Lithium ion batteries
The humble electric car is making a comeback.
Electric vehicles were invented in the 19th century, soon after Alessandro Volta invented the electrochemical battery in 1800. Mass-produced lead-acid batteries started to become successful EVs started rolling on US roads in 1890, albiet very quietly. By 1900, the electric vehicle was in its heyday in the US - New York City even had 60 electric taxis at one point. The first EVs suffered from low range and they were heavy due to the battery technology available at the time. When the Ford Model T became available at a third of the cost of an EV, they started disappearing from the road
In the 1990s, commercial lithium ion batteries started being produced for electronic devices. Lithium ion batteries have a much higher energy density than most other batteries - meaning they store more energy per unit mass - and they do not require unpleasant heavy metals like cadmium, mercury or lead. LIB technology matured in the subsequent decades, and it was Tesla in 2008 that made the first production EV with the Roadster. LIB costs per kWh have seen a 90% drop since 2008, and today they are ubiquitous.
Components
Batteries are electrochemical cells containing a cathode and an anode, a separator, and electrolyte to carry the internal current. LIBs also has copper and/or aluminum glued to the cathode to collect electrons from the anode and distribute them to the cathode as electric current after passing through an external circuit. (Note that the familiar definition of “current” flows in the opposite direction - from “+” to “-” - by convention for historical reasons). Inside the battery, lithium ions shift travel in the opposite direction to balance charge and complete the circuit, since they are solvated and can pass through the separator.
Courtesy EnergyLink
The cathode can have various compositions, while the anode is typically carbon/graphite. The major performance improvements achieved over the years involved developing advanced cathode designs and manufacturing methods. These electrodes feature a layered crystal structure where lithium atoms can intercalate between the layers. There are also lithium ions in the electrolyte between the electrodes, typically lithium hexafluorophosphate. This allows lithium ions to shuffle back and forth from one electrode to the other depending on its charging state.
When discharging, metal ions in the cathode accept the electrons from the anode, and lithium ions collect around the cathode to balance charge. When charging, external voltage is applied across the battery, electrons flow from cathode to anode, and lithium ions nestle in between the graphite layers of the anode, where they balance charges now collecting within the anode.
Materials of construction
In the schematic above, several different elements are noted, particularly for the cathode: cobalt, manganese, aluminum, iron and lithium (plus oxygen). Other than lithium, all the elements come from the middle columns of the periodic table. This is because those metallic elements readily participate in redox reactions: their valence electrons are loosely held. The energy required to reduce a species is related to E° (the half-cell reduction potential), which generally ranges from +3 to -3 V vs SCE. Lower (more negative) reduction potentials indicates a stronger reductant, readily accepting electrons, while higher (more positive) values indicate a stronger oxidant. The difference between them is equal to the cell potential at standard conditions. To create cells with higher voltages, one would use something with a high positive E°, such as cobalt, and a negative reduction potential such as lithium:
Manganese and nickel can have similar reduction potentials in the appropriate environment, and both are used in LIBs as illustrated in the cell schematic in the previous section.
There is a high demand for EVs, and demand is projected to increase by about 15-20% per year. This is driving up the price of battery raw materials because there is a limited supply of different elements on the planet, and they are not distributed evenly. For example, the price of lithium has increased by seven fold since 2020, and cobalt and nickel prices increased by 2x-3x since 2020 as well.
Sources: Ycharts.com and Canary Media
Furthermore, many countries – including the United States – have very few reserves of critical battery elements, so they must rely on imports, which are subject to supply chain disruptions. Nickel, for example, has experienced recent shortages due to sanctions on Russia, which produced 10% of global production. The United States has set a goal to convert 50% of all vehicles sold in the country by 2030, and California will stop selling gas-powered cars by 2035. That’s a lot of batteries. This is why cobalt, nickel and lithium are now listed as critical materials by the US Department of Energy.
Conclusion
Lithium ion batteries are the dominant battery technology in 2023, and they are prone to catching on fire and burning. Their lifespan is also shorter than nickel metal hydride batteries, the previous iteration of EV battery technology. Electrochemical engineers and chemists are working on what could be the next major shift in battery technologies to address these issues.
