A high-performance garnet structure lithium ion solid electrolyte sheet normal pressure sintering method

Abstract

The application discloses a normal-pressure sintering method for high-performance garnet structure lithium ion solid-state electrolyte sheets, which fills the gap between the electrolyte green body and the crucible wall by using twice-recovered buried powder, and buries and seals the top, thereby saving cost, forming a semi-sealed sintering environment with uniform temperature and high lithium vapor concentration, reducing the loss of internal lithium, reducing the lithium ion migration activation energy of the electrolyte, making the electrolyte sintered uniformly and densely, and obtaining a pure cubic phase solid-state electrolyte sheet sintered body; and the lithium addition parameters of the bottom buried powder are adjusted to promote the improvement of the sintering performance of the electrolyte.

Description

Technical fields:

[0001] This invention belongs to the field of lithium-ion solid-state battery technology, specifically relating to an atmospheric pressure sintering method for a high-performance garnet-structured lithium-ion solid electrolyte sheet. Background technology:

[0002] Lithium-ion batteries are considered to have a very broad development prospect in energy storage due to their high energy density and long lifespan. However, currently commercial lithium-ion batteries often use organic electrolytes, which pose significant safety hazards due to their flammability and leakage. Furthermore, the presence of the electrolyte complicates the battery structure, hindering the development of miniaturized battery structures. All-solid-state batteries, due to their high thermal stability and good safety performance, have received widespread attention in recent years and are considered a key development direction for next-generation lithium-ion batteries.

[0003] The core of all-solid-state batteries is the solid electrolyte, which can generally be divided into oxide solid electrolytes and sulfide solid electrolytes. Sulfide solid electrolytes often have high ionic conductivity, but due to their high hygroscopicity, their environmental stability is poor, and they are still far from practical commercial applications. Currently, oxide solid electrolyte systems are more widely studied. The preparation of solid electrolytes requires a large amount of embedded powder to encapsulate the electrolyte green body for high-temperature sintering. The embedded powder is difficult to reuse after sintering, which not only increases costs but also poses potential environmental risks. Furthermore, the solid electrolytes sintered using conventional methods have unsatisfactory performance and low ionic conductivity. Summary of the Invention:

[0004] This invention provides an atmospheric pressure sintering method for high-performance garnet-structured lithium-ion solid electrolyte sheets. It utilizes recycled embedded powder as cover powder for the next sintering. At high temperature, the cover powder shrinks, encapsulating and burying the green solid electrolyte sheet, creating a semi-sealed sintering environment with uniform temperature and high lithium vapor concentration. This improves the performance of the solid electrolyte sheet, reduces sintering costs, and produces a high-performance pure cubic phase solid electrolyte sheet under atmospheric pressure sintering conditions. This solves the problems of difficult reuse of the embedded powder after sintering and low ionic conductivity of the sintered solid electrolyte sheet in existing technologies.

[0005] This invention is achieved through the following technical solutions:

[0006] A method for atmospheric pressure sintering of a high-performance garnet-structured lithium-ion solid electrolyte sheet, characterized in that the stoichiometric formula of the lithium-ion solid electrolyte sheet is Li 7-x La3Zr 2-x Ta x O 12 Where 0 ≤ x ≤ 0.5; the atmospheric pressure sintering method includes the following steps:

[0007] 1) Green pressing: Weighing the material according to the metering formula Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The masterbatch powder is added into a steel pressing mold and pressed into a solid electrolyte tablet blank;

[0008] 2) High-temperature sintering: The solid electrolyte sheet green blanks prepared in step 1) are stacked in a crucible with a certain thickness of embedded powder at the bottom. The green electrolyte sheet green blanks are separated from each other by embedded powder. A layer of embedded powder is placed on top of the uppermost layer of green electrolyte sheet green blanks. Then, the gap between the green electrolyte sheet and the crucible wall is filled with recycled embedded powder and sealed. After covering the crucible with the lid, it is calcined at 1150-1200℃ for 3-10 hours. After cooling to room temperature, it is removed to obtain the sintered solid electrolyte sheet body. The embedded powder is obtained from the mother powder Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 Add no more than 5 wt% LiOH·H2O to the mixture, then place it in a covered MgO crucible and calcine at 900℃-950℃ for 3-6 hours at a heating rate of 5℃ / min. After cooling to room temperature, grind the mixture to obtain the final product. The secondary recycled embedded powder is the embedded powder that fills the crucible to bury the solid electrolyte sheet green body. After calcining at a high temperature above 1150℃ for 3-8 hours, cool to room temperature and remove the solid electrolyte sheet sintered body. The remaining powder that encapsulates the electrolyte sheet is then ground to obtain the final product.

