Electrolytic Sn/Li2O coatings for thin-film lithium ion battery anodes

Sn/Li₂O composite coatings on stainless steel substrate, as anodes of thin-film lithium battery are carried out in SnCl₂ and LiNO₃ mixed solutions by using cathodic electrochemical synthesis and subsequently annealed at 200 °C. Through cathodic polarization tests, three major regions are verified: (I) O₂ + 4H⁺ + 4e⁻ → 2H₂O (∼0.25 to −0.5 V), (II) 2H⁺ + 2e⁻ → H₂, Sn²⁺ + 2e⁻ → Sn, and NO₃⁻ + H₂O + 2e⁻ → NO₂⁻ + 2OH⁻ (−0.5 to −1.34 V), and (III) 2H₂O + 2e⁻ → H₂ + 2OH⁻ (−1.34 to −2 V vs. Ag/AgCl). The coated specimens are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and charge/discharge tests. The nano-sized Sn particles embedded in Li₂O matrix are obtained at the lower part of region II such as −1.2 V, while the micro-sized Sn with little Li₂O at the upper part, such as −0.7 V. Charge/discharge cycle tests elucidated that Sn/Li₂O composite film showed better cycle performance than Sn or SnO₂ film, due to the retarding effects of amorphous Li₂O on the further aggregation of Sn particles. On the other hand, the one tested for cut-off voltage at 0.9 V (vs. Li/Li⁺) is better than those at 1.2 and 1.5 V since the incomplete de-alloy at lower cut-off voltage may inhibit the coarsening of Sn particles, revealing capacity 587 mAh g⁻¹ after 50 cycle, and capacity retention ratio C50/C2 81.6%, higher than 63.5% and 49.1% at 1.2 and 1.5 V (vs. Li/Li⁺), respectively.     

Electrochemical properties of Li2ZrO3-coated silicon/graphite/carbon composite as anode material for lithium ion batteries

Silicon/graphite/disordered carbon (Si/G/DC) is coated by Li₂ZrO₃ using Zr(NO₃)₄·5H₂O and CH₃COOLi·2H₂O as coating reagents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize Li₂ZrO₃-coated Si/G/DC composite. The Li₂ZrO₃-coated Si/G/DC composite exhibits a high reversible capacity with no capacity fading from 2nd to 70th cycle, indicating its excellent cycleability when used as anode materials for lithium ion batteries. A compact and stable solid-electrolyte interphase (SEI) layer is formed on the surface of Li₂ZrO₃-coated Si/G/DC electrode. Analysis of electrochemical impedance spectra (EIS) shows that the resistance of the coated material exhibits less variation during cycling, which indicates the integrity of electrode structure is kept during cycling. XPS shows that F and P elements do not appear in the SEI layers of Li₂ZrO₃-coated Si/G/DC electrode, while they have a relatively high content in SEI layers of Si/G/DC electrode. The improvement of Li₂ZrO₃-coated Si/G/DC is attributed to the decrease of lithium insertion depth and the formation of stable SEI film.     

Electrochemical characteristics of manganese oxide/carbon composite as a cathode material for Li/MnO2 secondary batteries

Electrolytic manganese dioxide (EMD) recovered from a simulated leaching solution of spent alkaline batteries using a modified cyclone cell is tested as a cathode material for Li secondary batteries. An EMD/C(Super P) composite heat-treated at 400 °C after high-energy mechanical milling shows better electrochemical performance than that of pure EMD in terms of cycleability and capacity fading. The electrochemical characteristics of the EMD/C(Super P) composite are investigated by various analytical techniques. The irreversible capacity during the first cycle is mainly due to the formation of a Li₂MnO₃ phase. The carbon composite also retards the dissolution of Mn during cycling.     

Dynamic behavior of surface film on LiCoO2 thin film electrode

Electrochemical oxidation behavior of non-aqueous electrolytes on LiCoO₂ thin film electrodes were investigated by in situ polarization modulation Fourier transform infrared (PM-FTIR) spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy (XPS). LiCoO₂ thin film electrode on gold substrate was prepared by rf-sputtering method. In situ PM-FTIR spectra were obtained at various electrode potentials during cyclic voltammetry measurement between 3.5 V vs. Li/Li⁺ and 4.2 V vs. Li/Li⁺. During anodic polarization, oxidation of non-aqueous electrolyte was observed, and oxidized products remained on the electrode at the potential higher than 3.75 V vs. Li/Li⁺ as a surface film. During cathodic polarization, the stripping of the surface film was observed at the potential lower than 3.9 V vs. Li/Li⁺. Depth profile of XPS also showed that more organic surface film remained on charged LiCoO₂ than that on discharged one. AFM images of charged and discharged electrodes showed that some decomposed products deposited on charged electrode and disappeared from the surface of discharged one. These results indicate that the surface film on LiCoO₂ is not so stable.     

