Pre-lithiated composite separator, lithium ion battery and preparation method thereof

Abstract

This disclosure provides a pre-lithiation composite separator, a lithium-ion battery, and a method for preparing it. The pre-lithiation composite separator includes a separator substrate; a pre-lithiation layer disposed on at least one side of the separator substrate; and a protective layer disposed on at least one side of the pre-lithiation layer. The protective layer includes a network framework and a filler filled in the network framework, wherein the network framework is an organic material and the filler is a conductive material. This protective layer, while ensuring isolation from water and oxygen, simultaneously increases the ionic conductivity of the separator and the electronic conductivity of the pre-lithiation reaction when used in a battery system, thereby reducing the battery's internal resistance and improving the pre-lithiation effect.

Description

Technical Field

[0001] This disclosure relates to the field of batteries, and more specifically, to a pre-lithium composite separator, a lithium-ion battery, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long lifespan, and good environmental performance, have become an indispensable energy storage method in mobile electronic devices, electric vehicles, and energy storage systems. The performance of a lithium-ion battery largely depends on its internal separator material. The separator is a highly porous thin film whose main function is to prevent direct contact between the positive and negative electrode active materials while allowing lithium ions to pass through.

[0003] To improve battery energy density and cycle life, researchers have proposed a pre-lithiation design to compensate for lithium loss caused by SEI film formation, thereby enhancing energy density and cycle performance. Pre-lithiation techniques include positive electrode pre-lithiation, negative electrode pre-lithiation, and separator pre-lithiation. However, the pre-lithiated layer, containing active lithium, is sensitive to water and oxygen, necessitating the addition of a protective layer to enhance its stability and shelf life.

[0004] In related technologies, the pre-lithiated composite negative electrode sheet includes a pre-lithiated negative electrode sheet and a protective layer. The pre-lithiated negative electrode sheet includes a negative electrode current collector, a film layer, and a pre-lithiated layer connected in sequence, with the protective layer located on the surface of the pre-lithiated layer. Although the protective layer can isolate water and oxygen, the inert material in the protective layer does not have ionic conductivity, and the binder is insoluble in the electrolyte. In actual use, the protective layer increases the ionic resistance of the separator, reduces the porosity of the separator, and thus significantly reduces the lithium-ion conductivity of the separator, increasing the internal resistance of the battery. Summary of the Invention

[0005] In view of the above, this disclosure provides a pre-lithium composite separator, a lithium-ion battery and a method for preparing the same, to solve or at least alleviate at least one technical problem existing in the above-mentioned pre-lithium composite separator, lithium-ion battery and method for preparing the same.

[0006] According to specific embodiments of this disclosure, this disclosure provides a pre-lithium composite separator, comprising:

[0007] Diaphragm substrate;

[0008] A pre-lithiation layer is disposed on at least one side of the separator substrate; and

[0009] A protective layer is disposed on at least one side of the pre-lithiation layer; the protective layer includes a network skeleton and a filler filled in the network skeleton, the network skeleton being an organic material and the filler being a conductive material.

[0010] In some embodiments, the organic material is at least one of the following: polyacrylic acid, waterborne polyurethane, or polyacrylonitrile material.

[0011] In some embodiments, the conductive material is an inorganic solid electrolyte material;

[0012] Optionally, the inorganic solid electrolyte material is at least one of the following: lithium aluminum titanium phosphate (LATP), lithium phosphorus sulfide chloride (LPSCL), lithium lanthanum titanate (LLTO), and tantalum-doped lithium lanthanum zirconium oxide (LLZTO).

[0013] Optionally, the inorganic solid electrolyte material is at least one of the following: li 1.3 Al 0.3 Ti 1.7 P3O 12 Li6PS5Cl, Li 0.33 La 0.55 TiO3, Li 6.6 La3Zr 1.6 Ta 0.4 O 12 Li 1+x+y Al X Ti 2-x Si y P 3-y O 12 .

[0014] In some embodiments, the conductive material D 50 The particle size is between 0.3 and 10 μm.

[0015] In some embodiments, the mass ratio of the inorganic solid electrolyte material to the organic material is between 20-50%, preferably 35%.

[0016] In some embodiments, the protective layer further includes a binder soluble in the electrolyte; and / or, the protective layer further includes an electronically conductive material.

