CN116646463A

CN116646463A - Pole piece preparation method, pole piece, battery and battery pack

Info

Publication number: CN116646463A
Application number: CN202310617604.XA
Authority: CN
Inventors: 李玲霞
Original assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Current assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2023-05-29
Filing date: 2023-05-29
Publication date: 2023-08-25

Abstract

The application provides a preparation method of a pole piece, the pole piece, a battery and a battery pack. The preparation method of the pole piece comprises the following steps: mixing an active material, an additive, a pore-forming agent and a solvent to obtain a first slurry; mixing the active material, the additive and the solvent to obtain second slurry; coating the first slurry on a current collector, and baking the coated first slurry to decompose the pore-forming agent to form a first active layer; and coating the second slurry on one side of the first active layer, which is far away from the current collector, and baking the coated second slurry to form a second active layer, wherein the average porosity of the first active layer is larger than that of the second active layer. The pole piece prepared by the pole piece preparation method provided by the application can obviously improve the electrolyte infiltration effect and obviously improve the energy efficiency of the battery.

Description

Pole piece preparation method, pole piece, battery and battery pack

Technical Field

The application relates to the field of batteries, in particular to a preparation method of a pole piece, the pole piece, a battery and a battery pack.

Background

The secondary battery is widely used in the fields of electronic consumer goods, energy storage, power and the like due to the advantages of high output voltage, high energy density, high power density, long cycle life, environmental friendliness and the like.

At present, the problem of incomplete electrolyte infiltration can appear in the electrode of secondary cell, especially appear easily under the thicker circumstances of electrode coating, pole piece upper strata electrolyte infiltration effect is better, and the conductibility is better, and pole piece lower floor infiltration effect is relatively poor, and the conductibility is relatively poor for lithium ion's transmission is hindered, leads to the pole piece upper strata to be great with the lithium ion concentration difference of pole piece lower floor, and lithium ion can not take off completely to inlay, and then makes the battery discharge incomplete, and the energy of battery can not be fully utilized, and the energy efficiency of battery is lower.

Disclosure of Invention

In order to solve the technical problems, the application provides a preparation method of a pole piece, the pole piece, a battery and a battery pack, which can remarkably improve the electrolyte infiltration effect of the pole piece and remarkably improve the energy efficiency of the battery.

The first aspect of the application provides a method for preparing a pole piece, which comprises the following steps: mixing an active material, an additive, a pore-forming agent and a solvent to obtain a first slurry; mixing the active material, the additive and the solvent to obtain second slurry; coating the first slurry on a current collector, and baking the coated first slurry to decompose the pore-forming agent to form a first active layer; and coating the second slurry on one side of the first active layer, which is far away from the current collector, and baking the coated second slurry to form a second active layer, wherein the average porosity of the first active layer is larger than that of the second active layer.

According to the preparation method of the pole piece, the pore-forming agent is added into the first slurry for forming the first active layer, and the pore-forming agent is not added into the second slurry for forming the second active layer, so that the average porosity of the first active layer close to the current collector is larger than the average porosity of the second active layer far away from the current collector, namely, the porosity of the pole piece is increased along the direction close to the current collector, the first active layer with increased porosity is easily infiltrated after the electrolyte infiltrates the second active layer, and the electrolyte infiltration effect of the pole piece is improved, particularly, the electrolyte infiltration effect of the pole piece is obviously improved when the slurry is coated with the thicker pole piece, more electrolyte is favorable for transmitting and diffusing lithium ions, the concentration polarization of the lithium ions can be reduced, further lithium ion deintercalation is facilitated, battery discharge is promoted, and the energy efficiency of the battery can be obviously improved.

The second aspect of the application also provides a pole piece, which comprises a current collector, and a first active layer and a second active layer which are sequentially formed on the current collector, wherein the average porosity of the first active layer is larger than that of the second active layer.

A third aspect of the application provides a battery comprising a pole piece as described above.

A fourth aspect of the application provides a battery pack comprising the battery as described above.

Drawings

In order to more clearly illustrate the technical solutions of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a flowchart of a method for manufacturing a pole piece according to an embodiment of the present application.

Fig. 2 is a schematic cross-sectional structure of a pole piece according to an embodiment of the present application.

Reference numerals illustrate:

100-pole pieces; 10-current collector; 20-a first active layer; 30-a second active layer.

Detailed Description

The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without any inventive effort, are intended to be within the scope of the application.

In the description of the present application, the terms "first," "second," and the like are used for distinguishing between different objects and not for describing a particular sequence, and furthermore, the terms "upper," "lower," "inner," "outer," and the like indicate an orientation or a positional relationship based on that shown in the drawings, merely for convenience of describing the present application and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present application.

