LiFePO4固相碳热合成法研究

以碳热还原法为原理，采用Fe2O3、Li2CO3、NH3H2PO4和碳黑为原料，以一定计量比和顺序混合，经过球磨、干燥、造粒、预烧、烧成等几道工序，制备出黑色的LiFePO4粉末。利用化学分析、XRD、SEM等手段研究了工艺流程对合成产物晶体结构、表面形貌的影响。利用合成材料组装电池，通过充放电试验测试电化学性能。结果表明，以0．1C速率充放电，首次充放电容量在150mAh／g。从长远看来，这种低成本，工艺简单，绿色无污染的合成方法很具有工业实用化生产价值。     

共沉淀法制备正极材料LiFePO4的研究

以氢氧化锂、硫酸亚铁铵和磷酸氢二铵为原料，研究了液相共沉淀法制备LiFePO4正极材料和掺杂Co^2＋的LiFePO4改性正极材料，并对其进行XRD、SEM分析和电化学性能测试。结果表明掺杂Co^2＋对正极材料的初始充电比容量为156．7mAh·g^-1，且循环60次后，容量仍有138．7mAh·g^-1，容量衰减率仅为11．4％。     

高密度锂离子电池正极复合材料LiFePO4/C

以FeC2O4-2H2O、NH4H2PO4、Li2CO3和乙炔黑为原料,采用两步固相反应法制备了高密度LiFePO4/C正极复合材料.利用差热(DSC),热重(TGA)和X射线衍射(XRD)等分析手段具体探讨了第一步固相反应中可能存在的反应过程和中间产物.利用扫描电镜表征了复合材料LiFePO4/C中LiFePO4微粒形貌和接触状态.结果表明,乙炔黑的含量是影响LiFePO4微粒尺寸和微粒间接触界面的重要因素.在一次热处理的基础上,二次球磨和烧结有利于第二次固相反应过程中反应物质的接触和传质,较一步固相法提高了生成的LiFePO4的振实密度.当乙炔黑的含量(质量分数)为0.1%～1.5%时,两步固相法所制正极材料LiFePO4/C的振实密度可达到1.7 g/cm3,初次放电容量达到105 mA.h/g.     

钇掺杂LiFePO4锂离子电池正极材料的制备与性能

用固相法合成LiFe1-xYxPO4 (x=0, 0.01, 0.02, 0.03, 0.04)锂离子电池正极材料,采用X射线衍射仪、扫描电子显微镜、粉末比电阻法和充放电性能测试表征材料的晶体结构、微观形貌、电子电导率和电化学性能。结果表明,少量的钇掺杂并未改变材料的晶体结构,但改善了材料的微观结构,提高其电子电导率,改善可逆容量和电化学性能。在10 mA/g的电流密度下,LiFe0.97Y0.03PO4首次放电容量可达146.54 mAh/g。     

液相沉淀-多元醇还原法合成LiFePO4/C正极材料的电化学性能

以钛白工业副产物七水硫酸亚铁为铁源,用液相沉淀制得无定形FePO4·xH2O前躯体,然后在多元醇中与锂源反应制得LiFePO4材料,过程在常压下进行,无需煅烧与惰性气体保护。用XRD、SEM及电化学分析考察多元醇乙二醇(EG)、二甘醇(DEG)和三甘醇(TEG)对材料物相和形貌的影响。结果表明:三甘醇所得样品的锂离子扩散速率最小;此样品的晶粒尺寸最小,结晶最完整,无明显杂相生成。在室温下放电倍率为0.1C、1C和5C时,该正极材料的首次放电比容量分别达到148.8、129.3和102.8 mA·h/g,其碳包覆样品的首次放电比容量分别达到155.6、139.9和112.2 mA·h/g,且循环性能良好。     

前驱体体系pH值对LiFePO4/C正极材料性能的影响

采用溶胶-凝胶法制备了LiFePO4/C正极材料.采用X射线衍射(XRD)、扫描电镜(SEM)和电化学手段对材料进行了结构表征和性能测试.研究了其前驱体体系pH值对材料性能的影响.结果表明:当前驱体体系pH值为8.4时,LiFePO4/C正极材料具有最佳的电化学性能.在0.1C倍率下充放电,磷酸铁锂首次放电比容量为16...     

