5 V正极材料LiNi0.5Mn1.5O4的自蔓延燃烧合成及性能

通过自蔓延燃烧方法合成了性能优良的高电位5V锂离子电池正极材料LiNi0.5Mn1.5O4,利用傅立叶红外光谱(FTIR)、热分析(DSC/TG)、X射线衍射(XRD)、透射电镜(TEM)等方法对前驱物及样品的结构和物化性质等进行了分析和表征,考察了材料的电化学性能。结果表明,所制备样品具有单一的尖晶石相结构,具有4.7V充放电平台;在3.5V到5.2V之间进行充放电性能测试具有131mAh·g-1以上的可逆容量;在2C倍率下循环100次后的容量保持率为96%以上。     

Electrochemical performance of nano-sized ZnO-coated LiNi0.5Mn1.5O4 spinel as 5 V materials at elevated temperatures

ZnO-coated LiNi_0.5Mn_1.5O₄ powders with excellent electrochemical cyclability and structural stability have been synthesized. The electrochemical performance and structural stability of ZnO-coated LiNi_0.5Mn_1.5O₄ electrodes in the 5 V region at elevated temperature has been studied as function of the level of ZnO coating. The 1.5 wt% ZnO-coated LiNi_0.5Mn_1.5O₄ electrode delivers an initial discharge capacity of 137 mAh g⁻¹ with excellent cyclability at elevated temperature even at 55 °C. The reason for the excellent cycling performance of ZnO-coated LiNi_0.5Mn_1.5O₄ electrode is largely attributed to ZnO playing an important role of HF getting in the electrolyte.     

Glycine-assisted combustion synthesis and electrochemical behavior of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>2</Subscript> nanoparticles under microwave irradiation

Layered LiNi_0.5Mn_0.5O₂ nanoparticles have been successfully prepared by the glycine-assisted combustion method under microwave irradiation. The exothermic reaction can generate a large quantity of heat rapidly leading to the formation and crystallization of LiNi_0.5Mn_0.5O₂. From the X-ray diffraction and scanning electronic microscopy results, the resulting powders have a well-developed layered structure and average particle-size is about 80 nm. The chemical composition analysis and electrochemical characteristics of the obtained LiNi_0.5Mn_0.5O₂ nanoparticles as cathode material for rechargeable lithium-ion battery were also investigated. The improved electrochemical performances of the layered LiNi_0.5Mn_0.5O₂ nanoparticles might be ascribed to the nanostructure of the powders and the unique combustion synthesis under microwave irradiation.     

凝胶燃烧法合成5V级正极材料LiNi_(0.5)Mn_(1.5)O_4及其高倍率放电性能

采用聚乙烯吡咯烷酮(PVP)作为络合剂和燃料以凝胶燃烧法制备了具有优异高倍率放电性能的亚微米LiNi0.5Mn1.5O4材料.用热重/差热分析(TG/DTA)研究了凝胶的燃烧过程,用X射线衍射(XRD)、扫描电镜(SEM)和循环伏安(CV)研究了LiNi0.5Mn1.5O4材料的结构和形貌.结果表明材料为结晶良好的纯尖晶石相结构,由5μm左右的二次颗粒组成,颗粒大小分布均匀,一次晶粒发育良好,粒径在500nm左右.充放电测试表明材料的倍率性能和循环性能十分优异.在3.5至4.9V进行充放电测试,0.5C、1C、4C、8C和10C倍率下放电容量分别为131.9、127.6、123.4、118.4和113.7mAh·g-1.在10C大倍率放电条件下循环100、500和1000次的容量保持率分别为91.4%、80.9%和73.5%.     

不同组分下富锂正极材料xLi_2MnO_3·(1-x)LiNi_(0.5)Mn_(0.5)O_2(x=0.1-0.8)的晶体结构与电化学性能

采用溶胶-凝胶法制备了一系列富锂锰基正极材料xLi2MnO3?(1-x)LiNi0.5Mn0.5O2(x=0.1-0.8),通过X射线衍射(XRD)仪,扫描电子显微镜(SEM)和电化学测试等检测手段表征了所得样品的晶体结构与电化学性能,研究了不同组分下富锂材料的结构与电化学性能.结果表明:Li2MnO3组分含量较高时,材料的首次放电容量较高,但循环稳定性较差;该组分含量较少时,所得样品中出现尖晶石杂相,且放电容量较低,但循环稳定性较好;综合来看,x=0.5时材料的电化学性能最优.x=0.4,0.6时材料也表现出了较好的电化学性能,值得关注.     

