A high-performance hybrid supercapacitor with Li4Ti5O12-C nano-composite prepared by in situ and ex situ carbon modification

In this work, we report on the synthesis of in situ and ex situ carbon-modified Li₄Ti₅O₁₂-C (LTO-C) nano-composite and its application in a hybrid supercapacitor constructed using activated carbon (AC) and LTO-C nano-composite as positive and negative electrodes, respectively. The hybrid capacitors are characterized by galvanostatic charge–discharge, cycle life testing, and electrochemical impedance spectroscopy. The results reveal that the AC/LTO-C hybrid capacitors exhibit high rate capability and long cycle life. In the potential range of 1.5–3.0 V, the AC/LTO-C hybrid system can deliver a specific capacitance of 83 F?g^?1 based on the total mass of AC and LTO-C electrodes at a current density of 60 mA g^?1 (2 C rate). At a higher discharge rate of 980 mA g^?1 (32 C), the capacity is 68 F?g^?1, about 82?% of that at 2 C rate. After 9,000 deep cycles at 32 C, the hybrid capacitor still maintains 84?% of its initial capacitance. The specific energy of such hybrid system is 20 Wh kg^?1, which is at least twice that of an AC/AC system. Combining the high energy density with power capability, the AC/LTO-C hybrid supercapacitor has demonstrated high performance for applications needing high power output.     

预嵌锂硬碳和软碳用于锂离子电容器负极的比较研究

锂离子电容器是一种应用前景广阔的电化学储能器件. 目前,活性炭作为锂离子电容器正极被广泛使用. 然而,锂离子电容器负极却有多种不同选择,如硬碳和软碳等碳材料. 本文使用两种具有不同结构和电化学特性的硬碳和软碳材料作为锂离子电容器负极,进行了对比研究. 研究表明,软碳相比于硬碳有更好的电子导电性和更高的可逆容量. 通过在电流范围0.1 ~ 12 A·g^-1下进行充放电测试,分别研究了两种碳基电极在不同涂覆厚度下的倍率性能. 结果显示,硬碳电极在大电流下有更好的倍率特性. 然后,以活性炭为正极,预嵌锂的硬碳和软碳为负极,锂片为锂源和参比电极,分别组装了三电极软包锂离子电容器. 根据三电极充放电测试,分别研究了不同预嵌锂量的硬碳和软碳所组装的锂离子电容器的电化学性能. 结果表明,合适的负极预嵌锂容量可以提升锂电容的能量密度、功率密度和循环稳定性. 最后,大容量硬碳和软碳基软包锂离子电容器被分别组装,软碳基锂电容实现了最高的能量密度21.2 Wh·kg^-1（基于整个器件质量）,硬碳基锂电容实现最高的功率密度5.1 kW·kg^-1.     

以预锂化中间相碳微球为负极的锂离子电容器的电化学性能

以商品活性炭(AC)为正极, 预锂化中间相碳微球(LMCMBs)为负极, 组装成锂离子电容器(LICs). 用X射线衍射(XRD)对LMCMB 电极材料的晶体结构进行了表征和分析, 预锂化量(PIC)小于200 mAh·g^-1 时,LMCMB电极材料基本保持了原始的石墨晶体结构. 利用三电极装置, 测试了充放电过程中LICs 的正、负极及整电容器的电压变化曲线. 以LMCMB为电极, 锂离子电容器负极的工作电压变低, 并且电压曲线更加平坦, 同时正极也可以利用到更低的电压区间. 对比锂离子电容器MCMB/AC, LMCMB/AC在比能量密度、循环性能和库仑效率电化学性能方面都得到了改善. 在电压区间2.0-3.8 V 下, 100 次循环后, 放电比容量的保持率从74.8%增加到100%, 库仑效率从95%增加到100%. LMCMB/AC电容器容量不衰退的直接原因是由于AC正极极化变小. 在2.0-3.8 V和1.5-3.8 V电压区间内, LMCMB/AC锂离子电容器的比能量密度分别可达85.6和97.9 Wh·kg^-1.     

Carbon-coated Li3VO4 with optimized structure as high capacity anode material for lithium-ion capacitors

Due to the high capacity, moderate voltage platform, and stable structure, Li₃VO₄ (LVO) has attracted close attention as feasible anode material for lithium-ion capacitor. However, the intrinsic low electronic conductivity and sluggish kinetics of the Li⁺ insertion process severely impede its practical application in lithium-ion capacitors (LICs). Herein, a carbon-coated Li₃VO₄ (LVO/C) hierarchical structure was prepared by a facial one-step solid-state method. The synthesized LVO/C composite delivers an impressive capacity of 435 mAh/g at 0.07 A/g, remarkable rate capability, and nearly 100% capacity retention after 500 cycles at 0.5 A/g. The superior electrochemical properties of LVO/C composite materials are attributed to the improved conductivity of electron and stable carbon/LVO composite structures. Besides, the LIC device based on activated carbon (AC) cathode and optimal LVO/C as anode reveals a maximum energy density of 110 Wh/kg and long-term cycle life. These results provide a potential way for assembling the advanced hybrid lithium-ion capacitors.     

