Low Ion Diffusion Research Articles

Synergistic structure and oxygen-vacancies engineering of lithium vanadate for kinetically accelerated and pseudocapacitance-dominated lithium storage

The high reversibility, capacity, and safety make lithium vanadate (LVO) an attractive anode to Li-ion batteries, yet they still suffer from the low intrinsic electrical conductivity and ion diffusion rate. Modulating the electronic and crystal structure of materials by vacancies engineering could significantly affect the lithium storage performance. Herein, high concentration of oxygen-vacancies incorporated Li3VO4 nanowires (HLVO) were prepared to make up conductivity and ion diffusion kinetics of LVO as a competitive fast-charging anode. The oxygen-vacancies were derived from the controllable oxidation of local V4+ ions via the thermal treatment, enabling the redistribution of electrons and optimized charge‐transport properties of LVO on the basis of the experimental results and theoretical calculations. The reduced reaction energy barriers, enhanced Li-ion diffusion, improved electrical conductivity, and additional active sites induced by oxygen-vacancies drastically accelerate the redox kinetics, enhancing the capacitive behavior. Thus, the HLVO anode delivers superior electrochemical performance with large specific capacities of 553.8 mA h g−1, exceptional rate capacity of 312.2 mA h g−1 even at 4.0 A g−1 and excellent cycling stability. This finding provides the credence to the prospect of vacancy engineering contributing to develop the matter-of-fact transition metal oxides as high-performance anodes for Li-ion batteries.

Flexible construction of three-dimensional continuous conductive structure by hollow carbon sphere and CNT for promoted ions transport in flow-electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) emerges as a promising desalination technique, characterized by its unlimited desalination capacity, seamless operation, and easy scalability. However, challenges such as discontinuous electronic network, inadequate dispersion of suspended carbon particles, and hindered electron/ion transport pathways have impeded the full potential of FCDI. This study addresses the above issues by synergistically leveraging the advantage of hollow carbon sphere (HCS) and CNT to construct a flexible, continuous three-dimensional conductive network (HCS@CNT) as the flow-electrode for FCDI. The incorporation of HCS substantially improves the fluidity and effective collision of the flow-electrode slurry. Simultaneously, the bridging effect of CNT facilitates smooth ion transport routes and rapid electron/ion transfer. Moreover, the spherical structure of HCS as a node can effectively alleviate the agglomeration of CNT due to its inherent good fluidity. As a result, the meticulously designed HCS@CNT flow-electrode demonstrates outstanding rheological behavior with excellent hydrophilicity, a large specific capacitance, and low ion diffusion resistance. During desalination tests, the HCS@CNT flow-electrode exhibited a high average salt removal rate (0.56 µmol min−1 cm−2), appropriate energy-normalized removal salt (15 µmol J−1), and notable charge efficiency (89 %) in a 1 g L-1 NaCl solution. Impressively, it maintained good stability and continuity over a continuous 10-hour desalination process, showcasing substantial potential for treating highly concentrated saline water. In addition, density functional theory (DFT) calculations provided additional insights, confirming that the construction of HCS@CNT facilitated interfacial charge transfer and electron transport from HCS to CNT. This innovative approach sheds light on enhancing electron/ion transfer by harnessing the unique structural characteristics of the flow-electrode.

Surface modification boosting amorphous vanadium oxides anode toward stable and rapid sodium ion storage

