Negative pole piece, preparation method thereof and battery

Abstract

The invention discloses a negative pole piece, a preparation method thereof and a battery, and belongs to the technical field of batteries. According to the method provided by the invention, the silicon-based material and the premixed material comprising the first binder are premixed, and the protective film with relatively high mechanical stability is formed on the surface of the silicon-based material through the first binder, so that side reactions caused by cracks generated by expansion of the silicon-based material can be reduced, corrosion of electrolyte to the surface of the silicon-based material is isolated, and the service life of the silicon-based material is prolonged. And on the premise of not increasing impedance, gas production and active lithium loss are reduced, so that the high-temperature storage life of the negative pole piece is prolonged. Moreover, at least one of the graphite material, the first binder, the second binder, the linear conductive agent and the nonlinear conductive agent is added in batches, so that the agglomeration of active particles can be reduced, the dispersion uniformity of each component can be optimized, and the structural stability of the negative pole piece can be better maintained, thereby further prolonging the high-temperature storage life of the negative pole piece.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode plate and a preparation method thereof, and a battery. Background Art

[0002] Silicon-based negative electrode materials experience a large volume expansion during the charge and discharge process. This volume expansion will affect the calendar storage life of the silicon-based negative electrode materials and shorten their high-temperature storage life.

[0003] Related technologies improve silicon-based negative electrode materials through coating, modification and other means. For example, a coating layer is added to the surface of the silicon-based negative electrode material. However, this improvement effect is limited and will cause the growth of silicon grains, sacrificing cycle life and causing increased impedance. Summary of the invention

[0004] The embodiment of the present application provides a negative electrode sheet and a preparation method thereof, and a battery, which can improve the high temperature storage life of the negative electrode sheet. The technical solution is as follows:

[0005] In one aspect, a method for preparing a negative electrode sheet is provided, the method comprising:

[0006] Mixing the silicon-based material and the premixed material uniformly to obtain a first premixed material, wherein the premixed material includes a portion of the first binder;

[0007] The remaining materials constituting the negative electrode sheet are uniformly mixed with the first premix to obtain a second premix, wherein the remaining materials constituting the negative electrode sheet include graphite material, the remaining first binder, the second binder, a linear conductive agent, and a nonlinear conductive agent, and at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches;

[0008] The second premix is ​​mixed with a solvent and a third binder to obtain a negative electrode slurry;

[0009] The negative electrode sheet is prepared by using the negative electrode slurry and the current collector.

[0010] In a possible implementation, the premixed material further includes a portion of the nonlinear conductive agent; or,

[0011] The premixed material also includes a portion of the graphite material.

[0012] In another possible implementation, when the premixed material includes only a portion of the first binder, the remaining material constituting the negative electrode sheet is uniformly mixed with the first premixed material to obtain a second premixed material, comprising:

[0013] The first premix, part of the nonlinear conductive agent and part of the graphite material are mixed evenly to obtain a third premix; or the first premix, part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent are mixed evenly to obtain a third premix;

[0014] Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix;

[0015] Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0016] In another possible implementation, when the premixed material further includes a portion of the nonlinear conductive agent, the remaining material constituting the negative electrode plate is uniformly mixed with the first premixed material to obtain a second premixed material, comprising:

[0017] The first premix and a part of the graphite material are mixed evenly to obtain a third premix, or the first premix, a part of the graphite material and the linear conductive agent are mixed evenly to obtain a third premix;

[0018] Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix;

[0019] Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0020] In another possible implementation, when the premixed material further includes part of the graphite material, the remaining material constituting the negative electrode plate is uniformly mixed with the first premixed material to obtain a second premixed material, comprising:

[0021] The first premix and part of the nonlinear conductive agent are mixed evenly to obtain a third premix; or the first premix, part of the nonlinear conductive agent and the linear conductive agent are mixed evenly to obtain a third premix;

[0022] Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix;

[0023] Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0024] In another possible implementation, the step of uniformly mixing the third premix with the remaining portion of the remaining material to obtain the second premix comprises:

[0025] The third premix, part of the second binder, the remaining part of the graphite material, and the remaining part of the nonlinear conductive agent are uniformly mixed to obtain a fourth premix; or the third premix, part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and the linear conductive agent are uniformly mixed to obtain a fourth premix;

[0026] uniformly mixing the fourth premix with another remaining part of the remaining material to obtain the second premix;

[0027] The first binder contained in the other remaining part of the remaining material is added in batches.

[0028] In another possible implementation, the third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are uniformly mixed to obtain a fourth premix, comprising:

[0029] The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the solvent are uniformly mixed, and the solid content of the slurry is adjusted to 60% to 90% by the solvent to obtain the fourth premix.

[0030] In another possible implementation, the mixing the fourth premix with the other remaining part of the remaining material to obtain the second premix comprises:

[0031] The fourth premix, the remaining part of the second binder, the remaining part of the first binder, and the linear conductive agent are uniformly mixed to obtain a fifth premix; or the fourth premix, the remaining part of the second binder, and the remaining part of the first binder are uniformly mixed to obtain a fifth premix;

[0032] The fifth premix is ​​mixed evenly with the remaining portion of the first binder to obtain the second premix.

[0033] In another possible implementation, in the first premix, the mass ratio of the solid component in the first binder to the silicon-based material is 0.02% to 2%.

[0034] In another possible implementation, when the premixed material further includes a portion of the nonlinear conductive agent, the mass of the nonlinear conductive agent included in the premixed material is 40% to 60% of the total mass of the nonlinear conductive agent;

[0035] When the premixed material further includes a portion of the graphite material, the mass of the graphite material contained in the premixed material is 30% to 70% of the total mass of the graphite material.

[0036] In another possible implementation, the mass of the second binder contained in the fourth premix is ​​10% to 30% of the total mass of the second binder;

[0037] The mass of the first binder included in the fifth premix is ​​5% to 10% of the total mass of the first binder.

[0038] In another possible implementation, the silicon-based material is selected from at least one of silicon carbon, pre-magnesium silicon oxide, and pre-lithium silicon oxide;

[0039] The first binder is selected from at least one of polyacrylic acid, polyethylene oxide and polyethyleneimine;

[0040] The nonlinear conductive agent is selected from at least one of carbon black, conductive graphite, carbon fiber and graphene;

[0041] The second binder is selected from at least one of sodium hydroxymethyl cellulose and lithium hydroxymethyl cellulose;

[0042] The linear conductive agent is selected from at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes;

[0043] The third binder is selected from styrene-butadiene rubber.

[0044] On the other hand, a negative electrode plate is provided, wherein the negative electrode plate is prepared by any of the above-mentioned methods for preparing a negative electrode plate.

[0045] On the other hand, a battery is provided, comprising: an electrolyte, a negative electrode plate disposed in the electrolyte, a positive electrode plate and a separator, wherein the negative electrode plate is a negative electrode plate prepared by the preparation method provided in the present application, and the negative electrode plate and the positive electrode plate are separated by the separator.

[0046] The embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the method premixes a silicon-based material with a premixed material including a first binder, and forms a protective film with strong mechanical stability on the surface of the silicon-based material through the first binder, thereby reducing the side reactions caused by cracks generated by the expansion of the silicon-based material, isolating the electrolyte from eroding the surface of the silicon-based material, and reducing gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode sheet. In addition, at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches, thereby reducing the agglomeration of active particles, optimizing the uniformity of the dispersion of each component, and better maintaining the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0047] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of a method for preparing a negative electrode sheet provided in an embodiment of the present application;

[0049] Figure 2 is a flow chart of another method for preparing a negative electrode sheet provided in an embodiment of the present application;

[0050] Figure 3 is a flow chart of another method for preparing a negative electrode sheet provided in an embodiment of the present application;

[0051] Figure 4 It is a flow chart of another method for preparing a negative electrode sheet provided in an embodiment of the present application. DETAILED DESCRIPTION

[0052] In order to make the technical solutions and advantages of the present application clearer, the implementation methods of the present application are described in further detail below.

