A gradient lithium-supplemented separator and its preparation method and battery

Abstract

This invention provides a gradient lithium replenishment separator, its preparation method, and a battery, belonging to the field of battery technology. The gradient lithium replenishment separator includes a base film, a first lithium replenishment coating, and a second lithium replenishment coating stacked sequentially. The first lithium replenishment coating includes a first lithium replenishing agent, a ceramic material, and a first binder. The second lithium replenishment coating includes a second lithium replenishing agent, a conductive agent, and a second binder. The lithium replenishment rate of the second lithium replenishing agent is greater than that of the first lithium replenishing agent. This invention achieves a gradient-controlled lithium replenishment effect—rapid lithium replenishment in the early stage and slow lithium replenishment in the later stage—while ensuring the stability of the lithium replenishment reaction.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a gradient lithium-filling separator, its preparation method, and a battery. Background Technology

[0002] Because batteries experience irreversible capacity loss during charging and discharging, additional lithium replenishment is required to overcome this loss. Existing separator lithium replenishment methods often employ a single or mixed lithium replenishment agent coating design. This design suffers from two major problems: first, the lithium replenishment agent reacts violently with the electrolyte in the initial stages, leading to low lithium replenishment efficiency and the generation of numerous byproducts, affecting battery interface stability; second, the lithium replenishment process cannot match the lithium-ion migration patterns during battery charging and discharging, easily resulting in excessive lithium replenishment in the early stages leading to lithium plating, and insufficient lithium replenishment in the later stages causing rapid capacity decay.

[0003] In existing technologies, lithium replenishment can be achieved by coating the membrane surface with lithium metal powder or lithium alloy lithium replenishing agent. However, lithium metal powder has high reactivity and is prone to causing local overheating when in contact with electrolyte, and the amount of lithium replenishment is difficult to control precisely. In other existing technologies, lithium salt lithium replenishing agents are used for lithium replenishment. Although the reaction stability is improved, the lithium replenishment rate is slow and cannot meet the rapid lithium replenishment requirements of the battery's first charge and discharge.

[0004] Therefore, there is an urgent need to provide a lithium replenishment membrane that can achieve "gradient rate control and stable reaction" to resolve the contradiction between lithium replenishment efficiency, safety, and long-term cycle stability in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a gradient lithium replenishment separator, its preparation method, and a battery. The gradient lithium replenishment separator includes two lithium replenishment coatings, wherein the lithium replenishment rate of the second lithium replenishment agent in the second lithium replenishment coating is greater than the lithium replenishment rate of the first lithium replenishment agent in the first lithium replenishment coating, thereby achieving a gradient-controlled lithium replenishment effect of rapid lithium replenishment in the early stage and slow lithium replenishment in the later stage. At the same time, ceramic materials are added to the first lithium replenishment coating to ensure the stability of the lithium replenishment reaction.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a gradient lithium replenishment separator, the gradient lithium replenishment separator comprising a base film, a first lithium replenishment coating and a second lithium replenishment coating stacked sequentially;

[0008] The first lithium replenishing coating includes a first lithium replenishing agent, a ceramic material, and a first binder; the second lithium replenishing coating includes a second lithium replenishing agent, a conductive agent, and a second binder.

[0009] The lithium replenishment rate of the second lithium replenishing agent is greater than that of the first lithium replenishing agent.

[0010] In some embodiments, the second lithium supplement includes any one or a combination of at least two of lithium powder, Li-Si alloy, Li-Al alloy, LiH, LiBH4, Li3N, Li2O2 or Li2S.

[0011] In some embodiments, the first lithium replenishing agent includes any one or a combination of at least two of Li2C2O4, Li5FeO4, LiNiO2, Li2MnO3, xLi2MnO3·(1-x)LiMO2, Li2FeS2 or Li2CO3, wherein M in xLi2MnO3·(1-x)LiMO2 includes any one or a combination of at least two of Ni, Co or Mn, and 0 < x < 1.

[0012] In some embodiments, the mass ratio of the first lithium supplement, the ceramic material and the first binder is (0.1-99):(0.1-99):(0.1-20), preferably (0.1-20):(80-99):(0.1-20).

[0013] In some embodiments, the mass ratio of the second lithium supplement, the conductive agent, and the second binder is (0.1-99):(0.1-99):(0.1-20), preferably (80-99):(0.1-20):(0.1-20).

