Separator, method for preparing the same, and battery

Abstract

This application relates to a separator, a preparation method thereof, and a battery. The separator includes a base film and a porous layer located on at least one surface of the base film. The porous layer contains a polymer solid electrolyte and an oxide solid electrolyte, and the oxide solid electrolyte is dispersed in the polymer solid electrolyte in a particulate form. There are also pores distributed in the polymer solid electrolyte. On the one hand, the separator improves the difficulty of being pierced by lithium dendrites by enhancing its own mechanical strength. On the other hand, it reduces the concentration polarization inside the battery by improving the path of lithium ion transmission, thereby increasing the difficulty of lithium dendrite growth. The two cooperate with each other, making the separator not easily pierced, and thus improving the cycle life of the battery.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly relates to a separator and a preparation method thereof and a battery. Background Art

[0002] Due to the relatively high theoretical energy density, lithium metal batteries have attracted much attention in the fields of 3C consumer batteries, energy storage, and electric vehicle batteries. A lithium metal battery is a battery with lithium metal as the negative electrode. Lithium metal batteries mainly include liquid lithium metal batteries and solid lithium metal batteries. Among them, the liquid metal battery uses an electrolyte as the electrolyte. As an intermediate transition form between lithium-ion batteries and solid lithium metal batteries, it has a higher energy density than lithium-ion batteries, and the related processes are more mature than those of solid lithium metal batteries, and recently it has received extensive attention from enterprises. However, the existing liquid lithium metal batteries still have the following technical problems: in the existing liquid lithium metal batteries, the growth of lithium dendrites may cause the separator to be punctured, which may lead to short circuits in the battery and a short cycle life. Summary of the Invention

[0003] Embodiments of the present application provide a separator and a preparation method thereof and a battery to at least partially solve the above technical problems.

[0004] To achieve the above object, according to the first aspect of the present application, a separator is provided. The separator includes a base film and a porous layer located on at least one surface of the base film. The porous layer includes a polymer solid electrolyte and an oxide solid electrolyte. The oxide solid electrolyte is dispersed in the polymer solid electrolyte in a particulate form, and pores are also distributed in the polymer solid electrolyte.

[0005] Optionally, the porosity of the porous layer is 30% - 75%.

[0006] Optionally, by weight, the porous layer includes 70 - 85 parts of the polymer solid electrolyte and 5 - 25 parts of the oxide solid electrolyte.

[0007] Optionally, by weight, the porous layer further includes 2 - 5 parts of a binder and 0.05 - 2 parts of a dispersant.

[0008] Optionally, the porous layer includes 75 - 83 parts of the polymer solid electrolyte and 10 - 20 parts of the oxide solid electrolyte.

[0009] Optionally, when the porous layer further includes a binder, the binder includes at least one of polyvinyl alcohol, polyacrylate, carboxymethyl cellulose, polyvinylidene fluoride, and polyurethane.

[0010] Optionally, when the porous layer further contains a dispersant, the dispersant includes at least one of polyethylene glycol, sodium polyacrylate, polyamide, polyvinyl alcohol, calcium carbonate, and silica powder.

[0011] Optionally, the polymer solid electrolyte includes an aramid-based polymer electrolyte.

[0012] Optionally, the aramid-based polymer electrolyte includes at least one of meta-aramid electrolyte and para-aramid electrolyte.

[0013] Optionally, the oxide solid electrolyte includes at least one of lithium titanium phosphate, lithium lanthanum titanium oxide, and lithium lanthanum zirconium oxide.

[0014] Optionally, the average particle size of the oxide solid electrolyte is 0.1 μm to 1.5 μm.

[0015] Optionally, the base film includes at least one of a polypropylene base film, a polyethylene base film, and a polyimide base film.

[0016] Optionally, the thickness of the base film is 3 μm to 30 μm, and the porosity is 25% to 60%.

[0017] Optionally, the thickness of the porous layer is 0.5 μm to 5 μm.

[0018] Optionally, the separator includes a buffer layer, and the buffer layer is located on the surface of the porous layer facing away from the base film or on the surface of the base film facing away from the porous layer.

[0019] Optionally, the buffer layer includes a plurality of island-shaped elastic protrusions.

[0020] Optionally, the elastic protrusion includes at least one of polyvinylidene fluoride and polymethyl methacrylate.

[0021] Optionally, the thickness of the buffer layer is 1 μm to 5 μm.

[0022] Optionally, the coating amount of the buffer layer is 0.2 g / m 2 ~0.8 g / m 2 。

[0023] According to the second aspect of the present application, a method for preparing a separator is provided for preparing the separator as described above, and the method for preparing the separator includes:

[0024] Providing a base film;

[0025] Providing a first slurry, the first slurry includes a solvent, a pore former, a polymer solid electrolyte, and an oxide solid electrolyte, and the polymer solid electrolyte is dissolved in the solvent;

[0026] Form a film of the first slurry on at least one surface of the base film to obtain a first wet film layer;

[0027] Heat-treat the first wet film layer to volatilize the solvent and thermally decompose the pore-forming agent, thereby obtaining a porous layer and further obtaining a separator.

[0028] Optionally, by weight, the first slurry includes 160 parts to 265 parts of the solvent, 0.5 parts to 2 parts of the pore-forming agent, 70 parts to 85 parts of the polymer solid electrolyte, and 5 parts to 25 parts of the oxide solid electrolyte.

[0029] Optionally, by weight, the first slurry further includes 2 parts to 5 parts of a binder and 0.05 parts to 2 parts of a dispersant.

[0030] Optionally, the solid content of the first slurry is 25 wt% to 65 wt%.

[0031] Optionally, the pore-forming agent includes at least one of ammonium carbonate, ammonium bicarbonate, ammonium chloride, sodium carbonate, and sodium bicarbonate.

[0032] Optionally, the first slurry further includes an auxiliary salt, the auxiliary salt is dissolved in the solvent, and the auxiliary salt is used to promote the dissolution of the polymer solid electrolyte in the solvent.

[0033] Optionally, the solvent is a polar solvent, and the polar solvent includes at least one of N-methylpyrrolidone, dimethylformamide, and N,N-dimethylacetamide, dimethyl sulfoxide.

[0034] Optionally, the auxiliary salt includes at least one of lithium chloride and calcium chloride.

[0035] Optionally, the mass ratio of the auxiliary salt to the solvent is 0.015 to 0.08.

[0036] According to the third aspect of the present application, there is provided a battery including the separator as described above or a separator prepared by the method for preparing the separator as described above.

[0037] Optionally, the battery includes a lithium metal battery, the lithium metal battery includes a lithium metal negative electrode, the lithium metal negative electrode is located on one side of the separator, and in the case where the separator includes a buffer layer, the buffer layer is located between the lithium metal negative electrode and the porous layer.

[0038] Optionally, the lithium metal battery is a liquid lithium metal battery, and the separator is infiltrated with an electrolyte solution.

