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15. Energy Applications I: Batteries

15. Energy Applications I: Batteries. Battery types: Primary Battery: Non reversible chemical reactions (no recharge) Secondary Battery: Rechargeable Common characteristics Electrode complex coposite of powders of active material and conductive

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15. Energy Applications I: Batteries

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  1. 15. Energy Applications I: Batteries

  2. Battery types: Primary Battery: Non reversible chemical reactions (no recharge) Secondary Battery: Rechargeable Common characteristics Electrode complex coposite of powders of active material and conductive diluent, polymer matrix to bind the mix typically 30% porosity, with complex surface throughout the material allows current production to be uniform in the structure Current distribution primary – cell geometry secondary – production sites within the porous electrode parameters affecting the secondarycurrent distribution are conductivity of diluent (matrix) electrolyte conductivity, exchange current diffusion characteristics of reactants and products total current flow porosity, pore size, and tortuosisity What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd

  3. We will briefly look at: Lead and Lithium insertion What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd

  4. What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd

  5. Require very good conductivity Throughout the system Which tends to lower the energy Content of the system In the lead acid system a significant amount Of the weight Is in the grids required To hold the paste What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd

  6. Equivalent Circuit for a Battery External Resistance, Rext Terminals, Resistance To current flow of, RM Capacitance of electrode Internal Discharge Rate (e.t.) Resistance of electrolyte

  7. Basic requirements for a battery 1. chemical energy stored near the electrode ( if too far away current will be controlled by time to get to electrode) 2. The chemical form coating the electrode must allow ion transport, or better yet, electronic conduction 3. The chemical form of the energy must be mechanically robust 4. The chemical form of the energy should generate a large voltage Lead Acid Battery

  8. The capacity of the battery depends on The type of material present. Support grids Fitch lead book

  9. One possible mechanism:. simultaneous dissolution of PbO2 and introduction of 2e Requires electronic conductivity of PbO2 and pore space for motion of water • Add e, H+ and OH- to PbO2 • Add 2nd e to reduce valence of Pb • Add 3rd e to reduce valence while removing OH- for charge nuetrality • PbO is more soluble than PbO2 so it dissolves and reacts with sulfate to • Initiate formation of PbSO4, nucleation rate rises with lg conc. Sulfate, which reduces growth of large sized crystals • PbSO4 structure is rhombic which matches the PbO2 so it can easily attach • Therefore need to control the alletropes of PbO2 and PbO

  10. Beta PbO2 is formed under acid and can be compressed to shorten bonds overlap induces semiconductor behavior which increases the performance Of the battery Add antiomony To drive reaction To beta phase Alpha forms when Pb metal Corrodes – reduces lifetime of Battery, is more compressible.

  11. Lead Acid battery a.What is the potential associated with a lead acid battery with the overall reaction: at the following concentration: [H2SO4]= 4.5 M

  12. Vo 1.69 -0.35 1.69 -(-0.35) 2.04

  13. Lead Acid battery energy

  14. c. What is the free energy associated with the lead acid battery?

  15. Dendrites are Good: porous (makes more Of possible energy available) Bad: fragile, break and fall from underlying electrode = NO CURRENT e No e

  16. The type of structure that forms depends upon the rate of crystallization which Depends upon rate of reaction which depends upon: Loss/production of products (current) Which depends also upon the rate constant (potential dependent)

  17. One way to “image” the various processes described above is by an Equivalent Circuit

  18. In a simplified system As the battery is discharged the discharge voltage is the Difference between what we started with and the remaining Voltage in the battery

  19. Lead acid batteries can be valve regulated to control the pressure associated With No pressure 1.29 V 1.38 V Suggests higher Degree of interparticle Contact under pressure Lower CT resistance Under pressure pressurized

  20. Insulating layer which can conduct only protons and lead Solubility Diffusion Et at conducting PbO2

  21. Solubility Diffusion Et at conducting PbO2 Modeled effect of diffusion

  22. Solubility Diffusion Et at conducting PbO2 Modeled effect of proton conc

  23. Solubility Diffusion Et at conducting PbO2 Different magnitude of discharge Changes the solubility and proton conc As well as the conductivity of the film

  24. Based on V. S. Bagotsky text, Fundamentals of Electrochemistry

  25. For the simplified model

  26. Monitor structural changes at electrode as a function of the discharge power

  27. Charge transfer resistance Decreases due formation of more porous PbO2 Small diameter Of impedance Circle here indicates The fast et kinetics of O2 reaction. High charge transfer Resistance due to insulating PbSO4 layer Increasing Charge transfer Resistance due To layer of PbSO4

  28. Reaction Vo Li++e Li -3.0 K+ + e K -2.95 Na+ + e Na -2.71 NCl3_4H+ + 6e 3Cl- + NH4+ -1.37 2H2O + 2e H2 + 2OH- -0.828 Fe2+ + 2e Fe -0.44 Pb2+ + 2e Pb -0.13 2H+ + 2e H2(gas) 0 N2(g) + 8H+ + 6e 2NH4+ 0.275 Cu2+ + 2e Cu 0.34 O2 + 2H2O + 4e 4OH- 0.40 O2 + 2H+ + 2e H2O2 0.68 Ag+ + e Ag 0.799 NO3- + 4H+ + 3e NO(g) +2H2O 0.957 Br2 + 2e 2Br- 1.09 2NO3- + 12H+ + 10e N2(g) +6H2O 1.246 Cl2 + 2e 2Cl- 1.36 Au+ + e Au 1.83 F2 + 2e 2F- 2.87 7g/mol 207g/mol

  29. Lithium oxidation proceeds a little too uncontrollably Lithium reduction does not not result in good attachment back to the lithium metal Forms dendrites which can grow to Short circuit Lithium intercalated in graphite is close to metallic, formal potential differs by only 0.1 to .3 V = -2.7 to -2.9V

  30. Anode – Solid electroactive metal salt (Can change overall charge so that it can electrostatically stabilize & localize Li+ ) Potential should be very positive (far from -2.5 V for Li/C reaction Solid should conduct charge throughout Solid should allow ion motion Should have fast kinetics (open and porous) Should be stable (does not convert to alleotropes) Low cost Environmentally benign M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  31. Group II Group I Group III Spinels M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  32. Smooth galvanostatic curve indicates That there are no sites nucleating Alleotropes of the compound. Allotropes would alter the structure, Porosity, and the ease of intercalation, Potential, and conductivity Single phase Light weight Conducting, but not Reactive (oxidised or reduced) Li ion intercalates in response to double layer charging Went to market In the late 1970s M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  33. Indicates various crystal forms octahedral Lithium ion inserts in response To reduction of vanadium 2nd is tetrahedral Different phases of VSe2 have similar structures So the distortion is not great M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  34. Group II M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  35. Major phase changes in LixV2O5  (x<0.01) is well ordered Є ( 0.35<x<0.7)is more puckered  (x=1) shifting of layers  (x>1) results in permanent structural change ω (x>>1) is a rock salt form

  36. Sol gel processes of the V2O5 materials

  37. Group III Spinels • These materials have a major change in • Unit cell dimensions when Mn changes • Oxidation state (see B). Need to keep the • Lattice parameter less than 8.23 A for good • Cycling, which • Keeps Mn in higher oxidation state, therefore • less soluble • Prevents distortion in the coordination of oxygen (Jahn-Teller) • around the manganese. These distortions will alter the oxidation and • reduction potential as seen in the next slide M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

  38. M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301

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