Negative electrode sheet, preparation method therefor, battery cell and electrical device

Abstract

A negative electrode sheet, a preparation method therefor, a battery cell and an electrical device. The negative electrode sheet comprises a current collector and an active layer, the active layer containing graphite which satisfies: 0 < OIa ≤ 5, and 2 ≤ OIb ≤ 20, wherein OIa is the ratio of the peak area of a characteristic diffraction peak of a graphite (004) surface to the peak area of a characteristic diffraction peak of a graphite (110) surface obtained by a XRD test on the surface of the negative electrode sheet, and OIb is the ratio of the peak area of a characteristic diffraction peak of the graphite (004) surface to the peak area of a characteristic diffraction peak of the graphite (110) surface obtained by a XRD test on a cross section of the negative electrode sheet.

Description

Negative electrode sheet and preparation method thereof, battery cell and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 30, 2023, with application number 202311632169.4 and invention name “Negative electrode sheet and preparation method thereof, battery cell and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a negative electrode sheet and a preparation method thereof, a battery cell and an electrical device. Background Art

[0003] The energy density of the battery directly affects the endurance of electrical equipment. Improving the surface density and compaction of the electrode, so that the active material has a higher volume share in a limited space, is an effective way to increase the energy density of the battery.

[0004] However, the increase in electrode surface density and compaction will cause the diffusion path of lithium ions to become longer; at the same time, the porosity will decrease, the tortuosity will increase, and the effective diffusion coefficient of ions will become smaller, which will ultimately lead to a decrease in the liquid phase diffusion impedance of the battery, affecting the power performance of the battery and making it difficult to meet fast charging requirements.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a negative electrode sheet and its preparation method, a battery cell and an electrical device, which can improve the liquid-phase lithium ion diffusion capacity of the electrode and improve the dynamic performance and fast charging performance of the thick electrode.

[0007] To achieve the purpose of this application, this application provides the following technical solutions:

[0008] In a first aspect, the present application provides a negative electrode sheet, comprising a current collector and an active layer, wherein the active layer is stacked on the current collector, wherein the active layer comprises graphite, and the graphite satisfies: 0<OI a ≤5, 2≤OI b ≤20; among them, OI a OI is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD test on the surface of the negative electrode sheet; b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet.

[0009] In one embodiment, the graphite satisfies: 0<OI a ≤2, 2≤OI b ≤10.

[0010] In a second aspect, the present application also provides a method for preparing a negative electrode sheet, comprising: providing a current collector; stacking an active layer on the current collector, wherein the active layer comprises graphite; and the graphite satisfies: 0<OI a ≤5, 2≤OI b ≤20; among them, OI a OI is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD test on the surface of the negative electrode sheet; b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet.

[0011] In one embodiment, stacking the active layer on the current collector includes: coating a slurry on the current collector, wherein the slurry includes graphite particles; applying an alternating electric field to the negative electrode sheet to generate an induced current in the active layer; and / or applying a magnetic field to the negative electrode sheet to orient the graphite particles.

[0012] In one embodiment, the voltage of the alternating electric field is U, and the frequency is F, which satisfies: 0V<U≤400V, 30Hz≤F≤150Hz.

[0013] In one embodiment, the voltage of the alternating electric field is U, and the frequency is F, which satisfies: 24V≤U≤130V, 50Hz≤F≤100Hz.

[0014] In one embodiment, the magnitude of the magnetic field is B, which satisfies: 0T<B≤2T.

[0015] In one embodiment, the magnitude of the magnetic field is B, which satisfies: 0.6T≤B≤1.2T.

[0016] In one embodiment, applying a magnetic field to the negative electrode sheet also includes: the magnetic field is a square magnetic field, and the direction of the magnetic field has a first angle θ1 with the thickness direction of the negative electrode sheet, and / or the magnetic field is a cylindrical magnetic field, and the direction of the magnetic field has a second angle θ2 with the length direction of the negative electrode sheet, satisfying: 45°≤θ1≤90°, 45°≤θ2≤80°.

[0017] In one embodiment, after applying a magnetic field to the negative electrode sheet, the method further comprises: baking the negative electrode sheet at a baking temperature T satisfying: 80° C. ≤ T ≤ 140° C.

[0018] In one embodiment, the surface density of the negative electrode sheet is C, the compaction density is D, and the surface density is 140 g / m 2 ≤C≤300g / m 2 , 1.1g / cm3 ≤D≤1.8g / cm 3 .

[0019] In a third aspect, the present application also provides a battery cell comprising a diaphragm, a positive electrode sheet, and a negative electrode sheet prepared according to any one of the embodiments of the first aspect or a negative electrode sheet prepared according to any one of the embodiments of the second aspect, wherein the positive electrode sheet, the diaphragm, and the negative electrode sheet are stacked.

[0020] In a fourth aspect, the present application also provides a battery, comprising the battery cell according to the third aspect.

