Large-scale carbon framework microbelts anchoring ultrafine SnO2 nanoparticles with enhanced lithium storage properties

GeO2 Nanoparticles Decorated in Amorphous Carbon Nanofiber Framework as Highly Reversible Lithium Storage Anode

Germanium oxide (GeO2) is a high theoretical capacity electrode material due to its alloying and conversion reaction. However, the actual cycling capacity is rather poor on account of suffering low electron/ion conductivity, enormous volume change and agglomeration in the repeated lithiation/delithiation process, which renders quite a low reversible electrochemical lithium storage reaction. In this work, highly amorphous GeO2 particles are uniformly distributed in the carbon nanofiber framework, and the amorphous carbon nanofiber not only improves the conduction and buffers the volume changes but also prevents active material agglomeration. As a result, the present GeO2 and carbon composite electrode exhibits highly reversible alloying and conversion processes during the whole cycling process. The two reversible electrochemical reactions are verified by differential capacity curves and cyclic voltammetry measurements during the whole cycling process. The corresponding reversible capacity is 747 mAh g-1 after 300 cycles at a current density of 0.3 A g-1. The related reversible capacities are 933, 672, 487 and 302 mAh g-1 at current densities of 0.2, 0.4, 0.8 and 1.6 A g-1, respectively. The simple strategy for the design of amorphous GeO2/carbon composites enables potential application for high-performance LIBs.

High-capacity and ultrastable lithium storage in SnSe2-SnO2@NC microbelts enabled by heterostructures

The ingenious design of high-performance tin-based lithium-ion batteries (LIBs) is challenging due to their poor conductivity and drastic volume change during continuous lithiation/delithiation cycles. Herein, we present a strategy to confine heterostructured SnSe₂-SnO₂ nanoparticles into macroscopic nitrogen-doped carbon microbelts (SnSe₂-SnO₂@NC) as anode materials for LIBs. The composites exhibit an excellent specific capacity of 436.3 mA h g^-1 even at 20 A g^-1 and an ultrastable specific capacity of 632.7 mA h g^-1 after 2800 cycles at 5 A g^-1. Density Functional Theory (DFT) calculations reveal that metallic SnSe₂-SnO₂ heterostructures endow the lithium atoms at the interface with high adsorption energy, which promotes the anchoring of Li atoms, and enhances the electrical conductivity of the anode materials. This demonstrates the superior Li⁺ storage performance of the SnSe₂-SnO₂@NC microbelts as anode materials.

Insight into Reversible Conversion Reactions in SnO2 -Based Anodes for Lithium Storage: A Review

Various anode materials have been widely studied to pursue higher performance for next generation lithium ion batteries (LIBs). Metal oxides hold the promise for high energy density of LIBs through conversion reactions. Among these, tin dioxide (SnO₂ ) has been typically investigated after the reversible lithium storage of tin-based oxides is reported by Idota and co-workers in 1997. Numerous in/ex situ studies suggest that SnO₂ stores Li⁺ through a conversion reaction and an alloying reaction. The difficulty of reversible conversion between Li₂ O and SnO₂ is a great obstacle limiting the utilization of SnO₂ with high theoretical capacity of 1494 mA h g^-1 . Thus, enhancing the reversibility of the conversion reaction has become the research emphasis in recent years. Here, taking SnO₂ as a typical representative, the recent progress is summarized and insight into the reverse conversion reaction is elaborated. Promoting Li₂ O decomposition and maintaining high Sn/Li₂ O interface density are two effective approaches, which also provide implications for designing other metal oxide anodes. In addition, some in/ex situ characterizations focusing on the conversion reaction are emphatically introduced. This review, from the viewpoint of material design and advanced characterizations, aims to provide a comprehensive understanding and shed light on the development of reversible metal oxide electrodes.

Hierarchical Ni3S2nanorod@nanosheet arrays on Ni foam for high-performance supercapacitor

We successfully designed and prepared hierarchical Ni₃S₂nanorod@nanosheet arrays on three-dimensional Ni foam via facile hydrothermal sulfuration. We conducted a series of time- and temperature-dependent experiments to determine the Ostwald ripening process of hierarchical Ni₃S₂nanorod@nanosheet arrays. The rationally hierarchical architecture creates an excellent supercapacitor electrode for Ni₃S₂nanorod@nanosheet arrays. The areal capacitance of this array reaches 5.5 F cm^-2at 2 mA cm^-2, which is much higher than that of Ni₃S₂nanosheet arrays (1.5 F cm^-2). The corresponding asymmetric supercapacitor exhibits a wide potential window of 1.6 V and energy density up to 1.0 Wh cm^-2when the proposed array is utilized as the positive electrode with activated carbon as the negative electrode. This electrochemical performance enhancement is attributable to the hierarchical structure and synergistic cooperation of macroporous Ni foam and well-aligned Ni₃S₂nanorod@nanosheet arrays. Our results represent a promising approach to the preparation of hierarchical nanorod@nanosheet arrays as high-performing electrochemical capacitors.

