Structural,microstructural and electrochemical studies on LiMn2-x(GdAl)xO4 with spinel structure as cathode material for Li-ion batteries

Gd and Al co-doped LiMn_2-x(GdAl)_xO₄ (x?=?0, 0.01, 0.02, 0.03, 0.04 and 0.05) materials with spinel structure were synthesized by sol–gel method. Powder X-ray diffraction results confirm the formation of cubic spinel structure and average particle sizes are found to be between 80 and 110?nm from FE-SEM and TEM analysis. Decrease in peak potential difference as a function of doping in Cyclic Voltammetry results establishes enhancement in Li⁺ intercalation and de-intercalation. Electrochemical Impedance Spectroscopy (EIS) results showed that accumulation of charges on electrode has improved with doping over pristine samples. At a doping of x?=?0.02 charge transfer resistance values were found to be least. First cycle charge–discharge profiles for LiMn_1.96(GdAl)_0.02O₄ shows 139.2?mAh/g discharge capacity over other doped derivatives and pure LiMn₂O₄ (119.6?mAh/g) in aqueous Li₂SO₄ electrolyte. Doping of x?=?0.02 exhibit good cycling performance with only a total 4% capacity loss after 30 cycles.     

Synthesis and electrochemical characterizations of nano-scaled Zn doped LiMn2O4 cathode materials for rechargeable lithium batteries

The LiZn_xMn_2−xO₄ (x = 0.00-0.15) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol-gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valance state of Mn in the synthesized materials. The sample exhibited a well-defined spinel structure and the lattice parameter was linearly increased with increasing the Zn contents in LiZn_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmission electron microscopy, respectively. Electrochemical properties were characterized for the assembled Li/LiZn_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5 C rate and cyclic voltammetry technique in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them Zn doped spinel LiZn_0.10Mn_1.90O₄ has improved the structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.     

Spray pyrolysis synthesis of nanostructured LiFexMn2−xO4 cathode materials for lithium-ion batteries

A series of partially Fe-substituted lithium manganese oxides LiFe_xMn_2−xO₄ (0 ≦ x ≦ 0.3) was successfully synthesized by an ultrasonic spray pyrolysis technique. The resulting powders were spherical nanostructured particles which comprised the primary particles with a few tens of nanometer in size, while the morphology changed from spherical and porous to spherical and dense with increasing Fe substitution. The densification of particles progressed with the amount of Fe substitution. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns.The as-prepared powders were then sintered at 750 °C for 4 h in air. However, the particles morphology and pure spinel phase of LiFe_xMn_2−xO₄ powders did not change after sintering. The as-sintered powders were used as cathode active materials for lithium-ion batteries, and cycle performance of the materials was investigated using half-cells Li/LiFe_xMn_2−xO₄. The first discharge capacity of Li/LiFe_xMn_2−xO₄ cell in a voltage 3.5-4.4 V decreased as the value x increased, however these cells exhibited stable cycling performance at wide ranges of charge-discharge rates.     

Carbon modified Li2Ti3O7 ramsdellite electrode for Li-ion batteries

An original carbothermal synthesis of ramsdellites phases under specific atmosphere (Ar, Ar/H₂, N₂, N₂/H₂) allowed creating in situ composites which showed good electrochemical properties as negative active materials of Li-ion batteries. The combination of chemical, XRD and electrochemical analyses enabled to identify the as-formed composite electrodes. It consists in ramsdellite/spinel for the synthesis under Ar/H₂, TiO₂ ramsdellite/Li₂TiO₃ for the synthesis under N₂/H₂, and Li_2±xTi₃O₇/Li_2±x′Ti₃O₇ for the samples prepared under both N₂ and Ar. Carbon is partially inserted inside channels of titanate structure for the sample obtained under Ar/H₂. For the first time, one of these composites allowed reaching a specific capacity close to the theoretical value of 198 mAh g⁻¹.     

Improvement of the high-rate discharge capability of phosphate-doped spinel LiMn2O4 by a hydrothermal method

Micrometer-scale pristine and phosphate-doped spinel LiMn₂O₄ materials with homogeneous size distribution were synthesized by a one-step hydrothermal method. The composition, structure and morphology of the as-prepared samples were characterized using inductively coupled plasma atomic emission spectroscopy (ICP-AES), chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of phosphate doping on the structural and electrochemical properties of spinel LiMn₂O₄ was investigated by Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The phosphate-doped LiMn₂O₄ cathode (with a molar ratio of PO₄³⁻:LiMn₂O₄ = 1.5%) exhibits good high-rate discharge capability with 94 mAh/g at a current density of 2960 mA/g. The analyses demonstrate that compared with the pristine LiMn₂O₄ sample, the phosphate-doped samples have a relatively large Li-ion diffusion coefficient and smaller charge-transfer resistance due to the increase of the unit cell volume of spinel LiMn₂O₄ caused by the doping of phosphate.     

