Co-precipitation synthesis of spherical Li1.05M0.05Mn1.9O4 (M = Ni, Mg, Al) spinel and its application for lithium secondary battery cathode

Metal-doped spinel lithium manganese oxides were successfully synthesized via co-precipitation. The synthesized Li_1.05M_0.05Mn_1.9O₄ (M = Ni, Mg, Al) had highly crystalline cubic spinel phase with the space group Fd3m, as confirmed by X-ray diffraction study. From scanning electron microscopic observation, it was found that the prepared materials had spherical morphology with high tap-density. The Li_1.05M_0.05Mn_1.9O₄ (M = Ni, Mg, Al) electrode exhibited improved cycling performance at elevated temperature. Especially, the Li_1.05Al_0.05Mn_1.9O₄ showed capacity retention of 91.5% during 100 cycles at elevated temperature (55 °C). Also the thermal stability of the Li_1.05M_0.05Mn_1.9O₄ (M = Ni, Mg, Al) was also significantly improved.     

Improvement of electrochemical stability of LiMn2O4 by CeO2 coating for lithium-ion batteries

CeO₂-coated LiMn₂O₄ spinel cathode was synthesized using two-step synthesis method. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The results of the electrochemical performances on CeO₂-coated electrode are compared to those of electrodes based on LiMn₂O₄ spinel without CeO₂ coating. CeO₂-coated LiMn₂O₄ cathode improved the cycling stability of the electrode. The capacity retention of 2 wt% CeO₂-coated LiMn₂O₄ was more than 82% after 150 cycles between 3.0 and 4.4 V at room temperature and 82% after 40 cycles at elevated temperature of 60 °C. The amounts of dissolved manganese-ions in CeO₂-coated LiMn₂O₄ significantly are smaller than pristine LiMn₂O₄ systems especially at elevated temperatures. Surface-modified LiMn₂O₄ can suppress the dissolution reaction of manganese-ions at elevated temperature and clearly improve the cyclability of the spinel LiMn₂O₄ cathode materials.     

Enhanced rate performance of nano–micro structured LiFePO4/C by improved process for high-power Li-ion batteries

A spherical carbon-coated nano–micro structured LiFePO₄ composite is synthesized for use as a cathode material in high-power lithium-ion batteries. The composites are synthesized through carbothermal reduction with two sessions of ball milling (before and after pre-sintering of precursor) followed by spray-drying with the dispersant of polyethylene glycol added. The structure, particle size, and surface morphology of the cathode active material and the properties of the coated carbon are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Results indicate that the LiFePO₄/C composite has a spherical micro-porous morphology composed of a large number of carbon-coated nano-spheres linked together with an ordered olivine structure. The carbon on the surface of LiFePO₄ effectively reduces inter-particle agglomeration of the LiFePO₄ particles. A galvanostatic charge–discharge test indicates that the LiFePO₄/C composites exhibit initial discharge capacities of 155 mAh g⁻¹ and 88 mAh g⁻¹ at 0.2 C and 20 C rates with the end of discharge voltage of 2.5 V, respectively. This behavior is ascribed to the unique spherical structure, which shortens lithium ions diffusion length and improves the electric contact between LiFePO₄ particles.     

Comparison of 4 V and 3 V electrochemical properties of nanocrystalline LiMn2O4 cathode particles in lithium ion batteries prepared by ultrasonic spray pyrolysis

Nanocrystalline LiMn₂O₄ particles were prepared by an ultrasonic spray pyrolysis method using nitrate salts at 800 °C in air atmosphere. Particle properties were characterized by the X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy. In addition, cyclic voltammetry and galvanostatic tests were performed to investigate the effects of structure on electrochemical behavior of both the 4 V and 3 V potential plateaus. Particle characterization studies show that the nanocrystalline particles have spinel structure of submicron size with spherical morphology. Particles, ranging between 75 and 1250 nm, were formed by aggregation of nanoparticles. Discharge capacity of LiMn₂O₄ particles between 3.0 and 4.5 V is 70 mA h g⁻¹ and cumulative capacity between 2.2 and 4.5 V is 111 mA h g⁻¹ at 0.5 C rate. Discharge capacity at the 4 V potential region reduces to 47% of initial capacity, whereas cumulative capacity fade is 62% after 100 cycles at 0.5 C rate. Although nanocrystalline LiMn₂O₄ cathode particles exhibit good rate capability at the 4 V plateau, capacity decreased rapidly by increasing C- rates and cycling between 2.2 and 4.5 V. The loss of capacity can be attributed to phase transformation and dissolution of electrode material. Particle characterization of used cathodes showed that nanocrystalline LiMn₂O₄ electrodes partly dissolve during electrochemical cycling.     

