KIT has developed a non-flammable electrolyte that is intended to bring more energy density and service life to nickel-rich batteries.
After years of research, researchers at the Helmholtz Institute Ulm (HIU), associated with the Karlsruhe Institute of Technology (KIT), have presented a battery cell with "extremely high energy density of 560 watt hours per kilogram with remarkably good stability". . The prototype uses an (almost) market-ready cathode from an Asian manufacturer with an 88 percent nickel content and a lithium-metal anode. Lithium-ion batteries currently in use use graphite for the anode and a combination of nickel, manganese and cobalt for the cathode material. Most recently, attempts were made to steadily reduce the proportion of the problematic cobalt (Tesla is less than three percent) and increased the proportion of nickel to do so. The new KIT battery also uses such a nickel-rich cathode (the prototype still contains nine percent cobalt).
New, non-flammable electrolyte
What is special about the KIT battery is the electrolyte, which is based on liquid containing various anions. The electrolyte ensures good cycle stability. It consists of a molten salt that is non-volatile, flame retardant but easy to recycle, according to Professor Stefano Passerini, Director of the Helmholtz Institute Ulm (HIU). In addition, the new substance prevents the formation of toxic hydrofluoric acid when it comes into contact with (extinguishing) water or if the heat is too high electrolyte keeps its capacity much longer; Previously used electrolytes interact unfavorably with the highly reactive nickel in the cathode, causing micro-fractures and making the material porous. With commercially available nickel-rich materials, additives or sealers on the nickel provide protection against excessively rapid aging. ,
Dr. Michael Hess, whose start-up company does market analyzes for new battery concepts, sees the comparatively poor charging and discharging rate of the new cell as a disadvantage. Apparently, the conductivity of the ionic electrolyte is not so good, which makes series production less desirable. Passerini says there are some industrial partners showing interest, including automakers.,
Potential for solid state batteries?
Maybe with regard to solid state batteries. Beyond the published research results, Passerini points out that the ionic electrolyte can be used as an intermediate layer between lithium-metal electrodes and inorganic solid electrolytes and could thus reduce the resistance during the transition of (lithium) ions into the electrolytes of solid-state batteries.Currently, these boundary layers in solid-state batteries, especially in the case of ceramic electrolytes, have to be brought under high pressure in order to allow as little distance as possible, even in the nanometer range. Because it prevents the simple ion transfer.
Solid-state batteries, which mainly have lithium metal on the anode, which is the goal of the technology, otherwise work with electrolytes based on polymers, such as the battery in Daimler's E-Citaro. However, their working temperature is between 60 and 80 degrees; the anionic electrolyte of the KIT, on the other hand, works at room temperature. In addition, Passerini believes that the cells can be mass-produced on production lines using standard components from well-known production plants for lithium-ion and lithium-metal batteries.
The publication of the KIT shows once again how intensively research is being done on the battery of the future. After a number of further developments on cathodes and anodes, the KIT has recently also dealt intensively with the electrolyte. It is difficult to estimate what effects laboratory developments in particular will have on the electric car batteries of the future. The charging capability of the KIT battery does not appear very promising, but the ionic electrolyte may have the potential to accelerate the market maturity of the solid-state battery, which is being worked on intensively in many places.