CN211088397U

CN211088397U - Secondary battery and pole piece thereof

Info

Publication number: CN211088397U
Application number: CN202020013754.1U
Authority: CN
Inventors: 张芹
Original assignee: Shenzhen Haihong New Energy Technology Co ltd
Current assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2020-01-03
Filing date: 2020-01-03
Publication date: 2020-07-24
Anticipated expiration: 2030-01-03

Abstract

The application provides a secondary battery and a pole piece thereof, belonging to the technical field of secondary batteries. The conductive layer of the current collector in the pole piece of the secondary battery comprises a first area and a second area, and the thickness of the first area is larger than that of the second area. The active material layer is coated on the second region and a portion of the first region near the second region. This secondary battery's pole piece, the regional utmost point ear district that does not coat the active material layer in first region, utmost point ear district thickness is thicker and is used for connecting utmost point ear, the second region and the first regional part that is close to the second region are as coating the district, be used for coating the active material layer, can make the ability reinforcing of overflowing of utmost point ear district and utmost point ear department, also can make the ability reinforcing of overflowing of utmost point ear district and coating district, improve the holistic conducting capacity of pole piece, reduce the internal resistance of electric core, improve the 3C capacity retention rate of electric core, and the electric core of same volume, can coat more active material layers, improve the energy density of electric core.

Description

Secondary battery and pole piece thereof

Technical Field

The application relates to the technical field of secondary batteries, in particular to a secondary battery and a pole piece thereof.

Background

Generally, a composite current collector of a secondary battery comprises an insulating layer and two conductive layers respectively arranged on two surfaces of the insulating layer, generally, the conductive layer is divided into two regions, one region is a pole ear region and is used for connecting a metal foil (pole ear), and after the pole ear region is welded with the pole ear, current on a pole piece is guided and collected to a pole through the pole ear; the other region is a coating region for coating an active material layer.

The inventors have found that the over-current capacity between the tab region and the tab is insufficient.

SUMMERY OF THE UTILITY MODEL

An object of this application is to provide a secondary battery and pole piece thereof, not only can improve the ability of overflowing of utmost point ear district and utmost point ear department, can also make the ability of overflowing reinforcing in utmost point ear district and coating district, improve the holistic electrically conductive ability of pole piece, improve the energy density of electric core.

In a first aspect, an embodiment of the present application provides a pole piece of a secondary battery, including a current collector and an active material layer. The current collector comprises an insulating layer and two conducting layers positioned on two surfaces of the insulating layer, each conducting layer comprises a first area and a second area, and the thickness of the first area is larger than that of the second area. The active material layer is coated on the second region and a portion of the first region near the second region.

In the current collector, the region for connecting the tabs (the region of the first region without the active material layer) is the tab region, and because the first region is thick, after the tab region is connected with the tabs, the overcurrent capacity between the tab region and the tabs can be ensured. The region (the second region and the part of the first region close to the second region) coated with the active material layer is a coating region, the first region is thicker, the second region is thinner, and the part of the thicker region close to the thinner region and the thinner region are coated with the active material layer, so that the overcurrent capacity between the thinner region of the coating region and the thicker region of the coating region can be enhanced, the conductive capacity of the whole pole piece is improved, the internal resistance of the battery cell is reduced, and the capacity retention rate of the battery cell 3C is improved. And because the thickness of the second area is reduced, correspondingly, the thickness of the active material layer at the second area is increased, and more active material layers can be coated on the battery core with the same volume so as to improve the energy density of the secondary battery.

In one possible embodiment, the active material layer extends from a boundary between the first region and the second region to the first region by a distance of 1 to 5 mm.

The pole lug area can be effectively connected with the pole lug, the overcurrent capacity between a thicker area and a thinner area in the coating area can be considered under the condition that the overcurrent capacity of the pole lug and the pole lug area is ensured, and the conductive capacity of the pole piece is further improved.

In one possible embodiment, the maximum thickness difference between the first region and the second region is 1-600 nm; optionally, the maximum thickness difference between the first region and the second region is 200-500 nm.

The difference in thickness between the two regions can be made within a suitable range so that the flow-through capability between the thicker region and the thinner region in the coating region is stronger and the active material layer at the second region is made uniform in thickness.

In one possible embodiment, the second region includes a first subregion and a second subregion, the thickness of the first region is greater than that of the second subregion, the first subregion is located between the first region and the second subregion, the first subregion becomes thicker gradually along the direction from the second subregion to the first region, and the second subregion, the first subregion and the portion of the first region close to the first subregion are all coated with the active material layer.

First subregion thickens gradually along the direction of second subregion to first region, can avoid two conducting layers of mass collector to appear the face defects such as fold, drum muscle to first subregion department coating has the active material layer, can make the ability of overflowing of coating district become strong gradually along the direction of keeping away from utmost point ear district to utmost point ear district, so that the conducting property of pole piece is stronger, and the conducting property of each part can both be satisfied.

In one possible embodiment, a boundary between the first region and the first sub-region is a first boundary, a boundary between the first sub-region and the second sub-region is a second boundary, and a surface of the first sub-region, which is away from the insulating layer, protrudes from the reference surface with a surface passing through the first boundary and the second boundary as the reference surface.

If the first subregion that becomes thicker gradually satisfies above-mentioned condition, can make the discharge capacity of pole piece better, energy density is higher.

In a possible embodiment, the pole piece is a negative pole piece, the conductive layer includes a functional layer and a protective layer that are overlapped, a surface of the functional layer that faces away from the protective layer is disposed on a surface of the insulating layer, a thickness of the functional layer at the first region is greater than a thickness of the functional layer at the second region, and a surface of the protective layer at the second region and a surface of the protective layer at the first region that is close to the second region are both coated with a negative active material layer.

The functional layer mainly plays a conductive role, the protective layer protects the functional layer, and the functional layer is of a structure with different thicknesses and is more favorable for improving the conductive capability of the whole pole piece.

In one possible embodiment, the thickness of the functional layer at the first region is 100 to 2500nm, and the thickness of the functional layer at the second region is 50 to 2000 nm; optionally, the thickness of the functional layer in the first region is 600-1500 nm, and the thickness of the functional layer in the second region is 300-1000 nm.

