Structural Insight into Layer Gliding and Lattice Distortion in Layered Manganese Oxide Electrodes for Potassium‐Ion Batteries

Abstract

grids. Current growth rates in lithiumion battery (LIB) manufacturing are not sustainable given our limited lithium resources. In this context, alternative battery systems with low cost are sought, with sodium-and potassium-ion batteries (SIBs and PIBs, respectively) regarded as suitable replacements due to the high natural abundance of sodium and potassium and their similar working mechanism to LIBs. [1] Of these, PIBs are more promising due to the closeness of the K + /K redox potential (−2.9 V vs H + /H 2 O) to that of Li + /Li (−3.0 V vs H + /H 2 O), as compared to Na + /Na (−2.7 V vs H + /H 2 O), and the consequential ease of reversible K + intercalation into the most common LIB negative electrode, graphite. [2][3][4] The slow kinetics of the reversible insertion of K + in electrode materials as a result of its relatively large ionic radius of 1.38 Å is a major issue for the realization of high-performance PIBs. [5][6][7] For PIB technology to be successful, scientists need to find stable electrode materials capable of reversibly hosting K + relatively quickly. Transition metal layered oxides possess a 2D structure that can accommodate large ions and are attracting interest as potential PIB electrode materials. [8][9][10][11][12][13][14] Among these, manganese layered oxides are particularly promising due to the high natural abundance and nontoxicity of manganese. A range of layered K x MnO 2 structure types can be prepared [15,16] including Potassium-ion batteries (PIBs) are an emerging, affordable, and environmentally friendly alternative to lithium-ion batteries, with their further development driven by the need for suitably performing electrode materials capable of reversibly accommodating the relatively large K + . Layer-structured manganese oxides are attractive as electrodes for PIBs, but suffer from structural instability and sluggish kinetics of K + insertion/extraction, leading to poor rate capability. Herein, cobalt is successfully introduced at the manganese site in the K x MnO 2 layered oxide electrode material and it is shown that with only 5% Co, the reversible capacity increases by 30% at 22 mA g -1 and by 92% at 440 mA g -1 . In operando synchrotron X-ray diffraction reveals that Co suppresses Jahn-Teller distortion, leading to more isotropic migration pathways for K + in the interlayer, thus enhancing the ionic diffusion and consequently, rate capability. The detailed analysis reveals that additional phase transitions and larger volume change occur in the Co-doped material as a result of layer gliding, with these associated with faster capacity decay, despite the overall capacity remaining higher than the pristine material, even after 500 cycles. These results assert the importance of understanding the detailed structural evolution that underpins performance that will inform the strategic design of electrode materials for high-performance PIBs.

Hierarchical Engineering of Porous P2‐Na2/3Ni1/3Mn2/3O2 Nanofibers Assembled by Nanoparticles Enables Superior Sodium‐Ion Storage Cathodes

“…The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials. [36,[54][55][56] To gain insight into the underlying Na-storage reaction mechanism of the P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofiber electrode, in operando XRD was performed between 1.5 and 4.0 V using Al foil as both the current collector and testing window. Figure 2d displays the rate capability of the P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofiber cathode.…”

Review on Recent Advances of Cathode Materials for Potassium‐ion Batteries

“…b) Schematic structure of P3‐type K 0.5 MnO 2 structure. Reproduced with permission . Copyright 2017, John Wiley and Sons; c) schematic structure of O3‐type KCrO 2 ; d) In situ XRD patterns of KCrO 2 between 5° and 25°; e,f) XRD patterns of highlighted regions (e, yellow; f, green) in d. Reproduced with permission .…”

Toward a Reversible Mn4+/Mn2+ Redox Reaction and Dendrite‐Free Zn Anode in Near‐Neutral Aqueous Zn/MnO2 Batteries via Salt Anion Chemistry

“…Rechargeable batteries are one of the most promising methods for energy storage. [1][2][3][4] For large-scale energy storage to be feasible, however, the electrodes employed need to be cost-effective, and the systems should be long lasting and safe during operation. Aqueous batteries are favorable candidates owing to their intrinsic safety and environmental friendliness.…”