Electrode assembly and battery

Abstract

The present invention discloses an electrode assembly and a battery. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a first diaphragm, wherein the first diaphragm is located between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet includes a current collector, a negative electrode material coating and a first multifunctional coating arranged between the current collector and the negative electrode material coating, wherein the first multifunctional coating includes a first ester-based quaternary ammonium salt, and the negative electrode material coating includes a negative electrode material, wherein the negative electrode material includes hard carbon. The present invention can effectively improve the peeling force of the electrode sheet, reduce the powder loss rate of the electrode sheet, and improve the winding yield and Hi-pot yield by arranging a first multifunctional coating containing an ester-based quaternary ammonium salt between the current collector and the negative electrode material coating. The first-cycle coulomb efficiency and cycle performance of the sodium ion battery assembled using the negative electrode sheet provided by the present invention are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrode assembly and a battery. Background Art

[0002] As market demand increases, the development of lithium-ion batteries may be constrained by lithium resources. The content of lithium in the earth's crust is only 0.0065%, and the reserves of lithium resources are not abundant, and the geographical distribution is also relatively uneven.

[0003] Sodium-ion batteries are another type of energy storage battery with a similar working mechanism and battery structure to lithium-ion batteries. Sodium-ion batteries have received increasing attention recently. Since sodium is easily available and inexpensive, and the negative current collector of sodium batteries can use aluminum foil instead of copper foil like lithium batteries, sodium-ion batteries have great potential price advantages. The material cost of sodium-ion batteries has room to drop by 30%-40% compared to lithium-ion batteries. With the continuous deepening of research, the potential advantages of sodium-ion batteries are constantly being explored, especially the excellent performance at high and low temperatures and high safety, which lays a good foundation for the application of sodium-ion batteries in the fields of energy storage and power.

[0004] As a key component for cost reduction of sodium-ion batteries, negative electrode materials have attracted much attention in recent years. Among them, hard carbon materials have become the mainstream negative electrode materials due to their advantages of high charge capacity, excellent rate capacity, long cycle capability and good low-temperature performance. However, hard carbon materials have some disadvantages after being used as negative electrode materials to make negative electrode sheets, such as poor sheet stripping rate, poor flexibility, and easy water absorption during placement, resulting in serious sheet powder loss, high defective rates of battery cell winding and Hi-pot (high potential testelectrical safety stress test), and poor long-cycle performance of the manufactured batteries.

[0005] In summary, finding a negative electrode that has good long-cycle battery performance and a high cell production yield is of great significance to the commercialization of sodium-ion batteries. Summary of the invention

[0006] In view of the above technical problems existing in the prior art, the object of the present invention is to provide an electrode assembly and a battery.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet and a first separator, wherein the first separator is located between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet comprises a current collector, a negative electrode material coating and a first multifunctional coating arranged between the current collector and the negative electrode material coating, wherein the first multifunctional coating comprises a first ester-based quaternary ammonium salt, the negative electrode material coating comprises a negative electrode material, and the negative electrode material comprises hard carbon.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0010] Preferably, the chemical structure formula of the first ester quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0011] Preferably, the first multifunctional coating further includes a first conductive agent and a first binder, and the mass ratio of the first ester quaternary ammonium salt, the first conductive agent and the first binder is (90~94):(1~6):(2~4).

[0012] Preferably, the thickness of the first multifunctional coating is 3 μm to 6 μm.

[0013] Preferably, the thickness of the negative electrode material coating is 40 μm to 60 μm.

[0014] Preferably, the negative electrode material coating further includes a negative electrode conductor and a negative electrode binder, and the mass ratio of the negative electrode material, the negative electrode conductor and the negative electrode binder is (90-94):(1-6):(2-4).

[0015] As a preferred technical solution of the electrode assembly of the present invention, a second multifunctional coating is further provided between the first separator and the negative electrode sheet, and the second multifunctional coating includes a second ester-based quaternary ammonium salt.

[0016] Preferably, the chemical structure formula of the second ester quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0017] Preferably, the second multifunctional coating further includes a second conductive agent and a second binder, and the mass ratio of the second ester quaternary ammonium salt, the second conductive agent and the second binder is (88~92):(1~4):(3~6).

[0018] Preferably, the second multifunctional coating has a thickness of 2 μm to 4 μm.

[0019] Preferably, the second multifunctional coating is disposed on the surface of the negative electrode sheet.

[0020] As a preferred technical solution of the electrode assembly described in the present invention, the electrode assembly is a wound electrode assembly, and the electrode assembly also includes a second diaphragm, the second diaphragm is located on the side of the negative electrode sheet away from the first diaphragm, and a third multifunctional coating is also arranged between the second diaphragm and the negative electrode sheet, and the third multifunctional coating includes a third ester-based quaternary ammonium salt.

[0021] Preferably, the chemical structure formula of the third ester group quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0022] Preferably, the third multifunctional coating also includes a third conductive agent and a third binder, and the mass ratio of the third ester quaternary ammonium salt, the third conductive agent and the third binder is (88~92):(1~4):(3~6).

[0023] Preferably, the thickness of the third multifunctional coating is 2 μm to 4 μm.

[0024] Preferably, the third multifunctional coating is disposed on the surface of the negative electrode sheet.

[0025] As a preferred technical solution of the electrode assembly of the present invention, the electrode assembly includes a bent portion and a straight portion.

[0026] Preferably, the thickness of the first multifunctional coating at the bent portion is greater than the thickness of the first multifunctional coating at the straight portion.

[0027] Preferably, the thickness of the third multifunctional coating at the bent portion is greater than the thickness of the third multifunctional coating at the straight portion.

[0028] As a preferred technical solution of the electrode assembly of the present invention, the thickness of the first multifunctional coating gradually decreases from the starting end to the end of the winding.

[0029] Preferably, the thickness of the third multifunctional coating gradually decreases from the starting end to the ending end of the winding.

[0030] In a second aspect, the present invention provides a battery, comprising a housing and the electrode assembly as described in the first aspect, wherein the electrode assembly is accommodated in the housing.

[0031] Preferably, the battery further comprises an electrolyte contained in the shell, the electrolyte comprises a solvent, the solvent comprises a nucleophilic group, and the nucleophilic group comprises at least one of esters and ethers.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a first multifunctional coating between the current collector and the negative electrode material coating, wherein the ester-based quaternary ammonium salt has a certain degree of softness and smoothness, which can improve the flexibility of the negative electrode, reduce the powder loss rate of the pole piece, and improve the winding yield and Hi-pot yield; moreover, the -COO- contained in the ester-based quaternary ammonium salt exhibits polyanion characteristics after absorbing water, so that the first multifunctional coating has a certain degree of viscosity, thereby improving the peeling force of the pole piece; in addition, the ester-based quaternary ammonium salt can form ion pairs with nucleophilic groups in the electrolyte, accelerate the reaction rate, contribute to the rapid formation of the SEI film, and improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of an electrode assembly in one embodiment of the present invention, wherein a is a concave surface, b is a convex surface, A is a straight portion, and B is a bent portion;

[0035] Figure 2 is a positional relationship diagram of a positive electrode sheet, a negative electrode sheet, a first separator, a second separator, a second multifunctional coating, and a third multifunctional coating in one embodiment of the present invention;

[0036] Figure 3 is a schematic structural diagram of a negative electrode sheet in one embodiment of the present invention;

[0037] Among them, 1. positive electrode sheet; 2. first separator; 3. second multifunctional coating; 4. negative electrode sheet; 5. third multifunctional coating; 6. second separator;

[0038] 41. Current collector; 42. First multifunctional coating; 43. Negative electrode material coating. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0040] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Example 1

[0042] In the present invention, the terms "first", "second" and "third" are only used to distinguish in description and have no special meanings.

