LixCo0.4Ni0.3Mn0.3O2 electrode materials: Electrochemical and structural studies

LiCo_0.4Ni_0.3Mn_0.3O₂ layered oxide in a member of the LiCo_1?2xNi_xMn_xO₂ solid solution between LiCoO₂ and LiNi_0.5Mn_0.5O₂. Compositions from this solid solution have attracted much attention and have been extensively studied as promising cathode candidates to replace the most popular LiCoO₂ cathode material used in the commercial lithium-ion batteries (LiBs). LiCo_0.4Ni_0.3Mn_0.3O₂ positive electrode material was prepared via the combustion method followed by a thermal treatment at 900 °C for 12 h. This material was characterized by a high homogeneity and a granular shape. The Rietveld refinement evidenced that the structure of this compound exhibits no Ni/Li disorder revealing that the LiCo_1?2xNi_xMn_xO₂ system presents the ideal structure for LiBs application when x < 0.4. The electrochemical performances of the LiCo_0.4Ni_0.3Mn_0.3O₂ sample were measured at different current rates in the 2.7–4.5 V potential range. Its discharge capacity reached 178, 161 and 145 mAhg^?1 at C/20, 1C and 2C, respectively. Structural changes in LiCo_0.4Ni_0.3Mn_0.3O₂ upon delithiation were studied using ex situ X-ray diffraction. A continuous solid solution with a rhombohedral symmetry was detected in the whole composition range. This structural stability during the cycling combined with the obtained electrochemical features make this material convenient for the LiBs applications.     

Surface modification of LiCo1/3Ni1/3Mn1/3O2 with CoAl-MMO for lithium-ion batteries

Layered LiCo_1/3Ni_1/3Mn_1/3O₂ has been modified with Co–Al-mixed metal oxide (CoAl-MMO). The surface-modified materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and galvanostatic charge–discharge cycling. The CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ had an initial discharge specific capacity of 178.1 mAh g⁻¹ within the potential range of 2.75–4.5 V (vs. Li⁺/Li), and its discharge specific capacity is 175.0 mAh g⁻¹ after 50 cycles, much higher than that of the pristine LiCo_1/3Ni_1/3Mn_1/3O₂ (148.4 mAh g⁻¹). The improvement could be attributed to the CoAl-MMO coating layer that would hinder interaction between LiCo_1/3Ni_1/3Mn_1/3O₂ and electrolyte and stabilize the structure of LiCo_1/3Ni_1/3Mn_1/3O₂. Moreover, DSC showed that the CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ had a higher thermal stability than the pristine LiCo_1/3Ni_1/3Mn_1/3O₂. Therefore, the CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ could be a high-performance cathode material for lithium-ion batteries.     

Synthesis and electrochemical performance of Li1+xNi0.5Mn0.3Co0.2O2+δ (0 ≤ x ≤ 0.15) cathode materials for lithium-ion batteries

In this work, layered lithium-excess materials Li_1+xNi_0.5Mn_0.3Co_0.2O_2+δ (x = 0, 0.05, 0.10 and 0.15), of spherical morphology with primary nanoparticles assembled in secondary microspheres, were synthesized by a coprecipitation method. The effects of lithium content on the structure and electrochemical performance of these materials were evaluated by employing X-ray diffraction (XRD), inductive coupled plasma (ICP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge tests. It is found that Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ, i.e., Li[(Ni_0.5Mn_0.3Co_0.2)_0.95Li_0.05]O₂ showed the best electrochemical performance due to the highly ordered layered structure, reduced cation mixing and the lowest charge transfer resistance. Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ delivered a discharge capacity of 145 mA h g^?1 at 125 mA g^?1 in the cut-off voltage of 2.5–4.3 V, and had a capacity retention of 100% after 50 cycles at room temperature.     

