Worldwide trends in mobile electrification, largely driven by the popularity of electric vehicles (EVs) will skyrocket demands for lithium‐ion battery (LIB) production. As such, up to four million metric tons of LIB waste from EV battery packs could be generated from 2015 to 2040. LIB recycling directly addresses concerns over long‐term economic strains due to the uneven geographic distribution of resources (especially for Co and Li) and environmental issues associated with both landfilling and raw material extraction. However, LIB recycling infrastructure has not been widely adopted, and current facilities are mostly focused on Co recovery for economic gains. This incentive will decline due to shifting market trends from LiCoO2 toward cobalt‐deficient and mixed‐metal cathodes (eg, LiNi1/3Mn1/3Co1/3O2). Thus, this review covers recycling strategies to recover metals in mixed‐metal LIB cathodes and comingled scrap comprising different chemistries. As such, hydrometallurgical processes can meet this criterion, while also requiring a low environmental footprint and energy consumption compared to pyrometallurgy. Following pretreatment to separate the cathode from other battery components, the active material is dissolved entirely by reductive acid leaching. A complex leachate is generated, comprising cathode metals (Li+, Ni2+, Mn2+, and Co2+) and impurities (Fe3+, Al3+, and Cu2+) from the current collectors and battery casing, which can be separated and purified using a series of selective precipitation and/or solvent extraction steps. Alternatively, the cathode can be resynthesized directly from the leachate.

A novel sodium hybrid capacitor (NHC) is constructed with an intercalationtype sodium material [carbon coated-Na 3 V 2 (PO 4 ) 3 , C-NVP] and high surface area-activated carbon derived from an eco-friendly resource cinnamon sticks (CDCs) in an organic electrolyte. This novel NHC possesses a combination of high energy and high power density, along with remarkable electrochemical stability. In addition, the C-NVP/CDC system outperforms present, well-established lithium hybrid capacitor systems in all areas, and can thus be added to the list of candidates for future electric vehicles. A careful optimization of mass balance between electrode materials enables the C-NVP/CDC cell to exhibit extraordinary capacitance performance. This novel NHC produces an energy density of 118 Wh kg −1 at a specifi c power of 95 W kg −1 and retains an energy density of 60 Wh kg −1 with high specifi c power of 850 W kg −1 . Furthermore, a discharge capacitance of 53 F g −1 is obtained from the C-NVP/CDC cell at a 1 mA cm −2 current density, along with 95% capacitance retention, even after 10 000 cycles. The sluggish kinetics of the Na ion battery system is successfully overcome by developing a stable, high-performing NHC system.

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In this study, we report a novel route via microwave irradiation to synthesize a bio-inspired hierarchical graphene--nanotube--iron three-dimensional nanostructure as an anode material in lithium-ion batteries. The nanostructure comprises vertically aligned carbon nanotubes grown directly on graphene sheets along with shorter branches of carbon nanotubes stemming out from both the graphene sheets and the vertically aligned carbon nanotubes. This bio-inspired hierarchical structure provides a three-dimensional conductive network for efficient charge-transfer and prevents the agglomeration and restacking of the graphene sheets enabling Li-ions to have greater access to the electrode material. In addition, functional iron-oxide nanoparticles decorated within the three-dimensional hierarchical structure provides outstanding lithium storage characteristics, resulting in very high specific capacities. The anode material delivers a reversible capacity of ~1024 mA · h · g(-1) even after prolonged cycling along with a Coulombic efficiency in excess of 99%, which reflects the ability of the hierarchical network to prevent agglomeration of the iron-oxide nanoparticles.

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