Ultrahigh Rate Capability Research Articles

Enhancing the ultra-high rate capability of manganese-based olivine cathode by in situ catalytic growth of graphene carbon layer

Manganese-based olivine is a high energy and low-cost cathode material for lithium-ion batteries. However, its low electronic and ionic conductivity limits its further application. Herein the graphene-modified LiMn0.8Fe0.2PO4 (LMFP/C-Fe) composites are prepared by in-situ pyrolysis and catalytic graphitization through trace ferrocene as catalyst precursor. The average thickness of graphene carbon layer grown in situ is about 2–3 nm, which forms a dense and uniform carbon layer along the face of LMFP granules. It has been found that this unique structure can make a significant improvement to the electrical conductivity of LMFP. The as-prepared LMFP/C-Fe composite has a high discharge capacity of 155.9 mAh/g at 0.5C, and the capacity retention is 93.8 % after 300 charge-discharge cycles. In addition, the material can still provide reversible capacity of 94.4 mAh/g even at an ultra-high current rate of 30C. Therefore, this work offers new tactics for layout and preparation of long-life, low cost and high-energy density lithium-ion batteries, which will present a promising application in electric automobile and other applications.

MXene-Integrated Perylene Anode with Ultra-Stable and Fast Ammonium-Ion Storage for Aqueous Micro Batteries.

The aqueous micro batteries (AMBs) are expected to be one of the most promising micro energy storage devices for its safe operation and cost-effectiveness. However, the performance of the AMBs is not satisfactory, which is attributed to strong interaction between metal ions and the electrode materials. Here, the first AMBs are developed with NH4 + as charge carrier. More importantly, to solve the low conductivity and the dissolution during the NH4 + intercalation/extraction problem of perylene material represented by perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), the Ti3 C2 Tx MXene with high conductivity and polar surface terminals is introduced as a conductive skeleton (PTCDA/Ti3 C2 Tx MXene). Benefitting from this, the PTCDA/Ti3 C2 Tx MXene electrodes exhibit ultra-high cycle life and rate capability (74.31% after 10000 galvanostatic chargedischarge (GCD) cycles, and 91.67 mAh g-1 at 15.0 A g-1 , i.e., capacity retention of 45.2% for a 30-fold increase in current density). More significantly, the AMBs with NH4 + as charge carrier and PTCDA/Ti3 C2 Tx MXene anode provide excellent energy density and power density, cycle life, and flexibility. This work will provide strategy for the development of NH4 + storage materials and the design of AMBs.

Unveiling the Double‐Edged Behavior of Controlled Selenium Substitution in Cobalt Sulfide for Balanced Na‐Storage Capacity and Rate Capability

AbstractTransition metal sulfide‐based anodes usually suffer from huge volumetric change and sluggish reaction kinetics, hindering their application for long‐term and high‐power/energy sodium‐ion batteries. Herein, a new design of CoS2‐xSex (0≤x≤2) nanocrystals with highly controllable selenium substitution and S, Se‐codoped graphene immobilization (CoS2‐xSex@SG) is proposed to tune the reaction kinetics and structural stability. The nanocrystal‐on‐graphene structure and robust C─S &C─Se bonding rivets between CoS2‐xSex and SG greatly improve the structural stability of the CoS2‐xSex@SG. Electrochemical performance, kinetic analysis, and theoretical calculation reveal that Se substitution plays a double‐edged role in sodium storage: the increase of Se substitution content enhances the Na+ diffusion kinetics but decreases the Na‐storage capacity. When the Se substitution content is 0.4, the CoS1.6Se0.4@SG electrode demonstrates the best performance: high initial Coulombic efficiency (95.5%), ultrahigh rate capability (412.8 mAh g−1 at 30 A g−1), and ultra‐stable cycling performance (97.6% capacity retention after 1000 cycles). In situ/ex situ measurements further unveil that the conversion reaction between Co0 and Na2S/Na2Se generates the micro‐scaled CoSe2–CoS2 heterostructure, synergistically improving the Na‐storage active sites and reaction kinetics. This work provides a controllable anion substitution strategy to balance the Na+ storage active sites and kinetics with potential applications for high‐power/energy sodium‐ion batteries.

