Lithium ion battery

Abstract

The application provides a lithium ion battery, which comprises a positive electrode sheet and a negative electrode sheet, and a diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on one side or both sides of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprises a modified element, the mass content a of the modified element in the positive electrode active material and the air permeability b of the diaphragm satisfy the following relationship: 0.06<=a*b<=5.4 (I), the modified element is selected from metal elements and / or non-metal elements, and the bond energy of the modified element combined with oxygen atoms is greater than the bond energy of nickel elements combined with oxygen atoms. When a and b satisfy the above relationship (I), the cross talk between the positive electrode and the negative electrode can be reduced, the active lithium loss and the side reaction can be reduced, and the lithium ion battery with excellent fast charging performance and cycle life is obtained.

Description

Technical Field

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

[0002] Lithium-ion batteries, as the leading technology in modern rechargeable batteries, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density, long cycle life, and fast charge / discharge capabilities. However, with technological advancements and increasing application demands, the battery industry faces a new challenge: how to improve the fast-charging performance of lithium-ion batteries.

[0003] Improving the fast-charging performance of batteries requires increasing the lithium-ion transport rate within the battery, which places higher demands on the porosity of the separator. The separator, an essential component of lithium-ion batteries, primarily functions to isolate the positive and negative electrodes to prevent short circuits, while simultaneously providing channels for lithium-ion transport. Theoretically, increased porosity can accelerate lithium-ion diffusion in the electrolyte, thereby shortening charging time and improving fast-charging performance. However, with increased porosity, the contact opportunities between the positive and negative electrode active materials and the electrolyte increase, leading to more side reactions. Byproducts from these reactions shuttle between the active materials and the electrolyte, consuming active lithium and reducing battery cycle life.

[0004] Based on this, it is necessary to research and develop a lithium-ion battery that combines excellent fast-charging performance and cycle life. Summary of the Invention

[0005] The main objective of this invention is to provide a lithium-ion battery that solves the problem that improving the fast-charging performance of lithium-ion batteries in the prior art is often accompanied by increased crosstalk between the positive and negative electrodes, making it difficult for lithium-ion batteries to simultaneously have excellent fast-charging performance and cycle life.

[0006] To achieve the above objectives, in one aspect, the present invention provides a lithium-ion battery, which includes a positive electrode and a negative electrode, with a separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on one or both surfaces of the positive current collector. The positive active material layer includes a positive active material, which contains modifying elements. The mass content of the modifying elements in the positive active material and the permeability of the separator satisfy the following relationship:

[0007] 0.06≤a×b≤5.4(I)

[0008] Where 'a' represents the mass content of the modifying element in the positive electrode active material; 'bs / 100mL' represents the air permeability of the membrane; the modifying element is selected from metallic and / or non-metallic elements, and the modifying element is a modifying element whose bond energy with oxygen atoms is greater than that of nickel with oxygen atoms.

[0009] Furthermore, 0.5 ≤ a × b ≤ 3.15.

[0010] Furthermore, a ranges from 0.001 to 0.015.

[0011] Furthermore, a ranges from 0.004 to 0.010.

[0012] Furthermore, b is 50 to 400.

[0013] Furthermore, b is 100 to 350.

[0014] Furthermore, the bond energy between the modified element and the oxygen atom is 400 kJ / mol to 1000 kJ / mol.

[0015] Furthermore, the positive electrode active material includes nickel-cobalt-based ternary materials or lithium iron phosphate.

[0016] Furthermore, the positive electrode active material includes nickel-cobalt-based ternary materials, in which the molar percentage of nickel is 50 mol% to 98 mol%.

[0017] Furthermore, nickel-cobalt-based ternary materials include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0018] Furthermore, nickel-cobalt-based ternary materials include lithium nickel cobalt manganese oxide, which includes single-crystal particles and / or polycrystalline particles.

[0019] Furthermore, lithium nickel cobalt manganese oxide includes monocrystalline particles and polycrystalline particles, with monocrystalline particles accounting for 20wt% to 80wt% by mass.

[0020] Furthermore, the nickel-cobalt-based ternary material contains modifying elements, including one or more of Zr, Al, W, B, Y, Sr, La, Si, Mo, and Ta.

[0021] Furthermore, the modifying elements include Zr, Al, and W.

[0022] Furthermore, the modifying elements also include one or more of B, Y, Sr, La, Si, Mo, and Ta.

[0023] Furthermore, in the nickel-cobalt-based ternary material, the mass percentage content of Zr is 2000ppm to 6000ppm, and / or the mass percentage content of Al is 1000ppm to 3000ppm, and / or the mass percentage content of W is 1000ppm to 3000ppm, and / or the mass percentage content of B, Y, Sr, La, Si, Mo, and Ta is independently 1000ppm to 3000ppm.

[0024] Furthermore, the positive electrode active material includes lithium iron phosphate, which contains modifying elements, including one or more of Ti, V, Mn, Na, Cr, Co, Al, Zr, and Nb.

[0025] Furthermore, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the Dv50 of the negative electrode active material is 8μm to 20μm.

[0026] Furthermore, the negative electrode active material includes silicon-based materials, and 1.5≤a×b≤3.15.

[0027] Furthermore, lithium-ion batteries also include an electrolyte with a viscosity of 1.5 mPa / s to 10 mPa / s at 25°C.

[0028] Furthermore, the viscosity of the electrolyte at 25°C is 3 mPa / s to 5 mPa / s.

[0029] Furthermore, the electrolyte includes a solvent selected from carbonate solvents; and / or, the mass percentage of carbonate solvents in the electrolyte is 75 wt% to 95 wt% of the total mass of the electrolyte.

[0030] Furthermore, carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0031] Furthermore, the lithium-ion battery is a cylindrical battery, and b is 150 to 300; or, the lithium-ion battery is a prismatic battery, and b is 200 to 350.

[0032] By applying the technical solution of this invention, this application achieves a balance between the fast-charging performance and cycle life of lithium-ion batteries by controlling the relationship between the mass content 'a' of the modified elements in the positive electrode active material and the permeability 'b' of the separator. When 'a' and 'b' satisfy the above relationship (I), it can ensure that while improving the fast-charging rate of the lithium-ion battery, crosstalk between the positive and negative electrodes is reduced, active lithium loss and side reactions are reduced, thereby significantly improving the cycle stability of the lithium-ion battery and obtaining a lithium-ion battery with both excellent fast-charging performance and cycle life. Detailed Implementation

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0034] As described in the background section, existing lithium-ion batteries often suffer from increased crosstalk between the positive and negative electrodes while improving their fast-charging performance, making it difficult for lithium-ion batteries to simultaneously achieve excellent fast-charging performance and cycle life. To address this technical problem, one aspect of this application provides a lithium-ion battery comprising a positive electrode and a negative electrode, with a separator disposed between them. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer comprises a positive active material containing modifying elements. The mass content of the modifying elements in the positive active material and the permeability of the separator satisfy the following relationship: 0.06 ≤ a × b ≤ 5.4 (I), where a represents the mass content of the modifying elements in the positive active material; bs / 100mL represents the permeability of the separator; the modifying elements are selected from metallic and / or non-metallic elements, and the modifying elements are those whose bond energy with oxygen atoms is greater than that of nickel with oxygen atoms.

[0035] This application achieves a balance between excellent fast-charging performance and cycle life in lithium-ion batteries by adjusting the relationship between the mass content (a wt%) of modified elements in the positive electrode active material and the permeability (bs / 100mL) of the separator. While reducing the permeability of the separator increases ion transport rate and thus improves fast-charging performance, it also causes byproducts from the positive and negative electrode active materials and electrolyte to migrate between pores, consuming active lithium and reducing cycle life. This application uses positive electrode active materials containing modified elements, which improves crystal stability, reduces byproduct formation, and increases cycle life. However, a high mass content of modified elements in the positive electrode active material makes lithium-ion extraction difficult, and low separator permeability hinders lithium-ion transport, leading to decreased fast-charging performance. This application achieves a balance between fast-charging performance and cycle life by controlling the relationship between the mass content (a) of modified elements in the positive electrode active material and the permeability (b) of the separator.

