Batteries

What is the difference between a primary and secondary cell?

Primary cannot be recharged- Irreversible reaction

Secondary can be recharged- Reversible reaction

Battery

Defining any electrochemical device

Calvanic cell

Fundamental device that stores energy

Battery pack

The assembly of many galvanic cells, to provide larger energy storage device

Optimisation of personal electronics

Energy density

Cost

Lifetime

Optimisation of transport

Faster charging

Optimisation of stationary energy storage

Specific energy

What is specific energy?

How much energy can be stored per unit mass

What is energy density?

How much energy can be stored per unit volume

What is happening in a cell when the cell is fuly charged? (anode, cathode, potentials, charge)

Anode has low potential

Cathode has high potential

-ve charged electrons leave anode and go to cathode

No electrical connection between anode and cathode

What is happening in a cell when the cell is discharged? (anode, cathode, potentials, charge)

Anode loses electrons

Cathode accepts electrons

Ion transfer from anode to cathode through electrolyte

What happens if it is not a spontaneous process?

A charge buildup occurs at different points of the cell

Include us putting work into the system

What is a redox reaction?

Reduction and oxidation half-processes combined

Gibbs free energy

The maximum amount of non-expansion work that can be extracted from a thermodynamically closed system

Form of potential energy that can be converted into useful work

The change to the amount of potential energy that may one day be converted to useful work

What is entropy?

The degree of disorder in the universe

What occurs when a reaction is spontaneous?

Increases universe entropy

What happens to entropy when reactions are not spontaneous?

Requires us to put work in, so a resuction in universe entropy

Thermodynamically closed system

A system where no mass is exchanged into or out of it, only energy is transferred

How would you find total energy extraction?

Area under a OCV V discharge graph

How would you graphically find the Total energy required?

Area below an OCV V charge grph

How would you graphically find the losses during charge/discharge?

Area between OCV and charge/discharge curves

Why is there cell resistance?

When a current passes through a resistor, a voltage drop will occur

What is overpotential?

Volage drop over the cell

When do we extract more energy?

Slow discharge

What is a C-rate?

They define the rate at which the batteries charge is being depleted

Number of times you could charge/discharge a battery at a constant current in a 1 hour period

What is the state of charge?

Amount of charge contained within the cell, relative to the total charge storage capacity of the cell

What is OCV?

Open circuit voltage

Difference between two half-reaction potentials

Pseudo OCV

Completing a very slow constant current discharge

What is the potential for an idealised cell?

Abundance of material so we say Eanode=Ecathode

What is happening in an engineered cell?

Start:

High reactant concentration and low product concentration at cathode

High product concentration and low reactant concentration at anode

What happens to lithiation when discharged?

Lithium at cathode increases

Electrons and ions moving

Half reaction potential decreases

Reactant to product ratio decreases

Anode becomes Delithiated