Xiaobo Ji

Carbon Quantum Dots and Their Derivative 3D Porous Carbon Frameworks for Sodium-Ion Batteries with Ultralong Cycle Life.

A new methodology for the synthesis of carbon quantum dots (CQDs) for large production is proposed. The as-obtained CQDs can be transformed into 3D porous carbon frameworks exhibiting superb sodium storage properties with ultralong cycle life and ultrahigh rate capability, comparable to state-of-the-art carbon anode materials for sodium-ion batteries.

NiCo2O4-based materials for electrochemical supercapacitors

Nickel cobaltite (NiCo2O4), with excellent electrochemical performance, has become a new class of energy storage material for electrochemical supercapacitors, which facilitates to relieve the pressure of energy crisis and environmental pollution. It possesses richer electroactive sites and at least two magnitudes higher electrical conductivity than that of NiO and Co3O4, which exhibit not only large power density, but also high energy density of up to 35 W h kg−1. Furthermore, it shows comparable capacitive performances with noble metal oxides of RuO2, but with much lower cost and more abundant resources. This feature article briefly analyses the energy storage mechanism of NiCo2O4, summarizes the methodologies and nanostructures discovered in recent years, and points out the potential problems and future prospects of utilizing NiCo2O4-based materials as supercapacitor electrodes. Moreover, composite electrodes based on nickel cobaltite are also elaborated with considerable interest. Since the pioneering work of Hu and his group in 2010, numerous research studies have also demonstrated NiCo2O4 electrodes to show remarkable supercapacitive performances; however, more specialized work should be performed to further develop the potential of this novel electrode material so as to realize their massive commercial applications.

Electrochemical capacitors utilising transition metal oxides: an update of recent developments

Transition metal oxides receive considerable attention in the area of electrochemistry not only due to their beneficial reported structural, mechanical or electronic properties, but because of their capacitive properties ascribed to their multiple oxide states they exhibit pseudo capacitances which carbon counterparts generally cannot. Typically transition metal oxides may be classified as noble transition metal oxides which exhibit excellent capacitive properties but have the drawback of generally being relatively expensive. Alternatively base metal oxides may also be utilised which are considerably cheaper and more environment friendly than noble transition metals as well as exhibiting good capacitive properties. In considering that nanostructured materials can help ameliorate the electrochemical performances of transition metal oxides, this review summarizes the recent investigations of fundamental advances in understanding the electrochemical reactivity of transition metal oxides, thus leading to an improved capacitive performance, which is essential for their continual use in a plethora of supercapacitor applications.

A carbon quantum dot decorated RuO2 network: outstanding supercapacitances under ultrafast charge and discharge

Carbon quantum dots (CQDs) due to their unique properties have recently attracted extensive attention from researchers in many fields. In the present work, a new application in the form of a CQD-based hybrid as an excellent electrode material for supercapacitors is reported for the first time. The CQDs are fabricated by a facile chemical oxidation method following which they are thermally reduced, and further decorated with RuO2 to obtain the composites. The hybrid exhibits a specific capacitance of 460 F g−1 at an ultrahigh current density of 50 A g−1 (41.9 wt% Ru loading), and excellent rate capability (88.6, 84.2, and 77.4% of capacity retention rate at 10, 20, and 50 A g−1 compared with 1 A g−1, respectively). Surprisingly, the hybrid shows exceptional cycling stability with 96.9% capacity retention over 5000 cycles at 5 A g−1. Such remarkable electrochemical performances can be primarily ascribed to the significantly enhanced utilization of RuO2 achieved by the efficient dispersion of tiny reduced CQDs and the formation of a CQD-based hybrid network structure that can facilitate the fast charge transport and ionic motion during the charge–discharge process. Additionally, the contact resistance at the interface between active materials and current collectors is concluded to be a key factor in determining the performance of the hybrid. These results above demonstrate the great potential of CQD-based hybrid materials in the development of high-performance electrode materials for supercapacitors.

Porous NiCo2O4 spheres tuned through carbon quantum dots utilised as advanced materials for an asymmetric supercapacitor

Carbon quantum dots (CQDs) tuned porous NiCo2O4 sphere composites are prepared for the first time via a reflux synthesis route followed by a post annealing treatment. Benefiting from the advantages of the unique porous structure with a large specific surface area, high mesoporosity and superior electronic conductivity, the as-obtained CQDs/NiCo2O4 composite electrode exhibits high specific capacitance (856 F g−1 at 1 A g−1), excellent rate capability (83.9%, 72.5% and 60.8% capacity retention rate at 20, 50 and 100 A g−1, respectively) and exceptional cycling stability (98.75% of the initial capacity retention over 10000 cycles at 5 A g−1). Furthermore, the assembled AC//CQDs/NiCo2O4 asymmetric supercapacitor manifests a high energy density (27.8 W h kg−1) at a power density of 128 W kg−1 or a high power density (10.24 kW kg−1) at the reasonable energy density of 13.1 W h kg−1 and remarkable cycling stability (101.9% of the initial capacity retention over 5000 cycles at 3 A g−1). The results above suggest a great potential of the porous CQDs/NiCo2O4 composites in the development of high-performance electrochemical energy storage devices for practical applications.

