21650 full tab cylindrical lithium-ion battery cell and electric device

Abstract

The application provides a 21650 full-tab cylindrical lithium ion battery cell and an electric device, and relates to the technical field of lithium ion batteries. The cell defines a negative electrode hole impedance-compaction coupling coefficient K1 and limits the numerical range thereof, so that the negative electrode can maintain high capacity bearing capacity under a short high structure and can guarantee the connectivity of ion transmission paths under low temperature conditions. Meanwhile, the negative electrode unit area electrolyte retention amount η is limited, so that the electrolyte supply capacity at the interface of the negative electrode active material layer is stably guaranteed, thereby supporting the continuous electrochemical reaction in the low-temperature large-current discharge process. The 21650 full-tab cylindrical lithium ion battery cell of the application cooperatively limits K1 and η, so that the cell can simultaneously meet the capacity target and the low-temperature cold start output requirement under the constraint of the short high size, and a reproducible and verifiable matching relationship is formed.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a 21650 all-tab cylindrical lithium-ion cell and its power application device. Background Technology

[0002] 21mm-class cylindrical lithium-ion cells (such as 21700) typically need to meet multiple performance requirements, including capacity, rate discharge, low-temperature start-up, and cycle safety, within a limited casing space. For a conventional 21700 cell with a height of approximately 70mm, its core axial space, electrode unfolding length, electrolyte filling space, and end assembly allowance are relatively ample, providing sufficient coordination margin between structure and performance.

[0003] When the cell height is reduced to the 65mm level (i.e., the 21650 short-height platform), while the outer diameter, cap, roller groove, and part of the winding platform are still compatible with the existing 21700 production line as much as possible, the cell must maintain a capacity target of approximately 5Ah within a shorter axial space. Under this constraint, the contradiction between negative electrode capacity capacity, negative electrode channel connectivity, liquid retention capacity, and ion transport capacity under low-temperature conditions is significantly aggravated.

[0004] In systems employing high-nickel cathodes and graphite / silicon-carbon composite anodes, while silicon-carbon materials can enhance the anode's capacity carrying capacity, they are prone to increased polarization, insufficient electrolyte supply in pores, and the risk of localized lithium plating under high loading density and low temperature conditions (e.g., -20°C or -40°C). Increasing the anode compaction density alone, while beneficial to volumetric capacity, may reduce pore connectivity and liquid retention capacity, leading to a sharp increase in low-temperature pulsed DC resistance (DCR). Decreasing compaction density alone while increasing porosity may sacrifice areal capacity, making it difficult to achieve the 5Ah capacity target. Relying solely on local surface grooving, separator orientation adjustment, or central support structures makes it difficult to stably characterize the ion transport state along the thickness and in-plane directions of the entire anode, and also hinders reverse verification and consistency validation from finished cells.

[0005] In existing technologies, some solutions focus on increasing the specific capacity of the positive and negative electrode materials or extending the electrode unfolding length; some focus on increasing the total electrolyte injection volume or improving the end wetting uniformity; and some focus on modeling the relationship between cell volume, surface area, and rate-dependent temperature rise. However, none of the above solutions systematically address the coupling problem between the negative electrode hole impedance, negative electrode compaction density, negative electrode electrolyte retention per unit area, and low-temperature cold start capability in 21650 short-height full-tab cylindrical cells. Traditional solutions improve electrolyte retention by simply increasing the injection volume, but the short-height structure results in high axial penetration resistance, and uneven electrolyte distribution leads to localized dry areas, causing a sudden increase in DCR and lithium plating even at low temperatures.

[0006] Therefore, it is both necessary and urgent to research and develop a 21650 all-tab cylindrical lithium-ion cell that can be reverse-tested from finished cells and can reliably support high-current cold start output at -40℃.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] Parameter definitions in this invention: H1 represents the total height of the cylindrical shell, in mm.

[0009] D represents the outer diameter of the cylindrical shell, in mm.

[0010] C 0.2 This indicates the discharge capacity of the battery cell under discharge conditions of 25℃ and 0.2C, and the unit is Ah.

[0011] Mn represents the surface density of the negative electrode active material layer, in mg / cm².

[0012] P1 represents the negative electrode compaction density, with units of g / cm³.

[0013] tn represents the thickness of the negative electrode active material layer on one side, in μm.

[0014] e represents the porosity of the negative electrode active material layer.

[0015] R represents the equivalent pore impedance of the negative electrode active material layer. R is obtained by fitting the EIS of the negative electrode symmetrically blocked electrode, and the unit is Ω•cm².

[0016] K1 represents the negative electrode hole resistance-compact coupling coefficient, K1=R×P1.

[0017] K2 represents the unit capacity orifice resistance of the negative electrode, K2=R / C 0.2 .

[0018] η represents the electrolyte content per unit area of ​​the negative electrode, η=M1 / An, where M1 is the electrolyte content in the active material layer of the negative electrode; M1 represents the electrolyte content in the negative electrode active material layer, expressed in mg.

[0019] An represents the effective area of ​​both sides of the negative electrode active material layer, in cm². 2 .

[0020] DCR 25 This indicates the pulsed DC internal resistance at 50% SOC at 25℃.

[0021] DCR -20 This indicates the pulsed DC internal resistance at -20℃ with 50% SOC.

[0022] DCR -40This indicates the pulsed DC internal resistance at -40℃ with 50% SOC.

[0023] Vmin represents the lowest voltage during the low-temperature cold start test.

[0024] 21650 indicates a 21650 short-high platform (cell height approximately 65mm, outer diameter approximately 21mm) all-tab cylindrical lithium-ion cell.

