For electrochemical devices, electrode performances are fundamentally linked to cations' distribution. While simulations and modelling have revealed that current-collector geometry induces uneven current and charge distributions, and partial aging, experimental evidence, intrinsic mechanisms and solutions have remained unexplored. Herein, the 3D distribution of inserted ions in transition-metal-oxide cathodes and its ubiquitous bottom effect (i.e., accumulation of trapped cations at the bottom area far from the pole ear and the induced bottom aging) induced by the size effect of current collectors is depicted. Uneven distribution of embedded ions, accumulation of trapped cations, and bottom aging are experimentally visualized. An "end reflection model" is proposed and verified by designing the current collector with an extra-wide bottom or with a tiny blank at the bottom. Notably, these two designs solved the bottom effect and doubled the electrodes' cyclic life. This finding represents a milestone in the current-collector-geometry study and open new insights for regulating ion distribution.

Dendrite growth and interfacial side reactions severely impair the stability of lithium negative electrodes. A deeper understanding of the structure-performance relationship between current collectors (CCs) and lithium deposition is crucial for addressing these challenges. In this study, a "random-to-aligned hierarchical porous carbon nanofibers" (r/a-HPCNFs) CC strategy was proposed to realize uniform bottom-up lithium-ion (Li+) deposition by analyzing the ion transport within aligned CNF channels. By constructing a top-random/bottom-aligned interface with different charge centers, the dielectric constant can be effectively adjusted, thereby promoting a polarization transformation of the intrinsic electric field and strengthening the driving force for Li+ migration toward the bottom of the CC. The symmetric cell assembled with Li-predeposited r/a-HPCNFs operates stably for over 6500 h at 5 mA cm-2. With less Li predeposition (∼3 mAh, N/P = 2), r/a-HPCNF-based full cells (LiFePO4, LiNi0.8Co0.1Mn0.1O2, and sulfur) deliver >80% capacity over 400, 260, and 200 cycles at 3, 2, and 0.5 C, respectively. These results highlight the key role of the random-aligned hierarchical architecture in intrinsic field regulation, enabling dendrite suppression and stable cycling.

Sodium-ion batteries (SIBs) have attracted increasing attention as a cost-effective and sustainable alternative to lithium-ion batteries (LIBs) for large-scale energy storage owing to the abundance of sodium and its electrochemical similarity to lithium. However, the development of suitable anode materials remains a key challenge. Alloy-type metals are considered promising anode candidates because they offer high theoretical capacities and multiple electron transfer reactions. In this study, we investigate a Bi-Sn alloy foil anode prepared by rolling to a thickness of 36 μm and punching into 4 mm-diameter discs. The foil is employed directly as the anode without the addition of conducting agents or binders, enabling the intrinsic electrochemical behavior of the active material to be evaluated. Electrochemical tests were performed in Swagelok-type cells using sodium metal as the counter electrode and two different electrolytes: 1 M NaPF6 in 1,2-dimethoxyethane (DME) and 1 M NaPF6 in ethylene carbonate/diethyl carbonate (EC/DEC). The Bi-Sn foil demonstrates excellent cycling performance in DME, retaining a capacity of 530 mAh g-1 (14.84 mAh cm-2) after 100 cycles at 0.1 Cequivalent to 91.5% of its theoretical capacity. In contrast, rapid capacity fading is observed in EC/DEC, underscoring the critical role of electrolyte chemistry in alloy-type anodes. Morphological analyses reveal that during cycling in DME, the Bi-Sn foil undergoes significant mechanical deformation, including cracking and pulverization into nanoscale domains. However, the fragmented particles spontaneously reconstruct into a porous structurea phenomenon referred to as self-healing. This porous structure maintains electrical connectivity to the current collector, enabling capacity retention. These findings demonstrate that pulverization is not inherently detrimental to alloy-type anodes; rather, it can be mitigated by using an ether-type electrolyte to facilitate self-healing. This strategy offers a new pathway for the development of alloy-type anodes composed of low-melting-temperature metals, such as Bi, Sn, and Pb.

