Positive pole piece, secondary battery and electric device

Abstract

The invention provides a positive pole piece, a secondary battery and an electric device. 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 film layer comprises a positive active material and an additive, and the additive comprises at least one compound represented by a formula (I); in the formula (I), R1 comprises an electron withdrawing group, n is an integer greater than or equal to 1, and when n is an integer greater than 1, R1 is the same or different; r2 comprises a group for loading R1 and-B (OH) 2. According to the positive pole piece disclosed by the invention, the capacity, the rate capability, the reliability, the storage performance and the cycle performance of the secondary battery can be improved. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their performance.

[0003] As an important component of secondary batteries, the positive electrode has a significant impact on their performance. However, in current secondary batteries, the performance of the positive electrode cannot meet the requirements of secondary batteries. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode sheet, a secondary battery and an electrical device, wherein the positive electrode sheet can improve the capacity, rate performance, reliability, storage performance and cycle performance of the secondary battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and an additive, wherein the additive comprises at least one compound represented by formula (I),

[0006]

[0007] In the formula (I), R1 includes an electron-withdrawing group, n is an integer greater than or equal to 1, and when n is an integer greater than 1, R1 is the same or different; R2 includes a group for supporting R1 and -B(OH)2.

[0008] By including an additive having an electron-withdrawing group and a boric acid group (-B(OH)2) in the positive electrode film layer of the positive electrode sheet, the boric acid group in the additive undergoes a neutralization reaction with the lithium-containing compound (hereinafter sometimes referred to as "miscellaneous lithium") remaining on the surface of the positive electrode active material, and the electron-withdrawing group in the additive undergoes a coordination reaction with the transition metal ions dissolved from the surface of the positive electrode active material, thereby improving the capacity, rate performance, reliability, storage performance and cycle performance of the secondary battery.

[0009] In some embodiments, n = 1 to 5. By making the number of R1 groups within the above range, it is beneficial to disperse the additive in the positive electrode slurry, and the stability of the positive electrode slurry can be improved.

[0010] In some embodiments, R1 comprises a nitro group, a cyano group, a trihalomethyl group, a fluorine atom, a chlorine atom, a sulfonic acid group, a vinyl group, or a propenyl group; and / or R2 comprises an aromatic group. In some embodiments, R2 comprises a phenyl group, a biphenyl group, or a fluorenyl group.

[0011] In some embodiments, the compound represented by formula (I) includes at least one of 3-nitrophenylboronic acid, 2-cyanophenylboronic acid, 3-cyanophenylboronic acid, 4-cyanophenylboronic acid, 3-trifluoromethylphenylboronic acid, 3-sulfonylphenylboronic acid, 4-vinylphenylboronic acid, 2,3,4,5-tetrafluorophenylboronic acid and 2,3,4,6-tetrafluorophenylboronic acid.

[0012] The electron-withdrawing ability of nitro, cyano, trihalomethyl, fluorine, chlorine, sulfonic acid, vinyl or propenyl groups is relatively strong. By making the additive include the above-mentioned strong electron-withdrawing groups, the coordination effect with the transition metal ions dissolved from the surface of the positive electrode active material is stronger. By making R2 an aromatic compound, the electron-withdrawing ability of R1 can be further enhanced through the conjugation effect, thereby further improving the cycle performance of the secondary battery.

[0013] In some embodiments, the additive further comprises a lithium salt of a compound represented by formula (I). The boric acid group in the compound represented by formula (I) reacts with the lithium-containing compound remaining on the surface of the positive electrode active material to form a lithium borate compound and exists in the positive electrode sheet, thereby reducing the adverse effects caused by miscellaneous lithium. In some embodiments, the positive electrode active material comprises lithium nickel cobalt aluminum oxide and / or lithium nickel cobalt manganese oxide. In some embodiments, the chemical formula of the lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M 1 (1-b-c-d) O n , 0.5≤a≤1.2, 0.65≤b≤1, 0≤c≤0.35, 0≤d≤0.35, 1.9≤n≤2.2, M 1 A combination of one or more selected from Zr, Zn, Ti, Sr, Sb, Y, W, Al and B; the chemical formula of the lithium nickel cobalt aluminum oxide is Li e Ni f Co g Al h M 2 (1-f-g-h) O n , 0.5≤e≤1.2, 0.5≤f≤1, 0≤g≤0.5, 0≤h≤0.5, 1.9≤n≤2.2, M 2 A combination of one or more selected from the group consisting of Zr, Mg, Ba, Ti, Sr, Sb, Y, W and B.