[0053] Figure 1 is a flow chart of a method for preparing a negative electrode sheet according to an exemplary embodiment, see Figure 1 , the preparation method comprises:

[0054] Step 101: Evenly mix the silicon-based material and the premixed material to obtain a first premixed material.

[0055] The premix material includes a portion of the first binder.

[0056] The specific process may be: adding the silicon-based material and the premixed material into a container, stirring and mixing them evenly to obtain a first premixed material.

[0057] The container may be a stirring tank or any other stirring device, which is not specifically limited.

[0058] In a possible implementation manner, the premix material includes only a portion of the first binder.

[0059] In another possible implementation, in addition to a portion of the first binder, the premixed material further includes a portion of the nonlinear conductive agent, that is, the premixed material includes both a portion of the first binder and a portion of the nonlinear conductive agent.

[0060] In another possible implementation, in addition to a portion of the binder in the first binder, the premixed material further includes a portion of graphite material, that is, the premixed material includes both a portion of the first binder and a portion of the graphite material.

[0061] Regardless of whether the premixed material includes part of the nonlinear conductive agent or part of the graphite material, in the first premixed material, the mass ratio of the solid component in the first binder to the silicon-based material is 0.02% to 2%.

[0062] The mass ratio of the solid component in the first adhesive to the silicon-based material may be 0.02%, 0.03%, 0.05%, 0.08%, 1%, 1.2%, 1.5%, 1.8%, or 2%.

[0063] In an embodiment of the present application, the first binder is a solid-liquid mixture. Based on the proportion of solid components in the first binder, the mass fraction of the silicon-based material and the mass percentage, the mass fraction of the first binder contained in the premix can be calculated. The process can be: determine the product of the mass fraction of the silicon-based material and the mass percentage to obtain the mass fraction of the solid components in the first binder, determine the ratio of the mass fraction of the solid components in the first binder to the proportion of the solid components in the first binder, and obtain the mass fraction of the first binder contained in the premix.

[0064] If the premixed material only includes a portion of the first binder, step 101 may be: uniformly mixing the silicon-based material and a portion of the first binder to obtain a first premixed material.

[0065] In an embodiment of the present application, the silicon-based material is premixed with the above-mentioned part of the first binder, and a protective film with strong mechanical stability is formed on the surface of the silicon-based material by the first binder. This can reduce the side reactions caused by cracks generated by the expansion of the silicon-based material, isolate the corrosion of the electrolyte on the surface of the silicon-based material, and reduce gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode plate.

[0066] If the premixed material further includes a portion of nonlinear conductive agent in addition to a portion of the first binder, step 101 may be: uniformly mixing the silicon-based material, a portion of the first binder, and a portion of the nonlinear conductive agent to obtain a first premixed material.

[0067] The mass of the nonlinear conductive agent contained in the premix is ​​40% to 60% of the total mass of the nonlinear conductive agent. For example, the mass of the nonlinear conductive agent contained in the premix is ​​40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60% of the total mass of the nonlinear conductive agent.

[0068] In the embodiment of the present application, when the silicon-based material and part of the first binder are uniformly mixed, adding the nonlinear conductive agent in the above mass percentage can enhance the conductivity of the silicon-based material.

[0069] If the premixed material further includes a portion of graphite material in addition to a portion of the first binder, step 101 may be: uniformly mixing the silicon-based material, a portion of the first binder, and a portion of the graphite material to obtain a first premixed material.

[0070] The mass of the graphite material contained in the premix is ​​30% to 70% of the total mass of the graphite material. For example, the mass of the graphite material contained in the premix is ​​30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% of the total mass of the graphite material.

[0071] In the embodiment of the present application, when the silicon-based material and a portion of the first binder are uniformly mixed, adding the graphite material in the above mass percentage can promote full mixing of the silicon-based material and the graphite.

[0072] In an embodiment of the present application, the negative electrode plate includes the following components in proportions by mass: 1 to 15 parts of silicon-based material, 1.5 to 3 parts of a first binder, 81 to 95 parts of a graphite material, 0.1 to 0.6 parts of a nonlinear conductive agent, 0.1 to 0.5 parts of a second binder, 0.01 to 0.1 parts of a linear conductive agent, and 0.5 to 1.2 parts of a third binder.

[0073] Among them, the mass fraction of the silicon-based material can be 1 part, 2 parts, 3 parts, 4 parts, 6 parts, 8 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, and 15 parts, the mass fraction of the first binder can be 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.3 parts, 2.5 parts, 2.6 parts, 2.8 parts, and 3 parts, the mass fraction of the graphite material can be 81 parts, 82 parts, 85 parts, 86 parts, 87 parts, 88 parts, 90 parts, 91 parts, 93 parts, and 95 parts, and the mass fraction of the nonlinear conductive agent can be 0.1 parts, 0.2 parts, The mass fractions of the first and second adhesives can be 0.1, 0.2, 0.25, 0.3, 0.4, and 0.5, the mass fractions of the linear conductive agent can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1, and the mass fractions of the third adhesive can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, and 1.2.

[0074] The silicon-based material is selected from at least one of silicon carbon, pre-magnesium silicon oxide and pre-lithium silicon oxide, the first binder is selected from at least one of polyacrylic acid, polyethylene oxide and polyethyleneimine, the nonlinear conductive agent is selected from at least one of carbon black, conductive graphite, carbon fiber and graphene, the second binder is selected from at least one of sodium hydroxymethyl cellulose and lithium hydroxymethyl cellulose, the linear conductive agent is selected from at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes, and the third binder is selected from styrene-butadiene rubber. The solid content of the first binder is 6% to 10%.

[0075] The silicon carbon in the silicon-based material may be silicon carbon prepared by ball milling or by gas phase method, and there is no specific limitation on this. The type of carbon black in the nonlinear conductive agent may be set and changed as needed, for example, the carbon black may be granular carbon black SP or flake graphite carbon black FG5, and there is no specific limitation on this. The solid content in the first binder may be 6%, 7%, 8%, 9%, or 10%.

[0076] In the embodiments of the present application, the negative electrode plate prepared by the preparation method provided in the present application using the above-mentioned components can reduce gas production and active lithium loss without increasing the battery impedance, thereby improving the high-temperature storage life of the negative electrode plate.

[0077] Step 102: Evenly mix the remaining materials constituting the negative electrode plate with the first premix to obtain a second premix.

[0078] Among them, the remaining materials constituting the negative electrode plate include graphite material, the remaining first binder, the second binder, the linear conductive agent, and the non-linear conductive agent, and at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the non-linear conductive agent is added in batches.

[0079] One point that needs to be explained is that at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches. Each component of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent may be added in batches. Alternatively, some components of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent may be added in batches, such as the graphite material, the first binder, the second binder, and the nonlinear conductive agent. There is no specific limitation on this.

[0080] In addition, adding in batches may be adding in two times, three times, or even more times, which is not specifically limited. For example, the graphite material is added in two times, and the first binder is added in three times.

[0081] In an embodiment of the present application, adding at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent in batches can reduce the agglomeration of active particles, optimize the uniformity of dispersion of each component, and better maintain the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0082] When the components included in the premixed material are different, the remaining materials constituting the negative electrode plate are different, and the corresponding process of step 102 is also different. The specific process will be described in detail in the subsequent embodiments and will not be repeated here.

[0083] Step 103: Evenly mix the second premix with the solvent and the third binder to obtain a negative electrode slurry.

[0084] The second premix is ​​mixed evenly with the solvent, the solid content in the slurry is adjusted to 35% to 55% by the solvent, and then the third binder is added and mixed evenly to obtain the negative electrode slurry.

