Seeing inside lead-acid batteries using neutron imaging

J. M. Campillo-Robles, D. Goonetilleke, N. Sharma, D. Soler, U. Garbe, P. Türkyilmaz

1

2

3

Causes of aging

- Electrode degradation: sulfating, corrosion, non-cohesion of active mass (shedding/degradation).

- Electrolyte degradation: stratification, water loss.

- Faulty manufacturing of cell: paste production, pasting, grid manufacturing, formation of the cell.

4

Limitations of lead acid battery

≈ 35 Wh/kg

5

What is happening inside?

We will try to see inside using neutrons

First time

6

Gaston Planté (1834-1889)

1.- In operando monitoring.

2.- Neutron imaging techniques.

3.- Cell design.

4.- Results

5.- Conclusions

7

1.- In operando monitoring

Monitoring of inner processes to optimize and improve the cell. A lot of sensors developed to check the SOC of the cell (using electrolyte concentration). Unfriendly environment: acid, electrical, small place.

8

1.- In operando monitoring

Intrusive techniques: - Optic techniques: point measurement. - Equilibrium potential: point measurement.

Non-intrusive techniques:

- Electric potential of the cell. - Ultrasounds: line measurement. - Holographic Laser Interferometry (HLI): plane measurement. - Neutron Imaging

9

2.- Neutron imaging techniques

Non-destructive testing for industrial/engineering applications. Advantages over other imaging techniques: - Neutron interaction only with the nucleus.

- Neutron pictures are related to the elemental composition of the object.

- Greater penetration than gamma rays.

Opaque to X rays.

Transparent to neutrons. Pb

10

2.- Neutron imaging techniques

Different elements/compounds have different attenuation coefficients. Two mean attenuation processes: absorption and scattering.

scattering

absorption

transmission Neutron source Target Detector

collimator

Nuclear reactor Spallation source

2.- Neutron imaging techniques

11

Two techniques: - Radiography (2D) Shadow image of the investigated sample. - Tomography (3D) Full three-dimensional image of the object is reconstructed from 2D pictures.

Already applied in energy storage:

Fuel cells, Lithium-Ion Batteries (LIBs), hydrogen storage, nuclear fuel, etc.

First time neutron imaging has been used for monitoring lead acid batteries!

12

2.- Neutron imaging techniques: Dingo instrument

Open Pool Australian Lightwater (OPAL) Reactor

Fuel: 30 kg low enriched uranium

T = 60 °C 20 MW

13 neutron beam instruments

Opened in 2007

13

2.- Neutron imaging techniques: Dingo instrument

Neutron radiography/tomography - Thermal neutrons (∼25 meV). - Detector:

CCD camera + scintillator. Measured area 20 × 20 cm.

- Spatial resolution: 27 µm. - Average flux at sample (n cm-2 s-1):

∼107 (centre of image) ∼ 7 × 106 (corner of image)

Opened in 2014

14

3.- Cell design

Only one cell: 1.2 Ah.

Neutron friendly case Teflon (PTFE)

15

3.- Cell design: electrodes

Dry charged commercial plates.

2 positive electrodes 3 negative electrodes

16

3.- Cell design: separators

Commercial separators in positive plates (not in all cells). Polyethylene → hydrogen → high attenuation of the beam.

17

3.- Cell design: electrical connections

18

3.- Cell design: electrolyte

Deuterated electrolyte:

D2SO4 (Sigma-Aldrich) 96-98 wt. % in D2O, 99.5 atom % D.

D2O (Cambridge Isotope Laboratories) 99.9 atom % D.

Initial concentration (previous activation): 5 M.

4.- Results

19

4.- Results: electrical behaviour

20

C/3

C/3 C/4

Charge-discharge processes:

C/5 (0.182 A)

C/2 (0.38 A)

Problems at higher intensities!

4.- Results: attenuation

21

Beer-Lambert law of attenuation of radiation valid for neutrons: 𝐼𝐼 = 𝐼𝐼0𝑒𝑒−𝜇𝜇𝜇𝜇. µ - linear attenuation coefficient of the target: µ = µabsorption + µ scattering . d - thickness of the sample.

Intensity reduction for different attenuation coefficients

4.- Results: attenuation

22

Neutron linear attenuation coefficient, µ , for λ = 1.54 Å:

Less attenuation in concentrated electrolyte!!!

Data obtained from: NIST, Center for neutron research, https://www.ncnr.nist.gov/

ρ (g/cm3) µ (cm-1)

Pb (porous) 4.97 0.002

PbO2 (porous) 5.5 0.002

Pb (metal) 11.34 0.005 PbSO4 6.29 0.008

D2SO4 (liquid) 1.86 0.051

D2O (liquid) 1.107 0.137

4.- Results: open beam / as measured picture

23

Cell without separators as measured

Open beam profile not homogeneous

not centred

4.- Results: as measured pictures

24

Intensity profile as measured in air Electrodes

More attenuation at electrodes and separators

Cell with separators

Separators

25

4.- Results: as measured pictures

Intensity profile as measured Electrodes

Separators cause measurement problems

Cell with separators

Separators

4.- Results: as measured pictures

26

Intensity profile as measured

Electrodes

More attenuation at electrolyte than at electrodes

Cell without separators

4.- Results: corrections

27

Corrections to be performed:

- Subtraction of noise (gamma rays). - Correction of open beam profile:

∼30 % reduction from maximum to minimum. - Correction of battery case.

- Fluctuations of reactor beam.

4.- Results: empty cell

28

More than 70% of the neutrons pass through the cell

4.- Results: cell with electrodes

29

The electrodes reduce the transmittance from 70% to 40%

4.- Results: electrolyte

30

Final state after slow charging Final state after fast charging

4.- Results: neutron tomography

31

Same principle as in X-R tomography. Only one difference: rotating sample. We can decide the cutting plane to analyse. Detailed inner structure.

Full image of the cell.

4.- Results: neutron tomography

32

What can we see? - Inner structure of the electrodes (also through separators). - Active material behaviour. - Inner structural problems. - Sulfation of the electrodes. - Corrosion.

Grid

Active material

Separator

Electrode.

33

5.- Conclusions

- Neutron imaging is complementary to other monitoring techniques. - Only technique with capability to see inside electrodes. - We can see changes in the electrolyte concentration. - Need to improve the experiment.

34

We are working on …

- Optimization of cell design. - Quantification of electrolyte concentration. - Electrolyte stratification analysis. - Active material degradation analysis. - Transport properties of deuterated acid in heavy water.

35

Thanks to …

Cell design: I. Urrutibeaskoa (MU), B. Turhan (YIGITAKU). Cell manufacturing: G. Arrizabalaga (MU), A. Arrillaga (MU), Parra Mekanizatuak. CAD drawing: E. Ruiz de Samaniego (MU), F. Zugasti (MU), I. Perez (MU). FEM simulations: X. Artetxe (MU), L. Oca (MU). Help at ANSTO: J. Pramudita (UNSW), N. Booth (ANSTO).

Data processing: F. Rossi (ANSTO), A. Velasco (ANSTO), J. Coslovich (ANSTO).

36

Any question?

Aramaio valley (Basque Country)

Thank you! Eskerrik asko!