Through the functional layer thickness of injecing first region and second region department respectively, can make thinner region (second region) bear the weight of active material layer to can guarantee certain overcurrent capacity, and the utmost point ear district of first region can be firm connects utmost point ear, and guarantees the overcurrent capacity in utmost point ear and utmost point ear district.

In one possible embodiment, the second region includes a first subregion and a second subregion, the thickness of the first region is greater than that of the second subregion, the first subregion is located between the first region and the second subregion, the first subregion becomes thicker gradually along the direction from the second subregion to the first region, and the surface of the protective layer at the second subregion, the surface of the protective layer at the first subregion, and the surface of the protective layer at the first region near the first subregion are coated with the negative electrode active material layer.

The film surface defects of folds, ribs and the like of the two functional layers of the current collector and the protective layer on the functional layers can be avoided.

In one possible embodiment, an adhesive layer is also provided between the functional layer and the insulating layer.

The arrangement of the bonding layer improves the connection strength of the functional layer and the insulating layer, and prevents the functional layer from being peeled off from the insulating layer.

In a second aspect, embodiments of the present application provide a secondary battery, including a pole piece of the secondary battery.

The pole piece with higher overcurrent capacity is used, so that the internal resistance of the battery cell is reduced, the 3C capacity retention rate of the battery cell is improved, the secondary battery with higher energy density is obtained, and the manufacturing cost of the secondary battery can be reduced.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments are briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive efforts and also belong to the protection scope of the present application.

Fig. 1 is a schematic structural diagram of a first layer of a negative electrode tab provided in an embodiment of the present application;

fig. 2 is a schematic view of a first sub-region of a negative electrode current collector provided in an embodiment of the present application;

FIG. 3 is a schematic view of a first structure of a baffle according to an embodiment of the present disclosure;

fig. 4 is a schematic view of a second layer structure of a negative electrode tab provided in an embodiment of the present application;

fig. 5 is a schematic view of a second sub-region of a negative electrode current collector provided in an embodiment of the present application;

fig. 6 is a cross-sectional view of a surface of a functional layer of a negative electrode current collector away from an insulating layer according to an embodiment of the present disclosure;

FIG. 7 is a second structural schematic diagram of a baffle according to an embodiment of the present disclosure;

fig. 8 is a schematic view of a third layer structure of a negative electrode tab provided in an embodiment of the present application;

fig. 9 is a schematic diagram of a third partial area of the negative electrode current collector provided in the embodiment of the present application.

Icon: 10-a negative current collector; 11-an insulating layer; 12-a tie layer; 13-a functional layer; 14-a protective layer; 15-a first region; 16-a second region; 161-a first sub-region; 162-a second sub-region; 20-an active material layer; 30-a baffle plate; 31-a hollowed-out part; 32-shielding part.

Detailed Description

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

The secondary battery comprises an electrode assembly and a shell, wherein the shell comprises a shell and a top cover plate, the electrode assembly is arranged in the shell, the top cover plate is covered on the shell, and a positive pole column and a negative pole column are fixed on the top cover plate. The electrode assembly includes a pole piece of the secondary battery, wherein the pole piece of the secondary battery includes a positive pole piece and a negative pole piece. The current on the positive pole piece is collected on the positive pole column through the first tab, and the current on the negative pole piece is collected on the negative pole piece through the second tab.

The current collector in positive pole piece and the negative pole piece all includes two conducting layers on insulating layer and insulating layer two surfaces, and the conducting layer divide into coating district and utmost point ear district, and the coating district is used for coating active substance layer, and utmost point ear district is used for connecting utmost point ear. The inventor finds that under the condition that the thicknesses of a tab area and a coating area of a conductive layer are the same, if the thicknesses of the tab area and the coating area are both thinner, the overcurrent capacity cannot be ensured at the joint of the tab area and a tab; if the thickness of both the tab region and the coating region is relatively thick, the flow capacity of the coating region is too high, wasting material.

In order to better collect the current on the positive pole piece on the positive pole, the current on the negative pole piece can be better collected on the negative pole, the over-design of the overcurrent capacity of the coating area is avoided, the structures of the positive pole piece and the negative pole piece are improved, the improvement principle of the positive pole piece and the improvement principle of the negative pole piece (the pole pieces of the secondary battery comprise the positive pole piece and the negative pole piece) are the same, the negative pole piece is taken as an example for explanation, and the specific improvement mode is as follows:

referring to fig. 1 to 8, the method for preparing the negative electrode plate includes the following steps:

s10, an insulating layer 11 (base film) is provided. Wherein, insulating layer 11 is the flexible film material, and insulating layer 11 plays the effect of basic support.

Alternatively, the insulating layer 11 (base film) may be PP (Polypropylene), BOPP (Biaxially oriented Polypropylene film), Biaxially oriented Polypropylene film, Biaxially oriented BOPP, PE (Polyethylene), OPP (O-phenylphenol), PET (Polyethylene terephthalate), PI (Polyimide), PS (Polystyrene), PPs (polyphenylene sulfide), CPP (Cast Polypropylene film), Cast Polypropylene), PEN (Polyethylene naphthalate) polyester acrylate), PVC (Polyvinyl chloride), non-woven fabric, or the like.

Further, the thickness of the insulating layer 11 may be 1.2 to 12 μm, and the thickness of the insulating layer 11 may be 2 to 6 μm. For example: the thickness of the insulating layer 11 is 1.2 μm, 2 μm, 4 μm, 6 μm or 12 μm.

S20, adhesive layers 12 are provided on both surfaces of the insulating layer 11. Alternatively, the adhesive layer 12 may be deposited on both surfaces of the insulating layer 11. The thickness of the bonding layer 12 may be 1 to 100nm, and optionally, the thickness of the bonding layer 12 may be 3 to 40 nm. For example: the thickness of the adhesive layer 12 is 2nm, 3nm, 10nm, 40nm or 100 nm. In other embodiments, the adhesive layer 12 may not be provided.