[0014] In some embodiments, the thickness ratio of the first lithium replenishing coating and the second lithium replenishing coating is (1.5-5):1.

[0015] In some embodiments, the thickness of the first lithium replenishment coating is 0.5 μm-10 μm.

[0016] In some embodiments, the thickness of the second lithium replenishment coating is 0.1 μm-10 μm.

[0017] In some embodiments, the ceramic material includes any one or a combination of at least two of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, or SiC.

[0018] In some embodiments, the first adhesive and the second adhesive independently comprise any one or a combination of at least two of the following: styrene-butadiene rubber, sodium carboxymethyl cellulose, PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), PMMA (polymethyl methacrylate), waterborne acrylate, or PMMA-PBA (polymethyl methacrylate-polybutyl acrylate copolymer, which may be core-shell type).

[0019] In some embodiments, the conductive agent includes any one or a combination of at least two of Super P, CNT, graphene, carbon nanofibers, or graphite.

[0020] In some embodiments, the base membrane includes a PP microporous membrane and / or a PE microporous membrane.

[0021] In some embodiments, the thickness of the base film is 3μm-50μm.

[0022] In a second aspect, the present invention provides a method for preparing a gradient lithium-supplemented separator as described in the first aspect, the method comprising the following steps:

[0023] The slurry of the first lithium replenishment coating is coated on one side surface of the base film. After drying, the first lithium replenishment coating is obtained on one side surface of the base film. The slurry of the second lithium replenishment coating is coated on the surface of the first lithium replenishment coating. After drying, the gradient lithium replenishment separator is obtained.

[0024] Thirdly, the present invention provides a battery comprising a gradient lithium-filling separator as described in the first aspect, wherein one side of the gradient lithium-filling separator having a second lithium-filling coating faces the negative electrode of the battery.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) In this invention, a first lithium replenishment coating is first set on one side surface of the base film, and then a second lithium replenishment coating is set on the surface of the first lithium replenishment coating. The lithium replenishment rate of the second lithium replenishment agent in the second lithium replenishment coating is greater than that of the first lithium replenishment agent in the first lithium replenishment coating. Therefore, the second lithium replenishment coating can quickly release lithium ions during the first charge and discharge stage of the battery to compensate for the initial irreversible lithium loss of the negative electrode. The first lithium replenishment coating slowly releases lithium ions in subsequent cycles to avoid the problem of insufficient lithium replenishment in the later stage. This achieves a precise match of "fast replenishment in the early stage and slow replenishment in the later stage", and improves the first coulombic efficiency and cycle performance of the battery.

[0027] (2) The second lithium replenishing agent of the present invention has a fast lithium replenishing speed and high reactivity. The ceramic material is set in the first lithium replenishing coating to isolate the second lithium replenishing coating from the base film, thereby reducing the risk of reaction between the highly active second lithium replenishing agent and the base film. At the same time, the first lithium replenishing agent has a low lithium replenishing speed and low reactivity, which slows down the initial reaction rate between the lithium replenishing agent and the electrolyte, reduces the generation of by-products, thereby reducing the impedance growth rate during battery cycling, improving the overall lithium replenishing reaction stability, and solving the contradiction between lithium replenishing efficiency and safety and long-term cycling stability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the gradient lithium-supplementing separator described in Embodiment 1 of the present invention.

[0029] Wherein, 1-base film, 2-first lithium replenishment coating, 3-second lithium replenishment coating. Detailed Implementation

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0031] In a first aspect, the present invention provides a gradient lithium replenishment separator, the gradient lithium replenishment separator comprising a base film, a first lithium replenishment coating and a second lithium replenishment coating stacked sequentially;

[0032] The first lithium replenishing coating includes a first lithium replenishing agent, a ceramic material, and a first binder; the second lithium replenishing coating includes a second lithium replenishing agent, a conductive agent, and a second binder.

[0033] The lithium replenishment rate of the second lithium replenishing agent is greater than that of the first lithium replenishing agent.

