Precise carbon structure control by salt template for high performance sodium-ion storage

Carbon materials are considered to be one of the most promising anode materials for sodium-ion batteries(SIBs),but the well-ordered graphitic structure limits the intercalation of sodium ions.Besides,the sluggish intercalation kinetics of sodium ions impedes the rate performance.Thus,the precise structure control of carbon materials is important to improve the battery performance.Herein,a 3D porous hard-soft composite carbon(3DHSC)was prepared using the NaCl as the template and phenolic resin and pitch as carbon precursors.The NaCl template restrains the growth of the graphite crystallite during the carbonization process,resulting in small graphitic domains with expanded interlayer spacing which is favorable for the sodium storage.Moreover,the Na Cl templates help to create abundant mesopores and macropores for fast sodium ion diffusion.The porous structure and the graphite crystalline structure can be precisely controlled by simply adjusting the mass ratio of Na Cl,and thus,the suitable structure can be prepared to reach high capacity and rate performance while keeping a relatively high Coulombic efficiency.Typically,a high reversible capacity(215 mA h g^(-1)at 0.05 A g^(-1)),an excellent rate capability(97 mA h g^(-1)at 5 A g^(-1)),and a high initial Coulombic efficiency(60%)are achieved.

Multifunctional binder designs for lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries are promising next-generation high energy density batteries but their practical application is hindered by several key problems,such as the intermediate polysulfide shuttling and the electrode degradation caused by the sulfur volume changes.Binder acts as one of the most essential components to build the electrodes of Li-S batteries,playing vital roles in improving the performance and maintaining the integrity of the cathode structure during cycling,especially those with high sulfur loadings.To date,tremendous efforts have been devoted to improving the properties of binders,in terms of the viscosity,elasticity,stability,toughness and conductivity,by optimizing the composition and structure of polymer binders.Moreover,the binder modification endows them strong polysulfide trapping ability to suppress the shuttling and decreases the swelling to maintain the porous structure of cathode.In this review,we summarize the recent progress on the binders for Li-S batteries and discuss the various routes,including the binder combination use,functionalization,in-situ polymerization and ion cross-linking,etc.,to enhance their performance in stabilizing the cathode,building the high sulfur loading electrode and improving the cyclic stability.At last,the design principles and the problems in further applications are also highlighted.

Dual-ion hybrid supercapacitor:Integration of Li-ion hybrid supercapacitor and dual-ion battery realized by porous graphitic carbon

Lithium-ion hybrid supercapacitors(Li-HSCs) and dual-ion batteries(DIBs) are two types of energy storage devices that have attracted extensive research interest in recent years. Li-HSCs and DIBs have similarities in device structure, tendency for ion migration, and energy storage mechanisms at the negative electrode. However, these devices have differences in energy storage mechanisms and working potentials at the positive electrode. Here, we first realize the integration of a Li-HSC and a DIB to form a dual-ion hybrid supercapacitor(DIHSC), by employing mesocarbon microbead(MCMB)-based porous graphitic carbon(PGC) with a partially graphitized structure and porous structure as a positive electrode material. The MCMB-PGC-based DIHSC exhibits a novel dual-ion battery-capacitor hybrid mechanism: it exhibits excellent electronic double-layer capacitor(EDLC) behavior like a Li-HSC in the low-middle wide potential range and anion intercalation/de-intercalation behavior like a DIB in the high-potential range. Two types of mechanisms are observed in the electrochemical characterization process, and the energy density of the new DIHSC is significantly increased.

Design and modification of metal sulfide-based catalysts for lithiumsulfur batteries

Metal sulfide(MS)have good conductivity,strong adsorption ability,and excellent catalytic activity for the conversion of sulfur species,and thus,show great promise as the catalysts in LieS batteries.However,the relationship between their properties and electrochemical performance is still unclear.Thus,further in-depth discussions are required to improve their design in Li-S batteries.This review systematically summarizes the basic structural and electrochemical properties of MSs and highlights the advantages that guarantee them as high-performance catalysts in Li-S batteries.Then,various modification strategies for MSs to enhance the catalytic activity,efficiency,and stability are also reviewed.At last,future opportunities for MS catalysts in Li-S batteries are proposed.

