Rate Capability Performance Research Articles

Trace Cu Doping Enabled High Rate and Long Cycle Life Sodium Iron Phosphate Cathode for Sodium-Ion Batteries.

Na4Fe3(PO4)2(P2O7) (NFPP) is currently receiving a lot of attention, as it combines the advantages of NaFePO4 and Na2FeP2O7 in terms of cost, energy density, and cycle stability. However, the issues of intrinsic poor electronic conductivity and difficult high-purity preparation may impede its practical application. Herein, the pivotal role of Cu doping in strengthening the polyanion structure and improving its electrochemical properties is comprehensively investigated. It is found that trace Cu doping not only expands the lattice volume of NFPP but also suppresses the formation of the inactive NaFePO4 impurity phase. In addition, Cu doping can effectively reduce the structural variations of NFPP during sodiation/desodiation processes (2.02%) while decreasing the band gap and lowering the ion mobility energy barrier (from 0.46 to 0.426 eV). Consequently, the Cu-doped NFPP electrode exhibits superior rate capability and long-term cycling performance. The computational simulations reveal a strong electronic interaction between Fe and Cu that tunes the electron localization and distribution, and additional Na+ transport channels can be created in NFPP by distorting the [PO4] units adjacent to the doping site, which provides a reference to enhance the performance of NFPP and reveals the great application potential of NFPP materials.

Deciphering the Basis of Enhanced Na+ Storage Induced by Halogen Doping in Na2VTi(PO4)3

AbstractElemental doping is a widely adopted strategy to enhance the electrochemical performance of electrode materials, yet limited studies have explored the resulting variations in the bonding environments and the interactions between dopant atoms and their neighboring atoms. In this study, halogen‐doped (fluorine, chlorine, and bromine) polyanionic phosphates are synthesized to investigate the effects of halogen doping on the fine crystal structure, chemical micro‐environment, and electronic structure of Na2VTi(PO4)3 for Na ion storage. Density functional theory analysis reveals that halogen doping strengthens interactions at the Na sites while disrupting their symmetry, thereby promoting Na+ conductivity. Simultaneously, the increased electron density and expanded electron cloud potentially bridge the electron clouds previously isolated by [PO4] tetrahedra, facilitating electron transport. As a result, the doped samples demonstrate improved performance in rate capability, capacity, and cycling stability. This study provides deeper insights into the influence of elemental doping on electrode materials properties.

Suppressed P3-O3' Phase Transition and Enhanced Na+ Diffusion Kinetics of O3-Type Layered Oxide Cathode via Multivariate Doping.

O3-NaNi1/3Fe1/3Mn1/3O2 has attracted much attention as a cathode for sodium-ion batteries, because of its low cost and high sodium-ion storage capacity. However, its slow Na+ diffusion kinetics and harmful P3-O3' phase transition with severe bulk strain at high voltage leads to poor rate capability and fast capacity fading. Herein, we propose a multivariate doping strategy with Cu, Mg, and Ti ions to solve the above problems of the O3-NaNi1/3Fe1/3Mn1/3O2 cathode. The O3-Na(Ni1/3Fe1/3Mn1/3)0.9Cu0.03Mg0.02Ti0.05O2 (NFMCMT) cathode exhibits enlarged Na+ diffusion channels and a strengthened layered structure, which improves the Na+ diffusion kinetics, suppresses the harmful P3-O3' phase transition at high voltages, and inhibits the intragranular fatigue cracks, leading to enhanced rate capability and cycling performance. As a result, the NFMCMT exhibits outstanding performance in the 2-4.1 V voltage window, delivers a discharge capacity of 151.2 mAh g-1 with the 81.5% capacity retention for 100 cycles at 0.1 C, and 83.1% capacity retention for 300 cycles at 5 C. Especially in the rate performance, the NFMCMT delivers a 115.6 mAh g-1 and 100.1 mAh g-1 discharge capacity even at 5 and 10 C. This work provides an effective multivariate doping strategy for development of high-performance layered oxide cathodes for sodium-ion batteries.

