Composite oxide solid electrolyte and method for manufacturing the same

Abstract

The application discloses a kind of composite oxides solid electrolyte, the composite oxides solid electrolyte including LLZO film band two sides MgO film band is symmetrical structure, consistent shrinkage when sintering two sides, the electrolyte sheet obtained is relatively flat and will not appear bending condition;The electrolyte sheet of the application is better, LLZO film band two sides MgO film band play the supporting role, improve the strength of electrolyte sheet;The electrolyte sheet of the application does not adhere to supporting plate, LLZO film band two sides MgO film band play the role of isolation, will not adhere to supporting plate;The electrolyte sheet of the application does not need to add protective powder to embed during sintering process, MgO isolation layer will inhibit the excessive volatilization of Li2O, so that it can be sintered dense without a large amount of sacrificial protective powder.The interface impedance of the electrolyte sheet of the application and positive and negative pole is small, and the two sides are porous structure, increase the contact between positive and negative pole and electrolyte.

Description

TECHNICAL FIELD

[0001] The present application relates to all-solid-state lithium ion batteries, in particular, to a composite oxide solid electrolyte and a manufacturing method thereof. BACKGROUND

[0002] To meet the growing demand for lithium batteries in consumer electronics and electric vehicles, all-solid-state lithium batteries have attracted widespread attention in recent years due to their superior safety and ultra-high energy density. Traditional lithium batteries containing organic liquid electrolytes exhibit serious safety problems such as toxicity, flammability, corrosiveness, and poor chemical stability. Using solid electrolytes as a substitute for electrolytes and separators can fundamentally eliminate the above safety problems. All-solid-state lithium batteries are divided into three categories according to the type of solid electrolyte: polymers, oxides, and sulfides. Oxide solid electrolytes have been widely studied due to their high ionic conductivity and good mechanical strength, with LLZO being the most studied. LLZO electrolyte powder is usually prepared by solid-phase reaction, specifically by mechanically mixing a lithium source (LiOH·H2O or Li2CO3), La2O3, and ZrO2 and then sintering at high temperature. To obtain a thinner LLZO electrolyte sheet, the tape casting method is the most common means: the LLZO powder is prepared into a slurry, and a film is cast on a high-temperature sintering belt to obtain a thinner LLZO electrolyte sheet. For example, the patent CN104916869A Porous-dense double-layer electrolyte ceramic sintered body, lithium ion battery, lithium-air battery by Ren Yaoyu Nan Ce Wen of Tsinghua University discloses a porous-dense double-layer structure of LLZO solid electrolyte. The electrolyte structure is asymmetric, and during the sintering process, there will be inconsistent shrinkage, resulting in bending of the electrolyte sheet; the material of the two-layer structure of the electrolyte is LLZO, which needs to be sintered in LLZO protective powder during the sintering process, and it cannot be guaranteed that the electrolyte sheet and the protective powder are not adhered. Therefore, in the field of oxide solid electrolyte preparation, there are still problems such as difficulty in sintering thinner LLZO electrolyte sheets, poor strength, severe bending, adhesion to the sintering plate, and inability to separate. SUMMARY

[0003] Therefore, in order to solve the problems of difficulty in sintering thinner LLZO electrolyte sheets, poor strength, severe bending, adhesion to the sintering plate, and inability to separate, the present application provides a composite oxide solid electrolyte and a manufacturing method thereof, and the specific technical solutions are as follows:

[0004] A composite oxide solid electrolyte, comprising a first film belt, a second film belt arranged on one side of the first film belt, and a third film belt arranged on the other side of the first film belt, and the second film belt and the third film belt both form a porous structure of spherical grain packing;

[0005] The first film strip comprises the following raw materials: LLZO powder, a first dispersant, a first solvent, a first binder, and a first plasticizer.

[0006] The second film strip and the third film strip each comprise the following raw materials: MgO powder, a second dispersant, a second solvent, a second binder, a second plasticizer, and a pore-forming agent.

[0007] Further, the first dispersant and the second dispersant are one or a mixture of both of triethanolamine and fish oil.

[0008] Further, the first solvent and the second solvent are one or a mixture of more than one of ethanol, isopropyl alcohol, and toluene.

