Advances in Lithium-Ion Battery Materials Expected to Lower US Electric Vehicle Costs

While a variety of commercial electric vehicles (EVs) are available on the US market, there are several barriers to address before they achieve widespread adoption. Consumers are cost-conscious, averse to long charge times, and concerned about vehicle safety. A current CTMA collaboration is addressing these issues, aiming to increase the public’s adoption of electric vehicles and reduce the country’s petroleum dependence.

“If you think about what’s going to stop somebody from buying an electric vehicle, the two main things are high cost and concerns about safety,” said Sam Esarey, Ph.D., Senior Research Chemist at PPG. “We’re working to help reduce the manufacturing cost of batteries for electric vehicles, along with making thermal management coatings for battery fire protection.”

The initiative, Advanced Materials for Lithium-Ion Batteries, brings together experts from PPG, US Army Ground Vehicle Systems Center (GVSC), and North Dakota State University. The team is researching new coating technologies and thermal management systems for improved lithium-ion battery energy density, life, and safety, particularly to provide protection against temperature extremes that can lead to catastrophic battery failure. Results will lead to cheaper, longer-lasting batteries that would be usable for consumer products, industrial use, and electric vehicles.

“The battery pack is the most expensive component of an electric vehicle,” said John DiMeglio, Research Chemist at PPG. “Any technology that can help with improving batteries, realizing economies of scale or a cheaper, more efficient manufacturing process, will decrease the cost of EVs. With our system, we’ve found a five to six percent cost savings from the cathode coating process.”

The team is working on improving lithium-ion batteries for ground vehicles. Lithium-ion battery cells are composed of an anode and cathode, layered with a separator, surrounded by electrolyte and capped with two current collectors (i.e., electrodes). A chemical process allows ions to separate from electrons, delivering negatively charged electrons to an electrical circuit and allowing positively charged ions to travel through the electrolyte. Cathodes are made by coating active materials, frequently lithium iron phosphate (LFP) or lithium nickel manganese cobalt oxide (NMC), onto an aluminum foil current collector. Anodes are typically graphite or other carbon materials coated onto copper foil. During charging, lithium ions are driven through the separator to intercalate into the graphite, building up a negative charge at the anode’s electrode and a positive charge at the cathode’s electrode. During discharge, the electrons carry current from the negative electrode into an electrical circuit, and the ions travel back through the separator from the negative to positive electrode. The binder or the binder system is essentially the polymers that hold all the other components of the battery together.

“The chemistry that we use in our binder system ultimately helps with increasing the cycle life of our batteries,” said Esarey. “Our binder system contains components that are better at distributing the cathode coating to yield better results over time, over many cycles, compared to traditional binder systems. We’re incorporating particular binders in our system that help with the ultimate performance of cathode, such as better carbon dispersion, active material dispersion, adhesion to the current collector, and better flexibility so that during processing, you don’t have any cracks.”

In Phase I, the team focused on improving cathodes to improve the batteries’ energy density and power density. The novel cathode coating formulas can deliver a balance of power and energy so batteries can store enough power to fuel a vehicle over long distances, all while providing a high-enough power draw to support the onboard electrical equipment. In addition, they worked to reduce the batteries’ environmental impact by creating and successfully demonstrating a cathode coating formula that eliminated N-methyl pyrrolidine (NMP).

“NMP is being regulated out in Europe and will eventually be phased out elsewhere, so we seek an alternative for battery manufacturing that does not contain NMP,” said Esarey. “The new system that we have developed is an NMP-free solvent binder system that actually allows us to use less solvent overall compared to traditional NMP-containing cathode formulations, and that allows us then to use less heat to evaporate less solvent and cure the cathode coatings faster. Ultimately, lowering the amount of energy required to coat and dry cathode materials will lower the overall cost.”

The new formulation brings other improvements that reduce the batteries’ environmental impact.

“One consideration we have is that batteries are made in a sustainable way so that there are not a lot of emissions associated with the production of the raw materials that go into the battery and the battery itself,” said DiMeglio. “We’ve done some life cycle analyses for our NMP-free solvent that have shown that the PPG binder system and the PPG NMP-free solvent emits 39 percent less CO2 when compared to standard NMP systems.”

In the second phase, the team shifted their attention to improving anodes.

“In Phase II, we designed some new binders for the anode, which is carbon-based material that can allow the active materials to be more well distributed throughout the coating, and which we found to significantly improve the performance of the anode,” said DiMeglio.

Currently, the project team is concurrently working on the third and fourth phases to leverage research benefits between efforts and maximize information-sharing of technical knowledge. In Phase III, the team is incorporating the advanced high-energy-density cathodes and anodes demonstrated in the previous phases into single-layer pouch cells to assess performance. The anticipated results will bring new levels of both power and energy capacity compared to current energy storage technology.

“The first three phases focused on making cells that will ultimately go into a 6-T battery,” said Esarey. “We looked at the cell level, rather than the pack level. We weren’t testing 6-T batteries. Rather, we’re looking to build pouch cells that will be tested at the cell level to meet 6-T specifications. In phase three, we’re trying new formulations to further improve energy density and power, particularly by looking at anode formulations.”

The team is also working on the fourth phase, which is focused on developing solid-state battery capabilities, and on high-power supercapacitor cells that are meant to complement a Li-ion battery electrode with decreased flammability and size versus traditional supercapacitors. As complementary technology to a battery, a supercapacitor can take the extreme load off the Li-ion battery during high power applications such as turning over an engine, extending the lifetime of the Li-ion 6T battery.

“We’re working to make these devices smaller and safer so they can be used more readily in mobility applications,” said Esarey.

The project is scheduled to be completed in September 2023, when the team will perform a manufacturability study to determine if there are any roadblocks to making a 6T battery at scale. Results will be of interest to the entire Department of Defense (DOD), since the DOD, as the largest federal government consumer of fossil fuel, has identified vehicle electrification as an area of high priority. In the long road to full electrification, the ability to utilize a lithium-ion 6T battery in place of lead-acid batteries would allow the DOD to begin reaping benefits much sooner. Lithium-ion batteries are lighter weight and can last five times as long as lead acid-based batteries.

This project’s improvements to the performance, efficiency, energy density, safety, charging speed, and cost of lithium-ion batteries will lead to more affordable EVs and possibly more widespread public adoption of EVs.

“Working in the alternative energy battery space is a really exciting opportunity,” said DiMeglio. “After working on this project over the past few years, I’ve seen the real-world positive impact.”

“I went into science to work on renewable energy,” said Esarey. “It’s been really motivating to work with the military to help convert their vehicles to something that are more hybrid, not purely run on fossil fuels. I think this project will have an impact on improving lithium-ion batteries.”