Vertical aligned V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoneedle arrays grown on Ti substrate as binder-free cathode for lithium-ion batteries

V₂O₅ nanoneedle arrays were grown directly on titanium (Ti) substrate by a facile solvothermal route followed with calcination at 350 °C for 2 h. The as-prepared V₂O₅ nanoneedles are about 50 nm in diameter and 800 nm in length. The electrochemical behavior of V₂O₅ nanoarrays as binder-free cathode for lithium-ion batteries (LIBs) was evaluated by cyclic voltammetry and galvanostatic discharge/charge tests. Compared with V₂O₅ powder electrode, V₂O₅ nanoneedle arrays electrode exhibited improved electrochemical performance in terms of high discharge capacity of 262.5 mA h g^?1 between 2.0 and 4.0 V at 0.2 C, and high capacity retention up to 77.1% after 100 cycles. Under a high current rate of 2 C, a discharge capacity of about 175.6 mA h g^?1 can be maintained. The enhanced performance are mainly due to the intimate contact between V₂O₅ nanoneedle active material and current collector, which enable shortened electron transfer pathway and improved charge transfer kinetics, demonstrating their potential applications in high rate electrochemical storage devices.     

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.     

Enhanced electrochemical performance of lithium ion battery cathode Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C

Li-ion battery cathode material lithium-vanadium-phosphate Li₃V₂(PO₄)₃ was synthesized by a carbon-thermal reduction method, using stearic acid, LiH₂PO₄, and V₂O₅ as raw materials. And stearic acid acted as reductant, carbon source, and surface active agent. The effect of its content on the crystal structure and electrochemical performance of Li₃V₂(PO₄)₃/C were characterized by XRD and electrochemical performance testing, respectively. The results showed that the content of carbon source has no significant effect on the crystal structure of lithium vanadium phosphate. Lihtium vanadium phosphate obtained with 12.3% stearic acid demonstrated the best electrochemical properties with a typical discharge capacity of 119.4 mAh/g at 0.1 C and capacity retention behavior of 98.5% after 50 cycles. And it has high reversible discharge capacity of 83 mAh/g at 5 C with the voltage window of 3 to 4.3 V.     

Ultra-rapid combustion synthesis of Na<Subscript>2</Subscript>FePO<Subscript>4</Subscript>F fluorophosphate host for Li-ion and Na-ion insertion

Exploring soft-chemistry synthesis of Fe-based battery cathode materials, we have optimized combustion synthesis as an ultra-rapid approach to produce Na₂FePO₄F fluorophosphate cathode. It yields nanoscale, carbon-coated target product by annealing (at 600 °C) for just 1 min. The purity of the material crystallizing in the orthorhombic structure was confirmed by powder X-ray diffraction pattern and XPS analysis, while the morphology was studied by scanning electron microscopy. The as-synthesized material exhibits good electrochemical performance delivering a first discharge capacity of more than 70 mAh/g at C/10 rate versus both Li⁺/Li and Na⁺/Na, hence acting as an efficient host for both Li-ion and Na-ion insertion. Combustion synthesis can be employed as an economic route for synthesis and rapid screening of various phosphate-based insertion materials.     

Low-temperature synthesis of Cu-doped Li<Subscript>1.2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> as cathode for reversible lithium storage

Li_{1 .2}V₃O₈ and Cu-doped Li_1.2V₃O₈ were prepared at a temperature as low as 300 °C by a sol-gel method. The structure, morphology, and electrochemical performance of the as-prepared samples were characterized by means of X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and the galvanostatic discharge–charge techniques. It is found that the Cu-doped Li_1.2V₃O₈ sample exhibits less capacity loss during repeated cycling than the undoped one. The Cu-doped Li_1.2V₃O₈ sample demonstrates the first discharge capacity of 275.9 mAh/g in the range of 3.8–1.7 V at a current rate of 30 mA/g and remains at a stable discharge capacity of 264 mAh/g within 30 cycles. Furthermore, the possible role that copper plays in enhancing the cycleability of Li_1.2V₃O₈ has also been elucidated.     