[0009] Further, the first binder and the second binder are both PVB.

[0010] Further, the first plasticizer and the second plasticizer are one or a mixture of more than one of DOP, DEP, and DBP.

[0011] Further, the pore-forming agent is one or a mixture of more than one of PMMA microspheres, PS microspheres, and graphite spheres.

[0012] Further, the first film strip is an LLZO film strip, and the second film strip and the third film strip are both MgO film strips.

[0013] In addition, the application also provides a manufacturing method of a composite oxide solid-state electrolyte, comprising the following steps:

[0014] After the LLZO powder, the first dispersant, and the first solvent are mixed, ball milling treatment is performed for 5 hours, then the first binder and the first plasticizer are added and ball milling treatment is continued for 2 hours to obtain LLZO slurry;

[0015] The LLZO slurry is cast on a PET base strip using a fixed scraper, and after room temperature drying treatment, an LLZO film strip is obtained.

[0016] After the MgO powder, the second dispersant, and the second solvent are mixed, ball milling treatment is performed for 5 hours, then the second binder and the second plasticizer are added and ball milling treatment is continued for 2 hours, and finally a pore-forming agent with a particle size of 1-10 microns is added and mixed for 1 hour to obtain MgO slurry;

[0017] The MgO slurry is cast on a PET base strip using a fixed scraper, and after room temperature drying treatment for 1 hour, an MgO film strip is obtained.

[0018] After the LLZO film strip after drying treatment is placed with MgO film strips on both sides, hot pressing treatment is performed, high-temperature sintering treatment is performed, and then cooling to room temperature to obtain a composite oxide solid-state electrolyte.

[0019] Further, the temperature of the hot-pressing treatment is 70-80 DEG C, and the time of the hot-pressing treatment is 1h.

[0020] Further, the sintering treatment is: increasing the temperature to 700-800 DEG C at 2 DEG C / min, keeping warm for 2h to remove glue, then increasing the temperature to 1100-1300 DEG C at 10 DEG C / min and keeping warm for 10-60min to perform the sintering treatment.

[0021] The electrolyte sheet manufactured by the scheme has a symmetrical structure with the MgO film strips on both sides of the LLZO film strip being flat, and the obtained electrolyte sheet is relatively flat and does not appear to be bent; the electrolyte sheet has good strength, the MgO film strips on both sides of the LLZO film strip play a supporting role, and the strength of the electrolyte sheet is improved; the electrolyte sheet does not adhere to the supporting plate, the MgO film strips on both sides of the LLZO film strip play an isolation role, and do not adhere to the supporting plate; the electrolyte sheet does not need to be embedded with protective powder during the sintering process, the MgO isolation layer can inhibit the excessive volatilization of Li2O, so that the sintering can be dense without a large amount of sacrificial protective powder. The electrolyte sheet has small interface impedance with the positive and negative electrodes, and both sides are porous structures, which increases the contact between the positive and negative electrodes and the electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A cross-sectional SEM schematic diagram of the composite oxide solid-state electrolyte prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with its embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the protection scope of the present application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0025] A composite oxide solid-state electrolyte in an embodiment of the present application comprises a first film strip, a second film strip arranged on one side of the first film strip, and a third film strip arranged on the other side of the first film strip, and the second film strip and the third film strip both form a porous structure of spherical grain stacking.

[0026] The first film strip comprises the following raw materials: LLZO powder, a first dispersant, a first solvent, a first binder, and a first plasticizer.

[0027] The second film strip and the third film strip each comprise the following raw materials: MgO powder, a second dispersant, a second solvent, a second binder, a second plasticizer, and a pore-forming agent.

[0028] In one embodiment, the LLZO powder, the first dispersant, the first solvent, the first binder, and the first plasticizer are present in a weight ratio of 18-25:0.1-1:18-25:1-5:0.1-1.

[0029] In one embodiment, the MgO powder, the second dispersant, the second solvent, the second binder, the second plasticizer, and the pore-forming agent are present in a weight ratio of 18-25:0.1-1:18-25:1-5:0.1-1:1-25.

[0030] In one embodiment, the first dispersant and the second dispersant are one or a mixture of both of triethanolamine and fish oil.

