•Co3O4 & LiCoO2 complex layer with nutty-cake structure improves the rate and storage performance of LiNi0.8Co0.15Al0.05O2.•Lithium impurity on NCA surface can be synchronously transformed to LiCoO2 when coating Co3O4.•LiCoO2 with the similar structure to LiNiO2 tightly immobilizes Co3O4 layer on NCA surface.Co3O4 & LiCoO2 complex cladding layer with nutty-cake structure effectively improves high rate and storage properties of high nickel material LiNi0.8Co0.15Al0.05O2 (NCA), using a simple one-step wet-coating process, and the degradation of NCA is successfully restrained. The structure and morphology of samples are demonstrated by X-ray diffraction (XRD), scanning electron microscope (SEM), and field-emission high resolution transmission electron microscope (FEHRTEM). The elemental composition and distribution are determinate by energy dispersive spectrometer (EDS). In comparison with pristine NCA, 0.25 wt.% Co3O4-modified NCA has a better electrochemical performance with more capacity of approximate 30 mAh g−1 at 1C after 150 cycles. At 5C and 10C, it also exhibits better capacity retentions and higher capacities. After exposed to the air for 100 days, 0.25 wt. % Co3O4-modified NCA still shows better electrochemical performance than pristine NCA stored at the same condition. The improved comprehensive performance of Co3O4 & LiCoO2 coated NCA is related with the facile coating method in which Co3O4 is formed and the lithium impurity on NCA surface is consumed to produce LiCoO2 concurrently during calcining process. The reaction mechanism of Co3O4 & LiCoO2 composite layer is analyzed using the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS).

•LaMnO3 coated LiMn2O4 exhibits excellent high rate charge-discharge performance.•LaMnO3 with high electronic conductivity facilitates Li+ diffusion at the interface.•LaMnO3-coated LiMn2O4 shows lower charge and higher discharge potential plateau.The effect of LaMnO3 with high electronic conductivity on the fast charge-discharge rate performance of LiMn2O4 is studied. X-ray diffraction patterns confirm the existence of LaMnO3 and also indicate LaMnO3 has no influence on the crystal structure of pristine LiMn2O4. The transmission electron microscopy (TEM) images indicate that LaMnO3 coating layer, about 15 nm thickness, covers the surface of LiMn2O4 well. The electrochemical performances are evaluated by galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). At 0.5 C/0.5 C, LaMnO3 coated LiMn2O4 delivers an initial capacity of about 114 mAh g− 1 along with the coulombic efficiency of 95.0%, which are higher than those of uncoated LiMn2O4 (106 mAh g− 1 and 89.1%). Furthermore, LaMnO3 coated LiMn2O4 can exhibit higher capacities at high charge-discharge rates than uncoated LiMn2O4. It can deliver about 90.6 mAh g− 1 at 10 C/10 C and 68.0 mAh g− 1 at 20 C/20 C, but there are only 53.6 mAh g− 1 and 43.3 mAh g− 1 for bare LiMn2O4. Electrochemical impedance spectroscopy (EIS) demonstrates that LaMnO3 coating layer can effectively reduce the electrodes' resistances and improve the kinetics of electrodes. The improved high rate properties of LaMnO3 coated LiMn2O4 are ultimately ascribed to the easier phase conversion from λ-MnO2 to Li0·5Mn2O4 which is related to LaMnO3 coating layer with high electronic conductivity.

•Hybrid CeO2/C coating layer is formed to synergistically improve performance of LiMnPO4.•The interconnector of CeO2 in carbon network can enhance the electronic conductivity.•CeO2 can facilitate lithium ions diffusion and improve structural stability of LiMnPO4.•LiMnPO4/C modified with 0.25 wt.% CeO2 shows the best electrochemical performances.The CeO2/C hybrid coated LiMnPO4 composites are prepared via a simple and effective wet chemical process followed by heat treatment at 550 °C. The nanometer-sized CeO2 acts as an interconnector in carbon network, and its influence on the electrochemical performance is investigated in detail. The 0.25 wt.% CeO2-modified LiMnPO4/C (sample-0.25) exhibits the highest discharge capacity and the best cycle life, which can deliver an initial capacity of 139.9 mAh g−1 at 0.1C and still retain a reversible capacity of 120.4 mAh g−1 after 50 cycles (capacity retention of 86.1%). While for pristine LiMnPO4/C (sample-0), only 94.4 mAh g−1 can be obtained at the 50th cycle, corresponding to 72.9% of its initial discharge capacity (129.5 mAh g−1). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) results confirm that an integrated and hybrid CeO2/C coating layer is formed on LiMnPO4 surface and its existence has no influence on the structure of LiMnPO4. The reason for the improved electrochemical properties of the CeO2-modified LiMnPO4/C composites has also been studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements.

