Reversible facile Rb⁺and K⁺ions de/insertion in a KTiOPO₄-type RbVPO₄F cathode material

Abstract

In this paper, we report on a novel RbVPO4F fluoride phosphate, which adopts the KTiOPO4 (KTP) type structure and complements the AVPO4F (A = alkali metal) family of positive electrode (cathode) materials for metal-ion batteries.

Tuning the Crystal Structure of A2CoPO4F (A = Li, Na) Fluoride‐Phosphates: A New Layered Polymorph of LiNaCoPO4F

“…Generally, the PBE flavor of the exchange‐correlation potential overestimates experimental lattice constants of phosphates by 1–2 % . Considering a similar behavior of PBE for the LiNaCoPO 4 F phases, the cell parameters for Co 2+ in a high spin state indeed exceed the experimental values by 0–2 %, confirming that Co 2+ is in a high spin state, which was also previously validated by magnetic susceptibility measurements for 3D‐LiNaCoPO 4 F …”

Safe, Low‐Cost, Fast‐Kinetics and Low‐Strain Inorganic‐Open‐Framework Anode for Potassium‐Ion Batteries

“…[16] Galvanostatic intermittent titration technique (GITT) analysis further confirms the fast K + diffusion within the KTP structure ( Figure S16). Electrochemical impedance spectroscopy (EIS) show that, upon activation, the charge transfer resistance (R ct )d ecreases from 4387 to 773 W after 100 cycles,w hich is substantially smaller than those of WS 2 ( % 1671 W), Dynamics simulations using bond balance energy landscape (BVEL) and climbing image nudged elastic band (CI-NEB) methods are conducted to unveil the origin of the fast K + -diffusion kinetics.A ss hown in Figures 4a-c and S17, the BVEL method reveals that K + ions preferentially migrate through aone-dimensional (1D) helical pathway along the baxis,similar to that of Rb + in RbVPO 4 F. [18] K + migration along the a-and c-axis are considered impassable due to extremely high energy barriers.W efurther calculate the energy barriers of the possible K + pathways via the CI-NEB method, the corresponding energy profiles are presented in Figures 4d-f. It is shown that the energy barriers along path 1, path 2, path 3 and path 4are 0.11, 0.15, 1.18 and 1.77 eV,respectively.These results again confirm the 1D helical K + -migration trajectory that is composed of path 1a nd path 2a nd possesses at otal energy barrier of as low as 0.15 eV (Figures 4d,S 17).…”

Investigation of Alkali‐Ion (Li, Na, and K) Intercalation in KxVPO4F (x ∼ 0) Cathode

“…In this work, we investigated and contrasted alkali ion (Li, Na, and K) intercalation properties in K x VPO 4 F ( x ∼ 0) by a combined experimental and computational study. Related work has been done by Fedotov et al and Nikitina et al Fedotov et al demonstrated that depotassiated K x VPO 4 F ( x ∼ 0.15) can intercalate Li ions reversibly, and found that Li ions occupy under‐coordinated sites, compared to K sites . Later, alkali ion diffusivity in K x VPO 4 F ( x ∼ 0.5) and Rb x VPO 4 F ( x ∼ 0.5) was investigated and compared by Nikitina et al and Fedotov et al, respectively .…”

“…Related work has been done by Fedotov et al and Nikitina et al Fedotov et al demonstrated that depotassiated K x VPO 4 F ( x ∼ 0.15) can intercalate Li ions reversibly, and found that Li ions occupy under‐coordinated sites, compared to K sites . Later, alkali ion diffusivity in K x VPO 4 F ( x ∼ 0.5) and Rb x VPO 4 F ( x ∼ 0.5) was investigated and compared by Nikitina et al and Fedotov et al, respectively . These authors found that K migration along the c ‐axis has a low barrier (≈200 meV) and the Li ion diffusivity is lower than for Na and K ions in the K x VPO 4 F ( x ∼ 0.5) structure despite its smaller ionic size .…”

“…Later, alkali ion diffusivity in K x VPO 4 F ( x ∼ 0.5) and Rb x VPO 4 F ( x ∼ 0.5) was investigated and compared by Nikitina et al and Fedotov et al, respectively . These authors found that K migration along the c ‐axis has a low barrier (≈200 meV) and the Li ion diffusivity is lower than for Na and K ions in the K x VPO 4 F ( x ∼ 0.5) structure despite its smaller ionic size . There are some differences between the Fedotov et al's compound and ours in the voltage profile, which is attributable to different V‐oxidation and O/F between the two as previously discussed .…”