CN116190766A

CN116190766A - Composite oxide solid electrolyte and manufacturing method thereof

Info

Publication number: CN116190766A
Application number: CN202211097704.6A
Authority: CN
Inventors: 刘亭; 杨文科
Original assignee: Foshan Southern China Institute For New Materials
Current assignee: Foshan Southern China Institute For New Materials
Priority date: 2022-09-08
Filing date: 2022-09-08
Publication date: 2023-05-30

Abstract

The invention discloses a composite oxide solid electrolyte, which comprises MgO membrane strips on two sides of an LLZO membrane strip, wherein the MgO membrane strips are of symmetrical structures, the two sides shrink uniformly during sintering, and an obtained electrolyte sheet is smoother and can not generate bending conditions; the electrolyte sheet has good strength, the MgO membrane belts at the two sides of the LLZO membrane belt play a supporting role, and the strength of the electrolyte sheet is improved; the electrolyte sheet is not adhered to the burning plate, the MgO film strips on two sides of the LLZO film strip play a role in isolation, and the electrolyte sheet is not adhered to the burning plate; the electrolyte sheet of the invention does not need to be added with protective powder for embedding in the sintering process, and the MgO isolating layer can inhibit Li ₂ Excessive volatilization of O, so that there is no need for a large amount of sacrificial protective powderCan be sintered and compacted under the condition. The interface impedance between the electrolyte sheet and the positive electrode and the negative electrode is small, and the porous structures are arranged on the two sides, so that the contact between the positive electrode and the negative electrode and the electrolyte is increased.

Description

Composite oxide solid electrolyte and manufacturing method thereof

Technical Field

The invention relates to an all-solid-state lithium ion battery, in particular to a composite oxide solid electrolyte and a manufacturing method thereof.

Background

In order to meet the increasing demands of consumer electronics and electric vehicles for lithium batteries, all-solid-state lithium batteries have attracted considerable attention in recent years due to their superior safety and ultra-high energy density. Conventional lithium batteries containing organic liquid electrolytes exhibit serious safety problems of toxicity, flammability, corrosiveness, and chemical stability. The use of a solid electrolyte instead of an electrolyte and a separator fundamentally eliminates the above-mentioned safety problems. All-solid-state lithium batteries are classified into three types according to the types of solid electrolytes: polymers, oxides and sulfides. Oxide solid state electrolytes have been widely studied due to their higher ionic conductivity and better mechanical strength, with LLZO being the most studied. The LLZO electrolyte powder is generally prepared by solid phase reaction, specifically, is prepared by mechanically mixing La2O3 and ZrO2 using a lithium source (LiOH H2O or Li2CO 3) and then sintering at high temperature. To obtain thinner LLZO electrolyte sheets, casting is the most common approach: the LLZO powder is prepared into slurry, and the slurry is cast into a film strip, and the film strip is sintered at high temperature, so that a thinner LLZO electrolyte sheet is obtained. For example, patent CN104916869a porous-dense double-layer electrolyte ceramic sintered body, lithium ion battery, lithium-air battery of the university of Qinghai Ren Yaoyu south-zebra discloses a porous-dense double-layer structured LLZO solid electrolyte. The electrolyte structure is an asymmetric structure, and the phenomenon of inconsistent shrinkage still exists in the sintering process, so that the electrolyte sheet is bent; the electrolyte two-layer structure is made of LLZO, and the electrolyte sheet and the protective powder cannot be guaranteed to be not adhered to each other because the electrolyte two-layer structure is sintered by being buried in LLZO protective powder in the sintering process. Therefore, in the field of oxide solid electrolyte preparation, the problems that a thinner LLZO electrolyte sheet is difficult to sinter successfully, has poor strength and serious bending, is adhered to a burning-rate plate and cannot be separated still exist.

Disclosure of Invention

Based on the problems that a thinner LLZO electrolyte sheet is difficult to sinter successfully, has poor strength and serious bending, is adhered to a burning plate and cannot be separated, the invention provides a composite oxide solid electrolyte and a manufacturing method thereof, and the specific technical scheme is as follows:

a composite oxide solid electrolyte comprising a first membrane strip, a second membrane strip arranged on one side of the first membrane strip, and a third membrane strip arranged 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 grain stacking;

wherein, the first membrane strip comprises the following preparation raw materials: LLZO powder, a first dispersing agent, a first solvent, a first binder and a first plasticizer;

the second membrane strip and the third membrane strip comprise the following preparation raw materials: mgO powder, a second dispersant, a second solvent, a second binder, a second plasticizer and a pore-forming agent.