Sodium-ion batteries (SIBs) are receiving increasing attention for their flexibility and low cost, showing potential to replace the well-studied lithium-ion batteries (LIBs). Compared to lithium ion, sodium ion possesses larger radius, leading to the volume expansion during insertion/extraction. Therefore, amorphous anode materials with low volume expansion and fast ion diffusion are more suitable for the SIBs. Among them, vanadium-based oxides are regarded as promising alternatives according to their advantages of high theoretical capacity, abundance, and low cost. However, the shortcomings such as poor conductivity, aggregation, and pulverization restrict their development as the anode of SIBs. Herein, the vanadium oxide is modified by graphene sheets, and a VOx/rGO-5 % composite is reported as the anode material for SIBs, which has promising electrochemical performance. The VOx/rGO-5 % anode remains a discharge specific capacity of 185 mAh g−1 over 400 cycles under 0.5 A g−1. Meanwhile, VOx/rGO-5 % anode also exhibits a rate capability of 189 mAh g−1 at 2 A g−1. Moreover, the sodium ion storage kinetics in VOx/rGO-5 % is investigated. This work affirms the possibility of vanadium-based oxides being the anode materials of SIBs.

Flexible carbon nanofibers with multichannel and porous structure as freestanding anode for excellent sodium storage

Hard carbon is the most commonly used anode material for sodium-ion batteries (SIBs). However, it has the drawback of having inferior capacity at high rates due to low ion-diffusion kinetics. Rational design of hard carbon with a hierarchical pore structure and multichannel structure can address this issue. Herein, we introduced an electrospinning method for preparing flexible carbon nanofibers as a freestanding anode for SIBs. The pore structure can be modified by adjusting the amount of Pluronic F-127 (F127) added to the spinning solution. This strategy results in the formation of numerous micropores and mesopores, along with pore-derived defects, effectively increasing the number of sites available for sodium storage. The existence of multichannel facilitates the migration of sodium ions. PCNF-1 possesses an appropriate pore structure with the least amount of added pore-forming agent exhibits exceptional electrochemical performance. It delivers a reversible capacity of 286 mA h g−1 at a current density of 50 mA g−1 with an initial Coulombic efficiency (ICE) of 82 %. At 5 A g−1, it delivers a capacity of 211 mAh g−1. Furthermore, it demonstrates a high retention rate of 79 % at 1 A g−1 even after 1000 cycles. Notably, in full-cell tests, PCNF-1, when paired with a Na3V2(PO4)3 cathode, achieved a specific capacity of 253 mA h g−1 in the second cycle and maintained a retention rate of 51 % after 200 cycles at a current density of 1 A g−1.

Enhancing Zn2+ Storage Performance by Constructing the Interfaces Between VO2 and Co-N-C Layers.

Vanadium oxides have aroused attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their low cost and high safety. However, low ion diffusion and vanadium dissolution often lead to capacity decay and deteriorating stability during cycling. Herein, vanadium dioxides (VO2) nanobelts are coated with a single-atom cobalt dispersed N-doped carbon (Co-N-C) layer via a facile calcination strategy to form Co-N-C layer coated VO2 nanobelts (VO2@Co-N-C NBs) for cathodes in AZIBs. Various in-/ex situ characterizations demonstrate the interfaces between VO2 layers and Co-N-C layers can protect the VO2 NBs from collapsing, increase ion diffusion, and enhance the Zn2+ storage performance. Additional density functional theory (DFT) simulations demonstrate that Co─O─V bonds between VO2 and Co-N-C layers can enhance interfacial Zn2+ storage. Moreover, the VO2@Co-N-C NBs provided an ultrahigh capacity (418.7mAhg-1 at 1Ag-1), outstanding long-term stability (over 8000 cycles at 20Ag-1), and superior rate performance.

ZnONR Microstructure Modification and their Potential for High Reversibillity Performance of AC-Mn<sub>2</sub>O<sub>3</sub> Supercapacitor

