Lithium ion batteries are here to stay. Yet there are aspects of these electrochemical storage devices that can be improved. One such area is the electrolyte. Neville Pavri, research chemist at Halocarbon Products Corp., will give a talk at The Battery Show in Novi, MI on September 12 titled, “Fluorinated Materials to Help Improve Performance in Lithium-ion Batteries.” Pavri has worked on fluorinated electrolytes for several years and spoke with Design News about some of the advantages of this new concept.

Organic Issues

The liquid electrolyte inside a commercial lithium ion battery is an organic solvent. Its job is to allow the passage of lithium ions between the positive (cathode) and negative (anode) electrodes during charging and discharging. It also must prevent self-discharge that would occur if electrons could pass through the electrolyte between the anode and cathode. As long as voltages remain below 4.2 volts, the organic solvent electrolytes are stable. To increase energy density and storage capacity, researchers would like to increase the cell operating voltage to 4.4 volts or higher. But there is a problem.

Normal organic solvent electrolytes begin to oxidize when the voltages reach the 4.3 to 4.4 volt range. “The main goal with lithium ion batteries in the near future is two-fold. You want to make the battery safer and you want to enable higher energy density,” Neville Pavri told Design News. “The currently used materials that are used for electrolytes in the batteries today tend to not be stable as you go to higher voltages. As you go to 4.3 or 4.4 volts, the materials that are used to make the electrolyte today start breaking down because they do not have good oxidative stability,” he explained.

Despite having an energy density among the highest of all electrochemical batteries, lithium ion cells are still far behind liquid hydrocarbon fuels, such as gasoline. Increasing energy density would improve laptop or cellphone life or distance traveled by an EV on a charge.

Fluorinated electrolytes have been demonstrated to help drive new levels of safety and performance in high-voltage cells. (Image source: Halocarbon)

Fluorine

Pavri heads a research effort at Halocarbon to examine fluorinated materials as additives or co-solvents for the organic electrolytes. “Using fluorinated solvents, that we prepare, they tend to be much more oxidatively stable,” said Pavri. “You need a lot more energy to break a carbon fluorine bond compared to a carbon hydrogen bond. Since you need a lot more energy, the compounds are more stable and they can be used at these higher voltages without as many issues,” he told us. “Fluorinated co-solvents and additives have much greater oxidative stability. They will tend not to decompose as you go to 4.3, 4.4, 4.5 volts.”

Halocarbon is particularly well-placed to do this type of research. “We have a lot of experience making different fluorinated molecules,” said Pavri. “About two years ago, we were looking for new markets to enter and figured that we could enter into the lithium ion battery market. We have the ability to put fluorine on different parts of molecules and then study how they will behave inside the system, which in this case is a battery system. We quickly realized that our specialty is making organic compounds, so we went ahead and partnered with electrolyte manufacturers and battery companies and started to test our materials in the batteries with their help,” he explained.

Structured Approach

“We are using this structured activity relationship (SAR) approach to narrow down the candidates that have the best efficacy, not only in cycling, but also in reducing the flammability of the electrolyte and other additive properties, such as anti-gassing and making better SEI (solid−electrolyte interphase ) layers,” said Pavri. In most photographs of spectacular battery fires, it is this electrolyte that provides the fuel. “When you replace hydrogen with fluorine in a compound, you usually reduce the flammability,” noted Pavri.

Thanks to Halocarbon’s open innovation approach to the lithium ion electrolyte additives that it is developing, the company is finding real power in working together with its industry partners. “We are not coming into this market with just one compound. Halocarbon is a specialty fluorocarbon company, and we already make a wide variety of fluorinated compounds,” said Pavri. “Many of them are made in up to hundreds if not thousands of metric ton scale. Other products that Halocarbon makes are specialty oils, greases and waxes, pharma compounds, and fluorinated anesthetics.” This gives Halocarbon the flexibility to produce a range of different fluorocarbons at additive quantities.

The ability to make large quantities of potential additives also means that some new battery chemistries could be available in as short as six months, although the expected time frame for adoption by automotive customers is probably more like 2-3 years, according to Pavri.

Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.