Negative electrode sheet and preparation method therefor, battery, battery pack, and electronic device

Abstract

The present disclosure provides a negative electrode sheet and a preparation method therefor, a battery, a battery pack, and an electronic device. The negative electrode sheet comprises a negative electrode active material layer. The surface of the negative electrode active material layer comprises N concentric circular stripe lines, a region between an N-th concentric circular stripe line and an (N-1)-th concentric circular stripe line is a diffusion region, and a region surrounded by the diffusion region is an orientation region. The negative electrode sheet satisfies the following relationships: 0.8<VC / VQ<1, 1.6≤QOI≤9, and 0.5≤COI<1.6, wherein VC is the electrolyte solution infiltration rate of the orientation region with a unit of mm / 100 s, VQ is the electrolyte solution infiltration rate of the diffusion region with a unit of mm / 100 s, QOI is the OI value of the diffusion region, and COI is the OI value of a region surrounded by a first concentric circular stripe line in the orientation region. The negative electrode sheet provided in the present disclosure can simultaneously improve the longitudinal liquid-phase diffusion capability and the lateral liquid-phase diffusion capability of lithium ions, thereby facilitating regulation of a balance between lithium ion reaction kinetics of the negative electrode sheet and long-term cycling performance.

Description

A negative electrode sheet and its preparation method, a battery, a battery pack, and electronic equipment.

[0001] This disclosure claims priority to Chinese Patent Application No. 202410946861.2, filed on July 12, 2024, entitled "A negative electrode sheet and its preparation method, a battery, a battery pack, and an electronic device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of battery technology, and more specifically, to a negative electrode and its preparation method, a battery, a battery pack, and an electronic device. Background Technology

[0003] The arrangement of graphite particles and their crystal structure in the negative electrode has a significant impact on the lithium-ion diffusion and electron transport capabilities of the electrode. However, the graphite particles in a typical negative electrode are randomly arranged, which is not conducive to the diffusion of lithium ions and the transport of electrons.

[0004] By magnetically inducing and controlling the arrangement of graphite particles in the negative electrode, the lithium-ion liquid phase diffusion capability in the thickness direction (longitudinal liquid phase diffusion capability) of the electrode 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 lithium-ion liquid phase diffusion capability in the length direction (lateral liquid phase diffusion capability) of the negative electrode, which is not conducive to the long cycle life of the battery.

[0005] Application content

[0006] This disclosure provides a negative electrode sheet that, by defining a dispersion region, an orientation region, and the relationship between their OI values ​​and their electrolyte wetting rates, can simultaneously improve the longitudinal and lateral liquid phase diffusion capabilities of lithium ions passing through the negative electrode sheet, thereby facilitating the regulation of lithium ion reaction kinetics and the balance between long-term cycling.

[0007] This disclosure also provides a method for preparing a negative electrode sheet, which can prepare the above-mentioned negative electrode sheet and is simple in nature.

[0008] This disclosure also provides a battery including the above-mentioned negative electrode sheet. Compared with conventional magnetically induced batteries, the battery of this disclosure has relatively low 50% SOC DC internal resistance and liquid phase diffusion impedance, while having better cycle performance.

[0009] This disclosure also provides a battery pack that, because it includes the aforementioned battery, has better electrical performance and a longer cycle life.

[0010] This disclosure also provides an electronic device that, because it includes the aforementioned battery, has superior electrical performance and a relatively long service life.

[0011] In detail, in a first aspect, this disclosure provides a negative electrode sheet, including 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 the surface of the negative electrode active material layer includes N concentric circular stripes, the region between the Nth concentric circular stripe and the (N-1)th concentric circular stripe is a dispersion region, and the region surrounded by the dispersion region is an orientation region, the negative electrode sheet satisfying the following equations 1 to 3: 0.8 <V C / V Q <1 Equation 1; 1.6≤Q OI ≤9 Equation 2; 0.5≤C OI <1.6 Equation 3;

[0012] Among them, V C Electrolyte wetting rate of the orientation region, unit: mm / 100s, V Q Q represents the electrolyte wetting rate in the dispersed region, expressed in mm / 100s. OI C represents the OI value of the diffusion region. OI The OI value is the region enclosed by the first concentric circular stripe in the orientation region.

