Download - 2.3 He Li (Rui Zhen Li)

8/2/2019 2.3 He Li (Rui Zhen Li)

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RuizhenLiSchool of Chemistry and Environment

South China Normal University

Guangzhou China

Study on Lead Based Rare Earth Alloys for

Positive Grids of Power and Energy StorageLead-acid Battery


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Contents

Introduction1

Experimental2

Results and discussion3

Conclusion4


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1 Introduction

Possessing of the potentials of development, solar energy has wide

prospects, as the key part of the solar electric generation system, storage

energy battery becomes the restrictive factors. Meanwhile, acted as a

green intelligent and efficiency transportation vehicle, electric bikesencounter opportunity and challenge too.

Valve regulated lead-acid battery was the first selection for solar

system and E-bikes for many years, service life is the most important

which restrict the development of the two fields


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There are many literatures on the passive film, but the problem stillexists. Premature capacity loss (PCL) of the traditional lead-calcium alloywas very severe and the passive film had bad conductivity.The rare earthelements were often used as additives to lead alloys in order to get betterproperties for lead-acid batteries, cerium was added to improve thehydrogen evolution performance, corrosion resistance would be increasedtoo , lanthanum and cerium could inhibit the anodic film formation indeep discharge at the potential of 0.9v.

In this paper, ratio optimization on the most widely used alloy Pb-Ca-Sn-Al was made, argentine and mixed rare earth of lanthanum andcerium were introduced to the alloy, and a new practical grid alloy Pb-Ca-Sn-Al-Ag-La-Ce was developed.


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2 Experimental

Lead-calcium tin aluminum argentine alloys (with 0.07, 1.2, 0.05,

0.1wt.%) were processed in the laboratory by melting weighed mixtures

of pure materials, mixed rare earth lanthanum and cerium was added

with mass ratios of 0, 0.01, 0.15, 0.5wt.%, respectively. In this paper, 1#,

2#, 3#, 4# were used to represent these alloys, respectively.

Electrochemical tests were performed in a three-electrode cell, the

counter electrode and reference electrode were a platinum plate and

Hg/Hg2SO4 electrode (1.28g.cm-3 H2SO4 solution, E=+0.658 vs. SHE),

respectively.


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3.1 Alternating current voltammetry (ACV)

Fig1 Z'vs.E plots of the anodic films

formed on electrodes at 0.9Vfor 1h (v=

1mV.s-1 ,f=1000Hz)

-1.5 -1.0 -0.5 0.0 0.5 1.0

0

10

20

30

40

50

4

3

2

1

Z'/O.c

m-2

E/V(vs.Hg/Hg2SO

4)

Alloys with mixed rare earth elements

have lower resistance at the Pb()film reduced potential about 0.75V,

the same phenomenon appeared at the

potential of -0.75V, where is theelectric resistance peak of PbSO4. It

can be concluded that the addition of

the mixed rare earth lanthanum and

cerium can hinder the growth of the

anodic Pb() film, the deep cyclic lifewill be improved.


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Fig.2 The open circuit decay curves of the

electrodes

-5000 0 5000 10000 15000 20000 25000

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

F

E

4 3 2 1

E

/V

Time/S

3.2 Open-circuit potential (OCP)

The depression curves of the alloys

after oxidation at 0.9V for 1h are

shown in Fig.2. A platform EF appears

at -0.5V, which corresponding with the

transformation time(TEF) of Pb() toPb, the length of TEF represent the

amount of Pb(). The electrodewithout additive has the longest

platform, the amount of Pb()decrease as the content of rare earth

increase, This indicated that theaddition of rare earth can inhibit the

growth of Pb() film. This result isconsistent with ACV.