A facile method to synthesize carbon coated Li1.2Ni0.2Mn0.6O2 with improved performance

Carbon-coated Li_1.2Ni_0.2Mn_0.6O₂ powders have been synthesized with Bakelite and heat process in air. The effect of carbon coating on the physical and electrochemical properties have been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), discharge and rate tests. The carbon-coated cathode exhibits much improved first discharge capacity and rate capability than the pristine sample. The discharge capacity at 0.1 and 5.0 C rates are 246 and 125 mAhg⁻¹, while that of pristine are only about 222 and 49 mAhg⁻¹, respectively. The capacity retention of Li_1.2Ni_0.2Mn_0.6O₂ electrode after 50 cycles is improved from 89.8 to 97.5% after carbon coating. EIS results indicate that R_ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode is decreased from 62 to 37 Ω after carbon coating.     

Synthesis and electrochemical characterization of LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by radiated polymer gel method

Layered LiCo_1/3Ni_1/3Mn_1/3O₂ as a lithium insertion positive-electrode material was prepared by a radiated polymer gel method. The synthesis conditions and microstructure, morphology and electrochemical properties of the products were investigated by XRD, SEM and electrochemical cell cycling. It was found that the positive-electrode material annealed at 950 °C showed the best electrochemical property with the first specific discharge capacity of 178 mAh/g at C/6 and stable cycling ability between 2.8 and 4.5 V versus Li/Li⁺. The optimized LiCo_1/3Ni_1/3Mn_1/3O₂ exhibited rather good rate capability with the specific capacity of 173 mAh/g at 0.2C and 116 mAh/g at 4C under a fast charge and discharge mode in rate performance test.     

The LiyNi0.2Mn0.2Co0.6O2 electrode materials: A structural and magnetic study

Layered LiNi_0.2Mn_0.2Co_0.6O₂ phase, belonging to a solid solution between LiNi_1/2Mn_1/2O₂ and LiCoO₂ most commercialized cathodes, was prepared via the combustion method at 900 °C for a short time (1 h). Structural and magnetic properties of this material during chemical extraction were investigated. The powders adopted the α-NaFeO₂ structure with almost none of the well-known Li/Ni cation disorder. The analysis of the magnetic properties in the paramagnetic domain agrees with the combination of Ni²⁺ (S = 1), Co³⁺ (S = 0) and Mn⁴⁺ (S = 3/2) spin-only values. X-ray analysis of the chemically delithiated Li_yNi_0.2Mn_0.2Co_0.6O₂ reveals no structural transition. The process of lithium extraction from and insertion into LiNi_0.2Mn_0.2Co_0.6O₂ was discussed on the basis of ex situ EPR experiments and magnetic susceptibility. Oxidation of Ni²⁺ (S = 1) to Ni³⁺ (S = 1/2) and to Ni⁴⁺ (S = 0) was observed upon lithium removal.     

Effect of Cu-doping on the electrochemical performance of FeS2

FeS₂ reportedly has a high specific capacity of 893 mAh/g; however, its poor cyclic performance limits its commercialization. To circumvent this limitation, strategies such as preparation of high-purity FeS₂ and Ni-doping were adopted to modify the electrochemical properties of FeS₂. Nevertheless, these approaches resulted only in limited improvements in the electrochemical properties. Therefore, in this study, we synthesized Cu-doped FeS₂ via a solvothermal process, aiming at improved electrochemical properties. Systematic studies indicated that Cu doping changed the morphology of FeS₂ from larger irregular particles to smaller spherical ones. The charge–discharge measurements indicated that the Cu-doped FeS₂ exhibited two discharge plateaus, at 1.6 V and 1.4 V. The initial specific discharge capacity of Cu-doped FeS₂ was about 866 mAh/g at a current density of 90 mA/g, which is approximately 11% higher than that of the undoped FeS₂. The initial discharge capacity of the Cu-doped FeS₂ at a current density of 2700 mA/g was 518 mAh/g, and its cyclic discharge capacity exceeded 105 mAh/g at the 20th cycle. Cyclic voltammetry and resistance measurements revealed that Cu-doping reduces both the internal resistance and polarization of Li/FeS₂ batteries.     