Li3PO4‐Coated LiNi0.5Mn1.5O4: A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi_0.5Mn_1.5O₄ is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li₃PO₄ on LiNi_0.5Mn_1.5O₄ to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ is prepared by a solid‐state reaction and noncoated LiNi_0.5Mn_1.5O₄ is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li₃PO₄ layer (<6 nm) is successfully coated on the LiNi_0.5Mn_1.5O₄ primary particles. XRD and FT‐IR reveal that the synthesized Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ has a cubic spinel structure with a space group of Fd$\bar 3$ m, whereas noncoated LiNi_0.5Mn_1.5O₄ shows a cubic spinel structure with a space group of P4₃32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ shows dramatically enhanced cycling performance compared with noncoated LiNi_0.5Mn_1.5O₄.     

BiFeO<Subscript>3</Subscript>-coated spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> with improved electrochemical performance as cathode materials for lithium-ion batteries

Spinel LiNi_0.5Mn_1.5O₄ cathode material is a promising candidate for next-generation rechargeable lithium-ion batteries. In this work, BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials were prepared via a wet chemical method and the structure, morphology, and electrochemical performance of the materials were studied. The coating of BiFeO₃ has no significant impact on the crystal structure of LiNi_0.5Mn_1.5O₄. All BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials exhibit cubic spinel structure with space group of Fd3m. Thin BiFeO₃ layers were successfully coated on the surface of LiNi_0.5Mn_1.5O₄ particles. The coating of 1.0 wt% BiFeO₃ on the surface of LiNi_0.5Mn_1.5O₄ exhibits a considerable enhancement in specific capacity, cyclic stability, and rate performance. The initial discharge capacity of 118.5 mAh g^?1 is obtained for 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ with very high capacity retention of 89.11% at 0.1 C after 100 cycles. Meanwhile, 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ electrode shows excellent rate performance with discharge capacities of 117.5, 110.2, 85.8, and 74.8 mAh g^?1 at 1, 2, 5, and 10 C, respectively, which is higher than that of LiNi_0.5Mn_1.5O₄ (97.3, 90, 77.5, and 60.9 mAh g^?1, respectively). The surface coating of BiFeO₃ effectively decreases charge transfer resistance and inhibits side reactions between active materials and electrolyte and thus induces the improved electrochemical performance of LiNi_0.5Mn_1.5O₄ materials.     

Synthesis and electrochemical properties of high-voltage LiNi0.5Mn1.5O4 electrode material for Li-ion batteries by the polymer-pyrolysis method

A submicron LiNi_0.5Mn_1.5O₄ cathode was synthesized via the pyrolysis of polyacrylate salts as precursor polymerized by reaction of the metal salts with acrylate acid. The structure and morphology of the resulting compound was characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal that the prepared LiNi_0.5Mn_1.5O₄ cathode material has a pure cubic spinel structure and submicron-sized morphology even if calcined at 900 °C and quenched to room temperature. The LiNi_0.5Mn_1.5O₄ electrodes exhibited promising high-rate characteristics and delivered stable discharge capacity (90 mAh/g) with excellent retention capacity at the current density of 50 mA/g between 3.5 and 4.9 V. The capacity of the LiNi_0.5Mn_1.5O₄ electrodes remains stable even after 30 cycles at low or high current density. This polymer-pyrolysis method is simple and particularly suitable for preparation of the spinel LiNi_0.5Mn_1.5O₄ cathode material compared to the conventional synthesis techniques.     

The influence of Li sources on physical and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials for lithium-ion batteries

LiNi_0.5Mn_1.5O₄ cathode materials were successfully prepared by sol–gel method with two different Li sources. The effect of both lithium acetate and lithium hydroxide on physical and electrochemical performances of LiNi_0.5Mn_1.5O₄ was investigated by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, and electrochemical method. The structure of both samples is confirmed as typical cubic spinel with Fd3m space group, whichever lithium salt is adopted. The grain size of LiNi_0.5Mn_1.5O₄ powder and its electrochemical behaviors are strongly affected by Li sources. For the samples prepared with lithium acetate, more spinel nucleation should form during the precalcination process, which was stimulated by the heat released from the combustion of extra organic acetate group. Therefore, the particle size of the obtained powder presents smaller average and wider distribution, which facilitates the initial discharge capacity and deteriorates the cycling performance. More seriously, there exists cation replacement of Li sites by transition metal elements, which causes channel block for Li ion transference and deteriorates the rate capability. The compound obtained with lithium hydroxide exhibits better electrochemical responses in terms of both cycling and rate properties due to higher crystallinity, moderate particle size, narrow size distribution and lower transition cation substitute content.     