LiFePO4/C锂离子电池正极材料的电化学性能

以碳凝胶作为碳添加剂,采用固相法制备了复合型LiFePO4/C锂离子电池正极材料.研究了不同掺碳量对样品性能的影响.利用X射线衍射仪、扫描电镜和碳硫(质量分数)分析方法对所得样品的晶体结构、表面形貌、含碳量进行分析研究.结果表明:样品中的碳含量(质量分数)分别为0%、5%、10%、22%,所得样品均为单一的橄榄石型晶体结构,碳的加入使LiFePO4颗粒粒径减小.另外,碳分散于晶体颗粒之间,增强了颗粒之间的导电性.合成样品的电化学性能测试结果表明,掺碳后的LiFePO4放电比容量和循环性能都得到显著改善.其中,含碳量为22%的LiFePO4/C在0.1 C倍率下放电,首次放电容量达143.4 mA·h/g,充放电循环6次后电容量为142.7 mA·h/g,容量仅衰减0.7%.     

固相法制备LiFePO4正极材料的研究

采用固相法合成橄榄石型LiFePO4锂离子电池正极材料,研究了烧结时间和温度对材料性能的影响,采用XRD、SEM和激光粒度分析等方法对材料的成分、结构和形貌进行了分析.结果表明:在600℃下烧结24h合成的LiFePO4材料具有完整的结晶度、规则的晶体形貌和均匀的粒径(约0.8 μm).     

Synthesis and characterization of LiFePO4／C composite used as lithium storage electrodes

LiFePO4/C composites with good rate capability and high energy density were prepared by adding sugar to the synthetic precursor, A significant improvement in electrode performance was achieved. The resulting carbon contents in the sample 1 and sample 2 are 3.06% and 4.95% (mass fraction), respectively. It is believed that the synthesis of LiFePO4 with sugar added before heating is a good method because the synthesized particles having uniform small size are covered by carbon. The performance of the cathodes was evaluated using coin cells. The samples were characterized by X-ray diffraction and scanning electron microscope observation. The addition of carbon limits the particles size growth and enables high electron conductivity. The LiFePO4/C composites show very good electrochemical performance delivering about 142 mAh/g specific capacity when being cycled at the C/10 rate. The capacity fade upon cycling is very small.     

利用新颖的三层电极提高LiFePO4／C正极材料的电化学性能

对常用的两层电极（活性材料层｜集电极）进行改进,提出一种新颖的夹心状三层电极（导电材料层｜活性材料层｜集电极）以提高 LiFePO4/C 的电化学性能。充放电测试表明：相比两层电极,三层电极中 LiFePO4/C 表现出更优的倍率性能。循环伏安和电化学阻抗测试表明：相比两层电极,三层电极中LiFePO4/C材料中的Fe3＋/Fe2＋氧化还原电对表现出更快的氧化还原速度。更好的可逆性能以及更低的电荷转移阻抗。在三层电极中,活性材料层表层中与LiFePO4/C颗粒尺寸相当的孔洞被粒径小得多的乙炔黑微粒填充,形成LiFePO4/C颗粒间的导电连接,为暴露在电解液主体LiFePO4/C颗粒中的LiFePO4晶体提供更多运输电子到达或离开的路径。     

用β-环糊精制备LiFePO4/C锂离子电池正极材料

采用高温固相法制备了β-环糊精为碳源前驱体、具有橄榄石结构的LiFePO4/C复合正极材料.与采用相同工艺制备的LiFePO4和以碳黑作为碳源制备的LiFePO4/C产物比较,该复合材料粉体粒度小,电化学性能优良,体现在:占体积分数为26.88%的产物粒度小于1 μm;0.1C放电比容量可达到147 mA·h·g-1,相对纯净LiFePO4提高66 mA·h·g-1.此外,初步分析了β-环糊精在制备过程中细化颗粒的机理.     

溶胶-凝胶法制备LiFePO_4/C复合材料及其性能

为了提高LiFePO4的电化学性能,以柠檬酸为络合剂和碳源,采用溶胶-凝胶法制备LiFePO4/C复合正极材料。采用FTIR和XRD等对前驱体及产物进行表征,并测试样品的电化学性能。结果表明:经700℃烧结10h所得产物具有单一的橄榄石型晶体结构,碳含量为10.81%(质量分数)。样品在0.1C下首次放电比容量为127.1mA·h/g,在0.2C、0.5C、1C下首次放电比容量分别为106.1、83.3、70.6mA·h/g。该样品在0.1C下经过20次循环后,容量还保持为126.3mA·h/g,衰减仅为0.035%。循环伏安和交流阻抗测试表明该材料具有较好的电化学性能。     

Conducting network interface modulated rate performance in LiFePO4/C cathode materials

Carbon can play a critical role in electrode,especially for LiFePO4 cathode,not only serving as con-tinuous conducting network for electron pathway,but also boo...     

