Electrochemical properties of carbon-coated LiFePO4 cathode using graphite, carbon black, and acetylene black

Design of LiFePO4 and porous carbon composites with excellent High-Rate charging performance for Lithium-Ion secondary battery

Lithium iron phosphate (LFP) is one of the promising cathode materials of lithium ion battery (LIB), but poor electrical conductivity restricts its electrochemical performance. Carbon coating can improve electrical conductivity of LFP without changing its intrinsic property. Uniform coating of carbon on LFP is significant to avoid charge congregation and unpreferable redox reactions. It is the first time to apply the commercial organic binder, Super P® (SP), as carbon source to achieve uniform coating on LFP as cathode material of LIB. The simple and economical mechanofusion method is firstly applied to coat different amounts of SP on LFP. The LIB with the cathode material of optimized SP-coated LFP shows the highest capacity of 165.6 mAh/g at 0.1C and 59.8 mAh/g at 10C, indicating its high capacity and excellent high-rate charge/discharge capability. SP is applied on other commercial LFP materials, M121 and M23, for carbon coating. Enhanced high-rate charge/discharge capabilities are also achieved for LIB with SP-coated M121 and M23 as cathode materials. This new material and technique for carbon coating is verified to be applicable on different LFP materials. This novel carbon coating method is expected to apply on other cathode materials of LIB with outstanding electrochemical performances.

Improvement of the Battery Performance of Indigo, an Organic Electrode Material, Using PEDOT/PSS with d-Sorbitol

Rare-metal-free and high-performance secondary batteries are necessary for improving the efficiency of renewable energy systems. Organic compounds are attractive candidates for the active material of such batteries. Many studies have reported organic active materials that show high energy density per active material weight. However, organic active materials, most of which exhibit low conductivity and low specific density, typically require a large amount of a conductive additive (>50 wt %) to obtain a high utilization rate. Therefore, organic active materials rarely display high energy density per electrode weight. High energy densities per electrode weight can be obtained using high weight fractions of active materials and low weight fractions of conductive additives. Herein, we report that a low-conductivity organic active material, indigo, showed improved net discharge capacity density when even a small amount of a conductive polymer composite, poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSS) with d-sorbitol, was used as both a binder and conductive additive. The cycle life was also improved by coating one side of the separator with the composite, which probably hindered the dissolution of the active material. A discharge capacity of 96% of the theoretical capacity of indigo and an improved cycle life were achieved with an electrode containing 80 wt % indigo and with a PEDOT/PSS-coated separator. The optimal fraction of the conductive binder was examined, and the mechanism of conductivity enhancement was discussed. The present scheme allows us to replace the dispersion solvent of the slurry, N-methylpyrrolidone, with water, which can reduce the environmental load during battery manufacturing processes.

Effect of Combined Conductive Polymer Binder on the Electrochemical Performance of Electrode Materials for Lithium-Ion Batteries

The electrodes of lithium-ion batteries (LIBs) are multicomponent systems and their electrochemical properties are influenced by each component, therefore the composition of electrodes should be properly balanced. At the beginning of lithium-ion battery research, most attention was paid to the nature, size, and morphology peculiarities of inorganic active components as the main components which determine the functional properties of electrode materials. Over the past decade, considerable attention has been paid to development of new binders, as the binders have shown great effect on the electrochemical performance of electrodes in LIBs. The study of new conductive binders, in particular water-based binders with enhanced electronic and ionic conductivity, has become a trend in the development of new electrode materials, especially the conversion/alloying-type anodes. This mini-review provides a summary on the progress of current research of the effects of binders on the electrochemical properties of intercalation electrodes, with particular attention to the mechanisms of binder effects. The comparative analysis of effects of three different binders (PEDOT:PSS/CMC, CMC, and PVDF) for a number of oxide-based and phosphate-based positive and negative electrodes for lithium-ion batteries was performed based on literature and our own published research data. It reveals that the combined PEDOT:PSS/CMC binder can be considered as a versatile component of lithium-ion battery electrode materials (for both positive and negative electrodes), effective in the wide range of electrode potentials.

