Helical silicon/silicon oxide core-shell anodes grown onto the surface of bulk silicon

We demonstrate a simple route for preparing Si/SiO(x) urchin-like structures in which Si/SiO(x) core-shell nanocoils protruded out from the surface of bulk Si, via high-temperature annealing of Pt-decorated Si powders. The carbon-coated urchin-like anodes with micro- and nanostructured composite exhibit a significantly improved electrochemical performance with a high specific capacity of 1600 mAh/g and a superior cycling performance of 70 cycles at a rate of 0.2 C due to the nanocoil conformation and SiO(x) buffer layer. More importantly, the composite results in a significantly enhanced the volumetric capacity with ～3780 mAh/cc, compared to bulk Si (～2720 mAh/cc) after fully lithiation to 0 V.     

多孔碳纳米管纸负载中空硅微球作为阳极的高容量锂硅电池

为提高硅基锂离子电池的电化学性能,制备了一种多微孔结构的集流体。以纸纤维为基体,多壁碳纳米管（MWCNTs）为导电剂,制得MWCNTs/纸纤维复合多孔导电纸代替铜箔作为负极集流体。MWCNTs负载中空Si微球复合材料作为负极活性材料。FESEM分析显示,中空Si-MWCNTs复合活性物质均匀分布在MWCNTs构建的三维导电网络的孔隙中,从而保证了材料的结构稳定性和化学稳定性。所制备的中空Si-MWCNTs/纸纤维复合锂离子电池具有良好的循环稳定性和较高的比容量,同时具有可逆性。在0.02 C的电流密度下,循环30次后其比容量稳定在1 300 mAh/g。在3 C的大电流密度下,比容量仍可稳定保持在330 mAh/g。恢复0.25 C充放电后,容量恢复为1 150 mAh/g。     

Ultrathin graphite foam: a three-dimensional conductive network for battery electrodes

We report the use of free-standing, lightweight, and highly conductive ultrathin graphite foam (UGF), loaded with lithium iron phosphate (LFP), as a cathode in a lithium ion battery. At a high charge/discharge current density of 1280 mA g(-1), the specific capacity of the LFP loaded on UGF was 70 mAh g(-1), while LFP loaded on Al foil failed. Accounting for the total mass of the electrode, the maximum specific capacity of the UGF/LFP cathode was 23% higher than that of the Al/LFP cathode and 170% higher than that of the Ni-foam/LFP cathode. Using UGF, both a higher rate capability and specific capacity can be achieved simultaneously, owing to its conductive (～1.3 × 10(5) S m(-1) at room temperature) and three-dimensional lightweight (～9.5 mg cm(-3)) graphitic structure. Meanwhile, UGF presents excellent electrochemical stability comparing to that of Al and Ni foils, which are generally used as conductive substrates in lithium ion batteries. Moreover, preparation of the UGF electrode was facile, cost-effective, and compatible with various electrochemically active materials.     

Roll-Pressed Silicon Anodes with High Reversible Volumetric Capacity Achieved by Interfacial Stabilization and Mechanical Strengthening of a Silicon/Graphene Hybrid Assembly

Application of Si anodes is hindered by severe capacity fading due to pulverization of Si particles during the large volume changes of Si during charge/discharge and repeated formation of the solid-electrolyte interphase. To address these issues, considerable efforts have been devoted to the development of Si composites with conductive carbons (Si/C composites). However, Si/C composites with high C content inevitably show low volumetric capacity because of low electrode density. For practical applications, the volumetric capacity of a Si/C composite electrode is more important than gravimetric capacity, but volumetric capacity in pressed electrodes is rarely reported. Herein, a novel synthesis strategy is demonstrate for a compact Si nanoparticle/graphene microspherical assembly with interfacial stability and mechanical strength achieved by consecutively formed chemical bonds using 3-aminopropyltriethoxysilane and sucrose. The unpressed electrode (density: 0.71 g cm⁻³) shows a reversible specific capacity of 1470 mAh g⁻¹ with a high initial coulombic efficiency of 83.7% at a current density of 1 C-rate. The corresponding pressed electrode (density: 1.32 g cm⁻³) exhibits high reversible volumetric capacity of 1405 mAh cm⁻³ and gravimetric capacity of 1520 mAh g⁻¹ with a high initial coulombic efficiency of 80.4% and excellent cycling stability of 83% over 100 cycles at 1 C-rate.     

