Electrode sheet and battery

Abstract

Provided in the present application are an electrode sheet and a battery. Provided in the first aspect of the present application is an electrode sheet, comprising a current collector and a functional layer, wherein the current collector comprises a first surface and a second surface that are arranged opposite each other; the first surface comprises a first coating area, and the second surface comprises a second coating area; the functional layer is arranged on the first coating area and the second coating area of the current collector; the second coating area comprises a first area and a second area; and the thickness of the functional layer arranged in the second area is W1, the total thickness of the functional layer arranged in the first coating area and the first area is W2, and W1 / W2*100％≥70％. The electrode sheet provided in the present application is beneficial for improving the cycle performance of a battery.

Description

A pole piece and a battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 14, 2023, with application number 202311713765.5 and application name “A Pole and Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to a pole piece and a battery, and to the technical field of batteries. Background Art

[0003] Batteries, as energy storage devices, face increasing demands for performance with the rapid development of new energy. Electrodes, as crucial components of batteries, include current collectors, functional layers, and tabs. Tab glue is also applied to the tabs to prevent short circuits.

[0004] In most areas of the electrode, only the current collector and the functional layer are included, and the thickness of this area is relatively uniform. However, the thickness of the tab is generally higher than that of the functional layer, and tab glue is also pasted on the surface of the tab. As a result, the closer to the tab position, the more complex the electrode structure is, and the poorer the thickness uniformity is, which can easily affect the cycle performance of the battery.

[0005] Summary of the Invention

[0006] The present application provides a pole piece for improving the cycle performance of a battery.

[0007] The present application also provides a battery comprising the above-mentioned electrode.

[0008] In a first aspect, the present application provides a pole piece, comprising a current collector 1 and a functional layer 2, wherein the current collector 1 comprises a first surface a and a second surface b disposed opposite to each other, the first surface a comprising a first coating area 111, the second surface b comprising a second coating area 121, and the functional layer 2 is disposed on the first coating area 111 and the second coating area 121 of the current collector 1;

[0009] The second coating area 121 includes a first area 1211 and a second area 1212. The projection of the first area 1211 on the current collector 1 coincides with the projection of the first coating area 111 on the current collector 1. The projection of the second area 1212 on the current collector 1 is located outside the projection of the first coating area 111 on the current collector 1.

[0010] Along the thickness direction of the pole piece, the maximum thickness of the functional layer 2 arranged in the first coating area 111 is W1, the minimum thickness of the functional layer 2 arranged in the first area 1211 is W2, and the average thickness of the functional layer 2 arranged in the second area 1212 is W3, W3 / W1+W2≥0.7.

[0011] In a specific embodiment, at least a portion of the first region 1211 is bent in a direction toward the first coating area 111 to form a bent portion, and the bent portion is connected to the second region 1212 .

[0012] In a specific embodiment, along the thickness direction of the pole piece, the minimum thickness of the functional layer 2 located on the bent portion of the second surface b is equal to W2, and the maximum thickness is equal to W3;

[0013] The minimum thickness of the functional layer 2 located on the bending portion of the first surface a is 0, and the maximum thickness is equal to W1.

[0014] In a specific embodiment, the first surface a of the current collector further includes a first empty foil area 112, and the second surface b further includes a second empty foil area 122, and the projection of the second empty foil area 122 on the current collector 1 is located within the projection of the first empty foil area 112 on the current collector 1.

[0015] In a specific embodiment, the total area of ​​the second empty foil region 122 and the second region 1212 is not greater than the area of ​​the first empty foil region 112 .

[0016] In a specific embodiment, the area of ​​the second region 1212 is 10% to 100% of the area of ​​the first empty foil region 112 .

[0017] In a specific embodiment, the first empty foil area 112 or the second empty foil area 122 is connected to a tab 3 .

[0018] In a specific embodiment, the functional layer 2 includes a protective layer 21 and an active material layer 22, and the protective layer 21 and the active material layer 22 are sequentially stacked on the surface of the current collector 1;

[0019] Along the length direction of the electrode sheet, the distance between the active material layer 22 and the electrode tab 3 is D1, and the distance between the protective layer 21 and the electrode tab 3 is D2, where |D1-D2|≤0.5mm.

[0020] In a specific embodiment, the distance D2 between the protective layer 21 and the electrode tab 3 is smaller than the distance D1 between the active material layer 22 and the electrode tab 3 , and (D1-D2)≤0.1 mm.