The adhesive layer 12 may be a metallic layer or a non-metallic layer. When the adhesive layer 12 is a metal layer, the metal layer may be a metal plating film including one of Ni, Cr, a Ni alloy, and a Cr alloy. For example: the bonding layer 12 is a metal Ni plating film, or the bonding layer 12 is a metal Cr plating film, or the bonding layer 12 is a Ni alloy plating film, or the bonding layer 12 is a Cr alloy plating film.

When the adhesion layer 12 is a Ni alloy plating film, the Ni alloy may be an NiCu alloy, an NiCr alloy, or an NiV alloy. Further, if the Ni alloy coating is an NiCu alloy coating, the NiCu alloy consists of 20-40% of Ni and 60-80% of Cu in percentage by mass; if the Ni alloy coating is an NiCr alloy coating, the NiCr alloy consists of 10-30 percent of Ni and 70-90 percent of Cr according to mass percentage; if the Ni alloy coating is NiV alloy, the NiV alloy consists of 80-95% of Ni and 5-20% of V in percentage by mass.

When the bonding layer 12 is a Cr alloy plating film, the Cr alloy may be a CrCu alloy, a CrV alloy or a CrCo alloy. Further, if the Cr alloy coating is a CrCu alloy, the CrCu alloy consists of 10-40% of Cr and 60-90% of Cu in percentage by mass; if the Cr alloy coating film is a CrV alloy, the CrV alloy consists of 40-80% of Cr and 20-60% of V in percentage by mass; if the Cr alloy coating is a CrCo alloy, the CrCo alloy consists of 60-90% of Cr and 10-40% of Co by mass percent.

When the bonding layer 12 is a non-metal layer, the non-metal layer may be a non-metal plating film including PTFE (polytetrafluoroethylene), PP (Polypropylene), PE (polyethylene), SiC, Si₃N₄、SiO_x(1.5≤x≤2)、AlO_x(1≤x≤1.5)、AlO_xAnd melamine.

Alternatively, the adhesive layer 12 may be deposited on the surface of the base film, and the method of depositing the adhesive layer 12 may be: magnetron sputtering, high-frequency heating evaporation in crucible, resistance heating evaporation, electron gun-accelerated electron beam thermal evaporation, and chemical vapor deposition. The embodiments of the present application are not limited as long as the method capable of forming the adhesive layer 12 is within the scope of the present application.

S30, the functional layer 13 is formed on the surface of the adhesive layer 12. The provision of the adhesive layer 12 can improve the bonding strength between the insulating layer 11 and the functional layer 13, and prevent the functional layer 13 from peeling off from the insulating layer 11. In the embodiment of the present application, the functional layer 13 is disposed on the surface of the bonding layer 12 away from the insulating layer 11, the functional layer 13 mainly plays a role in conducting electricity, and the protective layer 14 is disposed on the surface of the functional layer 13 away from the bonding layer 12.

Fig. 1 is a schematic structural diagram of a first layer of a negative electrode tab provided in an embodiment of the present application; fig. 2 is a schematic view of a first sub-region of a negative electrode current collector provided in an embodiment of the present application. Referring to fig. 1 and fig. 2, each of the conductive layers includes a first region 15 and a second region 16 (the dotted boxes in fig. 2 are the first region 15 and the second region 16, respectively), and the thickness of the first region 15 is greater than that of the second region 16. The difference in thickness between the first region 15 and the second region 16 is that the functional layer 13 at different positions has a difference in thickness. That is, the thickness of the functional layer 13 at the first region 15 is greater than the thickness of the functional layer 13 at the second region 16.

Optionally, the maximum thickness difference between the first region 15 and the second region 16 is 1-600 nm. Optionally, the maximum thickness difference between the first region 15 and the second region 16 is 200-500 nm. That is, the maximum thickness difference between the functional layer 13 at the first region 15 and the functional layer 13 at the second region 16 is 1 to 600nm, and optionally, the maximum thickness difference between the functional layer 13 at the first region 15 and the functional layer 13 at the second region 16 is 200 to 500 nm.

Further, the thickness of the functional layer 13 in the first region 15 is 100 to 2500nm, and the thickness of the functional layer 13 in the second region 16 is 50 to 2000 nm. Optionally, the thickness of the functional layer 13 in the first region 15 is 600nm to 1500nm, and the thickness of the functional layer 13 in the second region 16 is 300nm to 1000 nm.

For example: the thickness of the functional layer 13 at the first region 15 is 600nm, and the thickness of the functional layer 13 at the second region 16 is 300 nm; the thickness of the functional layer 13 at the first region 15 is 1500nm, and the thickness of the functional layer 13 at the second region 16 is 900 nm; the thickness of the functional layer 13 at the first region 15 is 1000nm, and the thickness of the functional layer 13 at the second region 16 is 500 nm; the thickness of the functional layer 13 at the first region 15 was 700nm, and the thickness of the functional layer 13 at the second region 16 was 699 nm; the thickness of the functional layer 13 at the first region 15 is 800nm, and the thickness of the functional layer 13 at the second region 16 is 600 nm; the thickness of the functional layer 13 at the first regions 15 is 2500nm and the thickness of the functional layer 13 at the second regions 16 is 2000 nm; or a thickness of 100nm at the first region and a thickness of 50nm at the second region.

In the embodiment of the present application, the first regions 15 and the second regions 16 are alternately arranged in sequence, that is, the deposited functional layer 13 is sequentially thin, thick, thin, and thick, which are alternately arranged in sequence. A wound battery or a laminated battery may be prepared.

In order to achieve a greater thickness of the functional layer 13 at the first area 15 than at the second area 16, there are several implementations, which are illustrated below by way of example (but not limited to the following three ways):

first, please refer to fig. 1 and fig. 2, the thickness variation between the first region 15 and the second region 16 is an abrupt process, that is, there is a thickness difference between the functional layer 13 in the first region 15 and the functional layer 13 in the second region 16, but the thickness difference is a fixed value, and the thickness difference between the functional layer 13 in the first region 15 and the functional layer 13 in the second region 16 is 1 to 600 nm. Optionally, the difference between the thickness of the functional layer 13 at the first region 15 and the thickness of the functional layer 13 at the second region 16 is 200-500 nm.