Li6V10O28, a novel cathode material for Li-ion battery

A novel cathode material, lithium decavanadate Li₆V₁₀O₂₈ with a large tunnel within the framework structure for lithium ion battery has been prepared by hydrothermal synthesis and annealing dehydration treatment. The structure and electrochemical properties of the sample have been investigated. The novel material shows good reversibility for Li⁺ insertion/extraction and long cycle life. High discharge capacity (132 mAh/g) is obtained at 0.2 mA/cm² discharge current and potential range between 2.0 and 4.2 V versus Li⁺/Li. AC impedance of the Li/Li₆V₁₀O₂₈ cell reveals that the cathode process is controlled mainly by Li⁺ diffusion in the active material. The novel material would be a promising cathode material for Li-ion batteries.     

Synthesis and electrochemical characterizations of nano-scaled Zn doped LiMn2O4 cathode materials for rechargeable lithium batteries

The LiZn_xMn_2−xO₄ (x = 0.00-0.15) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol-gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valance state of Mn in the synthesized materials. The sample exhibited a well-defined spinel structure and the lattice parameter was linearly increased with increasing the Zn contents in LiZn_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmission electron microscopy, respectively. Electrochemical properties were characterized for the assembled Li/LiZn_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5 C rate and cyclic voltammetry technique in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them Zn doped spinel LiZn_0.10Mn_1.90O₄ has improved the structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.     

Synthesis of spinel Li4Mn5O12 with an aid of mechanochemical treatment

A mechanochemically assisted method for synthesizing spinel Li₄Mn₅O₁₂ has been proposed in this paper. The method involves grinding a mixture of LiOH·H₂O and γ-MnO₂ in ambient air, followed by heating the ground product. The grinding of the mixture was conducted by using a planetary ball mill, causing their structural changes into amorphous state, which is lithium manganese oxides hydrated (Li-Mn-O·nH₂O). The ground product can be crystallized into lithium manganese oxide by heating at about 400 °C or more. Heating the ground product at around 600 °C for 12 h results in the formation of pure phase of the spinel. Temperature in the heating stage is an important factor in crystallization of the spinel from the amorphous mixture, and heating up to about 600 °C is suitable for the formation of pure phase spinel. The product synthesized is very fine powder with mean grain size of 100 nm.     

Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel prepared by radiated polymer gel method

LiNi_0.5Mn_1.5O₄ as a 4.7 V-class cathode material was prepared through the radiated polymer gel method that allowed homogeneous mixing of starting materials at the atomic scale. After calcinations of the polymer gels containing the metal salts at different temperatures from 750 to 1150 °C, powders of a pure LiNi_0.5Mn_1.5O₄ phase were obtained. X-ray diffraction and transmission electron microscopy were used to characterize the structures of the powders. Galvanostatic cell cycling and a simultaneous DC resistance measurement were performed on Li/LiNi_0.5Mn_1.5O₄ cells. It is found that the powder calcined at 950 °C shows the best electrochemical performance with the initial discharge capacity of 139 mAh g⁻¹ and 96% retention after 50 cycles. Adopting a slow cooling procedure for the powder calcination can increase the capacity of LiNi_0.5Mn_1.5O₄ at the 4.7 V plateau. Besides, a “w”-shape change of the DC resistance of Li/LiNi_0.5Mn_1.5O₄ cells is a good indication of the structural change of LiNi_0.5Mn_1.5O₄ electrode during charge and discharge courses.     

Enhanced cycling stability of LiMn2O4 by surface modification with melting impregnation method

The surface of as-prepared LiMn₂O₄ was modified with Al₂O₃ by a melting impregnation method. X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies indicated that Al₂O₃ nano-particles are distributed around the spinel. X ray absorption fine structure analysis (XAFS) further demonstrated that Al atoms were also doped to the surface of LiMn₂O₄ particles. The nano-Al₂O₃ particle coating improves the capacity retention of spinel LiMn₂O₄ efficiently at both room temperature and 55 °C. The mechanism of improvement for surface modified LiMn₂O₄ can be attributed to the inhibition of a surface Jahn-Teller distortion and the decrease of manganese dissolution, leading to good electric contact among particles.     

