Carbon-coated Lithium Iron Phosphate Research Articles

Re-Functionalization of Aged Lithium Iron Phosphate Cathode Materials

As lithium-ion batteries continue to be implemented in everyday technologies, it is imperative to repurpose these battery materials upon their degradation. Carbon-coated lithium iron phosphate (LFP/C) is considered one of the most stable cathode materials for application in lithium-ion batteries. Due to this stability, LFP/C possesses a remarkably long cycle life of greater than 3000 cycles.1 Extended cycling of these cathode materials may result in multiple modes of degradation, including degradation of the carbon coating, and loss of contact between the cathode and the current collector.2,3 In this work, a suitable process and reagents have been selected to isolate and purify the LFP/C from the cathodes of cycled batteries. Isolating and purifying aged LFP/C materials enables the diagnosis of the mode(s) of degradation of these materials and their coatings using a variety of techniques including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy methods.Furthermore, additional work was pursued to give new life to these isolated, spent cathode materials. The addition of a coating with a relatively high lithium conductivity to the aged LFP/C particles was sought to provide a second life to these electrochemically aged materials. Half-cells were fabricated using the coated, aged LFP/C cathode materials to compare their performance to both pristine LFP/C nanoparticles and aged LFP/C nanoparticles without the addition of this custom coating. Electrochemical testing techniques such as galvanostatic cycling, cyclic voltammetry, and electrochemical impendence spectroscopy were used to probe the performance of each type of LFP/C nanoparticle as cathode materials in lithium-ion batteries. The coated, aged LFP/C particles were also characterized using transmission electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy techniques. The techniques developed herein can be used to isolate, purify, and re-functionalize other cathode materials from lithium-ion batteries. Lewerenz, M.; Munnix, J.; Schmalstieg, J.; Kabitz, S.; Knips, M.; Sauer, D. U. Systematic aging of commercial LiFePO4|Graphite cylindrical cells including a theory explaining rise of capacity during aging. Power Sources. 2017, 345, 254-263.Wang, L.; Qiu, J.; Wang, X.; Chen, L.; Cao, G.; Wang, J.; Zhang, H.; He, X. Insights for understanding multiscale degradation of LiFePO4 cathodes. eScience 2022, 2(2), 125-137.

Compensation of capacitive currents in high-throughput dielectrophoretic separators

Separation and classification are important operations in particle technology, but they are still limited in terms of suspended particles in the micrometer and nanometer size-range. Electrical fields can be beneficial for sorting such particles according to material properties. A mechanism based on strong and inhomogeneous fields is dielectrophoresis (DEP). It can be used to separate microparticles according to their material properties, such as conductivity and permittivity, by selectively trapping one particle type while the other can pass the separator. Conventional DEP-separators show either a limitation in throughput or frequency bandwidth. A low throughput limits the economical feasibility in many cases. A lower frequency bandwidth limits the variety of materials that can be sorted by DEP. To separate semiconducting particles from a mixture containing particles with higher conductivity according to their material, high frequencies are required. Possible applications are the separation of semiconducting and metallic carbon nanotubes or the separation of carbon-coated lithium iron phosphate particles from graphite in the recycling process of spent lithium-ion batteries. In this publication, we aim to display how to tune the electrical impedance of a high-throughput DEP separator based on custom-designed printed circuit boards to increase its frequency bandwidth. By adding inductors to the electrical circuit, we were able to increase the frequency bandwidth from 500 kHz to over 11 MHz. The experiments in this study act as proof-of-principle. Furthermore, a non-deterministic way to increase the impedance of the setup is shown, yielding a maximum frequency of 39.16 MHz.

