Synthesis and electrochemical performance of the high voltage cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with improved rate capability

The high voltage layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode material, which is a solid solution between Li₂MnO₃ and LiMn_0.4Ni_0.4Co_0.2O₂, has been synthesized by co-precipitation method followed by high temperature annealing at 900 °C. XRD and SEM characterizations proved that the as prepared powder is constituted of small and homogenous particles (100-300 nm), which are seen to enhance the material rate capability. After the initial decay, no obvious capacity fading was observed when cycling the material at different rates. Steady-state reversible capacities of 220 mAh g⁻¹ at 0.2C, 190 mAh g⁻¹ at 1C, 155 mAh g⁻¹ at 5C and 110 mAh g⁻¹ at 20C were achieved in long-term cycle tests within the voltage cutoff limits of 2.5 and 4.8 V at 20 °C.     

Basic molten salt process—A new route for synthesis of nanocrystalline Li4Ti5O12-TiO2 anode material for Li-ion batteries using eutectic mixture of LiNO3-LiOH-Li2O2

A nanocrystalline Li₄Ti₅O₁₂-TiO₂ duplex phase has been synthesized by a simple basic molten salt process (BMSP) using an eutectic mixture of LiNO₃-LiOH-Li₂O₂ at 400-500 °C. The microstructure and morphology of the Li₄Ti₅O₁₂-TiO₂ product are characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sample prepared by heat-treating at 300 °C for 3 h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li₄Ti₅O₁₂; with heat treatment at 400 °C for 3 h (S-2), there is a duplex crystallite size (fine < 10 nm, and coarse > 20 nm) of Li₄Ti₅O₁₂-TiO₂; at 500 °C for 3 h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size ∼15-30 nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193 mAh g⁻¹ at 0.2 C, 168 mAh g⁻¹ at 0.5 C, 146 mAh g⁻¹ at 1 C, 135 mAh g⁻¹ at 2 C, and 117 mAh g⁻¹ at 5 C. After 100 cycles, the discharge capacity is 138 mAh g⁻¹ at 1 C with a capacity retention of 95%. The S-2 sample yields the best electrochemical performance in terms of charge-discharge capacity and rate capability compared with other samples. Its superior electrochemical performance can be mainly attributed to the duplex crystallite structure, composed of fine (<10 nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li₄Ti₅O₁₂ and the anatase TiO₂.     

Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode

Li₂FeSiO₄/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li₂FeSiO₄/C cathode were investigated. The XRD patterns of the Li₂FeSiO₄/C samples indicate that all the samples are of good crystallinity, and a little Fe₃O₄ impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750 °C. The Li₂FeSiO₄/C sample synthesized at 650 °C has good electrochemical performances with an initial discharge capacity of 144.9 mAh g⁻¹ and the discharge capacity remains 136.5 mAh g⁻¹ after 10 cycles. The performance of Li₂FeSiO₄/C cathode is further improved by modification of Ni substitution. The Li₂Fe_0.9Ni_0.1SiO₄/C composite cathode has an initial discharge capacity of 160.1 mAh g⁻¹, and the discharge capacity remains 153.9 mAh g⁻¹ after 10 cycles. The diffusion coefficient of lithium in Li₂FeSiO₄/C is 1.38 × 10⁻¹² cm² s⁻¹ while that in Li₂Fe_0.9Ni_0.1SiO₄/C reaches 3.34 × 10⁻¹² cm² s⁻¹.     

Electrochemical performance of In2O3 thin film electrode in lithium cell

Indium oxide (In₂O₃) coating on Pt, as an electrode of thin film lithium battery was carried out by using cathodic electrochemical synthesis in In₂(SO₄)₃ aqueous solution and subsequently annealing at 400 °C. The coated specimens were characterized by X-ray photoelectron spectroscopy (XPS) for chemical bonding, X-ray diffraction (XRD) for crystal structure, scanning electron microscopy (SEM) for surface morphology, cyclic voltammetry (CV) for electrochemical properties, and charging/discharging test for capacity variations. The In₂O₃ coating film composed of nano-sized particles about 40 nm revealing porous structure was used as the anode of a lithium battery. During discharging, six lithium ions were firstly reacted with In₂O₃ to form Li₂O and In, and finally the Li_4.33In phase was formed between 0.7 and 0.2 V, revealing the finer particles size about 15 nm. The reverse reaction was a removal of Li⁺ from Li_4.33In phase at different oxidative potentials, and the rates of which were controlled by the thermodynamics state initially and diffusion rate finally. Therefore, the total capacity was increased with decreasing current density. However, the cell delivering a stable and reversible capacity of 195 mAh g⁻¹ between 1.2 and 0.2 V at 50 μA cm⁻² may provide a choice of negative electrode applied in thin film lithium batteries.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.     

