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

Abstract

The application relates to the technical field of energy storage devices, in particular to a positive electrode sheet, a preparation method thereof and a battery. The positive electrode sheet comprises a current collector and a positive electrode active coating layer coated on at least one side surface of the current collector, wherein the positive electrode active coating layer comprises a positive electrode active material; the positive electrode active material comprises first active particles and second active particles, and the particle size of the first active particles is smaller than that of the second active particles; along the direction away from the current collector, the mass content of the first active particles is distributed in a gradient decreasing manner, and the mass content of the second active particles is distributed in a gradient increasing manner. The structure of the positive electrode sheet in the application is beneficial to the infiltration and diffusion of electrolyte, shortens the transmission path of lithium ions, increases the porosity of the electrode sheet, reduces the internal resistance of the battery, and improves the dynamic performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage devices, and particularly relates to a positive electrode sheet, a preparation method thereof and a battery. BACKGROUND

[0002] With the rapid development of lithium ion secondary battery technology, lithium ion batteries have been widely used in various aspects of people's daily life, such as portable digital devices such as mobile phones and cameras, and fields such as electric bicycles, electric buses and electric vehicles, due to their high energy density, green environmental protection and other significant advantages.

[0003] In the prior art, the energy density of the battery is generally improved by increasing the coating weight and improving the compaction of the positive and negative electrode sheets. However, due to the increase in coating weight, the thickness of the electrode sheet increases and the lithium ion transmission path increases, and the dynamic performance of the battery is deteriorated. Moreover, blindly increasing the compaction will cause the structure of the material to be damaged, thereby reducing the cycle life of the battery. How to improve the energy density of the battery and improve the dynamic and cycle performance of the battery is the key development direction of the lithium battery industry.

[0004] Therefore, it is necessary to develop a positive electrode sheet, a preparation method thereof and a battery to further improve the dynamic performance of the battery. SUMMARY

[0005] The present application aims to provide a positive electrode sheet, a preparation method thereof and a battery, which further improve the dynamic performance of the battery by optimizing the structure.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] A positive electrode sheet, comprising a current collector and a positive active coating layer coated on at least one side surface of the current collector, wherein the positive active coating layer comprises a positive active material.

[0008] The positive active material comprises first active particles and second active particles, and the particle size of the first active particles is smaller than that of the second active particles.

[0009] In the direction away from the current collector, the mass ratio of the first active particles to the second active particles is distributed in a gradient decreasing manner.

[0010] Optionally, the particle size D50 of the first active particles is 50-400nm, and the particle size D50 of the second active particles is 700-1300nm.

[0011] Optionally, the positive electrode active coating layer comprises at least two layers of coating layers arranged in a stack, each layer of coating layer comprising the first active particles and the second active particles; in two adjacent layers of coating layers, the mass ratio of the first active particles and the second active particles in the coating layer close to the side of the current collector is A, and the mass ratio of the first active particles and the second active particles in the coating layer away from the side of the current collector is B, and B is less than A.

[0012] Optionally, the positive electrode active coating layer comprises two layers of coating layers arranged in a stack, the two layers of coating layers comprising a first coating layer coated on the current collector and a second coating layer coated on the first coating layer.

[0013] The mass ratio of the second active particles to the first active particles in the first coating layer is (6-5):(4-5).

[0014] The mass ratio of the second active particles to the first active particles in the second coating layer is (9-5):(1-5).

[0015] Optionally, the positive electrode active coating layer further comprises a conductive agent and a binder; in the positive electrode active coating layer, the mass content of the positive electrode active material is 94-98%, the mass content of the conductive agent is 1-3%, and the mass content of the binder is 1-2%.

[0016] Optionally, the first active particles and the second active particles are both lithium iron phosphate particles.

[0017] A preparation method of a positive electrode sheet, the preparation method comprising:

[0018] S01, preparing an active slurry, the active slurry comprising a positive electrode active material, the positive electrode active material comprising first active particles and second active particles, and the particle size of the first active particles being smaller than the particle size of the second active particles;

[0019] S02, coating the active slurry to at least one side surface of a current collector to form a positive electrode active coating layer, to obtain a positive electrode sheet; wherein the mass ratio of the first active particles to the second active particles is in a gradient decreasing distribution.

[0020] Optionally, the active slurry is prepared, in particular:

[0021] S011, uniformly stirring the first active particles and the second active particles according to a mass ratio of (9-5):(1-5) to obtain a uniformly mixed lithium iron phosphate material; wherein the particle size D50 of the first active particles is 50-400 nm; and the particle size D50 of the second active particles is 700-1300 nm.

