatment of thecoated NCA samples produced Ni3(PO4)2 in the coated layers, and
Li3PO4 disappeared from the surface of NCA during the heat
treatment. The process with and without heat treatment did notchange the oxidation state of Ni on the NCA surfaces.
To identify the crystal structures of the coated layers andNCAs, pXRD patterns of the coated NCA samples were

measured (Fig. 6(A-1) and (B-1)). The pXRD proles obtained
matched that of a layered a-NaFeO2-type structure with them,43 in which the Na sites are occupied by Li+
space group R3
ions and the Fe sites by transition metal (Ni, Co and Al) ions.
The (003) peaks of the coated NCA samples shi to higher
angles, and the degree of the (003) peak shi increases with thetemperature of the heat treatment (Fig. 6(A-2) and (B-2)),

Fig. 5 XPS spectral proﬁles in the P 2p region of (a) Li3PO4 powder, (b) pristine NCA and (c–i) coated NCA. Sample (c) was not heat-treated, andsamples (d–i) were heat-treated at (d) 200, (e) 250, (f) 300, (g) 350, (h) 400 and (i) 450  C in (A) Ar and (B) air atmospheres.

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RSC AdvancesFig. 6 pXRD patterns of (a) pristine NCA and (b–h) coated NCA with standard peak patterns of Li3PO4 (JCPDS 83-0339) and Ni3(PO4)2 (JCPDS
46-1388). Sample (b) was not heat-treated, and samples (c–h) were heat-treated at (c) 200, (d) 250, (e) 300, (f) 350, (g) 400 and (h) 450  C in (A) Ar
and (B) air atmospheres.

indicating that the coated layers aﬀect the crystal structure of
the NCA surface themselves. In addition, the coated NCA
samples prepared under an air atmosphere exhibited larger
peak shis than those prepared under an Ar atmosphere. The
pXRD peaks corresponding to Li3PO4 (ref. 44) and Li2CO3 can beobserved in the enlarged pXRD patterns of the samples(Fig. 6(A-3) and (B-3)). However, the peaks for Ni3(PO4)2, which
are considered to exist in the coated layers with the XPS results,
cannot be observed in the enlarged pXRD patterns. The heat
treatment of the coated NCA samples might produce amorphous Ni3(PO4)2 on the surface of the coated layer of NCAs.
Taken together with the results of TG-DTA, XPS and pXRD, it
can be considered that the formation of the coated layer containing Ni3(PO4)2 and Li3PO4 in the heat treatment occurs, as
shown in Fig. 7. H3PO4 added to the mixture of ethanol/water
adsorbs on the surface of NCA and is a source of protons forthe exchange of Li+/H+ (intercalation/deintercalation of Li+/H+
into/from NCA). Following the intercalation of protons, nickel
ions (Ni2+) dissolve, and Ni(OH)2 forms on the NCA surfaces. At
the same time, Li+ deintercalated from the NCA surfaces forms
LiOH and Li3PO4 on the NCA surfaces. As mentioned above,© 2021 The Author(s). Published by the Royal Society of Chemistry

Li3PO4 is formed also in eqn (1). The coated layers containing
Li3PO4, LiOH, H3PO4 and Ni3(PO4)2 are very thick on the NCA
surfaces. During the heat treatment, the coated layer is dehydrated, and then Li3PO4 and Ni3(PO4)2 are le. The dense coatedlayers constructed by Li3PO4 and Ni3(PO4)2 have water-stableproperties. Based on the XPS results, the dense coated layers
consist mainly of Ni3(PO4)2. Ni3(PO4)2 does not have a crystal
structure in the coated layers. Heat treatment under an air
atmosphere enhanced the formation of dense Li3PO4/Ni3(PO4)2.
The reason for the diﬀerence between the coated layers
prepared with the heat treatments under the Ar and air atmosphere, that is the heat treatment under air atmosphere
produce thinner Ni3(PO4)2-rich coat layers, cannot be madeclear yet. However, although clear evidence is not obtained, we
think that oxygen in air contributes to the formation of thinnercoated layers; for example, during heat treatment, oxygen
repairs the dissolved oxide surface of NCAs, and then thecondensation reaction of PO34 ions and the formation reactionof Ni3(PO4)2 occurs eﬀectively on the repaired NCA surfaces.
Fig. 8 shows the SEM images of (a) pristine NCA particles, (b)uncoated NCA particles and (c–g) coated NCA particles that were

