A negative electrode sheet, a method for manufacturing the same, and a battery

Abstract

The present application relates to a kind of negative pole piece and its preparation method and battery, the negative pole piece includes current collector, and active material layer is arranged on the at least one side surface of the current collector, the active material layer includes: first graphite layer;Second graphite layer;And third graphite layer;The first graphite layer is arranged on the at least one side surface of the current collector, the second graphite layer is arranged on the surface of the first graphite layer away from the side of the current collector, the third graphite layer is arranged on the surface of the second graphite layer away from the side of the current collector;And the OI value of the first graphite layer is 25.0~35.0;The OI value of the second graphite layer is 4.0~12.0;The OI value of the third graphite layer is 20.0~30.0.The negative pole piece guarantees the fast charging capacity at the same time, effectively inhibits pole piece fold and has lower full charge rebound rate.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, and in particular to a negative electrode sheet, its preparation method, and the battery thereof. Background Technology

[0002] In recent years, with the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and energy storage systems, the demand for fast-charging performance of lithium-ion batteries has been increasing. However, the rapid insertion and extraction of lithium ions during fast charging leads to increased structural stress in the electrode materials, resulting in mechanical damage, capacity decay, and decreased safety performance. Especially under high-rate charging conditions, the uneven distribution of lithium ions in the electrodes is exacerbated, increasing the risk of battery short circuits.

[0003] To match the distribution of lithium ions in the electrode during high-rate charging, one solution to improve the fast-charging performance of the battery at the electrode level is to use a double-layer coating technology, which usually requires improving the fast-charging capability of the coating on the electrode side close to the separator.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] In view of this, the present application provides a negative electrode sheet, a method for preparing the same, and a battery to solve at least one problem existing in the prior art.

[0006] A first aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprising:

[0007] First graphite layer;

[0008] The second graphite layer; and

[0009] The third graphite layer;

[0010] The first graphite layer is disposed on at least one surface of the current collector, the second graphite layer is disposed on the surface of the first graphite layer away from the current collector, and the third graphite layer is disposed on the surface of the second graphite layer away from the current collector; and

[0011] The OI value of the first graphite layer is 25.0 to 35.0; the OI value of the second graphite layer is 4.0 to 12.0; and the OI value of the third graphite layer is 20.0 to 30.0.

[0012] The OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer.

[0013] Preferably, based on the thickness of the active material layer being 100%, the thickness of the first graphite layer in the active material layer accounts for 25% to 45%, the thickness of the second graphite layer in the active material layer accounts for 50% to 70%, and the thickness of the third graphite layer in the active material layer accounts for 5% to 15%.

[0014] Preferably, the thickness of the active material layer is 120μm to 220μm; the thickness of the first graphite layer is 40μm to 100μm; the thickness of the second graphite layer is 70μm to 130μm; and the thickness of the third graphite layer is 10μm to 30μm.

[0015] Preferably, the material of the first graphite layer includes first graphite; the OI value of the first graphite is 3.0 to 6.0;

[0016] The material of the second graphite layer includes second graphite; the OI value of the second graphite is 0.2 to 1.5;

[0017] The material of the third graphite layer includes third graphite; the OI value of the third graphite is 1.5 to 4.0;

[0018] The OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of graphite to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of graphite.

[0019] Preferably, the tap density of the first graphite is 0.95 g / cm³. 3 ~1.10g / cm 3 The tap density of the second graphite is 0.90 g / cm³. 3 ~1.05g / cm 3 The tap density of the third graphite is 1.10 g / cm³. 3 ~1.25g / cm 3 .

[0020] Preferably, the graphitization degree of the first graphite is 93% to 95%; the graphitization degree of the second graphite is 92% to 94%; and the graphitization degree of the third graphite is 92.5% to 94.5%.

[0021] Preferably, the material of the first graphite layer further includes a first binder and a first conductive agent, the material of the second graphite layer further includes a second binder and a second conductive agent, and the material of the third graphite layer further includes a third binder and a third conductive agent; the negative electrode sheet satisfies at least one of the following features (a) to (f):

[0022] (a) The first adhesive comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride;

[0023] (b) The second adhesive comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride;

[0024] (c) The third adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride;

[0025] (d) The first conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0026] (e) The second conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes;

[0027] (f) The third conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0028] Preferably, based on the mass of the first graphite layer being 100%, the mass percentage of the first graphite in the first graphite layer is 93.5% to 98.5%, the mass percentage of the first binder in the first graphite layer is 1% to 5%, and the mass percentage of the first conductive agent in the first graphite layer is 0.1% to 2%.

