一种新型的锂离子电池正极材料——LiFePO4

介绍了1种新型的锂离子电池正极活性材料LiFePO4并解释了材料的结构特征和电化学过程。LiFePO4具有较高的比容量和良好的循环稳定性等优良的电化学性能,但是目前还存在着制约容量释放的锂离子扩散系数小以及材料导电性能不太好等问题。在回顾该材料研究状态的基础上,说明了只要通过选取适当的制备工艺和进行合适的表面改性可以制备出具有优良电化学性能的LiFePO4粉体。这种粉体具有环境相容性、便宜以及资源丰富等诸多优点,是1种颇具潜力的锂离子电池正极替代材料。     

Ni^2+掺杂对LiFePO_4正极材料电化学性能的影响

采用固相反应法在惰性气氛下合成了橄榄石型LiFePO4及其Ni^2＋掺杂正极材料,采用XRD,SEM和充放电等方法对目标材料进行了表征。XRD分析表明,掺杂少量Ni^2＋后的LiFePO4晶体结构并未发生变化;SEM观察发现,掺杂后,样品的粒径变小;充放电测试得出,比未掺杂的LiFePO4具有更好的电化学性能,首次放电比容量达145mAh·g^-1,高于纯的LiFePO4正极材料的容量90mAh·g^-1,经100次循环后掺杂Ni^2＋的LiFePO4和LiFePO4样品的容量保有率分别为91％和53％。     

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.     

Optimized synthesis technology of LiFePO4 for Li-ion battery

The influence of factors of the carbon black content, sintering temperature, sintering time, molar ratio of Li to Fe, as well as the electrochemical properties of LiFePO4 for lithium ion battery were studied. The only technology was obtained by using range analysis through Latin orthogonal experiment of L4^4 (16). The results show that the optimization synthesis technology of LiFePO4 is content of 5% doping carbon, sintering temperature of 700℃,molar ratio of Li to Fe of 1.03 : 1 and sintering time of 16 h. The optimized cathode synthesis techniques can make LiFePO4 have good electrochemical properties.     

锂离子电池正极材料磷酸铁锂研究进展

电极材料是推进电池技术发展及应用的关键。作为锂离子电池正极材料的LiFePO4表现出优异的电池性能(大容量、优异循环特性),但也有本征低电导率的缺点。具有橄榄石结构的LiFePO4在电池充放电过程发生FePO4与LiFePO4之间的相变,已有实验证明充放电过程中出现固溶体LixFePO4。掺杂是提高材料电导率的常用手段,但LiFePO4的掺杂却一直饱受争议;缺陷化学的研究初步认定通过适当点缺陷的电荷补偿,晶体内引入掺杂元素是可以实现的,并且提出几种缺陷补偿机制。导电相复合可降低电极颗粒间的接触电阻,特别是LiFePO4的碳包覆有效地改善其电化学性能,促进其工业化推广;碳包覆的有效性取决于碳的sp2杂化键的比例及碳含量。由于电极材料形貌影响电池的充放电动力学过程,LiFePO4的颗粒尺寸、形状、表面粗糙度等的控制都成为提高电池性能的重要手段;LiFePO4的薄膜制备及三维构架技术则进一步推动微型电池的应用发展。     

反应物中锂元素的量对LiFePO4/C电化学性能的影响

以Fe2O3和LiH2PO4为原料,葡萄糖为碳源,采用碳热还原法合成了LiFePO4/C正极材料,考察了反应物中锂元素的量对正极材料LiFePO4/C电化学性能的影响。用X射线衍射、扫描电镜(SEM)和恒电流充放电测试和循环伏安法对正极材料的结构、形貌以及电化学性能进行了研究。结果表明:当反应物中额外添加锂元素的量是理论量的10%时,制得的正极材料的电化学性能最佳,在0.2和1C(1C=170mA/g)的充放电倍率下,首次放电比容量分别为156.3和137.5mAh/g,经过20次充放电循环后,容量基本保持不变。     

Synthesis and electrochemical performances of spherical LiFePO4 cathode materials for Li-ion batteries

Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g -1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g -1.The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.     

Electrochemical performance of carbon nanotube-modified LiFePO_4 cathodes for Li-ion batteries

Carbon nanotubes (CNTs) and acetylene black (AB) were dispersed synchronously or separately between LiFePO4 (LFP) particles as conducting agents during the course of manufacture of LiFePO4 cathodes. The morphology and electrochemical performances of as-prepared LiFePO4 were evaluated by means of transmission electron microscopy (TEM), charge-discharge test, electrochemical impedance spectroscope (EIS) and cyclic voltammetry (CV). CNTs contribute to the interconnection of the isolated LiFePO4 or carbon particles. For the CNTs-modified LiFePO4, it exhibits excellent performance in terms of both specific capacity and cycle life. The initial discharge capacity is 147.9 mA·h/g at 0.2C rate and 134.2 mA·h/g at 1C rate, keeping a capacity retention ratio of 97% after 50 cycles. The results from EIS indicate that the impedance value of the solid electrolyte interface decreases. The cyclic voltammetric peak profiles is more symmetric and spiculate and there are fewer peaks. CNTs are promising conductive additives candidate for high-power Li-ion batteries.     

