Negative plate and preparation method thereof, battery, battery pack and electronic equipment

Abstract

The invention provides a negative plate and a preparation method thereof, a battery, a battery pack and electronic equipment. The negative plate comprises a negative active material layer; the surface of the negative electrode active material layer comprises N concentric circle stripe lines, an area between the Nth concentric circle stripe line and the (N-1) th concentric circle stripe line is a dispersion area, an area surrounded by the dispersion area is an orientation area, and the negative electrode sheet meets the following relations: 0.8 lt; vC / VQlt; 1, 1.6 < = QOI < = 9, 0.5 < = COIlt; 1.6); wherein VC is the electrolyte infiltration rate of the orientation area with the unit of mm / 100s, VQ is the electrolyte infiltration rate of the dispersion area with the unit of mm / 100s, QOI is the OI value of the dispersion area, and COI is the OI value of the area surrounded by the first concentric circle stripe line in the orientation area. The negative plate provided by the invention can improve the longitudinal liquid phase diffusivity and the transverse liquid phase diffusivity of lithium ions at the same time, so that the balance between lithium ion reaction kinetics and long circulation of the negative plate can be regulated and controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode sheet and a preparation method thereof, a battery, a battery pack, and an electronic device. Background Art

[0002] The arrangement of graphite particles and their crystal structure in the negative electrode sheet has an important influence on the lithium ion diffusion capacity and electron transmission capacity of the electrode. However, the graphite particles in the negative electrode sheet are generally arranged randomly, which is not conducive to the diffusion of lithium ions and the transmission of electrons.

[0003] By regulating the arrangement of graphite particles in the negative electrode sheet through magnetic induction, the liquid-phase diffusion capacity of lithium ions in the thickness direction of the electrode sheet (the ability of longitudinal liquid-phase diffusion) can be improved to a certain extent, which is beneficial to the improvement of lithium-ion reaction kinetics. However, at the same time, it will also deteriorate the liquid-phase diffusion capacity of lithium ions in the length direction of the negative electrode sheet (the ability of lateral liquid-phase diffusion), which is not conducive to the long cycle of the battery. Summary of the Invention

[0004] The present invention provides a negative electrode sheet. By defining the relationship between the diffusion zone, the orientation zone, the OI value of the two, and the electrolyte infiltration rate of the two, the negative electrode sheet can simultaneously improve the longitudinal liquid phase diffusion capacity and the transverse liquid phase diffusion capacity of lithium ions through the negative electrode sheet, thereby facilitating the regulation of the balance between the lithium ion reaction kinetics of the negative electrode sheet and long cycle.

[0005] The present invention also provides a method for preparing a negative electrode sheet, which can be used to prepare the negative electrode sheet and is simple.

[0006] The present invention also provides a battery comprising the above-mentioned negative electrode sheet. Compared with conventional magnetic induction batteries, the battery of the present invention has relatively lower 50% SOC DC internal resistance and liquid phase diffusion impedance and better cycle performance.

[0007] The present invention also provides a battery pack. Since the battery pack includes the battery, the battery pack has better electrical performance and longer cycle life.

[0008] The present invention also provides an electronic device. Since the electronic device includes the battery, the electronic device has excellent electrical performance and a relatively long service life.

[0009] 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, the surface of the negative electrode active material layer comprises N concentric circular stripe lines, the region between the Nth concentric circular stripe line and the N-1th concentric circular stripe line is a diffuse region, and the region surrounded by the diffuse region is an oriented region, wherein the negative electrode sheet satisfies the following equations 1 to 3:

[0010] 0.8 <V C / V Q <1 formula 1;

[0011] 1.6≤Q OI ≤9 Formula 2;

[0012] 0.5≤C OI <1.6 Equation 3;

[0013] Among them, V C is the electrolyte infiltration rate of the orientation zone, unit: mm / 100s, V Q Q is the electrolyte infiltration rate in the diffusion zone, unit: mm / 100s, OI is the OI value of the diffusion zone, C OI It is the OI value of the area surrounded by the first concentric circle stripe line in the orientation zone.

[0014] Furthermore, N≥5.