[0017] This disclosure also provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode, and the separator is a pre-lithiated composite separator as described in any of the preceding claims.

[0018] This disclosure also provides a method for preparing a pre-lithium composite separator as described in any of the preceding claims, comprising the following steps:

[0019] Provide diaphragm substrate;

[0020] A pre-lithium layer is deposited on at least one side of the diaphragm substrate;

[0021] The protective layer is coated on the surface of the pre-lithiation layer away from the membrane substrate. The protective layer includes a network skeleton and a filler filled in the network skeleton. The network skeleton is an organic material and the filler is a conductive material.

[0022] In some embodiments, the method further includes a step of preparing a protective layer adhesive, comprising:

[0023] An inorganic solid electrolyte material is ultrasonically dispersed in an NMP solution, wherein the inorganic solid electrolyte accounts for 30%-60% of the mass of the NMP solution.

[0024] The organic material is added to the well-dispersed solution, and the mass ratio of the inorganic solid electrolyte material to the organic material is between 20-50%, preferably 35%. The mixture is stirred for 12-24 hours to complete the preparation of the protective layer adhesive.

[0025] This disclosure also provides a method for preparing a lithium-ion battery, comprising the following steps:

[0026] A positive electrode active material is uniformly coated on the surface of the positive electrode current collector to form a positive electrode sheet;

[0027] A negative electrode active material is uniformly coated on the surface of the negative electrode current collector to form a negative electrode sheet;

[0028] The pre-lithium composite membrane was prepared using the method described above.

[0029] The pre-lithiation composite separator is placed between the positive electrode and the negative electrode, and the positive electrode, the pre-lithiation composite separator and the negative electrode are placed in the housing. Electrolyte is injected into the housing and then the housing is sealed.

[0030] Compared with the prior art, the above-described solutions of this disclosure have at least one of the following beneficial effects:

[0031] This disclosure provides a pre-lithiation separator protective layer with high lithium-ion conductivity. While ensuring isolation from water and oxygen, it simultaneously increases the ionic conductivity of the separator and the electronic conductivity of the pre-lithiation reaction when used in a battery system, reducing battery internal resistance and improving the pre-lithiation effect. On one hand, this protective layer can isolate the lithium layer in the separator from moisture in the air in an atmospheric environment; on the other hand, the organic matter in the protective layer is soluble in the electrolyte in the battery system, but retains the conductive network support, thus maintaining its ability to conduct lithium ions. By combining the inorganic protective layer and the conductive layer into a single layer, the complexity of multi-layer processes in separator production is avoided, preventing an increase in battery internal resistance.

[0032] This disclosure uses a solid electrolyte as the conductive material in the protective layer and a binder soluble in the electrolyte. When used in the battery system, the binder dissolves in the electrolyte, which greatly increases the porosity of the separator. Furthermore, the addition of the solid electrolyte further enhances the conductivity of lithium ions, thereby reducing internal resistance. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0034] Figure 1 This is a schematic diagram of the pre-lithium composite separator in an embodiment of this disclosure;

[0035] Figure 2 This is a schematic diagram of the pre-lithium composite membrane in another embodiment of the present disclosure;

[0036] Figure 3 This is a schematic diagram of the pre-lithium composite membrane in another embodiment of the present disclosure;

[0037] Figure 4 This is a schematic diagram of the pre-lithium composite membrane in another embodiment of the present disclosure;

[0038] Figure 5 This is a schematic diagram of the microstructure of the protective layer in the atmosphere according to an embodiment of the present disclosure;

[0039] Figure 6 This is a schematic diagram of the microstructure of the protective layer in the electrolyte according to an embodiment of the present disclosure;

[0040] Figure 7 A flowchart illustrating the preparation method of the pre-lithium composite separator provided in this embodiment.

[0041] The reference numerals in the detailed embodiments are as follows:

[0042] The pre-lithiation composite separator 100 comprises a separator substrate 10, a pre-lithiation layer 20, a protective layer 30, a network skeleton 31, a filler 32, an electronically conductive material 33, and an adhesive 34. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this disclosure clearer, the disclosure will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure.

[0045] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0046] In the description of the embodiments of this disclosure, the technical terms "upper," "lower," "thickness," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this disclosure and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this disclosure.