[0029] Preferably, based on the mass of the second graphite layer being 100%, the mass percentage of the second graphite in the second graphite layer is 95.5% to 98.5%, the mass percentage of the second binder in the second graphite layer is 1% to 3%, and the mass percentage of the second conductive agent in the second graphite layer is 0.1% to 2%.

[0030] Preferably, based on the mass of the third graphite layer being 100%, the mass percentage of the third graphite in the third graphite layer is 95.5% to 98.5%, the mass percentage of the third binder in the third graphite layer is 1% to 3%, and the mass percentage of the third conductive agent in the third graphite layer is 0.1% to 2%.

[0031] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect of the present invention, the method comprising:

[0032] S1: The first graphite, the first binder, and the first conductive agent are mixed with deionized water in a mass ratio of (93.5-98.5):(1-5):(0.1-2) to form a first graphite layer slurry;

[0033] The second graphite, the second binder, and the second conductive agent are mixed with deionized water in a mass ratio of (95.5–98.5):(1–3):(0.1–2) to form a second graphite layer slurry.

[0034] The third graphite, the third binder, and the third conductive agent are mixed with deionized water in a mass ratio of (95.5–98.5):(1–3):(0.1–2) to form a third graphite layer slurry.

[0035] S2: The first graphite layer slurry, the second graphite layer slurry, and the third graphite layer slurry obtained in step S1 are sequentially coated onto at least one side surface of the current collector, dried, and rolled to obtain the negative electrode sheet.

[0036] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the first aspect of the present invention or the negative electrode sheet prepared by the preparation method described in the second aspect of the present invention.

[0037] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0038] This invention provides a negative electrode sheet, its preparation method, and a battery. The negative electrode sheet has three graphite coating layers. By controlling the OI value of the first and third graphite layers to be greater than that of the second graphite layer, and the thickness of the second graphite layer to be greater than that of the first and third graphite layers, wrinkles on the electrode sheet can be effectively suppressed while ensuring its fast-charging capability. Furthermore, by controlling the difference in graphitization degree between the layers, the electrode sheet can achieve both fast-charging capability and a low full-charge rebound rate. Attached Figure Description

[0039] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0040] Figure 1 This is a cross-sectional schematic diagram of the negative electrode sheet in some embodiments of this application.

[0041] Explanation of reference numerals in the attached figures

[0042] 100. Current collector;

[0043] 200. Active material layer;

[0044] 201. First graphite layer;

[0045] 202. Second graphite layer;

[0046] 203. Third graphite layer. Detailed Implementation

[0047] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below by listing specific embodiments. The accompanying drawings are not necessarily drawn to scale, and local features may be enlarged or reduced to more clearly show the details of the local features. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0048] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0049] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0050] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0051] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0052] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0053] Currently, one approach to improving battery fast-charging performance at the electrode level, to match the distribution of lithium ions in the electrodes during high-rate charging, is to employ a double-layer coating technique. This typically requires enhancing the fast-charging capability of the coating near the separator. Existing technologies primarily utilize graphite materials with lower OI values ​​to improve this capability. However, graphite materials with lower OI values ​​often exhibit excessive rebound in the electrode planar direction during charging, leading to electrode wrinkling.

[0054] In view of the above, the present invention provides the following technical solution:

[0055] [Negative electrode plate]

[0056] A first aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector 100 and an active material layer 200 disposed on at least one side surface of the current collector 100, the active material layer 200 comprising:

[0057] First graphite layer 201;

[0058] Second graphite layer 202; and

[0059] Third graphite layer 203;

[0060] The first graphite layer 201 is disposed on at least one surface of the current collector 100, the second graphite layer 202 is disposed on the surface of the first graphite layer 201 away from the current collector 100, and the third graphite layer 203 is disposed on the surface of the second graphite layer 202 away from the current collector 100; and

[0061] The OI value of the first graphite layer 201 is 25.0 to 35.0; the OI value of the second graphite layer 202 is 4.0 to 12.0; and the OI value of the third graphite layer 203 is 20.0 to 30.0.

[0062] The OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer.

