Lithium ion battery

Abstract

The invention provides a lithium ion battery, belongs to the technical field of lithium ion batteries, and overcomes the defect that Ni ions in a ternary lithium battery are easy to migrate in the prior art. The lithium ion battery comprises a positive plate, a negative plate, a diaphragm and an electrolyte, the positive plate comprises a positive current collector and a positive material layer arranged on at least one surface of the positive current collector, and the positive material layer comprises a ternary material; the general formula of the ternary material is LiNixCoyM1-x-yO2, x is more than or equal to 0.5 and less than or equal to 0.9, y is more than or equal to 0.05 and less than or equal to 0.3, and M is Mn or Al; the diaphragm comprises a base membrane and a zeolite coating arranged on at least one surface of the base membrane, the zeolite coating comprises zeolite, and the zeolite has micropores with the pore diameter of F nm; x / F is equal to 0.5 to 2.8; wherein F is equal to 0.3 to 1.2. The lithium ion battery provided by the invention has excellent cycle performance and safety performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a lithium - ion battery. Background Art

[0002] With the increasing demand for high - energy - density and long - cycle - life batteries in the fields of new - energy vehicles, portable electronic devices, and energy - storage systems, ternary lithium batteries (especially the NCM / NCA system) have attracted much attention due to their excellent electrochemical performance. However, a key problem faced by ternary lithium batteries in practical applications is the migration phenomenon of Ni ions.

[0003] During the charge - discharge cycle of ternary lithium batteries, especially under high - temperature, high - voltage, or fast - charge - discharge conditions, Ni ions in the positive - electrode active material are prone to migrate. This migration not only causes damage to the structure of the positive - electrode active material, reducing the electrochemical performance of the battery, but also may trigger side reactions, such as reacting with solvents or lithium salts in the electrolyte to form insoluble precipitates, blocking the pores of the separator, and affecting the normal transmission of lithium ions. More seriously, the migrated ions may also penetrate the separator and reach the surface of the negative electrode, causing corrosion of the negative - electrode material and internal short - circuit of the battery, thus seriously threatening the safety and service life of the battery. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that Ni ions in ternary lithium batteries are prone to migrate in the prior art, so as to provide a lithium - ion battery.

[0005] To this end, the present invention provides the following technical solutions:

[0006] A lithium - ion battery, comprising a positive - electrode sheet, a negative - electrode sheet, a separator, and an electrolyte. The positive - electrode sheet includes a positive - electrode current collector and a positive - electrode material layer provided on at least one surface of the positive - electrode current collector, and the positive - electrode material layer includes a ternary material;

[0007] The general formula of the ternary material is LiNi x Co y M 1-x-y O 2 , where 0.5 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.3, and M is Mn or Al;

[0008] The separator includes a base film and a zeolite coating provided on at least one surface of the base film. The zeolite coating includes zeolite, and the zeolite has micropores with a pore diameter of F nm;

[0009] x / F = 0.5 - 2.8;

[0010] where F = 0.3 - 1.2.

[0011] In a possible implementation, the zeolite includes hierarchical pore zeolite;

[0012] Optionally, the porosity of the hierarchical pore zeolite is C%, and 100x / C = 0.8 to 2.5;

[0013] Optionally, C = 35 to 70;

[0014] Optionally, the hierarchical pore zeolite further includes mesopores and / or macropores with pore diameters of 2 to 500 nm.

[0015] In a possible implementation, F = 0.3 to 0.7;

[0016] In a possible implementation, x / F = 0.7 to 2.3.

[0017] In a possible implementation, the specific surface area of the zeolite is Am 2 / g, and the particle size Dv50 of the zeolite 1 is B μm, and A / B = 100 to 1500;

[0018] Optionally, A = 20 to 700;

[0019] Optionally, B = 0.01 to 5.

[0020] In a possible implementation, the particle size Dv50 of the ternary material 2 is 3 to 15 μm.

[0021] In a possible implementation, the thickness of the zeolite coating is h μm, and B / h = 0.1 to 0.8;

[0022] Optionally, h = 0.5 to 10.

[0023] In a possible implementation, the pore volume of the zeolite is 0.5 to 1.5 cm 3 / g;

[0024] In a possible implementation, the ternary material is a nickel-cobalt-manganese ternary material;

[0025] In a possible implementation, the separator further includes an adhesive layer provided on at least one surface of the base film and / or the zeolite coating;

[0026] Optionally, the thickness of the adhesive layer is 0.1 to 4 μm;

[0027] In a possible implementation, the base film includes one or more of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone;

[0028] Optionally, the thickness of the base film is 3 - 20 μm;

[0029] Optionally, the pore size of the base film is 0.02 - 0.5 μm.