[0047] In the description of the embodiments of this disclosure, the term "and / or" is merely a description of the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following associated objects have an "or" relationship.

[0048] In the description of the embodiments of this disclosure, the symbol "-" represents the data of the two endpoints before and after "-" and all data between the two endpoints. For example, AB represents all data that is greater than or equal to A and less than or equal to B.

[0049] In this disclosure, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this disclosure can be combined with other embodiments.

[0050] In the preparation of lithium-ion battery separators, after pre-lithiation, a protective layer is typically designed on the lithium layer to isolate the lithium layer from water and oxygen in the air, prevent the lithium layer from reacting, and increase the stability and shelf life of the pre-lithiated separator. This protective layer is often made of inorganic materials such as metal oxides, lithium carbonate, and lithium nitride, or a mixture of ceramic materials, binders, and conductive agents. However, these protective layers reduce the ionic conductivity of the pre-lithiated separator to some extent, increasing the battery's internal resistance. Furthermore, to improve the initial efficiency of pre-lithiation and increase the electronic conduction of the pre-lithiation reaction, an additional electronically conductive layer is usually added on top of the protective lithium layer, leading to a more complex process and further increasing the battery's internal resistance.

[0051] Based on this, this disclosure provides a pre-lithiation composite separator, comprising: a separator substrate; a pre-lithiation layer disposed on at least one side of the separator substrate; and a protective layer disposed on at least one side of the pre-lithiation layer; the protective layer includes a network skeleton and a filler filled in the network skeleton, wherein the network skeleton is an organic material and the filler is a conductive material. This disclosure provides a pre-lithiation separator protective layer with high lithium-ion conductivity, which, while ensuring the isolation of water and oxygen, can simultaneously increase the ionic conductivity of the separator and the electronic conduction of the pre-lithiation reaction when used in a battery system, thereby not only reducing the internal resistance of the battery but also improving the pre-lithiation effect.

[0052] The optional embodiments of this disclosure are described in detail below with reference to the accompanying drawings.

[0053] Please see Figure 1 This disclosure provides a pre-lithiation composite separator 100, which includes a separator substrate 10; a pre-lithiation layer 20 disposed on at least one side of the separator substrate 10; and a protective layer 30 disposed on the side of the pre-lithiation layer 20 away from the separator substrate 10.

[0054] In some embodiments, such as Figure 2 As shown, the protective layer 30 is disposed on the side of the pre-lithiation layer 20 away from the membrane substrate 10 and on the side of the membrane substrate 10 away from the pre-lithiation layer 20.

[0055] In some embodiments, such as Figure 3As shown, the protective layer 30 is disposed on the side of the pre-lithiation layer 20 away from the membrane substrate 10 and on the side of the membrane substrate 10 close to the pre-lithiation layer 20.

[0056] In some embodiments, such as Figure 4 As shown, the protective layer 30 is disposed on the side of the pre-lithiation layer 20 away from the membrane substrate 10, on the side of the membrane substrate 10 close to the pre-lithiation layer 20, and on the side of the membrane substrate 10 away from the pre-lithiation layer 20.

[0057] By setting one, two, or three protective layers 30, while ensuring the isolation of water and oxygen, the ionic conductivity of the separator and the electronic conduction of the pre-lithiation reaction can be increased when the battery system is used. This not only reduces the internal resistance of the battery but also improves the pre-lithiation effect.

[0058] Among them, such as Figures 5-6 As shown, Figure 5 This is a schematic diagram of the internal structure of the protective layer 30 in the atmosphere. Figure 6 This is a schematic diagram of the internal structure of the protective layer 30 in the electrolyte. The protective layer 30 includes a network skeleton 31 and a filler 32 filled within the network skeleton 31. The network skeleton 31 forms an irregular, hollow structure. The material of the network skeleton 31 is an organic material, and the filler 32 is a conductive material filled within the hollow network skeleton 31. The protective layer 30 provided in this disclosure, due to its hollow network skeleton 31 and the conductive material filling it, can simultaneously increase the ionic conductivity of the pre-lithiation composite separator 100 and the electronic conductivity of the pre-lithiation reaction when used in a battery system, while ensuring the isolation of water and oxygen. This not only reduces the battery's internal resistance but also improves the pre-lithiation effect. Figure 5 As shown, the protective layer 30 can isolate the pre-lithiation layer 20 in the pre-lithiation composite membrane 100 from moisture in the air in an atmospheric environment, preventing lithium from reacting with water and oxygen. Figure 6 As shown, the organic network framework 31 in the protective layer 30 is soluble in the electrolyte in the battery system, but retains the conductive network support to conduct lithium ions; the filler 32 acts as a conductive material to enhance the ionic conductivity of the pre-lithium composite separator 100. This disclosure avoids the complexity of multi-layer processes in separator production by combining the traditional inorganic protective layer and conductive layer into one layer, thus reducing the internal resistance of the battery.

