A cylindrical battery

Abstract

The application provides a cylindrical battery, comprising a battery cell, a shell and an electrolyte; the group margin of the cylindrical battery is a, the height of the battery cell is h mm, the concentration of lithium salt in the electrolyte is b mol / L, and 38<=a*h / b<=112. The application reduces the group margin and the height of the battery cell to improve the uneven concentration distribution of lithium ions in the cylindrical battery, thereby avoiding local lithium precipitation and lithium dendrite generation and improving the cycle life. Meanwhile, by adjusting the concentration of lithium salt in the electrolyte, the problem of DCR increase caused by the reduction of the group margin and the height of the battery cell is solved. The application realizes the technical effect of improving the fast-charging performance and the cycle life of the battery by comprehensively regulating the relationship among a, b and c.

Description

Technical Field

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

[0002] Cylindrical batteries are a type of lithium-ion battery characterized by their cylindrical shape. Large cylindrical batteries are considered the mainstream technology due to their advantages in energy density, safety, and fast charging.

[0003] However, existing cylindrical batteries generally suffer from the technical problem of localized lithium plating. Summary of the Invention

[0004] The purpose of this invention is to provide a cylindrical battery that can improve the local lithium plating phenomenon and enhance the cycle performance of the cylindrical battery.

[0005] This invention provides a cylindrical battery, comprising a cell, a casing, and an electrolyte. The cylindrical battery has a group margin of 'a', a cell height of 'h' mm, and a lithium salt concentration of 'b' mol / L in the electrolyte, where 38 ≤ a × h / b ≤ 112. This invention improves the uneven distribution of lithium ion concentration in the cylindrical battery by reducing the group margin and cell height, thereby avoiding localized lithium plating and lithium dendrite formation, and improving cycle life. Simultaneously, by adjusting the lithium salt concentration in the electrolyte, it addresses the increased drain-rate-compression (DCR) caused by reducing the group margin and cell height. This invention achieves improved fast-charging performance and cycle life by comprehensively controlling the relationship between 'a', 'b', and 'h'. Detailed Implementation

[0006] This invention provides a cylindrical battery, comprising a cell, a casing, and an electrolyte. The cylindrical battery has a group margin of 'a', a cell height of 'h' mm, and a lithium salt concentration of 'b' mol / L in the electrolyte, where 38 ≤ a × h / b ≤ 112. A larger cell height 'h' results in a more pronounced effect of gravity on the electrolyte during resting or cycling, exacerbating uneven electrolyte distribution within the cell, leading to excessive electrolyte accumulation at the bottom and insufficient electrolyte at the top, thus intensifying lithium deposition and reducing the battery's cycle life. Reducing the group margin 'a' allows more space for the electrolyte to fully wet the cell, improving electrolyte distribution uniformity, suppressing lithium dendrite formation, and increasing cycle life. However, a too small 'a' increases the gaps between electrodes and between electrodes and the separator, lengthening the lithium ion transport path and increasing the die charge rate (DCR). Further increasing the lithium salt concentration 'b' in the electrolyte increases the number of mobile lithium ions per unit volume, thereby improving electrolyte conductivity and reducing the battery's DCR. Therefore, by comprehensively regulating a, h, and b, making 38≤a×h / b≤112, the uniform distribution of the electrolyte is promoted, lithium plating is reduced, and the fast-charging performance and cycle life of the battery are improved.

[0007] In some embodiments of the present invention, 38 ≤ a×h / b ≤ 112, such as a×h / b being 38, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 110, 112, or any of the above values ​​as the upper or lower limit.

[0008] For further optimization, 49≤a×h / b≤81.5.

[0009] In some embodiments of the present invention, the group margin 'a' of the cylindrical battery is the ratio of the core volume of the cell to the casing volume, with a group margin of 90% ≤ a ≤ 98.5%. If the group margin is too low, there will be excessive gaps inside the core, increasing the gaps between electrodes and between electrodes and the separator, thus lengthening the lithium-ion transport path and leading to an increase in DCR. If the group margin is too high, after charging expansion, the electrolyte will be squeezed out from inside the electrodes, and the charging expansion stress will accumulate inside the battery pack, causing side effects such as electrode material cracking and accelerated SEI film repair, resulting in a reduction in cycle life. Preferably, 92% ≤ a ≤ 97.5%, such as a being 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or 98.5%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0010] In some embodiments of the present invention, the cell height hmm is preferably 60~120mm. If h is too high, the lithium-ion transport path is long, which easily leads to uneven lithium-ion concentration and lithium plating, thus reducing cycle life. If h is too low, it is difficult to implement a multi-tab or all-tab structure design for the cell, resulting in concentrated current transport path and significantly increasing DCR. The cell height hmm is more preferably 70~100mm, such as 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, preferably within the range of any of the above values ​​as the upper or lower limit.