[0022] S012. Adding a conductive agent and a binder to the lithium iron phosphate material and stirring uniformly to obtain a positive electrode slurry, wherein the mass ratio of the lithium iron phosphate material, the conductive agent, and the binder in the positive electrode slurry is (94-98):(1-3):(1-2);

[0023] S013, changing the mass ratio of the first active particles to the second active particles, and maintaining the mass ratio of the first active particles to the second active particles in the range of (9-5): (1-5), repeating steps S011 and S012 to obtain n different positive electrode slurries, wherein the active slurry includes n different positive electrode slurries;

[0024] The active slurry is applied to at least one side of the current collector to form a positive electrode active coating to obtain a positive electrode sheet, comprising the following steps:

[0025] S021, coating n different positive electrode slurries on a current collector in order of a gradient-decreasing distribution of the mass ratio of the first active particles to the second active particles, to obtain a current collector coated with n layers of coating;

[0026] S022. Cold-pressing the current collector coated with the n-layer coating to obtain the desired positive electrode sheet.

[0027] A battery comprises a shell and a wound cell installed in the shell, wherein the wound cell is formed by stacking and winding a positive electrode sheet, a separator and a negative electrode sheet, and the positive electrode sheet is the positive electrode sheet as described in any one of the above items.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] By coating a positive electrode active coating comprising first active particles and second active particles on the surface of the current collector, wherein the particle size of the first active particles is smaller than the particle size of the second active particles, and the mass content of the first active particles is distributed in a gradient decreasing manner along the direction away from the current collector, while the mass content of the second active particles is distributed in a gradient increasing manner, the packing density and porosity of the positive electrode active coating are improved, which is more conducive to the infiltration and diffusion of the electrolyte, thereby improving the dynamic performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] The structure, proportion, size and the like shown in the drawings of the specification are only used to cooperate with the content disclosed in the specification, to be understood and read by those skilled in the art, and do not have technical significance in defining the conditions for implementing the application, so any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the application, should still fall within the scope of the disclosed technology.

[0032] Figure 1 A first positive plate structure schematic diagram provided by an embodiment of the application is shown in the figure.

[0033] Figure 2 A second positive plate structure schematic diagram provided by an embodiment of the application is shown in the figure.

[0034] Figure 3 A third positive plate structure schematic diagram provided by an embodiment of the application is shown in the figure.

[0035] Illustration: 1, current collector; 2, positive active coating; 11, first coating; 12, second coating; 101, first active particle; 102, second active particle. DETAILED DESCRIPTION

[0036] In order to make the purposes, features and advantages of the application more obvious and easy to understand, the technical solutions in the embodiments of the application will be described clearly and completely below in combination with the drawings in the embodiments of the application. Obviously, the embodiments described below are only some of the embodiments of the application, not all. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the application.

[0037] In the description of the application, it should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there can be a component disposed therebetween.

[0038] The technical solutions of the application will be further described below in combination with the drawings and through specific embodiments.

[0039] The positive electrode sheet provided by the embodiment of the present application can effectively improve the packing density of the positive electrode active material and the porosity of the positive electrode sheet, and is beneficial to the rapid infiltration and rapid diffusion of the electrolyte, thereby further improving the kinetic performance of the battery.

[0040] Embodiment one

[0041] As shown in Figure 1 and Figure 2 , the positive electrode sheet comprises a current collector 1 and a positive electrode active coating 2 coated on at least one side surface of the current collector 1, wherein the positive electrode active coating 2 comprises a positive electrode active material; the positive electrode active material comprises first active particles 101 and second active particles 102, and the particle size of the first active particles 101 is smaller than that of the second active particles 102. Both the first active particles 101 and the second active particles 102 are lithium iron phosphate particles.

[0042] In the direction away from the current collector 1, the mass ratio of the first active particles 101 and the second active particles 102 is in a gradient increasing distribution.

[0043] It should be noted that the positive electrode active coating 2 can be a whole layer, or can be formed by at least two layers of coating. In addition, the positive electrode active coating 2 can be arranged on one side surface of the current collector 1, or can be arranged on the opposite two side surfaces of the current collector 1. When the positive electrode active coating 2 is a whole layer, the positive electrode active coating 2 is formed by multiple coating, and the proportion of the first active particles 101 and the second active particles 102 in the slurry for each coating is different, so that in the direction away from the side surface of the current collector 1, the mass content of the first active particles 101 in the positive electrode active coating 2 is in a gradient decreasing distribution, and the mass content of the second active particles 102 in the positive electrode active coating 2 is in a gradient increasing distribution.