Electrochemical deposition of porous Co3O4 nanostructured thin film for lithium-ion battery

Porous Co₃O₄ nanostructured thin films are electrodeposited by controlling the concentration of Co(NO₃)₂ aqueous solution on nickel sheets, and then sintered at 300 °C for 3 h. The as-prepared thin films are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The electrochemical measurements show that the highly porous Co₃O₄ thin film with the highest electrochemically active specific surface area (68.64 m² g⁻¹) yields the best electrochemical performance compared with another, less-porous film and with a non-porous film. The highest specific capacity (513 mAh g⁻¹ after 50 cycles) is obtained from the thinnest film with Co₃O₄ loaded at rate of 0.05 mg cm⁻². The present research demonstrates that electrode morphology is one of the crucial factors that affect the electrochemical properties of electrodes.     

Structural and electrochemical characterization of xLi[Li1/3Mn2/3]O2·(1 − x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) as cathode materials for lithium ion batteries

A series of cathode materials with molecular notation of xLi[Li_1/3Mn_2/3]O₂·(1 − x)Li[Ni_1/3Mn_1/3Co_1/3]O₂ (0 ≤ x ≤ 0.9) were synthesized by combination of co-precipitation and solid state calcination method. The prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, and their electrochemical performances were investigated. The results showed that sample 0.6Li[Li_1/3Mn_2/3]O₂·0.4Li[Ni_1/3Mn_1/3Co_1/3]O₂ (x = 0.6) delivers the highest capacity and shows good capacity-retention, which delivers a capacity ∼250 mAh g⁻¹ between 2.0 and 4.8 V at 18 mA g⁻¹.     

High-density spherical Li4Ti5O12/C anode material with good rate capability for lithium ion batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. To improve the material's rate capability and pile density is considered as the important researching direction. One effective way is to prepare powders composed of spherical particles containing carbon black. A novel technique has been developed to prepare spherical Li₄Ti₅O₁₂/C composite. The spherical precursor containing carbon black is prepared via an “outer gel” method, using TiOCl₂, C and NH₃ as the raw material. Spherical Li₄Ti₅O₁₂/C powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃ in N₂. The investigation of TG/DSC, SEM, XRD, Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂/C composite prepared by this method are spherical, has high tap-density and excellent rate capability. It is observed that the tap-density of spherical Li₄Ti₅O₁₂/C powders (the mass content of C is 4.8%) is as high as 1.71 g cm⁻³, which is remarkably higher than the non-spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, the initial discharge specific capacity of the sample is as high as 144.2 mAh g⁻¹, which is still 128.8 mAh g⁻¹ after 50 cycles at a current density of 1.6 mA cm⁻².     

A novel method for synthesis of layered LiNi1/3Mn1/3Co1/3O2 as cathode material for lithium-ion battery

The layered LiNi_1/3Mn_1/3Co_1/3O₂ materials with good crystalline are synthesized by a novel method of hydrothermal method followed by a short calcination process. The crystalline structure and morphology of the synthesized materials are characterized by XRD, SEM. Their electrochemical performances are evaluated by CV, EIS and galvonostatic charge/discharge tests. The material synthesized at 850 °C for 6 h shows the highest initial discharge capacity of 187.7 mAh g⁻¹ at 20 mA g⁻¹. And the capacity retention of 97.9% is maintained at the end of 40 cycles at 1.0 C. CV test reveals almost no shift of anodic and cathodic peaks after first cycle, which indicates good reversible deintercalation and intercalation of Li⁺ ions.     

Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries

Nano-CuCo₂O₄ is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10–20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo₂O₄ at 60 mA g⁻¹ in the voltage range 0.005–3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g⁻¹ per cycle. Good rate capability is also found in the range 0.04–0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g⁻¹ (∼6.9 mol of Li per mole of CuCo₂O₄) and 745(±10) mAh g⁻¹ (∼6.8 mol of Li), respectively at a current of 60 mA g⁻¹. The average discharge and charge potentials are ∼1.2 and ∼2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co₃O₄ and Cu ↔ CuO aided by Li₂O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo₂O₄ compares well with that of iso-structural nano-Co₃O₄ as reported in the literature.     

