Revision•Define a battery•State five practical applications of batteries•What is electrolysis?•What is an electrolyte?•What are positive and negative terminal are called?•Make a labelled sketch of a simple cell•What is a difference between primary and a secondary cell? name two types and three applications of each.

Secondary (Rechargeable) Batteries• Nickel cadmium

• Nickel metal hydride

• Alkaline

• Lithium ion

• Lithium ion polymer

• Lead acid

Lead acid battery;• Invented by French physicist GASTAN PLANTE

• Oldest rechargeable battery

• Nominal cell voltage is 2.105v

• Second lowest energy-to-weight ratio (next to the nickel-iron battery)

Construction; • consist of Lead &Lead Oxide

electrodes

• Which are dipped in Sulphuric

acid

• Normal Lead acid battery is

six cell battery

• Separators are present in between electrodes

Separators• wood

• rubber

• glass fiber mat

• cellulose

• sintered PVC

• micro porous PVC/polyethylene.

Cells and Batteries

Construction of lead-acid battery (cont....)

Cells and Batteries

Working of Lead-acid battery (cont….)

Discharging reactions

Anode reaction:

Cathode reaction:

Cells and Batteries

Working of Lead-acid battery (cont….) Recharging reactions

Anode reaction:

Cathode reaction:

Figure 7 One of the Cells in a 12-V Lead Storage Battery (LSM 14.1C)

applications• Submarines

• Motor car ignition

• Industries

• To maintain required

voltages in sub stations

Cells and Batteries

Limitations of Lead acid battery

• More amounts of materials should be taken. Because, the products lead sulphate and water are poor conductors of electricity. Moreover, acid gets progressively diluted.

• Optimal charging and discharging should be done to avoid the loss of efficiency.

• Wrong polarity connection should be avoided.

• Acid concentration and proper connections should be monitored /checked frequently.

ALKALINE BATTERIESDescription• Alkaline batteries and alkaline cells (a battery

being a collection of multiple cells) are a type of disposable battery or rechargeable battery dependent upon the reaction between zinc and manganese(IV) oxide (Zn/MnO2).

• Alkaline battery is an improved dry cell.

• The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide, as opposed to the acidic electrolyte of the zinc-carbon batteries

• Zinc in a powdered form increases the surface area of the anode, allowing more particle interaction. This lowers the internal resistance and increases the power density

Construction• A cylindrical cell is contained in a drawn steel can, which

is the cathode current collector.

• The cathode mixture is a compressed paste of manganese dioxide with carbon powder added for increased conductivity.

• The hollow center of the cathode is lined with a separator, which prevents mixing of the anode and cathode materials and short-circuiting of the cell.

• The separator is made of a non-woven layer of cellulose or a synthetic polymer. The separator must conduct ions and remain stable in the highly alkaline electrolyte solution.

• The anode is composed of a dispersion of zinc powder in a gel containing the potassium hydroxide electrolyte. To prevent gassing of the cell at the end of its life, more manganese dioxide is used than required to react with all the zinc.

Chemistry

Anode : Zinc Powder

Cathode : Manganese dioxide(MnO2) powder

Electrolyte : Potassium hydroxide(KOH)

Half cell reactions

• Anode(Oxidation) :

Zn (s) + 2OH− (aq) → ZnO(s) + H2O (l) + 2e−

• Cathode(Reduction) :

2MnO2 (s) + H2O (l) + 2e− →Mn2O3 (s) + 2OH− (aq)

• The overall reaction is:

Zn + 2MnO2 —> ZnO + Mn2O3 ;E=1.5 V

Advantages

• Better low temperature performance than zinc carbon. Continue to function in sub-zero temperatures.

• Available in a wide range of sizes including AAA, AA, C, D and 9Volt sizes.

• Suitable for a wide range of consumer applications

• Made from non toxic chemicals

• No voltage drop and longer shell life than dry cell because of alkaline electrolyte

• Up to ten times the service life of regular zinc-carbon cells.

