Negative plate and preparation method thereof, battery cell and electric equipment

Abstract

The invention relates to a negative plate and a preparation method thereof, a battery cell and electric equipment, the negative plate comprises a current collector and an active layer, the active layer is laminated on the current collector, the active layer contains graphite, and the graphite satisfies 0 < OIa < = 5 and 2 < = OIb < = 20; wherein OIa is a ratio of a peak area of a characteristic diffraction peak of a graphite (004) surface to a peak area of a (110) characteristic diffraction peak obtained by performing an XRD test on the surface of the negative plate; and OIb is the ratio of the peak area of a characteristic diffraction peak of a graphite (004) surface to the peak area of a (110) characteristic diffraction peak obtained by carrying out XRD test on the cross section of the negative plate. The parameters are met by regulating and controlling the orientation of the graphite in the active layer, the liquid-phase lithium ion diffusivity of the electrode can be improved, and the dynamic performance and the fast charging performance of the thick electrode can be improved.

Description

Technical Field

[0001] 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

[0002] 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.

[0003] 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. Summary of the invention

[0004] The purpose of the present application is to provide a negative electrode sheet and a preparation method thereof, a battery cell and an electrical device, 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.

[0005] To achieve the purpose of this application, this application provides the following technical solutions:

[0006] 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;

[0007] 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 (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 (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet.

[0008] In one embodiment, the graphite satisfies: 0<OI a ≤2, 2≤OI b ≤10.

[0009] 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 contains graphite; and the graphite satisfies: 0<OI a ≤5,2≤OI b ≤20;

[0010] Among them, OI aOI 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 (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 (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, the slurry including graphite particles; applying an alternating electric field to the negative electrode sheet to cause the active layer to generate an induced current; and / or applying a magnetic field to the negative electrode sheet to orient the graphite particles.

[0012] In one embodiment, applying an alternating electric field to the negative electrode sheet includes: the voltage of the alternating electric field is U, the frequency is F, and it satisfies: 0V<U≤400V, 30Hz≤F≤150Hz; preferably, 24V≤U≤130V, 50Hz≤F≤100Hz.

[0013] In one embodiment, applying a magnetic field to the negative electrode plate includes: the magnitude of the magnetic field is B, satisfying: 0T<B≤2T; preferably, 0.6T≤B≤1.2T.

[0014] 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°.

[0015] In one embodiment, after applying a magnetic field to the negative electrode sheet, the method further comprises: baking the negative electrode sheet, wherein the baking temperature is T and satisfies: 80°C≤T≤140°C.

[0016] In one embodiment, the negative electrode sheet 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 .

[0017] In a third aspect, the present application also provides a battery cell, comprising a separator, a positive electrode sheet, and a negative electrode sheet as described in any one of the embodiments of the first aspect or a negative electrode sheet prepared by the preparation method of the negative electrode sheet as described in any one of the embodiments of the second aspect, wherein the positive electrode sheet, the separator, and the negative electrode sheet are stacked.

[0018] In a fourth aspect, the present application also provides an electrical device, comprising the battery cell described in the third aspect.

[0019] 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

[0020] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. 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.

[0021] Figure 1 is a schematic diagram of a pole piece of an embodiment;

[0022] Figure 2 is a schematic diagram of applied electric and magnetic fields according to an embodiment;

[0023] Figure 3 is a schematic diagram of applying different magnetic fields according to an embodiment;

[0024] Figure 4 is a process flow chart of preparing a negative electrode sheet according to an embodiment;

[0025] Figure 5 The present invention is a process flow chart of preparing an active layer according to an embodiment.

[0026] Description of reference numerals:

[0027] 100-negative electrode;

[0028] 10-current collector, 20-active layer, 30-graphite particles;

[0029] B1-square magnetic field, B2-cylindrical magnetic field. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there can be a central component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there can be a central component at the same time.

[0032] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items.