Synthesis of a High-Capacity α-Fe2O3@C Conversion Anode and a High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode and Their Combination in a Li-Ion Battery

A Li-conversion α-Fe₂O₃@C nanocomposite anode and a high-voltage LiNi_0.5Mn_1.5O₄ cathode are synthesized in parallel, characterized, and combined in a Li-ion battery. α-Fe₂O₃@C is prepared via annealing of maghemite iron oxide and sucrose under an argon atmosphere and subsequent oxidation in air. The nanocomposite exhibits a satisfactory electrochemical response in a lithium half-cell, delivering almost 900 mA h g^-1, as well as a significantly longer cycle life and higher rate capability compared to the bare iron oxide precursor. The LiNi_0.5Mn_1.5O₄ cathode, achieved using a modified co-precipitation approach, reveals a well-defined spinel structure without impurities, a sub-micrometrical morphology, and a reversible capacity of ca. 120 mA h g^-1 in a lithium half-cell with an operating voltage of 4.8 V. Hence, a lithium-ion battery is assembled by coupling the α-Fe₂O₃@C anode with the LiNi_0.5Mn_1.5O₄ cathode. This cell operates at about 3.2 V, delivering a stable capacity of 110 mA h g^-1 (referred to the cathode mass) with a Coulombic efficiency exceeding 97%. Therefore, this cell is suggested as a promising energy storage system with expected low economic and environmental impacts.

Nitrogen and boron doped carbon layer coated multiwall carbon nanotubes as high performance anode materials for lithium ion batteries

Lithium ion batteries (LIBs) are at present widely used as energy storage and conversion device in our daily life. However, due to the limited power density, the application of LIBs is still restricted in some areas such as commercial vehicles or heavy-duty trucks. An effective strategy to solve this problem is to increase energy density through the development of battery materials. At the same time, a stable long cycling battery is a great demand of environmental protection and industry. Herein we present our new materials, nitrogen and boron doped carbon layer coated multiwall carbon nanotubes (NBC@MWCNTs), which can be used as anodes for LIBs. The electrochemical results demonstrate that the designed NBC@MWCNTs electrode possesses high stable capacity over an ultra-long cycling lifespan (5000 cycles) and superior rate capability even at very high current density (67.5 A g⁻¹). Such impressive lithium storage properties could be ascribed to the synergistic coupling effect of the distinctive structural features, the reduced diffusion length of lithium ions, more active sites generated by doped atoms for lithium storage, as well as the enhancement of the electrode structural integrity. Taken together, these results indicate that the N, B-doped carbon@MWCNTs materials may have great potential for applications in next-generation high performance rechargeable batteries.

Ultrafine antimony (Sb) nanoparticles encapsulated into a carbon microfiber framework as an excellent LIB anode with a superlong life of more than 5000 cycles

Antimony (Sb) anode has attracted increasing attention given its high theoretical capacity and suitable working potential. Nonetheless, its practical application is largely hindered by huge volume changes during the cyclic process, resulting in unsatisfactory long-term cycled stabilities at high current density. In this work, large-scale ultrafine Sb nanoparticles are functionally designed to encapsulate into a 3D carbon microfiber framework (CMF) via a scalable electrospinning approach followed by a thermal treatment process. This fabrication strategy effectively avoids the change in the volume of the Sb anode and provides a fast conductive network to serve as an efficient 3D e/Li⁺ transport pathway. Benefiting from this novel structural design, an ultrafine Sb nanoparticles@carbon microfiber framework (U-Sb-NPs@CMF) composite anode used for lithium-ion batteries (LIBs) delivers a high reversible capacity of 622 mAh g^-1 after 200 cycles at 0.5 A g^-1 and 507 mAh g^-1 after 2000 cycles at 2 Ag^-1 and a high-capacity retention of 350 mAh g^-1 even after 5000 long-term cycles. These outstanding charge-discharge performances suggest that the U-Sb-NPs@CMF composite is a promising candidate for an anode material in the application of LIBs.