CN115692604A - Positive plate, preparation method thereof and battery - Google Patents

Abstract

The invention relates to the technical field of energy storage devices, in particular to a positive plate and a preparation method thereof, and a battery, wherein the positive plate comprises a current collector and a positive active coating coated on the surface of at least one side of the current collector, and the positive active coating comprises a positive active material; the positive electrode active material includes first active particles and second active particles, and a particle size of the first active particles is smaller than a particle size of the second active particles; along the direction of keeping away from the current collector, the mass content of first active particle is the distribution that decreases progressively of gradient, the mass content of second active particle is the distribution that increases progressively of gradient. The structure of the positive plate is beneficial to the infiltration and diffusion of electrolyte, the transmission path of lithium ions is shortened, the porosity of the positive plate is increased, the internal resistance of the battery is reduced, and the dynamic performance of the battery is improved.

Description

Positive plate, preparation method thereof and battery

Technical Field

The invention relates to the technical field of energy storage devices, in particular to a positive plate, a preparation method of the positive plate and a battery.

Background

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 the fields of electric bicycles, electric buses, electric automobiles, etc., due to their significant advantages of high energy density, environmental protection, etc.

In the prior art, the energy density of the battery is generally improved by increasing the coating weight and improving the compaction of a positive pole piece and a negative pole piece. However, the electrode plate becomes thicker and the lithium ion transmission path increases due to the increase of the coating weight, so that the dynamic performance of the battery cell becomes worse; and blindly increasing compaction can result in damage to the material structure and reduced battery cycle life. How to improve the energy density of the battery and improve the dynamic and cycle performance of the battery is a key development direction of the lithium battery industry.

In view of the above, it is necessary to develop a positive plate, a method for preparing the positive plate, and a battery, so as to further improve the dynamic performance of the battery.

Disclosure of Invention

The invention aims to provide a positive plate, a preparation method thereof and a battery, which further improve the dynamic performance of the battery by optimizing the structure.

In order to achieve the purpose, the invention adopts the following technical scheme:

the positive plate comprises a current collector and a positive active coating coated on at least one side surface of the current collector, wherein the positive active coating comprises a positive active material;

the positive electrode active material includes first active particles and second active particles, and a particle size of the first active particles is smaller than a particle size of the second active particles;

the mass ratio of the first active particles to the second active particles is distributed in a gradient decreasing mode along the direction far away from the current collector.

Optionally, the first active particle has a particle size D50 of 50-400nm; the second active particles have a particle diameter D50 of 700 to 1300nm.

Optionally, the positive active coating layer comprises at least two coating layers arranged in a stacked manner, and each coating layer is provided with first active particles and second active particles; in two adjacent layers of coating, the mass ratio of the first active particles to the second active particles in the coating layer close to the current collector side is A, the mass ratio of the first active particles to the second active particles in the coating layer far away from the current collector side is B, and B is smaller than A.

Optionally, the positive active coating comprises two coating layers which are arranged in a stacked manner, wherein the two coating layers comprise a first coating layer coated on the current collector and a second coating layer coated on the first coating layer;

the mass ratio of the second active particles to the first active particles in the first coating layer is (6-5): (4-5);

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

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

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

A method for preparing a positive electrode sheet, the method comprising:

s01, preparing an active slurry, wherein the active slurry 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;

s02, coating the active slurry on at least one side surface of a current collector to form a positive active coating to obtain a positive plate; wherein the mass ratio of the first active particles to the second active particles is distributed in a gradient decreasing manner.

Optionally, the preparing of the active slurry is specifically:

s011, mixing the first active particles and the second active particles according to the ratio of (9-5): (1-5) stirring uniformly to obtain a uniformly mixed lithium iron phosphate material; wherein the first active particles have a particle size D50 of 50 to 400nm; the particle size D50 of the second active particles is 700-1300nm;

s012, adding a conductive agent and an adhesive into the lithium iron phosphate material and uniformly stirring to obtain positive slurry, wherein the mass ratio of the lithium iron phosphate material to the conductive agent to the adhesive is (94-98) to (1-3) to (1-2);

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 at (9-5): (1-5) repeating the step S011 and the step S012 to obtain n different cathode pastes, and the active paste includes n different cathode pastes;

the method for preparing the positive plate comprises the following steps of coating the active slurry on at least one side surface of a current collector to form a positive active coating, and obtaining the positive plate, wherein the steps comprise:

s021, sequentially coating n different kinds of positive electrode slurry on a current collector according to the order that the mass ratio of the first active particles to the second active particles is in gradient decreasing distribution, and obtaining the current collector coated with n layers of coatings;

and S022, cold-pressing the current collector coated with the n layers of coatings to obtain the required positive plate.

