A lithium battery positive electrode sheet, a preparation method and application thereof

Abstract

The application discloses a lithium battery positive plate and a preparation method and application thereof, the edge of the positive plate is coated with an insulating coating of special material, the coating position of the insulating coating is between an active material layer and a tab blank; the components of the insulating coating include ethylene-vinyl acetate polymer, a plasticizer, a binder and an antioxidant; the insulating coating is coated on the active material layer and covers a certain width. The insulating coating of the application has low viscosity, is in a solid state at normal temperature and is in a liquid state above 140 DEG C, can be stably and uniformly coated on the surface of a current collector, meanwhile, the high temperature generated in the laser cutting process can melt the insulating coating, at this time, the coating has certain fluidity, and the cutting process in the molten state can effectively coat the edge notch burrs of the positive plate. Therefore, the insulating coating has the functions of insulating protection of the edge surface of the positive plate and burr coating protection of the notch end surface of the positive plate, and the double protection can effectively solve the problems of membrane puncture and positive and negative short circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium battery positive plate and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of new energy vehicles and consumer electronic products, the market demand for lithium batteries as an efficient and portable energy storage device continues to grow. However, how to ensure the safety of the battery has always been the focus of the industry during the manufacturing process of the lithium battery.

[0003] During the manufacturing process of the lithium battery, some abnormal battery cells are often encountered, such as 0 resistance in the assembly short circuit test, low formation voltage, large self-discharge, large module pressure difference, etc. Through the disassembly analysis of the abnormal battery cells, it is found that the edge blank of the positive plate of the battery cell corresponds to a point where the diaphragm is broken, which is mainly caused by the fact that the metal beads generated at the cross-section port of the current collector during the laser cutting process are not effectively covered by the insulating layer. At the same time, the existing manufacturing process generally adopts a method of coating ceramic materials as the insulating layer through a coating process. However, this method generates a large amount of dust during the laser cutting process, which not only affects the production environment, but also may have an adverse effect on the product quality. In addition, the ceramic coating mainly acts on the surface of the foil, and the covering effect on the edge of the laser cutting incision is not good, and the burrs generated during the cutting process may still cause the risk of short circuit.

[0004] Patent CN113488743A proposes a coating method of modified ceramic slurry, which improves the insulation performance by changing the peeling force after coating. However, this method is still limited to the protection effect of ceramic materials, and the effective covering of the cross-section of the laser cutting incision has not been fundamentally solved.

[0005] Therefore, developing an insulating coating technology that can effectively cover the edge of the laser cutting incision becomes an important measure to improve the safety of the lithium battery. At the same time, in order to avoid the problem of mutual solubility of the insulating slurry and the active material slurry during the process processing or the difficulty in controlling the gap of the integrated die coating, a new type of insulating layer coating process needs to be developed to meet the safety requirements in the manufacturing process of the lithium battery. SUMMARY

[0006] In view of the deficiencies of the prior art, the application provides a lithium battery positive plate and a preparation method and application thereof, which transfers the difficulty to the laser cutting process and directly coats an insulating coating on the dry material (active material) positive plate, thereby effectively solving the mutual solubility problem between wet materials.

[0007] The application is implemented through the following technical solutions:

[0008] A lithium battery positive electrode sheet, the edge of the positive electrode sheet is coated with a special material insulation coating, the coating position of the insulation coating is between the active material layer and the tab blank; the composition of the insulation coating includes ethylene-vinyl acetate polymer, plasticizer, binder and antioxidant; the insulation coating is coated on the active material layer and covers a certain width.

[0009] By coating a special material insulation coating (in a molten state when coated, and forming a hot melt adhesive layer after cooling and solidification) on the active material layer (dry material), the problem of mutual solubility between wet materials can be effectively solved.

[0010] Preferably, the width of the insulation coating is 6-8mm, and the thickness is 10-15μm.

