S udy o Zinc Deposi ed in he P esence o
O ganic Addi i es o Zinc-based Seconda y
Ba e ies
CHLADIL, L.; ČECH, O.; SMEJKAL, J.; VANÝSEK, P.
Jou nal o Ene gy S o age
Volume 21, Feb ua y 2019, Pages 295-300
ISSN: 2352-152X
DOI: h ps://doi.o g/10.1016/j.es .2018.12.001
Accep ed manusc ip
© 2019. This manusc ip e sion is made a ailable unde he CC-BY-NC-ND 4.0 license
h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/
dspace. u b .cz
S udy o Zinc Deposi ed in he P esence o O ganic Addi i es o Zinc-Based
Seconda y Ba e ies
L. Chladila,b, O.Čecha,b, J. Smejkala and P. Vanýseka,b
a Depa men o Elec ical and Elec onic Technology, B no Uni e si y o Technology,
Technicka 10, 616 00 B no, Czech Republic
b Cen e o Resea ch and U iliza ion o Renewable Ene gy, Facul y o Elec ical
Enginee ing and Communica ion, BUT, Technicka 10, 616 00 B no, Czech Republic
Abs ac
This wo k is ocused on he e ec o selec ed o ganic addi i es on zinc deposi
p ope ies in ela ion o a possible u ilizing he addi i es o a zinc based ba e y sys ems
wo ked wi h alkaline elec oly e. The Zn laye s we e deposi ed on in subs a e om he
KOH based elec oly es sa u a ed by zinc oxide and wi h addi ion o di e en o ganic
su ac an s - CTAB, Slo asol 2520/2, Tween 20 and Lugal an G 35 in concen a ion
500 ppm. Deposi ions we e held unde low cu en densi ies 10 mA/cm2 whe e he mossy
po ous deposi g ows om pu e KOH solu ions. All addi i es we e examined wi h
emphasis on he s udy o zinc deposi mo phology and hei abili y o c ea e uni o mly
dis ibu ed po ous s uc u e which could exhibi as elec ode kine ic. All deposi s we e
s udied by X- ay c ys allog aphy and p e e ed s uc u e o ien a ions a e epo ed. Fo he
pu pose o using addi i es di ec ly in he ba e y sys ems we e alua ed also he co osion
p ope ies o he KOH solu ion wi h addi ion o he abo e men ioned su ac an s. I has
been ound ha he p esence o CTAB and Slo asol 2520/2 lead o a py amidal ex u e,
Lugal an G 35 p oduced mic o-c ys alline deposi wi h opened po ous s uc u e and
inally p esence o Tween 20 lead o nano-c ys alline highly po ous deposi almos wi hou
p e e ed o ien a ion.
In oduc ion
Elec ochemical deposi ion o zinc is a p ocess u ilized mainly in pla ing indus y
and in he ield o ene gy s o age. Al hough elec odeposi ion o zinc o o m a p o ec i e
laye is s ill mo e comme cially exploi ed and he e o e is mo e widely s udied [1], [2], [3],
de elopmen o uncon en ional elec ochemical ene gy s o age (EES) sys ems ha could
be based on zinc elec odes [4] b ings a new impe us o s udy he zinc deposi ion upon he
condi ions o hese ba e y sys ems. Using zinc o ene gy s o age seems o be p ospec i e
mainly due o i s abundance, low cos and ease o ecycling. This gi es an ad an age o he
zinc based sys em o e con en ional Li-ion [5] o anadium edox low ba e ies [6], [7].
The g oup o zinc based ene gy s o age sys ems is wide and con ains long- e m
in es iga ed nickel zinc cells [8], [9], zinc-sil e [10] and many di e en ypes o zinc-
based hyb id low ba e ies like zinc-ai , zinc-i on, zinc-ce ium, zinc-iodine, zinc-b omine,
zinc-polyme e c. [11]. Al hough bo h applica ion ields – pla ing indus y and ba e y
sys ems ha e di e en equi emen s on zinc deposi s (co osion p o ec ion needs a compac
zinc laye wi hou po osi y whe eas ba e y applica ion bene i s o m high su ace
s uc u es wi h as eac ion kine ics and good di usion p ope ies) hey a e uni ed in he
e o o a oid dend i ic g ow h o zinc. G ow h o zinc dend i es occu s mainly a high
cu en densi ies and depends on he concen a ion o soluble zinc ions.
