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 PS-b-PEO NaPF6 PS PEO salt Energy Signal 100 200 500 PS PEO Salt

TEM of block copolymer electrolytes PS-b-PEO NaPF6 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

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 - anode at 0.2 V (vs Li/Li+) Li Li+ + e- Li+ current collector - anode: Li/graphite anode at 0.2 V (vs Li/Li+) Li Li+ + e- alkyl carbonates/ Li+X- Li+ cathode: FePO4 cathode at 4 V Li+ + e- + FePO4 LiFePO4 current collector + conductive carbon and binder Components of electrodes: active particles, electron conductor, ion conductor

Miracle of lithium battery electrodes conductive carbon inactive binder reaction sites active particle e- Li+ Li+ + e- + FePO4 LiFePO4 Need equal electronic and ionic conductivity electrolyte 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

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. active particle e- Li+ 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 McCloskey et al., JACS 2011 electrolyte: carbonate/ether ether

- - - - - - Li-S needs miracles + + + + + + Sulfur Lithium - + + - - + - + + - - + Quoting Venkat: Milk-to-cheese-to-milk-…

Ideal speciation spectroscopy Signal Li2S4 Li2S6 Li2S2 100 200 500 Energy

Work in a pristine environment (computer) Simulation of Li2Sx and S8 dissolution in tetraglyme (oligomeric PEO) Tod Pascal Tod Pascal and David Prendergast

Simulations show clustering Li2S6

These simulations show clustering that is not limited by box Li2S8

Work in a real environment XAS measurements of Li2Sx in PEO or SEO Wujcik, Velasco-Velez, Cabana, Salmeron, Guo Kevin Wujcik XAS predictions Li2Sx in tetraglyme (in progress…) Bottom line: No clear distinction between species…

Principal Component Analysis Juan Velasco Velez Eigenvalue Indicator 72.1 8.58 7.2 2.78 1.29 1.15 0.49 0.993 Truncate at 3 Unconstrained PCA analysis gives unphysical underlying spectra. Iterative transformation factor analysis (Marcus)

Theory vs Experiment

Ideal speciation spectroscopy Signal Li2S4 Li2S6 Li2S2 100 200 500 Energy Waiting for this is not an option…..but developing such tools is!

Prototype Electrode Project Active particle Tab Electron and ion conducting binder (electron side street) C nanotubes (electron highway) Ensure that electron and ion are delivered to particle. contamination

Characterization Task: Make the miracle happen. Respect the intuition of Stan Wittinghams of the day. (You cannot convince me to work on binder for Sn5Fe.) 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. active particle e- Li+ 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