The new material, described in the journal Ionics, was produced by a process called in-situ copolymerization. The researchers mixed two liquid monomers—sulfobetaine methacrylate (SBMA), a zwitterionic molecule, and pentaerythritol triacrylate, a three-armed crosslinker—directly into the liquid carbonate electrolyte of an assembled cell. When polymerized, the monomers form a solid yet solvent-swollen gel that fills the separator and electrode pores without the need to disassemble or re-stack the cell. This in-situ strategy is industrially attractive because it preserves intimate contact between the electrolyte and the rough, porous surfaces of battery electrodes, a contact that is notoriously difficult to achieve with pre-made polymer films.

The chemical trick at the heart of the material lies in how it treats the two charged species in a battery. In a standard liquid electrolyte, lithium ions travel surrounded by a shell of solvent molecules and, often, PF6- anions; when current flows, both cations and anions drift in opposite directions. This coupled motion wastes driving force, builds up concentration gradients under high current, and delivers anions to the anode surface where they decompose. In the zwitterionic gel, however, the permanently charged sulfobetaine groups act as electrostatic anchors that immobilize the PF6- anions, while the same framework offers dynamic coordination sites where lithium ions can briefly bind and then hop to the next site. The result is a hopping transport mechanism in which lithium migration is decoupled from both anion flux and the sluggish segmental motion of the polymer backbone itself.

The measured numbers underscore why this matters. The gel achieves a room-temperature ionic conductivity of 6.72 millisiemens per centimeter—approaching the range of free-flowing liquid electrolytes and far above most solid polymer electrolytes. More striking is the lithium-ion transference number of 0.69, meaning nearly seven of every ten charge carriers moving through the electrolyte are lithium ions rather than anions. Typical liquid electrolytes have transference numbers around 0.3 to 0.4, which means most of the current is carried by anions that contribute nothing to storing energy and much to degrading the cell. A high transference number reduces concentration polarization, allowing the cell to sustain high charging rates without the lithium depletion at the anode that triggers damaging lithium plating.

To test the concept under realistic fast-charging stress, the researchers built 1 ampere-hour pouch cells pairing an NCM523 layered oxide cathode—nickel-rich lithium nickel cobalt manganese oxide—with graphite anodes, the same chemistry family used in commercial electric vehicle batteries. The cells were cycled at a punishing regime of 2C charging, meaning a full charge in half an hour, combined with 5C discharging, or twelve minutes to empty. After 500 such cycles, the cells with the zwitterionic gel retained 80.7 percent of their original capacity. Both the pristine liquid electrolyte and a non-zwitterionic gel counterpart faded substantially faster under the same conditions, demonstrating that the zwitterionic solvation strategy, not merely the gelling itself, was responsible for the endurance.

The mechanistic story behind this durability lies in the interfacial films that form on the electrodes. Every lithium-ion battery contains two crucial passivation layers: the solid electrolyte interphase (SEI) on the anode and the cathode electrolyte interphase (CEI) on the cathode. When anions and solvent molecules decompose uncontrollably, these films grow thick, porous and chemically heterogeneous, adding resistance and consuming lithium inventory. In the zwitterionic gel, the regulated solvation environment—where lithium ions are coordinated by the polymer’s charged sites rather than by reactive solvent clusters—changes the decomposition chemistry itself. On the graphite anode, the team observed a robust interphase enriched in lithium fluoride (LiF), an inorganic compound prized for its chemical stability and high interfacial energy that suppresses parasitic side reactions.

On the cathode side, the improvement was equally pronounced. The NCM523 cathode developed an ultrathin CEI of only about 5 nanometers—roughly a hundred times thinner than a human red blood cell is wide—that was uniform and dominated by inorganic species. Thin, inorganic-rich interphases conduct lithium ions efficiently while blocking electrons and solvent, protecting the high-voltage cathode from transition-metal dissolution and electrolyte oxidation. Together, the LiF-rich SEI and the nanometer-scale CEI explain how the cells survived half a thousand aggressive cycles: the electrolyte spent its early cycles building near-ideal protective layers, then simply kept working.

The decoupling of ion transport also has a subtle kinetic benefit for fast charging. During rapid charge, lithium ions are consumed at the graphite anode far faster than they can diffuse through the electrolyte and through the SEI. If anions must move to balance the charge, large salt concentration gradients form, lowering the local lithium concentration at the anode surface until metallic lithium plates directly instead of intercalating into graphite—an effect that both erodes capacity and, in the worst case, short-circuits the cell. With anions largely pinned in place by the zwitterionic network, the concentration gradient is shallower, and the effective lithium supply at the anode remains adequate even at 2C charging rates.

