A 21650 cylindrical lithium ion battery

Abstract

The application discloses a 21650 cylindrical lithium ion battery and belongs to the technical field of lithium ion batteries. The 21650 cylindrical lithium ion battery comprises a positive electrode sheet and a negative electrode sheet. The porosity epsilon p of the positive electrode sheet is 20% to 35%, and the median pore diameter dp is 0.3 mu m to 0.8 mu m. The porosity epsilon n of the negative electrode sheet is 22% to 45%, and the median pore diameter dn is 0.5 mu m to 1.5 mu m. Epsilon p, dp, epsilon n and dn satisfy the following formula: P1=(epsilon n / epsilon p) x (dn / dp) x (Hj / Dj) >=2.5. Wherein, Hj / Dj is the ratio of the height to the diameter of the winding core, and Hj / Dj is 3.09 to 3.14. The 21650 cylindrical lithium ion battery satisfying the above characteristics has a longer cycle life, a lower internal resistance and a more excellent infiltration performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a 21650 cylindrical lithium-ion battery. Background Technology

[0002] With the increasing demands for battery power density and cycle life from power tools, drones, and portable electronic devices, the electrode aperture structure design of cylindrical lithium-ion batteries has become a key factor affecting battery performance. 21650 cylindrical batteries have specific dimensional specifications, and this unique geometry requires a balance between radial and axial ion transport in the electrode aperture structure. However, in existing technologies, the ion transport rates between the positive and negative electrodes of this type of battery often mismatch, leading to polarization accumulation and consequently affecting the battery's rate performance and cycle life.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a 21650 cylindrical lithium-ion battery to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows: In a first aspect, the present invention provides a 21650 cylindrical lithium-ion battery, comprising a positive electrode and a negative electrode, wherein the porosity εp of the positive electrode is 20%~35% and the median pore size dp is 0.3μm~0.8μm; and the porosity εn of the negative electrode is 22%~45% and the median pore size dn is 0.5μm~1.5μm. εp, dp, εn, and dn satisfy: 2.5≤P1≤7.6, P1=(εn / εp)×(dn / dp)×(Hj / Dj); where Hj / Dj is the ratio of the core height to the diameter, and Hj / Dj is 3.09~3.14.

[0006] In an optional implementation, 3.0 ≤ P1 ≤ 7.6.

[0007] In an optional implementation, 5.0 ≤ P1 ≤ 7.6.

[0008] In an optional embodiment, the porosity εp of the positive electrode is 25%~30%, and the porosity εn of the negative electrode is 35%~40%.

[0009] In an optional embodiment, the median pore size dp of the positive electrode is 0.4 μm to 0.7 μm, and the median pore size dn of the negative electrode is 0.5 μm to 1.2 μm.

[0010] In an optional implementation, the median pore size dp of the positive electrode is 0.5 μm to 0.6 μm, and the median pore size dn of the negative electrode is 0.5 μm to 0.8 μm.

[0011] In an optional implementation, the tortuosity kp of the positive electrode sheet is 1.5 to 3.0, and the tortuosity kn of the negative electrode sheet is 2.0 to 4.0.

[0012] In an optional implementation, the tortuosity kp of the positive electrode sheet is 1.8 to 2.5, and the tortuosity kn of the negative electrode sheet is 2.5 to 3.5.

[0013] In an optional embodiment, the compaction density of the positive electrode sheet is 3.45 g / cm³. 3 ~3.55g / cm 3 The compaction density of the negative electrode sheet is 1.50 g / cm³. 3 ~1.60g / cm 3 .

[0014] In an optional implementation, the core height Hj is 62.1mm~63.5mm and the core diameter Dj is 19.9mm~20.5mm.

[0015] In an optional embodiment, the outer diameter D of the 21650 cylindrical lithium-ion battery casing is 20.8 mm to 21.5 mm, and the height H is 64.8 mm to 66.2 mm.

[0016] In an optional embodiment, the battery further includes a negative electrode current collector with a diameter of 17.3 mm to 20.1 mm and a thickness of 0.12 mm to 0.17 mm.

