Glass ceramic solid electrolyte

Abstract

The present invention relates to a glass ceramic solid electrolyte mixture comprising a glass ceramic solid electrolyte comprising a ternary glass ceramic of a borate, Li2SO4 and a lithium halide. The invention further relates to a glass ceramic solid electrolyte obtained from the mixture, a solid state battery comprising the glass ceramic solid electrolyte, and a method for preparing the glass ceramic solid electrolyte and the solid state battery.

Description

Technical Field

[0001] This invention relates to glass-ceramic solid electrolytes and solid-state battery packs, particularly lithium-ion battery packs, comprising said glass-ceramic solid electrolytes. The invention further relates to methods for preparing said glass-ceramic solid electrolytes. Background Technology

[0002] Inorganic materials, such as ceramics, are widely used in electronics, energy storage, and extreme environments due to their high thermal, mechanical, and chemical stability. The conventional synthesis of such inorganic materials typically involves a solid-state reaction that forms an inorganic component from a precursor and sintersulates said inorganic component to obtain a solid (inorganic) component. Each step usually requires high temperatures and long processing times.

[0003] The long processing time is also one of the problems with conventional methods for preparing inorganic (e.g., ceramic-based) solid electrolytes (SSEs). Such SSEs are promising alternatives to, for example, liquid electrolytes, which can leak from the battery pack, thus raising safety concerns. In particular, phosphorus oxynitride and thio-Li... x A 1-y M y S4 (where A is Si or Ge, and M is P, Al, Zn, Ga, or Sb) materials are promising for SSE, showing performance at 10 -4 These materials exhibit excellent ionic conductivity in the S / cm range. However, they are costly to manufacture, particularly due to high energy consumption caused by high sintering temperatures, and frequent contact losses between the electrodes and the SSE are observed during prolonged charge / discharge cycles, thus limiting the lifespan of battery packs containing these solid electrolytes.

[0004] Glassy and glass-ceramic solid electrolytes have therefore attracted interest because they are known to allow sintering at relatively, but still fairly high, temperatures. In particular, borate-based glass-ceramics have attracted interest and are known to include two-component phases using B₂O₃, LiBO₂, and occasionally Li₃BO₃.

[0005] Study of electrical conductivity of Li₂O-B₂O₃-SiO₂-Li₂SO₄ glasses and glass-ceramics, S.S. Gundale, V.V. Vehare et al., Solid State Ionics, Vol. 298 (2016), pp. 57-62, discloses the synthesis of glasses and glass-ceramics for SSE in the Li₂O-B₂O₃-SiO₂-Li₂SO₄ system. The method includes melt quenching and single-stage heat treatment. The highest electrical conductivity (4.08 × 10⁻⁶) was measured at 250 °C for the synthesized glass with a composition of 40Li₂O:30B₂O₃:15SiO₂:15Li₂SO₄. -4 (S / cm), although it is noted that the ionic conductivity of glass ceramics is lower than that of glass.

[0006] The aforementioned method has the disadvantage of complexity, requiring a suitable environment and equipment for melt quenching. Another disadvantage is the need for high temperatures during heat treatment due to the presence of SiO2 (silicates) with a high melting temperature.

[0007] Optimization of a heterogeneous ternary Li3PO4–Li3BO3–Li2SO4 mixture for Li-ion conductivity by machine learning, Kenji Homma, Yu Liu et al., The Journal of Physical Chemistry C 124, 24 (2020), pp. 12865-12870, discloses the use of machine learning to optimize the composition ratio of a ternary Li3PO4–Li3BO3–Li2SO4 mixture for Li-ion conductivity. After determining the optimal composition (25:14:61 Li3PO4:Li3BO3:Li2SO4, in mol%) via machine learning, the mixture was prepared and sintered at temperatures determined by the melting point and phase transition of the mixture (lasted for 12 hours in the range of 620-1000 °C). The Li-ion conductivity of this mixture was 4.9 × 10⁻⁶ at 300 °C. -4 S / cm.

[0008] The drawback of the aforementioned method is that it still requires a relatively high sintering temperature, which is believed to be due to the use of Li3PO4, which has a high melting temperature.