[0036] The mass content 'a' of modifying elements in positive electrode active materials is closely related to their crystal stability. A smaller 'a' indicates a lower content of modifying elements, resulting in poorer stability of the positive electrode active material. This makes it easier for transition metals to dissolve into the negative electrode, damaging the solid electrolyte interphase (SEI) film and leading to more side reactions with the electrolyte, thus reducing the cycle life of the lithium-ion battery. Conversely, a larger 'a' makes it more difficult for lithium ions to escape during charging and discharging, resulting in decreased fast-charging performance of the lithium-ion battery.

[0037] The higher the porosity of the separator, the better the air permeability; conversely, the higher the air permeability 'b', the worse the air permeability. The air permeability 'b' of the separator is closely related to lithium-ion transport and the contact between the positive electrode material and the electrolyte. Specifically, the smaller 'b' is, the greater the probability of chemical substances in the lithium-ion battery passing through the separator, the more opportunities for contact between the positive and negative electrode active materials and the electrolyte, and the more side reactions occur. This leads to more intense movement of byproducts from the positive and negative electrode active materials and the electrolyte within the pores, consuming active lithium and reducing the cycle life of the lithium-ion battery. Conversely, the larger 'b' is, the more obstructed lithium-ion transport becomes, resulting in lower lithium-ion transport efficiency and a decrease in the fast-charging performance of the lithium-ion battery.

[0038] This application achieves a balance between fast-charging performance and cycle life of lithium-ion batteries by controlling the relationship between the mass content 'a' of modified elements in the positive electrode active material and the permeability 'b' of the separator. If the relationship (I) is too large, the mass content of modified elements in the positive electrode active material is high, making lithium-ion extraction difficult; the permeability of the separator is low, hindering lithium-ion transport and reducing fast-charging performance. If the relationship (I) is too small, the mass content of modified elements in the positive electrode active material is low, making it easier for transition metals to dissolve into the negative electrode, damaging the SEI film; the permeability of the separator is high, increasing side reactions between the electrolyte and the interface, resulting in poor cycle life of the lithium-ion battery. When 'a' and 'b' satisfy the above relationship (I), it is possible to ensure that while improving the fast-charging rate of the lithium-ion battery, active lithium loss and side reactions are reduced, thereby significantly improving the cycle stability of the lithium-ion battery and obtaining a lithium-ion battery with both excellent fast-charging performance and cycle life.

[0039] It should be noted that the positive electrode active material layer is disposed on one or both surfaces of the positive electrode current collector. When disposed on one surface, the positive electrode active material layer is disposed on the surface of the positive electrode current collector closest to the separator; when the positive electrode and negative electrode are stacked (e.g., in cylindrical or prismatic batteries), the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector.

[0040] In a preferred embodiment, 0.5 ≤ a × b ≤ 3.15. Compared to other ranges, when a × b meets the above range, it is beneficial to improve the fast charging performance of lithium-ion batteries, reduce crosstalk between positive and negative electrodes, reduce active lithium loss and side reactions, thereby improving the cycle stability of lithium-ion batteries.

[0041] In a preferred embodiment, a is 0.001 to 0.015. Limiting the mass content 'a' of the modifying element in the positive electrode active material within the above range is beneficial for improving the stability of the positive electrode active material, suppressing side reactions with the electrolyte, and facilitating the extraction of lithium ions, thereby extending the cycle life of the lithium-ion battery and improving its fast-charging performance. Specifically, 'a' can be 0.0010, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015, 0.0016, 0.0017, 0.0018, 0.0019, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045, 0.0050, 0.0055, 0.0060, 0.0065, 0.0070, 0.0075, 0.0080, 0.0085, 0.0090, 0.0095, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, or a range between any two of the above values.

[0042] To further improve the stability of the positive electrode active material, suppress its side reactions with the electrolyte, and further improve lithium ion extraction, thereby extending the cycle life of the lithium-ion battery and improving its fast-charging performance, in a preferred embodiment, 'a' is 0.004 to 0.010. Specifically, 'a' can be 0.004, 0.0045, 0.005, 0.0055, 0.006, 0.0065, 0.007, 0.0075, 0.0080, 0.010, or a range between any two of the above values.

[0043] In a preferred embodiment, b is 50 to 400. Limiting the membrane's permeability (bs / 100mL) within this range helps suppress side reactions between the positive and negative electrode active materials and the electrolyte, improves lithium-ion transport efficiency, and thus extends the cycle life of the lithium-ion battery while improving its fast-charging performance. Specifically, bs / 100mL can be 50s / 100mL, 60s / 100mL, 70s / 100mL, 80s / 100mL, 90s / 100mL, 100s / 100mL, 110s / 100mL, 120s / 100mL, 130s / 100mL, 140s / 100mL, 150s / 100mL, 160s / 100mL, 170s / 100mL, 180s / 100mL, 190s / 100mL, 200s / 100mL, 210s / 100mL, 220s / 100mL, etc. 00mL, 230s / 100mL, 240s / 100mL, 250s / 100mL, 260s / 100mL, 270s / 100mL, 280s / 100mL, 290s / 100mL, 300s / 100mL, 310s / 100mL, 320s / 100mL, 330s / 100mL, 340s / 100mL, 350s / 100mL, 360s / 100mL, 370s / 100mL, 380s / 100mL, 390s / 100mL, or 400s / 100mL.

[0044] In order to further suppress side reactions between the positive and negative electrode active materials and the electrolyte, and to further improve the lithium-ion transport efficiency, thereby improving the fast charging performance of the lithium-ion battery and extending its cycle life, in a preferred embodiment, b is 100-350. Specifically, bs / 100mL can be 100s / 100mL, 105s / 100mL, 110s / 100mL, 115s / 100mL, 120s / 100mL, 125s / 100mL, 130s / 100mL, 135s / 100mL, 140s / 100mL, 145s / 100mL, 150s / 100mL, 155s / 100mL, 160s / 100mL, 165s / 100mL, 170s / 100mL, 175s / 100mL, 180s / 100mL, 185s / 100mL, 190s / 100mL, 195s / 100mL, 200s / 100mL, 205s / 100mL, 210s / 100mL, 215s / 100mL, 220s / 100mL, 230s / 100mL, 240s / 100mL, 250s / 100mL, 260s / 100mL, 270s / 100mL, 280s / 100mL, 290s / 100mL, 300s / 100mL, 310s / 100mL, 320s / 100mL, 330s / 100mL, 340s / 100mL, or 350s / 100mL.

[0045] In a preferred embodiment, the bond energy between the modified element and the oxygen atom is 400 kJ / mol to 1000 kJ / mol. Using modified elements with higher bond energies improves the structural stability of the positive electrode active material, inhibits redox reactions that generate byproducts, and thus extends the battery's cycle life. Specifically, the bond energies of the modified elements bonded to oxygen atoms are: Mo-O 523 kJ / mol, La-O 799 kJ / mol, Al-O 512 kJ / mol, BO 515 kJ / mol, Si-O 452 kJ / mol, Ba-O 562 kJ / mol, Ti-O 662 kJ / mol, WO 530 kJ / mol, Zr-O 760 kJ / mol, Y-O 715 kJ / mol, Sr-O 414 kJ / mol, VO 628 kJ / mol, and Ta-O 680 kJ / mol.

[0046] In a preferred embodiment, the positive electrode active material includes nickel-cobalt-based ternary materials or lithium iron phosphate.

[0047] In a preferred embodiment, the positive electrode active material comprises a nickel-cobalt-based ternary material, wherein the molar percentage of nickel in the positive electrode active material is 50 mol% to 98 mol%. The molar percentage of nickel in the positive electrode active material includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the stability of the positive electrode active material and reducing byproducts generated from the reaction with the electrolyte, thereby improving the cycle life of the lithium-ion battery while ensuring battery energy density. Specifically, the molar percentage of nickel in the positive electrode active material is 50 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol%, 94 mol%, 98 mol%, or any two of the above values.