功能化石墨烯/活性炭复合电极及不对称电容器脱盐

以3-氨丙基三乙氧基硅烷(AMPTS)修饰氧化石墨(GO)还原合成氨基功能化石墨烯(GP-NH₂). 傅里叶变换红外(FTIR)光谱和X射线能谱(EDX)分析证明了氨基基团的成功接枝. 以GP-NH₂为添加剂, 制备胺化石墨烯/活性炭(GP-NH₂/AC)复合电极, 并以GP-NH₂/AC 为正极, AC电极为对电极, 组装不对称电容器(AC||GPNH₂/AC)用于电容脱盐. 实验表明, AC||GP-NH₂/AC 单循环脱盐量为7.63 mg·g^-1, 电流效率达77.6%. 利用磺酸重氮盐接枝石墨烯制备磺化石墨烯(GP-SO₃H)及磺化石墨烯/活性炭(GP-SO₃H/AC)复合电极. 并以GPSO₃H/AC为负极, GP-NH₂/AC 为正极, 组装不对称电容器(GP-SO₃H /AC||GP-NH₂/AC)用于电容脱盐, 其平均脱盐速率可达0.99 mg·g^-1·min^-1, 比纯AC电极提高了接近5倍. 充放电速率提高了30%; 而且由于正、负极表面固有电荷的存在, 大大降低了反离子效应, 电流效率由40% (纯AC||AC对称电容器)提高到92.8%. 表明电极内功能化导电石墨烯的存在既提高了导电性, 又兼具离子选择性的作用, 从而明显改善电极的脱盐性能.     

A hybrid nonaqueous electrochemical supercapacitor using nano-sized iron oxyhydroxide and activated carbon

A beta-iron oxyhydroxide (FeOOH) was synthesized via a hydrolyzing route and investigated as a lithium intercalation host. It delivers a capacity of about 170 mAh/g and exhibits good cycling performance when charged/discharged in the voltage range from 1.6 V to 3.3 V. For the first time we have confirmed that FeOOH is suitable for using it as a negative electrode for hybrid electrochemical supercapacitor assembled with an activated carbon positive electrode in 1.0 M LiPF₆ ethylene carbonate/dimethyl carbonate (EC/DMC, 1:2 in volume) solution. The cell reveals a slightly sloping voltage profile from 0 V to 2.8 V and gives an estimated specific energy of 45 Wh/kg based on the total weight of two electrode materials, approximately two times of carbon/carbon electrochemical double layer capacitors. The hybrid supercapacitor shows a good cycling performance, it remains approximately 96% of initial capacity after 800 cycles at a charge/discharge rate of 4 C. The capacitor also shows a desirable rate capability, even at 10 C discharge rate, it holds 80% of capacity compared with that at 1 C discharge rate.     

High Power Density Electric Double Layer Capacitor with Improved Activated Carbon

Introduction　　Recently ,therehasbeenanincreasinginterestinthedevelopmentofelectricdoublelayercapacitors (EDLCs)us inghighlyporouscarbonsastheelectrodematerialsduetotheirpossibletechnologicalapplicationsasenergystoragede vicespossessinghighpowerdensitycapability .1,2 Themainadvantagesofsuchdevicesaretheirpossiblehighratecapa bilityandlongcyclelifeascomparedtorechargeablebatter ies,butitsenergydensityislowerthanthatofrechargeablebatteries.Inordertoobtaintherequiredenergyandpowerdensity,EDLC…     

均匀负载氧化镍纳米颗粒多孔硬碳球的制备及其高性能锂离子电池负极材料应用

利用水热法制备了粒径为90-130 nm的多孔硬碳球, 并通过浸渍与煅烧的方法制备了硬碳球均匀负载纳米氧化镍颗粒(~10 nm)复合材料. 硬碳球的表面官能团和内部的微孔保证了氧化镍颗粒在硬碳上的均匀分布. 在100 mA·g^-1的电流密度下, 复合材料电极首次充电比容量高达764 mAh·g^-1; 在100 mA·g^-1的电流密度下循环100 个周期后电极充电比容量保持在777 mAh·g^-1, 容量保持率为101%; 800 mA·g^-1电流密度下电极的充电比容量达380 mAh·g^-1, 显示复合材料电极具有优异的循环性能和倍率性能. 硬碳的表面官能团和内部微孔为氧化镍提供了优先形核位点, 保证了二者的牢固结合, 使复合材料获得了“协同效应”, 从而使复合电极具备更短的锂离子扩散路径、更高的电导率和更多的锂离子脱嵌位点. 这种方法还可用于制备硬碳/其他金属氧化物复合材料.     