[0013] Furthermore, N≥5.

[0014] Furthermore, 5.9mm / 100s≤V Q ≤6.7mm / 100s; 5.2mm / 100s≤V C ≤6.39mm / 100s.

[0015] Furthermore, the negative electrode also satisfies the following equation 4: 0.6≤R C / R Q <1 Equation 4;

[0016] Among them, R Q R is the straight-line distance from the center of the Nth concentric circular stripe. C It is the straight-line distance from the center of the (N-1)th concentric circular stripe.

[0017] Furthermore, 0.65≤R C / R Q ≤0.75.

[0018] Furthermore, in the negative electrode active material layer, the mass percentage of graphite is 70% to 99%.

[0019] Secondly, this disclosure provides a method for preparing the aforementioned negative electrode sheet, comprising the following steps:

[0020] An electrode slurry comprising an active material, a binder, and a conductive agent is coated onto at least one surface of a current collector. The current collector coated with the electrode slurry is then induced by a rotating magnetic field and dried to obtain the negative electrode sheet. The rotating magnetic field includes a magnet. The perpendicular distance between the current collector coated with the electrode slurry and the magnet is m, and the rotational speed of the rotating magnetic field is n, where 0 mm... <m≤5mm;0r / min<n≤400r / min。

[0021] Furthermore, 0.5mm≤m≤2mm, 75r / min <n≤250r / min。

[0022] Thirdly, this disclosure provides a battery comprising the negative electrode sheet described in the first aspect.

[0023] Fourthly, this disclosure provides a battery pack comprising the battery described in the third aspect.

[0024] Fifthly, this disclosure provides an electronic device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0025] The negative electrode provided in this disclosure, by defining the dispersion region, the orientation region, and the relationship between their OI values ​​and their electrolyte wetting rates, can simultaneously improve the longitudinal liquid phase diffusion capability and the lateral liquid phase diffusion capability of lithium ions through the negative electrode, thereby facilitating the regulation of the lithium ion reaction kinetics of the negative electrode and the balance between long-term cycling. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies of this disclosure are briefly introduced below. Obviously, the accompanying drawings described below are merely some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0027] Figure 1 is a schematic diagram of the concentric stripe area of ​​a negative electrode sheet according to a specific embodiment of the present disclosure;

[0028] Figure 2 is a physical image of the concentric stripe area of ​​a negative electrode sheet according to a specific embodiment of this disclosure. Detailed Implementation

[0029] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0030] Conventional ellipsoidal graphite with a particle size D50 of 8-15 μm and a compaction density of 1.6 g / cm³. 3 The graphite anode has a high electrolyte wetting rate, indicating a fast lateral electrolyte transport speed, but lacks longitudinal electrolyte wetting ability and lithium-ion diffusion speed. Magnetic induction to regulate the vertical alignment of graphite particles can usually improve the longitudinal electrolyte wetting ability of the graphite anode. However, existing magnetic induction methods cannot simultaneously improve both the lateral and longitudinal electrolyte wetting abilities of the graphite anode. To solve the above problems, this disclosure adopts the following technical solution:

[0031] In a first aspect, this disclosure 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 and the (N-1)th concentric circular stripe is a dispersion region, and the region surrounded by the dispersion region is an orientation region (see Figure 1), and the negative electrode sheet satisfies the following equations 1 to 3: 0.8 <V C / V Q <1 Equation 1; 1.6≤Q OI ≤9 Equation 2; 0.5≤C OI <1.6 Equation 3;

[0032] Among them, V C Electrolyte wetting rate of the orientation region, unit: mm / 100s, V Q Q represents the electrolyte wetting rate in the dispersed region, expressed in mm / 100s. OI C represents the OI value of the diffusion region. OI The OI value is the region enclosed by the first concentric circular stripe in the orientation region.