The illustrations provided in the embodiments of the application are merely schematic illustrations of the basic concepts of the application, in which only the components related to the application are shown rather than being drawn according to the number, shape and size of the components in actual implementation, the form, number and proportions of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.

Referring to fig. 1, fig. 1 is a flowchart of a method for manufacturing a pole piece according to an embodiment of the application. As shown in fig. 1, the preparation method of the pole piece comprises the following steps:

s10: and mixing the active material, the additive, the pore-forming agent and the solvent to obtain first slurry.

S20: and mixing the active material, the additive and the solvent to obtain second slurry.

S30: and coating the first slurry on a current collector, and baking the coated first slurry to decompose the pore-forming agent to form a first active layer.

S40: and coating the second slurry on one side of the first active layer, which is far away from the current collector, and baking the coated second slurry to form a second active layer, wherein the average porosity of the first active layer is larger than that of the second active layer.

Referring to fig. 2, a schematic cross-sectional structure of a fabricated pole piece 100 according to an embodiment of the present application is shown in fig. 2, where the fabricated pole piece 100 includes the current collector 10, the first active layer 20 and the second active layer 30. The average porosity of the first active layer 20 is greater than the average porosity of the second active layer 30.

According to the preparation method of the pole piece 100 provided by the embodiment of the application, by adding the pore-forming agent into the first slurry for forming the first active layer 20 and not adding the pore-forming agent into the second slurry for forming the second active layer 30, the average porosity of the first active layer 20 close to the current collector 10 is larger than the average porosity of the second active layer 30 far away from the current collector 10, namely, the porosity of the pole piece 100 is increased along the direction close to the current collector 10 (the Y direction shown in fig. 2), compared with the condition that the porosity is unchanged or the porosity is reduced along the direction close to the current collector 10, the increase of the porosity along the direction close to the current collector 10 can enable electrolyte to infiltrate into the first active layer 20 with the increased porosity easily, so that the electrolyte infiltration effect of the pole piece 100 can be improved, particularly, the electrolyte can be remarkably improved for the thick pole piece 100 coated with the slurry, more electrolyte is beneficial to the transmission and diffusion of lithium ions, the concentration polarization of lithium ions can be reduced, and the lithium ion concentration de-intercalation can be facilitated, and the energy discharge capacity of a battery can be remarkably improved. In addition, since the average porosity of the first active layer 20 is higher, the absorbed electrolyte is more, and lithium ions rapidly diffuse into the surface layer of the electrode sheet 100, i.e., the second active layer 30, when the battery is charged or discharged, the concentration of lithium ions in the first active layer 20 is lower than that in the second active layer 30, and the concentration difference of lithium ions between the first active layer 20 and the second active layer 30 may cause lithium ions to easily migrate into the first active layer 20.

Wherein, in the process of baking the first slurry, the pore-forming agent generates gas by thermal decomposition, and the generated gas is discharged to form pores in situ.

The preparation method of the pole piece can be used for preparing a positive pole piece or a negative pole piece.

In some embodiments, the above-described methods of preparing a pole piece may be used to prepare a positive pole piece. The active material may include one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganate, ternary materials, wherein the ternary materials may include one or more of lithium nickel cobalt manganate and lithium nickel cobalt aluminate.

In some embodiments, the pore-forming agent may include one or more of glucose, starch, sucrose, urea, methyl methacrylate, and epoxy. The pore-forming agent does not react with the active material and the additive when mixed with the active material and the additive, does not affect the active material and the additive, does not react with other substances in the first slurry when the first slurry is baked at a high temperature to decompose the pore-forming agent, and does not participate in electrochemical reaction inside the battery even if the pore-forming agent is not completely decomposed.

In some embodiments, the additive includes one or more of a binder, a conductive agent, and a dispersant. The binder may be selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN) or modified derivatives thereof. The conductive agent can be selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The dispersing agent can be one or more selected from polyether polyurethane, polymethyl methacrylate and amino alcohol.

In some embodiments, the additive includes a binder, a conductive agent, and a dispersant, the mass ratio of the pore former, the active material, the conductive agent, the binder, and the dispersant in the first slurry being (5-10): (94.5-98.5): (0.5-2.5): (1-3): (0-1). The first active layer 20 prepared and formed in the mass ratio has higher porosity and uniform pore distribution, and is favorable for infiltration of electrolyte. Illustratively, 8kg of a pore-forming agent, 95kg of an active material, 1kg of a conductive agent, 2kg of a binder, and 0.5kg of a dispersing agent are weighed, and the weighed substances are mixed with a solvent and stirred uniformly to obtain a first slurry. In some embodiments, the dispersant may not be added, i.e., the dispersant is added in an amount of 0, or the dispersant is added with a mass ratio of less than or equal to 1.

