Positive electrode electrolyte membrane slurry, positive electrode electrolyte membrane, preparation method of positive electrode electrolyte membrane and sulfide all-solid-state battery

Abstract

The invention provides positive electrode electrolyte membrane slurry, a positive electrode electrolyte membrane, a preparation method of the positive electrode electrolyte membrane and a sulfide all-solid-state battery, and relates to the technical field of sulfide all-solid-state batteries. The positive electrode film slurry comprises slurry I, slurry II and an emulsifier; the slurry I contains a binder, a conductive agent and a polar organic solvent; the slurry II contains an electrolyte, an active substance and a non-polar organic solvent; the electrolyte is sulfide electrolyte; the active substance is at least one selected from the group consisting of iFePO4, LiCoO2, NCM, NCA and LiMn2O4; the emulsifier is selected from one or more of sorbitol ester glyceride, fatty acid ester, polyoxyethylene ether, a block copolymer emulsifier and an anionic emulsifier. By improving the preparation method of the positive electrode membrane, the reaction activity of the positive electrode membrane is reduced, and the cohesiveness is improved.

Description

Technical Field

[0001] This invention relates to the field of sulfide all-solid-state battery technology, and particularly to positive electrode electrolyte membrane slurry, positive electrode electrolyte membrane and its preparation method, and sulfide all-solid-state battery. Background Technology

[0002] All-solid-state sulfide batteries (ASSBs) are highly favored in the energy storage field due to their excellent safety and high energy density. In solution processing, the appropriate combination of solvent and binder has a significant impact on battery performance. An ideal solvent is highly compatible with the sulfide solid electrolyte (SE), preventing its degradation and ensuring the inherent properties of the electrolyte; a suitable binder enhances the stability of the electrode structure, ensures close contact between the active materials and the electrolyte, and improves the battery's cycle performance and processability.

[0003] However, sulfide all-solid-state batteries face a significant challenge in solution processing: the synergistic effect between solvents and binders. On one hand, the easy degradation of sulfide (SE) in polar solvents necessitates the use of non-polar solvents, severely limiting the choice of binders. On the other hand, low-polarity binders soluble in non-polar solvents exhibit weak interactions with the active material and sulfide SE, making it difficult to maintain good solid-state contact and impacting battery performance. These problems severely hinder the commercialization of sulfide-based all-solid-state batteries through scalable solution processing, thus urgently requiring an innovative approach to overcome this technological bottleneck. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for preparing a positive electrode film with low reactivity and high adhesion. By improving the preparation method of the positive electrode film, the reactivity of the positive electrode film is reduced and the adhesion is improved.

[0005] In a first aspect, the present invention provides a positive electrode electrolyte membrane slurry, the positive electrode membrane slurry comprising slurry I, slurry II, and an emulsifier; slurry I is a polar phase containing a binder, a conductive agent, and a polar organic solvent, utilizing the solubility characteristics of the polar organic solvent to achieve efficient dispersion of the binder, and various suitable combinations of polar organic solvent and binder can be configured to expand the applicable scenarios of the system; slurry II is a non-polar phase containing an electrolyte, an active substance, and a non-polar organic solvent, utilizing the compatibility of the non-polar organic solvent with the sulfide electrolyte to effectively reduce the structural instability problem caused by the sulfide electrolyte contacting the polar system; the emulsifier includes, but is not limited to, one or more of the following: sorbitol esters, glycerol esters, fatty acid esters, polyoxyethylene ethers, block copolymer emulsifiers, and anionic emulsifiers; the electrolyte is a sulfide electrolyte; the active substance is at least one selected from LiFePO4, LiCoO2, NCM, NCA, and LiMn2O4.

[0006] In a preferred embodiment, the mass ratio of the adhesive, conductive agent, and polar organic solvent is 1 : (0.1-0.5) : (8-20); In a preferred embodiment, the mass ratio of the electrolyte, the active substance, and the nonpolar organic solvent is 1:(1-4):(1-8). In a preferred embodiment, the mass ratio of the emulsifier to slurry I and slurry II is 1:(50-150):(20-80).

