A positive electrode sheet, its preparation method and application

Abstract

This invention provides a positive electrode sheet, its preparation method, and its application. The positive electrode sheet includes a positive current collector and a base layer, an intermediate layer, and an active layer sequentially stacked on the surface of the positive current collector. The base layer, intermediate layer, and active layer all contain bisphenol-S epoxy resin. This invention ensures that BPSER does not affect the normal operation of lithium-ion batteries by designing the proportion and thickness of bisphenol-S epoxy resin (BPSER) material in the base layer, intermediate layer, and active layer, as well as the mixing sequence of key materials.

Description

Technical Field

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

[0002] With the rapid development of science and technology, lithium-ion batteries, as an ideal chemical energy source recognized by society today, are widely used in electronic products such as cameras, mobile phones, and laptops due to their advantages such as small size, large capacity, and small capacity loss after repeated use. However, their safety issues, such as leakage, expansion, combustion, and even explosion, are receiving increasing attention and seriously hindering the promotion and application of lithium-ion batteries in the fields of power and large-scale energy storage. People have had to reduce the harm caused by their drawbacks by adding high-temperature safety materials and other means.

[0003] The rapid development of electric vehicles has placed increasingly higher demands on lithium-ion batteries, encompassing aspects such as long lifespan, high power, fast charging, and high safety. Existing conventional lithium-ion battery cathodes are obtained by coating current collectors with electrode active materials. The primary cause of thermal runaway in lithium-ion batteries using this type of cathode is internal short circuits.

[0004] Lithium-ion batteries may be subjected to thermal shock, puncture, compression and violent collision under abnormal operation, which may cause internal short circuits and release a large amount of heat. This can cause the separator to shrink in volume and fail, which may further lead to thermal runaway and cause safety problems such as fire and explosion.

[0005] CN109004175A discloses a positive electrode sheet and a lithium-ion battery. The positive electrode sheet includes: a current collector; a first active material layer including a first active material; and a second active material layer. The first active material layer is disposed between the current collector and the second active material layer. The first active material layer includes a first active material selected from at least one combination of modified ternary positive electrode materials and modified nickel-cobalt-manganese ternary materials.

[0006] CN112531174A discloses a positive electrode sheet and a battery, wherein the positive electrode sheet has a third coating, a first positive electrode coating, and a second positive electrode coating sequentially stacked on a positive electrode current collector. In the event of an internal short circuit in the battery, the first positive electrode coating can increase the contact resistance of the positive electrode sheet, reduce the internal short-circuit current, thereby reducing the heat generated inside the battery and lowering the risk of battery runaway.

[0007] The positive electrode sheet described in the above scheme cannot simultaneously achieve good cycle performance and high-temperature safety performance, which limits its practical application. In this case, a lithium-ion battery with good cycle performance and high-temperature safety is needed. Summary of the Invention

[0008] The purpose of this invention is to provide a positive electrode sheet, its preparation method and application. This invention ensures that BPSER does not affect the normal operation of lithium-ion batteries by designing the proportion and thickness of bisphenol-S epoxy resin (BPSER) material in the base layer, intermediate layer and active layer, and the mixing sequence of key materials.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a base layer, an intermediate layer and an active layer sequentially stacked on the surface of the positive current collector, wherein the base layer, the intermediate layer and the active layer all contain bisphenol-S epoxy resin.

[0011] This invention incorporates bisphenol-S epoxy resin (BPSER) into the coating of traditional lithium-ion battery cathode materials. BPSER is insoluble in electrolyte and can rapidly and effectively form an insulating layer in the event of a sudden temperature rise due to a short circuit or malfunction, causing the separator to fail. This interrupts the electrochemical reaction and improves the battery's high-temperature safety performance.

[0012] Since BPSER is non-conductive and does not participate in electrochemical reactions, this invention uses differentiated design of the base layer, intermediate layer, and active layer, and the mixing sequence of key materials. The base layer is close to the current collector, and the active layer is far from the current collector and close to the separator. This ensures that BPSER does not affect the normal operation of lithium-ion batteries while improving battery safety performance.

[0013] Preferably, the substrate layer further includes a positive electrode active material, a conductive agent, and a binder.

[0014] Preferably, based on the mass of the substrate layer as 100%, the mass fraction of the positive electrode active material is 60-75%, for example: 60%, 68%, 70%, 72% or 75%, etc.

[0015] Preferably, the bisphenol-S epoxy resin has a mass fraction of 1-3%, for example: 1%, 1.5%, 2%, 2.5% or 3%, etc.

[0016] Preferably, the mass fraction of the conductive agent is 15-25%, for example: 15%, 18%, 20%, 22% or 25%, etc.

