Secondary battery, preparation method thereof and electric device

Abstract

The invention provides a secondary battery, a power utilization device and a preparation method of the secondary battery. The secondary battery comprises a positive pole piece, wherein the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector; the positive electrode film layer comprises a positive electrode active material and an additive, the additive comprises blocked isocyanate, and blocking molecules used for blocking comprise one or more of compounds with the structure shown in the formula I. And the isocyanate comprises one or more of compounds with a structure as shown in the following formula II. According to the secondary battery, the blocked isocyanate is adopted as an additive to be contained in a positive electrode film layer, unsaturated bonds in the blocked isocyanate can react with oxygen free radicals generated by a positive electrode active material to generate a stable compound, and therefore gas generated by the secondary battery is reduced. R2-[OH] n (I) and R3-[NCO] m (II).

Description

Technical Field

[0001] This application relates to the field of lithium-ion secondary battery technology, and more particularly to additives for positive electrodes. Background Technology

[0002] In recent years, with the increasingly wide application of lithium-ion secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, and aerospace.

[0003] However, gas is generated during battery cycling and storage, which can affect battery life. Therefore, improvements are needed to address the issue of gas generation in batteries. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery with reduced gas production. Furthermore, this application also provides a method for preparing the secondary battery and an electrical device including the secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery. The secondary battery includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material and an additive, the additive including a capped isocyanate, wherein the capping molecule for capping includes one or more compounds having the structure of Formula I:

[0006] R2-[OH] n (I)

[0007] Isocyanates include one or more compounds having the structure of Formula II:

[0008] R3-[NCO] m (II)

[0009] In Equations I and II above, when n = 1, m is any integer from 1 to 3, or when m = 1, n is any integer from 1 to 3;

[0010] R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-10 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-10 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-10 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-10 Alkyl and substituted or unsubstituted C 2-10 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group;

[0011] R3 includes R1 and R6-[OC(=O)NH-R1] which have monovalent to trivalent valences. p - one of them, in which

[0012] R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 3-20 Contains alkyl groups with three to six-membered rings,

[0013] R6 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl group, p=m

[0014] The substitution is performed by one or more substances selected from halogens, -N(=O)2OR c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metal ions and C 1-4 alkyl.

[0015] In this disclosure, the aforementioned end-capped isocyanate is included as an additive in the positive electrode film layer. The unsaturated bonds therein can preferentially react with oxygen free radicals generated by the positive electrode active material to produce stable compounds, thereby reducing the generation of gas due to side reactions between oxygen free radicals and components in the battery.

[0016] In some embodiments, R2 comprises substituted or unsubstituted monovalent to trivalent C. 3-6 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-6 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups.

[0017] In some embodiments, R1 includes substituted or unsubstituted monovalent to trivalent C. 2-8 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 5-18 Contains an alkyl group with a five- or six-membered ring; R6 includes substituted or unsubstituted monovalent to trivalent C. 1-6 alkyl.

[0018] The optional end-capping molecules and isocyanate molecules have smaller molecular weights, resulting in a relatively larger number of unsaturated bonds at the same addition amount, which is more beneficial for reducing gas generation in secondary batteries. In addition, smaller end-capping isocyanate molecules are easier to disperse in the positive electrode slurry without making the slurry too viscous.

[0019] In some embodiments, the substitution is R2 or R3, optionally R2 or R6, and is selected from one or more of -S(=O)2OR. c F-, -P(=O)2OR c -N(=O)2OR c and -NHC(=O)OR c The groups in the group are substituted, wherein each R c It is independently selected from methyl and ethyl.

[0020] These functional substituents enable the capped isocyanate molecules to reduce gas production in secondary batteries while providing further functionality. For example, halogen and phosphate groups can provide flame retardancy; fluorine can form lithium fluoride with lithium ions in the SEI film, and the nitrogen in the nitrate group can form lithium nitride with lithium ions in the SEI film, improving the stability of the SEI film; sulfonic acid groups can improve the conductivity of the positive electrode film; and amide groups readily form hydrogen bonds with the binder in the positive electrode film, which can improve the adhesion of the positive electrode film.

[0021] In some implementations, n = 1, m = 2 or 3. Optionally, R2 includes substituted or unsubstituted C. 3-6 alkenyl, substituted or unsubstituted C 3-6 Alkyne, substituted or unsubstituted C 3-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups; R3 includes substituted or unsubstituted C. 1-6 Alkylene and C 5-10 Divalent alkyl groups containing three to six-membered rings.

[0022] In this embodiment, a monohydric alcohol is used as a capping agent to cap binary or ternary isocyanate groups. The resulting capped isocyanate can introduce more unsaturated bonds, thereby further improving gas production in the secondary battery.

[0023] In a specific embodiment, the isocyanate includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, and hexamethylene diisocyanate trimer; the end-capping molecule includes one or more of N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxyethylmethylacrylamide, 3-hydroxypropylcyanamide, and 3-hydroxybutylcyanamide.

[0024] In some embodiments, the molecular weight of the capped isocyanate is less than or equal to 1,000, optionally less than or equal to 800, and more optionally less than or equal to 600. A smaller molecular weight is beneficial for the uniform dispersion of the additive, which can better capture the free radicals generated by the positive electrode active material and is beneficial to reducing the gas generation level of the secondary battery.

[0025] In some embodiments, the capped isocyanate is obtained by reacting the isocyanate and the capping molecule at an isocyanate index R of 1.0 - 1.2, optionally 1.05 - 1.1. Optionally, the reaction system after the reaction is directly used as the additive.

[0026] Within the above R value range, the capping reaction can be promoted, and the hydroxyl groups of the capping molecules can react almost completely, so that hydroxyl groups will not be introduced into the battery in an unfavorable amount. In addition, a slight excess of isocyanate can cause the reactants to form almost all capped isocyanate molecules according to the stoichiometric ratio, which helps to increase the addition amount of the active ingredient in the additive. Moreover, directly using the reaction system after the reaction as the additive saves the treatment process, and a small amount of unreacted isocyanate groups can also play a role in removing water and acid, reducing the occurrence of side reactions between water or acid and the electrolyte, thereby further improving the gas generation performance of the secondary battery.

[0027] In some embodiments, based on the total weight of the positive electrode film layer, the content of the additive is 0.2 wt% to 1 wt%, optionally 0.3 wt% to 0.8 wt%, and more optionally 0.4 wt% - 0.6 wt%. Using an additive with an addition amount within the above range can effectively play the role of inhibiting gas generation, and at the same time, it basically has no effect on the energy density of the positive electrode and the first Coulomb efficiency of the secondary battery.

