Low-residual alkali oxide solid electrolyte as well as preparation method and application thereof

Abstract

The invention provides a low-residual alkali oxide solid electrolyte as well as a preparation method and application thereof. Raw materials of the low-residual-alkali oxide solid electrolyte comprise an oxide electrolyte and a fluorine-containing polymer, and the residual alkali content of the surface of the low-residual-alkali oxide solid electrolyte is less than 0.3%. The preparation method comprises the following steps: mixing a fluorine-containing polymer and an oxide electrolyte to obtain a blend, and co-sintering the blend to obtain the low-residual alkali oxide solid electrolyte. According to the method, the oxide electrolyte is subjected to fluorination treatment of the fluorine-containing polymer, F2 or HF generated by decomposition of the fluorine-containing polymer reacts with residual alkali groups on the surface of the oxide solid electrolyte, and residual alkali is removed.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion batteries and relates to a low-residual alkali oxide solid electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have high energy density, high average output voltage, low self-discharge, no memory effect, wide operating temperature range, excellent cycle performance, fast charge and discharge, charging efficiency up to 100%, and high output power. Long service life. These advantages have made them widely used in various commercial rechargeable and dischargeable chemical energy storage devices. As the requirements for lithium-ion safety performance gradually increase, the existing mature liquid lithium-ion batteries are no longer suitable for existing production and life. Researchers have begun to seek to replace electrolytes with solid electrolytes to further improve the safety performance of batteries. Among them, inorganic oxide electrolytes have become a research hotspot in solid electrolytes due to their good stability, high ionic conductivity, and low cost. However, oxide electrolytes easily form LiOH and LiO2 at the interface with moisture, carbon dioxide, etc. in the air. 2 CO 3 The presence of substances such as alkali in the electrolyte causes a high content of "residual alkali" on the surface of the electrolyte, which hinders the transmission of lithium ions and makes the prepared electrolyte membrane easy to break, which is not conducive to the cycle performance of the battery.

[0003] CN114142082A discloses a composite solid electrolyte membrane, a preparation method thereof and a solid-state battery. An inorganic barrier layer for isolating water vapor and / or air is combined on the surface of the oxide solid electrolyte membrane body, including at least one of metal oxide, silicon dioxide and metal halide. However, the requirement for the addition amount of the inorganic barrier layer is relatively high, which will reduce the contact between the internal oxide solid electrolyte and the positive and negative electrodes to a certain extent, making the electrochemical performance worse.

[0004] CN115360430A discloses a solid electrolyte coated with a low surface energy material and a preparation method thereof. A method is provided in which a fluorine-containing polymer solution and electrolyte powder are mixed and then heated at a temperature of 150 to 600°C. However, heating the solution and powder wastes raw materials, easily volatilizes or produces some harmful substances, is not conducive to green environmental protection, cannot be prepared on a large scale, and the prepared solid electrolyte cannot solve the problem that the surface of the original oxide solid electrolyte becomes low alkaline.

[0005] Therefore, it is very important to develop an oxide solid electrolyte with low residual alkali content and a method to reduce the residual alkali content of the oxide solid electrolyte. Summary of the invention

[0006] The object of the present invention is to provide a low-residual alkali oxide solid electrolyte and a preparation method and application thereof.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a low residual alkali oxide solid electrolyte, wherein the raw materials of the low residual alkali oxide solid electrolyte include an oxide electrolyte and a fluorine-containing polymer, and the residual alkali content on the surface of the low residual alkali oxide solid electrolyte is less than 0.3%, wherein the residual alkali content can be 0, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25% or 0.29%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0009] In the present invention, the oxide electrolyte is subjected to fluorination treatment of the fluorinated polymer, and the fluorinated polymer is decomposed to generate F 2 Or HF reacts with the residual alkali groups on the surface of the oxide solid electrolyte to remove the residual alkali.

[0010] Preferably, the molar fraction of residual alkali on the surface of the residual alkali oxide solid electrolyte is ≤0.12mmol / g, wherein the molar fraction can be 0, 0.01mmol / g, 0.02mmol / g, 0.03mmol / g, 0.04mmol / g, 0.05mmol / g, 0.06mmol / g, 0.07mmol / g, 0.08mmol / g, 0.09mmol / g, 0.10mmol / g, 1.11mmol / g or 0.12mmol / g, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0011] As a preferred technical solution of the present invention, the diffraction angle 2θ of the low residual alkali oxide solid electrolyte has peaks in the entire ranges of 38.35-39.15°, 44.65-45.25° and 64.95-65.55°.

[0012] Preferably, the diffraction angle 2θ of the oxide solid electrolyte has peaks in the entire ranges of 38.65 to 38.95°, 44.65 to 44.95°, and 64.95 to 65.15°.

