羧甲基壳聚糖水性粘结剂改性及其在磷酸铁锂正极的应用研究

羧甲基壳聚糖（C-CTS）作为磷酸铁锂（LiFePO4, LFP）正极水系粘结剂的两种改性方式分别是：（1）与聚环氧乙烷（PEG）共混制备C-CTS/PEG复合粘结剂;（2）在C-CTS/PEG混合体系中,以三羟甲基丙烷-三[3-(2-甲基吖丙啶基)丙酸酯]（XR-104）作为交联剂制备可交联的C-CTS/PEG/XR-104水系粘结剂。本文考察了不同C-CTS/PEG质量比复合粘结剂对LFP正极的电化学性能的影响,C-CTS/PEG的优化重量比为3∶1,此时LFP正极表现出最佳的循环稳定性。电池在0.5 C下充放电测试,140次循环后容量保持率为99%。采用差示扫描量热法（DSC）、傅里叶红外光谱仪（FTIR）和溶解实验等研究C-CTS/PEG与XR-104的交联反应,当交联剂XR-104的重量为C-CTS的1%时,LFP正极表现出最佳的电化学性能。     

石墨负极材料形态对LiFePO4动力电池性能的影响

本文分别以树脂包覆天然石墨（RCNG）、人造石墨（AG）和中间相碳微球（MCMB）为负极材料,制备了三种不同的圆柱形磷酸铁锂（LiFePO4）动力电池。通过X射线衍射分析仪（XRD）和扫描电子显微镜（SEM）对材料的晶体结构与形貌进行表征,并采用多种手段测试了各动力电池的电化学性能。结果显示,磷酸铁锂/中间相碳微球（LFP/MCMB）电池表现出较为优异的电化学低温、倍率和循环性能,其在 −20℃下的1 C容量保持率为61.04%,6 C高倍率容量保持率和温升分别为87.52%和24.8℃,3 C循环1 000次后容量保持率为93.81%。     

分级多孔纳米碳球的制备及其在锂硫电池中的应用

以戊二醛（GA）与3-氨丙基三乙氧基硅烷（KH-550）为原料,通过醛胺缩合反应、高温煅烧以及碱刻蚀,制备了分级多孔纳米碳球（HPCN）。扫描电子显微镜（SEM）测试表明,制备的HPCN为平均粒径85.3 nm的单分散纳米球。将HPCN与单质S混合,通过熔融-扩散法制备HPCN/S正极材料,组装成锂硫（Li-S）电池后进行电化学测试。测试结果表明,HPCN/S具有优良的电化学性能,使用铝箔集流体时,在0.2 C循环100圈后放电比容量为472.1 mA∙h/g;采用碳纸替代铝箔集流体制备的HPCN/S-CP正极,显示出更加优异的循环稳定性与倍率性能,在0.2 C循环100圈后放电比容量为636.1 mA∙h/g,在1.0 C与2.0 C下的倍率比容量分别为702.7 mA∙h/g、249.4 mA∙h/g。     

Preparation and electrochemical performance of a type 622 ternary cathode materials

将622型前驱体与0.24 Li₂CO₃-0.76 LiOH锂盐体系、氯化钾熔盐混合,在通空气气氛中采用熔盐法制备了622型三元电池正极材料（LNCM）,采用XRD和SEM表征考察了锂源和钾盐的比例及焙烧温度和时间对LNCM晶体结构的影响,得出最佳制备条件为：锂源与钾盐1：5,前驱体和锂源1：1.1,焙烧温度为750℃,焙烧时间为15 h。将LNCM作为正极材料组装成扣式电池,对其进行了多项电化学性能指标测试,结果表明该材料在2.7~4.3 V内,0.1 C放电倍率下,具有182.5 mA·h/g首次放电容量,库仑效率为89.1%;在2.7~4.5 V,0.1 C条件下循环100圈后容量仍有183.2 mA·h/g,容量保持率为91.5%。     