Electrochemical performance of SrF2-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

SrF₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials with improved cycling performance over 2.5–4.6 V were investigated. The structural and electrochemical properties of the materials were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), charge–discharge tests and electrochemical impedance spectra (EIS). The results showed that the crystalline SrF₂ with about 10–50 nm particle size is uniformly coated on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particles. As the coating amount increased from 0.0 to 2.0 mol%, the initial capacity and rate capability of the coated LiNi_1/3Co_1/3Mn_1/3O₂ decreased slightly owing to the increase of the charge-transfer resistance; however, the cycling stability was improved by suppressing the increase of the resistance during cycling. 4.0 mol% SrF₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ showed remarkable decrease of the initial capacity. 2.0 mol% coated sample exhibited the best electrochemical performance. It presented an initial discharge capacity of 165.7 mAh g⁻¹, and a capacity retention of 86.9% after 50 cycles at 4.6 V cut-off cycling.     

Synthesis and characterization of submicron-sized LiNi1/3Co1/3Mn1/3O2 by a simple self-propagating solid-state metathesis method

Submicron-sized LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials were synthesized using a simple self-propagating solid-state metathesis method with the help of ball milling and the following calcination. A mixture of Li(ac)·2H₂O, Ni(ac)₂·4H₂O, Co(ac)₂·4H₂O, Mn(ac)₂·4H₂O (ac = acetate) and excess H₂C₂O₄·2H₂O was used as starting material without any solvent. XRD analyses indicate that the LiNi_1/3Co_1/3Mn_1/3O₂ materials were formed with typical hexagonal structure. The FESEM images show that the primary particle size of the LiNi_1/3Co_1/3Mn_1/3O₂ materials gradually increases from about 100 nm at 700 °C to 200–500 nm at 950 °C with increasing calcination temperature. Among the synthesized materials, the LiNi_1/3Co_1/3Mn_1/3O₂ material calcined at 900 °C exhibits excellent electrochemical performance. The steady discharge capacities of the material cycled at 1 C (160 mA g⁻¹) rate are at about 140 mAh g⁻¹ after 100 cycles in the voltage range 3–4.5 V (versus Li⁺/Li) and the capacity retention is about 87% at the 350th cycle.     

High rate capabilities of all-solid-state lithium secondary batteries using Li4Ti5O12-coated LiNi0.8Co0.15Al0.05O2 and a sulfide-based solid electrolyte

Rate capability of LiNi_0.8Co_0.15Al_0.05O₂ in solid-state cells was investigated with 70Li₂S-30P₂S₅ glass-ceramics as a sulfide solid electrolyte. It showed higher rate capability than LiCoO₂; discharge capacity observed at a current density of 10 mA cm⁻² was ca. 70 mAh g⁻¹. Surface coating with Li₄Ti₅O₁₂ onto the LiNi_0.8Co_0.15Al_0.05O₂ particles further improved the high-rate performance to give ca. 110 mAh g⁻¹. The rate capability promises to realize all-solid-state lithium secondary batteries with very high performance.     

High power and high capacity cathode material LiNi0.5Mn0.5O2 for advanced lithium-ion batteries

Single-phase lithium nickel manganese oxide, LiNi_0.5Mn_0.5O₂, was successfully synthesized from a solid solution of Ni_1.5Mn_1.5O₄ that was prepared by means of the solid reaction between Mn(CH₃COO)₂·4H₂O and Ni(CH₃COO)₂·4H₂O. XRD pattern shows that the product is well crystallized with a high degree of Li–M (Ni, Mn) order in their respective layers, and no diffraction peak of Li₂MnO₃ can be detected. Electrochemical performance of as-prepared LiNi_0.5Mn_0.5O₂ was examined in the test battery by charge–discharge cycling with different rate, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The cycling behavior between 2.5 and 4.4 V at a current rate of 21.7 mA g⁻¹ shows a reversible capacity of about 190 mAh g⁻¹ with little capacity loss after 100 cycles. High-rate capability test shows that even at a rate of 6C, stable capacity about 120 mAh g⁻¹ is retained. Cyclic voltammetry (CV) profile shows that the cathode material has better electrochemical reversibility. EIS analysis indicates that the resistance of charge transfer (R_ct) is small in fully charged state at 4.4 V and fully discharged state at 2.5 V versus Li⁺/Li. The favorable electrochemical performance was primarily attributed to regular and stable crystal structure with little intra-layer disordering.     

