Lithium-ion battery electrode sheets and their preparation methods

Abstract

This invention relates to the field of lithium battery technology, specifically to a lithium battery electrode sheet and its preparation method. The lithium battery electrode sheet includes a substrate and a positive electrode active material, and also includes a mesh with multiple mesh openings, the mesh being woven from graphene fibers. The mesh is fixedly connected to one side of the substrate, and the positive electrode active material is coated on the side of the mesh away from the substrate, filling the mesh openings and contacting the substrate. The method for preparing the lithium battery electrode sheet involves bonding the graphene fiber woven mesh to the side of the substrate; then coating the positive electrode active material on the side of the mesh away from the substrate; and finally drying. This solution solves the technical problems of low electronic conductivity and low lithium-ion diffusion rate in lithium iron phosphate positive electrode sheets.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a lithium battery electrode sheet and its preparation method. Background Technology

[0002] A lithium battery consists of a positive electrode and a negative electrode, separated by a separator to prevent short circuits caused by contact between the two electrodes. The charging and discharging of the lithium battery is achieved by the movement of lithium ions in the electrolyte between the positive and negative electrodes.

[0003] The positive electrode of a lithium-ion battery consists of a substrate and a positive electrode active material located on the substrate. The positive electrode active material is typically lithium iron phosphate (LFP). LFP is chosen because it has certain advantages, such as low cost and ease of preparation. However, LFP has the following disadvantages: its electronic conductivity and lithium-ion diffusion rate are relatively low, thus affecting the volumetric capacity and energy density of the lithium-ion battery. It also limits the charging speed and results in poor rate performance and cycle performance. Summary of the Invention

[0004] The present invention aims to provide lithium battery electrode sheets and their preparation methods to solve the technical problems of low electronic conductivity and low lithium-ion diffusion rate of positive electrode sheets.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a lithium battery electrode sheet, comprising a substrate and a positive electrode active material, and further comprising a mesh having multiple mesh openings, the mesh being woven from graphene fibers; the mesh is fixedly connected to one side of the substrate, the positive electrode active material is coated on the side of the mesh away from the substrate, and the positive electrode active material is filled in the mesh openings, the positive electrode active material located in the mesh openings being in contact with the substrate.

[0006] The principle and advantages of this scheme are: the thickness of the mesh is less than 0.2mm. Since the positive electrode active material accounts for more than half of the weight of the entire electrode sheet, the weight of the mesh is relatively small. Therefore, setting the mesh on the electrode sheet has almost no impact on the thickness and weight of the electrode sheet.

[0007] Meanwhile, the mesh is made of graphene fiber. According to the properties of graphene fiber, graphene has excellent mechanical strength. When the positive electrode active material is coated onto the mesh, the mesh can act as a skeleton for the positive electrode active material, supporting it. As a supporting substance on which the positive electrode active material is attached, the positive electrode active material will not break or be damaged, and the stability of the entire electrode sheet is good.

[0008] Furthermore, based on the properties of graphene, it is known that graphene possesses excellent electrical and thermal conductivity. By coating the positive electrode active material onto a mesh woven from graphene fibers, the excellent electrical conductivity effectively improves the electronic conductivity of the positive electrode; the excellent thermal conductivity allows for rapid heat dissipation from the electrode sheet, enabling the positive electrode active material to heat up uniformly and quickly, avoiding slow localized heating. Since the lithium-ion diffusion rate is temperature-dependent, the rapid and uniform heating of the positive electrode active material thus improves the overall lithium-ion diffusion rate. In summary, this solution can improve the volumetric specific capacity and energy density of lithium batteries, thereby contributing to improved rate performance and cycle performance.

[0009] Furthermore, it is worth noting that although coating the substrate with graphene slurry, creating a mesh-like structure, and then drying the slurry before coating the positive electrode active material into the mesh can solve the technical problem of this solution, the dried graphene slurry itself is not as flexible as graphene fibers. After the electrode sheet is prepared, it may crack or break during installation and movement, thus failing to provide stable support for the positive electrode active material and failing to achieve the effect of the mesh in preventing breakage and damage to the positive electrode active material. The cracks in the dried graphene slurry create gaps, affecting the conductivity of the electrode sheet. Therefore, a mesh woven from graphene fibers is superior to graphene slurry.