[0017] In an optional embodiment, the 21650 cylindrical lithium-ion battery also has at least one of the following features: Feature 1: The capacity retention rate of the 21650 cylindrical lithium-ion battery is ≥90% after 1000 cycles at 25℃ and 1C / 1C conditions; Feature 2: The DC internal resistance of the 21650 cylindrical lithium-ion battery at 25℃ and 50% SOC is ≤6.5mΩ; Feature 3: The electrolyte immersion time of the 21650 cylindrical lithium-ion battery electrode is ≤95s.

[0018] The beneficial effects of this invention include: This invention creatively limits the porosity εp of the positive electrode sheet of the 21650 cylindrical lithium-ion battery to 20%~35%, the median pore size dp of the positive electrode sheet to 0.3μm~0.8μm, the porosity εn of the negative electrode sheet to 22%~45%, and the median pore size dn of the negative electrode sheet to 0.5μm~1.5μm. At the same time, by using 2.5≤P1≤7.6, P1=(εn / εp)×(dn / dp)×(Hj / Dj), εp, εn, and dn are integrated with the height-to-diameter ratio of the core, so that the 21650 cylindrical lithium-ion battery that meets the above conditions can have a longer cycle life, lower internal resistance, and better wetting performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the 21650 cylindrical lithium-ion battery provided by the present invention.

[0021] Icons: 10-Shell; 20-Negative current collector; 30-Core. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] Some performance parameters in this article can be obtained using the following methods: Electrode porosity: determined by mercury intrusion porosimetry (MIP) or helium true density method, with mercury intrusion pressure ranging from 0.01 to 400 MPa and pore size ranging from 3 nm to 100 μm.

[0024] Median pore size of the electrode: The pore size value corresponding to the cumulative pore volume reaching 50% is read from the pore size distribution curve obtained by mercury intrusion porosimetry.

[0025] Pore ​​tortuosity: The electrochemical impedance spectroscopy (EIS) combined with symmetrical cell testing was used to calculate the tortuosity by the relationship between ionic resistance Rion, porosity ε, and electrolyte conductivity σe: k = ε × σe / (Rion × L), where L is the electrode thickness.

[0026] Compacted density: The compacted thickness and areal density of the coating on one side of the positive and negative electrode sheets are measured using vernier calipers. The compacted density is calculated as: compacted density = areal density / compacted coating thickness.

[0027] Height Hj and diameter Dj of core 30: Before battery assembly, the axial height and radial diameter of core 30 are measured with vernier calipers (accuracy 0.01mm), and each is measured 3 times and the average value is taken.

[0028] Outer diameter D and height H of housing 10: After the battery is packaged, the outer diameter and total height of the middle part of housing 10 are measured with a vernier caliper (accuracy 0.01mm), and the average value is taken for each measurement 3 times.

[0029] The following describes the 21650 cylindrical lithium-ion battery (e.g., provided by the present invention) Figure 1 (As shown) will be explained in detail.

[0030] The 21650 cylindrical lithium-ion battery provided by this invention includes a positive electrode and a negative electrode; the porosity εp of the positive electrode is 20%~35%, and the median pore size dp is 0.3μm~0.8μm; the porosity εn of the negative electrode is 22%~45%, and the median pore size dn is 0.5μm~1.5μm. εp, dp, εn, and dn satisfy: 2.5≤P1≤7.6, P1=(εn / εp)×(dn / dp)×(Hj / Dj); where Hj / Dj is the ratio of the height to the diameter of the core 30, and Hj / Dj is 3.09~3.14.

[0031] The εn / εp ratio represents the abundance ratio of ion transport channels between the negative and positive electrodes; a larger ratio indicates more ion-accommodating space on the negative electrode side. The dn / dp ratio represents the size ratio of ion transport channels between the negative and positive electrodes; a larger ratio indicates a higher proportion of large pores and lower ion transport resistance on the negative electrode side. Hj / Dj is the height-to-diameter ratio of the core 30, representing the radial and axial geometric proportions of the 21650 cell. Multiplying these three values ​​yields P1, which comprehensively reflects the degree of matching between the positive and negative electrode pore structures under the specific geometric constraints of the 21650 cell. If P1 is less than 2.5, the corresponding 21650 cylindrical lithium-ion battery will struggle to simultaneously achieve a long cycle life, low internal resistance, and excellent wetting performance.

