Positive electrode pole piece and preparation method therefor, battery and preparation method therefor

Abstract

The present application relates to the technical field of batteries, and in particular relates to a positive electrode pole piece and a preparation method therefor, as well as a battery and a preparation method therefor. The positive electrode pole piece comprises a current collector, a non-active layer, an active material layer and a tab, the non-active layer and the active material layer being disposed on at least one side surface of the current collector. The active substance layer comprises an active substance, and the non-active layer does not comprise an active substance. Along an extension direction of the tab, the edge of the non-active layer extends past the edge of the active substance layer. The non-active layer provided by the present application not only has the function of protecting the current collector, but can also prevent transition band capacity loss without affecting the capacity utilization of the active substance.

Description

Positive electrode sheet and preparation method thereof, battery and preparation method thereof Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode sheet and a preparation method thereof, a battery and a preparation method thereof.

[0002] Background of the Invention

[0003] The battery cell with a multi-tab winding and stacked structure has tabs extending from the electrode. To prevent burrs during the manufacturing process and to ensure that the positive active material is completely covered by the negative active material to prevent lithium deposition, the current industry practice is to apply an insulating layer to the side of the positive electrode tab to improve safety. The schematic diagram is shown in Figures 9A and 9B. Figure 9A is a top view of the electrode, and Figure 9B is a left view of the electrode along the dotted area of ​​Figure 9A. On the side of the positive electrode tab, near the edge of the electrode and on the tab, there is usually an insulating layer of 0.5 to 5 mm. The insulating layer and the active material layer penetrate each other, forming a transition zone of a certain width. The insulating layer and the active material layer are irregularly distributed in the transition zone. Because the insulating layer does not have the ability to conduct electrons, the active material in the transition zone has difficulty participating in the electrochemical reaction and it is difficult to deintercalate and extract lithium ions. The capacity of this part of the positive electrode active material is lost, reducing the overall capacity of the battery.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a positive electrode sheet and a method for preparing the same, as well as a battery and a method for preparing the same. The positive electrode sheet includes an inactive layer between the current collector and the active material layer, which not only protects the current collector but also prevents capacity loss in the transition zone, without affecting the capacity of the active material.

[0006] In order to achieve the above-mentioned invention objectives, this application provides the following technical solutions:

[0007] The present application provides a positive electrode sheet, which includes a current collector, an inactive layer, an active material layer and a tab; the inactive layer and the active material layer are arranged on at least one side surface of the current collector, and the inactive layer is arranged between the current collector and the active material layer; the active material layer includes an active material, and the inactive layer does not include an active material; along the direction in which the tab extends, the edge of the inactive layer exceeds the edge of the active material layer.

[0008] This application eliminates the insulating layer at the edge of the electrode near the pole ear end and extends the inactive layer to the position where the insulating layer was originally set, so that there is no transition zone between the inactive layer and the active material layer where the insulating layer and the active material layer penetrate each other, thereby avoiding the capacity loss in the transition zone and not affecting the capacity of the active material.

[0009] In the present application, the inactive layer is a coating that does not provide a lithium source and has a conductive effect.

[0010] Preferably, the vertical distance that the edge of the inactive layer exceeds the edge of the active material layer is 0.5 to 5 mm.

[0011] In the embodiment of the present application, the width of the inactive layer is 10.5 to 150 mm, and the width of the active material layer is 10 to 145 mm. However, the present application is not limited thereto, as long as the edge of the inactive layer extends vertically beyond the edge of the active material layer by 0.5 to 5 mm.

[0012] In an embodiment of the present application, at least one side surface of the current collector includes a first region and a second region, and the tab is arranged at one end of the current collector close to the first region; the inactive layer includes region A and region B, region A is arranged in the first region and part of the tab surface, and region B is arranged in the second region.

