CN219917211U - Cathode pole piece structure and secondary battery - Google Patents

Abstract

The utility model relates to a cathode pole piece structure and a secondary battery, comprising: the solar cell comprises a first electrode sheet body, a second electrode sheet body and a third electrode sheet body, wherein the third electrode sheet body comprises a third current collector, a third coating layer and a fourth coating layer, the first surface of the third current collector is provided with the first electrode sheet body, the third current collector is provided with the third coating layer, and the first electrode sheet body is in contact with the two third coating layers; a fourth coating layer is arranged on the second surface of the third current collector, and the second pole piece body is contacted with the two fourth coating layers; the first pole piece body comprises a first current collector and a first coating layer, and the first coating layer is coated on one surface, far away from the third pole piece body, of the first current collector; the second pole body comprises a second current collector and a second coating layer, and the second coating layer is coated on one surface, far away from the third pole body, of the second current collector. The utility model effectively reduces the expansion degree of the battery.

Description

Cathode pole piece structure and secondary battery

Technical Field

The utility model relates to the technical field of batteries, in particular to a cathode pole piece structure and a secondary battery.

Background

Under the dual stimulus of national policy and market demand, the power battery has been developed rapidly in recent years, and compared with batteries such as lead acid, the power battery has the advantages of high energy density, stable voltage platform and long service life, and is favored by consumers. With further expansion of the market, the competition between power battery manufacturers is increasing, and the performance requirements for battery products are also increasing, and high safety, long cycle life, and fast charging capability are necessary.

The battery core can expand after a period of charging and discharging processes of the existing battery, and the lithium active substances on the cathode stage sheet are inserted into the anode stage sheet when the battery is charged each time, so that the anode stage sheet becomes thick, the lithium active substances on the anode cannot be completely released and inserted back into the cathode stage sheet after each discharging process of the battery, the anode stage sheet becomes thicker, the middle of the stage sheet is more expanded due to smaller stress, larger expansion, the middle of the battery core is more expanded when the battery is seen from the outside, potential safety hazards exist when the battery is used for a long time, the battery performance is continuously deteriorated, the cycle life of the battery is influenced, for example, the power performance of the battery is continuously reduced, the cycle life is rapidly attenuated, and the like.

Disclosure of Invention

Therefore, the utility model aims to solve the technical problems that the service life of the battery is influenced due to the reduced battery performance in the prior art, and further provides a cathode plate structure and a secondary battery capable of reducing the expansion degree of the middle part of the electrode plate.

In order to solve the technical problems, the cathode pole piece structure of the utility model comprises: the third pole piece body comprises a third current collector, a third coating layer and a fourth coating layer, wherein the third current collector is provided with a first surface and a second surface in the thickness direction, the first surface of the third current collector is provided with a first pole piece body, the first surface of the third current collector and the two sides of the first pole piece body in the width direction are respectively provided with the third coating layer, and the first pole piece body is contacted with the two third coating layers;

the second surface of the third current collector is provided with a second electrode sheet body, the second surface of the third current collector and the two sides of the second electrode sheet body in the width direction are provided with fourth coating layers, and the second electrode sheet body is contacted with the two fourth coating layers;

the widths W1 of the two third coating layers are equal, and the thickness of the first pole piece body is equal to the thickness T3 of the third coating layers; the widths W2 of the two fourth coating layers are equal, and the thickness of the second electrode sheet body is equal to the thickness T4 of the fourth coating layer;

a first electrode sheet including a first current collector in contact with the first current collector and a first coating layer; the first coating layer is coated on one surface, far away from the third pole piece body, of the first current collector;

a second electrode sheet comprising a second current collector in contact with the first current collector and a second coating layer; the second coating layer is coated on one surface, far away from the third pole piece body, of the second current collector.

In one embodiment of the present utility model, the ratio of the width W4 of the first pole piece body to the width W3 of the third current collector is 0.1-0.9; the ratio of the width W5 of the second pole piece body to the width W3 of the third current collector is 0.1-0.9.

In one embodiment of the utility model, the width W1 of the third coating layer is equal to the width W4 of the first pole piece body; the width W2 of the fourth coating layer is equal to the width W5 of the second electrode sheet body.