[0011] In some embodiments of the present invention, the electrolyte comprises a lithium salt and a solvent. The concentration of the lithium salt in the electrolyte, b mol / L, is preferably 0.9~1.8 mol / L. If the lithium salt concentration is too high, the electrolyte viscosity will increase, making lithium-ion transport difficult and increasing the DCR (discharge rate). If the lithium salt concentration is too low, the number of carriers available for lithium-ion migration in the electrolyte will decrease. During charging, the deposition of lithium ions on the negative electrode surface may become more uneven, leading to the formation of a large number of lithium dendrites and reducing cycle life. The lithium salt concentration b mol / L is more preferably 1.1~1.6 mol / L, such as 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, and 1.8 mol / L, preferably within the range of any of the above values ​​as the upper or lower limit.

[0012] In some embodiments of the present invention, a, h, and b satisfy the relationship 38 ≤ a × h / b ≤ 112. If the value of a × h / b exceeds 112, it indicates a high group margin, a small internal space in the battery, a large cell height, a low lithium salt concentration, and uneven lithium ion distribution in the height direction, resulting in a large amount of local lithium plating and a reduced cycle life. If the value of a × h / b is less than 38, it indicates a low group margin, a large internal space in the battery, a small cell height, a high lithium salt concentration, which leads to increased electrolyte viscosity, difficulty in lithium ion transport, and an increase in DCR.

[0013] In some embodiments of the present invention, the lithium salt is preferably one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6, and lithium tetrafluoroborate (LiBF4). Among them, LiPF6 has a high degree of dissociation, lithium bis(fluorosulfonyl)imide (LiFSI) has high molecular structural symmetry and a lower lithium ion migration activation energy, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium tetrafluoroborate (LiBF4) are both interface-optimized lithium salts, which both help to improve the lithium ion diffusion rate.

[0014] In some embodiments of the present invention, the solvent in the electrolyte preferably includes one or more of cyclic carbonates, chain carbonates, and carboxylic acid ester solvents; the cyclic carbonates include ethylene carbonate (EC) and / or propylene carbonate (PC), which are high dielectric constant solvents that can improve the dissociation degree of lithium salts; the chain carbonates include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), which are low viscosity solvents that improve the lithium ion migration rate; the carboxylic acid ester solvents include methyl acrylate (MA) and / or ethyl acetate (EA), which are lower viscosity solvents compared to chain carbonates, further improving the lithium ion migration rate.

[0015] In some embodiments of the present invention, the mass fraction of ethylene carbonate in the electrolyte is preferably 10% to 30%, such as 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, preferably within the range of any of the above values ​​as the upper or lower limit; the mass fraction of propylene carbonate in the electrolyte is preferably 10% to 20%, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, preferably within the range of any of the above values ​​as the upper or lower limit; the mass fraction of dimethyl carbonate in the electrolyte is preferably 0% to 70%, such as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%. The mass fraction of ethyl acetate in the electrolyte is preferably 0-30%, such as 0%, 5%, 10%, 15%, 20%, 25%, 30%, preferably within the range of any of the above values ​​as the upper or lower limit; the mass fraction of ethyl acetate in the electrolyte is preferably 0-50%, such as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, preferably within the range of any of the above values ​​as the upper or lower limit; the mass fraction of methyl acetate in the electrolyte is preferably 0-40%, such as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, preferably within the range of any of the above values ​​as the upper or lower limit.

[0016] In some embodiments of the present invention, the battery cell includes a negative electrode, a positive electrode, and a separator.

[0017] In some embodiments of the present invention, the negative electrode sheet preferably includes a negative electrode current collector and a negative electrode material layer composited on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode material.

[0018] In some embodiments, the negative electrode current collector may include negative electrode current collectors conventionally used in the art. For example, the negative electrode current collector may include at least one of copper foil, chromium foil, nickel foil, and titanium foil.

[0019] In some embodiments, the negative electrode material layer includes a negative electrode material, which includes a negative electrode active material. The negative electrode active material can be graphite or silicon-carbon material; the primary particle size D50 of the graphite is 5.5~7 μm; the primary particle size D50 of the silicon-carbon material is 6~15 μm. If the primary particle size is too large, the lithium-ion transport path is prolonged, and the die charge rate (DCR) increases; if the primary particle size is too small, side reactions with the electrolyte increase, and the cycle life decreases. In the negative electrode material, the mass fraction of the negative electrode active material is preferably 94%~98.5%, such as 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, preferably within a range where any of the above values ​​is the upper or lower limit.

