A secondary battery, its design method and electrical device

Abstract

This application discloses a secondary battery, its design method, and an electrical device thereof, belonging to the field of battery technology. This application controls the change in specific surface area (BET2-BET1) of the positive electrode active material before and after rolling, the single-sided areal density (CW) of the positive electrode active material layer, the compaction density (PD) of the positive electrode sheet, and the electrolyte mass (A) per unit capacity. EL Satisfying 0.05 ≤ (BET2-BET1)·CW·PD·A EL ≤20 effectively improves the fast charging and discharging performance of secondary batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a secondary battery, its design method, and an electrical device thereof. Background Technology

[0002] Secondary batteries possess significant advantages such as high energy density, high power density, long lifespan, and no memory effect, and have been gradually applied in fields such as electronics, home appliances, and aerospace. Compared with ternary cathode materials, lithium iron phosphate cathode materials have the advantage of low cost, but their lithium-ion diffusion rate is relatively low, which can easily lead to poor charge-discharge rates. Therefore, it is necessary to design a secondary battery with fast-charging performance to effectively alleviate range anxiety in electric vehicles. Summary of the Invention

[0003] Based on the deficiencies of existing technologies, the purpose of this invention is to provide a secondary battery, its design method, and an electrical device, aiming to enable the secondary battery to have good fast charging performance.

[0004] In a first aspect, the present invention provides a secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode.

[0005] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material;

[0006] The secondary battery satisfies: 0.05 ≤ (BET2 - BET1)·CW·PD·A EL ≤20;

[0007] Wherein, BET2 is the specific surface area of ​​the positive electrode active material after rolling, in m². 2 / g,

[0008] BET1 is the specific surface area of ​​the positive electrode active material before rolling, in m². 2 / g,

[0009] CW represents the areal density of the positive electrode active material layer on one side, expressed in g / 1540.25 mm². 2 ,

[0010] PD is the compaction density of the positive electrode, expressed in g / cm³. 3 ,

[0011] A EL The value represents the mass of electrolyte per unit capacity, expressed in g / Ah.

[0012] Preferably, 0 < BET2 - BET1 ≤ 15m 2 / g.

[0013] Preferably, BET1 is 5-15m. 2 / g, wherein BET2 is 5-20m 2 / g.

[0014] Preferably, the CW is 0.1–0.5 g / 1540.25 mm. 2 .

[0015] Preferably, the PD is 2.0–2.5 g / cm³. 3 .

[0016] Preferably, the A EL The concentration is 1.0–5.0 g / Ah.

[0017] Preferably, the positive electrode active material comprises lithium iron phosphate, and the microstructure of the lithium iron phosphate is secondary spherical particles.

[0018] Preferably, the secondary battery satisfies at least one of the following conditions:

[0019] (1) The negative electrode sheet includes a negative electrode active material, which includes at least one of carbon material and silicon-based material. The carbon material includes at least one of graphite, soft carbon, hard carbon, carbon fiber, and mesophase carbon microspheres. The silicon-based material includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, and silicon alloy.

[0020] (2) The electrolyte includes an electrolyte salt, an organic solvent and an additive. The electrolyte salt includes lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide; the organic solvent includes at least one of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate; and the additive includes vinylene carbonate and / or fluoroethylene carbonate.

[0021] Secondly, this application provides a design method for a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode;

[0022] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material;

[0023] The design method includes the following steps: designing a secondary battery that satisfies 0.05 ≤ (BET2 - BET1)·CW·PD·A EL ≤20;

[0024] Wherein, BET2 is the specific surface area of ​​the positive electrode active material after rolling, in m². 2 / g,

[0025] BET1 is the specific surface area of ​​the positive electrode active material before rolling, in m². 2 / g,

[0026] CW represents the areal density of the positive electrode active material layer on one side, expressed in g / 1540.25 mm². 2 ,

[0027] PD is the compaction density of the positive electrode, expressed in g / cm³. 3 ,

[0028] A EL The value represents the mass of electrolyte per unit capacity, expressed in g / Ah.

[0029] Thirdly, this application provides an electrical device, including the secondary battery and / or the secondary battery designed by the design method.

[0030] Compared with the prior art, the beneficial effects of this application are as follows: This application effectively improves the fast charge and discharge performance of secondary batteries by controlling the change in specific surface area of ​​the positive electrode active material before and after rolling, the single-sided surface density of the positive electrode active material layer, the compaction density of the positive electrode sheet and the product of the electrolyte mass per unit capacity within a certain range. Attached Figure Description

[0031] Figure 1 This is a SEM image of the positive electrode active material described in Example 1 before rolling.