A battery comprises a shell and a winding battery cell installed in the shell, wherein the winding battery cell is formed by overlapping and winding a positive plate, a diaphragm and a negative plate, and the positive plate is the positive plate as described in any one of the above.

Compared with the prior art, the invention has the following beneficial effects:

the positive active coating comprising the first active particles and the second active particles is coated on the surface of the current collector, wherein the particle size of the first active particles is smaller than that of the second active particles, the mass content of the first active particles is in gradient decreasing distribution along the direction far away from the current collector, and the mass content of the second active particles is in gradient increasing distribution, so that the stacking density and the porosity of the positive active coating are improved, the infiltration and the diffusion of electrolyte are facilitated, and the dynamic performance of the battery can be improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

The structure, proportion, size and the like shown in the drawings are only used for matching with the content disclosed in the specification, so that the person skilled in the art can understand and read the description, and the description is not used for limiting the limit condition of the implementation of the invention, so the method has no technical essence, and any structural modification, proportion relation change or size adjustment still falls within the range covered by the technical content disclosed by the invention without affecting the effect and the achievable purpose of the invention.

Fig. 1 is a schematic structural diagram of a first positive electrode plate according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a second positive electrode plate according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a third positive electrode tab according to an embodiment of the present invention.

Illustration of the drawings: 1. a current collector; 2. a positive active coating layer; 11. a first coating layer; 12. a second coating layer; 101. a first active particle; 102. a second active particle.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. It should be noted that when one component is referred to as being "connected" to another component, it can be directly connected to the other component or intervening components may also be present.

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The embodiment of the invention provides a positive plate, which is provided with firstactive particles 101 and secondactive particles 102 with different diameters, and a distribution structure between the firstactive particles 101 and the secondactive particles 102 is reasonably arranged, so that the stacking density of a positive active material and the porosity of the positive plate can be effectively improved, the rapid infiltration and rapid diffusion of electrolyte can be promoted, and the dynamic performance of a battery can be further improved.

Example one

As shown in fig. 1 and 2, the positive electrode sheet includes acurrent collector 1 and a positiveactive coating 2 coated on at least one side surface of thecurrent collector 1, wherein the positiveactive coating 2 includes a positive active material; the positive electrode active material includes firstactive particles 101 and secondactive particles 102, and a particle size of the firstactive particles 101 is smaller than a particle size of the secondactive particles 102. The firstactive particles 101 and the secondactive particles 102 are both lithium iron phosphate particles.

The mass ratio of the firstactive particles 101 to the secondactive particles 102 is distributed in a gradient increasing manner in a direction away from thecurrent collector 1.

It should be noted that the positiveactive coating layer 2 may be a single integral layer, or may be formed by laminating at least two coating layers. In addition, the positiveactive coating layer 2 may be provided on one side surface of thecurrent collector 1, or may be provided on both opposite side surfaces of thecurrent collector 1. When the positiveactive coating 2 is an integral layer, the positiveactive coating 2 needs to be formed by multiple coating, in slurry coated each time, the proportions of the firstactive particles 101 and the secondactive particles 102 are different, so that the mass content of the firstactive particles 101 in the positiveactive coating 2 is in gradient decreasing distribution along the direction away from the surface of one side of thecurrent collector 1, and the mass content of the secondactive particles 102 in the positiveactive coating 2 is in gradient increasing distribution.

It should be further noted that the mass ratio of the firstactive particles 101 to the secondactive particles 102 is distributed in a gradient increasing manner, and the mass content of the firstactive particles 101 may be smaller as they are farther from the current collector, and the mass content of the secondactive particles 102 may be constant or higher.

