Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a negative pole piece and a diaphragm, the negative pole piece comprises a negative pole material layer, and the negative pole material layer is provided with a plurality of grooves. The diaphragm comprises a modified base membrane, the surface of the modified base membrane comprises a first functional group, and the first functional group is at least one of carboxyl, hydroxyl, epoxy group, amino or ester group; the number of moles per unit area of the first functional group on the surface of the modified base membrane is n mmol / cm2, the surface energy of the separator is gamma mJ / m2, 1 < = n < = 4, and 50 < = gamma < = 300. The secondary battery meets the characteristics, so that the electrolyte has better wettability, the cohesiveness between the diaphragm and the negative pole piece is improved, the practical application capability of a laser processing technology in the manufacturing process of the negative pole piece is widened, the problem of purple spots caused by bonding failure and the problem of cycle failure caused by lithium precipitation are improved, and the service life of the secondary battery is prolonged. And meanwhile, the secondary battery also has relatively good dynamic performance and relatively high energy density.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Lithium ion batteries have high energy density and power density, making them the preferred technology for portable electronic devices, power tools and hybrid / electric vehicles. Therefore, as consumers demand higher performance from products, the market demand for high-performance lithium ion batteries is also increasingly urgent.

[0003] The electrolyte is an important component of the lithium ion battery, and has an important influence on the cycle stability and high temperature performance of the battery system. Therefore, how to improve the wettability of the electrolyte and improve the uniformity of the electrolyte distribution of the lithium ion battery during the cycle process is of great significance to improve the cycle stability of the lithium ion battery. SUMMARY

[0004] The purpose of the present application is to provide a secondary battery and an electronic device, which has good wettability of the electrolyte, improves the adhesion between the separator and the negative electrode sheet, broadens the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and improves the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, while the secondary battery also has good kinetic performance and high energy density. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a secondary battery, which comprises a negative electrode sheet and a separator, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer is provided with a plurality of grooves, and the surface of the groove comprises at least one of a hydroxyl group and a carboxyl functional group. The separator comprises a modified base film, the surface of the modified base film comprises a first functional group, the first functional group is at least one of a carboxyl group, a hydroxyl group, an epoxy group, an amino group or an ester group; the number of moles of the first functional group on the surface of the modified base film per unit area is n mmol / cm 2 , and the surface energy of the separator is γmJ / m 2, 1≤n≤4, 50≤γ≤300. When the laser processing technology is used to construct the groove on the negative electrode sheet, the negative electrode sheet can introduce functional groups such as hydroxyl and carboxyl during the process of manufacturing the groove structure by the laser processing technology. The surface of the modified base film includes carboxyl, hydroxyl, epoxy or amino functional groups, and the functional groups on the surface of the modified base film can interact with the functional groups introduced by the negative electrode sheet during the process of manufacturing the groove structure by the laser processing technology. Specifically, for hydroxyl or carboxyl, esterification can occur during the dehydration process at high temperature, i.e. R-OH + R'COOH → R-O-CO-R' + H2O; for epoxy, curing can occur with hydroxyl during the high temperature process, i.e. O=CH-CH2-O + HO-R” → HO-CH2-CH2-O-R”; for amino, dehydration polymerization can occur with hydroxyl, i.e. R”'-NH2 + R””-OH → R”'-NHR”” + H2O; such polymerization reactions can provide molecular forces, which can improve the adhesion between the separator and the negative electrode sheet. Therefore, when the laser processing technology is used to construct the groove on the negative electrode sheet, by adjusting the type, the number of moles per unit area of the first functional groups on the surface of the modified base film and the surface energy of the separator, the electrolyte has good wettability, and at the same time, the functional groups on the surface of the modified base film can interact with the functional groups introduced by the laser processing technology during the process of manufacturing the groove structure on the negative electrode sheet, form molecular forces, improve the adhesion between the separator and the negative electrode sheet, expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the adhesion between the separator and the negative electrode sheet is high, the separator can not include a bonding layer, the amount of the bonding agent in the separator is reduced, and the gap between the negative electrode sheet and the separator is reduced, which is beneficial to the transmission of lithium ions, improves the kinetic performance of the secondary battery, and also improves the energy density of the secondary battery.

[0006] In some embodiments of the present application, 0.01≤n / γ≤0.05. By adjusting the value of n / γ within the above range, the adhesion between the separator and the negative electrode sheet is further improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is further expanded, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, and at the same time, the kinetic performance and energy density of the secondary battery are further improved.

[0007] In some embodiments of the present application, the contact angle between the separator and water is θ°, and 0≤θ≤90. The contact angle between the separator and water within the above range indicates that the wettability of the electrolyte by the separator is good, which is beneficial to the transmission of lithium ions, and at the same time, the separator has good adhesion, which can improve the cycle stability and rate performance of the secondary battery.

[0008] In some embodiments of the present application, the material of the modified base film comprises at least one of polyamide, polypropylene or polyethylene. The base film is selected from the group consisting of the base film with a low glass transition temperature, the base film with high chemical stability and the base film with a low possibility of shrinkage at high temperature, which can improve the safety performance of the secondary battery.

[0009] In some embodiments of the present application, the thickness of the separator is h1 μm, 2≤h1≤8. By adjusting the thickness of the separator within the above range, the safety performance and the kinetic performance of the secondary battery can be improved, and the secondary battery can have a high energy density.

[0010] In some embodiments of the present application, the plurality of grooves extend along a first direction and are arranged at intervals along a second direction; the first direction is the extension direction of the grooves, and the second direction is the arrangement direction of the grooves; in the cross section of the negative electrode material layer along the thickness direction of the negative electrode material layer, along the second direction, the maximum size of a single groove is L1 μm, and the minimum size of a single groove is L2 μm, 20≤L1≤300, and 10≤L2≤200. By adjusting the maximum size and the minimum size of a single groove along the second direction within the above range, the adhesion between the separator and the negative electrode sheet is further improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is further widened, the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, and the kinetic performance and the energy density of the secondary battery are further improved.

[0011] In some embodiments of the present application, 1≤L1 / L2≤1.5. By adjusting the value of L1 / L2 within the above range, the adhesion between the separator and the negative electrode sheet is further improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is further widened, the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, and the kinetic performance and the energy density of the secondary battery are further improved.

[0012] In some embodiments of the present application, the ratio of the grooving area S1 of the plurality of grooves on the surface of the negative electrode material layer to the total area S2 of the surface of the negative electrode material layer is Z, 5%≤Z×100%≤40%, and preferably, 10%≤Z×100%≤30%. By adjusting the value of Z×100% within the above range, the adhesion between the separator and the negative electrode sheet is further improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is further widened, the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, and the kinetic performance and the energy density of the secondary battery are further improved.

[0013] In some embodiments of the present application, 0.02≤Z / n≤0.35. By adjusting the value of Z / n within the above range, the adhesion between the separator and the negative electrode sheet is further improved, the practical application capability of the laser processing technology in the negative electrode sheet manufacturing process is further widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, while the kinetic performance and energy density of the secondary battery are further improved.

[0014] In some embodiments of the present application, the cross-sectional shape of the groove includes a square, a rectangle, or a trapezoid. The cross-sectional shape of the groove meets the above characteristics, further improves the adhesion between the separator and the negative electrode sheet, further widens the practical application capability of the laser processing technology in the negative electrode sheet manufacturing process, and further improves the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, while further improving the kinetic performance and energy density of the secondary battery.

[0015] In some embodiments of the present application, the adhesion between the separator and the negative electrode material layer is F N / m, and 5≤F≤40. By adjusting the adhesion between the separator and the negative electrode material layer within the above range, the adhesion between the separator and the negative electrode sheet is better, which can better improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, while improving the kinetic performance and energy density of the secondary battery.

[0016] In some embodiments of the present application, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes at least one of graphite, a silicon material, or lithium titanate, and the silicon material includes at least one of elemental silicon, silicon oxide, or silicon carbide. The above-mentioned negative electrode active material is selected and applied to the secondary battery, and the secondary battery has good cycle stability, kinetic performance, and high energy density.

[0017] The second aspect of the present application provides an electronic device including the secondary battery in any of the foregoing embodiments. Thus, the electronic device provided by the present application has good use performance.

[0018] The beneficial effects of the present application are as follows:

[0019] The present application provides a secondary battery and an electronic device. The secondary battery includes a negative electrode sheet and a separator. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer is provided with a plurality of grooves. The surface of the groove includes at least one of a hydroxyl group and a carboxyl functional group. The separator includes a modified base film. The surface of the modified base film includes a first functional group. The first functional group is at least one of a carboxyl group, a hydroxyl group, an epoxy group, an amino group, or an ester group. The number of moles per unit area of the first functional group on the surface of the modified base film is n mmol / cm 2 The surface energy of the separator is γ mJ / m2 The secondary battery satisfies the above characteristics, while having good wettability of the electrolyte, improving the adhesion between the separator and the negative electrode sheet, expanding the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and improving the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, and the secondary battery also has good kinetic performance and high energy density.

[0020] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0022] Figure 1 is a schematic diagram of the contact angle between the separator and water;

[0023] Figure 2 is a schematic diagram of the structure of the negative electrode material layer in the first direction and the second direction of an embodiment of the present application;

[0024] Figure 3 is a schematic diagram of the cross section of the negative electrode material layer along the thickness direction of an embodiment of the present application;

[0025] Figure 4 is a schematic diagram of the structure of the negative electrode material layer in the first direction and the second direction of another embodiment of the present application;

[0026] Figure 5 is a schematic diagram of the structure of the negative electrode material layer in the first direction and the second direction of another embodiment of the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0028] It should be noted that in the specific embodiments of the present application, lithium ion batteries are used as examples of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium ion batteries.

