A carbon–LiFePO<Subscript>4</Subscript> nanocomposite as high-performance cathode material for lithium-ion batteries

A cathode material of an electrically conducting carbon–LiFePO₄ nanocomposite is synthesized by wet ball milling and spray drying of precursor powders prior to a solid-state reaction. The structural characterization shows that the composite is composed of LiFePO₄ crystals and 4.8 wt.% amorphous carbon. Galvanostatic charge/discharge measurements indicate that the composite exhibits a superior high energy and high cycling stability. This composite delivers a discharge capacity of 159.1 mAh g⁻¹ at 0.1 C, 150.8 mAh g⁻¹ at 1 C, and 140.1 mAh g⁻¹ at 2 C rate. The capacity retention of 99% is achieved after 200 cycles at 2 C. The 18,650 cylindrical batteries are assembled using the composite as cathode materials and demonstrate the capacity of 1,400 mAh and the capacity retention of 97% after 100 cycles at 1 C. These results reveal that the as-prepared LiFePO₄–carbon composite is one of the promising cathode materials for high-performance, advanced lithium-ion batteries directed to the hybrid electric vehicle and pure electric vehicle markets.     

Electrochemical performances of FePO<Subscript>4</Subscript>-positive active mass prepared through a new sol–gel method

This investigation is a contribution to the research on alternative cathode materials with much more promising performances for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO₄, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor at temperatures (T _c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with the decrease in T _c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S _BET, as high as 28 m² g⁻¹ for the sample annealed at 400°C. The electrochemical properties of FePO₄-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum reversible capacity of 132 mAh g⁻¹, which fell with the increase in T _c. A direct correlation was established between the activity of the material and its active surface area.     

Preparation and electrochemical properties of nano Al<Subscript>0.2</Subscript>V<Subscript>2</Subscript>O<Subscript>5.3−<Emphasis Type="BoldItalic">δ</Emphasis></Subscript> cathode materials for rechargeable lithium batteries

Nano-sized Al³⁺-doped V₂O₅ cathode materials, Al_0.2V₂O_5.3−δ , were prepared by an oxalic acid assisted sol–gel method at 350 °C (sample A) and 400 °C (sample B). X-ray diffraction confirmed that samples A and B were pure phase Al_0.2V₂O_5.3−δ with an orthorhombic structure close to that of V₂O₅. Scanning electron microscopy showed that sample A was in nanoscale with a mean particle size about 50 nm. Cyclic voltammetry showed the good electrochemical and structural reversibility of the Al_0.2V₂O_5.3−δ nanoparticles during the Li⁺ insertion/extraction process. The Al_0.2V₂O_5.3−δ nanoparticles exhibited excellent charge–discharge cycling performance and rate capability compared to that of bulky V₂O₅ electrodes. For instance, the materials delivered a reversible specific capacity about 180 mAh g⁻¹ (sample A) and 150 mAh g⁻¹ (sample B), in the potential window of 4.0–2.0 V at the current density of 150 mA g⁻¹. The Al_0.2V₂O_5.3−δ nanoparticles in particular showed almost no capacity fading for at least 50 cycles.     

Synthesis of LiFePO4-C cathode materials using a green and low-cost method

LiFePO₄-C was prepared by the solid-state reaction using LiH₂PO₄, Fe₂O₃, and glucose as raw materials, which is a green and low-cost method. Thermogravimetry, differential scanning calorimetry, X-ray diffraction, and element analyzer were used to study the phase and carbon content of the synthesized samples. The optimum conditions for synthesizing LiFePO₄ are identified. The discharge capacity of 120 mAh g⁻¹ was achieved at a current density of 100 mA g⁻¹ between 2.5 and 4.2 V during the first 50 cycles.     

