While lithium-ion battery chemistry dominates the current electric vehicle market, scientists are working to develop innovative battery chemistries that address the known challenges the existing chemistry presents.
By Adam Kimmel for Mouser Electronics
Sales of electric vehicles (EVs) continue to outpace the overall automotive segment, with EV market shares of 5.2% in Q1 and 5.6% in Q2 of 2022 in the US, with global values increasing to nearly half of all new vehicles sold. This growth is happening in the face of continued supply challenges, chip, and skilled labor shortages, and slowing economic growth. Nevertheless, consumers are undeterred, and new vehicle registrations continue to climb.
The limitation to when automakers can meet this unconstrained demand will be cost-limiting components. For fuel cell electric vehicles (FCEVs), reducing the cost of hydrogen fuel from the current $6.50/kg to $1.50/kg is the light-off point. Battery costs will pace the adoption of battery electric vehicles (BEV) and electric hybrid vehicles (PHEVs), with the battery pack consuming 30% of the total cost to consumers. Still, with vehicle demand exponentially increasing, the cost per kilowatt-hour (kWh) is dropping at a similar rate, down to $137/kWh at the end of 2020. In addition, at $100/kWh, electric cars will be at cost parity with gasoline-powered vehicles, according to a BloombergNEF estimate.
While the debate between hydrogen and battery vehicles is far from over, BEVs will likely dominate the market soon, especially for light-duty vehicles that would not require a battery big enough to power a Class VIII truck. But even within the battery segment, there is no clear choice for the best battery technology. Lithium-Ion (Li-ion) dominates the market, but other viable and technically superior battery chemistries exist today.
With the costs of Li-ion projected to plateau soon, coupled with existing technical opportunities, there is an opportunity for innovation with alternate chemistries to gain a share of the battery segment. While several chemistries have emerged, vehicle designers have observed some clear trends.
Li-Ion batteries and the leading alternatives
Most EV batteries are Li-ion-based. Li-ion is a liquid-state technology that employs lithium to carry the electric charge between the electrodes. To put the scale of EV batteries into perspective, they use 10,000 times the amount of lithium in mobile phones, ramping up the demand for lithium and driving up its commodity price. However, Li-ion carries known challenges, leading battery manufacturers to develop alternatives such as zinc-air, lithium iron phosphate, and solid-state batteries.
Li-ion battery technology has become popular in consumer electronics due to its high power-to-mass ratio. This trait is highly desirable for vehicles whose mass limits driving range. However, heavy components siphon battery power when starting and stopping the car, reducing the driving range. In addition, Li-ion batteries have high energy density and better performance than their alternatives at elevated temperatures.
The decreasing size of electronics and the desire for longer operating hours per charge spurred innovation in this parameter. As a result, Li-ion’s energy density is more than 2.5 times greater than both NMH and lead-acid batteries. In addition, Li-ion batteries are recyclable, making them a good choice for environmentally-focused consumers.
Lithium batteries consist of the following:
- A cathode (made of cobalt, nickel, or manganese) that determines the capacity and voltage of the battery
- An anode (made of graphite or silicon) that enables electric current to flow through an external circuit
- An electrolyte comprises salts and other additives that transfer ions from the cathode to the anode. It is what gives the name to the battery type (“Li-ion” means lithium carries the electrons in the form of a negative ion)
- A separator to prevent direct contact between the anode and the cathode
Though Li-ion is inexpensive and offers some technical advantages, exploding demand for this kind of battery coupled with commodity inflation affecting its raw materials has buoyed the costs, stopping prices from continuing downward. In addition, the batteries themselves pose the risk of swelling from excessive temperature change or sharp impact. Because Li-ion is liquid-based, it may leak upon intense contact. Another drawback is that lithium is an alkali metal, meaning it is highly reactive and flammable. This feature represents another critical safety hurdle to clear.
Finally, many Li-ion batteries contain cobalt, such as nickel cobalt manganese (NCM) and nickel cobalt aluminum (NCA). While these deliver the low-cost, high-energy-density performance OEMs desire, cobalt mining has negative environmental and social impacts through hazardous sourcing and is highly flammable.