• Low internal resistance.

• Good low temperature performance.

• Excellent leakage resistance.

• Alkaline batteries do not have a carbon rod cathode, which allow them to be smaller.

CONSTRUCTION OF ALKALINE BATTERIES• http://www.youtube.com/watch?v=ksxSOwA933M

Nickel-Cadmium Battery

Cathode NiO(OH) 

Anode Cd

Separator  NaOH

NICKEL CADMIUM BATTERIES• NICKEL HYDROXIDE (POSITIVE ELCTRODE)

• CADMIUM HYDROXIDE (NEGATIVE ELECTRODE)

• POTASSIUM HYDROXIDE (ELECTROLYTE)

• SEPERATOR

• CHEMICAL REACTION:

• NORMALLY 19 TO 20 CELLS ARE USED

WORKING OF NiCd BATTERIES

• Nickel-Cadmium battery:- the reactions look something like this: 

Oxidation:-

Cd(s) + 2 OH- (aq) → Cd(OH)2(s) + 2 e-

Reduction:-

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

Net:-

Cd(s) + 2NiO(OH)(s) + 2 H2O(l) → Cd(OH)2(s) + 2Ni(OH)2(s)

Electrons moving from one place to another – this is electricity

Numbers of electrons in oxidation and reduction must be same.

Nickel cadmium batteries

• Advantages

• Fast and simple charge even after prolonged storage.

• High number of charge/discharge cycles — if properly maintained, the NiCd provides over 1000 charge/discharge cycles.

• Long shelf life – in any state-of-charge.

• Simple storage and transportation — most airfreight companies accept the NiCd without special conditions.

• Good low temperature performance.

• Forgiving if abused — the NiCd is one of the most rugged rechargeable batteries.

• Economically priced — the NiCd is the lowest cost battery in terms of cost per cycle.

• Available in a wide range of sizes and performance options (most NiCd cells are cylindrical.)

• Limitations:

• Relatively low energy density compared with newer systems.

• Memory effect: The NiCd must periodically be exercised to prevent memory.

• Environmentally unfriendly: the NiCd contains toxic metals. Some countries are limiting the use of the NiCd battery.

• Has relatively high self-discharge: needs recharging after storage.

NICKEL CADMIUM BATTERIES

Lithium Manganese Dioxide• Chemistry

Lithium (-), manganese dioxide (+)

Alkali metal salt in organic solvent electrolyte

• Features

+ High energy density

+ Long shelf life (20 years at 70°C)

+ Capable of high rate discharge

• Expensive

Nickel Metal Hydride (NiMH)

• The nickel-metal hydride battery chemistry is a

hybrid of the proven positive electrode chemistry of

the sealed nickel-cadmium battery with the energy

storage features of metal alloys developed for

advanced hydrogen energy storage concepts. This

heritage in a positive-limited battery design results in

batteries providing enhanced capacities while

retaining the well-characterized electrical and

physical design features of the sealed nickel-

cadmium battery design.

Nickel Metal Hydride (NiMH)• ADVANTAGES:

• 30 – 40 percent higher capacity over a standard NiCd. The NiMH has potential for yet higher energy densities.

• Less prone to memory than the NiCd. Periodic exercise cycles are required less often.

• Simple storage and transportation — transportation conditions are not subject to regulatory control.

• Environmentally friendly — contains only mild toxins; profitable for recycling.

• Elimination of the constraints on battery manufacture

• Simplified incorporation into products

• Greater service advantage over other primary battery types at low temperature extremes operating at -20°C

limitations• High self-discharge — the NiMH has about

50 percent higher self-discharge compared to the NiCd. New chemical additives improve the self-discharge but at the expense of lower energy density.

• High maintenance — battery requires regular full discharge to prevent crystalline formation.

• About 20 percent more expensive than NiCd — NiMH batteries designed for high current draw are more expensive than the regular version.