[0028] In some embodiments, the positive electrode active material includes LiNi 10-x-y Co x M y O2, where M includes at least one of Al, Y, Zr, La, Ti, Mg, Nb, Mn, W, Sr, where 1 < x < 5 and 1 < y < 5. Optionally, M is Al or Mn. Optionally, (10 - x - y) ≥ 7.

[0029] The second aspect of the present application provides an electrical device including the above secondary battery. The electrical device includes the secondary battery of any of the above embodiments. The beneficial effects of all aspects of the secondary battery are also reflected in the electrical device.

[0030] The third aspect of this application provides a method for preparing the aforementioned secondary battery. The secondary battery includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material and an additive, the additive including a capped isocyanate, wherein the preparation method includes the step of adding the reaction product of the isocyanate and the capping molecule as the additive to a positive electrode slurry. The capping molecule and the isocyanate are as defined in the first aspect above, and will not be repeated here.

[0031] In some embodiments, the isocyanate and the capping molecule react in a ratio of 1.0 to 1.2, optionally 10.5 to 1.10, with an isocyanate index R of 1.0 to 1.2. When the R value is within this range, the reaction can be promoted to complete, thereby minimizing the introduction of hydroxyl groups into the positive electrode, while also allowing for a higher proportion of capping isocyanate molecules added to the positive electrode.

[0032] In some embodiments, the reaction product is obtained by reacting the isocyanate and the capping molecule at 70°C to 90°C. Optionally, adding the reaction product of the isocyanate and the capping molecule as an additive to the positive electrode slurry includes directly adding the reaction system after the reaction is completed to the positive electrode slurry.

[0033] Using the entire reaction system as an additive after the reaction is complete simplifies the process. Furthermore, small amounts of unreacted isocyanate groups can react with trace amounts of water or acid in the battery, further reducing gas generation issues caused by these substances.

[0034] In some embodiments, the amount of additive added is 0.2 wt% to 1 wt%, optionally 0.3 wt% to 0.8 wt%, and more preferably 0.4 wt% to 0.6 wt%, based on the total weight of the positive electrode film. Within the range of the amount added, the added additive can reduce gas production in the secondary battery without significantly affecting the energy density and initial coulombic efficiency of the secondary battery. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0036] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0037] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0038] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0039] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0040] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0041] Figure 7 The infrared spectrum of the reaction system during the preparation process of Preparation Example 1 of this application is shown.

[0042] Figure 8 The volume growth rate of the secondary batteries prepared in Examples 1-4 and Comparative Example 1 of the present invention during storage at 70°C is shown.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0045] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and electrical device of this application. However, unnecessary details 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0046] 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.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0049] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating 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.

[0050] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0051] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0052] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery.

[0053] In this application, the term "monovalent to trivalent" group refers to a group capable of forming bonds with 1 to 3 groups.

[0054] In this application, the term "monovalent to trivalent C" is used. 1-10 "Alkyl" refers to a straight-chain or branched alkyl group containing 1 to 10 carbon atoms, ranging from monovalent to trivalent. The C atoms can be monovalent to trivalent. 1-6 Alkyl groups. Examples include methyl, methylene, ethyl, ethylene, methine, propyl, propylene, methine, butyl, butylene, methine, pentyl, pentylene, methine, hexyl, hexylene, methine, etc. The term "C" 1-10 "Alkyl" refers to a straight-chain or branched alkyl group containing 1 to 10 carbon atoms, ranging from monovalent to trivalent. Examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, etc.

[0055] In this application, the term "monovalent to trivalent C" is used. 3-10 "Alkenyl" refers to a straight-chain or branched alkenyl group containing 2 to 10 carbon atoms, with at least one carbon-carbon double bond, and characterized by monovalent to trivalent oxidation. Monovalent to trivalent carbon atoms can be selected. 3-6 Alkenyl. Examples include propenyl, propenylene, propenylene, butenyl, butadienyl, butenylene, butenylene, pentenyl, pentadienyl, pentenylene, pentenylene, hexenyl, hexadienyl, hexene, pentenylene, etc. The term "C" 2-10 "Alkenyl" refers to a straight-chain or branched alkenyl group containing 2 to 10 carbon atoms with at least one carbon-carbon double bond, ranging from monovalent to trivalent. Examples include vinyl, propenyl, butenyl, pentenyl, pentadienyl, hexenyl, hexadienyl, heptene, heptadiene, octene, octadiene, etc.

[0056] In this application, the term "monovalent to trivalent C" is used. 3-10 "Alynyl" refers to a straight-chain or branched alkynyl group containing 2 to 10 carbon atoms, with at least one carbon-carbon triple bond, and is monovalent to trivalent. Monovalent to trivalent carbon atoms can be selected. 3-6 Alkyne group. Examples include, but not limited to, propynyl, propynyl, butynyl, butynyl, pseudobutynyl, penynyl, pseudopentynyl, pseudopentenyl, hexenyl, and hexenyl.

[0057] In this application, the term "monovalent to trivalent C" is used. 2-10 "Cyano" refers to a group having at least one cyano group substituted on an alkyl chain with 2-10 carbon atoms that is monovalent to trivalent. The cyano group can be monovalent to trivalent. 2-6Cyanoyl. Examples include, but not limited to, propylcyano-3-yl, butyrylcyano-3-yl, butyrylcyano-4-yl, pentancyano-3,5-diyl, hexanocyano-3,6-diyl, 1,5-pentadicyano-3-yl, etc.

[0058] In this application, the term "monovalent to trivalent C" is used. 3-20 "Alkyl groups containing three to six-membered rings" refers to monocyclic, spirocyclic (sharing one atom), or fused (sharing at least one bond) saturated carbocyclic systems with 3 to 6 members, wherein the carbocyclic ring has one or more alkyl groups with a total of 3 to 12 carbon atoms, and the monovalent to trivalent carbon is located on the ring and / or the alkyl group. The carbon atoms can be monovalent to trivalent. 5-18 Alkyl groups containing five or six-membered rings. Examples include cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, cycloheptylene, bicyclo[4,3,0]nonylene, norbornylene, isophorone, cyclohexane-[1,3,5-tris(butyl-1-yl)-4-yl], etc.

