Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, the negative pole piece comprises a negative pole current collector and a negative pole material layer located on at least one surface of the negative pole current collector, the negative pole material layer comprises hydrophobic modified polyacrylic acid and graphite, the graphite coating degree of the negative pole piece is F, and 80% < = F < = 100%. Through the arrangement, the cycle performance and the hot box performance of the secondary battery can be improved.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, offer high specific energy, high operating voltage, low self-discharge, compact size, and light weight, making them widely used in portable consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, the demand for the long-cycle performance of lithium-ion batteries has become increasingly stringent.

[0003] In the prior art, the cycle performance of secondary batteries is often improved by adjusting the electrolyte, but this will also reduce other performance of the secondary batteries, such as the hot box performance. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to improve the cycle performance and hot box performance of the secondary battery.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer comprises hydrophobically modified polyacrylic acid and graphite. The graphite coating degree of the negative electrode sheet is F, 80%≤F≤100%. The combination of the hydrophobically modified polyacrylic acid and the graphite facilitates a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode sheet, which helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0007] In some embodiments of the present application, the oil absorption value of the graphite is X mL / 100 g, and 0.67 ≤ 0.01X / F ≤ 1.25. By regulating the value of 0.01X / F within the above range, the synergistic effect of the graphite and the hydrophobically modified polyacrylic acid is maximized, thereby improving the cycle performance and hot box performance of the secondary battery.

[0008] In some embodiments of the present application, the oil absorption value of the graphite is X mL / 100 g, where 60 ≤ X ≤ 100. By regulating the value of X within the above range, the oil absorption capacity of the graphite is relatively strong, which is beneficial for reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0009] In some embodiments of the present application, the hydrophobically modified acrylic acid is an alkalized hydrophobically modified acrylic acid, and the monomers forming the alkalized hydrophobically modified polyacrylic acid include a hydrophobic monomer, a hydrophilic monomer, and a functional monomer, wherein the hydrophobic monomer includes a long carbon chain monomer of C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide. In this case, the alkalized hydrophobically modified polyacrylic acid has high viscosity and good dispersibility, and synergistically acts with graphite with high oil absorption value, facilitating a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate, and facilitating reducing side reactions between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0010] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of ethers, esters, or hydrocarbons containing an unsaturated double bond; and / or the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid, or acrylic acid. The use of these hydrophobic monomers improves the viscosity and dispersibility of the alkalized hydrophobically modified polyacrylic acid. Furthermore, the synergistic effect with graphite having a high oil absorption value helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0011] In some embodiments of the present application, the degree of swelling of the alkaline hydrophobically modified polyacrylic acid in the electrolyte is c, 1% ≤ c ≤ 10%. By regulating the value of c within the above range, the viscosity of the negative electrode dispersant is relatively high. When used in the negative electrode slurry to prepare the negative electrode sheet, this has a strong binding ability for the negative electrode active material particles. In combination with graphite with high oil absorption, it also reduces side reactions between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0012] In some embodiments of the present application, the mass percentage of the alkalized hydrophobically modified polyacrylic acid is a, 0.8% ≤ a ≤ 2%, based on the mass of the negative electrode material layer. By regulating the mass percentage of the alkalized hydrophobically modified polyacrylic acid within the above range, the alkalized hydrophobically modified polyacrylic acid exhibits good viscosity and dispersibility, and synergistically interacts with the high-oil-absorption graphite, thereby reducing side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot-box performance of the secondary battery.

[0013] In some embodiments of the present application, the mass percentage of graphite is b, based on the mass of the negative electrode material layer, and 97% ≤ b ≤ 98.7%. By regulating the mass percentage of graphite within the above range, the proportion of negative electrode active material in the negative electrode material layer is high, and the secondary battery has a higher energy density. The addition of alkaline hydrophobically modified polyacrylic acid helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery while maintaining a balanced energy density.

[0014] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) the graphite includes at least one of artificial graphite, natural graphite or mesophase carbon microbeads; (2) the specific surface area of the graphite is Sm 2 / g, 0.8≤S≤2.0; (3) the average particle size of graphite is Dμm, 5≤D≤18; (4) the compacted density of graphite is ρ1g / cm 3 , 1.7≤ρ1≤2.1; (5) The tap density of graphite is ρ2g / cm 3 , 0.7≤ρ2≤0.95; (6) 85%≤F≤95%. The use of graphite with a high oil absorption value including the above characteristics and the combination with the alkaline hydrophobically modified polyacrylic acid is conducive to forming a more comprehensive and uniform coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate, which is conducive to reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0015] In some embodiments of the present application, the electrolyte conductivity is κmS / cm, and 0.08≤F / κ≤0.13. By regulating the F / κ value within the above range, the negative electrode active material on the surface of the negative electrode plate is more comprehensively coated. When used with a high-conductivity electrolyte, the cycling performance and hot box performance of the secondary battery are improved while maintaining the kinetic performance of the secondary battery.

[0016] In some embodiments of the present application, 8≤κ≤10. By regulating the value of κ within the above range, the conductivity of the electrolyte is high, while taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are improved.

[0017] In some embodiments of the present application, the electrolyte includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes at least one of vinylene carbonate or fluoroethylene carbonate. The mass percentage of the negative electrode film-forming additive is x, 5%≤x≤10%, based on the mass percentage of the electrolyte. By selecting the above-mentioned types of negative electrode film-forming additives and regulating the content of the negative electrode film-forming additives within the above-mentioned range, it is beneficial to form a stable solid electrolyte interface (SEI) film on the surface of the negative electrode plate. In combination with the more fully coated negative electrode active material, while taking into account the secondary battery's kinetic performance, the cycle performance and hot box performance of the secondary battery are further improved.

[0018] In some embodiments of the present application, 8≤F / x≤16. By regulating the value of F / x within the above range, the negative electrode film-forming agent is combined with a high degree of graphite coverage, which is conducive to further reducing the side reactions between the negative electrode active material and the electrolyte, while taking into account the kinetic performance of the secondary battery, and further improving the cycle performance and hot box performance of the secondary battery.

[0019] In some embodiments of the present application, the electrolyte includes a non-aqueous solvent, the non-aqueous solvent including at least one of a linear ester or a cyclic ester, and the mass percentage of the non-aqueous solvent is y, 75% ≤ y ≤ 85%, based on the mass percentage of the electrolyte. By selecting the aforementioned non-aqueous solvent and regulating the mass percentage of the non-aqueous solvent within the aforementioned range, the electrolyte exhibits excellent stability and ion transport properties. When used with the negative electrode plate of the present application, the cycling performance and hot box performance of the secondary battery are further improved while maintaining the kinetic performance of the secondary battery.

[0020] In some embodiments of the present application, the electrolyte includes a lithium salt, including at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide. The mass percentage of the lithium salt, z, based on the mass percentage of the electrolyte, is 10% ≤ z ≤ 15%. By selecting the aforementioned lithium salts and regulating the lithium salt content within the aforementioned range, the cycling performance and hot box performance of the secondary battery are further improved while taking into account the kinetic performance of the secondary battery.

[0021] The second aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device of the present application has good performance.

[0022] Beneficial effects of this application:

[0023] The present application provides a secondary battery and electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer includes hydrophobically modified polyacrylic acid and graphite. The graphite coating degree of the negative electrode sheet is F, 80%≤F≤100%. The combination of the hydrophobically modified polyacrylic acid and graphite with a high oil absorption value facilitates a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode sheet, which helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0024] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0027] A first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer comprising hydrophobically modified polyacrylic acid and graphite, and the graphite coverage of the negative electrode sheet is F, 80% ≤ F ≤ 100%, preferably 85% ≤ F ≤ 95%. For example, the value of F can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or a range consisting of any two of these values.