[0025] The primary objective of this invention is to provide a 21650 all-tab cylindrical lithium-ion cell, which achieves a balance between high capacity carrying capacity and low-temperature high-current output capability under the constraints of the 21650 short-height structure by synergistically controlling K1 and η.

[0026] A third objective of this invention is to provide an electrical device.

[0027] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention provides a 21650 all-tab cylindrical lithium-ion battery cell, comprising a cylindrical shell, a core and an electrolyte, wherein the core is formed by winding a positive electrode sheet, a separator and a negative electrode sheet, and the ends of the positive electrode sheet and the negative electrode sheet are flattened to form an all-tab end face; The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes graphite material and silicon carbon material. With the equivalent pore impedance of the negative electrode active material layer as R and the negative electrode compaction density as P1, the negative electrode pore impedance-compaction coupling coefficient K1 is defined as R × P1, and K1 is 0.85~2.15. This coupling coefficient indirectly characterizes the nonlinear superposition effect of the increase in pore tortuosity caused by the increase in compaction density and the ion transport resistance.

[0028] Given that the negative electrode active material layer has a double-sided effective area An and the electrolyte content in the negative electrode active material layer is M1, the electrolyte content per unit area of ​​the negative electrode is defined as η = M1 / An, where η is 2.20 mg / cm² to 3.60 mg / cm². Furthermore, the battery cell meets the following requirements: at 50% SOC, the ratio of the pulsed DC internal resistance at -20℃ to the pulsed DC internal resistance at 25℃ is ≤7.8; and the trough voltage in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.80V.

[0029] Furthermore, the total height H1 of the cylindrical housing of the battery cell is 63.5 mm to 66.5 mm, and the outer diameter D is 20.6 mm to 21.5 mm; And / or, the total height H1 of the cylindrical housing of the battery cell is 64.7 mm to 65.5 mm, the outer diameter D is 20.8 mm to 21.2 mm, and H1 / D is 3.06 to 3.14; And / or, the discharge capacity of the battery cell under the conditions of 25°C and 0.2C discharge is 4.9 Ah to 5.2 Ah, preferably 4.98 Ah to 5.05 Ah.

[0030] Furthermore, the single-sided areal density Mn of the negative electrode active material layer is 5.3 mg / cm² to 6.2 mg / cm², preferably 5.50 mg / cm² to 6.05 mg / cm²; The compaction density P1 of the negative electrode is 1.50 g / cm³ to 1.65 g / cm³, preferably 1.54 g / cm³ to 1.62 g / cm³; The thickness tn of the negative electrode active material layer on one side is 38μm~44μm, preferably 39.5μm~42.5μm; The single-cell porosity e of the negative electrode active material layer is 28%~38%, preferably 31%~36%.

[0031] The equivalent pore impedance R of the negative electrode active material layer is 0.55Ω•cm² to 1.35Ω•cm², preferably 0.70Ω•cm² to 1.05Ω•cm².

[0032] Furthermore, R is related to the discharge capacity C. 0.2 The ratio defines the negative electrode unit capacity orifice resistance K2; K2=R / C 0.2 K2 is 0.11Ω•cm² / Ah to 0.27Ω•cm² / Ah, preferably 0.14Ω•cm² / Ah to 0.21Ω•cm² / Ah.

[0033] Furthermore, the negative electrode hole impedance-compaction coupling coefficient K1 is 1.10~1.70; The electrolyte retention η per unit area of ​​the negative electrode is 2.55 mg / cm² to 3.25 mg / cm².

[0034] Furthermore, the contribution ratio Rs of silicon-carbon material in the negative electrode active material layer to the reversible capacity of the negative electrode is 40%~50%, preferably 43%~48%.

[0035] And / or, the ratio of the negative electrode capacity of the negative electrode to the positive electrode capacity of the positive electrode, N / P, is 1.02~1.10, preferably 1.035~1.075.

[0036] Furthermore, the cell has a DCR of 50% at 50% SOC. -20 / DCR 25The value is 5.5~7.8, preferably 6.0~7.2; And / or, the cell's -40°C pulsed DC internal resistance DCR -40 With DCR 25 The ratio is ≤18.0.

[0037] And / or, the trough voltage Vmin of the battery cell in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.88V; And / or, the trough voltage in the cold start test at -40℃, 100% SOC, and 20A discharge is ≥1.60V.

[0038] Preferably, the testing method for the 21650 all-tab cylindrical lithium-ion cell of the present invention includes the following steps: Measure the total height, outer diameter, and discharge capacity of the battery cell under test; Disassemble the battery cell under an inert atmosphere to obtain the negative electrode plate; Test the compaction density P1 and equivalent pore resistance R of the negative electrode sheet, and calculate K1 = R × P1; Test the electrolyte retention M1 and the effective double-sided area An of the negative electrode sheet, and calculate η = M1 / An; The pulse DC internal resistance ratio of the cell under test was tested at -20℃ and 25℃, and the cold start trough voltage was tested at -40℃. The measured K1, η, impedance ratio, and trough voltage are compared with the above-described limits of the present invention.

[0039] Furthermore, the equivalent aperture impedance R is obtained by AC impedance spectroscopy testing of a negative electrode symmetrical blocking electrode, with a test frequency range of 100kHz~10mHz. The electrolyte content M1 is obtained by measuring the difference between the wet and dry mass of the negative electrode sample, and the time interval from disassembly to wet mass weighing is ≤120s.

[0040] Furthermore, the cell's -40℃ pulsed DC internal resistance (DCR) -40 With DCR 25 The ratio is ≤18.0.