[0011] Preferably, the ethylene-vinyl acetate polymer is prepared by emulsion method from ethylene and vinyl acetate, and the molecular weight is 1280, and the structural formula is as follows:

[0012]

[0013] Preferably, the mass ratio of each component in the insulation coating is as follows:

[0014] Ethylene-vinyl acetate polymer: plasticizer: binder: antioxidant = 80-85: 0.5-1: 10-15: 1-2.

[0015] Preferably, the plasticizer is dibutyl phthalate or dioctyl phthalate; the binder is polyvinylidene fluoride or polystyrene; and the antioxidant is butylated hydroxyanisole or dibutylated hydroxytoluene.

[0016] Preferably, the active material layer is lithium iron phosphate or ternary lithium.

[0017] The preparation method of the above lithium battery positive electrode sheet includes the following steps:

[0018] Step 1) In a high-pressure reaction kettle, first add vinyl acetate and K2S2O8 or (NH4)2S2O8 initiator to the prepared emulsion reaction medium, then add ethylene, and polymerize at 85℃, 90kg / cm 2 pressure to prepare ethylene-vinyl acetate polymer latex with a vinyl acetate content of 75%;

[0019] Step 2) At 150℃, add plasticizer, binder and antioxidant to the ethylene-vinyl acetate polymer latex prepared in step 1) in a mass ratio of 0.5-1: 10-15: 1-2; after uniform dispersion and stirring at 220℃, an insulation coating glue is obtained; after filtration, cool to room temperature to prepare a solid insulation coating;

[0020] Step 3) heating the solid insulation coating prepared in step 2) to above 170℃ using a heating furnace to melt it into a flowable glue solution; the melt flow rate is 170℃ / 2.0kg, 190℃ / 2.2kg;

[0021] Step 4) introducing the molten glue solution obtained in step 3) to the glue coating head through an electric heating pipe, wherein the temperature of the heating furnace and the electric heating pipe is controlled at 170℃, and continuous heating is achieved;

[0022] Step 5) starting the electric heating module, and the heating temperature is 220℃, further melting the insulation coating;

[0023] Step 6) after the entire glue coating device is installed at the laser cutting and unwinding position, and before the laser cutting position, the laser cuts the horizontal electrode sheet after unwinding through the conveying roller, and the glue coating device is installed directly above the conveying roller; uniform coating is achieved on the edge of the positive electrode sheet current collector, i.e. the junction of the positive electrode material area and the blank area, by moving up and down through the telescopic cylinder during the laser cutting and unwinding process; after completing the front coating, the back surface needs to be coated with a buffer return mechanism;

[0024] Step 7) applying the molten hot melt adhesive to the tab forming area, covering at least part of the active material layer, and cooling and solidifying to form a hot melt adhesive layer;

[0025] Step 8) laser direct cutting of the insulation coating surface to obtain a pre-designed tab shape and excess waste edge.

[0026] Preferably, in step 8), the width of the insulation coating left on the electrode sheet after laser cutting is 3-4mm, and the coating area and the cutting area are both located on the tab side.

[0027] The above-mentioned lithium battery positive electrode sheet, or the lithium battery positive electrode sheet prepared by the above-mentioned preparation method, is used in the preparation of a lithium battery. The lithium battery positive electrode sheet is combined with a separator and a negative electrode sheet through a winding or stacking process to obtain a qualified roll core, and then combined with an electrolyte and a shell structure to form a lithium battery.

[0028] Preferably, the winding or stacking process adopts a staggered wrapping method to realize the correspondence between the negative electrode cutout and the positive electrode insulation layer, which is as follows: in the laser cutting process, the positive electrode cuts the insulation layer, and the negative electrode cuts the active material area; in the assembly process, the negative electrode active material area wraps the positive electrode active material area, and the positive electrode insulation layer wraps the negative electrode active material area.

[0029] Preferably, the phase difference between the negative electrode active material area wrapping the positive electrode active material area is 3.5mm; and the phase difference between the positive electrode insulation layer wrapping the negative electrode active material area is 1mm.

[0030] A lithium battery comprising the above-mentioned lithium battery positive electrode sheet, or the lithium battery positive electrode sheet prepared by the above-mentioned preparation method.