[0015] Furthermore, 5.9 mm / 100 s ≤ V Q ≤6.7mm / 100s; 5.2mm / 100s≤V C ≤6.39mm / 100s.

[0016] Furthermore, the negative electrode sheet also satisfies the following formula 4:

[0017] 0.6≤R C / R Q <1 formula 4;

[0018] Among them, R Q R is the straight-line distance from the Nth concentric circle stripe line to the center of the circle, C is the straight-line distance from the N-1th concentric circle stripe line to the center of the circle.

[0019] Furthermore, 0.65≤R C / R Q ≤0.75.

[0020] Furthermore, in the negative electrode active material layer, the mass proportion of graphite is 70% to 99%.

[0021] In a second aspect, the present invention provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0022] The electrode slurry comprising an active material, a binder and a conductive agent is coated on at least one surface of a current collector, and the current collector coated with the electrode slurry is induced by a rotating magnetic field and dried to obtain the negative electrode sheet; wherein the rotating magnetic field comprises a magnet; the vertical distance between the current collector coated with the electrode slurry and the magnet is m, and the rotation speed of the rotating magnetic field is n, wherein 0 mm <m≤5mm;0r / min<n≤400r / min。

[0023] Furthermore, 0.5mm≤m≤2mm, 75r / min <n≤250r / min。

[0024] In a third aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0025] In a fourth aspect, the present invention provides a battery pack comprising the battery described in the third aspect.

[0026] In a fifth aspect, the present invention provides an electronic device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0027] The negative electrode sheet provided by the present invention can simultaneously improve the longitudinal liquid phase diffusion capacity and the transverse liquid phase diffusion capacity of lithium ions through the negative electrode sheet by limiting the relationship between the diffusion zone, the orientation zone, the OI value of the two, and the electrolyte infiltration rate of the two, thereby facilitating the regulation of the balance between the lithium ion reaction kinetics of the negative electrode sheet and long cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present invention or related technologies. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0029] Figure 1 Schematic diagram of concentric circle stripe areas of a negative electrode sheet according to a specific embodiment of the present invention;

[0030] Figure 2 This is a physical picture of the concentric circle stripe area of the negative electrode sheet according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] Conventional ellipsoidal graphite, particle size D50 is 8-15μm, compaction 1.6g / cm 3 The stacking structure has a large electrolyte infiltration rate, which means that its lateral electrolyte transmission speed is faster, but its longitudinal electrolyte infiltration ability and lithium ion diffusion rate are insufficient. Magnetic induction regulates the vertical arrangement of graphite particles, which can usually improve the longitudinal electrolyte infiltration ability of the graphite negative electrode. However, the existing magnetic induction method cannot take into account the lateral electrolyte infiltration ability and the longitudinal electrolyte infiltration ability of the graphite negative electrode at the same time. To solve the above problems, the present invention adopts the following technical solutions:

[0033] 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; the surface of the negative electrode active material layer comprises N concentric circular stripes, the region between the Nth concentric circular stripe line and the N-1th concentric circular stripe line is a diffuse region, and the region surrounded by the diffuse region is an oriented region (see Figure 1 ), the negative electrode sheet satisfies the following formulas 1 to 3:

[0034] 0.8 <V C / V Q <1 formula 1;

[0035] 1.6≤Q OI ≤9 Formula 2;

[0036] 0.5≤C OI <1.6 Equation 3;

[0037] Among them, V C is the electrolyte infiltration rate of the orientation zone, unit: mm / 100s, V Q Q is the electrolyte infiltration rate in the diffusion zone, unit: mm / 100s, OI is the OI value of the diffusion zone, C OI It is the OI value of the area surrounded by the first concentric circle stripe line in the orientation zone.

