Extra Plateau Research Articles

Heterostructure of Ta5+-substituted Na3V2(PO4)3–TaN promoting the activation of V4+/V5+ redox couple for high performance sodium-ion batteries

Currently, low capacity with poor kinetics seriously hinders the development of Na3V2(PO4)3 (NVP). Herein, a simultaneous optimized scheme of Ta5+ substitution and carbon nanotubes (CNTs) enwrapping is proposed. The substitution of hypervalent Ta5+ at V3+ site introduces a favorable n-type doping effect to generate extra electrons, increasing electron concentration to accelerate electronic conductivity. Ta5+ behaves as a pillar ion to expand Na + migration channel and stabilize the skeleton. Moreover, a new phase of TaN is produced, which embeds into the Na3V2(PO4)3 phase to generate grain boundary. Benefiting from this heterojunction, Na+ diffusion rate could be effectively promoted. The addition of CNTs further restricts agglomeration growth of particles, making the grains smaller and more uniform. Benefiting from the synergetic improved kinetics, a higher voltage platform at 3.9 V is activated. Due to the investigations of ex-situ X-ray photoelectron spectroscopy, the extra plateau is derived from the V4+/V5+ redox couple. Moreover, Density Functional Theoretical calculation suggests the favorable Ta5+ substitution optimizes the electronic structure of NVP to reduce the band gap. Accordingly, the modified NVPT/C@CNTs0.15 submits 125.5 mA h g−1 at 0.1C, and delivers a high value of 77.5 mA h g−1 at 100 C with retention rate of 81.03% after 12000 cycles.

Lithium-ion storage mechanism in closed pore-rich hard carbon with ultrahigh extra plateau capacity

A closed pore-rich hard carbon is fabricated from mildly cured phenolic-formaldehyde resin. It can deliver a high capacity of 550 mAh g−1, including a low-voltage plateau capacity of 230 mAh g−1 from lithium-ion insertion in closed ultramicropores.

Surface Structure Evolution and its Impact on the Electrochemical Performances of Aqueous‐Processed High‐Voltage Spinel LiNi0.5Mn1.5O4 Cathodes in Lithium‐Ion Batteries

AbstractLiNi0.5Mn1.5O4 (LNMO) is a promising cathode in lithium‐ion batteries (LIBs) due to its high operating voltage and open Li+ diffusion framework. However, the instability of the electrode–electrolyte interface and the negative environmental impact of electrode fabrication processes limit its practical application. Therefore, switching electrode processing conditions to aqueous and understanding the accompanying surface structural evolution are imperative. Here, water‐treated, poly(acrylic acid) (PAA)‐treated, and H3PO4‐treated LNMO, labeled as W‐LNMO, A‐LNMO, and H‐LNMO, are studied systematically. W‐LNMO shows a high concentration of Mn3+ induced by Li loss while a conformal PAA layer formed on A‐LNMO reduces this phenomenon. H‐LNMO displays a second MnPO4∙H2O phase. Upon cycling, a fast capacity decay is observed in W‐LNMO while an extra plateau at ≈2.7 V appears in the initial charging, corresponding to a two‐phase transition. A surface reconstruction layer from a spinel to a rock‐salt phase with a reductive Mn2+ segregation is observed in W‐LNMO after 105 cycles. The PAA layer persists on A‐LNMO and alleviates the capacity decay. H‐LNMO delivers a relatively low capacity due to the formation of a MnPO4∙H2O phase. This study provides new insights into manipulating the surface chemistry of LNMO cathodes to enable aqueous, large‐scale processingin LIBs.

Role of Bloch oscillation in high-order harmonic generation from periodic structure**Project supported by the NSAF, China (Grant No. U1730449) and the National Natural Science Foundation of China (Grant Nos. 11904341, 11774322, 91850201, and 11874066).

The high-order harmonic generation from a model solid structure driven by an intense laser pulse is investigated using the semiconductor Bloch equations (SBEs). The main features of harmonic spectrum from SBEs agree well with the result of the time-dependent Schrödinger equation (TDSE), and the cut-off energy can be precisely estimated by the recollision model. With increasing the field strength, the harmonic spectrum shows an extra plateau. Based on the temporal population of electron and the time–frequency analysis, the harmonics in the extra plateau are generated by the Bloch oscillation. Due to the ultrafast time response of the Bloch electron, the generated harmonics provide a potential source of shorter isolated attosecond pulse.