[0014] The problem of the generation of impure lithium and the dissolution of transition metals on the surface of ternary positive electrode materials is relatively serious. By adding the above-mentioned additives to the ternary positive electrode materials, the boric acid groups in the additives react with the lithium-containing compounds remaining on the surface of the above-mentioned ternary materials to neutralize each other, and the electron-withdrawing groups in the additives coordinate with the nickel, cobalt and other transition metal ions dissolved from the surface of the above-mentioned ternary materials, thereby more effectively solving the above-mentioned problems of the ternary materials and improving the performance of the ternary battery.

[0015] In some embodiments, the positive electrode active material comprises a chemical formula of Li(Ni x Co y M z )O2 material, wherein M is Al or Mn, 0.7≤x≤1, 0≤y+z≤0.3, x+y+z=1.

[0016] The higher the nickel content in the ternary high-nickel material (x≥0.7), the higher the energy density. However, the problem of surface impurity lithium and transition metal dissolution in the ternary high-nickel material is particularly serious. By adding the above-mentioned additives to the ternary high-nickel material, the adverse effects caused by surface impurity lithium and transition metal dissolution are reduced. As a result, while achieving high energy density, the battery capacity, rate performance, reliability, storage performance and cycle performance can be improved.

[0017] In some embodiments, the mass ratio of the additive to the positive electrode active material is 0.001:1 to 0.03:1, optionally, 0.003:1 to 0.007:1.

[0018] By making the content of the additive within the above range, the additive can better play its role, which helps to improve the above performance of the secondary battery. In some embodiments, the additive covers at least a portion of the surface of the positive electrode active material.

[0019] By making the additive cover at least a portion of the surface of the positive electrode active material, the contact area between the additive and the positive electrode active material is larger, the effect is more complete, and it is more helpful to improve the performance of the secondary battery.

[0020] The second aspect of the present application provides a secondary battery comprising the positive electrode sheet of the first aspect of the present application. The secondary battery has excellent capacity, rate performance, reliability, storage performance and cycle performance.

[0021] A third aspect of the present application provides an electrical device comprising the secondary battery according to the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a battery cell according to one embodiment of the present application.

[0023] Figure 2 yes Figure 1 FIG. 1 is an exploded view of a battery cell according to an embodiment of the present application.

[0024] Figure 3 Schematic diagram of a battery module according to one embodiment of the present application.

[0025] Figure 4 Schematic diagram of a battery pack according to one embodiment of the present application.

[0026] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0027] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0028] Description of reference numerals:

[0029] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. DETAILED DESCRIPTION

[0030] Below, the embodiments of the positive electrode sheet, its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, the terms used in this application have the common meanings generally understood by those skilled in the art.

[0035] Unless otherwise specified, the values of the parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in this application.

[0036] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0037] Lithium-ion batteries are currently attracting significant attention for their long lifespan, high energy density, and low maintenance costs. However, their performance currently fails to fully meet various demands. Cathode materials are crucial for improving battery performance. Lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary, nickel-cobalt-aluminum ternary, and lithium iron phosphate are widely used. However, during the production process, these materials inevitably retain residual lithium compounds ("miscellaneous lithium") on their surfaces. These miscellaneous lithium compounds generate oxidizing gases during battery charge and discharge, leading to battery flatulence and reduced reliability. Furthermore, the presence of miscellaneous lithium also reduces battery storage performance. Furthermore, the dissolution of transition metals from the cathode material is a significant factor affecting battery life. Metals such as Ni, Co, and Mn, after forming ions, travel through the electrolyte and separator to the anode, catalyzing the decomposition of the SEI film. This SEI film continuously forms at the anode, consuming active lithium and resulting in reduced cycling performance. These issues are particularly pronounced in ternary materials, particularly high-nickel ternary materials.

