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Int. J. Electrochem. Sci., 6 (2011) 2859 - 2868

International Journal of

ELECTROCHEMICAL

SCIENCE

www.electrochemsci.org

A Solid-State Method for Preparing Cobalt-Doped

Li5FeO !"ing Fe(#O$)$ a" the %ron So&r'e

Keqiang Ding 1 , Li Wang

2,* , Jianjun Li

2 , Haitao Jia

1 , Xiangming He

2

1College of Chemistry and Materials Science, Heei !ormal "ni#ersity, Shi$ia%h&ang, Heei '5''16,(.). China2*nstit&te o f !&clear + !ew nergy echnology, ei$ing /ey 0a of ine Ceramics, singh&a"ni#ersity, ei$ing 1'''8, China3-mail4 wang-ltsingh&a.ed&.cn

ecei!e"# 7ril 2'11 $cce%te"# 15 :&ne 2'11 &u'li(he"# 1 :&ly 2'11

*n the asence of inert gas rotection, a cathode material of Co-doed 0i 5e; was s&ccessf&lly reared y a solid-state method, i.e., a mi?9H2;, 0i;H?H2; andCo=!;>2?6H2; was thoro&ghly gro&nd leading to a owder, and then this mi, scanning electron microscoe =SM>, and its secific caacity,cycle roerty and rate caailities were also meas&red. 7 no#el iron so&rce was emloyed in the worB tho&gh the electrochemical erformance of the Co-doed 0i5e; was not #ery satisfactory. hismethod &sing caron coating as rotection is a #ery simle and &sef&l tool to synthesi%e 0i 5e;,esecially for the ind&strial alication.

e*ord"+ Caron rotection, lithi&m attery, 0i5e;, coalt doing

1, %#.OD!C%O#

7ltho&gh many Binds of cathode materials, s&ch as 0i2Co;2, 0iMn2; and 0ie(;, ha#e

een de#eloed so far, there are still more saces for &rs&ing no#el cathodes since these de#eloed

cathodes materials ha#e some o#io&s flaws 1D. *t was reorted that 0i2Co;2 is related to a n&mer of

economic and en#ironmental rolems tho&gh it has good electrochemical erformance 2D. Comared

to the coalt-ased materials, Mn-ased cathode raw materials are #ery chea and friendly to the

en#ironment -5D, &t the caacity loss rolems at ele#ated temerat&res and an inherent lower

caacity at E ha#e &ndermined 0iMn2;Fs alication as a s&itale electrode 6D. eca&se of its

relati#e lacB of to

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Int. J. Electrochem. Sci., )ol. , 2+11 286'

generation cathode material in lithi&m ion atteries, 0ie(; has een widely in#estigated recently.

Howe#er, with the de#eloment of researching worB on 0ie(;, it was re#ealed that oli#ine 0ie(;

has a low electronic cond&cti#ity and a low lithi&m diff&si#ity which greatly re#ents its large-scale

alication in electric #ehicles =Es> and hyrid electric #ehicles =HEs>, th&s, de#eloing no#el

cathode materials is still a hot toic esecially in the field of electrochemistry.o o&r Bnowledge, as far as in 19G1, Aemois-son et al. ha#e de#eloed new 0ithi&m iron

o is 1G m7hg-1

, and it wastho&ght that in the relationshi etween ant-fl&orite and fl&orite str&ct&res, 0i ions in anti-fl&orite

0i5e; occ&y the o

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Int. J. Electrochem. Sci., )ol. , 2+11 2861

2, /P/.%M/#AL

riefly, stoichiometric amo&nt of 0i;H?H2; and e=!;>?9H2; were mi and @-ray diffraction =@)A, r&Ber 7@S, A8 7AE7!C, Lermany> was &sed to e inder in a

weight ratio of 8541'45. wo-electrode electrochemical cells consisting of lithi&m metal foil as thenegati#e electrode, Celgard 2'' searator, and an electrolyte of 1M 0iCl; in C4AC4AMC

=245411, #ol.> were assemled in an nitrogen-filled glo#e o at #ario&s C rates =1CI1Gm7g-1

> etween 2.G and .2 E at amient temerat&re=25N2OC>.

$, ./S!LS A#D D%SC!SS%O#

.1. -haracteriation o/ the -o0"o%e" o/ Li e34

7s reorted re#io&sly, the doing of coalt element can greatly increase the electrochemical

erformance of 0i5e;. ig.1 shows the @-ray diffraction rofiles of 0i5e; synthesi%ed at 85'OC

with #ario&s molar ratio of e to Co. *t can e seen that the intensities of the diffraction eaBs of @)A

attern for the &re 0i5e; are too weaB to e oser#ed, indicating a oor crystal str&ct&re. hile,

the intensity of eaBs are greatly enhanced y Co doing, s&ggesting an imro#ed crystal str&ct&re.