[0041] Furthermore, the trough voltage Vmin of the battery cell in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.88V; and / or, the trough voltage in the cold start test at -40℃, 100% SOC, and 20A discharge is ≥1.60V.

[0042] The present invention provides an electrical device comprising a plurality of the aforementioned 21650 omni-tab cylindrical lithium-ion cells.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a 21650 all-tab cylindrical lithium-ion cell. By defining and limiting the negative electrode pore impedance-compaction coupling coefficient K1, the cell maintains high capacity carrying capacity and ensures ion transport pathway connectivity under low-temperature conditions within a short-height structure. Simultaneously, by limiting the electrolyte content η per unit area of ​​the negative electrode, the electrolyte supply at the interface of the negative electrode active material layer is stably guaranteed, thus supporting continuous electrochemical reactions during low-temperature, high-current discharge. This 21650 all-tab cylindrical lithium-ion cell, by synergistically limiting K1 and η, and using the low-temperature pulse DC internal resistance ratio and cold-start trough voltage as performance verification indicators, enables the cell to simultaneously meet capacity targets and low-temperature cold-start output requirements under short-height size constraints, forming a reproducible and verifiable matching relationship.

[0044] The present invention also provides an electrical device comprising a plurality of the aforementioned 21650 all-tab cylindrical lithium-ion cells. Based on the capacity consistency and low-temperature output stability of the cells in the present invention under a short-height structure, the module of the present invention can maintain a coordinated response in overall electrical performance under wide temperature range operating conditions and dynamic power demands. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] According to one aspect of the present invention, a 21650 all-tab cylindrical lithium-ion battery cell includes a cylindrical shell, a core and an electrolyte, wherein the core is wound together by a positive electrode, a separator and a negative electrode, and the ends of the positive electrode and the negative electrode are flattened to form all-tab end faces. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes graphite material and silicon carbon material. With the equivalent pore impedance of the negative electrode active material layer as R and the negative electrode compaction density as P1, the negative electrode pore impedance-compaction coupling coefficient K1 is defined as R×P1, and K1 is 0.85~2.15. Given that the negative electrode active material layer has a double-sided effective area An and the electrolyte content in the negative electrode active material layer is M1, the electrolyte content per unit area of ​​the negative electrode is defined as η = M1 / An, where η is 2.20 mg / cm² to 3.60 mg / cm². Furthermore, the battery cell meets the following requirements: at 50% SOC, the ratio of the pulsed DC internal resistance at -20℃ to the pulsed DC internal resistance at 25℃ is ≤7.8; and the trough voltage in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.80V.

[0047] This invention provides a 21650 all-tab cylindrical lithium-ion cell. By defining and limiting the negative electrode pore impedance-compaction coupling coefficient K1, the cell maintains high capacity carrying capacity and ensures ion transport pathway connectivity under low-temperature conditions within a short-height structure. Simultaneously, by limiting the electrolyte content η per unit area of ​​the negative electrode, the electrolyte supply at the interface of the negative electrode active material layer is stably guaranteed, thus supporting continuous electrochemical reactions during low-temperature, high-current discharge. This 21650 all-tab cylindrical lithium-ion cell, by synergistically limiting K1 and η, and using the low-temperature pulse DC internal resistance ratio and cold-start trough voltage as performance verification indicators, enables the cell to simultaneously meet capacity targets and low-temperature cold-start output requirements under short-height size constraints, forming a reproducible and verifiable matching relationship.

[0048] In a preferred embodiment of the present invention, the total height H1 of the cylindrical housing of the battery cell is 63.5mm~66.5mm, and the outer diameter D is 20.6mm~21.5mm; In a preferred embodiment, the total height H1 of the cylindrical housing of the battery cell is 63.5mm to 66.5mm, and the outer diameter D is 20.6mm to 21.5mm. This size range is compatible with the 21650 short-height specification, and while maintaining compatibility with key components of the existing 21700 production line, it provides a basis for the coordinated control of the negative electrode channel structure and electrolyte interface supply.

[0049] Preferably, the total height H1 of the cylindrical housing of the battery cell is 64.7 mm to 65.5 mm, the outer diameter D is 20.8 mm to 21.2 mm, and the H1 / D ratio is 3.06 to 3.14. In a preferred embodiment of the present invention, the discharge capacity of the battery cell under the conditions of 25°C and 0.2C discharge is 4.9 Ah to 5.2 Ah, preferably 4.98 Ah to 5.05 Ah.

[0050] As a preferred embodiment, the aforementioned discharge capacity range of the battery cell ensures that the battery cell still has an energy output capability comparable to that of the 21700 battery cell under the constraints of the 21650 short-height structure, thereby maintaining the system-level energy density while supporting the synergistic optimization of the negative electrode hole impedance-compact coupling coefficient K1 and the electrolyte retention η per unit area.

[0051] In a preferred embodiment of the present invention, the single-sided areal density Mn of the negative electrode active material layer is 5.3 mg / cm² to 6.2 mg / cm², preferably 5.50 mg / cm² to 6.05 mg / cm²; The compaction density P1 of the negative electrode is 1.50 g / cm³ to 1.65 g / cm³, preferably 1.54 g / cm³ to 1.62 g / cm³; The thickness tn of the negative electrode active material layer on one side is 38μm~44μm, preferably 39.5μm~42.5μm; The single-cell porosity e of the negative electrode active material layer is 28%~38%, preferably 31%~36%.

[0052] The equivalent pore impedance R of the negative electrode active material layer is 0.55Ω•cm² to 1.35Ω•cm², preferably 0.70Ω•cm² to 1.05Ω•cm².