Simple Construction of Multistage Stable Silicon–Graphite Hybrid Granules for Lithium-Ion Batteries

Because of its high specific capacity, the silicon–graphite composite (SGC) is regarded as a promising anode for new-generation lithium-ion batteries. However, the frequently employed two-section preparation process, including the modification of silicon seed and followed mixture with graphite, cannot ensure the uniform dispersion of silicon in the graphite matrix, resulting in a stress concentration of aggregated silicon domains and cracks in composite electrodes during cycling. Herein, inspired by powder engineering, the two independent sections are integrated to construct multistage stable silicon–graphite hybrid granules (SGHGs) through wet granulation and carbonization. This method assembles silicon nanoparticles (Si NPs) and graphite and improves compatibility between them, addressing the issue of severe stress concentration caused by uncombined residue of Si NPs. The optimal SGHG prepared with 20% pitch content exhibits a highly reversible specific capacity of 560.0 mAh g⁻¹ at a current density of 200 mA g⁻¹ and a considerable stability retention of 86.1% after 1000 cycles at 1 A g⁻¹. Moreover, as a practical application, the full cell delivers an outstanding capacity retention of 85.7% after 400 cycles at 2 C. The multistage stable structure constructed by simple wet granulation and carbonization provides theoretical guidance for the preparation of commercial SGC anodes.     

锂离子电池Si/C/石墨复合负极材料的电化学性能

采用热裂解方法, 热解分散于聚偏二氟乙烯溶液中的硅和石墨, 得到了具有稳定电化学循环性能的Si/C/石墨复合负极材料。透射电子显微镜观察发现, 复合材料形貌为无定型碳包裹硅颗粒的核壳结构。通过系统研究不同Si粒径和石墨含量对电极电化学性能的影响, 发现Si颗粒粒径越小复合材料电化学循环稳定性能越优越, 适当的降低石墨含量有利于电极材料剩余比容量的提高。当Si粒径为50 nm, Si与石墨质量比1:1时, 电极材料具有1741.6 mAh/g的首次放电比容量和72.5%的首次库仑效率, 60次循环后, 可逆比容量保持在820 mAh/g。热解有机物形成碳包覆的结构能有效地改善硅基类负极材料的电化学循环性能。     

One-step strategy to graphene/Ni(OH)2 composite hydrogels as advanced three-dimensional supercapacitor electrode materials

Graphene-based three-dimensional (3D) macroscopic materials have recently attracted increasing interest by virtue of their exciting potential in electrochemical energy conversion and storage. Here we report a facile one-step strategy to prepare mechanically strong and electrically conductive graphene/Ni(OH)₂ composite hydrogels with an interconnected porous network. The composite hydrogels were directly used as 3D supercapacitor electrode materials without adding any other binder or conductive additives. An optimized composite hydrogel containing ～82 wt.% Ni(OH)₂ exhibited a specific capacitance of ～1,247 F/g at a scan rate of 5 mV/s and ～785 F/g at 40 mV/s (～63% capacitance retention) with excellent cycling stability. The capacity of the 3D hydrogels greatly surpasses that of a physical mixture of graphene sheets and Ni(OH)₂ nanoplates (～309 F/g at 40 mV/s). The same strategy was also applied to fabricate graphene-carbon nanotube/Ni(OH)₂ ternary composite hydrogels with further improved specific capacitances (～1,352 F/g at 5 mV/s) and rate capability (～66% capacitance retention at 40 mV/s). Both composite hydrogels obtained here can deliver high energy densities (～43 and ～47 Wh/kg, respectively) and power densities (～8 and ～9 kW/kg, respectively), making them attractive electrode materials for supercapacitor applications. This study opens a new pathway to the design and fabrication of functional 3D graphene composite materials, and can significantly impact broad areas including energy storage and beyond.      