Lithium-Sulfur Batteries at Extreme Temperatures:Challenges,Strategies and Prospects

High-energy-density-batteries working at a wide-temperature range are urgently required in many performance-critical areas.Lithium-sulfur batteries(LSB)are promising high-energy-density batteries that have the potential to maintain high performance at extreme temperatures.However,some problems like severe shuttling and safety issues at high temperatures or sluggish reaction kinetics and charge-transfer process at low temperatures decrease the performance and hinder their practical uses in extreme temperature conditions.Therefore,broadening the working temperature of LSB with stable electrochemical performance becomes a crucial topic.In this paper,the key stumbling blocks for high and low-temperature LSB are comprehensively discussed.The solutions from the aspects of electrolyte and electrode materials are discussed to solve the aggravating shuttle effect and thermal safety issues under high temperature and the sluggish reaction kinetics under low temperature.Moreover,some specific promising solutions to extend the operating temperature range of LSB are also proposed and highlighted,which provide potential research directions on the practical LSB application in future.

Promoted conversion of polysulfides by MoO_2 inlaid ordered mesoporous carbons towards high performance lithium-sulfur batteries

As polar materials, transition-metal oxides have shown great potentials to improve the adsorption of lithium polysulfides in lithium-sulfur batteries. Herein, a MoO_2-ordered mesoporous carbon (M-OMC)hybrid was designed as the sulfur host, in which MoO_2 is inlaid on the surface of ordered mesoporous carbons that can store active materials and provide fast electron transfer channel due to its ordered pore structure. The MoO_2 can effectively prevent the migration of polysulfides through the chemical adsorption and promote the conversion of polysulfides towards Li-sulfur battery.

g-C_(3)N_(4) templated mesoporous carbon with abundant heteroatoms as high-rate anode material for dual-carbon sodium ion hybrid capacitors

Sodium ion hybrid capacitors(SIHCs)are regarded as advanced power supply systems.Nevertheless,the kinetics imbalance of cathode and anode suppresses the further performance improvement of SIHCs.The carbonaceous anode materials are promising and many strategies have been utilized to increase the capacity of sloping region or accelerate the reaction rate of plateau region.However,it is still challenging to simultaneously realize high mesopore/micropore volume ratio,large interlayer distance(>0.37 nm),and abundant and favorable heteroatoms-doping by a simple method.Herein,we report N,P,O ternarydoped mesoporous carbon(PNPOC-T,T=700,800 or 900)with large interlayer distance(~0.4 nm)as anode materials.The PNPOC-T were prepared by a simple in-situ polymerization of aniline and phytic acid on the exfoliated graphitic nitrogen carbide(g-C3N4)and subsequent carbonization.The obtained PNPOC-800 exhibits an excellent rate performance(101.5 mA·h·g^(-1) at 20 A·g^(-1)),which can be attributed to the high surface-controlled capacitive behavior ratio and rapid ion diffusion.The optimum SIHCs display a high energy density of 105.48 W·h·kg^(-1) and a high power density of 13.59 kW$kg1.Furthermore,the capacitance retention rate of SIHCs can reach 87.43%after 9000 cycles at 1 A·g^(-1).

Strategies to Realize Compact Energy Storage for Lithium-Sulfur Batteries

High volume energy density(Ev)means more energy can be stored in a small space,which helps ease the“space anxiety”faced by electrochemical energy storage(EES)devices such as batteries.Lithium-sulfur batteries(LSBs)are promising next-generation EES devices due to their high theoretical energy density.However,its E_(v) is unsatisfactory due to the low density of sulfur and excess use of lightweight nanocarbon in the cathode,severely limiting its practical applications.In this review,the recent progress in improving the E_(v) is summarized from the aspects of materials,electrodes,and devices.First,the key factors affecting E_(v) are discussed.Then at the material level,the design of materials with high density and rich pore structure,and the key roles of catalysts are discussed.At the electrode level,the design of the compact electrode structure is summarized.Increasing the thickness of the cathodes or reducing the use of the anodes(low N/P ratio)to improve E_(v) from the device level is highlighted.Finally,the E_(v) of solid-state LSBs system has been prospected.

Catalyzing polysulfide conversion by g-C3N4 in a graphene network for long-life lithium-sulfur batteries

The practical application of lithium-sulfur batteries with a high energy density has been plagued by the poor cycling stability of the sulfur cathode, which is a result of the insulating nature of sulfur and the dissolution of polysulfides. Much work has been done to construct nanostructured or doped carbon as a porous or polar host for promising sulfur cathodes, although restricting the polysulfide shuttle effect by improving the redox reaction kinetics is more attractive. Herein, we present a well-designed strategy by introducing graphitic carbon nitride （g-C3N4） into a three-dimensional hierarchical porous graphene assembly to achieve a synergistic combination of confinement and catalyzation of polysulfides. The porous g-CBN4 nanosheets in situ formed inside the graphene network afford a highly accessible surface to catalyze the transformation of polysulfides, and the hierarchical porous graphene-assembled carbon can function as a conductive network and provide appropriate space for g-C3N4 catalysis in the sulfur cathode. Thus, this hybrid can effectively improve sulfur utilization and block the dissolution of polysulfides, achieving excellent cycling performance for sulfur cathodes in lithium-sulfur batteries.

