Solid Electrolyte Li1 Research Articles

(Invited) Advanced Hybrid Supercapacitors with “Water-in-Salt” Electrolyte and Protected Lithium Anode

Aqueous supercapacitors are attracting increasing attention owing to their high power density, cyclability and environmental friendliness. However, thermodynamic limit of water electrolysis limits the cell voltage and window of common aqueous supercapacitors, restricting the energy density. We have previously demonstrated that advanced hybrid supercapacitors that employ aqueous electrolyte with a multi-layered water-stable protected negative electrode consisting of laminated metallic lithium or lithiated graphite, polymer electrolyte and water-stable lithium ion conducting solid electrolyte Li1+x+yTi2-xAlxSiyP3-yO12 (LTAP), can extend the negative electrode potential close to 0 V vs Li/Li+, thus providing a cell voltage close to 4 V with aqueous catholytes. In this work this hybrid supercapacitor concept is further extended to high concentration electrolytes or “water-in-salt (WIS)” electrolytes. We will demonstrate that 4 V-class cell voltage with wide voltage window can be delivered for advanced hybrid supercapacitors with capacitive or pesudocapacitive positive electrodes in WIS electrolytes combined with a protected Li anode. A typical advanced hybrid supercapacitor with MnO2 electrode shows a 4.4 V maximum cell voltage with a 1.5 V window, an energy density of 405 Wh/(kg-MnO2) at a power density of 0.88 kW kg/(kg-MnO2). A high energy density of 163 Wh kg/(kg-MnO2) is maintained at a power density of 16.7 kW kg/(kg-MnO2). These advanced hybrid supercapacitors show acceptable cycle stability and good energy retentions (around 90% within 3000 cycles). Fig. Galvanostatic charge/discharge curves for advanced hybrid supercapacitor with MnO2 in 21m LiTFSI and protected lithium negative electrode at (a) a current density of 0.1 mA/cm2 and U cell varized from 1.0 to 1.5 V (U min = 2.9 V and U max = 3.9→4.4 V) and (b) a fixed U cell = U max – U min = 4.4 – 2.9 V = 1.5 V) and various current densities (Left axis: cell voltage; Right axis: electrode potentials of MnO2 electrode and multi-layered water-stable protected lithium anode). (c) Specific capacity (1) and capacitance (2) extracted from the discharge curves of MnO2 electrode from advanced hybrid supercapacitor with MnO2 in 1 M Li2SO4 at U cell = U max – U min = 4.3 – 3.3 V = 1.0 V. Specific capacity (3) and capacitance (4) extracted from the discharge curves of MnO2 electrode from advanced hybrid supercapacitor with MnO2 in 21 m LiTFSI at the U cell = U max – U min = 4.4 – 2.9 V = 1.5 V. Figure 1

Correlative electrochemical strain and scanning electron microscopy for local characterization of the solid state electrolyte Li1.3Al0.3Ti1.7(PO4)3.

Correlative microscopy has been used to investigate the relationship between Li-ion conductivity and the microstructure of lithium aluminum titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3, LATP) with high spatial resolution. A key to improvement of solid state electrolytes such as LATP is a better understanding of interfacial and ion transport properties on relevant length scales in the nanometer to micrometer range. Using common techniques, such as electrochemical impedance spectroscopy, only global information can be obtained. In this work, we employ multiple microscopy techniques to gain local chemical and structural information paired with local insights into the Li-ion conductivity based on electrochemical strain microscopy (ESM). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) have been applied at identical regions to identify microstructural components such as an AlPO4 secondary phase. We found significantly lower Li-ion mobility in the secondary phase areas as well as at grain boundaries. Additionally, various aspects of signal formation obtained from ESM for solid state electrolytes are discussed. We demonstrate that correlative microscopy is an adjuvant tool to gain local insights into interfacial properties of energy materials.

