NEC Corporation announced on 9 October that it had developed a next-generation manganese lithium-ion battery prototype featuring cathodes that support high voltage operations and an electrolyte solution that improves the stability of high voltage operations. NEC expects the format’s energy density to help increase EVs’ range while reducing their batteries’ weight.
NEC currently develops and produces lithium-ion batteries with cathodes made with manganese (an inexpensive and abundant resource), which are used in traction batteries for EVs as well as in residential use. To improve these batteries’ capacity per weight (energy density), NEC introduced higher voltage and made progress in the development of an electrolyte solution that suppresses the oxidative decomposition of the electrolyte solution generated on the surface of cathodes from the higher voltage.
This new cathode and electrolyte solution improve battery energy density by approximately 30%, increase battery capacity and reduce battery weight, all while maintaining a high level of safety.
“These new batteries provide high voltage drive and the same long operating life as conventional 4V lithium-ion batteries,” noted Hidenori Shimawaki, General Manager, Smart Energy Research Laboratories at NEC.
Higher voltages are achieved by substituting nickel for another material in existing spinel-structured, manganese-based cathodes. These cathodes, with graphite anodes, enable average operating voltage to be increased to 4.5V from the previous technologies’ 3.8V, thereby increasing energy density by about 30% from 150Wh/kg to 200Wh/kg.
The conventional carbonate-based electrolyte was changed to a fluorinated solvent which is highly resistant to oxidation. This enables the suppression of oxidative decomposition where the electrolyte solution and the cathodes interface, which has posed a challenge for existing techniques. NEC says these new batteries maintain approximately 80% of their original capacity after undergoing tests with 500 full charge and discharge cycles in conditions below room temperature (20 degrees Celsius), while maintaining roughly 60% when above room temperature (45 degrees Celsius). The batteries have demonstrated life span performance equivalent to that of conventional 4V batteries. The suppression of gas formation within cells affords a significant reduction in the battery swelling ratio to just 10% (vs more than 100% swelling in conventional batteries) after cycle tests conducted at above room temperature.
NEC says it will continue to drive R&D to achieve greater capacity, life span and reliability for these batteries in preparation for their adoption by EVs and large, stationary storage applications.
