Fabrication of all-solid-state rechargeable lithium-ion battery using mille-feuille structure of Li0.35La0.55TiO3

A mille-feuille structure, which comprises both sides of dense layer are sandwiched by porous layers, is one of the promising structures for 3-dimensional (3D) all-solid-state battery. The porous layers should have 3-dimensionally ordered macroporous structure to obtain large contact area between electrolyte and electrode. Li_0.35La_0.55TiO₃ (LLT) solid electrolyte with the mille-feuille structure was fabricated by the suspension filtration method. The dense layer was sintered well, no grain boundary was observed. The porous layers contacted well with dense layer. Thicknesses of dense and porous layers were 30 and 26 μm, respectively. To check compatibility of the mille-feuille LLT with all-solid-state Li ion battery, chronopotentiometry of symmetric cell with LiMn₂O₄/mille-feuille LLT/LiMn₂O₄ configuration was measured. Charge and discharge currents were clearly observed, indicating that the cell was successfully operated.     

Al-doped Li7La3Zr2O12 synthesized by a polymerized complex method

Li₇La₃Zr₂O₁₂ electrolytes doped with different amounts of Al (0, 0.2, 0.7, 1.2, and 2.5 wt.%) were prepared by a polymerized complex (Pechini) method. The influence of aluminum on the structure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscopy (SEM), and thermal dilatometry. It was found that even a small amount of Al (e.g. 0.2 wt.%) added to Li₇La₃Zr₂O₁₂ can greatly accelerate densification during the sintering process. SEM micrographs showed the existence of a liquid phase introduced by Al additions which led to the enhanced sintering rate. The addition of Al also stabilized the higher conductivity cubic form of Li₇La₃Zr₂O₁₂ rather than the less conductive tetragonal form. The combination of these two beneficial effects of Al enabled greatly reduced sintering times for preparation of highly conductive Li₇La₃Zr₂O₁₂ electrolyte. With optimal additions of Al (e.g. 1.2 wt.%), Li₇La₃Zr₂O₁₂ electrolyte sintered at 1200 °C for only 6 h showed an ionic conductivity of 2.0 × 10⁻⁴ S cm⁻¹ at room temperature.     

Interfacial lithium-ion transfer at the LiMn2O4 thin film electrode/aqueous solution interface

Interfacial lithium-ion transfer at the LiMn₂O₄ thin film electrode/aqueous solution was investigated. The cyclic voltammograms of the film electrode conducted in the aqueous solution was similar to an adsorption-type voltammogram of reversible system, suggesting that fast charge transfer reaction proceed in the aqueous solution system. We found that the activation energy for this interfacial lithium-ion transfer reaction obtains 23–25 kJ mol⁻¹, which is much smaller than that in the propylene carbonate solution (50 kJ mol⁻¹). This small activation energy will be responsible for the fast interfacial lithium-ion transfer reaction in the aqueous solution. These results suggest that fast lithium insertion/extraction reaction can be realized by decreasing the activation energy for interfacial lithium-ion transfer reaction.     

Characterization of the interface between LiCoO2 and Li7La3Zr2O12 in an all-solid-state rechargeable lithium battery

The interfacial layer formed between a lithium-ion conducting solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZ), and LiCoO₂ during thin film deposition was characterized using a combination of microscopy and electrochemical measurement techniques. Cyclic voltammetry confirmed that lithium extraction occurs across the interface on the first cycle, although the nonsymmetrical redox peaks indicate poor electrochemical performance. Using analytical transmission electron microscopy, the reaction layer (∼50 nm) was analyzed. Energy dispersive X-ray spectroscopy revealed that the concentrations of some of the elements (Co, La, and Zr) varied gradually across the layer. Nano-beam electron diffraction of this layer revealed that the layer contained neither LiCoO₂ nor LLZ, but some spots corresponded to the crystal structure of La₂CoO₄. It was also demonstrated that reaction phases due to mutual diffusion are easily formed between LLZ and LiCoO₂ at the interface. The reaction layer formed during high temperature processing is likely one of the major reasons for the poor lithium insertion/extraction at LLZ/LiCoO₂ interfaces.     

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.     

Synthesis and characterization of Nd doped LiMn2O4 cathode for Li-ion rechargeable batteries

Spinel powders of LiMn_1.99Nd_0.01O₄ have been synthesized by chemical synthesis route to prepare cathodes for Li-ion coin cells. The structural and electrochemical properties of these cathodes were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, and charge-discharge studies. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation and deintercalation in the electrochemical cell. The charge-discharge characteristics for LiMn_1.99Nd_0.01O₄ cathode materials were obtained in 3.4–4.3 V voltage range and the initial discharge capacity of this material were found to be about 149 mAh g⁻¹. The coin cells were tested for up to 25 charge-discharge cycles. The results show that by doping with small concentration of rare-earth element Nd, the capacity fading is considerably reduced as compared to the pure LiMn₂O₄ cathodes, making it suitable for Li-ion battery applications.     