一步固相合成Nb掺杂LiFePO4/C及其电化学性能

用廉价的三价铁离子化合物为铁源,以聚丙烯为还原剂和碳源,在一步固相法合成Nb掺杂LiFePO4的同时实现颗粒表面碳导电膜的原位包覆。结果表明:一步固相合成的Nb掺杂LiFePO4/C具有完整的橄榄石型LiFePO4晶体结构和近似球状的颗粒形貌,颗粒尺寸为100~500 nm;聚丙烯分解后在颗粒表面和颗粒之间形成连通的网络状碳膜。电化学测试结果表明,当Nb的掺入量为1.0%(摩尔分数)时具有最好的倍率放电性能和循环性能;在2C充放电时具有130 mA.h/g的放电容量,循环100次容量无衰减,在4C充放电时仍具有105 mA.h/g的放电容量。     

Electrochemical performance of LiFePO4 cathode material for Li-ion battery

In the search for improved materials for rechargeable lithium batteries, LiFePO4 offers interesting possibilities because of its low raw materials cost, environmental friendliness and safety. The main drawback with using the material is its poor electronic conductivity and this limitation has to be overcome. Here Al-doped LiFePO4/C composite cathode materials were prepared by a polymer-network synthesis technique. Testing of X-ray diffraction, charge-discharge, and cyclic voltammetry were carried out for its performance. Results show that Al-doped LiFePO4/C composite cathode materials have a high initial capacity, good cycle stability and excellent low temperature performance. The electrical conductivity of LiFePO4 material can be obviously improved by doping Al. The better electrochemical performances of Al-doped LiFePO4/C composite cathode materials have a connection with its conductivity.     

固相法制备Y3+掺杂LiFePO4/C的反应机理及其电化学性能

以Fe2O3为铁源,采用高温固相法制备了Y3+掺杂的LiFePO4/C复合材料。利用TG-DSC、XRD、SEM、恒电流充放电等手段对材料的合成反应历程、粉体颗粒形貌以及电化学性能进行了研究。结果表明:Fe3+在300～550℃间被还原为Fe2+,经过650℃煅烧后,形成晶型单一的橄榄石结构晶体。LiFe0.98Y0.02PO4/C样品在0.2 C倍率下的首次放电比容量达到了151.6 mA.h/g。     

Electrochemical performance of Ti4+-doped LiFePO4 synthesized by co-precipitation and post-sintering method

Ti4+-mixed FePO4·xH2O precursor was prepared by co-precipitation method,with which Ti4+ cations were added in the process of preparing FePO4·xH2O to pursue an effective and homogenous doping way.Ti4+-doped LiFePO4 was prepared by an ambient-reduction and post-sintering method using the as-prepared precursor,Li2CO3 and oxalic acid as raw materials.The samples were characterized by scanning electron microscopy (SEM),X-ray diffractometry (XRD),electrochemical impedance spectroscopy (EIS),and electrochemical charge/discharge test.Effects of Ti4+-doping and sintering temperature on the physical and electrochemical performance of LiFePO4 powders were investigated.It is noted that Ti4+-doping can improve the electrochemical performance of LiFePO4 remarkably.The Ti4+-doped sample sintered at 600 ℃ delivers an initial discharge capacity of 150,130 and 125 mA·h/g with 0.1C,1C and 2C rates,respectively,without fading after 40 cycles.     

Electrochemical performance of LiVPO4F/C synthesized by different methods

LiVPO₄F/C samples were synthesized by one-step solid-state reaction and two-step solid-state reaction methods, respectively. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance tests were adopted to characterize the properties of LiVPO₄F/C. XRD results show that the LiVPO₄F/C samples prepared by one-step solid-state reaction method have the same triclinic structure (space group as that synthesized by conventional two-step solid-state reaction. SEM image exhibits that the particle size of LiVPO₄F/C prepared by one-step solid-state reaction method is smaller than that of the sample synthesized by two-step solid-state reaction. The improved electrochemical properties of the LiVPO₄F/C are attributed to the depressed grain size and enhanced electrical conductivity produced via one-step solid-state reaction method using oxalic acid as both reduction agent and carbon sources. AC impedance measurements also show that the LiVPO₄F/C synthesized by one-step solid-state reaction route significantly decreases the charge-transfer resistance.