July 2016    Print this article

Metals: at the heart of transportation electrification

Denis Blackburn, Eng.
Ministère de l'Énergie et des Ressources naturelles

In 2012, the transportation sector was the largest contributor to greenhouse gas emissions in Québec, accounting for 44.7% of emissions. From 1990 to 2012, greenhouse gas emissions from transportation activities increased by 25.7%, while emissions in other sectors (industrial, agricultural, residential, institutional, waste and electricity generation) decreased by 24.3% over the same period.

Transportation electrification appears to be one of the best ways to reduce emissions of greenhouse gases, especially carbon dioxide (CO2). Although the use of electric motors is a technologically proven way to power all forms of land vehicles, the question of operating range remains crucial.

There are two methods for supplying an electrically-powered vehicle:   

Method 1 is not a way to reduce greenhouse gas emissions, but several innovations have been introduced to optimize performance.

This article offers a brief overview of the use of batteries as a source of energy for electrically-powered land vehicles.

Basic electro-chemical notions

Some chemical reactions release electrons which, using appropriate means, can be harnessed and forced to run through a motor. The circulation of electrons then causes the motor to turn.

The basic unit allowing the electro-chemical process to generate a flow of electrons is called a cell. A battery is an assembly of several cells. In everyday language "cell" and "battery" are often used interchangeably, but technically a battery contains several cells.

Figure 1 is a simplified diagram showing the operation of a cell in discharge mode. In short, the metallic (M) portion of the anode decomposes—or ionizes—when submerged in an electrolytic solution. The metal (ion) migrates from the anode to the cathode through the electrolyte, and is then deposited on the cathode.

The electrolytic solution is composed of a solvent and an active metal salt, and facilitates the movement of the metal from one electrode to the other.

The decomposition, or ionisation, of the metal at the anode releases electrons (e-) which are then free to move through an electric circuit and power a motor or any other load (light, TV, sound system, etc.). The electrons, after completing their task, move to the cathode to complete the circuit.

The discharge continues until the metallic portion of the anode is completely exhausted. The discharge can be shown symbolically as follows:

M (anode) → M+ (electrolyte) + e- (circuit)

Some cells can be recharged. Figure 2 is a simplified diagram showing the operation of a cell in charge mode. In short, a source of electrons is directed to the anode; this abundance of electrons allows the anode to be reconstructed by attracting the metal present in the electrolyte. At the end of the process, metal migrates from the deposit on the cathode to the anode, via the electrolyte.

Once the anode has been reconstructed, the charging cycle is complete. This can be shown symbolically as follows:

M+ (electrolyte) + e- (circuit) → M (anode)

A discharge is a spontaneous phenomenon that creates a movement of ions and electrons in one or more specific directions, whereas a charge reverses the same flow using an outside source.

It is important to note two key elements:

Performance criteria for a rechargeable battery

There would not be much point in using non-rechargeable batteries to power the electric motor of a land vehicle. Once discharged, they would have to be replaced. As a result, rechargeable batteries are the only viable option for the electric vehicle market.    

Several criteria are used to rank battery performance. We will use two of these criteria:

The difference between energy and power is the time element. Energy measures the work performed regardless of the time needed; power measures the quantity of energy supplied each second.

For example, running a marathon requires far more energy than a 100-metre sprint—but an Olympic sprinter is more powerful than a marathon runner.

Ideally, a battery would be able to supply energy over a long period (criterion 1) and also be able to respond to a peak energy demand over a short period (criterion 2).

A third criterion can also be used to measure the performance of a rechargeable battery: the number of charge-discharge cycles it can support without a significant decrease in performance. For the purposes of this article, this third criterion will not be used to compare battery types, since it is not covered in the literature consulted.

Performance of different battery types

Table I ranks battery types based on the criterion energy versus mass (Wh/kg).

Table I: Ranking of batteries using the criterion energy versus mass

Type

Energy (Wh/kg)

Lead-Lead oxide

35

Nickel-Cadmium

50

Nickel-metal hydride

55

Nickel-Zinc

60

Lithium-Titanium oxide

90

Lithium-Iron/Phosphate

100

Lithium-Cobalt oxide

150

Lithium-ion Polymer

165

Table II ranks battery types based on the criterion power versus mass (W/kg).

Table II: Ranking of batteries using the criterion power versus mass

Type

Power (W/kg)

Nickel-Cadmium

150

Lead-Lead oxide

180

Nickel-metal hydride

625

Nickel-Zinc

900

Lithium-Iron/Phosphate

1400

Lithium-Cobalt oxide

1800

Lithium-ion Polymer

3000

Lithium-Titanium oxide

4000

Of the battery types presented in Tables I and II, two deserve particular attention:

Lead-Lead oxide: This battery, the well-known "car battery", was invented over one hundred years ago. It is used mainly to supply energy to a starter motor to turn an internal combustion engine, over a short period of time. The battery does not have the necessary characteristics to power a car over a longer period.

Lithium-Cobalt oxide: This battery was a pioneer in the world of lithium batteries, with early versions dating back to the 1990s. The Lithium-Cobalt oxide battery was first used to supply small electronic devices such as cell phones. It now dominates the electric vehicle market, and is expected to do so for many years.

The anode is made of graphite impregnated with lithium, and the cathode is made of a mixture of cobalt and lithium oxide (LiCoO2). The electrolyte is a solvent containing a dissolved lithium salt.

Obviously, any growth in the battery market to supply electric vehicles will result in increased demand for lithium, and also for cobalt and graphite.

Conclusion

Transportation electrification will lead to increased demand for metals and industrial minerals such as lithium and graphite. The mining industry will be directly affected by this trend and will have an important contribution to make.

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