A cylindrical lithium-ion battery

Abstract

This invention provides a cylindrical lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte; the negative electrode comprises a negative electrode material layer containing a negative electrode active material, the negative electrode active material comprising a silicon-based material; the non-aqueous electrolyte comprises a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent comprising a chain carbonate containing DMC, and the lithium salt comprising LiPF6 and lithium fluorinated sulfonyl imide; the cylindrical lithium-ion battery satisfies the following conditions: 0.05≤(100-D)*F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, 5≤S≤20. This invention effectively improves the rate performance, room temperature cycle performance, and high temperature storage performance of cylindrical lithium-ion batteries and extends their service life by controlling the mass percentage D of DMC in the non-aqueous electrolyte, the ratio F of the molar content of lithium fluorinated sulfonyl imide to LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer to satisfy 0.05≤(100-D)*F / S≤8.75, 50≤D≤75, 0.012≤F≤1, and 5≤S≤20.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a cylindrical lithium-ion battery. Background Technology

[0002] Cylindrical batteries are favored by major manufacturers due to their advantages of simple design, standardized manufacturing, simple process, low cost, and high application flexibility. Traditional cylindrical batteries, however, are disadvantageous as power batteries due to their small size. To address this issue, current cylindrical batteries are increasingly larger, with diameters reaching up to 46mm, resulting in a further increase in energy density. Because the electrodes in cylindrical batteries are wound, the winding tension effectively suppresses electrode expansion, making them more suitable for silicon anodes that expand significantly during charging and discharging. The cylindrical battery cell design is also well-suited for high-energy-density material systems.

[0003] Silicon-containing anodes exhibit significant volume effects. The lithium-silicon alloying and dealloying processes are accompanied by dramatic expansion and contraction of the anode, causing the solid electrolyte interphase (SEI) film on its surface to continuously rupture and regenerate. This leads to electrolyte consumption and loss of active lithium, increasing interfacial impedance and thus deteriorating cycle performance. Simultaneously, as charging and discharging progress, the thickness of the anode electrode increases, potentially causing the battery casing to crack and posing a safety hazard due to pressure. Furthermore, increased thickness worsens the contact between the active material and the copper foil current collector, affecting electronic conductivity and resulting in a sharp capacity drop in the later stages of cycling, leading to a "capacity plunge."

[0004] Currently, the industry primarily improves the energy density of cylindrical batteries by using high-specific-capacity positive and negative electrode materials. The theoretical specific capacity of silicon-based negative electrodes is approximately 10 times that of currently used graphite negative electrodes. Therefore, increasing the silicon content in the negative electrode material of the battery cell is one of the important development directions for achieving high specific energy of batteries. For every 10% increase in energy density, cycle life will decrease by 25%. The cycle life of cells made using high-energy-density materials is a bottleneck, and existing cylindrical batteries struggle to improve their cycle life while maintaining high energy density.

[0005] Therefore, it is necessary to develop a cylindrical lithium-ion battery to solve the aforementioned problems of existing technologies. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide a cylindrical lithium-ion battery with advantages such as high energy density, good room temperature cycle performance and good high temperature storage performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A cylindrical lithium-ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte; the negative electrode includes a negative electrode material layer containing a negative electrode active material, and the negative electrode active material includes a silicon-based material; the non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent includes a chain carbonate containing DMC, and the lithium salt includes LiPF6 and lithium fluorosulfonylimide;

[0009] The cylindrical lithium-ion battery satisfies the following conditions:

[0010] 0.05 ≤ (100 - D) * F / S ≤ 8.75, and 50 ≤ D ≤ 75, 0.012 ≤ F ≤ 1, 5 ≤ S ≤ 20;

[0011] Where, D is the mass percentage content of DMC in the non-aqueous electrolyte, with the unit of wt%;

[0012] F is the ratio of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte;

[0013] S is the mass percentage content of silicon element in the negative electrode material layer, with the unit of wt%.

[0014] Optionally, the cylindrical lithium-ion battery satisfies the following condition: 0.1 ≤ (100 - D) * F / S ≤ 7.5.

[0015] Optionally, the mass percentage content D of DMC in the non-aqueous electrolyte is 55 wt% to 67 wt%.

[0016] Optionally, the ratio F of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte is 0.06 to 0.85.

