Pole piece and related lithium-ion secondary battery, battery, and power-using device

Abstract

The application provides an electrode sheet and a lithium ion secondary battery, a battery and a power utilization device related thereto. The electrode sheet comprises a current collector and an active material layer arranged on at least one surface of the current collector, wherein the active material layer comprises an active material and an aldehyde ketone polymer, and the active material layer satisfies formula (1) to formula (3). The aldehyde ketone polymer as a component of the active material layer can form a uniform high wetting point inside the active material layer, uniformly improve the wetting performance of the active material layer, thereby improving the liquid absorption speed of the whole active material layer and the cycle performance of the lithium ion secondary battery.v / λ>1.00 formula (3).

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to an electrode and related lithium-ion secondary batteries, batteries, and electrical devices. Background Technology

[0002] Lithium-ion rechargeable batteries have the characteristics of high capacity and long life, and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] As battery applications become increasingly widespread, the performance requirements for lithium-ion rechargeable batteries are becoming more stringent. To improve the safety performance of lithium-ion rechargeable batteries, the performance of the electrodes is typically optimized. However, the active materials in the electrodes currently have poor liquid absorption properties, resulting in poor cycle performance when used in lithium-ion rechargeable batteries. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide an electrode and related lithium-ion secondary batteries, batteries and power-consuming devices.

[0005] A first aspect of this application provides an electrode, the electrode comprising a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprising an active material and an aldehyde-ketone polymer, the active material layer satisfying the following:

[0006]

[0007]

[0008] v / λ>1.00 Equation (3),

[0009] In equations (1) to (3),

[0010] λ represents the porosity of the active material layer;

[0011] P1 represents the actual compacted density of the active material layer, with units of g / cm³. 3 ;

[0012] P2 represents the actual compacted density of the active material, with units of g / cm³. 3 ;

[0013] v represents the liquid absorption rate of the active material layer, with units of mg / s.

[0014] d represents the diameter of the capillary in the capillary test of the active material layer, and its unit is mm;

[0015] h represents the height of the liquid level in the capillary tube, and its unit is mm;

[0016] ρ represents the density of the electrolyte in the capillary test, and its unit is g / cm³. 3 ;

[0017] t represents the time it takes for the electrolyte to be absorbed within the capillary, and its unit is seconds (s).

[0018] Therefore, the aldehyde-ketone polymer of this application, when introduced during the preparation of the active material layer, can form a uniform high wetting point inside the active material layer, uniformly improving the wetting performance of the active material layer, thereby increasing the overall liquid absorption rate of the active material layer and thus improving the cycle performance of the lithium-ion secondary battery using the electrode.

[0019] In some embodiments, the active material includes a positive electrode active material, and the active material layer satisfies: 1.00 < v / λ < 4.00; optionally, 1.20 ≤ v / λ ≤ 3.80.

[0020] In some embodiments, the active material includes a positive electrode active material, and the mass percentage of the aldehyde-ketone polymer is A% based on the mass of the active material layer; wherein 0.1 ≤ A ≤ 1.5. When the mass percentage of the aldehyde-ketone polymer is within the above range, the liquid absorption capacity of the positive electrode active material layer can be significantly improved.

[0021] In some embodiments, the active material includes a negative electrode active material, and the active material layer satisfies: 3.00 < v / λ < 50.00; optionally, 3.40 ≤ v / λ ≤ 30.00.

[0022] In some embodiments, the active material includes a negative electrode active material, and the mass percentage of the aldehyde-ketone polymer is B% based on the mass of the active material layer; wherein 0.2 ≤ B ≤ 5.0. When the mass percentage of the aldehyde-ketone polymer is within the above range, the liquid absorption capacity of the negative electrode active material layer can be significantly improved.

[0023] In some embodiments, the aldehyde-ketone polymer is formed into a sheet-like structure; the sheet-like structure is in (T m The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K, 0.8≤K<∞, optionally, 0.8≤K≤100, and further optionally, 0.8≤K≤10. m °C represents the melting temperature of the aldehyde-ketone polymer.

[0024] Therefore, when the polymer of this application meets the above-mentioned range, it can further reduce the molecular chain entanglement state, which is conducive to the diffusion of solvent molecules in the electrolyte between molecular chains; and the polymer still maintains a certain molecular chain entanglement state, which can lock the solvent molecules in situ inside the polymer and reduce the risk of polymer dissolving in the electrolyte, thereby improving the stability of polymer performance; and it is also conducive to the formation of a protective layer on the surface of the active material by the polymer, improving the solid-liquid interface performance, reducing side reactions between the active material and the electrolyte, and improving the cycle performance and storage performance of lithium-ion secondary batteries.

[0025] In some embodiments, the glass transition temperature of the aldehyde-ketone polymer is Tg, expressed in °C, where -100 ≤ Tg ≤ 50; alternatively, -80 ≤ Tg ≤ 30. The relatively low glass transition temperature of the aldehyde-ketone polymer results in better segmental flexibility of the molecular chains, making it easier for adjacent molecular chains to open and for in-situ gel formation to occur. This improves the wetting performance of the electrolyte on the active material layer, thereby enhancing the cycle performance of the lithium-ion secondary battery.

[0026] In some embodiments, the aldehyde-ketone polymer comprises the structural unit shown in formula (I).

[0027]

[0028] In formula (I), R1 includes a single bond, a substituted or unsubstituted C1-C6 methylene group; R2 includes a hydrogen atom, a substituted or unsubstituted C1-C6 alkyl group; optionally, R1 includes a single bond, a substituted or unsubstituted C1-C2 methylene group; and R2 includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group.

[0029] In some embodiments, the aldehyde-ketone polymer includes at least one of the structural units shown in formula (I-1) to formula (I-6).

[0030]

[0031] In some embodiments, the aldehyde-ketone polymer comprises the structural unit shown in formula (II).