Ionic and electronic conductivity of solid electrolyte Li0.5La0.5TiO3 doped with LiO2-SiO2-B2O3 glass

The LiO2-SiO2-B2O3 (LBS) glass doped solid electrolyte Li0.5La0.5TiO3 (LLTO) ceramics were prepared by solid-state reaction method. The results show that the samples present mainly tetragonal perovskite structure and grain size increase with glass content increases. The frequency dependent AC conductivity shows two plateaus that correspond to the bulk and grain boundary responses associated with two semi-circles observed in AC impedance spectrum. The maximum bulk ionic conductivity appeared at 1.0 wt% glass addition calculated by equivalent circuit at a value of 1.12 × 10−3 S/cm, which is nearly 1.7 times compared to pure LLTO at room temperature. The overall electronic conductivity is about 10−9 S/cm calculated from a long time leakage current measurement, which is 6 orders of magnitude lower than the ionic conductivity σbulk. These results would be helpful for us to adjust and control the conductivity of glass added solid electrolyte composite for use of all-solid-state lithium batteries.

Compatibility study of oxide and olivine cathode materials with lithium aluminum titanium phosphate

The compatibility of the solid electrolyte Li1.5Al0.5Ti1.5(PO4)3 (LATP) with the cathode materials LiCoO2, LiMn2O4, LiCoPO4, LiFePO4, and LiMn0.5Fe0.5PO4 was investigated in a co-sintering study. Mixtures of LATP and the different cathode materials were sintered at various temperatures and subsequently analyzed by thermal analysis, X-ray diffraction, and electron microscopy. Oxide cathode materials display a rapid decomposition reaction with the electrolyte material even at temperatures as low as 500 °C, while olivine cathode materials are much more stable. The oxide cathode materials tend to decompose to lithium-free compounds, leaving lithium to form Li3PO4 and other metal phosphates. In contrast, the olivine cathode materials decompose to mixed phosphates, which can, in part, still be electrochemically active. Among the olivine cathode materials, LiFePO4 demonstrated the most promising results. No secondary phases were detected by X-ray diffraction after sintering a LATP/LiFePO4 mixture at temperatures as high as 700 °C. Electron microscopy revealed a small secondary phase probably consisting of Li2FeTi(PO4)3, which is ionically conductive and should be electrochemically active as well.

Characterization of Sputter-Deposited LiCoO2 Thin Film Grown on NASICON-type Electrolyte for Application in All-Solid-State Rechargeable Lithium Battery.

All-solid-state Li-rechargeable batteries using a 500 nm-thick LiCoO2 (LCO) film deposited on two NASICON-type solid electrolyte substrates, LICGC (OHARA Inc.) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), are constructed. The postdeposition annealing temperature prior to the cell assembly is critical to produce a stable sharp LCO/electrolyte interface and to develop a strong crystallographic texture in the LCO film, conducive to migration of Li ions. Although the cells deliver a limited discharge capacity, the cells cycled stably for 50 cycles. The analysis of the LCO/electrolyte interfaces after cycling demonstrates that the sharp interface, once formed by proper thermal annealing, will remain stable without any evidence for contamination and with minimal intermixing of the constituent elements during cycling. Hence, although ionic conductivity of the NASICON-type solid electrolyte is lower than that of the sulfide electrolytes, the NACSICON-type electrolytes will maintain a stable interface in contact with a LCO cathode, which should be beneficial to improving the capacity retention as well as the rate capability of the all-solid state cell.

Facile Synthesis of Nanosized Lithium-Ion-Conducting Solid Electrolyte Li1.4Al0.4Ti1.6(PO4)3 and Its Mechanical Nanocomposites with LiMn2O4 for Enhanced Cyclic Performance in Lithium Ion Batteries.

