Strategies and Roadblocks to Commercialization of High Capacity Lithium Ion Batteries

1. Strategies and Roadblocks to Commercialization of High Capacity Lithium Ion Batteries Nicholas Gurnon Scientist – Polaris Battery Labs ngurnon@polarisbatterylabs.com

2. Lithium Ion Battery Prototyping at Polaris The Polaris Team • Artisanal Batteries • Hand-made • Highly customizable Electrode raw materials Separator Current collectors (metal foil) Wide variety of cell formats

3. Composite Cathode Material for Li-Ion Batteries Based on LiFePO4 System. DOI: 10.5772/21635 ~1960 mAh 508 mg Li Separator ~2940 mAh 761 mg Li 372 mAh/g 175 mAh/g 3862 mAh/g Low Potential Full charge ~ 0.01 V vs. Li/Li+ High Potential Full charge ~ 4.3 V vs. Li/Li+ • 1mA = 1 = 6.242 x 1015 elementary charges passing through a given point per second • 1mAh = unit of capacity equal to a current of 1 mA, sustained for 1 hour = 2.247 x 1019 elementary charges = 0.26 mg lithium

4. Solid Electrolyte Interphase (SEI): Complex, Heterogeneous, Difficult to Study, Magical 2Li + H2O → 2LiOH + H2 + heat = caustic mess + FIRE Image Source: Webb Group website, University of Texas at Austin Image Source: MIT Technology Review Website

5. Not All Anode Materials Created Equal Fully Charged Graphite: LiC6 ~372 mAh/g Fully Charged Silicon: Li22Si5 ~4200 mAh/g Intercalation Alloying

6. All of That Lithium Has to Go Somewhere Si Si Li4.4Si Lithiated Graphite: 10% Volume Expansion SEI SEI SEI Discharge Charge Li C6 C C SEI Mater. Chem. Front., 2017, Advance Article (DOI: 10.1039/C6QM00302H)  SEI SEI Particle cracking, continuous SEI growth, loss of electrical connection, unstable anode voltage lead to rapid capacity fade Lithiated Silicon: 300% Volume Expansion

7. Use Smaller Particles Less severe differential expansion = decreased internal stress = reduced cracking 10x surface area means at least 10x SEI per gram of anode material • Silicon - 50 nm diameter • Surface area ~20 m2 per gram Chem. Commun., 2012,48, 7268-7270 • Graphite - 20 µm diameter • Surface area ~2 m2 per gram

8. Build a Better SEI with Electrolyte Additives Chem. Commun., 2012,48, 7268-7270

9. Limit Expansion/Contraction by Controlling State of Charge (SOC) Li1.2Si Li3.2Si Si Si Si Li4.4Si • Anode capacity ~1200 mAh/g silicon • Moderate ICL – comparable cell capacity to graphite • LowerCell Voltage than graphite • Reduced volumetric energy density Full Contraction Voltage ~ 1.5 V Full Charge Partial Discharge Full Discharge Partial Charge • Anode capacity ~1200 mAh/g silicon • Large ICL - lower cell capacity than graphite • Comparable Cell Voltage to graphite • Reduced volumetric energy density Journal of The Electrochemical Society, 163 (6) A1020-A1026 (2016) ~100% Expansion Voltage ~ 0.15 V Partial Contraction Voltage ~ 0.4 V Cell Voltage () = Volumetric Energy Density () = 300% Expansion Voltage ~ 0.01 V

10. Engineered Silicon MorphologiesPeople are Creative! Encapsulated Silicon Silicon Nanowires (Amprius) Nano Lett., 2012, 12 (6), pp 3315–3321 Nature Nanotechnology3, 31 - 35 (2008)  Graphene-coated Silicon Nanoparticles Scientific Reports4, Article number: 3863 (2014)

11. Thank You! Want to talk batteries? ngurnon@polarisbatterylabs.com https://www.linkedin.com/in/nicholasgurnon