[0053] In a preferred embodiment, the synergistic effect of the parameters of the above-mentioned negative electrode active material layer ensures the high capacity carrying capacity of the negative electrode while maintaining the connectivity of the pore structure and the effective distribution of electrolyte in the active layer, providing a repeatable process basis for the stable control of K1 and η.

[0054] In a preferred embodiment of the present invention, R is related to the discharge capacity C. 0.2 The ratio defines the negative electrode unit capacity orifice resistance K2; K2=R / C 0.2 K2 is 0.11Ω•cm² / Ah to 0.27Ω•cm² / Ah, preferably 0.14Ω•cm² / Ah to 0.21Ω•cm² / Ah.

[0055] In a preferred embodiment, the present invention defines the negative electrode unit capacity orifice impedance K2 as the ratio of the negative electrode equivalent orifice impedance R to the discharge capacity C0.2. This parameter correlates the orifice impedance characteristics with the actual capacity level of the cell, ensuring that the coordinated regulation of K1 and η maintains a consistent evaluation benchmark under different capacity fluctuation conditions.

[0056] In a preferred embodiment of the present invention, the negative electrode hole impedance-compaction coupling coefficient K1 is 1.10~1.70; In a preferred embodiment of the present invention, the electrolyte content η per unit area of ​​the negative electrode is 2.55 mg / cm² to 3.25 mg / cm².

[0057] In a preferred embodiment of the present invention, the contribution ratio Rs of silicon-carbon material in the negative electrode active material layer to the reversible capacity of the negative electrode is 40%~50%, preferably 43%~48%.

[0058] And / or, the ratio of the negative electrode capacity of the negative electrode to the positive electrode capacity of the positive electrode, N / P, is 1.02~1.10, preferably 1.035~1.075.

[0059] In a preferred embodiment of the present invention, the cell has a DCR of 50% SOC. -20 / DCR 25 The value is 5.5~7.8, preferably 6.0~7.2; And / or, the cell's -40°C pulsed DC internal resistance (DCR) -40 With DCR 25 The ratio is ≤18.0.

[0060] And / or, the trough voltage Vmin of the battery cell in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.88V; And / or, the trough voltage in the cold start test at -40℃, 100% SOC, and 20A discharge is ≥1.60V.

[0061] As a preferred embodiment, the battery cell of the present invention, at 50% SOC, exhibits a pulse DC internal resistance ratio between -20℃ and 25℃ that falls within a specific range. Furthermore, it defines an upper limit for the pulse DC internal resistance ratio between -40℃ and 25℃, and a lower limit for the cold start trough voltage under different discharge currents at -40℃. These performance indicators collectively constitute a multi-dimensional verification of the low-temperature output capability of the short-capacity battery cell, ensuring that the synergistic control effect of K1 and η is consistently reflected across a wide temperature range and under various current conditions, thereby enhancing the reliability and adaptability of the technical solution in practical applications.

[0062] Preferably, the testing method for the above-mentioned 21650 all-tab cylindrical lithium-ion cell of the present invention includes the following steps: Measure the total height, outer diameter, and discharge capacity of the battery cell under test; disassemble the battery cell under an inert atmosphere to obtain the negative electrode plate; Test the compaction density P1 and equivalent pore resistance R of the negative electrode sheet, and calculate K1 = R × P1; Test the electrolyte retention M1 and the effective double-sided area An of the negative electrode sheet, and calculate η = M1 / An; The pulse DC internal resistance ratio of the cell under test was tested at -20℃ and 25℃, and the cold start trough voltage was tested at -40℃. The measured K1, η, impedance ratio, and trough voltage are compared with the ranges defined above in this application.

[0063] In a preferred embodiment of the present invention, the equivalent aperture impedance R is obtained by AC impedance spectroscopy testing of a negative symmetrical blocking electrode, with a test frequency range of 100kHz to 10mHz. In a preferred embodiment of the present invention, the electrolyte content M1 is obtained by measuring the difference between the wet and dry mass of the negative electrode sample, and the time interval from disassembly to wet mass weighing is ≤120s.

[0064] In a preferred embodiment of the present invention, the trough voltage Vmin of the battery cell in the cold start test at -40°C, 100% SOC, and 15A discharge is ≥1.88V; and / or, the trough voltage in the cold start test at -40°C, 100% SOC, and 20A discharge is ≥1.60V.

[0065] According to one aspect of the present invention, an electrical device includes a plurality of the aforementioned 21650 omni-tab cylindrical lithium-ion cells.

[0066] The present invention also provides an electrical device comprising a plurality of the aforementioned 21650 all-tab cylindrical lithium-ion cells. Based on the capacity consistency and low-temperature output stability of the cells in the present invention under a short-height structure, the module of the present invention can maintain a coordinated response in overall electrical performance under wide temperature range operating conditions and dynamic power demands.

[0067] The technical solution of the present invention will be further described below with reference to the embodiments.

[0068] Example 1 A 21650 all-tab cylindrical lithium-ion battery cell is prepared by the following method: (I) Preparation of positive electrode sheet: The positive electrode active material includes, by mass percentage: 97.25% layered high-nickel lithium transition metal oxide with a nickel content of 88 mol% to 92 mol%, 1.50% carbon black conductive agent, 0.10% carbon nanotube conductive agent, and 1.15% polyvinylidene fluoride (PVDF) binder. The above components are dispersed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry; the slurry is coated on both sides of an aluminum foil current collector with a thickness of 12 μm, and after drying, rolling and slitting, the positive electrode sheet is obtained.