[0013] As a preferred technical solution of the present invention, the mass ratio of the oxide electrolyte and the fluorine-containing polymer is 100:(0.01~10), wherein the mass ratio can be 100:0:01, 100:0.05, 100:0.1, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9 or 100:10, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In the present invention, the oxide electrolyte and the fluorine-containing polymer are selected in a ratio of 100:(0.01-10), which can more effectively remove the alkali. Within the ratio range, the higher the content of the fluorine-containing polymer, the better the effect of removing the residual alkali.

[0015] As a preferred technical solution of the present invention, the oxide electrolyte includes any one of a perovskite electrolyte, a NASICON electrolyte, a LISICON electrolyte or a garnet electrolyte, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of a perovskite electrolyte and a NASICON electrolyte, a combination of a NASICON electrolyte and a LISICON electrolyte, or a combination of a LISICON electrolyte and a garnet electrolyte, etc.

[0016] Preferably, the perovskite electrolyte comprises Li 3x La 2 / 3-x TiO 3 .

[0017] Preferably, the perovskite electrolyte comprises Li 0.5 La 0.5 TiO 3 , Li 0.33 La 0.57 TiO 3 , Li 0.29 La 0.57 TiO 3 , Li 0.33 Ba 0.25 La 0.39 TiO 3 、(Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O 3 or Li 0.5 La 0.5 Ti 0.95 Zr 0.05 O 3 Any one or a combination of at least two of the above, wherein a typical but non-limiting example of the combination is: Li 0.5 La 0.5 TiO 3 and Li 0.33 La 0.57 TiO 3 Combination of Li 0.33 La 0.57 TiO 3 and Li 0.29 La 0.57 TiO 3 Combination of Li 0.29La 0.57 TiO 3 and Li 0.33 Ba 0.25 La 0.39 TiO 3 Combination or Li 0.33 Ba 0.25 La 0.39 TiO 3 and (Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O 3 combinations of etc.

[0018] Preferably, the NASICON-type electrolyte comprises Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 .

[0019] Preferably, the garnet-type electrolyte comprises Li 7 La 3 Zr 2 O 1.2 , Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 or Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Any one or a combination of at least two of the above, wherein a typical but non-limiting example of the combination is: Li 7 La 3 Zr 2 O 1.2 and Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 Combination of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 and Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Combination or Li 7 La 3 Zr 2 O1.2 and Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 combinations of etc.

[0020] As a preferred technical solution of the present invention, the fluorine-containing polymer includes any one of polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer or polyvinyl fluoride, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of polyvinylidene fluoride and polyvinylidene fluoride-trifluoroethylene copolymer, a combination of polyvinylidene fluoride-trifluoroethylene copolymer and polyvinylidene fluoride-hexafluoropropylene copolymer, a combination of polyvinylidene fluoride-hexafluoropropylene copolymer and polytetrafluoroethylene, a combination of polytetrafluoroethylene and ethylene-tetrafluoroethylene copolymer, or a combination of ethylene-tetrafluoroethylene copolymer and polyvinyl fluoride, etc.

[0021] The second object of the present invention is to provide a method for preparing the low residual alkali oxide solid electrolyte as described in the first object, the preparation method comprising:

[0022] The fluorine-containing polymer and the oxide electrolyte are mixed to obtain a blend, and the blend is co-sintered to obtain the low residual alkali oxide solid electrolyte.

[0023] The fluorine-containing polymer in the present invention decomposes during the sintering process and has a gas-solid two-phase reaction with the oxide solid electrolyte, which can more thoroughly remove the residual alkali on the surface of the oxide solid electrolyte material and improve the removal efficiency.

[0024] As a preferred technical solution of the present invention, the mixing is dry mixing.

[0025] The present invention can also use wet mixing to dissolve the fluorine-containing polymer and the oxide solid electrolyte in a solvent, and the boiling point of the solvent should be lower than the decomposition temperature of the fluorine-containing polymer.

[0026] As a preferred technical solution of the present invention, the co-sintering temperature is greater than the decomposition temperature of the fluorine-containing polymer.

[0027] Preferably, the co-sintering temperature is 650-800°C, wherein the temperature may be 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C or 800°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the co-sintering time is 1.5 to 2.5 hours, wherein the time may be 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours or 2.5 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] The decomposition temperature of the fluorine-containing polymer in the present invention refers to the lowest temperature at which the fluorine-containing polymer decomposes under a certain atmosphere. When the fluorine-containing polymer decomposes, F 2 or hydrogen fluoride, the above gases react with the residual "OH" on the surface of the oxide solid electrolyte during the co-sintering reaction - ” and “CO 3 2- " reacts to reduce the residual alkali in the oxide solid electrolyte and form a protective layer on the surface of the oxide solid electrolyte. The generated inorganic protective layer is a LiF layer, which has low electronic conductivity and surface diffusion barrier, which is beneficial to improving the interface properties of the oxide electrolyte.