[0021] In one embodiment, the battery further includes a shell, which includes a bottom plate and multiple side plates, the side plates are connected to the bottom plate and enclosed to form a accommodating cavity, the accommodating cavity is open at one end opposite to the bottom plate, and the battery cell is accommodated in the accommodating cavity.

[0022] In one embodiment, the battery further includes a cover plate, which is connected to the opening of the shell to close the accommodating cavity.

[0023] In a fifth aspect, the present application also provides an electrical device comprising the battery cell according to the third aspect.

[0024] By regulating the orientation of graphite in the active layer, the liquid-phase lithium ion diffusion capacity of the electrode can be improved, and the kinetic performance and fast charging performance of the thick electrode can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation methods or the description of the prior art. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] FIG1 is a schematic diagram of a pole piece according to an embodiment;

[0027] FIG2 is a schematic diagram of applying electric and magnetic fields according to an embodiment;

[0028] FIG3 is a schematic diagram of applying different magnetic fields according to an embodiment;

[0029] FIG4 is a flow chart of a process for preparing a negative electrode sheet according to an embodiment;

[0030] FIG5 is a process flow chart of preparing an active layer according to an embodiment.

[0031] Description of reference numerals:

[0032] 100-negative electrode;

[0033] 10-current collector, 20-active layer, 30-graphite particles;

[0034] B1-square magnetic field, B2-cylindrical magnetic field. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be an intermediate component. When a component is referred to as being "connected to" another component, it may be directly connected to the other component or there may be an intermediate component.

[0037] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used in this application includes any and all combinations of one or more of the relevant listed items.

[0038] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0039] The present invention provides an electrical device including the battery cell of the present invention. The electrical device may be an electric vehicle, a hybrid vehicle, a base station, a household electrical load, or the like.

[0040] The electrical device uses a battery including the battery cell provided in the embodiment of the present application. The battery can be a square laminated battery, an energy storage battery, etc.

[0041] The battery also includes a housing, which includes a bottom plate and a plurality of side plates, the side plates being connected to the bottom plate and enclosing a receiving cavity. The receiving cavity is open at one end opposite to the bottom plate, and the battery cell is received in the receiving cavity.

[0042] The material of the shell is similar to that of the aforementioned battery pack shell, so it can be used as a reference and will not be described in detail.

[0043] Optionally, the housing may be a one-piece structure, i.e., the bottom and side panels are formed using an integrated molding process, such as stamping or casting, without limitation. The housing may also be a split-piece structure, with the side and bottom panels connected and secured by welding, bonding, clamping, screwing, or the like. The wall thickness of the housing may be substantially uniform throughout, i.e., the thickness of the side panels may be substantially uniform, and the thickness of the bottom and side panels may also be substantially the same.

[0044] The battery also includes a cover plate, which is connected to the opening of the outer shell to seal the receiving cavity. The cover plate and the outer shell can be connected by welding, bonding, clamping, screwing, etc., without limitation. The shape of the cover plate can be roughly the same as that of the base plate.

[0045] The battery uses the battery cell in the embodiment of the present application, which can effectively increase the liquid phase diffusion rate of lithium ions and improve battery performance.

[0046] The embodiment of the present application also provides a battery cell, including a separator, a positive electrode sheet and a negative electrode sheet in the embodiment of the present application, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence.

[0047] Optionally, the positive electrode sheet includes a positive electrode current collector having a positive electrode active layer thereon. The positive electrode active layer includes components such as a positive electrode material, a conductive agent, and a binder. This application does not specifically limit these materials, and suitable materials can be selected according to actual application requirements. The positive electrode current collector includes, but is not limited to, aluminum foil. The positive electrode active material can be a phosphate positive electrode active material or a ternary positive electrode active material. In specific embodiments, it includes one or more of lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadium phosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum oxide. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. The type of binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives, without specific limitation.

[0048] Optionally, the separator can be selected based on actual needs. For example, polyethylene film, polypropylene film, polyvinylidene fluoride film, and non-woven fabric can be selected. The separator can also have various coatings, such as alumina coating, boehmite coating, PVDF coating, etc., without limitation.

[0049] The battery cell adopts the negative electrode sheet in the embodiment of the present application, which can improve the diffusion capacity of liquid-phase lithium ions in the electrode and improve the dynamic performance and fast charging performance of the thick electrode.

[0050] The negative electrode sheet in the embodiment of the present application is introduced in detail below.

[0051] An embodiment of the present application provides a negative electrode sheet 100 , as shown in FIG1 , including a current collector 10 and an active layer 20 . The active layer 20 is stacked on at least one side of the current collector 10 , and the active layer 20 contains graphite.

[0052] First, let's define the directions. Referring to FIG. 1 , the width direction of the negative electrode sheet 100 is the X direction, the length direction of the negative electrode sheet 100 is the Y direction, and the thickness direction of the negative electrode sheet 100 is the Z direction.