The positiveactive coating layer 2 comprises at least two coating layers which are arranged in a stacked mode, and each coating layer is provided with a firstactive particle 101 and a secondactive particle 102; in the two adjacent coating layers, the mass ratio of the firstactive particles 101 to the secondactive particles 102 in the coating layer on the side close to the current collector is a, and the mass ratio of the firstactive particles 101 to the secondactive particles 102 in the coating layer on the side far from the current collector is B, and B is smaller than a.

The current collector coated with two layers of coatings in fig. 2 is mainly used as a main description object in the present embodiment, that is, the positiveactive coating 2 includes two layers of coatings, and the two layers of coatings include afirst coating 11 coated on thecurrent collector 1 and asecond coating 12 coated on thefirst coating 11.

The mass ratio of the secondactive particles 102 to the firstactive particles 101 in thefirst coating layer 11 is 6:4; the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thesecond coating layer 12 is 9:1. in this embodiment, the particle diameter D50 of the firstactive particles 101 is 200nm; the secondactive particles 102 have a particle size D50 of 800nm.

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

The embodiment also provides a preparation method of the positive plate, which comprises the following steps

S01, preparing an active slurry, wherein the active slurry comprises a positive electrode active material, the positive electrode active material comprises firstactive particles 101 and secondactive particles 102, and the particle size of the firstactive particles 101 is smaller than that of the secondactive particles 102;

s02, coating the active slurry on at least one side surface of acurrent collector 1 to form a positive active coating to obtain a positive plate; wherein, along the direction far away from thecurrent collector 1, the mass ratio of the firstactive particles 101 to the second active particles is distributed in a gradient decreasing manner.

Optionally, the preparing of the active slurry is specifically:

s011, mixing the firstactive particles 101 and the secondactive particles 102 according to (9-5): (1-5) stirring uniformly to obtain a uniformly mixed lithium iron phosphate material; wherein the particle diameter D50 of the firstactive particles 101 is 50 to 400nm; the particle size D50 of the secondactive particles 102 is 700 to 1300nm;

s012, adding a conductive agent and an adhesive into the lithium iron phosphate material and uniformly stirring to obtain positive slurry, wherein the mass ratio of the lithium iron phosphate material to the conductive agent to the adhesive is (94-98) to (1-3) to (1-2);

s013, changing the mass ratio of the firstactive particles 101 to the secondactive particles 102, and maintaining the mass ratio of the firstactive particles 101 to the secondactive particles 102 at (9-5): (1-5) repeating the step S011 and the step S012 to obtain n different cathode pastes, and the active paste includes n different cathode pastes;

the method for coating the active slurry on at least one side surface of acurrent collector 1 to form a positiveactive coating 2 to obtain the positive plate comprises the following steps:

s021, sequentially coating n different kinds of positive electrode slurry on acurrent collector 1 according to the order that the mass ratio of the firstactive particles 101 to the secondactive particles 102 is in gradient descending distribution, and obtaining a current collector coated with n layers of coatings;

s022, cold pressing the current collector coated with the n layers of coatings to obtain a compacted density of 2.30-2.55g/cm³ The positive electrode sheet of (1). The positive electrodeactive coating layer 2 includes n coating layers.

Note that, where n is not less than 2, i.e., the number of active coating layers on the current collector is at least two.

The embodiment also provides a battery prepared by the method, the battery comprises a shell and a winding battery cell installed in the shell, the winding battery cell is formed by overlapping and winding a positive plate, a diaphragm and a negative plate, and the positive plate is the positive plate as described in any one of the above.

In another specific embodiment, the positiveactive coating layer 2 includes several layers of coating layers arranged in a layer-by-layer manner; in the coating layer on the surface on the side farther from thecurrent collector 1, the mass content of the firstactive particles 101 is lower, and the mass content of the secondactive particles 102 is higher.

Referring to fig. 3, as long as different coatings are in a direction away from the surface of one side of thecurrent collector 1, the requirement that the mass ratio of the firstactive particles 101 to the secondactive particles 102 in the positiveactive coating 2 is in gradient increasing distribution is met, and the electrochemical performance of the battery is effectively improved.