Learning heterogeneous reaction kinetics from X-ray videos pixel by pixel

Reaction rates at spatially heterogeneous, unstable interfaces are notoriously difficult to quantify, yet are essential in engineering many chemical systems, such as batteries1 and electrocatalysts2. Experimental characterizations of such materials by operando microscopy produce rich image datasets3–6, but data-driven methods to learn physics from these images are still lacking because of the complex coupling of reaction kinetics, surface chemistry and phase separation7. Here we show that heterogeneous reaction kinetics can be learned from in situ scanning transmission X-ray microscopy (STXM) images of carbon-coated lithium iron phosphate (LFP) nanoparticles. Combining a large dataset of STXM images with a thermodynamically consistent electrochemical phase-field model, partial differential equation (PDE)-constrained optimization and uncertainty quantification, we extract the free-energy landscape and reaction kinetics and verify their consistency with theoretical models. We also simultaneously learn the spatial heterogeneity of the reaction rate, which closely matches the carbon-coating thickness profiles obtained through Auger electron microscopy (AEM). Across 180,000 image pixels, the mean discrepancy with the learned model is remarkably small (<7%) and comparable with experimental noise. Our results open the possibility of learning nonequilibrium material properties beyond the reach of traditional experimental methods and offer a new non-destructive technique for characterizing and optimizing heterogeneous reactive surfaces.

Enhanced stability and high-yield LiFePO4/C derived from low-cost iron precursors for high-energy Li-ion batteries

The present work focuses on developing carbon-coated lithium iron phosphate (LFP/C) cathode material from economical, high-dense Fe3O4 iron precursor resulting in good capacity, high atomic economy, and appreciable tap density for lithium-ion battery (LIB) fabrication. In addition, Fe2O3 and Fe were also used as Fe precursor for LFP/C synthesis and the results were compared with Fe3O4-LFP/C. Less gas evolution during heating and high-density precursors resulted in ~20–25% more atomic efficiency and ~1.5 to 1.8 times higher tap density over FeC2O4-LFP/C. Further, the synthesized materials have been characterized for their phase purity, morphology, and oxidation states using various characterization techniques. Electrochemical studies showed that Fe3O4-LFP/C delivers a high capacity of 137 mAh g−1 at 1C when compared with Fe2O3-LFP/C and Fe-LFP/C. Interestingly, Fe3O4-LFP/C retained 83 % capacity after 600 cycles at 1C, illustrating the long cyclic stability. In addition, Fe3O4-LFP/C with the high atomic economy (73%) and tap density equivalent to the commercially available LFP/C paves the path for affordable LFP synthesis for high-energy density batteries. Hence, the LFP/C developed in this work can be used as a cathode material for high-density electrodes that are appropriate for high-energy applications.

Prominent enhancement of stability under high current density of LiFePO4-based multidimensional nanocarbon composite as cathode for lithium-ion batteries

A facile method for synthesizing carbon-coated lithium iron phosphate (LiFePO4, LFP) and an LFP-based multidimensional nanocarbon composite to enhance the electrochemical performance of lithium-ion batteries is presented herein. Three types of cathode materials are prepared: carbon-coated LFP (LC), carbon-coated LFP with carbon nanotubes (LC@C), and carbon-coated LFP with carbon nanotubes/graphene quantum dots (LC@CG). The electrochemical performances of the LC-nanocarbon composites are compared, and both LC@C and LC@CG show improved electrochemical performance than LC. Compared with both the LC and LC@C electrodes, the LC@CG electrode exhibits the highest specific capacity of 107.1 mA h g−1 under 20C of current density, as well as higher capacities and greater stability over all measured current densities. Moreover, after 300 charge–discharge cycles, the LC@CG electrode exhibits the best stability than the LC and LC@C electrodes. This is attributable to the graphene quantum dots, which enhance the morphological stability of the LC@CG electrode during electrochemical measurements. Our findings suggest that LFP-nanocarbon composites are promising as cathode materials and highlight the potential of graphene quantum dots for improving the stability of cathodes.

