Lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and provides a lithium ion battery, which comprises a negative plate and an electrolyte, the negative plate comprises a negative active material, the negative active material comprises a graphite matrix and a coating layer, and the coating layer comprises an amorphous carbon material; the electrolyte comprises a carbonic ester additive and a chalcogenide additive; based on the total mass of the electrolyte, the mass ratio of the carbonic ester additive is 0.01%-8%, and the mass ratio of the sulfur additive is 0.01%-3%; the mass ratio of the carbonic ester additive to the sulfur additive is 0.3-300. In the lithium ion battery, the negative electrode active material used by the negative electrode is the graphite matrix surface coated amorphous carbon material, so that the low-temperature charging performance of the battery can be improved. Meanwhile, the carbonic ester additive and the sulfur additive are added into the electrolyte, so that the reaction activity of the negative electrode active material can be reduced, side reactions are reduced, the high-temperature performance of the battery is improved, and the battery has high and low temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields due to their advantages such as high specific energy, no memory effect and long cycle life. In the field of energy storage, lithium-ion batteries are an electrochemical energy storage device that converts electrical energy into chemical energy during charging and chemical energy into electrical energy during discharge. The normal use temperature of lithium-ion batteries is ≥25°C, but when used in low-temperature scenarios (below 0°C), lithium deposition will pierce the diaphragm and cause a short circuit in the battery, causing fire, explosion and other safety issues. At present, the energy storage field mainly adds additional heating systems during PACK design to enable lithium-ion batteries to work normally at low temperatures, but this brings huge costs, so there is an urgent need to develop a lithium-ion battery that can take both high and low temperatures into account. Summary of the invention

[0003] The purpose of the present invention is to overcome the above problems existing in the prior art and provide a lithium ion battery, in which the negative electrode active material used in the negative electrode is a graphite substrate surface coated with an amorphous carbon material, which can improve the low temperature charging performance of the battery. At the same time, adding carbonate additives and sulfur additives to the electrolyte can reduce the reaction activity of the negative electrode active material, reduce side reactions, improve the high temperature performance of the battery, and make the battery have both high and low temperature performance.

[0004] In order to achieve the above-mentioned object, the present invention provides a lithium-ion battery in a first aspect, the battery comprising a negative electrode sheet and an electrolyte;

[0005] The negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a graphite matrix and a coating layer, and the coating layer comprises an amorphous carbon material;

[0006] The electrolyte comprises a carbonate additive and a sulfur additive; based on the total mass of the electrolyte, the mass proportion of the carbonate additive is 0.01%-8%, and the mass proportion of the sulfur additive is 0.01%-3%; the mass ratio of the carbonate additive to the sulfur additive is 0.3-300.

[0007] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0008] In the lithium-ion battery provided by the present invention, the negative electrode active material is a graphite matrix surface coated with an amorphous carbon material, which can improve the low-temperature charging performance of the battery; at the same time, adding carbonate additives and sulfur additives to the electrolyte can reduce the reaction activity of the negative electrode active material, reduce side reactions, and improve the high-temperature performance of the battery, so that the battery has both high and low temperature performance.

[0009] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In this article, unless otherwise specified, data ranges include endpoints. Detailed Embodiments

[0010] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0011] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention pertains.

[0012] In a first aspect of the present invention, a lithium-ion battery is provided. The battery includes a negative electrode sheet and an electrolyte;

[0013] The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes a graphite matrix and a coating layer, and the coating layer includes an amorphous carbon material;

[0014] The electrolyte includes a carbonate additive and a sulfur-based additive; based on the total mass of the electrolyte, the mass ratio of the carbonate additive is 0.01% - 8%, and the mass ratio of the sulfur-based additive is 0.01% - 3%; the mass ratio of the carbonate additive to the sulfur-based additive is 0.3 - 300.

[0015] In some embodiments, the mass ratio of the carbonate additive to the sulfur-based additive is 0.3 - 300. For example, the mass ratio can be 0.3, 0.33, 0.67, 1, 5, 8, 9, 10, 12, 15, 18, 20, 25, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, or any point value within the range formed by any two of the above point values.

[0016] In some embodiments, based on the total mass of the electrolyte, the mass ratio of the carbonate additive is 0.01% - 8%. For example, it can be 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any point value within the range formed by any two of the above point values.

[0017] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the chalcogen-based additive is 0.01% - 3%, for example, it can be 0.01%, 0.1%, 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3% or any value within the range formed by any two of the above values.

[0018] In the present invention, among the anode active materials used for the anode, the graphite matrix has anisotropy, with large impedance and polarization during low-temperature charging. Coating the surface of the graphite matrix with an amorphous carbon material can increase its lithium-ion insertion active sites, enhance the isotropy of the graphite matrix, and can greatly reduce the lithium-ion insertion impedance and improve the low-temperature charging performance of the graphite matrix. However, coating the surface of the graphite matrix with an amorphous carbon material will result in strong electrochemistry reaction activity and an increase in side reactions of the electrolyte, generating more by-products at high temperatures, which affect the stability of the solid electrolyte interface (SEI) film, consume more lithium ions and electrolyte components, and deteriorate the high-temperature performance of the battery. To compensate for and improve the high-temperature performance of the battery, a carbonate-based additive and a chalcogen-based additive are added to the electrolyte of the present invention. The carbonate-based additive forms a polycarbonate organic component on the anode surface, improving the conductivity and stability of the SEI film, but the formed film is thicker and has a larger impedance; the chalcogen-based additive forms a sulfite component (such as Li2O, Li2SO3) at the anode interface, improving the stability of the SEI film, and the formed film is thinner and has a lower impedance; when adjusting the addition content and mass ratio of the carbonate-based additive and the chalcogen-based additive within a specific range, an SEI film component composed of organic and inorganic components is formed on the anode surface, which can make the SEI film have high ionic conductivity and stability, can reduce the reaction activity of the anode active material, reduce side reactions of the electrolyte, improve the high-temperature performance of the battery, and enable the battery to take into account both high and low temperature performances.

