PNNL’s New EV Battery: 7x Longer Lifespan, 2 to 3 Times Longer Range
The transport sector remains a major contributor to greenhouse gas emissions and electric vehicles can eliminate this generation of pollutants. Still, there are factors that remain challenges to electric mobility.
The miles an electric vehicle can drive before it runs out of charge is almost half of the miles a petroleum/diesel-fueled vehicle can drive before it runs out of gas. Moreover, the availability of charging stations and the service life of batteries are also reasons for car owners to choose conventional vehicles.
So, efforts to improve electric mobility experience are seen globally and currently, researchers from the Pacific Northwest National Laboratory (PNNL) have developed a new formula for battery’s electrolyte solution to enhance its performance unprecedentedly in terms of its service life and storage capacity or an electric vehicle’s range.
In a separate project, engineers from the University of Colorado, Boulder are currently developing a technology for electric vehicles that would allow them to recharge wirelessly while running on the road.
Lithium-Metal vs Lithium-Ion Battery
Briefly, a battery is composed of two electrodes (anode and cathode) and an electrolyte solution. The solution is a special liquid that contains charges or electrolytes, which transports from one electrode to the other.
For lithium-ion batteries, the electrodes are made up of graphite, while lithium-metal batteries use lithium metal as their electrodes. Comparing the two electrode materials, lithium metal is a much better option as it can store two to three times more energy than graphite.
This means that with lithium-metal batteries, electric vehicles can drive two to three times farther in a single charge compared with the currently commonly used lithium-ion batteries powering our personal electronic devices. As such, they are considered as the “holy grail” of energy-storing devices.
New Electrolyte Solution Brings 7 Times Longer Battery Lifespan and 2-3 Times Longer EV Range
Acknowledging this fact, PNNL focused on the current challenges and problems of lithium-metal batteries. The main problem lies with its electrolyte solution that easily corrodes its electrodes, causing shorter battery life or lower number of recharging cycles.
Their study published in the journal Advanced Materials found out that increasing the concentration of lithium-based salt in the electrolyte solution forms a barrier around the electrodes, protecting them from corrosion and ultimately, lengthening the battery life.
This technique, however, has two disadvantages: first, the lithium-based salt is expensive and second, increasing the salt’s concentration results in increasing the viscosity and lowering the conductivity of the electrolyte solution.
So, the researchers had to optimize the salt concentration. PNNL senior battery researcher Ji Guang “Jason” Zhang said, “We were trying to preserve the advantage of the high concentration of salt, but offset the disadvantages. By combining a fluorine-based solvent to dilute the high concentration electrolyte, our team was able to significantly lower the total lithium salt concentration yet keep its benefits.”
By adding the fluorine-based solvent into the electrolyte solution, the lithium-based salts become clusters. These salt clusters, in effect, function as balls of localized high-concentration lithium salt within the solution that can still act as protection to electrodes from corrosion, but its “cluster” form avoids its formation of dendrites.
Crystals, such as the lithium-based salt, tend to form dendrites or the branch-like structure during crystallization. They are like snowflake formation and frost patterns on a glass. Lithium-based salt dendrites are undesirable for the battery as they cause short circuits and thus, end the battery’s life.
The performance of this new formulation of electrolyte solution was tested on an experimental battery cell as small as a watch battery. While a conventional electrolyte solution can maintain its charging capability after just 100 charge/discharge cycles, the newly developed electrolyte solution can withstand up to 700 cycles. That is, the lifespan of a battery is 7 times more than the existing batteries.
Wireless Battery Charging
“On a highway, you could have one lane dedicated to charging,” said Khurram Afridi, who leads a team of engineers and scientists at CU Boulder on developing a technology that enables wireless transferring of electrical energy and electric vehicles to charge on the go.
The concept of wireless transfer through electric fields is actually deemed impossible because of the very small capacitance created by the large airgap between a car and a road. Nevertheless, for Afridi, “As a scientist, you feel challenged by things that people tell you are impossible to do.”
Afridi said, “Everybody said that it’s not possible to transfer that much energy through such a small capacitance. But we thought: What if we increase the frequency of electric fields?”
Afridi and his team devised pairs of parallel metal plates with each pair comprised of a bottom plate and a top plate separated by a 12-centimeter gap. The top plates represent the receiving plate attached to a vehicle, while the bottom plates are the transmitting plates to be fixed on the road.
The device was shown to transmit kilowatts of power at megahertz-scale frequencies. “When we broke the thousand-watt barrier by sending energy across the 12-centimeter gap, we were just exhilarated,” said Afridi.