One of Indonesia's most significant issues with technological growth is the lack of electrical energy storage devices. Active materials have low electrical conductivity, accessibility, and ion diffusion. Therefore, it is urgently required to study the combination of higher electrical conductivity ZnO and high surface area of AC-Mn2O3. However, ZnO nanorods (ZnONR) can be modified from ZnO nanoparticles (ZnONP). The structure modification may increase energy density due to having a higher surface area than ZnONP. Three different electrodes with AC-Mn2O3 addition various spin coated of 1000 rpm (MZnONR1), 2500 rpm (MZnONR2), and 3000 rpm (MZnONR3). The electrodes were then packaged in a sandwich flat symmetric supercapacitor. The characterization was carried out using X-RD, SEM-EDX cross-section, FTIR, and Cyclic Voltammetric. It is obtained that the highest specific capacitance showed by symmetric supercapacitor MZnONR1 with low speed of spin coating. We also found that the greater the deposited ZnNR content, the lowest thickness until 43.76 μm, the crystallinity until 62% and the highest porosity until 79%. This shows that the MZnONR1 sample exhibits the best electrochemical performance, which is supported by its morphological properties. It is shown that the higher the Zn content, the stability performance AC-Mn2O3 supercapacitor higher. ZnONR1 sandwich flat symmetric supercapacitor have a specific capacitance 0.0086 Fg-1 with an 0.00433 Whg-1 energy density. Furthermore, it was found that the addition of the AC-Mn2O3 increased 2800x compared to the ZnONR1, which reached 28.04 Fg-1 and an 14.09 Whg-1 of capacitance specific and energy density, respectively.

Flexible CNT@Porous carbon sponge cathode with large mesopores for high-rate zinc-ion hybrid capacitors

Zinc ion hybrid capacitor (ZIHC) is promising in achieving both high energy density and power density at a large scale. However, the poor rate capability of carbon-based cathodes limits the fast-charging performance of ZIHCs due to mismatch between micropores in the carbon matrix and large hydrated Zn ions. Herein, we prepare a flexible carbon nanotube@porous carbon (CNT@PC) sponge with large mesopores (average mesopore size of 14.3 nm), which can achieve a high specific capacity of 175.3 mAh/g (0.1 A/g) and a high rate capability of 93.1 mAh/g (50 A/g). The effects of pore size of PC cathodes on rate capability are investigated by various electrochemical methods. Large mesopores facilitate rapid ion transport with low IR drop and ion diffusion resistance, and high ion diffusion coefficient and surface capacitive contributions. CNT@PC sponge-based ZIHC delivers high energy densities of 150.8 Wh/kg (80 W/kg) and 74.4 Wh/kg (40 kW/kg). The flexible pouch cell can maintain high performance in various bending states. Multilayer stacked sponges show increased mass loading and high areal capacities. This work provides insight into the pore structure design for high-rate ZIHC PC cathodes.

Hierarchical porous LiVO3/N-doped carbon hollow microspheres as a high-performance anode for lithium-ion batteries

LiVO3 has been considered as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, the rate capability and cycling stability of LiVO3 are limited by its poor electronic conductivity and low ion diffusion efficiency. In this work, hierarchical porous LiVO3/N-doped carbon hollow microspheres (LiVO3/NC HSs) are designed and synthesized via a simple spray drying method. As an anode material for LIBs, LiVO3/NC HSs show high reversible capacity (557.6 mAh g−1 at 0.5 A g−1) and excellent rate capability (411.5 mAh g−1 at 2.0 A g−1). Even at a high current density of 10.0 A g−1, a capacity retention of 77.0 % can be achieved over 4000 cycles. Such outstanding performance can be attributed to the unique structure, in which LiVO3 particles are in-situ encapsulated in the N-doped carbon network to enhance the electronic conductivity, and the porous and hollow structure enable rapid ion transport and accommodate large volume changes. This work provides novel insights into the design of vanadium-based materials for LIBs.