[0043] In one embodiment, the present invention provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42 arranged between the current collector 41 and the negative electrode material coating 43, wherein the first multifunctional coating 42 includes a first ester-based quaternary ammonium salt, and the negative electrode material coating 43 includes a negative electrode material, and the negative electrode material includes hard carbon.

[0044] It should be noted that the negative electrode material coating 43 is disposed on at least one side of the current collector 41 in the thickness direction. Specifically, the negative electrode material coating 43 may be disposed on one side of the current collector 41 in the thickness direction, or Figure 3 The negative electrode material coating 43 is disposed on both sides of the current collector 41 in the thickness direction.

[0045] In one embodiment of the present invention, a first multifunctional coating 42 is provided between the current collector 41 and the negative electrode material coating 43, wherein the ester-based quaternary ammonium salt has a certain softness and smoothness, which can improve the flexibility of the negative electrode, reduce the powder loss rate of the electrode sheet, and improve the winding yield and Hi-pot yield; moreover, the -COO- contained in the ester-based quaternary ammonium salt exhibits polyanion characteristics after absorbing water, so that the first multifunctional coating has a certain viscosity, thereby improving the peeling force of the electrode sheet; in addition, the ester-based quaternary ammonium salt can form ion pairs with nucleophilic groups in the electrolyte, accelerate the reaction rate, contribute to the rapid formation of the SEI film, and improve the electrochemical performance of the battery.

[0046] In one embodiment, the chemical structure formula of the first ester quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0047] In one embodiment, the first ester group quaternary ammonium salt includes at least one of dipalmitoyl carboxyethyl hydroxyethyl methyl ammonium salt, distallow ester group hydroxyethyl methyl ammonium sulfate, disoleyl ester group hydroxyethyl methyl ammonium sulfate, dicocoyl ester group hydroxyethyl methyl ammonium sulfate, difatty alkyl ethyl ester group hydroxyethyl methyl ammonium sulfate, octadecyl diester group quaternary ammonium salt, methyl diisopropanolamine ester group quaternary ammonium salt, triethanolamine ester group quaternary ammonium salt or imidazoline ester group quaternary ammonium salt.

[0048] In one embodiment, the first multifunctional coating 42 further includes a first conductive agent and a first binder, and the mass ratio of the first ester quaternary ammonium salt, the first conductive agent and the first binder is (90-94): (1-6): (2-4). The selection range of the first ester quaternary ammonium salt is "90-94", for example, it can be 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5 or 94; the selection range of the first conductive agent is "1-6", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6; the selection range of the first binder is "2-4", for example, it can be 2, 2.5, 3, 3.5 or 4. If the content of the first ester quaternary ammonium salt in the first multifunctional coating 42 is too much, it will affect the capacity of the negative electrode material; if the content of the first ester quaternary ammonium salt in the first multifunctional coating 42 is too little, the performance improvement effect on the negative electrode is not obvious.

[0049] In one embodiment, the first conductive agent includes at least one of Super P (SP), acetylene black, Ketjen black, conductive graphite, and carbon black.

[0050] In one embodiment, the first binder includes at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylate binder (LA) and polyacrylic acid binder (PAA).

[0051] In one embodiment, the thickness of the first multifunctional coating 42 is 3 μm to 6 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm, etc. If the first multifunctional coating 42 is too thick, it will affect the kinetic performance of the negative electrode, so that the capacity of the negative electrode material is hindered; if the first multifunctional coating 42 is too thin, it will not significantly inhibit the powdering of the electrode sheet, and the peeling force will be limited.

[0052] In one embodiment, the thickness of the negative electrode material coating 43 is 40 μm to 60 μm, for example, 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm, 53 μm, 55 μm, 57 μm or 60 μm, etc. If the negative electrode material coating 43 is too thick, the coulombic efficiency of the battery will be reduced and the capacity will be affected; if the negative electrode material coating 43 is too thin, lithium is easily deposited at a high rate.

[0053] In one embodiment, the negative electrode material coating 43 further includes a negative electrode conductive agent and a negative electrode binder, and the mass ratio of the negative electrode material, the negative electrode conductive agent and the negative electrode binder is (90-94): (1-6): (2-4). The selection range of the negative electrode material is "90-94", for example, it can be 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5 or 94, etc.; the selection range of the negative electrode conductive agent is "1-6", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.; the selection range of the negative electrode binder is "2-4", for example, it can be 2, 2.5, 3, 3.5 or 4, etc.

[0054] In one embodiment, the negative electrode conductive agent includes at least one of Super P (SP), acetylene black, Ketjen black, conductive graphite, and carbon black.

[0055] In one embodiment, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylate binder (LA) and polyacrylic acid binder (PAA).

[0056] In one embodiment, if Figure 2 As shown, a second multifunctional coating 3 is further provided between the first separator 2 and the negative electrode sheet 4, and the second multifunctional coating 3 includes a second ester-based quaternary ammonium salt. By providing the second multifunctional coating 3 between the first separator 2 and the negative electrode sheet 4, the stripping rate and flexibility of the negative electrode sheet 4 can be further optimized, the powder loss rate can be reduced, and the formation of SEI can be facilitated, thereby improving the electrochemical performance of the battery assembled with the negative electrode.

[0057] By setting a first multifunctional coating 42 in the negative electrode sheet 4 and further setting a second multifunctional coating 3 between the negative electrode sheet 4 and the first separator 2, the powder loss rate of the electrode sheet can be further reduced, the winding yield and Hi-pot yield can be improved, the peeling force of the electrode sheet can be improved, and the formation of the SEI film can also be facilitated.

[0058] In one embodiment, the chemical structure formula of the second ester quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0059] In one embodiment, the second ester group quaternary ammonium salt includes at least one of dipalmitoyl carboxyethyl hydroxyethyl methyl ammonium salt, distallow ester group hydroxyethyl methyl ammonium sulfate, disoleyl ester group hydroxyethyl methyl ammonium sulfate, dicocoyl ester group hydroxyethyl methyl ammonium sulfate, difatty alkyl ethyl ester group hydroxyethyl methyl ammonium sulfate, octadecyl diester group quaternary ammonium salt, methyl diisopropanolamine ester group quaternary ammonium salt, triethanolamine ester group quaternary ammonium salt or imidazoline ester group quaternary ammonium salt.

[0060] In one embodiment, the second multifunctional coating 3 further includes a second conductive agent and a second binder, and the mass ratio of the second ester quaternary ammonium salt, the second conductive agent and the second binder is (88-92): (1-4): (3-6). The selection range of the second ester quaternary ammonium salt is "88-92", for example, it can be 88, 89, 90, 90.5, 91, 91.5 or 92, etc.; the selection range of the second conductive agent is "1-4", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5 or 4, etc.; the selection range of the second binder is "3-6", for example, it can be 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc.

[0061] Since the second multifunctional coating 3 is in direct contact with the first separator 2 and is located between the first separator 2 and the negative electrode sheet 4, the capacity of the negative electrode material can be better guaranteed by limiting the composition of the second multifunctional coating 3 within the above range.

[0062] In one embodiment, the second conductive agent includes at least one of Super P, acetylene black, Ketjen black, conductive graphite, and carbon black.

[0063] In one embodiment, the second binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate binder and polyacrylic acid binder.

