Positive pole piece and battery

Abstract

The invention discloses a positive pole piece and a battery. The positive pole piece meets the following conditions: 34.8 P + 0.1 H is more than or equal to 12.5 and less than or equal to 18.5; wherein P is the porosity of the positive pole piece, the unit is%, H is the height of the positive pole piece infiltrated by the electrolyte in the first direction, and the unit is mm. Therefore, the electrolyte wettability of the positive pole piece is relatively good, and the ion transmission impedance is reduced, so that the energy density and the cycling stability of the battery are improved.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage systems due to their high safety, long cycle life, and low cost. Related technologies commonly employ increasing electrode compaction density to improve battery energy density. However, high compaction density leads to reduced electrode porosity, causing problems such as difficulty in electrolyte wetting and increased ion transport impedance, ultimately affecting the battery's rate performance and cycle life.

[0003] Currently, most methods for solving electrolyte wettability problems focus on optimizing electrolyte formulations, extending wetting time, and adjusting process parameters. However, these methods have limited effectiveness and lack clear theoretical guidance.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a positive electrode sheet that satisfies: 12.5 ≤ 34.8P + 0.1H ≤ 18.5; where P is the porosity of the positive electrode sheet in %, and H is the height of the electrolyte wetting the positive electrode sheet along a first direction in mm. Therefore, this positive electrode sheet exhibits good electrolyte wettability and reduced ion transport impedance, thereby contributing to improved battery energy density and cycle stability.

[0006] In some embodiments, 15.0 ≤ 34.8P + 0.1H ≤ 16.0. This is beneficial for further improving the energy density and cycle stability of the battery.

[0007] In some embodiments, 20% ≤ P ≤ 45%. This provides sufficient space to store the electrolyte, which helps to improve the ion diffusion rate.

[0008] In some embodiments, the compaction density of the positive electrode sheet is 2.4 mg / mm². 3 -2.7mg / mm 3 This facilitates the construction of a stable and efficient electron-ion hybrid conductive network, enabling the battery to possess both high energy density and excellent cycle stability.

[0009] In some embodiments, 15mm ≤ H ≤ 55mm. This allows the electrolyte to achieve a sufficient and uniform wetting state inside the positive electrode, resulting in a more complete ion transport network and helping to improve the battery's capacity.

[0010] In some embodiments, the electrolyte comprises a lithium salt and a solvent; wherein the lithium salt comprises at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate; and / or the solvent comprises at least one selected from cyclic carbonates, chain carbonates, phosphate esters, and carboxylic acid esters. Thus, the electrolyte can provide and conduct lithium ions, improving ionic conductivity.

[0011] In some embodiments, the concentration of lithium salt in the electrolyte is 0.9 mol / L to 1.2 mol / L; and / or, the viscosity of the electrolyte is 3.5 mPa·s to 4.0 mPa·s. Thus, the electrolyte can provide sufficient active ions while adequately wetting the positive electrode.

[0012] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes at least one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide. Therefore, a wide range of positive active materials can be selected, facilitating large-scale deployment.

[0013] In some embodiments, the thickness of the positive electrode sheet is 150 μm-300 μm; the thickness of the positive electrode active material layer ranges from 140 μm-280 μm. This allows the battery to achieve both high energy density and fast ion transport rate.

[0014] In a second aspect, this application proposes a battery including the positive electrode sheet described in the first aspect. Therefore, this battery exhibits high energy density and cycle stability. Attached Figure Description

[0015] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 This is a schematic diagram of the electrolyte wetting direction according to an embodiment of this application.

[0016] Explanation of reference numerals in the attached figures: 100-Positive electrode sheet. Detailed Implementation

[0017] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description 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.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0019] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0020] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article; "0-5" is just a shortened representation of these numerical combinations.

[0022] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Porosity of lithium battery positive electrode is the core structural parameter that affects the electrochemical and mechanical properties of the electrode. Compared with structural parameters such as thickness, areal density, and compaction density, its special features are mainly: (1) Directly related to ion transport channels: Porosity is the "physical basis" of electrolyte wetting and lithium ion migration. Too low porosity will lead to ion transport obstruction and rate performance decline, while too high porosity will reduce the energy density and structural stability of the electrode. Parameters such as thickness and areal density describe the characteristics of the electrode from a geometric or mass dimension and have little impact on ion transport efficiency; (2) Key link for coupling multiple parameters: Porosity is negatively correlated with compaction density. The compaction process will change the size, distribution and connectivity of the electrode pores. At the same time, porosity will also affect the adhesion and flexibility of the electrode, while other structural parameters usually only affect one performance and it is difficult to achieve synergistic regulation of multiple performances.

