Batteries: Chemistry And Categories

Electricity is the flow of electrons through a conductive path called a circuit. Batteries consist of an anode (-), a cathode (+), and an electrolyte. The battery produces chemical reactions, causing a buildup of electrons at the anode, which results in an electrical difference between the anode and cathode. The electrons attempt to eliminate this difference by repelling each other and attempting to go somewhere with fewer electrons. In a battery, the only place for the electrons to go is to the cathode, but the electrolyte keeps them from doing this. When a wire connects the cathode to the anode, the circuit becomes closed, thus allowing the electrons into the cathode. This is how electrical potential causes electrons to flow through the circuit. The chemistry of battery reactions in batteries In any battery, an electrochemical reaction moves electrons from one pole to the other. The metals and electrolytes in the battery control the voltage, with each different reaction causing a characteristic voltage. Modern batteries use a variety of chemistries including:
- Alkaline - commonly found in Energizer and Duracell brands, alkaline batteries have zinc and manganese-oxide electrodes and an alkaline electrolyte.
- Lithium-iodide - this type of battery chemistry is long lasting, and typically used in hearing aids and pacemakers.
- Silver-zinc - designed with a high power-to-weight ratio, silver-zinc batteries are most often used in aeronautical applications.
- Zinc-carbon (aka standard carbon battery) - is used in nearly all AA, C, and D dry-cell batteries. The electrodes are made entirely of zinc and carbon, with an acidic paste acting as the electrolyte.
- Lead-acid - used in automobile batteries, lead-acid chemistry contains lead and lead-oxide electrodes and a strong, rechargeable electrolyte.
- Lithium-ion - often found in high-end laptops and cell phones, this rechargeable battery chemistry offers excellent power-to-weight ratio.

Electrochemical battery cells can be further divided into four distinct categories:

- Primary cell - is a battery that not rechargeable, and must be discarded after use. Most primary cells use liquid-free electrolytes, and are thus named 'dry cells.'
- Secondary cell - these types of batteries can be recharged by passing current through the circuit in the opposite direction. Secondary batteries can be used as energy storage devices, or as primary cells that can be recharged instead of being discarded.
- Reserve cell - in this kind of battery, a key component of the cell (most often the electrolyte) is separated from the remaining components until just before activation. This structure is most often used in thermal batteries, due to the fact that its structure effectively eliminates the possibility of self-discharge and chemical deterioration.
- Fuel cell - active materials in this type of battery are fed into the cell from an outside source. Fuel cells differ from standard batteries in that they possess the capability to produce electrical energy as long as active materials are fed to the electrodes.