[0033] In this disclosure, due to the lower OI value of the oriented region electrode, the graphite particles in this area are mostly distributed perpendicular to the electrode direction, which can improve the longitudinal electrolyte wetting ability of the graphite negative electrode, thereby ensuring faster longitudinal liquid phase diffusion and rapid insertion of lithium ions, and helping to improve the reaction kinetics of lithium ions. Due to the higher OI value of the dispersed region electrode, the active material particles in this region have a gentler orientation, 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 transport of lithium ions in the battery, and avoid excessive diffusion resistance of electrolyte entering from the electrode edge, leading to a lack of electrolyte in the middle of the electrode core, thus affecting the battery cycle performance. The electrolyte wetting rate of both regions satisfies: 0.8 <V C / V Q <1 ensures that the negative electrode has a reasonable match between the longitudinal liquid phase diffusion capability and the lateral liquid phase diffusion capability of lithium ions, so that the negative electrode has both good lithium ion reaction kinetics and cycle performance.

[0034] It should be noted that the electrolyte wetting rate test method disclosed herein includes the following steps: After drying the 0SOC negative electrode in a glove box, cut it into 4×4cm pieces and place it on the sample stage, ensuring the surface of the negative electrode is 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 graduation label can be attached to the outer wall of the tube for easy observation of liquid level changes) to draw a certain amount of electrolyte (liquid level H = 14mm), clamp the capillary glass tube in a clamp, further adjust the image for clarity, lower the capillary tube until it contacts the test point on the negative electrode, and start recording and timing as the liquid level in the capillary glass tube descends; stop recording and timing after the liquid level has descended completely. Compare the wetting time of the same volume of electrolyte to obtain the electrolyte wetting rate V, i.e., V = ΔV / ΔT, where ΔV: electrolyte volume (total electrolyte volume in the capillary glass tube - remaining volume); ΔT: wetting time. Regarding the composition of the electrolyte, this disclosure does not impose any particular limitations, and it is generally consistent with the electrolyte used in batteries. For example, an electrolyte composed of an organic solvent and an electrolyte salt may be selected. The organic solvent may be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte salt may be lithium hexafluorophosphate (LiPF6).

[0035] Q OI The test can be performed by taking a sample from the negative electrode along the diffuse region, placing the sample horizontally, and performing X-ray diffraction spectroscopy. The scanning angle is 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 diffuse region, i.e., b = C(004) / C(110); similarly, C OI The test can be referred to Q. OI The only difference in the testing method is that the negative electrode sample to be tested is cut along the area enclosed by the first concentric circle stripe in the orientation region. In addition, the area enclosed by the first concentric circle stripe can also be understood as the area enclosed by the concentric circle stripe closest to the center, as shown in Figure 1.

[0036] This disclosure does not specifically limit the type or source of the graphite mentioned above. Those skilled in the art may use conventional graphite for electrode materials, such as natural graphite or artificial graphite.

[0037] As for the material of the current collector, this disclosure 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.

[0038] To further balance the longitudinal and lateral diffusion of lithium ions in the negative electrode, thereby ensuring improved lithium-ion reaction kinetics without excessively affecting cycle performance, in a preferred embodiment, the negative electrode also satisfies: N≥5; and / or 0.85 <V C / V Q <1.

[0039] Furthermore, in one specific embodiment, 5.9mm / 100s≤V Q ≤6.7mm / 100s; 5.2mm / 100s≤V C ≤6.39mm / 100s.

[0040] 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.

[0041] In a preferred embodiment, the negative electrode also satisfies the following equation 4: 0.6≤R C / R Q <1 Equation 4;

[0042] In conjunction with Figure 1, R Q R is the straight-line distance from the center of the Nth concentric circular stripe. C It is the straight-line distance from the center of the (N-1)th concentric circular stripe.

[0043] If the RC / RQ value is less than 0.6, the battery's kinetic performance is poor. If the RC / RQ value is greater than 1, there is a problem with the electrolyte wetting ability, making it difficult for lithium ions to transport laterally and reducing the battery's long-cycle stability.

[0044] In one specific implementation, 0.65 ≤ R Q / 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.

[0045] In one specific embodiment, the graphite content in the negative electrode active material layer is 70% to 99% by mass. This embodiment, by limiting the proportion of graphite, can further optimize the conductivity of the negative electrode sheet.

[0046] For example, the adhesives mentioned above include, but are not limited to, at least one of the following: carboxymethyl cellulose, styrene-butadiene rubber, 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.

