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Due to the abundant reserves and low cost of sodium resources, sodium metal batteries (SMBs) can be used as a promising energy storage technology with high energy density. Recently, ultralow-concentration electrolytes (ULCEs) with 0.3 mol/L (M) NaPF6 are greatly attractive because of their low cost and high permeability. However, the cycle life and rate performance of SMBs in ULCEs are limited by the high reactivity of sodium metal anodes. Here, an acetamide additive, N, O-bis(trimethylsilyl) trifluoroacetamide (BSTFA), is introduced into an ULCE (0.3 M NaPF6 in EC/PC, 1:1 vol %) for stabilizing the electrolyte and fabricating a highly conductive interface in SMBs. Theoretical and experimental results prove that BSTFA can scavenge HF and H2O in the NaPF6-based electrolyte spontaneously and inhibit the hydrolysis reaction of NaPF6. Owing to protective interface layers on sodium metal anode and Na3V2(PO4)3 (NVP) cathode, the Na||NVP battery in 2% BSTFA-containing ULCE shows a high-capacity retention rate of 92.63% after 1955 cycles at 2 C and a superior rate capability of exceeding 105 mAh g−1 at 40 C.

P2-type layered oxide Na0.67Fe0.5Mn0.5O2 is recognized as a very promising cathode material for sodium-ion batteries due to the merits of high capacity, high voltage, low cost, and easy preparation. However, its unsatisfactory cycle and rate performances remain huge obstacles for practical applications. Here, we report a strategy of SnO2 modification on P2-type Na0.67Fe0.5Mn0.5O2 to improve the cycle and rate performance. Scanning electron microscope(SEM) and transmission electron microscope(TEM) images indicate that an insular thin layer SnO2 is coated on the surface of Na0.67Fe0.5Mn0.5O2 after medication. The coating layer of SnO2 can protect Na0.67Fe0.5Mn0.5O2 from corrosion by electrolyte and the cycle performance is well enhanced. After 100 cycles at 1 C rate(1 C=200 mA/g), the capacity of SnO2 modified Na0.67Fe0.5Mn0.5O2 retains 83 mA·h/g(64% to the initial capacity), while the capacity for the pristine Na0.67Fe0.5Mn0.5O2 is only 38 mA·h/g(33.5% to the initial capacity). X-Ray photoelectron spectroscopy reveals that the ratio of Mn4+ increases after SnO2 modification, leading to less oxygen vacancy and expanded lattice. As a result, the capacity of Na0.67Fe0.5Mn0.5O2 increases from 178 mA·h/g to 197 mA·h/g after SnO2 modification. Furthermore, the rate performance of Na0.67Fe0.5Mn0.5O2 is enhanced with SnO2 coating, due to high electronic conductivity of SnO2 and expanded lattice after SnO2 coating. The capacity of SnO2 modified Na0.67Fe0.5Mn0.5O2 at 5 C increases from 21 mA·h/g(pristine Na0.67Fe0.5Mn0.5O2) to 35 mA·h/g.

A lithium metal anode and high nickel ternary cathode are considered viable candidates for high energy density lithium metal batteries (LMBs). However, unstable electrode-electrolyte interfaces and structure degradation of high nickel ternary cathode materials lead to serious capacity decay, consequently hindering their practical applications in LMBs. Herein, we introduced N,O-bis(trimethylsilyl) trifluoro acetamide (BTA) as a multifunctional additive for removing trace water and hydrofluoric acid (HF) from the electrolyte and inhibiting corrosive HF from disrupting the electrode-electrolyte interface layers. Furthermore, the BTA additive containing multiple functional groups (C-F, Si-O, Si-N, and C═N) promotes the formation of LiF-rich, Si- and N-containing solid electrolyte interfacial films on a lithium metal anode and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode surfaces, thereby improving the electrode-electrolytes interfacial stability and mitigating the capacity decay caused by structural degradation of the layered cathode. Using the BTA additive had tremendous benefits through modification of both anode and cathode surface layers. This was demonstrated using a Li||NMC811 metal battery with the BTA electrolyte, which exhibits remarkable cycling and rate performances (122.9 mA h g-1 at 10 C) and delivers a discharge capacity of 162 mA h g-1 after 100 cycles at 45 °C. Likewise, this study establishes a cost-effective approach of using a single additive to improve the electrochemical performance of LMBs.

Graphene materials have recently experienced rapid developments, but large-scale production of high-quality graphene is still desired. Electrochemical exfoliation method is considered as a promising approach to meet this requirement. Here we demonstrate a non-electrified electrochemical exfoliation method to produce high-quality graphene (NEEG) sheets. By direct electrochemical reaction between graphite powders and metallic Li in 1 M LiPF6/propylene carbonate electrolyte, continuous graphite exfoliation is achieved with a high yield of excess 80% without any consumption of electric energy. The as-prepared NEEG has high quality with few defects (ID/IG = 0.45), a high C/O ratio of 27.74 and excellent electronic conductivity of 102.5 S cm−1. As conductive additives in Li4Ti5O12 electrode for lithium ion batteries, NEEG contributes to higher capacity and initial coulombic efficiency than common thermally reduced graphene oxide. Given the advantages of NEEG, the non-electrified electrochemical exfoliation method is promising for the large-scale preparation of high-quality graphene sheets.

MoO2 nanoparticle-modified Li4Ti5O12 materials were prepared via a facile solution-based method. X-ray diffraction patterns (XRD) and high resolution transmission electron microscopy (HRTEM) analyses revealed that the MoO2 nanoparticles were anchored on the surface of spinel Li4Ti5O12, and energy dispersive X-ray spectroscopy (EDX) mapping indicated the MoO2 nanoparticles distributed uniformly. Compared with the pristine Li4Ti5O12, the appropriate amount of MoO2 on the surface of the Li4Ti5O12 could not only effectively reduce the electrochemical polarization of Li4Ti5O12, but also contribute to specific capacity for lithium storage. The 3% MoO2 modified Li4Ti5O12 exhibited excellent rate capability of 116 mA h g−1 at 10 C, and superior cycling performance of 124 mA h g−1 after 450 cycles at 5 C. Since the MoO2 modification process was easy to handle and the source of Mo has affordable costs, MoO2-modified Li4Ti5O12 would be promising for industrial application.

Owing to the abundant resource and tunable structure, amorphous carbon materials have been widely studied as anode for alkali-metal ion batteries. However, it is still a huge space to promote their electrochemical performance for potassium ion batteries (PIBs), especially rate capability, because of the sluggish kinetics of potassium ions. In this work, 3D amorphous carbon with nitrogen and oxygen dual doping (N/O-3DC) is elaborately designed and facilely synthesized for high performance PIBs. Benefit from the synergistic effect of structural advantages, N/O-3DC electrode delivers a high reversible capacity (345 mA h g−1 at 0.03 A g−1), excellent rate performance (132 mA h g−1 at 9.6 A g−1) and ultralong lifespan (0.02% capacity decay per cycle over 1000 cycles at 3 A g−1). Combined with control experiment and structural characterization, it demonstrates the interaction between introduction of heteroatoms, construction of 3D open pore network and tailored microstructure, obtaining more active sites and enlarged interlayer spacing. Kinetic analysis and density functional theory calculations reveal dual N/O doping can not only facilitate the adsorption/desorption of K+ and elevate electronic conductivity, but also reduce energy barrier for K+ diffusion, hence promote the reaction kinetics. This work presents an appealing development of high performance carbon anode with multi-strategy coupling for PIBs.