(Invited) Improving Low-Temperature Lithium-Ion Battery Performance through 3D Structure-Controlled Anodes with Optimized Charge Storage Mechanisms

The performance of lithium (Li)-ion batteries (LIBs) significantly decreases at low temperatures, primarily due to the slow diffusion of Li ions within the graphite anode. This issue often necessitates the use of complex thermal control systems to safeguard the batteries, enhancing their cost, mass, and volume, especially under extreme conditions. Here, we introduce both structure-controlled graphene and graphite composite anodes, which employ controlled charge storage mechanisms to accelerate Li-ion charge storage kinetics and maintain structural stability under low-temperature conditions. [1-3] By transitioning from layered graphite to crumpled graphene or expanded graphite (composite), we effectively utilize diffusion- and surface-controlled charge storage mechanisms. These structure-controlled anodes exhibit superior rate capability and exceptional performance at temperatures as low as -50 °C. Through comprehensive low-temperature analyses, this research provides a detailed understanding of the relationships between anode structure, charge storage mechanisms, and performance under low-temperature conditions. Our findings offer valuable insights for the development of advanced energy storage devices optimized for low-temperature operation.

Laser Ablation of High-Loading Electrodes to Improve Performance of Li-Ion Batteries in Behind-the-Meter Storage (BTMS) Applications

Behind-the-Meter Storage (BTMS) is a battery-based, stationary energy storage system that is connected to the residential or industrial customer’s side of the electrical grid utility service meter. BTMS systems enable consumers to (A) economically schedule charging and usage of stored energy, (B) store and use energy from on-site generation, especially from inconstant, renewable sources like solar and wind, and (C) avoid overworking the grid during peak hours via supplementation with stored energy. BTMS battery performance requirements and general priorities differentiate from other applications, like EVs, which has prompted the development of batteries with tailored electrode and electrolyte materials. These materials prioritize low cost, avoiding critical materials; high safety, mitigating thermal runaway; and longevity, achieving 8000 cycle and 20-year shelf lives.Lithium titanate (Li4Ti5O12, LTO) is a promising anode candidate for BTMS applications due to its high safety and stability, while maintaining an acceptable 160 mAhg-1 reversable capacity and composition of reasonably abundant materials.[1] Specifically, LTO has a high working voltage, which helps to prevent Li dendrite formation, improving safety. Furthermore, LTO, a “zero strain” material, has negligible lithiation-based volume change, leading to less active material loss upon cycling. Lithium manganese oxide (LiMn2O4, LMO) has been paired with LTO for BTMS applications in the past due to its safety, low cost (abundancy and critical material-free), and decently high operating voltage.[2-4] However, the low specific capacity of LMO limits energy density. While not the highest priority for BTMS applications, increasing energy density will enable BTMS deployment in space constrained applications as well as decrease total cost of the system. Therefore, improving volumetric energy density via the use of high-loading electrodes is of interest. A concern with the use of high-thickness, high-tortuosity, and low-porosity electrodes is that limitations arise with regard to electrode wettability, rate capability, and general performance, especially when paired with the high-stability, but also high-viscosity, ethylene carbonate-based electrolytes.[4] Previous studies have shown that limitations in electrode wettability and rate capability may be addressed by employing a scalable laser structuring technique on the electrodes prior to cell assembly.[5] Therefore, the study presented here focuses on the understanding of how structuring of high-loading LTO/LMO electrodes via laser ablation will impact cell performance. Specifically, a comparison is provided for cells with standard electrodes, a standard anode and ablated cathode, an ablated anode and standard cathode, and both electrodes ablated. Details of a novel laser structuring method will be provided in addition to material characterization as well as electrochemical characterization focused on rate capability and cycle life as they apply to BTMS requirements.This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by the U.S. Department of Energy's Vehicle Technologies Office under the Behind-the-Meter Storage (BTMS) Consortium directed by Fernando Salcedo and managed by Anthony Burrell. The electrodes used in this manuscript are from Argonne's Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is fully supported by the DOE Vehicle Technologies Office (VTO). The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Design of Poly(ethylene oxide)-Based Polymer-in-High Concentrated Ionic Liquid Electrolyte for All-Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) have emerged as promising candidates for solid-state lithium metal batteries (LMBs) due to their inherent safety advantages and potential to facilitate high energy density devices [1]. Poly(ethylene oxide) (PEO) has been the most prominent representative polymer host in SPEs since 1970s because of their excellent ability to solvate Li ions and support ion transport [2,3]. However, it suffers from limited oxidation stability (<4 V vs. Li) and low ambient temperature conductivity (up to 10−6 S cm−1), thus hindering its practical application in high voltage (>4V) high energy density LMBs. In this study, a new type of polymer-in-“high concentrated ionic liquid” solid electrolyte is designed with high molecular weight PEO, N-propyl-N-methylpyrrolidinium bis(fuorosulfonyl) imide (C3mpyrFSI) ionic liquid and lithium bis(fluorosulfonyl)imide (LiFSI). The EO: [LiFSI/C3mpyrFSI] ratio has been widely varied and the resulting physicochemical and electrochemical properties have been explored. The optimal electrolyte provides promisingly high oxidative stability exceeding 5V and ambient temperature conductivity of 5.6 x10-4 S cm-1. It induces stable solid electrolyte interface with Li metal and demonstrates prolonged reversible Li plating-stripping in Li symmetrical cells even at high temperatures (up to 70°C). All solid-state Li metal cells assembled with LFP cathode show excellent rate capability and cycling performance (see Figure 1). The discharge capacity can be maintained at 47.3% when the current density increases 20 times from 0.1 C to 2 C (areal capacity ~0.4 mAh/cm2), and long-term cycling of Li||LFP cells showed 97% capacity retention after 100 cycles at 0.2 C. Based on the findings, an ion conduction network consisting of interconnected anion-rich clusters and pores is highlighted to help understand the structural change, ion dynamics and good battery performance of the designed SPE. Therefore, the novel approach of polymer-in-“high concentrated ionic liquid” solid electrolyte enables a new pathway to design high-performing SPEs for high energy density all-solid-state LMBs. Figure 1