电化学法制备BaMoO_4和SrMoO_4薄膜的生长特性比较研究(II):个性研究

采用恒电流电化学技术直接在金属钼片上制备了具有白钨矿结构的钼酸盐(BaMoO4、SrMoO4)薄膜,对制备时间分别为10s直到50min的BaMoO4薄膜和制备时间分别为1min直到100min的SrMoO4薄膜的生长情况进行了SEM测试,并对相应结果进行了对比分析。研究表明:用电化学法制备BaMoO4和SrMoO4晶态薄膜,其生长特性既具有共性,也具有鲜明的个性。其共性特征已在另文中给出。其鲜明的个性特征是:1)BaMoO4和SrMoO4这两种薄膜在生长初期晶粒的成核速率不同;两种薄膜晶粒的生长速率不同;2)两种薄膜晶粒的形貌不同,晶粒的尺寸大小明显不同;3)两种薄膜晶粒的生长取向不同。该研究结果对功能薄膜的电化学制备和了解及预测白钨矿结构的晶态薄膜的生长习性,具有重要意义。     

还原-插锂和碳包覆同步制备磷酸铁锂/碳复合材料及其性能

以聚丙烯酸为碳源,用低温还原-插锂与聚合物高温分解相结合的方法制备LiFePO4/C复合正极材料;FePO4被还原插锂与含碳聚合物化学包覆同时进行,简化了制备工艺,降低了制备成本。经X射线粉末衍射(XRD)、扫描电镜(SEM)以及恒电流充/放电测试,研究了不同焙烧温度对合成产物的物相、晶胞参数、表面形貌及电化学性能的影响。研究发现,焙烧温度为600℃时,合成产物的0.1 C倍率放电具有最高的放电容量和最好的循环稳定性。在0.1 C下LiFePO4/C复合材料的首次放电容量高达141.3 mAh/g,库伦效率为98.0%,100次循环后,其容量保持率为108.3%。     

多孔LiFePO4正极材料的研究进展

锂离子电池是高效、清洁的储能装置,在便携式电子产品、储能设施和电动汽车等领域具有广泛的应用前景,对于缓解能源危机和环境污染具有重要意义。橄榄石型LiFePO_4是最有前途的锂离子电池正极材料之一。然而,相对低的本征电子电导率与锂离子扩散速率限制了LiFePO_4倍率性能的发挥,阻碍其在动力锂离子电池领域的大规模商业化应用。纳米化是一种能有效改善LiFePO_4倍率性能的方法,但纳米粒子存在表面能高,易团聚结块,性能衰减较快等问题。近些年的研究表明,三维多孔结构的LiFePO_4兼具纳米与微米级活性材料的优点,是LiFePO_4正极材料的研究热点和重要的发展方向。本文从合成方法、形貌结构、电化学性能以及结构—性能关系等方面系统总结多孔LiFePO_4材料的研究进展,并展望其发展前景。     

微波功率对(100)晶面取向金刚石薄膜制备的影响

以H2和CH4的混合气体为气源,使用实验室自制10 kW新型装置,采用微波等离子体化学气相沉积法(MPCVD)在Si(100)基体上沉积金刚石薄膜,然后采用扫描电镜(SEM)、Raman光谱以及XRD光谱,以得到表面形貌、样品质量和晶面取向等信息,由此获得微波功率对金刚石薄膜取向的影响。结果表明,微波功率对金刚石膜的质量、表面形貌和晶面取向都有明显地影响,随着微波功率升高,金刚石薄膜的形貌变得规则,薄膜中Isp3/Isp2由1.52提高到6.58,其沉积晶面的I(100)/I(111)由0.38提高到3.93。当微波功率为4 900 W时,所得沉积样品晶面以(100)为主,形貌规则,纯度很高。     

复合金属掺杂的LiFePO4/C复合材料的制备与电化学性能研究

以超声波辅助沉淀法合成的纳米级球形FePO4·2H2O为原料,采用碳热还原法制备了复合金属掺杂的LiFePO4/C复合材料。通过X射线衍射(XRD),扫描电镜(SEM),恒电流充放电测试,循环伏安和交流阻抗测试表征了FePO4·2H2O和LiFePO4/C的物相、结构和电化学性能。结果表明,溶液浓度为0.1 mol/L时制备的FePO4·2H2O为分布均匀的纳米级球形颗粒。复合金属掺杂显著提高了LiFePO4的放电比容量,Ni和Nb复合掺杂的LiFePO4/C复合材料表现出了最佳的电化学性能,0.1 C倍率条件下首次放电容量158.8 mAh/g,1 C倍率下首次放电容量150.2 mAh/g,100次循环后容量保持率分别为98.30%和97.8%。Ni和Nb复合掺杂后提高了LiFePO4的锂离子扩散速率和电导率。     

