To lower the costs and environmental impact of hydrometallurgy leaching while improving safety, electrochemical leaching of spent lithium-ion battery (LIB) cathodes has gained attention. This study proposes the use of an active cathode and anode in the electrochemical leaching process and introduces a low-voltage electrochemical synergistic leaching process for spent LiNi_0.5Co_0.2Mn_0.3O₂(NCM) and LiFePO₄(LFP) cathodes in sulfuric acid solution. Thermodynamic analysis demonstrates that various elements can be leached without additional redox agents through electrochemical methods. Under optimal conditions (1 V, 1 M acid, 60 °C, and 120 min), leaching efficiencies of Li, Ni, Co, Mn, and Fe are above 98%. Fe leaching was identified as diffusion-controlled, while the leaching of other elements was primarily governed by chemical reactions. The ion diffusion inside the electrode during the electrochemical leaching process was analyzed through finite element simulations. Higher voltage restricted transition metal leaching due to diffusion-limited current densities and side reactions involving gas evolution. Fe²⁺/Fe³⁺ acting as an electron mediator between the cathode and anode achieved a synergistic effect and suppressed gas evolution reactions. This method solves the challenges for gas evolution in electrochemical leaching of spent LIBs using Fe ion cycling instead of conventional reductants, reduces energy consumption and provides a greener approach for LIB recovery.

Ti-6Al-4V alloy (TC4) with different concentrations of graphene nanoplatelets (GNPs) were fabricated by ball milling and spark plasma sintering (SPS). Microstructure characteristics of the composites were characterized by X-Ray Diffraction (XRD), Scanning electron microscopy (SEM), and Raman. Microhardness and the compressive mechanical properties were also investigated. Experimental results showed that in the process of SPS, most of the GNPs were still retained at high pressure and temperature, and a new phase of TiC was presented due to the in-situ reaction between TiC and GNPs. Also, the strength of the composites was depended on the concentration of GNPs in TC4 matrix. Consequently, the composite with 0.8 wt. % GNPs was increased 18% in microhardness. The maximum yield strength and ductility of the composite were increased by 22.2% and 43.2%, respectively. The strengthening mechanism of the composites was further discussed, and the Orowan strengthening mechanism was the main strengthening factor.

Ti₂AlNb alloys with few-layer graphene were fabricated by spark plasma sintering (SPS) to enhance the tribological properties (TP) of the composite materials. Microstructure characteristics of the original few-layer graphene (FLG), Ti₂AlNb powders, and the sintered composites were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The experimental results indicated that FLGs were homogeneously distributed in the composites. Tribological results indicated that the coefficient of friction (COF) of the composites was reduced as the content of FLG increased. Compared with the pure Ti₂AlNb alloy, the average COF of the composite with 1.0 wt.% FLG was decreased by 9.4% and the wear rate was decreased by 36%. Meanwhile, the microstructures of the worn surface showed that TiC particles and friction layers formed by residual FLGs were present on the surface of the composites after tribological test. It is proposed that Ti₂AlNb alloys with FLGs presented the enhanced wear resistance.