Synergy and Symbiosis Analysis of Capacity-Contributing Polypyrrole and Carbon-Coated Lithium Iron Phosphate Nanostructures for High-Performance Cathode Materials

To address the existing problems of commercial inorganic cathodes, including relatively low capacity, poor rate performance, structural instability, and low conductivity, it is critical to introduce a conductive matrix accompanied with electrochemical activity. Conductive polymers have great potential as electrodes with good conductivity, high redox activity, and potential. In this study, carbon-coated lithium iron phosphate (C-LiFePO4) nanoparticles were effectively dispersed in a polypyrrole (PPy) matrix by in situ pulverization. PPy, as an active nanostructure, significantly improves conductivity and accelerates Li+ diffusion. To further explore the synergy and symbiosis mechanism of PPy and C-LiFePO4 (hereinafter called C-LFP in the composite), the nanoparticle dispersion, carburization dependence, and heat treatment preference were investigated. Therefore, a reasonable amount of PPy (25 wt %) hybridization, a moderately wrapped carbon buffer layer (5.3 wt %), and a suitable heat treatment (100 °C) were employed to prepare the (C-LFP)0.75(PPy)0.25 nanocomposite. With a smaller particle size, uniformly dispersed morphology, and good synergy effect between PPy and C-LiFePO4, (C-LFP)0.75(PPy)0.25 delivers a high discharge capacity (209.1 mAh g–1 at 0.1C), a superior rate capability (86.1 mAh g–1 at 10C), and an outstanding capacity retention (83.5% of the initial values after 500 cycles at 0.5C).

An integrated study on the ionic migration across the nano lithium lanthanum titanate (LLTO) and lithium iron phosphate-carbon (LFP-C) interface in all-solid-state Li-ion batteries

A major challenge for the development of all-solid-state lithium-ion batteries (ASS-LIBs) relay on the development of an ideal electrolyte material and solving the interfacial issues at the electrode-electrolyte interface. Nano-crystalline lithium lanthanum titanate (LLTO) and lithium iron phosphate-carbon (LFP/C) has been prepared as electrolyte and cathode material for a solid-state lithium ion cell (LIBs). Prepared lithium lanthanum titanate, lithium iron phosphate-carbon and the composite powders were subjected to structural, optical, morphological and electrochemical characterizations. The high ionic conductivity of lithium lanthanum titanate (1.06 × 10−4), carbon coated lithium iron phosphate (5.01 × 10−5) and their interface (6.00 × 10−5) designate the pertinence of their full cell configurations. The full cell assembly has been characterized electrochemically to evaluate the performance of the interface. The assembled ASSBs show cyclability up to 55 initial cycles, with the nano-LLTO/LFP-C interface. The line scan analysis has been performed to identify the cation movement and accumulation of ions towards and across the cathode-electrolyte interface after cycling. The present study provides new direction and methodology for the detailed interface analysis across the nano-electrode- nano-solid electrolyte layer in all solid-state assemblies.

Understanding the Light-Triggered Process of a Photo-Rechargeable Battery via Fluorescence Studies of Its Constitutional Photo- and Electroactive Components

Solar energy is a standout clean and renewable energy source. Indeed, sunlight can efficiently be converted to electricity. However, solar energy must be stored for use during dark periods because of its intermittency. To address this challenge, we report a fundamental photophysical study for advancing an all-in-one photobattery for harvesting photons in addition to converting and storing energy. Focus was placed on assessing the photophysical properties of a light-harvesting organic dye, perelyene diimide (PDI), and its capacity to promote photo-oxidation of a lithium-ion battery’s electroactive positive material. Electron transfer kinetics between perelyene diimide and carbon-coated lithium iron phosphate (cLFP) were measured by both steady-state and time-revolved emission and they were ca. 1010 M–1 s–1. Lifetime analyses showed that the PDI’s intrinsic fluorescence was deactivated by cLFP through a mixed quenching mechanism. Various ceramics that are used as battery cathodes were also screened (LiCoO2, LiNi0.33Mn0.33Co0.33O2, LiNi0.8Co0.15Al0.05O2, and LiMn2O4) by fluorescence quenching of PDI. Both the carbon black coating and the oxidation state of the metal were found to play important roles in enabling the electronic transfer.

