Electrocatalytic CO₂ reduction reaction (CO₂RR) is widely recognized as a promising strategy for converting greenhouse gas CO₂ into value-added chemicals and fuels, thereby contributing to carbon neutrality and renewable energy storage. However, CO₂RR involves complex multi-electron and multi-proton transfer processes, leading to diverse reaction pathways and product distributions. The catalytic performance is fundamentally governed by the adsorption and transformation of key intermediates (e.g., *COOH, *CO,*OCHO), which are highly sensitive to the local structure and electronic properties of active sites.

Supported metal catalysts emerge as an important class of CO₂RR catalysts due to their structural tunability and versatile catalytic behavior. Recent studies reveal that catalytic reactions predominantly occur at localized active centers rather than the entire catalyst surface. These active centers can be described as "functional units" with specific geometric and electronic characteristics, including single-atom sites, dual-atom sites, and nanoparticle sites. The spatial arrangement and interaction of these functional units form a "structural ordering" feature, which plays a decisive role in determining adsorption behavior, reaction pathways, and energy barriers. Understanding the structure-performance relationship from the perspective of functional unit ordering is thus essential for rational catalyst design.

This review summarizes recent progress on supported metal catalysts for CO₂RR from the viewpoint of functional unit structural ordering. First, the structural characteristics and catalytic mechanisms of typical functional units are discussed. Single-atom sites exhibit highly tunable electronic structures through coordination engineering, enabling a precise control over intermediate adsorption and offering opportunities to break conventional scaling relationships. Dual-atom sites introduce metal-metal electronic coupling and spatial synergy, which can optimize intermediate binding and promote complex reactions such as C-C coupling. Nanoparticle sites, characterized by continuous surfaces and multiple active centers, provide cooperative platforms where size effects, facet engineering, and metal-support interactions collectively affect catalytic performance. In these systems, the synergy between geometric configuration and electronic structure governs the activity, selectivity, and stability of CO₂RR.

Despite significant progress, a rational catalyst design remains challenging due to the vast configurational space and complex coupling between geometric and electronic effects. To address these challenges, machine learning (ML) is increasingly integrated into catalyst research. This review further highlights recent advances on ML-assisted design of functional units. Descriptor-based ML models establish quantitative relationships between structural features and catalytic performance, enabling efficient high-throughput screening of candidate catalysts. In addition, machine learning potentials (MLPs) also provide near density functional theory (DFT) accuracy with a significantly reduced computational cost. These methods enable large-scale structure exploration and dynamic simulations, offering insights into the evolution of active sites under realistic reaction conditions.

Finally, some challenges and future perspectives are discussed. Key issues include the lack of realistic dynamic models for active sites under operating conditions, the absence of unified multiscale frameworks linking atomic-scale properties to macroscopic performance, and the limited transferability of ML models due to descriptor and data constraints. Future research should focus on developing multiscale theoretical-experimental approaches, constructing physically interpretable descriptor systems, and integrating ML with high-quality databases and advanced characterization techniques. Such efforts are expected to enable a precise regulation of functional unit ordering and accelerate the transition from empirical optimization to predictive catalyst design.

Overall, the paradigm shift from "global structure optimization" to "precise control of functional unit ordering," combined with the integration of theory, machine learning, and advanced characterization, provides a promising pathway for the rational design of high-performance CO₂RR catalysts and the advancement of sustainable energy technologies.

The strategy of units ordering offers a new approach to overcoming the conventional trade-off between strength and plasticity in metallic materials. Nano-twinned copper (Cu) serves as an ideal model system for constructing ordered materials and unraveling the mechanisms underlying their enhanced mechanical properties due to its stable microstructure, precisely controllable microstructures, and well-understood dislocation mechanisms during plastic deformation. Based on the existing research on ordered nanotwinned Cu, this review systematically elucidates the effects of two typical ordering configurations (i.e., layered and gradient structures) on the mechanical properties, deformation behavior, and plastic deformation mechanisms. The aim is to reveal the intrinsic mechanisms by which the units ordering regulates the mechanical performance. Also, this review outlines the existing opportunities and challenges in this field to provide a reference for the development of high-performance metallic materials.

