GLASS CERAMIC SOLID ELECTROLYTE

Abstract

A glass ceramic solid electrolyte mixture including glass ceramic solid electrolyte including a ternary glass ceramic of borate, Li.sub.2SO.sub.4 and a lithium halide. Also, a glass ceramic solid electrolyte obtained from the mixture, a solid state battery including the glass ceramic solid electrolyte, and methods of producing the glass ceramic solid electrolyte and the solid state battery.

Claims

1. A glass ceramic solid electrolyte mixture comprising a ternary glass ceramic of borate, Li.sub.2SO.sub.4 and a lithium halide.

2. The glass ceramic solid electrolyte mixture according to claim 1, comprising between 50 and 85% by weight of borate, between 10 and 40% by weight Li.sub.2SO.sub.4, and between 1 and 10% by weight of lithium halide, based on the total weight of the glass ceramic solid electrolyte mixture.

3. The glass ceramic solid electrolyte mixture according to claim 1, wherein the borate comprises Li.sub.3BO.sub.3.

4. The glass ceramic solid electrolyte mixture according to claim 1, wherein the lithium halide comprises LiCl.

5. A glass ceramic solid electrolyte obtainable by sintering the glass ceramic solid electrolyte mixture according to claim 1, wherein the glass ceramic solid electrolyte mixture comprises a ternary glass ceramic of borate, Li.sub.2SO.sub.4 and a lithium halide.

6. The glass ceramic solid electrolyte according to claim 5, comprising a matrix comprising the borate, and wherein the lithium halide and Li.sub.2SO.sub.4 are dispersed within the matrix.

7. The glass ceramic solid electrolyte according to claim 5, wherein the borate is at least partially comprised within the electrolyte as a glassy phase.

8. The glass ceramic solid electrolyte according to claim 5, wherein the borate comprises Li.sub.3BO.sub.3.

9. The glass ceramic solid electrolyte according to claim 5, having a total ionic conductivity between 10.sup.5 and 10.sup.9 S/cm at a temperature between room temperature and 100 C.

10. A solid state battery, comprising the glass ceramic solid electrolyte according to claim 5.

11. The solid state battery according to claim 10, being an all ceramic solid state battery.

12. A method of producing a glass ceramic solid electrolyte comprising a ternary glass ceramic of borate, Li.sub.2SO.sub.4 and a lithium halide, comprising sintering the mixture of claim 1 at a temperature between 600 C. and 1000 C. in an inert atmosphere.

13. A method of producing a solid state battery comprising the glass ceramic solid electrolyte of claim 5, comprising applying the glass ceramic solid electrolyte mixture to a surface of an anode or a cathode, sintering at a temperature between 600 C. and 1000 C. in an inert atmosphere, and providing a cathode or an anode at the exposed surface of the sintered mixture, thereby obtaining the solid state battery.

14. The method of producing a solid state battery according to claim 13, wherein both the anode and the cathode are provided prior to sintering, thereby providing the glass ceramic solid electrode mixture between the anode and the cathode, and wherein sintering comprises sintering of the anode-mixture-cathode assembly.

Description

DESCRIPTION OF THE FIGURES

[0046] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:

[0047] FIG. 1 shows the X-ray diffraction (XRD) pattern for a glass ceramic solid electrolyte of the invention after grinding the electrolyte to a powder;

[0048] FIGS. 2 and 3 show scanning electron microscope (SEM) images of the cross-section of an inventive glass ceramic solid electrolyte at different magnifications;

[0049] FIG. 4 shows the energy dispersive X-ray analysis (EDX) analysis from the cross-section of an inventive glass ceramic solid electrolyte;

[0050] FIG. 5 shows the total ionic conductivity for a LiLi symmetrical cell comprising an inventive glass ceramic solid electrolyte; and

[0051] FIG. 6 shows the galvanostatic cycling of an inventive battery cell.

DETAILED DESCRIPTION OF THE INVENTION

[0052] The glass ceramic solid electrolyte mixture and the glass ceramic solid electrolyte of the present disclosure comprise or substantially consist of a ternary glass ceramic of borate, Li.sub.2SO.sub.4 and a lithium halide.