[0085] The solid content in the slurry is the mass percentage of the solid components in the slurry. The solid content in the slurry can be 35%, 37%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%. The solvent can be water, and the form of water can be set and changed as needed, for example, distilled water or tap water, which is not specifically limited.

[0086] Step 104: Prepare a negative electrode sheet using negative electrode slurry and current collector.

[0087] The negative electrode slurry is coated on the negative electrode current collector and dried to obtain a negative electrode sheet.

[0088] The negative electrode current collector may be copper foil or other metal foils, which are not specifically limited.

[0089] The embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the method premixes a silicon-based material with a premixed material including a first binder, and forms a protective film with strong mechanical stability on the surface of the silicon-based material through the first binder, thereby reducing the side reactions caused by cracks generated by the expansion of the silicon-based material, isolating the electrolyte from eroding the surface of the silicon-based material, and reducing gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode sheet. In addition, at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches, thereby reducing the agglomeration of active particles, optimizing the uniformity of the dispersion of each component, and better maintaining the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0090] Above Figure 1 This is the basic process for preparing the negative electrode sheet. In the embodiment of the present application, when the components included in the premixed material are different, the remaining materials constituting the negative electrode sheet are different, and the process of obtaining the second premixed material is also different. Figures 2 to 4 The embodiments of the present invention are described in detail for different situations.

[0091] See also Figure 2 , Figure 2 is a flow chart of a method for preparing a negative electrode sheet according to an exemplary embodiment. This embodiment is described by taking the premixed material including only a part of the first binder as an example. Figure 2 , the preparation method comprises:

[0092] Step 201: Evenly mix the silicon-based material and a portion of the first binder to obtain a first premix.

[0093] The specific process may be: adding the silicon-based material and part of the first binder into a container, stirring and mixing them evenly to obtain a first premix.

[0094] In the embodiment of the present application, after obtaining the first premix, part of the nonlinear conductive agent and part of the graphite material may be added first, wherein when adding the nonlinear conductive agent and the graphite material, a linear conductive agent may be added or not. If no linear conductive agent is added when adding the nonlinear conductive agent and the graphite material, then after executing step 201, step 202 is executed, and step 203 is no longer executed; if a linear conductive agent is added when adding the nonlinear conductive agent and the graphite material, then after executing step 201, step 203 is directly executed.

[0095] Step 202: uniformly mix the first premix, part of the nonlinear conductive agent and part of the graphite material to obtain a third premix.

[0096] In a possible implementation, the first premix is ​​evenly mixed with any one of a portion of the nonlinear conductive agent and a portion of the graphite material, and then evenly mixed with the other component to obtain a third premix.

[0097] For example, the first premix is ​​mixed evenly with part of the nonlinear conductive agent, and then part of the graphite material is added and mixed evenly to obtain the third premix. For another example, the first premix is ​​mixed evenly with part of the graphite material, and then part of the nonlinear conductive agent is added and mixed evenly to obtain the third premix.

[0098] In another possible implementation manner, part of the nonlinear conductive agent and part of the graphite material are firstly mixed evenly, and then mixed evenly with the first premix to obtain a third premix.

[0099] Step 203: uniformly mix the first premix, part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent to obtain a third premix.

[0100] In a possible implementation, the first premix is ​​firstly mixed evenly with any one of a part of the nonlinear conductive agent, a part of the graphite material and the linear conductive agent, and then the second component is added and mixed evenly, and finally the third component is added and mixed evenly to obtain a third premix.

[0101] For example, the first premix is ​​mixed evenly with part of the nonlinear conductive agent, then part of the graphite material is added and mixed evenly, and then the linear conductive agent is added and mixed evenly to obtain a third premix. For another example, the first premix is ​​mixed evenly with the linear conductive agent, then part of the nonlinear conductive agent is added and mixed evenly, and then part of the graphite material is added and mixed evenly to obtain a third premix. The other implementation methods are similar to this method and are not listed here one by one.

[0102] In another possible implementation, firstly mix any two components among part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent, and then mix them with the third component, and finally mix the mixed slurry of the three components with the first premix to obtain a third premix.

[0103] For example, part of the nonlinear conductive agent and part of the graphite material are mixed evenly, and then mixed evenly with the linear conductive agent, and finally the mixed slurry of the three components is mixed evenly with the first premix to obtain a third premix. For another example, part of the nonlinear conductive agent and the linear conductive agent are mixed evenly, and then mixed evenly with part of the graphite material, and finally the mixed slurry of the three components is mixed evenly with the first premix to obtain a third premix. The remaining implementation methods are similar to this method and are not listed here one by one.

[0104] In another possible implementation, any two components among part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent are first mixed evenly, then mixed evenly with the first premix, and finally mixed evenly with the third component to obtain a third premix.

[0105] For example, firstly, a part of the nonlinear conductive agent and a part of the graphite material are mixed evenly, then mixed evenly with the first premix, and finally mixed evenly with the linear conductive agent to obtain a third premix. The other implementation methods are similar to this method and are not listed here one by one.

[0106] In the embodiment of the present application, the first premix, part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent may be uniformly mixed in other ways, which are not listed here one by one.

[0107] In the embodiment of the present application, when the first premix, part of the nonlinear conductive agent, and part of the graphite material are uniformly mixed, the linear conductive agent is added to form a conductive network between the graphite and the silicon-based material.

[0108] Step 204: uniformly mix the third premix with the remaining part of the remaining materials to obtain a second premix.

[0109] The second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0110] If step 202 is performed after step 201, step 204 can be implemented by the following steps (A1) to (A2), including:

[0111] (A1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are uniformly mixed to obtain a fourth premix.

[0112] In step (A1), the third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the solvent are uniformly mixed, and the solid content in the slurry is adjusted to 60% to 90% by the solvent to obtain a fourth premix.

[0113] The solid content in the slurry is the mass percentage of the solid components in the slurry. The solid content in the fourth premix can be 60%, 65%, 68%, 70%, 75%, 78%, 80%, 85%, 88%, 90%.

[0114] The mass of the second binder contained in the fourth premix is ​​10% to 30% of the total mass of the second binder. For example, the mass of the second binder contained in the fourth premix is ​​10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30% of the total mass of the second binder.

[0115] In one possible implementation, the third premix is ​​mixed evenly with part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent, and then the second component is added and mixed evenly, and then the third component is added and mixed evenly, and finally a solvent is added to adjust the solid content in the slurry to obtain a fourth premix.

[0116] For example, the third premix is ​​mixed evenly with part of the second binder, and then the remaining part of the graphite material is added and mixed evenly, and then the remaining part of the nonlinear conductive agent is added and mixed evenly, and finally the solvent is added to knead the powder, and the solid content in the slurry is adjusted by the amount of solvent added to obtain the fourth premix.

[0117] In another possible implementation, the third premix is ​​evenly mixed with part of the second binder, the remaining part of the graphite material, and the remaining part of the nonlinear conductive agent, and then the remaining two components are evenly mixed, and then the two mixed slurries are evenly mixed, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0118] For example, the third premix is ​​firstly mixed evenly with a part of the second binder, and then the remaining part of the graphite material is mixed evenly with the remaining part of the nonlinear conductive agent, and then the two mixed slurries are mixed evenly, and finally a solvent is added to knead the powder to obtain a fourth premix.

[0119] In another possible implementation, first, part of the second binder, the remaining graphite material, and any two of the remaining nonlinear conductive agent are evenly mixed, then evenly mixed with the third component, then the mixed slurry is evenly mixed with the third premix, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0120] For example, firstly mix the remaining graphite material and the remaining nonlinear conductive agent evenly, then add part of the second binder and mix evenly, then add the third premix and mix evenly, and finally add the solvent to adjust the solid content to obtain the fourth premix.

[0121] In the embodiment of the present application, the third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the solvent may be uniformly mixed in other ways, which are not listed here one by one.

[0122] (A2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0123] The first binder contained in the other remaining part of the remaining material is added in batches.