[0030] In a possible implementation, the mass percentage of zeolite in the zeolite coating is 10% - 90%;

[0031] In a possible implementation, the zeolite coating further includes a binder;

[0032] Optionally, the mass percentage of the binder in the zeolite coating is 0 - 90%;

[0033] In a possible implementation, the zeolite coating further includes an auxiliary agent;

[0034] Optionally, the mass percentage of the auxiliary agent in the zeolite coating is 0 - 10%.

[0035] In a possible implementation, the tensile strength of the separator is 2000 - 5500 gf;

[0036] In a possible implementation, the adhesion of the separator is 5 - 30 N / m;

[0037] In a possible implementation, the porosity of the base film is 35 - 45%;

[0038] In a possible implementation, the puncture strength of the separator is 150 - 600 gf.

[0039] In a possible implementation, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material;

[0040] The negative electrode active material includes silicon carbon and graphite;

[0041] Optionally, in the silicon carbon, the mass content of silicon element is 20 - 70%;

[0042] Optionally, the particle size Dv50 of the silicon carbon 3 is 5 - 15 μm.

[0043] The technical solution of the present invention has the following advantages:

[0044] 1. The lithium-ion battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a ternary material; the general formula of the ternary material is LiNi x Co y M 1-x-y O 2, where 0.5 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.3, and M is Mn or Al; the separator includes a base film and a zeolite coating provided on at least one surface of the base film, the zeolite coating includes zeolite, and the zeolite has micropores with a pore diameter of F nm; x / F = 0.5 - 2.8. An appropriate nickel content in the ternary material improves the energy density of the battery, while an appropriate pore diameter of the zeolite coating effectively promotes the rapid transport of lithium ions and significantly inhibits the migration of transition metal ions, thus ensuring the long life and high safety of the battery. The lithium-ion battery of the present application satisfying x / F = 0.5 - 2.8 exhibits excellent comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 It is a schematic diagram of the separator structure.

[0047] Reference numerals:

[0048] 1 - Base film; 2 - Zeolite coating; 3 - Adhesive layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] The following embodiments are provided to better understand the present invention further. It is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0050] For those steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specified by the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0051] During the charge and discharge cycle of the lithium battery, Ni ions in the ternary material are prone to migration, which seriously threatens the safety and service life of the battery.

[0052] Based on this, the present application provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, and the positive electrode material layer includes a ternary material;

[0053] The general formula of the ternary material is LiNi x Co y M 1-x-y O 2 , where 0.5 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.3, and M is Mn or Al;

[0054] The separator includes a base film and a zeolite coating provided on at least one surface of the base film. The zeolite coating includes zeolite, and the zeolite has micropores with a pore diameter of F nm;

[0055] x / F = 0.5 - 2.8;

[0056] Among them, F = 0.3 - 1.2. Optionally, x / F = 0.7 - 2.3.

[0057] Exemplarily, x can be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, or 0.90. y can be 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3. x / F can be 0.5, 0.6, 0.7, 0.8, 1.0, 1.3, 1.5, 1.8, 2.0, 2.2, 2.5, or 2.8. Exemplarily, F can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, or 1.2.

[0058] The higher the Ni content in the positive electrode, the relatively poorer the structural stability of the ternary material. During charge and discharge, especially under high-temperature or deep charge-discharge conditions, its crystal structure may undergo minor changes, resulting in the migration and redistribution of transition metal ions. These migrated ions may deposit on the surface of the negative electrode, forming a so-called "metal coating", which not only reduces the cycle performance of the battery but may also cause internal short circuits, further exacerbating self-discharge and thermal runaway problems.

[0059] Zeolite is a kind of aluminosilicate with a topological structure and has microporous channels inside, which can effectively adsorb metal ions. And the zeolite framework carries a negative charge and can attract positively charged metal ions (such as Ni, Co, Mn) through electrostatic interaction. This electrostatic interaction helps to block the migration of these metal ions. The functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the zeolite framework can form chemical adsorption bonds with Ni, Co, Mn ions, and this chemical adsorption can further enhance the blocking ability of the separator to these metal ions.

[0060] When the nickel content is relatively low and the pore size F of the zeolite is relatively large, the energy density of the battery is limited, and at the same time, the migration problem of transition metal ions is aggravated. The adsorption and blocking effects of the zeolite coating on ions are weakened, resulting in a decrease in the cycle stability of the battery and accelerating the capacity decay process. When the nickel content is relatively high and the small pore size of the zeolite is relatively small, although the energy density of the battery may be improved to a certain extent, it brings problems of decreased cycle performance and poor thermal stability. The migration of transition metal ions becomes difficult to control, exceeding the adsorption capacity of the zeolite coating, leading to the destruction of the negative electrode SEI film and the rapid decay of the battery capacity, increasing the safety hazards of the battery. Therefore, when x / F = 0.5 - 2.8, the lithium-ion battery exhibits excellent comprehensive performance. The appropriate nickel content in the ternary material improves the energy density of the battery, while the appropriate pore size of the zeolite coating effectively promotes the rapid transmission of lithium ions and significantly inhibits the migration of transition metal ions, thus ensuring the long life and high safety of the battery.

