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In this study, polyacrylonitrile and boric acid are used as the nitrogen source and boron source, respectively. The Na3V2(PO4)2F3 cathode material with a carbon layer coated by nitrogen and boron was successfully synthesized by using a mechanical ball milling assisted sol–gel method (represented as NVPF@NBC). Simultaneously, Na3V2(PO4)2F3 materials with single-atom-doped carbon have been successfully prepared in this study by using the same method. Among the above materials, NVPF@NBC exhibits appreciable electrochemical performance because of the synergistic effect of diatoms in carbon. NVPF@NBC shows an outstanding specific discharge capacity of 127.2 mA h g−1 at 0.2C, and the capacity retention after 100 cycles is 97.6%. In particular, NVPF@NBC exhibits a discharge specific capacity of 106.3 mA h g−1 at 5C, and the capacity retention after 500 cycles is 90.59%. The X-ray diffraction analysis of the synthesized materials shows that the NVPF@NBC material has good crystallinity, indicating that the diatoms of N and B do not change the crystal structure of the material. TEM shows that the NVPF@NBC material exhibits uniform distribution of particles and a uniform carbon coating of about 4 nm. Nitrogen–boron co-doping does not influence the valence state of V3+ in the material. The results indicate that the co-doping of nitrogen and boron reinforces the crystallinity of the material and strengthens the sodium storage performance of the material, thereby greatly ameliorating the electrochemical performance of the material. [ABSTRACT FROM AUTHOR]

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]

• Na 3 V 2 O 2 (PO 4) 2 F/C materials doped with Mg2+ were prepared successfully. • Mg2+ doping can boost cycling stability and rate performance of Na 3 V 2 O 2 (PO 4) 2 F/C. • The diffusion coefficients of Na+ in composites were enhanced by Mg2+ doping. Na 3 V 2 O 2 (PO 4) 2 F, a significant member of the polyanionic sodium superionic conductor family, exhibits high theoretical specific capacity and operating voltage. However, its application potential is hindered by its limited intrinsic conductivity. In this study, a series of Na 3 V 2–x Mg x O 2 (PO 4) 2 F/C cathode materials (x = 0, 0.05, 0.1, and 0.15) were synthesized using sol–gel and high-temperature solid-state methods. The impact of Mg2+ doping on the structural and electrochemical properties of Na 3 V 2 O 2 (PO 4) 2 F was examined. Na 3 V 1.9 Mg 0.1 O 2 (PO 4) 2 F/C demonstrated remarkable electrochemical performance, with a first cycle discharge specific capacity of 114.2 mAh/g and a capacity retention of 96.2 % after 500 cycles at 5C. The Na+ diffusion coefficient was 3.4 × 10–13 cm2 s−1. The full cell assembled with hard carbon as the counter electrode has a first cycle discharge specific capacity of 111.16 mAh/g at 0.1C and a capacity retention of 91.89 % after 50 cycles. This superior performance is attributed to the Mg2+ doping, which enhances the structural stability and accelerates sodium-ion diffusion. [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]

Nanoparticle Na3V2(PO4)3/C materials with different polyacrylonitrile contents can be successfully synthesized using precipitation method. As an energy storage material used in the production of lithium batteries which is also compared with pure of that, the Na3V2(PO4)3/C not only has a larger capacity, but also has a very high cycle stability. In particular, the initial discharge capacities of the Na3V2(PO4)3/C sample annealed at 750°C containing 10 wt% of polyacrylonitrile are 130.9 and 122.2 mAh g−1 at current densities of 0.5 and 1 C, respectively; the corresponding coulomb efficiencies are 97.3 and 99.5%. It is also worth noting that the capacity retention can reach as high as 92.7% for 500 cycles at 1 C. [ABSTRACT FROM AUTHOR]

A facile and highly efficient method was proposed for the separation and regeneration of LiFePO4 (LFP) cathode materials from spent lithium‐ion batteries (LIBs). The optimal separation conditions involved immersing the spent LFP materials in NaOH (0.5 mol/L) solutions at a temperature of 90 °C, with a solid‐liquid ratio of 30 g/L under stirring of 500 rpm. The high separation effect can be attributed to the synergistic action of several factors at the interface. Furthermore, the structure, composition, morphology, and electrochemical performance of the regenerated LFP (D‐LFP) materials at different temperatures were systematically investigated. Notably, the D‐LFP material generated through calcination at 650 °C for 10 h exhibited a initial discharge capacity of 154.4 mAh g−1 at 0.5 C and the capacity retention rate of 97.3 % after 100 cycles. Moreover, a detailed investigation of the kinetics of the separation and regeneration processes was carried out, along with an exploration of the underlying electrochemical mechanism. This idea not only mitigates the harmful impact of waste on both human health and the environment but also realizes the transformation of waste into valuable resource treasure, promoting a greener and more sustainable development of society. [ABSTRACT FROM AUTHOR]

