Pouch-typed cell from Li-rich LiFePO<Subscript>4</Subscript> prepared by low-cost carbothermal reduction method

Lithium iron phospho-olivine cathode material with optimized lithium amount for lithium-ion batteries was successfully prepared from low cost Fe₂O₃ as raw materials by thermal reduction method. The as-obtained material showed a reversible discharge capacity of 153.8 mAh g^–1 in the voltage window of 2.0–4.2 V at half-cell level. The pouch-typed cells with prepared Li_1.05FePO₄ were assembled to investigate electrochemical performance at level of full-cell. The results show that the assembled pouch-typed full-cells present better rate capability and cycle life. The low-cost approach reported here firstly sheds light on application of mass production of olivinestructured LiFePO₄ at level of full-cell.     

A novel method with low-cost Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> to synthesize small size LiFePO<Subscript>4</Subscript> by carbothermal reduction method

The phase-pure LiFePO₄/C cathode materials have been successfully fabricated by precursor containing Fe₂O₃ coated with polyaniline through carbothermal reduction method. The polyaniline coating at Fe₂O₃ could restrict the growth of crystal and subsequently become electric carbon at higher synthesis temperature. Compared with conventional carbothermal reduction method, the sample showed a better capacity and less than 3% capacity fading after 30 cycles at various charge and discharge rate.     

Optimization of preparing LiFePO<Subscript>4</Subscript> for lithium-ion batteries via carbothermal reduction route

Lithium iron phosphate olivines (LiFePO₄) have been considered as very promising cathode for lithium-ion batteries due to their energy storage capacity combined with electrochemical and thermal stability. A key issue in synthesizing this materials is to optimize the synthetic conditions for obtain materials with excellent electrochemical properties. Here, we report full studies that investigate the synthesis of the LiFePO₄ by promising carbothermal reduction methods to prepare LiFePO₄ coated with pyrolytic carbon. Variation of the synthesis parameters showed that the materials synthesized at 700°C for 12 h have appropriate particles size and electronically conductive carbon. This makes it have better performances than others prepared at different temperature.     

LiFePO<Subscript>4</Subscript> synthesized via melt synthesis using low-cost iron precursors

LiFePO₄/C material has been prepared using fast-melt synthesis method followed by grinding and carbon coating. The low-cost iron ore concentrate (IOC) and purified iron ore concentrate (IOP) were used as iron precursors in the melt process to reduce significantly the cost of LiFePO₄/C. The same product was also synthesized using pure Fe₂O₃ under similar conditions as reference. The physical-chemical and electrochemical properties of samples were investigated. The X-ray Diffraction (XRD) results confirm the formation of an olivine structure of LiFePO₄ with a minor amount of Li₃PO₄ and Li₄P₂O₇ impurities for all the samples but no Fe₂P. The power performances of LiFePO₄/C using low-cost iron precursors were close to the sample using pure Fe₂O₃ precursor although capacity in mAh g^?1 is somewhat lower. With the inherent presence of silicon and other metals species, multi-substitution may take place when using IOC as source of iron leading to a Li(Fe_1-yM_y)(P_1-xSi_x)O₄ general composition. Multi-substitution, however, allows a better cycling stability. Therefore, these iron precursors present a promising option in this field to reduce the cost of a large-scale synthesis of LiFePO₄/C for Li-ion batteries application.     

Preparation and characterization of LiFePO<Subscript>4</Subscript> from NH<Subscript>4</Subscript>FePO<Subscript>4</Subscript>·H<Subscript>2</Subscript>O under different microwave heating conditions

Olivine-type LiFePO₄ is a very promising polyanion-type cathode material for lithium-ion batteries. In this work, LiFePO₄ with high specificity capacity is obtained from a novel precursor NH₄FePO₄·H₂O via microwave processing. The grains grow up in the duration of sintering until they reach the decomposition temperature. The apparent conductivity of the samples rises rapidly with the irradiation time and influences the electrochemical performance of the material greatly at high current density. As a result, the LiFePO₄ cathode material obtained with a sintering time of 15 min has good electrochemical performance. Between 2.5 and 4.2 V versus Li, a reversible capacity is as high as 156 mAh g⁻¹ at 0.05 C.     