[0063] The negative electrode sheet provided by the present invention has three graphite coating layers. By controlling the OI value of the first and third graphite layers to be greater than the OI value of the second graphite layer and the thickness of the second graphite layer to be greater than the thickness of the first and third graphite layers, wrinkles on the electrode sheet can be effectively suppressed while ensuring the fast charging capability of the electrode sheet.

[0064] In some embodiments, the OI value of the first graphite layer 201 is 25.0; the OI value of the second graphite layer 202 is 9.1; and the OI value of the third graphite layer 203 is 20.0.

[0065] In some embodiments, the OI value of the first graphite layer 201 is 29.6; the OI value of the second graphite layer 202 is 9.1; and the OI value of the third graphite layer 203 is 22.7.

[0066] In some embodiments, the OI value of the first graphite layer 201 is 29.6; the OI value of the second graphite layer 202 is 9.1; and the OI value of the third graphite layer 203 is 20.1.

[0067] In some embodiments, the OI value of the first graphite layer 201 is 29.8; the OI value of the second graphite layer 202 is 9.1; and the OI value of the third graphite layer 203 is 20.2.

[0068] In some embodiments, the OI value of the first graphite layer 201 is 29.8; the OI value of the second graphite layer 202 is 9.3; and the OI value of the third graphite layer 203 is 20.4.

[0069] In some embodiments, the OI value of the first graphite layer 201 is 29.6; the OI value of the second graphite layer 202 is 9.2; and the OI value of the third graphite layer 203 is 20.2.

[0070] In some embodiments, the OI value of the first graphite layer 201 is 29.6; the OI value of the second graphite layer 202 is 10.5; and the OI value of the third graphite layer 203 is 20.2.

[0071] In some embodiments, the OI value of the first graphite layer 201 is 29.6; the OI value of the second graphite layer 202 is 11.9; and the OI value of the third graphite layer 203 is 20.2.

[0072] In some embodiments, based on the thickness of the active material layer 200 being 100%, the first graphite layer 201 accounts for 25% to 45% of the thickness of the active material layer 200, the second graphite layer 202 accounts for 50% to 70% of the thickness of the active material layer 200, and the third graphite layer 203 accounts for 5% to 15% of the thickness of the active material layer 200.

[0073] In some embodiments, with the thickness of the active material layer 200 being 100%, the first graphite layer 201 accounts for 40% of the thickness of the active material layer 200, the second graphite layer 202 accounts for 50% of the thickness of the active material layer 200, and the third graphite layer 203 accounts for 10% of the thickness of the active material layer 200.

[0074] In some embodiments, based on the thickness of the active material layer 200 being 100%, the first graphite layer 201 accounts for 30% of the thickness of the active material layer 200, the second graphite layer 202 accounts for 57% of the thickness of the active material layer 200, and the third graphite layer 203 accounts for 13% of the thickness of the active material layer 200.

[0075] In some embodiments, with the thickness of the active material layer 200 being 100%, the first graphite layer 201 accounts for 45% of the thickness of the active material layer 200, the second graphite layer 202 accounts for 50% of the thickness of the active material layer 200, and the third graphite layer 203 accounts for 5% of the thickness of the active material layer 200.

[0076] In some embodiments, the thickness of the active material layer 200 is 120 μm to 220 μm; the thickness of the first graphite layer 201 is 40 μm to 100 μm; the thickness of the second graphite layer 202 is 70 μm to 130 μm; and the thickness of the third graphite layer 203 is 10 μm to 30 μm.

[0077] In some embodiments, the thickness of the active material layer 200 is 220 μm; the thickness of the first graphite layer 201 is 88 μm; the thickness of the second graphite layer 202 is 110 μm; and the thickness of the third graphite layer 203 is 22 μm.

[0078] In some embodiments, the thickness of the active material layer 200 is 120 μm; the thickness of the first graphite layer 201 is 48 μm; the thickness of the second graphite layer 202 is 60 μm; and the thickness of the third graphite layer 203 is 12 μm.

[0079] In some embodiments, the thickness of the active material layer 200 is 220 μm; the thickness of the first graphite layer 201 is 66 μm; the thickness of the second graphite layer 202 is 125.4 μm; and the thickness of the third graphite layer 203 is 28.6 μm.

[0080] In some embodiments, the thickness of the active material layer 200 is 220 μm; the thickness of the first graphite layer 201 is 99 μm; the thickness of the second graphite layer 202 is 110 μm; and the thickness of the third graphite layer 203 is 11 μm.