[0047] 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 dodecyl sulfate.

[0048] The negative electrode active material layer may also include a dispersant, which may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0049] Regarding the thickness of the aforementioned negative electrode sheet and the thickness of the negative electrode active material layer, this disclosure does not specify any particular thickness. 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.; and 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.

[0050] Secondly, this disclosure provides a method for preparing the aforementioned negative electrode sheet, comprising the following steps:

[0051] An electrode slurry comprising an active material, a binder, and a conductive agent is coated onto at least one surface of a current collector. The current collector coated with the electrode slurry is then induced by a rotating magnetic field and dried to obtain the negative electrode sheet. The rotating magnetic field includes a magnet. The perpendicular distance between the current collector coated with the electrode slurry and the magnet is m, and the rotational speed of the rotating magnetic field is n, where 0 mm... <m≤5mm;0r / min<n≤400r / min。

[0052] The above preparation method can obtain a negative electrode sheet that satisfies Equation 1-3 by inducing the current collector coated with electrode slurry to pass through a rotating magnetic field under specific conditions. The principle is as follows: the orientation of graphite particles changes due to the action of the magnetic field. The rotating magnetic field affects the magnetic force action time. Since the rotational angular velocity is the same on the rotating table, the magnetic force effect changes with the distance from the center and the rotational angular velocity, thereby forming a negative electrode sheet with N concentric circular stripes on the surface. The OI value of the electrode sheet is related to the magnetic field action time and the magnetic field strength. Therefore, the above method can control the values ​​of m and n to make the electrode sheet satisfy the conditions of Equation 1-3.

[0053] In one specific embodiment, the aforementioned rotating magnetic field can be constructed from a permanent magnet and a rotating platform, and the rotation speed of the rotating magnetic field can be adjusted by adjusting the rotation speed of the rotating platform.

[0054] In a preferred embodiment, 0.5mm ≤ m ≤ 2mm, 75r / min <n≤250r / min。

[0055] Thirdly, this disclosure provides a battery comprising the negative electrode sheet described in the first aspect.

[0056] It should be noted that the aforementioned batteries may include, but are not limited to, lithium-ion power batteries, solar cells, and novel energy storage batteries. That is, the actual application form of the batteries provided in this disclosure may be, but is not limited to, the products listed, or may be other application forms. For example, when the battery is a lithium-ion power battery, it may include at least one of cylindrical batteries, prismatic batteries, etc.

[0057] Generally speaking, the above-mentioned battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0058] The aforementioned positive electrode 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.

[0059] In one specific embodiment, the positive electrode active material layer comprises, by weight percentage: 70-99% positive electrode active material, 0.5%-10% binder, and 0.7%-10% conductive agent.

[0060] 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 may be LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2.

[0061] The aforementioned adhesives include, but are not limited to, at least one of the following: carboxymethyl cellulose, styrene-butadiene rubber, 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.

[0062] 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 dodecyl sulfate.

[0063] The dispersant mentioned above can be at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0064] This disclosure 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 comprises an organic solvent and an electrolyte salt. The organic solvent serves as the ion transport medium in the electrochemical reaction and can be any organic solvent known in the art for use in 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-mentioned organic solvents may be selected.

[0066] 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).

[0067] Fourthly, this disclosure provides a battery pack comprising the battery described in the third aspect.

[0068] Fifthly, this disclosure provides an electronic device comprising the battery described in the third aspect or the battery pack described in the fourth aspect.

[0069] 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.

[0070] The technical solutions of this disclosure are 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.

[0071] Example 1

[0072] This example provides a negative electrode sheet, comprising a copper foil and negative electrode active material layers respectively disposed on two functional surfaces of the copper foil; the thickness of each negative electrode active material layer is 145 μm, and the double-sided areal density of the negative electrode sheet is 220 g / m³. 2 Compacted to 1.52 g / cm³ 3 The negative electrode active material layer, by mass percentage, comprises: 95% graphite, 1% conductive carbon black, 1% sodium carboxymethyl cellulose, and 3% styrene-butadiene rubber; the D50 of the graphite is 9.5 μm. Furthermore, the surface of the negative electrode active material layer includes N concentric circular stripes, the region between the Nth and (N-1)th concentric circular stripes is a dispersion region, and the region surrounded by the dispersion region is an orientation region (see Figures 1 and 2). OI C OI V Q and V C The specific values ​​are shown in Table 1.