Carbon Black Flow Electrode Enhanced Electrochemical Desalination Using Single-Cycle Operation

Flow-electrode electrochemical desalination (FEED) processes (e.g., flow-electrode capacitive deionization), which use flowable carbon particles as the electrodes, have attracted increasing attention, holding the promise for continuous desalination and high desalting efficiency. While it is generally believed that carbon particles with abundant microporous and large specific capacitances (e.g., activated carbon, AC) should be ideal candidates for FEED electrodes, we provide evidence to the contrary, showing that highly conductive electrodes with low specific surface area can outperform microporous AC-based electrodes. This study revealed that FEED using solely high surface area AC particles (∼2000 m² g^-1, specific capacitance of ∼44 F g^-1, average salt adsorption rate of ∼0.15 μmol cm^-2 min^-1) was vastly outperformed by electrodes based solely on low-surface area carbon black (CB, ∼70 m² g^-1, ∼0.5 F g^-1, ∼0.75 μmol cm^-2 min^-1). Electrochemical impedance spectroscopy results suggest that the electrode formed by CB particles led to more effective electronic charge percolation, likely contributing to the improved desalination performance. In addition, we propose and demonstrate a novel operation mode, termed single cycle (SC), which greatly simplified the FEED cell configuration and enabled simultaneous charging and discharging. Using SC mode with CB flow electrodes delivered an increased average salt removal rate relative to the more traditional short-circuited closed cycle (SCC) mode, achieving up to 1.13 μmol cm^-2 min^-1. Further investigations demonstrate that up to 50% of energy input would be avoided when using CB flow electrodes operated under SC mode as compared to that of AC flow electrodes operated under SCC mode. In summary, the FEED process presented in this study provided an innovative and promising approach toward high-efficient and low-cost brackish water desalination.

Redox mediators as charge agents for changing electrochemical reactions

This review provides a comprehensive discussion toward understanding the effects of RMs in electrochemical systems, underlying redox mechanisms, and reaction kinetics both experimentally and theoretically.

A mixed polyanion NaFe1−x(VO)xPO4 glass-ceramic cathode system for safe and large-scale economic Na-ion battery applications

In this paper, highly efficient mixed polyanion NaFe_1−x(VO)_xPO₄ series of glass-ceramic cathode samples have been synthesized for use in sodium-ion batteries with good specific capacity and capacity retention.

Carbon Black Oxidized by Air Calcination for Enhanced H2O2 Generation and Effective Organics Degradation

Carbon black (CB) has a high conductivity and a large surface area, which are the basis of an excellent electrocatalyst. However, CB itself is usually less active or even inactive toward two-electron oxygen reduction reaction (2e^- ORR) due to the absence of highly active functional groups with low oxygen content. To activate commercial CB for 2e^- ORR, oxygen-containing functional groups were introduced onto the CB surface by a simple air calcination method. After the oxidation treatment at 600 °C (CB600), the oxygen content increased from the initial 1.17 ± 0.15 to 4.08 ± 0.60%, leading to a dramatic increase of the cathodic current from only -8.1 mA (CB) to -117.6 mA (CB600). The air cathode made of CB600 achieved the maximum H₂O₂ production of 517.7 ± 2.4 mg L^-1 within 30 min, resulting in the removal of ∼91.1% rhodamine B in 2 min and an effective mineralization of ∼76.3% in an electro-Fenton reactor. This performance was much better than that obtained using the CB catalyst (65.3 ± 5.6 mg L^-1 H₂O₂ production, and ∼20.3% mineralization). This excellent activity of CB600 toward 2e^- ORR was greatly improved by the introduction of O═C-OH and C-O-C groups. The successful improvement of the 2e^- ORR activity of CB using air calcination enables its practical application in electrochemical advanced oxidation processes.