Oriented Gradient Doping of Zirconium in Ni-Rich Cathode to Achieve Ultrahigh Stability and Rate Capability.

Ni-rich layered oxide materials exhibit great prospects for practical applications in lithium-ion batteries due to their high specific capacity. However, the poor cycling performance and suboptimal rate performance have caused obstacles for their widespread application. Herein, we developed a gradient Zr element doping method based on the bulk gradient concentration of Ni-rich layered oxide material to reinforce the cycle stability and rate performance of the cathode. In particular, the orientations of the gradient Zr doping were achieved via coprecipitation in a positive or negative correlation between the concentrations of Zr and Ni, and it was revealed that the material behaves better when the Zr content is abundant in the core. The gradient doping of Zr decreases the content of Ni2+ and mitigates the mixing degree of Li+ and Ni2+, implying the superior performance of doped cathode material. Compared with the bare sample (70.7%, 121.4 mAh g-1), the Zr-doped sample delivered a higher capacity retention of 85.6% after 300 cycles at 1C (1C = 180 mA g-1) and exhibited a considerable rate performance of 122.5 mAh g-1 at 20C. In particular, the Zr-doped cathodes performed dramatically on high rate cycling at 10C, with an initial capacity of 143.6 and 103.9 mAh g-1 after 300 cycles. Furthermore, the Zr-doped cathode delivered significant stability at a high potential of 4.5 V with a capacity retention of 72.1% after 300 cycles, while that of the bare sample was only 37.4%. The concept of gradient doping strategies during coprecipitation offers new insight into the design of advanced cathodes with excellent cycling stability and rate capability.

Promoting OH- Adsorption and Diffusion Enables Ultrahigh Capacity and Rate Capability of Nickel Sulfide Cathode for Aqueous Alkaline Zn-Based Batteries.

Aqueous alkaline Zn-based batteries (AAZBs) possess great promise for large-scale applications thanks to their higher discharging plateau and unique reaction mechanism. However, the capacity and rate capability of Ni-based cathodes are still unsatisfactory due to their insufficient OH- adsorption and diffusion ability. Herein, heterostructured Ni3 S2 /Ni(OH)2 nanosheets with outstanding electrochemical performance are synthesized via a facile chemical etching strategy. The heterostructured Ni3 S2 /Ni(OH)2 nanosheet cathode shows significantly increased capacity and rate capability due to its boosted OH- adsorption and diffusion ability compared to Ni3 S2 . Consequently, the assembled Zn//Ni3 S2 /Ni(OH)2 cell can deliver an ultrahigh capacity of 2.26mAhcm-2 , an excellent rate performance (0.91mAhcm-2 at 100mAcm-2 ) and a satisfying cycling stability (1.01mAhcm-2 at 20mAcm-2 after 500 cycles). Moreover, a prominent energy density of 3.86mWhcm-2 is obtained, which exceeds the majority of recently reported AAZBs. This work is expected to provide a new modification direction for developing high-performance nickel sulfide cathode for AAZBs.

Hierarchical porous titanium dioxide nanosheets with surface-engineering for exceptional sodium storage performance

Structural reconstruction derived from surface engineering has substantially improved fast and high-efficient charge storage for sodium-ion batteries. Here, a surface engineering strategy including phosphorus doping and nitrogen-doped carbon coating simultaneously realizes surface structural reconstruction and establishes a conductive network, which significantly enhances Na+ storage kinetics of TiO2. Expectedly, functionalized TiO2 nanocrystals with phosphorus doping and nitrogen-doped carbon coating present expedited electron and Na+ transfer and enhanced structural stability during Na+ insertion/extraction, fueled by the enhanced surface electrochemical reactivity and unique hybrid structure. Therefore, surface-engineered two-dimensional (2D) TiO2 nanosheets achieve exceptional Na+ storage performance including the ultralong cycling stability with reversible capacities of 223 mAh/g at 5C for 10,000 cycles at 5C, 212 mAh/g at 10C for 20,000 cycles, and 203 mAh/g at 20C for 5000 cycles, as well as an ultrahigh rate capability of 181 mAh/g up to 50C. This functionalizing strategy fueled by surface engineering paves a new way for achieving high-performed anode materials for sodium-ion batteries.