• Limited service life

• Limited discharge current 

Negative Electrode

• The basic concept of the nickel-metal hydride battery

negative electrode emanated from research on the storage of

hydrogen for use as an alternative energy source in the

1970s. Certain metallic alloys were observed to form hydrides

that could capture (and release) hydrogen in volumes up to

nearly a thousand times their own volume. By careful

selection of the alloy constituents and proportions, the

thermodynamics could be balanced to permit the absorption

and release process to proceed at room temperatures. The

metal hydride electrode has a theoretical capacity >40

percent higher than the cadmium electrode in a nickel-

cadmium couple. As a result, nickel-metal hydride batteries

provide energy densities that are >20 percent higher than

the equivalent nickel-cadmium battery.

• Battery Construction

• The nickel-metal hydride couple lends itself to the wound construction shown in (Fig. 1), which is similar to that used by cylindrical nickel-cadmium, LI ion and primary lithium batteries. The basic components consist of the positive and negative electrodes insulated by separators. The sandwiched electrodes are wound together and inserted into a metallic can that is sealed after injection of electrolyte. Nickel-metal hydride batteries are typically sealed designs with metallic cases and tops that are electrically insulated from each other. The case serves, as the negative terminal for the battery while the top is the positive terminal. Finished battery designs may use a plastic insulating wrapper shrunk over the case to provide electrical isolation between cells in typical battery applications. Nickel-metal hydride batteries contain a resealable safety vent built into the top, as shown in (Fig. 4). The nickel-metal hydride battery is designed so the oxygen recombination cycle described earlier is capable of recombining gases formed during overcharge under normal operating conditions, thus maintaining pressure equilibrium within the battery. However, in cases of extended overcharge or incompatible battery/charger combinations for the operating environment, it is possible that oxygen, and hydrogen, will be generated faster than it can be recombined. In such cases the safety vent will open to reduce the pressure and prevent battery rupture. The vent reseals once the pressure is relieved. The expulsion of gas thru the resealable vent can carry electrolyte, which may form crystals or rust once outside the can.

Electrochemistry:• Discharge

• At the negative electrode, the hydrogen is desorbed and combines with a hydroxyl ion to form water while also

• contributing an electron to the circuit.

Alloy (H) + OH`‹----------------› Alloy + H2O + e`

• At the positive electrode, nickel oxyhydroxide is reduced to its lower valence state, nickel hydroxide.

NiOOH + H2O + e`‹------------------› Ni(OH)2 + OH`

Hazards: EXPLOSION

• A battery explosion is caused by the misuse or malfunction of a battery, such as attempting to recharge a primary (non-rechargeable) battery,[70] or short circuiting a battery.[71] With car batteries, explosions are most likely to occur when a short circuit generates very large currents

• When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and the possibility of bursting of the battery case. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury. Overcharging—

• That is, attempting to charge a battery beyond its electrical capacity—can also lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the charger or device in which the overcharged battery is later used. In addition, disposing of a battery in fire may cause an explosion as steam builds up within the sealed case of the battery.[71]

Leakage

• Many battery chemicals are corrosive, poisonous, or both. If leakage occurs, either spontaneously or through accident, the chemicals released may be dangerous.

• For example, disposable batteries often use zinc "can" as both a reactant and as the container to hold the other reagents. If this kind of battery is run all the way down, or if it is recharged after running down too far, the reagents can emerge through the cardboard and plastic that forms the remainder of the container. The active chemical leakage can then damage the equipment that the batteries were inserted into. For this reason, many electronic device manufacturers recommend removing the batteries from devices that will not be used for extended periods of time.

Environmental concerns

• The widespread use of batteries has created many environmental concerns, such as toxic metal pollution. Battery manufacture consumes resources and often involves hazardous chemicals. Used batteries also contribute to electronic waste.

Lithium v Alkaline Discharge