Silver-coated LiVPO4F composite with improved electrochemical performance as cathode material for lithium-ion batteries

Nano-structured LiVPO₄F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO₄F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO₄F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO₄F material exhibits high discharge capacity, good cycle performance (108.5 mAh g⁻¹ after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g⁻¹ for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (R_ct) of LiVPO₄F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO₄F for lithium-ion batteries cathode material.     

LiVPO4F: A new active material for safe lithium-ion batteries

In this paper, we report the latest findings for the new lithium vanadium fluorophosphate cathode material, LiVPO₄F. High quality samples have been prepared using a carbothermal reduction approach and extensive electrochemical and DSC measurements have been performed. In graphite based lithium-ion cells, the LiVPO₄F demonstrates reversible specific capacity behavior approaching theoretical. The lithium-ion system operates with an average discharge voltage around 4 V, low polarization and with good rate capability. These results indicate that the active material possesses exemplary electrochemical performance and may well be suitable as a replacement for LiCoO₂ in commercial lithium-ion cells. DSC measurements on charged cathodes indicate the thermal stability behavior expected for a phosphate based active material.     

Cation mixing （Li0.5Fe0.5）2SO4F cathode material for lithium-ion batteries

We study the crystal structure of a triplite-structured (Li_0.5Fe_0.5)SO₄F with full Li⁺/Fe2⁺ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li⁺/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li⁺ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO₄ with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.     

Effect of carbon coating on the electrochemical performance of LiFePO<Subscript>4</Subscript>/C as cathode materials for aqueous electrolyte lithium-ion battery

Organic electrolyte is widely used for lithium-ion rechargeable batteries but might cause flammable fumes or fire due to improper use such as overcharge or short circuit. That weakness encourages the development of tools and materials which are cheap and environmental friendly for rechargeable lithium-ion batteries with aqueous electrolyte. Lithium iron phosphate (LiFePO₄) with olivine structure is a potential candidate to be used as the cathode in aqueous electrolyte lithium-ion battery. However, LiFePO₄ has a low electronic conductivity compared to other cathodes. Conductive coating of LiFePO₄ was applied to improve the conductivity using sucrose as carbon source by heating to 600 °C for 3 h on an Argon atmosphere. The carbon-coated LiFePO₄ (LiFePO₄/C) was successfully prepared with three variations of the weight percentage of carbon. From the cyclic voltammetry, the addition of carbon coatings could improve the stability of cell battery in aqueous electrolyte. The result of galvanostatic charge/discharge shows that 9 % carbon exhibits the best result with the first specific discharge capacity of 13.3 mAh g^?1 and capacity fading by 2.2 % after 100 cycles. Although carbon coating enhances the conductivity of LiFePO₄, excessive addition of carbon could degrade the capacity of LiFePO₄.     

Synthesis of PANI/rGO composite as a cathode material for rechargeable lithium-polymer cells

Graphene oxide (GO) was synthesized by an improved Hummers method and then reduced with NaBH₄; GO became rGO with regular layered structure. Polyaniline (PANI)/rGO composite was prepared by a adsorption double oxidant method with rGO as a template. Some physical characterization methods (Fourier transform infrared spectroscopy analysis, X-ray diffraction, scanning electron microscope, and transmission electron microscope) were used to analyze the morphology and crystallinity of the composite. The electrochemical properties were characterized by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge, and rate capability. The first discharge specific capacity of the rPANI/rGO and PANI/rGO was 181.2 and 147.8 mAh/g. After 100 cycles, the capacity retention rate was still 90.2 and 88.9% separately, and the coulombic efficiency of batteries is close to 100%. These results demonstrate the composite has exciting potentials for the cathode material of lithium-ion battery.     

The synthesis, structure, and electrochemical properties of a novel rods-shaped Li6V10O28 for lithium-ion batteries

Rods-shaped Li₆V₁₀O₂₈ powders were synthesized by rheological phase reaction. The ratio of the Li/V of the product sintered at 600 °C for 8 h was characterized by inductively coupled plasma. The structure, composite, and morphology of the product have been investigated by X-ray diffraction, scan electron microscope, transmission electron microscopy, and X-ray photoelectron spectrometry, respectively. After charge–discharge test using the product as the cathode material of lithium-ion batteries, the product calcined at 600 °C for 8 h exhibited an initial high discharge specific capacity of 212.4 mAh/g at a rate of 1.0 mA/cm² in a potential range of 2.0 and 4.4 V, and its stabilized capacity still remained 167.7 mAh/g after 30 cycles, which indicates that the rods-shaped Li₆V₁₀O₂₈ are promising cathode materials in lithium-ion batteries.     