[0013] Preferably, the thickness of region A is greater than or equal to the thickness of region B. More preferably, the thickness of region A is greater than the thickness of region B. This design can more effectively prevent burrs from being generated, more effectively prevent the positive electrode active material from being completely covered by the negative electrode active material, and improve safety.

[0014] Preferably, the thickness of region A is 1 to 50 μm.

[0015] Preferably, the thickness of region A is 5 to 40 μm.

[0016] In a specific embodiment of the present application, the thickness of region A is 5 to 20 μm.

[0017] Preferably, the thickness of the region B is 0.1 to 20 μm.

[0018] Preferably, the thickness of region B is 1 to 10 μm.

[0019] In a specific embodiment of the present application, the thickness of region B is 1 to 5 μm.

[0020] Preferably, the width of region A is d1, the width of region B is d2, and the width of the active material layer is d3. d1, d2, and d3 satisfy the following relationship:

[0021] d2≤d3 <d1+d2。

[0022] In a specific embodiment of the present application, when d2=d3, as shown in FIG8 , the projections of region A and region B in the length direction are both rectangular.

[0023] In another specific embodiment of the present application, when d2 < d3 < d1 + d2, as shown in Figure 3, the projection of region A in the length direction is a pentagon-like right trapezoid, and the projection of region B in the length direction is a rectangle. However, the present application is not limited thereto, and any technical solution that can implement the concept of the present application is within the protection scope of the present application.

[0024] In an embodiment of the present application, the non-active layer includes inorganic particles without lithium and a binder.

[0025] In an embodiment of the present application, the inorganic particles without lithium refer to inorganic particles that do not include lithium-containing transition metal oxides.

[0026] Preferably, the mass percentage of the inorganic particles without lithium to the binder is (80 wt% - 99 wt%): (1 wt% - 20 wt%).

[0027] More preferably, the mass percentage of the inorganic particles without lithium to the binder is (90 wt% - 99 wt%): (1 wt% - 10 wt%).

[0028] Preferably, the inorganic particles without lithium include a conductive material and / or an insulating material.

[0029] More preferably, the inorganic particles without lithium include a conductive material, and the conductive material includes a first conductive material, and / or an insulating material coated with a second conductive material.

[0030] Preferably, the first conductive material includes at least one of, but is not limited to, ATO (antimony-doped SnO2), FTO (fluorine-doped SnO2), ITO (tin-doped In2O3), and AZO (aluminum-doped ZnO).

[0031] Preferably, the second conductive material includes at least one of, but is not limited to, carbon black, carbon nanotubes, graphene, ATO, FTO, ITO, and AZO.

[0032] In another embodiment of the present application, the inorganic particles without lithium only include an insulating material, and the non-active layer further includes a conductive agent.

[0033] Preferably, the conductive agent includes at least one of, but is not limited to, carbon black, carbon nanotubes, graphene, and carbon fibers.

[0034] Preferably, the insulating material includes at least one of, but is not limited to, alumina, magnesia, titanium oxide, zinc oxide, silicon oxide, boehmite, cobalt oxide, iron phosphate, aluminum phosphate, iron metaphosphate, and aluminum metaphosphate.

[0035] Preferably, the adhesive includes but is not limited to at least one of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, polyacrylic acid, polyacrylic salt, polyimide, styrene-butadiene rubber, and styrene-propylene rubber.

[0036] In an embodiment of the present application, the inorganic particles containing no lithium are a conductive material, and the weight ratio of the inorganic particles containing no lithium to the binder is (80 wt% to 99 wt%): (1 wt% to 20 wt%). Preferably, the weight ratio of the inorganic particles containing no lithium to the binder is (90 wt% to 99 wt%): (1 wt% to 10 wt%).

[0037] In an embodiment of the present application, the inorganic particles that do not contain lithium are an insulating material, and the inactive layer further includes a conductive agent. The weight percentages of the inorganic particles that do not contain lithium, the conductive agent, and the binder are (70 wt% to 98 wt%): (1 wt% to 15 wt%): (1 wt% to 15 wt%). Preferably, the weight percentages of the inorganic particles that do not contain lithium, the conductive agent, and the binder are (80 wt% to 98 wt%): (1 wt% to 10 wt%): (1 wt% to 10 wt%).

