石墨烯/富锂三元正极复合材料的制备及电化学性能研究

通过水热法制备了石墨烯包覆量不同的石墨烯/富锂三元正极复合材料。采用X射线衍射仪、扫描电子显微镜和电化学交流阻抗等对包覆后富锂三元正极复合材料的物相结构、形貌及电化学性能进行了研究。结果表明:石墨烯包覆量为2%(质量分数)时,包覆效果较好,石墨烯/富锂三元正极复合材料首次库仑效率为89.6%,比富锂三元正极材料提高了17.16%,放电比容量为226.41mAh/g,比原材料提高了21.38mAh/g;以0.5C循环100次后石墨烯/富锂三元正极复合材料放电比容量可保持在154mAh/g,容量保持率为88%,比富锂三元正极材料提高了5.3%;石墨烯/富锂三元正极复合材料阻抗为75Ω,比富锂三元正极材料阻抗低50Ω。     

Li1.15-xNi0.33Co0.33Mn0.33O2+δ溶胶-凝胶法合成、表征及合成机理

以可溶性盐为原料采用溶胶-凝胶法合成了具有六方层状结构的Li1．15-xNi0．33Co0．33-Mn0．33O2-δ（LNCMO）固溶体．用X射线衍射（XRD）、光电子能谱（XPS）、扫描电镜（SEM）、循环伏安（CV）、充放电测试等表征了其结构、形貌、过渡金属元素的离子价态及电化学性能，结合热重-差热分析（TG—DTA）及变温过程XRD结果分析了合成机理．950℃样品以0．1mA／cm^2的电流密度在2．5-4．5V间首次放电容量为190mAh／g，循环10次后为180mAh／g，表明样品具有较好的电化学性能．前驱物在较低温度下分解即可形成层状LNCMO主相，高温焙烧不仅可稳定材料的层状结构，而且能显著提高其结晶性，固溶体的形成可分为以下三步；（1）前驱物氧化分解的同时生成Li—Ni—Co-Mn-O固溶体；（2）残余的Li2CO3分解产生Li2O；（3）表面的Li2O逐步扩散到固溶体内部，形成单相Li—Ni—Co-Mn-O固溶体．     

LiLaPO4-coated Li[Ni0.5Co0.2Mn0.3]O2 and AlF3-coated Li[Ni0.5Co0.2Mn0.3]O2 blend composite for lithium ion batteries

A blended composite of LiLaPO₄-coated Li[Ni_0.5Co_0.2Mn_0.3]O₂ and AlF₃-coated Li[Ni_0.5Co_0.2Mn_0.3]O₂ was tested as the cathode of lithium secondary batteries. The rate capability, cyclic performance, and thermal stability of the blended electrode were characterized and compared with pristine, AlF₃-coated, and LiLaPO₄-coated electrodes. The blended sample showed good cyclic performance and thermal stability, which implies that blending these two cathode coatings were effective in obtaining their advantages and lessening their weaknesses.     

Novel hollow Ni0.33Co0.67Se nanoprisms for high capacity lithium storage

In this work, homogeneous Ni_0.33Co_0.67Se hollow nanoprisms were synthesized successfully in virtue of Kirkendall effect. It is the first time for bimetallic Ni-Co compounds Ni_0.33Co_0.67Se to be used in lithium-ion batteries (LIBs). Impressively, the Ni_0.33Co_0.67Se hollow nanoprisms show superior specific capacity (1,575 mAh/g at the current density of 100 mA/g) and outstanding rate performance (850 mAh/g at 2,000 mA/g) as anode material for LIBs. This work proves the potential of bimetallic chalcogenide compounds as high performance anode materials for LIBs.

     

Li2ZrO3包覆锂离子电池正极材料Li[Li0.2Ni0.2Mn0.6]O2的制备及其电化学性能

富锂锰基材料因其具有较高的充放电比容量而备受关注。针对其首次库仑效率低、循环和倍率性能差的问题,将具有三维Li^+通道的锂离子导体Li2ZrO3引入至富锂锰基正极材料Li[Li0.2Ni0.2Mn0.6]O2的表面对其进行包覆改性研究。通过XRD,TEM,SEM,EDS综合分析可知:Li2ZrO3成功包覆到样品表面。包覆层厚度为3 nm(包覆量1%,质量分数)时复合材料的电化学性能得到显著提升。0.1 C(1 C=200 mAh·g^-1)倍率下首次放电比容量可达271.5 mAh·g^-1,库仑效率为72.4%,降低了首次不可逆容量损失;0.5 C下循环100周次后放电比容量为191.5 mAh·g^-1,容量保持率为89.5%,5 C倍率放电比容量为75 mAh·g^-1,倍率性能提升。适当厚度的均匀Li2ZrO3包覆层可在样品表面形成核壳结构使样品更稳定,减少表面副反应,阻止生成较厚SEI膜,这得益于Li2ZrO3本身的高电导率、高电化学稳定性和较好的锂离子传导性。     

