Carbon materials are very important for the commercial production of supercapacitors and they are crucial electrode materials. The porous carbon prepared with biomass materials as a precursor is of significance due to its sustainability, environmental friendliness, and low cost. Biomass-derived carbon (BDC) has been widely investigated and reported as the electrode of supercapacitors due to its abundant pores and high surface areas. In this work, the recent advancement of BDC for supercapacitors in the last three years is reviewed. The energy storage mechanism, synthesis techniques, and biomass classification of BDC are briefly summarized at the beginning of this work. Some new typical cases with different biomass resources as raw materials are addressed. Then, effective strategies to further improve the specific capacitance of BDC, including heteroatoms doping, designing composites, novel processes, enhancing graphitic degree, and unique preparation methods, are discussed in detail. Finally, the challenges and future perspectives of porous BDC for supercapacitors are outlined.

Biomass hard carbon, serving as a negative electrode material for sodium-ion batteries, boasts advantages such as abundant sources, low cost, and high sodium storage capacity, thus earning its reputation as a highly promising negative electrode material. We utilized discarded peanut shells as raw materials and prepared high-performance hard carbon through a two-step process involving hydrothermal treatment and high-temperature carbonization. The application of the hydrothermal method significantly enhanced the nanoscale structure of the material, resulting in a highly dispersed sheet-like structure that facilitates the infiltration of the electrolyte and enhances the sodium storage capacity. The prepared hard carbon exhibits a specific surface area of 7.1 m2 g-1 and an interlayer spacing of 0.406 nm. Serving as a negative electrode material for sodium-ion batteries, it demonstrates a reversible sodium storage capacity of up to 357.55 mA h g-1 and a first coulombic efficiency of 63.4% at a current density of 30 mA g-1. PSHC-2 exhibits superior rate performance and good structural stability. The GITT test shows that PSHC-2 has good diffusion kinetics, which is beneficial for the insertion and extraction of sodium ions. The development of this new and efficient hard carbon negative electrode material has certain positive significance for the development of sodium ion batteries.

Hard carbon (HC) has excellent sodium storage capacity as anode materials of sodium-ion batteries (SIBs), and the properties of its precursor are also important to the electrochemical performance. In this work, bamboo- derived HC materials with four different particle sizes from 1.5 to 10 mu m are prepared by combination of acid etching and carbonization at 1300 degrees C, in order to identify the effects of particle size on the structure and electrochemical performance. Two HC materials with the medium sizes of 3.5 mu m and 6.5 mu m show higher specific capacities than the others. To enhance the performance further, two hybrids of HC/soft carbon are prepared by coating pitch-derived soft carbon films onto the above two HC materials with sizes of 3.5 mu m and 6.5 mu m. Comparing the two hybrids, the one originated from 3.5 mu m HC delivers a higher reversible specific capacity of 335.3 mAh g- 1 at 30 mA g- 1 and an initial coulombic efficiency of 86.8 %. Its capacity retention is 95.2 % after 150 cycles at 300 mA g- 1 , showing an excellent cycling stability. This work provides encouraging anode materials of SIBs for the industrial application.

To study the cutting mechanical properties of quinoa straw and reduce the cutting force and unit area cutting power consumption of quinoa straw, this study took quinoa from low-altitude areas as the research object. Through observation and experimental analysis of quinoa from low-altitude areas, the relevant external characteristics of quinoa straw were recognized, providing a certain research basis for the development of quinoa-specific harvesting machinery. In the cutting mechanical experiments, a reciprocating cutting test bench for straw was designed. Single-factor experiments were conducted on the moisture content, cutting speed, blade angle, and cutting angle of quinoa straw. Response surface experiments were conducted on cutting speed, blade inclination angle, and cutting inclination angle to reveal the variation laws of the cutting mechanical properties of quinoa straw, providing a scientific basis for the rational formulation of harvesting strategies. In the single-factor experiments, the ultimate cutting stress of the stem and the unit area cutting power consumption decreased with the increase in moisture content; the ultimate cutting stress of the stem and the unit area cutting power consumption decreased first and then increased with the increase in cutting inclination angle; the ultimate cutting stress of the stem decreased with the increase in blade inclination angle, while the unit area cutting power consumption decreased first and then increased; the ultimate cutting stress of the stem and the unit area cutting power consumption decreased first and then remained stable with the increase in average cutting speed. In the response surface experiments, the optimal parameter combination was an average cutting speed of 0.8 m/s, a cutting inclination angle of 9.8°, and a blade inclination angle of 33.2°. The verification test proved that the error was no more than 4%. Under the optimal parameters, the ultimate cutting stress and unit area cutting power consumption of the straw were 9.1% and 2.9%, respectively.