Fig. 3 is a schematic view of a first structure of a baffle 30 provided in an embodiment of the present application, in order to form the functional layer 13 of the first structure. Referring to fig. 1 to 3, optionally, a baffle 30 is disposed between the metal source and the portions of the composite film composed of the insulating layer 11 and the adhesive layer 12 corresponding to the first region 15 and the second region 16, the baffle 30 includes a shielding portion 32 and a hollow portion 31, and the ratio of the hollow portion 31 of the baffle 30 corresponding to the first region 15 is greater than the ratio of the hollow portion 31 of the baffle 30 corresponding to the second region 16.

Optionally, the hollowed-out portion 31 is a hole structure, in order to make the processing technology of the baffle 30 simple, a circular hole structure may be provided on the baffle 30 to form the hollowed-out portion 31, the hole diameter of each circular hole structure is consistent, the circular hole structures corresponding to the first region 15 of the baffle 30 are uniformly distributed, the circular hole structures corresponding to the second region 16 of the baffle 30 are also uniformly distributed, the number of the circular hole structures corresponding to the first region 15 of the baffle 30 is greater than the number of the circular hole structures corresponding to the second region 16 of the baffle 30, and thus the functional layer 13 with different thicknesses may be formed.

Of course, the shielding portion 32 corresponding to the first region 15 of the baffle 30 may be 0, and all the shielding portions 31 are hollow portions, that is, no baffle is disposed at the portion corresponding to the first region 15, and the metal source is more plated on the adhesive layer 12.

Secondly, fig. 4 is a schematic diagram of a second layer structure of the negative electrode plate provided in the embodiment of the present application; fig. 5 is a schematic view of a second sub-region of a negative electrode current collector provided in an embodiment of the present application; fig. 6 is a cross-sectional view of a surface of the functional layer 13 of the negative electrode current collector 10 away from the insulating layer 11 according to an embodiment of the present application. Referring to fig. 4-6, the thickness variation between the first region 15 and the second region 16 is a gradual process, that is, the thickness difference exists between the functional layer 13 in the first region 15 and the functional layer 13 in the second region 16, but the thickness difference varies within a certain range, and the maximum thickness difference h is 1 to 600 nm. Optionally, the maximum thickness difference h is 200-500 nm.

Optionally, the second region 16 includes a first sub-region 161 and a second sub-region 162 (the dotted square portions in fig. 4 are the first region 15, the first sub-region 161, and the second sub-region 162, respectively), the thickness of the first region 15 is greater than that of the second sub-region 162, the first sub-region 161 is located between the first region 15 and the second sub-region 162, and the first sub-region 161 becomes thicker gradually along the direction from the second sub-region 162 to the first region 15.

Due to the formation of the first sub-region 161, the second sub-region 162 to the first region 15 can be gradually thickened, so that the functional layer 13 can be prevented from generating film surface defects such as wrinkles and ribs at the boundary between the first region 15 and the second region 16, and the thickness protection layer 14 can be prevented from generating film surface defects.

The thickness difference h between the functional layer 13 at the first region 15 and the functional layer 13 at the second subregion 162 is 1 to 600 nm. Optionally, the thickness difference h between the functional layer 13 at the first region 15 and the functional layer 13 at the second subregion 162 is 200 to 500 nm. However, the functional layer 13 of the first sub-region 161 is a layer structure that becomes thicker gradually in the direction from the second sub-region 162 to the first region 15.

Further, a boundary between the first region 15 and the first sub-region 161 is a first boundary, that is, a boundary between the functional layer 13 at the first region 15 and the functional layer 13 at the first sub-region 161 is a first boundary; a boundary between the first sub-region 161 and the second sub-region 162 is a second boundary, and a boundary between the functional layer 13 in the first sub-region 161 and the functional layer 13 in the second sub-region 162 is a second boundary; with a surface passing through the first boundary line and the second boundary line as a reference surface, a surface of the first sub-region 161 remote from the insulating layer 11 protrudes from the reference surface.

Referring to fig. 6, optionally, a cross-section of the surface of the first sub-region 161 away from the insulating layer 11 is a curve, and the curve and the surface of the second sub-region 162 substantially form an included angle, wherein the included angle is a maximum angle α formed between a tangent of the curve and the surface of the second sub-region 162, and the included angle α may be 1 to 80 °, and further, the included angle α may be 1 to 30 °.

In other embodiments, the cross section of the surface of the first sub-region 161 away from the insulating layer 11 may also be a straight line.

Fig. 7 is a schematic diagram of a second structure of the stopper 30 provided in the embodiment of the present application, in order to form the functional layer 13 of the second structure. Referring to fig. 4 to 7, optionally, a baffle 30 is disposed between the metal source and the portions of the composite film composed of the insulating layer 11 and the adhesive layer 12 corresponding to the first region 15 and the second region 16, the baffle 30 includes a shielding portion 32 and a hollow portion 31, an occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the first region 15 is greater than an occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the second subregion 162, and an occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the first subregion 161 is gradually increased along a direction from the second subregion 162 to the first region 15.

Optionally, the circular hole structures at the corresponding first areas 15 of the baffle 30 are uniformly distributed, the circular hole structures at the corresponding second sub-areas 162 of the baffle 30 are also uniformly distributed, and the number of the circular hole structures at the corresponding first areas 15 of the baffle 30 is greater than the number of the circular hole structures at the corresponding second sub-areas 162 of the baffle 30. The number of the circular hole structures at the corresponding first sub-region 161 of the baffle 30 gradually increases, and the gradually increasing direction is along the direction from the second sub-region 162 to the first region 15.

Of course, in the second mode, the shielding portion 32 corresponding to the first region 15 of the baffle 30 may be 0, and all the shielding portions are the hollow portions 31, that is, no baffle is disposed at the portion corresponding to the first region 15, and the metal source is more plated on the adhesive layer 12.