[0032]

[0033] In formula (II), each of R3 to R6 independently comprises a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; each of r and s independently comprises an integer from 0 to 5, and at least one of r and s is selected from a positive integer; optionally, each of R3 to R6 independently comprises a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C2 hydroxyalkyl group, or a substituted or unsubstituted C1-C2 alkoxy group.

[0034] In some embodiments, the aldehyde-ketone polymer comprises at least one of the structural units shown in formula (II-1) to formula (II-4).

[0035]

[0036] In some embodiments, n is selected from positive integers from 500 to 15000; and / or the molecular weight of the aldehyde-ketone polymer is 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 When the molecular weight of the polymer is within the above range, it ensures that the polymer exhibits a certain solubility in the electrolyte, while being less likely to be completely dissolved and dispersed by the electrolyte. This is beneficial for controlling the distribution and dispersion of the polymer on the surface of the active material. Furthermore, it can further improve the flexibility between the polymer molecular chains, and the relatively weak interaction forces between the molecular chains facilitate the solvent molecules in the electrolyte to open the molecular chains and enter between the molecular chains, where they are encapsulated. This, in turn, facilitates the smooth and rapid migration of active ions into the active material through the solvent.

[0037] A second aspect of this application provides a lithium-ion secondary battery comprising electrodes as described in any embodiment of the first aspect of this application.

[0038] A third aspect of this application provides a battery, including a lithium-ion secondary battery as described in the second aspect of this application.

[0039] A fourth aspect of this application provides an electrical device including a battery as described in the third aspect of this application. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0041] Figure 1This is a schematic diagram of one embodiment of the lithium-ion secondary battery of this application.

[0042] Figure 2 yes Figure 1 An exploded view of an embodiment of a lithium-ion secondary battery.

[0043] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0044] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0045] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0046] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a lithium-ion secondary battery as a power source, including the present application.

[0047] The accompanying drawings may not be drawn to scale.

[0048] The annotations in the attached figures are explained as follows:

[0049] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0050] 5. Lithium-ion secondary battery; 51. Housing; 52. Electrode assembly;

[0051] 53. Cover plate;

[0052] 6. Electrical appliances. Detailed Implementation

[0053] The following detailed description discloses embodiments of the electrode sheet and related lithium-ion secondary batteries, batteries, and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0054] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0056] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0057] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0058] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0060] The term "alkyl" encompasses both straight-chain and branched alkyl groups. For example, an alkyl group can be C1-C5, C1-C4, C1-C3, or C1-C2 alkyl. In some embodiments, the alkyl group includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, etc. Additionally, the alkyl group may optionally be substituted. When substituted, the substituent includes a fluorine atom.

[0061] The term "alkoxy group" refers to a group in which an alkyl group is bonded to an oxygen atom by a single bond. For example, an alkoxy group can be a C1-C5 alkoxy group, a C1-C3 alkoxy group, or a C1-C2 alkoxy group. In some embodiments, an alkoxy group may include a methoxy group, an ethoxy group, or a propoxy group. Additionally, an alkoxy group may optionally be substituted.

[0062] The term "hydroxyalkyl" refers to a group in which a hydroxyl group is linked to an alkyl group by a single bond. For example, a hydroxyalkyl group can be a C1-C8 hydroxyalkyl group, a C1-C5 hydroxyalkyl group, a C1-C3 hydroxyalkyl group, or a C1-C2 hydroxyalkyl group. In some embodiments, the hydroxyalkyl group may include hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, etc. Additionally, the hydroxyalkyl group may optionally be substituted.

[0063] The term "halogen atom" refers to fluorine atoms, chlorine atoms, bromine atoms, etc.

[0064] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In various embodiments, "hydrogen" may be 1H (protium, H).

[0065] A lithium-ion secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The electrode assembly has a slot-pore structure. The electrolyte is immersed in the electrode assembly. The driving force for immersion is mainly capillary force, which is a spontaneous permeation process. Due to the obstruction of the current collector in the electrode, the electrolyte is absorbed from the end face of the electrode assembly through the separator into the interior of the electrode assembly. Therefore, the interlayer gap of the electrode assembly plays a guiding role, while the separator plays a diversion role. The steps of electrolyte immersion in the electrode assembly include: (1) the electrolyte is transported in the gap between the electrode and the separator under the action of capillary force; (2) the electrolyte preferentially permeates in the pores of the separator (the immersion rate of the electrolyte in the separator is much greater than that in the active material layer of the electrode); (3) the electrolyte diffuses through the separator to the surfaces of the positive and negative electrodes on both sides and permeates into the pores of the active material layer.

[0066] In related technologies, the poor affinity between the electrode and the electrolyte, as well as the poor wettability of the electrode, result in a slow diffusion rate of the electrolyte from the surface of the active material layer to the interior of the active material layer, and poor liquid absorption performance of the active material, thereby deteriorating the cycle performance of lithium-ion secondary batteries.

[0067] Therefore, the embodiments of this application improve the liquid absorption rate of the active material layer by modifying the substances in the active material layer, such as aldehyde-ketone polymers, in order to increase the liquid absorption rate and thereby improve the cycle performance of the lithium-ion secondary battery.

[0068] Polaroid

[0069] In a first aspect, this application proposes an electrode; the electrode includes a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprising an active material and an aldehyde-ketone polymer. The electrode can be a positive electrode and / or a negative electrode; correspondingly, the positive electrode includes a positive current collector and a positive active material layer; the negative electrode includes a negative current collector and a negative active material layer.

[0070] The electrode can be made by coating a slurry onto a current collector and then drying and cold pressing it. Alternatively, the electrode can be derived from a lithium-ion secondary battery. The lithium-ion secondary battery is disassembled, and the electrode immersed in the electrolyte is taken out. The electrode immersed in the electrolyte is placed in a vacuum dryer at 100°C for 12 hours to obtain the electrode, which is then used for electrode tests such as liquid absorption rate.

