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Ashlee N. Gordon Mentor: Dr. Quinton Williams 20 July 2018

Effect of Carbon Nanofibers on the Discharging Rate Performance of LiFePO 4 Cathodes. Ashlee N. Gordon Mentor: Dr. Quinton Williams 20 July 2018. Overview. Motivation LFP as a solution? Summer goal w/ CNFs Battery fabrication Results Conclusions Future work. Motivation.

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Ashlee N. Gordon Mentor: Dr. Quinton Williams 20 July 2018

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  1. Effect of Carbon Nanofibers on the Discharging Rate Performance of LiFePO4 Cathodes Ashlee N. Gordon Mentor: Dr. Quinton Williams 20 July 2018

  2. Overview • Motivation • LFP as a solution? • Summer goal w/ CNFs • Battery fabrication • Results • Conclusions • Future work

  3. Motivation • Need for portable energy • Currently use LiCoO2 batteries • Relatively low reversible specific capacity (140 mAh/g) • Cobalt is toxic and expensive • O2 poses safety concerns due to explosions (hover boards, cell phones)

  4. LiFePO4 Advantages Disadvantages Relatively low electronic conductivity Slow Li-ion diffusion kinetics • High theoretical specific capacity (160 mAh/g) • Non-toxic • Inexpensive source materials • Long cycle life • Excellent thermal stability

  5. Summer Goal To optimize the overall performance of Li-ion rechargeable batteries using carbon-nanofibers as conductive additives inLiFePO4 (LFP) cathodes to improve: • ionic diffusion • electrical conductivity

  6. Why carbon-nanofiber additives?

  7. Slurry for electrodes Cathode (on aluminum foil) • LFP – 80% (active material) • Polyvinylidene fluoride (PVDF, binder) – 10% • Carbon black – 10% - 7% - 5% - 3% • CNF – 0% - 3% - 5% - 7% Anode (on copper foil) • Carbon graphite – 70% • PVDF – 30%

  8. Battery fabrication

  9. Discharge Capacity at Different C-Rates C-rate is the time is takes for the battery to completely charge/discharge relative to its specific capacity Current settings: 1C = 150 mAh/g Voltage Window: 2.5V-3.6V 5% CNF batteries show better SDC at low c-rate of 0.1C (10 hours) and at high c-rate of 5C (12 minutes) *Average of 3 batteries each

  10. LFP + 3% CNF cathode Current settings: 1C = 100 mAh/g Voltage window: 2.5-3.6V 3% CNF batteries show slight improvement of SDC over 0% batteries *Average of 3 batteries each

  11. C-Rate Testing • 1 cycle is a complete charge and discharge • Improved rate performance for 5% CNF batteries vs 0% CNF • 5% CNF batteries maintained improvement after multiple cycles *Average of 3 batteries each

  12. LFP + 3% CNF cathodes At low c-rate, 3% shows slight improvement At high c-rate, 3% loses capacity rapidly *Average of 3 batteries each

  13. Conclusions

  14. Acknowledgements • Financial support from the REU site in Physics at Howard University NSF Award PHY 1659224 is gratefully acknowledged • Dr. Quinton Williams • Adewale Adepoju

  15. Questions?

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