[0064] In one embodiment, the thickness of the second multifunctional coating 3 is 2 μm to 4 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm or 4 μm, etc. If the second multifunctional coating 3 is too thick, it will affect the ion transmission speed of the positive electrode material; if the second multifunctional coating 3 is too thin, it will not significantly reduce the powder loss rate of the electrode, improve the peeling force of the electrode, and facilitate the formation of the SEI film.

[0065] In one embodiment, the second multifunctional coating 3 is disposed on the surface of the negative electrode sheet 4. Compared with disposing the second multifunctional coating 3 on the first separator 2, this method is more conducive to suppressing the powdering of the negative electrode sheet 4, ensuring the overall stability of the battery, and is conducive to the integrity of the negative electrode SEI film, thereby improving the stability of the battery.

[0066] In one embodiment, the electrode assembly is a wound electrode assembly, such as Figure 1As shown, the electrode assembly further includes a second diaphragm 6, which is located on the side of the negative electrode sheet 4 away from the first diaphragm 2, and a third multifunctional coating 5 is further provided between the second diaphragm 6 and the negative electrode sheet 4, wherein the third multifunctional coating 5 includes a third ester-based quaternary ammonium salt. Since the wound electrode assembly needs to be wound during the manufacturing process, the electrode sheet is prone to powder falling, and the third multifunctional coating 5 is provided to improve the problem of electrode sheet powder falling and reduced peeling force.

[0067] In one embodiment, the chemical structure formula of the third ester group quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO.

[0068] In one embodiment, the third ester group quaternary ammonium salt includes at least one of dipalmitoyl carboxyethyl hydroxyethyl methyl ammonium salt, distallow ester group hydroxyethyl methyl sulfate ammonium salt, disoleyl ester group hydroxyethyl methyl sulfate ammonium salt, dicocoyl ester group hydroxyethyl methyl sulfate ammonium salt, difatty alkyl ethyl ester group hydroxyethyl methyl sulfate ammonium salt, octadecyl diester group quaternary ammonium salt, methyl diisopropanolamine ester group quaternary ammonium salt, triethanolamine ester group quaternary ammonium salt or imidazoline ester group quaternary ammonium salt.

[0069] In one embodiment, the third multifunctional coating 5 further includes a third conductive agent and a third binder, and the mass ratio of the third ester quaternary ammonium salt, the third conductive agent and the third binder is (88-92): (1-4): (3-6). Among them, the selection range of the third ester quaternary ammonium salt is "88-92", for example, it can be 88, 89, 90, 90.5, 91, 91.5 or 92, etc.; the selection range of the third conductive agent is "1-4", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5 or 4, etc.; the selection range of the third binder is "3-6", for example, it can be 3, 3.5, 4, 4.5, 5, 5.5 or 6, etc. If the content of the third ester quaternary ammonium salt is too much, it will affect the gram capacity of the negative electrode material; if the content of the third ester quaternary ammonium salt is too little, the improvement of the powder falling phenomenon of the electrode piece is not obvious.

[0070] By limiting the composition of the third multifunctional coating layer 5 to the above range, the capacity of the negative electrode material can be better guaranteed.

[0071] In one embodiment, the third conductive agent includes at least one of Super P, acetylene black, Ketjen black, conductive graphite, and carbon black.

[0072] In one embodiment, the third binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate binder and polyacrylic acid binder.

[0073] In one embodiment, the thickness of the third multifunctional coating 5 is 2 μm to 4 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm or 4 μm. If the third multifunctional coating 5 is too thick, the capacity of the negative electrode material will be affected; if the third multifunctional coating 5 is too thin, the effect of suppressing the powder falling of the electrode sheet is not obvious, and the peeling force is limited.

[0074] In one embodiment, the third multifunctional coating 5 is disposed on the surface of the negative electrode sheet 4. Compared with disposing the third multifunctional coating 5 on the second separator 6, this method is more conducive to suppressing the powder falling of the negative electrode and ensuring the overall stability of the battery.

[0075] In one embodiment, if Figure 1 As shown, the electrode assembly includes a bent portion B and a straight portion A.

[0076] For wound electrode assemblies, such as Figure 1 As shown, during its preparation, the electrode assembly is usually hot-pressed after being wound. After hot-pressing, the curvature of the straight portion A is smaller, and the curvature of the bent portion B is larger. The side of the pole piece facing the outer ring corresponds to the convex surface b, and the side of the pole piece facing the inner ring corresponds to the concave surface a. The curvature of the convex surface b is smaller than that of the concave surface a. Therefore, powder shedding or even cracking is more likely to occur at the bent portion B, especially at the concave surface a of the bent portion B.

[0077] In one embodiment, the temperature of hot pressing can be 85°C to 95°C, for example, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0078] Since the probability of powder shedding in different parts of the wound electrode assembly is different, the probability of powder shedding at the bending portion B and / or the concave surface a is higher. Therefore, the first multifunctional coating 42, the second multifunctional coating 3 and the third multifunctional coating 5 are preferably arranged at the bending portion B and / or the concave surface a to better solve the problem of powder shedding.

[0079] In one embodiment, the first multifunctional coating 42 is disposed at least on the concave surface of the negative electrode sheet.

[0080] In one embodiment, the second multifunctional coating 3 is disposed at least on the concave surface of the negative electrode sheet.

[0081] In one embodiment, the third multifunctional coating 5 is disposed at least on the concave surface of the negative electrode sheet.

[0082] In one embodiment, the first multifunctional coating 42 , the second multifunctional coating 3 , and the third multifunctional coating 5 are disposed at least at the bending portion B.

[0083] In one embodiment, the thickness of the first multifunctional coating 42 at the bent portion B is greater than the thickness of the first multifunctional coating 42 at the straight portion A.

[0084] In one embodiment, the thickness of the third multifunctional coating 5 at the bent portion B is greater than the thickness of the third multifunctional coating 5 at the straight portion A.

[0085] In one embodiment, when the second multifunctional coating 3 is present in the electrode assembly, the thickness of the second multifunctional coating 3 at the bent portion B is greater than the thickness of the second multifunctional coating 3 at the straight portion A.

[0086] Since the bending portion B is more prone to powdering than the straight portion A, it is preferred that the thickness of the corresponding multifunctional coating at the bending portion B is greater than that at the straight portion A.

[0087] In one embodiment, the thickness of the first multifunctional coating 42 gradually decreases from the starting end to the end of the winding.

[0088] In one embodiment, the thickness of the third multifunctional coating 5 gradually decreases from the starting end to the end of the winding.

[0089] In one embodiment, when the second multifunctional coating 3 is present in the electrode assembly, the thickness of the second multifunctional coating 3 gradually decreases from the starting end of the winding to the end of the winding.

[0090] Since the curvature of the wound inner layer is greater than that of the wound outer layer, the thickness of the first multifunctional coating 42, the second multifunctional coating 3 and the third multifunctional coating 5 preferably decreases gradually with the increase in the number of winding turns, thereby ensuring the flexibility, stripping rate and performance of the negative electrode while alleviating the performance and safety degradation caused by powder shedding and cracking at the bending part, thereby improving the electrical performance, service life and safety of the battery.

[0091] In another embodiment, the present invention provides a method for preparing an electrode assembly, comprising the following steps:

[0092] (1) Preparation of negative electrode sheet 4:

[0093] S1: preparing negative electrode slurry A1, wherein the negative electrode slurry A1 includes hard carbon;

[0094] preparing a first multifunctional slurry B1, wherein the first multifunctional slurry B1 includes a first ester-based quaternary ammonium salt;

[0095] S2: coating the slurry B1 on the current collector and, after drying, obtaining a bottom-coated electrode;

[0096] S3: coating the slurry A1 on the base-coated electrode sheet, and after drying, obtaining the negative electrode sheet 4.