Heterostructure NaMnO2–Li0.5Mn2O4 cathode materials were prepared by adjusting the molar ratio of sodium in the materials by a solid phase method. X-ray diffraction (XRD) analysis showed that the prepared samples were a layered-spinel heterostructure NaMnO2–Li0.5Mn2O4. The lattice fingerprint region of NaMnO2–Li0.5Mn2O4 was studied by electron microscopy, and the results showed the (111) plane of Li0.5Mn2O4 and the (001) plane of NaMnO2. The heterostructure 0.5NaMnO2–0.5Li0.5Mn2O4 exhibits superior high-rate capability and excellent cycling performance. The proposed heterostructure 0.5NaMnO2–0.5Li0.5Mn2O4 cathode is investigated by in situ XRD and impedance analysis. The rate of discharge of heterostructure 0.5NaMnO2–0.5Li0.5Mn2O4 was 108.8 mA h g−1 at 500 mA g−1. The initial discharge of 0.5NaMnO2–0.5Li0.5Mn2O4 was 61.69 mA h g−1, and after 1000 cycles the discharge capacity remained 51.13 mA h g−1 at a current of 2 A g−1. The heterogeneous structure combines the advantages of high capacity of the layered structure NaMnO2 and the structural stability of the spinel Li0.5Mn2O4, which exert a synergistic effect and improve the electrochemical performance of the lithium-free layered NaMnO2 cathode material. [ABSTRACT FROM AUTHOR]

In this investigation, a lithium-free cathode material, Na0.7MnO2.05–Na0.91MnO2, was synthesized by the solid phase method. The intercalation mechanism and partial phase transformation mechanism of NMO600 were clarified by in situ X-ray diffraction and impedance. The design of the heterostructure is favourable for improving the lithium ion storage of NMO600, which can deliver a discharge capacity of 83.12 mA h g−1 at 1 A g−1 and keep 61.71 mA h g−1 after 700 cycles. [ABSTRACT FROM AUTHOR]

Summary: Herein, a series of lithium‐sodium hybrid ion Na3−xLixV2(PO4)3/C (x = 2.5, 2.0, 1.5, 1.0, 0.5) as cathode materials are prepared by sol‐gel method. The lithium storage properties of Na3−xLixV2(PO4)3/C reveal that the lithium sodium ratio has a strong influence on material structure and the electrochemical properties. The multiple voltage platforms are observed at charge and discharge curve for the Na0.5Li2.5V2(PO4)3 material, as it contains rhombohedral and monoclinic Li3V2(PO4)3 phases, whereas a single voltage platform can be observed when x is less than 2, which are mixtures of Na3V2(PO4)3 with rhombohedral structure and Li3V2(PO4)3 with rhombohedral structure. Notably, NaLi2V2(PO4)3/C prepared by the calcination at 700°C for 8 hours contains a single rhombohedral phase. And when the charging and discharging voltage at the range 2.5 to 4.5 V and current density at 0.5C, NaLi2V2(PO4)3/C and Na2.5Li0.5V2(PO4)3/C are prepared by the pre‐calcination at 400°C for 4 hours and subsequent calcination at 750°C for 8 hours exhibit high first‐cycle specific discharge capacities of 124.8 and 130.0 mAh·g−1. The capacities are 118.4 and 115.1 mAh·g−1 after 50 cycles, indicating excellent capacity retention. [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]