Nanoparticles of fast lithium-ion-conducting solid electrolyte Li1.4Al0.4Ti1.6(PO4)3 (LATP) are prepared by a modified citric-acid-assisted sol-gel method that involves a two-step heat treatment in which the dry gel is calcined first in argon and then in air. The obtained LATP exhibits smaller particle size (down to 40 nm) with a narrower size distribution and less aggregation than LATP prepared by a conventional sol-gel method because of a polymeric network that preserves during LATP crystallization. It has a high relative density of 97.0% and a high room-temperature conductivity of 5.9 × 10-4 S cm-1. The as-prepared superfine LATP is further used to composite with a spinel LiMn2O4 cathode in lithium ion batteries by simple grinding. This noncoating speckled layer over the LiMn2O4 particle surface has a minimal effect on the electronic conductivity of the electrode while offering excellent ionic conductivity. The cycling stability and rate capability of LiMn2O4 are greatly improved at both ambient and elevated temperatures. After 100 cycles at 25 and 55 °C, the capacity retentions are 96.0% and 89.0%, respectively, considerably higher than the values of pristine LiMn2O4 (61.0% at 25 °C; 51.5% at 55 °C) and mechanical LiMn2O4 composite with LATP made by a conventional sol-gel method (85.0% at 25 °C; 71.4% at 55 °C).

Preparation of NASICON-Type Nanosized Solid Electrolyte Li1.4Al0.4Ti1.6(PO4)3 by Evaporation-Induced Self-Assembly for Lithium-Ion Battery.

A simple and practicable evaporation-induced self-assembly (EISA) method is introduced for the first time to prepare nanosized solid electrolyte Li1.4Al0.4Ti1.6(PO4)3 (LATP) for all-solid-state lithium-ion batteries. A pure Na+ super ion conductor (NASICON) phase is confirmed by X-ray diffraction (XRD) analysis, and its primary particle size is down to 70 nm by optimizing evaporation rate of the solvent. Excellent room temperature bulk and total lithium-ion conductivities of 2.09 × 10−3 S cm−1 and 3.63 × 10−4 S cm−1 are obtained, with an ion-hopping activation energy as low as 0.286 eV.

Electrochemical Behaviors of All-Phosphate Lithium-Ion Battery and All-Phosphate Solid-State Lithium-Ion Battery

Lithium-ion batteries are in focus of research around the world, due to their high volumetric and gravimetric energy density. For inorganic all-solid-state batteries since many years considerable effort has been devoted to the development of thin film batteries for their application in microelectronics [1, 2]. Recent research activities are directed to develop high capacity all solid state batteries for automobile applications (Toyota) [3, 4]. These kinds of applications of all-solid-state lithium-ion batteries require high cycling performance, high thermal stability, high capacity and high rate capacity. The main objective of the current work is to build up an all-solid-state battery system which meets the previously listed. Electroactive phosphate materials with different microstructures were synthesized. Based on several combinations of materials, three phosphate compounds were synthesized and used as electrolyte and electrode materials, respectively. The carbon coated cathode (Li3V2(PO4)3/C) and anode (LiTi2(PO4)3/C) materials were first investigated in half-cells that use metallic lithium foil as counter electrode and reference electrode, 1 M LiPF6 in a 1:1 solvent mixture of ethylene carbonate (EC)/dimethyl carbonate (DMC) (LP30) was used as electrolyte. Afterwards, the selected electrode materials were used to make full cells by using LP30 liquid electrolyte. The working voltage, capacity as well as high-rate performance of the full cells were characterized. The optimum ratio of Li3V2(PO4)3/C and LiTi2(PO4)3/C in the full cell was investigated based on the electrochemical performances. Finally, an all-phosphate solid-state lithium-ion battery was made by using the electrode materials and Li1.3Al0.3Ti1.7(PO4)3 solid state electrolyte. The electrochemical behavior of the all-phosphate solid-state lithium-ion battery was investigated and compared with a full cell using liquid LP30 electrolyte. The working voltage of the Li3V2(PO4)3/C-LiTi2(PO4)3/C battery is in the range of 0.2-2.2V, which well matched with the electrochemical window of the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3. Applying materials with high Li-ion conductivities such as Li3V2(PO4)3 and LiTi2(PO4)3provides the advantage of high rate capability for all solid state batteries. Reference [1] M. Koo, K. Park, S. H. Lee, M. S. Duh, D. Y. Jeon, J. W. Choi, K. Kang and K. J. Lee, Nano Lett., 2012, 12, 4810–4816. [2] Y. J. Nam, S. J. Cho, D. Y. Oh, J. M. Lim, S. Y. Kim, J. H. Song, Y. G. Lee, S. Y. Lee and Y. S. Jung, Nano Lett., 2015, 15, 3317–3323. [3] M. S. Beal, B. E. Hayden, T. L. Gall, C. E. Lee, X. Lu, M. Mirsaneh, C. Mormiche, D. Pasero, D. C. A. Smith, A. Weld, C. Yada and S. Yokoishi, ACS Comb. Sci., 2011, 13, 375–381. [4] C. Yada, C. E. Lee, D. Laughman, L. Hannah, H. Iba and B. E. Hayden, J. Electrochem. Soc., 2015, 162, A722–A726.