沥青基软碳材料对硅负极锂离子电池性能的影响沥青基软碳材料对硅负极锂离子电池性能的影响

以沥青为软碳原料（质量分数为10%、20%、30%、50%）,通过高温热解法成功合成了不同软碳含量的碳/硅（C/Si）复合材料。实验结果表明,软碳材料的引入能有效抑制Si基材料的体积效应和提高其电子电导率,从而在极大的改善负极材料循环性能的同时,还提高了其比容量。其次,通过系统研究不同C含量的C/Si复合材料性能,发现最佳的沥青加入量为20%。该条件所合成样品具有高达2356.7 mAhg-1的首次充电比容量和86.6%的库伦效率。经过50次循环后依然有726.4 mAhg-1的充电比容量,远高于工业化石墨负极材料,应用前景广阔。本研究还详细研究和讨论了软碳材料的形成机制以及不同软碳含量对材料形貌的影响。      

Flexible Interface Design for Stress Regulation of a Silicon Anode toward Highly Stable Dual-Ion Batteries

Dual-ion batteries (DIBs) have attracted increasing attention due to their high working voltage, low cost, and environmental friendliness, yet their development is hindered by their limited energy density. Pairing silicon—a most promising anode due to its highest theoretical capacity (4200 mAh g⁻¹)—with a graphite cathode is a feasible strategy to address the challenge. Nevertheless, the cycling stability of silicon is unsatisfactory due to the loss of electrical contact resulting from the high interface stress when using rigid current collectors. In this work, a flexible interface design to regulate the stress distribution is proposed, via the construction of a silicon anode on a soft nylon fabric modified with a conductive Cu–Ni transition layer, which endows the silicon electrode with remarkable flexibility and stability over 50 000 bends. Assembly of the flexible silicon anode with an expanded graphite cathode yields a silicon–graphite DIB (SGDIB), which possesses record-breaking rate performance (up to 150 C) and cycling stability over 2000 cycles at 10 C with a capacity retention of 97%. Moreover, the SGDIB shows a high capacity retention of ≈84% after 1500 bends and a low self-discharging voltage loss of 0.0015% per bend after 10 000 bends, suggesting high potential for high-performance flexible energy-storage applications.     

球磨法制备锂离子液流电池石墨负极浆料的性能研究

采用球磨法制备锂离子液流电池所用的石墨负极浆料,并对石墨负极浆料的颗粒形貌、电导率、比容量性能及循环性能进行研究。结果表明:导电添加剂的加入有助于提高电极浆料的悬浮稳定性;球磨过程可以降低石墨和导电添加剂混合粉体的电阻率,球料比达到5∶1时即可实现较好的球磨效果,但球料比不宜过高,否则会造成石墨材料层状结构的破坏,影响电极浆料性能的稳定性。提高石墨和导电添加剂的含量可以在电极浆料中形成稳定的导电网络结构,使可逆比容量提高;在保证电极浆料可流动的情况下,可逆比容量可大于40mAh/g。石墨负极浆料的容量损失主要发生在首次充放电过程中,随着循环次数的增加,容量损耗的速率降低,第5次循环以后容量趋于稳定。     

Core–Shell Si/C Nanospheres Embedded in Bubble Sheet‐like Carbon Film with Enhanced Performance as Lithium Ion Battery Anodes

Due to its high theoretical capacity and low lithium insertion voltage plateau, silicon has been considered one of the most promising anodes for high energy and high power density lithium ion batteries (LIBs). However, its rapid capacity degradation, mainly caused by huge volume changes during lithium insertion/extraction processes, remains a significant challenge to its practical application. Engineering Si anodes with abundant free spaces and stabilizing them by incorporating carbon materials has been found to be effective to address the above problems. Using sodium chloride (NaCl) as a template, bubble sheet‐like carbon film supported core–shell Si/C composites are prepared for the first time by a facile magnesium thermal reduction/glucose carbonization process. The capacity retention achieves up to 93.6% (about 1018 mAh g^?1) after 200 cycles at 1 A g^?1. The good performance is attributed to synergistic effects of the conductive carbon film and the hollow structure of the core–shell nanospheres, which provide an ideal conductive matrix and buffer spaces for respectively electron transfer and Si expansion during lithiation process. This unique structure decreases the charge transfer resistance and suppresses the cracking/pulverization of Si, leading to the enhanced cycling performance of bubble sheet‐like composite.     