[0039] The separator provided by the embodiment of the present application further adds a porous layer on the basis of the base film. The combination of the porous layer and the base film can increase the mechanical strength of the separator, making it not easily pierced by lithium dendrites. Further, the porous layer includes a polymer solid electrolyte and an oxide solid electrolyte, wherein the polymer solid electrolyte serves as a base material layer, and the oxide solid electrolyte is dispersed in the polymer solid electrolyte base material layer as oxide solid electrolyte particles. In this way, the oxide solid electrolyte particles dispersed in the polymer solid electrolyte can stack with each other and form pores in the polymer solid electrolyte, and there are also holes distributed in the polymer solid electrolyte. These pores and holes can communicate with each other and form a flow channel for the electrolyte to flow through, improving the wetting effect of the separator on the electrolyte and reducing the concentration polarization inside the separator; at the same time, since both the polymer solid electrolyte and the oxide solid electrolyte are solid electrolytes containing lithium elements and can conduct ions themselves, by forming the polymer solid electrolyte and the oxide solid electrolyte into a porous layer and introducing it onto the surface of the base film, the lithium ion conductivity of the separator is further improved, and the transmission of lithium ions is improved. In this way, during the charging and discharging process of the battery, the electrolyte can first enter the inside of the separator through the flow channels inside the porous layer. If the flow channels are through channels penetrating the porous layer, the electrolyte can directly reach the base film and wet the base film, thus forming a continuous ion transmission channel; for some non-through flow channels, lithium ions can also continue to be transmitted through the polymer solid electrolyte and the oxide solid electrolyte in the porous layer, so that lithium ions can quickly pass through the separator during the charging and discharging process, reducing the concentration polarization inside the separator and the concentration polarization on the surface of the separator, and further improving the concentration polarization on the surface of the negative electrode, thereby reducing the risk of lithium dendrite precipitation.

[0040] Other features and advantages of the present application will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0042] In order to more completely understand the present application and its beneficial effects, the following will be described in conjunction with the drawings, in which the same reference numerals represent the same parts in the following description.

[0043] Figure 1 It is a schematic structural diagram of the separators provided in Embodiments 1 to 7 and Comparative Examples 1 to 3 of the present application;

[0044] Figure 2Schematic structural diagram of the separator provided in Embodiment 8 of the present application;

[0045] Figure 3 Schematic structural diagram of the separator provided in Embodiment 9 of the present application;

[0046] Figure 4 Schematic structural diagram of the separator provided in Embodiment 10 of the present application;

[0047] Figure 5 Schematic structural diagram of the separator provided in Comparative Example 4 of the present application;

[0048] Figure 6 Schematic structural diagram of the separator provided in Comparative Example 5 of the present application;

[0049] Figure 7 Schematic structural diagram of the separator provided in Comparative Example 6 of the present application.

[0050] Explanation of reference numerals:

[0051] 10 - base film, 20 - mixed coating, 201 - first mixed coating, 202 - second mixed coating, 30 - buffer layer, 301 - first buffer layer, 302 - second buffer layer. Detailed implementation manners

[0052] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application.

[0053] According to the first aspect of the present application, a separator is provided. The separator includes a base film and a porous layer located on at least one surface of the base film. The porous layer contains a polymer solid electrolyte and an oxide solid electrolyte, and the oxide solid electrolyte is dispersed in the polymer solid electrolyte in a particulate form. There are also pores distributed in the polymer solid electrolyte.

[0054] The oxide solid electrolyte is a compound composed of lithium, oxygen, and other elements (such as phosphorus, titanium, aluminum, etc.). The polymer solid electrolyte is mainly composed of a polymer matrix and a lithium salt.

[0055] The separator provided in the embodiments of the present application further adds a porous layer on the basis of the base film. The combination of the porous layer and the base film can increase the mechanical strength of the separator, making the separator not easily pierced by lithium dendrites.

[0056] Furthermore, the porous layer comprises a polymer solid electrolyte and an oxide solid electrolyte. The polymer solid electrolyte serves as a substrate layer, and the oxide solid electrolyte serves as oxide solid electrolyte particles dispersed in the polymer solid electrolyte substrate layer. In this way, the oxide solid electrolyte particles dispersed in the polymer solid electrolyte can stack with each other and form pores in the polymer solid electrolyte. There are also holes distributed in the polymer solid electrolyte. These pores and holes can be interconnected to form a flow channel for the electrolyte to flow through, improving the wetting effect of the separator on the electrolyte and reducing the concentration polarization inside the separator. At the same time, since both the polymer solid electrolyte and the oxide solid electrolyte are solid electrolytes containing lithium elements and can conduct ions themselves, by forming a porous layer with the polymer solid electrolyte and the oxide solid electrolyte and introducing it onto the surface of the base film, the lithium ion conductivity of the separator is further improved, and the transmission of lithium ions is improved. In this way, during the charge and discharge process of the battery, the electrolyte can first enter the inside of the separator through the flow channel inside the porous layer. If the flow channel is a through-channel penetrating the porous layer, the electrolyte can directly reach the base film and wet the base film, thus forming a continuous ion transmission channel. For some non-through flow channels, lithium ions can also continue to be transmitted through the polymer solid electrolyte and the oxide solid electrolyte in the porous layer, so that lithium ions can quickly pass through the separator during the charge and discharge process, reducing the concentration polarization inside the separator and the concentration polarization on the surface of the separator, and further improving the concentration polarization on the surface of the negative electrode, thereby reducing the risk of lithium dendrite precipitation.

[0057] That is, on the one hand, the separator provided by the embodiment of the present application improves the difficulty of being pierced by lithium dendrites by enhancing its own mechanical strength, and on the other hand, reduces the concentration polarization inside the battery by improving the path of lithium ion transmission, thereby increasing the difficulty of lithium dendrite growth. The two cooperate with each other, making the separator not easily pierced, and thus improving the cycle life of the battery.

[0058] In some embodiments, the porosity of the porous layer is 30% - 75%. It can be understood that the porosity of the porous layer will affect the mechanical strength of the porous layer and the wetting effect on the electrolyte. If the porosity of the porous layer is too large, the mechanical strength of the porous layer will decrease, and if the porosity of the porous layer is too small, it will make it difficult for the electrolyte to pass through the porous layer, and thus the base film is not easily wetted by the electrolyte. By controlling the porosity of the porous layer to be 30% - 75%, while making the separator have a good wetting effect on the electrolyte, the mechanical strength of the separator is improved as much as possible, and the risk of being pierced by lithium dendrites is reduced. As an example, the porosity of the porous layer is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%.

[0059] In some embodiments, by weight parts, the porous layer comprises 70 to 85 parts of polymer solid electrolyte and 5 to 25 parts of oxide solid electrolyte. It can be understood that in the porous layer, the polymer solid electrolyte serves as the base layer, and the oxide solid electrolyte is dispersed in the polymer solid electrolyte as oxide solid electrolyte particles. Although the oxide solid electrolyte has better hardness and thermal stability than the polymer solid electrolyte, and the mechanical properties and heat resistance of the separator can be improved by increasing the oxide solid electrolyte, the oxide solid electrolyte needs to be fixed and polymerized together by the polymer solid electrolyte. That is to say, the polymer solid electrolyte provides the cohesion for the formation of the porous layer, and increasing the polymer solid electrolyte can also improve the structural stability and toughness of the porous layer. Therefore, by controlling the content of the polymer solid electrolyte in the porous layer to be 70 to 85 parts and the oxide solid electrolyte to be 5 to 25 parts, not only can the porous layer have sufficient structural stability, but also the porous layer can have high mechanical strength and heat resistance. As an example, the mass parts of the polymer solid electrolyte in the porous layer are 70 parts, 72 parts, 74 parts, 76 parts, 78 parts, 80 parts, 82 parts, 84 parts or 85 parts; the mass parts of the oxide solid electrolyte in the porous layer are 5 parts, 10 parts, 15 parts, 20 parts or 25 parts.