[0028] The inventors have found that when the negative electrode material layer includes hydrophobically modified polyacrylic acid, especially alkalized hydrophobically modified polyacrylic acid, the alkalized hydrophobically modified polyacrylic acid has a higher viscosity and good dispersibility. The polyacrylic acid (PAA) is added with a hydrophobic segment, i.e., a long carbon chain monomer, and an alkali is added to the slurry. The acrylic acid in the polyacrylic acid molecule undergoes a neutralization reaction under the action of the alkali, and COO -It can be ionized to become a negative charge, and the PAA molecular chain can be opened. At this time, the hydrophobic groups on the PAA chain segments can have a strong interaction with graphite, which is conducive to forming a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-film formation on the surface of the negative electrode pole piece, which is conducive to reducing the side reactions between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery. When the value of F is too low, for example, lower than the lower limit of this application, the surface of the negative electrode active material fails to obtain a more comprehensive coating, the negative electrode active material is prone to side reactions with the electrolyte, and its cycle performance and hot box performance are difficult to improve. Therefore, in the secondary battery of this application, the hydrophobically modified polyacrylic acid is combined with graphite with a high oil absorption value, and the value of F is within the above range, which is conducive to improving the cycle performance and hot box performance of the secondary battery.

[0029] In some embodiments of the present application, the oil absorption value of the graphite is XmL / 100g, and 60≤X≤100. For example, the value of X can be 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two of these values. By regulating the value of X within the above range, the oil absorption capacity of the graphite is relatively strong, and it can react with more alkaline hydrophobically modified polyacrylic acid at the same coating degree, which is conducive to forming a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-film formation on the surface of the negative electrode plate, which is conducive to reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0030] In some embodiments of the present application, the oil absorption value of the graphite is X mL / 100 g, and 0.67≤0.01X / F≤1.25. For example, the value of 0.01X / F can be 0.67, 0.7, 0.72, 0.75, 0.78, 0.80, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, or a range consisting of any two of these values. By regulating the value of 0.01X / F within the above range, the synergistic effect of graphite with high oil absorption value and alkaline hydrophobically modified polyacrylic acid is maximized, which is conducive to forming a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-film formation on the surface of the negative electrode plate, which is conducive to reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, and is conducive to maintaining the integrity of the plate structure, reducing expansion and contraction at high temperature, thereby improving the cycle performance and hot box performance of the secondary battery.

[0031] In some embodiments of the present application, the hydrophobically modified acrylic acid is an alkalized hydrophobically modified acrylic acid, and the monomers forming the alkalized hydrophobically modified polyacrylic acid include a hydrophobic monomer, a hydrophilic monomer, and a functional monomer. The hydrophobic monomer includes a long carbon chain monomer of C4 to C21, preferably, the hydrophobic monomer includes a long carbon chain monomer of C7 to C15; the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide. By adding a hydrophobic segment, i.e., a long carbon chain monomer, to the alkalized hydrophobically modified polyacrylic acid, the long carbon chain molecule weakens the hydrogen bonding between the hydrophilic monomers on the one hand, thereby improving dispersion; on the other hand, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond to increase viscosity. At this time, the alkalized hydrophobically modified polyacrylic acid has a higher viscosity and good dispersibility, and synergizes with the graphite with a high oil absorption value, which is conducive to forming a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-filming on the surface of the negative electrode plate, which is conducive to reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery. In the present application, it is understood that the alkalized hydrophobically modified polyacrylic acid is prepared by polymerizing a hydrophobic monomer, a hydrophilic monomer, and a functional monomer.

[0032] In some embodiments of the present application, the structural formula of the structural unit of the hydrophobically modified polyacrylic acid is as shown in Formula I:

[0033]

[0034] Wherein, Y is selected from a long carbon chain monomer of C4 to C21, preferably, a long carbon chain monomer of C7 to C15; n1 is selected from a natural number within the range of 3,000 to 20,000, n3 is selected from a natural number within the range of 800 to 5,000, and n4 is selected from a natural number within the range of 0 to 5,000. By selecting the hydrophobically modified polyacrylic acid of the above structure and adding a hydrophobic segment, i.e., a long carbon chain monomer, the long carbon chain molecules weaken the hydrogen bonding between the hydrophilic monomers, improving dispersion; and furthermore, the hydrophobic monomers and the hydrophilic monomers form another form of hydrogen bonding, increasing viscosity. The alkalized hydrophobically modified polyacrylic acid exhibits high viscosity and good dispersibility, synergizing with the high oil absorption graphite to facilitate a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate. This helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery. It is understood that the number of monomers in the polymer, i.e., hydrophobically modified polyacrylic acid, meets the limitations of n1, n3, and n4 in the molecular formula, but the actual connection of the monomer units may be disordered. The structural formula in this application is drawn for schematic purposes.

[0035] In some embodiments of the present application, the structural formula of the structural unit of the hydrophobically modified polyacrylic acid is as shown in Formula II:

[0036]

[0037] Wherein, Y is selected from a long carbon chain monomer of C4 to C21, preferably, a long carbon chain monomer of C7 to C15; n1 is selected from a natural number within the range of 3,000 to 20,000, n2 is selected from a natural number within the range of 0 to 5,000, and n3 is selected from a natural number within the range of 800 to 5,000. By selecting the hydrophobically modified polyacrylic acid of the above structure and adding a hydrophobic segment, i.e., a long carbon chain monomer, the long carbon chain molecules weaken the hydrogen bonding between the hydrophilic monomers, improving dispersion; and furthermore, the hydrophobic and hydrophilic monomers form another form of hydrogen bonding, increasing viscosity. The alkalized hydrophobically modified polyacrylic acid exhibits high viscosity and good dispersibility, synergizing with the high oil absorption graphite to facilitate a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate. This helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery. It is understood that the number of monomers in the polymer, i.e., hydrophobically modified polyacrylic acid, meets the limitations of n1, n2, and n3 in the molecular formula, but the actual connection of the monomer units may be disordered. The structural formula in this application is drawn for schematic purposes.

[0038] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of ethers, esters, or hydrocarbons containing an unsaturated double bond. The use of such hydrophobic monomers improves the viscosity and dispersibility of the alkaline hydrophobically modified polyacrylic acid. Furthermore, the monomers further synergize with the high-oil-absorption graphite, thereby forming a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation. This achieves the effect of pre-forming a film on the surface of the negative electrode plate, which helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0039] In some embodiments of the present application, the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid, or acrylic acid. The use of these hydrophilic monomers improves the hydrophilicity of the alkaline hydrophobically modified polyacrylic acid, forming a uniform dispersion in an aqueous system. This allows for a more uniform distribution of the active material during negative electrode slurry coating. This, in synergistic effect with graphite having a high oil absorption value, facilitates a more comprehensive and uniform coating on the surface of the negative electrode active material after the drying step of the preparation, achieving the effect of pre-forming a film on the surface of the negative electrode electrode sheet. This helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0040] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of ethers, esters, or hydrocarbons containing an unsaturated double bond; and / or the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid, or acrylic acid. By selecting the aforementioned types of hydrophobic monomers and hydrophilic monomers, the hydrophobic monomers and the hydrophilic monomers act synergistically, and the alkaline hydrophobically modified polyacrylic acid has good viscosity and dispersibility, further synergizing with the high oil absorption value of graphite, thereby forming a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate, which is beneficial to reducing the side reactions between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0041] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of butadiene, isoprene, styrene, vinyl acetate, butyl acrylate, octyl acrylate, lauryl acrylate, hexadecyl acrylate, octadecyl acrylate, hydroxybutyl vinyl ether, ethyl vinyl ether, ethyl propylene ether, butyl vinyl ether, triethylene glycol divinyl ether, 1,4-cyclohexyl dimethanol divinyl ether, tetradecyl vinyl ether, octadecyl propylene ether, ethyl vinyl ether, octadecyl propylene ether, ethyl vinyl ether, vinyl acetate, or butyl acrylate. The selection of the above-mentioned long carbon chain monomers is beneficial for improving the viscosity and dispersibility of the alkalized hydrophobically modified polyacrylic acid. Furthermore, the long carbon chain monomers further synergistically act with the graphite with high oil absorption value, thereby forming a relatively comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate, and reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0042] In some embodiments of the present application, the degree of swelling of the alkaline hydrophobically modified polyacrylic acid in the electrolyte is c, 1% ≤ c ≤ 10%. For example, the value of c can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two values therein. By regulating the value of c within the above range, the viscosity of the negative electrode dispersant is relatively high. When applied to the negative electrode slurry to prepare the negative electrode sheet, the binding ability of the negative electrode active material particles is relatively strong. During the charge and discharge process of the secondary battery, it is beneficial to reduce the expansion of the negative electrode sheet, thereby improving the cycle performance and mechanical safety performance of the secondary battery; and the lower swelling degree is beneficial to reduce the expansion of the alkaline hydrophobically modified polyacrylic acid in the electrolyte, thereby reducing the side reactions caused by the expansion of the alkaline hydrophobically modified polyacrylic acid. Paired with graphite with high oil absorption value, it also reduces the side reactions between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0043] The swelling degree refers to the ratio of the mass of the polymer molecules after swelling to the mass before swelling, when the polymer molecules adsorb solvent molecules and reach swelling equilibrium. This application does not specifically limit the electrolyte used to test the swelling degree, as long as it can achieve the objectives of this application. For example, a conventional electrolyte composition can be used. Specifically, the electrolyte composition can be the same as the electrolyte composition described in the Examples section of this application.

