Rate Performance Modification of a Lithium-Rich Manganese-Based Material through Surface Self-Doping and Coating Strategies.

Lithium-rich manganese-based materials are currently considered to be highly promising cathode materials for next-generation lithium-ion batteries due to their high specific capacity (>250 mA h g-1) and low cost. A key challenge for the commercialization of these lithium-rich manganese-based materials is their poor rate performance, which is caused by the low electronic conductivity and increasing interface charge transfer resistance produced by the side reaction during the cycling procedure. In this work, we try to improve the rate performance of a lithium-rich manganese-based material Li1.2Mn0.54Co0.13Ni0.13O2 using a collaborative approach with Co-doping and NaxCoO2-coating methods. Cobalt doping can improve the electronic conductivity, and NaxCoO2 coating provides a convenient lithium-ion diffusion channel and moderately alleviates the inevitable decrease in cycling stability caused by cobalt doping. Under the synergistic effect of these two modification strategies, the surface and internal dynamics of the Li1.2Mn0.54Co0.13Ni0.13O2 material are enhanced and its rate performance is considerably improved without decay of the cycle stability.

A High-Energy-Density Hybrid Supercapacitor with P-Ni(OH)2 @Co(OH)2 Core-Shell Heterostructure and Fe2 O3 Nanoneedle Arrays as Advanced Integrated Electrodes.

Transition metal hydro/oxides (TMH/Os) are treated as the most promising alternative supercapacitor electrodes thanks to their high theoretical capacitance due to the various oxidation states and abundant cheap resources of TMH/Os. However, the poor conductivity and logy reaction kinetics of TMH/Os severely restrict their practical application. Herein, hierarchical core-shell P-Ni(OH)2 @Co(OH)2 micro/nanostructures are in situ grown on conductive Ni foam (P-Ni(OH)2 @Co(OH)2 /NF) through a facile stepwise hydrothermal process. The unique heterostructure composed of P-Ni(OH)2 rods and Co(OH)2 nanoflakes boost the charge transportation and provide abundant active sites when used as the intergrated cathode for supercapacitors. It delivers an ultrahigh areal specific capacitance of 4.4 C cm-2 at 1 mA cm-2 and the capacitance can maintain 91% after 10 000 cycles, showing an ultralong cycle life. Additionally, a hybrid supercapacitor composed with P-Ni(OH)2 @Co(OH)2 /NF cathode and Fe2 O3 /CC anode shows a wider voltage window of 1.6 V, a remarkable energy density of 0.21 mWh cm-2 at the power density of 0.8 mW cm-2 , and outstanding cycling stability with about 81% capacitance retention after 5000 cycles. This innovative study not only supplies a newfashioned electronic apparatus with high-energy density and cycling stability but offers a fresh reference and enlightenment for synthesizing advanced integrated electrodes for high-performance hybrid supercapacitors.

Construction of hierarchical V4C3-MXene/MoS2/C nanohybrids for high rate lithium-ion batteries.

MoS2 is a promising anode candidate for high-performance lithium-ion batteries (LIBs) due to its unique layered structure and high specific capacity. However, the poor conductivity and unsatisfactory structural stability limit its practical application. Recently, a new class of 2D materials, V4C3-Mxene, has been found to combine metallic conductivity, high structural stability and rich surface chemistries. Herein, a facile method has been developed to fabricate V4C3-MXene/MoS2/C nanohybrids. Ultrasmall and few-layered MoS2 nanosheets are uniformly anchored on the surface of V4C3-MXene with a thin carbon-coating layer. The ultrasmall and few-layered MoS2 nanosheets can enlarge the specific areas, reduce the diffusion distance of lithium ions, and accelerate the transfer of charge carriers. As a supporting substrate, V4C3-MXene endows the nanohybrid with high electrical conductivity, strong structural stability, and fast reaction kinetics. Moreover, the carbon-coating layer can further enhance the electrical conductivity and structural stability of the hybrid material. Benefiting from these advantages, the V4C3-MXene/MoS2/C electrode shows an excellent cycling stability with a high reversible capability of 622.6 mA h g-1 at 1 A g-1 after 450 cycles, and a superior rate capability of 500.0 mA h g-1 at 10 A g-1. Thus, the V4C3-MXene/MoS2/C nanohybrid could become a promising anode material for high rate LIBs.

Glucose-Induced Synthesis of 1T-MoS2 /C Hybrid for High-Rate Lithium-Ion Batteries.

1T phase MoS2 possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T-MoS2 /C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer-layer 1T-MoS2 nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T-MoS2 also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer-layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g-1 at 1 A g-1 and the capacity can maintain 870 mAh g-1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g-1 at 10 A g-1 . These results show that the 1T-MoS2 /C hybrid shows potential for use in high-performance lithium-ion batteries.

Hierarchical core-shell structures of P-Ni(OH)2 rods@MnO2 nanosheets as high-performance cathode materials for asymmetric supercapacitors.

The hierarchical porous structure with phosphorus-doped Ni(OH)2 (P-Ni(OH)2) rods as the core and MnO2 nanosheets as the shell is fabricated directly by growth on a three-dimensional (3D) flexible Ni foam (NF) via a two-step hydrothermal process. As a binder-free electrode material, this unique hybrid structure exhibits excellent electrochemical properties, including an ultrahigh areal capacitance of 5.75 F cm-2 at a current density of 2 mA cm-2 and great cyclic stability without capacitance loss at a current density of 20 mA cm-2 after 10 000 cycles. Moreover, an all-solid-state asymmetric supercapacitor (AAS) based on a P-Ni(OH)2@MnO2 hybrid structure on Ni foam as the cathode and activated carbon (AC) as the anode is successfully assembled to enhance value the electrochemical properties. The AAS device also shows excellent electrochemical properties including a large potential window of 0∼1.6 V, an areal capacitance is 911.3 mF cm-2 at a current density of 1 mA cm-2 and long-term cycling performance. Meanwhile, the AAS device also delivers a high energy density of 0.324 mW h cm-2 at a power density of 0.8 mW cm-2; and can easily light colorful light-emitting diode (LED) lights, suggesting that 3D P-Ni(OH)2@MnO2 hybrid composite has promising potential for practical use in high-performance supercapacitors.