[0038] In the present invention, since the OI value of the electrode in the orientation zone is low, the graphite particles here are mostly distributed in the direction perpendicular to the electrode, which can improve the longitudinal electrolyte wetting ability of the graphite negative electrode, thereby ensuring faster longitudinal liquid phase diffusion and rapid embedding ability of lithium ions, and helping to improve the reaction kinetics of lithium ions; since the OI value of the electrode in the diffusion zone is high, the active material particles in this area are gently oriented, which can ensure the lateral electrolyte wetting ability of the negative electrode, that is, ensure the lateral liquid phase diffusion ability of lithium ions, alleviate the difficulty of lateral transmission of lithium ions in the battery, and avoid the diffusion resistance of the electrolyte entering from the edge of the electrode being too large, resulting in poor liquid in the middle of the electrode core, thereby affecting the battery cycle performance; and the electrolyte infiltration rate of the two zones meets: 0.8 <VC / V Q <1, which can ensure that the negative electrode sheet reasonably matches the longitudinal liquid phase diffusion capacity of lithium ions and the transverse liquid phase diffusion capacity of lithium ions, so that the negative electrode sheet has both better lithium ion reaction kinetics and cycle performance.

[0039] It should be noted that the electrolyte infiltration rate test method disclosed herein includes the following steps: drying a 0SOC negative electrode sheet in a glove box, cutting it into a 4×4 cm area, and placing it on a sample stage, keeping the negative electrode sheet surface flat; turning on a microscope and adjusting the lens and sample stage until the image is clear; then using a 700 μm inner diameter capillary glass tube (a transparent scale label can be attached to the outer wall of the tube to facilitate observation of the liquid level change) to draw a certain amount of electrolyte (liquid level H = 14 mm), clamping the capillary glass tube on a clamp, further adjusting the image for clarity, and lowering the capillary glass tube until it contacts the test point of the negative electrode sheet. As the liquid level in the capillary glass tube descends, the video timing begins and stops when the liquid level has completely descended. Comparing the infiltration time of the same volume of electrolyte, the electrolyte infiltration rate V is obtained, that is, V = ΔV / ΔT, where ΔV is the electrolyte volume (total electrolyte volume in the capillary glass tube minus the remaining volume); ΔT is the infiltration time. As for the composition of the electrolyte, the present invention does not make any special limitation, and it is generally consistent with the electrolyte used in the battery, for example, an electrolyte composed of an organic solvent and an electrolyte salt is selected; 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); and the electrolyte salt is lithium hexafluorophosphate (LiPF6).

[0040] Q OI The test can be done by cutting the sample to be tested from the negative electrode along the diffusion zone, placing the sample to be tested horizontally for X-ray diffraction spectrum test, with a scanning angle of 10 to 80°. The ratio of the measured 004 characteristic diffraction peak intensity (or integrated area) to the 110 characteristic diffraction peak intensity (or integrated area) is described as the OI value of the diffusion zone, that is, b = C(004) / C(110); similarly, C OI The test can refer to Q OI The only difference is that the negative electrode sample to be tested is intercepted along the area surrounded by the first concentric circle stripe line in the orientation zone. In addition, the area surrounded by the first concentric circle stripe line can also be understood as the area surrounded by the concentric circle stripe line closest to the center of the circle. For details, see Figure 1 .

[0041] The present invention does not specifically limit the type or source of the graphite. Technicians can choose conventional graphite as electrode materials, such as natural graphite or artificial graphite.

[0042] The present invention does not specifically limit the material of the current collector. For example, the current collector may be any one or more selected from copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals.

[0043] In order to further balance the longitudinal diffusion and lateral diffusion of lithium ions in the negative electrode sheet, thereby ensuring that the lithium ion reaction kinetics of the negative electrode sheet are improved while not causing too much impact on the cycle performance, in a preferred embodiment, the negative electrode sheet also meets the following requirements: N≥5; and / or, 0.85 <V C / V Q <1.

[0044] Furthermore, in one embodiment, 5.9 mm / 100 s ≤ V Q ≤6.7mm / 100s; 5.2mm / 100s≤V C ≤6.39mm / 100s.

[0045] For example, V Q For 5.9mm / 100s, 6.0mm / 100s, 6.1mm / 100s, 6.2mm / 100s, 6.3mm / 100s, 6.4mm / 100s, 6.5mm / 100s, 6.6mm / 100s, 6.7mm / 100s, etc.; V C For 5.2mm / 100s, 5.3mm / 100s, 5.4mm / 100s, 5.5mm / 100s, 5.6mm / 100s, 5.7mm / 100s , 5.8mm / 100s, 5.9mm / 100s, 6.0mm / 100s, 6.1mm / 100s, 6.2mm / 100s, 6.3mm / 100s.

