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that are important indicators for use in photonics, biomedicine, catalysis, and advanced electrodes. [4] Current achievements related to porous carbon spheres mostly center on nanometer-sized spheres. [5] However, micrometer-sized spheres with refined hierarchical interior structures are highly desirable, because such structures not only enable spatiotemporal control of the chemical process occurring inside the spheres, but also reduce the difficulty of product separation compared with nanometersized spheres. [6] In particular, hierarchical porous carbon microspheres with large inner cavities, refined pore structure, and diverse functional groups are ideal hosts to anchor active guests through both physical and chemical interactions. [7] However, the fabrication of hierarchical porous carbon microspheres with such a refined structure is much more challenging than fabricating traditional carbon nanospheres, because it is extremely difficult to achieve the necessary delicate control of the interior structure and outer shell across the microscale to nanoscale.Although emulsion, spraying, dripping, and aerosol-assisted self-assembly methods have been explored to fabricate carbon microspheres, [6a,8] these microspheres do not possess complex interior structures because of the limitations of those methods in diversifying the assembly. [5] Solution synthetic methods have been widely applied for controllable fabrication of porous nanospheres. [9] It is nontrivial to extend solution synthetic methods to the fabrication of hierarchical porous carbon microspheres. Lu and co-workers reported a surface free energy-induced assembly approach to synthesize multicavity carbon nanospheres about 100 nm in diameter; this was the first direct synthesis of multicavity-structured carbon nanospheres by a controllable solution synthetic method. [7b] Yang and co-workers subsequently reported the synthesis of interiorstructured mesoporous carbon microspheres (50-200 µm in diameter) based on surfactant assembly within water droplet confined spaces. [5] To our knowledge, carbon microspheres of size ranging from sub-micrometer to a few micrometers with a refined hierarchical structure, based on a solution synthetic method, have not been reported. Moreover, the carbon precursors used by Lu and co-workers were both traditional phenolic resol; [5,7b] and the resultant carbons with homogeneousThe construction of refined architectures plays a crucial role in performance improvement and application expansion of advanced materials. The synthesis of carbon microspheres with a refined hierarchical structure is still a problem in synthetic methodology, because it is difficult to achieve the necessary delicate control of the interior structure and outer shell across the microscale to nanoscale. Nitrogen-doped multichamber carbon (MCC) microspheres with a refined hierarchical structure are realized here via a surfactant-directed spaceconfined polymerization strategy. The MCC precursor is not the traditional phenolic resol but a new kind of 2,6-di...

The safety problems of lithium ion batteries (LIBs) have been the main obstacles that hinder their broad applications in portable electronic devices, electric vehicles, and energy storage. Such problems originate from flammable solvent-containing liquid electrolytes that could be easily oxidized upon excessive heat, leading to further heat accumulation and, subsequently, thermal runaway. The design strategies of a safe electrolyte could control the flammability and volatility of the liquid electrolyte, might prevent the thermal runaway, and ultimately ensure the risk-free and fire-free operation of LIBs. This work is to explore the mechanism of thermal runaway and review the state-of-the-art of the designs of a safe electrolyte for LIBs, including the additions of flame retardant additives, overcharge additives, and stable lithium salts and the adoption of solid-state electrolytes, ionic liquid electrolytes, and thermosensitive electrolytes. The features, advantages, and drawbacks of these strategies are systematically summarized, compared, and discussed, while the development direction of a safer electrolyte for future LIBs is proposed in the end.

Developing safe and high-energy-density lithium metal batteries (LMBs) is considered to be the focus of next-generation rechargeable batteries. However, the inevitable lithium reaction with the liquid electrolyte and the subsequent formation of Li dendrites must be overcome, and upgrading traditional liquid electrolytes is a key strategy for achieving this goal. Here, we report a nano-SiO2-supported gel polymer electrolyte (SiO2-GPE) with a hierarchical structure fabricated via in situ gelation of a traditional organic liquid electrolyte supported on a functionally modified SiO2 layer, which displayed high ionic conductivity (1.98 × 10–3 S cm–1 at 25 °C) and wide electrochemical window (>4.9 V vs Li/Li+). The LiFePO4/SiO2-GPE/Li cells exhibited a high capacity of 125.5 mAh g–1 at 1 C with capacity retention of 88.42% after 700 cycles. The superior electrochemical performance is mainly due to the highly compatible electrode/electrolyte interface and the effective inhibition of Li dendrite growth provided by the synergistic effects of this SiO2-GPE membrane.

Decay in electrochemical performance resulting from the “shuttle effect” of dissolved lithium polysulfides is one of the biggest obstacles for the realization of practical applications of lithium–sulfur (Li–S) batteries. To meet this challenge, a 2D g‐C3N4/graphene sheet composite (g‐C3N4/GS) was fabricated as an interlayer for a sulfur/carbon (S/KB) cathode. It forms a laminated structure of channels to trap polysulfides by physical and chemical interactions. The thin g‐C3N4/GS interlayer significantly suppresses diffusion of the dissolved polysulfide species (Li2Sx; 2

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Lithium−sulfur batteries are considered as the most promising candidate for nextgeneration energy storage devices. However, they are subjected to the "shuttle effect" of soluble lithium polysulfides (LiPSs). Herein, a free-standing membrane composed of two-dimensional MXene material (Ti 3 C 2 T x ) and graphene oxide (GO) is synthesized by a simple vacuum-filtration method. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are carried out to determine structure, morphology, and composition of the Ti 3 C 2 T x /GO composite membrane, respectively. As a functional layer of trapping LiPS species, the Ti 3 C 2 T x /GO composite membrane and commercial polypropylene (PP) are successfully assembled to be a hybrid separator, Ti 3 C 2 T x /GO@ PP, to suppress the shuttle effect of LiPSs. The porous and rough surface of the Ti 3 C 2 T x /GO composite membrane is beneficial to improve the wettability of the commercial separator in an etherbased electrolyte. The cells with the Ti 3 C 2 T x /GO@PP hybrid separator exhibit a low polarization potential of 0.26 V in the conversion from Li 2 S 4 to Li 2 S 2 /Li 2 S and deliver a discharge capacity of 640.0 mA h g −1 for 5 C rate, indicating that the hybrid separator benefits the rate performance. According to the results of electrochemical impedance spectroscopy, increased discharge capacity is attributed to the reduced internal resistance and intensified Li + diffusion. The results of X-ray photoelectron spectroscopy focusing on the surfaces of both sides of the hybrid separator indicate that the shuttle effect of LiPSs is suppressed through a coefficient of the terminated groups' catalytic conversion on long-chain LiPSs and the titanium-reactive centers' Lewis acid−base pairs on short-chain LiPSs. Combining with digital photographs of the H-type electrolytic cell, the results of UV−visible absorption spectroscopy suggest that the concentration of long-chain polysulfides declines instantly under the redox effect of the terminated groups on Ti 3 C 2 T x surfaces and then infiltrate through the hybrid separator by virtue of concentration difference impetus. Generally, a Ti 3 C 2 T x /GO@PP hybrid separator restrains LiPS diffusion and improves the rate performance of Li−S batteries.