[0029] As an important component of a secondary battery, an electrolyte has an important influence on the cycle stability and high-temperature performance of a battery system. In order to improve the wettability of the electrolyte and make the electrolyte uniformly distributed in the whole secondary battery during the whole cycle process, a negative electrode laser etching, that is, a negative electrode laser processing technology, is usually used to construct grooves to improve the flowability and wettability of the electrolyte. To some extent, this method can reduce the edge lithium precipitation of the secondary battery and improve the cycle stability of the secondary battery. However, the grooves constructed by laser etching can reduce the actual contact area of the interface between the separator and the negative electrode sheet, indirectly weaken the adhesion between the separator and the negative electrode sheet, and cause the adhesion loss of the separator and the negative electrode sheet, which is not conducive to the cycle stability of the secondary battery. Based on this, the application provides a secondary battery and an electronic device. A plurality of grooves are arranged on the negative electrode material layer, and by adjusting the type and the number of moles per unit area of the first functional groups on the surface of the modified base film of the separator and the surface energy of the separator within the scope of the application, the electrolyte has good wettability. At the same time, the functional groups on the surface of the modified base film can interact with the functional groups introduced by the laser processing technology in the process of manufacturing the groove structure on the negative electrode sheet during the heat pressing of the secondary battery, form molecular forces, improve the adhesion between the separator and the negative electrode sheet, expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the secondary battery also has good kinetic performance and high energy density. The specific technical solutions are as follows:

[0030] The first aspect of the application provides a secondary battery, which comprises a negative electrode sheet and a separator. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector. A plurality of grooves are arranged on the negative electrode material layer, and the surface of the grooves comprises at least one of a hydroxyl group and a carboxyl functional group. The above-mentioned grooves can be grooves constructed on the negative electrode sheet by using a laser processing technology. The separator comprises a modified base film, and the surface of the modified base film comprises a first functional group. The first functional group is at least one of a carboxyl group, a hydroxyl group, an epoxy group, an amino group or an ester group. The number of moles per unit area of the first functional groups on the surface of the modified base film is n mmol / cm 2 The surface energy of the separator is γ mJ / m 2, 1≤n≤4, 50≤γ≤300. Illustratively, n can have a value of 1, 1.5, 2, 2.5, 3, 3.5, 4, or a range between any two of the aforementioned values; and γ can have a value of 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, or a range between any two of the aforementioned values. In some embodiments of the present application, the surface of the modified base film can further comprise a second functional group, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the second functional group can include, but is not limited to, an amide group, an alkenyl group, or an alkyl group. In the present application, the first functional group can be disposed on one surface of the modified base film, or on both surfaces of the modified base film, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The "negative electrode material layer disposed on at least one surface of the negative electrode current collector" described above means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or on both surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire area of the negative electrode current collector, or a partial area of the negative electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0031] In order to improve the electrolyte wettability and make the electrolyte evenly distributed in the whole secondary battery during the whole cycle process, the inventors found that grooves can be constructed on the negative electrode sheet by using laser processing technology. During the process of manufacturing the grooves on the negative electrode sheet by using laser processing technology, functional groups such as hydroxyl and carboxyl groups can be introduced. The specific process includes the following steps: (1) if the negative active material is graphite: first, high-energy photons bombard the surface of graphite, generating local high temperature. A part of the graphite is directly vaporized, and another part of the graphite reacts with oxygen to produce CO2. At the same time, water molecules in the air or hydrogen (H) atoms on the surface of graphite react to generate hydroxyl (-OH) or carboxyl (-COOH) due to the effect of local high temperature after graphite cracking. (2) if the negative active material is silicon material: first, high-energy photons bombard the surface of silicon material, vaporize the surface atoms of silicon material and cause them to react with oxygen ions to generate Si-O bonds. The above Si-O bonds form a silicon oxide (SiO2) layer on the surface of the silicon material. At the same time, some oxygen ions react with hydrogen (H) atoms on the surface of the silicon material to generate hydroxyl (-OH) or carboxyl (-COOH). The separator includes a modified base film, and the surface of the modified base film includes carboxyl, hydroxyl, epoxy or amino functional groups. During the hot pressing of the secondary battery, the above functional groups can interact with the hydroxyl, carboxyl and other functional groups introduced by the negative electrode sheet during the manufacturing of the groove structure by using laser processing technology. For example, the above functional groups can be connected on the surface of the modified base film by grafting. Specifically, for hydroxyl or carboxyl, esterification can occur during the dehydration process at high temperature to obtain ester groups, i.e. R-OH + R'COOH → R-O-CO-R' + H2O; for epoxy, curing reaction can occur with hydroxyl during the high temperature process, i.e. O=CH-CH2-O + HO-R” → HO-CH2-CH2-O-R”; for amino, dehydration polymerization can occur with hydroxyl, i.e. R”'-NH2 + R””-OH → R”'-NHR”” + H2O; such polymerization reactions can provide molecular forces, which can improve the adhesion between the separator and the negative electrode sheet, expand the practical application ability of laser processing technology in the manufacturing process of the negative electrode sheet, and improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the adhesion between the separator and the negative electrode sheet is high, the separator can not include a bonding layer, the amount of adhesive in the separator is reduced, and the gap between the negative electrode sheet and the separator is reduced, which is beneficial to the transmission of lithium ions, improves the kinetic performance of the secondary battery, and also can improve the energy density of the secondary battery. When the number of moles of the first functional group on the surface of the modified base film per unit area is too large, for example, greater than 4 mmol / cm 2 , the adhesion between the separator and the negative electrode sheet is too strong, which can affect the rapid transmission of lithium ions, leading to more serious lithium precipitation, which is not conducive to the improvement of the cycle stability of the secondary battery; when the number of moles of the first functional group on the surface of the modified base film per unit area is too small, for example, less than 1 mmol / cm 2, the functional groups on the surface of the modified base film interact less with the functional groups such as hydroxyl groups and carboxyl groups introduced by the laser processing technology when manufacturing the groove structure on the negative electrode sheet, cannot provide higher molecular forces, cannot effectively improve the adhesion between the separator and the negative electrode sheet, and cannot improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. When the surface energy of the separator is too large, for example, greater than 300 mJ / m 2 , the first functional groups on the surface of the modified base film are too many, the interaction between the separator and lithium ions will be enhanced, affecting the transmission speed of lithium ions, which will cause the degree of lithium precipitation to increase, affecting the cycle stability of the secondary battery. When the surface energy of the separator is too small, for example, less than 50 mJ / m 2 On the one hand, it indicates that the first functional groups on the surface of the modified base film are too few, the adhesion between the separator and the negative electrode sheet is poor, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation cannot be improved. On the other hand, it also indicates that the affinity between the separator and the electrolyte is too poor, which will affect the wettability of the electrolyte.

[0032] Therefore, when the laser processing technology is used to construct grooves on the negative electrode sheet, by adjusting the type, the number of moles per unit area of the first functional groups on the surface of the modified base film, and the surface energy of the separator within the scope of the present application, the electrolyte has good wettability, and at the same time, the functional groups on the surface of the modified base film can interact with the functional groups introduced by the laser processing technology during the process of manufacturing the groove structure on the negative electrode sheet to form molecular forces, improve the adhesion between the separator and the negative electrode sheet, expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the secondary battery also has good kinetic performance and high energy density.

[0033] In some embodiments of the present application, 0.01≤n / γ≤0.05. Illustratively, the value of n / γ can be 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, or a range composed of any two of the above values. By adjusting the value of n / γ within the above range, the number of moles of the functional groups on the surface of the modified base film is more moderate, the surface energy of the separator is relatively high, the functional groups on the surface of the modified base film can interact with the functional groups introduced by the laser processing technology during the process of manufacturing the groove structure on the negative electrode sheet to form molecular forces, further improve the adhesion between the separator and the negative electrode sheet, further expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and further improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the kinetic performance and energy density of the secondary battery are further improved.

[0034] In some embodiments of the present application, the contact angle of the separator with water is θ°, 0≤θ≤90. Exemplarily, the value of θ can be 0, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or a range between any two of the above values. In the present application, the contact angle refers to the angle between the solid-liquid interface, the interior of the liquid, and the gas-liquid interface, as shown in Figure 1 The contact angle of the separator with water is θ°, which refers to the angle between the separator-water interface, the interior of the water, and the air-water interface. The contact angle of the separator with water is within the above range, which indicates that the separator has good wettability to the electrolyte, is conducive to the transmission of lithium ions, and has good adhesion, which can improve the cycle stability and rate performance of the secondary battery.

[0035] In some embodiments of the present application, the material of the modified base film includes at least one of polyamide, polypropylene, or polyethylene. The above base film has a low glass transition temperature, high chemical stability, and low possibility of shrinkage at high temperature, which can improve the safety performance of the secondary battery.

[0036] In some embodiments of the present application, the thickness of the separator is h1μm, 2≤h1≤8. Exemplarily, the value of h1 can be 2, 2.3, 2.5, 2.7, 2.9, 3, 3.3, 3.5, 3.7, 3.9, 4, 4.3, 4.5, 4.7, 4.9, 5, 5.3, 5.5, 5.7, 5.9, 6, 6.3, 6.5, 6.7, 6.9, 7, 7.3, 7.5, 7.7, 7.9, 8, or a range between any two of the above values. By adjusting the thickness of the separator within the above range, the modified base film has a suitable thickness, high chemical stability, low possibility of shrinkage at high temperature, and good mechanical properties, which can improve the safety performance of the secondary battery. In addition, the small thickness of the separator can shorten the transmission distance of lithium ions, which is conducive to the transmission of lithium ions, improves the kinetic performance of the secondary battery, and also enables the secondary battery to have high energy density.