[0020] In some embodiments of the present invention, when the negative electrode active material is graphite, preferably, 96%≤a≤98%, such as 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit; when the negative electrode active material is silicon-carbon material, preferably, 93%≤a≤96%, within this range, it can ensure that the battery has a certain space buffer when expanding, such as a being 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit. When the negative electrode active material is silicon-carbon material, the mass fraction of silicon in the negative electrode sheet is preferably 1~30%, more preferably 5~25%. Within this range, the silicon content can improve the stability of the negative electrode sheet.

[0021] In some embodiments of the present invention, when the negative electrode active material contains a silicon-based material, the electrolyte preferably contains an additive, which preferably includes one or more of fluoroethylene carbonate, vinylene carbonate, propylene-1,3-sulfonyl lactone, and methanedisulfonate.

[0022] In some embodiments, the negative electrode material further includes a conductive agent. The conductive agent in the negative electrode material is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the negative electrode material includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (Super P), acetylene black, and Ketjen black. In some embodiments of the present invention, the carbon fibers may be carbon nanofibers; and the carbon black may be at least one of SP (Super P), acetylene black, and Ketjen black.

[0023] In some embodiments, the mass fraction of the conductive agent in the negative electrode material is preferably 0.2% to 1.5%, such as 0.2%, 0.5%, 0.7%, 1%, 1.2%, or 1.5%, preferably within a range where any of the above values ​​is the upper or lower limit.

[0024] In some embodiments, the negative electrode material further includes a binder. The binder in the negative electrode material is used to improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. Exemplary binders in the negative electrode material include, but are not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resins.

[0025] In some embodiments, the mass fraction of the binder in the negative electrode material is preferably 1% to 3%, such as 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, preferably within a range where any of the above values ​​are the upper or lower limits.

[0026] In some embodiments, the negative electrode material further includes a dispersant used to improve the dispersibility of the negative electrode active material. Any dispersant can be used without particular limitation, as long as it has suitable dispersibility and does not significantly cause adverse chemical changes in the battery. Exemplary examples include, but are not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and hydrogenated styrene-butadiene rubber (H-SBR).

[0027] In some embodiments, the mass fraction of the dispersant in the negative electrode material is preferably 0.3% to 1.5%, such as 0.3%, 0.5%, 0.7%, 1%, 1.2%, or 1.5%, preferably within a range where any of the above values ​​is the upper or lower limit.

[0028] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the negative electrode sheet includes the following steps: mixing a negative electrode active material, a conductive agent, a binder, a dispersant and a solvent to obtain a negative electrode slurry; coating the negative electrode slurry onto at least one side of a negative electrode current collector, drying it and then rolling and cutting it to obtain a negative electrode sheet.

[0029] In some embodiments of the present invention, the positive electrode sheet preferably includes a positive current collector and a positive electrode material layer composited on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode material.

[0030] In some embodiments, the positive current collector may include positive current collectors conventionally used in the art. For example, the positive current collector may include at least one of aluminum foil and composite foil. The composite foil includes a middle high-density layer and metal layers disposed on both sides of the polymer layer. The polymer layer includes polymer materials, including at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, their derivatives, their crosslinks, and their copolymers. The metal layers may include at least one of aluminum, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0031] In some embodiments, the cathode material includes a cathode active material, which preferably includes one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), ternary materials, and 5V spinel.

[0032] In some embodiments, the mass fraction of the positive electrode active material is preferably 97% to 98.8%, such as 97%, 97.2%, 97.5%, 97.8%, 98%, 98.2%, 98.5%, 98.6%, 98.7%, 98.8%, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0033] In some embodiments, the positive electrode material further includes a conductive agent. The conductive agent in the positive electrode material is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, activated carbon, carbon fibers, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, acetylene black, SP, Ketjen black, etc.

[0034] In some embodiments, the mass fraction of the conductive agent in the positive electrode material is preferably 0.6% to 1.5%, such as 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, preferably within a range where any of the above values ​​is the upper or lower limit.

[0035] In some embodiments, the positive electrode material further includes a binder. The binder in the positive electrode material is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder includes, but is not limited to, fluorinated polyolefin binders, including, but not limited to, polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0036] In some embodiments, the mass fraction of the binder in the positive electrode material is preferably 0.6% to 1.5%, such as 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, preferably within a range where any of the above values ​​is the upper or lower limit.