(Invited) Understanding Fast Charge Behavior and Limitations of Anodes and Cathodes for Hybrid Ion Capacitors and Libs

Sustained fast charge behavior is essential for many next-generation LIB applications as well as for emerging hybrid ion capacitors (HICs) that offer energies up to four times higher that EDLC systems. Fast charging anodes for both LIBs and HICs are often based on advanced disordered carbons where orderly ion intercalation is minimized while ion adsorption at bulk and surface sites is enhanced. This presentation covers several recent embodiments of such microstructures including crumpled activated graphene and low surface area nanoboxes. It is demonstrated that as long as the volume changes associated with charging are minimized, the structures are relatively stable over tens of thousands and even hundreds of thousands of fast charge cycles. A generally similar carbon structure design approach is effective for lithium ion capacitors (LICs), sodium ion capacitors (NICs) and potassium ion capacitors (KICs). With all three ions, a solid electrolyte interphase (SEI) can be stable as long as the carbons don't exfoliate or are otherwise structurally damaged. Attention then turns to the cathode, where the materials options are more limited. High surface area heteroatom-rich surface-adsorption carbons do work but offer very limited reversible capacity at high voltages. Their triangular discharge profile also substantially cuts into the device's energy, making it in effect a supercapacitor but with sub-par cyclability. To achieve reasonable fast charge capacity and voltage characteristics, carbon-coated lithium iron phosphate (LiFePO4) remains one of the best choices. However, the energy of LFP degrades with extended cycling, with the capacity-voltage fade mechanism not being understood. This presentation provides the first atomic-scale description of the fade process as well as the role of pyrrole coating in mitigating it. Cycling causes near-surface (∼ 30 nm) amorphization of the Olivine crystal structure, with isolated amorphous regions also being present deeper in the bulk crystal. Within this amorphous shell, some of the Fe2+ is transformed into Fe3+. Simulations predict that amorphization significantly impedes ion diffusion in LiFePO4 and even more severely in FePO4. A pyrrole coating suppresses the dissolution of Fe and allows for extended retention of the Olivine structure. It also reduces the level of crossover of iron to the metal anode and stabilizes its solid electrolyte interphase, thus also contributing to the half-cell cycling stability.

High‐performanceLiFePO4cathode material was prepared by multiple intensification process with acid‐washed iron red as raw material

LiFePO4 carbon coating technology has been widely used in the lithium ion industries. However, there are still many challenges such as low ionic conductivity. This paper compares the residual carbon rate and electrical conductivity of sucrose, glucose, and soluble starch, and proposes a secondary carbon coating technology. The carbon-coated lithium iron phosphate cathode material (LiFePO4/C) overcoated with soluble starch to improve the initial carbon layer. A variety of test methods are used to analyze the LiFePO4/C cathode. The results show that under the soluble starch coating of 20 wt%, particle size and morphology do not change significantly, surface graphitization degree and electrical conductivity increase, and thus electrochemical performance is improved. At the charge and discharge rate of 0.1 C, the specific discharge capacity of the first cycle is 27.7% higher than that of the initial sample, and the cycle stability is also significantly improved. The mechanism of soluble starch coating carbon layer on LiFePO4 cathode is studied.

MoSx surface-modified, hybrid core-shell structured LiFePO4 cathode for superior Li-ion battery applications

A hybrid core-shell cathode, composed of MoSxshell and carbon-coated lithium iron phosphate core (MoSx@c-LiFePO4or MoSx@c-LFP) is obtained by the post-annealing of a thermally decomposable ammonium thiomolybdate and commercial carbon-coated LiFePO4 (c-LFP) powder. The specific capacity of the commercially available amorphous carbon-coated LFP (c-LFP) is typically around 120–160 mAhg−1, which is usually lower than the theoretical values ~170 mAhg−1 due to the limited Li+ phase-boundary diffusion and low electrical conductivity. In the present investigation, we report that the specific capacity of surface-modified (~1.2 wt% of layered MoSx) c-LFP (MoSx@c-LFP) material can reach as high as ~228 mAhg−1 delivering high gravimetric energy density ~750–770 Whkg−1. The excess capacity can be attributed to the partial Li-ions intercalated/de-intercalated through the MoSx layers within a specific potential range (2.0–3.8 V). MoSx coating helps increase the c-LFP surface's stability by forming strong covalent bonding and is believed to enhance the electronic conduction by reducing the interparticle contact. During charge and discharge the hysteresis is substantially reduced by MoSx coating. The approach may open up a universal route to increase the cathode capacity, potentially attractive for further Li-ion battery research and industrial applications.