[0124] The specific process may be: uniformly mix the fourth premix, the remaining second binder, the remaining first binder, and the linear conductive agent to obtain a fifth premix; and uniformly mix the fifth premix with the remaining first binder to obtain a second premix.

[0125] The mass of the first binder contained in the fifth premix is ​​5% to 10% of the total mass of the first binder. For example, the mass of the first binder contained in the fifth premix is ​​5%, 6%, 7%, 8%, 9%, or 10% of the total mass of the first binder.

[0126] It can be seen that in the embodiment of the present application, the second binder is added in two times, and the first binder is added in three times.

[0127] In a possible implementation, the fourth premix is ​​mixed evenly with the remaining second binder, the remaining first binder, and any one of the linear conductive agents, and then mixed evenly with the second component, and finally the third component is added and mixed evenly to obtain the fifth premix.

[0128] For example, the fourth premix is ​​mixed evenly with the remaining part of the second binder, and then the remaining part of the first binder is added and mixed evenly, and finally the linear conductive agent is added and mixed evenly to obtain the fifth premix.

[0129] In another possible implementation, the fourth premix is ​​evenly mixed with the remaining portion of the second binder, the remaining portion of the first binder, and any one of the linear conductive agents, and then the remaining two components are evenly mixed, and then the two mixed slurries are evenly mixed to obtain the fifth premix.

[0130] For example, the fourth premix is ​​mixed evenly with the remaining portion of the second binder, and then the remaining portion of the first binder is mixed evenly with the linear conductive agent, and finally the two slurries are mixed evenly to obtain the fifth premix.

[0131] In another possible implementation, the remaining second binder, the remaining first binder, and any two of the linear conductive agents are first mixed evenly, then mixed evenly with the third component, and then the mixed slurry is mixed evenly with the fourth premix to obtain a fifth premix.

[0132] For example, firstly mix the remaining part of the second binder and the remaining part of the first binder evenly, then add the linear conductive agent and mix evenly, and finally add the fourth premix and mix evenly to obtain the fifth premix.

[0133] Of course, the fourth premix, the remaining second binder, the remaining first binder, and the linear conductive agent may be uniformly mixed in other ways, which are not listed here one by one.

[0134] In an embodiment of the present application, when the fourth premix, the remaining part of the second binder, and the remaining part of the first binder are evenly mixed, a linear conductive agent is added to form a conductive network between the silicon-based material and the graphite material, while enhancing the fluidity and dispersibility of the slurry.

[0135] If step 202 is executed after step 201, step 204 can also be implemented by the following steps (B1) to (B2), including:

[0136] (B1) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the linear conductive agent are uniformly mixed to obtain a fourth premix.

[0137] In step (B1), the third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, the linear conductive agent, and the solvent are uniformly mixed, and the solid content of the slurry is adjusted to 60% to 90% by the solvent to obtain a fourth premix.

[0138] In one possible implementation, the third premix is ​​mixed evenly with part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and the linear conductive agent, and then the second component is added and mixed evenly, the third component is added and mixed evenly, the fourth component is added and mixed evenly, and finally a solvent is added to adjust the solid content in the slurry to obtain a fourth premix.

[0139] For example, the third premix is ​​mixed evenly with part of the second binder, and then the remaining part of the graphite material is added and mixed evenly, and then the remaining part of the nonlinear conductive agent is added and mixed evenly, and then the linear conductive agent is added and mixed evenly, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0140] In another possible implementation, the third premix is ​​mixed evenly with part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and any one of the linear conductive agents, and then part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and the other two components of the linear conductive agent are mixed evenly, and then the two mixed slurries are mixed evenly, and then the fourth component is added and mixed evenly, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0141] For example, the third premix is ​​mixed evenly with part of the second binder, the remaining graphite material is mixed evenly with the linear conductive agent, the two mixed slurries are mixed evenly, the remaining nonlinear binder is added and mixed evenly, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0142] In another possible implementation, the third premix is ​​evenly mixed with part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and any one of the linear conductive agents, and then the second component is added and mixed evenly, and then the remaining two components are mixed evenly, the two mixed slurries are mixed evenly, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0143] For example, the third premix is ​​mixed evenly with part of the second binder, and then the linear conductive agent is added and mixed evenly, and then the remaining part of the graphite material and the remaining part of the nonlinear conductive agent are mixed evenly, the two mixed slurries are mixed evenly, and finally a solvent is added to adjust the solid content to obtain a fourth premix.

[0144] Of course, the third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the linear conductive agent may be uniformly mixed in other ways, which are not listed here one by one.

[0145] In an embodiment of the present application, when the third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are mixed evenly, the linear conductive agent is added to form a protective film on the surface of the silicon-based material in batches, and the binder is evenly dispersed to form a more complete protective conductive layer.

[0146] (B2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0147] The first binder contained in the other remaining part of the remaining material is added in batches.

[0148] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0149] In a possible implementation, the fourth premix is ​​mixed evenly with any one of the remaining part of the second binder and the remaining part of the first binder, and then the second component is added and mixed evenly to obtain the fifth premix.

[0150] For example, the fourth premix is ​​mixed evenly with the remaining portion of the second binder, and then the remaining portion of the first binder is added and mixed evenly to obtain the fifth premix.

[0151] In another possible implementation, the remaining part of the second binder and the remaining part of the first binder are firstly mixed evenly, and then the fourth premix is ​​added and mixed evenly to obtain the fifth premix.

[0152] If step 203 is performed after step 201, step 204 can be implemented by the following steps (C1) to (C2), including:

[0153] (C1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are uniformly mixed to obtain a fourth premix.

[0154] In step (C1), the third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the solvent are uniformly mixed, and the solid content of the slurry is adjusted to 60% to 90% by the solvent to obtain a fourth premix.

[0155] Step (C1) is the same as step (A1) and will not be described again here.

[0156] (C2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0157] The first binder contained in the other remaining part of the remaining material is added in batches.

[0158] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0159] Step (C2) is the same as step (B2) and will not be described again here.

[0160] In the embodiment of the present application, the linear conductive agent can be added in step 203, can be added in step (A2), and can also be added in step (B1). It can be seen that the order of adding the linear conductive agent is diversified, and any addition method can make the linear conductive agent better dispersed, forming a bridging structure between the silicon carbon and graphite materials, thereby improving the stability of the negative electrode plate, and then improving the high temperature storage life of the negative electrode plate.

[0161] In the related art, when preparing the negative electrode plate, the first binder and the linear conductive agent are prepared into a conductive glue, which is then mixed with other components. However, the conductive glue formed in this way has a high viscosity, which easily causes the linear conductive agent to agglomerate, which is not conducive to the dispersion of the linear conductive agent and instead reduces the high-temperature storage life of the negative electrode plate.

[0162] Step 205: Evenly mix the second premix with the solvent and the third binder to obtain negative electrode slurry.

[0163] This step is the same as step 103 and will not be repeated here.

[0164] Step 206: Prepare a negative electrode sheet using negative electrode slurry and current collector.

[0165] This step is the same as step 104 and will not be described again here.

[0166] The embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the method premixes a silicon-based material with a premixed material including a first binder, and forms a protective film with strong mechanical stability on the surface of the silicon-based material through the first binder, thereby reducing the side reactions caused by cracks generated by the expansion of the silicon-based material, isolating the electrolyte from eroding the surface of the silicon-based material, and reducing gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode sheet. In addition, at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches, thereby reducing the agglomeration of active particles, optimizing the uniformity of the dispersion of each component, and better maintaining the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0167] See also Figure 3 , Figure 3 is a flow chart of a method for preparing a negative electrode sheet according to an exemplary embodiment. This embodiment is described by taking the premixed material including part of the first binder and part of the nonlinear conductive agent as an example. Figure 3 , the preparation method comprises:

[0168] Step 301: Evenly mix the silicon-based material, part of the first binder, and part of the nonlinear conductive agent to obtain a first premix.