[0071] Aldehyde-ketone polymers can be synthesized through emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization. Alternatively, aldehyde-ketone polymers can be derived from lithium-ion secondary batteries. This involves disassembling the battery, removing the electrodes immersed in the electrolyte, and using external force to peel off the active material from the current collector to form a powder sample. This powder is then added to dimethyl carbonate (DMC) and stirred at 80°C for 8 hours at 500 rpm. After stirring, the mixture is allowed to stand at room temperature for 10 minutes. The supernatant is then dried at 80°C for 12 hours to obtain the aldehyde-ketone polymer. The resulting polymer may contain a small amount of lithium salt, but this has minimal impact on infrared and precipitation value measurements. To ensure the accuracy of the polymer, lithium salts can be further separated by rinsing the DMC at room temperature.

[0072] The active material layer satisfies:

[0073]

[0074]

[0075] v / λ>1.00 Equation (3),

[0076] In equations (1) to (3),

[0077] λ represents the porosity of the active material layer;

[0078] P1 represents the actual compacted density of the active material layer, with units of g / cm³. 3 ;

[0079] P2 represents the actual compacted density of the active material, with units of g / cm³. 3 ;

[0080] v represents the liquid absorption rate of the active material layer, with units of mg / s.

[0081] d represents the diameter of the capillary in the capillary test of the active material layer, and its unit is mm;

[0082] h represents the height of the liquid level in the capillary tube, and its unit is mm;

[0083] ρ represents the density of the electrolyte in the capillary test, and its unit is g / cm³. 3 ;

[0084] t represents the time it takes for the electrolyte to be absorbed within the capillary, and its unit is seconds (s).

[0085] In this application, the actual compaction density P1 refers to the ratio of the mass to the thickness of the active material layer per unit area in the electrode sheet. The actual compaction density is determined by the force applied during roller pressing after the electrode sheet is coated, and the unit is g / cm³. 3The specific testing steps are as follows: take an electrode sheet of a certain area S, weigh the mass M of its active material layer, and measure the thickness D of the active material layer. The actual compaction density is M / (S×D).

[0086] In this application, the actual compaction density P2 refers to the density of the active material itself in the active material layer. Using graphite as the negative electrode, the density of graphite is 2.25 g / cm³. 3 The actual compacted density of the active material is 2.25 g / cm³. 3 .

[0087] Taking positive electrode active material as an example, specifically, it refers to the mass of a unit "actual volume of solid material (excluding open and closed pores and interparticle pores)" in a compacted state. The actual volume V is obtained by testing, and then the actual compacted density is calculated using P = m / V. The test can be performed with reference to GB / T24586-2009. Specifically, the test steps are as follows:

[0088] 1) Pretreatment: Place a clean and dry sample cup on the balance, zero the balance, add the powder sample into the sample cup, filling about 1 / 2 of the sample cup volume, and record the sample mass;

[0089] 2) Place the sample cup containing the sample into the true density tester, seal the test system, and introduce helium gas according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the true volume is calculated according to Bohr's law (PV=nRT), and thus the true compaction density is calculated.

[0090] The sample cup volume is 3.5 cm³. 3 Analytical gas: Helium.

[0091] Equation (1) can be used to calculate the porosity λ of the active material layer using the actual compaction density and the true compaction density.

[0092] Specifically,

[0093] Where V1 represents the volume of the active material layer at mass m, and its unit is cm. 3 ;

[0094] V2 represents the volume occupied by active particles in the active material layer at mass m, and its unit is cm. 3 ;

[0095] m represents the mass of the active material layer, and its unit is g.

[0096] Equation (2) can characterize the rate at which a point on the electrode absorbs almost completely the liquid (e.g., electrolyte) in the capillary per unit time. In this application, a point on the electrode refers to a region of the electrode with a certain area, the area of ​​which corresponds to the cross-sectional area of ​​the capillary.

[0097] In this application, the method for detecting the liquid absorption rate of the electrode includes the following steps:

[0098] A predetermined amount of electrolyte is drawn using a capillary tube;

[0099] When the capillary tube is brought into contact with the electrode, the electrode under test absorbs the electrolyte in the capillary tube under capillary action.

[0100] After a predetermined time t, the liquid level h of the electrolyte absorbed in the capillary is recorded. The amount of electrolyte absorbed is calculated based on the liquid level h, diameter d, and electrolyte density ρ of the capillary. The absorption rate v of the electrode is then quantitatively calculated based on the ratio of the absorbed amount to the predetermined time t.

[0101] For example, d takes a value from 0.2 to 1, such as 0.2; h takes a value from 3 to 5, such as 3.

[0102] The capillary has capillary channels, allowing it to directly absorb electrolyte through capillary action without the need for an external drive unit. This provides two advantages: firstly, it allows for more precise control of the absorbed electrolyte volume; secondly, since the electrode absorbs electrolyte through its own capillary action, and the electrolyte is only drawn out of the capillary when the capillary comes into contact with the electrode under test, and stops flowing out when the contact is broken, the amount of electrolyte absorbed within the capillary can accurately reflect the corresponding volume of electrolyte absorbed by the electrode. This further improves the accuracy of the test results and enables quantitative calculation of the electrolyte absorption rate of the electrode.

[0103] This application uses a standard electrolyte as the test sample. The specific formulation of the electrolyte can be found in the electrolyte formulation in the examples.

[0104] Equation (3) represents the liquid absorption rate of the electrode under a porosity of λ, and can be used to characterize the liquid absorption speed of the electrode.

[0105] The aldehyde-ketone polymer of this application is introduced during the preparation of the active material layer, which can form a uniform high wetting point inside the active material layer, uniformly improve the wetting performance of the active material layer, thereby improving the overall liquid absorption rate of the active material layer and thus improving the cycle performance of the lithium-ion secondary battery using the electrode.

[0106] Optionally, 1.00 < v / λ < 50.00.

