CN106384801B

CN106384801B - Preparation method of oxide solid electrolyte diaphragm

Info

Publication number: CN106384801B
Application number: CN201610877257.4A
Authority: CN
Inventors: 赵鹏程; 曹高萍; 文越华; 徐艳; 程杰
Original assignee: 63971 Troops of PLA
Current assignee: 63971 Troops of PLA
Priority date: 2016-10-09
Filing date: 2016-10-09
Publication date: 2020-01-14
Anticipated expiration: 2036-10-09
Also published as: CN106384801A

Abstract

The invention relates to a preparation method of an oxide solid electrolyte diaphragm, belonging to the field of electrochemical engineering and ceramic industry. The method uses lithium carbonate or lithium hydroxide as a lithium source, and solid electrolyte powder prepared in advance is placed in a crucible and directly sintered at high temperature to obtain a compact block; and cutting and polishing the block to obtain the solid electrolyte diaphragm slice. The method avoids the complex die tabletting process in the conventional method, firstly converts mechanical energy into surface free energy of powder particles through ball milling, then utilizes excessive low-melting-point lithium salt to be melted at high temperature to generate a liquid phase to cover the surfaces of the powder particles, enables the powder to automatically agglomerate under the action of surface tension, reduces the surface free energy and forms a compact solid electrolyte block. The method has the advantages of simple process, flat and compact finished product, easy scale production and the like, and is particularly suitable for preparing the oxide solid electrolyte diaphragm in the solid secondary battery.

Description

Preparation method of oxide solid electrolyte diaphragm

Technical Field

The invention relates to a preparation method of an oxide solid electrolyte diaphragm, belonging to the field of electrochemical engineering and ceramic industry.

Background

The traditional lithium ion battery adopts organic electrolyte, so that potential dangers such as combustion, explosion and the like exist. The new generation of lithium ion battery, so-called 'all-solid-state battery', adopts solid electrolyte to replace flammable organic electrolyte, and fundamentally solves the safety problem of the battery. Solid electrolytes can be broadly classified into high molecular polymers and inorganic substances. High molecular polymers have low ionic conductivity at room temperature and are difficult to apply to all-solid-state batteries. Although the inorganic solid electrolyte is difficult to prepare a membrane on a large scale, the inorganic solid electrolyte has high ionic conductivity, good selectivity and long service life, and becomes the mainstream of research on all-solid-state battery separators.

Inorganic solid electrolytes are various in variety, and the current research focus is mainly on sulfide solid electrolytes, Lithium Lanthanum Titanate (LLTO) andLi₇La₃Zr₂O₁₂(LLZO), and the like. The sulfide solid electrolyte has the highest conductivity, but the preparation of the sulfide solid electrolyte needs to be carried out under Ar protective atmosphere, the operation is complex, the electrolyte is very sensitive to moisture, and the stability is poor. The LLTO ionic conductivity can reach 10 at room temperature^-3S/cm, but the redox potential of Ti in LLTO is lower than 1.8V vs. Li/Li⁺And the lithium ion battery is unstable in contact with metal lithium, and is not suitable for being directly used as a solid battery diaphragm. Murugan et al recently produced cubic phase LLZO solid electrolytes with ionic conductivities as high as 5X 10^-4S/cm. LLZO has the advantages of small electronic conductivity, small grain boundary resistance, good electrochemical stability and the like, and also shows good stability when contacting with metal lithium, thereby initiating the hot tide of research on LLZO solid electrolyte.

The existing LLZO powder synthesis method mainly comprises the traditional solid phase reaction method, the sol-gel method, the spray-pyrolysis method, the field-assisted sintering method, the chemical vapor deposition method and the like. However, regardless of the method used to prepare the LLZO powder, the LLZO powder is finally compacted into a sheet and then sintered at high temperature into a ceramic diaphragm. When the tablet is pressed by a die method, the tablet pressing process of the powder is time-consuming and labor-consuming, and the pollution of the grinding tool to the sample is difficult to stop. In addition, the thin slice sample is easy to be distorted and deformed and even cracked in the sintering process, and the sample is polluted by the sintering environment. Before the ceramic diaphragm is used as a battery diaphragm, surface cleaning and polishing are generally needed, and particularly, the ceramic diaphragm is easy to damage in the polishing process. If the ceramic diaphragm obtained by sintering is not completely flat, the ceramic diaphragm is easy to be stressed and broken in the process of pressurizing and assembling the solid-state battery, and the assembly is difficult.