高能量密度的锂离子混合型电容器

锂离子混合型电容器兼有锂离子电池和超级电容器的优点,在电化学储能领域具有广泛的应用前景. 但其产业化仍存在一系列的基础及工艺方面的问题,具体包括器件结构设计、电极材料筛选、预嵌锂工艺和电解液与电极的界面等. 本文结合作者课题组的研究工作介绍了近年来高能量密度的锂离子混合型电容器的研究进展,内容涉及锂离子电容器正/负极材料的筛选、预嵌锂工艺的优化、内并联结构的锂离子电池型超级电容器复合正极组成材料的调控、隔膜的选择、电解液的组成、以及器件的高/低温性能,分析了锂离子电容器的容量衰减机制,探讨了锂离子电池型超级电容器的储能机制,提出了未来对高能量密度的锂离子混合型电容器研究的展望.     

功能化石墨烯/活性炭复合电极及不对称电容器脱盐

以3-氨丙基三乙氧基硅烷(AMPTS)修饰氧化石墨(GO)还原合成氨基功能化石墨烯(GP-NH2).傅里叶变换红外(FTIR)光谱和X射线能谱(EDX)分析证明了氨基基团的成功接枝.以GP-NH2为添加剂,制备胺化石墨烯/活性炭(GP-NH2/AC)复合电极,并以GP-NH2/AC为正极,AC电极为对电极,组装不对称电容器(AC||GPNH2/AC)用于电容脱盐.实验表明,AC||GP-NH2/AC单循环脱盐量为7.63 mg·g-1,电流效率达77.6%.利用磺酸重氮盐接枝石墨烯制备磺化石墨烯(GP-SO3H)及磺化石墨烯/活性炭(GP-SO3H/AC)复合电极.并以GPSO3H/AC为负极,GP-NH2/AC为正极,组装不对称电容器(GP-SO3H/AC||GP-NH2/AC)用于电容脱盐,其平均脱盐速率可达0.99 mg·g-1·min-1,比纯AC电极提高了接近5倍.充放电速率提高了30%;而且由于正、负极表面固有电荷的存在,大大降低了反离子效应,电流效率由40%(纯AC||AC对称电容器)提高到92.8%.表明电极内功能化导电石墨烯的存在既提高了导电性,又兼具离子选择性的作用,从而明显改善电极的脱盐性能.     

Electrochemical study on lithium iron phosphate/hard carbon lithium-ion batteries

The electrochemical performances of lithium iron phosphate (LiFePO₄), hard carbon (HC) materials, and a full cell composed of these two materials were studied. Both positive and negative electrode materials and the full cell were characterized by scanning electron microscopy, transmission electron microscopy, charge–discharge tests, and alternating current (a.c.) impedance techniques. Experimental results show that the LiFePO₄/HC full cell exhibits a gradually decreased cell voltage, and it is capable of delivering a reversible discharge capacity of 122.1 mAh g⁻¹ at 0.2-C rate. At the higher rate of 10 C, the efficiency of the full cell remains almost unchanged from that of 0.2 C. Furthermore, the LiFePO₄/HC battery demonstrated a long life of 2,450 cycles with 40% of capacity change at a 10-C high rate. The internal resistance of the full cell is rather low as it is revealed from a.c. impedance measurements. These properties make the LiFePO₄/HC battery an attractive option for high rate and long cycle life power applications.     

High‐Power Electrochemical Energy Storage System Employing Stable Radical Pseudocapacitors

The development of electrical energy storage devices that can operate at high charge and discharge rates is fundamentally important, however although electrochemical capacitors (ECs) can charge and discharge at high rates, their electrochemical storage capacity remains an order of magnitude lower than that of conventional lithium‐ion batteries. Novel pseudocapasitors are developed, based on the stable persilyl‐susbtituted free radicals of the heavy group 14 elements, (tBu₂MeSi)₃E^. [E=Si ( 1 ), Ge ( 2 ), and Sn ( 3 )], as anode materials for energy storage system. Such systems showed a remarkable cycle stability without significant loss of power density, in comparison with similar characteristics of the known organic radical batteries, the dual carbon cell, and the electrochemical capacitor. Particularly important is that these novel electrochemical energy storage systems employing stable heavy group 14 element radicals are lithium‐free. The electrochemical properties and structures of the reduced and oxidized species were studied by the cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and X‐ray diffraction (XRD).     