[0107] In some embodiments, the aldehyde-ketone polymer is formed into a sheet-like structure; the sheet-like structure is subjected to dynamic frequency scanning test at (Tm+20)℃ to obtain an elastic modulus G'-energy dissipation modulus G” curve, the slope of the elastic modulus G'-energy dissipation modulus G” curve is K, 0.8≤K<∞, 0.8≤K≤100; optionally, 0.8≤K≤10; Tm℃ represents the melting temperature of the aldehyde-ketone polymer.

[0108] Specifically, the preparation process of the sheet-like structure is as follows: The polymer is vacuum dried at 80°C for 12 hours. The dried polymer is then hot-pressed into thin sheets using a flat vulcanizing machine. The hot-pressing temperature is set to (Tm+20)°C, the calendering thickness is 1-2 min, the calendering time is 2 min, and the pressure is 8 MPa. After calendering for 2 min, the sample is removed and placed on another vulcanizing machine of the same model for cold pressing at a pressure of 10 MPa. Polymer discs (sheet-like structures) of a fixed size can be obtained using a circular mold with a diameter of 25 mm. For example, the sheet-like structure can be a disc with a thickness of 1-2 mm and a diameter of 25 mm; alternatively, it can be prepared according to the sample standard required by the testing equipment.

[0109] According to the conclusions of classical linear viscoelasticity, for polymers, especially linear polymers, the elastic modulus G'-energy dissipation modulus G” curve exhibits frequency dependence in the terminal region (the range approaching the maximum angular velocity), and the longest chain of the polymer plays a role in viscoelastic behavior.

[0110] The specific steps of the dynamic frequency scanning test are as follows: A TA-AR2000EX rotational rheometer (TA Instruments, USA) is used for the dynamic frequency scanning test. The parallel plate diameter is 25mm and the thickness is 0.9mm. To ensure the test is conducted within the linear springback region, the strain is 2% during the dynamic frequency scanning test, the test temperature is Tm+20℃, and the frequency scanning range is 500rad / s≤w. 2 ≤0.05rad / s, so as to obtain data in the lowest possible frequency range.

[0111] Dynamic frequency scanning tests can characterize the degree of molecular chain entanglement during solid-state melting (molten state). Compared to linear or short-branched structures, long-branched, network, and low-crosslinked structures exhibit high entanglement and deviate from linear end-effector behavior, resulting in solid-state polymer behavior. When the polymer of this application meets the above-mentioned range, it can further reduce the molecular chain entanglement state, which is beneficial for the diffusion of solvent molecules in the electrolyte between molecular chains. Furthermore, the polymer still maintains a certain degree of molecular chain entanglement, which can lock solvent molecules in situ within the polymer and reduce the risk of polymer dissolution in the electrolyte, improving the stability of polymer performance. It also facilitates the formation of a protective layer on the surface of the active material, improving solid-liquid interface properties, reducing side reactions between the active material and the electrolyte, and improving the cycle performance and storage performance of lithium-ion secondary batteries.

[0112] In some embodiments, the glass transition temperature of the aldehyde-ketone polymer is Tg, which is in °C, and -100 ≤ Tg ≤ 50; alternatively, -80 ≤ Tg ≤ 30.

[0113] The glass transition temperature (GLT) is the temperature at which the chain segments of an aldehyde-ketone polymer transition from frozen to mobile. The GLT has a certain influence on the flexibility of the polymer molecular chains; the lower the GLT, the better the flexibility of the polymer molecular chains at room temperature, and vice versa. The GLT can be measured using differential scanning calorimetry (DSC). Specifically, the testing procedure is as follows: Take 0.5g to 0.8g of sample, place it in a crucible, and subject it to heating and cooling treatments under a nitrogen atmosphere. The temperature is increased at a rate of 10℃ / min from an initial temperature 20℃ lower than the intrinsic Tg of the material to a cutoff temperature 20℃ higher than the intrinsic Tm of the material. The actual GLT and Tm of the material are determined based on the endothermic and exothermic peak values ​​or transition points during the process.

[0114] Aldehyde-ketone polymers have relatively low glass transition temperatures, better segmental flexibility of molecular chains, and are more easily broken down into adjacent chains, facilitating the formation of in-situ gels. This improves the wetting performance of the electrolyte on the active material layer, thereby enhancing the cycle performance of lithium-ion secondary batteries. For example, the glass transition temperature of aldehyde-ketone polymers can be -100℃, -90℃, -80℃, -60℃, -30℃, 0℃, 30℃, 50℃, or any combination of two of these values.

[0115] In some embodiments, the aldehyde-ketone polymer comprises the structural unit shown in formula (I).

[0116]

[0117] In formula (I), R1 includes a single bond, a substituted or unsubstituted C1-C6 methylene group; R2 includes a hydrogen atom, a substituted or unsubstituted C1-C6 alkyl group;

[0118] Optionally, R1 includes a single bond, a substituted or unsubstituted C1-C2 methylene group; R2 includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group.

[0119] For example, the aldehyde-ketone polymer includes at least one of the structural units shown in formula (I-1) to formula (I-6).

[0120]

[0121] Exemplarily, the aldehyde-ketone polymer comprises the structural unit shown in formula (II).

[0122]

[0123] In formula (II), each of R3 to R6 independently comprises a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; each of r and s independently comprises an integer from 0 to 5, and at least one of r and s is selected from a positive integer; optionally, each of R3 to R6 independently comprises a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C2 hydroxyalkyl group, or a substituted or unsubstituted C1-C2 alkoxy group.

[0124] In some embodiments, the aldehyde-ketone polymer comprises at least one of the structural units shown in formula (II-1) to formula (II-4).

[0125]

[0126] The aforementioned aldehyde-ketone polymers have a low degree of molecular chain entanglement, which is beneficial to improving the flexibility of the molecular chains. The molecular chains can fully extend in the electrolyte, thereby further improving the interfacial properties of the active material.

[0127] The polymers described above are merely examples of structural groups in the main molecular chains. In the embodiments of this application, the polymers may also be obtained by copolymerizing the above structural groups with other types of structural groups (such as olefin structural units, acrylonitrile structural units, etc.).

