Anatomy of a lithium ion battery

Today’s lithium ion batteries use electrolytes that are either liquid or pastelike. That makes the batteries less efficient than they otherwise could be because lithium ions do not travel as freely as they do in a solid material. Automakers and battery companies are spending billions to change one part of the battery, the separator, from a liquid to a solid.

The goal is to create a lighter, safer, cooler and more energy-dense battery.

An EV battery pack contains thousands of cells, which look like normal flashlight batteries, connected together.

4 parts of a lithium ion battery

• Positive electrode: This is the cathode, and it determines the capacity and voltage of the battery cell.
• Negative electrode: This is the anode, and it stores and releases lithium ions into the cathode, allowing current to flow through an external circuit.
• Electrolyte: The liquid that enables lithium ions to move between the anode and the cathode.
• Separator: A physical barrier that keeps the anode and cathode apart.

How a liquid lithium ion battery works

• Discharging: Lithium ions flow from the anode into the cathode through the electrolyte and across the separator
• Charging: Lithium ions leave the cathode and make their way through the liquid electrolyte into the anode. 
• Disadvantages: Slow charge times, high heat, limited energy density

Solid-state lithium ion battery

Replaces the liquid electrolyte with a solid separator made from either ceramic, polymer or sulfide materials.

Advantages:

• Faster charging
• Lower fire risk
• Increased energy density
• Longer life
• Lower manufacturing costs

Battery engineers and chemists at Toyota, General Motors, Volkswagen and other automakers, as well as most major battery suppliers, are working to develop a solid separator robust enough for use in automobiles.

Challenges:

• Ceramic separators can crack.
• Solid-state batteries also can form dendrites, small growths of lithium that can short-circuit the battery.
• Developing a high-volume manufacturing system for solid-state batteries is another hurdle.

Because solid-state batteries are far more energy dense, automakers can use fewer of them without sacrificing driving range or performance. They have the potential to greatly reduce vehicle weight. And, because they operate at cooler temperatures and are far less prone to fires, battery pack cooling systems can be made less complex.

Images: KEVIN HEINL

Source: Automotive News research, Samsung, Chemical & Engineering News