[0021] In a specific embodiment, the second region 1212 includes a first side c, a second side d, and a third side e, and the first side c, the second side d, and the third side e form a tab connection region;

[0022] The distance difference between the protective layer 21 and the active material layer 22 and the first side c is D3, the distance difference between the protective layer 21 and the active material layer 22 and the second side d is D4, and the distance difference between the protective layer 21 and the active material layer 22 and the third side e is D5, D3>D4, D3>D5.

[0023] In a specific embodiment, along the width direction of the pole piece, the height difference of the current collector 1 located on both sides of the first side c is H1; along the length direction of the pole piece, the height difference of the current collector 1 located on both sides of the second side d is H2, and the height difference of the current collector 1 located on both sides of the third side e is H3, H1<H2, H1<H3.

[0024] A second aspect of the present application provides a battery comprising any of the above-mentioned pole pieces.

[0025] The pole piece provided in the present application increases the thickness of the functional layer in the second region to reduce the thickness difference between the functional layer and the pole lug, which helps to improve the uniformity of the pole piece thickness and improve the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0027] FIG1 is a schematic diagram of the structure of a pole piece provided by the prior art;

[0028] FIG2 is a schematic structural diagram of a pole piece provided in one embodiment of the present application;

[0029] FIG3 is a schematic diagram of partitions of the first surface of the current collector provided in one embodiment of the present application;

[0030] FIG4 is a schematic diagram of partitions of the second surface of the current collector provided in one embodiment of the present application;

[0031] FIG5 is a schematic structural diagram of a pole piece provided in another embodiment of the present application;

[0032] FIG6 is a schematic diagram of partitions of the first surface of the current collector provided in another embodiment of the present application;

[0033] FIG7 is a schematic diagram of partitions of the second surface of the current collector provided in another embodiment of the present application;

[0034] FIG8 is a schematic structural diagram of a pole piece provided in another embodiment of the present application;

[0035] FIG9 is a schematic structural diagram of a pole piece provided in another embodiment of the present application;

[0036] FIG10 is a schematic diagram of partitions of the second surface of the current collector provided in another embodiment of the present application;

[0037] FIG11 is a cross-sectional schematic diagram of a first side provided in yet another embodiment of the present application;

[0038] FIG12 is a schematic structural diagram of a functional layer provided in yet another embodiment of the present application;

[0039] FIG13 is a physical diagram of a tab connection area provided in one embodiment of the present application;

[0040] FIG14 is an EDS spectrum of a cross section of a pole piece near a first side provided in one embodiment of the present application;

[0041] FIG15 is an EDS spectrum of a cross section of a pole piece near the second side provided in one embodiment of the present application;

[0042] FIG16 is an EDS spectrum of a cross section of a pole piece near the third side provided in one embodiment of the present application;

[0043] FIG17 is an SEM image of a cross section of a tab welding region provided in one embodiment of the present application.

[0044] Description of reference numerals:

[0045] 1-current collector;

[0046] a-first surface;

[0047] b-second surface;

[0048] 111-first coating area;

[0049] 112-first empty foil area;

[0050] 121- second coating area;

[0051] 1211-First Area;

[0052] 1212-Second Area;

[0053] c-first side;

[0054] d-second side;

[0055] e-third side;

[0056] 122-second empty foil area;

[0057] 2-functional layer;

[0058] 21- protective layer;

[0059] 22-active material layer;

[0060] 3-Pole ear. DETAILED DESCRIPTION

[0061] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0062] The pole piece is an important component of the battery. Figure 1 is a structural schematic diagram of the pole piece provided by the prior art. As shown in Figure 1, the pole piece includes a current collector 1, a functional layer 2 arranged on the surface of the current collector 1, and a pole ear 3. Since the thickness of the pole ear 3 is generally higher than the thickness of the functional layer 2, and the pole ear glue is also pasted on the surface of the pole ear 3, the closer to the pole ear position, the more complex the pole piece structure is, the poorer the thickness uniformity is, and it is easy to affect the cycle performance of the battery; especially for the pole piece placed in the middle of the pole ear, how to adjust the pole piece structure and improve the cycle performance of the battery is a technical problem that needs to be solved urgently by those skilled in the art.

