Multi-hierarchical nanosheet-assembled chrysanthemum-structured Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as electrode materials for high-performance sodium-ion batteries

The structure and morphology of sodium vanadium phosphate (Na₃V₂(PO₄)₃) play a vital role in enhancing the electrochemical performance of sodium-ion batteries due to the inherent poor electronic conductivity of the phosphate framework. In order to improve this drawback, a new chrysanthemum-structured Na₃V₂(PO₄)₃/C material has been successfully assembled with multi-hierarchical nanosheets via a hydrothermal method. Continuous scattering nanosheets in chrysanthemum petals are beneficial in reducing energy consumption during the process of sodium ion diffusion, on which the carbon-coated surface can significantly increase overall conductivity. The as-prepared sample exhibits outstanding electrochemical performance due to its unique structure. It rendered a high initial specific capacity of 117.4?mAh?g^?1 at a current density of 0.05 C. Further increasing the current density to 10 C, the initial specific capacity still achieves 101.3?mAh?g^?1 and remains at 87.5?mAh?g^?1 after 1000 cycles. In addition, a symmetrical sodium-ion full battery using the chrysanthemum-structured Na₃V₂(PO₄)₃/C materials as both the cathode and anode has been successfully fabricated, delivering the capacity of 62?mAh?g^?1 at 1?C and achieving the coulombic efficiency at an average of 96.4% within 100 cycles. These results indicate that the new chrysanthemum-structured Na₃V₂(PO₄)₃/C can provide a new idea for the development of high-performance sodium-ion batteries.     

Investigations on the synthesis and electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C by different methods

Li₃V₂(PO₄)₃/C samples were synthesized by two different synthesis methods. Their influence on electrochemical performances of Li₃V₂(PO₄)₃/C as cathode materials for lithium-ion batteries was investigated. The structure and morphology of Li₃V₂(PO₄)₃/C samples were characterized by X-ray diffraction and scanning electron microscopy. Electrochemical performance was characterized by charge/discharge, cyclic voltammetry, and alternating current (AC) impedance measurements. Li₃V₂(PO₄)₃/C with smaller grain size showed better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of the Li₃V₂(PO₄)₃/C were attributed to the decreasing grain size and enhanced electrical conductivity produced via low temperature route. AC impedance measurements also showed that the Li₃V₂(PO₄)₃/C synthesized by low temperature route significantly decreased the charge-transfer resistance and shortened the migration distance of lithium ion.     

Improved structural stability and electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript> (PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material by Cr doping

Cr-doped sodium vanadium phosphate (NVP) in the form of Na₃V_2-xCr_x(PO₄)₃ (x = 0, 0.02, 0.04, 0.08, 0.10) is synthesized via a facile sol-gel route as cathode materials for sodium ion batteries. The structure and morphology of these materials are systematically characterized by x-ray diffraction (XRD), Fourier-infrared spectra (FT-IR), and scanning electron microscope (SEM). XRD analysis reveals that with the increasing amount of Cr, the crystallographic parameters show a descending trend. Electrochemical tests show that the cycle stability and the specific capacity of the sodium ion batteries can be significantly improved by doping Cr into NVP. Among all the Cr-doped cathode materials, Na₃V_1.92Cr_0.08(PO₄)₃ achieves the highest capacity of 112.2 mAh g^?1 and the capacity retention is 97.2 % after 50 cycles. Electrochemical impedance spectroscopy measurements demonstrate that Cr doping is an effective method to reduce the contact resistance of interparticles by suppressing irreversible phase transformation at low sodium contents.     