[0038] In the embodiment of the present application, in the insulating material coated with the second conductive material, the second conductive material and the insulating material can be composed of any ratio, and the coating can be complete or incomplete. Preferably, the mass ratio of the second conductive material to the insulating material is (1-10):(80-98).

[0039] In the embodiment of the present application, the active material layer includes a positive electrode active material, and the positive electrode active material is a lithium-containing transition metal oxide;

[0040] Preferably, the lithium-containing transition metal oxide includes but is not limited to at least one of 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.

[0041] Preferably, the active material layer in the positive electrode sheet further includes a conductive agent and / or a binder.

[0042] Preferably, the mass percentage of each component in the positive electrode active material layer is: 80 wt% to 99.8 wt% of the positive electrode active material, 0.1 wt% to 10 wt% of the conductive agent, and 0.1 wt% to 10 wt% of the binder.

[0043] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90 wt% to 99.6 wt% of the positive electrode active material, 0.2 wt% to 5 wt% of the conductive agent, and 0.2 wt% to 5 wt% of the binder.

[0044] The present application also provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0045] (1) mixing an inactive layer material and a first solvent to obtain an inactive layer slurry, and coating the inactive layer slurry on a current collector to form an inactive layer;

[0046] (2) The active material layer material and the second solvent are mixed to obtain an active material layer slurry, and the active material layer slurry is coated on the inactive layer of the current collector. After drying, rolling, and die-cutting the tabs, a positive electrode sheet is obtained.

[0047] In the embodiment of the present application, the inactive layer is prepared by gravure coating.

[0048] In the embodiment of the present application, the mesh size of the gravure coating of the preparation area A is 10 to 80 meshes.

[0049] In the embodiment of the present application, the mesh size of the gravure coating of the preparation area B is 100 to 150 meshes.

[0050] In the embodiment of the present application, the current collector is a material containing aluminum.

[0051] Preferably, the aluminum-containing material includes one of aluminum foil, carbon-coated aluminum foil, and aluminum-polymer composite current collector.

[0052] The present application also provides a battery, which includes a negative electrode sheet, a separator and the above-mentioned positive electrode sheet.

[0053] In the embodiment of the present application, the vertical distance between the projected edge of the negative electrode sheet on the side of the tab in the length direction and the projected edge of the inactive layer in the positive electrode sheet on the side of the tab in the length direction is d4, and the vertical distance between the projected edge of the active material layer in the positive electrode sheet on the side of the tab in the length direction and the projected edge of the inactive layer in the positive electrode sheet on the side of the tab in the length direction is d5. d4 and d5 satisfy the following relationship:

[0054] d4 <d5。

[0055] In the embodiments provided herein, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0056] Preferably, the mass percentage of each component in the negative electrode active material layer is: 80 wt% to 99.8 wt% of the negative electrode active material, 0.1 wt% to 10 wt% of the conductive agent, and 0.1 wt% to 10 wt% of the binder.

[0057] Preferably, the mass percentage content of each component in the negative electrode active material layer is: 90 wt% to 99.6 wt% of negative electrode active material, 0.2 wt% to 5 wt% of conductive agent, and 0.2 wt% to 5 wt% of binder.

[0058] Preferably, the negative electrode active material includes a carbon-based negative electrode material.

[0059] Preferably, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0060] Preferably, the negative electrode active material may further include a silicon-based negative electrode material.

[0061] Preferably, the silicon-based negative electrode material is selected from at least one of nano-silicon, silicon oxide negative electrode material (SiOx, 0 < x < 2), or silicon-carbon negative electrode material.

[0062] Preferably, in the negative electrode active material, the mass ratio of the carbon-based negative electrode material to the silicon-based negative electrode material is 10:0 to 1:19.