[0033] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0034] The embodiment of the present application provides an electric device, including the battery cell in the embodiment of the present application. The electric device may be an electric vehicle, a hybrid vehicle, a base station, a household power load, etc.

[0035] 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.

[0036] 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 enclosed to form 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.

[0037] 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.

[0038] Optionally, the shell can be an integrated structure, that is, the bottom plate and the side plate are an integrated structure made by an integrated molding process, and the integrated molding process can be stamping, casting, etc., without limitation. The shell can also be a split structure, and the side plate and the bottom plate can be connected and fixed by welding, bonding, clamping, screwing, etc. The wall thickness of the shell can be roughly uniform everywhere, that is, the thickness of the side plate can be roughly uniform, and the thickness of the bottom plate and the side plate can also be roughly the same.

[0039] The battery also includes a cover plate, which is connected to the opening of the shell to close the accommodating cavity. The connection between the cover plate and the shell can be welding, bonding, clamping, screwing, etc., without limitation. The shape of the cover plate can be roughly the same as that of the bottom plate.

[0040] The battery adopts 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.

[0041] 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.

[0042] Optionally, the positive electrode sheet includes a positive electrode current collector, and the positive electrode current collector has a positive electrode active layer, and the positive electrode active layer includes components such as positive electrode materials, conductive agents, and binders. The present 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 and a ternary positive electrode active material. In a specific embodiment, it includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, 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 types of binders include 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.

[0043] Optionally, the separator can be selected according to actual needs. For example, the separator can be selected from polyethylene film, polypropylene film, polyvinylidene fluoride film and non-woven fabric, etc. At the same time, the separator can have different coating layers, such as aluminum oxide coating, boehmite coating, PVDF coating, etc., without limitation.

[0044] 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.

[0045] The negative electrode sheet in the embodiment of the present application is described in detail below.

[0046] The present application embodiment provides a negative electrode sheet 100, such as Figure 1 As shown, the current collector 10 and the active layer 20 are included. The active layer 20 is stacked on at least one side of the current collector 10 , and the active layer 20 contains graphite.

[0047] First define the direction, please refer to Figure 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.

[0048] Optionally, the active layer 20 is coated along the length direction Y.

[0049] Graphite satisfies: 0<OI a ≤5,2≤OI b ≤20.

[0050] Among them, OIa 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 (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 (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet 100.

[0051] 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 layered 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, it can ensure that the path for lithium ions to be embedded in the negative electrode sheet 100 is short enough, which is most beneficial to the diffusion of lithium ions, thereby reducing the problems of lithium precipitation and poor cycle capacity caused by too long lithium insertion paths; however, it is difficult to achieve in actual preparation, and usually the orientation of the graphite electrode can only be controlled within a certain range.

[0052] The X-ray diffraction method can be used to test the orientation of graphite electrodes. 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 .

[0053] Section OI b The test principle is similar to the above, and the test is carried out by stacking multiple layers of electrodes. After multiple negative electrode sheets 100 are stacked along the Z direction, the test surface is parallel to the Y direction and the Z direction, and the active layer 20 is ensured to be 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.

[0054] It is understandable that in the negative electrode sheet 100 of the present application, in addition to the negative electrode active material graphite, the active layer 20 also includes a conductive agent and a binder. Both the conductive agent and the binder can be selected according to the needs. For example, the conductive agent can be selected from conductive carbon black (SP), carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, carbon nanofibers, 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.

[0055] Commonly used positive and negative 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, and the potential barrier to be overcome by embedding lithium ions along this direction is minimal. By regulating the orientation of the material, the lithium embedding direction is consistent with the diffusion direction of lithium ions during the battery charging and discharging process, which is beneficial to reducing the impedance of the battery.

[0056] On the other hand, under the existing electrode preparation process, the accumulation of active material particles is often disordered, resulting in large overall electrode tortuosity and long lithium ion diffusion paths. By regulating the particle orientation, the tortuosity of the electrode can be significantly reduced, and the diffusion capacity of lithium ions in the internal pores of the electrode can be improved.