[0037] The type of the separator is not particularly limited in the present application, as long as it can achieve the purpose of the present application. For example, the type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

[0038] In the present application, the surface energy of both surfaces of the separator is increased after the base film is modified. In some embodiments of the present application, the separator can further include an inorganic layer disposed on one surface of the modified base film. The inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application, for example, the inorganic particles can include at least one of aluminum oxide (AI2O3), silicon dioxide (SiO2), magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide (ZrO2), yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, for example, the binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, styrene butadiene rubber, or polyvinylidene fluoride. The coating weight of the inorganic layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the coating weight of the inorganic layer can be 1.5 mg / 1540.25 mm 2 to 3 mg / 1540.25 mm 2 In the present application, when the separator includes a modified base film and an inorganic layer, the inorganic layer is disposed opposite to the positive electrode material layer.

[0039] The method for preparing the modified base film is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the method for preparing the modified base film including a surface comprising a carboxyl functional group can include the following steps: performing surface modification treatment on an unmodified base film with an acid solution to obtain a modified base film including a surface comprising a carboxyl functional group. The acid solution is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the acid solution can include at least one of sulfuric acid, hydrochloric acid, or a mixed solution of sulfuric acid and hydrogen peroxide. The concentration of sulfuric acid or hydrochloric acid is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the concentration of sulfuric acid can be 0.1 mol / L to 18 mol / L; the concentration of hydrochloric acid can be 0.1 mol / L to 18 mol / L. The volume ratio of sulfuric acid to hydrogen peroxide in the mixed solution of sulfuric acid and hydrogen peroxide is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the volume ratio of sulfuric acid to hydrogen peroxide can be 5:1 to 10:1. Specifically, the method for preparing the modified base film including a surface comprising a carboxyl functional group can include the following steps: immersing the unmodified base film in the sulfuric acid, hydrochloric acid, or the mixed solution of sulfuric acid and hydrogen peroxide, heating at 50°C to 80°C for 6h to 16h, taking out the base film and performing vacuum drying, the temperature for vacuum drying is 60°C to 120°C, the time for vacuum drying is 12h to 24h, to obtain the modified base film including a surface comprising a carboxyl functional group.

[0040] For example, the method for preparing the modified base film having the surface including the hydroxyl functional group can include the steps of immersing the unmodified base film in HNO3 having a mass fraction of 35 wt% to 75 wt%, heating at 60°C to 120°C for 6h to 24h, washing with deionized water until neutral (pH value reaches 7), taking out the base film and performing vacuum drying, the temperature of the vacuum drying being 60°C to 120°C, the time of the vacuum drying being 12h to 24h, to obtain the modified base film having the surface including the hydroxyl functional group.

[0041] For example, the method for preparing the modified base film having the surface including the epoxy functional group can include the steps of immersing the unmodified base film in a glycidyl methacrylate (GMA) aqueous solution having a mass fraction of 5 wt% to 10 wt%, heating at 70°C to 90°C for 6h to 24h, taking out the base film and performing vacuum drying, the temperature of the vacuum drying being 60°C to 120°C, the time of the vacuum drying being 6h to 24h, to obtain the modified base film having the surface including the epoxy functional group. The glycidyl methacrylate aqueous solution contains ammonium persulfate (APS) having a mass fraction of 1 wt% to 10 wt%.

[0042] For example, the method for preparing the modified base film having the surface including the amino functional group can include the steps of immersing the unmodified base film in a 3-aminopropyltriethoxysilane (APTES) aqueous solution having a mass fraction of 2 wt% to 10 wt%, heating at 60°C to 90°C for 6h to 24h, then washing with ethanol, and then drying at 80°C to 120°C for 1h to 8h, to obtain the modified base film having the surface including the amino functional group.

[0043] For example, the method for preparing the modified base film having the surface including the ester functional group can include the steps of immersing the unmodified base film in a methyl methacrylate (MMA) monomer solution having a mass fraction of 10 wt% to 20 wt%, heating at 50°C to 120°C for 3h to 24h, and then removing homopolymer by Soxhlet extraction with acetone for 24h to 48h, to obtain the modified base film having the surface including the ester functional group. The methyl methacrylate monomer solution contains a mixed solvent of ethanol and water, and the mass ratio of ethanol to water in the mixed solvent is 1:9 to 3:1. The methyl methacrylate monomer solution contains dibenzoyl peroxide (BPO) having a mass fraction of 1 wt% to 12 wt%.

[0044] In the present application, the modified base film having the surface including the above-described functional group has more excellent hydrophilic properties and has a smaller contact angle with water than the unmodified base film.

[0045] The preparation method of the separator is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, when the separator includes a modified base film and an inorganic layer, the preparation method of the separator can include the following steps: after mixing the inorganic particles and the binder, a solvent is added and stirred uniformly to obtain an inorganic layer slurry; the inorganic layer slurry is coated on one surface of the modified base film, and dried to obtain a separator with an inorganic layer coated on one surface. The mass ratio of the inorganic particles and the binder is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the mass ratio of the inorganic particles and the binder can be (0.02:1) to (0.2:1). The solvent is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the solvent can include at least one of N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or tetramethylsilane (TMS). The solid content of the inorganic layer slurry is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the solid content of the inorganic layer slurry can be 20 wt% to 48 wt%.

[0046] The way of regulating the number of moles per unit area of the functional groups on the surface of the modified base film is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, when the surface of the modified base film includes carboxyl functional groups, the number of moles per unit area of the functional groups on the surface of the modified base film can be regulated by regulating the heating time. For example, when the surface of the modified base film includes hydroxyl functional groups, the number of moles per unit area of the functional groups on the surface of the modified base film can be regulated by regulating the mass fraction of the acid. For example, when the surface of the modified base film includes epoxy functional groups, the number of moles per unit area of the functional groups on the surface of the modified base film can be regulated by regulating the heating time. For example, when the surface of the modified base film includes amino functional groups, the number of moles per unit area of the functional groups on the surface of the modified base film can be regulated by regulating the heating temperature. For example, when the surface of the modified base film includes ester functional groups, the number of moles per unit area of the ester functional groups on the surface of the modified base film can be regulated by regulating the number of moles per unit area of the hydroxyl and carboxyl functional groups on the surface of the modified base film and / or the number of moles per unit area of the hydroxyl and carboxyl functional groups on the surface of the groove.

[0047] The way of regulating the surface energy of the separator is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the surface energy of the separator can be regulated by regulating the type, the treatment temperature, the treatment time, and the number of moles per unit area of the functional groups on the surface of the modified base film.

[0048] The method of regulating the value of n / γ is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the value of n / γ can be regulated by regulating the respective values of n and γ, and the regulation method of n and γ is as described above.

[0049] The method for regulating the contact angle of the separator with water is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the contact angle of the separator with water can be regulated by regulating the number of moles and the type of functional groups per unit area on the surface of the modified base film.

[0050] In some embodiments of the present application, as shown in Figure 2 The plurality of grooves 100 extend along a first direction and are arranged at intervals along a second direction; the first direction is the extension direction of the grooves, that is, the Y direction, and the second direction is the arrangement direction of the grooves, that is, the X direction; as shown in Figure 3 In the cross section of the negative electrode material layer along the thickness direction (that is, the Z direction) of the negative electrode material layer, the maximum size of a single groove along the second direction is L1 μm, L1 refers to the size of the groove on the surface of the negative electrode material layer, and the minimum size of a single groove is L2 μm, 20≤L1≤300, and 10≤L2≤200. Exemplarily, the value of L1 can be 20, 30, 50, 60, 80, 100, 120, 140, 150, 160, 180, 200, 220, 240, 250, 260, 280, 300, or a range composed of any two of the above values; the value of L2 can be 10, 30, 50, 70, 90, 100, 110, 130, 150, 170, 190, 200, or a range composed of any two of the above values. By regulating the maximum size and the minimum size of a single groove along the second direction within the above range, the electrolyte wettability is better, and the surface area of the groove constructed on the negative electrode plate by the laser processing technology is larger, there are more moles of functional groups such as hydroxyl and carboxyl on the surface of the groove, the above functional groups interact with the functional groups on the surface of the modified base film, form molecular forces, further improve the adhesion between the separator and the negative electrode plate, further expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode plate, and further improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, while further improving the kinetic performance and energy density of the secondary battery.

[0051] In some embodiments of the present application, the first direction and the second direction can be perpendicular at 90°. As shown in Figure 2 The first direction (Y direction) and the second direction (X direction) are perpendicular at 90°. In some embodiments of the present application, the angle between the first direction and the second direction can not be equal to 90°. As shown in Figure 4 The angle between the first direction (Y direction) and the second direction (X direction) is not equal to 90°.