[0017] Optionally, the mass percentage content S of silicon element in the negative electrode material layer is 7 wt% to 15 wt%.

[0018] Optionally, the silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials and silicon alloy materials; preferably, the negative electrode active material is selected from silicon-carbon composite materials;

[0019] Preferably, the silicon material is a nanosilicon material; the silicon oxide material is a SiOx material, where 0 < x < 2; the silicon-carbon composite material is a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, where 0 < y < 2; the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material.

[0020] Optionally, the lithium fluorosulfonylimide is selected from one or more of LiFSI and LiTFSI.

[0021] Optionally, the lithium salt further includes LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 One or more of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0022] Optionally, the total molar content of the lithium salt is 0.9 mol / L to 3.5 mol / L, and 0.012 ≤ F ≤ 1; preferably, the total molar content of the lithium salt is 1.1 mol / L to 1.5 mol / L, and 0.06 ≤ F ≤ 0.85.

[0023] Optionally, the non-aqueous organic solvent may further include one or more of cyclic carbonates, carboxylic acid esters, and ethers;

[0024] Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propylene carbonate, and butene carbonate;

[0025] The chain carbonate also includes one or more of diethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate;

[0026] The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, methyl isobutyrate, ethyl butyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0027] The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0028] Optionally, the non-aqueous electrolyte further includes additives, which are selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate ester compounds, and nitrile compounds; the content of the additives is 0.01% to 30% based on 100% of the total mass of the non-aqueous electrolyte.

[0029] Preferably, the cyclic carbonate compound is selected from one or more of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or compounds represented by structural formula 1:

[0030]

[0031] In structural formula 1, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0032] The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate;

[0033] The sulfonyl lactone compound is selected from one or more of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0034] The phosphate ester compounds are selected from tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and compounds shown in structural formula 2 below:

[0035]

[0036] In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group;

[0037] The borate esters are selected from one or more of tris(trimethylsilane)borate and tris(triethylsilane)borate;

[0038] The nitrile compound is selected from one or more of succinic acid, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

[0039] This invention provides a cylindrical lithium-ion battery, wherein the negative electrode active material comprises a silicon-based material, and the non-aqueous electrolyte uses a non-aqueous organic solvent containing DMC and a lithium salt containing LiPF6 and lithium fluorinated sulfonyl imide. For high-energy-density lithium-ion batteries with silicon-containing negative electrodes, selecting DMC as the non-aqueous organic solvent for the electrolyte can greatly improve the wettability and flowability of the non-aqueous electrolyte; selecting lithium fluorinated sulfonyl imide and LiPF6 as lithium salts can improve conductivity, electrochemical properties, thermal stability, and hydrolysis resistance. Based on their own experience and extensive research, the inventors discovered that when the mass percentage D of DMC in the non-aqueous electrolyte, the ratio F of the molar content of lithium fluorinated sulfonyl imide to the molar content of LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer satisfy 0.05≤(100-D)*F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, and 5≤S≤20, the volume change of the silicon negative electrode can be effectively suppressed, and problems such as electrolyte consumption and active lithium loss, increased interface impedance, deterioration of cycle performance, and sharp capacity decay in the later stages of cycling can be improved. This can enhance the rate performance, room temperature cycle performance, and ultra-high temperature storage performance of cylindrical lithium-ion batteries, and increase their service life. Detailed Implementation

[0040] Unless otherwise specified, the experimental methods described in the following embodiments of the present invention are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products.

[0041] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0042] The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or device that includes a series of steps is not limited to the steps or modules listed, but may optionally include steps not listed, or may optionally include other steps inherent to such process, method, product, or device.

[0043] In this invention, "multiple" refers to two or more kinds.

[0044] This embodiment provides a cylindrical lithium-ion battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte; the negative electrode includes a negative electrode material layer containing a negative electrode active material, the negative electrode active material including a silicon-based material; the non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent including a chain carbonate containing DMC, and the lithium salt including LiPF6 and lithium fluorinated sulfonyl imide;

[0045] The cylindrical lithium-ion battery meets the following conditions:

[0046] 0.05≤(100-D)*F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, 5≤S≤20;

[0047] Wherein, D is the mass percentage of DMC in the non-aqueous electrolyte, in wt%.

[0048] F is the ratio of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte.