Disclosure of Invention

The invention aims to solve the problems that the diaphragm needs to be pressed in advance before being sintered, is easy to deform in the sintering process, is easy to damage in post treatment and the like in the traditional solid phase method, and provides the preparation method of the oxide solid electrolyte diaphragm with high ionic conductivity, which has the advantages of simple process, flat and compact finished product and easiness in scale production.

The technical scheme adopted by the invention for solving the problems is as follows: ball-milling lithium carbonate or lithium hydroxide, lanthanum oxide, zirconium oxide and doped oxide for 1-24 h, and mixing to obtain a primary material; pre-sintering the primary material at 700-1200 ℃ for 1-15 h, and then ball-milling for 1-24 h to obtain oxide solid electrolyte powder, wherein the particle size of the powder is 1-30 microns; under the protection of gas, placing the powder in a crucible, and then preserving heat for 1-48 h at 1000-1500 ℃ to obtain an oxide solid electrolyte block; cutting the block into solid electrolyte diaphragm sheets with the thickness of 0.1-2 mm by adopting a cutting machine;

the mol ratio of the lithium carbonate, the lanthanum oxide, the zirconium oxide and the doped oxide is as follows: 3.5-6: 3: 2: 0.001-0.5; the molar ratio of lithium hydroxide, lanthanum oxide, zirconium oxide and doped oxide is as follows: 7-12: 3: 2: 0.001-0.5.

The doped oxide is more than one of aluminum oxide, tantalum oxide, niobium oxide, tungsten oxide and tin oxide.

The protective gas is more than one of oxygen, air, nitrogen, helium and argon.

The principle of the oxide solid electrolyte diaphragm preparation method of the invention is as follows: firstly, converting mechanical energy into surface free energy of powder particles through ball milling; then, melting excessive low-melting-point lithium salt at high temperature to generate a liquid phase to cover the surface of the LLZO powder particles, automatically agglomerating the powder under the action of surface tension, reducing the surface free energy, and forming a compact solid electrolyte block; and finally, the solid electrolyte diaphragm is obtained by cutting the block, so that the problem that the diaphragm is easy to deform in the sintering process by using a conventional method is solved, and only the outer surface of the block is easy to be polluted by the environment in the sintering process, so that the pollution probability of the diaphragm sample in the sintering process is greatly reduced.

The invention has the beneficial effects that: no adhesive is added, so that the influence of gas discharged in the sintering process of the adhesive on the solid electrolyte is avoided; the complicated die tabletting process in the conventional method is not needed, and the density of the finished solid electrolyte can reach more than 96 percent; the diaphragm is prepared by directly sintering powder into blocks and then cutting, and the finished product has high flatness and is easy for batch production. Therefore, the method has the advantages of simple process, flat and compact finished product, easy scale production and the like, and the lithium ion conductivity of the finished product prepared by the method at 30 ℃ can reach 10^-4S/cm ofThe oxide solid electrolyte membrane is particularly suitable for preparing an oxide solid electrolyte membrane in a solid secondary battery.

Drawings

FIG. 1 Electron micrograph of oxide solid electrolyte separator surface

Detailed Description

Example 1

Firstly according to Li₇La₃Zr₂O₁₂Proportioning, 12.3135g of lithium hydroxide (LiOH, excess 15%) and zirconia (ZrO) are weighed respectively₂)8.8930g lanthanum oxide (La)₂O₃)17.4594g, placing in a ball milling tank, adding 20ml of absolute ethyl alcohol, ball milling at the rotation speed of 400 r/m for 10 h; drying the obtained slurry at 120 ℃ for 10h, and then grinding to obtain an oxide primary material; placing the primary material in a corundum crucible in a temperature control furnace, quickly heating to 1150 ℃, and preserving heat for 10 hours; grinding and ball-milling the high-temperature treated primary material, directly crushing and uniformly mixing the high-temperature treated primary material, sieving the powder by using a 100-mesh sieve to obtain LLZO powder, and testing the average particle size of the LLZO powder to be 10.88 microns by using a Malvern laser particle sizer; placing the obtained powder in a corundum crucible, placing the corundum crucible in a temperature control furnace, and sintering the corundum crucible in air at 1150 ℃ for 15 hours to obtain a compact oxide solid electrolyte block; and cutting the block into 1.640cm multiplied by 1.178cm slices with the thickness of 1.456mm by adopting a table grinding cutting machine, and then grinding the surface of the slices by adopting a 1000-mesh diamond sheet to obtain the solid electrolyte diaphragm slice. The block density is 4.7336g/cm3 and the density is 92.64 percent by adopting a drainage method; coating silver paste on both sides of the diaphragm, testing in a constant temperature oven by adopting an alternating current impedance method, wherein the lithium ion conductivity is 6.47 multiplied by 10 at 30 DEG C^-5S/cm。

