Novel Electrolytes for High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material
Various methods have been proposed to inhibit the detrimental reactions on high voltage cathode materials. One of them is adopting inert surface coatings, such as Al2O3, ZnO, and Bi2O3 to prevent the oxidation of the electrolyte. Surface coated cathodes have cyclability superior to that of uncoated material; however, the surface coating method has a negative effect on the discharge capacity of the material and may be difficult to scale for commercial applications. Since the oxidative stability of current LiPF6/carbonate electrolyte is considered to be limited by the oxidative stability of the organic solvents, there has been significant interest in development of novel organic solvents with high anodic stability. Sulfone, lactone, organic nitriles, and fluorinated carbonates were reported to be stable over 5 V (vs. Li/Li+), but most of them have high viscosity or do not favor the formation of a protective solid electrolyte interface (SEI) on graphite anode. Alternatively, there have been several investigations of the incorporation of cathode film forming additives which are sacrificially oxidized on the cathode surface to generate a cathode passivation layer similar in nature to the anode SEI.
Some additives have been investigated which improve the performance of Li/LiNi0.5Mn1.5O4 cells, including dimethyl methyl phosphonate and Lithium bis(oxalato)borate (LiBOB). Most recently, the extension research work of LiBOB on Graphite/LiNi0.5Mn1.5O4 full cells was also reported. The incorporation of LiBOB significantly improves the cycling performance of graphite/LiNi0.5Mn1.5O4 cells when cycled at elevated temperature (55 oC) and high voltage (4.8 V vs Li/Li+). However, huge gas generation was observed upon cycling at high voltage and elevated temperature, which is not acceptable in practical applications. Therefore, novel electrolyte system is still highly need to drive the applications of high voltage cathode materials in lithium ion batteries.
Several types of novel additives are developing in our laboratory to meet the requirements of high voltage cathode materials upon cycling at over 4.5 V, vs. Li/Li+.
 M. Xu, L. Zhou, Y. Dong, Y. Chen, A. Garsuch, B. L. Lucht. J. Electrochem. Soc., 2013, 160: A2005.
 S. Dalavi, M. Xu, B. Knight, B. L. Lucht, J. Power Sources, 2011, 196, 2251.
 M. Xu, D. Lu, A. Garsuch, B. L. Lucht, J. Electrochem. Soc., 2012, 159, A2130.
 M. Xu, Y. Liu, W. Li, X. Li, S. Hu, Electrochem. Commun., 2012, 18, 123.
This research work is supported by the National Natural Science
Foundation of China (21373092, 21273084), the Joint Project of National Natural Science Foundation of China and Natural Science Foundation of Guangdong (No. U1134002).