Comprehensive reinvestigation on the initial coulombic efficiency and capacity fading mechanism of LiNi0.5Mn1.5O4 at low rate and elevated temperature

The effect of different membranes and aluminum current collectors on the initial coulombic efficiency of LiNi_0.5Mn_1.5O₄/Li was investigated, and the cycling performance at different rates and temperatures and the storage performance at 60 °C for a week are discussed for LiNi_0.5Mn_1.5O₄/Li. The results show that the lower initial coulombic efficiency is associated with the lower decomposition voltage of the commercial membrane and electrolyte, and the instability of aluminum current collector under the higher voltage. In addition, both versions of LiNi_0.5Mn_1.5O₄ can deliver about 115 mA?h g^?1 of initial discharge capacity at 1 C at 25 °C and 60 °C; however, it retains only 61.57 % of its initial capacity after the 130th cycles at 60 °C, which is much lower than the 94.46 % rate observed for LiNi_0.5Mn_1.5O₄ at 25 °C, and the cycling performance of the material at 1 C is better than that at 0.5 C. Meanwhile, the initial discharge capacity at 0.1 C after storing at 60 °C is 119.3 mA?h g^?1, which is only a little lower than 121.5 mA?h g^?1 recorded before storing; moreover, the spinel structure and surface state of LiNi_0.5Mn_1.5O₄ after storing at 60 °C has not been changed basically. These results indicate that the electrochemical stability of electrolyte is also related to the temperature. The serious capacity fading of LiNi_0.5Mn_1.5O₄ at 60 °C is attributed to the severe oxidation decomposition and the thermal decomposition in the range of cut-off voltage of the materials, and then the decomposition products interact with active materials to form a solid interface phase, leading to the larger electrode polarization and irreversible capacity loss. Meanwhile, the worse cycling performance at 0.5 C than that at 1 C is attributed to the longer interaction time between the electrolyte and the active materials. However, the storage performance of LiNi_0.5Mn_1.5O₄ corresponds to the thermal stability of electrolyte to a certain extent.     

High performance LiNi0.5Mn1.5O4 cathode materials synthesized by a combinational annealing method

High performance LiNi_0.5Mn_1.5O₄ was prepared by a combinational annealing method. All samples were characterized by X-ray diffraction, infrared, and cell measurements. With increasing the annealing time at 600 °C, LiNi_0.5Mn_1.5O₄ showed a decreased lattice parameter and an enhanced Ni-ordering. The electrochemical property of LiNi_0.5Mn_1.5O₄ was optimized by controlling the annealing time. It was found that after annealing at 600 °C for 8 h, LiNi_0.5Mn_1.5O₄ can discharge up to 138 mA h g⁻¹ with a superior cycling performance at the rate of 5/7 C. High-rate test indicated that LiNi_0.5Mn_1.5O₄ exhibited excellent electrochemical performance when charged and discharged at 1.2 C and 2.5 C, respectively. The findings reported in this work are expected to pave the way for the practical application of LiNi_0.5Mn_1.5O₄.     

Improved electrochemical performance of LiNi0.5Mn1.5O4 as cathode of lithium ion battery by Co and Cr co-doping

Three samples, LiNi_0.5Mn_1.5O₄, LiNi_0.4Mn_1.4Co_0.2O₄, and LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, were prepared by sol–gel method and characterized by powder X-ray diffraction, Fourier transformed infrared spectroscope, scanning electron microscopy, Brunauer–Emmett–Teller surface area, four-probe resistance, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge test. It is found that the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ exhibits an improved performance compared with the Co-doped sample LiNi_0.4Mn_1.4Co_0.2O₄ and the undoped sample LiNi_0.5Mn_1.5O₄, especially at elevated temperature. At 25 °C, the discharge capacity of LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ is 130 mAh g^?1 at 0.1 C and 103 mAh g^?1 at 10 C. At an elevated temperature (55 °C), its 1 C discharge capacity is 136 mAh g^?1 and maintains 95.6 % of its initial capacity after 100 cycles. Compared with the reported results of LiNi_0.4Mn_1.4Co_0.2O₄ and LiNi_0.475Mn_1.475Co_0.05O₄, the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, with least content of Co, 0.05, possesses not only the high C-rate capacity but also the structural stability. The mechanism on the electrochemical performance improvement of LiNi_0.5Mn_1.5O₄ by the co-doping was discussed.     

