Chapter 4: 4.4 Batteries

Question 1

Define:

Battery

Answer 1

A device that converts the chemical energy stored in its active materials into electrical energy

Question 2

How are batteries classified?

Answer 2

• Primary
• Secondary

Question 3

What are characteristics of primary batteries?

Answer 3

• Can only be used once
• Cannot be recharged, once it dies it is dead

Question 4

What are some characteristics of secondary batteries?

Answer 4

• Rechargeable

Question 5

What are the reasons that a battery dies?

Answer 5

1. ΔG = 0
2. Limiting reagent used up

Question 6

What was the world’s first recheargeable battery? Describe it

Answer 6

Lead-Acid Battery
* A spiral roll of two sheets of pure lead
* Separated by a linen cloth
* Immersed in a sulfuric acid solution

Later made into a 9-cell version

Question 7

What are key characteristics of a Lead-Acid Battery?

Answer 7

• Cheap, available components
• Low energy density
• High currents generated in short periods of time

Question 8

How is a lead-acid battery recharged? What can this reaction be classified as?

Answer 8

Recharged by the current provided by the alternator (in a car)
A disproportionation reaction

Question 9

What are the key characteristics of a Nickel-Cadmium (NiCd) Battery?

Answer 9

• Rechargeable
• Inexpensive
• Memory-effect
• Toxic
• Heavy

Question 10

State:

The reactions for the cathode and anode of a lead-acid battery

Answer 10

1. Anode: Pb to PbSO4
2. Cathode: PbO2 to PbSO4

Question 11

State:

The reactions for the cathode and anode of a nickel-cadmium battery

Answer 11

1. Anode: Cd to CdO
2. Cathode: NiO2 to NiO

Question 12

Define:

Memory effect

(in NiCd batteries)

Answer 12

Gradually lose their maximum energy capacity after repeated recharging when they are not fully discharged (remembers the smaller capacity and only charges tot that level)

Question 13

In a NiCd battery, what is memory effect caused by?

Answer 13

Due to crystal buildup; can be reversed by deep discharge and recharge

Question 14

What are key characteristics to Nickel-Metal Hydride (NiMH) batteries?

Answer 14

• “Improved” NiCd batteries
• No toxicity
• Much less memory effect
• Better energy-to-weight ratio

Question 15

State:

The reactions of the anode and cathode of a NiMH battery

Answer 15

1. Anode: MH to M (MH stands for metal alloy)
2. Cathode: NiO(OH) to Ni(OH)2

Question 16

What are key characteristics of Lithium ion (Li-ion) batteries?

Answer 16

• Lightweight
• High energy density/energy-to-weight ratio
• Expensive

Question 17

True or False:

Li+ ions are oxidized/reduced in a Li-ion battery

Answer 17

False, they undergo intercalation

Question 18

What happens in a Li-ion battery? Describe the reactions at the anode and cathode of the battery

Answer 18

• Electrons flow to maintain charge neutrality as Li+ move
• Co is reduced during discharge

1. Anode (graphite): LiC6 to Li+
2. Cathode (CoO2): CoO2 to LiCoO2

Question 19

True or False:

Various cathode materials can be used in an Li-ion battery

Answer 19

True

Question 20

What are the downsides of Li-ion batteries?

Answer 20

• Can rupture, ignite, and/or explode when sujected to high temperature or overcharging
• Short circuits and electrolyte breakdown, causing fires
• Cannot deliver high currents

Question 21

What is a Lithium-Polymer (Li-Pol) Battery?

Answer 21

A variation in lithium battery technology
* Uses a polymer (solid phase) electrolyte between the two electrodes
* As a result, a cyclindrical container is usually used to hold the max amount of reagents

Question 22

What is an advantage of using a polymer electrolyte as opposed to using a liquid electrolyte?

Answer 22

Allows materials to be stacked with little chance of two electrodes coming into contact (means that these batteries can be made into virtually any shape)