[0059] In this application, the terms "substituted" or "having substituents" refer to a compound or chemical group that is partially substituted by at least one substituent. Unless otherwise indicated, a "substituted" group has one substituent at one or more substituted positions of the group, and when more than one position is substituted in any given structure, the substituent is either the same or different at each position. The terms "unsubstituted" or "without substituents" refer to a parent compound or portion that does not have any other substituents except for an undetermined valence chemically saturated with hydrogen atoms. The substituents described in this application are selected from halogens, -N(=O)₂OR c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metals and C 1-4 Alkyl groups, such as Na + K + Methyl, ethyl, propyl, butyl.

[0060] In secondary batteries, positive electrode active materials, especially ternary positive electrode active materials, become unstable under high temperature or high voltage environments and during battery use. A mainstream view on the specific reasons for this instability is that ternary positive electrode active materials are prone to lattice oxygen loss, generating oxygen free radicals. These oxygen free radicals are highly reactive, triggering a series of chemical reactions, such as various side reactions with the electrolyte to produce gases like CO2, CO, H2, and C. x H y C x H y Oz C x H y Factors such as F can cause battery swelling, leading to safety hazards and consequently reducing battery performance and lifespan.

[0061] Based on this, this application proposes a secondary battery with reduced gas production, a method for preparing the same, and an electrical device including the secondary battery. The following provides a detailed description of this application and its optional embodiments.

[0062] Secondary batteries

[0063] The first aspect of this application provides a secondary battery.

[0064] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0065] The secondary battery of this application includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material and an additive, the additive including a capped isocyanate, wherein the capping molecule for capping includes one or more compounds having the structure of the following formula I:

[0066] R2-[OH] n (I)

[0067] Isocyanates include one or more compounds having the structure of Formula II:

[0068] R3-[NCO] m (II)

[0069] In Equations I and II above, when n = 1, m is any integer from 1 to 3, or when m = 1, n is any integer from 1 to 3;

[0070] R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-10 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-10 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-10 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-10 Alkyl and substituted or unsubstituted C 2-10 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group;

[0071] R3 includes R1 and R6-[OC(=O)NH-R1] which have monovalent to trivalent valences. p - one of them, in which

[0072] R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 3-20 Contains alkyl groups with three to six-membered rings,

[0073] R6 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl group, p=m

[0074] The substitution is performed by one or more substances selected from halogens, -N(=O)2OR c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metal ions and C 1-4 alkyl.

[0075] In this application, the capped isocyanate as defined above is used as an additive contained in the positive electrode film layer. The unsaturated bonds in this isocyanate preferentially react with oxygen free radicals generated by the positive electrode active material to produce stable compounds, thereby reducing gas generation. The capped isocyanate, as defined above, has good hydrophilicity due to the good dispersion of the urethane groups formed by the isocyanate groups and hydroxyl groups after the capping reaction, allowing it to be well dispersed in the positive electrode slurry and exhibiting good compatibility with the binder in the positive electrode film layer, thus ensuring uniform dispersion. Furthermore, the capped isocyanate exhibits good stability, does not undergo side reactions with the electrolyte, and can withstand the high temperature (e.g., approximately 70°C) and high voltage environment of the secondary battery, thus remaining stable in the positive electrode film layer. When the positive electrode active material is unstable and generates oxygen free radicals, it promptly captures these free radicals. Therefore, the secondary battery of this application has improved gas generation during storage, especially at high temperatures.

[0076] In addition, the end-capped isocyanate can increase the adhesion of the positive electrode film, making the positive electrode film more tightly bonded to the current collector.

[0077] In this application, the capped isocyanate can be determined using infrared spectroscopy. For example, the infrared spectrum of the additive material can be tested, and the additive can be identified by the characteristic peaks of the residual carbamate and unsaturated bond groups it contains. Alternatively, the additive can be substantially separated by disassembling the positive electrode film of the formed secondary battery, and then determined by infrared spectroscopy. Specifically, the material can be subjected to infrared spectral analysis using instruments and methods known in the art, such as an infrared spectrometer (e.g., a Nicolet IS10 Fourier transform infrared spectrometer) according to the General Rules for Infrared Spectroscopic Analysis in GB / T 6040-2019.

[0078] The end-capped molecule shown in Formula I above is a monohydric, dihydric, or trihydric alcohol, wherein the R2 group is as defined above. The end-capped molecule can also be an amine compound having -NH2 or -NH-. Amine compounds are too reactive and prone to causing localized thermal runaway and generating byproducts; therefore, they are not used in this application. As defined above, the end-capped molecule introduces an unsaturated carbon-carbon bond capable of capturing oxygen free radicals into the end-capped isocyanate through the R2 group; the hydroxyl group therein reacts with the isocyanate group in the isocyanate molecule to generate a urethane group (-OC(=O)NH-), thereby end-capping the isocyanate molecule.

[0079] The end-capping molecule may contain 1-3 hydroxyl groups, thus allowing it to react with 1-3 isocyanate groups. As defined above, when n=1 in the end-capping molecule of Formula I, i.e., when the end-capping molecule is a monohydric alcohol, the isocyanate molecule may contain 1-3 isocyanate groups (m is an integer from 1 to 3). When n=2 or 3 in the end-capping molecule of Formula I, the isocyanate molecule contains only 1 isocyanate group. This prevents the formation of polymers, thus making the end-capped isocyanate a small molecule compound. This allows the additive to be easily dispersed in the positive electrode slurry without causing excessively high slurry viscosity. Optionally, n=1 in the end-capping molecule of Formula I, i.e., the end-capping molecule is a monohydric alcohol.

[0080] According to some implementations, R2 includes monovalent to trivalent C, substituted or unsubstituted. 3-6 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-6 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group. Specifically, R2 includes a monovalent to trivalent C, whether substituted or unsubstituted. 3-6 One of alkenyl and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group. More specifically, the end-capping molecule may be a hydroxyalkyl-substituted acrylamide or a hydroxyalkyl-substituted (meth)acrylamide, wherein the hydroxyalkyl group may be one or more of the following: 1-4 carbon atoms (e.g., N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxyethyl(meth)acrylamide), hydroxyalkyl-substituted cyanides (e.g., 3-hydroxypropylcyanide, 3-hydroxybutylcyanide), but is not limited thereto.