[0061] When the micropore size of the zeolite is 0.3 - 1.2 nm, it can prevent Ni ions from entering the micropore channels of the zeolite, making them unable to shuttle through the zeolite channels, thereby inhibiting the migration of Ni ions. Moreover, the zeolite framework carries a negative charge and can attract metal ions with positive charges through electrostatic interaction. This electrostatic interaction helps to block the migration of these metal ions. The functional groups on the zeolite framework can form chemical adsorption bonds with Ni, Co, and Mn ions, and this chemical adsorption effect can further enhance the blocking ability of the separator for these metal ions. When the micropore size of the zeolite is 0.3 - 1.2 nm, lithium ions can pass through. That is, the zeolite used in the separator of the present application can increase the lithium ion transmission channels while inhibiting the migration of Ni ions, ensuring the rapid and efficient transmission of lithium ions.

[0062] In a possible implementation manner, the zeolite includes hierarchical zeolite;

[0063] Hierarchical zeolite is a zeolite material with a hierarchical pore structure. Compared with traditional zeolites, hierarchical zeolites not only have micropores but also introduce mesopores (2 - 50 nm) and / or macropores (greater than 50 nm) structures, thus forming a hierarchical pore system.

[0064] Optionally, the porosity of the hierarchical zeolite is C%, and 100x / C = 0.8 - 2.5;

[0065] Optionally, C = 35 - 70.

[0066] Exemplarily, C can be 35, 40, 45, 50, 55, 60, 65, or 70; exemplarily, 100x / C can be 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, or 2.5.

[0067] The structure of hierarchical pores can increase the specific surface area of zeolite, thereby enhancing the adsorption of transition metals by zeolite, which is beneficial to reducing the self-discharge rate of the battery and the risk of thermal runaway. By uniformly coating hierarchical pore zeolite particles on the surface of the base membrane, a three-dimensional hierarchical pore structure is constructed, enhancing the thermal stability, mechanical strength, and puncture strength of the separator, ensuring that its structure remains intact under high-temperature environments, effectively resisting internal battery stress, reducing structural damage during charge and discharge processes, and thus reducing the self-discharge rate.

[0068] Hierarchical pore zeolite particles (aluminosilicate) can improve the wettability of the separator to the electrolyte and the liquid retention capacity of the zeolite coating, thereby enhancing the fluidity of the electrolyte, reducing the mass transfer resistance of lithium ions in the battery, increasing the conductivity of lithium ions, and enhancing the kinetics of the battery; the increase in liquid retention capacity can prevent the evaporation of the electrolyte under high temperature or long-term use, and thus improve the reliability and lifespan of the battery.

[0069] Applying the zeolite coating to the separator of a ternary lithium battery and meeting 100x / C = 0.8 - 2.5 can effectively inhibit the migration of transition metals during high-temperature storage, reduce the phenomenon of transition metal elements dissolving from the positive electrode and depositing on the negative electrode, thereby slowing down the damage of the SEI on the negative electrode surface, reducing the consumption of active lithium ions, and contributing to improving the storage performance and cycle stability of the battery. When 100x / C is less than 0.8, the migration of transition metals may become relatively easy. An excessively high zeolite porosity may make the blocking effect of the zeolite coating on transition metals very limited, and may even lead to the formation of some overly large pores in the zeolite coating, enabling transition metals to migrate more easily through these pores. This migration will also damage the positive and negative electrode structures of the battery, resulting in a decline in battery performance. When 100x / C is greater than 2.5, due to the small porosity, the blocking effect of the separator on transition metals weakens, leading to the easier dissolution of transition metals from the positive electrode material and their migration to the negative electrode through the electrolyte. This migration will not only reduce the activity of the positive electrode material but also form poor deposits on the negative electrode surface, damaging the SEI (solid electrolyte interface) film on the negative electrode surface, and thus accelerating the consumption of active lithium ions and the attenuation of battery capacity. Meeting 100x / C = 0.8 - 2.5 can not only effectively inhibit the migration of Ni, Co, and Mn ions, protect the structure of the positive electrode material, extend the battery cycle life, but also improve the safety and electrochemical performance of the battery, providing strong technical support for the further development of ternary lithium batteries. It is expected to promote the development of the lithium-ion battery industry towards higher safety, higher energy density, and longer cycle life.

