制备温度对热解炭包覆磷酸铁锂/气相生长炭纤维复合正极材料的影响

采用微波化学气相沉积法一步合成了热解炭包覆磷酸铁锂/气相生长炭纤维复合正极材料. 借助X射线衍射仪、场发射扫描电子显微镜、高分辨透射电镜和电化学测试仪等测试手段研究了不同制备温度对材料晶体结构、显微形貌和电化学性能的影响. 结果表明, 当制备温度由500℃升至600℃时, 磷酸铁锂主晶相的颗粒尺寸没有发生明显变化, 而原位VGCF的网络程度却明显增加, 材料的放电比容量随之提高; 当制备温度进一步升高到700℃时, 磷酸铁锂颗粒异常生长现象加剧, VGCF直径较大且粗细不均, 材料的电化学性能变差. 研究发现, 当温度为600℃时, 材料表现出较优的电化学性能, 25℃在0.2C、0.5C、1C和3C倍率下的放电比容量分别可达163、159、153和143mAh/g.     

Synthesis and electrochemical analyses of vapor-grown carbon fiber/pyrolytic carbon-coated LiFePO<Subscript>4</Subscript> composite

A vapor-grown carbon fiber/pyrolytic carbon-coated LiFePO₄ (VGCF/PCLFP) composite has been prepared in one step through a solid-state reaction accompanied by a gas-phase decomposition process. This method leads to the formation of a conductive network composed of pyrolytic carbon layer and in situ vapor-grown carbon fiber in the composite. The amount of carbon in the composite has been determined by a modified formula based on thermogravimetric analysis to be around 3.0 wt%. The optimized electrode of VGCF/PCLFP composite can deliver 150 mAhg⁻¹ at 0.5 C rate, 137 mAhg⁻¹ at 1.0 C rate and 132 mAhg⁻¹ at 3.0 C rate. And its discharge capacity loses only ~4% at a higher rate of 3.0 C after 100 cycles. The area-specific impedance of a cell fabricated with VGCF/PCLFP composite is lower than that made of only pyrolytic carbon-coated LiFePO₄, reported here for the purpose of comparison. In comparison to the electrode made of carbon black/LiFePO₄ composite (10 wt% carbon), the charge transfer resistance of the VGCF/PCLFP composite electrode decreases from 165 to 91 Ω. This technique presents an attractive way to produce high-performance LiFePO₄ cathode material through a low-cost high-efficiency process.     

高温还原GO制备LiFePO_4/石墨烯复合正极材料及表征

通过对氧化石墨烯(GO)进行微观调控处理得到少层GO。采用喷雾干燥再高温改性的方法制备LiFePO_4/石墨烯锂离子电池复合正极材料;GO还原后即可得到石墨烯,其优良的导电性可以提高LiFePO_4的电子传输能力。通过X射线衍射(XRD)、红外光谱(FTIR)、扫描电镜(SEM)、透射电镜(TEM)和电化学测试技术等方法对复合材料的结构、形貌及电化学性能进行表征。石墨烯的复合使材料颗粒间构建空间三维导电网络,提高了电解质/电极材料界面的电荷转移速率,改善了LiFePO_4的电化学性能。电化学测试结果表明,在0.1C时LiFePO_4的放电比容量为155mAh/g,LiFePO_4/石墨烯复合材料的放电比容量为164mAh/g;1C和2C倍率时,LiFePO_4/石墨烯复合材料的放电比容量分别为140,119mAh/g。     