[0031] The beneficial effects of the present application are as follows:

[0032] (1) The principle of the present application is to use laser cutting to cut the tabs on the edge of the pole piece, and the colloid plays a light-absorbing role at a specific laser wavelength, thereby meeting the requirements of laser cutting of the pole piece at a specific power and no edge shrinkage of the glue layer. The insulating coating of the present application has low viscosity and is solid at room temperature, and is liquid above 140°C. It can be stably and uniformly coated on the current collector surface. The high temperature generated during the laser cutting process can melt the insulating coating. At this time, the coating has a certain fluidity, and the molten state during the cutting process can effectively cover the burrs on the edge of the pole piece. Therefore, the insulating coating can be used with different coating equipment, and has good wettability to the substrate, providing high adhesion. During use, it can better lock metal particles and cutting port burrs, providing double protection of the edge surface of the pole piece and the burr protection of the cut end surface of the pole piece, which can effectively solve the problems of diaphragm puncture and positive and negative short circuit.

[0033] (2) The preparation method of the insulating coating of the present application is simple, and the coating process avoids the coating process. It is different from the current market end insulating coating process which is coated in the wet film state of the active material. The present application breaks the convention and first uses the idea of coating the insulating coating in the dry film state of the active material, avoiding the problem of mutual solubility of the active material slurry and the insulating coating, and further improving the process consistency and the qualified rate. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a schematic diagram of the position structure of the insulating coating of the positive pole piece in Example 1 on the current collector.

[0035] Figure 2 It is a schematic diagram of the insulating coating device in the prior art.

[0036] Figure 3 It is a schematic diagram of the core misalignment coating in Example 1.

[0037] Figures 1-3 In the figure: 1, insulating coating; 2, active material layer; 3, tab blank; 4, positive current collector; 5, insulating coating area not cut by laser cutting; 6, insulating coating coating area; 7, positive active material area; 8, negative active material area; 9, diaphragm; 10, negative current collector; 11, negative pole piece; 12, positive pole piece; 13, glue coating head; 14, electric heating module; 15, telescopic air cylinder;

[0038] Figure 4 It is a laser cutting cross-section port electron microscope image of the positive pole piece prepared in Example 2 (1000x).

[0039] Figure 5 It is a laser cutting cross-section port electron microscope image of the positive pole piece prepared in Example 3 (2000x).

[0040] Figure 6 The image shows a laser-cut cross-section (5000×) of the positive electrode sheet prepared in Example 4.

[0041] Figure 7 The image shows a laser-cut cross-section (1000×) of the positive electrode sheet prepared in Comparative Example 1. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] A lithium battery positive electrode, such as Figure 1 As shown, the edge of the positive electrode is coated with an insulating coating 1 of a special material. The insulating coating 1 is applied between the active material layer 2 and the tab blank 3. The components of the insulating coating 1 include ethylene-vinyl acetate polymer, plasticizer, binder and antioxidant. The insulating coating 1 is applied to the active material layer 2 (dry active material) and is allowed to cover a certain width. In this embodiment, the width of the insulating coating 1 is 6-8 mm and the coating thickness is 10-15 μm.

[0045] The ethylene-vinyl acetate polymer is prepared from ethylene and vinyl acetate via an emulsion method, has a molecular weight of 1280, and its structural formula is as follows:

[0046]

[0047] In the formula: x and y are both natural numbers between 1 and 100.

[0048] In this embodiment, the mass ratios of each component in the insulating coating are as follows:

[0049] Ethylene-vinyl acetate polymer: plasticizer: binder: antioxidant = 80-85: 0.5-1: 10-15: 1-2.

[0050] In this embodiment, the plasticizer is dibutyl phthalate (DBP) or dioctyl phthalate (DOP); the binder is polyvinylidene fluoride or polystyrene resin; and the antioxidant is butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT).

[0051] In this embodiment, the active material layer is a traditional lithium iron phosphate or ternary lithium, and the core is fabricated by winding or stacking.

