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The cathode material Na 3 V 2 (PO 4) 2 F 3 of sodium-ion battery is well-known for its large number of ion migration channels and high working voltage. However, the electrochemical performance of Na 3 V 2 (PO 4) 2 F 3 is not very outstanding. Thus, in the present study, Na 3 V 2 (PO 4) 2 F 3 cathode materials were successfully synthesized by using the sol-gel method and mechanical milling method to enhance the electrochemical performance. The physicochemical properties of synthesized Na 3 V 2 (PO 4) 2 F 3 were investigated by using X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transition electron microscopy. X-ray diffraction spectroscopy indicates that the doping of nitrogen and sulfur did not alter the crystal form of Na 3 V 2 (PO 4) 2 F 3. Transition electron microscopy image shows that Na 3 V 2 (PO 4) 2 F 3 has a thin carbon layer, and x-ray photoelectron spectroscopy illustrates the successful doping of nitrogen and sulfur into the carbon layer. The cyclic voltammetry curves show that the nitrogen and sulfur co-doped Na 3 V 2 (PO 4) 2 F 3 samples have good reversibility and low polarization. Materials with 15% thiourea has a high discharge specific capacity (126.9 mA h g−1 at 0.2 C) at the first cycle and excellent cycle stability (126.3 mA h g−1 after 100 cycles, a capacity retention of 99.5%) among the synthesized cathode materials. In the present study, the electrochemical performance of the Na 3 V 2 (PO 4) 2 F 3 cathode material was enhanced by regulation of co-doping of nitrogen and sulfur atoms. [ABSTRACT FROM AUTHOR]

• The composite solid-state electrolytes were formed by NATP and PAN. • The ionic conductivity of Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN was 4.51 × 10−4 S/cm at 20 °C. • Al3+ doping NTP enlarged the electrochemical window to 5.2 V. • Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN exhibited excellent electrochemical performance. In this study, Na 1+x Al x Ti 2-x (PO 4) 3 (NATP) with oxygen vacancies was synthesized using a high-temperature solid-phase method. Then, NATP and polyacrylonitrile (PAN) were combined to form NATP-PAN composite solid-state electrolytes. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated the presence of oxygen defects in NATP. Al3+ doping created oxygen vacancies in NATP, which decreased the activation energy for Li+ ions transport; this increased the mobility of Li+ ions in the material, broadening the electrochemical window of the electrolyte. The Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN solid-state electrolytes achieved an excellent ionic conductivity of 4.51 × 10−4 S cm−1 at 20 °C and a wide electrochemical stability window of 5.2 V (vs. Li+/Li). Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN composite electrolyte was used to assemble a Li||Li symmetric half-cell, which exhibited good interface stability and an overpotential of approximately ±60 mV at a current density of 0.25 mA cm−2. Furthermore, Li׀Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN׀LiFePO 4 was assembled into an all-solid-state lithium metal battery, which exhibited excellent electrochemical performance, with the initial discharge capacity of 255.0 mA h g−1 at 0.1 C. After 100 cycles, the discharge capacity was maintained at 229.6 mA h g−1, and the capacity retention rate was 90.0 %. Increasing dopant concentration, the oxygen defect concentration is increasing, which plays a crucial role in the ionic conductivity as well as the interface stability. The Na 1.3 Al 0.3 Ti 1.7 (PO 4) 3 -PAN solid-state electrolytes achieved an excellent ionic conductivity of 4.51 × 10−4 S cm−1 at 20 °C and a wide electrochemical stability window of 5.2 V (vs. Li+/Li). Increasing dopant concentration, the oxygen defect concentration is increasing, which plays a crucial role in the ionic conductivity as well as the interface stability. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen-deficient Li 1.3 Al 0.3 Ti 1.7 (PO 4) 3 (LATP) was prepared using a hydrothermal method followed by high-temperature calcination. Comprehensive analyses using X-ray powder diffraction (XRD), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) conclusively demonstrated the successful preparation of oxygen-deficient LATPs under different calcination temperatures in an argon-hydrogen mixed atmosphere. These varying temperatures affected the concentration of oxygen defects in LATP. The hydrothermal precursor was calcined at 700 °C for 6 h to prepare an oxygen-deficient LATP, which was subsequently combined with polyacrylonitrile (PAN) to form a solid composite electrolyte. The composite exhibited a total ionic conductivity of 7.55 × 10−4 S cm−1 at 20 °C. Furthermore, when tested at 25 °C with a current density of 0.025 mA cm−2, the composite displayed good compatibility with a lithium metal anode. At a current density of 0.1 C, the initial discharge capacity was found to be 256.2 mA h g−1, which was maintained at 231.8 mA h g−1 after 100 cycles within the voltage range of 2.0–4.5 V. By judiciously modulating the oxygen defects concentration, it is possible to not only improve the ionic conductivity of the solid composite electrolyte but also to further enhance its discharge capacity. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) present the advantages of long cycle life, high voltage, and energy density and are widely made in the field of energy storage. LiVOPO 4 (LVOP), a cathode material used in LIBs, has a high conceptual capacity of 159 mAh g−1 and high operating voltage of 3.9 V. However, its low electrical conductivity and cycle performance limit its commercial applications. According to the X-ray diffraction results, orthogonal crystal LVOP and monoclinic crystal Li 3 V 2 (PO 4) 3 (LVP) coexisted in the synthesised composite material. The transmission electron microscopy results also indicated that the LVOP and LVP phases coexist, which were coated by carbon layer of about 2.5 nm. The discharge of LVOP–LVP composite material initially was 143.2 mAh g−1, and that after 120 cycles was 132.2 mAh g−1 (at 0.1 C and 3–4.5 V). Thus, the electronic conductivity and first discharge specific capacity of the material enhanced due to the introduction of fast ion conductor LVP into LVOP. Electrochemical performance improved because the introduction of LVP led to an increase in Li+ pervasion channels in the original material and the acceleration of the Li+ transmission speed. [ABSTRACT FROM AUTHOR]