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Fig. 7 Schematic description of the formation of the coated layer containing Ni3(PO4)2 and Li3PO4 in the heat treatment.

not (c) or were (d–g) heat-treated at 200 (d, e) and 400 (f, g)  C
under Ar (d, f) and air (e, g). Samples (b)–(g) were immersed inwater for 1 h to conrm the water stability of the samples before
SEM observations. When compared with the SEM image of thepristine NCA sample (a), the uncoated NCA sample that was
exposed to water for 1 h was damaged signicantly due to thedissolution of the surface into water (b). From the SEM imagesof coated NCA samples ((c)–(g)), it was conrmed that thesurface roughness of the coated NCA samples increased due tothe formation of coating moieties on the NCA surfaces and thatthe coated NCA samples did not suﬀer damage from watercontact.
Fig. S3† shows the results of the examination of changes inthe slurry pH. An aqueous slurry containing CMC and AB

Fig. 8 SEM images of NCA particles. (a) Pristine NCA, (b) uncoated NCA, (c) coated NCA without heat treatment, (d) coated NCA after heat

treatment at 200  C in Ar, (e) coated NCA after heat treatment at 200  C in air, (f) coated NCA after heat treatment at 400  C in Ar, and (g) coated
NCA after heat treatment at 400  C in air. SEM images of (b)–(g) samples were obtained after immersion of samples in water for 1 h and drying for
1 h at 130  C.

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without NCA as a blank slurry maintained a pH of approximately 7.5 until 90 min aer slurry preparation (a). On the other
hand, the pH of the slurry containing uncoated NCA was over
12.5 (b). The coated NCA without and with heat treatment
depressed the increase in pH of the slurries aer adding thecoated NCA to the slurry solutions. Among them, the pH of thecoated NCA samples aer heat treatment at 350 and 400  C
was lower than that of the other samples. The lowest pH wasobserved in the coated NCA sample aer heat treatment at
400  C in air. Although an increase in the pH of slurries could
be observed, the dissolution of Ni from NCA to the slurrysolutions could not be detected in the ICP-MS analysis of theslurry solutions. The reason for the increase in slurry pH evenwhen coated NCA was added to slurry solutions is considered
to be due to the exchange of H+ in H2O with Li+ in Li3PO4, andif Ni ions are dissolved from NCA, Ni ions remain on the NCA
surface by forming Ni(OH)2 and Ni3(PO4)2. Because thecoated layers formed in the 350 and 400  C heat treatments
block water contact with the NCA surface, the exchange
reaction of H+/Li+ was suppressed among the samples tested.
In contrast, the coated layers on NCAs that were heat-treatedat 200–300  C were sparse. Therefore, the exchange reactionof H+/Li+ occurred easily, resulting in the relatively high pHof slurry solutions.

RSC Advances
3.2 Charging/discharging cycle performance tests withcoated NCA materials and comparison of them with samples
prepared with other preparation methods
Fig. 9 shows the charging/discharging cycle performance obtained with the cathodes prepared from pristine NCA (a, b) andcoated NCA samples without (c) and with heat treatment at 200–450  C (d–i) under Ar (1) and air (2) atmospheres. The cathodes
were prepared with PVdF (a) or TRD202A (b–i) binders. In
addition, in the case of the TRD202A binder, the slurries containing NCA particles, AB, CMC and TRD202A binder werestored for 1 (A) and 24 (B) h before preparation of the cathodes.
The cathode (a) prepared with pristine NCA and PVdF binder
exhibited a discharge capacity of 200 mA h g1 in the rst cycle,
and the discharge capacity decreased with an increase in the cycle
number to 190 mA h g1 at 20 cycles. The decrease in discharge
capacity is an inherent property of pristine NCA. The noncoated
NCA cathode (b) prepared with the TRD202A binder exhibiteda large decrease in discharge capacity at the rst cycle and a large
degradation of the discharge capacity with the cycles. The cycle
performance of cathodes is in the order follow as(A-1) Slurry storage 1 h, Ar atmosphere in the heat-treatment.
Pristine NCA with PVdF ¼ Li3PO4-coated NCA with heat treatment at 300  C > 400  C > 350  C > 250  C > Li3PO4-coated NCA
without heat treatment > 450  C > 200  C.