General synthesis of high-performing magneto-conjugated polymer core-shell nanoparticles for multifunctional theranostics

Recently, increasing attention has been paid to magneto-conjugated polymer core-shell nanoparticles （NPs） as theranostic platforms. However, the utilization of surfactants and extra oxidizing agents with potential toxicity in synthesis, the lack of general methods for the controlled synthesis of various kinds of magnetic NP （MNP）@conjugated polymer NPs, and the difficulty of obtaining balanced magneto-optical properties have greatly limited the applications of magneto-conjugated polymers in theranostics. We developed an in situ surface polymerization method free of extra surfactants and oxidizing agents to synthesize MNP@polypyrrole （PPy） NPs with balanced, prominent magneto-optical properties. MNP@PPy NPs with an adjustable size, different shapes, and a controlled shell thickness were obtained using this method. The method was extended to synthesize other MNP-conjugated polymer core-shell NPs, such as MNP@polyaniline and MNP@poly（3,4-ethylenedioxythiophene）：poly（4- styrenesulfonate） （PEDOT：PSS）. We discuss the formation mechanism of the proposed method according to our experimental results. Finally, using the optical and magnetic properties of the obtained MNP@PEDOT：PSS NPs, in vivo multimodal imaging-guided hyperthermia was induced in mice, achieving an excellent tumor-ablation therapeutic effect. Our work is beneficial for extending the application of MNP-conjugated polymer core-shell NPs in the biomedical field.

Ultrafast presodiation of graphene anodes for high-efficiency and high-rate sodium-ion storage

The low initial Coulombic efficiency(ICE)is a significant problem hindering the practical uses of carbon anodes in sodium-ion batteries(SIBs),especially for the carbons with large surface area.Presodiation is an effective way to solve the above problem,but it always needs complicated operations and cannot suppress the unavoidable electrolyte decomposition in the assembled battery.Herein,we develop an ultrafast chemical presodiation method for reduced graphene oxide(rGO)using sodium naphthalene(Na-Nt)dissolved in dimethoxyethane(DME)solvent as a presodiation reagent.The presodiation effectively improves the ICE of rGO to 96.8%and forms an artificial solid electrolyte interphase(SEI)on its surface due to the decomposition of the formed complex between Na+and DME.The formed artificial SEI suppresses the excessive decomposition of electrolytes in the assembled battery,leading to a formation of uniform and inorganic component–rich SEI on rGO surface,which enables a rapid interfacial ion transfer.Therefore,the presodiated rGO showed excellent rate performance with a high capacity of 198.5 mAh g^(-1) at 5 A g^(-1).Moreover,excellent cycle stability indicated by the high capacity retention of 68.4%over 1000 cycles was also achieved,showing the poten-tial to promote the practical uses of high-rate rGO anode in SIBs.

Vertical Graphenes Grown on a Flexible Graphite Paper as an All-Carbon Current Collector towards Stable Li Deposition

Lithium(Li)metal has been regarded as one of the most promising anode materials to meet the urgent requirements for the next-generation high-energy density batteries.However,the practical use of lithium metal anode is hindered by the uncontrolled growth of Li dendrites,resulting in poor cycling stability and severe safety issues.Herein,vertical graphene(VG)film grown on graphite paper(GP)as an all-carbon current collector was utilized to regulate the uniform Li nucleation and suppress the growth of dendrites.The high surface area VG grown on GP not only reduces the local current density to the uniform electric field but also allows fast ion transport to homogenize the ion gradients,thus regulating the Li deposition to suppress the dendrite growth.The Li deposition can be further guided with the lithiation reaction between graphite paper and Li metal,which helps to increase lithiophilicity and reduce the Li nucleation barrier as well as the overpotential.As a result,the VG film-based anode demonstrates a stable cycling performance at a current density higher than 5mAcm^(-2)in half cells and a small hysteresis of 50mV at 1mAcm^(-2)in symmetric cells.This work provides an efficient strategy for the rational design of highly stable Li metal anodes.

