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Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed-alkali honeycomb layered oxide material, namely, NaKNi TeO . Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of Na and K atoms. We also investigate the possibility of mixed electrochemical transport and storage of Na and K ions in NaKNi TeO . In particular, we report an average discharge cell voltage of about 4 V and a specific capacity of around 80 mAh g at low specific currents (i.e., < 10 mA g ) when a NaKNi TeO -based positive electrode is combined with a room-temperature NaK liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for \"dendrite-free\" electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials.

Silver Degenerate States In article number 2204672, using high‐resolution transmission electron microscopy (HRTEM), Titus Masese, Godwill Mbiti Kanyolo, and co‐workers report novel honeycomb layered oxides exhibiting silveratom bilayers. The bilayers are theoretically understood via emergent SU(2) interactions with three distinct states of silver associated with fractional valency (sub‐valent) states, alongside conventional U(1) (electromagnetic) interaction. Breaking the SU(2)×U(1) symmetry, analogous to electroweak theory, generates silver mass terms manifesting as the bilayered structure.

The world is at the cusp of a new era where pivotal importance is being attached to the development of sustainable and high-performance energy storage systems. Potassium-ion batteries are deemed not only as cheap battery candidates, but also as the penultimate high-voltage energy storage systems within the monovalent-cation chemistries. However, their performance and sustainability are undermined by the lack of suitable electrolytes for high-voltage operation particularly due to the limited availability of cathode materials. Here, the potential of ionic liquids based on potassium bis(trifluoromethanesulfonyl)amide (KTFSA) as high-voltage electrolytes is presented by assessing their physicochemical properties, along with the electrochemical properties upon coupling with new high-voltage layered cathode materials. These ionic liquids demonstrate a lower redox potential for potassium dissolution / deposition (with a wide voltage tolerance of around \\(6.0\\) \\(\\rm V\\)), placing them as feasible and safe electrolytes for high-voltage potassium-ion battery configuration. This is proven by matching this electrolyte with new high-voltage layered cathode compositions, demonstrating stable electrochemical performance. The present findings of electrochemically stable ionic liquids based on potassium bis(trifluoromethanesulfonyl)amide will bolster further advancement of high-performance cathode materials, whose performance at high-voltage regimes were apparently restricted by the paucity of suitable and compatible electrolytes.

Honeycomb layered oxides with monovalent or divalent, monolayered cationic lattices generally exhibit myriad crystalline features encompassing rich electrochemistry, geometries and disorders, which particularly places them as attractive material candidates for next-generation energy storage applications. Herein, we report global honeycomb layered oxide compositions, \\({\\rm Ag_2}M_2{\\rm TeO_6}\\) (\\(M = \\rm Ni, Mg, \\textit{etc}.\\)) exhibiting \\(\\rm Ag\\) atom bilayers with sub-valent states within Ag-rich crystalline domains of \\({\\rm Ag_6}M_2{\\rm TeO_6}\\) and \\(\\rm Ag\\)-deficient domains of \\({\\rm Ag}_{2 - x}\\rm Ni_2TeO_6\\) (\\(0 < x < 2\\)). The \\(\\rm Ag\\)-rich material characterised by aberration-corrected transmission electron microscopy reveals local atomic structural disorders characterised by aperiodic stacking and incoherency in the bilayer arrangement of \\(\\rm Ag\\) atoms. Meanwhile, the global material not only displays high ionic conductivity, but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the \\(\\rm Ag\\)-rich domains, the bilayered structure, argentophilic interactions therein and the expected \\(\\rm Ag\\) sub-valent states (\\(1/2+, 2/3+, \\textit{etc}.\\)) are theoretically understood via spontaneous symmetry breaking of SU(\\(2\\))\\(\\times\\)U(\\(1\\)) gauge symmetry interactions amongst \\(3\\) degenerate mass-less chiral fermion states, justified by electron occupancy of silver \\(4d_{z^2}\\) and \\(5s\\) orbitals on a bifurcated honeycomb lattice. This implies that bilayered frameworks have research applications that go beyond the confines of energy storage.

Endowed with a multitude of exquisite properties such as rich electrochemistry, superb topology and eccentric electromagnetic phenomena, honeycomb layered oxides have risen to the top echelons of science with applications in diverse fields ranging from condensed matter physics, solid-state chemistry, materials science, solid-state ionics to electrochemistry. However, these oxides are vastly underutilised as their underlying atomistic mechanisms remain unexplored. Therefore, in this study, atomic-resolution imaging on pristine \\(\\rm K_2Ni_2TeO_6\\) along multiple zone axes was conducted using spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) to reveal hitherto unreported nanoscale topological defects and curvature which can be associated with various phase transitions. Furthermore, we discover the coexistence of a stacking variant with P3-type sequence alongside the well-reported P2-type stacking sequence in such honeycomb layered oxides. Our findings have the potential to inspire further experimental and theoretical studies into the role of stacking and topology in the functionality of honeycomb layered oxides, for instance, as high-performance electrode materials for rechargeable batteries.