[0081] In this invention, wrinkles in the intermediate second graphite layer are suppressed by constructing a coating with minimal wrinkles in the first and third graphite layers. If the third graphite layer is too thick, the fast-charging capability of the electrode will be insufficient; if the third graphite layer is too thin, it will not effectively suppress wrinkles. Similarly, if the first graphite layer is too thick, the fast-charging capability of the electrode will be insufficient; if the first graphite layer is too thin, the compaction capability of the electrode will be insufficient. By constructing the layers with the thicknesses described above, both the fast-charging performance of the electrode and the wrinkles can be effectively suppressed while ensuring the compaction capability of the electrode are maintained.

[0082] In some implementations:

[0083] The material of the first graphite layer 201 includes first graphite; the OI value of the first graphite is 3.0 to 6.0;

[0084] The material of the second graphite layer 202 includes second graphite; the OI value of the second graphite is 0.2 to 1.5;

[0085] The material of the third graphite layer 203 includes third graphite; the OI value of the third graphite is 1.5 to 4.0;

[0086] The OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of graphite to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of graphite.

[0087] In some embodiments, the tap density of the first graphite is 0.95 g / cm³. 3 ~1.10g / cm 3 The tap density of the second graphite is 0.90 g / cm³. 3 ~1.05g / cm 3 The tap density of the third graphite is 1.10 g / cm³. 3 ~1.25g / cm 3 .

[0088] When the tap density of graphite is too low, the graphite layer morphology is irregular, and the electrode is prone to wrinkling; when the tap density of graphite is too high, the fast-charging capability of the electrode is insufficient. In this invention, controlling the tap density of the first graphite within the above-mentioned range helps to ensure the compaction capability of the first graphite layer 201; controlling the tap density of the second graphite within the above-mentioned range helps to ensure the fast-charging performance of the electrode; and controlling the tap density of the third graphite within the above-mentioned range can improve the electrode's ability to suppress wrinkling. That is, by controlling the tap densities of the first, second, and third graphite within the above-mentioned range, both the fast-charging performance of the electrode and the wrinkling suppression and compaction capability of the electrode can be guaranteed.

[0089] In some embodiments, the tap density of the first graphite is 1.03 g / cm³. 3The tap density of the second graphite is 0.90 g / cm³. 3 The tap density of the third graphite is 1.12 g / cm³. 3 .

[0090] In some embodiments, the tap density of the first graphite is 1.05 g / cm³. 3 The tap density of the second graphite is 0.90 g / cm³. 3 The tap density of the third graphite is 1.12 g / cm³. 3 .

[0091] In some embodiments, the tap density of the first graphite is 0.99 g / cm³. 3 The tap density of the second graphite is 0.90 g / cm³. 3 The tap density of the third graphite is 1.13 g / cm³. 3 .

[0092] In some embodiments, the tap density of the first graphite is 0.95 g / cm³. 3 The tap density of the second graphite is 0.91 g / cm³. 3 The tap density of the third graphite is 1.11 g / cm³. 3 .

[0093] In some embodiments, the tap density of the first graphite is 1.09 g / cm³. 3 The tap density of the second graphite is 1.05 g / cm³. 3 The tap density of the third graphite is 1.25 g / cm³. 3 .

[0094] In some embodiments, the graphitization degree of the first graphite is 93% to 95%; the graphitization degree of the second graphite is 92% to 94%; and the graphitization degree of the third graphite is 92.5% to 94.5%.

[0095] In some embodiments, the degree of graphitization of the first graphite, the second graphite, and the third graphite satisfies the following condition: degree of graphitization of the first graphite > degree of graphitization of the third graphite > degree of graphitization of the second graphite.

[0096] When the graphitization is too high, wrinkles appear on the electrode because the higher the graphitization, the greater the electrode rebound. When the graphitization is too low, lithium plating is likely to occur on the electrode because the specific capacity of the electrode is insufficient, resulting in an insufficient charging NP value. In this invention, the graphitization of the first, second, and third graphites is controlled within the above-mentioned range. Since the graphitization of the first graphite is the highest, it is beneficial to the high-compaction design of the first graphite layer 201; the graphitization of the second graphite is the lowest, which is beneficial to the design of high fast-charging capability of the electrode; and the graphitization of the third graphite is moderate, which is beneficial to the electrode to ensure fast charging capability while also taking into account a low full-charge rebound rate.