Advantageous Li3PO4 Coating on Conductive Agents for Sulfide-Based All-Solid-State-Batteries

Sulfide-based all-solid-state-batteries (ASSBs) are garnering attentions as a next-generation battery system due to their high ionic conductivity and the ductility-derived processability. However, it is imperative to address the issue of side reactions between carbon additive-based conductive agents and solid electrolytes. Irreversible reactions of solid electrolytes, stemming from narrow electrochemical stability window, lead to capacity fading of ASSBs. Previous research has explored conductive agents in the form of fibers with a smaller specific surface area or reducing the proportion of conductive agents. Nevertheless, these approaches have not provided a fundamental solution.Herein, we apply an oxide coating to the surface of carbon nanofiber conductive agents to prevent interfacial side reactions between the electrolyte and the conductive agent. Through computational screening among various oxide-based coating candidates, Li3PO4 is identified as possessing the highest chemical interfacial stability and superior ionic conductivity when interfaced with cathode active materials and solid electrolytes. This approach not only preserves the electronic percolation pathway essential for high-rate capability but also effectively suppress the decomposition of solid electrolytes through a stable ceramic layer. The efficacy of the Li3PO4 coating is demonstrated through enhanced ionic conductivity by up to 150% and improved rate capability and cycle performance in ASSBs, without significant loss of electronic conductivity in the composite cathode. This work introduces a novel concept in conductive agent modification, offering significant advantages in both ionic and electronic conductivity aspects.

Enhanced Cycling Stability of Al-Doped Li1.20Mn0.52-x Al x Ni0.20Co0.08O2 as a Cathode Material for Li-Ion Batteries by a Supercritical-CO2-Assisted Method.

