ZIF-67 is a crystalline scaffold in which cobalt ions are linked by organic imidazolate ligands into a porous, cage-like architecture. Materials chemists love such frameworks because, when heated in an inert atmosphere, they collapse in a controlled way: the cobalt nodes catalyze the growth of carbon nanotubes while the organic struts supply the carbon and nitrogen. The result is a self-assembling composite in which conductive carbon tubes are threaded with metallic cobalt and doped with nitrogen atoms — precisely the combination of conductivity, catalytic activity and defect chemistry that battery engineers seek in an anode. But the final product is exquisitely sensitive to how hot the furnace gets, and until now the trade-offs had not been systematically mapped for this system.

The researchers prepared three samples, carbonized at 500, 700 and 900 degrees Celsius, and labeled them N-CNTs-500, N-CNTs-700 and N-CNTs-900. At 500 degrees the framework conversion is incomplete, leaving a poorly developed carbon network. At 900 degrees the tubes grow more fully but the nitrogen dopants begin to burn off and the structure coarsens. The 700-degree middle ground proved to be the sweet spot: semi-closed nitrogen-doped carbon nanotubes that encapsulate cobalt clusters, a high specific surface area of 352.66 square meters per gram, and an abundance of the pyrrolic and pyridinic nitrogen configurations, along with cobalt coordinated to nitrogen in Co-Nx sites, that give doped carbons their electrochemical personality.

One of the most intriguing findings concerns the atomic geometry of the carbon itself. In ordinary graphite, carbon atoms sit in flat hexagonal sheets stacked 0.335 nanometers apart. The 700-degree material instead shows an expanded interlayer spacing of 0.381 nanometers, which the authors attribute to five-membered carbon rings that warp the sheets into curved, saddle-shaped regions the paper describes as Riemann surfaces — a mathematical term borrowed from differential geometry to describe locally non-Euclidean curvature. Those five-membered rings act like wedges inserted into the hexagonal lattice, forcing the planes apart and creating extra room for lithium ions to slip between the layers and additional sites for them to bind.

The electrochemical payoff is striking. At a modest current density of 0.1 amperes per gram, the N-CNTs-700 anode delivers a reversible capacity of 970.1 milliampere-hours per gram — roughly two and a half times what commercial graphite manages. More importantly for real-world fast charging, it still retains 356.2 milliampere-hours per gram when the current is cranked up to 8 amperes per gram, an eighty-fold increase in rate, and it sustains 130 milliampere-hours per gram after 1,000 cycles at 3 amperes per gram. Both the 500-degree and 900-degree analogues fall well short on every count, confirming that the microstructure, not merely the chemical composition, governs performance.

The team traces the high-rate capability to a synergy between two features of the material. The first is the conductive nanotube network itself, which provides highways for electrons and short diffusion distances for ions. The second is the dense population of nitrogen defects, which does something subtler: it introduces what electrochemists call extrinsic pseudocapacitance, meaning lithium ions are stored at defect sites through fast, surface-like charge-transfer reactions rather than slow solid-state diffusion. Because pseudocapacitive storage does not depend on ions burrowing deep into a crystal lattice, it can keep pace with very high charging currents — the fundamental reason capacitors charge in seconds while batteries normally take hours.

The nitrogen defects also reshape the solid-electrolyte interphase, the thin reaction layer that forms on any anode the moment it touches electrolyte. The SEI is a double-edged entity: it must exist to passivate the surface, but if it is thick, resistive or chemically heterogeneous it throttles the very ions it is supposed to conduct. The authors report that their material promotes a bilayer SEI with an inorganic-rich inner layer and an organic-rich outer layer. Inorganic components such as lithium fluoride, which the paper’s keywords highlight, are mechanically robust and ionically conductive, while the organic exterior cushions the interface. This architecture effectively lowers the energy barrier for desolvation — the step in which a lithium ion sheds its shell of solvent molecules before entering the electrode — and reduces interfacial charge-transfer resistance, the kinetic bottleneck that most limits fast charging.

That desolvation insight connects this work to a broader frontier in battery science. In recent years, researchers have come to appreciate that the speed limit of a lithium-ion cell is often set not inside the electrode but at its surface, where ions must be stripped of their solvation shells and pushed across a resistive interface. Strategies ranging from electronegative surface coatings to dipole-engineered electrolytes have been pursued to lower this barrier. The Taiyuan study adds a materials-design route to that toolbox: by tuning the defect chemistry of the carbon itself, the interface that forms on it self-organizes into a structure that welcomes lithium ions rather than repelling them.

