June 16, 2022

Nickel Sodium Battery Chemistry FAQ

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Nickel/Sodium Cells
These are specialty cells made by one manufacturer in England, Beta Research. They have advantages for electric vehicles. The cell runs hot, about 300 degrees C, but this isn't a worry, since they heat themselves up during discharge. The discharge reaction is:

Location	Half Reaction	Voltage
Charge	2 NaCl + Ni Z —> 2Na +NiCl₂
Discharge	NiCl₂ + 2 Na —> Ni + 2NaCl	2.58 V

The electrolyte on the nickel side of the alumina separator is sodium tetracloroaluminate.NaAlCl₄, which melts at 151 degrees C.. Energy density is 100 to 150 Wh/kg. These use an aluminum oxide ceramic as a separator, similar to that of the sodium-sulfur cell. They have the same danger of rupture of the separator, but have a unique solution to the problem. The cell is encased in a two-wall steel thermally insulated package. If the separator breaks the energy is confined within this package. A cell that is broken in this way has a low resistance, so it can continue to reside in the battery pack without causing a vehicle break-down. This double-insulated case also prevents the cell from spilling in car crashes.

There are no higher-voltage reactions or other side reactions, so the inventors claim that up to the point of full charge the cell is 100% coulomb efficient–meaning that the amp-hours you put in is exactly the same as the amp-hours you get out. Overcharging does not damage the cell, so the battery packs are easy to keep in balance–just overcharge the whole pack.

It seems that the cell has no self-discharge if the batteries are cold, (solid blocks of sodium don't migrate at room temperature) and that a pack requires about 24 hours to get to temperature with a 230 VAC input to the pack heater.

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