The strength and ductility as critical mechanical properties of metallic materials often exhibit a trade-off relationship. This phenomenon becomes a formidable bottleneck in conventional strengthening strategies that rely on solid solution, second-phase particles, grain refinement, and dislocations, with homogeneous or randomly microstructure. Fortunately, the ordering architecture of units offers a promising pathway to overcome this limitation, attracting recent attention. Typical ordered configurations include laminated and gradient structures, where the units consist of common microstructural features such as grains, twins, dislocations, and phases. Numerous studies demonstrate that the laminated and gradient architectures both can achieve a superior combination of strength and ductility, thereby mitigating the strength-ductility trade-off. The underlying mechanism is often qualitatively attributed to heterogeneous plastic deformation across different sections and the associated formation of geometrically necessary dislocations (GNDs), promoting extra strengthening and work hardening through long-range back stress. However, a quantitative understanding of how the specific ordering strategy affects the mechanical properties, and the strengthening mechanisms remains elusive. In this review, we systematically compare the mechanical properties and deformation mechanisms of laminated nano-twinned (LNT) Cu and gradient nano-twinned (GNT) Cu to address this important issue.

LNT and GNT Cu both exhibit extra strengthening and enhanced work hardening, as demonstrated by their strengths, and the work-hardening rates at small strains exceed the corresponding rule-of-mixture predictions. These effects are further amplified via increasing the structural gradient, defined as the hardness variation per unit depth. GNT Cu demonstrates superior enhancements in both strength and work hardening, compared to LNT Cu, highlighting the advantage of gradient ordering over laminated ordering. Compared to conventional homogeneous or randomly heterogeneous structures, LNT and GNT architectures both achieve an enhanced strength-ductility synergy. In particular, the GNT structure maintains a considerable ductility with only a minor reduction as the strength increases. GNT Cu with the maximum structural gradient exhibits strength exceeding that of its strongest constituent unit, while retaining appreciable ductility. These results demonstrate that gradient ordering can induce stronger strengthening and superior strength-ductility synergy, compared to laminated ordering.

LNT and GNT Cu both display a characteristic gradient plastic deformation across their sections, which promotes the accumulation of GNDs and thereby enhances strengthening and work hardening. In LNT Cu, plastic strain gradients and GNDs concentrate mainly at interfaces. In contrast, in GNT Cu, they are distributed more homogeneously throughout all thesections, forming bundles of concentrated dislocations within grain interiors. Consequently, the dislocation density in GNT Cu is nearly an order of magnitude higher than that in its homogeneous counterparts. Moreover, these dispersed GNDs interact more frequently with other dislocations, generating higher back stresses, compared to the interface-accumulated GNDs in LNT Cu. This GND-distribution-dominated strengthening mechanism is responsible for the superior strength-ductility synergy achieved through gradient ordering.

Li-ion battery is used in fields such as transportation, electronics, and grid-scale energy storage. However, some challenges remain in achieving higher energy density, enhanced safety, and lower cost for large-scale energy storage and electric vehicles applications. To address these issues, a comprehensive understanding on the structural evolution of electrode materials, the stability of the electrolyte, and the reaction mechanism at the electrode interface is required. Nevertheless, conventional characterizations are limited by brightness, spectral range, and spatial/temporal coherence of light source, thus being unable to resolve the reaction details and structure/micro-structure evolution during the charge/discharge. Synchrotron radiation is an electromagnetic radiation emitted tangentially by relativistic electrons deflecting in a magnetic field. Compared with conventional light sources, synchrotron radiation shows high brightness, highly collimated, wide spectral range, etc.. These superior characters make it a powerful tool for battery study. For instance, synchrotron radiation XRD offers a superior lattice resolution as small as 0.10% or even 0.01%, thereby showing a subtle lattice collapse after lithium de-intercalation. Moreover, synchrotron radiation extended X-ray absorption fine structure (EXAFS) can determine the chemical valence of a selected element and the coordination structure of the element. Furthermore, the EXAFS can be combined with microscopy/imaging to directly provide the spatial distribution of oxidation state and coordination environments of a selected element within electrode materials. This review represents some challenges of Li-ion battery that can be strategically addressed by synchrotron radiation characterizations. In addition, the related progress in this field through a few case studies are described.

Synchrotron Radiation X-ray Diffraction: Compared with conventional X-ray diffraction, synchrotron radiation XRD can accurately capture the subtle lattice changes, phase transformation, and structure/micro-structure evolution during the charge/discharge. For instance, in polycrystalline and single-crystalline NCM523 materials, synchrotron radiation XRD reveals the~0.2% sudden changes in lattice constants and clarifies the significant differences in the phase transformation paths between different crystalline states. Synchrotron radiation XRD can also track the reversible structure evolution from trigonal to cubic to tetragonal during the charge/discharge of the sodium-ion battery cathode material Na_2-xFe[Fe(CN)₆ · nH₂O, and confirm its excellent structural reversibility and cycling stability.