The effect of ZnO coating on LiMn2O4 cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn₂O₄ was modified with zinc oxide by a chemical process to improve its electrochemical performance at high temperatures. The physical properties of the prepared products have been investigated by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-rays analysis (EDAX). The charge/discharge of the materials was carried at 1 mA/cm² in the range of 3.0 and 4.4 V at 55 °C. The discharge capacity of ZnO-coated LiMn₂O₄ (117 mAh/g) showed only 3% loss of the initial capacity (121 mAh/g) over 60 cycles. The cycle ability improvement of the spinel LiMn₂O₄ coated with ZnO is demonstrated at high temperatures. From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycle ability may be attributed to the suppression on the formation of the passivation film and the reduction of Mn dissolution, which result from the modifying the surface of the spinel LiMn₂O₄ with zinc oxide.     

Electrochemical properties of 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 composite cathode powders prepared by large-scale spray pyrolysis

0.3Li₂MnO₃·0.7LiNi_0.5Mn_0.5O₂ composite cathode powders with a mixed-layer crystal structure comprising Li₂MnO₃ and LiNi_0.5Mn_0.5O₂ phases are prepared by spray pyrolysis. The composition of the cathode powders is found to be Li_1.19Ni_0.39Mn_0.61O₂ by ICP analysis. At a constant current density of 30 mA g^?1, the initial discharge capacities of the composite cathode powders post-treated at 700, 750, 800, and 850 °C are 177, 202, 215, and 212 mAh g^?1, respectively. The discharge capacity of the composite cathode powders post-treated at 800 °C decreases from 215 mAh g^?1 to 205 mAh g^?1 by the 40th cycle, in which the capacity retention is 95%. The first cycle has a low Coulombic efficiency of 75%. However, in the subsequent cycles, the Coulombic efficiency is retained at nearly 100%. The dQ/dV curves show that Mn exists as Mn⁴⁺ in the sample. The Mn⁴⁺ ions in the cathode powders become increasingly active as the cycle number increases and participate in the electrochemical reaction.     

Solvothermal synthesis of Mn2P2O7 and its application in lithium-ion battery

Manganese pyrophosphate, Mn₂P₂O₇ was synthesized by a simple solvothermal method using Mn metal powder and P₂S₅ in ethylene glycol medium at 190–220 °C. Morphology and crystalline structure of the products were characterized by X-ray diffraction and scanning electron microscopy. The flower-like microspheres with diameters of about 2–5 μm are composed of a number of nanoplatelets with thickness of 20–40 nm. The effect of reaction temperature and reaction time on the microstructure of Mn₂P₂O₇ was investigated. The samples were used as active anode materials for lithium-ion battery and their electrochemical properties were examined by constant current charge–discharge cycling. The Mn₂P₂O₇ electrodes exhibited initial reversible capacities of 440–330 mAh g^? 1 depending on the synthetic conditions. From these results, a possible reaction mechanism of Mn₂P₂O₇ with lithium was proposed.     

X-ray absorption spectroscopy studies of the Ni ion of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with a core–shell structure and LiNi0.8Co0.15Al0.05O2 as cathode materials

Core–shell materials have attracted a great deal of interest since core–shell particles have superior physical and chemical properties compared to their single-component counterparts. The cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) with a core–shell structure was synthesized via a co-precipitation method and investigated as the cathode material for lithium ion batteries. The core–shell particle consisted of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and LiNi_0.5Mn_0.5O₂ as the shell. The cycling behavior between 2.8 and 4.3 V at a current of 0.1 C-rate showed a reversible capacity of ～195 mAh g^?1 with little capacity loss after 50 cycles. Extensive assessment of the electronic structures of the LNCAO and LNCANMO cathode materials was carried out using X-ray absorption spectroscopy (XAS). XAS has been used for structure refinement on the transition metal ion of the cathode. In particular, XAS studies of electrochemical reactions have been done from the viewpoint of the transition metal ion. In this study, Ni K-edge XAS spectra of the charge and discharge processes of LNCAO and LNCANMO were investigated.     

