Recent development of flexible and self-healable electro-conductive hydrogels (ECHs) are considered as promising soft materials towards intelligent applications. Nonetheless, realizing the integrated ...features of high electro-conductivity, viscoelasticity and mechanical toughness, as well as inherent mouldability, fast self-healing ability, and ideal electrochemical properties is still challenging. Herein, we report a kind of multifunctional ECHs based on a polyvinyl alcohol-borax (PVAB) hydrogel and carbon nanotube-cellulose nanofiber (CNT-CNF) nanohybrids that combines the conductivity of CNTs and template function of CNFs. CNFs serve as dispersant to uniformly stabilize CNTs in suspension. As-prepared CNT-CNF nanohybrids are uniformly dispersed into PVAB to construct freeze-standing CNT-CNF/PVAB composite hydrogels. Owing to a conductive and reinforcing dual-network structure, the compression stress (∼93 kPa) and storage modulus (∼7.12 kPa) of CNT-CNF/PVAB are 2.7 and 1.9-fold larger than those of CNF/PVAB. CNT-CNF/PVAB also exhibits low density (∼1.1 g cm−3), high water content (∼95%), pH sensitivity, intrinsic mouldability and 20s self-healing capability. The solid-state supercapacitor assembled by PVAB-based hydrogels has a specific capacitance of 117.1 F g−1 and a capacitance retention of 96.4% after 1000 cycles. The self-healable and flexible supercapacitor demonstrates an ideal capacitance retention (∼98.2%) after ten damaging/self-healing cycles and a capacitance retention (∼95%) after 1000 cycles under various deformation.
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Flexible aqueous zinc-ion batteries (AZIBs) are promising to satisfy the emerging wearable electronics. However, conventional hydrogel electrolytes are unable to work at subzero temperatures because ...they inevitably freeze. In this work, a borax-crosslinked polyvinyl alcohol (PVA)/glycerol gel electrolyte is developed, in which glycerol can strongly interact with PVA chains, thus effectively prohibiting the formation of ice crystals within the whole gel network. Thanks to this, the freezing point of this gel electrolyte is below −60 °C, which allows it to work in extremely cold environments. Even at −35 °C, it still exhibits a high ionic conductivity of 10.1 mS cm−1 and great mechanical properties. On the basis of this anti-freezing gel electrolyte, a flexible quasi-solid-state aqueous Zn–MnO2 battery is assembled and realizes an impressive energy density of 46.8 mW h cm−3 (1330 μW h cm−2) at a power density of 96 mW cm−3 (2.7 mW cm−2) at 25 °C, outperforming nearly all the reported AZIBs. More importantly, when the temperature is reduced to −35 °C, a rather high energy density (25.8 mW h cm−3, 732 μW h cm−2) can still be achieved, and 53.3% of that value can be retained when the power density is increased to about 10-fold. This battery also shows excellent cycling durability (around 90% capacity retention over 2000 cycles) and great tolerance to various extreme conditions even when the temperature is down to −35 °C. These findings provide valuable insights into designing aqueous batteries/supercapacitors that can work in cold climates and high-altitude areas.
•Novel porous SnO2@C micro/nanospheres were prepared for the first time.•The as-prepared SnO2@C had superior structural stability and electrochemical kinetics.•The as-prepared SnO2@C anode exhibited ...high capacity and superior rate performance.•It displayed 955 and 836 mAh g−1 at 200 and 1000 mA g−1 after 250 and 350 cycles, respectively.
With high theoretical specific capacity and relatively safe working potential, SnO2 has drawn widespread attention as a promising candidate of advanced anode for next generation lithium-ion batteries. However, the practical application of SnO2 anode in lithium-ion batteries is severely blocked by some shortcomings such as the inferior rate capability, fast capacity decay and low initial coulombic efficiency during charge/discharge process. Gratifyingly, there are many works which have demonstrated that the SnO2 anode achieves extra improvement in lithium storage performance after being reduced to nanoscale and embedded into porous carbon matrixes. Herein, porous SnO2@C micro-/nanospheres with a sandwiched buffer zone resulted from unevenly radial distribution of pores in carbon micro-/nanospheres are prepared for the first time. These SnO2@C micro-/nanospheres consist of small SnO2 nanoparticles embedded within porous carbon micro-/nanospheres with a sandwiched buffer zone. The results of this study indicate that the sandwiched buffer zone of carbon micro-/nanospheres and the confinement effect of nanopores on small SnO2 nanoparticles synergistically contribute to outstanding structural stability and excellent electrochemical performance of thus porous SnO2@C micro-/nanospheres. Besides, it is found that the lithium storage performance of the SnO2@C micro-/nanospheres can be tuned by adjusting the SnO2 contents. As a result, the as-prepared SnO2@C micro-/nanospheres with an optimalizing SnO2 content exhibit the best performance, delivering a high capacity of 955 mAh g−1 at 200 mA g−1 after 250 cycles as well as a high capacity of 836 mAh g−1 at even 1000 mA g−1 after 350 cycles.
The SnO2 nanoparticles are embedded within porous carbon micro/nanospheres with uneven diametrical porosity distribution by a well-designed strategy and exhibit excellent performance in terms of high capacity, long lifetime and superior rate capability. Display omitted
With the advantages of intrinsic safety, good affordability, environmental friendliness, moderate energy density, and large power density, aqueous zinc ion batteries (AZIBs) have gained considerable ...research interest. However, zinc dendrites, hydrogen evolution, inert byproducts, and zinc metal corrosion severely hinder practical applications of AZIBs. In order to address these issues, many research works have been carried out to modify the interface between zinc metal anode and aqueous electrolyte. In fact, the interface engineering takes effect at the surface and near the surface of separator. However, a specialized review on the separators of AZIBs is still lacking. Herein, basic requirements of separators and recent advances on the modification strategies including employment of functional groups, establishment of surface coatings, construction of hybrid architectures, regulations of porosity, and utilization of bipolar membrane are reviewed. Besides, the perspectives for further investigations on the separators of AZIBs are outlined. This review could offer useful guidance for the future explorations of separators for AZIBs.
