24M, a startup battery company founded as a spin-off from MIT, claims it has made a breakthrough in creating semi-solid lithium-ion battery cells with an energy density exceeding 350Wh per kg.

MIT professor yet Ming Chiang hit upon the idea of mixing active materials in electrolytes together before forming the cell, rather than ‘injecting’ the electrolyte into a slurry, thought to be a much more efficient process for creating cells.

In other words, compositionally distinct catholytes and anolytes are created, kept apart by an ionically conductive, non-permeable separator.

“Unlike a conventional technology where they use a solvent and sort of deposit the material and then throw it all up and then inject the electrolyte at the end, we mix the electrolyte at the beginning,” Joe Adiletta, senior director of products for 24M, said.

“Of course we mix the anode and the cathode separately so we can put a different electrolyte in the anode, called the anolyte or the cathode – catholyte. Typically the separator not only allows the ions to pass but allows the electrolyte to pass. So if you use a traditional separator, eventually the materials will diffuse and you get a homogenous mixture, which is exactly what you don’t want in this design.”

Keeping the anolyte and catholytes separated, Adiletta said, can open up “huge options” on which electrolytes to choose, meaning individual batteries or systems can be tailored to “specific approaches in the battery”. This means the ‘dual electrolyte’ technology can be applied to LFP cells, more commonly used in stationary storage, or NMC cells, higher energy density and typically used for electric cars, to give two prominent examples.

24M will open up its first pilot production line towards the end of this year, which Adiletta stressed is small, at 100MWh, but is nonetheless the first high volume production of this type of technology. This way of making higher energy density versions of lithium batteries will also enable ways to “tune the electrolyte, improve the voltage, make fast charge, slow discharge technologies – there’s a huge number of options,” Adiletta said.