Fig. 9 Plots of discharge capacity vs. charge/discharge cycle number obtained with the NCA cathodes. (a) Pristine NCA cathode prepared with
PVdF binder, (b) pristine NCA cathode prepared with TRD202A binder, (c–i) coated NCA cathodes. Sample (c) was not heat-treated, and samples(d–i) were heat-treated at (d) 200, (e) 250, (f) 300, (g) 350, (h) 400 and (i) 450  C in (1) Ar and (2) air atmospheres. When cathodes were preparedwith TRD202A binder, aqueous slurries were stored for (A) 1 and (B) 24 h.

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RSC Advances(A-2) Slurry storage 1 h, air atmosphere in the heat treatment.
Pristine NCA with PVdF ¼ 400  C > 350  C > Li3PO4-coated NCA
without heat treatment ¼ 450  C > 250  C > 200  C > 300  C.
(B-1) Slurry storage 24 h, Ar atmosphere in the heat-treatment.
Pristine NCA with PVdF > 400  C > 350  C ¼ 200  C > 250  C >450  C > 300  C > Li3PO4-coated NCA without heat treatment.
(B-2) Slurry storage 24 h, air atmosphere in the heattreatment. Pristine NCA with PVdF > 400  C > 350  C > 250  C¼ 200  C > 450  C > 300  C > Li3PO4-coated NCA without heat
treatment.
Although the order of cycle performance among the cathodes examined is not xed in the cases of (A-1), (A-2), (B-1) and(B-2), the cathodes ((g) and (h)) prepared with coated NCAs
treated at 350 and 400  C exhibited relatively high cathode
performance. This trend can be related to one of the pH values
in cathode slurries shown in Fig. S3.† Namely, the samples that
did not show a large increase in the pH of the slurry can exhibit
comparable discharge capacity and cyclability with thoseobserved with cathodes prepared with pristine NCA and PVdF
binders. In Fig. 10, the results of coated NCA in this study werecompared with coated NCA prepared with ethanol-35 andwater-37based slurries. The coated NCA samples were reproduced faithfully with ref. 35 and 37 as samples for comparison.
However, when cathodes were prepared with the Li3PO4-coated
NCA samples, all slurries in which the coated NCA samples, AB
and CMC were dispersed in water were stored for 1 h before
preparation of cathodes to conrm the water stability of thecoated NCA samples. The coated NCA sample prepared withethanol/water-based slurry, which was developed in this study,
exhibited the same cathode performance as that of a pristineNCA cathode prepared with PVdF. It means that the formationof (Ni3(PO4)2) and Li3PO4 in the coating layer does not aﬀect thePapercapacity of NCA cathode. The weight% of (Ni3(PO4)2) and Li3PO4
in the coated NCA is important. However, the weight% of(Ni3(PO4)2) and Li3PO4 in the coated NCA cannot be evaluatedbecause it is very small and the thickness is less than 10 nm as
can be expected from TEM image in Fig. 2. When the capacities(mA h g1) of the NCA and non-coated NCA cathodes were
evaluated, the weight% of (Ni3(PO4)2) and Li3PO4 was notconsidered. In the comparison between capacities of the coatedand non-coated NCA cathodes in Fig. 10, the diﬀerence in thecapacities cannot be observed. Therefore, the weight% of(Ni3(PO4)2) and Li3PO4 in the coated NCA is so small. The
cathodes prepared with ethanol- and water-based slurries show
a decrease in discharge capacity even in the rst cycle. In several
cycles since the rst cycle, the discharge capacity of the cathodes prepared with ethanol- and water-based slurries increased.
However, the capacities could not reach one of the cathodes
prepared with ethanol/water-based slurry. It can be conrmedthat the coated NCA sample examined in this study has thehighest water stability.
3.3 High rate performance test of coated NCA materials andcomparison of them with samples prepared with otherpreparation methods
The high rate performance of the abovementioned cathodes
prepared with ethanol/water-based slurries was examined, andthe results were compared with those of TiOx-, Li2CO3- andTiOx/Li2CO3-coated NCA cathodes (Fig. 11). TiOx-, Li2CO3- andTiOx/Li2CO3-coated NCA cathodes were examined in ourprevious papers.15,29 These samples have water stability enoughto exhibit inherent performance of NCA even aer exposing the