Lithium-rich layered oxide materials (Li-NMC) are considered a potential cathode material for next-generation batteries, thanks to their high theoretical specific capacity. Large potential drop and capacity loss after long cycles are the main obstacles to expanding commercial utilization of Li-NMC. In the past decade, great efforts have been made to overcome those issues of Li-NMCs. In this study, Al-doped Li1.20Mn0.52-x Al x Ni0.20Co0.08O2 cathode materials are for the first time synthesized by a supercritical-CO2-assisted method. Upon the electrochemical tests of Al-doped Li-rich NMCs, the optimal initial charge/discharge profile is obtained for the Li-NMC-Al02 cathode with 374.6/247.5 mAh/g compared with that of 320.7/235.1 mAh/g for the pristine Li-NMC-Al00 sample at the C/20 rate. In addition, the Li-NMC-Al02 cathode shows an enhanced rate-capability performance compared to the pristine sample at relatively low rates. When the current density is increased from C/10 to 3C, the charge/discharge capacity values of the Li-NMC-Al02 cathode are measured as 249.88/105.84 mAh/g. Last but not least, Li-NMC-Al02 demonstrates an excellent energy retention of 92.32%, which is notably higher than that of pristine Li-NMC-Al00 (86.4%) after 120 cycles at the C/20 rate. Overall, the present fabrication and doping strategy opens a new avenue for commercialization of Li-NMC cathode materials.

NiS2/FeS2 binary nanoparticles confined in interconnected carbon framework with regulated pore structure enabled by citric acid for enhanced sodium storage properties

Recently, pyrite iron disulfide (FeS2) has emerged as a promising anode candidate for sodium-ion batteries (SIBs) due to its high theoretical capacity, affordability, non-toxicity and abundant resource in nature. However, the utilization of FeS2 still confronts the challenges of inferior rate capability and cycling instability for sodium storage, stemming from its low electronic conductivity and substantial volume changes during cycling. Herein, to address these obstacles, NiS2/FeS2 binary nanoparticles encapsulated within a network of interconnected N-doped porous carbon framework (NiS2/FeS2@NPC) are prepared by a successive solid-state ball milling, carbonization and sulfurization strategy with coordination complex of nickel iron Prussian blue analogue (NiFe-PBA) as precursor. The introduction of citric acid plays a critical role for the formation of interconnected carbon framework with regulated internal porous structure, thereby achieving heterostructured NiS2/FeS2@NPC with modulated specific surface area and pore volume. The rational design of interconnected N-doped porous carbon framework and heterogeneous structure guarantees rapid ion/electron transport kinetics, alleviated mechanical stress, and enhanced structural integrity. Benefitting from these advantages, the optimal NiS2/FeS2@NPC-1 electrode exhibits a high reversible capacity (545 mAh/g at 1 A/g), superior rate capability (267 mAh/g at 5 A/g) and ultrastable long-term cycling performance (98.5 % retention over 1000 cycles at 5 A/g). This study presents a novel and efficient design approach for creating durable and high-rate anode materials based on metal sulfides for SIBs.

Laser exfoliated 2D MXene for supercapacitor applications

MXenes-based compounds, particularly Ti3C2Tx, have been studied intensively as electrodes for supercapacitors due to their layered structure and high conductivity, enabling facile ion diffusion and charge transfer. However, tight restacking of the 2D layers in these materials limits their practical, accessible surface area, thereby impeding their capacity and rate capability performance. To mitigate this phenomenon, we present a new approach using a processing method based on laser beam irradiation to modify Ti3C2Tx films. We found that the laser treatment induces chemical and morphological changes, ultimately optimizing the stacking arrangement of the MXene electrodes and consequently enhancing their capacity in both neutral and acidic electrolytes. Furthermore, the laser-modified MXene electrodes demonstrate excellent rate capabilities, showing 84 % retention at extreme rates of 0.5 V compared to only 33 % of the original Ti3C2Tx electrodes. Finally, we discuss the chemical and physical changes induced by the laser treatments and their influence on the electrochemical behavior of the lasered MXene. The principles of laser exfoliation discovered in this study can be implemented in broader 2D materials for various applications.

Mitigating the Kinetic Hysteresis of Co-Free Ni-Rich Cathodes via Gradient Penetration of Nonmagnetic Silicon.