In some embodiments, the current collector 10 may be a metal foil. The current collector 10 may be selected from at least one of aluminum foil, copper foil, stainless steel foil, porous aluminum foil, porous copper foil, porous stainless steel foil.

In some embodiments, in step S10, mixing the active material, the additive, the pore-forming agent, and the solvent to obtain a first slurry includes: dissolving the pore-forming agent in a solvent to obtain a pore-forming agent solution; mixing and uniformly stirring the active materials, the additive and the solvent; and adding the pore-forming agent solution and uniformly stirring to obtain the first slurry.

Wherein the pore-forming agent may be dissolved in an organic solvent to obtain the pore-forming agent solution, e.g., N-methyl-2-pyrrolidone (NMP). The pore-forming agent is dissolved in the organic solvent, and then is mixed with the active material and the additive to obtain first slurry, so that the pore-forming agent and the active material are uniformly mixed, and the pore-forming agent is uniformly dispersed in the first slurry, and agglomeration is avoided. In other embodiments, the pore former may be mixed with other organic solvents, such as Dimethylformamide (DMF), dimethylacetamide (DMAC), tetramethylurea (TMU), dimethylsulfoxide (DMSO), triethylphosphate, ethylene carbonate, propylene carbonate, and the like.

Wherein the active material, additive may be mixed with an organic solvent and stirred uniformly, for example, the active material, additive may be mixed with N-methyl-2-pyrrolidone (NMP). In other embodiments, the active materials, additives may be mixed with other organic solvents, such as Dimethylformamide (DMF), dimethylacetamide (DMAC), tetramethylurea (TMU), dimethylsulfoxide (DMSO), triethylphosphate, ethylene carbonate, propylene carbonate, and the like.

In some embodiments, in step S30, the first paste is coated on the current collector 10, and the coated first paste is baked so that the pore-forming agent is decomposed, including: the first slurry is coated on the current collector 10 and baked at a first temperature, which is less than the second temperature, and then baked at a second temperature such that the pore-forming agent is decomposed.

Wherein, when the coated first slurry is baked at the first temperature, the solvent in the first slurry is volatilized and removed to form pores; when the coated first paste is baked at the second temperature, the pore-forming agent in the first paste is thermally decomposed to generate gas, and the generated gas escapes from the first paste to further form pores, so that the first active layer 20 is formed to have a porous structure.

Wherein in some embodiments, the first slurry may be simultaneously baked while being coated on the current collector 10, i.e., the first slurry is coated while being baked at a first temperature and then baked at a second temperature. In other embodiments, the coated first slurry may be baked at the first temperature and the second temperature after the first slurry is coated.

The solvent in the first slurry is firstly removed by drying at a first temperature with a lower temperature, and then the pore-forming agent is thermally decomposed at a second temperature with a higher temperature, so that the decomposition process of the pore-forming agent is less influenced by solvent volatilization, the formed pores are more uniform, the decomposition process of the pore-forming agent is more gentle, the formed pore distribution is not too regular due to severe decomposition, and in addition, the complete decomposition of the pore-forming agent is also facilitated. And the pole piece 100 is prevented from being baked and cracked by adopting a lower temperature to bake first and then thermally decomposing the pore-forming agent at a higher temperature.

Wherein the first paste may be coated on the current collector 10 by a squeeze coating apparatus or a transfer coating apparatus, and the coated first paste may be baked.

In some embodiments, the first temperature is a value in the range of 50 ℃ to 200 ℃ at which the solvent in the first slurry volatilizes to be removed; the second temperature is a value in the range of 200 ℃ to 450 ℃ at which thermal decomposition of the pore-forming agent occurs to produce gas.

If the first temperature is less than 50 ℃, the solvent of the first slurry volatilizes slowly, which affects the preparation efficiency of the first active layer 20; if the first temperature is higher than 200 ℃, the volatilization of the solvent of the first slurry and the thermal decomposition of the pore-forming agent are performed simultaneously, and the thermal decomposition of the pore-forming agent is influenced.

If the second temperature is less than 200 ℃, the pore-forming agent is not easy to decompose, and the decomposition rate is reduced; if the second temperature is higher than 450 ℃, the pore-forming agent may decompose too rapidly, thereby affecting the uniformity of the pores of the first active layer 20, and possibly causing baking cracking of the pole piece 100.