[0053] Optionally, the active layer 20 is coated along the length direction Y.

[0054] Graphite satisfies: 0<OI a ≤5, 2≤OI b ≤20.

[0055] Among them, OI a OI is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD test on the surface of the negative electrode sheet 100; b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD testing the cross section of the negative electrode sheet 100.

[0056] In this application, OI represents the orientation of graphite in the electrode. After graphite is made into an electrode sheet, the arrangement direction (orientation) of the graphite layer structure has a great influence on the migration of lithium ions. Ideally, when the graphite layer structure is completely perpendicular to the plane direction of the electrode sheet, the path for lithium ions to be embedded in the negative electrode sheet 100 can be ensured to be short enough, which is most beneficial to the diffusion of lithium ions, thereby reducing the problems of lithium precipitation and poor cycling performance caused by excessively long lithium embedding paths; however, this is difficult to achieve in actual preparation, and the orientation of the graphite electrode can usually only be controlled within a certain range.

[0057] The X-ray diffraction method can be used to test the orientation of the graphite electrode. The principle is: when the diffraction spectrum of the negative electrode sheet 100 sample placed horizontally (the test surface is parallel to the X direction and the Y direction) is tested, the diffraction peaks of the (004) plane and the (110) plane of the graphite can be obtained respectively. The stronger the intensity of the (004) peak, the more particles of the (004) crystal plane parallel to the negative electrode sheet 100 current collector 10. The ratio of the (004) crystal plane diffraction peak intensity (or integrated area) to the (110) crystal plane diffraction peak intensity (or integrated area) OI can be used. a To measure the orientation of graphite. a The larger the value, the higher the orientation, which means that more layered structures of graphite particles 30 are arranged parallel to the current collector 10.

[0058] Section OI bThe test principle is similar to the above, and the test is carried out by stacking multiple layers of electrodes. After stacking multiple negative electrodes 100 along the Z direction, the test surface is parallel to the Y and Z directions, and the active layer 20 is exposed. b It is also the ratio of the diffraction peak intensity (or integrated area) of the (004) crystal plane to the (110) crystal plane. b The value is too large, the expansion of graphite is mainly in the X direction, the cross section OI b If the value is too small, the expansion is mainly in the Y direction. In both cases, the expansion stress is too concentrated, which is not conducive to the long-cycle performance of the graphite electrode and may cause material falling during the cycle, resulting in capacity attenuation.

[0059] It is understood that in the negative electrode sheet 100 of the present application, the active layer 20 includes, in addition to the negative electrode active material graphite, a conductive agent and a binder. Both the conductive agent and the binder can be selected according to needs. For example, the conductive agent can be selected from conductive carbon black (SP), carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, carbon nanofiber, etc.; the binder can be selected from polyacrylonitrile, polyvinylidene fluoride (PVDF), polyvinyl alcohol, sodium carboxymethyl cellulose (CMC), polymethacrylamide, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene-butadiene rubber (SBR), sodium alginate, chitosan, polyethylene glycol, guar gum, etc., without limitation.

[0060] Commonly used cathode and anode active materials in lithium-ion batteries, such as lithium iron phosphate, lithium nickel cobalt manganese oxide, and graphite, have specific active surfaces for lithium ion embedding, along which the potential barrier to lithium ion embedding is minimized. By manipulating the material's orientation so that the direction of lithium embedding aligns with the direction of lithium ion diffusion during battery charge and discharge, the battery's impedance is reduced.

[0061] On the other hand, under existing electrode preparation processes, the accumulation of active material particles is often disordered, resulting in large electrode tortuosity and long lithium ion diffusion paths. By manipulating particle orientation, the tortuosity of the electrode can be significantly reduced, improving the diffusion capacity of lithium ions in the pores within the electrode.

[0062] Therefore, studying how to reduce tortuosity is of great significance in high-areal-density, high-pressure electrode systems. This application modulates the tortuosity of the electrode and, at the same time, modulates the angle between the lithium-insertion surface of the electrode and the current collector 10, thereby shortening the diffusion path of lithium ions in the electrode.

[0063] The negative electrode sheet 100 provided in the embodiments of the present application includes a stacked current collector 10 and an active layer 20, wherein the active layer 20 contains graphite. By regulating the orientation of the graphite in the active layer 20, the liquid-phase lithium ion diffusion capacity of the electrode can be improved, thereby enhancing the kinetic performance and fast-charging performance of the thick electrode.

[0064] Optionally, graphite satisfies: 0<OI a ≤2, 2≤OI b ≤10.

[0065] Optional, OI a The value of OI can be 0.8, 1, 1.2, 1.3, etc. b The value can be 4, 4.8, 5.6, 6.2, etc., without specific restrictions.

[0066] By regulating the orientation of graphite, the plane OI a The value and cross-section OI b The values ​​of all meet the above ranges, which can improve the liquid-phase lithium ion diffusion capacity of the electrode and improve the kinetic performance and fast charging performance of the thick electrode.