[0049] S represents the mass percentage of silicon in the negative electrode material layer, expressed in wt%.

[0050] The cylindrical lithium-ion battery provided by this invention comprises a silicon-based material as its negative electrode active material, and uses a non-aqueous electrolyte consisting of a non-aqueous organic solvent containing DMC (dimethyl carbonate) and a lithium salt containing LiPF6 and lithium fluorinated sulfonyl imide. For high-energy-density lithium-ion batteries with silicon-containing negative electrodes, selecting DMC as the non-aqueous organic solvent for the electrolyte can greatly improve the wettability and flowability of the non-aqueous electrolyte; selecting lithium fluorinated sulfonyl imide and LiPF6 as lithium salts can improve conductivity, electrochemical properties, thermal stability, and hydrolysis resistance. Based on their own experience and extensive research, the inventors discovered that when the mass percentage D of DMC in the non-aqueous electrolyte, the ratio F of the molar content of lithium fluorinated sulfonyl imide to the molar content of LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer satisfy 0.05≤(100-D)*F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, and 5≤S≤20, the volume change of the silicon negative electrode can be effectively suppressed, and problems such as electrolyte consumption and active lithium loss, increased interface impedance, deterioration of cycle performance, and sharp capacity decay in the later stages of cycling can be improved. This can enhance the rate performance, room temperature cycle performance, and ultra-high temperature storage performance of cylindrical lithium-ion batteries, and increase their service life.

[0051] Specifically, the value of (100-D)*F / S can be, but is not limited to, 0.05, 0.07, 0.09, 0.1, 1.2, 1.5, 1.6, 1.8, 2, 2.1, 2.3, 2.5, 2.7, 3, 3.2, 3.6, 3.8, 4, 4.2, 4.5, 4.7, 5, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.5, 7.8, 8.0, 8.2, 8.5, 8.75.

[0052] In a preferred embodiment, the cylindrical lithium-ion battery satisfies the following condition: 0.1 ≤ (100-D)*F / S ≤ 7.5. Further optimizing the condition from 0.05 ≤ (100-D)*F / S ≤ 8.75, the optimal value of 0.1 ≤ (100-D)*F / S ≤ 7.5 can better suppress the volume expansion of the silicon anode and improve the cycle performance and lifespan of the high-energy-density lithium-ion battery system containing the silicon anode.

[0053] Specifically, the mass percentage D of DMC in the non-aqueous electrolyte may be, but is not limited to, 50wt%, 52wt%, 55wt%, 58wt%, 60wt%, 62wt%, 65wt%, 67wt%, 69wt%, 70wt%, 72wt%, 74wt%, or 75wt%.

[0054] In a preferred embodiment, the mass percentage D of DMC in the non-aqueous electrolyte is 55wt% to 67wt%.

[0055] Cylindrical batteries have a tightly wound structure, resulting in a compact material structure and relatively little internal space. For the electrolyte to function effectively, it must possess good wettability and flowability. Chain carbonates have lower viscosity than cyclic carbonates, and among commonly used non-aqueous organic solvents, DMC has the lowest viscosity, correspondingly offering the best effect on improving conductivity. However, DMC is prone to gas generation at high temperatures, requiring careful control of its dosage. Using 50wt%–75wt% DMC as a non-aqueous organic solvent component in the non-aqueous electrolyte can significantly improve its wettability and flowability. In particular, when the mass percentage D of DMC is 55wt%–67wt%, the wettability and flowability of the non-aqueous electrolyte of this invention are even better improved.

[0056] Silicon-based anodes exhibit lower conductivity than graphite anodes. In non-aqueous electrolytes, lithium fluorinated sulfonyl imide (LiPF6) offers better conductivity, higher electrochemical and thermal stability, and greater resistance to hydrolysis compared to LiPF6, helping to reduce internal resistance, decrease heat generation, improve discharge efficiency, and enhance battery safety. However, high LiPF6 content can easily cause aluminum foil corrosion. Therefore, controlling the molar ratio F of LiPF6 to LiPF6 in the non-aqueous electrolyte to be between 0.012 and 1 can largely mitigate this risk; especially when F is between 0.06 and 0.85, battery performance can be better balanced. When reducing the mass percentage D of DMC in the non-aqueous electrolyte to increase the (100-D) ratio, the molar ratio F of LiPF6 to LiPF6 needs to be adjusted to ensure sufficient system conductivity. Furthermore, introducing an appropriate amount of LiPF6 into the silicon-based cylindrical system can further optimize battery rate performance, extend battery cycle life, and improve high-temperature stability.