MOFs及衍生复合材料在锂硫电池中的设计应用

在能源危机与环境问题日益凸显的背景下,电化学储能技术得到了迅速发展。在“超越锂”储能领域的竞争者中,锂硫电池(Li-S)因其具有高理论比容量、高质量能量密度并且环境友好、价格低廉等优点,成为最有前途的新储能技术。但是,锂硫电池的发展仍存在一些瓶颈问题需要解决,例如正极材料导电性能差、多硫化物穿梭效应及在充放电过程中电极体积膨胀等。作为锂硫电池的关键组成部分,电极和隔膜材料的设计和制备对解决这些问题及电池整体性能提升起到了重要的作用。金属有机骨架(MOFs)及衍生的复合材料作为锂硫电池电极或隔膜修饰材料,具有质量轻、电子和离子传导性好、孔道丰富和活性位点均匀分布等优势。此外,这类复合材料还具备形貌和组分可控、来源丰富和孔径可调等特性,从而便于机制研究。本文全面介绍了锂硫电池组成、工作原理并综述了近几年MOFs及衍生复合材料在锂硫电池中的研究进展,重点讨论了其在正极材料和隔膜材料中的应用,并对未来该材料在锂硫电池研究方向上的前景和突破进行了展望。      

Preparation of nitrogen-doped three-dimensional hierarchical porous carbon/sulfur composite cathodes for high-performance aluminum-sulfur batteries

Abstract

Aluminum-ion batteries, as a feasible substitute for lithium-ion batteries, have the advantages of high safety, high capacity, low cost and environmental friendliness. However, the cathode material is one of the key factors restricting the performance and practical application of aluminum-ion batteries. Sulfur is becoming a promising cathode material for aluminum-ion batteries due to its considerable theoretical specific capacity. However, the poor conductivity of elemental sulfur seriously limits the development of aluminum-sulfur batteries. In this work, nitrogen doped three-dimensional multi-stage porous carbon materials (N-C/S) were prepared, which were compounded with sulfur to prepare carbon sulfur composite cathode materials. The microstructure, phase morphology, element composition and electrochemical performance were analyzed by various characterization methods. Then, N-C/S composite was used as a positive electrode to assemble a new type of aluminum-sulfur batteries, and its performance was evaluated. This novel high-performance N-C/S composite cathode holds great potential in future high-performance aluminum-sulfur batteries.     

Mesoporous nitrogen-doped carbon-glass ceramic cathodes for solid-state lithium-oxygen batteries

The composite of nitrogen-doped carbon (N-C) blend with lithium aluminum germanium phosphate (LAGP) was studied as cathode material in a solid-state lithium-oxygen cell. Composite electrodes exhibit high electrochemical activity toward oxygen reduction. Compared to the cell capacity of N-C blend cathode, N-C/LAGP composite cathode exhibits six times higher discharge cell capacity. A significant enhancement in cell capacity is attributed to higher electrocatalytic activity and fast lithium ion conduction ability of LAGP in the cathode.     

电化学合成磷酸铁锂正极材料的前驱体

以NH4H2PO4、锂盐和纯铁为主要原料,采用电化学法合成磷酸锂铁前驱体,再通过磷酸锂铁前驱体合成锂离子电池正极材料LiFePO4/C。通过X射线衍射(XRD)、扫描电镜(SEM)及充放电性能测试等方法对其晶体结构、微观形貌和电化学性能进行分析研究。结果表明,LiFePO4/C具有单一的橄榄石型晶体结构。其中在无水乙醇溶剂中合成的LiFePO4/C正极材料粒径细小且分布均匀,具有最好的电化学性能,在0.2C的放电电流下,首次放电比容量达到142.3mAh/g,充放电循环30次后放电比容量仍保持在141.2mAh/g。     

碳源对LiFePO_4/C正极材料性能的影响

以FePO_4·2H_2O、Li_2CO_3和柠檬酸/酒石酸/抗坏血酸为原料,经机械球磨后在惰性气氛中高温煅烧合成LiFePO_4/C正极材料.研究了不同碳源对LiFePO_4结构、形貌及电化学性能的影响.重点考察了碳源为酒石酸时,不同合成温度对材料性能的影响.采用XRD、SEM以及电化学测试等手段对目标产物进行了结构表征和性能测试.结果表明,以酒石酸做碳源时,合成的正极材料物相单一,颗粒细小,粒度均匀,并且具有优良的电化学性能.在室温下以0.1C倍率充放电,首次放电比容量可达155mAh/g,1.0C首次放电比容量为120mAh/g,经过100次循环以后容量仍有109mAh/g.     