[0026] Electrolyte wetting height is a parameter that can intuitively reflect the dynamic wetting process. Compared with parameters such as contact angle and wetting rate, its special features are mainly: (1) Contact angle is a parameter that statically characterizes the affinity of liquid-solid interface and can determine whether wetting is possible. Wetting height is dynamic data obtained through tests such as capillary rise method, which can directly quantify the degree and speed of wetting and is more in line with the verification requirements of actual production processes such as electrode rolling and cell liquid injection; (2) The numerical change of wetting height can simultaneously reflect the quality of structural parameters such as electrode porosity, pore connectivity, and coating flatness. Electrodes with suitable porosity and good connectivity will have a faster wetting height and a higher final value. Other wetting parameters mostly correspond to a single structural feature and cannot reflect the synergistic effect of multiple parameters.

[0027] The ultimate goal of lithium battery design is to achieve the highest and fastest electrolyte wettability while meeting the target porosity for energy density requirements. This requires controlling the particle size distribution of materials, binder networks, and compaction processes to construct a pore structure that meets performance requirements, namely a structure with appropriate pore size, high connectivity, and low tortuosity. This is related to the two parameters of electrode porosity and electrolyte wetting height, which is beneficial for balancing the energy density and cycle life of lithium batteries.

[0028] Currently, there is a lack of models in related technologies that can accurately and quantitatively describe the intrinsic relationship between the structural parameters (porosity) of the positive electrode and the electrolyte wetting behavior (wetting height). This leads to the design of positive electrode sheets often relying on experience and trial and error, making it impossible to accurately preset their power performance while ensuring high energy density.

[0029] This application utilizes the intrinsic quantitative relationship between the porosity (P) of the positive electrode sheet and the electrolyte wetting height (H) to control porosity in order to accurately predict and optimize electrolyte wettability, thereby producing a high-performance battery that achieves the best balance between energy density and cycle life.

[0030] In the first aspect of this application, reference is made to Figure 1 This application proposes a positive electrode 100 that satisfies the following: 12.5 ≤ 34.8P + 0.1H ≤ 18.5; where P is the porosity of the positive electrode, in %; and H is the height of the electrolyte wetting the positive electrode along a first direction (i.e., perpendicular to the thickness of the positive electrode), in mm. Therefore, this positive electrode has good electrolyte wettability and reduced ion transport impedance, which is beneficial for improving the energy density and cycle stability of the battery.

[0031] This application provides a model relating positive electrode design parameters to electrolyte wettability (12.5≤34.8P+0.1H≤18.5), making positive electrode design based on data. Before battery manufacturing, the model can predict the final battery performance, greatly shortening the R&D cycle and reducing development costs. It can also find the optimal wettability under a given energy density requirement, thereby achieving precise positioning of battery performance.

[0032] Specifically, the process of establishing the above-mentioned relationship model may include: taking positive electrode samples prepared with the same ratio and different compaction densities; measuring their porosity (P) using a porosimeter; and using an ETS1000 wettability testing system to test the wetting height (H) of the electrolyte along the direction perpendicular to the thickness of the positive electrode within 900 seconds under the same conditions. Linear regression analysis was performed on the obtained (P, H) data, revealing a strong correlation, and ultimately determining that it satisfies the following relationship: 12.5 ≤ 34.8P + 0.1H ≤ 18.5.

[0033] It should be noted that the positive electrode includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. Those skilled in the art can choose to provide the positive active material layer on one side of the positive current collector or on both sides of the positive current collector, depending on the specific circumstances. It is understood that in this application, the electrolyte wetting occurs within the positive active material layer.

[0034] As an example, 34.8P+0.1H can be 12.5, 13.5, 14.5, 15.5, 16.5, 17.5 or 18.5, etc.

[0035] In some embodiments, 15.0 ≤ 34.8P + 0.1H ≤ 16.0. This is beneficial for further improving the energy density and cycle stability of the battery.

[0036] In some embodiments, 20% ≤ P ≤ 45%, such as 20%, 25%, 30%, 35%, 40%, or 45%. This provides sufficient space to store the electrolyte, which helps to improve the ion diffusion rate.