Crystallization of LiMn2O4 observed with high temperature X-ray diffraction

We investigated the formation of LiMn₂O₄ phases by calcinating a stoichiometric mixture of Li₂CO₃ and various manganese compounds with high temperature X-ray diffraction (HT-XRD) technique to understand the influence of starting materials on the electrochemical performance. XRD measurements were carried out during heating processes from room temperature to 700 °C. In case of Li₂CO₃/electrolytic manganese dioxide and Li₂CO₃/MnCO₃ mixtures used as starting materials, Li_0.33MnO₂ phase and low crystalline phase, respectively, appeared as intermediate products during heating process followed by the crystallization into the spinel. HT-XRD observation confirmed that the LiMn₂O₄ phase was directly formed from starting Li₂CO₃/Mn₂O₃ and Li₂CO₃/Mn₃O₄ mixtures. The reactivity of the mixture, meant by the lower reaction temperature between Li and Mn compounds and the faster evolution of Li–Mn–O phase, depended on manganese compounds. The purity and stoichiometry of spinel type LiMn₂O₄ was not achieved only by the higher reactivity. From these results, the dependence of reversible capacities and cycleability of synthesized LiMn₂O₄s on the formation process which varied with the starting materials was discussed.     

Electrochemical performance of nanostructured spinel LiMn2O4 in different aqueous electrolytes

A nanostructured spinel LiMn₂O₄ electrode material was prepared via a room-temperature solid-state grinding reaction route starting with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O) and citric acid (C₆H₈O₇·H₂O) raw materials, followed by calcination of the precursor at 500 °C. The material was characterized by X-ray diffraction (XRD) and transmission electron microscope techniques. The electrochemical performance of the LiMn₂O₄ electrodes in 2 M Li₂SO₄, 1 M LiNO₃, 5 M LiNO₃ and 9 M LiNO₃ aqueous electrolytes was studied using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. The LiMn₂O₄ electrode in 5 M LiNO₃ electrolyte exhibited good electrochemical performance in terms of specific capacity, rate dischargeability and charge/discharge cyclability, as evidenced by the charge/discharge results.     

Electrochemical activity of Li2FeTiO4 and Li2MnTiO4 as potential active materials for Li ion batteries: A comparison with Li2NiTiO4

We demonstrate, for the first time, a considerable electrochemical activity of two members of lithium transition element titanates: Li₂FeTiO₄ and Li₂MnTiO₄. Both materials consist of 10–20 nm particles embedded in a conductive carbon coating. We show that not the coating but the small particle size is decisive for materials’ activity. Li₂FeTiO₄ shows a stable reversible capacity of up to 123 mA hg⁻¹ at C/20 and 60 °C which is 83% of the theoretical value for exchange of 1 electron (148 mA hg⁻¹). Li₂MnTiO₄ could only be prepared in a nanosized form that contained about 30% of impurities. The capacity of the whole material (including impurities) is comparable to that of Li₂FeTiO₄ but the cycling stability is much poorer. In contrast to the Fe and Mn analogues, the third member of the titanate family, Li₂NiTiO₄, shows a good electrochemistry even when the particle size is much larger (about 100 nm). During initial cycles at C/10 and 60 °C, exchange of more than 1 electron per compound formula has been observed. The cycling stability at high temperatures, however, is poor.     

Nonflammable electrolyte for 3-V lithium-ion battery with spinel materials LiNi0.5Mn1.5O4 and Li4Ti5O12

The compatibility between dimethyl methylphosphonate (DMMP)-based electrolyte of 1 M LiPF₆/EC + DMC + DMMP (1:1:2 wt.) and spinel materials Li₄Ti₅O₁₂ and LiNi_0.5Mn_1.5O₄ was reviewed, respectively. The cell performance and impedance of 3-V LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ lithium-ion cell with the DMMP-based nonflammable electrolyte was compared with the baseline electrolyte of 1 M LiPF₆/EC + DMC (1:1 wt.). The nonflammable DMMP-based electrolyte exhibited good compatibility with spinel Li₄Ti₅O₁₂ anode and high-voltage LiNi_0.5Mn_1.5O₄ cathode, and acceptable cycling performance in the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ full-cell, except for the higher impedance than that in the baseline electrolyte. All of the results disclosed that the 3 V LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ lithium-ion battery was a promising choice for the nonflammable DMMP-based electrolyte.     

