Consider the almost insulator for pure Li3VO4 with a band gap of 3.77 eV, to significantly improve the electrical conductivity, the novel Li3V1–xMoxO4 (x = 0.00, 0.01, 0.02, 0.05, and 0.10) anode materials were prepared successfully by simple sol–gel method. Our calculations show that, by substitute Mo6+ for V5+, the extra electron occupied the V 3p empty orbital and caused the Fermi level shift up into the conduction band, where the Mo-doped Li3VO4 presents electrical conductor. The V/I curve measurements show that, by Mo doping in V site, the electronic conductivity of the Li3VO4 was increased by 5 orders of magnitude. And thence the polarization was obviously reduced. EIS measurement results indicated that by Mo-doping a higher lithium diffusion coefficient can be obtained. The significantly increased electronic conductivity combined the higher lithium diffusion coefficient leads to an obvious improvement in reversible capacity and rate performance for the Mo-doped Li3VO4. The resulting Li3V1–xMoxO4 (x = 0.01) material exhibited the excellent rate capability. At a high rate 5 C, a big discharge capacity of the initial discharge capacity 439 mAh/g can be obtained, which is higher than that of pure Li3VO4 (only 166 mAh/g), and after 100 cycles the mean capacity fade is only 0.06% per cycle.Keywords: anode materials; band gap; first-principles calculations; Li3VO4; Mo-doping; rate capability;

•The nature of the inferior persistent performance of La3GaGe5O16 phosphor is uncovered.•The most like cause is the formation of ring structure and rather localized conduction band of La3GaGe5O16.•First-principles calculation is useful in evaluating the potential of a new persistent phosphor.Using first-principles calculations, we investigate the atomic and electronic structure of La3GaGe5O16 and its oxygen vacancies with an aim to evaluate the potential of La3GaGe5O16 as a new persistent phosphor. We find that oxygen vacancies prefer the bridging sites within [GemOn] groups over the bridging sites between groups. Oxygen vacancies are found to act as an electron trap center and their trap states are of conduction band character of the host. By comparison with other excellent persistent phosphors, we suggest that La3GaGe5O16 cannot emerge as an efficient persistent phosphor, and the most likely cause is the formation of ring structure and rather localized conduction band of the host. The ring structure makes most of oxygen atoms structurally inactive and the localized conduction band results in low concentration of trapping electrons. Our results thus provide fundamental explanations for the inferior persistent performance of La3GaGe5O16 phosphor.

•Mg-doping does not change the crystal structure of Li3VO4.•Electronic conductivity of Mg-doped Li3VO4 was increased by two orders of magnitude.•Mg-doped Li3VO4 showed a significant improved performance.•The reversible discharge capacity of Li2.97Mg0.03VO4 is 415.5 mAh/g at 2C rate.Mg-doped composite, Li2.97Mg0.03VO4, with an orthorhombic structure was prepared by a sol-gel method. The effects of the Mg doping on the structure and electrochemical performance of Li3VO4 were investigated. The X-ray diffraction pattern shows that the Mg doping does not change the crystal structure of Li3VO4. The EDS mappings indicated the fairly uniform distribution of Mg throughout the grains of Li2.97Mg0.03VO4. Electronic conductivity of Mg-doped Li3VO4 increased by two orders of magnitude compared to that of pure Li3VO4. CV and EIS measurement confirms that the Li2.97Mg0.03VO4 sample exhibits a smaller polarization and transfer resistance and a higher lithium diffusion coefficient compared with the pure Li3VO4. Due to the better electrochemical kinetics properties, Mg-doped Li3VO4 showed a significant improved performance compared to the pure Li3VO4, especially for the high rate capability. At the higher discharge/charge rate (2C), the discharge and charge capacities of 415.5 and 406.1 mAh/g have been obtained for the Li2.97Mg0.03VO4 which is more than three times higher the discharge/charge capacities of Li3VO4. The discharge and charge capacities of pure Li3VO4 are only 126.4 and 125.8 mAh/g respectively. The excellent electrochemical performance of Li2.97Mg0.03VO4 enables it as a promising anode material for rechargeable lithium-ion batteries.The electronic conductivity of the Mg-doped Li3VO4 was increased by two orders of magnitude. As a result, Li2.97Mg0.03VO4 have a significantly higher capacity and a relatively stable charge/discharge property.

Li2ZrO3 anode materials were prepared by the conventional solid-state reaction. The crystal structure has been determined by X-ray diffraction. Electrochemical tests show that Li2ZrO3 anode materials process a excellent cycle performance and rate capability due to the good structural stability and high lithium diffusion coefficients. For the Li2ZrO3 anode material, the change of the unit cell volume is only ∼0.3% at discharge or charge process. Except for the first several cycles, the coulombic efficiency of the Li2ZrO3 electrode was nearly 100% at a discharge/charge rate of 0.3 C. The lithium diffusion coefficients of Li2ZrO3 for the reduction and oxidation process are calculated to be 3.165 × 10−6 and 1.919 × 10−6 cm2 s−1 respectively which is much higher than that of the Li4Ti5O12 anode material (about 10−9 to 10−13 cm2 s−1). In situ XRD results, combined the sloping character of the charge/discharge voltage profiles and the lithium ion diffusion controlled mechanism in the charge and discharge process, show that the insertion/extraction mechanism of Li+ for Li2ZrO3 can be interpreted as a solid-solution behavior.