Synchrotron Radiation Extended X-ray Absorption Fine Structure: The EXAFS can provide the coordination information around a specific element, which is crucial for in-depth research on the structure changes of electrode materials. For instance, regarding the Jahn-Teller distortion of Ni in high-nickel layered cathode materials LiNi_0.9Mn_0.05Co_0.05O₂, the dynamic evolutions of Ni-O coordination environment during the battery cycling can be in-situ monitored. The results demonstrate that the modified coating layer can effectively buffer the Jahn-Teller distortion of Ni³⁺, thereby significantly reducing the lattice distortion and enhancing the structural stability of the high-nickel layered materials. For the issues of Mn dissolution and electrolyte decomposition in the LiNi_0.5Mn_1.5O₄ cathode, the EXAFS characterization confirms that Fe³⁺ in the additive can dynamically and uniformly dope the LNMO cathode, therefore significantly reducing the lattice damage caused by Mn dissolution and improving the cycling stability of the electrode material.

Synchrotron Radiation X-ray Imaging: Synchrotron radiation X-ray computed tomography (XCT) is a high-resolution, non-destructive, three-dimensional characterization technique. Combined with the wavelength tunability of synchrotron radiation, the XCT can dynamically image the internal structural evolution (such as crack propagation, phase distribution) inside the electrode materials and valence and coordination environment distribution through combination with the EXAFS. For instance, in a Li-rich NMC cathode grain, the XCT reveals the gradient distribution of Mn valence and its evolution during the charging/discharging, providing a key basis for understanding the reaction kinetics.

Synchrotron Radiation Infrared Spectroscopy: Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), as an interface-sensitive technique, can be effectively used to characterize the composition and structure evolution inside the SEI between the electrode and electrolyte. However, as the main vibrational modes of Li salts are located in the low-energy region while conventional Globar gives only a weak output in the corresponding mid-infrared range, high bright synchrotron radiation infrared source is expected to play an important role in the study of SEI. For instance, there is a significant difference between the mid-infrared spectra of LiF thin film obtained from ATR-FTIR and scanning infrared near-field spectroscopy (which should be a surface sensitive technique), indicating that the distribution and coordination environment inside the film is nonuniform. As the gradient is closely related to the reaction/diffusion dynamics, a comprehensive characterization of the distribution of various components eventually bring us a deeper understanding of the formation and dissolution of the Li inorganics in the SEI film.

Conventional carbon materials such as graphite and hexagonal boron nitride, as well as other difficult-to-sinter carbon-based materials, suffer from some challenges such as lengthy preparation processes and high energy consumption. The existing strategy of assembling and structurally regulating functional building blocks across scales leads to significant improvements in the mechanical and thermal properties of these materials.

In the preparation of high-performance hexagonal boron nitride ceramics, using onion boron nitride (oBN) as functional building blocks, cubic boron nitride (cBN) is introduced and transformed into oBN during the sintering process. The volume expansion associated with this phase transformation promotes densification, resulting in high-strength hexagonal boron nitride (HSHBN) with improved mechanical properties. Also, BN plastic ceramics are fabricated by a twisted architecture approach with nano-oBN as a raw material. The ceramics composed of twisted nanosheets are formed via spark plasma sintering (SPS), achieving a fracture strain of up to 14% and a compressive strength of 626 MPa, and demonstrating the superior plastic deformation capacity and impact resistance.

In the preparation of graphite materials, high-strength graphite is fabricated through a uniformly dispersed architecture via mixing nano-diamond (ND) with natural graphite. After sintering, ND is converted into onion carbon (OC), forming a "nano-scar" structure that significantly enhances mechanical properties, with flexural strength of > 90 MPa. In a one-dimensional functional building block architecture, ND is introduced into polyacrylonitrile fibers via electrospinning, forming a one-dimensional nanofiber-reinforced structure that further increases flexural strength to 145 MPa. The strengthening mechanisms include crack deflection and bridging effects. Furthermore, a mortise-and-tenon structure architecture is employed to fabricate carbon-carbon composites via introducing ND into carbon fiber cloth, which transforms into an OC "mortise-and-tenon" structure after sintering. This significantly improves interlaminar bonding, achieving a flexural strength of 1206.5 MPa.