Thirdly, fig. 8 is a schematic structural diagram of a third layer of the negative electrode tab provided in the embodiment of the present application; fig. 9 is a schematic diagram of a third partial area of the negative electrode current collector provided in the embodiment of the present application. Referring to fig. 8 and 9, the thickness variation between the first region 15 and the second region 16 is a gradual process (the dotted square blocks in fig. 8 are the first region 15 and the second region 16, respectively), that is, there is a thickness difference between the functional layer 13 in the first region 15 and the functional layer 13 in the second region 16, but the thickness difference changes at different positions of the second region 16, and the maximum thickness difference is 1 to 600 nm. Optionally, the maximum thickness difference is 200-500 nm.

Alternatively, the surface of the functional layer 13 facing away from the adhesive layer 12 in the second region 16 is of an arcuate concave configuration, the thickness being a gradual process throughout the second region 16. The maximum thickness difference between the functional layer 13 in the first region 15 and the functional layer 13 in the second region 16 is 1 to 600 nm. Optionally, the maximum thickness difference between the functional layer 13 at the first region 15 and the functional layer 13 at the second region 16 is 200-500 nm.

Since the thickness of the second region 16 gradually changes, film surface defects such as wrinkles and ribs can be prevented from occurring at the boundary between the first region 15 and the second region 16 of the functional layer 13, and film surface defects can be prevented from occurring in the thickness protective layer 14.

In order to form the functional layer 13 with the third structure, optionally, a baffle 30 is disposed between the metal source and the portions of the insulating layer 11 corresponding to the first region 15 and the second region 16, the baffle 30 includes a shielding portion 32 and a hollow portion 31, an occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the first region 15 is greater than an occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the second region 16, the occupation ratio of the hollow portion 31 of the baffle 30 corresponding to the second region 16 gradually changes, and the occupation ratio gradually increases from the portion of the baffle 30 corresponding to the second region 16 to the portion of the baffle 30 corresponding to the first region 15.

Optionally, the circular hole structures at the corresponding first regions 15 of the baffle 30 are uniformly distributed, the circular hole structures at the corresponding second regions 16 of the baffle 30 gradually change, and the number of the circular hole structures at the corresponding first regions 15 of the baffle 30 is greater than the number of the circular hole structures at the corresponding second regions 16 of the baffle 30. The number of the circular hole structures of the baffle 30 corresponding to the second area 16 is gradually increased, and the gradually increasing direction is along the direction from the second area 16 to the first area 15.

Of course, in the third mode, the shielding portion 32 corresponding to the first region 15 of the baffle 30 may be 0, and all the shielding portions are the hollow portions 31, that is, no baffle is disposed at the portion corresponding to the first region 15, and the metal source is more plated on the adhesive layer 12.

In the embodiment of the present application, the functional layer 13 mainly having the conductive function is a metal layer, and optionally, a metal Cu layer. Further, it may be a metallic Cu plating. For depositing the functional layer 13 on the surface of the adhesive layer 12, the deposition method of the functional layer 13 is not limited, and the method is within the scope of the present application as long as the above structure can be achieved.

S40, forming a protective layer 14 on the surface of the functional layer 13 away from the adhesive layer 12, where the protective layer 14 is mainly used to protect the functional layer 13, so as to prevent the functional layer 13 from being oxidized and even falling off, and prevent the functional layer 13 from being damaged. In the embodiment of the present application, the conductive layer includes the functional layer 13 and the protective layer 14 that are overlapped, and both the functional layer 13 and the protective layer 14 are made of conductive materials. The thickness of the protective layer 14 is 2 to 100nm, and optionally, the thickness of the protective layer 14 is 3 to 20 nm. For example: the thickness of the protective layer 14 is 2nm, 3nm, 10nm, 20nm or 100 nm.

The protective layer 14 may be a metal layer or a non-metal layer. When the protective layer 14 is a metal layer, the metal layer includes one of Ni, Cr, a Ni alloy, and a Cr alloy. For example: the protective layer 14 is a metal Ni layer, or the protective layer 14 is a metal Cr layer, or the protective layer 14 is a Ni alloy layer, or the protective layer 14 is a Cr alloy layer.

When the protective layer 14 is a Ni alloy layer, the Ni alloy layer may be a NiCu alloy layer, an NiCr alloy layer, or an NiV alloy layer. Further, if the Ni alloy layer is an NiCu alloy layer, the NiCu alloy layer consists of 20-40% of Ni and 60-80% of Cu in percentage by mass; if the Ni alloy layer is an NiCr alloy layer, the NiCr alloy layer consists of 10-30 percent of Ni and 70-90 percent of Cr according to mass percentage; if the Ni alloy layer is a NiV alloy layer, the NiV alloy layer consists of 80-95% of Ni and 5-20% of V in percentage by mass.

When the protective layer 14 is a Cr alloy layer, the Cr alloy layer may be a CrCu alloy layer, a CrV alloy layer, or a CrCo alloy layer. Further, if the Cr alloy layer is a CrCu alloy layer, the CrCu alloy layer consists of 10-40% of Cr and 60-90% of Cu in percentage by mass; if the Cr alloy layer is a CrV alloy layer, the CrV alloy layer consists of 40-80% of Cr and 20-60% of V in percentage by mass; if the Cr alloy layer is a CrCo alloy, the CrCo alloy layer consists of 60-90% of Cr and 10-40% of Co according to mass percentage.

When the protective layer 14 is a non-metallic layer, the non-metallic layer is a glucose complex layer or a potassium dichromate layer. For example: the protective layer 14 is a glucose complex layer or the protective layer 14 is a potassium dichromate layer.

Alternatively, the protective layer 14 is deposited on the surface of the functional layer 13, and the method for depositing the protective layer 14 may be: magnetron sputtering, high-frequency heating evaporation in crucible, resistance heating evaporation, electron gun-accelerated electron beam evaporation, chemical vapor deposition, water electroplating, and surface coating. The embodiments of the present application are not limited as long as the method capable of forming the protective layer 14 is within the scope of the present application.

And forming a negative electrode current collector 10 in steps S10 to S40, wherein the thickness of the functional layer 13 in the first region 15 is different from that of the functional layer 13 in the second region 16, so that the conductive layer in the first region 15 is different from that in the second region 16, the sheet resistance of the film in the first region 15 is 100 to 5m Ω, the sheet resistance of the film in the second region 16 is 300 to 10m Ω, and the sheet resistivity of the film is 1.8 × 10^-8～2.5×10^-8Omega.m; film surfaceThe longitudinal fracture elongation and the film surface transverse fracture elongation are not less than 3%; the longitudinal tensile strength of the film surface and the transverse tensile strength of the film surface are not less than 200 MPa; the surface tension test dyne value is more than or equal to 38.