The Riemann-surface concept likewise builds on an emerging theme. Previous work has shown that locally curved carbon surfaces, whether engineered in hard carbons or in sp2/sp3-hybridized networks, can unlock lithium storage at extreme low temperatures and boost capacity beyond what flat graphite allows, because curvature disrupts the ordered stacking that limits ion insertion. By showing that five-membered-ring-induced curvature arises naturally during the temperature-controlled pyrolysis of a cobalt zeolitic imidazolate framework, the new study suggests a scalable, synthesis-driven way to bake that geometry into an anode without exotic processing steps.

For a field racing toward batteries that charge in minutes without sacrificing lifespan, the message of the Ionics paper is that the furnace dial matters as much as the recipe. A 200-degree shift in pyrolysis temperature transformed the same starting framework from a sluggish electrode into one that pairs near-graphite-beating capacity with genuine high-rate endurance, thanks to expanded interlayer spacing, defect-rich nitrogen chemistry, encapsulated cobalt catalysts and a self-assembled, inorganic-rich protective film. The authors position their systematic temperature map as a foundation for the rational design of high-rate anodes based on ZIF-67-derived carbons — and, by extension, a template for anyone engineering MOF-derived carbons where atomic-scale curvature and interfacial chemistry, not just surface area, decide who wins the fast-charging race.

Subject of Research: Temperature-controlled pyrolysis of ZIF-67 into nitrogen-doped carbon nanotubes for high-rate lithium-ion battery anodes

Article Title: Temperature-tailored pyrolysis of ZIF-67 into N-Doped carbon nanotubes: Riemann Surface distortion, robust inorganic-rich SEI, and high-rate lithium storage

Article References: Temperature-tailored pyrolysis of ZIF-67 into N-Doped carbon nanotubes: Riemann Surface distortion, robust inorganic-rich SEI, and high-rate lithium storage. (n.d.). https://doi.org/10.1007/s11581-026-07527-7

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07527-7

Keywords: ZIF-67, metal-organic framework, nitrogen-doped carbon nanotubes, pyrolysis, lithium-ion batteries, anode materials, Riemann surfaces, solid-electrolyte interphase, pseudocapacitance, fast charging, cobalt clusters, Co-Nx sites

To appreciate why this combination of numbers matters, it helps to understand what a layered double hydroxide actually is. These materials, often described as synthetic analogues of the naturally occurring mineral hydrotalcite, consist of positively charged brucite-like metal hydroxide layers interspersed with charge-balancing anions and water molecules in the interlayer space. Because the metal cations sit within flexible, easily exfoliated sheets, layered double hydroxides offer an unusually rich palette for materials designers: the identity and ratio of the metal ions can be tuned almost continuously, and the layered geometry exposes an abundance of electrochemically active sites to the electrolyte. In supercapacitor electrodes, this translates into pseudocapacitance, a charge-storage mechanism in which fast, reversible faradaic reactions at or near the electrode surface store charge far more densely than the pure electrostatic adsorption that governs carbon-based double-layer capacitors.

The Indian team’s choice of metals was anything but arbitrary. Cobalt is a workhorse of pseudocapacitive chemistry, shuttling between oxidation states in alkaline electrolytes with respectable speed and capacity. Copper adds its own rich redox activity and excellent electronic conductivity, helping electrons move through the electrode rather than stalling at grain boundaries. Magnesium, by contrast, is essentially electrochemically inert in this context, but that is precisely its value: by substituting into the hydroxide lattice, magnesium ions act as structural spacers and stabilizers, helping to preserve the open, sheet-like morphology during repeated cycling and preventing the collapse that often degrades purely bimetallic hydroxides. The researchers describe the resulting CuCoMg layered double hydroxide as a heterostructure, meaning that the interplay among the three cations creates local electronic and structural environments that no single-metal or two-metal composition could replicate.