[0034] This invention first forms a first lithium replenishment coating on one side of the base film, and then forms a second lithium replenishment coating on the surface of the first lithium replenishment coating. The lithium replenishment rate of the second lithium replenishment agent in the second lithium replenishment coating is greater than that of the first lithium replenishment agent in the first lithium replenishment coating. Therefore, the second lithium replenishment coating can quickly release lithium ions during the first charge and discharge stage of the battery to compensate for the initial irreversible lithium loss of the negative electrode. The first lithium replenishment coating, on the other hand, slowly releases lithium ions in subsequent cycles to avoid the problem of insufficient lithium replenishment in the later stages. This achieves a precise match of "fast replenishment in the early stage and slow replenishment in the later stage", and at the same time improves the battery's initial coulombic efficiency and cycle performance.

[0035] Furthermore, the second lithium replenishing agent of this invention has a fast lithium replenishing rate and high reactivity. The ceramic material in the first lithium replenishing coating isolates the second lithium replenishing coating from the base film, reducing the risk of reaction between the highly active second lithium replenishing agent and the base film. At the same time, the first lithium replenishing agent has a low lithium replenishing rate and low reactivity, which slows down the initial reaction rate between the lithium replenishing agent and the electrolyte, reduces the generation of by-products, thereby reducing the impedance growth rate during battery cycling, improving the overall lithium replenishing reaction stability, and resolving the contradiction between lithium replenishing efficiency, safety, and long-term cycling stability.

[0036] It is understood that the lithium replenishment rate of the lithium replenishment agent described in this invention is related to the activity of the lithium replenishment agent and the decomposition potential of the lithium replenishment agent.

[0037] The gradient lithium replenishment separator of this invention has a first lithium replenishment coating and a second lithium replenishment coating on one side of the base film. When applied in a battery, the side with the first and second lithium replenishment coatings faces the negative electrode because the core of lithium replenishment is to replenish the lithium lost by the negative electrode. The ion transport path facing the negative electrode is short, resulting in high lithium replenishment efficiency. Furthermore, since highly active lithium replenishing agents will rapidly oxidize and decompose when in contact with the positive electrode oxidation environment, generating a large number of insulating byproducts and causing exothermic reactions, while the negative electrode reduction environment can reduce the initial reaction activity of the lithium replenishing agent. Combined with the gradient coarse layer design, byproduct generation is reduced and local overheating is avoided. Therefore, facing the negative electrode can avoid severe side reactions and ensure interface and structural stability.

[0038] In one specific embodiment, the second lithium replenishing agent includes any one or a combination of at least two of lithium powder, Li-Si alloy, Li-Al alloy, LiH, LiBH4, Li3N, Li2O2 or Li2S.

[0039] In one specific embodiment, the first lithium replenishing agent includes any one or a combination of at least two of Li2C2O4, Li5FeO4, LiNiO2, Li2MnO3, xLi2MnO3·(1-x)LiMO2, Li2FeS2, or Li2CO3, wherein M in xLi2MnO3·(1-x)LiMO2 includes any one or a combination of at least two of Ni, Co, or Mn, and 0 < x < 1, for example, it can be 0.1, 0.3, 0.5, 0.7, 0.9, or 0.95, but is not limited to the listed values, and other unlisted values ​​within the value range are also applicable.

[0040] In one specific embodiment, the mass ratio of the first lithium supplement, the ceramic material, and the first binder is (0.1-99):(0.1-99):(0.1-20), for example, it can be 0.1:89.1:10, 10:85:5, 15:70:15, 20:60:20, 50:40:10, 70:10:20, 90:5:5 or 89.1:0.1:10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is (0.1-20):(80-99):(0.1-20), and more preferably (5-20):(80-95):(2-10).

[0041] In one specific embodiment, the mass ratio of the second lithium replenishing agent, the conductive agent, and the second binder is (0.1-99):(0.1-99):(0.1-20), for example, it can be 0.1:89.1:10, 10:85:5, 15:70:15, 20:60:20, 50:40:10, 70:10:20, 90:5:5 or 89.1:0.1:10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is (80-99):(0.1-20):(0.1-20), and more preferably (80-90):(5-10):(5-10).