CoCx‑induced interfacial octahedral Co2+ sites of NiCo-LDH electrode with improved faradic reactivity toward high-performance supercapacitor

Battery-like electrode materials are characterized by large theoretical capacitance but suffer from poor surface reactivity and insufficient electroactive sites thus limiting their practical charge storage capacity. To overcome this challenge, an effective strategy for vacancy modulation on battery-like electrode materials is necessary. Herein, we report for the first time an elaborately designed three-dimensional (3D) hierarchical heterostructure consisting of CoCx@NiCo-LDH on conductive nickel foam as a freestanding supercapacitor electrode. Benefiting from the weakening of the coordination of CoO bonds, the CoCx structure induces in-situ reconstruction of the NiCo-LDH lattice, resulting in the formation of abundant oxygen vacancies (interfacial octahedral Co2+ sites) that lower the OH− adsorption energy as determined by the density functional theory (DFT) calculation. The resulting CoCx@NiCo-LDH/NF electrode exhibits an ultrahigh rate capability (2330 mF cm−2 at 0.3 mA cm−2, with capacitance retention of 51.5 % at 30 mA cm−2) and remarkable cycling performance (capacitance retention of 81.6 % after 10,000 cycles). Additionally, the assembled asymmetric devices deliver an extremely high energy density of 246 μWh cm−2 at the power density of 798 μW cm−2, with 87.8 % capacitance retention after 10,000 cycles at 8 mA cm−2. Overall, this study presents a simple yet effective strategy to construct high-performance battery-like electrodes for potential applications in energy storage, transportation, and communication.

Endowing V6O13/CeVO4 heterojunction with substantial improvements on zinc ion storage performance

The slow ion diffusion stemming from the high charge density of Zn2+ renders zinc-ion batteries (ZIBs) low reaction kinetics and cyclic stability. Herein, a series of nanoflake-shaped V6O13/CeVO4 composites containing oxygen vacancies with different feed ratios of cerium and vanadium are synthesized by one-step hydrothermal method. The design of V6O13-CeVO4 heterostructure can generate the built-in electric field, offering an additional driving force to accelerate electron transfer and thus enhance its overall electrical conductivity. Significantly, the enhanced adsorption energy of Zn2+ on the heterointerfaces is beneficial to stimulate the fast reaction kinetics. The induced abundant oxygen vacancies serve as the ample active sites to facilitate ion transport. Therefore, the construction of heterojunction and vacancy can be considered as a dual-drive strategy to promote the electrochemical performance. As a result, the ZIBs cathode based on the optimal V6O13/CeVO4-6 heterostructure exhibits an ultra-high capacity (280 mA h g−1 after 300 cycles at 1 A/g), rate capability, and long-cycle life (206.4 mA h g−1 after 4000 cycles at 10 A/g with a 78.2% capacity retention). Together with the deep investigation on the storage mechanism and kinetics analysis of Zn2+ through a series of ex situ characterizations and theoretical calculation, this study is valuable for the development of new vanadium-based cathodes for high-performance ZIBs.

Manipulating polysulfide catalytic conversion through edge site construction, hybrid phase engineering, and Se anion substitution for kinetics-enhanced lithium-sulfur battery

