Solid-state lithium microbatteries

Batteries of the size of microelectronic devices, less than 10 μm thick, are now being developed and built, using thin-film deposition technologies, i.e., flash-evaporation, rf-sputtering and sol-gel technique, that are compatible with integrated circuits. Their use in future micro-devices, microsensors, intergrated circuits, memories and very large-scale integration are envisaged. Advances have been made particularly in the engineering of lithium/amorphous inorganic electrolyte/layered compound cells. Physics of the solid-state microbatteries are reviewed and the latest advances presented. The adequacy and efficiency of materials is examined. New optimized lithium microbatteries including transition-metal oxides as intercalation cathodes, i.e., MoO₃, V₂O₅, and V₆O₁₃ films are presented and their advantages are discussed in detail. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, 10–16 Sept. 1995.     

Experimental routes to in situ characterization of the electronic structure and chemical composition of cathode materials for lithium ion batteries during lithium intercalation and deintercalation using photoelectron spectroscopy and related techniques

Three different experimental routes to in situ characterization of electronic structure and chemical composition of thin film cathode surfaces used in lithium ion batteries are presented. The focus is laid on changes in electronic structure and chemical composition during lithium intercalation and deintercalation studied by photoelectron spectroscopy and related techniques. At first, results are shown obtained from spontaneous intercalation into amorphous or polycrystalline V₂O₅ thin films after lithium deposition. Although this technique is simple and clean, it is nonreversible and only applicable to the first lithium intercalation cycle into the cathode only to be applied to host materials stable in the delithiated stage. For other cathode materials, as LiCoO₂, a real electrochemical setup has to be used. In our second approach, the experiments are performed in a specially designed electrochemical cell directly connected to the vacuum system. First experimental results of RF magnetron sputtered V₂O₅ and LiCoO₂ thin film cathodes are presented. In the third approach, an all solid-state microbattery cell must be prepared inside the vacuum chamber, which allows electrochemical processing and characterization by photoelectron spectroscopy in real time. We will present our status and experimental difficulties in preparing such cells.     

Structure and electrochemistry of thin-film oxides grown by laser-pulsed deposition

Thin films of V₂O₅, LiCoO₂ and LiMn₂O₄ were grown by pulsed-laser deposition in the view of their use in lithium microbatteries. Lithiated polycrystalline crystalline thin dense films grown without post-deposition annealing were formed onto substrates maintained at low temperature (300 °C) from a sintered composite target including Li₂O as additive. The structural characterizations of these films have been carried out by X-ray diffraction and Raman scattering spectroscopy. The electrochemical features of thin films are investigated by cyclic voltammetry and their charge-discharge profiles in lithium microbatteries are shown. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

氧化还原对SrVOx外延膜晶相及物性的可逆调控

本文揭示了SrVO₃和Sr₂V₂O₇薄膜通过氧气或真空气氛中热处理来相互转化的现象. 基于该现象,高质量的Sr₂V₂O₇外延薄膜被间接合成. 性能表征结果显示半透明金属性的SrVO₃与透明绝缘的Sr₂V₂O₇可以实现可逆转换,该现象在可控的电学、光学器件中具有潜在应用价值.     

4-Volt cathode materials for rechargeable lithium batteries wet-chemistry synthesis, structure and electrochemistry

Lithium transition-metal oxides used as intercalation compounds for rechargeable lithium batteries are widely studied in search of structural stability and improved electrochemical performance. Cathode materials belonging to the 4-volt class electrodes were synthesized by wet-chemistry methods, i.e., sol-gel, combustion or co-precipitation techniques. It is shown that synthesis greatly affects the electrochemistry and cycle life characteristics of the cathodes. Extensive damage including local strain variation, nanodomain formation, and changes in cation ordering, has been observed by local probes such as Raman and FTIR spectroscopy. In this work we wish to show the relationship between the local cationic environment and electrochemical characteristics of the 4-volt cathodes. Materials such as LiMn₂O₄, LiCoO₂, LiNi_1−yCo_yO₂, LiNi_1−yCo_yVO₄, and LiMoVO₆ are investigated.     

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY ON ELECTROCHROMIC V2O5 THIN FILM

Nanocrystalline V₂O₅ thin films were reactively radio-frequency magnetron-sputtered under optimal deposition parameters. Their electrochemical and electrochromic characteristics were investigated by cyclic voltammetry and in-situ monochromatic transmittance measurements. Upon lithium intercalation, V₂O₅ thin films showed a double electrochromic behavior depending on the wavelength and the intercalation extent. X-ray photoelectron spectroscopy results showed that part of the V⁵⁺ in V₂O₅ was reduced to V⁴⁺ during the Li⁺ intercalation process.     