[0081] The isocyanate molecule shown in Formula II above may have one, two, or three isocyanate groups (m = 1, 2, or 3), wherein the R3 group is as defined above. Optionally, when n = 1, m = 2 or 3. In this embodiment, R2 comprises substituted or unsubstituted C. 3-6 alkenyl, substituted or unsubstituted C 3-6 Alkyne, substituted or unsubstituted C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups. Optionally, R2 includes substituted or unsubstituted C. 3-6 alkenyl, substituted or unsubstituted C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups. R3 includes substituted or unsubstituted C. 1-6 Alkylene and C 5-10 Divalent alkyl groups containing three to six-membered rings.

[0082] In some embodiments, the isocyanate molecule is a molecule having a straight chain, a branched chain, or a saturated hydrocarbon group containing a carbide ring, with an isocyanate group substituted on the chain (i.e., R3 is selected from the R1 group defined above). Optionally, the isocyanate molecule is a binary or ternary isocyanate. Such molecules have a more compact molecular structure, which is beneficial for the cathode slurry to have a suitable viscosity.

[0083] In other embodiments, the isocyanate molecule may be formed by pre-conjugating a binary or ternary isocyanate (optionally those with different reactivity of isocyanates in the molecule, such as isophorone diisocyanate) with an isocyanate group in excess of the hydroxyl group (e.g., 2:1 or 3:1) to an alcohol (R6-(OH)). p R6 and p (as defined above) react to form R3 containing unreacted isocyanate groups, which is R6-[OC(=O)NH-R1]. p -A molecule with a specific structure. In this embodiment, another alcohol (R6-(OH)) can be used. p This involves introducing groups with additional functions (such as conductivity, flame retardancy, adhesion, etc.). In some embodiments, in the isocyanate molecule represented by Formula II, R1 includes a substituted or unsubstituted monovalent to trivalent C. 2-8 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 5-18 Contains an alkyl group with a five- or six-membered ring; R6 includes substituted or unsubstituted monovalent to trivalent C. 1-6Alkyl group. Optionally, R3 includes substituted or unsubstituted C3. 1-6 Alkylene and C 5-10 Contains a divalent alkyl group with a three- to six-membered ring. Specifically, the isocyanate represented by Formula II includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, and diphenylmethane diisocyanate.

[0084] In the above definition, "substituted or unsubstituted" groups can be substituted by the defined substituents. These substituents include halogens, -N(=O)₂OR, etc. c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metal ions and C 1-4 Alkyl group. Optionally, the halogen is F. Optionally, R c The substituents are independently selected from methyl and ethyl groups. Among these substituents, halogens (especially F) have a flame-retardant effect; nitrate groups or nitrate esters (-N(=O)2OR) c This can provide N atoms to form a stable lithium nitride-containing SEI film; sulfonic acid groups or sulfonates (-S(=O)2OR) c This can improve the conductivity of the positive electrode film, thereby reducing the DC resistance; phosphate groups or phosphate esters (-P(=O)2OR) c It also has flame-retardant properties; the amide group (-NHC(=O)OR) c It readily forms hydrogen bonds with the binder in the positive electrode film, which can improve the adhesion of the positive electrode film.

[0085] By introducing one or more of the aforementioned functional substituents, the additive can acquire the desired additional properties. Adding an additive molecule can reduce gas production while simultaneously obtaining additional performance. This reduces the amount of functional additive required, thus preventing excessive reduction in the amount of positive electrode active material, and minimizing the impact of additional additives on battery capacity, initial coulombic efficiency, and other properties.

[0086] In some embodiments, R2 in Formula I or R3 in Formula II has the aforementioned substituents.

[0087] In a further embodiment, R2 in Formula I has the aforementioned substituent, or R3 in Formula II is selected from R6-[OC(=O)NH-R1]. p - When R6 has the above-mentioned substituents.

[0088] In some embodiments, the molecular weight of the end-capped isocyanate is less than or equal to 1,000, optionally less than or equal to 800, and more preferably less than or equal to 600. Studies have found that while oligomeric polyurethanes can introduce more active groups and optional functional groups, their improvement on gas generation performance is not significant; in fact, when the molecular weight is greater than 2,000, they have no effect. Conversely, smaller molecular weights are beneficial for the uniform dispersion of additives, which allows for better capture of free radicals generated by the positive electrode active material, thus helping to reduce the gas generation level of the secondary battery.

[0089] In some embodiments, the capped isocyanate is obtained by reacting the isocyanate and the capping molecule in an isocyanate index R of 1.0-1.2, optionally 1.05-1.1. Exemplary R values ​​are 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.15, 1.18, etc. Within the above R value range, the hydroxyl groups of the capping molecule can react substantially completely, thus preventing the introduction of hydroxyl groups into the battery in an unfavorable amount. Furthermore, a slight excess of isocyanate groups can promote the capping reaction, bringing it closer to complete reaction, thereby ensuring that all reactants are converted into capped isocyanate molecules in stoichiometric proportions, increasing the amount of active ingredient added to the additive. In specific embodiments, when the R value is within the above range, the reaction rate of the capping reaction is 98% or higher, particularly 99% or higher (90% or higher in terms of isocyanate reaction rate, optionally 95% or higher), thereby ensuring that the capping molecule reacts substantially completely.

[0090] In an optional embodiment, the R value is greater than 1, optionally between 1.05 and 1.1, resulting in a certain amount of uncapped isocyanate groups. The introduction of a small amount of isocyanate groups (-N=C=O) into the battery allows them to react with residual hydrogen ions and water, thereby removing water and acid, reducing side reactions between water or acid and the electrolyte, and further improving the gas production performance of the secondary battery. A small amount of unreacted isocyanate molecules can also participate in the formation of the CEI or SEI membrane, increasing the organic content of the CEI or SEI membrane, thus improving the membrane's flexibility.

[0091] In some embodiments, after the capping reaction between the capping molecule and the isocyanate molecule is completed, the reaction system is directly used as an additive. In this embodiment, the additive contains capped isocyanates as defined above, and may also contain completely unreacted isocyanates, partially reacted isocyanates, and small amounts of unreacted and partially reacted capping molecules. In a further optional embodiment, the reaction system substantially does not contain unreacted and / or partially reacted capping molecules.

