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.

Mechanism studies of LiFePO4cathode material: lithiation/delithiation process, electrochemical modification and synthetic reaction

Olivine-structured lithium ion phosphate (LiFePO₄) is one of the most competitive candidates for fabricating energy-driven cathode material for sustainable lithium ion battery (LIB) systems.

Soft-templated LiFePO4/mesoporous carbon nanosheets (LFP/meso-CNSs) nanocomposite as the cathode material of lithium ion batteries

A soft-templated LFP/mesoporous carbon nanosheets (LFP/meso-CNSs) nanocomposite as the cathode of lithium ion batteries displays an excellent high-rate capability and stable cycling property, benefitting from its high electronic conductivity, open mesoporosity, and the nano-size of its active material.

Facile and economical synthesis for “plum pudding”-shaped porous LiFePO4/carbon composites for lithium ion batteries

The LiFePO₄/C composite shows plentiful LiFePO₄ nanospheres uniformly lodged in the 3D porous conductive carbon framework, and exhibits improved electrochemical performance.

Facile synthesis of hierarchical networks composed of highly interconnected V2O5 nanosheets assembled on carbon nanotubes and their superior lithium storage properties

Hierarchical networks with highly interconnected V2O5 nanosheets (NSs) anchored on skeletons of carbon nanotubes (CNTs) are prepared by a facile hydrothermal treatment and a following calcination for the first time. Benefiting from these unique structural features, the as-prepared CNT@V2O5 material shows dramatically excellent electrochemical performance with remarkable long cyclability (137-116 mA h g(-1) after 400 cycles) at various high rates (20 C to 30 C) and very good rate capability for highly reversible lithium storage. The excellent electrochemical performance suggests its promising use as a cathode material for future lithium-ion batteries.

Hierarchical hollow spheres of Fe2O3 @polyaniline for lithium ion battery anodes

Hierarchical hollow spheres of Fe2 O3 @polyaniline are fabricated by template-free synthesis of iron oxides followed by a post in- and exterior construction. A combination of large surface area with porous structure, fast ion/electron transport, and mechanical integrity renders this material attractive as a lithium-ion anode, showing superior rate capability and cycling performance.

Comparative advantages and limitations of the basic metrology methods applied to the characterization of nanomaterials

Fabrication of modern nanomaterials and nanostructures with specific functional properties is both scientifically promising and commercially profitable. The preparation and use of nanomaterials require adequate methods for the control and characterization of their size, shape, chemical composition, crystalline structure, energy levels, pathways and dynamics of physical and chemical processes during their fabrication and further use. In this review, we discuss different instrumental methods for the analysis and metrology of materials and evaluate their advantages and limitations at the nanolevel.

Hierarchical LiFePO4 with a controllable growth of the (010) facet for lithium-ion batteries

Hierarchically structured LiFePO4 was successfully synthesized by ionic liquid solvothermal method. These hierarchically structured LiFePO4 samples were constructed from nanostructured platelets with their (010) facets mainly exposed. To the best of our knowledge, facet control of a hierarchical LiFePO4 crystal has not been reported yet. Based on a series of experimental results, a tentative mechanism for the formation of these hierarchical structures was proposed. After these hierarchically structured LiFePO4 samples were coated with a thin carbon layer and used as cathode materials for lithium-ion batteries, they exhibited excellent high-rate discharge capability and cycling stability. For instance, a capacity of 95% can be maintained for the LiFePO4 sample at a rate as high as 20 C, even after 1000 cycles.

Solvothermal synthesis of monodisperse LiFePO4 micro hollow spheres as high performance cathode material for lithium ion batteries

A microspherical, hollow LiFePO4 (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li3PO4 as the self-sacrificed template and FeCl2·4H2O as the Fe(2+) source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ~1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe(2+) source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li3PO4 templates and Fe(2+) ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ~3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g(-1) at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.