The synthesis itself relied on the hydrothermal method, a technique in which precursor solutions are sealed in an autoclave and heated above the boiling point of water, allowing crystals to grow under elevated pressure in a controlled, homogeneous environment. Hydrothermal growth is prized in the energy-storage community because it tends to produce well-defined nanostructures with strong adhesion to substrates and good crystallinity, both of which matter enormously for electrode durability. In this case, the process yielded the two-dimensional nanosheet-like morphology that gives the material its high accessible surface area, with the trimetallic composition locked into the layered framework from the start rather than grafted on afterward.

Yet even the most elegantly grown nanosheets face a fundamental problem when used alone: layered double hydroxides are intrinsically poor electronic conductors. An electrode that stores charge quickly must also move electrons to and from those storage sites quickly, and in a bare hydroxide the sluggish conductivity becomes a bottleneck at high charging rates. The team’s solution was to coat the surface of the CuCoMg layered double hydroxide with carbon, creating a conductive skin that acts like a nanoscale wiring network threaded through the active material. The carbon coating serves a second, equally important function: it increases the effective surface area of the electrode, providing additional pathways for electrolyte ions to reach the redox-active hydroxide and for the resulting charge to be collected. The researchers attribute the improved electrochemical performance directly to this carbon-induced increase in surface area.

The performance figures reported for the coated material are striking when placed in context. A specific capacitance of 1115 farads per gram at 1 ampere per gram places the CuCoMg LDH/C composite among the more capable layered double hydroxide electrodes described in the recent literature, a field that includes nickel-manganese, nickel-cobalt and ternary nickel-cobalt-manganese hydroxides grown on foams, carbon cloths and metal-organic framework templates. What distinguishes the new work is not only the capacitance but the effort to translate single-electrode performance into a complete, working device, which is where many laboratory records quietly evaporate. Single-electrode measurements are made against a reference in a three-electrode cell; a real supercapacitor must balance a positive electrode against a negative one within a fixed voltage window, and every inefficiency in that pairing subtracts from the delivered energy.

For the full device, the researchers fabricated an asymmetric supercapacitor, pairing the CuCoMg LDH/C composite as the positive electrode with activated carbon as the negative electrode. Asymmetric designs exploit the different stable voltage windows of the two electrode materials, allowing the cell to operate at a higher overall voltage than a symmetric configuration could safely sustain, and because energy scales with the square of voltage, this architectural choice pays dividends directly in energy density. The assembled device delivered 89 watt-hours per kilogram at a power density of 890 watts per kilogram. For comparison, typical commercial carbon supercapacitors cluster in the range of roughly 5 to 10 watt-hours per kilogram, so a device approaching 90 watt-hours per kilogram, if the figures can be reproduced at scale, would represent a meaningful leap toward bridging the gap with lithium-ion batteries while retaining the capacitor’s characteristic speed of charge and discharge.

Perhaps the most commercially significant number in the study, however, is the cycling data. The asymmetric device retained 89 percent of its capacity after 10,000 charge-discharge cycles, a result the authors cite as evidence that the electrode is a strong candidate for fast-charging, cost-effective energy storage. Degradation in pseudocapacitive hydroxide electrodes usually stems from mechanical stress during repeated ion insertion and removal, dissolution of active material, and loss of electrical contact as the structure swells and shrinks. The magnesium-stabilized lattice and the conformal carbon coating appear to address these failure modes together, the former by maintaining the layered architecture and the latter by keeping the active material electrically tethered even as it breathes. The authors note that no datasets were generated or analyzed beyond those presented in the study, and they declare no competing interests; the work received no dedicated funding.

The broader significance of the research lies in its demonstration that rational composition design, rather than exotic processing, can still yield competitive energy-storage materials. All three constituent metals are comparatively abundant and inexpensive relative to the ruthenium oxides and rare-metal chemistries that once dominated high-performance pseudocapacitor research, and the hydrothermal synthesis route is scalable with standard laboratory equipment. The study also adds to a growing body of evidence, reflected in the surrounding literature on ternary carbonate hydroxides, hydrotalcite-derived sulfides and MOF-templated trimetallic hydroxide arrays, that three-metal layered double hydroxides consistently outperform their two-metal counterparts by distributing the burdens of conductivity, redox activity and structural resilience across different cations. If the fast-charging, long-lived behavior reported here survives the transition from coin-cell-scale devices to practical modules, carbon-coated trimetallic nanosheets could find a home in applications where batteries struggle, from regenerative braking and grid frequency regulation to portable electronics that recharge in minutes rather than hours.