[0092] In some embodiments, the weight percentage of the additive, based on the total weight of the positive electrode film, is 0.2 wt% to 1 wt%, optionally 0.3 wt% to 0.8 wt%, and further optionally 0.4 wt% to 0.6 wt%. For example, based on the total weight of the positive electrode film, the weight percentage of the additive is 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, or 0.8 wt%, 0.9 wt%, etc., and values ​​within any range of two such values. Using additives within the above ranges can effectively react with oxygen free radicals generated by the positive electrode active material, thereby inhibiting gas production, while also minimizing its impact on the positive electrode energy density and initial coulombic efficiency.

[0093] In this application, the positive electrode active material is a suitable positive electrode active material for lithium-ion secondary batteries, but there are no particular limitations. In some embodiments, the positive electrode active material includes LiNi. 1-x-y Co x M y O2, wherein M includes at least one of Al, Y, Zr, La, Ti, Mg, Nb, Mn, W, and Sr, wherein 0.01 ≤ x ≤ 0.05 and 0.01 ≤ y ≤ 0.05. The positive electrode active material can be a single material or two or more materials. In a specific embodiment, M is Al or Mn. The positive electrode active material includes a ternary positive electrode active material. Optionally, (10-xy) ≥ 7. That is, the positive electrode active material includes a high-nickel ternary positive electrode active material. Exemplarily, the positive electrode active material is a 7-series or 8-series ternary positive electrode active material, such as ternary material 811, but is not limited thereto.

[0094] Ni in the aforementioned positive electrode active materials, especially when the Ni content is high, is more likely to cause crystal structure instability and generate oxygen free radicals. Therefore, the additives mentioned above can effectively capture the oxygen free radicals generated by such positive electrode active materials, reducing the gas generation problems they cause.

[0095] The content of the positive electrode active material in the positive electrode film layer is not particularly limited in this disclosure and can be determined as needed. Exemplarily, the mass percentage of the positive electrode active material in the positive electrode film layer is more than 95%, and optionally 95%-98%.

[0096] In some embodiments, the battery undergoes Li deintercalation and consumption during charging and discharging, resulting in different molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0097] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0098] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0099] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum 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 (aluminum, aluminum 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.).

[0102] A single secondary battery cell also includes a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0103] Negative electrode sheet

[0104] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0105] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0106] 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] 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.

[0108] In some embodiments, the negative electrode film layer may optionally include a binder. The 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).

[0109] In some embodiments, the negative electrode film 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.

[0110] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0111] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, 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.

[0112] electrolytes

[0113] The electrolyte 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.

[0114] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0115] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0116] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0117] 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.

[0118] Separating membrane

[0119] In some embodiments, the battery cell also 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.

[0120] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0121] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0122] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0123] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0124] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 A quasi-square battery cell 5 is shown as an example.

[0125] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0126] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0127] Figure 4 Battery module 4 is shown as an example. (Refer to...) Figure 4 In battery module 4, multiple battery cells 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 battery cells 5 can be fixed in place using fasteners.

[0128] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0129] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0130] Figure 5 and Figure 6 Battery pack 1 is shown as an example. (Refer to...) Figure 5 and Figure 6 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, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0131] Methods for preparing secondary batteries

[0132] This application also provides a method for preparing the above-mentioned secondary battery. The preparation method includes...

[0133] The reaction product of isocyanate and capping molecule is added to the positive electrode slurry as the additive, wherein the isocyanate and the capping molecule are the same as defined above and will not be repeated here.

[0134] In some embodiments, the isocyanate and the capping molecule react at an isocyanate index R of 1.0 to 1.2, optionally 10.5 to 1.10. The capping reaction of the isocyanate can be carried out according to conventional methods. Specifically, the isocyanate and the capping molecule are mixed uniformly at 70°C to 90°C and reacted for 5 to 10 hours.

[0135] When the isocyanate index R is greater than 1, a slight excess of isocyanate groups further favors the reaction. Advantageously, the reaction rate is greater than 98%, even 99%. This can be calculated by measuring the amount of unreacted isocyanate groups in the reaction system. When the isocyanate groups are in slight excess in the reactants (e.g., R is 1.02, 1.04, 1.05, 1.06, 1.08, 1.10, 1.12, 1.14, etc.), the reaction rate of the isocyanate groups can reach over 90%, even over 95%. In this way, the hydroxyl groups in the alcohol, which is the end-capping molecule, react almost completely.

[0136] Using the reaction system directly as an additive after the reaction is complete means that it is not necessary to separate and purify the capped isocyanate molecules; the additive also includes unreacted reactants. This simplifies the preparation process. Moreover, as mentioned earlier, using the entire reaction system as the additive not only allows the capped isocyanate to capture oxygen free radicals, but also enables the unreacted isocyanate groups to react with trace amounts of water and / or acid in the battery cell, thereby further improving the performance of high-temperature gas generation.

[0137] In the above reaction, infrared spectroscopy was used to qualitatively characterize the functional groups contained in the synthesized product. The infrared spectrum at 2240 cm⁻¹... -1 The absorption peak intensity of the -NOC group can reflect the reaction process over time, and the reaction is complete when the peak position basically disappears.

[0138] In addition, the toluene-di-n-butylamine NCO titration experiment can be used to quantitatively characterize the experimental process. According to the method for determining the isocyanate group content in polyurethane prepolymers (HG-T2409-1992), the isocyanate content can be quantitatively and accurately determined by titrating the -NCO group content in the reaction system. Since -NCO can react with di-n-butylamine, the reaction conversion rate can be calculated, and the reaction endpoint can be determined.

[0139] The method further includes the step of preparing a positive electrode sheet. First, a positive electrode slurry is prepared: The additives containing end-capped isocyanates prepared above (0.2 wt% to 1 wt%, optionally 0.3 wt% to 0.8 wt%, more preferably 0.4 wt% to 0.6 wt%), the aforementioned positive electrode active material (95% to 98%), a conductive agent (1 wt% to 2 wt%), and an optional binder (1 wt% to 2 wt%) are mixed at appropriate weight percentages, and an organic solvent (e.g., N-methylpyrrolidone) is added to adjust the viscosity to obtain the positive electrode slurry. Next, a positive electrode sheet is prepared: The positive electrode slurry is coated onto at least one surface of the positive electrode current collector, cold-pressed, and then cut to a suitable size to obtain the positive electrode sheet.

[0140] The method further includes the steps described above for preparing the negative electrode sheet. Finally, the positive and negative electrode sheets are alternately stacked, with a separator placed between adjacent electrodes, and an electrode assembly is formed using a winding or stacking process. The electrode assembly is then encapsulated in an outer package, and finally, an electrolyte is injected to immerse the electrode assembly in the electrolyte, thereby completing the assembly of the battery cell. As mentioned above, the battery cell can be further assembled into a battery module, and further assembled into a battery pack. This yields the secondary battery.