Further, the first dispersing agent and the second dispersing agent are one or two of triethanolamine and fish oil.

Further, the first solvent and the second solvent are one or more of ethanol, isopropanol and toluene.

Further, the first binder and the second binder are both PVB.

Further, the first plasticizer and the second plasticizer are each a mixture of one or more of DOP, DEP, DBP.

Further, the pore-forming agent is one or more of PMMA microspheres, PS microspheres and graphite spheres.

Further, the first film strip is a LLZO film strip, and the second film strip and the third film strip are MgO film strips.

In addition, the invention also provides a manufacturing method of the composite oxide solid electrolyte, which comprises the following steps:

mixing LLZO powder, a first dispersing agent and a first solvent, performing ball milling for 5 hours, adding a first binder and a first plasticizer, and performing ball milling for 2 hours to obtain LLZO slurry;

casting the LLZO slurry on a PET base band by using a fixed scraper, and drying at room temperature to obtain a LLZO film band;

mixing MgO powder, a second dispersant and a second solvent, performing ball milling for 5 hours, adding a second binder and a second plasticizer, performing ball milling for 2 hours, and finally adding a pore-forming agent with the particle size of 1-10 mu m, and mixing for 1 hour to obtain MgO slurry;

casting the MgO slurry on a PET base band by using a fixed scraper, and drying at room temperature for 1h to obtain a MgO film band;

and respectively placing MgO film strips on two sides of the LLZO film strips after the drying treatment, performing hot pressing treatment, high-temperature sintering treatment, and cooling to room temperature to obtain the composite oxide solid electrolyte.

Further, the temperature of the hot pressing treatment is 70-80 ℃, and the time of the hot pressing treatment is 1h.

Further, the sintering process is: heating to 700-800 ℃ at 2 ℃/min, preserving heat for 2h to remove glue, heating to 1100-1300 ℃ at 10 ℃/min, preserving heat for 10-60 min to perform sintering treatment.

The electrolyte sheet manufactured by the scheme is flat, mgO membrane belts on two sides of the LLZO membrane belt are of symmetrical structures, the two sides shrink in a consistent manner during sintering, and the obtained electrolyte sheet is relatively flat and cannot be bent; the electrolyte sheet has good strength, the MgO membrane belts at the two sides of the LLZO membrane belt play a supporting role, and the strength of the electrolyte sheet is improved; the electrolyte sheet is not adhered to the burning plate, the MgO film strips on two sides of the LLZO film strip play a role in isolation, and the electrolyte sheet is not adhered to the burning plate; the electrolyte sheet of the invention does not need to be added with protective powder for embedding in the sintering process, and the MgO isolating layer can inhibit Li ₂ Excessive volatilization of O can lead to compact sintering without great sacrifice of protective powder. The interface impedance between the electrolyte sheet and the positive electrode and the negative electrode is small, and the porous structures are arranged on the two sides, so that the contact between the positive electrode and the negative electrode and the electrolyte is increased.

Drawings

Fig. 1 is a schematic cross-sectional SEM of a composite oxide solid electrolyte prepared in example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following examples thereof in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.

Unless defined otherwise, 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 invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The invention relates to a composite oxide solid electrolyte, which comprises a first membrane strip, a second membrane strip arranged on one side of the first membrane strip and a third membrane strip arranged on the other side of the first membrane strip, wherein the second membrane strip and the third membrane strip form a porous structure with spherical grain stacking;

In one embodiment, 18 to 25 parts by weight of LLZO powder, 0.1 to 1 part by weight of a first dispersant, 18 to 25 parts by weight of a first solvent, 1 to 5 parts by weight of a first binder and 0.1 to 1 part by weight of a first plasticizer.

In one embodiment, the weight ratio of the MgO powder is 18 to 25 parts, the second dispersant is 0.1 to 1 part, the second solvent is 18 to 25 parts, the second binder is 1 to 5 parts, the second plasticizer is 0.1 to 1 part, and the pore-forming agent is 1 to 25 parts.