[0097] (2) After stacking the positive electrode sheet 1 , the negative electrode sheet 4 and the first separator 2 , they are wound from the starting end to the end to obtain an electrode assembly.

[0098] The embodiment of the present invention does not limit the preparation order of slurry A1 and slurry B1.

[0099] In the method for preparing an electrode assembly provided in one embodiment of the present invention, steps S2 and S3 solidify the slurry by drying.

[0100] The preparation method of the electrode assembly provided in one embodiment of the present invention is simple and suitable for industrial production.

[0101] Preferably, the drying temperatures in step S2 and step S3 are independently 100°C to 150°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, wherein "independently" means that the drying temperatures of step S2 and step S3 are both selected within this range, and the respectively selected values ​​are independent of each other and are not affected by each other.

[0102] In one embodiment, the drying time in step S2 and step S3 is independently 0.5h to 12h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, etc. Wherein, "independently" means that the drying time in step S2 and the drying time in step S3 are both selected within this range, and the values ​​selected by each are independent of each other and are not affected by each other.

[0103] In one embodiment, the drying method in step S2 is air drying.

[0104] In one embodiment, the drying method in step S3 is air drying. In step S3, air drying solidifies the slurry and also melts the two contacting slurry layers, increasing the contact area between the slurries, thereby improving the flexibility of the negative electrode, reducing the powder loss rate of the pole piece, and improving the winding yield and Hi-pot yield.

[0105] In one embodiment, the method for preparing the electrode assembly further includes preparing a second multifunctional slurry B2, and performing step S41 after step S3. The second multifunctional slurry B2 includes a second ester-based quaternary ammonium salt; step S41 is: coating the second multifunctional slurry B2 on the surface of the negative electrode sheet 4 obtained in step S3, drying, to obtain a negative electrode sheet 4 having a second multifunctional layer 3 formed on the surface, and using it in the lamination process of step (2).

[0106] In one embodiment, the drying method in step S4 is to first dry by air blast and then dry by vacuum blast. The air blast drying not only solidifies the slurry, but also melts the two contacting slurries, increasing the contact area between the slurries, thereby improving the flexibility of the negative electrode, reducing the powder loss rate of the pole piece, and improving the winding yield and Hi-pot yield. The vacuum drying can remove moisture from the pole piece.

[0107] In one embodiment, the time of the blast drying and the vacuum drying in step S4 are independently 0.5h to 12h, for example, 0.5h, 1h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 10h, 10.5h, 11h or 12h, etc. Wherein, "independently" means that the time of the blast drying and the time of the vacuum drying in step S4 are both selected within this range, and the values ​​selected by each are independent of each other and are not affected by each other.

[0108] In one embodiment, the method for preparing the electrode assembly further includes preparing a second multifunctional slurry B2, and coating the second multifunctional slurry B2 on the surface of the first diaphragm 2, and after drying, obtaining a first diaphragm 2 having a second multifunctional layer 3 formed on the surface, and using it in the stacking process of step (2).

[0109] In the embodiment of the present invention, the compositions of slurry B1 and slurry B2 may be the same or different, preferably different. Since slurry B1 and slurry B2 are used to form the first multifunctional coating 42 and the second multifunctional coating 3, respectively, the two are located in different positions and play different roles. Therefore, the compositions of the two are different. Specifically, slurry B1 and slurry B2 can be prepared according to the composition requirements of the first multifunctional coating 42 and the second multifunctional coating 3.

[0110] In one embodiment, the method for preparing the electrode assembly further includes preparing a third multifunctional slurry B3, and performing step S42 after step S3. The third multifunctional slurry B3 includes a second ester-based quaternary ammonium salt; step S42 is: coating the third multifunctional slurry B3 on the surface of the negative electrode sheet obtained in step S3, drying, to obtain a negative electrode sheet 4 having a third multifunctional layer 5 formed on the surface, and stacking a second separator 6 on the surface of the third multifunctional layer 5.

[0111] In one embodiment, the method for preparing the electrode assembly further includes preparing a third multifunctional slurry B3, and coating the second multifunctional slurry B3 on the surface of the second diaphragm 6, and after drying, obtaining a second diaphragm 6 with a third multifunctional layer 5 formed on the surface, and laminating the second diaphragm 6 with the third multifunctional layer 5 formed on the surface to the surface of the negative electrode sheet 4, wherein the third multifunctional layer 5 is located between the negative electrode sheet 4 and the second diaphragm 6.

[0112] In another embodiment, the present invention provides a battery, comprising a housing and the electrode assembly as described above, wherein the electrode assembly is accommodated in the housing.

[0113] The embodiment of the present invention does not specifically limit the type of battery, for example, it can be a sodium ion battery.

[0114] In one embodiment, the battery further comprises an electrolyte contained in the shell, the electrolyte comprises a solvent, the solvent carries a nucleophilic group, and the nucleophilic group comprises at least one of esters and ethers.

[0115] In one embodiment, the esters include, but are not limited to, at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0116] In one embodiment, the ethers include, but are not limited to, at least one of ethylene glycol dimethyl ether, epoxy ether, phosphate ether, dodecyl ether or butyl ether.

[0117] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0118] Example 1

[0119] This embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 42 and a first multifunctional coating 43, the first multifunctional coating 42 is arranged between the current collector 41 and the negative electrode material coating 42, and a second multifunctional coating 3 is arranged between the first separator 2 and the negative electrode sheet 4;

[0120] The first multifunctional coating 42 contains ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), conductive agent (SP) and binder (PVDF), the mass ratio of ester quaternary ammonium salt, conductive agent and binder is 90:6:4, and the thickness of the first multifunctional coating 42 is 3 μm;

[0121] The second multifunctional coating 3 contains an ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), a conductive agent (SP) and a binder (PVDF), the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 90:6:4, and the thickness of the second multifunctional coating 3 is 3 μm;

[0122] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 90:6:4, and the thickness of the negative electrode material coating 43 is 40 μm;

[0123] The current collector 41 is made of aluminum foil.

[0124] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0125] (1) Preparation of negative electrode sheet 4:

[0126] S1: weigh hard carbon material, SP and PVDF respectively according to a mass ratio of 90:6:4, add NMP according to a mass ratio of hard carbon material to N-methylpyrrolidone (NMP) of 1:2, disperse at high speed, and mix well to obtain slurry A1;

[0127] S2: Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:6:4, add NMP in an amount of octadecyl diester quaternary ammonium salt and NMP in a mass ratio of 1:2, disperse at high speed, and mix well to obtain slurry B;

[0128] S3: Setting the coating machine parameters so that the coating thickness of the first multifunctional coating 42 is 3 μm, coating the slurry B evenly on the aluminum foil, and drying the electrode piece after coating at 110° C. for 0.5 h to obtain the electrode piece A;

[0129] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 40 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, namely negative electrode sheet 4.

[0130] (2) Forming a second multifunctional coating 3 on the surface of the negative electrode sheet 4:

[0131] S5: Slurry B is evenly coated on the dried electrode piece B, so that the coating thickness of the second multifunctional coating 3 is 3 μm. The coated electrode piece is air-dried at 110° C. for 0.5 h, and then vacuum-dried at 120° C. for 12 h to obtain an electrode piece C, which is a negative electrode piece 4 with a second multifunctional coating 3 formed on the surface.

