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How are rechargeable batteries made? A guide to NiMH batteries

With a lemon, some copper wire and a paper clip, everyone can create a battery. It wouldn’t stand a chance against a single household battery’s power output, but the principle is very similar.

Today, millions of batteries are produced, used and recycled all around the world. By choosing better materials and more specific structures, manufacturers are trying to continually improve the quality and reliability of their batteries.

But how are batteries made, exactly? What makes a battery reliable, safe and good for use in everyday situations? In this article, we’re explaining how we create rechargeable batteries.

The same, but different

There are several types, most of which can be categorised into two main groups: primary batteries and secondary (rechargeable) batteries.

In terms of usage, the differences between the types may not be as significant: a battery is simply a tool which stores energy and releases it whenever required. But in terms of structure, differences between the types could be more notable. This also applies to how batteries are manufactured.

To simplify matters, we’ll only focus on the structure of eneloop batteries in this article. For a more detailed explanation of other types, please refer to our extensive battery guide.

A newer, better battery

Panasonic eneloop batteries are NiMH (Nickel-Metal Hybride) batteries. In terms of structure, this type is very similar to its older brother, the NiCd (Nickel Cadmium) battery, but eneloop NiMH batteries have a larger capacity and therefore are more suitable for longer operating times. Due to their different chemical composition, they’re also more resistant to the memory effect.

How are batteries made up, then? As the name suggests, a NiMH battery is mostly of nickel and a metal compound. An eneloop battery is organised in three layers: a positive electrode, a separator and a negative electrode. These are rolled up into a coil, which is placed into a metal casing. The latter is then filled up with a liquid electrolyte before being closed off with a cap. The cap itself has a gas release vent to allow the release of gases if the battery is overcharged.

What’s different about eneloop batteries?

NiMH batteries have been criticised of having high self-discharge rates, often requiring people to have to recharge their batteries right before use. This low shelf life was caused by impurities in certain materials.

Panasonic eneloop has made an effort to make NiMH batteries more reliable, both in terms of self-discharge and performance. By improving the composition of the positive electrode and the separator, the batteries could hold up to 80% of their original capacity after one year of storage. The negative electrode has better coating technology to improve cycle life.

Additionally, eneloop uses a thinner yet stronger protective case. Without noticeable changes to the exterior size, the inside of the battery is organised more efficiently. As a result, the battery has a larger capacity and can be recharged up to 2100 times.

How are batteries made into a reliable source of energy for everyone? It’s a combination of basic principles and continual improvement for the many years to come.