In one embodiment of the present utility model, the width W4 of the first pole piece and the width W5 of the second pole piece are equal.

In one embodiment of the present utility model, the thickness D1 of the first current collector, the thickness D2 of the second current collector, and the thickness D3 of the third current collector are all 5 μm to 20 μm.

In one embodiment of the present utility model, the thickness D1 of the first current collector, the thickness D2 of the second current collector, and the thickness D3 of the third current collector are all equal.

In one embodiment of the present utility model, the thickness T1 of the first coating layer, the thickness T2 of the second coating layer, the thickness T3 of the third coating layer, and the thickness T4 of the fourth coating layer are all 50 μm to 200 μm, wherein the ratio of the thickness T1 of the first coating layer to the thickness T3 of the third coating layer is 0.1 to 0.9; the ratio of the thickness T2 of the second coating layer to the thickness T4 of the fourth coating layer is 0.1-0.9.

In one embodiment of the utility model, the thickness T3 of the third coating layer and the thickness T4 of the fourth coating layer are equal.

In one embodiment of the utility model, the active substance content of the first coating layer is 1% -10% lower than the active substance content of the third coating layer; the active substance content of the second coating layer is 1% -10% lower than the active substance content of the fourth coating layer.

The utility model also provides a secondary battery, which comprises the cathode pole piece structure of any one of the above.

Compared with the prior art, the technical scheme of the utility model has the following advantages:

the cathode pole piece structure and the secondary battery adopt a split structure, the cathode pole piece is divided into three pole pieces, and the first pole piece body is arranged in the middle of the first surface of the third pole piece body, and the second pole piece body is arranged in the middle of the second surface of the third pole piece body, so that a current collector with thick middle and thin two sides is formed, the active substance content in the middle position of the pole piece can be reduced, and a coating layer with thin middle and thick two sides is formed, so that the lithium ion intercalation quantity in the middle position of the pole piece is reduced when the battery is charged, the lithium intercalation degree is small, the potential safety hazard is effectively reduced, and the battery performance is ensured.

Drawings

In order that the utility model may be more readily understood, a more particular description of the utility model will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings, in which

FIG. 1 is an exploded schematic view of the cathode pole piece structure of the present utility model;

fig. 2 is a schematic view of the cathode sheet structure of the present utility model.

Description of the drawings: 10. a first pole piece body; 11. a first current collector; 12. a first coating layer; 20. a second pole piece body; 21. a second current collector; 22. a second coating layer; 30. a third pole piece; 31. a third current collector; 32-a third coating layer; 33-fourth coating layer.

Detailed Description

As shown in fig. 1 and 2, the present embodiment provides a cathode sheet structure, including:

the third pole piece 30 comprises a third current collector 31, a third coating layer 32 and a fourth coating layer 33, wherein the third current collector 31 is provided with a first surface and a second surface in the thickness direction, the first surface of the third current collector 31 is provided with a first pole piece body 10, the first surface of the third current collector 31 and the two sides of the first pole piece body 10 in the width direction are respectively provided with a third coating layer 32, and the first pole piece body 10 is contacted with the two third coating layers 32;

the second surface of the third current collector 31 is provided with a second electrode sheet 20, the second surface of the third current collector 31 and the two sides of the second electrode sheet 20 in the width direction are provided with fourth coating layers 33, and the second electrode sheet 20 is contacted with the two fourth coating layers 33;

wherein the widths W1 of the two third coating layers 32 are equal, and the thickness of the first electrode body 10 is equal to the thickness T3 of the third coating layer 32; the widths W2 of the two fourth coating layers 33 are equal, and the thickness of the second electrode body 20 is equal to the thickness T4 of the fourth coating layer 33;

a first electrode body 10 including a first current collector 11 and a first coating layer 12, the first current collector 11 being in contact with the first current collector 11; the first coating layer 12 is coated on one surface of the first current collector 11 far from the third pole piece body 30;

a second electrode sheet 20 including a second current collector 21 and a second coating layer 22, the second current collector 21 being in contact with the first current collector 11; the second coating layer 22 is coated on a surface of the second current collector 21 away from the third electrode sheet 30.