Structural evolution of NASICON-type Li1+xAlxGe2−x(PO4)3 using in situ synchrotron X-ray powder diffraction

In situ synchrotron X-ray diffraction study of the synthesis of solid-electrolyte Li1+xAlxGe2−x(PO4)3 (LAGP) from the precursor glass reveals that an initially crystallized dopant poor phase transforms into the Al-doped LAGP at 800 °C.

Fabrication and Performance of All-Solid-State Li–Air Battery with SWCNTs/LAGP Cathode

The all-solid-state Li-air battery has been fabricated, which is constructed by a lithium foil anode, a NASICON-type solid state electrolyte Li1+xAlyGe2-y(PO4)3 (LAGP) and single-walled carbon nanotubes (SWCNTs)/LAGP nanoparticles composite as air electrode. Its electrochemical performance was investigated in air atmosphere. Particularly, this battery exhibited a larger capacity about 2800 mAh g(-1) for the first cycle, while comparatively the battery with multiwalled carbon nanotubes (MWCNTs)/LAGP as cathode had a capacity of only about 1700 mAh g(-1). Also, the battery with SWCNTs/LAGP showed improved cycling performance with a reversible capacity of 1000 mAh g(-1) at a current density of 200 mA g(-1). Our result demonstrated that the all-solid-state Li-air battery with SWCNTs/LAGP as cathode catalyst has a considerable potential for practical application.

Preparation and properties of Li1.3Al0.3Ti1.7(PO4)3 by spray-drying and post-calcining method

Solid state electrolyte Li1.3Al0.3Ti1.7(PO4)3 is synthesized by spray-drying and post-calcining method. X-ray diffraction is employed to characterize the powders calcined in the range of 700–900°C for 2h, which indicates powders are well crystallized. FTIR shows trivalent cation Al3+ is substituted by Ti4+. The composite material appears as 2–5μm spherical particle. TG–DTA results confirm that the thermal decomposition of precursors obtained by spray-drying method occurred at lower temperature compares with solid phase synthesis method and sol–gel method. The ionic conductivity of the pellets reaches a maximum of 0.622mScm−1 at calcining temperature of 800°C.

Production of an electrode material modified by a lithium-conducting solid electrolyte

The process for producing the electrode material LiCoPO4 modified by the lithium-conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) was studied. To create a composite consisting of an electrochemically active substance and an electrically conductive additive distributed uniformly between LiCoPO4 particles, a peroxide solution of a LATP precursor was used. After annealing at 700°C, the two-phase composite LiCoPO4/LATP was obtained, the conductivity of which was two orders of magnitude higher than that of binary lithium cobalt phosphate at room temperature.