Sn-Sb and Sn-Bi alloys as anode materials for lithium-ion batteries

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH₄ and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH₄ yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g⁻¹, ∼ 350 – 400 mAh g⁻¹, and ∼ 500 mAh g⁻¹ were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

The preparation and characterization of olivine LiFePO4/C doped with MoO3 by a solution method

Composite Li_0.99Mo_0.01FePO4/C cathode materials were prepared by an easy solution method followed by heat-treating at various temperatures. XRD, SEM, TGA/DTA, EA, CV, XPS and charge–discharge cycles were used to evaluate the Li_0.99Mo_0.01FePO₄/C composite powders. The results indicate that mix-doping method does not affect the olivine structure of the cathode but considerably improves its capacity delivery and cycle performance. Among the prepared cathode materials, the sample heat-treated at 700 °C for 12 h shows best electrochemical performances. It shows initial specific discharge capacities of 161 and 124 mAh g^− 1 with C rates of 0.2C and 2C, respectively, which is ascribed to the enhancement of the electronic conductivity by ion doping and carbon coating.     

Synthesis of high performance Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C cathode material by ultrasonic-assisted sol–gel method

A novel ultrasonic-assisted sol–gel method is proposed to prepare Li₃V₂(PO₄)₃/C cathode material. X-ray diffraction analyses show that both Li₃V₂(PO₄)₃/C(A) synthesized by the ultrasonic-assisted sol–gel method and Li₃V₂(PO₄)₃/C(B) synthesized by a traditional sol–gel method have monoclinic structure. Scanning electron microscopy images indicate that the Li₃V₂(PO₄)₃/C(A) composite has a more uniform morphology than that of the Li₃V₂(PO₄)₃/C(B) composite. In the voltage range of 3.0–4.3 V (vs. Li/Li⁺), the initial specific discharge capacities of the Li₃V₂(PO₄)₃/C(A) and Li₃V₂(PO₄)₃/C(B) samples are 129.8 and 125.9 mAh g⁻¹ at 1C rate (1C = 133 mA g⁻¹), respectively. Furthermore, at 2-C charge/10-C discharge rate, the specific discharge capacity of the Li₃V₂(PO₄)₃/C(A) composite retains 113.2 mAh g⁻¹ after 50 cycles, but the Li₃V₂(PO₄)₃/C(B) composite only presents a capacity of 94.8 mAh g⁻¹.     

Sn(II)-Treated MoO3 as cathode material for rechargeable lithium batteries

We report on the synthesis and structural, thermal and electrochemical characterisation of reduced molybdenum oxides with layered α-MoO₃ type structure. The samples have been prepared by reactions of various amounts of water-free tin dichloride with fine-particulated orthorhombic molybdenum trioxide in n-hexane (non-aqueous media) or in aqueous media, which yielded materials with different Sn:Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO₃ has been maintained after the reduction process. No crystalline impurity phases (e.g. tin oxides) could be detected by XRD. The tin-reduced samples exhibited a drastically improved cycling stability and capacity retention on cycling in 1 M LiClO₄/propylene carbonate, i.e. the discharge capacities were well above 100 mAh g⁻¹ after 20 cycles whereas the non-treated MoO₃ (reference sample) has retained only about 45 mAh g⁻¹. At higher cycle numbers (approx. cycle 100) the discharge capacity of the reduced molybdenum oxides stabilises at a level of approx. 100 mAh g⁻¹. This significant improvement of the rechargeability may be related to improved electronic conductivity and/or higher structural stabilisation of the layered MoO₃ structure either due to (i) a coating of the MoO₃ particles with a protective thin layer of a tin containing compounds, and/or (ii) an amorphisation of the structure after reductive treatment. Further efforts of this study were devoted to a variation of the conductive carbon content in the electrode composition and to changes of cut-off voltages and current densities. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Improved of cathode performance of LiFePO<Subscript>4</Subscript>/C composite using different carboxylic acids as carbon sources for lithium-ion batteries

Among the several materials under development for use as a cathodes in lithium-ion batteries olivine-type LiFePO₄ is one of the most promising cathode material. However, its poor conductivity and low lithium-ion diffusion limits its practical application. In this study, we report seven different carboxylic acids used to synthesize LiFePO₄/C composite, and influences of carbon sources on electrochemical performance were intensively studied. The structure and electrochemical properties of the LiFePO₄/C were characterized by X-ray diffraction, scanning electron microscopy, electrical conductivity, and galvanostatic charge–discharge measurements. Among the materials studied, the sample E with tartaric acid as carbon source exhibited the best cell performance with a maximum discharge capacity of 160 mAh g⁻¹ at a 0.1 C-rate. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.     

