Masashi Kotobuki

Compatibility of Li7La3Zr2O12 Solid Electrolyte to All-Solid-State Battery Using Li Metal Anode

Electrochemical properties of Li 7 La 3 Zr z O 12 (LLZ) were investigated to reveal its availability as a solid electrolyte for all-solid-state rechargeable batteries with a Li metal anode. After calcination at 1230°C, a well-sintered LLZ pellet with a garnet-like structure was obtained, and its conductivity was 1.8 × 10 ―4 S cm ―1 at room temperature. The cyclic voltammogram of the Li/LLZ/Li cell showed that the dissolution and deposition reactions of lithium occurred reversibly without any reaction with LLZ. This indicates that a Li metal anode can be applied for an LLZ system. A full cell composed of a LiCoO 2 /LLZ/Li configuration was also operated successfully at expected voltage estimated from the redox potential of Li metal and LiCoO 2 . Simultaneously, an irreversible behavior was observed at the first discharge and charge cycle due to an interfacial problem between LiCoO 2 and LLZ. The discharge capacity of the full cell was 15 μA h cm ―2 . These results reveal that LLZ is available for all-solid-state lithium batteries.

Fabrication of Three-Dimensional Battery Using Ceramic Electrolyte with Honeycomb Structure by Sol–Gel Process

Li 0.35 La 0.55 TiO 3 (LLT) with a honeycomb structure, which has microsized holes on both sides of a membrane, was prepared as an electrolyte for three-dimensional all-solid-state rechargeable lithium-ion batteries. In this study, LiCoO 2 and Li 4 Mn 5 O 12 were used as cathode and anode materials, respectively, and their particles were fabricated by the sol-gel method, which provided not only small particles to inject into the microsized holes of the honeycomb electrolyte (0.6 and 0.3 μm for LiCoO 2 and Li 4 Mn 5 O 12 , respectively) but also particles with high discharge capacities (98.6 and 90.2% of their theoretical capacities for LiCoO 2 and Li 4 Mn 5 O 12 , respectively). The impregnation of active material particles mixed with the precursor sol into the honeycomb holes provided a good contact between the LLT electrolyte and the active materials, which reduced the internal resistance of the cell and improved the discharge capacity. Accordingly, the LiCoO 2 /LLT/Li 4 Mn 5 O 12 all-solid-state battery was successfully operated at 1.1 V with a discharge capacity of 7.3 μAh cm -2 .

First-principles density functional calculation of electrochemical stability of fast Li ion conducting garnet-type oxides

The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).

A hybrid polymer/oxide/ionic-liquid solid electrolyte for Na-metal batteries

The development of solid electrolytes with superior electrical and electrochemical performances for the room-temperature operation of sodium (Na)-based batteries is at the infant stage and still remains a challenge. Herein, we, for the first time, report hybrid solid electrolytes consisting of PEO20–NaClO4–5% SiO2–x% Emim FSI (x = 50, 70) designed for solid-state Na-metal batteries. The hybrid design yields a solid electrolyte featuring a high room-temperature ionic conductivity of 1.3 × 10−3 S cm−1, suitable mechanical property, a wide voltage stability window of 4.2 V and a high Na+ transference number of 0.61. A prototypical Na-metal battery using this hybrid solid electrolyte demonstrates promising long-term cycling performances at room temperature and at an elevated temperature of 60 °C for 100 cycles. The finding implies that the hybrid solid electrolyte is promising for Na-metal batteries operating at room temperature.

Na-rich layered Na 2 Ti 1−x Cr x O 3−x/2 (x = 0, 0.06): Na-ion battery cathode materials with high capacity and long cycle life

Rechargeable lithium batteries have been well-known and indispensable for portable electronic devices, and have the potential to be used in electric vehicles and smart grids. However, the growing concerns about the availability of lithium resources for large-scale applications have revived interest in sodium ion batteries. Of many obstacles to commercialization of Na-ion batteries, achieving simultaneously a large reversible capacity and good cycling capability of electrode materials remains a major challenge. Here, we report a new cathode material, Na-rich layered oxide Na2Ti0.94Cr0.06O2.97, that delivers high reversible capacity of 336 mAh g−1 at current density of 18.9 mA g−1 along with promising cycling capability of 74% capacity retention over 1000 cycles at current of 378 mA g−1. The high capacity is associated to the redox reaction of oxygen, which is confirmed here by a combined experimental and theoretical study. The present work therefore shows that materials beyond mainstream layered oxides and polyanion compounds should be considered as candidate high-performance cathodes for Na-ion batteries.

All-Solid-State Li Battery for Future Energy Technology

Rechargeable lithium ion battery has been utilized to power sources for portable devices, such as cellar phone and laptop computer. Recently, this battery has been investigated as energy storage system for electric vehicles, natural energy, and so on. Many of researches have been done and still continued to develop rechargeable lithium ion batteries with high energy and power densities. In addition, several types of new generation batteries have been proposed in order to realize higher energy density of battery. All-solid-state battery is one of new type of rechargeable batteries with excellent safety and high energy density. However, there are some problems to construct all-solid-state rechargeable battery. Most important point is battery design for all-solid-state battery, due to usage of solid electrolyte, especially ceramic electrolyte. This means that new structure concept is needed for construction of rechargeable lithium battery in micro or nm scale. Recently, three-dimensionally ordered macroporous solid electrolyte has been proposed to establish new concept for electrode system. In addition, macro structure of all-solid-state battery was examined based on three-dimensional batteries. In this chapter, some of such unique structure for construction of practical battery system with ceramic solid electrolyte was described. In this part, oxide materials with high ionic conductivity were discussed.