纯相磷酸铁锂PLD靶材合成和表征

本研究着眼于确定制备纯相Li Fe PO4脉冲激光沉积靶材的合成条件。通过TG-DTA实验分析合成过程,XRD检测确定晶相,SEM观察表面形貌。结果表明,采用液相法在800℃、通有氩气(93%)和氢气(7%)的混合气体中焙烧制得纯相的Li Fe PO4粉末,经压合焙烧获得了纯相、高结晶度、大晶粒的Li Fe PO4靶材。利用脉冲激光技术沉积Li Fe PO4薄膜,薄膜结构致密,晶粒粒径达纳米级别。     

Mg-Co复合掺杂对LiFePO4电化学性能的影响（英文）

通过固相反应制备了Mg2+和Co4+复合掺杂的LiFePO4电极材料。采用X射线衍射、恒电流充放电和循环伏安研究复合掺杂对 LiFePO4结构和电化学性能的影响。结果表明:复合掺杂能够提高 LiFePO4的首次放电比容量,0.1C和1C的放电容量分别达到147.2mA·h/g 和133.3mA·h/g。循环伏安测试结果表明:复合掺杂改善了LiFePO4的导电性能,增强了Li+的脱嵌可逆性。     

镍镁掺杂LiFePO4的电子结构

采用基于密度泛函理论的第一性原理研究锂离子电池正极材料LiFePO4掺杂Ni和Mg的电子结构。结果表明:Ni氧化物的电子结构和能量性质受d轨道中电子影响,用于掺杂改性时,结构稳定,带隙降低使电子电导率增加,充放电速率提高;Mg掺杂改性时,当掺杂在Li位时,带隙和总能均降低,同时Li离子的扩散运动也提高,有利于改性,而在Fe位掺杂时,费米面附近Fe-d轨道中电子影响能带,使带隙增加,不利于电子电导,键的布居分析也表明Li—O共价性增强,不利于离子扩散,即不利于改性。因此,通过掺杂可对LiFePO4的微观结构产生影响,从而影响其电化学性能,但这种微观结构主要受d轨道中电子运动对费米面附近能带的影响,而与掺杂离子的化合价和半径无关。     

球形磷酸铁锂正极材料制备中试研究

用湿法球磨-喷雾干燥法制备LiFe0.98Mg0.02PO4/C复合正极材料;用激光粒度分析仪、X射线衍射仪、扫描电镜和恒流充放电等对前驱体和磷酸铁锂样品进行表征;考察不同球磨工艺对磷酸铁锂颗粒形貌、粒度分布、振实密度和电化学性能的影响。结果表明:用湿法球磨-喷雾干燥法可以制得球形颗粒、高振实密度且电化学性能优良的磷酸铁锂正极材料,原料经粗磨后再超细球磨制得的材料性能更佳,振实密度达1.67 g/cm3,在0.1 C、0.5 C和1.0 C倍率下的首次放电比容量分别为151、143和132 mA·h/g。     

The Growth Habit of Electrodeposited Copper

By plating under base reproduction conditions in an acidified copper sulphate solution, the growth processes occurring at polycrystalline cathodes have been studied and compared with those at single crystal cathodes. It has been found that the surface topography of the deposit formed on any one grain of the polycrystalline aggregate is identical to that of a deposit, grown under similar conditions, on a single crystal of the same orientation. The growth habit is in each case related to the atomic configuration of the initial cathode surface. The thickness of the deposit formed on electropolished polycrystalline strip has been found to vary from grain to grain. This may be explained in terms of electrochemical anisotropy. It has been found that the growth habit of thick deposits (10 microns) formed on deeply etched surfaces is similar to that on electropolished surfaces. Mechanical polishing of the basis metal causes the development of a polycrystalline, textured deposit, although some base influence can be detected even through very thick deposits (40 microns). Under certain conditions, deposits of the base-reproduction type can be obtained from cyanide copper solutions. Such deposits develop well-defined surface structures, with large, regular features and highly reflecting facets.     

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.     

液相法制备磷酸铁锂的研究进展

介绍了锂离子电池正极材料磷酸铁锂（LiFePO4）的晶体结构和充放电特性,评述了固相法和液相法制备LiFePO4。系统介绍了近几年液相法制备LiFePO4的研究进展,包括水热法,溶胶-凝胶法,共沉淀法等。并对LiFePO4正极材料的应用前景做了展望。