[0057] Specifically, the mass percentage content S of silicon element in the negative electrode material layer can be, but is not limited to, 5wt%, 7wt%, 9wt%, 10wt%, 12wt%, 14wt%, 15wt%, 17wt%, 19wt%, 20wt%.

[0058] Silicon-based materials can effectively improve the energy density of the battery, but their huge volume effect cannot be ignored. Especially as the silicon content increases, this negative impact will increase exponentially. The high-strength shell of the cylindrical battery can, to a certain extent, inhibit the decomposition of the electrolyte to generate gas and the damage of the battery body caused by the volume expansion of the material. At the same time, through the coordinated regulation of the silicon content and key components in the electrolyte design, the volume effect can be further optimized: taking (100 - D) as the control parameter, and coordinating the change of the silicon content S to regulate the content of DMC (reducing the content, reducing the gas production pressure) and the value of F, taking into account the electrolyte compatibility of cylindrical batteries with different silicon contents.

[0059] In some embodiments, the silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials, and silicon alloy materials.

[0060] In some embodiments, the silicon material is a nanosilicon material; the silicon oxide material is a SiOx material, where 0 < x < 2; the silicon-carbon composite material is a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, where 0 < y < 2; the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material.

[0061] The silicon material has a high specific capacity, but due to its lithium intercalation mechanism, it is extremely easy to undergo volume expansion, resulting in the rupture and failure of the electrode material; the carbon material has better stability than the silicon material. In some preferred embodiments, the negative electrode active material is selected from silicon-carbon composite materials. The silicon and carbon in the silicon-carbon composite material form a complementary relationship. The high specific capacity of the silicon-based and the cycle stability of the carbon-based are combined, which can effectively solve the problem of material expansion and failure, while taking into account good cycle performance.

[0062] Specifically, the ratio F of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte can be, but is not limited to, 0.012, 0.05, 0.06, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.

[0063] In a preferred embodiment, the molar content of lithium fluorosulfonylimide in the non-aqueous electrolyte is 0.01 mol / L to 0.9 mol / L; more preferably, the molar content of lithium fluorosulfonylimide in the non-aqueous electrolyte is 0.1 mol / L to 0.6 mol / L.

[0064] In a preferred embodiment, the molar content of LiPF6 in the non-aqueous electrolyte is 0.5 mol / L to 2.0 mol / L; more preferably, the molar content of LiPF6 in the non-aqueous electrolyte is 0.6 mol / L to 1.3 mol / L.

[0065] In a preferred embodiment, the lithium fluorosulfonylimide is selected from one or more of lithium bis(fluorosulfonylimide) (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0066] In some embodiments, the lithium salt further includes LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 One or more of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0067] In some embodiments, the total molar content of the lithium salt is 0.9 mol / L to 3.5 mol / L, and 0.012 ≤ F ≤ 1; preferably, the total molar content of the lithium salt is 1.1 mol / L to 1.5 mol / L, and 0.06 ≤ F ≤ 0.85. Specifically, the total molar content of the lithium salt can be 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, or 3.5 mol / L.

[0068] In some embodiments, the non-aqueous organic solvent further includes one or more of cyclic carbonates, carboxylic esters, and ethers.

[0069] Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate (FEC), vinylene carbonate, propylene carbonate, and butene carbonate;

[0070] The chain carbonate also includes one or more of diethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate;

[0071] The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, methyl isobutyrate, ethyl butyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0072] The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0073] In some preferred embodiments, the non-aqueous organic solvent includes chain carbonates and cyclic carbonates, wherein the cyclic carbonates include at least FEC. The FEC content is 6% to 30% based on 100% of the total mass of the non-aqueous electrolyte. In the electrolyte of silicon-containing battery systems, FEC not only aids in interfacial film formation but also helps suppress lithium consumption.

[0074] In some embodiments, the non-aqueous electrolyte further includes additives selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate ester compounds, and nitrile compounds.