[0128] The functional groups of the polymer in this application can be detected by infrared spectrophotometry (IR). Specifically, the polymer is tested using a Thermo Nicolet Nexus 670 attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), and then tested according to standard GB / T6040-2002. The test range is 600–4000 cm⁻¹ using the ATR method. -1 Repeatability: ±2cm -1 Resolution: better than 4cm -1 ; Transmission depth 0.2~0.6μm.

[0129] The structure of the polymer in this application can be determined by nuclear magnetic resonance (NMR). Specifically, 1H NMR and 13CN MR are performed on a Varian MercuryPlus-400 NMR spectrometer at a test temperature of 20°C, with TMS as an internal standard, CDCl3 as a solvent, and a proton resonance frequency of 400 MHz.

[0130] The polymer monomer types described in this application (especially suitable for monomers that constitute a small proportion of the polymer) can be analyzed using pyrolysis-gas chromatography-mass spectrometry (GC-MS). The specific testing steps are as follows: Accurately weigh 0.5 mg of sample into a sample cup, fix it to the injection rod, and then place it into the pyrolyzer installed near the GC (gas chromatograph) injection port. After the pyrolyzer reaches the set temperature, press the injection button. The sample cup will rapidly fall into the core of the pyrolysis furnace through free fall. In an inert N2 atmosphere, the volatile components will instantly vaporize and be carried into the gas chromatography column by the carrier gas for separation. Finally, the components will be detected by flame ionization detector (FID) or mass spectrometer (MS) to obtain a gas chromatogram or total ion chromatogram.

[0131] When the above groups are substituted, the substituents may include one or more of the following: nitrile (-CN), nitro, sulfonyl, carboxyl, ester, chlorine, fluorine, and bromine. These substituents are high-pressure resistant and are more conducive to stabilizing the polymer structure.

[0132] In some implementations, n is selected from a positive integer from 500 to 15000.

[0133] Optionally, n is selected from a positive integer between 500 and 10000.

[0134] In some embodiments, the polymer has a molecular weight of 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 g / mol.

[0135] When the polymer's molecular weight is within the aforementioned range, it ensures a certain degree of solubility in the electrolyte while preventing complete dissolution and dispersion. This facilitates the control of the polymer's distribution and dispersion on the surface of the active material. Furthermore, it enhances the flexibility between the polymer's molecular chains, resulting in relatively weaker intermolecular forces. This allows solvent molecules in the electrolyte to open the molecular chains and enter between them, where they are encapsulated. This, in turn, facilitates the smooth and rapid migration of active ions into the active material. For example, the polymer's molecular weight can be 1.2 × 10⁻⁶. 5 g / mol, 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol or a range consisting of any two of the above values.

[0136] The molecular weight of aldehyde-ketone polymers is known in the art and can be determined using commonly used equipment and methods. Gel permeation chromatography (GPC) can be used for testing. The specific test steps are as follows: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, determine the sample according to GB / T19077-2016 / ISO13320:2009 standard.

[0137] Alternatively, a multi-angle laser scattering (MALLS) instrument can be used for testing. Specifically, an instrument combining a GPC with a Dawn Heleos II multi-angle laser light scattering device, an Optilab T-rEX refractive index (RI) detector, and a ViscoStar II viscometer (Wyatt Technology Corporation, USA) is employed. Tests are conducted at 30°C using tetrahydrofuran as the mobile phase at a flow rate of 1.0 ml / min. SEC-SAMLL data are processed using the commercial software ASTRA6 to obtain molecular weight parameters.

[0138] The aldehyde-ketone polymer in the embodiments of this application can further improve the cycle performance of lithium-ion secondary batteries when it meets one or more of the following conditions.

[0139] In some embodiments, the aldehyde-ketone polymer is added to a first solvent at 45°C to form an aldehyde-ketone polymer system. After standing at 45°C for 8 hours and then standing at 25°C for ≥24 hours, the aldehyde-ketone polymer system undergoes two stages of standing treatment, resulting in partial or complete in-situ transformation into a gel state. The aldehyde-ketone polymer system is then filtered through a 200-mesh filter, leaving the first substance. The mass of the aldehyde-ketone polymer is n (in grams); the mass of the first substance is m (in grams); the aldehyde-ketone polymer and the first substance satisfy: 5 ≤ m / n ≤ 1000; optionally, 10 ≤ m / n ≤ 1000; further optionally, 10 ≤ m / n ≤ 50. Exemplarily, m / n can be 5, 10, 20, 25, 28, 30, 32, 35, 40, 50, 80, 100, 200, 500, 1000, or a range of any two of the above values.

[0140] For example, based on the mass of the aldehyde-ketone polymer system, the ratio of the mass content of the aldehyde-ketone polymer to the mass content of the first solvent ranges from 1:100 to 1:10, for example, 3:50.

[0141] For example, the first solvent is the same as or similar to the solvent of the electrolyte, and the first solvent may include carbonate solvents. For example, carbonate solvents include cyclic carbonate solvents and / or linear carbonate solvents.

[0142] Examples of cyclic carbonate solvents include one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC.

[0143] As examples of linear carbonate solvents, linear carbonate solvents include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), diphenyl carbonate (DPC), methyl allyl carbonate (MAC), and polycarbonate (VA).

[0144] Optionally, the first solvent may also contain lithium salts and electrolyte additives, such as lithium hexafluorophosphate, vinylene carbonate (VC), and fluorovinylene carbonate (FEC).

[0145] In this application, m / n is also referred to as precipitation value, which characterizes the ability of aldehyde-ketone polymers and solvents to transform into a gel-state substance.

[0146] The first substance mainly includes gel-state substances formed by aldehyde-ketone polymers and a first solvent. In this type of gel-state substance, the molecular structure of the aldehyde-ketone polymer remains basically unchanged.

[0147] In some embodiments, the first substance is dried at 80°C for 12 hours to remove the first solvent from the first substance, and then detected by infrared spectrophotometry (IR) or nuclear magnetic resonance (NMR). After drying, the main component of the first substance is the aldehyde-ketone polymer described above.

