Because of its high theoretical specific capacity, Si negative electrodes and lithium-rich positive electrodes are the research hotspots for the next generation of electrode materials for high energy density lithium-ion batteries. However, due to the large volume expansion of Si negative electrodes during cycling and the irreversible phase transition of lithium-rich positive electrodes, limitations Its practical application.
Recently, Professor Jaephil Cho, Professor Sung You Hong, and Professor Nam-Soon Choi of Ulsan University of Technology in South Korea published the title of 'Unsymmetrical fluorinatedmalonatoborate as an amphoteric additive for high-energy-density lithium-ion battery' as a co-corresponding author in Energy & Environmental Science. 'The research article. The researchers introduced the electrolyte additive LiFMDFB, which has a double modification of the positive and negative electrodes. With the help of FEC, improved the electrochemical performance of the full cell based on lithium-rich positive electrode and silicon-carbon negative electrode.
Figure 1: (a): LiFMDFB Synthesis Roadmap
(b): Comparison of HOMO/LUMO energy levels of EC, FEC, VC, LiDFOB, LiFMDFB, etc.
Comparing the highest occupied molecular orbital (HOMO) energy level and the lowest unoccupied molecular orbital (LUMO) energy level of the materials EC, FEC, VC, LiDFOB, LiFMDFB, etc., it can be found that the LUMO level of LiFMDFB is lower than the LUMO of FEC. The energy level indicates that LiFMDFB has stronger electron affinity and will be reduced by electrons before FEC decomposes and adheres to the surface of the negative electrode material. At the same time, LiFMDFB has higher HOMO energy level than EC, and FEC has preferential oxidation loss. Preferential reduction is accompanied by preferential oxidation. It is possible to use LiFMDFB to form a protective barrier at both positive and negative electrodes. Apply it to a full battery with a lithium-rich positive electrode and a silicon-carbon negative electrode. The energy density, Coulomb efficiency, and cycle stability of the battery are both It has been significantly improved. The improvement of the battery performance is due to the fact that the LiFMDFB-induced positive electrode protective layer prevents the intergranular crack generation of the lithium-rich material and the irreversible transformation from the layered to the spinel phase, while being induced by LiFMDFB+FEC. The negative SEI film effectively suppresses the volume expansion of silicon.
Figure 2: (a) Comparison of cycle stability of lithium-rich/silicon-carbon full cells with and without LiFMDFB additives
(b): Comparison of lithium-rich/silicon-carbon full battery rate performance with or without LiFMDFB additive
Figure 3: LiFMDFB-induced protection of lithium-rich cathode materials
Figure 4: SEM Morphology of Lithium-enriched Cathode Materials after Cycling
Figure 5: Comparison of the effect of LiFeDFB+FEC-induced SEI layer on silicon carbon anode materials