•La-doped Li2MnSiO4/C materials are prepared by polyol-assisted hydrothermal method.•High capacity for Li2MnSiO4/C is obtained by doping 1 at.% La3+.•The utilization ratio of active mass of La-doped Li2MnSiO4/C is obviously improved.•La3+ doping enhances Li+ diffusion and decreases charge transfer resistance.Li2Mn1LaxSiO4/C (x = 0, 0.01 and 0.04) composites are prepared via a polyol-assisted hydrothermal method followed by carbon coating. X-ray diffraction patterns confirm that the unit cell volume of Li2MnSiO4 has been enlarged by doping a small amount of La3+. The scanning electron micrographs and elemental maps indicate that the sizes of the Li2MnSiO4 particles can be reduced by homogeneously doping La3+. The transmission electron microscopy shows the well crystallized Li2MnSiO4 nanoparticles. The electrochemical performances of all samples are evaluated by galvanostatic charge/discharge tests and electrochemical impedance spectroscopy. 1 at.% La3+ doped Li2MnSiO4 (AL1) delivers the highest initial discharge capacity of about 257 mAh g−1, corresponding to the intercalation of about 1.55 lithium ions per formula unit. AL1 also exhibits improved capacity retentions of about 51.1%. The above improvements of electrochemical properties are related to the decreased charge transfer resistance and enhanced lithium ion diffusion for La-doped samples, whose crystal structure is maintained and lattice has been slightly enlarged.

•A delicate polyol-assisted hydrothermal method to synthesize LiMnPO4 is present.•Pre-synthesized hollow-sphere Li3PO4 particles are used as precursor.•Influence of water–DEG ratio on the LiMnPO4 morphology is investigated.•Excellent capacity retentions indicate the weaker Jahn–Teller effect.•The flaky shaped sample delivers 60% initial capacity (154.1 mA h g−1) at 4 C rate.With the hollow-sphere Li3PO4 as precursor, a delicate polyol-assisted hydrothermal method is devised to synthesize high-performance LiMnPO4. Orthorhombic shaped, irregular flaky shaped and sphere-like LiMnPO4 are sequentially prepared by decreasing the water–diethylene glycol (DEG) ratio. The capacity, cycling stability and rate performance of all samples prepared by the new synthesis method are improved significantly. And the C/LiMnPO4 with irregular flaky shape exhibits a capacity of 154.1 mA h g−1 at C/20, 147.4 mA h g−1 at C/10 and 102.5 mA h g−1 at 2 C, which is the best performance ever reported for LiMnPO4 active material with similar carbon additives.

•A nutty-cake structural C–LiMn1−xFexPO4–LiFePO4 cathode material is synthesized.•The calcination temperature has obvious influence on the crystal structure.•Fe2+ diffused from the LiFePO4 core to the outer LiMnPO4 layer during calcination.The extremely low electronic conductivity, slow ion diffusion kinetics, and the Jahn–Teller effect of LiMnPO4 limit its electrochemical performance. In this work, a nutty-cake structural C–LiMn1−xFexPO4–LiFePO4 cathode material is synthesized by hydrothermal method and further calcined at different temperatures. The influence of calcination temperature on the electrochemical behavior is investigated by X-ray diffractometer, scanning electron microscope, field-emission high-resolution transmission electron microscope, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and charge–discharge tests. And the performance of C–LiMn1−xFexPO4–LiFePO4 materials has a relationship with its crystal structure. The well-crystallized Sample-600 calcined at 600 °C shows the smallest charge transfer resistance, the largest lithium ion diffusion coefficient (DLi) and the best cycling stability. The discharge capacity of Sample-600 holds around 112 mAh g−1 after the 3rd cycle at 0.1 C rate. The performances improvement of C–LiMn1−xFexPO4–LiFePO4 material can be mainly attributed to the iron diffusion from the LiFePO4 core to the outer LiMnPO4 layer under appropriate calcination temperature.