[0069] (II) Preparation of negative electrode sheet: The negative electrode active material includes, by mass percentage: 83.0% artificial graphite, 13.4% silicon-carbon composite material, 0.6% conductive carbon black, 1.2% sodium carboxymethyl cellulose (CMC) binder, and 1.8% styrene-acrylic emulsion (SBR) binder. CMC is dissolved in deionized water, and artificial graphite, silicon-carbon composite material, and conductive carbon black are added for pre-dispersion. Then, SBR emulsion is added to adjust the viscosity to obtain a negative electrode slurry. The slurry is coated on both sides of a copper foil current collector with a thickness of 6 μm to 8 μm, and after segmented drying, rolling, and slitting, the negative electrode sheet is obtained.

[0070] The compaction density of the negative electrode is P1 = 1.58 g / cm³, the porosity of the negative electrode is 33.0%, and the equivalent pore resistance of the negative electrode is R = 0.88 Ω•cm².

[0071] (III) Diaphragm and electrolyte: The diaphragm is a coated diaphragm composed of a polyolefin-based membrane and an inorganic ceramic coating, with a total thickness of 11 μm to 13 μm, wherein the thickness of the polyolefin-based membrane is 8 μm to 10 μm and the thickness of the inorganic ceramic coating is 2 μm to 3 μm; the inorganic ceramic coating comprises, by mass percentage, 94.0% boehmite particles, 3.5% polyvinylidene fluoride binder and 2.5% acrylic binder.

[0072] The electrolyte comprises, by total mass, 12.5% ​​lithium hexafluorophosphate (LiPF6), 2.0% lithium bis(fluorosulfonyl)imide (LiFSI), 3.0% fluoroethylene carbonate (FEC), 1.0% vinylene carbonate (VC), 0.5% ethylene sulfate (DTD), and the balance being a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), with a mass ratio of EC, EMC, and DMC of 25:45:30.

[0073] (iv) Cell assembly and formation: The positive electrode, separator, and negative electrode are wound to form a core. The ends of the positive and negative electrode are flattened to form full-tab end faces. The core is then installed into a cylindrical shell with an outer diameter D of 21.0 mm and a total height H1 of 65.1 mm. The current collector is welded, electrolyte is injected, and the shell is sealed. After formation and capacity testing, the finished battery cell is obtained.

[0074] (v) Key parameter testing: 1. The total height of the cylindrical shell is H1 = 65.1 mm, and the outer diameter is D = 21.0 mm; 2. The discharge capacity C0.2 = 5.02 Ah under the conditions of 25℃ and 0.2C discharge. 3. The surface density M of the negative electrode active material layer on one side n = 5.75 mg / cm², negative electrode compaction density P1 = 1.58 g / cm³, negative electrode active material layer single-sided thickness t n = 41.0 μm; 4. Negative electrode equivalent aperture resistance R = 0.88 Ω·cm², negative electrode aperture resistance – compaction coupling coefficient K1 = R × P1 = 1.39; 5. Electrolyte retention per unit area of ​​the negative electrode η = 2.90 mg / cm²; 6. At 50% SOC, the pulsed DC internal resistance (DCR) at -20℃ -20 With 25℃ pulsed DC internal resistance DCR25 The ratio of DCR -20 / DCR 25 = 6.71; 7. In the cold start test at -40℃, 100% SOC, and 15 A discharge, the trough voltage Vmin = 1.96 V; 8. After 100 cycles of charging at 25℃ and 8 A and discharging at 40 A, no continuous lithium plating was observed on the surface of the negative electrode when it was fully charged and disassembled.

[0075] Example 2 The difference between this embodiment and Embodiment 1 is that by adjusting the negative electrode roller pressure to about 12% higher than that in Embodiment 1 and reducing the roller gap to the target roller gap, the negative electrode compaction density P1 changes from 1.58 g / cm³ to 1.64 g / cm³, the negative electrode porosity changes from 33.0% to 29.5%, and R changes from 0.88 Ω•cm² to 1.18 Ω•cm²; the rest is the same as in Embodiment 1.

[0076] This embodiment illustrates that when the compaction density is close to the upper limit, the negative electrode can still maintain low-temperature output within the K1 and η windows.

[0077] Example 3 The difference between this embodiment and Embodiment 1 is that by adjusting the negative electrode roller pressure to about 10% lower than that in Embodiment 1 and appropriately increasing the roller gap, the negative electrode compaction density P1 changes from 1.58 g / cm³ to 1.52 g / cm³, the negative electrode porosity changes from 33.0% to 36.8%, and R changes from 0.88 Ω•cm² to 0.74 Ω•cm²; the rest is the same as in Embodiment 1.

[0078] This example illustrates that a low compaction boundary can reduce hole resistance, but it is still necessary to maintain a capacity of 4.9 Ah or higher.

[0079] Example 4 The difference between this embodiment and Embodiment 1 is that by adjusting the pore-forming control component in the negative electrode slurry to a lower level and increasing the subsequent drying temperature, the pore connectivity of the negative electrode is reduced, and the equivalent pore impedance R of the negative electrode changes from 0.88Ω•cm² to 1.28Ω•cm², and K1 changes from 1.39 to 2.02; otherwise, it is the same as Embodiment 1.

[0080] Example 5 The difference between this embodiment and Embodiment 1 is that the electrolyte immersion and standing time is adjusted to 36 hours, and the number of negative pressure immersions before formation is adjusted from 1 to 2, so that the electrolyte retention η per unit area of ​​the negative electrode is changed from 2.90 mg / cm² to 3.35 mg / cm²; otherwise, it is the same as Embodiment 1.

[0081] This embodiment illustrates the effect of the upper limit of negative electrode liquid retention on improving low-temperature cold start.