[0148] This application achieves the expansion of aldehyde-ketone polymer molecular chains within the safe operating temperature range of lithium-ion secondary batteries by increasing the temperature, promoting mutual attraction and physical bonding between the aldehyde-ketone polymer molecular chains and the solvent, thereby improving liquid absorption capacity. At room temperature, the activity of aldehyde-ketone polymer molecular chain segments decreases, maintaining their attachment to the surface of the active material and locking the electrolyte in the space environment of the aldehyde-ketone polymer, forming a state similar to in-situ gel, improving liquid retention capacity and cycle performance.

[0149] [Positive electrode plate]

[0150] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material and an aldehyde-ketone polymer. In this application, the aldehyde-ketone polymer includes the aldehyde-ketone polymer as described above.

[0151] For example, the positive electrode current collector has two surfaces opposite each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0152] In some implementations, 1.00 < v / λ < 4.00; alternatively, 1.20 ≤ v / λ ≤ 3.80; further alternatively, 1.4 ≤ v / λ ≤ 3.6. Exemplarily, v / λ can be 1.20, 1.40, 1.80, 2.00, 2.50, 3.00, 3.50, 3.60, 3.80, 3.90, or a range consisting of any two of the above values.

[0153] In some embodiments, the mass percentage of the aldehyde-ketone polymer is A% based on the mass of the positive electrode active material layer; wherein, 0.1 ≤ A ≤ 1.5.

[0154] When the mass percentage of the aldehyde-ketone polymer is within the above range, it can significantly improve the liquid absorption capacity of the positive electrode active material layer. For example, the mass percentage A% of the aldehyde-ketone polymer can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or any combination of two of the above values.

[0155] The positive electrode active material layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in lithium-ion secondary batteries. As an example, the positive electrode active material may include at least one of the following materials: layered structure positive electrode active materials (e.g., ternary, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered, and rock salt phase layered materials), olivine-type phosphate active materials, and spinel structure positive electrode active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.).

[0156] For example, the general formula of a layered positive electrode active material is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y z Wherein, 0≤x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0≤a≤1, 0≤b≤1, 0≤c≤1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y is selected from one or more of O and F. Optionally, y=0. Specifically, the layered structure positive electrode active material may include lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 One or more of O2 (NCM523).

[0157] For example, the general formula of olivine-type phosphate active substances is: Li x A y Me a M b P 1-c X c Y zWherein, 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A is selected from one or more of Na, K, and Mg; Me is selected from one or more of Mn, Fe, Co, and Ni; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X is selected from one or more of S, Si, Cl, B, C, and N; Y is selected from one or more of O and F. Specifically, the olivine-type phosphate active substances include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0158] For example, the general formula of a spinel-structured positive electrode active material is: Li x A y Mn a M 2-a Y z Wherein, 0≤x≤2, 0≤y≤1, and 0.9≤x+y≤2; 0.5≤a≤2; 3≤z≤5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of Ni, Co, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y is selected from one or more of O and F. Specifically, the positive electrode active materials with spinel structure include LiMn2O4 and LiNi. 0.5 Mn 1.5 O4, LiCr 0.3 Mn 1.7 O4, Li 1.1 Al 0.1 Mn 1.9 O4, Li2Mn2O4 and Li 1.5 One or more of Mn2O4.

[0159] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0160] In some embodiments, the positive electrode active material layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more combinations selected from superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode active material layer.

[0161] In some embodiments, the positive electrode active material layer may optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder; as an example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF). In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode active material layer. The crystallinity of the positive electrode binder is higher than that of the aldehyde-ketone polymers described above, and the melting temperature of the positive electrode binder is higher than that of the aldehyde-ketone polymers described above.

[0162] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, the aldehyde-ketone polymer, an optional conductive agent, an optional positive electrode binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to it.

[0163] [Negative electrode plate]

[0164] A negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material and an aldehyde-ketone polymer. In this application, the aldehyde-ketone polymer includes the aldehyde-ketone polymer as described above.

[0165] For example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0166] In some implementations, 3.00 < v / λ < 50.00; alternatively, 3.40 ≤ v / λ ≤ 30.00. For example, v / λ can be 3.20, 3.40, 3.50, 4.00, 4.50, 5.00, 5.50, 6.00, 6.50, 7.00, 8.00, 9.00, 9.50, 10.00, 10.50, 11.00, 12.00, 13.00, 14.00, or a range consisting of any two of the above values.

[0167] In some embodiments, the mass percentage of the aldehyde-ketone polymer is B% based on the mass of the negative electrode active material layer; wherein 0.2 ≤ B ≤ 5.0. When the mass percentage of the aldehyde-ketone polymer is within the above range, the liquid absorption capacity of the negative electrode active material layer can be significantly improved. Exemplarily, the mass percentage B% of the aldehyde-ketone polymer can be 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range of any two of the above values.

[0168] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0170] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. The negative electrode binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The crystallinity of the negative electrode binder is higher than that of the aldehyde-ketone polymers described above, and the melting temperature of the negative electrode binder is higher than that of the aldehyde-ketone polymers described above.

[0171] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0172] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0173] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the aldehyde-ketone polymer, the conductive agent, the negative electrode binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0174] Lithium-ion secondary batteries

[0175] Secondly, this application provides a lithium-ion secondary battery, which includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The lithium-ion secondary battery can be a lithium-ion battery or the like.

[0176] In some embodiments, the positive electrode can be a positive electrode of any embodiment of the first aspect of this application, thereby improving the cycle performance of the lithium-ion secondary battery. The negative electrode can be a conventional electrode.

[0177] In some embodiments, the negative electrode can be a negative electrode of any embodiment of the first aspect of this application, thereby improving the cycle performance of the lithium-ion secondary battery. The positive electrode can be a conventional electrode.