[0048] In a preferred embodiment, the nickel-cobalt-based ternary material includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0049] Single-crystal particles consist of a single crystal with atoms arranged continuously and orderly in one direction, without grain boundaries. This means that single-crystal particles exhibit high homogeneity and directionality at the microscale, resulting in good consistency in physical and chemical properties. Polycrystalline materials consist of multiple small crystals (grains), each with ordered atomic arrangement, but the atomic arrangement directions differ between grains, which are connected by grain boundaries. Grain boundaries are the main defects in polycrystalline materials, and their presence can affect the material's mechanical, electrical, and electrochemical properties. In a preferred embodiment, the nickel-cobalt-based ternary material includes lithium nickel cobalt manganese oxide, which comprises single-crystal particles and / or polycrystalline particles.

[0050] In a preferred embodiment, lithium nickel cobalt manganese oxide comprises monocrystalline particles and polycrystalline particles, with the mass percentage of monocrystalline particles ranging from 20 wt% to 80 wt%. When lithium nickel cobalt manganese oxide comprises monocrystalline particles and polycrystalline particles, limiting the mass percentage of monocrystalline particles within the aforementioned range is beneficial for leveraging the advantages of high structural stability of monocrystalline materials and good stress resistance of polycrystalline materials. This can increase the compaction density of the positive electrode active material, thereby improving the energy density and cycle life of the lithium-ion battery.

[0051] In a preferred embodiment, the nickel-cobalt-based ternary material includes modifying elements, such as one or more of Zr, Al, W, B, Y, Sr, La, Si, Mo, and Ta. Compared to other types, using the above-mentioned modifying elements is beneficial for further improving the structural stability of the positive electrode active material and further inhibiting its redox reaction to generate byproducts, thereby helping to further extend the cycle life of the battery.

[0052] In order to further improve the structural stability of the positive electrode active material, suppress the redox reaction that generates byproducts, and extend the cycle life of the battery, in a preferred embodiment, the modifying elements include Zr, Al and W.

[0053] In order to further improve the structural stability of the positive electrode active material, suppress the redox reaction that generates byproducts, and extend the cycle life of the battery, in a preferred embodiment, the modifying element also includes one or more of B, Y, Sr, La, Si, Mo, and Ta.

[0054] In a preferred embodiment, in the nickel-cobalt-based ternary material, the mass percentage of Zr is 2000ppm to 6000ppm, and / or the mass percentage of Al is 1000ppm to 3000ppm, and / or the mass percentage of W is 1000ppm to 3000ppm, and / or the mass percentages of B, Y, Sr, La, Si, Mo, and Ta are each independently 1000ppm to 3000ppm. Limiting the mass percentage of modifying elements in the nickel-cobalt-based ternary material within the above range is beneficial for improving the stability of the positive electrode active material, suppressing side reactions with the electrolyte, and facilitating lithium ion extraction, thereby extending the cycle life of the lithium-ion battery and improving its fast-charging performance.

[0055] In a preferred embodiment, the positive electrode active material includes lithium iron phosphate, which contains modifying elements, including one or more of Ti, V, Mn, Na, Cr, Co, Al, Zr, and Nb. Compared to other types, using the above-mentioned modifying elements is beneficial to further improve the structural stability of the positive electrode active material, further suppress its redox reaction to generate byproducts, and thus further extend the cycle life of the battery.

[0056] The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. In this application, the positive electrode binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. This application does not have any particular limitation on the type of positive electrode binder for the positive electrode sheet; in this application, the positive electrode binder can be a conventional choice in the battery field.

[0057] In a preferred embodiment, the weight ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (97.5–98.5):(0.5–1.5):(0.8–1.5). The weight ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the coatability of the positive electrode slurry and for improving the cycle life and fast-charging performance of the lithium-ion battery.

[0058] In a preferred embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material with a Dv50 of 8 μm to 20 μm. The Dv50 of the negative electrode active material includes, but is not limited to, the range described above. Limiting it to this range helps to shorten the ion transport path, improve the fast-charging performance of the lithium-ion battery, and also helps to suppress side reactions, thereby extending the cycle life of the lithium-ion battery.

[0059] In a preferred embodiment, the negative electrode active material comprises a silicon-based material, and 1.5 ≤ a × b ≤ 3.15. When a silicon-based material is used as the negative electrode active material, its specific capacity is high, which helps to improve the fast-charging performance of the lithium-ion battery. In this case, limiting the permeability b of the separator within the above-mentioned range is beneficial to controlling the permeability of the separator within a small range, thereby helping to suppress side reactions, reduce crosstalk between the positive and negative electrodes, and extend the cycle life of the lithium-ion battery.

[0060] In a preferred embodiment, the lithium-ion battery further includes an electrolyte with a viscosity of 1.5 mPa / s to 10 mPa / s at 25°C. The viscosity of the electrolyte includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving lithium-ion transport efficiency and also helps to suppress side reactions between the electrolyte and the interface, thereby improving the fast-charging performance and cycle life of the lithium-ion battery.

[0061] To further improve lithium-ion transport efficiency and suppress side reactions between the electrolyte and the interface, in a preferred embodiment, the viscosity of the electrolyte at 25°C is 3 mPa / s to 5 mPa / s. Specifically, the viscosity of the electrolyte can be 3 mPa / s, 3.5 mPa / s, 4 mPa / s, 4.5 mPa / s, 5 mPa / s, or any two of these values.

[0062] In a preferred embodiment, the electrolyte includes a solvent, which includes, but is not limited to, carbonate solvents. Preferably, the carbonate solvent includes one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Compared to other types, the above-mentioned solvents are less prone to decomposition and heat generation, and facilitate the adjustment of the electrolyte viscosity within a suitable range, thereby improving the fast-charging performance and cycle life of the lithium-ion battery.

[0063] In a preferred embodiment, the solvent content in the electrolyte is 75-95 wt% based on the total mass of the electrolyte. The solvent content in the electrolyte includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving lithium-ion transport efficiency, thereby improving the fast-charging performance of the lithium-ion battery.

[0064] A separator is disposed between the positive and negative electrode plates to separate them and prevent short circuits caused by contact. In a preferred embodiment, the separator includes, but is not limited to, at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. A coating may also be provided on the separator surface, which can be an inorganic coating and / or an organic coating. The inorganic coating includes, but is not limited to, at least one of alumina, silicon oxide, titanium oxide, magnesium oxide, zirconium oxide, alumina ceramic, and boehmite. The organic coating may be at least one of aramid coating and polyvinylidene fluoride (PVDF).

[0065] A cylindrical battery is a rechargeable battery with a cylindrical shape. Its characteristic is that it is made by winding positive and negative electrodes and separators alternately, stacking and winding them into a cylindrical shape, and then encapsulating them in a shell.

[0066] In a preferred embodiment, the lithium-ion battery is a cylindrical battery, and b is 150-300. When the lithium-ion battery is a cylindrical battery, the gap between the positive and negative electrode plates is smaller than that of other types of batteries, and the lithium-ion transport path is relatively shorter. Limiting the value of b within the above range can reduce the permeability of the separator, thereby helping to reduce crosstalk between the positive and negative electrodes and thus extending the cycle life of the lithium-ion battery.

[0067] A prismatic battery is a type of lithium-ion battery with a rectangular or flat shape and a stacked internal structure.

[0068] In a preferred embodiment, the lithium-ion battery is a prismatic battery, and b is 200-350. When the lithium-ion battery is a prismatic battery, the gap between the positive and negative electrode plates is larger than that of other types of batteries, and the lithium-ion transport is relatively slow. Limiting the permeability b of the separator within the above range can increase the permeability of the separator, thereby improving the lithium-ion transport efficiency and thus improving the fast-charging performance of the lithium-ion battery.

[0069] Another aspect of this application provides a method for preparing a lithium-ion battery, the method comprising: step S1, preparing a positive electrode sheet, a negative electrode sheet, and a separator; step S2, sequentially stacking and winding the positive electrode sheet, separator, and negative electrode sheet to obtain a bare cell; or, sequentially stacking the positive electrode sheet, separator, and negative electrode sheet to obtain a bare cell; step S3, placing the bare cell in an outer packaging shell, drying it, and then injecting an electrolyte to obtain a lithium-ion battery. The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector, the positive active material layer comprising a positive active material.

