摘要
随着能源环境问题的日益突出以及现代化科技的高速发展,提高电池性能已是迫切需求。锂离子电池以其高能量密度、不污染环境、长循环寿命、高工作电压等优势而成为人们的首选。开发成本低、容量高的新型正极材料是当今国际的发展趋势。锂离子电池LiNixCo1-2xMnxO2正极材料正是具有比容量高、成本低等优点而被认为是最有潜力的新型正极材料之一。
首先,本文采用高温固相法合成了锂离子电池正极材料LiNixCo1-2xMnxO2。通过XRD和SEM对其结构和形貌进行表征,通过考察x值、Li/(Ni+Co+Mn)摩尔比、焙烧温度、煅烧时间对其电化学性能的影响,确定了最佳烧结条件。研究结果发现,提高Co含量可以改善材料的循环性能;当n(Li)/n(M)=1.10,950℃煅烧20h时,可得到电化学性能优良的正极材料。
研究了不同合成方法对LiNi0.4Co0.2Mn0.4O2正极材料的表面形貌、晶格常数、粒径分布、比表面积和电化学性能的影响,研究发现共沉淀法合成的材料粒径和形貌可以得到有效控制。接下来又进一步研究了不同沉淀剂对LiNi0.4Co0.2Mn0.4O2性能的影响。研究发现以NaOH+NH3和Na2CO3为沉淀剂均可以得到性能较好的正极材料,但选用Na2CO3作为沉淀剂制备更为方便。
通过掺杂对LiNixCo1-2xMnxO2正极材料进行改性方面的研究。采用高温固相法制备了阴离子掺杂型LiNi0.45Co0.1Mn0.45O2-xFx正极材料。结果表明当掺杂量x=0.25时,在3-4.3V充放电条件下,首次放电容量为138.58 mAh/g,20周循环后的容量保持率为92.47% ,循环性能得到了很大提高。采用共沉淀法制备了阳离子掺杂型Li(Ni0.4Co0.2Mn0.4)1-yCryO2正极材料。结果表明当y=0.02时,在3-4.3V充放电条件下,20周循环后的容量保持率为90.35%,循环性能得到一定程度的改善。
Along with the increase of energy and environment problems, and the rapid development of modern science and technology, how to increase the performances of the lithium ion batteries becomes more and more important. The lithium-ion battery is the first choice for its high energy density, amity to the environment, long cycle life and the high working voltage. Researches on the new cathode materials with low cost and high capacity are the developing trend of conventional cathode materials. As a new generation cathode materials, LiNixCo1-2xMnxO2 cathode material has great potential for being a new kind of cathode candidate for its excellent electrochemical performance and low cost .
Firstly, the LiNixCo1-2xMnxO2 cathode material for lithium-ion battery was synthesized by high temperature solid-state method. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the structure and appearance of the products.The effect of x values,Li/(Ni+Co+Mn) molar ratios,sintering temperatures and sintering times on performances of LiNixCo1-2xMnxO2 were studied, on this basis, the optimized flowsheet was obtained. The results showed that the cycling performance was improved with higher Co content. The cathode material with excellent electrochemical performance was obtained by sintering the mixed raw materials with n(Li)/n(M)=1.10 at 950℃for 20h.
The effect of synthesis method, on surface topography, lattice parameter, particle size distribution, specific surface area and electrochemical performance were studied. It was found that the particle size and morphology can be controlled by co-precipitation method. Further studies with different precipitating agent on the performance of LiNi0.4Co0.2Mn0.4O2 had been made. The sample prepared by co-precipitation method with NaOH+NH3 and Na2CO3 as precipitating agent exhibited good properties and Na2CO3 as precipitating agent is more easily carried out for preparation.
Layered cathode material was modified by doping method. The anion-doping LiNi0.45Co0.1Mn0.45O2-xFx cathode material was synthesized by high temperature solid-state method. The results showed that when x=0.25, LiNi0.45Co0.1Mn0.45O2-xFx exhibited the initial capacity of 138.58 mAh/g in the voltage range of 3-4.3V, its capacity retained 92.47% after 20 cycles. The cycling performance of LiNi0.45Co0.1Mn0.45O2-xFx had been improved significantly. The cation-doping Li(Ni0.4Co0.2Mn0.4)1-yCryO2 cathode material was synthesized by co-precipitation method. The results showed that when y=0.02, Li(Ni0.4Co0.2Mn0.4)1-yCryO2 exhibited that its capacity retained 90.35% after 20 cycles in the voltage range of 3-4.3V. The cycling performance of Li(Ni0.4Co0.2Mn0.4)1-yCryO2 had been improved.
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