[0063] In order to solve the above technical problems, the first aspect of the present application provides a pole piece, as shown in Figures 2 to 4, the pole piece includes a current collector 1 and a functional layer 2, wherein the current collector 1 serves as a conductive substrate, including a first surface a and a second surface b arranged opposite to each other, the first surface a includes a first coating area 111, and the second surface b includes a second coating area 121, and the functional layer 2 is arranged on the first coating area 111 and the second coating area 121 of the current collector 1.

[0064] According to the different thicknesses of the functional layer 2 arranged on the second coating area 121, the second coating area 121 includes a first area 1211 and a second area 1212. The projection of the first area 1211 on the current collector 1 coincides with the projection of the first coating area 111 on the current collector 1. The first area 1211 and the first coating area 111 constitute a double-sided coating area, that is, the functional layer 2 is provided on both the upper and lower surfaces of the current collector 1; the projection of the second area 1212 on the current collector 1 is located outside the projection of the first coating area 111 on the current collector 1. The second area 1212 is a single-sided coating area, that is, only one surface in the second area of ​​the current collector 1 is provided with a functional layer 2.

[0065] Furthermore, the second region 1212 is located near the tab, and the first region 1211 is located away from the tab. For a pole piece placed in the middle of the tab, the second region 1212 is located on both sides of the tab, and the first region 1211 is located on the side of the second region 1212 away from the tab.

[0066] Those skilled in the art will appreciate that a pole piece is typically a long sheet, with its longer side being the length direction, its shorter side being the thickness direction, and the side between the longer and shorter sides being the width direction. The length, width, and thickness directions are perpendicular to each other. Referring to Figures 2 to 4 , in this application, the x-direction of the pole piece is the pole piece length direction, the z-direction is the pole piece thickness direction, and the y-direction is the pole piece width direction.

[0067] Along the thickness direction of the electrode, the maximum thickness of the functional layer 2 arranged in the first coating area 111 is W1, the minimum thickness of the functional layer 2 arranged in the first area 1211 is W2, and the average thickness of the functional layer 2 arranged in the second area 1212 is W3, W3 / (W1+W2)≥0.7, that is, the thickness of the functional layer in the single-sided coating area is not less than 70% of the total thickness of the functional layer in the double-sided coating area. By increasing the thickness of the functional layer in the second area, the height difference between the functional layer near the pole ear and the pole ear is compensated, which helps to improve the uniformity of the pole sheet thickness and improve the cycle performance of the battery.

[0068] In this application, the maximum thickness refers to the maximum value of the thickness of the functional layer 2 in the first coating area 111; the minimum thickness refers to the minimum value of the thickness of the functional layer 2 set in the first area 1211, and the average thickness refers to the average value of the thickness of the functional layer 2 set in the second area 1212.

[0069] During the electrode preparation process, a functional layer slurry is first prepared and coated on different areas of the current collector according to the thickness requirements. Subsequently, the electrode is rolled. During the rolling process, the functional layer 2 arranged in the second area 1212 of the current collector 1 will squeeze the current collector 1 downward, causing the second area 1212 to be recessed downward toward the first coating area 111, resulting in a recessed portion in the current collector 1. The space formed by the recessed portion can accommodate the functional layer 2 of the second area 1212, so that the functional layer 2 is located in the same plane away from the surface of the current collector 1, thereby ensuring the flatness of the electrode.

[0070] 2 , as the second region 1212 is recessed, at least a portion of the first region 1211 is bent toward the first coating area 111 to form a bent portion, which is connected to the second region 1212 .

[0071] Further, referring to Figure 2 , along the z-direction of the electrode sheet, the thickness of the functional layer 2 located on the bend of the second surface b ranges from a minimum value of W2 to a maximum value of W3. The thickness of the functional layer 2 located on the bend of the first surface a ranges from a minimum value of 0 to a maximum value of W1. That is, along the length of the current collector 1, the thickness of the functional layer 2 located on the bend of the second surface b gradually increases, while the thickness of the functional layer 2 located on the bend of the first surface a gradually decreases. This variation in the thickness of the functional layer in the bend helps improve the uniformity of the electrode sheet thickness and enhance the battery's cycling performance.

[0072] 3-4 , the first surface a of the current collector 1 further includes a first empty foil area 112 , and the second surface b further includes a second empty foil area 122 . The first empty foil area 112 or the second empty foil area 122 is used to connect the tab 3 .

[0073] Furthermore, the projection of the second empty foil area 122 on the current collector 1 is located within the projection of the first empty foil area 112 on the current collector 1 , that is, the length of the first empty foil area 112 is greater than the length of the second empty foil area 122 .