[0009] While the ionic conductivity values ​​of the two publications mentioned above appear acceptable, it should be noted that these values ​​were obtained only at 250°C and 300°C, respectively, which are impractical temperatures for battery packs. It is known in the art that ionic conductivity decreases with decreasing test temperature, meaning that at temperatures between room temperature and 100°C, the ionic conductivity values ​​of the sintered material can be expected to be unacceptably low, making the material unsuitable for use as a solid electrolyte in a battery pack. Summary of the Invention

[0010] One object of the present invention is to overcome one or more of the aforementioned disadvantages. One object of the present invention is to provide a glass-ceramic solid electrolyte (i.e., a solid electrolyte, SSE) that exhibits good total ionic conductivity when used in battery packs at both room temperature and elevated temperatures.

[0011] Meanwhile, one object of the present invention is to provide a method for preparing glass-ceramic SSEs that consumes less energy compared to methods known in the art. Another object is to provide a method for preparing glass-ceramic SSEs comprising sintering at a temperature lower than that of prior art sintering methods, wherein the obtained SSE has properties equal to or better than those of glass-ceramic SSEs obtained by conventional high-temperature sintering processes, particularly in terms of total ionic conductivity when used in battery packs.

[0012] Another objective is to provide a method for preparing solid-state battery packs (SSBs), particularly all-ceramic SSBs, in which some or all of the components—including the anode and / or cathode—can be assembled and subsequently sintered together, thereby reducing the total energy consumption of the method for preparing the SSBs, as well as the complexity of the process and the number of steps required.

[0013] According to a first aspect of this disclosure, a glass-ceramic solid electrolyte mixture is provided.

[0014] The glass-ceramic solid electrolyte mixture comprises or is substantially composed of ternary glass-ceramics containing borate, Li2SO4, and lithium halides.

[0015] Advantageously, based on the total weight of the glass-ceramic solid electrolyte mixture, the glass-ceramic solid electrolyte mixture contains 50 to 85% by weight, preferably 60 to 80% by weight, more preferably 65 to 75% by weight, for example 70% by weight, of borate.

[0016] Advantageously, based on the total weight of the glass-ceramic solid electrolyte mixture, the glass-ceramic solid electrolyte mixture contains 10 to 40% by weight, preferably 15 to 35% by weight, more preferably 20 to 30% by weight, for example 25% by weight of Li2SO4.

[0017] Advantageously, based on the total weight of the glass-ceramic solid electrolyte mixture, the glass-ceramic solid electrolyte mixture contains 1 to 10% by weight, preferably 2 to 8% by weight, more preferably 3 to 7% by weight, for example 5% by weight of lithium halide.

[0018] Advantageously, based on the total weight of the glass-ceramic solid electrolyte mixture, the glass-ceramic solid electrolyte mixture contains 50 to 85 wt% borate, 10 to 40 wt% Li2SO4 and 1 to 10 wt% lithium halide, preferably 65 to 75 wt% borate, 20 to 30 wt% Li2SO4 and 3 to 7 wt% lithium halide.

[0019] Advantageously, the borate comprises or is substantially composed of Li3BO3.

[0020] Advantageously, the lithium halide is LiCl, that is, the halide is advantageously a chloride.

[0021] According to a second aspect of this disclosure, a glass-ceramic solid electrolyte is provided.

[0022] Advantageously, the glass-ceramic solid electrolyte is obtained by sintering the glass-ceramic solid electrolyte mixture of the first aspect or can be obtained by sintering the glass-ceramic solid electrolyte mixture of the first aspect.

[0023] The glass-ceramic solid electrolyte comprises or is substantially composed of ternary glass-ceramics containing borate, Li2SO4, and lithium halide, wherein the borate and the lithium halide are as described above.

[0024] Advantageously, the glass-ceramic solid electrolyte comprises or is substantially composed of a matrix, which comprises or is substantially composed of a borate. Advantageously, lithium halide and Li₂SO₄ are dispersed within the matrix.

[0025] Advantageously, the borate exists at least partially as a glassy phase (e.g., a glass network) in or is contained within the glass-ceramic solid electrolyte.