[0059] In some embodiments, the diaphragm substrate 10 may include, but is not limited to, a base film, a base film / ceramic composite diaphragm, a base film / adhesive composite diaphragm, or a base film / ceramic / adhesive composite diaphragm. The base film includes, but is not limited to, at least one of the following: polyethylene base film, polyethylene nonwoven base film, polypropylene base film, polypropylene nonwoven base film, polypropylene / polyethylene / polypropylene composite base film, polyimide base film, polyimide nonwoven base film, polytetrafluoroethylene film, polytetrafluoroethylene nonwoven base film, polyvinyl chloride film, and polyvinyl chloride nonwoven base film. The ceramic includes, but is not limited to, at least one of the following: alumina, zirconium oxide, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide, titanium dioxide, yttrium oxide, and cerium oxide. The adhesive includes, but is not limited to, at least one of the following: polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, sodium carboxymethyl cellulose, styrene-butadiene rubber, hydroxypropyl methylcellulose, carboxylated styrene-butadiene latex, and polyvinyl alcohol. The thickness of the diaphragm substrate 10 is preferably, but not limited to, 5-50 μm. In this embodiment, the thickness of the diaphragm substrate 10 is 13 μm, etc.

[0060] In some embodiments, the pre-lithiation layer 20 can compensate for irreversible lithium loss during the first charge-discharge and cycling processes of the lithium-ion battery, thereby improving the battery's capacity and energy density. The material of the pre-lithiation layer 20 can be, but is not limited to, metallic lithium, lithium-silicon alloy, lithium-magnesium alloy, lithium-copper alloy, lithium-silver alloy, lithium-beryllium alloy, lithium-zinc alloy, lithium-cadmium alloy, lithium-aluminum alloy, lithium-gold alloy, and lithium-boron alloy. The thickness of the pre-lithiation layer 20 is preferably, but not limited to, 0.1-10 μm. In this embodiment, the thickness of the pre-lithiation layer 3 is 1 μm.

[0061] In some embodiments, the protective layer 30 includes a network skeleton 31 and a filler 32 filled in the network skeleton 31. The network skeleton 31 is an organic material, and the filler 32 is a conductive material. The thickness of the protective layer 30 is 3-10 μm, for example, 4 μm, 6 μm, 8 μm, etc. Optionally, the thickness of the protective layer 30 is 4-6 μm, which ensures that the gaps in the network skeleton 31 are large enough to accommodate the conductive material filler 32, allowing conductive particles to move freely in the gaps of the network skeleton 31 to enhance conductivity. The material of the organic network skeleton 31 is at least one of the following: polyacrylic acid, waterborne polyurethane, or polyacrylonitrile.

[0062] In some embodiments, the conductive material is an inorganic solid electrolyte material, which can form conductive particles dispersed in the network framework 31 to enhance the ionic conductivity of the pre-lithium composite membrane 100. Optionally, the inorganic solid electrolyte material is at least one of the following: lithium aluminum titanium phosphate (LATP), lithium phosphorus sulfide chloride (LPSCL), lithium lanthanum titanate (LLTO), and tantalum-doped lithium lanthanum zirconium oxide (LLZTO).

[0063] Optionally, the inorganic solid electrolyte material is at least one of the following: li 1.3 Al 0.3 Ti 1.7 P3O 12 Li6PS5Cl, Li 0.33 La 0.55 TiO3, Li 6.6 La3Zr 1.6 Ta 0.4 O 12 Li 1+x+y Al X Ti 2-x Si y P 3-y O 12 .