Zwitterionic materials have been drawing growing attention in electrolyte research, and this work builds on a broader trend. Zwitterions and zwitterionic polymers have previously been explored for lithium-sulfur batteries, for low-temperature lithium metal cells, and as additives that modulate the solvation sheath of lithium ions. What distinguishes the new study is the combination of a practical in-situ fabrication route, compatibility with standard carbonate electrolytes and commercial electrode chemistries, and demonstration in genuine 1 Ah pouch cells rather than small coin cells—a scale where many laboratory breakthroughs quietly fail. The collaboration with Tianjin Lishen Battery, a major Chinese cell manufacturer, suggests the researchers are attentive to manufacturability from the start.

The work was supported by the Natural Science Foundation of Hunan Province and the National Natural Science Foundation of China, and the research team included Yan Tong, Maohui Bai, Xuhui Wang, Xihao Zou, Shu Hong, Bo Hong and Yanqing Lai. Fast charging has become one of the most fiercely contested battlegrounds in battery development, because charging time is consistently cited by consumers as a barrier to electric vehicle adoption, and because grid storage operators value the flexibility that rapidly rechargeable systems provide. Yet pushing current through a cell heats it, stresses its interfaces and invites lithium plating; nearly every proposed solution involves trade-offs among conductivity, safety, cost and cycle life.

Gel polymer electrolytes occupy a compelling middle ground in this trade-off landscape: they retain most of the ionic conductivity of liquids while offering the leak resistance, mechanical robustness and improved safety of solids. What they have historically lacked is control—control over which ions move, control over how lithium is solvated, and control over the interfacial chemistry that ultimately determines whether a cell lives for a decade or dies in a year. The zwitterionic design described in Ionics shows that this control can be engineered directly into the polymer architecture rather than bolted on through additives.

If the approach proves scalable, the implications extend beyond fast-charging electric cars. High-transference-number electrolytes could ease thermal management burdens, permit thinner electrodes and higher energy densities, and improve the low-temperature behavior of cells by reducing concentration polarization in sluggish electrolytes. The researchers describe their zwitterionic solvation strategy as a general pathway—one that other labs can adapt by tuning the balance between anion immobilization and lithium coordination in related polymer chemistries. For now, the demonstration of 500 stable fast-charge cycles at pouch-cell scale with a transference number of 0.69 marks a significant step toward batteries that can drink from a high-power charger as casually as they deliver power on the road.

The traditional bottleneck arises because lithium ions, solvated in the electrolyte, must first shed their solvent shells—a process called desolvation—before they can intercalate into graphite layers. Under rapid charging conditions, this desolvation step becomes rate-limiting, causing lithium ions to deposit as metallic lithium on the anode surface, which leads to hazardous dendrite growth and rapid capacity degradation. Conventional approaches such as the use of highly concentrated electrolytes or surface coatings have provided incremental improvements but often at the cost of reduced rate capabilities, increased manufacturing complexity, or higher production costs.

Addressing this multifaceted challenge, the research team led by Professors Zhi Chang and Haoshen Zhou designed and fabricated an ultrathin (~5 nm) glassy MOF coating that transforms the graphite anode’s surface chemistry and interface dynamics. This novel coating performs two critical functions through its dynamic structural evolution during the initial electrochemical cycle. In its initial state, it acts as a uniform gatekeeper layer. With cycling, it evolves into a dual-layer architecture comprising an outer sub-nanometer pore MOF glass layer and an inner lithium phosphide (Li₃P) enriched layer on the graphite surface.

The outer MOF glass layer is engineered with highly selective pores measuring approximately 2.93 angstroms in diameter. These nanoscale channels function as an effective molecular sieve, enforcing lithium-ion pre-desolvation by stripping off solvent molecules from lithium ions before their entry into the electrode. This pre-desolvation mechanism not only accelerates ion kinetics but also fosters a highly concentrated ionic environment at the interface, crucial for the formation of a robust, LiF-rich solid electrolyte interphase (SEI). This unique SEI chemistry is pivotal in suppressing dendritic lithium growth and enhancing long-term battery safety and stability.

Simultaneously, the inner layer enriched with Li₃P serves as an ultrafast ionic conductor. Li₃P boasts excellent lithium-ion conductivity, effectively acting as an ion accelerator that facilitates the rapid diffusion of partially desolvated lithium ions into the graphite bulk. By decoupling the slow desolvation stage from subsequent solid-state ion transport within the anode, this dual-layer configuration significantly enhances the overall ion transport rates, enabling extremely fast charging without compromising electrode integrity.

Experimentally, the coated Glass@Graphite anode exhibits extraordinary electrochemical performance. In half-cell configurations, it delivers a specific capacity exceeding 250 mAh/g at ultrahigh rates of 5C—over five times the capacity retention compared to uncoated graphite electrodes under identical conditions. These impressive capabilities translate effectively to practical full-cell architectures, where the Glass@Graphite anode is paired with commercial nickel-rich NCM-811 cathodes. The resulting batteries demonstrate remarkable operational durability, retaining 88% of their initial capacity even after 1,000 cycles at a stringent 4C charging rate.