[0032] This invention creatively limits the εp, dp, εn, and dn of the 21650 cylindrical lithium-ion battery to the above-mentioned ranges. At the same time, by using 2.5≤P1≤7.6 and P1=(εn / εp)×(dn / dp)×(Hj / Dj), εp, dp, εn, and dn are integrated with the height-to-diameter ratio of the core, so that the 21650 cylindrical lithium-ion battery that meets the above conditions can have a longer cycle life, lower internal resistance, and better wetting performance.

[0033] In some optional embodiments, the porosity εp of the positive electrode sheet can be 20%, 22%, 25%, 28%, 30%, 32%, or 35%, or other values ​​within the range of 20% to 35%. In some preferred embodiments, the porosity εp of the positive electrode sheet is 25% to 30%.

[0034] If the porosity εp of the positive electrode is less than 20%, it will easily lead to a longer immersion time, higher DCIR, and a lower cycle retention rate. If the porosity εp of the positive electrode is greater than 35%, it will easily lead to a loose electrode structure and damage to the electronic conductivity network, thus reducing the cycle retention rate of the battery.

[0035] The median pore size dp of the positive electrode can be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, or 0.8 μm, or other values ​​within the range of 0.3 μm to 0.8 μm. In some preferred embodiments, the median pore size dp of the positive electrode is 0.4 μm to 0.7 μm. In some even more preferred embodiments, the median pore size dp of the positive electrode is 0.5 μm to 0.6 μm.

[0036] If the median pore size dp of the positive electrode is less than 0.3 μm, it can easily lead to increased ion transport resistance; if the median pore size dp of the positive electrode is greater than 0.8 μm, it can easily lead to a loose electrode structure, damage to the electronic conductivity network, and reduced cycle retention rate of the battery.

[0037] The porosity εn of the negative electrode sheet can be 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, or 45%, or other values ​​within the range of 22% to 45%. In some preferred embodiments, the porosity εn of the negative electrode sheet is 35% to 40%.

[0038] If the porosity εn of the negative electrode is less than 22%, it will easily lead to a longer immersion time, higher DCIR, and lower cycle retention rate. If the porosity εn of the negative electrode is greater than 45%, it will easily lead to a loose electrode structure and damage to the electronic conductivity network, thus reducing the cycle retention rate of the battery.

[0039] The median pore size dn of the negative electrode can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, or 1.5 μm, or other values ​​within the range of 0.5 μm to 1.5 μm. In some preferred embodiments, the median pore size dn of the negative electrode is 0.5 μm to 1.2 μm. In some even preferred embodiments, the median pore size dn of the negative electrode is 0.5 μm to 0.8 μm.

[0040] If the median pore size dn of the negative electrode is less than 0.5 μm, it can easily lead to increased ion transport resistance; if the median pore size dn of the negative electrode is greater than 1.5 μm, it can easily lead to a loose electrode structure, damage to the electronic conductivity network, and reduced cycle retention rate of the battery.

[0041] Hj / Dj can be 3.09, 3.10, 3.11, 3.12, 3.13 or 3.14, or other values ​​in the range of 3.09 to 3.14.

[0042] In some preferred embodiments, 3.0 ≤ P1 ≤ 7.6. In some even more preferred embodiments, 5.0 ≤ P1 ≤ 7.6.

[0043] In some optional embodiments, the tortuosity kp of the positive electrode sheet can be 1.5 to 3.0, such as 1.5, 2.0, 2.5 or 3.0, or other values ​​within the range of 1.5 to 3.0. In some preferred embodiments, the tortuosity kp of the positive electrode sheet is 1.8 to 2.5.

[0044] The tortuosity kn of the negative electrode sheet can be 2.0~4.0, such as 2.0, 2.5, 3.0, 3.5 or 4.0, or other values ​​within the range of 2.0~4.0. In some preferred embodiments, the tortuosity kn of the negative electrode sheet is 2.5~3.5.

[0045] Pore ​​tortuosity affects electrolyte wetting efficiency and the smoothness of ion transport paths. If the pore tortuosity kp of the positive electrode is less than 1.5, the ion transport path is too straight, resulting in insufficient utilization of the pore volume inside the electrode, which is detrimental to sufficient electrolyte wetting and ion diffusion within the electrode. If the pore tortuosity kp of the positive electrode is greater than 3.0, the ion transport path is excessively tortuous, significantly lengthening the actual diffusion distance of lithium ions, increasing concentration polarization, and negatively impacting high-rate performance. If the pore tortuosity kn of the negative electrode is less than 2.0, it is detrimental to the electrode pores' ability to fully accommodate solvated lithium ions. If the pore tortuosity kn of the negative electrode is greater than 4.0, the excessively tortuous pore structure will significantly increase liquid-phase ion transport resistance, increase polarization, and negatively impact cycle stability and wetting uniformity.