Co/S co-doped Li4Ti5O12 as lithium-ion batteries anode for high-rate

The low capacity and low ion diffusion coefficient are issues that need further addressed in the practical application of Li4Ti5O12 (LTO) at high-rate. In this study, Co/S co-doped nano-LTO was prepared as an anode material for lithium-ion batteries using a sulfur-cobalt synergistic strategy. The XRD and XPS results showed that Co ions were doped into the Ti sites of LTO, while S ions were doped into the Ti and O sites. And the cell volume was expanded by Co/S co-doping, which was beneficial for inserting more Li+ into the 8a site in nano-LTO to increase the capacity. Meanwhile, the Co/S co-doping increased the Ti3+/Ti4+ ratio to improve the electronic conductivity, which was beneficial for electron transport. With the synergistic effect of ion co-doping and nanosizing, the Li+ diffusion coefficient was increased from 2.75 × 10−13 to 2.02 × 10−11 cm2 s−1, resulting in the first discharge-specific capacity of 163, 158.6 and 146.5 mA h/g for LPCS at 10 C, 20 C and 50 C. And the capacity retention rate of LPCS was 85.3 % after 1000 cycles at 20 C; at this time, the discharge-specific capacity remained at 135.3 mA h/g at 20 C, which was 1.43 times that of LTO.

Efficient Self-Assembly Preparation of 3D Carbon-Supported Ti3 C2 Tx Hollow Spheres for High-Performance Potassium Ion Batteries.

MXenes are considered a promising negative electrode material for potassium ion batteries (PIBs) in view of their low potassium ion diffusion barrier and excellent electrical conductivity. However, the stacking phenomenon in practical applications severely reduces their active surface and leads to slow K+ diffusion. Herein, a facile composite template method is proposed to construct stacking-resistance 3D carbon-supported Ti3 C2 Tx (3D-C@Ti3 C2 Tx ) hollow spheres. Due to the unique structure, when used as a negative electrode material, as-prepared 3D-C@Ti3 C2 Tx hollow spheres show not only improved rate capability with 160.4 mAh g-1 at 100mA g-1 and 133.7 mAh g-1 at 500mA g-1 , but also stable cycling performance with 142.5 mAh g-1 specific capacity remained at 2 A g-1 after 4200 cycles. Furthermore, the full cells with 3D-C@Ti3 C2 Tx anode can operate stably for 1000 cycles at 100mA g-1 . Moreover, the linear fit analysis demonstrates that 3D-C@Ti3 C2 Tx hollow spheres have a fast and stable capacitive potassium storage mechanism. This method is simple and easy to implement, which provide a feasible path to solve the stacking problem of 2D materials.

Fast Ionic Conducting Hydroxyapatite Solid Electrolyte Interphase Enables Ultra-Stable Zinc Metal Anodes.

Zn metal has been extensively utilized as an anode in aqueous zinc-ion batteries attributed to its affordable cost and superior theoretical capacity. Nevertheless, the presence of dendrites and undesirable side reactions poses challenges to its widespread commercialization. To address these issues, herein, a surface coating composed of hydroxyapatite (HAP) was developed on the Zn anode to create an artificial solid electrolyte interphase. After the application of a hydroxyapatite layer, dendrites and corrosion of the Zn anode are sufficiently inhibited. Furthermore, the hydroxyapatite interphase with a low ionic diffusion barrier enables fast anodic redox kinetics. Consequently, the Zn@HAP symmetric cell possesses a durable lifespan over 2000 h at 1 mA cm-2, while maintaining minimal polarization. Moreover, the practical feasibilities of the Zn@HAP anode are also manifested in full batteries combined with MnO2 cathodes, exhibiting exceptional cycling performance up to 500 cycles at 1 A g-1 and excellent rate capability with a retention of 109 mAh g-1 at 5 A g-1.

Asymmetric Trihalogenated Aromatic Lithium Salt Induced Lithium Halide Rich Interface for Stable Cycling of All-Solid-State Lithium Batteries.

