Ultralong lifespan of SuperRedox Capacitor using Ti-doped Li3V2(PO4)3 cathode with suppressed vanadium dissolution

Abstract

In this study, we successfully synthesized highly dispersed composites of multiwalled carbon nanotubes (MWCNTs). This was achieved by stoichiometrically substituting various metal ions, namely Ti⁴⁺, Al³⁺, and/or Mn²⁺, into monoclinic Li₃V_2−X M_X(PO₄)₃ (LVP), where X varies from 0 to 0.5. The substituted LVP materials, including Ti-, Al-, and Mn-LVP, consistently exhibited enhanced electrochemical performance, surpassing 10 000 cycles in cycling tests. Notably, Ti-LVP (X = 0.1) displayed a remarkable capacity retention of 88.6% after 10 000 cycles. Our investigation entailed comprehensive characterization of the electrochemical behavior of Ti-LVP over the entire doping range (X = 0–0.5). This characterization considered the crystal structure and its potential dependence on V-sites and Li-sites, along with their interplay with the proposed mechanism. Remarkably, a significant reduction (>50%) of vanadium dissolution was observed in immersion tests in polar solvents under extreme conditions with Ti-doped LVP. To gain further insights into this groundbreaking suppression behavior, we employed a combination of X-ray absorption fine structure (XAFS) analysis and precise molecular orbital calculations via the DV-Xα method. This approach unveiled a potential reduction in the ionicity of V³⁺ in V–O bonds within the bulk of LVP crystals and underscored surface interactions with electrodes and particles as contributing factors. The impact of suppressing parasitic reactions at the anode due to vanadium dissolution was evident in full-cell tests employing a configuration of Li₄Ti₅O₁₂/(1 M LiPF₆/EC:DEC)/Li_2.9V_1.9Ti_0.1(PO₄)₃, which demonstrated exceptional performance. Overall, the findings of this study hold significant promise for advancing the development of ultrafast and reliable energy storage technologies such as SuperRedox Capacitors, paving the way for a more sustainable and environmentally friendly future.