The properties research of ferrum additive on Li [Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>] O<Subscript>2</Subscript> cathode material for lithium ion batteries

Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3] O₂(x?=?0.0, 0.1, 0.3, 0.5, 0.7, and 0.9) cathode materials have been synthesized via hydroxide co-precipitation method followed by a solid state reaction. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The crystal structure features were characterized by X-ray diffraction (XRD). The electrochemical properties of Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3]O₂ were compared by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy(EIS), and galvanostatic charge/discharge test. Electrochemical test results indicate that Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ decrease charge transfer resistance and enhance Li⁺ ion diffusion velocity and thus improve cycling and high-rate capability compared with Li[Ni_1/3Co_1/3Mn_1/3]O₂. The initial discharge specific capacity of Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ was 178.5 mAh/g and capacity retention was 87.11 % after 30 cycles at 0.1C, with the battery showing good cycle performance.     

Antisite defects and valence state of vanadium in Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Electron paramagnetic resonance (EPR) studies have been performed with the aim of determining the valence state and local crystal structure of the nearest environment of vanadium ions in the initial, charged, and discharged samples of the cathode material Na_xV₂(PO₄)₃ (1 ≤ x ≤ 3). It has been found that the charged sample (x = 1) is characterized by an intense signal corresponding to V⁴⁺ ions located in a highly distorted octahedral crystal field. An EPR signal with the g-factor close to the g-factor of the V⁴⁺ ion has also been observed in the initial sample (x = 3), where the intensity of the resonance signal is one order of magnitude lower than that in the charged sample. It has been revealed that the resonance signal under consideration is associated with the formation of antisite defects when a part of vanadium ions are located in sites of sodium ions. It has also been found that the intensity of this signal increases after a complete charge–discharge cycle (x = 3).     

Improved electrochemical performance of Li<Subscript>1.2</Subscript>Ni<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>O<Subscript>2</Subscript> cathode material with fast ionic conductor Li<Subscript>3</Subscript>VO<Subscript>4</Subscript> coating

Layered lithium-enriched nickel manganese oxides Li_1.2Ni_0.2Mn_0.6O₂ have been synthesized and coated by fast ionic conductor Li₃VO₄ with varying amounts (1, 3, and 5 wt%) in this paper. The effect of Li₃VO₄ on the physical and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), discharge, cyclic performance, rate capability, and electrochemical impedance spectroscopy (EIS). The discharge capacity and coulomb efficiency of Li_1.2Ni_0.2Mn_0.6O₂ in the first cycle have been improved after Li₃VO₄ coating. And, the 3 wt% Li₃VO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ shows the best discharge capacity (246.8 mAh g^?1), capacity retention (97.3 % for 50 cycles), and rate capability (90.4 mAh g^?1 at 10 C). Electrochemical impedance spectroscopy (EIS) results show that the R _ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode decreases after Li₃VO₄ coating, which is due to high lithium ion diffusion coefficient of Li₃VO₄, is responsible for superior rate capability.     

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.     

Nanocrystalline Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> electrodes for supercapattery application

Nanocrystalline Li₂TiO₃ was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ～40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li₂TiO₃ cell in 1 mol L^?1 Li₂SO₄ aqueous electrolyte. The Li₂TiO₃ electrode exhibits a specific discharge capacity of 122 mAh g^?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g^?1 at a current density of 1 mA g^?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li₂TiO₃ is a suitable electrode material for supercapattery application.     

Lithium diffusion in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based electrodes: a joint analysis of electrochemical impedance,cyclic voltammetry,pulse chronoamperometry,and chronopotentiometry data

In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li₃V₂(PO₄)₃), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10^?9 and 3 × 10^?10 cm² s^?1, respectively, for transfer in the bulk and 10^?12 cm² s^?1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10^?10 and 0.9–5 × 10^?10 cm² s^?1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10^?10 cm² s^?1 for lithiated (at a potential of 3.5 V) and 2.3 × 10^?9 cm² s^?1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10^?11 cm² s^?1 for anodic and 3.4 × 10^?11 cm² s^?1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li₃V₂(PO₄)₃ electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Properties of Ca-containing LiCoPO<Subscript>4</Subscript>-graphitic carbon foam composites