Solid polymer electrolytes (SPEs) are the key components for all-solid-state lithium metal batteries with high energy density and intrinsic safety. However, the low lithium ion transference number (t+) of a conventional SPE and its unstable electrolyte/electrode interface cannot guarantee long-term stable operation. Herein, asymmetric trihalogenated aromatic lithium salts, i.e., lithium (3,4,5-trifluorobenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiFFF) and lithium (4-bromo-3,5-difluorobenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiFBF), are synthesized for polymer electrolytes. They exhibit higher t+ values and better compatibility with Li metal than conventional lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Due to the trihalogenated aromatic anions, LiFFF- and LiFBF-based electrolytes are prone to generate an LiF- and LiBr-rich solid electrolyte interphase (SEI), therefore increasing the stability of the solid electrolyte/anode interface. Particularly, LiFBF could induce a LiF/LiBr hybrid SEI, where LiF shows a high Young's modulus and high surface energy for homogenizing Li ion flux and LiBr exhibits an extremely low Li ion diffusion barrier in the SEI layer. As a result, the Li/Li symmetric cells could remain stable for more than 1200 h without a short circuit and the LiFePO4/Li batteries showed superb electrochemical performance over 1200 cycles at 1 C. This work provides valuable insights from the perspective of lithium salt molecular structures for high-performance all-solid-state lithium metal batteries.

Electrolyte Design for Intermediate-Temperature Na-S Batteries with High Energy Density

The conventional high-temperature sodium sulfur battery is an attractive technology for grid-level energy storage due to its low cost, high energy density and long cycle life. However, this system operates at 300-350 oC, which not only increases cost, but also accelerates degradation and causes potential safety issues. On the other side, Na-S batteries working at intermediate temperatures (e.g., 100-150 oC) have a much worse kinetics due to the formation of solid Na2S2 and Na2S with low ionic diffusivity and electronic conductivity. In this study, we have developed a new electrolyte solvent that can dissolve all sulfides and polysulfides, which avoids the poor kinetics in Na2S2 and Na2S, and allows Na-S batteries to operate at ~75 oC. Based on the 1 molL−1 sulfur catholyte, a high specific capacity of 1640 mAhg−1 is achieved at 0.13 mAcm−2. When increased to the 4 molL−1, the capacity is achieved 830 mAhg−1 and decays only 0.029%/cycle over 250 cycles at 1 mAcm−2. Such a system has potential applications for long-duration energy storage.

Synthesis of nanosphere-like vanadium selenide cathode for high performance asymmetric hybrid supercapacitors

Vanadium selenide electrodes exhibit promising candidates for supercapacitor application, owing to their exotic electronic properties. Exploring more facile synthesis strategies undoubtedly promote the development of vanadium selenide electrodes that from laboratory to practical application, while it was still a challenging. In this work, we provided a facile electrodeposition method to prepare vanadium selenide cathodes for asymmetric hybrid supercapacitors. By controlling the deposition technique, nanosphere-like vanadium selenide cathode or microrod-like selenium were achieved. Electrochemical tests indicated that the prepared vanadium selenide cathode exhibited high capacitance feature (921.6 F/g at a current density of 1 A/g), due to the high ion diffusion ability in the vanadium selenide nanosphere electrode. The charge storage mechanism and reaction kinetics of the prepared vanadium selenide were further investigated and results indicated a mixed effect of pseudocapacitance and battery-type together contributed to the energy storage, meaning a hybrid capacitor. The further assembly hybrid supercapacitor exhibited excellent rate performance and good cycling stability. Moreover, density functional theory calculations demonstrated that the electrode material possessed appropriate adsorption energy of OH− with a low ion diffusion barrier.

