The invention provides an electrochemical energy-storage battery and a battery system applied to an electric vehicle. The battery comprises a battery core which comprises a positive plate, a negative plate and a diaphragm, a rectangular casing which comprises two open ends and has a size suitable for accommodating the battery core, a cover plate which is matched with the open ends, an electrode terminal which extends out of the battery through the cover plate from the interior of the electrochemical energy-storage battery, and a space ring which is safely arranged between the cover plate in the rectangular casing and the battery core and separates the cover plate from the battery core. The battery system comprises a plurality of battery packs connected in series, and each battery pack comprises a plurality of batteries provided by the invention. The safety of the monomer batteries is improved dramatically so that the electrochemical energy-storage battery can be applied to the electric vehicle safely and supplies power to the same.