[0052] A method for preparing a lithium battery positive electrode sheet, the specific steps of which are as follows:

[0053] (1) Preparation of insulating coating

[0054] (1-1) In a high-pressure reactor, first add vinyl acetate and K2S2O8 or (NH4)2S2O8 initiator to the prepared emulsion reaction medium, then add ethylene, and polymerize at 85℃, 90kg / cm 2 pressure to obtain an ethylene-vinyl acetate polymer latex with a vinyl acetate content of 75%.

[0055] (1-2) At a high temperature of 150℃, add plasticizer, binder and antioxidant to the ethylene-vinyl acetate polymer latex prepared above in a mass ratio of 0.5-1:10-15:1-2, wherein the ethylene-vinyl acetate polymer accounts for 80-85wt%; after uniform dispersion and stirring at a high temperature of 220℃, an insulating coating glue is obtained; after filtration, cooling to room temperature, a solid insulating coating is prepared.

[0056] (2) Preparation of positive electrode sheet with insulating coating

[0057] (2-1) Use a heating furnace to heat the solid insulating coating prepared above to above 170℃ to melt it into a glue liquid that can flow; the melt flow rate is 2.0kg / 10min at 170℃ and 2.2kg / 10min at 190℃.

[0058] (2-2) Introduce the molten glue liquid obtained above to the glue coating head 13( Figure 2 ) through an electric heating pipe, wherein the temperature of the heating furnace and the electric heating pipe is controlled at 170℃ and continuous heating is achieved.

[0059] (2-3) Start the electric heating module 14( Figure 2 ), and the heating temperature is 220℃ to further melt the insulating coating.

[0060] (2-4) The entire glue coating device (prior art, as shown in Figure 2 ) is installed after the laser cutting and unwinding position and before the laser cutting position. The laser cutting and unwinding electrode sheet passes through the conveying roller horizontally, and the glue coating device installation position is located directly above the conveying roller. The laser cutting and unwinding process is uniformly coated on the edge of the positive electrode sheet current collector (the junction between the positive electrode material area and the blank area) by moving up and down through the telescopic cylinder 15( Figure 2 ); after completing the front coating, the back surface needs to be coated with a buffer return mechanism.

[0061] (2-5) Apply the molten hot melt adhesive to the tab forming area and cover at least part of the active material layer, and cool and solidify to form a hot melt adhesive layer.

[0062] (2-6) Cutting with a pulse laser, laser direct cutting of the insulating coating surface, obtaining a preset tab shape and excess waste edge, namely the lithium battery positive plate. Among them, the width of the insulating coating left on the plate after laser cutting is 3-4 mm, and the coating area and the cutting area are located on the tab side.

[0063] (3) The positive plate prepared by the above laser cutting process is wound or stacked with the separator and the negative plate to obtain a qualified roll core, as shown in Figure 3 , the separator 9 covers the negative plate 11 and the positive plate 12 as a whole, the negative plate 11 covers the positive plate 12 in the middle layer, and the positive plate 12 is located in the innermost layer.

[0064] Among them, the negative plate 11 includes a negative active material area 8 and a negative current collector 10 (copper foil), and the positive plate 12 includes a positive active material area 7, an insulating coating coating area 6 (located on the edge of the positive plate), an insulating coating area 5 (located on the tab) that is not cut off by laser cutting, and a positive current collector 4 (aluminum foil).

[0065] The winding or stacking process uses staggered coverage to realize the correspondence between the negative cutout and the positive insulating layer, as follows: in the laser cutting process, the positive cut insulating layer (insulating coating coating area 6 located on the edge of the positive plate), and the negative cut active material area (negative active material area 8); in the assembly process, the negative active material area (negative active material area 8) covers the positive active material area (positive active material area 7), and the positive insulating layer (insulating coating coating area 6) covers the negative active material area (negative active material area 8).

[0066] As shown in Figure 3 , the phase difference between the negative active material area (negative active material area 8) covering the positive active material area (positive active material area 7) is 3.5 mm; and the phase difference between the positive insulating layer (insulating coating coating area 6) covering the negative active material area (negative active material area 8) is 1 mm.