A PEG-assisted rheological phase reaction synthesis of 5LiFePO<Subscript>4</Subscript>⋅Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as cathode material for lithium ion cells

5LiFePO₄⋅Li₃V₂(PO₄)₃/C composite cathode material is synthesized by a polyethylene glycol (PEG)-assisted rheological phase method. As a surfactant and dispersing agent, PEG can effectively inhabit the aggregation of colloidal particles during the formation of the gel. Meanwhile, PEG will coat on the particles to play the role of carbon source during the sintering. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical methods. XRD results indicate that the 5LiFePO₄⋅Li₃V₂(PO₄)₃/C composites are well crystallized and contain olivine-type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. The composite synthesized at 650 °C exhibits the initial discharge capacities of 134.8 and 129.9 mAh g⁻¹ and the capacity retentions of 96.2 and 97.1 % after 50 cycles at 1C and 2C rates, respectively.     

An improved solid-state reaction route to Mg2+-doped LiFePO4/C cathode material for Li-ion battery

An improved solid-state reaction route has been employed to synthesize Mg²⁺-doped LiFePO₄/C nanocomposite cathode by calcining the precursor obtained via evaporating the mixture of ascorbic acid, LiCH₃COO·2H₂O, Mg(CH₃COO)₂·4H₂O, and amorphous FePO₄ nanoparticles in anhydrous ethanol under continuous stirring. Ascorbic acid used here acted as both reducing agent and carbon source. The amorphous FePO₄ was pre-prepared via a simple and fast oxidic precipitation method. Electrochemical tests showed that the final product exhibited good rate and cycling performance, with discharge capacities of 145.2 mAh g^?1 at 0.2 C, 129.8 mAh g^?1 at 1 C, 107.6mAh g^?1 at 5 C, and 81.4 mAh g^?1 at 20 C, respectively. The Mg²⁺-doped LiFePO₄/C showed enhanced charge–discharge performance compared with undoped LiFePO₄/C, especially at high rates. The enhanced electrochemical performance of the composite could be attributed to a combination result of the fine particle size with narrow particle size distribution, homogeneous carbon coating on the surface of the particles, and magnesium ion doping.     

Preparation of MnO<Subscript>2</Subscript>/WMNT composite and MnO<Subscript>2</Subscript>/AB composite by redox deposition method and its comparative study as supercapacitive materials

The manganese oxide/multi-walled carbon nanotube (MnO₂/MWNT) composite and the manganese oxide/acetylene black (MnO₂/AB) composite were prepared by translating potassium permanganate into MnO₂ which formed the above composite with residual carbon material using the redox deposition method and carbon as a reducer. The products were characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope. Electrochemical properties of both the MnO₂/MWNT and MnO₂/AB electrodes were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the MnO₂/MWNT electrode has better electrochemical capacitance performance than the MnO₂/AB electrode. The charge–discharge test showed the specific capacitance of 182.3 F·g⁻¹ for the MnO₂/MWNT electrode, and the specific capacitance of 127.2 F·g⁻¹ for the MnO₂/AB electrode had obtained, within potential range of 0–1 V at a charge/discharge current density of 200 mA·g⁻¹ in 0.5 mol·L⁻¹ potassium sulfate electrolyte solution in the first cycle. The specific capacitance of both the MnO₂/MWNT and MnO₂/AB electrodes were 141.2 F·g⁻¹ and 78.5 F·g⁻¹ after 1,200 cycles, respectively. The MnO₂/MWNT electrode has better cycling performance. The effect of different morphologies was investigated for both MnO₂/MWNT and MnO₂/AB composites.     

Nanosized IrO<Subscript>2</Subscript> electrocatalysts for oxygen evolution reaction in an SPE electrolyzer

Nanosized IrO₂ electrocatalysts (d ~ 7–9 nm) with specific surface area up to 100 m² g⁻¹ were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C. The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry (TG–DSC) and transmission electron microscopy (TEM). IrO₂ catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm⁻². A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm⁻². The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A maximum current density of 1.3 A cm⁻² was obtained at 1.8 V and 80 °C for the IrO₂ catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination between nanostructure and suitable morphology.     