Example two

The difference between this embodiment and the first embodiment is only:

the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thefirst coating layer 11 is 11:9; the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thesecond coating layer 12 is 8:2.

the rest of the process is the same as the examples.

EXAMPLE III

The difference between this embodiment and the first embodiment is only:

the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thefirst coating layer 11 is 5.5:4.5; the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thesecond coating layer 12 is 7.5:2.5.

the rest is consistent with the embodiment.

Example 4

The difference between this embodiment and the first embodiment is only:

the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thefirst coating layer 11 is 5.3:4.7; the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thesecond coating layer 12 is 7:3.

example 5

The difference between this embodiment and the first embodiment is only:

the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thefirst coating layer 11 is 5:5; the mass ratio of the secondactive particles 102 to the firstactive particles 101 in thesecond coating layer 12 is 6.5:3.5.

the rest is consistent with the embodiment.

Comparative example 1

In the comparative example, the difference from the first example is;

there is only one layer in the positive active coating, and only the secondactive particles 102 are distributed in the positive active coating, there is no firstactive particle 101, and the secondactive particles 102 are uniformly distributed in the positive active coating.

The rest is consistent with the embodiment.

Comparative example 2

In the comparative example, the difference from the first example is;

there is only one layer in the positive active coating, and only the firstactive particles 101 are distributed in the positive active coating, there is no secondactive particle 102, and the firstactive particles 101 are uniformly distributed in the positive active coating.

The rest is consistent with the embodiment.

1. And (3) energy density testing: charging the battery to 3.65V at a constant current and a constant voltage of 1C at 25 +/-2 ℃, and stopping current at 0.05C; standing for 60 min, discharging to 2.5V at a constant current of 1C, and recording discharge energy P; weighing the battery cell, and recording a weight value m; battery energy density = discharge energy P/weight value m;

2. testing direct current internal resistance:

a) Capacity calibration: charging the battery to 3.65V at a constant current and a constant voltage of 1C at 25 +/-2 ℃, and stopping current at 0.05C; discharging to 2.5V at constant current of 1C after standing for 30 min, and recording discharge capacity C₀ 。

B) Testing direct current internal resistance: the battery is charged with 1C₀ Discharging to 2.5V; standing for 60 min; 1C₀ Charging 30 min, standing for 2h, and recording the voltage V₀ (ii) a Rear battery 2C₀ Discharging for 10s, recording final discharge voltage V₁ (ii) a The direct current internal resistance of the battery is = (V)₀ -V₁ /2)/C₀

3. Testing the circulating internal resistance: charging the battery to 3.65V at a constant current and a constant voltage of 1C at 25 +/-2 ℃, and cutting off the current of 0.05C; 30 min was allowed to stand, then 1C discharged to 2.5V, and the process continued until the capacity had decayed to 80% of the initial capacity, and the number of cycles was recorded.

TABLE 1

To sum up, theembodiments 1 to 5 show that the structure of the positive electrode adopted by the invention is beneficial to the rapid infiltration and rapid diffusion of the electrolyte, reduces the polarization of the battery, shortens the transmission path of lithium ions, increases the porosity of the positive electrode sheet, reduces the internal resistance of the battery, and effectively improves the dynamic performance of the battery. The lithium ion battery prepared by the anode has better power performance and higher energy density.

As can be seen from comparative examples 1 to 5, if the firstactive particles 101 in thefirst coating layer 11 are defined by the mass ratio Q₁ The mass ratio of the firstactive particles 101 in thesecond coating layer 12 is Q₂ ，Q₁ /Q₂ When the ratio of (A) to (B) is close to 1, the direct current internal resistance of the battery is obviously reduced, the cycle performance of the battery is reduced to some extent, and the cycle life is gradually reduced.

It can be seen from comparison of examples 1 to 5 and comparative examples 1 to 2 that the provision of the firstactive particles 101 and the secondactive particles 102 having different particle diameters effectively reduces the direct current internal resistance of the battery and improves the cycle life of the battery.