纳米碳材料改善电化学电容器性能研究

通过在双电层电化学电容器的活性炭电极中添加纳米结构炭黑、碳纳米管等新型电子导体的方法,扩大电子导体与活性物质的有效接触面积,增大活性物质具有电化学反应活性的表面,从而提高电极的导电性能与容量性质,改善电化学电容器的充放电性能。实验结果表明新型的纳米碳材料可赋予电极良好的导电性能,优于常用的导电石墨、炭黑等电子导体,是较为理想的电化学电容器用电极导电剂。     

Plasma Treatment for Nitrogen‐Doped 3D Graphene Framework by a Conductive Matrix with Sulfur for High‐Performance Li–S Batteries

Carbon materials have received considerable attention as host cathode materials for sulfur in lithium–sulfur batteries; N‐doped carbon materials show particularly high electrocatalytic activity. Efforts are made to synthesize N‐doped carbon materials by introducing nitrogen‐rich sources followed by sintering or hydrothermal processes. In the present work, an in situ hollow cathode discharge plasma treatment method is used to prepare 3D porous frameworks based on N‐doped graphene as a potential conductive matrix material. The resulting N‐doped graphene is used to prepare a 3D porous framework with a S content of 90 wt% as a cathode in lithium–sulfur cells, which delivers a specific discharge capacity of 1186 mAh g^?1 at 0.1 C, a coulombic efficiency of 96% after 200 cycles, and a capacity retention of 578 mAh g^?1 at 1.0 C after 1000 cycles. The performance is attributed to the flexible 3D structure and clustering of pyridinic N‐dopants in graphene. The N‐doped graphene shows high electrochemical performance and the flexible 3D porous stable structure accommodates the considerable volume change of the active material during lithium insertion and extraction processes, improving the long‐term electrochemical performance.     

In situ construction of graded porous carbon matrix to strengthen structural stability of NiFe2O4 nanoparticles as high-capacity anodes of Li-ion batteries

Transition metal oxides are considered as promising anode materials of high-performance lithium-ion batteries because of their higher specific capacities than that of commercial graphite. However, they still suffer from huge volume expansion/contraction during cycling, leading to fast decay of the reversible capacity and poor cycle stability. In this work, a graded porous carbon matrix has been in situ constructed successfully to strengthen structural stability of NiFe₂O₄ nanoparticles via a facile and green low-temperature combustion method. The calcination temperature has a significant effect on the purity and electrochemical performances of the final NiFe₂O₄/C composites. NiFe₂O₄/C prepared at 350 °C shows a high first discharge capacity of 1385.8 mAh g^?1 at 200 mA g^?1, excellent cycle stability, and good rate capability. This excellent electrochemical performance may be attributed to its favorable graded porous structure. The carbon matrix can effectively protect the NiFe₂O₄ nanoparticles, buffer the surface stress caused by volume expansion/contraction, and facilitate the transmission of electrons and Li⁺ ions. The symbiotic relationship between NiFe₂O₄ active nanoparticles and graded porous carbon matrix strengthens the structural stability of the electrode, which expands the way of designing high-performance electrode materials for secondary rechargeable batteries.

     

Uniform Distribution of Alloying/Dealloying Stress for High Structural Stability of an Al Anode in High‐Areal‐Density Lithium‐Ion Batteries

Aluminum (Al) is one of the most attractive anode materials for lithium‐ion batteries (LIBs) due to its high theoretical specific capacity, excellent conductivity, abundance, and especially low cost. However, the large volume expansion, originating from the uneven alloying/dealloying reactions in the charge/discharge process, causes structural stress and electrode pulverization, which has long hindered its practical application, especially when assembled with a high‐areal‐density cathode. Here, an inactive (Cu) and active (Al) co‐deposition strategy is reported to homogeneously distribute the alloying sites and disperse the stress of volume expansion, which is beneficial to obtain the structural stability of the Al anode. Owing to the homogeneous reaction and uniform distribution of stress during the charge/discharge process, the assembled full battery (LiFePO₄ cathode with a high areal density of ≈7.4 mg cm^?2) with the Cu–Al@Al anode, achieves a high capacity retention of ≈88% over 200 cycles, suggesting the feasibility of the interfacial design to optimize the structural stability of alloying metal anodes for high‐performance LIBs.     