Applying catalytic materials in Li-S batteries can effectively enhance the lithium polysulfides (LiPSs) conversion kinetics and suppress the severe LiPSs shuttle effect. However, optimizing the catalytic activity of catalysts through synchronous geometrical/electronic structure design remains challenging. Here, we demonstrate that the highly stable MoSSe@graphene (MoSSe@rGO) electrocatalyst, with vertically aligned geometry configuration, 1T/2H hybrid phase engineering, and Se anion substitution, can effectively trap and catalyze the LiPSs conversion. The vertically grown MoSSe nanosheets on rGO expose abundant active edge sites and ensure that every MoSSe nanosheet participates in chemical adsorption and catalytic reaction. The 1T/2H hybrid phase possesses high electronic conductivity, enabling direct and fast adsorption/catalyzing of LiPSs. Moreover, the Se anion substitution in 1T/2H-MoS2 enhances the Li+ diffusion kinetics and accelerates the LiPSs redox reaction. Due to the synergy of geometrical (edge sites) and electronic (1T/2H phase and Se substitution) engineering, the 1T/2H-MoSSe@rGO affords strong chemical adsorption and enhanced bidirectional catalytic activity toward LiPSs, endowing the Li-S batteries with ultra-small voltage hysteresis (125 mV at 0.2 C), ultrahigh rate capability (747.2 mAh g−1 at 3 C), and long cycle life over 500 cycles. Further, theoretical simulation and ex-situ measurements verify the catalysis mechanism of 1T/2H-MoSSe@rGO and demonstrate its ultra-stable operation upon cycling. This work provides a geometrical/electronic multi-construction strategy to design superior Li-S catalysts.

Synthesis of Porous Bowl-like LiFePO4/C Composite with Ultrahigh Rate Capability

Synthesis of Porous Bowl-like LiFePO4/C Composite with Ultrahigh Rate Capability

Achieving Practical High-Energy-Density Lithium-Metal Batteries by a Dual-Anion Regulated Electrolyte.

Lithium-metal batteries (LMBs) using lithium-metal anodes and high-voltage cathodes have been deemed as one of the most promising high-energy-density battery technology. However, its practical application is largely hindered by the notorious dendrite growth of lithium-metal anodes, the fast structure degradation of the cathode, and insufficient electrode-electrolyte interphase kinetics. Here, a dual-anion regulated electrolyte is developed for LMBs using lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluoro(bisoxalato)phosphate (LiDFBOP) as anion regulators. The incorporation of TFSI- in the solvation sheath reduces the desolvation energy of Li+ , and DFBOP- promotes the formation of highly ion-conductive and sustainable inorganic-rich interphases on the electrodes. Significantly enhanced performance is demonstrated on Li||LiNi0.83 Co0.11 Mn0.06 O2 pouch cells, with 84.6% capacity retention after 150 cycles in 6.0 Ah pouch cells and an ultrahigh rate capability up to 5 C in 2.0 Ah pouch cells. Furthermore, a pouch cell with an ultralarge capacity of 39.0 Ah is fabricated and achieves an ultrahigh energy density of 521.3Wh kg-1 . The findings provide a facile electrolyte design strategy for promoting the practical utilization of high-energy-density LMBs.

Mechanochemical Pretreated Mn+1AXn (MAX) Phase to Synthesize 2D-Ti3C2Tx MXene Sheets for High-Performance Supercapacitors.

Two-dimensional (2D) MXenes sheet-like micro-structures have attracted attention as an effective electrochemical energy storage material due to their efficient electrolyte/cation interfacial charge transports inside the 2D sheets which results in ultrahigh rate capability and high volumetric capacitance. In this article, Ti3C2Tx MXene is prepared by a combination of ball milling and chemical etching from Ti3AlC2 powder. The effects of ball milling and etching duration on the physiochemical properties are also explored, as well as the electrochemical performance of as-prepared Ti3C2 MXene. The electrochemical performances of 6 h mechanochemically treated and 12 h chemically etched MXene (BM-12H) exhibit an electric double layer capacitance behavior with an enhanced specific capacitance of 146.3 F g-1 compared to 24 and 48 h treated samples. Moreover, 5000-cycle stability tested sample's (BM-12H) charge/discharge show increased specific capacitance due to the termination of the -OH group, intercalation of K+ ion and transformation to TiO2/Ti3C2 hybrid structure in a 3 M KOH electrolyte. Interestingly, a symmetric supercapacitor (SSC) device fabricated in a 1 M LiPF6 electrolyte in order to extend the voltage window up to 3 V shows a pseudocapacitance behavior due to Li on interaction/de-intercalation. In addition, the SSC shows an excellent energy and power density of 138.33 W h kg-1 and 1500 W kg-1, respectively. The ball milling pre-treated MXene exhibited an excellent performance and stability due to the increased interlayer distance between the MXene sheets and intercalation and deintercalation of Li+ ions.

