A negative electrode sheet, a battery, a battery pack, and an electronic device

Abstract

The application provides a negative electrode sheet, a battery, a battery pack and an electronic device. The negative electrode sheet comprises a current collector and a negative electrode active material layer arranged on at least one functional surface of the current collector. The negative electrode active material layer comprises graphite and a binder. The negative electrode sheet satisfies the following conditions: a 0.98 / b x 0.02c + 1.2 0.98 / b x 0.02c + 1.4, wherein 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. The negative electrode sheet provided by the application can simultaneously have high peel strength and low resistivity by limiting the median particle size of the graphite, the OI value of the graphite and the relationship between the OI value of the negative electrode sheet and the amount of the binder.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode, a battery, a battery pack, and an electronic device. Background Technology

[0002] Hexagonal graphite, as an active material in negative electrode materials, has a wide application in lithium-ion batteries. Graphite has a hexagonal layered structure, which makes it easy to generate preferred orientation during the electrode preparation process. The degree of orientation (usually expressed by OI value) directly affects the diffusion rate of lithium ions. However, the OI value of traditional graphite negative electrodes is generally high, which is not conducive to the diffusion of lithium ions.

[0003] Using a negative electrode with a lower OI value can significantly enhance the electron transport rate and lithium ion diffusion rate along the thickness direction of the electrode. However, as the OI value of the negative electrode decreases, the graphite tends to contact the current collector at the end face, which reduces the peel strength of the negative electrode. Summary of the Invention

[0004] This invention provides a negative electrode sheet that can have both high peel strength and conductivity.

[0005] The present invention also provides a battery comprising the above-mentioned negative electrode, which has a low 50% SOC DC internal resistance and a high mixed-material capacity.

[0006] The present invention also provides a battery pack including the above-mentioned battery, which has high electrical performance and stability.

[0007] The present invention also provides an electronic device, which, because it includes the above-mentioned battery or battery pack, has superior electrical performance and a relatively long service life.

[0008] In detail, in a first aspect, the present invention provides a negative electrode sheet, comprising a current collector and a negative electrode active material layer disposed on at least one functional surface of the current collector; the negative electrode active material layer comprises graphite and a binder, and the negative electrode sheet satisfies the following formula 1:

[0009] a 0.98 / b×0.02c+1.2≤X≤a 0.98 / b×0.02c+1.4 Equation 1,

[0010] In Formula 1, X represents the content of the binder, in g / 100g. 石墨 a is the OI value of graphite; b is the OI value of the negative electrode; c is the D50 of graphite, in μm.

[0011] In an optional embodiment, the adhesive contains styrene-butadiene rubber at a mass percentage of not less than 30 wt%.

[0012] In an alternative embodiment, the particle size of the graphite satisfies the following formula 2:

[0013] 1.3≤(D 90 -D 10 Equation 2, ) / c≤4.8

[0014] In Equation 2, D 90 D 10 D of graphite 90 and D 10 .

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

[0016] In an alternative implementation, c ≥ 12 μm.

[0017] In an alternative embodiment, the negative electrode also satisfies: 3.5 ≤ a ≤ 21.

[0018] In an alternative embodiment, the negative electrode also satisfies: 5 ≤ b ≤ 30.

[0019] In an optional embodiment, the negative electrode active material layer comprises, by weight, 87-98 parts graphite, 0.9-6 parts conductive agent, and 0.4-6 parts dispersant.

[0020] In a second aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0021] Thirdly, the present invention provides a battery pack comprising the battery described in the second aspect.

[0022] Fourthly, the present invention provides an electronic device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0023] The negative electrode provided by the present invention can simultaneously possess high peel strength and low resistivity by limiting the median particle size of graphite, the OI value, and the relationship between the electrode OI value and the amount of binder. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In order to improve the peel strength of the negative electrode without reducing its conductivity, the present invention adopts the following technical solution:

[0026] In a first aspect, the present invention provides a negative electrode sheet, comprising a current collector and a negative electrode active material layer disposed on at least one functional surface of the current collector; the negative electrode active material layer comprises graphite and a binder, and the negative electrode sheet satisfies the following formula 1:

[0027] a 0.98 / b×0.02c+1.2≤X≤a 0.98 / b×0.02c+1.4 Equation 1,

[0028] In Formula 1, X represents the content of the binder, in g / 100g. 石墨 a is the OI value of graphite; b is the OI value of the negative electrode; c is the D50 of graphite, in μm.