[0052] In some embodiments of the present application, the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and the electrode assembly in a wound structure can be obtained by winding, folding or other operations as needed. In some embodiments of the present application, when the electrode assembly is in a wound structure, the negative electrode material layer of the negative electrode sheet is provided with a plurality of grooves, as shown in FIG. 1A, the plurality of grooves extend along a first direction and are arranged at intervals along a second direction, the first direction is the extension direction of the grooves, and it can be understood that the first direction is also the width direction of the negative electrode sheet after being unfolded; the second direction is the arrangement direction of the grooves; and it can be understood that the second direction is also the length direction of the negative electrode sheet after being unfolded. In the cross section of the negative electrode material layer along the thickness direction thereof, along the second direction, the maximum size of a single groove is L1 μm, and the minimum size of a single groove is L2 μm, 20≤L1≤300, and 10≤L2≤200. Figure 2

[0053] In some embodiments of the present application, when the electrode assembly is in a wound structure, the negative electrode material layer of the negative electrode sheet is provided with a plurality of grooves, as shown in FIG. 1A, the plurality of grooves extend along a first direction and are arranged at intervals along a second direction, the first direction is the extension direction of the grooves, and it can be understood that the first direction is also the width direction of the negative electrode sheet after being unfolded; the second direction is the arrangement direction of the grooves; and it can be understood that the second direction is also the length direction of the negative electrode sheet after being unfolded. In the cross section of the negative electrode material layer along the thickness direction thereof, along the second direction, the maximum size of a single groove is L1 μm, and the minimum size of a single groove is L2 μm, 20≤L1≤300, and 10≤L2≤200. Figure 5

[0054] ​​In some embodiments of the present application, 1≤L1 / L2≤1.5. For example, the value of L1 / L2 can be 1, 1.12, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26, 1.28, 1.3, 1.32, 1.34, 1.36, 1.38, 1.4, 1.42, 1.44, 1.46, 1.48, 1.5, or a range consisting of any two of the above values. By regulating the value of L1 / L2 within the above range, the wettability can be effectively improved while minimizing the damage to the negative electrode surface caused by laser etching, reducing the mass loss of the negative electrode, and making the energy density loss of the secondary battery relatively small. In addition, there are functional groups such as hydroxyl and carboxyl groups with a large number of moles on the surface of the groove. The above functional groups interact with the functional groups on the surface of the modified base film to form molecular forces, further improving the adhesion between the diaphragm and the negative electrode sheet, further expanding the practical application capabilities of laser processing technology in the manufacturing process of the negative electrode sheet, and further improving the purple spot problem caused by adhesion failure and the cycle failure problem caused by lithium plating, while further improving the kinetic performance and energy density of the secondary battery.

[0055] In some embodiments of the present application, Figure 3 As shown, along the second direction, i.e., the X direction, the spacing between two adjacent grooves is A1 μm, 2≤A1≤50. For example, the value of A1 can be 2, 5, 7, 9, 10, 12, 15, 17, 19, 20, 22, 25, 27, 29, 30, 32, 35, 37, 39, 40, 42, 45, 47, 49, 50, or a range consisting of any two of the above values. In this application, the spacing between two adjacent grooves refers to the shortest distance from the edge of the upper surface of one groove to the edge of the upper surface of another adjacent groove. By regulating the distance between two adjacent grooves within the above range, the distance between two adjacent grooves is smaller, the number of grooves and / or the surface area of ​​the grooves on the negative electrode material layer are larger, the electrolyte wettability is better, and there are functional groups such as hydroxyl groups and carboxyl groups with a large number of moles on the groove surface. The above functional groups interact with the functional groups on the surface of the modified base film to form molecular forces, further improving the adhesion between the diaphragm and the negative electrode sheet, further expanding the practical application capabilities of laser processing technology in the manufacturing process of the negative electrode sheet, and further improving the purple spot problem caused by adhesion failure and the cycle failure problem caused by lithium plating, while further improving the kinetic performance and energy density of the secondary battery.

[0056] In some embodiments of the present application, the ratio of the grooving area S1 of the plurality of grooves on the surface of the negative electrode material layer to the total area S2 of the surface of the negative electrode material layer is Z, 5%≤Z×100%≤40%, preferably, 10%≤Z×100%≤30%. Exemplarily, the value of Z×100% can be 5%, 10%, 13%, 15%, 17%, 19%, 20%, 23%, 25%, 27%, 29%, 30%, 33%, 35%, 37%, 39%, 40%, or a range formed by any two of the above values. By adjusting the value of Z×100% within the above range, the ratio of the grooving area of the plurality of grooves on the surface of the negative electrode material layer to the total area of the surface of the negative electrode material layer is higher, the number and / or the surface area of the grooves on the negative electrode material layer are larger, the electrolyte wettability is better, and there are more functional groups such as hydroxyl and carboxyl on the surface of the grooves. The functional groups on the surface of the grooves interact with the functional groups on the surface of the modified base film to form molecular forces, further improve the adhesion between the separator and the negative electrode sheet, further expand the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet, and further improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, while further improving the kinetic performance and energy density of the secondary battery.

[0057] In some embodiments of the present application, 0.02≤Z / n≤0.35. Exemplarily, the value of Z / n can be 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.07, 0.09, 0.1, 0.2, 0.3, 0.35, or a range formed by any two of the above values. By adjusting the value of Z / n within the above range, the number and / or the surface area of the grooves on the negative electrode material layer are larger, the electrolyte wettability is better, and there are more functional groups such as hydroxyl and carboxyl on the surface of the grooves. The number of the functional groups such as hydroxyl and carboxyl on the surface of the grooves matches the number of the functional groups on the surface of the modified base film, the interaction between the functional groups on the surface of the grooves and the functional groups on the surface of the modified base film is more sufficient, molecular forces are formed, the adhesion between the separator and the negative electrode sheet is further improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is further expanded, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are further improved, while the kinetic performance and energy density of the secondary battery are further improved.

[0058] In some embodiments of the present application, the cross-sectional shape of the groove includes a square, a rectangle, or a trapezoid. In some embodiments of the present application, as shown in FIG. 1A, the cross-sectional shape of the groove is a square, and the length of the side of the square is a. In some embodiments of the present application, as shown in FIG. 1B, the cross-sectional shape of the groove is a rectangle, and the length of the long side of the rectangle is a and the length of the short side of the rectangle is b. In some embodiments of the present application, as shown in FIG. 1C, the cross-sectional shape of the groove is a trapezoid, and the length of the long side of the trapezoid is a, the length of the short side of the trapezoid is b, and the height of the trapezoid is c. Figure 3As shown, the cross-sectional shape of the groove is trapezoidal. The cross-sectional shape of the groove satisfies the above characteristics, the surface area of the groove is large, the electrolyte wettability is good, and there are a large number of functional groups such as hydroxyl groups and carboxyl groups on the surface of the groove. The above functional groups interact with the functional groups on the surface of the modified base film to form molecular forces, further improving the adhesion between the separator and the negative electrode sheet, further expanding the practical application ability of the laser processing technology in the negative electrode sheet manufacturing process, and further improving the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation. At the same time, the kinetic performance and energy density of the secondary battery are further improved.

[0059] In the present application, the thickness direction of the negative electrode material layer is the Z direction. It can be understood that the size of a single groove in the Z direction is the depth of a single groove, and the size of the negative electrode material layer in the Z direction is the thickness of the negative electrode material layer. In some embodiments of the present application, as shown in Figure 3 As shown, the depth of a single groove is H2 μm, 2≤H2≤60. In some embodiments of the present application, as shown in Figure 3 As shown, the thickness of the negative electrode material layer is H1 μm, 10≤H1≤150. The thickness H1 of the above-mentioned negative electrode material layer refers to the thickness of the negative electrode material layer after cold pressing. In some embodiments of the present application, 5≤H1 / H2≤30.

[0060] The present application does not have special restrictions on the way of regulating the maximum size of a single groove, the minimum size of a single groove, the slotting area S1 of a plurality of grooves on the surface of the negative electrode material layer, and the cross-sectional shape of the groove, as long as the purpose of the present application can be achieved. For example, the maximum size of a single groove, the minimum size of a single groove, the slotting area S1 of a plurality of grooves on the surface of the negative electrode material layer, and the cross-sectional shape of the groove can be regulated by regulating the laser frequency, laser power, and laser processing time in the laser processing technology. The present application does not have special restrictions on the laser processing time and laser power in the laser processing technology, as long as the purpose of the present application can be achieved. For example, the laser processing time can be 0.1 s to 2 s; the laser power can be 120 W to 1200 W.

[0061] The present application does not have special restrictions on the method of regulating the value of L1 / L2, as long as the purpose of the present application can be achieved. Illustratively, the value of L1 / L2 can be regulated by regulating the value of L1 and L2 respectively, and the regulation method of L1 and L2 is as described above.

[0062] In some embodiments of the present application, the surface formed along the first direction and the second direction, a single groove can be a straight line type, an oblique line type, a broken line type or a curve type.

[0063] In some embodiments of the present application, the distribution position of the groove can be the area of the negative material layer region, the area of 1 / 10 to 1 / 2 of the edge of the negative electrode tab, or the corner area of the negative electrode tab.

[0064] In some embodiments of the present application, the adhesion between the separator and the negative material layer is F N / m, and 5≤F≤40. Exemplarily, the value of F can be 5, 10, 20, 23, 25, 27, 29, 30, 33, 35, 37, 39, 40, or a range composed of any two of the above values. By adjusting the adhesion between the separator and the negative material layer within the above range, the adhesion between the separator and the negative material layer is higher, the adhesion between the separator and the negative electrode tab is better, which can better improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, and at the same time improve the kinetic performance and energy density of the secondary battery.

[0065] In some embodiments of the present application, when at least one functional group of carboxyl, hydroxyl, epoxy or amino is provided on one surface of the modified base film, compared to the case where the surface of the modified base film including the above functional group is arranged opposite to the negative material layer provided with the groove, when the surface of the modified base film including the above functional group is arranged opposite to the positive electrode tab, the adhesion between the separator and the negative electrode tab is relatively poor.

[0066] In some embodiments of the present application, when at least one functional group of carboxyl, hydroxyl, epoxy or amino is provided on one surface of the modified base film, preferably, the surface of the modified base film including the above functional group is arranged opposite to the negative material layer provided with the groove, which further improves the adhesion between the separator and the negative electrode tab, further broadens the practical application ability of the laser processing technology in the manufacturing process of the negative electrode tab, and further improves the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, and at the same time further improves the kinetic performance and energy density of the secondary battery.