[0178] In some embodiments, the positive electrode can be a positive electrode of any embodiment of the first aspect of this application, and the negative electrode can be a negative electrode of any embodiment of the first aspect of this application, thereby improving the cycle performance of the lithium-ion secondary battery.

[0179] [Electrolytes]

[0180] Lithium-ion secondary batteries also include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0181] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0182] As an example, lithium salts may include one or more combinations selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0183] As an example, the organic solvent may include one or more combinations selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0184] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0185] [Isolation membrane]

[0186] In some embodiments, the lithium-ion secondary battery further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0187] In some embodiments, the material of the separator may include one or more combinations selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0188] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding or stacking process.

[0189] This application does not impose any particular limitation on the shape of the lithium-ion secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured lithium-ion secondary battery.

[0190] In some embodiments, such as Figure 1 and Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 may be one or more, and can be adjusted according to requirements.

[0191] The method for preparing the lithium-ion secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a lithium-ion secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion secondary battery is obtained.

[0192] In some embodiments of this application, the lithium-ion secondary battery according to this application can be assembled into a battery module. The number of lithium-ion secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0193] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple lithium-ion secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion secondary batteries 5 can be fixed in place using fasteners.

[0194] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of lithium-ion secondary batteries 5 are received.

[0195] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0196] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0197] Both battery modules and battery packs can be used as examples of batteries in this application.

[0198] Electrical appliances

[0199] Thirdly, this application provides an electrical device, which includes at least one of the lithium-ion secondary battery, battery module, and battery pack described in this application. The lithium-ion secondary battery, battery module, and battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0200] Electrical devices can choose lithium-ion rechargeable batteries, battery modules, or battery packs according to their usage requirements. Figure 6 This is a schematic diagram of an example electrical device. This electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or a battery module can be used. Another example electrical device could be a mobile phone, tablet computer, laptop computer, etc. These devices typically require a slim and lightweight design, and can use lithium-ion rechargeable batteries as their power source.

[0201] Example

[0202] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0203] Example 1

[0204] (1) Preparation of the positive electrode sheet:

[0205] Aluminum foil with a thickness of 12μm was used as the positive electrode current collector.

[0206] A positive electrode slurry was prepared by combining an aldehyde-ketone polymer, the positive electrode active material LiFePO4, the conductive agent carbon black, and the binders polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP). The mass ratio of the aldehyde-ketone polymer, LiFePO4, conductive carbon black, PVDF, and N-methylpyrrolidone (NMP) in the positive electrode slurry was 0.5:96.8:2:0.7:29. The positive electrode slurry was coated onto a current collector aluminum foil and dried at 85°C, then cold-pressed. After edge trimming, cutting, and slitting, it was dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0207] (2) Preparation of negative electrode sheet:

[0208] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0209] An aldehyde-ketone polymer, artificial graphite (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), sodium carboxymethyl cellulose (CMC) (thickener), and deionized water were mixed evenly in a weight ratio of 2.5:94:0.5:2:1:100 to prepare a negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector and dried at 85°C. Then, it was cold-pressed, trimmed, cut into sheets, and slit. Finally, it was dried under vacuum at 120°C for 12 hours to produce the negative electrode sheet.

[0210] (3) Preparation of electrolyte

[0211] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate EC and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3:7 to obtain an electrolyte solvent. Then, lithium salt LiPF6 is mixed with the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0212] (4) Preparation of lithium-ion batteries:

[0213] A 16μm polyethylene film (PE) is used as the separator. The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0214] Comparative Example 1

[0215] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that no aldehyde-ketone polymer was added to the positive electrode of Comparative Example 1, and no aldehyde-ketone polymer was added to the negative electrode of Comparative Example 1.

[0216] Comparative Example 2

[0217] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that the positive and negative electrode materials of Comparative Example 2 were replaced with aldehyde-ketone polymers.

[0218] Examples 2 to 4

[0219] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the positive and negative electrode sheets in Examples 2 to 4 were made of aldehyde-ketone polymer instead of aldehyde-ketone polymer.

[0220] Example 5

[0221] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that an aldehyde-ketone polymer was added to the positive electrode of Example 5, while no aldehyde-ketone polymer was added to the negative electrode of Example 5.

[0222] Examples 6 to 9

[0223] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the content of aldehyde-ketone polymer was adjusted in the positive electrode sheets of Examples 6 to 9.

[0224] Examples 10 to 12

[0225] Lithium-ion batteries were prepared using a method similar to that of Example 1, except that the content of aldehyde-ketone polymers in the negative electrode sheets of Examples 10 to 12 was adjusted.

[0226] The data for the examples and comparative examples are shown in Table 1.

[0227] Test section

[0228] 1. Lithium-ion battery capacity retention test

[0229] The lithium-ion batteries prepared in the examples and comparative examples were charged at a constant current of 1C to 4.25V at 45°C, then charged at a constant voltage of 4.25V to a current of 0.05C, rested for 5 minutes, and then discharged at 1C to 2.8V. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The battery capacity retention rate after each cycle was Pn = Cn / C0*100%. A dot plot of battery capacity retention rate versus cycle number was obtained with 1200 points (P1, P2...P1200) as the vertical axis and the corresponding cycle number as the horizontal axis.

[0230] In this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 1200th cycle to n=1200. For example, the battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 1200 cycles under the above test conditions, i.e., the value of P1200. The test process for Comparative Example 1 and other examples is the same as above.

[0231] 2. Lithium-ion battery DC impedance test

[0232] The lithium-ion batteries prepared in the examples and comparative examples were charged at 45°C with a constant current of 1C to 4.25V, and then charged with a constant voltage of 4.25V to a current of 0.05C. After resting for 5 minutes, the voltage V1 was recorded. Then, the batteries were discharged at 1C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle was obtained by calculating (V2-V1) / 1 / 3C. The above steps were repeated for the same battery, and the internal resistance DCRn of the battery after the nth cycle (n=1, 2, 3...1200) was recorded. The 1200 points of DCR1, DCR2, DCR3...DCR1200 were plotted on the ordinate, and the corresponding cycle number was plotted on the abscissa to obtain the DCIR curve of the battery discharge versus the cycle number for the aldehyde-ketone polymers of the examples and comparative examples.

