Preparation of High-performance water-removing separator based on MOFs materials and its application in High-voltage Lithium-ion batteries

At present, the miniaturization of electronic devices and the long range of electric vehicles have put forward higher and higher requirements for the energy density of lithium-ion batteries, and there is an urgent need to develop battery systems with higher energy density. The use of layered metal oxide LiMO2 cathode materials is one of the effective solutions to improve the energy density of lithium-ion batteries. However, the water in the electrolyte could react with LiPF6 in the electrolyte to generate corrosive HF that corrodes LiMO2 cathode and causes dissolution of the transition metal, which in turn leads to the degradation of battery capacity. To address the above problems, we designed and prepared a novel separator based on metal-organic frameworks (MOFs) material. In addition to the regular pore network structure and larger specific surface area compared to molecular sieves with similar pores, this MOFs material can effectively remove water from the electrolyte by spontaneous water molecule adsorption at its open metal sites, while suppressing the side reactions and capacity degradation problems triggered by water. The results show that the cycling stability of the NCM811||Li battery based on this novel water-removing separator is higher than that of the conventional PP separator in electrolytes with different water contents. At 300 ppm of electrolyte water content, the discharge specific capacity of the cell based on the new separator is 142.22 mAh/g after 200 cycles, and its capacity retention rate is 71.11%, which is much higher than that of the cell based on PP separator (39.95%). Even with the electrolyte water content as high as 600 ppm, the NCM811||Li battery based on this novel separator still has a capacity retention of 79.54% after 100 cycles. The present work is carried out to provide useful theoretical guidance for the related design of functionalized separators and an effective solution for the practical application of high-performance high-voltage lithium-ion batteries.

Dr. Dejun Li, distinguished professor of Physics and Materials Science, Tianjin Normal University, China, received his Ph.D. degree from the Tsinghua University, China, in 1999, He entered Northwestern University, USA as a Postdoctor in 2001. His research is focused on nanomaterials, energy storage materials, biomedical materials, ion-beam and thin films for surface modification of various materials.