Modeling battery electrode properties

1. Modeling battery electrode properties Presentation to: Math Problems in Industry workshop David Clatterbuck Jacqueline Ashmore 6/16/08 Reference No.:

2. Overview Introduction to TIAX Batteries & electrodes MPI workshop project description MPI workshop, WPI, 2008

3. Overview Introduction to TIAX Batteries & electrodes MPI workshop project description MPI workshop, WPI, 2008

4. Introduction to TIAX Focus TIAX implements innovations, accelerating the transformation of ideas and technologies into significant and sustainable business growth for our clients. Ideas & Technologies Market Impact Implementation Focus Hospitals Universities National Labs Company A Company B Reach of Research Reach of Companies Corporate R&D Inventors Start-ups End Start Company C Company … • Internal laboratories • Development tools • 150+ technologists • Surround technologies MPI workshop, WPI, 2008

5. Introduction to TIAX Approach We incorporate several important elements into our approach, making TIAX unique in its ability to create value for our clients. Implementation Focus Approach: IP Blending Leveraging investments by accessing and incorporating the most appropriate IP from all available sources Collaboration Creating a team that really works—reliably accelerating development while building capabilities Linked Diversity Integrating deep technical expertise within a multidisciplinary business context Context Shifting Adapting proven solutions and insights from one industry to resolve issues and create opportunities in another Hands-On Delivering tangible results using our people, tools, and infrastructure MPI workshop, WPI, 2008

6. Introduction to TIAX Overview TIAX is a new, independent company that builds on the 116-year legacy of Arthur D. Little, Inc. • Founded in May 2002 by Dr. Kenan Sahin • Acquired assets of the ADL Technology & Innovation business • Dr. Charles Vest, MIT President Emeritus, chairs our Advisory Board • More than 150 scientists, engineers, and technicians, with PhD and MS degrees from top universities • More than 40,000ft2 of laboratory space • Extensive ties to research and industry • Headquartered in Cambridge, MA, with a West Coast presence in Silicon Valley, CA • An ISO 9001-registered and secure facility MPI workshop, WPI, 2008

7. Introduction to TIAX History TIAX advances a century-long track record of breakthrough innovation. Non-toxic foam neutralizes chemical & biological agents Commercialized scroll technology for automotive applications Sent five experiments on first moon mission Nonflammable motion picture film (sold to Eastman Kodak) Heat-pump water heater has 60% more efficiency Pioneered commercial cryogenics applications, founded HELIX Developed reformer technology— enabling fuel-cell vehicles to use gasoline & alternative fuels Non-CFC aerosol device Today 2002 Patented technology leads to development of Fiberglas MIT Holds Controlling Interest 90’s TIAX LLC founded (May 2002) 80’s 70’s Formulated Slim Fast line of drinks Flavor Profile method 60’s 50’s New line of cooking appliances for SubZero/Wolf 40’s Commercialized & patented synthetic penicillin 1920’s Advanced protective clothing used by industrial & agricultural workers 1886 APTAC chemical reactor measures process risk First iso-octane (later adopted as antiknock gas standard) Griffin & Little established 1886 Developed SABRE with IBM Developed and sold advanced lithium ion battery technology to major Japanese firm MPI workshop, WPI, 2008

8. Introduction to TIAX Mission TIAX’s mission is to help clients create an impact in the market and a difference in people’s lives across four interconnected themes: Health & Wellness Lifestyle Comfort & Convenience New ways to deliver care as well as improve wellness through the air we breath, our food and personal care products Enabling people be more effective in daily chores and make their time more enjoyable, satisfying and fulfilling Enhancing people’s safety and security at rest or while performing functions and missions Delivering energy/power efficiently, subject to cost effective resource and environmental constraints Human Safety & Security Energy Efficiency & Sustainability MPI workshop, WPI, 2008