[0067] The present embodiment further provides a method for preparing a negative electrode sheet 100, which specifically includes the following steps, as shown in FIG4 :

[0068] S10: providing a current collector 10;

[0069] S20 : ​​The active layer 20 is stacked on the current collector 10 .

[0070] Specifically, the active layer 20 contains graphite; the graphite satisfies: 0<OI a ≤5, 2≤OI b ≤20.

[0071] Among them, OI a OI is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD test on the surface of the negative electrode sheet 100; b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by XRD testing the cross section of the negative electrode sheet 100.

[0072] By setting a negative electrode sheet 100, the negative electrode sheet 100 includes a stacked current collector 10 and an active layer 20, and the active layer 20 contains graphite. By regulating the orientation of the graphite in the active layer 20, the liquid-phase lithium ion diffusion capacity of the electrode can be improved, and the dynamic performance and fast charging performance of the thick electrode can be improved.

[0073] Optionally, an active layer 20 is stacked on the current collector 10. Referring to FIG. 5 , the process specifically includes the following steps:

[0074] S21; coating the current collector 10 with a slurry comprising graphite particles 30;

[0075] S22: applying an alternating electric field to the negative electrode sheet 100 to generate an induced current in the active layer 20; and / or,

[0076] S23 : applying a magnetic field to the negative electrode sheet 100 to regulate the directional arrangement of the graphite particles 30 .

[0077] Optionally, the current collector 10 is copper foil, etc., without specific limitation.

[0078] Optionally, the slurry includes materials such as graphite, a conductive agent, a binder, a stabilizer, and water. The types of the conductive agent and the binder are as described above and will not be described in detail.

[0079] Optionally, an active layer 20 is stacked on the current collector 10, and an alternating electric field can be applied only to the negative electrode sheet 100 to cause the active layer 20 to generate an induced current; alternatively, a magnetic field can be applied only to the negative electrode sheet 100; alternatively, both an alternating electric field and a magnetic field can be applied to the negative electrode sheet 100. All of the above methods are possible and are not specifically limited.

[0080] Optionally, as shown in FIG2 , the slurry is coated on the current collector 10 using a continuous coating device. After coating, the graphite particles 30 can be arranged in a random or regular orientation, without limitation. Applying an alternating electric field in step S22 can cause the graphite particles 30 inside the electrode to generate an induced current, the direction of which is parallel to the layered structure of the graphite particles 30 (parallel to the Y direction); then applying a magnetic field in step S23 causes the graphite particles 30 to be subjected to a force, resulting in a directional arrangement.

[0081] By applying alternating electric and magnetic fields to the negative electrode sheet 100, the graphite particles 30 in the active layer 20 are regulated from a random arrangement to a directional arrangement, which can reduce the tortuosity of the electrode, improve the diffusion ability of lithium ions in the internal pores of the electrode, and at the same time reduce the angle between the material's lithium insertion channel and the lithium ion diffusion direction, thereby improving the kinetic performance of the electrode.

[0082] Optionally, applying an alternating electric field to the negative electrode sheet 100 includes: the voltage of the alternating electric field is U, the frequency is F, and the following conditions are satisfied: 0V<U≤400V, 30Hz≤F≤150Hz.

[0083] Optionally, the voltage range of the alternating current battery is 24V≤U≤130V, and 50Hz≤F≤100Hz. Specifically, the voltage can be 36V, 48V, 100V, etc., and the frequency can be 50Hz, 70Hz, 90Hz, etc., without limitation.

[0084] By applying an alternating electric field with appropriate voltage and frequency to the negative electrode sheet 100, the magnitude and frequency of the alternating electric field satisfy the above ranges, so that the graphite inside the electrode sheet generates an induced current.

[0085] Optionally, applying a magnetic field to the negative electrode sheet 100 includes: a magnitude of the magnetic field is B, and satisfies: 0T<B≤2T.

[0086] Optionally, the magnitude of the magnetic field is 0.6 T ≤ B ≤ 1.2 T. Specifically, the magnitude of the magnetic field may be 0.6 T, 0.8 T, 1.0 T, 1.2 T, etc., without limitation.

[0087] By applying a magnetic field to the negative electrode sheet 100, and the magnitude of the magnetic field satisfies the above range, the graphite particles 30 in the active layer 20 can be regulated from an irregular arrangement to a directional arrangement, which can reduce the tortuosity of the electrode, improve the diffusion ability of lithium ions in the internal pores of the electrode, and at the same time reduce the angle between the material's lithium insertion channel and the lithium ion diffusion direction, thereby improving the kinetic performance of the electrode.

[0088] Optionally, as shown in FIG3 , applying a magnetic field to the negative electrode sheet 100 further includes: the magnetic field is a square magnetic field B1 , and the direction of the magnetic field and the Z direction of the negative electrode sheet 100 have a first angle θ1 ; and / or,

[0089] The magnetic field is a cylindrical magnetic field B2 , and the direction of the magnetic field has a second angle θ2 with the Y direction of the negative electrode sheet 100 , satisfying: 45°≤θ1≤90°, 45°≤θ2≤80°.