Quantifying Reaction and Rate Heterogeneity in Battery Electrodes in 3D through Operando X-ray Diffraction Computed Tomography

In composite battery electrode architectures, local limitations in ionic and electronic transport can result in nonuniform energy storage reactions. Understanding such reaction heterogeneity is important to optimizing battery performance, including rate capability and mitigating degradation and failure. Here, we use spatially resolved X-ray diffraction computed tomography to map the reaction in a composite electrode based on the LiFePO₄ active material as it undergoes charge and discharge. Accelerated reactions at the electrode faces in contact with either the separator or the current collector demonstrate that both ionic and electronic transport limit the reaction progress. The data quantify how nonuniformity of the electrode reaction leads to variability in the charge/discharge rate, both as a function of time and position within the electrode architecture. Importantly, this local variation in the reaction rate means that the maximum rate that individual cathode particles experience can be substantially higher than the average, control charge/discharge rate, by a factor of at least 2-5 times. This rate heterogeneity may accelerate rate-dependent degradation pathways in regions of the composite electrode experiencing faster-than-average reaction and has important implications for understanding and optimizing rate-dependent battery performance. Benchmarking multiscale continuum model parameters against the observed reaction heterogeneity permits extension of these models to other electrode geometries.

A Review: Carbon Additives in LiMnPO4- and LiCoO2-Based Cathode Composites for Lithium Ion Batteries

Carbon plays a critical role in improving the electronic conductivity of cathodes in lithium ion batteries. Particularly, the characteristics of carbon and its composite with electrode material strongly affect battery properties, governed by electron as well as Li+ ion transport. We have reviewed here various types of carbon materials and organic carbon sources in the production of conductive composites of nano-LiMnPO4 and LiCoO2. Various processes of making these composites with carbon or organic carbon sources and their characterization have been reviewed. Finally, the type and amount of carbon and the preparation methods of composites are summarized along with their battery performances and cathode materials. Among the different processes of making a composite, ball milling provided the benefit of dense and homogeneous nanostructured composites, leading to higher tap-density and thus increasing the volumetric energy densities of cathodes.

Variation of carbon coatings on the electrochemical performance of LiFePO4 cathodes for lithium ionic batteries

Asphalt-derived and glucose-derived carbon proved to be soft carbon-coating (SCC) and hard carbon-coating (HCC), and it was found that LFP/SCC showed a superior performance in capacity and rate capability than that of LFP/HCC.

Advanced cathode materials for lithium-ion batteries using nanoarchitectonics

In recent years, the global climate has further deteriorated because of the excessive consumption of traditional energy sources. The replacement of traditional fossil fuels with limited reserves by alternative energy sources has become one of the main strategies to alleviate the increasingly serious environmental issues. As a sustainable and promising store of renewable energy, lithium-ion batteries have replaced other types of batteries for many small-scale consumer devices. Notwithstanding their worldwide applications, it has become abundantly clear that the design and fabrication of electrode materials is urgently required to adapt to meet the growing global demand for energy and the power densities needed to make electric vehicles fully commercially viable. To dramatically enhance battery performance, further advances in materials chemistry are essential, especially in novel nanomaterials chemistry. The construction of nanostructured cathode materials by reducing particle size can boost electrochemical performance. The present review is intended to provide readers with a better understanding of the unique contribution of various nanoarchitectures to lithium-ion batteries over the last decade. Nanostructured cathode materials with different dimensions (0D, 1D, 2D, and 3D), morphologies (hollow, core-shell, etc.), and composites (mainly graphene-based composites) are highlighted, aiming to unravel the opportunities for the development of future-generation lithium-ion batteries. The advantages and challenges of nanomaterials are also addressed in this review. We hope to simulate many more extensive and insightful studies on nanoarchitectonic cathode materials for advanced lithium-ion batteries with desirable performance.

Superior rate performance of Li3V2(PO4)3 co-modified by Fe-doping and rGO-incorporation

Reduced graphene oxide (rGO) incorporated Li₃V_1.94Fe_0.06(PO₄)₃/C cathode materials were successfully prepared by a sol–gel method.

A free-standing, flexible and bendable lithium-ion anode materials with improved performance

Bendable, flexible and self-supported anode materials with excellent electrochemical properties have highly attractive for the high performance lithium-ion batteries (LIBs).

Preparation and electrochemical properties of Li2MoO3/C composites for rechargeable Li-ion batteries

Li₂MoO₃/C composites provide reversible Li intercalation based on the Mo(iv/vi) redox couple via enhanced electron conduction.

