Insights into the Dual-Electrode Characteristics of Layered Na_0.5Ni_0.25Mn_0.75O₂ Materials for Sodium-Ion Batteries

Sodium-ion batteries are now close to replacing lithium-ion batteries because they provide superior alternative energy storage solutions that are in great demand, particularly for large-scale applications. To that end, the present study is focused on the properties of a new type of dual-electrode material, Na_0.5Ni_0.25Mn_0.75O₂, synthesized using a mixed hydroxy-carbonate route. Cyclic voltammetry confirms that redox couples, at high and low voltage ranges, are facilitated by the unique features and properties of this dual-electrode, through sodium ion deintercalation/intercalation into the layered Na_0.5Ni_0.25Mn_0.75O₂ material. This material provides superior performance for Na-ion batteries, as evidenced by the fabricated sodium cell that yielded initial charge–discharge capacities of 125/218 mAh g^–1 in the voltage range of 1.5–4.4 V at 0.5 <i>C</i>. At a low voltage range (1.5–2.6 V), the anode cell delivered discharge–charge capacities of 100/99 mAh g^–1 with 99% capacity retention, which corresponds to highly reversible redox reaction of the Mn^4+/3+ reduction and the Mn^3+/4+ oxidation observed at 1.85 and 2.06 V, respectively. The symmetric Na-ion cell, fabricated using Na_0.5Ni_0.25Mn_0.75O₂, yielded initial charge–discharge capacities of 196/187 μAh at 107 μA. These results encourage the further development of new types of futuristic sodium-ion-battery-based energy storage systems

High Performance LiMn₂O₄ Cathode Materials Grown with Epitaxial Layered Nanostructure for Li-Ion Batteries

Tremendous research works have been done to develop better cathode materials for a large scale battery to be used for electric vehicles (EVs). Spinel LiMn₂O₄ has been considered as the most promising cathode among the many candidates due to its advantages of high thermal stability, low cost, abundance, and environmental affinity. However, it still suffers from the surface dissolution of manganese in the electrolyte at elevated temperature, especially above 60 °C, which leads to a severe capacity fading. To overcome this barrier, we here report an imaginative material design; a novel heterostructure LiMn₂O₄ with epitaxially grown layered (<i>R</i>3̅<i>m</i>) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 °C. The unique characteristics of the heterostructure LiMn₂O₄ phase exhibited a discharge capacity of 123 mAh g^–1 and retained 85% of its initial capacity at the elevated temperature (60 °C) after 100 cycles

New Chemical Route for the Synthesis of β‑Na_0.33V₂O₅ and Its Fully Reversible Li Intercalation

To obtain good electrochemical performance and thermal stability of rechargeable batteries, various cathode materials have been explored including NaVS₂, β-Na_0.33V₂O₅, and Li_<i>x</i>V₂O₅. In particular, Li_<i>x</i>V₂O₅ has attracted attention as a cathode material in Li-ion batteries owing to its large theoretical capacity, but its stable electrochemical cycling (i.e., reversibility) still remains as a challenge and strongly depends on its synthesis methods. In this study, we prepared the Li_<i>x</i>V₂O₅ from electrochemical ion exchange of β-Na_0.33V₂O₅, which is obtained by chemical conversion of NaVS₂ in air at high temperatures. Crystal structure and particle morphology of β-Na_0.33V₂O₅ are characterized by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, in combination with electrochemical data, suggest that Na ions are extracted from β-Na_0.33V₂O₅ without irreversible structural collapse and replaced with Li ions during the following intercalation (i.e., charging) process. The thus obtained Li_<i>x</i>V₂O₅ delivers a high discharge capacity of 295 mAh g^–1, which corresponds to <i>x</i> = 2, with crystal structural stability in the voltage range of 1.5–4.0 V versus_. Li, as evidenced by its good cycling performance and high Coulombic efficiency (under 0.1 mA cm^–2) at room temperature. Furthermore, the ion-exchanged Li_<i>x</i>V₂O₅ from β-Na_0.33V₂O₅ shows stable electrochemical behavior without structural collapse, even at a case of deep discharge to 1.5 V versus Li