[0044] The present application has no particular restrictions on the preparation method of hydrophobically modified polyacrylic acid, as long as the purpose of the present application can be achieved. For example, the preparation method of hydrophobically modified polyacrylic acid includes but is not limited to the following steps: (1) taking 900 to 4900 parts of deionized water as a solvent; adding a chain transfer agent and an initiator to the solvent to obtain a mixture, wherein the chain transfer agent includes at least one of n-dodecyl mercaptan, secondary dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol or thioglycolic acid, and the addition amount of the chain transfer agent W2 is 0.2 to 0.8 parts; the initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile or azobisisoheptonitrile, and the initiator The amount of the added agent W3 is 0.5 to 1 part; (2) adding the hydrophobic monomer, the hydrophilic monomer and the functional monomer to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 10 to 50 parts, the mass fraction W5 of the hydrophobic monomer is 20 to 60 parts, the mass fraction W6 of the functional monomer is 20 to 60 parts; and the total mass fraction of the hydrophobic monomer, the hydrophilic monomer and the functional monomer is 100 parts; continuing to heat the polymerization reaction to a temperature T of 60°C to 80°C and a time t of 2h to 10h to obtain an aqueous dispersion of hydrophobically modified polyacrylic acid. The aqueous dispersion of the hydrophobically modified polyacrylic acid can subsequently be obtained by heat treatment or other methods to obtain hydrophobically modified polyacrylic acid.

[0045] When preparing the negative electrode slurry, the hydrophobically modified polyacrylic acid is generally added in the form of an aqueous dispersion of the hydrophobically modified polyacrylic acid.

[0046] In this application, it is understood that the difference between hydrophobically modified polyacrylic acid and alkalized hydrophobically modified polyacrylic acid lies in whether a base is added for neutralization during the preparation of the negative electrode slurry or in the prepared aqueous dispersion of the hydrophobically modified polyacrylic acid. After the neutralization reaction, the content of the alkalized hydrophobically modified polyacrylic acid is substantially the same as that of the hydrophobically modified polyacrylic acid.

[0047] In some embodiments of the present application, the base added when preparing the negative electrode slurry or the prepared aqueous dispersion of hydrophobically modified polyacrylic acid includes at least one of lithium hydroxide, sodium hydroxide or potassium hydroxide, and the mass ratio of the base to the hydrophobically modified polyacrylic acid is 1 / 8 to 1 / 4.

[0048] The present application does not particularly limit the parameter control of the alkalized hydrophobically modified polyacrylic acid, as long as the purpose of the present application can be achieved. For example, the swelling degree c of the alkalized hydrophobically modified polyacrylic acid in the electrolyte can be adjusted by regulating the type of hydrophobic monomer, the amount of hydrophilic monomer added, the polymerization reaction temperature, and the time. When other conditions remain unchanged, the amount of hydrophilic monomer added increases, and the amount of hydrophobic monomer and functional monomer added decreases accordingly. The higher the polymerization reaction temperature and the longer the time, the smaller the swelling degree of the alkalized hydrophobically modified polyacrylic acid in the electrolyte, and vice versa.

[0049] In some embodiments of the present application, based on the mass of the negative electrode material layer, the mass percentage of the alkalized hydrophobically modified polyacrylic acid is a, 0.8%≤a≤2%. For example, the value of a can be 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or a range consisting of any two of these values. By regulating the mass percentage of the alkalized hydrophobically modified polyacrylic acid within the above range, the alkalized hydrophobically modified polyacrylic acid has good viscosity and dispersibility, and synergizes with the graphite with high oil absorption value, which is conducive to forming a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-filming on the surface of the negative electrode plate, which is conducive to reducing the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0050] In some embodiments of the present application, based on the mass of the negative electrode material layer, the mass percentage of graphite is b, 97%≤b≤98.7%. For example, the value of b can be 97%, 97.2%, 97.5%, 97.8%, 98%, 98.2%, 98.5%, 98.7% or a range consisting of any two of these values. By regulating the mass percentage of graphite with a higher oil absorption value within the above range, the proportion of negative electrode active material in the negative electrode material layer is high, and the secondary battery has a higher energy density. When combined with alkaline hydrophobically modified polyacrylic acid, it is beneficial to form a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-filming on the surface of the negative electrode plate, which is beneficial to reduce the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery while taking into account the energy density.

[0051] In some embodiments of the present application, the graphite includes at least one of artificial graphite, natural graphite, or mesocarbon microbeads. By selecting the aforementioned graphite with high oil absorption, the cycle performance and hot box performance of the secondary battery are improved while also taking into account the production cost of the secondary battery.

[0052] In some embodiments of the present application, the specific surface area of graphite is Sm2 / g, 0.8≤S≤2.0. For example, the value of S can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or a range consisting of any two of these values. By regulating the specific surface area of graphite within the above range, the contact area with the electrolyte is increased, and the alkalized hydrophobically modified polyacrylic acid is used, while reducing the side reaction with the electrolyte, it is beneficial to the adsorption and desorption of lithium ions, and the graphite particles with a moderate specific surface area can better support and combine with each other in the negative electrode material layer to form a more stable structure, which can reduce expansion and contraction at high temperatures, thereby improving the cycle performance and hot box performance of the secondary battery.

[0053] In some embodiments of the present application, the average particle size of the graphite is D μm, 5≤D≤18. For example, the value of D can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a range consisting of any two of these values. By regulating the average particle size of the graphite within the above range, the contact area with the electrolyte is increased, and the alkaline hydrophobically modified polyacrylic acid is used to reduce the side reaction with the electrolyte while facilitating the adsorption and desorption of lithium ions. The graphite particles with a moderate specific surface area can better support and combine with each other in the negative electrode material layer to form a more stable structure, which can reduce expansion and contraction at high temperatures, thereby improving the cycle performance and hot box performance of the secondary battery.

[0054] It is understood that the average particle size of graphite can be purchased and the desired graphite can be obtained by combining the test method of "Average Particle Size Test of Graphite". The specific surface area of graphite can also be obtained by purchase or adjusted through coating, granulation, etc. It is understood that the average particle size of graphite can be maintained unchanged while the specific surface area of graphite can be changed through carbon coating.

[0055] In some embodiments of the present application, the compacted density of graphite is ρ1 g / cm 3 , 1.7≤ρ1≤2.1. For example, the value of ρ1 can be 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, or a range consisting of any two of these values. By regulating the compaction density of graphite within the above range, the structure of the negative electrode plate is relatively stable, which can reduce expansion and contraction at high temperatures, and the graphite particles are arranged more densely. Combined with the alkaline hydrophobically modified polyacrylic acid, it is beneficial to reduce the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0056] In some embodiments of the present application, the tap density of graphite is ρ2 g / cm 3, 0.7≤ρ2≤0.95. For example, the value of ρ2 can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. By regulating the tap density of graphite within the above range, the structure of the negative electrode plate is relatively stable, which can reduce expansion and contraction at high temperatures, and the graphite particles are arranged more densely. Combined with the alkaline hydrophobically modified polyacrylic acid, it is beneficial to reduce the side reaction between the negative electrode active material and the electrolyte during the cycle, thereby improving the cycle performance and hot box performance of the secondary battery.

