Electrode tabs and methods of making the same

Abstract

The present application relates to an electrode tab and a method of manufacturing the same. The electrode tab includes a current collector and an electrode active material layer disposed on at least one surface of the current collector, wherein the porosity of the outer surface side of the electrode active material layer is the largest. The porosity of the outer surface side of the electrode active material layer of the electrode tab of the present application is the largest, whereby the electrolyte impregnation rate of the electrode tab can be significantly improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to electrode sheets and their preparation methods. Background Technology

[0002] In recent years, with the increasing demand for clean energy, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, transportation vehicles, military equipment, aerospace, and many other fields. As the application areas of secondary batteries have greatly expanded, higher requirements have been placed on their performance.

[0003] The preparation process of electrode sheets for secondary batteries is a crucial step affecting battery performance. The microstructure of the electrode sheets (e.g., surface porosity and binder distribution) directly affects the wetting effect of the electrolyte, thus influencing important performance characteristics such as battery internal resistance, rate capability, and lifespan. Currently, the following wet coating process is commonly used in the preparation of electrode sheets for secondary batteries: preparation of active material slurry → coating → drying → rolling. During the drying process of the electrode sheets (especially near the transition point (the junction where the upper layer of the electrode sheet is dried while the lower layer is not), the upper solvent of the active material layer evaporates first, and the lower solvent rises rapidly. Therefore, the binder is carried by the solvent during the rising process due to the following reasons, resulting in the binder floating: (1) surface tension; (2) concentration gradient; (3) capillary action; (4) thermodynamic motion of solid particles; (5) density difference between particles (the density difference between the upper and lower layers is caused by particle sedimentation). Furthermore, as the coating speed increases, the drying temperature needs to be further increased, which further reduces the surface tension of the solvent. This leads to a greater difference in surface tension between the upper dried electrode active material layer and the solvent, making it easier for the solvent to migrate and spread upwards, and for the binder to float to the surface. Therefore, the final electrode sheet exhibits a state where the surface is rich in binder while the lower layer has less binder. Additionally, although lowering the drying temperature can alleviate binder floating, this reduces the productivity of secondary batteries.

[0004] During the drying process of the electrode sheets, the binder floats to the surface, leading to binder enrichment on the electrode sheet surface. After cold pressing, the electrode sheet surface tends to become denser. On the one hand, a dense electrode sheet surface makes electrolyte wetting difficult, severely affecting the productivity of secondary batteries. On the other hand, the low porosity of the electrode sheet surface makes it difficult for active ions to shuttle within the electrode sheet, resulting in reduced rate performance and low-temperature performance. Furthermore, if the electrode sheet has difficulty wetting, the insufficiently wetting areas cannot achieve electrochemical reactions, leading to abnormal battery performance and the risk of metal deposition of active materials (such as lithium plating) at the interface. Therefore, the microstructure of the electrode sheets directly affects the electrolyte wetting effect, thereby affecting important performance characteristics such as battery internal resistance, rate performance, and lifespan.

[0005] To address the aforementioned problems, existing technologies (such as CN111293273B) propose the following technical solution: An interface adhesive (acrylate-based) is pre-coated onto a first substrate (aluminum or copper foil), and then an electrode active material layer is coated onto the interface adhesive. After drying and rolling, a first pre-treated electrode sheet is prepared. A transfer adhesive (polyurethane, polystyrene, polyacrylate-based) is coated onto a second substrate (aluminum or copper foil) and then covered onto the surface of the first pre-treated electrode sheet to form a second pre-treated electrode sheet. The transfer of the electrode sheet is achieved by using a transfer adhesive and an interface adhesive with opposite adhesive properties (the interface adhesive has adhesive properties at room temperature while the transfer adhesive has no adhesive force; after being exposed to light or heat, the interface adhesive loses its activity while the transfer adhesive retains its adhesive properties). The entire active material layer of the electrode sheet is transferred from the surface of the first substrate to the second substrate by heating (100℃-200℃) or exposure to light, thereby reversing the gradient direction of the porosity of the electrode sheet, that is, the active material layer of the electrode sheet is dense in the middle and loose on the surface. Summary of the Invention

[0006] Technical issues

[0007] Through in-depth research, the inventors of this application have discovered that the above-mentioned technical solution still has at least the following problems.

[0008] Compared to the existing manufacturing process of electrode sheets for secondary batteries, the above technology requires additional interface adhesives and transfer adhesives, as well as heating or light irradiation processes. In particular, the heating or light irradiation process is complex, which increases costs and makes it difficult to achieve mass production.

[0009] The coated active material slurry and the interface binder will permeate each other, which will lead to the following risks: (1) Due to the permeation, the surface of the electrode active material layer is prone to cracking after drying, resulting in poor electrode sheet consistency and low yield; the surface of the electrode sheet is cracked, and during battery cycling, active material metal precipitation (such as lithium plating) is likely to occur at the interface (negative electrode) of the electrode sheet; (2) Due to the above permeation phenomenon, the electrode active material layer is not fully transferred during battery cycling, that is, the electrode active material remains in the interface binder layer, which causes the loss of electrode active material and the reduction of battery energy density.

[0010] The substrate and interface adhesive cannot be reused after transfer printing, which increases material costs; the transfer process requires light or heating, which increases energy consumption; and the light or heating process requires a certain amount of time for the interface adhesive to degrade, so the productivity of this method is low.

[0011] Transfer adhesives are mostly ester-based. Ester-based adhesives generally have low adhesion and swell significantly in the electrolyte (especially at high temperatures (50℃~60℃)). Therefore, the electrode sheets are prone to demolding (especially in the later stages of battery cycling). In addition, due to the large swelling, ester-based adhesives themselves are prone to migrate into the electrolyte, thereby causing side reactions and deteriorating battery performance.