Conformal Coating Strategy Comprising N-doped Carbon and Conventional Graphene for Achieving Ultrahigh Power and Cyclability of LiFePO4

Surface carbon coating to improve the inherent poor electrical conductivity of lithium iron phosphate (LiFePO4, LFP) has been considered as most efficient strategy. Here, we also report one of the conventional methods for LFP but exhibiting a specific capacity beyond the theoretical value, ultrahigh rate performance, and excellent long-term cyclability: the specific capacity is 171.9 mAh/g (70 μm-thick electrode with ∼10 mg/cm(2) loading mass) at 0.1 C (17 mA/g) and retains 143.7 mAh/g at 10 C (1.7 A/g) and 95.8% of initial capacity at 10 C after 1000 cycles. It was found that the interior conformal N-C coating enhances the intrinsic conductivity of LFP nanorods (LFP NR) and the exterior reduced graphene oxide coating acts as an electrically conducting secondary network to electrically connect the entire electrode. The great electron transport mutually promoted with shorten Li diffusion length on (010) facet exposed LFP NR represents the highest specific capacity value recorded to date at 10 C and ultralong-term cyclability. This conformal carbon coating approach can be a promising strategy for the commercialization of LFP cathode in lithium ion batteries.

Boron and Nitrogen Codoped Carbon Layers of LiFePO4 Improve the High-Rate Electrochemical Performance for Lithium Ion Batteries

An evolutionary composite of LiFePO4 with nitrogen and boron codoped carbon layers was prepared by processing hydrothermal-synthesized LiFePO4. This novel codoping method is successfully applied to LiFePO4 for commercial use, and it achieved excellent electrochemical performance. The electrochemical performance can be improved through single nitrogen doping (LiFePO4/C-N) or boron doping (LiFePO4/C-B). When modifying the LiFePO4/C-B with nitrogen (to synthesis LiFePO4/C-B+N) the undesired nonconducting N-B configurations (190.1 and 397.9 eV) are generated. This decreases the electronic conductivity from 2.56×10(-2) to 1.30×10(-2) S cm(-1) resulting in weak electrochemical performance. Nevertheless, using the opposite order to decorate LiFePO4/C-N with boron (to obtain LiFePO4/C-N+B) not only eliminates the nonconducting N-B impurity, but also promotes the conductive C-N (398.3, 400.3, and 401.1 eV) and C-B (189.5 eV) configurations-this markedly improves the electronic conductivity to 1.36×10(-1) S cm(-1). Meanwhile the positive doping strategy leads to synergistic electrochemical activity distinctly compared with single N- or B-doped materials (even much better than their sum capacity at 20 C). Moreover, due to the electron and hole-type carriers donated by nitrogen and boron atoms, the N+B codoped carbon coating tremendously enhances the electrochemical property: at the rate of 20 C, the codoped sample can elevate the discharge capacity of LFP/C from 101.1 mAh g(-1) to 121.6 mAh g(-1), and the codoped product based on commercial LiFePO4/C shows a discharge capacity of 78.4 mAh g(-1) rather than 48.1 mAh g(-1). Nevertheless, the B+N codoped sample decreases the discharge capacity of LFP/C from 101.1 mAh g(-1) to 95.4 mAh g(-1), while the commercial LFP/C changes from 48.1 mAh g(-1) to 40.6 mAh g(-1).

Multifunctional SA-PProDOT Binder for Lithium Ion Batteries

An environmentally benign, highly conductive, and mechanically strong binder system can overcome the dilemma of low conductivity and insufficient mechanical stability of the electrodes to achieve high performance lithium ion batteries (LIBs) at a low cost and in a sustainable way. In this work, the naturally occurring binder sodium alginate (SA) is functionalized with 3,4-propylenedioxythiophene-2,5-dicarboxylic acid (ProDOT) via a one-step esterification reaction in a cyclohexane/dodecyl benzenesulfonic acid (DBSA)/water microemulsion system, resulting in a multifunctional polymer binder, that is, SA-PProDOT. With the synergetic effects of the functional groups (e.g., carboxyl, hydroxyl, and ester groups), the resultant SA-PProDOT polymer not only maintains the outstanding binding capabilities of sodium alginate but also enhances the mechanical integrity and lithium ion diffusion coefficient in the LiFePO4 (LFP) electrode during the operation of the batteries. Because of the conjugated network of the PProDOT and the lithium doping under the battery environment, the SA-PProDOT becomes conductive and matches the conductivity needed for LiFePO4 LIBs. Without the need of conductive additives such as carbon black, the resultant batteries have achieved the theoretical specific capacity of LiFePO4 cathode (ca. 170 mAh/g) at C/10 and ca. 120 mAh/g at 1C for more than 400 cycles.

