High Energy, Long Cycle, and Superior Low Temperature Performance Aqueous Na–Zn Hybrid Batteries Enabled by a Low-Cost and Protective Interphase Film-Forming Electrolyte

A hybrid aqueous Na–Zn ion battery derived from the Na3V2(PO4)3 cathode is one of the most promising systems among aqueous batteries because it exhibits higher energy density than a pure Zn ion battery due to different ion intercalation mechanisms related to various electrolytes. However, it is more difficult to improve the electrochemical performance of the hybrid aqueous Na–Zn ion battery versus Zn ion battery. In addition, searching for suitable protective interphase film-forming electrolyte additives in order to increase cycling stability and developing a new electrolyte recipe to improve the low temperature performance are significant and still big challenges for the hybrid aqueous Na–Zn battery. Herein, the introduction of protective interphase film-forming additives (VC), an economical 10 M NaClO4–0.17 M Zn­(CH3COO)2-2 wt % VC electrolyte, was proposed. Based on such an electrolyte, the carbon-coated single crystalline Na3V2(PO4)3 nanofiber//Zn aqueous Na–Zn hybrid battery involving high energy, long cycle, and outstanding low temperature performance was successfully obtained. For example, it delivered a remarkable output voltage of 1.48 V and excellent cycle stability (retained 84% after 1000 cycles). The capacities were 94.4 mA h/g at 0.2 A/g at −10 °C and 90.0 mA h/g at 0.2 A/g at −20 °C, respectively

Tin Nanoparticles Encapsulated in Porous Multichannel Carbon Microtubes: Preparation by Single-Nozzle Electrospinning and Application as Anode Material for High-Performance Li-Based Batteries

Tin Nanoparticles Encapsulated in Porous Multichannel Carbon Microtubes: Preparation by Single-Nozzle Electrospinning and Application as Anode Material for High-Performance Li-Based Batterie

Carbon-Coated Na₃V₂(PO₄)₃ Embedded in Porous Carbon Matrix: An Ultrafast Na-Storage Cathode with the Potential of Outperforming Li Cathodes

Sodium ion batteries are one of the realistic promising alternatives to the lithium analogues. However, neither theoretical energy/power density nor the practical values reach the values of Li cathodes. Poorer performance is expected owing to larger size, larger mass, and lower cell voltage. Nonetheless, sodium ion batteries are considered to be practically relevant in view of the abundance of the element Na. The arguments in favor of Li and to the disadvantage of Na would be completely obsolete if the specific performance data of the latter would match the first. Here we present a cathode consisting of carbon-coated nanosized Na₃V₂(PO₄)₃ embedded in a porous carbon matrix, which not only matches but even outshines lithium cathodes under high rate conditions. It can be (dis)­charged in 6 s with a current density as high as 22 A/g (200 C), still delivering a specific capacity of 44 mAh/g, while up to 20 C, the polarization is completely negligible

Direct Observation of Lithium Staging in Partially Delithiated LiFePO₄ at Atomic Resolution

Lithium ions in LiFePO4 were observed directly at atomic resolution by an aberration-corrected annular-bright-field scanning transmission electron microscopy technique. In addition, it was found in partially delithiated LiFePO4 that the remaining lithium ions preferably occupy every second layer, along the b axis, analogously to the staging phenomenon observed in some layered intercalation compounds. This new finding challenges previously proposed LiFePO4/FePO4 two-phase separation mechanisms

Lithium Potential Variations for Metastable Materials: Case Study of Nanocrystalline and Amorphous LiFePO₄

Much attention has been paid to metastable materials in the lithium battery field, especially to nanocrystalline and amorphous materials. Nonetheless, fundamental issues such as lithium potential variations have not been pertinently addressed. Using LiFePO₄ as a model system, we inspect such lithium potential variations for various lithium storage modes and evaluate them thermodynamically. The conclusions of this work are essential for an adequate understanding of the behavior of electrode materials and even helpful in the search for new energy materials

Ge/C Nanowires as High-Capacity and Long-Life Anode Materials for Li-Ion Batteries

Germanium-based materials (Ge and GeO_<i>x</i>) have recently demonstrated excellent lithium-ion storage ability and are being considered as the most promising candidates to substitute commercial carbon-based anodes of lithium-ion batteries. Nevertheless, practical implementation of Ge-based materials to lithium-ion batteries is greatly hampered by the poor cyclability that resulted from the huge volume variation during lithiation/delithiation processes. Herein, uniform carbon-encapsulated Ge and GeO_<i>x</i> nanowires were synthesized by a one-step controlled pyrolysis of organic–inorganic hybrid GeO_<i>x</i>/ethylenediamine (GeO_<i>x</i>/EDA) nanowires in H₂/Ar and Ar atmospheres, respectively. The as-obtained Ge/C and GeO_<i>x</i>/C nanowires possess well-defined 0D-in-1D morphology and homogeneous carbon encapsulation, which exhibit excellent Li storage properties including high specific capacities (approximate 1200 and 1000 mA h g^–1 at 0.2C for Ge/C and GeO_<i>x</i>/C, respectively). The Ge/C nanowires, in particular, demonstrate superior rate capability with excellent capacity retention and stability (producing high stable discharge capacities of about 770 mA h g^–1 after 500 cycles at 10C), making them promising candidates for future electrodes for high-power Li-ion batteries. The improved electrochemical performance arises from synergistic effects of 0D-in-1D morphology and uniform carbon coating, which could effectively accommodate the huge volume change of Ge/GeO_<i>x</i> during cycling and maintain perfect electrical conductivity throughout the electrode

Low-Temperature Synthesis of Amorphous FePO₄@rGO Composites for Cost-Effective Sodium-Ion Batteries

The dramatic growth of the sodium-ion battery market evokes a high demand for high-performance cathodes. In this work, a nanosized amorphous FePO4@rGO composite is developed using coprecipitation combined with low-temperature hydrothermal synthesis, which registered a surface area of 179.43 m2 g–1. The composites maintain three-dimensional mesoporous morphology with a pore size in the range of 3–4 nm. Uniform distribution of amorphous FePO4 allows a reversible capacity of 175.4 mA h g–1 at 50 mA g–1 while maintaining a stable cycle life of 500 cycles at 200 mA g–1. The amorphous FePO4@rGO, obtained by energy-efficient synthesis, significantly improved the rate performance compared to the crystalline material prepared at high temperatures. Cyclic voltammetry tests reveal that the fast reaction kinetics can be attributed to the pseudocapacitive behavior of the electrode. In addition, we demonstrated the promise of FePO4@rGO cathodes for low-temperature sodium-ion batteries

Phase Boundary Propagation in Large LiFePO₄ Single Crystals on Delithiation

Large single crystals of LiFePO4 have been chemically delithiated. The relevance of chemical oxidation in comparison with electrochemical delithiation is discussed. Analyses of the Li content and profiles were done by electron energy loss spectroscopy and secondary ion mass spectrometry. The propagation of the FePO4 phase growing on the surface of the large single crystal was followed by in situ optical microscopy as a function of time. The kinetics were evaluated in terms of linear irreversible thermodynamics and found to be characterized by an induction period followed by parabolic growth behavior of the FePO4 phase indicating transport control. The growth rate was shown to depend on the crystallographic orientation. Scanning electron microscopy images showed cracks and a high porosity of the FePO4 layer due to the significant changes in the molar volumes. The transport was found to be greatly enhanced by the porosity and crack formation and hence greatly enhanced over pure bulk transport, a result which is supposed to be very relevant for battery research if coarse-grained powder is used