Electrochemical Performance Of LiNi0 Research Articles

Preparation and characterization of LiNi0.8Co0.15Al0.05O2 with high cycling stability by using AlO2- as Al source

We report the preparation of a series of LiNi0.8Co0.15Al0.05O2 materials with different reaction time (10, 20, 30 and 40h) of precursor and their electrochemical properties as cathode material for lithium-ion batteries (LIBs). The preparation of LiNi0.8Co0.15Al0.05O2 was divided into two steps: a co-precipitation process to obtain Ni0.8Co0.15Al0.05(OH)2 precursor and a calcination step with LiOH. During the co-precipitation process, AlO2- was employed as Al source so as to guarantee Ni2+, Co2+ and Al3+ co-precipitation. The impacts of different synthesis time of the precursor on crystal structure, morphology and electrochemical performance of LiNi0.8Co0.15Al0.05O2 were systematically investigated. The samples with various synthesis time of precursor possessed spherical morphology and a layered α-NaFeO2 structure with R-3m space group. Especially, when the reaction time of precursor was 30h, the LiNi0.8Co0.15Al0.05O2 had the weakest degree of Li+/Ni2+ ions mixing and the best uniformity and integrity. When used as cathode materials for LIBs, the LiNi0.8Co0.15Al0.05O2 with 30h exhibited high discharge capacity, good cycling performance and remarkable rate capability. The maximum discharge capacity was 202.3 mAh g−1 at 0.1C and the capacity retention approached 99.4% after 100 cycles at 1C. At 10C, the discharge capacity exceeded 140 mAh g−1, suggesting a possible application in the high rate LIBs. The excellent electrochemical performance might be attributed to the uniform co-precipitation of Ni2+, Co2+ and Al3+ and well layered structure with less Li+/Ni2+ mixing.

Effect of niobium doping on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries

Key issues including poor rate capability and limited cycle life span should be addressed for the extended application of LiNi0.5Co0.2Mn0.3O2 cathode. The suppressed Li+/Ni2+ site exchange, enlarged LiO2 inter-slab space and reduced impedance, which could facilitate the structure stability, were achieved by controlled Niobium (Nb) doping and contributed to enhanced performance even at elevated temperature (55°C). The detailed role of the doped Nb was investigated thoroughly and systematically with the help of XRD, SEM, XPS and related electrochemical tests. The full and accurate results demonstrate that the Li(Ni0.5Co0.2Mn0.3)0.99Nb0.01O2 sample with appropriate Nb doping amount possess high capacity retention of 93.77% after 100 cycles at 1.0C and improved rate performance with 125.5mAhg−1 at 5.0C, which are much better than that of the LiNi0.5Co0.2Mn0.3O2. Moreover, at high temperature of 55°C, Nb doping shows more remarkable effect on stabilizing the structure and 88.63% of the initial reversible capacity could be retained, which is ~20% higher than the LiNi0.5Co0.2Mn0.3O2. This study intensively determines that controlled Nb doping could be effectively maintain the structure stability of advanced LiNi0.5Co0.2Mn0.3O2 cathode and promote the development of high energy density lithium ion batteries.

Insights into the inner structure of high-nickel agglomerate as high-performance lithium-ion cathodes

In this paper, the intrinsic impact of inner structure features on the electrochemical performances of LiNi0.6Co0.2Mn0.2O2 cathodes is for the first time systematically investigated. Three different spherical Ni0.6Co0.2Mn0.2(OH)2 precursors are successfully synthesized by controlling pH values and ammonia concentrations. Interestingly, via a further lithiation process, the final cathodes can gradually inherit the structural features, showing distinct particle arrangement and genetic orientation characteristics in the inner structures. Such a hereditary property can be well reined for customizing the grain-orientation, helping the growth of the inert crystal direction, reducing cation mixing and exposing the high active (100) or (010) lattice planes for lithiation/delithiation processes via an intrinsical way. The degree of grain-orientation of the primary particles turns out to be a critical factor in determining the long-term stability and power performances. Due to the reduced cation mixing degree and favorable lithium diffusion pathways, the ordered agglomerates with the grain growth along with [003] direction exhibit superior rate capability and good cycle stability.