In the cathode pole piece structure of the present embodiment, the widths W1 of the two third coating layers 32 are equal, so that the first pole piece body 10 can be ensured to be positioned in the middle of the first surface of the third pole piece body 30, and the widths W2 of the two fourth coating layers 33 are equal, so that the second pole piece body 20 can be ensured to be positioned in the middle of the second surface of the third pole piece body 30, and further, after the first pole piece body 10, the second pole piece body 20 and the third pole piece body 30 are combined, a current collector with thick middle and thin two sides can be formed; the thickness of the first electrode sheet body 10 is equal to the thickness T3 of the third coating layer 32, and the thickness of the second electrode sheet body 20 is equal to the thickness T4 of the fourth coating layer 33, so that the middle thick and the thin current collectors on two sides can be formed, meanwhile, the middle thin and the thick coating layers on two sides can be formed, and then the active material content in the middle position of the electrode sheet can be effectively reduced, the lithium ion intercalation quantity in the middle position of the electrode sheet is reduced when the battery is charged, the lithium intercalation degree is small, the middle release heat quantity is less during charging and discharging, the rebound of the electrode sheet is less, and the lithium precipitation is reduced, thereby effectively reducing the expansion degree of the middle part of the cathode sheet, saving the space, improving the performance of the battery and achieving the purpose of prolonging the service life of the battery. In addition, the thickness of the first electrode sheet body 10 is equal to the thickness T3 of the third coating layer 32, and the thickness of the second electrode sheet body 20 is equal to the thickness T4 of the fourth coating layer 33, so that the surface of the cathode sheet structure is flat, and the subsequent manufacturing of the battery cell is convenient.

In this embodiment, the ratio of the width W4 of the first electrode sheet body 10 to the width W3 of the third current collector 31 is 0.1-0.9; the ratio of the width W5 of the second pole piece body 20 to the width W3 of the third current collector 31 is 0.1-0.9, so that the stability of the current collector structure is higher, the strength of the overall structure is stable, the strength is high, and the processing is easy while the content of active substances in the middle position of the pole piece is reduced.

Specifically, the ratio of the width W4 of the first electrode sheet body 10 to the width W3 of the third current collector 31 may be any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9; the ratio of the width W5 of the second electrode sheet 20 to the width W3 of the third current collector 31 may be any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9. Preferably, the ratio of the width W4 of the first pole piece body 10 to the width W3 of the third current collector 31 is the same as the ratio of the width W5 of the second pole piece body 20 to the width W3 of the third current collector 31, which is not only convenient for manufacturing and processing, but also is beneficial for ensuring that the content of active substances in the middle position of the pole piece is the same.

The width W1 of the third coating layer 32 is equal to the width W4 of the first electrode body 10; the width W2 of the fourth coating layer 33 is equal to the width W5 of the second electrode sheet 20, which is convenient for processing and manufacturing, and can make the current collector have higher structural stability, can bear larger strength, and has stable overall structure and high strength. Preferably, the width W4 of the first pole piece 10 is equal to the width W5 of the second pole piece 20.

The thickness D1 of the first current collector 11, the thickness D2 of the second current collector 21, and the thickness D3 of the third current collector 31 are all 5 μm-20 μm, so that wettability and uniformity of the current collectors can be effectively ensured. Specifically, the thickness D1 of the first current collector 11, the thickness D2 of the second current collector 21, and the thickness D3 of the third current collector 31 may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm. Preferably, the thickness D1 of the first current collector 11, the thickness D2 of the second current collector 21, and the thickness D3 of the third current collector 31 are equal.

Since the first electrode body 10 includes the first current collector 11 and the first coating layer 12, the thickness of the first electrode body 10 is equal to the sum of the thickness D1 of the first current collector 11 and the thickness T1 of the first coating layer 12; the second electrode body 2 includes a second current collector 21 and a second coating layer 22, and thus the thickness of the second electrode body 20 is equal to the sum of the thickness D2 of the second current collector 21 and the thickness T2 of the second coating layer 22.