[0007] In a preferred embodiment, the sulfide electrolyte is selected from at least one of LGPS (lithium germanium phosphorus sulfide), LPSC (lithium phosphorus sulfide chloride), and LPSI (lithium phosphorus sulfide iodide).

[0008] In a preferred embodiment, the polar organic solvent is selected from at least one of NMP (N-methylpyrrolidone), DMF (N,N-dimethylformamide), DMSO (dimethyl sulfoxide), acetone, THF (tetrahydrofuran), ethyl acetate, dichloromethane, and isopropanol.

[0009] In a preferred embodiment, the nonpolar organic solvent includes, but is not limited to, one or more of toluene, xylene, cyclohexane, and n-hexane.

[0010] In a preferred embodiment, the adhesive is selected from at least one of PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), SBR (styrene-butadiene rubber), CMC (sodium carboxymethyl cellulose), PAA (polyacrylic acid), and PVA (polyvinyl alcohol).

[0011] In a preferred embodiment, the conductive agent includes, but is not limited to, one or more of the following: Super P, acetylene black, carbon nanotubes (CNTs), graphene, and carbon fiber.

[0012] In a preferred embodiment, the active substance is one or two of LiFePO4, LiCoO2, NCM, NCA, and LiMn2O4.

[0013] Secondly, the present invention provides a method for preparing a positive electrode film with low reactivity and high adhesion, comprising the following steps: S1. Mix the binder, conductive agent and polar organic solvent evenly to obtain a mixed slurry I; S2. Mix the electrolyte, active material and non-polar organic solvent evenly to obtain a mixed slurry II; S3. Mix slurry II and emulsifier III into slurry I to obtain positive electrode electrolyte membrane slurry; S4. The positive electrode electrolyte membrane slurry is coated onto aluminum foil by casting or spraying, and then dried and hot-pressed to obtain the positive electrode electrolyte membrane.

[0014] The conditions for mixing I, mixing II, and mixing III are each independently selected from one or more of the following: ball milling dispersion, stirring dispersion, acoustic resonance dispersion, and vibration dispersion; the mixing and dispersion time is 0.5 to 3 hours.

[0015] The drying conditions include: the preferred drying method is baking, the drying temperature is 30-60℃, and the drying time is 20-80h.

[0016] The hot pressing conditions include: the hot pressing method is flat plate hot pressing, the hot pressing pressure is 0.1-5 MPa, the hot pressing temperature is 150-200°C, and the hot pressing time is 2-10 min.

[0017] The positive electrode film provided by this invention has the following technical effects: (1) Enhanced mechanical properties: By adding surfactants and fine two-phase (polar phase and non-polar phase) composite steps, the elastic modulus and tensile strength of the positive electrode film are greatly improved, the structural stability is enhanced, and the risk of cracking and deformation during use is reduced.

[0018] (2) Optimize interface characteristics: improve the interfacial compatibility of various components in the membrane, effectively reduce interfacial impedance, reduce charge transport energy loss, and improve the kinetic efficiency of the positive electrode reaction.

[0019] (3) Ensure cycle stability: While optimizing mechanical and interface performance, rationally control the positive electrode reaction activity to ensure high capacity retention rate, extend battery life and energy output stability. Attached Figure Description

[0020] Figure 1 Interface impedance curve. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0022] The instruments and materials used in the embodiments and comparative examples of this invention are described below.

[0023] Example 1: Preparation of a positive electrode electrolyte membrane with low reactivity and high adhesion. S1: Under argon protection, polyvinylidene fluoride (PVDF, 8 mg) was added to methyl isobutyl ketone (MIBK, 100 mg), and the mixture was kept at a constant temperature of 65℃±2℃. After mechanical stirring at 350 rpm for about 20 min, the stirring speed was increased to 800 rpm±50 rpm, and conductive carbon black (Super P, 2 mg) was added in 3 batches. The mixture was stirred for another 30 min until a uniform black colloid was formed, thus obtaining the polar phase.

[0024] S2: Mix toluene (60mg) and Li6PS5Cl (15mg), first stir at a low speed of 200rpm for 20 minutes to premix Li6PS5Cl, then increase to 700rpm±30rpm and add LiFePO4 (25mg), continue stirring for 40 minutes to obtain a nonpolar phase.