[0057] In some embodiments of the present application, the secondary battery satisfies the following characteristics: the graphite includes at least one of artificial graphite, natural graphite or mesocarbon microbeads; and / or the specific surface area of the graphite is Sm 2 / g, 0.8≤S≤2.0, for example, the value of S can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or a range consisting of any two values therein; and / or, the average particle size of the graphite is D μm, 5≤D≤18, for example, the value of D can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or a range consisting of any two values therein; and / or, the compacted density of the graphite is ρ1 g / cm 3 , 1.7≤ρ1≤2.1, the value of ρ1 can be 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1 or a range consisting of any two values therein; and / or, the tap density of graphite is ρ2 g / cm 3 , 0.7≤ρ2≤0.95. For example, the value of ρ2 can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. The use of graphite with the aforementioned characteristics, combined with an alkaline hydrophobically modified polyacrylic acid, facilitates a more comprehensive and uniform coating on the surface of the negative electrode active material after the drying step of the preparation, achieving the effect of pre-forming a film on the surface of the negative electrode sheet. This helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby improving the cycling performance and hot box performance of the secondary battery.

[0058] This application does not specifically limit the methods for controlling the various graphite parameters, as long as the objectives of this application are achieved. For example, the compacted density of graphite can be controlled by increasing the degree of graphitization or performing secondary granulation; the tap density can be controlled by increasing the degree of graphitization or reducing coating; and the oil absorption value can be controlled by performing secondary granulation or increasing coating. Alternatively, different commercially available graphites can be purchased based on the desired graphite parameters.

[0059] The present application does not impose any particular restrictions on the graphitization process, as long as the purpose of the present application can be achieved. For example, the graphitization process includes but is not limited to the following steps: carbonizing the precursor at high temperature in an inert atmosphere to increase the carbon content to more than 98%. The carbonized coke is mechanically crushed and the particle morphology is optimized by a shaping machine. Then, it is heated in an inert atmosphere and kept warm to rearrange the carbon atoms into an ordered layered graphite structure to obtain graphitized carbon with a carbon content of 99.99%. The present application does not impose any particular restrictions on the various parameters in the graphitization process, as long as the purpose of the present application can be achieved. For example, the precursor can include petroleum coke or needle coke; the inert atmosphere can be nitrogen or argon; the high-temperature carbonization temperature can be 1200°C to 1500°C; the high-temperature carbonization time can be 2h to 5h; the particle size after mechanical crushing can be 10μm to 30μm; the temperature can be heated to 2500°C to 3000°C in an inert atmosphere; and the holding time can be 10h to 50h. The degree of graphitization of graphite can be controlled by adjusting parameters such as the type of precursor, high-temperature carbonization temperature, high-temperature carbonization time, particle size after mechanical crushing, heating temperature in an inert atmosphere, and holding time.

[0060] The present application has no special restrictions on the coating process, as long as the purpose of the present application can be achieved. For example, the coating process includes but is not limited to the following steps: mixing graphite particles and coal tar pitch in a certain mass ratio and then pyrolyzing to form coated amorphous carbon layer graphite, and grading to obtain finished graphite. The present application has no special restrictions on the various parameters in the coating process, as long as the purpose of the present application can be achieved. For example, the softening point of coal tar pitch can be 80°C to 120°C; the mass ratio of graphite particles to coal tar pitch can be 95:5; the pyrolysis temperature can be 1000°C to 1500°C; the particle size of the coated amorphous carbon layer graphite can be 5nm to 50nm; grading can be performed using a vibrating screen; the Dv50 of the finished graphite obtained by grading can be 15μm to 25μm. Among them, the degree of graphite coating can be regulated by adjusting the parameters in the coating process.

[0061] The present application does not particularly limit the secondary granulation process, as long as it can achieve the purpose of the present application. Exemplarily, the secondary granulation process includes, but is not limited to, the following steps: mixing the graphite particles with a binder to uniformly disperse them, using a dry or wet granulation process, removing oversized or undersized particles using a vibrating screen or air classifier to retain the target particle size range; and performing a carbonization treatment under an inert atmosphere to carbonize the binder and form a stable structure with the graphite. The present application has no particular restrictions on the parameters in the secondary granulation process, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to water-based binders such as polyacrylic acid (PAA) or carboxymethyl cellulose (CMC), and oil-based binders such as polyvinylidene fluoride (PVDF), resin or asphalt; the mass ratio of graphite particles to binder may be 95 to 98:2 to 5; a high-speed mixer may be used for mixing and dispersion; the wet method may include but is not limited to the following steps: spraying a solvent (ethanol, acetone, etc.) to form a liquid bridge, and the particles agglomerate into spheres under shear force, and then removing the solvent at 60°C to 120°C to avoid cracking of the particles; the dry method may include but is not limited to the following steps: forcing the particles to combine by mechanical pressure (such as rolling); the inert atmosphere may be nitrogen or argon; the temperature of the carbonization treatment may be 1000°C to 1200°C.

[0062] In some embodiments of the present application, the negative electrode material layer further comprises at least one of styrene-butadiene rubber (SBR) or styrene-acrylic rubber (SAM). This configuration further increases the viscosity of the negative electrode slurry by combining the alkaline hydrophobically modified polyacrylic acid with the SBR and / or SAM in the negative electrode material layer. This facilitates more comprehensive coating of the negative electrode active material surface after the drying step, achieving the effect of pre-forming a film on the negative electrode electrode surface. This helps reduce side reactions between the negative electrode active material and the electrolyte during cycling, thereby further improving the cycling performance and hot box performance of the secondary battery.

[0063] In some embodiments of the present application, the negative electrode material layer further comprises styrene-butadiene rubber, and the weight percentage of the styrene-butadiene rubber is 0.5% to 1.5% based on the weight of the negative electrode material layer. When the weight percentage of the styrene-butadiene rubber is within the above range, the combination of the alkalized hydrophobically modified polyacrylic acid and the styrene-butadiene rubber further increases the viscosity of the negative electrode slurry, which facilitates a more comprehensive coating on the surface of the negative electrode active material after the drying step of the preparation is completed, achieving the effect of pre-forming a film on the surface of the negative electrode plate, which helps to reduce side reactions between the negative electrode active material and the electrolyte during the cycle, thereby further improving the cycle performance and hot box performance of the secondary battery.

[0064] It can be understood that in the process of preparing the negative electrode slurry, styrene-butadiene rubber emulsion and / or styrene-acrylic rubber emulsion is added to the negative electrode slurry, and the negative electrode plates in the secondary battery need to undergo a drying step during the preparation process to remove the solvent used in the plate preparation process, thereby improving the safety and reliability of the secondary battery, and the negative electrode material layer prepared includes styrene-butadiene rubber and / or styrene-acrylic rubber.

[0065] In some embodiments of the present application, the conductivity of the electrolyte is κmS / cm, and 0.08≤F / κ≤0.13. For example, the value of F / κ can be 0.08, 0.09, 0.1, 0.11, 0.12, 0.13 or a range consisting of any two values therein. By regulating the value of F / κ within the above range, the negative electrode active material on the surface of the negative electrode plate is more comprehensively coated, and with a high-conductivity electrolyte, while reducing the side reactions between the negative electrode active material and the electrolyte, the migration and transmission of lithium ions are promoted, the migration speed of lithium ions in the electrolyte is accelerated, and the overall internal resistance of the secondary battery is reduced. While taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are improved.

[0066] In some embodiments of the present application, 8≤κ≤10. For example, the value of κ can be 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10, or a range consisting of any two of these values. By regulating the value of κ within the above range, the conductivity of the electrolyte is high, which is conducive to the migration and transmission of lithium ions, accelerates the migration speed of lithium ions in the electrolyte, and reduces the overall internal resistance of the secondary battery. While taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are improved.

[0067] In some embodiments of the present application, the electrolyte includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes at least one of vinylene carbonate (VC) or fluoroethylene carbonate (FEC). Based on the mass percentage of the electrolyte, the mass percentage of the negative electrode film-forming additive is x, 5%≤x≤10%. For example, the value of x can be 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values. By selecting the above-mentioned types of negative electrode film-forming additives and regulating the content of the negative electrode film-forming additives within the above-mentioned range, it is beneficial to form a stable solid electrolyte interface (SEI) film on the surface of the negative electrode plate, and with the negative electrode active material that is more fully coated, it is beneficial to further reduce the side reactions between the negative electrode active material and the electrolyte, and the formed SEI film can provide a good ion transmission channel, thereby reducing the overall internal resistance of the secondary battery. While taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are further improved.