[0070] In a preferred embodiment, the positive electrode active material includes a nickel-cobalt-based ternary material, which includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. The preparation method includes: step SA1, mixing nickel salt, cobalt salt, manganese salt or aluminum salt with water to obtain a metal salt solution; step SA2, adjusting the pH of the metal salt solution to 11-13 and performing a co-precipitation reaction, and drying to obtain a precursor; step SA3, mixing lithium salt, precursor and modified metal source, and calcining to obtain the positive electrode active material; wherein, the modified metal source is an oxide and / or phosphate containing modified elements, and the mass content a of the modified elements in the above-mentioned positive electrode active material and the air permeability b of the separator satisfy the relationship shown in formula (I) above, and a and b have the same definition as the above content.

[0071] In another preferred embodiment, the positive electrode active material includes lithium iron phosphate, which is prepared by a solid-state method, specifically including: (1) mixing and dispersing the iron phosphate precursor, lithium source, carbon source, dopant, and solvent in a certain proportion to obtain slurry 1; (2) milling slurry 1 to obtain slurry 2; (3) spray drying the slurry 2 obtained in step (2) to evaporate the solvent and obtain raw material; preferably, the inlet air temperature is 180-220°C and the feed rate is 25-70 m / s. 3 / h; the outlet air temperature is 80~100℃, (4) the above raw material obtained in step (3) is sintered under an inert atmosphere or a weak reducing atmosphere to obtain sintered material; preferably, the sintering temperature is 700~820℃ and the constant temperature time is 6~12h, (5) the sintered material obtained in step (4) is crushed and depolymerized to obtain lithium iron phosphate; preferably, the crushing pressure is 300~500MPa; the grading frequency is 40~60Hz.

[0072] The lithium-ion battery preparation method of this application achieves a balance between fast-charging performance and cycle life by controlling the relationship between the mass content 'a' of the modified element in the positive electrode active material and the permeability 'b' of the separator. When 'a' and 'b' satisfy the above relationship (I), it can ensure that while improving the fast-charging rate of the lithium-ion battery, crosstalk between the positive and negative electrodes is reduced, active lithium loss and side reactions are reduced, thereby significantly improving the cycle stability of the lithium-ion battery and obtaining a lithium-ion battery with both excellent fast-charging performance and cycle life.

[0073] Moreover, the above-mentioned lithium-ion battery preparation method ensures the stability of the internal structure of the battery and the smooth flow of lithium-ion channels by controlling the stacking or winding of the positive and negative electrode sheets and the separator, which can improve the lithium-ion transport efficiency. The electrolyte injection in a dry environment avoids side reactions caused by moisture, enhances the quality of SEI film formation, and ensures the electrochemical performance and cycle life of the lithium-ion battery.

[0074] In the preparation process of the nickel-cobalt-based ternary material provided in this application, firstly, nickel salt, cobalt salt, manganese salt, or aluminum salt, which provide transition metal elements, are mixed with water; the pH is adjusted within the specific range mentioned above to carry out a co-precipitation reaction, which enables the nickel, cobalt, and manganese elements in the metal salt solution to form their corresponding hydroxides, and after drying, a precursor is obtained; then, lithium salt, the obtained precursor, and modified metal source are mixed and calcined in sequence, so that the modified elements are in situ doped into the lattice of the formed positive electrode active material and / or in situ coated on the surface of the positive electrode active material. In the preparation process of the lithium iron phosphate provided in this application, firstly, the iron phosphate precursor, lithium source, carbon source, dopant, and solvent are mixed and dispersed in a certain proportion to obtain slurry 1; then, slurry 2 is obtained by sand milling; then, spray drying and solvent evaporation are carried out to obtain raw material; finally, high-temperature sintering and pulverization and depolymerization are carried out in sequence to obtain lithium iron phosphate. Compared to undoped or uncoated cathode active materials, the introduction of modifying elements can improve the stability of the crystal structure of cathode active materials, reduce the dissolution of transition metals during charging and discharging, reduce the generation of by-products, and reduce crosstalk between the positive and negative electrodes.

[0075] In a preferred embodiment, in step SA1, the molar ratio of Ni in the nickel salt, Co in the cobalt salt, and Mn in the manganese salt is (50–98):(1–50):(1–50). Compared to other ranges, limiting the molar ratio of Ni, Co, and Mn in each raw material to the above range is beneficial to improving the electrochemical capacity of the positive electrode active material, thereby improving the energy density of the lithium-ion battery.

[0076] In a preferred embodiment, during step SA2, the coprecipitation reaction is stirred at a speed of 200–800 rpm. The stirring speed includes, but is not limited to, the above range; limiting it within this range is beneficial for improving the efficiency of the coprecipitation reaction and increasing the precursor formation rate.

[0077] To improve the efficiency of the coprecipitation reaction and increase the precursor formation rate, the coprecipitation reaction is preferably carried out at a temperature of 50–60°C for 10–36 h.

[0078] In a preferred embodiment, in step SA2, the drying temperature is 80–120°C, and the drying time is 12–20 hours. The drying temperature and time include, but are not limited to, the above ranges. Limiting them to these ranges is beneficial for improving the precursor formation rate and facilitating subsequent doping or coating.

[0079] To reduce the impurity content in the precursor, a washing process is preferably included between the coprecipitation reaction and drying.

[0080] The lithium salts used in the preparation method of the positive electrode active material in this application include, but are not limited to, one or more of LiOH-LiNO3 molten salt, LiOH, and Li2CO3. Compared with other types, using the above-mentioned lithium salts is advantageous.

[0081] In a preferred embodiment, in step SA3, the molar ratio of Li in the lithium salt to the metal element in the precursor is (0.98–1.06):(0.99–1.02). Compared to other ranges, limiting the molar ratio of Li to the metal element in each raw material to the above range is beneficial to improving the electrochemical capacity of the positive electrode active material, thereby improving the energy density of the lithium-ion battery.

[0082] In a preferred embodiment, the mixing process in step SA3 is a ball milling process. This mixing method allows for more uniform mixing of the raw materials, facilitating doping and / or coating.

[0083] In a preferred embodiment, step SA3, the calcination process includes a first holding stage, a second holding stage, and a third holding stage. The temperature of the first holding stage is 500–600°C, and the time is 3–6 hours; the temperature of the second holding stage is 850–950°C, and the time is 3–10 minutes; the temperature of the third holding stage is 780–840°C, and the time is 8–15 hours. Calcination using the above method is beneficial for improving the structural stability of the positive electrode active material, improving its crystal purity, thereby better utilizing its electrochemical capacity, and also helps to suppress the dissolution of transition metals, reduce side reactions, and reduce crosstalk between the positive and negative electrodes.

[0084] In a preferred embodiment, step SA3 further includes a crushing process. Specifically, the positive electrode active material is obtained by crushing after calcination using an air jet mill. Performing air jet milling after calcination helps improve the particle uniformity of the positive electrode active material, while also increasing its specific surface area and improving the contact between the positive electrode active material and the electrolyte. This, in turn, helps improve the insertion and extraction of lithium ions, thereby better utilizing its electrochemical capacity and increasing the energy density of the lithium-ion battery.

[0085] In a preferred embodiment, the Dv50 of the positive electrode active material is 1.5 μm to 20 μm. The Dv50 of the positive electrode active material includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the contact between the positive electrode active material and the electrolyte, thereby improving the insertion and extraction of lithium ions, and thus better utilizing its electrochemical capacity and improving the energy density of the lithium-ion battery.

[0086] In this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, positive electrode conductive agent, positive electrode binder and other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto one side surface of the positive electrode current collector, and after drying, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0087] In this application, the positive electrode binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. This application does not have any particular limitation on the type of positive electrode binder for the positive electrode sheet; the positive electrode binder can be a conventional choice in the battery field. Specifically, the positive electrode binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate.

[0088] The positive electrode conductive agent in this application includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, SuperP), carbon nanotubes, graphene, and carbon nanofibers.

[0089] This application does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0090] In this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, negative electrode conductive agent, negative electrode binder and any other components, in a solvent (e.g., water) to form a negative electrode slurry; coating the negative electrode slurry on one side surface of the negative electrode current collector, and after drying, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0091] This application does not impose specific limitations on the type of negative electrode conductive agent. In a preferred embodiment, as an example, the negative electrode conductive agent may be one or more of natural graphite, acetylene black, and carbon nanotubes.