[0075] Preferably, the cyclic carbonate compound is selected from one or more of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or compounds represented by structural formula 1:

[0076]

[0077] In structural formula 1, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0078] The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate;

[0079] The sulfonyl lactone compound is selected from one or more of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0080] The phosphate ester compounds are selected from tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and compounds shown in structural formula 2 below:

[0081]

[0082] In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group;

[0083] The borate esters are selected from one or more of tris(trimethylsilane)borate and tris(triethylsilane)borate;

[0084] The nitrile compound is selected from one or more of succinic acid, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

[0085] It should be noted that, unless otherwise specified, the content of any optional substance in the additive in the non-aqueous electrolyte is generally less than 10%, preferably 0.1% to 5%, and more preferably 0.1% to 3%. Specifically, the content of any optional substance in the additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0086] In some embodiments, the positive electrode includes a positive electrode material layer containing a positive electrode active material. The type and content of the positive electrode active material are not particularly limited and can be selected according to actual needs, as long as it is a positive electrode active material or a conversion type positive electrode material that can reversibly insert / deintercalate lithium metal ions.

[0087] In some embodiments, the positive electrode active material may be selected from LiFe1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2, wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, W, Zr, V, or Ti, and M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, W, Zr, V, or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. The positive electrode active material may also be selected from at least one of sulfides, selenides, and halides. More preferably, the positive electrode active material may be selected from LiCoO2, LiFePO4, or LiFe... 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 At least one of O2.

[0088] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector.

[0089] The positive current collector is selected from a metallic material that can conduct electrons. Preferably, the positive current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0090] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0091] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0092] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0093] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector may be the same as that of the positive electrode current collector, and will not be described in detail here.

[0094] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0095] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0096] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0097] The following description is based on specific embodiments.

[0098] Example 1

[0099] This embodiment illustrates the cylindrical lithium-ion battery and its preparation method disclosed in this invention, including the following steps:

[0100] Preparation of the positive electrode: High-nickel ternary positive electrode active material NCM811 (LiNi) was mixed at a mass ratio of 97:1.5:1.5. 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black and binder polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil. After drying, rolling and vacuum drying, a positive electrode material layer is formed on the aluminum foil. Aluminum leads are then welded on using an ultrasonic welding machine to obtain a positive electrode plate. The thickness of the electrode plate is between 120-150 μm.

[0101] Preparation of the negative electrode: Silicon-carbon composite material (silicon suboxide + graphite mixture), conductive carbon black, styrene-butadiene rubber binder and sodium carboxymethyl cellulose are mixed in a mass ratio of 94.2:1.2:3.0:1.5 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil. After drying, rolling and vacuum drying, a negative electrode material layer (with a Si content of 6%) is formed on the copper foil. Nickel leads are then welded on using an ultrasonic welding machine to obtain a negative electrode plate with a thickness between 120-150 μm.

[0102] Preparation of electrolyte: Dimethyl carbonate (DMC), ethylene carbonate (EC) and fluoroethylene carbonate (FEC) were mixed in a certain mass ratio, and then LiFSI and LiPF6 were added. The mass percentages of DMC and FEC in the electrolyte were 75% and 10%, respectively. The molar contents of LiFSI and LiPF6 are shown in Table 1.

[0103] Battery assembly: A separator is placed between the positive and negative plates, and then the sandwich structure consisting of the positive plate, negative plate and separator is wound up and then placed into a cylindrical aluminum metal shell.

[0104] Electrolyte injection and formation: The prepared electrolyte was injected into the cell, vacuum-sealed, and left to stand for 36 hours. Then, the first charge was carried out according to the following steps: 0.02C constant current charging for 30 minutes, 0.05C constant current charging for 30 minutes, 0.1C constant current charging for 120 minutes, and 0.2C constant current charging for 240 minutes, with the cutoff voltage set at 3.85V for all. After resting for 1 hour and then at room temperature for 24 hours (12 hours each in reverse orientation), the cell was charged to 4.2V with a 0.5C constant current and discharged to 2.75V with a 0.2C constant current.

[0105] Examples 2-33

[0106] Examples 2-33 illustrate the cylindrical lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, except that the battery composition shown in Table 1 is used. In Example 26, lithium fluorinated sulfonylimide is LiTFSI.

[0107] Comparative Examples 1-16

[0108] Comparative Examples 1-16 illustrate the cylindrical lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, except that they use the battery composition shown in Table 1. Specifically, the non-aqueous electrolyte in Comparative Example 1 does not contain FEC.

