metals and organic electrolytes, which are hazardous to the environment.Apparently, recycling spent LIBs is a far-sighted strategy for both resource recovery and environmental protection. Particularly, re-utilizing the cathode materials is the primary task for battery recycling since they make up approximately 35% of the cost and contain abundant valuable metals. [4] Conventional approaches to recycle cathodes are based on the hydrometallurgy [5] and pyrometallurgy [6] processes, which are either tedious or energy-consuming and produce massive liquid/gaseous pollutants. [7] Overall, both methods aim to extract metals through complete physical and chemical destruction of the cathode materials. [4,8] LIBs typically retire when losing more than 20% of the initial capacity, yet the bulk structure of the electrode materials remains largely intact. [8b,9] State-of-the-art recycling approaches focus on directly regenerating the cathodes by a non-destructive process to recover the losing capacity and restore the original structure. In a typical process, after harvesting the electrode materials from current collectors (e.g., by dissolution, [10] mechanical separation, [4] or heat treatment [11] ) and removing the inactive components (e.g., polymer binders and acetylene black), the spent cathode powders are treated with Li sources for relithiation. For example, wet chemistry [12] and solid state [4,13] approaches have been demonstrated to regenerate LiCoO 2 and Ni-poor NCM cathodes, in which the capacity loss is mainly ascribed to the Li loss. Nevertheless, precise control of the reaction condition and/or stoichiometry of reactants is generally required, making these two approaches less versatile.Different from the above liquid-or solid-state approaches, molten salts have recently emerged as promising reaction mediums to regenerate cathode materials due to their low melting point, favorable reaction medium, fast ion diffusivity, and so on. [8b,14] Binary eutectic molten salts such as LiOH+LiNO 3 , [8b] LiOH+Li 2 CO 3 , [14b] and LiNO 3 +sylvite [15] have been successfully applied to recover the spent NCM cathodes. Nevertheless, the capacity decay of NCM cathodes not only results from the loss of active Li but also comes from cation mixing and subsequent formation of undesirable rock salt/spinel phases. [12a,16] Although the above binary eutectic molten salts have been found to partially restore the crystallographic structure of NCM cathodes, full recovery of the lattice Li and elimination of the cation mixing remain unconquered challenges.Recycling spent lithium-ion batteries (LIBs) is an urgent task in view of the resource shortage and environmental concerns. Here, a facile ternary molten salt approach is presented for efficiently regenerating the LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode of spent LIBs. Such an approach involves the treatment of spent cathode powder in the ternary molten salt at a moderate temperature (400 °C) and subsequent annealing in oxygen. The Li loss and degraded phases in spent NCM that...

Carbonate-based electrolytes are incompatible with lithium (Li) metal anode because the generated solid electrolyte interphase (SEI) undergoes repeated breakage-repair, resulting in the accumulation of inactive Li including Li + compounds and electrically isolated dead Li 0 in the SEI. Therefore, exploiting a suitable strategy to construct a stable SEI while efficiently rejuvenating the inactive Li capacity is urgent and more thoughtful than just building a stereotyped SEI layer. Herein, an innovative strategy is proposed of high-concentration additive (HCA) of LiNO 3 inspired by (localized) high-concentration electrolyte and inactive Li restoration methodology via triiodide/iodide (I 3 − / I − ) redox couple to improve the compatibility of carbonate-based electrolytes. The HCA of LiNO 3 can maintain the cation-anion aggregates solvation structures in the carbonate-based bulk electrolyte and induce the in situ formation of superior-ionic-conductivity NO 3 − -derived SEI. Moreover, the reversible I 3 − / I − redox couple can further optimize the SEI and constantly rejuvenate the inactive Li including solvent/LiNO 3 -derived Li 2 O, a derivative has almost been acquiescent in LiNO 3 -additive electrolytes, and dead Li 0 into delithiated cathode. Consequently, epitaxy-like planar Li deposition, better reversibility, and higher capacity retention can be realized and are systematically verified by Li||Cu half cells, full cells with excess/limited Li (N/P ratio = 1.5) and anode-free lithium metal batteries.

Flocculation or restacking of different kinds of two-dimensional (2D) nanosheets into heterostructure nanocomposites is of interest for the development of high-performance electrode materials and catalysts. However, lacking a molecular-scale control on the layer sequence hinders enhancement of electrochemical activity. Herein, we conducted electrostatic layer-by-layer (LbL) assembly, employing oxide nanosheets (e.g., MnO2, RuO2.1, reduced graphene oxide (rGO)) and layered double hydroxide (LDH) nanosheets (e.g., NiFe-based LDH) to explore a series of mono- and bilayer films with various combinations of nanosheets and sequences toward oxygen evolution reaction (OER). The highest OER activity was attained in bilayer films of electrically conductive RuO2.1 nanosheets underlying catalytically active NiFe LDH nanosheets with mixed octahedral/tetrahedral coordination (NiFe LDHTd/Oh). At an overpotential of 300 mV, the RuO2.1/NiFe LDHTd/Oh film exhibited an electrochemical surface area (ECSA) normalized current density of 2.51 mA cm–2 ECSA and a mass activity of 3610 A g–1, which was, respectively, 2 and 5 times higher than that of flocculated RuO2.1/NiFe LDHTd/Oh aggregates with a random appearance of a surface layer. First-principles density functional theory calculations and COMSOL Multiphysics simulations further revealed that the improved catalytic performance was ascribed to a substantial electronic coupling effect in the heterostructure, in which electrons are transferred from exposed NiFe LDHTd/Oh nanosheets to underneath RuO2.1. The study provides insight into the rational control and manipulation of redox-active surface layers and conductive underlying layers in heteroassembled nanosheet films at molecular-scale precision for efficient electrocatalysis.

The regulation of lithium plating/stripping behavior is considered to be critical for next-generation safe and high-energy-density lithium metal batteries. Lithium deposition with maximum granular size and minimum microstructural tortuosity can significantly improve the lithium plating/stripping efficiency. Here, a self-assembled organosilane layer with nanopores is constructed on Cu current collector surface via a thiol-Cu reaction. In contrast to typical stacked-particle morphology with small grain size and high specific area in ether electrolyte, dough-like and lateral-growth lithium deposition can be plated on the modified Cu current collector due to the low surface energy of a lithiophilic SiOSi membrane. The planar and dense lithium deposition contributes to the stable implementation of up to near 500 cycles in full cells with high-loading LiFePO 4 cathode. Anticorrosion in rigorous Cl-ion containing solution can even be achieved due to the corrosive repellency of hydrophobic organosilane. A high Coulombic efficiency (97.12%) is remained after corroding for 300 min. Moreover, the irreversible capacity loss caused by galvanic corrosion, an ignored but crucial aspect, has been significantly suppressed due to the passivation of high-redox-potential Cu by organosilane coating.

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