Six-Membered-Ring Malonatoborate-Based Lithium Salts as Electrolytes for Lithium Ion Batteries

• Published in: ECS transactions 2011-09, Vol.33 (39), p.57-69
• Main Authors: Yang, Li, Zhang, Hanjun, Driscoll, Peter F., Lucht, Brett, Kerr, John B.
• Format: Article
• Language: English
• ISSN: 1938-5862; 1938-6737
• DOI: 10.1149/1.3589921

A new class of lithium salts of malonatoborate anions has been synthesized. These six-membered-ring salts provided slightly lower ionic conductivity than that of LiBOB and LiBF4. Nevertheless, compared with LiBOB and LiPF6, the lowered ring strains in the malonatoborate structures and reduced numbers of fluorine atoms in the molecules was found to enhance the thermal and water stabilities and compatibilities of these salts with ether solvents. Small amount LiDMMDFB when used as an additive, was found to stabilize LiPF6 in carbonate electrolytes at 80oC for one month. Employing LiMDFB as the electrolyte in Li/Li cells and full cells, large interfacial impedances were observed on lithium metal and the cathode. The large impedances are at least partially attributed to the acidic hydrogen atoms in the malonate structure. This issue can be addressed by replacing the acidic atoms with methyl groups.