Al Substitution For Co Research Articles

Study on electrochemical performance of Al-substitution for different cations in Li-rich Mn-based materials

Layered Li-rich Mn-based cathode materials have attracted immense interest for using in lithium-ion batteries, owing to their high energy density. However, the severe degradation of cycle and rate performances has impeded the actual commercial application. Herein, Al was selected as doping element to substitute for the metal elements of Li, Ni, Co and Mn in Li1.2Mn0.54Ni0.13Co0.13O2 material to promote electrochemical performances and optimize element proportion. Results indicate that when replacing Li with Al, it displays outstanding initial coulombic efficiency of 80.06%. Besides, Al-substitution for Co shows excellent rate performance of 147.3 mAh g−1 at 5.0 C. Particularly, the replacement of Mn not only shows the highest capacity and voltage retention within the potential range from 2.0 to 4.8 V, but also presents superior capacity retention up to the potential of 5.0 V. Unfortunately, the substitution of Ni displays the worst balanced electrochemical performance among Al-doped materials, which shows lower voltage retention than that of pristine. The reasons why Al-substitution for various cations displays difference on electrochemical performance were discussed from the perspective of migration, dissolution and valence reduction of transition metal ions to the structure evolution in detail. The proposed method and detected action mechanisms can provide guidance on how to optimize materials structure and composition for cathode materials in lithium-ion batteries to obtain electrode materials with excellent comprehensive electrochemical performance.

The functioning mechanism of Al valid substitution for Co in improving the cycling performance of Zr–Co–Al based hydrogen isotope storage alloys

In order to optimize the hydrogen isotope storage properties of ZrCo alloy and promote its application in the storage and delivery system (SDS), ZrCo alloy is modified by partial substitution of Co with Al and subsequent melt spinning process. The microstructure and hydrogen isotope storage properties, especially the cycling performance, of ZrCo1-xAlx (x = 0–0.15) samples were thoroughly investigated. It is found that all as-cast Al-substituted alloys are consisted of a main phase of ZrCo, while the segregation of Al element at grain boundary is more serious with the increase of Al doping content, which restrains the valid substitution content of Al for Co in ZrCo phase. The initial activation performances of the Al-substituted alloys are enhanced and excellent hydriding kinetics are maintained. With the increase of Al substitution content in ZrCo phase of ZrCo1-xAlx (x = 0–0.15) alloys, the initial saturated hydrogen capacities of α solid-solution phase are improved significantly, which is attributed to the decline of valence electron concentrations (VEC) for Al-substituted alloys. Further analysis shows that the hydrogenation-dehydrogenation process of ZrCo1-xAlx (x = 0–0.15) alloys after multiple cycles has been altered as intercalation and de-intercalation of hydrogen atoms between ZrCo phase and α phase, leading to cycling capacity stabilization. More importantly, the improved terminal saturated hydrogen capacities of α phase in the Al-substituted alloys, which represents enhanced final cycling stable capacities, is linked with the increase of initial saturated hydrogen capacities of α phase after Al substitution for Co in ZrCo phase. In addition, the valid substitution content of Al for Co in ZrCo phase is further increased without any element segregation for ZrCo0.9Al0.1 alloy processed by melt spinning, which behaves further optimized final cycling stable capacity of 0.93 wt%, and its variation of the hydrogenation and dehydrogenation paths is similar to those of the above samples. In this work, the mechanism of cycling capacity stabilization has been explored in detail, which provides guidance to improve the cycling stability of ZrCo-based hydrogen isotope storage alloys from point of phase structure of ZrCo alloy.

Electrochemical Characteristics of Layered Transition Metal Oxide Cathode Materials for Lithium Ion Batteries: Surface, Bulk Behavior, and Thermal Properties.

