Hexafluorocyclotriphosphazene (HFPN) is a promising flame retardant to be applied in lithium-ion batteries (LIBs) to decrease the fire risk during the treatment of electrolyte. In this manuscript, ...the influence of HFPN on the combustion characteristics of LIB electrolyte was investigated, the combustion behaviors and flame retardancy of the electrolyte with or without HFPN were systematically studied by using cone calorimeter, flash point meter and a series of standard equipment, as well as self-made water spray fire extinguishing platform. The flash points of 3 kinds of control group as base solution and 3 kinds of flame-retarded electrolyte were measured and obtained by SCKB3000 closed cup automatic flash point tester. The combustion characteristics of 6 types of electrolytes were analyzed by a cone calorimeter. The heat release rate (HRR), fire growth index (FGI), fire magnitude index (FMI) and other important combustion parameters of the electrolytes were studied. Based on the self-made water mist fire extinguishing platform, the fire extinguishing effect on 6 kinds of electrolytes under the same water mist condition was compared, and the influence of flame retardants in the fire extinguishing process was analyzed. The results showed that the change of flash point was obviously related to the composition of electrolyte. Flame retardant could reduce the peak HRR (pHRR) during electrolyte fire to a large extent, while it could also prolong the combustion duration of electrolyte pool fire. Under the action of fine water mist, the electrolyte pool fire would quickly extinguish, but there would remain a lot of smoke.
The dissolution of calcite in a full range of saturation conditions is investigated to explore the kinetic effect of Gibbs free energy, dislocation density, and the presence of atmospheric pCO₂. ...Experiments are carried out in a mixed-flow reactor at room temperature (25°C) in both closed and open (to air) settings, and calcite samples are prepared by fragmentation and milling to generate different defect densities. Experimental observations show a highly nonlinear dependence of the dissolution rates on the Gibbs free energy; however, the kinetics does not seem to be affected by the samples' dislocation density, nor the presence of atmospheric pCO₂ at any saturation condition. Fitting the conventional transition state model (TST) to the observed rate - free energy relationship indicates that, though the TST rate equation is sufficient to describe the dissolution kinetics near and far from equilibrium, it clearly overestimates the dissolution rate when the system sits in between. These results suggest that: (i) the classic TST model may not be sufficient to depict the relation between dissolution rate and Gibbs free energy once solution saturation falls from its extrema. (ii) The steps associated with increased crystal defects may be overwhelmed by those regenerated at corners and edges of calcite particles through layer-by-layer dissolution along the cleavage directions. (iii) The presence of CO₂ in ambient environments bears little importance to calcite dissolution possibly due to the slow response of aqueous HCO₃ ⁻ to pCO₂ change at low CO₂ partial pressure conditions.
Grain size- and crystallographic direction-dependence are among the fundamental characteristics of crystal solubility. However, such important material properties are routinely ignored and solubility ...is often conveniently approximated by a solubility product. In this study, we attempt to outline the relationship between solubility and solubility product using thermodynamic arguments, and to provide observations that demonstrate the occurrence of circumstances where the solubility product cannot properly approximate crystal solubility. Theoretical analysis shows that solubility is always greater than solubility product, but the difference is inversely related to the grain size. Furthermore, the difference can be crystallographic direction specific if the total surface energy change upon the attachment of an individual growth unit is nonequivalent for each symmetrically unrelated crystal faces.
In situ AFM experiments conducted on the cleavage face of calcite demonstrate that the
〈
4
¯
41
〉
±
steps exhibit direction- and length-dependent behavior. Specifically, the measured critical step lengths are consistent with the predicted inverse relationship to saturation states. Moreover, step retreat at
〈
4
¯
41
〉
+
and advance at
〈
4
¯
41
〉
-
are observed simultaneously in a narrow range of saturation at near equilibrium conditions, indicating the existence of direction specific solubility. Whereas these findings justify the rationale for approximating solubility by solubility product in cases where large crystals are concerned, the results imply that the size and direction effect should not be ignored if nanocrystal growth/dissolution is the subject of interest.
