High specific capacitance, high energy density, and high power density have always been important directions for the improvement of electrode materials for supercapacitors. In this paper, Co3O4 nanowire arrays with various Mn doping concentrations (Mn:Co molar ratio = 1:11, 1:5, 1:2) directly grown on nickel foam (NF) were prepared by a simple hydrothermal method and annealing process. The influence of Mn doping on the morphology, structure, and electrochemical behaviors of Co3O4 was investigated. The results show that partial substitution of Co ions with Mn ions in the spinel structure does not change the nanowire morphology of pure Co3O4 but increases the lattice parameter and decreases the crystallinity of cobalt oxide. Electrochemical measurements showed that Mn doping in Co3O4 could effectively enhance the redox activity, especially Co3O4 with a Mn doping ratio of 1:5, which exhibits the most excellent electrochemical performance, with the maximum specific capacitance of 1210.8 F·g–1 at 1 A·g–1 and a rate capability of 33.0% at 30 A·g–1. The asymmetric supercapacitor (ASC) device assembled with the optimal Mn–Co3O4 (1:5) and activated carbon (AC) electrode performs a high specific capacitance of 105.8 F·g–1, a high energy density of 33 Wh·kg–1 at a power density of 748.1 W·kg–1, and a capacitance retention of 60.2% after 5000 cycles. This work indicates that an appropriate Mn doping concentration in the Co3O4 lattice structure will have great potential in rationalizing the design of spinel oxides for efficient electrochemical performance.

Hollow nanostructures with enlarged surface areas are highly attractive electrode materials for supercapacitors. In this work, the size-dependent synthesis of hollow Co ₃ O ₄ nanocubes via a facile ionic exchange reaction between Co-Fe Prussian blue analogues (PBAs) and alkali solution is reported. By adjusting the concentration of sodium citrate to control the reaction kinetics during nucleation and growth, four different sizes of Co-Fe PBAs were synthesized. It was also found that a Co-Fe PBA of about 140 nm can be easily converted into a well-defined internal hollow structure, while Co-Fe PBAs with smaller or larger sizes are challenged in generating a hollow structure. Benefitting from the inner voids and thin shell architecture, the derived hollow Co ₃ O ₄ nanocubes exhibit a high specific capacity of 296.6C cm ⁻² at 2 mA cm ⁻² , and a rate capability of 64.5% when the current density is increased to 60 mA cm ⁻² . Furthermore, a hybrid supercapacitor (HSC) was fabricated with hollow Co ₃ O ₄ nanocubes as the cathode and activated carbon as the anode, respectively. The HSC provided a maximum energy density of 14.1 Wh kg ⁻¹ at 464.7 W kg ⁻¹ . Moreover, it retained the excellent cycling stability of 85.7% of the original capacity over 5000 continuous charging and discharging processes.

Metallic bismuth is a promising anode electrode material for sodium ion batteries due to its high theoretical specific capacity. However, the formation of Na₃Bi during the reaction process brings about significant volume changes and structural collapse of the electrode, resulting in the destruction of structures and a decrease in the cycling stability of sodium ion batteries. In this study, bismuth nanoparticles embedded in carbon fibers (Bi/CF) through a facile approach of electrospinning and calcination. Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed in the carbon fibers, as confirmed by relevant morphological and structural features. The carbon fiber substrate can serve as a flexible and free-standing electrode, forming a conductive network to accelerate electron transport and ion diffusion. In light of this, Bi/CF anodes exhibit a high reversible capacity (376.6 mA h g⁻¹ at 0.1 A g⁻¹) and long-term cycle stability (only attenuates 0.12% in each cycle after 2000 times). This work provides a convenient and effective strategy for the synthesis of flexible and free-standing anodes for high-performance sodium ion batteries.

Traditional hydro-pneumatic spring suspensions are limited to a single vertical degree of freedom, which cannot accommodate the significant technological changes introduced by the new in-wheel motor drive mode. Integrating the motor into the vehicle’s hub creates a direct motor drive mode, replacing the traditional engine–transmission–drive shaft configuration. Together with the dual in-wheel motor wheelset structure, this setup can achieve both drive and differential steering functions. In this study, we designed a six-arm suspension wheel-leg device based on hydro-pneumatic springs, and its structural composition and functional characteristics are presented herein. The external single-chamber hydro-pneumatic springs used in the six-arm structure suspension were analyzed and mathematically modeled, and the nonlinear characteristic curves of the springs were derived. To overcome the instability caused by inconsistent extension lengths of the hydro-pneumatic springs during horizontal steering, the spring correction force, horizontal rotational torque, consistency, and stiffness of the six-degree-of-freedom hydro-pneumatic spring wheel-leg device were analyzed. Finally, with the auxiliary action of tension springs, the rotational torque of the hydro-pneumatic springs and the tension resistance torque of the tension spring counterbalanced each other, keeping the resultant torque on the wheelset at approximately 0 N∙m. The results suggest that the proposed device has excellent self-stabilizing performance and meets the requirements for straight-line driving and differential steering applications. This device provides a new approach for the drive mode and suspension design of the dual in-wheel motor wheelset.

The step-stress accelerated degradation test (ADT) provides a feasible method for assessing the storage life of high-reliability, long-life products. However, this method results in a slower rate of performance degradation at the beginning of the test, significantly reducing the test efficiency. Therefore, this article proposes an assessment method for the step-down stress ADT that considers random effects and detection errors (SDRD). Firstly, a new Inverse Gaussian (IG) model is proposed. The model introduces the Gamma distribution to characterize the randomness of the product degradation path and uses the normal distribution to describe the detection errors of performance parameters. In addition, to solve the problem that the likelihood function of the IG model is complex and has no explicit expression, the Monte Carlo (MC) method is used to estimate unknown parameters of the model. This approach enhances computational accuracy and efficiency. Finally, to verify the effectiveness of the SDRD method, it is applied to the step-down stress ADT data from a specific missile tank to assess its storage life. Comparing the life assessment results of different methods, the conclusion shows that the SDRD method is more effective for assessing the storage life of high-reliability, long-life products.