[0092] This application does not impose specific limitations on the type of negative electrode binder. In a preferred embodiment, as an example, the binder may be one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), polyvinylidene fluoride (PVDF), and polyacrylic acid (PAA).

[0093] This application does not impose specific limitations on the type of negative electrode current collector. In a preferred embodiment, as an example, the negative electrode current collector can be one of the conventional negative electrode current collectors such as copper foil.

[0094] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. As an example, the electrolyte in this application can be any electrolyte suitable for electrochemical energy storage devices in the art. The electrolyte includes an electrolyte and a solvent; the electrolyte typically includes a lithium salt, and additives may also be added to the electrolyte.

[0095] Specifically, the electrolyte includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0096] In a preferred embodiment, as an example, the additive may be a conventional electrolyte additive such as fluoroethylene carbonate (FEC), chloroethylene carbonate (CEC), or vinylene carbonate (VC).

[0097] In a preferred embodiment, the secondary battery further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0098] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0099] It should be noted that the test methods in this application are as follows:

[0100] (1) The test methods for the mass content 'a' of the modifying elements in the positive electrode active material include:

[0101] Test method for modified element content in nickel-cobalt based ternary materials: (1.1) Pretreatment: Discharge the battery to the lower limit voltage of 2.5V at 0.33C, disassemble the empty lithium-ion battery, disassemble the lithium-ion battery to obtain the electrode sheet, soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature for 60min, take it out, and dry it at room temperature with humidity ≤15%; scrape off the positive active material layer on the surface of the positive current collector; (2.1) Test: Accurately weigh 0.5g of positive active material powder, disperse it in 20mL of water, add 10mL of nitric acid, mix evenly and heat it. After the positive active material powder dissolves, dilute the material with water to 100mL to obtain the original solution; dilute the original solution The sample is diluted 20 times to form the test solution for ICP testing. Before testing, a standard solution must be prepared. The linear correlation coefficient of the standard concentration should be above 0.999 to be used as a normal standard. The 1000 mg / L standard solution is diluted with deionized water to different concentrations (generally 0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL). The element detection wavelength is selected, and the experimental conditions are set as follows: Based on the characteristics of the sample and the element to be detected, appropriate ICP instrument operating conditions are set: gas flow rate 0.5 L / min, power 1150 W, and the corresponding test wavelength for the modified element is selected. The mass content of the modified element in the sample is obtained by ICP testing.

[0102] Test method for modified element content in lithium iron phosphate: Discharge the secondary battery at 0.33C to the lower limit voltage of 2.5V, disassemble the battery and remove the positive electrode. Soak it in DMC solution for 4 hours, dry it, and scrape off the positive electrode active material powder from the surface of the electrode with a ceramic knife; accurately weigh 0.5±0.0005g of powder, add 5mL of hydrochloric acid, place it in a dry, clean, and impurity-free quartz crucible, add 5mL of hydrochloric acid, digest at 190℃ for 15min, add 10mL of ultrapure water along the wall of the crucible, digest for another 15min, add 1mL of HNO3 dropwise, digest for 2min, remove and cool to room temperature, transfer the solution to a 50mL centrifuge tube, dilute to the mark with ultrapure water, mix well, and obtain the test solution; Before conducting ICP testing, a standard solution must be prepared. The linear correlation coefficient of the standard concentration must be above 0.999 to be used as a normal standard. The 1000 mg / L standard solution is diluted with deionized water to different concentrations (generally 0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL). The element detection wavelength is selected, and the experimental conditions are set: based on the sample characteristics and the element to be detected, appropriate ICP instrument operating conditions are set: gas flow rate 0.5 L / min, power 1150 W, and the detection wavelength corresponding to the modified element is selected. The mass content of the modified element in the sample is obtained by ICP testing. The standard solution refers to a solution containing the element to be tested, which can be obtained commercially.

[0103] (2) The air permeability b of the separator was tested according to the national standard GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries". Specifically, the secondary battery was discharged at 0.33C to the lower limit voltage of 2.5V, then the empty battery was disassembled, the separator was taken out, soaked in DMC solution for 2 hours, and dried to obtain the separator sample. Using a separator air permeability tester, in an environment with relative humidity <2%RH and 101.3KPa±5KPa, the test instrument applied a pressure of 1.21KPa, and the area through which 100mL of air passed was measured to be 6.45cm². 2 The time required for the diaphragm sample to mature is the air permeability b of the diaphragm.

[0104] (3) Test method for nickel content:

[0105] (3.1) Pretreatment: Discharge the battery to the lower limit voltage of 2.5V at 0.33C, disassemble the empty lithium-ion battery, disassemble the lithium-ion battery to obtain the electrode sheet, soak the positive electrode sheet or negative electrode sheet in DMC (dimethyl carbonate) at room temperature for 4 hours, take it out and dry it at room temperature with humidity ≤15%; scrape off the positive active material layer on the surface of the positive current collector; (3.2) Accurately weigh 0.5g of positive active material powder, disperse it in 20mL of water, add 10mL of nitric acid, mix evenly and heat it. After the positive active material powder dissolves, dilute the material with water to 100mL to obtain the original solution; dilute the original solution 100 times to obtain the test solution. For ICP testing, standard solutions must be prepared before testing. A linear correlation coefficient of 0.999 or higher for the standard concentration is required for normal standard use. The 1000 mg / L standard solution is diluted with deionized water to different concentrations (generally 0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL). The element detection wavelength is selected, and experimental conditions are set: based on the sample characteristics and the element to be detected, appropriate ICP instrument operating conditions are set: gas flow rate 0.5 L / min, power 1150 W, and the element detection wavelength is selected (Ni wavelength 231.604 nm, the element content in the sample is obtained through ICP testing).

[0106] (4) Test method for the ratio of monocrystalline to polycrystalline materials (Q):

[0107] The lithium-ion battery was disassembled to obtain the positive electrode active material as a sample; the SEM image of the sample was taken using a scanning electron microscope, and a 2k magnification image was selected. The number of large polycrystalline particles x and the number of small single crystal particles y were measured respectively, and the compounding ratio Q=x / y.

[0108] (5) Test method for fast charging performance:

[0109] When assembling a lithium-ion battery, a copper wire is added to the negative electrode side as a reference electrode. After assembly, the battery is left to stand for 24 hours, then charged at 0.02C to 4.1V, then charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage to 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 0.33C to 2.5V to complete formation. Then, it was charged at a constant current of 0.33C to 4.25V, followed by constant voltage charging to 0.05C. After resting for 10 minutes, it was discharged at a constant current of 0.33C to 2.5V, completing one cycle of capacity determination. After two cycles, the copper wire was lithium-plated at a rate of 0.02C for 4 hours. Then, 10% of the capacity from the second cycle was charged at a rate of 0.33C, followed by constant current charging at 4C until the negative parameter potential reached 0 or the terminal voltage reached 4.25V. Then, a 0.2C gradient was used for de-leveling charging, with the cutoff condition remaining unchanged, until the charging rate decreased to 0.33C or the capacity reached 80%. Finally, it was charged at a constant current and constant voltage of 0.33C to 4.25V. The test temperature was set to 25℃, and the device signal acquisition frequency was 100ms. After the test, the lithium-ion battery capacity was calculated from 10% to 80%. The charging time required for SOC is denoted as t (in minutes).

[0110] (6) Cycle life test method:

[0111] For the nickel-cobalt-manganese ternary material system, the cycle life test method includes: Capacity setting: The test object is placed in a 25°C chamber, and the test object (the lithium-ion battery prepared in the embodiments and comparative examples of this application) is subjected to the following operations: charged at 0.33C to 4.25V, then charged at constant voltage to the cutoff current of 0.05C; allowed to stand for 30 minutes, then discharged at 0.33C to the lower discharge limit voltage of 2.5V; the above operation is repeated 3 times, and the discharge capacity of the third cycle is taken as the battery's capacity setting; then the following steps are performed; Cyclic performance test: 1) Charged at a constant current rate of 1C to 4.25V, and charged at constant voltage until the current drops to 0.05C; 2) Allowed to stand for 20 minutes; 3) Discharged at a 1C rate to 2.5V; 4) Allowed to stand for 20 minutes, and the cycle test is performed according to steps 1) to 4) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and the number of cycles is recorded.

