Negative electrode plate, battery, battery pack, and electronic device

Abstract

The present application provides a negative electrode plate, a battery, a battery pack, and an electronic device. The negative electrode plate comprises a current collector, and a negative electrode active material layer provided on at least one functional surface of the current collector. The negative electrode active material layer comprises graphite and a binder. The negative electrode plate satisfies the following expression: a0.98 / b×0.02c+1.2≤X≤a0.98 / b×0.02c+1.4, X being the content of the binder, in units of g / 100 ggraphite, a being the OI value of the graphite, b being the OI value of the negative electrode plate, and c being the D50 of the graphite, in units of μm. The negative electrode plate provided by the present application can have both high peel strength and low resistivity, by means of defining a median particle size of graphite, an OI value, and a relationship between the OI value of the negative electrode plate and an amount of binder.

Description

An anode sheet, a battery, a battery pack, and an electronic device

[0001] The present application claims priority to the Chinese patent application No. 202410897996.4, filed on July 4, 2024, and entitled "An anode sheet, a battery, a battery pack, and an electronic device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium ion batteries, and in particular to an anode sheet, a battery, a battery pack, and an electronic device. BACKGROUND

[0003] Graphite with a hexagonal structure as an active material in a negative electrode material has a wide application in lithium ion batteries. Graphite has a hexagonal layered structure, and during the preparation of the electrode sheet, preferred orientation is easily generated, and the degree of orientation (generally represented by the OI value) will directly affect the diffusion rate of lithium ions. However, the OI value of the traditional graphite negative electrode is generally high, which is not conducive to the diffusion of lithium ions.

[0004] The use of anode sheets with a lower OI value can significantly enhance the electron transport rate and lithium ion diffusion rate of the electrode sheet along its thickness direction. However, as the OI value of the anode sheet decreases, the graphite tends to contact the current collector more, which reduces the peel strength of the anode sheet.

[0005] SUMMARY

[0006] The present application provides an anode sheet that can have both high peel strength and conductivity.

[0007] The present application also provides a battery comprising the above-mentioned anode sheet, which has a low 50% SOC direct current resistance and a high mixing capacity.

[0008] The present application also provides a battery pack comprising the above-mentioned battery, which has high electrical performance and stability.

[0009] The present application also provides an electronic device. Since the electronic device comprises the above-mentioned battery or battery pack, it has excellent electrical performance and a relatively long service life.

[0010] In detail, in a first aspect, the present application provides an anode sheet comprising a current collector and a negative active material layer disposed on at least one functional surface of the current collector; the negative active material layer comprises graphite and a binder, and the anode sheet satisfies the following formula 1: a 0.98 / b x 0.02c + 1.2 ≤ X ≤ a 0.98 / b x 0.02c + 1.4 Formula 1,

[0011] In formula 1, X is the content of the binder, in g / 100g 石墨 ; a is the OI value of the graphite; b is the OI value of the negative electrode sheet; and c is the D50 of the graphite, in μm.

[0012] In an optional embodiment, the mass percentage of the butadiene styrene rubber in the binder is not less than 30wt%.

[0013] In an optional embodiment, the particle size of the graphite satisfies the following formula 2: 1.3≤(D 90 -D 10 ) / c≤4.8 Formula 2,

[0014] In formula 2, D 90 , D 10 are the D 90 50 and D 10 90 of the graphite, respectively.

[0015] In an optional embodiment, the negative electrode sheet further satisfies: 5μm≤c≤19μm.

[0016] In an optional embodiment, c≥12μm.

[0017] In an optional embodiment, the negative electrode sheet further satisfies: 3.5≤a≤21.

[0018] In an optional embodiment, the negative electrode sheet further satisfies: 5≤b≤30.

[0019] In an optional embodiment, the negative electrode active material layer comprises, in mass parts: 87-98 parts of the graphite, 0.9-6 parts of the conductive agent, and 0.4-6 parts of the dispersing agent.

[0020] In a second aspect, the present application provides a battery comprising the negative electrode sheet of the first aspect.

[0021] In a third aspect, the present application provides a battery pack comprising the battery of the second aspect.

[0022] In a fourth aspect, the present application provides an electronic device comprising the battery of the second aspect or the battery pack of the third aspect.

