不同沉淀剂对Li_(1.1)Ni_(0.5)Mn_(0.5)O_2结构和电化学性能的影响

通过共沉淀-高温煅烧方法合成了层状结构的Li1.1Ni0.5Mn0.5O2正极材料,并通过XRD、SEM研究了不同沉淀剂对产物结构和形貌的影响。运用恒电流充放电测试、CV及EIS研究了其电化学性能。结果表明,不同沉淀剂合成的产物均具有良好的层状结构及形貌。碳酸盐为沉淀剂合成的产物锂镍混排度最小,颗粒更均匀,具有最低的极化及最小的电荷转移阻抗,具有最高的容量及最优的倍率性能。     

溶胶-凝胶法合成LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2及其性能研究

采用溶胶-凝胶法合成了层状正极材料LiNi0.4Co0.2Mn0.4O2,XRD、SEM、EDS和电化学性能测试表明,850℃为最佳煅烧温度,在此温度下合成的材料具有ɑ-NaFeO2层状结构,结晶度最好,Ni、Co、Mn分布均匀。充放电测试在2.0～4.6 V,0.2 C的电流下,材料首次放电比容量为185.6 mAh/g,库伦效率为93.2%;经40次循环后,容量保持率为92.5%,且该材料具有优良的倍率性能。     

细化颗粒固相法合成锂离子电池正极材料LiNi_(0.80)Co_(0.15)Al_(0.05)O_2及其结构和电化学性能研究

利用超细旋转盘式砂磨机细化颗粒固相烧结法,合成锂离子电池正极材料Li Ni0.80Co0.15Al0.05O2。原料经过砂磨后,混合均匀,粒径达到纳米级。根据塔曼定理,混合均匀的微小粒径可以在相同的烧结温度下,提高烧结的强度。SEM、XRD分别表征NCA材料的颗粒形貌和晶形结构。结果显示,通过细化颗粒烧结后的样品具有良好的形貌和层状结构。CV法测试样品的氧化还原性能,电池测试系统测试样品的电化学性能。测试结果显示,经过细化颗粒,在720℃合成的NCA材料具有良好的层状结构,018/110峰分裂明显。样品的电化学性能优良,0.2C下,首次放电容量达到182 m Ah?g?1,30次循环后容量保持率99.9%。1C下,首次放电容量153 m Ah?g?1,100次循环后容量保持率92.6%。     

层状锂离子正极材料Li_(1+x)(Co_(0.2)Ni_(0.4)Mn_(0.4))O_2的结构和电化学性能的研究

采用溶胶凝胶法,用柠檬酸作为鳌合剂,在不同的温度下合成制备均一的层状锂离子正极材料Li(Co0.2Ni0.4Mn0.4)O2。XRD、SEM实验数据表明,在较低温度700°C下便可制得层状Li1+x(Co0.2Ni0.4Mn0.4)O2,并具有均一的颗粒形貌,颗粒大小为300 nm左右。XPS显示其正极材料中的Co、Ni、Mn的化学价态分别为+3,+2,+4,均为它们的稳定价态。700°C下合成的材料在20mA/g,2.9~4.6 V电压范围内,首次放电比容量为210.2 mAh/g,50周后放电比容量仍高达185.3 mAh/g,容量损失为11.84%。     

Mg2+和F-共掺杂提高LiNi0.8Co0.15Al0.05O2电化学性能

采用传统固相法对锂离子电池富镍系LiNi0.8Co0.15Al0.05O2正极材料进行了Mg2+和F-共掺杂改性研究,借助X射线衍射(XRD)、XRD数据精修、扫描电子显微镜(SEM)、恒电流充放电测试、循环伏安曲线(CV)和电化学阻抗谱(EIS)等手段探究Mg2+和F-共掺杂对材料晶体结构、表面形貌和电化学性能的影响.物理测试表明,Mg2+和F-共掺杂后正极材料仍保持α-NaFeO2结构,无杂质生成,且共掺杂后正极材料晶胞参数增大,离子混排程度降低,这有利于Li+在晶格中的脱嵌迁移.此外,共掺杂后正极材料的微观形貌未发生明显变化.电化学性能表明,Mg2+和F-共掺杂样品表现出优异的电化学性能,1C倍率下循环200圈后,放电比容量仍保持有144.1mAh·g-1,容量保持率高达83.1％.优异的电化学性能归因于Mg2+和F-稳定了材料的晶体结构,减少了材料极化,抑制了电池电荷转移阻抗的增加.本工作的开展为其他锂离子电池正极材料性能提升提供了思路.     