[0090] Optionally, the square magnetic field B1 is used to adjust the angle between the graphite particles 30 and the Z direction. The first angle θ1 between the square magnetic field B1 and the Z direction of the negative electrode sheet 100 satisfies 60°≤θ1≤90°. Specifically, the first angle θ1 can be 60°, 70°, 80°, 90°, etc., without limitation.

[0091] Optional, flat OI a The value depends on the first angle θ1. Adjusting the first angle θ1 will affect the tortuosity of the electrode, and further affect the liquid phase diffusion capacity of lithium ions in the electrode.

[0092] Optionally, as shown in FIG3 , the cylindrical magnetic field B2 is used to adjust the angle between the graphite particles 30 and the Y direction. The cylindrical magnetic field B2 can rotate around the axis, and the axis has a second angle θ2 with the Y direction of the negative electrode sheet 100 .

[0093] Optionally, the second angle θ2 between the axis of the cylindrical magnetic field B2 and the Y direction of the negative electrode sheet 100 satisfies 45°≤θ2≤70°. Specifically, the second angle θ2 can be 50°, 55°, 60°, 65°, etc., without limitation.

[0094] Optionally, the second angle θ2 determines the cross section OI b The size of the cross section is parallel to the Y and Z directions, and the cross section OI b The value is too large, the expansion of graphite is mainly in the X direction, the cross section OI bIf the value is too small, the expansion is mainly in the Y direction. In both cases, the expansion stress is too concentrated, which is not conducive to the long-cycle performance of the graphite electrode and may cause material falling during the cycle, resulting in capacity attenuation.

[0095] Optionally, the square magnetic field B1 and the cylindrical magnetic field B2 can be used separately; or, the square magnetic field B1 and the cylindrical magnetic field B2 can be used at the same time. When used at the same time, the square magnetic field B1 and the cylindrical magnetic field B2 can be used in sections on the negative electrode sheet 100, or they can be used alternately on the entire negative electrode sheet 100, and so on, without limitation.

[0096] Optionally, a square magnetic field B1 and a cylindrical magnetic field B2 are applied to the entire negative electrode sheet 100 simultaneously to adjust the angles between the graphite particles 30 and the Z direction and the Y direction, respectively.

[0097] By applying two different magnetic fields to the negative electrode sheet 100 , the angles between the graphite particles 30 and the Z direction and the Y direction can be adjusted respectively, so that the graphite particles 30 are arranged in a directional manner.

[0098] Optionally, after applying the magnetic field to the negative electrode sheet 100 , the method further includes: baking the negative electrode sheet 100 , wherein the baking temperature is T and satisfies: 80° C. ≤ T ≤ 140° C.

[0099] Optionally, the negative electrode sheet 100 has a surface density of C and a compaction density of D, which satisfies: 140 g / m 2 ≤C≤300g / m 2 , 1.1g / cm 3 ≤D≤1.8g / cm 3 .

[0100] Optionally, the baking temperature T can be 80°C, 100°C, 120°C, etc., and the surface density C can be controlled to 225g / m 2 , 230g / m 2 , 235g / m 2 etc., the compaction density D can be controlled to 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 etc., without any specific limitation.

[0101] As can be understood, the coating density of the negative electrode sheet 100 significantly impacts the fast-charging performance of lithium-ion batteries. As the areal density of the negative electrode sheet 100 increases, the ionic and electronic impedances of the sheet increase, leading to increased battery internal resistance and deteriorating fast-charging and cycling performance. Therefore, selecting an appropriate areal density is crucial for minimizing the battery's internal resistance while ensuring the battery's discharge capacity and cycling performance.

[0102] The process of lithium ion extraction and insertion is closely related to the compaction density of the negative electrode sheet 100. On the one hand, as the compaction density of the electrode sheet increases, the contact between the particles of the negative electrode active material gradually becomes closer, the electronic conductive network in the electrode sheet is improved, and the internal resistance is reduced; however, if the compaction density is too high, it will cause the electrode sheet to rebound during the cycle, causing the contact chain between the conductive agent and adhesive and the negative electrode active material to break, resulting in the mutual peeling of the negative electrode active material particles, thereby increasing the resistance of charge transfer, and further deteriorating the battery's rate performance and cycle performance. On the other hand, increasing the compaction density of the negative electrode sheet 100 will also cause the porosity in the electrode sheet to continue to decrease, resulting in a continuous decrease in the amount of electrolyte retained in the electrode sheet, a decrease in the ionic conductivity of the electrode sheet, and an increase in the internal resistance of the battery. Therefore, choosing a suitable compaction density can both reduce the rebound of the negative electrode sheet 100 and ensure the power performance of the battery.