[0044] It should be noted that the mass ratio of the first active particles 101 and the second active particles 102 is in a gradient increasing distribution, which can mean that the farther the first active particles 101 are from the current collector, the less the mass content is, and the mass content of the second active particles 102 can remain unchanged or increase.

[0045] The positive electrode active coating 2 comprises at least two layers of coating arranged in a stack, each layer of coating comprising first active particles 101 and second active particles 102; in two adjacent layers of coating, the mass ratio of the first active particles 101 and the second active particles 102 in the coating close to the side of the current collector is A, and the mass ratio of the first active particles 101 and the second active particles 102 in the coating away from the side of the current collector is B, and B is less than A.

[0046] The embodiment mainly takes the current collector coated with two layers of coating in the positive electrode active coating 2 as the main object of illustration, that is, the positive electrode active coating 2 comprises two layers of coating, and the two layers of coating comprise a first coating 11 coated on the current collector 1 and a second coating 12 coated on the first coating 11. Figure 2

[0047] The mass ratio of the second active particles 102 and the first active particles 101 in the first coating 11 is 6:4; and the mass ratio of the second active particles 102 and the first active particles 101 in the second coating 12 is 9:1. In the embodiment, the particle size D50 of the first active particles 101 is 200 nm; and the particle size D50 of the second active particles 102 is 800 nm.

[0048] Optionally, the positive electrode active coating 2 further comprises a conductive agent and a binder; in the positive electrode active coating 2, the mass content of the positive electrode active material is 94-98%, the mass content of the conductive agent is 1-3%, and the mass content of the binder is 1-2%.

[0049] The embodiment further provides a preparation method of a positive electrode sheet, the preparation method comprising

[0050] S01, preparing an active slurry, the active slurry comprising a positive electrode active material, the positive electrode active material comprising first active particles 101 and second active particles 102, and the particle size of the first active particles 101 being smaller than the particle size of the second active particles 102;

[0051] S02, coating the active slurry to at least one side surface of a current collector 1 to form a positive electrode active coating, to obtain a positive electrode sheet; wherein along the direction away from the current collector 1, the mass ratio of the first active particles 101 to the second active particles decreases in a gradient distribution.

[0052] Optionally, the active slurry is prepared, in particular:

[0053] ​S011. The first active particles 101 and the second active particles 102 are uniformly stirred in a mass ratio of (9-5): (1-5) to obtain a uniformly mixed lithium iron phosphate material; wherein the particle size D50 of the first active particles 101 is 50-400 nm; and the particle size D50 of the second active particles 102 is 700-1300 nm;

[0054] S012. Adding a conductive agent and a binder to the lithium iron phosphate material and stirring uniformly to obtain a positive electrode slurry, wherein the mass ratio of the lithium iron phosphate material, the conductive agent, and the binder in the positive electrode slurry is (94-98):(1-3):(1-2);

[0055] S013, changing the mass ratio of the first active particles 101 to the second active particles 102, and maintaining the mass ratio of the first active particles 101 to the second active particles 102 within the range of (9-5):(1-5), repeating steps S011 and S012 to obtain n different positive electrode slurries, wherein the active slurries include n different positive electrode slurries;

[0056] The active slurry is applied to at least one side of the current collector 1 to form a positive electrode active coating 2 to obtain a positive electrode sheet, comprising the following steps:

[0057] S021, coating n different positive electrode slurries on the current collector 1 in order of a gradient-decreasing distribution of the mass ratio of the first active particles 101 to the second active particles 102, to obtain a current collector coated with n layers of coating;

[0058] S022, cold pressing the current collector coated with the n-layer coating to obtain a compaction density of 2.30-2.55 g / cm 3 The positive electrode active coating 2 includes n coating layers.

[0059] It should be noted that n is not less than 2, that is, the number of active coating layers on the current collector is at least two.

[0060] This embodiment also provides a battery prepared using the above method, wherein the battery includes a shell and a wound battery cell installed in the shell, the wound battery cell is formed by stacking and winding a positive electrode sheet, a separator and a negative electrode sheet, and the positive electrode sheet is the positive electrode sheet described in any one of the above items.

[0061] In another specific embodiment, the positive electrode active coating 2 includes several stacked layers of coatings; in the coating farther away from the surface of the current collector 1, the mass content of the first active particles 101 is lower, and the mass content of the second active particles 102 is higher.

[0062] See also Figure 3As long as the different coatings meet the requirement that the mass ratio of the first active particles 101 and the second active particles 102 in the positive electrode active coating 2 is distributed in a gradient increasing manner in the direction away from the surface of the current collector 1, the electrochemical performance of the battery is effectively improved.

