Breakthrough in Lithium Metal Battery Technology CIPA Electrolyte for High-Energy-Density and Long-Life Batteries
TapTechNews August 14th news, although the theoretical energy density of lithium metal batteries exceeds 500 Wh/kg (about 1700 Wh/lb), due to the very limited cycle life, the commercialization process is very restricted. This is mainly because the interface stability between the electrolyte and the electrode is poor, and the traditional electrolyte is difficult to be compatible with the lithium metal anode and the high-voltage cathode. Therefore, designing an electrolyte with high stability interfaces at both the anode and the cathode is the key to realizing high-energy-density lithium metal batteries.
The Chinese Academy of Sciences announced that the specially-appointed researcher Wang Xuefeng from the Institute of Physics / National Center for Condensed Matter Physics, Beijing, jointly with researchers from Peking University, University of Science and Technology of China, and Soochow University, proposed a dense ion pair aggregate (CIPA) electrolyte, which can develop a long-life lithium metal pouch battery under dilute electrolyte conditions.
According to the official introduction, this contact ion pair aggregate electrolyte with a unique nanoscale solvation structure. When assembled with a high-nickel cathode (LiNi0.905Co0.06Mn0.035O2), the 505.9 Wh/kg lithium metal pouch battery has an energy retention rate of 91% after 130 cycles.
Related research results have been published in the journal Nature Energy under the title of Towards long-life 500 Wh kg-1 lithium metal pouch cells via compaction-pair aggregate electrolytes (TapTechNews attached DOI: 10.1038/s41560-024-01565-z).
In structure, the CIPA electrolyte forms a thin and uniform SEI film on the surface of the lithium metal anode. The average thickness of this film is about 6.2 nm, which is lower than the SEI film formed in the local highly concentrated electrolyte. The SEI films formed in both electrolytes show an organic-inorganic composite structure, and the size and distribution of Li2O nanocrystals in the SEI film formed by the CIPA electrolyte show higher uniformity.
In terms of composition, compared with the CIPA electrolyte, the SEI formed by the LHCE-G3 electrolyte has less LiF content and stronger C- and O-signals, indicating that the decomposition of the FSI− anion is reduced and the solvent decomposition is more serious.
In terms of spatial distribution, the C- and S-elements in the SEI film derived from the CIPA electrolyte are more evenly distributed from the inside to the outside, while in the LHCE-G3 electrolyte, a significant C-signal is detected on the outer layer of the SEI film, and the S-signal is concentrated on the inner layer, indicating that the reduction behavior of the LHCE-G3 electrolyte is not uniform, which will trigger local lithium deposition and lead to the formation of lithium dendrites.
The comprehensive interface characterization results of the research found that the FSI− anion in the CIPA electrolyte is rapidly reduced through a collective electron transfer mechanism, forming an SEI film rich in LiF and Li2O and with low organic content. This stable SEI layer provides effective protection for the lithium metal anode and prevents further side reactions, the reby enhancing the cycle stability and safety of the lithium metal battery.