[0032] Figure 2 This is a SEM image of the positive electrode active material after rolling as described in Example 1. Detailed Implementation

[0033] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0034] (1) Secondary battery

[0035] According to a first aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrode.

[0036] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material;

[0037] The secondary battery satisfies: 0.05 ≤ (BET2 - BET1)·CW·PD·A EL ≤20;

[0038] Wherein, BET2 is the specific surface area of ​​the positive electrode active material after rolling, in m². 2 / g,

[0039] BET1 is the specific surface area of ​​the positive electrode active material before rolling, in m². 2 / g,

[0040] CW represents the areal density of the positive electrode active material layer on one side, expressed in g / 1540.25 mm². 2 ,

[0041] PD is the compaction density of the positive electrode, expressed in g / cm³. 3 ,

[0042] A EL The value represents the mass of electrolyte per unit capacity, expressed in g / Ah.

[0043] The inventors of this application have discovered a significant correlation between the degree of fragmentation of the secondary particle spherical morphology and the fast-charging performance of the secondary battery. The degree of fragmentation of the secondary particle spherical morphology can be controlled by adjusting key parameters such as the change in specific surface area of ​​the positive electrode active material before and after rolling, the load on the positive electrode sheet during coating, and the compaction density during electrode rolling. Furthermore, the increased specific surface area of ​​the positive electrode active material after rolling provides more interfaces for electrolyte wetting, necessitating a corresponding adjustment of the electrolyte weight per unit capacity to effectively reduce irreversible side reactions. Controlling the secondary battery to satisfy 0.05 ≤ (BET2 - BET1)·CW·PD·A EL A value of ≤20 allows the secondary battery to have very good fast charging performance.

[0044] In this application, the positive electrode active material layer can be provided on only one side of the positive electrode current collector, or the positive electrode active material layer can be provided on both sides of the positive electrode current collector.

[0045] In this application, (BET2-BET1)·CW·PD·A EL The value ranges from 0.05 to 20. Optional, (BET2-BET1)·CW·PD·A EL The value can also be in the range of 2–18, 4–16, 6–14, or 8–12. Optional, (BET2-BET1)·CW·PD·A EL The value can also be 1, 3, 5, 7, 9, 11, 13, 15, 17, or 19.

[0046] In some embodiments of this application, 0 < BET2 - BET1 ≤ 15m 2 / g. If BET2-BET1 is too high, it means that the specific surface area of ​​the positive electrode active material after rolling is large, which can easily induce side reactions in the electrolyte, thereby deteriorating the battery performance. Therefore, BET2-BET1 should be controlled within the above range to ensure that the secondary battery has a high discharge specific capacity and good cycle performance.

[0047] In some embodiments of this application, BET1 is 5-15m. 2 / g, BET2 is 5-20m 2 / g. A lower BET1 reduces the contact sites between the electrolyte and the positive electrode interface, and reduces the sites for redox reactions during electrochemical processes, thereby reducing the specific capacity of the positive electrode active material. A higher BET1 means a higher BET2, which can easily induce side reactions in the electrolyte, thus deteriorating the battery performance. In addition, a higher BET1 can also cause particle agglomeration of the positive electrode active material during the slurry preparation process, thereby increasing the processing cost of the positive electrode sheet.

[0048] In some embodiments of this application, CW is 0.1–0.5 g / 1540.25 mm. 2 Optionally, the CW can also be 0.15–0.45 g / 1540.25 mm. 2 Or 0.25~0.35g / 1540.25mm 2 Optionally, CW can also be 0.1g / 1540.25mm. 2 Or 0.2g / 1540.25mm 2 Or 0.3g / 1540.25mm 2 Or 0.4g / 1540.25mm 2 When CW is greater than 0.5g / 1540.25mm 2 At this time, the lithium-ion transport path is long, and the concentration polarization is large during charging and discharging, which hinders the rapid insertion and extraction of lithium ions and is not conducive to the release of the battery's fast charging performance; CW is less than 0.1g / 1540.25mm 2 At this time, there is a risk that the positive electrode sheet may be exposed during the rolling process, which will degrade the battery performance.

