P2 layered oxides have attracted more and more attention as cathode materials of high‐power sodium‐ion batteries (SIBs). During the charging process, the release of sodium ions leads to layer slip, which leads to the transformation of P2 phase into O2 phase, resulting in a sharp decline in capacity. However, many cathode materials do not undergo P2‐O2 transition during charging and discharging, but form a “Z” phase. It is proved that the iron‐containing compound Na0.67Ni0.1Mn0.8Fe0.1O2 formed the “Z” phase of the symbiotic structure of the P phase and O phase during high‐voltage charging through ex‐XRD and HAADF‐STEM. During the charging process, the cathode material undergoes a structural change of P2‐OP4‐O2. With the increase of charging voltage, the O‐type superposition mode increases to form an ordered OP4 phase, and the P2‐type superposition mode disappears after further charging to form a pure O2 phase. 57Fe‐Mössbauer spectroscopy revealed that no migration of Fe ions is detected. The O–Ni–O–Mn–Fe–O bond formed in the transition metal MO6 (M = Ni, Mn, Fe) octahedron can inhibit the elongation of the Mn–O bond and improve the electrochemical activity so that P2‐Na0.67Ni0.1Mn0.8Fe0.1O2 has an excellent capacity of 172.4 mAh g−1 and a coulombic efficiency close to 99% at 0.1C.

In the study, the waste polyvinylidene fluoride (PVDF) membranes were recovered and the obtained resin powders by a solvent recovery method were employed for the fabrication of a novel PVDF-based tribological composite.Herein, a new strategy was developed for applying the waste PVDF membranes to fabricate a self-lubricant composite, where the recycled PVDF powders acted as the polymer matrix and microcapsules with the configuration of polysulfone (PSF) capsuling lubricant oil (PAO) served as the filler. The morphologies, crystal phases, chemical components and groups as well as thermal stabilities of fabricated PAO@PSF/PVDF composites were characterized, and the self-lubricating and wear properties of fabricated composites were tested under the dry sliding condition using a ball-on-disc configuration. Experimental results suggest that the PAO@PSF/PVDF composite with an addition of 20 wt% PAO@PSF microcapsules exhibits the best tribological properties, in view of the lowest friction coefficient (0.077) and the smallest wear rate (2.34 Â 10 À15 m 3 /Nm). The incorporation of PAO@PSF microcapsules greatly reduces the friction coefficient of PVDF polymer. The tribological properties of fabricated PAO@PSF/PVDF composite will be expectable to that of the PVDF polymer with the dripping presence of lubricating oil.

In the study, the waste polyvinylidene fluoride (PVDF) membranes were recovered and the micropowders of this polymer were obtained by solvent recovery method. Moreover, the new direction for applying waste PVDF membranes to the field of tribology were developed. Thus, a novel PVDF-based tribological composite (PAO@PSF/PVDF) was fabricated with recycled PVDF micropowders acted as the matrix polymer and PAO@PSF microcapsules with the configuration of polysulfone (PSF) capsuling lubricant oil (PAO) served as the filler. The self-lubricating and wear properties of PAO@PSF/PVDF composite were tested under dry sliding condition using a ball-on-disc configuration. In particular, this kind of composite with the inclusion of 20 wt% PAO@PSF microcapsules exhibited the best tribological properties, i.e., the lowest friction coefficient (0.077) and the smallest wear rate (2.34×10-15 m3/Nm). The filling of PAO@PSF microcapsules greatly improved the antifriction and wear resistance of PVDF, guaranteeing the self-lubricating feature of this polymer. The tribological properties of PAO@PSF/PVDF composite can reach close to those under the condition of dripping lubricating oil, and the prepared PAO@PSF/PVDF self-lubricating composite can be applied to a large range of friction conditions. Furthermore, without any doubt, it will facilitate the reutilization of waste polymers.

Carbon fiber composite continuous sucker rod string is more and more widely used in deep and ultradeep wells because of its light weight, high strength, and corrosion resistance. In order to analyze the dynamic problems of carbon fiber sucker rod string in actual oil wells, a transverse vibration simulation model of carbon fiber and steel (carbon-steel) hybrid rod string excited by buckling deformation in vertical wells is established with the compression buckling deformation of weighting rod. Considering the influence of wellbore trajectory and the constraint of tubing, the transverse vibration simulation model of carbon-steel hybrid rod string in directional wells under borehole trajectory excitation is also established in this paper. The finite difference method is used to discretize the well depth node, the numerical integration method (Newmark-β) is used to discretize the reciprocating periodic time node, and simulation methods for the contact and collision dynamics of rod-tubing in vertical wells and directional wells are formed. Through programming calculation, the distribution laws of transverse displacement, contact force, collision force, and bending stress of carbon-steel hybrid sucker rod string in vertical wells and directional wells along well depth are obtained. The simulation results in vertical wells show that the strong collision between the rod and tubing occurs near the bottom steel rod, while the upper load is small and the rod-tubing collision load of the upper rod of the carbon-steel hybrid rod string is much lower than that of the traditional steel rod string at the same position. Furthermore, the bending stress of the upper carbon fiber is also much less than that of the bottom steel rod. The simulation results in directional wells show that the collision phenomenon of the deflecting section and the bottom weighting rod compression section are the strongest and the rod-tubing contact pressure is also the largest. Second, the impact force of the upper carbon fiber rod is also much lower than that of the steel rod. Again, the maximum bending stress of the whole well occurs near the deviation section where the deviation angle changes suddenly. The transverse vibration mechanical model in directional wells in this paper lays a theoretical foundation and provides theoretical support for the optimal design of fracture and splitting prevention measures of carbon fiber sucker rod.