The synthesis of high-performance electrode materials at a low cost is essential for the future application of supercapacitors. In this work, multilayer graphene (MLG) prepared by mechanical exfoliation is directly used as a conductive substrate, on which nickel hydroxychloride nanosheet networks are assembled by chemical bath deposition at 90 degrees C using EDTA (Ethylenediaminetetraacetic acid) as a complexing agent. The effect of EDTA amount on the morphology and electrochemical performance of nickel hydroxychloride (NHC)/MLG composites is studied in detail. The composite prepared with optimized EDTA (NHC/MLG-10) exhibits a specific capacitance of 1952.38 F g- 1 at 1 A g- 1 and a capacitance retention of 70.24 % at 10 A g- 1. An asymmetric supercapacitor is fabricated using NHC/MLG-10 as the positive electrode and activated carbon as the negative electrode. It demonstrates a high specific capacitance of 105.17 F g- 1 at 1 mA cm- 2, and a capacitance retention of 73.85 % at 10 mA cm- 2. A high energy density of 36.99 Wh kg- 1 can be delivered at a high power density of 3185.36 W kg- 1. It is a promising material for supercapacitors due to its facile synthesis, low cost and high specific capacitance.

Hard carbon made from bamboo has been considered as a promising anode material for sodium-ion batteries because of its renewability and high-performance. Nitrogen-doping can significantly improve the electrochemical performance of carbon materials through enhancing the conductivity and maintaining the stability. In this work, two series of N-doped hard carbon materials derived from bamboo were prepared by heating the mixture of hard carbon and melamine at different temperatures from 700 to 900 degrees C with various mass ratios of melamine to hard carbon 1:1, 2:1 and 3:1. The non-porous structure of the carbon particles made it difficult to achieve a high nitrogen content, and nitrogen would not be successfully doped into carbon at too high temperatures. Nitrogen doping into hard carbon would affect the structure and electrochemical properties. Among as-prepared samples, the one prepared with a mass ratio of 1:1 at 800 degrees C exhibited optimum performance with a high reversible specific capacity of 329.1 mAh center dot g- 1 and high initial Coulombic efficiency of 85.5 % at 30 mA center dot g- 1. Moreover, it had excellent rate capability of 206.2 mAh center dot g- 1 at 1.5 A center dot g- 1. After 100 cycles at 0.3 A center dot g- 1, the capacity retention rate was 92.9 %. The results showed that the electrochemical performance of samples was strongly related to the doped nitrogen content, the disordered degree and the conductivity of N-doped hard carbon.

Recent research on supercapacitors (SCs) has been attractive due to the potential application in a variety of fields related to energy storage. Electrode materials play a very important role for the performance of SCs and various metal nanoparticles are involved in the SC electrodes. In this paper, the roles of metal nanoparticles for SCs are reviewed and discussed. They can serve as a dopant to modify the surface of electrode materials, or be embedded in a composite to effectively reduce the resistance and lead to an enhanced specific capacitance. Some metal nanoparticles can be also employed as electrode materials directly, but easily being oxidized. Metallic nanoparticles can even act as current collectors, especially for these noble metals with excellent stability and high conductivity. Nanoporous metals prepared by dealloying and electrochemical method can be used as both pseudocapacitive materials and current collector of SCs. Some important experimental data on this issue are summarized. A brief discussion on the future directions, challenges and opportunities in this topic is also provided.

Hard carbon made from biomass-based precursors has many advantages as anode for sodium-ion batteries such as low cost and sustainability. In this work, three different hard carbon materials derived from bamboo, wood and coconut shell with the same particle size are screened, combining acid etching and carbonization at 1200 degrees C, to compare the sodium ion storage performances. The anode material originated from bamboo shows the highest specific capacity among them. Subsequently, the hard carbon from bamboo is optimized by the same process, but changing the carbonization temperature ranging from 1000 degrees C to 1400 degrees C. Among the hard carbon materials, the bamboo-derived one prepared at 1300 degree celsius exhibits excellent electrochemical performances at a current density of 30 mA g-1, with a high reversible specific capacity of 303.8 mAh/g and an initial coulombic efficiency of 83.7 %. After 150 cycles, a capacity retention of 94.7 % is achieved at a current density of 300 mA g-1. This work provides a potential hard carbon anode for sodium-ion batteries to realize large-scale energy storage due to the cheap sources of bamboo.