[0042] In one specific embodiment, the thickness ratio of the first lithium replenishing coating and the second lithium replenishing coating is (1.5-5):1, for example, it can be 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Since the second lithium replenishment layer only needs to meet the rapid lithium replenishment requirements of the first charge and discharge cycle, excessive lithium replenishment can easily lead to lithium deposition. Therefore, its thickness is thinner than that of the first lithium replenishment layer. If the second lithium replenishment layer is too thick, it will lead to excessive by-products, while if it is too thin, it will lead to insufficient lithium replenishment. The first lithium replenishment layer needs to continuously provide lithium ions for subsequent cycles and also plays a role in isolation. Therefore, its thickness needs to be thicker than that of the second lithium replenishment layer. The first lithium replenishment layer needs to fix the by-products with sufficient thickness, while avoiding excessive thickness that would hinder ion migration. Therefore, the present invention preferably has a thickness ratio of the first lithium replenishment coating and the second lithium replenishment coating within a specific range, thereby further ensuring the gradient lithium replenishment rate and the stability of the lithium replenishment reaction.

[0044] In one specific embodiment, the thickness of the first lithium replenishment coating is 0.5μm-10μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] In one specific embodiment, the thickness of the second lithium replenishment coating is 0.1μm-10μm, for example, it can be 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] In one specific embodiment, the ceramic material includes any one or a combination of at least two of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, or SiC.

[0047] In one specific embodiment, the first adhesive and the second adhesive each independently include any one or a combination of at least two of the following: styrene-butadiene rubber, sodium carboxymethyl cellulose, PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), PMMA (polymethyl methacrylate), waterborne acrylate, or PMMA-PBA (polymethyl methacrylate-polybutyl acrylate copolymer, which may be core-shell type).

[0048] In one specific embodiment, the conductive agent includes any one or a combination of at least two of Super P, CNT, graphene, carbon nanofibers, or graphite.

[0049] In one specific embodiment, the base membrane includes a PP microporous membrane and / or a PE microporous membrane, and the porosity of the base membrane is 30%-55%, for example, it can be 30%, 35%, 40%, 45%, 50% or 55%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] In one specific embodiment, the thickness of the base film is 3μm-50μm, for example, it can be 3μm, 5μm, 10μm, 20μm, 30μm, 40μm or 50μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0051] In a second aspect, the present invention provides a method for preparing a gradient lithium-supplemented separator as described in the first aspect, the method comprising the following steps:

[0052] The slurry of the first lithium replenishment coating is coated on one side surface of the base film. After drying, the first lithium replenishment coating is obtained on one side surface of the base film. The slurry of the second lithium replenishment coating is coated on the surface of the first lithium replenishment coating. After drying, the gradient lithium replenishment separator is obtained.

[0053] The method for preparing the gradient lithium-filling separator described in this invention has strong process compatibility. The preparation process can adopt the microgravure and slit coating processes commonly used in existing separator coating, without the need for additional special equipment. It can be directly connected to existing lithium-ion battery production lines, reducing the cost of industrial application.

[0054] Thirdly, the present invention provides a battery comprising a gradient lithium-filling separator as described in the first aspect, wherein one side of the gradient lithium-filling separator having a second lithium-filling coating faces the negative electrode of the battery.

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0056] Example 1

[0057] This embodiment provides a gradient lithium-supplementation separator, the structural schematic diagram of which is shown below. Figure 1 As shown, the gradient lithium replenishment membrane includes a base film 1, a first lithium replenishment coating 2, and a second lithium replenishment coating 3 stacked sequentially; the first lithium replenishment coating 2 includes a first lithium replenishing agent, a ceramic material, and a first binder in a mass ratio of 10:80:10, and the second lithium replenishment coating 3 includes a second lithium replenishing agent, a conductive agent, and a second binder in a mass ratio of 85:7.5:7.5.

[0058] The second lithium replenishing agent has a lithium replenishing rate greater than that of the first lithium replenishing agent. The second lithium replenishing agent is lithium powder, the first lithium replenishing agent is Li5FeO4, the ceramic material is SrTiO3, the first binder and the second binder are both PVDF, and the conductive agent is Super P.

[0059] The thickness ratio of the first lithium replenishing coating 2 to the second lithium replenishing coating 3 is 3:1, the thickness of the first lithium replenishing coating 2 is 7.5 μm, and the thickness of the second lithium replenishing coating 3 is 2.5 μm.

[0060] The base membrane 1 is a PP microporous membrane with a thickness of 25 μm (porosity of 40%).

