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