S50, the negative electrode active material layer 20 is coated on the surface of the functional layer 13. In step S10 to step S40, the negative electrode current collector 10 is formed, and in step S50, the negative electrode active material layer 20 is coated on the negative electrode current collector 10, thereby obtaining a negative electrode tab.

Here, the anode active material layer 20 is applied to the second region 16 and a portion of the first region 15 near the second region 16. That is, the negative electrode active material layer 20 is applied to the protective layer 14 of the second region 16 and the portion of the first region 15 near the protective layer 14 of the second region 16. That is, the anode active material layer 20 is coated on the protective layer 14, and the active material layer 20 is coated on the protective layer 14 corresponding to the second region 16, and the active material layer 20 is coated on the portion of the protective layer 14 corresponding to the first region 15, which is close to the second region 16.

In the negative electrode current collector 10, the region to which the tab is connected (the region of the first region 15 not coated with the active material layer 20) is the tab region, and since the functional layer 13 of the first region 15 is thick, after the tab region is connected to the tab, the overcurrent capacity between the tab region and the tab can be ensured. The region (the second region 16 and the part of the first region 15 close to the second region 16) coated with the active material layer 20 is a coating region, since the functional layer 13 of the first region 15 is thicker and the functional layer 13 of the second region 16 is thinner, and the part of the thicker region close to the thinner region and the thinner region are coated with the active material layer 20, the overcurrent capacity between the thinner region of the coating region and the thicker region of the coating region can be enhanced, so that the electric conductivity of the whole pole piece can be improved, and the energy density of the secondary battery can be improved.

Alternatively, the distance from the boundary between the first region 15 and the second region 16 to the first region 15 of the negative electrode active material layer 20 is 1 to 5 mm. For example: the distance that the anode active material layer 20 extends from the boundary between the first region 15 and the second region 16 to the first region 15 is 1mm, 2mm, 3mm, 4mm, or 5 mm.

Further, the surface of the negative electrode active material layer 20 facing away from the protective layer 14 is a flat surface.

If the anode active material layer 20 corresponds to the first structure in step S30, the anode active material layer 20 is coated on the protective layer 14 at the second region 16 and the protective layer 14 at the first region 15 near the second region 16, and the anode active material layer 20 is a sudden process, suddenly thinned, from the second region 16 to the first region 15.

If the anode active material layer 20 corresponds to the second structure in step S30, the second sub-region 162, the first sub-region 161, and the portion of the first region 15 close to the first sub-region 161 are all coated with the active material layer 20. The anode active material layer 20 is coated on the protective layer 14 at the second sub-region 162, the protective layer 14 at the first sub-region 161, and the protective layer 14 at the first region 15 near the first sub-region 161, and the anode active material layer 20 is gradually thinned in a process from the second sub-region 162 to the first region 15. And the active substance layer 20 is coated on the first sub-region 161, so that the overcurrent capacity of the coating region gradually becomes stronger along the direction from the tab region to the tab region, the conductive capacity of the pole piece is stronger, and the conductive capacity of each part can be satisfied.

If the anode active material layer 20 corresponds to the third structure in step S30, the anode active material layer 20 is coated on the protective layer 14 at the second region 16 and the protective layer 14 at the first region 15 near the second region 16, and the anode active material layer 20 is a gradual process at the second region 16, gradually thinning, and the side of the anode active material layer 20 contacting the protective layer 14 is an arc-shaped face structure. The overcurrent capacity of the coating area is gradually strengthened along the direction away from the lug area to the lug area, so that the conductive capacity of the pole piece is stronger, and the conductive capacity of each part can be met.

In the present embodiment, the coating manner of the anode active material layer 20 may be formed by spraying the slurry on the surface of the protective layer 14 through a coating die, so that part of the surface of the protective layer 14 is coated with the anode active material layer 20.

Because the current collector in the second region 16 is thinner, and the thickness of the negative active material layer 20 in the second region 16 can be increased for the pole pieces with the same thickness, so that the energy density of the battery cell is improved. And the current collector in the first region 15 is thicker, so that the tab can be conveniently connected, the connection strength between the tab and the tab region is higher, and the overcurrent capacity between the tab region and the tab is higher. Because the negative electrode active material layer 20 is coated on the protective layer 14 at the second region 16 and also coated on the protective layer 14 at the first region 15 close to the second region 16, the overcurrent capacity at the junction of the first region 15 and the second region 16 can be improved, the conductivity of the whole pole piece can be improved, the internal resistance of the battery cell can be reduced, and the 3C capacity retention rate of the battery cell can be improved.

Therefore, the negative pole piece is used for preparing the secondary battery, so that the cost of the obtained secondary battery can be reduced by 3-30%, and the energy density of the battery cell can be improved by 0.5-2%.

Example 1

The preparation method of the negative pole piece comprises the following steps:

(1) a PET film having a thickness of 3.2 μm was used as the insulating layer 11 (base film).

(2) Bonding layers 12 are arranged on two surfaces of the insulating layer 11. NiCr is selected as a material of the bonding layers 12, NiCr alloy is composed of 80% of Ni and 20% of Cr, the NiCr alloy is manufactured into a target material for magnetron sputtering, a base film coil is placed in a vacuum coating machine, a vacuum chamber is sealed, and the vacuum chamber is gradually vacuumized until the vacuum degree reaches 5 × 10^-3Pa, adopting magnetron sputtering method, charging 500SCCM Ar gas at 20-30m/min, at 3 × 10^-1Pa, a 4nm coating, i.e., the adhesive layer 12, is formed on the moving base film with a target power set to 40 Kw.