[0141] Electrical appliances

[0142] This application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, 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.

[0143] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0144] Figure 6 This is a schematic diagram of an electrical device using a lithium secondary battery as a power source according to one embodiment of this application. The electrical device 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 the secondary battery for this electrical device, a battery pack or battery module can be used.

[0145] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0146] Example

[0147] 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.

[0148] Preparation Example 1

[0149]

[0150] 88.2 g of compound 4 (hexamethylene diisocyanate, HDI) and 115 g of compound 3 (N-hydroxyethyl acrylamide, HEAA) were mixed at a molar ratio of 1.05:1, resulting in an isocyanate index R of 1.05 and an isocyanate conversion rate of 96.36%. The mixture was reacted at 80°C for 7 hours to obtain product PU-1, which was used directly in the following examples to prepare the cathode without further processing. Products obtained in other preparation examples were also used directly in the preparation of cathodes without further processing.

[0151] Samples were taken at 3 hours, 5 hours, and 5.5 hours of reaction and analyzed using an infrared spectrometer to obtain infrared spectra as follows: Figure 7As shown in the figure. It can be seen that the infrared spectrum of the product corresponds to 2200 cm⁻¹. -1 The NCO peak at the reaction site gradually decreases in intensity over time, indicating the successful introduction of a double bond. This reaction is essentially a reaction between isocyanate and alcohol to convert to urethane; the reaction rate must be ≥99%, meaning the alcohol must react almost completely. The reaction rate can be calculated by measuring the isocyanate conversion rate using the NCO group titration method (Standard No.: HGT 2409-1992 Determination of Isocyanate Group Content in Polyurethane Prepolymers).

[0152] It should be understood that the reaction product PU-1 mentioned here is the final reaction system mainly containing the compound PU-1 shown above, and also includes a small amount of unreacted reactants, such as excess compound 4. That is, the reaction product PU-1 contains compound PU-1, unreacted compound 4, and a very small amount of compound 3. In the following preparation examples, depending on the different isocyanate index and isocyanate conversion rate, the resulting reaction products contain a certain amount of unreacted reactants in addition to the corresponding compounds generated in the reaction, which will not be elaborated further.

[0153] Preparation Example 2

[0154]

[0155] 233.1 g of compound 1 (isophorone diisocyanate, IPDI) and 83 g of compound 2 (sodium 1,3-propanediol-2-sulfonate) (molar ratio of about 2.1:1) were reacted at 80 °C for 5 hours.

[0156] Subsequently, 115 g of compound 3 (HEAA, 1 mol) was added, and the reaction was carried out at 80 °C for 5 hours to obtain the reaction product PU-2. The isocyanate index R was 1.05. The isocyanate conversion rate was 97.88%.

[0157] Preparation Example 3

[0158]

[0159] 116.5g of compound 1 (IPDI) and 115g of compound 3 (HEAA) (molar ratio of 1.05:1, isocyanate index R of 1.05) were reacted at 80°C for 7 hours to obtain the reaction product PU-3.

[0160] According to Table 1 below, the amounts of compound 1 and compound 3 were further varied to obtain a series of products.

[0161] Table 1:

[0162]

[0163] Preparation Example 4

[0164] 146g of compound 6 (hexamethylene diisocyanate trimer, PHDI) and 115g of compound 3 (HEAA) (molar ratio of 1.05:1, isocyanate index R of 1.05) were reacted at 80°C for 7 hours to obtain the reaction product PU-4.

[0165]

[0166] 116.5g of compound 1 (hexamethylene diisocyanate trimer, PHDI) and 71g of compound 5 (3-hydroxypropionitrile) (molar ratio of 1.05:1, isocyanate index R of 1.05) were reacted at 80°C for 7 hours to obtain the reaction product PU-5.

[0167] Example 1

[0168] Preparation of the positive electrode sheet:

[0169] A high-nickel ternary cathode active material 811, conductive carbon black, additives (reaction product PU-1 prepared in Preparation Example 1), and PVDF were mixed in a mass ratio of 96.8:1.7:0.5:1 and then added to the solvent N-methylpyrrolidone to obtain a cathode slurry with a solid content of 79%. This slurry was then uniformly coated onto both surfaces of the cathode current collector aluminum foil, and after cold pressing and cutting, a cathode electrode sheet was obtained.

[0170] Preparation of negative electrode sheet:

[0171] Artificial graphite, conductive carbon black, carboxymethyl cellulose (CMC) binder, and additive (polystyrene rubber) are mixed in a mass ratio of 96.5:0.8:1.2:1.5 and then added to deionized water to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on both sides of a copper foil, and after cold pressing and cutting, a negative electrode sheet is obtained.

[0172] Electrolyte preparation:

[0173] Lithium salt LiPF6 (lithium hexafluorophosphate) was added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20 and mixed thoroughly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0174] Separating membrane

[0175] A polyethylene (PE) membrane with a thickness of 13 μm was used as the separator.

[0176] Assembly of secondary batteries

[0177] The electrodes are arranged in the following order: separator - negative electrode - separator - positive electrode. One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode, negative electrode, and two separators to obtain the electrode assembly. The electrode assembly is then encapsulated in an outer package and injected with electrolyte to obtain a wound battery.

[0178] Performance testing of secondary batteries

[0179] 1. Gas production test

[0180] 1) Store at 70°C and 100% SOC, without fixtures;

[0181] 2) Before storage, measure the capacity and adjust the SOC. Test the open circuit voltage (OCV), K value, and initial volume. Then, take the cells out of the furnace every 2 days, let them stand for 1 hour to cool to room temperature, and then test the OCV and K value. Use the water displacement method to test the cell volume.

[0182] 3) Adjust the SOC before each furnace storage, and add power if necessary to maintain the SOC at 100%;

[0183] 4) After storage, test the remaining capacity and reversible capacity of the battery cell at room temperature, and end the test in the discharged state;

[0184] 5) Stop the experiment when the volume of the control group (without additives) battery expands to 40% of its original size.

[0185] Record the percentage of volume growth during the experiment, such as Figure 8 As shown.