Wherein, when the pore-forming agent is glucose, the second temperature is a value in the range of 250 ℃ to 450 ℃, at which temperature thermal decomposition of glucose occurs. When the pore-forming agent is methyl methacrylate, the second temperature is a value in the range of 270 ℃ to 450 ℃, at which temperature thermal decomposition of methyl methacrylate occurs. When the pore-forming agent is an epoxy resin, the molecular weight of the epoxy resin may be 175-200, and the second temperature may be a value in the range of 200-450 ℃, at which thermal decomposition of the epoxy resin occurs.

In some embodiments, the baking time at the first temperature is 30min-60min, so that the solvent in the first slurry can be volatilized completely. The baking time at the second temperature is 60-120 min, so that the decomposition reaction of the pore-forming agent is more complete.

In some embodiments, in step S40, the applying the second paste to the side of the first active layer 20 facing away from the current collector 10 and baking the applied second paste includes: the second paste is coated on the side of the first active layer 20 facing away from the current collector 10, and the coated second paste is baked at 50-200 ℃.

Wherein, baking the second slurry at 50-200 ℃ can volatilize the solvent in the second slurry to be removed, and form pores, thus obtaining the second active layer 30 with a porous structure. Because the pore-forming agent is added to the first slurry, the pores of the first active layer 20 may be formed not only by solvent evaporation but also by decomposition of the pore-forming agent, so that the average porosity of the first active layer 20 is greater than the average porosity of the second active layer 30.

Wherein, if the second slurry is baked at a temperature of less than 50 ℃, the solvent of the second slurry volatilizes slowly, which affects the preparation efficiency of the second active layer 30; if the second slurry is baked at a temperature greater than 200 c, too fast a solvent evaporation may result in an uneven pore distribution of the formed second active layer 30.

Wherein in some embodiments, the second slurry may be applied simultaneously with the second slurry being applied to the first active layer 20, i.e., the second slurry may be applied simultaneously with the second slurry being baked at 50-200 ℃. In other embodiments, the coated second slurry may also be baked at 50 ℃ to 200 ℃ after the second slurry coating is completed.

Wherein the second paste may be coated on the first active layer 20 by a squeeze coating apparatus or a transfer coating apparatus, and the coated second paste is baked.

In some embodiments, the active material and additive of the first slurry are the same as the active material and additive of the second slurry, respectively, and the mass ratio of active material to additive in the first slurry is the same as the mass ratio of active material to additive in the second slurry. That is, the active material in the first slurry is the same as the active material in the second slurry, the additive in the first slurry is the same as the additive in the second slurry, and the mass ratio of active material to additive in the first slurry is the same as the mass ratio of active material to additive in the second slurry.

The first active layer 20 and the second active layer 30 are formed by using the first slurry and the second slurry which are the same in components except for the pore-forming agent, so that the electrochemical properties of the inner layer and the outer layer of the formed pole piece 100 are relatively consistent, and the electrical property of the battery is guaranteed.

In some embodiments, the mass ratio of the active material, the conductive agent, the binder, and the dispersant in the second slurry is (94.5-98.5): 0.5-2.5): 1-3): 0-1.

Wherein the solvent in the second slurry may be the same as or different from the solvent in the first slurry.

In some embodiments, the additive comprises a binder, a conductive agent, and a dispersant, the binder, the conductive agent, and the dispersant in the first slurry being the same as the binder, the conductive agent, and the dispersant in the second slurry, respectively, the mass ratio of the active material, the binder, the conductive agent, and the dispersant in the first slurry being the same as the mass ratio of the active material, the binder, the conductive agent, and the dispersant in the second slurry.

In other embodiments, the active material in the first slurry is different from the active material in the second slurry, and/or the additive in the first slurry is different from the additive in the second slurry.

In other embodiments, the mass ratio of active material to additive in the first slurry may be different than the mass ratio of active material to additive in the second slurry.

In some embodiments, the solid content of the first slurry is 40wt% to 80wt%, and the first slurry with the solid content in the range has good fluidity, is beneficial to the coating operation of the first slurry, reduces the coating difficulty, and can avoid the excessive thickness of the coated first active layer 20 because the solid content is not too low.

The solid content of the first slurry can be measured by a moisture meter, or the solid content of the first slurry can be obtained by weighing the first slurry before and after drying.

In some embodiments, the solid content of the second slurry is 40wt% to 80wt%, and the second slurry with the solid content in the range has good fluidity, is beneficial to the coating operation of the second slurry, reduces the coating difficulty, and can avoid the excessive thickness of the coated second active layer 30 because the solid content is not too low.

The solid content of the second slurry can be measured by a moisture meter, or the solid content of the second slurry can be obtained by weighing the second slurry before and after drying.