Developing high-performance anode materials is significantly important for further application of sodium ion batteries (SIBs). Constructing a rational hierarchical nanostructure of active materials with carbon materials can effectively improve the electrochemical performance. Here, thin films of carbon coated Sn/SnO2 nanoparticles are synthesized on multilayer graphene (MLG), which has flat surface and high electric conductivity. The synthesis includes the preparation of uniform thin films of amorphous SnO2 on MLG by a HCl controlled chemical bath deposition method, subsequent coating glucose and annealing at a high temperature. As anode of SIBs, the composite delivers specific discharge capacities of around 598.0 mAh/g at 100 mA g-1 and 244.2 mAh/g at 5 A/ g, showing a high reversible capacity and superior rate performance. It also shows high cycling stability with capacity retention of 490 mAh/g at 100 mA g-1 after 100 cycles, and 355.64 mAh/g at 500 mA g-1 after 300 cycles.

Ni-Fe battery is one of prospective aqueous alkaline batteries due to its high safety, eco-friendliness and cost-effectiveness. However, the electrochemical performance of Fe-based anodes is limited due to the particle aggregation and low electric conductivity. In this work, iron powder is used as a precursor in a chemical bath deposition method. By optimizing the concentration of HNO3 , a balanced dissolution-crystallization process is achieved to obtain uniform Fe2 O3 nanospheres in size between 60 and 90 nm, which are separately anchored on ultrasonically prepared multilayer graphene (MLG). This composite delivers specific discharge capacities of 191.1 and 160.8 mAh g-1 at the current densities of 2 and 10 A g-1 , respectively. A Ni-Fe battery with the as-prepared Fe2 O3 /MLG as anode and Ni(OH)2 /MLG as cathode exhibits an energy density of 69.5 Wh kg-1 at a high power density of 3931.6 W kg-1 .

Conductive polymer polypyrrole (PPy)-coated lithium-rich manganese-based Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) nanotube cathode materials were synthesized by electrospinning and subsequently subjected to low-temperature vapor-phase polymerization. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) results confirm that the successful coating of the PPy layer (~2 nm) on the surface of LMNCO nanotubes did not destroy their morphologies or structures. Electrochemical tests indicate that the electrochemical performance of PPy-coated LMNCO nanotubes has been significantly enhanced. At a rate of 1 C, the discharge capacity of the PPy-coated LMNCO cell is 200.1 mAh g−1, and the capacity retention is 99% after 120 cycles. This excellent stability is attributed to the inhibition of side reactions and the protective function of the tubular structure due to the PPy coating layer. Additionally, the rate capability is also improved at a high current density due to the higher electronic and ionic conductivity.

Although advanced anode materials for the lithium-ion battery have been investigated for decades, a reliable, high-capacity, and durable material that can enable a fast charge remains elusive. Herein, we report that a metal phosphorous trichalcogenide of MnPS3 (manganese phosphorus trisulfide), endowed with a unique and layered van der Waals structure, is highly beneficial for the fast insertion/extraction of alkali metal ions and can facilitate changes in the buffer volume during cycles with robust structural stability. The few-layered MnPS3 anodes displayed the desirable specific capacity and excellent rate chargeability owing to their good electronic and ionic conductivities. When assembled as a half-cell lithium-ion battery, a high reversible capacity of 380 mA h g(-1) was maintained by the MnPS3 after 3000 cycles at a high current density of 4 A g(-1), with a capacity retention of close to or above 100%. In full-cell testing, a reversible capacity of 450 mA h g(-1) after 200 cycles was maintained as well. The results of in-situ TEM revealed that MnPS3 nanoflakes maintained a high structural integrity without exhibiting any pulverization after undergoing large volumetric expansion for the insertion of a large number of lithium ions. Their kinetics of lithium-ion diffusion, stable structure, and high pseudocapacitance contributed to their comprehensive performance, for example, a high specific capacity, rapid charge-discharge, and long cyclability. MnPS3 is thus an efficient anode for the next generation of batteries with a fast charge/discharge capability.