[0026] The term "at least partially present as a glass phase or contained herein" is used in this disclosure to mean that at least 25%, preferably at least 50%, more preferably at least 75% of the borate is present as a glass phase in the glass-ceramic solid electrolyte.

[0027] Advantageously, the glass-ceramic solid electrolyte has a temperature range of 10°C from room temperature to 100°C. -5 Up to 10 -9 S / cm, preferred 10 -5 Up to 10 -8Total ionic conductivity (S / cm).

[0028] According to a third aspect of this disclosure, a solid-state battery pack is provided.

[0029] The solid-state battery pack includes an electrolyte according to the second aspect of this disclosure, namely an electrolyte comprising or substantially composed of a ternary glass-ceramic containing borate, Li2SO4 and lithium halide, or an electrolyte obtained by sintering a glass-ceramic solid electrolyte mixture according to the first aspect of this disclosure.

[0030] Advantageously, the solid-state battery pack is an all-ceramic solid-state battery pack. Advantageously, the solid-state battery pack is a secondary battery pack.

[0031] According to a fourth aspect of this disclosure, a method for preparing a glass-ceramic solid electrolyte is provided.

[0032] Advantageously, the prepared glass-ceramic solid electrolyte is, according to the second aspect of this disclosure, a ternary glass-ceramic comprising or substantially composed of borate, Li2SO4 and lithium halide, wherein the borate and the lithium halide are as described above.

[0033] The method includes sintering a glass-ceramic solid electrolyte mixture comprising, or substantially comprising, a ternary glass-ceramic of borate, Li₂SO₄, and lithium halide, as described above. Advantageously, the glass-ceramic solid electrolyte mixture is as described in the first aspect of this disclosure.

[0034] The mixture is sintered in an inert atmosphere at a temperature of 600°C to 1000°C, preferably 700°C to 900°C, and more preferably 750°C to 850°C.

[0035] According to a fifth aspect of this disclosure, a method for preparing a solid-state battery pack is provided. Advantageously, the solid-state battery pack is as described in a third aspect of this disclosure, i.e., advantageously an all-ceramic solid-state battery pack.

[0036] According to the first embodiment, the method includes:

[0037] - Apply the glass-ceramic solid electrolyte mixture according to the first aspect of this disclosure to the surface of the anode or cathode.

[0038] - Sintering the mixture-anode or mixture-cathode assembly in an inert atmosphere at a temperature of 600°C to 1000°C, preferably 700°C to 900°C, more preferably 750°C to 850°C, and

[0039] - A cathode or anode is provided at the exposed surface of the sintered mixture, thereby obtaining the solid-state battery pack.

[0040] According to a second embodiment, the method includes providing a glass-ceramic solid electrolyte mixture according to a first aspect of this disclosure between an anode and a cathode, and sintering the anode-mixture-cathode assembly, wherein the sintering is carried out at the temperature and atmosphere as described above for the first embodiment.

[0041] The inventors have surprisingly discovered that the presence of lithium halides in glass-ceramic solid electrolyte mixtures allows for a significant reduction in the sintering temperature of ternary glass-ceramics containing borate compounds, for example, from temperatures up to 1050°C and even higher, down to temperatures of 800°C to 850°C. Not wishing to be bound by any theory, the inventors believe that lower sintering temperatures can be achieved by the fact that lithium halides, having a melt temperature below the sintering temperature (e.g., 605°C for LiCl), will be in a molten state during sintering, thus leading to so-called liquid-phase sintering or liquid-assisted sintering—where the presence of liquid (molten lithium halides) accelerates the bonding between other components, thereby allowing for lower sintering temperatures.

[0042] The advantage of this significantly lower sintering temperature is that the mixture can be co-sintered with one or both of the anode and cathode, thereby making the fabrication of solid-state battery packs, especially all-ceramic solid-state battery packs, less complex and less energy-intensive. It is known that for all ceramic SSBs, the anode and / or cathode contain materials that need to be sintered at temperatures below 1000°C, preferably even below 900°C, to avoid any degradation or damage leading to inferior battery packs.

