Batteries are they key to making electric vehicles viable. The motor technology has not changed much at all in the last century. The motor controllers have improved remarkably in the last few decades. But all technologies prior to lithium ion were too large and heavy, and degraded too quickly.
Lithium Ion pros:
- Greater power output
- Can be charged in less than half an hour
- Longer lasting
Lithium Ion batteries are not all the same. There are many chemistries, and each provide different benefits and drawbacks. The qualities of greatest concern are: energy capacity, power output, safety, and durability. The composition of any lithium ion battery contains relatively little lithium by mass or volume compared to the other parts. Copper and aluminum - used to conduct the electricity - compose the majority of the material. There are three major components of any battery cell: the cathode, the anode, and the electrolyte.
The Cathode is where the lithium calls home. It is where most of the differences in lithium ion chemistries are found. When drawing power out of the cell, the lithium ions migrate back to the cathode. Applying a greater voltage to the cell shoves the lithium ions out of the cathode over to the anode. It is the various additives that give the different qualities. The more common additives in the cathode include Cobalt, Nickel, Manganese, and Iron Phosphate. For EV traction batteries, we endorse Lithium Iron Phosphate (LiFePO4) for its inherent stability, durability, and safety. LiFePO4 batteries will last two to three times as long as other lithium ion chemistries.
Almost universally the Anode is carbon. The lithium ions the travel across to it do not strongly bond with the carbon. Instead they intercalate. They are held amongst the carbon atoms by charge, almost like static cling. But they do not combine with the carbon. It is that stable, but weak holding strength that gives the battery such good power output.
The Electrolyte is usually a combination of solvents and lithium hexafluorophosphate. The electrolyte is liquid and provides a medium for the lithium ions to migrate across. It is absorbed into a permeable plastic insulator. The amount of electrolyte in a cell could be described as moistening the cell, but not flooding the cell. There certainly is not enough to slosh around.
- Lower initial cost, but only last a year or two
- Can be overcharged with little permanent damage
- Cannot be rapidly charged
- Rapidly degrade
- Require periodic maintenance
Lead Acid batteries are the most well known to be used in cars to start the gas engines. They are actually quite good for the purpose. They can deliver a large amount of current for a brief time. And are resilient to overcharging. Most are not sealed, but are "wet" cells. This means that when overcharged they just boil the electrolyte and release steam, oxygen, and hydrogen. The acid is also released and causes corrosion of all metals nearby. They are relatively inexpensive for the use.
To use lead acid batteries to power an EV requires very high quality batteries that are more expensive. These are still quite heavy. The heft is what makes them so inappropriate for EVs. It is quite difficult to build in enough capacity to travel more than 20 or 30 miles. As well, these batteries degrade quickly in EV use; typically losing range within months and become completely useless within a year or two.