Sulfide electrolyte membrane with high compaction density at room temperature, preparation method of sulfide electrolyte membrane and solid-state battery

Abstract

The invention discloses a sulfide electrolyte membrane with high compaction density at room temperature, a preparation method of the sulfide electrolyte membrane and a solid-state battery. The sulfide solid electrolyte membrane with high compaction density comprises a sulfide electrolyte, a binder A, a binder B and a lithium salt. The preparation method of the sulfide solid electrolyte membrane comprises the following steps: ball-milling and mixing a sulfide electrolyte, a binder A, a binder B, a lithium salt and an organic solvent according to a specific proportion, coating the surface of a base material with the mixture, and drying to obtain the sulfide solid electrolyte membrane. The high-molecular-weight binder A is in a solid state at room temperature and provides mechanical strength and a binding effect; and the low-molecular-weight binder B is in a liquid state at room temperature, and is used for filling gaps of the electrolyte membrane and improving the compaction density. The electrolyte membrane is prepared by using the two-phase binder, the room-temperature compaction density of the solid electrolyte membrane can be effectively improved while the self-supporting property of the electrolyte membrane is ensured, and the prepared low-porosity solid electrolyte membrane reduces the lithium dendrite penetration risk and improves the cycle stability of a solid battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid-state batteries, and particularly relates to a sulfide electrolyte film with high compaction density at room temperature, a preparation method thereof and a solid-state battery. BACKGROUND

[0002] The organic liquid electrolyte used in traditional lithium-ion batteries has the characteristics of flammability and leakage, and has safety hazards in practical application. Therefore, solid-state batteries using solid-state electrolytes are considered as the core solution in the field of new generation energy storage and electric vehicles due to their high safety and high energy density. However, the short circuit phenomenon caused by lithium dendrite penetration greatly limits the cycle life of the all-solid-state battery. This problem is exacerbated by the pre-existing microstructure defects on the surface and inside of the solid-state electrolyte film, such as cracks and voids. Therefore, it is crucial to obtain a dense solid-state electrolyte film layer that can resist dendrites.

[0003] In the solid-state electrolyte system, sulfide-based electrolytes are widely studied due to their significant ion transmissivity. Compared with the room temperature conductivity bottleneck of polymer-based electrolytes and the high Young's modulus and low fracture toughness of oxide ceramic electrolytes, sulfide materials exhibit better intrinsic ion conductivity and significantly improved room temperature plastic deformation ability, which makes them more advantageous in cold pressing and interface contact. However, in the preparation of thin sulfide solid-state electrolyte films, cracks and internal void defects are easily formed during cold pressing due to the frictional mechanical interlocking effect between particles.

[0004] At present, researchers often introduce high dielectric constant ceramic fillers or functional nanoparticles as void inhibiting components to inhibit the formation of voids in the solid-state electrolyte film during film formation. However, due to the high surface energy characteristics of nanoscale fillers, particles are prone to agglomeration through van der Waals forces, forming sub-micron secondary aggregates. This multi-level structural defect not only weakens the physical barrier effect of the filler on the pores, but also causes local ion flow distortion, which in turn accelerates the growth of lithium dendrites along the agglomerate-matrix interface, so a complex dispersion process is needed to effectively improve the uniformity of the solid-state electrolyte film.

[0005] In view of the above technical bottlenecks, it is urgent to develop a high compaction density solid-state electrolyte film with simple preparation process and easy scale-up production. SUMMARY

[0006] In view of the above problems, the present application aims to provide a solid-state electrolyte film preparation strategy with high room temperature compaction density and a full solid-state battery. On the one hand, through the synergistic effect of the dual-phase binder, the high molecular weight binder A provides a three-dimensional network skeleton, and the low molecular weight binder B penetrates between the particles through capillary action during cold pressing, reduces the friction coefficient between the electrolyte particles, and promotes the directional rearrangement and densification of the particles under stress transmission. Under the premise of maintaining high ionic conductivity of sulfide, the electrolyte film compaction density is increased to more than 92% of the theoretical density, significantly reducing the probability of lithium dendrite growth through the electrolyte film along the void. On the other hand, the ultra-thin sulfide solid-state electrolyte film is prepared by simple ball milling dispersion mixing and coating drying process, which is convenient for large-scale production of solid-state electrolyte film.