Lithiated c-V<Subscript>2</Subscript>O<Subscript>5</Subscript> thin-film as positive electrode for rocking-chair solid-state lithium microbattery

We report for the first time the use of lithiated crystalline V₂O₅ thin films as positive electrode in all-solid-state microbatteries. Crystalline Li_xV₂O₅ films (x ≈ 0.8 and 1.5) are obtained by vacuum evaporation of metallic lithium deposited on sputtered c-V₂O₅. An all-solid-state lithium microbattery of Li_1.5V₂O₅/LiPON/Li exhibited a typical reversible capacity of 50 μAh/cm² in the potential range 3.8/2.15 V which exceeds by far the results known on all-solid-state lithium batteries using amorphous V₂O₅ films and lithiated amorphous Li_xV₂O₅ thin films as positive electrode. Hence, the present work opens the possibility of using high performance crystalline lithiated V₂O₅ thin films in rocking-chair solid-state microbatteries.     

Electrochromic performance of the mixed V2O5–WO3 thin films synthesized by pulsed spray pyrolysis technique

Vanadium pentoxide (V₂O₅) mixed tungsten trioxide (WO₃) thin films have been synthesized by a novel pulsed spray pyrolysis technique (PSPT) on glass and fluorine doped tin oxide (FTO) coated glass substrates at 400 °C. Aqueous solutions of equimolar vanadium chloride and ammonium tungstate were mixed in volume proportions (5%, 10% and 15%) for the deposition of V₂O₅–WO₃ thin films. The structural, morphological, optical and electrochemical properties of V₂O₅–WO₃ thin films were investigated by FT-IR, XRD, SEM, cyclic voltammetry, chronoamperometry and chronocoulometry techniques. The results showed that the electrochemical properties of V₂O₅ were altered by mixing WO₃. All the films exhibited cathodic electrochromism in lithium containing electrolyte (0.5 M LiClO₄ + propylene carbonate (PC)). Maximum coloration efficiency (CE) of about 49 cm² C⁻¹ was observed for the V₂O₅ film mixed with 15% WO₃. The electrochemical stability of the sample was examined and it was found to be stable up to 1000 cycles.     

Investigation of the electrical properties and stability of HfInZnO thin-film transistors

In this study, amorphous HfInZnO (a-HIZO) thin films and related thin-film transistors (TFTs) were fabricated using the RF-sputtering method. The effects of the sputtering power (50–200 W) on the structural, surface, electrical, and optical properties of the a-HIZO films and the performance and NBIS stability of the a-HIZO TFTs were investigated. The films’ N_e increased and resistivity decreased as the sputtering power increased. The 100 W deposited a-HIZO film exhibited good optical and electrical properties compared with other sputtering powers. Optimization of the 100 W deposited a-HIZO TFT demonstrated good device performance, including a desirable μ_FE of 19.5 cm²/Vs, low SS of 0.32 V/decade, low V_th of 0.8 V, and high I_on/I_off of 10⁷, respectively. The 100 W deposited a-HIZO TFT with Al₂O₃ PVL also exhibited the best stability, with small V_th shifts of -2.2 V during NBIS testing. These high-performance a-HIZO thin films and TFTs with Al₂O₃ PVL have practical applications in thin-film electronics.     

Recent progress in solid oxide and lithium ion conducting electrolytes research

Recent material developments of fast solid oxide and lithium ion conductors are reviewed. Special emphasis is placed on the correlation between the composition, structure, and electrical transport properties of perovskite-type, perovskite-related, and other inorganic crystalline materials in terms of the required functional properties for practical applications, such as fuel or hydrolysis cells and batteries. The discussed materials include Sr- and Mg-doped LaGaO₃, Ba₂In₂O₅, Bi₄V₂O₁₁, RE-doped CeO₂, (Li,La,)TiO₃, Li₃La₃La₃Nb₂O₁₂ (M=Nb, Ta), and Na super-ionic conductor-type phosphate. Critical problems with regard to the development of practically useful devices are discussed.     