Layered lithium transition metal oxides, in particular, NMCs (LiNixCoyMnzO2) represent a family of prominent lithium ion battery cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety for electric vehicles and grid storage. Our work has focused on various strategies to improve performance and to understand the limitations to these strategies, which include altering compositions, utilizing cation substitutions, and charging to higher than usual potentials in cells. Understanding the effects of these strategies on surface and bulk behavior and correlating structure-performance relationships advance our understanding of NMC materials. This also provides information relevant to the efficacy of various approaches toward ensuring reliable operation of these materials in batteries intended for demanding traction and grid storage applications. In this Account, we start by comparing NMCs to the isostructural LiCoO2 cathode, which is widely used in consumer batteries. Effects of changing the metal content (Ni, Mn, Co) upon structure and performance of NMCs are briefly discussed. Our early work on the effects of partial substitution of Al, Fe, and Ti for Co on the electrochemical and bulk structural properties is then covered. The original aim of this work was to reduce the Co content (and thus the raw materials cost) and to determine the effect of the substitutions on the electrochemical and bulk structural properties. More recently, we have turned to the application of synchrotron and advanced microscopy techniques to understand both bulk and surface characteristics of the NMCs. Via nanoscale-to-macroscale spectroscopy and atomically resolved imaging techniques, we were able to determine that the surfaces of NMC undergo heterogeneous reconstruction from a layered structure to rock salt under a variety of conditions. Interestingly, formation of rock salt also occurs under abuse conditions. The surface structural and chemical changes affect the charge distribution, the charge compensation mechanisms, and ultimately, the battery performance. Surface reconstruction, cathode/electrolyte interface layer formation, and oxygen loss are intimately related, making it difficult to disentangle the effects of each of these phenomena. They are driven by the different redox activities of Ni and O on the surface and in the bulk; there is a greater tendency for charge compensation to occur on oxygen anions at particle surfaces rather than on Ni, whereas the Ni in the bulk is more redox active than on the surface. Finally, our latest research efforts are directed toward understanding the thermal properties of NMCs, which is highly relevant to their safety in operating cells.

Stabilization effects of Al doping for enhanced cycling performances of Li-rich layered oxides

Despite the promising high energy density, Li-rich layered oxides still suffer from capacity fade and voltage decay during prolonged cycling. Doping could be effective in addressing such problems, but current studies pay less attention on rhombohedral phases. To this end, Al incorporated Li1.14(Ni0.136Co0.10Al0.03Mn0.544)O2 oxides are investigated. Rietveld refined X-ray diffraction and transmission electron microscope results, along with electrochemical analyses, prove the substitution of Al for Co as well as its influence mainly on rhombohedral components. With slight capacity decreases, Al doped cathodes attain superior cycling performances, presenting a capacity retention up to 94.7% as compared to 81.7% for the pristine ones after 100 cycles. Most importantly, the fatal voltage decay, is alleviated as well through the obstructed formation of spinel-like phases, which are confirmed by the ex-situ XRD and further estimated by Raman spectra. Additionally, interfaces of Al doped electrodes are also somewhat enhanced as indicated by the electrochemical impedance study. These results suggest a notable stabilization effects on host framework in Li-rich layered oxides through manipulations on rhombohedral phases.

Magnetostructural phase transitions and magnetocaloric effect in Tb-Dy-Ho-Co-Al alloys with a Laves phase structure

The influence of simultaneous substitution within the rare earth (R) and Co sublattices on the structural, magnetic, and magnetocaloric properties of the Laves phase RCo2-type compounds is studied. Main attention is devoted to the studies of the magnetostructural phase transitions and the transition types with respect to the alloy composition. Multicomponent alloys Tbx(Dy0.5Ho0.5)1−xCo2 and Tbx(Dy0.5Ho0.5)1−xCo1.75Al0.25 were prepared with the use of high purity metals. Majority of the Tbx(Dy0.5Ho0.5)1−xCo2 alloys exhibit magnetic transitions of the first-order type and a large magnetocaloric effect. The substitution of Al for Co in Tbx(Dy0.5Ho0.5)1−xCo2 increases the Curie temperature (TC) but changes the transition type from first-to the second-order. The discussion of the physical mechanisms behind the observed phenomena is given on the basis of the first principles electronic-structure calculations taking into account both the atomic disorder and the magnetic disorder effects at finite temperatures. The advantage of Al-containing materials is that sufficiently high magnetocaloric effect values are preserved at T > TC.

