CN112820854B

CN112820854B - Electrode plate and application thereof

Info

Publication number: CN112820854B
Application number: CN202011628651.7A
Authority: CN
Inventors: 孙雷明; 张健; 张双虎; 彭冲
Original assignee: Zhuhai Cosmx Battery Co Ltd
Current assignee: Zhuhai Cosmx Battery Co Ltd
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-10-14
Anticipated expiration: 2040-12-30
Also published as: CN112820854A

Abstract

The invention provides an electrode plate and application thereof, wherein the electrode plate comprises a current collector, and the functional surface of the current collector comprises a tab area and an active layer area positioned on the periphery of the tab area; the active layer region comprises a first active layer region and a second active layer region which are adjacent; the first active layer is arranged in the first active layer area, the second active layer area is provided with a second coating, and the surface of the second coating is provided with a third active layer; the second coating comprises the following components in percentage by mass: 55-96% of inorganic particles, 3-40% of binder and 1-5% of conductive agent; in the first active layer, the relative molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%; in the second coating layer, the relative molecular weight of the binder is 800000-200000; in the third active layer, the relative molecular weight of the binder is 400000-800000 and the mass percentage content is 1-5%. The electrode sheet can improve the safety performance of the battery.

Description

Electrode plate and application thereof

Technical Field

The invention relates to an electrode plate, in particular to an electrode plate and application thereof, and belongs to the technical field of batteries.

Background

With the advent of the 5G era, the position of lithium ion batteries is becoming more important, and lithium ion batteries are also continuously developing in the direction of high energy density and high rate. However, lithium ion batteries

On the other hand, in order to reduce the impedance inside the lithium ion battery, at present, the connection position of the tab is usually adjusted from the edge of the pole piece to the inside of the pole piece, and the tab is brought into contact with the inside of the current collector to newly partition the functional layer on the surface of the current collector, thereby reducing the impedance.

On the other hand, the current collector of the lithium ion battery is made of metal foil, the positive electrode is usually made of metal aluminum foil, the negative electrode is usually made of metal copper foil, and internal short circuit can be caused under certain abuse conditions (such as needling, extrusion, impact and the like) to be incapable of cutting off current, so that heat accumulation is caused to cause thermal runaway, and safety accidents are finally caused. There is therefore an increasing interest in improving the safety performance of lithium ion batteries in which the tabs are located inside the current collector.

Disclosure of Invention

The invention provides an electrode plate, which can ensure the safety performance of a secondary battery comprising the electrode plate and prolong the service life of the secondary battery by adjusting the composition and distribution of an active layer of the electrode plate.

The present invention also provides a secondary battery including the electrode tab, so that safety performance is excellent.

The present invention also provides an apparatus including the above secondary battery, so that safety performance can be secured.

The invention provides an electrode plate, which comprises a current collector, wherein the functional surface of the current collector comprises a tab area and an active layer area positioned on the periphery of the tab area;

the active layer region comprises a first active layer region and a second active layer region which are adjacent, and the first active layer region is close to the tab region; a first active layer is arranged in the first active layer area, a second coating is arranged in the second active layer area, and a third active layer is arranged on the surface of the second coating;

the second coating comprises the following components in percentage by mass: 55-96% of inorganic particles, 3-40% of binder and 1-5% of conductive agent;

in the first active layer, the relative molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%;

in the second coating layer, the relative molecular weight of the binder is 800000-200000;

in the third active layer, the relative molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%.

The electrode sheet as described above, wherein the thickness of the second coating layer is 2 to 10 μm.

The electrode sheet as described above, wherein the inorganic particles are at least one selected from lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, nickel-cobalt-manganese-aluminum quaternary material, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganate, lithium-rich manganese base, alumina, and boehmite.

The electrode sheet as described above, wherein the inorganic particles have a median particle diameter D50 of 0.5 to 8 μm.

The electrode sheet as described above, wherein the median particle diameter D50 of the active material in the first active layer is 10 to 20 μm; and/or the presence of a gas in the gas,

the median particle diameter D50 of the active material in the first active layer is 10-20 μm.

The electrode sheet as described above, wherein the binder in the first active layer is 0.5% to 2% by mass of the first active layer; and/or the presence of a gas in the gas,

the mass percentage of the binder in the third active layer is 0.5-2%.

The electrode sheet as described above, wherein the thickness of the second coating layer is smaller than the thickness of the first active layer.