Fig. 11 Plots of discharge capacity retention vs. C-rate obtained with

Plots of discharge capacity vs. charge/discharge cycle number
obtained with the NCA cathodes. (a) Pristine NCA cathode preparedwith PVdF binder. (b) Pristine NCA cathode prepared with TRD202A
binder. Sample (c) was coated NCA prepared in a mixture of water andethanol. Sample (d) was coated NCA prepared in water. Sample (e) was
coated NCA prepared in ethanol. NCA slurries prepared with water/
ethanol, water or ethanol were stored for 1 h before preparing thecathodes.
Fig. 1037158 | RSC Adv., 2021, 11, 37150–37161

the cathodes prepared from (a) pristine NCA and PVdF binder, (b) TiOx/
Li2CO3-, (c) TiOx- and (d–h) the coated NCAs. Cathodes (b–h) wereprepared with a TRD202A water-based binder. Coated NCA (b) was
not heat-treated. The coated NCAs (c–h) were not heat-treated at (e,g) 350 and (f, h) 400  C in (e, f) Ar and (g, h) air atmospheres. In thecalculation of the discharge capacity retention, a discharge capacity of
200 mA h g1, which was observed at the pristine NCA cathodeprepared with PVdF binder, was considered 100% capacity retention.

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Paper
coated NCA particles in water-based slurries for long times.
However, the TiOx-, Li2CO3- and TiOx/Li2CO3-coated NCA cathodes exhibited lower rate performance than one of pristine NCA
cathodes prepared with PVdF binder because the TiOx-, Li2CO3and TiOx/Li2CO3-coating layers inhibited Li+-ion transfer
through the coating layers for the intercalation/deintercalation
processes to/from NCA surfaces. Four cathodes prepared withthe coated NCA samples heat-treated at 350 and 400  C under Ar
and air atmospheres clearly showed higher rate performance than
one of pristine NCAs prepared with PVdF. The purpose of thisstudy was to conrm that the coated NCA samples heat-treated at
350 and 400  C under Ar and air atmospheres, which were originally examined in this study, have both water stability and highcathode performance for the rst time. The reason for the
improvement of rate performance on the coated NCA samples
heat-treated at 350 and 400  C under Ar and air atmosphere might
be enhancement of Li+-ion transfer in the coating layers. It has
been reported that a coated NCA cathode prepared with PVdF
binder exhibited a higher rate performance than an uncoated NCA
cathode prepared with PVdF binder.37,45,46 In addition, the highrate performance of Ni3(PO4)2-coated NCA cathodes comparedwith uncoated NCA cathodes prepared with PVdF binders has beenreported.47 Although the composition of the coated layer cannot yet
be determined, Li3PO4 or Ni3(PO4)2 layers, which we assumed
based on the characterization results of the synthesized samples inthis study, could be formed on NCA surfaces to achieve therequired water stability and high cycle and rate performance.