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•Sc3+ is selected to replace V3+ and PAN is introduced to provide porous carbon substrate.•Sc bonds with oxygen to form ScO6, resulting in improved structural stability and ...kinetics.•PAN can induce a beneficial nitrogen-doped carbon skeleton with defects, resulting in enhanced electronic conductivity.•After cycling XRD/SEM confirms the stabilized porous carbon skeleton and improved crystal stability.•Ex-situ XRD analysis reveals the crystal volume change in Sc-3 is relatively slight but reversible.
The poor structural stability and conductivity of Na3V2(PO4)3 (NVP) have been serious limitations to its development. In this paper, Sc3+ is selected to replace partial site of V3+ which can enhance its ability to bond with oxygen, forming the ScO6 octahedral unit, resulting in improved structural stability and better kinetic properties for the NVP system. Moreover, due to the larger ionic radius of Sc3+ compared to V3+, moderate Sc3+ substitution can support the crystal framework as pillar ions and expand the migration channels for de-intercalation of Na+, thus efficiently promoting ionic conductivity. The introduction of polyacrylonitrile (PAN) to provide an N-doped porous carbon substrate is another key aspect. The low-cost carbon resource of PAN can induce a beneficial nitrogen-doped carbon skeleton with defects, enhancing electronic conductivity at the interface to reduce the polarization phenomenon. The established pore structure can serve as a buffer for unit cell deformation caused by Na+ migration. Furthermore, the enlarged specific surface area provides more active sites for electrolyte infiltration, improving the material utilization rate. The after cycling X-ray Diffraction/scanning electron microscope (XRD/SEM) further confirms the stabilized porous carbon skeleton and improved crystal stability of Sc-3 material. Ex-situ XRD analysis shows that the crystal volume change in the Sc-3 cathode is relatively slight but reversible during the charge/discharge process, indicating that Sc3+ doping plays a crucial role in stabilizing the unit cell structure. The hybrid Sc/VO6 and PO4 units jointly build a strong bone structure to resist stress and weaken deformation. Accordingly, the optimized Sc-3 sample reveals an initial capacity of 115.9 mAh/g at 0.1C, with a capacity retention of 78.6 % after 2000 cycles at 30C. The Sc-3//CHC full battery can release a capacity of 191.3 mAh/g at 0.05C, accompanied by successful illumination, showcasing its promising practical applications.
Porous carbon network-based phase change composites have been widely used in energy storage and thermal management related fields. At present, the demand of energy crisis for photothermal energy ...storage and the prevention and management of thermal abuse of electronic equipment constantly promote the development of carbon-based composite phase change materials (PCMs). Therefore, a series of new composite materials filled with PCMs and polyethylene glycol (PEG) and added with flame-retardant magnesium hydroxide were developed, which makes the composites show certain flame-retardant ability in high-temperature environments. The results show that the thermal conductivity increases from 0.25 to 0.94 W/m·K, and the latent heat of phase change remains at 142.7 J/g. In addition, due to the capillary effect caused by the synergistic effect of multi-pore carbon (MPC) structure and cellulose macromolecular chain, the composite material has good shape stability, which effectively prevents the leakage behavior of PCMs during solid-liquid phase change. Moreover, the absorbance of the composite material can reach 1.28 L/(g cm) in the ultraviolet–visible light range of 200 nm–800 nm, and its photothermal conversion efficiency can reach 90.8 %. Therefore, this material has a broad application prospect in the thermal management of electronic equipment and photothermal energy storage devices.
A series of composite membranes with enhanced mechanical properties were prepared by self-assembly of MPC, polyethylene glycol (PEG) and Mg(OH)2. It is an innovative application for composite phase change materials in thermal energy storage, battery thermal management system, microelectronics packaging and intelligent buildings. Display omitted
•Composite films with enhanced mechanical properties were prepared.•MPC@PEG/Mg(OH)2 is a novel composite with superior characteristics.•The addition of MPC in composite films effectively improved thermal conductivity.•The form-stable composite films had a phase change enthalpy of 142.7 J/g.•It is an innovative application for composite phase change materials.