[0049] In some embodiments of this application, PD is 2.0–2.5 g / cm³. 3 Optionally, the PD can also be 2.1–2.4 g / cm³. 3 Or 2.2~2.3g / cm 3 Optionally, the PD can also be 2.05 g / cm³. 3 Or 2.15g / cm 3Or 2.25g / cm 3 or 2.35g / cm 3 Or 2.45g / cm 3 When the PD (Power Distribution) is low, the secondary particle spherical morphology of the positive electrode active material is less fragmented, reducing the contact interface between the positive electrode active material and the electrolyte. This, to some extent, reduces the electrochemical active sites of the positive electrode active material, hindering the release of its specific capacity. Furthermore, a lower PD means a higher watt-hour cost per unit volume of the battery. Conversely, when the PD is high, the secondary particle spherical morphology of the positive electrode active material is more fragmented, increasing the specific surface area of ​​the positive electrode active material. This results in more active electrochemical reaction sites between the positive electrode active material and the electrolyte, which can improve the reversible specific capacity of the positive electrode to some extent. However, a higher specific surface area easily induces side reactions in the electrolyte, leading to irreversible capacity loss during cycling. The PD should be controlled between 2.0 and 2.5 g / cm³. 3 Within a certain range, this allows the positive electrode active material to obtain more electrochemical active sites while reducing side reactions in the electrolyte, resulting in secondary batteries with higher specific capacity and cycle performance, and also at a lower cost.

[0050] In some embodiments of this application, A EL The concentration is 1.0–5.0 g / Ah. Optional, A EL It can also be 1.0–4.0 g / Ah, or 2.0–3.0 g / Ah. Optional, A EL It can also be 2.5 g / Ah, 3.5 g / Ah, or 4.5 g / Ah. After rolling, the secondary particle spherical structure of the positive electrode active material is broken, increasing the specific surface area and improving its wettability with the electrolyte. Appropriately reducing the amount of electrolyte per unit capacity can effectively avoid side reactions of the electrolyte and, to some extent, reduce costs. However, too low an amount of electrolyte per unit capacity can easily lead to electrolyte drying during repeated charging, resulting in severe capacity decay. Therefore, controlling A... EL Within the range of 1.0 to 5.0 g / Ah.

[0051] In some embodiments of this application, the positive electrode active material includes lithium iron phosphate, which has a microstructure of secondary spherical particles. Lithium iron phosphate is low in cost, and using it as the positive electrode active material enables secondary batteries to combine low cost with good fast-charging performance.

[0052] In some specific embodiments of this application, the lithium iron phosphate surface is provided with a coating layer, but the type, content, and thickness of the coating layer are not limited. The coating layer may include at least one of carbon, metal oxides, etc., but is not limited to this.

[0053] In some specific embodiments of this application, the positive electrode active material also contains doping elements, but the type and content of doping elements are not limited. It can be doped with only one element or with two or more elements.

[0054] In some embodiments of this application, the positive electrode active material layer further includes a conductive agent and a binder. The type and amount of the conductive agent and binder are not specifically limited and can be selected according to actual needs.

[0055] In this application, the type of positive current collector is not specifically limited and can be selected according to actual needs.

[0056] In this application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material. The negative active material layer may be disposed on only one surface of the negative current collector, or it may be disposed on both surfaces of the negative current collector.

[0057] In this application, the type of negative electrode active material is not specifically limited and can be selected according to actual needs. In some embodiments of this application, the negative electrode active material includes at least one of carbon materials, silicon-based materials, etc., but the type of negative electrode active material is not limited to this. Among them, carbon materials include at least one of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, etc., but the type of carbon material is not limited to this, and graphite can be selected from at least one of artificial or natural graphite; silicon-based materials include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, etc., but the type of silicon-based material is not limited to this.

[0058] In some embodiments of this application, the negative electrode active material layer further includes a conductive agent and a binder. The type and amount of the conductive agent and binder are not specifically limited and can be selected according to actual needs.

[0059] In some embodiments of this application, the electrolyte comprises an electrolyte salt and an organic solvent, or an electrolyte salt, an organic solvent, and an additive. There are no specific limitations on the electrolyte salt, organic solvent, and additive. In some specific embodiments of this application, the electrolyte salt comprises lithium hexafluorophosphate and / or lithium bis(trifluoromethanesulfonyl)imide, but is not limited thereto. In some specific embodiments of this application, the organic solvent comprises at least one of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, but is not limited thereto. The additive may be selected from at least one of negative electrode film-forming additives, positive electrode film-forming additives, and other additives that can improve certain battery performance (such as additives that improve high or low temperature performance of the battery), such as ethylene carbonate and / or fluoroethylene carbonate, but is not limited thereto.

