An increase of the Zn-ion hybrid SC performance by carbon surface chemistry through the pseudocapacitance induced by proton transfer.

No abstract

The proton transfer mechanism on the carbon cathode surface has been considered as an effective way to boost the electrochemical performance of Zn-ion hybrid supercapacitors (SCs) with both ionic liquid and organic electrolytes. However, cheaper, potentially safer, and more environmental friendly supercapacitor can be achieved by using aqueous electrolyte. Herein, we introduce the proton transfer mechanism into a Zn-ion hybrid supercapacitor with the ZnSO4 aqueous electrolyte and functionalized activated carbon cathode materials (FACs). We reveal both experimentally and theoretically an enhanced performance by controlling the micropores structure and hydrogen-containing functional groups (–OH and –NH functions) of the activated carbon materials. The Zn-ion SCs with FACs exhibit a high capacitance of 435 F g−1 and good stability with 89% capacity retention over 10,000 cycles. Moreover, the proton transfer effect can be further enhanced by introducing extra hydrogen ions in the electrolyte with low pH value. The highest capacitance of 544 F g−1 is obtained at pH = 3. The proton transfer process tends to take place preferentially on the hydroxyl-groups based on the density functional theory (DFT) calculation. The results would help to develop carbon materials for cheaper and safer Zn-ion hybrid SCs with higher energy.

Lithium difluoro(axalato)borate (LiODFB) was synthesized in dimethyl carbonate (DMC) solvent and purified by the method of solventing-out crystallization. The structure characterization of the purified LiODFB was performed by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectrometry. The electrochemical properties of the cells using 1 mol/L LiPF 6 and 1 mol/L LiODFB in ethylene carbonate (EC)/DMC were investigated, respectively. The results indicate that LiODFB can be reduced at about 1.5 V and form a robust protective solid electrolyte interface (SEI) film on the graphite surface in the first cycle. The graphite/LiNi 1/3 Mn 1/3 Co 1/3 O 2 cells with LiODFB-based electrolyte have very good capacity retention at 55 , ℃ and show very good rate capability at 0.5C and 1C charge/discharge rate. Therefore, as a new salt, LiODFB is a most promising alternative lithium salt to replace LiPF 6 for lithium ion battery electrolytes in the future.

Supercabatteries, combining the energy of secondary batteries with the power of supercapacitors, have attracted significant attention in the energy storage research and market field. Herein, we continued our previous 3D electrode works and fabricated supercabatteries with the prelithiated ACNTs@MnOx positive and C/MnOy/ACNTs negative electrodes, which can offer ultrahigh discharge capacities and remarkable improved capabilities and stabilities. The theoretical specific capacities of the supercabatteries were calculated and predicted as function of the P/N mass ratios and initial potentials for the two electrodes, based on the half-cell results. The experimental specific capacities of the supercabatteries with different P/N mass ratios and charge injection pretreatments matched well with the prediction line. The supercabattery with a P/N mass ratio of 1.6 and optimized EPW delivered the maximum specific discharge capacity of 217 mAh g−1 and energy density of 208.6 Wh kg−1 based on the active materials. The supercabattery remained at 105.8 Wh kg−1 with a ultrahigh power density of 3000 W kg−1 and maintained 80% of the initial capacity after 1000 cycles.