Improved electrochemical properties of Li1+x(Ni0.3Co0.4Mn0.3)O2−δ (x = 0, 0.03 and 0.06) with lithium excess composition prepared by a spray drying method

Layered Li_1+x(Ni_0.3Co_0.4Mn_0.3)O_2−δ (x = 0, 0.03 and 0.06) materials were synthesized through the different calcination times using the spray-dried precursor with the molar ratio of Li/Me = 1.25 (Me = transition metals). The physical and electrochemical properties of the lithium excess and the stoichiometric materials were examined using XRD, AAS, BET and galvanostatic electrochemical method. As results, the lithium excess Li_1.06(Ni_0.3Co_0.4Mn_0.3)O_2−δ could show better electrochemical properties, such as discharge capacity, capacity retention and C rate ability, than those of the stoichiometric Li_1.00(Ni_0.3Co_0.4Mn_0.3)O_2−δ. In this paper, the effect of excess lithium on the electrochemical properties of Li_1+x(Ni_0.3Co_0.4Mn_0.3)O_2−δ materials will be discussed based on the experimental results of ex situ X-ray diffraction, transmission electron microscopy (TEM) and galvanostatic intermittent titration technique (GITT)     

Electrochemical performance of Li4Mn5O12 nano-crystallites prepared by spray-drying-assisted solid state reactions

Nanosized Li₄Mn₅O₁₂ has been synthesized by a spray-drying-assisted solid state method. The effect of spray drying and drying temperature on the microstructure and electrochemical performance of the final products has been investigated. The microstructure of the products has been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electrochemical performance of the products has been studied by galvanostatic cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It has been found that the products prepared with a spray-drying pretreatment of the precursor exhibit a smaller grain size and a narrower size distribution than that prepared without the pretreatment. Among the three samples with a precursor pretreatment, that pretreated at 250 °C shows the best electrochemical performance due to the smallest grain size of below 50 nm and the narrowest size distribution.     

Molten salt synthesis of LiNi0.5Mn1.5O4 spinel for 5 V class cathode material of Li-ion secondary battery

Well-ordered high crystalline LiNi_0.5Mn_1.5O₄ spinel has been readily synthesized by a molten salt method using a mixture of LiCl and LiOH salts. Synthetic variables on the synthesis of LiNi_0.5Mn_1.5O₄, such as synthetic atmosphere, LiCl salt amount, synthetic temperature, and synthetic time, were intensively investigated. X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images showed that LiNi_0.5Mn_1.5O₄ synthesized at 900 and 950 °C have cubic spinel structure () with clear octahedral dimension. LiNi_0.5Mn_1.5O₄ spinel phase began to decompose at around 1000 °C accompanied with structural and morphological degradation. LiNi_0.5Mn_1.5O₄ powders synthesized at 900 °C for 3 h delivered an initial discharge capacity of 139 mAh/g with excellent capacity retention rate more than 99% after 50 cycles.     

Hydrothermal synthesis of layered Li[Ni1/3Co1/3Mn1/3]O2 as positive electrode material for lithium secondary battery

In attempts to prepare layered Li[Ni_1/3Co_1/3Mn_1/3]O₂, hydrothermal method was employed. The hydrothermal precursor, [Ni_1/3Co_1/3Mn_1/3](OH)₂, was synthesized via a coprecipitation route. The sphere-shaped powder precursor was hydrothermally reacted with LiOH aqueous solution at 170 °C for 4 days in autoclave. From X-ray diffraction and scanning electron microscopic studies, it was found that the as-hydrothermally prepared powders were crystallized to layered α-NaFeO₂ structure and the particles had spherical shape. The as-prepared Li[Ni_1/3Co_1/3Mn_1/3]O₂ delivered an initial discharge of about 110 mA h g⁻¹ due to lower crystallinity. Heat treatment of the hydrothermal product at 800 °C was significantly effective to improve the structural integrity, which consequently affected the increase in the discharge capacity to 157 (4.3 V cut-off) and 182 mA h g⁻¹ (4.6 V cut-off) at 25 °C with good reversibility.     