[0061] The preparation method of the gradient lithium-supplemented separator includes the following steps:

[0062] According to the formula, a first lithium replenishing agent, ceramic material, first binder and N-methylpyrrolidone are mixed to prepare a slurry for the first lithium replenishing coating. The slurry for the first lithium replenishing coating is coated on one side surface of the base film. After drying, the first lithium replenishing coating is obtained on one side surface of the base film. A second lithium replenishing agent, conductive agent, second binder and N-methylpyrrolidone are mixed to prepare a slurry for the second lithium replenishing coating. The slurry for the second lithium replenishing coating is coated on the surface of the first lithium replenishing coating. After drying, the gradient lithium replenishing separator is obtained.

[0063] Example 2

[0064] This embodiment provides a gradient lithium replenishment separator, which includes a base film, a first lithium replenishment coating, and a second lithium replenishment coating stacked sequentially; the first lithium replenishment coating includes a first lithium replenishing agent, a ceramic material, and a first binder in a mass ratio of 5:85:10, and the second lithium replenishment coating includes a second lithium replenishing agent, a conductive agent, and a second binder in a mass ratio of 90:5:5.

[0065] The second lithium replenishing agent has a lithium replenishing rate greater than that of the first lithium replenishing agent. The second lithium replenishing agent is lithium powder, the first lithium replenishing agent is Li3N, the ceramic material is SnO2, the first binder and the second binder are both styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 1:1, and the conductive agent is Super P.

[0066] The thickness ratio of the first lithium replenishing coating and the second lithium replenishing coating is 5:1, the thickness of the first lithium replenishing coating is 10 μm, and the thickness of the second lithium replenishing coating is 2 μm.

[0067] The base membrane is a PP microporous membrane with a thickness of 50 μm and a porosity of 30%.

[0068] The preparation method of the gradient lithium-supplemented separator includes the following steps:

[0069] According to the formula, a first lithium replenishing agent, ceramic material, first binder and N-methylpyrrolidone are mixed to prepare a slurry for the first lithium replenishing coating. The slurry for the first lithium replenishing coating is coated on one side surface of the base film. After drying, the first lithium replenishing coating is obtained on one side surface of the base film. A second lithium replenishing agent, conductive agent, second binder and N-methylpyrrolidone are mixed to prepare a slurry for the second lithium replenishing coating. The slurry for the second lithium replenishing coating is coated on the surface of the first lithium replenishing coating. After drying, the gradient lithium replenishing separator is obtained.

[0070] Example 3

[0071] This embodiment provides a gradient lithium replenishment separator, which includes a base film, a first lithium replenishment coating, and a second lithium replenishment coating stacked sequentially; the first lithium replenishment coating includes a first lithium replenishing agent, a ceramic material, and a first binder in a mass ratio of 20:75:5, and the second lithium replenishment coating includes a second lithium replenishing agent, a conductive agent, and a second binder in a mass ratio of 80:10:10.

[0072] The second lithium replenishing agent has a lithium replenishing rate greater than that of the first lithium replenishing agent. The second lithium replenishing agent is lithium powder, the first lithium replenishing agent is LiNiO2, the ceramic material is Al2O3, the first binder and the second binder are both PVDF, and the conductive agent is Super P.

[0073] The thickness ratio of the first lithium replenishing coating and the second lithium replenishing coating is 1.5:1, the thickness of the first lithium replenishing coating is 2.5 μm, and the thickness of the second lithium replenishing coating is 1.67 μm.

[0074] The base membrane is a PE microporous membrane with a thickness of 10 μm and a porosity of 55%.

[0075] The preparation method of the gradient lithium-supplemented separator includes the following steps:

[0076] According to the formula, a first lithium replenishing agent, ceramic material, first binder and N-methylpyrrolidone are mixed to prepare a slurry for the first lithium replenishing coating. The slurry for the first lithium replenishing coating is coated on one side surface of the base film. After drying, the first lithium replenishing coating is obtained on one side surface of the base film. A second lithium replenishing agent, conductive agent, second binder and N-methylpyrrolidone are mixed to prepare a slurry for the second lithium replenishing coating. The slurry for the second lithium replenishing coating is coated on the surface of the first lithium replenishing coating. After drying, the gradient lithium replenishing separator is obtained.

[0077] Example 4

[0078] This embodiment provides a gradient lithium replenishment separator, which is the same as in Embodiment 1 except that the second lithium replenishing agent is a Li-Si alloy.

[0079] Example 5

[0080] This embodiment provides a gradient lithium replenishment separator, which is the same as that in Embodiment 1 except that the second lithium replenishing agent is a Li-Si alloy and the first lithium replenishing agent is Li3N.