Fe3O4/CNT composites are synthesized with ethylene glycol as solvent by a one-step solvothermal method and used as anode materials for asymmetric supercapacitors (ASC). An appropriate amount of water in ethylene glycol can accelerate the formation of Fe3O4 and reduce the average size of Fe3O4 to around 20 nm. However, spherical Fe3O4 particles larger than 100 nm will form in pure ethylene glycol for long reaction time. The Fe3O4/CNT composite with small Fe3O4 nanoparticles exhibits a high specific surface area, promoted electron transfer ability, as well as a high utilization rate of active materials. The optimized electrode shows a high specific capacity of 689 C g(-1) at 1 A g-1, and remains 443 C g(-1) at 10 A g(-1). The inferior long-term cycling stability is due to the phase transition of Fe3O4 and a reductive effect to form metallic Fe. An ASC using Fe3O4/CNT and NiCoO2/C composites as anode and cathode, respectively, delivers a high energy density of 58.1 Wh kg(-1) at a power density of 1007 W kg-1 in a voltage window of 1.67 V and has a capacity retention of 63% after 5000 cycles. The self-discharge behavior of the ASC is also investigated.

MnS has been explored as an anode material for lithium-ion batteries due to its high theoretical capacity, but low electronic conductivity and severe volume change induce low reversible capacity and poor cycling performance. In this work, the nanocapsule consisting of MnS nanopolyhedrons confined in independent, closed and conductive hollow polyhedral nanospheres is prepared by embedding MnCO3 nanopolyhedrons into ZIF-67, followed by coating of RF resin and gaseous sulfurization/carbonization. Benefiting from the unique nanocapsule structure, especially inner CoS/C shell and outer pure C shell, the MnS@CoS/C@C composite as anode material presents excellent cycling performance (674 mAh g−1 at 1 A g−1 after 300 cycles; 481 mAh g−1 at 5 A g−1 after 300 cycles) and superior rate capability (1133.3 and 650.6 mAh g−1 at 0.1 and 4 A g−1), compared to the control materials (MnS and MnS@CoS/C) and other MnS composites. Kinetics measurements further reveal a high proportion of the capacitive effect and low reaction impedance of MnS@CoS/C@C. SEM and TEM observation on the cycled electrode confirms superior structural stability of MnS@CoS/C@C during long-term cycles. Excellent lithium storage performance and the convenient synthesis strategy demonstrates that the MnS@CoS/C@C nanocapsule is a promising high-performance anode material.

The performances of energy storage devices are strongly dependent on the electrode materials. Owing to the high theoretical capacity, NiCoO2 is a promising transition metal oxide for supercapacitors. Despite many efforts have been devoted, it still lacks of effective methods to overcome its shortcomings such as low conductivity and poor stability, in order to achieve its theoretical capacity. Herein, utilizing the thermal reducibility of trisodium citrate and its hydrolyzate, a series of NiCoO2@NiCo/CNT ternary composites in which NiCoO2@NiCo core-shell nanospheres deposited on CNT surface with adjustable metal contents are synthesized. Benefiting from the enhanced synergistic effect of both metallic core and CNTs, the optimized composite exhibits an extremely high specific capacitance (2660 F g-1 at 1 A g-1, the effective specific capacitance of the loaded metal oxide is 4199 F g-1, close to the theoretical value), an excellent rate performance and stability, when the metal content is about 37%. After depolarized calculation, the energy storage mechanism of the composite is reasonably analyzed. By controlling the contents of hexamethylenetetramine, trisodium citrate and CNTs in the reactant, the roles of them are distinguished. This study reveals an efficient novel strategy for transition metal oxides to maximize the electrochemical performances.

The electrochemical performance of lithium-ion batteries, i.e. specific capacity and cyclability, is primarily determined by chemical reversibility and structural stability of the electrodes in cycling. Here we have investigated the fundamental reaction behaviors of nickel sulfide (NixSy) as lithium-ion battery anodes by in-situ TEM. We find that Ni3S2 is the electrochemically stable phase, which appears in the first cycle of the NixSy anode. From the second cycle, conversion between Ni3S2 and Li2S/Ni is the dominant electrochemical reaction. In lithiation, the NixSy nanoparticles evolve into a mixture of Ni nanocrystals embedded in Li2S matrix, which form a porous structure upon full lithiation, and with the recrystallization of the Ni3S2 phase in delithiation, a compact and interconnected network is built. Structural stability in cycles is susceptible to particle size and substrate restraint. Carbon substrate can certainly improve the tolerance for size-dependent pulverization of NixSy nanoparticles. When NixSy nanoparticle exceeds the critical size value, the morphology of the particle is no longer well maintained even under the constraints of the carbon substrate. This work deepens the understanding of electrochemical reaction behavior of conversion-type materials and helps to rational design of high-energy density battery anodes.