Enhancements of rate capability and cyclic performance of spinel LiNi0.5Mn1.5O4 by trace Ru-doping

The rate capability and cyclic performance of the LiNi_0.5Mn_1.5O₄ under high current density have been significantly improved by doping a small amount of ruthenium (Ru). Specifically, Li_1.1Ni_0.35Ru_0.05Mn_1.5O₄ and LiNi_0.4Ru_0.05Mn_1.5O₄ synthesized by solid state reaction can respectively deliver a discharge capacity of 108 and 117 mAh g^?1 at 10 C rate between 3 and 5 V. At 10 C charge/discharge rate, Li_1.1Ni_0.35Ru_0.05Mn_1.5O₄ and LiNi_0.4Ru_0.05Mn_1.5O₄ can respectively maintain 91% and 84% of their initial capacity after 500 cycles, demonstrating that Ru-doping could be a way to enhance the electrochemical performance of spinel LiNi_0.5Mn_1.5O₄.     

层状Li(Ni1/3Co1/3Mn1/3)O2正极材料的合成与电化学性能研究

采用共沉淀-喷雾造粒法制备前驱体, 于750 ℃在空气中煅烧20 h合成出层状Li(Ni_1/3Co_1/3Mn_1/3)O₂正极材料, 并用XRD, SEM, 粒度分析和电性能测试考察了所得材料结构、形貌及电化学性能. 本层状Li(Ni_1/3Co_1/3Mn_1/3)O₂正极材料具有α-NaFeO₂结构, 六方晶系, R3m空间群, 其晶胞参数为a＝0.2865 nm, c＝1.4238 nm. 当材料分别在2.8～4.2, 2.8～4.5 V间进行充放电时, 其首次放电容量分别为173.5和185.4 mAh•g^－1, 首次充放电效率分别为90%和83.8%, 40次循环后容量保持率分别为96%和84%.     

Co-precipitation spray-drying synthesis and electrochemical performance of stabilized LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials

In this paper, the LiNi_0.5Mn_1.5O₄ cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi_0.5Mn_1.5O₄ particles with a cubic crystal structure, a specific surface area of 60.1 m² g^?1, a tap density of 1.15 g mL^?1, and a specific capacity of 132.9 mAh g^?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi_0.5Mn_1.5O₄. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g^?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi_0.5Mn_1.5O₄ material without CNF, the LiNi_0.5Mn_1.5O₄ with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi_0.5Mn_1.5O₄ cathode material.

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Graphical Abstract Micro/nanostructured LiNi_0.5Mn_0.5O₄ cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.

     

Preparation of hierarchical LiNixCoyMnzO2 from solvothermal [NixCoyMnz](OH)2 via regulating the ratio of Ni,Co, and Mn and its excellent properties for lithium-ion battery cathode

The ternary-layered oxide (LiNi_xCo_yMn_zO₂) has become the most promising cathode material for lithium-ion batteries due to the advantages of higher discharge platform, better conductivity, and higher theoretical capacity. The [Ni_xCo_yMn_z](OH)₂ with different ratios of nickel, cobalt, and manganese (NCM) was prepared by solvothermal method, and then ternary cathode material LiNi_xCo_yMn_zO₂ was obtained by mixing lithium and calcining. In this paper, ternary cathode materials with different ratios of NCM were prepared by the solvothermal method. The structure and morphology of the materials were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The effects of the ratio on the electrochemical properties of the materials were investigated by constant current charge and discharge test and electrochemical impedance spectroscopy test. The synthesized lithium-nickel-cobalt-manganese oxide belongs to the hexagonal system and has an α-NaFeO₂ layered structure, which is an R-3m space group. The NCM ternary cathode materials with different morphologies were obtained by changing the ratio of NCM. The sample with NCM ratio of 5:3:2 has a unique sheet-like spherical shape and has the best rate performance.     