[0029] As an inactive component of the negative electrode, excessive addition of binder will reduce the specific capacity of the negative electrode, while insufficient addition will weaken the adhesion between the layers of the negative electrode active material and between the current collector and the negative electrode active material, affecting the peel strength of the negative electrode. To solve this problem, this invention limits the relationship between the D50 size of graphite, OI value, the OI value of the negative electrode, and the specific amount of binder to satisfy the conditions of Equation 1, so that the negative electrode has both high peel strength and low resistivity. If the amount of binder is less than the value set in Equation 1, the peel strength of the negative electrode will be low, while if it is greater than the value set in Equation 1, it will affect the conductivity of the negative electrode, thereby affecting the battery capacity. Among them, the OI value of the electrode mainly affects the peeling between the negative electrode active material layer and the current collector. The smaller the OI value of the electrode, the more the graphite tends to be vertically aligned on the surface of the current collector, resulting in a reduction in the bonding surface between the graphite and the current collector. More binder needs to be added to ensure the peeling strength of the electrode. Therefore, the OI value of the negative electrode is negatively correlated with the amount of binder. The OI value of graphite mainly affects the peeling between the layers of the negative electrode active material. The larger the OI value of graphite, the more binder is required. Therefore, the OI value of graphite is positively correlated with the amount of binder. In addition, generally speaking, the smaller the graphite particle size, the larger the surface area, and the more binder needs to be added to ensure the peeling strength of the electrode. However, for electrodes with low OI values, since the graphite tends to be vertically aligned on the surface of the current collector, the smaller the graphite particle size, the more contact surface with the current collector. The amount of binder required does not increase or is even less. Taking all factors into account, there is a positive correlation between the graphite particle size and the amount of binder.

[0030] It should be noted that the D50 of graphite mentioned above refers to the particle size value corresponding to 50% (by volume) of the cumulative particle size distribution curve, which can be regarded as the median particle size of the material. It is generally obtained by laser diffraction particle size distribution instrument. The OI value of graphite refers to the inherent OI value of graphite. Graphite can be tested by X-ray diffraction spectroscopy with a scanning angle of 10-80°. The OI value of graphite is the ratio of the intensity (or integrated area) of the 004 characteristic diffraction peak to the intensity (or integrated area) of the 110 characteristic diffraction peak, i.e., a = C. 石墨 (004) / C石墨 (110) The OI value of the negative electrode can be determined by X-ray diffraction testing of a horizontally placed negative electrode sample at a scanning angle of 10–80°. The ratio of the intensity (or integrated area) of the 004 characteristic diffraction peak to the intensity (or integrated area) of the 110 characteristic diffraction peak is described as the OI value of the negative electrode, i.e., b = C. 负极片 (004) / C 负极片 (110). The source of the graphite mentioned above is not particularly limited in this invention. Those skilled in the art may use conventional graphite for electrode materials, such as natural graphite or artificial graphite.

[0031] The present invention does not specifically limit the preparation method of the above-mentioned negative electrode sheet. Those skilled in the art can use the magnetic induction method, for example, by a method including the following processes:

[0032] 1) First determine the required OI values ​​of graphite and negative electrode, and then calculate the binder content according to Equation 1;

[0033] 2) Mix graphite, binder and other raw materials and solvent, stir to prepare a base coating slurry, and then coat the base coating slurry on both sides of a copper foil with a thickness of 8μm 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 slurry in an oven, and then roll and cut to obtain the above negative electrode sheet.

[0034] In a preferred embodiment, the styrene-butadiene rubber (SBR) in the adhesive comprises at least 30 wt% of the material. When the main component of the adhesive is SBR, the conditions of Formula 1 can better guarantee the peel strength and conductivity of the negative electrode sheet; furthermore, the SBR in the adhesive comprises at least 80 wt% of the material.