[0060] In some embodiments, by weight parts, the porous layer comprises 75 to 83 parts of polymer solid electrolyte and 10 to 20 parts of oxide solid electrolyte. By further controlling the content of the polymer solid electrolyte and the oxide solid electrolyte in the porous layer, the mechanical properties and heat resistance of the porous layer can be further improved. As an example, the mass parts of the polymer solid electrolyte in the porous layer are 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts or 83 parts; the mass parts of the oxide solid electrolyte in the porous layer are 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts.

[0061] In some embodiments, by weight parts, the porous layer further comprises 2 to 5 parts of binder. By increasing the binder, the bonding effect between the oxide solid electrolytes and between the oxide solid electrolyte and the polymer solid electrolyte can be improved, and the mechanical strength and structural stability of the porous layer can be enhanced. As an example, the mass parts of the binder in the porous layer are 2 parts, 3 parts, 4 parts or 5 parts. As an example, the binder includes at least one of polyvinyl alcohol, polyacrylate, carboxymethyl cellulose, polyvinylidene fluoride, and polyurethane.

[0062] In some embodiments, by weight parts, the porous layer further comprises 0.05 part to 2 parts of a dispersant. The dispersant can be used to improve the dispersion effect of the oxide solid electrolyte in the polymer solid electrolyte, thereby improving the overall mechanical properties of the separator and the wetting effect on the electrolyte. As an example, the mass parts of the dispersant in the porous layer are 0.05 part, 0.1 part, 0.5 part, 1 part, 1.5 parts or 2 parts. As an example, the dispersant includes at least one of polyethylene glycol, sodium polyacrylate, polyamide, polyvinyl alcohol, calcium carbonate, and silica powder.

[0063] In some embodiments, the polymer solid electrolyte includes an aramid-based polymer electrolyte. The aramid-based polymer electrolyte refers to a solid electrolyte material composed of aramid as the polymer matrix and a lithium salt. The aramid-based polymer electrolyte has good heat resistance, thereby increasing the membrane breakage temperature of the separator and reducing the risk of fire and explosion when the battery is thermally punctured by a needle. It can be understood that when the separator is punctured by a hot needle (i.e., a needle-like structure at a relatively high temperature), usually the base film is easily melted by the temperature brought by the hot needle to generate a first perforation, and the polymer solid electrolyte in the porous layer is also melted by the temperature brought by the hot needle to generate a second perforation. The second perforation corresponds to the first perforation. In this way, the positive and negative electrodes in the battery are easily in contact through the first perforation and the second perforation, resulting in a short circuit and then triggering a battery fire or explosion. Then, due to the good heat resistance of the aramid-based polymer electrolyte, the heat resistance of the porous layer is also improved. In this way, the aperture of the formed second perforation can be controlled, and the risk of the second perforation being enlarged can be reduced. Even if the aperture of the first perforation is relatively large, but because the aperture of the second perforation is relatively small, the probability of the positive and negative electrodes being in contact through the first perforation and the second perforation can be reduced, thereby increasing the thermal puncture passing rate of the battery.

[0064] In some embodiments, the aramid-based polymer electrolyte includes at least one of meta-aramid electrolyte and para-aramid electrolyte. Both the meta-aramid electrolyte and the para-aramid electrolyte have good thermal stability, thereby increasing the thermal puncture passing rate of the battery.

[0065] In some embodiments, the oxide solid electrolyte includes at least one of lithium aluminum titanium phosphate (LATP), lithium lanthanum titanium oxide (LLTO), and lithium lanthanum zirconium oxide (LLZO). LATP is a NASICON-type solid electrolyte. As an example, the chemical formula of LATP is Li 1.5 Al 0.5 Ti 1.5 (PO4)3 or Li 1.3 Al 0.3 Ti 1.7 (PO4)3. LLTO belongs to the perovskite structure. As an example, the chemical formula of LLTO is Li 0.5 La 0.5TiO3. The crystal structure of LLZO is a garnet structure, which is mainly composed of lithium (Li), lanthanum (La), zirconium (Zr) and oxygen (O). As an example, the chemical formula of LLZO is Li7La3Zr2O 12 . LATP, LLTO and LLZO all have high ionic conductivity and good chemical stability, which is beneficial to improving the effect of the separator in transporting lithium ions.

[0066] In some embodiments, the average particle size of the oxide solid electrolyte is 0.1 μm to 1.5 μm. By controlling the average particle size of the oxide solid electrolyte, the oxide solid electrolyte can have a good dispersion effect in the polymer solid electrolyte, thereby ensuring the performance of the porous layer. Generally, if the average particle size of the oxide solid electrolyte is too large, the dispersibility of the oxide solid electrolyte will decrease, while if the average particle size of the oxide solid electrolyte is too small, the oxide solid electrolyte will agglomerate, which will also affect the dispersion effect of the oxide solid electrolyte. As an example, the average particle size of the oxide solid electrolyte is 0.1 μm, 0.5 μm, 1.0 μm, 1.2 μm, 1.4 μm or 1.5 μm.

[0067] In some embodiments, the thickness of the porous layer is 0.5 μm to 5 μm. Generally, if the thickness of the porous layer is too large, the difficulty for lithium ions to pass through the porous layer will increase, affecting the concentration polarization inside the battery, and further increasing the risk of lithium deposition in the battery. While if the thickness of the porous layer is too small, the mechanical strength of the separator will be insufficient, increasing the risk of the separator being pierced by lithium dendrites. By controlling the thickness of the porous layer, the risk of the separator being pierced by lithium dendrites in the battery can be reduced. As an example, the thickness of the porous layer is 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm or 5 μm.

[0068] In some embodiments, the base film includes at least one of a polypropylene (PP) base film, a polyethylene (PE) base film and a polyimide (PI) base film. In the separator, the performance of the base film will affect the performance of the separator. The base film is a porous thin film that allows ions to pass through and has the function of retaining the electrolyte. Here, the base film can be a single-layer structure or a multi-layer composite structure. As an example, the base film only includes one of the polypropylene base film, the polyethylene base film and the polyimide base film, or the base film includes two or three of the polypropylene base film, the polyethylene base film and the polyimide base film.

[0069] In some embodiments, the thickness of the base film is 3 μm to 30 μm, and the porosity is 25% to 60%. By controlling the thickness and porosity of the base film, the separator can have good mechanical strength and electrolyte infiltration effect. As an example, the thickness of the base film is 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm; the porosity of the base film is 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%.

[0070] In some embodiments, the diaphragm includes a buffer layer, and the buffer layer is located on the surface of the side of the porous layer away from the base membrane or on the surface of the side of the base membrane away from the porous layer. It is understood that the buffer layer can be arranged on the porous layer or directly on the base membrane, but the buffer layer is not arranged between the base membrane and the porous layer. As an example, the base membrane has a first surface and a second surface opposite to each other, the porous layer is arranged on the first surface, and the buffer layer is arranged on the second surface; or the porous layer is arranged on the first surface and the second surface of the base membrane, and the buffer layer is arranged on the porous layer and away from the base membrane; or the porous layer is arranged on the first surface, the buffer layer is arranged on the porous layer, and the second surface is exposed. In the battery, the diaphragm is usually arranged between the positive electrode and the negative electrode to isolate the positive electrode and the negative electrode. By arranging the buffer layer, when the electrode expands, the buffer layer can buffer the electrode expansion, reducing the risk of the diaphragm being punctured by lithium dendrites due to strong confrontation between lithium dendrites and the diaphragm.