Synthesis and electrochemical characterization of Li2MnO3–LiNixCOyMnzO2 cathode for lithium battery using co-precipitation method

The Li_xNi_0.23Co_0.12Mn_0.65O₂ electrode system with various compositions (x = 1.19, 1.33, 1.46, 1.58) was synthesized from a metal oxide precursor synthesized by co-precipitation method. The XRD patterns of the prepared powders revealed a hexagonal α-NaFeO₂ structure (space group: R-3m, 166) and the existence of a Li₂MnO₃ phase in the composite structure. In particular, the low Li content sample shows a three integrated structure (spinel, Li₂MnO₃, LiMO₂) for a Li/Metal(Ni/Co/Mn) mol ratio of 1.2. Scanning electron microscopy showed that all the synthesized samples contained spherical agglomerates with a size of 8–10 μm. Among the samples tested, Li_1.46Ni_0.23Co_0.12Mn_0.65O₂ shows relatively high charge and discharge capacity for the first cycle is 287, 192.9 mA h g^?1, respectively. Also, charge transfer resistance was also significantly improved compare with other samples.     

Electrochemical studies on cathode blends of LiMn2O4 and Li[Li1/15Ni1/5Co2/5Mn1/3O2]

Composite cathodes were prepared by blending LiMn₂O₄ spinel and Li[Li_1/15Ni_1/5Co_2/5Mn_1/3O₂] layer by simple mixing/ball milling followed by calcination at 800 °C. The prepared blend materials were subjected to XRD and charge–discharge studies. The cycling results revealed that the discharge capacity and cycleability of LiMn₂O₄ can be considerably increased upon blending the material with layered Li[Li_1/15Ni_1/5Co_2/5Mn_1/3O₂].     

Submicron size Li(Ni1/3Co1/3Mn1/3)O2 particles prepared by spray pyrolysis from polymeric precursor solution

Submicron-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles were prepared by spray pyrolysis. A polymeric precursor solution containing citric acid and ethylene glycol enabled the formation of submicron-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ spherical particles with narrow-sized distribution and non-aggregation characteristics in the spray pyrolysis. The mean sizes of the particles post-treated at temperatures of 800 and 900^∘C were 380 and 770 nm. On the other hand, the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles obtained from the aqueous solution had irregular morphology and broad-sized distribution. The discharge capacity of the particles prepared from polymeric precursor solution decreased from 88 mAh/g to 135 mAh/g after 50 cycles. The particles prepared from polymeric precursor solution had high discharge capacity and good cyclic properties than those of the particles prepared from the aqueous solution.     

Improvement of cycle stability at elevated temperature and high rate for LiNi0.5−xCuxMn1.5O4 cathode material after Cu substitution

A series of Cu-substituted LiNi_0.5−xCu_xMn_1.5O₄ (x = 0, 0.03, 0.05 and 0.08) spinels have been synthesized using a sol–gel method. The results demonstrate that when x = 0.05, the sample (LiNi_0.45Cu_0.05Mn_1.5O₄) exhibits the best electrochemical performance, achieving 124.5 mAh g⁻¹ and 115.0 mAh g⁻¹ at the discharge rates of 5 C and 20 C with the capacity retention of 97.7% and 95.7% after 150 cycles, respectively. Besides, the excellent cycle stability at 55 °C has been demonstrated to retain 96.8% of the maximum attainable discharge capacity (127.3 mAh g⁻¹) at the discharge rate of 5 C after 100 cycles. These data indicate that the LiNi_0.45Cu_0.05Mn_1.5O₄ cathode material has the real potential to be used for high power and high energy lithium ion battery in electric vehicle applications.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Lithium selective adsorption on 1-D MnO2 nanostructure ion-sieve