[0103] By baking the negative electrode sheet 100 after applying the electric field and the magnetic field to obtain the negative electrode sheet 100 meeting the above parameters, the discharge specific capacity, cycle performance and power performance of the battery can be optimized.

[0104] The technical solution of the present invention is described in detail below through specific embodiments.

[0105] Example 1

[0106] The negative electrode sheet in this embodiment includes a current collector and an active layer, wherein the current collector is a copper foil, and a slurry is coated on the copper foil to form the active layer. The slurry includes materials such as graphite, a conductive agent, a binder, a stabilizer, and water.

[0107] 1) Coating: Use continuous coating equipment to coat the slurry on the copper foil along the length direction;

[0108] 2) Control, while applying an alternating electric field with a voltage of 36 V and a frequency of 50 Hz and a magnetic field of 0.4 T to the current collector copper foil to magneto-electrically induce graphite orientation, with the first angle θ1 = 90° between the square magnetic field and the thickness direction of the negative electrode sheet, and the second angle θ2 = 60° between the cylindrical magnetic field and the length direction of the electrode sheet, to keep the magnetic field uniform and stable.

[0109] 3) Baking, baking temperature 100 ℃, adjust the surface density to 230g / m 2 , compaction density is controlled at 1.6g / cm 3 .

[0110] Example 2

[0111] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the magnetic field size is 0.8T.

[0112] Example 3

[0113] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the voltage is 100V.

[0114] Example 4

[0115] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that there is no cylindrical magnetic field.

[0116] Example 5

[0117] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and embodiment 4 is that there is no electric field.

[0118] Example 6

[0119] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and embodiment 5 is that the magnetic field size is 0.6T.

[0120] Example 7

[0121] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and embodiment 5 is that the magnetic field size is 0.8T.

[0122] Example 8

[0123] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that it does not have a square magnetic field.

[0124] Example 9

[0125] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the eighth embodiment is that there is no electric field.

[0126] Example 10

[0127] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and embodiment 9 is that the magnetic field size is 0.6T.

[0128] Example 11

[0129] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and embodiment 9 is that the magnetic field size is 0.8T.

[0130] Example 12

[0131] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the voltage is 24V.

[0132] Example 13

[0133] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the voltage is 130V.

[0134] Example 14

[0135] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the magnetic field size is 0.6T.

[0136] Example 15

[0137] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the magnetic field size is 1.2T.

[0138] Example 16

[0139] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that there is no electric field.

[0140] Example 17

[0141] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that the electric field frequency is 100 Hz.

[0142] Comparative Example 1

[0143] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that there is no magnetic field.

[0144] Comparative Example 2

[0145] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the first embodiment is that there is no electric field and magnetic field.

[0146] Comparative Example 3

[0147] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator. The difference between this embodiment and the embodiment 1 is that: θ2 = 90°.

[0148] Comparative Example 4

[0149] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and is different from the embodiment 1 in that: θ1 = 30°.

[0150] Comparative Example 5

[0151] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and is different from the embodiment 1 in that: θ2 = 30°.

[0152] Table 1 is a summary table of parameter settings for the above embodiments and comparative examples.

[0153] The electrochemical properties of the negative electrode sheets prepared in Examples 1-17 and Comparative Examples 1-5 were characterized and tested:

[0154] OI value: Through the XRD test of the pole piece, the graphite (004) peak intensity (peak integrated area) and (110) peak intensity (peak integrated area) in each pole piece are measured to calculate the OI value of the graphite crystal structure. a It is obtained by testing the XRD spectrum of the electrode surface, which can be used to characterize the angle between the graphite (004) crystal plane and the Z direction, OI b The XRD spectrum obtained by testing the cross section of the electrode can be used to characterize the angle between the graphite (004) plane and the Y direction.

[0155] It should be noted that the OI value of the graphite crystal structure in this application is the OI value of the graphite in the negative electrode sheet. The OI value of the material in the electrode sheet reflects the arrangement of the material in the electrode sheet. In addition to being affected by the OI value of the graphite material itself, the OI value of the graphite in the electrode sheet is also affected by the electrode sheet manufacturing process.

[0156] Peeling force test: Evenly stick the transparent tape on one side of the electrode and tear off one end to fix it on the test fixture. Use a tensile tester to measure the force when the tape peels off the electrode, so as to evaluate the bonding strength between the graphite particles in the negative electrode and with the current collector copper foil. a It has a great influence on the peeling force, OI a The smaller it is, the greater the peeling force is.

[0157] Liquid phase diffusion impedance test: The electrode, diaphragm, and electrode stack are made into a symmetrical battery. At a frequency of 0.02-200000HZ and a voltage of 5V, the AC impedance of the symmetrical battery is tested and analyzed as the liquid phase diffusion impedance.