层状正极材料Li[Li0.2Mn0.54Ni0.13Co0.13-xAlx]O2的合成及其电化学性能研究

采用溶胶-凝胶法合成层状正极材料Li[Li0.2Mn0.54Ni0.13Co0.13-xAlx]O2(x=0,0.05,0.13)。用X射线衍射(XRD)、循环伏安(CV)和充放电测试等手段对产物的结构及电化学性能进行了表征。结果表明:采用溶胶-凝胶法在900℃空气氛围下煅烧12h制备的Li[Li0.2Mn0.54Ni0.13Co0.08Al0.05]O2晶型较好,具有α-NaFeO2型层状结构。室温,2.0～4.8V下,0.1C倍率下最高放电比容量达到268.3mAh/g,0.2C倍率下循环50次后比容量依然高达238.1mAh/g,具有良好的电化学性能。     

钠离子电池正极材料P2-Nax[Mg0.33Mn0.67]O2的电化学活性研究

钠离子电池具有成本低廉、原料分布广泛等优点,是锂离子电池正极材料的最佳替代材料.在具有层状结构的P2相NaMnO2正极材料中,对过渡金属层进行二元固溶可有效提升电极材料的电化学性能.本研究利用库仑模型构建了Mg离子固溶的Nax[Mg0.33Mn0.67]O2结构模型.通过第一性原理计算发现,在钠离子含量小于0.67时,...     

TiO2(B)表面修饰富锂层状氧化物Li(Li0.17Ni0.2Mn0.58Co0.05)O2正极材料

采用喷雾干燥法和沉淀法, 制备了表面修饰TiO₂(B) (2wt%、4wt%、6wt%和8wt%)的富锂层状氧化物Li(Li_0.17Ni_0.2Mn_0.58Co_0.05)O₂正极材料。X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)结构测试分析结果表明, 修饰TiO₂(B)后样品的体相结构仍然保持初始样品的层状结构, 仅氧化物颗粒表面附着有少量TiO₂(B)纳米晶。示差扫描量热测试(DSC)表明, 与初始样品比较, 修饰TiO₂(B)后样品的热稳定性得到明显改善。在2.0~4.8 V范围内进行恒流电化学性能测试。研究显示, 在0.1C(1C=300 mA/g)倍率下, 修饰4wt%TiO₂(B)样品的首次放电比容量可达296.4 mAh/g, 首次库伦效率则由初始样品的77.7%提升到修饰TiO₂(B)后样品的84.3%, 100周循环后电极容量保持率由初始样品的69.5%提升到修饰TiO₂(B)后样品的80.2%。即使在阶梯倍率的2C倍率下, 修饰4wt%TiO₂(B)的样品仍具有较高的电化学容量(166.5 mAh/g)。以上研究结果表明, 表面修饰TiO₂(B)纳米晶可以显著改善富锂层状氧化物Li(Li_0.17Ni_0.2Mn_0.58Co_0.05)O₂的热稳定性和电化学性能。     

Layered K0.54Mn0.78Mg0.22O2 as a high-performance cathode material for potassium-ion batteries

Layered Mn-based oxides are one of the promising cathode materials for potassium-ion batteries(KIBs)owing to their high theoretical capacities,abundant material...     

铝掺杂的富锂正极材料Li[Li0.2Mn0.4Fe0.3Al0.1]O2的合成及电化学性能研究

用共沉淀法合成了用铝掺杂的铁部分取代锰的富锂正极材料Li[Li0.2Mn0.4Fe0.3Al0.1]O2。采用XRD、SEM、电化学测试等方法对样品进行表征。结果表明,与Li[Li0.2Mn0.45Fe0.35]O2相比,Li[Li0.2Mn0.4Fe0.3Al0.1]O2具有较好的电化学性能,其初始容量达到241mAh/g左右,经50次充放电循环后,容量衰减率在7%左右。     

Influence of solvents on the synthesis and electrochemical properties of Li[Li1/5Ni1/10Co1/5Mn1/2]O2 for the applications in lithium-ion batteries

The solid solution of Li[Li_1/5Ni_1/10Co_1/5Mn_1/2]O₂ was synthesized using starting materials with two different functional groups (hydroxide and acetate) in the presence of a reaction medium ethanol or acetone using solid-state reaction method. The prepared samples were found to posses layered structure and their electrochemical properties were greatly influenced by the functional group of the starting materials. The samples which were prepared with same functional group offered better electrochemical properties and addition of solvents during the ball milling of the samples has considerably enhanced the diffusivity of the chemical species in the layered compound. The electrochemical properties and the influence of starting materials on the added solvents are discussed.     