微波辅助固相法合成锂离子电池正极复合材料Li2FeSiO4/C

以Na2SiO3.9H2O和FeCl2.4H2O为原料,采用低热固相反应获得了分散均匀的β-FeOOH/SiO2前驱体;再以Li2CO3为锂源、聚乙烯醇和超导电炭黑为复合碳源,通过微波辅助固相法合成了Li2FeSiO4/C材料.通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征.650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li2FeSiO4/C材料;在选用的微波合成体系下,超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行,而且提高了Li2FeSiO4的整体导电性能.制备的复合正极材料在60℃下0.05C倍率首次放电容量为129.6 mAh/g,0.5C倍率下为107.5 mAh/g,0.5C下15次循环后保持为104.8 mAh/g,具有较好的放电比容量和良好的循环稳定性能.结果表明,微波辅助固相合成工艺是制备Li2FeSiO4/C复合材料的一种很有前景的方法.     

Carbon Nanotube-Reinforced Dual Carbon Stress-Buffering for Highly Stable Silicon Anode Material in Lithium-Ion Battery

Silicon (Si) anode suffers from huge volume expansion which causes poor structural stability in terms of electrode material, solid electrolyte interface, and electrode, limiting its practical application in high-energy-density lithium-ion batteries. Rationally designing architectures to optimize the stress distribution of Si/carbon (Si/C) composites has been proven to be effective in enhancing their structural stability and cycling stability, but this remains a big challenge. Here, metal-organic frameworks (ZIF-67)-derived carbon nanotube-reinforced carbon framework is employed as an outer protective layer to encapsulate the inner carbon-coated Si nanoparticles (Si@C@CNTs), which features dual carbon stress-buffering to enhance the structural stability of Si/C composite and prolong their cycling lifetime. Finite element simulation proves the structural advantage of dual carbon stress-buffering through significantly relieving stress concentration when Si lithiation. The outer carbon framework also accelerates the charge transfer efficiency during charging/discharging by the improvement of lithium-ion diffusion and electron transport. As a result, the Si@C@CNTs electrode exhibits excellent long-term lifetime and good rate capability, showing a specific capacity of 680 mAh g⁻¹ even at a high rate of 1 A g⁻¹ after 1000 cycles. This work provides insight into the design of robust architectures for Si/C composites by stress optimization.     

静电纺TiO2改性联苯型聚酰亚胺锂离子电池隔膜

先采用高压静电纺丝技术制备二氧化钛/聚酰胺酸(TiO₂/PAA)复合纤维膜,然后对其进行热亚胺化处理制备出二氧化钛/聚酰亚胺(TiO₂/PI)复合纤维隔膜。使用扫描电子显微镜(SEM)、傅里叶红外光谱分析仪(FTIR)、热失重分析仪和电化学工作站测试了TiO₂/PI复合纤维隔膜的基本性能和电化学性能,结果表明：隔膜具有明显的三维网状结构,与未改性的纯PI隔膜相比,改性后TiO₂/PI复合纤维隔膜的拉伸强度、孔隙率和吸液率分别提高到16.74 MPa、77.5%和550%;其热收缩性能较好,整体电化学性能优异。制备的LiFePO₄(磷酸铁锂正极)/TiO₂/PI/C(石墨负极)电池具有优异的循环稳定性和高放电容量,在1 C条件下进行100个循环后,其库伦效率在25℃和120℃高达96.7%和90.7%。     

Mechanical properties and oxidation resistance of C–B–Si coated silicon nitride fiber reinforced Si–N–C composites with cross-ply structure

To enhance the oxidation resistance of a ceramic matrix composite, a C–B–Si interface layer was applied between the fiber and the matrix. The layer was deposited on the fiber by chemical vapor deposition. Three types of coatings were prepared: A1, A2 (multilayers of graphite layer/B–C–Si crystalline layer/graphite layer) and B1 (monolayer of B and C containing graphite). The multilayer coated CMC retained 88–97% of the original strengths after oxidation at 1523 K for 36 ks. The monolayer coated CMC degraded to 55% of its original strength after oxidation, but had a high fracture toughness (28 MPa m^1/2) before oxidation. The differences of the oxidation resistance and fracture toughness were discussed in relation to the microstructure of the coatings.     