Subject of Research: Carbon-coated trimetallic CuCoMg layered double hydroxide nanosheets for fast-charging asymmetric supercapacitor electrodes

Article Title: Carbon coated two dimensional trimetallic layered double hydroxide nanosheet like structure for fast charging supercapacitor applications

Article References: Sathiya, V., Ramabalan, S., Vignesh, M., & Seenivasan, S. (2026). Carbon coated two dimensional trimetallic layered double hydroxide nanosheet like structure for fast charging supercapacitor applications. Ionics. https://doi.org/10.1007/s11581-026-07561-5

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07561-5

Keywords: supercapacitors, layered double hydroxide, nanosheets, carbon coating, pseudocapacitance, energy storage, asymmetric supercapacitor, hydrothermal synthesis, trimetallic electrode, fast charging, energy density, cycling stability

The new work, published in the open-access journal iScience, describes a low-frequency bidirectional pulsed current heating method that operates at frequencies of one hertz or below. The central innovation is adaptivity: rather than applying fixed pulse parameters, the system continuously adjusts the pulse currents according to the battery’s real-time state, ensuring that the anode potential never crosses the lithium-plating threshold throughout the entire heating process. The result, according to the authors, is the fastest possible heating that a given battery chemistry can safely tolerate, a genuine non-destructive approach validated on both lithium iron phosphate and nickel-cobalt-manganese cells.

To understand why this matters, it helps to consider the landscape of existing solutions. External heating methods, which rely on thermal fluids, heat pipes, or phase change materials placed outside the cell, tend to produce uneven temperature distributions and accelerate aging. Internal heating, by contrast, exploits the battery’s own internal resistance to generate Joule heat directly where it is needed, minimizing losses. Alternating current heating and mutual pulse heating, in which battery modules alternately charge and discharge one another, have both been explored extensively. Bidirectional pulsed current strategies, in which positive and negative pulses alternate to keep the state of charge nearly constant, have shown particular promise, but earlier high-frequency implementations demanded costly power electronics that limited real-world adoption.

The research team began by systematically mapping how pulse parameters influence heat generation. Using 2 ampere-hour LFP soft-pack cells placed in a temperature chamber, they varied the ratio of positive to negative pulse amplitudes from 1:1 up to 1:5 while holding the pulse period fixed at six seconds. Across both low and high states of charge, a larger amplitude ratio produced a greater temperature rise, a consequence of the fundamental relationship that heat generation scales with the square of current. They then varied the pulse period from fractions of a second up to 36 seconds and found that longer periods heated the battery more effectively, although the benefit plateaued beyond roughly ten seconds. That plateau defined their operating point: a ten-second pulse period, well within the low-frequency regime that avoids expensive high-frequency excitation hardware.

The truly distinctive element of the study is its use of three-electrode cells to police the lithium-plating boundary in real time. The researchers modified commercial cells by implanting a lithium titanate reference electrode at the center of the electrode stack, allowing them to measure the anode potential directly during operation, something impossible with conventional two-terminal cells. Through hybrid pulse power characterization tests conducted at temperatures from minus ten to twenty-five degrees Celsius and across a range of states of charge, they constructed a three-dimensional map of the maximum charging current the battery could tolerate at each condition without lithium deposition. This boundary current map became the adaptive brain of the heating algorithm, dictating the positive pulse amplitude as temperature and state of charge evolved.

The preheating experiments themselves were conducted under conditions mimicking a real electric vehicle arriving at a charger on a frigid winter day. With cells adjusted to ten percent state of charge and stabilized at minus fifteen degrees Celsius, the bidirectional pulses were applied. For the LFP cell, heating from minus fifteen to ten degrees took 2,068 seconds, an average temperature rise of 0.73 degrees Celsius per minute. Crucially, the measured anode potential, corrected against the reference electrode’s equilibrium potential of 1.565 volts versus lithium, remained above zero volts throughout the entire process, the electrochemical signature that no metallic lithium was plating onto the graphite anode at any moment.

