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EC > Batteries and Fuel Cells > Flashcards

Batteries and Fuel Cells Flashcards

1
Q

What is a “Battery“?

A

Portable Source of Electrical Power
* Energy Storage/Conversion Device
* Converts Chemical Energy Into Electrical Energy
* Works on Electrochemistry Principles
* Volta invented in 1800

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2
Q

Battery :- Definition :

A

A battery is a storage device used for the storage of chemical energy and for the transformation of chemical energy into electrical energy

Battery consists of group of two or more electric cells connected together electrically in series.

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3
Q

Chemical

A

Chemical energy converted to thermal energy
* Energy producing chemicals: Fuel and Oxidant
* Fuel and oxidant are brought together. Resultant combustion reaction produces heat
* Fuel + Oxidant → Heat

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4
Q

Electrochemical

A

Chemical energy converted to electrochemical energy
* Energy Producing chemicals: Anode Material, Cathode material * Anode and cathode materials are kept separately
* electrons pass through out side loop
* electrolyte to complete circuit

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5
Q

Battery Terminology

A

Cell-Basic Unit: Contains Anode, Cathode, Electrolyte, Separator etc. * Battery: Contains 2 or more cells in series or parallel
* Discharging: Removing energy from the cell/Battery
* Charging: Returning energy to the cell/battery

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6
Q

Basic Electrochemical Cell: Five essential components of a cell

A

The Anode
* The Cathode
* The Ionic Conductor (electrolyte)
* The Metallic Conductor (electrical connection)
* The separator

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7
Q

The Anode

A

The anode has the lowest potential and is oxidized in the process by a loss of electrons:
Anodic reaction
Oxidation reaction
Electron generation

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8
Q

The Cathode

A

The cathode has a high potential, leading to a consumption of electrons. Cathodic reaction
Reduction reaction
Electron consumption

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9
Q

The Electrolyte

A

A solution conducting ions

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10
Q

The Separator

A

Electrical insulator membrane, allowing ionic transfer and solvent wetting.

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11
Q

Electrical Connections

A

The anode and cathode in an electrochemical cell must be in electrical contact in order to generate power and energy. Difference in free energies between the anode and the cathode produces electrical potential which is the driving force for electrochemical reaction.

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12
Q

Batteries are of 3 types:

A
  1. Primary Batteries (or) Primary Cells
  2. Secondary Batteries (or) Secondary Cells
  3. Fuel Cells (or) Flow Batteries
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13
Q

Primary Batteries (or) Primary Cells

A

Those cells in which the chemical reaction
occurs only once and the cell becomes dead after sometime and it cannot be used again.
These batteries are used as source of DC power. Eg. Dry cell (Leclanche Cell) and Mercury cell.

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14
Q

Requirements of Primary cell:

A

1) It must be convenient to use.
2) Cost of discharge should be low.
3) Stand-by power is desirable.

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15
Q

Dry Cell (Leclanche Cell)

A

Components:
Anode: Zinc (Zn) container
Cathode: Graphite rod surrounded by MnO2 and carbon paste
Electrolyte: Paste of NH4Cl, ZnCl2, MnO2, and starch (thick paste prevents leakage)
Named “dry cell” because: There is no liquid electrolyte, only a thick paste.
Advantages:
Voltage: 1.25V - 1.50V
Low price
Disposable (primary cell)
Used in many devices (torches, radios, etc.)
Disadvantages:
Short lifespan:
NH4Cl corrodes zinc container (even when not in use).
Limited capacity for storing electrical energy.
Not rechargeable (primary cell)

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16
Q

Secondary Cells (Accumulator Batteries)

A

Definition: Rechargeable cells that can be used again and again by passing an electric current through them.
Examples: Lead-acid batteries, Nickel-Cadmium (NiCd) batteries, Lithium-ion (Li-ion) batteries
Applications: Cars, trains, motors, electronics (laptops, cameras), power storage (power stations, emergency lights)
Reversible Cells:
Behave as a galvanic cell during discharge (electricity produced)
Behave as an electrolytic cell during charging (electrical energy used to drive a chemical reaction)

17
Q

Desired Characteristics for Commercial Batteries:

A

High energy density: More energy stored in a smaller volume.
High power density: Can deliver high current quickly.
Good low-temperature performance: Maintain functionality in cold environments.
Stable voltage: Minimal voltage variation during discharge.
High energy efficiency: Maximize the amount of usable energy obtained during discharge (calculated as % of energy recovered compared to energy put in during charging).
Reliability: Consistent performance over time.
Durability: Tolerance to shock, vibration, and temperature extremes.
Cycle life: High number of charge/discharge cycles before failure.