Example 2

Separately weighing lithium carbonate (Li)₂CO₃Excess 10%) 10.3704g, zirconia (ZrO2)8.8930g, lanthanum oxide (La)₂O₃)17.4594g and tantalum oxide (Ta)₂O₅)1.0525g, placing in a ball milling tank, adding 20ml of absolute ethyl alcohol, and ball milling for 10 hours at the ball milling rotation speed of 400 r/min; drying the obtained slurry at 120 ℃ for 10h, and grinding to obtain an oxide primary material; placing the initial material in a corundum crucible in a temperature control furnace, and quickly heatingKeeping the temperature for 10h at 1150 ℃; directly crushing and uniformly mixing the high-temperature treated primary material by grinding, ball milling and other modes, and sieving by using a 100-mesh sieve to obtain LLZO powder; placing the obtained powder in a corundum crucible, placing the corundum crucible in a temperature control furnace, and sintering the corundum crucible in air at 1150 ℃ for 20 hours to obtain a compact oxide solid electrolyte block; cutting the block into 1.730cm × 1.528cm sheets with the thickness of 1.490mm by using a bench grinder cutting machine, and then performing surface grinding by using a 1000-mesh diamond sheet to obtain the solid electrolyte diaphragm sheet. The block density is 4.9261g/cm3 and the density is 96.44 percent by adopting a drainage method; SEM testing indicated that the membrane sheet surface was dense and non-porous, as shown in figure 1; coating silver paste on both sides of the diaphragm, testing in a constant temperature oven by adopting an alternating current impedance method, wherein the lithium ion conductivity is 3.60 multiplied by 10 at 30 DEG C^-4S/cm。

The density of the finished solid electrolyte in the above examples 1 and 2 is respectively 92.64% and 96.44%, which are higher than 70-90% of the density of the sample prepared by sintering by the conventional die tabletting method reported in the literature; the lithium ion conductivity of the sample doped with tantalum oxide in example 2 was significantly improved.

Claims

1. A preparation method of an oxide solid electrolyte membrane is characterized by comprising the following steps:

according to the LLZO ratio, placing lithium carbonate or lithium hydroxide, lanthanum oxide, zirconium oxide and doped oxide into a ball milling tank, adding 20ml of absolute ethyl alcohol for ball milling for 10 hours, drying the obtained slurry at 120 ℃ for 10 hours, and then grinding to obtain an oxide primary material, wherein the rotating speed of the ball mill is 400 r/min, and the lithium carbonate or lithium hydroxide is excessively prepared;

rapidly heating the primary material to 1150 ℃, preserving the heat for 10 hours, directly crushing and uniformly mixing the primary material by ball milling, and sieving the primary material by a 100-mesh sieve to obtain LLZO powder;

under the protection of gas, putting the LLZO powder into a crucible, and sintering at 1150 ℃ for 15h to obtain an oxide solid electrolyte block;

the die tabletting process in the conventional method is not needed before sintering, and the density of the solid electrolyte block is up to more than 96%;

cutting the block into solid electrolyte diaphragm sheets with the thickness of 0.1-2 mm by adopting a cutting machine;

the gas is more than one of oxygen, air, nitrogen, helium and argon.

2. The method of claim 1, wherein the LLZO ratio is: 12.3135g of lithium hydroxide, 8.8930g of zirconium oxide and 17.4594g of lanthanum oxide, wherein the lithium hydroxide is in excess of 15%.

3. The method of claim 1, wherein the LLZO ratio is: 10.3704g of lithium carbonate, 8.8930g of zirconium oxide, 17.4594g of lanthanum oxide and 1.0525g of tantalum oxide, wherein the lithium carbonate is in excess of 10%.