[0057] Therefore, studying how to reduce tortuosity is of great significance in high surface density and high compaction electrode systems. The present application can adjust the tortuosity of the electrode and at the same time adjust 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.

[0058] The negative electrode sheet 100 provided in the embodiment of the present application includes a current collector 10 and an active layer 20 which are stacked, and graphite is contained in the active layer 20. 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 kinetic performance and fast charging performance of the thick electrode can be improved.

[0059] Optionally, graphite satisfies: 0<OI a ≤2, 2≤OI b ≤10.

[0060] Optional, OI a The value of can be 0.8, 1, 1.2, 1.3, etc. b The value of can be 4, 4.8, 5.6, 6.2, etc., without specific limitation.

[0061] By regulating the orientation of graphite, the plane OI a Value and cross-sectional OI bThe values ​​of all satisfy the above range, 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.

[0062] The present application also provides a method for preparing a negative electrode sheet 100. Figure 4 , specifically including the following steps:

[0063] S10: providing a current collector 10;

[0064] S20 : ​​stacking the active layer 20 on the current collector 10 .

[0065] Specifically, the active layer 20 contains graphite; the graphite satisfies: 0<OI a ≤5,2≤OI b ≤20.

[0066] 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 (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 (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet 100.

[0067] 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 adjusting 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 kinetic performance and fast charging performance of the thick electrode can be improved.

[0068] Optionally, an active layer 20 is stacked on the current collector 10, see Figure 5 , specifically including the following steps:

[0069] S21; coating the current collector 10 with a slurry, wherein the slurry includes graphite particles 30;

[0070] S22: applying an alternating electric field to the negative electrode sheet 100 to cause the active layer 20 to generate an induced current; and / or,

[0071] S23: applying a magnetic field to the negative electrode sheet 100 to adjust the directional arrangement of the graphite particles 30 .

[0072] Optionally, the current collector 10 is copper foil or the like, without any specific limitation.

[0073] 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 mentioned above and will not be described in detail.

[0074] Optionally, an active layer 20 is stacked on the current collector 10, and an alternating electric field may be applied only to the negative electrode sheet 100 to cause the active layer 20 to generate an induced current; or, a magnetic field may be applied only to the negative electrode sheet 100; or, both an alternating electric field and a magnetic field may be applied to the negative electrode sheet 100, and all of the above methods are possible and are not specifically limited.

[0075] Optional, such as Figure 2 As shown, the slurry is coated on the current collector 10 by a continuous coating device. After coating, the graphite particles 30 can be arranged irregularly or regularly, without limitation. Applying an alternating electric field in step S22 can cause the graphite particles 30 inside the pole piece to generate an induced current, and the direction of the induced current 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 stressed and oriented.

[0076] By applying an alternating electric field and a magnetic field to the negative electrode sheet 100, the graphite particles 30 in the active layer 20 are regulated from an irregular arrangement to a directional arrangement, which can reduce the tortuosity of the electrode, improve the diffusion capacity 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.

[0077] 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.

[0078] Optionally, the voltage range of the alternating current battery is 24V≤U≤130V, 50Hz≤F≤100Hz. Specifically, the voltage may be 36V, 48V, 100V, etc., and the frequency may be 50Hz, 70Hz, 90Hz, etc., without limitation.

[0079] By applying an alternating electric field with a suitable 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.

[0080] Optionally, applying a magnetic field to the negative electrode sheet 100 includes: a magnitude of the magnetic field is B, satisfying: 0T<B≤2T.

[0081] 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.

[0082] By applying a magnetic field to the negative electrode sheet 100, the magnitude of the magnetic field satisfies the above range, and 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 capacity of lithium ions in the internal pores of the electrode, and at the same time reduce the angle between the material lithium insertion channel and the lithium ion diffusion direction, thereby improving the kinetic performance of the electrode.