Platinum decorated functionalized defective acetylene black; a promising cathode material for the oxygen reduction reaction

Enormously enhanced oxygen reduction reaction of Pt-np/functionalized acetylene black.

Direct Observation of Active Material Concentration Gradients and Crystallinity Breakdown in LiFePO4 Electrodes During Charge/Discharge Cycling of Lithium Batteries

The phase changes that occur during discharge of an electrode comprised of LiFePO₄, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO₄ electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate.

Mesoporous carbon-coated LiFePO4 nanocrystals co-modified with graphene and Mg2+ doping as superior cathode materials for lithium ion batteries

In this work, mesoporous carbon-coated LiFePO4 nanocrystals further co-modified with graphene and Mg(2+) doping (G/LFMP) were synthesized by a modified rheological phase method to improve the speed of lithium storage as well as cycling stability. The mesoporous structure of LiFePO4 nanocrystals was designed and realized by introducing the bead milling technique, which assisted in forming sucrose-pyrolytic carbon nanoparticles as the template for generating mesopores. For comparison purposes, samples modified only with graphene (G/LFP) or Mg(2+) doping (LFMP) as well as pure LiFePO4 (LFP) were also prepared and investigated. Microscopic observation and nitrogen sorption analysis have revealed the mesoporous morphologies of the as-prepared composites. X-ray diffraction (XRD) and Rietveld refinement data demonstrated that the Mg-doped LiFePO4 is a single olivine-type phase and well crystallized with shortened Fe-O and P-O bonds and a lengthened Li-O bond, resulting in an enhanced Li(+) diffusion velocity. Electrochemical properties have also been investigated after assembling coin cells with the as-prepared composites as the cathode active materials. Remarkably, the G/LFMP composite has exhibited the best electrochemical properties, including fast lithium storage performance and excellent cycle stability. That is because the modification of graphene provided active sites for nuclei, restricted the in situ crystallite growth, increased the electronic conductivity and reduced the interface reaction current density, while, Mg(2+) doping improved the intrinsically electronic and ionic transfer properties of LFP crystals. Moreover, in the G/LFMP composite, the graphene component plays the role of "cushion" as it could quickly realize capacity response, buffering the impact to LFMP under the conditions of high-rate charging or discharging, which results in a pre-eminent rate capability and cycling stability.

Effects of Vapor Grown Carbon Fiber Substitution for Conductive Carbon in Anode Systems for LiB Applications

Isotropic and anisotropic conductive carbon particles, carbon black (CB) and vapor grown carbon fiber (VGCF), were incorporated into a Lithium Titanate (LTO) battery anode material composition, and their effect on conductivity and electrochemical properties investigated. Nanocomposite electrodes comprised of LTO, polyvinyldine floride (PVDF) and as little as 5 wt% VGCF are reported to manifest more than one order of magnitude enhancement in conductivity over their CB counterparts. VGCF-based anodes are also found to exhibit more stable voltage discharge profiles and as much as 20% improvement in capacity retention during extended electrochemical cycling at charge/discharge rates as high as 2.625 A/g (15 C). Remarkably, we find that the benefits of VGCF relative to CB conductivity aids diminish at higher particle loadings and that a LTO anode formulation containing 5 wt% CB | 5 wt% VGCF yields optimal capacity retention. At 5C, this composite system outperformed both the 10 wt% VGCF and 10 wt% CB electrode systems by delivering 20% higher capacity during extended charge/discharge cycling. We explain this finding in terms of two synergetic effects: enhanced electrode conductivity facilitated by incorporation of a percolated network of anisotropic VGCF particles; and shorter transport distances between the insulative LTO and high surface area CB.