The thickness T1 of the first coating layer 12, the thickness T2 of the second coating layer 22, the thickness T3 of the third coating layer 32 and the thickness T4 of the fourth coating layer 33 are all 50 μm-200 μm, so that wettability and uniformity of the current collector can be effectively ensured.

Specifically, the thickness T1 of the first coating layer 12, the thickness T2 of the second coating layer 22, the thickness T3 of the third coating layer 32, and the thickness T4 of the fourth coating layer 33 may be 50 μm, 60 μm, 70 μm, 80 μm, 85 μm, 90 μm, 100 μm, 104 μm, 110 μm, 120 μm, 130 μm, 140 μm, 146 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm.

Wherein the ratio of the thickness T1 of the first coating layer 12 to the thickness T3 of the third coating layer 32 is 0.1-0.9; the ratio of the thickness T2 of the second coating layer 22 to the thickness T4 of the fourth coating layer 33 is 0.1-0.9, so that a coating layer with a thin middle and thick two sides is formed, the active material content in the middle of the pole piece is effectively reduced, and the cell expansion phenomenon is reduced.

Specifically, the ratio of the thickness T1 of the first coating layer 12 to the thickness T3 of the third coating layer 32 may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9. The ratio of the thickness T2 of the second coating layer 22 to the thickness T4 of the fourth coating layer 33 may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9.

The thickness T3 of the third coating layer 32 is equal to the thickness T4 of the fourth coating layer 33, thereby facilitating processing and manufacturing and assembly.

In some embodiments, the active material content of the first coating layer 12 is 1% -10% lower than the active material content of the third coating layer 32; the content of the active substances in the second coating layer 22 is 1% -10% lower than that in the fourth coating layer 33, so that the active substances in the middle coating layer are smaller, the active substances in the coating layers on the two sides are larger, and the active substance content in the middle position of the pole piece is effectively reduced.

Specifically, the active material content of the first coating layer 12 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% lower than the active material content of the third coating layer 32. The active substance content of the second coating layer 22 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% lower than the active substance content of the fourth coating layer 33.

In the cathode plate structure of this embodiment, the first plate body 10, the second plate body 20 and the third plate body 30 are combined together to form the cathode plate structure, which is specifically as follows: coating a first coating layer 12 on the first current collector 11 to form a first electrode sheet body 10;

coating a second coating layer 22 on the second current collector 21 to form a second electrode sheet 20;

coating a third coating layer 32 on two sides of the first surface of the third current collector 31, and coating a fourth coating layer 33 on two sides of the second surface of the third current collector 31 to form a third pole piece body 30;

the first electrode body 10 and the second electrode body 20 are respectively disposed on the first surface and the second surface of the third current collector 31, the first electrode body 10 is disposed between the two third coating layers 32, and the second electrode body 20 is disposed between the two fourth coating layers 33.

It should be noted that the order of coating the first coating layer 12, the second coating layer 22, the third coating layer 32 and the fourth coating layer 33 is not limited, that is, the first current collector 11 and the second current collector 21 are respectively disposed on the first surface and the second surface of the third current collector 31, and then the first coating layer 12, the second coating layer 22, the third coating layer 32 and the fourth coating layer 33 are disposed; the first electrode sheet body 10 may be formed by coating the first coating layer 12 on the first current collector 11, the second electrode sheet body 20 may be formed by coating the second coating layer 22 on the second current collector 21, the first electrode sheet body 10 and the second electrode sheet body 20 may be respectively disposed on the first surface and the second surface of the third current collector 31, and finally the third coating layer 32 and the fourth coating layer 33 may be disposed.

In the cathode sheet structure of this embodiment, the first current collector 11, the second current collector 21, and the third current collector 31 refer to structures for collecting current, and in this embodiment, aluminum foil may be used. The first coating layer 12, the second coating layer 22, the third coating layer 32 and the fourth coating layer 33 are cathode coating layers, and are composed of a main material and an auxiliary material, wherein the main material is one of lithium iron phosphate, ternary lamellar material, lithium manganate and lithium cobaltate, and the auxiliary material is composed of a conductive agent and a binder; the proportion of active material content in the cathode coating (comprising main material and auxiliary material) is Loading, and the range is 80% -100%. Specifically, the proportion Loading of the active material content to the cathode coating is: 80%, 85%, 90%, 95%, 98%, 100%.