[0074] Furthermore, the total area of ​​the second empty foil area 122 and the second region 1212 is not greater than the area of ​​the first empty foil area 112. Furthermore, the area of ​​the second region 1212 is 10% to 100% of the area of ​​the first empty foil area 112.

[0075] When the area of ​​the second region 1212 is 100% of the area of ​​the first empty foil area 112, its structure is shown in Figures 5 to 7. It can be seen that the second surface b of the current collector 1 does not include the second empty foil area, that is, the area corresponding to the first empty foil area 112 is coated with the functional layer 2, which helps to increase the coating area of ​​the functional layer and improve the energy density of the battery.

[0076] As shown in FIG8 , the electrode sheet provided in the present application further includes a tab 3. One end of the tab 3 is connected to the surface of the current collector 1, and the other end extends outward along the y direction. The tab 3 is disposed in the first hollow foil region 112 or the second hollow foil region 122. Depending on the type of electrode sheet, different materials can be selected as the current collector 1 and the tab 3. For example, aluminum foil can be used as the current collector for the positive electrode sheet, while copper foil can be used as the current collector for the negative electrode sheet. The material for the tab 3 varies depending on the type of electrode sheet and can be metal materials such as copper, nickel, and aluminum.

[0077] Furthermore, in order to facilitate the preparation of the pole piece, the distance between the functional layer 2 and the pole tab 3 along the x direction of the pole piece is 0.5 to 4 mm.

[0078] In a specific embodiment, the functional layer 2 includes a protective layer 21 and an active material layer 22, which are sequentially stacked on the surface of the current collector 1. The provision of the protective layer 21 helps to reduce the probability of short circuit between the current collector and the electrode, thereby improving the safety of the battery. Based on the current coating process, the distances between the protective layer 21 and the active material layer 22 and the electrode 3 cannot be completely consistent. There is a situation where the protective layer 21 exceeds the active material layer 22, or the active material layer 22 exceeds the protective layer 21. However, both of the above situations are not conducive to improving battery performance. Specifically, when the protective layer 21 exceeds the active material layer 22, the thickness of the exceeding area is reduced compared with other areas. During the hot pressing process, the area is not subjected to sufficient force, resulting in an unreliable interface contact between the electrode and the diaphragm in this area. During the battery's charge and discharge cycle, the migration of ions is affected, resulting in a battery cycle failure. After a certain number of times, ions are precipitated, resulting in capacity loss; when the active material layer 22 exceeds the protective layer 21, this area is in direct contact with the current collector, and the electrons in this area are directly conducted from the current collector to the active material layer. Compared with most areas of the electrode, the electrons are conducted from the current collector to the protective layer and then to the active material layer. The electron conduction in this area is faster, and during the charging process, it is more conducive to the escape of ions, resulting in better positive electrode kinetics in this area, thereby increasing the ion embedding pressure of the corresponding electrode. Compared with the negative electrode in other areas, the risk of ion precipitation of the negative electrode corresponding to this area is increased, affecting the cycle stability of the battery.

[0079] Based on the above reasons, the present application keeps the edges of the protective layer 21 and the active material layer 22 close to the tab 3 as consistent as possible. Specifically, the difference in distance between the protective layer 21 and the active material layer 22 and the tab 3 is no more than 0.5 mm.

[0080] Furthermore, the distance D2 between the protective layer 21 and the tab 3 is smaller than the distance D1 between the active material layer 22 and the tab 3 , and the difference in distances between the protective layer and the active material layer and the tab ( D1 − D2 ) is no greater than 0.1 mm.

[0081] In a specific embodiment, as shown in Figures 9 to 12, when the width of the second empty foil area 122 is smaller than the width of the current collector 1, the second region 1212 includes a first side c, a second side d, and a third side e. The first side c, the second side d, and the third side e form the second empty foil area 122 for placing the tab 3.

[0082] The difference in distance between the protective layer 21 and the active material layer 22 and the first side c is D3, the difference in distance between the protective layer 21 and the active material layer 22 and the second side d is D4, and the difference in distance between the protective layer 21 and the active material layer 22 and the third side e is D5, where D3>D4 and D3>D5. In other words, the length of the protective layer 21 exposed below the tab should be greater than the length of the protective layer exposed on both sides of the tab. The lengths D4 and D5 of the protective layer exposed on both sides of the tab can be the same or different.