[0063] In the specific embodiment provided by the present application, the negative electrode current collector is a copper foil.

[0064] In the embodiment of the present application, in the positive electrode sheet or the negative electrode sheet, the conductive agent is selected from at least one of conductive carbon black (acetylene black and / or Ketjen black), conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

[0065] In the embodiment of the present application, in the positive electrode sheet or the negative electrode sheet, the binder is selected from at least one of PVDF, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0066] The present application also provides a preparation method for the above battery, including the following steps:

[0067] Stack the positive electrode sheet, the separator, and the negative electrode sheet to obtain a stacked core, or stack the positive electrode sheet, the separator, and the negative electrode sheet and then wind them to obtain a wound core, place the stacked core or the wound core in an outer package, inject electrolyte into the outer package, and perform vacuum packaging, standing, and formation to obtain the battery of the present application.

[0068] Compared with the prior art, the beneficial effects of the present application are as follows:

[0069] (1) In the positive electrode sheet of the present application, the non-active layer is located between the current collector and the active material layer, which has a protective effect on the current collector and further improves the mechanical abuse safety of the battery.

[0070] (2) In the positive electrode sheet of the present application, the protective layer uses a conductive inactive layer instead of an insulating layer at the edge of the positive electrode tab side, thereby avoiding the capacity loss in the transition zone and not affecting the capacity of the active material.

[0071] (3) The inactive layer in the positive electrode sheet of the present application does not include a lithium-containing transition metal oxide, and due to the setting of the inactive layer region A, the width of the inactive layer exceeds the width of the positive electrode active material layer, reducing the risk of lithium plating.

[0072] (4) The thickness of the inactive layer region A in the positive electrode sheet of the present application is greater than that of the region B, the thickness uniformity of the positive electrode sheet is better, the interface between the positive electrode sheet near the tab and the diaphragm and the negative electrode sheet is stronger, and the capacity retention rate is higher.

[0073] BRIEF DESCRIPTION OF THE DRAWINGS

[0074] FIG1 is a left side view of the positive electrode sheet of Example 1.

[0075] FIG2 is a distribution diagram of the first region and the second region of the current collector in Example 1.

[0076] FIG3 is a left side view of a positive electrode sheet according to another embodiment.

[0077] Figure 4 is a schematic cross-sectional view of the battery cell structure.

[0078] Figure 5 is a schematic diagram of the core structure.

[0079] FIG6A is a top view of the positive electrode undercoat sheet before die-cutting the tabs.

[0080] FIG6B is a top view of the positive electrode sheet after the tabs are die-cut.

[0081] FIG7 is a left side view of the positive electrode sheet of Example 9.

[0082] FIG8 is a left side view of the positive electrode sheet of Example 11.

[0083] FIG9A is a top view of the positive electrode sheet of Comparative Example 1. FIG.

[0084] FIG9B is a left side view of the positive electrode sheet of Comparative Example 1 along the dotted line area of ​​FIG9A .

[0085] The figures are numbered as follows: positive electrode sheet 100, positive electrode current collector 110, inactive layer 120, active material layer 130, edge of active material layer 131, positive electrode tab 140, first region 111, second region 112, region A 121, region B 122, edge of inactive layer 123, insulating layer 150, transition zone 160; separator 200; negative electrode sheet 300, negative electrode tab 340; X represents the thickness direction of the electrode sheet, and Y represents the direction in which the electrode sheet (current collector, inactive layer or active material layer) extends along the tab or the width direction.

[0086] Modes for Carrying Out the Invention

[0087] The present application discloses a positive electrode sheet and a method for preparing the same, and a battery and a method for preparing the same. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art and are deemed to be included in this application. The methods and applications of this application have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of this application to implement and apply the technology of this application.

[0088] The reagents, instruments, and materials used in this application can all be obtained through commercial channels.

[0089] The present application is further described below with reference to the embodiments.