4 Conclusion
Optimization of the concentration of H3PO4 added to the slurryfor cathode preparation, the ratio of ethanol and water used toprepare the cathode slurry as solvents and the temperature forheat-treatment of coated NCA samples realized water-stable
NCA samples, which can be applied to aqueous processes forcathode preparation. Coating layers containing Ni3(PO4)2 andLi3PO4 were formed on NCA surfaces and contributed to theimprovement of the water stability of NCA cathode materials.
The coating layers could prohibit the NCA surface from damage
due to water contact for 24 h. The Ni3(PO4)2 and Li3PO4 species
in the coated layers collaborate to improve cathode performance, such as cyclability and high-rate performance. Ni3(PO4)2
protects the NCA surface from water contact, and Li3PO4
enhances the transfer of Li+ through the coated layers. In thisstudy, the analysis of coated layers formed on NCA surfaces has
not been completed, and the distribution and atomic ratio of
Ni3(PO4)2 and Li3PO4 in the coated layers are still unknown.
Deep examination of the coated layers and the reasons why thecoated layers of Ni3(PO4)2 and Li3PO4 can improve waterstability and high-rate performance and why the performance
diﬀerence between air and Ar treated samples can be observed
are in progress.

Author contribution
T. W. and T. Y. performed charge/discharge test and preparation of coated cathode materials. M. Y and T. G. characterized© 2021 The Author(s). Published by the Royal Society of Chemistry

RSC Advances
the synthesized materials with STEM and EDS. S. K., S. U. and
H. L. performed coating treatment of cathode materials. Y. I.
and F. M. performed a preparation of bare cathode material andpreparation of gures. J. W., T. O. and F. M. wrote the manuscript, summarized the work.

Conﬂicts of interest
There are no conicts to declare.

Acknowledgements
This work was supported by NIMS microstructural characterization platform as a program of “Nanotechnology Platform” of
the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

References
1 G. Zubi, R. Dufo-López, M. Carvalho and G. Pasaoglu, The
lithium-ion battery: state of the art and future perspectives,
Renew. Sustain. Energy Rev., 2018, 89, 292–308.
2 M. Broussely and G. Archdale, Li-ion batteries and portable
power source prospects for the next 5–10 years, J. Power
Sources, 2004, 136, 386–394.
3 M. A. Hannan, M. M. Hoque, A. Mohamed and A. Ayob,
Review of energy storage systems for electric vehicle
applications: Issues and challenges, Renew. Sustain. EnergyRev., 2017, 69, 771–789.
4 F. T. Wagner, B. Lakshmanan and M. F. Mathias,
Electrochemistry and the future of the automobile, J. Phys.
Chem. Lett., 2010, 1, 2204–2219.
5 J. B. Goodenough and Y. Kim, Challenges for Rechargeable
Li Batteries, Chem. Mater., 2010, 22, 587–603.
6 J. M. Tarascan and M. Armand, Issues and challenges facing
rechargeable lithium batteries, Nature, 2001, 414, 359–367.
7 W. Li, B. Song and A. Manthiram, High-voltage positiveelectrode materials for lithium-ion batteries, Chem. Soc.
Rev., 2017, 46, 3006–3059.
8 J.-L. Shi, R. Qi, X.-D. Zhang, P.-F. Wang, W.-G. Fu, Y.-X. Yin,
J. Xu, L.-J. Wan and Y.-G. Guo, High-thermal- and air-stability
cathode material with concentration-gradient buﬀer for Liion batteries, ACS Appl. Mater. Interfaces, 2017, 9, 42829–
42835.
9 K. Liu, Y. Liu, D. Lin, A. Pei and Y. Cui, Materials for lithiumion battery safety, Sci. Adv., 2018, 4, eaas9820.
10 J. Cabana, B. J. Kwon and L. Hu, Mechanisms of degradationand strategies for the stabilization of cathode–electrolyte
interfaces in Li-ion batteries, Acc. Chem. Res., 2018, 51,
299–308.
11 J. Wang, Y. Yamada, K. Sodeyama, E. Watanabe, K. Takada,Y. Tateyama and A. Yamada, Fire-extinguishing organic
electrolytes for safe batteries, Nat. Energy, 2018, 3, 22–29.
12 W. He, P. Liu, B. Qu, Z. Zheng, H. Zheng, P. Deng, P. Li, S. Li,
H. Huang, L. Wang, Q. Xie and D.-L. Peng, Uniform Na+
doping-induced defects in Li- and Mn-rich cathodes for

RSC Adv., 2021, 11, 37150–37161 | 37159

View Article Online

Open Access Article. Published on 18 November 2021. Downloaded on 10/8/2024 5:02:43 PM.
This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.

