Hard carbon derived from cellulose as anode for sodium ion batteries:Dependence of electrochemical properties on structure

Cellulose, the most abundant organic polymer on Earth, is a sustainable source of carbon to use as a negative electrode for sodium ion batteries. Here, hard carbons(HC) prepared by cellulose pyrolysis were investigated with varying pyrolysis temperature from 700 °C to 1600 °C. Characterisation methods such as Small Angle X-ray Scattering(SAXS) measurements and N2adsorption were performed to analyse porosity differences between the samples. The graphene sheet arrangements were observed by transmission electron microscopy(TEM): an ordering of the graphene sheets is observed at temperatures above 1150 °C and small crystalline domains appear over 1400 °C. As the graphene sheets start to align, the BET surface area decreases and the micropore size increases. To correlate hard carbon structures and electrochemical performances, different tests in Na//HC cells with 1 M NaPF6ethylene carbonate/dimethyl carbonate(EC/DMC) were performed. Samples pyrolysed from 1300 °C to 1600 °C showed a 300 m Ah/g reversible capacity at C/10 rate(where C = 372 mA/g) with an excellent stability in cycling and a very good initial Coulombic efficiency of up to 84%. Furthermore, hard carbons showed an excellent rate capability where sodium extraction rate varies from C/10 to 5C. At 5C more than 80% of reversible capacity remains stable for hard carbons synthesized from 1000 °C to 1600 °C.

A green route to synthesize low-cost and high-performance hard carbon as promising sodium-ion battery anodes from sorghum stalk waste

Sodium-ion batteries(SIBs) have been considered to be potential candidates for next-generation low-cost energy storage systems due to the low-cost and abundance of Na resources. However, it is a big challenge to find suitable anode materials with low-cost and good performance for the application of SIBs. Hard carbon could be a promising anode material due to high capacity and expectable low-cost if originating from biomass. Herein, we report a hard carbon material derived from abundant and abandoned biomass of sorghum stalk through a simple carbonization method. The effects of carbonization temperature on microstructure and electrochemical performance are investigated. The hard carbon carbonized at 1300 ℃ delivers the best rate capability(172 mAh g^(-1) at 200 mA g^(-1)) and good cycling performance(245 mAh g^(-1) after 50 cycles at 20 mA g^(-1),96% capacity retention). This contribution provides a green route for transforming sorghum stalk waste into "treasure"of promising low-cost anode material for SIBs.

Study on Hardness of Ion Implantation Layer

The surface layer of beryllium, specimen, has been strengthened by ion implantation. Its microhardness was measured. The hardness of surface layer has been calculated from the microhardness. The experimental data of the wear rate indirectly Confirmed the reasonableness of the result of calculation. It is shown that the hardness of the surface layer strengthened, by ion implantation is nine times higher than that of beryllium itself. The relation between hardness and implantation dose was analysed and the best dose was obtained.

Composition Gradient Hard Coatings by Arc Ion Plating

Arc Ion Plating can be used to synthesize multi-component composition gradient hard coatings by adjusting arc currents of metal targets. The present work aims at a comprehensive description of such a technique. The examples of TiAl multi-layer alloy coatings and (Ti, M) N composition-gradient films were taken (M representing Zr, Nb etc.) for the purpose of explaining the working process and evaluating practical effects. The results show that this technique has the advantages of easy manipulation, rapid deposition, and wide composition range.

Hard carbons derived from pine nut shells as anode materials for Na-ion batteries

Hard carbons as promising anode materials for Na-ion batteries(NIBs) have captured extensive attention because of their low operation voltage, easy synthesis process, and competitive specific capacity. However, there are still several disadvantages, such as high cost and low initial coulombic efficiency, which limit their large-scale commercial applications.Herein, pine nut shells(PNSs), a low-cost biomass waste, are used as precursors to prepare hard carbon materials. Via a series of washing and heat treatment procedures, a pine nut shell hard carbon(PNSHC)-1400 sample has been obtained and delivers a reversible capacity of around 300 mAh/g, a high initial coulombic efficiency of 84%, and good cycling performance. These excellent Na storage properties indicate that PNSHC is one of the most promising candidates of hard carbon anodes for NIBs.