An In Situ Electrochemical Amorphization Electrode Enables High‐Power High‐Cryogenic Capacity Aqueous Zinc‐Ion Batteries

AbstractQuick‐charge technology is of great significance for the development of aqueous zinc‐ion batteries. In this study, an unreported in situ electrochemical amorphization mechanism is highlighted to unlock the ultrafast‐kinetics electrode. Multiple characterizations, density functional theory calculation, and molecular dynamic simulation are applied to uncover the storage mechanism of electrodes, as well as the evolution of structure, and reaction kinetics after reconstruction. As revealed, the long‐range ordered ZnV2O4 crystalline can be reconstructed to a short‐range ordered Zn0.44V2O4 electrode, which exhibits significantly improved active sites, shortened diffusion path, and enhanced zinc ions capture ability. Notably, by pairing with the modified Zn anode, it can display ultrahigh rate capability (212 mAh g−1 at 50 A g−1) with a maximum power density of 23.2 kW kg−1, as well as good cycle performance (217.2 mAh g−1 after 3000 cycles at 20 A g−1). Unexpectedly, such reconstructed amorphous electrodes can also retain superior storage capability even at cryogenic conditions. A high specific capacity of 251 mAh g−1 can be delivered at −25°C and 1 A g−1, as well as an 84.3% capacity retention after 500 cycles. This brand‐new in‐situ electrochemical amorphization mechanism is expected to provide new insight into understanding the high‐performance aqueous zinc‐ion batteries.

Exploiting the Coordination Effect in Fe-Phenanthroline Complex for the Catalytic Carbonization of Phenanthroline toward the High Capacity Anode Grade Carbon

Aromatic organic molecules (AOMs) present an appealing precursor option for anode-grade hard carbon for sodium-ion batteries (SIBs) because of their prevalence, diverse chemical functionalities, and huge scope for nanostructure engineering at the molecular level. However, most small organic molecules decompose before actual carbonization is initiated unless reactions are carried out under high pressures or in the presence of catalysts. Herein, we report a facile carbonization of aromatic monomeric phenanthroline (phen) by exploiting the strong molecule-level coordination effect of the Fe-phen complex and in situ catalysis affected by Fe. With this carbonization strategy, we achieve better scalability with appreciable carbon yield, while carbonization of simple phen molecule returns zero carbon yields. The as-prepared N-doped microporous carbon (NMC) possesses desirable microstructural features with optimum nitrogen content to be employed as an anode for SIB. As an anode, the NMC delivers a high reversible capacity of 271 mAh g–1 at 100 mA g–1, an ultrahigh rate capability of 101 mAh g–1 at 1 A g–1, and a stable cycle life. The galvanostatic intermittent titration technique (GITT) depicts sodium ion diffusion coefficients of the order of ∼10–13 (cm2 s–1) in the intercalation region, which implies a faster sodium ion diffusion rate compared to most of the reported hard carbons. Given the vast diversity of AOMs, this work encourages new research interests to produce advanced carbon materials with nanostructure engineering at the molecular level for sodium-ion battery applications.

Engineering single-atom catalysts as multifunctional polysulfide and lithium regulators toward kinetically accelerated and durable lithium-sulfur batteries