Co-free Ni-rich layered oxides are considered a promising cathode material for next-generation Li-ion batteries due to their cost-effectiveness and high capacity. However, they still suffer from the practical challenges of low discharge capacity and poor rate capability due to the hysteresis of Li-ion diffusion kinetics. Herein, based on the regulation of the lattice magnetic frustration, the Li/Ni intermixing defects as the primary origin of kinetic hysteresis are radically addressed via the doping of the nonmagnetic Si element. Meanwhile, by adopting gradient penetration doping, a robust Si-O surface structure with reversible lattice oxygen evolution and low lattice strain is constructed on Co-free Ni-rich cathodes to suppress the formation of surface dense barrier layer. With the remarkably enhanced Li-ion diffusion kinetics in atomic and electrode particle scales, the as-obtained cathodes (LiNixMn1-xSi0.01O2, 0.6≤x≤0.9) achieve superior performance in discharge capacity, rate capability, and durability. This work highlights the coupling effect of magnetic structure and interfacial chemicals on Li-ion transport properties, and the concept will inspire more researchers to conduct an intensive study.

Mitigating the Kinetic Hysteresis of Co‐Free Ni‐Rich Cathodes via Gradient Penetration of Nonmagnetic Silicon

AbstractCo‐free Ni‐rich layered oxides are considered a promising cathode material for next‐generation Li‐ion batteries due to their cost‐effectiveness and high capacity. However, they still suffer from the practical challenges of low discharge capacity and poor rate capability due to the hysteresis of Li‐ion diffusion kinetics. Herein, based on the regulation of the lattice magnetic frustration, the Li/Ni intermixing defects as the primary origin of kinetic hysteresis are radically addressed via the doping of the nonmagnetic Si element. Meanwhile, by adopting gradient penetration doping, a robust Si−O surface structure with reversible lattice oxygen evolution and low lattice strain is constructed on Co‐free Ni‐rich cathodes to suppress the formation of surface dense barrier layer. With the remarkably enhanced Li‐ion diffusion kinetics in atomic and electrode particle scales, the as‐obtained cathodes (LiNixMn1−xSi0.01O2, 0.6≤x≤0.9) achieve superior performance in discharge capacity, rate capability, and durability. This work highlights the coupling effect of magnetic structure and interfacial chemicals on Li‐ion transport properties, and the concept will inspire more researchers to conduct an intensive study.

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

NiCo2S4 nanoparticles encapsulated within hollow mesoporous carbon spheres enabling rapid and stable sodium storage

Poor rate capability and cycling performance significantly impair the utilization of NiCo2S4 as an anode material in sodium-ion batteries. Herein, hollow mesoporous carbon spheres (HMCSs) are synthesized using a hard-template method. NiCo2S4 nanoparticles with sizes ranging from 15 to 43 nm are grown in-situ within HMCSs (NiCo2S4@HMCS) by melt adsorption, solution impregnation, and gas-phase sulfurization. Specifically, NiCo2S4 nanoparticles are uniformly distributed on the inner walls of HMCSs and within the mesoporous channels of spherical shells. In half-cells, NiCo2S4@HMCS exhibits reversible capacities of 482 mAh g−1 after 340 cycles at 1.0 A g−1, 340 mAh g−1 after 600 cycles at 5.0 A g−1, and 271 mAh g−1 after 700 cycles at 10.0 A g−1. In NiCo2S4@HMCS//Na3V2(PO4)3 full-cells, NiCo2S4@HMCS maintain reversible capacities of 203 mAh g−1 after 1200 cycles at 1.0 A g−1 and 122 mAh g−1 after 2000 cycles at 5.0 A g−1. The unique nano-encapsulated structure prevents the detachment of NiCo2S4 from HMCSs, maintaining electrochemical activity and stability of NiCo2S4. Additionally, the nano-encapsulated structure also facilitates electrolyte penetration and enhances the electronic conductivity of NiCo2S4. These effects synergistically result in rapid and stable sodium storage performance.

Nb1.60Ti0.32W0.08O5−δ as negative electrode active material for durable and fast-charging all-solid-state Li-ion batteries

Li-based all-solid-state batteries (ASSBs) are considered feasible candidates for the development of the next generation of high-energy rechargeable batteries. However, ASSBs are detrimentally affected by a limited rate capability and inadequate performance at high currents. To circumvent these issues, here we propose the use of Nb1.60Ti0.32W0.08O5-δ (NTWO) as negative electrode active material. NTWO is capable of overcoming the limitation of lithium metal as the negative electrode, offering fast-charging capabilities and cycle stability. Physicochemical and electrochemical characterizations of NTWO in combination with the Li6PS5Cl (LPSCl) solid-state electrolyte demonstrate that the formation of LiWS2 at the electrode|electrolyte interphase is the main responsible for the improved battery performance. Indeed, when an NTWO-based negative electrode and LPSCl are coupled with a LiNbO3-coated LiNi0.8Mn0.1Co0.1O2-based positive electrode, the lab-scale cell is capable of maintaining 80% of discharge capacity retention after 5000 cycles at 45 mA cm−2 at 60 °C and 60 MPa.

