Disordered Rock Salt And Transition Metal Anodes — Engineering The Batteries Of The Future

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People like to say nothing is sure but death and taxes. But there is something else we can be sure of — announcements about blockbuster new battery technologies that promise higher energy density and shorter charging times. Given that discoveries in the lab usually take years to make their way into production, two such announcements this week suggest the children of tomorrow will think about today’s lithium-ion batteries the way children today think about transistors.

Disordered Rock Salt

Scientists at UC San Diego have discovered a new anode material they call disordered rock salt that enables lithium-ion batteries to be safely recharged within minutes and last for thousands of cycles. They are composed of lithium, vanadium, and oxygen atoms that are arranged much the same as ordinary kitchen table salt except distributed randomly. The research was conducted by Professors Ping Liu and Shyue Ping Ong and was published September 2 in the journal Nature.

At the present time, the two materials most commonly used as anodes in commercially available lithium-ion batteries are graphite, which is energy dense, and lithium titanate, which allows faster charging with no risk of fires but has lower energy density. Disordered rock salt anode has properties that are somewhere between the two. It is safer to use than graphite yet has an energy density at least 70% greater than lithium titanate.

“The capacity and energy will be a little bit lower than graphite, but it’s faster, safer and has a longer life. It has a much lower voltage and therefore much improved energy density over current commercialized fast charging lithium-titanate anodes,” said Haodong Liu, a postdoctoral scholar in Professor Ping Liu’s lab and first author of the paper. “So with this material we can make fast-charging, safe batteries with a long life, without sacrificing too much energy density.” According to Science Daily, the first uses for batteries with the new anodes will be electric buses and power tools, since the characteristics of disordered rock salt make it ideal for use in devices where recharging can be easily scheduled.

“For a long time, the battery community has been looking for an anode material operating at a potential just above graphite to enable safe, fast charging lithium-ion batteries. This material fills an important knowledge and application gap,” said Ping Liu. “We are excited for its commercial potential since the material can be a drop-in solution for today’s lithium-ion battery manufacturing process.”

In the study, the researchers found the disordered rock salt anode could reversibly cycle two lithium ions at an average voltage of 0.6 V — higher than the 0.1 V of graphite, eliminating lithium metal plating at a high charge rate which makes the battery safer, but lower than the 1.5 V at which lithium-titanate intercalates lithium, and therefore storing much more energy. In testing the new anode was cycled more than 6,000 times with negligible capacity loss. It can charge and discharge energy rapidly, delivering over 40 percent of its capacity in 20 seconds.

Postdoctoral candidate Zhuoying Zhu says, “We discovered that Li3V2O5 operates via a charging mechanism that is different from other electrode materials. The lithium ions rearrange themselves in a way that results in both low voltage as well as fast lithium diffusion.”

Transition Metal Oxides

Scientists have long been fascinated by a group of metal oxides that store more energy than theoretically possible. Now an international research team from the University of Texas at Austin, Massachusetts Institute of Technology, the University of Waterloo in Canada, Shandong University China, Qingdao University, and the Chinese Academy of Sciences think they have solved the mystery. The research, published in Nature Materials, found several types of metal compounds with up to three times the energy storage capability compared with materials common in today’s commercially available lithium-ion batteries.

“For nearly two decades, the research community has been perplexed by these materials’ anomalously high capacities beyond their theoretical limits,” says Guihua Yu, an associate professor in the Walker Department of Mechanical Engineering at the Cockrell School of Engineering. “This work demonstrates the very first experimental evidence to show the extra charge is stored physically inside these materials via space charge storage mechanism.”

At the head of the discovery are transition metal oxides — compounds that include oxygen bonded with iron, nickel, or zinc. Energy can be stored inside the metal oxides as opposed to the changes in the crystalline structure that conventional lithium-ion batteries require to store energy, according to Science Daily.

The key technique employed in this study, called in situ magnetometry, is a real-time magnetic monitoring method used to investigate the evolution of a material’s internal electronic structure. It is able to quantify the charge capacity by measuring variations in magnetism. This technique can be used to study charge storage at a very small scale — a capability unavailable using many conventional characterization tools. “The most significant results were obtained from a technique commonly used by physicists but very rarely in the battery community,” Yu says. “This is a perfect showcase of a beautiful marriage of physics and electrochemistry.”

QuantumScape To Go Public

All of the research above is theoretical stuff taking place inside laboratories. The time needed to go from research to commercialization is demonstrated by QuantumScape, a spin off from research at Stanford University founded by Jagdeep Singh a decade ago. Now ten years later, the company thinks it is nearly ready for prime time and is planning an IPO to raise funds to get its first prototype manufacturing process up and running.

The IPO will be accomplished by something called a reverse merger using special purpose acquisition company Kensington Capital Acquisition — a technique that is all the rage on Wall Street. It has been used recently to go public by Lordstown Motors, Nikola, and Fisker. Canoo is about to conduct its IPO the same way. The QuantumScape IPO is expected to raise $3.3 billion.

According to Tech Crunch, a conventional lithium-ion battery has two electrodes. There’s an anode on one side and a cathode on the other. An electrolyte in the middle acts as the courier that moves ions between the electrodes when charging and discharging. Solid state batteries use a solid electrolyte instead of the liquid or gel based electrolyte found in most lithium-ion batteries.  The company claims solid electrolytes have greater energy density, which translates into more range from smaller, lighter (and hopefully less expensive) batteries. Solid electrolytes also are supposed to reduce the risk of fire and the need for cooling systems associated with traditional lithium-ion batteries.

So often today we hear about astonishing breakthroughs in battery technology that are little more than vaporware. QuantumScape seems to be the real deal. No less an authority than JB Straubel, former chief technical officer of Tesla and now founder of Redwood Materials, a company developing ways to recapture the raw materials inside lithium-ion batteries for re-use, calls the QuantumScape solid state anode-less design, “the most elegant architecture I’ve seen for a lithium-based battery system.” High praise from someone who should know.