[0037] In some embodiments, the compaction density of the positive electrode sheet is 2.4 mg / mm². 3 -2.7mg / mm 3 For example, it could be 2.4 mg / mm 3 2.5 mg / mm 3 2.6 mg / mm 3 Or 2.4 mg / mm 3 This facilitates the construction of a stable and efficient electron-ion hybrid conductive network, enabling the battery to possess both high energy density and excellent cycle stability.

[0038] In some embodiments, 15mm ≤ H ≤ 55mm, for example, it can be 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, or 55mm. Therefore, the electrolyte can achieve a sufficient and uniform wetting state inside the positive electrode sheet, resulting in a more complete ion transport network, which helps to improve the battery's capacity.

[0039] In some embodiments, the electrolyte comprises a lithium salt and a solvent; wherein the lithium salt comprises at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate; and / or the solvent comprises at least one selected from cyclic carbonates, chain carbonates, phosphate esters, and carboxylic acid esters. Thus, the electrolyte can provide and conduct lithium ions, improving ionic conductivity.

[0040] In some embodiments, the concentration of lithium salt in the electrolyte is 0.9 mol / L-1.2 mol / L, for example, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, or 1.2 mol / L; and / or, the viscosity of the electrolyte is 3.5 mPa·s-4.0 mPa·s, for example, 3.5 mPa·s, 3.6 mPa·s, 3.7 mPa·s, 3.8 mPa·s, 3.9 mPa·s, or 4.0 mPa·s. Thus, the electrolyte can provide sufficient active ions while adequately wetting the positive electrode.

[0041] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes at least one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide. Therefore, a wide range of positive active materials can be selected, facilitating large-scale deployment.

[0042] In some embodiments, the thickness of the positive electrode sheet is 150μm-300μm, for example, it can be 150μm, 180μm, 200μm, 230μm, 250μm, 280μm, or 300μm; the thickness of the positive electrode active material layer is in the range of 140μm-280μm, for example, it can be 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 260μm, or 280μm. This allows the battery to achieve both high energy density and fast ion transport rate.

[0043] In a second aspect, this application proposes a battery including the positive electrode sheet described in the first aspect. Therefore, this battery exhibits high energy density and cycle stability.

[0044] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0045] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of 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 this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0046] Example 1 (1) Preparation of positive electrode slurry The positive electrode active material lithium iron phosphate, the positive electrode conductive agent carbon nanotubes (CNT), and the positive electrode binder polyvinylidene fluoride (PVDF) were mixed evenly in a mass ratio of 96:2:2. Then, N-methylpyrrolidone (NMP) solvent was added and the viscosity was adjusted to 12000 mPa·s by stirring to obtain the positive electrode slurry.

[0047] (2) Preparation of positive electrode sheet The prepared positive electrode slurry was coated onto one side of the positive electrode current collector aluminum foil. After the coating process was completed, the roller compaction density was designed to be 2.40 mg / mm². 3 Rolling is performed to obtain lithium iron phosphate positive electrode sheets.

[0048] The differences between other embodiments and comparative examples and embodiment 1 are shown in Table 1.

[0049] The positive electrode sheets prepared in the above embodiments and comparative examples were subjected to the following tests, and the test results are shown in Table 1.

[0050] (1) Porosity P: Measured using a porosity meter.

[0051] (2) Electrolyte wetting height H: The ETS1000 wettability test system was used to test the wetting height of the electrolyte along the direction perpendicular to the thickness of the positive electrode sheet within 900 seconds under the same conditions.

[0052] Linear regression analysis was performed on the (P, H) data obtained above, and a strong correlation was found. Finally, it was determined that the relationship satisfies the formula: 12.5≤34.8P+0.1H≤18.5.

[0053] Table 1

[0054] Battery assembly: (1) Preparation of negative electrode sheet: The negative electrode active material graphite, the negative electrode conductive agent carbon black, the negative electrode binder styrene-butadiene rubber (SBR), and the negative electrode thickener sodium carboxymethyl cellulose (CMC) are mixed evenly in a mass ratio of 96:1:1.5:1.5. Deionized water solvent is added and the viscosity is adjusted to 8000 mPa·s by stirring to obtain a negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector copper foil to obtain a negative electrode sheet. (2) Separator: A commercially available 13μm polyethylene (PE) membrane is used; (3) Battery preparation: The positive electrode sheets with different compaction densities are used as positive electrodes. The N / P ratio of the cell is kept constant and fixed at 1.13. The negative electrode sheets are used as negative electrodes. The same separator and electrolyte are selected for winding and assembly and coating. The battery is left to stand for 24 hours and then the electrical performance is tested. The N / P ratio is (specific capacity of negative electrode active material × surface density of negative electrode × content ratio of negative electrode active material) / (specific capacity of positive electrode active material × surface density of positive electrode × content ratio of positive electrode active material).