[0063] Example 2

[0064] The only difference between this embodiment and the first embodiment is that:

[0065] The mass ratio of the second active particles 102 to the first active particles 101 in the first coating layer 11 is 11:9; the mass ratio of the second active particles 102 to the first active particles 101 in the second coating layer 12 is 8:2.

[0066] The rest are consistent with the first embodiment.

[0067] Example 3

[0068] The only difference between this embodiment and the first embodiment is that:

[0069] The mass ratio of the second active particles 102 to the first active particles 101 in the first coating layer 11 is 5.5:4.5; the mass ratio of the second active particles 102 to the first active particles 101 in the second coating layer 12 is 7.5:2.5.

[0070] The rest are consistent with the first embodiment.

[0071] Example 4

[0072] The only difference between this embodiment and the first embodiment is that:

[0073] The mass ratio of the second active particles 102 to the first active particles 101 in the first coating layer 11 is 5.3:4.7; the mass ratio of the second active particles 102 to the first active particles 101 in the second coating layer 12 is 7:3.

[0074] Example 5

[0075] The only difference between this embodiment and the first embodiment is that:

[0076] The mass ratio of the second active particles 102 to the first active particles 101 in the first coating layer 11 is 5:5; the mass ratio of the second active particles 102 to the first active particles 101 in the second coating layer 12 is 6.5:3.5.

[0077] The rest are consistent with the first embodiment.

[0078] Comparative Example 1

[0079] The difference between the present comparative example and Example One is that:

[0080] There is only one layer of positive active coating, and only the second active particles 102 are distributed in the positive active coating, without the first active particles 101, and the second active particles 102 are uniformly distributed in the positive active coating.

[0081] The rest is consistent with Example One.

[0082] Comparative Example 2

[0083] The difference between the present comparative example and Example One is that:

[0084] There is only one layer of positive active coating, and only the second active particles 102 are distributed in the positive active coating, without the first active particles 101, and the second active particles 102 are uniformly distributed in the positive active coating.

[0085] The rest is consistent with Example One.

[0086] I. Energy density test: at 25±2℃, the battery is charged at 1C current constant current constant voltage to 3.65V, and the cutoff current is 0.05C; after standing for 60min, it is discharged at 1C constant current to 2.5V, and the discharge energy P is recorded; the weight of the cell is weighed, and the weight value m is recorded; the energy density of the battery = discharge energy P / weight value m;

[0087] II. DC resistance test:

[0088] A) Capacity calibration: at 25±2℃, the battery is charged at 1C current constant current constant voltage to 3.65V, and the cutoff current is 0.05C; after standing for 30min, it is discharged at 1C constant current to 2.5V, and the discharge capacity C0 is recorded.

[0089] B) DC resistance test: the battery is discharged at 1C0 to 2.5V; stand for 60min; after 1C0 charging for 30min, stand for 2h, record the voltage V0 at this time; then the battery is discharged at 2C0 for 10s, and the final discharge voltage V1 is recorded; then the DC resistance of the battery = (V0-V1 / 2) / C0

[0090] III. Cycle resistance test: at 25±2℃, the battery is charged at 1C constant current constant voltage to 3.65V, and the cutoff current is 0.05C; after standing for 30min, it is discharged at 1C to 2.5V, and the above process is continued until the capacity attenuation is 80% of the initial capacity, and the cycle number is recorded.

[0091] Table 1

[0092]

[0093] As shown in Examples 1-5, the cathode structure employed in the present invention facilitates rapid electrolyte infiltration and diffusion, reduces battery polarization, shortens the lithium ion transport pathway, increases the porosity of the cathode sheet, reduces the battery's internal resistance, and effectively improves the battery's dynamic performance. Lithium-ion batteries fabricated using this cathode exhibit superior power performance and high energy density.

[0094] By comparing Examples 1-5, it can be seen that if the mass ratio of the first active particles 101 in the first coating 11 is defined as Q1 and the mass ratio of the first active particles 101 in the second coating 12 is defined as Q2, when the ratio Q1 / Q2 approaches 1, the DC internal resistance of the battery is significantly reduced, the battery cycle performance is reduced, and the cycle life gradually decreases.

[0095] Comparison of Examples 1-5 and Comparative Example 1-2 shows that providing the first active particles 101 and the second active particles 102 with different particle sizes can effectively reduce the DC internal resistance of the battery and increase the cycle life of the battery.

