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.     

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.     

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.     

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.     

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.     

Li4Ti5O12/CNTs composite anode material for large capacity and high-rate lithium ion batteries

Li₄Ti₅O₁₂ sub-micro crystallites are synthesized by ball-milling and one-step sintering under different heat treatment temperature from 700 °C to 900 °C. The composite electrode of Li₄Ti₅O₁₂/carbon nanotubes (CNTs) is prepared by mixing powders of Li₄Ti₅O₁₂ and CNTs in different weight ratios. Before mixing, in order to disperse CNTs in Li₄Ti₅O₁₂ particles preferably, the CNTs are cut and dispersed by hyperacoustic shear method and the composite electrodes of low resistance of about 20–30 Ω are obtained. The composite electrodes have steady discharge platform of 1.54 V and large specific capacity, initial discharge capacities are 168, 200, 196, 176 mAh g⁻¹ in different Li₄Ti₅O₁₂:CNTs weight ratios of 94:1, 92:3, 90:5, 88:7 respectively at 0.1 C discharge rate for the Li₄Ti₅O₁₂ synthesized in an optimized heat treatment temperature of 800 °C. In our experimental range, the composite electrode in a CNTs weight ratio of 3:92 shows the best performance under different discharge rate such as the initial capacity is 200 mAh g⁻¹ with discharge capacities retention rate of nearly 100%. Its capacity is about 151 mAh g⁻¹ under 20 C rate discharge condition with excellent high-rate performance. There is almost no decline after 20th cycles under 10 C rate discharging condition.     

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.     

Synthesis, structure and electrochemical Li insertion behaviour of Li2Ti6O13 with the Na2Ti6O13 tunnel-structure

Li₂Ti₆O₁₃ has been prepared from Na₂Ti₆O₁₃ by Li ion exchange in molten LiNO₃ at 325 °C. Chemical analysis and powder X-ray diffraction study of the reaction product respectively indicate that total Na/Li exchange takes place and the Ti-O framework of the Na₂Ti₆O₁₃ parent structure is kept under those experimental conditions. Therefore, Li₂Ti₆O₁₃ has been obtained with the mentioned parent structure. An important change is that particle size is decreased significantly which is favoring lithium insertion. Electrochemical study shows that Li₂Ti₆O₁₃ inserts ca. 5 Li per formula unit in the voltage range 1.5-1.0 V vs. Li⁺/Li, yielding a specific discharge capacity of 250 mAh g⁻¹ under equilibrium conditions. Insertion occurs at an average equilibrium voltage of 1.5 V which is observed for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. However, a capacity loss of ca. 30% is observed due to a phase transformation occurring during the first discharge. After the first redox cycle a high reversible capacity is obtained (ca. 160 mAh g⁻¹ at C/12) and retained upon cycling. Taking into consideration these results, we propose Li₂Ti₆O₁₃ as an interesting material to be further investigated as the anode of lithium ion batteries.     

Li4Ti5O12/Sn composite anodes for lithium-ion batteries: Synthesis and electrochemical performance

Li₄Ti₅O₁₂/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li₄Ti₅O₁₂ matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li₄Ti₅O₁₂/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge-discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li₄Ti₅O₁₂ at a calcination of 500 °C, due to the steric effect of Li₄Ti₅O₁₂ and chemical interaction between Li₄Ti₅O₁₂ and tin oxide. The experimental results indicate that Li₄Ti₅O₁₂/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g⁻¹ is maintained after 50 cycles at 100 mA g⁻¹ current density, which is still higher than 195 mAh g⁻¹ for the pure Li₄Ti₅O₁₂ after the same charge/discharge cycles. It suggests Li₄Ti₅O₁₂/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.     

TiO2(B) as a promising high potential negative electrode for large-size lithium-ion batteries

Needle-like TiO₂(B) powder was obtained from K₂Ti₄O₉ precursor by ion exchange to protons, followed by dehydration. The charge and discharge characteristics of the TiO₂(B) powder were investigated as a high potential negative electrode in lithium-ion batteries. It had a high discharge capacity of 200–250 mAh g⁻¹ at around 1.6 V vs. Li/Li⁺, which was comparable with that of TiO₂(B) nanowires and nanotubes prepared via a hydrothermal reaction in alkaline solution. It showed very good cycleability, and gave a discharge capacity of 170 mAh g⁻¹ even in the 650th cycle. It also had a high rate capability, and gave a discharge capacity of 106 mAh g⁻¹ even at 10 °C.     

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.     

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.     

Hybrid supercapacitor with nano-TiP2O7 as intercalation electrode

Nano-size (≤100 nm) TiP₂O₇ is prepared by the urea assisted combustion synthesis, at 450 and 900 °C. The compound is characterized by powder X-ray diffraction, Rietveld refinement, high resolution transmission electron microscopy and surface area methods. Lithium cycling properties by way of galvanostatic cycling and cyclic voltammetry (CV) showed a reversible and stable capacity of 60 (±3) mAh g⁻¹ (0.5 mole of Li) up to 100 cycles, when cycled at 15 mA g⁻¹ between 2-3.4 V vs. Li. Non-aqueous hybrid supercapacitor, TiP₂O₇ (as anode) and activated carbon (AC) (as cathode) has been studied by galvanostatic cycling and CV in the range, 0-3 V at 31 mA g⁻¹ and exhibited a specific discharge capacitance of 29 (±1) F g⁻¹stable in the range, 100-500 cycles. The Ragone plot shows a deliverable maximum of 13 Wh kg⁻¹ and 371 W kg⁻¹ energy and power density, respectively.     