[0055] The assembled batteries were subjected to the following electrical performance tests, and the test results are shown in Table 2.

[0056] The square aluminum-cased lithium iron phosphate battery composed of the above positive electrode sheets was weighed, with the weight as m (in kg). After standing at room temperature (25℃) for 12 hours, the battery's cycle performance was determined by repeated constant current charge-discharge cycles at a constant current density. Specifically, the ambient temperature was maintained at 25±2℃ in a high-low temperature chamber. The battery was charged at a constant current rate of 1C to 3.65V, rested for 30 minutes, and then discharged at a constant current rate of 1C to 2.5V, rested for 30 minutes, and then subjected to long-term cycling. The ratio of the discharge energy of the first cycle to the weight m was taken as the energy density; the ratio of the discharge capacity of the first cycle to the charge capacity was taken as the initial coulombic efficiency; the ratio of the discharge capacity of the 200th cycle to the maximum discharge capacity during the cycle was taken as the capacity retention rate of the 200th cycle; and the ratio of the discharge capacity of the 500th cycle to the maximum sustained discharge capacity during the cycle was taken as the capacity retention rate of the 500th cycle.

[0057] Table 2

[0058] Referring to the results of the above comparative examples and embodiments, it can be seen that, under the same battery size, when the positive electrode compaction is small, the energy density of the batteries composed of comparative examples 1-2 is very low, the production cost is high, and they cannot meet market demand; when the positive electrode compaction is continuously increased, the capacity decay of comparative examples 3 and 4 after 500 charge-discharge cycles is significantly faster than that of other comparative examples and embodiments, and they cannot meet the standard requirement of 80% capacity decay after 4000 long-term cycles at 25°C.

[0059] Compared to Comparative Examples 1-4, the positive electrode sheets in Examples 1-5 satisfy 12.5 ≤ 34.8P + 0.1H ≤ 18.5, resulting in batteries with both high energy density and capacity retention, exhibiting better overall performance. The 34.8P + 0.1H value in Comparative Examples 1-2 is too large, leading to low battery energy density and failing to meet market demands. Conversely, the 34.8P + 0.1H value in Comparative Examples 3-4 is too small, resulting in short battery cycle life and failing to meet warranty requirements. By satisfying the aforementioned relationship model, optimal electrolyte wettability can be achieved under given energy density requirements, thereby enabling precise positioning of battery performance.

[0060] 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 positive electrode plate, characterized in that, Satisfies: 12.5 ≤ 34.8P + 0.1H ≤ 18.5; Wherein, P is the porosity of the positive electrode sheet, in %, and H is the height of the electrolyte wetting the positive electrode sheet along the first direction, in mm.

2. The positive electrode sheet according to claim 1, characterized in that, 15.0≤34.8P+0.1H≤16.

0.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, 20%≤P≤45%。 4. The positive electrode sheet according to claim 1 or 2, characterized in that, The compaction density of the positive electrode sheet is 2.4 mg / mm². 3 -2.6mg / mm 3 .

5. The positive electrode sheet according to claim 1 or 2, characterized in that, 15mm≤H≤55mm.

6. The positive electrode sheet according to claim 1 or 2, characterized in that, The electrolyte comprises a lithium salt and a solvent; wherein... The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate; and / or, The solvent includes at least one of cyclic carbonates, chain carbonates, phosphate esters, and carboxylic acid esters.

7. The positive electrode sheet according to claim 6, characterized in that, The concentration of lithium salt in the electrolyte is 0.9 mol / L-1.2 mol / L; and / or, The viscosity of the electrolyte is 3.5 mPa·s-4.0 mPa·s.

8. The positive electrode sheet according to claim 1 or 2, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes at least one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

9. The positive electrode sheet according to claim 8, characterized in that, The thickness of the positive electrode sheet is 150μm-300μm; the thickness of the positive electrode active material layer ranges from 140μm-280μm.

10. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-9.

Images