Effect of mixed LiBOB and LiPF6 salts on electrochemical and thermal properties in LiMn2O4 batteries

The effects of mixed LiBOB and LiPF₆ salts as electrolyte for lithium ion batteries are investigated by electrochemical testing and thermal stability analysis. Elevated temperature cycle, specific power, DCIR and EIS tests reveal that mixed salts electrolyte has a distinct effect on cycle life and effectively stabilize impedance increase, as optimum concentration of LiBOB is between 0.1 and 0.25 M. Fading mechanism analyses demonstrate that the mixed salts system could decrease Mn dissolution and LiBOB decomposition at elevated temperature application. Accelerating rate calorimetry (ARC) shows that the thermal stability of mixed salts electrolyte is also acceptable. In short, the mixed salts of LiBOB and LiPF₆ provide a possible solution to improve the instability of LiMn₂O₄ as cathode in lithium ion batteries at elevated temperature conditions and show a promising capability in high current discharge for high power application such as hybrid electrical vehicles.     

Synthesis of spinel LiMn2O4 nanoparticles through one-step hydrothermal reaction

Phase pure spinel LiMn₂O₄ nanoparticles can be directly synthesized by one-step hydrothermal reaction of γ-MnO₂ with LiOH in an initial Li/Mn ratio of 1 at 200 °C. The reaction might involve a redox reaction between Mn⁴⁺ and OH⁻, and the formation of LiMn₂O₄ at the same time under the proposed hydrothermal conditions. This hydrothermal process is simple since only γ-MnO₂ powders are used as the Mn source, whereas without use of any oxidants, reductants, or low valence Mn source. The electrochemical performance of the as-synthesized LiMn₂O₄ nanoparticles towards Li⁺ insertion/extraction was examined. Rather good capacity and cycle performance, and an especially excellent high rate capability, were observed for the sample that was hydrothermally reacted for 3 days.     

Al2O3-coated nanoporous TiO2 electrode for solid-state dye-sensitized solar cell

This paper reports the preparation of a core-shell nanoporous electrode consisting of an inner TiO₂ porous matrix and a thin overlayer of Al₂O₃, and its application for solid-state dye-sensitized solar cell using p-CuI as hole conductor. Al₂O₃ overlayer was coated onto TiO₂ porous film by the surface sol–gel process. The role of Al₂O₃ layer thickness on the cell performance was investigated. The solar cells fabricated from Al₂O₃-coated electrodes showed superior performance to the bare TiO₂ electrode. Under illumination of AM 1.5 simulated sunlight (89 mW/cm²), a ca. 0.19 nm Al₂O₃ overlayer increased the photo-to-electric conversion efficiency from 1.94% to 2.59%.     

Flame co-synthesis of LiMn2O4 and carbon nanocomposites for high power batteries

A novel method to produce LiMn₂O₄/carbon nanocomposites in a rapid, one-step and industrially scalable process is presented. A flame spray and a diffusion flame are combined to continuously produce LiMn₂O₄ nanoparticles and carbon black, respectively. Powder carbon content is varied by adjusting the diffusion flame conditions. The powders are characterized by X-ray diffraction (XRD), transmission electron microscopy, cyclic voltammetry and galvanostatic cycling for a range of current densities. These LiMn₂O₄/carbon nanocomposites retain over 80% of their initial galvanostatic discharge capacity for current densities ranging from 5 to 50C-rates, significantly better than pure LiMn₂O₄ nanoparticles mixed conventionally with commercial carbon blacks. The improved performance of the LiMn₂O₄/carbon nanocomposites is attributed to the carbon particle contact and/or film coating of the freshly-made LiMn₂O₄ nanoparticles. This additional well-distributed carbon provides an electrically conductive network that induces a more homogeneous charge transfer throughout the electrode. The suitability of these nanocomposites as a hybrid material is discussed by considering the layout of a thin-layer lithium-ion battery containing these flame-made nanocomposites as positive electrode and LiC₆ as negative electrode. The battery’s specific energy is calculated to be 78 Wh kg⁻¹ (50C-rate) based on the results of lithium-ion insertion capacity experiments and reasonable engineering assumptions on the lithium-ion battery design.     