A chemically activated graphene-encapsulated LiFePO4 composite for high-performance lithium ion batteries

A composite of modified graphene and LiFePO4 has been developed to improve the speed of charging-discharging and the cycling stability of lithium ion batteries using LiFePO4 as a cathode material. Chemically activated graphene (CA-graphene) has been successfully synthesized via activation by KOH. The as-prepared CA-graphene was mixed with LiFePO4 to prepare the composite. Microscopic observation and nitrogen sorption analysis have revealed the surface morphologies of CA-graphene and the CA-graphene/LiFePO4 composite. Electrochemical properties have also been investigated after assembling coin cells with the CA-graphene/LiFePO4 composite as a cathode active material. Interestingly, the CA-graphene/LiFePO4 composite has exhibited better electrochemical properties than the conventional graphene/LiFePO4 composite as well as bare LiFePO4, including exceptional speed of charging-discharging and excellent cycle stability. That is because the CA-graphene in the composite provides abundant porous channels for the diffusion of lithium ions. Moreover, it acts as a conducting network for easy charge transfer and as a divider, preventing the aggregation of LiFePO4 particles. Owing to these properties of CA-graphene, LiFePO4 could demonstrate enhanced and stably long-lasting electrochemical performance.

Synthesis of Microspherical LiFePO₄-Carbon Composites for Lithium-Ion Batteries

This paper reports an “all in one” procedure to produce mesoporous, micro-spherical LiFePO₄ composed of agglomerated crystalline nanoparticles. Each nanoparticle is individually coated with a thin glucose-derived carbon layer. The main advantage of the as-synthesized materials is their good performance at high charge-discharge rates. The nanoparticles and the mesoporosity guarantee a short bulk diffusion distance for both lithium ions and electrons, as well as additional active sites for the charge transfer reactions. At the same time, the thin interconnected carbon coating provides a conductive framework capable of delivering electrons to the nanostructured LiFePO₄.

Li3V2(PO4)3@C core-shell nanocomposite as a superior cathode material for lithium-ion batteries

Li3V2(PO4)3@C core-shell nanoparticles with typical sizes of 20-40 nm were synthesized using a hydrothermal-assisted sol-gel method. Ascorbic acid and PEG-400 were adopted as carbon sources and reductants. The uniform Li3V2(PO4)3@C nanocomposite obtained was composed of a Li3V2(PO4)3 core with high-phase purity and a graphitized carbon shell, which was characterized using XRD, SEM, TEM, and Raman analysis. The nanocomposite exhibited a remarkably high rate capability and long cyclability, delivering a discharge capacity of 138 mA h g(-1) at 5 C within a voltage range of 3-4.8 V and the capacity retention was 86% after 1000 cycles. The superior electrochemical performance of Li3V2(PO4)3@C indicates that it has potential for application as a cathode material in advanced rechargeable lithium-ion batteries.

Olivine-type nanosheets for lithium ion battery cathodes

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 μs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

LiMn2O4 nanotube as cathode material of second-level charge capability for aqueous rechargeable batteries

LiMn2O4 nanotube with a preferred orientation of (400) planes is prepared by using multiwall carbon nanotubes as a sacrificial template. Because of the nanostructure and preferred orientation, it shows a superfast second-level charge capability as a cathode for aqueous rechargeable lithium battery. At the charging rate of 600C (6 s), 53.9% capacity could be obtained. Its reversible capacity can be 110 mAh/g, and it also presents excellent cycling behavior due to the porous tube structure to buffer the strain and stress from Jahn-Teller effects.

Defect effects on the physical and electrochemical properties of nanoscale LiFe0.92PO4 and LiFe0.92PO4/C/graphene composites

Nanoscale LiFe0.92PO4 and LiFe0.92PO4/C/graphene composites including defects as performance-improved cathode materials for lithium-ion batteries were prepared by a carbothermal reduction method. The physical and electrochemical properties of samples were characterized by means of X-ray diffraction, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical testing techniques. The results confirmed that defects existed within the nanoscale LiFe0.92PO4 lattice and had significant effects on improving the electrochemical properties of samples. The excellent graphene sheets covered on nanoparticles and formed a three-dimensional conductive network in nanoscale LiFe0.92PO4/C/graphene composites. The composites exhibited a discharge capacity of 90 mA h g(-1) at 10 C and capacity retention ratios of 98% after 100 cycles at various rates, implying outstanding high-rate capability and cycling stability.