[0009] Preferably, in step 1), the mass of the masterbatch powder is 0.6-1.2g, the diameter of the steel tableting mold is 16-19mm, and the pressing pressure is 10-15Mpa.

[0010] Preferably, in step 2), the crucible is made of MgO material with a lid, the inner height of the crucible is 3-8cm, and the inner diameter of the crucible is 2-5mm larger than the diameter of the pressed solid electrolyte sheet blank.

[0011] In step 2), the number of solid electrolyte sheet blanks is 2-8.

[0012] Step 2) Increase the temperature to calcination temperature of 1150-1200℃ at a rate of 5℃ / min.

[0013] In step 2), the thickness of the buried powder at the bottom of the crucible is greater than 0.5 cm. The buried powder recovered from the second time is used to fill the gap between the side wall of the crucible and the electrolyte green blank to cover and bury all the solid electrolyte green blanks. The distance between the uppermost end of the buried layer and the upper surface of the uppermost solid electrolyte green blank is greater than 0.5 cm, preferably 0.6-0.8 cm.

[0014] The method of this invention uses recycled buried powder as cover powder. During the high-temperature calcination process, the cover powder shrinks and wraps around the solid electrolyte sheet green blank, forming a semi-sealed sintering environment with uniform internal temperature and high lithium vapor concentration. This reduces the loss of internal lithium and lowers the lithium ion migration activation energy of the electrolyte, resulting in uniform and dense electrolyte sintering.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. Cost savings: Solid electrolyte sheets require a large amount of powder to cover the green sheet during sintering before high-temperature sintering. The powder is difficult to reuse after sintering. This invention recycles the powder after sintering as the cover powder for the next sintering, reducing the use of powder and saving costs.

[0017] 2. Improved sintering performance of solid electrolyte sheets. The recycled powder, used as a cover powder, readily agglomerates and shrinks minimally during high-temperature sintering. It encapsulates and covers the green solid electrolyte sheet, forming a dome. Inside this dome, a semi-sealed sintering environment with uniform temperature and high lithium vapor concentration is created, significantly reducing internal lithium loss and lowering the lithium-ion migration activation energy of the electrolyte. Furthermore, by controlling the excess lithium parameter of the bottom powder, the sintering performance of the electrolyte sheet is promoted, resulting in a uniform and dense solid electrolyte sheet with a pure cubic phase sintered body and a room temperature ionic conductivity of 8.24*10⁻⁶. -4 S * cm -2 It has a density as high as 94.78% and an activation energy as low as 0.102 eV. Attached image description:

[0018] Figure 1 This is a schematic diagram of solid electrolyte sintering using the burial method of the present invention in Example 1.

[0019] Figure 2 This is a schematic diagram of solid electrolyte sintering using conventional burial methods in Comparative Example 1.

[0020] Figure 3 This is the SEM X-ray diffraction pattern of the solid electrolyte after sintering in Example 1.

[0021] Figure 4 This is the SEM X-ray diffraction pattern of the solid electrolyte after sintering in Comparative Example 1.

[0022] Figure 5 This is an AC impedance diagram of the solid electrolyte at different temperatures after sintering in Example 1.

[0023] Figure 6 This is the AC impedance diagram of the solid electrolyte at different temperatures after sintering in Comparative Example 1.

[0024] Figure 7 This is a graph showing the lithium-ion migration activation energy of the solid electrolyte after sintering in Example 1.

[0025] Figure 8 This is a graph showing the lithium-ion migration activation energy of the solid electrolyte after sintering in Comparative Example 1. Detailed implementation method:

[0026] Those skilled in the art will understand that the techniques disclosed in the following embodiments represent those discovered by the inventors that work well in the practice of this invention. However, many changes can be made to the specific embodiments disclosed, still obtaining the same or similar results without departing from the spirit and scope of the invention.