[0046] In some alternative embodiments, the compaction density of the positive electrode sheet can be 3.45 g / cm³. 3 ~3.55g / cm 3 For example, 3.45 g / cm 3 3.5g / cm 3 Or 3.55g / cm 3 The value can also be 3.45 g / cm³. 3 ~3.55g / cm 3 Other values ​​within the range.

[0047] The compaction density of the negative electrode sheet can be 1.50 g / cm³. 3 ~1.60g / cm 3 For example, 1.5g / cm 3 1.55g / cm 3 Or 1.6g / cm 3 etc., can also be 1.50 g / cm 3 ~1.60g / cm 3 Other values ​​within the range.

[0048] The compaction density of the electrode affects the contact tightness between active material particles in the electrode coating and the electrolyte containment space. If the compaction density of the positive electrode is less than 3.45 g / cm³... 3 If the coating is too porous, poor electronic contact between particles hinders the construction of the electronic conductivity network and the improvement of volumetric energy density; if the compaction density of the positive electrode sheet is greater than 3.55 g / cm³, it will further impede the overall structure. 3 An excessively dense coating reduces porosity, hinders electrolyte wetting, and impedes ion transport, negatively impacting rate performance and cycle life. If the compaction density of the negative electrode sheet is less than 1.50 g / cm³... 3 This is detrimental to the contact between negative electrode active material particles and the volumetric energy density; if the compaction density of the negative electrode sheet is greater than 1.60 g / cm³, it will hinder the contact between the particles and the volumetric energy density. 3 This can lead to excessively low negative electrode porosity, insufficient expansion buffer space for silicon-carbon negative electrodes, and poor electrolyte wetting, which is detrimental to cycle stability and lithium plating control.

[0049] In some alternative implementations, the height Hj of the core 30 can be 62.1mm to 63.5mm, such as 62.1mm, 62.2mm, 62.3mm, 62.4mm, 62.5mm, 63mm or 63.5mm, or other values ​​within the range of 62.1mm to 63.5mm.

[0050] The diameter Dj of the core 30 can be 19.9mm to 20.5mm, such as 19.9mm, 20.0mm, 20.1mm or 20.5mm, or other values ​​within the range of 19.9mm to 20.5mm.

[0051] In some alternative embodiments, the outer diameter D of the casing 10 of the 21650 cylindrical lithium-ion battery can be 20.8mm to 21.5mm, such as 20.8mm, 20.9mm, 21mm, 21.1mm, 21.2mm, 21.3mm, 21.4mm or 21.5mm, or other values ​​within the range of 20.8mm to 21.5mm.

[0052] The height H of the housing 10 can be 64.8mm to 66.2mm, such as 64.8mm, 64.9mm, 65mm, 65.1mm, 65.2mm, 65.5mm, 65.8mm, 66mm or 66.2mm, or other values ​​within the range of 64.8mm to 66.2mm.

[0053] In some alternative embodiments, the battery also includes a negative electrode current collector 20, the diameter of which can be 17.3mm to 20.1mm, such as 17.3mm, 17.5mm, 18mm, 18.5mm, 19mm, 19.5mm, 20mm or 20.1mm, or other values ​​within the range of 17.3mm to 20.1mm.

[0054] The thickness of the negative electrode current collector 20 can be 0.12mm to 0.17mm, such as 0.12mm, 0.13mm, 0.14mm, 0.15mm, 0.16mm or 0.17mm, or other values ​​within the range of 0.12mm to 0.17mm.

[0055] The structural parameters of the negative electrode current collector 20 are related to the current collection efficiency, and its relationship with the hole structure of the electrode affects the battery's internal resistance and power performance. By controlling the diameter and thickness of the negative electrode current collector 20 within the aforementioned range, this invention can effectively reduce the battery's internal resistance and improve its power performance by cooperating with the specific hole structure of the electrode in this application.