[0071] In some embodiments, the buffer layer includes a plurality of island-shaped elastic protrusions. That is, a large number of island-shaped elastic protrusions grow on the surface of the porous layer or the surface of the base film and form a buffer layer. As an example, the cross-section of the island-shaped elastic protrusions is semicircular, triangular, trapezoidal or square along the thickness direction of the buffer layer. It can be understood that there are gaps between the island-shaped elastic protrusions, so that these gaps can be formed to provide growth space for the deposition of lithium dendrites, alleviate the excessive growth of lithium dendrites and cause the diaphragm to be pierced, and improve the cycle life of the battery. In addition, compared to the continuous film-like buffer layer, the buffer layer is set to be composed of a plurality of island-shaped elastic protrusions, and the island-shaped elastic protrusions have better deformation ability, which can effectively improve the buffer performance of the buffer layer. As an example, the buffer layer can be prepared by spraying, and the buffer layer formed in this way is composed of a large number of island-shaped elastic protrusions. The gaps between the island-shaped elastic protrusions can also be formed as channels for the circulation of electrolytes, which promote the infiltration of electrolytes into the diaphragms.

[0072] In some embodiments, the elastic protrusion comprises at least one of polyvinylidene fluoride and polymethyl methacrylate. That is, the material of the elastic protrusion can be polyvinylidene fluoride, polymethyl methacrylate, or polyvinylidene fluoride and polymethyl methacrylate. These materials usually have a certain degree of adhesion, and when the separator is used in a battery, the buffer layer can also be bonded to the electrode.

[0073] In some embodiments, the thickness of the buffer layer is 1 μm to 5 μm. It can be understood that when the buffer layer includes a plurality of elastic protrusions, the average height of the elastic protrusions is equal to the thickness of the buffer layer. By controlling the thickness of the buffer layer, the separator has better buffer effect and ion transport performance. As an example, the thickness of the buffer layer can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0074] In some embodiments, the coating amount of the buffer layer is 0.2 g / m 2 ~0.8 g / m 2 。As an example, the coating amount of the buffer layer can be 0.2 g / m 2 、0.3 g / m 2 、0.4 g / m 2 、0.5 g / m 2 、0.6 g / m 2 、0.7 g / m 2 or 0.8 g / m 2 。

[0075] According to the second aspect of the present application, a method for preparing a separator is provided, which is used to prepare the separator as described above. The method for preparing the separator includes:

[0076] S1. Provide a base film;

[0077] S2. Provide a first slurry, the first slurry includes a solvent, a pore former, a polymer solid electrolyte and an oxide solid electrolyte, and the polymer solid electrolyte is dissolved in the solvent;

[0078] S3. Perform a film-forming treatment on at least one surface of the base film with the first slurry to obtain a first wet film layer;

[0079] S4. Perform a heat treatment on the first wet film layer to volatilize the solvent and thermally decompose the pore former, thereby obtaining a porous layer, and then obtaining a separator.

[0080] In the method for preparing a separator provided by the embodiments of the present application, since the first slurry for preparing the first wet film layer includes a solvent, a pore former, a polymer solid electrolyte and an oxide solid electrolyte mixed together, and the polymer solid electrolyte is dissolved in the solvent, when the first wet film layer is heat-treated, the solvent volatilizes, causing the polymer solid electrolyte to precipitate, solidify and form a base material layer. During the curing process of the polymer solid electrolyte, not only the oxide solid electrolyte dispersed in the polymer solid electrolyte is cured in the polymer solid electrolyte, but also the pore former simultaneously undergoes thermal decomposition. In this way, the positions originally filled by the pore former will leave holes in the polymer solid electrolyte, so that the first wet film layer is transformed into a porous layer, and the porous layer is combined with the base film to obtain a separator.

[0081] The preparation method of the separator provided by the embodiments of the present application is not only simple, but also, on the one hand, the prepared separator has strong mechanical strength, thus increasing the difficulty for lithium dendrites to pierce it. On the other hand, the separator can also improve the path of lithium ion transmission, thereby reducing the concentration polarization inside the battery, and further increasing the difficulty of lithium dendrite growth. The two cooperate with each other, making the separator not easily pierced, and thus improving the cycle life of the battery.

[0082] In some embodiments, by weight, the first slurry includes 160 to 265 parts of a solvent, 0.5 to 2 parts of a pore former, 70 to 85 parts of a polymer solid electrolyte, and 5 to 25 parts of an oxide solid electrolyte. Within this ratio range, the polymer solid electrolyte is effectively dissolved in the solvent, while the oxide solid electrolyte and the pore former are uniformly mixed with the polymer solid electrolyte, so that in the prepared porous layer, the oxide solid electrolyte and the pores can be uniformly dispersed in the polymer solid electrolyte. As an example, in the first slurry, the mass parts of the solvent can be 160 parts, 170 parts, 180 parts, 190 parts, 200 parts, 210 parts, 220 parts, 230 parts, 240 parts, 250 parts or 265 parts, the mass parts of the pore former can be 0.5 parts, 1.0 parts, 1.5 parts or 2 parts, the mass parts of the polymer solid electrolyte can be 70 parts, 72 parts, 74 parts, 76 parts, 78 parts, 80 parts, 72 parts, 74 parts or 85 parts, and the mass parts of the oxide solid electrolyte can be 5 parts, 10 parts, 15 parts, 20 parts or 25 parts.

[0083] In some embodiments, by weight, the first slurry further includes 2 to 5 parts of a binder and 0.05 to 2 parts of a dispersant. As an example, in the first slurry, the mass parts of the binder can be 2 parts, 3 parts, 4 parts or 5 parts, and the mass parts of the dispersant can be 0.05 parts, 0.1 parts, 0.5 parts, 1.0 parts, 1.5 parts or 2 parts.

[0084] In some embodiments, the solid content of the first slurry is 25wt% to 65wt%. As an example, the solid content of the first slurry is 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt% or 65wt%. By controlling the solid content of the first slurry, the forming effect of the first wet film layer can be improved, and further the forming effect of the porous layer can be improved.

[0085] In some embodiments, the pore-forming agent includes at least one of ammonium carbonate, ammonium bicarbonate, ammonium chloride, sodium carbonate, and sodium bicarbonate. By using carbonate or ammonium salt as the pore-forming agent, these substances generally have a low thermal decomposition temperature, so that a lower temperature can be used to convert the first wet film layer into a porous layer, reducing the risk of high-temperature damage to the structures and chemical properties of the polymer solid electrolyte and the oxide solid electrolyte; in addition, these substances mainly decompose into gases after thermal decomposition, and the gases can be discharged from the porous layer, reducing the adverse effects of residual substances on the porous layer.

[0086] In some embodiments, the first slurry further includes an auxiliary salt, which is dissolved in the solvent and is used to promote the dissolution of the polymer solid electrolyte in the solvent. By adding an auxiliary salt in the solvent to promote the dissolution of the polymer solid electrolyte in the solvent, on the one hand, the amount of the solvent can be reduced, and on the other hand, the time for preparing the first slurry and the drying time of the first wet film layer can also be shortened, thereby reducing the production cost of the separator. As an example, the auxiliary salt includes at least one of lithium chloride and calcium chloride.

[0087] In some embodiments, the solvent is a polar solvent. The polar solvent can promote the rapid dissolution of the polymer solid electrolyte. Especially when the polymer solid electrolyte is an aramid-based polymer electrolyte, the polar solvent can improve the dissolution effect of the aramid-based polymer electrolyte. Optionally, the polar solvent is an organic polar solvent. As an example, the polar solvent includes at least one of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0088] In some embodiments, the mass ratio of the auxiliary salt to the solvent is 0.015 to 0.08. As an example, the mass ratio of the auxiliary salt to the solvent is 0.015, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or 0.08.