[0035] For example, the adhesive may also include adhesives other than styrene-butadiene rubber, including but not limited to: at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0036] In a preferred embodiment, the particle size of the graphite satisfies the following formula 2:

[0037] 1.3≤(D 90 -D 10 Equation 2, ) / c≤4.8

[0038] In Equation 2, D 90 D 10 D of graphite 90 and D 10 .

[0039] This embodiment can further improve battery capacity and charge / discharge rate by limiting the particle size distribution of graphite. However, if the particle size distribution of graphite is too narrow (D...),... 90 -D 10 If the ratio of graphite to carbon (D) is less than 1.3, it affects the compaction ability of the negative electrode, thus affecting the capacity of the battery; if the graphite particle size distribution is too wide, i.e., (D) 90 -D 10 When the ratio of ) / c is greater than 4.8, the graphite particles are more tightly packed, which affects the diffusion of lithium ions in the electrode and thus affects the charge and discharge rate of the battery.

[0040] The D99 and D10 values ​​mentioned above represent the particle size values ​​corresponding to 99% and 10% (by volume) of the cumulative particle size distribution curve, respectively, and are generally obtained by testing with a laser diffraction particle size distribution instrument.

[0041] For example, (D 90 -D 10 The value of ) / c is any one of the following: 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.

[0042] In a preferred embodiment, the negative electrode sheet further satisfies the following condition: 5μm ≤ c ≤ 19μm. Lowering the D50 of graphite increases the number of effective reaction sites for lithium-ion insertion / extraction, resulting in a shorter lithium-ion transport distance, which is beneficial for improving the specific capacity of the negative electrode material. However, if the D50 of graphite is less than 5μm, a larger amount of binder is required, affecting the conductivity of the negative electrode sheet. Conversely, if the D50 of graphite exceeds 19μm, insufficient binder is added, affecting the peel strength of the negative electrode sheet.

[0043] In a more preferred embodiment, c ≥ 12 μm, i.e., c is in the range of 12-19 μm, which can give the negative electrode a lower resistivity and a higher peel strength. Exemplarily, c is any value among 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc.

[0044] As for the D of graphite 90 and D 10 The present invention does not impose specific limitations on the value of , as long as it meets the conditions of Equation 2.

[0045] In a preferred embodiment, the negative electrode sheet further satisfies: 3.5 ≤ a ≤ 21. Here, a is positively correlated with X. If a is less than 3.5, the amount of binder used is less, resulting in lower peel strength of the negative electrode sheet. If a is greater than 21, the amount of binder used is more, affecting the conductivity of the electrode sheet and thus impacting the battery capacity.

[0046] For example, 'a' is any value among 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

[0047] In a preferred embodiment, the negative electrode sheet further satisfies: 5 ≤ b ≤ 30. Here, b is positively correlated with negative. If b is less than 5, the amount of binder used is excessive, affecting the conductivity of the electrode sheet and thus impacting the battery capacity. If b is greater than 30, the amount of binder used is excessive, resulting in lower peel strength of the negative electrode sheet.

[0048] For example, b is any value among 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.

[0049] In a preferred embodiment, the negative electrode active material layer comprises, by weight, 87-98 parts graphite, 0.9-6 parts conductive agent, and 0.4-6 parts dispersant. This embodiment further optimizes the conductivity of the negative electrode by limiting the proportions of components such as graphite.

[0050] For example, the conductive agent is a non-graphite conductive agent, such as at least one selected from carbon black, acetylene black, Ketjen black, carbon fiber, and carbon nanotubes; the dispersant can be at least one selected from carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0051] The present invention does not specifically limit the thickness, areal density, and thickness of the negative electrode active material layer of the aforementioned negative electrode sheet. However, in order to balance battery capacity, cycle life, and energy density, in one specific 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 areal density of the negative electrode sheet is 3-10 mg / cm³. 2 Specifically, including but not limited to: 3.5 mg / cm³ 2 4mg / cm 2 4.5 mg / cm 2 5mg / cm 2 5.5 mg / cm 2 6mg / cm 2 6.5 mg / cm2 7mg / cm 2 7.5 mg / cm 2 8mg / cm 2 8.5 mg / cm 2 9mg / cm 2 9.5 mg / cm 2 The thickness of the negative electrode active material layer is 20-60μm, specifically including but not limited to: 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, etc.