[0186] 2. Adhesion of the positive electrode sheet

[0187] Cut 2*15cm strips of the positive electrode sheet prepared by cold pressing in Example 1 above, fix them to a steel plate with double-sided adhesive, and then fix them on the platform of an Instron 3365 tensile testing machine. Perform a 90-degree peel test at a speed of 50mm / min, and record the force when the electrode sheet and the current collector are completely separated, which is the electrode sheet adhesion force.

[0188] Examples 2-5

[0189] Except for the use of the reaction products PU-2 to PU-5 additives obtained in Preparation Examples 2 to 5 in the preparation of the positive electrode sheet, the battery was prepared and tested in the same manner as in Example 1 (wherein the volume change rate during the gas production test was not recorded in Example 5), and the results are shown in Table 2 below. Figure 8 As shown.

[0190] Comparative Example 1

[0191] In the preparation of the positive electrode sheet, only the high-nickel ternary active material 811, conductive carbon black, and PVDF were mixed at a mass ratio of 97.3:1.7:1.0, without adding any additional additives. The battery was prepared and tested in the same manner as in Example 1, and the results are shown in Table 2 below. Figure 8 (i.e., the baseline group) is shown.

[0192] Table 2:

[0193] serial number additive Gas production (%) during storage at 70℃ Pole piece adhesion force (N / m 2 )]]> Example 1 PU-1 34.62％ 14.85 Example 2 PU-2 39.23％ 17.95 Example 3 PU-3 28.85％ 12.21 Example 4 PU-4 37.34％ 18.65 Example 5 PU-5 33.45％ 15.28 Comparative Example 1 / 44.65％ 9.51

[0194] The additives in all examples in Table 2 had an isocyanate index of 1.05 during preparation, and the addition amount in the positive electrode film was 0.5 wt%. As can be seen from Table 2, compared with Comparative Example 1 (without any additive), adding the additives according to the present invention to the positive electrode significantly reduced gas generation during high-temperature storage of the battery, while also improving the adhesion of the positive electrode sheet. Among them, the compound PU-2 in Preparation Example 2 has a larger molecule, and at the same mass percentage, introduces relatively fewer reactive unsaturated bonds, thus its effect on reducing gas generation is relatively weaker. The additives in Examples 3 and 5, which react isophorone diisocyanate with monools containing unsaturated bonds, showed relatively better results. In particular, the additive obtained in Example 3 by reacting isophorone diisocyanate with N-hydroxyethylacrylamide has good hydrophilicity and can be more uniformly dispersed in the positive electrode film, thereby better capturing oxygen free radicals generated by the positive electrode active material and reducing gas generation.

[0195] Figure 8 This demonstrates the volume increase of the batteries prepared in Comparative Example 1 and Examples 1-4 during high-temperature storage. Specifically, after approximately 20 days of storage, the volume growth rate of the batteries in Examples 1-4, which had additives PU1-PU4 added, began to be significantly lower than that of the batteries prepared in Comparative Example 1 (the baseline group).

[0196] Examples 6-8

[0197] The battery was prepared and tested using the same method as in Example 1, except that PU-3 was added to the positive electrode slurry in different proportions during the preparation of the positive electrode sheet. Based on Example 3, the mass ratio of high-nickel ternary active material 811: conductive carbon black: reaction product PU-3: PVDF was 96.8:1.7:0.5:1.0. In other examples, an increase in the amount of PU-3 resulted in a corresponding decrease in the amount of high-nickel ternary active material 811, and vice versa. The test results are shown in Table 3.

[0198] Table 3:

[0199] serial number PU-3 addition amount Gas production (%) during storage at 70℃ Example 6 0.2wt% 42.43％ Example 3 0.5wt% 28.85％ Example 7 0.6wt% 32.70％ Example 8 0.8wt% 37.22％

[0200] As shown in Table 3, the effect of reducing gas production is significantly weakened when the amount added decreases. However, when the amount added increases, the viscosity of the cathode slurry is increased by the end-capped isocyanate, leading to a decrease in dispersion uniformity, which also weakens the effect of reducing gas production.

[0201] Examples 9-10

[0202] The battery was prepared and tested using the same method as in Example 1, except that in the preparation of the positive electrode, a series of PU-3 reaction products prepared in Example 3 with an isocyanate index R of 1.0 to 1.10 were used as additives. The mixture was prepared according to a mass ratio of high-nickel ternary active material 811: conductive carbon black: reaction product PU-3: PVDF of 96.8:1.7:0.5:1.0. The test results are shown in Table 4.

[0203] Table 4:

[0204] serial number additive Gas generation during storage at 70℃ Example 9 PU-3-00 39.12％ Example 3 PU-3-05 28.85％ Example 10 PU-3-10 34.58％

[0205] As shown in Table 4, the best gas generation suppression effect was observed when the R value was 1.05 (Example 3). In Example 9, with an R value of 1.0, the reaction completion rate decreased due to the equimolarity of reactants, resulting in a relative reduction in end-capping products and ultimately a lower amount of end-capped isocyanate added to the positive electrode film. Furthermore, the amount of unreacted alcohol in the additive of Example 9 also increased. All of these factors affected the gas generation reduction effect. When the R value was 1.10 (Example 10), the isocyanate excess was slightly greater, and the same reduction in end-capping products resulted in a relative decrease in the amount of end-capped isocyanate added to the positive electrode film, further reducing the effect to some extent. This indicates that the end-capped isocyanate added to the positive electrode film, especially the unsaturated bonds, plays a crucial role in reducing gas generation in secondary battery storage. Increasing the amount of unsaturated bonds in the positive electrode film at the same addition level is more beneficial for reducing gas generation.

[0206] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer comprises a positive electrode active material and an additive, the additive comprising a capped isocyanate, wherein the capping molecule for capping comprises one or more compounds having the structure of Formula I: R2-[OH] n (I) Isocyanates include one or more compounds having the structure of Formula II: R3-[NCO] m (II) In Equations I and II above, when n = 1, m is any integer from 1 to 3, or when m = 1, n is any integer from 1 to 3; R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-10 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-10 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-10 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-10 Alkyl and substituted or unsubstituted C 2-10 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group; R3 includes R1 and R6-[OC(=O)NH-R1] which have monovalent to trivalent valences. p - one of them, in which R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 3-20 Contains alkyl groups with three to six-membered rings, R6 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl group, p=m The substitution is performed by one or more substances selected from halogens, -N(=O)2OR c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metal ions and C 1-4 alkyl.

2. The secondary battery according to claim 1, characterized in that, R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-6 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-6 Alkyne, substituted or unsubstituted monovalent to trivalent C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups.

