The important thing to know here is that Li-ion batteries are not solid state, they've got a gel in them. TDK are claiming this new solid state battery provide

The important thing to know here is that Li-ion batteries are not solid state, they've got a gel in them. TDK are claiming this new solid state battery provides "1000 watt-hours per liter" Whereas for comparison a Panasonic Li-ion battery like a UPF496171Z offers 650 watt hours per litre. So compared to competing Li-ion batteries, they're claiming a 50% improvement in energy density.