Synthesis and electrochemical performance of lithium iron phosphate/carbon composites based on controlling the secondary morphology of precursors

In this study, dihydrate iron phosphates with primary and secondary morphology were first prepared with ferric sulfate and phosphoric acid as the major raw materials, which were then taken as the precursor to prepare carbon-coated lithium iron phosphate composite material. Results show that structures of synthesized lithium iron phosphate/Carbon materials are the same, however, the morphologies are significantly different, especially the one synthesized with the secondary morphology iron phosphate precursor. Thus, the particle size, specific surface area and carbon coating effect of the material are changed accordingly, which can affect the electrochemical performance of the composite. The lithium iron phosphate/Carbon synthesized with spherical aggregation morphology (secondary morphology) iron phosphate precursor showed the best electrochemical property. At 0.5C and 10C rates, the first specific discharge capacity is 155.6 and 103.8 mA h/g respectively, which is better than that prepared with cabbage shape aggregation morphology (secondary morphology) and near-spherical simplex (primary morphology), increasing 1.38%, 1.37% and 3.58%, 9.05%, respectively. This research result provided new thoughts to further improve the electrochemical property of lithium iron phosphate/Carbon composites.

Plasma-treated Bombyx mori cocoon separators for high-performance and sustainable lithium-ion batteries

The success of lithium-ion batteries (LIBs) and their unique advantages for electrochemical energy storage have sped up research in this field. A critical component of LIBs is the separator. Here, Bombyx mori silk cocoon separators have been treated with oxygen (O2) and nitrogen (N2) plasmas at different exposure times. The goal was to improve the electrochemical characteristics of these natural separators, without jeopardizing the major attributes of silk fibers. Major physical and chemical modifications have been identified at the submicrometer scale on the application of the plasmas: (1) Etching of the silk nanofibrils and concomitant increase of roughness (more effective with O2 plasma), corresponding to the destruction of the 5th structural hierarchy level of the silk fibers. (2) Creation of oxygen-containing functional groups carrying negative charges at the surface, causing a superhydrophobic-to-superhydrophilic transition, and favoring Li+ transport. The optimized cocoon separator exposed to O2 plasma for 30 s exhibited high electrolyte uptake (289%), high ionic conductivity (2.33 mS/cm at 25 °C), and low overall resistance. A cathodic half-cell of carbon-coated lithium iron phosphate incorporating this separator sample soaked in the ethylene carbonate/dimethyl carbonate/lithium hexafluorophosphate electrolyte demonstrated a performance boost with respect to the battery, including a raw cocoon separator: an outstanding increase (ca. 270%) of the discharge capacity (from 26.1 to 96.7 mAh/g at 5C-rate) and an impressive increase (291%) of the capacity retention (from 22.3% to 87.2%, from C/5 to 5C). This work proves that the O2 plasma exposure is a valid, simple, fast, clean, and safe top-down methodology to improve the properties of B. mori cocoon separators. The features of these plasma-treated separators, which surpass those of commercial separators, help in upgrading the performance of LIBs. This plasma-enhanced natural biomaterial separator technological platform pushes LIBs to the next performance-level, while guaranteeing the eco-friendly, sustainability, and safety labels.