[0031] In one embodiment, the first solvent and the second solvent are one or a mixture of more than one of ethanol, isopropyl alcohol, and toluene.

[0032] In one embodiment, the first binder and the second binder are both PVB.

[0033] In one embodiment, the first plasticizer and the second plasticizer are one or a mixture of more than one of DOP, DEP, and DBP.

[0034] In one embodiment, the pore-forming agent is one or a mixture of more than one of PMMA microspheres, PS microspheres, and graphite spheres.

[0035] In one embodiment, the first film strip is an LLZO film strip, and the second film strip and the third film strip are both MgO film strips. The first film strip and the second film strip each form a porous structure of spherical grain stacking, which can serve as a protective layer to inhibit lithium volatilization in the LLZO at high temperatures and promote densification in the sintering process of the LLZO. The first film strip and the second film strip can also serve as an isolation layer to prevent the LLZO from being in contact with a sintering plate during the sintering process of the LLZO.

[0036] In addition, the application also provides a method for manufacturing a composite oxide solid-state electrolyte, comprising the following steps:

[0037] The LLZO powder, the first dispersant, and the first solvent are mixed, ball-milled for 5h, then the first binder and the first plasticizer are added and ball-milled for 2h to obtain an LLZO slurry;

[0038] The LLZO slurry is cast on a PET base strip using a fixed scraper, and an LLZO film strip is obtained after room temperature drying treatment;

[0039] The MgO powder, the second dispersant, and the second solvent are mixed, ball-milled for 5h, then the second binder and the second plasticizer are added and ball-milled for 2h, and finally a pore-forming agent with a particle size of 1-10μm is added and mixed for 1h to obtain a MgO slurry;

[0040] The MgO slurry is cast on a PET base strip using a fixed scraper, and a MgO film strip is obtained after room temperature drying treatment for 1h;

[0041] After drying treatment, the MgO film strips are placed on both sides of the LLZO film strip, and then hot-pressing treatment, high-temperature sintering treatment, and cooling to room temperature are performed to obtain a composite oxide solid-state electrolyte.

[0042] In one embodiment, the temperature of the hot-pressing treatment is 70-80℃, and the time of the hot-pressing treatment is 1h.

[0043] In one embodiment, the sintering treatment is as follows: heating to 700-800℃ at a rate of 2℃ / min, holding for 2h to remove glue, then heating to 1100-1300℃ at a rate of 10℃ / min and holding for 10-60min for sintering treatment.

[0044] In one embodiment, the thickness of the composite oxide solid-state electrolyte is 10-200μm.

[0045] The electrolyte sheet manufactured by the scheme of the present application is flat, the MgO film strips on both sides of the LLZO film strip are symmetrical structures, the shrinkage on both sides is consistent during sintering, and the obtained electrolyte sheet is relatively flat and does not appear to be curved; the electrolyte sheet of the present application has good strength, the MgO film strips on both sides of the LLZO film strip play a supporting role, and the strength of the electrolyte sheet is improved; the electrolyte sheet of the present application does not adhere to the supporting plate, the MgO film strips on both sides of the LLZO film strip play an isolation role and do not adhere to the supporting plate; the electrolyte sheet of the present application does not need to be added with a protective powder for embedding during sintering, and the MgO isolation layer can inhibit the excessive volatilization of Li2O, so that the electrolyte sheet can be sintered to be dense without the need for a large amount of sacrificial protective powder. The interface impedance of the electrolyte sheet of the present application and the positive and negative electrodes is small, and the two sides are porous structures, which increases the contact between the positive and negative electrodes and the electrolyte.

[0046] The embodiments of the present application will be described in detail below with reference to specific examples.

[0047] Example 1:

[0048] 20 g of LLZO powder, 0.2 g of fish oil, 20 g of isopropyl alcohol were added to a ball mill tank, and ball milling was performed at a speed of 300 rpm / min for 5 h. Then, 1 g of PVB and 0.5 g of DOP were added, and ball milling was continued for 2 h to obtain an LLZO slurry. The LLZO slurry was cast on a PET base tape using a fixed scraper, and after drying at room temperature for 1 h, an LLZO film tape was obtained.