[0046] In a preferred embodiment, the negative electrode sheet further satisfies the following formula 4:

[0047] 0.6≤R C / R Q <1 formula 4;

[0048] Among them, combined Figure 1 , R Q R is the straight-line distance from the Nth concentric circle stripe line to the center of the circle, C is the straight-line distance from the N-1th concentric circle stripe line to the center of the circle.

[0049] Among them, if the RC / RQ value is less than 0.6, the battery kinetic performance is poor, and if the RC / RQ value is greater than 1, there are problems with the electrolyte wetting ability, the lateral transmission of lithium ions is difficult, and the long-cycle stability of the battery is reduced.

[0050] In one embodiment, 0.65≤RQ / R C ≤0.75. For example, R Q / R C The values are 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, etc.

[0051] In one embodiment, the mass percentage of graphite in the negative electrode active material layer is 70% to 99%. This embodiment can further optimize the conductive properties of the negative electrode sheet by limiting the percentage of graphite.

[0052] Illustratively, the above-mentioned binder includes, but is not limited to, at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0053] The conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium lauryl sulfate.

[0054] The negative electrode active material layer may further include a dispersant, and the dispersant may be at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium lauryl sulfate.

[0055] As for the thickness of the above-mentioned negative electrode sheet and the thickness of the negative electrode active material layer, the present invention does not make specific limitations. However, in order to balance the battery capacity, cycle life and energy density, in a 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 thickness of the negative electrode 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.

[0056] In a second aspect, the present invention provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0057] The electrode slurry comprising an active material, a binder and a conductive agent is coated on at least one surface of a current collector, and the current collector coated with the electrode slurry is induced by a rotating magnetic field and dried to obtain the negative electrode sheet; wherein the rotating magnetic field comprises a magnet; the vertical distance between the current collector coated with the electrode slurry and the magnet is m, and the rotation speed of the rotating magnetic field is n, wherein 0 mm <m≤5mm;0r / min<n≤400r / min。

[0058] The above preparation method can obtain a negative electrode sheet that satisfies formulas 1-3 by inducing a rotating magnetic field under specific conditions on a current collector coated with an electrode slurry. The principle is: the change in the orientation of graphite particles is due to the action of the magnetic field, and the rotating magnetic field affects the magnetic action time. Since the angular velocity of rotation on the rotating table is the same, the effect of the magnetic action changes with the distance from the center and the angular velocity of rotation, thereby forming a negative electrode sheet with N concentric circular stripes on the surface, and the OI value of the electrode sheet is related to the magnetic field action time and the strength of the magnetic field. Therefore, the above method can control the values of m and n to make the electrode sheet satisfy the conditions of formulas 1-3.

[0059] In a specific embodiment, the rotating magnetic field may be constructed by a permanent magnet and a rotating table, and the rotation speed of the rotating magnetic field may be adjusted by adjusting the rotation speed of the rotating table.

[0060] In a preferred embodiment, 0.5 mm ≤ m ≤ 2 mm, 75 r / min <n≤250r / min。

[0061] In a third aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0062] It should be noted that the above-mentioned batteries may include but are not limited to lithium-ion power batteries, solar cells, new energy storage batteries, 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, and may also be other application forms. For example, when the battery is a lithium-ion power battery, it includes at least one of a cylindrical battery, a square battery, etc.

[0063] Generally speaking, the above-mentioned battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0064] The positive electrode sheet generally includes a current collector and a positive electrode active material layer disposed on at least one functional surface of the current collector; the positive electrode active material layer includes an active material.

[0065] In a specific embodiment, the positive electrode active material layer comprises, by weight percentage, 70-99% of positive electrode active material, 0.5%-10% of binder, and 0.7%-10% of conductive agent.

[0066] For example, the above-mentioned positive electrode active materials include but are not limited to: one or more of lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate; the lithium nickel cobalt manganese oxide material can be LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2.

[0067] The above-mentioned binder includes but is not limited to: at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0068] The conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium lauryl sulfate.