[0038] In view of the above situation, the first aspect of the present application provides a positive electrode plate, which can improve the capacity, rate performance, reliability, storage performance and cycle performance of a secondary battery. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material and an additive, the additive including at least one compound represented by formula (I),

[0039]

[0040] In the formula (I), R1 includes an electron-withdrawing group, n is an integer greater than or equal to 1, and when n is an integer greater than 1, R1 may be the same or different; R2 includes a group for supporting R1 and -B(OH)2.

[0041] The boric acid group (-B(OH)2) in the additive represented by the above formula (I) is an acidic group. Through the basic principle of acid-base neutralization, the boric acid group reacts with the lithium-containing compound (also known as "stray lithium") remaining on the surface of the positive electrode active material to form a chemical bond, neutralizing the stray lithium, thereby effectively avoiding the degradation of battery reliability and storage performance caused by the stray lithium. For example, when the residual lithium-containing compound is Li2CO3, the compound represented by formula (I) reacts with Li2CO3 as shown in the following reaction formula (1); when the residual lithium-containing compound is LiOH, the compound represented by formula (I) reacts with LiOH as shown in the following reaction formula (2).

[0042] [R1] n -R2-B-(OH)2+Li2CO3→[R1] n -R2-B-(OLi)2+CO2+H2O (1)

[0043] [R1]n -R2-B-(OH)2+2LiOH→[R1] n -R2-B-(OLi)2+2H2O (2)

[0044] Furthermore, the above product [R1] n The Li in -R2-B-(OLi)2 can be converted into active lithium during the battery cycle, achieving the effect of "replenishing lithium" for the battery, thereby increasing the battery capacity.

[0045] In addition, the reaction products generated in the reaction of removing impurity lithium contain BO bonds, among which the B element helps to form the CEI film (catholyte interface film) and inhibits the interface side reaction. Moreover, the CEI film containing the B element can increase the Li + The electrical conductivity can effectively improve the rate performance of the positive electrode.

[0046] In addition, in the additive represented by the above formula (I), R1 is an electron-withdrawing group. These electron-withdrawing groups can effectively coordinate with transition metal ions such as Co, Mn, and Ni on the surface of the positive electrode active material, stabilizing the transition metal ions on the surface of the positive electrode active material to reduce the dissolution of the transition metal ions. Moreover, the above electron-withdrawing groups can also capture the Ni ions, Co ions, and Mn ions that have been detached. Thus, by containing electron-withdrawing groups in the additive, the battery capacity decay caused by the dissolution of the transition metal is avoided, thereby improving the cycle life of the secondary battery.

[0047] Furthermore, the inventors discovered that compounds with only boronic acid groups but no electron-withdrawing groups can react with heterolithium to form chemical bonds and thus be fixed on the surface of the positive electrode active material, but cannot coordinate with transition metal ions; while compounds with only electron-withdrawing groups but no boronic acid groups can coordinate with transition metal ions, compounds with electron-withdrawing groups alone are generally soluble and easily migrate in the electrolyte, making it difficult to stably fix on the surface of the positive electrode active material. In contrast, the present application achieves a synergistic effect by making the additive contain both boronic acid groups and electron-withdrawing groups. That is, the additive containing the electron-withdrawing group can be stabilized on the surface of the positive electrode active material, while the additive containing the boronic acid group is easily soluble in the electrolyte. The combination of the two enables the additive molecules to be firmly adsorbed on the positive electrode surface, thereby reducing the impact on the negative electrode and the electrolyte, and effectively improving the capacity, reliability, rate performance, storage performance and cycle life of the secondary battery.

[0048] In the additive represented by the above formula (I), R2 is a group for supporting R1 and -B(OH)2. This group acts as a carrier and can connect the boronic acid group and the electron-withdrawing group through a covalent bond.

[0049] In some embodiments, n = 1 to 5. The compound represented by formula (I) may include multiple electron-withdrawing groups (R1). By making the number of R1 groups within the above range, it is beneficial to disperse the additive in the positive electrode slurry and improve the stability of the positive electrode slurry.

[0050] In some embodiments, R1 is a nitro group, a cyano group, a trihalomethyl group, a fluorine atom, a chlorine atom, a sulfonic acid group, a vinyl group, or a propenyl group; and / or R2 is an aromatic group.