Examinations on 2.5 V Li[Li1/3Ti5/3]O4/Li[Li0.1Al0.1Mn1.8]O4 cells at −10, 25, and 55 °C for the first-generation 12 V lead-free batteries

Electrochemical behaviors of 2.5 V Li[Li_1/3Ti_5/3]O₄ (LTO)/Li[Li_0.1Al_0.1Mn_1.8]O₄ (LAMO) cells for the first-generation 12 V lead-free battery were examined at −10, 25, and 55 °C. The LTO/LAMO cells showed the same rechargeable capacity in temperature ranging from −10 to 55 °C when the cells were examined at 0.5 mA cm⁻² in cell potential ranging from 0 to 3.0 V. Capacity fading after 250 cycles was negligibly small at −10 °C. Rechargeable capacities, however, faded 5% at 25 °C and 15% at 55 °C after 250 cycles. In the discharged LTO/LAMO cell after 250 cycles at 55 °C, the state of charge (SOC) of the positive electrode was 16% while SOC of the negative electrode was 0%, indicated that the capacity fading was due to an imbalance in SOC between the positive and negative electrodes. To understand the progress of an imbalance in SOC, the LTO/LAMO cell with a lithium auxiliary electrode was fabricated and examined at 55 °C for 400 cycles, and the possible origin of capacity fading was discussed.     

Optimizing preparation conditions for 5 V electrode performance, and structural changes in Li1−xNi0.5Mn1.5O4 spinel

A new lithium-excess method is used for the synthesis of LiNi_0.5Mn_1.5O₄ electrode materials at temperatures in the 600-800 °C range. Higher average manganese oxidation state and lower impurity contents are detected from X-ray diffraction in the spinel samples, as compared with stoichiometric synthesis. These properties cause the virtual elimination of the 4 V capacity, thus allowing a higher performance of these 5 V materials. A two-phase model of lithium extraction-insertion is detected by X-ray diffraction of electrodes prepared at different extensions of charge.     

High performance Li3V2(PO4)3/C composite cathode material for lithium ion batteries studied in pilot scale test

Li₃V₂(PO₄)₃/C composite cathode material was synthesized via carbothermal reduction process in a pilot scale production test using battery grade raw materials with the aim of studying the feasibility for their practical applications. XRD, FT-IR, XPS, CV, EIS and battery charge-discharge tests were used to characterize the as-prepared material. The XRD and FT-IR data suggested that the as-prepared Li₃V₂(PO₄)₃/C material exhibits an orderly monoclinic structure based on the connectivity of PO₄ tetrahedra and VO₆ octahedra. Half cell tests indicated that an excellent high-rate cyclic performance was achieved on the Li₃V₂(PO₄)₃/C cathodes in the voltage range of 3.0-4.3 V, retaining a capacity of 95% (96 mAh/g) after 100 cycles at 20C discharge rate. The low-temperature performance of the cathode was further evaluated, showing 0.5C discharge capacity of 122 and 119 mAh/g at −25 and −40 °C, respectively. The discharge capacity of graphite//Li₃V₂(PO₄)₃ batteries with a designed battery capacity of 14 Ah is as high as 109 mAh/g with a capacity retention of 92% after 224 cycles at 2C discharge rates. The promising high-rate and low-temperature performance observed in this work suggests that Li₃V₂(PO₄)₃/C is a very strong candidate to be a cathode in a next-generation Li-ion battery for electric vehicle applications.     

Isothermal calorimetry investigation of Li1+xMn2−yAlzO4 spinel

The heat generation of LiMn₂O₄, Li_1.156Mn_1.844O₄, and Li_1.06Mn_1.89Al_0.05O₄ spinel cathode materials in a half-cell system was investigated by isothermal micro-calorimetry (IMC). The heat variations of the Li/LiMn₂O₄ cell during charging were attributed to the LiMn₂O₄ phase transition and order/disorder changes. This heat variation was largely suppressed when the stoichiometric spinel was doped with excess lithium or lithium and aluminum. The calculated entropy change (dE/dT) from the IMC confirmed that the order/disorder change of LiMn₂O₄, which occurs in the middle of the charge, was largely suppressed with lithium or lithium and aluminum doping. The dE/dT values obtained did not agree between the charge and the discharge at room temperature (25 °C), which was attributed to cell self-discharge. This discrepancy was not observed at low temperature (10 °C). Differential scanning calorimeter (DSC) results showed that the fully charged spinel with lithium doping has better thermal stability.     

