LiClO_4浓度对Li-MnO_2电池高低温性能的影响

考察了碳酸丙烯酯(PC)+乙二醇二甲醚(DME)电解液中LiClO_4浓度对Li-MnO_2一次电池内阻、开路电压及高低温放电性能的影响。在-25℃,LiClO_4浓度为1.2 mol/L时,电池性能最好;300 mA放电时LiClO_4浓度为1.2 mol/L比1.0 mol/L的电池放电平台约高90 mV,放电比容量约高14%。随着温度的升高,电池放电性能的差异逐渐减小;在50℃时,不同LiClO_4浓度的电池放电平台和比容量相近。     

锂电池正极材料多硫化碳炔的制备及性能研究

设计并制备了一种新型正极材料多硫化碳炔,并通过拉曼光谱扫描、X射线衍射等手段对其结构进行了表征。电化学性能研究表明,该材料具有较高的充放电效率与良好的循环性能,0.4mA/cm2放电制度下60次循环后比容量仍能达到400mAh/g,容量保持率可达64.5%,充放电效率接近100%。     

乙炔黑在锂离子电池负极中的贮锂功能

对乙炔黑在负极中的贮锂功能进行了研究。以乙炔黑和PTFE按955质量比制成负极,在9种电解液中进行了恒电流充放电实验,结果表明:在所有的电解液中乙炔黑都有一定的贮锂容量,其中以在1mol/LLi-ClO4/(EC DEC)(11)电解液中的贮锂功能最好,其第三循环的放电容量QD3=182.1mA·h/g,充、放电效率η3=83.75%。     

用作锂电池负极材料的多孔生物质碳的合成及表征

以藕片为碳源制备生物质多孔碳用作锂电池负极材料,在不同电流密度下的倍率性能测试中,0.1 A/g电流密度下电池首次充放电容量最高可达500 mAh/g,经过60圈循环后电流密度再次恢复到0.1 A/g,生物质多孔碳放电比容量仍然高达500 mAh/g。在电流密度0.5 A/g下,比容量最高可达212 mAh/g左右,经过700次循环比容量仍可维持200 mAh/g,其放电容量保持率为99.4%,显示出材料良好的循环稳定性。说明该碳材料不仅具有较高的循环稳定性还具有较好的倍率性能。     

锂离子电池正极材料LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2与电解液的相容性

研究LiNi1/3Co1/3Mn1/3O2正极材料在四种不同的电解液体系中(LiPF6/EC+DEC(1∶1)、LiPF6/EC+DMC(1∶1)、LiPF∶6/EC+EMC(1∶1)和LiPF∶6/EC+PC+DMC(1∶1∶1))的电化学性能,讨论了正极材料与电解液的相容性。结果表明在1 mol·L-1LiPF6/EC+PC+DMC(1∶1∶1)电解液体系中,2.8~4.6 V电压范围内,LiNi1/3Co1/3Mn1/3O2的电化学性能最好,其首次放电比容量可达202.17 mA·h·g-1,50次的容量保持率可达88.58%。     

天然石墨的氧化改性及其电化学性能研究北大核心

采用双氧水对天然石墨进行氧化改性研究,考察改性过程中反应温度和双氧水浓度对天然石墨微观结构和电化学性能的影响。结果表明:天然石墨经过双氧水氧化改性后,石墨层间距增大,结晶度降低,表面官能团的含量升高;天然石墨经60℃、4 mol/L的双氧水改性后,放电比容量由335.2 mAh/g增加到403.6 mAh/g,30次充放电后的放电比容量为338.3 mAh/g,容量保持率为83.8%。     

硫包覆改性磷酸铁锂材料的性能研究

锂硫电池因其较高的理论比容量受到广泛关注,实验采用硫包覆改性磷酸铁锂,以期兼顾两者的优点。硫包覆改性处理的磷酸铁锂材料LFP-0.05S与初始磷酸铁锂材料LFP相比,形貌相近,均为100～300 nm一次颗粒。在碳酸酯类电解液和醚类电解液中,LFP的放电比容量均为160 mAh/g。在醚类电解液中,LFP-0.05S的放电比容量可以达到190 mAh/g,在3.4 V出现磷酸铁锂的放电平台,在2.4 V和2.1 V出现硫的放电平台。但是LFP-0.05S的循环稳定性较差,循环20圈后,容量保持率为74.9%。     