•Electrochemical performance of Li[Ni0.5Co0.2Mn0.3]O2 is improved by Li3VO4 coating.•Li[Ni0.5Co0.2Mn0.3]O2 coated with 3 wt.% Li3VO4 shows the best high-rate capability.•Cycle stability of Li3VO4-coated Li[Ni0.5Co0.2Mn0.3]O2 at 10 C is obviously improved.•Li3VO4-coated Li[Ni0.5Co0.2Mn0.3]O2 shows better high voltage cycliability (4.8 V).Li3VO4-coated Li[Ni0.5Co0.2Mn0.3]O2 cathode material exhibits much better cycling stability, rate capability, and high voltage cycling behavior than pristine Li[Ni0.5Co0.2Mn0.3]O2 at room temperature. The sample coated with 3 wt.% Li3VO4 shows the optimum electrochemical performance. It delivers a capacity of 61.5 mAh g−1 at 10 C (1800 mA g−1) after 100 cycles. The capacity retention at 1 C (180 mA g−1) is 63.5% at cut-off voltage 4.6 V, and 63.0% at a higher cut-off voltage 4.8 V. XRD and XPS results reveal that the Li3VO4 coating layer reinforces the surface of matrix material, which benefits structural stability of Li[Ni0.5Co0.2Mn0.3]O2 during long-term cycling. CV and EIS tests indicate that the improvement of electrochemical performances could be attributed to higher Li+ conductivity, suppression of Co and Mn dissolution from Li[Ni0.5Co0.2Mn0.3]O2, and decreased polarization during cycling since Li3VO4 layer on Li[Ni0.5Co0.2Mn0.3]O2 surface acts as a relatively stable protective barrier as well as an excellent Li-ion conductor.

•Electrochemical performance of LiNi0.5Co0.2Mn0.3O2 is improved by Y2O3 coating.•Y2O3-coated samples show excellent high rate capability (10C and 20C).•Good cycling stability at 10C under high voltages (4.6 V and 4.8 V) can be obtained.•Y2O3 layer facilitates the diffusion of Li+ at the electrode/electrolyte interface.Y2O3-coated LiNi0.5Co0.2Mn0.3O2 cathode materials show excellent cycling stability and higher rate capability than the bare LiNi0.5Co0.2Mn0.3O2 at higher cut-off voltages of 4.6 V and 4.8 V. The thickness of Y2O3-coating layer is about 5–15 nm, and the original structure of the LiNi0.5Co0.2Mn0.3O2 isn't influenced by Y2O3 coating layer. The 2 wt% Y2O3-coated LiNi0.5Co0.2Mn0.3O2 can deliver 114.5 mAh g−1 (76.3% of its initial discharge capacity) after 100 cycles at 10C (1800 mA g−1) between 2.8 and 4.6 V, while the bare LiNi0.5Co0.2Mn0.3O2 delivers only 11.5 mAh g−1 with 8.3% capacity retention left. When the high cut-off voltage increases to 4.8 V, the capacity retention of 2 wt% Y2O3-coated sample is 49.0%, which is much higher than that of the bare sample (5.9%) at 10C after 100 cycles. The rate capabilities of 2 wt% Y2O3-coated LiNi0.5Co0.2Mn0.3O2 are also improved significantly, especially at high rates (10C and 20C). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are carried out to confirm the existence of Y2O3 layer on the LiNi0.5Co0.2Mn0.3O2 surface. Electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) are applied to analyze the role of Y2O3-coating layer on the long cycling life and high rate capability.

•Layered Li[Li0.2Ni0.2−xMn0.6−xMg2x]O2 (2x = 0, 0.01, 0.02, 0.05) were synthetized.•Li[Li0.2Ni0.2−xMn0.6−xMg2x]O2 exhibit enhanced electrochemical properties.•The improved performance is attributed to enhanced structure stability.Mg-doped Li[Li0.2Ni0.2Mn0.6]O2 as a Li-rich cathode material of lithium-ion batteries were prepared by co-precipitation method and ball-milling treatment using Mg(OH)2 as a dopant. Scanning electron microscopy (SEM), ex situ X-ray powder diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvantatic charge/discharge were used to investigate the effect of Mg doping on structure and electrochemical performance. Compared with the bare material, Mg-doped materials exhibit better cycle stabilities and superior rate capabilities. Li[Li0.2Ni0.195Mn0.595Mg0.01]O2 displays a high reversible capacity of 226.5 mAh g−1 after 60 cycles at 0.1 C. The excellent cycle performance can be attributed to the improvement in structure stability, which is verified by XRD tests before and after 60 cycles. EIS results show that Mg doping decreases the charge-transfer resistance and enhances the reaction kinetics, which is considered to be the major factor for higher rate performance.