Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential

Abstract

The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO 4 F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

Electrochemical Redox Processes Involved in Carbon-Coated KVPO4F for High Voltage K-Ion Batteries Revealed by XPS Analysis

“…Instead, these results likely originate from structural constraints hindering the extraction (and insertion) of K + from x=0.5 to x=0 as proposed previously. 19,31 To evaluate the possibility to further extract the remaining K + , a cell was hold at 5 V for 18h during the 3 rd cycle and the corresponding DOxps was +3.9 ( Fig. S10), in agreement with the evolution of the cell parameters determined by XRD (not shown).…”

“…This structural constraint could increase the K + migration barrier, inducing a decrease in the K + diffusion coefficient, 31 slowing the global extraction process.…”

Fluoro(Phosphates,Sulfates) or (Phosphate,Sulfate) Fluorides: Why Does It Matter?

“…Specifically, the group of E. V. Antipov has been thoroughly studying the crystallochemistry and the electrochemistry of various transition metals phosphate fluorides. [ 5,9,26,27 ] We also found one paper about Li 2 CoPO 4 F from Okada et al. [ 8 ] dating from 2005.…”

“…Specifically, the group of E. V. Antipov has been thoroughly studying the crystallochemistry and the electrochemistry of various transition metals phosphate fluorides. [5,9,26,27] We also found one paper about Li 2 CoPO 4 F from Okada et al [8] dating from 2005. To the best of our knowledge, these are the only groups using the correct denomination "fluoride phosphates" for such materials, and probably the use of this accurate nomenclature is lowering their visibility.…”

Solid state chemistry for developing better metal-ion batteries

“…In practice, shifting the ionocovalency of the M–L bond through the inductive effect appears a useful tool to tune the redox potentials in quite a broad range. For instance, a cumulative inductive effect of fluoride and phosphate anion species in KTiPO 4 F allowed for a substantial boost of the Ti 4+ /Ti 3+ redox potential up to 3.6 V vs. K + /K turning it into a prospective cathode despite the well-establish perception of Ti-containing compounds as “only-anode” materials 98 . …”