[0017] Preferably, the adhesive has a mass fraction of 8-15%, for example: 8%, 9%, 10%, 12% or 15%, etc.

[0018] Preferably, the thickness of the substrate layer is 10~30μm, for example: 10μm, 15μm, 20μm, 25μm or 30μm, etc.

[0019] Preferably, the intermediate layer further includes a positive electrode active material, a conductive agent, and a binder.

[0020] Preferably, based on the mass of the intermediate layer as 100%, the mass fraction of the positive electrode active material is 70-85%, for example: 70%, 72%, 75%, 80% or 85%, etc.

[0021] Preferably, the bisphenol-S epoxy resin has a mass fraction of 0.5% to 1%, for example: 0.5%, 0.6%, 0.7%, 0.8% or 1%, etc.

[0022] Preferably, the mass fraction of the conductive agent is 10-15%, for example: 10%, 11%, 12%, 13%, 14% or 15%, etc.

[0023] Preferably, the adhesive has a mass fraction of 5-10%, for example: 5%, 6%, 7%, 8% or 10%.

[0024] Preferably, the thickness of the intermediate layer is 20~50μm, for example: 20μm, 25μm, 30μm, 40μm or 50μm, etc.

[0025] Preferably, the active layer further includes a positive electrode active material, a conductive agent, and a binder.

[0026] Preferably, based on the mass of the active layer as 100%, the mass fraction of the positive electrode active material is 75-90%, for example: 75%, 78%, 80%, 85% or 90%, etc.

[0027] Preferably, the bisphenol-S epoxy resin has a mass fraction of 0.5% to 1%, for example: 0.5%, 0.6%, 0.7%, 0.8% or 1%, etc.

[0028] Preferably, the mass fraction of the conductive agent is 5-10%, for example: 5%, 6%, 7%, 8% or 10%.

[0029] Preferably, the adhesive has a mass fraction of 4-10%, for example: 4%, 5%, 6%, 8% or 10%.

[0030] Preferably, the thickness of the active layer is 50~100μm, for example: 50μm, 60μm, 70μm, 80μm or 100μm, etc.

[0031] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0032] (1) According to the proportion of each material in the base layer, intermediate layer and active layer, mix the entire designed mass of positive electrode active material and 2 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 1. Mix the entire designed mass of bisphenol-S epoxy resin and 1 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 2. Mix slurry 1 and slurry 2 evenly and wait for coating.

[0033] (2) The base layer slurry, intermediate layer slurry and active layer slurry are coated onto the surface of the positive current collector in sequence and dried to obtain the positive electrode sheet.

[0034] Preferably, the drying temperature in step (2) is <120°C.

[0035] Thirdly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the first aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) This invention ensures that BPSER does not affect the normal operation of lithium-ion batteries by designing the proportion of bisphenol-S epoxy resin (BPSER) material in the base layer, intermediate layer and active layer, as well as the layer thickness and the mixing sequence of key materials.

[0038] (2) The positive electrode sheet of the present invention can maintain a capacity retention rate of more than 97% after 500 cycles, and can pass the needle penetration, extrusion and midday impact tests 100% of the time, showing good electrochemical performance and safety performance. Attached Figure Description

[0039] Figure 1 This is a cross-sectional schematic diagram of the positive electrode sheet described in Embodiment 1 of the present invention, 1.1-active layer, 1.2-intermediate layer, 1.3-base layer, 2-current collector. Detailed Implementation

[0040] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0041] The positive electrode sheets described in Examples 1-9 of this invention are all prepared by the following method:

[0042] (1) According to the proportion of each material in the base layer, intermediate layer and active layer, mix the entire designed mass of positive electrode active material and 2 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 1. Mix the entire designed mass of bisphenol-S epoxy resin and 1 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 2. Mix slurry 1 and slurry 2 evenly and wait for coating.

[0043] (2) The base layer slurry, intermediate layer slurry and active layer slurry are coated sequentially on the surface of the positive electrode current collector and dried at 110°C to obtain the positive electrode sheet.

[0044] Example 1

[0045] This embodiment provides a positive electrode sheet, which includes an aluminum foil current collector and an active layer with a thickness of 80 μm, an intermediate layer with a thickness of 30 μm, and a base layer with a thickness of 20 μm disposed on the surface of the aluminum foil current collector. The active layer is composed of a nickel-cobalt-manganese ternary cathode material, bisphenol-S epoxy resin, conductive carbon black SP, and polyvinylidene fluoride, with mass percentages of 85%, 0.5%, 9.5%, and 5%, respectively. The intermediate layer is composed of the same material, but with mass percentages of 80%, 1%, 11%, and 8%. The base layer is composed of the same material, but with mass percentages of 75%, 3%, 12%, and 10%.