The effects of Al substitution on the phase abundance, structure and electrochemical performance of La0.7Mg0.3Ni2.8Co0.5−xAlx (x = 0, 0.1, 0.2) alloys

A series of (La, Mg)Ni2.8Co0.5 metal hydride alloys was studied in order to understand the effects of partial Al-substitution for Co on the alloy's structure, gaseous phase hydrogen storage properties, and electrochemical performance. The alloys were characterized by X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, pressure-concentration-temperature characterization, half-cell electrochemical tests, and sealed full-cell tests. After an annealing process at 960 °C for 5 h, the main matrix of the Al-free base alloy shifted from AB3 phase into an A2B7 phase. Annealed alloy samples incorporating Al promoted the AB5 phase over the A2B7 phase. The annealing treatment (AB3 to A2B7) increased the gaseous phase hydrogen storage capacity and lowered the plateau pressure and hysteresis in the absorption–desorption isotherms. The addition of Al in the annealed samples (A2B7 to AB5) decreased gaseous phase hydrogen storage and electrochemical capacities, decreased high rate dischargeability, but increased cycle stability. Continuous pulverization of the metal hydride alloy at the negative electrode appeared to be the main failure mode of this series of alloys despite the lower starting rate of pulverization when compared to commercially available AB5 alloys.

The microstructures and electrochemical performances of La0.6Gd0.2Mg0.2Ni3.0Co0.5−xAlx (x=0–0.5) hydrogen storage alloys as negative electrodes for nickel/metal hydride secondary batteries

La0.6Gd0.2Mg0.2Ni3.0Co0.5−xAlx (x = 0–0.5) hydrogen storage alloys were prepared by induction melting followed by annealing treatment at 1173 K for 8 h. The effects of substitution Al for Co on the microstructures and electrochemical performances were studied systematically. The structure analyses show that all alloys consist of multiphase structures such as (La, Mg)2Ni7 phase, (La, Mg) Ni3 phase and LaNi5 phase. The abundance of (La, Mg)2Ni7 phase decreases while the abundance of LaNi5 phase and (La, Mg)Ni3 phase increases directly as the Al content increasing. The electrochemical tests show that the maximum discharge capacity of alloy electrodes are almost unchanged when x ≤ 0.2 while the cyclic stability of the alloy electrode are improved significantly after proper amount of Al substitution for Co. The alloy electrode with x = 0.1 exhibits the better balance between discharge capacity and cycling life than any others. Moreover, at the discharge current density of 900 mA g−1, the high rate dischargeability (HRD) of the alloy electrodes decreases with increasing Al substitution and the relative analyses reveal that the charge transfer on alloy surface is more important than the hydrogen diffusion in alloy bulk for the kinetic properties of the alloy electrodes.

Thermoelectric properties of Al substituted misfit cobaltite Ca3(Co1−x Al x )4O9 at low temperature

Thermoelectric properties of Al substituted compounds Ca3(Co1−x Al x )4O9 (x = 0, 0.03, 0.05), prepared by a sol-gel process, have been investigated in the temperature range 305–20 K. The results indicate that after Al substitution for Co in Ca3(Co1−x Al x )4O9, the direct current electrical resistivity and thermopower increase due to the reduction of carrier concentration. Experiments show that Al substitution results in decreased lattice thermal conductivity. The figure of merit of temperature behavior suggests that Ca3(Co0.97Al0.03)4O9 would be a promising candidate thermoelectric material for high-temperature thermoelectric application.

Effect of partial magnetic order on resistivity and thermopower of Ho(Co1−x Al x )2 alloys

The electrical resistivity ρ and the thermopower S of Ho(Co1−xAlx)2 alloys (x = 0 to 0.2) were measured at temperatures from 2 K to 300 K in magnetic fields up to 10 T. While ρ(T) and S(T) of pure HoCo2 reveal abrupt changes at the magnetic ordering temperature TC, indicating a firstorder transition, the temperature variations of both properties across the ordering temperature in Ho(Co1−xAlx)2 alloys clearly show that the type of magnetic transition changes under substitution of Al for Co from first order to second order around x ≈ 0.06. ρ(T) of the Al-substituted samples (x = 0.15 and 0.2) has a very unusual variation at temperatures below TC: in contrast to the expected and usually-observed decrease of ρ(T), the resistivity of Ho(Co1−xAlx)2 alloys (x = 0.15 and 0.2) increases at temperatures below TC. Moreover, the magnetoresistance of these alloys is positive around TC; this is also in a sharp contrast to the usually observed negative magnetoresistance. We show that the anomalous resistivity and magnetoresistance in these alloys are related to the metamagnetic instability of the Co 3d subsystem and to the fluctuating local magnetic susceptibility due to atomic substitution. Due to this fluctuating local magnetic susceptibility, the uniform exchange field of 4f moments induces a non-uniform polarization of the 3d system, with static spatial fluctuations of the local magnetization. This static magnetic disorder gives an additional contribution (ρm) to the electrical resistance in the alloys at temperatures below TC. The degree of this disorder changes with decreasing temperature, resulting in specific variation of ρm with temperature.