[0083] Furthermore, to avoid wrinkles in the tab connection area caused by deformation in different directions and to improve the flatness of the electrode sheet, the flatness of the first side c is better than that of the second side d and the third side e. Continuing to refer to Figures 9 and 11, along the y-direction of the electrode sheet, the height difference of the current collector 1 on both sides of the first side c is H1; along the length direction of the electrode sheet, the height difference of the current collector 1 on both sides of the second side d is H2, and the height difference of the current collector 1 on both sides of the third side e is H3, where H1 < H2 and H1 < H3.

[0084] In a specific embodiment, the protective layer 21 includes inorganic particles and a binder, wherein the inorganic particles are materials that do not contain active lithium, including at least one of an insulating material and a conductive material; the insulating material is selected from one or more of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, cobalt oxide, iron phosphate, aluminum phosphate, iron metaphosphate, and aluminum metaphosphate; the conductive material is selected from at least one of ATO (Sb-doped SnO2), FTO (F-doped SnO2), ITO (Sn-doped In2O3), and AZO (Al-doped ZnO), or at least one of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, cobalt oxide, iron phosphate, aluminum phosphate, iron metaphosphate, aluminum metaphosphate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium titanate coated with at least one of carbon black, carbon nanotubes, graphene, ATO, FTO, ITO, and AZO.

[0085] Furthermore, when the inorganic particles of the protective layer are selected from insulating materials, the protective layer further comprises a conductive agent. Furthermore, the inorganic particles are preferably conductive materials.

[0086] The binder includes one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, styrene-butadiene rubber, and styrene-propylene rubber.

[0087] The active material layer 22 includes an active material, a conductive agent and a binder. The active material can be selected according to the type of electrode. For example, when the electrode is a positive electrode, the positive electrode active material is a lithium-containing transition metal oxide, such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, and lithium-rich manganese-based materials. One or more of the following materials: when the electrode is a negative electrode, the negative electrode active material is silicon, silicon carbon, SiOx (0<X<2), lithium silicon alloy, silicon alloy, artificial graphite, natural graphite, hard carbon, soft carbon, and mesophase carbon microbeads.

[0088] Generally, the thickness of the protective layer 21 is 1 / 20 to 1 / 5 of the thickness of the active material layer 22 .

[0089] The method for preparing a pole piece provided in this application includes the following steps: first, preparing a protective layer slurry and an active material layer slurry, applying them to the surface of a current collector, and drying them to obtain a functional layer 2; second, removing the functional layer 2 to form a first hollow foil area 112 and a second hollow foil area 122. To completely remove the protective layer and the active material layer from the current collector, the adhesion between the protective layer and the current collector after spraying with NMP is less than 100 N / m. To achieve the above requirements, the formula of the protective layer is specifically limited, and the binder content should not be greater than 8%. Otherwise, the adhesion between the functional layer and the current collector is good and difficult to completely remove; finally, welding the pole tab 3 to the first hollow foil area 112 or the second hollow foil area 122, and affixing the pole tab tape to obtain the pole piece.

[0090] The electrode structure provided in this application is applicable to positive electrode sheets and / or negative electrode sheets and can be configured according to actual needs.

[0091] A second aspect of the present application provides a battery comprising any of the above-mentioned pole pieces.

[0092] Based on the uniformity of the thickness of the electrode provided in the first aspect of the present application, the battery including the electrode has good cycle performance.

[0093] The preparation method of the battery provided in this application can be prepared according to conventional methods in the art.

[0094] In a specific embodiment, first, the positive electrode sheet and the negative electrode sheet are prepared according to the electrode sheet structure described above, and a separator is used to prepare a battery cell. Then, the battery cell is packaged and injected with liquid to prepare a battery.

[0095] The diaphragm and electrolyte are both conventional materials in this field and can be configured according to specific needs.

[0096] The technical solution provided by this application is further described below with reference to specific embodiments.

[0097] Example 1

[0098] The electrode sheet provided in this embodiment is a positive electrode sheet, and its structure is shown in FIG9 , including a current collector aluminum foil, a protective layer, a positive electrode active material layer, and an electrode tab. Specifically:

[0099] The current collector includes a first surface and a second surface. The first surface includes a first empty foil area and a first coated area. Along the x-direction of the pole piece, the size of the first empty foil area is 11 mm, and along the y-direction of the pole piece, the size of the first empty foil area is 20 mm. The second surface includes a second empty foil area and a second coated area. Along the x-direction of the pole piece, the size of the second empty foil area is 10 mm, and along the y-direction of the pole piece, the size of the second empty foil area is 20 mm.