[0010] Preferably, as an improvement, an adhesive layer is provided between the mesh and the substrate. The adhesive layer is mesh-shaped, and its planar shape is the same as that of the mesh. The mesh openings of the adhesive layer are opposite to those of the mesh. An adhesive is applied between the mesh and the substrate to bond the substrate and the mesh together. After the adhesive is applied, an adhesive layer is formed between the mesh and the substrate.

[0011] Because the planar shape of the adhesive layer is the same as that of the mesh, and the adhesive layer is also mesh-like with the mesh openings of the adhesive layer opposite to those of the mesh, the adhesive layer is not located at the mesh openings of the mesh. Instead, the adhesive layer is located between each mesh wire and the substrate. The adhesive layer does not block the mesh openings, so the positive electrode active material located in the mesh openings is not blocked by the adhesive layer. The positive electrode active material located in the mesh openings can still contact the substrate, avoiding the adhesive layer completely blocking the positive electrode active material and the substrate, which would affect the conductivity between the positive electrode active material and the substrate. In this way, the substrate can normally transfer current with the positive electrode active material.

[0012] Preferably, as an improvement, the adhesive used in the adhesive layer is a conductive adhesive. Therefore, the conductive adhesive is conductive, which reduces the impact of the adhesive on the conductivity of the electrode sheet.

[0013] Preferably, as an improvement, the positive electrode active material is lithium iron phosphate, or a ternary material of lithium cobalt oxide, lithium manganese oxide, or nickel cobalt manganese.

[0014] The method for preparing lithium battery electrode sheets includes the following steps:

[0015] Step 1: Attach the graphene fiber woven mesh to the side of the substrate.

[0016] Step 2, then the positive electrode active material is coated on the side of the mesh away from the substrate;

[0017] Step 3, finally, dry it.

[0018] The method described above for preparing lithium-ion battery electrode sheets involves first attaching a mesh to a substrate, which then blocks the mesh openings. The positive electrode active material is then coated, preventing leakage through the mesh openings. The coated material is positioned within the mesh openings and directly contacts the substrate. This method achieves efficient preparation of lithium-ion battery electrode sheets; the operation is simple and convenient, requiring only the drying of the coated positive electrode active material without needing to dry other parts of the electrode sheet.

[0019] Preferably, as an improvement, in step 1, the adhesive is first applied to the side of the mesh, and then the mesh is adhered to the substrate;

[0020] When applying adhesive to the mesh, the belt body is attached to the mesh. The belt body has multiple protrusions on its side, which are inserted into the mesh openings of the mesh. Then, the adhesive is applied to the side of the mesh away from the belt body.

[0021] After the adhesive is applied, separate the tape and the mesh, and attach the side of the mesh coated with adhesive to the side of the substrate.

[0022] Therefore, when the protrusion is inserted into the mesh and adhesive is applied to the side of the mesh, because the protrusion passes through the mesh and blocks it, the adhesive can only be applied to the ends of the protrusion and each mesh line, avoiding application into the mesh itself. This prevents the adhesive from clogging the mesh. After the adhesive is applied, the belt separates from the mesh, and the protrusion emerges from the mesh, at which point the mesh remains open.

[0023] Furthermore, while the mesh is woven from fibers, the interlacing of the fibers can be uneven during weaving, with some fibers being too close together. This results in smaller mesh openings formed by multiple intersecting fibers, affecting the uniform distribution of the mesh on the electrode sheet. In this solution, protrusions are inserted into the mesh openings. These protrusions enlarge the smaller openings, preventing the mesh from becoming too small due to close-knit fibers. The protrusions also cause the smaller mesh openings to shift, increasing the distance between them and resulting in a more uniform distribution of the fibers. This ensures even contact between the mesh and the positive electrode active material, improving the performance of the electrode sheet.