Synthesis and characterization of macroporous tin oxide composite as an anode material for Li-ion batteries

A macroporous SnO₂/C composite anode material was synthesized using an organic template-assisted method. Polystyrene spheres were synthesized and used as template and lead to macroporous morphology with pores of 300-500 nm in diameter and a surface area of 54.7 m² g⁻¹. X-ray diffraction showed that the SnO₂ nanoparticles are crystallized in a rutile P42/mnm lattice with the presence of Sn metal traces. The synthesized macroporous SnO₂/C composite provided promising performance in lithium half cells showing a discharge capacity of 607 mAh g⁻¹ after 55 cycles. It was found that the macroporous SnO₂/C composite is stable and resistant to pulverization upon cycling.     

Nanosized Zn–Sn metal composite oxide: a new anode material for Li ion battery

Abstract

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g^?1, and the first charge specific capacity is up to 903 mAh g^?1 for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.     

Electrochemical behavior of Sn/SnO2 mixtures for use as anode in lithium rechargeable batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li₂O generated in situ by the electrochemical reduction of SnO₂ can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li_4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO₂, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO₂ = 1:2 exhibited a specific capacity of 549 mAh g⁻¹ (13% higher than that for SnO₂) with an irreversible capacity, which was 7% lower than that for SnO₂ and a capacity fade of 1.4 mAh g⁻¹ cycle⁻¹. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.     

A novel CuO-nanotube/SnO2 composite as the anode material for lithium ion batteries

A novel CuO-nanotubes/SnO₂ composite was prepared by a facile solution method and its electrochemical properties were investigated as the anode material for Li-ion battery. The as-prepared composite consisted of monoclinic-phase CuO-nanotubes and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were dramatically decorated on the CuO-nanotubes. The composite showed higher reversible capacity, better durability and high rate performance than the pure SnO₂. The better electrochemical performance could be attributed to the introducing of the CuO-nanotubes. It was found that the CuO-nanotubes were reduced to metallic Cu in the first discharge cycle, which can retain tube structure of the CuO-nanotubes as a tube buffer to alleviate the volume expansion of SnO₂ during cycling and act as a good conductor to improve the electrical conductivity of the electrodes.     

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.     

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).     

Fabrication of all solid-state lithium-ion batteries with three-dimensionally ordered composite electrode consisting of Li0.35La0.55TiO3 and LiMn2O4

A composite electrode between three-dimensionally ordered macroporous (3DOM) Li_0.35La_0.55TiO₃ (LLT) and LiMn₂O₄ was fabricated by colloidal crystal templating method and sol–gel process. A close-packed PS beads with the opal structure was prepared by filtration of a suspension containing PS beads. Li–La–Ti–O sol was injected by vacuum impregnation process into the voids between PS beads, and then was heated to form 3DOM-LLT. Three-dimensionally ordered composite material consisting of LiMn₂O₄ and LLT was prepared by sol–gel process. The prepared composite was characterized with SEM and XRD. All solid-state Li-ion battery was fabricated with the LLT–LiMn₂O₄ composite electrode as a cathode, dry polymer electrolyte and Li metal anode. The prepared all solid-state cathode exhibited a volumetric discharge capacity of 220 mAh cm⁻³.     

Nanocrystalline Ti2/3Sn1/3O2 as anode material for Li-ion batteries

We prepared nanocrystalline Ti_2/3Sn_1/3O₂ by a coprecipitation method starting from Ti(isopropoxide)₄ and SnCl₄·5H₂O followed by calcination at 600 °C. TEM and XRD measurements reveal crystallite sizes of about 5 nm and a crystal structure equivalent to those of TiO₂ rutile and SnO₂ cassiterite. The local structure was investigated with ¹¹⁹Sn NMR and Sn Mössbauer spectroscopy. The material was cycled with C/20 at voltages between 3.0 and 0.02 V against Li metal. Specific capacities of 300 mAh g⁻¹ were obtained for 100 cycles with voltage profiles very similar to those of pure SnO₂. Faster cycling leads to strong decrease of the capacities but after returning to C/20 the initial values are obtained.     

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.     

Effect of electrolytes on the structure and evolution of the solid electrolyte interphase (SEI) in Li-ion batteries: A molecular dynamics study

We have studied the formation and growth of solid-electrolyte interphase (SEI) for the case of ethylene carbonate (EC), dimethyl carbonate (DMC) and mixtures of these electrolytes using molecular dynamics simulations. We have considered SEI growth on both Li metal surfaces and using a simulation framework that allows us to vary the Li surface density on the anode surface. Using our simulations we have obtained the detailed structure and distribution of different constituents in the SEI as a function of the distance from the anode surfaces. We find that SEI films formed in the presence of EC are rich in Li₂CO₃ and Li₂O, while LiOCH₃ is the primary constituent of DMC films. We find that dilithium ethylene dicarbonate, LiEDC, is formed in the presence of EC at low Li surface densities, but it quickly decomposes to inorganic salts during subsequent growth in Li rich environments. The surface films formed in our simulations have a multilayer structure with regions rich in inorganic and organic salts located near the anode surface and the electrolyte interface, respectively, in agreement with depth profiling experiments. Our computed formation potentials 1.0 V vs. Li/Li⁺ is also in excellent accord with experimental measurements. We have also calculated the elastic stiffness of the SEI films; we find that they are significantly stiffer than Li metal, but are somewhat more compliant compared to the graphite anode.     