[0169] In a possible implementation manner, the silicon-based material is uniformly mixed with any one of a portion of the first binder and a portion of the nonlinear conductive agent to obtain a first premix.

[0170] For example, the silicon-based material and part of the first binder are mixed evenly, and then part of the nonlinear conductive agent is added and mixed evenly to obtain a first premix. The specific process may be: the silicon-based material and part of the first binder are added into a container and stirred, after mixing evenly, part of the nonlinear conductive agent is added and mixed evenly to obtain a first premix.

[0171] In another possible implementation, part of the first binder and part of the nonlinear conductive agent are evenly mixed, and then evenly mixed with the silicon-based material to obtain a first premix.

[0172] The specific process may be: adding part of the first binder and part of the nonlinear conductive agent into a container and stirring them, and after mixing them evenly, adding the silicon-based material and mixing them evenly to obtain a first premix.

[0173] In the embodiment of the present application, after obtaining the first premix, part of the graphite material may be added first. When adding the graphite material, a linear conductive agent may be added or not. If no linear conductive agent is added when adding the graphite material, then after executing step 301, step 302 is executed, and step 303 is no longer executed; if a linear conductive agent is added when adding the graphite material, then after executing step 301, step 303 is directly executed.

[0174] Step 302: Evenly mix the first premix and part of the graphite material to obtain a third premix.

[0175] A portion of the graphite material is added to the container containing the first premix and mixed evenly to obtain a third premix.

[0176] Step 303: uniformly mix the first premix, part of the graphite material and the linear conductive agent to obtain a third premix.

[0177] In a possible implementation, the first premix is ​​evenly mixed with a portion of the graphite material and any one of the linear conductive agents, and then evenly mixed with the other component to obtain a third premix.

[0178] For example, the first premix is ​​mixed evenly with a portion of the graphite material, and then the linear conductive agent is added and mixed evenly to obtain the third premix.

[0179] In another possible implementation, part of the graphite material and the linear conductive agent are firstly mixed evenly, and then mixed evenly with the first premix to obtain a third premix.

[0180] In the embodiment of the present application, when the first premix and part of the graphite material are mixed evenly, a linear conductive agent is added to promote uniform dispersion of the silicon-based material and the graphite, and the linear conductive agent adheres to the surface of the silicon-based material and the graphite.

[0181] Step 304: uniformly mix the third premix with the remaining part of the remaining materials to obtain a second premix.

[0182] The second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0183] If step 302 is executed after step 301, step 204 can be implemented by the following steps (D1) to (D2), including:

[0184] (D1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are mixed uniformly to obtain a fourth premix.

[0185] Step (D1) is the same as step (A1) in step 204 and will not be described again here.

[0186] (D2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0187] The first binder contained in the other remaining part of the remaining material is added in batches.

[0188] The specific process may be: uniformly mix the fourth premix, the remaining second binder, the remaining first binder, and the linear conductive agent to obtain a fifth premix; and uniformly mix the fifth premix with the remaining first binder to obtain a second premix.

[0189] Step (D2) is the same as step (A2) in step 204 and will not be described again here.

[0190] If step 302 is executed after step 301, step 204 can also be implemented by the following steps (E1) to (E2), including:

[0191] (E1) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the linear conductive agent are uniformly mixed to obtain a fourth premix.

[0192] Step (E1) is the same as step (B1) in step 204 and will not be described again here.

[0193] (E2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0194] The first binder contained in the other remaining part of the remaining material is added in batches.

[0195] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0196] Step (E2) is the same as step (B2) in step 204 and will not be described again here.

[0197] If step 303 is performed after step 301, step 304 can be implemented by the following steps (F1) to (F2), including:

[0198] (F1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are mixed uniformly to obtain a fourth premix.

[0199] Step (F1) is the same as step (A1) in step 204 and will not be described again here.

[0200] (F2) mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0201] The first binder contained in the other remaining part of the remaining material is added in batches.

[0202] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0203] Step (F2) is the same as step (B2) in step 204 and will not be described again here.

[0204] Step 305: Evenly mix the second premix with the solvent and the third binder to obtain negative electrode slurry.

[0205] This step is the same as step 103 and will not be repeated here.

[0206] Step 306: Prepare a negative electrode sheet using negative electrode slurry and current collector.

[0207] This step is the same as step 104 and will not be described again here.

[0208] The embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the method premixes a silicon-based material with a premixed material including a first binder, and forms a protective film with strong mechanical stability on the surface of the silicon-based material through the first binder, thereby reducing the side reactions caused by cracks generated by the expansion of the silicon-based material, isolating the electrolyte from eroding the surface of the silicon-based material, and reducing gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode sheet. In addition, at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches, thereby reducing the agglomeration of active particles, optimizing the uniformity of the dispersion of each component, and better maintaining the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0209] See also Figure 4 , Figure 4 is a flow chart of a method for preparing a negative electrode sheet according to an exemplary embodiment. This embodiment is described by taking the premixed material including part of the first binder and part of the graphite material as an example. Figure 4 , the preparation method comprises:

[0210] Step 401: Evenly mix the silicon-based material, part of the first binder, and part of the graphite material to obtain a first premix.

[0211] In a possible implementation manner, the silicon-based material is uniformly mixed with any one of a portion of the first binder and a portion of the graphite material to obtain a first premix.

[0212] For example, the silicon-based material and part of the first binder are mixed evenly, and then part of the graphite material is added and mixed evenly to obtain the first premix. The specific process can be: the silicon-based material and part of the first binder are added into a container and stirred, after mixing evenly, part of the graphite material is added and mixed evenly to obtain the first premix.

[0213] In another possible implementation, part of the first binder and part of the graphite material are evenly mixed, and then evenly mixed with the silicon-based material to obtain a first premix.

[0214] The specific process may be: adding part of the first binder and part of the graphite material into a container and stirring them, and after mixing them evenly, adding the silicon-based material and mixing them evenly to obtain the first premix.

[0215] In the embodiment of the present application, after obtaining the first premix, part of the nonlinear conductive agent may be added first. When adding part of the nonlinear conductive agent, a linear conductive agent may be added or not. If no linear conductive agent is added when adding the nonlinear conductive agent, then after executing step 401, step 402 is executed, and step 403 is no longer executed; if a linear conductive agent is added when adding the nonlinear conductive agent, then after executing step 401, step 403 is directly executed.

[0216] Step 402: Evenly mix the first premix and part of the nonlinear conductive agent to obtain a third premix.

[0217] A portion of the nonlinear conductive agent is added to the container containing the first premix and mixed evenly to obtain a third premix.

[0218] Step 403: uniformly mix the first premix, part of the nonlinear conductive agent and the linear conductive agent to obtain a third premix.

[0219] In a possible implementation, the first premix is ​​evenly mixed with a portion of any one of the nonlinear conductive agent and the linear conductive agent, and then evenly mixed with the other component to obtain a third premix.

[0220] For example, the first premix is ​​mixed evenly with a portion of the nonlinear conductive agent, and then the linear conductive agent is added and mixed evenly to obtain the third premix.

[0221] In another possible implementation, part of the nonlinear conductive agent and the linear conductive agent are firstly mixed evenly, and then mixed evenly with the first premix to obtain a third premix.

[0222] In the embodiment of the present application, when the first premix and part of the nonlinear conductive agent are uniformly mixed, the linear conductive agent is added to form a conductive slurry to promote effective dispersion of the nonlinear conductive agent without forming conductive agent agglomerates.

[0223] Step 404: uniformly mix the third premix with the remaining portion of the remaining materials to obtain a second premix.

[0224] The second binder and the first binder contained in the remaining part of the remaining material are added in batches.

[0225] If step 402 is performed after step 401, step 404 can be implemented by the following steps (G1) to (G2), including:

[0226] (G1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are mixed uniformly to obtain a fourth premix.