*nterestingly, the @)A atterns change e#idently with the molar ratio of e to Co. his indicated that

Co content is a Bey factor infl&encing crystal str&ct&re of the samles. hen the molar ratio of e to

Co is G4, the eaB aro&nd 65P atten&ates o#io&sly, imlying that too m&ch Co will destroy the crystal

str&ct&re of 0i5e;. herefore, the samle of 0i5e'.8Co'.2; is &sed in the following worB.

o determine the comonent of the otained samle, A@ meas&rements are also carried o&t,

as shown in ig.2. Since lithi&m element cannot e detected &sing o&r resent e&iment, only e, Co,

; are detected in the A@ attern of 0i5e'.8Co'.2;, strongly indicating that the samle as-reared

ha#e ao#e three elements. "nfort&nately, it is re#ealed that the molar ratio of e4Co4; in the as-

reared samle is 84141', which does not accord with the molec&lar form&la of 0i5e'.8Co'.2;.

Considering that A@ is a semi&antitati#e sectrograhic analysis, this indicates that some im&rities

may e in#ol#ed in the reared samle.

he infl&ence of sintering temerat&re on crystalline str&ct&re of 0i5e'.8Co'.2; is also

investigated. As shown in Fig.3, all starting mixtures are heated for 3h, but the sinteringtemperatures are dierent.

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1 . 1 . 1

（）

4 . 0 . 0

（）

4 . 4 . 0

）

（ d

I n t e n ( i t 5 , a . u

c

b

a

0 20 40 60 80 100

2theta,degree

Fig&re 1, @)A atterns of Co-doed 0i5 e; samle sintered at 85'OC for h. a4 0i5e;Q b4

0i5e'.9Co'.1;Q '4 0i5e'.8Co'.2;Q d4 0i5e'.GCo'.;.

Co

C o u n

t s / a . u

O Fe

FeCo

0 5 10 15 20

B e E

Fig&re 2, A@ atterns of 0i5e'.8Co'.2;.

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a . u ， d

I n t e n ( i t 5 c

b

a

0 20 40 60 80 100

2theta,degree

Fig&re $, @)A atterns of 0i5e'.8Co'.2; sintered for h at different temerat&res. a4 65'OCQ b4

G5'OCQ '4 85'OCQ d4 95'OC

*t can e seen that when the temerat&re is 95'oC, the diffraction eaBs are significantly atten&ated,

indicating a oor crystal str&ct&re. (roaly, when the temerat&re is too high, more lithi&m ise#aorated, leading to a material with oor crystal str&ct&re. *nterestingly, as the sintering temerat&re

is 85'oC, more diffraction eaBs similar to the standard @)A attern of 0i 5e; are dislayed.

herefore, 85'oC is set as the otimi%ed sintering temerat&re to reare samles.

d

a . u ， c

I n t e n s i t

y

b

a

0 20 40 60 80 100

2th etade gree

Fig&re , @)A atterns of 0i5e'.8Co'.2; reared at 85'OC for #ario&s sintering time. a4 1hQ b4 hQ '4 6hQ d: h

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a

Fig&re 5, SM images of Co-doed 0i5e;. a4 0i5e'.8Co'.2;Q b4 0i5e'.GCo'.;.

he effect of calcination time on the str&ct&re of 0i5e'.8Co'.2; is roed as shown in ig..

*t can e seen that the sintering time has a strong effect on the shae of the @)A atterns and the

intensity of the eaBs as well. *nstead of enhancing the eaB intensities, when the sintering time is 9h,

as lotted y line d weaB eaBs are oser#ed, imlying that a material with a oor crystal str&ct&re

was reared.

SM images for 0i5e; doed with #ario&s content of Co are shown in ig.5. *mages a and b

is for 0i5e'.8Co'.2; and 0i5e'.8Co'.2;, resecti#ely. *t seems that Co content shows no o#io&seffect on the morhology of the as-reared samles. 7lso, one can see that there are some small

articles on the s&rface of the ig articles, indicating that the samle is not a &re material, and moreworBs sho&ld e done to re#eal the relationshi etween the rearation conditions and the crystal

str&ct&re. o o&r Bnowledge, the SM images of 0i5e; doed with #ario&s content of Co is not

reorted so far tho&gh the reort on 0i5e; has een &lished y other research gro&s.

.2 Electrochemical %er/ormance o/ the -o0"o%e" Li e+.6-o+.234

he cyclic #oltammograms =CEs> of the cathode material can clearly reflect the intercalation

and deintercalation of lithi&m in the charge-discharge rocess. he CEs of 0i 5e'.8Co'.2; are shown

in ig. 6, it can e seen that se#eral eaBs are dislayed. he o

sho&ld corresond to the rocess as shown elow4

0i5 e'.8Co'.2; R0i e'.8Co'.2; K0iK Ke =1>

he eaBs at ao#e .G5E =#s 0i0iK! probably correspond to the reaction as shown below:

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0i 1e'.8Co'.2;R0i- and '.5C =line a and aF> rate.

h&s, the red&ction eaBs corresond to the intercalation of 0iK. herefore, it can e concl&ded

that there sho&ld e two #oltage latea&s in the charge-discharge c&r#es. 7lso, one can see that as the

scan rates increased the eaB c&rrent enhanced corresondingly, s&ggesting that 0i ion can intercalateand deintercalate freely.