[0025] S3: Place the polar phase (140 mg) in a high-speed shear emulsifier (1300 rpm ± 100 rpm), and inject the non-polar phase (60 mg) at a rate of 1.2 mL / min using a precision metering pump. When the non-polar phase injection volume reaches 30 mL, simultaneously add Span-80 and Tween-80 (mass ratio 1:1, total addition 1.4 mg). After the addition is complete, increase the speed to 2000 rpm ± 150 rpm and continue for 55 minutes to obtain a micron-sized dispersion slurry.

[0026] S4: Pour the prepared slurry onto aluminum foil, use a scraper to smooth it out, place it in a vacuum drying oven at 30-60℃ for 48 hours, and then hot press it on a flat plate at 130℃, 5MPa for 3 minutes to obtain the positive electrode film.

[0027] Example 2: Preparation of a positive electrode electrolyte membrane with low reactivity and high adhesion. S1: Under argon protection, polyvinylidene fluoride (PVDF, 8 mg) was added to methyl isobutyl ketone (MIBK, 100 mg), and the mixture was kept at a constant temperature of 65℃±2℃. After mechanical stirring at 350 rpm for about 20 min, the stirring speed was increased to 800 rpm±50 rpm, and conductive carbon black (Super P, 2 mg) was added in 3 batches. The mixture was stirred for another 30 min until a uniform black colloid was formed, thus obtaining the polar phase.

[0028] S2: Mix toluene (60mg) and Li6PS5Cl (15mg), first stir at a low speed of 200rpm for 20 minutes to premix Li6PS5Cl, then increase to 700rpm±30rpm and add LiFePO4 (25mg), continue stirring for 40 minutes to obtain a nonpolar phase.

[0029] S3: Place the polar phase (140 mg) in a high-speed shear emulsifier (1300 rpm ± 100 rpm) and inject the non-polar phase (60 g) at a rate of 1.2 mL / min using a precision metering pump. When the non-polar phase injection volume reaches 30 mL, simultaneously add Span-80 and Tween-80 (mass ratio 1:1, total addition 1.0 mg). After the addition is complete, increase the speed to 2000 rpm ± 150 rpm and continue for 55 minutes to obtain a micron-sized dispersion slurry.

[0030] S4: Pour the prepared slurry onto aluminum foil, use a scraper to smooth it out, place it in a vacuum drying oven at 30-60℃ for 48 hours, and then hot press it on a flat plate at 130℃, 5MPa for 3 minutes to obtain the positive electrode film.

[0031] Comparative Example 1: No Two-Phase Composite S1: Under argon protection, polyvinylidene fluoride (PVDF, 8 mg) was added to methyl isobutyl ketone (MIBK, 100 mg), and the mixture was kept at a constant temperature of 65℃±2℃. After mechanical stirring at 350 rpm for about 20 minutes, the stirring speed was increased to 800 rpm±50 rpm. Conductive carbon black (Super P, 2 mg) was added in 3 batches, and stirring was continued for 30 minutes until a uniform black colloid was formed.

[0032] S2: Increase the rotation speed to 700rpm±30rpm, add Li6PS5Cl (15mg) and LiFePO4 (25mg), and stir continuously for 40 minutes to form a homogeneous slurry.

[0033] S3: Pour the prepared slurry onto aluminum foil, use a scraper to smooth it out, place it in a vacuum drying oven at 30-60℃ for 48 hours, and then hot press it on a flat plate at 130℃, 5MPa for 3 minutes to obtain the positive electrode film.

[0034] Comparative Example 2: No Two-Phase Composite S1: Mix toluene (160mg) and polyvinylidene fluoride (PVDF, 8mg), first premix by stirring at low speed of 200rpm for 20 minutes, keep the temperature constant at 65℃±2℃, and then mechanically stir at 350rpm for about 20 minutes. Then increase the speed to 800rpm±50rpm, add conductive carbon black (Super P, 2mg) in 3 batches, and continue stirring for 30 minutes.