[0132] (3) Preparation of positive electrode sheet 1:

[0133] Sodium vanadium phosphate Na3V2(PO4)3, SP and PVDF were weighed according to a mass ratio of 95.5:2:2.5, and NMP was added in a mass ratio of Na3V2(PO4)3 to NMP of 1:2, and high-speed dispersion was performed. After mixing evenly, a positive electrode slurry was obtained, and the positive electrode slurry was evenly coated on an aluminum foil with a coating thickness of 20 μm. After the coating, the electrode was blow-dried at 110°C for 0.5h, and then vacuum-dried at 120°C for 12h to obtain a positive electrode sheet 1.

[0134] (4) Assembling electrode components:

[0135] Using PE film as the first separator 2, the positive electrode sheet 1, the negative electrode sheet 4 with the second multifunctional coating 3 formed on the surface, and the first separator 2 are stacked, wherein winding is performed from the starting end to the end, and after winding, hot pressing is performed at 90°C to obtain an electrode assembly.

[0136] Example 2

[0137] The present embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42, the first multifunctional coating 42 is arranged between the current collector 41 and the negative electrode material coating 43, and a second multifunctional coating 3 is arranged between the first separator 2 and the negative electrode sheet 4;

[0138] The first multifunctional coating 42 contains ester quaternary ammonium salt (bis-palmitoyl carboxyethyl hydroxyethyl methyl sulfate ammonium salt), a conductive agent (SP) and a binder (PVDF), the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 92:5:3, and the thickness of the first multifunctional coating 42 is 4.5 μm;

[0139] The second multifunctional coating 3 contains ester quaternary ammonium salt (bis-palmitoyl carboxyethyl hydroxyethyl methyl sulfate ammonium salt), a conductive agent (SP) and a binder (PVDF), the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 92:5:3, and the thickness of the second multifunctional coating 3 is 4.5 μm;

[0140] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 92:5:3, and the thickness of the negative electrode material coating 43 is 50 μm;

[0141] The current collector 41 is made of aluminum foil.

[0142] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0143] (1) Preparation of negative electrode sheet 4:

[0144] S1: The hard carbon material, SP and PVDF were weighed respectively in a mass ratio of 92:5:3, and NMP was added in a mass ratio of the hard carbon material to NMP of 1:2, and the mixture was dispersed at a high speed and mixed evenly to obtain slurry A1.

[0145] S2: Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:6:4, add NMP in a mass ratio of 1:2 of dispalmitate carboxyethyl hydroxyethyl methyl ammonium sulfate and NMP, disperse at high speed, and mix well to obtain slurry B.

[0146] S3: Setting the coating machine parameters so that the coating thickness of the first multifunctional coating 42 is 4.5 μm, coating the slurry B evenly on the aluminum foil, and drying the electrode piece after coating at 110° C. for 0.5 h to obtain the electrode piece A;

[0147] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 50 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, namely negative electrode sheet 4.

[0148] (2) Forming a second multifunctional coating 3 on the surface of the negative electrode sheet:

[0149] S5: Slurry B is evenly coated on the dried electrode B, so that the coating thickness of the second multifunctional coating 3 is 4.5 μm. The coated electrode is blown dried at 110° C. for 0.5 h, and then vacuum dried at 120° C. for 12 h to obtain an electrode C, which is a negative electrode 4 with a second multifunctional coating 3 formed on the surface.

[0150] (3) Preparation of positive electrode sheet 1:

[0151] Same as Example 1.

[0152] (4) Assembling electrode components:

[0153] Using PE film as the first separator 2, the positive electrode sheet 1, the negative electrode sheet 4 with the second multifunctional coating 3 formed on the surface, and the first separator 2 are stacked, wherein winding is performed from the starting end to the end, and after winding, hot pressing is performed at 90°C to obtain an electrode assembly.

[0154] Example 3

[0155] The present embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42, the first multifunctional coating 42 is arranged between the current collector 41 and the negative electrode material coating 43, and a second multifunctional coating 3 is arranged between the first separator 2 and the negative electrode sheet 4;

[0156] The first multifunctional coating 42 contains ester quaternary ammonium salt (bis-fatty alkyl ester hydroxyethyl methyl sulfate ammonium salt), conductive agent (SP) and binder (PVDF), the mass ratio of ester quaternary ammonium salt, conductive agent and binder is 94:4:2, and the thickness of the first multifunctional coating 42 is 6 μm;

[0157] The second multifunctional coating 3 contains ester quaternary ammonium salt (bis-fatty alkyl ester hydroxyethyl methyl sulfate ammonium salt), a conductive agent (SP) and a binder (PVDF), the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 94:4:2, and the thickness of the second multifunctional coating 3 is 6 μm;

[0158] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 94:4:2, and the thickness of the negative electrode material coating 43 is 60 μm;

[0159] The current collector 41 is made of aluminum foil.

[0160] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0161] (1) Preparation of negative electrode sheet 4:

[0162] S1: weigh hard carbon material, SP and PVDF respectively at a mass ratio of 94:4:2, add NMP at a mass ratio of hard carbon material to N-methylpyrrolidone (NMP) of 1:2, disperse at high speed, and mix well to obtain slurry A1;

[0163] S2: Weigh di-fatty alkyl ester hydroxyethyl methyl sulfate ammonium salt, SP and PVDF in a mass ratio of 94:4:2, add NMP in an amount of octadecyl diester quaternary ammonium salt and NMP in a mass ratio of 1:2, disperse at high speed, and mix well to obtain slurry B;

[0164] S3: Setting the coating machine parameters so that the coating thickness of the first multifunctional coating 42 is 6 μm, coating the slurry B evenly on the aluminum foil, and drying the electrode piece after coating at 110° C. for 0.5 h to obtain the electrode piece A;

[0165] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 60 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, which is the negative electrode sheet.

[0166] (2) Forming a second multifunctional coating 3 on the surface of the negative electrode sheet:

[0167] S5: Slurry B is evenly coated on the dried electrode piece B, so that the coating thickness of the second multifunctional coating 3 is 6 μm. The coated electrode piece is air-dried at 110° C. for 0.5 h, and then vacuum-dried at 120° C. for 12 h to obtain an electrode piece C, which is a negative electrode piece 4 with a second multifunctional coating 3 formed on the surface.

[0168] (3) Preparation of positive electrode sheet 1:

[0169] Same as Example 1.

[0170] (4) Assembling electrode components:

[0171] Using PE film as the first separator 2, the positive electrode sheet 1, the negative electrode sheet 4 with the second multifunctional coating 3 formed on the surface, and the first separator 2 are stacked, wherein winding is performed from the starting end to the end, and after winding, hot pressing is performed at 90°C to obtain an electrode assembly.

[0172] Example 4

[0173] This embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42, and the first multifunctional coating 42 is disposed between the current collector 41 and the negative electrode material coating 43;

[0174] The first multifunctional coating 42 contains ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), conductive agent (SP) and binder (PVDF), the mass ratio of ester quaternary ammonium salt, conductive agent and binder is 90:6:4, and the thickness of the first multifunctional coating 42 is 3 μm;

[0175] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 90:6:4, and the thickness of the negative electrode material coating 43 is 40 μm;

[0176] The current collector 41 is made of aluminum foil.

[0177] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0178] (1) Preparation of negative electrode sheet 4:

[0179] S1: The hard carbon material, SP and PVDF were weighed respectively in a mass ratio of 90:6:4, and NMP was added in a mass ratio of hard carbon material to N-methylpyrrolidone (NMP) of 1:2, and the mixture was dispersed at a high speed and mixed evenly to obtain slurry A1.

[0180] S2: Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:6:4, add NMP in a mass ratio of octadecyl diester quaternary ammonium salt to NMP of 1:2, disperse at high speed, and mix well to obtain slurry B.