[0064] In some embodiments, the conductive material D 50 The particle size is between 0.3-10 μm, thus ensuring the conductivity of the material D. 50 The particle size is smaller than the thickness of the protective layer 30, allowing the conductive particles to move freely within the gaps of the network skeleton 31 to enhance conductivity. In this embodiment, the conductive material D... 50 The particle size is 0.3μm or 0.4μm, which is much smaller than the thickness of the protective layer 30, thus enhancing its conductivity.

[0065] In some embodiments, the mass ratio of the inorganic solid electrolyte material to the organic matter is between 20-50%, preferably 35%. A reasonable mass ratio of the inorganic solid electrolyte material to the organic matter ensures that the inorganic solid electrolyte material fills the gaps in the organic network framework appropriately, avoiding both overfilling leading to reduced conductivity and underfilling resulting in insufficient conductive particles, which would also affect conductivity. Therefore, experimental verification shows that a mass ratio of 20-50% for the inorganic solid electrolyte material to the organic matter exhibits excellent conductivity.

[0066] In some embodiments, such as Figure 6 As shown, the protective layer 30 further includes a binder 34 dissolved in the electrolyte; the binder may be, for example, ethylene carbonate, and the mass ratio of ethylene carbonate to the organic network skeleton is 0%-20%, for example, 10%. In the presence of an inorganic solid electrolyte, ethylene carbonate can undergo dipole-dipole interactions with the organic network skeleton material, which is beneficial to the formation of a complete skeleton; in addition, in the electrolyte system, ethylene carbonate can dissolve in the electrolyte, providing porous channels for lithium ion shuttle, which is beneficial to lithium ion conduction.

[0067] In some embodiments, the protective layer 30 further includes an electronically conductive material 33. The electronically conductive material 33 is, for example, at least one of graphite, carbon nanotubes, graphene, etc. The electronically conductive material 33 serves as an electron channel for the pre-lithiation layer 20 to form lithium ions; during the pre-lithiation process, the electronically conductive material 33 (e.g., graphite) loses electrons, which are transferred to the pre-lithiation layer 20 through the conductive material in the protective layer 30; the pre-lithiation layer 20 gains electrons, transforming from lithium to lithium ions; the lithium ions then embed into the graphite through the protective layer 30; wherein the mass ratio of the electronically conductive material to the inorganic solid electrolyte is 20%-60%, for example, 30%-40%.

[0068] This disclosure also provides a lithium-ion battery, comprising: a pre-lithiation composite separator 100, a positive electrode, and a negative electrode, wherein the pre-lithiation composite separator 100 is located between the positive electrode and the negative electrode. The positive electrode, negative electrode, and pre-lithiation composite separator 100 are stacked and assembled into a cell, and then subjected to baking, encapsulation, electrolyte injection, high-temperature pressure treatment, electrolyte extraction, encapsulation, and volume determination processes to obtain the lithium-ion battery.

[0069] Please see Figure 7 This disclosure also provides a method for preparing any of the aforementioned pre-lithium composite separators, comprising the following steps:

[0070] Step S701: Provide a diaphragm substrate;

[0071] Step S703: Deposit a pre-lithium layer on at least one side of the diaphragm substrate;

[0072] Step S705: Coat the protective layer on the surface of the pre-lithiation layer away from the membrane substrate. The protective layer includes a network skeleton and a filler filled in the network skeleton. The network skeleton is an organic material and the filler is a conductive material.

[0073] In step S701, the diaphragm substrate is dried in a vacuum high-temperature drying oven at 70°C-90°C, or optionally 80°C, for 5-7 hours, or optionally 6 hours, thereby effectively removing moisture from the diaphragm substrate.

[0074] In step S703, a lithium plating process is performed on the separator substrate. Lithium is deposited on the separator substrate by vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering to form a pre-lithiation layer.

[0075] In some embodiments, before step S705, coating the protective layer onto the surface of the pre-lithiation layer away from the separator substrate, a step of preparing a protective layer adhesive is further included, comprising:

[0076] Step S705-1: The inorganic solid electrolyte material is ultrasonically dispersed in NMP (N-methylpyrrolidone).

[0077] In the solution, the inorganic solid electrolyte accounts for 30%-60% of the mass of the NMP solution, so that the inorganic solid electrolyte material is fully dispersed in NMP to form a uniform mixed solution; the mixed solution is heated to 80℃-100℃ and stirred for 3-4 hours to further disperse the inorganic solid electrolyte material in the NMP solution.