[0073] The above-mentioned method for preparing the negative electrode includes the following steps:

[0074] Graphite, conductive agent, binder and water are mixed to make the solid content of the slurry reach 45.7% (by mass), and stirred to prepare the electrode slurry. The electrode slurry is then coated on both sides of a copper foil with a thickness of 6μm. Then, the copper foil is fixed at a position 2mm away from the permanent magnet at a vertical distance. The permanent magnet is fixed to the surface of the rotating table with strong adhesive double-sided tape. The size of the permanent magnet and the size of the electrode coating are not more than 5mm apart. The rotation speed of the rotating table is adjusted to 75r / min to make concentric circular stripes appear on the surface of the electrode. The electrode is baked in an oven, and then cold-pressed, slit and cut to obtain the above-mentioned negative electrode.

[0075] Examples 2-7

[0076] 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 and / or the rotation speed of the rotating stage are changed, as detailed in Table 1.

[0077] Comparative Example 1

[0078] The negative electrode sheet provided is basically the same as that in Example 1, except that magnetic field induction is not used, and the electrode paste is directly placed in an oven for baking after being coated with copper foil.

[0079] Comparative Example 2

[0080] 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.

[0081] Test Example 1

[0082] The following performance characteristics of the negative electrode sheets of the above embodiments and comparative examples were tested, and the results are recorded in Table 1.

[0083] Wetting rate: After drying the 0SOC electrode in a glove box, cut it into 4×4cm pieces 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 graduation label can be attached to the outer wall of the tube for easy observation of liquid level changes) to draw a certain amount (liquid level height H = 14mm) of electrolyte (to avoid evaporation of the electrolyte during the test, 12.8% mass fraction LiPF6 is used here, and the solvent is DMC). Clamp the capillary glass tube to the clamp, further adjust the image to be clear, lower the capillary tube until it contacts the test point on the negative electrode. Start recording and timing as the liquid level drops, and stop recording and timing after the liquid level has dropped completely. Compare the wetting time of the same volume of electrolyte to obtain the wetting rate V of the electrode, i.e., V = ΔV / ΔT, where V: wetting rate, ΔV: electrolyte volume; ΔT: wetting time.

[0084] OI value test: Q OI The test involves taking a sample from the negative electrode along the diffuse region, placing the sample horizontally, and performing X-ray diffraction spectroscopy. The scanning angle is 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 Q. OI The value is b = C(004) / C(110); C OI The test can be referred to Q. OI The only difference in the testing method is that the negative electrode sample is cut out along the area enclosed by the first concentric circle stripe in the orientation region.

[0085] Table 1: Note: " / " in the table indicates that there is no corresponding test data.

[0086] As shown in Table 1, the embodiments can adjust the area of ​​the dispersion region and the orientation region, as well as the electrolyte wetting rate of each region, by changing the vertical distance between the current collector and the permanent magnet and / or the rotation speed of the rotary table. However, since no magnetic field induction is used in Comparative Example 1, its negative electrode does not have a dispersion region or an orientation region, and the electrolyte wetting rate of the negative electrode is a fixed value of 6.89 mm / 100 s. Since the magnetic field of Comparative Example 2 does not rotate, its negative electrode only has an orientation region and no dispersion region, and the electrolyte wetting rate of the orientation region is 5.13 mm / 100 s.

[0087] Application Example 1

[0088] The negative electrode sheets of Examples 1-7 and Comparative Examples 1-2 were assembled into batteries. The assembly process included the following steps:

[0089] (1) Electrolyte preparation

[0090] In an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) solvents were uniformly mixed at mass fractions (25%, 0%, 58.5%, 0%, 0). Then, fluoroethylene carbonate (FEC), 1,3-propanesulfonyl lactone (PS), 1,3,6-hexanetrionitrile, and adiponitrile (ADN) were added to the solvents at a certain mass ratio (3.2% FEC, 0.5% PS, and the remainder 0%) and mixed uniformly. Finally, 12.8% by mass of LiPF6 was added.