• The crystal structures of pyrophosphate fluorides A 2 Mg 2 P 2 O 7 F 2 (A = K , Rb) were determined for the first time. • The unit of [Mg 2 O 7 F 3 ] is first reported. • K 2 Mg 2 P 2 O 7 F 2 shows a short UV cutoff edge, which indicates that it has a potential application value in the UV region. • The first-principle theoretical studies for A 2 Mg 2 P 2 O 7 F 2 (A = K , Rb) are carried out to understand the electronic structures. Two new alkali/alkaline-earth metal pyrophosphate fluorides, A 2 Mg 2 P 2 O 7 F 2 (A = K , Rb) have been synthesized, structurally analyzed, and characterized for the first time. They both crystallize in the Pbcn space group and show similar crystal structures. Their structures contain 1[M g 2 O 7 F 3 ] ∞ chains made up of edge-sharing MgO 4 F 2 octahedra and 2[ A 2 O 11 F 4 ] ∞ layers built by face-sharing [ A 2 O 11 F 4 ] clusters, which are bridged by isolated P 2 O 7 units to construct a 3D framework. It's worth noting that A 2 Mg 2 P 2 O 7 F 2 (A = K , Rb) are the first pyrophosphate fluoride in the A -Mg-P-O-F (A = alkali metal) system. Furthermore, the optical measurements of the title compounds show that they all possess UV absorption cutoff edges. First-principles theoretical studies were conducted to understand the electronic structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• LiVOPO 4 -Li 2.72 Ti 2 (PO 4) 3 was successfully synthesized by a two-step method. • The LiVOPO 4 -Li 2.72 Ti 2 (PO 4) 3 has a heterogeneous structure. • The lithium superior conductor improves electrochemical performance of the LiVOPO 4. The heterostructure LiVOPO 4 -Li 2.72 Ti 2 (PO 4) 3 (LVOP-LTP) was synthesized using a hydrothermal process combined with a high-temperature solid-phase method. The electron microscopic analysis demonstrates that the sample has a heterojunction. The electrochemical performance tests reveal that the heterostructure LVOP-LTP has initial discharge-specific capacity of 88.4 mAh/g at 100 mA g−1, which is superior to the single-phase LiVOPO 4 (LVOP, 25.1 mAh/g) and Li 2.72 Ti 2 (PO 4) 3 (LTP, 37.1 mAh/g). The improved electrochemical performance of heterostructure LVOP-LTP can be ascribed to the introduction of lithium superionic conductor (LISICON) and the formation of a heterojunction, which increases the lithium-ion pervasion channels and accelerates the lithium-ion transmission speed. [ABSTRACT FROM AUTHOR]

The oxygen vacancy modulated LiTiOPO4‐y was synthesized by simple hydrothermal and high‐temperature solid‐phase methods. X‐ray diffraction (XRD) test data analyses reveal that the density of oxygen defects in LiTiOPO4‐y can be affected by the hydrothermal reaction time. The electron paramagnetic resonance (EPR) showed signal peaks at g=2.003, which proved that oxygen defects were generated. X‐ray photoelectron spectroscopy (XPS) further demonstrated that oxygen defects exist in LiTiOPO4‐y, which led to the partial conversion of Ti4+ to Ti3+. The capacity of LiTiOPO4 was limited (less than 161 mAh g−1) by cycling potential range (0.5–3.0 V). The oxygen‐deficient LiTiOPO4‐y was used to enhance lithium‐ion storage performance by mediating voltage from 0.01 to 3.0 V. The initial capacity of oxygen‐deficient LiTiOPO4‐y, which was synthesized after hydrothermal treatment for 18 h, with an exposed (121) face, reached 563.5 mAh g−1 at the current density of 500 mA g−1. After 1500 cycles, the specific discharge capacity kept at 397.2 mAh g−1. In the oxygen‐defective LiTiOPO4‐y, multiple coordination unsaturated sites are exposed, which can not only significantly enhance ion diffusion and charge transfer, but also promote Li+ to more storage sites. [ABSTRACT FROM AUTHOR]

The heterostructures, xNa0.7MnO2–yLi4Mn5O12(0 < x < 1, 0 < y ≤ 1), were synthesized by a solid-phase method. X-Ray diffraction (XRD) analyses revealed that the as-prepared samples were heterostructures Na0.7MnO2 and Li4Mn5O12. Electron microscopy was used to study the lattice fingerprint area of 0.6Na0.7MnO2–0.4Li4Mn5O12 that showed (111) crystal surface of Li4Mn5O12 and (002) crystal surface of Na0.7MnO2. With different molar ratios of lithium and sodium, Li4Mn5O12 and Na0.7MnO2 in the formed heterostructure will change accordingly, during the synthesis process. The XPS data also showed that Mn3+/Mn4+ in the materials presented different ratios. The heterostructure, 0.6Na0.7MnO2–0.4Li4Mn5O12, exhibits superior high-rate capability and excellent cycle performance. The rate discharge capacity of 0.6Na0.7MnO2–0.4Li4Mn5O12 was maintained at 163.25 mA h g−1 at 500 mA g−1. When cycled at 100 mA g−1, the discharge capacity was maintained at 189.80 mA h g−1 after 50 cycles. The construction of heterostructure can take the advantage of the high capacity of the layered structure of Na0.7MnO2 and the stable spinel structure of Li4Mn5O12, which can form a synergistic effect and improve the electrochemical performance of cathode materials. [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]