[0067] In some embodiments of the present application, when at least one functional group of carboxyl, hydroxyl, epoxy or amino is provided on both surfaces of the modified base film, not only the adhesion between the separator and the negative electrode tab can be further improved, but also the adhesion between the separator and the positive electrode tab can be improved, which can further broaden the practical application ability of the laser processing technology in the manufacturing process of the negative electrode tab, further improve the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation, and at the same time further improve the kinetic performance and energy density of the secondary battery.

[0068] The application does not have a particular restriction on the way of regulating the adhesion between the separator and the negative material layer, as long as the purpose of the application can be achieved. For example, the adhesion between the separator and the negative material layer can be regulated by regulating the number of moles per unit area of the first functional group on the surface of the modified base film and / or the number of moles of the functional groups such as hydroxyl, carboxyl, etc. on the groove surface.

[0069] In some embodiments of the application, the negative material layer comprises a negative active material, the negative active material comprises at least one of graphite, a silicon material or lithium titanate, and the silicon material comprises at least one of elemental silicon, silicon oxide or silicon carbide. The graphite comprises at least one of natural graphite or artificial graphite. The above-mentioned negative active material is selected and applied to a secondary battery, and the secondary battery has good cycle stability, kinetic performance and high energy density.

[0070] The application does not have a particular restriction on the negative current collector, as long as the purpose of the application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper or a composite current collector. Exemplarily, the composite current collector can be 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.

[0071] In some embodiments of the application, the negative material layer can further comprise a conductive agent and a negative binder. The application does not have a particular restriction on the type of conductive agent and negative binder, as long as the purpose of the application can be achieved. For example, the conductive agent can include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned conductive carbon black can include but is not limited to at least one of Super P, acetylene black or Ketjen black. The above-mentioned carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include but are not limited to vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal materials can include but are not limited to metal powder and / or metal fibers, and specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer can include but is not limited to at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene or polypyrrole. For example, the negative binder can be at least one of the above-mentioned binders. The application does not have a particular restriction on the mass ratio of the negative active material, the conductive agent and the negative binder in the negative material layer, and the person skilled in the art can select according to the actual needs, as long as the purpose of the application can be achieved.

[0072] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent, a negative electrode binder, and a thickening agent. The present application does not have a particular limitation on the types of the conductive agent, the negative electrode binder, and the thickening agent as long as the purpose of the present application can be achieved. For example, the conductive agent and the negative electrode binder can be at least one of the above-mentioned conductive agents and the above-mentioned binders. The thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not have a particular limitation on the mass ratio of the negative electrode active material, the conductive agent, the negative electrode binder, and the thickening agent in the negative electrode material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0073] The present application does not have a particular limitation on the thickness of the negative electrode current collector as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0074] Optionally, the negative electrode tab can further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The present application does not have a particular limitation on the composition of the conductive layer, which can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The present application does not have a particular limitation on the conductive agent and the binder in the conductive layer, which can be at least one of the above-mentioned conductive agents and the above-mentioned binders.

[0075] In the present application, the secondary battery further includes a positive electrode tab, and the positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned “positive electrode material layer disposed on at least one surface of the positive electrode current collector” means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be disposed on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the “surface” here can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector. The present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0076] The present application does not have a particular limitation 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 can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc.

[0077] The positive electrode material layer includes a positive electrode active material. The present application does not have a particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (for example, NCM811, NCM622, NCM523, NCM111), lithium manganese oxide, lithium nickel oxide, or lithium iron phosphate.

[0078] The positive electrode material layer can further include a conductive agent and a positive electrode binder. The type of the conductive agent and the positive electrode binder is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the conductive agent and the positive electrode binder can be at least one of the above-described conductive agent and the above-described binder. The mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode material layer is not particularly limited in the present application, and can be selected by a person skilled in the art according to the actual needs, as long as the object of the present application can be achieved.

[0079] The thickness of the positive electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness H3 of the positive electrode material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, 40 μm ≤ H3 ≤ 100 μm.

[0080] Optionally, the positive electrode sheet can further include a conductive layer between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and can be at least one of the above-described conductive agent and the above-described binder.

[0081] In the present application, the secondary battery further includes an electrolyte including a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiAlCl4, Li2SiF6, LiCl, lithium bis(oxalato)borate (LiBOB), LiBr, or lithium difluoroborate. For example, LiPF6 is selected as the lithium salt, because LiPF6 has a higher ionic conductivity and can improve the cycle stability of the secondary battery. The content of the lithium salt in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved.

[0082] The non-aqueous solvent is not particularly limited as long as the object of the present application can be achieved, for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, or an aprotic solvent. The carbonate compound can include at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate compound can include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The ester-based compound can include at least one of methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valerolactone, methylvaleronolactone, hexanolactone, or methyl formate. The ether-based compound can include at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The ketone-based compound can include cyclohexanone. The alcohol-based compound can include at least one of ethanol or isopropyl alcohol. The aprotic solvent can include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a phosphate ester. The content of the non-aqueous solvent in the electrolyte is not particularly limited as long as the object of the present application can be achieved.

[0083] The secondary battery also includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte solution, and other components known in the art of secondary batteries, which are not limited by the present application. The case is not particularly limited by the present application and can be any case known in the art as long as the purpose of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be metal, which is not particularly limited by the present application and can be any metal known in the art as long as the purpose of the present application is achieved. The flexible case can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, or the like.

[0084] The secondary battery is not particularly limited by the present application and can include any device that undergoes an electrochemical reaction. In the present application, the secondary battery can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.

[0085] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited by the present application. For example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and performing operations such as winding, folding, or the like as needed to obtain an electrode assembly in a wound structure, placing the electrode assembly in the case, injecting the electrolyte solution into the case and sealing it to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in order, and then the four corners of the entire stack structure can be fixed with adhesive tape to obtain an electrode assembly in a stack structure, the electrode assembly can be placed in the case, the electrolyte solution can be injected into the case and sealed to obtain the secondary battery. In addition, a current overprotection element, a guide plate, or the like can also be placed in the case as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0086] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the preceding embodiments. Thus, the electronic device provided by the present application has good use performance.

[0087] The electronic device is not particularly limited by the present application and can be any electronic device known in the art. In some embodiments of the present application, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, and the like.

[0088] Examples

[0089] Hereinafter, examples and comparative examples are cited to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0090] Test method and apparatus:

[0091] Separator sampling method:

[0092] The lithium ion battery was discharged at a constant current of 0.5C to a discharge cutoff voltage at 25°C, the lithium ion battery was disassembled under an argon atmosphere, and the separator was soaked in dimethyl carbonate solvent, washed several times and dried at 60°C for 1 h to obtain the separator. In the examples and comparative examples of the present application, the discharge cutoff voltage of the lithium ion battery was 3.0V. It can be understood that when the voltage range marked on the factory battery packaging is 3.0V to 4.5V, the charge cutoff voltage is 4.5V and the discharge cutoff voltage is 3.0V. The lithium ion battery of the present application as an example has a charge cutoff voltage of 4.5V and a discharge cutoff voltage of 3.0V.

[0093] The X-ray photoelectron spectroscopy (XPS) test, the surface energy test of the separator, the contact angle test of the separator and water, and the surface energy test of the separator were all tested using the separator obtained in the above manner.

[0094] X-ray photoelectron spectroscopy (XPS) test:

[0095] The number of moles per unit area of functional groups on the surface of the separator was tested by XPS, and the functional groups were hydroxyl, carboxyl, amino, ester, and epoxy. Sample pretreatment: Take a 2cm x 2cm separator, clean the separator with acetone and ethanol in sequence and vacuum dry, transfer under argon protection to prevent contamination, and obtain the pretreated separator sample. Then the above separator sample was tested by XPS, Al Kα monochromatic source (1486.6eV) was used for high resolution O1s scanning (528eV to 536eV), the pass energy was set to 10eV, and the surface composition of the sample was calculated by electron gun and low-energy Ar +The charge in the beam is neutralized. In the peak fitting, the characteristic peak of the hydroxyl group is located at 531.0 eV to 532.5 eV, the characteristic peak of the carboxyl group is located at 531.8 eV to 532.5 eV, the characteristic peak of the amino group is located at 532.0 eV to 533.0 eV, the characteristic peak of the ester group is located at 533.2 eV to 533.8 eV, and the characteristic peak of the epoxy group is located at 532.8 eV to 533.5 eV. The content ratio of the above functional groups is calculated by the ratio of the functional group characteristic peak area to the total area of the O1s XPS spectrum. In the test, the X-ray exposure time needs to be controlled (<15 min / point) and the surface sensitivity is improved by using 80° grazing incidence, and the data reliability is verified by using SiO2 or TiO2 standard sample. The calculation is carried out according to the following formula:

[0096] The number of moles of oxygen atoms per unit area on the surface of the separator = XPS scanning area × XPS test thickness × surface density of the separator / molar mass of the separator × mass ratio of oxygen atoms on the surface of the separator;

[0097] The number of moles of functional groups per unit area on the surface of the separator = functional group content ratio × the number of moles of oxygen atoms per unit area on the surface of the separator.

[0098] Wherein, the mass ratio of oxygen atoms on the surface of the separator is obtained by XPS test; the molecular formula of each substance in the separator is obtained by XPS test of the mass ratio of each atom, and the molar mass of the separator is calculated.