[0027] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0028] Example 1

[0029] Powder embedded in Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The mother powder was calcined at 900℃ for 6 hours with a heating rate of 5℃ / min after being added to 5 wt% LiOH·H2O and then cooled to room temperature before grinding. The secondary recycled embedded powder was obtained by calcining the embedded powder, which was used to fill the crucible to embed the electrolyte sheet green body, at 1150℃ for 5 hours, then cooling to room temperature, removing the solid electrolyte sheet sintered body, and grinding the remaining powder that encapsulated the electrolyte sheet.

[0030] Weigh out the mother powder Li 6.4 La3Zr 1.4 Ta 0.6 O 12 0.7g of powder was poured into a 19mm steel tableting mold, spread evenly, and pressed into solid electrolyte sheet preforms using a pressure of 10MPa. A total of 5 preforms were pressed. A 22mm inner diameter, 33ml capacity MgO covered crucible was selected. 3.5g of lithium-added powder (5wt%) was placed at the bottom of the crucible, with a thickness of 5.2mm. The pressed solid electrolyte sheet preforms were stacked on top of the powder, with the preforms separated from each other by the powder to prevent direct contact. A layer of powder was placed on top of the top layer of preforms. The gaps between the preforms and the crucible wall were then filled with recycled powder and sealed (see schematic diagram). Figure 1The distance between the top edge of the buried layer and the top surface of the top solid electrolyte sheet blank is 8 mm, and the crucible is covered. The crucible containing the sample is placed in a muffle furnace and heated to 1150℃ at a heating rate of 5℃ / min, and calcined at 1150℃ for 5 hours. Then it is naturally cooled to room temperature, and the sintered solid electrolyte sheet is removed. The solid electrolyte sheet has a pure cubic phase crystal structure and an ionic conductivity of 8.24 × 10⁻⁶. -4 S * cm -2 The activation energy is 0.102 eV, and the actual densities are 4.891, 4.892, and 4.891 g. * cm -3 Theoretical density: 5.16g * cm -3 The average actual density is taken as 4.891g. * cm -3 The density was 94.78%.

[0031] Comparative Example 1

[0032] Referring to Example 1, the difference is that, using Figure 2 The conventional burial method shown utilizes buried powder to fill the gap between the electrolyte green body and the crucible wall and encapsulates the electrolyte green body, using only the secondary recycled buried powder for burial and sealing (see schematic diagram). Figure 2 The top of the recycled powder is 6 mm higher than the top surface of the top solid electrolyte sheet. Other steps are the same as in Example 1.

[0033] The solid electrolyte sheet has a pure cubic crystal structure and a room temperature ionic conductivity of 4.23 × 10⁻⁶. -4 S * cm -2 Actual density (4.768, 4.769, 4.768 g) * cm -3 Theoretical density: 5.16g * cm -3 The average actual density is taken as 4.768g. * cm -3 The density was 92.4%.

[0034] The solid electrolyte sheets prepared in Example 1 and Comparative Example 1 were subjected to SEM X-ray diffraction and electrochemical impedance spectroscopy (EIS) tests. The EIS test conditions were as follows: a silver-blocked electrode was used for AC impedance testing; a conductive silver layer was brushed onto both ends of the solid electrolyte sheet, tabs were led out, and the sheet was connected to an electrochemical workstation; impedance testing was selected; the open-circuit voltage was 0V; and the test frequency was 1-1MHz. The relevant results are shown in […]. Figures 3-8 .

[0035] Depend on Figure 3 and Figure 4 It can be seen that the solid electrolyte in Example 1 is more uniform and dense after sintering.