[0227] Step (G1) is the same as step (A1) in step 204 and will not be described again here.

[0228] (G2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0229] The first binder contained in the other remaining part of the remaining material is added in batches.

[0230] The specific process may be: uniformly mix the fourth premix, the remaining second binder, the remaining first binder, and the linear conductive agent to obtain a fifth premix; and uniformly mix the fifth premix with the remaining first binder to obtain a second premix.

[0231] Step (G2) is the same as step (A2) in step 204 and will not be described again here.

[0232] If step 402 is executed after step 401, step 404 can also be implemented by the following steps (H1) to (H2), including:

[0233] (H1) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the linear conductive agent are uniformly mixed to obtain a fourth premix.

[0234] Step (H1) is the same as step (B1) in step 204 and will not be described again here.

[0235] (H2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0236] The first binder contained in the other remaining part of the remaining material is added in batches.

[0237] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0238] Step (H2) is the same as step (B2) in step 204 and will not be described again here.

[0239] If step 403 is performed after step 401, step 404 can be implemented by the following steps (I1) to (I2), including:

[0240] (I1) The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are mixed uniformly to obtain a fourth premix.

[0241] Step (I1) is the same as step (A1) in step 204 and will not be described again here.

[0242] (I2) uniformly mixing the fourth premix with another remaining portion of the remaining materials to obtain a second premix.

[0243] The first binder contained in the other remaining part of the remaining material is added in batches.

[0244] The specific process may be: uniformly mixing the fourth premix, the remaining part of the second binder, and the remaining part of the first binder to obtain a fifth premix; and uniformly mixing the fifth premix with the remaining part of the first binder to obtain a second premix.

[0245] Step (I2) is the same as step (B2) in step 204 and will not be described again here.

[0246] Step 405: Evenly mix the second premix with the solvent and the third binder to obtain a negative electrode slurry.

[0247] This step is the same as step 103 and will not be repeated here.

[0248] Step 406: Prepare a negative electrode sheet using negative electrode slurry and current collector.

[0249] This step is the same as step 104 and will not be described again here.

[0250] The embodiment of the present application provides a method for preparing a negative electrode sheet, wherein the method premixes a silicon-based material with a premixed material including a first binder, and forms a protective film with strong mechanical stability on the surface of the silicon-based material through the first binder, thereby reducing the side reactions caused by cracks generated by the expansion of the silicon-based material, isolating the electrolyte from eroding the surface of the silicon-based material, and reducing gas production and active lithium loss without increasing impedance, thereby improving the high-temperature storage life of the negative electrode sheet. In addition, at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches, thereby reducing the agglomeration of active particles, optimizing the uniformity of the dispersion of each component, and better maintaining the structural stability of the negative electrode sheet, thereby further improving the high-temperature storage life of the negative electrode sheet.

[0251] The embodiment of the present application also provides a negative electrode plate, which is prepared by the preparation method shown in any of the above embodiments.

[0252] An embodiment of the present application also provides a battery, which includes: an electrolyte, a negative electrode plate disposed in the electrolyte, a positive electrode plate and a separator, wherein the negative electrode plate is prepared by the preparation method provided in the present application, and the negative electrode plate and the positive electrode plate are separated by the separator.

[0253] The positive electrode sheet can be a ternary positive electrode material, lithium cobalt oxide, or other materials, which are not specifically limited. The ternary positive electrode material is mainly composed of three elements: nickel, cobalt, and manganese. According to the different proportions of nickel, cobalt, and manganese, it can be divided into different models, such as NCM523, NCM811, and other models.

[0254] The diaphragm is a commercially available diaphragm, and the material of the diaphragm may be PP (polypropylene), PE (polyethylene), a three-layer material of PP and PE composite, or other materials, and there is no specific limitation on this.

[0255] The technical solution of the present application will be described in detail below through specific embodiments.

[0256] In the following specific examples, operations involved without specifying conditions were performed under conventional conditions or conditions recommended by the manufacturer.

[0257] The silicon-based material is selected from ball-milled silicon carbon, gas-phase silicon carbon, and pre-lithium silicon oxygen; wherein the ball-milled silicon carbon is silicon carbon prepared by ball milling, and the gas-phase silicon carbon is silicon carbon prepared by gas phase method;

[0258] The first binder is selected from polyacrylic acid (solid content is 7%) and polyethyleneimine (solid content is 7%);

[0259] The nonlinear conductive agent is selected from granular carbon black SP;

[0260] The second binder is selected from sodium hydroxymethyl cellulose (solid content is 4%) and lithium hydroxymethyl cellulose (solid content is 4%);

[0261] The linear conductive agent is selected from multi-walled carbon nanotubes and single-walled carbon nanotubes;

[0262] The third binder is selected from styrene-butadiene rubber;

[0263] The positive electrode plate is made of NCM811 and the diaphragm is made of PE matrix diaphragm.

[0264] Example 1

[0265] This embodiment is described by taking the example that the premixed material only includes a part of the first binder, and the linear conductive agent, the graphite material and the nonlinear conductive agent are added together.

[0266] In this embodiment, the silicon-based material is selected from ball-milled silicon carbon, the first binder is selected from polyacrylic acid, the nonlinear conductive agent is selected from granular carbon black SP, the second binder is selected from sodium hydroxymethyl cellulose, the linear conductive agent is selected from multi-walled carbon nanotubes, and the third binder is selected from styrene-butadiene rubber;

[0267] The weight proportion of the silicon-based material is 5, the weight proportion of the first binder is 1.8, the weight proportion of the nonlinear conductive agent is 0.5, the weight proportion of the second binder is 0.5, the weight proportion of the linear conductive agent is 0.08, the weight proportion of the third binder is 1, and the weight proportion of the graphite material is 91.12.

[0268] The preparation process is as follows:

[0269] (1) The silicon-based material and a portion of the first binder are mixed uniformly to obtain a first premix.

[0270] The mass of the first binder contained in the first premix is ​​20% of the total mass of the first binder.

[0271] (2) The first premix, part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent are stirred and mixed uniformly to obtain a third premix.

[0272] The mass of the part of the nonlinear conductive agent is 50% of the total mass of the nonlinear conductive agent, and the mass of the part of the graphite material is 50% of the total mass of the graphite material.

[0273] (3) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent and water are stirred and mixed evenly, and the solid content of the slurry is adjusted to 65% by water to obtain a fourth premix.

[0274] The mass of the second binder contained in the fourth premix is ​​30% of the total mass of the second binder.

[0275] (4) The fourth premix, the remaining part of the second binder, and the remaining part of the first binder are stirred and mixed uniformly to obtain a fifth premix.

[0276] The mass of the first binder contained in the fifth premix is ​​30% of the total mass of the first binder.

[0277] (5) The fifth premix is ​​stirred with the remaining first binder to obtain a second premix.

[0278] (6) The second premix is ​​mixed with water to be uniformly mixed, and the solid content in the slurry is adjusted to 45% by water, and then the third binder is added and stirred to obtain a negative electrode slurry.

[0279] (7) The negative electrode slurry is coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0280] Example 2

[0281] This embodiment is described by taking the example that the premix material only includes a part of the first binder, and the linear conductive agent, a part of the second binder, the remaining part of the graphite material and the remaining part of the nonlinear conductive agent are added together.

[0282] The types and weight proportions of the components in this embodiment are the same as those in Embodiment 1.

[0283] The preparation process is as follows:

[0284] (1) The silicon-based material and a portion of the first binder are mixed uniformly to obtain a first premix.

[0285] The mass of the first binder contained in the first premix is ​​20% of the total mass of the first binder.

[0286] (2) The first premix, part of the nonlinear conductive agent and part of the graphite material are stirred and mixed uniformly to obtain a third premix.