[0051] The electron-withdrawing ability of nitro, cyano, trihalomethyl, fluorine, chlorine, sulfonic, vinyl or propenyl groups is relatively strong. By making the additive include the above-mentioned strong electron-withdrawing groups, the coordination effect with the transition metal ions contained in the positive electrode active material is stronger, which can better stabilize the transition metal ions contained in the positive electrode active material to reduce the dissolution of the transition metal ions; at the same time, the stronger electron-withdrawing groups can also better capture the transition metal ions that have been detached, thereby more advantageously reducing the transition metal ions from reaching the negative electrode through the electrolyte and the isolation membrane, effectively reducing the risk of SEI film decomposition and consumption of active lithium, and more conducive to improving the cyclability of the secondary battery.

[0052] In some embodiments, R2 is an aromatic group, such as phenyl, biphenyl, fluorenyl, etc. When R2 is an aromatic group, the electron-withdrawing ability of R1 can be increased through conjugation effect, thereby improving the effect of reducing metal dissolution.

[0053] In some embodiments, the compound represented by the above formula (I) may be, for example, 3-nitrophenylboronic acid, 2-cyanophenylboronic acid, 3-cyanophenylboronic acid, 4-cyanophenylboronic acid, 3-trifluoromethylphenylboronic acid, 3-sulfonicphenylboronic acid, 4-vinylphenylboronic acid, 2,3,4,5-tetrafluorophenylboric acid, 2,3,4,6-tetrafluorophenylboric acid, 4-fluorophenylboric acid, 2-cyano-4-fluoro-phenylboric acid, (7-bromo-9,9-dimethyl-9H-fluoren-2-yl)boric acid, (3',4'-dichloro[1,1'-biphenyl]-4-yl)boric acid, etc. From the perspective of stronger electron-withdrawing ability, the compound represented by the above formula (I) is preferably 3-nitrophenylboric acid, 2-cyanophenylboric acid, 3-cyanophenylboric acid, 4-cyanophenylboric acid, 3-trifluoromethylphenylboric acid, 3-sulfonylphenylboric acid, 4-vinylphenylboric acid, 2,3,4,5-tetrafluorophenylboric acid and 2,3,4,6-tetrafluorophenylboric acid.

[0054] In some embodiments, the additive further comprises a lithium salt of a compound represented by formula (I). The lithium salt is formed by a neutralization reaction between the boric acid group in the compound represented by formula (I) and the lithium salt on the surface of the positive electrode active material, for example, according to the above reaction formulas (1) and (2), and its chemical formula is [R1] n-R2-B-(OLi)2. The formation of the lithium salt indicates that the surface impurity lithium is reduced, thereby reducing the adverse effects caused by the impurity lithium.

[0055] In some embodiments, the positive electrode active material is lithium nickel cobalt aluminum oxide and / or lithium nickel cobalt manganese oxide. The chemical formula of the lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M 1 (1-b-c-d) O n , 0.5≤a≤1.2, 0.65≤b≤1, 0≤c≤0.35, 0≤d≤0.35, 1.9≤n≤2.2, M 1 A combination of one or more selected from Zr, Zn, Ti, Sr, Sb, Y, W, Al, B, etc.; the chemical formula of the lithium nickel cobalt aluminum oxide is Li e Ni f Co g Al h M 2 (1-f-g-h) O n , 0.5≤e≤1.2, 0.5≤f≤1, 0≤g≤0.5, 0≤h≤0.5, 1.9≤n≤2.2, M 2 A combination of one or more selected from Zr, Mg, Ba, Ti, Sr, Sb, Y, W, and B.

[0056] The problem of surface lithium and transition metal dissolution is particularly prominent during the production of nickel-cobalt-manganese and nickel-cobalt-aluminum ternary materials. By adding the above-mentioned additives to the above-mentioned ternary materials, the boric acid groups react with the lithium-containing compounds remaining on the surface of the above-mentioned ternary materials to neutralize them, and the electron-withdrawing groups can coordinate with the nickel, cobalt, manganese, aluminum and other metal ions dissolved from the surface of the above-mentioned ternary materials, thereby significantly improving the capacity, reliability, rate performance, storage performance and cycle performance of the ternary battery.

[0057] In some embodiments, the positive electrode active material comprises a chemical formula of Li(Ni x Co y M z )O2 material, wherein M is Al or Mn, 0.7≤x≤1, 0≤y+z≤0.3, x+y+z=1; optionally, x≥0.8; further optionally, x≥0.95.