[0078] Step S705-2: Add the organic material to the well dispersed solution. The mass ratio of the inorganic solid electrolyte material to the organic material is between 20-50%, preferably 35%. Then stir at 40℃-60℃ for 12-24 hours to complete the preparation of the protective layer adhesive.

[0079] In some embodiments, in step S705-2 above, while adding organic matter, a binder solution and / or an electronically conductive material may be selectively added. The electronically conductive material is, for example, at least one of graphite, carbon nanotubes, graphene, etc. The mass ratio of binder solution to organic matter is (0-0.2):1, optionally, such as 0.2:1. The mass ratio of electronically conductive material to inorganic solid electrolyte is (0.2-0.6):1, optionally, such as 0.4:1.

[0080] In some embodiments, step S705, coating the protective layer on the surface of the pre-lithiation layer away from the membrane substrate, includes: applying the above-mentioned protective layer adhesive to a preset surface of the pre-lithiation composite membrane by scraping, with the wet thickness of the coating controlled at 3-10 μm; after coating, placing it in a vacuum drying oven at a drying temperature of 60-100°C for 30-60 min to form a protective layer.

[0081] The preparation process, testing methods, and test data of the examples and comparative examples are described below:

[0082] Example 1:

[0083] Inorganic solid electrolyte material Li 6.6 La3Zr 1.6 Ta 0.4 O 12 (D50 = 0.3 μm) The inorganic solid electrolyte was ultrasonically dispersed in NMP solution (the mass ratio of inorganic solid electrolyte to NMP solvent was 40%), and then stirred at 100°C for 3 hours. Next, the polyacrylic acid organic material was added to the dispersed solution at a mass ratio of 3:1 (organic material to inorganic solid electrolyte). After addition, the solution was stirred at 50°C for 18 hours to complete the preparation of the adhesive. Simultaneously, a binder solution and artificial graphite electronically conductive material were added, with a binder solution to organic material mass ratio of 0.2:1 and an electronically conductive material to inorganic solid electrolyte mass ratio of 0.4:1.

[0084] The above-mentioned adhesive solution was applied to the surface of the pre-lithiation layer by a scraping method, and the wet thickness of the coating was controlled at 3 μm. After coating, it was placed in a vacuum drying oven at 80°C for 60 min.

[0085] Method for testing the ionic conductivity of pre-lithium composite membranes:

[0086] A pre-lithiated composite separator was assembled with positive and negative electrodes to form a button-type half-cell. Both the positive and negative electrodes were made of stainless steel. The pre-lithiated composite separator had 1, 2, and 3 layers, respectively. Electrolyte was added, the cells were sealed, and allowed to stand for 6 hours before testing their EIS impedance. The EIS test conditions were 0.01-106 Hz with a 5 mV disturbance. The ionic conductivity σ was calculated as follows: σ = d / (R*S), where d is the thickness of the pre-lithiated composite separator, R is the measured impedance, and S is the effective measurement area of ​​the pre-lithiated composite separator.

[0087] Example 2:

[0088] Inorganic solid electrolyte material li 1.3 Al 0.3 Ti 1.7 P3O 12 (D50 = 0.3 μm) The inorganic solid electrolyte was ultrasonically dispersed in NMP solution (the mass ratio of inorganic solid electrolyte to NMP solvent was 40%), and then stirred at 100°C for 3 hours. Next, the polyacrylic acid organic material was added to the dispersed solution at a mass ratio of 3:1 (organic material to inorganic solid electrolyte). After addition, the solution was stirred at 50°C for 18 hours to complete the preparation of the adhesive. Simultaneously, a binder solution and artificial graphite electronically conductive material were added, with a binder solution to organic material mass ratio of 0.2:1 and an electronically conductive material to inorganic solid electrolyte mass ratio of 0.4:1.

[0089] The above-mentioned adhesive solution was applied to the surface of the pre-lithiation layer by a scraping method, and the wet thickness of the coating was controlled at 3 μm. After coating, it was placed in a vacuum drying oven at 80°C for 60 min.