钴掺杂对Li1.2Mn0.6Ni0.2O2电化学性能的影响

利用共沉淀法制备了锂离子电池正极材料Li1.2Mn0.6Ni0.2O2和Li1.2Mn0.588Ni0.196Co0.016O2,并利用XRD、SEM和充放电测试对其晶体结构、形貌和电化学性能进行了表征.XRD结果表明:掺杂钴材料后,材料的层状结构保持完整,阳离子混排程度降低.电化学性能测试结果表明:掺钴材料的首次充放电效率和倍率放电性能明显优于Li1.2Mn0.6Ni0.2O2,且表现出较优的循环性能,其1、2、5C放电比容量分别为230.3、215.6、155.6 mA·h/g,1 C下循环50次的容量保持率为90.9％.     

共沉淀法制备Li[Ni_(l/3)Co_(1/3)Mn_(1/3)]O_2及电化学性能研究

采用NH3-NaOH共沉淀法合成了Li[Nil/3Co1/3Mn1/3]O2正极材料,通过改变NH3·H2O浓度及加料方式研究材料的电化学性能。采用XRD、SEM对晶体的结构和形貌作表征。将正极材料Li[Nil/3Co1/3Mn1/3]O2制成电极极片,组装成电池进行测试。分析测试结果表明,合成的极材料Li[Nil/3Co1/3Mn1/3]O2具有典型的α-NaFeO2结构,粒径分布较好,呈类球形。     

正极材料LiNi_(0.7)Co_(0.3)O_2合成条件及电化学性能研究

采用溶胶凝胶法制备了LiNi0.7Co0.3O2。结果表明,煅烧温度为800℃、时间为12 h、Li/(Ni+Co)=1.05的正极材料LiNi0.7Co0.3O2具有α-NaFeO2型的六方晶体结构,在0.1 C下,首次充放电比容量分别为218.0 mAh/g和190.2 mAh/g,首次充放电效率为87.2%,经过20次循环仍有171.5 mAh/g,容量保持率为90.3%。     

锂离子电池正极材料Li_(1.2)Ni_(0.16)Co_(0.12)Mn_(0.52)O_2的溶胶-凝胶制备与电化学性能研究

以柠檬酸作为螯合剂,通过简单的溶胶-凝胶法制备了富锂层状氧化物Li1.2Ni0.16Co0.12Mn0.52O2纳米颗粒。X射线衍射(XRD)和透射电子显微镜(TEM)结果显示:尺寸在100~300 nm的产物具有良好的六方层状结构。作为锂离子电池正极活性物质,在0.1C电流密度和2.0~4.7 V电压区间,Li1.2Ni0.16Co0.12Mn0.52O2电极的初始放电比容量为245.9 mAh·g-1;在0.5C的电流密度下,经过60次循环容量保持率达到97.3%;同时在5C这样高的电流密度下,放电容量也能稳定在115.8 mAh·g-1。     

金属离子浓度对LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2材料结构及电化学性能影响研究

采用液相共沉淀+高温煅烧法制备正极材料LiNi0.5Co0.2Mn0.3O2,利用XRD、SEM及恒电流充放电等等分析手段,研究不同金属离子浓度合成镍钴锰酸锂前驱体对最终产品晶体结构、形貌及其电化学性能的影响。结果表明:金属离子浓度为2.0 mol/L时,所制备材料晶型层状结构发育完整,粒径分布均匀,球形度高且表面光滑,材料首次放电比容量达172.5 mAh/g,首次库伦效率为90.84%。     

LiNi0.8Co0.15Al0.05O2 cathode materials prepared by TiO2 nanoparticle coatings on Ni0.8Co0.15Al0.05(OH)2 precursors

Synthesis, electrochemical, and structural properties of LiNi_0.8Co_0.15Al_0.05O₂ cathodes prepared by TiO₂ nanoparticles coating on a Ni_0.8Co_0.15Al_0.05(OH)₂ precursor have been investigated by the variation of coating concentration and annealing temperature. TiO₂-coated cathodes showed that Ti elements were distributed throughout the particles. Among the coated cathodes, the 0.6 wt% TiO₂-coated cathode prepared by annealing at 750 °C for 20 h exhibited the highest reversible capacity of 176 mAh g⁻¹ and capacity retention of 92% after 40 cycles at a rate of 1C (=190 mA g⁻¹). On the other hand, an uncoated cathode showed a reversible first discharge capacity of 186 mAh g⁻¹ and the same capacity retention value to the TiO₂-coated sample at a 1C rate. However, under a 1C rate cycling at 60 °C for 30 cycles, the uncoated sample showed a reversible capacity of 40 mAh g⁻¹, while a TiO₂-coated one showed 71 mAh g⁻¹. This significant improvement of the coated sample was due to the formation of a possible solid solution between TiO₂ and LiNi_0.8Co_0.15Al_0.05O₂. This effect was more evident upon annealing the charged sample while increasing the annealing temperature, and at 400 °C, the coated one showed a more suppressed formation of the NiO phase from the spinel LiNi₂O₄ phase than the uncoated sample.     

