The use of analytical techniques to study battery chemistry

by Ernst Ferg, uYilo at Nelson Mandela University, Port Elizabeth

• Brief background of two battery chemistries

• Common materials analysis (PXRD, XRF, SEM etc)

• Common electrochemical analysis (Cyclic Voltammetry, cell capacity performance, EIS)

• Examples of voltage limit issues (BMS): LFP 12V battery

• : 18650 LNMC

• Conclusion

Content of Talk

Introduction • When working with batteries, understand chemical processes.

• Pb-acid or Li-ion battery chemistry (others: Zn-air, V-Redox etc)

• Different understandings of material changes.

• Cannot break 1st law of thermodynamics. (conservation of energy: only transform from one type to another)

Discharge reactions

-ve Plate Electrolyte +ve Plate

Pb 2H2SO4 and 2H2O PbO2Original material used

Ionization stepSO4

2-; SO42-; 4H+ 4OH-; Pb4+

Current producing step

Final products of

discharge

Pb2+ + 2e-

Pb2+

PbSO4PbSO4 4H2O

.

Introduction

• Battery science and engineering stretches across disciplines

• Good understanding of analytical chemistry, physical electrochemistry and materials chemistry.

• Scaling-up of materials requires good process engineering understating.

• Once in a cell, move into cell to pack configuration Mechatronic understanding (mechanics and electrical)

• Mechanical pack design and electrical performance for specific application

When life gives you lemons,

add electrodes and make a

battery

Cu

Zn

Chemistry (Analytical/Physical)

• At the battery material (lab) level:– Good understanding of analytical chemistry, physical electrochemistry

material chemistry

– Range of analytical disciplines required. Elemental analysis requires low level determination (ICP-MS, AA, XRF)

– Recently XPS (x-ray photoelectron spectroscopy): better understanding of chemical and electronic state of compounds in material

http://www.xpsfitting.com/2012/06/xps-instrument-manufacturers.html

Chemistry (Analytical/Physical) Some challenges elemental analysis (eg: XRF).Misinterpretation

• Large metal matrix (Zn, Pb, Fe influence on minor components)• Geological mode indicates elemental composition as CaO: SiO2; Al2O3; K2O, Fe2O3 etc• Not necessary a true reflection of phase composition.

• Homogeneity of sample is critical. Particle size (hard and soft material in one sample influence results.)

• Overlap of peaks: Need a look at original spectra carefully.• Preparation of good set of standards for accurate quantification.

Chemistry (Analytical/Physical)

• At the battery material (lab) level:– Powder X-ray diffraction gives crystallographic information of

materials: phase composition, crystallite size (nano), solid solution effect and relate to electrochemical process of charging discharging and life cycling.

– Has developed to in-situ analysis: temperature and electrochemical

2Th Degrees706560555045403530252015105

Counts

40,000

35,000

30,000

25,000

20,000

15,000

10,000

5,000

0

-5,000

-10,000

Pb 7.88 %

A-PbO 84.49 %

B-PbO 7.64 %

• Powder X-ray Diffraction continued

• Able to look at multiple phases: Relies on good Interpretation of powder diffraction pattern. Need crystal structure data for Rietveld refinement

• Can do quantification with amorphous and or partial crystal structure information (PONKCS)

• IC Madsen, NVY Scarlet, LMD Cranswick and T Lwin, Outcomes of the International Union of Crystallography Commission on powderdiffraction round robin on quantitative phase analysis: samples 1a to 1h, J App Cryst 34(4); (2001) 409–426

• EE Ferg and B Simpson, Using PXRD and PONKCS to determine the kinetics of crystallization of highly concentrated NH4NO3 emulsions; J. Chem. Crystallogr 43; (2013) 197-206.

2Th Degrees706560555045403530252015105

Co

un

ts

2 000

1 500

1 000

500

0

-500

amorphous silica 50.00 %

Corundum 50.00 %

Chemistry (Analytical/Physical)

• Temperature in-situ PXRD

• Battery cathode (anode) materials (Pb-acid & Li-ion) that are synthesized by thermal heating processes ( 800oC and higher).

• Track phase transitions.