(3) Forming a functional layer 13 on the surface of the bonding layer 12, placing the film roll with the bonding layer 12 into a double-sided vacuum coating machine, sealing the vacuum chamber, and gradually vacuumizing until the vacuum degree reaches less than 5 × 10^-2Pa, heating the copper with the purity of more than or equal to 99.9% by adopting a crucible high-frequency heating evaporation mode, arranging a water-cooling baffle plate (the structure of the water-cooling baffle plate is a first baffle plate 30 of the three baffle plates 30; the conveying direction of the coil relative to the baffle plate 30 is the direction indicated by an arrow in the figure) with the width requirement corresponding to the coil between the film of the evaporation coating area and the evaporation source, walking the film at the speed of 300m/min, gradually increasing the heating power of the crucible, continuously melting and evaporating the copper in the evaporation source, and forming a copper-plated layer on the surface of the film plated with the bonding layer 12. Due to the existence of the baffle, 25nm of copper is deposited at the position corresponding to the first area 15 every time, 20nm of copper is deposited at the shielded second area every time, the functional layer 13 with different thicknesses can be obtained by repeating 40 times, the thickness of the functional layer 13 corresponding to the first area 15 is 600nm, and the thickness of the functional layer 13 corresponding to the second area 16 is 300 nm.

(4) A protective layer 14 is formed on the surface of the functional layer 13 facing away from the adhesive layer 12. The protective layer 14 is non-metallic, and the non-metallic layer is a potassium dichromate layer. The method for depositing the protective layer 14 may be to place the roll material with the functional layer 13 into a roll-to-roll water electroplating device or apparatus, where the roll-to-roll water electroplating apparatus may be included in the water electroplating device in step S30, and immerse the material into the solution in the solution tank by winding the film, and the solution in the solution tank is dissolved with the proper concentration of potassium dichromate, and the proper winding and unwinding speed, current, concentration, pH value, and temperature are adjusted, so as to form a layer of coating, i.e., the protective layer 14, on the surface of the functional layer 13.

(5) The negative electrode active material layer 20 is coated on the protective layer 14, thereby obtaining a negative electrode sheet. The distance from the boundary between the first region 15 and the second region 16 to the first region 15 of the negative electrode active material layer 20 was 3 mm.

Example 2

(1) A BOPP film having a thickness of 3.6 μm was used as the insulating layer 11 (base film).

(2) Setting adhesive layers 12 on two surfaces of the insulating layer 11, selecting AlOx (x is more than 1 and less than or equal to 1.5) as the material of the adhesive layers 12, placing the base film coil in a vacuum coating machine, sealing the vacuum chamber, and gradually vacuumizing until the vacuum degree reaches less than 5 × 10^-2Pa, using resistive typeThe heating method is used as an evaporation source, compressed oxygen is introduced into an oxygen introducing structure obtained by an oxygen delivering mechanism near the evaporation source or between the evaporation source and the surface close to the tympanic membrane or near the main drum, and the ventilation quantity is adjusted. The evaporation source evaporation raw material is metal aluminum wire with the purity more than or equal to 99.9 percent, the winding and unwinding speed is adjusted, and evaporated atoms react with oxygen to form a layer of AlO on the moving base layer_x(x is more than or equal to 1 and less than or equal to 1.5), namely the bonding layer 12.

(3) The functional layer 13 is formed on the surface of the adhesive layer 12. The film coil stock plated with the conductive bonding layer 12 is placed in a reel-to-reel hydroelectric plating device, the square resistance of the film surface of the conductive bonding layer 12 is 0.5-1 omega, a water-cooling baffle (the structure of the water-cooling baffle is the structure of the second baffle 30 of the three baffles 30, wherein, relative to the baffles 30, the conveying direction of the coil stock is the direction indicated by the arrow in the figure) corresponding to the width requirement of the coil stock is arranged in a hydroelectric plating bath, and the proper winding and unwinding speed, current, copper ion concentration, brightener concentration, adjuvant concentration, pH value and electrolyte temperature are adjusted. 600nm copper can be deposited in the first area at a time, and 300nm copper can be deposited in the area shielded by the baffle at a time.

(4) A protective layer 14 is formed on the surface of the functional layer 13 facing away from the adhesive layer 12. The roll material with the functional layer 13 is placed into roll-to-roll surface coating equipment or device, the roll-to-roll surface coating device may be included in the equipment in step S30, or may be an independent set of equipment, the material is made to pass through the coating device by adopting a film winding and removing manner, the coating device can uniformly coat organic matter with oxidation resistance at a proper concentration on the surface of the functional layer 13, and a coating layer, that is, a protective layer 14, can be formed on the surface of the functional layer 13 by adjusting a proper winding and unwinding speed.

(5) The negative electrode active material layer 20 is coated on the negative electrode current collector 10, thereby obtaining a negative electrode sheet. The distance from the boundary between the first region 15 and the second region 16 to the first region 15 of the negative electrode active material layer 20 was 3 mm.

Example 3

Example 3 differs from example 2 in that: the structure of the water-cooled baffle plate used in the step (3) of the manufacturing method provided in example 3 is the structure of the third baffle plate 30 of the above-mentioned three baffle plates 30; wherein the conveying direction of the roll material is the direction indicated by the arrow in the figure with respect to the baffle 30. The other method steps are consistent.

Comparative example 1

Comparative example 1 differs from example 1 in that: in the case of coating the active material layer 20 in step (5) of the production method provided in comparative example 1, only the second region 16 is coated, and coating is not performed on the first region 15. Examples of the experiments

In order to examine the performance of the negative electrode sheets provided in examples 1 to 3 and comparative example 1. Firstly, preparing a battery cell: the volume of the inner cavity adopted in the experiment is 300cm³The aluminum shell of (2) is used for manufacturing the battery cell.

The anode and the cathode of each group adopt the same formula:

preparing a negative pole piece: the negative electrode sheets provided in examples 1 to 3 and comparative example 1 were used. After drying, cold pressing, trimming, slitting and cutting. The preparation method of the negative electrode slurry of the negative electrode plate comprises the following steps: mixing graphite, conductive carbon, styrene butadiene rubber and sodium carboxymethylcellulose according to the weight ratio of 97: 0.7: 1.5: 0.8 mass ratio in water.

