Graphene quantum dot is one of the most important derivants of graphene. With the quantum size effect, graphene quantum dots show a distinct semiconductive nature, compared with intrinsic graphene. Graphene quantum dots have a high application value in fluorescent anti-counterfeiting materials, biological imaging, tumor diagnosis and treatment, and photo/electrocatalysis due to their superior photoluminescence properties, high stability, low biotoxicity, modulated interface structure. This review represented the photoluminescence properties of graphene quantum dots. The bandgap structure of graphene quantum dots, which is related to the important basic physical properties of the material in various applications was summarized. This review can provide a reference for the future studies on the photoluminescence performance modulation and mechanism of graphene quantum dots.

As one of carbon nanomaterials, carbon dots have attracted widespread attention due to their ultra-small size, abundant surface functional groups, good chemical stability, and superior optoelectronic properties. In this review, the structures, classifications, characteristics, and preparation methods of carbon dots were introduced. Recent research studies on carbon dots as various components or additives in dye-sensitized solar cells were represented. The challenges of controllable synthesis, structure-property relationship, and performance optimization of carbon dots were analyzed. In addition, the development directions of large-scale controllable preparation for carbon dots and their application in dye-sensitized solar cells were proposed.

Hard carbon (HC) materials are considered as promising anode materials for sodium-ion batteries (SIBs) due to their advantages of high capacity, low working potential, and low cost. The most important feature of HC materials is a rich microcrystalline structure that is conducive to the sorption and insertion/extraction of sodium ions, which in turn enables HC materials to exhibit a superior sodium ion storage performance. However, HC materials have some problems such as low initial Coulombic efficiency (ICE), insufficient long-cycle stability, and poor rate performance in the application. A functional design can be an effective strategy to improve these problems of HC. This review mainly summarized recent studies on the modification of HC anode for SIBs, and provided the related information on some typical optimization strategies and the latest research progress in the functional design of HC anodes. The advantages and disadvantages of functional design were also discussed, providing a theoretical basis and technical support for guiding the commercial application of HC anodes for SIBs.

In the application of the third-generation semiconductors, the power density of electronic devices increases and the size is miniaturization. A problem of high temperature becomes more prominent. Diamond is one of the optimum heat dissipation materials because of its ultra-high thermal conductivity and stable properties. In this review, the design principle and development process of different microwave plasma chemical vapor deposition equipment were introduced. Recent developments on different thermal applications of single crystal, polycrystalline and nanocrystal diamond were represented. Some challenges in the industrialization process combined with the 3rd-generation-semiconductors and the development direction of "larger, purer and faster" were summarized. In addition, the future research direction of diamond heat dissipation application was also prospected.

Spinel LiMn₂O₄ cathode materials suffer a serious capacity decay and a poor cycle stability during the charge-discharge process due to the Jahn-Teller effect and Mn dissolution. A cathode material of truncated octahedral single crystal LiFe_0.12Mn_1.88O₄ with {111}, {100} and {110} surfaces was prepared by a solid-state combustion method and element doping and single crystal morphology controlling strategies. The results show that the crystal structure of spinel LiMn₂O₄ is not changed by Fe doping, the Jahn-Teller effect is effectively inhibited, the crystallinity and the selective growth of {400} and {440} diffraction peak crystal planes are promoted, and the material has superior rate performance and capacity retention. The initial discharge specific capacities at 1 C and 5 C at 25 ℃ are 105.2 mA·h/g and 92.4 mA·h/g, and the capacity retentions after 1 000 cycles are 71.1% and 75.2%, respectively. Moreover, the capacity retention reaches 88.4% after 1 000 cycles at 10 C. The initial discharge capacity of the material is 108.6 mA·h/g at 55 ℃ and 1 C, and the capacity retention rate is 79.1% after 150 cycles, and the capacity retention rate is 79.1% after 150 cycles. By using cyclic voltammetry and electrochemical impedance spectroscopy, we found that the Fe-doped sample has superior circulation reversibility and large Li⁺ diffusion coefficient. The Fe-doped material of truncated octahedral LiMn₂O₄ inhibits the Jahn-Teller effect, and slows down the Mn dissolution, thus stabilizing the crystal structure, increasing the Li⁺ migration channel, and improving the electrochemical rate performance and long cycle life.

The preparation of silicon anode materials via reduction of silicate minerals can improve the electrochemical properties and reduce the production cost. In this paper, silicon-carbon composites were prepared by a simple evaporation solvent method with natural halloysite aluminothermic reductive product as a raw material and asphalt as a carbon source. The results show that silicon exists in the form of nanotubes with a diameter of approximately 30 nm. The carbon layer is uniformly coated on the silicon nanotubes, which increases the diameter of the silicon carbon composite. The thickness of the carbon layer is approximately 7 nm. The carbon exists in an amorphous structure, and the carbon coating leads to the decrease of the specific surface area. According to the results of electrochemical tests, the optimum electrochemical performance of silicon-carbon composites can be obtained at a mass fraction of coated carbon of 15%, i.e., the first charge and discharge capacities of 1 387.8 mA∙h/g and 1 615.7 mA∙h/g, respectively, and the first coulomb efficiency of 85.9%. The silicon-carbon composites maintain the first charge discharge efficiency of silicon nanotubes, and greatly improve the cycle performance. Compared with the 200 cycles capacity retention rate of silicon nanotubes of 38%, the 200 cycles capacity retention rate of silicon-carbon composites coated with a carbon content of 15% is increased by 45.8%. The specific capacity of silicon-carbon composites coated with a carbon content of 15% is 1 065.6 mA∙h/g after 500 cycles. The capacity retention rate is 76.8%.