Improvement of the high rate capability of hierarchical structured Li4Ti5O12 induced by the pseudocapacitive effect

Hierarchical structured Li₄Ti₅O₁₂, assembling from randomly oriented nanosheets with a thickness of about 10-16 nm, is fabricated by a facile hydrothermal route and following calcination. It is demonstrated that the as-prepared sample has good cycle stability and excellent high rate performance. In particular, the discharge capacity of 128 mAh g⁻¹ can be obtained at the high current density of 2000 mA g⁻¹, which is about 87% of that at the low current density of 200 mA g⁻¹ upon cycling, indicating that the as-prepared sample can endure great changes of various discharge current densities to retain a good stability. In addition, the pseudocapacitive effect based on the hierarchical structure, also contributes to the high rate capability of Li₄Ti₅O₁₂, which can be confirmed in cyclic voltammograms.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

The influence of compositional change of 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.5, y = x − 0.1) cathode materials prepared by co-precipitation

Cathode materials prepared by a co-precipitation are 0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g⁻¹. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life.     

Morphology and electrochemical performance of Li[Ni1/3Co1/3Mn1/3]O2 cathode material by a slurry spray drying method

The spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders with appropriate porosity, small particle size and good particle size distribution were successfully prepared by a slurry spray drying method. The Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were characterized by XRD, SEM, ICP, BET, EIS and galvanostatic charge/discharge testing. The material calcined at 950 °C had the best electrochemical performance. Its initial discharge capacity was 188.9 mAh g⁻¹ at the discharge rate of 0.2 C (32 mA g⁻¹), and retained 91.4% of the capacity on going from 0.2 to 4 C rate. From the EIS result, it was found that the favorable electrochemical performance of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material was primarily attributed to the particular morphology formed by the spray drying process which was favorable for the charge transfer during the deintercalation and intercalation cycling.     

Nano-sized LiMn2O4 spinel cathode materials exhibiting high rate discharge capability for lithium-ion batteries

Nano-sized LiMn₂O₄ spinel with well crystallized homogeneous particles (60 nm) is synthesized by a resorcinol-formaldehyde route. Micro-sized LiMn₂O₄ spinel with micrometric particles (1 μm) is prepared by a conventional solid-state reaction. These two samples are characterized by XRD, SEM, TEM, BET, and electrochemical methods. At current rate of 0.2C (1C = 148 mA g⁻¹), a discharge capacity of 136 mAh g⁻¹ is obtained on the nano-sized LiMn₂O₄, which is higher than that of micro-sized one (103 mAh g⁻¹). Furthermore, compared to the micro-sized sample, nano-sized LiMn₂O₄ shows much better rate capability, i.e. a capacity of 85 mAh g⁻¹, 63% of that at 0.2C, is realized at 60C. The excellent high rate performance of nano-sized LiMn₂O₄ spinel may be attributed to its impurity-free nano-sized particles, higher surface area and well crystalline. The outstanding electrochemical performances demonstrate that the nano-sized LiMn₂O₄ spinel will be the promising cathode materials for high power lithium-ion batteries used in hybrid and electric vehicles.     

Nanosized high voltage cathode material LiMg0.05Ni0.45Mn1.5O4: Structural,electrochemical and in situ investigation

In this study a modified solid state synthesis (auto-ignition method) is used to form nanosized spinel type material LiMg_0.05Ni_0.45Mn_1.5O₄. This material presents a high voltage plateau at 4.75 V vs. Li/Li⁺. Structural and electrochemical characterisations have been performed using a wide range of techniques (TEM, neutron diffraction, galvanostatic measurements, and impedance spectroscopy). Besides, in situ XAS has been performed to monitor the evolution of Ni and Mn oxidation state during Li intercalation. The material presents an ordered cubic spinel structure, good capacity retention upon cycling (131 mAh g⁻¹ at C/10 and 117 mAh g⁻¹ at 1C) and good electronic conductivity (10⁻⁶ S cm⁻¹ at RT). The simultaneous presence of Mn³⁺/Mn⁴⁺ in the structure has been investigated and explained by inclusion of disordered nanodomains in the structure.