Preparing a positive pole piece: mixing a positive electrode active substance, conductive acetylene black and polyvinylidene fluoride according to a ratio of 97: 1.5: 1.5 mass ratio in NMP, and coated on 14um aluminum foil. After drying, cold pressing, trimming, slitting and cutting.

Assembling the positive electrode, the negative electrode and the isolating membrane into a battery, putting the battery into an aluminum shell, and testing the capacity, the internal resistance and the rate performance after baking, electrolyte injection, sealing and formation.

The method for detecting the performance of the battery cell comprises the following steps:

internal resistance: testing the internal resistance of the 3.85V charging cell by adopting a daily internal resistance instrument;

the capacity is measured by charging the battery cell to 4.2V at a rate of 1C, then charging the battery cell to a constant voltage until the current is less than or equal to 0.05C, standing the battery cell for 5 minutes, then discharging the battery cell to 3.0V at a constant current of the rate of 1C to obtain a 1C capacity C1, then charging the battery cell to 4.2V at a rate of 1C, then charging the battery cell to a constant voltage until the current is less than or equal to 0.05C, standing the battery cell for 5 minutes, discharging the battery cell to 3.0V at a constant current of the rate of 3C to obtain a capacity retention rate of 3C capacity C3.3C which is C3/C1 × 100%, and detecting the capacity.

TABLE 1 Properties of the cells

	Internal resistance m omega of battery core	Capacity retention ratio of cell 3C
			Example 1	31	78％
Example 2	25	83％
			Example 3	23	88％
Comparative example 1	32	75％

As can be seen from table 1, compared with comparative example 1, the internal resistance of the battery cells provided in examples 1 to 3 is reduced, and the capacity retention rate of the battery cell 3C is increased, which indicates that the performance of the battery prepared by using the negative electrode plate provided in the present application is better.

Of course, the positive electrode plate can also be improved in the above manner, and a battery cell with better performance can be obtained by designing the conducting layer of the positive electrode plate with different thicknesses and the coating manner of the positive active material layer.

According to the above content, the electrode plate of the secondary battery and the preparation method thereof provided by the application have the beneficial effects that:

(1) the functional layer 13 in the first region 15 is thicker, the connection strength between the tab and the tab region (part of the first region 15) is enhanced, and the overcurrent capacity between the tab region and the tab is enhanced.

(2) The thickness of the functional layer 13 in the second area 16 is smaller, and the thickness of the functional layer 13 in most of the coating areas (the second area 16) is reduced, so that the use amount of the functional layer 13 in the second area 16 can be reduced, and the cost of the battery cell is reduced by 3-30%.

(3) For the same cell volume, the thickness of the functional layer 13 at the second region 16 is reduced, so that the thickness of the active material layer 20 coated at the second region 16 is increased, more active material can be contained, and the energy density of the cell is improved by 0.5-2%.

(4) Since the active material layer 20 is coated on the thin second region 16 and the thick first region 15 at the portion close to the second region 16, the overcurrent capacity between the thin region of the coating region and the thick region of the coating region can be enhanced, so that the conductive capacity of the whole pole piece is improved, the internal resistance of the battery cell is reduced, and the 3C capacity retention rate of the battery cell is improved.

(5) Through the arrangement of the first sub-region 161, the thickness of the functional layer 13 between the second sub-region 162 and the first region 15 is in a gradual change process, so that defects such as wrinkles and ribs formed at the boundary between the first region 15 and the second region 16 can be avoided, and the electric conductivity of the obtained pole piece is better.

The above description is only a few examples of the present application and is not intended to limit the present application, and various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pole piece for a secondary battery, comprising:

the current collector comprises an insulating layer and two conducting layers positioned on two surfaces of the insulating layer, each conducting layer comprises a first area and a second area, and the thickness of the first area is greater than that of the second area;

an active material layer applied to the second region and a portion of the first region adjacent to the second region.

2. The pole piece according to claim 1, wherein the active material layer extends from a boundary between the first region and the second region to the first region by a distance of 1 to 5 mm.

3. The pole piece of claim 1, wherein the maximum thickness difference between the first region and the second region is 1-600 nm;

optionally, the maximum thickness difference between the first region and the second region is 200-500 nm.

4. The pole piece according to any one of claims 1 to 3, wherein the second region comprises a first subregion and a second subregion, the thickness of the first region is greater than that of the second subregion, the first subregion is positioned between the first region and the second subregion, the first subregion becomes thicker gradually along the direction from the second subregion to the first region, and the second subregion, the first subregion and the part of the first region close to the first subregion are all coated with the active material layer.

5. The pole piece of claim 4, wherein a boundary between the first region and the first sub-region is a first boundary line, a boundary between the first sub-region and the second sub-region is a second boundary line, and a surface of the first sub-region, which is away from the insulating layer, protrudes from the reference surface with a surface passing through the first boundary line and the second boundary line as a reference surface.

6. The pole piece according to any one of claims 1 to 3, wherein the pole piece is a negative pole piece, the conductive layer comprises a functional layer and a protective layer which are overlapped, the surface of the functional layer facing away from the protective layer is arranged on the surface of the insulating layer, the thickness of the functional layer at the first area is larger than that of the functional layer at the second area, and the surface of the protective layer at the second area and the surface of the protective layer at the first area close to the second area are both coated with a negative pole active material layer.

7. The pole piece of claim 6, wherein the thickness of the functional layer at the first region is 100 to 2500nm and the thickness of the functional layer at the second region is 50 to 2000 nm;

optionally, the thickness of the functional layer at the first region is 600 to 1500nm, and the thickness of the functional layer at the second region is 300 to 1000 nm.

8. The pole piece of claim 6, wherein the second region comprises a first subregion and a second subregion, the thickness of the first region is greater than that of the second subregion, the first subregion is located between the first region and the second subregion, the first subregion becomes thicker gradually along the direction from the second subregion to the first region, and the surface of the protective layer at the second subregion, the surface of the protective layer at the first subregion, and the surface of the protective layer at the first region near the first subregion are coated with a negative electrode active material layer.

9. The pole piece of claim 6, wherein an adhesive layer is further disposed between the functional layer and the insulating layer.

10. A secondary battery comprising the electrode sheet for a secondary battery according to any one of claims 1 to 9.