As a modification, the present utility model also provides a secondary battery including the cathode tab structure of the above embodiment.

In the cyclic charge and discharge process of the secondary battery, the expansion of the cathode electrode plate mainly results from the expansion of cathode active material particles in the cathode membrane, and the expansion direction of the cathode active material particles mainly results from the expansion of cathode active material particles in which the layered structure plane is parallel to the cathode current collector, i.e., the thickness increase of the cathode membrane mainly results from the expansion of the layered structure plane in the cathode membrane. When the expansion of the cathode plate is overlarge, the battery core, namely the battery body, can transmit expansion force from inside to outside, the toughness of the cathode current collector relative to the anode current collector is poorer, the phenomenon that the cathode membrane is broken easily occurs in a region with large local stress of the cathode current collector, the broken membrane pierces the isolating membrane to cause the probability of short circuit in the battery to be increased, and the battery has higher potential safety hazard. The expansion of the cathode plate can also generate direct extrusion action on the cathode plate, so that electrolyte infiltration is poor, polarization of the battery is increased when the battery is charged at a larger multiplying power, and local lithium is separated out from a cathode interface, so that potential safety hazard of the battery is increased, and circulating capacity of the battery is accelerated and attenuated. The expansion of the cathode electrode plate can also cause mutual stripping of cathode active material particles, the particle gap is increased, the cathode conductive network is destroyed, the polarization of the battery is increased when the battery is charged at a larger multiplying power, and then the charge and discharge power of the battery is reduced and the heat generation is increased. In the secondary battery, the split structure is adopted in the cathode pole piece structure, the cathode pole piece is divided into three pole pieces, and the first pole piece body is arranged in the middle of the first surface of the third pole piece body, and the second pole piece body is arranged in the middle of the second surface of the third pole piece body, so that a current collector with thick middle and thin two sides is formed, the active substance content in the middle position of the pole piece can be reduced, and a coating layer with thin middle and thick two sides is formed, so that the lithium ion intercalation quantity in the middle position of the pole piece is reduced when the battery is charged, the lithium intercalation degree is small, the expansion is reduced, the expansion gap reserved in the battery is reduced, the problem of expansion of the battery is reduced, the potential safety hazard is effectively reduced, and the battery performance is ensured.

The following specifically describes the structure of the cathode sheet and various performances of the secondary battery according to the present utility model in combination with data.

Example 1

The width of the cathode plate structure is 100mm, that is, the width of the third current collector 31 is 100mm, the width of the first and second electrode plates 10 and 20 is 50mm (that is, the width of the middle region is 50 mm), the thickness of the first and second current collectors 11 and 21 is 14 μm, the thickness of the third current collector is 10 μm, the thickness of the first and second coating layers 12 and 22 is 100 μm, the thickness of the third and fourth coating layers 32 and 33 is 104 μm, the middle loading of the coating layers is 90%, the loading of the two sides is 98%, that is, the loading of the first and second coating layers 12 and 22 is 90%, and the loading of the third and fourth coating layers 32 and 33 is 98%.

Example 2

In comparative example 1, the loading of the first and second coating layers 12 and 22 was 95%, and the loading of the third and fourth coating layers 32 and 33 was 98%, namely: middle loading95% and two sides loading98%.

Example 3

In comparative example 1, the width of each of the first and second electrode sheets 10 and 20 was 70mm, i.e., the intermediate width was 70mm.

Example 4

Comparative example 1, the middle current collector had a thickness of 12 μm and the two side current collectors had a thickness of 10 μm, namely: the total thickness of the first current collector 11, the second current collector 21 and the third current collector 31 is 12 μm, and the thickness of the third current collector 31 is 10 μm, forming a current collector structure with a thick middle and thin sides.

Comparative example 1

Comparative example 1, the loading difference between the middle and the two sides of the coating layer was not distinguished.

Comparative example 2

Comparative example 1, the thickness of the middle and both sides of the diversity fluid and coating layers were not distinguished.

