Optimized Solid Electrolyte Interphase and Solvation Structure of Potassium Ions in Carbonate Electrolytes for High-Performance Potassium Metal Batteries.

The introduction of electrolyte additives is one of the most potential strategies to improve the performance of potassium metal batteries (PMBs). However, designing an additive that can alter the K+ solvation shell and essentially inhibit K dendrite remains a challenge. Herein, the amyl-triphenyl-phosphonium bromide was introduced as an additive to build a stable solid electrolyte interphase layer. The amyl-TPP cations can form a cation shielding layer on the metal surface during the nucleation stage, preventing K+ from gathering at the tip to form K dendrites. Besides, the cations can be preferentially reduced to form Kx Py with fast K+ transport kinetics. The Br- anions, as Lewis bases with strong electronegativity, can not only coordinate the Lewis acid pentafluoride to inhibit the formation of HF, but also change the K+ solvation structure to reduce solvent molecules in the first solvation structure. Therefore, the symmetrical battery exhibits a low deposition overpotential of 123 mV at 0.1 mA cm-2 over 4200 h cycle life. The full battery, paried with a perylene-tetracarboxylic dianhydride (PTCDA) cathode, possesses a cycle life of 250 cycles at 2 C and 81.9% capacity retention. This work offers a reasonable electrolyte design to obtain PMBs with long-term stablity and safety.

Novel Polymer/Barium Intercalated Vanadium Pentoxide with Expanded Interlayer Spacing as High-Rate and Durable Cathode for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) exhibit great potential in large-scale energy storage systems. However, limited reaction kinetics and poor long-cycle stability restrict the application of vanadium oxide cathode materials. Herein, we designed and successfully synthesized a novel composite material with polyethylene glycol (PEG) and barium cation (Ba2+) preintercalated between the layers of vanadium pentoxide, denoted as PEG-Ba0.38V2O5·nH2O (PEG-BVO), as a cathode material of AZIBs. The optimized PEG-BVO material shows a uniform nanobelt-like structure with the expanded interlayer spacing of 1.07 nm, significantly promoting the transport kinetics of zinc ions. The theoretical calculation results unravel that an interlayer spacing of 1.07 nm may be at the most stable state for this layered composite structure, ensuring a robust architecture for rapid reversible (de)intercalation of zinc ions. As a result, the PEG-BVO electrode (with a large mass loading of 4 mg cm-2) exhibits an outstanding electrochemical performance including a high specific capacity (345 mAh g-1 at 0.1 A g-1), decent rate capability (up to 175 mAh g-1 at 10 A g-1), and long-term cycling stability (98.8% capacity retention upon 4000 cycles at 6 A g-1). Our discovery provides a new guest preinsertion strategy to construct a robust layered vanadium-based electrode with the expanded interlayer spacing, and the as-prepared PEG-Ba0.38V2O5·nH2O shows great potential as a high-rate positive electrode for AZIBs.

Construction of a High-Stability and Low-Nucleation-Barrier Cu3Sn Alloy Layer on Carbon Paper for Dendrite-Free Li Metal Deposition.

The construction of three-dimensional lithiophilic hosts is one of the most effective approaches for achieving the uniform nucleation and alleviating the volume changes of the Li metal. Unfortunately, some lithiophilic materials suffer from severe mechanical degradation resulting from the large volume expansion during lithiation, which causes a heterogeneous Li deposition. Herein, a low-nucleation-barrier Cu3Sn alloy layer on a carbon paper (Cu3Sn/CP) is constructed by a facile co-electrodeposition method for the Li anode framework. Density functional theory calculations show that the Cu3Sn alloy has a higher binding energy (-2.31 eV) than pure Sn (-1.97 eV) due to the electron-deficient state of Sn in the alloy phase, which enables the lithiophilic Sn to have increased affinity for Li. Additionally, the uniformly distributed Cu particles can evenly disperse the electric field on the surface of the carbon fiber and act as a "metal barrier" to inhibit the volume expansion of the Sn particles during lithiation, thereby enhancing the electrochemical stability of the alloy modification layer. As a result, the Cu3Sn/CP anode framework exhibits an exceptionally low nucleation overpotential (∼10 mV), a high and steady Coulombic efficiency (>98.5% for more than 200 cycles), and a long lifespan up to 1150 h. The full cells with LiFePO4 as a cathode show favorable cycling performance at 1 C with a capacity retention rate of 95.2%. The construction of the Cu3Sn alloy layer in this work sheds light on the design of a high-stability lithiophilic host for the dendrite-free Li metal anode.