[0012] Technical solution

[0013] The inventors of this application completed this invention in order to solve the above-mentioned problems.

[0014] A first aspect of this application provides an electrode sheet comprising a current collector and an electrode active material layer disposed on at least one surface of the current collector.

[0015] The outer surface of the electrode active material layer has the highest porosity.

[0016] In some embodiments, the porosity of the bottom surface side of the electrode active material layer opposite to the outer surface side can be minimized.

[0017] In some embodiments, when the electrode sheet is a positive electrode sheet, the compaction density can be 2.1 g / cm³. 3 ~3.8g / cm 3 When the electrode sheet is a negative electrode sheet, the compaction density can be 1.3 g / cm³. 3 ~1.8g / cm 3 .

[0018] A second aspect of this application provides a method for preparing an electrode sheet, comprising the following steps:

[0019] Step (1): Provide an electrode active material slurry, coat the electrode active material slurry onto at least one surface of a polymer substrate, and then dry it to obtain an initial electrode sheet having an electrode active material layer; and

[0020] Step (2): Provide a metal substrate, stack the metal substrate and the initial electrode sheet with the surface of the metal substrate facing the electrode active material layer, and perform a pressing process to transfer the electrode active material layer onto the surface of the metal substrate.

[0021] In some embodiments, the pressure of the pressing process can be 20 to 80T.

[0022] In some embodiments, the pressing process can be roller pressing.

[0023] In some embodiments, the polymer substrate may be at least one selected from polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene (PE) film, polyvinyl alcohol (PVA) film, polyvinylidene fluoride (PVDF) film, polytetrafluoroethylene (PTFE) film, polycarbonate (PC) film, polyvinyl chloride (PVC) film, polymethyl methacrylate (PMMA) film, polyimide (PI) film, polystyrene (PS) film, and polybenzimidazole (PBI) film.

[0024] In some embodiments, the thickness of the polymer substrate can be from 25 μm to 500 μm.

[0025] In some embodiments, the metal substrate may be aluminum foil or copper foil.

[0026] A third aspect of this application provides a secondary battery comprising the electrode plates described in any of the above embodiments.

[0027] A fourth aspect of this application provides a battery module that includes the secondary battery provided in the third aspect of this application.

[0028] A fifth aspect of this application provides a battery pack that includes the battery module provided in the fourth aspect of this application.

[0029] A sixth aspect of this application provides an electrical device comprising at least one selected from the third aspect of this application, the fourth aspect of this application, or the fifth aspect of this application.

[0030] Beneficial effects

[0031] This application provides an electrode sheet and its preparation method. The electrode sheet prepared by the method of this application has the highest porosity on the outer surface of the electrode active material layer, which can significantly improve the electrolyte wetting rate of the electrode sheet. From the perspective of battery productivity, the improved electrolyte wetting rate of the electrode sheet can shorten the electrolyte wetting time of the battery cell, greatly improving battery productivity. From the perspective of battery performance, the improved wettability of the electrolyte to the electrode sheet can improve the interfacial characteristics of the battery and increase the electrochemical reactivity of the electrode sheet; in addition, the high porosity on the outer surface of the electrode sheet is conducive to the shuttle of active ions in the electrode sheet, thereby improving the kinetic performance and high and low temperature performance of the battery.

[0032] Furthermore, the electrode preparation method of this application does not require additional interface binders, transfer adhesives, or heating or light irradiation processes. Therefore, the aforementioned electrode sheets can be produced easily, at low cost, and on a large scale (the electrode slurry can use currently mature mass-produced materials and formulation systems, without the need for new materials, formulation adjustments, or special treatment of the current collector, thus simplifying control and making mass production easier). In addition, compared to existing technologies, since the electrode preparation method of this application does not involve interpenetration between the coated active material slurry and the interface binder, the prepared electrode sheets exhibit excellent consistency and yield. During battery cycling, the electrode sheets are less prone to problems such as active material metal deposition (e.g., lithium plating), and there is no issue of reduced battery energy density due to loss of electrode active material remaining in the interface binder layer. Moreover, since no transfer binder (such as ester binder) is required, the electrode sheet of this application is less prone to demolding risk under high temperature (50℃~60℃) conditions (especially in the later stages of battery cycling), and will not cause side reactions and deteriorate battery performance due to the migration of ester binder into the electrolyte.

[0033] Furthermore, this application provides a secondary battery, a battery module, a battery pack, and an electrical device comprising the aforementioned electrode plates. The secondary battery, battery module, battery pack, and electrical device also possess the advantages of the aforementioned electrode plates. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0035] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0036] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0037] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0038] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0039] Figure 6 This is a schematic diagram of an electrical device in which a secondary battery is used as a power source, according to one embodiment of this application.

[0040] Figure 7 This is a schematic diagram of an electrode manufacturing apparatus according to one embodiment of this application.

[0041] Figure 8This is a schematic diagram of the transfer process of the electrode active material layer in one embodiment of this application.

[0042] Figure 9 This is a SEM image of the outer surface of the positive electrode sheet in Comparative Example 1.

[0043] Figure 10 This is a SEM image of the outer surface of the positive electrode sheet in Example 1.

[0044] Figure 11 This is a SEM image of the outer surface of the positive electrode sheet in Comparative Example 2.

[0045] Figure 12 This is a SEM image of the outer surface of the positive electrode sheet in Example 4.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 6 Cold press roller; 7 Metal substrate unwinding device; 8 Initial electrode sheet unwinding device; 9 Polymer substrate winding device; 10 Electrode sheet winding device; 11 Metal substrate; 12 Initial electrode sheet; 101 Polymer substrate; 102 Electrode active material layer. Detailed Implementation

[0048] The electrode plates of this application will be described in detail below, but unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description and embodiments are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] The following provides a detailed description of the electrode plates of this application and the secondary battery, battery module, battery pack and power device containing them.