[0070] In a possible embodiment, the hierarchical zeolite further includes mesopores and / or macropores with pore diameters of 2 to 500 nm; for example, the hierarchical zeolite includes mesopores with pore diameters of 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm; for example, the hierarchical zeolite includes macropores with pore diameters of 60 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm.

[0071] In a possible embodiment, F = 0.3 to 0.7.

[0072] In a possible embodiment, the specific surface area of the zeolite is Am 2 / g, and the particle size Dv50 of the zeolite 1 is B μm, and A / B = 100 to 1500.

[0073] When A / B is in the range of 100 to 1500, the separator has sufficient adsorption sites for Ni ions, Co ions, Mn ions, and Al ions, which can well inhibit their migration; at the same time, excessive water absorption of the zeolite can be avoided, resulting in an excessive water content inside the battery. A high water content will cause the capacity of the battery to decay rapidly during cycling, and water decomposes to generate gas (such as H 2 ) during the charge and discharge process of the battery, resulting in the battery bulging and swelling. A / B = 100 to 1500 can ensure the cycling performance of the battery, reduce the transmission resistance of the separator layer, and improve the rate performance of the battery.

[0074] Optionally, A = 20 to 700; for example, A can be 20, 50, 100, 150, 200, 300, 400, 500, 600, or 700.

[0075] Optionally, B = 0.01 to 5. For example, it can be 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. The present invention uses zeolite particles (aluminosilicate) with better affinity for the electrolyte, and by controlling the particle size of the zeolite to be 0.01 to 5 μm, the wettability of the separator to the electrolyte can be improved. And by controlling the particle size of the zeolite particles, it helps to form a uniform and stable coating, thereby improving the adsorption effect on transition metal ions and mechanical stability, and further improving the safety performance of the battery.

[0076] In a possible embodiment, the particle size Dv50 of the ternary material 2is 3 to 15 μm. Exemplarily, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0077] When the particle size of the ternary material is within this range, it can avoid the increase in the liquid-phase diffusion resistance and the decline in the rate performance caused by too small a particle size; at the same time, it can avoid too large a particle size, resulting in structural stress and material fragmentation during the cycling process. When the particle size of the ternary material meets the above range, it can inhibit the migration of Ni ions, improve the battery safety, and at the same time improve the cycling performance and rate performance of the battery.

[0078] In a possible implementation manner, the thickness of the zeolite coating is h μm, and B / h = 0.1 to 0.8; optionally, h = 0.5 to 10. Exemplarily, B / h can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8. Exemplarily, h can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0079] When B / h is in the range of 0.1 to 0.8, the packing density of the zeolite particles is moderate, which can ensure a good porosity of the coating, less hindrance to ion transport, and at the same time can ensure the adsorption of more Ni ions, Co ions, Mn ions, and Al ions, inhibit their migration, and maintain better cycling and rate performance of the battery.

[0080] When the thickness of the hierarchical pore zeolite coating is controlled within the above range, it can provide a sufficient physical barrier effect while maintaining good mechanical strength, and further prevent the penetration of transition metal ions.

[0081] In a possible implementation manner, the zeolite is a lithium-exchanged zeolite; optionally, the lithium exchange amount in the lithium-exchanged zeolite is 90% to 99%. Exemplarily, the lithium exchange amount in the lithium-exchanged zeolite can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%.

[0082] The lithium-exchanged zeolite refers to a zeolite in which at least part of the cations (such as Na, K, Ca, etc.) contained in the zeolite body are replaced by lithium ions. The replacement amount is the lithium exchange amount.

[0083] The use of lithium-exchanged zeolite can achieve the effect of lithium supplementation, while avoiding the adsorption of lithium by zeolite during the battery cycle, thereby increasing the content of free lithium, improving ionic conductivity, enhancing kinetics, improving rate performance and cycling performance. It can also improve the chemical stability of the zeolite coating, enabling it to maintain good performance even under extreme conditions such as high temperature and high pressure. Lithium-exchanged zeolite not only provides additional lithium ions for the battery system, but also significantly improves the ion transport efficiency, while effectively inhibiting the dissolution and migration of transition metal ions such as Ni, Co, and Mn, preventing the deposition of these ions on the negative electrode to form dendrites, and avoiding the problem of battery self-discharge caused by dendrite piercing of the separator.

[0084] In a possible implementation, the pore volume of the zeolite is 0.5 - 1.5 cm 3 / g; exemplarily, it can be 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4 cm 3 / g or 1.5 cm 3 / g. Zeolite with a higher pore volume can effectively adsorb transition metal ions, and a pore volume of 0.5 - 1.5 cm 3 / g can further inhibit the migration of transition metal elements.