Impact of pH on preparation of LiFePO4@C cathode materials by a sol-gel route assisted by biomineralization

A carbon-coated lithium iron phosphate (LiFePO4@C) cathode materials were synthesized by a sol-gel method assisted by biomineralization. Yeast acted as a template and biocarbon source. NH3·H2O was used to adjust the pH in the preparation process, which effectively controlled the morphology. The LiFePO4@C synthesized at pH = 7 exhibited an optimal electrochemical performance, with a discharge capacity of 159.6 mAh/g at 0.1 C rate. Electrochemical impedance spectroscopy and cyclic voltammetry were applied to further analyze the impact of pH value. The optimized electrode also exhibited stable cycling characteristics. The improved electrochemical properties were ascribed to uniform spherical morphology and low electrochemical impedance. The biosynthetic sol-gel route can be desired to prepare LiFePO4@C cathode materials.

An aqueous hybrid lithium ion capacitor based on activated graphene and modified LiFePO4 with high specific capacitance

Aqueous Li-ion capacitors (ALICs) have been extensively studied in recent years due to their safety, environmental friendliness and low availability. In this paper, we constructed an ALIC using carbon-coated lithium iron phosphate (LFP) as the positive electrode, activated reduced graphene oxide as the negative electrode and studied its electrochemical performance in 1 M Li2SO4 electrolyte. Here, coating of LFP particles is carried out by dopamine polymerization to form a uniform carbon layer on the surface of the particles, which increases the conductivity and cycle performance of LFP. The optimal ALIC can achieve 82.8 F g−1 (based on the total mass of the positive and negative materials) at a current density of 0.2 A g−1, and shows good cycling stability. The specific capacitance can still retain 73% of the initial value after 1000 charge and discharge cycles. The specific energy density can reach 11.5 Wh kg−1 at a power density of 100 W kg−1.

A novel low-cost and simple colloidal route for preparing high-performance carbon-coated LiFePO4 for lithium batteries

Abstract Nanosized carbon-coated lithium iron phosphate (LiFePO4/C) particles were synthesized using a novel low-cost colloidal process with LiH2PO4, FeCl2 and anhydrous N-methylimidazole (NMI) as starting materials, following by a short annealing step at 600 °C. The ∼3–5 nm thick carbon coating comes from the carbonization of molten salt NMIH+Cl− derived from NMI; the resulting carbon contents of the LiFePO4/C powder is 2.53 wt.%. The materials were characterized by thermogravimetric and differential thermal analysis, differential scanning calorimetry, powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, Raman spectroscopy, four-point probe method, cyclic voltammetry and galvanostatic cycling experiments in coin cells. The LiFePO4 phase reveals agglomeration of semi-spherically particles with an average individual size of 35 ± 4 nm. Carbon-coated LiFePO4 posseses electronic conductivity of 1.4 × 10−3 S cm−1 at room temperature causing a markable increase in rate capability. Cycling the cells between 2.2 and 4.2 V vs. Li+/Li resulted in a discharge capacity of 164 mAh g−1 at the first cycle of C/20 and 162 mA hg−1 after 35 cycles, which corresponds to over 95% of the theoretical capacity of olivine LiFePO4.

Characteristics of Vanadium Doped And Bamboo Activated Carbon Coated LiFePO4 And Its Performance For Lithium Ion Battery Cathode

Vanadium doped and bamboo activated carbon coated lithium iron phosphate (LiFePO 4 ) used for lithium ion battery cathode has been successfully prepared. Lithium iron phosphate was prepared through a wet chemical method followed by a hydrothermal process from the starting materials of LiOH, NH 4 H 2 PO 4 , and FeSO 4 .7H 2 O. The dopant variations of 0 wt.%, 3 wt.%, 5 wt.%, and 7 wt.% of vanadium and a fixed 3 wt.% of bamboo activated carbon were carried out via a solid-state reaction process each by using NH 4 VO 3 as a source of vanadium and carbon pyrolyzed from bamboo tree, respectively. The characterization was carried out using X-ray Diffraction (XRD) for the phase formed and its crystal structure, Scanning Electron Microscope (SEM) for the surface morphology, Electrochemical Impedance Spectroscopy (EIS) for the conductivity, and battery analyzer for the performance of lithium ion battery cathode. The XRD results show that the phase formed has an olivine based structure with an orthorhombic space group. Morphology examination revealed that the particle agglomeration decreased with the increasing level of vanadium concentrations. Conductivity test showed that the impedance of solid electrolyte interface decreased with the increase of vanadium concentration indicated by increasing conductivity of 1.25 x 10 -5 S/cm, 2.02 x 10 -5 S/cm, 4.37 x 10 -5 S/cm, and 5.69 x 10 -5 S/cm, each for 0 wt.%, 3 wt.%, 5 wt.%, and 7 wt.% vanadium, respectively. Vanadium doping and bamboo activated carbon coating are promising candidate for improving lithium ion battery cathode as the initial charge and discharge capacity at 0.5C for LiFePO 4 /C at 7 wt.% vanadium is in the range of 8.0 mAh/g.