Ruthenium doped cubic-garnet structured solid electrolyte Li7La3Zr2−xRuxO12

The cubic garnet solid electrolyte Li7La3Zr2O12 (LLZO) is recognised as a promising solid electrolyte for the all solid-state batteries. In this study, an effect of Ru doping to Zr site on electrochemical properties of the cubic LLZO is examined. The Ru-doped LLZO is prepared by a conventional solid-state reaction using Ga as a stabilise agent for the cubic phase. X-ray diffraction, scanning electron microscopy, and electrochemical impedance are used to characterise it. A lattice constant of the Ru-doped LLZO decreases with increase in doping amount of Ru. Also, a formation of perovskite LaRuO3 is confirmed in the Ru-doped LLZO. The Li ion conductivity of the Ru-doped LLZO is higher than that of the pure LLZO. The highest ionic conductivity of 2.56 × 10−4 S/cm was obtained in Li7La3Zr1.6Ru0.4O12. A promotion of sintering and shrinkage of lattice constant by the Ru doping would be reason for the improvement of Li ion conductivity in the Ru-doped LLZO.

Study on stabilization of cubic Li7La3Zr2O12 by Ge substitution in various atmospheres

Stabilization of high Li ion conductive cubic Li7La3Zr2O12 (LLZ) by Ge substitution in air, N2/O2 and N2 atmospheres are studied by high temperature XRD (HT-XRD) of Ge-added tetragonal LLZ (Ge-LLZ). A formation of low temperature cubic phase caused by CO2 absorption during storage of the Ge-LLZ is observed at about 160∘C in all atmospheres. Additionally, impurity formation of La2Zr2O7 and La2O3 also occurs in all atmospheres. On the other hand, stabilization of cubic phase by substitution of Ge is largely influenced by the atmosphere. The cubic phase is observed at 40∘C after heating Ge-LLZ to 700∘C in air while only tetragonal phase appeared after heating in N2/O2. It is concluded that the heating atmosphere largely influences substitution of Ge, resulting in stabilization of the high Li ion conductive cubic phase.

Ceramic Electrolytes for All-Solid-State Li Batteries

All-solid-state batteries have gained much attention as the next-generation batteries. This book is about various Li ion ceramic electrolytes and their applications to all-solid-state battery. It contains a wide range of topics from history of ceramic electrolytes and ion conduction mechanisms to recent research achievements. Here oxide-type and sulfide-type ceramic electrolytes are described in detail. Additionally, their applications to all-solid-state batteries, including Li-air battery and Li-S battery, are reviewed.Consisting of fundamentals and advanced technology, this book would be suitable for beginners in the research of ceramic electrolytes; it can also be used by scientists and research engineers for more advanced development.

Research Update: Ca doping effect on the Li-ion conductivity in NASICON-type solid electrolyte LiZr2(PO4)3: A first-principles molecular dynamics study

In this work, we used a density functional theory-based molecular dynamics simulation to investigate the Ca content-dependent Li-ion conductivity of NASICON-type Li1+2xCaxZr2-x(PO4)3 (LCZP) solid electrolytes (0.063 ≤ x ≤ 0.375) which exhibit a Li-excess chemical composition. The LCZP systems show a higher room temperature Li-ion conductivity and a lower activation energy than pristine LiZr2(PO4)3 (LZP), and the tendencies of those properties agree with the experimental results. In addition, the Li-ion conduction mechanisms in LCZP were clarified by analyzing the radial distribution functions and site displacement functions obtained from our molecular dynamics simulations. For minimal Ca substitution for LZP, the Li-ion conductivity is enhanced because of the creation of interstitial Li ions by Ca doping in the LCZP systems; the frequency of collisions with Li ions dramatically increases. For substantial Ca substitution for LZP, the Li-ion conductivity gradually worsened because some Li ions were trapped at the M1 (most stable) and M2 (metastable) sites near Ca atoms.In this work, we used a density functional theory-based molecular dynamics simulation to investigate the Ca content-dependent Li-ion conductivity of NASICON-type Li1+2xCaxZr2-x(PO4)3 (LCZP) solid electrolytes (0.063 ≤ x ≤ 0.375) which exhibit a Li-excess chemical composition. The LCZP systems show a higher room temperature Li-ion conductivity and a lower activation energy than pristine LiZr2(PO4)3 (LZP), and the tendencies of those properties agree with the experimental results. In addition, the Li-ion conduction mechanisms in LCZP were clarified by analyzing the radial distribution functions and site displacement functions obtained from our molecular dynamics simulations. For minimal Ca substitution for LZP, the Li-ion conductivity is enhanced because of the creation of interstitial Li ions by Ca doping in the LCZP systems; the frequency of collisions with Li ions dramatically increases. For substantial Ca substitution for LZP, the Li-ion conductivity gradually worsened because some Li ions were trapped ...