Synthesis and lithium-ion storage performances of LiFe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>PO<Subscript>4</Subscript>/C nanoplatelets and nanorods

Carbon-coated olivine-structured LiFe_0.5Co_0.5PO₄ solid solution was synthesized by a facile rheological phase method and applied as cathode materials of lithium-ion batteries. The nanostructure’s properties, such as morphology, component, and crystal structure for the samples, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET) determination, X-ray photoelectron spectroscopy (XPS), and the electrochemical performances were evaluated using constant current charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that nanoplatelet- and nanorod-structured LiFe_0.5Co_0.5PO₄/C composites were separately obtained using stearic acid or polyethylene glycol 400 (PEG400) as carbon source, and the surfaces of particles for the two samples are ideally covered by full and uniform carbon layer, which is beneficial to improving the electrochemical behaviors. Electrochemical tests verify that the nanoplatelet LiFe_0.5Co_0.5PO₄/C shows a better capacity capability, delivering a discharge specific capacity of 133.8, 112.1, 98.3, and 74.4 mAh g^?1 at 0.1, 0.5, 1, and 5 C rate (1 C?=?150 mA g^?1); the corresponding cycle number is 5th, 11th, 15th, 20th, and 30th, respectively, whereas the nanorod one possesses more excellent cycling ability, with a discharge capacity of 83.3 mAh g^?1 and capacity retention of 86.9% still maintained after cycling for 100 cycles at 0.5 C. Results from the present study demonstrate that the LiFe_0.5Co_0.5PO₄ solid solution nanomaterials with favorable carbon coating effect combine the characteristics and advantage of LiFePO₄ and LiCoPO₄, thus displaying a tremendous potential as cathode of lithium-ion battery.     

花状磷酸铁锂的聚乙二醇辅助水热合成及其电化学性能

通过聚乙二醇辅助水热法制备了厚度为200 nm的片状磷酸铁锂晶体,并由此自组装为花状磷酸铁锂颗粒．聚乙二醇在水热体系中作为共溶剂使用,它能有效地降低磷酸铁锂片的厚度,并且作为软模板,使磷酸铁锂片自组装成花状结构．这样的花状磷酸铁锂虽然没经过碳包覆改性,在锂离子电池中仍具有高达140 mAh/g的放电容量,并且表现出优异的循环性能,在循环50次后,容量未出现衰减．这种未经碳包覆的磷酸铁锂材料表现出良好的电化学性能．     

Structure change analysis in γ-Fe2O3/carbon composite in the process of electrochemical lithium insertion

It was previously shown that γ-Fe₂O₃/carbon composite synthesized by the aqueous solution method exhibit good high-speed charge/discharge and cycle characteristics as the cathode material in lithium-ion rechargeable batteries. We examined the crystal structure of γ-Fe₂O₃ in γ-Fe₂O₃/carbon composite by X-ray diffraction and the Rietveld analysis before and during electrochemical insertion of lithium ions. Before insertion, the sample has a spinel structure belonging to the Fd3¯m space group with the following iron occupancies: 8a site, 0.92, 16c site, 0 and 16d site, 0.87. During insertion, iron occupancy at 16d site remains virtually constant, at 8a site decreases from 0.92 to 0, and at 16c site increases from 0 to 0.53. These results suggest that, during insertion, iron migrates from 8a to 16c site. In the most highly lithiated sample, iron occupancy at 8a site decreases to 0 and occupancies at 16c and 16d sites were not equalized. Thus, the crystal structure for this sample belongs not to the Fm3¯m space group that represents the rock salt structure, but rather to the Fd3¯m space group.     

Synthesis of LiCoPO4 as a cathode material for lithium-ion battery by a polymer method

A polymer method has been used to synthesize high operation voltage LiCoPO₄ cathode material. Thermogravimetric analysis and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM),galvanostatic charge–discharge test and cyclic voltammetry (CV) are used to study the LiCoPO ₄ . The results show LiCoPO₄ has a well-crystallized olivine structure with submicron size. In the range of 3.0–5.1 V, the initial discharge capacities of polymer material are 97.3, 91.5, and 86.5 mAh g^?1 at 0.1, 0.2. and 1 C, respectively. Thus, the polymer method has a great potential in preparing electrode materials for lithium-ion batteries.     

