“Secondary-Batteries”

Chemistry for Engineers

Submitted by

Ratnesh kanungo

15BIT0257

B.Tech (IT) “VIT University, (Vellore)”

……….What is Battery………. A battery is an electrochemical cell (or enclosed and protected material) that can be charged electrically to provide a static potential for power or released electrical charge when needed.

OR

A container consisting of one or more cells, in which chemical energy is converted into electricity and used as a source of power.

OR

THE COMBINATIONS OF TWO OR MORE CELL IS CALLED “BATTERY”

Secondary Batteries

OR Rechargeable Batteries

• Rechargeable batteries are batteries that can be restored to full charge by the application of electrical energy.

• Rechargeable batteries come in different designs using different chemical reactions.

• Rechargeable batteries are also called storage batteries or secondary cells.

TYPES OF SECONDARY BATTERY:

Lead-acid Batteries

Nickel-cadmium Battery

Nickel-metal Hydride Battery

Lithium-ion Battery

Lead-acid battery

This battery is used in automobiles. The electrodes are made of lead and lead-oxide with a strong acidic electrolyte.

Lead-acid batteries are the most commonly used rechargeable batteries today.

Lead-acid battery• The chemical reactions are (charged to

discharged):

Anode (oxidation):

Pb(s) + SO42- (aq) « PbSO4 (s) + 2e-

• Cathode (reduction):

PbO2(s) + SO42- (aq) + 4H+ + 2e- « PbSO4 (s) +

2H2O (l)

NICKEL-CADMIUM BATTERY

The electrodes are nickel-hydroxide and cadmium, with potassium-hydroxide as the electrolyte.

The nickel–cadmium battery (NiCd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.

Nickel Cadmium Batteries (Ni-Cd)

Normal service life is 20-25 years.

Nominal cell voltage is 1.2 V/cell

Initial cost may be approximately three times

Used in hazardous environment such as chemical, fertilizer, cement industry.

Batteries occasionally demand boost charging, 1.4 V/cell

Nickel-metal Hydride Battery

This battery does not contain cadmium and is used in hybrid or electric vehicles. The electrodes are nickel-hydroxide and rare earth metals, with potassium-hydroxide as the electrolyte.

• The reaction occurring in a NiMH battery is as follows: H2O + Mm + 2e- « OH− + ½ H2 (stored as Mm-Hx)

• The battery is charged in the right direction of this equation and discharged in the left direction.

• Mm stands for misch metal (from German: "mixed metals") is an unintentional alloy of rare earth elements in various naturally-occurring proportions.

Nickel-metal Hydride Battery

Anode (NiCad):

Cd(s) + 2OH- (aq) X Cd (OH)2(s) + 2e- (NiMH) MH(s) + OH- (aq) X M(s) + H2O(l) + e

Cathode:

NiO (OH) (s) + H2O (l) + e- X Ni(OH)2(l) + OH- (aq)

Ecell = 1.2-1.4 V

(Fairly constant during discharge)

Products adhere to electrodes - reactions can be reversed by charging.

Disposal of cadmium a problem (NiCad). Used in calculators, cordless appliances and portable power tools.

Lithium Ion Battery anode

This battery has a large ratio of power to weight and is used in high-end laptop computers and cell phones.

Lithium Ion Battery anode: Li(in polymer) X Li+ (in polymer) + e cathode: Li+ (in CoO2) + e- + CoO2 X LiCoO2 Rechargeable, long life, higher voltage (Ecell = 3.4

V) . Used in portable computers, cellular phones,

cameras.

Lithium Ion Battery anode

• The anode is made from carbon.

• The cathode is a metal oxide such as CoO2.

• The electrolyte is a lithium salt in an organic solvent, such as ether.

• Since the lithium metal is very reactive and explosive, Li-ion cells usually have built-in protective electronics and/or fuses to prevent polarity reversal, over-voltage and over-heating.

SECONDARY BATTERY:-

Higher initial cost. Lower life-cycle cost ($/kWh) if charging in

convenient and inexpensive. Regular maintenance required. Periodic recharging required. Replacements while available are not produced in the

same sheer numbers as primary batteries. May need to be pre-ordered.

Traditionally less suited for portable applications, although recent advances in Lithium battery technology have lead to the development of smaller/lighter secondary batteries.

Relative to primary battery systems, traditional secondary batteries (particularly aqueous secondary batteries) exhibit inferior charge retention.

Superior high discharge rate performance at heavy loads

 

…..Conclusion….. • Secondary batteries are able to

undergo the reverse chemical reaction changes efficiently to allow them to be restored to almost the same fully charged condition on each recharging.

………………THANK YOU…………….