In situ synthesis of Ag-doped CuO microflowers on multilayer graphene (MLG) and their application in non-enzymatic detection of glucose are studied here. Mechanically exfoliated MLG has particular advantages such as low defects and cost efficiency. However, the deposition of CuO on its surface is still a challenge due to the lack of active sites on the MLG surface. In this work, a one-step chemical bath deposition approach is developed to synthesize homogeneous CuO microflowers and Ag-doped CuO microflowers on MLG surfaces. The CuO structures are composed of ultra-small CuO nano-spindles and internal nano-gaps. The materials are well characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive spectrometry (EDS) and evaluated as glucose sensors. The electrode of Ag-doped CuO microflowers on MLG exhibits a sensitivity of 1527 μA mM−1cm−2 in a linear response range of 0.01 mM ~ 6.0 mM with an excellent selectivity and a long-term stability. The composite is a promising material for glucose sensors due to its facile synthesis and highly detective performance.

Metal–organic framework (MOF)-derived pure ZnO and Cu-doped ZnO nanocages were fabricated by calcining a zeolitic imidazole framework (ZIF-8) and Cu-doped ZIF-8. The morphology and crystal structure of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that Cu doping did not change the crystal structures and morphologies of MOF-derived ZnO nanocages. The H2S-sensing properties of the sensors based on ZnO and Cu-doped ZnO nanocages were investigated. The results indicated that the H2S-sensing properties of MOF-derived ZnO nanocages were effectively improved by Cu doping, and the optimal doping content was 3 at%. Moreover, 3 at% Cu-doped ZnO nanocages showed the highest response of 4733 for 5 ppm H2S at 200 °C, and the detection limit could be as low as 20 ppb. The gas-sensing mechanism was also discussed.

Antimony-based electrodes have earned a place among anodes for sodium-ion batteries (SIBs) on account of their high specific capacity and appropriate reaction potential. However, significant volume changes during charge/discharge cycles directly lead to poor cycling ability, prohibiting their further practical application. Doping is recognized as a valid approach to tuning the electrochemical properties of electrodes for better electrochemical performances. In this work, Se-doped Sb solid solution (Sb1-xSex) nanoparticles are reported as a variety of anode materials for SIBs via a straightforward solvothermal method. The nanoparticles are uniformly distributed with a small size of about 20 nm. The diffusion properties of Na+ are studied by the galvanostatic intermittent titration technique (GITT), and the coefficient is acquired by calculation to be 1.8 x 10(-12) cm(2) s(-1). The electrochemical measurement results show that the nanoparticle electrode yields reversible capacities of 514, 500, 464, and 313 mAh g(-1) at 0.5, 1, 2, and 5 A g(-1), respectively. An initial charging specific capacity of 556.3 mAh g(-1) could be stable for 100 cycles at 100 mA g(-1), retaining up to 96.8% of battery capacity. It is believed that a solution is provided based on our findings to polish the electrochemical characteristics applied in SIBs by means of doping.

For rapid charge/discharge application, capacitive energy storage technology is an attractive approach. The low energy density, one of disadvantages, can be ameliorated by promising pseudocapacitive materials that harvest energy through redox reactions. In this work, a composite of bimetal oxide and carbon nanotubes (CNTs), NiCoO2@CNT, with a novel mesoporous grape-like structure is prepared by a mild method, in which metal oxide nanoparticles are bonded to CNTs like vines tightly. Due to the synergistic effect and the unique structure as well as the facilitation of CNTs, impressive properties are performed for the NiCoO2@CNT composite. With an excellent stability and rate capability, it achieves 1587 F g(-1) at 1 A g(-1). As revealed in the charge storage mechanism, the surface-controlled process plays a dominant role, which can be ascribed to the large proportion of redox reactions on the surface of small NiCoO2 nanoparticles and the presence of CNTs. NiCoO2@CNT and activated carbon are then applied to fabricate an asymmetric supercapacitor. It exhibits a high energy density of 41.8 Wh kg(-1) at 412 W kg(-1) and an outstanding cycling property with 92% maintained after 5000 cycles, indicating a great potential for the actual application. (C) 2021 Elsevier Ltd. All rights reserved.