[0068] In some embodiments of the present application, 8≤F / x≤16. For example, the value of F / x can be 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16 or a range of any two values thereof. By regulating the value of F / x within the above range, the negative electrode film-forming agent is combined with a higher degree of graphite coating, which is conducive to further reducing the side reactions between the negative electrode active material and the electrolyte, and the SEI film formed by the negative electrode film-forming additive can provide a good ion transport channel, thereby reducing the overall internal resistance of the secondary battery. While taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are further improved.

[0069] In some embodiments of the present application, the electrolyte includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of a linear ester or a cyclic ester. Based on the mass percentage of the electrolyte, the mass percentage of the non-aqueous solvent is y, and 75%≤y≤85%. For example, the value of y can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85% or a range consisting of any two values therein. By selecting the above-mentioned types of non-aqueous solvents and regulating the mass percentage of the non-aqueous solvent within the above-mentioned range, the electrolyte now has good stability and ion transport performance. When used with the negative electrode plate of the present application, while taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are further improved.

[0070] In some embodiments of the present application, the linear ester includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or ethylmethyl carbonate (MEC), and the cyclic ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC). By selecting the aforementioned non-aqueous solvents, the electrolyte now has excellent stability and ion transport properties. When used with the negative electrode plate of the present application, the cycling performance and hot box performance of the secondary battery are further improved while taking into account the kinetic performance of the secondary battery.

[0071] In some embodiments of the present application, the electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Based on the mass percentage of the electrolyte, the mass percentage of the lithium salt is z, and 10%≤z≤15%. For example, the value of z can be 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or a range consisting of any two of these values. By selecting the above-mentioned types of lithium salts and regulating the content of the lithium salts within the above-mentioned range, it is beneficial to provide sufficient lithium ion concentration for the electrolyte, ensure the transmission of lithium ions during the cycle, reduce the capacity loss caused by insufficient lithium ion concentration, and help to form a stable SEI film on the surface of the negative electrode. When used with the negative electrode of the present application, while taking into account the kinetic performance of the secondary battery, the cycle performance and hot box performance of the secondary battery are further improved.

[0072] The present application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, other non-aqueous solvents may include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of other non-aqueous solvents in the electrolyte, as long as the purpose of the present application can be achieved. Exemplarily, based on the mass of the electrolyte, the mass percentage of other non-aqueous solvents is 0% to 90%.

[0073] In some embodiments of the present application, the electrolyte may include a lithium salt and other non-aqueous solvents, wherein the weight percentage of the lithium salt is as described above, and the weight percentage of the other non-aqueous solvent is 85% to 90%. The secondary battery including the above electrolyte has good cycle performance and hot box performance.

[0074] In some embodiments of the present application, the electrolyte may include a lithium salt, a negative electrode film-forming additive, and other non-aqueous solvents. The weight percentages of the lithium salt and the negative electrode film-forming additive are as described above, and the weight percentage of the other non-aqueous solvent is 75% to 85%. Secondary batteries including the above electrolytes have good cycle performance and hot box performance.

[0075] In some embodiments of the present application, the electrolyte may include a lithium salt, a non-aqueous solvent, and other non-aqueous solvents. The weight percentages of the lithium salt and the non-aqueous solvent are as described above, and the weight percentage of the other non-aqueous solvent is 0% to 15%. A secondary battery including the above electrolyte has good cycle performance and hot box performance.

[0076] In some embodiments of the present application, the electrolyte may include a lithium salt, a negative electrode film-forming additive, a non-aqueous solvent, and other non-aqueous solvents. The weight percentages of the lithium salt, the negative electrode film-forming additive, and the non-aqueous solvent are as described above, and the weight percentage of the other non-aqueous solvent is 0% to 10%. A secondary battery including the above electrolyte has good cycle performance and hot box performance.

[0077] In the present application, "the negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of itself, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or it can be a partial area of the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). In the present application, the negative electrode material layer also includes a conductive agent. The negative electrode material layer can also include a conductive agent. This application has no special restrictions on the type of conductive agent, as long as the purpose of this application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material or a conductive polymer, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0078] The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer may also include a binder and a conductive agent. The present application has no particular restriction on the type of binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, conductive agent and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0079] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven membrane or a composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the diaphragm can be 3 μm to 30 μm.

[0080] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0081] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one or more embodiments, the secondary battery may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0082] The second aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device of the present application has good performance.

[0083] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0084] Example

[0085] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0086] Test methods and equipment:

[0087] Powder sampling of negative electrode material layer:

[0088] At 25°C, the lithium-ion battery was discharged at a constant current of 0.5C to a discharge cut-off voltage. The lithium-ion battery was disassembled under an argon atmosphere, and the negative electrode sheet was soaked in dimethyl carbonate solvent for 4 hours and dried at 60°C for 1 hour to obtain the negative electrode sheet. The negative electrode material layer on the negative electrode sheet was scraped off and the powder of the negative electrode material layer was collected.

[0089] The discharge cut-off voltage of the lithium-ion batteries in the examples and comparative examples of this application is 3.0 V. It is understood that when the voltage range marked on the factory battery packaging is 3.0 V to 4.5 V, the charge cut-off voltage is 4.5 V and the discharge cut-off voltage is 3.0 V. Unless otherwise specified, the charge cut-off voltage of the lithium-ion batteries used as examples in this application is 4.5 V and the discharge cut-off voltage is 3.0 V.

[0090] Unless otherwise specified, the following test methods use the negative electrode obtained in the above manner for testing.

[0091] Graphite sampling of the negative electrode material layer:

[0092] The lithium-ion battery was discharged at a constant current of 0.5C at 25°C to the discharge cutoff voltage. The lithium-ion battery was disassembled under an argon atmosphere, and the negative electrode sheet was soaked in dimethyl carbonate solvent for 4 hours and dried at 60°C for 1 hour to obtain the negative electrode sheet. The negative electrode material layer on the negative electrode sheet was scraped off and the powder of the negative electrode material layer was collected. The product was then calcined in a muffle furnace at 400°C in a conventional air atmosphere for 4 hours and cooled to obtain graphite powder.

[0093] It is understandable that, since the content of the conductive agent in the negative electrode material layer is too low, the influence of the conductive graphite can be ignored when conducting graphite-related tests.

[0094] Electrolyte sampling for lithium-ion batteries:

[0095] At 25° C., the lithium-ion battery was discharged at a constant current of 0.5 C to a discharge cutoff voltage, and the lithium-ion battery was disassembled in an argon atmosphere, centrifuged, and the electrolyte was collected.

[0096] Graphite coating test:

[0097] 1g of the negative electrode material layer powder was placed in a sample tube, followed by the addition of 5mL of a buffer solution containing 0.25% osmium tetroxide (OsO2), and the sample was placed on a horizontal shaker for 15 minutes. The sample was then removed and rinsed with 100% acetone for 15 minutes and placed in a 65°C thermostat for 48 to 72 hours. The sample was placed on the sample stage of a scanning electron microscope (SEM) for scanning electron microscopy (SEM) to obtain an SEM image. The area of graphite in the SEM image and the area of alkalized hydrophobically modified polyacrylic acid coated on the graphite surface were calculated using software. The graphite coating degree was calculated as: area of alkalized hydrophobically modified polyacrylic acid / graphite area × 100%.

[0098] Graphite oil absorption test:

[0099] Using the graphite sampling method described above, 100g of graphite is placed in the mixing tank of an oil absorptometer. Castor oil is then added dropwise to the sample using a constant-rate titrator. The mixture changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continues to increase. This viscosity is transmitted to the torque sensing system. When the mixture reaches saturation (i.e., no further oil is absorbed by the material), the torque reaches its maximum value (i.e., maximum torque). The titrator automatically shuts off, and the volume of castor oil added (VmL) is directly read from the reading burette. The graphite's oil absorption value (X) is VmL / 100g.

[0100] Swelling test of alkalized hydrophobically modified polyacrylic acid in electrolyte:

[0101] At 25°C, an aqueous dispersion of alkalized hydrophobically modified polyacrylic acid with a solids content of 6 wt% was placed in a rectangular glass template (60 mm × 150 mm × 1 mm). After air-drying until no appreciable surface moisture was present, the film was then baked in an 80°C oven until its weight stopped decreasing. This yielded a film. The film was then weighed, recorded as m1, and then sealed and immersed in an electrolyte solution. The film was then placed in an 85°C oven for 48 hours. The film was then removed and the electrolyte on the film surface was blotted dry with paper until no electrolyte remained. The weight was then weighed and recorded as m2. The degree of swelling of the alkalized hydrophobically modified polyacrylic acid in the electrolyte, c, = (m2 - m1) / m1 × 100%.