[0023] The negative electrode sheet provided by the present application can have both high peel strength and low resistivity by limiting the median particle size, OI value of the graphite, and the relationship between the OI value of the negative electrode sheet and the content of the binder. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0025] In order to improve the peel strength of the negative electrode sheet without reducing the conductivity thereof, the present application adopts the following technical solutions.

[0026] In a first aspect, the present application provides a negative electrode sheet, comprising a current collector and a negative active material layer arranged on at least one functional surface of the current collector; the negative active material layer comprises graphite and a binder, and the negative electrode sheet satisfies the following formula 1: a 0.98 / b x 0.02c + 1.2 ≤ X ≤ a 0.98 / b x 0.02c + 1.4 Formula 1,

[0027] In formula 1, X is the content of the binder, in units of g / 100g 石墨 ; a is the OI value of the graphite; b is the OI value of the negative electrode sheet; and c is the D50 of the graphite, in units of μm.

[0028] The binder is a non-active component of the negative electrode sheet, and too much addition of the binder will result in a decrease in the specific capacity of the negative electrode sheet, and too little addition of the binder will result in a poor adhesion between the negative active material layers and between the current collector and the negative active material layer, thereby affecting the peel strength of the negative electrode sheet. To solve this problem, the present application limits the size of the D50 of the graphite, the OI value of the graphite, the OI value of the negative electrode sheet, and the relationship between the specific amount of the binder to satisfy the condition of formula 1, so that the negative electrode sheet has both high peel strength and low resistivity. If the amount of the binder is less than the set value of formula 1, the peel strength of the negative electrode sheet is low, and if the amount of the binder is greater than the set value of formula 1, the conductivity of the negative electrode sheet is affected, thereby affecting the battery capacity. The OI value of the electrode sheet mainly affects the peel between the negative active material layer and the current collector, and the smaller the OI value of the electrode sheet, the more the graphite tends to be vertically arranged on the surface of the current collector, resulting in a decrease in the bonding surface between the graphite and the current collector, and thus more binder needs to be added to ensure the peel strength of the electrode sheet. Therefore, the OI value of the negative electrode sheet is negatively correlated with the amount of the binder. The OI value of the graphite mainly affects the peel between the negative active material layers, and the more the binder needed, the greater the OI value of the graphite. Therefore, the OI value of the graphite is positively correlated with the amount of the binder. In addition, generally speaking, the smaller the particle size of the graphite, the greater the surface area, and more binder needs to be added to ensure the peel strength of the electrode sheet. However, compared with the electrode sheet with a low OI value, since the graphite tends to be vertically arranged on the surface of the current collector, the smaller the particle size of the graphite, the more the contact surface between the graphite and the current collector, and thus the amount of the binder needed is not increased or is less. In summary, the particle size of the graphite is positively correlated with the amount of the binder.

[0029] It should be noted that the D50 of the above-mentioned graphite refers to the particle size value corresponding to the cumulative amount of 50% (by volume) in the particle size cumulative distribution curve, which can be regarded as the median particle size of the material, and is generally tested by a laser diffraction particle size distribution instrument; the OI value of the graphite refers to the inherent OI value of the graphite, which can be tested by X-ray diffraction spectrum, the scanning angle is 10-80°, and the OI value of the graphite is the ratio of the 004 characteristic diffraction peak intensity (or integral area) to the 110 characteristic diffraction peak intensity (or integral area), i.e. a = C 石墨 (004) / C 石墨 (110). The OI value of the negative electrode sheet can be tested by X-ray diffraction spectrum of the horizontally placed negative electrode sheet sample, the scanning angle is 10-80°, and the ratio of the 004 characteristic diffraction peak intensity (or integral area) to the 110 characteristic diffraction peak intensity (or integral area) measured is described as the OI value of the negative electrode sheet, i.e. b = C 负极片 (004) / C 负极片 (110). The source of the above-mentioned graphite is not particularly limited in the present application, and the skilled person can select a conventional graphite for electrode materials, for example, natural graphite or artificial graphite.

[0030] The preparation method of the above-mentioned negative electrode sheet is not particularly limited in the present application, and the skilled person can select a magnetic induction method, for example, by a method comprising the following processes:

[0031] 1) First, determine the OI values of the required graphite and negative electrode sheet, then calculate the content of the binder according to formula 1;

[0032] 2) Mix the raw materials such as graphite, binder, etc. and solvent, stir to prepare the primer layer slurry, then coat the primer layer slurry on both sides of the copper foil with a thickness of 8 μm in a magnetic field environment, adjust the magnetic field parameters to make the negative electrode sheet reach the required OI value, then bake the copper foil coated with the slurry in an oven, and then roll, cut to obtain the above-mentioned negative electrode sheet.