Durability is where many preheating schemes have quietly failed, so the team subjected cells to one hundred repeated heating cycles at fixed state of charge. Because the bidirectional pulses deliver equal charge and discharge capacity within each cycle, the state of charge never drifts, allowing every cycle to begin from identical conditions. The authors note that with typical weekly charging and a three-month winter, one hundred heating cycles correspond to roughly seven years of real-world service, comparable to the lifetime of a traction battery. Capacity measurements taken before the test, after fifty cycles, and after one hundred cycles showed essentially no degradation. Post-mortem analysis sealed the case: transmission electron microscopy revealed an intact, uncracked SEI film, scanning electron microscopy showed an orderly lamellar electrode structure with no dendritic deposits, and energy-dispersive spectroscopy confirmed the elemental composition was unchanged.

To test whether the framework generalizes beyond one chemistry, the researchers repeated the entire procedure with a 1.75 ampere-hour commercial NCM811 pouch cell, independently recalibrating its lithium-plating boundary rather than simply copying LFP parameters. The results were striking. The NCM811 cell heated from minus fifteen to ten degrees in just 865.8 seconds, an average rise of 1.75 degrees Celsius per minute, nearly double the LFP rate. The reason lies in the interplay of resistance and allowable current: the NCM cell’s internal resistance is roughly half that of the LFP cell, but its lithium-plating boundary current is nearly twice as large, so its heating power, proportional to current squared times resistance, is consistently higher across all temperatures. The NCM cell likewise survived one hundred heating cycles with no measurable capacity loss and no lithium plating detected.

The physics underlying these results rewards aggressive current within safe limits. Because heat generation is proportional to the square of current, the alternating charge and discharge pulses of the bidirectional strategy allow larger amplitudes than constant-current heating would, since the alternating polarity alleviates anode polarization and prevents the anode potential from collapsing below zero volts. The authors point out an encouraging trend for the future: as battery technology improves fast-charging capability, the allowable lithium-plating boundary current grows, which in turn permits even larger pulse currents and faster heating, even as falling internal resistance reduces the Joule heating contribution per ampere.

The study is candid about its limitations. The pulse period was optimized at zero degrees and extrapolated to minus fifteen, an assumption supported but not exhaustively characterized across the full temperature range. The long-term stability of the implanted reference electrodes under repeated pulsing remains an open question, the durability test did not combine heating with subsequent fast charging, and the hardware costs and system-level energy efficiency of the required bidirectional power electronics were not quantified. Even so, the demonstration that a low-frequency, adaptive, chemistry-agnostic pulse strategy can warm frozen batteries at up to 1.75 degrees per minute without any detectable damage represents a meaningful step toward electric vehicles and stationary storage that shrug off winter. For the millions of drivers who watch their range evaporate on cold mornings, the prospect of a battery that heats itself safely and swiftly may be the most welcome news of the season.

Subject of Research: Non-destructive low-temperature pulse preheating of lithium-ion batteries

Article Title: Low-frequency non-destructive adaptive fastest pulse preheating for lithium-ion batteries

Article References: Li, C., Mao, S., Gao, M., He, M., Sun, Y., Wang, D., Han, X., Xia, C.-J., Wang, X., Lu, Y., & Gao, W. (2026). Low-frequency non-destructive adaptive fastest pulse preheating for lithium-ion batteries. iScience, 29(10), Article 117715. https://doi.org/10.1016/j.isci.2026.117715

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117715

Keywords: lithium-ion batteries, preheating, bidirectional pulse current, lithium plating, cold climate, electric vehicles, anode potential, three-electrode cells, LFP, NCM811, fast charging, battery degradation

The study, published in Nature Synthesis, introduces what the researchers call a descriptor-informed multi-component dopant selection strategy. Rather than testing dopant elements one by one in the laboratory, an approach that can consume months of synthesis and electrochemical testing for every candidate, the team identified two quantitative descriptors that predict how any given dopant will behave inside a nickel-rich layered oxide lattice. The first descriptor is the dopant’s charge density, which governs the electrostatic environment that lithium ions must navigate as they hop between sites in the crystal. The second is the strength of the chemical bond that forms between the dopant and the surrounding oxygen atoms, which determines how well the oxygen sublattice, the structural backbone of the material, resists degradation.

