Recently, Yan Jian, a professor at the School of Materials Science and Engineering, Hefei University of Technology, collaborated with Mao Wenping, a researcher at the Strong Magnetic Field Science Center of the Hefei Research Institute of Materials Science, Chinese Academy of Sciences, to study the Al. 3+The electrochemical cycling stability of doped manganese dioxide was reported in the ACS Appl. Mater. Interfaces magazine.
Supercapacitors have the characteristics of high specific capacity, long cycle life, and environmental friendliness. They play a role of green energy in electronic products and hybrid power systems. Supercapacitor electrode materials are the key factors affecting the electrochemical performance of supercapacitors. MnO 2) Not only theoretical high specific capacity, but also rich in raw materials, is an electrode material with good application prospects. However, due to its poor conductivity and cycle stability, the capacity retention rate during electrochemical cycling needs to be improved. Metal ions can improve the electrochemical performance and cycling stability of manganese dioxide.
The researchers prepared Al by chemical precipitation 3+Doped MnO 2(Al-MO) and pure MnO 2(MO) Two kinds of electrode materials and analysis of the electrochemical performance of the two. The test found that: The Al-MO electrode has a specific capacity of 264.6 F/g at a current density of 1 A/g, which is higher than that of an MO electrode (180.6 F/g). And at room temperature and 50 °C high temperatures have good cycle stability. By field emission scanning electron microscopy observation of the electrode in different cycles after the micro-morphology, found that Al-MO electrode gradually changed from granular to the needle The structure, but the crystal shape did not change, while the MO electrode at the same time in the cycle of morphology and crystal shape changes.
To further understand the relationship between electrode morphology evolution and electrochemical stability, the researchers used in situ solid-state NMR to observe Na in different charge and discharge cycles. +In the process of intercalation/deintercalation of Al-MO and MO positive electrodes, it was found that the 23Na peak of the MO electrode during charge and discharge showed different changes at different potentials and cycles, indicating that the MO electrode undergoes structural changes in the cycle. The peak of 23Na spectrum did not change significantly during the charge-discharge process of Al-MO electrode, and there was no change even in the first cycle. This indicates that Na+ has a rapid and reversible intercalation/deintercalation reaction on the Al-MO electrode surface. It shows that the Al-MO electrode structure is stable.
Based on the above test results, the investigators speculate that the morphology evolution of MO electrodes during the cycle may follow the process of 'powdering-self-assembly'. The insertion/deintercalation of Na+ leads to MnO 2The volume of the nanoparticle changes to cause powdering of the surface, and these powderized nanoparticles show a change in morphology after reassembly. In the case of weak bonding, the reassembled microparticles may dissociate from the parent and dissolve in the electrolyte. With the loss of active electrode material, the capacitance will gradually decrease. For MnO 2Perform Al 3+Doping can enhance the bonding between the powdered particles, which helps to improve MnO 2The structural stability.
Some of the experiments in this study were combined with self-made static probes on the 600 MHz solid-state NMR spectrometer at the Regional Center for Large Instruments in Hefei Strategic Energy and Material Science at the Chinese Academy of Sciences.
Fig. 23Na spectrum of Al3+ doped MnO2 during charging and discharging, microscopic morphology and specific capacity at room temperature and 50°C