[0102] The composition and preparation steps of the electrolyte are the same as those of the electrolyte in Example 1.

[0103] Test of mass percentage of alkalized hydrophobically modified polyacrylic acid and mass percentage of graphite:

[0104] Following the same sampling method for the negative electrode material layer powder as described above, weigh 2 mg of the collected negative electrode material layer powder into a sample holder (a precision electronic balance with automatic weighing). Place the sample in a thermogravimeter and introduce nitrogen (N2) at a purge current of 60 mL / min. Turn on the thermogravimeter and set the temperature ramp from 35°C to 1000°C at a rate of 10°C / min. Once the temperature is complete, the instrument automatically records the weight-temperature curve.

[0105] The peak at 200℃ to 350℃ is alkaline hydrophobically modified polyacrylic acid, and the corresponding weight loss ratio is its percentage content. The peak above 500℃ is graphite, and the corresponding weight loss ratio is its percentage content.

[0106] Graphite specific surface area test:

[0107] Graphite was collected according to the graphite sampling method described above. The graphite to be tested was dried in a vacuum drying oven and placed in a sample tube. The specific surface area of the graphite to be tested was measured by nitrogen adsorption / desorption using a specific surface area analyzer (Tristar II 3020M) to obtain the specific surface area S of the graphite. The specific test was conducted in accordance with GB / T 19587-2017 Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method.

[0108] Average particle size test of graphite:

[0109] Graphite was taken according to the above graphite sampling method, and the graphite to be measured was taken, and the particle size distribution of the graphite was measured using a laser particle size analyzer (Malvern, UK, model: Mastersizer 2000E) according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, and the average particle size of the graphite, i.e., the average particle size D of the graphite, was calculated.

[0110] Compaction density test of graphite:

[0111] Graphite is sampled using the graphite sampling method described above. A weight of graphite powder (m) is weighed and placed in a dedicated compaction mold, with a metal disc sandwiched between the upper and lower hollow spaces. The graphite powder is placed between the metal discs and a metal cylinder placed on top. The mold is then placed in a compaction density meter. The desired pressure is set, and the thickness of the powder at the corresponding pressure can be read on the instrument. The volume v is calculated based on the powder thickness and the surface area of the metal disc. The compacted density (ρ1) of the graphite is then calculated using the density formula ρ1 = m / v.

[0112] Tap density test of graphite:

[0113] Take graphite according to the graphite sampling method above, connect the tap density analyzer (Geopyc 1365) to the power supply, and turn on the equipment. Wipe the sample tube with dust-free paper, place the sample tube in the specified position of the analyzer, and tighten the bottom of the sample tube clockwise. Open the program, select the empty tube test program, click Start, and test the zero volume baseline. Weigh the sample with a mass of M and put it into the sample tube, place the sample tube in the specified position of the analyzer, and tighten the bottom of the sample tube clockwise. Select the sample test program, enter the sample mass, click Start, the test is completed, and the tap density is directly read, that is, the tap density ρ2 of graphite.

[0114] Conductivity test of electrolyte:

[0115] The test was performed using a conductivity meter DDST-319L with a measuring range of 0 to 20ms / cm.

[0116] Place the standard solution in a centrifuge tube and incubate at 25°C for 30 minutes. Place the electrode in the standard electrode and shake it until the value stabilizes. This is the "calibration" of the electrode. The standard solution is a 0.1 mol / L potassium chloride solution.

[0117] Following the electrolyte sampling method described above, place the electrolyte sample in a centrifuge tube and incubate at 25°C for 30 minutes. Place the electrode in the sample tube and shake it until the value stabilizes, then read the value. Lift the electrode and place it back in again, repeating this process twice and recording the measured data.

[0118] Electrolyte component test:

[0119] The electrolyte components were tested using a gas chromatography-mass spectrometer (GC-MS, model: Agilent GC 7890A), and the external standard method was used to test the components to determine the mass percentage of each component in the electrolyte.

[0120] Cyclic performance test:

[0121] Place the lithium-ion battery of the embodiment or comparative example being tested on a charge and discharge instrument, set the temperature to 25°C, and set the charging process as follows: 0.7C constant current charging to 4.5V, 4.5V constant voltage charging to 0.025C; discharge process: 0.5C DC discharge to 3.0V. The above charge and discharge process is recorded as one cycle (cl). After each discharge cycle, the discharge capacity Qn is recorded. The discharge capacity at the end of the first discharge cycle is Q1. The number of cycles when the discharge capacity Qn = 80% of Q1 is recorded, and recorded as N1.

[0122] Place the battery from the embodiment or comparative example being tested on a charge-discharge instrument at 45°C. Set the charging cycle to 0.7C constant current charging to 4.5V, then 4.5V constant voltage charging to 0.025C. Discharging cycle: 0.5C DC discharge to 3.0V. Each charge and discharge cycle is counted as one cycle (cl). Record the discharge capacity Q'n at the end of each discharge cycle. The discharge capacity at the end of the first discharge cycle is Q'1. Record the cycle number N2 when the discharge capacity Q'n reaches 80% of Q'1.

[0123] Hot box performance test:

[0124] Five lithium-ion batteries were prepared for each set of Examples or Comparative Examples. Each set of five lithium-ion batteries was placed in a hot box furnace and discharged to 3.0V at 0.2C. The batteries were then charged to 4.5V at 0.7C constant current and then to 0.025C at 4.5V constant voltage. The temperature was raised to 130°C at a rate of 5±2°C and held for 30 minutes. Each battery was then photographed to observe whether it exploded, smoked, or caught fire. If the battery did not explode, smoke, or catch fire, it was considered passed. Otherwise, it was considered failed. If all batteries passed, five fresh batteries from the same set were placed in the hot box furnace again and cycled through the above steps. After further heating to 131°C and holding for 30 minutes, the test was repeated. If all batteries passed, fresh batteries from the same set were tested again at this temperature until all batteries in the set failed to pass. The highest temperature at which the battery in the set passed was recorded. The higher the highest temperature, the better the hot box performance of the battery in the set.

[0125] Impedance test:

[0126] The kinetic performance of lithium-ion batteries is evaluated by their impedance. The smaller the impedance of a lithium-ion battery, the better its kinetic performance, and the larger the impedance, the worse its kinetic performance. At 25°C, the lithium-ion battery is charged at a constant current of 0.7C to a voltage of 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.05C, so that the lithium-ion battery reaches a fully charged state. The lithium-ion battery is discharged at 0.1C for 5s, and the voltage value at this time is recorded as V1 and the current value is I1. Then it is discharged at 1C for 1s, and the voltage value at this time is recorded as V2 and the current value is I2. Repeat the above operation until the lithium-ion battery is discharged to 3.0V. The impedance (DCR) of the lithium-ion battery is calculated by the following formula: DCR (Ω) = (V1-V2) / (I1-I2).

[0127] Example 1-1

[0128] <Preparation of Hydrophobically Modified Polyacrylic Acid>

[0129] (1) 1566.7 parts of deionized water (W1) was used as a solvent, and a chain transfer agent, n-dodecyl mercaptan, and an initiator, sodium persulfate, were added to the solvent to obtain a mixture, wherein the amount of the chain transfer agent added, W2, was 0.5 parts, and the amount of the initiator added, W3, was 0.5 parts;

[0130] (2) Adding a hydrophobic monomer triethylene glycol divinyl ether, a hydrophilic monomer acrylic acid, and a functional monomer acrylamide to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 40 parts; the mass fraction W5 of the hydrophobic monomer is 30 parts, the mass fraction W6 of the functional monomer is 30 parts, and the total mass fraction of the hydrophobic monomer, the hydrophilic monomer, and the functional monomer is 100 parts; continuing to heat to 70°C, keeping the temperature for 4 hours, and removing the residual monomers by reduced pressure distillation for 4 hours to obtain an aqueous dispersion of hydrophobically modified polyacrylic acid.