Ce-modified LiNi0.5Co0.2Mn0.3O2 cathode with enhanced surface and structural stability for Li ion batteries

The well-established LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode materials possess a broad prospect for Li-ion batteries. However, the NCM523 still suffers severe capacity fading and structural instability. In this research, Ce-doped and CeO₂-coated NCM523 cathode materials are synthesized by a smart one-step calcination process. It is found that the CeO₂ coating layer is formed during high-temperature calcination. The CeO₂ coating layers stop the electrode from being exposed to the electrolyte directly and promote the kinetics of lithium deintercalation. Besides, Ce doping could suppress the bulk cation-mixing degree. Electrochemical tests suggest that Ce-modification improves the capacity retention of cathode materials. The optimized Ce-modification cathode material, among 2.7 V and 4.6 V, not only shows the best capacity retention of 76.2%, but also delivers a discharge capacity of 178.2 mAh g^?1 at 1 C. This smart modification strategy provides novel ideas for advanced LIBs.     

Electrochemical and thermal behaviour of Li[Li(x)(Ni0.3Co0.1Mn0.6)1 - x]O2 (x = 0.09, 0.11) cathode Materials for lithium rechargeable batteries

High rate capable Mn-rich layered Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, 0.11) cathode materials that are fully charged are investigated with respect to stability. Differential scanning calorimetry is used to determine the thermal stability of cathode material compositions together with PVdF binder and a conductive agent by heating from 30 degrees C to 400 degrees C at 10 degrees C/min. In the Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, x = 0.11) cathode materials, the exothermic reaction started at 100 degrees C. Due to thermal runway, a sharp peak was observed at 279.25 degrees C for the material of x = 0.09 with exothermic heat generation of 168.4 J/g. For the Mn-rich cathode material, where x = 0.11, two relatively smaller peaks appeared at 250.72 degrees C and 268.60 degrees C with heat evolution of 71.49 J/g and 93.67 J/g, respectively. These layered cathode materials are thermally stable. The x = 0.09 composition shows huge heat flow occurrence when compared to the x = 0.11. It is concluded from a heat generation analysis that the two Mn-rich cathode materials are thermally stable for lithium rechargeable batteries.     

Preliminary studies of mn-rich Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, 0.11) as cathode active materials for lithium rechargeable batteries

Novel cathode active materials, Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, 0.11) composed of rod-like primary particles, but aggregated spherical shape in appearance, were synthesized. The newly Mn-rich cathode active materials were then adopted as cathodes to show the benefits for Li-ion rechargeable batteries. The results show that to use proper nano-scaled particles as a cathode and to make homogeneous particle sizes have great improvements on electrochemical performances, probably ascribed to enhancement of charge transfer kinetics and lower cell impedance at high voltage region (approximately 4.6 V). The electrochemical performances of Mn-rich cathodes were investigated by cycler (BT2000, Arbin), comparing electrochemical behaviors between room and elevated temperature, 55 degtees C. The morphology of cathodes having nano-scaled particles of active materials and the Mn-rich cathode active materials were investigated using field emission scanning electron microscope (FE-SEM) and field emission transmission electron microscope (FE-TEM), also the crystalline phase identification was analyzed by high power X-ray diffractometer (XRD).     

Electrochemical Aging Protocol Governed Capacity Losses and Structure Degradations in Layered LiNi0.8Co0.1Mn0.1O2 Oxides

The comparatively poor endurance of Ni-rich cathode materials restricts their application in high-energy lithium-ion batteries. A thorough understanding of the degradation characteristics of such materials under complex electrochemical aging protocols is required to further improve their reliability. In this work, the irreversible capacity losses of LiNi_0.8Mn_0.1Co_0.1O₂ under different electrochemical aging protocols are quantitatively evaluated via a well-designed experiment. In addition, it is discovered that the origin of irreversible capacity losses is highly related to electrochemical cycling parameters and can be divided into two types. Type I is heterogeneous degradation caused by low C-rate or high upper cut-off voltage cycling and features abundant capacity loss during H2-H3 phase transition. Such capacity loss is attributed to the irreversible surface phase transition that limits the accessible state of charge during the H2-H3 phase transition stage via the pinning effect. Type II is fast charging/discharging induced homogeneous capacity loss that occurs consistently throughout the whole phase transition time. This degradation pathway shows a distinctive surface crystal structure, which is dominated by a bending layered structure rather than a typical rock-salt phase structure. This work offers detailed insight into the failure mechanism of Ni-rich cathodes and provides guidance on designing long-cycle life, high-reliability electrode materials.     

The effect of addition of alcohol and calcination methods on the synthesis of layered Li[Li1/5Ni1/10Co1/5Mn1/2]O2 using solid-state reaction method

Li[Li_1/5Ni_1/10Co_1/5Mn_1/2]O₂ solid solutions were prepared by four different routes using a solid-state reaction method. All the prepared samples were of a layered manganese oxide structure. The prepared samples were subjected to XRD, Raman and charge–discharge studies. The addition of ethyl alcohol in the starting materials during the synthesis process has exhibited superior electro-chemical properties and offered higher discharge capacity than the samples calcinated in the form of pellets without solvent. The added ethyl alcohol not only assists to get a homogeneous mixing of reacting species, but also influences the chemical reaction during the synthesis process. The materials are found to be superior in terms of minimum capacity fading per cycle than the materials so far reported. The other electro-chemical properties like irreversible capacity and discharge capacity of the synthesized materials have also been discussed based on the experimental observations.