[0085] In a possible implementation, the ternary material is a nickel-cobalt-manganese ternary material.

[0086] In a possible implementation, the separator further includes an adhesive layer provided on at least one surface of the base film and / or the zeolite coating;

[0087] Optionally, the thickness of the adhesive layer (the thickness of the adhesive layer on one surface) is 0.1 - 4 μm; exemplarily, the thickness of the adhesive layer can be 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm.

[0088] In a possible implementation, the base film includes one or more of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone;

[0089] Optionally, the thickness of the base film is 3 - 20 μm; exemplarily, it can be 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 18 μm or 20 μm.

[0090] Optionally, the pore size of the base film is 0.02 - 0.5 μm. Exemplarily, it can be 0.02 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0091] In a possible implementation, the tensile strength of the separator is 2000 - 5500 gf; within this range of tensile strength, the expansion of the silicon negative electrode can be effectively inhibited while avoiding the reduction of separator dynamics.

[0092] In a possible implementation, the adhesion of the separator is 5 - 30 N / m;

[0093] In a possible implementation, the porosity of the base film is 35 - 45%; Exemplarily, it can be 35%, 38%, 40%, 42% or 45%.

[0094] In a possible implementation, the puncture strength of the separator is 150 - 600 gf.

[0095] In a possible implementation, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material;

[0096] The negative electrode active material includes silicon carbide and graphite.

[0097] The zeolite coating can enhance the puncture strength of the separator. This design can better adapt to the volume expansion of the silicon carbide negative electrode, reduce the potential damage to the battery structure, and further reduce the self-discharge rate.

[0098] Optionally, in the silicon carbide, the mass content of silicon element is 20 - 70%; Exemplarily, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0099] Optionally, the particle size Dv50 of the silicon carbide 3 is 5 - 15 μm; Exemplarily, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0100] Optionally, the average sphericity of the silicon carbide is 0.5 - 1. Exemplarily, it can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0101] Through the optimized combination of these parameters, the hierarchical pore zeolite coating can significantly reduce the migration of transition metal ions, thereby reducing the side reactions with the electrolyte caused by these ions, avoiding the formation of an unstable solid electrolyte interface (SEI) film, which affects the intercalation and deintercalation processes of lithium ions, improving the performance of the battery; meanwhile, reducing the formation of dendrites, ultimately reducing the self-discharge rate of the battery, and improving the overall performance and stability of the battery.

[0102] In summary, in the present invention, the cathode active material using LiNi x Co y M 1-x-y O 2 , where 0.5 ≤ x ≤ 0.9, can effectively solve the problems of poor wetting of the battery cell, low liquid retention, and large self-discharge rate by regulating the coating thickness and hierarchical pore size of the hierarchical pore zeolite in the battery separator, and coordinating the adjustment of the particle size of the zeolite particles.

[0103] In one possible implementation, the configuration of the hierarchical pore zeolite includes one or more of MEI, BEA, DDR, STT, MWW, MFI, LTA, FAU, SOD, CHA, MOR.

[0104] By regulating the zeolite synthesis method, zeolite particles with various pore structures can be prepared, such as hierarchical pore zeolite MFI, which includes macropores larger than 100 nm and micropores of 0.58 nm.

[0105] In one possible implementation, the adhesive layer includes at least one polymer of polytetrafluoroethylene, polyvinylidene fluoride, modified polyvinylidene fluoride hexafluoropropylene and its copolymer, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymer-modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrenesulfonate, pure benzene latex, polyvinylidene fluoride trichloroethylene, polyvinylidene fluoride chlorotrifluoroethylene, polyvinylpyrrolidone, poly(ethylene oxide), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylated amylose, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, cyanoethylated sucrose.

[0106] In a possible implementation, the binder is a polymer binder. Optionally, the polymer binder is selected from polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyimide, polyacrylonitrile, poly(methyl)methacrylate, aramid resin, poly(methyl)acrylic acid, styrene - butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMCNa), carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water - borne polyurethane, ethylene - vinyl acetate copolymer, polyacrylic acid copolymer, lithium polystyrene sulfonate, water - borne silicone resin, nitrile - polyvinyl chloride blend, styrene - acrylic latex, pure benzene latex, etc., and one or more combinations of blends and copolymers derived from the modification of the aforementioned polymers.

[0107] In a possible implementation, the additives include at least one of multi - branched alcohols, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, polyethylene oxide, stearic acid, sodium dodecylbenzenesulfonate, sodium hexadecylsulfonate, glycerol fatty acid ester, sorbitan fatty acid ester, and polysorbate.

[0108] The electrolyte can be a conventional electrolyte in the art. In a possible implementation, the electrolyte is a non - aqueous electrolyte, and the electrolyte includes a carbonate solvent and a lithium salt.