[0007] To achieve the above object, the technical scheme adopted by the present application is: The present application provides a preparation method of sulfide electrolyte film with high room temperature compaction density, comprising the following process steps: (1) Under room temperature conditions, high molecular weight solid-state polymer binder A and low molecular weight liquid-state polymer binder B are dissolved in solvents respectively by stirring and dispersing to obtain binder A glue and binder B glue; (2) Under room temperature conditions, lithium salt is dissolved in solvent by stirring and dispersing to obtain lithium salt solution; (3) The sulfide electrolyte is mixed with the binder A glue, the binder B glue, the lithium salt solution and the solvent, and the electrolyte slurry is obtained after ball milling dispersion. The electrolyte slurry is coated on a release film, and the release film is peeled off after standing and drying to obtain the sulfide electrolyte film.

[0008] Further, the high molecular weight solid-state polymer binder A in step (1) is at least one of hydrogenated nitrile rubber, nitrile rubber, styrene-ethylene-butylene-styrene block copolymer, polyvinylidene fluoride, polyacrylonitrile, and polyethylene oxide, and the high molecular weight is 10000 < Mn < 200000, and the solid-state polymer binder A is solid at room temperature.

[0009] Further, the low molecular weight liquid-state polymer binder B in step (1) is at least one of polyethylene glycol diacrylate, hydroxyl-terminated polybutadiene, carboxyl-terminated nitrile rubber, hydrogenated nitrile rubber, and polyisoprene rubber methacrylate, and the low molecular weight is 4000 < Mn < 10000, and the liquid-state polymer binder B is liquid at room temperature.

[0010] Further, the lithium salt in step (2) is at least one of lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium perchlorate, and lithium bis(trifluoromethanesulfonyl)imide.

[0011] Further, the sulfide electrolyte in step (3) is at least one of Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, Li6PS5I, Li6PS5Cl 0.25 Br 0.75 , Li 5.3 PS 4.3 ClBr 0.7 , Li2S-P2S5, Li 10 GeP2S 12 , and the particle size of the sulfide electrolyte is D50=0.5-5μm.

[0012] Further, the solvent in steps (1)-(3) is at least one of toluene, xylene, isobutyl isobutyrate, butyl butyrate, anisole, diethyl ether, n-heptane, and acetonitrile.

[0013] Further, the ball milling speed in step (3) is 300-500rpm, and the ball milling time is 5-20h.

[0014] Further, the solid content of the electrolyte slurry in step (3) is 25%-30%, the mass ratio of the sulfide electrolyte, the binder, and the lithium salt in the electrolyte film is (94-96.5):(3-5):(0.5-1), and the mass ratio of the binder A and the binder B is 1:(0.05-0.5). The lithium salt is added to improve the ionic conductivity and the electrochemical stability of the electrolyte film.

[0015] The application further provides a sulfide electrolyte film with high room temperature and high pressure density prepared by the preparation method, which comprises a sulfide electrolyte, a solid-state polymer binder A, a liquid-state polymer binder B, and a lithium salt, and the thickness of the sulfide electrolyte film is 30-60μm.

[0016] The application further provides a full solid-state lithium battery, which uses the sulfide electrolyte film prepared by the preparation method, and is packaged after the positive electrode, the electrolyte film, and the negative electrode are stacked in the order of positive electrode-electrolyte film-negative electrode and the tab is welded, and then is subjected to isostatic pressing treatment to obtain the solid-state battery.

[0017] Compared with the prior art, the technical scheme of the application has the following beneficial effects: 1、The application uses the synergistic effect of the two-phase binder, the binder A with high molecular weight and solid state characteristics provides a three-dimensional network skeleton support, guarantees the mechanical integrity and self-supporting property of the electrolyte membrane; the binder B with low molecular weight and liquid state characteristics further flows through capillary penetration during cold pressing, rapidly fills into the tiny gaps between the solid electrolyte particles, reduces the inter-particle gap and membrane surface cracks. The liquid state binder reduces the friction coefficient between the solid electrolyte particles, promotes the sliding and rearrangement of the particles under the action of cold pressing, so that the particles can be more closely packed together, thereby significantly improving the compaction density of the electrolyte membrane.

[0018] 2、The application only introduces part of the easily mixed and dispersed liquid binder in the existing binder component, thereby improving the membrane forming characteristics of the electrolyte and the packing behavior of the powder particles, and bypassing the complex route of relying on the introduction of filler components and ultra-high cold pressing pressure or high temperature hot pressing to improve the compaction density of the electrolyte membrane. The application provides a simple, mature and moderate equipment requirement electrolyte membrane preparation method which can be compacted at room temperature, and is more suitable for large-scale and economic production.