Characterization of yttrium substituted LiNi0.33Mn0.33Co0.33O2 cathode material for lithium secondary cells

LiNi_0.33−xMn_0.33Co_0.33Y_xO₂ materials are synthesized by Y³⁺ substitute of Ni²⁺ to improve the cycling performance and rate capability. The influence of the Y³⁺ doping on the structure and electrochemical properties are investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and galvanostatic charge/discharge tests. LiNi_0.33Mn_0.33Co_0.33O₂ exhibits the capacity retentions of 89.9 and 87.8% at 2.0 and 4.0 C after 40 cycles, respectively. After doping, the capacity retentions of LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ are increased to 97.2 and 95.9% at 2.0 and 4.0 C, respectively. The discharge capacity of LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ at 5.0 C remains 75.7% of the discharge capacity at 0.2 C, while that of LiNi_0.33Mn_0.33Co_0.33O₂ is only 47.5%. EIS measurement indicates that LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ electrode has the lower impedance value during cycling. It is considered that the higher capacity retention and superior rate capability of Y-doped samples can be ascribed to the reduced surface film resistance and charge transfer resistance of the electrode during cycling.     

Electrochemical performance of high specific capacity of lithium-ion cell LiV3O8//LiMn2O4 with LiNO3 aqueous solution electrolyte

The electrochemical performance of aqueous rechargeable lithium battery (ARLB) with LiV₃O₈ and LiMn₂O₄ in saturated LiNO₃ electrolyte is studied. The results indicate that these two electrode materials are stable in the aqueous solution and no hydrogen or oxygen produced, moreover, intercalation/de-intercalation of lithium ions occurred within the range of electrochemical stability of water. The electrochemical performance tests show that the specific capacity of LiMn₂O₄ using as the cathode of ARLB is similar to that of ordinary lithium-ion battery with organic electrolyte, which works much better than the formerly reported. In addition, the cell systems exhibit good cycling performance. Therefore, it has great potential comparing with other batteries such as lead acid batteries and alkaline manganese batteries.     

High capacity ZnFe2O4 anode material for lithium ion batteries

A nanostructured ternary transition metal oxide, ZnFe₂O₄, is synthesized via the simple polymer pyrolysis method. The characteristics of the material are examined by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical test results show that this method of ZnFe₂O₄ synthesis produces high specific capacities and good cycling performance, with an initial specific capacity as high as 1419.6 mAh g⁻¹ at first discharge that is maintained at over 800 mAh g⁻¹ even after 50 charge–discharge cycles. The electrode also presents a good rate capability, with a high rate of 4C (1C = 928 mA g⁻¹), a reversible specific capacity that can be as high as 400 mAh g⁻¹. ZnFe₂O₄ is a potential alternative to high-performance nanostructured anode material in lithium ion batteries.     

Enhanced cycling stability of LiMn2O4 cathode by amorphous FePO4 coating

The cycling performance of LiMn₂O₄ at room and elevated temperatures is improved by FePO₄ modification through chemical deposition method. The pristine and FePO₄-coated LiMn₂O₄ materials are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Their cycling performances are thoroughly investigated and compared. The 3 wt.% FePO₄-coated LiMn₂O₄ exhibits capacity losses of only 32% and 34% at room temperature and 55 °C, respectively, after 80 cycles, much better than those of the pristine material, 55% and 72%. The cyclic voltammograms at 55 °C reveal that the improvement in the cycling performance of FePO₄-coated LiMn₂O₄ electrodes can be attributed to the stabilization of spinel structures. The separation of FePO₄ between active materials and electrolyte and its interaction with SEI (solid electrolyte interphase) film are believed to account for the improved performances.     

