Presentation on theme: "Characterization of Battery Failure Nitash Balsara University of California, Berkeley Lawrence Berkeley National Laboratory Intellectual support: John."— Presentation transcript:
Characterization of Battery Failure Nitash Balsara University of California, Berkeley Lawrence Berkeley National Laboratory Intellectual support: John Newman (Berkeley) Support: Soft Matter EM Program (BES), Lithium sulfur LDRD and Program (BATT, EERE)
Ideal speciation spectroscopy Energy Signal PS PEOSalt PS PEO salt PS-b-PEONaPF 6
Intense plasmon peak is sensitive to the material’s chemical structure. One big fat broad peak regardless of chemical details. Typically, we record a series of EFTEM images from 5-60eV in 1eV steps using a 5eV energy slit. EFTEM SI datasets analyzed by Principle Component Analysis TEM of block copolymer electrolytes PS-b-PEONaPF 6
Species identification Principal component analysis (PCA) enables speciation in spite of big fat highly overlapping ugly peaks! Frances Allen, Andy Minor, et al., Ultromicroscopy, 2012
Lithium Battery current collector cathode: FePO 4 current collector anode: Li/graphite conductive carbon and binder + alkyl carbonates/ Li + X - anode at 0.2 V (vs Li/Li + ) Li Li + + e - Li + cathode at 4 V Li + + e - + FePO 4 LiFePO 4 Components of electrodes: active particles, electron conductor, ion conductor
Miracle of lithium battery electrodes reaction sites active particle e-e- Li + electrolyte conductive carbon inactive binder Li + + e - + FePO 4 LiFePO 4 Need equal electronic and ionic conductivity Components of electrodes: active particles, electron conductor, ion conductor. Every active particle needs to have access to electron and ion conducting pathways at all times! It is a miracle that any electrode works.
Time-honored Approach Synthesize a new cathode or anode material. Make a full cell (not half cell with excess lithium). Make sure that the cathodes are thick enough to be commercially viable. Count electrons coming in and out of the battery. Measure voltage. Usual result: terrible Once in a while: result better than terrible base line Publish! Advantage: If it works you can go directly to the market. Disadvantage: You might be throwing out a perfectly good material. Perhaps the binder failed.
Example of approach
active particle e-e- Li + Why did the miracle not happen? What if the binder was not holding the structure together? What if the electrons were reacting with the electrolyte? What if ionic pathways were blocked? What if the electronic pathways were blocked? What if the top half of the cell is working fine but the bottom half is not? PIs who go through the pains of establishing a new synthesis route may no be great cell builders. JCESR desperately needs a facile lab to answer these questions. We cannot afford to throw out good active materials. The prototyping and characterization group has an opportunity to create such an infrastructure.
Balsara’s Version of the Time-honored Approach Synthesize a polymer binder. Make a full cell (not half cell with excess lithium). Make sure that the cathodes are thick enough to be commercially viable. Count electrons coming in and out of the battery. Measure voltage. Usual result. Joke: Balsara drops his keys in front of his home and the area around the door is pitch-dark. An hour later a neighbor drives by and sees Balsara searching for something on the street near lamppost. “What’s up?” he asks. “Looking for my keys”. “Why are you searching here?” he asks. “Because there is light here and I can see.”
Lithium-air saves the day Perfect for fundamental studies because… Easy to detect gasses!
Detect something other than electrons electrolyte: carbonate/ether ether McCloskey et al., JACS 2011
Ideal speciation spectroscopy Energy Signal Li 2 S 2 Li 2 S 4 Li 2 S 6
Simulation of Li 2 S x and S 8 dissolution in tetraglyme (oligomeric PEO) Work in a pristine environment (computer) Tod Pascal and David Prendergast Tod Pascal
Li2S6 Simulations show clustering
Li2S8 These simulations show clustering that is not limited by box
XAS measurements of Li 2 S x in PEO or SEO Wujcik, Velasco-Velez, Cabana, Salmeron, Guo Work in a real environment XAS predictions Li 2 S x in tetraglyme (in progress…) Bottom line: No clear distinction between species… Kevin Wujcik
EigenvalueIndicator Truncate at 3 Unconstrained PCA analysis gives unphysical underlying spectra. Principal Component Analysis Iterative transformation factor analysis (Marcus) Juan Velasco Velez
Theory vs Experiment
Ideal speciation spectroscopy Energy Signal Li 2 S 2 Li 2 S 4 Li 2 S 6 Waiting for this is not an option…..but developing such tools is!
Prototype Electrode Project Tab C nanotubes (electron highway) Electron and ion conducting binder (electron side street) Active particle Ensure that electron and ion are delivered to particle. contamination
active particle e-e- Li + Characterization Task: Make the miracle happen. Respect the intuition of Stan Wittinghams of the day. (You cannot convince me to work on binder for Sn 5 Fe.) We must work under our lampposts. Need to find lampposts near the key. Make sure we do not discard gem. Get your hands dirty and help the synthetic folks succeed. Concerted deployment of tools: theory, experiment, statistics. Nobody can afford to throw out good active materials. JCESR prototyping and characterization groups have an opportunity to create the necessary infrastructure. Credit: Frances Allen, Kevin Wujcik, Juan Velasco Velez, Tod Pascal Andy Minor, Jinguha Guo, Miquel Salmeron, David Prendergast