[0049] 20 g of MgO powder, 0.2 g of fish oil, 20 g of isopropyl alcohol were added to a ball mill tank, and ball milling was performed at a speed of 300 rpm / min for 5 h. Then, 1 g of PVB and 0.5 g of DOP were added, and ball milling was continued for 2 h. Finally, 8.6 g (30%) of PMMA microspheres (average particle size 5 μm) were added, and mixing was continued for 30 min to obtain a MgO slurry. The obtained slurry was cast on a PET base tape using a fixed scraper, and after drying at room temperature for 1 h, a MgO film tape was obtained.

[0050] The MgO film tapes were placed on both sides of the dried LLZO film tape, and hot pressing was performed at 80 °C for 1 h to obtain a composite film tape.

[0051] The composite film tape was clamped between two MgO supporting plates and placed in a MgO crucible with a cover. The temperature was raised to 700 °C at a rate of 2 °C / min, and degassing was performed for 2 h. Then, the temperature was raised to 1200 °C at a rate of 10 °C / min, and sintering was performed for 20 min. After cooling to room temperature, a composite solid-state electrolyte sheet was obtained.

[0052] Example 2:

[0053] The difference from Example 1 is that 2.2 g (10%) of PMMA was added, and the rest remained unchanged.

[0054] Example 3:

[0055] The difference from Example 1 is that 20 g (50%) of PMMA was added, and the rest remained unchanged.

[0056] Example 4:

[0057] The difference from Example 1 is that isopropyl alcohol was replaced by ethanol, and the rest remained unchanged.

[0058] Example 5:

[0059] The difference from Example 1 is that isopropyl alcohol was replaced by toluene, and the rest remained unchanged.

[0060] Example 6:

[0061] The difference from Example 1 is that the temperature is increased to 700 DEG C at 2 DEG C / min, and the glue is discharged for 2h, then the temperature is increased to 1200 DEG C at 10 DEG C / min, and the sintering treatment is performed for 40min, and the rest remains unchanged.

[0062] Example 7:

[0063] The difference from Example 1 is that the temperature is increased to 700 DEG C at 2 DEG C / min, and the glue is discharged for 2h, then the temperature is increased to 1200 DEG C at 10 DEG C / min, and the sintering treatment is performed for 60min, and the rest remains unchanged.

[0064] Comparative Example 1:

[0065] The LLZO film strip is sintered, and the sintering process is consistent with the composite film strip in Example 1.

[0066] Comparative Example 2:

[0067] The LLZO film strip is sintered, and is buried in the LLZO protective powder for sintering, and the sintering process is consistent with the composite film strip in Example 1.

[0068] Comparative Example 3:

[0069] The difference from Example 1 is that the composite film strip of the LLZO film strip on one side of the MgO film strip is sintered, and the sintering process is unchanged.

[0070] The performance comparison tests are performed on Examples 1-7 and Comparative Examples 1-3, and the results are shown in Table 1.

[0071] Table 1:

[0072]

[0073] From the analysis in Table 1, it can be seen that the composite electrolyte sheets with porous MgO structure on both sides of the LLZO film strip prepared by the application do not appear to be adhered to the burning plate, and the surface is smooth, but Comparative Example 1 is tightly adhered to the burning plate, Comparative Example 2 is tightly adhered to the protective powder, and Comparative Example 3 is tightly adhered to the burning plate on one side, and it is difficult to take out the complete and smooth surface electrolyte sheet; the affinity performance of the electrolyte sheet prepared by the application to molten lithium is also far superior to that of the comparative examples (the specific surface area of the porous layer is increased, and the wettability with molten lithium is improved).