[0097] In some embodiments, the graphitization degree of the first graphite is 93.2%; the graphitization degree of the second graphite is 92%; and the graphitization degree of the third graphite is 92.5%.

[0098] In some embodiments, the degree of graphitization of the first graphite is 95.0%; the degree of graphitization of the second graphite is 93.9%; and the degree of graphitization of the third graphite is 94.5%.

[0099] In some embodiments, the degree of graphitization of the first graphite is 93.3%; the degree of graphitization of the second graphite is 92.1%; and the degree of graphitization of the third graphite is 92.8%.

[0100] In some embodiments, the graphitization degree of the first graphite is 93.4%; the graphitization degree of the second graphite is 92.2%; and the graphitization degree of the third graphite is 92.6%.

[0101] In some embodiments, the material of the first graphite layer 201 further includes a first binder and a first conductive agent, the material of the second graphite layer 202 further includes a second binder and a second conductive agent, and the material of the third graphite layer 203 further includes a third binder and a third conductive agent.

[0102] In some embodiments, the first adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride.

[0103] In some embodiments, the second adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride.

[0104] In some embodiments, the third adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride.

[0105] In some embodiments, the first conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0106] In some embodiments, the second conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0107] In some embodiments, the third conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

[0108] In some embodiments, based on the mass of the first graphite layer 201 being 100%, the mass percentage of the first graphite in the first graphite layer 201 is 93.5% to 98.5%, the mass percentage of the first binder in the first graphite layer 201 is 1% to 5%, and the mass percentage of the first conductive agent in the first graphite layer 201 is 0.1% to 2%.

[0109] In some embodiments, based on the mass of the second graphite layer 202 being 100%, the mass percentage of the second graphite in the second graphite layer 202 is 95.5% to 98.5%, the mass percentage of the second binder in the second graphite layer 202 is 1% to 3%, and the mass percentage of the second conductive agent in the second graphite layer 202 is 0.1% to 2%.

[0110] In some embodiments, based on the mass of the third graphite layer 203 being 100%, the mass percentage of the third graphite in the third graphite layer 203 is 95.5% to 98.5%, the mass percentage of the third binder in the third graphite layer 203 is 1% to 3%, and the mass percentage of the third conductive agent in the third graphite layer 203 is 0.1% to 2%.

[0111] [Preparation method of negative electrode]

[0112] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect of the present invention, the method comprising:

[0113] S1: The first graphite, the first binder, and the first conductive agent are mixed with deionized water in a mass ratio of (93.5-98.5):(1-5):(0.1-2) to form a first graphite layer slurry;

[0114] The second graphite, the second binder, and the second conductive agent are mixed with deionized water in a mass ratio of (95.5–98.5):(1–3):(0.1–2) to form a second graphite layer slurry.

[0115] The third graphite, the third binder, and the third conductive agent are mixed with deionized water in a mass ratio of (95.5–98.5):(1–3):(0.1–2) to form a third graphite layer slurry.

[0116] S2: The first graphite layer slurry, the second graphite layer slurry, and the third graphite layer slurry obtained in step S1 are sequentially coated onto at least one side surface of the current collector 100, dried, and rolled to obtain the negative electrode sheet.

[0117] [Battery]

[0118] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the first aspect of the present invention or the negative electrode sheet prepared by the preparation method described in the second aspect of the present invention.

[0119] In some embodiments, the battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery can be a lithium-ion battery, but it is not limited thereto. The battery structures of this application include, but are not limited to, pouch-type lithium-ion batteries, prismatic hard-shell batteries, or cylindrical hard-shell batteries.

[0120] In some embodiments, the battery further includes a positive electrode, an electrolyte, and a separator. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator disposed between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0121] The positive electrode sheet includes a positive current collector and a layer of positive active material disposed on the positive current collector. The positive current collector can be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive active material layer includes a positive active material. The positive active material suitable for this invention can be any known positive active material used in lithium-ion batteries, capable of reversibly inserting and de-intercalating lithium ions. The positive active material can be selected from composite oxides containing lithium and at least one selected from cobalt, manganese, nickel, and iron, preferably lithium-containing composite oxides. The lithium-containing composite oxide is preferably LiMnO2. x O y LiM x PO4 or LiNi x Co y Mn 1-x-y One or more of O2, wherein M is a combination of one or more transition metals, 0 < x ≤ 3, 0 < y ≤ 4. Examples of positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate (LiFePO4), etc.