[0058] Increasing nickel content helps improve the energy density of batteries. However, high nickel content in ternary materials poses a significant problem of surface lithium and transition metal dissolution, which can severely impact battery performance. Therefore, in this application, by adding an additive such as the one represented by formula (I), it is possible to achieve high energy density while also improving the battery's capacity, rate capability, reliability, storage performance, and cycle performance.

[0059] In some embodiments, the mass ratio of the additive to the positive electrode active material is 0.001:1 to 0.03:1, optionally 0.003:1 to 0.007:1, specifically 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, etc.

[0060] In some embodiments, the additive coats at least a portion of the surface of the positive electrode active material. Coating the additive with at least a portion of the surface of the positive electrode active material increases the contact area between the additive and the positive electrode active material, allowing for a more complete reaction and facilitating the reaction between the boric acid group and electron-withdrawing group in the additive and the heterolithium and transition metal.

[0061] In some embodiments, the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0062] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0063] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0064] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In addition, the method for preparing the positive electrode sheet of the first aspect of the present application comprises the following steps:

[0066] Step (a): Add the positive electrode active material and the above-mentioned additives to prepare a positive electrode slurry; the additives are the same as the additives in the positive electrode plate of the first aspect of the present application, and will not be repeated here.

[0067] Step (b): coating the positive electrode slurry on the positive electrode current collector to obtain a positive electrode sheet.

[0068] The present application adds an additive containing a boric acid group and an electron-withdrawing group during the slurrying process of the positive electrode material, causing the additive to react with residual lithium and initially forming BO bonds on the surface of the positive electrode material particles. After drying to form pole pieces and assembling into a battery, in the subsequent initial charge and discharge formation stage, while consuming the remaining miscellaneous lithium, the electron-withdrawing group interacts with transition metal ions such as Co, Mn, and Ni on the surface of the positive electrode active material, stabilizing or capturing Ni, Co, and Mn, reducing transition metal dissolution, and significantly improving battery life. The present application makes the additive and the positive electrode active material into a slurry, allowing the additive to directly interact with the positive electrode active material, reducing side reactions with the electrolyte, improving interface stability, and thereby improving the capacity, reliability, rate performance, cycle performance, and storage performance of the secondary battery.

[0069] In some embodiments, in the above step (a), after the positive electrode active material and the additive are mixed to form a composite slurry, the composite slurry is sintered at 200-800° C., and then a conductive agent and a binder are added to form a positive electrode slurry.

[0070] The positive electrode active material and additive are mixed to form a composite slurry, which is then sintered. During the sintering process, the boric acid groups in the additive initially react with the lithium ions on the surface of the positive electrode active material, forming B-O bonds, allowing the additive to coat at least a portion of the surface of the positive electrode active material, forming a coating layer on at least a portion of the surface of the positive electrode active material, preferably forming a coating layer on the entire surface of the positive electrode active material. This increases the contact area between the additive and the positive electrode active material, allowing for a more complete reaction and further improving the performance of the secondary battery.

[0071] In some embodiments, the above step (a) may specifically include the following steps.

[0072] (1) adding the above-mentioned additives and positive electrode active materials to an organic solvent and stirring uniformly to obtain a composite slurry, wherein the mass ratio of the additives to the positive electrode active materials is 0.001:1 to 0.03:1, and optionally 0.003 to 0.007:1;

[0073] (2) placing the composite slurry prepared in (1) above into a clean sagger;

[0074] (3) Then, the material is placed in an oven and dried at 80-110° C. for 0.01-5 h. Through the drying process, some of the impurity lithium in the ternary material can be removed.

[0075] (4) The composite slurry treated in (3) is placed in a box furnace and sintered at 200-800° C. under inert gas protection for 2-24 hours.

[0076] (5) The product obtained by the treatment in (4) above is dispersed in a solvent (eg, N-methylpyrrolidone) with a conductive agent, a binder, and any other components to form a positive electrode slurry.

[0077] In some embodiments, the mass ratio of the additive to the positive electrode active material is 0.001:1 to 0.03:1, optionally 0.003:1 to 0.007:1, specifically 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, etc.

[0078] In some embodiments, in the above step (a), the positive electrode active material may be mixed with the conductive agent and the binder to form a slurry, and then additives may be added to form the positive electrode slurry.