Zinc Air (Zn-air)
Like solid-state, Zn-air contains greater energy density than the incumbent Li-ion batteries. It also uses more available materials, helping to minimize cost, and carries a flat discharge voltage to reduce thermal runaway risk. In addition, the chemistry has a higher potential for recyclability, improving the sustainability footprint of the technology, and exhibits a long shelf life. Current development focuses on enhancing the reaction kinetics via catalysis.
Lithium Iron Phosphate (LFP)
Lithium Iron Phosphate (LFP) is an attractive long-term option over Li-ion due to its long lifespan, non-active maintenance, safe operation, lightweight, and high discharge rates. However, the specific energy density is lower than Li-ion chemistry due to the lithium ions’ lower maximum voltage and unilateral spatial movement. This lower energy density limits LFP’s applicability for heavy-duty commercial vehicles or high-performance applications.
Furthermore, LFP carries a higher first cost but avoids critical materials like cobalt and nickel and operates in a wide temperature range. In addition, a robust operating window makes LFP advantaged in extreme weather and rugged applications.
Li-Ion vs. Solid-State Electrolytes for BEV
Given the above comparison, it is not surprising that liquid-state electrolytes remain dominated by Li-ion battery chemistry. But that realization is not the end of the story; as discussed above, Li-ion is susceptible to higher costs due to skyrocketing demand. In addition, there is an opportunity to improve the top safety concern of flammable liquid catching fire. Safety is one of the most critical success criteria for EVs to inspire public confidence, so the industry and safety regulators would welcome an opportunity to step up the safety features. These reasons are why Tesla, BYD, GM, Ford, VW, and others are developing LFP vehicles. In fact, Tesla confirmed that nearly half of its Q1 vehicles used LFP.
One other technology, the solid-state battery (comprised of lithium metal), addresses the most pressing safety challenges of Li-ion. It is more stable, has a higher energy density than the already high Li-ion, comes from readily-available materials, and offers lower flammability, faster charging, and a more extended range.
Barriers to wide-scale adoption
At the moment, a combination of solid-state and LFP is the future of EV batteries. However, there are a few barriers to widescale adoption that battery developers must solve. Solid-state batteries will carry a higher development cost due to a lack of capital to produce mass quantities. It is crucial to reduce this cost to encourage consumers to buy solid-state electric vehicles.
There are gaps in the solid Li electrolyte material that degrades battery performance and service life when implemented into BEVs. In addition, solid-state batteries are prone to cracking, and it is best to charge them at 140 degrees Fahrenheit for optimal performance.
As with any development material, it will be critical for the manufacturing process to be efficient. There has not been a mass-produced solid-state battery for electric vehicles to date. As a result, manufacturing challenges through the lack of experience with solid electrolyte materials would substantially delay wide-scale adoption. A manufacturing issue could also cause the EV battery plant to shut down, delaying most of the public’s first interaction with the new battery and affecting consumer confidence.
Securing the automakers’ investment commitments during commercialization planning will enable higher technology adoption. In addition, companies are investing hundreds of millions of dollars into the technology to find a better solution to Li-ion, avoid using cobalt, and decrease solid-state manufacturing costs.
The major automakers are pivoting their strategies to solid-state and LFP electrolyte chemistry, given their numerous benefits and safety improvements. For example, as solid-state batteries will become the standard electrolyte technology of the future for many EVs, Toyota announced it will invest $13.5B by 2030 into that chemistry. In addition, a group including VW, Ford, and BMW are among the OEMs committing to solid-state batteries in the coming years for electric vehicles.
Not without its challenges, solid-state batteries address flammability safety concerns with liquid-state batteries, charge faster, and provide a more extended driving range. Installing capital equipment and increasing the battery supply will smooth the market’s transition from liquid-state Li-ion to solid-state and LFP. Once the market moves, the industry and consumers will all benefit from the shift.