Electrochemical properties of nano-crystalline LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> synthesized by polymer-pyrolysis method

LiNi_0.5Mn_1.5O₄ powders were prepared through polymer-pyrolysis method. XRD and TEM analysis indicated that the pure spinel structure was formed at around 450 °C due to the very homogeneous intermixing of cations at the atomic scale in the starting precursor in this method, while the well-defined octahedral crystals appeared at a relatively high calcination temperature of 900 °C with a uniform particle size of about 100 nm. When cycled between 3.5 and 4.9 V at a current density of 50 mA/g, the as prepared LiNi_0.5Mn_1.5O₄ delivered an initial discharge capacity of 112.9 mAh/g and demonstrated an excellent cyclability with 97.3% capacity retentive after 50 cycles.     

Nearly monodispersed LiFePO<Subscript>4</Subscript>F nanospheres as cathode material for lithium ion batteries

Tavorite-structured lithium transition metal fluorophosphates have been considered as a good alternative to olivine-type cathode for lithium-ion batteries due to its exceptional ionic conductivity and excellent thermal stability. In this work, nearly monodisperse LiFePO₄F nanospheres with high purity are successfully synthesized by a solid-state route associated with chemically induced precipitation method for the first time. The synthesized LiFePO₄F presents nearly monodisperse nanospheres particles with average particle size of ~?500 nm. Cyclic voltammetry data exhibit a clear indication of the Fe³⁺/Fe²⁺ redox couple that involves a two-phase transition. Its electrochemical behaviors are examined by galvanostatic charge-discharge. The results show that the initial discharge capacity is 110.2 mAh g^?1 at 0.5 C, after 200 cycles is still retained 104.0 mAh g^?1 with the retention rate of 94.4%. The excellent cycle performance is mainly attributed to the uniform nanospheres-like morphology which is not only beneficial to shorten the transport distance of ions and electrons, but also improve the interface area between electrode and electrolyte, and thus improve the kinetics of Li ions.     

Preparation of LiFePO<Subscript>4</Subscript>/graphene composites by microwave-assisted solvothermal method

Well-crystallized and nano-sized LiFePO₄/graphene composite have been successfully synthesized by in-situ disperse graphene oxide (GO) in precursor via a rapid microwave-solvothermal process at 200°C within 10 min. In spite of the low synthesis temperature, the structural and morphological properties of as-prepared composites present high specific capacity, an excellent high rate capability, and stable cycling performance.The short reaction times of just 10 min show the basis for an efficient and time-saving synthesis of LiFePO₄ρaphene composite.     

Electrochemical and magnetic characterization of LiFePO<Subscript>4</Subscript> and Li<Subscript>0.95</Subscript>Mg<Subscript>0.05</Subscript>FePO<Subscript>4</Subscript> cathode materials

A series of lithium iron phosphates was synthesized via the sol–gel route. Iron phosphides, which are electronic conductors, were formed when sintered at 850°C. Magnetic susceptibility measurements on the samples show antiferromagnetic behaviour with T _N=50±2 K for LiFePO₄ and Li_0.95Mg_0.05PO₄ sintered at temperatures below 850°C. The LiFePO₄ and Li_0.95Mg_0.05FePO4 cathodes show a stable electrochemical capacity in the range of 150–160 mA h/g on cycling. The cyclability deteriorates with increasing sample sintering temperature due to the increased crystal size and impurities.     

Enhanced electrochemical performance of LiFePO<Subscript>4</Subscript>/C nanocomposites due to in situ formation of Fe<Subscript>2</Subscript>P impurities

We have studied LiFePO₄/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO₄ phase, all the samples show a varying amount of in situ Fe₂P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe₂P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO₄/C sample calcined at 700 °C which contains ～15 wt% Fe₂P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g^?1 at a rate of 1 C, 121 mA h g^?1 at 10 C (～70 % of the theoretical capacity of LiFePO₄), and excellent cycleability. Although further increase in the amount of Fe₂P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li⁺ diffusion coefficient (～1.3?×?10^?13 cm² s^?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe₂P for obtaining the best capacity for the high power batteries.     