Electrostatic spray deposition of spinel Li4Ti5O12 thin films for rechargeable lithium batteries

Spinel Li₄Ti₅O₁₂ thin films are important for the fabrication of rechargeable lithium microbatteries. Porous thin films of Li₄Ti₅O₁₂ were prepared by electrostatic spray deposition (ESD) technique with lithium acetate and titanium butoxide as the precursors. The structures of these films were analyzed by scanning electron microscopy and X-ray diffraction. Coin-type cells with a liquid electrolyte were made with the Li₄Ti₅O₁₂ films against metallic lithium. Their electrochemical performance was investigated by means of galvanostatic cell cycling, cyclic voltammetry and Ac impedance spectroscopy. It was found that pure spinel phase of Li₄Ti₅O₁₂ was obtained. After annealing at the optimal temperature of 700 °C, the films can deliver a reversible specific capacity of about 150 mAh/g with excellent capacity retention after 70 cycles. Their electrochemical characteristics were quite comparable with those of the Li₄Ti₅O₁₂ laminate electrodes containing carbon black additive.     

Tailoring of electrochemical properties of V2O5 thin films grown on flexible substrates using plasma-assisted activated reactive evaporation

The vanadium pentoxide (V₂O₅) thin films have been deposited using home built activated reactive evaporation technique on indium tin oxide-coated flexible Kapton substrates and investigated their microstructural and electrochemical properties. X-ray diffraction pattern displayed predominant (001) orientation designating the orthorhombic structure of the films deposited at optimised growth conditions. The surface of the films is observed to be composed of vertical elliptical-shaped grains of size 98 nm distributed uniformly over the surface of the films provided with root mean square surface roughness of 9 nm as evidenced from atomic force microscopy studies. As-deposited V₂O₅ thin films demonstrated constant discharge capacity of about 60 μAh/(cm² _?μm) for 10 cycles at room temperature in the potential window of 4.0–2.5 V. The influence of silver (Ag) interlayer on electrochemical properties of V₂O₅ films was investigated and observed appreciable improvement in electrochemical performance of ‘V₂O₅/Ag/V₂O₅’ films. The multilayered V₂O₅/Ag/V₂O₅ films exhibited a discharge capacity of about 75 μAh/(cm² _?μm) provided with enhanced cycliability.     

Sub-10 nm V2O5 Crystals on Carbon Nanosheets for Advanced All-Solid-State Lithium Metal Batteries

V₂O₅, as a lithium-free cathode material, has inherent defects such as sluggish kinetics and volume change and, at the same time, requires a lithium metal anode that tends to form dendrites in liquid electrolytes. Both the lithium dendrite and the flammable electrolyte solvent bring longtime safety issues. This work introduces nonflammable inorganic–organic composite solid electrolyte to inhibit the growth of the lithium dendrite and suppress the instability caused by V₂O₅ nanometerization. However, the long-term cycling and rate performances are still insufficient even when reducing V₂O₅ size to about 50 nm. As an improvement, sub-10 nm V₂O₅/C nanosheets are designed and prepared using corn stalks as precursors through simple impregnation and calcination process. The V₂O₅/C offers a much better electrode/electrolyte contact and interface stability than bulk V₂O₅ and commercial V₂O₅ in the inorganic–organic composite solid electrolyte. The discharge capacity is 228 mAh g⁻¹ at 0.1 C after 50 cycles and ≈110 mAh g⁻¹ at 2.0 C.     

Antiferromagnetic Heisenberg S=5/2 spin chain compound SrMn2V2O8

Large single crystals of the new compound SrMn₂V₂O₈ have been grown by the floating-zone method. This transition-metal based oxide is isostructural to SrNi₂V₂O₈, described by the tetragonal space group I4₁cd. Magnetic properties were investigated by means of susceptibility, magnetization, and specific-heat measurements. The compound behaves like a 1D magnetic system above the ordering temperature (T_N=43 K). The magnetic ground state can be described as a classical long-range ordered antiferromagnet with weak anisotropy.     

Charge Movement through Electrochromic Thin-Film Tungsten Trioxide

A detailed survey is given of the models devised to describe the kinetics of charge movement, both electronic and ionic, through thin-film tungsten trioxide WO₃ during either reduction or oxidation. The principal models are those of Faughnan and Crandall, Green, Ingram Duffy and Monk, and of Bohnke. Adjuncts and adaptations of these models are discussed also. The inherent assumptions and kinetic details of each model are outlined, and comparisons made both between each model, and with additional data from the extensive literature on WO₃ and other solid electrochromes. Because thin-film WO3 is electrochromic, much additional information can be gleaned from optical data regarding the electro-coloration and electro-bleaching reactions, as optical effects allow an additional ‘probe’ of the physicochemical processes occurring within the solid-state WO₃ during electrochemical change. Many of the implications of this work may also be applied to charge transport through films of other transition-metal oxides—electrochromic or otherwise—so many other electrochromic metal oxides are also mentioned and discussed.     

