Li2S-P2S5 Glass-ceramic Electrolyte Research Articles

Ionic Conductivity and Crystal Structure of Li5GaS4 Solid Electrolytes Prepared via Mechanochemical Process

High-performance batteries attract attention as the power sources for electric cars with cruising long distance and Smart Grid to balance supply with demand in electric power. All-solid-state batteries using solid electrolytes without leakage are attracting with high safety and reliability. For realization of all-solid-state batteries, the solid electrolytes are needed to have a high ionic conductivity, good ductility, and chemical stability.Various sulfide solid electrolytes were reported as Li2S-P2S5 glass-based electrolytes, thio-LISICON-type crystals, and the class of argyrodites. We reported Li2S-P2S5 glass and glass-ceramic electrolytes have high ionic conductivities, wide potential windows, and good ductility [1]. In other systems, the electrolytes with thio-LISICON-type and Li10GeP2S12-type crystal structure were reported to have high conductivity [2-4].The solid electrolytes of Li4GeS4-Li3PS4 and Li4GeS4-Li5GaS4 with thio-LISICON-type crystal structure have the conductivity of 2.2×10−3 and 6.5×10−5 S cm−1 at 25°C, respectively [2,3]. The crystal structures and conductivities at room temperature of Li4GeS4 and Li3PS4, which are the terminal composition in the binary systems, were reported [3,5]. Another terminal composition Li5GaS4 had the low conductivity of 5.1×10−8 S cm−1 at 100°C, but has not been reported its crystal structure [3].In this study, we prepared Li5GaS4 electrolytes with low crystallinity by mechanochemical process in order to increase their conductivity.The Li5GaS4 solid electrolytes were prepared by mechanochemical process and subsequent heat treatment at 600°C. In the XRD pattern of the sample after mechanochemical process, weak unidentified peaks were observed and different from the peaks of the starting material. This indicated that the sample with low crystallinity including amorphous matrix was obtained. On the other hand, the diffraction pattern of the heated sample was not reported and different from that after mechanochemical process. The peaks in the pattern were able to be indexed in monoclinic system. The sample of Li5GaS4 after mechanochemical treatment showed the highest ionic conductivity of 2.2×10−5 S cm−1 at 25°C. The ionic conductivity of the sample decreased with increasing the crystallinity by heat treatment, and the sample heated at 600°C showed a low value of 2.1×10−8 S cm−1 at 25°C. This suggests that the structure of Li5GaS4 crystal is not suitable for ionic conduction. On the other hand, the ionic conductivity of the Li5GaS4 sample increased due to the amorphization by mechanochemical process, and increasing of the free volume in the sample is effective in increasing the conductivity. Reference s : [1] M. Tatsumisago and A. Hayashi, Int. J. Appl. Glass Sci., 5, 226 (2014).[2] R. Kanno and M. Murayama, J. Electrochem. Soc., 148, A742 (2001).[3] R. Kanno et al., Solid State Ionics, 130, 97 (2000).[4] N. Kayama et al., Nat. Mater., 10, 682 (2011).[5] M. Tachez et al., Solid State Ionics, 14, 181 (1984).

Synergistic effect of processing and composition x on conductivity of xLi2S-(100 − x)P2S5 electrolytes

Highly Li-ion conductive Li2S-P2S5 glass-ceramic electrolytes were prepared by controlling the compositions and heat treatment process of the glass. In the systems xLi2S·(100−x)P2S5 (65≤x≤75,mol%) glass phase substrates were prepared by mechanical ball milling. After melting, rapidly quenching and tempering, glass-ceramic electrolytes were prepared. Among them, the 70Li2S·30P2S5 sample showed a highest conductivity of 1.58×10−3Scm−1 and an activation energy of 39kJmol−1. The outstanding property was attributed to both the precipitation of the high conductivity thio-LISICON III phase and the heat treatment, which reduces the grain boundary and improves the grain morphology. Moreover, ball milling method was applied to prepare the composite cathode. Significant high capacity all-solid-state cell with commercial Li2S as active material and 70Li2S·30P2S5 glass ceramic as electrolyte was prepared. First discharge capacity of 1055mAhg−1, high capacity retention of 57.2% after ten cycle and excellent coulombic efficiency were achieved.

Invited paper: Recent development of bulk-type solid-state rechargeable lithium batteries with sulfide glass-ceramic electrolytes

The recent development of bulk-type solid-state rechargeable lithium batteries with sulfide glass-ceramics as a solid electrolyte was reviewed. Sulfide glasses and glass-ceramics in the system Li2S-P2S5 have an advantage of high conductivity, wide electrochemical window and low grain-boundary resistance. Bulk-type solid-state batteries composed of compressed powder layers of electrode and electrolyte were fabricated with Li2S-P2S5 glass-ceramic electrolytes. Formation of a favorable solid-solid interface between electrode and electrolyte is a key to achieving excellent performance in solid-state batteries. The mechanochemical preparation of nanocomposite electrodes and surface modification of active materials by softening of the electrolyte, or PLD coating, were useful for increasing the electrode-electrolyte contact area and improving battery performance.

Nanostructured all-solid-state supercapacitor based on Li2S-P2S5 glass-ceramic electrolyte

While today’s lithium-ion batteries offer acceptable energy storage capability, they lack the ability to be cycled repeatedly more than a couple thousand times. Electrochemical capacitors, i.e., supercapacitors, are being developed whose lifetimes exceed 1 × 106 cycles and power densities surpass those of batteries by several times. Here, we present an all-solid-state supercapacitor using a Li2S-P2S5 glass-ceramic electrolyte as both separator and ion conductor. Three device architectures are examined including two with nanostructured electrodes which incorporate multi-walled carbon nanotubes (MWCNTs). Cyclic voltammograms and electrochemical impedance measurements demonstrate that these devices develop reversible double layer capacitance, and a maximum of 7.75 F/g is achieved in the device constructed by mechanically mixing the nanostructured electrodes. Electrochemical impedance spectroscopy explains non-idealities observed when MWCNTs are incorporated in the electrode layers.

All-solid-state rechargeable lithium batteries using SnX-P2X5 (X = S and O) amorphous negative electrodes

SnS-P2S5 and SnO-P2O5 amorphous materials were prepared by a mechanical milling technique. The SnO-P2O5 milled materials worked as a reversible electrode with higher capacity than SnO crystal in rechargeable lithium cells with conventional liquid electrolytes. All-solid-state cells with a SnX-P2X5 (X = S and O) amorphous electrode and the Li2S-P2S5 glass-ceramic electrolyte were charged and discharged at room temperature. The sulfide electrodes exhibited better charge-discharge performance than the oxide electrodes, suggesting that SnS-P2S5 electrodes are more compatible with Li2S-P2S5 sulfide solid electrolytes. All-solid state batteries 80SnS·20P2S5/LiCoO2 showed a charge-discharge plateau of about 3.4 V and high reversible capacity of over 400 mAh/g, even after 50 cycles. The SnX (X = S and O)-based amorphous materials are promising negative electrode materials with high capacity for rechargeable lithium batteries using not only liquid electrolytes but solid electrolytes.