[0037] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the positive electrode sheet includes the following steps: mixing positive electrode active material, conductive agent, binder and solvent to obtain positive electrode slurry; coating the positive electrode slurry onto at least one side of the positive electrode current collector, drying and then rolling and cutting to obtain the positive electrode sheet.

[0038] In some embodiments of the present invention, the capacity ratio of the negative electrode to the positive electrode is preferably 1.0 to 1.12. If this ratio is too large, excess negative electrode material increases interfacial side reactions and reduces charge-discharge efficiency. If this ratio is too small, the negative electrode capacity is insufficient to fully accept the lithium ions released from the positive electrode during charging, causing lithium ions to deposit on the negative electrode surface, forming lithium metal dendrites and reducing cycle life. In some embodiments of the present invention, the capacity ratio of the negative electrode to the positive electrode is 1.04.

[0039] In some embodiments of the present invention, the lithium-ion battery further includes a separator disposed between the positive electrode and the negative electrode to separate the positive and negative electrode and prevent short circuits caused by contact between the positive and negative electrode. The separator can be at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. A coating can also be provided on the surface of the separator, which can be an inorganic coating and / or an organic coating. The inorganic coating material includes at least one of alumina, silicon oxide, titanium oxide, magnesium oxide, zirconium oxide, and boehmite; the organic coating includes at least one of aramid coating and polyvinylidene fluoride (PVDF) coating.

[0040] In some embodiments, the porosity of the membrane is preferably 40-60%, more preferably 45-55%. If the porosity of the membrane is too large, the side reactions between the material interface and the electrolyte will increase, resulting in a decrease in cycle life. If the porosity of the membrane is too small, lithium-ion transport will be hindered, leading to an increase in DCR.

[0041] This invention provides a cylindrical battery, comprising a cell and an electrolyte; the cylindrical battery has a group margin of 'a', a cell height of 'h' mm, and a lithium salt concentration of 'b' mol / L in the electrolyte, where 38 ≤ a × h / b ≤ 112. This invention improves the uneven distribution of lithium ion concentration in the cylindrical battery by reducing the group margin and cell height, thereby avoiding localized lithium plating and lithium dendrite formation, and improving cycle life. Simultaneously, by adjusting the lithium salt concentration in the electrolyte, it addresses the increased drain-rate-compression (DCR) caused by reducing the group margin and cell height. This invention achieves improved fast-charging performance and cycle life by comprehensively controlling the relationship between 'a', 'b', and 'c'.

[0042] To further illustrate the present invention, the following describes a cylindrical battery provided by the present invention in detail with reference to embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0043] Example 1

[0044] (1) Preparation of positive electrode sheet

[0045] The positive electrode active material (high-nickel ternary material: LiNi9Co) 0.5 Mn 0.5 O2), conductive agent acetylene black, and binder PVDF are mixed in a mass ratio of 98.2:0.8:0.8, and solvent NMP is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0046] (2) Preparation of negative electrode sheet

[0047] The negative electrode active material graphite and silicon-carbon material (mass ratio = 9:1 (w:w)), conductive agent acetylene black, thickener CMC, and binder SBR were mixed at a mass ratio of 96:1:1.4:1.6. Deionized water was added as solvent, and the mixture was stirred in a vacuum mixer until the system was homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing with different compaction densities and slitting, negative electrode sheets were obtained. The mass fraction of silicon in the negative electrode material was 30%, and the capacity ratio of the negative electrode sheet to the positive electrode sheet was 1.04.

[0048] (3) Preparation of electrolyte

[0049] In an argon-filled glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 20:50:20:10 to obtain an organic solvent. Then, thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1.35 mol / L and stirred until completely dissolved to prepare an electrolyte.

[0050] (4) Preparation of the separating membrane.

[0051] The diaphragm is commercially available. Its base membrane is a 6μm thick PE membrane. One side surface of the base membrane has a 2μm thick alumina coating and a 1μm thick PVDF coating, respectively. The other side surface of the base membrane has a 1μm thick PVDF coating. The diaphragm porosity is 45%.

[0052] (5) Preparation of lithium-ion batteries

[0053] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode is then wound 102 times to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and volume adjustment, a lithium-ion battery is obtained.

[0054] The lithium-ion batteries of Examples 2-16 and Comparative Examples 1-4 were prepared according to the method in Example 1 and the parameters listed in Table 1.

