BATTERY CHEMISTRY and CORROSION chemistry.pptx

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1. BATTERY CHEMISTRY & CORROSION By Dr. Saumyaprava Acharya

2. Introduction It is a device consisting of two or more galvanic cells connected in series or parallel or both to obtain higer potential An active Chemical Material which Convert into an Electrical Energy. The size & design of battery varies from w.r.t. the applications.

3. Components of Battery Anode Material/ Alloy: Oxidation Cathode Material/ Alloy: Reduction Separator : to avoid Electrical contact between two Anode and Cathode electrodes Electrolyte: conducting ion moves between two electrode

4. Types of Battery Batteries are Classified into Three types: Primary Cells Secondary Cells Reserved Battery Primary Cells: the potential of battery as use of Free energy of active material as long as present inside the battery. These cell reaction are not reversible and not rechargeable. Ex: Dry cell (Zn-MnO 2 )

5. 2. Secondary Cells : Batteries are Rechargeable. The cell reactions are reversible so called reversible batteries. During discharging the cell works galvanic cell converting chemical energy into electrical energy. During charging the cell works electrolytic cell by converting electric energy into chemical energy, hence these batteries are called as storage battery. Ex: Lead acid Battery, Ni- Cd battery etc.

6. 3. Reserve Battery Reserve batteries are high current battery and long shelf life. The electrolyte component of battery is isolated(missing) These battery activated by contacting active isolated component when ever need high potential. Used to deliver high potential for shorter periods of time such as missiles, military applications etc. Ex: Zn-Ag 2 O- active material water. Mg-AgCl activated by water

7. Bbasic requirement for Battery: EMF Current: Current is a measure of the rate at which the battery is discharging. Higher the surface area of the electrodes, higher is the rate of reaction. Current is measured in A. Capacity: total energy obtained until the end of battery failure Efficiency Cycle life Power Density (w/Kg) Shelf Life

8. Zinc-air batteries Zinc-air batteries and Zinc-air Fuel Cells are metal air batteries which are powered by oxidizing Zinc with oxygen from the air. Zinc-air batteries have high energy density Zinc air batteries range from Button Cell, Film Cameras, Electric Vehicle Propulsion

9. ZINC AIR BATTERIES

10. CONSTRUCTION & WORKING PRIMARY (NON-RECHARGEABLE) Button cell type and 1Ah type SECONDARY (RECHARGEABLE)

11. WORKING In Zinc-air battery the Oxygen from the air reacts at the cathode and forms hydroxyl ions which migrate into the zinc paste and form zincate (Zn(OH) 2− 4 ), releasing electrons to travel to the cathode. The zincate decays into zinc oxide and water returns to the electrolyte. The water and hydroxyl from the anode are recycled at the cathode, so the water is not consumed. The reactions produce a theoretical 1.65 volts, but this is reduced to 1.35–1.4 V in available cells.

12. REACTIONS SIZE – AAA CAPACITY – 3600 mAh VOLT – 1.3 V WEIGHT – 11.7 Gms Sp. ENERGY – 400 mW /gm SHELF LIFE- 3 Years

13. advantages

14. Disadvantages

15. Lithium-ion battery (Li-ion Battery) 16 Li-ion batteries are secondary batteries. The battery consists of a anode of Lithium, dissolved as ions, into a carbon. The cathode material is made up from Lithium liberating compounds, typically the three electro-active oxide materials, Lithium Cobalt-oxide (LiCoO 2 ) Lithium Manganese-oxide (LiMn 2 O 4 ) Lithium Nickel-oxide (LiNiO 2 )

16. 17 Principle During the charge and discharge processes, lithium ions are inserted or extracted from interstitial space between atomic layers within the active material of the battery. Simply, the Li-ion is transfers between anode and cathode through lithium Electrolyte. Since neither the anode nor the cathode materials essentially change, the operation is safer than that of a Lithium metal battery. The chemical reaction that takes place inside the battery is as follows, during charge and discharge operation:

17. Li-ion Battery

18. Advantages They have high energy density than other rechargeable batteries They are less weight They produce high voltage out about 4 V as compared with other batteries. They have improved safety, i.e. more resistance to over voltage. No liquid electrolyte means they are immune from leaking. . Fast charge and discharge rate Disadvantage They are expensive They are not available in standard cell types .

19. 20 Applications The Li-ion batteries are used in cameras, calculators They are used in cardiac pacemakers and other implantable device They are used in telecommunication equipment, instruments, portable radios and TVs, pagers They are used to operate laptop computers and mobile phones and aerospace application

20. The cell that converts energy of combustion of fuels like Hydrogen, Methane to electrical energy. Fuels are usually gas or liquid, with oxygen as the oxidant..… Different fuel cells are The direct conversion of chemical energy to electrical energy has 100%. The cell representation is as follows. Fuel/electrode//electrolyte//electrode//oxidant Types of Fuels: 1.Hydrogen – Oxygen Fuel cell 2.Methanol –Oxygen fuel cell FUEL CELLS