[0099] The number of moles of hydroxyl and carboxyl functional groups per unit area on the surface of the groove is tested:

[0100] The number of moles of hydroxyl and carboxyl functional groups per unit area on the surface of the groove is tested by XPS. First, the area containing grooves on the negative electrode sheet after laser grooving is cut into a small piece of 5mm×5mm, and nitrogen is blown to dry to prevent pollution; during the test, the XPS spot is aligned with the groove surface, the C1s spectrum (280eV-295eV) is scanned, the energy is set to 20eV, and the charge correction is carried out with C-C peak (284.8eV) as the reference. In the peak fitting of C1s spectrum, the hydroxyl group (C-OH) is located at 286.2eV to 286.5eV, and the carboxyl group (-COOH) is located at 288.8eV to 289.2eV. The C-C peak position (284.8eV) needs to be fixed first, the peak width of the hydroxyl group is about 1.1 times that of the C-C peak, and the peak width of the carboxyl group is about 1.3 times that of the C-C peak. The calculation is carried out according to the following formula:

[0101] The number of moles of carbon atoms on the surface of the groove = XPS test thickness × groove surface area × surface density of the negative electrode material layer / molar mass of carbon atoms;

[0102] The number of moles of hydroxyl functional groups on the surface of the groove = (the area of the hydroxyl peak in the C1s spectrum ÷ the total area of the peaks in the C1s spectrum) × 100% × the number of moles of carbon atoms on the surface of the groove;

[0103] Moles of hydroxyl functional groups per unit area of the groove surface = moles of hydroxyl functional groups of the groove surface / groove surface area, unit: mmol / pm 2 ;

[0104] Moles of carboxyl functional groups of the groove surface = (carboxyl peak area of C1s spectrum ÷ total peak area of C1s spectrum) x 100% x moles of carbon atoms of the groove surface;

[0105] Moles of carboxyl functional groups per unit area of the groove surface = moles of carboxyl functional groups of the groove surface / groove surface area, unit: mmol / pm 2 ;

[0106] Wherein, the groove surface area is calculated by the maximum size of a single groove L1, the minimum size of a single groove L2, and the depth of a single groove H2, which are obtained by the following method: the maximum size of a single groove L1, the minimum size of a single groove L2, the distance between two adjacent grooves A1, and the depth of a single groove H2 test.

[0107] Surface energy test of the separator:

[0108] First, clean and dry the surface of the separator to ensure no contaminants; then use a contact angle measuring instrument to drop 3 pL of water on the surface of the separator, record the droplet shape by a high-speed camera and calculate the contact angle; repeat the measurement at least 5 different positions and take the average value; finally, according to the Owens-Wendt or Van Oss theoretical model, substitute the contact angle data into the formula: the surface energy of the separator = the dispersion component of water (intermolecular non-polar interaction) + the polarity component (intermolecular polarity interaction, such as hydrogen bond) = √(21.8 x S^d x contact angle) + √(51.0 x S^p x contact angle). In the formula, S^d and S^p represent the actual test dispersion component and polarity component, respectively, which are directly given by the instrument according to the actual drop quality, the test needs to be completed in a constant temperature (23 ± 1 ℃) and humidity (50 ± 5% RH) environment, and the accuracy can reach ± 0.1 mJ / m 2 .

[0109] Contact angle test of the separator and water:

[0110] The sessile drop method is used to test the contact angle of the separator and water. First, lay the separator flat on the substrate (so that the separator remains flat), then drop 0.02 mL of water onto the separator sample, the image of the droplet is taken by a high-resolution camera, and the angle is measured automatically by software using an optical contact angle measuring instrument, and the test result is the contact angle of the separator and water.

[0111] The maximum size L1 of a single groove, the minimum size L2 of a single groove, the spacing A1 of two adjacent grooves, the depth H2 of a single groove are tested:

[0112] The lithium ion battery is disassembled, the negative electrode sheet is taken out, the negative electrode sheet is cleaned with DMC, and then the negative electrode sheet is dried. The dried negative electrode sheet is cut into a negative electrode sheet sample with a size of 10 mm x 10 mm.

[0113] The spacing A1 of two adjacent grooves on the negative electrode sheet is tested by a scanning electron microscope (SEM, model ZEISS Sigma / X-max). The test conditions are: an acceleration voltage of 10 kV, a grating of 10 spot, a working distance of 10 mm, and a magnification of 10,000 times. A scanning electron microscope image of the surface of the negative electrode material layer is obtained. The shortest distance from the edge of the upper surface of one groove to the edge of the upper surface of the adjacent groove is observed and measured, which is the spacing A1 of two adjacent grooves.

[0114] The cross section of the negative electrode sheet is prepared by ion beam cross section grinding (CP), and the maximum size L1 of a single groove, the minimum size L2 of a single groove, and the depth H2 of a single groove on the negative electrode sheet are tested by a scanning electron microscope (SEM, model ZEISS Sigma / X-max). The test conditions are: an acceleration voltage of 10 kV, a grating of 10 spot, a working distance of 10 mm, and a magnification of 5000 times. A scanning electron microscope image of the cross section of the negative electrode sheet is obtained. The maximum size L1 of a single groove, the minimum size L2 of a single groove, and the depth H2 of a single groove are observed and measured. The value of L1 / L2 can be calculated.

[0115] The grooving area S1 of a plurality of grooves on the surface of the negative electrode material layer, the total area S2 of the surface of the negative electrode material layer, and the Z value are tested:

[0116] The cross section of the negative electrode sheet is prepared by ion beam cross section grinding (CP), and the maximum size L1 of a single groove on the negative electrode sheet is tested by a scanning electron microscope (model ZEISS Sigma / X-max). The test conditions are: an acceleration voltage of 10 kV, a grating of 10 spot, a working distance of 10 mm, and a magnification of 5000 times. A scanning electron microscope image of the cross section of the negative electrode sheet is obtained. The maximum size L1 of a single groove is observed and measured. Then the length of the groove is tested using a steel ruler, as shown in Figure 2 The length of the groove is the size of the groove along the first direction (Y direction). Then the length and width of the negative electrode material layer are tested using a steel ruler, as shown in Figure 2As shown, the width of the negative material layer is the dimension of the negative material layer along the first direction (Y direction), and the length of the negative material layer is the dimension of the negative material layer along the second direction (X direction). S1 = L1 x length of the groove x number of grooves, S2 = length of the negative material layer x width of the negative material layer, and the value of Z can be obtained by calculation.

[0117] Adhesion test between the separator and the negative material layer:

[0118] The lithium ion battery was discharged at 0.2C constant current to 3.0V, at which time the lithium ion battery was fully discharged, and then the lithium ion battery was disassembled, and the separator and negative electrode sheet adhered together were taken out. The separator and negative electrode sheet adhered together were cut into a sample with a width of 30mm and a length of 100mm, and the sample was peeled off along the second direction by a special separator adhesion test tension machine (model QT-6203), to obtain the adhesion between the separator and the negative material layer. The tensile speed was 50mm / min, the tensile displacement was 50mm, and the angle between the separator and the negative electrode sheet along the second direction was 180°.

[0119] Lithium precipitation performance test:

[0120] The voltage range marked on the factory battery packaging was used as the reference, for example, when the factory battery was marked with a voltage range of 3.0V to 4.5V, the charging cutoff voltage was 4.5V and the discharge cutoff voltage was 3.0V.

[0121] After charging the lithium ion batteries of the examples and the comparative examples using the following charging process at a test environment temperature of 25℃, the lithium ion batteries were disassembled and the interface of the negative electrode sheet was observed. The charging process was as follows: the lithium ion battery was charged at 2C constant current to 4.5V, and charged at 4.5V constant voltage to 0.05C.

[0122] In order to describe the lithium precipitation of the interface of the negative electrode sheet, the interface condition was classified: the image of the surface of the negative electrode sheet was collected, the lithium precipitation area of the surface was calculated using image recognition method, and the ratio of the lithium precipitation area to the total area was taken as the lithium precipitation area ratio. If the lithium precipitation area ratio of the negative electrode sheet ≤0.5%, it was determined that the negative electrode sheet had no lithium precipitation; if the negative electrode sheet had a lithium precipitation area, the lithium precipitation color was slight, and 0.5% < lithium precipitation area ratio ≤8%, it was determined that the negative electrode sheet had slight lithium precipitation; if the lithium precipitation area ratio of the negative electrode sheet appeared ≥15%, it was determined that the negative electrode sheet had serious lithium precipitation; and the rest was determined as moderate lithium precipitation of the negative electrode sheet.

[0123] Cycle stability test:

[0124] The voltage range marked on the battery packaging at the factory is used as the reference, for example, when the battery marked at the factory has a voltage range of 3.0V to 4.5V, the charging cut-off voltage is 4.5V and the discharging cut-off voltage is 3.0V.

[0125] At a test environment temperature of 25°C, the lithium ion batteries of the examples and the comparative examples were charged and discharged using the following charge and discharge procedure, and the discharge capacity of the first cycle and the discharge capacity of the 1000th cycle of the lithium ion batteries were recorded. The discharge capacity of the 1000th cycle of the lithium ion battery divided by the discharge capacity of the first cycle of the lithium ion battery is the capacity retention rate of the lithium ion battery after 1000 cycles. The charge and discharge procedure is as follows:

[0126] Step (1): the lithium ion battery was charged at 2C constant current to 4.5V, and charged at 4.5V constant voltage to 0.05C;

[0127] Step (2): stand for 5 minutes;

[0128] Step (3): discharge at 0.5C constant current to 3.0V;

[0129] Step (4): stand for 5 minutes;

[0130] Step (5): cycle the above steps (1) to (4) for 1000 cycles.

[0131] Example 1-1

[0132] <Preparation of positive electrode sheet>

[0133] The positive active material lithium cobaltate (LiCoO2), the positive electrode binder polyvinylidene fluoride (PVDF) and the conductive agent Super P were mixed in a weight ratio of 97.6:1.3:1.1, then N-methyl pyrrolidone (NMP) was added as the positive electrode solvent, and the mixture was stirred and mixed uniformly to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 70wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and was subjected to drying treatment at 120°C for 1h to obtain a positive electrode sheet coated with a positive electrode material layer with a thickness of 100μm on one surface. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both surfaces. After drying at 120°C under vacuum conditions for 1h, cold pressing, cutting and slitting, a positive electrode sheet with a specification of 42mm×86mm was obtained. The compaction density of the cold pressing process was 4.2g / cm 3 .