[0043] Therefore, since the method of the present invention and the glass-ceramic solid electrolyte mixture allow sintering at temperatures below 1000°C, the anode and / or cathode can be assembled together with the glass-ceramic solid electrolyte mixture first, followed by a single sintering step. This contrasts with prior art methods, which require separate sintering steps for the anode and / or cathode—at temperatures below 1000°C—and for the SSE—at temperatures above 1000°C.

[0044] The advantages of the method and glass-ceramic solid electrolyte mixture of the present invention include lower energy consumption during sintering and a less complex process for preparing solid-state battery packs, especially all-ceramic solid-state battery packs. Attached Figure Description

[0045] Aspects of the invention will now be described in more detail with reference to the accompanying drawings, wherein like reference numerals indicate like features, and wherein:

[0046] - Figure 1The X-ray diffraction (XRD) pattern of the glass-ceramic solid electrolyte of the present invention after it has been ground into powder is shown.

[0047] - Figure 2 and 3 The images show scanning electron microscope (SEM) images of the cross-section of the invented glass-ceramic solid electrolyte at different magnifications.

[0048] - Figure 4 Energy dispersive X-ray (EDX) analysis of the cross-section of the invented glass-ceramic solid electrolyte is shown.

[0049] - Figure 5 The total ionic conductivity of the Li-Li symmetric cell containing the invented glass-ceramic solid electrolyte is shown; and

[0050] - Figure 6 The invention demonstrates the constant current cycling of the battery pack. Detailed Implementation

[0051] The glass-ceramic solid electrolyte mixtures and glass-ceramic solid electrolytes disclosed herein comprise ternary glass-ceramics containing or substantially composed of borates, Li2SO4, and lithium halides.

[0052] Advantageously, the borate comprises or is substantially composed of Li3BO3. Alternatively or additionally, but advantageously, the borate may comprise one or more of B2O3, LiBO2, Li4B2O5, and Li6B4O9.

[0053] The halide can be any one of chloride, bromide, iodide, and fluoride, preferably chloride or fluoride, and more preferably chloride. The lithium halide can thus be any one of LiCl, LiBr, LiI, and LiF, preferably LiCl or LiF, and more preferably LiCl. The glass-ceramic solid electrolyte can contain two or more lithium halides, advantageously two or more of LiCl, LiBr, LiI, and LiF.

[0054] Advantageously, based on the total weight of the glass-ceramic solid electrolyte, the glass-ceramic solid electrolyte contains 50 to 85% by weight, preferably 60 to 80% by weight, more preferably 65 to 75% by weight, for example 70% by weight, of borate.

[0055] Advantageously, based on the total weight of the glass-ceramic solid electrolyte, the glass-ceramic solid electrolyte contains 10 to 40 wt%, preferably 15 to 35 wt%, more preferably 20 to 30 wt%, for example 25 wt% of Li2SO4.

[0056] Advantageously, based on the total weight of the glass-ceramic solid electrolyte, the glass-ceramic solid electrolyte contains 1 to 10% by weight, preferably 2 to 8% by weight, more preferably 3 to 7% by weight, for example 5% by weight of lithium halide.

[0057] Advantageously, based on the total weight of the glass-ceramic solid electrolyte, the glass-ceramic solid electrolyte comprises 50 to 85 wt% borate, 10 to 40 wt% Li2SO4 and 1 to 10 wt% lithium halide, preferably 65 to 75 wt% borate, 20 to 30 wt% Li2SO4 and 3 to 7 wt% lithium halide.

[0058] Advantageously, the glass-ceramic solid electrolyte of this disclosure is a dense electrolyte, i.e., an electrolyte with low porosity. More particularly, the electrolyte advantageously has a density equal to or higher than 70% of its theoretical density. The theoretical density is calculated from the density of the compounds contained in the electrolyte and the composition of the electrolyte (the amount of each compound). The density of the electrolyte is calculated by dividing its weight by its volume.

[0059] The present invention further relates to solid-state battery packs (i.e., all-solid-state battery packs) (SSBs) incorporating the glass-ceramic solid electrolyte of the present invention, particularly secondary battery packs.