[0036] Depend on Figure 5 and Figure 6 It can be seen that the room temperature impedance R of the solid electrolyte sheets prepared in Example 1 and Comparative Example 1 are 46.21Ω and 61.87Ω, respectively; the thickness L of the solid electrolyte sheet in Example 1 is measured to be 0.065cm, and the effective area S is 1.70cm². 2 Comparative Example 1: The solid electrolyte sheet has a thickness L of 0.05 cm and an effective area S of 1.70 cm². 2 The formula σ = L / (S·R) (where σ is the ionic conductivity; L is the thickness of the sample in cm; R is the bulk impedance of the sample in ohms; and S is the effective area of ​​the electrode in cm²) is used. 2 The calculated room-temperature ionic conductivity σ of the solid electrolyte sheet in Example 1 is 8.24 × 10⁻⁶. -4 S * cm -2 The room temperature ionic conductivity of the solid electrolyte sheet in Comparative Example 1 is 4.23 × 10⁻⁶. -4 S * cm -2 .Depend on Figure 7 and Figure 8 It can be seen that the activation energy of the solid electrolyte sheet in Example 1 is 0.102 eV, and the activation energy of the solid electrolyte sheet in Comparative Example 1 is 0.251 eV.

[0037] The density of the prepared solid electrolyte sheets was tested using the specific gravity bottle method, and the actual densities obtained in Example 1 were 4.891, 4.892, and 4.891 g. * cm -3 (Measured three times), the actual density of Comparative Example 1 was 4.768, 4.769, and 4.768 g. * cm -3 (Measured three times.)

Claims

1. A method for pressureless sintering of high performance garnet-structured lithium ion solid state electrolyte sheets, characterized by, The stoichiometric formula of the lithium ion solid-state electrolyte sheet is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ; the normal pressure sintering method comprises the following steps: 1) green compact pressing: a mother powder of Li 6.4 La3Zr 1.4 Ta 0.6 O 12 is added to a steel tabletting die to press a solid electrolyte tablet green compact; 2) high temperature sintering: the green body of solid state electrolyte sheet prepared in step 1) is stacked in a crucible with a certain thickness of buried powder on the bottom, the green body of electrolyte sheet is separated by buried powder between the sheets, a layer of buried powder is laid on the top of the uppermost layer of green body of electrolyte sheet, then the gap between the green body of electrolyte and the wall of the crucible is filled with the secondary recovered buried powder and buried for sealing, then the lid of the crucible is covered, and calcination is carried out at 1150-1200℃ for 3-10h, cooled to room temperature, taken out, and the sintered body of solid state electrolyte sheet is obtained; the buried powder is prepared by adding not more than 5wt% of LiOH·H2O to the mother powder Li 6.4 La3Zr 1.4 Ta 0.6 O 12 and then placed in a MgO crucible with a cover, calcined at 900-950℃ at a heating rate of 5℃ / min for 3-6h, cooled to room temperature, and then ground to obtain; the secondary recovered buried powder is the buried powder for filling the green body of solid state electrolyte sheet in the crucible, which is obtained after the solid state electrolyte sheet sintered body is taken out after high temperature calcination at 1150℃ or above for 3-8h and cooled to room temperature, and the powder wrapped around the electrolyte sheet is ground.

2. The method of claim 1, wherein, In step 1), the mass of the mother powder is 0.6-1.2 g, the steel tabletting die has a diameter of 16-19 mm, and the compression pressure is 10-15 MPa.

3. The method of claim 1, wherein, In step 2), the crucible is made of MgO with a cover, the inner height of the crucible is 3-8 cm, and the inner diameter of the crucible is 2-5 mm larger than the diameter of the green compact of the solid-state electrolyte tablet.

4. The method of claim 1, wherein, In step 2), the number of the green compacts of the solid-state electrolyte tablet is 2-8.

5. The method of claim 1, wherein, In step 2), the temperature is raised to 1150-1200℃ at a rate of 5℃ / min.

6. The method of claim 1, wherein, In step 2), the thickness of the buried powder at the bottom of the crucible is greater than 0.5 cm, the gap between the side wall of the crucible and the green compacts of the solid-state electrolyte tablet is filled with the secondly recycled buried powder to wrap and bury all the green compacts of the solid-state electrolyte tablet, and the distance between the upper end of the burying layer and the upper surface of the uppermost green compact of the solid-state electrolyte tablet is greater than 0.5 cm.

7. The method of claim 6, wherein, In step 2), the gap between the side wall of the crucible and the green compacts of the solid-state electrolyte tablet is filled with the secondly recycled buried powder to wrap and bury all the green compacts of the solid-state electrolyte tablet, and the distance between the upper end of the burying layer and the upper surface of the uppermost green compact of the solid-state electrolyte tablet is 0.6-0.8 cm.

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