Design and comparison of ex situ and in situ devices for Raman characterization of lithium titanate anode material

In this paper, ex situ and in situ devices for Raman observations are designed and compared with each other by using lithium titanate as working electrode. In situ cell is made for Raman spectroscopy based on a confocal microscope Raman spectrometer. The instant evolutions of lithium titanate anode material during cycle can be recorded by in situ Raman in detail. Although the in situ technique is an important method to monitor the structure evolution of lithium titanate, it is difficult to conduct an in situ experiment in most laboratories. Moreover, the existence of electrolyte and surface deposits weakens the Raman signals of sample. Therefore, the structure evolution of Li₄Ti₅O₁₂ cannot be described accurately. For comparison, air-free ex situ device is a simple and cheap tool to achieve the information from lithiated and delithiated samples. By removing the electrolyte and deposits on the sample with dimethyl carbonate, the ex situ Raman pattern shows higher signal to noise ratio than that of in situ Raman result. As a result, the shift and recovery of ex situ Raman bands confirms that the electrochemical reaction of Li₄Ti₅O₁₂ with Li in 0.0–2.0 V is not a fully reversible process but a partially reversible process.     

Synthesis and characterization of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>·LiMn<Subscript>0.33</Subscript>Fe<Subscript>0.67</Subscript>PO<Subscript>4</Subscript>/C cathode materials

A new polyanionic cathode material, Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C for lithium-ion batteries, was synthesized using a sol-gel method and with N,N-dimethyl formamide as a dispersion agent. The analysis of electron transmission spectroscopy and X-ray diffraction revealed that the composite contained two phases. The material has high crystallinity with a grain size of 20–50 nm. The valence states of Mn, V, and Fe in the composite were analyzed by X-ray photoelectron spectroscopy. The electrochemical kinetics in Li₃V₂(PO₄)₃ is effectively enhanced by the incorporation of LiMnPO₄ and LiFePO₄, via structure modification and reduced Li diffusion length. The Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C materials displayed high rate capacity and steady cycle performance with discharge capacity remained 148 mAh g^?1 after 50 cycles at the rate of 0.2C. In particular, the composite exhibited excellent reversible capacities, with the values of 157, 134, 120, 102, and 94 mAh g^?1 at charge/discharge 0.2, 0.5, 1, 2, and 5C rates, respectively.     

Vertically aligned α-MnO<Subscript>2</Subscript> nanosheets on carbon nanotubes as cathodic materials for aqueous rechargeable magnesium ion battery

In this work, vertically aligned α-MnO₂ nanosheets on carbon nanotubes are synthesized simply by a solution process and the electrochemical performance as host materials of magnesium ion is tested in aqueous solution. Cyclic voltammetry analysis confirms the enhanced electrochemical activity of carbon nanotube-supported samples. Moreover, carbon nanotubes skeleton could reduce the charge transfer resistant of the cathode materials, which is confirmed by electrochemical impedance spectroscopy. Furthermore, when tested as magnesium ion batteries cathodic electrode, the α-MnO₂/carbon nanotube sample registers a prominent discharge capacity of 144.6 mAh g^?1 at current density of 0.5 A g^?1, which is higher than the discharge capacity of α-MnO₂ (87.5 mAh g^?1) due to the synergistic effect of insertion/deinsertion reaction and physical adsorption/desorption process. After the 1000th cycle, a remarkable discharge capacity of 48.3 mAh g^?1 is collected for α-MnO₂/carbon nanotube at current density of 10 A g^?1, which is 85% of the original. It is found that the carbon skeleton not only improved the capacity but also enhanced the cycling performance of the α-MnO₂ electrode significantly. Therefore, α-MnO₂/carbon nanotube is a very promising candidate for further application in environmentally benign magnesium ion batteries.     

A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi_0.5Mn_1.5O₄ as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C₆H₅)₂SnCl₂ and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi_0.5Mn_1.5O₄ is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.     

Electrochemical properties of thin TiO2 electrode on Li1 + xAlxGe2 − x(PO4)3 solid electrolyte

A fabrication of all-solid-state thin-film rechargeable lithium ion batteries by sol-gel method is expected to achieve both the simplification and cost reduction for fabrication process. TiO₂ thin film electrode was prepared by PVP (polyvinylpyrrolidone) sol-gel method combined with spin-coating on Li_1 + xAl_xGe_2 − x(PO₄)₃ (LAGP) solid electrolyte which has wide electrochemical window. The thin film was composed of anatase TiO₂ that is the most active phase for Li insertion and extraction and contacted well with LAGP substrate. In the cyclic voltammogram, a redox couple was observed at 1.8 V vs. Li/Li⁺ assigned to Li insertion/extraction into/from anatase TiO₂, indicating that the thin film worked as electrode for lithium battery. The charge and discharge test in various charge and discharge rates revealed that the discharge process (delithiation) is thought to be faster than charge process (lithiation). It is attested that the sol-gel process, which derives both simplification and cost reduction for fabrication process, can be applied to thin film battery using LAGP solid electrolyte.     