Improvement in electrochemical performance of V2O5 by Cu doping

Cu_0.04V₂O₅ was prepared by a precipitation method followed by heat treatment at 300 and 600 °C. The material prepared at 300 °C showed porous morphology, whereas that prepared at 600 °C was highly crystalline. X-ray diffraction, Raman scattering and Fourier transform infrared spectroscopy showed both materials exhibiting the same structure as that of V₂O₅, with a slight lattice expansion. X-ray absorption spectroscopy confirmed the presence of V⁴⁺ cations in Cu_0.04V₂O₅, which would increase the electronic conductivity of V₂O₅. Cu_0.04V₂O₅ showed better electrochemical performance than V₂O₅ because of its high electronic conductivity and good structural stability. The material prepared at 600 °C delivered a reversible discharge capacity over 160 mAh g⁻¹ after 60 cycles at a C rate of C/5.6. The material prepared at 300 °C showed good high-rate performance, which delivered a reversible capacity ∼100 mAh g⁻¹ when cycled at C/1.9. The discrepancy in the rate performance of Cu_0.04V₂O₅ was attributed to the morphology of materials.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

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.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

Characterization of electrolytic Co3O4 thin films as anodes for lithium-ion batteries

The electrolytic deposition of Co₃O₄ thin films on stainless steel was conducted in Co(NO₃)₂ aqueous solution for anodes in lithium-ion thin film batteries. Three major electrochemical reactions during the deposition were discussed. The coated specimens and the coating films carried out at −1.0 V (saturated KCl Ag/AgCl) were subjected to annealing treatments and further characterized by XRD, TGA/DTA, FE-SEM, Raman spectroscopy, cyclic voltammetry (CV) and discharge/charge cyclic tests. The as-coated film was β-Co(OH)₂, condensed into CoO and subsequently oxidized into nano-sized Co₃O₄ particles. The nano-sized Co₃O₄, CoO, Li₂O and Co particles revealed their own characteristics different from micro-sized ones, such as more interfacial effects on chemical bonding and crystallinity. The initial maximum capacity of Co₃O₄ coated specimen was 1930 mAh g⁻¹ which much more than its theoretical value 890 mAh g⁻¹, since the nano-sized particles offered more interfacial bondings for extra sites of Li⁺ insertion. However, a large ratio of them was trapped, resulting in a great part of irreversible capacity during the first charging. Still, it revealed a capacity 500 mAh g⁻¹ after 50 discharged-charged cycles.     

Study of the Li insertion into V2O5 films deposited by CVD onto various substrates

Vanadium oxide films were synthesised by chemical vapour deposition (CVD) from pure of triisopropoxyvanadium oxide (VO(OC₃H₇)₃) and oxygen as precursors. The influence of the substrate on the crystallinity of the vanadium oxide films was studied before and after annealing at 500 °C. On mica substrates, as-deposited film was composed of crystalline V₂O₅ as revealed by XRD. On Pt, Ti, stainless steel, glass and F-doped SnO₂ substrates, an annealing procedure was required to get V₂O₅. SEM investigations have clearly evidence V₂O₅ plates but the kinetics growth seems to be strongly dependent on the nature of the substrate. The insertion/extraction of Li⁺ into the host structure was investigated in 1 M LiClO₄-PC with annealed V₂O₅ films deposited on Ti, Pt and stainless steel substrates. The best electrochemical performances were obtained in the potential range 3.8–2.8 V versus Li/Li⁺ with V₂O₅ films deposited onto stainless steel substrate: the reversible capacity reaches after subsequent cycles was about 115 mAh g⁻¹ (rate C/23). In a wider potential range (between 3.8 and 2.2 V versus Li/Li⁺), V₂O₅ deposited onto Ti substrate exhibited the higher electrochemical performances (220 mAh g⁻¹ for a rate of C/23).     

Pyroxene LiVSi2O6 as an electrode material for Li-ion batteries

Lithium vanadium metasilicate (LiVSi₂O₆) with pyroxene structure has been exploited as an electrode material for Li-ion batteries. Galvanostatic charge and discharge tests show that LiVSi₂O₆ is able to deliver a capacity of 85 mAh g⁻¹ at 30 °C, and a high capacity of 181 mAh g⁻¹ at 60 °C. The high capacity is believed to be due to the reactions of V³⁺/V⁴⁺ and V²⁺/V³⁺redox couples, accompanied by the excess 0.42 Li⁺ insertion into the lattice forming a Li-rich phase Li_1.42VSi₂O₆. High-energy synchrotron XRD combined with the Rietveld refinement analysis confirms that the electrochemical delithiation-lithiation reaction proceeds by a single phase redox mechanism with an overall volume variation of 1.9% between LiVSi₂O₆ and its delithiated state, indicating a very stable framework of LiVSi₂O₆ for Li⁺ ions extraction-insertion.