Over the last several years, increasing the energy density of batteries has been a top priority in battery technology development, congruent with increasing demands for faster mobile devices and longer-lasting electronic vehicles. The energy density of lithium-ion batteries can be enhanced by either increasing the capacity of electrodes, or by enhancing the cell voltage (V).
Extensive research has been devoted to exploring the pairing of various materials in the search for the most efficient cathode/anode mix, but until now, only limited advances have been achieved due to the narrow electrochemical stability window of traditional electrolyte.
Researchers at the University of Maryland (UMD) led by Chunsheng Wang—a professor with joint appointments in the Departments of Chemical & Biomolecular Engineering (ChBE), and Chemistry & Biochemistry—have developed a highly reversible 5.3 V battery offering a Mn3+-free LiCoMnO4 cathode, and graphite and Li-metal anodes.
A specially designed electrolyte was also created, which is stable to 5.5V for both the LiCoMnO4 cathode and (graphite and Li-metal) anodes. This resulted in a 5.3V Li-metal cell, delivering a high energy density of 720 Wh/kg for 1k cycles. This battery chemistry features a Coulombic efficiency of >99%, offering new development opportunity for high-voltage and energy Li-ion batteries. A paper on their work is published in the journal Chem.
The energy density of current Li-ion batteries is limited by the low capacity of intercalation cathode, which leaves relatively little room to further improve because the specific capacities of these cathodes approach the theoretical levels. Increasing the cell output voltage is a possible direction to largely increase the energy density of the batteries.
Extensive research has been devoted to exploring >5.0 V cells, but only limited advances have been achieved because of the narrow electrochemical stability window of the electrolytes (<5.0 V). Herein, we report a 5.5 V electrolyte (1 M LiPF 6 in fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and hydrofluoroether [FEC/FDEC/HFE] with a Li difluoro(oxalate)borate [LiDFOB] additive) that enables 5.3 V LiCoMnO4 cathodes to provide an energy density of 720 Wh kg−1 for 1,000 cycles and 5.2 V graphite||LiCoMnO4 full cells to provide an energy density of 480 Wh kg−1 for 100 cycles. The 5.5 V electrolytes provide a large step toward developing high-energy Li batteries.—Chen et al.
The key, said Long Chen—a ChBE post-doctoral research associate and one of the first authors on the paper, is the super electrolytes with an especially wide electrochemical window of 0 - 5.5V. This is due to the formation of a robust interfacial layer on the electrodes, he explained.
The high voltage electrolytes enable us to use high voltage cathode and high capacity Si- and potential Li-metal anodes, which will significantly increase the cell energy density. However, the Coulombic efficiency of >99% for 5.3V LiCoMnO4 still needs improvement to achieve a long cycle life.—Chunsheng Wang
Chen, L., Fa, X., Hu, E., Ji, X., Chen, J., HouS., Deng, T., Li, J., Su, D., Yang, X., Wang, C. (2019) “Achieving High Energy Density through Increasing the Output Voltage: A Highly Reversible 5.3 V Battery.” Chem doi: XXX10.1016/j.chempr.2019.02.003XX