Carbon dots supported upon N-doped TiO2 nanorods applied into sodium and lithium ion batteries

N-doped TiO2 nanorods decorated with carbon dots with enhanced electrical-conductivity and faster charge-transfer have been fabricated utilizing a simple hydrothermal reaction process involving TiO2 powders (P25) and NaOH in the presence of carbon dots followed by ion exchange and calcination treatments. Due to the merits of the carbon dots, doping and nanostructures, the as-designed N–TiO2/C-dots composite utilized as anode materials for lithium-ion batteries can sustain a capacity of 185 mA h g−1 with 91.6% retention even at a high rate of 10 C over 1000 cycles. It is interesting to note that the ratios of capacitive charge capacity during such high rates for the N–TiO2/C-dots composite electrodes are higher than those at low rates, which likely explains the observed excellent rate capabilities. In contrast to lithium-ion batteries, sodium-ion batteries have gained more interest in energy storage grids because of the greater abundance and lower cost of sodium-containing precursors. The as-obtained N–TiO2/C-dots composites reported here and utilized as anode materials for sodium-ion batteries exhibit excellent electrochemical performances, including substantial cycling stabilities (the capacity retention ratios after 300 cycles at 5 C is 93.6%) and remarkable rate capabilities (176 mA h g−1 at 5 C, 131 mA h g−1 at 20 C); such performances are the greatest ever reported to date over other structured TiO2 or TiO2 composite materials.

Sodium/Lithium storage behavior of antimony hollow nanospheres for rechargeable batteries.

Sodium-ion batteries (SIBs) have come up as an alternative to lithium-ion batteries (LIBs) for large-scale applications because of abundant Na storage in the earths crust. Antimony (Sb) hollow nanospheres (HNSs) obtained by galvanic replacement were first applied as anode materials for sodium-ion batteries and exhibited superior electrochemical performances with high reversible capacity of 622.2 mAh g(-1) at a current density of 50 mA g(-1) after 50 cycles, close to the theoretical capacity (660 mAh g(-1)); even at high current density of 1600 mA g(-1), the reversible capacities can also reach 315 mAh g(-1). The benefits of this unique structure can also be extended to LIBs, resulting in reversible capacity of 627.3 mAh g(-1) at a current density of 100 mAh g(-1) after 50 cycles, and at high current density of 1600 mA g(-1), the reversible capacity is 435.6 mAhg(-1). Thus, these benefits from the Sb HNSs are able to provide a robust architecture for SIBs and LIBs anodes.

One-Dimensional Rod-Like Sb2S3-Based Anode for High-Performance Sodium-Ion Batteries

Due to the high theoretical capacity of 946 mAh g(-1), Sb2S3 can be employed as promising electrode material for sodium-ion batteries (SIBs). Herein, the sodium storage behaviors of one-dimensional (1D) Sb2S3-based materials (Sb2S3 and Sb2S3@C rods) are successfully studied for the first time, displaying good cyclability and rate capability owing to their unique morphology and structure. Specifically, the Sb2S3@C rods electrode presents greatly enhanced electrochemical properties, resulting from the introduction of thin carbon layers which can effectively alleviate the strain caused by the large volume change and simultaneously improve the conductivity of electrode during cycling. At a current density of 100 mA g(-1), it delivers a high capacity of 699.1 mAh g(-1) after 100 cycles, which corresponds to 95.7% of the initial reversible capacity. Even at a high current density of 3200 mA g(-1), the capacity can still reach 429 mAh g(-1). This achievement may be a significant exploration for develpoing novel 1D Sb-based materials or metal sulfide SIBs anodes.

Graphene‐Rich Wrapped Petal‐Like Rutile TiO2 tuned by Carbon Dots for High‐Performance Sodium Storage

Carbon dots inducing petal-like rutile TiO2 wrapped by ultrathin graphene-rich layers are proposed to fabricate superior anodes for sodium-ion batteries, featuring high-rate capabilities and long-term cyclelife, benefiting from promoted electron transport and a shortened Na+ diffusion length. High capacities of 144.4 mA h g-1 (at 837.5 mA g-1 ) after 1100 cycles and 74.6 mA h g-1 (at 3350 mA g-1 ) after 4000 cycles are delivered outstandingly.

Anatase TiO2 nanocubes for fast and durable sodium ion battery anodes

With the aim of advancing anatase TiO2 anodes for sodium ion batteries, crystalline titania nanocubes were employed and they delivered a gradually increasing capacity during the initial cycles, termed as an activation process. The number of necessary discharge–charge loops for total activation is dependent on the galvanostatic current density (about 20 cycles at 0.2 C, or 90 cycles at 1 C). A percentage of Ti3+ was detected after the activation, indicating an amount of irreversibly trapped sodium ions in the lattice. After the activation process, an excellent rate capability and outstanding cycling stability were presented. The reversible capacity reached 174, 132, and 108 mA h g−1 at rates of 1 C, 5 C, and 10 C, respectively. The capacity was sustained with a loss of less than 10% after 1000 discharge–charge cycles at a rate of 2 C or 10 C. The superior battery performance achieved by the nanocubes is related to the encircled {100} facets that are more favorable for sodium ion attachment compared to the {001} and {101} facets, as supported by first-principles calculations. From this work we can see the feasibility of optimizing electrode materials via rational surface structure construction based on theoretical calculations.