Li+Intercalation of Manganese Ferrocyanide as Investigated by In situ Valence-Differential Absorption Spectroscopy

Manganese ferrocyanide is a promising cathode material for lithium-ion secondary battery (LIB) with a high discharge rate (\(v\)). The open-circuit-voltage (OCV) discharge curve for LixMn[Fe(CN)6]0.813.0H2O films consists of plateaus I and II, which are due to the reduction of Mn3+ and Fe3+, respectively. Systematic investigations of the discharge curve revealed that an extra plateau, plateau III, appears between plateaus I and II. In situ valence-differential (VD) absorption spectroscopy indicates that the reduction sites in plateaus I and III are Mn3+. We ascribed plateaus I and III to the reduction of the Jahn–Teller (JT)-released and JT-distorted Mn3+N6 octahedra, respectively.

Gate-Defined Graphene Quantum Point Contact in the Quantum Hall Regime

We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5h/e2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.

Hematite nanoflakes as anode electrode materials for rechargeable lithium-ion batteries

Hematite (α-Fe 2O 3) nanoflakes and nanocubes were synthesized by liquid–solid-solution method and their properties as anode electrode materials for rechargeable Li +-ion batteries were measured. When changing the water to ethanol volume ratio in the synthesis system, the nanocrystals can be changed from α-Fe 2O 3 to α-FeOOH, with shapes being tuned from nanoflakes to nanocubes, non-uniform particles and nanowires. When assembled as the anode electrode materials in rechargeable Li +-ion batteries, the hematite nanoflakes showed one more plateau in the first discharge progress of the voltage–composition curves than hematite nanocrystals with other shapes in the literature. X-ray diffraction, high-resolution transmission electron microscope and electrochemical data showed that this extra plateau came from the formation of Li 2Fe 3O 4 nanoclusters and amorphous Li 2O. This experiment showed that like sizes, shapes of nanocrystals may also affect the detailed electrochemical progress.

Low-temperature fate of the 0.7 structure in a point contact: a Kondo-like correlated state in an open system.

Besides the usual conductance plateaus at multiples of 2e(2)/h, quantum point contacts typically show an extra plateau at approximately 0.7(2e(2)/h), believed to arise from electron-electron interactions that prohibit the two spin channels from being simultaneously occupied. We present evidence that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state. Evidence includes a zero-bias conductance peak that splits in a parallel field, scaling of conductance to a modified Kondo form, and consistency between peak width and the Kondo temperature.

Alternating-spin ladders in a magnetic field: Formation of magnetization plateaux

We study numerically the formation of magnetization plateaux with the Lanczos method in 2-leg ladders with mixed spins of magnitudes $(S_1,S_2)=(1,1/2)$ located at alternating positions along the ladder and with dimerization $\gamma$. For interchain coupling $J'>0$ and $\gamma=0$, we find normalized plateaux at $m=1/3$ starting at zero field and $m=1$ (saturation), while when $\gamma \ne 0$ is columnar, another extra plateau at $m=2/3$ shows up. For $J'<0$, when $\gamma<\gamma_c(J')$ we find no plateau while for $\gamma>\gamma_c(J')$ we find four plateaux at $m=0,1/3,2/3,1$. We also apply several approximate analytical methods (Spin Wave Theory, Low-Energy Effective Hamiltonians and Bosonization) to understand these findings and to conjeture the behaviour of ferrimagnetic ladders with a bigger number of legs.

Excitonic Effect on the Electron Tunneling Through a Quantum Well**The project supported by National Natural Science Foundation of China and the Doctoral Program Foundation of Institution of Higher Education

We proposed a simplified model to describe the excitonic effect on electron tunneling through a quantum well (QW). Using nonequilibrium-Green-function method self consistently, we calculated the dc current of electron tunneling through QW. The extra plateau in the J-V characteristics appears dearly, which shows the existence of exciton in QW. This result is in good agreement with the experiment qualitatively. We also studied the density of electrons and holes in the quantum well.