The preparation and lithium mobility of zinc based NASICON-type solid electrolyte Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12

A series of Nasicon-type solid electrolytes Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12 was synthesized by conventional solid state ceramic route. X-ray diffraction and Rietveld whole pattern refinement were applied to investigate the phase, structure and the unit cell parameters of those solid electrolytes. EIS complex impedance method was carried out to study the Li+ conductivity. The results showed that Li1+2x+2yAlxZnyTi2−x−ySixP3−xO12 with x=0.1 y=0.5 presents highest ionic conductivity 7.2×10−5Scm−1 at ambient temperature and 2.0×10−3Scm−1 at 473K. The activation energy of Li+ migration was calculated to be ca. 20kJmol−1. The influence of Zn2+ element on the structure and Li+ mobility was preliminary explained.

Lithium conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 obtained via solution chemistry

NaSICON-type lithium conductor Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is synthesized with controlled grain size and composition using solution chemistry. After thermal treatment at 850 °C, sub-micronic crystallized powders with high purity are obtained. They are converted into ceramic through Spark Plasma Sintering at 850–1000 °C. By varying the processing parameters, pellet with conductivities up to 1.6 × 10 −4 S/cm with density of 97% of the theoretical density have been obtained. XRD, FEG-SEM, ac-impedance and Vickers indentation were used to characterize the products. The influence of sintering parameters on pellet composition, microstructure and conductivity is discussed in addition to the analysis of the mechanical behavior of the grains interfaces.

Preparation of powders and films of the lithium ion conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3

This paper describes a process for the preparation of powders and films of the lithium ion conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 from peroxide solutions. The use of peroxide solutions ensures the preparation of Li1.3Al0.3Ti1.7(PO4)3 with a room-temperature electrical conductivity of (4–5) × 10−4 S/cm by calcining a precursor at 800°C. The synthesized Li1.3Al0.3Ti1.7(PO4)3 powders were characterized by X-ray diffraction, thermal analysis (DTA/TG), and ionic and electronic conductivity measurements. The growth of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte films is described.

Synthesis and orientation control of Li-ion conducting epitaxial Li0.33La0.56TiO3 solid electrolyte thin films by pulsed laser deposition

Epitaxial thin films of the Li-ion conducting solid electrolyte Li0.33La0.56TiO3 were grown by pulsed laser deposition. The growth temperature and oxygen partial pressure required for crystallization were higher than 900°C and 5Pa, respectively. Further optimization of growth conditions led to the formation and orientation control of Li-ion conducting epitaxial Li0.33La0.56TiO3 thin films.

The determination of Li+ mobility in solid electrolyte Li1.3Al0.1Zn0.1Ti1.8P3O12 in view of ionic diffusivity and conductivity

Nasicon-type solid electrolyte Li1.3Al0.1Zn0.1Ti1.8P3O12 was prepared by citric acid-assisted acrylamide polymerisation gel method. X-ray diffraction pattern showed that the introduction of Zn2+ in the parent matrix Li1+xAlxTi2−xP3O12 made it easier to get high-purity rhombohedral structure (space group \( R\overline 3 C \)) Li1.3Al0.1Zn0.1Ti1.8P3O12 without the evidence of impurity secondary phase. The Li+ kinetics were investigated by complex impedance in bulk pellet and ionic conductivity in battery-type composite cathode, respectively. Grain-interior resistance measured by galvanostatic intermittent titration technique, potential step chronoamperometry, and AC impedance spectroscopy at 20 °C varies in the range 1.2–1.95 × 10−4 S cm−1, which is in good agreement with that obtained by complex impedance method 1.5 × 10−4 S cm−1.

Effect of sintering conditions on the properties of sol-gel-derived Li1.3Al0.3Ti1.7(PO4)3

Solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li1.3Al0.3Ti1.7(PO4)3 sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li1.3Al0.3Ti1.7(PO4)3 sintered pellets. The Li1.3Al0.3Ti1.7(PO4)3 pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li1.3Al0.3Ti1.7(PO4)3. Among the Li1.3Al0.3Ti1.7(PO4)3 pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10−4 S cm−1 and the lowest activation energy of 0.2821 eV.