By Dan Hagopian

In the last two articles we addressed how and why rechargeable batteries have limited charge cycles. We reviewed in detail the effect of a charge-discharge cycle - a chemical change in a battery system that results in degradation and power loss. But there is one aspect in my last article that deserves special attention. This one factor is the basis of battery degradation. It is the reason why batteries can never just keep going and going and going. The fact is, is that all batteries degrade and lose power because there is a reduction in the battery's active material.

We know that a battery is a device that converts chemical energy into electrical energy. In order to convert chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of electrical energy. The chain of events have been discussed in depth in previous articles which you can access on my blog but what is key to the creation of electricity is that in batteries electrical energy is produced from two chemicals in a solution. After discharging you recharge the battery via a charger. The charge process involves intercalation: the joining of a molecule (or molecule group) between two other molecules (or groups). Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is one of the chemical components used to create electrical energy in batteries. Lithium compounds have minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current. Ionizing lithium loads the crystal planes to the point where they are forced into a current flow. Intercalation replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive property. You could say if you use it you will lose it!

Why then is lithium used as the chemical to create electricity in batteries? There are a number of good reasons - let's look at a few!

General Characteristics of Lithium

• Name: lithium
• Symbol: Li
• Atomic number: 3
• Atomic weight: [6.941 (2)] g m r
• CAS Registry ID: 7439-93-2
• Group number: 1
• Group name: Alkali metal
• Period number: 2
• Block: s-block
• Standard state: solid at 298 K
• Color: silvery white/grey
• Classification: Metallic

Lithium is one of the metals in the alkali group (the other metals include Sodium, Potassium, Rubidium, Cesium, and Francium). Lithium is a highly reactive metal. Lithium has only one electron in its outer shell (two electrons in its inner shell), which makes it chemically "ready" to lose that one electron in ionic bonding with other elements. Lithium is used as a battery anode material (due to its high electrochemical potential). Electrochemical potential is the sum of the chemical potential and the electrical potential. The higher the electrochemical potential the better the electrical current yields. In some lithium-based cells the electrochemical potential can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries. One other core advantage that lithium has is that it is soft and bendable which allows for tight configurations in small cell designs (PDAs. Laptops, Cameras etc...).

Lithium, even with all of its good chemical properties will eventually, however, react to the point where the electrochemical potential will yield a charge that is simply not enough to create current to pass to power a device.

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© Dan Hagopian You have permission to publish this article electronically or in print, free of charge, as long as the bylines are included with link. Dan Hagopian of http://www.batteryship.com has been writing about consumer electronics since 1996. Dan has a personal passion for understanding how electronic devices can be powered, for learning about various types of battery devices and their internal systems, as well as the interaction of batteries with interfacing systems, and finally about the internal control mechanisms of batteries. Dan writes on battery power related devices for mobile computing and portable power. Dan writes about this technology extensively and his work can be found at http://www.batteryeducation.com

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