Performance of layered Li(Ni1/3Co1/3Mn1/3)O2 as cathode for Li-ion batteries

Layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ was prepared by mixed hydroxide method and characterised by means of X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and charge-discharge cycling. The hexagonal lattice parameters obtained for the compound are: a=2.864 and c=14.233 Å. XPS studies show that the predominant oxidation states of Ni, Co and Mn in the compound are 2+, 3+ and 4+, respectively with small content of Ni³⁺ and Mn³⁺ ions. Initial discharge capacity of 160 mAh/g was obtained in the range 2.5-4.4 V and at a specific current of 30 mA/g of which 143 mAh/g was retained at the end of 40 charge-discharge cycles. At lower current (10 mA/g) and in the voltage window 2.5-4.7 V, discharge capacity of 215 mAh/g is obtainable. From the voltage profile and cyclic voltammetry, the redox processes occurring at ∼3.8 and ∼4.6 V are assigned to the Ni^2+/4+ and Co^3+/4+ couples, respectively.     

Novel chemical method for synthesis of LiV3O8 nanorods as cathode materials for lithium ion batteries

A novel method which is based on the hydrothermal reaction was employed to synthesize LiV₃O₈. First, the mixture solution of LiOH, V₂O₅, and NH₄OH was subjected to the hydrothermal reaction. The hydrothermal treatment yielded a clear, homogeneous solution. The evaporation of this solution led to the formation of a precursor gel. The gel was then heated at different temperatures in the range of 300-600 °C. The characterization by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) indicated that LiV₃O₈ nanorods have been obtained by this novel synthesis method. The electrochemical performance of the LiV₃O₈ nanorods have been investigated, which indicates that the highest discharge specific capacity of 302 mAh/g in the range of 1.8-4.0 V was obtained for the sample heated at 300 °C, and its capacity remained 278 mAh/g after 30 cycles.     

One-step synthesis of recoverable CuCo2S4 anode material for high-performance Li-ion batteries

A facile one-step hydrothermal method has been adopted to directly synthesize the CuCo₂S₄ material on the surface of Ni foam. Due to the relatively large specific surface area and wide pore size distribution, the CuCo₂S₄ material not only effectively increases the reactive area, but also accommodates more side reaction products to avoid the difficulty of mass transfer. When evaluated as anode for Li-ion batteries, the CuCo₂S₄ material exhibits excellent electrochemical performance including high discharge capacity, outstanding cyclic stability and good rate performance. At the current density of 200 mA·g⁻¹, the CuCo₂S₄ material shows an extremely high initial discharge capacity of 2510 mAh·g⁻¹, and the cycle numbers of the material even reach 83 times when the discharge capacity is reduced to 500 mAh·g⁻¹. Furthermore, the discharge capacity can reach 269 mAh·g⁻¹ at a current of 2000 mA·g⁻¹. More importantly, when the current density comes back to 200 mA·g⁻¹, the discharge capacity could be recovered to 1436 mAh·g⁻¹, suggesting an excellent capacity recovery characteristics.     

Li-ion diffusion kinetics in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films were deposited on Au substrates by pulsed laser deposition (PLD). The Li-ion chemical diffusion coefficients of the films, , were measured by cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). It was found that the values by CV and PITT were in the order of 10⁻¹³ cm² s⁻¹, and those by EIS and GITT were in the range of 10⁻¹³ to 10⁻¹¹ and 10⁻¹⁴ to 10⁻¹¹ cm² s⁻¹, respectively. These data were compared with the previously reported values.     

Li-storage and cyclability of urea combustion derived ZnFe2O4 as anode for Li-ion batteries

The cubic ZnFe₂O₄ with the spinel structure is prepared by the urea combustion method. Powder X-ray diffraction and HR-TEM studies confirm the single-phase nature with particle size in the range, 100-300 nm. A stable and reversible capacity, 615(±10) mAh g⁻¹ (5.5 moles of Li per mole of ZnFe₂O₄) when cycled in the range, 0.005-3.0 V vs. Li at a current of 60 mA g⁻¹(0.1C) has been achieved between 15 and 50 cycles. The underlying reaction mechanism contributing to the observed capacity is the combination of ‘de-alloying-alloying’ and ‘conversion’ reactions of ‘LiZn-Fe-Li₂O composite’. Ex situ HR-TEM and SAED data on the charged-electrode confirmed the proposed reaction mechanism.     