[0079] In some embodiments, in the above step (b), the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode sheet is obtained.

[0080] In addition, the second aspect of the present application provides a secondary battery comprising the positive electrode sheet according to the first aspect of the present application. The secondary battery has excellent storage performance and cycle life.

[0081] In addition to the aforementioned positive electrode sheet, the secondary battery of the present application also includes the negative electrode sheet, electrolyte, and separator described below. During the battery's charge and discharge process, active ions are embedded and released back and forth between the positive and negative electrode sheets. The electrolyte acts as an ion conductor between the positive and negative electrode sheets. The separator is disposed between the positive and negative electrode sheets, primarily to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0082] Negative electrode

[0083] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0084] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0085] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In some embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. 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. The above-mentioned silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The above-mentioned tin-based material can be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0087] In some embodiments, the negative electrode film layer may further 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).

[0088] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0090] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0091] electrolytes

[0092] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0093] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0094] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0095] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0096] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0097] Isolation film

[0098] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0099] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0100] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0101] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0102] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0103] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 5 is a square structure as an example.

[0104] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the above opening to close the above receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the above receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0105] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0106] Figure 3 4 is an example of a battery module. Figure 3In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of battery cells 5 may further be fixed by fasteners.

[0107] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0108] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0109] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0110] In addition, the third aspect of the present application further provides an electrical device, which includes the secondary battery provided in the second aspect of the present application. The secondary battery can be used as a power source for the above-mentioned electrical device, and can also be used as an energy storage unit for the above-mentioned electrical device. The above-mentioned electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but is not limited thereto.

[0111] As the above-mentioned electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0112] Figure 6 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0113] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0114] Example

[0115] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0116] Example 1

[0117] 1. Preparation of positive electrode sheet

[0118] 1000g of lithium nickel cobalt manganese oxide ternary positive electrode active material Li (Ni 0.83 Co 0.12 Mn 0.05 )O2 and 5g of the additive 4-cyanophenylboric acid are added to N-methylpyrrolidone (NMP) and stirred evenly to obtain a composite slurry, wherein the mass ratio of 4-cyanophenylboric acid to the positive electrode active material is 0.005:1. Then, the composite slurry is placed in a clean sagger. Next, the sagger is placed in an oven and dried at 90°C for 2 hours. Thereafter, the composite material obtained after drying is placed in a box furnace and sintered at 400°C for 12 hours under the protection of inert gas.

[0119] 0.9 g of the sintered product was taken and dissolved in N-methylpyrrolidone (NMP) with acetylene black as a conductive agent and polyvinylidene fluoride as a binder at a weight ratio of 90:5:5. The mixture was thoroughly stirred and mixed to obtain a positive electrode slurry.

[0120] Afterwards, the positive electrode slurry was evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain a single-side positive electrode film with a weight of 250 mg / 1540.25 mm 2 The positive electrode.

[0121] 2. Preparation of secondary batteries

[0122] The negative electrode active material, artificial graphite (Dv50, 15μm, purchased from Ningbo Shanshan Co., Ltd.), the conductive agent, carbon black (SuperP), the binder, styrene-butadiene latex, and sodium carboxymethyl cellulose were thoroughly mixed in a suitable amount of deionized water (solvent) at a mass ratio of 0.94:0.03:0.015:0.015 to form a negative electrode slurry with a solid content of 50%. The negative electrode slurry was coated on the surface of the negative electrode current collector copper foil, dried at 85°C, and cold pressed to obtain the negative electrode sheet.

[0123] The positive and negative electrodes, along with a separator (12 μm polyethylene film), were assembled and 0.5 g of electrolyte was injected to produce a laminated soft-pack secondary battery. The electrolyte was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC, EMC, and DEC of 3:5:2.

[0124] Examples 2 to 7

[0125] A secondary battery was prepared in the same manner as in Example 1, except that the additives shown in Table 1 were used instead of 4-cyanophenylboronic acid.

[0126] Comparative Example 1

[0127] No additive 4-cyanophenylboric acid was added in the preparation of the positive electrode slurry, and the nickel cobalt manganese oxide ternary positive electrode active material Li (Ni 0.83 Co 0.12 Mn 0.05 )O2, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and the mixture was thoroughly stirred and mixed to obtain a positive electrode slurry. Otherwise, a secondary battery was prepared in the same manner as in Example 1.