[0089] According to the third aspect of the present application, a battery is provided, including the separator as described above or the separator prepared by the method for preparing the separator as described above.

[0090] In some embodiments, the battery includes a lithium metal battery, the lithium metal battery includes a lithium metal negative electrode, the lithium metal negative electrode is located on one side of the separator, and when the separator includes a buffer layer, the buffer layer is located between the lithium metal negative electrode and the porous layer. In this case, the buffer layer can also block the lithium metal negative electrode and the porous layer, reducing the risk of direct contact between the lithium metal negative electrode and the porous layer, thereby reducing the risk of the oxide solid electrolyte in the porous layer being reduced by the lithium metal. Especially when the oxide solid electrolyte includes LATP, the risk of the tetravalent titanium in LATP being reduced to trivalent titanium by the lithium metal can be effectively reduced, thereby improving the stability of LATP and the stability of the performance of the porous layer.

[0091] In some embodiments, the lithium metal battery is a liquid lithium metal battery, and the separator is impregnated with an electrolyte. A liquid lithium metal battery refers to a battery with a lithium metal negative electrode and an electrolyte.

[0092] This will be described below in conjunction with specific embodiments.

[0093] I. Preparation of separator

[0094] Example 1

[0095] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 1.

[0096] Table 1

[0097]

[0098] In Example 1, the average particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%. It should be noted here that in this application, the calculation method of the solid content of the first slurry is: the solid content of the first slurry = (the mass of the polymer solid electrolyte + the mass of the oxide solid electrolyte + the mass of the binder + the mass of the dispersant + the mass of the pore former) / the total mass of the first slurry × 100%.

[0099] The steps for preparing the first slurry include:

[0100] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0101] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former to the polymer electrolyte solution, and stir at room temperature at a stirring rate of 4000 r / min to mix evenly to obtain the first slurry.

[0102] S2. Prepare the separator. Please refer to Figure 1 , and the preparation process of the separator includes:

[0103] S21. Provide a base film 10, and the base film 10 is a polyethylene film; the thickness of the polyethylene film is 9 μm, and the porosity is 40%;

[0104] S22. Coating the prepared first slurry on one side surface of the base film 10 by a microgravure extrusion coating process, and then baking at a temperature of 60 °C for 140 min, and cooling to form a single-layer mixed coating 20 (i.e., a porous layer) with a thickness of 3 μm on the surface of the base film 10;

[0105] S23. Coating on the surface of the mixed coating at a coating amount of 0.5 g / m 2Spray a buffer layer 30 (specifically a polyvinylidene fluoride coating), and then bake it at a temperature of 60 °C for 140 min, and cool it to obtain a separator.

[0106] Example 2

[0107] The difference between Example 2 and Example 1 lies in step S1:

[0108] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 2.

[0109] Table 2

[0110]

[0111] In Example 2, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0112] The steps for preparing the first slurry include:

[0113] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 500 r / min for 20 h to form a polymer electrolyte solution;

[0114] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former to the polymer electrolyte solution, and stir at room temperature at a stirring rate of 1000 r / min to mix evenly to obtain the first slurry.

[0115] The others are the same as in Example 1.

[0116] Example 3

[0117] The difference between Example 3 and Example 1 lies in step S1:

[0118] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 3.

[0119] Table 3

[0120]

[0121] In Example 3, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0122] The steps for preparing the first slurry include:

[0123] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 8000 r / min for 1 h to form a polymer electrolyte solution;

[0124] S12. Add an oxide solid electrolyte, a binder, a dispersant, and a pore former to the polymer electrolyte solution, stir at room temperature at a stirring rate of 8000 r / min until well mixed to obtain a first slurry.

[0125] Example 4

[0126] The difference between Example 4 and Example 1 lies in step S1:

[0127] S1. Prepare a first slurry, and the composition of the first slurry is shown in Table 4.

[0128] Table 4

[0129]

[0130] In Example 4, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0131] The steps for preparing the first slurry include:

[0132] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 6000 r / min for 5 h to form a polymer electrolyte solution;

[0133] S12. Add an oxide solid electrolyte, a binder, a dispersant, and a pore former to the polymer electrolyte solution, stir at room temperature at a stirring rate of 6000 r / min until well mixed to obtain a first slurry.

[0134] Example 5

[0135] The difference between Example 5 and Example 1 lies in step S1:

[0136] S1. Prepare a first slurry, and the composition of the first slurry is shown in Table 5.

[0137] Table 5

[0138]

[0139] In Example 5, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0140] The steps for preparing the first slurry include:

[0141] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 2000 r / min for 15 h to form a polymer electrolyte solution;

[0142] S12. Add the oxide solid electrolyte, binder, dispersant, and pore-forming agent into the polymer electrolyte solution, stir at room temperature at a stirring rate of 2000 r / min until evenly mixed to obtain the first slurry.

[0143] Example 6

[0144] The difference between Example 6 and Example 1 lies in step S1:

[0145] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 6.

[0146] Table 6

[0147]

[0148] In Example 6, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0149] The steps for preparing the first slurry include:

[0150] S11. First, add the polymer solid electrolyte into the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0151] S12. Add the oxide solid electrolyte, binder, dispersant, and pore-forming agent into the polymer electrolyte solution, stir at room temperature at a stirring rate of 4000 r / min until evenly mixed to obtain the first slurry.

[0152] Example 7

[0153] The difference between Example 7 and Example 1 lies in step S1:

[0154] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 7.

[0155] Table 7

[0156]

[0157] In Example 7, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0158] The steps for preparing the first slurry include:

[0159] S11. First, add the polymer solid electrolyte into the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0160] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former into the polymer electrolyte solution, stir at room temperature at a stirring rate of 4000 r / min until evenly mixed to obtain the first slurry.

[0161] Example 8

[0162] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 8.

[0163] Table 8

[0164]

[0165] In Example 8, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 38.1 wt%.

[0166] The steps for preparing the first slurry include:

[0167] S11. First, add the polymer solid electrolyte into the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0168] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former into the polymer electrolyte solution, stir at room temperature at a stirring rate of 4000 r / min until evenly mixed to obtain the first slurry.

[0169] S2. Prepare the separator. Please refer to Figure 2 , and the preparation process of the separator includes:

[0170] S21. Provide the base film 10, and the base film 10 is a polypropylene base film; the thickness of the polypropylene base film is 3 μm, and the porosity is 32%;

[0171] S22. Coat the two surfaces of the base film 10 with the prepared first slurry by microgravure extrusion coating process, and then bake at a temperature of 40 °C for 240 min and cool; mixed coatings 20 (i.e., porous layers) are formed on both surfaces of the base film 10, including a first mixed coating 201 and a second mixed coating 202. The thickness of the first mixed coating 201 is 2.5 μm, and the thickness of the second mixed coating 202 is 2.5 μm;

[0172] S23. Spray buffer layers 30 (specifically, polymethyl methacrylate coatings) on both the first mixed coating 201 and the second mixed coating 202 of the base film 10, including a first buffer layer 301 and a second buffer layer 302; the coating amount of the first buffer layer 301 is 0.25 g / m 2 , and the coating amount of the second buffer layer 302 is 0.25 g / m 2, and then bake at a temperature of 40 °C for 240 min and cool to obtain a separator.