[0181] (2) Preparation of negative electrode sheet 4:

[0182] S3: Setting the coating machine parameters so that the coating thickness of the first multifunctional coating 42 is 3 μm, coating the slurry B evenly on the aluminum foil, and drying the electrode piece after coating at 110° C. for 0.5 h to obtain the electrode piece A;

[0183] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 40 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, which is negative electrode sheet 4.

[0184] (3) Preparation of positive electrode sheet 1:

[0185] Same as Example 1.

[0186] (4) Assembling electrode components:

[0187] The PE film is used as the first separator 2, and the positive electrode sheet 1, the above-mentioned negative electrode sheet 4 and the first separator 2 are stacked, wherein they are wound from the starting end to the end, and after winding, they are hot-pressed at 90° C. to obtain an electrode assembly.

[0188] Example 5

[0189] The difference between this embodiment and embodiment 1 is that the thickness of the first multifunctional coating 42 is 2 μm, and the other parameters and preparation conditions are the same as those of embodiment 1.

[0190] Example 6

[0191] The difference between this embodiment and embodiment 1 is that the thickness of the first multifunctional coating 42 is 7 μm, and the other parameters and preparation conditions are the same as those of embodiment 1.

[0192] Example 7

[0193] The difference between this embodiment and embodiment 1 is that in the first multifunctional coating 42, based on the total mass of octadecyl diester quaternary ammonium salt, SP and PVDF as 100%, the mass proportion of the ester quaternary ammonium salt is 88%, and the mass ratio of the conductive agent to the binder is the same as that in embodiment 1.

[0194] Example 8

[0195] The difference between this embodiment and embodiment 1 is that in the first multifunctional coating 42, based on the total mass of octadecyl diester quaternary ammonium salt, SP and PVDF as 100%, the mass proportion of the ester quaternary ammonium salt is 96%, and the mass ratio of the conductive agent to the binder is the same as that in embodiment 1.

[0196] Example 9

[0197] The present embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42, the first multifunctional coating 42 is arranged between the current collector 41 and the negative electrode material coating 43, and a second multifunctional coating 3 is arranged between the first separator 2 and the negative electrode sheet 4;

[0198] The first multifunctional coating 42 contains ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), conductive agent (SP) and binder (PVDF), and the mass ratio of ester quaternary ammonium salt, conductive agent and binder is 90:6:4;

[0199] The second multifunctional coating 3 contains ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), a conductive agent (SP) and a binder (PVDF), and the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 90:6:4;

[0200] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 90:6:4, and the thickness of the negative electrode material coating is 40 μm;

[0201] The current collector 41 is made of aluminum foil.

[0202] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0203] (1) Preparation of negative electrode sheet 4:

[0204] S1: The hard carbon material, SP and PVDF were weighed respectively in a mass ratio of 90:6:4, and NMP was added in a mass ratio of hard carbon material to N-methylpyrrolidone (NMP) of 1:2, and the mixture was dispersed at a high speed and mixed evenly to obtain slurry A1.

[0205] S2: Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:6:4, add NMP in a mass ratio of octadecyl diester quaternary ammonium salt to NMP of 1:2, disperse at high speed, and mix well to obtain slurry B.

[0206] S3: According to the length of the negative electrode sheet of the single winding core, the coating machine parameters are set so that the coating thickness of the first multifunctional coating 42 gradually decreases from 6 μm to 3 μm as the length of the electrode sheet gradually increases, and the slurry B is evenly coated on the aluminum foil. After the coating, the electrode sheet is dried at 110° C. for 0.5 h to obtain the electrode sheet A;

[0207] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 40 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, namely negative electrode sheet 4.

[0208] (2) Forming a second multifunctional coating 3 on the surface of the negative electrode sheet 4:

[0209] S5: Slurry B is evenly coated on the dried electrode B, so that the coating thickness of the second multifunctional coating 3 gradually decreases from 4 μm to 2 μm as the length of the electrode increases. The coated electrode is air-dried at 110° C. for 0.5 h, and then vacuum-dried at 120° C. for 12 h to obtain an electrode C, which is a negative electrode 4 with a second multifunctional coating 3 formed on the surface.

[0210] (3) Preparation of positive electrode sheet 1:

[0211] Same as Example 1.

[0212] (4) Assembling electrode components:

[0213] Using PE film as the first separator 2, the positive electrode sheet 1, the negative electrode sheet 4 with the second multifunctional coating 3 formed on the surface, and the first separator 2 are stacked, wherein they are wound from the starting end to the end, and after winding, they are hot pressed at 90°C. The thickness of the first multifunctional coating 42 gradually decreases from the starting end to the end of the winding, and the thickness of the second multifunctional coating 3 gradually decreases from the starting end to the end of the winding, to obtain an electrode assembly.

[0214] Example 10

[0215] This embodiment provides an electrode assembly and a method for preparing the same.

[0216] The difference between the electrode assembly and Example 9 is that the electrode assembly further includes a second diaphragm 6, which is located on the side of the negative electrode sheet 4 away from the first diaphragm 2, and a third multifunctional coating 5 is further provided between the second diaphragm 6 and the negative electrode sheet 4, and the third multifunctional coating 5 includes a third ester-based quaternary ammonium salt. The third multifunctional coating 5 contains an ester-based quaternary ammonium salt (octadecyl diester-based quaternary ammonium salt), a conductive agent (SP) and a binder (PVDF), and the mass ratio of the ester-based quaternary ammonium salt, the conductive agent and the binder is 90:3:4.

[0217] The difference between the preparation method of the electrode assembly and that of Example 1 is that steps (2) to (4) are:

[0218] Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:3:4, add NMP in an amount of octadecyl diester quaternary ammonium salt and NMP in a mass ratio of 1:2, disperse at high speed, and mix well to obtain slurry C;

[0219] The slurry C is uniformly coated on the surface of the negative electrode sheet 4 on the side where the second multifunctional coating 3 is not provided, and the third multifunctional coating 5 is formed after drying, and the coating thickness of the third multifunctional coating 5 is gradually reduced from 4 μm to 2 μm as the length of the electrode sheet gradually increases. The coated electrode sheet is air-dried at 110° C. for 0.5 h, and then vacuum-dried at 120° C. for 12 h to obtain a negative electrode sheet 4 with the second multifunctional coating 3 and the third multifunctional coating 5 formed on the surface.

[0220] The positive electrode sheet 1 was prepared in the same manner as in Example 9:

[0221] A PE film is used as the first separator 2 and the second separator 6, and the positive electrode sheet 1, the negative electrode sheet 4 having the second multifunctional coating 3 and the third multifunctional coating 5 formed on the surface thereof, are stacked with the first separator 2 and the second separator 6, wherein the electrode sheet is wound from the starting end to the end, and after winding, it is hot pressed at 90°C, and the thickness of the first multifunctional coating 42 gradually decreases from the starting end to the end of the winding, the thickness of the second multifunctional coating 3 gradually decreases from the starting end to the end of the winding, and the thickness of the third multifunctional coating 5 gradually decreases from the starting end to the end of the winding, to obtain an electrode assembly.

[0222] Embodiment 11

[0223] This embodiment provides an electrode assembly and a method for preparing the same.

[0224] The difference between the electrode assembly and Example 1 is that the second multifunctional coating 3 is formed on the first separator 2 instead of the negative electrode sheet 4 .