Abstract Herein, the hexagonal NaTi 2 (PO 4) 3 /C was successfully synthesized by mechanical ball-milling using citric acid as the carbon source and characterized the structure and morphology of as-obtained samples, revealing that their surface was covered with a thin carbon layer. Charge/discharge testing revealed that the NaTi 2 (PO 4) 3 /C sample with a carbon content of 4.4 wt% (prepared at 800 °C at a citric acid loading of 10 wt%) exhibited the highest initial discharge capacity of 869.5 mAh/g and featured excellent cycling stability. Thus, mechanical ball-milling coupled with carbon coating enabled the facile and practical preparation of NaTi 2 (PO 4) 3 /C with enhanced electrochemical properties. [ABSTRACT FROM AUTHOR]

Triclinic α-LiVOPO 4 with excellent electrochemical properties is prepared, using δ-VOPO 4 , LiNO 3, and a highly conductive carbon material (acetylene black) as raw materials, by a two-step method, for the first time. Transmission electron microscopy reveals that the synthesized nanoscale α-LiVOPO 4 is approximately 50–100 nm in size, and its surface is covered by 1.68 nm thick acetylene black, which not only improves the ionic conductivity of the material, but prevents material-size growth at high temperature, and particle agglomeration. In addition, the initial discharge capacity of α-LiVOPO 4 sintered at 600 °C over 10 h is the highest, reaching 111.7 mAh g −1 at 0.05 °C. The capacity retention rate is 95.1%, which is 106.3 mAh g −1 after 50 cycles. [ABSTRACT FROM AUTHOR]

A series of LiFe 1−x Mn x PO 4 /C composites (x=0, 0.1, 0.3, 0.5, 1) are synthesized via an ion exchange method, utilizing LiOH·H 2 O, FeSO 4 ·7H 2 O, MnSO 4 ·H 2 O, Na 3 PO 4 ·12H 2 O, and H 3 PO 4 as the raw materials, citric acid as the carbon source, and reductant, and H 2 O as the solvent. The composites containing Mn have larger lattice parameters compared to pure LiFeMnPO 4 /C, due to the larger ionic size of Mn 2+ compared to Fe 2+ . The composites also consist of spherical nanoparticles with a thicker carbon coating. LiFe 0.9 Mn 0.1 PO 4 /C exhibited the best electrochemical properties as the cathode in lithium-ion batteries, with a discharge capacity close to the theoretical value of LiFePO 4 , better capacity retention rate (98.5% vs. 94.5%) and excellent cycle stability. The improvements were attributed to the Mn-complex. Electrochemical impedance spectra demonstrate that the Mn-composites can improve electronic and ionic conductivity, indicating that introduction of Mn is a viable way to improve the conductivity in olivine-like LiFePO 4 cathode materials, and enhance the battery performance. [ABSTRACT FROM AUTHOR]