[0082] Example 6 The difference between this embodiment and Embodiment 1 is that by adjusting the proportion of silicon-carbon composite material in the negative electrode active material to 15.2wt%, the contribution ratio of silicon-carbon material to the reversible capacity of the negative electrode, Rs, is changed from 45% to 48%. At the same time, P1 is adjusted to 1.56g / cm³, so that R is controlled to 0.95Ω•cm². The rest is the same as in Embodiment 1.

[0083] This example illustrates that even with a high silicon capacity ratio, low-temperature output can still be maintained through pore resistance and liquid retention window.

[0084] Comparative Example 1 The difference between this comparative example and Example 1 is that by adjusting the negative electrode roller pressure to about 25% higher than that in Example 1 and reducing the roller gap to an over-compacted state, the negative electrode compaction density P1 changes from 1.58 g / cm³ to 1.70 g / cm³, the negative electrode porosity changes from 33.0% to 25.0%, and R changes from 0.88 Ω•cm² to 1.65 Ω•cm²; otherwise, it is the same as Example 1.

[0085] Comparative Example 2 The difference between this comparative example and Example 1 is that by adjusting the surface density of the negative electrode coating to 5.05 mg / cm² and reducing the roller pressure, the compaction density P1 of the negative electrode changes from 1.58 g / cm³ to 1.43 g / cm³, and R changes from 0.88 Ω•cm² to 0.62 Ω•cm²; otherwise, it is the same as Example 1.

[0086] Comparative Example 3 The difference between this comparative example and Example 1 is that, by adjusting the injection volume and the soaking and standing time, the electrolyte retention per unit area of ​​the negative electrode η is changed from 2.90 mg / cm² to 1.95 mg / cm², and R is changed from 0.88 Ω•cm² to 1.42 Ω•cm²; otherwise, it is the same as Example 1.

[0087] Comparative Example 4 The difference between this comparative example and Example 1 is that the negative electrode pore connectivity is reduced by adjusting the dispersion time and drying regime of the negative electrode slurry, so that R changes from 0.88 Ω•cm² to 1.52 Ω•cm² and K1 changes from 1.39 to 2.40; otherwise, it is the same as Example 1.

[0088] Comparative Example 5 The difference between this comparative example and Example 1 is that by adjusting the proportion of silicon-carbon composite material to 18.5 wt%, the contribution ratio of silicon-carbon material to the reversible capacity of the negative electrode, Rs, changes from 45% to 53%, and R changes from 0.88 Ω•cm² to 1.10 Ω•cm²; otherwise, it is the same as Example 1.

[0089] Comparative Example 6 The difference between this comparative example and Example 1 is that by setting a local trench structure on the surface of the negative electrode, but without adjusting the overall pore impedance and liquid retention per unit area of ​​the negative electrode, R changes from 0.88 Ω•cm² to 1.38 Ω•cm², and η changes from 2.90 mg / cm² to 2.15 mg / cm²; otherwise, it is the same as Example 1. This comparative example is used to illustrate that relying solely on local surface structures cannot replace the overall coupled control of negative electrode pore impedance, compaction density, and liquid retention.

[0090] The test results of key parameters for Examples 1-6 and Comparative Examples 1-6 are shown in Table 1.

[0091] Table 1:

[0092] Experimental Example 1 This experiment tests the performance of the battery cells prepared in Examples 1-6 and Comparative Examples 1-6. The specific testing methods are as follows: Unless otherwise stated, the number of samples for the overall electrical performance test in each embodiment and comparative example is n=3, and the negative electrode is disassembled and sampled at no less than 3 locations. The results in the table are average values.

[0093] Capacity test at 25℃ and 0.2C: Capacity testing was conducted using a battery charge-discharge testing system with a sample size of n=3. The cells were left to stand at 25℃ for 3 hours, then charged at a constant current of 0.5C to 4.2V, followed by constant voltage charging to a cutoff current of 0.05C. After standing for 30 minutes, they were discharged at a constant current of 0.2C to 2.5V, and the discharge capacity C was recorded. 0.2 And discharge energy. Each sample was tested three times, and the average of the second and third tests was taken as the capacity result. The judgment method was C. 0.2 It fell between 4.9Ah and 5.2Ah.

[0094] 25℃, 50% SOC DCR test: A power battery pulse internal resistance testing device was used. The battery cell was adjusted to 50% SOC and left to stand at 25℃ for 2 hours. A 40A discharge pulse was applied for 10 seconds, and the voltage V0 before the pulse and the voltage V10 at the 10th second of discharge were recorded. The DCR (Discharge Rate) was also recorded. 25 =(V0-V10) / 40A. For each sample, n=3, the average value is taken. The judgment method is DCR. 25 It falls within 6.5mΩ to 8.8mΩ or meets the DCR low-temperature rate ratio requirement in this invention.

[0095] DCR test at -20℃ and -40℃ 50% SOC battery cells were placed in -20℃ and -40℃ incubators for 6 hours respectively to stabilize the cell surface and core temperature. DCR was tested using the same 40A, 10s pulse method as at 25℃. -20 and DCR -40 Calculate DCR -20 / DCR 25 and DCR -40 / DCR 25 The determination method is DCR. -20 / DCR 25 ≤7.8, preferably ≤7.2; DCR -40 / DCR 25 Preferably ≤18.0.

[0096] -40℃ cold start test: Charge the battery cells to 100% SOC, let them stand at 25℃ for 1 hour, then transfer them to a -40℃ chamber and let them stand for 6 hours. Discharge in steps of 5A, 10A, 15A, and 20A, discharging for 10 seconds per current step, with a 60-second rest period between steps. The cutoff voltage is 1.5V or the process is stopped according to the safety strategy. Record the lowest voltage of each step, using the lowest voltage of the 15A step as Vmin,-40,15A, and the lowest voltage of the 20A step as Vmin,-40,20A. The determination method is Vmin,-40,15A ≥ 1.80V, preferably ≥ 1.88V.