Effect of LiBOB as additive on electrochemical properties of lithium–sulfur batteries

The effect of varying amounts (in the range 1–10 wt.%) of LiBOB (lithium bis(oxalato) borate) as additive in mixed liquid electrolyte on the electrochemical performance of lithium–sulfur batteries is investigated at room temperature. The electrochemical impedance spectroscopy (EIS) of lithium anode with LiBOB has two semicircles, corresponding to charge transfer impedance and ion migration impedance, respectively. The lithium anode with LiBOB shows a higher ion migration impedance, which could reduce the ionic diffusion rate in the anode. Scanning electron microscopy (SEM) observations shows that lithium anode with LiBOB has a smoother and denser surface morphology than the anode without LiBOB. The lithium–sulfur batteries with LiBOB shows the improvement of both the discharge capacity and cycle performance, a maximum discharge capacity of 1,191 mA h g⁻¹ is obtained with 4 wt.% LiBOB. The lithium–sulfur batteries with 4 wt.% LiBOB can maintain a reversible capacity of 756 mA h g⁻¹ after 50 cycles.     

Nanoporous carbon microspheres as matrix of sulfur to prepare sulfur/carbon cathode material for lithium–sulfur battery

A high specific surface area (2798.8 m² g^?1) of nanoporous carbon microsphere (NPCM) is prepared by activated carbon microsphere in hot CO₂ atmosphere, which is used as matrix material of sulfur to prepare NPCM/sulfur composite cathode material by a melt-diffusion method. The NPCM/sulfur composite cathode material with the sulfur content of 53.5% shows high discharge capacity; the initial discharge capacity is 1274 mAh g^?1 which maintains as high as 776.4 mAh g^?1 after 50 cycles at 0.1 C current. At high current density of 1 C, the NPCM/sulfur cathode material still shows initial discharge capacity of 830.3 mAh g^?1, and the reversible capacity retention is 78% after 50 cycles. To study the influence of different sulfur content of NPCM/sulfur cathode material to the performance of Li–S battery, the different sulfur content of NPCM/sulfur composite cathode materials is prepared by changing the thermal diffusion time and the ratio of sulfur powder to NPCM. The performance of NPCM/sulfur cathode material with different sulfur content is studied at a current of 0.1 C, which will be very important to the preparation of high-performance sulfur/carbon cathode material with appropriate sulfur content.     

Enhanced electrochemical properties of LiMnPO<Subscript>4</Subscript>/C via Li-site substitution with Mg

Li_0.94Mg_0.03MnPO₄/C composite cathode materials for lithium ion battery with different carbon contents are synthesized by sol–gel method followed by heat treatment in the air. Environmental scanning electron microscopy measurements show that both firing temperature and carbon content affect the morphology of the end products. X-ray powder diffraction analysis indicates that the samples are olivine-structured. The galvanostatic charge–discharge results show that the optimal firing temperature registers 400 °C and that the electrochemical performances of Li_0.94Mg_0.03MnPO₄/C are improved by elevating its carbon amount. The sample with an initial conductive carbon content of 20 wt.% gives the best performances; when tested at the rate of 0.02C, 0.1C, and 1.0C between 2.8 and 4.4 V, its initial discharge capacity reaches 145.8, 103.0, and 72.8 mAhg⁻¹, respectively, and maintains at 100.1, 77.6, and 65.4 mAhg⁻¹, respectively, after 100 cycles.     

All-solid-state lithium-based polymer cells for high-temperature applications

A lithium salt doped siloxane/methacrylate copolymer membrane, prepared by a rapid UV curing process, has been characterised and tested as a fully solid electrolyte in rechargeable lithium test cells using low cost materials as electrodes. In addition, results of a laboratory-scale Li-ion polymer cell, assembled by contacting a LiFePO₄ cathode with a graphite anode and using the solid polymer as electrolyte, are presented. The polymer electrolyte production process is simple and versatile and the highly cross-linked membrane demonstrates mechanical integrity, low T _g and large thermal stability. It is an extra soft, non-crystalline, transparent solid and shows sufficient ionic conductivity (>10⁻⁴ S cm⁻¹ at 60 °C) along with a wide electrochemical stability window and improved interfacial stability with respect to lithium. The performances in Li-based cells have been determined by cycling tests carried out at 80 °C. Good rate capability, along with high charge/discharge efficiency even at 1C-rate, and a satisfactory cyclability have been obtained. These results outline the practical relevance of the use of this solid electrolyte membrane (which serves as the separator simultaneously) in Li-based cells conceived for high-temperature applications.     