[0096] Comparing Examples 1-5 and Comparative Examples 1-2, it can be seen that the configuration of first active particles 101 and second active particles 102 of different particle sizes, and a gradient distribution structure, can also increase the packing density of the positive electrode active material, thereby facilitating an increase in the compaction density of the positive electrode sheet and the energy density of the battery cell. It should be further explained that the smaller-sized first active particles 101 are more abundant on the side closest to the current collector. As a result, during the compaction process, the larger-diameter second active particles 102 apply pressure to the smaller-diameter first active particles 101, allowing more of the first active particles 101 to adhere to the current collector, thereby effectively ensuring the high energy density of the battery.

[0097] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0098] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0099] The above-described embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalent replacements; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode sheet characterized by comprising: The positive electrode active coating (2) comprises a current collector (1) and a positive electrode active coating (2) coated on at least one side surface of the current collector (1), wherein the positive electrode active coating (2) comprises a positive electrode active material; The positive electrode active material is composed of first active particles (101) and second active particles (102), and the particle size of the first active particles (101) is smaller than that of the second active particles (102); In the direction away from the current collector (1), the mass ratio of the first active particles (101) to the second active particles (102) is in a gradient decreasing distribution; The particle size D50 of the first active particles (101) is 50-400 nm, and the particle size D50 of the second active particles (102) is 700-1300 nm; The positive electrode active coating (2) comprises at least two layers of coating arranged in a stack, and each layer of coating has first active particles (101) and second active particles (102); in the adjacent two layers of coating, the mass ratio of the first active particles (101) and the second active particles (102) in the coating close to the current collector is A, and the mass ratio of the first active particles (101) and the second active particles (102) in the coating away from the current collector is B, and B is less than A; The positive electrode active coating (2) comprises two layers of coating arranged in a stack, and the two layers of coating comprise a first coating (11) coated on the current collector (1) and a second coating (12) coated on the first coating (11); The mass ratio of the second active particles (102) to the first active particles (101) in the first coating (11) is (6-5):(4-5); The mass ratio of the second active particles (102) to the first active particles (101) in the second coating (12) is (9-5):(1-5); The compacted density of the positive electrode sheet is 2.30-2.55 g / cm 3 .

2. The positive electrode sheet according to claim 1, characterized by The positive electrode active coating (2) further comprises a conductive agent and a binder; in the positive electrode active coating (2), the mass content of the positive electrode active material is 94-98%, the mass content of the conductive agent is 1-3%, and the mass content of the binder is 1-2%.

3. The positive electrode sheet according to claim 1, characterized by The first active particles (101) and the second active particles (102) are both lithium iron phosphate particles.

4. A method for producing a positive electrode sheet for producing the positive electrode sheet according to any one of claims 1 to 3, characterized by, The preparation method comprises: S01, preparing an active slurry, wherein the active slurry comprises a positive electrode active material, the positive electrode active material comprises first active particles (101) and second active particles (102), and the particle size of the first active particles (101) is smaller than that of the second active particles (102); S02, coating the active slurry to at least one side surface of a current collector (1) to form a positive electrode active coating (2), thereby obtaining a positive electrode sheet; wherein in the direction away from the current collector (1), the mass ratio of the first active particles (101) to the second active particles (102) is in a gradient decreasing distribution.

5. The preparation method according to claim 4, characterized in that The preparation of the active slurry is specifically: S011, stirring the first active particles (101) and the second active particles (102) in a mass ratio of (9-5): (1-5) to obtain a uniformly mixed lithium iron phosphate material; wherein the particle size D50 of the first active particles (101) is 50-400 nm; and the particle size D50 of the second active particles (102) is 700-1300 nm; S012. Adding a conductive agent and a binder to the lithium iron phosphate material and stirring uniformly to obtain a positive electrode slurry, wherein the mass ratio of the lithium iron phosphate material, the conductive agent, and the binder in the positive electrode slurry is (94-98):(1-3):(1-2); S013, changing the mass ratio of the first active particles (101) to the second active particles (102), and maintaining the mass ratio of the first active particles (101) to the second active particles (102) within the range of (9-5): (1-5), repeating steps S011 and S012 to obtain n different positive electrode slurries, wherein the active slurries include n different positive electrode slurries; The active slurry is applied to at least one side of the current collector (1) to form a positive electrode active coating (2) to obtain a positive electrode sheet, comprising the following steps: S021, coating n different positive electrode slurries on a current collector (1) in order of a gradient distribution of the mass ratio of the first active particles (101) to the second active particles (102), to obtain a current collector coated with n layers of coating; S022. Cold-pressing the current collector coated with the n-layer coating to obtain the desired positive electrode sheet.

6. A battery, characterized by The battery comprises a shell and a wound cell installed in the shell, wherein the wound cell is formed by stacking and winding a positive electrode sheet, a separator and a negative electrode sheet, and the positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 3.

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