Electrochemical Cycling Stability of Doped Manganese Oxide in Supercapacitor Electrode Material Has Been Developed

The researchers prepared chemically precipitated Al3+-doped MnO2 (Al-MO) and pure MnO2 (MO) electrode materials and analyzed their electrochemical performance. It was found that the specific capacity of the Al-MO electrode at the current density of 1 A/g was 264.6 F/g, which was higher than that of the MO electrode (180.6 F/g), and the cycle stability was good at both room temperature and 50°C. Sex. The micro-morphology of the electrode after various cycles was observed by field emission scanning electron microscope. It was found that the Al-MO electrode gradually changed from granular to needle-like structure, but the crystal shape did not change, and the MO electrode was in the cycle At the same time, changes in morphology and crystal form occurred.

To further understand the relationship between electrode morphology evolution and electrochemical stability, the researchers used in-situ solid-state NMR to observe the process of embedding/deintercalating Na+ in Al-MO and MO positive electrodes during different charge and discharge cycles. The 23Na spectrum peak of MO electrode showed significant changes at different potentials and cycles during the discharge process, indicating that the structure of MO electrode changed during the cycle; the peak of 23Na spectrum did not change significantly during the charge-discharge process of Al-MO electrode. Even in the first cycle, there was no change, indicating that Na+ rapidly and reversibly intercalates/deintercalates on the Al-MO electrode surface, indicating that the Al-MO electrode structure is stable.

Based on the above test results, the researchers speculate that the morphology evolution of the MO electrode during the cycle may follow the "powdering-self-assembly" process. The intercalation/deintercalation of Na+ resulted in the change of the volume of MnO2 nanoparticles, which led to the powdering of the surface. These powdered nanoparticles exhibited a change in morphology after reassembly. In the case of a weak bond, the reassembled microparticles may dissociate from the matrix and dissolve in the electrolyte. With the loss of active electrode material, the capacitance will gradually decrease. The Al3+ doping of MnO2 can enhance the bonding between the powdered particles, which is beneficial to improve the structural stability of MnO2.

Some of the experiments in this study were carried out on a 600 MHz solid-state NMR spectrometer at the Regional Center for Large Instruments of Hefei Strategic Energy and Material Science at the Chinese Academy of Sciences in conjunction with a self-made static probe.