[0055] The lithium-ion batteries prepared in the examples and comparative examples were tested according to the following methods, and the performance data are shown in Table 2.

[0056] ① Test method for battery pack margin:

[0057] Remove the battery cell and measure the core diameter d and height h. According to the formula: [π(d / 2)] 2 The core volume is calculated by multiplying h. According to the definition: core volume / shell volume = group margin;

[0058] ② Test method for cell height:

[0059] Place the battery cell on a flat surface and use a high-precision ruler to measure the battery height;

[0060] ③ Test method for lithium salt concentration:

[0061] 1. Discharge the battery completely; 1) Charge at a constant current of 0.33C to 4.25V, and then charge at a constant voltage until the current drops to 0.05C; 2) Let it stand for 30 minutes; 3) Discharge at a constant current of 0.33C to 2.5V; 4) Let it stand for 30 minutes;

[0062] 2. After recording the battery number / barcode, disassemble the battery in a glove box (H2O≤0.1ppm, O2≤0.1ppm) to collect the electrolyte. There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage. ② if there is no free electrolyte, use a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) to continuously pressurize until free electrolyte appears, collect it into a sample tube and seal it. ③ Add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing glue.

[0063] Remove the internal core of the battery and place it in a press to squeeze out the electrolyte; 1) Break the battery casing and remove the internal core; 2) Place the core in a press to squeeze out the electrolyte; 3) Place the collected electrolyte in a centrifuge to separate liquid and solid impurities; 4) Take the supernatant for testing.

[0064] 3. The collected electrolyte sample was injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe for testing, obtaining GC-MS chromatograms. Electrolyte additives were dissolved in EMC solvent to prepare solutions of different concentrations, and these solutions were injected into the Agilent Intuvo 9000 gas chromatograph-mass spectrometer to obtain standard GC-MS chromatograms. The GC-MS chromatogram of the electrolyte to be tested was compared with the standard GC-MS chromatogram to confirm the presence of corresponding components. The content of each component was then determined based on its peak area in the electrolyte to be tested.

[0065] ④ Battery DCR test method:

[0066] Place the target battery cell in a constant temperature environment of 25℃ for 30 minutes;

[0067] (1) Charge the battery to 50% SOC (50% of rated capacity) at 0.33C; record V1.

[0068] (2) Let stand for 10 minutes;

[0069] (3) 2C constant current (I1) discharge for 30s; record V2

[0070] (4) Let stand for 10 minutes;

[0071] Define DCR value: (V1-V2) / I1=R1

[0072] ⑤ Test method for cycle life:

[0073] The lithium-ion batteries prepared in the examples and comparative examples were subjected to cycle tests at 25°C according to the following procedure:

[0074] 1) Charge at a constant current rate of 0.33C to 4.25V, and then charge at a constant voltage until the current drops to 0.05C;

[0075] 2) Let it stand for 30 minutes;

[0076] 3) Discharge to 2.5V at a rate of 0.33C;

[0077] 4) Let it stand for 30 minutes.

[0078] Perform cycle tests according to steps 1)-4) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0079] The test results are shown in Table 1.

[0080] Table 1. Process parameters for preparing lithium-ion batteries in the examples and comparative examples.

[0081]

[0082] Table 2 Performance data of lithium-ion batteries prepared in the examples and comparative examples

[0083]

[0084] According to the data in Tables 1 and 2, when the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery meet the condition 38 ≤ a × h / b ≤ 112 (Examples 1-16), the DCR of the lithium-ion battery is controlled between 1.45 and 2.1Ω, and the cycle life is between 450 and 1200 cycles. However, when the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery do not meet the condition 38 ≤ a × h / b ≤ 112 (Comparative Examples 1-4), the DCR of the lithium-ion battery increases to between 1.85 and 2.35Ω, the cycle life decreases to between 352 and 853 cycles, and it is difficult to simultaneously optimize fast charging performance and cycle life.

[0085] When the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery, as well as a×h / b, are all within the further preferred range of this application (Examples 1-5), it is possible to simultaneously optimize the DCR and cycle life of the lithium-ion battery. The DCR is reduced to 1.45~1.78Ω, and the cycle life is increased to 816~1200 cycles. While improving the fast charging performance of the battery, excellent cycle life is also taken into account.