In some embodiments, the thickness of the first active layer 20 is equal to the thickness of the second active layer 30, so that the electrolyte wettability of the electrode sheet 100 is improved while the electrode sheet 100 is maintained to have a higher areal density, thereby enabling a battery to have a higher energy density.

Wherein the thickness of the first active layer 20 and the thickness of the second active layer 30 are both dimensions along a direction perpendicular to the current collector 10.

In other embodiments, the thickness of the first active layer 20 may be different from the thickness of the second active layer 30.

In some embodiments, the average porosity of the pole piece 100 prepared by using the preparation method is 18% -58%, the average porosity of the pole piece 100 is in the above range, and the diffusion paths of lithium ions in the pole piece 100 are more, which is beneficial to the transmission and diffusion of lithium ions, and the average porosity of the pole piece 100 is not too high, which can ensure that the pole piece 100 has higher areal density, and is beneficial to keeping the battery with higher energy density.

The average porosity of the pole piece 100 may be measured by Scanning Electron Microscopy (SEM) or mercury porosimetry, among others. During testing, the pole piece 100 can be divided into three equal parts, each equal part is divided into a plurality of sub equal parts, each sub equal part is subjected to a porosity test by using an SEM or a mercury porosimeter to obtain the porosities of all sub equal parts of each equal part, the average porosity of each equal part is obtained by taking the average value, the average porosities of all equal parts are obtained, and the average porosity of all equal parts is obtained by taking the average value of the average porosities of all equal parts. For example, each sub-aliquot is imaged by SEM and analyzed by image analysis software to obtain the porosity of the sub-aliquot, and thus the porosity of all sub-aliquots of each aliquot. The Image analysis software may be, for example, aviZO software, image J software, or the like.

In order to further understand the preparation method of the pole piece of the present application, the preparation method of the pole piece is described in further detail in conjunction with examples 1 to 9 and comparative example 1, and the scope of the present application is not limited by the following examples.

Example 1 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving glucose in NMP to obtain glucose solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding glucose solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of glucose to lithium iron phosphate to conductive agent to binder to dispersant is 6 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

Preparing a second slurry: mixing and stirring uniformly lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP to obtain second slurry with the solid content of 40-80 wt%, wherein the mass ratio of the lithium iron phosphate to the conductive agent to the binder to the dispersing agent is (94.5-98.5) (0.5-2.5) (1-3) (0-1).

Uniformly coating the first slurry on the positive electrode current collector, baking for 30-60 min at 50-200 ℃, and then baking for 60-120 min at 250 ℃ to form a first active layer; uniformly coating the second slurry on one side of the first active layer far away from the positive electrode current collector, and baking at 50-200 ℃ for 30-60 min; and rolling and slitting to obtain the positive pole piece.

Preparing a negative electrode plate:

preparing a negative electrode slurry: mixing and uniformly stirring graphite, a negative electrode dispersing agent, a conductive agent, a negative electrode adhesive, a plasticizer and a solvent to obtain negative electrode slurry with the solid content of 40-60 wt%, wherein the mass ratio of the graphite to the negative electrode dispersing agent to the conductive agent to the negative electrode adhesive to the plasticizer is (97-98.5) (1.2-1.6) (0.4-2.0) (1.3-2.3) (1-2); uniformly coating the negative electrode slurry on a negative electrode current collector and drying; and rolling and slitting to obtain the negative electrode plate.

Preparation of the battery:

and winding the positive electrode plate, the diaphragm and the negative electrode plate, welding the positive electrode lug and the negative electrode lug, packaging in an aluminum plastic film, baking for 10-20 h in vacuum, and carrying out liquid injection, standing, high-temperature high-pressure formation, degassing packaging and capacity division to obtain the battery.

Example 2 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving glucose in NMP to obtain glucose solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding glucose solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of glucose to lithium iron phosphate to conductive agent to binder to dispersant is 7 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

The preparation method of the negative electrode tab in example 2 and the preparation method of the battery are the same as in example 1.

Example 3 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving glucose in NMP to obtain glucose solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding glucose solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of glucose to lithium iron phosphate to conductive agent to binder to dispersant is 8 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

The preparation method of the negative electrode tab in example 3 and the preparation method of the battery are the same as in example 1.

Example 4 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving methyl methacrylate in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the methyl methacrylate solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the methyl methacrylate to the lithium iron phosphate to the conductive agent to the adhesive to the dispersing agent is 8 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

Uniformly coating the first slurry on the positive electrode current collector, baking for 30-60 min at 50-200 ℃, and then baking for 60-120 min at 300 ℃ to form a first active layer; uniformly coating the second slurry on one side of the first active layer far away from the positive electrode current collector, and baking at 50-200 ℃ for 30-60 min; and rolling and slitting to obtain the positive pole piece.