[0233] During this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 1200th cycle to n=1200. For example, in Table 1, the battery internal resistance increase rate of Example 1 is (DCRn-DCR1) / DCR1*100%, and the test process for Comparative Example 1 and other examples is the same. The data in Table 1 were measured after 1200 cycles under the above test conditions.

[0234] Test Results

[0235] Table 1

[0236]

[0237] In Table 1, 100% formaldehyde refers to the total mass of monomer 1 and monomer 2, where the mass percentage of formaldehyde is 100%.

[0238] 30% polyvinyl alcohol refers to a polyvinyl alcohol content of 30% based on the total mass of monomer 1 and monomer 2.

[0239] As shown in Table 1, compared with Comparative Example 1, the embodiments of this application add the aldehyde-ketone polymer of this application to the positive electrode and / or negative electrode. The aldehyde-ketone polymer can form a uniform high wetting point inside the active material layer, uniformly improve the wetting performance of the active material layer, thereby improving the overall liquid absorption speed of the active material layer, and thus improving the cycle performance of the lithium-ion secondary battery using the electrode.

[0240] Compared to Comparative Example 2, the embodiments of this application can more significantly improve the cycle performance of lithium-ion batteries when v / λ>1 is satisfied.

[0241] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An electrode comprising a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprising an active material and an aldehyde-ketone polymer, the active material layer satisfying: Equation (1), Equation (2), v / λ>1.00 Equation (3); In equations (1) to (3), λ represents the porosity of the active material layer; P1 represents the actual compacted density of the active material layer, with units of g / cm³. 3 ; P2 represents the actual compacted density of the active material, with units of g / cm³. 3 ; v represents the liquid absorption rate of the active material layer, with units of mg / s; d represents the diameter of the capillary in the capillary test of the active material layer, and its unit is mm; h represents the height of the liquid level in the capillary tube, and its unit is mm; The density of the electrolyte in the capillary test is expressed in g / cm³. 3 ; t represents the time it takes for the electrolyte to be absorbed in the capillary, and its unit is s. The aldehyde-ketone polymer is made into a sheet-like structure. The elastic modulus G' - energy dissipation modulus G” curve of the sheet-like structure was obtained by dynamic frequency scanning test at (Tm+20)℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K, 0.8≤K<∞, and Tm℃ represents the melting temperature of the aldehyde-ketone polymer.

2. The electrode according to claim 1, wherein, The active material includes a positive electrode active material. The active material layer satisfies: 1.00 < v / λ < 4.

00.

3. The electrode according to claim 2, wherein, The active material layer satisfies: 1.20≤v / λ≤3.

80.

4. The electrode according to claim 1, wherein, The active material includes a positive electrode active material. Based on the mass of the active material layer, the mass percentage of the aldehyde-ketone polymer is A%. Where 0.1≤A≤1.

5.

5. The electrode according to claim 1, wherein, The active material includes a negative electrode active material. The active material layer satisfies: 3.00 < v / λ < 50.

00.

6. The electrode according to claim 5, wherein, The active material layer satisfies: 3.40≤v / λ≤30.

00.

7. The electrode according to claim 1 or 5, wherein, The active material includes a negative electrode active material. Based on the mass of the active material layer, the mass percentage of the aldehyde-ketone polymer is B%. Where 0.2≤B≤5.

0.

8. The electrode according to claim 1, wherein, 0.8≤K≤100。 9. The electrode according to claim 1, wherein, 0.8≤K≤10。 10. The electrode according to any one of claims 1 to 6, wherein, The glass transition temperature of the aldehyde-ketone polymer is Tg, which is in °C, and -100≤Tg≤50.

11. The electrode according to claim 10, wherein, -80≤Tg≤30.

12. The electrode according to any one of claims 1 to 6, wherein, The aldehyde-ketone polymer comprises the structural unit shown in formula (I). Equation (I); In formula (I), R1 includes a single bond or a substituted or unsubstituted C1-C6 methylene group; R2 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group; n is selected from positive integers from 500 to 15000.

13. The electrode according to claim 12, wherein, R1 includes a single bond or a substituted or unsubstituted C1-C2 methylene group; R2 includes a hydrogen atom or a substituted or unsubstituted C1-C3 alkyl group.

14. The electrode according to claim 12, wherein, The aldehyde-ketone polymer comprises at least one of the structural units shown in formula (I-1) to formula (I-6). Equation (I-1), Equation (I-2), Equation (I-3), Equation (I-4), Formula (I-5), Equation (I-6); n is selected from positive integers from 500 to 15000.

15. The electrode according to any one of claims 1 to 6, wherein the aldehyde-ketone polymer comprises the structural unit shown in formula (II), Formula (II); In formula (II), R3 to R6 each independently include a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; r and s each independently select an integer from 0 to 5, and at least one of r and s is selected from a positive integer; n is selected from a positive integer from 500 to 15000.

16. The electrode according to claim 15, wherein, R3 to R6 each independently include a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C2 hydroxyalkyl group, or a substituted or unsubstituted C1-C2 alkoxy group.

17. The electrode according to claim 15, wherein the aldehyde-ketone polymer comprises at least one of the structural units shown in formula (II-1) to formula (II-3). Formula (II-1) Formula (II-2) Formula (II-3) Equation (II-4); n is selected from positive integers from 500 to 15000.

18. The electrode according to claim 12, wherein, and / or The molecular weight of the aldehyde-ketone polymer is 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 g / mol.

19. A lithium-ion secondary battery, comprising the electrode as described in any one of claims 1 to 18.

20. A battery comprising the lithium-ion secondary battery as claimed in claim 19.

21. An electrical device comprising the battery as claimed in claim 20.

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