Low-temperature synthesis of highly crystallized LiMn2O4 from alpha manganese dioxide nanorods

One-dimensional alpha manganese dioxide (α-MnO₂) nanorods synthesized by a hydrothermal route were explored as the starting material for preparing lithium manganese spinel LiMn₂O₄. Pure and highly crystalline spinel LiMn₂O₄ was easily obtained from α-MnO₂ nanorods through a low-temperature solid-state reaction route, while Mn₂O₃ impurity was present along with the spinel phase when commercial MnO₂ was used as starting material. The particle size of LiMn₂O₄ prepared from α-MnO₂ nanorods was about 100 nm with a homogenous distribution. Electrochemical tests demonstrated that the LiMn₂O₄ thus prepared exhibited a higher capacity than that prepared from commercial MnO₂. Therefore, α-MnO₂ nanorods are proved to be a promising starting material for the preparation of high quality LiMn₂O₄.     

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.     

Preparation of manganese oxide with high density by decomposition of MnCO3 and its application to synthesis of LiMn2O4

Manganese oxide with high tap density was prepared by decomposition of spherical manganese carbonate, and then LiMn₂O₄ cathode materials were synthesized by solid-state reaction between the manganese oxide and lithium carbonate. Structure and properties of the samples were determined by X-ray diffraction, Brunauer–Emmer–Teller surface area analysis, scanning electron microscope and electrochemical measurements. With increase of the decomposition temperature from 350 °C to 900 °C, the tap density of the manganese oxide rises from 0.91 g cm⁻³ to 2.06 g cm⁻³. Compared with the LiMn₂O₄ cathode made from chemical manganese dioxide or electrolytic manganese dioxide, the LiMn₂O₄ made from manganese oxide of this work has a larger tap density (2.53 g cm⁻³), and better electrochemical performances with an initial discharge capacity of 117 mAh g⁻¹, a capacity retention of 93.5% at the 15th cycle and an irreversible capacity loss of 2.24% after storage at room temperature for 28 days.     

High-strength all-solid lithium ion electrodes based on Li4Ti5O12

A Li₄Ti₅O₁₂-Li_0.29La_0.57TiO₃-Ag electrode composite was fabricated via sintering the corresponding powder mixture. The process achieved a final relative density of 97% the theoretical. Relatively thick, ∼100 μm, electrodes were fabricated to enhance the energy density relatively to the traditional solid-state thin film battery electrodes. The sintered electrode composite delivered full capacity in the first discharge at C/40 discharge rate. Full capacity utilization resulted from the 3D percolated network of both solid electrolyte and metal, which provide paths for ionic and electronic transport, respectively. The electrodes retained 85% of the theoretical capacity after 10 cycles at C/40 discharge rate. The tensile strength and the Young's modulus of the sintered electrode composite are the highest reported values to date, and are at least an order of magnitude higher than the corresponding value of traditional tapecast “composite electrodes”. The results demonstrate the concept of utilizing thick all-solid electrodes for high-strength batteries, which might be used as multifunctional structural and energy storage materials.     

Fabrication and electrochemical properties of three-dimensional net architectures of anatase TiO2 and spinel Li4Ti5O12 nanofibers

As a new type of electrodes engineering method with three-dimensional (3D) architecture for 3D rechargeable lithium ion batteries, an electrospinning has been successfully employed to prepare 3D net architectures of anatase TiO₂ and spinel Li₄Ti₅O₁₂ nanofibers. Scanning electron microscopy, X-ray diffraction, cyclic voltammetry and the discharge/charge measurements were used to characterize their structures and electrochemical properties. Our results demonstrated that 3D architectures stacked from a cross-bar array of electrospun anatase TiO₂ nanofibers could be accomplished but were destroyed after the insertion of Li ion. Significantly, spinel Li₄Ti₅O₁₂ could be selected as one of promise candidates for the realization of 3D batteries considering its structure stability of 3D spinel Li₄Ti₅O₁₂ nanofibers associated with well cyclability.     

Electrochemistry of LiMn2O4 epitaxial films deposited on various single crystal substrates

LiMn₂O₄ epitaxial thin films were synthesized on SrTiO₃:Nb(1 1 1) and Al₂O₃(0 0 1) single crystal substrates by pulsed laser deposition (PLD) method and the electrochemical properties were discussed comparing with that of amorphous LiMn₂O₄ film on polycrystalline Au substrate. LiMn₂O₄ epitaxial film showed only a single plateau in charge–discharge curves and a single redox peak at the corresponding voltage of cyclic voltammograms. This phenomenon seems to originate from the effect of the epitaxy: the film is directly connected with the substrate by the chemical bond and this connection would suppress the phase transition of Li_xMn₂O₄ film during lithium (de-)intercalation. The discharge voltage of LiMn₂O₄ epitaxial film on SrTiO₃ was lower than that of LiMn₂O₄ film on Al₂O₃. This lowered discharge voltage may be caused by the electronic interaction between LiMn₂O₄ film and SrTiO₃:Nb n-type semiconductor substrate.