[0035] S2: Increase the rotation speed to 700rpm±30rpm, add Li6PS5Cl (15mg) and LiFePO4 (25mg), and stir continuously for 40 minutes to form a homogeneous slurry.

[0036] S3: Pour the prepared slurry onto aluminum foil, use a scraper to smooth it out, place it in a vacuum drying oven at 30-60℃ for 48 hours, and then hot press it on a flat plate at 130℃, 5MPa for 3 minutes to obtain the positive electrode film.

[0037] Test Example 1: Methods for Testing Elastic Modulus (GPa) and Tensile Strength (MPa) Test samples: The positive electrode films prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were cut into rectangular samples with a length of 80 mm and a width of 10 mm. The thickness was measured with a micrometer (the average value of 5 different points was taken).

[0038] Test conditions: A universal testing machine was used, with a tensile rate of 5 mm / min, an ambient temperature of 25℃, and a relative humidity of 45%. The stress-strain curve was recorded, and the elastic modulus (GPa) was calculated from the slope of the linear phase of the curve. The tensile strength (MPa) was calculated from the ratio of the maximum load at fracture to the initial cross-sectional area. Five sets of tests were conducted on each sample, and the average value was taken.

[0039] Test Example 2: Test Method for Interface Impedance (Ω) Test samples: The positive electrode films prepared in Examples 1, 2, Comparative Example 1, and Comparative Example 2 were assembled with Li6PS5Cl lithium metal negative electrodes to form coin cells (CR2032 type). The assembly process was completed in an argon atmosphere glove box (water and oxygen content <0.1ppm).

[0040] Test conditions: An electrochemical workstation was used, and the test was performed using electrochemical impedance spectroscopy (EIS). The frequency range was set to 10. 5 Hz~10 - 2Hz, AC disturbance voltage of 5mV; test environment temperature of 25℃, record Nyquist plot, calculate interface impedance (Ω) by equivalent circuit fitting; 3 sets of tests for each sample, and take the average value.

[0041] Test Example 3: Test Method for Capacity Retention (After 100 Cycles) Test sample: coin cell structure with the same interfacial impedance test.

[0042] Test conditions: A battery testing system was used, with the charge / discharge voltage range set (adjusted according to the all-solid-state battery system, such as 2.5~4.2V), and the charge / discharge rate set to 0.5C. 100 charge / discharge cycles were performed at 25℃, recording the first discharge capacity (initial capacity) and the 100th discharge capacity. The capacity retention rate was calculated using the formula: (100th discharge capacity / First discharge capacity × 100%). Three sets of tests were performed for each sample, and the average value was taken.

[0043] Table 1 shows the test results of the positive electrode films prepared in each embodiment and comparative example:

[0044] Through Table 1 and Figure 1 The test results show that, compared with Comparative Examples 1 and 2, Examples 1 and 2 of the present invention exhibit significant advantages in high adhesion-related indicators (elastic modulus, tensile strength) and low reactivity-related indicators (interfacial impedance, capacity retention), which fully meet the core invention goal of "a composite cathode with low reactivity and high adhesion".

[0045] Comparative Example 1 uses a polar solvent, which has insufficient interfacial compatibility with the sulfide electrolyte. This directly weakens the effective bonding effect of the binder in the composite positive electrode film. The decrease in adhesion leads to a weakening of the mechanical connection strength between the active particles, conductive agent, and current collector, which macroscopically manifests as a significant reduction in the elastic modulus and tensile strength of the electrolyte film. During battery cycling, this poor mechanical integrity cannot maintain a stable electrode structure, resulting in interfacial contact failure, increased impedance, and ultimately, a capacity retention rate far lower than that of Examples 1 and 2.

[0046] Comparative Example 2 used a non-polar solvent, but this solvent had poor solubility for the binder, resulting in insufficient dispersion and uniform film formation of the binder. This significantly weakened the bonding network inside the composite cathode, macroscopically manifested as a marked decrease in the elastic modulus and tensile strength of the electrolyte membrane. Poor bonding further exacerbated contact losses inside the electrode and increased the solid-solid interface impedance, ultimately leading to its overall electrochemical performance being far inferior to that of Examples 1 and 2 after solvent optimization.