The preparation method of the negative electrode tab in example 4 and the preparation method of the battery were the same as in example 1.

Example 5 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving methyl methacrylate in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the methyl methacrylate solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the methyl methacrylate to the lithium iron phosphate to the conductive agent to the binder to the dispersing agent is 9 (94.5-98.5) to 0.5 to 1-3 to 0-1.

The preparation method of the negative electrode tab in example 5 and the preparation method of the battery are the same as in example 1.

Example 6 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving methyl methacrylate in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the methyl methacrylate solution and stirring uniformly to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the methyl methacrylate to the lithium iron phosphate to the conductive agent to the adhesive to the dispersing agent is 10 (94.5-98.5) to 0.5 to 1-3 to 0-1.

The preparation method of the negative electrode tab in example 6 and the preparation method of the battery were the same as in example 1.

Example 7 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving epoxy resin in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the epoxy resin solution and uniformly stirring to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the epoxy resin to the lithium iron phosphate to the conductive agent to the adhesive to the dispersing agent is 5 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

Uniformly coating the first slurry on the positive electrode current collector, baking for 30-60 min at 150 ℃, and then baking for 60-120 min at 200 ℃ to form a first active layer; uniformly coating the second slurry on one side of the first active layer far away from the positive electrode current collector, and baking at 50-200 ℃ for 30-60 min; and rolling and slitting to obtain the positive pole piece.

The preparation method of the negative electrode tab in example 7 and the preparation method of the battery were the same as in example 1.

Example 8 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving epoxy resin in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the epoxy resin solution and uniformly stirring to obtain first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the epoxy resin to the lithium iron phosphate to the conductive agent to the adhesive to the dispersing agent is 6 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

The preparation method of the negative electrode tab in example 8 and the preparation method of the battery were the same as in example 1.

Example 9 of the embodiment

Preparing a positive electrode plate:

preparing a first slurry: dissolving epoxy resin in NMP to obtain methyl methacrylate solution; mixing and uniformly stirring lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP; and adding the epoxy resin solution and uniformly stirring to obtain a first slurry with the solid content of 40-80 wt%, wherein the mass ratio of the epoxy resin to the lithium iron phosphate to the conductive agent to the adhesive to the dispersing agent is 7 (94.5-98.5) (0.5-2.5) (1-3) (0-1).

The preparation method of the negative electrode tab in example 9 and the preparation method of the battery were the same as in example 1.

Comparative example 1

Preparing a positive electrode plate:

preparing positive electrode slurry: mixing and stirring uniformly lithium iron phosphate, a conductive agent, a binder, a dispersing agent and NMP to obtain second slurry with the solid content of 40-80 wt%, wherein the mass ratio of the lithium iron phosphate to the conductive agent to the binder to the dispersing agent is (94.5-98.5) (0.5-2.5) (1-3) (0-1).

Uniformly coating the anode slurry on an anode current collector, and baking at 50-200 ℃ for 30-60 min; and rolling and slitting to obtain the positive pole piece.

The preparation method of the negative electrode tab in comparative example 1 and the preparation method of the battery were the same as those of example 1.

The positive electrode sheets prepared in examples 1 to 9 and comparative example 1 were subjected to average porosity measurement and the corresponding batteries were subjected to cycle performance test, and the average porosity measurement method was referred to the aforementioned measurement method, and the cycle performance test method included: and (3) charging the battery to 3.65V at a charging rate of 1P, discharging to 2.5V at a discharging rate of 1P, performing full charge discharge cycle test until the capacity of the battery is less than 80% of the initial capacity, recording the charging energy and discharging energy in each cycle of cycle test, and dividing the discharging energy by the charging energy to obtain energy efficiency. Average porosities of the positive electrode sheets prepared in examples 1 to 9 and comparative example 1 and energy efficiencies of the corresponding batteries are recorded in table 1 below.

TABLE 1

As can be seen from the average porosities and energy efficiencies of examples 1 to 9 and comparative example 1, the pole piece made by adding the pore-forming agent has higher average porosities and higher energy efficiencies than the pole piece made by not adding the pore-forming agent, which indicates that the pole piece made by adding the pore-forming agent can remarkably improve the porosities and electrolyte infiltration effects of the pole piece, increase the diffusion path of lithium ions, improve the transmission effect of lithium ions, reduce the concentration polarization of lithium ions, facilitate the deintercalation of lithium ions, promote the discharge of batteries, and thereby remarkably improve the energy efficiency of the batteries.