Du ing ca hodic pola iza ion o he zinc elec ode he zinca e ions s a o educe o
me allic zinc. In his p ocess, he zinc is deposi ed om he elec oly e o he cu en
collec o o he nega i e elec ode. The eagen s a e in he o m o zinca e ions Zn(OH)42-
dilu ed in he solu ion and in he elec ode a e in he o m o ZnO [12]. The o al deposi ion
mo phology is highly dependen on cu en densi ies a which he dend i ic g ow h occu s
[13]. Supp ession o he dend i ic g ow h is possible unde he condi ions suppo ing
anspo o zinc ions such as inc ease concen a ion o zinc ions in he elec oly e and low
iscosi y o he elec oly e o o ced elec oly e con ec ion in he case o low-ba e ies.
Ano he way how o a oid dend i e o ma ion is a con olled zinc deposi ion by
special cu en p o ile [14], [15], [16], [17]. This app oach was b oadly s udied o Ni-Zn
o Ni-ai ba e y applica ions [15], [17], [18] and he cu en p o ile ypically consis s o
high cu en pulses complemen ed by elec oless pe iods and in some cases also by coun e -
pulses. While he deposi ion a high cu en peak ensu es a su icien le el o o e po en ial
o zinc c ys al g ow h in all c ys allog aphic di ec ion, he cu en less gaps we e used as
eco e y imes when he c ea ed di usion laye ge s he ime o balance he eac an
g adien , and inally, he high cu en coun e -pulses should dissol e he ips o he
dend i es and edeposi he dend i e ma e ial in a le el o m on he elec ode. Fo example
Lin e al. used he pulses o p epa a ion o a zinc-ai anode and hey ound he bes esul s
o a 500 Hz equency [17] which is consis en wi h ou p e ious esul s [16].
The o he app oach o inhibi ion o dend i e o ma ion is u ilizing o special
o ganic addi i es (su ac an s) ha should p e en a non-uni o m zinc deposi ion and hus
keep up he smoo h and b igh su aces wi hou dend i es [19], [20]. The su ac an s ha e
he abili y o o m a ba ie o he eac an s (zinca e) on he elec ode su ace, he eby
balancing hei une en deposi ion on he su ace o he elec ode. This phenomenon is
called a blocking e ec [19]. The su ac an molecule ypically has a hyd ophilic and
hyd ophobic pa . The hyd ophobic pa is o ien ed owa ds he solid su ace. By adso bing
on a solid su ace, i c ea es a ba ie which p e en s access o he ions o he su ace o
he elec ode. This a highe cu en densi ies leads o supp ession o he p e e ed g ow h
o dend i es. Fo his eason, zinc deposi ion will begin o slow down. Impac o he a e o
elec on ans e includes blocking o ac i e si es using su ac an s and elec os a ic
in e ac ion be ween elec oac i e pa icles o zinc ions and abso bed su ac an s [14]. As a
esul we can ob ain a po ous laye wi hou he p esence o dend i es. No only su ac an s,
bu also o he me al ions, and o ganic and ino ganic compounds a e impo an addi i es
ha can a ec he shape and size and hus change he mo phology o he deposi [21], [22].
As a esul , bo h app oaches, pulse cha ging and using o addi i es, could
e ec i ely educe dend i e o ma ion and bo h we e applied on zinc-based EES sys ems.
Ou con ibu ion aims o ex end he g oup o usable su ac an s ha a e able o c ea e a
highly po ous s uc u e wi hou any p esence o dend i es. Addi i es o his s udy ha e
been selec ed based on hei al eady known bene i s o Ni-Zn cell (CTAB), based on hei
using in gal anic indus y (Lugal an G 35) and based on ou p e ious esea ch p ojec in
he ield o Ni-Zn accumula o s. Deposi s we e e alua ed om hei s uc u al p ope ies
using X- ay c ys allog aphy wi h emphasis on e alua ion o a p e e ed o ien a ion.
In luence o addi i es on co osion p ope ies o zinc we e s udy on wi e zinc elec ode in
o de o in es iga e changes in co osion beha io o alkaline en i onmen en ich by
selec ed addi i es.
Ma e ial and Me hods
Cu en collec o s o deposi ion we e p epa ed om a olled in (Sn) shee o
0.5 mm hickness. Tin me al has been chosen because o i s high alue o o e -po en ial
o hyd ogen e olu ion and because i s in e nal (c ys allog aphic) s uc u e is simila o
me allic zinc. The equi emen o ano he collec o ma e ial han zinc is based on he need
o measu e he deposi pa ame e s and i is he e o e necessa y o dis inguish he s uc u e
o he unde lying ma e ial and he deposi in he di ac og am. The measu ing a ea was
2 cm2; he emaining pa o he elec ode was insula ed wi h an epoxy adhesi e and hen
cu ed a 100 °C o 60 minu es.