三氧化钼——一种新型有机系钠离子储能器件负极材料

由于锂资源短缺,我们尝试使用三氧化钼作为钠离子储能装置负极材料。通过一种简单的方法合成了三氧化钼,使用XRD、SEM和TEM等测试手段对其物性进行了表征。利用三氧化钼作为有机系钠离子储能器件的负极材料,通过循环伏安和恒流充放电测试探讨了负极材料的储钠机理。以三氧化钼(MoO3)作为负极材料,活性炭(AC)和石墨(graphite)作为正极材料,组装成新型的电化学储能器件,研究了两种器件在1mol/L NaPF6的碳酸丙烯酯(PC)中的电化学性能。两种器件的电压范围分别为0~3.2V和0~3.5V,能量密度最高可分别达到31.6和53 Wh/kg,长循环性能远远优于AC/AC对称电容器。此种储能装置有望成为锂离子电池的一个很好的替代。     

水系锌离子电容器

本文首次提出了一种水系锌离子电容器的新型储能体系,其中以五氧化二钒（V₂O₅）为正极,具有高比表面积的活性炭（AC）为负极,以及三氟甲基磺酸锌（Zn(TfO)₂）为电解质. X射线衍射（XRD）证明二价锌离子作为电荷载体,可以在五氧化二钒（V₂O₅）中进行可逆的嵌入与脱出. 该锌离子电容器的电位窗口可达1.4 V,具有良好的倍率特性及循环稳定性. 电流密度为1000 mA·g^-1 时,电容器的比能量密度为4.5 Wh·kg^-1,功率密度可达181 W·kg^-1. 本工作为发展新型基于多价离子电化学电容器提供了新思路和新方法.     

LiNi0.8Co0.2O2/CNTs Composite used as the Materials for Supercapacitor Electrodes

Stupercapacitors or electrochemical capacitors(ECs) have attracted considerable attentionas an intermediate power source between conventional capacitors and batteries since they possesshigh power density and energy density, exhibit excellent reversibility, and have long cycle life1.Conductive polymers2, electrically conductive metal oxide3,4, activated carbon5 and carbonnanotubes(CNTs) 6-9 have been used as supercapacitor electrode materials. LiNi0.sCo0.2O2 is apromising lithium battery material because it has some advantages of both LiNiO2 and LiCoO2besides its low cost and high power10.In this paper, the electrochemical properties of supercapacitors based on LiNi0.8Co0.2O2/carbonnanotubes composite and LiNi0.8Co0.2O2/acetylene black composite and CNTs in 1 mol/LLiClO4/EC+DEC [V(EC):V(DEC)=1:1] electrolyte have been investigated by means of constantcharge/discharge current tests. The experiment results show that the LiNi0.8Co0.2O2/carbon nanotubescomposite has better properties than others, and the maximun specific capacitance of thesupercapacitor can reach 284.88F/g, while the energy density is up to 158.27Wh/Kg.That discharge capacities, coulombic efficiencies and energy densities at the first cycle and themaximum value and capacity retention at the 100th cycle for supercapacitors using differentelectrode materials (A) LiNi0.8Co0.2O2/acetylene black, (B) LiNi0. 8Co0.2O2/CNTs, (C) CNTs is listedin table 1*Capacity retention rate obtained by dividing the discharge capacity at the 100th cycle by themaximum valueFrom above, the LiNi0. 8Co0.2O2/carbon nanotubes composite should be a good candidatesupercapacitor electrode material.     

Enhanced Capacitive Characteristics of Activated Carbon by Secondary Activation

The effect of the improvement of commercial activated carbon(AC) on its specific capacitance and high rate capability of double layer(dl) charging/discharging process has been studied. The improvement of AC was carried out via a secondary activation under steam in the presence of catalyst NiCl2, and the suitable condition was found to be a heat treatment at about 875 ℃ for 1 h. Under those conditions, the discharge specific capacitance of the improved AC increases up to 53. 67 F/g, showing an increase of about 25% as compared with that of as-received AC. The good rectangular-shaped voltammograms and A.C. impedance spectra prove that the high rate capability of the capacitor made of the improved AC is enhanced significantly. The capacitance resistance (RC) time constant of the capacitor containing the improved AC is 1.74 s, which is much lower than that of the one containing as-received AC(an RC value of 4. 73 s). It is noted that both kinds of AC samples show a similar specific surface area and pore size distribution, but some changes have taken place in the carbon surface groups, especially a decrease in the concentration of surface carbonyl groups after the improvement, which have been verified by means of X-photoelectron spectroscopy. Accordingly, it is suggested that the decrease in the concentration of surface carbonyl groups for the improved AC is beneficial to the organic electrolyte ion penetrating into the pores, thus leading to the increase in both the specific capacitance and high rate capability of the supercapacitor.     