[0109] Table 1

[0110]

[0111]

[0112]

[0113]

[0114] Performance testing

[0115] The cylindrical lithium-ion batteries in the above embodiments and comparative examples were subjected to the following performance tests, and the results are recorded in Table 2.

[0116] 1) Rate Discharge Efficiency Test: At 25℃, the formed battery was charged to 4.2V using a 0.5C constant current and constant voltage method, then discharged to 2.75V using a 0.5C constant current and constant voltage method, then charged to 4.2V again using a 0.5C constant current and constant voltage method, and finally discharged to 2.75V using a 4C constant current method. Calculate the ratio of the 4C discharge capacity to the 0.5C discharge capacity. The calculation formula is as follows:

[0117] 4C / 0.5C rate discharge efficiency (%) = (4C discharge capacity / 0.5C discharge capacity) × 100%;

[0118] 2) Room Temperature Cycling Performance Test: At 25℃, the formed battery was charged to 4.2V using a 1C constant current and constant voltage method, and then discharged to 2.75V using a 1C constant current method. The capacity retention rate after 1000 charge / discharge cycles was calculated. The calculation formula is as follows:

[0119] Capacity retention rate after 1000 cycles (%) = (Discharge capacity after 1000 cycles / Discharge capacity after 1st cycle) × 100%;

[0120] 3) Ultra-high temperature storage performance: After formation, the battery was charged to 4.2V at room temperature using a 1C constant current and constant voltage method, then discharged to 2.75V using a 1C constant current and constant voltage method. The initial discharge capacity was recorded. The battery was then charged to 4.2V again using a 1C constant current and constant voltage method, and then stored at 85℃ for 12 hours. Finally, after the battery cooled to room temperature, it was discharged to 2.75V using a 1C method to measure the battery's retention capacity. The calculation formula is as follows:

[0121] Capacity retention rate (%) = Retained capacity / Initial capacity × 100%.

[0122] Table 2

[0123]

[0124]

[0125] As can be seen from the data in Table 2, when the mass percentage D of DMC in the non-aqueous electrolyte, the ratio F of the molar content of lithium fluorinated sulfonyl imide to LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer satisfy 0.05≤(100-D)*F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, 5≤S≤20, the rate discharge efficiency, room temperature cycle performance, and ultra-high temperature storage performance of cylindrical lithium-ion batteries can be effectively improved (Examples 1-33). In particular, when the cylindrical lithium-ion battery satisfies 0.1≤(100-D)*F / S≤7.5, and 55≤D≤67, 0.06≤F≤0.85, 7≤S≤15, the battery performance is even better (e.g., Examples 3, 5, 7, 13, and 14). When at least one of the values ​​of (100-D)*F / S, D, F, or S is outside the preferred range, the relevant performance of the battery will slightly deteriorate. For example, compared to Example 3, in Example 24, D is above the preferred range, resulting in decreased ultra-high temperature storage performance; in Example 25, D is below the preferred range, resulting in decreased rate discharge efficiency and room temperature cycling performance. Compared to Example 3, in Example 20, F is below the preferred range, resulting in decreased room temperature cycling performance; in Example 21, F is above the preferred range, resulting in decreased room temperature cycling performance. Compared to Example 5, in Example 22, S is above the preferred range, resulting in decreased room temperature cycling performance; in Example 23, S is below the preferred range, resulting in decreased room temperature cycling performance and ultra-high temperature storage performance. When two or more of the values ​​of (100-D)*F / S, D, F, or S are outside the preferred range, the relevant performance of the battery deteriorates more significantly, as shown in the comparison of battery performance in Examples 10-12; when the values ​​of (100-D)*F / S, D, F, or S are all outside the preferred range, the battery performance is relatively worse (e.g., Example 10).

[0126] In the non-aqueous electrolyte of the lithium-ion battery of the present invention, lithium fluorinated sulfonyl imide can be selected from one or more of LiFSI (Examples 1-25, Examples 27-33) and LiTFSI (Example 26), all of which can meet the requirements. LiFSI is preferred, which can enable the battery to obtain better performance (Example 3 vs Example 26).