Electrocatalytic nitrate reduction (NO₃RR) emerges as a promising strategy for simultaneously addressing nitrogen pollution and enabling renewable energy conversion, thereby underpinning the emerging concept of an electrochemical nitrogen cycle. As a fundamental biogeochemical process, the nitrogen cycle is profoundly perturbed by anthropogenic activities, particularly excessive fertilizer application and fossil fuel combustion, resulting in the widespread accumulation of nitrate species in aquatic and terrestrial environments. This imbalance poses severe ecological and human health risks, rendering nitrate remediation on urgent global priority. Conventional nitrate removal technologies, including biological denitrification and physicochemical treatments, are extensively developed, but remain constrained by high energy consumption, stringent operating conditions, and the potential for secondary pollution. In contrast, NO₃RR employs electrons as clean reducing agents and water as a proton source to drive nitrate conversion under mild conditions, enabling seamless integration with a renewable electricity. Beyond pollutant removal, this process also facilitates the synthesis of value-added chemicals, such as ammonia, thereby offering a sustainable route for energy storage and chemical production. Reflecting its strategic significance, the electrochemical nitrogen cycle is identified as a key emerging direction in modern chemistry.

Despite rapid progress, the NO₃RR field remains fragmented and lacks a unifying framework. This challenge primarily stems from the intrinsic complexity of NO₃RR as a multistep proton-coupled electron transfer process involving numerous nitrogen-containing intermediates, leading to convoluted reaction pathways and ambiguous rate-determining steps. In addition, competing reactions such as hydrogen evolution also complicate the evaluation of catalytic selectivity. The existing studies are organized according to material categories, where catalytic performance typically originates from multi-site synergistic effects. Although such systems can deliver a high activity, they obscure the identification of true active centers and impede the establishment of clear relationships among structure, adsorption behavior, and catalytic performance, thereby limiting mechanistic insight and cross-study comparability. This lack of structural clarity also hinders the development of generalizable descriptors capable of linking electronic structure to reaction energetics. To overcome these limitations, increasing attention is directed toward atomically ordered catalysts as an emerging research paradigm. These systems allow for the construction of structurally well-defined and identifiable active centers via enabling precise control over atomic species, spatial distribution, and coordination environments. Such an atomic-level determinacy facilitates direct correlations among electronic structure, adsorption energetics, and reaction pathways, providing a foundation for descriptor-based understanding of catalytic behavior. In this context, representative systems, including single-atom alloys, intermetallic compounds, demonstrate an enhanced catalytic performance and an improved mechanistic clarity relative to conventional materials. Moreover, these model systems offer opportunities to examine the validity and limitations of scaling relationships and to explore strategies for breaking conventional activity and selectivity constraints.

This review proposes a unified classification framework for atomically ordered NO₃RR catalysts based on three key dimensions, i.e., active site scale, local bonding and coordination environment, and atomic arrangement order. This multidimensional perspective enables a systematic comparison across diverse catalyst systems and supports the extraction of fundamental design principles. Furthermore, recent progress on rational catalyst design, descriptor development, and device-level integration is summarized, with an emphasis on bridging the gap between fundamental understanding and practical implementation. Collectively, this framework aims to provide a basis for the development of more predictive and transferable strategies in NO₃RR catalyst design.

Metal-organic frameworks (MOFs) are crystalline porous materials constructed from metal ions or metal clusters and organic linkers through coordination bonds. MOFs become one of the most actively studied functional porous materials due to their long-range structural order, high porosity, exceptionally large specific surface areas, and tunable pore environments. Researchers can design framework topologies in an atomic level and regulate channel dimensions, pore shapes, and surface chemistry in a nanoscale via selecting metal nodes with different coordination geometries and organic linkers with tailored sizes, conformations, and functional groups. These characteristics endow MOFs with a broad application potential in gas storage, molecular separation, heterogeneous catalysis, chemical sensing, optoelectronics, and emerging micro/nano devices. In particular, continuous progress on component design and post-synthetic modification make it possible to modulate the electrical, optical, and interfacial properties of MOFs systems, thereby creating opportunities for their integration into microelectronic, photonic, and sensing platforms.