[0081] Example 6

[0082] This embodiment provides a gradient lithium replenishment separator, which is the same as that in Embodiment 1 except that the first lithium replenishment agent is LiH.

[0083] Example 7

[0084] This embodiment provides a gradient lithium replenishment separator, which is the same as that in Embodiment 1 except that the first lithium replenishment agent is LiBH4.

[0085] Example 8

[0086] This embodiment provides a gradient lithium replenishment separator. Except that the thickness ratio of the first lithium replenishment coating and the second lithium replenishment coating is 0.8:1, that is, the thickness of the first lithium replenishment coating is 2μm, the gradient lithium replenishment separator is the same as that in Embodiment 1.

[0087] Example 9

[0088] This embodiment provides a gradient lithium replenishment separator. Except for the thickness ratio of the first lithium replenishment coating and the second lithium replenishment coating being 6:1, i.e., the thickness of the first lithium replenishment coating being 15μm, the gradient lithium replenishment separator is the same as that in Embodiment 1.

[0089] Comparative Example 1

[0090] This comparative example provides a lithium replenishing membrane, which is the same as in Example 1 except that the first and second lithium replenishing agents are both lithium powder.

[0091] Comparative Example 2

[0092] This comparative example provides a lithium replenishing membrane, which is the same as in Example 1 except that the first and second lithium replenishing agents are both Li5FeO4.

[0093] Comparative Example 3

[0094] This comparative example provides a lithium replenishing membrane, which is the same as in Example 1 except that the first lithium replenishing agent is lithium powder and the second lithium replenishing agent is Li5FeO4.

[0095] Comparative Example 4

[0096] This comparative example provides a lithium-replenishing separator, which is identical to Example 1 except that the ceramic material is replaced by the conductive agent Super P.

[0097] The separators obtained in the above embodiments and comparative examples were used to prepare lithium-ion batteries with NCM811 positive electrode, graphite negative electrode and lithium hexafluorophosphate electrolyte (wherein, when the separator has a coating on one side, the side with the coating faces the negative electrode); the first efficiency and cycle performance of the lithium-ion batteries were tested at a test temperature of 25°C and a charge / discharge voltage range of 2.5V-4.2V.

[0098] The types of the first and second lithium supplementers in the above embodiments and comparative examples, and the electrochemical performance test results are shown in Table 1.

[0099] Table 1

[0100]

[0101] As can be seen from Table 1 above:

[0102] (1) As can be seen from Example 1 and Comparative Examples 1-2, the present invention uses a first lithium replenishing agent and a second lithium replenishing agent with different lithium replenishing rates. The second lithium replenishing agent can replenish lithium quickly in the early stage, while the first lithium replenishing agent replenishes lithium slowly in the later stage, thus ensuring the battery's first efficiency and cycle performance. As can be seen from Example 1 and Comparative Example 3, the lithium replenishing rate of the second lithium replenishing agent in the present invention is greater than that of the first lithium replenishing agent. If the two are interchanged, the highly active fast lithium replenishing agent is located in the first lithium replenishing coating, and the low-activity slow lithium replenishing agent is located in the second lithium replenishing coating. In this case, the first lithium replenishing efficiency is low, the irreversible lithium loss of the negative electrode cannot be compensated, resulting in a low first coulombic efficiency of the battery. Furthermore, when the lithium release of the low-activity lithium replenishing agent decreases in the later stage, the lithium ions of the highly active lithium replenishing agent are released in a concentrated manner, which may trigger lithium plating, thereby affecting the battery's cycle and safety performance. As can be seen from Example 1 and Comparative Example 4, the present invention sets ceramic materials in the first lithium replenishing coating, which can reduce the risk of reaction between the lithium replenishing agent and the base film and improve the stability of the lithium replenishing reaction.