[0100] A protective layer and a positive electrode active material layer are sequentially arranged on the first coating area and the second coating area. The protective layer includes 92 parts by mass of ATO-coated TiO2 and 8 parts by mass of binder PVDF; the positive electrode active material layer includes 96 parts by mass of lithium cobalt oxide, 1 part by mass of carbon black, 1 part by mass of carbon nanotubes and 2 parts by mass of binder PVDF.

[0101] The total thickness of the protective layer and the positive electrode active material layer in the first coating area is 70 μm. The second coating area includes the first region and the second region. The thickness of the second region is 60 μm. The ratio between the two is 85.7%.

[0102] The second empty foil area is connected to the positive electrode tab. The distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab. The distance difference D1-D2 between the two is less than 0.1 mm.

[0103] The method for preparing the electrode provided in this embodiment includes the following steps:

[0104] Step 1: Prepare protective layer slurry and positive electrode active material layer slurry: Mix 92 parts by mass of ATO-coated TiO2 and 8 parts by mass of PVDF, add a certain amount of NMP, adjust the slurry solid content to 40%, and stir to prepare protective layer slurry. Mix 96 parts by mass of lithium cobalt oxide, 1 part by mass of carbon black, 1 part by mass of carbon nanotubes, and 2 parts by mass of PVDF, add a certain amount of NMP, adjust the slurry solid content to 70%, and stir to prepare positive electrode active material layer slurry.

[0105] Step 2: coating the protective layer slurry prepared in step 1 on the positive electrode current collector, and then coating the positive electrode active material layer slurry on the protective layer, and drying to obtain the positive electrode sheet.

[0106] Step 3: Use a scraper to remove part of the active material layer and protective layer of the positive electrode (spray NMP before cleaning). The cleaning size of the first surface is 20*11mm to obtain the first empty foil area; the cleaning size of the second surface is 20*10mm to obtain the second empty foil area.

[0107] Step 4: Weld the positive electrode tabs onto the second empty foil area and apply protective tape. Use a roller press to roll the positive electrode sheets to the designed thickness.

[0108] Figure 13 is a physical picture of the tab connection area provided in one embodiment of the present application. As shown in Figure 13, the tab connection area is a rectangular hollow foil, and the three sides are adjacent to the functional layer. Figures 14 to 16 are EDS spectra of the cross-section of the tab connection area, where orange represents cobalt, representing the active material layer, blue represents titanium, representing the protective layer, and yellow represents aluminum, representing aluminum foil. It can be seen that the protective layer slightly protrudes beyond the active material layer, and the length of the excess is less than 0.1mm. And compared with the second and third sides on both sides of the tab shown in Figures 15 to 16, the first side shown in Figure 14 has more exposed protective layer, and the current collector is relatively flat.

[0109] FIG17 is an SEM image of the cross section of the tab connection area. As shown in FIG17 , the thickness of the single-sided coating area is 60 μm, the average thickness of the double-sided coating area is 70 μm, and the thickness ratio of the single-sided area to the double-sided area is 85.7%.

[0110] Example 2

[0111] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is less than 0.5 mm.

[0112] Example 3

[0113] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is less than 0.3 mm.

[0114] Example 4

[0115] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is 0 mm.

[0116] Example 5

[0117] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the cleared size of the first surface is 20*12mm, that is, the size of the first empty foil area along the length direction is 12mm, and the size of the first empty foil area along the width direction is 20mm.

[0118] Example 6

[0119] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the cleared size of the first surface is 20*13mm, that is, the size of the first empty foil area along the length direction is 13mm, and the size of the first empty foil area along the width direction is 20mm.

[0120] Example 7

[0121] The positive electrode sheet provided in this embodiment can refer to Example 1, except that the cleared size of the first surface is 20*14mm, that is, the length of the first empty foil area is 14mm along the length direction, and the size of the first empty foil area is 20mm along the width direction.

[0122] Example 8

[0123] The structure of the positive electrode plate provided in this embodiment is shown in Figure 5, that is, the first surface includes a first empty foil area and a first coating area, the second surface includes a second coating area, and does not include a second empty foil area. Along the length direction, the size of the first empty foil area is 10 mm, and along the width direction, the size of the first empty foil area is 20 mm.