RSC Advances
high-performance lithium-ion batteries, Adv. Sci., 2019, 6,
1802114.
13 T. Liu, S.-X. Zhao, L.-L. Gou, X. Wu and C.-W. Nan,
Electrochemical performance of Li-rich cathode material,
0.3Li2MnO3–0.7LiMn1/3Ni1/3Co1/3O2 microspheres with Fdoping, Rare Met., 2019, 38, 189–198.
14 W.-W. Li, X.-J. Zhang, J.-J. Si, J. Yang and X.-Y. Sun, TiO2coated LiNi0.9Co0.08Al0.02O2 cathode materials withenhanced cycle performance for Li-ion batteries, Rare Met.,
2021, 40, 1719–1726.
15 T. Tanabe, Y. B. Liu, K. Miyamoto, Y. Irii, F. Maki, F. Maki,
T. Gunji, S. Kaneko, S. Ugawa, H. Lee, T. Ohsaka and
F. Matsumoto, Synthesis of Water-Resistant Thin TiOx
Layer-Coated High-Voltage and High-Capacity LiNiaCobAl1a-bO2 (a > 0. > 0.85) Cathodeand Its Cathode Performance
to Apply a Water-Based Hybrid Polymer Binder Binder to
Li-Ion Batteries, Electrochim. Acta, 2017, 258, 1348–1355.
16 T. Tanabe, T. Gunji, Y. Honma, K. Miyamoto, T. Tsuda,
Y. Mochizuki, S. Kaneko, S. Ugawa, H. Lee, T. Ohsaka and
F. Matsumoto, Preparation of Water-Resistant Surface
Coated High-Voltage LiNi0.5Mn1.5O4 Cathode and Its
Cathode Performance to Apply a Water-Based Hybrid
Polymer Binder to Li-Ion Batteries, Electrochim. Acta, 2017,
224, 429–438.
17 D. Bresser, D. Buchholz, A. Moretti, A. Varzi and S. Passerini,
Alternative binders for sustainable electrochemical energy
storage – the transition to aqueous electrode processing
and bio-derived polymers, Energy Environ. Sci., 2018, 11,3096–3127.
18 A. Iturrondobeitia, A. Kvasha, J.-M. Lopez del Amo,
J. F. Colin, D. Sotta, I. Urdampilleta and M. CasasCabanas, A comparative study of aqueous and organic
processed Li1.2Ni0.2Mn0.6O2 Li-rich cathode materials foradvanced lithium-ion batteries, Electrochim. Acta, 2017,
247, 420–425.
19 D. L. Wood III, J. Li and C. Daniel, Prospects for reducing theprocessing cost of lithium ion batteries, J. Power Sources,
2016, 275, 234–242.
20 W. Liu, P. Oh, X. Liu, M.-J. Lee, W. Cho, S. Chae, Y. Kim and
J. Cho, Nickel-rich layered lithium transition-metal oxide forhigh-energy lithium-ion batteries, Angew. Chem., Int. Ed.,
2015, 54, 4440–4457.
21 K. Hoang and M. Johannes, Defect physics and chemistry inlayered mixed transition metal oxide cathode materials:(Ni,Co,Mn) vs (Ni,Co,Al), Chem. Mater., 2016, 28, 1325–1334.
22 S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp,
S.-J. Kim and Y.-K. Sun, Nickel-rich layered cathodematerials
forautomotive
lithium-ion
batteries:
achievements and perspectives, ACS Energy Lett., 2017, 2,
196–223.
23 Y. Makimura, T. Sasaki, T. Nonaka, Y. F. Nishimura,
T. Uyama, C. Okuda, Y. Itou and Y. Takeuchi, Factors
aﬀecting cycling life of LiNi0.8Co0.15Al0.05O2 for lithium-ion
batteries, J. Mater. Chem. A, 2016, 4, 8350–8358.
24 S. Hwang, S. M. Kim, S.-M. Bak, B.-W. Cho, K. Y. Chung,J. Y. Lee, W. Chang and E. A. Stach, Investigating local
degradation and thermal stability of charged nickel-based