[0052] In one specific embodiment, the peel force between the negative electrode active material layer and the current collector is greater than 0.25 N / m.

[0053] The peel force between the negative electrode active material layer and the current collector refers to the force required for at least a portion of the negative electrode active material layer to peel off from the surface of the current collector. The test method for this peel force may include the following procedure: bonding pressure-sensitive tape to a stainless steel plate, and then fixing an area (40 × 100 mm)... 2 The negative electrode active material layer of the negative electrode sheet is bonded to one side of the pressure-sensitive adhesive tape. The tensile testing machine clamps the negative electrode sheet and peels it off at 180°, and records the peeling force required at this time.

[0054] As for the material of the current collector, the present invention does not make specific limitations. For example, it can be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil and composite foils of the above metals.

[0055] In one specific embodiment, the longitudinal resistivity of the negative electrode is less than 0.8 Ω·m.

[0056] The longitudinal resistivity test method for negative electrode sheets may include the following process: cut the negative electrode sheets into 4×10cm samples, place the samples into a resistivity test stage, set the test pressure to 25Kpa, and the holding time to 20s. The test result is the longitudinal resistivity of the electrode sheet.

[0057] The present invention does not specifically limit the method for preparing the negative electrode sheet. For example, it can be prepared by a method including the following process:

[0058] Graphite, conductive agent, binder and solvent are mixed to make the solid content of the slurry reach 40-50% (by volume), and stirred to prepare a base coating slurry. The base coating slurry is then coated on at least one side of the current collector in a magnetic field environment and then dried. After rolling and slitting, the negative electrode sheet is obtained.

[0059] It is understandable that the purpose of coating and drying in a magnetic field environment is to change the OI value of graphite and / or the OI value of the negative electrode. Therefore, the specific parameters of the magnetic field environment can be adjusted by technicians according to the required OI value of graphite and / or the OI value of the negative electrode.

[0060] In a second aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0061] It should be noted that the above-mentioned battery may include, but is not limited to, single cell, battery module, battery pack, etc. That is, the actual application form of the battery provided by the present invention may be, but is not limited to, the listed products, or other application forms. When the battery is a single cell, it includes at least one of cylindrical battery, prismatic battery, etc.

[0062] Generally speaking, the above-mentioned battery also includes a positive electrode, a separator, and an electrolyte; the positive electrode includes a positive electrode active material, a conductive agent, and a binder.

[0063] The specific capacity of the positive electrode active material directly affects the energy density of the battery. This invention does not impose any particular limitation on the positive electrode active material. Exemplarily, the positive electrode active material can be one or more commonly used in the art, such as lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, and lithium iron phosphate.

[0064] This invention does not impose any particular limitation on the aforementioned diaphragm; any known porous diaphragm with electrochemical and chemical stability can be selected, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The diaphragm can be single-layered or multi-layered.

[0065] The electrolyte described above includes an organic solvent and an electrolyte salt. The organic solvent acts as a medium for transporting ions in the electrochemical reaction, and organic solvents known in the art for use in battery electrolytes can be employed.

[0066] For example, 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 specific embodiments, two or more of the above-mentioned organic solvents can be selected.

[0067] The electrolyte salt serves as the ion source and can be any electrolyte salt known in the art for use in battery electrolytes. Exemplarily, 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).

[0068] The above-mentioned positive electrode, separator and negative electrode can be stacked in sequence to obtain a battery cell, or the above-mentioned positive electrode, separator and negative electrode can be stacked in sequence and then wound to obtain a battery cell; the battery cell is placed in a battery packaging film shell (such as an aluminum-plastic film shell), electrolyte is injected into the outer packaging and sealed to prepare the battery of the present invention.

