A sulfide electrolyte film with high room-temperature high-density and a preparation method thereof and a solid-state battery

Abstract

The application discloses a sulfide electrolyte film with high compactness at room temperature, a preparation method thereof and a solid-state battery. The sulfide solid-state electrolyte film with high compactness comprises a sulfide electrolyte, a binder A, a binder B and a lithium salt. The preparation method of the sulfide solid-state electrolyte film comprises the following steps: ball-milling the sulfide electrolyte, the binder A, the binder B, the lithium salt and an organic solvent according to specific proportions, coating on the surface of a substrate and drying to obtain the sulfide solid-state electrolyte film. The binder A with high molecular weight is in a solid state at room temperature, and provides mechanical strength and a binding effect; the binder B with low molecular weight is in a liquid state at room temperature, fills the gaps of the electrolyte film and improves the compactness. The electrolyte film is prepared by using the dual-phase binder, the room-temperature compactness of the solid-state electrolyte film can be effectively improved while the self-supporting property of the electrolyte film is ensured, the prepared solid-state electrolyte film with low porosity reduces the risk of lithium dendrite penetration, and the cycle stability of the solid-state battery is improved.

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 during cold pressing through capillary action, 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 along the gap and penetrating the electrolyte film. 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:

[0008] The present application provides a preparation method of sulfide electrolyte film with high room temperature compaction density, which comprises the following process steps:

[0009] (1) Under room temperature conditions, high molecular weight solid-state polymer binder A and low molecular weight liquid polymer binder B are dissolved in solvents respectively by stirring and dispersing to obtain binder A glue and binder B glue;

[0010] (2) Under room temperature conditions, lithium salt is dissolved in solvent by stirring and dispersing to obtain lithium salt solution;

[0011] (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 and dispersion. The electrolyte slurry is coated on the release film, and the release film is peeled off after standing and drying to obtain the sulfide electrolyte film.

[0012] 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, the high molecular weight is 10000 < Mn < 200000, and the solid-state polymer binder A is solid at room temperature.

[0013] Further, the low molecular weight liquid 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, the low molecular weight is 4000 < Mn < 10000, and the liquid polymer binder B is liquid at room temperature.

[0014] 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, lithium bis(trifluoromethanesulfonyl)imide.

[0015] 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=0.5-5 μm.

[0016] 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.

[0017] Further, the rotation speed of the ball mill in step (3) is 300-500 rpm, and the ball milling time is 5-20 h.

[0018] Further, the solid content of the electrolyte slurry in step (3) is 25%-30%, and 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); 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.

[0019] The application further provides a sulfide electrolyte film with high room-temperature packing 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 30-60 μm.

[0020] 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.

[0021] Compared with the prior art, the technical scheme of the application has the following beneficial effects:

[0022] 1. This invention utilizes a synergistic effect of two-phase binders. High-molecular-weight, solid-state binder A provides a three-dimensional network framework, ensuring the mechanical integrity and self-support of the electrolyte membrane. Low-molecular-weight, liquid-state binder B further flows through capillary action during cold pressing, rapidly filling the tiny gaps between solid electrolyte particles, reducing interparticle voids and membrane surface cracks. Furthermore, the liquid binder lowers the coefficient of friction between solid electrolyte particles, promoting particle sliding and rearrangement under cold pressing, allowing the particles to pack more tightly together, thereby significantly improving the compaction density of the electrolyte membrane.

[0023] 2. This invention introduces only a portion of easily mixable and dispersible liquid binder into the existing binder components, thereby improving the film-forming properties of the electrolyte and the packing behavior of the powder particles, bypassing the complex route of relying on the introduction of filler components and ultra-high cold pressing pressure or high-temperature hot pressing to increase the compaction density of the electrolyte membrane. This invention provides a simple, mature process with moderate equipment requirements for preparing electrolyte membranes that can be compacted at room temperature, making it easier to achieve large-scale and economical production.