[0131] <Preparation of negative electrode sheet>

[0132] The negative electrode active material artificial graphite (manufacturer: Ningbo Shanshan Co., Ltd.), conductive carbon black, and an aqueous dispersion of hydrophobically modified polyacrylic acid were mixed at a solid mass ratio of 98.0:0.5:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 45wt%. Alkali lithium hydroxide was then added and stirred evenly using a ROSS double planetary mixer to prepare the coating layer negative electrode slurry. The coating was applied using an extrusion double-layer coater at a coating speed of 18m / min and a coating weight of 160mg / 1540.25cm. 2 The above negative electrode slurry was applied to the surface of the negative electrode current collector copper foil with a thickness of 6 μm. Then, it was baked in an oven until the electrode was dry and cold pressed to 1.80 mg / mm using a cold press. 2After cold pressing, the negative electrode sheet is placed in a high-temperature vacuum furnace for heat treatment at 320°C, and then cut into pieces and welded to the tabs to obtain a negative electrode sheet with a specification of 78mm×875mm. Among them, the oil absorption value X of artificial graphite is 80mL / 100g, and the specific surface area S is 1.3m 2 / g, the average particle size D is 14 μm, and the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2.

[0133] <Preparation of positive electrode sheet>

[0134] The positive electrode active material lithium titanate, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 6μm and dried at 120℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 267.8mg / 1540mm 2 Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. Dry at 120°C and then cold press. Cut into pieces to obtain a positive electrode sheet with a specification of 74mm×867mm for use. The cold pressed density of the positive electrode material layer is 4.15mg / mm 2 .

[0135] <Preparation of Separator>

[0136] A 5 μm thick polyethylene film was used as the base layer of the diaphragm. A 2 μm thick alumina ceramic layer was coated on one surface of the base layer, and then a 2.5 mg / 1540.25 mm thick alumina ceramic layer was coated on the surface of the alumina ceramic layer and the other surface of the base layer. 2 The adhesive layer is dried to obtain a diaphragm. The alumina ceramic layer comprises aluminum oxide and polyvinylidene fluoride in a ratio of 70:30 by mass; the adhesive layer is made of polyvinylidene fluoride-hexafluoroethylene, and the porosity of the diaphragm is 39%.

[0137] <Preparation of Electrolyte>

[0138] In an environment with a water content of less than 10 ppm, a non-aqueous solvent, linear ester diethyl carbonate, and cyclic ester ethylene carbonate, are mixed in a mass ratio of 1:1 to obtain an organic solvent. Fluoroethylene carbonate (FEC), a negative electrode film-forming additive, and lithium hexafluorophosphate (LiPF6), a lithium salt, are then added to the organic solvent and mixed uniformly to obtain an electrolyte. The electrolyte comprises a lithium salt content (z) of 12% by mass, a negative electrode film-forming additive content (x) of 8% by mass, and a total non-aqueous solvent content (y) of 80% by mass.

[0139] <Preparation of lithium-ion batteries>

[0140] The prepared positive and negative electrode sheets were welded to the positive and negative tabs, respectively. The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide insulation, and then wound to form an electrode assembly. The electrode assembly was packaged in an aluminum-plastic film bag and baked under vacuum for 24 hours to remove moisture. The electrolyte was then injected and allowed to stand at high temperature. The battery was then formed and sorted to produce a square soft-pack lithium-ion polymer battery with a thickness, width, and height of 3.8 mm, 64 mm, and 82 mm, respectively.

[0141] Example 1-2 to Example 1-17

[0142] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0143] Examples 1-18

[0144] Except that the hydrophobically modified polyacrylic acid was prepared as follows and the relevant preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0145] <Preparation of Hydrophobically Modified Polyacrylic Acid>

[0146] (1) 1566.7 parts of deionized water (W1) was used as a solvent, and a chain transfer agent, n-dodecyl mercaptan, and an initiator, sodium persulfate, were added to the solvent to obtain a mixture, wherein the amount of the chain transfer agent added, W2, was 0.5 parts, and the amount of the initiator added, W3, was 0.5 parts;

[0147] (2) Adding a hydrophobic monomer triethylene glycol divinyl ether, a hydrophilic monomer acrylic acid, and a functional monomer acrylonitrile to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 40 parts; the mass fraction W5 of the hydrophobic monomer is 20 parts, the mass fraction W6 of the functional monomer is 40 parts, and the total mass fraction of the hydrophobic monomer, the hydrophilic monomer, and the functional monomer is 100 parts; continuing to heat to 80°C, keeping the temperature for 10 hours, and performing reduced pressure distillation for 4 hours to remove the residual monomers to obtain a hydrophobically modified polyacrylic acid.

[0148] Examples 1-19

[0149] Except that the hydrophobically modified polyacrylic acid was prepared as follows and the relevant preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0150] <Preparation of Hydrophobically Modified Polyacrylic Acid>

[0151] (1) 1566.7 parts of deionized water (W1) was used as a solvent, and a chain transfer agent, n-dodecyl mercaptan, and an initiator, sodium persulfate, were added to the solvent to obtain a mixture, wherein the amount of the chain transfer agent added, W2, was 0.5 parts, and the amount of the initiator added, W3, was 0.5 parts;

[0152] (2) Adding a hydrophobic monomer triethylene glycol divinyl ether, a hydrophilic monomer acrylic acid, and a functional monomer acrylonitrile to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 50 parts; the mass fraction W5 of the hydrophobic monomer is 25 parts, the mass fraction W6 of the functional monomer is 25 parts, and the total mass fraction of the hydrophobic monomer, the hydrophilic monomer, and the functional monomer is 100 parts; continuing to heat to 70°C, keeping the temperature for 4 hours, and removing the residual monomers by reduced pressure distillation for 4 hours to obtain a hydrophobically modified polyacrylic acid.

[0153] Examples 1-20

[0154] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, and the aqueous dispersion of hydrophobically modified polyacrylic acid are mixed according to a solid mass ratio of 98.7:0.5:0.8, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest are the same as Example 1-1.

[0155] Examples 1-21

[0156] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, and the aqueous dispersion of hydrophobically modified polyacrylic acid are mixed according to a solid mass ratio of 97.5:0.5:2.0, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest are the same as Example 1-1.

[0157] Examples 1-22

[0158] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, and the aqueous dispersion of hydrophobically modified polyacrylic acid are mixed according to a solid mass ratio of 97.0:0.5:2.5, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest are the same as Example 1-1.

[0159] Example 1-23 to Example 1-24

[0160] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0161] Examples 1-25

[0162] Except that the functional monomer for preparing the hydrophobically modified polyacrylic acid is acrylonitrile and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0163] Examples 1-26

[0164] Except that the hydrophilic monomer for preparing the hydrophobically modified polyacrylic acid is methacrylic acid and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0165] Examples 1-27

[0166] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, the hydrophobically modified polyacrylic acid, and the styrene-butadiene emulsion are mixed in a solid mass ratio of 97.5:0.5:1.5:0.5, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest are the same as Example 1-1.

[0167] Examples 1-28

[0168] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, the hydrophobically modified polyacrylic acid, and the styrene-butadiene emulsion are mixed in a solid mass ratio of 98.2:0.5:0.8:0.5, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Tables 1 and 2, the rest are the same as Example 1.

[0169] Example 2-1 to Example 2-11

[0170] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-14. When the composition of the electrolyte changes, the mass ratio of the linear ester to the cyclic ester remains unchanged.

[0171] Comparative Example 1

[0172] The process was the same as in Example 1-1, except that the negative electrode active material artificial graphite, the conductive agent conductive carbon black, sodium carboxymethyl cellulose, and the styrene acrylic rubber in the styrene acrylic emulsion were mixed in a mass ratio of 97.3:0.5:1.2:1.0 as described in <Preparation of Negative Electrode Sheet> and the relevant preparation parameters were adjusted according to Table 1.

[0173] Comparative Example 2

[0174] The process was the same as Example 1-1, except that the negative electrode active material artificial graphite, the conductive agent conductive carbon black, polyacrylic acid, and the styrene acrylic rubber in the styrene acrylic emulsion were mixed in a mass ratio of 97.3:0.5:1.2:1.0 as described in <Preparation of Negative Electrode Sheet> and the relevant preparation parameters were adjusted according to Table 1.

