Batteries

Question 1

What is the purpose of a battery?

Answer 1

To store energy in electrochemical form and release that energy on demand.

Question 2

Define a redox reaction.

Answer 2

A type of chemical reaction where the reactions are either reduced or oxidized by gaining or losing electrons (respectively).

Question 3

Which electrode does oxidation occur at in a galvanic cell?

Answer 3

Anode (remember: AnOx)

Question 4

Which electrode does reduction occur at in a galvanic cell?

Answer 4

Cathode (remember: RedCat)

Question 5

Which is the difference between a cell and a battery?

Answer 5

A cell is the smallest individual electrochemical storage unit. A battery is a group of cells connected together to form a larger storage unit.

Question 6

In what ways can cells be connected to form a battery?

Answer 6

Either in series or in parallel

Question 7

What is the difference between a primary and secondary cell? What is a secondary cell often termed?

Answer 7

Primary cells are single discharge, secondary cells can be recharged and discharged multiple times. Secondary cells are often called ‘rechargeable.’

Question 8

When a galvanic cell discharges, electrons are removed from the cathode and released into the anode. How does the cell still stay electrically neutral?

Answer 8

Charged species are drawn across the electrolyte/salt bridge to balance out the movement of charge.

Question 9

What is the relationship between a spontaneous reaction and Gibb’s free energy?

Answer 9

If the change in Gibb’s free energy is negative for a reaction, that reaction will be spontaneous.

Question 10

True or False: ΔrG = ΣΔG(products) - ΣΔG(reactants)

Answer 10

True

Question 11

True or False: ΔrG = ΣΔG(reactants) - ΣΔG(products)

Answer 11

False

Question 12

True or False: E(cell) = E(red) + E(ox)

Answer 12

True

Question 13

How can we tell where the energy of a cell is stored?

Answer 13

If | Δmetal G | > | Δion G | then more energy is stored as “lattice cohesive energy”, rather than “ionization energy of metal atoms in water.” Vice versa.

Question 14

What is the energy transformation that occurs during the discharge of a galvanic cell?

Answer 14

Chemical energy -> electrical energy

Question 15

What type of system is a battery?

Answer 15

Close system (mass and charged conserved, energy transfer through system boundary)

Question 16

A battery will be labelled with its ‘nominal voltage’ and ‘nominal capacity’. In these cases, what does ‘nominal’ mean?

Answer 16

Average or typical

Question 17

A battery will be labelled with its ‘nominal capacity’. Give the definition and the units for this quantity.

Answer 17

It is the (average) steady quantity of charge the battery can release over an hour. It is the integral of current with respect to time. Typical units are ampere hours (Ah).

Question 18

What are three factors that the voltage of a battery depends on?

Answer 18

Internal resistance of battery, chemical components, arrangement of cells (i.e. series or parallel).

Question 19

What component of a cell is often called a ‘charge reservoir’?

Answer 19

Electode

Question 20

Fill in the blank:

A cell inside a rechargeable battery is similar to a galvanic cell, but the salt bridge is replaced with a _____ _____.

Answer 20

Electrolyte solution

Question 21

What electrolyte is used in a PbA (lead acid) battery? Which species inside the cell is reduced when the battery discharges? Which is oxidised?

Answer 21

Electrolyte = dilute sulfuric acid. Pb4+ ions (part of the PbO2 lattice) are reduced. Pb(s) atoms are oxidised.

Question 22

When a PbA battery discharges, there is a movement of electrons across each cell. How does conservation of charge still hold true across the cell?

Answer 22

Movement of charged ions inside the electrolyte solution (H+ and HSO4 -)

Question 23

Discuss the movement of electrons at each anode of a PbA cell.

Answer 23

Pb (s) anode releases electrons and so is oxidised. PbO2 cathode accepts electrons and is reduced. Oppose of both is true when battery is recharged.

Question 24

What electrical properties does a separator have in a PbA cell? State a couple of examples of suitable materials.

Answer 24

Electrical insulator. Examples: glass mats, plastic polymers usually

Question 25

List three pros of Li-ion batteries.

Answer 25

High energy density due to chemical species present, can provide high currents, relatively low self-discharge

Question 26

List three cons of Li-ion batteries.

Answer 26

Requires a protection circuit to prevent overcharging, high manufacturing cost, human rights violations, environmental damage

Question 27

What material is the anode of a Li-ion battery made of? How about the cathode?

Answer 27

Anode = graphite, cathode = complex lithium alloy

Question 28

Complete the sentence: 70% of today’s mined cobalt comes from the _______.

Answer 28

Democratic Republic of Congo

Question 29

Complete the sentence: 60% of today’s cobalt ore refining operations are in _____.

Answer 29

China

Question 30

List some social and environmental impacts of the battery supply chain.

Answer 30

Child labor, slavery (forced labor), environmental pollution, corruption, unsafe working conditions

Question 31

How does the Paris Agreement relate to the battery supply chain?

Answer 31

The battery supply chain accelerates climate change, possibility going over the 2 C scenario in the agreement.

Question 32

Complete the sentence: An improvement to the battery supply chain is to incorporate the ________ and _______ sectors, forming a ______ supply chain, opposed to a _____ one.

Answer 32

An improvement to the battery supply chain is to incorporate the transport and power sectors, forming a circular supply chain, opposed to a linear one.

Question 33

What are the downsides of current battery recycling methods?

Answer 33

Costly, emit environmental pollutants during the recycling process.

Question 34

Complete the sentence: All practicing NZ engineers are bound by the __________ __ _______ code of _____.

Answer 34

Engineering New Zealand Code of Ethics

Question 35

List some examples of the rare earth elements used in solar panels.

Answer 35

Silver, Indium, Neodymium, Praseodymium, Dysprosium, Terbium