[0112] For lithium iron phosphate systems, the cycle life test method includes: Capacity setting: Place the test subject in a 25°C chamber (the specific test temperature will be adjusted according to the case), and perform the following operations: charge at 0.33C to the upper limit voltage of 3.65V, then charge at constant voltage to the cutoff current of 0.05C; let stand for 30 minutes, then discharge at 0.33C to the lower limit voltage of 2.5V; repeat the above operation 3 times, and use the discharge capacity of the third cycle as the battery's capacity setting; then proceed to the following steps; Cyclic performance test: At 25°C, perform cycle tests on the lithium-ion batteries prepared in the examples and comparative examples according to the following procedure: 1) Charge at a constant current rate of 1C to 3.65V, and then charge at constant voltage until the current drops to 0.05C; 2) Let stand for 30 minutes; 3) Discharge at a 1C rate to 2.5V; 4) Let stand for 30 minutes, and perform cycle tests according to steps 1) to 4) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0113] Example 1

[0114] (1) Preparation of positive electrode active material:

[0115] Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water in a molar ratio of 94:4:2 to obtain a metal salt solution. The pH of the metal salt solution was adjusted to 12.1, and a coprecipitation reaction was carried out at 55°C with stirring at 500 rpm. After the reaction was completed, the solution was washed with deionized water and dried at 110°C for 12 h to obtain a precursor. This precursor was a hydroxide containing the three metal salts.

[0116] According to the molar ratio Li:M (Ni+Co+Mn) =1.04:1, LiOH-LiNO3 molten salt, precursor, ZrO2, Al2O3, and W3O4 were mixed and ground; the mixture was transferred to a muffle furnace and heated to 500℃, held for 3 hours, then heated to 850℃ and held for 5 minutes, then cooled to 820℃ and held for 10 hours. After cooling to room temperature in the furnace, it was crushed by air jet milling to finally obtain D. V LiNi, a cathode active material doped with modified elements with a diameter of 50 = 3.02 μm. 0.94 Co 0.04 Mn 0.02 O2 (with a nickel molar percentage of 94 mol%, and modified elements being Zr, Al, and W, with Zr content of 2000 ppm, Al content of 1000 ppm, and W content of 1000 ppm); confirmed by SEM to be a single-crystal material.

[0117] (2) Preparation of the positive electrode:

[0118] The positive electrode active material LiNi doped with modified elements obtained in step (1) was prepared at a mass ratio of 98:1:1. 0.94 Co0.04 Mn 0.02 O2, acetylene black, and PVDF are mixed, and NMP solvent is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is coated on one side of an aluminum foil and dried at 80°C. Then it is coated on the other side in sequence, dried at room temperature, and transferred to an oven for further drying. Finally, it is cold-pressed and slit to obtain a positive electrode sheet.

[0119] (3) Preparation of negative electrode:

[0120] Natural graphite (D) was mixed in a mass ratio of 96.4:1:1.2:1.4. 50 =12μm), SP, CMC, and SBR are mixed evenly and dispersed in deionized water to obtain a negative electrode slurry; the negative electrode slurry is coated onto one side of a copper foil and dried at 80℃, then coated onto the other side and dried at 80℃, resulting in an areal density of 185g / m². 2 After rolling and compaction, the density is 1.55 g / cm³. 3 The negative electrode sheet is obtained by cutting.

[0121] (4) Preparation of electrolyte:

[0122] EC, EMC, and DEC were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a molar concentration of 1 mol / L.

[0123] (5) Preparation of the diaphragm:

[0124] A PE base film with an alumina coating on one side was used as the separator, wherein the alumina coating thickness was 1.8 μm and the total coating weight on one side was 3.24 g / m. 2 The PE base film thickness is 7.8μm;

[0125] (6) Assembly and formation of lithium-ion batteries:

[0126] 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 cells are then wound to obtain a bare cell. The winding tension during the winding process is 180N, and the winding speed is 200mm / s.

[0127] The bare cell is placed in an outer packaging shell, dried, and then injected with an electrolyte with a viscosity of 2.3 mPa / s (1.0 mol / L LiPF6, with the solvent being EC, EMC, and DEC in a volume ratio of 1:1:1). After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0128] Example 2

[0129] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 3000 ppm, the content of Al is 1000 ppm, and the content of W is 1000 ppm; In step (5), the base film thickness is 7.0 μm, the alumina coating thickness is 1.6 μm, and the total coating amount of the single-sided alumina coating is 2.88 g / m². 2 .

[0130] Example 3

[0131] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 3000 ppm, the content of Al is 2000 ppm, and the content of W is 1000 ppm; In step (5), the base film thickness is 8.8 μm, the alumina coating thickness is 2.3 μm, and the total coating amount of the single-sided alumina coating is 4.14 g / m. 2 .

[0132] Example 4

[0133] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 3000 ppm, the content of Al is 2000 ppm, and the content of W is 2000 ppm; In step (5), the thickness of the base film is 10.3 μm, the thickness of the alumina coating is 3.3 μm, and the total coating amount of the single-sided alumina coating is 5.94 g / m. 2 .

[0134] Example 5

[0135] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 4000 ppm, the content of Al is 3000 ppm, and the content of W is 2000 ppm; In step (5), the thickness of the base film is 8.9 μm, the thickness of the alumina coating is 2.4 μm, and the total coating amount of the single-sided alumina coating is 4.32 g / m. 2 .

[0136] Example 6

[0137] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 5000 ppm, the content of Al is 3000 ppm, and the content of W is 2000 ppm; in step (5), the thickness of the base film is 9.2 μm, the thickness of the alumina coating is 2.55 μm, and the total coating amount of the single-sided alumina coating is 4.59 g / m. 2 .

[0138] Example 7

[0139] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and Sr, wherein the content of Zr is 4000 ppm, the content of Al is 1000 ppm, and the content of Sr is 1000 ppm; in step (5), the thickness of the base film is 8.4 μm, the thickness of the alumina coating is 2.1 μm, and the total coating amount of the single-sided alumina coating is 3.78 g / m. 2 .

[0140] Example 8

[0141] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and Si, wherein the content of Zr is 4000 ppm, the content of Al is 3000 ppm, and the content of Si is 1000 ppm; In step (5), the base film thickness is 9.0 μm, the alumina coating thickness is 2.4 μm, and the total coating amount of the single-sided alumina coating is 4.32 g / m. 2 .

[0142] Example 9

[0143] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 2000 ppm, the content of Al is 500 ppm, and the content of W is 300 ppm; In step (5), the thickness of the base film is 11.4 μm, the thickness of the alumina coating is 3.6 μm, and the total coating amount of the single-sided alumina coating is 6.48 g / m 2 .

[0144] Example 10

[0145] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and Y, wherein the content of Zr is 7000 ppm, the content of Al is 3500 ppm, and the content of Y is 3500 ppm; In step (5), the base film thickness is 6.3 μm, the alumina coating thickness is 1.5 μm, and the total coating amount of the single-sided alumina coating is 2.7 g / m². 2 .

[0146] Example 11

[0147] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 4000 ppm, the content of Al is 3000 ppm, and the content of W is 2500 ppm; In step (5), the base film thickness is 9.8 μm, the alumina coating thickness is 3.15 μm, and the total coating amount of the single-sided alumina coating is 5.67 g / m. 2 .

[0148] Example 12

[0149] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 2000 ppm, the content of Al is 1000 ppm, and the content of W is 1000 ppm; in step (5), the base film thickness is 7.5 μm, the alumina coating thickness is 1.7 μm, and the total coating amount of the single-sided alumina coating is 3.06 g / m. 2 .

[0150] Example 13

[0151] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and Si, wherein the content of Zr is 2500 ppm, the content of Al is 1000 ppm, and the content of Si is 1000 ppm; In step (5), the thickness of the base film is 7.2 μm, the thickness of the alumina coating is 1.65 μm, and the total coating amount of the single-sided alumina coating is 2.97 g / m. 2 .

[0152] Example 14

[0153] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 500 ppm, the content of Al is 300 ppm, and the content of W is 200 ppm; In step (5), the base film thickness is 5.7 μm, the alumina coating thickness is 1.1 μm, and the total coating amount of the single-sided alumina coating is 1.98 g / m. 2 .