Behaviors of fine(IG-110)and ultra-fine(HPG-510)grain graphite irradiated by 7 MeV Xe^26+ions

Developing a molten salt reactor needs molten salt-impermeable nuclear graphite. Ultra-fine grain graphite is a good choice as it is better in permeability than fine grain graphite. In this paper, ultra-fine grain graphite(HPG-510) and fine grain graphite(IG-110) samples are irradiated at room temperature by 7 MeV Xe ions to doses of 1 × 10^(14)-5 × 10^(15) ions/cm^2. Scanning electron microscopy, transmission electron microscopy(TEM), Raman spectroscopy and nano-indentation are used to study the radiation-induced changes. After irradiation of different doses, all the HPG-510 samples show less surface fragment than the IG-110 samples. The TEM and Raman spectra,and the hardness and modulus characterized by nano-indentation, also indicate that HPG-510 is more resistant to irradiation.

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.

The Power-Energy Coupling Effect of Mixed Hard-Carbon/Graphite Anode

As the anode materials of lithium-ion battery, the hard carbon has the higher power performance while the graphite has the higher energy performance, respectively. In this work, novel mixed hard carbon/graphite anodes are presented showing the coupling effect of power and mixed anodes was investigated at the varying charging rates, showing the tunable behaviors dependent on the hard carbon/graphite ratios. By studying the specific capacity evolution in different split potential ranges, we found that the mixed anodes with a higher proportion of hard carbon were advantageous when working in the cut-off potential greater than 0.10 V. The electrochemical impedance spectroscopy was measured at various anode potentials, which depicted the evolution of cell resistance with the state of charge. With the aid of electrochemical impedance spectroscopy, we found that the capacity evolution with mixed ratio is attributed to the lithiation-level induced difference of charge transfer resistance and Warburg resistance. A coupling effect was discovered showing a great potential in balancing the power-energy performance of mixed anode by simply controlling the ratio of hard-carbon/graphite.

钠离子电池用生物质基硬碳的研究进展

生物质基硬碳具有原材料资源丰富、可持续、成本低和储钠容量高等特点,是钠离子电池的理想负极材料。生物质基硬碳材料的微结构是决定钠离子存储性能的关键。本综述回顾了硬碳负极对钠离子存储机理的研究现状。从生物质原料的角度,分类总结了高性能生物质基硬碳材料的制备方法。探讨了生物质基硬碳结构的调控与钠离子存储性能提升的关系,对钠离子电池用生物质基硬碳负极材料的研究方向进行了展望。

采用两步炭化法和熔盐模板法制备N、S共掺杂煤基硬炭及共储钠性能

硬炭因资源丰富、结构稳定及安全性高等优势,已成为钠离子电池常用阳极材料。其中,煤基衍生硬炭受到了广泛的关注。本工作以长焰煤为碳源,硫脲为氮硫源,NaCl为模板,通过两步炭化工艺和杂原子掺杂相结合的方法合成了N和S共掺杂的煤基硬炭(NSPC1200)。两步炭化过程在调节碳微晶结构和扩大层间距方面发挥了重要的作用。N和S的共掺杂调节了炭材料的电子结构,赋予其更多的活性位点;此外,引入NaCl作为模板有助于孔结构的构建,有利于电极和电解质之间的接触,从而实现Na+和电子的有效传输。在协同作用下,样品NSPC1200表现出优异的储钠能力,在20 mA g^(−1)电流密度下呈现314.2 mAh g^(−1)的可逆容量。即使在100 mA g^(−1)下循环200次,仍保持224.4 mAh g^(−1)的比容量。这项工作成功实现了策略性调整煤基炭材料微观结构的目标,最终获得了具有优异的电化学性能的硬炭阳极。