LiFePO4/C cathode material prepared with sphere mesoporous-FePO4 as precursors for lithium-ion batteries

The spherical mesoporous iron phosphate (P-FP) were prepared by liquid phase crystallization method, and then Carbon-coated lithium iron phosphate was synthesized by high temperature solid phase method using the spherical mesoporous iron phosphate as precursors (P-LFP/C) or using the non-mesoporous iron phosphate as precursors (LFP/C). The P-LFP/C were characterized by X-Ray-Diffraction, Scanning-Electron-Microscope, Fourier-Transform Infrared Spectrometer and electrochemical tests. The results show that the initial discharge capacity of the P-LFP/C at 0.1 C increase by 27.10%, reaching 159.29 mAh g−1, and the electrode charge transfer resistance reduce by 88.16%, just 48.32 Ω. compare with the LFP/C. And the P-LFP/C exhibited better discharge capacity at initial 151.78 and 112.11 mAh g−1 at 0.2 C and 5 C rate, respectively. It is beneficial to the lithium ion escaped and embed in the process of charging and discharging and enhanced the electronic conductivity and rate performance of the cathode materials.

Formation of size-dependent and conductive phase on lithium iron phosphate during carbon coating

Carbon coating is a commonly employed technique for improving the conductivity of active materials in lithium ion batteries. The carbon coating process involves pyrolysis of organic substance on lithium iron phosphate particles at elevated temperature to create a highly reducing atmosphere. This may trigger the formation of secondary phases in the active materials. Here, we observe a conductive phase during the carbon coating process of lithium iron phosphate and the phase content is size, temperature, and annealing atmosphere dependent. The formation of this phase is related to the reducing capability of the carbon coating process. This finding can guide us to control the phase composition of carbon-coated lithium iron phosphate and to tune its quality during the manufacturing process.

Effects of α-Fe2O3 size and morphology on performance of LiFePO4/C cathodes for Li-ion batteries

In this study, carbon-coated lithium iron phosphate (LiFePO4/C, denoted as LFP/C) composite cathode materials were prepared through wet ball milling and spray drying. Ground and spherical α-Fe2O3 precursors were used to synthesize LFP samples. Wet ball milling and a solvothermal method were used to prepare α-Fe2O3 particles with a smaller size and spherical morphology, respectively. The as-prepared α-Fe2O3 was used to synthesize LFP/C composites in order to investigate the effects of α-Fe2O3 size and morphology on the electrochemical performance of LFP/C cathode materials. Charge–discharge measurements revealed that the LFP/C cathode materials prepared from the ground and spherical α-Fe2O3 precursors delivered a similar specific discharge capacity of approximately 150 mAh/g at 0.1 C and 96 mAh/g at 10 C, which was higher than that of the LFP/C cathode materials prepared using the irregular and unground α-Fe2O3 (the discharge capacity was 135 mAh/g at 0.1 C and 62 mAh/g at 10 C). The results reveal that the size and morphology of iron precursors have a profound influence on the electrochemical properties of LFP/C materials. The results obtained in this study can serve as a reference in the use of the solid-state method to produce low-cost LFP/C cathode materials with favorable consistent properties and high electrochemical performance.