MOF-based electrolyte effectively inhibits lithium dendrites and promotes the performance of lithium titanate anode materials for lithium metal batteries

Lithium metal has a specific capacity as high as 3,860mAh/g and an oxidation-reduction potential as low as -3.04V (relative to a standard hydrogen electrode). Therefore, the rechargeable lithium metal battery has become one of the most promising high-energy secondary rechargeable battery systems. However, the problem of lithium dendrites has seriously plagued the development of lithium metal batteries. Uncontrolled growth of lithium dendrites can quickly reduce battery performance, shorten battery life, and even pierce the membrane between electrodes, causing safety problems such as battery short-circuits. Therefore, how to achieve effective inhibition of lithium dendritic growth under the conditions of large current density, large energy density, and long cycle cycles becomes the key issue. In view of this, Dr. Songyan Bai and Dr. Yang Sun of the Japan Institute of Industrial Technology and Professor Haoshen Zhou of Nanjing University have developed a new type of MOF-based electrolyte that can inhibit the growth of lithium dendrites under high current and high capacity. Research highlights: 1. MOF-based electrolytes can effectively inhibit the growth of lithium dendrites under high current density, high energy density, and long cycle cycles. 2. Through calculations, it is proved that the MOF structure can effectively regulate TFSI ions and achieve uniform Li+ ion transmission. TOC diagram MOF-based electrolyte uses the ordered ultra-microporous structure of MOF (HKUST-1) as an ion sieve to achieve effective regulation of anion and cation transmission in ordinary electrolyte (1MLiTFSIDOL/DME), and exhibits a high ion mobility coefficient And high ionic conductivity. Compared with the disordered transmission of anions and cations in the ordinary electro-hydraulic solution and causes uneven lithium deposition, the MOF structure can provide efficient ion channels and selectively slow down the passage of TFSI? anions in it, thereby achieving uniform lithium ion transmission. , To achieve homogeneous lithium deposition. In order to clarify the mechanism by which MOF channels play a role in the transport of anions and cations, the researchers made a series of theoretical calculations. Calculated by density functional theory (DFT). In two extreme cases, TFSI® anions pass through the energy barrier in the MOF channel in the horizontal (Path-I) or vertical (Path-II) situations. When the MOF frame is in a rigid or relaxed state, the energy barrier difference between them (point F and F') reaches 1.26 eV and 0.63 eV, respectively. Correlation calculations show that the space limitation of the MOF channel selectively delays the transport of TFSI? anions in the channel. The results of molecular dynamics simulation (MD) prove that the MOF structure can achieve uniform Li+ ion transport through effective regulation of TFSI? anions. In ordinary electro-hydraulic (1MLiTFSIDOL/DME), due to the solvation process, the mean square shift of TFSI? anions is faster than that of solvated Li+ ions. In the MOF-based electrolyte, the MOF pores will delay the passage of TFSI? anions, which makes the mean square displacement of Li+ ions diffuse faster. Compared with the disordered transmission of anions and cations in ordinary electro-liquid and causing uneven lithium deposition, the MOF structure can provide efficient ion channels and selectively delay the passage of TFSI? anions in it, thereby achieving uniform lithium ion transmission. , To achieve homogeneous lithium deposition. Symmetrical battery tests are carried out under high current density (5mA/cm2, 10mA/cm2 and 10mA/cm2), and the corresponding energy density is (2.5mAh/cm2, 5mAh/cm2 and 10mAh/cm2). Symmetrical batteries can be Long cycle time, at least more than 800 hours without obvious signs of short circuit. The growth of lithium dendrites in the lithium metal negative electrode after the cycle was observed by SEM. Symmetrical batteries using traditional electrolyte, under the conditions of 10mAh/cm2 and 10mAh/cm2, the battery short-circuited after 120 hours. On the surface of the lithium metal negative electrode, a large number of lithium dendrites with a length of 10 μm pierce the diaphragm and cause a short circuit. In symmetric batteries using MOF-based electrolytes, the growth of lithium dendrites is significantly suppressed. Under the conditions of three large current densities, there is no obvious lithium dendritic growth. The use of lithium titanate as the electrode material verifies that the lithium metal battery using the MOF-based electrolyte can also exhibit stable long-cycle performance under high current conditions. When the current density reaches 7mA/cm2, the lithium titanate-lithium metal battery has only a capacity loss of 7mAh/cm2 after 2000 cycles. The capacity loss rate per lap is as low as 0.0025%. In short, this study reported for the first time the role of MOF-based electrolytes in the protection of lithium negative electrodes, which is of great significance to the further development of lithium metal batteries. In addition, the study also demonstrated the potential of MOF's ultra-microporous structure in battery systems.