[0019] 3、The electrolyte membrane with high compaction density at room temperature provided by the application has extremely low porosity, and the low porosity structure makes it difficult for lithium dendrites to find sufficient channels for growth and expansion. In addition, the good interfacial bonding between the flowable binder B and the sulfide electrolyte, as well as the regulation effect of lithium salt on ion transport, enables lithium ions to migrate more uniformly in the electrolyte membrane, avoiding the phenomenon of lithium dendrite growth caused by excessive local lithium ion concentration, thereby effectively reducing the risk of lithium dendrite penetrating the electrolyte membrane and improving the cycle stability and safety of the solid-state battery.

[0020] In summary, the application optimizes the microstructure of the sulfide electrolyte membrane through the synergistic effect of the two-phase binder. Due to the improved compaction density of the electrolyte membrane, the ion transport path is more continuous and stable, reducing the obstacles in the ion transport process, thereby improving the ionic conductivity of the solid-state battery. At the same time, the low risk of lithium dendrite penetration ensures the structural integrity of the battery during charging and discharging, reduces the possibility of internal short circuit of the battery, prolongs the cycle life of the battery, and improves the overall performance of the solid-state battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The rate performance comparison chart of the sulfide electrolyte membrane prepared by the application for each embodiment for preparing a solid-state battery; Figure 2 The charge-discharge coulomb efficiency curve of the rate performance test of the sulfide electrolyte membrane prepared by the application for example 1 for preparing a solid-state battery; Figure 3Prepare the cycle performance of the solid-state battery at 0.5C rate for the sulfide electrolyte film prepared in Example 1 of the present application; Figure 4 Prepare the charge-discharge curves of the 1st, 3rd, 5th, 7th weeks of the solid-state battery for the sulfide electrolyte film prepared in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0023] Example 1

[0024] The solid-state hydrogenated nitrile rubber binder with a molecular weight of 100000 and the liquid carboxyl-terminated nitrile rubber with a molecular weight of 6000 were added into toluene solutions respectively, and the binder A glue and the binder B glue were obtained respectively after magnetic stirring dispersion, and the glue concentrations were both 5wt%. Lithium bis(trifluoromethylsulfonyl)imide was added into isobutyl isobutyrate solution, and the lithium salt solution was obtained after stirring dispersion, and the concentration was 5w%. A certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, the binder A glue, the binder B glue, the lithium salt solution and the toluene solvent were mixed, and the mass ratio of the sulfide electrolyte, the binder A, the binder B and the lithium salt was 94.5:4:0.5:1. The electrolyte slurry was obtained after 12h of ball milling at a speed of 500rpm, and the solid content of the slurry was 27%. The slurry was coated on a release PET film, and the PET release film was peeled off after standing and drying to obtain the sulfide electrolyte film.

[0025] Example 2

[0026] The preparation methods of the glue and the lithium salt solution were the same as those in Example 1. A certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, the binder A glue, the binder B glue, the lithium salt solution and the toluene solvent were mixed, and the mass ratio of the sulfide electrolyte, the binder A, the binder B and the lithium salt was 94.5:4.3:0.2:1. The electrolyte slurry was obtained after 12h of ball milling at a speed of 500rpm, and the solid content of the slurry was 27%. The slurry was coated on a release PET film, and the PET release film was peeled off after standing and drying to obtain the sulfide electrolyte film.

[0027] Example 3

[0028] Solid styrene-ethylene-butylene-styrene block copolymer with a molecular weight of 90000 and liquid carboxyl-terminated butylnitrile rubber with a molecular weight of 6000 were added into toluene solution respectively, and then dispersed by magnetic stirring to obtain adhesive A glue and adhesive B glue respectively, with a glue concentration of 5wt%. The lithium salt solution, electrolyte slurry and electrolyte membrane were prepared by the same method as in Example 1 to obtain a sulfide electrolyte membrane.

[0029] Comparative Example 1 Solid hydrogenated butylnitrile rubber adhesive with a molecular weight of 100000 was added into toluene solution, and then dispersed by magnetic stirring to obtain adhesive glue, with a glue concentration of 5wt%. Lithium bis(trifluoromethylsulfonyl)imide was added into isobutyl isobutyrate solution, and then stirred and dispersed to obtain lithium salt solution, with a concentration of 5w%. A certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, adhesive glue, lithium salt solution and toluene solvent were mixed, with a mass ratio of sulfide electrolyte, adhesive, lithium salt being 94.5:4.5:1, and then ball-milled at a speed of 500 rpm for 12 h to obtain electrolyte slurry, with a solid content of 27%. The slurry was coated on a release PET film, and then the PET release film was peeled off after standing and drying to obtain a sulfide electrolyte membrane.