[0090] Example 1

[0091] 1. Battery structure

[0092] 1 to 4 , the battery of this embodiment includes a positive electrode sheet 100 , a separator 200 , a negative electrode sheet 300 , and an electrolyte.

[0093] As shown in Figure 1, the positive electrode sheet 100 (only the coating structure on one side of the positive electrode sheet is shown; the inactive layer and active layer structure on the other side are not shown) includes a current collector 110, an inactive layer 120, an active material layer 130, and a tab 140. The inactive layer 120 and the active material layer 130 are provided on both sides of the current collector 110, and the inactive layer 120 is provided between the current collector 110 and the active material layer 130.

[0094] As shown in FIG. 2 , both side surfaces of the current collector 110 include a first region 111 and a second region 112 , and the tab 140 is disposed at one end of the current collector 110 close to the first region 111 .

[0095] As shown in Figure 3 (Figure 3 only shows the structure of one side of the positive electrode sheet, and the inactive layer and active layer structure on the other side are not shown), the inactive layer 120 includes region A 121 and region B 122, wherein region A 121 is arranged in the first region 111 and a portion of the tab surface, and region B 122 is arranged in the second region 112, and the thickness of region A 121 is greater than the thickness of region B 122.

[0096] The width of the inactive layer 120 is 102.5 mm, the width of the active material layer 130 is 100 mm, and the vertical distance from the edge of the inactive layer 120 to the edge of the active material layer 130 is 2.5 mm.

[0097] The width of region A 121 is d1, the width of region B 122 is d2, and the width of active material layer 130 is d3. d1, d2, and d3 satisfy the following relationship:

[0098] d2≤d3 <d1+d2。

[0099] As shown in FIG4 , FIG4 is a cross-sectional schematic diagram of a battery cell structure composed of a positive electrode sheet 100 , a separator 200 , and a negative electrode sheet 300 (the negative electrode tab is not shown).

[0100] The vertical distance between the projected edge of the negative electrode sheet 300 on the tab side in the length direction and the projected edge of the inactive layer 120 of the positive electrode sheet 100 on the tab side in the length direction is d4.

[0101] The vertical distance between the projected edge of the active material layer 130 on the tab side in the length direction of the positive electrode sheet 100 and the projected edge of the inactive layer 120 on the tab side in the length direction of the positive electrode sheet 100 is d5, and d4 and d5 satisfy the following relationship:

[0102] d4 <d5。

[0103] The schematic diagram of the core structure is shown in Figure 5.

[0104] 2. Preparation method

[0105] Step 1: Prepare the inactive layer slurry. Mix 97% by weight of ATO-coated TiO2 (3% ATO, 94% TiO2) and 3% by weight of PVDF. Add a certain amount of NMP and adjust the solid content of the slurry to 40%. Stir to prepare the inactive layer slurry.

[0106] Step 2: Prepare the positive electrode slurry. Mix 96% lithium cobalt oxide, 1% carbon black, 1% carbon nanotubes, and 2% PVDF. Add a certain amount of NMP to adjust the solid content of the slurry to 70%. Stir to prepare the positive electrode slurry.

[0107] Step 3: Prepare the negative electrode slurry. Mix 96% artificial graphite, 1% carbon black, 1.5% styrene-butadiene rubber, and 1.5% sodium carboxymethyl cellulose. Add deionized water and adjust the solid content of the slurry to 40%. Stir to prepare the negative electrode slurry.

[0108] Step 4: Preparation of the positive electrode sheet. The inactive layer slurry of step one is coated on aluminum foil by gravure coating (the gravure roller is prepared by engraving different meshes in different areas, corresponding to the engraving area of ​​the inactive layer area A is 40 mesh, and the engraving area of ​​area B is 120 mesh) to obtain a positive electrode bottom coating. The thickness of the inactive layer of the bottom coating varies in different areas, where the thickness of area A is 20μm, the thickness of area B is 5μm, and the thickness of area A near one end of area B shows a gradual trend. In the left view of the positive electrode sheet, area A is a pentagonal right-angled trapezoid, and area B is a rectangle. The positive active material of step 2 is then coated on the inactive layer and dried to obtain a positive electrode sheet, as shown in Figure 6A.

