Microstructure and electrochemical studies on carbon nano material additives for positive active mass of industrial cells Varna│June 13 th , 2017
Microstructure and electrochemical studies on carbon nano material additives for positive active mass of industrial cells Varna│June 13th , 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 2
Agenda
Introduction
3
• New developments on Nanomaterials may help to improve performance and cycle life
of lead-acid batteries.
• Recently it has been proposed the use of Carbon Nano-Tubes (CNT) as additives for
the negative plates, but the high cost of these materials and the use of cheaper
alternatives (Conductive Carbons) make difficult an industrial application.
• On the other hand, their possible use in the positive plate is not fully explored although
the potential benefits are even greater, which could justify the material cost.
• Multi walled CNT dispersions are being investigated, with the aim to modify the
internal structure of the PbO2 electrodes (reducing particle size, increasing surface
area and inter-particle conductivity).
• Preliminary studies in laboratory cells showed that very small amounts of conductive
Carbon Nano-Tubes (CNT) act as crystallization nuclei of active material, improving
the contact between the insulating particles of basic Lead Sulfates.
• The aim is to improve the energy efficiency, both during formation and along the
charge and discharge cycles, i.e. to increase the durability of lead acid batteries.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 4
Agenda
Experimental procedure
5
• Several batches of positive mass (leady oxide and sulfuric acid) were prepared in a
laboratory mixer and then pasted on PbSnCa grids (10 Ah), cured and formed.
• Multi-walled CNT water dispersions were added to leady oxide at two different
concentrations (0.025% and 0.05%) and then mixed with sulfuric acid (1.4 g/cc) to
prepare the positive paste.
• The paste was applied to PbSnCa grids, cured for 24h at two different temperatures
(60ºC & 80ºC) with 85% relative humidity and then dried 24h at 70ºC.
• The dry unformed positive plates were formed in diluted sulfuric acid (1.1 g/cc),
washed, dried and assembled as electrochemical cells (2 negative / one positive).
• Three initial performance tests were performed in sequence:
• Capacity test (C20) at low current (0.5A) until 1.75V
• Recharge at 0.5A for 24 hours with a voltage limitation of 2.67V
• Charge acceptance (CA) measurement was done after a rest period (24h) at 90%
State of Charge (SOC) with a maximum Voltage (2.42V/cell).
• Finally, a teardown analysis of formed and tested active material was performed.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 6
Agenda
TEM of CNT dispersion
Analytical and microstructural studies
7
• Multi Walled CNT particles were analyzed by Transmission Electron Microscopy (TEM)
to study their characteristics and stability during the dispersion process.
• The pictures show the CNT particles that were deposited and dried over the TEM grid.
• As expected, there is a range of different CNT particle sizes, being the most common
values around 12 nm diameter and 12 walls per particle.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
EDX analysis
Analytical and microstructural studies
8
• The EDX analysis show certain particles coming from the production processes, like
the presence of metals such as Fe (more abundant), Zn and Cr.
• It is important to note that no drastic changes are observed after the mechanical
dispersion process: the CNT remain undamaged, apart from maybe a possible
shortening of the tubes (not quantified).
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
Active material composition and pore distribution
Analytical and microstructural studies
9
• The presence of CNT do not affect significantly the apparent density and phase
composition of the active material (mainly composed by α-PbO and 3BS).
• However, It has been found that the addition of CNT modify the pore structure of the
active material, showing a linear dependence of the pore size with the carbon content.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
CNT
Content
(%)
MERCURY
POROSIMETRY
X-RAY DIFFRACTION
Porosity
(%)
Density
(g/cc)
Pore
size
(µm)
-P
bO
-P
bO
1B
S
3 B
S
4 B
S
0 49.4 4.29 0.44 85 - - 11 -
0.025 47.8 4.42 0.32 76 - - 8 -
0.05 47.2 4.36 0.25 74 1 - 11 -
y = -0,038x + 0,4317 R² = 0,9774
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
0,50
0 1 2 3 4 5 6
Po
re S
ize
(µ
m)
CNT content (x 0.01%)
Average Pore size
SEM and surface area (BET)
Analytical and microstructural studies
10
• CNT particles can be clearly observed in the unformed active material.