9. Overview Introduction to TIAX Batteries & electrodes MPI workshop project description MPI workshop, WPI, 2008

10. Batteries & electrodes Li-ion batteries Applications Advanced Li-ion battery technology is one of TIAX’s key market areasTIAX has the largest independent Li-ion battery research group in the USOur research spans the Li-ion field: cathode, anode, electrolyte, separator, battery safety modeling, material synthesis, characterization, performance testing Applications: Hybrid electric vehicles (HEVs) – Toyota Prius Portable electronics Power Tools Laptops Plug-in hybrid electric vehicles (PHEVs) – Chevy Volt MPI workshop, WPI, 2008

11. C3H8 C3H7 H O O M M Batteries & electrodes Modeling We use a wide range of linked models which span the range from atomistic calculations, to cost models for entire systems. Customer Model New Products & Processes Value - in - Use Model Market Model Ef QuantumChemistry Microkinetics $ ¥ € Transport phenomena – Battery engineering Device engineering Cost model Examples Quantum Chemistry: Designing new cathode materials with improved cycle life (stability). Battery Engineering: Determining the role of internal short circuits in battery safety incidents. Cost Modeling: Evaluating the impact of different cathode materials on the cost of PHEV battery systems. MPI workshop, WPI, 2008

12. Batteries & electrodes Key Battery Attributes Li–ion batteries must meet a range of performance criteria which vary in importance depending on the application. Key Battery Attributes • Energy Density: Total amount of energy that can be stored per unit mass or volume. How long will your laptop run before it must be recharged? • Power Density: Maximum rate of energy discharge per unit mass or volume. Low power: laptop, i-pod. High power: power tools. • Low-Temperature Energy Density: The amount of energy that can be recovered decreases at low temperatures due to slower charge and mass transfer. • Safety: At high temperatures, certain battery components will breakdown and can undergo exothermic reactions. • Life: Stability of energy density and power density with repeated cycling is needed for the long life required in many applications. • Cost: Must compete with other energy storage technologies. MPI workshop, WPI, 2008

13. Batteries & electrodes Li-ion battery chemistry/physics A Li-ion battery is a electrochemical device which converts stored chemical energy directly into electricity. • During charging an external voltage source pulls electrons from the cathode through an external circuit to the anode and causes Li-ions to move from the cathode to the anode by transport through an liquid electrolyte. • During discharge the processes are reversed. Li-ions move from the anode to the cathode through the electrolyte while electrons flow through the external circuit from the anode to the cathode and produce power. To a large extent, the cathode material limits the performance of current Li-ion batteries V + - Separator Cathode Anode Li Li Li Li Li Li Li Li Li Li Li Li LiMO2 Graphite Non-aqueous electrolyte MPI workshop, WPI, 2008

14. Anode Current Collector Batteries & electrodes Li-ion battery chemistry/physics More details on the transport of Li-ions. • Both the anode and cathode are made from a collection of powder particles which are bonded together into a 3-D porous body (electrode). • During discharge, ion transport in the electrode occurs as follows (green line) • Li-ion starts in the bulk of a cathode particle. • It undergoes solid state diffusion in the particle. • At the surface it disassociates from the e- and enters the electrolyte which occupies the pores of the electrode. • The ion is transported through the electrolyte (liquid phase diffusion) to the anode. • In enters the anode. • It undergoes solid state diffusion in the anode. • At the same time, the electron must pass through the collection of solid particles to a metal current collector where it can be extracted from the cell and used to power a device (red line). It can not travel in the electrolyte. 6 5 4 4 Electrolyte 4 3 1 2 Cathode Current Collector MPI workshop, WPI, 2008

15. Batteries & electrodes Battery Electrodes Real electrodes are more complex. • Electrodes typically contain high surface area carbon to increase the electrical conductivity between particles. • A small amount of polymer binder is used to hold the particles in place. • Typical particle size ~10um. • Typical electrode thickness 50-75um. Cathode Current Collector MPI workshop, WPI, 2008

16. Batteries & electrodes Particle size distribution Real powder particles can have different morphologies and surface roughness. 10mm 10mm 1mm MPI workshop, WPI, 2008