Constructing N, Se co-doped carbon nanofibers encapsulated with hollow FeSe2 nanospheres as electrodes for energy storage

Iron selenide (FeSe2), a p-type narrow band gap (1.0 eV) semiconductor, has been considered as a potential electrode material for electrochemical energy storage owing to its many benefits, including quick electron transfer, excellent electrical conductivity and exceptional theoretical specific capacity. Nevertheless, the volumetric expansion, agglomeration, low ion-diffusion capacity and other inadequacies in the process of discharging and charging. Therefore, FeSe2 is far short of high initial coulomb efficiency, long-cycle stability, and excellent rate performance. The greatest obstacle to the practical use of energy storage systems is these drawbacks. Herein, the electrospinning and a thermally-induced selenization route are adopted to encapsulate the FeSe2 hollow nanospheres into the intertwined Se, N co-doped carbon nanofibers (Se, N-FeSe2CNFs). Density functional theory calculation delivers that Se, N-FeSe2CNFs nanocomposite presents extremely low bandgap and high density of states at the Femi level, demonstrating significantly increased conductivity. When assembling into the all-solid-state symmetric supercapacitors (ASSSCs), the Se, N-FeSe2CNFs ASSSCs provide a remarkable specific capacity of 330.2 F g−1 and maintain 92.0% after 5000 cycles at 2 A g−1. Meanwhile, the resistance of charge transfer decreases from 0.73 Ω (FeSe2) to 0.28 Ω (Se, N-FeSe2CNFs). Moreover, the Se, N-FeSe2CNFs ASSSCs deliver 128.6 Wh kg−1 (energy density) at about 800 W kg−1 (power density). Additionally, the Se, N-FeSe2CNFs anodes also have outstanding reversible capacity (549.5 mAh g−1 at 0.1 A g−1) and stability of long-circulation (481.3 mAh g−1 after 100 circles and 480.9 mAh g−1 after 200 circles at 0.1 A g−1) for sodium-ion batteries (SIBs). The superb property of energy storage can be due to the encapsulated structure that can maintain the integrity of structures for electrodes during electrochemical reactions and the Se, N heteroatoms doped CNFs that can conducive to ions/charges transport and storage. The designed encapsulated structure and synthesis approach have broad application prospects in electrochemical energy storage.

Enhanced electrical conductivity and lithium ion diffusion rate of LiFePO4 by Fe site and P site doping

Lithium iron phosphate (LiFePO4) with an olivine-type structure has garnered great interest due to its electrochemical activity. It is considered one of the most promising cathode materials for lithium-ion batteries because of its high discharge platform, large theoretical capacity, and excellent cycling performance and stability. However, the typical crystal structure of LiFePO4 restricts the formation of efficient electron conduction pathways and hampers the embedding and removal motion of lithium ions, resulting in low electron conductivity and a low ion diffusion rate. The experimental results show that element doping can reduce the activation energy of diffusion, increase the diffusion rate of lithium ions, improve the rate capability of lithium-ion batteries, and contribute to the improvement of its conductivity. In this work, the electronic structure and diffusion mechanism of a S/Co/Mn co-doped LiFePO4 system are systematically studied. The introduction of S, Co, and Mn atoms leads to the formation of impurity bands, resulting in a significant reduction in the bandgap from 3.593 eV to 0.190 eV, which is beneficial for improving the conductivity of LiFePO4. Moreover, the diffusion activation energy of lithium ions decreases from 0.73 eV to 0.34 eV, and the diffusion rate of lithium ions increases from 2.7 × 109 cm/s to 1.0 × 1016 cm/s. These results demonstrate that co-doping of S, Co, and Mn can effectively enhance the conductivity and diffusion rate of lithium ions in LiFePO4, providing a reliable reference for improving the electrochemical performance of lithium iron phosphate.

Electrodeposition of nanoporous conjugated copolymer on functionalized carbon cloth with extraordinary cycling stability for high-performance flexible supercapacitors

Conjugated polymers (CPs) have been widely used as pseudocapacitive materials in supercapacitors owing to their excellent conductivity and low processing costs. However, their low ionic diffusivity, sluggish charge transfer kinetics, and volume shrinkage/expansion during charging/discharging seriously reduce the capacity and cycle stability. Here, electrochemical copolymerization of aniline and 1,5-diaminoanthraquinone (DAA) was conducted on functionalized carbon cloth (FCC) to tune the structure and morphology of CPs for a better application in high-performance flexible supercapacitors. At an optimized feeding ratio, nanoporous conjugated copolymer coated FCC (FCC@PDA-AN-4) was obtained, possessing a high areal specific capacitance of 2847 mF cm−2 at 1 mA cm−2 with superior cycle life of 127.3% of its initial capacitance after 10,000 cycles.

