The use of analytical techniques to study battery chemistry. by Ernst Ferg, uyilo at Nelson Mandela University, Port Elizabeth

Transcription

1 The use of analytical techniques to study battery chemistry by Ernst Ferg, uyilo at Nelson Mandela University, Port Elizabeth

2 Content of Talk 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 Conclusion : LNMC

3 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 1 st law of thermodynamics. (conservation of energy: only transform from one type to another) Discharge reactions -ve Plate Electrolyte +ve Plate Original material used Pb 2H 2 SO 4 and 2H 2 O PbO 2 Ionization step SO 4 2- ; SO 4 2- ; 4H + 4OH - ; Pb 4+ Current producing step Pb e - Pb 2+ Final products of discharge PbSO 4 4H 2 O PbSO 4.

4 Cu Introduction Zn 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

5 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

6 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: SiO 2 ; Al 2 O 3 ; K 2 O, Fe 2 O 3 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.

7 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 40,000 35,000 Pb 7.88 % A-PbO % B-PbO 7.64 % 30,000 25,000 Counts 20,000 15,000 10,000 5, ,000-10, Th Degrees

8 Chemistry (Analytical/Physical) 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) amorphous silica % Corundum % Th Degrees IC Madsen, NVY Scarlet, LMD Cranswick and T Lwin, Outcomes of the International Union of Crystallography Commission on powder diffraction round robin on quantitative phase analysis: samples 1a to 1h, J App Cryst 34(4); (2001) EE Ferg and B Simpson, Using PXRD and PONKCS to determine the kinetics of crystallization of highly concentrated NH 4 NO 3 emulsions; J. Chem. Crystallogr 43; (2013)

9 Chemistry (Analytical/Physical) Temperature in-situ PXRD Battery cathode (anode) materials (Pb-acid & Li-ion) that are synthesized by thermal heating processes ( 800 o C 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) 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

10 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

11 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

12 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.

13 Electrochemical Analysis Poteniodynamic Scans Tafel Plots EIS Lissajous figure for I=1.5 V 1.5 x Sine (angle + 60) Sin angle

14 Electrochemical Analysis Cyclic Voltametry Discharge/Charge; capacity cycling The use of Ref electrode

15 Example of unbalanced cells A battery (12V) built with 4 new 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

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

17 Example of unbalanced cells Connected a simple cell voltage limit protection circuit (BMS) Battery started loosing capacity upon cycling (2.4% after 65 cycles)

18 Example of over-(charge & -discharge) A LNMC 2.5Ah 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

19 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.

20 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

21 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.

22 Conclusion uyilo hosted 2 day Shmuel De-Leon workshop in July Shmuel De-Leon is an international consultant in Energy Storage. Publishes a range of market related studies and technology information

23 Thank you Mandela University / uyilo