[0053] Advantageously, the borate comprises or substantially consists of Li.sub.3BO.sub.3. Alternatively or additionally, yet advantageously, the borate can comprise one or more of B.sub.2O.sub.3, LiBO.sub.2, Li.sub.4B.sub.2O.sub.5, and Li.sub.6B.sub.4O.sub.9.

[0054] The halide can be any one of chloride, bromide, iodide, fluoride, preferably chloride or fluoride, more preferably chloride. The lithium halide can thus be any one of LiCl, LiBr, LiI and LiF, preferably LiCl or LiF, more preferably LiCl. The glass ceramic solid electrolyte can comprise two or more lithium halides, advantageously two or more of LiCl, LiBr, LiI and LiF.

[0055] Advantageously, the glass ceramic solid electrolyte comprises between 50 and 85% by weight, preferably between 60 and 80% by weight, more preferably between 65 and 75% by weight, for example 70% by weight of borate, based on the total weight of the glass ceramic solid electrolyte.

[0056] Advantageously, the glass ceramic solid electrolyte comprises between 10 and 40% by weight, preferably between 15 and 35% by weight, more preferably between 20 and 30% by weight, for example 25% by weight Li.sub.2SO.sub.4, based on the total weight of the glass ceramic solid electrolyte.

[0057] Advantageously, the glass ceramic solid electrolyte comprises between 1 and 10% by weight, preferably between 2 and 8% by weight, more preferably between 3 and 7% by weight, for example 5% by weight of lithium halide, based on the total weight of the glass ceramic solid electrolyte.

[0058] Advantageously, the glass ceramic solid electrolyte comprises between 50 and 85% by weight of borate, between 10 and 40% by weight Li.sub.2SO.sub.4 and between 1 and 10% by weight of lithium halide, preferably between 65 and 75% by weight of borate, between 20 and 30% by weight Li.sub.2SO.sub.4 and between 3 and 7% by weight of the lithium halide, based on total weight of the glass ceramic solid electrolyte.

[0059] Advantageously, the glass ceramic solid electrolytes of the present disclosure are dense electrolytes, i.e. electrolytes having a low porosity. More particularly, the electrolytes advantageously have a density equal to or higher than 70% of the theoretical density of the electrolyte. The theoretical density is calculated from the densities of the compounds comprised in the electrolyte and the composition of the electrolyte (amount of each compound). The density of the electrolyte is calculated by dividing its weight by its volume.

[0060] The present invention further relates to solid state batteries (i.e. all solid batteries) (SSBs), in particular secondary batteries, comprising the inventive glass ceramic solid electrolyte.

[0061] Advantageously, the battery further comprises a cathode, which can be any suitable cathode known in the art. Advantageously, the battery further comprises an anode, which can be any suitable anode known in the art.

[0062] Advantageously, the SSB is an all ceramic SSB, i.e. a SSB wherein all components-anode, cathode and electrolyte, are ceramic materials.

[0063] The present invention also relates to methods of producing the glass ceramic SSE. The method advantageously comprises an operation of preparing a mixture, a shaping operation and a sintering operation.

[0064] Advantageously, the mixture preparation operation comprises mixing a borate, Li.sub.2SO.sub.4 and a lithium halide, wherein the borate and the lithium halide are as hereinabove described. To obtain a homogeneous mixture, mixing techniques known in the art can be used, for example ball-milling or pearl-milling.

[0065] Advantageously, the mixture comprises between 50 and 85% by weight of borate, preferably Li.sub.3BO.sub.3, between 10 and 40% by weight Li.sub.2SO.sub.4 and between 1 and 10% by weight of lithium halide, preferably LiCl, preferably between 65 and 75% by weight of borate, between 20 and 30% by weight Li.sub.2SO.sub.4 and between 3 and 7% by weight of lithium halide, based on the total weight of the mixture.

[0066] Advantageously, the mixture is shaped during a shaping operation. Shaping can be performed by methods known in the art, for example by pressing the mixture into a predetermined shape or by laser cutting the mixture into a predetermined shape. Upon shaping, a green body is obtained. The green body can have a variety of shapes, such as a sheet, a pellet, a disk, etc., wherein the shape is defined by the shape required for the composite solid electrolyte.