The logic behind the two descriptors is elegantly complementary. Dopants with low charge density weaken the electrostatic barriers that lithium ions encounter during migration, effectively widening the ionic highways through the crystal and accelerating transport. Dopants with high metal-oxygen bond energy, by contrast, act like structural rivets, reinforcing the oxygen framework and stabilizing the metal-oxygen network against the repeated expansion and contraction that occurs as lithium ions are extracted and reinserted during cycling. By combining dopants chosen for each property into a single multi-component formulation, the researchers achieved what single-element doping has rarely managed: simultaneous enhancement of rate capability and long-term structural stability, without sacrificing either one for the other.

The material that emerged from this strategy, which the team refers to as MD-LNMO, is a cobalt-free, nickel-rich layered oxide. The researchers subjected it to a battery of electrochemical tests, and the results are striking. At a charging and discharging rate of 25 C, meaning the battery is fully discharged in under three minutes, the cathode delivered 130.9 milliampere-hours per gram at room temperature. For comparison, conventional nickel-rich cathodes typically lose most of their capacity at such extreme rates because lithium ions simply cannot move through the lattice fast enough to sustain the current. The descriptor-guided doping scheme appears to have cleared that kinetic bottleneck.

Longevity is equally impressive. When cycled at 10 C over 350 cycles, the material retained 82.4 percent of its initial capacity, a level of durability that suggests the structural reinforcement provided by the high-bond-energy dopants is doing its job. Nickel-rich cathodes are notorious for cycling-induced phase transitions, in which the layered structure gradually transforms into spinel-like and rock-salt phases that are electrochemically inert. These transitions are driven by cation migration, oxygen loss and the accumulation of mechanical strain, a phenomenon the researchers describe as chemomechanical fatigue. The multi-component doping strategy suppresses all of these degradation pathways, keeping the crystal structure intact through hundreds of aggressive charge-discharge cycles.

Perhaps the most eye-catching result is the material’s low-temperature performance. At minus 20 degrees Celsius, a temperature at which most lithium-ion batteries lose a large fraction of their usable capacity because lithium diffusion slows dramatically in the cold, the doped cathode still delivered 112.2 milliampere-hours per gram at a 1 C rate. This is a significant achievement for a nickel-rich chemistry and points toward applications in cold climates, where electric vehicle range can plummet and fast charging becomes hazardous. The enhanced lithium-ion mobility engineered into the lattice appears to hold up even when thermal energy is scarce.

To understand why the doped material performs so well, the team deployed a comprehensive suite of characterization techniques. Synchrotron-based X-ray absorption near-edge structure and extended X-ray absorption fine structure measurements, performed at the Shanghai Institute of Applied Physics, probed the local chemical environment and bonding of the dopant atoms. Transmission electron microscopy, supported by the Jihua Laboratory and the Institute of Metal Research, revealed the atomic-scale structural evolution of the cathode during cycling. Electron paramagnetic resonance experiments tracked changes in the electronic structure and redox behavior of nickel. Together, these multimodal measurements confirmed that the dopants occupy their intended sites, that the oxygen sublattice is stabilized, and that the deleterious phase transitions and microcracking that normally destroy nickel-rich cathodes are largely suppressed.

The theoretical side of the work relied on density functional theory calculations, using the generalized gradient approximation and projector augmented-wave methods, to compute the migration barriers for lithium ions in doped lattices and the bond energies of candidate dopants with oxygen. These calculations provided the quantitative foundation for the two descriptors, allowing the team to screen candidate elements computationally before committing to synthesis. The approach mirrors a broader trend in materials science, where computational descriptors and machine-learned correlations are replacing Edisonian trial-and-error screening, but the demonstration here is notable for its direct translation from descriptor to working cathode with exceptional measured performance.

The implications extend beyond a single cathode formulation. Cobalt-free, nickel-rich chemistries are widely regarded as essential for reducing the cost and ethical footprint of lithium-ion batteries at the scale required by global electrification. Previous efforts have explored compositionally complex doping, gradient structures, surface coatings and strain engineering, each addressing part of the stability or kinetics problem. The descriptor-informed strategy offers a unifying design principle: choose dopants by their fundamental physical properties, charge density and bond strength, rather than by empirical screening, and combine them deliberately to address multiple failure modes simultaneously. The authors frame this as a transition from empirical, trial-based selection to a targeted selection regime, and the phrase captures a genuine methodological shift.