[0069] Thirdly, the present invention provides a battery pack comprising the battery described in the second aspect.

[0070] Fourthly, the present invention provides an electronic device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0071] It should be noted that the aforementioned electronic devices can be any conventional device that requires electricity, such as, but not limited to, computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0072] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. All parts, percentages and ratios recorded in the following embodiments are based on weight. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0073] Example 1

[0074] This example provides a negative electrode sheet, comprising a copper foil and negative electrode active material layers respectively disposed on both surfaces of the copper foil; the thickness of each negative electrode active material layer is 120 μm, and the areal density of the negative electrode sheet is 200 mg / cm³. 2 The negative electrode active material layer comprises, by mass parts: 95.7 parts graphite, 0.96 parts conductive carbon black, 1.91 parts carboxymethyl cellulose (CMC) and styrene-butadiene rubber; wherein, the amount of styrene-butadiene rubber, the OI value of the negative electrode sheet, the OI value of graphite, and the D50 of graphite are shown in Table 1; the D90 of the graphite is 4 μm and the D10 is 16 μm.

[0075] The above-mentioned method for preparing the negative electrode includes the following steps:

[0076] Graphite, conductive carbon black, binder and NMP solvent are mixed to make the solid content of the slurry reach 45% (by volume), and stirred to prepare a base coating slurry. Then the base coating slurry is coated on both sides of a copper foil with a thickness of 8μm in a magnetic field environment. The copper foil coated with slurry is baked in an oven. Then the negative electrode sheet is obtained by rolling and slitting.

[0077] Example 2-19

[0078] The negative electrode provided is basically the same as that in Example 1, except that the parameters shown in Table 1 are changed.

[0079] Example 20

[0080] The provided negative electrode sheet is basically the same as that in Example 1, except that the negative electrode active material layer includes: 87 parts of graphite material, 5.76 parts of conductive carbon black, 5.76 parts of carboxymethyl cellulose and styrene-butadiene rubber; wherein, the amount of styrene-butadiene rubber, the OI value of the negative electrode sheet, the OI value of graphite, and the D50 of graphite are shown in Table 1.

[0081] Example 21

[0082] The provided negative electrode sheet is basically the same as that in Example 1, except that, by weight, the negative electrode active material layer includes: 98 parts of graphite material, 0.27 parts of conductive carbon black, 0.27 parts of sodium carboxymethyl cellulose and styrene-butadiene rubber; wherein, the amount of styrene-butadiene rubber, the OI value of the negative electrode sheet, the OI value of graphite, and the D50 of graphite are shown in Table 1.

[0083] Comparative Examples 1-2

[0084] The negative electrode provided is basically the same as that in Example 1, except that the parameters shown in Table 1 are changed.

[0085] Test Example 1

[0086] The peeling force and longitudinal resistivity of the negative electrode sheets of the above embodiments and comparative examples were tested, and the results are recorded in Table 1.

[0087] The peel force test method involves bonding pressure-sensitive tape to a stainless steel plate, and then fixing the area (40×100mm). 2 The negative electrode active material layer of the negative electrode sheet is bonded to pressure-sensitive tape on one side. The tensile testing machine clamps the negative electrode sheet and peels it off at 180°. The force that at least part of the negative electrode active material layer is peeled off from the copper foil is the peeling force.

[0088] Longitudinal resistivity test method: Cut the negative electrode sheet into 4×10cm samples, place the samples into the resistivity test stage, set the test pressure to 25Kpa, and the holding time to 20s. The test result is the longitudinal resistivity of the electrode sheet.

[0089] Table 1:

[0090]

[0091] As shown in Table 1, compared with the comparative example, the embodiment, by limiting the median particle size of graphite, the OI value, and the relationship between the OI value of the negative electrode and the amount of binder, enables the negative electrode to simultaneously possess high peel strength and low resistivity.