纳米Si/C/N复相粉体的制备及其在不同基体中的微波介电特性

以六甲基二硅胺烷（（Ｍｅ_３Ｓｉ）_２ＮＨ）（Ｍｅ：ＣＨ_３）为原料,用双反应室激光气相合成纳米粉体装置制备了纳米Ｓｉ／Ｃ／Ｎ复相粉体．研究了纳米Ｓｉ／Ｃ／Ｎ复相粉体在不同基体中８．２～１２．４ＧＨｚ的微波介电特性,纳米粉体介电常数的实部（ε’）和虚部（ε”）随频率增大而减小,介电损耗（ｔｇδ＝ε”／ε’）较高·纳米Ｓｉ／Ｃ／Ｎ复相粉体中的ＳｉＣ微晶固溶了大量的Ｎ原子,在纳米Ｓｉ／Ｃ／Ｎ复相粉体中形成大量的带电缺陷;极化弛豫是吸收电磁波的主要原因．     

Si@环化聚丙烯腈/多壁碳纳米管负极复合材料的制备及电化学性能

通过简单高能球磨和高温热解法制备了锂离子电池Si/C电极复合材料,聚丙烯腈（PAN）包覆的纳米颗粒（Si@PAN）与多壁碳纳米管（MWCNTs）混合,制得Si@环化PAN/MWCNTs（Si@c-PAN/MWCNTs）复合材料作为锂离子电池的负极材料。包覆在纳米Si外层的高温热解后的PAN能够有效缓冲Si在充放电过程中巨大的体积变化产生的应力,同时MWCNTs作为Si@c-PAN的基体阻止Si@c-PAN颗粒的团聚,也提高了Si@c-PAN/MWCNTs复合材料电极的导电性能。电化学测试结果表明,Si@c-PAN/MWCNTs复合材料电极在电流密度为0.2 A/g时,其首次放电比容量达到2 098 mA?h/g,库伦效率达到86%;循环50次后Si@c-PAN/MWCNTs复合材料电极的可逆比容量仍能够达到1 278 mA?h/g,在2 A/g放电时其比容量为600 mA?h/g,仍保持良好的循环稳定性。      

纳米硅/石墨负极材料的炭包覆改性研究

硅颗粒的低负载量及其与石墨基体的弱相互作用严重制约了硅/石墨负极材料的商业化应用。本研究通过浓硫酸和高锰酸钾的氧化处理增大石墨基体的比表面积,利用十二烷基苯磺酸钠作为表面活性剂,改善纳米硅与氧化石墨湿法混合的均匀性,采用柠檬酸催化蔗糖碳源的水解,以便热解后在复合材料表面形成完整的炭包覆层。XRD与SEM分析表明,改进的炭包覆工艺可促进氧化石墨的还原,获得高石墨化度的碳硅复合材料,并实现硅颗粒在石墨基体中的均匀分散。上述协同效应使炭包覆的纳米硅/石墨负极材料在100 mA·g^-1的电流密度下循环100圈后比容量仍能稳定在400 mAh·g^-1左右,在提升比容量的基础上,有效抑制了硅在循环过程中的体积膨胀。     

多组元掺杂石墨微观结构及其性能的研究

制备了Si,Ti比组元和Si,Ti,B4C三组元掺杂石墨材料并研究了其结构和性能,实验结果表明,与相同条件下制得的纯石墨材料相比,掺杂石墨材料具有高密度,高强度以及极低的电阻率等特点,双组元掺杂石墨的导电性略优于三组元掺杂石墨,但其机械强度却明显低于后者,分析表明,各组元在材料中所起的作用各不相同,钛,硼添加剂对材料的机械强度有增强作用,对材料的石经具有催化作用,少量硅的添加有利于石墨材料的石墨化和蔼以及导电性能的提高,但含量较多时,由于Si的大量逸失导致气率增大,使掺杂石墨的导电极性及机械性能降低。     

多孔兰尼镍作单质硫载体的锂硫电池性能

提出以导电多孔兰尼镍（RNi）为锂硫电池中单质S的新载体材料,探究了S/RNi复合材料在溶剂法、研磨高温法及球磨高温法下的电化学性能差异。结果表明,溶剂法制备的S/RNi复合材料的电化学性能最好。预处理后的RNi为海绵状的导电多孔结构,孔径分布在12.5~50 nm之间。SEM和XRD表明,溶剂法制备的S/RNi复合材料具备良好的孔结构,单质S颗粒较小,均匀分布在深层孔结构中,S与RNi充分接触。其首次放电比容量达到1 479 mAh/g,经过200次充放电循环后放电比容量保持在765 mAh/g,库伦效率约为99%。其循环性能也优于传统S/C复合材料。溶剂法制备的S/RNi复合材料的循环稳定性和高倍率性能得益于RNi的导电性及对单质S的物理和化学吸附。