[0047] The core of Examples 1 and 2 lies in employing a two-phase mixing strategy of polar and non-polar phases. This process fundamentally reduces the reactivity of the cathode material, effectively suppressing side reactions and lowering interfacial impedance. Simultaneously, the addition of surfactants significantly optimizes the interfacial compatibility and dispersibility within the electrode, thereby constructing a robust structure with high adhesion, resulting in a significant improvement in elastic modulus and tensile strength. Through this synergistic effect, the battery achieves excellent mechanical properties and interfacial stability while maintaining high capacity retention.

[0048] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0049] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A positive electrode electrolyte membrane slurry, characterized in that, The positive electrode film slurry includes slurry I, slurry II, and an emulsifier; The slurry I contains a binder, a conductive agent, and a polar organic solvent; The slurry II contains an electrolyte, an active substance, and a nonpolar organic solvent; the electrolyte is a sulfide electrolyte; the active substance is at least one selected from LiFePO4, LiCoO2, NCM, NCA, and LiMn2O4. The emulsifier is selected from one or more of sorbitan glycerides, fatty acid esters, polyoxyethylene ethers, block copolymer emulsifiers, and anionic emulsifiers.

2. The positive electrode electrolyte slurry according to claim 1, characterized in that, The mass ratio of the binder, conductive agent, and polar organic solvent is 1 : (0.1-0.5) : (8-20); And / or, the mass ratio of the electrolyte, active substance, and nonpolar organic solvent is 1 : (1-4) : (1-8). And / or, the mass ratio of the emulsifier to slurry I and slurry II is 1:(50-150):(20-80).

3. The positive electrode electrolyte membrane slurry according to claim 1, characterized in that, The sulfide electrolyte is selected from at least one of LGPS, LPSC, and LPSI. And / or, the adhesive is selected from at least one of PVDF, PTFE, SBR, CMC, PAA, and PVA.

4. The positive electrode electrolyte membrane slurry according to claim 1, characterized in that, The conductive agent is selected from at least one of Super P, acetylene black, carbon nanotubes, graphene, and carbon fiber.

5. The positive electrode electrolyte membrane slurry according to claim 1, characterized in that, The polar organic solvent is selected from at least one of NMP, DMF, DMSO, acetone, THF, ethyl acetate, dichloromethane, and isopropanol; And / or, the nonpolar organic solvent is selected from one or more of toluene, xylene, cyclohexane, and n-hexane.

6. A method for preparing a positive electrode electrolyte membrane, characterized in that, Including the following steps: S1. Mix the binder, conductive agent and polar organic solvent to obtain slurry I; S2. Mix the electrolyte, active material and non-polar organic solvent to obtain slurry II; S3. Mix slurry II, emulsifier and slurry I together to obtain positive electrode film slurry; S4. The positive electrode slurry is coated onto aluminum foil by casting or spraying, and then dried and hot-pressed to obtain the positive electrode electrolyte membrane.

7. The method for preparing the positive electrode electrolyte membrane according to claim 6, characterized in that, The conditions for mixing I, mixing II, and mixing III are each independently selected from one or more of ball milling, stirring, acoustic resonance, and vibration; the mixing time is 0.5 to 3 hours. The drying conditions include: the preferred drying method is baking, the drying temperature is 30-60℃, and the drying time is 20-80 hours; The hot pressing conditions include: the hot pressing method is flat plate hot pressing, the hot pressing pressure is 0.1-5 MPa, the hot pressing temperature is 150-200°C, and the hot pressing time is 2-10 min.

8. A positive electrode electrolyte membrane prepared from the positive electrode electrolyte membrane slurry according to any one of claims 1-5 or prepared by the method according to claim 6 or 7.

9. The positive electrode electrolyte membrane according to claim 8, characterized in that, The elastic modulus of the positive electrode electrolyte membrane is 0.1 GPa to 1 GPa. The tensile strength of the positive electrode electrolyte membrane is 1 MPa to 35 MPa.

10. A sulfide all-solid-state battery, comprising the positive electrode electrolyte membrane as described in claim 8 or 9.

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