Synergistic Engineering of Ni-Decorated Composite Current Collector and Hollow CoS Nanocages for Ultrahigh Areal Capacity Lithium-Ion Battery Anodes

Lithiophilic alloyed metal anodes (LAMAs) are emerging as a transformative platform for enabling practical Li metal batteries. By harnessing alloy chemistry, LAMAs combine favorable Li nucleation and growth behavior, robust interfacial chemistry, and mechanical integrity, thereby mitigating the long-standing challenges of manufacturability and cycling stability that have hindered large-scale deployment of Li metal anodes. Nevertheless, a unifying framework that quantitatively defines lithiophilicity, the central design parameter of LAMAs, remains underdeveloped. This review establishes a descriptor-based paradigm to systematically elucidate lithiophilicity, bridging empirical observations with thermodynamic, kinetic, and electronic-structure descriptors, while also addressing the temporal stability of lithiophilic interfaces. Building upon these insights, we critically analyze state-of-the-art strategies for designing and fabricating LAMAs, including alloy-embedded architectures, interfacial engineering approaches, modified current collector substrates, Li-free anode concepts, and all-solid-state configurations. We conclude by outlining key research opportunities and design principles that couple materials chemistry, interfacial science, and scalable manufacturing, aiming to accelerate the rational development of LAMAs for high-energy, industrially viable Li metal batteries.

Improving cycling stability and capacity retention is critical for the development of high-energy-density and low-cost anode-free sodium batteries (AFSBs). However, unstable Na plating/stripping and uncontrolled solid electrolyte interphase (SEI) evolution still hinder their practical application. In this work, we investigate the impact of grain-boundary density in the Cu substrate on the performance of AFSBs. The results reveal that higher grain-boundary density Cu exhibits a stronger affinity for sodium and can lower the sodium nucleation energy barriers, facilitating the formation of highly crystalline and densely packed sodium deposits. Moreover, the high surface energy at grain-boundaries strengthens anion adsorption, leading to an anion-rich interfacial solvation structure, which results in the formation of a thin, NaF-rich stable SEI film. Anode-free cells constructed with ultrahigh-grain-boundary density Cu (UGB-Cu) and Na3V2(PO4)3 (NVP) cathode achieved stable cycling for 800 cycles at 5C with an average coulombic efficiency (CE) of 99.97%. This work elucidates the dual role of grain-boundary in improving both substrate-sodium affinity and interfacial SEI chemistry, highlighting grain-boundary engineering of Cu foils as a practical and scalable pathway toward high-performance AFSBs.

Silicon (Si) has emerged as an ideal material for next-generation high-energy-density lithium (Li)-ion batteries owing to its ultrahigh theoretical capacity and low working voltage. However, severe volume changes during electrochemical reactions cause the pulverization of active Si and continuous degradation of interfacial structures amongst internal components, resulting in rapid capacity fading. To address these challenges, designing functional nanoscale interfaces in Si anodes is critical for enhancing the Li-ion storage stability. This review systematically elaborates the recent advances in the interface engineering of Si-based anodes from a multiscale interface perspective, mainly focusing on the interfaces generated by the functional coatings, liquid/solid electrolytes, polymer binders, and modified current collectors. The principles of interface design and dynamic structural evolution as well as the regulation of Li-ion-transfer or charge-transfer kinetics at various interfaces are comprehensively analyzed. Feasible strategies to enhance electrochemical performance through the interface design are also highlighted. This review concludes by summarizing the current challenges in interface engineering and outlining future research directions. It provides fundamental theoretical guidance and practical insights from the perspective of interface design for developing high performance Si anodes.

Enhanced hydrophobicity of the current collector modifier for Zn anode endows improved longevity.

Anode-free lithium metal batteries (AFLMBs) leverage a bare current collector (CC) as a lithium deposition substrate to achieve high energy density and reduced manufacturing costs. However, severe nucleation overpotential and dendritic growth, rooted in the Cu–Li lattice mismatch, hinder their practical deployment. Herein, a dense zeolitic imidazolate framework-67 (ZIF-67) polycrystalline membrane is epitaxially grown in situ on Cu CC via liquid-phase epitaxy and subsequently converted into a CoN-doped carbon skeleton membrane (67 MC@Cu) through thermal treatment. The embedded CoN nanoparticles, evolved from {CoN4} units in ZIF-67, serve as highly lithiophilic sites that dynamically regulate lithium nucleation and suppress dendrite formation. The binder-free fabrication maximizes the exposure of active sites while preserving the functionality of the MOF-derived architecture. As a result, full cells assembled with 67 MC@Cu exhibit markedly enhanced cycling stability, retaining 92.0% capacity after 280 cycles—far surpassing 20.2% retention of commercial carbon-coated Cu (C@Cu). This work provides an effective interfacial engineering strategy to advance the practical implementation of AFLMBs.