[0287] The mass of the part of the nonlinear conductive agent is 50% of the total mass of the nonlinear conductive agent, and the mass of the part of the graphite material is 50% of the total mass of the graphite material.

[0288] (3) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the linear conductive agent are stirred and mixed uniformly, and the solid content of the slurry is adjusted to 65% by water to obtain a fourth premix.

[0289] The mass of the second binder contained in the fourth premix is ​​30% of the total mass of the second binder.

[0290] (4) The fourth premix, the remaining part of the second binder, and the remaining part of the first binder are stirred and mixed uniformly to obtain a fifth premix.

[0291] The mass of the first binder contained in the fifth premix is ​​30% of the total mass of the first binder.

[0292] (5) The fifth premix is ​​stirred with the remaining first binder to obtain a second premix.

[0293] (6) The second premix is ​​mixed with water to be uniformly mixed, and the solid content in the slurry is adjusted to 45% by water, and then the third binder is added and stirred to obtain a negative electrode slurry.

[0294] (7) The negative electrode slurry is coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0295] Example 3

[0296] This embodiment is described by taking the example that the premix material only includes a part of the first binder, and the linear conductive agent, the remaining part of the second binder, and the remaining part of the first binder are added together.

[0297] The types and weight proportions of the components in this embodiment are the same as those in Embodiment 1.

[0298] The preparation process is as follows:

[0299] (1) The silicon-based material and a portion of the first binder are uniformly mixed to obtain a first premix.

[0300] The mass of the first binder contained in the first premix is ​​20% of the total mass of the first binder.

[0301] (2) The first premix, part of the nonlinear conductive agent and part of the graphite material are stirred and mixed uniformly to obtain a third premix.

[0302] The mass of the part of the nonlinear conductive agent is 50% of the total mass of the nonlinear conductive agent, and the mass of the part of the graphite material is 50% of the total mass of the graphite material.

[0303] (3) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent and water are stirred and mixed uniformly, and the solid content in the slurry is adjusted to 65% by water to obtain a fourth premix.

[0304] The mass of the second binder contained in the fourth premix is ​​30% of the total mass of the second binder.

[0305] (4) The fourth premix, the remaining part of the second binder, the remaining part of the first binder, and the linear conductive agent are stirred and mixed uniformly to obtain a fifth premix.

[0306] The mass of the first binder contained in the fifth premix is ​​30% of the total mass of the first binder.

[0307] (5) The fifth premix is ​​stirred with the remaining first binder to obtain a second premix.

[0308] (6) The second premix is ​​mixed with water to be uniformly mixed, and the solid content in the slurry is adjusted to 45% by water, and then the third binder is added and stirred to obtain a negative electrode slurry.

[0309] (7) The negative electrode slurry is coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0310] Example 4

[0311] This embodiment is described by taking the example that the premix material includes part of the first binder and part of the nonlinear conductive agent, and the linear conductive agent, the remaining part of the second binder, and the remaining part of the first binder are added together.

[0312] In this embodiment, the silicon-based material is selected from pre-lithium silicon oxide, the first binder is selected from polyacrylic acid, the nonlinear conductive agent is selected from granular carbon black SP, the second binder is selected from lithium hydroxymethyl cellulose, the linear conductive agent is selected from single-walled carbon nanotubes, and the third binder is selected from styrene-butadiene rubber;

[0313] The weight fraction of the silicon-based material is 7, the weight fraction of the first binder is 2, the weight fraction of the nonlinear conductive agent is 0.5, the weight fraction of the second binder is 0.4, the weight fraction of the linear conductive agent is 0.04, the weight fraction of the third binder is 1.2, and the weight fraction of the graphite material is 88.86.

[0314] The preparation process is as follows:

[0315] (1) The silicon-based material, part of the first binder, and part of the nonlinear conductive agent are uniformly mixed to obtain a first premix.

[0316] The mass of the first binder contained in the first premix is ​​20% of the total mass of the first binder, and the mass of the nonlinear conductive agent contained in the first premix is ​​50% of the total mass of the nonlinear conductive agent.

[0317] (2) Stirring the first premix and part of the graphite material to mix them evenly to obtain a third premix.

[0318] The partial graphite material accounts for 50% of the total mass of the graphite material.

[0319] (3) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent and water are stirred and mixed uniformly, and the solid content of the slurry is adjusted to 69% by water to obtain a fourth premix.

[0320] The mass of the second binder contained in the fourth premix is ​​30% of the total mass of the second binder.

[0321] (4) The fourth premix, the remaining part of the second binder, the remaining part of the first binder, and the linear conductive agent are stirred and mixed uniformly to obtain a fifth premix.

[0322] The mass of the first binder contained in the fifth premix is ​​30% of the total mass of the first binder.

[0323] (5) The fifth premix is ​​stirred with the remaining first binder to obtain a second premix.

[0324] (6) The second premix is ​​mixed with water to be uniformly mixed, and the solid content in the slurry is adjusted to 45% by water, and then the third binder is added and stirred to obtain a negative electrode slurry.

[0325] (7) The negative electrode slurry is coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0326] Example 5

[0327] This embodiment is described by taking the example that the premixed material includes part of the first binder and part of the graphite material, and the linear conductive agent, the remaining part of the second binder, and the remaining part of the first binder are added together.

[0328] In this embodiment, the silicon-based material is selected from gas phase silicon carbon, the first binder is selected from polyethylene imine, the nonlinear conductive agent is selected from granular carbon black SP, the second binder is selected from sodium hydroxymethyl cellulose, the linear conductive agent is selected from single-walled carbon nanotubes, and the third binder is selected from styrene-butadiene rubber;

[0329] The weight fraction of the silicon-based material is 4, the weight fraction of the first binder is 2.3, the weight fraction of the nonlinear conductive agent is 0.6, the weight fraction of the second binder is 0.4, the weight fraction of the linear conductive agent is 0.06, the weight fraction of the third binder is 1.1, and the weight fraction of the graphite material is 91.54.

[0330] The preparation process is as follows:

[0331] (1) The silicon-based material, part of the first binder, and part of the graphite material are uniformly mixed to obtain a first premix.

[0332] The mass of the first binder contained in the first premix is ​​10% of the total mass of the first binder, and the mass of the graphite material contained in the first premix is ​​50% of the total mass of the graphite material.

[0333] (2) The first premix and part of the nonlinear conductive agent are stirred and mixed uniformly to obtain a third premix.

[0334] The mass of the part of the nonlinear conductive agent is 50% of the total mass of the nonlinear conductive agent.

[0335] (3) The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent and water are stirred and mixed uniformly, and the solid content of the slurry is adjusted to 70% by water to obtain a fourth premix.

[0336] The mass of the second binder contained in the fourth premix is ​​30% of the total mass of the second binder.

[0337] (4) The fourth premix, the remaining part of the second binder, the remaining part of the first binder, and the linear conductive agent are stirred and mixed uniformly to obtain a fifth premix.

[0338] The mass of the first binder contained in the fifth premix is ​​30% of the total mass of the first binder.

[0339] (5) The fifth premix is ​​stirred with the remaining first binder to obtain a second premix.

[0340] (6) The second premix is ​​mixed with water to be uniformly mixed, and the solid content in the slurry is adjusted to 45% by water, and then the third binder is added and stirred to obtain a negative electrode slurry.

[0341] (7) The negative electrode slurry is coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0342] Comparative Example 1

[0343] The types and weight proportions of the components in this embodiment are the same as those in Embodiment 1.

[0344] The preparation process is as follows:

[0345] (1) Stir the silicon-based material and the graphite material to mix them evenly.

[0346] (2) Add a nonlinear conductive agent to the powder obtained in step (1), stir, and mix well.

[0347] (3) Add the first binder to the powder obtained in step (2), stir and mix well.

[0348] (4) Add a linear conductive agent to the mixed slurry obtained in step (3), stir, and mix well.