[0097] EIS testing and pore resistance fitting: The overall battery EIS test was conducted at 25℃ and 50% SOC, with a frequency range of 100kHz to 10mHz and a perturbation voltage of 5mV. The negative electrode pore impedance test used a symmetrically blocked electrode prepared from disassembled negative electrode sheets. The electrolyte and separator were consistent with the cell system. After standing at 25℃ for 12 hours, the EIS test was performed. An equivalent circuit fitting method incorporating ohmic resistance, interfacial charge transfer resistance, transmission line pore impedance, and Warburg diffusion elements was used. The result was normalized to the electrode area to obtain R, in Ω•cm². At least three negative electrode locations were taken for each sample, and the average value was calculated.

[0098] Negative electrode disassembly and structural testing: Discharge the cell to 2.5V, disassemble it in an inert atmosphere glove box, and remove the negative electrode sheet. Clean the negative electrode sheet three times with DMC and vacuum dry it at 40℃ for 12 hours. Punch out 14mm diameter discs using a punching machine, weigh the dried mass, and calculate Mn after deducting the mass of the copper foil. Measure the thickness of the negative electrode sheet and the thickness tn of the negative electrode active material layer using a micrometer or CP cross-section. P1 is calculated by dividing the mass of the negative electrode active material layer by the volume of the active material layer. Porosity e is calculated based on the theoretical solid density and compacted density, or verified using mercury intrusion porosimetry / gas adsorption.

[0099] Negative electrode liquid retention test: Disassemble a fully charged or specified SOC battery cell in an inert atmosphere, quickly remove the negative electrode sheet, and cut the sample according to area An, obtaining the wet mass M1. Extract with DMC and vacuum dry to constant weight, then weigh to obtain the dry mass m2. ΔM = M1 - m2, η = ΔM / An. To reduce volatility error, the time from disassembly to initial weighing should not exceed 120 seconds. Take three samples from each location and average the results.

[0100] Lithium plating observation and post-cycling verification: The sample was subjected to 100 cycles of charging at 25°C and 8A / discharging at 40A. After each cycle, the sample was fully charged and the negative electrode was disassembled in an inert atmosphere. The presence of a continuous silvery-white lithium plating band on the negative electrode surface was observed visually, using an optical microscope, and with SEM. Further confirmation of residual lithium metal could be made using titration or XPS. The determination was based on the absence of a continuous lithium plating band in the sample.

[0101] See Table 2 for specific test results.

[0102] Table 2:

[0103] Based on the data in Tables 1 and 2 above, the 21650 all-tab cylindrical lithium-ion cells of Examples 1-6 and Comparative Examples 1-6 are analyzed as follows: Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that increasing the compaction density of the negative electrode can increase the loading per unit volume. However, when P1 increases from 1.58 g / cm³ to 1.70 g / cm³, the porosity decreases from 33.0% to 25.0%, R increases to 1.65 Ω•cm², and K1 exceeds the scope of this invention. At low temperatures, the electrolyte viscosity increases, and the increased pore shrinkage and tortuosity amplify ion transport resistance, causing DCR to decrease. -20 / DCR 25 The voltage rose to 8.44, and the trough voltage at -40°C and 15A dropped to 1.58V. Although Example 2 was at the upper boundary of compaction, K1 was still controlled, indicating that the scope of the invention can achieve a balance between 5Ah capacity and low-temperature output.

[0104] Comparing Example 1, Example 3, and Comparative Example 2, it can be seen that reducing the negative electrode compaction density can improve pore connectivity and reduce R. Therefore, Example 3 has a lower DCR. -20 / DCR 25 And a higher cold start trough voltage. However, when P1 drops to 1.43 g / cm³ and Mn drops to 5.05 mg / cm², although Comparative Example 2 shows better low-temperature DCR, C 0.2 With a capacitance of only 4.78Ah, it cannot meet the 5Ah capacity window of the 21650 short-high circuit. Therefore, this invention does not simply pursue low orifice impedance, but rather establishes a common window for capacity and cryogenic transport between Mn, P1, and R.

[0105] Comparing Examples 1 and 5 with Comparative Example 3, it can be seen that the liquid retention capacity η per unit area of ​​the negative electrode directly affects the liquid phase pathway that can participate in ion transport within the negative electrode channels under low-temperature conditions. In Example 5, after increasing η to 3.35 mg / cm², the DCR... -20 / DCR 25 The voltage dropped to 6.51, and the cold start trough voltage rose to 2.01V. In Comparative Example 3, η dropped to 1.95 mg / cm². Even though the negative electrode areal density and compaction density were the same as in Example 1, insufficient liquid phase in the pores at low temperatures still caused increased concentration polarization, resulting in Vmin dropping to 1.55V and lithium plating. Therefore, the η range can support the low-temperature interface liquid supply of short-capacity 5Ah cells.

[0106] Comparing Examples 1 and 4 with Comparative Example 4, it is evident that R is a crucial parameter connecting the negative electrode channel structure and low-temperature polarization. In Example 4, increasing R to 1.28 Ω•cm² still maintained Vmin at 1.84 V, indicating that the present invention allows for a certain degree of process variation over a wide range. In Comparative Example 4, R was increased to 1.52 Ω•cm², and K1 was 2.40, exceeding the range of the present invention, resulting in a simultaneous increase in the low-temperature DCR rate ratio and the risk of lithium plating. This result demonstrates that the negative electrode pore impedance cannot be separated from the evaluation of compaction density, and the K1 window can more accurately reflect the ion transport state of a highly loaded silicon-carbon negative electrode at low temperatures.