Chelation-assisted method for the preparation of cathode material LiFePO<Subscript>4</Subscript>

LiFePO₄/C composite cathode material is prepared by ball milling with the assistance of EDTA chelation with using water as the media of ball mill procedure. FePO₄ and LiOH are used as starting materials; a certain amount of glucose is used as carbon sources and reduction agent. The structure and morphology of the composite are characterized by X-ray diffraction and scanning electron microscopy. Cyclic voltammetry, AC impedance measurements, and galvanostatic charge–discharge and cycling performances are used to characterize its electrochemical properties. The results indicate that the performances of composites prepared by chelation-assisted method are much better than common ball milling method which using alcohol or acetone as the media of ball mill procedure. The stable discharge capacity of the prepared composite is 150 and 105 mAh g⁻¹ at 1 and 10 C rate, respectively.     

Orientational disorder in crystal structures of (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>ZrF<Subscript>7</Subscript> and (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>NbOF<Subscript>6</Subscript>

Crystal structures of (NH₄)₃ZrF₇ (I) and (NH₄)₃NbOF₆ (II) are refined by X-ray diffraction at room temperature. The compounds are isostructural and belong to the structural type of elpasolite: space group F23; a(I) = 9.4185(3) Å, a(II) = 9.3371(5) Å; V(I) = 835.50(5) ų, V(II) = 814.02(8) ų; Z = 4; R(I) = 0.0145, and R(II) = 0.0138. The refinement of the structures in the space group Fm3m yields abnormally short X-X distances in the pentagonal bipyramid MX₇ (X = F, O). The oxygen atom in II is identified by Nb-X distances and occupies one of the axial vertices of the bipyramid. The Nb atom in II is statistically distributed over the position 24f, while Zr in I resides in the symmetry center. The pentagonal bipyramid MX₇ has six independent orientations in I and twelve in II. One of three crystallographically independent ammonium groups of the structures is disordered over six or twelve equivalent orientations.     

Degradation of organic compounds on TiO<Subscript>2</Subscript> photocatalysts prepared by a hydrothermal method in the presence of NH<Subscript>4</Subscript>F

TiO₂ photocatalysts were synthesized by a hydrothermal method from tetraisopropyl orthotitanate (TPOT) in the presence of NH₄F with different NH₄F/Ti molar ratios (0, 0.25, and 1). The formation of a well-crystallized anatase phase of TiO₂ and the suppression of phase transition to rutile were observed, even at high calcination temperature, owing to the effects of NH₄F. The TiO₂ synthesized hydrothermally with NH₄F exhibited absorption with a shift to the longer wavelengths of the visible-light region. The hydrothermally synthesized TiO₂ with a moderate amount of NH₄F exhibited high photocatalytic activity for the degradation of alcohol diluted in water under both UV-light and visible-light irradiations.     

Crystal structures of Ti(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript> and Sn(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>

The characteristics of crystal structures of the titanium(IV) diammonium (Ti(NH₄)₂P₄O₁₃) and tin(IV) diammonium (Sn(NH₄)₂P₄O₁₃) tetraphosphates, which are isostructural with similar silicon(IV) and germanium(IV) salts, have been obtained by the Rietveld method using X-ray powder diffraction data. The compounds crystallize in the triclinic system, space group P \(\overline 1 \), Z = 2, a = 15.0291(7) Å, b = 7.9236(4) Å, c = 5.0754(3) Å, α = 99.168(3)°, β = 97.059(3)°, γ = 83.459(3)° for Ti(NH₄)₂P₄O₁₃ and a = 15.1454(7) Å, b = 8.0103(5) Å, c = 5.1053(3) Å, α = 99.898(6)°, β = 96.806(3)°, γ = 83.881(4)° for Sn(NH₄)₂P₄O₁₃. The structure is refined in the isotropic approximation using the pseudo-Voigt function: R _p = 0.077, R _Bragg = 0.045, R _F = 0.057 for Ti(NH₄)₂P₄O₁₃; R _p = 0.082, R _Bragg = 0.044, R _F = 0.046 for Sn(NH₄)₂P₄O₁₃. The hydrogen atoms of the ammonium cations are placed in the calculated positions. A comparative analysis of the structures of the compounds of the M^IV(NH₄)₂P₄O₁₃ (M^IV = Si, Ge, Ti, Sn) series has been carried out.     