Z-scheme heterostructures confining rGO/protonated C3N5 junction supported CoCu LDH positive electrode and Fe3O4 negative electrode for supercapacitors

CoCu LDH stabilized reduced graphene oxide-linked N-rich protonated C3N5 (CoxCuy@rGO/P–CN) as a power source Z-scheme nanocomposite was rationally tailored engineered an electrodeposition approach. The electrochemical performance was regulated by adjusting the electrodeposition potential and manipulating the Co/Cu molar ratio. Hence, affording compelling evidence for fine-tuning the performance of pseudo-active compounds. Benefiting from abundant heterointerfaces and synergistic effects between LDH nanoarrays and rGO/P–CN heterojunction, the hierarchical −1.2V Co3Cu1@rGO/P–CN Z-scheme positive electrode achieves a higher capacitance of 1184 F g−1 at 1 A g−1 and good rate capability performance. Theoretical simulation outcomes illustrate that the Co3Cu1@rGO/P–CN nanocomposite has higher electronic conductivity and superior electronic transition capability, originating from robust interactions between valence and conduction bands, interfacial charge transfer, and built-in electric field at the LDH/rGO/P–CN interface. We also explore the Fe3O4@rGO/P–CN Z-scheme as a negative electrode material via a simple annealing process with a capacitance of 402 F g−1 at 1 A g−1 and an enhanced cyclic performance. Consequently, the as-assembled −1.2V Co3Cu1@rGO/P–CN//Fe3O4@rGO/P–CN asymmetric supercapacitor (ASC) cell acquires a remarkable energy density of 63.4 Wh kg−1 at 750 W kg−1 and displays an exceptional cycling activity with 88 % retention after 11,000 cycles.

Elevating electrochemical performance of Na4MnCr(PO4)3 cathode material for sodium ion batteries through the synergistic effect of Sc doping and RuO2/C coating

The widespread interest in Na4MnCr(PO4)3 (NMCP) for sodium-ion batteries (SIBs) derives from its high energy density and earth abundance. Nevertheless, the poor rate capability and unsatisfactory cycle performance restrict the application of NMCP cathodes in commercialized SIBs. Herein, we designed and prepared the dual-modified NMCP cathode materials by combining doping Sc3+ and hybrid coating with RuO2/C. Benefiting from the synergistic effects of two approaches, the structural stability and the Na+ diffusion as well as the electronic conductivity have been elevated synchronously. Therefore, the optimized Na4MnCr0.95Sc0.05(PO4)3@RuO2/C composite (NMCSP@RC) presents a superior rate capability (163.4 mAh/g at 50 mA g−1 and 87.6 mAh/g at 1000 mA g−1) and extended cycle stability (capacity retention of 66.3 % after 500 cycles at 1000 mA g−1) compared to pure NMCP. Moreover, a full SIB cell with NMCSP@RC cathode demonstrates a praiseworthy energy density of 469.8 Wh kg−1. This study proves the effectiveness of the dual modification strategy on NMCP, which could provide a fresh idea to optimizing the performance for NMCP cathode materials and contribute to the final fulfillment of their commercialized application.