[0349] (5) Add the second binder to the mixed slurry obtained in step (4), stir and mix well.

[0350] (6) Add water to the mixed slurry obtained in step (5) to adjust the solid content of the slurry to 45%, add a third binder, and disperse and stir to obtain a negative electrode slurry.

[0351] (7) The negative electrode slurry is evenly coated on the copper foil current collector and dried to obtain a negative electrode sheet.

[0352] Performance Testing:

[0353] Examples 1 to 5 and Comparative Example 1 all use NCM811 as the positive electrode plate and a PE matrix separator. Batteries are prepared using the negative electrode plates and positive electrode plates and separators prepared in Examples 1 to 5 and Comparative Example 1.

[0354] Impedance test: At 25±2°C, the batteries prepared in Examples 1 to 5 and Comparative Example 1 were charged at 0.5C constant current to 4.2V, discharged at 0.5C to 50% SOC, left to stand for 1h, and the cut-off voltage V1 was recorded; the battery was discharged at 0.5C for 10s, and the voltage V2 was recorded. Impedance = (V1-V2) / 0.5C.

[0355] Storage life test: At 25±2°C, the batteries prepared in Examples 1 to 5 and Comparative Example 1 were charged to 4.2V at 0.5C constant current, left to stand for 10 minutes, discharged to 2.5V, and the capacity was recorded as Q1; then charged to 4.2V at 0.5C constant current, and stored at 60±2°C for 50 days. After 50 days, they were discharged to 2.5V at 0.5C, and the capacity was recorded as Q2; they were charged to 4.2V at 0.5C constant current, left to stand for 10 minutes, discharged to 2.5V, and the capacity was recorded as Q3.

[0356] Capacity retention rate = Q2 / Q1*100;

[0357] Capacity recovery rate = Q3 / Q1*100.

[0358] The test data is shown in Table 1 below.

[0359] Table 1

[0360]

[0361] It can be seen from Table 1 that the impedance of the batteries prepared in Examples 1 to 5 is similar to that of the battery prepared in Comparative Example 1, but the capacity retention rate and capacity recovery rate of the batteries prepared in Examples 1 to 5 at high temperatures are greater than those of the battery prepared in Comparative Example 1. This shows that the method provided in the present application can indeed improve the high-temperature storage life of the negative electrode sheet without increasing the impedance.

[0362] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solution of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: The preparation method comprises: Mixing the silicon-based material and the premixed material uniformly to obtain a first premixed material, wherein the premixed material includes a portion of the first binder; The remaining materials constituting the negative electrode sheet are uniformly mixed with the first premix to obtain a second premix, wherein the remaining materials constituting the negative electrode sheet include graphite material, the remaining first binder, the second binder, a linear conductive agent, and a nonlinear conductive agent, and at least one of the graphite material, the first binder, the second binder, the linear conductive agent, and the nonlinear conductive agent is added in batches; The second premix is ​​mixed with a solvent and a third binder to obtain a negative electrode slurry; The negative electrode sheet is prepared by using the negative electrode slurry and the current collector.

2. The preparation method according to claim 1, characterized in that: The premixed material also includes part of the nonlinear conductive agent; or, The premixed material also includes a portion of the graphite material.

3. The preparation method according to claim 1, characterized in that: When the premixed material includes only a part of the first binder, the remaining material constituting the negative electrode plate is mixed evenly with the first premixed material to obtain a second premixed material, comprising: The first premix, part of the nonlinear conductive agent and part of the graphite material are mixed evenly to obtain a third premix; or the first premix, part of the nonlinear conductive agent, part of the graphite material and the linear conductive agent are mixed evenly to obtain a third premix; Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix; Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

4. The preparation method according to claim 2, characterized in that: When the premixed material further includes part of the nonlinear conductive agent, the remaining material constituting the negative electrode plate is mixed evenly with the first premixed material to obtain a second premixed material, comprising: The first premix and a part of the graphite material are mixed evenly to obtain a third premix, or the first premix, a part of the graphite material and the linear conductive agent are mixed evenly to obtain a third premix; Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix; Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

5. The preparation method according to claim 2, characterized in that: When the premixed material further includes part of the graphite material, the remaining material constituting the negative electrode plate is uniformly mixed with the first premixed material to obtain a second premixed material, comprising: The first premix and part of the nonlinear conductive agent are mixed evenly to obtain a third premix; or the first premix, part of the nonlinear conductive agent and the linear conductive agent are mixed evenly to obtain a third premix; Evenly mixing the third premix with the remaining part of the remaining material to obtain the second premix; Wherein, the second binder and the first binder contained in the remaining part of the remaining material are added in batches.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The step of uniformly mixing the third premix with the remaining part of the remaining material to obtain the second premix comprises: The third premix, part of the second binder, the remaining part of the graphite material, and the remaining part of the nonlinear conductive agent are uniformly mixed to obtain a fourth premix; or the third premix, part of the second binder, the remaining part of the graphite material, the remaining part of the nonlinear conductive agent, and the linear conductive agent are uniformly mixed to obtain a fourth premix; uniformly mixing the fourth premix with another remaining part of the remaining material to obtain the second premix; The first binder contained in the other remaining part of the remaining material is added in batches.

7. The preparation method according to claim 6, characterized in that: The third premix, part of the second binder, the remaining graphite material, and the remaining nonlinear conductive agent are uniformly mixed to obtain a fourth premix, comprising: The third premix, part of the second binder, the remaining graphite material, the remaining nonlinear conductive agent, and the solvent are uniformly mixed, and the solid content of the slurry is adjusted to 60% to 90% by the solvent to obtain the fourth premix.

8. The preparation method according to claim 6, characterized in that: The step of uniformly mixing the fourth premix with the other remaining part of the remaining material to obtain the second premix comprises: The fourth premix, the remaining part of the second binder, the remaining part of the first binder, and the linear conductive agent are uniformly mixed to obtain a fifth premix; or the fourth premix, the remaining part of the second binder, and the remaining part of the first binder are uniformly mixed to obtain a fifth premix; The fifth premix is ​​mixed evenly with the remaining portion of the first binder to obtain the second premix.

9. The preparation method according to claim 1, characterized in that: In the first premix, the mass ratio of the solid content in the first binder to the silicon-based material is 0.02% to 2%.

10. The preparation method according to claim 2, characterized in that: When the premixed material further includes a portion of the nonlinear conductive agent, the mass of the nonlinear conductive agent contained in the premixed material is 40% to 60% of the total mass of the nonlinear conductive agent; When the premixed material further includes a portion of the graphite material, the mass of the graphite material contained in the premixed material is 30% to 70% of the total mass of the graphite material.

11. The preparation method according to claim 8, characterized in that: The mass of the second binder contained in the fourth premix is ​​10% to 30% of the total mass of the second binder; The mass of the first binder included in the fifth premix is ​​5% to 10% of the total mass of the first binder.

12. The preparation method according to any one of claims 1 to 11, characterized in that: The silicon-based material is selected from at least one of silicon carbon, pre-magnesium silicon oxide and pre-lithium silicon oxide; The first binder is selected from at least one of polyacrylic acid, polyethylene oxide and polyethyleneimine; The nonlinear conductive agent is selected from at least one of carbon black, conductive graphite, carbon fiber and graphene; The second binder is selected from at least one of sodium hydroxymethyl cellulose and lithium hydroxymethyl cellulose; The linear conductive agent is selected from at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes; The third binder is selected from styrene-butadiene rubber.

13. A negative electrode plate, characterized in that: The negative electrode sheet is prepared by the method for preparing a negative electrode sheet according to any one of claims 1 to 12.

14. A battery, characterized in that: The battery comprises: an electrolyte, a negative electrode sheet disposed in the electrolyte, a positive electrode sheet and a separator, wherein the negative electrode sheet is as described in claim 13, and the negative electrode sheet and the positive electrode sheet are separated by the separator.

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