[0090] A pre-lithiated composite separator was assembled with positive and negative electrodes to form a button-type half-cell. Both the positive and negative electrodes were made of stainless steel. The pre-lithiated composite separator had 1, 2, and 3 layers, respectively. Electrolyte was added, the cells were sealed, and allowed to stand for 6 hours before testing their EIS impedance. The EIS test conditions were 0.01-106 Hz with a 5 mV disturbance. The ionic conductivity σ was calculated as follows: σ = d / (R*S), where d is the thickness of the pre-lithiated composite separator, R is the measured impedance, and S is the effective measurement area of ​​the pre-lithiated composite separator.

[0091] Example 3:

[0092] Inorganic solid electrolyte material Li 0.33 La 0.55 TiO3 (D50 = 0.4 μm) was ultrasonically dispersed in NMP solution (the inorganic solid electrolyte accounted for 40% of the NMP solvent by mass), and then stirred at 100°C for 3 hours. Next, polyacrylic acid organic material was added to the dispersed solution at a mass ratio of 3:1 to the inorganic solid electrolyte. After addition, the mixture was stirred at 50°C for 18 hours to complete the preparation of the adhesive solution. Simultaneously, a binder solution and artificial graphite electronically conductive material were added, with a binder solution to organic material mass ratio of 0.2:1 and an electronically conductive material to inorganic solid electrolyte mass ratio of 0.4:1.

[0093] The above-mentioned adhesive solution was applied to the surface of the pre-lithiation layer by a scraping method, and the wet thickness of the coating was controlled at 3 μm. After coating, it was placed in a vacuum drying oven at 80°C for 60 min.

[0094] A pre-lithiated composite separator was assembled with positive and negative electrodes to form a button-type half-cell. Both the positive and negative electrodes were made of stainless steel. The pre-lithiated composite separator had 1, 2, and 3 layers, respectively. Electrolyte was added, the cells were sealed, and allowed to stand for 6 hours before testing their EIS impedance. The EIS test conditions were 0.01-106 Hz with a 5 mV disturbance. The ionic conductivity σ was calculated as follows: σ = d / (R*S), where d is the thickness of the pre-lithiated composite separator, R is the measured impedance, and S is the effective measurement area of ​​the pre-lithiated composite separator.

[0095] Comparative Example 1:

[0096] Polyacrylic acid organic material was added to NMP solution, with polyacrylic acid accounting for 80% of the NMP solvent by mass. After addition, the mixture was stirred at 50 degrees Celsius for 18 hours to complete the preparation of the adhesive solution. Simultaneously, an adhesive solution and artificial graphite electronically conductive material were added. The mass ratio of the adhesive solution to the organic material was 0.2:1, and the mass ratio of the electronically conductive material to the polyacrylic acid organic material was 0.7:1.

[0097] The adhesive solution described above was applied to the surface of the diaphragm by scraping, and the wet thickness of the coating was controlled at 3 μm. After coating, the diaphragm was placed in a vacuum drying oven at 80°C for 60 min.

[0098] Comparative Example 2:

[0099] Traditional lithium carbonate particles were ultrasonically dispersed in an NMP solution (lithium carbonate comprising 40% of the NMP solvent by mass) and then stirred at 100°C for 3 hours. PVDF binder particles, comprising 5% of the lithium carbonate by mass, were then added to the dispersed NMP solution. The solution was stirred at 50°C for 18 hours after addition to complete the preparation of the adhesive. Simultaneously with the addition of the binder, artificial graphite electronically conductive material, comprising 20% ​​of the lithium carbonate by mass, could be added.

[0100] The adhesive solution described above was applied to the surface of the diaphragm by scraping, and the wet thickness of the coating was controlled at 3 μm. After coating, the diaphragm was placed in a vacuum drying oven at 80°C for 60 min.

[0101] The ionic conductivity of the membranes in Examples 1-3 and the comparative examples was tested, and the test data are shown in Table 1.

[0102] Table 1 Test data for each embodiment and comparative example

[0103]

[0104] The test results show that the pre-lithiated composite membrane with added inorganic solid electrolyte has a significant advantage in lithium-ion conductivity. The lithium-ion conductivity of Examples 1-3 is significantly greater than that of Comparative Examples 1 and 2. In particular, Example 1 has a lithium-ion conductivity of 0.707 mS / cm, which is nearly 30% higher.