聚乙烯吡咯烷酮包覆硫/碳复合材料的制备及其电化学性能

采用液相化学沉积法,并引入聚乙烯吡咯烷酮（PVP）制备得到聚乙烯吡咯烷酮包覆硫/碳复合材料。采用热重分析（TGA）、扫描电子显微镜（SEM）、X射线衍射（XRD）、恒流充放电和循环伏安（CV）表征其物化性能和电化学性能,结果表明,聚乙烯吡咯烷酮可有效提高硫/碳复合材料的电化学性能。0.35 C充放电时,所得聚乙烯吡咯烷酮包覆硫/碳复合材料首次放电比容量达到1 415.3 mAh/g(按单质硫的质量计算),120次后比容量保留为903.3 mAh/g,容量保持率为63.8%;2 C充放电时,首次放电比容量可达到904 mAh/g,200次后比容量仍能保持在486.8 mAh/g。     

ZnF2包覆对锂离子电池正极材料LiNi0.5Mn1.5O4的性能影响

本文用溶胶凝胶法制备了LiNi0.5Mn1.5O4正极材料,然后用ZnF2对其进行表面包覆。XRD测试表明,包覆处理没有影响材料的晶体结构,EDS、SEM和TEM测试表明,2wt%ZnF2在LiNi0.5Mn1.5O4表面形成了约7 nm厚的均匀包覆层。对未包覆、1wt%、2wt%、3wt%包覆后的材料进行电化学性能测试对比,发现包覆后都能减弱电解液与基体间的相互作用,较大地稳定电极表面,提高了材料的电化学性能。其中,2wt%ZnF2包覆样品表现出最佳的电化学性能,0.2 C倍率下循环200圈后,其放电比容量维持在109 mAh/g,容量保持率为79.7%;在10 C时,放电比容量依然高达102.1 mAh/g;5 C高倍率下循环500圈后,放电比容量维持在94.2 mAh/g,容量保持率为85.6%。     

碳掺杂改善LiFePO4电化学性能

采用葡萄糖为碳源,通过固相合成法制备了掺碳的LiFePO4正极材料,并对样品的性能进行了研究分析.结果表明,少量的碳掺杂并未改变LiFePO4的晶体结构但显著改善了其电化学性能,LiFePO4/C样品的粒度较小粒径分布均匀,0.1 C首次放电比容量为141.9 mAh/g,循环50次后容量下降11.2 mAh/g,以1 C倍率首次放电比容量为126.5 mAh/g,循环50次后容量保持率为87.2%.     

偏氟乙烯-六氟丙烯共聚物电解质研究

以偏氟乙烯-六氟丙烯共聚物〔P(VdF-HFP)〕、LiClO4/碳酸二甲酯(DMC)/碳酸乙烯酯(EC)或LiPF6/EC/DMC/碳酸二乙酯(DEC)和纳米SiO2为原料,用自然挥发法和相转移法制成聚合物电解质膜。测试结果表明:对LiClO4/DMC/EC体系,c(LiClO4)=1mol/L,w(SiO2)=7%时,室温(21℃)电导率达最大值2 81mS/cm,72℃时达9 6mS/cm;对LiPF6/EC/DMC/DEC体系,c(LiPF6)=1mol/L,m〔P(VdF-HFP)〕∶m(SiO2)=3∶2时,室温电导率为3 68mS/cm,72℃时达13 8mS/cm。扫描电镜(SEM)和X射线衍射分析(XRD)结果表明,电解质膜为非晶态的多孔结构,纳米SiO2粉末掺入可使微孔的数目明显增多,孔隙率增加,孔分布更均匀;傅里叶红外光谱(FTIR)结果显示,P(VdF-HFP)、增塑剂与LiClO4间存在相互作用。     