β-MnO₂, spinel-type Li₄Mn₅O₁₂ and pure cubic phase MnO₂ nanorod, with the size about 20–140 nm in diameter and 0.8–4 μm in length, were synthesized via a combination of hydrothermal synthesis and low temperature solid-phase reaction, more favorable to control the nanocrystalline structure with well-defined pore size distribution and high surface area than the traditional high temperature calcination process. Further, the MnO₂ ion-sieves with lithium selective adsorption property were prepared by the acid treatment process to completely extract lithium from the spinel Li₄Mn₅O₁₂ precursor with little change to the Mn–O lattice structure and the 1-D nanorod morphology. The effects of hydrothermal and solid-phase reaction process on the nanostructure, chemical stability and ion-exchange property of the ion-sieve material were examined with powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), N₂ adsorption–desorption at 77 K, and Li⁺ selective adsorption measurements. The lithium selective adsorption capacity was improved remarkably to 6.62 mmol g^?1 at equilibrium and about 5 mmol g^?1 at the initial lithium concentration of only 5.0 mmol l^?1, which is significant for lithium extraction from aqueous solutions with very low lithium content.     

Influence of isovalent ion substitution on the electrochemical performance of LiCoPO4

LiCo_1−xM_xPO₄ (M = Mg²⁺, Mn²⁺ and Ni²⁺; 0 ≤ x ≤ 0.2) compounds have been synthesized by solid-state reaction method and studied as cathode materials for secondary lithium batteries. LiCoPO₄ exhibits a discharge plateau at ∼4.7 V with an initial discharge capacity of 125 mAh/g and on cycling capacity falls. Substitution of Co²⁺ with Mg²⁺/Mn²⁺/Ni²⁺ in LiCoPO₄ has an influence on the initial discharge capacity and on cycling behaviour. The capacity retention of LiCoPO₄ is improved by manganese substitution. Among the manganese substituted phases, LiCo_0.95Mn_0.05PO₄ shows good reversible capacity of ∼50 mAh/g.     

Electrochemical properties of LiNi1−yTiyO2 and LiNi0.975M0.025O2 (M = Zn,Al, and Ti) synthesized by the solid-state reaction method

LiNi_1?yTi_yO₂ (y = 0.000, 0.012, 0.025, 0.050, 0.100, and 0.150) and LiNi_0.975M_0.025O₂ (M = Zn, Al, and Ti) were synthesized by the solid-state reaction method. The voltage vs. discharge capacity curves for y = 0.012 and y = 0.025 exhibit four distinct plateaus corresponding to phase transitions. Among LiNi_1?yTi_yO₂, LiNi_0.975Ti_0.025O₂ has the largest first discharge capacity, 154.8 mAh/g, at a rate of 0.1 C, and a relatively good cycling performance (77% at n = 10). Among LiNi_0.975M_0.025O₂ (M = Zn, Al, and Ti) samples, the LiNi_0.975Ti_0.025O₂ sample had the largest first discharge capacity. The LiNi_0.975Ti_0.025O₂ sample has sharper peaks for the ?dx/|dV| vs. V curves than the LiNi_0.975M_0.025O₂ (M = Zn and Al). The LiNi_0.975Al_0.025O₂ sample, with the first discharge capacity of 128.5 mAh/g at a rate of 0.1 C, has the best cycling performance (98% at n = 10).     

A new strategy to diminish the 4 V voltage plateau of LiNi0.5Mn1.5O4

As for spinel LiNi_0.5Mn_1.5O₄, there is 4 V voltage plateau in the charge–discharge profiles. This voltage plateau can be reduced by an annealing process, however it is hard to avoid it completely. In this study, a new strategy of partial substitution for Mn by Mg is applied. There is no 4 V voltage plateau in the charge–discharge profiles of Mg-doped compound LiNi_0.5Mn_1.45Mg_0.05O₄. This compound exhibits good electrochemical properties which can be used as cathode material of lithium ion batteries. At 1 C rate, it can deliver a capacity of around 129 mAh g⁻¹ and remain good cycle performance.