[0173] Example 9

[0174] The difference between Example 9 and Example 1 lies in step S1:

[0175] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 9.

[0176] Table 9

[0177]

[0178] In Example 9, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.6 wt%.

[0179] The steps for preparing the first slurry include:

[0180] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0181] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former to the polymer electrolyte solution, and stir at room temperature at a stirring rate of 4000 r / min to mix evenly to obtain the first slurry.

[0182] S2. Prepare the separator, please refer to Figure 3 , and the preparation process of the separator includes:

[0183] S21. Provide a base film 10, and the base film 10 is a PP / PE / PP three-layer co-extruded base film; the thickness of the base film 10 is 30 μm, and the porosity is 45%;

[0184] S22. Coat the prepared first slurry on both surfaces of the base film 10 by a microgravure extrusion coating process, and then bake at a temperature of 80 °C for 30 min and cool; a mixed coating 20 (i.e., a porous layer) is formed on both surfaces of the base film 10, including a first mixed coating 201 and a second mixed coating 202. The thickness of the first mixed coating 201 is 2.5 μm, and the thickness of the second mixed coating 202 is 2.5 μm;

[0185] S23. Spray a buffer layer 30 on the surface of the first mixed coating 201 of the base film 10 at a coating amount of 0.6 g / m 2 (specifically, coat after mixing polymethyl methacrylate and polyvinylidene fluoride in a mass ratio of 1:1), do not coat the buffer layer 30 on the surface of the second mixed coating 202 of the base film 10, and then bake at a temperature of 80 °C for 30 min and cool to obtain the separator.

[0186] Example 10

[0187] The difference between Example 10 and Example 1 lies in step S1:

[0188] S1. Prepare the first slurry, and the composition of the first slurry is shown in Table 10.

[0189] Table 10

[0190]

[0191] In Example 10, the particle size of the oxide solid electrolyte is 0.6 μm, and the solid content of the first slurry is 33.3 wt%.

[0192] The steps for preparing the first slurry include:

[0193] S11. First, add the polymer solid electrolyte to the mixed solution and dissolve it. Stir at a temperature of 100 °C and a stirring rate of 4000 r / min for 10 h to form a polymer electrolyte solution;

[0194] S12. Add the oxide solid electrolyte, binder, dispersant, and pore former to the polymer electrolyte solution, and stir at room temperature at a stirring rate of 4000 r / min until evenly mixed to obtain the first slurry.

[0195] S2. Prepare the separator. Please refer to Figure 4 , and the preparation process of the separator includes:

[0196] S21. Provide the base film 10, and the base film 10 is a polyimide base film; the thickness of the polyimide base film is 15 μm, and the porosity is 60%;

[0197] S22. Coat the first slurry prepared onto one surface of the base film 10 using the microgravure extrusion coating process, and then bake at a temperature of 50 °C for 100 min and cool; a mixed coating 20 with a thickness of 4 μm is formed on the surface of the base film 10;

[0198] S23. Spray the first buffer layer 301 (specifically a polymethyl methacrylate coating) on the surface of the mixed coating 20 at a coating amount of 0.2 g / m 2 and spray the second buffer layer 302 (specifically a polymethyl methacrylate coating) on the other surface of the base film 10 that is not coated with the mixed coating 20 at a coating amount of 0.2 g / m 2 , and then bake at a temperature of 50 °C for 100 min and cool; the separator is obtained.

[0199] Comparative Example 1

[0200] The difference between Comparative Example 1 and Example 1 lies in that the first slurry does not contain an oxide solid electrolyte. Others are the same as in Example 1.

[0201] Comparative Example 2

[0202] The difference between Comparative Example 2 and Example 1 lies in that the first slurry does not contain a pore former. Others are the same as in Example 1.

[0203] Comparative Example 3

[0204] The difference between Comparative Example 3 and Example 1 lies in that the first slurry does not contain an oxide solid electrolyte and a pore former. Others are the same as in Example 1.

[0205] Comparative Example 4

[0206] The difference between Comparative Example 4 and Example 1 lies in that the buffer layer 30 is not provided in the separator, and the structure of the obtained separator is as Figure 5 shown. Others are the same as in Example 1.

[0207] Comparative Example 5

[0208] The difference between Comparative Example 5 and Example 1 lies in that the mixed coating 20 is not provided in the separator, and the structure of the obtained separator is as Figure 6 shown. Others are the same as in Example 1.

[0209] Comparative Example 6

[0210] The difference between Comparative Example 6 and Example 1 lies in that the buffer layer 30 and the mixed coating 20 are not provided in the separator, that is, the separator only includes the base film 10, and the structure of the obtained separator is as Figure 7 shown. Others are the same as in Example 1.

[0211] II. The following performance tests were carried out on the separators prepared in Examples 1 to 10 and Comparative Examples 1 to 6, and the results were recorded in Table 11:

[0212] 1. Puncture strength: Using a universal tensile testing machine, a needle with a diameter of 1 mm was moved downward at a rate of 200 mm / min, and the maximum force used to pierce the separator was recorded.

[0213] 2. Thermal shrinkage at 130 °C / 0.5 h: The separator was cut into a rectangular sample of 120 mm × 60 mm. A rectangular stamp with a size of 100 mm × 50 mm was used to cover a 100 mm × 50 mm rectangle on it. The sample was sandwiched between two A4 papers. After being fixed, it was placed in a forced-air drying oven at 130 °C for baking for 0.5 h. After completion, the length and width of the baked rectangle were measured, and its thermal shrinkage rate = (size before baking - size after baking) / size before baking × 100% was calculated.

[0214] 3. Coating internal pore volume ratio: Tested by the isopropanol penetration method, the pore channel porosity of the coating (here the coating refers to the coating except the base film) is tested by measuring the penetration amount of the unit area separator. First, weigh the mass m0 of the separator, then place the separator in the isopropanol solution. After the isopropanol solution is completely infiltrated into the pore channels of the separator coating, take out the separator and measure the mass m1 of the separator. The mass m2 of the isopropanol adsorbed by the separator coating can be calculated. The mass m of the isopropanol adsorbed by the base film is tested by the same method. 基膜 The volume ratio of the internal pores and channels of the coating is calculated by calculating the mass of the isopropanol adsorbed by the separator coating:

[0215] The mass m2 of the isopropanol adsorbed by the coating = m1 - m0 - m 基膜 ;

[0216] The volume ratio of the internal pores and channels of the coating = (the mass m2 of the isopropanol adsorbed by the coating / the density of isopropanol) / the volume of the whole coating × 100%.

[0217] 4. The electrolyte infiltration test method is as follows: Use a pipette to take a quantitative 10 μL of electrolyte and drop it on the surface of the separator, and record the diameter of the electrolyte diffusion within 30 s.

[0218] 5. Isolation lithium ion conductivity: Assemble a copper foil / separator / copper foil symmetric cell, and test the impedance of 1 - 4 layers of separators at 25 °C under the condition of 100 k~0.01 H. The ionic conductivity of the separator is calculated through a linear fitting formula. The formula is σ = d / (R×S), where σ is the ionic conductivity, d is the separator thickness, R is the resistance of a single layer of separator, and S is the effective area for lithium ions to pass through the separator.

