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To explore the influence of cation doping with cation radius variation on LiNi0.8Co0.1Mn0.1O2, a series of layered Li0.99M0.01Ni0.8Co0.1Mn0.1O2 (M-NCM, M=Ca, Sr, Ba) cathode materials were synthesized. Through density functional theory (DFT) calculations, all doped models have low band gaps and more relative electrons near the Fermi energy level than the pristine model. With increasing cation radius, the improvement in electronic conductivity diminishes. X-ray diffraction data and structural refinement results show that lattice parameters and lithium layer increase with increasing doping cation radius. The Ba-NCM sample, which has the largest radius, has the highest initial capacity (246.6 mAh·g−1) at 0.1 C. The Ca-NCM sample, with the least doping cation radius, has the highest capacity retention, which reaches to 90.06% after 100 cycles at 1 C. The Sr-NCM sample exhibits the highest remaining capacity, which could retain 146.5 mAh·g−1 at 5 C and 158.7 mAh·g−1 after 100 cycles at 1 C. This is attributed to the highest Li+ diffusion coefficient (8.49 × 10−11 cm2·s−1) and moderate electronic conductivity and radius of Sr2+. Doping Li sites in LiNi0.8Co0.1Mn0.1O2 with divalent cations of proper radius could be effectively improved the comprehensive electrochemical performance. This effect is based on not only the pillar effect and high electronic conductivity but also the trade-off between the expansion of lithium layer thickness and introduction of steric hindrance, as a consequence of the cations doping. [ABSTRACT FROM AUTHOR]

Na3–2xMgxV2(PO4)3/C (0 ≤ x ≤ 0.2) were synthesized by a sol–gel method. According to X-ray diffraction (XRD) Rietveld refinement and energy dispersive spectroscopy (EDS) mapping results, Mg ions were approved to occupy the Na2 (18e) site in Na3–2xMgxV2(PO4)3/C for the first time. The amount of Mg substitution in Na3–2xMgxV2(PO4)3/C was optimized. The specific discharge capacities of Na2.9Mg0.05V2(PO4)3/C at 10 C, 20 C, and 30 C were 98.9%, 91.5%, and 76.2% of the value obtained at 1 C, respectively. Na2.9Mg0.05V2(PO4)3/C exhibited the highest capacity retention of 80.3% with a discharge capacity of 77.3 mAh·g−1 after 1200 cycles at 10 C. Na2.9Mg0.05V2(PO4)3/C exhibited superior rate performance, resulting from a high sodium diffusion coefficient (DNa) of 3.91 × 10–12 cm2·s−1 and the excellent electrical conductivity (5.7 × 10–2 s·cm−1). Combining the X-ray photoelectron spectroscopy (XPS) and Electrochemical impedance spectroscopy (EIS) results, the mechanism of Mg substitution was investigated. Since two Na+ were replaced by one Mg2+, V Na ′ was produced to maintain valence equilibrium. This phenomenon benefited Na+ migration by broadening the diffusion channel in the structure of Na3V2(PO4)3. According to the EPR results, the signal intensity of Na2.9Mg0.05V2(PO4)3/C was much stronger than that of Na3V2(PO4)2/C, thus confirming the existence of V Na ′ after Mg substitution. When the amount of Mg substitution was further increased to 0.1, the DNa decreased because of the small radius of Mg2+, which led to severe lattice distortion and volumetric shrinkage of the unit cell. [ABSTRACT FROM AUTHOR]

Boron-modified Li(Ni0.8Co0.1Mn0.1)1−xBxO2 cathode materials(NCM811) were successfully prepared by a nano-milling assisted solid-state approach. X-ray diffraction investigations showed that the materials are solid solutions with a layered structure. SEM observations implied that the doped B ions promoted the growth of the target crystal with well-developed facets since it will form liquid phase at lower temperature. The intensity ratio of I(003)/I(104) raised with the increase in Boron doping concentration, until a maximum value of 1.453 was observed at x = 0.01. Further Rietveld refinements revealed that boron ions occupy the crystal lattice in the transition metal slab which helps to promote the lattice ordering by decreasing the Li/Ni ionic mixing. Such B promoted NCM811 cathode materials were confirmed to have an improved diffusion coefficient with a reduced interfacial resistance by subsequent CV and EIS measurements. From the electrochemical test, those B modified NCM811 cathode materials presented enhanced electrochemical performance. Among the synthesized samples, Li(Ni0.8Co0.1Mn0.1)0.99B0.01O2 exhibited the best specific capacity, with 194.7 mAh g−1 and 166.8 mAh g−1 at 0.1C and 5C respectively. The capacity retention at 0.5C was also confirmed as 98.2% after 100 cycles. Such improvement can be explained by the reduced Li/Ni ionic mixing, the increased Li ionic diffusion and the reduced interfacial resistance caused by the promoted growth of the B doped NCM811 crystals. Compared to those NCM811 materials reported elsewhere, the material obtained by this approach showed high potential for future application. [ABSTRACT FROM AUTHOR]

A cost effective and eco-friendly approach for the preparation of LiFePO4/C cathode material is proposed in this paper. High-purity natural mineral magnetite (Fe3O4 ≥ 99%) was employed as the only ferric source in the synthesis routine. By ultrafine ball milling and subsequent oxidation, the magnetite was converted into FePO4·2H2O. After dehydration, the iron phosphate reacted with Li2CO3 and sucrose to form the target LiFePO4/C composite. Mössbauer result revealed that all the Fe cations exhibited + 2 valence state in the LiFePO4 lattice although redox process of the species occurred during the synthesis. SEM observations indicated that the pure phase LiFePO4 powders with round shape were constructed by fine primary grains with size of 100–200 nm. Such micro-nano structure offered an increased Li diffusion by increasing the surface area and reducing the migration pathway. LiFePO4/C composite synthesized by this magnetite approach exhibited excellent performance with a specific capacity of 161.1 mAh g−1 at 0.1 C and a capacity retention rate of 98.8% after 100 cycles at 1 C. The new approach we proposed presents the remarkable advantages of low cost and environmental friendliness, and therefore suggest significant potential in mass production. [ABSTRACT FROM AUTHOR]

Rubidium modified Ni-rich LiNi0.8Co0.15Al0.05O2 cathode materials were successfully synthesized through a nano-milling assisted solid-state method. Rietveld refinement revealed that the Rb ions were incorporated into the lattice by replacing the original Li ions. It resulted in the enlarging of Li layer spacing together with the reducing of the thickness of the transition metal slab. Such changes in crystal structure led to the increase in the diffusion coefficient of Li ions in the lattice (DLi). Calculated diffusion coefficient presented the highest Li-ion diffusion coefficient of 1.54 × 10−10 cm2 s−1 for the sample Rb0.01Li0.99Ni0.8Co0.15Al0.05O2. It was also in good accordance with the changes in Li slab thickness. Improved electrochemical performance in specific capacity, capacity retention and rate performance were observed. Among the samples synthesized, the Rb0.01Li0.99Ni0.8Co0.15Al0.05O2 sample exhibited the highest initial discharge capacity and the best rate performance. It delivered specific discharge capacities of 190.5, 177, 169, 161 and 151 mAh g−1 at 0.1C, 0.2C, 0.5C, 1C and 5C, respectively. It also showed the best cycle stability with capacity retention of 91.31% after 100 cycles at 2C. [ABSTRACT FROM AUTHOR]