37160 | RSC Adv., 2021, 11, 37150–37161

Papercathode materials through real-time electron microscopy,
ACS Appl. Mater. Interfaces, 2014, 6, 15140–15147.
25 W. B. Hawley, A. Parejiya, Y. Bai, H. M. Meyer III, D. L. Wood
III and J. Li, Lithium and transition metal dissolution due toaqueous processing in lithium-ion battery cathode active
materials, J. Power Sources, 2020, 466, 228315.
26 L. Hartmann, D. Pritzl, H. Beyer and H. A. Gasteiger,
Evidence for Li+/H+ exchange during ambient storage of
Ni-rich cathode active materials, J. Electrochem. Soc., 2021,
168, 070507.
27 I. Hamam, N. Zhang, A. Liu, M. B. Johnson and J. R. Dahn,
Study of the reactions between Ni-rich positive electrodematerials and aqueous solutions and their relation to thefailure of Li-ion cells, J. Electrochem. Soc., 2020, 167, 130521.
28 M. Hofmann, M. Kapuschinski, U. Guntow and G. A. Giﬃn,
Implications of aqueous processing for high energy density
cathode materials: part I. Ni-rich layered oxides, J.
Electrochem. Soc., 2020, 167, 140512.
29 T. Watanabe, K. Hirai, F. Ando, S. Kurosumi, S. Ugawa,H. Lee, Y. Irii, F. Maki, T. Gunji, J. Wu, T. Ohsaka and
F. Matsumoto, Surface double coating of a LiNiaCobAl1-abO2 (a > 0.85) cathode with TiOx and Li2CO3 to apply
a water-based hybrid polymer binder to Li-ion batteries,
RSC Adv., 2020, 10, 13642–13654.
30 K. Kimura, K. Onishi, T. Sakamoto, K. Asami and
M. Yanagida, Achievement of the high-capacity retention
rate for the Li[Ni0.8Co0.15Al0.05]O2 (NCA) cathodecontaining an aqueous binder with CO2 gas treatmentusing the cavitation eﬀect (CTCE), J. Electrochem. Soc.,
2019, 166, A5313–A5317.
31 W. B. Hawley, H. M. Meyer III and J. Li, Enabling aqueous
processing for LiNi0.80Co0.15Al0.05O2 (NCA)-based lithiumion battery cathodes using polyacrylic acid, Electrochim.
Acta, 2021, 380, 138203.
32 W. Bauer, F. A. Çetinel, M. Müller and U. Kaufmann, Eﬀects
of pH control by acid addition at the aqueous processing ofcathodes for lithium ion batteries, Electrochim. Acta, 2019,
317, 112–119.
33 K. Soeda, M. Yamagata and M. Ishikawa, Alginic acid asa new aqueous slurry-based binder for cathode materialsof LIB, ECS Trans., 2015, 64, 13–22.
34 M. Hofmann, F. Nagler, M. Kapuschinski, U. Guntow and
G. A. Giﬃn, Surface modication of LiNi0.8Co0.15Al0.05O2
particles via Li3PO4 coating to enable aqueous electrodeprocessing, ChemSusChem, 2020, 13, 5962–5971.
35 M. Hofmann, F. Nagler, U. Guntow, G. Sextl and G. A. Giﬃn,Long-term cycling performance of aqueous processed Nirich LiNi0.8Co0.15Al0.05O2 cathodes, J. Electrochem. Soc.,
2021, 168, 060511.
36 X. Bian, Q. Fu, X. Bie, P. Yang, H. Qiu, Q. Pang, G. Chen,
F. Du and Y. Wei, Improved electrochemical performanceand thermal stability of Li-excess Li1.18Co0.15Ni0.15Mn0.52O2
cathode material by Li3PO4 surface coating, Electrochim.
Acta, 2015, 174, 875–884.
37 S. Chen, T. He, Y. Su, Y. Lu, L. Bao, L. Chen, Q. Zhang,
J. Wang, R. Chen and F. Wu, Ni-rich LiNi0.8Co0.1Mn0.1O2oxide coated by dual-conductive layers as high© 2021 The Author(s). Published by the Royal Society of ChemistryView Article Online

Open Access Article. Published on 18 November 2021. Downloaded on 10/8/2024 5:02:43 PM.
This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.