In one embodiment, the first dispersant and the second dispersant are both one or two of triethanolamine and fish oil.

In one embodiment, the first solvent and the second solvent are each one or more of ethanol, isopropanol, toluene.

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

In one embodiment, the first plasticizer and the second plasticizer are each a mixture of one or more of DOP, DEP, DBP.

In one embodiment, the pore-forming agent is one or more of PMMA microspheres, PS microspheres and graphite spheres.

In one embodiment, the first film strip is a LLZO film strip, and the second film strip and the third film strip are MgO film strips. And the first membrane belt and the second membrane belt both form a porous structure with spherical grains stacked, and can be used as a protective layer to inhibit lithium volatilization in LLZO at high temperature and promote densification of the LLZO sintering process. Can also be used as an isolation layer to prevent the LLZO from being burnt with the burning plate in the sintering process.

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

In one embodiment, the sintering process is: heating to 700-800 ℃ at 2 ℃/min, preserving heat for 2h to remove glue, heating to 1100-1300 ℃ at 10 ℃/min, preserving heat for 10-60 min to perform sintering treatment.

In one embodiment, the composite oxide solid state electrolyte has a thickness of 10 μm to 200 μm.

Embodiments of the present invention will be described in detail below with reference to specific examples.

Example 1:

adding 20g of LLZO powder, 0.2g of fish oil and 20g of isopropanol into a ball milling tank, performing ball milling treatment for 5 hours at a rotating speed of 300rpm/min, adding 1g of PVB and 0.5g of DOP, and performing ball milling treatment for 2 hours to obtain LLZO slurry; casting the LLZO slurry on a PET base band by using a fixed scraper, and drying for 1h at room temperature to obtain a LLZO film band;

adding 20g of MgO powder, 0.2g of fish oil and 20g of isopropanol into a ball milling tank, performing ball milling treatment for 5 hours at a rotating speed of 300rpm/min, then adding 1g of PVB and 0.5g of DOP, performing ball milling treatment for 2 hours, and finally adding 8.6g (30%) of PMMA microspheres (with an average particle size of 5 mu m), and mixing for 30 minutes to obtain MgO slurry; casting the obtained slurry on a PET base band by using a fixed scraper, and drying for 1h at room temperature to obtain an MgO film band;

placing MgO film strips on two sides of the dried LLZO film strips respectively, and then carrying out hot pressing treatment at 80 ℃ for 1h to obtain composite film strips;

and clamping the composite film belt between two MgO burning plates, and placing the composite film belt into an MgO crucible with a cover. Heating to 700 ℃ at 2 ℃/min, preserving heat for 2 hours to remove glue, heating to 1200 ℃ at 10 ℃/min, preserving heat for 20 minutes to sinter, and cooling to room temperature to obtain the composite solid electrolyte sheet.

Example 2:

the difference from example 1 is that 2.2g (10%) of PMMA is added, the remainder remaining unchanged.

Example 3:

the difference from example 1 is that 20g (50%) of PMMA is added, the remainder remaining unchanged.

Example 4:

the difference from example 1 is that isopropanol is changed to ethanol, the remainder remaining unchanged.

Example 5:

the difference from example 1 is that isopropanol is changed to toluene and the rest remains unchanged.

Example 6:

the difference from example 1 is that the temperature is raised to 700 ℃ at 2 ℃/min, the glue is discharged after heat preservation for 2h, then the temperature is raised to 1200 ℃ at 10 ℃/min, the sintering treatment is carried out after heat preservation for 40min, and the rest is kept unchanged.

Example 7:

the difference from example 1 is that the temperature is raised to 700 ℃ at 2 ℃/min, the glue is discharged after heat preservation for 2h, then the temperature is raised to 1200 ℃ at 10 ℃/min, the sintering treatment is carried out after heat preservation for 60min, and the rest is kept unchanged.

Comparative example 1:

the LLZO tape was subjected to a sintering treatment, which was identical to the composite tape of example 1.

Comparative example 2:

the LLZO tape was subjected to sintering treatment, and buried in LLZO protective powder for sintering, and the sintering treatment process was identical to that of the composite tape in example 1.