[0109] In a possible implementation, the carbonate solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0110] In a possible implementation, the negative electrode current collector is selected from one or more of aluminum foil, carbon - coated aluminum foil, and perforated aluminum foil.

[0111] In a possible implementation, the positive electrode current collector is selected from one or more of aluminum foil, carbon - coated aluminum foil, and perforated aluminum foil.

[0112] In a possible implementation, the battery housing can include one of aluminum - plastic film, aluminum alloy, and stainless steel.

[0113] "Parts" in the examples and comparative examples are all "parts by mass".

[0114] The preparation method of lithium - exchanged zeolite in the examples includes: soaking the zeolite in a lithium salt solution, so that the original cations can be replaced by lithium ions, and then centrifuging and washing to obtain lithium - exchanged zeolite. The lithium exchange amount can be controlled by controlling the soaking time.

[0115] Example 1

[0116] This example provides a lithium - ion battery, and the preparation method includes:

[0117] 85 parts of lithium-exchanged hierarchical pore FAU zeolite particles (particle size Dv50 1 is 1 μm, micropore diameter is 0.5 nm, macropore diameter is 204 nm, and the Li exchange amount in the zeolite is 95%), 10 parts of polyvinylidene fluoride-hexafluoropropylene, and 5 parts of polyethylene glycol are added to 860 parts of DMAC (N,N-dimethylacetamide). After uniform mixing, a mixed slurry is obtained. The mixed slurry is coated on one side surface of the base film 1 (the thickness of the base film 1 is 7 μm, the pore diameter of the base film 1 is 0.05 μm, and the porosity is 38%) by microgravure printing. After drying, a separator with a hierarchical pore FAU zeolite coating 2 is obtained. The thickness of the hierarchical pore FAU zeolite coating 2 is 3 μm. The obtained separator is coated with a 1-μm-thick polyvinylidene fluoride-hexafluoropropylene adhesive layer 3 on both sides by gravure printing. The puncture strength of the separator prepared in this example is 350 gf.

[0118] The negative electrode sheet selects artificial graphite: a silicon-carbon composite graphite material with a mass ratio of silicon to carbon of 90:10 as the negative electrode active material. In the silicon-carbon, the mass content of silicon element is 40%, and the particle size Dv50 3 of the silicon-carbon is 8 μm. The positive electrode sheet selects the ternary material LiNi 0.8 Co 0.1 Mn 0.1 O 2 as the positive electrode active material. The above-mentioned separator, positive electrode sheet, and negative electrode sheet are wound in the order of negative electrode sheet, separator, positive electrode sheet, and separator by the winding method to prepare a lithium-ion battery core. After baking, injecting electrolyte, forming, and encapsulating, a high-safety lithium-ion battery is obtained.

[0119] This application also provides lithium-ion batteries of Example 2 - Example 25 and Comparative Example 1, Comparative Example 21, which are basically the same as Example 1, but with different parameters, as shown in Table 1 and Table 2.

[0120] Comparative Example 3 is basically the same as Example 1, except that a conventional separator (using alumina to replace the lithium-exchanged hierarchical pore FAU zeolite particles) is used.

[0121] The test methods for each parameter are as follows:

[0122] (1) Base film thickness: Measure the thickness of the base film with a micrometer.

[0123] (2) Thickness (h μm) of the zeolite coating: Use a scanning electron microscope (SEM) to observe the cross-section of the coated separator. Through the SEM image measurement software, measure the coating thickness 3 times and take the average value.

[0124] (3) Thickness of the adhesive layer: After coating the separator, cross-sectional observation was carried out using a scanning electron microscope (SEM). Through the SEM image measurement software, the thickness of the adhesive layer was measured 3 times and the average value was taken.

[0125] (4) Pore size of the base film: Obtained by testing with a PMI separator micropore analyzer.

[0126] (5) Puncture strength of the separator: Can be tested using a universal tensile machine with reference to GB / T 36363-2018.

[0127] (6) Test method for the tensile strength of the separator: Tested using a tensile testing machine and stretched at a strain rate of 1 mm / min.

[0128] (7) Test method for the adhesion of the separator: Cut out specimens with a width of 20 mm * a length of 80 mm from the separators prepared in the examples and comparative examples and the positive or negative electrode plates. Press them together on a hot press. Under the conditions of a temperature of 65 °C and a pressure of 1 MPa, the hot pressing time is 30 s. Fix one end of the separator and one end of the electrode plate on the left and right clamps of a universal tensile machine respectively, and peel them at a constant speed of 10 mm / min. The experiment is repeated 5 times and the average value is taken.

