Lithium ion Rechargeable Batteries

Lithium ion rechargeable batteries, similar to the ones seen at are by far one of the most important technologies that have been developed over the last 10 years. Lithium based batteries are used in most portable devices from PDAs to laptops to digital cameras. Lithium ion rechargeable batteries are not hazardous when sealed and used according to the recommendations of the manufacturer.

There a number of electrochemical components contained inside a lithium battery that can cause it to be dangerous. Again let me stress that when sealed and used according to the recommendations of the manufacturer lithium ion rechargeable batteries are not hazardous.

However contained inside a battery are components that convert chemical energy into electrical energy and these components if not carefully designed can become dangerous. Why? Because it is basis of the design!

The basic design of a battery includes two electrodes, an anode and a cathode.  The battery’s purpose: to create current, from which we get voltage, the power to make our devices work while on the go. But the same power can also be quite dangerous if not manufactured and or used correctly. Let’s look closer at the battery’s design.

The two electrodes contained within the battery are the anode and the cathode. The anode is where oxidation occurs. During oxidation oxygen is added to the electrode which causes the removal of electrons from the specific chemical compound (e.g. lithium). The cathode is where reduction (gain of electrons) takes place. A Redox reaction is one where electrons are gained from an oxidizing source. In a battery it is in the anode where oxidation occurs to pass electrons to the cathode.

From the anode to the cathode electrons are passed through an electrolyte. An electrolyte is a scientific term for salt, specifically ions. The term electrolyte means that an ion is electrically-charged and moves to either a negative or positive electrode. The electrolyte is a substance containing free ions which behaves as an electrically conductive medium.

Electrolytes are typically formed when the force of salt is placed into a solution. The force of the salt (not to mention the salt itself) separate the atomic components of the solute molecules in a process called chemical dissociation. The solution can be any number of things such as a solution of lithium hexaflourophosphate (LiPF6) in a mixture of Organic Solvents: [Ethylene Carbonate (EC) + DiEthyl Carbonate (DMC) + DiEthyl Carbonate (DEC) + Ethyl Acetate (EA).

In batteries electrolytes are used to store energy as chemical fuel on the surface of the metal plates within battery cell and the electrolyte also serves as a conductor, which connects the plates electrically.

In some of the lithium batteries at for example the electrolyte is a gel-like polymer film that allows ion exchange. The dry polymer electrolyte design offers simplifications with respect to fabrication, ruggedness, safety, a razor thin-profile geometry, and enhanced conductivity. The electrolyte is held within a dry cell which is a galvanic electrochemical cell containing the pasty electrolyte.

Under normal conditions of use, the solid electrode materials and liquid electrolyte they contain are non reactive provided the battery integrity is maintained and seals remain intact. There is risk of exposure ONLY in cases of abuse (mechanical, thermal, electrical), which leads to the activation of the safety valve and/or the rupture of the battery container. Electrolyte leakage, electrode materials reaction with moisture/water or battery vent/explosion/fire may follow, depending upon the circumstances. Consequently the battery may bulge, bubble, smoke, or catch on fire in extreme circumstances. However if constructed and used according to the manufacturers recommendations lithium rechargeable batteries are perfectly safe and very useful.

Until next time – Dan Hagopian,
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