[0083] Optional, such as Figure 3 As shown, applying a magnetic field to the negative electrode sheet 100 also 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,

[0084] 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°.

[0085] 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.

[0086] 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.

[0087] Optional, such as Figure 3 As shown, 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 .

[0088] 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.

[0089] 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 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.

[0090] 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 can be used alternately on the entire negative electrode sheet 100, and so on, without limitation.

[0091] Optionally, a square magnetic field B1 and a cylindrical magnetic field B2 are simultaneously applied to the entire negative electrode sheet 100 to adjust the angles between the graphite particles 30 and the Z direction and the Y direction, respectively.

[0092] 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 can be arranged in a directional manner.

[0093] 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.

[0094] 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 .

[0095] Optionally, the baking temperature T can be 80°C, 100°C, 120°C, etc., and the surface density C can be controlled to be 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 specific limitation.

[0096] It is understandable that the coating surface density of the negative electrode sheet 100 has a significant impact on the fast charging performance of the lithium-ion battery. As the surface density of the negative electrode sheet 100 increases, the ionic impedance and electronic impedance of the electrode sheet increase, the internal resistance of the battery increases, and the fast charging and cycle performance deteriorate. Therefore, choosing a suitable surface density can both reduce the internal resistance of the battery and ensure the discharge specific capacity and cycle performance of the battery.

[0097] The process of lithium ion extraction and embedding 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; but if the compaction density is too high, the electrode sheet will rebound during the cycle, causing the contact chain between the conductive agent and the 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 rate performance and cycle performance of the battery. On the other hand, the increase in the compaction density of the negative electrode sheet 100 will also cause the porosity in the electrode sheet to continue to decrease, causing the electrolyte retention in the electrode sheet to continue to decrease, the ionic conductivity of the electrode sheet to decrease, and the internal resistance of the battery to increase. 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.

[0098] 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.

[0099] The technical solution of the present invention is described in detail below through specific embodiments.

[0100] Example 1

[0101] 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.

[0102] 1) Coating: using a continuous coating device to coat the slurry on the copper foil along the length direction;

[0103] 2) Regulation, at the same time, an alternating electric field with a voltage of 36V and a frequency of 50Hz and a magnetic field of 0.4T are applied to the current collector copper foil to perform magneto-electrically induced graphite orientation. The first angle θ1 between the square magnetic field and the thickness direction of the negative electrode sheet is 90°, and the second angle θ2 between the cylindrical magnetic field and the length direction of the electrode sheet is 60°, so as to keep the magnetic field uniform and stable.

[0104] 3) Baking, baking temperature 100℃, adjusting the surface density to 230g / m 2 , compaction density is controlled at 1.6g / cm 3 .

[0105] Example 2

[0106] 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 the magnitude of the magnetic field is 0.8T.

[0107] Example 3

[0108] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that the voltage is 100V.

[0109] Example 4

[0110] 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 it has no cylindrical magnetic field.

[0111] Example 5

[0112] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and is different from the embodiment 4 in that there is no electric field.

[0113] Example 6

[0114] 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 5 is that the magnitude of the magnetic field is 0.6T.

[0115] Example 7

[0116] 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 5 is that the magnitude of the magnetic field is 0.8T.

[0117] Example 8

[0118] 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 it has no square magnetic field.

[0119] Example 9

[0120] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and is different from the embodiment 8 in that there is no electric field.

[0121] Example 10

[0122] 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 9 is that the magnitude of the magnetic field is 0.6T.

[0123] Embodiment 11

[0124] 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 9 is that the magnitude of the magnetic field is 0.8T.

[0125] Example 12

[0126] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that the voltage is 24V.

[0127] Embodiment 13

[0128] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that the voltage is 130V.

[0129] Embodiment 14

[0130] 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 magnitude of the magnetic field is 0.6T.