酚醛树脂改性沥青基硬碳的制备及储钠性能研究

石油沥青作为炼油副产品被用作多种碳质材料前驱体,但在高温碳化过程中易石墨化,不利于钠离子储存。将酚醛树脂引入硬质沥青共碳化,促进沥青分子与酚醛树脂分子间的交联,抑制碳层熔融重排,得到酚醛树脂改性沥青基硬碳材料。当酚醛树脂添加质量比例为1∶1时,在1200℃碳化所得硬碳材料具有最佳的储钠电化学性能。在0.05 A/g电流密度下,比容量达270.2 mAh/g,首次库仑效率为63.8%。在0.3 A/g电流密度下,循环1200圈后容量保持率达71.6%。

全木质素衍生硬碳电极的制备及储钠性能研究

钠离子电容器结合了电池型负极的高能量密度和电容型正极的高功率密度,成为新一代储能器件,硬碳材料作为电池型负极,是当前的研究热点。本研究以制浆黑液为原料,通过提纯、预碳化和高温热解碳化制备木质素衍生硬碳材料,分析其石墨层间距、微晶结构等性质随碳化温度变化的规律,研究了木质素衍生硬碳电极的电化学性能及储钠机理。研究结果表明,随着碳化温度从800℃升高至1600℃,木质素衍生硬碳材料的石墨层间距从0.406 nm减小至0.378 nm,赝石墨层比例从52.69%升高至77.60%。此外,在木质素衍生硬碳电极充放电过程中,更多的Na^(+)在石墨层间嵌入和脱嵌,电极的平台容量从56.8 mAh/g提高至236.0 mAh/g;在斜坡容量变化不大的情况下,平台容量的大幅增加使木质素衍生硬碳电极的可逆容量高达333.7 mAh/g。根据恒电流间歇滴定技术(GITT)分析可知,Na+在木质素衍生硬碳电极中的存储机制符合“吸附-嵌入/填充”模型。

提高硬碳材料钠离子电池首次库仑效率的研究进展

钠离子电池(SIBs),得益于钠资源的高丰度、分布均匀、较低的成本、优异的低温性能和快充特性等优势,被认为是潜力巨大的大规模储能技术。SIBs的电化学性能很大程度上由电极材料决定,在负极材料中,硬碳(HC)材料由于具有较低的氧化/还原电势、合适的比容量、对环境友好、制造方法简单以及来源广泛等优势,被认为是目前最为理想的SIBs负极材料。然而,HC作为负极材料的SIBs首次库仑效率(ICE)的不足导致在全电池中阴极的钠被过度消耗,因而严重限制了HC在SIBs的实际应用。因此,结合导致硬碳材料ICE较低的关键科学问题,本文总结、分析了提高SIBs硬碳负极材料ICE的研究进展,包括调节热解温度、减少缺陷、孔隙调控以及金属原子催化调控碳层这4种方式。并简要介绍了硬碳材料的碳层间距、缺陷以及孔隙这3个基本结构,以及不同的结构影响钠离子储存行为的最新研究进展,论述了不同类型HC负极材料的设计思路及其商业化进展,最后分析探讨了SIBs硬碳负极材料的发展方向。

氮掺杂淀粉基硬碳负极材料制备及其储钠性能研究

钠离子电池(sodium-ion batteries,SIBs)作为未来极具竞争力的大型储能装置之一,由于没有合适的负极材料,其商业化应用受到严重阻碍,因此,开发新型高性能SIBs负极材料是目前亟待解决的问题之一。硬碳材料由于来源丰富和成本低廉受到广泛关注,使用马铃薯淀粉为前驱体,采用不同的氮源对马铃薯淀粉进行掺杂改性,从而制备出氮掺杂硬碳材料。测试结果表明氮掺杂硬碳材料相比于未掺杂改性材料,其电化学性能显著提高。以二氰二胺为氮源掺杂的硬碳材料在0.1 A/g的电流密度下循环100圈后,仍能保持220.47 mA·h/g的可逆比容量,以尿素为氮源的硬碳材料能保持233.36 mA·h/g可逆比容量。结果表明,氮元素的掺杂可以有效地提升硬碳材料的离子电导率、增加硬碳材料的可逆比容量,从而整体提升硬碳材料的电化学性能。