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•Mn2+ substitution generates beneficial holes to accelerate electron transport while supporting the structure to stabilize the framework.•Al2O3 coating has the triple effect of ...reducing HClO4 concentration, inhibiting the dissolution of Mn and acting as a conductive agent.•NVMP@CNTs@1wt.%Al2O3 possesses a porous structure, effectively promoting the rapid Na+ transport.•The excellent structural stability is confirmed by in situ XRD.•NVMP@CNTs@1wt.%Al2O3 reveals a remarkable sodium storage property in both half and full cells.
Na3V2(PO4)3 (NVP) encounters significant obstacles, including limited intrinsic electronic and ionic conductivities, which hinder its potential for commercial feasibility. Currently, the substitution of V3+ with Mn2+ is proposed to introduce favorable carriers, enhancing the electronic conductivity of the NVP system while providing structural support and stabilizing the NASICON framework. This substitution also widens the Na+ migration pathways, accelerating ion transport. Furthermore, to bolster stability, Al2O3 coating is applied to suppress the dissolution of transition metal Mn in the electrolyte. Notably, the Al2O3 coating serves a triple role in reducing HClO4 concentration in the electrolyte, inhibiting Mn dissolution, and functioning as the ion-conducting phase. Likewise, carbon nanotubes (CNTs) effectively hinder the agglomeration of active particles during high-temperature sintering, thereby optimizing the conductivity of NVP system. In addition, the excellent structural stability is investigated by in situ XRD measurement, effectively improving the volume collapse during Na+ de-embedding. Moreover, the Na3V5.92/3Mn0.04(PO4)3/C@CNTs@1wt.%Al2O3 (NVMP@CNTs@1wt.%Al2O3) possesses unique porous structure, promoting rapid Na+ transport and increasing the interface area between the electrolyte and the cathode material. Comprehensively, the NVMP@CNTs@1wt.%Al2O3 sample demonstrates a remarkable reversible specific capacity of 122.6 mAh/g at 0.1 C. Moreover, it maintains a capacity of 115.9 mAh/g at 1 C with a capacity retention of 90.2 mAh/g after 1000 cycles. Even at 30 C, it achieves a capacity of 87.9 mAh/g, with a capacity retention rate of 84.87 % after 6000 cycles. Moreover, the NVMP@CNTs@1wt.%Al2O3//CHC full cell can deliver a high reversible capacity of 205.5 mAh/g at 0.1 C, further indicating the superior application potential in commercial utilization.
Na3V2(PO4)3 (NVP) has been extensively researched as an ideal cathode material. However, the limitations of its structural stability and electronic conductivity have hindered its further ...applications. To address these challenges, this study proposes a modification strategy centered on the synergistic effects of Nd doping and carbon nanotubes (CNTs) coating. The Nd element shows a stronger affinity for oxygen. When replacing the V site, it can form a more stable Nd-O bond, meanwhile, it can inhibit the oxygen evolution. Furthermore, due to the super large ionic radius of Nd3+ (1.81 Å vs. 0.64 Å of V3+), the introduction of Nd doping serves to enhance the stability of the crystal structure, thereby ensuring the effective de-intercalation of Na+. Furthermore, Nd doping widens the transport channels, thereby increasing the speed of Na+ transport. Concurrently, the CNTs coating network, which is integrated onto the material surface, offers diverse pathways for electronic transport, significantly improving electronic conductivity. Comprehensively, Nd-3 sample shows the optimal performance at different doping gradients. It displays a reversible capacity of 114.8 mAh g−1 at 0.1 C. When cycling at 40 C, it can remain 90.2 % after 2500 cycles. According to the ex-situ XRD measurements, the Nd-3 sample shows favourable structural reversibility and very small volume shrinkage, indicating the significantly improved structural stability. Finally, the Nd-3//CHC full cell reveals a high capacity of 134.4 mAh g−1 at 0.1 C, indicating its great potential for applications.