[0024] 3. The electrolyte membrane with high solid density proposed in this invention has extremely low porosity at room temperature. This low porosity structure makes it difficult for lithium dendrites to find sufficient channels for growth and expansion. Furthermore, the good interfacial bonding between the fluid binder B and the sulfide electrolyte, along with the regulatory effect of the lithium salt on ion transport, allows lithium ions to migrate more uniformly within the electrolyte membrane. This avoids lithium dendrite growth caused by excessively high local lithium ion concentrations, effectively reducing the risk of lithium dendrites penetrating the electrolyte membrane and improving the cycle stability and safety of the solid-state battery.

[0025] In summary, this invention optimizes the microstructure of the sulfide electrolyte membrane through the synergistic effect of the biphase binder. The increased compaction density of the electrolyte membrane leads to a more continuous and stable ion transport path, reducing obstacles during ion transport and thus improving the ionic conductivity of the solid-state battery. Simultaneously, the low risk of lithium dendrite penetration ensures the structural integrity of the battery during charge and discharge, reduces the possibility of internal short circuits, extends the battery's cycle life, and enhances the overall performance of the solid-state battery. Attached Figure Description

[0026] Figure 1 A comparison chart of the rate performance of solid-state batteries prepared from sulfide electrolyte membranes obtained in various embodiments of the present invention;

[0027] Figure 2 The charge-discharge coulombic efficiency curves of the solid-state battery prepared by the sulfide electrolyte membrane in Example 1 of this invention are used for rate performance testing.

[0028] 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;

[0029] 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

[0030] 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 of ordinary skill in the art without creative labor fall within the scope of the present application.

[0031] Example 1

[0032] A solid-state hydrogenated nitrile rubber binder with a molecular weight of 100000 and a liquid carboxyl-terminated nitrile rubber with a molecular weight of 6000 were added to toluene solutions, respectively, and after magnetic stirring and dispersion, binder A glue and binder B glue were obtained, and the glue concentrations were both 5wt%. Lithium bis(trifluoromethylsulfonyl)imide was added to isobutyl isobutyrate solution, stirred and dispersed to obtain a lithium salt solution with a concentration of 5w%. A certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, binder A glue, binder B glue, lithium salt solution and toluene solvent were mixed, and the mass ratio of the sulfide electrolyte, binder A, binder B and lithium salt was 94.5:4:0.5:1. An electrolyte slurry was obtained by ball milling at a speed of 500 rpm for 12 h, and the solid content of the slurry was 27%. The slurry was coated on a release PET film, and after standing and drying, the PET release film was peeled off to obtain a sulfide electrolyte film.

[0033] Example 2

[0034] The preparation methods of the glue and the lithium salt solution were the same as in Example 1. A certain amount of Li 5.5 PS 4.5 Cl 1.5 The sulfide electrolyte, binder A glue, binder B glue, lithium salt solution and toluene solvent were mixed, and the mass ratio of the sulfide electrolyte, binder A, binder B and lithium salt was 94.5:4.3:0.2:1. An electrolyte slurry was obtained by ball milling at a speed of 500 rpm for 12 h, and the solid content of the slurry was 27%. The slurry was coated on a release PET film, and after standing and drying, the PET release film was peeled off to obtain a sulfide electrolyte film.

[0035] Example 3

[0036] Solid styrene-ethylene-butene-styrene block copolymer with a molecular weight of 90,000 and liquid carboxyl-terminated nitrile butadiene rubber with a molecular weight of 6,000 were added to toluene solution, respectively. After magnetic stirring and dispersion, binder A solution and binder B solution were obtained, with a solution concentration of 5 wt% for both. The preparation methods of lithium salt solution, electrolyte slurry and electrolyte membrane were the same as in Example 1, resulting in a sulfide electrolyte membrane.