To showcase industrial viability, the researchers scaled up the technology to a 2.36 Ah pouch cell format. This larger cell maintained a competitive energy density of 283 Wh/kg and preserved more than 80% capacity after 300 fast-charge cycles. Post-mortem characterization of the electrodes confirmed a pristine graphite surface void of lithium dendrites and a stable crystal lattice structure, underscoring the coating’s protective function over extended cycling.

What sets this innovation apart is the marriage of nanoscale precision engineering with scalable, low-temperature synthesis techniques. Unlike many nano-coating approaches requiring high-temperature or complex processing steps incompatible with current battery manufacturing lines, the MOF glass coating can be applied using cost-effective, industry-friendly methods, paving the way for seamless adoption in existing production infrastructures.

Fundamentally, this work redefines the role of interfacial layers in high-performance lithium-ion batteries. Rather than simply blocking or passivating the electrode surface, the glassy MOF coating acts as an active interface that orchestrates ion dynamics—accelerating desolvation and enhancing lithium-ion mobility while concurrently promoting the growth of a stable, protective SEI. This sophisticated multifunctionality resolves the enduring trade-off between rapid charging capability and long-term cycle life.

Looking ahead, the implications of this technology extend beyond graphite anodes. The principles of selective ion sieving coupled with fast ionic conduction could inform the design of next-generation interfaces for other electrode materials where ion transport limitations govern performance. Moreover, the ability to precisely control interfacial chemistry through dynamic, self-adaptive coatings potentially opens new horizons in battery material science, helping usher in a new era of energy storage devices that combine speed, safety, and longevity.

In essence, the glassy MOF nano-sieve coating represents a quantum leap in lithium-ion battery technology. It addresses the central challenge of desolvation kinetics without sacrificing the essential attributes of electrode stability and manufacturability. As global demand for rapid, reliable battery charging continues to intensify, this breakthrough offers a promising avenue to accelerate the electrification of transportation, grid storage solutions, and myriad portable electronics, fundamentally transforming the battery landscape for decades to come.

Subject of Research:
Article Title:
News Publication Date:
Web References: http://dx.doi.org/10.1093/nsr/nwaf349
References:
Image Credits: ©Science China Press

Keywords
Lithium-ion battery, fast charging, graphite anode, metal-organic framework, MOF glass coating, lithium-ion desolvation, solid electrolyte interphase, SEI, lithium phosphide, Li₃P, electrochemical performance, molecular sieve, battery interface engineering

Graphite has long served as the standard anode in lithium-ion batteries due to its structural stability and well-understood electrochemistry. However, its inherent limitations—including a relatively low theoretical capacity and inadequate ionic transport rates—hinder its applicability in fast-charging, high-power scenarios. In response, the research team devised a composite approach marrying the advantageous ion diffusion properties of hard carbon with the high capacity potential of tin, an element historically plagued by volumetric instability during charge-discharge cycles. This composite architecture strategically leverages the benefits of each component, overcoming their individual shortcomings.

Hard carbon, characterized by its disordered microstructure rich with micropores and interconnected diffusion pathways, facilitates rapid ion mobility, which is essential for swift charge and discharge kinetics. This intrinsic porosity combined with mechanical robustness enables the material to endure the stresses of prolonged electrochemical cycling, fulfilling the criteria for long-life battery performance. Yet, while hard carbon offers a favorable framework, it alone cannot achieve the desired volumetric energy densities needed for cutting-edge energy storage.

The integration of tin nanoparticles within the hard carbon matrix presents a nuanced challenge. Tin, while boasting a high theoretical capacity — significantly surpassing graphite — suffers from substantial volume expansion close to 260% during lithiation, which compromises the structural integrity of the anode. Moreover, synthesizing tin nanoparticles under 10 nanometers is complicated by tin’s low melting point around 230°C, which typically results in particle agglomeration. The research team overcame this obstacle using a sol–gel method followed by a controlled thermal reduction process that crafted sub-10 nm tin nanodots homogeneously embedded in the carbon structure, ensuring consistent distribution and enhanced stability.

The synergy between the hard carbon matrix and the tin nanoparticles is more than additive; it emerges as a catalytic interaction that fundamentally enhances the crystallinity of the surrounding carbon. The tin serves not only as an electrochemically active species but also as a nucleation catalyst during thermal treatments, improving the structural order of hard carbon. This coalescence has a profound impact on the electrochemical performance, as it facilitates reversible Sn–O bond formation during battery cycling. These conversion reactions contribute to supplementary capacity beyond intercalation mechanisms, effectively amplifying the battery’s energy density and overall efficiency.