B_(2)O_(3)包覆NaNi_(1/3)Fe_(1/3)Mn_(1/3)O_(2)正极材料制备及其电化学性能北大核心CSCD

O3型层状氧化物正极材料NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)具有高比容量、低成本和环境友好性等优点,被认为是最有前途的钠离子电池正极材料之一,但在充放电过程中会发生一系列复杂的相变,导致电化学性能较差。本研究报道了一种协同改性方法,以同时提高NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料的循环稳定性和倍率性能。通过将硼酸粉末和正极材料固相球磨混匀后低温煅烧,在NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料表面包覆纳米非金属氧化物B_(2)O_(3)。借助X射线衍射仪(XRD)、扫描电子显微技术(SEM)、透射电子显微镜(TEM)和电化学技术等测试手段,对比分析不同包覆量和原材料的形貌和电化学性能,筛选得到最优包覆量为2%(质量分数,余同)。该方法实现了B_(2)O_(3)的均匀包覆,并且没有改变NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)正极材料的晶体结构。通过电化学性能测试表明2%B_(2)O_(3)包覆材料在1 C倍率下循环200圈容量保持率从78%提升至87%。同时,2%B_(2)O_(3)包覆材料的高倍率性能也得到了改善,10 C高倍率下放电比容量从75 mAh/g提升至99 mAh/g。结果表明,这是一种有效且可靠的表面改性策略,可以增强钠离子电池层状氧化物正极材料的电化学性能。     

锂离子电池正极材料低温性能衰退机理研究

锂离子电池凭借其高能量密度、长循环寿命等突出优势被广泛应用于便携式设备、电动汽车以及大规模储能领域。然而,锂离子电池对外界温度敏感,尤其是在较低的工作温度下,能量密度和功率密度急剧下降,这严重限制了其在寒冷地区的应用。为探究锂离子电池在低温环境下的性能衰减机理,选择磷酸铁锂(LiFePO₄)、钴酸锂(LiCoO₂)、层状三元(LiNi_0.6Co_0.2Mn_0.2O₂)三种商业化正极材料作为研究对象,结合恒流充放电测试、电化学阻抗测试、恒电流间歇滴定技术以及X射线衍射分析和扫描电子显微镜表征技术,全面系统地比较了三种材料在室温(25℃)和低温(-20℃)下的电化学性能。恒流充放电测试结果显示三种正极材料在低温下均会出现比容量明显降低,三元NCM622表现出最佳的低温循环稳定性,在-20℃循环400圈时容量保持率为95.89%。进一步的交流阻抗测试分析和Li⁺扩散速率计算表明,在低温条件下电解液电导率的降低、正极材料电荷转移阻抗的增加和Li...     

La掺杂对523型镍钴锰酸锂正极材料电化学性能的影响

文章研究了稀土元素La掺杂对镍钴锰酸锂Li Ni_(0.5-x)La_xCo_(0.2)Mn_(0.3)O_2(x=0,0.05,0.08,0.12)的物相和电化学性能的影响。利用液相共沉淀法+固相煅烧工艺制备了目标产物,并综合利用XRD、恒电流充放电技术及交流阻抗技术对材料物理和电化学性能进行了表征。La掺杂量x=0.05样品的首次放电比容量为152.6 mAh/g,库伦效率为93.6%,在1C电流密度下,经过30次电化学循环后的容量保持率为95.9%;在5C充放电电流密度下,掺杂样品的放电比容量为115.3 mAh/g,达到0.2C下放电比容量的76.4%。La掺杂增加了三元材料沿c轴方向的晶格常数,为锂离子在晶格内部的脱嵌提供了更大的空间,提高了锂离子在晶体中的扩散速度,从而显著增强了材料高倍率充放电性能。     

Preparation and electrochemical performance of LiFePO4/S composite cathode materials

以提高磷酸铁锂体系动力电池的能量密度为目的,在LiFePO₄正极材料中加入少量S材料球磨制得LiFePO₄/S复合正极材料。使用X射线衍射（XRD）和扫描电子显微镜（SEM）表征了结构和形貌,并分别组装扣式电池和软包电池测试其电化学性能。结果表明,磷酸铁锂纳米颗粒致密均匀附着在硫材料表面,构成具有包覆性结构的复合材料。在不同比例的LiFePO₄/S复合材料中,硫的添加量为15%的LiFePO₄/S复合正极材料表现出最优异的电化学性能,0.1 C下的初始容量为251.5mA·h/g,循环100周之后容量保持率达94.9%。以该比例的复合材料为正极的0.5A·h软包电池,循环100周后容量保持率为86.7%。LiFePO₄作为一种极性载体,对多硫化物有一定的吸附能力,少量硫的加入可以在大幅度提高LiFePO₄材料放电容量的同时,维持优异的循环稳定性。LiFePO₄/S复合材料可为磷酸铁锂体系动力电池的发展提供新的思路。     