As can be seen from comparison between examples 1 to 5 and comparative examples 1 to 2, the firstactive particles 101 and the secondactive particles 102 having different particle diameters are provided, and satisfy the gradient distribution structure, and the stacking density of the positive electrode active material can also be increased, thereby facilitating to increase the compaction density of the positive electrode sheet and the energy density of the battery cell. It should be further added that the amount of the firstactive particles 101 with smaller particle size is larger at the side close to the current collector, so that during the compaction process, the secondactive particles 102 with larger diameter apply pressure to the firstactive particles 101 with smaller diameter, so that more firstactive particles 101 are attached to the current collector, thereby effectively ensuring the high energy density of the battery.

It should be noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (9)

1. The positive plate is characterized by comprising a current collector (1) and a positive active coating (2) coated on at least one side surface of the current collector (1), wherein the positive active coating (2) comprises a positive active material;

the positive electrode active material includes first active particles (101) and second active particles (102), and a particle diameter of the first active particles (101) is smaller than a particle diameter of the second active particles (102);

the mass ratio of the first active particles (101) to the second active particles (102) is distributed in a gradient decreasing manner along the direction away from the current collector (1).

2. The positive electrode sheet according to claim 1, wherein the first active particles (101) have a particle diameter D50 of 50 to 400nm; the second active particles (102) have a particle size D50 of 700-1300nm.

3. The positive electrode sheet according to claim 1, wherein the positive electrode active coating layer (2) comprises at least two coating layers arranged in a stack, each coating layer having therein a first active particle (101) and a second active particle (102); in two adjacent layers of coating, the mass ratio of the first active particles (101) to the second active particles (102) in the coating layer close to the current collector is A, the mass ratio of the first active particles (101) to the second active particles (102) in the coating layer far away from the current collector is B, and B is less than A.

4. The positive electrode sheet according to claim 3, wherein the positive electrode active coating layer (2) comprises two coating layers arranged in a stack, the two coating layers comprising a first coating layer (11) arranged on the current collector (1) and a second coating layer (12) arranged on the first coating layer (11);

the mass ratio of the second active particles (102) to the first active particles (101) in the first coating layer (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 layer (12) is (9-5): (1-5).

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

6. The positive electrode sheet according to claim 1, wherein the first active particles (101) and the second active particles (102) are each lithium iron phosphate particles.

7. A positive electrode sheet production method for producing the positive electrode sheet according to any one of claims 1 to 6, characterized by comprising:

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 on at least one side surface of a current collector (1) to form a positive active coating (2) to obtain a positive plate; wherein the mass ratio of the first active particles (101) to the second active particles (102) is distributed in a gradient decreasing manner along the direction away from the current collector (1).

8. The method according to claim 7, characterized in that the preparation of the active paste is in particular:

s011, and enabling the first active particles (101) and the second active particles (102) to be in the following ratio (9-5): (1-5) stirring uniformly to obtain a uniformly mixed lithium iron phosphate material; wherein the first active particles (101) have a particle size D50 of 50-400nm; the second active particles (102) have a particle size D50 of 700-1300nm;

s012, adding a conductive agent and an adhesive into the lithium iron phosphate material and uniformly stirring to obtain positive slurry, wherein the mass ratio of the lithium iron phosphate material to the conductive agent to the adhesive is (94-98) to (1-3) to (1-2);

s013, changing the mass ratio of the first active particles (101) to the second active particles (102), and keeping the mass ratio of the first active particles (101) to the second active particles (102) at (9-5): (1-5) repeating the step S011 and the step S012 to obtain n different cathode pastes, and the active paste includes n different cathode pastes;

the method comprises the following steps of coating the active slurry on at least one side surface of a current collector (1) to form a positive active coating (2) to obtain a positive plate, and comprises the following steps:

s021, sequentially coating n different kinds of positive electrode slurry on a current collector (1) according to the order that the mass ratio of the first active particles (101) to the second active particles (102) is in gradient decreasing distribution, and obtaining the current collector coated with n layers of coatings;

and S022, cold-pressing the current collector coated with the n layers of coatings to obtain the required positive plate.

9. A battery, characterized in that the battery comprises a shell and a winding cell arranged in the shell, the winding cell is formed by winding a positive plate, a diaphragm and a negative plate in an overlapping manner, and the positive plate is the positive plate as claimed in any one of claims 1 to 6.

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