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•Recent advances on the separators of aqueous zinc ion batteries are reviewed.•The basic requirements for separators of aqueous zinc ion batteries are introduced.•The modification strategies on the separators are systematically discussed.•The cyclability of Zn//Zn cells with different separators is compared.•The remaining challenges and perspectives on the separators are outlined.
Electrode structure design and interfacial nitrogen engineering enabling Si-N-MXene anode for high energy density solid-state battery.
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Replacing the conventional carbonate electrolyte ...by solid-state electrolyte (SSE) will offer improved safety for lithium-ion batteries. To further improve the energy density, Silicon (Si) is attractive for next generation solid-state battery (SSB) because of its high specific capacity and low cost. High energy density and safe Si-based SSB, however, is plagued by large volume change that leads to poor mechanical stability and slow lithium ions transportation at the multiple interfaces between Si and SSE. Herein, we designed a self-integrated and monolithic Si/two dimensional layered T3C2Tx (MXene, Tx stands for terminal functional groups) electrode architecture with interfacial nitrogen engineering. During a heat treatment process, the polyacrylonitrile not only converts into amorphous carbon (a-C) that shells Si but also forms robust interfacial nitrogen chemical bonds that anchors Si and MXene. During repeated lithiation and delithiation processes, the robust interfacial engineered Si/MXene configuration enhances the mechanical adhesion between Si and MXene that improves the structure stability but also contributes to form stable solid-electrolyte interphase (SEI). In addition, the N-MXene provides fast lithium ions transportation pathways. Consequently, the Si/MXene with interfacial nitrogen engineering (denoted as Si-N-MXene) deliveres high-rate performance with a specific capacity of 1498 mAh g−1 at a high current of 6.4 A g−1. A Si-N-MXene/NMC full cell exhibited a capacity retention of 80.5% after 200 cycles. The Si-N-MXene electrode is also applied to SSB and shows a relative stable cycling over 100 cycles, demonstrating the versatility of this concept.
To address the issues of the particle fracture and loss of electrical connectivity of high capacity silicon anodes, herein, we propose a novel strategy that combines surface carbon coating and bulk ...boron doping. Heavily boron doped polycrystalline photovoltaic Si particles are used as starting materials. The bulk boron doping is demonstrated to enhance both electron transportation and lithium-ion diffusion, which contributes to superior high-rate performance. Taking advantage of the fast kinetics and stable interphase with the electrolyte, the carbon coated boron doped Si electrode exhibits higher capacity retention. For example, the capacity retentions are 668 mA h g
−1
, 293 mA h g
−1
and 79 mA h g
−1
at a high rate of 0.5C (1C = 4000 mA g
−1
) after 500 cycles for 3900 ppm, 120 ppm, and 10 ppm boron doped Si, respectively. In addition, an improved mass loading of 2.0 mg cm
−2
, high areal capacity (3.9 mA h cm
−2
) and high-volume capacity (2111 mA h cm
−3
) are achieved. Our work opens a new horizon for designing stable high loading Si anodes, which is applicable for other alloy electrode materials.
Surface carbon coating and bulk boron doping enabling high-rate and long durable Si anode.
Wood has unique advantages. However, the rigid structure and intrinsic insulating nature of wood limit its applications. Herein, a two-step process is developed to render wood veneers conductive and ...flexible. In the first step, most of the lignin and hemicellulose in the wood veneer are removed by hydrothermal treatment. In the second step, electroless Ni plating and subsequent pressing are carried out. The obtained Ni-plated veneer is flexible and bendable, and has a high tensile strength of 21.9 and 4.4 MPa along and across the channel direction, respectively, the former of which is considerably higher than that of carbon cloth and graphene foam. Moreover, this product exhibits high electrical conductivity around 1.1 × 103 S m−1, which is comparable to that of carbon cloth and graphene foam, and significantly outperforms previously reported wood-based conductors. This work reveals an effective strategy to transform cheap and renewable wood into a high value-added product that rivals expensive carbon cloth and graphene foam. The obtained product is particularly promising as a current collector for flexible and wearable electrochemical energy storage devices such as supercapacitors and Li-ion batteries.
It remains a great challenge for aqueous zinc-ion batteries to work at subzero temperatures, since the water in aqueous electrolytes would freeze and inhibit the transportation of electrolyte ions, ...inevitably leading to performance deterioration. In this work, we propose an anti-freezing gel electrolyte that contains polyacrylamide, graphene oxide, and ethylene glycol. The graphene oxide can not only enhance the mechanical properties of gel electrolyte but also help construct a three-dimensional macroporous network that facilitates ionic transport, while the ethylene glycol can improve freezing resistance. Due to the synergistic effect, the gel electrolyte exhibits high ionic conductivity (e.g., 14.9 mS cm-1 at -20 °C) and good mechanical properties in comparison with neat polyacrylamide gel electrolyte. Benefiting from that, the assembled flexible quasi-solid-state Zn-MnO2 battery exhibits good electrochemical durability and superior tolerance to extreme working conditions. This work provides new perspectives to develop flexible electrochemical energy storage devices with great environmental adaptability.
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