The electrode sheet as described above, wherein a total thickness of the third active layer and the second coating layer is greater than a thickness of the first active layer.

The invention also provides a secondary battery, which comprises the electrode plate.

The present invention also provides a device whose driving source or energy storage source is the above-described secondary battery.

According to the electrode plate, the binding agent in the active layer region around the electrode tab region is limited, so that the binding force between the active layer far away from the electrode tab region and the current collector is higher than the binding force between the active layer close to the electrode tab region and the current collector, the safety performance of a battery comprising the electrode plate is ensured, the connection strength between the electrode tab and the current collector is not influenced, and the service life of the battery is prolonged by improving the yield of the electrode plate.

The secondary battery of the invention has good safety performance and long service life because of the electrode plate.

The device of the invention comprises the secondary battery, thereby having good safety performance and service life and high customer satisfaction.

Drawings

Fig. 1 is a schematic top view of an embodiment of a current collector of an electrode sheet according to the present invention;

fig. 2 is a schematic top view of another embodiment of the current collector of the electrode sheet according to the present invention;

FIG. 3 is a front view of an embodiment of the electrode sheet of the present invention;

FIG. 4 is a schematic structural view of another embodiment of an electrode sheet according to the present invention;

fig. 5 is a schematic structural view of another embodiment of the electrode sheet of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to 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.

The invention provides an electrode plate, which comprises a current collector, wherein the functional surface of the current collector comprises a tab area and an active layer area positioned on the periphery of the tab area; the active layer region comprises a first active layer region and a second active layer region which are adjacent, and the first active layer region is close to the tab region; a first active layer is arranged in the first active layer area, a second coating is arranged in the second active layer area, and a third active layer is arranged on the surface of the second coating; the second coating comprises the following components in percentage by mass: 55-96% of inorganic particles, 3-40% of binder and 1-5% of conductive agent; in the first active layer, the molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%; in the second coating, the molecular weight of the binder is 800000-200000; in the third active layer, the molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%.

The electrode sheet of the present invention may specifically be a positive electrode sheet, in one embodiment, a current collector of the electrode sheet may be an aluminum foil, and the active material of the first active layer and the active material of the third active layer in the electrode sheet may be independently selected from at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, a lithium-rich manganese-based material, and lithium nickel cobalt aluminate.

In one embodiment, the inorganic particles in the second coating layer may be at least one of lithium cobaltate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, nickel cobalt manganese aluminum quaternary material, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganate, lithium rich manganese base, alumina, boehmite. The inorganic particles serve primarily as framework supports in the second coating.

The electrode sheet of the present invention includes a current collector and an active layer on a functional surface of the current collector, wherein the functional surface refers to the largest and opposite two surfaces of the current collector for coating the active layer, and the active layer sheet in the electrode sheet of the present invention may be coated on only one functional surface of the current collector or simultaneously coated on both functional surfaces of the current collector. Wherein the functional surfaces for welding the tab are defined below.

The functional surface of the current collector of the electrode plate for welding the electrode lug comprises a lug area and an active layer area, wherein the functional surface of the lug area is used for connecting the electrode lug and is positioned in the functional surface; the region around the tab region is the active layer region, which is used for arranging the active layer (the active layer regions of the current collector functional surface are all covered by the active layer). It should be noted here that the length (dimension in the width direction of the current collector) of the tab region may be equal to the width of the functional surface of the current collector. Fig. 1 is a schematic top view of an embodiment of a current collector of an electrode sheet according to the present invention, and as shown in fig. 1, a length n of a tab region a is equal to a width m of a functional surface of a current collector 100, so that the tab region a divides an active layer region B on two adjacent sides into two independent portions, where the two independent portions are both active layer regions B. Fig. 2 is a schematic top view of another embodiment of the current collector of the electrode sheet according to the present invention. As shown in fig. 2, the length n of the tab region a may be smaller than the width m of the functional surface of the current collector 100, and the active layer region B located on three surfaces of the tab region a may be a continuous region. Generally, the active layer regions B on both sides of the tab region a are symmetrically distributed about the center of the tab region a.

Taking fig. 1 as an example, the active layer region B is divided into a first active layer region B1 and a second active layer region B2 according to the distance from the tab region a, wherein the first active layer region B1 is close to the tab region a, and the second active layer region B2 is far away from the tab region a and is adjacent to the first active layer region B2.