[0154] Example 15

[0155] The difference from Example 1 is as follows: In step (1), the positive electrode active material includes single-crystal particles and polycrystalline particles, and the mass percentage of single-crystal particles is 80wt%; the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 1000ppm, the content of Al is 500ppm, and the content of W is 500ppm; in step (5), the thickness of the base film is 5.0μm, the thickness of the alumina coating is 1.0μm, and the total coating amount of the single-sided alumina coating is 1.8g / m 2 .

[0156] Example 16

[0157] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 1500 ppm, the content of Al is 1000 ppm, and the content of W is 500 ppm; In step (5), the base film thickness is 6.3 μm, the alumina coating thickness is 1.5 μm, and the total coating amount of the single-sided alumina coating is 2.7 g / m². 2 .

[0158] Example 17

[0159] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 6000 ppm, the content of Al is 3000 ppm, and the content of W is 3000 ppm; in step (5), the thickness of the base film is 11.4 μm, the thickness of the alumina coating is 3.6 μm, and the total coating amount of the single-sided alumina coating is 6.48 g / m. 2 .

[0160] Example 18

[0161] The difference from Example 1 is as follows: In step (1), the positive electrode active material includes single-crystal particles and polycrystalline particles, and the mass percentage of single-crystal particles is 50wt%; the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 6000ppm, the content of Al is 2500ppm, and the content of W is 2000ppm; in step (5), the thickness of the base film is 11.9μm, the thickness of the alumina coating is 3.95μm, and the total coating amount of the single-sided alumina coating is 7.11g / m 2 .

[0162] Example 19

[0163] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 3000 ppm, the content of Al is 1000 ppm, and the content of W is 1000 ppm; in step (5), the thickness of the base film is 11.0 μm, the thickness of the alumina coating is 3.5 μm, and the total coating amount of the single-sided alumina coating is 6.3 g / m. 2 .

[0164] Example 20

[0165] The difference from Example 1 is that in step (1), the positive electrode active material is LiNi. 0.7 Co 0.2 Mn 0.1O2, the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 500 ppm, the content of Al is 500 ppm, and the content of W is 200 ppm; in step (5), the thickness of the base film is 5.0 μm, the thickness of the alumina coating is 1.0 μm, and the total coating amount of the single-sided alumina coating is 1.8 g / m 2 .

[0166] Example 21

[0167] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 500 ppm, the content of Al is 500 ppm, and the content of W is 200 ppm; In step (5), the thickness of the base film is 11.9 μm, the thickness of the alumina coating is 3.95 μm, and the total coating amount of the single-sided alumina coating is 7.11 g / m 2 .

[0168] Example 22

[0169] The difference from Example 1 is that in step (1), the positive electrode active material is LiNi. 0.7 Co 0.2 Mn 0.1 O2, the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 8000 ppm, the content of Al is 4000 ppm, and the content of W is 3000 ppm; in step (5), the thickness of the base film is 10.6 μm, the thickness of the alumina coating is 3.4 μm, and the total coating amount of the single-sided alumina coating is 6.12 g / m 2 .

[0170] Example 23

[0171] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Mg, and Y, wherein the content of Zr is 2000 ppm, the content of Mg is 500 ppm, and the content of Y is 500 ppm; In step (5), the base film thickness is 5.8 μm, the alumina coating thickness is 1.2 μm, and the total coating amount of the single-sided alumina coating is 2.16 g / m 2 .

[0172] Example 24

[0173] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, B, W, and Y, wherein the content of Zr is 6000 ppm, the content of Al is 2000 ppm, the content of B is 1000 ppm, the content of W is 2000 ppm, and the content of Y is 1000 ppm; In step (5), the thickness of the base film is 11.9 μm, the thickness of the alumina coating is 3.95 μm, and the total coating amount of the single-sided alumina coating is 7.11 g / m 2 .

[0174] Example 25

[0175] (1) Preparation of positive electrode active material:

[0176] Ferric phosphate precursor (Fe / P ratio 0.960:1), lithium carbonate, glucose, PEG, phosphoric acid, and water were mixed and dispersed in a mass ratio of 100:25:7:4.5:0.8:204, and titanium dioxide was added as a dopant to obtain a first slurry. The first slurry was then milled to obtain a second slurry with a D50 of 400 nm. The second slurry was then spray-dried at an inlet air temperature of 200°C and a feed rate of 50 m / s. 3 / h, with an outlet air temperature of 100℃, after solvent evaporation, a raw material with a D50 of 40μm is obtained; the raw material is sintered under a nitrogen atmosphere at a temperature of 800℃ for 8h to obtain a sintered material; the sintered material is then pulverized and depolymerized at a pulverizing pressure of 450MPa and a grading frequency of 50Hz to obtain lithium iron phosphate doped with Ti (with a Ti content of 1000ppm).

[0177] (2) Preparation of the positive electrode:

[0178] The lithium iron phosphate, acetylene black and PVDF obtained in step (1) were mixed in a mass ratio of 98:1:1. NMP solvent was added and the mixture was stirred in a vacuum mixer until the system was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated on one side of an aluminum foil and dried at 80°C. Then it was coated on the other side in sequence, dried at room temperature and transferred to an oven for further drying. The positive electrode sheet was then obtained by cold pressing and slitting.

[0179] (3) Preparation of negative electrode:

[0180] Natural graphite (D) was mixed in a mass ratio of 96.4:1:1.2:1.4. 50 =12μm), SP, CMC, and SBR are mixed evenly and dispersed in deionized water to obtain a negative electrode slurry; the negative electrode slurry is coated onto one side of a copper foil and dried at 80℃, then coated onto the other side and dried at 80℃, resulting in an areal density of 185g / m². 2After rolling and compaction, the density is 1.55 g / cm³. 3 The negative electrode sheet is obtained by cutting.

[0181] (4) Preparation of electrolyte:

[0182] EC, EMC, and DEC were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a molar concentration of 1 mol / L.

[0183] (5) Preparation of the diaphragm:

[0184] A PE base film with an alumina coating on one side was used as the separator, wherein the alumina coating thickness was 1.1 μm and the total coating weight of the alumina coating on one side was 1.98 g / m. 2 The PE base film thickness is 5.7μm;

[0185] (6) Assembly and formation of lithium-ion batteries:

[0186] 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 cells are then wound to obtain a bare cell. The winding tension during the winding process is 180N, and the winding speed is 200mm / s.

[0187] The bare cell is placed in an outer packaging shell, dried, and then injected with an electrolyte with a viscosity of 2.3 mPa / s (1.0 mol / L LiPF6, with the solvent being EC, EMC, and DEC in a volume ratio of 1:1:1). After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0188] Example 26

[0189] The difference from Example 31 is that: in step (1), the dopants are titanium dioxide and vanadium pentoxide, and the modifying elements in the positive electrode active material include Ti and V, wherein the content of Ti is 8000 ppm and the content of V is 3000 ppm; in step (5), the base film thickness is 12.0 μm, the alumina coating thickness is 4.0 μm, and the total coating amount of the single-sided alumina coating is 7.2 g / m 2 .

[0190] Example 27

[0191] The difference from Example 1 is as follows: In step (1), the positive electrode active material includes single-crystal particles and polycrystalline particles, and the mass percentage of single-crystal particles is 20wt%; the modifying elements in the positive electrode active material include Zr, Al and W, wherein the content of Zr is 500ppm, the content of Al is 300ppm, and the content of W is 100ppm; in step (5), the thickness of the base film is 12.7μm, the thickness of the alumina coating is 4.1μm, and the total coating amount of the single-sided alumina coating is 7.38g / m 2 .

[0192] Example 28

[0193] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, B, W, and Y, wherein the content of Zr is 6000 ppm, the content of Al is 3200 ppm, the content of W is 3000 ppm, the content of B is 2000 ppm, and the content of Y is 1000 ppm; In step (5), the thickness of the base film is 10.3 μm, the thickness of the alumina coating is 3.3 μm, and the total coating amount of the single-sided alumina coating is 5.94 g / m 2 .