[0056] In some optional implementations, the capacity retention rate of the 21650 cylindrical lithium-ion battery after 1000 cycles at 25°C and 1C / 1C is ≥90%, such as 90.1%~93.5%.

[0057] In some alternative implementations, the DC internal resistance of the 21650 cylindrical lithium-ion battery at 25°C and 50% SOC is ≤6.5mΩ, such as 5.0mΩ~6.5mΩ.

[0058] In some optional embodiments, the electrolyte immersion time of the 21650 cylindrical lithium-ion battery electrode is ≤95s, such as 68s~95s.

[0059] It should be noted that other structures and preparation methods of the 21650 cylindrical lithium-ion battery not further elaborated in this invention can be found in the relevant prior art, and will not be described in detail here.

[0060] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0061] Example 1 This embodiment provides a 21650 cylindrical lithium-ion battery, the preparation method of which includes: S1: Prepare the positive electrode sheet.

[0062] LiNi 0.88 Co 0.05 Mn 0.05 Al 0.02 O2, conductive carbon black SuperP, carbon nanotubes (CNTs), and PVDF were dispersed in NMP at a mass ratio of 96.0:1.5:1.0:1.5 and coated onto an aluminum foil with a thickness of 12 μm. This resulted in a positive electrode material region width of 55 mm, a positive electrode empty foil region width of 4 mm, and a positive electrode sheet areal density of 24 mg / cm³. 2 The compacted density is 3.50 g / cm³. 3 The positive electrode has a porosity of εp = 28%, a median pore diameter of dp = 0.5 μm, and a pore tortuosity of kp = 2.2.

[0063] S2: Prepare the negative electrode sheet.

[0064] Artificial graphite (Dv50=11μm) and silicon-carbon composite material (silicon mass fraction 15%) were mixed at a mass ratio of 82:18. This mixture was then combined with conductive carbon black, CMC, and SBR at a mass ratio of 95.0:2.0:1.5:1.5 to form a slurry. This slurry was then coated onto an 8μm thick copper foil, resulting in a negative electrode material area width of 56mm, a negative electrode empty foil area width of 3.5mm, and a negative electrode sheet areal density of 14mg / cm³. 2 The compacted density is 1.55 g / cm³. 3 The negative electrode has a porosity of εn = 40%, a median pore diameter of dn = 0.8 μm, and a pore tortuosity of kn = 3.0.

[0065] S3: Negative current collector 20. A negative current collector 20 with a diameter of 18.5 mm and a thickness of 0.15 mm is used.

[0066] S4: Core 30 and assembly.

[0067] A full-ear core 30 structure is adopted, in which the positive electrode, negative electrode, and ceramic-coated separator are wound into an electrode assembly. The height Hj of the core 30 is measured to be 62.3 mm, and the diameter Dj of the core 30 is 20.0 mm. The core 30 is placed into a cylindrical shell 10 with an outer diameter D of 21.0 mm and a height H of 65.0 mm. After electrolyte injection, it is encapsulated, formed, and capacity tested.

[0068] The electrolyte is a 1.2 mol / L LiPF6 EC / EMC / DEC mixed solution (mass ratio 3:4:3).

[0069] Example 2 The difference between this embodiment and Embodiment 1 is that the porosity of the positive electrode sheet εp=25%, the porosity of the negative electrode sheet εn=35%, the median pore size of the negative electrode dn=0.6μm, and the median pore size of the positive electrode dp=0.5μm.

[0070] Example 3 The difference between this embodiment and Embodiment 1 is that the porosity of the positive electrode sheet εp=30%, the porosity of the negative electrode sheet εn=38%, the median pore size of the negative electrode dn=0.5μm, and the median pore size of the positive electrode dp=0.6μm.

[0071] Example 4 The difference between this embodiment and Embodiment 1 is that: εp is 20%, dp is 0.3μm, εn is 22%, and dn is 0.5μm; Example 5 The difference between this embodiment and Embodiment 1 is that εp is 35%, dp is 0.8μm, εn is 45%, and dn is 1.5μm.

[0072] Example 6 The difference between this embodiment and Embodiment 1 is that kp is 1.5, kn is 2.0, and the compaction density of the positive electrode sheet is 3.45 g / cm³. 3 The compaction density of the negative electrode sheet is 1.50 g / cm³. 3 The height Hj of the core 30 is 62.1 mm, and the diameter Dj of the core 30 is 19.9 mm; the outer diameter D of the shell 10 is 20.8 mm, and the height H is 64.8 mm; the diameter of the negative electrode current collector 20 is 17.3 mm, and the thickness is 0.12 mm.