Synthesis of sea urchin-like LiMn2O4 hollow macrospheres via in situ conversion for rechargeable lithium-ion batteries

Among several materials (transition metal oxide) under development for use as a cathode in lithium-ion batteries, cubic spinel LiMn₂O₄ is one of the most promising cathode materials. In this study, the sea urchin-like LiMn₂O₄ hollow macrospheres were synthesized by using sea urchin-like α-MnO₂ precursors through solid-state in situ self-sacrificing conversion route. The as-prepared LiMn₂O₄ was assembled by many single-crystalline “thorns” of ca.10–20 nm in diameter and ca. 400–500 nm in length. Galvanostatic battery testing showed that sea urchin-like LiMn₂O₄ had an initial discharge capacity of 126.8 mAh/g at the rate of 0.2 C in the potential range between 3.0 and 4.5 V. More than 96.67 % of the initial discharge capacity was maintained for over 50 cycles. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by the materials. This particular sea urchin-like structured composite conceptually provides a new strategy for designing electrodes in energy storage applications.     

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.     

Oxalate precursor preparation of Li1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery positive electrode

Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ powders have been prepared through co-precipitation of metal oxalate precursor and subsequent solid state reaction with lithium carbonate. X-ray diffraction pattern shows that the massive rock-like structure has a good layered structure and solid solution characteristic. Scanning electron microscope and transition electron microscope images reveal that the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ composed of nanoparticles have the size of 1–2 μm. As a lithium ion battery positive electrode, the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ has an initial discharge capacity of 285.2 mAh g^?1 at 0.1 C within 2.0–4.8 V. When the cutoff voltage is decreased to 4.6 V, the cycling stability of product can be greatly improved, and a discharge capacity of 178.5 mAh g^?1 could be retained at 0.5 C after 100 cycles. At a high charge–discharge rate of 5 C (1,000 mAh g^?1), a stable discharge capacity of 121.4 mAh g^?1 also can be reached. As the experimental results, the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ prepared from oxalate precursor route is suitable as lithium ion battery positive electrode.     

Electrochemical properties of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C cathode materials synthesized via ethylene glycol-assisted solvothermal method

The Li₃V₂(PO₄)₃/C (LVP/C) cathode materials for lithium-ion batteries were synthesized via ethylene glycol-assisted solvothermal method. The phase composition, phase transition temperature, morphology, and fined microstructure were studied using X-ray diffraction (XRD), differential thermal analyzer (DTA), scanning electron microscope (SEM), and transmission electron microscope (TEM), respectively. The electrochemical properties, impedance, and electrical conductivity of LVP/C cathode materials were tested by channel battery analyzer, the electrochemical workstation, and the Hall test system, respectively. The results shown that the appropriate amount of water added to ethylene glycol solvent contributes to the synthesis of pure phase LVP. The LVP₁₀/C cathode material can exhibit discharge capacities of 128, 126, 126, 123, 124, and 114 mAh g^?1 at 0.1, 0.5, 2, 5, 10, and 20 C in the voltage range of 3.0–4.3 V, respectively. Meanwhile, it shows also a stable cycling performance with the capacity retention of 89.6% after 180 cycles at 20 C.     

Layered lithium-rich oxide nanoparticles: low-temperature synthesis in mixed molten salt and excellent performance as cathode of lithium-ion battery

Layered lithium-rich oxide, 0.5Li₂MnO₃·0.5LiMn_1/3Ni_1/3Co_1/3O₂, is synthesized in a mixed molten salt of KCl and LiCl under 750 °C. Its morphology and structure are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption and desorption isotherm, and its performances as cathode of lithium-ion battery are investigated by charge–discharge test and electrochemical impedance spectroscopy, with a comparison of the samples synthesized via solid-state reaction. It is found that the resulting product consists of uniform nanoparticles, 50 nm in average, which possesses a well crystallite layered structure although its synthesis temperature is low and thus exhibits excellent cyclic stability and rate capability. The resulting product delivers an initial discharge capacity of 268 mAh g^?1 at 0.1 C and has a capacity retention of 82% after 100 cycles at 1 C, compared to the 243 mAh g^?1 and 73% for the sample synthesized by solid-state reaction under 900 °C.     