[0225] The present embodiment provides an electrode assembly, including a positive electrode sheet 1, a negative electrode sheet 4 and a first separator 2, wherein the first separator 2 is located between the positive electrode sheet 1 and the negative electrode sheet 4, the negative electrode sheet 4 includes a current collector 41, a negative electrode material coating 43 and a first multifunctional coating 42, the first multifunctional coating 42 is arranged between the current collector 41 and the negative electrode material coating 43, and a second multifunctional coating 3 is arranged between the first separator 2 and the negative electrode sheet 4 and on the first separator 2;

[0226] The first multifunctional coating 42 contains ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), conductive agent (SP) and binder (PVDF), the mass ratio of ester quaternary ammonium salt, conductive agent and binder is 90:6:4, and the thickness of the first multifunctional coating 42 is 3 μm;

[0227] The second multifunctional coating 3 contains an ester quaternary ammonium salt (octadecyl diester quaternary ammonium salt), a conductive agent (SP) and a binder (PVDF), the mass ratio of the ester quaternary ammonium salt, the conductive agent and the binder is 90:6:4, and the thickness of the second multifunctional coating 3 is 3 μm;

[0228] The negative electrode material coating 43 includes a negative electrode material (hard carbon material), a conductive agent (SP) and a binder (PVDF), the mass ratio of the negative electrode material, the conductive agent and the binder is 90:6:4, and the thickness of the negative electrode material coating 43 is 40 μm;

[0229] The current collector 41 is made of aluminum foil.

[0230] This embodiment also provides a method for preparing the above-mentioned electrode assembly, comprising the following steps:

[0231] (1) Preparation of negative electrode sheet 4:

[0232] S1: weigh hard carbon material, SP and PVDF respectively according to a mass ratio of 90:6:4, add NMP according to a mass ratio of hard carbon material to N-methylpyrrolidone (NMP) of 1:2, disperse at high speed, and mix well to obtain slurry A1;

[0233] S2: Weigh octadecyl diester quaternary ammonium salt, SP and PVDF in a mass ratio of 90:6:4, add NMP in an amount of octadecyl diester quaternary ammonium salt and NMP in a mass ratio of 1:2, disperse at high speed, and mix well to obtain slurry B;

[0234] S3: Setting the coating machine parameters so that the coating thickness of the first multifunctional coating 42 is 3 μm, coating the slurry B evenly on the aluminum foil, and drying the electrode piece after coating at 110° C. for 0.5 h to obtain the electrode piece A;

[0235] S4: Slurry A1 is evenly coated on the dried electrode sheet A, so that the coating thickness of the negative electrode material coating 43 is 40 μm, and the coated electrode sheet is blown dry at 110° C. for 0.5 h to obtain electrode sheet B, namely negative electrode sheet 4.

[0236] (2) forming a second multifunctional coating 3 on the surface of the first diaphragm 2:

[0237] S5: Using a PE film as the first separator 2, slurry B is evenly coated on the first separator 2, so that the coating thickness of the second multifunctional coating 3 is 3 μm. The coated separator is air-dried at 110° C. for 0.5 h, and then vacuum-dried at 120° C. for 12 h to obtain a first separator 2 with a second multifunctional coating 3 formed on the surface.

[0238] (2) Preparation of positive electrode sheet 1:

[0239] Same as Example 1.

[0240] (3) Assembling electrode components:

[0241] The positive electrode sheet 1, the first separator 2 having the second multifunctional coating 3 formed on the surface thereof, and the negative electrode sheet 4 including the first multifunctional coating 42 are stacked, wherein they are wound from the starting end to the end, and after winding, they are hot pressed at 90° C. The thickness of the first multifunctional coating 42 gradually decreases from the starting end to the end of the winding, and the thickness of the second multifunctional coating 3 gradually decreases from the starting end to the end of the winding, to obtain an electrode assembly.

[0242] Comparative Example 1

[0243] This comparative example provides an electrode assembly and a preparation method thereof. The difference between the electrode assembly and Example 1 is that the electrode assembly does not include the first multifunctional coating 42 and the second multifunctional coating 3.

[0244] The difference between the method for preparing the electrode assembly and Example 1 is that slurry B is not prepared and coating of slurry B is not involved.

[0245] Comparative Example 2

[0246] This comparative example provides an electrode assembly and a preparation method thereof. The difference between the electrode assembly and Example 2 is that the electrode assembly does not include the first multifunctional coating 42 and the second multifunctional coating 3.

[0247] The difference between the method for preparing the electrode assembly and Example 1 is that slurry B is not prepared and coating of slurry B is not involved.

[0248] Comparative Example 3

[0249] This comparative example provides an electrode assembly and a preparation method thereof. The difference between the electrode assembly and Example 3 is that the electrode assembly does not include the first multifunctional coating 42 and the second multifunctional coating 3.

[0250] The difference between the method for preparing the electrode assembly and Example 1 is that slurry B is not prepared and coating of slurry B is not involved.

[0251] Test Case

[0252] 1. Preparation of batteries

[0253] Battery assembly: Using 1 mol / L NaPF6 solution of diethylene glycol dimethyl ether as the electrolyte, the electrode assemblies of Examples 1-10 and Comparative Examples 1-3 were installed in an aluminum shell and the electrolyte was injected to seal the shell to obtain a square aluminum shell sodium ion battery.

[0254] 2. Test methods

[0255] (1) Negative electrode peeling force:

[0256] 1. Cut a piece of 3M strong double-sided tape (strong adhesion, easy to clean) with a length of 100mm and a width of 15~40mm, stick one side on the peel test steel sheet, and flatten the tape to avoid bubbles;

[0257] 2. Use a cutting knife to cut a length greater than 70mm (150mm if long enough) and a width of 10~50mm;

[0258] 3. Tear off the release paper of the double-sided tape, stick the cut battery electrode sample on the double-sided tape, and roll it back and forth 3 times at a speed of 10mm / s with a 2kg rolling roller;

[0259] 4. Place the peeled steel sheet into the 90-degree lower fixture of the YL-S90 peel force tester, fix both ends of the steel sheet, and place one end of the pole piece into the upper fixture and clamp it;

[0260] 5. Clamp the sample, set the peeling interval (the peeling start and end sections are not included in the peeling interval, the interval between them is the peeling interval) and the test speed, click program reset, click test, and the electrode is peeled at a speed of 100 mm / min.

[0261] (2) Powder shedding of the negative electrode sheet before winding: Spread out the negative electrode sheet before winding and visually inspect the overall powder shedding of the sheet.

[0262] (3) Powder shedding at the bent part of the negative electrode after hot pressing: After hot pressing, spread out the negative electrode and visually inspect the overall powder shedding at the bent part of the electrode.

[0263] (4) Cell winding yield: the number of cells that have been wound without abnormalities divided by the total number of cells that have been wound.

[0264] (5) Hi-pot yield: the number of cells after Hi-pot divided by the number of cells before Hi-pot.

[0265] (6) First-cycle coulombic efficiency: A fresh battery is charged and discharged at 0.5C, charged to 2.0V and discharged to 0.01V. The first-cycle discharge capacity divided by the first-cycle charge capacity is the first-cycle coulombic efficiency.

[0266] (7) 0.5C / 0.5C cycle life test: The square aluminum shell sodium ion batteries prepared in Examples 1-8 and Comparative Examples 1-3 were respectively taken for capacity separation at 25°C, 0.1C rate, charge cut-off voltage 2.0 V, and discharge cut-off voltage 0.01 V. Then, a 0.5C / 0.5C cycle test was performed at 25°C. The number of cycles when the discharge specific capacity decayed to zero was the battery life (charge cut-off voltage 2.0 V, discharge cut-off voltage 0.01 V).

[0267] See Table 1 for the results.