The four examples and two comparative examples were tested for the expanded thickness and capacity retention of the cells, and the test results obtained are shown in the following table:

from the above table it can be derived that: the current collector adopted by the utility model has a structure with thick middle and thin two sides, which not only can effectively reduce the expansion degree of the middle part of the cathode pole piece, but also can improve the capacity retention rate of the battery, and the purpose of prolonging the service life of the battery is achieved due to the improvement of the performance of the battery.

It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present utility model will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the utility model.

Claims (10)

1. A cathode sheet structure, comprising:

the third pole piece body (30) comprises a third current collector (31), a third coating layer (32) and a fourth coating layer (33), wherein the third current collector (31) is provided with a first surface and a second surface in the thickness direction, the first surface of the third current collector (31) is provided with a first pole piece body (10), the first surface of the third current collector (31) and two sides which are positioned in the width direction of the first pole piece body (10) are respectively provided with the third coating layer (32), and the first pole piece body (10) is contacted with the two third coating layers (32);

a second electrode body (20) is arranged on the second surface of the third current collector (31), fourth coating layers (33) are arranged on the second surface of the third current collector (31) and positioned on two sides of the second electrode body (20) in the width direction, and the second electrode body (20) is in contact with the two fourth coating layers (33);

wherein the widths W1 of the two third coating layers (32) are equal, and the thickness of the first pole piece body (10) is equal to the thickness T3 of the third coating layers (32); the widths W2 of the two fourth coating layers (33) are equal, and the thickness of the second pole piece body (20) is equal to the thickness T4 of the fourth coating layers (33);

a first pole piece body (10) comprising a first current collector (11) and a first coating layer (12), the first current collector (11) being in contact with the first current collector (11); the first coating layer (12) is coated on one surface, far away from the third pole piece body (30), of the first current collector (11);

-a second pole body (20) comprising a second current collector (21) and a second coating layer (22), said second current collector (21) being in contact with said first current collector (11); the second coating layer (22) is coated on one surface of the second current collector (21) far away from the third pole piece body (30).

2. The cathode pole piece structure of claim 1, wherein: the ratio of the width W4 of the first polar plate body (10) to the width W3 of the third current collector (31) is 0.1-0.9; the ratio of the width W5 of the second pole piece body (20) to the width W3 of the third current collector (31) is 0.1-0.9.

3. The cathode pole piece structure of claim 1, wherein: the width W1 of the third coating layer (32) is equal to the width W4 of the first pole piece body (10); the width W2 of the fourth coating layer (33) is equal to the width W5 of the second pole piece body (20).

4. The cathode pole piece structure of claim 1, wherein: the width W4 of the first pole piece body (10) is equal to the width W5 of the second pole piece body (20).

5. The cathode pole piece structure of claim 1, wherein: the thickness D1 of the first current collector (11), the thickness D2 of the second current collector (21) and the thickness D3 of the third current collector (31) are all 5-20 mu m.

6. The cathode pole piece structure of claim 5, wherein: the thickness D1 of the first current collector (11), the thickness D2 of the second current collector (21) and the thickness D3 of the third current collector (31) are equal.

7. The cathode pole piece structure of claim 1, wherein: the thickness T1 of the first coating layer (12), the thickness T2 of the second coating layer (22), the thickness T3 of the third coating layer (32) and the thickness T4 of the fourth coating layer (33) are all 50-200 mu m, wherein the ratio of the thickness T1 of the first coating layer (12) to the thickness T3 of the third coating layer (32) is 0.1-0.9; the ratio of the thickness T2 of the second coating layer (22) to the thickness T4 of the fourth coating layer (33) is 0.1-0.9.

8. The cathode pole piece structure of claim 1, wherein: the thickness T3 of the third coating layer (32) and the thickness T4 of the fourth coating layer (33) are equal.

9. The cathode pole piece structure of claim 1, wherein: the active substance content of the first coating layer (12) is 1% -10% lower than the active substance content of the third coating layer (32); the active substance content of the second coating layer (22) is 1% -10% lower than the active substance content of the fourth coating layer (33).

10. A secondary battery characterized in that: a cathode sheet structure comprising any one of claims 1-9.