[0091] (2) Preparation of positive electrode

[0092] Lithium iron phosphate (LiFePO4), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.3:0.8:1.9. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. This slurry was then uniformly coated onto an Al foil current collector. After drying at 100°C, the mixture was cold-pressed, slit, and cut into sheets. Finally, it was dried under vacuum at 100°C for 4 hours to obtain the positive electrode sheet.

[0093] (3) Preparation of the separating membrane

[0094] The separator is made of polyethylene (PE).

[0095] (4) Preparation of lithium-ion batteries

[0096] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound up and placed in an outer packaging foil. The prepared electrolyte is injected into the dried battery. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery is completed.

[0097] Test Example 2

[0098] The battery in Application Example 1 was tested for 50% SOC DC internal resistance, liquid phase diffusion impedance, and long cycle test. The test results are shown in Table 2.

[0099] Test method:

[0100] 50% SOC DC internal resistance test: 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 rest for 30 minutes; discharged at 1.5C constant current for 30 seconds, and the DC internal resistance of the battery at 50% SOC is measured.

[0101] Liquid phase diffusion impedance test: Assemble the two negative electrode plates and the separator in sequence to form the electrode core; place the electrode core in the outer packaging shell, bake and inject electrolyte, and after encapsulation, wetting and other processes, use an electrochemical workstation to conduct liquid phase diffusion impedance test in the frequency range of 300,000Hz-0.05Hz.

[0102] Table 2

[0103] As shown in 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 resistance within a relatively ideal range. Moreover, the 50% SOC DC internal resistance, liquid phase diffusion resistance, 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 rotary table. In contrast, the negative electrode sheet of Comparative Example 1, due to the lack of magnetic field induction, produces a battery with a cycle capacity retention rate that is not much different from that of the embodiment, but the 50% SOC DC internal resistance and liquid phase diffusion resistance are significantly higher than those of the embodiment. The negative electrode sheet of Comparative Example 2, due to the lack of rotating magnetic field induction, produces a battery with a lower 50% SOC DC internal resistance and liquid phase diffusion resistance, but its cycle capacity retention rate is significantly lower than that of the embodiment.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure 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 therein. Such 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 this disclosure.

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; said negative electrode active material layer comprising graphite, characterized in that, The surface of the negative electrode active material layer includes N concentric circular stripes. The region between the Nth and (N-1)th concentric circular stripes is a dispersion region, and the region surrounded by the dispersion region is an orientation region. The negative electrode sheet satisfies the following equations 1 to 3: 0.8 <V C / V Q <1 Equation 1; 1.6≤Q OI ≤9 Equation 2; 0.5≤C OI <1.6 Equation 3; Among them, V C Electrolyte wetting rate of the orientation region, unit: mm / 100s, V Q Q represents the electrolyte wetting rate in the dispersed region, expressed in mm / 100s. OI C represents the OI value of the diffusion region. OI The OI value is the region enclosed by the first concentric circular stripe in the orientation region.

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 1-3, characterized in that, The negative electrode also satisfies the following equation 4: 0.6≤R C / R Q <1 Equation 4; Among them, R Q R is the straight-line distance from the center of the Nth concentric circular stripe. C It is the straight-line distance from the center of the (N-1)th concentric circular stripe.

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 1-5, characterized in that, In the negative electrode active material layer, the mass percentage of graphite is 70% to 99%.

7. A method for preparing a negative electrode sheet as described in any one of claims 1-6, characterized in that, Includes the following steps: An electrode slurry comprising graphite, a binder, and a conductive agent is coated onto at least one surface of a current collector. The current collector coated with the electrode slurry is then induced by a rotating magnetic field and dried to obtain the negative electrode sheet. The rotating magnetic field includes a magnet. The perpendicular distance between the current collector coated with the electrode slurry and the magnet is m, and the rotational speed of the rotating magnetic field is n, where 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 negative electrode comprises the negative electrode sheet according to any one of claims 1-6 or the negative electrode sheet prepared by any one of claims 7-8.

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

11. An electronic device, characterized in that, Includes the battery of claim 9 or the battery pack of claim 10.

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