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.     

Oligo(ethylene oxide)-functionalized trialkoxysilanes as novel electrolytes for high-voltage lithium-ion batteries

Oligo(ethylene oxide)-functionalized trialkoxysilanes were synthesized through hydrosilylation reaction by reacting trialkoxysilane with oligo(ethylene oxide) allyl methyl ether using PtO₂ as a catalyst. The physical properties of these compounds, such as viscosity, dielectric constant, and ionic conductivity, were characterized. Among them, [3-(2-(2-methoxyethoxy)ethoxy)-propyl]triethoxysilane (TESM2) exhibited a commercial viable ionic conductivity of 1.14 mS cm^?1 and a wide electrochemical window of 5.2 V. A preliminary investigation was conducted by using TESM2 as an electrolyte solvent for high-voltage applications in lithium-ion batteries. Using 1 M LiPF₆ in TESM2 with 1 vol% vinyl carbonate as an electrolyte, LiCoO₂/Li half-cell delivered a specific capacity of 153.9 mAh g^?1 and 90 % capacity retention after 80 cycles (3.0–4.35 V, 28 mA g^?1); Li_1.2Ni_0.2Mn_0.6O₂/Li₄Ti₅O₁₂ full cell exhibited the initial capacity of 161.3 mAh g^?1 and 86 % capacity retention after 30 cycles (0.5–3.1 V, 18 mA g^?1).     

Preparation and characterization of LiTi<Subscript>2</Subscript>O<Subscript>4</Subscript> anode material synthesized by one-step solid-state reaction

LiTi₂O₄ anode material for lithium-ion battery has been prepared by a novel one-step solid-state reaction method using Li₂CO₃, TiO₂, and carbon black as raw materials. X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and the determination of electrochemical properties show that the single phase of LiTi₂O₄ with spinel crystal structure is formed at 850?°C by this new method, and the lattice parameter is about 8.392?Å. The primary particle size of the LiTi₂O₄ powder is about 0.5–1.0 μm and its morphology is similar to a sphere. The lithium ion insertion voltage of LiTi₂O₄ anode material is about 1.50 V versus lithium metal, the initial discharge capacity is about 133.6 mAh g^-1, the charge–discharge voltage plateau is very flat, and no solid electrolyte interface film is formed when working potential is more than 1.0 V. The reaction reversibility and the cycling stability are excellent, and the high rate performance is good.     

Preparation and electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>4</Subscript>O<Subscript>7</Subscript> composite for lithium-ion batteries

In order to improve the rate capability of Li₄Ti₅O₁₂, Ti₄O₇ powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li₄Ti₅O₁₂/Ti₄O₇ has been synthesized as anode material for lithium-ion batteries. It is found that the Li₄Ti₅O₁₂/Ti₄O₇ composite shows higher reversible capacity and better rate capability compared to Li₄Ti₅O₁₂. According to the charge-discharge tests, the Li₄Ti₅O₁₂/Ti₄O₇ composite exhibits excellent rate capability of 172.3 mAh g^?1 at 0.2 C, which is close to the theoretical value of the spinel Li₄Ti₅O₁₂. More impressively, the reversible capacity of Li₄Ti₅O₁₂/Ti₄O₇ composite is 103.1 mAh g^?1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li₄Ti₅O₁₂ is only 22.3 mAh g^?1 with a capacity retention of 31.1%. The results indicate that Li₄Ti₅O₁₂/Ti₄O₇ composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries.     

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.     