[0030] Comparative Example 2 The adhesive glue and lithium salt solution were prepared by the same method as in Example 1, and a certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, adhesive A glue, adhesive B glue, lithium salt solution and toluene solvent were mixed, with a mass ratio of sulfide electrolyte, adhesive A, adhesive B, lithium salt being 94.5:2.25:2.25:1, and then ball-milled at a speed of 500 rpm for 12 h to obtain electrolyte slurry, with a solid content of 27%. The slurry was coated on a release PET film, and then the PET release film was peeled off after standing and drying to obtain a sulfide electrolyte membrane.

[0031] Comparative Example 3 Solid hydrogenated butylnitrile rubber adhesive with a molecular weight of 6000 was added into toluene solution, and then dispersed by magnetic stirring to obtain adhesive glue, with a glue concentration of 5wt%. The lithium salt solution, electrolyte slurry and electrolyte membrane were prepared by the same method as in Comparative Example 1 to obtain a sulfide electrolyte membrane.

[0032] Performance test and analysis: The sulfide electrolyte membranes obtained in each example and comparative example were collected respectively, and then subjected to die cutting treatment, with an electrolyte membrane area of 30 cm 2The thickness of each electrolyte film after isostatic pressing at 500 MPa was tested at room temperature using a thickness gauge, and the mass of the electrolyte film was measured to calculate the compaction density and porosity of the sulfide electrolyte film obtained in each example and comparative example, and the results are shown in Table 1: Table 1: Ion conductivity, compaction density and porosity of the sulfide electrolyte film obtained in each example and comparative example after compaction at 500 MPa

[0033] As can be seen from the above comparative data, a certain proportion of liquid small molecule binder is introduced in Examples 1-3, and the compaction density is improved compared with Comparative Example 1 which does not introduce a small molecule binder. The porosity after isostatic pressing is significantly reduced, which verifies that the introduction of a liquid binder helps to improve the compaction density of the sulfide electrolyte film at room temperature and reduce the internal voids of the electrolyte film in the full battery. Moreover, as the compaction density increases, the particles in the electrolyte film are in closer contact, and the ion conductivity of the sulfide solid electrolyte film of Examples 1-3 is improved compared with Comparative Example 1, which helps to improve the ion transmission efficiency in the full battery.

[0034] In Comparative Example 2, the same proportion of liquid binder as the solid binder is introduced, and the proportion of high molecular weight solid binder is reduced, resulting in a weakening of the network skeleton support and adhesion of the electrolyte film. After peeling off the release film, the sulfide electrolyte film is partially cracked and difficult to form a continuous film. In Comparative Example 3, only a low molecular weight liquid binder is used, and the prepared electrolyte film has insufficient mechanical strength, cannot be peeled off from the release film, and cannot form a self-supporting sulfide electrolyte film. However, through the synergistic effect of the two-phase binder components in Examples 1-3, the high molecular weight solid binder ensures good mechanical properties of the electrolyte film, and a certain amount of liquid small molecule binder is introduced to improve the room temperature compaction density of the sulfide electrolyte film.

[0035] Figure 1 and Figure 2 are comparative diagrams of the rate performance of the solid soft pack battery prepared from the sulfide electrolyte film prepared in each example of the present application, and the Coulomb efficiency curve of Example 1 under different rate charge and discharge tests. As can be seen, after introducing an appropriate amount of small molecular weight liquid binder, the compaction density of the electrolyte film is improved, enabling the solid-state battery to have a first week Coulomb efficiency close to 92% at 0.1C rate, and a subsequent stable charge and discharge cycle Coulomb efficiency of more than 99% at 1C rate. Among them, the soft pack battery prepared from the sulfide electrolyte film prepared in Example 1 has higher compaction density, higher ion transmission efficiency, and exhibits more excellent rate performance.

[0036] Figure 3The cycle performance of the solid-state soft pack battery prepared by the sulfide electrolyte film prepared in Example 1 was prepared at 0.5C rate. It can be seen that the solid-state soft pack battery prepared by using the electrolyte film prepared in Example 1 can be stably cycled at more than 99% coulombic efficiency at 0.5C rate for more than 100 weeks, and no short circuit phenomenon occurs.

[0037] Figure 4 The charge-discharge curves of the first, third, fifth, and seventh weeks of the solid-state soft pack battery prepared by the sulfide electrolyte film prepared in Comparative Example 1 were prepared. It can be seen that the soft pack battery assembled by the electrolyte film prepared without using the two-phase binder can only be cycled at 0.3C rate; when the cycle rate is increased to 0.5C (7th week), the battery occurs soft short circuit, indicating that lithium dendrites have penetrated and grown along the electrolyte gap or crack. While Example 1 can be stably cycled at 0.5C rate, it shows that the high-compactness, low-porosity electrolyte film prepared using the two-phase binder can effectively resist the growth of lithium dendrites, and improve the cycle performance and rate performance of the solid-state soft pack battery.