• Thermal characterization of tetrabasic lead sulfate used in the lead acid battery technology; E. Ferg, D. Billing and A Venter; Solid State Sci.64 (2017) 13-22

• An investigation into the temperature phase transitions of synthesized materials with Al and Mg doped lithium manganese oxide spinels by in-situ powder x-ray diffraction; C.D. Snyders, E.E. Ferg and D. Billing; Powder Diffraction. 32(1) (2017) 23-30

Chemistry (Analytical/Physical)

• Electrochemistry in-situ PXRD.

• Early stages showing that the method of analysis is possible.

• Best done on Synchrotron to understand transition under various conditions.

• A novel high-throughput setup for in situ powder diffraction on coin cell batteries Markus Herklotz, Jonas Weiß, Eike Ahrens, Murat Yavuz, Liuda Mereacre, Nilu¨fer Kiziltas-Yavuz, Christoph Drager, Helmut Ehrenberg, Ju¨rgen Eckert, Francois Fauth, Lars Giebeler and Michael Knapp J Appl Chryst 2016 49 1-6

Chemistry (Analytical/Physical)

Chemistry: Surface/ Particle • SEM/HRTEM are usually located at universities or research institutes.

• Answer questions around material morphology

• Looking at surface characteristics: Use Scanning Probe Microscope (AFM) – Possible to do in-situ electrochemistry.

FIBSEM TEM

Analysis process in a battery

• Make material Analyse Build Cell Capacity test until failure Remove material Analyse

• Especially when a battery does not do what it intended to do.

• Euphemistic term: Premature battery (capacity) failure.

• Look at electrode material failure, cell assembly and environment.

• Partly destructive analysis. Battery needs to be cut open and material removed.

• Move towards understanding analysis in-situ.

Electrochemical Analysis

• Poteniodynamic Scans Tafel Plots • EIS

Lissajous figure for I=1.5 V

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-1.5 -1 -0.5 0 0.5 1 1.5

Sin angle

1.5

x S

ine (

an

gle

+ 6

0)

Electrochemical Analysis

• Cyclic Voltametry

• Discharge/Charge; capacity cycling

The use of Ref electrode

Example of unbalanced cells

• A battery (12V) built with 4 new 32650 LFP cells (5Ah)

• Capacity cycle at different rates between voltage limits (as specified)

• EIS analysis done of new cells

• Voltage limits of individual cells monitored

Example of unbalanced cells • Voltage limits of certain individual cells exceeded specifications

Example of unbalanced cells • Connected a simple cell voltage limit protection circuit (BMS)

• Battery started loosing capacity upon cycling (2.4% after 65 cycles)

Example of over-(charge & -discharge)

• A LNMC 2.5Ah 18650 cell that was deliberately

overcharged to 4.7V instead of 4.5V and discharge to 2V instead of 2.5V during cycling at 1C.

• Monitor voltage and external cell temperature.

• Do CT scans of new and damaged cell

Example of over-(charge & -discharge)

• Lasted only 224 cycles, before noticeable drop in capacity was noticed.

• But gradual build up of internal resistance was observed with increase in current required to charge cell and temperature

• No EIS was done, but would be useful to track as cell ages.

Example of over-(charge & -discharge) • CT scanned images show significant internal damage.

• Significant temperature difference between internal and external of cell (up to 20 deg)*

• *T Waldmann, S Gorse, T Samtleben, V Knoblauch and M Wohlfahrt-Mehrens; A mechanical aging mechanism

in Lithium-Ion Batteries; Electrochem. Soc 161(10); (2014) A1742-A1747

Conclusion • Battery science and engineering covers a wide field of disciplines

• Understanding of fundamental material and electrochemistry to application engineering.

• Move to in-situ studies of chemical processes in cell electrochemistry.

• Good engineering practices of “fit for use” design of packs with BMS

• Understand and build into system configuration the influence of external factors on the battery.

• Range of good resources available.

Conclusion • uYilo hosted 2 day Shmuel De-Leon workshop in July 2017.• Shmuel De-Leon is an international consultant in Energy Storage. Publishes

a range of market related studies and technology information

Thank you Mandela University / uYilo