[0131] Embodiment 15

[0132] 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 magnitude of the magnetic field is 1.2T.

[0133] Example 16

[0134] 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 there is no electric field.

[0135] Embodiment 17

[0136] 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 the electric field frequency is 100 Hz.

[0137] Comparative Example 1

[0138] 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 there is no magnetic field.

[0139] Comparative Example 2

[0140] 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 there is no electric field and magnetic field.

[0141] Comparative Example 3

[0142] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that: θ2 = 90°.

[0143] Comparative Example 4

[0144] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that: θ1 = 30°.

[0145] Comparative Example 5

[0146] The battery of this embodiment includes a negative electrode sheet, a positive electrode sheet and a separator, and the difference between this embodiment and the embodiment 1 is that: θ2 = 30°.

[0147] Table 1 is a summary table of parameter settings for the above embodiments and comparative examples.

[0148] Experiment number electric field magnetic field <![CDATA[θ1]]> <![CDATA[θ2]]> Example 1 36V, 50Hz 0.4T 90° 60° Example 2 36V, 50Hz 0.8T 90° 60° Example 3 100V, 50Hz 0.4T 90° 60° Example 4 36V, 50Hz 0.4T 90° —— Example 5 —— 0.4T 90° —— Example 6 —— 0.6T 90° —— Example 7 —— 0.8T 90° —— Example 8 36V, 50Hz 0.4T —— 60° Example 9 —— 0.4T —— 60° Example 10 —— 0.6T —— 60° Embodiment 11 —— 0.8T —— 60° Example 12 24V, 50Hz 0.4T 90° 60° Embodiment 13 130V, 50Hz 0.4T 90° 60° Embodiment 14 36V, 50Hz 0.6T 90° 60° Embodiment 15 36V, 50Hz 1.2T 90° 60° Example 16 —— 0.4T 90° 60° Embodiment 17 36V, 100Hz 0.4T 90° 60° Comparative Example 1 36V, 50Hz —— —— —— Comparative Example 2 —— —— —— —— Comparative Example 3 36V, 50Hz 0.4T 90° 90° Comparative Example 4 36V, 50Hz 0.4T 30° 90° Comparative Example 5 36V, 50Hz 0.4T 90° 30°

[0149] The electrochemical properties of the negative electrode sheets prepared in Examples 1-17 and Comparative Examples 1-5 were characterized and tested:

[0150] 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 It is obtained by testing the XRD spectrum of the electrode cross section and can be used to characterize the angle between the graphite (004) plane and the Y direction.

[0151] It should be noted that the OI value of the graphite crystal structure in the present application is the OI value of the graphite in the negative electrode sheet, and the OI value of the material in the electrode sheet reflects the arrangement of the material in the electrode sheet. The OI value of the graphite in the electrode sheet is affected not only by the OI value of the graphite material itself, but also by the electrode sheet manufacturing process.

[0152] Peeling force test: Stick the transparent tape evenly 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 strength of the tape peeling off the electrode, so as to evaluate the bonding strength between the graphite particles of the negative electrode and 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.

[0153] Liquid phase diffusion impedance test: The pole piece, diaphragm, and pole piece 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.

[0154] Specifically, through electrochemical impedance spectroscopy (EIS), a small amplitude sine wave potential signal of a certain frequency is applied to the electrode based on the reference potential, and the impedance of the electrode system is measured as the sine wave frequency changes. Then, the spectrum is analyzed and fitted to obtain the electrode process kinetic information and electrode interface structure. Generally, the diffusion impedance value of lithium ions in the electrolyte can be obtained by fitting the equivalent circuit to characterize the impedance value inside the battery.

[0155] Battery preparation and capacity ratio test method:

[0156] The battery of this embodiment further includes a separator and a positive electrode sheet.

