Lithium ion batteries are different from NI-CD rechargeable batteries. No water is used in the electrolyte of NI-CD rechargeable batteries. They use a non-aqueous electrolyte instead, which is composed of organic liquids and salts of lithium to provide ionic conductivity. It has much higher cell voltages than the aqueous electrolyte systems. They also require a more complex assembly, as it must be done in a nearly perfectly dry atmosphere.

A number of non-rechargeable batteries were first developed with lithium metal as the anode. Commercial coin cells used for watch batteries are mostly lithium chemistry. These batteries use a variety of cathode systems that are safe for consumer use. The cathodes are made of various materials, like carbon monoflouride, copper oxide, or vanadium pentoxide. All solid cathode systems are limited in the discharge rate they will support.

To obtain a higher discharge rate, liquid cathode systems were developed. The electrolyte is reactive in these designs and reacts at the porous cathode, which provides catalytic sites and electrical current collection. Examples of these systems include lithium-thionyl chloride and lithium-sulfur dioxide. The batteries are used in space and for military applications, as well as for emergency beacons. They are generally not available to the public because they are less safe than the solid cathode systems.

The next step in lithium ion battery technology is believed to be the lithium polymer battery. This battery replaces the liquid electrolyte with either a gelled electrolyte or a true solid electrolyte. These batteries are supposed to be even lighter than lithium ion batteries, but there are currently no plans to fly this technology in space. It is also not commonly available in the commercial market.

We have come a long way since the leaky flashlight 18650 batteries of the sixties, when space flight was born. There is a wide range of solutions available to meet the many demands of space flight. It is possible to handle massive radiation, decades of service, and loads reaching tens of kilowatts. There will be a continued evolution of this technology and a constant striving toward improved batteries.