Improving the electrochemical performances of spherical LiNi0.5Mn1.5O4 by Fe2O3 surface coating for lithium-ion batteries

The spherical LiNi0.5Mn1.5O4 cathode material synthesized by a co-precipitation method has been modified by Fe2O3 through a simple chemical precipitation method. The effects of Fe2O3 coating on the structure and property of LiNi0.5Mn1.5O4 cathode have been carefully investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and atomic absorption spectroscopy (AAS). The results show that the Fe2O3 coating layer covered the surfaces of the spherical LiNi0.5Mn1.5O4 particles does not change the crystallographic structure of LiNi0.5Mn1.5O4, but it can protect the surface of the active materials from electrolyte erosion and suppresses the dissolution of transition metal elements. The effects of Fe2O3 coating layer on the electrochemical performances of LiNi0.5Mn1.5O4 have also been investigated systematically by the charge-discharge testing and AC impedance spectroscopy. Compared with the pristine LiNi0.5Mn1.5O4, the Fe2O3 modified material exhibits remarkably enhanced cyclic stability and excellent rate capability. In addition, surface modification of the LiNi0.5Mn1.5O4 is found to be an effective route for suppressing the increase of the impedance during the storage process at elevated temperatures.

Enhanced electrochemical performances of layered LiNi0.5Mn0.5O2 as cathode materials by Ru doping for lithium-ion batteries

The pristine and Ru-doped LiNi0.5Mn0.5O2 cathode materials are synthesized by a wet chemical method, followed by a high-temperature calcination process. The influence of Ru substitution on the microstructure and electrochemical performances of the prepared materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and galvanostatic charge/discharge test. The XRD results show that, compared to the Ru-undoped sample, the LiNi0.5Mn0.45Ru0.05O2 owns a better hexagonal α-NaFeO2 structure and a smaller amount of cation mixing. The galvanostatic charge/discharge measurements demonstrate that the electrochemical properties of the LiNi0.5Mn0.5O2 sample are enhanced by Ru doping. At 5 and 10 C, the discharge capacity of LiNi0.5Mn0.45Ru0.05O2 is 118.61 and 105.43 mAh g−1, respectively, which is higher than those of LiNi0.5Mn0.5O2 (101.24 and 78.94 mAh g−1) due to the reduced charge-transfer resistance and the improved lithium-ion diffusion coefficient. On the basis of these results, Ru doping is considered an effective way to enhance the electrochemical performances of LiNi0.5Mn0.5O2 cathode materials.

Optimized structure stability and electrochemical performance of LiNi0.8Co0.15Al0.05O2 by sputtering nanoscale ZnO film

LiNi0.8Co0.15Al0.05O2 (NCA) is one of the most promising cathode material for lithium-ion batteries (LIBs) in electric vehicles, which is successfully adopted in Tesla. However, the dissolution of the cation into the electrolyte is still a one of the major challenges (fading capacity and poor cyclability, etc.) presented in pristine NCA. Herein, a homogeneous nanoscale ZnO film is directly sputtered on the surface of NCA electrode via the magnetron sputtering (MS). This ZnO film is evidenced by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results clearly demonstrate that ZnO film is fully and uniformly covered on the NCA electrodes. After 90 cycles at 1.0C, the optimized MS-2min coated NCA electrode delivers much higher discharge capacity with 169 mAh g−1 than that of the pristine NCA electrode with 127 mAh g−1. In addition, the discharge capacity also reaches 166 mAh g−1 at 3.0C, as compared to that of 125 mAh g−1 for the pristine electrode. The improved electrochemical performance can be ascribed to the superiority of the MS ZnO film that reduce charge transfer resistance and protect the NCA electrode from cation dissolution.

Comparison on Electrochemical Performances of LiNi0.5Mn1.5O4 Cathode Materials Synthesized Using Different Precursors

In this work, LiNi0.5Mn1.5O4 has been synthesized by using acetate and carbonate precursors, respectively and ball-milled with citric acid, followed by heat treatment at high temperature. The structure, morphology and electrochemical performances of all samples were investigated using X-ray diffraction, scanning electron microscope, and galvanostatic testing. The high crystallinity and small particle size are affected by the homogeneity of the samples with the presence of citric acid. It was shown that the electrochemical performances of LiNi0.5Mn1.5O4 prepared from acetate precursor exhibit the highest discharge capacity of 120 mAh g-1 at 1C rate.