Block Copolymer Directed Ordered Mesostructured TiNb₂O₇ Multimetallic Oxide Constructed of Nanocrystals as High Power Li-Ion Battery Anodes

In order to achieve high-power and -energy anodes operating above 1.0 V (vs Li/Li⁺), titanium-based materials have been investigated for a long time. However, theoretically low lithium charge capacities of titanium-anodes have required new types of high-capacity anode materials. As a candidate, TiNb₂O₇ has attracted much attention due to the high theoretical capacity of 387.6 mA h g^–1. However, the high formation temperature of the TiNb₂O₇ phase resulted in large-sized TiNb₂O₇ crystals, thus resulting in poor rate capability. Herein, ordered mesoporous TiNb₂O₇ (denoted as m-TNO) was synthesized by block copolymer assisted self-assembly, and the resulting binary metal oxide was applied as an anode in a lithium ion battery. The nanocrystals (∼15 nm) developed inside the confined pore walls and large pores (∼40 nm) of m-TNO resulted in a short diffusion length for lithium ions/electrons and fast penetration of electrolyte. As a stable anode, the m-TNO electrode exhibited a high capacity of 289 mA h g^–1 (at 0.1 C) and an excellent rate performance of 162 mA h g^–1 at 20 C and 116 mA h g^–1 at 50 C (= 19.35 A g^–1) within a potential range of 1.0–3.0 V (vs Li/Li⁺), which clearly surpasses other Ti-and Nb-based anode materials (TiO₂, Li₄Ti₅O₁₂, Nb₂O₅, etc.) and previously reported TiNb₂O₇ materials. The m-TNO and carbon coated m-TNO electrodes also demonstrated stable cycle performances of 48 and 81% retention during 2,000 cycles at 10 C rate, respectively

Highly Stable Cesium Lead Halide Perovskite Nanocrystals through in Situ Lead Halide Inorganic Passivation

Highly Stable Cesium Lead Halide Perovskite Nanocrystals through in Situ Lead Halide Inorganic Passivatio

Quantum Confinement and Its Related Effects on the Critical Size of GeO₂ Nanoparticles Anodes for Lithium Batteries

This work has been performed to determine the critical size of the GeO₂ nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO₂ nanoparticles with different sizes of ∼2, ∼6, ∼10, and ∼35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO₂ nanoparticles, the ∼6 nm sized GeO₂ showed the best electrochemical performance. Unexpectedly smaller particles of the ∼2 nm sized GeO₂ showed the inferior electrochemical performances compared to those of the ∼6 nm sized one. This was due to the low electrical conductivity of the ∼2 nm sized GeO₂ caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed

Mesoporous Ge/GeO₂/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility

We report mesoporous composite materials (m-GeO₂, m-GeO₂/C, and m-Ge-GeO₂/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO₂/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g^–1), and stable cycle life compared with the other mesoporous and bulk GeO₂ electrodes. m-Ge/GeO₂/C exhibits one of the highest areal capacities (1.65 mA h cm^–2) among previously reported Ge- and GeO₂-based anodes. The superior electrochemical performance in m-Ge/GeO₂/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge

Metal-Free Ketjenblack Incorporated Nitrogen-Doped Carbon Sheets Derived from Gelatin as Oxygen Reduction Catalysts

Electrocatalysts facilitating oxygen reduction reaction (ORR) are vital components in advanced fuel cells and metal-air batteries. Here we report Ketjenblack incorporated nitrogen-doped carbon sheets derived from gelatin and apply these easily scalable materials as metal-free electrocatalysts for ORR. These carbon nanosheets demonstrate highly comparable catalytic activity for ORR as well as better durability than commercial Vulcan carbon supported Pt catalysts in alkaline media. Physico-chemical characterization and theoretical calculations suggest that proper combination of graphitic and pyridinic nitrogen species with more exposed edge sites effectively facilitates a formation of superoxide, [O_2(ad)]⁻, via one-electron transfer, thus increasing catalytic activities for ORR. Our results demonstrate a novel strategy to expose more nitrogen doped edge sites by irregular stacked small sheets in developing better electrocatalysts for Zn-air batteries. These desirable architectures are embodied by an amphiphlilic gelatin mediated compatible synthetic strategy between hydrophobic carbon and aqueous water