Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm–2 with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.

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Despite the extremely high ionic conductivity, the commercialization of LiGePS-type materials is hindered by the poor stability against Li metal. Herein, to address that issue, a simple strategy is proposed and demonstrated for the first time, i.e., in situ modification of the interface between Li metal and LiSnPS (LSPS) by pretreatment with specific ionic liquid and salts. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy results reveal that a stable solid electrolyte interphase (SEI) layer instead of a mixed conducting layer is formed on Li metal by adding 1.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/ N-propyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrTFSI) ionic liquid, where ionic liquid not only acts as a wetting agent but also improves the stability at the Li/LSPS interface. This stable SEI layer can prevent LSPS from directly contacting the Li metal and further decomposition, and the Li/LSPS/Li symmetric cell with 1.5 M LiTFSI/PyrTFSI attains a stable cycle life of over 1000 h with both the charge and discharge voltages reaching about 50 mV at 0.038 mA cm. Furthermore, the effects of different Li salts on the interfacial modification is also compared and investigated. It is shown that lithium bis(fluorosulfonyl) imide (LiFSI) salt causes the enrichment of LiF in the SEI layer and results in a higher resistance of the cell upon a long cycling life.

Tin (Sn) has been considered as one of the most promising anode materials for high-capacity lithium-ion batteries (LIBs) due to its high energy density, abundance, and environmentally benign nature. However, the problems of fast capacity fading at prolonged cycling and poor rate capacity hinder its practical use. Herein, we report the development of a novel architecture of Sn nanoparticle-decorated three-dimensional (3D) foothill-like graphene as an anode in LIBs. Electrochemical measurements demonstrated that the 3D Sn-graphene anode delivered a reversible capacity of 466 mA h g(-1) at a current density of 879 mA g(-1) (1 C) after over 4000 cycles and 794 mA h g(-1) at 293 mA g(-1) (1/3 C) after 400 cycles. The capacity at 1/3 C is over 200% that of conventional graphite anodes, suggesting that the 3D Sn-graphene structure enables a significant improvement in the overall performance of a LIB in aspects of capacity, cycle life, and rate capacity.

The high-energy lithium ion battery is an ideal power source for electric vehicles and grid-scale energy storage applications. Germanium is a promising anode material for lithium ion batteries due to its high specific capacity, but still suffers from poor cyclability. Here, we report a facile preparation of a germanium-graphene nanocomposite using a low-pressure thermal evaporation approach, by which crystalline germanium particles are uniformly deposited on graphene surfaces or embedded into graphene sheets. The nanocomposite exhibits a high Coulombic efficiency of 80.4% in the first cycle and a capacity retention of 84.9% after 400 full cycles in a half cell, along with high utilization of germanium in the composite and high rate capability. These outstanding properties are attributed to the monodisperse distribution of high-quality germanium particles in a flexible graphene framework.This preparation approach can be extended to other active elements that can be easily evaporated (e.g., sulfur, phosphorus) for the preparation of graphene-based composites for lithium ion battery applications.

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However, several severe obstacles, particularly the large overpotential and the limited capacity far less than theory, have hindered the practical application of Li-O 2 batteries. [2] Many authors have revealed that the high overpotential of Li-O 2 batteries is mainly attributed to the sluggish oxygen redox kinetics, [2a,3] electrical passivation of the cathode by the poorly conducting Li 2 O 2 , [4] inferior Li 2 O 2 /cathode contact interface, [5] and undesired parasitic reactions. [6] As a gas electrode, two factors, structural factor and catalytic factor, are crucial in the electrochemical performance. Although the two factors are interrelated and interplayed, basically, the structural factor will determine the O 2 electrode capacities and the O 2 active species diffusions, while the catalytic factor will determine the oxygen redox kinetics. In the past few years, tremendous efforts have been devoted to developing effective oxygen cathodes for improving the electrochemical performance of Li-O 2 batteries. [7] A variety of carbon catalysts with well-designed architecture have been proposed to serve as frameworks for insoluble Li 2 O 2 storage mainly for improving the discharge capacity but with very limited overpotential improvement. [7a-e] On the other hand, different kinds of noble metals [7f-i] and transition metal oxides (TMOs) [7j-q] were widely used to reduce the large overpotential of Li-O 2 batteries but with relatively low capacity. In fact, these investigations which only focused on either the structural factor or catalytic factor are not The nonaqueous lithium-oxygen (Li-O 2 ) battery is considered as one of the most promising candidates for next-generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li 2 O 2 deposition, inferior Li 2 O 2 /cathode contact interface, and difficult oxygen transport. Herein, an open-structured Co 9 S 8 matrix with sisal morphology is reported for the first time as an oxygen cathode for Li-O 2 batteries, in which the catalyzing for oxygen redox, good Li 2 O 2 /cathode contact interface, favorable oxygen evolution, and a promising Li 2 O 2 storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li-O 2 batteries. The intrinsic oxygen-affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co 9 S 8 electrode are found to play an important role in the remarkable enhancement in specific capacity and round-trip efficiency for Li-O 2 batteries. As expected, the Co 9 S 8 electrode can deliver a high discharge capacity of ≈6875 mA h g −1 at 50 mA g −1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g −1 , outperforming most of the current metal-oxide-based cathodes.