Nonlinear Conductivities and Electrochemical Performances of LiNi0.5Co0.2Mn0.3O2 Electrodes

There is increasing research attention on optimizing the carbon black nanoparticles’ structure and loading procedure for improving conductivities and thus, electrochemical performances of cathodes in lithium-ion batteries. Recently, LiNi0.5Co0.2Mn0.3O2 (NCM523) has been actively investigated due to its larger specific capacity and lower cost compared to conventional cathode materials. Presented here is a high energy density NCM523 cathode obtained by reducing the carbon content using the state-of-the-art carbon nanoparticles developed at Cabot Corporation. It is the first time that the nonlinear conductivity of NCM523 electrodes has been discovered, which is significantly impacted by the dispersion and surface crystalline quality of carbon black nanoparticles, especially when the loading of carbon black is only 1 wt%. The nonlinear conductivity of the cathodes can dramatically affect their electrochemical performances at high rates (≧3C), which is close to the tunneling saturated current. In addition, there is no discernable difference in terms of the rate and cycle performance of the NCM523 electrodes, when reducing the loading of novel carbon black nanoparticles from 5 wt% to 1 wt% in the cathode. Therefore, the energy density of the electrode can be increased by 9% by using existing commercially available electrode materials.

Effect of Mg doping on the structural and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials

LiNi0.6Co0.2Mn0.2O2 and Mg-substituted LiNi0.6Co0.2Mn0.2O2 cathode materials have been prepared by co-precipitation and high-temperature solid state method. The effects of partial substitution of Ni with Mg in LiNi0.6Co0.2Mn0.2O2 material on its chemical component, crystal structure, surface valence states, electrochemical properties, and Li+ diffusion barrier have been extensively studied. The Rietveld refinement results reveal that cation mixing has been suppressed effectively, and the lattice parameters a and c decrease while the c/a ratio increases induced by Mg doping. The X-ray photoelectron spectroscopy (XPS) indicates that Mg substitution reduces the relative ratio of Ni2+/Ni3+ ions on surface. Electrochemical studies indicate that the Mg-substituted material exhibits better cycling performance. First-principles calculations indicate that Mg doping increase the activation barriers of Li+ migration, thus excesses of Mg substitution lead to rate performance degradation.

Influence of Using Additives in Spray Drying Process on Structural and Electrochemical Properties of LiNi0.5Mn1.5O4 cathode Material

As one of the most promising candidates for the next generation lithium ion batteries, LiNi0.5Mn1.5O4 (LNMO) has attracted much attention since its discovery in 1997.1,2 With a theoretical capacity of 146.7 mAh g-1 and a high average operational voltage of 4.7 V from Ni2+/Ni4+ redox couple, it offers a larger energy density compared to the common cathode materials like LiCoO2, LiFePO4 or LiMn2O4.3 The LNMO provides three dimensional diffusion channels for Li+-ion insertion/extraction, leading to a good rate capability and good safety characteristics. In addition, it is more economical and less toxic than the materials employing cobalt. The spinel structure of LNMO is reported to exist in two polymorphs, depending on synthesis conditions: an ordered structure (P4332), where the Mn and the Ni ions are ordered, occupying different lattice sites (12d and 4a, respectively) and a disordered structure (Fd-3m), where the transition metal ions are randomly distributed on 16d sites. These polymorphs are reported to possess different properties for instance in terms of ion conductivity or manganese dissolution. Besides of the obtained phase after synthesis process, the morphology of primary particles and the way of their agglomeration into secondary particles plays a crucial rule on the electrochemical performance. In this work, LiNi0.5Mn1.5O4 spinel material was synthesized by a spray drying process using different additives as well as different heating devices. The additives used were urea, citric acid and polyvinylpyrrolidon (PVP). For the heat treatment, a conventional muffle furnace and a microwave assisted muffle furnace were employed. The microwave assisted muffle furnace offers advantages over conventional heating in terms of higher heating, more homogeneous temperature profiles in the sample or a reduction of activation energies for reactions during calcination, leading to reduced energy costs and/or purer products. The effect of the additives and heating method on the structure and electrochemical performance of LiNi0.5Mn1.5O4 is studied in detail. First results show an influence of the additive on the primary and secondary particle morphology. Adding Polyvinylpyrrolidon (PVP) in the spray drying process leads to smaller particle of precursor and the formation of flake-like secondary LNMO particles after high temperature thermal treatment. Also the cycling stability and the rate capability could be increased when using PVP. A further improvement in terms of cycling stability and rate capability, as being showed in figure 2, can be achieved when heating the precursor rapidly by using the microwave assisted muffle furnace. From the SEM image in figure 1, this can be attributed to the formation of thermodynamically unfavorable lattice planes like {110} or {100} in which the Li+ ion diffusion rate is higher than for the more stable {111}.4,5 References 1 K. Amine, H. Tukamoto, and Y. Fujita, J. Electrochem. Soc., 1996, 143, 1607-1613. 2 Q. M. Zhong, A. Bonakdarpour, M. J. Zhang, Y. Gao and J. R. Dahn, J. Electrochem. Soc., 1997, 144, 205-213. 3 G. B. Zhong, Y. Y. Wang, Z. C. Zhang, and C. H. Chen, Electrochim. Acta, 2011, 56, 6554-6561. 4 J. Mao, K. H. Dai, and Y. C. Zhai, Electrochim. Acta, 2012, 63, 381-390. 5 M. Hirayama, H. Ido,K. Kim, W.Cho, K. Tamura, J. Mizuki, R. Kanno, J. Am. Chem. Soc., 2010, 132, 15268–15276 Figure 1