[0128] Comparative Example 2

[0129] No additive 4-cyanophenylboric acid was added in the preparation of the positive electrode slurry, and the nickel cobalt manganese oxide ternary positive electrode active material Li (Ni 0.83 Co 0.12 Mn 0.05 )O2, conductive agent acetylene black, and binder polyvinylidene fluoride are dissolved in N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and the mixture is fully stirred and mixed to obtain a positive electrode slurry.

[0130] Furthermore, 2 mg of 4-cyanophenylboronic acid was added to 0.5 g of the electrolyte solution of Example 1.

[0131] A secondary battery was prepared in the same manner as in Example 1 except for the above.

[0132] Comparative Example 3

[0133] In the preparation of the positive electrode slurry, phenylboric acid and 4-cyanobenzene (the mass ratio of phenylboric acid to 4-cyanobenzene is 1:1, and the total amount of the two is the same as the amount of the additive in Example 1) are added as additives instead of 4-cyanophenylboric acid. Except for this, a secondary battery is prepared in the same manner as Example 1.

[0134] The following tests were conducted on the above examples and comparative examples, and the results are shown in Table 1 below.

[0135] Performance Testing

[0136] (1) Capacity test

[0137] In a 25°C environment, the theoretical capacity of the secondary battery is calculated to be C1 based on the gram capacity and weight of the positive electrode active material provided by the merchant.

[0138] The capacity of the secondary batteries provided in the examples and comparative examples was tested as follows: first, discharge at a constant current of 1 / 3C1 to 2.8V; second, charge at a constant current of 1 / 3C1 to 4.25V; then, charge at a constant voltage of 1 / 3C1 to 0.05C1; then, let stand for 5 minutes; and finally, discharge at a constant current of 1 / 3C1 to 2.8V. The capacity tested in this step is the secondary battery capacity C0.

[0139] (2) DC internal resistance test

[0140] In an environment of 25°C, adjust the secondary battery to 50% SOC and use 4C0 constant current discharge for 30s. Then, in an environment of 25°C, the calculation formula of DC resistance is: DC internal resistance = (V 放电前 -V 放电后 ) / current.

[0141] (3) Gas production test

[0142] First, the secondary battery was fully charged and stored in a 70°C oven, and the volume V1 of the secondary battery was recorded. The battery was charged to 100% SOC every day, and the volume of the secondary battery was tested using the drainage method every day after being taken out of the oven. The volume V2 of the secondary battery after 100 days of storage was recorded.

[0143] The volume increase rate (%) of the secondary battery after storage at 70° C. for 100 days = (V2 − V1) / V1.

[0144] (4) Cyclic performance test

[0145] In an environment of 25°C, the battery is charged and discharged using a 0.5C0 current cycle, with a voltage range of 2.8 to 4.25V.

[0146] Capacity retention rate (%) of the secondary battery after 800 cycles at 25° C. = discharge capacity after 800 cycles / discharge capacity at the first cycle×100%.

[0147] (5) Storage performance test

[0148] At 25°C, the secondary battery prepared above was charged to 4.25V at a constant current of 0.33C0, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged to 2.8V at a constant current of 0.33C, and the discharge capacity at this time was recorded, which was the discharge capacity before storage.

[0149] At 25°C, the secondary battery prepared above was charged to 4.25V at a constant current of 0.33C0, and then charged to a current of 0.05C at a constant voltage. The secondary battery was then stored in a 60°C constant temperature oven for 300 days. After the storage time was up, the battery was removed from the oven and placed at 25°C for 48 hours; then discharged to 2.8V at 0.33C0, allowed to stand for 30 minutes, and then charged to 4.25V at a constant current of 0.33C0, followed by constant voltage charging to 0.05C0, allowed to stand for 30 minutes; and then discharged to 2.8V at 0.33C0. The resulting capacity was the discharge capacity after 300 days of storage at 60°C.

[0150] Capacity retention rate (%) of the secondary battery after storage at 60° C. for 300 days = discharge capacity after storage for 300 days / discharge capacity before storage × 100%.