[0268] Table 1

[0269] Negative electrode peeling force (N / m) Negative electrode sheet powder falling off before winding Powder falling off at the bending part of the negative electrode after hot pressing Cell winding yield (%) Hi-pot yield (%) First cycle coulomb efficiency (%) 0.5C / 0.5C cycle life (number of cycles) Example 1 5.25 none slight 99.2 99.9 98.45 1786 Example 2 5.16 none slight 98.8 99.6 97.32 1620 Example 3 5.09 none slight 98.6 99.3 95.61 1569 Example 4 4.51 slight slight 97.3 98.2 90.8 1365 Example 5 3.89 slight slight 96.4 97.6 90.45 1221 Example 6 5.54 slight slight 96.3 97.7 90.13 1210 Example 7 4.19 slight slight 96.0 96.8 89.64 1209 Example 8 4.23 slight slight 96.1 97.0 89.15 1196 Example 9 5.10 none none 99.0 99.8 97.53 1606 Example 10 5.26 none none 99.3 99.9 98.47 1801 Embodiment 11 4.89 slight slight 95.8 96.5 89.12 1159 Comparative Example 1 0.95 serious serious 68.6 67.4 85.76 1098 Comparative Example 2 0.76 serious serious 63.2 62.1 83.15 1041 Comparative Example 3 0.64 serious serious 60.9 59.4 82.02 1007

[0270] By comparing Examples 1-10 with Comparative Examples 1-3, it can be seen that the present invention sets a first multifunctional coating 42 between the current collector 41 and the negative electrode material coating 43, wherein the ester-based quaternary ammonium salt has a certain softness and smoothness, which can improve the flexibility of the negative electrode, reduce the powder loss rate of the pole piece, and improve the winding yield and Hi-pot yield. Moreover, the -COO- contained in the ester-based quaternary ammonium salt exhibits polyanionic properties after absorbing water, so that the first multifunctional coating has a certain viscosity and improves the peeling force of the pole piece; in addition, the ester-based quaternary ammonium salt can form an ion pair with the nucleophilic group in the electrolyte, accelerate the reaction rate, contribute to the rapid formation of the SEI film, and improve the electrochemical performance of the battery.

[0271] By comparing Examples 1-3 with Example 4, it can be seen that further, by providing a second multifunctional coating 3 between the first diaphragm 2 and the negative electrode sheet 4, the peeling force of the electrode sheet can be better improved, the powder loss of the negative electrode sheet before winding can be avoided, and the winding yield, Hi-pot yield and electrochemical performance of the battery cell can be improved.

[0272] By comparing Examples 1-3 with Example 9, it can be seen that by adjusting the thickness of the first multifunctional coating 42 and the second multifunctional coating 43 to gradually decrease from the starting end to the end of winding, the powder falling phenomenon at the bending part of the negative electrode sheet after hot pressing can be improved. At the same time, it can take into account the high negative electrode sheet peeling force, avoid the powder falling phenomenon of the negative electrode sheet before winding, and high battery cell winding yield, Hi-pot yield and electrochemical performance.

[0273] By comparing Example 9 and Example 10, it can be seen that further, providing a third multifunctional coating 5 between the second separator 6 and the negative electrode sheet 4 is beneficial to further reduce the powder loss and low peeling force of the negative electrode, while improving the coulombic efficiency and cycle performance.

[0274] By comparing Example 1 with Example 11, it can be seen that setting the second multifunctional coating 3 on the negative electrode 4 can significantly reduce the powder loss and low peeling force of the negative electrode material compared to setting it on the first diaphragm 2, and also improves the winding yield, Hi-pot yield and electrochemical performance of the battery cell.

[0275] By comparing Example 1 with Examples 5-6, it can be seen that a first multifunctional coating 42 that is too thin does not have obvious beneficial effects and does not improve mass production enough; a first multifunctional coating 42 that is too thick reduces the electrochemical performance of the battery.

[0276] By comparing Example 1 with Examples 7-8, it can be seen that if there is too little ester-based quaternary ammonium salt in the first multifunctional coating 42, the electrode peeling rate and powder falling phenomenon will not be significantly improved; if there is too much ester-based quaternary ammonium salt in the first multifunctional coating 42, the electrochemical performance of the battery will be reduced.

[0277] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrode assembly, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a first separator, wherein the first separator is located between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet comprises a current collector, a negative electrode material coating and a first multifunctional coating arranged between the current collector and the negative electrode material coating, wherein the first multifunctional coating comprises a first ester-based quaternary ammonium salt, the negative electrode material coating comprises a negative electrode material, and the negative electrode material comprises hard carbon.

2. The electrode assembly according to claim 1, characterized in that: The chemical structure formula of the first ester quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO; and / or, The first multifunctional coating further includes a first conductive agent and a first binder, and the mass ratio of the first ester quaternary ammonium salt, the first conductive agent and the first binder is (90-94):(1-6):(2-4); and / or, The thickness of the first multifunctional coating is 3 μm to 6 μm; and / or, The thickness of the negative electrode material coating is 40 μm to 60 μm; and / or, The negative electrode material coating also includes a negative electrode conductor and a negative electrode binder. The mass ratio of the negative electrode material, the negative electrode conductor and the negative electrode binder is (90-94):(1-6):(2-4).

3. The electrode assembly according to claim 1, characterized in that: A second multifunctional coating is also provided between the first separator and the negative electrode sheet, and the second multifunctional coating includes a second ester-based quaternary ammonium salt.

4. The electrode assembly according to claim 3, characterized in that: The chemical structure formula of the second ester group quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO; and / or, The second multifunctional coating further comprises a second conductive agent and a second binder, and the mass ratio of the second ester quaternary ammonium salt, the second conductive agent and the second binder is (88-92):(1-4):(3-6); and / or, The thickness of the second multifunctional coating is 2 μm to 4 μm; and / or, The second multifunctional coating is disposed on the surface of the negative electrode sheet.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that: The electrode assembly is a wound electrode assembly, and the electrode assembly also includes a second diaphragm, which is located on the side of the negative electrode sheet away from the first diaphragm. A third multifunctional coating is also arranged between the second diaphragm and the negative electrode sheet, and the third multifunctional coating includes a third ester-based quaternary ammonium salt.

6. The electrode assembly according to claim 5, characterized in that: The chemical structure formula of the third ester group quaternary ammonium salt is R4NX, wherein R is a hydrocarbon group and X is R1-COO; and / or, The third multifunctional coating further comprises a third conductive agent and a third binder, and the mass ratio of the third ester quaternary ammonium salt, the third conductive agent and the third binder is (88-92):(1-4):(3-6); and / or, The thickness of the third multifunctional coating is 2 μm to 4 μm; and / or, The third multifunctional coating is disposed on the surface of the negative electrode sheet.

7. The electrode assembly according to claim 5, characterized in that: The electrode assembly includes a bent portion and a straight portion; the thickness of the first multifunctional coating in the bent portion is greater than the thickness of the first multifunctional coating in the straight portion; and / or, The thickness of the third multifunctional coating at the bent portion is greater than the thickness of the third multifunctional coating at the straight portion.

8. The electrode assembly according to claim 5, characterized in that: The thickness of the first multifunctional coating gradually decreases from the winding start end to the winding end end; and / or, The thickness of the third multifunctional coating gradually decreases from the starting end to the end of the winding.

9. A battery, characterized in that: The battery comprises a housing and the electrode assembly according to any one of claims 1 to 8, wherein the electrode assembly is accommodated in the housing.

10. The battery according to claim 9, characterized in that The battery further comprises an electrolyte contained in the shell, the electrolyte comprises a solvent, the solvent comprises a nucleophilic group, and the nucleophilic group comprises at least one of esters and ethers.

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