[0124] Example 9

[0125] The positive electrode plate provided in this embodiment can refer to Example 1, except that the total thickness of the protective layer and the positive electrode active material layer in the first coating area is 70 μm, the second coating area includes the first area and the second area, the thickness of the second area is 49 μm, and the ratio W1 / W2 between the two is 70%.

[0126] Example 10

[0127] The positive electrode plate provided in this embodiment can refer to Example 1, except that the total thickness of the protective layer and the positive electrode active material layer in the first coating area is 70 μm, and the second coating area includes the first area and the second area. The thickness of the second area is 63 μm, and the ratio of the two is 90%.

[0128] Comparative Example 1

[0129] The positive electrode sheet provided in this comparative example can refer to Example 1, except that the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is 2.5 to 3 mm.

[0130] The preparation process can be referred to Example 1, except that the protective layer slurry is applied to the positive electrode current collector using a gravure coater. The gravure roller reserves space for the tabs, leaving the protective layer uncoated at the tab welding location. The uncoated area is 16 mm in the length direction of the electrode sheet and 20 mm in the width direction. The positive electrode active material from step 2 is then applied to the protective layer, and the positive electrode sheet is obtained after drying.

[0131] A first empty foil area of ​​20*11 mm was cleaned out on the first surface of the positive electrode current collector, and a second empty foil area of ​​20*10 mm was cleaned out on the second surface. That is to say, on the first surface, the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is 2.5 mm. On the second surface, the distance between the protective layer and the positive electrode tab is smaller than the distance between the positive electrode active material layer and the positive electrode tab, and the distance difference between the two is 3 mm.

[0132] Comparative Example 2

[0133] The positive electrode plate provided in this comparative example can refer to Example 1, with the difference that along the length direction of the plate, the size of the first empty foil area and the second empty foil area are both 11 mm, and the second coating area corresponds to the first coating area, that is, the second coating area does not include the second region.

[0134] Comparative Example 3

[0135] The positive electrode sheet provided in this comparative example can refer to Example 1, except that the size of the first empty foil area along the length direction of the sheet is 25 mm.

[0136] Comparative Example 4

[0137] The positive electrode plate provided in this embodiment can refer to Example 1, except that the total thickness of the protective layer and the positive electrode active material layer in the first coating area is 70 μm, and the second coating area includes the first area and the second area. The thickness of the second area is 40 μm, and the ratio between the two is 57%.

[0138] Test example

[0139] The positive electrode sheets provided in Examples 1 to 10 and Comparative Examples 1 to 4 were matched with negative electrode sheets and separators to prepare battery cells through a winding process, and the battery cells were packaged, injected, formed, and sorted using an aluminum-plastic film to prepare lithium-ion batteries; wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector, and the negative electrode active material layer includes 96 parts by mass of artificial graphite, 1 part by mass of carbon black, 1.5 parts by mass of styrene-butadiene rubber, and 1.5 parts by mass of sodium carboxymethyl cellulose.

[0140] The prepared lithium-ion battery was subjected to cycle capacity retention and energy density tests. The test method is as follows. The test results are shown in Table 1:

[0141] 25℃ cycle capacity retention test: At 25℃, the battery is charged and discharged at a rate of 1.5C charge / 0.5C discharge, and the ratio of the 1000th discharge capacity to the first discharge capacity is tested.

[0142] Energy density test: The battery is fully charged at 0.2C and then discharged at 0.2C to 3.0V. The discharged energy is recorded as E. The energy density is ED = E / (L*W*H), where L, W, and H are the length, width, and height of the battery.

[0143] Table 1

[0144] According to the data provided in Examples 1 to 4 and Comparative Example 1, as the distance difference between the protective layer and the positive electrode active material layer and the tab increases, the cycle performance of the battery deteriorates. Therefore, the distance difference between the protective layer and the active material layer and the tab should be no more than 0.5 mm, and further no more than 0.1 mm.

[0145] According to the data provided in Examples 1, 5 to 7 and Comparative Example 2, there is a single-sided area near the tab. The existence of the single-sided area causes the tab to bend toward the empty foil, so that the empty foil area has more space to accommodate the tab, thereby improving the interface stability between the tab connection area and the adjacent coating, and improving the cycle capacity retention rate of the battery.

[0146] According to the data provided in Example 8 and Example 1, the second surface does not have an empty foil area, and this area does not need to be protected by tab tape, which is beneficial to reducing the thickness of the electrode, increasing the coverage area of ​​the positive electrode active material layer, and improving the energy density of the battery.