高阻燃硫正极的制备及其性能北大核心CSCD

本工作系统研究了锂硫电池硫正极中添加不同含量的六氯环三磷腈对硫正极阻燃性能和电化学性能的影响。通过燃烧实验,发现六氯环三磷腈的加入可使硫正极表现出优异的阻燃性能。此外,通过借助扫描电镜(SEM)、X射线衍射(XRD)技术和电化学性能测试等手段,对比了添加和未添加六氯环三磷腈硫正极循环前后的表面形貌、组成成分和电化学性能。结果表明,当六氯环三磷腈添加量为10%时,硫正极表现出最优的循环性能和库仑效率。在0.2 C电流密度下,硫正极中添加量为10%六氯环三磷腈的锂硫电池在100次循环后放电比容量仍保持在975.2 mAh/g,明显优于硫正极中未添加六氯环三磷腈的锂硫电池。而且,添加六氯环三磷腈的硫正极材料分散均匀,即使循环100次后,也未出现明显的裂纹,阻抗也未明显增加。此外,通过六氯环三磷腈和多硫化锂的反应实验,发现六氯环三磷腈的存在有助于锚定充放电中间产物多硫化锂,进而抑制多硫化锂的穿梭,提升锂硫电池的电化学性能,这为提高阻燃锂硫正极材料的电化学性能提供了新的思路。     

Novel ionic plastic crystal-polymeric ionic liquid all-solid-state electrolytes for lithium ion batteries

离子塑性晶体作为一类新型的固态电解质材料,近年来受到研究人员的极大关注。本文合成了一种新型离子塑性晶体：N,N-二甲基吡咯双氟磺酰亚胺（P₁₁FSI）,并将其与吡咯阳离子离子液体聚合物-聚二甲基二烯丙基铵双氟磺酰亚胺（PILFSI）和锂盐（LiFSI）复合制备了P₁₁FSI-PILFSI-LiFSI全固态电解质。采用差示扫描量热法、热重分析、阻抗测试、线性扫描伏安法及对称锂电池测试等一系列表征技术对全固态电解质的热性能和电化学性能进行了系统研究。所制备的电解质膜具有好的柔韧性和热稳定性,高的离子电导率和电化学稳定性,以及与金属锂良好的界面相容性。将全固态电解质应用于Li/LiFePO₄电池中,在50℃、0.2 C充放电倍率时,电池放电比容量在60次循环后仍可达151.1 mA·h/g,容量保持率为96.8%;且在0.5 C、1.0 C倍率下放电比容量仍然高达138.1 mA·h/g和128.1 mA·h/g,展现出高的放电比容量,好的循环性能和倍率性能,有望应用于全固态锂离子电池中。     

Theoretical study on discharge behavior of LiFePO4 battery

使用多孔电极理论对LiFePO4（LFP）锂离子电池的放电行为进行了详细探讨,发现随着放电过程进行,电极内部的电化学反应从隔膜侧向集流体侧移动,并且移动过去之后LFP基本完成放电过程,放电截止时电化学反应截止在电极的某个位置,并不是所有的LFP颗粒都完成了放电。随后对放电速率、电极电导率和电解液扩散系数对放电过程的影响进行了研究。随着放电倍率增加,电化学反应推进的距离不断减少,并且峰值不断增大,峰值区域变窄。提高电极电导率可以保证电化学反应从隔膜侧开始进行,但是继续提高电极电导率并不能进一步将电化学反应的峰值向电极深处推进。较高的扩散系数可以保证所有的活性材料都能发生电化学反应。以上结论可对高性能LFP锂离子电池的设计和制备提供了有效的指导作用。     

Surface modification of LiNi0.5Co0.2Mn0.3O2 cathode materials with Li2O‐B2O3‐LiBr for lithium‐ion batteries

LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode material suffers from phase transformation and electrochemical performance degradation as its main drawbacks, which are strongly dependent on the surface state of NCM523. Herein, an effective surface modification approach was demonstrated; namely, the fast lithium‐ion conductor (Li₂O‐B₂O₃‐LiBr) was coated on NCM523. The Li₂O‐B₂O₃‐LiBr coating layer as a protecting shell can prevent NCM523 particles from corrosion by the acidic electrolyte, leading to a superior discharge capacity, rate capability, and cycling stability. At room temperature, the Li₂O‐B₂O₃‐LiBr–coated NCM523 exhibited an excellent capacity retention of 87.7% after 100 cycles at the rate of 1 C, which is remarkably better than that (29.8%) without the uncoated layer. Furthermore, the coating layer also increased the discharge capacity of NCM523 cathode material from 68.7 to 117.0 mAh g^?1 at 5 C. Those can be attributed to the reduction in the electrode polarization and improvement in the electrode conductivity, which was supported by electrochemical impedance spectroscopy and cyclic voltammetry measurements.     