3. The secondary battery according to claim 1 or 2, characterized in that, R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 2-8 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 5-18 Contains an alkyl group with a five- or six-membered ring; R6 includes substituted or unsubstituted monovalent to trivalent C. 1-6 alkyl.

4. The secondary battery according to any one of claims 1-3, characterized in that, The substitution is R2 or R3, optionally R2 or R6, and is selected from one or more of -S(=O)2OR. c F-, -P(=O)2OR c -N(=O)2OR c and -NHC(=O)OR c The groups in are substituted, wherein each R c It is independently selected from methyl and ethyl.

5. The secondary battery according to any one of claims 1-4, characterized in that, n = 1, m = 2 or 3; Optionally, R2 includes substituted or unsubstituted C. 3-6 alkenyl, substituted or unsubstituted C 3-6 Alkyne group, substituted or unsubstituted C 2-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups; R3 includes substituted or unsubstituted C. 1-6 Alkylene and C 5-10 Divalent alkyl groups containing three to six-membered rings.

6. The secondary battery according to claim 5, characterized in that, The isocyanate includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, and hexamethylene diisocyanate trimer; The capping molecule includes one or more of N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxyethylmethylacrylamide, 3-hydroxypropylcyanamide, and 3-hydroxybutylcyanamide.

7. The secondary battery according to any one of claims 1-5, characterized in that, The end-capped isocyanate has a molecular weight of less than or equal to 1,000, optionally less than or equal to 800, and more preferably less than or equal to 600.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The capped isocyanate is obtained by reacting the isocyanate and the capping molecule in a ratio of isocyanate index R of 1.0-1.2, optionally 1.05-1.1; optionally, the reaction system after the reaction is completed is directly used as the additive.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, Based on the total weight of the positive electrode film, the content of the additive is from 0.2 wt% to 1 wt%, optionally from 0.3 wt% to 0.8 wt%, and more preferably from 0.4 wt% to 0.6 wt%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The positive electrode active material includes LiNi 10-x-y Co x M y O2, where M includes at least one of Al, Y, Zr, La, Ti, Mg, Nb, Mn, W, Sr, where 1 < x < 5 and 1 < y < 5; optionally, M is Al or Mn.

11. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1 to 10.

12. A method for preparing a secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material and an additive, the additive including a capped isocyanate. The preparation method includes: The reaction product of isocyanate and end-capping molecules is added as the additive to the positive electrode slurry, wherein... The capped molecule includes one or more compounds having the structure of Formula I: R2-[OH] n (I) The isocyanate includes one or more compounds having the structure of Formula II: R3-[NCO] m (II) In Equations I and II above, when n = 1, m is any integer from 1 to 3, or when m = 1, n is any integer from 1 to 3; R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-10 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-10 Alkyne, substituted or unsubstituted monovalent to trivalent C 3-10 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-10 Alkyl and substituted or unsubstituted C 2-10 One of the alkenyl groups, and at least one of R4 and R5 is an alkenyl group; R3 includes R1 and R6-[OC(=O)NH-R1] which have monovalent to trivalent valences. p - one of them, in which R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 3-20 Contains alkyl groups with three to six-membered rings, R6 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-10 Alkyl group, p=m The substitution is performed by one or more elements selected from halogens, -N(=O)2OR. c -S(=O)2OR c -P(=O)2OR c and -NHC(=O)OR c Substituents in, wherein each R c Independently selected from alkali metal ions and C 1-4 alkyl.

13. The preparation method according to claim 12, characterized in that, R2 includes monovalent to trivalent C, whether substituted or unsubstituted. 3-6 Alkenyl, substituted or unsubstituted monovalent to trivalent C 3-6 Alkyne, substituted or unsubstituted monovalent to trivalent C 3-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups.

14. The preparation method according to claim 12 or 13, characterized in that, R1 includes monovalent to trivalent C, whether substituted or unsubstituted. 2-8 Alkyl groups and substituted or unsubstituted monovalent to trivalent Cs 5-18 Alkyl groups containing five- or six-membered rings; R6 includes monovalent to trivalent C, whether substituted or unsubstituted. 1-6 alkyl.

15. The preparation method according to any one of claims 12-14, characterized in that, The substitution is R2 or R3, optionally R2 or R6, and is selected from one or more of -S(=O)2OR. c F-, -P(=O)2OR c -N(=O)2OR c and -NHC(=O)OR c The groups in are substituted, wherein each R c It is independently selected from methyl and ethyl.

16. The preparation method according to any one of claims 12-15, characterized in that, n = 1, m = 2 or 3; Optionally, R2 includes substituted or unsubstituted C. 3-6 alkenyl, substituted or unsubstituted C 3-6 Alkyne group, substituted or unsubstituted C 3-6 One of cyano and -R4-NHC(=O)-R5, wherein R4 and R5 each independently include a substituted or unsubstituted C. 1-4 Alkyl and substituted or unsubstituted C 2-4 One of the alkenyl groups; R3 includes substituted or unsubstituted C. 1-6 Alkylene and C 5-10 Divalent alkyl groups containing three to six-membered rings.

17. The preparation method according to claim 16, characterized in that, The isocyanate includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, and hexamethylene diisocyanate trimer; The capping molecule includes one or more of N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxyethylmethylacrylamide, 3-hydroxypropylcyanamide, and 3-hydroxybutylcyanamide.

18. The preparation method according to any one of claims 12-16, characterized in that, The end-capped isocyanate has a molecular weight of less than or equal to 1,000, optionally less than or equal to 800, and more preferably less than or equal to 600.

19. The preparation method according to any one of claims 12-18, characterized in that, The isocyanate and the capping molecule react in a ratio of 1.0 to 1.2, optionally 10.5 to 1.10, with an isocyanate index R of 1.0 to 1.

2.

20. The preparation method according to any one of claims 12-19, characterized in that, The reaction product is obtained by reacting the isocyanate and the end-capping molecule at 70°C to 90°C; optionally, adding the reaction product of the isocyanate and the end-capping molecule as the additive to the positive electrode slurry includes directly adding the reaction system after the reaction is completed to the positive electrode slurry.

21. The preparation method according to any one of claims 12-20, characterized in that, Based on the total weight of the positive electrode film, the amount of the additive added is 0.2wt% to 1wt%, optionally 0.3wt% to 0.8wt%, and more preferably 0.4wt% to 0.6wt%.

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