[0052] A first embodiment of this application may provide an electrode sheet, including a current collector and an electrode active material layer disposed on at least one surface of the current collector.

[0053] The outer surface of the electrode active material layer has the highest porosity.

[0054] Because the outer surface of the electrode active material layer of the electrode sheet in this application has the highest porosity, this application can significantly improve the electrolyte wetting rate of the electrode sheet. From the perspective of battery productivity, the improved electrolyte wetting rate of the electrode sheet can shorten the electrolyte wetting time of the battery cell, greatly improving battery productivity. From the perspective of battery performance, the improved wettability of the electrolyte to the electrode sheet can improve the interfacial characteristics of the battery and increase the electrochemical reactivity of the electrode sheet; in addition, the high porosity of the outer surface of the electrode sheet is beneficial to the shuttle of active ions within the electrode sheet, thereby improving the battery's kinetic performance and high and low temperature performance.

[0055] In some embodiments, the porosity of the bottom surface side of the electrode active material layer, opposite to the outer surface side, is minimized. In this application, the outer surface side refers to the side of the electrode active material layer facing the negative electrode. In some embodiments, the porosity of the electrode active material layer of the electrode sheet of this application can decrease monotonically from the outer surface side towards the bottom surface side. The bottom surface side of the electrode active material layer of this application can have minimal porosity due to the enrichment of binder relative to the outer surface side, thereby increasing the adhesion between the electrode active material layer and the current collector. Furthermore, the minimal porosity of the bottom surface side of the electrode active material layer of this application makes it less likely for the electrolyte to come into contact with the binder enriched on the bottom surface side, thus reducing the risk of electrode sheet demolding due to binder swelling.

[0056] In some embodiments, when the electrode sheet is a positive electrode sheet, the compaction density is 2.1–3.8 g / cm³. 3 When the electrode sheet is a negative electrode sheet, the compaction density is 1.3–1.8 g / cm³. 3 Optionally, the compaction density of the positive electrode sheet can be 2.2–3.7 g / cm³. 3 2.3~3.6g / cm 3 2.4~3.5g / cm 3 2.5~3.7g / cm 3 2.5~3.4g / cm 3 2.3~3.3g / cm 3 2.6~3.7g / cm 3 2.7~3.6g / cm 3 2.8~3.5g / cm 3 2.9~3.7g / cm 3 3.0~3.7g / cm 3 3.1~3.7g / cm 3 3.2~3.7g / cm 3 and 3.3~3.7g / cm 3The compaction density of the negative electrode sheet can be 1.3–1.8 g / cm³. 3 1.4~1.8g / cm 3 1.4~1.7g / cm 3 1.4~1.6g / cm 3 1.3~1.6g / cm 3 1.3~1.7g / cm 3 1.3~1.5g / cm 3 1.4~1.5g / cm 3 1.5~1.7g / cm 3 and 1.5~1.8g / cm 3 .

[0057] In this application, both the positive and negative electrode sheets can be fabricated by transfer printing. Therefore, electrode sheets with different compaction densities can be prepared according to specific needs. Electrode sheets with higher compaction densities than conventional electrode sheets can also be prepared (because the porosity of the outer surface of the electrode sheet is the largest, so the outer surface is not easily densified by pressing), thereby improving the energy density of the battery while maintaining the battery's rate performance and high and low temperature performance.

[0058] The second embodiment of this application can provide a method for preparing an electrode sheet, including the following steps:

[0059] Step (1): Provide an electrode active material slurry, coat the electrode active material slurry onto at least one surface of a polymer substrate, and then dry it to obtain an initial electrode sheet having an electrode active material layer; and

[0060] Step (2): Provide a metal substrate, stack the metal substrate and the initial electrode sheet with the surface of the metal substrate facing the electrode active material layer, and perform a pressing process to transfer the electrode active material layer onto the surface of the metal substrate.

[0061] In this application, it can be done by, for example Figure 7 The electrode manufacturing equipment shown continuously and on a large scale manufactures electrode sheets. Specifically, the initial electrode sheet unwinding device 8 and the polymer substrate winding device 9, as well as the metal substrate unwinding device 7 and the electrode sheet winding device 10, are controlled to rotate continuously at corresponding speeds, so that the initial electrode sheet 12 and the metal substrate 11 pass through the gap between the cold pressure rollers 6 with the electrode active material layer of the initial electrode sheet 12 facing the surface of the metal substrate 11 to achieve a pressing process, thereby transferring the electrode active material layer to the surface of the metal substrate in one step.

[0062] In this application, the structure of the (initial) electrode sheets before and after the pressing process is as follows: Figure 8As shown. By Figure 8 It can be seen that before the pressing and transfer, the electrode active material layer 102 was adhered to the polymer substrate 101; after the pressing and transfer, the electrode active material layer 102 was transferred to the metal substrate 11.

[0063] In step (1), except for selecting a polymer substrate to replace the conventional metal current collector, the other processes in step (1) can directly use the conventional electrode coating process (or can be finely adjusted according to actual needs).

[0064] In this application, the metal substrate in step (2) can refer to a substrate composed of metal and / or its alloys, or a composite substrate formed by forming a metal layer on a polymer substrate (as long as there is a difference in ductility between the composite substrate and the polymer substrate used in conjunction, and the electrode active material layer can be transferred in one step to the surface of the metal layer therein through a pressing process). The composite substrate may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite substrate can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In step (2), since there is a difference in ductility between the polymer substrate and the metal substrate (such as aluminum foil or copper foil) of the initial electrode sheet during pressing, the electrode active material layer on the polymer substrate can be directly transferred to the metal substrate in one step through the pressing process, thereby realizing the flipping of the upper and lower layers of the electrode sheet. Finally, the obtained electrode sheet has less adhesive on the upper layer (outer surface side), more adhesive on the lower layer (bottom surface side), and the porosity of the outer surface side of the electrode active material layer is the largest.