The basic solu ions we e p epa ed by dissol ing 30 g ZnO in 1000 ml o
6 mol/dm3 KOH. The solu ion was close o a sa u a ed s a e, which co esponds o he s a e
o he elec oly e in alkaline ba e ies a he end o he discha ging p ocess. Tes ed solu ions
we e p epa ed om s ock solu ions by adding addi i es. Mo e in o ma ion abou chemical
composi ion and dis ibu o o used addi i es is in Table 1.
Table 1. Chemical composi ion and applica ion ield o selec ed addi i es.
Addi i es
Chemical composi ion
Mo e de ails
CTAB
ce yl ime hylammonium
b omide
Ca ionic su ac an , used in he syn hesis o
gold nanopa icles. I is supplied by Sigma-
Ald ich.
Lugal an G 35
polye hyleneimine
Aqueous solu ion. Is used as a zinc ba h polish
in he gal anic indus y. I is supplied as a 50%
solu ion by BASF company.
Slo asol 2520
alkylpolyglycole he
P oduc could be used a co osion inhibi o and
in he cosme ics indus y. Supplied by
Slo chema.
Tween 20
polyoxye hylene
so bi anes e
Non-ionic de e gen widely used o s able oil-
in-wa e emulsion in he cosme ics indus y. I
was supplied by Sigma-Ald ich
Selec ed addi i es con ains bo h nonionic (Slo asol 2520/2 and Tween 20) and ca ionic
su ac an s (CTAB) and also indus ial addi i e used in gal anic zinc pla ing (Lugal an
G 35). The addi i es we e added o he solu ion in concen a ion 500 ppm by weigh . Fo
solu ions was used demine alized wa e wi h speci ic conduc i i y 0.1 µS/cm.
The zinc deposi ion was ealized in a h ee-wi e connec ion a a cons an cu en o
10 mA/cm2 o 30 minu es. The wo king elec ode was a in elec ode, a zinc wi e was used
as he e e ence elec ode and he coun e elec ode was a nickel wi e mesh. The coun e
elec ode had a 2.5 imes la ge a ea han he wo king elec ode. Upon comple ion o he
deposi ion, he elec odes we e emo ed om he solu ion and placed in o a la ge essel o
dis illed wa e o 1 minu e o emo e he alkaline solu ion and addi i es om he deposi s.
The ea e , he elec odes we e placed in a cons an empe a u e chambe and d ied o 48
hou s a 40 °C.
The co osion es s we e also pe o med in a h ee-wi e connec ion, bu as he e e ence
elec ode a s anda d calomel elec ode was used and as a wo king elec ode a 10 mm long
zinc wi e o 2 mm diame e was used (ac i e su ace 0.659 cm2). The elec oly es o he
co osion es s we e based on pu e 6 mol/dm3 KOH wi hou any zinca e ions. Only
addi i es in 500 ppm concen a ions we e added.
X- ay measu emen was pe o med by Rigaku Mini lex 600 HR wi h selec ed kβ
il e o 0.003 mm hickness and a 0.1 mm di e gence sli . The measu ing ange was om
20° o 120° wi h a s ep 0.02°. Measu emen s we e made on samples ha we e placed on a
low backg ound holde wi hou any X- ay e lec ions. Pa icle sizes we e calcula ed using
he Sche e equa ion:
𝐷
=
𝐾𝜆
𝛽 𝑐𝑜𝑠 𝜃
whe e D is he mean size o he c ys alli e, shape ac o K was 0.9, β is he line b oadening
a hal maximum in ensi y ( e e ed also as FWHM) and θ is he B agg angle [23]. Fo
c ys alli es size calcula ion o samples wi h s ong p e e ed o ien a ion we sub ac ed
β om he peaks wi h he highes in ensi y.
Mo phology was s udied on scanning elec on mic oscope Vega 3 XMU wi h LaB6
Ca hode by Tescan. All pic u es we e ob ained in acuum and wi h accele a ing ol age
20 kV.
Resul s and Discussion
Zinc Deposi ion
Zinc deposi ion is close o he p ocess inside a zinc based low-ba e y du ing
cha ging. Ba e y cha ging could p oceed in wo egimes: cons an cu en (gal anos a ic)
o cons an po en ial (po en ios a ic). The second men ioned is ypically used du ing inal
s age o ba e y cha ging in o de o p e en inc ease o hyd ogen e olu ion bu usually a
ba e y cha ging is ca ied ou unde gal anos a ic con ol. The e o e we used he
gal anos a ic mode al hough po en ios a ic egime is ypically p e e ed by in es iga o s
o he s udy o changes in deposi mo phology du ing zinc deposi ion [19]. I he
gal anos a ic deposi ion is unde mass- anspo con ol, changes in mo phology such as a
dend i ic g ow h can be de ec ed by changes (dec ease) o po en ial du ing he
gal anos a ic deposi ion.