The higher the average porosity and energy efficiency between comparative examples 1-3 and the average porosity and energy efficiency between comparative examples 4-6 and the average porosity and energy efficiency between comparative examples 7-9, the higher the addition amount of the pore-forming agent is, the higher the average porosity of the prepared pole piece is, and the higher the energy efficiency of the corresponding battery is, which means that the addition amount of the pore-forming agent is increased, the more pores are formed, the electrolyte infiltration effect of the pole piece, the transmission and diffusion effect of lithium ions and the concentration polarization of lithium ions are further improved, and the battery discharge is further promoted, thereby further improving the energy efficiency of the battery. The average porosity of the pole piece and the energy density of the battery can be improved by improving the addition amount of the pore-forming agent.

The embodiment of the application also provides a pole piece, which comprises a current collector, and a first active layer and a second active layer which are sequentially formed on the current collector, wherein the average porosity of the first active layer is larger than that of the second active layer.

According to the pole piece provided by the embodiment of the application, the average porosity of the first active layer close to the current collector is larger than that of the second active layer far away from the current collector, namely, the porosity of the pole piece is increased along the direction close to the current collector, compared with the situation that the porosity is unchanged or the porosity is reduced along the direction close to the current collector, the increase of the porosity along the direction close to the current collector can enable electrolyte to infiltrate the first active layer with increased porosity easily after infiltrating the second active layer, so that the electrolyte infiltration effect of the pole piece can be improved, particularly for pole pieces with thicker slurry coating, the infiltration effect can be obviously improved, more electrolyte is beneficial to the transmission and diffusion of lithium ions, the concentration polarization of the lithium ions can be reduced, and further lithium ion deintercalation is facilitated, and the discharge of a battery comprising the pole piece is promoted, and therefore, the energy efficiency of the battery can be obviously improved. And, since the average porosity of the first active layer is higher, the absorbed electrolyte is more, the lithium ion concentration of the first active layer is lower than that of the second active layer, and the lithium ion concentration difference between the first active layer and the second active layer can make the lithium ions easily migrate to the first active layer.

The pole piece can be manufactured by the manufacturing method of the pole piece in any embodiment.

The embodiment of the application also provides a battery, which comprises the pole piece and electrolyte. Wherein the battery may be a lithium ion secondary battery.

The electrode plate provided by the embodiment of the application comprises the electrode plate, wherein the average porosity of the first active layer close to the current collector is larger than that of the second active layer far away from the current collector, namely, the porosity of the electrode plate is increased along the direction close to the current collector, compared with the situation that the porosity is unchanged or the porosity is reduced along the direction close to the current collector, the increase of the porosity along the direction close to the current collector can enable electrolyte to infiltrate the first active layer with increased porosity after infiltrating the second active layer, so that the electrolyte infiltration effect of the electrode plate can be improved, particularly for thick electrode plates coated with slurry, the infiltration effect can be remarkably improved, more electrolyte is beneficial to the transmission and diffusion of lithium ions, the concentration polarization of lithium ions can be reduced, and lithium ion deintercalation is facilitated, and the battery discharge is promoted, so that the energy efficiency of the battery can be remarkably improved. And, because the average porosity of the first active layer is higher, the absorbed electrolyte is more, and when the battery is charged or discharged, lithium ions rapidly diffuse to the surface layer of the pole piece, namely, the second active layer, wherein the lithium ion concentration of the first active layer is lower than that of the second active layer, and the lithium ion concentration difference between the first active layer and the second active layer can enable lithium ions to easily migrate to the first active layer.

In some embodiments, the battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, where the positive electrode sheet may be manufactured by the method for manufacturing a sheet provided in any of the foregoing embodiments.

The active material of the negative electrode plate can be one or more selected from graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microsphere and petroleum coke.

Wherein the electrolyte may include a carbonate electrolyte.

The embodiment of the application also provides a battery pack, which comprises the battery provided by any one of the embodiments.