[0024] Preferably, as an improvement, an adhesive is applied to the mesh using an adhesive coating device;

[0025] The coating equipment includes a mesh roller, a coating roller, and a conveyor belt mechanism. The protrusion is located on the outer side of the conveyor belt mechanism. The conveyor belt mechanism is arranged laterally. After the mesh on the mesh roller is pulled out, it is attached to the outer side of the belt. The coating roller is located on the outer side of the belt, and the side of the coating roller is in contact with the side of the mesh on the belt away from the belt.

[0026] Therefore, through this adhesive coating equipment, the mesh is pulled from the mesh roller and conveyed to the outer surface of the conveyor belt. The protrusions on the belt automatically enter the mesh openings. The conveyor belt follows the mesh, thus achieving automatic protrusion into the mesh openings during mesh conveying, eliminating the need for manual operation. The mesh then moves with the conveyor belt to the coating roller, which automatically applies adhesive to the side of the mesh. After adhesive application, the mesh and belt automatically separate as they continue to be conveyed. In summary, the adhesive coating equipment in this solution achieves automatic bonding of the belt and mesh, automatic adhesive application, and automatic separation of the mesh and belt, all without manual operation, resulting in a high degree of automation and improving the efficiency of lithium battery electrode sheet preparation.

[0027] Preferably, as an improvement, a substrate roller is provided on the outer side of the conveyor belt mechanism. After the mesh is coated with adhesive, it separates from the belt body and adheres to the substrate pulled out from the substrate roller. Thus, after the mesh is coated with adhesive, it immediately adheres to the substrate pulled out from the substrate roller, thereby automatically bonding the two together and improving the preparation efficiency of lithium battery electrode sheets.

[0028] Preferably, as an improvement, the cross-sectional shape of the protrusion is trapezoidal or triangular, with the end of the protrusion furthest from the belt being the smaller end. This way, even if the mesh wires around the mesh holes stick together, making the holes smaller, it is still easy for the protrusion to be inserted into the mesh holes. At the same time, the end of the protrusion closest to the belt is larger, ensuring that the two ends of the protrusion are not the same size, thus guaranteeing that the protrusion can enlarge the small mesh holes after entering the mesh holes.

[0029] Preferably, as an improvement, bristles are fixedly provided on the surface of the coating roller. Thus, the bristles can extend into the gaps between the plurality of protrusions away from the ends of the belt and contact the mesh, thereby applying the adhesive to the mesh. Attached Figure Description

[0030] Figure 1 This is a planar schematic diagram of the lithium battery electrode sheet in Example 1.

[0031] Figure 2 This is a front view of the adhesive application equipment.

[0032] Figure 3 for Figure 2 A partial schematic diagram showing the fit between the inner mesh and the belt.

[0033] Figure 4 This is a schematic diagram of each layer of a lithium battery electrode sheet.

[0034] Figure 5 This is a planar schematic diagram of the adhesive layer.

[0035] Figure 6 This is a schematic diagram of a planar mesh with uneven interlacing. Detailed Implementation

[0036] The following detailed description illustrates the specific implementation method:

[0037] The reference numerals in the accompanying drawings include: substrate 1, mesh 2, positive electrode active material 3, mesh opening 4, bump 5, belt 6, mesh roller 7, first guide roller 8, conveyor roller 9, adhesive box 10, coating roller 11, substrate roller 12, pressure roller 13, second guide roller 14, winding roller 16, brush bristles 17, and adhesive layer 18.

[0038] The basic implementation examples are as follows: Figures 1-5 As shown.

[0039] Combination Figure 1 , Figure 4 and Figure 5 As shown, the lithium battery electrode sheet includes a substrate 1 (substrate 1 is aluminum foil), an adhesive layer 18, a mesh 2, and a positive electrode active material 3, which are combined with... Figure 1As shown, the mesh 2 is a mesh structure with multiple mesh openings 4. The mesh 2 is woven from graphene fibers. Graphene fibers are existing technology and will not be elaborated further here. For example, patent publication number CN103388197B discloses a method for preparing graphene fibers. The graphene fibers prepared using this patented method have high electrical conductivity and high flexibility, and can be woven into any shape. Furthermore, graphene fibers can also be graphene composite fibers (graphene composite fibers have advantages such as good flexibility, electrical conductivity, and excellent thermal properties). Dong Zelin et al. from Beijing Institute of Technology used graphene composite fibers as conductors to weave conductive fabrics (fabric is a flat, soft sheet-like material formed by crossing, knotting, and connecting small, flexible elongated materials; the small, flexible elongated materials cross each other to form mesh openings, therefore the fabric has a mesh structure; hence, the fabric is the mesh 2 in this embodiment). In this embodiment, the thickness of the mesh 2 is less than 0.2 mm.