Developing electrocatalyst to ameliorate the shuttling effect of lithium polysulfides (LiPSs), sluggish sulfur redox reaction kinetics and the rampant dendrite growth is of paramount importance for lithium-sulfur (Li-S) batteries. Yet still, the utilization of the most mainstream traditional metal electrocatalytic nanoparticles is far below expectation. Herein, we engineer an exclusive single-atom catalyst with planar Co-N4 coupling of nitrogen-doped graphene mesh (SA-Co/NGM) to achieve exceptional atom utilization efficiency for catalytic conversion of LiPSs. High surface area and ultra-thin two-dimensional texture can not only accommodate high concentration monodispersed lithiophilic atomic Co sites, but also guarantee homogenize high-flux Li ion transport, alleviating the formation of Li-dendrites. Critically, the maximized exposure of Co-N4 as a regulator in sulfur electrochemistry can conspicuously suppress the shuttle effect and accelerate bidirectional sulfur redox kinetics via electron delocalization, as demonstrated by a judicious combination of electro-kinetic analysis, in situ spectroscopy and density functional theory (DFT) computations. As expected, the batteries based on a SA-Co/NGM modified separator achieve an ultrahigh rate capability, exceptionally long cycle life and a distinguished favorable areal capacity under high sulfur loading. This work provides a rational design of single-atom catalysts for kinetics-boosted electrocatalysis towards long-lasting Li-S batteries.

Turbostratic Lattice and Electronegativity Modification Jointly Enabled an Ultra-High-Rate and Long-Lived Carbon Anode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are considered as a promising technology alternative to lithium-ion batteries due to more abundance of potassium than lithium and a lower redox potential of K/K+ than that of Na/Na+. The critical limitation in PIBs is the electrode with poor rate capability and cycling stability induced by the sluggish reaction kinetics and large volume change during potassiation and depotassiation. In this work, we report a turbostratic lattice iodine-doped carbon (TLIC) nanosheet as an advanced innovative anode for PIBs displaying fast charge/discharge and electrode stability. The turbostratic lattice caused by doping of large-sized iodine and the unique charge transfer between iodine/carbon atoms creates more active sites and a shorter transport distance for K ions, improves the electrochemical activity, promotes rapid ion diffusion, and enhances pseudocapacitive behavior. The TLIC exhibits a high capacity of 433.5 mAh g-1 at 50 mA g-1, an ultrahigh rate capability of 162.1 mAh g-1 at 20 A g-1, and an excellent capacity retention of ∼96% (206 mAh g-1) after 4000 cycles. The combination of turbostratic lattice and pseudocapactive storage is an effective approach to designing carbon electrodes with the transformational performance of high capacity, rate performance, and long lifetime for practical applications of PIBs.

Hexaindium Heptasulfide/Nitrogen and Sulfur Co-Doped Carbon Hollow Microspindles with Ultrahigh-Rate Sodium Storage through Stable Conversion and Alloying Reactions.

Group IIIA-VA metal sulfides (GMSs) have attracted increasing attention because of their unique Na-storage mechanisms through combined conversion and alloying reactions, thus delivering large theoretical capacities and low working potentials. However, Na+ diffusion within GMSs anodes leads to severe volume change, generally representing a fundamental limitation to rate capability and cycling stability. Here, monodispersed In6 S7 /nitrogen and sulfur co-doped carbon hollow microspindles (In6 S7 /NSC HMS) are produced by morphology-preserved thermal sulfurization of spindle-like and porous indium-based metal organic frameworks. The resulting In6 S7 /NSC HMS anode exhibits theoretical-value-close specific capacity (546.2 mAhg-1 at 0.1Ag-1 ), ultrahigh rate capability (267.5mAhg-1 at 30.0Ag-1 ), high initial coulombic efficiency (≈93.5%), and ≈92.6% capacity retention after 4000 cycles. This kinetically favored In6 S7 /NSC HMS anode fills up the kinetics gap with a capacitive porous carbon cathode, enabling a sodium-ion capacitor to deliver an ultrahigh energy density of 136.3Whkg-1 and a maximum power density of 47.5kWkg-1 . The in situ/ex situ analytical techniques and theoretical calculation both show that the robust and fast Na+ charge storage of In6 S7 /NSC HMS arises from the multi-electron redox mechanism, buffered volume expansion, negligible morphological change, and surface-controlled solid-state Na+ transport.

In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries.