Influence of co-precipitation temperature on microstructure and electrochemical properties of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials for lithium ion batteries

The layered Li-rich Mn-based cathode materials Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ were prepared by using co-precipitation technique at different temperatures, and their crystal microstructure and particle morphology were observed and analyzed by XRD and SEM. The electrochemical properties of these samples were investigated by using charge-discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results indicated that all samples are of high purity. When the precursors were co-precipitated at 50 °C, their cathode materials have the most uniform and full particles and exhibit the highest initial discharge capacity (289.4 mAh/g at 0.1C), the best cycle stability (capacity retention rate of 91.2 % after 100 cycles at 0.5C), and the best rate performance. The EIS results show that the lower charge transfer resistance of 50 °C sample is responsible for its superior discharge capacity and rate performance.     

Synthesis and performance of Li2NiTi3O8 as a new anode material for lithium-ion batteries

The titanate spinel Li₂NiTi₃O₈ is proposed for the first time as a new anode for lithium-ion batteries and successfully synthesized via a facile ball-milling assisted solid-state reaction method. The sample is characterized by X-ray diffraction patterns (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, cyclic voltammetry (CV) tests, and electrochemical impedance spectroscopy (EIS). The results reveal that the Li₂NiTi₃O₈ nanoparticles have well-distributed morphology, and the particle size ranges between 100 and 300 nm. Although the initial coulombic efficiency is only 56.3 %, the Li₂NiTi₃O₈ electrode still exhibits a high rate capability and excellent cycling stability. The Li₂NiTi₃O₈ anode provides a large capacity of 212.3 mAh g^?1 at 0.1 A g^?1 after 10 cycle, which is close to its theoretical capacity (223.6 mAh g^?1). Even after 100 cycles, it still delivers a quite high capacity of 203.98 mAh g^?1, with no significant capacity fading. This indicates that the as-synthesized Li₂NiTi₃O₈ material is a promising anode material for lithium-ion batteries.     

V<Subscript>2</Subscript>O<Subscript>5</Subscript>-SiO<Subscript>2</Subscript> hybrid as anode material for aqueous rechargeable lithium batteries

V₂O₅-SiO₂ hybrid material was fabricated by heat-treating a mixture of H₂SiO₃ and V₂O₅. SEM, TEM, XRD, and N₂ isotherm analyses were performed to characterize the morphology and structure details of the as-prepared V₂O₅-SiO₂. The possibility of using the as-prepared V₂O₅-SiO₂ as anode material for aqueous lithium-ion batteries was investigated. Potentiostatic and galvanostatic results indicated that the intercalation/de-intercalation of Li⁺ in this material in aqueous electrolyte was quasi-reversible. It was also found that a discharge capacity of up to 199.1 mAh g^?1 was obtained at a current density of 50 mA g^?1 in aqueous solution of 1 M Li₂SO₄, a value which is much higher than the available reported capacities of vanadium (+5) oxides in aqueous electrolytes.     

Preparation and electrochemical performances of submicro-TiP2O7 cathode for lithium ion batteries

The TiP₂O₇ with a cubic 3?×?3?×?3 superstructure was synthesized by a liquid-assisted solid-state reaction, and characterized by x-ray diffraction, scanning electron microscopy, cyclic voltammogram, galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy (EIS) technique. The results showed that there was only one step of intercalation into TiP₂O₇, corresponding to a pair redox (E _Li/Li ⁺?=?2.74/2.48 V). The initial discharge capacity of TiP₂O₇ was 110 mAh/g at a current density of 15 mA/g, and the capacity retention was 76.12 % of the initial discharge capacity after 100 cycles. The EIS of TiP₂O₇ electrode consisted of two semicircles in organic electrolyte, which was attributed to SEI resistance as well as the contact resistance, and charge transfer process, respectively. A suitable model was proposed to explain the impedance response of the insertion TiP₂O₇ material of lithium ion batteries.     

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.