[0040] Combination Figure 1 and Figure 4 As shown, the mesh 2 is bonded to one side of the substrate 1 via an adhesive layer 18. The positive electrode active material 3 is coated on the side of the mesh 2 away from the substrate 1, and the positive electrode active material 3 fills the mesh openings 4, making contact between the positive electrode active material 3 located in the mesh openings 4 and the substrate 1. Figure 5 As shown, the adhesive layer 18 in this embodiment is mesh-shaped. The planar shape of the adhesive layer 18 is the same as that of the mesh 2. The mesh openings of the adhesive layer 18 are opposite to the mesh openings 4 of the mesh 2. In this way, the adhesive layer 18 will not block the mesh openings 4 of the mesh 2, and the positive electrode active material 3 in the mesh openings 4 of the mesh 2 will not be blocked by the adhesive layer 18. The positive electrode active material 3 in the mesh openings 4 of the mesh 2 can contact the substrate 1.

[0041] In this embodiment, the adhesive used in the adhesive layer 18 is a conductive adhesive, such as epoxy resin conductive adhesive, phenolic resin conductive adhesive, polyurethane conductive adhesive, thermoplastic resin conductive adhesive, and polyimide conductive adhesive. The positive electrode active material 3 is lithium iron phosphate, or a ternary material of lithium cobalt oxide, lithium manganese oxide, or nickel-cobalt-manganese. In this embodiment, the positive electrode active material 3 is preferably lithium iron phosphate, specifically including lithium iron phosphate, polyvinylidene fluoride, and N-methylpyrrolidone. N-methylpyrrolidone is used as a solvent to dissolve polyvinylidene fluoride. The weight ratio of lithium iron phosphate to polyvinylidene fluoride is 10:1, and it is prepared by ball milling.

[0042] In addition, this embodiment also discloses a method for preparing lithium battery electrode sheets, including the following steps:

[0043] Step 1: Adhere the graphene fiber woven mesh 2 to the side of the substrate 1; specifically, first apply adhesive to the side of the mesh 2, and then adhere the mesh 2 to the substrate 1.

[0044] Step 2, then the positive electrode active material 3 is coated on the side of the mesh 2 away from the substrate 1;

[0045] Step 3: Finally, dry the product at a temperature of 70℃ for 3-4 hours.

[0046] In this embodiment, an adhesive coating device is used to coat the mesh 2 with adhesive. Figure 2 and Figure 3 As shown, the adhesive coating equipment in this embodiment includes a frame, a first guide roller 8, a mesh roller 7, a coating roller 11, and a conveyor belt mechanism. The conveyor belt mechanism is arranged laterally and includes two conveyor rollers 9 and a belt body 6 located on the two conveyor rollers 9. Multiple protrusions 5 are integrally formed on the outer surface of the belt body 6. The cross-sectional shape of the protrusions 5 is trapezoidal or triangular. In this embodiment, the cross-sectional shape of the protrusions 5 is trapezoidal. The end of the protrusion 5 away from the belt body 6 is the small end, and the other end of the protrusion 5 is the large end.