中空炭微球的喷雾法制备及其储钠性能研究

以酚醛树脂和马铃薯淀粉为前驱体,采用喷雾干燥和炭化法制备中空炭微球。采用扫描电子显微镜法(SEM)、透射电子显微镜法(TEM)、X射线衍射光谱法(XRD)、小角X射线散射(SAXS)、拉曼光谱等表征方法对其形貌、微观结构进行表征,并研究了中空硬炭微球负极的储钠性能。结果表明:当酚醛树脂与马铃薯淀粉以质量比7∶3混合时,中空炭微球的粒径及其分布减小,具有最低的振实密度,有利于缩短离子传输路径,缓解循环过程中造成的体积变化。该样品具有大的层间距(0.41 nm)、较多的闭孔结构,提供了较快的插层反应动力学,有效提高了样品的平台容量。在0.1 A/g电流密度下,其展现出396.5 mAh/g的可逆比容量,循环200次后容量保持率为97.1%;在2 A/g电流密度下保持254.3 mAh/g的可逆比容量,表现出优异的大电流充放电能力。

锂/钠离子电池硬碳负极材料的研究进展

随着锂离子电池的发展和钠离子电池的兴起,硬碳材料作为一种新型负极材料,受到了广泛关注。硬碳来源丰富,价格便宜,具有比锂离子电池石墨负极更高的储锂容量和优异的倍率性能,并且是最有商业化潜质的钠离子电池负极材料。然而,硬碳普遍存在电池首周库仑效率低的问题,且对于硬碳的储锂/钠机制仍存在争论,其比容量仍有较大的提升空间。近年来,研究人员围绕硬碳负极材料的电化学机理展开了各种研究和模型假设,针对硬碳负极存在的问题,提出了各种解决策略。本文介绍了硬碳的基本结构和常用的制备方法,并结合硬碳的优势,梳理了硬碳在锂离子电池和钠离子电池中的应用情况,重点介绍了其在快充、包覆等细分领域的应用进展,并分别针对硬碳提升比容量和改善首周库仑效率的需求,归纳了孔结构设计、元素掺杂、优化材料与电解液界面等不同改性策略。

钠离子电池硬碳负极的优化设计研究进展

开发合适的负极材料是促进钠离子电池实现商业化的关键,其中硬碳具有高容量、低成本、环保、低工作电位,被认为是最理想的选择。然而,硬碳负极在实际应用中也面临着初始库伦效率低、长循环稳定性及倍率性能较差等问题。近年来,研究学者在对硬碳负极的优化方面取得了突破性成效,实现了从实验室研制到批量生产的重大转型。总结了钠离子电池硬碳负极性能优化的研究进展,在深入了解前驱体特性的基础上,分析了碳化温度、预氧化工艺、孔隙结构、异质原子掺杂等对硬碳性能的影响,展望了未来的发展方向。

钠离子电池中硬碳负极的结构调控及研究进展

因地壳中丰富的钠资源和低廉的成本,钠离子电池(SIBs)成为了继锂离子电池(LIBs)后最有希望商业化的碱金属离子电池。硬碳材料具有较多的缺陷、丰富孔结构、较合适的嵌钠电位和较高的比容量等,因而被认为是最有潜力的SIBs负极材料之一。但是,实际应用中硬碳用作SIBs负极仍存在系列问题,如:初始库仑效率(ICE)低、倍率性能差和循环稳定性不理想等。基于此主要从孔结构调控、杂原子掺杂、硬-软(硬)碳复合这3个结构调控策略进行总结,为促进硬碳材料商业化提供思路。

钠离子电池硬碳负极研究进展

锂离子电池(LIB)因其能量密度高、循环寿命长而被广泛用于移动储能。然而,锂资源的有限严重限制了其在大规模储能领域的应用。近年来,钠离子电池(SIB)由于成本低、安全性高等优点,成为了LIB有前途的替代品。硬碳具有较低的氧化还原电位、稳定的结构、较大层间距和相对较低的成本,被广泛用作SIB的负极材料。然而,硬碳负极较差的倍率性能和较低的首次库仑效率限制了SIB的性能。综述了钠离子电池硬碳负极的研究进展,包括硬碳储钠机理、前驱体选择以及制备工艺对硬碳性能的影响。