Eliminating the irreversible capacity loss of high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode by blending with other lithium insertion hosts

The large irreversible capacity loss generally encountered with the high capacity layered oxide solid solutions between layered Li[Li_1/3Mn_2/3]O₂ and LiMO₂ (M = Mn, Ni, and Co) has been reduced by blending layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂, which is a solid solution between Li[Li_1/3Mn_2/3]O₂ and Li[Mn_1/3Ni_1/3Co_1/3]O₂, with spinel Li₄Mn₅O₁₂ or LiV₃O₈. The irreversible capacity loss decreases from 68 to 0 mAh g⁻¹ as the Li₄Mn₅O₁₂ content increases to 30 wt.% in the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-Li₄Mn₅O₁₂ composite and the LiV₃O₈ content increases to 18 wt.% in the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-LiV₃O₈ composite. The decrease in irreversible capacity loss is due to the ability of Li₄Mn₅O₁₂ or LiV₃O₈ to insert the extracted lithium that could not be inserted back into the layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ during the first cycle. The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-LiV₃O₈ composite with ∼18 wt.% LiV₃O₈ exhibits a high capacity of ∼280 mAh g⁻¹ with little or no irreversible capacity loss and good cyclability.     

In situ X-ray diffraction studies of mixed LiMn2O4-LiNi1/3Co1/3Mn1/3O2 composite cathode in Li-ion cells during charge-discharge cycling

The structural changes of the composite cathode made by mixing spinel LiMn₂O₄ and layered LiNi_1/3Co_1/3Mn_1/3O₂ in 1:1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ∼5.2 V vs. Li/Li⁺, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the LiNi_1/3Co_1/3Mn_1/3O₂ component only. When the cell voltage reaches at ∼4.0 V vs. Li/Li⁺, lithium extraction from the spinel LiMn₂O₄ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of LiMn₂O₄. When the voltage passed 4.3 V, the major structural changes are from the LiNi_1/3Co_1/3Mn_1/3O₂ component, while the LiMn₂O₄ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel LiMn₂O₄ component, with much less changes in the layered LiNi_1/3Co_1/3Mn_1/3O₂ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research.     

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.     

Li ion exchange in CeO2-TiO2 sol-gel layers studied by electrochemical quartz crystal microbalance

The paper reports first on the electrochemical behavior in liquid Li⁺ electrolytes of 200 nm thick single sol-gel (CeO₂)_0.81-TiO₂ electrochromic (EC) layers deposited by the dip-coating process. The electrolytes were solutions of 1 M LiClO₄ dissolved in dry propylene carbonate (PC) (containing 0.03 wt% of water) and wet PC containing up to 10 wt% of water, respectively. Then an electrochemical quartz crystal microbalance was used as a sensitive detector to analyze the mass changes occurring during the Li⁺ ion exchange processes. These electrochemical processes were studied for 370 nm thick double layers, deposited on gold-coated quartz crystal electrodes and sintered at 450 °C in air. The electrolytes were the same solutions with water content varying from 0.03 up to 3 wt% of water. The processes have been studied in the potential range from −2.0 to +1.0 V vs. Ag/AgClO₄ during 100 voltammetry cycles. The composition of the (CeO₂)_0.81-TiO₂ layers was found to change during the early cycles, mainly because of an irreversible Li⁺ intercalation. It was found, however, that the mass change observed during cycling is not due only to a pure Li⁺ ion exchange process but also involves the adsorption/desorption or exchange of other cations and anions contained in the electrolyte. These ions are Li⁺ and ClO₄⁻ in dry electrolyte and Li⁺, hydrated Li(H₂O)_n⁺ and ClO₄⁻ in wet electrolyte. The improvement of the reversibility of the intercalation and deintercalation processes as well as the faster kinetics observed in wet electrolytes are finally discussed in terms of a model in which the formation of hydrated Li⁺ ions takes an important role.     

Implications of the first cycle irreversible capacity on cell balancing for Li2MnO3-LiMO2 (M = Ni, Mn, Co) Li-ion cathodes

Much of the research on lithium-ion cathodes consisting of layered solid solutions of Li₂MnO₃-LiMO₂ (M = Mn, Co, Ni) has focused on identifying the causes of the irreversible capacity loss on the first cycle. However, a key issue that must be addressed is whether the high irreversible capacity observed seen on the first cycle is associated with intercalated lithium at the anode, or if it is associated with irretrievable capacity (i.e., film formation, and/or decomposition reactions). To this end, we have quantified the amount of utilizable lithium that is made available for the anodes when employing Li₂MnO₃-LiMO₂ as cathodes. Using a MoS₂ anode lithiation plateau transition as a reference point to the amount of lithium transferred to the anode during charge, it has been shown that almost none of the cathode irreversible charge capacity resulted in lithiation of the anode. Further, by reacting charged graphitic anodes that were retrieved from C anode-Li_1.2Ni_0.175Co_0.1Mn_0.52O₂ cathode cells with water to generate H₂ gas to measure the active amount of lithium in the anode, we confirmed the results with the MoS₂ titration experiments, demonstrating that lithium released from the cathode during the first charge is not proportionate to the cathode charge capacity.