As a promising candidate for large-scale energy storage, aqueous zinc-ion batteries (ZIBs) still lack cathode materials with large capacity and high rate capability. Herein, a spherical carbon-confined nanovanadium oxynitride with a polycrystalline feature (VNxOy/C) was synthesized by the solvothermal reaction and following nitridation treatment. As a cathode material for ZIBs, it is interesting that the electrochemical performance of the VNxOy/C cathode is greatly improved after the first charging process viain situ electrochemically oxidative activation. The oxidized VNxOy/C delivers a greatly enhanced reversible capacity of 556 mAh g-1 at 0.2 A g-1 compared to the first discharge capacity of 130 mAh g-1 and a high capacity of 168 mAh g-1 even at 80 A g-1. The ex situ characterizations verify that the insertion/extraction of Zn2+ does not affect the crystal structure of oxidized VNxOy/C to promise a stable cycle life (retain 420 mAh g-1 after 1000 cycles at 10 A g-1). The experimental analysis further elucidates that charging voltage and H2O in the electrolyte are curial factors to activate VNxOy/C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VNxOy/C to VNx-mOy+2m/C and then resulting in considerably strengthened rate performance and improved Zn2+ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.

Ultra-high rate capability of in-situ anchoring FeF3 cathode onto double-enhanced conductive Fe/graphitic carbon for high energy density lithium-ion batteries

The FeF3 cathode shows some promising potentials for lithium-ion batteries (LIBs) because of its high theoretical capacity induced by conversion reactions, but the poor electrical conductivity and inferior reaction kinetics severely limit battery performance. Herein, the FeF3 nanoparticles embedded in double Fe/graphitized carbon (GC) matrices (FeF3/Fe/GC) are fabricated using low-temperature fluorination, where the spongy structure originates from the unique self-expanding process. It was found that the pseudocapacitive contribution of the optimized FeF3/Fe/GC nanocomposite is as high as 98%, which contributes to a high specific capacity of 151.2 mA h g−1 at a high rate of 10 C after 1000 cycles, with a capacity decay rate of only 0.03% per cycle. Surprisingly, even at an ultra-high rate of 100 C, the composite cathode still delivers a discharge capacity as high as 106.7 mA h g−1, which is superior to those reported in the previous studies. The excellent cycle stability and ultra-high rate performance can be attributed to the intimate contact between double Fe/GC matrices and ultrafine FeF3 nanoparticles, which can effectively reduce the diffusion barrier of ions and electrons to enhance the redox pseudocapacitive process. It has been demonstrated that optimizing the pseudocapacitive behavior may be a simple yet effective strategy to obtain the cathode materials with ultra-high rate capability.

Hybrid nanotubes constructed by confining Ti0.95Nb0.95O4 quantum dots in porous bamboo-like CNTs: superior anode materials for boosting lithium storage.

Current commercial lithium ion battery (LIB) anodes comprising graphite and Li4Ti5O12 inevitably suffer from safety risk and low energy density. Hence, a novel anode material of Ti0.95Nb0.95O4/C hybrid nanotubes was developed via a modified sol-gel method combined with subsequent calcination. The hybrids consist of Ti0.95Nb0.95O4 quantum dots that are homogeneously embedded in the walls of porous bamboo-like CNTs. The high capacity feature of multiple redox couples of Ti-Nb-O based anodes is demonstrated by ex situ XPS in the hybrids. With the advantages of stimulative lithium storage, increased conductivity and robust mechanical properties due to the unique hybrid structure, the hybrids exhibit a high capacity (516.8 mA h g-1 at 0.2 A g-1), superior long-term cycling stability (142.7 mA h g-1 at 5 A g-1 after 3000 cycles) and an ultra-high rate capability (234.6 mA h g-1 at 1 A g-1 and 125 mA h g-1 at 8 A g-1). Meanwhile, the hybrids showed superior electrochemical performance compared with the reported Li4Ti5O12 and Ti-Nb-O based anodes. Furthermore, the GITT measurements revealed the fast Li+ transport for the charge-discharge processes of the hybrids. Such prominent merits of the Ti0.95Nb0.95O4/C hybrid nanotubes make them more likely candidates that can replace graphite and Li4Ti5O12 anodes in LIBs.