Scientists from the Bulgarian Academy of Sciences and the Sofia University Saint Kliment Ohridski invented a new-generation battery that will make a revolution in energy conservation. The original Bulgarian development of safe, cheap and environmentally-friendly rechargeable battery based on sodium can be combined with lithium-ion batteries in electric mobiles or entirely replace the lithium--ion batteries in other machinery and appliances. The sodium-ion battery uses new types of electrodes of sulfate salts which are widely used, cheaper, safer, more environmentally-friendly and accessible in nature.