LiCo_1???x Ca _x PO₄–graphitic carbon foam composites are prepared using a sol–gel method. The structural analysis reveals LiCoPO₄ as major crystalline phase and Co₂P₂O₇ (for x?=?0.0) and Co₂P, Li₃PO₄, and (Ca,Co)₃(PO₄)₂ (for x?≥?0.05) as secondary phases. The morphology consists of microcrystalline “islands” with acicular crystallites (5–50 μm size). Transmission electron microscopy (TEM) of the powders showed that the Ca is incorporated into the crystal structure evoking exaggerated grain growth. The voltammetric profiles show a decrease of the voltammetric surface between anodic and cathodic sweeps and a shift of the reduction potentials toward higher values (～4.6 V, x?=?0.1). The electrochemical measurements, at a discharge rate of C/10 (room temperature), show an increase of the discharge-specific capacity from 100 mAhg^?1 for x?=?0.0 to 104 mAhg^?1 for x?=?0.1. The ac impedance spectroscopy data revealed an improvement of the Li-ion conductivity at high content of Ca ions (x?=?0.1).     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

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.     

Synthesis and electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C by organic solvent replacement drying method

A series of Li₃V₂(PO₄)₃/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g^?1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10^?7 cm² s^?1) which can facilitate to the Li⁺ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.     

Synthesis and electrochemical characterization of graphene nanoflakes and LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C for lithium-ion battery

The graphene nanoflakes and olivine-type LiFe_0.97Ni_0.03PO₄/C (LFNP3/C) samples have been synthesized as anode and cathode materials, respectively. Physicochemical characterization of the graphene nanoflakes and LFNP3/C material were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD patterns reveal the formation of the pure phase of both the synthesized samples. SEM micrographs disclose the formation of spherically shaped nanosized particles for LFNP3/C while graphene shows flake-type morphology. CR2032 half and full coin cells were assembled for electrochemical testing of the synthesized samples. Cyclic voltammetry (CV) results indicate that the graphene-based half-cells, i.e., GN1H and GN2H, possess reduction peak/plateau around 0.17 V while LFNP3/C cathode shows discharging voltage plateau at 3.4 V vs. Li/Li⁺. The discharge capacities were found to be 700, 900, and 153 mAhg^?1 for GN1H, GN2H, and LFNP3/C half-cells vs. Li/Li⁺, respectively. Among full cells, LFPGN1F with γ = 0.75 (mass/capacity balancing factor) shows better charging/discharging profile at each C-rate as compared to LFPGN2F with γ = 0.55. LFPGN1F delivered an initial discharge capacity of around 154 mAhg^?1 at 0.1C and even at a high discharge rate of 1C, it retained ~97% of the discharge capacity as compared to the initial cycle at the same rate.     

The effects of copper and titanium co-substitution on LiNi<Subscript>0.6</Subscript>Co<Subscript>0.15</Subscript>Mn<Subscript>0.25</Subscript>O<Subscript>2</Subscript> for lithium ion batteries

The Li(Ni_0.6Co_0.15Mn_0.25)_1?x (CuTi) _x O₂ (x = 0.00, 0.01, 0.02, 0.03) cathode materials were synthesized via a hydroxide co-precipitation method followed by a solid-state reaction. The elementary composition, crystal structure features, morphology, and electrochemical performances of the powders were investigated in detail by inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results of XRD and Rietveld refinements demonstrate that Cu and Ti co-substitution does not destroy the crystal structure, but can decrease cation ordering level and improve structural integrity. Electrochemical results show that Cu and Ti addition also results in an improved rate and cycling performances compared to pristine LiNi_0.6Co_0.15Mn_0.25O₂. An increase in rate performance and cycle stability upon copper and titanium co-substitution is related to the better hexagonal structure and enhanced kinetics of the intercalation process. Especially, Li(Ni_0.6Co_0.15Mn_0.25)_0.99(CuTi)_0.01O₂ exhibits the best rate performance and cycle stability among all samples with discharge specific capacity of 178.8 mAh/g and capacity retention of 90.6% after 30 cycles at 0.2C, which are higher than those of other materials.     