[0073] Example 7 The difference between this embodiment and Embodiment 1 is that kp is 3.0, kn is 4.0, and the compaction density of the positive electrode sheet is 3.55 g / cm³. 3 The compaction density of the negative electrode sheet is 1.60 g / cm³. 3 The height Hj of the core 30 is 62.5 mm, and the diameter Dj of the core 30 is 20.1 mm; the outer diameter D of the shell 10 is 21.2 mm, and the height H is 65.2 mm; the diameter of the negative electrode current collector 20 is 20.1 mm, and the thickness is 0.17 mm.

[0074] Comparative Example 1 The difference between this comparative example and Example 1 is that the porosity of the positive electrode sheet εp=18%, the porosity of the negative electrode sheet εn=20%, the median pore size of the negative electrode dn=0.3μm, and the median pore size of the positive electrode dp=0.3μm.

[0075] Comparative Example 2 The difference between this comparative example and Example 1 is that the porosity of the positive electrode sheet εp=38%, the porosity of the negative electrode sheet εn=50%, the median pore size of the negative electrode dn=2.0μm, and the median pore size of the positive electrode dp=1.0μm.

[0076] Comparative Example 3 The difference between this comparative example and Example 1 is that εp is 18%.

[0077] Comparative Example 4 The difference between this comparative example and Example 1 is that εp is 38%.

[0078] Comparative Example 5 The difference between this comparative example and Example 1 is that εn is 20%.

[0079] Comparative Example 6 The difference between this comparative example and Example 1 is that εn is 48%.

[0080] Comparative Example 7 The difference between this comparative example and Example 1 is that dp is 0.1 μm.

[0081] Comparative Example 8 The difference between this comparative example and Example 1 is that dp is 1 μm.

[0082] Comparative Example 9 The difference between this comparative example and Example 1 is that dn is 0.2 μm.

[0083] Comparative Example 10 The difference between this comparative example and Example 1 is that dn is 1.8 μm.

[0084] Test case The 21650 cylindrical lithium-ion batteries obtained in Examples 1-7 and Comparative Examples 1-10 were subjected to performance tests. The test methods are as follows, and the test results are shown in Table 1.

[0085] Capacity retention rate after 1C / 1C cycles of 1000: At 25℃, charge at 1C constant current and constant voltage to full charge, then discharge at 1C constant current to cutoff voltage, cycle 1000 times, and calculate the ratio of discharge capacity in the 1000th cycle to discharge capacity in the first cycle.

[0086] DC internal resistance DCIR: At 25℃ and 50% SOC, the voltage drop is recorded after 1C constant current pulse discharge for 10s. DCIR = ΔV / ΔI.

[0087] Electrolyte wetting time: Add electrolyte to the electrode and record the time required for the electrolyte to completely wet the surface of the electrode.

[0088] Table 1 Test Results

[0089] As can be seen from Table 1, all of Examples 1 to 7 satisfy P1≥2.5 under the premise of meeting the constraints of each individual parameter (among which Examples 1, 2, 4 to 7 further satisfy P1≥5.0 or even ≥7.0). The corresponding 21650 cylindrical lithium-ion batteries have a capacity retention rate ≥90%, DCIR ≤6.5mΩ, and wetting time ≤95s after 1000 cycles, which are excellent in terms of cycle life, low internal resistance and wetting performance.

[0090] Although Comparative Example 1 had P1≥2.5, its εp was less than 20% and εn was less than 22%, which led to an extended soaking time of 135s, an increase in DCIR to 8.5mΩ, and a decrease in cycle retention rate to 86.5%.

[0091] Although Comparative Example 2 has a high P1 of 8.20, its εp is greater than 35%, dp is greater than 0.8 μm, εn is greater than 45%, and dn is greater than 1.5 μm. The excessive porosity and pore size lead to a loose electrode structure and damage to the electronic conductivity network, resulting in a cycle retention rate of only 82.5%.