Modeling the impedance versus voltage characteristics of LiNi0.8Co0.15Al0.05O2

The power-delivery capability of lithium-ion cells based on LiNi_0.8Co_0.15Al_0.05O₂-based positive electrodes shows a significant dependence on the cell's state-of-charge. One reason for this behavior is the variation of the positive electrode's impedance with the oxide's lithium content. In this article, an electrochemical model based on concentrated solution porous electrode theory is used to model impedance data obtained on LiNi_0.8Co_0.15Al_0.05O₂-based positive electrodes charged to potentials ranging from 3.55 to 4.55 V versus Li. The parameters obtained from model fits include the exchange-current density and Li-ion diffusion coefficients in the oxide. The variations in these parameters with oxide potential are correlated with structural changes in the material observed during Li-ion intercalation-deintercalation reactions.     

Improved electrochemical properties of Li1.2Ni0.18Mn0.59Co0.03O2 by surface modification with LiCoPO4

Lithium-rich nickel–manganese–cobalt oxide, Li_1.2Ni_0.18Mn_0.59Co_0.03O₂, prepared by spray-dry process, exhibits rapid capacity fade and poor rate capability. The surface of Li_1.2Ni_0.18Mn_0.59Co_0.03O₂ can be modified with LiCoPO₄ through co-precipitation method in order to improve its electrochemical properties. The resultant LiCoPO₄ particles are in nano-scale and accumulate on the surface of the Li_1.2Ni_0.18Mn_0.59Co_0.03O₂ particles. The surface modification by LiCoPO₄ is shown to significantly improve both the cyclic performance and the rate capability of Li_1.2Ni_0.18Mn_0.59Co_0.03O₂.     

X-ray absorption study on LiNi0.8Co0.15Al0.05O2 cathode material for lithium-ion batteries

LiNi_0.8Co_0.15Al_0.05O₂, being one of the promising cathode materials for lithium-ion batteries, shows distinct capacity fades after charge/discharge cycling and/or storage at high temperatures. The origin of the capacity fade has been explored by investigating the electronic and structural changes of the cathode material using X-ray absorption spectroscopy (XAS). Ni K-edge XAS measurements were performed in two different modes: surface-sensitive conversion electron yield (CEY) mode and bulk-sensitive transmission mode. Ni K-edge XANES data revealed that, after the cycling and aging tests, the bulk-averaged Ni valences were reduced, implying the existence of divalent Ni atoms. Further reductions of Ni atoms were observed at the surface of the cathode material particles, and the ranges of the Ni valence change upon charging became narrower, indicating the existence of the Ni atoms that did not oxidize. These changes which occur prominently at the surface are probably the main causes of the capacity fade.     

Aging characteristics of high-power lithium-ion cells with LiNi0.8Co0.15Al0.05O2 and Li4/3Ti5/3O4 electrodes

The impedance rise that results from the accelerated aging of high-power lithium-ion cells containing LiNi_0.8Co_0.15Al_0.05O₂-based positive and graphite-based negative electrodes is dominated by contributions from the positive electrode. Data from various diagnostic experiments have indicated that a general degradation of the ionic pathway, apparently caused by surface film formation on the oxide particles, produces the positive electrode interface rise. One mechanistic hypothesis postulates that these surface films are components of the negative electrode solid electrolyte interphase (SEI) layer that migrate through the electrolyte and separator and subsequently coat the positive electrode. This hypothesis is examined in this article by subjecting cells with LiNi_0.8Co_0.15Al_0.05O₂-based positive and Li_4/3Ti_5/3O₄-based negative electrodes to accelerated aging. The impedance rise in these cells was observed to be almost entirely from the positive electrode. Because reduction products are not expected on the 1.55 V Li_4/3Ti_5/3O₄ electrode, the positive electrode impedance cannot be attributed to the migration of SEI-type fragments from the negative electrode. It follows then that the impedance rise results from mechanisms that are “intrinsic” to the positive electrode.     