Electrochemical performance of rare-earth doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel cathode materials for Li-ion rechargeable battery

Spinel powders of LiMn_2−x RE _x O₄ (RE = La, Ce, Nd, Sm; 0 ≤ x ≤ 0.1) have been synthesized by solid-phase reaction. The structure and electrochemical properties of these electrode materials were characterized by X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge–discharge experiment. The part substitution of rare-earth element RE for Mn in LiMn₂O₄ decreases the lattice parameter, resulting in the improvement of structural stability, and decreases the charge transfer resistance during the electrochemical process of LiMn₂O₄. As a result, the cycle ability, 55 °C high-temperature and high-rate performances of LiMn_2−x RE _x O₄ electrode materials are significantly improved with increasing RE addition, compared to the pristine LiMn₂O₄.     

[Zn(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][PtCl<Subscript>6</Subscript>] and [Cd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][PtCl<Subscript>6</Subscript>] as precursors for intermetallic compounds PtZn and PtCd

Double complex salts (tetraamminezinc and tetraamminecadmium hexachloroplatinates) have been synthesized. Their thermal properties have been studied, as well as the products of their degradation in hydrogen and helium atmospheres. Optimal thermolysis schedules have been determined. Thermolysis under hydrogen yields intermetallic compounds PtZn and PtCd.     

Effect of Li excess content and Ti dopants on electrochemical properties of LiFePO<Subscript>4</Subscript> prepared by thermal reduction method

Carbon coated Li_{1 + x} FePO₄ (x = 0, 0.01, 0.02, 0.03, 0.04) and doped compositions Li_1.03Fe_0.99Ti_0.01PO₄ have been synthesized by thermal reduction method in this paper. The results showed that increasing the content in Li_{1 + x} FePO₄ result in better electrochemical properties and cyclic performances until x = 0.03, which had similar change law with the particle size of samples; and the initial discharge capacity and cycle life of Li_1.03Fe_0.9Ti_0.01PO₄ was better than other samples under 1 C rate. When the Li_1.03Fe_0.99Ti_0.01PO₄/C sample cycled before 60 times, this sample exhibited a trend of increased capacity, and reached the highest discharging rate capacity of 156 mA h g⁻¹ at 60 cycles. The electrochemical performances of LiFePO₄ compositions synthesized by thermal reduction method, to some extent, can be improved by Li excess content and Ti doping.     

Crystal structure of NH<Subscript>4</Subscript>-substituted chabazite

The structure of NH₄-substituted chabazite, (NH₄)_3.30Ca_0.30Na_0.07K_0.01[Al_3.98Si_8.02O₂₄]·8.4H₂O, (trigonal, space group \(R\bar 3m\), rhombohedral unit cell: a = 9.423(1) Å, α = 94.66(2)°, V = 827.9(2) Å ³, Z = 1) has been determined by single crystal X-ray diffraction. The structure is compared to that of the natural chabazite. NH ₄ ⁺ cations occupy two of four cationic positions of original chabazite, one position being shared with H₂O. Hydrogen atoms were localized and the orientation of NH₄ tetrahedra was revealed. Their low coordination on H₂O determined a substantial decrease of H₂O content in the modified structure.     

Electrochemical performance of LiVPO<Subscript>4</Subscript>F/C composite cathode prepared through amorphous vanadium phosphorus oxide intermediate

LiVPO₄F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus oxide (VPO) intermediate synthesized by a sol–gel method using H₃PO₄, V₂O₅ and citric acid as raw materials. The properties of LiVPO₄F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel method is amorphous and VPO₄ may exist in VPO intermediate. The compositions of LiVPO₄F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO₄F. The electrochemical tests show that LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This LiVPO₄F/C composite displays discharge capacity of 133 mAh g⁻¹ at 0.5 C (78 mA g⁻¹) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge capacity of 115 mAh g⁻¹ and capacity retention of 97% after 100 cycles.