[0103] (2) As can be seen from Examples 1 to 5, the difference in lithium replenishment rate between the first lithium replenisher and the second lithium replenisher in Examples 2 and 5 is small. The first lithium replenisher is not preferred. Moreover, the lithium replenishment activity of both the first and second lithium replenishers is high. Therefore, the performance of Examples 2 and 5 is lower than that of Examples 1 and 3-4. The present invention prefers that the materials selected for the first and second lithium replenishers correspond to each other, which can improve the difference in lithium replenishment rate between the first and second lithium replenishers, thereby further improving the overall performance of the battery. As can be seen from Examples 1 and Examples 6-7, although the lithium replenishment rate of the second lithium replenisher in Examples 6-7 is greater than that of the first lithium replenisher, the first lithium replenisher in Examples 6-7 is also a highly reactive lithium replenisher with a faster lithium replenishment rate. Therefore, the effect of "fast replenishment in the early stage and slow replenishment in the later stage" is reduced, and the safety of the battery is also reduced accordingly. As can be seen from Examples 1 and Examples 8-9, the present invention prefers that the thickness ratio of the first lithium replenishment coating and the second lithium replenishment coating be within a specific range, thereby further ensuring the gradient lithium replenishment rate and the stability of the lithium replenishment reaction.

[0104] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A gradient lithium supplementing separator, characterized by, The gradient lithium supplement diaphragm comprises a base film, a first lithium supplement coating layer and a second lithium supplement coating layer arranged in sequence. The first lithium supplement coating layer comprises a first lithium supplement agent, a ceramic material and a first binder, and the second lithium supplement coating layer comprises a second lithium supplement agent, a conductive agent and a second binder. The lithium supplement speed of the second lithium supplement agent is greater than that of the first lithium supplement agent.

2. The gradient lithium supplementing separator of claim 1, wherein, The second lithium supplement agent comprises any one or a combination of at least two of lithium powder, Li-Si alloy, Li-Al alloy, LiH, LiBH4, Li3N, Li2O2 or Li2S.

3. The gradient lithium supplementing separator according to claim 1 or 2, characterized by, The first lithium supplement agent comprises any one or a combination of at least two of Li2C2O4, Li5FeO4, LiNiO2, Li2MnO3, xLi2MnO3·(1-x)LiMO2, Li2FeS2 or Li2CO3, wherein M in xLi2MnO3·(1-x)LiMO2 comprises any one or a combination of at least two of Ni, Co or Mn, and 0 4. The gradient lithium supplementing separator according to claim 1 or 2, characterized by, The mass ratio of the first lithium supplement agent, the ceramic material and the first binder is (0.1-99):(0.1-99):(0.1-20); And / or, the mass ratio of the second lithium supplement agent, the conductive agent and the second binder is (0.1-99):(0.1-99):(0.1-20).

5. The gradient lithium supplementing separator of claim 4, wherein, The mass ratio of the first lithium supplement agent, the ceramic material and the first binder is (0.1-20):(80-99):(0.1-20); And / or, the mass ratio of the second lithium supplement agent, the conductive agent and the second binder is (80-99):(0.1-20):(0.1-20).

6. The gradient lithium supplementing separator of claim 1 or 2, wherein, The thickness ratio of the first lithium supplement coating layer and the second lithium supplement coating layer is (1.5-5):1; And / or, the thickness of the first lithium supplement coating layer is 0.5μm-10μm; And / or, the thickness of the second lithium supplement coating layer is 0.1μm-10μm.

7. The gradient lithium supplementing separator of claim 1 or 2, wherein, The ceramic material comprises any one or a combination of at least two of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2 or SiC; And / or, the first binder and the second binder independently comprise any one or a combination of at least two of styrene-butadiene rubber, sodium carboxymethyl cellulose, PVDF, PVDF-HFP, PMMA, water-based acrylate or PMMA-PBA; And / or, the conductive agent comprises any one or a combination of at least two of Super P, CNT, graphene, carbon nanofiber or graphite.

8. The gradient lithium supplementing separator of claim 1 or 2, wherein, The base film comprises a PP microporous film and / or a PE microporous film; And / or, the thickness of the base film is 3μm-50μm.

9. A method for preparing the gradient lithium supplementing separator according to any one of claims 1-8, characterized in that, The preparation method comprises the following steps: The slurry of the first lithium supplement coating layer is coated on one side surface of the base film, and after drying, the first lithium supplement coating layer is obtained on one side surface of the base film, the slurry of the second lithium supplement coating layer is coated on the surface of the first lithium supplement coating layer, and after drying, the gradient lithium supplement diaphragm is obtained.

10. A battery, characterized by The battery comprises the gradient lithium supplementing separator as claimed in any one of claims 1-8, and the side of the gradient lithium supplementing separator where the second lithium supplementing coating is arranged faces the negative electrode of the battery.

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