Despite these advantages, the practical use of MOFs in integrated devices remains strongly limited by their common physical forms. Most of MOFs are still prepared and utilized as polycrystalline powders, bulk crystals, or randomly deposited particles, which are difficult to position precisely on substrates or to incorporate into device architectures with controlled dimensions. As modern microelectronics, integrated photonics, and high-density sensor technologies continue to evolve toward miniaturization, multifunctionality, and on-chip integration, it is important to convert the intrinsic physicochemical properties of MOFs into device-relevant thin films and micro-/nano-structures. In this context, patterning technology plays a central role. It provides an essential bridge between the unique properties of MOFs and the fabrication requirements of practical devices via enabling high-quality MOF films or well-defined micro/nanopatterns to be formed on silicon wafers, glass, metals, and flexible polymer substrates. The development of reliable and precise patterning strategies is thus a key prerequisite for the implementation of MOFs in integrated circuits, sensor arrays, optical components, and other miniaturized functional systems.

However, MOFs also present some distinctive challenges for micro-/nano-fabrication. Their frameworks are mainly stabilized by coordination bonds, which are generally weaker than the covalent or ionic bonds in conventional inorganic semiconductors. As a result, many MOFs possess a limited mechanical robustness and are sensitive to heat, moisture, irradiation, reactive chemicals, and aggressive processing environments. Furthermore, their interconnected nanoporous channels can be easily blocked or damaged during conventional lithographic and etching procedures. Standard microfabrication methods such as plasma etching, wet chemical corrosion, and resist-assisted processing often involve high-energy species or chemical agents that may degrade framework integrity, alter surface functionality, or collapse pore structures. In addition, the compatibility of many MOFs with established semiconductor processing conditions is also insufficient, especially with respect to thermal stability, solvent tolerance, and interface adhesion. These factors motivate the development of MOF-specific patterning methods that can deliver a high spatial precision, while preserving crystallinity, porosity, and functionality.

According to whether the intrinsic structure of the MOF is directly transformed during processing, the existing MOF patterning technologies can be broadly divided into indirect and direct strategies. Indirect patterning does not primarily rely on structural modification of preformed MOFs. Instead, it controls where MOFs nucleate, grow, or deposit through external spatial confinement, surface chemical guidance, or material transfer. Representative approaches include template-assisted growth, inkjet printing, microcontact printing, selective growth on chemically modified substrates, and other spatially guided assembly methods. These routes are attractive because they are relatively simple, often mild, and generally effective for preserving the original porous framework. They play an important role in the early development of patterned MOF films and arrays, especially on nontraditional substrates and in proof-of-concept sensing devices. Nevertheless, their pattern fidelity is often restricted by template dimensions, droplet spreading, solvent evaporation, or interfacial diffusion. As a consequence, it remains difficult for many indirect methods to achieve high-resolution submicron-sized features, excellent film uniformity over large areas, and precise three-dimensional integration. Direct patterning strategies emerge as a major focus of recent research. Unlike indirect routes, they directly process pre-deposited MOF films or their precursor-derived layers through localized irradiation or other targeted energy inputs. Ultraviolet light, electron beams, X-rays, and lasers are the most widely explored tools. Their underlying mechanisms can be generally categorized into two types. The first involves irradiation-induced chemical changes, such as ligand crosslinking, framework decomposition, bond cleavage, or surface functionalization, which create solubility or wettability contrast between exposed and unexposed regions and thus enable selective development. The second involves direct material removal or transformation through physical ablation, decomposition, densification, or phase change. Compared with conventional resist-based lithography, direct patterning often reduces the need for sacrificial organic photoresists and can minimize residue-induced pore blockage. The carefully-designed direct methods can achieve a higher resolution, while retaining a large fraction of the crystallinity, pore accessibility, and chemical functionality of MOFs. Recent studies demonstrate that X-ray and electron-beam lithography can produce features well below 50 nm, ultraviolet-based chemistry can offer an effective balance between resolution and scalable processing, and laser-induced methods can enable localized consolidation, shaping, and even three-dimensional structuring.

From a broader perspective, the evolution of MOF patterning reflects a transition from externally guided deposition toward irradiation-driven in-situ material transformation. This transition is essential for addressing several key demands simultaneously, including precise positioning, high-resolution micro-/nano-structuring, heterogeneous integration, and compatibility with existing device fabrication workflows. Also, patterning requirements for MOFs can be understood as progressive levels of spatial control, i.e., one-dimensional control over film thickness, two-dimensional control over in-plane location and geometry, and three-dimensional control over complex architectures and multilayer arrangements. Expanding from simple film formation to sophisticated three-dimensional pattern construction will be crucial for realizing advanced device concepts in optics, sensing, electronics, and biomedicine.

