Electrochemical performance of multiphase nickel hydroxide

Available online at www.sciencedirect.com SCIENCE @DIRECT*

Scie nc:e Press

Transactions of Nonferrous Metals Society of China

Trans. Nonlkrrotis Met. Soc. China I7(3007) 654-65X \\\\I\, C\LI cciu L l l / > \ \ b

Electrochemical performance of multiphase nickel hydroxide

I . School of Chemistry and Chemical Engineering, Central South University, Changsha 4 10083, China; 2. Jiangxi Kingan High-Tech Co. Ltd, Nanchang 330508, China Received 6 March 2006; accepted 28 June 2006

Abstract: The high density nano-crystalline inultiphase nickel hydroxide containing at least three doping elements was synthesized and its clcctrochemical characteristics were studied. The electrocheinical behavior of the high density splierical multiphases rr-Ni(O14)2 wcrc also invcstigatcd. The results show that the structure of the material is a mixed phase of a-Ni(OH)? and ,!-Ni(OH)?, which has a the same stabilized structure as r/-Ni(OH)2 during long-term chargddischarge proccss. High dcnsity spherical multiphases u-Ni(OH): have a much better redox rcvcrsibility. a iiiuch lower oxidation potential of' Ni( 11 ) than the corresponding oxidation state in the casc ofp-Ni(OH)?, and a much higher reduction potential. They exchange one electron during clccti-ochcmical reaction and Iiavc a higher proton diffusion coefficient. The mechanisiii of the electrode reaction is proton diffusion, and the proton diftiision coefficient is 5 . 6 7 ~ 1 0I" cni'is. Morcovcr, they rcvcal a higher discharge capacity than fl-Ni(OH)2/P-Ni00F1because they exchange one electron per nickel atom during chargc!dischargc process. Key words: multiphase nickel hydroxide; elcctrocheinical performance; voltammogram; exchange electron number; manganese -

1 Introduction Rechargeable batteries are critical components in exploding new technologies of portable electronics, power tools and electric vehicles. The N K d , NilMH, Niifl? and NiiZn batteries belong to alkaline secondary batteries. A coininon feature of these batteries is electrochcmical active Ni(OH), electrode used as positive electrode and the Ni(OH), electrode is the essential limited factor in the overall battery encrgy dcnsity. Therc arc two polymorphs about the nickel hydroxidc denoted a-Ni(OH)? and p-Ni(OH),. Both form crystals in the hexagonal system with the brucite-type structure with Ni(OH)? layers stacked along the c-axis. Thc main difference between the p- and a-Ni(OH)., phase resides in the stacking of the layers along the c-axis. For p-Ni(OH)2 layers are perfectly stacked along the c-axis with an interlamellar distance of 0.46 nm; whilc for n-Ni(OH)2 layers are completely misoriented relative to each other corresponding to a turbostratic phase i n the presence of water molecules and anionic

species at the van der WAALS gap. The intcrlaniellar distance for the cx-Ni(OH)-,is about 0.78 nm[ 1-61, Conventional electrode reaction of p-Ni(OH)? is considered to be a one-electron proccss involving oxidation of divalcnt nickel hydroxide to trivalcnt nickcl oxyhydroxide in charge and subsequcnt discharge of trivalent nickel oxyhydroxidc to divalcnt nickel hydroxide. Thus, P-Ni(OH)? has a maximum theoretical specific capacity of 289 mA.h/g. However, it has also been reported that cx-Ni(OH), has bcttcr clcctrochemical properties than P-Ni(OH)2[7-1 I]. cx-Ni(OH): can bc oxidized to y-NiOOH at a lower potential than the corresponding oxidation state coniparcd with p-Ni(OH),, and has a higher discharge capacity than p-Ni(OH),/ P-NiOOH since the valence of nickel in y-NiOOH exceeds 3, due to Ni4+defects (3.3-3.7)[ 12-13]. It is also reported that a-Ni(OH), is not stable in presence of the high concentratc basic electrolyte incdia and is transformed into p-Ni(OH).,. Attempts to improve stability of the cx-Ni(OH)? have a lot of reports[7-l I]. In this paper, a high density multiphase cx-Ni(OH)? with stabilized a-Ni(OH)zly-NiOOH cycle during charge/ discharge process was synthesized through adding at

Corresponding author: L U O Fang-chen; Tcl: +X6-79 1.3432 146; E-mail: fcluo2003((~~yalioo.cn

LUO Fang-chen, et aliTrans. Nonferrous Met. Soc. China I7(2007)

lcast three modifier elements. It can improve capacity, cycle life and electrochemical performance. And the electrochemical performances of the high density spherical multiphase cx-Ni(OH)? were investigated.