21. Large weight and volume of hydrogen gas fuel storage system High cost of Hydrogen gas, technological advances should bring the cost down Lack of infrastructure for distribution and marketing of Hydrogen gas. Most basic fuel cells suffer from carbon di oxide leakages and should be prevented from entering the cell and reacting with the electrolyte. LIMITATIONS OF FUEL CELLS

22. CH 3 OH-oxygen fuel cell At anode: CH 3 OH + H 2 O CO 2 + 6H + + 6e - At cathode : 3/2 O 2 + 6H + + 6e -  3H 2 O Net rxn : CH 3 OH + 3/2 O 2  CO 2 + 2H 2 O  Electrolyte- sulphuric acid . Through the anode , Methanol and H 2 O T hrough the cathode O 2 gas bubbled. Emf:1.2 V

23. Methanol – Oxygen Fuel Cell Direct methanol fuel cells or DMFCs are using methanol as the fuel. Methanol and H 2 O is passed through anodic compartment. Oxygen is passed through cathodic compartment. Electrolyte consists of sulphuric acid. A membrane is provided which prevents the diffusion of methanol into the cathode. Advantages Methanol has low carbon content The OH group is easily oxidisable Methanol is highly soluble in water Product CO 2 is less toxic

24. Application They can produce a small amount of power over a long period of time. This makes them ill-suited for powering large vehicles, but ideal for smaller vehicles. Military applications of DMFCs are an emerging application since they have low noise and thermal signatures and no toxic effluent. Used in space craft : due to their lightness & product water is available as source of fresh water for astronauts ( ex: Apollo space craft)

25. Solid Oxide Fuel Cells (SOFC) are a type of fuel cell that use a solid oxide material as the electrolyte to conduct negative oxygen ions from the cathode to the anode. Fuels using in this type must contain hydrogen ions. EMF = 1V (0.6 to 0.7 V practically) Anode : Co-ZrO 2 to which fuel is passing and hydrogen from the fuel is electrochemically oxidized to water 2H 2 + 2O 2- → 2H 2 O + 4e Cathode : LaMnO 3 porous layered material to which air/oxygen is passing and electrochemical reduction of oxygen occurs here. This oxide ions migrate through electrolyte to the anodic part O 2 + 4e → 2O 2- Electrolyte : Oxygen ion conducting ceramic such as Yttria-doped zirconia (YSZ). SOLID OXIDE FUEL CELLS (SOFC)

26. The driving force for the migration of O 2– is the oxygen chemical potential gradient between the anode (low) and cathode (high). Overall Reaction: 2H 2 + O 2 → 2H 2 O + Heat + Electrical energy

27. Principle Oxygen supplied at the cathode (air electrode) reacts with incoming electrons from the external circuit to form oxide ions, which migrate to the anode (fuel electrode) through the oxide ion conducting electrolyte. At the anode, oxide ions combine with H 2 (and/or CO) in the fuel to form H 2 O (and/or CO 2 ), liberating electrons. Electrons (electricity) flow from the anode through the external circuit to the cathode. Work at high temperature. Advantages Because the electrolyte is solid, the cell can be cast into various shapes, such as tubular, planar etc and also reduces corrosion Less cost

28. Due to high temperature, no need of precious catalyst like platinum Waste heat from SOFC can be reused Disadvantages: The high temperature of the SOFC has its drawbacks. The high operating temperature places severe constraints on materials selection and results in difficult fabrication processes. Slow startup time, so less useful for mobile applications Applications Transport sector: auxiliary power in vehicles, bus, car etc Using planar SOFCs in stationary power generation systems

29. Recap : Photo means light in Greek and Volt is the name of a pioneer in the study of electricity Alessandro Volta Solar cell: Solar cell is a photovoltaic device that converts the light energy into electrical energy based on the principles of photovoltaic effect Albert Einstein was awarded the 1921 Nobel Prize in physics for his research on the photoelectric effect—a phenomenon central to the generation of electricity through solar cells . In the early stages, the solar cell was developed only with 4 to 6 % efficiency( because of inadequate materials and problems in focusing the solar radiations). But, after 1989, the solar cells with more than 50% efficiency was developed. 1. Introduction

30. Three generations of solar cells First Generation First generation cells consist of large-area, high quality and single junction devices. First Generation technologies involve high energy and labour inputs which prevent any significant progress in reducing production costs. Second generation Second generation materials have been developed to address energy requirements and production costs of solar cells. Alternative manufacturing techniques such as vapour deposition and electroplating are advantageous as they reduce high temperature processing significantly

31. Materials for Solar cell Solar cells are composed of various semiconducting materials Crystalline silicon Cadmium telluride Copper indium diselenide Gallium arsenide Indium phosphide Zinc sulphide Note: Semiconductors are materials, which become electrically conductive when supplied with light or heat, but which operate as insulators at low temperatures

32. Over 95% of all the solar cells produced worldwide are composed of the semiconductor material Silicon (Si). As the second most abundant element in earth`s crust, silicon has the advantage, of being available in sufficient quantities. To produce a solar cell, the semiconductor is contaminated or "doped". "Doping" is the intentional introduction of chemical elements into the semiconductor. By doing this, depending upon the type of dopant, one can obtain a surplus of either positive charge carriers (called p-conducting semiconductor layer) or negative charge carriers (called n-conducting semiconductor layer).