[0046] A cross-sectional schematic diagram of the positive electrode sheet is shown below. Figure 1 As shown, 1.1 is the active layer, 1.2 is the intermediate layer, 1.3 is the base layer, and 2 is the current collector.

[0047] Example 2

[0048] This embodiment provides a positive electrode sheet, which includes an aluminum foil current collector and an active layer with a thickness of 80 μm, an intermediate layer with a thickness of 30 μm, and a base layer with a thickness of 20 μm disposed on the surface of the aluminum foil current collector. The active layer is composed of a nickel-cobalt-manganese ternary cathode material, bisphenol-S epoxy resin, conductive carbon black SP, and polyvinylidene fluoride, with mass percentages of 90%, 0.5%, 5%, and 4.5%, respectively. The intermediate layer is composed of the same material, but with mass percentages of 80%, 1%, 10%, and 9%. The base layer is composed of the same material, but with mass percentages of 70%, 3%, 17%, and 10%.

[0049] Example 3

[0050] The only difference between this embodiment and Embodiment 1 is that the material composition of the base layer, intermediate layer and active layer is exactly the same (all use the material ratio of the base layer).

[0051] Example 4

[0052] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the active layer bisphenol-S epoxy resin is 0.3% (the reduced portion is replaced with nickel-cobalt-manganese ternary material), while the other conditions and parameters are exactly the same as in Embodiment 1.

[0053] Example 5

[0054] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the active layer bisphenol-S epoxy resin is 1.5% (the increased portion is deducted from the nickel-cobalt-manganese ternary material). All other conditions and parameters are exactly the same as in Embodiment 1.

[0055] Example 6

[0056] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the intermediate bisphenol-S epoxy resin is 0.3% (the reduced portion is replaced with nickel-cobalt-manganese ternary material), while the other conditions and parameters are exactly the same as in Embodiment 1.

[0057] Example 7

[0058] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the intermediate bisphenol-S epoxy resin is 1.5% (the increased portion is deducted from the nickel-cobalt-manganese ternary material). All other conditions and parameters are exactly the same as in Embodiment 1.

[0059] Example 8

[0060] The only difference between this embodiment and Embodiment 1 is that the mass fraction of bisphenol-S epoxy resin in the base layer is 0.5% (the reduced portion is replaced with nickel-cobalt-manganese ternary material). All other conditions and parameters are exactly the same as in Embodiment 1.

[0061] Example 9

[0062] The only difference between this embodiment and Embodiment 1 is that the mass fraction of bisphenol-S epoxy resin in the base layer is 4% (the increased portion is deducted from the nickel-cobalt-manganese ternary material). All other conditions and parameters are exactly the same as in Embodiment 1.

[0063] Comparative Example 10

[0064] The only difference between this comparative example and Example 1 is that, in the process of preparing each layer of slurry, the nickel-cobalt-manganese ternary cathode material, bisphenol-S epoxy resin, conductive carbon black SP, and polyvinylidene fluoride are directly mixed with the solvent. All other conditions and parameters are exactly the same as in Example 1.

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 1 is that bisphenol-S epoxy resin (BPSER) material is not added; all other conditions and parameters are exactly the same as in Example 1.

[0067] Comparative Example 2

[0068] The only difference between this comparative example and Example 1 is that no active layer is set; all other conditions and parameters are exactly the same as in Example 1.

[0069] Performance testing:

[0070] The positive electrode sheets obtained in Examples 1-9 and Comparative Examples 1-2 were combined with corresponding graphite negative electrode sheets, 12μm PP+PE separators, and 1.0M LiPF6 EC+EMC electrolyte, with the separator positioned between the positive and negative electrodes. The sheets were then wound or stacked to obtain bare cells. These bare cells were then assembled into battery cells within an outer aluminum-plastic film or aluminum shell. Electrolyte was injected into the dried battery cells. After aging, formation, shaping, and packaging processes, a lithium-ion battery was obtained. Cycle performance and safety performance tests were conducted on the lithium-ion batteries. The test results are shown in Table 1.

[0071] Table 1

[0072]

[0073] As can be seen from Table 1, as shown in Examples 1-2, the positive electrode sheet of the present invention can achieve a capacity retention rate of over 97% after 500 cycles, and can pass 100% of the needle penetration, extrusion and midday impact tests, demonstrating good electrochemical performance and safety performance.

[0074] As can be seen from the comparison of Examples 1 and 3 and Comparative Example 2, the present invention ensures that BPSER does not affect the normal operation of lithium-ion batteries through the differentiated design of the base layer, intermediate layer and active layer and the mixing sequence design of key materials.