Biomass‐Derived Carbon Materials as Prospective Electrodes for High‐Energy Lithium‐ and Sodium‐Ion Capacitors

Biomass‐derived carbon materials have received special attention as efficient, low‐cost, active materials for charge‐storage devices, regardless of the power system, such as supercapacitors and rechargeable batteries. In this Minireview, we discuss the influence of biomass‐derived carbonaceous materials as positive or negative electrodes (or both) in high‐energy hybrid lithium‐ion configurations with an organic electrolyte. In such hybrid configurations, the electrochemical activity is completely different to conventional electrical double‐layer capacitors; that is, one of the electrodes undergoes a Faradaic reaction, whilst the counter electrode undergoes a non‐Faradaic reaction, to achieve high energy density. The use of a variety of biomass precursors with different properties, such as surface functionality, the presence of inherent heteroatoms, tailored meso‐/microporosity, high specific surface area, various degrees of crystallization, calcination temperature, and atmosphere, are described in detail. Sodium‐ion capacitors are also discussed, because they are an important alternative to lithium‐ion capacitors, owing to the low abundance and high cost of lithium. The electrochemical performance of carbonaceous electrodes in supercapacitors and rechargeable batteries are not discussed.     

磺化石墨烯/活性炭复合电极的制备及其不对称电容器脱盐

在还原剂NaBH₄存在下, 采用对氨基苯磺酸重氮盐与氧化石墨(GO)表面共价键合制备磺化石墨烯(GP-SO₃H). 傅里叶变换红外光谱(FTIR)证明磺酸基团在石墨烯表面接枝. 采用扫描电子显微镜(SEM)研究了磺化石墨烯的表面形貌. 以磺化石墨烯为添加剂, 制备了磺化石墨烯/活性炭(GP-SO₃H/AC)复合电极. 循环伏安及阻抗分析结果表明, 该复合电极的电容特性及导电性有明显改善. 以活性炭电极为对电极组装了不对称电容器(GP-SO₃H/AC|AC), 研究了该不对称电容器的电化学脱盐性能. 与对称电容器(AC|AC)相比, 不对称电容器中由于电极内磺酸基团对反离子的屏蔽作用, 电容器的电流效率达到89.4%以上, 脱盐量提高2.4倍, 单个循环脱盐量达到10.87 mg/g.     

新型非对称电化学电容器的电极匹配研究

活性炭负极容量的有效利用率是导致双电层电化学电容器和C/Ni(OH)2非对称电化学电容器容量性质差异的主要因素,并可将其作为非对称电化学电容器容量设计和测算的依据;本文引入Ni(OH)2正极有效活性物质概念,以正极有效活性物质的量匹配负极的设计容量,从而优化正、负极的容量匹配,改善非对称电化学电容器的容量和大电流性能.     

二次包覆法制备煤沥青基硅/碳复合物及其锂离子电池性能

本文采用市售纳米硅为硅源,以软化点低、得碳率高、价格便宜的煤沥青作为碳源,通过两步包覆法制备了煤沥青基硅/碳(Si/C/C)复合物,并研究其作为锂离子电池负极材料的电化学性能。 结果表明,所得复合物的粒径在300~350 nm间,Si纳米粒子被C包覆并相互连结成C-Si-C网络结构,其中Si含量为27%的硅/碳复合物(Si/C/C-27%)作为锂电池电极材料表现了良好的储锂性能。 在0.1 A/g的小电流密度下,Si/C/C-27%的放电比容量为1281 mA·h/g;在3 A/g的大电流密度下,其放电比容量仍能保持在582 mA·h/g,表现了良好的倍率性能。Si/C/C-27%在2 A/g的电流密度下经过100次的循环后其比容量保持率为76.61%,表现了良好的循环稳定性。 相比于煤沥青基碳的一次包覆所得的硅/碳复合材料(Si/C),Si/C/C有效提高了Si纳米粒子的导电性并抑制了其在嵌锂和脱锂过程中的体积膨胀。 本文提出的二次包覆的新方法为制备具有优异电化学性能的锂离子电池负极材料提供了新的研究思路。