[0134] <Preparation of negative electrode sheet>

[0135] The negative active material artificial graphite, the negative binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC-Na) are mixed according to a weight ratio of 98:1:1, deionized water is added as a negative solvent, and the mixture is stirred and uniformly mixed to obtain a negative slurry, wherein the solid content of the negative slurry is 75 wt%. The negative slurry is uniformly coated on one surface of a negative current collector copper foil with a thickness of 5 μm, and is dried at 120 °C to obtain a negative electrode sheet coated with a negative material layer with a thickness of 150 μm on one surface. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative material layer on both surfaces. After drying under vacuum at 120 °C for 1 h, cold pressing, sheet cutting, and slitting, a negative electrode sheet with a size of 44 mm x 88 mm is obtained. After cold pressing, the thickness H1 of the negative material layer is 115 μm.

[0136] Then, a laser processing technique is used to construct grooves on both surfaces of the negative electrode sheet, the laser frequency is 600 Hz, the laser power is 800 W, and the laser processing time is 0.7 s, to obtain a negative electrode sheet provided with a plurality of grooves on both surfaces. In the cross section of the negative material layer along the thickness direction of the negative material layer, along the second direction, the maximum size L1 of a single groove is 132 μm, the minimum size L2 of a single groove is 110 μm, L1 / L2 = 1.2, the pitch A1 of two adjacent grooves is 30 μm, the grooving area S1 of the plurality of grooves on the surface of the negative material layer is 774 mm 2 , the total area S2 of the surface of the negative material layer is 3872 mm 2 , Z x 100% = 20%, since a laminated structure is used, S2 here is the total area of a single negative electrode sheet; the depth H2 of a single groove is 35 μm; and the cross-sectional shape of the groove is trapezoidal.

[0137] <Preparation of electrolyte>

[0138] In an argon glove box with a water content of less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), and vinylene carbonate are mixed in a mass ratio of 8:85:5:2 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added and uniformly mixed to obtain an electrolyte. The mass percentage of lithium salt based on the mass of the electrolyte is 8%, and the balance is the base solvent.

[0139] <Preparation of separator>

[0140] The unmodified base film polyethylene is immersed in 65wt% HNO3, heated at 80°C for 12h, washed with deionized water until neutral (pH value reaches 7), the base film is taken out and vacuum dried, the temperature of vacuum drying is 60°C, and the time of vacuum drying is 12h, to obtain a modified base film with surface including hydroxyl functional groups. The above modified base film is used as the separator. The thickness h1 of the separator is 5μm.

[0141] <Preparation of lithium ion battery>

[0142] The above prepared positive electrode sheet, separator, negative electrode sheet, and separator are stacked in sequence, with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, to obtain an electrode assembly. After welding the tab, the electrode assembly is placed in an aluminum plastic film shell, dried, and then injected with electrolyte, and then subjected to vacuum packaging, standing, formation, degassing, and edge cutting processes to obtain a lithium ion battery.

[0143] Example 1-2

[0144] Except that the separator is prepared according to the following method, the rest is the same as Example 1-1.

[0145] <Preparation of separator>

[0146] The unmodified base film polyethylene is immersed in 6mol / L sulfuric acid, heated at 80°C for 12h, the base film is taken out and vacuum dried, the temperature of vacuum drying is 60°C, and the time of vacuum drying is 12h, to obtain a modified base film with surface including carboxyl functional groups. The above modified base film is used as the separator. The thickness h1 of the separator is 5μm.

[0147] Example 1-3

[0148] Except that the separator is prepared according to the following method, the rest is the same as Example 1-1.

[0149] <Preparation of separator>

[0150] The unmodified base film polyethylene is immersed in a mixed solution of 4.5mol / L sulfuric acid and 35wt% HNO3, heated at 80°C for 16h, the base film is taken out and vacuum dried, the temperature of vacuum drying is 60°C, and the time of vacuum drying is 12h, to obtain a modified base film with surface including hydroxyl and carboxyl functional groups. The mass ratio of 4.5mol / L sulfuric acid to 35wt% HNO3 is 1:1. The above modified base film is used as the separator. The thickness h1 of the separator is 5μm.

[0151] Example 1-4

[0152] Except that the separator is prepared according to the following method, the rest is the same as Example 1-1.

[0153] <Preparation of the separator>

[0154] The unmodified base film polyethylene was immersed in a 5wt% aqueous solution of glycidyl methacrylate (GMA) and heated at 70°C for 12h. The base film was removed and vacuum dried at 70°C for 10h to obtain a modified base film having epoxy functional groups on the surface. The aqueous solution of glycidyl methacrylate contained 1wt% of ammonium persulfate (APS). The modified base film was used as the separator. The thickness h1 of the separator was 5μm.

[0155] Examples 1-5

[0156] The separator was prepared according to the following method, and the rest was the same as Example 1-1.

[0157] <Preparation of the separator>

[0158] The unmodified base film polyethylene was immersed in a 2wt% aqueous solution of 3-aminopropyltriethoxysilane (APTES) and heated at 60°C for 6h. The film was then washed with ethanol and vacuum dried at 80°C for 1h to obtain a modified base film having amino functional groups on the surface. The modified base film was used as the separator. The thickness h1 of the separator was 5μm.

[0159] Examples 1-6 to 1-7

[0160] The rest was the same as Example 1-1 except that the relevant preparation parameters were adjusted according to Table 1.

[0161] Examples 1-8 to 1-9

[0162] The rest was the same as Example 1-1 except that the number of moles per unit area of the first functional groups on the surface of the modified base film was adjusted by adjusting the mass fraction of nitric acid as shown in Table 1.

[0163] Examples 1-10 to 1-13

[0164] The rest was the same as Example 1-1 except that the relevant preparation parameters were adjusted according to Table 1.

[0165] Example 1-14

[0166] The rest was the same as Example 1-1 except that the separator was prepared according to the following method and the inorganic layer was arranged opposite the positive electrode material layer in the preparation of the lithium ion battery.

[0167] <Preparation of the separator>

[0168] The unmodified base film polyethylene was immersed in a solution of 65wt% HNO3 and 20wt% methyl methacrylate (MMA) monomer solution mixed solution, heated at 120°C for 24h, washed with deionized water until neutral (pH value reached 7), the base film was taken out and vacuum dried, the vacuum drying temperature was 60°C, the vacuum drying time was 12h, to obtain a modified base film with surface including hydroxyl and ester functional groups. Among them, the mass ratio of 65wt% HNO3 and 20wt% MMA monomer solution was 1:2. The solvent in the above methyl methacrylate monomer solution was a mixed solvent of ethanol and water, and the mass ratio of ethanol and water in the mixed solvent was 1:9. The above methyl methacrylate monomer solution contains 1wt% of dibenzoyl peroxide (BPO). The above modified base film is used as a separator. Among them, the thickness h1 of the separator is 5μm. 2 The thickness of the inorganic layer is 1μm, and the thickness h1 of the separator is 6μm.

[0169] Examples 1-15

[0170] Except that the separator was prepared according to the following method, the rest was the same as Example 1-1.

[0171] <Preparation of the separator>

[0172] The unmodified base film polyethylene was immersed in a solution of 65wt% HNO3 and 20wt% methyl methacrylate (MMA) monomer solution mixed solution, heated at 120°C for 24h, washed with deionized water until neutral (pH value reached 7), the base film was taken out and vacuum dried, the vacuum drying temperature was 60°C, the vacuum drying time was 12h, to obtain a modified base film with surface including hydroxyl and ester functional groups. Among them, the mass ratio of 65wt% HNO3 and 20wt% MMA monomer solution was 1:2. The solvent in the above methyl methacrylate monomer solution was a mixed solvent of ethanol and water, and the mass ratio of ethanol and water in the mixed solvent was 1:9. The above methyl methacrylate monomer solution contains 1wt% of dibenzoyl peroxide (BPO). The above modified base film is used as a separator. Among them, the thickness h1 of the separator is 5μm.

[0173] Examples 2-1 to 2-11

[0174] Except that the relevant preparation parameters were adjusted according to Table 2, the rest was the same as Example 1-3.

[0175] Comparative Example 1-1

[0176] Except that the separator and lithium ion battery were prepared according to the following method, the rest was the same as Example 1-1.

[0177] <Preparation of the separator>

[0178] The binder polyvinylidene fluoride (PVDF) was dissolved in solvent NMP to prepare a binder layer slurry with a solid content of 45 wt%. The binder layer slurry was coated on one surface of a polyethylene-based film using a manual draw coater, and dried at 70°C for 10 min to obtain a separator with a binder layer on one side. The coating weight of the binder layer was 1.4 mg / 1540.25 cm 2 , the thickness of the binder layer was 1 μm, the thickness of the separator was 6 μm, and the thickness of the base film was 5 μm.

[0179] <Preparation of a lithium ion battery>

[0180] The positive electrode sheet, the separator, the negative electrode sheet, and the separator prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator, and the binder layer of the separator was arranged opposite the negative electrode material layer provided with grooves. The stack was placed in an aluminum-plastic film housing after the tab was welded, and after drying, electrolyte was injected. The lithium ion battery was obtained after the processes of vacuum packaging, standing, formation, degassing, and edge cutting.

[0181] Comparative Example 1-2

[0182] Except that an unmodified polyamide-based film was used as the separator, the rest was the same as in Example 1-1.