[0075] A comparison of Examples 1 and 4-9 shows that the mass percentage of bisphenol-S epoxy resin (BPSER) material in the base layer, intermediate layer, and active layer of the positive electrode sheet of the present invention significantly affects the electrical and safety performance of the electrode sheet. By controlling the mass percentage of bisphenol-S epoxy resin (BPSER) material in the base layer to 0.5-1%, the mass percentage of bisphenol-S epoxy resin (BPSER) material in the intermediate layer to 0.5-1%, and the mass percentage of bisphenol-S epoxy resin (BPSER) material in the active layer to 1-3%, the positive electrode sheet can achieve both good electrical and safety performance. If the mass percentage of bisphenol-S epoxy resin (BPSER) material in each layer is too high, the safety performance is not affected, but the electrochemical performance is significantly affected. If the mass percentage of bisphenol-S epoxy resin (BPSER) material is too low, the safety performance drops sharply.

[0076] As can be seen from the comparison between Example 1 and Example 10, in the preparation process of the positive electrode sheet of the present invention, the amount of conductive agent and bisphenol-S epoxy resin added in each step will significantly affect the performance of the obtained positive electrode sheet and needs to be strictly controlled. BPSER is non-conductive and does not participate in electrochemical reaction. If the traditional homogenization method is used, BPSER will significantly reduce the electrochemical performance of the positive electrode sheet.

[0077] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention adds bisphenol-S epoxy resin (BPSER) material to the coating of traditional lithium-ion battery positive electrode material. It is insoluble in electrolyte and can quickly and effectively form an insulating layer in the event of sudden temperature rise due to short circuit or fault in lithium-ion battery and failure of separator, thereby cutting off electrochemical reaction and improving the high-temperature safety performance of battery.

[0078] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a base layer, an intermediate layer and an active layer sequentially stacked on the surface of the positive current collector. The base layer, intermediate layer and active layer all contain bisphenol-S epoxy resin. The base layer, intermediate layer and active layer also include a positive electrode active material, a conductive agent and a binder; Based on the mass of the base layer being 100%, the mass fraction of the bisphenol-S epoxy resin is 1.5~3%; Based on the mass of the intermediate layer as 100%, the mass fraction of the bisphenol-S epoxy resin is 0.5-1%, and the mass fraction of the positive electrode active material is 70-80%. Based on the mass of the active layer as 100%, the mass fraction of the bisphenol-S epoxy resin is 0.5-1%, and the mass fraction of the positive electrode active material is 85-90%. The thickness of the base layer is 10~30μm; the thickness of the intermediate layer is 20~50μm; and the thickness of the active layer is 50~100μm. The positive electrode sheet is prepared by the following method: (1) According to the proportion of each material in the base layer, intermediate layer and active layer, mix the entire designed mass of positive electrode active material and 2 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 1. Mix the entire designed mass of bisphenol-S epoxy resin and 1 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 2. Mix slurry 1 and slurry 2 evenly and wait for coating. (2) The base layer slurry, intermediate layer slurry and active layer slurry are coated onto the surface of the positive current collector in sequence and dried to obtain the positive electrode sheet.

2. The positive electrode sheet as described in claim 1, characterized in that, With the mass of the substrate layer being 100%, the mass fraction of the positive electrode active material is 60-75%.

3. The positive electrode sheet as described in claim 1, characterized in that, The mass fraction of the conductive agent in the substrate layer is 15-25%.

4. The positive electrode sheet as described in claim 1, characterized in that, The adhesive in the base layer has a mass fraction of 8-15%.

5. The positive electrode sheet as described in claim 1, characterized in that, The mass fraction of the conductive agent in the intermediate layer is 10-15%.

6. The positive electrode sheet as described in claim 1, characterized in that, The adhesive in the intermediate layer has a mass fraction of 5-10%.

7. The positive electrode sheet as described in claim 1, characterized in that, The mass fraction of the conductive agent in the active layer is 5-10%.

8. The positive electrode sheet as described in claim 1, characterized in that, The mass fraction of the binder in the active layer is 4-10%.

9. A method for preparing a positive electrode sheet as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) According to the proportion of each material in the base layer, intermediate layer and active layer, mix the entire designed mass of positive electrode active material and 2 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 1. Mix the entire designed mass of bisphenol-S epoxy resin and 1 / 3 of the designed mass of conductive agent evenly, then add 1 / 2 of the designed mass of binder and continue mixing evenly to form slurry 2. Mix slurry 1 and slurry 2 evenly and wait for coating. (2) The base layer slurry, intermediate layer slurry and active layer slurry are coated onto the surface of the positive current collector in sequence and dried to obtain the positive electrode sheet.

10. The preparation method according to claim 9, characterized in that, The drying temperature in step (2) is <120℃.

11. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a positive electrode as described in any one of claims 1-8.

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