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3.3 Chronoamperometry (CA)

0 200 400 600 800

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0.0045

4

3

2

1

I/A

Time/S

0 200 400 600 800

0.000

0.002

0.004

0.006

0.008

0.010

0.012

4

32

1I/A

Time/S

Fig.3 Current-time curves different electrodes at(a 1.5V, b 1.6V)

Fig.3 provides the plots of current vs. time at 1.3V, peak a appeared in the

curve corresponding with the formation of PbO2. It can be seen from the curve

that the peaks of the electrodes with lanthanum and cerium are lower thantheir counterpart. It seems that adding this material can inhibit the formation

process, however, when the additive is higher than 0.5wt. %, this phenomenon

disappears. In this case, proper amount of mixed rare earth lanthanum and

cerium can promote the anti-corrosion performance of the grid.


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3.4 hydrogen evolution study

Fig.4 Cathodic polarization curves alloy electrodes in 1.28 g.cm-3H2SO4 solution

(v=5mV.s-1)

-1.2 -1.3 -1.4 -1.5 -1.6 -1.7

0.002

0.000

-0.002

-0.004

-0.006

-0.008

-0.010

-0.012

-0.014

4

321

I/A

E/V

Table 1 kinetic parameters of the hydrogen evolution reaction on different

electrodes

electrode 1# 2# 3# 4#

a -1.8190 -1.9273 -2.0341 -2.0177

b -0.1407 -0.1658 -0.1835 -0.2140


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The rate of hydrogen evolution was studied by LSV andthe results are shown in Fig.4. The kinetic parameters ofthe reaction on the electrodes are presented in table 1. Itcan be seen that a value is different, which represents theover-potential of the hydrogen evolution reaction, thevalue increased with the amount of the mixed La and Ce.This indicates that the addition in the alloys inhibitshydrogen evolution reaction.


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3.5 Oxygen evolution study

- 20 0 0 20 0 4 00 6 00 8 00 1 00 0 12 00 1 40 0 16 00 1 80 0

-100

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

-Z''/ohmcm

-2

Z' / ohm cm-2

4

3

2

1

1.4V

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

-Z''/ohm

cm

-2

Z' / ohm cm-2

3

2

4

1

1.6V

Rs

Rct

C

Rs

Rct

C

Fig.5 Electrochemical impedance spectra of the oxygen

evolution reaction on electrodes ata 1.4 b 1.6VFig.6 The equivalent circuit of Fig.5

The plots for these electrodes are similar and exhibit a semicircular part at

high frequency that indicates control by electron transfer. The semicircular

radius of the electrode without additive is much larger than otherelectrodes, which demonstrate that the additive of mixed rare earth

elements can inhibit the oxygen evolution. This suggests that the oxygen

evolution reaction is influenced by the addition of mixed La and Ce.


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3.6 SEM micrographs of the corrosion test

1# 1000X 2# 1000X

3# 1000X 4# 1000X


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1# 5000X 2# 5000X

3# 5000X 4# 5000X

Fig.7 Cross-sectional views of the corrosion layer on electrodes


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The SEM micrographs reveal the differences in the

morphology of the corrosion layers after corrosion test of the

electrodes are shown in Fig.7. A loose and porous corrosion

layer is formed on the electrodes with mixed La and Ce. Thisis beneficial to the charge/discharge of the battery, for the

active materials can reach the grid more easily, utilization ratio

of the active materials can be increased. The deep

charge/discharge performance of the battery will be improved

by the addition of mixed La and Ce.


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4. Conclusion

1

Mixed rare earth elements La and Ce

can inhibit the growth of anodic Pb()film at 0.9V, and decrease the

resistance of the oxide film, the deep

cyclic life will be improved.

2

Both hydrogen and oxygen evolution

performance can be improved by this

addition. The hydrogen evolution over-

potential and oxygen evolution over-

potential are higher and thecharge/discharge property of the

battery will be better.

3

Proper amount of mixed La and Ce can

inhibit the growth of lead dioxide, what

is beneficial to the anti-corrosion of the

alloy. However, the content must lower

than 0.5wt. %. The optimal content is

0.15wt. %.

4

The corrosion products of the new

alloy Pb-Ca-Sn-Al-Ag-La-Ce are

loose and porous that the active

material can contact to the grid

surface easily.


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