[0033] In a preferred embodiment, the mass fraction of the butadiene styrene rubber in the binder is not less than 30 wt%. When the main component of the binder is butadiene styrene rubber, the peel strength and conductivity of the negative electrode sheet can be more optimally guaranteed under the condition of formula 1; further, the mass fraction of the butadiene styrene rubber in the binder is not less than 80 wt%.

[0034] Exemplarily, the above-mentioned binder can also include a binder other than butadiene styrene rubber, including but not limited to at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyvinyl alcohol, and sodium polyacrylate.

[0035] In a preferred embodiment, the particle size of the graphite satisfies the following formula 2: 1.3≤(D 90 -D 10 ) / c≤4.8 Formula 2,

[0036] In formula 2, D 90 , D 10 are D 90 and D 10 of the graphite, respectively.

[0037] This embodiment can further improve the capacity performance and the charge-discharge rate of the battery by limiting the particle size distribution of the graphite. If the particle size distribution of the graphite is too narrow, i.e., (D 90 -D 10 ) / c is less than 1.3, the compaction ability of the negative electrode sheet is affected, and thus the capacity performance of the battery is affected. If the particle size distribution of the graphite is too wide, i.e., (D 90 -D 10 ) / c is greater than 4.8, the close packing effect between the graphite particles is generated, and thus the diffusion of lithium ions in the electrode is affected, and thus the charge-discharge rate of the battery is affected.

[0038] D99 and D10 above represent the particle size values corresponding to the cumulative amounts of 99% and 10% (by volume) in the particle size cumulative distribution curve, which are generally obtained by a laser diffraction particle size distribution instrument.

[0039] For example, (D 90 -D 10 ) / c is specifically any one of 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.36, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.5, 4.7, etc.

[0040] In a preferred embodiment, the negative electrode sheet also satisfies 5 μm≤c≤19 μm. If the D50 of the graphite is reduced, the effective reaction sites for lithium ion intercalation / deintercalation increase, and the lithium ion transmission distance is shorter, which is beneficial to improve the gram capacity of the negative electrode material. However, if the D50 of the graphite is less than 5 μm, the amount of the required binder is relatively large, which affects the conductivity of the negative electrode sheet. However, if the D50 of the graphite exceeds 19 μm, the amount of the binder is insufficient, which affects the peel strength of the negative electrode sheet.

[0041] In a more preferred embodiment, c is greater than or equal to 12 μm, i.e. c is in the range of 12-19 μm, which can make the negative electrode sheet have lower resistivity and higher peel strength. For example, c is specifically any one of 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc.

[0042] As for the D 90 and D 10 of the graphite, the present application does not make specific limitation, as long as it meets the condition of formula 2.

[0043] In a preferred embodiment, the negative electrode sheet further satisfies 3.5≤a≤21. Wherein, a is positively correlated with X, if a is less than 3.5, the amount of binder is less, and the peel strength of the negative electrode sheet is low, if a is greater than 21, the amount of binder is more, which affects the conductivity of the electrode sheet, thereby affecting the capacity of the battery.

[0044] For example, a is specifically any one of 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

[0045] In a preferred embodiment, the negative electrode sheet further satisfies 5≤b≤30. Wherein, b is negatively correlated with X, if b is less than 5, the amount of binder is more, which affects the conductivity of the electrode sheet, thereby affecting the capacity of the battery; if b is greater than 30, the amount of binder is more, which leads to the peel strength of the negative electrode sheet being low.

[0046] For example, b is specifically any one of 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, etc.

[0047] In a preferred embodiment, the negative electrode active material layer comprises, in terms of mass fraction, 87-98 parts of graphite, 0.9-6 parts of conductive agent, and 0.4-6 parts of dispersing agent. Wherein, this embodiment can further optimize the conductivity of the negative electrode sheet by limiting the proportion of components such as graphite.

[0048] For example, the above-mentioned conductive agent is a non-graphite conductive agent, which can be selected from at least one of carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube; the dispersing agent can be selected from at least one of carboxymethyl cellulose, triethylhexyl phosphoric acid, sodium dodecyl sulfate.