[0147] According to the data provided in Examples 9 to 10 and Comparative Example 4, by increasing the thickness of the functional layers on both sides of the tab and making the thickness of the functional layer in the second region greater than 70% of the total thickness of other regions, it helps to improve the uniformity of the thickness of the electrode sheet, make the interface more stable, and improve the cycle capacity retention rate of the battery.

[0148] In the description of this application, it should be understood that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on this application.

[0149] The terms "first" and "second" in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can be practiced in orders other than those illustrated or described herein.

[0150] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pole piece, wherein: The invention comprises a current collector (1) and a functional layer (2), wherein the current collector (1) comprises a first surface (a) and a second surface (b) arranged opposite to each other, the first surface (a) comprises a first coating area (111), the second surface (b) comprises a second coating area (121), and the functional layer (2) is arranged on the first coating area (111) and the second coating area (121) of the current collector (1); The second coating area (121) comprises a first area (1211) and a second area (1212), the projection of the first area (1211) on the current collector (1) coincides with the projection of the first coating area (111) on the current collector (1), and the projection of the second area (1212) on the current collector (1) is located outside the projection of the first coating area (111) on the current collector (1); Along the thickness direction of the pole piece, the maximum thickness of the functional layer (2) arranged in the first coating area (111) is W1, the minimum thickness of the functional layer (2) arranged in the first area (1211) is W2, and the average thickness of the functional layer (2) arranged in the second area (1212) is W3, and W3 / (W1+W2)≥0.

7.

2. The pole piece according to claim 1, wherein: At least a portion of the first region (1211) is bent in a direction toward the first coating area (111) to form a bent portion, and the bent portion is connected to the second region (1212).

3. The pole piece according to claim 2, wherein: Along the thickness direction of the pole piece, the minimum value of the thickness of the functional layer (2) located on the bent portion of the second surface (b) is equal to W2, and the maximum value is equal to W3; The minimum value of the thickness of the functional layer (2) located on the bending portion of the first surface (a) is 0, and the maximum value is equal to W1.

4. The pole piece according to claim 1, wherein: The first surface (a) of the current collector further comprises a first empty foil area (112), and the second surface (b) further comprises a second empty foil area (122), wherein the projection of the second empty foil area (122) on the current collector (1) is located within the projection of the first empty foil area (112) on the current collector (1).

5. The pole piece according to claim 4, wherein: The total area of ​​the second empty foil area (122) and the second region (1212) is not greater than the area of ​​the first empty foil area (112).

6. The pole piece according to claim 5, wherein: The area of ​​the second region (1212) is 10% to 100% of the area of ​​the first empty foil region (112).

7. The pole piece according to claim 4, wherein: The first empty foil area (112) or the second empty foil area (122) is connected to a pole lug (3).

8. The pole piece according to claim 7, wherein: The functional layer (2) comprises a protective layer (21) and an active material layer (22), wherein the protective layer (21) and the active material layer (22) are sequentially stacked on the surface of the current collector (1); Along the length direction of the pole piece, the distance between the active material layer (22) and the pole tab (3) is D1, the distance between the protective layer (21) and the pole tab (3) is D2, and |D1-D2|≤0.5mm.

9. The pole piece according to claim 8, wherein: The distance D2 between the protective layer (21) and the electrode tab (3) is smaller than the distance D1 between the active material layer (22) and the electrode tab (3), and (D1-D2)≤0.1 mm.

10. The pole piece according to claim 9, wherein: The second region (1212) comprises a first side edge (c), a second side edge (d) and a third side edge (e), wherein the first side edge (c), the second side edge (d) and the third side edge (e) form a tab connection region; The distance difference between the protective layer (21) and the active material layer (22) and the first side (c) is D3, the distance difference between the protective layer (21) and the active material layer (22) and the second side (d) is D4, and the distance difference between the protective layer (21) and the active material layer (22) and the third side (e) is D5, D3>D4, D3>D5.

11. The pole piece according to claim 10, wherein: Along the width direction of the pole piece, the height difference of the current collector (1) located on both sides of the first side (c) is H1; along the length direction of the pole piece, the height difference of the current collector (1) located on both sides of the second side (d) is H2, and the height difference of the current collector (1) located on both sides of the third side (e) is H3, H1<H2, H1<H3.

12. A battery, wherein: A pole piece comprising any one of claims 1 to 11.

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