Layered P3-Type K_0.4Fe_0.1Mn_0.8Ti_0.1O₂ as a Low-Cost and Zero-Strain Electrode Material for both Potassium and Sodium Storage

Abstract

Layered transition metal oxides are ideal Na + /K + host materials due to their high theoretical capacities and appropriate working potentials, and the pursuit of cost-effective and environmentally friendly alternatives with high energy density and structural stability has remained a hot topic. Herein, we design and synthesize a low-cost and zero-strain cathode material, P3-type K 0.4 Fe 0.1 Mn 0.8 Ti 0.1 O 2 , which demonstrates superior properties for both potassium and sodium storage. The cathode delivers a reversible potassium storage capacity of 117 mA h g −1 at 20 mA g −1 and a fast rate capability of 71 mA h g −1 at 1000 mA g −1 . In situ Xray diffraction reveals a solid−solution transition with a negligible volume change of 0.5% upon K + insertion/deinsertion that ensures long cycling stability over 300 cycles. When the material is employed for sodium storage, a spontaneous ion-exchange process with Na + -containing electrolytes occurs. Thanks to the positive effects of the remaining K + ions that protect the layered structure from collapse as well as expand the interlayer structure, and the resulting K 0.12 Na 0.28 Fe 0.1 Mn 0.8 Ti 0.1 O 2 demonstrates a high sodium storage capacity of 160 mA h g −1 and superior cycling stability with capacity retention of 81% after 300 cycles as well as fast kinetics.

Recent Advances in Layered Metal‐Oxide Cathodes for Application in Potassium‐Ion Batteries

“…Despite the specific capacity loss caused by the electrochemically inactive Ti 4+ , it minimized the step-like voltage transitions and thus improved the electrochemical behavior. Zhang et al [102] developed a P3-type K 0.4 Fe 0.1 Mn 0.8 Ti 0.1 O 2 electrode by incorporating inexpensive and environmentally friendly Fe and Ti. This electrode showed a rapid rate capability (71 mAh g −1 at 1000 mA g −1 ) and excellent cycling stability over 300 cycles with a negligible volume change of 0.5% upon K + extraction/insertion, which was attributed to the suppression of multiple irreversible phase transitions originating from the presence of inactive Ti 4+ and strong Ti-O bonds relative to Fe/Mn-O bonds.…”

“…The stronger Ti-O bonds may increase the number of Mn-O and Fe-O covalencies and thus sup-press the movement of (Mn, Fe)O 6 octahedra by sharing oxygen atoms with Ti, resulting in structural stability and highrate performance. [102] Dang et al studied the influence of Mg 2+ and Al 3+ substitution in P3-type K 0.45 Ni 0.1 Co 0.1 Mn 0.8 O 2 . [99] The Mg/Al-doped compounds exhibited superior cycling and rate performance to the pristine compound owing to their displayed enlarged K + diffusion layers and reduced J-T distortions.…”

“…The P3‐K 0.4 Fe 0.1 Mn 0.8 Ti 0.1 O 2 cathode delivered an initial capacity of 117 mAh g −1 and exhibited long stability over 300 cycles and negligible volumetric change (0.5%). [ 102 ] Similarly, the P2‐K 0.6 Mn 0.8 Ni 0.1 Ti 0.1 O 2 solid solution did not exhibit any other phase transition (including OP4 or O2) and even charged to a high voltage of 4.2 V. In contrast, pristine P2‐K 0.6 MnO 2 exhibited complex P2‐OP4‐ X phase transitions during K + ‐ion extraction. [ 103 ] Furthermore, complex phase transitions considerably changed the pristine cathode c ‐axis lattice parameter (Δ c = 31%), whereas the doped P2‐K 0.6 Mn 0.8 Ni 0.1 Ti 0.1 O 2 cathode exhibited much less variation in the c ‐axis parameter (Δ c = 2.4%).…”

“…The stronger Ti—O bonds may increase the number of Mn—O and Fe—O covalencies and thus suppress the movement of (Mn, Fe)O 6 octahedra by sharing oxygen atoms with Ti, resulting in structural stability and high‐rate performance. [ 102 ] Dang et al. studied the influence of Mg 2+ and Al 3+ substitution in P3‐type K 0.45 Ni 0.1 Co 0.1 Mn 0.8 O 2 .…”

Hydration Enables Air‐Stable and High‐Performance Layered Cathode Materials for both Organic and Aqueous Potassium‐Ion Batteries

“…The total shrinkage of the interlayer distance between the full potassiation and depotassiation of KFMTO ⋅ 0.16H 2 O was only 2.7%, more minor than that of KFMTO (3.3%). [16] Note that the in situ XRD patterns of KFMTO ⋅ 0.16H 2 O were collected using the same instrument with the same experimental parameters as KFMTO in our previous published result to ensure the rationality of the comparison. This appealing phenomenon reveals the critical role of the preintercalated water molecules, as interlayer pillars in propping the structure and reducing the strain during cycling.…”