[0047] The shaft of the mesh roller 7 is rotatably connected to the frame. The mesh roller 7 is located on the left side of the conveyor belt mechanism. A mesh 2 is wound on the mesh roller 7. After the mesh 2 on the mesh roller 7 is pulled out, it is in contact with the outer side of the belt body 6. In this embodiment, the mesh 2 on the mesh roller 7 is pulled out to the right and is in contact with the outer side of the belt body 6 on the lower side of the conveyor belt mechanism. The first guide roller 8 is located between the left end of the conveyor belt mechanism and the mesh roller 7, and the first guide roller 8 is in contact with the mesh 2. The shaft of the coating roller 11 is rotatably connected to the frame. The coating roller 11 is located below the belt body 6 on the lower side of the conveyor belt mechanism. Brush bristles 17 are adhered to the outer circumference of the coating roller 11. The brush bristles 17 at the top of the coating roller 11 are in contact with the lower side of the mesh 2 on the belt body 6. An adhesive box 10 is fixed to the frame by bolts. The adhesive box 10 contains adhesive, and the bottom of the coating roller 11 is immersed in the adhesive in the adhesive box 10.

[0048] A substrate roller 12 is provided on the outer side of the conveyor belt mechanism. The roller shaft of the substrate roller 12 is rotatably connected to the frame. The substrate 1 is wound on the substrate roller 12, which is located at the lower right of the right end of the conveyor belt mechanism. A second guide roller 14 is provided on the right side of the substrate roller 12 and is rotatably connected to the frame. After the substrate 1 on the substrate roller 12 is pulled out, it passes to the right through the second guide roller 14. The mesh 2 on the belt 6 is conveyed to the right along with the belt 6. The mesh 2 separates from the belt 6 and adheres to the upper surface of the substrate 1 pulled out from the substrate roller 12. The substrate 1 and the mesh 2 are adhered together and pass through two pressure rollers 13, which are rotatably connected to the frame. The two pressure rollers 13 press the mesh 2 and the substrate 1 tightly together. A take-up roller 16 is provided on the frame. The roller shaft of the take-up roller 16 is rotatably connected to the frame. After the mesh 2 and the substrate 1 are combined, they are conveyed to the right and wound onto the take-up roller 16.

[0049] In this embodiment, the frame is equipped with a motor that drives the conveyor belt mechanism, the take-up roller 16, and the coating roller 11 to rotate.

[0050] Combination Figure 6 As shown, the mesh 2 in this embodiment is woven from fibers. However, during the weaving process, the interlacing of the mesh threads on the mesh 2 may be uneven. This results in some adjacent mesh threads being too close together, leading to smaller mesh openings formed by the intersection of multiple mesh threads. This uneven interlacing of the mesh threads affects the uniform distribution of the mesh threads on the electrode sheet, thus impacting the conductivity uniformity of the electrode sheet.

[0051] When preparing lithium battery electrode sheets using the above-mentioned equipment, the conveyor belt mechanism moves counterclockwise, the take-up roller 16 rotates clockwise, and the coating roller 11 rotates clockwise. The mesh 2 on the mesh roller 7 is pulled out, and the mesh 2 moves to the right. The mesh 2 passes through the first guide roller 8 and moves to the lower side of the conveyor belt 6, where it comes into contact with the outer surface of the lower side of the belt 6. The protrusions 5 on the belt 6 enter the mesh holes 4 of the mesh 2. When the protrusions 5 enter the smaller mesh holes 4, they enlarge them and adjust any misplaced mesh lines, thus moving two closely spaced mesh lines away from each other and ensuring that the mesh lines on the mesh 2 are distributed as evenly as possible. The protrusions 5 then enter the mesh holes 4 and block them. The mesh 2 then moves to the right along with the belt 6.

[0052] The coating roller 11 rotates clockwise. Adhesive adheres to the bottom of the coating roller 11 and rotates with it. When the roller reaches the top, the brush 17 applies the adhesive to the lower end of the protrusion 5 and the mesh 2. Since the protrusion 5 is located within the mesh opening 4, the adhesive is not applied into the mesh opening 4, preventing clogging. As the mesh 2 continues to move to the right, it separates from the belt 6 when it reaches the right end of the conveyor belt mechanism, and the protrusion 5 emerges from the mesh opening 4. The mesh 2 continues to be conveyed to the right, and it combines with the substrate 1 pulled from the substrate roller 12, passing through two pressure rollers 13. The two pressure rollers 13 press the mesh 2 and substrate 1 together. Finally, the combined mesh 2 and substrate 1 are wound together onto the take-up roller 16 for later use.