Fig. 3 is a front view of an embodiment of an electrode sheet according to the present invention, and a tab region a and an active layer region B of the current collector 100 in fig. 3 are divided as shown in fig. 1. In the electrode sheet of this embodiment, the tab region a does not contain any coating layer, so that the tab can be directly connected to the functional surface of the tab region a; the first active layer region B1 is provided with a first active layer 1, the second active layer region B2 is provided with a second coating layer 2, and the surface of the second coating layer is provided with a third active layer 3, wherein the adhesive force in the second coating layer 2 is respectively higher than the adhesive force of the first active layer 1 and the third active layer 3. Specifically, the molecular weight of the binder in the second coating 2 is 800000-2000000, and the mass percentage content of the binder in the second coating is 3-40%; the molecular weight of the binder in the first active layer 1 is 400000-800000, and the mass percentage of the binder in the first active layer is 1-5%; the molecular weight of the binder in the third active layer 3 is 400000 to 800000, and the mass percentage of the binder in the third active layer 3 is 1 to 5%. Wherein, the binder in the first active layer 1, the binder in the second coating layer 2, and the binder in the third active layer 3 may be the same or different from each other, or partially the same; the mass percentage of the binder in the first active layer 1 and the mass percentage of the binder in the third active layer 3 may be the same or different.

In the invention, because the second coating 2 has higher adhesive force, even if external force is applied in the application process of the battery, the current collector can not easily fall off to expose, thereby avoiding the short circuit phenomenon caused by the contact of the current collector and ensuring the safety performance of the lithium ion battery. It can be understood that the higher the mass percentage of the binder in the second coating 2, the higher the binding power between the second coating 2 and the functional surface of the current collector 100, the less likely it will be separated from the current collector 100 in the process of long-term application or under the action of external force, thereby further ensuring the safety performance and capacity retention rate of the battery.

In addition, the third active layer 3 on the upper surface of the second coating 2 is mainly used for ensuring that the positive plate has a proper positive active layer material, so that negative influence on the capacity of the lithium ion battery due to too little positive active material in the second coating is avoided. Specifically, with respect to two surfaces of the second coating layer 2 which are in contact with the current collector 100 and the third active layer 3, respectively, the second coating layer 2 has four sides perpendicular to the two surfaces, including a side a1 distant from the tab region a; similarly, with respect to both surfaces of the third active layer 3 which are in contact with the second coating layer 2 and are distant from the second coating layer 2, respectively, the third active layer 3 has four sides perpendicular to the two surfaces, including a side a2 distant from the tab area a, and a side b close to the tab area a. In the present embodiment, the side surface a1 and the side surface a2 are flush, and the length of the third active layer 3 (the length of the bottom surface of the third active layer 2 in contact with the second coating layer 2) is less than or equal to the length of the second coating layer 2, and in fig. 3, the length of the third active layer 3 is less than the length of the second coating layer 2.

When preparing electrode plate, prior art all is at the mass flow body functional surface coating active layer first, then will need the active layer of welding utmost point ear to dispose the welding of carrying out utmost point ear. However, the second coating layer 2 of the present invention has a strong adhesive force, and thus the second coating layer 2 is difficult to remove and easily remains on the functional surface, and the connection strength between the tab and the functional surface is affected, for example, the tab is separated from the current collector to damage the electrode sheet. Therefore, when the positive plate is prepared, the area of the current collector functional surface, which is prepared for welding the tab, can be reserved, and then the slurry of the second coating 2 is coated on the other area of the current collector functional surface. Because when the active layer is coated on the functional surface of the current collector, the welding position of the tab cannot be accurately positioned, the reserved area comprises a tab area and a partial area around the tab area. The slurry of the third active layer 3 is then applied to the surface of the second coating layer 2, and the slurry of the first active layer is applied to the reserved area and dried.

It can be understood that, because the first active layer has low cohesive force and is easy to remove, the first active layer in the region where the tab is to be welded (i.e., the tab region of the present invention) can be removed before the tab is welded, so as to obtain the electrode sheet of the present invention.

According to the molecular weight of the binder in the second coating 2 and the proportion of the binder in the second coating 2, the second coating 2 has a very strong binding force with the current collector 100, and the second coating 2 cannot be degraded in the capacity of the battery due to the peeling of the second coating 2 from the functional surface of the current collector 100 in the long-term application process of the battery; and when the battery receives great external force, the second coating 2 can be used as the protective layer of the current collector 100 to avoid the current collector 100 from exposing due to the high adhesive force between the second coating 2 and the current collector 100, so that the short circuit phenomenon caused by the contact of the current collector 100 and the active layer of another electrode plate or the current collector is effectively prevented, and the battery safety performance is remarkably improved.