[0127] The silicon-based material in the negative electrode active material of the lithium-ion battery of the present invention can be selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials, and silicon alloy materials, all of which can meet the requirements. In particular, when the silicon-based material is selected from silicon-carbon composite materials, the battery can obtain better performance (Example 7 vs Examples 27-28, Example 5 vs Examples 29-30).

[0128] The non-aqueous electrolyte of the lithium-ion battery of the present invention may further include conventional additives in the art, which can further improve the overall performance of the battery. For example, compared with Example 5, the non-aqueous electrolyte of Example 31 battery also added 1% DTD, which further improved the battery's rate discharge efficiency, room temperature cycle performance and ultra-high temperature storage performance; the non-aqueous electrolyte of Example 32 battery also added 1% PS, which further improved the battery's rate discharge efficiency and ultra-high temperature storage performance; the non-aqueous electrolyte of Example 33 battery also added 1% propargyl phosphate, which further improved the battery's ultra-high temperature storage performance.

[0129] When the cylindrical lithium-ion battery does not satisfy 0.1≤(100-D)*F / S≤7.5, and 55≤D≤67, 0.06≤F≤0.85, and 7≤S≤15, the battery's performance deteriorates significantly.

[0130] Compared with Example 2, the DMC content D in the non-aqueous electrolyte of Comparative Example 1 battery is higher than the range of the present invention, and there is no FEC in the non-aqueous electrolyte, resulting in insufficient interface protection. The battery's rate discharge efficiency, room temperature cycle performance and ultra-high temperature storage performance are severely degraded.

[0131] Compared with Example 1, the DMC content D in the non-aqueous electrolyte of Comparative Example 3 battery is lower than the range of the present invention, the electrolyte wettability is poor, and the battery performance is significantly degraded.

[0132] Compared to Example 2, the ratio F of the molar content of lithium fluoride sulfonyl imide to the molar content of LiPF6 in the non-aqueous electrolyte of Comparative Example 2 battery is lower than the range of the present invention, resulting in insufficient conductivity and corresponding degradation of battery performance. Compared to Example 1, the ratio F of the molar content of lithium fluoride sulfonyl imide to the molar content of LiPF6 in the non-aqueous electrolyte of Comparative Example 4 battery is higher than the range of the present invention, resulting in severe interfacial corrosion and significant degradation of battery performance.

[0133] Compared with Example 4, the mass percentage S of silicon in the negative electrode material layer of Comparative Example 5 battery is lower than the range of the present invention, and the mass percentage S of silicon in the negative electrode material layer of Comparative Example 6 battery is higher than the range of the present invention. Both of these results in a mismatch in battery composition, material damage, and significant deterioration of battery performance.

[0134] Compared to Example 1, the DMC content D in the non-aqueous electrolyte of Comparative Example 7 is lower than the range of this invention, and the molar ratio F of lithium fluorinated sulfonyl imide to LiPF6 is also lower than the range of this invention, resulting in a significant deterioration in battery performance. Compared to Comparative Example 3, the F value in the non-aqueous electrolyte of Comparative Example 7 is lower than that of this invention, further deteriorating battery performance. Compared to Comparative Example 7, the mass percentage S of silicon in the negative electrode material layer of Comparative Example 8 is lower. Although the battery performance is slightly improved, it is still significantly deteriorated compared to this invention.

[0135] The parameters of the comparative example 9 battery did not meet the requirements of this invention, the battery performance was severely degraded, the water pressure dropped significantly, and the ultra-high temperature storage performance could not be tested.

[0136] In Comparative Example 10, the mass percentage S of silicon in the negative electrode material layer does not match the ratio F of the molar content of lithium fluorinated sulfonyl imide to the molar content of LiPF6 in the non-aqueous electrolyte; in Comparative Example 11, the mass percentage S of silicon in the negative electrode material layer does not match the DMC content D in the non-aqueous electrolyte, and the value of (100-D)*F / S is not within the range of this invention, resulting in severe degradation of battery performance and inability to test ultra-high temperature storage performance.

[0137] Compared with Example 5, the DMC content D in the non-aqueous electrolyte of Comparative Example 12 battery is higher than the range of the present invention, and the ultra-high temperature storage performance cannot be tested.