[0129] (8) Test method for the pore size Fμm, specific surface area (Am 2 / g), and pore volume of the zeolite micropores: Use a specific surface area and pore size analyzer. Put 0.1 g of the sample into the analyzer, and calculate the pore size, specific surface area, and pore volume of the zeolite micropores by using the adsorption-desorption behavior of nitrogen molecules in the zeolite pores.

[0130] (9) Pore sizes of the mesopores and macropores of the hierarchical zeolite: Take 1 g of the hierarchical zeolite sample and put it into the expansion chamber of a mercury intrusion porosimeter. Apply different pressures to make mercury penetrate into the pores of the powder sample. According to the relationship between the volume of mercury entering the pores and the pressure, use the Washburn equation to calculate the pore size distribution.

[0131] (10) Dv50 1 (Bμm), Dv50 2 、Dv50 3 : Measured using a laser particle size analyzer.

[0132] (11) Test method for the porosity of the base film: The porosity is tested using a PMI instrument AAQ series water pressure meter in the United States: Specifically, the produced base film is sampled: Cut a 1.5 - 2.0 g base film sample; Record the thickness, length, and width of the sample, and calculate the density of the base film = weight / (length * width * thickness), with the unit of g / cm3, and the gram weight = weight / (length * width), with the unit of g / m 2; Then place the sample in a pure water tank to expel the gas; then conduct the test. Read the porosity value according to the output report.

[0133] (12) Test method for the porosity C% of hierarchical pore zeolite: Press mercury into the pores of hierarchical pore zeolite by applying an external pressure. The smaller the pore diameter, the greater the required pressure. By measuring the volume of mercury entering the pores at different pressures, the pore volume and pore size distribution can be calculated, and thus the porosity of the material can be obtained.

[0134] (13) Test method for lithium exchange amount: First, dissolve 0.1 g of zeolite sample in an appropriate acid to extract lithium ions from the zeolite structure. Use ICP-MS (Inductively Coupled Plasma Mass Spectrometry) equipment to test the sample to obtain the molar concentrations of lithium and sodium ions in the sample.

[0135] Lithium exchange amount = molar concentration of lithium ions / (molar concentration of lithium ions + molar concentration of sodium ions)

[0136] The parameters of each example and comparative example are shown in Table 1 - Table 2.

[0137] Table 1

[0138]

[0139]

[0140] Table 2

[0141]

[0142] Test methods for separator and lithium-ion battery performance

[0143] (1) Ion conductivity meter

[0144] Place the separator fully soaked in the electrolyte into an ion conductivity tester. The wetted separator sample is clamped between the same stainless steel electrodes to form a button battery or a similar test unit. Set an appropriate scanning frequency range (such as 0.1 - 100000 Hz) on an electrochemical workstation and conduct impedance testing to obtain the ion conductivity of the separator.

[0145] (2) After the lithium-ion battery is charged at 2C and discharged at 1C for 1000 cycles, disassemble the battery and test the metal content in the separator:

[0146] Use X-ray fluorescence spectroscopy (XRF) to test the content of metal elements in the battery separator. Cut the battery separator sample into a square with a side length of 10 mm, fix the separator sample with a fixture, and use XRF to detect the separator sample.

[0147] The test results of Example 1 are shown in Table 3.

[0148] Content of each metal in the separator (%)

[0149] Al Li Na Ni Co Mn Example 1 36.2 35.3 4.6 15.7 3.8 4.1

[0150] As can be seen from Table 3, the separator of the present application can successfully inhibit the migration of Ni, Co, and Mn ions.

[0151] Based on the total mass of metals in the separator, the Al content is 33.5 - 44%, the Li content is 33 - 37%, the Na content is 4 - 5.1%, the Ni content is 12 - 16%, the Co content is 3.5 - 4.2%, and the Mn content is 3.5 - 4.2%.

[0152] (3) Test of cycle capacity retention rate and thickness expansion rate at 25°C

[0153] Test the initial voltage and initial thickness of the incoming battery. Then place the lithium-ion battery at 25°C and charge it at a constant current of 2C to the upper limit voltage (4.5V), and then charge it at a constant voltage of 4.5V to 0.05C. Record the initial thickness P0, then discharge it at a constant current of 1C to 3.0V, and record the initial discharge capacity as C0. Let it stand for 5 minutes, which is one charge-discharge cycle. Charge / discharge in this way, and record the discharge capacity of the lithium-ion battery at 1000T as C1 and the final thickness as P1. Capacity retention rate: C = C1 / C0 * 100%, thickness expansion rate: P = (P1 - P0) / P0 * 100%.

[0154] (4) Liquid retention capacity test: Calculate the liquid retention capacity of the battery by the weight difference between after encapsulation and before injecting liquid.

[0155] (5) Wettability test: Test the contact angle of the separator through a contact angle tester to obtain its wettability.