[0038] In summary, the present application proposes to use the synergistic effect of two-phase binder, the network skeleton structure constructed by high molecular weight solid-state binder to ensure the mechanical integrity and self-supporting ability of the electrolyte film, and the appropriate amount of low molecular weight liquid binder to fill the gap between the particles during cold pressing, reduce the formation of gaps and cracks, and reduce the friction coefficient between the particles, promote the sliding and rearrangement of the particles to densify. This strategy effectively improves the room temperature compaction density of the sulfide electrolyte film, reduces the voids in the film, optimizes the continuity and stability of the ion transport path, effectively suppresses the risk of lithium dendrite penetration, and improves the cycle stability and rate performance of the solid-state battery.

[0039] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane, characterized in that, The process includes the following steps: (1) Under room temperature conditions, high molecular weight solid polymer binder A and low molecular weight liquid polymer binder B are dissolved in solvent by stirring and dispersing to obtain binder A solution and binder B solution. (2) At room temperature, the lithium salt is dissolved in the solvent by stirring to obtain a lithium salt solution; (3) The sulfide electrolyte is mixed with binder A liquid, binder B liquid, lithium salt solution and solvent, and dispersed by ball milling to obtain electrolyte slurry. The electrolyte slurry is coated on release film, and after standing and drying, the release film is peeled off to obtain sulfide electrolyte film.

2. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The high molecular weight solid polymer binder A mentioned in step (1) is at least one of hydrogenated nitrile rubber, nitrile rubber, styrene-ethylene-butene-styrene block copolymer, polyvinylidene fluoride, polyacrylonitrile, and polyethylene oxide. The high molecular weight is 10000 < Mn < 200000. The solid polymer binder A is solid at room temperature.

3. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The low molecular weight liquid polymer binder B mentioned in step (1) is at least one of polyethylene glycol diacrylate, hydroxyl-terminated polybutadiene, carboxyl-terminated nitrile rubber, hydrogenated nitrile rubber, and polyisoprene rubber methacrylate. The low molecular weight is 5000 < Mn < 10000. The liquid polymer binder B is liquid at room temperature.

4. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The lithium salt mentioned in step (2) is at least one of lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(trifluoromethane) yellow imide, lithium hexafluorophosphate, lithium perchlorate, and lithium bis(trifluoromethane) sulfonyl imide.

5. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The sulfide electrolyte mentioned in step (3) is Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, Li6PS5I, Li6PS5Cl 0.25 Br 0.75 Li 5.3 PS 4.3 ClBr 0.7 Li₂S-P₂S₅, Li 10 GeP2S 12 At least one of them, the sulfide electrolyte has a particle size of D50 = 0.5~5μm.

6. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The solvent mentioned in steps (1) to (3) is at least one of toluene, xylene, isobutyl isobutyrate, butyl butyrate, anisole, diethyl ether, n-heptane, and acetonitrile.

7. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, In step (3), the ball milling speed is 300~500 rpm and the ball milling time is 5~20h.

8. The method for preparing a room-temperature, high-pressure, high-density sulfide electrolyte membrane according to claim 1, characterized in that, The solid content of the electrolyte slurry in step (3) is 25%~30%, and the mass ratio of sulfide electrolyte, binder and lithium salt in the electrolyte membrane is (94~96.5):(3~5):(0.5~1); the mass ratio of binder A to binder B is 1:(0.05~1).

9. The room-temperature high-pressure, high-density sulfide electrolyte membrane prepared by the preparation method according to any one of claims 1-8, characterized in that, The room temperature high pressure density sulfide electrolyte membrane comprises a sulfide electrolyte, a solid polymer binder A, a liquid polymer binder B, and a lithium salt; the thickness of the room temperature high pressure density sulfide electrolyte membrane is 30~60μm.

10. A solid-state lithium battery, comprising a positive electrode, a negative electrode, and a room-temperature high-density sulfide electrolyte membrane prepared by the method described in any one of claims 1-8, wherein the positive electrode, negative electrode, and electrolyte membrane are stacked in the order of positive electrode-electrolyte membrane-negative electrode and then welded with tabs and encapsulated, and after completion, isostatic pressing is performed to obtain the solid-state battery.

Images