• Surface area of the active material was estimated from N2 adsorption analysis (BET)
with up to 13 experimental points.
• The figure below shows that CNT addition increases the specific surface area.
• Results also suggest that low (LT) curing yields slightly higher surface areas than high
temperature (HT) curing process (although no 4BS was detected by XRD).
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 11
Agenda
Influence of CNT on plate formation
Electrochemical test results
12 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Dry unformed plates were formed in diluted sulfuric acid (1.1 g/cc) at constant current.
• The figure shows the electrode potential average (4 plates each) along the formation.
• CNT addition increase the positive potential but also delay the onset of gassing
(oxygen evolution) thus potentially improving formation efficiency.
Influence of CNT on initial performance
Electrochemical test results
13
• After formation, the plates were washed for two hours and dried at 80°C for 24h, then
assembled (as 1+/2- cells) and immersed in sulfuric acid (1.28 g/cc) for testing.
• Initial performance is slightly improved with 0.05% CNT content, however, the capacity
remain stable whereas with 0.025% CNT and the control samples actually increase.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
0.025%
0.025% 0.025%
0.05% 0.05%
0.05%
0
20
40
60
80
100
120
140
FIRST CAPACITY SECOND CAPACITY THIRD CAPACITY
Cap
acit
y (
mA
h/g
)
Specific Capacity of Positive Electrode
Influence of CNT on charge acceptance (90% SoC)
Electrochemical test results
14
• After initial performance tests, the cells were fully charged at 2.67V for 16 hours, then
discharged for 2h at 0.5A (90% SoC), rest for 24h and charged at 2.42V for 60s.
• CNT addition reduce in fact charge acceptance, results that confirm the previous
finding during formation (probably due to the increase of the oxygen overvoltage).
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 15
Agenda
Phase composition and surface area
Teardown analysis of formed active material
16
• Samples of dry formed active material were also analyzed by XRD, BET, SEM and
Raman spectroscopy.
• The main component observed is β-PbO2, together with some α-PbO and α-PbO2.
• As expected, the BET measurements showed higher surface areas than unformed
plates (2-3 times), but the effect of CNT on surface is not relevant after formation.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
SEM and Raman spectroscopy
Teardown analysis of formed active material
17
• It is worth noting that no CNT have been observed in the charged plates by SEM or
Raman spectroscopy, so apparently they could have been oxidized during the
formation process or remain unseen in the skeleton of the active material.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
• Introduction
• Experimental procedure
• Analytical and microstructural studies
• Electrochemical test results
• Teardown analysis of formed active material
• Conclusions
June 13, 2017 Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL 18
Agenda
Conclusions
19
• Multi-Walled Carbon Nano Tubes (CNT) dispersions were characterized by TEM
showing 12 walls with average diameter of 12 nm and variable length.
• The addition of CNT reduces the pore size and increase surface area of the unformed
active material showing a linear dependence with the Nano-material dosage.
• No influence of CNT was observed in the phase composition of the active material.
• CNT increase positive potential and delay the onset of gassing during formation.
• There is an increase of the initial capacity that remain stable afterwards, whereas the
control and lower CNT dosage actually increase capacity in the initial cycling.
• Charge acceptance is reduced with the addition of CNT to positive active material,
possibly due to the increase of the oxygen over-potential.
• After formation, surface area is not affected by CNT neither it has been observed any
CNT particle in the positive formed active material by SEM observations.
• Raman spectroscopy detected the presence of CNT before formation but the
characteristic peaks disappear after formation, either because they are not stable or
remain inside the skeleton of the positive active material.
Exide Technologies Europe | Nanostructured PAM | COMPANY CONFIDENTIAL June 13, 2017
Thank you for your attention!
June 13, 2017 Exide Technologies Europe 20
Contact
Name: Francisco Trinidad
Position Title: Director Basic Research
Division: Europe
Phone: +34949277544
Mobile: +34616927664
Exide Technologies Europe | COMPANY CONFIDENTIAL 21 June 13, 2017