[0066] In step (2), when transferring the electrode active material layer to the metal substrate, no additional interface binder and transfer adhesive, as well as heating or light exposure processes, are required. Consequently, there are no issues such as increased energy consumption, interpenetration between the coated active material slurry and the interface binder, loss of battery energy density due to electrode active material residue in the interface binder layer, or the risk of electrode sheet demolding under high temperature conditions (especially in the later stages of battery cycling) or deterioration of battery performance due to the use of transfer adhesives (such as ester binders).

[0067] Therefore, the electrode preparation method of this application can easily, cheaply and on a large scale produce the electrode of this application (the electrode slurry can use the currently mature mass-produced materials and formulation system, without the need to add new materials, adjust the formulation, or special treatment of the current collector, so the control is simple and it is easier to achieve mass production (it can be easily and quickly applied to the current battery production process)).

[0068] Furthermore, as mentioned above, compared to the prior art, since the electrode preparation method of this application does not involve the interpenetration between the coated active material slurry and the interface binder, the prepared electrode has excellent consistency and yield. The electrode is less prone to problems such as active material metal precipitation (e.g., lithium plating) during battery cycling, and there is no problem of reduced battery energy density due to loss of electrode active material remaining in the interface binder layer. In addition, since no transfer binder (e.g., ester binder) is needed, the electrode of this application is less prone to demolding risk under high temperature (50℃~60℃) conditions (especially in the later stages of battery cycling), and there is no side reaction and deterioration of battery performance due to the migration of ester binder into the electrolyte.

[0069] In some embodiments, the pressure of the pressing process can be 20-80T. In this application, when the pressure of the pressing process is within the above range, it can be ensured that the electrode active material layer on the polymer substrate is directly transferred to the metal substrate in one step through the pressing process, and problems such as the electrode active material layer breaking due to excessive pressure of the pressing process, or the electrolyte failing to wet the electrode sheet due to excessive compaction density, and active ions failing to shuttle in the electrode sheet (thereby degrading the rate performance of the battery) are avoided.

[0070] In some embodiments, the pressing process can be roll forming. In this application, using roll forming in the pressing process is compatible with current battery manufacturing processes.

[0071] In some embodiments, the polymer substrate may be at least one selected from polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene (PE) film, polyvinyl alcohol (PVA) film, polyvinylidene fluoride (PVDF) film, polytetrafluoroethylene (PTFE) film, polycarbonate (PC) film, polyvinyl chloride (PVC) film, polymethyl methacrylate (PMMA) film, polyimide (PI) film, polystyrene (PS) film, and polybenzimidazole (PBI) film. In this application, there are no particular limitations on the composition of the polymer substrate, as long as there is a difference in ductility between it and the metal substrate used in conjunction with it, and the electrode active material layer on it can be transferred to the metal substrate in one step through a pressing process.

[0072] In some embodiments, the thickness of the polymer substrate can be from 25 μm to 500 μm. In this application, there is no particular limitation on the thickness of the polymer substrate, as long as it allows for a suitable difference in ductility between the polymer substrate and the metal substrate used in conjunction, and allows the electrode active material layer on the polymer substrate to be transferred to the metal substrate in one step via a pressing process.

[0073] In some embodiments, the metal substrate may be aluminum foil or copper foil. In this application, there are no particular limitations on the composition of the metal substrate; conventional metal substrates in the art can be used, as long as there is a difference in ductility between it and the polymer substrate used in conjunction with it, and the electrode active material layer can be transferred to its surface in one step through a pressing process.

[0074] A third embodiment of this application may provide a secondary battery comprising electrode plates as described in any of the above embodiments.

[0075] In this embodiment, there is no particular limitation on the type of electrode. For example, the electrode can be a positive electrode or a negative electrode.

[0076] Detailed Description of Embodiments of the Invention

[0077] The secondary battery, battery module, battery pack, and power supply device of this application will be described in detail below with appropriate reference to the accompanying drawings.

[0078] In one embodiment of this application, a secondary battery is provided. Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions, such as lithium ions, repeatedly insert and extract between the positive and negative electrodes. The electrolyte, acting as a conductor for the active ions, lies between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing the passage of active ions.

[0079] [Positive electrode plate]

[0080] The positive electrode sheet of this application is a positive electrode sheet prepared by the above-described electrode sheet preparation method. The positive electrode sheet may include a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer may include a positive active material and optionally a binder and a conductive agent.

[0081] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0082] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0083] In some embodiments, the positive electrode active material can be a known positive electrode active material for secondary batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2 and LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0084] When the secondary battery is a sodium-ion battery, the positive electrode may contain at least one positive electrode active material selected from the following: layered transition metal oxides, polyanionic compounds, Prussian blue compounds, sulfides, nitrides, carbides, and titanates. Optionally, the positive electrode active material may include, but is not limited to, NaCrO2, Na2Fe2(SO4)3, molybdenum disulfide, tungsten disulfide, vanadium disulfide, titanium disulfide, hexagonal boron nitride, carbon-doped hexagonal boron nitride, titanium carbide, tantalum carbide, molybdenum carbide, silicon carbide, Na2Ti3O7, and Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 At least one of the group consisting of NaTi2(PO4)3.