2 Experimental The material was synthesized by coprecipitation of scvcral metal ions from thc aqueous solution. The rcsull.ing brownish precipitate was filtcred by a laboratory suction filter and washed with distilled water until it was free from neutral salts, then dried at 80 "C to prodiice powder. The powder was subjected to chemical and X-ray diffraction analysis. The doped metal ions are most preferably Co, Zn and Mn. For comparison all samples had the same Co and Zn contents, and only Mn content was changed. The electrochemical behavior of the spherical multiphase nickel hydroxide in 6 moliL KOH electrolyte was studied. A typical three-electrode one-compartment clectrolysis cell was used for the experimental measurements. The working electrode was a platinum powder microelectrode with diarnetcr of 200 pm. Nickel sheet counter electrode was placed on the side and the working electrode was positioned at the center. A LUGGIN capillary with a salt bridge was used to connect the cell to the reference electrode. All potentials were measured and quoted with respect to a AgiAgCl (3 moliL NaCI) reference electrode. Cyclic vultammetric experiments were performed using EC & (3 PAR Mode 273A potentiostatigalvanostat, and a computer interface for experimental control and automatic data acquisition was used.

oxidation reaction shifts to more positive potentials, and cathodic peak potential Corresponding to nickel hydroxide reduction reaction shifts to less positive compared to the characteristics of thc abovc results. The cyclic voltammetric results i n Fig. 1 arc listcd in Table 1 . To comparc the effect of multiphase a-Ni(OH)2 on oxygen evolution reaction, the difference between the oxidation peak potential and the oxygen evolution potential( DOP) on the rcversc swccp rcquired to produce 50 pA of anodic current is also estimatcd from voltammograms.

-

5

3 0

0

0 0. I

1

0.2 0.3 0.4 Potent I a I ( v s A g/Ag('l)/ V

0.5

50

1

2

5

0

3 Results and discussion

655

25

0 -25

-50 Fig. 1 shows the typical cyclic voltammograms for multiphase nickel hydroxide microelectrode with various Mn contents, which was activated by 15 cyclic voltammograms at a rate of 5 mVis. In the range of scanning potentials employed, an anode oxidation peak for the electrode with various Mn contents, appearing between 0.34 and 0.38 V, was recorded prior to oxygen evolution. One oxyhydroxide reduction peak at about 0.162-0.177 V was observed on the reverse sweep. As shown in Fig.1, the potential of oxidation peak that corresponds to the formation of higher-valence nickel species apparently decreases with the increase of Mn content in nickel hydroxide, while the potential of reduction peak changes a little. Similar voltammogram is also observed (Fig.l(a)) for the electrode without Mn. The anodic oxidation peak corresponding to Ni( I1 )

-75

0

0.1

0.2 0.3 0.4 Potential (vs Ag/AgC'I)/V

0.3

Fig.1 Cyclic voltammograins of inultiphase nickel hydroxide with various mass fractions of Mn at 15th chargeidischarge

cycle: (a) Without Mn; (b) 10 % Mn, 15 % Mn and 20% Mn The results in Fig.1 and Table 1 illustrate that multiphase a-Ni(OH)2 allows the clectrodc to charge at a significantly less positive potential (387, 352 and 346 mV) instead of 412 mV. In addition, the charge process occurs more reversibly (AEL,cis 210, 168 and 184 mV instead of 254 mV). Moreover, their oxygen evolution overpotentials have nearly the same values. Thus, these results clearly indicate that multiphase a - N i ( O H ) 2

LUO Fang-chen, et alITrans. Nonferrous Met. Soc. China 17(2007)

656

Table 1 Parameters for nickel hydroxide electrode with various mass fraction of Mn CV(

E,,(vs Ag1AgCI)IV

E,,(vs AglAgC1)lV

AE,,,(vs Ag1AgCI)IV

E,,? (vs Ag1AgCI)IV

0

0.412

0.158

0.254

0.423

10

0.387

0.177

0.210

0.422

15

0.352

0. I84

0.168

0.423

20

0.346

0.162

0.184

0.426

Mn)/Yo

electrodes rnake the charge process perform more easily and more rzversibly, suggesting that much more active materials can be utilized during charge. From Figs.1-3, it can be seen that the nickel hydroxide microelectrodes with different Mn contents, which were activated by IS cyclic voltammograms at a rate of 5 mV/s, have a single diffusion-limited peak vs AgiAgCI. Theoretically, potential difference of peak to peak on a voltammogram for a reversible electrode reaction should be equal to 59 mV/n, howcvcr the values in Table 1 are markedly higher than the theoretical value. Therefore, electrode reaction of nickel hydroxide is usually considered as a quasi-reversible electrode reaction[ 12 141. The dependence of E,, and E , , can be exprcsscd using Nicholson and Shain equation (Eqn.( 1 ))[I Ls] and can be used to calculate the number of electrons ( n )participating in the rate determining stages:

1

,

,

0

2

4

0.12

,

,

8 10 12 Scan ratel(n1V * s 1 ) 6

14

10

~

E,,;,-E,,.=

1 .857RTI(anF')

(1)

where Epa12is the potential of half peak height, R is gas constant, T is absolute temperature, a is transfer coefficient and F is faraday constant. According to Fig. 1 and Eqn.( I ) , the number of electrons participating in electrode reaction for nickel hydroxide microelectrode can be calculated, and the results are listed in Table 2. In addition, since oxygcn evolution is a parasitic reaction

Fig.3 Effect of sweep rate on anodic and cathodic potentials for 15Y' M n electrode

during charge of nickel electrode, it will obscure the basic line of reduction peak current. Fig.4 shows that the anodic peak current (Ipr,)in Fig.2 depends linearly on the square root of the potential sweep rate. As seen in Fig.4, there exists a linear relationship between thc pcak current and the potential sweep rate square root. The charge-discharge process of thc nickel hydroxide in alkaline solution can be described as a proton deintercalation-intercalation mechanism: Diachargc

Ni00H+H20+e~Ni(OH)2+0H~ Chargc

(E" (vs Ag/AgC1)=0.29 1

I, 7 -8.0 mVIs 8 - 10.0 mV/s 9 - 12.0 mvis 10- IS.OmV/s 0.1

(2)

As a stationary elcctrode, a linear relationship between peak current and the square root of potential sweep rate (v'12)over the range of sweep rate in Fig.2 can be expressed as

6 -5 0 mV/s

0

V)

0.2 0.3 0.4 Potential (vs Ag/AgCI)/V

0.5

Fig.2 Cyclic voltammograms of 15% Mn electrode at various sweep rates

= 2.99 X

105n(an)i~2AD,1"C,"~"'

(3)

where Do is the proton diffusion coefficient in nickel hydroxide, C,," is the concentration of hydrogen in the solid (assuming the density of Ni(OH)2 is 3.5 g/cm' and thus the maximum concentration of electrochemically active material hydrogen in the lattice, C,", is 0.038 3 mol/cm3[16]), and A is the area of electrode. According to Fig.2, Fig.4, Table 2 and Eqn.(3), difhsion coefficient of H+ for 15% Mn multiphase nickel hydroxide is found

LUO Fang-chen, ct aliTI-ans. Nonfcrrous Met. Soc. China 17(2007)

657

Table 2 Diffusion cocfticicnts of H ' for nickcl hydroxide electrode with various mass fractions of M n 1t'(Mn)/%,

Epa(vsAg1AgCl)iV

E,,, ?(vsAg/AgCI)/V

1pAPA

n

Diffusion coefficient, D,,/(cm'.s

0

0.4 12

0.307

282.0

0.900

3.21 x 10

10

0.387

0.30 I

134.0

1.255

4.47x 10

15

0.352

0.286

94.0

1.440

6.67 X 10

"I

;!0

0.346

0.258

89.9

I .080

9 . 9 4 x 10

'I

I)

I'

alkaline rechargeable batterics. 16

.t

~

4 Conclusions

12 -

2c.

x401

' 0.5

1.0

1.5

2.0

2.5 3 0 1'1 2/(111V *s-l)l 2

3.5

4.0

Fig.4 Depcndcnce of anodic peak current on square root of

potential sweep rate for 15% Mn electrode to bc 6.67 X 10-I" cm'is. Similarly, the others can also be

calculated, the results are listed in Table 2. In Table 2, the proton diffusion coefficients in the multiphase nickel hydroxide exhibit higher values, which are higher than those in Al-substituted rx-Ni(OH)?, 3.6X l o - ' ' cm2/s reported in Refs.[6-71. As seen from Fig.1, Tables 1 and 2, the multiphase n-Ni(OH)? doped with different amounts of Mn reveals much better electrochemical performance than Mnundoped P-Ni(OH)?, such as much lower oxidation potential of nickel ( 11 ), much higher electrochemical reversibility, and much more exchange electron number, thus the inaterial has greater discharge capacity and higher utilization of' active material. The anions strongly anchor the positive charged brucite layers and stabilize the structure under a variety of stressful conditions. However, sample with lower anion content, namely that with 5% Mn is less stable in alkali media. As seen from Fig.1 and Table 2, the multiphase nickel hydroxide electrode that consists of 15% Mn has much better electrochemical performance, much more exchange electron number, and thus the electrode has greater discharge capacity than the theoretical capacity of P-Ni(OH)? (289 mA.h/g). As a consequence, it can be concluded that cx-Ni(OH)2 doped with 15% Mn is an excellent positive active material for

I ) Nickel hydroxide active materials internally containing at least three modifier elements, have a modified proton diffusion coefficient, excellent electrochemical performance and wider use of the available storage sites through improved proton transport. 2) The nickel hydroxide dopcd with 15%" Mn has much lower oxidation peak potential and much higher reduction peak potential. The presence of Mn in nickel hydroxide lattice can increase electronic conductivity and protonic conductivity of nickel hydroxide, thus improving the performance of nickel hydroxide electrode, such as greater discharging capacity and better reversibility of Ni( I1 )/Ni(lll) redox reaction.