[0194] Comparative Example 1

[0195] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 8000 ppm, the content of Al is 4000 ppm, and the content of W is 3000 ppm; in step (5), the thickness of the base film is 11.9 μm, the thickness of the alumina coating is 3.95 μm, and the total coating amount of the single-sided alumina coating is 7.11 g / m 2 .

[0196] Comparative Example 2

[0197] The difference from Example 1 is as follows: In step (1), the positive electrode active material includes single-crystal particles and polycrystalline particles, and the mass percentage of single-crystal particles is 10wt%; the modifying elements in the positive electrode active material include Zr and Al, wherein the content of Zr is 800ppm and the content of Al is 200ppm; in step (5), the base film thickness is 5.0μm, the alumina coating thickness is 1.0μm, and the total coating amount of the single-sided alumina coating is 1.8g / m 2 .

[0198] Comparative Example 3

[0199] The difference from Example 25 is that: in step (1), the content of the modified element Ti in the positive electrode active material is 1000 ppm; in step (5), the base film thickness is 5.5 μm, the alumina coating thickness is 1.1 μm, and the total coating amount of the single-sided alumina coating is 1.98 g / m.2 .

[0200] Comparative Example 4

[0201] The difference from Example 1 is as follows: In step (1), the modifying elements in the positive electrode active material include Zr, Al, and W, wherein the content of Zr is 700 ppm, the content of Al is 200 ppm, and the content of W is 1000 ppm; In step (5), the thickness of the base film is 4.3 μm, the thickness of the alumina coating is 0.9 μm, and the total coating amount of the single-sided alumina coating is 1.62 g / m. 2 .

[0202] Comparative Example 5

[0203] The difference from Example 25 is that: in step (1), the dopants are titanium dioxide and vanadium pentoxide, and the modifying elements in the positive electrode active material include Ti and V, wherein the content of Ti is 6000 ppm and the content of V is 200 ppm; in step (5), the base film thickness is 4.3 μm, the alumina coating thickness is 0.9 μm, and the total coating amount of the single-sided alumina coating is 1.62 g / m. 2 .

[0204] The microstructure of the positive electrode active material, the mass content a of the modified element in the positive electrode active material, the air permeability b of the separator, the formula value of a×b, the fast charging performance and capacity retention of the lithium-ion battery in all the above embodiments and comparative examples of this application are shown in Tables 1-1 and 1-2.

[0205] Table 1-1

[0206]

[0207] Table 1-2

[0208]

[0209] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0210] Comparing Example 1 with Comparative Examples 1, 2, and 4, it can be seen that the fast-charging performance and cycle life of the lithium-ion batteries prepared in Comparative Examples 1, 2, and 4 are all worse than those in Example 1. In Comparative Example 1, the relationship shown in formula (I) exceeds the upper limit of the above range, indicating a low mass content of modified elements in the positive electrode active material, easy dissolution of transition metals into the negative electrode, damage to the SEI film, high membrane permeability, increased side reactions between the electrolyte and the interface, and poor cycle life of the lithium-ion battery. In Comparative Examples 2 and 4, the relationship shown in formula (I) exceeds the lower limit of the above range, indicating a high mass content of modified elements in the positive electrode active material, difficulty in lithium-ion extraction, low membrane permeability, hindering lithium-ion transport, and decreased fast-charging performance.

[0211] Comparing Examples 25 and 26 with Comparative Examples 3 and 5, it can be seen that the fast-charging performance and cycle life of the lithium-ion batteries prepared in Comparative Examples 3 and 5 are worse than those of Examples 25 and 26. The relationship shown in Equation (I) in Comparative Examples 3 and 5 exceeds the lower limit of the above range, indicating a high mass content of modified elements in the positive electrode active material, making lithium ion extraction difficult, low permeability of the separator, hindering lithium ion transport, and reducing fast-charging performance.

[0212] This application achieves a balance between fast-charging performance and cycle life of lithium-ion batteries by controlling the relationship between the mass content 'a' of the modified elements in the positive electrode active material and the permeability 'b' of the separator. When 'a' and 'b' satisfy the above relationship (I), it ensures that while improving the fast-charging rate of the lithium-ion battery, crosstalk between the positive and negative electrodes is reduced, active lithium loss and side reactions are reduced, thereby significantly improving the cycle stability of the lithium-ion battery and obtaining a lithium-ion battery with both excellent fast-charging performance and cycle life.

[0213] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0214] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode and a negative electrode, wherein a separator is disposed between the positive electrode and the negative electrode, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on one or both surfaces of the positive current collector. The positive active material layer includes a positive active material containing modifying elements. The mass content of the modifying elements in the positive active material and the air permeability of the membrane satisfy the following relationship: 0.06≤a×b≤5.4(I) Wherein, a represents the mass content of the modified element in the positive electrode active material; bs / 100mL represents the air permeability of the membrane; the modified element is selected from metallic elements and / or non-metallic elements, and the modified element is a modified element whose bond energy with oxygen atoms is greater than the bond energy between nickel and oxygen atoms.

2. The lithium-ion battery according to claim 1, characterized in that, 0.5≤a×b≤3.

15.

3. The lithium-ion battery according to claim 1, characterized in that, The value of a is 0.001 to 0.

015.

4. The lithium-ion battery according to claim 3, characterized in that, The value of a is 0.004 to 0.

010.

5. The lithium-ion battery according to claim 1, characterized in that, The value of b is 50 to 400.

6. The lithium-ion battery according to claim 4, characterized in that, The value of b is 100 to 350.

7. The lithium-ion battery according to claim 1, characterized in that, The bond energy between the modified element and the oxygen atom is 400 kJ / mol to 1000 kJ / mol.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes nickel-cobalt-based ternary materials or lithium iron phosphate.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode active material includes a nickel-cobalt based ternary material, wherein the molar percentage of nickel in the positive electrode active material is 50 mol% to 98 mol%.

10. The lithium-ion battery according to claim 8, characterized in that, The nickel-cobalt-based ternary materials include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

11. The lithium-ion battery according to claim 10, characterized in that, The nickel-cobalt-based ternary material includes lithium nickel cobalt manganese oxide, which comprises single-crystal particles and / or polycrystalline particles.

12. The lithium-ion battery according to claim 11, characterized in that, The lithium nickel cobalt manganese oxide includes single crystal particles and polycrystalline particles, with the single crystal particles accounting for 20wt% to 80wt% by mass.

13. The lithium-ion battery according to claim 8, characterized in that, The nickel-cobalt-based ternary material includes the modifying element, which includes one or more of Zr, Al, W, B, Y, Sr, La, Si, Mo, and Ta.

14. The lithium-ion battery according to claim 13, characterized in that, The modifying elements include Zr, Al, and W.

15. The lithium-ion battery according to claim 14, characterized in that, The modifying elements also include one or more of B, Y, Sr, La, Si, Mo, and Ta.

16. The lithium-ion battery according to claim 15, characterized in that, In the nickel-cobalt-based ternary material, the mass percentage content of Zr is 2000ppm to 6000ppm, and / or the mass percentage content of Al is 1000ppm to 3000ppm, and / or the mass percentage content of W is 1000ppm to 3000ppm, and / or the mass percentage content of B, Y, Sr, La, Si, Mo, and Ta is each independently 1000ppm to 3000ppm.

17. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes lithium iron phosphate, and the lithium iron phosphate contains the modifying element, which includes one or more of Ti, V, Mn, Na, Cr, Co, Al, Zr, and Nb.

18. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the Dv50 of the negative electrode active material is 8μm to 20μm.

19. The lithium-ion battery according to claim 18, characterized in that, The negative electrode active material includes silicon-based materials, and 1.5 ≤ a × b ≤ 3.

15.

20. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery also includes an electrolyte, the viscosity of which is 1.5 mPa / s to 10 mPa / s at 25°C.

21. The lithium-ion battery according to claim 20, characterized in that, The electrolyte includes a solvent selected from carbonate solvents; and / or, based on the total mass of the electrolyte, the carbonate solvent content in the electrolyte is 75wt% to 95wt%.

22. The lithium-ion battery according to claim 21, characterized in that, The carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

23. The lithium-ion battery according to any one of claims 1 to 22, characterized in that, The lithium-ion battery is a cylindrical battery, and b is 150 to 300; or, the lithium-ion battery is a prismatic battery, and b is 200 to 350.

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