[0158] Specifically, electrochemical impedance spectroscopy (EIS) observes how the impedance of the electrode system changes with the frequency of the sine wave, applying a small-amplitude sinusoidal potential signal of a certain frequency to the electrode based on a baseline potential. The spectrum is then analyzed and fitted to obtain information about the electrode process kinetics and the electrode interface structure. Generally, an equivalent circuit can be fitted to obtain the diffusion impedance of lithium ions in the electrolyte, which is used to characterize the internal impedance of the battery.

[0159] Battery preparation and capacity ratio test method:

[0160] The battery of this embodiment further includes a separator and a positive electrode sheet.

[0161] 4) Cut the above negative electrode sheet into electrodes of appropriate size, matching the corresponding size and surface density of 500g / m 2 The positive electrode lithium iron phosphate electrode;

[0162] 5) dissolving 1 mol of lithium salt -LiPF6 in 1 L of an organic solvent (including ethylene carbonate and diethyl carbonate, with a volume ratio of ethylene carbonate to diethyl carbonate of 1:1) to obtain an electrolyte;

[0163] 6) Under a dew point environment, the positive electrode sheet, separator, and negative electrode sheet prepared in step 4) are stacked in sequence and injected with electrolyte to prepare a soft-pack battery with a designed battery capacity of 2.0 Ah.

[0164] Capacity calibration: In the voltage range of 2.0-3.8V, the battery is tested with 0.33C / 0.33C charge / discharge cycles for three cycles, and the capacity of the last cycle is taken as the battery capacity.

[0165] 50% SOC DC internal resistance test: The state of charge of the above soft-pack batteries was adjusted to 50% SOC at 25°C, and then charged at 1.5C for 30s. The voltage drop of each soft-pack battery was recorded to calculate the DC internal resistance (DCIR).

[0166] Charge capacity ratio: After discharging at 0.1C at 25°C, the battery was charged at 0.2C and 3C, respectively, with a voltage range of 2.0-3.8V. Calculate the ratio of the charge capacity at 3C to the charge capacity at 0.2C.

[0167] 45℃ cycle capacity retention rate: At 45℃, the battery was charged and discharged at a constant current of 1C / 1C, with a 30min rest period between each charge and discharge. The capacity retention rate of the battery after 500 cycles was recorded.

[0168] The electrochemical properties of the negative electrode sheet and the assembled battery were characterized. Table 2 summarizes the results of the characterization tests.

[0169] It can be seen from the experimental results of Examples 1 to 17 and Comparative Examples 1 to 2 in Tables 1 to 2 that by applying an electric field and / or a magnetic field to the negative electrode sheet, the bonding ability between the graphite particles and with the current collector copper foil can be improved, the resistivity and liquid phase diffusion impedance of the electrode sheet can be reduced, and the intercalation and deintercalation efficiency of lithium ions in the electrode sheet can be improved, which is beneficial to improving the charge and discharge performance of the battery.

[0170] It can be seen from Example 1, Example 3, and Examples 12 to 13 in Table 1 to Table 2 that the applied electric field strength is preferably 36V-130V, and the stronger the applied electric field, the better the power performance of the battery; it can be seen from Example 1 and Example 17 that the frequency of the applied electric field is preferably 50Hz-100Hz, and the higher the frequency of the applied electric field, the better the power performance of the battery; it can be seen from Examples 1 to 2, Examples 5 to 7, Examples 9 to 11, and Examples 14 to 15 that, whether a square magnetic field or a cylindrical magnetic field is applied alone, or a square magnetic field and a cylindrical magnetic field are applied simultaneously, the applied magnetic field strength is preferably 0.6T-1.2T, and the stronger the applied magnetic field, the better the power performance of the battery.

[0171] From the experimental results of Example 1 and Comparative Examples 3 to 5 in Tables 1 and 2, it can be seen that when the same electric field and the same magnitude of magnetic field are applied to the negative electrode sheet, the angle of the magnetic field will affect the durability of the electrode. a The value becomes larger, and the plane OI a The increase of the value will affect the deintercalation efficiency of lithium ions in the electrode, and further affect the liquid phase diffusion capacity of lithium ions in the electrode, which is not conducive to reducing the liquid phase diffusion impedance. At the same time, it can be found that the plane OI a The smaller the value, the higher the charging ratio. The change of the second angle θ2 between the cylindrical magnetic field and the Y direction will affect the cross-sectional OI b Value, cross-section OI b If the value is too large or too small, the expansion stress will be too concentrated, which is not conducive to the long-cycle performance of the graphite electrode. It may cause material falling during the cycle and cause capacity attenuation.

[0172] From the experimental results of Examples 1 to 17 and Comparative Examples 1 to 5 in Tables 1 and 2, it can be seen that applying electric and magnetic fields to the negative electrode can significantly improve the performance of the electrode in all aspects, and the stronger the magnetic and electric field strengths, the better the orientation adjustment effect of the electrode and the better the power performance of the electrode. At the same time, the angle of the magnetic field has a great influence on the durability of the electrode and needs to be controlled within a reasonable range so that the plane OI of the electrode is a and cross-sectional OI b The value can be controlled within an appropriate range to disperse the expansion stress of the electrode in the X and Y directions, avoiding stress concentration that may cause peeling of the active material during the cycle and reduce the cycle retention rate of the battery.