Magnetic properties and crystal structure of melt-spun Sm(Co, M)7 (M = Al and Si) ribbons

Effect of Si and Al contents on the magnetic properties and crystal structure of melt-spun SmCo7-xMx (M = Al and Si) ribbons have been investigated. The Rietveld refinement results show that Al and Si prefer to occupy the 3g site in the TbCu7-type structure. The changes in both the magnetocrystalline anisotropy field and the microstructure with Si or Al substitution may account for the variation of magnetic properties. The coercivity of SmCo7−xSix ribbons is enhanced from 1.9 kOe for SmCo7 to 4.7 kOe for SmCo6.5Si0.5 and 2.6 kOe for SmCo6.95Al0.05, which is mainly because of the enhancement of magnetic anisotropy field by the Si and Al substitution for Co in 3g sites. Furthermore, in melt-spun SmCo7−xMx ribbons system, with increasing x, the grain size is slightly reduced for M = Si, but increased for M = Al. In addition, with further increasing x, the enhancement of coercivity is attributed to both the third element substitution for Co in 3g sites and grain refinement.

Average and Local Structure Analyses of Li(Mn1/3Ni1/3Co1/3−xAlx)O2 Using Neutron and Synchrotron X-ray Sources

We prepared Li(Mn1/3Ni1/3Co1/3-xAlx)O2 by a solution method, and then investigated the electrode characteristics and average and local structures. From the charge-discharge cycle tests, it was found that Li(Mn1/3Ni1/3Co2/9Al1/9)O2 exhibited a worse cycle performance than Li(Mn1/3Ni1/3Co1/3)O2. In order to clarify the reason for this decrease from the viewpoint of the crystal structure, the average structures of the samples were studied by the Rietveld and Maximum Entropy Method (MEM) techniques using the neutron and synchrotron X-ray diffraction patterns. As a result, it was found that the Al substitution did not have a significant effect on the average structure. In order to reveal the local structures, we also performed X-ray absorption fine structure (XAFS) and Pair Distribution Function (PDF) analysis using neutron scattering data. These analyses implied that the stacking of the transition-metal layers varied by the partial substitution of Al for Co, and the arrangement had an influence on the cathode properties.

Self-Organized Core–Shell Structure for High-Power Electrode in Solid-State Lithium Batteries

Effect of Al-substitution for Co on the electrode properties of LiCoO2 is investigated in a sulfide solid electrolyte. The substitution decreases the electrode resistance and thus improves the high-rate capability. Investigation of the post-annealing effect revealed that, although the crystal structure or morphology of the LiAlxCo1–xO2 are not significantly changed by the post-annealing, the electrode properties are highly dependent on the post-annealing conditions, which suggests that the improvement in high-rate capability comes from the change in surface structure of the LiAlxCo1–xO2 particles (i.e., self-organized core–shell structure). The Al-substituted LiCoO2 obtained through this study delivers a discharge capacity of 115 mAh g–1 at 1 C and 84 mAh g–1 even at a high discharge rate of 5 C at 25 °C, which is one of the highest rate capabilities observed in solid-state cells.