[0067] Example 2

[0068] A preparation method of a lithium battery positive plate, the specific steps are the same as in Example 1, and the composition ratio of the insulating coating is as follows:

[0069] The proportion of ethylene-vinyl acetate polymer is 83.5wt%, the proportion of plasticizer is 0.5wt%, the proportion of adhesive is 15wt%, and the proportion of antioxidant is 1wt%.

[0070] Example 3

[0071] A preparation method of a lithium battery positive plate, the specific steps are the same as in Example 1, and the composition ratio of the insulating coating is as follows:

[0072] Ethylene-vinyl acetate polymer accounts for 85wt%, plasticizer accounts for 0.5wt%, binder accounts for 13wt%, antioxidant accounts for 1.5wt%.

[0073] Example 4

[0074] A preparation method of a lithium battery positive electrode sheet, the specific steps are the same as example 1, wherein the component ratio of the insulating coating is as follows:

[0075] Ethylene-vinyl acetate polymer accounts for 87.5wt%, plasticizer accounts for 0.5wt%, binder accounts for 10wt%, antioxidant accounts for 2wt%.

[0076] Comparative Example 1

[0077] A preparation method of a lithium battery positive electrode sheet, the specific steps are as follows:

[0078] (1) Use the traditional PVDF (polyvinylidene fluoride) + boehmite + NMP (N-methyl pyrrolidone) scheme, and uniformly coat the edge of the active material in the coating process.

[0079] (2) The positive electrode sheet obtained above is cut using a pulse laser to obtain a shaped tab, and the process is completed.

[0080] Test Example 1

[0081] 1. Test item

[0082] (1) Test the insulating layer resistance data of the positive electrode sheet prepared in examples 2-4 and comparative example 1, and record the data, and observe the insulating layer coating condition at the laser cutting position with electron microscope.

[0083] (2) Soak the positive electrode sheet prepared in examples 2-4 and comparative example 1 in electrolyte at two high temperatures, wherein the soaking time at 45℃ is 20 days, and the soaking time at 60℃ is 10 days, and observe the material dropping condition of the insulating layer.

[0084] 2. Test results

[0085] The test results are shown in the following table 1:

[0086] Table 1 test results

[0087]

[0088]

[0089] From table 1 and Figures 4-7It can be seen that the examples 2-4 and the comparative example 1 are basically equivalent in insulation level, and can meet the basic insulation requirement; but the examples 2-4 are superior to the comparative example 1 in the high-temperature electrolyte immersion resistance; at the same time, the examples 2-4 are superior to the comparative example 1 in the laser cutting burr coating Figures 4-6 The electron microscope pictures of different magnifications of the examples 2-4 are respectively shown, wherein Figure 4 is the picture under 1000 times magnification, and is the same magnification as the comparative example 1, and the two form a sharp contrast. Figure 7

[0090] It can be seen from the above test results that the application meets the process processing requirement in the laser cutting insulation protection ability, and is superior to the current traditional insulation coating method.

[0091] The above-described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. The protection scope of the present application is subject to the scope of the claims, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor fall within the protection scope of the present application.​

