Was it all too good to be true? It made for a great story: The 92-year-old inventor of the first lithium-ion battery was at it again. This time with new research on a chemistry that could store up to three times as much energy, charge in minutes instead of hours, and operate higher voltages and at much colder temperatures, down to -20˚C.
The implications for energy storage applications, from automobiles to sustainable energy such as solar and wind, are enormous, but now the skeptics are emerging, as they should.
In the 37 years since John Goodenough invented the lithium-ion (Li-ion) cathode, improvements in portable energy storage have been very much incremental. In the meantime, the electronics industry surged ahead with exponential improvements in performance and power consumption, enabled by Moore’s Law and driven in large part by the emergence of mobile communications and computing.
More recently, however, low power consumption has been coupled to rising concerns around atmospheric pollution and climate change. Owners of line-powered systems, such as datacenters and manufacturing plants, are under pressure to reduce both their carbon footprint, as well as energy bills. To this end many large installations, as even home owners, are turning to alternative energy sources such as solar and wind turbines, which depend upon batteries to store energy for times when energy generation is at its lowest. The stored energy can also be fed back to the grid to gain credit to offset electricity bills, while also reducing peak energy generation requirements. These storage applications stand to benefit from high-capacity, rechargeable batteries that are smaller, lower cost, and can operate at the lower temperatures.
However, for Goodenough, the key driver toward a more energy-dense battery is to reduce dependency on fossil fuel and enable electric vehicles to compete more effectively with combustion engines. While Tesla is content with incremental improvements, Goodenough wants step increases in volumetric density and much longer life cycles. At 92, he believed they had made a big leap in that direction through the development of an all-metal anode, with a glass electrolyte.
In a paper published in December of 2016, with the low-key title of, “Alternative Strategy for a Safe Rechargeable Battery,” Goodenough and his team at the University of Texas, Austin’s, Cockrell School of Engineering, disclosed details of solid-state rechargeable lithium or sodium battery with an energy density suited to automotive applications. They concluded it would invite, “a complete rethink of rechargeable battery strategies” due to the higher energy density and operating voltages (>3 V, versus today’s 1.5 V).
The cells use a solid glass electrolyte to enable low-temperature, high-voltage operation while allowing reversible plating/stripping of the alkali-metal anode, without forming dendrites. Dendrites form in conventional Li-ion batteries when they are charged too quickly and can cause shorts, leading to explosive reactions.
But not so fast: before getting too excited about Goodenough’s research, it’s worth taking a look at the analysis of the research by Dan Steingart, a researcher at Princeton University. In his blog “Redox without Redox,” Steingart posits that the findings of Goodenough, and his fellow researchers, including Helena Braga, violates the law of conservation of energy.
Long story short the effective energy density of a battery, if this can be utilized to its full extent, approaches 8x the current energy density of lithium ion cells (based on our current understanding of electrodes the projected ranges is somewhere between 2 and 5 times modern lithium ion capacity).
This is because in standard battery design the capacity of the battery is determined by the mass of the anode and cathode. The striking claim in this paper is that there effectively just needs to be an “image” of an oxidizing species in this reaction, and that is enough to drive a significant discharge capacity limited only by the amount of reductant available.
Another way to think about this: it’s like having an air electrode without the need for breathing air in or out: just the mere scent of air is enough to drive the cathodic potential. Another analogy: it’s like having an air fuel ratio that is exceptionally fuel rich yet reacting almost all of the fuel nonetheless.
Steingart did his own, “back-of-the-napkin” analysis and determined that the only change was the position of the reactants and not their chemical state (Figure 1).
Steingart states: “If nothing changes oxidation state, no energy can be released.”
Steingart emphasizes that his analysis is not in any way done to discredit Goodenough’s work, simply to raise questions, even going so far as to offer alternative reasons for the result. These include the possibility of oxygen having leaked into the cell or of accidental mis-measurement.
In a Computerworld interview, Goodenough, said:
“In this case, scientists wonder how it is possible to strip lithium from the anode and plate it on a cathode current collector to obtain a battery voltage since the voltage is the difference in the chemical potentials (Fermi energies) between the two metallic electrodes,” Goodenough stated. “The answer is that if the lithium plated on the cathode current collector is thin enough for its reaction with the current collector to have its Fermi energy lowered to that of the current collector, the Fermi energy of the lithium anode is higher than that of the thin lithium plated on the cathode current collector.”
His response was to a question that around how the, “solid-state Li-ion battery could produce energy when two different materials are needed to create an electrochemical reaction between two opposing battery electrodes.” Goodenough’s battery contained only one: metallic lithium sodium.
Computerworld also cited other skeptics, such as Jeff Dahn, a researcher at Dalhousie University in Nova Scotia, who compared the battery to cold fusion. That said, the article author noted that Dahn’s lab has a contract with Tesla.
While questions are a natural process for any breakthrough, it’s hard to not be hopeful that Goodenough has done enough to prove out the experiment and repeat it on demand. If he hasn’t yet done enough, well, he’s only 92. Lots of time to do more.