Resistivity and Thermopower of Ho(Co1-xAlx)2-Effects of Pressure and Magnetic Field

The electrical resistivity ρ and thermopower S of the cubic Laves phase compounds Ho(Co 1- x Al x ) 2 ( x =0, 0.15 and 0.20) have been measured at temperatures from 2 to 300 K in magnetic fields up to 10 T. The measurements of ρ under pressures up to 3 GPa have been performed in the temperature range between 2 K and 300 K. Both ρ( T ) and S ( T ) of the pure HoCo 2 reveal abrupt changes at the magnetic ordering temperature T C , indicating the first order transition. ρ( T ) of the Al substituted samples ( x =0.15 and 0.20) show anomalous behavior in the form of an increase below T C . The variations of ρ and S at T C clearly indicate that the type of the magnetic transition changes under substitution of Al for Co from the first order to the second order. The residual resistivity of Ho(Co 1- x Al x ) 2 shows a rapid increase with increasing x . T C increases linearly for x < 0.15, having a maximum at x ≈0.15 and decreases with further increase of x . The peculiar x dependence of T C and the anomalous behav...

The correlative effects of Al and Co on the structure and electrochemical properties of a La–Mg–Ni-based hydrogen storage electrode alloy

Replacing Co in the La–Mg–Ni-based alloys by other cheap materials is an expected goal to reduce the cost of the hydrogen storage alloys. The present study aims to partially substitute Co by Al for the La–Mg–Ni-based hydrogen storage alloys and to get the correlative effects of Al and Co on the structure and electrochemical properties of the alloys. Alloys with composition of La 0.7Mg 0.3Ni 2.75Co 0.75− x Al x ( x = 0–0.4) were investigated. The results from X-ray diffraction analyses show that all of the alloys mainly consist of a LaNi 5 phase and a (La, Mg)Ni 3 phase. While LaNi 5 phase increases, the (La, Mg)Ni 3 phase decreases and the cell volumes of both the phases are enlarged with the increasing substitution of Al for Co. Results of the electrochemical studies indicate that the substitution of Al for Co can enhance the cycle stability of the alloy electrode effectively. The capacity retention after 100 cycles is improved from 45.9% ( x = 0) to 82.1% ( x = 0.4). However, the maximum capacity and the electrochemical kinetics decrease. The correlative actions of Al and Co on the corrosion and pulverization resistance of the alloys and hence on the cycle stability and electrochemical kinetics of the alloy electrodes were discussed.

Solid-State Synthesis as a Method for the Substitution of Al for Co in LiNi1 ∕ 3Mn1 ∕ 3Co ( 1 ∕ 3 − z ) AlzO2

Al was substituted for Co in by two different routes: during coprecipitation of the hydroxide precursor or afterward as introduced during solid-state sintering. The latter method avoids the formation of layered double hydroxides during the coprecipitation, but may not ensure uniform distribution of the Al atoms in the mixed cation layers. The electrochemical performance and thermal stability of Al-substituted was studied by coin cell testing and accelerating rate calorimetry tests, respectively. High resolution compositional analysis showed that the Al distribution was not uniform in material prepared by solid-state synthesis at , unlike materials prepared by coprecipitation at 900 or or by solid-state synthesis at . Nonuniform Al distribution does not affect the electrochemical properties strongly, but has a strong negative impact on the thermal stability of the charged electrode materials. The solid-state sintering substitution of Al for Co can be successful if the sintering temperature is high enough to ensure a uniform Al distribution.

Effect of substituting Al for Co on the hydrogen-storage performance of La0.7Mg0.3Ni2.6AlxCo0.5−x (x=0.0–0.3) alloys

La0.7Mg0.3Ni2.6AlxCo0.5−x (x = 0.0–0.3) alloys were prepared by induction melting, and the effects of partially substituting Al for Co on the structure and hydrogen-storage properties of the alloys were investigated systematically. It is found that La(Ni, Co, Al)5 phase with hexagonal CaCu5-type structure, LaNi3 phase with PuNi3 structure and MgNi2 phase exist as the main phases in La0.7Mg0.3Ni2.6AlxCo0.5−x (x = 0.0–0.3) alloys, and the cell volume of the La(Ni, Co, Al)5 phase increases with the amount of Al added. The results show that the substitution of Al for Co can reduce the plateau pressure and the hysteresis between hydrogen absorption and desorption, and improve the hydrogen-absorption capacity and thermal stability of the hydride. Moreover, the addition of Al can delay the oxidation of the surface layer of the alloy electrodes in electrolyte, slow down the capacity degradation and prolong the cycling lifetime, and enhance the electrocatalytic activity of the hydrogen-storage electrodes for hydrogen oxidation.