[0069] The dispersant may be at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium lauryl sulfate.

[0070] The present invention is not particularly limited to the above-mentioned separator. Any known porous structure separator with electrochemical and chemical stability can be selected, for example, at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be single-layer or multi-layer.

[0071] The electrolyte includes an organic solvent and an electrolyte salt. The organic solvent acts as a medium for ion transport during the electrochemical reaction and can be any organic solvent known in the art for battery electrolytes. 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 organic solvents can be selected.

[0072] The electrolyte salt, as a source of ions, may be any electrolyte salt known in the art for use in battery electrolytes. For example, the electrolyte salt may be at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium nitrate (LiNO3), and lithium fluoride (LiF).

[0073] In a fourth aspect, the present invention provides a battery pack comprising the battery described in the third aspect.

[0074] In a fifth aspect, the present invention provides an electronic device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0075] It should be noted that the above-mentioned electronic devices can be any conventional devices that require electricity, for example, including but not limited to computers, electric cars, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0076] The technical solutions of the present invention are further illustrated below with reference to specific examples. All parts, percentages, and ratios described in the following examples are based on weight. All reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment. The instruments used in the examples are commercially available.

[0077] Example 1

[0078] This example provides a negative electrode sheet, comprising a copper foil and negative electrode active material layers disposed on two functional surfaces of the copper foil; the thickness of the negative electrode active material layers is 145 μm, and the double-sided surface density of the negative electrode sheet is 220 g / m 2 , compaction 1.52g / cm 3 The negative electrode active material layer comprises, by mass percentage, 95% graphite, 1% conductive carbon black, 1% sodium carboxymethyl cellulose, and 3% styrene-butadiene rubber; the graphite has a D50 of 9.5 μm. In addition, the surface of the negative electrode active material layer comprises N concentric circular stripes, the region between the Nth concentric circular stripe and the N-1th concentric circular stripe is a diffuse region, and the region surrounded by the diffuse region is an oriented region (see Figure 1 and Figure 2 ), Q OI 、C OI 、V Q and V C See Table 1 for specific values.

[0079] The method for preparing the negative electrode sheet comprises the following steps:

[0080] Graphite, a conductive agent, a binder and water are mixed to make the solid content of the slurry reach 45.7% (by mass), stirred to prepare an electrode slurry, and the electrode slurry is coated on both sides of a copper foil with a thickness of 6 μm; then, the copper foil is fixed at a position 2 mm vertically away from the permanent magnet, and the permanent magnet is fixed to the surface of the rotating table with a strong adhesive double-sided tape. The size of the permanent magnet is not more than 5 mm different from the size of the pole piece dressing. The rotation speed of the rotating table is adjusted to 75 r / min so that concentric circle stripes appear on the surface of the pole piece. It is baked in an oven and then cold pressed, slit and cut to obtain the above-mentioned negative electrode sheet.

[0081] Examples 2-7

[0082] The negative electrode sheet provided is basically the same as that in Example 1, with the only difference being that the vertical distance between the copper foil and the permanent magnet and / or the rotation speed of the rotating table are changed, as shown in Table 1 for details.

[0083] Comparative Example 1

[0084] The negative electrode sheet provided is basically the same as that in Example 1, except that no magnetic field induction is used, and the electrode slurry is directly placed in an oven for baking after being coated on the copper foil.

[0085] Comparative Example 2

[0086] The negative electrode sheet provided is basically the same as that in Example 1, except that the vertical distance between the copper foil and the permanent magnet is changed, and the rotation speed of the rotating table is 0, see Table 1 for details.

[0087] Test Example 1

[0088] The following properties of the negative electrode sheets of the above embodiments and comparative examples were tested, and the results are recorded in Table 1.

[0089] Wetting rate: After drying the 0SOC electrode in a glove box, cut it into 4×4 cm squares and place it on the sample stage, keeping the electrode surface flat. Turn on the microscope and adjust the lens and sample stage until the image is clear. Then, use a 700μm inner diameter capillary glass tube (a transparent scale label can be attached to the outer wall of the tube to facilitate observation of the liquid level) to draw a certain amount of electrolyte (liquid level H = 14mm). Clamp the capillary glass tube on a clamp, further adjust the image clarity, and lower the capillary tube until it contacts the test point of the negative electrode. As the liquid level drops, the video timing starts and stops when the liquid level has completely dropped. Comparing the immersion time of the same volume of electrolyte, the electrolyte immersion rate V of the electrode is obtained, that is, V = ΔV / ΔT, where V is the immersion rate, ΔV is the electrolyte volume, and ΔT is the immersion time.