Composite polymer electrolyte is one of the most promising electrolyte candidates for future solid state lithium batteries, but inorganic fillers used are prone to an agglomeration, thus being difficult to form a continuous ion transport pathway. Flexible SiO₂ nanofiber porous membranes were fabricated by an electrospinning technique and a heating treatment process. The samples were characterized by scanning electron microscope, fourier transform infrared spectrometer, X-ray diffractometer, and thermogravimetry analyzer. The effects of TEOS proportion and polymer concentration in electrospinning precursor on the morphology and flexibility of the nanofiber porous membranes were investigated. Moreover, the electrochemical properties of PEO based composite polymer electrolyte (CPE-SiO₂) were analyzed. The ionic conductivity of this composite electrolyte can reach 2.52×10^-5 S/cm at 30 ℃. LiFePO₄|CPE-SiO₂|Li can be steadily charged/discharged for 50 times at 1 C rate and 60 ℃. Li|CPE-SiO₂|Li symmetric cell can keep a stable overpotential profile for 300 h with a low hysteresis at 60 ℃. This work provides an effective approach for the commercialization of next generation high-performance all-solid-state batteries.

Anthracite has a great application potential in energy storage because of its low cost, but the reversible capacity of raw anthracite as an anode material for the sodium-ion battery is rather low. In this paper, anthracite was pyrolyzed at different temperatures. The results show that the reversible capacity of anthracite pyrolyzed at 1 300 ℃ (A-1300) is 307 mA·h/g at 20 mA/g, which is the maximum value among the pyrolyzed anthracites. However, the reversible capacity of A-1300 at 500 mA/g is only 105 mA·h/g, exhibiting an inferior rate performance. The two-step strategy via hydrogenation and pyrolysis can decrease the pyrolyzed temperature and improve the rate performance. Hydrogenated anthracite turns into an easy-graphitized precursor. The reversible capacity of hydrogenated anthracite pyrolyzed at 900 ℃ (H300-3-900) can retain 113 mA·h/g at 500 mA/g after 500 cycles, exhibiting a superior rate performance and an easier commercial production at a lower temperature.

The manufacture of flexible, miniature, large-area and low-cost energy storge units has attracted much attention with a rapid development of flexible electronic devices. In this paper, NiCo₂S₄/g-C₃N₄ nanocomposite material was prepared via a one-step solvothermal process with nickel and cobalt nitrate hexahydrate as raw materials, thiourea as a vulcanizing agent and pyrolysis g-C₃N₄. The interdigital electrode of NiCo₂S₄/g-C₃N₄ was created via mask printing on a polyethylene glycol terephthalate flexible substrate with the well-prepared ink. The flexible interdigital supercapacitor was obtained by coating a layer of gel electrolyte. Based on the structure and electrochemical performance characterizations, NiCo₂S₄ nanoparticles dispersedly grow on g-C₃N₄ nanoplates, thus improving the charge transfer and accommodating the volume expansion of NiCo₂S₄ during charge-discharge cycles. The area specific capacitance of the nanocomposite electrode is 9.1 F/cm² at a current density of 10 mA/cm². The assembled supercapacitor can operate at -0.2-0.6 V and remainsstable at a scanning rate of 500 mV/s, revealing a good rate performance. The area specific capacitance of the device is 5.7 mF/cm² at a scanning rate of 20 mV/s, and the energy density is 0.56 mW·h/cm³ at a power density of 17.5 mW/cm³.

High-conductivity titanium nitride nanowire can be used as a growth substrate of polyaniline to reduce the charge transfer resistance of the electrode material and improve the supercapacitor behavior of polyaniline. A polyaniline/titanium nitride nanowire (PANI/TiN) was synthesized as a supercapacitor electrode material via seed-assisted hydrothermal process and high-temperature calcinations with flexible carbon fiber as a substrate. PANI/TiN nanowires have a highly ordered coaxial core-shell nanowire structure, and the nanowires split each other to favor the ion diffusion and electron transportation and improve the energy storage performance. PANI/TiN exhibits a higher specific capacitance of 403 F/g at 1 A/g and a higher capacitance retention of 53.4% when the current density increases from 0.5 A/g to 10.0 A/g. The capacitance retention rate of PANI/TiN is 79.1% after 1 000 cycles of charging and discharging at 5 A/g. Compared with PANI, PANI/TiN has the improved electrochemical energy storage properties. The flexible all-solid-state symmetric supercapacitor (i.e., PANI/TiN supercapacitor) was assembled by using PANI/TiN as an electrode. PANI/TiN//PANI/TiN supercapacitor has the specific capacitance of 100.2 F/g at 1 A/g, and there is little attenuation of the specific capacitance after bending at different angles. PANI/TiN//PANI/TiN supercapacitor can obtain an energy density of 50.1 W·h/kg at a power density of 500 W/kg. Red light emitting diode (a rated voltage of 1.8 V) can be lighted up by one unit of the supercapacitor, indicating a promising potential application for energy storage.