Li2ZrO3包覆锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的制备及其电化学性能

富锂锰基材料因其具有较高的充放电比容量而备受关注。针对其首次库仑效率低、循环和倍率性能差的问题,将具有三维Li^+通道的锂离子导体Li2ZrO3引入至富锂锰基正极材料Li[Li0.2Ni0.2Mn0.6]O2的表面对其进行包覆改性研究。通过XRD,TEM,SEM,EDS综合分析可知:Li2ZrO3成功包覆到样品表面。包覆层厚度为3 nm(包覆量1%,质量分数)时复合材料的电化学性能得到显著提升。0.1 C(1 C=200 mAh·g^-1)倍率下首次放电比容量可达271.5 mAh·g^-1,库仑效率为72.4%,降低了首次不可逆容量损失;0.5 C下循环100周次后放电比容量为191.5 mAh·g^-1,容量保持率为89.5%,5 C倍率放电比容量为75 mAh·g^-1,倍率性能提升。适当厚度的均匀Li2ZrO3包覆层可在样品表面形成核壳结构使样品更稳定,减少表面副反应,阻止生成较厚SEI膜,这得益于Li2ZrO3本身的高电导率、高电化学稳定性和较好的锂离子传导性。     

Interface Chemistry Engineering of Protein‐Directed SnO2 Nanocrystal‐Based Anode for Lithium‐Ion Batteries with Improved Performance

A novel uniform amorphous carbon‐coated SnO₂ nanocrystal (NCs) for use in lithium‐ion batteries is formed by utilizing bovine serum albumin (BSA) as both the ligand and carbon source. The SnO₂–carbon composite is then coated by a controlled thickness of polydopamine (PD) layer through in situ polymerization of dopamine. The PD‐coated SnO₂–carbon composite is finally mixed with polyacrylic acid (PAA) which is used as binder to accomplish a whole anode system. A crosslink reaction is built between PAA and PD through formation of amide bonds to produce a robust network in the anode system. As a result, the designed electrode exhibits improved reversible capacity of 648 mAh/g at a current density of 100 mA/g after 100 cycles, and an enhanced rate performance of 875, 745, 639, and 523 mAh/g at current densities of 50, 100, 250, and 500 mA/g, respectively. FTIR spectra confirm the formation of crosslink reaction and the stability of the robust network during long‐term cycling. The great improvement of capacity and rate performance achieved in this anode system is attributed to two stable interfaces built between the active material (SnO₂–carbon composite) and the buffer layer (PD) and between the buffer layer and the binder (PAA), which effectively diminish the volume change of SnO₂ during charge/discharge process and provide a stable matrix for active materials.     

锂硫电池S@pPAN正极用柔性黏结剂研究

硫化聚丙烯腈(S@pPAN)作为锂硫电池正极材料实现了固–固转化反应机制,没有多硫离子溶解现象,但电化学循环过程中出现明显的体积变化,其表界面特性对电化学性能具有重要影响.本研究以单壁碳纳米管(SWCNT)与羧甲基纤维素钠(CMC)复配作为S@pPAN正极黏结剂,调控S@pPAN表界面并缓解充放电过程中的体积变化.在2...     