[0060] (2) Design method of secondary battery

[0061] Secondly, this application provides a design method for a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode.

[0062] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material;

[0063] The design method includes the following steps: designing the secondary battery to satisfy 0.05 ≤ (BET2 - BET1)·CW·PD·A EL ≤20;

[0064] Wherein, BET2 is the specific surface area of ​​the positive electrode active material after rolling, in m². 2 / g,

[0065] BET1 is the specific surface area of ​​the positive electrode active material before rolling, in m². 2 / g,

[0066] CW represents the areal density of the positive electrode active material layer on one side, expressed in g / 1540.25 mm². 2 ,

[0067] PD is the compaction density of the positive electrode, expressed in g / cm³. 3 ,

[0068] A EL The value represents the mass of electrolyte per unit capacity, expressed in g / Ah.

[0069] (3) Electrical appliances

[0070] According to a third aspect of this application, an electrical device is provided, comprising the aforementioned secondary battery and / or a secondary battery designed using the aforementioned design method. The type of electrical device is not specifically limited, and may include electric vehicles and energy storage devices, etc.

[0071] The present application will be further illustrated below through specific embodiments.

[0072] Example 1

[0073] This embodiment provides a lithium-ion battery, the preparation method of which is as follows:

[0074] Preparation of the positive electrode sheet: The positive electrode active material lithium iron phosphate (microscopic morphology of secondary spherical particles), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed at a mass ratio of 96:2:2. The solvent N-methylpyrrolidone is added, and then the mixture is stirred in a vacuum mixer until the system is a homogeneous positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of the positive electrode current collector (carbon-coated aluminum foil). The coated electrode sheet is dried in an oven, and then cold-pressed and slit to obtain the positive electrode sheet.

[0075] Preparation of negative electrode sheet: Graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), styrene-butadiene rubber (adhesive), and acetylene black (conductive agent) are mixed in a mass ratio of 97:1:1:1. Deionized water is added, and a negative electrode slurry is obtained under vacuum stirring. The negative electrode slurry is uniformly coated on both sides of the copper foil (negative electrode current collector). The coated electrode sheet is transferred to an oven for drying, and then cold-pressed and slit to obtain the negative electrode sheet.

[0076] Electrolyte preparation: EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DEC (diethyl carbonate) were mixed uniformly at a volume ratio of 20:20:60 to obtain a mixed solvent. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium salt LiPF6 was dissolved in the aforementioned mixed solvent and mixed uniformly to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L.

[0077] The preparation of lithium-ion batteries involves stacking positive electrode sheets, polypropylene separators, and negative electrode sheets in sequence, with the separator acting as a separator between the positive and negative electrode sheets. After being wound into a square bare cell, the cells are placed in a casing, baked at 80°C to remove water, injected with electrolyte, sealed, and then subjected to processes such as standing, hot and cold pressing, formation, clamping, and capacity testing to obtain the finished battery.

[0078] Examples 2-28 and Comparative Examples 1-2

[0079] Examples 2-28 and Comparative Examples 1-2 each provide a lithium-ion battery. These lithium-ion batteries were prepared using a method similar to that of Example 1. Specific differences are shown in Table 1, where the BET1 and BET2 test methods are as follows:

[0080] BET1 was determined by directly taking raw materials from the positive electrode active material.

[0081] Powder samples were directly scraped from the surface of the rolled positive electrode sheet. The powder samples scraped from the electrode sheet were then dissolved in NMP (N-methylpyrrolidone) solution to wash away the binder in the powder. Finally, the powder was transferred to clean water to wash away the conductive agent in the powder. The powder was then filtered, dried, and collected for the determination of BET2.

[0082] BET1 and BET2 tests were performed according to GB / T 19587-2017, the standard for determining the specific surface area of ​​solid substances by gas adsorption BET method.

[0083] Sample pretreatment and degassing conditions: 220℃ / 2hrs (vacuum degassing);

[0084] Sample volume: 2 / 3 of the bulb volume;

[0085] Methods for determining the amount of adsorbed gas: static volumetric method, multi-point method to measure P / P0, specifically P / P0 values ​​of: 0.060, 0.080, 0.120, 0.160, 0.20;

[0086] Adsorbate: N2, purity 99.999 wt%;

[0087] Balancing time: 10s;

[0088] Volume: Measurement mode (measured with N2);

[0089] Liquid nitrogen temperature: -196℃.