Fine-sized LiNi0.8Co0.15Mn0.05O2 cathode particles prepared by spray pyrolysis from the polymeric precursor solutions

Fine-sized LiNi_0.8Co_0.15Mn_0.05O₂ cathode particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from the polymeric precursor solutions. The cathode particles obtained from the spray solution without polymeric precursors had irregular morphology and hardly aggregated morphology. On the other hand, the cathode particles obtained from the spray solution with citric acid and ethylene glycol had fine size and regular morphologies. The cathode particles obtained from the spray solution containing adequate amounts of citric acid and ethylene glycol had several hundreds nanometer and narrow size distribution. The maximum discharge capacity of the cathode particles was 218 mAh/g when the excess of lithium component added to the spray solution was 6 mol% of the stoichiometric amount to obtain the LiNi_0.8Co_0.15Mn_0.05O₂ particles. The discharge capacities of the fine-sized LiNi_0.8Co_0.15Mn_0.05O₂ particles dropped from 218 to 213 mAh/g by the 50th cycle at a current density of 0.1 C.     

Impact of cobalt substitution for manganese on the structural and electrochemical properties of LiNi0.5Mn0.5O2

A series of LiNi_0.5Mn_0.5−xCo_xO₂ (0 ≤ x ≤ 0.5) compounds was prepared by a solid state reaction, and their structure, surface state and electrochemical characteristics were also investigated by XRD, XPS, EIS and charge-discharge cycling. The non-equivalent substitution of cobalt for manganese induced an increase in the average valence of nickel, thereby shrinking in the lattice volume. Moreover, Co non-equivalent substitution could not only reduce the impurity content but also significantly decreased the charge transfer resistance, thereby improving the rate capabilities.     

A comparison of preparation method on the electrochemical performance of cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion battery

Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m² g⁻¹). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g⁻¹ at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.     

Study on the phase structure and electrochemical properties of RE0.93Mg0.07Ni2.96Co0.60Mn0.37Al0.17 hydrogen storage alloy

In our endeavor to improve overall properties of the La-Mg-Ni-Co type alloys, RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 hydrogen storage electrode alloy with low magnesium content was obtained by inductive melting. The phase structure and electrochemical characteristics of the alloy were investigated by XRD and electrochemical measurement. The results indicate that RE_0.93Mg_0.07Ni_2.96Co_0.60 Mn_0.37Al_0.17 alloy has multi-phase microstructure containing the CaCu₅ structure of LaNi₅ phase as matrix phase and a little of LaNi₃ phase as the secondary phase. The maximum discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy reaches 359 mAh/g, which is 7.2% higher than that of commercial AB₅ alloy electrode. The discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy electrode at 233 K is up to 147 mAh/g, which is 308.3% higher than that of commercial AB₅ alloy electrode. Meanwhile, the discharge capacity of RE_0.93Mg_0.07Ni_2.96Co_0.60Mn_0.37Al_0.17 alloy can reach 92.7% of commercial AB₅ alloy after 100 charge/discharge cycles.     

Effects of gradient concentration on the microstructure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials

Nickel(Ni)-rich layered materials have attracted considerable interests as promising cathode materials for lithium ion batteries (LIBs) owing to their higher capacities and lower cost. Nevertheless, Mn-rich cathode materials usually suffer from poor cyclability caused by the unavoidable side-reactions between Ni⁴⁺ ions on the surface and electrolytes. The design of gradient concentration (GC) particles with Ni-rich inside and Mn-rich outside is proved to be an efficient way to address the issue. Herein, a series of LiNi_0.6Co_0.2Mn_0.2O₂ (LNCM622) materials with different GCs (the atomic ratio of Ni/Mn decreasing from the core to the outer layer) have been successfully synthesized via rationally designed co-precipitation process. Experimental results demonstrate that the GC of LNCM622 materials plays an important role in their microstructure and electrochemical properties. The as-prepared GC3.5 cathode material with optimal GC can provide a shorter pathway for lithium-ion diffusion and stabilize the near-surface region, and finally achieve excellent electrochemical performances, delivering a discharge capacity over 176 mAh·g⁻¹ at 0.2 C rate and exhibiting capacity retention up to 94% after 100 cycles at 1 C. The rationally-designed co-precipitation process for fabricating the Ni-rich layered cathode materials with gradient composition lays a solid foundation for the preparation of high-performance cathode materials for LIBs.