33. If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers. By doping trivalent element, we get p-type semiconductor. (with excess amount of hole) By doping pentavalent element, we get n-type semiconductor ( with excess amount of electron) n-type semiconductor p- type semiconductor p-n junction layer

34. Photovoltaic effect Definition: The generation of voltage across the PN junction in a semiconductor due to the absorption of light radiation is called photovoltaic effect. The Devices based on this effect is called photovoltaic device. Light energy n-type semiconductor p- type semiconductor Electrical Power p-n junction

35. electron-hole formation Photovoltaic energy conversion relies on the number of photons strikes on the earth . (photon is a flux of light particles) On a clear day, about 4.4 x 10 17 photons strike a square centimeter of the Earth's surface every second. Only some of these photons - those with energy in excess of the band gap - can be converted into electricity by the solar cell. When such photon enters the semiconductor, it may be absorbed and promote an electron from the valence band to the conduction band.

36. Therefore, a vacant is created in the valence band and it is called hole. Now, the electron in the conduction band and hole in valence band combine together and forms electron-hole pairs . hole Valence band Conduction band electron Photons

37. A solar panel (or) Solar array Single solar cell The single solar cell constitute the n- typpe layer sandwiched with p-type layer. The most commonly known solar cell is configured as a large-area p-n junction made from silicon wafer . A single cell can produce only very tiny amounts of electricity It can be used only to light up a small light bulb or power a calculator. Single photovoltaic cells are used in many small electronic appliances such as watches and calculators

38. N-type P-type Single Solar cell

39. Solar panel (or) solar array (or) Solar module The solar panel (or) solar array is the interconnection of number of solar module to get efficient power. A solar module consists of number of interconnected solar cells. These interconnected cells embedded between two glass plate to protect from the bad whether. Since absorption area of module is high, more energy can be produced.

40. A proper metal contacts are made on the n-type and p- type side of the semiconductor for electrical connection Working: When a solar panel exposed to sunlight , the light energies are absorbed by a semiconduction materials. Due to this absorded enrgy , the electrons are libereted and produce the external DC current. The DC current is converted into 240-volt AC current using an inverter for different applications.

41. Mechanism: First, the sunlight is absorbed by a solar cell in a solar panel. The absorbed light causes electrons in the material to increase in energy . At the same time making them free to move around in the material. However, the electrons remain at this higher energy for only a short time before returning to their original lower energy position. Therefore, to collect the carriers before they lose the energy gained from the light, a PN junction is typically used.

42. A PN junction consists of two different regions of a semiconductor material (usually silicon), with one side called the p type region and the other the n-type region. During the incident of light energy, in p-type material, electrons can gain energy and move into the n-type region . Then they can no longer go back to their original low energy position and remain at a higher energy. The process of moving a light- generated carrier from p-type region to n-type region is called collection . These collections of carriers (electrons) can be either extracted from the device to give a current , or it can remain in the device and gives rise to a voltage. The electrons that leave the solar cell as current give up their energy to whatever is connected to the solar cell, and then re-enter the solar cell . Once back in the solar cell, the process begins again

43. The mechanism of electricity production- Different stages Conduction band High density Valence band Low density E The above diagram shows the formation of p-n junction in a solar cell. The valence band is a low-density band and conduction band is high-density band.

44. Stage-1 Therefore, the hole (vacancy position left by the electron in the valence band) is generates. Hence, there is a formation of electron-hole pair on the sides of p-n junction. When light falls on the semiconductor surface, the electron from valence band promoted to conduction band. Conduction band High density Valence band Low density E

45. Stage-2 In the stage 2, the electron and holes are diffuse across the p-n junction and there is a formation of electron-hole pair. Conduction band High density Valence band Low density E junction

46. Stage-3 In the stage 3, As electron continuous to diffuse, the negative charge build on emitter side and positive charge build on the base side. Conduction band High density Valence band Low density E junction

47. Stage-4 When the PN junction is connected with external circuit, the current flows . Conduction band High density Valence band Low density E junction Power

48. Advantage, disadvantage and application of Solar cell Advantage It is clean and non-polluting It is a renewable energy Solar cells do not produce noise and they are totally silent. They require very little maintenance They are long lasting sources of energy which can be used almost anywhere They have long life time There are no fuel costs or fuel supply problems

49. Disadvantage Soar power can be obtained in night time Soar cells (or) solar panels are very expensive Energy has not be stored in batteries Air pollution and whether can affect the production of electricity They need large are of land to produce more efficient power supply

50. Applications Soar pumps are used for water supply. Domestic power supply for appliances include refrigeration, washing machine, television and lighting Ocean navigation aids: Number of lighthouses and most buoys are powered by solar cells Telecommunication systems: radio transceivers on mountain tops, or telephone boxes in the country can often be solar powered Electric power generation in space : To providing electrical power to satellites in an orbit around the Earth