[0090] Method for testing the single-sided areal density (CW) of the positive electrode active material layer: First, weigh a sample with an area of ​​1540.25 mm². 2 The mass m1 of the positive current collector is then weighed, and a sample with an area of ​​1540.25 mm² is also weighed. 2 The mass m2 of the positive electrode sheet uniformly coated with positive electrode active material on both sides is calculated using the formula CW=(m2-m1) / 2, where m1 and m2 are in g.

[0091] Test method for compaction density (PD) of positive electrode sheet: Measure the thickness L1 of the positive current collector and the thickness L2 of the positive electrode sheet uniformly coated with positive active material on both sides. Calculate PD using the formula PD = 2 * CW / (L2 - L1), where CW is in g / 1540.25 mm. 2 L1 and L2 are in mm, and PD is in g / cm³. 3 .

[0092] Table 1

[0093]

[0094]

[0095] The lithium-ion batteries of each embodiment and comparative example were tested using the following test methods.

[0096] (1) 0.33C discharge specific capacity test

[0097] ① Place the battery in an insulated box, adjust the temperature of the insulated box to 25℃, and let it stand for 2 hours; ② Charge the battery with a constant current of 0.33C to 3.65V, and then charge it with a constant voltage to the cutoff current of 0.05C; ③ Let it stand for 5 minutes; ④ Discharge the battery with a constant current of 0.33C to 2.5V; ⑤ Let it stand for 5 minutes and record the discharge specific capacity.

[0098] (2) 4C cycle capacity retention test

[0099] ① Place the battery in an insulated box, adjust the temperature of the insulated box to 25℃, and let it stand for 2 hours; ② Charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage to the cutoff current of 0.05C; ③ Let it stand for 5 minutes; ④ Discharge at a constant current of 0.33C to 2.5V; ⑤ Let it stand for 5 minutes; ⑥ Charge at a constant current of 4C to 3.65V, then charge at a constant voltage to the cutoff current of 0.05C; ⑦ Let it stand for 5 minutes; ⑧ Discharge at a constant current of 4C to 2.5V; ⑨ Let it stand for 5 minutes; ⑩ Repeat steps ⑥ to ⑨, record the capacity retention rate of each cycle, until the battery capacity remains below 80% and record the number of cycles at this point, which is the maximum number of cycles.

[0100] (3) 4C rate discharge performance

[0101] ① Place the battery in an insulated box, adjust the temperature of the insulated box to 25℃, and let it stand for 2 hours; ② Charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage to the cutoff current of 0.05C; ③ Let it stand for 5 minutes; ④ Discharge at a constant current of 0.33C to 2.5V; ⑤ Let it stand for 5 minutes; ⑥ Charge at a constant current of 4C to 3.65V, then charge at a constant voltage to the cutoff current of 0.05C; ⑦ Let it stand for 5 minutes; ⑧ Discharge at a constant current of 0.33C to 2.5V; ⑨ Let it stand for 5 minutes, and calculate the ratio of the discharge capacity at the 4C rate to the discharge capacity at the 0.33C rate.

[0102] The test results are shown in Table 2.

[0103] Table 2

[0104]

[0105]

[0106] Table 2 shows that the change in specific surface area of ​​the positive electrode active material before and after rolling, the areal density of the positive electrode active material layer on one side, the compaction density of the positive electrode sheet, and the electrolyte mass per unit capacity all affect the battery's fast charge and discharge performance. (BET2-BET1)·CW·PD·A EL Lower comparative example 1 and (BET2-BET1)·CW·PD·A EL In the higher comparative example 2, each embodiment controls (BET2-BET1)·CW·PD·A ELValues ​​in the range of 0.05 to 20 exhibit better fast charge and discharge performance, such as a 0.33C discharge capacity of over 135 mAh / g, a 4C discharge capacity retention rate of over 84.5%, and a maximum number of cycles of over 4350.

[0107] A comparison of Examples 1-5 and Examples 6-8 shows that the change in specific surface area (BET2-BET1) of the positive electrode active material before and after rolling affects the battery's fast charge and discharge performance; compared to BET2-BET1 > 15m 2 When / g, BET2-BET1≤15m 2 At / g, the battery has better fast charge and discharge performance.