Enhanced rate performance of carbon-coated LiNi0.5Mn1.5O4 cathode material for lithium ion batteries

Conductive carbon has been coated on the surface of LiNi_0.5Mn_1.5O₄ cathode material by the carbonization of sucrose for the purpose of improving the rate performance. The effect of carbon coating on the physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), cycling and rate tests. Results demonstrate that the carbon coating can greatly enhance the discharge capacity, rate capability and cycling stability of the LiNi_0.5Mn_1.5O₄ without degrading the spinel structure. The sample modified with 1 wt.% sucrose displays the best performance. A large capacity of 130 mAh g⁻¹ at 1 C discharge rate with a high retention of 92% after 100 cycles and a stable 114 mAh g⁻¹ at 5 C discharge rate can be delivered. The remarkably improved rate properties of the carbon-coated samples are due to the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li⁺ diffusion and the charge transfer reaction.     

锂离子电池正极材料LiMn_2O_4的合成与性能改进

用传统的高温固相法合成了尖晶石型LiMn_(195)La_(0.05O4)锂离子电池正极材料.通过充-放电测试,其最高容量为117.1mAh/g,经过50次循环后容量为108.4 mAh/g,平均每次循环的容量衰减率为0.15%.利用X射线衍射仪(XRD)和电子扫描电镜(SEM)对材料进行表征.XRD测试结果表明,样品为尖晶石结构;SEM结果表明,样品颗粒形状理想,粒径分布均匀.     

Preparation and electrochemical profile of Li0.33MnO2 nanorods as cathode material for secondary lithium batteries

We report the preparation of Li_0.33MnO₂ nanorods from γ-MnO₂ nanorods reacted with LiNO₃ by a low temperature solid-state reaction method. The Li_0.33MnO₂ nanorods tend to be oriented along the b-axis, and show an improved rate capability and cycling performance as positive electrode for lithium battery. It delivers a discharge capacity of 199 and 129 mAh/g at the current rate of 0.1 C (20 mA/g) and 2 C, respectively, and keeps 92% of initial capacity over 100 cycles. Li_0.33MnO₂ nanorods reduce both the electrode bulk resistance and charge-transfer resistance for lithium-ion intercalation. The advantage of nanorods results from good electrical conduction, appropriate length of nanorod and small volume expansion from appropriate orientations of tunnels structure.     

Facile molten salt synthesis of Li2NiTiO4 cathode material for Li-ion batteries

Well-crystallized Li₂NiTiO₄ nanoparticles are rapidly synthesized by a molten salt method using a mixture of NaCl and KCl salts. X-ray diffraction pattern and scanning electron microscopic image show that Li₂NiTiO₄ has a cubic rock salt structure with an average particle size of ca. 50 nm. Conductive carbon-coated Li₂NiTiO₄ is obtained by a facile ball milling method. As a novel 4 V positive cathode material for Li-ion batteries, the Li₂NiTiO₄/C delivers high discharge capacities of 115 mAh g^-1 at room temperature and 138 mAh g^-1 and 50°C, along with a superior cyclability.     

Three-dimensional porous amorphous SnO2 thin films as anodes for Li-ion batteries

Three-dimensional (3D) porous amorphous SnO₂ thin films were deposited on Ni foam substrates by Electrostatic Spray Deposition (ESD) technique as anodes for Li-ion batteries. These films display good capacity retention of 94.8% after 100 cycles at 0.5 C and rate capability of 362 mAh/g at 10 C. The improved performance originates from the fact that the 3D porous structure offers a “buffer zone” to accommodate the large volume change during cycling, and the foam-like substrate maximizes the contact area between electrode and electrolyte. The facile ESD method can be potentially extended to prepare other 3D porous functional materials.     

Relationship between glass network structure and conductivity of Li2O-B2O3-P2O5 solid electrolyte

Solid state glass electrolyte, xLi₂O-(1 − x)(yB₂O₃-(1 − y)P₂O₅) glasses were prepared with wide range of composition, i.e. x = 0.35 - 0.5 and y = 0.17 - 0.67. This material system is one of the parent compositions for chemically and electrochemically stable solid-state electrolyte applicable to thin film battery. Lithium ion conductivity of Li₂O-B₂O₃-P₂O₅ glasses was studied in the correlation to the structural variation of glass network by using FTIR and Raman spectroscopy. The measured ionic conductivity of the electrolyte at room temperature increased with x and y. The maximum conductivity of this glass system was 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for 0.45Li₂O-0.275B₂O₃-0.275P₂O₅ at room temperature. It was shown that the addition of P₂O₅ reduces the tendency of devitrification and increases the maximum amount of Li₂O added into glass former without devitrification. As Li₂O and B₂O₃ contents increased, the conductivity of glass electrolyte increased due to the increase of three-coordinated [BO₃] with a non-bridging oxygen (NBO).