18
Q

Nickel-Cadmium Cell (NiCad Cell)

A

Type: Rechargeable secondary cell
Anode: Cadmium (Cd)
Cathode: Nickel hydroxide (NiO(OH))
Electrolyte: Potassium hydroxide (KOH)
EMF: 1.4 V
Advantages:

Small size and high rate charge/discharge: Makes them versatile for various devices.
Very low internal resistance: Allows for efficient delivery of current.
Wide temperature range (up to 70°C): Can function in extreme temperatures.
Longer life than lead-acid cells: Offers more recharge cycles.
Relatively high voltage (around 1.4V): Provides good power output.
Applications:

Electronic devices: calculators, flash units, transistors
Medical equipment
Emergency lighting
Toys
Note: Due to environmental concerns, Nickel-Metal Hydride (NiMH) batteries are becoming a more preferable alternative to NiCad batteries in many applications.

19
Q

Fuel Cell Definition

A

An electrochemical cell that converts chemical energy from fuel and oxidant into electrical energy.

20
Q

Principle of fuel cell

A

Similar to a regular electrochemical cell, but fuel and oxidant are continuously supplied from external sources.

21
Q

Reactions of fuel cell:

A

Fuel undergoes oxidation at the anode, releasing electrons.
Electrons flow through an external circuit, generating electricity.
Oxidant accepts electrons at the cathode, undergoing reduction.
Overall reaction: Fuel + Oxidant → Oxidation Products + Electricity + Heat (and sometimes water vapor)

22
Q

Examples of fuel cell

A

Examples: Hydrogen-oxygen (H2-O2) fuel cell, propane-oxygen, methanol-oxygen

23
Q

Hydrogen-Oxygen Fuel Cell:

A

Anode: Hydrogen (H2) gas
Cathode: Oxygen (O2) gas
Electrodes: Porous graphite impregnated with platinum (Pt), nickel (Ni), or palladium-silver (Pd-Ag) alloy
Electrolyte: Potassium hydroxide (KOH) solution (2.5%)
Reactions:
Anode: H2 → 2H+ + 2e- (oxidation)
Cathode: ½ O2 + 2H+ + 2e- → H2O (reduction)
Byproducts: Heat, water (H2O), minimal pollutants

24
Q

Applications of fuel cell

A

Auxiliary power source in space vehicles, submarines, military vehicles
Source of fresh water for astronauts (byproduct water)
Preferred power source in spacecraft due to lightweight design

25
Q

Advantages of fuel cell

A

High efficiency (around 70% vs 15-35% for traditional engines)
Efficiency independent of power plant size
Low maintenance cost
More efficient power generation for vehicles, reducing energy consumption

26
Q

Disadvantages of fuel cell

A

High initial cost
Unknown long-term lifespan
Challenges with hydrogen storage and durability

27
Q

Type and application of lead acid battery cell

A

Type: Rechargeable secondary battery (stores and releases energy through chemical reactions)
Applications:
Automobiles (12V battery typically uses 6 cells connected in series)
Power supplies (UPS, etc.)
Railways, mines, laboratories, hospitals
Many other applications requiring portable power

28
Q

Components of lead acid battery cell

A

Components per Cell:
Anode: Lead (Pb)
Cathode: Lead dioxide (PbO2)
Electrolyte: Dilute sulfuric acid (H2SO4) - concentration around 20.22%
Separators: Thin separators between electrodes (may be different materials in modern batteries)

29
Q

Discharging and charging of lead acid battery cell

A

Discharging:
Anode reaction: Pb → PbSO4 + 2e- (oxidation)
Cathode reaction: PbO2 + 4H+ + 4e- → PbSO4 + 2H2O (reduction)
Sulfuric acid (H2SO4) consumed, density decreases (< 1.20 g/cm3 indicates recharge needed)
Charging (reverse of discharge):
Anode reaction: PbSO4 + 2H+ + 2e- → Pb + H2SO4 (reduction)
Cathode reaction: PbSO4 - 2e- → PbO2 + SO4²⁻ (oxidation)
Sulfuric acid (H2SO4) regenerated

30
Q

Advantages and disadvantages of lead acid fuel cell

A

Advantages:
Rechargeable
Portable
Relatively constant voltage
Low cost
Disadvantages:
Concentrated sulfuric acid is dangerous (corrosive)
Lead is toxic (environmental and health concerns)
Limited cycle life compared to some batteries
Requires maintenance (electrolyte level and density)
Not ideal for high-drain applications (slower discharge rates)

EC (10 decks)

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