[0060] Advantageously, the battery pack further includes a cathode, which can be any suitable cathode known in the art. Advantageously, the battery pack further includes an anode, which can be any suitable anode known in the art.

[0061] Advantageously, the SSB is an all-ceramic SSB, meaning that all components—anode, cathode, and electrolyte—are made of ceramic materials.

[0062] The present invention also relates to a method for preparing the glass-ceramic SSE. This method advantageously includes operations for preparing a mixture, a molding operation, and a sintering operation.

[0063] Advantageously, the mixture preparation operation involves mixing borates, Li₂SO₄, and lithium halides, wherein the borates and lithium halides are as described above. To obtain a homogeneous mixture, mixing techniques known in the art, such as ball milling or bead milling, can be used.

[0064] Advantageously, based on the total weight of the mixture, the mixture contains 50 to 85 wt% borates, preferably Li3BO3, 10 to 40 wt% Li2SO4 and 1 to 10 wt% lithium halides, preferably LiCl, preferably 65 to 75 wt% borates, 20 to 30 wt% Li2SO4 and 3 to 7 wt% lithium halides.

[0065] Advantageously, the mixture is shaped during the molding operation. Molding can be carried out by methods known in the art, such as by pressing the mixture into a predetermined shape or by laser-cutting the mixture into a predetermined shape. During molding, a green body is obtained. The green body can have various shapes, such as flakes, pellets, discs, etc., wherein the shape is defined by the desired shape of the composite solid electrolyte.

[0066] The green blank is then sintered during a sintering operation. The sintering operation includes heating the green blank to a sintering temperature and holding the green blank at the sintering temperature for a predetermined sintering duration, during which the green blank is sintered.

[0067] Advantageously, the sintering operation is carried out in an atmosphere known in the art. Preferably, the sintering operation is carried out in an inert atmosphere, more preferably in an inert atmosphere containing argon or consisting essentially of argon.

[0068] Advantageously, the sintering temperature is 600°C to 1000°C, preferably 700°C to 900°C, and more preferably 750°C to 850°C.

[0069] Advantageously, the green blank is heated to the sintering temperature at a heating rate of 5°C / s to 500°C / s, that is, at a conventional heating rate or an ultrafast heating rate.

[0070] Advantageously, the sintering duration is 5 to 600 seconds, preferably 10 to 300 seconds, more preferably 20 to 200 seconds, such as 30 to 150 seconds, or 45 to 100 seconds.

[0071] It will be understood that the sintering duration depends in particular on the heating rate, sintering temperature, and the equipment used.

[0072] Example

[0073] Example 1

[0074] A mixture of 7.0 g Li3BO3, 2.5 g Li2SO4, 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 pellets using a uniaxial press.

[0075] The green pellets were then heated to 825°C and sintered at 825°C for 100 seconds, followed by cooling to room temperature. The resulting glass-ceramic solid electrolyte pellets were then partially ground into powder and partially cut into fragments for analysis.

[0076] Figure 1X-ray diffraction (XRD) patterns of Li₂SO₄, Li₃BO₃, and glass-ceramic solid electrolyte powders (referred to as 1, 2, and 3, respectively) are shown. The comparison of the XRD patterns clearly indicates the presence of Li₂SO₄ and Li₃BO₃ in the electrolytes. The signal at 2θ from 0° to 20° further indicates the presence of a glassy phase, which is believed to be formed from Li₃BO₃.

[0077] Scanning electron microscopy (SEM) analysis was performed on fragments of glass-ceramic solid electrolytes under high vacuum using a high-resolution scanning electron microscope FEI (Teneo). Figure 2 and 3 SEM images of the cross-section of the glass-ceramic solid electrolyte at different magnifications are shown. At low magnification ( Figure 2 A dense structure is visible. At higher magnifications ( Figure 3 The glassy matrix (attributed to Li3BO3) – the crystalline phase dispersed within it – is clearly visible.

