The work performed in ASTRABAT wishes to find optimal solid-state cell materials, components and architecture that could well suited to the demands of the electric vehicle market and identification of process for manufacturing in mass production.
Five ambitious objectives were assessed during the project.
1. Development of materials for a solid hybrid electrolyte and electrodes enabling high energy, high voltage and reliable all-solid state Li-ion cells. The ASTRABAT cell is based on a hybrid electrolyte (two polymers) and an inorganic conductive ceramic filler : Li7La3Zr2O12 (LLZO). The two polymers were tailored to the specific materials electrodes, ORMOCER® as anolyte and fluoropolymer as catholyte. Series of Li-salt were synthesised to optimise the ionic conductivity in polymers electrolyte. The ionic conductivity of the solid electrolytes reached 0.4 mS/cm at 50°C. Electrode materials considered at the cathode is a NMC-based material with low cobalt content and at the anode, new nanostructured composite Silicium based material allowing achieving high energy density. To achieve this objective of high energy cell density, adaptation of interface material was done.
2. Development of a cell considering processing techniques compatible in a large scale manufacturing For this purpose, we developped the formulation of electrodes and electrolyte considering the case of electrode-electrolyte architecture based on the use of classical process of electrode coating (tape casting) with polymer electrolyte and conductive ionic ceramic electrolyte (LLZO) infiltrated inside electrode material. 1 Ah cell prototypes were manufactured with a pre-pilot line and reached 176 Wh/kg and 501 Wh/l, lower than the expected KPI due to Si irreversibility and low electrode loadings. Lower C-rates were required to maintain a high discharge capacity (C/10) while lab-scale cells could be cycled at higher C-rates (C/2). Up to 70 cycles were realized and a capacity loss of 25% was recorded for the 1 Ah prototypes.
3. Considering next generation of all solid state battery, we developed eco-designed P-Type (power) and E-Type (energy) of all-solid state battery in pre-prototype. Two type of electrode structure was considered. The first electrode structure is based on the use of nano-wire or nano-rods of LLZO to favour the ionic conduction inside the electrode. Secondly, nano-structured electrodes with different designs (pillars, honeycombs) were fabricated by ink-jet printing and screen-printing. This work was supported by modelling. Despite the strong benefits of ink-jet printing, we demonstrated the difficulty to print uniform layers with good electrochemical properties.
4. All these cells development must support the definition of an efficient cell architecture to comply with improved safety demands. We demonstrated no thermal runaway of the cells at 180°C and no flammable electrolyte, no leakage, no gas formation during cycling.
5. The eco-design of the new cells was developed through a life cycle assessment as well as recycling tests. 65% of the cell compounds is recyclable, reaching the KPI of the project. The cost of the cell prototypes was evaluated and reached 180 €/kWh, still higher than the targeted KPI.
In conclusion, the ASTRABAT solid-state cell offers promising properties but it is still in a rather early stage of development before industrialization.