[0122] The positive electrode active material layer may also include one or both selected from conductive agents and binders. The conductive agent is used to improve the electrode conductivity. Examples of conductive agents for the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene, and carbon nanotubes. The binder for the positive electrode improves the adhesion between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders for the positive electrode include at least one of fluoropolymers, polypropylene resins, fiber-type binders, rubber-type binders, and polyimide-type binders. In some embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black and single-walled carbon nanotubes, and the binder is polyvinylidene fluoride. The mass ratio of the components in the positive electrode active material layer can be conventional.

[0123] The positive electrode active material layer is obtained by coating a positive electrode slurry containing the components of the positive electrode active material layer and a solvent onto a positive electrode current collector, followed by rolling and slitting. The solvent for the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0124] The separator can be a polymer porous separator, an inorganic porous separator, or a polymer-inorganic composite porous separator. Polymer porous separators include single-layer polymer porous separators and multi-layer polymer porous separators.

[0125] Electrolytes consist of organic solvents and electrolyte salts.

[0126] The organic solvent suitable for the electrolyte of the present invention may include carbonate solvents, carboxylic acid ester solvents, ether solvents, or other aprotic solvents. In some embodiments, the electrolyte includes a carbonate solvent. In the electrolyte of the present invention, the mass of the carbonate solvent may be 80% to 100% of the total mass of the organic solvent, for example, 85%, 90%, or 95%. Examples of carbonate solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, etc. In some embodiments, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate. In some embodiments, the organic solvent comprises at least one cyclic carbonate and at least one linear carbonate. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, etc. Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.

[0127] The electrolyte salt may include or be selected from lithium salts. The lithium salt may be selected from one or more organic and inorganic lithium salts. In some embodiments, the electrolyte salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFB, and LiPO2F2. In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.5–2 mol / L, for example, 1 mol / L or 1.5 mol / L.

[0128] The battery of this application also includes a packaging shell for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for lithium-ion batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging shell; it can be a packaging shell known in the art, as long as it can achieve the purpose of this application.

[0129] This invention does not impose any special restrictions on the battery preparation method; any technical solution known to those skilled in the art for preparing a battery, such as a secondary battery, from a negative electrode material can be used.

[0130] It should be understood that since the battery provided in this application includes the negative electrode sheet provided in the first aspect of the present invention or the negative electrode sheet prepared by the preparation method provided in the second aspect of the present invention, the beneficial effects of the negative electrode sheet or its preparation method described in any of the above embodiments are applicable to the battery.

[0131] [Electrical appliances]

[0132] A fourth aspect of the present invention provides an electrical device comprising the battery described in the third aspect of the present invention.

[0133] The application of the battery in this application is not particularly limited, and it can be used in any electrical device known in the prior art. In some embodiments, the battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, drones, and lithium-ion capacitors, etc.

[0134] It should be understood that since the electrical device provided in this application includes the battery described in the third aspect of the present invention, the beneficial effects of the negative electrode sheet or its preparation method described in any of the above embodiments are applicable to the electrical device.

[0135] The method of the present invention will be described below through specific embodiments. It should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0136] Examples and Comparative Examples

[0137] The first artificial graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black (Super-P) were placed in a mixing tank in a ratio of 95.5:1.5:2:1. After adding pure water and stirring evenly, the first graphite layer slurry was obtained.

[0138] The second artificial graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black (Super-P) were placed in a mixing tank in a ratio of 95.5:1.5:2:1. After adding pure water and stirring evenly, the second graphite layer slurry was obtained.

[0139] The third artificial graphite, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon black (Super-P) were placed in a mixing tank in a ratio of 95.5:1.5:2:1. After adding pure water and stirring evenly, the third graphite layer slurry was obtained.

[0140] A first graphite layer is obtained by uniformly coating a first graphite layer slurry onto a current collector. A second graphite layer slurry is then coated onto the surface of the first graphite layer away from the current collector to form a second graphite layer. A third graphite layer slurry is then coated onto the surface of the second graphite layer away from the current collector to form a third graphite layer. The weight and thickness distribution of the three graphite layers in each embodiment and comparative example are controlled according to Table 1.