[0175] Comparative Example 3

[0176] The preparation process was the same as in Example 1-1, except that the negative electrode active material artificial graphite, the conductive agent conductive carbon black, polyvinyl alcohol, and the styrene acrylic rubber in the styrene acrylic emulsion were mixed in a mass ratio of 97.3:0.5:1.2:1.0 as described in <Preparation of Negative Electrode Sheet> and the relevant preparation parameters were adjusted according to Table 1.

[0177] Comparative Example 4 to Comparative Example 5

[0178] The preparation process was the same as in Example 1-1, except that the negative electrode active material artificial graphite, the conductive agent conductive carbon black, and the aqueous dispersion of hydrophobically modified polyacrylic acid were mixed in a solid mass ratio of 98.0:0.5:1.5, deionized water was added as a solvent, and a slurry with a solid content of 45 wt% was prepared. The negative electrode slurry was stirred evenly with a vacuum mixer, that is, no alkali was added during the preparation of the negative electrode slurry. Before use, the aqueous dispersion of hydrophobically modified polyacrylic acid was dispersed at a high speed of 2000 rpm for 10 hours, and the relevant preparation parameters were adjusted according to Tables 1 and 2.

[0179] Comparative Example 6

[0180] Except that in <Preparation of Negative Electrode Sheet> the negative electrode active material artificial graphite, the conductive agent conductive carbon black, and the hydrophobically modified polyacrylic acid are mixed according to a solid mass ratio of 97.5:0.5:2.0, the mass ratio of alkali lithium hydroxide to hydrophobically modified polyacrylic acid is 0.2, and the relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 1-1.

[0181] It can be understood that in the above embodiments and comparative examples, the mass ratio of the substances added to prepare the negative electrode slurry is the mass ratio of the solids contained in the substances.

[0182] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0183]

[0184]

[0185]

[0186] From Examples 1-1 to 1-28 and Comparative Examples 1 to 6, it can be seen that by adding hydrophobically modified polyacrylic acid to the negative electrode material layer and matching it with graphite with a high oil absorption value, the value of F is within the scope of this application. At this time, the lithium-ion battery has a large number of cycles at 25°C and 45°C, and the maximum temperature at which the hot box test is fully passed is high, indicating that the lithium-ion battery of this application has good cycle performance and hot box performance. Conventional negative electrode dispersants are used in Comparative Examples 1 to 3. At this time, the lithium-ion battery has a small number of cycles at 25°C and 45°C, and the maximum temperature at which the hot box test is fully passed is low. The graphite coating degree of the negative electrode sheets in Comparative Examples 4 to 6 is not within the scope of this application. At this time, the lithium-ion battery has a small number of cycles at 25°C and 45°C, and the maximum temperature at which the hot box test is fully passed is low.

[0187] The value of 0.01X / F generally affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-22, when the value of 0.01X / F is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0188] The type of hydrophobic monomer generally affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-14, when the type of hydrophobic monomer is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0189] The type of functional monomer generally affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1 and 1-25, when the type of functional monomer is within the scope of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0190] The type of hydrophilic monomer generally affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1 and 1-26, when the type of hydrophilic monomer is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, demonstrating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0191] The value of c typically affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-12, and 1-18 to 1-19, when the value of c is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0192] The value of a typically affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-22, and 1-27 to 1-28, when the value of c is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0193] The value of b generally affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-20 to 1-22, and 1-27 to 1-28, when the value of b is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0194] The value of S typically affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11, and 1-12, when the value of S is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0195] The value of D typically affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-23, and 1-24, when the value of D is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0196] The value of ρ1 typically affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-23, and 1-24, when the value of ρ1 is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0197] The value of ρ2 typically affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11, and 1-12, when the value of ρ2 is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0198] The value of X generally affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11, and 1-17, when the value of X is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0199] The value of F / κ generally affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14 and Examples 2-1 to 2-11, when the value of F / κ is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum temperature at which the hot box test passes. This indicates that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0200] The value of κ typically affects the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14 and 2-1 to 2-4, when the value of κ is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0201] The type and content of negative electrode film-forming additives generally affect the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14 and 2-1 to 2-4, when the type and content of negative electrode film-forming additives are within the ranges of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0202] The F / x value generally affects the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14 and 2-1 to 2-11, when the F / x value is within the range of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum temperature at which the hot box test passes. This indicates that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0203] The type and content of non-aqueous solvents generally affect the cycling and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14 and 2-1 to 2-10, when the type and content of non-aqueous solvents are within the ranges of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum pass temperature for the hot box test, indicating that the lithium-ion batteries of this application have good cycling and hot box performance.

[0204] The type and content of lithium salts generally affect the cycling performance and hot box performance of lithium-ion batteries. As can be seen from Examples 1-14, 2-1, and 2-5 to 2-9, when the type and content of lithium salts are within the ranges of this application, the lithium-ion batteries achieve a high number of cycles at 25°C and 45°C, and a high maximum temperature at which they pass the hot box test. This demonstrates that the lithium-ion batteries of this application have good cycling performance and hot box performance.

[0205] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0206] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0207] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises hydrophobically modified polyacrylic acid and graphite, and the graphite coating degree of the negative electrode sheet is F, 80%≤F≤100%.

2. The secondary battery according to claim 1, wherein The oil absorption value of the graphite is X mL / 100 g, and 0.67≤0.01X / F≤1.

25.

3. The secondary battery according to claim 1, wherein The oil absorption value of the graphite is X mL / 100 g, and 60≤X≤100.

4. The secondary battery according to any one of claims 1 to 3, wherein The hydrophobically modified acrylic acid is an alkalized hydrophobically modified acrylic acid. The monomers forming the alkalized hydrophobically modified polyacrylic acid include a hydrophobic monomer, a hydrophilic monomer and a functional monomer. The hydrophobic monomer includes a long carbon chain monomer of C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide.

5. The secondary battery according to claim 4, wherein The C4 to C21 long carbon chain monomer includes at least one of ethers, esters or hydrocarbons containing unsaturated double bonds; and / or the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid or acrylic acid.

6. The secondary battery according to claim 4, wherein The swelling degree of the alkalized hydrophobically modified polyacrylic acid in the electrolyte is c, 1%≤c≤10%.

7. The secondary battery according to claim 4, wherein Based on the mass of the negative electrode material layer, the mass percentage of the alkalized hydrophobically modified polyacrylic acid is a, and 0.8%≤a≤2%.

8. The secondary battery according to claim 4, wherein Based on the mass of the negative electrode material layer, the mass percentage of the graphite is b, and 97%≤b≤98.7%.

9. The secondary battery according to any one of claims 1 to 3, which satisfies at least one of the following characteristics: (1) The graphite includes at least one of artificial graphite, natural graphite or mesophase carbon microbeads; (2) The specific surface area of the graphite is Sm 2 / g, 0.8≤S≤2.0; (3) The average particle size of the graphite is D μm, 5≤D≤18; (4) The compacted density of the graphite is ρ1g / cm 3 , 1.7≤ρ1≤2.1; (5) The tap density of the graphite is ρ2 g / cm 3 , 0.7≤ρ2≤0.95; (6)85％≤F≤95％。 10. The secondary battery according to any one of claims 1 to 3, wherein The conductivity of the electrolyte is κmS / cm, and 0.08≤F / κ≤0.

13.

11. The secondary battery according to claim 10, wherein 8≤κ≤10.

12. The secondary battery according to claim 10, wherein The electrolyte includes a negative electrode film-forming additive, which includes at least one of vinylene carbonate or fluoroethylene carbonate. Based on the mass percentage of the electrolyte, the mass percentage of the negative electrode film-forming additive is x, 5%≤x≤10%.

13. The secondary battery according to claim 12, wherein 8≤F / x≤16.

14. The secondary battery according to claim 10, wherein The electrolyte includes a non-aqueous solvent, which includes at least one of a linear ester or a cyclic ester. Based on the mass percentage of the electrolyte, the mass percentage of the non-aqueous solvent is y, and 75%≤y≤85%.

15. The secondary battery according to claim 10, wherein The electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide. Based on the mass percentage of the electrolyte, the mass percentage of the lithium salt is z, 10%≤z≤15%. 16 . An electronic device comprising the secondary battery according to claim 1 .

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