[0053] Subsequently, the material wound on the take-up roller 16 can be removed and cut, and then the positive electrode active material 3 can be coated onto the mesh 2. The positive electrode active material 3 enters the mesh 4 and contacts the substrate 1. After the positive electrode active material 3 is coated, it is placed in a drying oven for drying.

[0054] In this embodiment, the operating parameters of the coating equipment (e.g., the rotation speed of the take-up roller 16, the conveyor belt mechanism, and the coating roller 11) are controlled by a PLC controller.

[0055] The prepared electrode sheets were assembled into lithium batteries in a glove box where the water and oxygen content were both less than 0.5 ppm. After cyclic voltammetry testing (using a CHI 660E electrochemical workstation, with a test voltage range of 0.05-2V, a scan rate of 0.2 mV / s, and a current density of 300 mA / g) and constant current charge-discharge testing (using a CT-400 battery testing system from Newwell, with a test voltage range of 0.05-2V and a current density of 300 mA / g), the tests showed that the rate performance of the lithium batteries was improved by about 20% compared to the previous ones, and the cycle performance was improved by about 15%.

[0056] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a lithium battery electrode sheet, wherein the lithium battery electrode sheet comprises a substrate and a positive electrode active material, characterized in that: It also includes a mesh screen with multiple mesh openings, the mesh screen being woven from graphene fibers; the mesh screen is fixedly connected to one side of the substrate, the positive electrode active material is coated on the side of the mesh screen away from the substrate, and the positive electrode active material is filled in the mesh openings, the positive electrode active material located in the mesh openings is in contact with the substrate; The method for preparing lithium battery electrode sheets includes the following steps: Step 1: Attach the graphene fiber woven mesh to the side of the substrate. Step 2, then the positive electrode active material is coated on the side of the mesh away from the substrate; Step 3, finally, dry it; In step 1, the adhesive is first applied to the side of the mesh, and then the mesh is glued to the substrate. When applying adhesive to the mesh, the belt body is attached to the mesh, and multiple protrusions are provided on the side of the belt body. The protrusions are inserted into the mesh openings of the mesh, and then adhesive is applied to the side of the mesh away from the belt body. After the adhesive is applied, separate the tape and the mesh, and attach the side of the mesh coated with adhesive to the side of the substrate.

2. The method for preparing lithium battery electrode sheets according to claim 1, characterized in that: An adhesive layer is provided between the mesh and the substrate. The adhesive layer is mesh-shaped, and the planar shape of the adhesive layer is the same as that of the mesh. The mesh openings of the adhesive layer are opposite to those of the mesh.

3. The method for preparing lithium battery electrode sheets according to claim 2, characterized in that: The adhesive used in the adhesive layer is a conductive adhesive.

4. The method for preparing lithium battery electrode sheets according to any one of claims 1-3, characterized in that: The positive electrode active material is lithium iron phosphate, or a ternary material of lithium cobalt oxide, lithium manganese oxide, or nickel cobalt manganese.

5. The method for preparing lithium battery electrode sheets according to claim 1, characterized in that: Apply adhesive to the mesh using a coating equipment; The coating equipment includes a mesh roller, a coating roller, and a conveyor belt mechanism. The protrusion is located on the outer side of the conveyor belt mechanism. The conveyor belt mechanism is arranged laterally. After the mesh on the mesh roller is pulled out, it is attached to the outer side of the belt. The coating roller is located on the outer side of the belt, and the side of the coating roller is in contact with the side of the mesh on the belt away from the belt.

6. The method for preparing lithium battery electrode sheets according to claim 5, characterized in that: The outer side of the conveyor belt mechanism is equipped with a substrate roller. After the mesh is coated with adhesive, it is separated from the belt body. After the mesh is separated from the belt body, it is attached to the substrate pulled out from the substrate roller.

7. The method for preparing lithium battery electrode sheets according to claim 1, characterized in that: The cross-sectional shape of the protrusion is trapezoidal or triangular, and the end of the protrusion away from the belt body is the small end.

8. The method for preparing lithium battery electrode sheets according to claim 5, characterized in that: The coating roller is fixedly provided with bristles.

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