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In recent years, sodium-ion batteries have received increasing attention as an alternative to lithium-ion batteries, and O3-type layered oxides are considered one of the candidates for commercial sodium-ion battery cathode materials. Here, we report a novel O3-NaNi0.3Fe0.2Mn0.5O2 sodium-ion battery cathode material, characterized by SEM, XRD, XPS, EIS, CV, and charge/discharge tests for the structural and electrochemical properties of O3-NaNi0.3Fe0.2Mn0.5O2. O3-NaNi0.3Fe0.2Mn0.5O2 has a discharge capacity of 139 mAh/g at 1 C and still has 77% capacity after 100 cycles, while it has a discharge capacity of 116 mAh/g at 5 C. The excellent cycling and rate performance is mainly due to the stability of the transition metal layer and the large spacing of the Na layer. These outstanding properties make O3-NaNi0.3Fe0.2Mn0.5O2 a potential candidate for sodium-ion battery cathode materials, and the experiments in this paper also provide suitable ideas for the discovery of new sodium-ion battery cathode materials. [ABSTRACT FROM AUTHOR]

P2-Na0.67Mn0.5Fe0.5O2 has been thought to be one of the potential cathode materials for sodium-ion batteries because of its economic efficiency and high specific capacity (260 mAh g−1). However, its practical applicability was limited by rapid capacity degradation and poor rate performance. In this work, the Spherical Ce-modified Na0.67Mn0.5Fe0.5O2 materials were successfully synthesized by the hydrothermal method, which simultaneously realized Ce doping and CeO2 coating. During the high-temperature calcination process, a section of Ce was doped into the lattice, and the stronger Ce–O bonding reduces the TMO2 layer spacing and enhanced the structural stability of the material, in addition, the larger radius of Ce4+ provides a larger interlayer gap for the diffusion of sodium ions and reduces the migration potential of Na+. The other section of Ce was coated on the material surface in the form of CeO2, which protects the electrode from electrolyte erosion and avoids side reactions. Electrochemical tests demonstrated that the 3 wt% Ce-modified FM sample (FM-3) displays good cycling performance and rate capability, with a capacity retention of 61.8% after 100 cycles at 1 C, compared to just 52.6% for the pristine sample (FM-0). Even at 2 C, the FM-3 has a discharge-specific capacity of 99.7 mAh g−1, whereas FM-0 only has 79.6 mAh g−1. An efficient modification technique for creating high-performance sodium-ion battery cathode materials is presented in this work. [ABSTRACT FROM AUTHOR]

During the charging and discharging process of LiNi0.5Mn1.5O4(LNMO) battery, Ni2+ and Mn2+ dissolve into the electrolyte and cause oxidation decomposition, which seriously affects the cycle life of the battery. In addition, the impurity phase in the material can also make the structure unstable, causing poor cycle and rate performance. In this paper, LNMO and LiNi0.5-xTi4xMn1.5-3xO4 ((x)Ti-LNMO, x = 0.02, 0.03, 0.04, 0.06) with spinel structure are synthesized by hydrothermal and high-temperature calcination using metal–organic frameworks (MOFs) as precursors. The obtained LNMO and Ti-LNMOs are further analyzed by a series of characterization and electrochemical performance tests. The XRD results and the Rietveld refinements show that the impurity phases gradually disappear and the lattice parameters of the materials increase with the doping of Ti4+. From the TEM and XPS results, we have observed the Ti-LNMO surface has a uniform Li2CO3 coating layer, which can isolate the direct contact between the electrolyte and the cathode material. The rate and cyclic performance of LNMO are simultaneously improved by a dual modification of Ti doping and in situ coating. When x(Ti) = 0.03, discharge specific capacity is 91.2 mAh/g at 15 C, while the undoped LNMO is only 72.1 mAh/g. Besides, the capacity retention rates of LNMO and 0.03 Ti-LNMO after 200 cycles are 83.2% and 93.8%, respectively. These excellent electrochemical properties are mainly attributed to the more stable crystal structure of the material after titanium doping, the generation of in situ coating layers, the reduction of impurity phases, the suitable particle size, and the stable chemical interface. [ABSTRACT FROM AUTHOR]

Na2FePO4F is a promising cathode material for sodium ion batteries because of its high capacity, good cyclic stability, and small volume expansion rate. In this paper, Na2FePO4F samples with different microstructures were synthesized by hydrothermal reaction with three different solvents and carbon coating process. The structures of the synthesized materials were characterized by X-ray diffraction, thermogravimetric analysis, scanning/transmission electron microscopy, and their electrochemical properties were tested. Based on the test results, a reasonable explanation is given for the reason leading to the morphology difference of the samples. The NFPF-EG sample synthesized with 30% ethylene glycol and 70% deionized water as the mixed solvent show the best electrochemical performance (112.3 mAh g−1 at the rate of 0.1 C and 93.2% capacity retention rate after 200 cycles at 1 C). The results of cyclic voltammetry and electrochemical impedance spectrum suggest that NFPF-EG sample has small irreversible polarization and high conductivity, which is attributed to its uniform microscopic morphology and small particle size to shorten the transport path of Na+ and electrons. [ABSTRACT FROM AUTHOR]

A thin and uniform Li3PO4 layer was successfully converted on the surface of LiNi0.5Mn1.5O4 (LNMO) via H3PO4 pretreatment. H3PO4 was converted to Li3PO4 by reacting with the in situ Li2CO3 layer on the surface of LNMO, which was obtained by one-step calcination method based on MOFs. The in situ conversion coating strategy not only improved the tight bonding between the coating layer and the host structure but also effectively enhanced the structural stability and acid corrosion resistance of LNMO. Therein, the 1 wt% Li3PO4-coated LNMO delivered the discharge specific capacities of 107 mA h g−1 at 10 C and exhibited a capacity retention ratio of 92.86% after 200 cycles at 2 C. All results demonstrated that the in situ Li3PO4 coating layer is beneficial to improve the cyclic and rate properties of LNMO. This finding provided a simple and effective modification strategy to obtain the cathode materials for high energy density Li-ion batteries. [ABSTRACT FROM AUTHOR]