Influence of cooling mode on the electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode materials for lithium-ion batteries

Li₄Ti₅O₁₂ (LTO) was synthesized with two different cooling methods by solid-state method, namely fast cooling and air cooling. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), galvanostatic charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. XRD revealed that the basic LTO structure was not changed. FESEM images showed that fast cooling effectively reduced the particle sizes and the agglomeration of particles. Galvanostatic charge–discharge test showed that the air cooling sample exhibited a mediocre performance, having an initial discharge capacity of 136.3mAh?·?g^?1 at 0.5 C; however, the fast cooling sample demonstrated noticeable improvement in both of its discharge capacity and rate capability, with a high initial capacity value of 142.7 mAh?·?g^?1 at 0.5 C. CV measurements also revealed that fast cooling enhanced the reversibility of the LTO. EIS confirmed that fast cooling resulted in lower electrochemical polarization and a higher lithium-ion diffusion coefficient. Therefore, fast cooling have a great impact on discharge capacity, rate capability, and cycling performance of LTO anode materials for lithium-ion batteries.     

Electrochemical impedance spectroscopic study of the lithium storage mechanism in commercial molybdenum disulfide

The first lithiation and delithiation processes of commercial molybdenum disulfide (MoS₂) electrode as anode material for lithium-ion batteries were studied by electrochemical impedance spectroscopy (EIS). It is found that the typical EIS is composed of four parts, namely, high-frequency semicircle, middle-frequency semicircle, low-frequency short sloping line, and low-frequency arc in the Nyquist diagram, and they can be attributed to the solid electrolyte interphase (SEI) film and ionic resistance in pores, charge transfer step, solid state diffusion process, and phase transformation, respectively. An equivalent circuit that includes elements related to the SEI film and charge transfer process, in addition to phase transformation, is proposed to simulate the experimental EIS data. The change of kinetic parameters for lithiation and delithiation of MoS₂ electrode as a function of potential in the first charge–discharge cycle is analyzed, and the reason for the rapid degradation in capacity of the MoS₂ electrode when cycled between 3.00 and 0.01 V is discussed in detail.     

Research status in preparation of FePO4: a review

The cathode is the most important component of a lithium-ion battery. The olivine structure lithium iron phosphate (LiFePO₄) with its numerous appealing features, such as high theoretical capacity, acceptable operating voltage, increased safety, environmental benignity, and low cost, has attracted extensive interest as a potential cathode material for Li-ion batteries. As a precursor, FePO₄ can be used to produce LiFePO₄ on a large scale with high bulk density, discharge rate, and capacity. This can be realized by controlling the crystal size and morphology of FePO₄. The characteristics, structure, and synthesis methods of FePO₄ are discussed in this review. The relative merits of these synthetic methods, as well as some suggestions on how to improve them, are also presented.     

Lithium electrochemistry of SiO2 thin film electrode for lithium-ion batteries

The lithium electrochemistry of SiO₂ thin film prepared by reactive radio frequency sputtering has been investigated for the first time. The reversible discharge capacities of SiO₂/Li cells cycled between 0.01 and 3.0 V are found in the range from 416 to 510 mAh/g during the first 100 cycles. By using ex situ transmission electron microscopy, selected-area electron diffraction and X-ray photo-electron spectroscopy measurements, both Li-Si alloying process and the reversible conversion reaction of SiO₂ into Li₂Si₂O₅ are proposed in the lithium electrochemical reaction of SiO₂. SiO₂ film electrode with high-reversible capacity and good cycle performance exhibits it potential anode material for future lithium-ion batteries.     

Facile and green fabrication of silver nanoparticles on a polyoxometalate for Li-ion battery

In the present study, we report the green and one-pot synthesis of silver nanoparticles (AgNPs) on as-prepared novel polyoxometalate {[Ni_2,5(Hpen)₄(PW₉O₃₄)]?·?5H₂O} (POM) without any reducing agent and its application as improved anode material for lithium-ion batteries (LIBs). The structure of the AgNPs involved POM (AgNPs/POM) nanocomposite was characterized by transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The synthesized POM was also characterized by elemental analysis and thermal analysis. The electrochemical performances of the POM, AgNPs, and AgNPs/POM composites were measured for charge/discharge specific capacities at different current rates in CR2032 coin-type cells. The prepared AgNPs/POM composite showed a high specific gravimetric capacity of about 1760 mAh g^?1 and long-term cycle stability.