[0108] A comparison of Examples 9-11 and Examples 14-15 shows that the compaction density (PD) of the positive electrode sheet affects the battery's fast charge / discharge performance. Both low and high PD of the positive electrode sheet are detrimental to the battery's fast charge / discharge performance. When the PD of the positive electrode sheet is between 2.0 and 2.5 g / cm³... 3 Within a certain range, it is more conducive to the battery's rapid charging and discharging performance.

[0109] A comparison of Examples 16-21 shows that the electrolyte mass A per unit capacity is... EL It will affect the battery's fast charge and discharge performance; the mass of electrolyte per unit capacity A EL Both excessively low and excessively high electrolyte levels are detrimental to the battery's rapid charge and discharge performance. When the electrolyte mass A per unit capacity... EL Within the range of 1.0 to 5.0 g / Ah, it is more conducive to the rapid charging and discharging performance of the battery, and the amount of electrolyte used is small, resulting in low cost.

[0110] A comparison of Examples 22-27 shows that the areal density (CW) of the positive electrode active material layer affects the battery's fast charge / discharge performance. A higher CW results in a longer lithium-ion transport path and greater concentration polarization during charging and discharging, which in turn worsens the battery's fast charging performance. Conversely, a lower CW increases the likelihood of foil leakage during coating, reducing the electrode manufacturing yield. Furthermore, a higher proportion of inactive materials (such as positive and negative current collectors) in the battery reduces its energy density. To ensure a high yield in the electrode manufacturing process and achieve good fast charging performance, a CW of 0.1–0.5 g / 1540.25 mm is preferred for the positive electrode active material layer. 2 Within the range.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet, The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material; The secondary battery satisfies: 0.05 ≤ (BET2 - BET1) · CW · PD · A EL ≤ 20, BET2 is the specific surface area of the positive active material after rolling, unit: m2 / g 2 / g, BET1 is the specific surface area before rolling of the positive active material, in m2 / g 2 / g, CW is the single-sided area density of the positive electrode active material layer, in g / 1540.25 mm 2 , the CW is 0.1 to 0.3 g / 1540.25 mm 2 ; PD is the compacted density of the positive electrode sheet, in g / cm 3 , the PD is 2.0-2.5 g / cm 3 ; A EL is the mass of the electrolyte in the unit volume, in g / Ah; the A EL is 3.0-5.0 g / Ah 0 < BET2 - BET1 < 15 m 2 / g.

2. The secondary battery according to claim 1, wherein The BET1 is 5-15 m 2 / g, and the BET2 is 5-20 m 2 / g.

3. The secondary battery according to claim 1, wherein The positive electrode active material comprises lithium iron phosphate, and the micro-morphology of the lithium iron phosphate is spherical secondary particles.

4. The secondary battery according to claim 1, wherein At least one of the following conditions is met: (1) The negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises at least one of a carbon material and a silicon-based material, the carbon material comprises at least one of graphite, soft carbon, hard carbon, carbon fiber, and mesocarbon microbeads, and the silicon-based material comprises at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, and a silicon alloy; (2) The electrolyte comprises an electrolyte salt, an organic solvent, and an additive, the electrolyte salt comprises lithium hexafluorophosphate and / or lithium bis(trifluoromethylsulfonyl)imide, the organic solvent comprises at least one of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, and the additive comprises vinylene carbonate and / or fluoroethylene carbonate.

5. A design method of a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, characterized in that, The design method includes the following steps: designing a secondary battery to satisfy: 0.05 ≤ (BET2 - BET1) · CW · PD · A EL ≤ 20; BET2 is the specific surface area of the positive active material after rolling, unit: m2 / g 2 / g, BET1 is the specific surface area before rolling of the positive active material, in m2 / g 2 / g, CW is the single-sided area density of the positive electrode active material layer, in g / 1540.25 mm 2 , the CW is 0.1 to 0.3 g / 1540.25 mm 2 ; PD is the compacted density of the positive electrode sheet, in g / cm 3 , the PD is 2.0-2.5 g / cm 3 ; A EL is the mass of the electrolyte in the unit volume, unit g / Ah; the A EL is 3.0-5.0 g / Ah 0 < BET2 - BET1 < 15 m 2 / g.

6. An electrical device, characterized by The secondary battery comprises the secondary battery of any one of claims 1 to 4 and / or the secondary battery designed by the design method of claim 5.

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