A novel and efficient water-based composite binder for LiCoO2 cathodes in lithium-ion batteries

The dispersion, adhesion strength, electrical, and electrochemical properties of LiCoO₂ cathodes in lithium-ion batteries with the addition of a new composite binder composed of two acrylic emulsions, poly(butyl acrylate)-based (PBA) and polyacrylonitrile-based (PA) latex in a ratio of 3:7, were evaluated. PBA binder has a low-glass transition temperature of 10 °C, which can improve the flexibility of the electrode. This new composite binder has a very good binding ability as same as the typical organic solvent-based binder, poly(vinylidene fluoride). The dispersions of the water-based cathode slurries with the composite binder were measured by analyzing the viscosity and sedimentation behaviors. The results show that the new composite binder can well disperse the LiCoO₂. Moreover, using the new composite binder could greatly improve the rate capabilities and the cycle stability of water-based LiCoO₂ cathodes.     

Graphene oxide coated nanosheet-like γ-MnS@KB-S fabricated by spray drying for high energy density Li-S batteries

In order to prohibit the shuttle influence of lithium polysulfides in lithium sulfur battery, a kind of graphene oxide (GO) coated γ-MnS@KB-S (GO@MKB-S) composite cathode material was successfully fabricated. First of all, the γ-MnS@KB (MKB) composite powders were prepared via a solvothermal reaction, then a spray drying method was used to obtain GO@MKB-S composites, which displays core/shell nanostructure. SEM, TEM, XRD as well as Raman spectrum are implemented to look into the microstructures and the functions of the 2D nanosheet-like γ-MnS in setting in KB on the battery performance were carefully analyzed. It is demonstrated that electrochemical discharge capacity and rate performance are clearly improved by using GO@MKB-S composites compared to the cathode electrode of the GO coated KB-S (GO@KB-S). With a sulfur loading of 5 mg cm⁻², the cathode electrode of GO@MKB-S shows a considerable discharge capacity of 749.9 mAh g⁻¹ at 0.36 C. Additionally, the Li-S battery cycle retention of GO@MKB-S sample maintains 97.36% after 100 cycles and 78.69% after 200 cycles.     

Effect of mechanical activation process parameters on the properties of LiFePO4 cathode material

Pure, nano-sized LiFePO₄ and carbon-coated LiFePO₄ (LiFePO₄/C) positive electrode (cathode) materials are synthesized by a mechanical activation process that consists of high-energy ball milling and firing steps. The influence of the processing parameters such as firing temperature, firing time and ball-milling time on the structure, particle size, morphology and electrochemical performance of the active material is investigated. An increase in firing temperature causes a pronounced growth in particle size, especially above 600 °C. A firing time longer than 10 h at 600 °C results in particle agglomeration; whereas, a ball milling time longer than 15 h does not further reduce the particle size. The electrochemical properties also vary considerably depending on these parameters and the highest initial discharge capacity is obtained with a LiFePO₄/C sample prepared by ball milling for 15 h and firing for 10 h at 600 °C. Comparison of the cyclic voltammograms of LiFePO₄ and LiFePO₄/C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO₄/C in lithium batteries cycled at room temperature. At the high current density of 2C, an initial discharge capacity of 125 mAh g⁻¹ (73.5% of theoretical capacity) is obtained with a low capacity fading of 0.18% per cycle over 55 cycles.     

Self-assembled mesoporous LiFePO4 with hierarchical spindle-like architectures for high-performance lithium-ion batteries

Self-assembled mesoporous LiFePO₄ (LFP) with hierarchical spindle-like architectures has been successfully synthesized via the hydrothermal method. Time dependent X-ray diffraction, scanning electron microscopy, and cross section high resolution transmission electron microscopy are used to investigate the detailed growth mechanism of these unique architectures. Reaction time and pH value play multifold roles in controlling the microstructures of LFP. The LFP particles are uniform mesoporous spindles, which are comprised of numerous single-crystal LFP nanocrystals. As the cathode material for lithium batteries, LFP exhibits high initial discharge capacity (163 mAh g⁻¹, 0.1 C), excellent high-rate discharge capability (111 mAh g⁻¹, 5 C), and cycling stability. These enhanced electrochemical properties can be attributed to this unique microstructure, which will remain structural stability for long-term cycling. Furthermore, nanosizing of LFP nanocrystals can increase the electrochemical reaction surface, enhance the electronic conductivity, and promote lithium ion diffusion.