[0078] Figure 4 Energy-dispersive X-ray diffraction (EDX) analysis of the cross-section of the electrolyte is shown. All elements of Li3BO3, Li2SO4, and LiCl were detected. This confirms that all components of the mixture are retained in the obtained glass-ceramic solid electrolyte.

[0079] Example 2

[0080] A Li-Li symmetric cell comprising the glass-ceramic solid electrolyte of Example 1 was prepared to measure the total ionic conductivity and electrochemical properties. The Li-Li symmetric cell of this invention was prepared using 800 μm thick glass-ceramic solid electrolyte pellets as prepared in Example 1, 50 μm thick lithium metal as electrodes, and 5-8 μm thick copper foil as current collectors.

[0081] Figure 5 The total ionic conductivity is shown at temperatures between room temperature and 100°C. At room temperature, the total ionic conductivity is 2 × 10⁻⁶. -8 The total ionic conductivity is 4*10⁻⁶ S / cm, while at 100℃, the total ionic conductivity is 4*10⁻⁶. -7 S / cm.

[0082] The constant current cycling of the Li-Li symmetric cell of this invention also showed up at 100°C and 0.1 mA / cm². 2 The experiment was conducted at a current density. From Figure 6 It is clear that a stable loop was observed over a test duration exceeding 4500 seconds.

[0083] Table of contents

[0084] 1. XRD pattern of Li2SO4

[0085] 2. XRD pattern of Li3BO3

[0086] 3. The XRD pattern of the glass-ceramic solid electrolyte of the present invention.

Claims

1. A glass-ceramic solid electrolyte mixture comprising ternary glass-ceramics containing borate, Li2SO4 and lithium halide.

2. The glass-ceramic solid electrolyte mixture according to claim 1, wherein, based on the total weight of the glass-ceramic solid electrolyte mixture, it comprises 50 to 85% by weight of borate, 10 to 40% by weight of Li₂SO₄ and 1 to 10% by weight of lithium halide.

3. The glass-ceramic solid electrolyte mixture according to any one of the preceding claims, wherein the borate comprises Li3BO3.

4. The glass-ceramic solid electrolyte mixture according to any one of the preceding claims, wherein the lithium halide comprises LiCl.

5. A glass-ceramic solid electrolyte obtainable by sintering the glass-ceramic solid electrolyte mixture according to any one of the preceding claims, wherein the glass-ceramic solid electrolyte mixture comprises a ternary glass-ceramic of borate, Li2SO4 and lithium halide.

6. The glass-ceramic solid electrolyte according to claim 5, comprising a matrix containing the borate, wherein the lithium halide and Li2SO4 are dispersed within the matrix.

7. The glass-ceramic solid electrolyte according to any one of claims 5 to 6, wherein the borate is at least partially contained in the electrolyte as a glassy phase.

8. The glass-ceramic solid electrolyte according to any one of claims 5 to 7, wherein the borate comprises Li3BO3.

9. The glass-ceramic solid electrolyte according to any one of claims 5 to 8, wherein it has a strength of 10 at a temperature from room temperature to 100°C. -5 Up to 10 -9 Total ionic conductivity (S / cm).

10. A solid-state battery pack comprising a glass-ceramic solid electrolyte according to any one of claims 5 to 9.

11. The solid-state battery pack according to claim 10, wherein it is an all-ceramic solid-state battery pack.

12. A method for preparing a glass-ceramic solid electrolyte comprising a ternary glass-ceramic material containing borate, Li2SO4 and lithium halide, comprising sintering the mixture of any one of claims 1 to 4 at a temperature of 600°C to 1000°C in an inert atmosphere.

13. A method for preparing a solid-state battery pack comprising the glass-ceramic solid electrolyte according to any one of claims 5 to 9 or the glass-ceramic solid electrolyte obtained by the method of claim 12, comprising: - Apply the glass-ceramic solid electrolyte mixture according to any one of claims 1 to 4 to the surface of the anode or cathode. - Sintered in an inert atmosphere at a temperature of 600°C to 1000°C, and - A cathode or anode is provided at the exposed surface of the sintered mixture, thereby obtaining the solid-state battery pack.

14. The method of preparing a solid-state battery pack 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 an anode-mixture-cathode assembly.

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