[0049] The thickness, the area density, and the thickness of the negative active material layer of the negative electrode sheet are not specifically limited in the present application, but in order to balance the battery capacity, the cycle life, and the energy density, in an embodiment, the thickness of the negative electrode sheet is 40-120 μm, specifically including but not limited to 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, etc.; the area density of the negative electrode sheet is 3-10 mg / cm 2 , specifically including but not limited to 3.5 mg / cm 2 , 4 mg / cm 2 , 4.5 mg / cm 2 , 5 mg / cm 2 , 5.5 mg / cm 2 , 6 mg / cm 2 , 6.5 mg / cm 2 , 7 mg / cm 2 , 7.5 mg / cm 2 , 8 mg / cm 2 , 8.5 mg / cm 2 , 9 mg / cm 2 , 9.5 mg / cm 2 , etc.; and the thickness of the negative active material layer is 20-60 μm, specifically including but not limited to 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, etc.

[0050] In an embodiment, the peeling force between the negative active material layer and the current collector is greater than 0.25 N / m.

[0051] The peeling force between the negative active material layer and the current collector refers to the force required for at least part of the negative active material layer to peel off from the surface of the current collector. The test method of the peeling force can include the following process: bonding a pressure-sensitive adhesive tape on a stainless steel plate, then bonding the negative active material layer of a negative electrode sheet with a fixed area (40 x 100 mm 2 ) on one side of the pressure-sensitive adhesive tape, clamping the negative electrode sheet with a tensile testing machine to perform 180° peeling, and recording the required peeling force at this time.

[0052] As for the material of the current collector, the present application is not specifically limited, for example, it can be selected from any one or several of copper foil, titanium foil, tin foil, chromium foil, and composite foil materials of the above metals, etc.

[0053] In an embodiment, the longitudinal resistivity of the negative electrode sheet is less than 0.8 Ω·m.

[0054] The negative electrode sheet longitudinal resistivity test method can include the following process: cutting the negative electrode sheet into 4x10 cm samples, placing the samples in a resistivity test table, setting the test pressure to 25 KPa, and maintaining the pressure for 20 s, and the test result is the longitudinal resistivity of the electrode sheet.

[0055] The negative electrode sheet preparation method is not particularly limited in the present application, for example, it can be prepared by a method comprising the following process:

[0056] Mixing graphite, conductive agent, binder and solvent to make the solid content of the slurry to 40-50% (by volume), stirring to prepare the primer slurry, then coating the primer slurry on at least one side of the current collector in a magnetic field environment, and then drying; after rolling and cutting, the negative electrode sheet is obtained.

[0057] It can be understood that the purpose of coating and drying in a magnetic field environment in the above method is to change the graphite OI value and / or the OI value of the negative electrode sheet, therefore, the specific parameters of the magnetic field environment can be adjusted by the skilled person according to the required graphite OI value and / or the OI value of the negative electrode sheet.

[0058] In a second aspect, the present application provides a battery comprising the negative electrode sheet of the first aspect.

[0059] It should be noted that the above-mentioned battery can include but is not limited to single battery, battery module, battery pack, etc., i.e., the actual application form of the battery provided by the present application can be but is not limited to the listed products, but also other application forms, when the battery is a single battery, it includes at least one of cylindrical battery, square battery, etc.

[0060] Generally, the above-mentioned battery further comprises a positive electrode sheet, a separator and an electrolyte; the positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder.

[0061] The gram capacity of the positive electrode active material will directly affect the energy density of the battery. The present application does not make special limitation to the positive electrode active material, for example, the positive electrode active material can be selected from the commonly used positive electrode active materials in the art, for example, one or more of lithium cobaltate, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, lithium manganese phosphate, lithium iron phosphate.

[0062] The above-mentioned separator is not particularly limited in the present application, and any known porous structure separator with electrochemical stability and chemical stability can be selected, for example, it can be at least one of glass fiber, non-woven fabric, polyethylene, polypropylene or polyvinylidene fluoride. The separator can be single layer or multi-layer.

[0063] The above-mentioned electrolyte comprises an organic solvent and an electrolyte salt. The organic solvent acts as a medium for transporting ions in electrochemical reactions, and the organic solvent known in the art for battery electrolyte can be used.

[0064] Exemplarily, the organic solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). In a specific embodiment, two or more of the above organic solvents can be selected.