[0085] In some embodiments, the positive electrode active material layer may optionally include other additives such as lithium replenishing agents. The lithium replenishing agent may include lithium replenishing agents commonly used in the art. Specifically, the lithium replenishing agent may include those selected from Li6CoO4, Li5FeO4, Li3VO4, Li2MoO3, Li2RuO3, Li2MnO2, Li2NiO2, and Li2Cu. x Ni 1-x M y At least one of O2, wherein 0 < x ≤ 1, 0 ≤ y < 0.1, and M is at least one selected from Zn, Sn, Mg, Fe, and Mn. From the viewpoint of improving the specific capacity and rate performance of secondary batteries, especially the rate performance after high-temperature storage, the lithium replenishing agent preferably includes a selection from Li6CoO4, Li5FeO4, Li2NiO2, Li2CuO2, and Li2Cu. 0.6 Ni 0.4 At least one of O2.

[0086] In some embodiments, the binder included in the positive electrode active material layer may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] In some embodiments, the positive electrode active material layer may also selectively include a conductive agent. As an example, conductive agents commonly used in the art can be used. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, carbon nanorods, graphene, and carbon nanofibers.

[0088] [Negative electrode plate]

[0089] The negative electrode sheet may include a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer may include a negative active material and optionally a binder, a conductive agent, and other additives.

[0090] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0091] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may comprise a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In embodiments where the secondary battery is a lithium-ion battery, the negative electrode active material can be any negative electrode active material known in the art for lithium-ion batteries. As an example, the negative electrode active material may contain at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials. The silicon-based material may contain at least one selected from elemental silicon, silicon oxide, silicon-carbon composites, and silicon-based alloys. When the negative electrode active material contains a silicon-based material, the mass percentage of the silicon-based material in the total negative electrode active material may be 0% to 30% by mass, optionally 0% to 10% by mass. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0093] In embodiments where the secondary battery is a sodium-ion battery, the negative electrode active material may include at least one selected from natural graphite, modified graphite, artificial graphite, graphene, carbon nanotubes, carbon nanofibers, porous carbon, tin, antimony, germanium, lead, ferric oxide, vanadium pentoxide, tin dioxide, titanium dioxide, molybdenum trioxide, elemental phosphorus, sodium titanate, and sodium terephthalate. Optionally, the negative electrode active material is at least one selected from natural graphite, modified graphite, artificial graphite, and graphene.

[0094] In some embodiments, the negative electrode active material layer may also selectively include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0095] In some embodiments, the negative electrode active material layer may also selectively contain a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, carbon nanorods, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative electrode active material layer may also selectively contain other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0097] In some embodiments, the negative electrode can be prepared by dispersing the components used to prepare the negative electrode, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode through processes such as drying and cold pressing. Alternatively, in another embodiment, the negative electrode can be manufactured by casting the negative electrode slurry used to form the negative electrode active material layer onto a separate carrier, and then pressing the film layer obtained by peeling it from the carrier onto the negative electrode current collector.

[0098] [Electrolytes]

[0099] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid or gel-like.

[0100] Furthermore, the electrolyte in the embodiments of this application includes additives. These additives may include those commonly used in the art. The additives may include, for example, alkylene carbonates (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinyl ethers, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the additives may be included in an amount from 0.1% to 5% by weight, or the amount of additives may be adjusted by those skilled in the art as needed.

[0101] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0102] In embodiments where the secondary battery is a lithium-ion battery, the electrolyte salt may contain at least one selected from LiPF6, LiBF4, LiN(SO2F)2 (LiFSI), LiN(CF3SO2)2 (LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (LiBOB), and LiBF2C2O4 (LiDFOB).

[0103] In embodiments where the secondary battery is a sodium-ion battery, the electrolyte salt may contain at least one selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0104] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0105] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0106] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0107] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0108] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 through a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to actual needs.

[0109] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0110] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 are arranged sequentially along the length of battery module 4. Of course, the multiple secondary batteries 5 can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0111] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0112] In some embodiments, the battery modules described above can also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0113] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0114] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0115] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0116] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0117] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0118] Example

[0119] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0120] Preparation of electrode sheets

[0121] The preparation method of the electrode sheet in this application is described in detail below. An electrode active material slurry containing electrode active material is coated onto a polyethylene terephthalate (PET) film, which serves as a polymer substrate, and then dried. When the electrode sheet is a positive electrode sheet and a negative electrode sheet, the ratio of the electrode active material is as follows: positive electrode active material: binder: conductive carbon: dispersant = (93–98.2%):(1–4%):(0.7–2%):(0–1%); negative electrode active material: binder: thickener: conductive carbon = (93–98.5%):(0.5–2.5%):(0.5–2.5%):(0.5–2%). A copper / aluminum foil, serving as a metal substrate, is placed between two layers of polyethylene terephthalate (PET) film, with the side coated with the electrode active material layer facing the copper / aluminum foil (i.e., serving as the current collector). Because of the difference in ductility between polyethylene terephthalate (PET) film and current collector (copper / aluminum foil), the electrode active material layer can be transferred from the PET film to the current collector through a pressing process, thereby achieving the flipping of the upper and lower layers of the electrode active material layer to obtain the electrode sheet of this application.

[0122] The compacted density of the positive electrode sheet after pressing is 2.3-3.6 g / cm³. 3 The compacted density of the negative electrode sheet is 1.3-1.7 g / cm³. 3 Table 1 below lists the types of electrode active materials and the pressure of the pressing process.

[0123] The preparation of the secondary batteries in the examples and comparative examples is described in detail below.

[0124] Example 1

[0125] Preparation of positive electrode sheet

[0126] Lithium iron phosphate (LiFePO4), a positive electrode active material, polyvinylidene fluoride (PVDF), a binder, acetylene black, a conductive agent, and polyacrylic acid (PAA), a dispersant, were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:2.2:0.7:0.1. The mixture was thoroughly stirred and mixed to obtain a positive electrode slurry. The positive electrode sheet was then prepared according to the above-described electrode sheet preparation method. The compacted density of the positive electrode sheet after the pressing process was 2.5 g / cm³. 3 .