[0151] Table 1

[0152]

[0153] As can be seen from Table 1, compared with Comparative Examples 1 to 3, the present application increases the battery capacity, reduces the DC internal resistance (indicating that the battery's rate performance is improved), reduces gas production (indicating that the amount of miscellaneous lithium on the surface of the positive electrode material is reduced), and improves the battery reliability. In addition, the cycle performance and storage performance of the secondary battery are improved.

[0154] It is particularly noted that in Comparative Example 2, although 2 mg of 4-cyanophenylboronic acid was added as an additive to the electrolyte, and the amount of the additive was much higher than that in Example 1, the technical effect of the present application could not be obtained. The inventors analyzed that the reason may be that the solubility of the additive in the electrolyte is very limited, and the proportion that can effectively act on the positive electrode is very small, resulting in the failure to achieve the expected effect. In addition, the electrolyte will contact the positive and negative electrodes at the same time during the infiltration process. The electrolyte additive acting on the positive electrode will affect the performance of the negative electrode. The cyano group will deteriorate the DC resistance of the negative electrode and affect the battery rate performance.

[0155] Examples 8 to 13

[0156] A secondary battery was prepared in the same manner as in Example 1 except that the mass ratio of the additive to the positive electrode active material was adjusted as shown in Table 2. The performance of the battery was evaluated. The results are shown in Table 2 below.

[0157] Table 2

[0158]

[0159] It can be seen from Table 2 that, compared with Example 8, the battery performance of Examples 9 to 12 is further improved by adjusting the mass ratio of the additive to the positive electrode active material within the range of 0.001:1 to 0.03:1.

[0160] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and an additive. The additive comprises at least one compound represented by formula (I), In formula (I), R1 includes an electron-withdrawing group, n is an integer greater than or equal to 1, and when n is an integer greater than 1, R1 are the same or different; R2 includes a group for supporting R1 and -B(OH)2.

2. The positive electrode sheet according to claim 1, characterized in that: n＝1～5。 3. The positive electrode sheet according to claim 1 or 2, characterized in that: R1 includes a nitro group, a cyano group, a trihalomethyl group, a fluorine atom, a chlorine atom, a sulfonic acid group, a vinyl group or a propenyl group; and / or, R2 includes an aromatic group.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: R2 includes phenyl, biphenyl or fluorenyl.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The compound represented by formula (I) includes at least one of 3-nitrophenylboric acid, 2-cyanophenylboric acid, 3-cyanophenylboric acid, 4-cyanophenylboric acid, 3-trifluoromethylphenylboric acid, 3-sulfonylphenylboric acid, 4-vinylphenylboric acid, 2,3,4,5-tetrafluorophenylboric acid and 2,3,4,6-tetrafluorophenylboric acid.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The additive further includes a lithium salt of the compound represented by formula (I).

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The positive electrode active material includes lithium nickel cobalt aluminum oxide or lithium nickel cobalt manganese oxide.

8. The positive electrode sheet according to claim 7, characterized in that: The chemical formula of the lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M 1 (1-b-c-d) O n , 0.5≤a≤1.2, 0.65≤b≤1, 0≤c≤0.35, 0≤d≤0.35, 1.9≤n≤2.2, M 1 A combination of one or more selected from Zr, Zn, Ti, Sr, Sb, Y, W, Al and B; The chemical formula of the lithium nickel cobalt aluminum oxide is Li e Ni f Co g Al h M 2 (1-f-g-h) O n , 0.5≤e≤1.2, 0.5≤f≤1, 0≤g≤0.5, 0≤h≤0.5, 1.9≤n≤2.2, M 2 A combination of one or more selected from the group consisting of Zr, Mg, Ba, Ti, Sr, Sb, Y, W and B.

9. The positive electrode sheet according to claim 7 or 8, characterized in that: The positive electrode active material includes a chemical formula of Li(Ni x Co y M z )O2 materials, Wherein, M is Al or Mn, 0.7≤x≤1, 0≤y+z≤0.3, and x+y+z=1.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The mass ratio of the additive to the positive electrode active material is 0.001:1 to 0.03:

1.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The mass ratio of the additive to the positive electrode active material is 0.003:1 to 0.007:

1.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The additive covers at least a portion of the surface of the positive electrode active material.

13. A secondary battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 12.

14. An electrical device, characterized in that: The secondary battery according to claim 13 is included.

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