[0219] Table 11

[0220]

[0221] III. Battery preparation

[0222] The separators prepared in Examples 1 to 10 and Comparative Examples 1 to 6 are respectively applied to the ternary cathode lithium metal batteries of NCM523 system, NCM622 system, and NCM811 system. When the separator is used, the surface coated with the buffer layer 30 is close to the negative electrode. If one surface of the base film 10 is coated with the mixed coating 20 and the buffer layer 30, and the other surface of the base film 10 is only coated with the buffer layer 30, then the surface only coated with the buffer layer 30 is close to the negative electrode.

[0223] IV. The following performance tests are carried out on the batteries prepared using the separators prepared in Examples 1 to 10 and Comparative Examples 1 to 6, and the results are recorded in Table 12:

[0224] 1. 130°C Hot Box Test Pass Rate: Charge the battery to full charge at a rate of 0.2C, then place it in an oven at 130°C for 1 hour. Observe the ignition state at 30 minutes and the explosion state at 60 minutes. If there is no ignition or explosion, it is considered to pass.

[0225] 2. Penetration Test Pass Rate: Charge the battery to full charge at a rate of 0.2C. Pierce the battery cell with a 0.8mm needle at a rate of 200mm / min. Observe the ignition and explosion states of the battery cell. If there is no ignition or explosion after piercing, it is considered to pass.

[0226] 3. Cycle Life (Number of Cycles): In a constant-temperature oven at 25°C, charge and discharge the battery at a rate of 0.33C / 1C, and record the number of cycles when the capacity retention rate is ≤80%.

[0227] Table 12

[0228]

[0229] (1) For the separators in Examples 1 - 10 of this application, on the basis of the base film 10, by designing the coating structure, a porous layer is prepared on the surface of the base film 10 after mixing the polymer solid electrolyte, oxide solid electrolyte, pore former, and solvent. This reduces the 130°C / 0.5h thermal shrinkage of the separator from 7% to below 3.5%, increases the 130°C hot box test pass rate from 20% to 100%, and increases the penetration test pass rate from 0 to 100%. Compared with Comparative Examples 1 - 6, for the separators in Examples 1 - 10 of this application, the overall thermal shrinkage, hot box test, and penetration test have all been improved.

[0230] (2) In the NCM523 ternary cathode material system, compared with the separators in Comparative Examples 1-6, the cycle life of the separators in Examples 1-10 of this application has been increased from 145 cycles to more than 190 cycles. The main reason is that the combined use of the oxide solid electrolyte, pore former and solvent in the hybrid coating 20 forms a large number of pores and channels in the polymer solid electrolyte. After the structural design of the hybrid coating 20 of the separator is modified, its electrolyte wettability increases. Moreover, the hybrid coating 20 has a three-dimensional network structure, with relatively uniform pore structures and channel structures, good pore connectivity, and a high tortuosity of the channels. First, it can improve the transport of lithium ions, enable the uniform passage of lithium ions, and achieve the uniformity of current density. Second, when lithium dendrites grow, it can extend the growth path of lithium dendrites, delay the piercing of the separator caused by the growth of lithium dendrites, thereby delaying the occurrence of the short circuit due to the contact between the positive and negative electrodes and improving the cycle life of the battery. Also, in the hybrid coating 20, the introduction of the oxide solid electrolyte, especially the introduction of LATP, LLTO, and LLZO, since LATP, LLTO, and LLZO themselves can conduct ions, after their introduction into the polymer solid electrolyte, the lithium ion conductivity is further improved, enabling lithium ions to quickly pass through the separator during charge and discharge, reducing the generation of concentration polarization, and preventing the generation of lithium dendrites induced by uneven current density. At the same time, the introduction of the buffer layer 30 is equivalent to setting up a buffer layer for the growth of lithium dendrites, which can provide sufficient space for the growth of lithium dendrites and induce the uniform deposition of lithium dendrites, preventing the piercing of the separator, thereby avoiding the occurrence of the short circuit due to the contact between the positive and negative electrodes and further improving the long-term cycling performance of the lithium metal battery.

[0231] In Examples 1-10, the design of the hybrid structure of the polymer solid electrolyte and the oxide solid electrolyte and the combined use of the buffer layer 30 extend the time for the separator to be pierced due to the growth of lithium dendrites, and their cycle life is longer than that of Comparative Examples 1-6;

[0232] Comparing Examples 5-6, due to the increase in the oxide solid electrolyte component, the internal filling material of the hybrid coating 20 increases, the pore and channel structures increase, and its ionic conductivity increases, resulting in an increase in cycle life.

[0233] In Examples 1-10, the introduction of LATP, LLTO, and LLZO enables lithium ions to quickly pass through during charge and discharge, further inhibiting the growth of lithium dendrites, and their cycle life is further improved. Moreover, as the components of LATP, LLTO, and LLZO increase, their ionic conductivity increases, and the cycle life increases.

[0234] Comparing Example 1 with Comparative Example 1, in Comparative Example 1, no oxide solid electrolyte is added to the separator slurry used for the mixed coating 20. Based on Comparative Example 1, Example 1 adds an oxide solid electrolyte. Due to the interface of the material itself and the mutual stacking between the oxide solid electrolyte particles, pore structures and pore channels are formed in the mixed coating 20, increasing the proportion of internal pores and pore volume in the mixed coating 20, enhancing the electrolyte wettability, increasing the puncture passing rate, increasing the ionic conductivity of the separator, and improving the cycle life.

[0235] Comparing Example 1 with Comparative Example 2, in Comparative Example 2, no pore former is added to the separator slurry used for the mixed coating 20. Based on Comparative Example 2, Example 1 adds a pore former. The addition of the pore former will form small bubbles during the baking process and will be removed, thus forming pores, increasing the proportion of internal pore volume in the mixed coating 20, enhancing the electrolyte wettability, increasing the ionic conductivity of the separator, increasing the puncture passing rate, and improving the cycle life.

[0236] Comparing Example 1 with Comparative Example 3, in Comparative Example 3, no oxide solid electrolyte or pore former is added to the separator slurry used for the mixed coating. Based on Comparative Example 3, Example 1 adds an oxide solid electrolyte and a pore former. Due to the interface of the material itself and the mutual stacking between the oxide solid electrolyte particles, pore structures are formed in the mixed coating 20. And the addition of the pore former will form small bubbles during the baking process and will be removed, thus forming a uniform pore structure. Moreover, the pore structure formed by part of the pore former will form pore channels with the pore structures formed between the oxide solid electrolyte and the polymer solid electrolyte. Additionally, the combined use of the solvent further increases the pores and pore channels inside the mixed coating 20. Therefore, compared with Comparative Example 3, in Example 1, the simultaneous addition of the oxide solid electrolyte, pore former, and solvent significantly increases the proportion of internal pores and pore volume in the mixed coating 20. At the same time, the electrolyte wettability, puncture passing rate, ionic conductivity of the separator, and cycle life are all greatly improved, indicating that the simultaneous use of the oxide solid electrolyte, pore former, and solvent in the separator slurry plays an obvious synergistic effect.

[0237] Comparing Example 1 with Comparative Example 4, the separator in Comparative Example 4 is not coated with a buffer layer. Based on Comparative Example 4, Example 1 adds a buffer layer, which can better provide sufficient space for the deposition of lithium dendrites, alleviate the piercing of the separator caused by the excessive growth of lithium dendrites, and improve the cycle life of the battery cell.