[0090] OI value test: Q OI The test can be done by cutting the sample from the negative electrode along the diffusion area, placing the sample horizontally for X-ray diffraction spectrum test, with a scanning angle of 10 to 80 degrees, and the ratio of the measured 004 characteristic diffraction peak intensity (or integrated area) to the 110 characteristic diffraction peak intensity (or integrated area) is Q OI value, that is, b=C(004) / C(110); C OI The test can refer to Q OI The only difference is that the negative electrode sample to be tested is intercepted along the area surrounded by the first concentric circle stripe line in the orientation zone.

[0091] Table 1:

[0092]

[0093]

[0094] Note: “ / ” in the table indicates that there is no corresponding test data.

[0095] As can be seen from Table 1, the embodiment can adjust the area of the diffusion zone and the orientation zone and the electrolyte infiltration rate of each zone by changing the vertical distance between the current collector and the permanent magnet and / or the rotation speed of the rotating table. In Comparative Example 1, since no magnetic field induction is used, the negative electrode sheet does not have a diffusion zone and an orientation zone, and the electrolyte infiltration rate of the negative electrode sheet is a fixed value of 6.89 mm / 100 s. Since the magnetic field in Comparative Example 2 does not rotate, the negative electrode sheet only has an orientation zone, no diffusion zone, and the electrolyte infiltration rate of the orientation zone is 5.13 mm / 100 s.

[0096] Application Example 1

[0097] The negative electrode sheets of Examples 1-7 and Comparative Examples 1-2 were assembled into batteries, respectively. The assembly process included the following steps:

[0098] (1) Preparation of electrolyte

[0099] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) solvents were uniformly mixed in a certain mass ratio, and then fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3,6-hexanetrionitrile, and adiponitrile (ADN) were added to the solvent in a certain mass ratio and uniformly mixed, and finally LiPF6 was added.

[0100] (2) Preparation of positive electrode sheet

[0101] The positive electrode active material, lithium iron phosphate (LiFePO4), the conductive agent, carbon nanotubes (CNT), and the specific binder, polyvinylidene fluoride, were mixed in a mass ratio of 97.3:0.8:1.9. N-methylpyrrolidone (NMP) was added and stirred in a vacuum mixer until the system formed a uniform positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector, Al foil. After drying at 100°C, the slurry was cold pressed, slit, and cut into pieces, and then dried under vacuum at 100°C for 4 hours to obtain the positive electrode sheet.

[0102] (3) Preparation of isolation membrane

[0103] The isolation membrane is made of polyethylene (PE) membrane.

[0104] (4) Preparation of lithium-ion batteries

[0105] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to serve as an isolation. The sheets are then wound and placed in outer packaging foil. The prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, formation, shaping, and other processes, the preparation of the lithium-ion battery is completed.

[0106] Test Example 2

[0107] The battery of Application Example 1 was tested for 50% SOC DC internal resistance, liquid phase diffusion impedance test, and long cycle test. The test results are shown in Table 2.

[0108] Test method:

[0109] 50% SOC DC internal resistance test: At room temperature (25±5°C), discharge the battery at a constant current of 1 / 3C to 2.0V, charge at a constant current of 1 / 3C to 50% SOC, and leave for 30 minutes. Discharge at a constant current of 1.5C for 30 seconds, and then test the battery's DC internal resistance at 50% SOC.

[0110] Liquid-phase diffusion impedance test: Assemble the two negative electrode sheets and the separator in sequence to form a core; place the core in an outer packaging shell, bake, inject electrolyte, and go through packaging, infiltration and other processes. Use an electrochemical workstation to perform a liquid-phase diffusion impedance test in the frequency range of 300,000 Hz-0.05 Hz.