[0141] Table 1

[0142]

[0143]

[0144] Preparation of lithium-ion batteries

[0145] (1) Positive electrode sheet: Lithium iron phosphate, polyvinylidene fluoride (PVDF) and conductive carbon black (Super-P) are mixed in a ratio of 97:2:1 and stirred to form a positive electrode slurry. The positive electrode slurry is coated on aluminum foil, dried in an oven, and then rolled and cut to obtain a positive electrode sheet.

[0146] (2) Negative electrode: The negative electrode obtained in Examples 1 to 10 or Comparative Examples 1 to 6 is used.

[0147] (3) Separating membrane: PE porous polymer film is used as the separating membrane.

[0148] (4) Electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:5:2. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1.2 mol / L to prepare the electrolyte.

[0149] (5) Assembly: Arrange the positive electrode, separator, and negative electrode in sequence, place a separator between each pair of positive and negative electrodes, and wind them to obtain a bare cell. Place the bare cell in an outer packaging shell, inject the prepared electrolyte into the dried bare cell, and obtain a lithium-ion battery through vacuum sealing, settling, formation, and shaping processes.

[0150] Performance testing

[0151] The performance of lithium-ion batteries, including Examples 1-10 and Comparative Examples 1-6, was tested according to the following methods:

[0152] 1. Electrode Full-Charge Rebound Rate Test: Measure the thickness of the current collector without negative electrode slurry coating using a micrometer and record it as dfoil; measure the thickness of the negative electrode sheet (including the active material layer and current collector) after rolling using a micrometer and record it as dpressure. Place the battery in a 25℃ incubator for 6 hours; first charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C; disassemble the battery and measure the thickness of the negative electrode sheet (including the active material layer and current collector) using a micrometer and record it as dfull; calculate the rebound rate, which is the ratio of the difference between the thickness of the fully charged active material layer and the thickness of the active material layer after rolling to the thickness of the active material layer after rolling; that is, the rebound rate ρ = (dfull - dpressure) / (dpressure - dfoil).

[0153] 2. Electrode Wrinkle Degree Test: Place the battery in a 25℃ incubator for 6 hours; first, charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C; disassemble the battery, observe and record the degree of wrinkling of the negative electrode. Wrinkles are defined as those observed on the surface of the negative electrode with abnormalities such as black spots or lithium plating; slight wrinkles are defined as those observed without black spots or lithium plating; and no wrinkles are defined as those observed on the surface of the negative electrode.

[0154] 3. 4C Fast Charging Lithium Placing Test: Place the battery in a 25℃ incubator for 6 hours; first, charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, and let stand for 10 minutes; then discharge at a constant voltage of 0.33C to 2.5V, and let stand for 10 minutes; repeat the above cycle 3 times, and record the discharge capacity of the last cycle as C0. First, charge at a constant current of 4C0 to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, and let stand for 10 minutes; then discharge at a constant current of 4C0 to 2.5V, and let stand for 10 minutes; repeat the above cycle 50 times, then remove the battery for disassembly and observe the lithium plating at the negative electrode interface.

[0155] The test results are shown in Table 2.

[0156] Table 2

[0157]

[0158]

[0159] As shown in the table above, the negative electrode sheets obtained in Examples 1-10 have low full-charge rebound rates and do not exhibit wrinkling or lithium plating. Comparison of Examples 1, 2, and Comparative Example 1 shows that increasing the OI value of the electrode significantly improves wrinkling, but does not significantly affect fast charging capability. Comparison of Examples 2, 3, and Comparative Example 2 shows that when the electrode thickness is within 220µm, the battery's 4C fast charging capability is unaffected; however, when the electrode thickness reaches 250µm, significant lithium plating occurs after 4C fast charging. Comparison of Examples 2, 4, 3, and 4 shows that when graphitization is too high, wrinkling occurs on the electrode, because higher graphitization results in greater electrode rebound; when graphitization is too low, lithium plating occurs, due to insufficient electrode specific capacity, leading to insufficient charging NP value. Comparing Examples 5, 6, 5, and 6, it is evident that when the material tap density is too low, the material morphology is irregular, easily leading to electrode wrinkles; when the material tap density is too high, the fast-charging capability of the electrode is insufficient, causing lithium plating. Comparing Examples 6, 7, and 8, it is evident that when the graphite layer thickness is within the scope of protection of this application, electrode wrinkles and lithium plating do not occur. Comparing Examples 6, 9, and 10, it is evident that when the OI value of the second graphite layer is between 4 and 12, electrode wrinkles do not occur; when the OI value of the second graphite layer exceeds the above range, insufficient orientation may occur, leading to lithium plating.

