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Design of Stoichiometric Layered Potassium Transition Metal Oxide for K-Ion Batteries

Wednesday, 3 October 2018: 08:00
Galactic 7 (Sunrise Center)
H. Kim (Lawrence Berkeley National Laboratory), D. H. Seo, A. Urban, J. Lee, D. H. Kwon (University of California, Berkeley), S. H. Bo (Lawrence Berkeley National Laboratory), T. Shi (UC Berkeley), J. K. Papp (Department of Chemical Engineering, UC Berkeley), B. D. McCloskey, and G. Ceder (University of California, Berkeley)
The layered transition metal oxides (TMOs) which have been investigated as cathode materials for K-ion batteries (KIBs) have so far exhibited moderate specific capacity and rate capability. [1-6] However, all the layered K-TMOs reported to date are K-deficient phases (x ≤ 0.7 in KxTMO2),[1-6] which limits their use in practical rocking-chair batteries because a pre-potassiation process of the electrodes would be required to insert enough K in the cells. In this respect, it is important to understand the factors that destabilize (or stabilize) the layered structure of KxTMO2 (x = 1) and then design a stoichiometric KxTMO2 (x = 1) cathode material.

In this work, we find that the strong electrostatic repulsion between K ions due to the short K+-K+ distance destabilizes the layered structure in a stoichiometric composition of KTMO2. However, a stoichiometric KCrO2 is thermodynamically stable in the layered structure despite short K+-K+ distance unlike other KTMO2 compounds that form non-layered structures. The unique stability of layered KCrO2 is attributable to the unusual ligand field preference of Cr3+ in octahedral sites that can compensate for the energy penalty from the short K+-K+ distance. Therefore, we develop the stoichiometric layered KCrO2 cathode material for KIBs and investigate its K-storage properties. In K-half cells, the KCrO2 cathode delivers a reversible specific capacity of ~90 mAh/g with an average voltage of ~2.73 V (vs. K/K+). In-situ diffraction and electrochemical characterization further demonstrate multiple phase transitions via reversible topotatic reactions occurring as the K content changes.

References

  1. Vaalma, C., et al. Non-aqueous K-ion battery based on layered K0.3MnO2 and hard carbon/carbon black. J. Electrochem. Soc. 163, A1295 (2016)
  2. Kim, H. et al. K-ion batteries based on a P2-type K0.6CoO2 cathode. Adv. Energy Mater. 7, 1700098 (2017)
  3. Hironaka Y. et al. P2- and P3-KxCoO2 as an electrochemical potassium intercalation host. Chem. Commun. 53, 3693 (2017)
  4. Kim, H. et al. Investigation of potassium storage in layered P3-type K0.5MnO2 cathode. Adv. Mater. 29, 1702480 (2017)
  5. Wang, X. et al. Earth Abundant Fe/Mn-based layered oxide interconnected nanowires for advanced K-ion full batteries. Nano Lett. 17, 544 (2017)
  6. Liu, C. et al. K0.67Ni0.17C0.17Mn0.66O2: A cathode material for potassium-ion battery. Electrochem. Commun. 82, 150 (2017)