[0111] Table 2

[0112] 50% SOC DCIR (Ω) Liquid phase diffusion impedance (Ω) Cycle capacity retention rate Example 1 0.779 0.597 0.909 Example 2 0.741 0.502 0.917 Example 3 0.613 0.438 0.939 Example 4 0.609 0.436 0.928 Example 5 0.604 0.428 0.911 Example 6 1.055 0.712 0.940 Example 7 0.606 0.433 0.893 Comparative Example 1 1.436 0.981 0.942 Comparative Example 2 0.599 0.422 0.791

[0113] As can be seen from Table 2, the battery assembled with the negative electrode sheet of the embodiment can simultaneously maintain the cycle capacity retention rate, 50% SOC DC internal resistance and liquid phase diffusion impedance in a relatively ideal range, and the 50% SOC DC internal resistance, liquid phase diffusion impedance or cycle capacity retention rate of the battery can be flexibly adjusted by changing the vertical distance between the current collector and the permanent magnet and / or the rotation speed of the turntable; while the negative electrode sheet of Comparative Example 1 is not subjected to magnetic field induction, the cycle capacity retention rate of the battery assembled therefrom is not much different from that of the embodiment, but the 50% SOC DC internal resistance and liquid phase diffusion impedance are significantly higher than those of the embodiment. Since the negative electrode sheet of Comparative Example 2 is not subjected to rotating magnetic field induction, although the 50% SOC DC internal resistance and liquid phase diffusion impedance of the battery assembled therefrom are lower, its cycle capacity retention rate is significantly lower than that of the embodiment.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 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, characterized in that: The surface of the negative electrode active material layer includes N concentric circular stripes, the area between the Nth concentric circular stripe line and the N-1th concentric circular stripe line is a diffuse area, and the area surrounded by the diffuse area is an oriented area; the negative electrode sheet satisfies the following equations 1 to 3: 0.8 <V C / V Q <1 formula 1; 1.6≤Q OI ≤9 Formula 2; 0.5≤C OI <1.6 Equation 3; Among them, V C is the electrolyte infiltration rate of the orientation zone, unit: mm / 100s, V Q Q is the electrolyte infiltration rate in the diffusion zone, unit: mm / 100s, OI is the OI value of the diffusion zone, C OI It is the OI value of the area surrounded by the first concentric circle stripe line in the orientation zone.

2. The negative electrode sheet according to claim 1, characterized in that: N≥5。 3. The negative electrode sheet according to claim 2, characterized in that: 5.9mm / 100s≤V Q ≤6.7mm / 100s;5.2mm / 100s≤V C ≤6.39mm / 100s。 4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The negative electrode sheet also satisfies the following formula 4: 0.6≤R C / R Q <1 formula 4; Among them, R Q R is the straight-line distance from the Nth concentric circle stripe line to the center of the circle, C is the straight-line distance from the N-1th concentric circle stripe line to the center of the circle.

5. The negative electrode sheet according to claim 4, characterized in that: 0.65≤R C / R Q ≤0.75。 6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: In the negative electrode active material layer, the mass proportion of graphite is 70% to 99%.

7. A method for preparing a negative electrode sheet according to any one of claims 1 to 6, characterized in that: The following steps are involved: The electrode slurry comprising graphite, a binder and a conductive agent is coated on at least one surface of a current collector, and the current collector coated with the electrode slurry is induced by a rotating magnetic field and dried to obtain the negative electrode sheet; wherein the rotating magnetic field comprises a magnet; the vertical distance between the current collector coated with the electrode slurry and the magnet is m, and the rotation speed of the rotating magnetic field is n, wherein 0 mm <m≤5mm;0r / min<n≤400r / min。 8. The preparation method according to claim 7, characterized in that 0.5mm≤m≤2mm, 75r / min <n≤250r / min。 9. A battery, characterized in that: The invention relates to a negative electrode sheet according to any one of claims 1 to 6 or a negative electrode sheet prepared by the preparation method according to any one of claims 7 to 8.

10. A battery pack, characterized in that: A battery comprising the battery of claim 9.

11. An electronic device, characterized in that: Comprising the battery according to claim 9 or the battery pack according to claim 10.

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