[0109] Step 5: Preparation of negative electrode sheet: the negative electrode slurry prepared in step 3 is coated on copper foil through an extrusion coating process to obtain a negative electrode sheet.

[0110] Step 6: Roll the positive and negative electrode sheets to the designed thickness, and then die-cut the tabs. The schematic diagram of the positive electrode sheet after die-cutting the tabs is shown in Figure 6B.

[0111] Step 7: Place the diaphragm between the positive and negative electrode sheets and wind them to obtain a roll core. Use external Al (aluminum) tabs to weld the tabs of the positive electrode sheet together. Use external nickel-plated copper tabs to weld the tabs of the negative electrode sheet together. Use aluminum-plastic film to encapsulate the roll core and inject electrolyte.

[0112] Step 8: Use lithium-ion battery formation equipment to charge and discharge the battery cells to harden them and sort out the capacity of the battery cells.

[0113] Step 9: The battery cell is sealed for the second time and folded to make the battery cell basically formed.

[0114] Step 10: Perform an OCV test on the battery to determine its K value, and select products with qualified K values.

[0115] Example 2

[0116] The component of the inactive layer 120 is AZO-coated TiO 2 , and the rest is the same as in Example 1.

[0117] Example 3

[0118] The component of the inactive layer 120 is ATO, and the rest is the same as in Example 1.

[0119] Example 4

[0120] The component of the inactive layer 120 is AZO, and the rest is the same as in Example 1.

[0121] Example 5

[0122] The composition of the inactive layer 120 is 97% carbon black-coated Al2O3 (the amount of carbon black is 3%, the amount of Al2O3 is 94%) + 3% PVDF, and the rest is the same as in Example 1.

[0123] Example 6

[0124] The composition of the inactive layer 120 is 94% Al2O3+3% carbon black+3% PVDF, and the rest is the same as in Example 1.

[0125] Example 7

[0126] The thickness of region A 121 of the inactive layer 120 is 20 μm, and the thickness of region B 122 is 3 μm. The rest is the same as in Example 1.

[0127] Example 8

[0128] The thickness of region A 121 of the inactive layer 120 is 20 μm, and the thickness of region B 122 is 1 μm. The rest is the same as in Example 1.

[0129] Example 9

[0130] The thickness of region A 121 of the inactive layer 120 is 5 μm, and the thickness of region B 122 is 5 μm, and the rest is the same as in Example 1. The structure is shown in FIG7 .

[0131] Example 10

[0132] The inactive layer 120 and the active material layer 130 are disposed on one surface of the current collector 110 , and the rest are the same as in Example 1.

[0133] Example 11

[0134] As shown in FIG8 , both region A 121 and region B 122 are rectangular, and the rest are the same as in the first embodiment.

[0135] Example 12

[0136] The width of the inactive layer 120 is 10.5 mm, the width of the active material layer 130 is 10 mm, and the vertical distance between the edge of the inactive layer 120 and the edge of the active material layer 130 is 0.5 mm.

[0137] Example 13

[0138] The width of the inactive layer 120 is 150 mm, the width of the active material layer 130 is 145 mm, and the vertical distance between the edge of the inactive layer 120 and the edge of the active material layer 130 is 5 mm.

[0139] Comparative Example 1

[0140] The positive electrode sheet does not contain an inactive layer. The insulating layer 150 of boehmite + PVDF (the mass ratio of boehmite to PVDF is 9:1) is located near the tab. Its structure is shown in FIG9A and FIG9B . The rest is the same as in Example 1.