[0065] The electrolyte salt can be at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium nitrate (LiNO3), and lithium fluoride (LiF), which are known electrolyte salts for battery electrolytes.

[0066] The positive electrode sheet, the separator, and the negative electrode sheet can be sequentially stacked to obtain a battery cell, or sequentially stacked and then wound to obtain a battery cell. The battery cell is placed in a packaging battery film shell (such as an aluminum plastic film shell), and an electrolyte is injected and sealed to obtain the battery of the present application.

[0067] In a third aspect, the present application provides a battery pack comprising the battery of the second aspect.

[0068] In a fourth aspect, the present application provides an electronic device comprising the battery of the second aspect or the battery pack of the third aspect.

[0069] It should be noted that the electronic device described above can be any conventional device that requires power, such as, but not limited to, a computer, an electric vehicle, an air conditioner, a refrigerator, a washing machine, a microwave oven, a printer, a fax machine, etc.

[0070] The technical solutions of the present application are further illustrated below in conjunction with specific embodiments. All the parts, percentages, and ratios in the following embodiments are based on weight, and all the reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are commercially available.

[0071] Example 1

[0072] This example provides a negative electrode sheet, which comprises a copper foil and negative electrode active material layers respectively arranged on both surfaces of the copper foil; the thickness of each negative electrode active material layer is 120 μm, and the surface density of the negative electrode sheet is 200 mg / cm 2, the negative active material layer comprises, by mass fraction: 95.7 parts of graphite, 0.96 parts of conductive carbon black, 1.91 parts of carboxymethyl cellulose (CMC) and butadiene-styrene rubber; wherein the butadiene-styrene rubber amount, the OI value of the negative electrode sheet, the OI value of the graphite, and the D50 of the graphite are shown in Table 1; the D90 of the graphite is 4 μm, and the D10 is 16 μm.

[0073] The preparation method of the above negative electrode sheet comprises the following steps:

[0074] The graphite, conductive carbon black, binder and NMP solvent are mixed to make the solid content of the slurry to 45% (by volume), and the base coating slurry is prepared by stirring, and then the base coating slurry is coated on both sides of a copper foil with a thickness of 8 μm in a magnetic field environment, and the copper foil coated with the slurry is baked in an oven; and then the above negative electrode sheet is obtained by rolling and slitting.

[0075] Examples 2-19

[0076] The negative electrode sheet provided is basically the same as that of Example 1, and the only difference is that the parameters shown in Table 1 are changed.

[0077] Example 20

[0078] The negative electrode sheet provided is basically the same as that of Example 1, and the only difference is that the negative active material layer comprises: 87 parts of graphite material, 5.76 parts of conductive carbon black, 5.76 parts of carboxymethyl cellulose and butadiene-styrene rubber; wherein the butadiene-styrene rubber amount, the OI value of the negative electrode sheet, the OI value of the graphite, and the D50 of the graphite are shown in Table 1.

[0079] Example 21

[0080] The negative electrode sheet provided is basically the same as that of Example 1, and the only difference is that, by mass fraction, the negative active material layer comprises: 98 parts of graphite material, 0.27 parts of conductive carbon black, 0.27 parts of sodium carboxymethyl cellulose and butadiene-styrene rubber; wherein the butadiene-styrene rubber amount, the OI value of the negative electrode sheet, the OI value of the graphite, and the D50 of the graphite are shown in Table 1.

[0081] Comparative Examples 1-2

[0082] The negative electrode sheet provided is basically the same as that of Example 1, and the only difference is that the parameters shown in Table 1 are changed.

[0083] Test Example 1

[0084] The peel strength and longitudinal resistivity of the negative electrode sheets of the above examples and comparative examples are tested, and the results are shown in Table 1.

[0085] The peel strength test method is as follows: a pressure-sensitive adhesive tape is bonded on a stainless steel plate, and then a fixed area (40 x 100 mm 2The peel strength is the force at which at least part of the negative active material layer is peeled off from the copper foil when the negative electrode sheet is adhered to the negative side of the negative electrode active material layer of the negative electrode sheet on a pressure-sensitive adhesive tape, and a tensile testing machine grips the negative electrode sheet to perform 180° peeling.

[0086] Longitudinal resistivity test method: the negative electrode sheet is uniformly cut into a sample of 4x10 cm, the sample is placed in a resistivity test table, the test pressure is set to 25 KPa, and the pressure holding time is 20 s, and the test result is the longitudinal resistivity of the electrode sheet.