The ime cou se o he ca hodic po en ial du ing he gal anos a ic deposi ion is
shown in Figu e 1. E en hough he ca hodic po en ial p o ile o he deposi ion om he
blank elec oly e seems o be almos linea , he second pa o he cu e ( > 0.3 h) exhibi s
a dec easing end and he ca hodic po en ial a he end o deposi ion is educed o 75 % o
he maximum ca hodic o e po en ial. I indica es he o ma ion o a mo e-open s uc u e
in he second pa o he zinc deposi ion. Indeed, Figu e 2 e ealed he o ma ion o mossy
po ous i egula ly shaped bunches ha s a o g ow h on he compac zinc deposi . This is
he ypical s uc u e ob ained mainly a low-cu en densi ies when he o e po en ial o he
deposi ion dec eases unde he le el o a mo e-dimensional nuclea ion. This o e po en ial
d op may no be e iden om he measu ed cu es because i can be only a local e ec
occu ing pa icula ly in he su ace dimples o dep essions.

Figu e 1. Vol age- ime p o ile a gal anos a ic deposi ion (j = 10 mA/cm2) o
elec opla ing zinc laye s in blank elec oly e (6 mol/dm3 KOH + 30 g/dm3 ZnO) and
elec oly e wi h addi ion o addi i es wi h a concen a ion o 500 ppm a cu en densi ies
10 mA/cm2.
Deposi Mo phology
Mo phology o he zinc deposi ob ained by a scanning elec on mic oscope is
shown in Figu e 3. The mos s able po en ial p o ile exhibi s he addi i e Lugal an G 35,
whe e only small decline o he ca hodic po en ial du ing he i s 90 s could be iden i ied
(Figu e 3). I is caused by ini ial changes in po osi y o he zinc laye sho ly a e zinc
nuclea ion ha is on he o he hand s able h oughou he deposi ion.
Po en ial du ing deposi ion in he elec oly e wi h addi ion o Slo asol 2520/2 and
CTAB we e s abilized o e a longe pe iod o ime (≈ 6 minu es). Ini ial ca hodic
o e po en ial inc eases apidly in he i s seconds and hen is educed o 60 %.
Mo phology o he deposi s in Figu e 3 e ealed he p esence o c ys alli e clus e s o
diame e en hs o mic ome e s. The in subs a e o he elec ode deposi ed in Slo asol
2520/2 in some pa exhibi s he p esence o hin g oo es ha a e he emains o su ace
polishing. Thus i e eals ha he elec ode con ains si es ha a e no co e ed by a zinc
deposi and mos o he zinc olume is s o ed in hese clus e s. Fo ma ion o hese clus e s
will mos likely be he eason why he ca hodic o e po en ial dec eases in he i s s age o
deposi ion.
Deposi ion in he p esence o Tween 20 has occu ed a he highes ca hodic
o e po en ial which eached 310 mV. P esence o he spikes in he po en ial p o ile
indica es p esence o hyd ogen e olu ion (bubble o ma ion) o some ex en . High
o e po en ial slowly dec eases du ing he whole deposi ion. The SEM images in Figu e 3
e ealed he p esence o isola ed spongy-like clumps placed on a sligh ly co e ed in
subs a e by zinc pa icles. G ow h o he clumps and inc easing o he elec ode su ace
could be ound in ela ion o o e po en ial decline. Rega ding he la ge changes he mic o-
po osi y (ob ious om he de ails o su ace in he igh pic u es o Figu e 3) we can
assume ha g adual dec ease in he ca hodic o e po en ial a e mo e likely caused by
mac oscopic changes in he elec odes su ace (g ow h o clus e s, clumps o la ge
dend i es) hen by an inc ease o ac i e su ace due o highe mic o- o nano-po osi y o
he laye .
High o e ol age o he elec ode in espec o he zinc equilib ium po en ial
(especially in he case o Tween 20) exp esses loss o cha ging ene gy and hus educes
he e iciency o ene gy s o ing. I has o be conside ed mo e mainly in he ba e y sys ems
wi h low alue o he cell ol age.
50 µm
2 µm
Figu e 2. Zn deposi ob ained om 6 mol/dm3 KOH solu ion sa u a ed wi h 30 g/dm3
ZnO a cu en densi ies 10 mA/cm2.