[0074] Therefore, from the comprehensive comparison in Table 1, it can be seen that the performance of Example 1 is the best. The corresponding best formula and process are: the solvent isopropanol is selected; the PMMA content is 30%; the sintering temperature is 1200℃, and the time is 20min. If the PMMA content is too low (10%), the porous MgO layer is easy to be sintered to be dense (the porosity is only 5%); if the content is too high (50%), the porosity of the porous layer is too large (60%), which cannot inhibit the volatilization of Li2O, resulting in that the LLZO is not dense after sintering. The PMMA content is the best when it is 30%, the porosity of the MgO layer is 46%, which can inhibit the volatilization of Li2O and ensure a certain pore. The solvent ethanol has a low melting point and volatilizes too fast, which is not conducive to the preparation of the slurry; toluene can dissolve PMMA, resulting in that the porosity of the porous layer is reduced and the sintering is dense. When the sintering time is 20min, the LLZO density is the highest, and with the increase of the sintering time, the density is continuously reduced. When the sintering time is long, the MgO porous layer is also difficult to block the excessive volatilization of Li2O, resulting in that the density of the LLZO is continuously reduced.

[0075] In addition, Figure 1 The cross-sectional SEM diagram of the composite oxide solid-state electrolyte prepared in Example 1 of the present application is shown in the figure, from which Figure 1 It can be clearly seen that the porous MgO film is distributed on both sides of the dense LLZO film.

[0076] The technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered that it is within the scope of the present application.

[0077] The above-described embodiments only express several embodiments of the present application, the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A composite oxide solid electrolyte, characterized in that, It includes a first membrane strip, a second membrane strip disposed on one side of the first membrane strip, and a third membrane strip disposed on the other side of the first membrane strip, wherein the second membrane strip and the third membrane strip both form a porous structure with spherical grains stacked together. The first membrane tape comprises the following raw materials: LLZO powder, a first dispersant, a first solvent, a first binder, and a first plasticizer; Both the second and third membrane tapes include the following raw materials: MgO powder, a second dispersant, a second solvent, a second binder, a second plasticizer, and a pore-forming agent; The first membrane strip is an LLZO membrane strip, and the second and third membrane strips are all MgO membrane strips.

2. The composite oxide solid electrolyte according to claim 1, characterized in that, The first dispersant and the second dispersant are both triethanolamine and fish oil, or a mixture of two of them.

3. The composite oxide solid electrolyte according to claim 1, characterized in that, Both the first solvent and the second solvent are one or a mixture of ethanol, isopropanol, and toluene.

4. The composite oxide solid electrolyte according to claim 1, characterized in that, Both the first adhesive and the second adhesive are PVB.

5. The composite oxide solid electrolyte according to claim 1, characterized in that, The first plasticizer and the second plasticizer are both mixtures of one or more of DOP, DEP, and DBP.

6. The composite oxide solid electrolyte according to claim 1, characterized in that, The pore-forming agent is one or more of PMMA microspheres, PS microspheres, and graphite spheres, or a mixture thereof.

7. A method for manufacturing a composite oxide solid electrolyte as described in any one of claims 1-6, characterized in that, Includes the following steps: After mixing LLZO powder, the first dispersant and the first solvent, the mixture is ball-milled for 5 hours. Then, the first binder and the first plasticizer are added and the mixture is ball-milled for another 2 hours to obtain LLZO slurry. The LLZO slurry was cast onto a PET substrate using a fixed doctor blade and dried at room temperature to obtain an LLZO film tape. After mixing MgO powder, a second dispersant, and a second solvent, the mixture is ball-milled for 5 hours. Then, a second binder and a second plasticizer are added and the mixture is ball-milled for another 2 hours. Finally, a pore-forming agent with a particle size of 1 μm-10 μm is added and the mixture is mixed for another 1 hour to obtain MgO slurry. The MgO slurry was cast onto a PET substrate using a fixed scraper and dried at room temperature for 1 hour to obtain an MgO film. After drying, MgO film strips were placed on both sides of the LLZO film strip, and then hot-pressed, sintered at high temperature, and cooled to room temperature to obtain a composite oxide solid electrolyte.

8. The method for manufacturing the composite oxide solid electrolyte according to claim 7, characterized in that, The hot pressing temperature is 70℃-80℃, and the hot pressing time is 1 hour.

9. The method for manufacturing the composite oxide solid electrolyte according to claim 7, characterized in that, The sintering process is as follows: heat the temperature to 700℃-800℃ at 2℃ / min, hold for 2 hours to remove the binder, and then heat the temperature to 1100℃-1300℃ at 10℃ / min and hold for 10min-60min for sintering.

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