石墨制品废料用作锂离子电池负极活性材料的研究

以某电炭厂石墨制品的废料为原样,对其进行了不同最高热处理温度(HTTmax)的热处理。用XRD图谱分析结合密度测定对原样及热处理试样的微观结构进行了表征。测定了部分试样的灰分含量。用恒电流充、放电法检测了所有试样的充、放电性能。实验结果表明:当HTTmax<2 800 时,随着HTTmax的升高,虽然试样中的石墨微晶数量增多、尺寸变大,但其充、放电容量并未增加。为了揭示这一反常现象的实质,将测定试样灰分含量所得结果和Aclaeson炉在石墨化过程中所发生的化学反应联系起来进行了分析。在此基础上,提出了该电炭厂石墨制品废料进行热处理时的最佳方案,最佳HTTmax为2 800 。将HTTmax=2 800的试样在1 mol／L LiCIO4／EC+DEC(1:1)电解液中进行恒电流充、放电时,第三循环的放电容量D3可达338.7mAh／g,充、放电效率η3为96.1％。     

High flash point electrolyte for use in lithium-ion batteries

The high flash point solvent adiponitrile (ADN) was investigated as co-solvent with ethylene carbonate (EC) for use as lithium-ion battery electrolyte. The flash point of this solvent mixture was more than 110 °C higher than that of conventional electrolyte solutions involving volatile linear carbonate components, such as diethyl carbonate (DEC) or dimethyl carbonate (DMC). The electrolyte based on EC:ADN (1:1 wt) with lithium tetrafluoroborate (LiBF₄) displayed a conductivity of 2.6 mS cm⁻¹ and no aluminum corrosion. In addition, it showed higher anodic stability on a Pt electrode than the standard electrolyte 1 M lithium hexafluorophosphate (LiPF₆) in EC:DEC (3:7 wt). Graphite/Li half cells using this electrolyte showed excellent rate capability up to 5C and good cycling stability (more than 98% capacity retention after 50 cycles at 1C). Additionally, the electrolyte was investigated in NCM/Li half cells. The cells were able to reach a capacity of 104 mAh g⁻¹ at 5C and capacity retention of more than 97% after 50 cycles. These results show that an electrolyte with a considerably increased flash point with respect to common electrolyte systems comprising linear carbonates, could be realized without any negative effects on the electrochemical performance in Li-half cells.     

Conductivity and viscosity studies of ethylene carbonate based solutions containing lithium perchlorate

Specific conductivities and viscosities of lithium perchlorate at four different concentrations (0.5, 1.0, 1.5 and 2.0 M) in ethylene carbonate (EC) based binary mixed solvent systems at 25°C are reported. The co-solvents chosen were tetrahydrofuran (THF), 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL). Viscosity variations in all the three mixed solvent systems without electrolyte showed negative deviation from ideal behaviour thereby indicating the occurrence of a structure breaking effect in these three different binary systems. The increase in viscosity with increase in concentration of LiClO₄ is attributed to the structural enhancement through the formation of a solvated complex which occupies interstitials in the solvent mixtures. 1 M LiClO₄ solution shows maximum specific conductivity at 30 vol % EC for EC + DME and EC + DOL mixtures and at 50 vol % EC for EC + THF mixtures. Conductivity variations are explained on the basis of preferential solvation of lithium perchlorate by co-solvents (THF, DME and DOL) in their respective mixtures with ethylene carbonate.     

微孔碳材料修饰的隔膜用于高性能锂硫电池

锂硫电池具有较高的能量密度,是有发展前景的能量存储体系之一。但“穿梭效应”严重制约了锂硫电池的实际应用,为解决该问题,本文通过简单的一步热解法合成了孔径均匀的微孔碳材料,探究了微孔碳材料修饰隔膜后对锂硫电池性能的影响。结果表明,制备的微孔碳材料孔径集中在0.56nm左右,修饰隔膜后不仅能够有效抑制“穿梭效应”的产生,还有利于加快锂离子的传输,确保正极一侧溶解的多硫化物的再次利用。在0.1C的电流密度下,采用微孔碳材料修饰隔膜的电池首次放电比容量为1359mAh/g,循环100次之后容量能保持在966mAh/g,而修饰之前的传统聚丙烯隔膜,循环100次之后的比容量仅为409mAh/g;在1C的电流密度下循环500圈后,采用微孔碳材料修饰隔膜的电池容量保持率为88%,表现出优异的循环稳定性。     