Synthesis of Ni0.8Co0.1Mn0.1(OH)2 precursor and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode material for lithium batteries

Spherical and homogeneously mixed metal hydroxide Ni0.8Co0.1Mn0.1(OH)2 precursor was successfully synthesized by co-precipitation method in a simple and small vessel with the volume of 1 L. The conditions of synthetic process including amount of chelating agent, stirring speed and temperature were studied. LiNi0.8Co0.1Mn0.1O2 samples were obtained by calcinating the precursors. The crystal structure, morphology and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge test, AC impedance and cyclic voltammetry. In the voltage range of 2.8–4.3 V, the initial discharge capacities of LiNi0.8Co0.1Mn0.1O2 at 0.1C and 1C rates were 199 and 170 mA·h/g, respectively. After 80 cycles at 1C, the discharge capacity retention was 92%, suggesting its promising application as the cathode material for Li-ion batteries.

Effects of fluorine doping on structure, surface chemistry, and electrochemical performance of LiNi0.8Co0.15Al0.05O2

The performance of LiNi0.8Co0.15Al0.05O2 is shown to be improved by fluorine doping via a modified low-temperature method. Scanning electron microscopy shows that fluorine doping catalyzes the growth of the primary particles. X-ray diffraction (XRD) results reveal that all the synthesized materials have typical hexagonal structure without impurities. The lattice parameters calculated from the XRD data by Rietveld refinement methods indicate that the interslab spacing distance is enlarged by fluorine doping. Inductively coupled plasma atomic emission spectroscopy and energy-dispersive X-ray spectroscopy show that fluorine atoms are preferentially enriched on the surface of the particle. X-ray photoelectron spectroscopy indicates that the valence state of nickel ions at the surface is lowered. The cycling performance of modified samples at room temperature, at high temperature (55°C), and at high upper cut-off potentials is improved. Electrochemical impedance spectroscopy measurements reveal that fluorine doping could lower the impedance rise during cycling and suppress the degradation of the cathode material.

Preparation and Electrochemical Performances of LiNi0.5Mn0.5O2 Cathode Materials for Lithium-Ion Batteries

Preparation and Electrochemical Performances of LiNi0.5Mn0.5O2 Cathode Materials for Lithium-Ion Batteries

Influence of Co doping on crystal structure and electrochemical performances of LiNi0.5Mn1.5O4

To investigate the influence of Co doping on spinel LiNi0.5Mn1.5O4 cathode, LiNi0.4Co0.1Mn1.5O4 and LiNi0.35Co0.1Mn1.5O4 were designed and successfully synthesised through a polymer assisted method. Inductively coupled plasma, X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy tests have been carried out. Results show that the compositions of the synthesised samples are consistent with the designed compositions, and Co doping could decrease the degree of cation ordering; Co doping together with octahedral vacancies could induce higher concentration of Mn3+ in the spinel structure. The result of cyclic voltammetry test suggests LiNi0.35Co0.1Mn1.5O4 has the best conductivity, and LiNi0.35Co0.1Mn1.5O4 exhibited the best rate capability among the three spinel cathodes.

Correlation of oxygen non-stoichiometry to the instabilities and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 utilized in lithium ion battery

In this work, we investigate the influence of oxygen non-stoichiometry on the characteristics of LiNi0.8Co0.1Mn0.1O2 cathode material. Among the investigated samples, the level of Ni/Li disorder in the bulk and the thickness of auto-generated layer on the surface share the same trend as the amount of oxygen loss in LiNi0.8Co0.1Mn0.1O2 materials. It indicates that the aforementioned key structural instabilities should be tightly related to the oxygen defects and the induced structural relaxation. As a consequence of structural entirety, the sample with the least defects presents the highest discharge capacity (192.9 mAhg−1 at 0.1C), the best rate capability (160.1 mAhg−1 at 5C), and the most stable cyclibility (89.9% at 200th). Our results demonstrate that oxygen deficiency plays a key role to determine the electrochemical performance of high-nickel cathode materials.