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•A simultaneous optimized strategy of Nd substitution and CNT coating is proposed for the first time.•Nd3+ replacing V3+ make the lattice spacing enlarged to improve the structural stability of electrode materials.•Nd-3 shows favourable structural reversibility and small volume shrinkage, indicating improved structural stability.•The dense coating of CNTs can form an efficient conductive network structure.•Nd-3 sample reveals high performance in both half and full cells.
Fsigure GA. Synthesis and application of composite materials. Ni Al-LDH was originally grown on MPC. After PEG was compounded, the light absorption capacity of CuS was utilized to carry out ...photothermal energy storage through the phase change heat storage capacity of PEG, and the composite material showed electromagnetic shielding performance as well as excellent mechanical properties.
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•MPC@Ni Al-LDH was synthesized and then combined with PEG to form composites.•Multifunctional bilayer films were synthesized two-step filtration method.•CuS and MPC in MLPC composite film effectively improve the thermal conductivity.•Latent heat of MLPC is 155.2 J/g, and its conversion efficiency is high.•It is an innovative application for composite phase change materials.
CuS-based composites are widely used in the fields related to photothermal energy storage and electromagnetic shielding and are excellent candidates for composites with phase change materials. To meet the requirements of micro-integration and electromagnetic resistance of electronic products and optimize the thermal management of electronic products, it is necessary to prepare new flexible composite phase change materials. In this paper, through the design of MPC@Ni Al-LDH/CuS double-layer structure, two-step vacuum filtration method is used, and the highly conductive materials CuS and MPC are introduced into the manufacture of PCM films. With the help of Ni Al-LDH, flame retardancy is introduced. The electromagnetic wave absorption performance is enhanced, and the existence of nano-cellulose (CNF) makes the film have excellent mechanical properties. Ni Al-LDH/MPC and CuS substrates with stable and high mechanical properties are prepared by ultrasonic treatment. According to scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and thermogravimetry (TG) characterizations, PEG successfully entered the MPC/CuS skeleton by vacuum filtration, and flexible phase change composite bilayers (MLPC) were obtained. Due to the synergistic effect of structure and components, the obtained composite film has many different excellent functions. Specifically, when MPC@Ni Al-LDH is 15 wt%, the phase transition enthalpy, thermal conductivity, electromagnetic shielding, and electrical conductivity are 146.8 J/g, 1.07 W/m·K, 38.8 dB and 126.4 S/m, respectively. The 3600 s infrared temperature measurement results show that the sample has stable thermal properties. Due to the presence of CuS, when MPC@Ni Al-LDH is 5 wt%, its absorbance can be kept at 1.51 L/(g·cm), and its photothermal conversion efficiency can reach 90.6 %. The MPC/CuS structure in the composite film provides many heat transfer channels, which reduces the phonon scattering in the heat transfer process and significantly increases thermal conductivity. Therefore, this multifunctional flexible phase change film can be used in photothermal conversion devices and for thermal management of electronic equipment, and it has broad application prospects in wearable equipment design due to its excellent electromagnetic shielding ability and infrared thermal stealth ability.
The behaviour of gypsum {010} cleavage faces, both (010) and (01¯0), in undersaturated conditions is studied at real time to probe the mineral dissolution process. The observations in surface ...topographic change and step motion made by in situ fluid cell atomic force microscopy show that: (i) the only type of etch pits on the cleavage faces is that embraced by the 100 and 001 steps, disagreeing with previous reports that suggested the involvement of the 101 direction; (ii) compared to calcite, the anisotropy in step velocity is much more pronounced, presumably due to the more significant difference in atomic structure between the 100 and 001 steps on gypsum relative to that between the <4¯41>
+ and <4¯41>
− on calcite; (iii) the step kinetic behavior follows the prediction of the transition state theory; (iv) the dissolution process on gypsum {010} faces is not characterized by the formation of deep etch pits, even at conditions far from equilibrium. The lack of deep pits most likely results from the observed faster dissolution of unstable steps in which the increase in pit depth is out-paced by that in the lateral dimension.