[0086] When the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery are not within the further preferred range of this application, but a×h / b is within the further preferred range of this application (Examples 6-7), the DCR of the lithium-ion battery is 1.67~1.72Ω, and the cycle life is 902~1076 cycles; when the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery are within the further preferred range of this application, but a×h / b is not within the further preferred range of this application (Examples 8-9), the DCR of the lithium-ion battery is 1.54~1.81Ω, and the cycle life is 754~1108 cycles. This proves that the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery, as well as a×h / b, have a significant impact on the fast charging performance and cycle life of the lithium-ion battery.

[0087] When the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery, as well as a×h / b, are all outside the further preferred range of this application (Examples 10-14), the DCR of the lithium-ion battery is 1.73-20.3Ω and the cycle life is 484-939 cycles. Compared with Examples 1-9, all of these show significant deterioration, but are still better than Comparative Examples 1-4.

[0088] When the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery do not meet the range of 90%≤a≤98.5%, 70≤h≤110, and 0.9≤b≤1.8 as specified in this application, but a×h / b still meets the requirement of 38≤a×h / b≤112 (Examples 15-16), the DCR and cycle life of the lithium-ion battery show a slight decrease compared to Examples 10-14, but are still better than Comparative Examples 1-2 (where the values ​​of the group margin a, cell height h, and lithium salt concentration b of the cylindrical battery meet the range of 90%≤a≤98.5%, 70≤h≤110, and 0.9≤b≤1.8 as specified in this application, but a×h / b does not meet the requirement of 38≤a×h / b≤112). This demonstrates the importance of the a×h / b parameter for simultaneously optimizing the fast-charging performance and cycle life of lithium-ion batteries.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cylindrical battery, characterized in that, It includes a battery cell, a casing, and an electrolyte; the cylindrical battery has a group margin of a, a cell height of h mm, and a lithium salt concentration of b mol / L in the electrolyte, where 38 ≤ a × h / b ≤ 112.

2. The cylindrical battery according to claim 1, characterized in that, 49≤a×h / b≤81.

5.

3. The cylindrical battery according to claim 1, characterized in that, 90%≤a≤98.5%， And / or, 70≤h≤110, And / or, 0.9≤b≤1.

8.

4. The cylindrical battery according to claim 1, characterized in that, The lithium salt in the electrolyte includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, LiPF6, and lithium tetrafluoroborate.

5. The cylindrical battery according to claim 1, characterized in that, The electrolyte also includes a solvent, which includes one or more of cyclic carbonates, chain carbonates, and carboxylic acid ester solvents; The cyclic carbonates include ethylene carbonate and / or propylene carbonate; The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; The carboxylic acid ester solvents include methyl acrylate and / or ethyl acetate.

6. The cylindrical battery according to claim 5, characterized in that, The mass fraction of ethylene carbonate in the electrolyte is 10%~30%; The mass fraction of propylene carbonate in the electrolyte is 10%~20%; The mass fraction of dimethyl carbonate in the electrolyte is 0-70%; The mass fraction of methyl ethyl carbonate in the electrolyte is 0-30%; The mass fraction of ethyl acetate in the electrolyte is 0-50%; The mass fraction of methyl acetate in the electrolyte is 0-40%.

7. The cylindrical battery according to claim 1, characterized in that, The battery cell includes a negative electrode sheet, the negative electrode sheet includes a negative electrode material, the negative electrode material includes a negative electrode active material, and the negative electrode active material is graphite and / or silicon-carbon material.

8. The cylindrical battery according to claim 7, characterized in that, The primary particle size Dv50 of the graphite is 5.5~7μm; the primary particle size Dv50 of the silicon carbide material is 6~15μm.

9. The cylindrical battery according to claim 7, characterized in that, When the negative electrode active material is graphite, 96%≤a≤98%.

10. The cylindrical battery according to claim 7, characterized in that, When the negative electrode active material contains silicon-carbon material, 93%≤a≤96%, and the mass fraction of silicon in the negative electrode material is 1~30%.

11. The cylindrical battery according to claim 7, characterized in that, When the negative electrode active material contains silicon-carbon material, the electrolyte contains additives, the additives including one or more of fluoroethylene carbonate, vinylene carbonate, propylene-1,3-sulfonyl lactone and methane disulfonate.

12. The cylindrical battery according to claim 1, characterized in that, The battery cell also includes a positive electrode, and the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.0 to 1.

12.

13. The cylindrical battery according to claim 12, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes one or more of lithium iron phosphate, lithium manganese iron phosphate, ternary materials, and 5V spinel.

14. The cylindrical battery according to claim 1, characterized in that, The battery cell also includes a separator, the porosity of which is 40-60%.

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