Improved electrochemical performance of the spherical LiNi0.5Mn1.5O4 particles modified by nano-Y2O3 coating

The large-scale use of LiNi0.5Mn1.5O4 as the cathode material for lithium-ion battery has so far been hindered by some drawbacks, for example, the interfacial side reactions between the high-voltage charged LiNi0.5Mn1.5O4 and the liquid electrolyte. Herein, the spherical LiNi0.5Mn1.5O4 is synthesized via co-precipitation method, and then the as-prepared LiNi0.5Mn1.5O4 is modified by nano-Y2O3 coating through heterogeneous nucleation route in order to improve its electrochemical performance. The effects of nano-Y2O3 coating on structural and electrochemical performance of LiNi0.5Mn1.5O4 are systematically investigated by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, and electrochemical measurements. The results demonstrate that the surface of LiNi0.5Mn1.5O4 particle is uniformly encapsulated by nano-Y2O3 coating. Meanwhile, although the nano-Y2O3 coating can still keep the spinel structure of LiNi0.5Mn1.5O4, it can apparently improve its electrochemical performance. The nano-Y2O3-coated LiNi0.5Mn1.5O4 sample can deliver an initial discharge capacity of 126.1 mAh g−1 with the capacity retention of 97.7 % after 300 cycles at current rate of 1 C at 25 °C. Particularly, the nano-Y2O3-coated LiNi0.5Mn1.5O4 sample exhibits excellent capacity retention of 91.6 % after 100 cycles even at elevated temperature and a rate of 2 C.

Electrochemical Performance of LiNi0.5Mn1.5O4 by Sol-gel Self-combustion Reaction Method in Different Kinds of Electrolyte for High-voltage Rechargeable Lithium Cells

AbstractLiNi

Electrochemical performance of LiNi0.5Mn1.5O4 composite electrodes featuring carbons and reduced graphene oxide

LiNi0.5Mn1.5O4 (LNMO) composite electrodes having the same formulation as to percentage of active material mass, binder and carbons, including reduced graphene oxide, were characterized in EC: DMC – 1M LiPF6 by cyclic voltammetry, charge/discharge cycles and impedance spectroscopy. The results demonstrate the beneficial effect on the electrode cycling stability in increasing C-rate to 1C, in limiting the charge voltage at 4.8 V and in covering the LNMO by partially reduced graphene oxide. The paper also discusses the evaluation of lithium diffusion coefficient in LNMO from cyclic voltammetry data in regard to the discrepancies reported in literature on this matter.

Effect of sintering temperature on cycling performance and rate performance of LiNi0.8Co0.1Mn0.1O2

LiNi0.8Co0.1Mn0.1O2 powder was prepared by mixing LiOH·H2O and co-precipitated Ni0.8Co0.1Mn0.1(OH)2 at a molar ratio of 1:1.05, followed by sintering at different temperatures. The effects of temperature on the morphology, structure and electrochemical performance were extensively studied. SEM and XRD results demonstrate that the sintering temperature has large influence on the morphology and structure and suitable temperature is very important to obtain spherical materials and suppresses the ionic distribution. The charge–discharge tests show that the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 powders becomes better with the increase of temperature from 700 °C to 750 °C and higher temperature will deteriorate the performance. Although both of materials obtained at 750 °C and 780 °C demonstrate almost identical cyclic stability at 2C rate, which delivers 71.9% retention after 200 cycles, the rate performance of powder calcined at 780 °C is much poorer than that at 750 °C. The XRD results demonstrate that the poor performance is ascribed to more severe ionic distribution caused by higher temperature.

Modified electrochemical performance of high potential cathode using a sand-like carbonate electrolyte

The electrochemical performance of LiNi0.5Mn1.5O4 is investigated in a sand-like carbonate electrolyte containing 4wt.% lithium metasilicate (Li2SiO3). The capacity fading rate of the LiNi0.5Mn1.5O4 electrode working in the sand-like electrolyte (2-5V) is reduced to 0.171 mAh g−1 per cycle, quite smaller than the value of 0.613 mAh g−1 per cycle in the electrolyte without Li2SiO3. The capacity of 159.5 mAh g−1 is delivered at 0.5C after 118 cycles while it is only 99.4 mAh g−1 for the Li2SiO3-free counterpart. Cyclic voltammetry, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopic measurements are conducted to explore the modification mechanism. It is found that the anodic stability of the sand-like electrolyte is improved compared to the base electrolyte. The Li2SiO3 precipitates on the electrode surface make contribution to the performance enhancement of the cathode at high potential.