Characteristics of the Li<Superscript>+</Superscript>-Ion Conductivity of Li<Subscript>3</Subscript>R<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> Crystals (R = Fe,Sc) in the Superionic State

The characteristics of Li+-ion conductivity σdc of structural γ modifications of Li₃R₂(PO₄)₃ compounds (R = Fe, Sc) existing in the superionic state have been investigated by impedance spectroscopy. The type of structural framework [R₂P₃O₁₂]_∞^3- affects the σdc value and the σdc activation enthalpy in these compounds. The ion transport activation enthalpy in γ-Li₃R₂(PO₄)₃ (ΔH_σ = 0.31 ± 0.03 eV) is lower than in γ-Li₃Fe₂(PO₄)₃ (ΔH_σ = 0.36 ± 0.03 eV). The conductivity of γ-Li₃Fe₂(PO₄)₃ (σ_dc = 0.02 S/cm at 573 K) is twice as high as that of γ-Li₃R₂(PO₄)₃. A decrease in temperature causes a structural transformation of Li₃R₂(PO₄)₃ from the superionic γ modification (space group Pcan) through the intermediate metastable β modification (space group P2₁/n) into the “dielectric” α modification (space group P2₁/n). Upon cooling, σdc for both phosphates decreases by a factor of about 100 at the superionic TSIC transition. In Li₃Fe₂(PO₄)₃ σdc gradually decreases in the temperature range T_SIC = 430–540 K, whereas in Li₃R₂(PO₄)₃ σdc undergoes a jump at T_SIC = 540 ± 25 K. Possible crystallochemical factors responsible for the difference in the σdc and ΔH_σ values and the thermodynamics and kinetics of the superionic transition for Li₃R₂(PO₄)₃ are discussed.     

Study on electrochemical performance of Mg-doped Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript> cathode material for Li-ion batteries

In this paper, Li₂Fe_1?yMg_ySiO₄/C (y?=?0, 0.01, 0.02, 0.03, 0.05), a cathode material for lithium-ion battery was synthesized by solid-state method and modified by doping Mg²⁺ on the iron site. The effects of Mg²⁺ doping on the crystal structure and electrochemical performance Li₂FeSiO₄ was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical tests. Electrochemical methods of measurement were applied including constant current charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), to determine the electrochemical performance of the material and the optimal doping ion and ratio. The results showed that Li₂Fe_0.98Mg_0.02SiO₄/C has the higher specific capacity and better cycle stability as well as lower impedance and better reversibility. The enhanced electrochemical performance can be attributed to the increased electronic conductivity, the decreased charge transfer impedance, and the improved Li-ion diffusion coefficient. Then, further study on the synthesis conditions was performed to find the optimal combustion temperature and time. According to the study, the material which has the best electrochemical performance, shows initial discharge specific capacity of 142.3 mAh g^?1 at 0.1 C (1 C?=?166 mA g^?1) and coulomb efficiency of 95.6%, under the condition that the temperature is 700 °C and the calcining time is 10 h.     

Enhanced electrochemical performance of Cu<Subscript>2</Subscript>O-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode material for lithium-ion batteries

Li₄Ti₅O₁₂/Cu₂O composite was prepared by ball milling Li₄Ti₅O₁₂ and Cu₂O with further heat treatment. The structure and electrochemical performance of the composite were investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Li₄Ti₅O₁₂/Cu₂O composite exhibited much better rate capability and capacity performance than pristine Li₄Ti₅O₁₂. The discharge capacity of the composite at 2 C rate reached up to 122.4 mAh g^?1 after 300 cycles with capacity retention of 91.3 %, which was significantly higher than that of the pristine Li₄Ti₅O₁₂ (89.6 mAh g^?1). The improvement can be ascribed to the Cu₂O modification. In addition, Cu₂O modification plays an important role in reducing the total resistance of the cell, which has been demonstrated by the electrochemical impedance spectroscopy analysis.     

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.