[0183] Comparative Example 1-3

[0184] Except that an unmodified polypropylene-based film was used as the separator, the rest was the same as in Example 1-1.

[0185] Comparative Example 1-4

[0186] Except that an unmodified polyethylene-based film was used as the separator, the rest was the same as in Example 1-1.

[0187] Comparative Examples 1-5 to 1-6

[0188] Except that the number of moles of functional groups per unit area on the surface of the modified base film was as shown in Table 1 by adjusting the mass fraction of nitric acid, the rest was the same as in Example 1-1.

[0189] Comparative Example 2-1

[0190] Except that a mechanical etching method was used to construct grooves on both surfaces of the negative electrode sheet in the <Preparation of a negative electrode sheet>, the rest was the same as in Example 1-3.

[0191] Comparative Example 2-2

[0192] Except that the negative electrode sheet was not treated using laser processing technology, the rest was the same as in Example 1-3.

[0193] Comparative Examples 2-3 to 2-4

[0194] The rest is the same as Examples 1-3, except that the relevant preparation parameters are adjusted according to Table 2.

[0195] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1-2.

[0196] Table 1

[0197]

[0198]

[0199] Note: In Table 1, " / " means no relevant preparation parameter.

[0200] As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-6, when grooves are constructed on the negative electrode sheet by using laser processing technology, by regulating the type of the first functional group on the surface of the modified base film, the number of moles per unit area, and the surface energy of the separator, the adhesion between the separator and the negative electrode material layer is higher within the scope of the present application, the degree of lithium precipitation of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density. The base film of Comparative Example 1-1 is not modified and the separator also includes a bonding layer, the base film of Comparative Examples 1-2 to 1-4 is not modified, the number of moles per unit area of the functional group on the surface of the modified base film of Comparative Examples 1-5 to 1-6 and the surface energy of the separator are not within the scope of the present application, the adhesion between the separator and the negative electrode material layer is lower, the degree of lithium precipitation of the prepared lithium ion battery is severe, the capacity retention rate after 500 cycles is lower, which indicates that the adhesion between the separator and the negative electrode sheet is lower, the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are more serious, the kinetic performance of the lithium ion battery is poorer, and the energy density is lower.

[0201] The material of the modified base film can affect the safety performance of the lithium ion battery. As can be seen from Examples 1-1, 1-6 to 1-7, the material of the modified base film is within the scope of the present application, the adhesion between the separator and the negative electrode material layer is higher, the degree of lithium precipitation of the prepared lithium ion battery is slight, and the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0202] The value of n / γ affects the lithium precipitation performance, cycle stability, kinetic performance, and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-15, by adjusting n / γ within the range of the present application, the adhesion between the separator and the negative electrode material layer is high, the lithium precipitation degree of the prepared lithium ion battery is slight, and the capacity retention rate after 500 cycles is high, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0203] The contact angle of the separator with water affects the cycle stability and rate performance of the lithium ion battery. As can be seen from Examples 1-1 to 1-15, by adjusting the contact angle of the separator with water within the range of the present application, the adhesion between the separator and the negative electrode material layer is high, the lithium precipitation degree of the prepared lithium ion battery is slight, and the capacity retention rate after 500 cycles is high, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0204] The thickness of the separator affects the safety performance, kinetic performance, and energy density of the lithium ion battery. As can be seen from Examples 1-1, 1-10 to 1-14, the thickness of the separator is within the range of the present application, the adhesion between the separator and the negative electrode material layer is high, the lithium precipitation degree of the prepared lithium ion battery is slight, and the capacity retention rate after 500 cycles is high, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0205]

[0206] As can be seen from Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-4, when the laser processing technology is used to construct the grooves on the negative electrode sheet, by regulating the type, the number of moles per unit area of the first functional groups on the surface of the modified base film and the surface energy of the separator within the scope of the present application, the adhesion between the separator and the negative electrode material layer is higher, the degree of lithium precipitation of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density. Comparative Example 2-1 uses a mechanical etching method to construct grooves on both surfaces of the negative electrode sheet, the negative electrode sheet of Comparative Example 2-2 is not processed by the laser processing technology, and the number of moles per unit area of the first functional groups on the surface of the modified base film of Comparative Examples 2-3 to 2-4 is not within the scope of the present application, the adhesion between the separator and the negative electrode material layer is lower, the degree of lithium precipitation of the prepared lithium ion battery is serious, the capacity retention rate after 500 cycles is lower, which indicates that the adhesion between the separator and the negative electrode sheet is lower, the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are more serious, the kinetic performance of the lithium ion battery is poorer, and the energy density is lower.

[0207] The maximum size of a single groove and the minimum size of a single groove can affect the lithium precipitation performance, cycle stability, kinetic performance and energy density of the lithium ion battery. As can be seen from Examples 1-3 and 2-1 to 2-4, when the maximum size of a single groove and the minimum size of a single groove are within the scope of the present application, the adhesion between the separator and the negative electrode material layer is higher, the degree of lithium precipitation of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0208] The value of L1 / L2 can affect the lithium precipitation performance, cycle stability, kinetic performance and energy density of the lithium ion battery. As can be seen from Examples 1-3 and 2-1 to 2-4, when the value of L1 / L2 is within the scope of the present application, the adhesion between the separator and the negative electrode material layer is higher, the degree of lithium precipitation of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0209] The ratio Z of the slotted area S1 of the plurality of grooves on the surface of the negative material layer to the total area S2 of the surface of the negative material layer will affect the lithium precipitation performance, cycle stability, kinetic performance and energy density of the lithium ion battery. As can be seen from Examples 1-3, Examples 2-1 to 2-6, within the scope of the present application, the adhesion between the separator and the negative material layer is higher, the lithium precipitation degree of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0210] The value of Z / n will affect the lithium precipitation performance, cycle stability, kinetic performance and energy density of the lithium ion battery. As can be seen from Examples 1-3, Examples 2-1 to 2-7, Examples 2-10, and Examples 2-11, within the scope of the present application, the adhesion between the separator and the negative material layer is higher, the lithium precipitation degree of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0211] The cross-sectional shape of the groove will affect the lithium precipitation performance, cycle stability, kinetic performance and energy density of the lithium ion battery. As can be seen from Examples 1-3, Examples 2-3, and Examples 2-8, within the scope of the present application, the adhesion between the separator and the negative material layer is higher, the lithium precipitation degree of the prepared lithium ion battery is slight, the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet can be improved, the practical application ability of the laser processing technology in the manufacturing process of the negative electrode sheet is widened, and the purple stain problem caused by adhesion failure and the cycle failure problem caused by lithium precipitation are improved, and the lithium ion battery also has good kinetic performance and high energy density.

[0212] As can be seen from Examples 1-3 and Example 2-9, the adhesion between the separator and the negative material layer is higher, the lithium precipitation degree of the prepared lithium ion battery is slight, and the capacity retention rate after 500 cycles is higher, which indicates that the adhesion between the separator and the negative electrode sheet is higher, and the lithium ion battery has good cycle stability, kinetic performance and high energy density.

[0213] It is to be noted that, in the present document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily implying any actual relationship or order between such entities or actions. Also, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0214] Various embodiments of the present specification are described in a related manner, and the same or similar parts between various embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0215] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery comprising a negative electrode plate and a separator, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer has a plurality of grooves, and the surfaces of the grooves include at least one of hydroxyl and carboxyl functional groups; The diaphragm includes a modified base film, the surface of the modified base film includes a first functional group, the first functional group is at least one of a carboxyl group, a hydroxyl group, an epoxy group, an amino group, or an ester group; the number of moles per unit area of ​​the first functional group on the surface of the modified base film is n mmol / cm 2 , the surface energy of the membrane is γmJ / m 2 , 1≤n≤4, 50≤γ≤300.

2. The secondary battery according to claim 1, wherein 0.01≤n / γ≤0.

05.

3. The secondary battery according to claim 1, wherein The contact angle between the membrane and water is θ°, 0≤θ≤90.

4. The secondary battery according to claim 1, wherein The material of the modified base film includes at least one of polyamide, polypropylene or polyethylene.

5. The secondary battery according to claim 1, wherein The thickness of the separator is h1 μm, 2≤h1≤8.

6. The secondary battery according to claim 1, wherein The plurality of grooves extend along a first direction and are spaced apart along a second direction; the first direction is an extending direction of the grooves, and the second direction is an arrangement direction of the grooves; In a cross section of the negative electrode material layer along its thickness direction, along the second direction, the maximum size of a single groove is L1 μm, the minimum size of a single groove is L2 μm, 20≤L1≤300, 10≤L2≤200.

7. The secondary battery according to claim 6, wherein 1≤L1 / L2≤1.

5.

8. The secondary battery according to claim 6, wherein A ratio of a groove area S1 of the plurality of grooves on the surface of the negative electrode material layer to a total surface area S2 of the negative electrode material layer is Z, and 5%≤Z×100%≤40%.

9. The secondary battery according to claim 8, wherein 10％≤Z×100％≤30％。 10. The secondary battery according to claim 8, wherein 0.02≤Z / n≤0.

35.

11. The secondary battery according to claim 6, wherein The cross-sectional shape of the groove includes square, rectangle or trapezoid.

12. The secondary battery according to claim 1, wherein The bonding force between the separator and the negative electrode material layer is FN / m, 5≤F≤40.

13. The secondary battery according to claim 1, wherein The negative electrode material layer includes a negative electrode active material. The negative electrode active material includes at least one of graphite, silicon material, or lithium titanate. The silicon material includes at least one of elemental silicon, silicon oxide, or silicon carbide. 14 . An electronic device comprising the secondary battery according to claim 1 .

Images