Nanowormlike Li2FeSiO4-C composites as lithium-ion battery cathodes with superior high-rate capability

Nanoworm-like Li2FeSiO4-C composites are synthesized using triblock copolymer Pluronic P123 (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), EO20PO70EO20) as the structure directing agent (SDA) and under the effects of ethanol. As a polar nonaqueous cosolvent, ethanol has effects on the self-organization behavior of Pluronic P123 in water, which determines the final morphologies of the Li2FeSiO4-C composites synthesized. Li2FeSiO4-C composite nanoparticles are obtained if no ethanol is added into the system during the synthesis process. When tested as lithium-ion battery cathodes, the Li2FeSiO4-C nanoworms show superior electrochemical performances. At the rate of 1 C (1 C=166 mA g(-1)) the discharge capacity of the Li2FeSiO4-C nanoworms can reach 166 mAh g(-1) in the voltage window of 1.5-4.8 V at room temperature. At the rates of 5, 10, and 20 C, the discharge capacities of the Li2FeSiO4-C nanoworms can stabilize at 120, 110, and 90 mAh g(-1), respectively, and do not show obvious declines after hundreds of cycles. This performance of the Li2FeSiO4-C nanoworms at high rates is better than that of the Li2FeSiO4-C nanoparticles synthesized and many other Li2FeSiO4/C composites reported in the literature. The excellent electrochemical performances of the Li2FeSiO4-C nanoworms are believed to be related to the small sizes of the Li2FeSiO4 nanocrystals inside the nanoworms and the carbon that coats and embeds the nanocrystals.

In situ fabrication of porous graphene electrodes for high-performance energy storage

In the development of energy-storage devices, simultaneously achieving high power and large energy capacity at fast rate is still a great challenge. In this paper, the synergistic effect of structure and doping in the graphene is demonstrated for high-performance lithium storage with ulftrafast and long-cycling capabilities. By an in situ constructing strategy, hierarchically porous structure, highly conductive network, and heteroatom doping are ideally combined in one graphene electrode. Compared to pristine graphene, it is found that the degree of improvement with both structure and doping effects is much larger than the sum of that with only structure effect or doping effect. Benefitting from the synergistic effect of structure and doping, the novel electrodes can deliver a high-power density of 116 kW kg(-1) while the energy density remains as high as 322 Wh kg(-1) at 80 A g(-1) (only 10 s to full charge), which provides an electrochemical storage level with the power density of a supercapacitor and the energy density of a battery, bridging the gap between them. Furthermore, the optimized electrodes exhibit long-cycling capability with nearly no capacity loss for 3000 cycles and wide temperature features with high capacities ranging from -20 to 55 °C.

Carbon-coated LiFePO4-porous carbon composites as cathode materials for lithium ion batteries

This work introduces a facile strategy for the synthesis of carbon-coated LiFePO(4)-porous carbon (C-LiFePO(4)-PC) composites as a cathode material for lithium ion batteries. The LiFePO(4) particles obtained are about 200 nm in size and homogeneously dispersed in porous carbon matrix. These particles are further coated with the carbon layers pyrolyzed from sucrose. The C-LiFePO(4)-PC composites display a high initial discharge capacity of 152.3 mA h g(-1) at 0.1 C, good cycling stability, as well as excellent rate capability (112 mA h g(-1) at 5 C). The likely contributing factors to the excellent electrochemical performance of the C-LiFePO(4)-PC composites could be related to the combined effects of enhancement of conductivity by the porous carbon matrix and the carbon coating layers. It is believed that further carbon coating is a facile and effective way to improve the electrochemical performance of LiFePO(4)-PC.

MoO2-ordered mesoporous carbon nanocomposite as an anode material for lithium-ion batteries

In the present work, the nanocomposite of MoO2-ordered mesoporous carbon (MoO2-OMC) was synthesized for the first time using a carbon thermal reduction route and the mesoporous carbon as the nanoreactor. The synthesized nanocomposite was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), N2 adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. Furthermore, this nanocomposite was used as an anode material for Li-ion intercalation and exhibited large reversible capacity, high rate performance, and good cycling stability. For instance, a high reversible capacity of 689 mAh g(-1) can remain after 50 cycles at a current density of 50 mA g(-1). It is worth mentioning that the MoO2-OMC nanocomposite electrode can attain a high reversible capacity of 401 mAh g(-1) at a current density as high as 2 A g(-1). These results might be due to the intrinsic characteristics of nanocomposite, which offered a better accommodation of the strain and volume changes and a shorter path for Li-ion and electron transport, leading to the improved capacity and enhanced rate capability.