Aluminothermal synthesis and characterization of Li3V2−xAlx(PO4)3 cathode materials for lithium ion batteries

Monoclinic Li₃V_2−xAl_x(PO₄)₃ with different Al³⁺ doping contents (x = 0, 0.05, 0.08, 0.10 and 0.12) have been prepared by a facile aluminothermal reaction. Aluminum nanoparticles have been used as source for Al³⁺ and nucleus for Li₃V_2−xAl_x(PO₄)₃ nucleation as well as reducing agent in the aluminothermal strategy. The products were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electrochemical methods. The XRD results show that the as-obtained Li₃V_2−xAl_x(PO₄)₃ has a phase-pure monoclinic structure, irrespective of the Al³⁺ doping concentration. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results reveal that the charge-transfer resistance of the Li₃V₂(PO₄)₃ is reduced and the reversibility is enhanced after V³⁺ substituted by Al³⁺. In addition, The Li₃V_2−xAl_x(PO₄)₃ phases exhibit better cycling stability than the pristine Li₃V₂(PO₄)₃.     

Lithium-deficient LiYMn2O4 spinels (0.9 ≤ Y < 1): Lithium content, synthesis temperature, thermal behaviour and electrochemical properties

Lithium-deficient Li_YMn₂O₄ spinels (LD-Li_YMn₂O₄) with nominal composition (0.9 ≤ Y < 1) have been synthesized by melt impregnation from Mn₂O₃ and LiNO₃ at temperatures ranging from 700 °C to 850 °C. X-ray diffraction data show that LD-Li_YMn₂O₄ spinels are obtained as single phases in the range Y = 0.975-1 at 700 °C and 750 °C. Morphological characterization by transmission electron microscopy shows that the particle size of LD-Li_YMn₂O₄ spinels increases on decreasing the Li-content. The influence of the Li-content and the synthesis temperature on the thermal and electrochemical behaviours has been systematically studied. Thermal analysis studies indicate that the temperature of the first thermal effect in the differential thermal analysis (DTA)/thermogravimetric (TG) curves, T_C1, linearly increases on decreasing the Li-content. The electrochemical properties of LD-Li_YMn₂O₄ spinels, determined by galvanostatic cycling, notably change with the synthesis conditions. So, the first discharge capacity, Q_disch., at C rate increases on rising the Li-content and the synthesis temperature. The sample Li_0.975Mn₂O₄ synthesized at 700 °C has a Q_disch. = 123 mAh g⁻¹ and a capacity retention of 99.77% per cycle. This LD-Li_YMn₂O₄ sample had the best electrochemical characteristics of the series.     

Electrochemical performance and local cationic distribution in layered LiNi1/2Mn1/2O2 electrodes for lithium ion batteries

LiNi_1/2Mn_1/2O₂ electrodes with layered structure were synthesized by solid-state reaction between lithium hydroxide and mixed Ni,Mn oxides obtained from co-precipitated Ni,Mn carbonates and hydroxides and freeze-dried Ni,Mn citrates. The temperature of the solid-state reaction was varied between 800 and 950 °C. This method of synthesis allows obtaining oxides characterized with well-crystallized nanometric primary particles bounded in micrometric aggregates. The extent of particle agglomeration is lower for oxides obtained from freeze-dried Ni,Mn citrates. The local Mn⁴⁺ surrounding in the transition metal layers was determined by X-band electron paramagnetic resonance (EPR) spectroscopy. It has been found that local cationic distribution is consistent with α,β-type cationic order with some extent of disordering that depends mainly on the precursors used. The electrochemical extraction and insertion of lithium was tested in lithium cells using Step Potential Electrochemical Spectroscopy. The electrochemical performance of LiNi_1/2Mn_1/2O₂ oxides depends on the precursors used, the synthesis temperature and the potential range. The best electrochemical response was established for LiNi_1/2Mn_1/2O₂ prepared from the carbonate precursor at 900 °C. The changes in local environment of Mn⁴⁺ ions during electrochemical reaction in both limited and extended potential ranges were discussed on the basis of ex situ EPR experiments.