[0127] Preparation of negative electrode sheet

[0128] Artificial graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) were dissolved in deionized water at a mass ratio of 96.6:0.7:1.5:1.2. The mixture was thoroughly stirred and mixed to obtain a negative electrode slurry. The negative electrode sheet was then prepared according to the aforementioned electrode sheet preparation method. The compacted density of the negative electrode sheet after the pressing process was 1.6 g / cm³. 3 .

[0129] Preparation of electrolyte

[0130] In an argon atmosphere glove box (atmosphere: H2O < 0.1 ppm, O2 < 0.1 ppm), 1 mol / L LiPF6 was dissolved in an organic solvent (EC / DMC / EMC = 1 / 1 / 1 (mass ratio)) and stirred until homogeneous to obtain the corresponding electrolyte.

[0131] Preparation of secondary batteries

[0132] The positive electrode, the 14μm thick polyethylene film as a separator, and the negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes, and then wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film bag in the battery casing, dried, and then injected with the electrolyte. After formation and settling processes, a secondary battery is obtained.

[0133] Example 2

[0134] The secondary battery was fabricated according to the method of Example 1, except that the mass ratio of the positive electrode active material lithium iron phosphate (LiFePO4), binder polyvinylidene fluoride (PVDF), conductive agent acetylene black, and dispersant polyacrylic acid (PAA) was 96.6:2.6:0.7:0.1.

[0135] Example 3

[0136] The secondary battery was prepared according to the method of Example 1, except that the mass ratio of the positive electrode active material lithium iron phosphate (LiFePO4), binder polyvinylidene fluoride (PVDF), conductive agent acetylene black and dispersant polyacrylic acid (PAA) was 97.4:1.8:0.7:0.1.

[0137] Example 4

[0138] The secondary battery was fabricated according to the method of Example 1, except that a ternary oxide LiNi was used. 0.5 Mn 0.3 Co 0.2 O2 replaces lithium iron phosphate (LiFePO4), and the ternary oxide LiNi0.5 Mn 0.3 Co 0.2 The mass ratio of O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black is 96.2:2.7:1.1, and the compacted density of the prepared positive electrode sheet is 3.45 g / cm³. 3 .

[0139] Example 5

[0140] The secondary battery was fabricated according to the method of Example 1, except that a ternary oxide LiNi was used. 0.5 Mn 0.3 Co 0.2 O2 replaces lithium iron phosphate (LiFePO4), and the ternary oxide LiNi 0.5 Mn 0.3 Co 0.2 The mass ratio of O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black is 95.7:3.2:1.1, and the compacted density of the prepared positive electrode sheet is 3.45 g / cm³. 3 .

[0141] Example 6

[0142] The secondary battery was fabricated according to the method of Example 1, except that a ternary oxide LiNi was used. 0.5 Mn 0.3 Co 0.2 O2 replaces lithium iron phosphate (LiFePO4), and the ternary oxide LiNi 0.5 Mn 0.3 Co 0.2 The mass ratio of O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black is 95.2:3.7:1.1, and the compacted density of the prepared positive electrode sheet is 3.45 g / cm³. 3 .

[0143] Examples 7 to 19

[0144] The secondary batteries of Examples 7 to 19 were prepared according to the method of Example 1, except that the parameters of Examples 7 to 19 shown in Table 1 below are different from those of Example 1.

[0145] Comparative Example 1

[0146] The secondary battery was prepared according to the method of Example 1, except that the positive electrode and the negative electrode were prepared according to the following conventional method.

[0147] Preparation of positive electrode sheet

[0148] Lithium iron phosphate (LiFePO4), a positive electrode active material, polyvinylidene fluoride (PVDF), a conductive agent, acetylene black, and a dispersant, polyacrylic acid (PAA), were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:2.2:0.7:0.1. The mixture was thoroughly stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto an aluminum foil current collector, followed by drying, cold pressing, and slitting to obtain a positive electrode sheet. The compacted density of the prepared positive electrode sheet was 2.5 g / cm³. 3 .

[0149] Preparation of negative electrode sheet

[0150] Artificial graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) are dissolved in deionized water at a mass ratio of 96.6:0.7:1.5:1.2. The mixture is thoroughly stirred and mixed to obtain a negative electrode slurry. This slurry is then uniformly coated onto a copper foil (negative electrode current collector) one or more times. After drying, cold pressing, and slitting, the negative electrode sheet is obtained. The pressing process involves a pressure of 50-80T, and the compacted density of the resulting negative electrode sheet is 1.6 g / cm³. 3 .

[0151] Comparative Example 2

[0152] The secondary battery was fabricated using the method of Comparative Example 1, the difference being the use of a ternary oxide, LiNi. 0.5 Mn 0.3 Co 0.2 O2 replaces lithium iron phosphate (LiFePO4), and the ternary oxide LiNi 0.5 Mn 0.3 Co 0.2 The mass ratio of O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black is 96.2:1.1:2.7, and the compacted density of the prepared positive electrode sheet is 3.45 g / cm³. 3 .

[0153] Experimental Example

[0154] First-effect test:

[0155] For the secondary battery with LiFePO4 as the positive electrode active material: at 25°C, the prepared secondary battery was allowed to stand for 30 minutes, then charged at a constant current of 0.33C to a voltage of 3.65V, further charged at a constant voltage of 3.65V to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to a voltage of 2.5V. The charging capacity and discharging capacity at this point are C10 and C11, respectively.