Solvothermal synthesis and electrochemical performance of Ag-doped V6O13 as cathode material for lithium-ion battery

For the first time, belt-like V₆O₁₃ precursor was synthesized via a simple solvothermal method. Rod-like Ag-doped V₆O₁₃ was successfully synthesized by this method followed by heating at 350 °C. Both crystal domain size, electronic conductivity, and the lithium diffusion coefficient of the Ag-doped V₆O₁₃ samples are influenced by the added amount of AgNO₃. When the amount of AgNO₃ is 0.008 g, the product is rod-like particles, which are 0.1–0.3 μm wide and 1–2 μm long, and exhibits the best electrochemical performance. The enhanced electrochemical performance originates from its higher total conductivity, higher lithium diffusion coefficient, and better structural reversibility.     

On the thermal oxidation of V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>–InP heterostructures formed by the centrifugation of vanadium(V) oxide gel

The optimal mode for the application of a nanoscale layer of vanadium-pentoxide gel on the surface of indium phosphide by centrifugation is determined via spectroscopic ellipsometry and atomic-force microscopy. By oxidizing the formed V _x Oy—InP heterostructures, films are obtained with a grain structure, with the height of the relief not exceeding 70 nm. The presence of incompletely oxidized chemostimulator components (VO₂, V₂O₃) in the films and the presence of InVO₄, which binds the V₂O₅ chemostimulator and thereby blocks the regeneration cycle of V⁺⁵ ? V⁺⁴, suggest implementation of the transit mechanism of the chemostimulated oxidation of indium phosphide. The data of spectroscopic ellipsometry indicate incomplete kinetic blocking of the diffusion of indium into the films upon oxidation.     

The sol-gel mixed oxide Cr0.11V2O5.16: An attractive cathodic material for secondary lithium batteries

Preliminary results of the properties of a new mixed oxide Cr_0.11V₂O_5.16 which was synthesized by a sol-gel process and may be used as cathode material for secondary lithium batteries are presented in this paper. The electrochemical properties are investigated and compared with those exhibited by the sol-gel vanadium pentoxide V₂O₅. The results are discussed with respect to the structural data available from these compounds. The presence of Cr³⁺ and additional O^2- ions in the structure notably emphasizes the attractive performances of the material both in terms of specific capacity and cycle life. In particular, a high capacity is still available even for the pure material used without addition of electronic conductor. The cyclability, as well as the behaviour at high discharge rates are found to be significantly better than for the parent oxide V₂O₅. These results are consistent with structural considerations from which less severe structural deformations are expected during lithium insertion. Paper presented at the 4th Euroconference on Solid State Ionics, Connemara, Galway, Ireland, Sept. 13–19, 1997     

Hybrid solid electrolytes with excellent electrochemical properties and their applications in all-solid-state cells

Three types of inorganic electrolytes [Li₁₀GeP₂S₁₂ (LGPS), 75Li₂S·24P₂S₅·1P₂O₅ (LPOS), Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP)] with different particle sizes and electrochemical properties are selected as active fillers incorporated into poly(ethylene oxide) (PEO) matrix to fabricate hybrid solid electrolytes. The optimum composition of each filler is found in consideration of ionic conductivity. Their electrochemical characteristics are investigated. The optimal conductivities are 1.60 × 10^?5, 1.18 × 10^?5, and 2.12 × 10^?5 S cm^?1 at room temperature for PEO-1%LGPS, PEO-1%LPOS, and PEO-20%LAGP, respectively. The electrochemical stability windows of these hybrid solid electrolytes are all above 5 V (vs. Li⁺/Li). The results show that these fillers have positive effects on the ionic conductivity, lithium ion transference number, and electrochemical stability. The relationship between the type of filler and electrochemical properties has been investigated. All-solid-state cells LiFePO₄/Li are fabricated and present fascinating electrochemical performance with high capacity retention and good cycling stability. This work provides promising electrolytes prepared by a simple method.     

Ultrafast synthesis of Li1 + αV3O8 gel precursors for lithium battery applications

A versatile route has been developed to synthesize the Li_1 + αV₃O₈ gel precursor 50 times faster than the standard path without heating by using H₂O₂ and V₂O₅ and lithium salts as precursors. Upon heat treatment it leads to stoechiometric Li_1.1V₃O₈ with an electrochemical behavior similar to the one observed from the standard material. The role of the pH and the nature of the counter ion on the structural type and the morphology of the condensed Li_1 + αV₃O_8,nH₂O compound have been investigated. pH close to the zero charge point (≈ 2) lead to intercalated Li_xV₂O₅,nH₂O type gels whereas at pH 4 condensation drives to hewettite like structures.