battery

A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars. When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode.

Batteries  are widely  used as  sources of  direct-current  electrical  energy  in automobiles, boats, aircraft, ships, portable  electric/electronic  equipment, and  lighting  equipment. In  some  instances, they  are used as the only  source of  power;  while  in others,  they  are used as  a secondary  or standby  power source. 

                                       A battery  consists of  a number of  cells assembled  in a  common container  and connected together to function  as  a source  of  electrical power.

 THE CELL 

                        A cell is  a device that  transforms chemical energy  into  electrical  energy.  The  simplest  cell, known as either  a galvanic  or voltaic  cell, It  consists of  a piece of  carbon (C)  and a  piece of zinc (Zn) suspended in  a  jar  that contains  a solution of  water  (H20)  and sulfuric acid  (H2So⁴)  called  the electrolyte. 

Simple  voltaic  or  galvanic  cell. The  cell  is  the  fundamental  unit  of  the battery.  A  simple cell consists of  two  electrodes placed in  a container  that  holds the  electrolyte. In  some  cells  the  container  acts  as one of  the electrodes and,  in  this case,  is acted  upon by  the electrolyte.  This will  be  covered in more detail  later. 

Components of Batteries 

A battery / cell consist of three major components and they are cathode, anode and electrolyte. 

Anode (Negative Electrode): 

                                          The anode is an electrode, where the oxidation reaction occurs, which releases electrons to the external circuit and reduced during the electrochemical reaction. In practical, anode is selected based on their efficiency as a reducing agent, high coulombic output (AWg), good conductivity, etc. The following materials can be used for the negative electrode in batteries,

 (i) Metals: Li, Na, Zn, Cd, Pb, etc. 

 (ii) Metal alloys (for example, lithium alloys, where           the alloying elements can be Al, Sn, Si, etc.) and          metal hydrides 

         (LaKi5H,, ZrMn?H,, MgzNiH,, etc.).

 (iii) Carbons (for example graphite carbons, non-graphite carbons).

 (iv) Redox polymers with negative redox potentials. 

Cathode (Positive Electrode): 

                                                The cathode is an electrode where the reduction reaction occurs, which accepts electrons from external circuit and oxidized during the electrochemical reaction. The cathode must be an efficient oxidizing agent, high stability when it is in contact with the electrolyte with use full working voltage. The following are the commonly used cathode materials in batteries, 

(i) Metal oxides (such as Mn02, PbO, etc.) and metal sulfides (such as TiS?, NbS3, MoS2, etc) 

(ii) Insertion or host materials like metal oxides (for example; LIMO?, where M= Co, Ni, Cr, Fe: V and Mn). (iii) Metal oxyhydroxides (NiOOH, PbOOH and MnOOH). 

(iv) Redox polymers with positive redox potentials. 

Electrolyte: 

                The electrolyte is an ionic conductor with negligibly small electronic conduction, which provides the medium for transfer of ions from one electrode to another electrode and also prevent short circuit. Important properties of the electrolyte are non reactivity with electrode materials, small property change with respective to temperature variation, safety in handling, etc. In majority of conventional batteries, the electrolytes are aqueous solutions such as ZnCl*, KOH, etc., but some advanced batteries are fabricated with non aqueous solutions, ion conducting solids or polymers as electrolytes.

How do Batteries Work?

When in operation the electrochemical cell essentially discharges its chemical energy in favor of electric energy. If the cell is connected via an external circuit from the cathode to the anode, electrons flow from the oxidized anode and are received by the cathode, which is subsequently reduced. The electric circuit is completed by cations and anions, within the electrolyte, which flow to the cathode and anode, respectively.