It is to be noted that the binder in the first active layer 1 and the third active layer 3 and the binder in the second coat layer 2 may be the same kind of compound having different molecular weights, and the binder in the first active layer 1 and the third active layer 3 and the binder in the second coat layer 2 may also be different compounds having different molecular weights.

The present invention is not limited to the other components in the first, second, and third

active layers

1, 2, and 3 except that the respective binders of the first, second, and third

active layers

1, 2, and 3 are defined, for example, the other components (e.g., conductive agents) in the first, second, and third

active layers

1, 2, and 3 may be different from or the same as each other.

In the electrode sheet of the present invention, since the first active layer region B1 has the first active layer 1, in order to prevent the first active layer 1 from falling off from the current collector during long-term use of the battery and under an external force, the mass percentage of the binder in the first active layer 1 may be relatively high, for example, 0.5 to 2%, without affecting the battery capacity.

Similarly, in order to avoid the detachment of the third active layer 3, the content of the binder in the third active layer 3 is 0.5 to 2% by mass in the third active layer 3.

In the process of preparing the slurry of the second coating layer using the inorganic particles, the binder, the conductive agent, the solvent, and the like, the binder wraps the inorganic particles and forms a system in which the inorganic particles are uniformly dispersed by filling gaps between the inorganic particles. When the particle size of the inorganic particles is smaller, the specific surface area of the inorganic particles is larger, so that the inorganic particles can contact with more binders, and when the slurry is coated on the functional surface of the current collector and dried to form the active layer, the binding force of the second coating layer to the current collector is larger, thereby improving the safety performance of the battery.

In one embodiment, the inorganic particles of the second coating layer 2 according to the invention therefore have a median particle diameter D50 of from 0.5 to 8 μm. Within this range, the smaller the median particle diameter D50 of the inorganic particles, the more advantageous the improvement of safety performance.

Based on the need for adhesion between the first active layer 1 and the current collector 100 and the need for adhesion between the third active layer 3 and the second coating layer 2, in one embodiment, the median particle diameter D50 of the active material in the first active layer 1 is 10 to 20 μm; and/or the median particle diameter D50 of the active material in the third active layer 3 is 10 to 20 μm.

In the specific implementation process, when the composition of the third active layer 3 is completely the same as that of the first active layer 1, the electrode plate preparation process is more facilitated to be simplified.

As shown in fig. 3, in order to avoid that the second coating layer has an excessive influence on the mass density of the lithium ion battery, in a specific embodiment, the thickness of the second coating layer 2 is smaller than the thickness of the first active layer 1.

Fig. 4 is a schematic structural view of another embodiment of the electrode sheet of the present invention. Generally, in order to secure the capacity of the battery, the thickness of the active layer on the functional surface of the current collector of the electrode sheet is uniform. However, when the tab is positioned inside the current collector, a lithium deposition phenomenon may occur around the tab due to an excessive current density around the tab, thereby causing deterioration in the cycle performance of the battery. Therefore, the sum of the thickness H2 of the second coating layer 2 and the thickness H3 of the third active layer 3 in the present embodiment is greater than the thickness H1 of the first active layer 1, based on the demand for the cycle performance of the battery, as shown in fig. 4 in particular. At this time, the first active layer area B1 close to the tab area a has less active layer distribution relative to the second active layer area B2 far away from the tab area a, and the distribution of lithium ions in the first active layer area B1 is reduced, so that the occurrence of a lithium dendrite phenomenon caused by an excessively high current density in the first active layer area B1 during the working process of the electrode plate can be avoided to a certain extent, and the cycle performance of the battery is remarkably improved.

Fig. 5 is a schematic structural view of another embodiment of the electrode sheet of the present invention. Further, the side surface b of the third active layer 3 is an inclined surface. In fig. 5, the side b of the third active layer includes a first edge contacting the second coating layer, and a second edge opposite to the first edge, wherein the second edge of the inclined surface b is inclined toward a direction away from the tab area a.

Of course, the first edge of the inclined surface b may also be inclined in a direction away from the tab region a.