Comparative example 3:

the difference from example 1 is that the composite film tape of the LLZO film tape, in which the MgO film tape is hot-pressed on one side, is subjected to a sintering process, and the sintering process is unchanged.

Performance comparison tests were performed on examples 1 to 7 and comparative examples 1 to 3, and the results are shown in table 1 below.

Table 1:

from the analysis in table 1, it can be seen that: the composite electrolyte sheets with porous MgO structures on two sides of the LLZO membrane belt prepared by the invention have no phenomenon of adhering to the burning plate and have smooth surfaces, but the adhesion between the comparative example 1 and the burning plate is tight, the adhesion between the comparative example 2 and the protective powder is tight, and the adhesion between one side of the comparative example 3 and the burning plate is tight, so that the complete electrolyte sheets with smooth surfaces are difficult to take out; the electrolyte sheet prepared by the application has far better adhesion performance with molten lithium than that of the comparative example (the specific surface area of the porous layer is increased, and the wettability with molten lithium is improved).

Thus, as can be seen from the comprehensive comparison in table 1, the performance of example 1 is optimal. The corresponding optimal formula and process are as follows: the solvent is isopropanol; PMMA content is 30%; the sintering temperature is 1200 ℃ and the sintering time is 20min. The PMMA content is too low (10%), and the porous MgO layer is easily sintered and densified (the porosity is only 5%); too high a content (50%), too high a porosity of the porous layer (60%), and an effect of suppressing volatilization of Li2O was not achieved, resulting in non-densification of LLZO sintering. The PMMA content is optimal at 30 percent, and the porosity of the MgO layer is 46 percent, so that the Li can be inhibited ₂ O volatilizes, and certain holes can be ensured. The solvent ethanol has a low melting point and is too fast to volatilize, so that the preparation of slurry is not facilitated; toluene dissolves PMMA, resulting in a decrease in porosity of the porous layer and densification of the sinter. When the sintering time is 20min, LLZO density is highest, and the density is continuously reduced along with the increase of the sintering time. The MgO porous layer is also difficult to block excessive volatilization of Li2O when the sintering time is long, so that the LLZO density is reduced continuously.

In addition, fig. 1 is a schematic cross-sectional SEM view of the composite oxide solid electrolyte prepared in example 1 of the present invention, and it is apparent from fig. 1 that porous MgO film tapes are distributed on both sides of a dense LLZO film tape.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. The composite oxide solid electrolyte is characterized by comprising a first membrane strip, a second membrane strip arranged on one side of the first membrane strip and a third membrane strip arranged on the other side of the first membrane strip, wherein the second membrane strip and the third membrane strip form a porous structure with spherical grain stacking;

2. The solid state composite oxide electrolyte of claim 1, wherein the first dispersant and the second dispersant are each one or a mixture of triethanolamine and fish oil.

3. The solid state composite oxide electrolyte of claim 1, wherein the first solvent and the second solvent are each one or more of ethanol, isopropanol, toluene.

4. The solid state composite oxide electrolyte of claim 1, wherein the first binder and the second binder are both PVB.

5. The composite oxide solid state electrolyte of claim 1, wherein the first plasticizer and the second plasticizer are each a mixture of one or more of DOP, DEP, DBP.

6. The composite oxide solid electrolyte of claim 1, wherein the pore-forming agent is one or more of PMMA microspheres, PS microspheres, graphite spheres.

7. The composite oxide solid state electrolyte of claim 1, wherein the first membrane strip is a LLZO membrane strip, and the second membrane strip and the third membrane strip are both MgO membrane strips.

8. A method for producing the composite oxide solid electrolyte according to any one of claims 1 to 7, comprising the steps of:

9. The method for producing a solid electrolyte of composite oxide according to claim 8, wherein the temperature of the hot pressing treatment is 70 ℃ to 80 ℃ and the time of the hot pressing treatment is 1h.

10. The manufacturing method of the composite oxide solid electrolyte according to claim 8, wherein the sintering process is: heating to 700-800 ℃ at 2 ℃/min, preserving heat for 2h to remove glue, heating to 1100-1300 ℃ at 10 ℃/min, preserving heat for 10-60 min to perform sintering treatment.