Synthesis, Electrochemical Properties, and Thermal Stability of Al-Doped LiNi1 ∕ 3Mn1 ∕ 3Co ( 1 ∕ 3 − z ) AlzO2 Positive Electrode Materials

Al-doped samples were synthesized using a coprecipitation method followed by calcination with at for and for . Electrochemical testing showed that had a high initial discharge capacity and good charge–discharge cycle performance in the voltage ranges of either 2.5–4.3 or . The impact of Al doping on the thermal stability of was studied by accelerating rate calorimetry. Al substitution for Co in caused a dramatic improvement in thermal stability over the material without aluminum. Al-doped with displays an energy density greater than and equivalent or higher thermal stability, making it a possible choice as an electrode material for large Li-ion batteries.

The effect of Al substitution on the reactivity of delithiated LiNi 1/3Mn 1/3Co (1/3−z)Al zO 2 with non-aqueous electrolyte

The high temperature reactions between 1 M LiPF 6 EC:DEC and Al-doped LiNi 1/3Mn 1/3Co (1/3− z )Al z O 2 charged to 4.3 V were studied by accelerating rate calorimetry (ARC) and compared with those of charged LiNi 1/3Mn 1/3Co 1/3O 2 and LiMn 2O 4. Al substitution for Co in LiNi 1/3Mn 1/3Co 1/3O 2 improves the thermal stability. Materials with z > 0.06 are less reactive with electrolyte than spinel LiMn 2O 4 at all temperatures studied. The maximum self-heating rate (SHR) attained and the specific capacity decrease as the Al content increases. There is a range of compositions near z = 0.1 that show excellent promise as materials which are both safer than and more energy dense than spinel LiMn 2O 4.

Structure and electrochemical properties of LaCo 11− x− yNi xM y (M = Fe, Mn and Al) compounds

In this work, the crystal structure and electrochemical charge–discharge properties of LaCo 13− x− y Ni x M y (M = Fe, Mn and Al) were studied. It was found that, in Co-rich region, except for the LaCo 11.4Ni 0.8Mn 0.8 sample, all the samples are composed mainly of the LaCo 13-type compounds. However, the 1:13 structure is difficult to obtain in Ni-rich samples. For the 1:13-type structure compounds. The lattice parameter and cell volume of compounds decrease with the substitution of Ni for Co and increase with the substitution of Al, Mn, Fe for Co. The electrochemical capacities of LaCo 12.2− y Ni 0.8M y (M = Fe, Mn, Al and y = 0.4 or 0.8) and LaCo 11− y Ni 2Al y ( y = 0, 0.5, 1.0) increase with increasing temperature. Compared with LaCo 13− x Ni x ( x = 0.8 and 2) compounds, the substitution of Mn or Al for Co results in decreasing of electrochemical capacity in the temperature range of 25–80 °C. The lowest electrochemical capacity was obtained from LaCo 11.8Ni 0.8Mn 0.4 compound. For the LaCo 13− x Ni x compounds, the electrochemical capacity increases in the temperature range 25–70 °C and decreases in the temperature range 70–80 °C with increasing Ni content x from 0.8 to 2. The best electrochemical properties of all the compounds studied here were obtained from LaCo 11.4Ni 0.8Fe 0.8 compound. The electrochemical stability increases and active property decreases markedly when Co is substituted by Al.

Effect of Al substitution for Co on the hydrogen storage characteristics of Ml 0.8Mg 0.2Ni 3.2Co 0.6− xAl x ( x=0–0.6) alloys

Ml 0.8Mg 0.2Ni 3.2Co 0.6− x Al x ( x=0–0.6) hydrogen storage alloys were prepared by induction melting and the effect of Al substitution for Co on the structure and hydrogen storage characteristics was investigated. These alloys are confirmed to be composed of LaNi 5 as matrix and (LaMg)Ni 3 as the secondary phase. The Al substitution leads to an expansion of the unit cell volume of matrix and an enhancement of the stability of the alloy hydrides. The thermodynamic properties such as Δ H and Δ S and the diffusion coefficient of hydrogen in these alloys were also evaluated.