Paper
performance cathode material for lithium-ion batteries, ACS
Appl. Mater. Interfaces, 2017, 9, 29732–29743.
38 W. Zhang, L. Liang, F. Zhao, Y. Liu, L. Hou and C. Yuan, Nirich LiNi0.8Co0.1Mn0.1O2 coated with Li-ion conductive
Li3PO4 as competitive cathodes for high-energy-density
lithium ion batteries, Electrochim. Acta, 2020, 340, 135871.
39 Q. Gan, N. Qin, Z. Wang, Z. Li, Y. Zhu, Y. Li, S. Gu, H. Yuan,
W. Luo, L. Lu, Z. Xu and Z. Lu, Revealing Mechanism of
Li3PO4 Coating Suppressed Surface Oxygen Release forCommercial Ni-Rich Layered Cathodes, ACS Appl. Energy
Mater., 2020, 3, 7445–7455.
40 A. T. Appapillai, A. N. Mansour, J. Cho and Y. Shao-Horn,
Microstructure of LiCoO2 with and without “AlPO4”
nanoparticle coating: combined STEM and XPS studies,
Chem. Mater., 2007, 19, 5748–5757.
41 J. Chang, Q. Lv, G. Li, J. Ge, C. Liu and W. Xing, Core-shellstructured
Ni12P5/Ni3(PO4)2
hollow
spheresasdifunctionaland eﬃcient electrocatalysts for overall waterelectrolysis, Appl. Catal., B, 2017, 204, 486–496.
42 M. Bichon, D. Sotta, N. Dupré, E. D. Vito, A. Boulineau,
W. Porcher and B. Lestriez, Study of immersion of
LiNi0.5Mn0.3Co0.2O2 material in water for aqueous© 2021 The Author(s). Published by the Royal Society of Chemistry

RSC Advances
processing of positive electrode for Li-ion batteries, ACS
Appl. Mater. Interfaces, 2019, 11, 18331–18341.
43 J. Xie, J. F. M. Oudenhoven, P.-P. R. M. L. Harks, D. Li and
P. H. L. Notten, Chemical vapor deposition of lithium
phosphate thin-lms for 3D all-solid-state Li-ion batteries,
J. Electrochem. Soc., 2015, 162(3), A249–A254.
44 M. A. Al-Omair, M. M. Khalaf, A. H. Touny, H. Elsawy and
M. M. Saleh, Antimicrobial activities of mesoporous nickel
phosphate synthesized with low-temperature method,
Microchem. J., 2019, 145, 113–118.
45 M. Wang, R. Zhang, Y. Gong, Y. Su, D. Xiang, L. Chen,
Y. Chen, M. Luo and M. Chu, Improved electrochemical
performance of the LiNi0.8Co0.1Mn0.1O2 material withlithium-ion conductor coating for lithium-ion batteries,
Solid State Ionics, 2017, 312, 53–60.
46 Y. Lee, J. Lee, K. Y. Lee, J. Mun, J. K. Lee and W. Choi, Facile
formation of a Li3PO4 coating layer during the synthesis ofa lithium-rich layered oxide for high-capacity lithium-ion
batteries, J. Power Sources, 2016, 315, 284–293.
47 D.-J. Lee, B. Scrosati and Y.-K. Sun, Ni3(PO4)2-coated Li[Ni0.8Co0.15Al0.05]O2 lithium battery electrode withimproved cycling performance at 55  C, J. Power Sources,
2011, 196, 7742–7746.

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