The C@Fe 1−x S/FeS 2 heterostructure was designed using a facile hydrothermal and vulcanization method. The as-prepared sample exhibits significant electrical conductivity, excellent electrochemical performance. The heterostructure not only makes the crystalline framework of the material more stable, but also accelerates ionic diffusion kinetics. [Display omitted] • Synthesized C@Fe 1−x S/FeS 2 heterostructure by hydrothermal and vulcanization method. • Heterostructure provides stable framework, it accelerates ionic diffusion kinetics. • As one of cathode, the C@Fe 1−x S/FeS 2 shows excellent cycle performances. The high theoretical capacity of iron-based sulfide makes it a promising cathode material for sodium-ion batteries. However, the extensive application of Na+ is limited by numerous issues, such as poor electrical conductivity stemming from slow ionic conduction kinetics. In this study, a diphase heterostructure nanocomposite (C@Fe 1−x S/FeS 2) was designed by combining heterostructure engineering with carbonaceous materials. According to X-ray diffraction (XRD) analyses, the as-prepared sample exhibited a diphase structure. Microscopic examinations revealed a dragon fruit-like morphology formed by carbon and Fe 1−x S/FeS 2 , where carbon is wrapped by Fe 1−x S/FeS 2. The C@Fe 1−x S/FeS 2 composite exhibited remarkable electrochemical performance as cathode materials for sodium-ion batteries. Notably, the discharge capacity maintained a value of 370.4 mA h g−1 after 500 cycles at a current density of 500 mA g−1 within the voltage range of 0.8–3.0 V. Remarkably, the discharge capacity remained at 253.6 mA h g−1 after 2000 cycles, even when cycled at a current density of 1000 mA g−1. Additionally, the diphase heterostructure C@Fe 1−x S/FeS 2 improves the conductivity of the material and buffers capacity loss. These advantageous features are attributed to the dragon fruit-like structure constructed from carbon and Fe 1−x S/FeS 2. [ABSTRACT FROM AUTHOR]

Europium-modified TiO2 with different valence states was prepared by a hydrothermal method and calcined in air. Microscopic analyses revealed that the average particle size of europium-modified TiO2 nanoparticles is approximately 11.03 nm, and the particle size distribution is narrow. In addition, defects were introduced into TiO2 by doping with europium. X-ray photoelectron spectroscopy (XPS) showed different valence states of Eu3+/Eu2+ in Ti1−xEuxO2 (x = 0.04). A mechanism for europium-modified TiO2 with different valence states is proposed. Europium-modified TiO2 features excellent rate performance and long-term stability. The discharge capacity of Ti1−xEuxO2 (x = 0.04) reached 417.5 mA h g−1 at the initial cycle and retained 219.1 mA h g−1 at 5C after 600 cycles. When it is cycled at 50C, the rate discharge capacity is maintained at 134.9 mA h g−1. The electronic conductivity of TiO2 was significantly improved by doping with different valence states of europium (Eu3+/Eu2+) due to the existence of mixed valence states of Ti4+/Ti3+. [ABSTRACT FROM AUTHOR]

Oxygen‐deficient TiP2O7‐y is synthesized by solvothermal and high‐temperature solid‐phase methods. X‐ray powder diffraction (XRD) test data analyses reveal that the solvothermal reaction time can affect the density of oxygen defects in the TiP2O7‐y. Fourier transform infrared spectra (FT‐IR) shows that there is a blue shift in the P−O bond because of the presence of oxygen vacancies. It is strongly demonstrated that oxygen vacancies exist in TiP2O7‐y because electron paramagnetic resonance (EPR) shows sharp peaks at g=2.003. Oxygen vacancy modulated TiP2O7‐y with exposed (541) face shows long cycling stability and super high‐rate capabilities. The initial discharge capacity of TiP2O7‐y, which was prepared after solvothermal reaction for 18 h, reached 828.4 mAh g−1. It can still maintain 246.9 mAh g−1, at 0.5 A g−1, after 500 cycles. Even cycled at 5 A g−1, the reversible rate capacity was maintained at 209.7 mAh g−1. Oxygen vacancies can not only improve the electronic conductivity of TiP2O7‐y but also increase the lithium‐ion diffusion rate. [ABSTRACT FROM AUTHOR]