[0087] Table 1:

[0088] As can be seen from Table 1, compared with the comparative examples, the examples limit the median particle size of graphite, the OI value, and the relationship between the OI value of the negative electrode sheet and the amount of binder, so that the negative electrode sheet can simultaneously have high peel strength and low resistivity.

[0089] Application Example

[0090] The negative electrode sheets of the above examples and comparative examples are assembled into batteries, including the following steps:

[0091] Preparation of the positive electrode sheet: the positive electrode active material LiFePO4, polyvinylidene fluoride and acetylene black are mixed in a weight ratio of 95.7:0.96:1.91, then N-methyl pyrrolidone is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a homogeneous positive electrode slurry (N-methyl pyrrolidone accounts for 55% by volume); the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 8 μm; the coated aluminum foil is baked in an oven with different temperature gradients, and then dried in an oven at 120°C for 8 h, followed by rolling and cutting to obtain the required positive electrode sheet;

[0092] Preparation of the electrolyte: after mixing ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC) in a mass ratio of 2:5:3, 5% of fluoroethylene carbonate (FEC) based on the total mass of the electrolyte and 13% of lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte are added, and the mixture is stirred to obtain the electrolyte

[0093] Assembly of the battery: each battery is composed of one electrode core, and each electrode core is composed of 7 positive electrode sheets, 8 negative electrode sheets and 16 separators.

[0094] Test Example 2

[0095] The 50% SOC direct current resistance and the mixing capacity of the batteries made of the corresponding negative electrode sheets are tested, and the test results are shown in Table 2.

[0096] The 50% SOC direct current resistance test method is as follows: at normal temperature 25±5℃, the battery is discharged at 1 / 3C constant current to 2.0V, charged at 1 / 3C constant current to 50% SOC, and rested for 30min; then discharged at 1.5C constant current for 30s, and the 50% SOC direct current resistance is detected.

[0097] The mixing capacity test method is as follows: at normal temperature 25±5℃, the battery is discharged at 1 / 3C constant current to 2.0V, charged at 1 / 3C constant current to 3.8V, and the current is cut off at 0.05C, and cycled for 3 times; the discharge capacity of the third cycle is the battery capacity, and the mixing capacity is the battery capacity / the positive electrode coating amount.

[0098] Table 2:

[0099] As can be seen from Table 2, compared with the comparative examples, the battery assembled by the negative electrode sheet of the examples has lower 50% SOC direct current resistance and higher mixing capacity.

[0100] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

A negative electrode sheet characterized by comprising: The negative electrode sheet includes a current collector and a negative active material layer provided on at least one functional surface of the current collector; the negative active material layer includes graphite and a binder, and the negative electrode sheet satisfies the following formula 1: a 0.98 / b x 0.02c + 1.2 ≤ X ≤ a 0.98 / b x 0.02c + 1.4 Equation 1, In formula 1, X is the content of the binder, unit: g / 100g 石墨 ; a is the OI value of the graphite; b is the OI value of the negative electrode sheet; c is the D50 of the graphite, unit: pm. The negative electrode sheet according to claim 1, wherein In the binder, the mass ratio of butadiene styrene rubber is not less than 30wt%. The negative electrode sheet according to claim 1 or 2, characterized by The particle size of the graphite satisfies the following formula 2: 1.3 < (D 90 - D 10 ) / c ≤ 4.8 Equation 2, In Equation 2, D 90 D 10 D of graphite 90 and D 10 . The negative electrode sheet according to any one of claims 1 to 3, characterized in that, Also satisfies: 5μm≤c≤19μm. The negative electrode sheet according to claim 4, characterized by c≥12μm. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, Also satisfies: 3.5≤a≤21. The negative electrode sheet according to any one of claims 1 to 6, characterized in that Also satisfies: 5≤b≤30. The negative electrode sheet according to any one of claims 1 to 7, characterized in that According to the mass fraction, the negative active material layer includes: 87-98 parts of graphite, 0.9-6 parts of a conductive agent, and 0.4-6 parts of a dispersing agent. A battery characterized by The negative electrode sheet according to any one of claims 1-8. A battery pack characterized by The battery according to claim 9. An electronic device, characterized by comprising: The battery according to claim 9 or the battery pack according to claim 10.

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