[0107] Comparing Examples 1 and 6 with Comparative Example 5, it can be seen that increasing the capacity contribution of silicon-carbon materials can improve the capacity of short-cell high-performance batteries, but an excessively high silicon-carbon ratio will increase low-temperature polarization and lithium plating tendency. In Example 6, Rs is 48%, C 0.2 The output reaches 5.15Ah, while the cold start trough voltage is maintained at 1.85V by controlling P1, R, and η. In Comparative Example 5, Rs rises to 53%, C 0.2 The optimal window was exceeded, but the low-temperature DCR rate ratio increased to 8.33 and significant lithium plating occurred. This indicates that the present invention uses silicon capacity ratio as a subordinate limitation, in conjunction with pore impedance and liquid retention capacity, rather than pursuing high silicon capacity alone.

[0108] Comparing Example 1 and Comparative Example 6, it is evident that relying solely on the local surface trench structure of the negative electrode cannot replace the combined control of overall pore impedance, compaction density, and liquid retention per unit area. Although Comparative Example 6 incorporates local trenches, R remains at 1.38 Ω•cm², η is only 2.15 mg / cm², the low-temperature DCR ratio is close to or exceeds the upper limit, and the trough voltage at -40℃ and 15A is only 1.66V. This indicates that the low-temperature cold-start capability depends not only on the local surface liquid channels but also on the continuous channels and liquid retention status along the thickness and in-plane directions of the entire negative electrode. This invention does not rely on local trenching as its core, but rather defines the protection range based on the overall pore impedance and liquid retention parameters that can be measured in reverse.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 21650 all-tab cylindrical lithium-ion battery cell, characterized in that, It includes a cylindrical shell, a core and an electrolyte. The core is formed by winding a positive electrode, a diaphragm and a negative electrode. The ends of the positive electrode and the negative electrode are flattened to form full-tab end faces. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes graphite material and silicon carbon material. With the equivalent pore impedance of the negative electrode active material layer as R and the negative electrode compaction density as P1, the negative electrode pore impedance-compaction coupling coefficient K1 is defined as R × P1, and K1 is 0.85~2.

15. Given that the negative electrode active material layer has a double-sided effective area An and the electrolyte content in the negative electrode active material layer is M1, the electrolyte content per unit area of ​​the negative electrode is defined as η = M1 / An, where η is 2.20 mg / cm² to 3.60 mg / cm². Furthermore, the battery cell meets the following requirements: at 50% SOC, the ratio of the pulsed DC internal resistance at -20℃ to the pulsed DC internal resistance at 25℃ is ≤7.8; and the trough voltage in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.80V.

2. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The total height H1 of the cylindrical shell is 63.5 mm to 66.5 mm, and the outer diameter D is 20.6 mm to 21.5 mm; And / or, the total height H1 of the cylindrical shell is 64.7 mm to 65.5 mm, the outer diameter D is 20.8 mm to 21.2 mm, and H1 / D is 3.06 to 3.14; And / or, the discharge capacity of the battery cell under the conditions of 25°C and 0.2C discharge is 4.9 Ah to 5.2 Ah, preferably 4.98 Ah to 5.05 Ah.

3. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The single-sided areal density Mn of the negative electrode active material layer is 5.3 mg / cm² to 6.2 mg / cm², preferably 5.50 mg / cm² to 6.05 mg / cm²; The compaction density P1 of the negative electrode is 1.50 g / cm³ to 1.65 g / cm³, preferably 1.54 g / cm³ to 1.62 g / cm³; The thickness tn of the negative electrode active material layer on one side is 38μm~44μm, preferably 39.5μm~42.5μm; The single-cell porosity e of the negative electrode active material layer is 28%~38%, preferably 31%~36%; The equivalent pore impedance R of the negative electrode active material layer is 0.55Ω•cm² to 1.35Ω•cm², preferably 0.70Ω•cm² to 1.05Ω•cm².

4. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, Using equivalent aperture resistance R and discharge capacity C 0.2 The ratio defines the negative electrode unit capacity orifice resistance K2; K2=R / C 0.2 K2 is 0.11Ω•cm² / Ah to 0.27Ω•cm² / Ah, preferably 0.14Ω•cm² / Ah to 0.21Ω•cm² / Ah.

5. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The negative electrode hole impedance-compaction coupling coefficient K1 is 1.10~1.70; The electrolyte retention η per unit area of ​​the negative electrode is 2.55 mg / cm² to 3.25 mg / cm².

6. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The contribution of silicon-carbon material to the reversible capacity of the negative electrode in the negative electrode active material layer is 40%~50%, preferably 43%~48%.

7. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The cell has a DCR of 50% SOC. -20 / DCR 25 The value is 5.5~7.8, preferably 6.0~7.

2.

8. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, Cell -40℃ Pulse DC Internal Resistance (DCR) -40 With DCR 25 The ratio is ≤18.

0.

9. The 21650 all-tab cylindrical lithium-ion cell according to claim 1, characterized in that, The cell's trough voltage Vmin in the cold start test at -40℃, 100% SOC, and 15A discharge is ≥1.88V. And / or, the trough voltage in the cold start test at -40℃, 100% SOC, and 20A discharge is ≥1.60V.

10. An electrical appliance, characterized in that, The electrical device includes the 21650 all-tab cylindrical lithium-ion battery cell as described in any one of claims 1 to 9.

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