用于锂金属负极的轻质、高掺氮量碳纳米纤维基三维集流体（英文）

锂金属是未来二次电池实现高能量密度化的关键负极材料,然而,如何实现锂金属的均匀和无枝晶沉积是目前制约其实际应用的关键问题.本论文采用静电纺丝技术及高温碳化方法制备了一种轻质、高掺氮量(9.5 at%)的三维碳纳米纤维集流体.该集流体较低的密度能提升基于整个电池的能量密度,而且高掺氮量使其具备亲锂的特性,从而有效降低锂离子在其表面的初始形核过电位,得到均匀的金属锂种子层,实现后续金属锂的均匀沉积.这种三维结构有效抑制了锂枝晶的产生,降低了电池的极化,金属锂沉积/脱除测试中其库伦效率在循环250圈后仍可保持在98%以上.将其沉积金属锂后与LiFePO_4组装全电池,电池极化降低,在循环300圈后容量保持率可达82.4%,表现出很好的应用前景.

锂硫电池:电极材料致密化与体积能量密度优化（英文）

随着人们对于储能器件微型化、长寿命需求的日益增加,电化学储能器件的体积能量密度成为其重要性能指标.锂硫电池作为下一代重点发展的高比能量二次电池,其先进电极材料的研发受到越来越多的关注.碳材料的使用可有效提高器件性能,然而较低的电极密度导致锂硫电池体积能量密度较低.通过对电极材料的设计以及结构调控,实现电极材料致密化,可以有效解决这一问题.一方面,提高复合电极材料中硫的含量,可以提高材料整体密度,减少非活性组分,提升电极体积比容量;另一方面,通过实现碳材料的致密化,也可以提高碳/硫复合电极材料密度的调控,获得具有高体积比容量的电极材料.本文对目前关于高体积比容量锂硫电池电极材料的研究工作进行了评述,虽然目前这一方向的研究尚处起步阶段,但其必将成为未来锂硫电池研究的重点.通过集成材料设计、组装、器件结构优化等多方面工作,能够实现高体积比容量电极材料和高体积能量密度锂硫电池的应用,推动电化学储能领域的发展.

氧化石墨烯水凝胶的毛细收缩机制

以两亲性氧化石墨烯为结构单元,可控组装构建三维网络石墨烯水凝胶,通过溶剂蒸发驱动网络致密化,获得高密多孔碳,解决了传统多孔碳电极体积容量低的应用瓶颈.本文旨在探究氧化石墨烯水凝胶致密化机理,阐明了毛细作用力是使溶剂脱出并引发石墨烯网络收缩的驱动力.溶剂表面张力决定毛细作用力,因此通过调节溶剂表面张力或采用不同表面张力的溶剂,可以实现"孔"与"密"的"收放自如"调控,从而得到不同密度和孔隙率的高密多孔碳,实现高密和多孔连续精确调控.氧化石墨烯水凝胶的毛细收缩也为纳米材料致密化提供了方法论支持.

二维材料的快速三维自组装:从氧化石墨烯到二硫化钼（英文）

本工作借助1,4-丁二醇二缩水甘油醚(BDGE)与氧化石墨烯上羧基的相互作用,实现了氧化石墨烯的快速三维组装.基于此方法,我们通过表面活性剂分散其他二维材料并实现材料表面官能化,借助于这些表面官能团与BDGE的相互作用,发展出一种普适的二维材料快速三维自组装方法.以二硫化钼为例,组装形成的三维结构显著提高了表面利用率,极大地改善了其作为钠离子电池负极材料的电化学性能.

聚苯乙烯微乳液的凝胶化及其块体的快速制备和结构调控

本文利用一种新的聚苯乙烯(PS)微乳液的凝胶化现象,制备了结构稳定的PS凝胶,并通过可控的毛细收缩过程获得了具有不同孔隙结构的PS块体.对PS微乳液的凝胶化机制的系统研究表明,在PS微乳液中加入适量特定的水溶性有机溶剂后,可实现PS微乳液的破乳,PS乳胶粒子周围的表面活性剂完全解吸附,并自发团聚成二次颗粒,在适当温度条件下可通过分子链缠结组装形成三维多孔凝胶.不同溶剂实现PS微乳液凝胶化的能力可以通过d2T/η参数的大小衡量和评估.通过进一步调整成胶时间与溶剂置换程度,PS凝胶可在后续的干燥过程中实现不同程度的收缩,从而得到密度范围在0.06–1.14 g cm^(-3)的多孔或致密PS块体.这种PS凝胶化策略是一种简单高效的PS成型方法,避免了成型设备、模板、成孔剂以及大量表面活性剂的应用,有望成为制备功能高分子聚合物块体材料的新方法.