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• 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]

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]

Abstract Li metal has been regarded as the most promising anode material for next high-energy batteries. However, the dendrite growth during the lithium deposition and low Coulombic efficiencies have restricted their practical applications. In the paper, we investigate the electrodeposition process of lithium metal under different current density in detail and firstly use diethylenetriamine as additive to adjust the deposition of lithium metal in LiPF 6 -PC and LiPF 6 -EC/DEC electrolyte. The result shows that trace diethylenetriamine can react with lithium anode producing R-N-Li and LiF, which greatly improves the morphology of lithium deposition by adjusting the components of the SEI film. The content of fast ionic conductors in SEI film (e.g., R-N-Li and LiF) can be identified by the X-ray photoelectron spectroscopy. The electrochemical impedance spectroscopy confirms diethylenetriamine could increase the ionic conductivity of the interface between the anode and electrolyte. Galvanostatic curves also show that the LiPF 6 -PC electrolyte with 0.2 vol% diethylenetriamine and LiPF 6 -EC/DEC electrolyte with 0.1 vol% diethylenetriamine has better cycling stability than blank group. Highlights • Our research has clearly demonstrated the behavior of metallic lithium in cathode deposition, lithium deposition law related to current density. • We firstly developed diethylenetriamine as nitrogenous organic additive to stabilize lithium electrode with 0.2 vol% amount. • The LiPF 6 -PC electrolyte with 0.2 vol% diethylenetriamine shows better stability of lithium electrode and high ionic conductivity than blank electrolyte. [ABSTRACT FROM AUTHOR]

• PES is first time used to modify the li electrode which shows excellent lithium affinity. • PES film with polar functional groups (O = S = O) can realize the redistribution of the lithium ion flow and a uniform nano-columnar lithium layer can be obtained even in the high current density of 5 mA cm−2. • (3) the PES film prolongs the half-cell life three times than control group with higher coulombic efficiency. The dendrite problem and low Coulombic efficiency of lithium anode have hindered its commercial application for long time. In this paper, the Polyethersulfone (PES) film is spin-coated to construct a composite lithium anode. With the polar functional groups of PES, the lithiophilicity of the anode is greatly improved. Non-conductive uniform structure with polar functional groups (O = S = O) constructed on the lithium metal anode can realize the redistribution of the lithium ion flow and reduce the probability of dendrite formation in the "hot spot" area. A uniform nano-columnar lithium layer can be obtained even in the high current density of 5 mA cm−2. Electrochemical interface studies have illustrated that PES film can increase the migration speed of lithium ion among the electrodes, increase the reduction reaction rate of lithium ion. Finite element simulation calculations show that the PES film can effectively reduce the concentration of lithium ion near the dendrite tip. In addition, with the Cu-PES structure modified by 3.3 mg mL−1 PES, the average Coulombic efficiency of half-cell reaches 90%, and the cell can run for 220 cycles stably which is three times than control group in 0.5 mA cm−2. [Display omitted] [ABSTRACT FROM AUTHOR]