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Int. J. Electrochem. Sci., )ol. , 2+11

4.0a c

3.9

b 3.63.8 3.3

) o l t a g e 8 )

9 3.6

) o l t a g e 8 )

9 3.0

2.7

3.4

2.43.2 2.1

1.8

3.0

0 5 10 15 20 25 30

Capacity(mAh!"

2866

a' b' c'

0 5 10 15 20 25 30 35

Capacity(mAh!"

Fig&re 4, Charge =a>-discharge => c&r#es for the cell assemled y the Co-doed 0i5e; at '.1C.

C&r#e a a4 0i5e'.GCo'.;Q c&r#e b b4 0i 5e'.9Co'.1;Q c&r#e ' '4 0i5e'.8Co'.2;.

c840

630 b

- Z ’ ’ / Ω 420

a

210

0

0 250 500 750 1000 1250 1500

Z’/Ω

Fig&re 6, -!y&ist lots for the cell assemled y 0i and Co-doed 0i5e;.0ine a4 0i5.'e'.GCo'.;,

line b40i5.'e'.8Co'.2;,line '4 0i5.'e'.9Co'.1;.

ig.G shows charge-discharge c&r#es of the cell assemled y the 0i5 e'.8Co'.2;. ;ne can see

that as the charge-discharge rate changed the caacity of the cell altered dramatically, s&ggesting thatthe roerties of 0i5e'.8Co'.2; should be improved in the further investigation. At ".#$, the

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Int. J. Electrochem. Sci., )ol. , 2+11 286G

discharge caacity of the 0i- 0i5 e'.8Co'.2; cell is ao&t Gm7hg, while as the discharge rate is

'.5C, the caacity was decreased greatly to e aro&nd 1Gm7hg. his indicated that the olari%ation of

the cathode of 0i5e'.8Co'.2; increased when the c&rrent enhanced. he infl&ence of Co content on

the charge-discharge c&r#e at '.1C of the cell assemled y Co-doed 0i5e; was also roed, as

shown in ig.8a and ig.8. *t indicated that when the molar ratio of e to Co is , the largest caacityof the cell was dislayed. 7s shown in the re#io&s worB 12D, *S is one of the most owerf&l tools to

analy%e electrochemical reactions, s&ch as those rocesses occ&rring at electrodeelectrolyte interfaces

and the lithi&m ion intercalationdeintercalation. *n this e were lotted at oen circ&it otential as shown in ig.9. Lenerally, the semicircle

aearing at the high fre&ency region corresonds to a circ&it containing a resistance element arallel

to a caacitance element, and the larger semicircle is dislayed, the igger resistance element is

otained. h&s, it can e concl&ded that the smallest charge transfer resistance was resented y the

cell of 0i-0i5e'.8Co'.2;, which is consistent with the res&lts otained from ig.8a and ig.8 #ery

well. e do admit the caacity #al&e of the as-reared 0i5e'.8Co'.2; is lower than the reorted

date y !. *manishi 1'D. &t in this worB the e so&rce is e=!; > and no inert gas was introd&ced,

which is the no#elty of this reliminary worB.

, CO#CL!S%O#S

0i5e; is synthesi%ed y a solid-state method &sing e=!;> as the iron so&rces. More

imortantly, in this rocess, instead of inert gas rotection, caron-coating rotection was introd&ced,which is #ery helf&l for the rearation of 0i5e; in a large scale. @)A atterns and SM images

strongly demonstrated that the Co content in 0i5e; is a Bey factor, affecting not only the crystal

str&ct&re &t also the electrochemical erformance of 0i5e;. secially, 0i5e'.8Co'.2; resents

the est electrochemical erformance among as-reared Co doed 0i 5e;. (resenting a no#el way

for rearing Co-doed 0i5e; is the main contri&tion of this reliminary worB. e do admit that

more worBs sho&ld e done to imro#e the electrochemical erformance of 0i5e;.

7C/!;0ALM!S

his worB is s&orted y the !SC =Lrand !o.2'9'1'6> and the M;S =Lrant !o. 2'11C959'2and Lrant !o. 2'1'A7G2G6'>.

.eferen'e

1. /. S&ryaBala, /. MariBBann&, L.(. /alaignan , . Eas&de#an, Int. J. Electrochem. Sci., =2''8> 16-1

2. S.-. Ti, H.-. Ch&ng , H.-L. /im, Electrochem. -ommun., 9 =2''G> 591.

. @. &, S. Chen, M. Ma, :. 0i&, Ionic(, 1G =2'11> 5

. . Ti, T. Uh&, @. Uh&, :. Sh&, C. T&e, 7. Uho&, Ionic( 15 =2''9> GG9

5. V. 0i& , T. 0i , U. H& , A. Mao , C. Chang, . H&ang, Electrochim. $cta 5 =2''8> G298

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