17. Batteries & electrodes Impact of electrode structure The internal structure of the electrode plays an important role in the performance of a battery. Energy vs. Power • For a given battery chemistry, the energy stored in the battery is proportional to the amount of active materials (i.e. anode + cathode powder). • For a cell of a given size, the higher the packing fraction of the powders, the more energy the battery can store and the longer your device can run before it needs recharging. • The power (rate of energy delivery) depends on having sufficient mass and electrical transport throughout the electrodes. In theory, higher power can be achieved with: • smaller particles • higher surface area • larger fraction of porosity (i.e. more electrolyte) • thinner electrodes • Careful design of electrodes is required in order to produce electrodes with the desired balance between high power and high energy. • Commercial electrode design is currently dominated by empirical experimental approaches. MPI workshop, WPI, 2008

18. Batteries & electrodes Property trade-offs For a given cathode material, you can vary the electrode morphology to gain power at the expense of energy density.Different applications require different combinations of properties (laptop vs. cordless drill). Power and energy from a high-power cell design MPI workshop, WPI, 2008

19. Batteries & electrodes Impact of electrode structure The internal structure of the electrode plays an important role in the performance of a battery. Electrodes for cathodes with slow solid state diffusion • Some cathode materials suffer from poor kinetics (slow solid state diffusion) • Some success has been achieved by using very small cathode particles (~100nm) because the average diffusion distance a Li-ion must travel in the particle is much smaller. • However, these nano-powders typically have a low tap density and are difficult to tightly pack due to surface effects. This causes the batteries to have lower energy densities. • Selecting a the best particle size will involve a trade-off between energy density and rate behavior. MPI workshop, WPI, 2008

20. Overview Introduction to TIAX Batteries & electrodes MPI workshop project description MPI workshop, WPI, 2008

21. MPI workshop problem description Overview TIAX would benefit from algorithms, methods, models, scaling relations, or frameworks to analyze the effect of different particle characteristics on electrode properties. • Knowledge of qualitative and/or quantitative relationships between electrode structure and performance will be useful in: • Isolating which features of current electrode structures are critical in achieving good performance, • Predicting improvements to current empirically determined relationships, • Identifying tradeoffs in structural features and performance. • The inputs for the problem for the MPI workshop are particle properties; the outputs are electrode properties. • TIAX can link the predicted electrode properties to key parameters quantifying electrode performance, such as energy density. MPI workshop, WPI, 2008

22. MPI workshop problem description Input variables The inputs for the problem for this workshop are particle properties. • Some particle characteristics to consider might include: • Size of monodisperse spheres • Roughness of monodisperse spheres • Radii of bidisperse spheres • Particle sizes with more realistic distributions of sizes (i.e. Gaussian distribution) • Deviations from sphericity, e.g., ellipsoidal particles (Zamponi, Nature, 2008) MPI workshop, WPI, 2008

23. MPI workshop problem description Output variables The outputs for the problem for this workshop are electrode properties. • Some electrode properties of interest include: • Packing fraction or void volume • Total surface area • Average path lengths for transport through the individual solid particles to the particle surface • Average path length for diffusion through the void volume from the surface of a particle to the surface of a collection of particles (electrode) of a certain thickness. • Effective cross-sectional area for this type of mass transport. • Average path length to travel through the collection of particles of a certain thickness, if you must travel only through the particles (passing from particle to particle only at points where they meet). Effective cross-sectional area for this type of transport. MPI workshop, WPI, 2008

24. Finally, experiments involving M&Ms may contribute to understanding the packing fraction of different shaped particles. http://www.physics.nyu.edu/~pc86/packing.html MPI workshop problem description Problem scope Determining all of the electrode properties for all possible combinations of particle characteristics is probably not a manageable task! • It may be useful to consider some of the more complex electrode properties for the case of simple particle size distributions (i.e., monodisperse spheres). • For more complex particles, determining the packing fraction may be a sufficiently challenging problem. • We would also like to increase our understanding of the literature in this area; any information you can provide on relevant references will be useful. MPI workshop, WPI, 2008

25. MPI workshop problem description Contact information David and Jacquie will be a “tag team” at the workshop part-time. • When we are not here you can reach either of us in the following way: • Jacquie mobile tel. 617 899-8935 • David office tel. 617 498-6088 (mobile tel. 510 290-0982) • We look forward to seeing the results, and thank you in advance for your efforts! MPI workshop, WPI, 2008