Moderate Specific Surface Areas Help Three-Dimensional Frameworks Achieve Dendrite-Free Potassium-Metal Anodes.

The inevitable problem of dendrites growth has hampered the further development of K metal anodes. Constructing a three-dimensional anode framework and potassiophilic nanocoating is an effective way to enlarge the specific surface area, reduce the local current density, and inhibit the formation of K dendrites. However, the effects of the electrochemically active surface area (ECSA) of the framework on deposition behavior have not been clarified. Hence, SnS2 nanosheets with different sizes are loaded on the surface of carbon paper (SnS2@CP) to improve the potassiophilicity and realize dendrite-free K-metal anodes. Experiments reveal that the size of SnS2 nanosheets would determine the ECSA of the framework, while the ECSA reveals the relative sizes of specific surface areas of frameworks. Excessive or limited specific surface areas will cause morphological collapse or weak potassiophilicity during potassiation, respectively, thus leading to high nucleation overpotential. The moderate specific surface area and abundant and stable potassiophilic sites prompt the SnS2@CP framework to achieve uniform electrodeposition of K. A low nucleation overpotential of 11.2 mV and a cycle life of more than 800 h are exhibited at a current density of 0.25 mA cm-2, indicating the directional strategy for stable and safe K metal anodes.

A novel interlayer-expanded tin disulfide/reduced graphene oxide nanocomposite as anode material for high-performance sodium-ion batteries.

As a kind of negative electrode material for sodium-ion batteries (SIBs), tin-based active compounds have attracted numerous research efforts in recent years due to relatively high theoretical capacity. However, sluggish reaction kinetics for large-radius sodium ions hinders the practical application of layered tin-based anodes such as tin disulfide (SnS2) in SIBs. In this study, polyethylene glycol (PEG) is introduced as an intercalant and reduced graphene oxide (rGO) is utilized as the substrate to prepare a novel PEG-SnS2/rGO composite with expanded layer spacing (0.921 nm) through a facile hydrothermal process. SnS2 flakes in a size range of 50-100 nm are uniformly grown on the graphene sheet, the CS covalent bonding demonstrates a tight connection between the active SnS2 particles and the graphene skeleton, which is conductive to convenient charge transfer during the electrochemical process. Owing to the significantly improved sodium ions transport kinetics and fast electronic conductive network, the PEG-SnS2/rGO composite presents a high capacitance contribution of 90.69% at a scan rate of 0.6 mV s-1. It delivers a high reversible capacity of 960.6 mAh g-1 at 0.1 A g-1, good cycling performance with 770 mAh g-1 remained after 100 charge/discharge cycles, and excellent rate capability with an ultrahigh capacity of 720 mAh g-1 at 5 A g-1. This work provides new insights into the design of a kinetically favorable anode material for SIBs.

Realizing Spherical Lithium Deposition by In Situ Formation of a Li2S/Li-Sn Alloy Mixed Layer on Carbon Paper for Stable and Safe Li Metal Anodes.

Uncontrollable formation of Li dendrites and volume expansion have always been serious obstacles to the practical application of Li metal anodes. Three-dimensional (3D) frameworks are proven to accommodate Li to suppress volume expansion, but the lithiophobic surface tends to cause uncontrollable formation of Li dendrites. Here, uniform SnS2 nanosheets are coated on the carbon paper (SnS2@CP) skeleton and then transformed into a mixed layer of Li2S/Li-Sn after lithiation. Under the joint action of the lithiophilic Li-Sn alloy and low-diffusion energy barrier Li2S, the dual effects of strong adsorption and rapid diffusion of Li are realized. As a result, Li deposits homogeneously within the whole framework; as the plating amount increases, dendrite-free spherical Li is demonstrated, and the thickness of the electrode stays almost unchanged even at a high areal capacity of 10 mA h cm-2. The SnS2@CP electrodes present an ultralow nucleation overpotential (ca. 4 mV), high Coulombic efficiency (above 96.6% for more than 450 cycles), and stable cycle life (>1500 h), indicating that the 3D framework with the Li2S/Li-Sn alloy mixed coating has excellent lithiophilicity and fast Li transport kinetics, thus effectively inhibiting the formation of Li dendrites. All the findings give new insights into the design strategy for stable and safe Li metal anodes.