Kuang-Che Hsiao. Supervisor: Prof. Tony West

Transcription

1 New Potential Cathode Materials for Lithium-ion ion Battery - Synthesis and characterization of Li 1+x FePO 4-x N x cathode - Kuang-Che Hsiao Supervisor: Prof. Tony West 08/06/ dtp09kh@sheffield.ac.uk TEL: +44(0)

2 Presentation Outline Introduction to Li-ion battery Applications of Li-ion battery New cathode materials LiFePO 4 -based cathode material Experimental procedure Results and discussion Conclusions

3 Battery chemistry over the years Source: M. Armand, J.-M. Tarascon, Nature 2008, 451, 652.

4 Energy Density of Various Batteries Lighter Weight Volumetric energy density (Wh/L) Smaller Size Source: SANYO battery comparison, 2006 brochure

5 Mechanism and Components of Li-ion Battery Both anode and cathode materials are intercalation compounds Anode reaction: xli + + 6C Li x C 6 Cathode reaction: LiCoO 2 Li 1-x CoO 2 + xli + Overall reaction: LiCoO 2 + 6C Li x C 6 + Li 1-x CoO 2 Components Common Materials Electrolyte Li 1-x CoO 2 Li x C 6 Solid Electrolyte Interface (SEI) is a surface film that generally forms between an electrode and electrolyte. It is an internal resistor that limits power output and generates heat build-up in a standard Li-ion battery. Cathode Anode Separator Electrolyte Active material: LiCoO 2, LiMnO 4, LiFePO 4 Conducting additives: Acetylene black Binder: PVDF, PTFE Current collector: Al foil Active material: graphite, MCMB Conducting additives: Acetylene black Binder: PVDF, PTFE Current collector: Cu foil porous polyolefin Solvent: EC, PC, DMC, DEC, DME Solute: LiClO 4, LiPF 6, LiBF 4 Source: Brian J. Landi, Potential Environmental Benefits of Nanotechnology: Fostering Safe Innovation-Led Growth, July 17th, 2009

6 Typical Configurations of Li-ion Battery a. Cylindrical Cell b. Coin Cell size 3.3 V 1.1 Ah 65 mm LiFePO 4 18 mm c. Prismatic Cell d. Thin and Flat Cell LTO 2.5 V 1.8 Ah Source: J.-M. Tarascon & M. Armand, Nature 2001, 414, ALB

7 Applications of Li-ion Battery 3C Portable Products LIB Driving Power Sources Energy Storage Systems

8 New Cathode Materials xli 2 MnO 3 /(1-x)LiMO 2 Cathode demands: high capacity high safety low cost long life cycle Source: Andreas Jossen, Margret Wohlfahrt-Mehrens, Second International Renewable Energy Storage Conference, Nov , 2007, Germany

9 LiFePO 4 Cathode Electrode Material LiFePO 4 Li forms one-dimensional chains along the [010] direction (b axis) Average working voltage (V) 3.4 Density (g/cm 3 ) 3.5 Structure (orthorhombic) Theoretic specific capacity (mah/g) Practical specific capacity (mah/g) 1-D, Olivine Energy Density (kwh/l) 1.9 Fe O P c b Fe 2+ Fe 3+ (stable) a LiCoO 2 : Co 3+ Co 4+ (untable!) Li (Li+ deintercalation upon charging) Conductivity (S/cm) ~10-9 Li ion diffusivity (cm 2 /s) ~ Cycle life Safety > 1000 cycle superior Literature Review: solid-state electrolyte (1992) Low ionic conductivity: S/cm Cross-Linked Structure Higher ionic conductivity: S/cm Li 3 PO 4 sputtering of Li 3 PO 4 with N 2 Li 3.3 PO 3.9 N 0.17 Cost 18 US/Kg Source: F. Zhou et al., Phys. Rev. B 2004, 69, J.B. Bates et al., Solid State Ionics 1992, 53-56, 647.

10 Synthesis of LiFePO 4 -based cathode materials Valence Mechanism (Solid State Chemistry): Li 1+x FePO 4-x N x where, Li: +1 Fe: +2 P: +5 O:-2 N: -3 if x=0 LiFePO 4 if x=0.2 Li 1.2 FePO 3.8 N 0.2 Li 2 CO 3 Grounding with mortar and reacted at 800 o C for 12 h under N 2 atmosphere FeC 2 O 4.2H 2 O NH 4 H 2 PO 4 LiFePO 4 XRD X Li 3 N (1-2X/2) Li 2 CO 3 Grounding with mortar and at reacted 800 o C for 12 h under N 2 atmosphere Li 1+X FePO 4-X N X FeC 2 O 4.2H 2 O NH 4 H 2 PO 4

11 XRD Results: Li 1+x FePO 4-x N x Li 3 PO 4 or Li 2.88 PO 3.73 N 0.14 X=0.2 Fe 2 O 3 Intensity (a.u.) X=0.1 X=0.05 X=0 Single phase LiFePO θ (deg)

12 Test temperature: 25 o C AC Impedance Results LiFePO 4 Li 1.05 FePO 3.95 N Z ''/10 5. Ω 2 -Z ''/10 7. Ω Z'/10 5. Ω Z'/10 7. Ω Results and Discussion: The impedance results at room temperature show the Li 1.05 FePO 3.95 N 0.05 is more resistive than that of pure LiFePO 4. More impedance studies at higher temperature for these two materials should be done to check the electronic and/or ionic effect contributed to their conductive differences. In addition, it is necessary to try to understand why the impure phase of Fe 2 O 3 in Li 1.05 FePO 3.95 N 0.05, using more experimental studies.

13 Conclusions Li-ion batteries show the highest specific energy (up to 200 Wh/kg) of available rechargeable battery systems, and they are market leader in portable power sources. The development of new cathode materials is a challenge for meeting current and future energy storage requirements aimed at high energy and power density, good cycle retention as well as low cost manufacture. The single phase LiFePO 4 cathode can be synthesized by solid state method, but more studies need to be done to check the Li 1.05 FePO 3.95 N 0.05 material. Coming Future Works - Scanning electron microscope (SEM)/Energy Dispersive Spectrometer (EDS): to check N composition because of the 3% limitation of XRD. - High temperature impedance testing: to understand the electronic and/or ionic effect for pure LiFePO 4 and Li 1.05 FePO 3.95 N 0.05.

14 Acknowledgements Inorganic Material Laboratory/Department of Engineering Materials: - Supervisor: Prof. Tony West (research discussion) - Jordi Jacas Biendicho (experimental discussion) - Andrew Mould (AC Impedance Training) Thank you for your kind attention!