[0030] Preferably, the co-sintering temperature is lower than the crystal transformation temperature of the oxide electrolyte.

[0031] The crystal transformation temperature of the oxide in the present invention: the crystal transformation is also called polycrystalline transformation, which refers to the phenomenon that the crystal structure of the same substance changes accordingly due to the change of environmental temperature.

[0032] The third object of the present invention is to provide an application of the low residual alkali oxide solid electrolyte as described in the first object, wherein the low residual alkali oxide solid electrolyte is applied in the field of lithium ion batteries.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The low residual alkali oxide solid electrolyte prepared by the present invention has a low residual alkali rate, which effectively improves the powder ion conductivity of the oxide solid electrolyte. The powder ion conductivity can be as high as 10 -5 S / cm or more.

[0035] (2) During the preparation of the low residual alkali oxide solid electrolyte of the present invention, the fluorine-containing polymer decomposes during the sintering process and reacts with the oxide solid electrolyte in a gas-solid two-phase manner, thereby removing the residual alkali on the surface of the oxide solid electrolyte material more thoroughly and improving the removal efficiency.

[0036] (3) Compared with the conventional method of adding a slight acid to the oxide solid electrolyte for neutralization, the low residual alkali oxide solid electrolyte in the present invention is more suitable for industrial production and does not generate wastewater, thus having the advantage of being green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the XRD diagram of the low residual alkali oxide solid electrolyte of Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0039] Example 1

[0040] The present embodiment provides a low residual alkali oxide solid electrolyte LLZTO-PVDF, wherein raw materials of the low residual alkali oxide solid electrolyte include lithium lanthanum zirconium titanate (LLZTO) and polyvinylidene fluoride (PVDF).

[0041] This embodiment also provides a method for preparing the above-mentioned residual alkali oxide solid electrolyte, and the preparation method comprises:

[0042] PVDF and LLZTO with a residual alkali content of 0.35mmol / g are dry-mixed at a mass ratio of 100:1.5 to obtain a blend, which is placed in a tubular furnace or a muffle furnace, and the blend is co-sintered at 750°C for 2 hours. After being taken out and cooled, the low residual alkali oxide solid electrolyte is obtained. It has been determined that the residual alkali content on the surface of the low residual alkali oxide solid electrolyte is 0.12mmol / g. The XRD pattern of the low residual alkali oxide solid electrolyte prepared in this embodiment is as follows: Figure 1 shown.

[0043] Example 2

[0044] This embodiment provides a low residual alkali oxide solid electrolyte LLZO-PVDF, wherein raw materials of the low residual alkali oxide solid electrolyte include lithium lanthanum zirconium titanium oxide (LLZO) and polyvinylidene fluoride (PVDF).

[0045] This embodiment also provides a method for preparing the above-mentioned residual alkali oxide solid electrolyte, and the preparation method comprises:

[0046] PVDF and LLZO with a residual alkali content of 0.87 mmol / g are dry-mixed in a mass ratio of 100:1.5 to obtain a blend, which is placed in a tubular furnace or a muffle furnace, and the blend is co-sintered at 750° C. for 2 hours. After being taken out and cooled, the low residual alkali oxide solid electrolyte is obtained.

[0047] Example 3

[0048] This embodiment provides a low residual alkali oxide solid electrolyte LATP-PVDF, wherein raw materials of the low residual alkali oxide solid electrolyte include lithium lanthanum zirconium titanium oxide (LATP) and polyvinylidene fluoride (PVDF).

[0049] This embodiment also provides a method for preparing the above-mentioned residual alkali oxide solid electrolyte, and the preparation method comprises:

[0050] PVDF and LATP with a residual alkali content of 0.7 mmol / g are dry-mixed at a mass ratio of 100:1.5 to obtain a blend, which is placed in a tubular furnace or a muffle furnace, and the blend is co-sintered at 750° C. for 2 hours. After being taken out and cooled, the low residual alkali oxide solid electrolyte is obtained.

[0051] Comparative Example 1

[0052] This comparative example uses the LLZTO used in Example 1 that has not been fluorinated.

[0053] Comparative Example 2

[0054] This comparative example uses the LLZO used in Example 2 that has not been fluorinated.

[0055] Comparative Example 3

[0056] This comparative example uses the LATP used in Example 3 that has not been fluorinated.

[0057] The powder conductivity test and the residual alkali content test on the electrolyte surface of the low residual alkali oxide solid electrolyte are carried out. The determination method is as follows:

[0058] 1. Powder conductivity test method:

[0059] 1) Reset the running height to zero; 2) Load the weighed sample into the mold cavity; 3) Fix the upper electrode knob; 4) Set the parameters on the display; 5) Reach the set pressure or pressure value; 6) Read the sample compression height data and input it; 7) Obtain resistance, resistivity, and conductivity data; 8) Record the data; 9) De-mold the sample and the test is over, ρ=RS / L, where ρ is the resistivity (kΩ×mm), R is the resistance value, L is the material length, and S is the area. The conductivity can be calculated based on the resistivity, where the conductivity is the reciprocal of the resistivity.