超级电容器MnO_2/活性炭复合电极的研究

采用机械混合物理方法将电解MnO2进行细化并与活性炭组成复合电极材料。循环伏安、恒流充放电等测试结果表明,复合电极材电极具有更好的电化学可逆性和理想的电化学电容行为。当MnO2和活性炭混合物的平均粒径在3μm左右,并且其配比达到某一值时,电极呈现出良好的大电流充放电性能,解决了活性炭大电流充放电效果差的问题。     

S,N-codoped carbon capsules with microsized entrance: Highly stable S reservoir for Li-S batteries

Nanostructured carbon materials are extensively applied as host materials to improve the utilization rate and reversibility of elemental sulfur in lithium sulfur (Li-S) batteries. Here, S, N-codoped carbon capsules (SNCCs) with microporous walls, prepared by a self-assembly process, are used as the sulfur host material in Li-S batteries. The SNCCs provide plenty of micron-sized cavities to accommodate a high S loading, which are sealed by thick walls with microsized entrance to efficently suppress the shuttle effect of lithium polysulfides. As the cathode in Li-S battery, the SNCCs/sulfur composite with a sulfur mass loading of 70 wt% exhibits a high average reversible capacity of 1220 and 1116 mA h g^?1 at 0.5C and 1C, respectively, superior rate performance (905 and 605 mAh g^?1 at 5C and 10C, respectively) and excellent cycling stability (capacity fading rate of 0.03% per cycle in 500 cycles). Even at a high sulfur areal loading of 7.3 mg/cm², the SNCCs/0.7S electrode still deliver a high initial discharge capacity of 838 mAh g^?1 and keeps at 730 mAh g^?1 after 100 cycles, corresponding to an extraordinary capacity retention of 87.1%, showing an excellent cyclic stability. The outstanding electrochemical performance is associated with the unique capsule structure with abundant volume, microsized entrance and high conductivity. Our results provides a new strategy to prepare highly stable sulfur-carbon composites for the application in Li-S batteries.     

煤基球形多孔碳用于锂离子电池负极材料的性能研

因具有较短的锂离子扩散路径、大的比表面积等优势, 球形碳材料在锂离子电池负极材料中展露出良好的应用前景。研究以新疆库车产煤为原料, 采用电弧放电法及化学活化法制备出了具有多孔结构的煤基球形碳。通过X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱(Raman)、氮气吸脱附法和恒电流充放电等测试手段对材料结构、形貌和电化学性能进行了表征。结果表明, 在100 mA/g的电流密度下, 煤基球形多孔碳的首次放电比容量可达到1188.9 mAh/g, 远高于商业石墨负极372 mAh/g的理论比容量。此外, 该材料还表现出了良好的循环稳定性, 经历200圈循环后的放电比容量为844.9 mAh/g。煤基球形多孔碳优异的电化学性能得益于活化过程所产生的分级孔道结构能为锂离子提供更多储存空间, 从而提高了电极的容量及循环稳定性。     

PAn/DMcT复合膜电极的电化学性能

PAn/DMcT复合膜电极的氧化还原峰电位差和电化学阻抗比DMcT的小得多,这表明PAn对DMcT具有电催化性能,使DMcT的氧化还原反应速度大大提高.而且DMcT使几乎所有的PAn都能保持电化学活性,复合膜电极的CV曲线经过100次循环几乎没有变化.PAn/DMcT复合膜电极的首次充放电比容量分别为275mAh·g-1和200mAh·g-1,首次充放电效率为72.7%.和粉末混合法制备的复合膜相比,溶液法制备的PAn/DMcT复合膜电极具有较高的放电比容量和优良的循环稳定性.     

Hydrothermal synthesis of ultra-thin LiFePO<Subscript>4</Subscript> platelets for Li-ion batteries

Ultra-thin LiFePO₄ platelets are prepared by a hydrothermal process using tetraethylene glycol as co-solvent. The prepared LiFePO₄ platelets have a very thin thickness of about 50–80 nm, which is beneficial for Li ions to fast transfer in the bulk of the electrode. It is found that the as-synthesized LiFePO₄ cathode material exhibits a quite high reversible capacity of 137 mAh g⁻¹ at 0.2 C. After carbon coating, the obtained LiFePO₄/C composite cathode has the enhanced electronic conductivity, and thus the rate capability has been improved significantly. At 8 and 12 C, the composite has the discharge capacity of 104 and 95 mAh g⁻¹, respectively, which suggests that the ultra-thin LiFePO₄ platelets are a promising candidate for the large-scale Li-ion batteries.