Claims

1. A method for producing a lithium battery positive electrode sheet, characterized by, The method comprises the following steps: Step 1) In a high pressure reactor, the vinyl acetate and K2S2O8or (NH4)2S2O8initiator are first added to the emulsion medium prepared, then ethylene is added, and the polymerization is carried out at 85°C, 90 kg / cm 2 pressure, obtaining a vinyl acetate content of 75% ethylene-vinyl acetate polymer latex; Step 2) At a high temperature of 150 DEG C, the ethylene-vinyl acetate polymer latex prepared in step 1) is added with a plasticizer, a binder and an antioxidant in a mass ratio of 0.5-1:10-15:1-2 in sequence; after being uniformly dispersed and stirred at a high temperature of 220 DEG C, an insulating coating glue solution is obtained; after being filtered and cooled to room temperature, a solid insulating coating is prepared; Step 3) The solid insulating coating prepared in step 2) is heated to above 170 DEG C by using a heating furnace to melt into a glue solution that can flow; the melt flow rate is 170 DEG C / 2.0 kg, 190 DEG C / 2.2 kg; Step 4) The melted glue solution obtained in step 3) is introduced into a glue coating head by an electric heating pipe, wherein the temperature of the heating furnace and the electric heating pipe is controlled at 170 DEG C and continuous heating is realized; Step 5) An electric heating module is started, and the heating temperature is 220 DEG C to further melt the insulating coating; Step 6) After the whole glue coating device is installed at a laser cutting and unwinding position and before the laser cutting position, the laser cuts the horizontal electrode sheet after unwinding and walking on the conveying roller, and the installation position of the glue coating device is located directly above the conveying roller; the laser cutting walking belt process is uniformly coated on the edge of the positive electrode sheet current collector, i.e. the junction of the positive electrode material area and the blank area, by moving up and down through the telescopic cylinder; after completing the front coating, the back surface needs to be coated by matching the buffer return mechanism; Step 7) The melted hot melt adhesive is coated on the tab forming area and covers at least part of the active material layer, and is cooled and solidified to form a hot melt adhesive layer; Step 8) The surface of the insulating coating is directly cut by laser to obtain a preset tab shape and excess waste edge.

2. The method of claim 1, wherein the lithium battery cathode sheet is prepared by the steps of: In step 8), the width of the insulating coating left on the electrode sheet after laser cutting is 3-4 mm, and the coating area and the cutting area are both located on the tab side. ​ 3. The lithium battery positive electrode sheet prepared by the preparation method according to claim 1 or 2, characterized in that, The edge of the positive electrode sheet is coated with an insulating coating of special material, and the coating position of the insulating coating is between the active material layer and the tab blank; the composition of the insulating coating includes ethylene-vinyl acetate polymer, plasticizer, binder and antioxidant; the insulating coating is coated on the active material layer and covers a certain width; The mass ratio of each component in the insulating coating is as follows: Ethylene-vinyl acetate polymer: plasticizer: binder: antioxidant = 80-85:0.5-1:10-15:1-2.

4. The lithium battery cathode sheet according to claim 3, characterized in that, The width of the insulating coating is 6-8 mm, and the thickness is 10-15 μm.

5. The lithium battery cathode sheet according to claim 3, wherein The ethylene-vinyl acetate polymer is prepared by emulsion method from ethylene and vinyl acetate, and the molecular weight is 1280, and the structural formula is as follows: 。 6. The lithium battery cathode sheet according to claim 3, wherein The plasticizer is dibutyl phthalate or dioctyl phthalate; the binder is polyvinylidene fluoride or polystyrene; the antioxidant is butylated hydroxyanisole or dibutylhydroxytoluene.

7. The lithium battery cathode sheet according to claim 3, wherein The active material layer is lithium iron phosphate or ternary lithium.

8. Use of the lithium battery positive electrode sheet according to any one of claims 3 to 7 in the production of a lithium battery, characterized in that, The positive electrode sheet of the lithium battery is prepared by winding or stacking process, matched with a separator and a negative electrode sheet to prepare a qualified roll core, and then matched with an electrolyte and a shell structure to jointly form a lithium battery.

9. Use according to claim 8, characterized in that, The winding or lamination process realizes that the negative cutout corresponds to the positive insulating layer by staggered covering, specifically as follows: in the laser cutting process, the positive cut insulating layer and the negative cut active material area; in the assembling process, the negative active material area covers the positive active material area, and the positive insulating layer covers the negative active material area.

10. Use according to claim 9, characterized in that, The phase difference of the negative active material area covering the positive active material area is 3.5 mm; and the phase difference of the positive insulating layer covering the negative active material area is 1 mm.

11. A lithium battery, characterized by The lithium battery positive plate comprises the lithium battery positive plate according to any one of claims 3-7.

Images