[0173] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", and "outside" are based on the orientation or positional relationship described in the accompanying drawings. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present application.

[0174] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present application are still within the scope covered by the present application.

Claims

1. A negative electrode sheet (100), characterized in that: include: current collector(10); An active layer (20) stacked on at least one side of the current collector (10), wherein the active layer (20) contains graphite; The graphite satisfies: 0<OI a ≤5,2≤OI b ≤20; Among them, OI a is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing an XRD test on the surface of the negative electrode sheet (100); OI b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing an XRD test on the cross section of the negative electrode sheet (100).

2. The negative electrode sheet (100) according to claim 1, characterized in that: The graphite satisfies: 0<OI a ≤2, 2≤OI b ≤10.

3. A method for preparing a negative electrode sheet (100), characterized in that: include: Providing (S10) a current collector (10); An active layer (20) is stacked and arranged (S20) on at least one side of the current collector (10), wherein the active layer (20) contains graphite; The graphite satisfies: 0<OI a ≤5,2≤OI b ≤20; Among them, OI a is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing an XRD test on the surface of the negative electrode sheet (100); OI b It is the ratio of the peak area of ​​the characteristic diffraction peak of the graphite (004) plane to the peak area of ​​the characteristic diffraction peak of the graphite (110) plane obtained by performing an XRD test on the cross section of the negative electrode sheet (100).

4. The method for preparing the negative electrode sheet (100) according to claim 3, characterized in that: The active layer (20) is stacked on the current collector (10) and comprises: coating (S21) a slurry on the current collector (10), wherein the slurry includes graphite particles (30); applying (S22) an alternating electric field to the negative electrode sheet (100) so that the active layer (20) generates an induced current; and / or, A magnetic field is applied (S23) to the negative electrode sheet (100) to orient the graphite particles (30).

5. The method for preparing the negative electrode sheet (100) according to claim 4, characterized in that: The voltage of the alternating electric field is U, and the frequency is F, which satisfies: 0V<U≤400V, 30Hz≤F≤150Hz.

6. The method for preparing the negative electrode sheet (100) according to claim 5, characterized in that: The voltage of the alternating electric field is U, and the frequency is F, which satisfies: 24V≤U≤130V, 50Hz≤F≤100Hz.

7. The method for preparing the negative electrode sheet (100) according to claim 4, characterized in that: The magnitude of the magnetic field is B, which satisfies: 0T<B≤2T.

8. The method for preparing the negative electrode sheet (100) according to claim 7, characterized in that: The magnitude of the magnetic field is B, which satisfies: 0.6T≤B≤1.2T.

9. The method for preparing the negative electrode sheet (100) according to claim 7, characterized in that: The magnetic field is a square magnetic field (B1), and the direction of the magnetic field has a first angle θ1 with the thickness direction of the negative electrode sheet (100), and / or the magnetic field is a cylindrical magnetic field (B2), and the direction of the magnetic field has a second angle θ2 with the length direction of the negative electrode sheet (100), satisfying: 45°≤θ1≤90°, 45°≤θ2≤80°.

10. The method for preparing the negative electrode sheet (100) according to claim 4, characterized in that: After applying a magnetic field to the negative electrode sheet (100), the method further comprises: baking the negative electrode sheet (100), wherein the baking temperature is T and satisfies: 80°C≤T≤140°C.

11. The method for preparing the negative electrode sheet (100) according to claim 4, characterized in that: The surface density of the negative electrode sheet (100) is C, and the compaction density of the negative electrode sheet (100) is D, which satisfies: 140 g / m 2 ≤C≤300g / m 2 , 1.1g / cm 3 ≤D≤1.8g / cm 3 .

12. A battery cell, characterized in that: The invention comprises a separator, a positive electrode sheet, and a negative electrode sheet (100) prepared according to the method for preparing the negative electrode sheet (100) according to claim 1 or 2 or the negative electrode sheet (100) according to any one of claims 3 to 11, wherein the positive electrode sheet, the separator, and the negative electrode sheet (100) are stacked.

13. A battery, characterized in that: Comprising the battery cell according to claim 12.

14. The battery according to claim 13, characterized in that The battery also includes a shell, which includes a bottom plate and a plurality of side plates. The side plates are connected to the bottom plate and enclose a receiving cavity. The receiving cavity is open at one end opposite to the bottom plate, and the battery cell is received in the receiving cavity.

15. The battery according to claim 14, characterized in that A cover plate is also included, and the cover plate is connected to the opening of the shell to close the accommodating cavity.

16. An electrical equipment, characterized in that: Comprising the battery cell according to claim 12.

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