When the third active layer comprises the inclined surface b, the distribution of the active layer around the tab region a can be controlled by adjusting the inclination direction of the inclined surface b and the inclination angle of the inclined surface b, and then the adjustment and control of the lithium precipitation phenomenon are realized.

The first active layer and the third active layer of the electrode of the present invention include a conductive agent and the like in addition to the active material and the binder, respectively.

For example, the conductive agent may be at least one selected from Acetylene Black (AB), conductive carbon black (Super-P), ketjen Black (KB), carbon Nanotube (CNT), and graphene.

The second aspect of the invention also provides a secondary battery including the electrode tab of the first aspect described above.

It should be emphasized here that the advantages of the present invention are all explained on the basis of the same areal density of the first active layer, the second coating layer and the third active layer.

The secondary battery of the present invention includes, but is not limited to, a lithium ion battery, a sodium ion battery.

Taking a lithium ion battery as an example, the lithium ion battery further comprises electrolyte and a diaphragm besides the electrode plates, wherein the diaphragm is arranged between the positive plate and the negative plate, and the electrolyte is filled between the positive plate and the negative plate.

The electrolyte selection is not strictly limited in the present invention, and may include one or more of the solvents commonly used in the current lithium battery electrolytes, and the electrolyte lithium salts commonly used in the current lithium ion electrolytes, such as: the solvent may be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methylethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ -butyrolactone, etc.; the lithium salt is selected from lithium hexafluorophosphate (LiPF) ₆ ) One or more of lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethylsulfonyl) imide (LiTFSI).

The material selection of the diaphragm is not strictly limited, and the diaphragm can be one of the diaphragm materials commonly used in the current lithium battery, such as a polypropylene diaphragm (PP), a polyethylene diaphragm (PE), a polypropylene/polyethylene double-layer composite film (PP/PE), a polyimide electrostatic spinning diaphragm (PI), a polypropylene/polyethylene/polypropylene three-layer composite film (PP/PE/PP), a cellulose non-woven fabric diaphragm and a diaphragm with a ceramic coating.

When the lithium ion battery is prepared, the positive plate, the diaphragm and the negative plate are wound or laminated to obtain a bare cell, and the bare cell is packaged into an aluminum-plastic film bag which is formed in a stamping mode in advance. And after the packaged battery is dried at 85 ℃, injecting the electrolyte into the dried battery, and after the battery is laid aside, formed and sealed for the second time, finishing the preparation of the lithium ion battery.

The secondary battery of the invention has outstanding advantages in safety performance and service life because of the electrode plate.

A third aspect of the present invention is to provide an apparatus whose driving source or energy storage source is the secondary battery of the foregoing second aspect.

For example, the device may be any device using a secondary battery as a driving source or an energy storage source, such as a mobile phone, a navigator, an unmanned aerial vehicle, or an electric vehicle.

The device of the invention has outstanding advantages in safety performance and service life because of the inclusion of the secondary battery, and has high customer satisfaction.

Hereinafter, the electrode sheet and the secondary battery according to the present invention will be described in detail by way of specific examples.

Example 1

The positive plate structure and the relative position relationship of the embodiment are similar to those in fig. 3, the tab region is located in the middle of the current collector functional surface, the two sides of the tab region are respectively the first active layer region and the second active layer region which are symmetrically distributed, and the first active layer region is close to the tab region. And the first active layer, the second coating layer and the third active layer on two sides of the tab region are respectively symmetrical.

Wherein the content of the first and second substances,

the current collector is an aluminum foil, the length of the current collector is 1000mm, and the width of the current collector is 90mm;

the total length of the first active layer was 40mm and the thickness was 80 μm;

the total length of the second coating was 950mm and the thickness was 5 μm

The third flexible layer has a total length of 950mm and a thickness of 80 μm.

The first active layer and the third active layer comprise the following components in percentage by mass: 97% of lithium cobaltate (the median particle diameter D50 is 15 μm), 1.5% of PVDF (the relative molecular weight is 800000), 1.5% of carbon black conductive agent;

the second coating comprises the following components in percentage by mass: 68% of lithium cobaltate (the median particle diameter D50 is 3 μm), 30% of PVDF (the relative molecular weight is 1200000) and 2% of carbon black conductive agent.

Example 2

The positive electrode sheet of this example was substantially the same as that of example 1 except that the composition of the second coating layer of this example was different from that of example 1.