[0037] Comparative Example 1

[0038] A solid hydrogenated nitrile butadiene rubber adhesive with a molecular weight of 100,000 was added to a toluene solution and dispersed by magnetic stirring to obtain an adhesive solution with a concentration of 5 wt%. Lithium bis(trifluoromethanesulfonyl)imide was added to an isobutyl isobutyrate solution and dispersed by stirring to obtain a lithium salt solution with a concentration of 5 wt%. Certain amounts of Lithium bis(trifluoromethanesulfonyl)imide with a D50 of 2 μm were then taken... 5.5 PS 4.5 Cl 1.5 A mixture of sulfide electrolyte, binder solution, lithium salt solution and toluene solvent is prepared, wherein the mass ratio of sulfide electrolyte, binder and lithium salt is 94.5:4.5:1. The mixture is ball-milled at 500 rpm for 12 hours to obtain an electrolyte slurry with a solid content of 27%. The slurry is coated onto a release PET film, allowed to stand and dry, and then the PET release film is peeled off to obtain a sulfide electrolyte film.

[0039] Comparative Example 2

[0040] The preparation methods for the adhesive solution and lithium salt solution are the same as in Example 1. A certain amount of Li₂ with a D50 of 2 μm is taken respectively. 5.5 PS 4.5 Cl 1.5 A mixture of sulfide electrolyte, binder A solution, binder B solution, lithium salt solution, and toluene solvent was prepared, wherein the mass ratio of sulfide electrolyte, binder A, binder B, and lithium salt was 94.5:2.25:2.25:1. The mixture was ball-milled at 500 rpm for 12 hours to obtain an electrolyte slurry with a solid content of 27%. The slurry was coated onto a release PET film, allowed to stand and dry, and then the PET release film was peeled off to obtain a sulfide electrolyte film.

[0041] Comparative Example 3

[0042] A solid hydrogenated nitrile butadiene rubber binder with a molecular weight of 6000 was added to a toluene solution and dispersed by magnetic stirring to obtain a binder solution with a concentration of 5 wt%. The lithium salt solution, electrolyte slurry, and electrolyte membrane were prepared using the same methods as in Comparative Example 1 to obtain a sulfide electrolyte membrane.

[0043] Performance testing and analysis:

[0044] Compaction density and porosity test: collect the sulfide electrolyte films obtained in each example and comparative example, after die cutting treatment, the area of the electrolyte film is 30 cm 2 After isostatic pressing of each electrolyte film at room temperature under 500 MPa, the thickness of the isostatic pressed electrolyte film is tested using a thickness gauge, and the mass of the electrolyte film is weighed, and the compaction density and porosity of the sulfide electrolyte film obtained in each example and comparative example are calculated, and the results are shown in Table 1:

[0045] Table 1: Ion conductivity, compaction density and porosity of the sulfide electrolyte film after compaction under 500 MPa in each example and comparative example

[0046]

[0047] From the above comparative data, it can be seen that a certain proportion of liquid small molecule binder is introduced in Examples 1-3, and compared with Comparative Example 1 without introducing a small molecule liquid binder, the compaction density is improved, and 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. And with the increase of the compaction density, the internal particle contact of the electrolyte film is more closely, and compared with Comparative Example 1, the ion conductivity of the sulfide solid electrolyte film of Examples 1-3 is improved, which helps to improve the ion transmission efficiency in the full battery.

[0048] 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, and after peeling off the release film, the sulfide electrolyte film appears to be 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 peel off the release film, and fails to form a self-supporting sulfide electrolyte film. While Examples 1-3 use the synergistic effect of two-phase binder components, the introduction of a certain amount of liquid small molecule binder improves the room temperature compaction density of the sulfide electrolyte film while ensuring good mechanical properties of the electrolyte film with high molecular weight solid binder.

[0049] Figure 1 and Figure 2The rate performance comparison chart of the solid-state soft pack battery prepared by the sulfide electrolyte film of each embodiment of the present application, and the coulomb efficiency curve of Example 1 in different rate charge and discharge tests. It can be seen that after introducing an appropriate amount of small molecular weight liquid binder, the compaction density of the electrolyte film is improved, so that the solid-state battery can be charged and discharged at 0.1C rate near 92% coulomb efficiency in the first week, and more than 99% coulomb efficiency in subsequent stable charge and discharge cycles to 1C rate. Among them, the soft pack battery prepared by the sulfide electrolyte film prepared by Example 1 has higher compaction density, higher ion transport efficiency, and better rate performance.

