Recently, a research team has made key progress in the development and application of high-voltage electrolyte systems, and the relevant research results have recently been published in an international journal.
issue
According to reports, the current lithium-ion battery due to its excellent electrochemical properties have been widely used in electric vehicles, cathode material is one of the key factors affecting the performance of lithium-ion batteries, the use of high specific energy cathode materials (such as NCM811) and improve the battery operating voltage (>4.2V) is the most effective way to obtain higher energy density. However, the traditional carbonate-based electrolyte cannot be adapted to the high-voltage battery system, and various side reactions occur in the ternary cathode material at high voltage, which eventually leads to system degradation and capacity attenuation.
breakthrough
The research team developed a new type of high-pressure fluorinated electrolyte system, which broke through the working voltage of NCM811 cathode material from 4.2V to 4.6V, expanded the upper limit and application scope of the ternary system, and solved two important problems: greatly improved the specific capacity and working voltage of the high-nickel ternary cathode system, suppressed the structural phase change of the NCM811 cathode at high voltage, dissolved transition metal ions and cracking of secondary particles, and reduced polarization. Thereby improving the energy density and cycle performance of the system. Stable CEI and SEI are constructed to achieve reversible and stable cycling of high-load and high-nickel ternary system batteries at high voltages.
According to the researchers, the reasons for the performance improvement of the high-voltage battery system are explained through the density functional theory (DFT) calculation system. The fluorine substituent (-F) has a strong electron-absorbing effect, reducing the solvent's highest occupied molecular orbital (HOMO), thereby increasing the oxidation potential of the electrolyte. By forming a thin and uniform B-rich and F-rich inorganic electrolyte interface on the surface of the cathode, the cracking of secondary particles is reduced, the contact area between the positive electrode and the electrolyte is reduced, and the poor electrical contact, side reactions and transition metal ion dissolution are greatly inhibited, thus breaking through the obstacles such as severe capacity attenuation of the high nickel ternary cathode at high voltage, providing a new idea and way for the design and development of high energy density lithium-ion batteries.
Article source: Science and Technology Daily