Electrochemical performance of LiNi0.5Mn1.5O4 doped with la and its compatiblity with new electrolyte system

Cathode materials LiNi_0.5Mn_1.5O₄ and LiNi_{0.5 ? x/2}La _x Mn_{1.5 ? x/2}O₄ (x = 0.04, 0.1, 0.14) were successfully prepared by the sol-gel self-combustion reaction (SCR) method. The X-ray diffraction (XRD) patterns indicated that, a few of doping La ions did not change the structure of LiNi_0.5Mn_1.5O₄ material. The scanning electronic microscopy (SEM) showed that the sample heated at 800°C for 12 h and then annealed at 600°C for 10 h exhibited excellent geometry appearance. A novel electrolyte system, 0.7 mol L^?1 lithium bis(oxalate)borate (LiBOB)-propylene carbonate (PC)/dimethyl carbonate (DMC) (1: 1, v/v), was used in the cycle performance test of the cell. The results showed that the cell with this novel electrolyte system performed better than the one with traditional electrolyte system, 1.0 mol L^?1 LiPF₆-ethylene carbonate (EC)/DMC (1: 1, v/v). And the electrochemical properties tests showed that LiNi_0.45La_0.1Mn_1.45O₄/Li cell performed better than LiNi_0.5Mn_1.5O₄/Li cell at cycle performance, median voltage, and efficiency.     

Electrochemical properties of nano-crystalline LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> synthesized by polymer-pyrolysis method

LiNi_0.5Mn_1.5O₄ powders were prepared through polymer-pyrolysis method. XRD and TEM analysis indicated that the pure spinel structure was formed at around 450 °C due to the very homogeneous intermixing of cations at the atomic scale in the starting precursor in this method, while the well-defined octahedral crystals appeared at a relatively high calcination temperature of 900 °C with a uniform particle size of about 100 nm. When cycled between 3.5 and 4.9 V at a current density of 50 mA/g, the as prepared LiNi_0.5Mn_1.5O₄ delivered an initial discharge capacity of 112.9 mAh/g and demonstrated an excellent cyclability with 97.3% capacity retentive after 50 cycles.     

三(三甲基硅烷)类添加剂助力5 V镍锰酸锂电池实用化

基于LiNi_0.5Mn_1.5O₄的5 V电池尚未实现实际应用,解决这一问题的关键在于电解液调控和电极界面优化。我们系统性研究了三（三甲基硅烷）硼酸酯（TMSB）和三（三甲基硅烷）亚磷酸酯（TMSPi）作为常规碳酸乙烯酯（EC）-LiPF₆基电解液添加剂在LiNi_0.5Mn_1.5O₄电池体系中的应用。结合理论计算、物理化学表征以及电化学手段分析了三（三甲基硅烷）类添加剂在高压电解液中的作用机制。研究发现,TMSB和TMSPi均可以通过优化电极/电解液界面来提高LiNi_0.5Mn_1.5O₄循环稳定性和库仑效率。TMSB中缺电子B可与阴离子相互作用,稳定PF₆^-,抑制LiNi_0.5Mn_1.5O₄正极阻抗的持续增加。TMSPi具有更高的最高占据分子轨道（HOMO）能级,可在更低电位下钝化高压正极,提高LiNi_0.5Mn_1.5O₄放电电压平台和放电容量。此外,TMSPi还可通过亲核反应参与石墨界面组分优化,改善负极循环性能。石墨LiNi_0.5Mn_1.5O₄软包电池在含1% TMSPi电解液中1C循环100次后的容量保持率为88.9%,优于基础电解液（60.5%）和含1% TMSB的电解液（77.4%）。     

High capacity lithium-manganese-nickel-oxide composite cathodes with low irreversible capacity loss and good cycle life for lithium ion batteries

We report a method to eliminate the irreversible capacity of 0.4Li_2MnO_3·0.6LiNi_(0.5)Mn_(0.5)O_2(Li_(1.17)Ni_(0.25)Mn_(0.583)O_2) by decreasing lithium content to yield integrated layered-spinel structures.XRD patterns,High-resolution TEM image and electrochemical cycling of the materials in lithium cells revealed features consistent with the presence of spinel phase within the materials.When discharged to about 2.8 V,the spinel phase of LiM_2O_4(M=Ni,Mn) can transform to rock-salt phase of Li_2M_2O_4(M=Ni,Mn) during which the tetravalent manganese ions are reduced to an oxidation state of 3.0.So the spinel phase can act as a host to insert back the extracted lithium ions(from the layered matrix) that could not embed back into the layered lattice to eliminate the irreversible capacity loss and increase the discharge capacity.Their electrochemical properties at room temperature showed a high capacity(about 275 mAh g~(-1) at 0.1 C) and exhibited good cycling performance.