The rapid proliferation of new energy vehicles (NEVs) leads to an unprecedented surge in the demand for lithium-ion batteries (LIBs). Among various LIBs, lithium iron phosphate (LFP) batteries have a significant market due to their inherent advantages, including superior thermal and chemical stability, low manufacturing cost, long cycle life (i.e., 2000-6000 cycles), and environmental friendliness. However, the service life of LFP batteries in NEVs is normally 6-10 years. These batteries are retired after decaying their capacity to below 80% of the initial value. The massive and growing volume of spent LFP batteries presents both a critical environmental challenge and a waste of valuable metal resources. Improper disposal can lead to the release of toxic substances from the electrolyte and heavy metals. Conversely, the spent cathodes contain abundant lithium (Li) and iron (Fe) that hold a significant economic value for recovery. Therefore, developing green, efficient, and economically viable recycling technologies is crucial for closing the material loop, ensuring resource security, and mitigating environmental hazards. This review represents the existing research status of two primary routes for managing spent LFP cathode materials, i.e., direct regeneration and hydrometallurgical/pyrometallurgical recycling. The underlying mechanisms, advantages, limitations, and key technological bottlenecks of each method are critically analyzed. Furthermore, future perspectives for the sustainable and efficient utilization of spent LFP materials are proposed to guide both academic research and industrial application.

This review systematically analyzes and compares the principal technologies for processing spent LFP cathode materials based on their structural integrity. For LFP materials that the olivine crystal structure remains largely intact despite Li⁺ loss, some direct regeneration methods are applicable. These motheds include (1) solid-state sintering, which involves supplementing missing Li, Fe, or P sources and calcining at high temperatures (i.e., typically 600-800 ℃) under an inert atmosphere to restore stoichiometry and repair defects; (2) hydrothermal synthesis, which uses aqueous lithium salts (e.g., LiOH, Li₂SO₄) and reducing agents (e.g., organic acids) at lower temperatures (i.e., 80-220 ℃) to re-lithiate the material and reduce Fe³⁺ back to Fe²⁺; and (3) electrochemical re-lithiation, where an external electric field drives Li⁺ insertion into the degraded cathode, potentially without dismantling the battery cell. For severely degraded LFP with an irreversibly damaged structure, full recycling methods are employed to extract valuable metals. These are primarily based on hydrometallurgy, i.e., acid leaching (using inorganic acids like H₂SO₄, H₃PO₄ or organic acids like oxalic, citric, formic acid), alkaline leaching (using NaOH for selective Li extraction), and bioleaching (using microbial metabolites). Pyrometallurgical processes that are often assisted by some additives like Na₂CO₃ or NaOH are also reviewed for their ability to convert LFP into separable metal compounds at high temperatures.

Direct regeneration is advantageous due to its short process flow, low cost, and high resource efficiency, making it a preferred industrial approach when applicable. Solid-state sintering offers high throughput and excellent recovery of electrochemical performance (discharge specific capacity up to ~147 mA·h·g^-1), but suffers from high energy consumption and potential impurity introduction. Hydrothermal synthesis operates under milder conditions (as low as 80 ℃), yielding repaired LFP with performance comparable to virgin material (>145 mA·h·g^-1), though it requires a strict control of pH value and a specialized autoclave equipment. Electrochemical methods avoid disassembly but face some challenges in scaling up due to the low repair efficiency. For full recycling, acid leaching achieves the maximum metal extraction rates (i.e., Li > 98%), but generates large volumes of acidic waste and introduces impurities. Organic acids offer a greener alternative but are costly and often less effective for Fe/P recovery. Selective Li leaching with oxalic acid or formic acid shows a promising potential via leaving Fe as a solid residue. Alkaline leaching is highly selective, but requires harsh conditions. Bioleaching is environmentally friendly, but suffers from slow kinetics and low efficiency. Pyrometallurgy is robust and feedstock-flexible, effectively converting LFP into soluble Li salts and magnetic Fe compounds, with Li recovery of exceeding 99% with Na₂CO₃ as an additive. However, it is energy-intensive and can emit toxic gases like HF and P₂O₅ from fluorinated binders and electrolytes, necessitating costly gas treatment. A key bottleneck across all the methods is a pretreatment step (i.e., discharging, disassembly, separation of cathode material from Al foil), which is often labor-intensive and inconsistent. Furthermore, the presence of impurities like Al, Cu, and residual carbon significantly affects the purity and performance of regenerated or recovered products. Most novel technologies remain in a lab-scale, with some challenges in industrial scalability, economic viability, and secondary waste management.