[0105] The test results show that the batteries assembled with the pre-lithium composite separator containing inorganic solid electrolyte also have lower internal resistance, all below 10mΩ. In particular, in Example 1, the battery internal resistance was reduced by more than 1mΩ, a reduction of nearly 10%, which is a significant advantage.

[0106] The test results show that the pre-lithium composite separator with added inorganic solid electrolyte also produces batteries with better first coulombic efficiency.

[0107] The test results show that the pre-lithium composite membrane battery with added inorganic solid electrolyte has a higher capacity retention rate after 100 cycles, which is nearly 2 percentage points higher, thus improving the battery performance.

[0108] The difference in ionic conductivity for different embodiments in Table 1 is due to the difference in conductivity of the solid electrolyte itself. Different solid electrolytes can be selected to form a pre-lithium composite membrane according to specific circumstances, which will significantly improve battery performance.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and not to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure, and they should all be covered within the scope of the claims and specification of this disclosure. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. This disclosure is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A pre-lithium composite separator, characterized in that, include: Diaphragm substrate; A pre-lithiation layer is disposed on at least one side of the separator substrate; as well as A protective layer is disposed on at least one side of the pre-lithiation layer; the protective layer includes a network skeleton and a filler filled in the network skeleton, the network skeleton being an organic material and the filler being a conductive material.

2. The pre-lithiation composite separator according to claim 1, characterized in that, The organic material is at least one of the following: polyacrylic acid, waterborne polyurethane, or polyacrylonitrile.

3. The pre-lithiation composite separator according to claim 1, characterized in that, The conductive material is an inorganic solid electrolyte material; Optionally, the inorganic solid electrolyte material is at least one of the following: lithium aluminum titanium phosphate (LATP), lithium phosphorus sulfide chloride (LPSCL), lithium lanthanum titanate (LLTO), and tantalum-doped lithium lanthanum zirconium oxide (LLZTO). Optionally, the inorganic solid electrolyte material is at least one of the following: li 1.3 Al 0.3 Ti 1.7 P3O 12 Li6PS5Cl, Li 0.33 La 0.55 TiO3, Li 6.6 La3Zr 1.6 Ta 0.4 O 12 Li 1+x+y Al X Ti 2-x Si y P 3-y O 12 .

4. The pre-lithiation composite separator according to claim 1, characterized in that, The conductive material D 50 The particle size is between 0.3 and 10 μm.

5. The pre-lithium composite separator according to claim 3, characterized in that, The mass ratio of the inorganic solid electrolyte material to the organic matter is between 20% and 50%.

6. The pre-lithiation composite separator according to claim 1, characterized in that, The protective layer further includes a binder soluble in the electrolyte; and / or, the protective layer further includes an electronically conductive material.

7. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode, characterized in that, The separator is a pre-lithium composite separator as described in any one of claims 1-6.

8. A method for preparing a pre-lithium composite separator as described in any one of claims 1-6, characterized in that, Includes the following steps: Provide diaphragm substrate; A pre-lithium layer is deposited on at least one side of the diaphragm substrate; The protective layer is coated on the surface of the pre-lithiation layer away from the membrane substrate. The protective layer includes a network skeleton and a filler filled in the network skeleton. The network skeleton is an organic material and the filler is a conductive material.

9. The method for preparing the pre-lithium composite separator according to claim 8, characterized in that, It also includes the step of preparing the protective layer adhesive, including: An inorganic solid electrolyte material is ultrasonically dispersed in an NMP solution, wherein the inorganic solid electrolyte accounts for 30%-60% of the mass of the NMP solution. The organic material is added to the well-dispersed solution, and the mass ratio of the inorganic solid electrolyte material to the organic material is between 20-50%. The mixture is stirred for 12-24 hours to complete the preparation of the protective layer adhesive.

10. A method for preparing a lithium-ion battery, characterized in that, Includes the following steps: A positive electrode active material is uniformly coated on the surface of the positive electrode current collector to form a positive electrode sheet; A negative electrode active material is uniformly coated on the surface of the negative electrode current collector to form a negative electrode sheet; The pre-lithium composite membrane is prepared using the preparation method of the pre-lithium composite membrane as described in claim 8 or 9; The pre-lithiation composite separator is placed between the positive electrode and the negative electrode, and the positive electrode, the pre-lithiation composite separator and the negative electrode are placed in the housing. Electrolyte is injected into the housing and then the housing is sealed.

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