[0092] Application examples

[0093] Assembling the negative electrode sheets of the above embodiments and comparative examples into a battery includes the following steps:

[0094] Preparation of positive electrode sheet: The positive electrode active material LiFePO4, polyvinylidene fluoride and acetylene black were mixed in a weight ratio of 95.7:0.96:1.91, and then N-methylpyrrolidone was added. The mixture was stirred under vacuum until a homogeneous and fluid positive electrode slurry (N-methylpyrrolidone accounted for 55% by volume) was formed. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 8 μm. The coated aluminum foil was baked in ovens at different temperature gradients and then dried in an oven at 120°C for 8 hours. Finally, it was rolled and slit to obtain the desired positive electrode sheet.

[0095] Electrolyte preparation: Ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) were mixed in a mass ratio of 2:5:3. Then, 5% fluoroethylene carbonate (FEC) and 13% lithium hexafluorophosphate (LiPF6) were added to the mixture, and the mixture was stirred to obtain the electrolyte.

[0096] Assemble the battery: Each battery consists of one electrode core, and each electrode core consists of 7 positive electrode sheets, 8 negative electrode sheets and 16 separators prepared as described above.

[0097] Test Example 2

[0098] The DC internal resistance and mixed capacity of the battery made with the corresponding negative electrode sheet at 50% SOC were tested, and the test results are shown in Table 2.

[0099] The 50% SOC DC internal resistance test method is as follows: at room 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 left to stand for 30 minutes; discharged at 1.5C constant current for 30 seconds, and the 50% SOC DC internal resistance is measured.

[0100] Mixed material specific capacity test method: At room temperature (25±5℃), the battery is discharged at 1 / 3C constant current to 2.0V, and then charged at 1 / 3C constant current and constant voltage to 3.8V. The cutoff current is 0.05C, and the cycle is repeated 3 times. The discharge capacity of the third cycle is the battery capacity. Mixed material specific capacity = battery capacity / positive electrode coating amount.

[0101] Table 2:

[0102]

[0103]

[0104] As shown in Table 2, compared with the comparative example, the battery assembled from the negative electrode sheet of the embodiment has a lower 50% SOC DC internal resistance and a higher mixed capacity.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The device includes a current collector and a negative electrode active material layer disposed on at least one functional surface of the current collector; the negative electrode active material layer includes graphite and a binder, and the negative electrode sheet satisfies the following formula 1: a 0.98 / b×0.02c+1.2≤X≤a 0.98 / b×0.02c+1.4 Equation 1, In Formula 1, X represents the content of the binder, in g / 100g. 石墨 a is the OI value of graphite; b is the OI value of the negative electrode; c is the D50 of graphite, in μm. 5μm≤c≤12μm; the particle size of the graphite satisfies the following formula 2: 1.3≤(D 90 -D 10 Equation 2, ) / c≤4.8 In Equation 2, D 90 D 10 D of graphite 90 and D 10 .

2. The negative electrode sheet according to claim 1, characterized in that, The adhesive contains styrene-butadiene rubber at a mass ratio of not less than 30 wt%.

3. The negative electrode sheet according to any one of claims 1-2, characterized in that, It also satisfies: 3.5≤a≤21.

4. The negative electrode sheet according to any one of claims 1-2, characterized in that, It also satisfies: 5≤b≤30.

5. The negative electrode sheet according to any one of claims 1-2, characterized in that, The negative electrode active material layer comprises, by weight, 87-98 parts graphite, 0.9-6 parts conductive agent, and 0.4-6 parts dispersant.

6. The negative electrode sheet according to claim 3, characterized in that, The negative electrode active material layer comprises, by weight, 87-98 parts graphite, 0.9-6 parts conductive agent, and 0.4-6 parts dispersant.

7. The negative electrode sheet according to claim 4, characterized in that, The negative electrode active material layer comprises, by weight, 87-98 parts graphite, 0.9-6 parts conductive agent, and 0.4-6 parts dispersant.

8. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-7.

9. A battery pack, characterized in that, Includes the battery as described in claim 8.

10. An electronic device, characterized in that, Includes the battery as described in claim 8 or the battery pack as described in claim 9.

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