The electrochemical performance of lithium–sulfur batteries with LiClO4 DOL/DME electrolyte

The electrochemical performance of lithium–sulfur batteries with LiClO₄ DOL/DME as electrolyte was investigated. Impedance and SEM analysis indicated that too high content of DME(Dimethoxy ethane) in electrolyte could raise the interfacial resistance of battery due to the impermeable layer formed on the surface of the sulfur cathode, which led to bad cycle performance, while the increase of DOL(1,3-dioxolane) could change those phenomena. The optimal composition of electrolyte was DME:DOL = 2:1 (v/v). With this electrolyte, the lithium–sulfur battery obtained a high initial discharge capacity of 1,200 mA h g^?1 and still remained 800 mA h g^?1 after 20 cycles.     

Spherical graphene and Si nanoparticle composite particles for high-performance lithium batteries

Silicon/carbon composite electrodes are in the spotlight as an anode with a high capacity and a long cycle life. For this purpose, it is important to make a uniformly dispersed composite material. We fabricated spherical composite particles of reduced graphene oxide (rGO) and silicon nanoparticle (Si NP) using a spray drying method. The composite microparticle fabricated by drying the suspended droplets forms a well-agglomerated rGO/Si NP composite and forms a pore structure by crumpled rGO. The rGO/Si NP microparticles were applied as the anode of the lithium-ion battery. We achieved a reversible capacity of 1,246 mAh/g at 1A/g after 200 charge/discharge cycles and a capacity retention of 83%. Considering that the Si NP microparticle without rGO showed a capacity of 365 mAh/g and a retention of 12%, the rGO matrix improves the electrical conductivity and effectively alleviates stress during charge and discharge cycles.     

Electrospun carbon nanofibers decorated with MnO nanoparticles as a sulfur-absorbent for lithium-sulfur batteries

Shuttle effect of the dissolved polysulfide is a main disadvantage for Li-S batteries, which has been explored by several polar materials to absorb lithium polysulfide with physical and chemical effect. Herein, for the first time, a composite of carbon nanofibers decorated with MnO nanoparticles (CNF-MnO) has been prepared by the facile electrospinning method followed by thermal treatment. SEM and TEM characterization delivered that the MnO NPs on CNF did not change the morphology but decrease the electronic conductivity of CNF-MnO composite. The CNF-MnO composite exhibited excellent electrochemical cyclic stability because of its strong chemical absorption for polysulfide. Interestingly, CNF-MnO composite served as both cathode as well interlayer for Li-S batteries. The CNF-MnO-S as cathode material showed an initial discharge capacity of 683.2 mAh g^-1 at 1.0?C and remained 592.0 mAh g^-1 even after 250 cycles with the capacity decay of 0.053% per cycle. As well, CNF-MnO as interlayer delivered superior cycling stability even at high current density of 3.0?C, where the capacity still maintained 542.2 mAh g^-1 over 200 cycles.     

氟化处理对La0.94Mg0.06Ni3.49Co0.73Mn0.12Al0.20储氢合金的性能影响

为了提高La_(0.94)Mg_(0.06)Ni_(3.49)Co_(0.73)Mn_(0.12)Al_(0.20)合金的性能,研究了氟化处理对其电化学性能的影响。X射线衍射和扫描电镜分析表明:氟化处理后,合金的相组成发生改变,有新相Mg F2生成;合金的表面有一层Mg F2颗粒。电化学测试表明:当NH4F浓度为0.3 mol/L时,合金电极的最大放电容量(Cmax)从346.4 m Ah/g提高到378.0 m Ah/g,容量保持率(S50)从69.5%提高到74.3%,交换电流密度由122.3 m A/g提高到188.5 m A/g,极限电流密度由891.7 m A/g提高到1162.1 m A/g,腐蚀电位由-0.895 V提高到-0.849 V,电化学反应阻抗减小。