A new member of the cuspidine family without the structural disorder, Na 2 Mg 2 P 2 O 7 F 2 exhibits an intricate three-dimensional framework that consists of the 2D herring-shaped layers [Mg 4 O 12 F 2 ] ∞ and the 1D s-shaped chain [Na 2 O 8 F 3 ] ∞ interlinked by isolated P 2 O 7 groups via sharing edge or vertex. [Display omitted] • A new member of the cuspidine family, Na 2 Mg 2 P 2 O 7 F 2 without the structure disorder was prepared by targeted structural modulation. • Na 2 Mg 2 P 2 O 7 F 2 exhibits an intricate three-dimensional (3D) framework that consists of the 2D herring-shaped layers [Mg 4 O 12 F 2 ] ∞ and the 1D s-shaped chain [Na 4 O 18 F 6 ] ∞ interlinked by isolated P 2 O 7 groups. • It can be seen that the larger size difference Δ R enables Na 2 Mg 2 P 2 O 7 F 2 to overcome the structural disorder, which is conducive to the exploration of new structures in phosphates fluoride. • Na 2 Mg 2 P 2 O 7 F 2 with cuspidine type has a large band gap (7.1 eV) and the structural template cuspidine is suitable for exploring UV/DUV optical materials. A new alkali/alkali-earth metal pyrophosphate fluoride Na 2 Mg 2 P 2 O 7 F 2 without the structural disorder in the cuspidine family has been successfully prepared in the sealed system. Na 2 Mg 2 P 2 O 7 F 2 crystallizes in the space group P 2 1 / c (No. 14) of the monoclinic crystal system. The structure of Na 2 Mg 2 P 2 O 7 F 2 is shown to be an intricate three-dimensional (3D) framework that consists of the 2D layers [Mg 4 O 12 F 2 ] ∞ and the 1D chain [Na 2 O 8 F 3 ] ∞ interlinked by isolated P 2 O 7 groups, which demonstrates the precise coordination environment of cations and the framework in inorganic alkali/alkaline earth metal pyrophosphate fluoride. By comparing with other phosphate structures, we found that the introduction of F is conducive to the consistent arrangement of anionic group P 2 O 7 and enriches the diversity of cationic polyhedra. In addition, first-principle theoretical studies were also carried out to aid the understanding of microstructures, and Na 2 Mg 2 P 2 O 7 F 2 possesses a large band gap (7.1 eV) and has potential applications in the deep ultraviolet region. [ABSTRACT FROM AUTHOR]

• LiTiOPO 4 /CeO 2 was synthesized by hydrothermal and solid phase method. • The different valence states of Ce3+/Ce4+ exist in LiTiOPO 4 /CeO 2. • The Ce3+-doped and CeO 2 modified LiTiOPO 4 enhance Lithium-Ion storage. LiTiOPO 4 /CeO 2 composites as high-performance anodes for lithium-ion batteries (LIBs) were synthesized by a simple hydrothermal and high-temperature solid-phase method. X-ray diffraction (XRD) analysis results showed that CeO 2 -motified LiTiOPO 4 was successfully prepared. Electron microscopy observation of the structural and morphological analysis data of the prepared materials further showed that CeO 2 was coated on the surface of LiTiOPO 4. X-ray photoelectron spectroscopy (XPS) showed different valence states of Ce4+/Ce3+ exist in LiTiOPO 4 /CeO 2. The Ce3+-doped LiTiOPO 4 with CeO 2 surface modification was used to enhance lithium-ion storage performance by mediating voltage from 0.01 to 3.0 V. The rate capacity of the LiTiOPO 4 /CeO 2 was maintained at 295.5 mAh g−1. The specific discharge capacity was maintained at 206.5 mAh g−1 after 1000 cycles, at 5 A g−1. The CeO 2 not only significantly enhances ion diffusion and charge transfer, but also reduces polarization, promotes transport of Li+ to more storage sites in LiTiOPO 4. [ABSTRACT FROM AUTHOR]