The second coating of this embodiment comprises, by mass: 63% of lithium cobaltate (the median particle diameter D50 is 3 μm), 35% of PVDF (the relative molecular weight is 1200000) and 2% of carbon black conductive agent.

Example 3

The positive electrode sheet of this example was substantially the same as example 1 except that the thickness of the second coating layer was 1 μm.

Example 4

The positive electrode sheet of this example was substantially the same as example 1, except that the median particle diameter D50 of the lithium cobaltate in the second coating layer was 6 μm in this example.

Comparative example

The positive electrode sheet of this comparative example had the same structure as that of the positive electrode sheet in example 1, except that the first active layer was provided in both the first active layer region and the second active layer region of this comparative example, wherein the composition and thickness of the first active layer were the same as those of the first active layer in example 1, respectively.

Test examples

Matching the positive plate (after the pole lug is ultrasonically welded in the pole lug area) in the embodiment 1 with a graphite negative electrode (96% of artificial graphite, 1.5% of SBR adhesive, 1% of carbon black conductive agent and 1.5% of carboxymethyl cellulose), stacking the positive plate, the isolating film and the negative plate in sequence to ensure that the isolating film is positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a naked battery cell without liquid injection; placing the naked cell in an outer packaging foil, and adding electrolyte (1 mol/L LiPF) ₆ EC/DMC (volume ratio 1).

According to the same process, the number 2# -4# of the lithium ion battery comprising the positive plate of the embodiment 2-4 and the number 1a # of the lithium ion battery comprising the positive plate of the comparative example are respectively prepared.

The lithium batteries obtained in the above examples and comparative examples are fully charged (the charge cut-off voltage is 4.45V), and then subjected to a needling safety test, wherein the test method refers to the GB/T31485-2015 standard, 20 batteries are tested in parallel in each group, and the pass rate is calculated. The test results are shown in table 1.

TABLE 1

	Needle penetration Rate (%)
		Example 1	80％
Example 2	90％
		Example 3	60％
Example 4	75％
		Comparative example 1	50％

As can be seen from table 1, the second coating of the present invention can significantly improve the safety performance of the lithium ion battery.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The electrode plate is characterized by comprising a current collector, wherein the functional surface of the current collector comprises a tab region and an active layer region positioned on the periphery of the tab region; the lug area is positioned in the middle area in the length direction of the current collector, and both sides of the middle area in the length direction of the current collector are the active layer areas;

the total thickness of the third active layer and the second coating layer is greater than the thickness of the first active layer;

in the second coating layer, the relative molecular weight of the binder is 800000-2000000;

in the third active layer, the relative molecular weight of the binder is 400000-800000, and the mass percentage content is 1-5%;

the composition of the second coating layer is different from the composition of the third active layer;

the third active layer includes a side surface close to the first active layer, the side surface being an inclined surface.

2. The electrode sheet of claim 1, wherein the thickness of the second coating layer is 2-10 μm.

3. The electrode sheet according to claim 1 or 2, wherein the inorganic particles are selected from at least one of lithium cobaltate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, nickel cobalt manganese aluminum quaternary material, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganate, lithium-rich manganese base, alumina, boehmite.

4. The electrode sheet according to claim 3, wherein the inorganic particles have a median particle diameter D50 of 0.5 to 8 μm.

5. The electrode sheet according to any one of claims 1, 2 or 4, wherein the median particle diameter D50 of the active material in the first active layer is 10-20 μm; and/or the presence of a gas in the gas,

the median particle diameter D50 of the active material in the third active layer is 10 to 20 μm.

6. The electrode sheet according to claim 3, wherein the median particle diameter D50 of the active material in the first active layer is 10 to 20 μm; and/or the presence of a gas in the gas,

7. The electrode sheet according to claim 1, wherein the binder in the first active layer is 1-2% by mass of the first active layer; and/or the presence of a gas in the atmosphere,

the mass percentage of the binder in the third active layer is 1-2%.

8. An electrode sheet as defined in any one of claims 1, 2, 4, 6 or 7, wherein the thickness of the second coating layer is less than the thickness of the first active layer.

9. The electrode sheet of claim 3, wherein the thickness of the second coating layer is less than the thickness of the first active layer.

10. The electrode sheet of claim 5, wherein the thickness of the second coating layer is less than the thickness of the first active layer.

11. A secondary battery comprising the electrode tab according to any one of claims 1 to 10.

12. A device characterized in that a drive source or an energy storage source of the device is the secondary battery according to claim 11.