By a simple wet ball-milling method, Li3VO4-coated LiMnPO4 samples were prepared successfully for the first time. The thin Li3VO4 coating layer with a three-dimensional Li+-ion transport path and high mobility of Li+-ion strongly adhered to the LiMnPO4 material reduces Mn dissolution and increases the Li+ flux through the surface of the LiMnPO4 itself by preventing formation of phases on the surface that would normally block Li+ as well as Li+-ion permeation into the surface of the LiMnPO4 electrode and therefore improve the rate capability as well as the cycling stability of LiMnPO4 materials. The electrochemical testing shows that the 5% Li3VO4-coated LiMnPO4 sample shows a clear voltage plateau in the charge curves and a much higher reversible capacity at different discharge rates compared with the pristine LiMnPO4. EIS results also show that the surface charge transfer resistance and Warburg impedance of the Li3VO4-coated LiMnPO4 samples significantly decreased. The surface charge transfer resistance and Warburg impedance for the pristine LiMnPO4 are 955.1 Ω and 400.3 Ω, respectively. While, for the 5% Li3VO4-coated LiMnPO4, the value are only 400.2 Ω and 283.6 Ω, respectively. The surface charge transfer resistance decreases more than half. All of the improved performance will be favorable for application of the LiMnPO4 in high-power lithium ion batteries.

The Mg-doped Li3V2−xMgx(PO4)3 (x = 0.00, 0.01, 0.02, 0.05, 0.10, 0.20, 0.30, 0.33, 0.50, 1.00 and 1.33) compounds have been prepared by a sol–gel method in reducing atmosphere (70%Ar + 30%H2) using citric acid as a chelating agent and a carbon source coated on the samples. The Mg-doped effects on the structural and electrochemical performance of Li3V2(PO4)3 are investigated by X-ray diffraction, galvanostatic, charge/discharge and four-point probe measurement method. The Li3V2−xMgx(PO4)3 solid solution phase can exist stable in the composition range between x = 0.00 and 0.27. The simple improve mechanism of the electrochemical performance for Mg-doped Li3V2−xMgx(PO4)3 system is discussed too. In the Mg-doped Li3V2−xMgx(PO4)3 system, at a lower charge/discharge rate (0.1C), the cycle performance has no much improvement with the increasing Mg doping content. However, at higher rates, there has an excited improvement in both cycle performance and rate capability due to the increase of electrical conductivity (more than one order of magnitude). At 5C charge/discharge rate, for the Li3V1.95Mg0.05(PO4)3 sample, the discharge capacities for the 1st and 100th cycle were 138.9 and 123.3 mAh g−1. The discharge capacity retention reached to 89% (more than 51% for undoped Li3V2(PO4)3 system). More important is that, except for the first 15 cycles, the discharge capacities kept almost a constant. Based on the excellent electrochemical performance, Li3V1.95Mg0.05(PO4)3 will be a promising cathode material for rechargeable lithium-ion batteries.Highlights► The Mg-doping content has an important effect on the structural and electrochemical performance of Li3V2(PO4)3 materials. ► The solid solution phase range of the Li3V2−xMgx(PO4)3 materials is 0 ≤ x ≤ 0.27. ► x = 0.5 is an optimal doping content for the electrochemical performance of the materials.

Lithium iron phosphate (LiFePO4) cathode material has been synthesized by a solid-state reaction. The XRD patterns and SEM images of the samples show that the LiFePO4 compounds prepared at 650 °C by using carbon gel in reaction have a single-phase, small grain-size and regular shapes. By using Rietveld refinement method, we calculated the Li–O interatomic distance in LiO6 octahedra and the cross section area of the lithium ion one-dimension tunnel, and analyze the reason of the improvement of the Lithium ion diffusion. The electrochemical test results of the sample show the LiFePO4 prepared by using carbon gel exhibits excellent electrochemical properties. Such a significant improvement in electrochemical performance should be partly related to the enhanced Lithium ion diffusion and electric conductivity due to the use of carbon gel.Highlights► Carbon gel has an important influence on the electrochemical properties of the LiFePO4 materials. ► By using the carbon gel, the lithium ion diffusion was enhanced due to the increase of the Li–O interatomic distance and the cross section area of the lithium ion one-dimension tunnel. ► In addition, the electric conductivity was obviously increased due to the small grains and good grain contact.