| Construction |
Rechargeable Nickel-metal hydride batteries consist of a positive plate containing nickel hydroxide as its principal active material, and a negative plate mainly composed of hydrogen-absorbing alloys, a separator, an alkaline electrolyte, a metal case and a sealing plate provided with a self-resealing safety vent. Their basic structure is identical to that of Ni-Cd batteries. A cylindrical nickel-metal hydride batteries, the positive and negative plates are separated by the separator, wound into a coil, inserted into the case, and sealed by the sealing plate through an electrically insulated gasket.
|
| Battery Reactions |
Nickel-metal hydride batteries employ nickel hydroxide for the positive electrode similar to Ni-Cd batteries. The hydrogen is stored in a hydrogen-absorbing alloy for the negative electrode, and an aqueous solution consisting mainly of potassium hydroxide for the electrolyte. Their charge and discharge reactions are shown below.
|
| In positive: |
| Charge: Ni(OH)2 +OH→NiOOH+H2O+e |
| Over charge:4OH-→2H2O + O2 + 4e |
| Discharge:NiOOH+H2O +e→Ni(OH)2+OH |
| Over discharge:2 H2O+2e→H2+2OH
|
| |
| In Negative plate: |
M+ H2O +e→MH+OH |
2H2O + O2+4e→4OH |
MH+ OH→M+ H2O +e |
H2+2OH→2H2O +2e
|
| Over rall: |
Ni ( OH )2 +M <-------> NiOOH + MH ?Q
|
| As can be seen by the overall reaction given above, the chief characteristics of the principle behind a nickel-metal hydride battery is that hydrogen moves from the positive to negative electrode during charge and reverse during discharge, with the electrolyte taking no part in the reaction; which means that there is no accompanying increase or decrease in the electrolyte. |
|
