The CORNERSTONE project, led by the Paul Scherrer Institute, aims to develop safer and more sus-tainable sodium-ion batteries by improving the performance of Prussian Blue Analogues (PBAs) - a promising class of cathode materials. Unlike lithium-ion batteries, which rely on scarce and expensive elements like lithium, cobalt, and nickel, PBAs are made from abundant, non-toxic materials and can be synthesized using low-energy, water-based methods. The project introduces a hypothesis-driven defect engineering approach to control crystal defects, water content, and sodium levels in PBAs. This strategy is designed to enhance battery performance, extend lifespan, and reduce gas evolution - especially toxic gases like cyanogen - during operation. Key goals include achieving high specific charge (≥140 mAh/g), maintaining capacity at low tempera-tures (-20°C), and reducing gas release by at least 20% compared to commercial PBAs. CORNERSTONE combines advanced material synthesis, operando diagnostics, and scalable produc-tion methods to support Switzerland’s energy transition and sustainability goals. The project also lays the groundwork for industrial collaboration, intellectual property development, and future commerciali-zation of sodium-ion battery technologies.