References KOSTECKI R. M O L A R N O N F. Elcctrochcmical and

in

situ Raman

spectroscopic characterization of nickel hydroxide electrodes [J]. Journal of Elcctrocliemical Society. 1997. 144(2): 4XS -493. KIM M S, HWANG T S. KIM K B. A study o f the clcctrochcmical

rcdox behavior of elcctrochcmically pi-ccipitatcd nickel hydroxides using elcctrochemical quartz crystal microbalance [J 1. .lourlial o f Elcctrochemical Society. 1997. 144(5): 1537- IS43 [31

R A M E S H T N, V l S H N l l K P. Synthesis of nickel hydroxide: Effect of precipitation conditions on ph

selectivity and structural

disorder [J]. Journal of Power Sources. 2006, 156: 6SS 661. 141

R A M E S H T N. VISHNU KAMATll P. SIIIVAKUMARA C.

Corrclation of structural disorder uitli thc rcvcrsiblc discharge capacity of nickel hydroxide electi-ode [J]. Journal of Elcctrochemical Society. 2005. IS2(4): AX06-AX 10. M O R G A N D, M E N G Y S. Phaae stability of nickel hydroxides and

oxyhydroxides[J]. Journal of Elcctrochcmical Society. 2006. IS3(2): A 2 10-A2 IS. KAMATH P V, DIXlT M , INDIRA L. S H U K L A A K. LUMAR V G. M U N I C H A N D R A I A H N.

Stabilized rx-Ni(Otl)2 as electrode

material for alkaline secondary cclls [J]. Journal of

Elcctrochemical

Society. 1994. 141(11): 7956-2959. DlXlT M, JAYASHREE R S, VISHNU K P. Elcctrochemically

iinpreiiated aluininum-stabili~ed rr-nickel hydroxide electrodes [J]. Elcctrochemical and Solid-State Letters. 1999, 2: I70 17 I E M O I J K G U E S L. DI:LMAS

(',

Elcctrochcmical hchavior of the

manganese-substitiitcd nickel hydroxidcs[.ll.

.Iowniil

of Electro-

658

LUO Fang-chcn, ct aVTrans. Nonfcrrous Met. SOC.China I7(2007) cliciiiicill Society, 1906, 143: S61 ~ 5 6 6 .

101

[ 131

I l l J W K. GAO X P, NOREUSD. Evaluation of nano-ciystal ai/ed

clcctrochciiiical studies 01' sphei-ical nickel hydroxide 1.11. .1wrii;iI 01'

cr-nickel hydroxide as an electrode material for alkaline rechargeable ccIIs [J]. .lournal of Power Sour

LlOl

Power Sources. 1998. 7 2 ( 2 ) .221-225. [I41

DAI J X . SAM. LI Y. Structul-al stability of aluminum stabilized

\ IIJ

[ 121

Z H A N G C'. PARK S M The anodic oxidation ofnickcl

iii

alkaline

media studied by spccti-oclectrocliciiiic~iltcchiiiqucs 1.11. Journal 01'

nickel hydroxide as a positive electrode material for alkaline secondary batteries [J]. Journal of Power Sources. 2000, 89: 40-45.

\?'.4NCi X Y. YAN J. Y UAK T. ZI IAN(; Y Siirf:icc inodilicatioii eiid

Elccti-ochciiiical Society, 19x7. I34( 12): 2Uh6-2')70. 1151

WANG X. L U O I-I. PARKHUTIK P V. Studies ofthe pcrfoi-inance of

Southainpton

Elccti-o-cheiii

group.

Iii\tiniiiiciital

Electrochcmistiy [MI. New York: l
Methods

I lorwood Ltd.

in

1990:

iiaiiostructural iiiultiphasc nickel hydroxide [J]. Joumal of Powei-

178- 227.

Sotircca. 2003. I I S : 153--160

Z I M M E R M A N A 11. EFFA P K. [)ischarge kiiictics 01' the nickel clectrodc [.I].Journal 01' tlcctrochciiiical Society. 10x4. 13 I :

('ORRIGAN D A. RENDERT R M. Effect of coprecipitatcd metal ioiis on the clcctrocheinistry of nickel hydroxidc t h i n films: Cyclic voltaiiiinetry i n 1 iiiolVL K O H [J]. Jouinal of Elccti-ochciiiical Society.

1989. 136(3): 723-728.

[ 161

709-7 13. (Edited hy CHKN Wei-ping)