Search

• The reduced graphene oxide (rGO)/Li-Al-LDH composite nanosheets by hydrothermal method. • This kind of rGO/Li-Al-LDH nanosheets layer is expected to improve the wettability of liquid electrolytes and thermal stability. • The rGO/Li-Al-LDH@PP composite separator exhibits enhanced lithium-ion transport property. • The rGO/Li-Al-LDH@PP composite separator can be applied in Li||LiFePO 4 half cells. Lithium metal batteries (LMBs) with ultra-high theoretical energy density are a prospective candidate to replace current lithium-ion batteries (LIBs). However, there are still two non-negligible problems of lithium dendrites and the volume expansion effect of LMBs. In this study, reduced graphene oxide (rGO)/Li-Al-LDH composite nanosheets were firstly prepared via a hydrothermal method and then vacuum filtered onto commercial polypropylene (PP) separator. This kind of rGO/Li-Al-LDH nanosheets layer is expected to improve the wettability of liquid electrolytes and thermal stability. Furthermore, rich- Li-Al LDH can promote more ionic carriers and channels, which exhibits higher-efficiency lithium-ion transport properties. Meanwhile, rGO with a graphitic-like structure is able to disperse the concentration of electrons at the sharp point when lithium dendrites arise. As a result, the discharge capacity of the Li||LiFePO 4 cells based on the rGO/Li-Al-LDH@PP separator is still 1.852 mAh after 250 cycles and the capacity decay rate is just 4.24%. It is demonstrated that a feasible and effective strategy for the modified separator can enhance the electrochemical performance of LMBs. [Display omitted] The functional coat is a superior strategy to optimize the interface among the electrode, separator, and liquid electrolyte. In our study, we have synthesized reduced graphene oxide (rGO)/Li-Al-LDH composite nanosheets by hydrothermal method. Li-Al-LDH possesses plenty of octahedral vacancies and abundant lithium-ion diffusion pathways. Meanwhile, rGO with a graphitic-like structure is able to disperse the concentration of electrons at the sharp point when lithium dendrites arise. The prepared rGO/Li-Al-LDH@PP composite separator exhibits increased lithium-ion transference number (0.39) and enhanced ionic conductivity (0.74 mS cm−1) when compared with bare PP separator. The cell has excellent cycle performance. The discharge capacity of the Li||LiFePO 4 cells based on the rGO/Li-Al-LDH@PP separator is still 1.852 mAh after 250 cycles and the capacity decay rate is just 4.24%. At the same time, it also improves the rate performance and Coulomb efficiency of the cell. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flower-like calcium phosphate coating is successfully formed on the surface of modified PE separator. • The obtained composite separator exhibits stronger affinity to electrolyte and absorbs more liquid electrolyte. • CaP@PE separator possess an improved ionic conductivity (0.52 mS cm−1) and lithium-ion transference number (0.36). • Cell assembled with CaP@PE separator exhibits excellent cycle performance and rate performance. The organic–inorganic composite separator possesses great thermal stability and electrolyte wettability, which is normally prepared via the slurry containing binder. However, this preparation is involved with large amounts of organic solvent that is harmful to health. In this paper, we design a novel method that combines the crosslinking technology and biomimetic mineralization process to prepare a Ca 3 (PO 4) 2 inorganic coating modified polyethylene separator (CaP@PE). The obtained composite separator exhibits stronger affinity to electrolyte, and its porous coating structure can store more liquid electrolyte, thus the ionic conductivity is promoted from 0.27 mS cm−1 to 0.52 mS cm−1 and the lithium-ion transference number is increased from 0.26 to 0.36. Compared with PE separator, CaP@PE separator shows better thermal stability at high temperature. Due to the improved ionic transport performance and reduced charge transfer impedance, LiCoO 2 /Li half-cell employing CaP@PE separator displays superior cycle stability and capacity retention ability after 150 cycles at a current density of 1C. Even at a high rate of 5C (7.5 mA cm−2), the cell with CaP@PE separator still exhibits a discharge capacity of 0.80 mAh. This work provides a promising separator to optimize the electrochemical performance and safety performance in lithium-ion battery. [ABSTRACT FROM AUTHOR]

Thermally induced phase separation (TIPS) is used to prepare polyethylene (PE) micro-porous membrane, consisting of melt blending, fast cooling, stretching and extracting process, which determine the pore-structure of the PE membrane. In this study, we tried to extract PE/liquid paraffin (LP) oil membrane to obtain PE porous membrane by n-hexane (n-PE) and dichloromethane (d-PE). The n-PE membrane would shrink by 10% for extractant volatilizing, less than 15% of the d-PE membrane after the extraction. These PE membranes were applied into symmetrical cells and LiCoO 2 /Li cells. As a result, the LiCoO 2 /Li cell based on n-PE separator exhibited better capacity retention (98%) than d-PE separator (91%) after 80 cycles at a current density of 1C rate for higher ionic conductivity. And the LiCoO 2 /Li cell with d-PE separator had higher capacity at 2C and 3C, it could be attributed to stronger interaction between solvent and wall of d-PE separator with the smaller and curved pore. In addition, the method that electrochemical impedance spectroscopy (EIS) technique carried out with cyclic voltammetry (CV) and charge-discharge curves is successfully applied to monitor the variety of impedance during the cycles, which is helpful to explore the mechanism of capacity attenuation. • The effect of extraction process on electrochemical performance of PE separator was explored. • n-PE membrane exhibited better capacity retention during the cycles, while d-PE membrane had a better C-rate performance. • EIS could be applied to monitor the variety of impedance inside the cell. • The equivalent circuit of EIS results of LiCoO 2 should contain positive region, separator region and negative region. [ABSTRACT FROM AUTHOR]

For sodium-ion batteries, polyanionic cathode materials have been mainly studied due to their advantages of high safety, low-cost and environmental friendliness. However, some shortcomings of low intrinsic conductivity and slow reaction kinetics limit its further application. In our study, a uniform and dense amorphous carbon layer is coated onto the surface of fluorophosphate (Na 2 FePO 4 F/C) via high-energy ball milling and heat-treatment process. According to the results of SEM and TEM, it is seen that the surface of the active particles would be composited with a carbon layer. When the heat treatment temperature is 650 °C, the ratio of I D /I G of Raman is the largest, indicating that the highest disorder degree of the carbon layer. The obtained Na 2 FePO 4 F/C-650 has the largest initial discharge specific capacity (120 mAh·g−1 at 0.1 C), and the specific capacity retention rate is 76.54% at 10 C for 1000 cycles. Furthermore, the sodium-ion diffusion coefficient of Na 2 FePO 4 F/C-650 measured using AC impedance is up to 4.91 × 10−12 cm2·s−1. It could be resulted from the fact that amorphous carbon layer can absorb more sodium ions and is beneficial to ion diffusion kinetics according to the DFT calculation. This study has proposed a new idea to modify cathode material and facilitated the commercial application of Na 2 FePO 4 F. The functional carbon layer is an effective strategy to improve the conductivity and ionic reaction kinetics of cathode materials. In this study, Na 2 FePO 4 F/C composite cathode material with a uniform and dense amorphous carbon layer have been synthesized through high-energy ball milling and heat treatment process. This amorphous carbon layer can absorb more sodium ions and is beneficial to the ion diffusion kinetics. What's more, the sodium-ion diffusion coefficient of the obtained Na 2 FePO 4 F/C-650 is up to 4.91 × 10−12 cm2· s −1. [Display omitted] [ABSTRACT FROM AUTHOR]