[0092] In Comparative Examples 3-10, each comparative example deviated from the scope of this application only by one parameter among εp, εn, dp, and dn; the remaining parameters were the same as in Example 1 and met the relevant requirements of P1. Comparative Examples 3 (εp=18%) and 5 (εn=20%) had excessively low porosity, resulting in prolonged wetting times of 125s and 122s, increased DCIR to 7.8mΩ and 7.5mΩ, and decreased capacity retention to 83.0% and 81.5%, respectively. Comparative Examples 4 (εp=38%) and 6 (εn=48%) had excessively high porosity, resulting in loose electrode structures and damaged electronic conductivity networks, further reducing cycle retention to 83.2% and 82.5%. Example 7 (dp=0.1μm) and Comparative Example 9 (dn=0.2μm) suffered from increased ion transport resistance, prolonged wetting time to 155s and 160s, increased DCIR to 9.0mΩ and 9.2mΩ, and decreased capacity retention to 80.2% and 82.8% due to excessively small pore size. Comparative Example 8 (dp=1.0μm) and Comparative Example 10 (dn=1.8μm) suffered from loose electrode structure due to excessively large pore size, and their cycle retention dropped to 81.3% and 81.5%.

[0093] In summary, only by integrating and limiting the positive electrode porosity, negative electrode porosity, positive electrode median pore size, negative electrode median pore size, and the height-to-diameter ratio of the core 30 through P1, and ensuring that each individual parameter falls within a specific range, can a high-performance 21650 cylindrical lithium-ion battery with long cycle life, low internal resistance, and excellent wetting performance be obtained.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A 21650 cylindrical lithium-ion battery, characterized in that, It includes a positive electrode and a negative electrode. The positive electrode has a porosity εp of 20% to 35% and a median pore size dp of 0.3 μm to 0.8 μm. The negative electrode has a porosity εn of 22% to 45% and a median pore size dn of 0.5 μm to 1.5 μm. εp, dp, εn, and dn satisfy: 2.5≤P1≤7.6, P1=(εn / εp)×(dn / dp)×(Hj / Dj); where Hj / Dj is the ratio of the core height to the diameter, and Hj / Dj is 3.09~3.

14.

2. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, 3.0≤P1≤7.6； Preferably, 5.0 ≤ P1 ≤ 7.

6.

3. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The porosity εp of the positive electrode is 25%~30%, and the porosity εn of the negative electrode is 35%~40%.

4. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The median pore size dp of the positive electrode is 0.4 μm to 0.7 μm, and the median pore size dn of the negative electrode is 0.5 μm to 1.2 μm. Preferably, the median pore size dp of the positive electrode is 0.5μm~0.6μm, and the median pore size dn of the negative electrode is 0.5μm~0.8μm.

5. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The tortuosity kp of the positive electrode sheet is 1.5~3.0, and the tortuosity kn of the negative electrode sheet is 2.0~4.

0. Preferably, the tortuosity kp of the positive electrode sheet is 1.8~2.5, and the tortuosity kn of the negative electrode sheet is 2.5~3.

5.

6. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The compaction density of the positive electrode sheet is 3.45 g / cm³. 3 ~3.55g / cm 3 The compaction density of the negative electrode sheet is 1.50 g / cm³. 3 ~1.60g / cm 3 .

7. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The height Hj of the core is 62.1mm~63.5mm, and the diameter Dj of the core is 19.9mm~20.5mm.

8. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The outer diameter D of the casing of the 21650 cylindrical lithium-ion battery is 20.8mm~21.5mm, and the height H is 64.8mm~66.2mm.

9. The 21650 cylindrical lithium-ion battery according to claim 1, characterized in that, The battery also includes a negative electrode current collector, which has a diameter of 17.3mm to 20.1mm and a thickness of 0.12mm to 0.17mm.

10. The 21650 cylindrical lithium-ion battery according to any one of claims 1 to 9, characterized in that, The 21650 cylindrical lithium-ion battery also has at least one of the following characteristics: Feature 1: The 21650 cylindrical lithium-ion battery retains ≥90% of its capacity after 1000 cycles at 25℃ and 1C / 1C conditions; Feature 2: The DC internal resistance of the 21650 cylindrical lithium-ion battery at 25℃ and 50% SOC is ≤6.5mΩ; Feature 3: The electrolyte immersion time of the electrodes of the 21650 cylindrical lithium-ion battery is ≤95s.

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