Exploring the new breakthroughs made by BIT in 3.7v 18650 battery pack research

Recently, the team of Academician Wu Feng of BIT has made a breakthrough in the research of positive electrode materials for aluminum-ion batteries. AlxMnO2·nH2O compound was synthesized as the positive electrode material for aluminum-ion batteries for the first time through in-situ electrochemical conversion reaction, and the aqueous 3.7v 18650 battery pack Al/Al(OTF)3-H2O/AlxMnO2·nH2O was successfully constructed using Al(OTF)3-H2O electrolyte. The aqueous 3.7v 18650 battery pack achieved an ultra-high three-electron reaction discharge capacity of 467mAhg-1, and the energy density based on the material can be as high as 481Whkg-1. In addition, this aqueous 3.7v 18650 battery pack also has the important advantages of high safety, easy assembly and low cost. The research results were published in the international journal "Nature Communications" under the title "Electrochemically activated spinelmanganese oxide for rechargeable aqueous aluminum battery". This progress was made by a research team led by Professor Wu Chuan in the team, and was supported by researchers from the Institute of Physics, Chinese Academy of Sciences and Argonne National Laboratory. Among all the metal electrode materials currently available, aluminum has the highest volumetric capacity. In addition, it has the advantages of light weight, high reliability, safe use, low price and abundant resources. Its typical multi-electron reaction characteristics make aluminum ion batteries an ideal choice for energy storage systems. However, due to the high charge of three electrons, aluminum ions have poor electrode reaction kinetics, which easily destroys the material structure during charging and discharging. The overpotential of the three-electron reaction is high, resulting in poor cyclability. It is currently difficult to have both high energy density and excellent cycle performance. These technical difficulties have led to the fact that aluminum ion batteries have not been successfully applied in electrochemical energy storage and conversion technologies. The development of high-performance cathode materials and new electrolytes is an urgent problem to be solved for aluminum ion batteries. The research team designed an in-situ conversion electrochemical reaction to convert spinel Mn3O4 into a layered, amorphous mixed phase AlxMnO2·nH2O containing water. In order to verify the feasibility of this method, the chemical state and element types of the reaction products were analyzed and characterized by electron energy loss method (EELS), X-ray photoelectron analysis and transmission electron microscopy-energy dispersive X-ray spectroscopy. Through analysis, the Mn element was converted from 2-valent/3-valent to 4-valent after the electrochemical conversion reaction. Thermogravimetric analysis showed that the reaction product showed a more obvious mass decline trend at 50-300 ° C, indicating the loss of crystal water during the conversion reaction. The above series of characterizations and analyses further proved the occurrence of the in-situ conversion reaction of Mn3O4→AlxMnO2·nH2O. The researchers observed the changes in the material structure in the in-situ conversion reaction more intuitively through X-ray diffraction and transmission electron microscopy, and found that during the in-situ conversion reaction, the spinel phase of Mn3O4 gradually became amorphous, and only a small part of the layered phase was retained. It can be seen from the high-resolution transmission electron microscopy results that compared with the spinel Mn3O4 before the reaction, the reaction product AlxMnO2·nH2O has an obvious amorphous layer. The atomic-level arrangement of the material can be observed using a spherical aberration-corrected electron microscope. Under the action of electric current and aqueous electrolyte, tetrahedral Mn2+ and part of octahedral Mn3+ are dissolved from the spinel structure, and the amorphous phase formed by oxidation under the action of electric current is redeposited on the surface of the original nanoparticles. Therefore, the mixed existence of spinel, layered and amorphous phases can be clearly seen in the spherical aberration electron microscope. The surface water-containing amorphous layer structure is conducive to the insertion and extraction of aluminum ions, so that the positive electrode material has the ability to quickly extract and extract aluminum ions. Aqueous aluminum ion batteries were assembled with AlxMnO2·nH2O as the positive electrode, metal aluminum sheet as the negative electrode, and Al(OTF)3-H2O as the electrolyte. It was found that AlxMnO2·nH2O showed a short charging platform and a long charging platform at 1.3V and 1.65V, respectively, corresponding to the extraction reaction of aluminum ions. The first-week discharge capacity of up to 467mAhg-1 and the high discharge platform voltage (average value reaches 1.1V) make the energy density of this electrode material as high as 481Whkg-1, which is leading in the current related research reports. This work is the first to apply the spinel-layered conversion reaction to an aqueous three-electron battery system, providing a new path for the development of 3.7v 18650 battery pack electrode materials and new electrolytes, demonstrating the application potential of transition metal oxide electrode materials in the construction of high-energy 3.7v 18650 battery pack systems, and providing new ideas and methods for realizing large-scale energy storage systems with high safety and high performance. The above work was supported by the National 973 Program and the National Natural Science Foundation of China.

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