There remain, of course, the usual steps between laboratory success and commercial deployment: scaling synthesis, validating performance in full cells and pouch cells over thousands of cycles, and confirming safety under abuse conditions. But the numbers reported here, ultrahigh rate capability, robust cycling retention and genuine low-temperature operation, all achieved without a gram of cobalt, make a compelling case that the bottleneck for nickel-rich cathodes was never the chemistry itself but the way chemists searched for improvements. With a rational, descriptor-based compass now in hand, the path to high-performance, cobalt-free batteries looks considerably shorter than it did before.

Subject of Research: Descriptor-informed multi-component doping of cobalt-free nickel-rich layered oxide cathodes for high-performance lithium-ion batteries

Article Title: Descriptor-informed multi-component doping enables high-performance Co-free Ni-rich cathodes

Article References: Guan, S., Yu, T., Tang, P., Wu, H., Wei, Q., Piao, N., Li, L., Zhu, J., Zhang, L., An, B., Niu, Y., Hu, G., Sun, Z., Wang, C., Cheng, H.-M., & Li, F. (2026). Descriptor-informed multi-component doping enables high-performance Co-free Ni-rich cathodes. Nature Synthesis. https://doi.org/10.1038/s44160-026-01152-y

Image Credits: AI Generated

DOI: 10.1038/s44160-026-01152-y

Keywords: lithium-ion batteries, cathode materials, cobalt-free, nickel-rich cathodes, doping strategy, descriptors, lithium-ion transport, structural stability, fast charging, low-temperature performance, layered oxides, Nature Synthesis

The separator is a thin polymer membrane, typically around nine micrometers thick, that sits between the cathode and anode. Its job sounds simple: keep the two electrodes from touching each other electrically while allowing lithium ions dissolved in the electrolyte to pass freely through its microscopic pores. But that porous architecture carries consequences. A separator with high porosity offers abundant channels for ion transport, reducing the internal resistance of the cell. A low-porosity separator provides better mechanical stability but throttles the flow of ions. For decades, engineers have treated this as a straightforward trade-off, and most studies have optimized separators in isolation from the rest of the cell.

The Korean team, led by Seungyeop Choi, Yeseo Lim, Jaejin Lim, and corresponding author Yong Min Lee, decided to ask a more subtle question: what happens when you pair separators of different porosities with electrodes whose intrinsic lithium diffusion kinetics differ dramatically? To find out, they built coin cells using a nickel-rich NCM622 cathode paired with an artificial graphite anode, and swapped in two polyethylene separators of identical thickness but very different microstructures. The high-porosity separator, dubbed HPPE, had a porosity of 58.2 percent, while the low-porosity LPPE came in at 37.2 percent. Every other design variable, from electrode composition and loading to electrolyte volume, was held constant, ensuring that any performance differences could be traced back to the separator alone.

The physical measurements told a clear story. Scanning electron microscopy revealed that the LPPE possessed a denser fiber network, which translated into a Gurley air-permeability number of 159.3 seconds per 100 milliliters, nearly three times the 58.9 seconds recorded for HPPE. Impedance measurements on stainless steel/separator/stainless steel cells confirmed the consequence: the LPPE carried roughly 60 percent more internal resistance, 0.855 ohms compared with 0.538 ohms for HPPE. Since both separators are made of the same polyethylene with equivalent wettability, the difference in ionic transport stemmed purely from microstructure, not surface chemistry.

Then came the surprise. When the cells were cycled under fast-discharge conditions, with a 0.5C charge followed by a 3C discharge, the HPPE cell clearly outperformed its low-porosity counterpart, delivering 136.0 mAh per gram of cathode material against 123.0 mAh per gram for the LPPE cell, a gap of 9.6 percent. But when the test was flipped to fast charging, a 3C charge followed by a 0.5C discharge, the two cells behaved almost identically. Rate capability tests reinforced the asymmetry: the LPPE cell’s capacity fell off a cliff above 3C during discharge, yet both cells tracked each other closely through 3C charging, with only a modest divergence appearing at 5C and beyond. Direct-current internal resistance measurements painted the same picture, showing a pronounced separator effect during discharge but only a faint one during charge.