[0160] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode includes a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprising: First graphite layer; The second graphite layer; and The third graphite layer; The first graphite layer is disposed on at least one surface of the current collector, the second graphite layer is disposed on the surface of the first graphite layer away from the current collector, and the third graphite layer is disposed on the surface of the second graphite layer away from the current collector; and The OI value of the first graphite layer is 25.0~35.0; the OI value of the second graphite layer is 4.0~12.0; and the OI value of the third graphite layer is 20.0~30.

0. Wherein, the OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the graphite layer. Based on the thickness of the active material layer being 100%, the first graphite layer accounts for 25%~45% of the thickness of the active material layer, the second graphite layer accounts for 50%~70% of the thickness of the active material layer, and the third graphite layer accounts for 5%~15% of the thickness of the active material layer; the thickness of the active material layer is 120μm~220μm; the thickness of the first graphite layer is 40μm~100μm; the thickness of the second graphite layer is 70μm~130μm; and the thickness of the third graphite layer is 10μm~30μm. The first graphite layer is made of first graphite; the OI value of the first graphite is 3.0~6.0; the second graphite layer is made of second graphite; the OI value of the second graphite is 0.2~1.5; the third graphite layer is made of third graphite; the OI value of the third graphite is 1.5~4.

0. Wherein, the OI value is the ratio of the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of graphite to the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of graphite. The tap density of the first graphite is 0.95 g / cm³ to 1.10 g / cm³; the tap density of the second graphite is 0.90 g / cm³ to 1.05 g / cm³; and the tap density of the third graphite is 1.10 g / cm³ to 1.25 g / cm³. The graphitization degree of the first graphite is 93%~95%; the graphitization degree of the second graphite is 92%~94%; and the graphitization degree of the third graphite is 92.5%~94.5%.

2. The negative electrode sheet according to claim 1, characterized in that, The material of the first graphite layer further includes a first binder and a first conductive agent; the material of the second graphite layer further includes a second binder and a second conductive agent; and the material of the third graphite layer further includes a third binder and a third conductive agent. The negative electrode sheet satisfies at least one of the following characteristics (a) to (f): (a) The first adhesive comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride; (b) The second adhesive comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride; (c) The third adhesive includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride; (d) The first conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (e) The second conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes; (f) The third conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes.

3. The negative electrode sheet according to claim 2, characterized in that, Based on the first graphite layer having a mass of 100%, the first graphite accounts for 93.5% to 98.5% of the mass of the first graphite layer, the first binder accounts for 1% to 5% of the mass of the first graphite layer, and the first conductive agent accounts for 0.1% to 2% of the mass of the first graphite layer. And / or, based on the second graphite layer being 100% by mass, the second graphite in the second graphite layer accounts for 95.5% to 98.5% by mass, the second binder in the second graphite layer accounts for 1% to 3% by mass, and the second conductive agent in the second graphite layer accounts for 0.1% to 2% by mass; And / or, based on the mass of the third graphite layer being 100%, the mass percentage of the third graphite in the third graphite layer is 95.5% to 98.5%, the mass percentage of the third binder in the third graphite layer is 1% to 3%, and the mass percentage of the third conductive agent in the third graphite layer is 0.1% to 2%.

4. A method for preparing a negative electrode sheet according to any one of claims 1-3, characterized in that, The method includes: S1: The first graphite, the first binder and the first conductive agent are mixed with deionized water in a mass ratio of (93.5~98.5):(1~5):(0.1~2) to form a first graphite layer slurry; The second graphite, the second binder, and the second conductive agent are mixed with deionized water in a mass ratio of (95.5~98.5):(1~3):(0.1~2) to form a second graphite layer slurry. The third graphite, the third binder, and the third conductive agent are mixed with deionized water in a mass ratio of (95.5~98.5):(1~3):(0.1~2) to form a third graphite layer slurry. S2: The first graphite layer slurry, the second graphite layer slurry, and the third graphite layer slurry obtained in step S1 are sequentially coated onto at least one side surface of the current collector, dried, and rolled to obtain the negative electrode sheet.

5. A battery, characterized in that, The negative electrode sheet includes any one of claims 1-3 or the negative electrode sheet prepared by the preparation method according to claim 4.

Images