Electrochemical behavior of Mg-doped 7LiFePO4–Li3V2(PO4)3 composite cathode material for lithium-ion batteries

Mg-doping effects on the electrochemical property of LiFePO₄–Li₃V₂(PO₄)₃ composite materials, a mutual-doping system, are investigated. X-ray diffraction study indicates that Mg doping decreases the cell volume of LiFePO₄ in the composite. The cyclic voltammograms reveal that the reversibility of the electrode reaction and the diffusion of lithium ion is enhanced by Mg doping. Mg doping also improves the conductivity and rate capacity of 7LiFePO₄–Li₃V₂(PO₄)₃ composite material and decreases the polarization of the electrode reaction. The discharge capacity of the Mg-doped composite was 93 mAh?g^?1 at the current density of 1,500 mA?g^?1, and Mg-doped composite has better discharge performance than the original 7LiFePO₄–Li₃V₂(PO₄)₃ composite at low temperature, too. At ?30 °C, the discharge capacity of Mg-doped LFVP is 89 mAh?g^?1, higher than that of the original composite. Electrochemical impedance spectroscopy study shows that Mg²⁺ doping could enhance the electrochemical activity of 7LiFePO₄–Li₃V₂(PO₄)₃ composite. Mg doping has a positive influence on the electrochemical performance of the LiFePO₄–Li₃V₂(PO₄)₃ composite material.     

Synthesis of Li3V2(PO4)3/reduced graphene oxide cathode material with high-rate capability

The Li₃V₂(PO₄)₃/reduced graphene oxide (LVP/rGO) composite is successfully synthesized by a conventional solid-state reaction with a high yield of 10 g, which is suitable for large-scale production. Its structure and physicochemical properties are investigated using X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The rGO content is as low as ~3 wt%, and LVP particles are strongly adhered to the surface of the rGO layer and/or enwrapped into the rGO sheets, which can facilitate the fast charge transfer within the whole electrode and to the current collector. The galvanostatic charge–discharge tests show that the LVP/rGO electrode delivers an initial discharge capacity of 177 mAh g^?1 at 0.5 C with capacity retention of 88 % during the 50th cycle in a wide voltage range of 3.0–4.8 V. A superior rate capability is also achieved, e.g., exhibiting discharge capacities of 137 and 117 mAh g^?1 during the 50th cycle at high C rates of 2 and 5 C, respectively.     

Anhydrous proton-conducting organic–inorganic hybrid membranes synthesized from tetramethoxysilane/methyltrimethoxysilane/diisopropyl phosphite and ionic liquid

Inorganic–organic hybrid membranes were prepared by sol–gel process with tetramethoxysilane/methyltrimethoxysilane/diisopropyl phosphite and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) ionic liquid as precursors. The Fourier transform infrared spectroscopy (FT-IR) and ³¹P, ²⁹Si, ¹H, ¹³C, and ¹⁹F nuclear magnetic resonance measurements have shown good chemical stability and complexation of (POH[(CH₃)₂CHO]₂) with [BMIMBF₄] ionic liquid in the fabricated hybrid membranes. The influence of the textural properties of all the prepared composite membranes could be interpreted from nitrogen adsorption–desorption measurements. The average pore size was increased proportionally with the ionic liquid weight percent ratio in the host phosphosilicate matrix from 2.59 to 11.71 nm, respectively. Thermogravimetric analysis and differential thermal analysis measurements confirmed that the hybrid membranes were thermally stable up to 260 °C. Thermal stability of the hybrid membranes was significantly enhanced by the presence of inorganic SiO₂ framework and high stability of [BF₄] anion. For all the composite membranes, the conductivities were measured within the temperature range (−30 °C) to 150 °C, and a maximum conductivity of 7 × 10⁻³ S/cm at 150 °C was achieved for 40 wt.% ionic liquid-based composite membrane under nonhumidified conditions.