Why would a component that sits symmetrically between the two electrodes behave so differently depending on the direction of current flow? The answer, the researchers found, lies in the electrodes themselves. Using electrochemical impedance spectroscopy combined with galvanostatic intermittent titration technique measurements across the full state-of-charge range, they calculated the chemical lithium-ion diffusion coefficients of both active materials. The result was striking: NCM622 diffused lithium at roughly 3.28 times ten to the minus twelve square centimeters per second, while graphite managed 2.28 times ten to the minus nine, nearly three orders of magnitude faster. During discharge, lithium ions must travel through the separator and then insert into the sluggish NCM622 particles, so any extra resistance imposed by a dense separator compounds the cathode’s inherent slowness. During charging, lithium ions leave the fast-diffusing graphite, and the anode’s rapid internal redistribution masks the separator’s limitations.

To test this coupling hypothesis directly, the team fabricated four cells with bilayer separators, stacking high- and low-porosity films in different orientations: HP-HP, HP-LP, LP-HP, and LP-LP, where the first layer faced the cathode and the second faced the anode. Although the HP-LP and LP-HP configurations should have similar total cell resistance, the HP-LP cell, with its porous layer adjacent to the slow-diffusing cathode, delivered better high-rate discharge capacity than the LP-HP cell. The explanation is interfacial: when a restrictive separator sits next to an electrode that already struggles to redistribute lithium, local ion accumulation and concentration polarization build up, inflating the discharge overpotential. Placing the high-porosity layer against the cathode smooths the lithium flux at precisely the point where the cell is most vulnerable.

The quantitative details sharpen the picture further. Under 3C charging, the constant-current portion of the total charge capacity was highest for the HP-HP cell at 65.9 percent and lowest for the LP-LP cell at 55.1 percent, while the HP-LP and LP-HP cells landed nearly tied at 60.4 and 59.5 percent. Under 3C discharge, however, the discharge capacity contribution ranked strictly by configuration: HP-HP beat HP-LP, which beat LP-HP, which beat LP-LP. In other words, the direction of ion flow through a porosity gradient matters, and the gradient should be arranged to favor the electrode with the weaker diffusion kinetics.

The implications reach well beyond the laboratory coin cell. The authors note that the coupling effect they identified is expected to be even more pronounced in material systems where the diffusion disparity between cathode and anode is large. High-nickel layered oxides such as NCM811 and NCA, which power many of today’s long-range electric vehicles, diffuse lithium even more slowly than NCM622 relative to graphite, making them especially sensitive to separator resistance. Olivine-structured lithium iron phosphate, with its restrictive one-dimensional diffusion channels, is another candidate for strong separator-coupled behavior. For battery designers chasing fast-charging and high-power applications, this means separator selection cannot be treated as a generic materials choice; it must be matched to the specific electrochemical fingerprints of the electrodes it separates.

The study also reframes how the field should think about so-called inactive components. A separator’s properties, the researchers conclude, may either emerge as a limiting factor or remain effectively invisible, depending on the diffusion kinetics of the surrounding electrodes. That duality helps explain why previous studies have reached seemingly conflicting conclusions about how much separators matter: the answer depends on what is on either side of the membrane. As the industry pushes toward extreme fast charging and high-power discharge in electric vehicles, grid storage, and electrified aviation, this work offers a practical design principle, orient and engineer separator porosity gradients to shield the slowest-diffusing electrode, and a conceptual one: in a lithium-ion battery, no component is truly inactive. Every layer participates in the intricate choreography of ion transport, and the weakest link is revealed only when the current flows in the right direction.

Subject of Research: Coupled effects of separator porosity and electrode lithium-ion diffusion kinetics on the fast-charge and fast-discharge performance of lithium-ion batteries

Article Title: Coupled effects of separator microstructure and active material diffusion kinetics on high-power performance of lithium-ion batteries

Article References: Choi, S., Lim, Y., Lim, J., Kang, D., Park, K. T., Hong, R., & Lee, Y. M. (2025). Coupled effects of separator microstructure and active material diffusion kinetics on high-power performance of lithium-ion batteries. Advances in Industrial and Engineering Chemistry, 1(1), Article 32. https://doi.org/10.1007/s44405-025-00033-w

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00033-w

Keywords: lithium-ion batteries, separator, porosity, polyethylene separator, NCM622 cathode, graphite anode, diffusion coefficient, fast charging, fast discharging, ionic resistance, electrochemical impedance spectroscopy, high-power batteries