[0156] For the positive electrode active material is LiNi 0.5 Mn 0.3 Co 0.2 O2 secondary battery: At 25°C, the prepared secondary battery was left to stand for 30 minutes, then charged at a constant current of 0.33C to a voltage of 4.2V, further charged at a constant voltage of 4.2V to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a voltage of 3V. The charging capacity and discharging capacity at this point are C20 and C21, respectively.

[0157] The initial efficiency of a secondary battery can be calculated as follows:

[0158] The initial efficiency (%) of a secondary battery = (C11 / C10) × 100%; or

[0159] The initial efficiency (%) of a secondary battery = (C21 / C20) × 100%.

[0160] Testing of DCR (Direct Current Resistance) performance:

[0161] Test method:

[0162] ① At 25℃, charge to full charge at 0.33C, then discharge at 0.33C for 0.1Cn (Cn represents the battery capacity) to adjust the secondary battery to 90% SOC. Let it stand for 30 minutes. The voltage at the end of the stand is V1. Then discharge at 3C for 30 seconds. The discharge cutoff voltage is V2. Let it stand for 40 seconds. Then charge at 3C for 30 seconds.

[0163] ② At 25℃, charge to full charge at 0.33C, then discharge at 0.33C for 0.5Cn (Cn represents the battery capacity) to adjust the secondary battery to 50% SOC. Let it stand for 30 minutes. The voltage at the end of the standing period is V1. Then discharge at 3C for 30 seconds. The discharge cutoff voltage is V2. Then discharge at 3C for 30 seconds, stand for 40 seconds, and then charge at 3C for 30 seconds.

[0164] ③ At 25℃, charge to full charge at 0.33C, then discharge at 0.33C to 0.9Cn (Cn represents the battery capacity) to adjust the secondary battery to 10% SOC. Let it stand for 30 minutes. The voltage at the end of the standing period is V1. Then discharge at 3C for 30 seconds. The discharge cutoff voltage is V2. Then discharge at 3C for 30 seconds, stand for 40 seconds, and then charge at 3C for 30 seconds.

[0165] Calculation method: DCR=(V1-V2) / I, where V1 is the static end voltage, V2 is the discharge cutoff voltage, and I is the discharge current.

[0166] High and low temperature performance testing:

[0167] Test method: Charge the secondary battery to full charge at 0.5C at 25℃, let it stand for 30 minutes, then discharge it to the cutoff voltage at 0.5C and measure the discharge capacity.

[0168] Adjust the temperature of the secondary battery to 60℃ and let it stand for 2 hours. Charge it at 0.5C to full charge, let it stand for 30 minutes, and then discharge it at 0.5C to the cutoff voltage and measure the discharge capacity.

[0169] Adjust the temperature of the secondary battery to 0℃ and let it stand for 2 hours. Charge it at 0.5C to full charge, let it stand for 30 minutes, and then discharge it at 0.5C to the cutoff voltage and measure the discharge capacity.

[0170] Adjust the secondary battery temperature to -20℃ and let it stand for 2 hours. Charge it at 0.5C to full charge, let it stand for 30 minutes, and then discharge it at 0.5C to the cutoff voltage and measure the discharge capacity.

[0171] Among them, the discharge cutoff voltage of the secondary battery with LiFePO4 as the positive electrode active material is 2.5V, and the positive electrode active material is LiNi. 0.5 Mn 0.3 Co 0.2 The discharge cutoff voltage of the O2 secondary battery is 3V.

[0172] Calculation method for capacity retention at different temperatures: discharge capacity at different temperatures / discharge capacity at 25℃.

[0173] Testing of rate charge / discharge performance:

[0174] Rate charging: 0.33C charging to full charge, rest for 30 minutes, discharge at 0.33C to the cutoff voltage and measure the charging capacity during this period, then rest for 30 minutes; 1C charging to full charge, rest for 30 minutes, discharge at 0.33C to the cutoff voltage and measure the charging capacity during this period, then rest for 30 minutes; 3C charging to full charge, rest for 30 minutes, discharge at 0.33C to the cutoff voltage and measure the charging capacity during this period, then rest for 30 minutes; 6C charging to full charge, rest for 30 minutes, discharge at 0.33C to the cutoff voltage and measure the charging capacity during this period, then rest for 30 minutes.

[0175] Among them, the secondary battery with LiFePO4 as the positive electrode active material has a discharge cutoff voltage of 2.5V and a charging cutoff voltage of 3.65V; the secondary battery with LiNi as the positive electrode active material... 0.5 Mn 0.3 Co 0.2 The discharge cutoff voltage of the O2 secondary battery is 3V, and the charging cutoff voltage is 4.2V.

[0176] Capacity retention rate at different rates: charging capacity at different rates / charging capacity at 0.33C.

[0177] Discharge rate tests: Charge to full charge at 0.33C, let stand for 30 minutes, discharge at 0.33C to the cutoff voltage and measure the discharge capacity during this period, then let stand for 30 minutes; Charge to full charge at 0.33C, let stand for 30 minutes, discharge at 1C to the cutoff voltage and measure the discharge capacity during this period, then let stand for 30 minutes; Charge to full charge at 0.33C, let stand for 30 minutes, discharge at 3C to the cutoff voltage and measure the discharge capacity during this period, then let stand for 30 minutes; Charge to full charge at 0.33C, let stand for 30 minutes, discharge at 6C to the cutoff voltage and measure the discharge capacity during this period, then let stand for 30 minutes.

[0178] Among them, the secondary battery with LiFePO4 as the positive electrode active material has a discharge cutoff voltage of 2.5V and a charging cutoff voltage of 3.65V; the secondary battery with LiNi as the positive electrode active material... 0.5 Mn 0.3 Co 0.2 The discharge cutoff voltage of the O2 secondary battery is 3V, and the charging cutoff voltage is 4.2V.