[0067] The green body is then sintered during the sintering operation. The sintering operation comprises heating the green body to a sintering temperature, and maintaining the green body at the sintering temperature for a predetermined sintering duration, during which the green body is sintered.

[0068] Advantageously, the sintering operation is performed in an atmosphere known in the art. Preferably, the sintering operation is performed in an inert atmosphere, more preferably in an inert atmosphere comprising or substantially consisting of argon.

[0069] Advantageously, the sintering temperature is between 600 C. and 1000 C., preferably between 700 C. and 900 C., more preferably between 750 C. and 850 C.

[0070] Advantageously, heating the green body to the sintering temperature is performed at a heating rate between 5 C./s and 500 C./s, i.e. can be at a traditional heating rate or at an ultrafast heating rate.

[0071] Advantageously, the sintering duration is between 5 seconds and 600 seconds, preferably between 10 seconds and 300 seconds, more preferably between 20 seconds and 200 seconds, such as between 30 seconds and 150 seconds, or between 45 seconds and 100 seconds.

[0072] It will be understood that the sintering duration depends, amongst others, on the heating rate, the sintering temperature and the equipment used.

EXAMPLES

Example 1

[0073] A mixture of 7.0 g Li.sub.3BO.sub.3, 2.5 g Li.sub.2SO.sub.4 and 0.5 g LiCl was ball-milled at 400 rpm for 2 hours under an argon atmosphere. The mixture was then pressed into green body pellets with an uniaxial press.

[0074] The green body pellets were then heated to 825 C. and sintered at 825 C. for 100 seconds, followed by cooling down to room temperature. The obtained glass ceramic solid electrolyte pellets were then partially ground to powder and partially cut into pieces for analysis.

[0075] FIG. 1 shows the X-ray diffraction (XRD) pattern for the Li.sub.2SO.sub.4, Li.sub.3BO.sub.3 and the glass ceramic solid electrolyte powder (referenced to as 1, 2 and 3, respectively). Comparison of the XRD patterns clearly indicates the presence of Li.sub.2SO.sub.4 and Li.sub.3BO.sub.3 in the electrolyte. The signal at 2 between 0 and 20 further indicates the presence of glassy phases, which are believed to be formed by Li.sub.3BO.sub.3.

[0076] Scanning Electron Microscopy (SEM)-analysis was performed on pieces of the glass ceramic solid electrolyte using a high resolution scanning electron microscope FEI (Teneo) under high-vacuum. FIGS. 2 and 3 show SEM-images at different magnifications of the cross-section of the glass ceramic solid electrolyte. At low magnification (FIG. 2) a dense structure is visible. At higher magnification (FIG. 3) a glassy phase matrix is clearly visiblecontributed to Li.sub.3BO.sub.3with crystalline phases dispersed therein.

[0077] FIG. 4 shows the energy dispersive X-ray analysis (EDX) analysis from the cross-section of the electrolyte. All elements of Li.sub.3BO.sub.3, Li.sub.2SO.sub.4 and LiCl were detected. This confirms that all components of the mixture are retained in the obtained glass ceramic solid electrolyte.

Example 2

[0078] A LiLi symmetric cell comprising the glass ceramic solid electrolyte of Example 1 was prepared to measure the total ionic conductivity and the electrochemical properties. The inventive LiLi symmetric cell was prepared with a 800 m thick glass ceramic solid electrolyte pellet as prepared in Example 1, metallic lithium with a thickness of 50 m as electrodes and copper foils with a thickness of 5-8 m as current collectors.

[0079] FIG. 5 shows the total ionic conductivity at temperatures varying between room temperature and 100 C. At room temperature, the total ionic conductivity was 2*10.sup.8 S/cm, whereas at 100 C. the total ionic conductivity was 4*10.sup.7 S/cm.

[0080] Galvanostatic cycling of the inventive LiLi symmetric cell was also performed at 100 C. and at a current density of 0.1 mA/cm.sup.2. From FIG. 6 it is clear that a stable cycling was seen for a test duration of more than 4500 seconds.

Nomenclature

[0081] 1. XRD pattern for Li.sub.2SO.sub.4 [0082] 2. XRD pattern for Li.sub.3BO.sub.3 [0083] 3. XRD pattern for an inventive glass ceramic solid electrolyte