[0141] Comparative Example 2

[0142] The thickness of region A 121 of the inactive layer 120 is 20 μm, and the thickness of region B 122 is 0 μm. The rest is the same as in Example 1.

[0143] Comparative Example 3

[0144] The width of the inactive layer 120 is 75 mm, the width of the active material layer 130 is 75 mm, and the edge of the inactive layer 120 is flush with the edge of the active material layer 130. Other aspects are the same as those of Example 1.

[0145] Battery performance test

[0146] (1) Acupuncture test:

[0147] A fully charged lithium-ion battery is placed on the test bench of a needle penetration tester. A tungsten steel needle with a diameter of 3mm and a tip length of 3.62mm is inserted through the center of the battery at a speed of 100mm / s. The battery passes the test if it does not catch fire or explode. The pass rate is calculated by dividing the number of passes by the number of tests. The number of tests is 30.

[0148] (2) Energy density:

[0149] Charge the lithium-ion battery to an upper voltage of 4.45V, then discharge it at 0.2C to a lower voltage of 3.0V. The discharge energy is recorded as E. The energy density of the lithium-ion battery is then calculated using the following formula:

[0150] Energy density = E / (length × width × height of lithium-ion battery).

[0151] (3) Capacity retention after 500 cycles at 45°C:

[0152] The lithium-ion battery is placed in a constant temperature environment of 45°C and charged and discharged at the designed charge and discharge rate for 500 cycles. The first discharge capacity is recorded as C1, and the 500th discharge capacity is recorded as C500. The capacity retention rate after 500 cycles at 45°C is C500 / C1.

[0153] (4) Lithium deposition

[0154] The battery was cycled at 25°C and 3C / 0.7C charge and discharge conditions, and disassembled at 200T\700T to confirm the degree of lithium plating. 0, 1, 2, 3, 4, and 5 were used to represent the degree of lithium plating. The larger the value, the more serious the lithium plating.

[0155] Table 1 shows the comparative data of the inactive layer composition, inactive layer thickness, needle penetration rate, energy density and capacity retention rate after 500 cycles at 45°C for each embodiment and comparative example.

[0156] Table 1 Comparison of different embodiments and comparative examples

[0157] In Examples 1-13, compared with Comparative Example 1, an inactive layer 120 is provided between the active material layer 130 and the current collector 110 , and the needle penetration rate is improved. When the thickness of the inactive layer 120 exceeds 3 μm, the improvement is obvious.

[0158] Compared with Comparative Example 1, Comparative Example 2 has an inactive layer 120 between the active material layer 130 and the current collector 110, and the conductive inactive layer 120 is located near the electrode tab 140, while the insulating layer 150 is located near the electrode tab 140 in Comparative Example 1. The capacity of Comparative Example 2 is higher than that of Comparative Example 1, and the energy density is increased by 5Wh / L.

[0159] Compared with Example 9, in Example 1, the thickness of region A 121 of the inactive layer 120 is greater than the thickness of region B 122 of the inactive layer 120, the thickness uniformity of the positive electrode sheet is better, the interface between the positive electrode sheet near the tab and the separator and the negative electrode sheet is stronger, and the capacity retention rate is higher.

[0160] Compared with Example 6, the inorganic particles in the inactive layer 120 of Example 5 are made of conductive materials. Compared with the design of insulating material inorganic particles + conductive agent in Example 6, Example 5 uses conductive agent to coat inorganic particles of insulating material. The conductive stability of its inactive layer 120 is better and the high-temperature cycle capacity retention rate is better, which is the preferred formula design.

[0161] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a current collector, an inactive layer, an active material layer and a tab; the inactive layer and the active material layer are arranged on at least one side of the current collector, and the inactive layer is arranged between the current collector and the active material layer; The active material layer includes active material, and the inactive layer does not include active material; Along the extending direction of the electrode tab, the edge of the inactive layer exceeds the edge of the active material layer.

