Energy Storage & Batteries Flashcards
What does more energy from renewable sources provide, and what are the key components in achieving this goals?
The transition to zero-carbon economy.
Key:
1. Increased electrification rates
2. Increased storage
What is the problem with energy supply from renewables, and why is energy storage important?
Problem: more difficult to control due to intermittence of supply (weather changes etc.)
Significance: excess energy produces can be stored, and used when renewable sources are insufficient.
What is a battery, give an example?
An electrochemical cell using two different metals (Zn and Cu) in contact with an electrolyte.
Example: hybrid cars / fully electric cars.
What does the voltage produced by the cell depend on?
The type of electrodes used and electrolyte.
How does the separator in the battery operate?
Allows ions to move selectively.
Prevents other species of moving.
How do batteries work?
- Cu deposits on Cu cathode.
Cu(2+) (aq) + 2e- => Cu (s) - Ion transport charge equivalent to electron flow.
- Porous barrier allows (SO4)2- to pass, blocks Zn and Cu ions.
- Zn gives 2e -> goes into aq.
Zn (s) => Zn2+ (aq) + 2e- - Zn loses e more readily than Cu.
- Electrode with oxidation : anode.
CuSO4 => (SO4)2- => ZnSO4
What does the potential of batteries determine?
=> determines the potential of the cell.
What is the order of the reactivity of metals?
Highest
1. K
2. Na
3. Ca
4. Mg
5. Al
6. C
7. Zn
8. Fe
9. Pb
10. H
11. Cu
12. Ag
13. Au
Lowest
What are the two types of batteries?
- Primary - disposable, electrochemical reaction cannot be reversed.
- Secondary - rechargeable, electrochemical reaction can be reversed by applying certain voltage to the battery (in opposite direction of the discharge).
Which are common disposable commercial batteries?
DISPOSABLE
- Zinc-Carbon: in all drycell batteries, cheap.
Electrodes are Zn & C, with acidic paste serving as the electrolyte. - Alkaline: in duracell and energizer batteries.
Electrodes are Zn & MnO2, with alkaline electrolyte.
Which are common rechargeable batteries?
- Nickel-Cadmium: NiCd
- Nickel-metal hydride: NiMH (Less stable than NiCd)
- Lead-Acid: used in cars.
Electrodes are Pb & PbO2, with an acidic (H2SO4) electrolyte. - Lithium-ion: Li-ion
High energy density, power rate, cycle life.
BUT, more expensive.
Give a brief explanation about Zinc-Carbon batteries.
- Electrodes are Zn & C, with an acidic paste serving as the electrolyte.
- disposable.
- Zinc as anode, MnO2 as cathode.
- Redox chemistry takes place in the battery.
How does a Zn-C battery operate? Give the overall reaction.
- The C added to cathode increasing conductivity & retaining moisture.
= non-conducting tube
= separating layer
= C electrode surrounded by carbon black.
= Manganese dioxide - cathode
= Zinc metal sleeve - anode
= Ion transfer accomplished in a paste of ammonium chloride and zinc chloride. - Reaction:
Zn + 2MnO2 -> ZnO + Mn2O3
Give a brief explanation about Alkaline batteries.
- Used in Duracell and Energizer batteries.
- Electrodes are Zn & MnO, with alkaline electrolyte (e.g. KOH).
- disposable.
- Zinc as anode, MnO2 as cathode.
- Redox chemistry takes place in the battery.
Write the redox reactions, at the cathode and anode, and the overall reaction.
Anode: Zn + 2OH- => Zn(OH)2 + 2e-
Cathode: MnO2 + 2H2O + 2e- => Mn(OH)2 + 2OH-
Full discharge: Zn + MnO2 + 2H2O => Mn(OH)2 + Zn(OH)2
Give a brief explanation about NiCd batteries.
- rechargeable.
- Cd as anode, Ni as cathode (discharge)
- Ni as anode, Cd as cathode (charging)
- Advantage: stability, long life.
- Problem: toxicity of Cd.
Write the reactions of the anode and cathode upon discharge for NiCd.
Anode: Cd + 2OH- => Cd(OH)2 + 2e-
Cathode: Ni(OH)4 + 2K+ + 2e- => 2KOH + Ni(OH)2
Write the reactions of the anode and cathode upon charging for NiCd.
Cathode: Ni(OH)2 + 2OH- => Ni(OH)4 + 2e-
Anode: Cd(OH)2 + 2K+ + 2e- => Cd + 2KOH
Give a brief explanation about Lead-Acid batteries.
- used in cars.
- Electrodes are Pb & PbO2, with an acidic (H2SO4) electrolyte.
- Rechargeable.
Write the reactions of the anode and cathode upon discharge for Lead-Acid along with the overall reaction.
Anode: Pb + HSO4- => PbSO4 + H+ + 2e-
Cathode: PbO2 + 3H+ + HSO4- + 2e- => PbSO4 + 2H2O
Overall: Pb + PbO2 + 2H2SO4 => 2PbSO4 + 2H2O
Give a brief explanation about Lithium-ion batteries.
- High energy density.
- High power rate.
- High cycle life.
- Rechargeable.
Write the reactions of the anode and cathode for Lithium-ion along with the overall reaction.
Cathode: Reduction, with CoO2 combines with Li-ions, forming LiCoO2.
Half reaction is CoO2 + Li+ + e- => LiCoO2
Co(IV) => Co(III)
Anode: Oxidation, with graphite intercalation compound LiC6 forming graphite C6, and Li-ions.
Half reaction is LiC6 => C6 + Li+ + e-
Li(0) => Li(I)
Full Reaction: LiC6 + CoO2 <=> C6 + LiCoO2
- Left to Right = discharging
- Right to Left = charging
Charging and discharging of batteries.
Page 29.
What are the improvements required to replace the internal combustion engine by electric engine?
- Reduce price of batteries.
- Improve energy density.
- Increase power density.
- Improve their lifetimes.
What is the problem of Li-ion batteries and suggest an alternative?
Eventhough ideal for automotive industry, it is too expensive.
Cheaper alternatives: Na-ion batteries.
