Preparation of alkali solution for Nickel-Cadmium alkaline battery


Nowadays I am reading more and more descriptions full with chemical, mathematical and conceptual errors about making alkali solutions for alkaline batteries used mainly in military radios, so I thought I, as a chemist, I make a simple, understandable recipe that could be used by anyone. Simple logical thinking is required and there is no magic in the matter.

As a starting point, we assume the following things:
- the recipe is not made for chemists,
- we do not want to make an analytically accurate solution, nor do we want to make a factory solution,
- in our case, we are preparing for non-combat conditions where the life and capacity of the batteries are not critical,
- we assume very simple, home available appliances.
If someone needs a factory description, it can also be found in the attached document collection.

The best known alkaline batteries are Nickel-Iron (Ni-Fe), Nickel-Cadmium (Ni-Cd) and Zinc-Silver (Zn-Ag). Military radios used Ni-Cd type batteries, so the recipe was also made for this type.

Let's start by clarifying two important basic concepts on a everyday level :)

The original recipes all give solution densities. The reason is very simple: density can be measured directly, while any concentration can only be measured indirectly. In this recipe, I’m going to refer to weight percent concentration, but we’re not really going to measure, it is for illustration only.
Concentration by weight: how many parts of the desired substance are 100 parts of a mixture. That "part" can be anything / whatever, not moored. All that is stipulated is that we refer to the weight of the "part".
Thus, for example, if 1 part of table salt is dissolved in 3 parts of water, the resulting solution consists of a total of 4 parts, so that the solution is 25% by weight of the soluted material, the salt. If 2 parts of water are added to 1 part of salt, the resulting solution will be 33.33%.
To measure density, we use a density meter - formerly an aerometer. For example, in brandy brewing, density meteres are still used today, which are certified for the density of an alcohol solution :)
It can be purchased if someone really wants it, but in our present case, we don’t need it.

The other important thing we need to clarify is density. Simply put, the density of a given substance expresses how many kg per 1 m3 of substance, the standard unit of measurement is kg/m3. It also has a smaller unit, g/cm3. It is VERY important to know about density that it is temperature dependent.
The reference base is water, as 1 m3 of water at sea level and 4 degrees Celsius weighs about 1000 kg. This 4 degrees Celsius has HUGE natural significance. At 20 degrees Celsius, the water is slightly lighter than 1000 kg, but this does not cause a significant difference in the present case, so we will not deal with this.
If e.g. we say to something that the density of substance X is 2, then it means that it is 2x heavier than water. So 1 liter of substance X will weigh 2 kg, which also means that 1 kg of substance X will occupy a volume of 0.5 liters.
So if we want to weigh 1 kg of water, we take a 1 liter bottle and fill it with water. However, if we want to weigh 1 kg from the previous material X, the above bottle is only half filled.

The alkali we use, potassium hydroxide - KOH - has a density of 2.04 g/cm3 or 2040 kg/m3. Put simply, it is twice heavier then the water.

I hope you understand the above basic math :)

From a chemical point of view, we want to make an alkali SOLUTION, so I will refer to a solution.

To operate the alkaline batteries, we need a solution of potassium hydroxide, hereinafter referred to as KOH.
Experience has shown that the best conductivity 26-27% KOH solution has, but we are satisfied with the roughly 25% solution.
In order to increase the capacity, lithium hydroxide (hereinafter referred to as LiOH) is even added to the solution, but on the one hand it is significantly more expensive than KOH, and on the other hand it is a bit more problematic to purchase, so we will dispense with it now.

Factory description suggests the following (included in the document collection):
- 1.17 - 1.19 g / cm3 in summer
- in winter till -10 degrees Celsius 1.19 - 1.21 g / cm3
- in winter below -10 degrees Celsius 1.27 - 1.28 g / cm3
density KOH solution should be used.

For their preparation, the factory description recommends the following (measured by weight in terms of solid KOH):
- 1.17 - 1.19 g / cm3 = 1 part KOH + 3.5 parts water => 22.22%
- 1.19 - 1.21 g / cm3 = 1 part KOH + 3    parts water => 25%
- 1.27 - 1.28 g / cm3 = 1 part KOH + 2    parts water => 33.3%

In principle, we should use distilled water as solvant. But if there isn’t then rainwater or melted snow will do. In the worst case, drinking tap water will do, but not recommended.
CAUTION! Deionized water used in cars is NOT distilled water! Deionized water is actually chemically treated water so that it does not precipitate when heated, but it still contains small amounts of chemicals, so it should be avoided for making solution.
There is nothing other than really pure water in distilled water. It is also available in stores.

Use goggles AND rubber gloves when preparing the solution !!!! Have kitchen vinegar on hand (yellow cap 10%).

Prepare eg 25% KOH solution - alkali:
- take a unit of measurement, such as a wine glass with as parallel a wall as possible, in which it is easiest to determine half the volume,
- take a plastic washbasin,
- take a glazed pot or a wide-mouthed plastic container (pot is better for heat transfer / cooling), use of any other material pot is forbidden,
- place the pot in the washbasin,
- weigh 3 glasses of water into the pot,
- fill the washbasin with cold water until the pot just starts to float,
- weigh out half a glass of solid KOH, making sure the glass is DRY
- while mixing with iron / steel, glass, plastic, in the worst case a wooden stick, slowly add the solid KOH to the water in the pot,
- continue to stir for a few more minutes,
- after cooling, our solution is ready to fill the batteries.

From an occupational safetyness, it is advisable to consider the following things:
- KOH is a very aggressive substance, handled VERY cautiosly, it has a very strong degreasing effect, it is advisable to wear protective gloves and goggles,
- it is usually said to corrode, which is why it is also called corrosive potassium, because, like fire, it severely destroys living tissues and forms burn-like wounds,
- if it gets on your skin wash very quickly with plenty of water,
- dust is expected when working with KOH, so not even dust should be inhaled / swallowed,
- if spilled anywhere, whether solid or solution, neutralize with vinegar, for body parts it is FORBIDDEN to use vinegar / any other acid, wash that part with plenty of water for minutes,
- if on clothing / shoes, take off immediately, wash with plenty of water,
- in case of contact with eyes, rinse immediately with plenty of water and seek medical advice,
- its dissolution in water or its reaction with an acid (even vinegar) is a very heat-producing - exothermic - process, therefore ALWAYS to pour KOH into the water and NOT REVERSE!
- if water is poured onto solid KOH, due to sudden heat production the solution may splash suddenly, causing very serious injuries,
- KOH chemical data sheets are attached to the document collection.

I hope I have described everything clearly :) If anyone has any questions then I will be happy to answer :)

Document collection : Alcaline battery documents