[0179] Capacity retention at different rates: discharge capacity at different rates / discharge capacity at 0.33C.

[0180] Test of adhesive float ratio:

[0181] Test method: Scrape powder from the outer and bottom surfaces of the electrode sheet, weigh 10-30 mg of sample, place it in an Al2O3 crucible, spread it evenly, cover the crucible, and test by differential scanning gravimetric analysis. Set parameters: nitrogen atmosphere, purge gas flow rate 60 mL / min, protective gas flow rate 20 mL / min, temperature range 35-600℃, heating rate 10-30℃, and conduct the experiment. Use an electronic balance with an accuracy of 0.01% to evaluate the difference in powder mass before and after heating, and obtain the weight loss rate as a function of temperature to determine the binder content.

[0182] Adhesive float ratio calculation method: (Outer surface adhesive content - Bottom surface adhesive content) / Bottom surface adhesive content * 100%

[0183] Testing of electrolyte wetting rate of electrode plates:

[0184] Test method: A certain amount of electrolyte (2 cm high) is drawn into a capillary tube (1 mm in diameter), and the liquid-absorbing end of the capillary tube is brought into contact with the surface of the electrode plate. The electrode plate has a porous structure, and under the capillary force, the electrolyte in the capillary tube can be drawn out. The time required for the electrolyte to be completely absorbed is recorded, and the electrolyte wetting rate is calculated from this.

[0185] Electrolyte wetting rate calculation method: electrolyte density * electrolyte volume in capillary / time required for complete electrolyte absorption.

[0186] The results of the above tests and the parameters of the electrode plates are shown in Tables 1 to 3 below.

[0187]

[0188]

[0189]

[0190]

[0191] Table 3

[0192]

[0193] Table 1 shows that, under the same preparation conditions, the secondary battery containing the electrode sheet of the embodiment of this application is superior to the corresponding secondary battery of the comparative example in at least one aspect of first-time efficiency, DC resistance and high and low temperature performance (even when the pressure of the pressing process is greater than that of the comparative example, such as Example 10), and the effect is more significant when the charging and discharging conditions are more demanding.

[0194] Table 2 shows that, under the same preparation conditions, the secondary battery containing the electrode sheets of the embodiments of this application is superior to the corresponding secondary batteries of the comparative examples in terms of both charge rate performance and discharge rate performance.

[0195] Table 3 shows a comparison between Examples 1 to 19 and Comparative Examples 1 and 2. It can be seen that, under the same preparation conditions, the secondary batteries containing the electrode sheets of the embodiments of this application exhibit superior electrolyte wetting rates in the electrode sheets compared to the corresponding comparative examples (approximately four times that of the comparative examples). Therefore, considering battery productivity, the improved electrolyte wetting rate of the electrode sheets can shorten the electrolyte wetting time of the battery cell, significantly increasing battery productivity.

[0196] Figures 9 to 12 The images shown are SEM images of the outer surface of the positive electrode sheets of Comparative Example 1, Example 1, Comparative Example 2, and Example 2, respectively. A comparison between Examples 1 and 2 and Comparative Examples 1 and 2 shows that the porosity of the outer surface of Examples 1 and 2 is significantly greater than that of Comparative Examples 1 and 2.

[0197] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing an electrode sheet, comprising the following steps: Step (1): Provide an electrode active material slurry, coat the electrode active material slurry onto at least one surface of a polymer substrate, and then dry it to obtain an initial electrode sheet having an electrode active material layer; and Step (2): A metal substrate is provided, and the metal substrate is laminated with the initial electrode sheet with the surface of the metal substrate facing the electrode active material layer. A pressing process is then performed to transfer the electrode active material layer onto the surface of the metal substrate to obtain the electrode sheet. There is a difference in ductility between the metal substrate and the polymer substrate used in conjunction. The electrode sheet includes a current collector and an electrode active material layer disposed on at least one surface of the current collector. The porosity of the outer surface side of the electrode active material layer is the largest, and the porosity of the bottom surface side of the electrode active material layer opposite to the outer surface side is the smallest.

2. The method for preparing the electrode sheet according to claim 1, wherein, When the electrode sheet is a positive electrode sheet, the compaction density is 2.1–3.8 g / cm³. 3 When the electrode sheet is a negative electrode sheet, the compaction density is 1.3–1.8 g / cm³. 3 .

3. The method for preparing the electrode sheet according to claim 1, wherein the pressure of the pressing process is 20-80T.

4. The method for preparing the electrode sheet according to any one of claims 1 to 3, wherein the pressing step is roll pressing.

5. The method for preparing the electrode sheet according to any one of claims 1 to 3, wherein the polymer substrate is at least one selected from polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene (PE) film, polyvinyl alcohol (PVA) film, polyvinylidene fluoride (PVDF) film, polytetrafluoroethylene (PTFE) film, polycarbonate (PC) film, polyvinyl chloride (PVC) film, polymethyl methacrylate (PMMA) film, polyimide (PI) film, polystyrene (PS) film, and polybenzimidazole (PBI) film.

6. The method for preparing the electrode sheet according to any one of claims 1 to 3, wherein the thickness of the polymer substrate is 25 μm to 500 μm.

7. The method for preparing the electrode sheet according to any one of claims 1 to 3, wherein the metal substrate is aluminum foil or copper foil.

8. A secondary battery comprising an electrode sheet prepared by the method described in any one of claims 1 to 7.

9. A battery module comprising the secondary battery of claim 8.

10. A battery pack comprising the battery module of claim 9.

11. An electrical device comprising at least one selected from the secondary battery of claim 8, the battery module of claim 9, or the battery pack of claim 10.

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