[0157] 4) Cut the above negative electrode sheet into electrode sheets of appropriate size, matching the corresponding size and surface density of 500g / m 2 The positive electrode lithium iron phosphate electrode;

[0158] 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;

[0159] 6) Under a dew point environment, the positive electrode sheet, separator, and negative electrode sheet prepared in step 4) are stacked in sequence, and the electrolyte is injected to prepare a soft-pack battery with a designed battery capacity of 2.0 Ah.

[0160] Capacity calibration: Within the voltage range of 2.0-3.8V, the battery is tested for three cycles of 0.33C / 0.33C charge / discharge, and the capacity of the last cycle is taken as the battery capacity.

[0161] 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 respectively, and the voltage drop of each soft-pack battery was recorded to calculate the DC impedance (DCIR).

[0162] Charge capacity ratio: After each battery is discharged at 0.1C at 25°C, the gram capacity at different rates of 0.2C and 3C is tested, and the voltage range is 2.0-3.8V. Calculate the ratio of the charge capacity at 3C rate to the charge capacity at 0.2C.

[0163] 45℃ cycle capacity retention rate: At 45℃, the battery was charged and discharged at 1C / 1C constant current, and left to stand for 30 minutes between each charge and discharge. The capacity retention rate of the battery after 500 cycles was recorded.

[0164] The electrochemical properties of the negative electrode sheet and the assembled battery were characterized. Table 2 summarizes the results of the characterization tests.

[0165]

[0166]

[0167] It can be seen from the experimental results of Examples 1 to 17 and Comparative Examples 1 to 2 in Tables 1 and 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 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.

[0168] 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.

[0169] 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, while the plane OI a The larger the value, the lower the efficiency of lithium ion deintercalation in the electrode, which in turn affects 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.

[0170] 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 sheet can significantly improve the performance of the electrode in various 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 sheet 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 active material peeling during the cycle and reduce the cycle retention rate of the battery.

[0171] 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, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0172] What is disclosed above is only a preferred embodiment of the present application, and it 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 implementing the above embodiment and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A negative electrode sheet, characterized in that: include: current collector; An active layer, stacked on at least one side of the current collector, wherein the active layer contains graphite; The graphite satisfies: 0<OI a ≤5,2≤OI b ≤20; 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 (110) plane obtained by performing an XRD test on the surface of the negative electrode sheet; 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 (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet.

2. The negative electrode sheet 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, characterized in that: include: providing a current collector; An active layer is stacked on at least one side of the current collector, wherein the active layer 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 (110) plane obtained by performing an XRD test on the surface of the negative electrode sheet; 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 (110) plane obtained by performing XRD test on the cross section of the negative electrode sheet.

4. The method for preparing a negative electrode sheet according to claim 3, characterized in that: The active layer is stacked on the current collector and comprises: Applying a slurry on the current collector, wherein the slurry includes graphite particles; applying an alternating electric field to the negative electrode sheet to cause the active layer to generate an induced current; and / or, A magnetic field is applied to the negative electrode sheet to orient the graphite particles.

5. The method for preparing a negative electrode sheet according to claim 4, characterized in that: Applying an alternating electric field to the negative electrode sheet 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; preferably, 24V≤U≤130V, 50Hz≤F≤100Hz.

6. The method for preparing a negative electrode sheet according to claim 4, characterized in that: Applying a magnetic field to the negative electrode plate includes: the magnitude of the magnetic field is B, satisfying: 0T<B≤2T; preferably, 0.6T≤B≤1.2T.

7. The method for preparing a negative electrode sheet according to claim 6, characterized in that: 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°.

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

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

10. A battery cell, characterized in that: The invention comprises a separator, a positive electrode sheet and a negative electrode sheet as claimed in any one of claims 1 to 2 or a negative electrode sheet prepared by the method for preparing a negative electrode sheet as claimed in any one of claims 3 to 9, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked.

11. An electrical device, characterized in that: Comprising the battery cell as claimed in claim 10.

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