In the recycling process of spent lithium-ion batteries (SLIBs), rapid and effective separation of the cathode material and current collector aluminium (Al) foil is a significant and difficult step. However, traditional separation methods have some drawbacks, including high energy consumption and cost and toxicity. In this study, we selected oxalic acid (OA), a green and low-cost simple organic acid, as the separating agent. Within 6 minutes of oxalic acid treatment, more than 99% of the nickel-manganese-cobalt (NCM) cathode materials are separated from the current collector Al foil. The mechanism analysis shows that the reaction of oxalic acid with the surface of the Al foil destroys the connection between the Al foil and the adhesive, while the oxalate protective layer formed on the surface of the NCM cathode material prevents further corrosion of the NCM cathode material, maintaining a good structural integrity. This green and efficient separation method provides an economical and viable solution for SLIB regeneration or upcycling.

The thiourea-crosslinked poly(acrylic acid- co -acrylamide) binder interacts strongly with Si, enhances interfacial adhesion with the Cu current collector, and alleviates Si's volume expansion to form a stable SEI layer.

Water-assisted delamination of cathode active materials from aluminum foil during electrical pulsed discharge for direct lithium-ion battery recycling.

A novel "all in one" anti-corrosion Cu current collector with an inner-outer synergistic electrolyte solvents shielding effect in long lifespan lithium-ion batteries

From the perspective of cross-scale collaborative design, this review systematically summarizes the multi-dimensional modification strategies for copper foil current collectors in anode-free lithium metal batteries (AFLMBs).

Aluminum foil anodes offer a lightweight and scalable design by integrating the active material and current collector, but their practical deployment has been limited by rapid mechanical degradation from ∼100% volume expansion during lithiation. Previous strategies to stabilize Al foils have primarily relied on grain refinement, alloying, or prelithiation, which improve either mechanical robustness or electrochemical reversibility, but rarely both. Here, we introduce a fundamentally different microstructural strategy in Al-1 wt% Si foils, where the large atomic size mismatch between Al and Si, combined with the presence of dispersed Si particles, generates pronounced lattice distortions and heterogeneous stored energy that drive the formation of partially recrystallized, laminated grain-boundary architectures. This architecture coordinates grain boundaries: vertical LAGBs/MAGBs guide Li, and periodic horizontal HAGBs drive β-LiAl nucleation and directional growth, forming an alternating α-β lamellar structure during cycling. This laminated α-β network, conceptually akin to a "stack dam" that regulates ion flow and dissipates strain energy, orchestrates phase evolution in a manner distinct from all previously reported Al foil anodes. When coupled with controlled electrochemical prelithiation, this tailored microstructural design fully realizes its potential, simultaneously delivering high energy density and long cycle life.

Failure mechanisms and current collector design for sodium metal anodes: from thermodynamic-kinetic coupling to structural-functional optimization

The etching and graphene oxide co-modified Al current collector for stable and ultrafast lithium-ion batteries

Controlling edge profiles in slot-die coating is critical for high-quality battery electrode manufacturing, yet the underlying mechanisms remain inadequately understood, particularly for thick electrodes. The slot-coating process deposits a slurry containing active materials onto a current collector, which constitutes a fundamental step in battery electrode production. While widely used in industry, controlling electrode edge quality remains a challenge, as elevated edges can cause wrinkles and reduce production yield. This study investigates edge profile formation mechanisms and control strategies for thick-film anode electrode slot-coating processes through comprehensive experimental and theoretical analysis. More than 500 experiments across various process conditions were analyzed using statistical and machine learning methods, revealing key process variables and underlying physical mechanisms through a visco-capillary model. The results demonstrate that edge profiles depend primarily on pressure distribution within the coating bead and downstream leveling flows. Optimal edge quality is achieved when the gap between the slot-die and substrate equals the wet coating thickness, providing practical guidelines for slot-die configuration and process conditions in battery electrode manufacturing.