[0060] 2. Determination of residual alkali content on electrolyte surface:

[0061] A certain amount of oxide solid electrolyte material is dispersed in deionized water, stirred for 30 minutes, filtered to obtain a clear solution, and titrated with calibrated dilute hydrochloric acid. Methyl orange is used as an indicator of the titration end point to calculate the residual alkali content, wherein the residual alkali amount a=Vc / m, a is the residual alkali amount per unit mass of the oxide solid electrolyte, in mol / g (the alkali (including hydroxide and carbonate) that can consume hydrogen ions in a unit mass of the oxide solid electrolyte), V is the volume of hydrochloric acid titrated, in ml, c is the hydrochloric acid concentration, in mmol / ml, and m is the mass of the oxide solid electrolyte.

[0062] The resistivity, the peak position of the powder conductivity and the residual alkali content of the low residual alkali solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 were measured. The test results are shown in Table 1.

[0063] Table 1

[0064]

[0065] It can be seen from the above table that the residual alkali content of the oxide solid electrolyte treated by the method of the present application is significantly reduced, thereby improving the ionic conductivity of the powder and reducing the electrical conductivity. The examples confirm that the method of the present application is suitable for oxide solid electrolytes.

[0066] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A low residual alkali oxide solid electrolyte, It is characterized in that The raw materials of the low residual alkali oxide solid electrolyte include oxide electrolyte and fluorine-containing polymer, and the residual alkali content on the surface of the low residual alkali oxide solid electrolyte is less than 0.3%.

2. The low residual alkali oxide solid electrolyte according to claim 1, It is characterized in that The molar fraction of residual alkali on the surface of the residual alkali oxide solid electrolyte is ≤0.12 mmol / g.

3. The low residual alkali oxide solid electrolyte according to claim 1 or 2, It is characterized in that The diffraction angle 2θ of the low residual alkali oxide solid electrolyte has peaks in the entire range of 38.35-39.15°, 44.65-45.25° and 64.95-65.55°; Preferably, the diffraction angle 2θ of the oxide solid electrolyte has peaks in the entire ranges of 38.65 to 38.95°, 44.65 to 44.95°, and 64.95 to 65.15°.

4. The low residual alkali oxide solid electrolyte according to any one of claims 1 to 3, It is characterized in that The mass ratio of the oxide electrolyte to the fluorine-containing polymer is 100:(0.01-10).

5. The low residual alkali oxide solid electrolyte according to any one of claims 1 to 4, It is characterized in that The oxide electrolyte includes any one of a perovskite electrolyte, a NASICON electrolyte, a LISICON electrolyte or a garnet electrolyte, or a combination of at least two thereof; Preferably, the perovskite electrolyte comprises Li 3x La 2 / 3-x TiO 3 ; Preferably, the perovskite electrolyte comprises Li 0.5 La 0.5 TiO 3 , Li 0.33 La 0.57 TiO 3 , Li 0.29 La 0.57 TiO 3 , Li 0.33 Ba 0.25 La 0.39 TiO 3 、(Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O 3 or Li 0.5 La 0.5 Ti 0.95 Zr 0.05 O 3 Any one or a combination of at least two of the following: Preferably, the NASICON-type electrolyte comprises Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 ; Preferably, the garnet-type electrolyte comprises Li 7 La 3 Zr 2 O 1.2 , Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 or Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Any one or a combination of at least two of the following.

6. The low residual alkali oxide solid electrolyte according to any one of claims 1 to 5, It is characterized in that The fluorine-containing polymer includes any one of polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer or polyvinyl fluoride, or a combination of at least two thereof.

7. A method for preparing the low residual alkali oxide solid electrolyte according to any one of claims 1 to 6, It is characterized in that The preparation method comprises: The fluorine-containing polymer and the oxide electrolyte are mixed to obtain a blend, and the blend is co-sintered to obtain the low residual alkali oxide solid electrolyte.

8. The preparation method according to claim 7, It is characterized in that The mixing is dry mixing.

9. The preparation method according to claim 7 or 8, It is characterized in that The co-sintering temperature is greater than the decomposition temperature of the fluorine-containing polymer; Preferably, the co-sintering temperature is less than the crystal transformation temperature of the oxide electrolyte; Preferably, the co-sintering temperature is 650-800°C; Preferably, the co-sintering time is 1.5 to 2.5 hours.

10. An application of the low residual alkali oxide solid electrolyte as claimed in any one of claims 1 to 6, It is characterized in that The low residual alkali oxide solid electrolyte is applied in the field of lithium ion batteries.

Images