2. The positive electrode sheet according to claim 1, characterized in that: The vertical distance that the edge of the inactive layer exceeds the edge of the active material layer is 0.5 to 5 mm.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: At least one side surface of the current collector includes a first region and a second region, and the electrode tab is arranged at one end of the current collector close to the first region; The inactive layer includes region A and region B, wherein region A is arranged in the first region and a portion of the surface of the tab, and region B is arranged in the second region; The thickness of region A is greater than or equal to the thickness of region B.

4. The positive electrode sheet according to claim 3, characterized in that: The thickness of the region A is 1 to 50 μm; the thickness of the region B is 0.1 to 20 μm.

5. The positive electrode sheet according to claim 3, characterized in that: The width of the region A is d1, the width of the region B is d2, the width of the active material layer is d3, and d1, d2, and d3 satisfy the following relationship: d2≤d3 <d1+d2。 6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The inactive layer includes inorganic particles not containing lithium and a binder; the inorganic particles not containing lithium include conductive materials and / or insulating materials.

7. The positive electrode sheet according to claim 6, characterized in that: The inorganic particles not containing lithium include a conductive material, wherein the conductive material includes a first conductive material and / or an insulating material coated with a second conductive material.

8. The positive electrode sheet according to claim 7, characterized in that: The first conductive material includes at least one of ATO, FTO, ITO, and AZO; And / or, the second conductive material includes at least one of carbon black, carbon nanotubes, graphene, ATO, FTO, ITO, and AZO.

9. The positive electrode sheet according to claim 6, characterized in that: The inorganic particles not containing lithium include only insulating materials, and the inactive layer further includes a conductive agent.

10. The positive electrode sheet according to claim 9, characterized in that: The conductive agent includes at least one of carbon black, carbon nanotubes, graphene, and carbon fiber.

11. The positive electrode sheet according to any one of claims 6 to 10, characterized in that: The insulating material includes at least one of aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, boehmite, cobalt oxide, iron phosphate, aluminum phosphate, iron metaphosphate, and aluminum metaphosphate; And / or, the adhesive includes at least one of PVDF, acrylic acid-modified PVDF, polyacrylate polymers, polyacrylic acid, polyacrylic salt, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The active material layer includes a positive electrode active material, and the positive electrode active material is a transition metal oxide containing lithium; The lithium-containing transition metal oxide includes at least one of 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; The current collector is a material containing aluminum; The aluminum-containing material includes one of aluminum foil, carbon-coated aluminum foil, and aluminum-polymer composite current collector.

13. A battery, characterized in that: The battery comprises a negative electrode sheet, a separator and a positive electrode sheet according to any one of claims 1 to 12; and / or, the vertical distance between the projection edge of the negative electrode sheet on one side of the electrode ear in the length direction and the projection edge of the inactive layer in the positive electrode sheet on one side of the electrode ear in the length direction is d4, The vertical distance between the projection edge of the active material layer on the side of the pole ear in the length direction of the positive electrode sheet and the projection edge of the inactive layer on the side of the pole ear in the length direction of the positive electrode sheet is d5, and d4 and d5 satisfy the following relationship: d4 <d5。 14. A method for preparing a positive electrode sheet, characterized in that: include: Mixing the inactive layer material and the first solvent to obtain an inactive layer slurry, and coating the inactive layer slurry on the current collector to form an inactive layer; The active material layer material and the second solvent are mixed to obtain an active material layer slurry, and the active material layer slurry is coated on the inactive layer of the current collector. After drying, rolling, and die-cutting the tabs, the positive electrode sheet is obtained.

15. A method for preparing a battery, characterized in that: include: The positive electrode sheet, separator and negative electrode sheet described in any one of claims 1 to 12 are stacked to obtain a stacked core, or the positive electrode sheet, separator and negative electrode sheet are stacked and then wound to obtain a wound core, the stacked core or wound core is placed in an outer package, electrolyte is injected into the outer package, and vacuum packaging, standing and formation are performed to obtain the battery.

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