Lithium Iron Phosphate/Carbon (LFP/C) Composite Using Nanocellulose as a Reducing Agent and Carbon Source.

Lithium iron phosphate (LiFePO4, LFP) is the most promising cathode material for use in safe electric vehicles (EVs), due to its long cycle stability, low cost, and low toxicity, but it suffers from low conductivity and ion diffusion. In this work, we present a simple method to obtain LFP/carbon (LFP/C) composites with different types of NC: cellulose nanocrystal (CNC) and cellulose nanofiber (CNF). Microwave-assisted hydrothermal synthesis was used to obtain LFP with nanocellulose inside the vessel, and the final LFP/C composite was achieved by heating the mixture under a N2 atmosphere. The resulting LFP/C indicated that the NC in the reaction medium not only acts as the reducing agent that aqueous iron solutions need (avoiding the use of other chemicals), but also as a stabiliser of the nanoparticles produced in the hydrothermal synthesis, obtaining fewer agglomerated particles compared to synthesis without NC. The sample with the best coating-and, therefore, the best electrochemical response-was the sample with 12.6% carbon derived from CNF in the composite instead of CNC, due to its homogeneous coating. The utilisation of CNF in the reaction medium could be a promising method to obtain LFP/C in a simple, rapid, and low-cost way, avoiding the waste of unnecessary chemicals.

Refined Grain Enhancing Lithium-Ion Diffusion of LiFePO4 via Air Oxidation

LiFePO4 is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO4 in the field of electric vehicles. In this paper, FePO4 with different grain sizes was prepared via the air oxidation precipitation method and then sintered to prepare LiFePO4. The refined grain can shorten the diffusion distance of Li+, accelerate the diffusion of Li+, and improve the diffusion coefficient of Li+. The results show that LiFePO4 with a smaller grain size has better electrochemical performance. The discharge capacity of the first cycle is 151.3 mAh g−1 at 1 C, and the capacity retention rate is 95.04% after 230 cycles. Its rate performance is more outstanding, not only at 0.2 C, where the discharge capacity is as high as 155 mAh g−1, but also at 10 C, the capacity fade is less, and it can still reach 131 mAh g−1. The air oxidation precipitation method reduces the production cost, shortens the production process, and prepares FePO4 with small grains, which provides a reference for further improving the properties of precursors and LiFePO4.

An inexpensive preparation of unique nano-micro porous LiFePO4 cathode with excellent rate capability for lithium-ion batteries

The application of LiFePO4 cathode material in the field of power lithium-ion batteries is seriously hampered by its poor rate performance that is triggered by its inherent poor electrical conductivity and low ion diffusion coefficient. Herein, an inexpensive and facile preparation method is developed to fabricate a novel nano-micro porous structural LiFePO4 cathode using 30 nm carbon black and iron powder as direct raw materials. It is found that the added amount of carbon black is an important factor affecting the phase and morphology of the products. Optimizing the amount of carbon black, the LiFePO4 cathode with the unique nano-micro porous structure and high specific surface area could be obtained. Such unique porous architecture with a high specific surface area can accelerate lithium-ion diffusion during charge/discharge to promote its rate performance. Meanwhile, the residual graphitized carbon derived from carbon black can not only enlarge the surface pseudocapacitance under high C rates but also enhance its electronic conductivity. Benefit from the suitable pseudocapacitive behavior and high Li+ diffusion coefficient, the LFP-1.5 electrode exhibits a discharge specific capacity of 166.27 mAh/g at 0.1C and 124.95 mAh/g at 20C, indicating prominent discharge specific capacity and excellent high-rate charge/discharge capability.