MadSci Network: Chemistry |
Dear Jennifer,
The clue to a rechargeable battery is that the redox chemical reactions which produce electricity (flow of electrons during discharge) are reversible. That is, during a charge cycle electrons are forced to flow in the opposite direction as that during discharge. A special charger is used to contol the charge rate and time. Not all reactions are easily reversible, and not all battery construction allow it either. Single use "one-way" batteries are called primary cells. Rechargeable ones are called secondary cells.
There are a number of secondary cells in use, most notably
The NICAD serves to illustrate the reversible nature of a secondary cell well:
At the first electrodeDISCHARGE CYCLE
Cd(0) => Cd(II) + 2e-
Ni(III) +2e- => Ni(II)
CHARGE CYCLE
Cd(II) + 2e- => Cd(0)
Ni(II) => Ni(III) +2e-
The efficiency of these processes can be enhanced by various additives such as lithium ions to the aqueous potassium hydroxide electrolyte, and cobalt hydroxide to the nickel hydroxide(see References).
This whole question of rechargeable batteries was actually addressed a little while back on this network. I have included some WEBlinks from that answer and provided a few more in the WEBOGRAPHY table below:
Title/Subject | Author |
Ni-Cd seminar | "Red" Scholefield |
Nickel-based Cells | Chris Dreyer |
Nickel- metal hydride rechargeable batteries, Structure and Chemistry | Maxell Batteries |
NiCd Battery FAQ | Ken A. Nishimura |
What makes some cells rechargeable and others not | Michael Lerner & Frank McLarnon |
New Technology Batteries Guide | National Institute of Standards and Technology (NIST) |
References
"The Nickel Hydroxide Electrode: Structural and Thermodynamic Aspects"
C.Greaves, M.A.Thomas and M.Turner, Power Sources 9 (1983)
153-182
"Structural and Electrochemical Characteristics of Plastic (PTFE) Bonded
Nickel Hydroxide Electrodes" C.Greaves, M.A.Thomas and M.Turner,
Journal of Power Sources 12 (1984) 195-202
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