Modification of polypropylene separator with multifunctional layers to achieve highly stable sodium metal anode

Separator modification is an effective approach to suppress dendrite growth to realize high-energy sodium metal batteries (SMBs) in practical applications, however, its success is mainly subject to surface modification. Herein, a separator with multifunctional layers composed of N-doped mesoporous hollow carbon spheres (HCS) as the inner layer and sodium fluoride (NaF) as the outer layer on commercial polypropylene separator (PP) is proposed (PP@HCS-NaF) to achieve stable cycling in SMB. At the molecular level, the inner HCS layer with a high content of pyrrolic-N induces the uniform Na+ flux as a potential Na+ redistributor for homogenous deposition, whereas its hollow mesoporous structure offers nano-porous buffers and ion channels to regulate Na+ ion distribution and uniform deposition. The outer layer (NaF) constructs the NaF-enriched robust solid electrolyte interphase layer, significantly lowering the Na+ ions diffusion barrier. Benefiting from these merits, higher electrochemical performances are achieved with multifunctional double-layered PP@HCS-NaF separators compared with single-layered separators (i.e. PP@HCS or PP@NaF) in SMBs. The Na||Cu half-cell with PP@HCS-NaF offers stable cycling (280 cycles) with a high CE (99.6%), and Na||Na symmetric cells demonstrate extended lifespans for over 6000 h at 1 mA cm−2 with a progressively stable overpotential of 9 mV. Remarkably, in Na||NVP full-cells, the PP@HCS-NaF separator grants a stable capacity of ∼81 mA h g−1 after 3500 cycles at 1 C and an impressive rate capability performance (∼70 mA h g−1 at 15 C).

High performance potassium/sodium-ion storage enabled by anchoring cobalt atoms on sulfur vacancies in WS2 nanosheets

Transition metal dichalcogenides (TMDs) as anodes have presented significant potential in alkali-ion batteries. Nevertheless, they are generally vulnerable to low conductivity and sluggish ion diffusion as well as severe volume variation. Here, a strategy of filling metal atoms into anion vacancies is proposed and applied to the example of WS2. More specifically, sulfur vacancies are produced and partially filled by Co atoms simultaneously in WS2 (denoted as Co@WS2-SV), creating a highly reactive micro-structure composed of Co-W-S, which can not only effectively provide more active sites, but also boost the charge transfer and reaction kinetics. Consequently, the as-prepared Co@WS2-SV exhibits superior K+ storage performance, which includes an ultrahigh reversible capacity of 382.9 mAh g−1 at 0.05 A g−1. Besides, Co@WS2-SV still maintain a capacity of 112.6 mAh g−1 after 1100 cycles at 2 A g−1 while the capacity fades to ∼0 mAh g−1 after only 800 cycles for WS2. Simultaneously, Co@WS2-SV also displays outstanding rate capability (338.7 mA h g−1 at 2 A g−1) and acceptable cycling performance (264.2 mA h g−1 at 1 A g−1 after 100 cycles) for sodium storage. The strategy in our study provides new way of precisely designing the other TMDs anodes for metal-ion batteries.

Surface modification of LiFePO4 cathode enabled by highly Li+ mobility wrapping layer towards high energy and power density

Surface-modified cathode materials have been developed to achieve high-performance lithium secondary batteries with higher capacity, rate capability, and longer cycle performance than bulk active materials. In this study, a new surface-modified active material was explored through a low-temperature in situ-solution wrapping method (LiFePO4@Li4SiO4 composite). In addition, high Li-ion and electronic conductivity materials with amorphous nanostructures, in which the bulk LiFePO4 nanoparticles were covered with a Li4SiO4 layer, were demonstrated. In lithium-ion batteries, the LiFePO4@Li4SiO4 composite demonstrated enhanced charge transfer kinetics, which lowered the interfacial resistance between electrode and electrolyte and resulted in enhanced electrochemical performance when compared to that of bulk LiFePO4. Furthermore, Li4SiO4 is introduced as a surface stabilizer and effective Li-ion conductor to avoid side reactions and prevent the dissolution of active materials into the electrolyte. The designed cathode delivers a high specific discharge capacity of 171.8 mAh g-1 at 0.1 C with 99.76 % capacity retention after 150 cycles and a high capacity of 121.2 mAh g-1 at 10 C. Moreover, Li-ion full batteries employing LiFePO4@Li4SiO4 and graphite displayed a high specific energy density of 416.078 Wh kg-1 at a power density of 69.34 W kg-1 at 5 C. In summary, this paper reports a new strategy based on low-temperature in situ solution phase wrapping materials for developing active materials for high energy-power density energy storage devices.