[0138] In Comparative Examples 13-16, although the mass percentage D of DMC in the non-aqueous electrolyte, the molar ratio F of lithium fluorinated sulfonyl imide to LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer all met the requirements of this invention, the value of (100-D)*F / S was outside the range of this invention, which also led to severe degradation of battery performance. This illustrates that only when appropriate key components are selected in the battery, and the relationship between the amount and content of the key components meets the specific requirements of this invention, can the excellent performance of the lithium-ion battery as described in this invention be guaranteed.

[0139] In summary, by controlling the mass percentage D of DMC in the non-aqueous electrolyte, the ratio F of the molar content of lithium fluorinated sulfonyl imide to LiPF6 in the non-aqueous electrolyte, and the mass percentage S of silicon in the negative electrode material layer, this invention can effectively suppress the volume change of silicon negative electrode, improve problems such as electrolyte consumption and active lithium loss, increased interface impedance, deterioration of cycle performance, and sharp capacity decay in the later stages of cycling, thereby improving the rate performance, room temperature cycle performance, and ultra-high temperature storage performance of cylindrical lithium-ion batteries and extending their service life.

[0140] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A cylindrical lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the negative electrode includes a negative electrode material layer containing a negative electrode active material, the negative electrode active material including a silicon-based material; the non-aqueous electrolyte includes a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent including a chain carbonate containing DMC, and the lithium salt including LiPF6 and lithium fluorosulfonylimide; The cylindrical lithium-ion battery meets the following conditions: 0.05≤(100-D) F / S≤8.75, and 50≤D≤75, 0.012≤F≤1, 5≤S≤20; Where D represents the mass percentage of DMC in the non-aqueous electrolyte, in wt%; F is the ratio of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte. S represents the mass percentage of silicon in the negative electrode material layer, expressed in wt%.

2. The cylindrical lithium-ion battery as described in claim 1, characterized in that, The cylindrical lithium-ion battery satisfies the following condition: 0.1 ≤ (100 - D) F / S≤7.

5.

3. The cylindrical lithium-ion battery as described in claim 1 or 2, characterized in that, The mass percentage D of DMC in the non-aqueous electrolyte is 55wt%~67wt%.

4. The cylindrical lithium-ion battery as described in claim 1 or 2, characterized in that, The ratio F of the molar content of lithium fluorosulfonylimide to the molar content of LiPF6 in the non-aqueous electrolyte is 0.06~0.

85.

5. The cylindrical lithium-ion battery as described in claim 1 or 2, characterized in that, The mass percentage S of silicon in the negative electrode material layer is 7wt%~15wt%.

6. The cylindrical lithium-ion battery as described in claim 1, characterized in that, The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon composite materials, and silicon alloy materials.

7. The cylindrical lithium-ion battery as described in claim 1, characterized in that, The lithium fluorosulfonylimide is selected from one or more of LiFSI and LiTFSI.

8. The cylindrical lithium-ion battery as described in claim 1 or 7, characterized in that, The total molar content of the lithium salt is 0.9 mol / L to 3.5 mol / L, and 0.012 ≤ F ≤ 1.

9. The cylindrical lithium-ion battery as described in claim 8, characterized in that, The total molar content of the lithium salt is 1.1 mol / L to 1.5 mol / L, and 0.06 ≤ F ≤ 0.

85.

10. The cylindrical lithium-ion battery as described in claim 1, characterized in that, The non-aqueous organic solvents also include one or more of cyclic carbonates, carboxylic esters, and ethers.

11. The cylindrical lithium-ion battery as described in claim 10, characterized in that, The cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propylene carbonate, and butene carbonate; The chain carbonate also includes one or more of diethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate; The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate; The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

12. The cylindrical lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte also includes additives, which are selected from one or more of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate ester compounds and nitrile compounds; the content of the additives is 0.01% to 10% based on the total mass of the non-aqueous electrolyte of 100%.

13. The cylindrical lithium-ion battery as described in claim 12, characterized in that, The cyclic carbonate compound is selected from one or more of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or compounds represented by structural formula 1: Structural Formula 1 In structural formula 1, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group; The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate; The sulfonyl lactone compound is selected from one or more of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone. The phosphate ester compounds are selected from tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and compounds shown in structural formula 2 below: Structural Formula 2 In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; The borate esters are selected from one or more of tris(trimethylsilane)borate and tris(triethylsilane)borate; The nitrile compound is selected from one or more of succinic acid, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

Images