Showing papers by "Toshiyuki Matsunaga published in 2020"

Sequential delithiation behavior and structural rearrangement of a nanoscale composite-structured Li1.2Ni0.2Mn0.6O2 during charge-discharge cycles.

Abstract: Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries Herein, the structural evolution of Li12Ni02Mn06O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 48 V In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi025Mn075O2 After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure

Capacity Improvement by Nitrogen Doping to Lithium-Rich Cathode Materials with Stabilization Effect of Oxide Ions Redox

Abstract: Lithium-rich cathode materials show higher theoretical capacity than conventional cathode materials because the redox activity of oxide ions in addition to the transition metal valence change contr...

High capacity manganese layered-perovskite cathode for fluoride ion batteries involving cationic and anionic redox reaction

Abstract: Developing electrochemical high-energy storage systems is of crucial importance towards a green and sustainable energy supply. A promising candidate is fluoride ion batteries (FIBs), which can deliver a higher energy density than is possible with lithium ion batteries1,2. However, conversion-type reactions with metal fluorides causes a poor electrochemical reversibility1,3,4. Recently, layered perovskite oxides such as LaSrMnO4 have been shown to undergo topotactic electrochemical (de)fluorination, but they have low reversible discharge capacities (25 ~ 100 mAh/g) and poor rate capabilities. Here we show that a double-layered perovskite oxyfluoride La1.2Sr1.8Mn2O7–δF2 exhibits topotactic (de)intercalation reaction inside the rock-salt slabs, achieving a large reversible capacity of 535 mAh/cm3 (0 ≤ x ≤ 2 in La1.2Sr1.8Mn2O7–δFx), with excellent cycle stability and rate capability. Surprisingly, despite the close-packed perovskite-based structure, two extra fluoride ions are (de)intercalated beyond x = 2, leading to a reversible capacity of 1168 mAh/cm3 (0 ≤ x ≤ 4). During the further intercalation, oxygen molecules are formed in the perovskite layer, as in Na0.75[ Li0.25Mn0.75 ]O25, which is responsible for the charge compensation (i.e. anion redox)5,6 and the concomitant formation of oxygen vacancies that allow the incorporation of the excess fluoride ions. These results highlight the layered perovskite oxide/oxyfluorides as a new class of active materials for the construction of high-performance FIBs. More generally, the concept of anion-intercalation through O2 formation in the mixed-anion perovskite materials can be used to develop new functionalities.

Stacking Disorders in MixedAlkali Honeycomb Layered Oxide NaKNi2TeO6 and Feasibility for Mixed-Cation Transport

Abstract: We demonstrate the feasibility of using a combination of alkali atoms (Na and K) to develop a robust mixed-alkali honeycomb layered oxide NaKNi2TeO6. Through a series of atomic-resolution transmission electron microscopy in multiple zone axes, we reveal for the first time the local atomic structural disorders characterised by aperiodic stackings and incoherency in the alternating arrangement of Na and K atoms. Our findings indicate great structural versatility that renders NaKNi2TeO6 an ideal platform for investigating other fascinating properties such as mixed ionic transport and intriguing electromagnetic and quantum phenomena amongst honeycomb layered oxides. Finally, we unveil the possibility of inducing mixed Na- and K-ion transport electrochemistry of NaKNi2TeO6 at high voltages (~ 4V), thus epitomising it as a competent cathode candidate for the emerging dendrite-free batteries based on NaK liquid metal alloy as anodes. The results not only betoken a new avenue for developing functional materials with fascinating crystal versatility, but also prefigure a new age of ‘dendrite-free’ energy storage system designs that rely on mixed-cation electrochemistry.