[0238] Comparing Example 1 with Comparative Example 5, the separator in Comparative Example 5 is not coated with the mixed coating 20 but only coated with the buffer layer 30. Example 1 is equivalent to adding the mixed coating 20 on the basis of Comparative Example 5. The introduction of the mixed coating 20 has greatly improved the thermal stability of the separator. It contains a large number of pores and channels inside, which is beneficial to improving the wettability of the electrolyte. And the oxide solid electrolyte particles can improve the ionic conductivity of the separator. This not only improves the volume ratio of the pores and channels inside the mixed coating 20, the wettability of the electrolyte, the thermal stability, and the ionic conductivity of the separator, but also significantly improves the passing rate of the heat box test and the acupuncture passing rate of the separator, and the cycle life is also significantly improved.

[0239] Comparing Example 1 with Comparative Example 6, the base film in Example 1 is used as the separator in Comparative Example 6. Example 1 is based on Example 6 with the addition of the mixed coating and the buffer layer. This not only improves the thermal stability and the wettability of the electrolyte of the separator, thus improving the ionic conductivity of the separator, but also improves the passing rate of the heat box test and the acupuncture passing rate of the battery cell. And the buffer layer 30 can better provide enough space for the deposition of lithium dendrites, alleviating the piercing of the separator caused by the excessive growth of lithium dendrites, and the cycle life is improved. The cycle life of the separator in Comparative Example 4 is 146 cycles, the cycle life of the separator in Comparative Example 5 is 126 cycles, the cycle life of the separator in Comparative Example 6 is 109 cycles, while the cycle life of the separator in Example 1 is 193 cycles. Compared with Comparative Examples 4 to 6, the cycle life of the separator in Example 1 has been significantly improved, indicating that the combined use of the mixed coating 20 and the buffer layer 30 has an obvious synergistic effect, and the cycle life of the separator is significantly improved.

[0240] Comparing Example 1 with Comparative Examples 1 to 3, the combined use of the polymer solid electrolyte, the oxide solid electrolyte, the pore former, and the solvent has significantly improved the acupuncture passing rate of the separator.

[0241] (3) The same effect also exists in the NCM622 and NCM811 ternary cathode material systems.

[0242] The above are only the preferred embodiments of the present application, and do not impose any form of limitation on the present application. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still fall within the scope of the technical solution of the present application.

Claims

1. A separator for a battery, characterized in that, The separator includes a base film and a porous layer located on at least one surface of the base film. The porous layer contains a polymer solid electrolyte and an oxide solid electrolyte. The oxide solid electrolyte is dispersed in the polymer solid electrolyte in a particulate form, and the particles of the oxide solid electrolyte are stacked with each other to form pores in the polymer solid electrolyte. There are also pores distributed in the polymer solid electrolyte, and the pores and the holes communicate with each other to form a flow channel for the electrolyte to flow through. The polymer solid electrolyte includes an aramid-based polymer electrolyte, which is a solid electrolyte material composed of aramid as a polymer matrix and a lithium salt. The porosity of the porous layer is 62% - 68%.

2. The diaphragm according to claim 1, characterized in that, By weight, the porous layer contains 70 - 85 parts of the polymer solid electrolyte and 5 - 25 parts of the oxide solid electrolyte.

3. The diaphragm according to claim 2, characterized in that, By weight, the porous layer further contains 2 - 5 parts of a binder and 0.05 - 2 parts of a dispersant; and / or, The porous layer contains 75 - 83 parts of the polymer solid electrolyte and 10 - 20 parts of the oxide solid electrolyte.

4. The diaphragm according to claim 2, wherein When the porous layer further contains a binder, the binder includes at least one of polyvinyl alcohol, polyacrylate, carboxymethyl cellulose, polyvinylidene fluoride, and polyurethane; and / or, When the porous layer further contains a dispersant, the dispersant includes at least one of polyethylene glycol, sodium polyacrylate, polyamide, polyvinyl alcohol, calcium carbonate, and silica powder.

5. The diaphragm according to claim 1, characterized in that, The aramid-based polymer electrolyte includes at least one of meta-aramid electrolyte and para-aramid electrolyte.

6. The diaphragm according to any one of claims 1 to 5, characterized in that The oxide solid electrolyte includes at least one of lithium titanium aluminum phosphate, lithium lanthanum titanium oxide, and lithium lanthanum zirconium oxide; and / or, The average particle size of the oxide solid electrolyte is 0.1 μm - 1.5 μm; and / or, The base film includes at least one of a polypropylene base film, a polyethylene base film, and a polyimide base film; and / or, The thickness of the base film is 3 μm - 30 μm, and the porosity is 25% - 60%; and / or, The thickness of the porous layer is 0.5 μm - 5 μm.

7. The diaphragm according to any one of claims 1 to 5, characterized in that The separator includes a buffer layer, which is located on the surface of the porous layer facing away from the base film or on the surface of the base film facing away from the porous layer.

8. The diaphragm according to claim 7, characterized in that, The buffer layer includes a plurality of island-shaped elastic protrusions.

9. The diaphragm according to claim 8, characterized in that, The elastic protrusion contains at least one of polyvinylidene fluoride and polymethyl methacrylate; and / or, The thickness of the buffer layer is 1 μm - 5 μm; and / or, The coating amount of the buffer layer is 0.2 g / m 2 ~0.8 g / m 2 .

10. A method for preparing a separator, which is used to prepare the separator according to any one of claims 1 to 9, characterized in that, The preparation method of the separator includes: Providing a base film; Providing a first slurry, which includes a solvent, a pore-forming agent, a polymer solid electrolyte, and an oxide solid electrolyte, and the polymer solid electrolyte is dissolved in the solvent; Performing a film-forming treatment on the first slurry on at least one surface of the base film to obtain a first wet film layer; Performing a heating treatment on the first wet film layer to volatilize the solvent and thermally decompose the pore-forming agent, thereby obtaining a porous layer and further obtaining a separator.

11. The method for preparing a separator according to claim 10, characterized in that, By weight parts, the first slurry includes 160 to 265 parts of the solvent, 0.5 to 2 parts of the pore former, 70 to 85 parts of the polymer solid electrolyte, and 5 to 25 parts of the oxide solid electrolyte.

12. The method for preparing a separator according to claim 10 or 11, characterized in that, By weight parts, the first slurry further includes 2 to 5 parts of a binder and 0.05 to 2 parts of a dispersant; and / or, The solid content of the first slurry is 25wt% to 65wt%; and / or, The pore former includes at least one of ammonium carbonate, ammonium bicarbonate, ammonium chloride, sodium carbonate, and sodium bicarbonate.

13. The method for preparing a separator according to claim 10, wherein, The first slurry further includes an auxiliary salt, the auxiliary salt is dissolved in the solvent, and the auxiliary salt is used to promote the dissolution of the polymer solid electrolyte in the solvent.

14. The method for preparing the diaphragm according to claim 13, wherein The solvent is a polar solvent, and the polar solvent includes at least one of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; and / or, The auxiliary salt includes at least one of lithium chloride and calcium chloride; and / or, The mass ratio of the auxiliary salt to the solvent is 0.015 to 0.

08.

15. A battery, characterized in that, A separator prepared by the preparation method of the separator according to any one of claims 1-9 or the separator according to any one of claims 10-14.

16. The battery according to claim 15, characterized in that, The battery includes a lithium metal battery, the lithium metal battery includes a lithium metal negative electrode, the lithium metal negative electrode is located on one side of the separator, and when the separator includes a buffer layer, the buffer layer is located between the lithium metal negative electrode and the porous layer.

17. The battery according to claim 16, characterized in that, The lithium metal battery is a liquid lithium metal battery, and the separator is infiltrated with an electrolyte.

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