[0156] The test results are shown in Table 4 and Table 5.

[0157] Table 4

[0158] Capacity retention rate at 1000T / % Thickness swelling rate / % Example 1 86.21 15.36 Example 2 85.25 17.99 Example 3 85.49 17.33 Example 4 83.85 21.82 Example 5 82.97 24.23 Example 6 84.36 20.42 Example 7 84.05 21.27 Comparative Example 1 80.4 31.26 Comparative Example 2 81.2 29.07 Comparative Example 3 75.1 30.42 Example 8 84.61 19.74 Example 9 85.26 17.96 Example 10 84.87 19.03 Example 11 82.58 25.29 Example 12 82.34 25.95 Example 13 83.11 23.84 Example 14 82.68 25.02 Example 15 82.35 25.92 Example 16 82.26 26.17 Example 17 83.59 22.53 Example 18 82.47 25.60 Example 19 82.34 25.95 Example 20 82.38 25.84 Example 21 82.05 26.74 Example 22 82.12 26.55 Example 23 83.72 22.17 Example 24 83.28 23.38 Example 25 82.49 25.54

[0159] As can be seen from the comparison between the examples and the comparative examples in Table 4, the capacity retention rate of the battery of the present application at 1000T is significantly increased, the cycle life is extended, the expansion rate is reduced, and the safety performance of the battery is improved.

[0160] Table 5

[0161] <![CDATA[Ionic conductivity / mS / cm 2 > Liquid retention amount / g Contact angle of diaphragm / ° Example 1 1.48 8.57 62 Example 25 0.95 8.31 67

[0162] The smaller the contact angle of the separator, the better the wettability. As can be seen from Table 5, using hierarchical pore zeolite can significantly improve the ionic conductivity, liquid retention capacity and wettability of the battery.

[0163] Obviously, the above embodiments are merely examples given for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises a ternary material; The general formula of the ternary material is LiNi x Co y M 1-x-y O2, where 0.5≤x≤0.9, 0.05≤y≤0.3, and M is Mn or Al; The diaphragm includes a base membrane and a zeolite coating disposed on at least one surface of the base membrane, wherein the zeolite coating includes zeolite, and the zeolite has micropores with a pore size of F nm; x / F=0.5-2.8; Among them, F=0.3~1.

2.

2. The lithium-ion battery according to claim 1, characterized in that The zeolite includes a hierarchical pore zeolite; Optionally, the porosity of the hierarchical pore zeolite is C%, 100x / C=0.8-2.5; Optional, C = 35 to 70; Optionally, the hierarchical pore zeolite further includes mesopores and / or macropores with a pore size of 2 to 500 nm.

3. The lithium ion battery according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1)F＝0.3～0.7； (2)x / F=0.7~2.

3.

4. The lithium ion battery according to claim 1 or 2, characterized in that: The specific surface area of ​​the zeolite is Am 2 / g, the particle size Dv501 of zeolite is Bμm, A / B=100~1500; Optional, A = 20 ~ 700; Optionally, B=0.01~5.

5. The lithium ion battery according to claim 1 or 2, characterized in that: The particle size Dv502 of the ternary material is 3 to 15 μm.

6. The lithium ion battery according to claim 1 or 2, characterized in that: The thickness of the zeolite coating is h μm, B / h=0.1-0.8; Optionally, h=0.5~10.

7. The lithium ion battery according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The pore volume of the zeolite is 0.5 to 1.5 cm 3 / g; (2) The ternary material is a nickel-cobalt-manganese ternary material; (3) The diaphragm further comprises a glue layer disposed on at least one side of the base film and / or the zeolite coating; Optionally, the thickness of the adhesive layer is 0.1 to 4 μm; (4) The base film comprises one or more of polyethylene, polypropylene, polyimide, polyacrylonitrile, and polyethersulfone; Optionally, the base film has a thickness of 3-20 μm; Optionally, the pore size of the base membrane is 0.02-0.5 μm.

8. The lithium ion battery according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The mass percentage of zeolite in the zeolite coating is 10% to 90%; (2) The zeolite coating further comprises a binder; Optionally, the mass percentage of the binder in the zeolite coating is 0 to 90%.

9. The lithium ion battery according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The tensile strength of the diaphragm is 2000 to 5500 gf; (2) The adhesive force of the diaphragm is 5 to 30 N / m; (3) The porosity of the base film is 35-45%; (4) The puncture strength of the diaphragm is 150 to 600 gf.

10. The lithium ion battery according to claim 1 or 2, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material; The negative electrode active material includes silicon carbon and graphite; Optionally, the mass content of silicon in the silicon carbon is 20 to 70%; Optionally, the particle size Dv503 of the silicon carbon is 5 to 15 μm.

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