Toyota Motor Corporation has been trying to avoid the use of lithium-ion batteries as much as possible due to their high cost. However, the company does use them for the Prius Plug-in Electric Vehicle and the RAV4 EV. But it has said that it is now betting on solid-state and lithium-air batteries for use in electric vehicles by 2020.
Comparison of Battery Chemistries.
Image Credit: Toyota Global.
“As Toyota anticipates the widespread use of electric vehicles in the future, we have begun research in developing next-generation secondary batteries with performance that greatly exceeds that of lithium-ion batteries,” Toyota writes.
Figure 2: All-solid-state battery. Directly connected cells enables smaller package.
“Beginning in 2010, we plan to accelerate our research through collaboration with production technologies. We are currently conducting research and development on two types of batteries, all-solid-state (shown in Figure 2) batteries and lithium-air batteries (shown in Figure 3).”
Figure 3: Lithium-air battery. Using oxygen in the air for the cathode and lithium metal for the anode allows for a smaller and lighter package.
It is important that I mention that “lithium-ion” is the name of a family of batteries. There is a wide variety of lithium-ion batteries in existence, and a few are in mainstream use already, including lithium-cobalt, lithium-iron-phosphate, and lithium-polymer batteries. The latter two are commonly used in electric vehicles.
Solid-state batteries utilize a solid electrolyte and solid electrodes, unlike most batteries, which utilize liquid electrolytes.
Some of the benefits of solid-state batteries include:
- The lack of liquid in solid-state battery cells enables them to be connected to each other without being placed in their own individual cases, which enables more compact packaging (cells are just tiny batteries connected to each other to form battery packs, hence the term “packs”).
- Solid-state batteries have the potential to outperform lithium-ion batteries (power-to-weight ratio). However their strength is a high energy density, which translates into long range.
- They can be created using thin films.
- They tend to be good conductors of ions, and are insulating towards electrons.
According to Technology Review, more than half the bulk of lithium-ion batteries is attributable to materials that don’t even store energy, but insulators and materials designed to protect and cool the components of the batteries. Solid-state batteries reduce that extra material greatly.
Lithium-air batteries, which Toyota is also pursuing, have the theoretical potential to store 50 times more energy than typical li-ion batteries. These batteries “use oxygen in the air as the cathode active material.” The have much better energy density and benefit from weight savings “by changing negative-electrode material into metallic lithium from black lead than solid batteries.”
It seems a lot of progress is being made in the field of electric vehicle batteries. What do you think of these two options?
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