5 µm
50 µm
5 µm
50 µm
50 µm
5 µm
50 µm
2 µm
a)
b)
c)
d)
Figu e 3. Deposi s uc u es a cu en densi ies10 mA/cm2. Blank solu ion was
6 mol/dm3 KOH + 30 g/dm3 ZnO. Selec ed addi i es we e a) CTAB, b) Lugal an G 35,
c) Slo asol 2520/2 d) Tween 20 and we e added in concen a ion o 500 ppm. The images
on he igh a e a de ailed iew o he su aces aken a he clus e ea u es on he le
side.
Deposi XRD E alua ion
De ailed SEM pic u es o zinc deposi s in Figu e 3 ( igh ) e eal impo an changes
o mic o-po osi y and ex u e o zinc, when o ganic addi i es a e p esen . This is also
con i med by he Rie eld simula ion o he ob ained di ac ion pa e ns (Figu e 4). We
analyzed he p e e ed o ien a ion o he zinc deposi and he esul ing Ma ch coe icien s
(MC) o selec ed c ys allog aphic planes which a e summa ized in Table 2. I should be
no ed ha when MC is highe han 1 i indica es a dec ease o e lec ion in he selec ed
c ys allog aphic di ec ions and ice e sa, MC below 1 indica es highe e lec ion in he
selec ed planes. Sil a Filho and Lins [3] s udied he c ys allog aphic ex u e o an
elec odeposi ed zinc laye h ough a wide ange o cu en densi ies om 150 mA/cm2 o
1500 mA/cm2. They iden i ied a signi ican changes in e lec ion o basal (0002) plane and
py amidal (10 5), (10 2) and (10 1) planes when he cu en densi y was inc easing (in
1
1
1
he p esen a icle he planes a e desc ibed using he s anda d Mille -B a ais no a ion). Ou
deposi ions p oceeded a much lowe cu en s (10 mA/cm2) and o longe ime pe iod.
P esence o addi i es d ama ically inc eases o e po en ial o he deposi ion which could
be simila o highe cu en condi ion.
Deposi g own in he blank elec oly e is compac ly laye ed wi h mossy po ous zinc
clumps. Bes i s o he Rie eld simula ion (e o pa ame e s Rp < 10) we e ob ained o
selec ed basal (0002) plane and he MC was sligh ly abo e 1.2 ha indica es sligh
dec ease in ela i e in ensi y o he selec ed plane. Simila esul s we e ob ained by Sil a
Filho and Lins [3] s ill a cu en densi ies 150 mA/cm2. The b igh su ace appea ance o
elec ode is also ypical ea u e o deposi wi h basal ex u e.
In he case o he CTAB addi i e, he deposi ed zinc s uc u e has g own o e he
en i e su ace o he elec ode in py amidal-like s uc u es. Indeed, he esul s o he
Rie eld e inemen e ealed signi ican dep ession o he (10 5) plane, which is a ypical
1
ea u e o zinc deposi ob ained a high cu en densi ies.
Lugal an G 35 addi i e esul ed in a deposi ed laye composed o insula ed
pa icles in he shape o small scales. The de ail o he scales is shown in Figu e 3 b). These
scales we e a anged close o each o he and we e g own pe pendicula ly o subs a e i.e.
in he di ec ion o he eac an low. XRD di ac ion pa e n and alue o he MC e ealed
he s onges p e e ed o ien a ion o deposi in compa ison o o he deposi s. S ong
e lec ion om he py amidal plane (10 1) exp essed by alue o MC 0.467 is a ypical
1
ea u e o a s ongly py amidal su aces ypically ob ained a cu en densi ies a ound
1500 mA/cm2 achie ed by agi a ion o he elec oly e. Zinc laye s composed o hin scales
will ha e he la ge su ace a ea due o pa ially opened s uc u e.
Mic os uc u e o deposi ob ained using Slo asol 2520/2 seems o be simila o he
zinc laye deposi ed in he p esence o CTAB bu a much s onge X- ay e lec ion om
he py amidal (10 2) plane was de ec ed. Deposi ion was pe o med a lowe alues o
1
o e po en ial in espec o he o he addi i es and high in ensi y o he (10 2) plane
1
co esponds o he deposi ob ained a middle cu en densi ies o 600 mA/cm2.
The addi i e Tween 20 p oduces clus e s ha we e made up o small s icks. A de ail
o he small s icks is shown in Figu e 3 d) ( igh ). Ci cula shapes o he clus e s indica e
ha he g ow h o hese clus e s was iden ical in e e y di ec ion. Because he clus e s a e