When subjected to rigorous electrochemical assessments in lithium-ion systems, the nanocomposite anode sustains stable capacity retention exceeding 1,500 cycles under rapid 20-minute fast-charging conditions. Notably, the battery achieves a volumetric energy density approximately 1.5 times greater than that of conventional graphite anodes. Such performance delineates a paradigm shift where high power delivery, impressive energy storage, and exceptional cycle life coexist, resolving a trilemma that has long limited lithium-ion battery commercialization potential.

The versatility of this material extends beyond lithium-ion configurations, demonstrating remarkable effectiveness in sodium-ion battery systems as well. Sodium ions, due to their larger ionic radius and distinct electrochemical characteristics, tend to interact poorly with conventional anode compounds such as graphite or silicon. The hard carbon–tin composite circumvents these limitations, operating with excellent kinetic stability and mechanical resilience in sodium environments. This adaptability broadens the scope of the anode’s applicability, paving the way for low-cost, abundant, and sustainable sodium-ion battery technologies suitable for large-scale energy storage solutions.

This breakthrough holds consequential implications for the future of electric vehicles and renewable energy integration, sectors that demand batteries with enhanced charge rates without compromising lifespan or energy density. Professor Soojin Park of POSTECH elaborates, emphasizing that the research marks a critical milestone, blending multidisciplinary expertise to realize anodes that can meet and exceed evolving energy storage criteria. Her insights highlight the strategic relevance of coupling advanced materials engineering with electrochemical innovations to meet global energy demands.

Echoing this sentiment, Dr. Gyujin Song from KIER underscores the transformative potential catalyzed by this dual compatibility with lithium and sodium-ion chemistries. This capability is poised to influence a broad spectrum of energy markets, accelerating the adoption of high-performance rechargeable batteries tailored to diverse industrial and grid applications. The breakthrough effectively heralds a pivotal phase in the evolution of battery technologies, responding simultaneously to power, stability, and sustainable resource considerations.

The rigorous research effort, led by Professors Soojin Park, Sungho Choi, and Dong-Yeob Han at POSTECH alongside Dr. Gyujin Song at KIER, harnessed a combination of advanced material synthesis, nanoscale characterization, and electrochemical evaluation methods. Their findings, recently published in the journal ACS Nano, received support from the Ministry of Trade, Industry and Energy and the Ministry of Science and ICT of Korea. This confluence of academic and governmental collaboration underscores the strategic priority of advancing battery science to meet socio-economic and environmental imperatives.

In dissecting the underlying mechanisms, the fabricated nanocomposite’s structure operates on finely balanced physicochemical principles. The hard carbon’s porous morphology reduces ion diffusion resistance, while the catalytic tin nanodots stabilize the carbon structure during lithiation and sodiation by mediating conversion reactions. These synergistic effects minimize mechanical degradation, phase transformations, and undesirable side reactions common in traditional electrodes, thereby enhancing cycle retention and capacity stability. This multi-faceted approach exemplifies a forward-thinking blueprint for material design in energy storage research.

Looking forward, the material’s scalability and cost-effectiveness remain critical aspects for industrial translation. The utilization of a sol–gel process combined with thermal reduction presents a viable route for large-scale electrode fabrication, crucial for meeting the burgeoning demand in electric vehicle production lines and renewable energy storage systems. Moreover, the adaptability toward sodium-ion systems implies a strategic advantage in addressing resource scarcity concerns associated with lithium, positioning this technology at the forefront of sustainable energy solutions.

In summary, this pioneering work transcends conventional electrode design by introducing a hybrid nanocomposite that achieves a rare confluence of high volumetric energy density, rapid charge capability, and prolonged cycling stability in both lithium-ion and sodium-ion battery frameworks. This advancement is anticipated to galvanize further research into multifunctional battery materials and expedite the deployment of high-performance batteries across diverse applications, including transportation electrification and grid resilience.

Subject of Research: Development of Hard Carbon–Tin Nanocomposite Anodes for Enhanced Lithium-Ion and Sodium-Ion Batteries

Article Title: Catalytic Tin Nanodots in Hard Carbon Structures for Enhanced Volumetric and Power Density Batteries

News Publication Date: 5-Mar-2025

Web References:
DOI: 10.1021/acsnano.5c00528

Image Credits: POSTECH

Keywords

Applied sciences and engineering; Anodes; Tin; Hardness; Chemical stability; Kinetic stability; Thermodynamic stability; Electrochemical energy; Kinetic energy; Thermal energy; Electric charge; Mechanical systems; Power industry; Electric vehicles; Lithium ion batteries; Ions; Nanoparticles