The electrode plate provided by the embodiment of the application has the advantages that the average porosity of the first active layer close to the current collector is larger than that of the second active layer far away from the current collector, namely, the porosity of the electrode plate is increased along the direction close to the current collector, compared with the situation that the porosity is unchanged or the porosity is reduced along the direction close to the current collector, the increase of the porosity along the direction close to the current collector can enable electrolyte to infiltrate the first active layer with increased porosity after infiltrating the second active layer, so that the electrolyte infiltrating effect of the electrode plate can be improved, particularly for thick electrode plates coated with slurry, the infiltrating effect can be remarkably improved, more electrolyte is beneficial to the transmission and diffusion of lithium ions, the concentration polarization of lithium ions can be reduced, and then the deintercalation of lithium ions is facilitated, and the discharge of the battery is promoted, so that the energy efficiency of the battery can be remarkably improved, and the energy efficiency of the battery pack can be remarkably improved. And, since the average porosity of the first active layer is higher, the absorbed electrolyte is more, the lithium ion concentration of the first active layer is lower than that of the second active layer, and the lithium ion concentration difference between the first active layer and the second active layer can make the lithium ions easily migrate to the first active layer.

It should be noted that, for simplicity of description, the foregoing method embodiments are all described as a series of acts, but it should be understood by those skilled in the art that the present application is not limited by the order of acts described, as some steps may be performed in other orders or concurrently in accordance with the present application. Further, those skilled in the art will also appreciate that the embodiments described in the specification are all preferred embodiments, and that the acts and modules referred to are not necessarily required for the present application.

The foregoing is a description of embodiments of the present application, and it should be noted that, for those skilled in the art, modifications and variations can be made without departing from the principles of the embodiments of the present application, and such modifications and variations are also considered to be within the scope of the present application.

Claims

1. The preparation method of the pole piece is characterized by comprising the following steps:

mixing an active material, an additive, a pore-forming agent and a solvent to obtain a first slurry;

mixing the active material, the additive and the solvent to obtain second slurry;

coating the first slurry on a current collector, and baking the coated first slurry to decompose the pore-forming agent to form a first active layer; and

And coating the second slurry on one side of the first active layer, which is far away from the current collector, and baking the coated second slurry to form a second active layer, wherein the average porosity of the first active layer is larger than that of the second active layer.

2. The method for preparing a pole piece according to claim 1, wherein the pore-forming agent comprises one or more of glucose, starch, sucrose, urea, methyl methacrylate and epoxy resin.

3. The method for preparing the pole piece according to claim 1 or 2, wherein the additive comprises a binder, a conductive agent and a dispersing agent, and the mass ratio of the pore-forming agent, the active material, the conductive agent, the binder and the dispersing agent in the first slurry is (5-10): (94.5-98.5): (0.5-2.5): (1-3): (0-1).

4. The method of manufacturing a pole piece of claim 1, wherein the first slurry is coated on a current collector and the coated first slurry is baked to decompose the pore-forming agent, comprising:

the first slurry is coated on a current collector, and the coated first slurry is baked at a first temperature, and then baked at a second temperature such that the pore-forming agent is decomposed, wherein the first temperature is less than the second temperature.

5. The method of manufacturing a pole piece of claim 4, wherein the first temperature is a value in the range of 50 ℃ to 200 ℃ and the second temperature is a value in the range of 200 ℃ to 450 ℃.

6. The method of preparing a pole piece of claim 1, wherein the applying the second slurry to the side of the first active layer facing away from the current collector and baking the applied second slurry comprises:

the second slurry is coated on the side of the first active layer facing away from the current collector, and the coated second slurry is baked at 50-200 ℃.

7. The method of manufacturing a pole piece according to claim 1, wherein the active material and the additive of the first slurry are the same as the active material and the additive of the second slurry, respectively, and the mass ratio of the active material to the additive in the first slurry is the same as the mass ratio of the active material to the additive in the second slurry.

8. The method for preparing a pole piece according to claim 1, wherein the mixing the active material, the additive, the pore-forming agent and the solvent to obtain the first slurry comprises:

dissolving the pore-forming agent in a solvent to obtain a pore-forming agent solution;

Mixing and uniformly stirring the active materials, the additive and the solvent;

and adding the pore-forming agent solution and uniformly stirring to obtain the first slurry.

9. The method of manufacturing a pole piece of claim 1, wherein the first slurry has a solids content of 40wt% to 80wt% and the second slurry has a solids content of 40wt% to 80wt%.

10. The method of claim 1, wherein the thickness of the first active layer is equal to the thickness of the second active layer, and the thickness of the first active layer and the thickness of the second active layer are both sized in a direction perpendicular to the current collector.

11. The method of making a pole piece of claim 1, wherein the average porosity of the pole piece is 18% -58%.

12. The method of manufacturing a pole piece of claim 1, wherein the pole piece is a positive pole piece.

13. The pole piece is characterized by comprising a current collector, and a first active layer and a second active layer which are sequentially formed on the current collector, wherein the average porosity of the first active layer is larger than that of the second active layer.

14. A battery comprising the pole piece of claim 13.

15. A battery pack comprising the battery of claim 14.