[0050] Figure 3 The cycle performance of the solid-state soft pack battery prepared by the sulfide electrolyte film prepared in Example 1 of the present application at 0.5C rate. It can be seen that the solid-state soft pack battery prepared by the electrolyte film prepared by Example 1 can be stably cycled at more than 99% coulomb efficiency at 0.5C rate for more than 100 cycles, and no short circuit phenomenon occurs.

[0051] Figure 4 The charge and 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 of the present application. It can be seen that the soft pack battery assembled by the electrolyte film prepared without using 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, indicating that the high-compaction, low-porosity electrolyte film prepared using 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.

[0052] In summary, the present application proposes to use two-phase binders to work together, high molecular weight solid-state binders to construct network skeleton structure, to ensure the mechanical integrity and self-supporting ability of the electrolyte film, and an appropriate amount of low molecular weight liquid binder to fill the gap between particles during cold pressing, reduce the formation of gaps and cracks, and reduce the friction coefficient between particles, promote particle sliding and rearrangement densification. This strategy effectively improves the room temperature compaction density of the sulfide electrolyte film, reduces the gap 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.

[0053] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope 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 producing a sulfide electrolyte film with a high density at room temperature, characterized by, The method comprises the following steps: (1) dissolving the high-molecular-weight solid-state polymer binder A and the low-molecular-weight liquid-state polymer binder B in solvents respectively by stirring and dispersing at room temperature to obtain binder A glue and binder B glue; (2) dissolving lithium salt in a solvent by stirring and dispersing at room temperature to obtain a lithium salt solution; (3) mixing the sulfide electrolyte, the binder A glue, the binder B glue, the lithium salt solution and the solvent, and obtaining electrolyte slurry after ball milling and dispersing, coating the electrolyte slurry on a release film, and peeling off the release film after standing and drying to obtain a sulfide electrolyte film; 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, the high-molecular-weight is 10000 < Mn < 200000, and the solid-state polymer binder A is solid at room temperature; 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 and hydrogenated nitrile rubber, the low-molecular-weight is 5000 < Mn < 10000, and the liquid-state polymer binder B is liquid at room temperature; The solid content of the electrolyte slurry in step (3) is 25% to 30%, the mass ratio of the sulfide electrolyte, the binder and the lithium salt in the electrolyte film is (94 to 96.5):(3 to 5):(0.5 to 1), and the mass ratio of the binder A to the binder B is 1:(0.05 to 1).

2. The method of claim 1, wherein the method is characterized by: The lithium salt in step (2) is at least one of lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide.

3. The method of claim 1, wherein the method is characterized by: 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 with a sulfide electrolyte particle size of D50=0.5-5 μm.

4. The method of claim 1, wherein the sulfide electrolyte film is prepared at room temperature and high compaction density. The solvent in steps (1) to (3) is at least one of toluene, xylene, isobutyl isobutyrate, butyl butyrate, anisole, diethyl ether, n-heptane and acetonitrile.

5. The method of claim 1, wherein the method is characterized by: The ball milling speed in step (3) is 300 to 500 rpm, and the ball milling time is 5 to 20 h.

6. The sulfide electrolyte film of high packing density at room temperature prepared by the production method according to any one of claims 1 to 5, characterized in that, The room-temperature high-density sulfide electrolyte film comprises the sulfide electrolyte, the solid-state polymer binder A, the liquid-state polymer binder B and the lithium salt, and the thickness of the room-temperature high-density sulfide electrolyte film is 30 to 60 μm.

7. A full-solid-state lithium battery comprising a positive electrode, a negative electrode and a room-temperature high-density sulfide electrolyte film prepared by the method of any one of claims 1 to 5, the positive electrode, the negative electrode and the electrolyte film being laminated in the order of positive electrode-electrolyte film-negative electrode and then being welded with tabs, and the full-solid-state lithium battery being obtained after encapsulation and isostatic pressing.

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