The selectivity of metal extraction from multi-element waste using the hydrometallurgical process is an urgent task. To extract lithium selectively from a waste, the leaching reagent should ideally react only with lithium, while FePO4 and graphite should remain in a solid state. The use of H2O2 allows one to control the degree of oxidation of the solution by oxidizing Fe2+ to Fe3+, followed by light precipitation, thus effectively suppressing iron leaching. The paper presents a method for processing the “black mass”, after mechanical separation from the current collector, using a solution of acetic acid with addition of hydrogen peroxide. In contrast to the above studies, where the object of processing was exclusively the cathode mass of a lithium iron-phosphate battery, our team used "black mass" as a raw material, which is an intermediate product in the processing of LIB, and raw materials in the processes of hydrometallurgical leaching of metals. The source of the “black mass” in our research was a lithium iron-phosphate battery HWE200A, LF54174200 3.2 V 200Ah (China). The phase composition, morphology, and particle size of the resulting compounds were analyzed by X-ray diffraction and scanning electron microscopy. Quantitative analysis of the concentration of lithium and iron, aluminum, and copper impurities in solutions was performed by Optical Emission Spectroscopy from inductively coupled plasma (ICP-OES) with an ICP spectrometer iCAP 6500 DUO (Thermo Electron Corp.) Using XRD analysis, the phase composition and crystallographic parameters of the obtained compounds and available impurities were determined. According to the results of research by the proposed method of processing the “black mass” with selective extraction of lithium compounds from spent LFP batteries, the degree of lithium extraction from the “black mass” is achieved by about 98 % with two times treating in the mixture of 0.8 M Hac + 5 wt. % H2O2. The presence of lithium in the form of SEI layer on the surface of the anode material was noted, which accounted for about 14 % of the total amount of lithium in the “black mass”. It is proved that the addition of hydrogen peroxide to a solution of acetic acid promotes the oxidation of Fe2+ to Fe3+in the crystal structure of lithium iron phosphate, which leads to a decrease in the solubility of iron. It was determined that the total amount of impurities (Fe, Al and Cu) in solutions of lithium salts did not exceed 1 %, which was precipitated in the form of corresponding hydroxides. The purity of the obtained Li2CO3, FePO4 compounds and graphite is more than 99.9 wt. %, which meets the battery purity standard and allows them to be used for LiFePO4/C synthesis and reuse in LFP batteries.

ABSTRACT Anode‐free lithium‐metal batteries (AFLMBs), wherein Li is plated onto a bare Cu current collector during the initial charge, feature a simplified architecture and high energy density. However, in AFLMBs employing high‐mass‐loading cathodes, the intrinsically poor lithiophilicity of bare Cu induces uncontrolled dendrite growth, irreversible lithium loss, and an unstable solid electrolyte interphase (SEI), resulting in rapid capacity decay and a low Coulombic efficiency (CE). Herein, an ultrathin, cross‐linked polyethylenimine (PEI) coating is proposed as a simple yet effective interfacial engineering strategy to stabilize the anode–electrolyte interface through dual mechanisms. Abundant amine groups coordinate strongly with Li⁺, promoting homogeneous nucleation and vertical deposition while restricting lateral diffusion. The flexible polymer matrix acts as a robust barrier against parasitic reactions and corrosion. Consequently, Cu||Li half‐cells with PEI‐coated Cu sustain 350 cycles at 0.5 mA cm −2 and 0.5 mAh cm −2 , delivering an average CE of 95.29%. Full cells with high‐loading LiFePO 4 cathodes (26.52 mg cm −2 ) retain 57.65% of their initial capacity (3.26 to 1.87 mAh cm −2 ) after 100 cycles. These findings highlight nanoscale polymer coatings as a promising strategy for constructing stable artificial SEI layers in AFLMBs, yielding high‐energy and durable Li‐ion batteries.