[0019] In some embodiments, the mass ratio of the carbonate-based additive to the chalcogen-based additive is 5 - 25, for example, the mass ratio can be 5, 8, 10, 12, 15, 18, 20, 25 or any value within the range formed by any two of the above values.

[0020] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the carbonate-based additive is 1% - 5%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any value within the range formed by any two of the above values.

[0021] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the chalcogen-based additive is 0.2% - 1.5%, for example, it can be 0.2%, 0.4%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5% or any value within the range formed by any two of the above values.

[0022] The present invention further preferably controls the contents of the carbonate additive and the sulfur-based additive, as well as their mass ratio, which can further optimize the components of the organic layer and the inorganic layer in the SEI film interface, better improve the ionic conductivity and stability of the SEI film, reduce the reactivity of the negative electrode active material, and make the battery perform better at both high and low temperatures.

[0023] The type of the carbonate additive is not specifically limited, and carbonate additives commonly used in the field of lithium batteries can be selected. For example, in some embodiments, the carbonate additive includes at least one of vinylene carbonate (VC), ethylene vinylene carbonate (VEC), fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate (TFEC), 1,2-difluoroethylene carbonate (DFEC), and bis(ethylene carbonate) (bis-EC). The present invention further preferably selects the type of the carbonate additive, which can form a polycarbonate organic component on the surface of the negative electrode, improve the conductivity and stability of the SEI film, facilitate reducing the reactivity of the negative electrode active material, reducing side reactions, and improving the high-temperature performance of the battery.

[0024] The type of the sulfur-based additive is not specifically limited, and sulfur-based additives (i.e., additives containing S element) commonly used in the field of lithium batteries can be selected. In some embodiments, the sulfur-based additive includes one or more of the following compounds:

[0025]

[0026]

[0027] The present invention further preferably selects the type of the sulfur-based additive, which can form an inorganic sulfite component on the surface of the negative electrode, facilitate reducing the impedance at the SEI film interface and improving the stability of the SEI film, reducing the reactivity of the negative electrode active material, reducing side reactions, and improving the high-temperature performance of the battery.

[0028] In some embodiments, the electrolyte further includes a lithium salt additive. Based on the total mass of the electrolyte, the mass percentage of the lithium salt additive is 0.01% - 1%, for example, it can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or any point value within the range composed of the above two values, preferably 0.1% - 1%. Preferably, the lithium salt additive includes at least one of lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium difluoro(oxalato)phosphate (LiODFP), lithium tetrafluoroborate (LiBF4), and lithium tetrafluoro(oxalato)phosphate (LiTFOP). The present invention further introduces a lithium salt additive into the electrolyte and adjusts the content and type of the lithium salt additive, which can increase the inorganic components at the negative electrode interface. The binding energy between the inorganic components and lithium ions is smaller, reducing the lithium ion migration resistance, lowering the polarization internal resistance, improving the ionic conductivity of the electrolyte, improving the properties of the positive electrode interface film and / or the negative electrode interface film, and helping to construct a stable and low-impedance positive electrode interface film and / or negative electrode interface film, thereby effectively reducing the decomposition of the electrolyte and further improving the power performance and low-temperature performance of the battery.

[0029] In some embodiments, the mass ratio of the total mass of the carbonate additive and the lithium salt additive to the mass of the chalcogen additive is 0.5 - 200, for example, it can be 0.5, 1, 1.2, 5, 8, 9, 10, 12, 15, 18, 20, 25, 50, 65, 80, 100, 120, 150, 180, 200 or any point value within the range composed of the above two values, preferably 1.2 - 65. Further preferably, when the mass ratio of the total mass of the carbonate additive and the lithium salt additive to the mass of the chalcogen additive is within the above range, it can further optimize the formation of organic and inorganic components on the negative electrode surface, which can not only enhance the stability of the negative electrode interface, reduce the reaction activity of the negative electrode active material, reduce side reactions, and improve the high-temperature performance of the battery; but also promote the lithium ion transport of the positive electrode interface film and / or the negative electrode interface film, improve the low-temperature performance of the battery, and make the battery have better high and low temperature comprehensive performance.

[0030] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI). Based on the total mass of the electrolyte, the mass fraction of the lithium salt is 2.5%-20%, such as 2.5%, 3.5%, 5.5%, 6.5%, 8.5%, 10.5%, 12.5%, 13.5%, 14.5%, 15.5%, 16.5%, 17.5%, 18.5%, 20%, or any value within the range formed by any two of the above values. When a lithium salt is added to the electrolyte and the content of the lithium salt is adjusted within the above range, the ionic conductivity of the lithium-ion battery is improved, and the cycle performance of the battery is enhanced.

[0031] In some embodiments, the electrolyte further includes a silicon-containing additive, that is, an additive containing silicon element and applied to the electrolyte. The type of the silicon-containing additive is not specifically limited, and a silicon-containing additive commonly used in the field of lithium batteries can be selected. For example, the silicon-containing additive includes at least one of trimethylfluorosilane, hexamethyldisilazane (HDMS), heptamethyldisilazane, tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB). Lithium hexafluorophosphate, a commonly used lithium salt in the electrolyte, will generate HF during the decomposition process. HF will change the composition of the SEI film, destroy its stability, damage the negative electrode interface, cause the recombination of the negative electrode interface, and result in the thickening of the interface film. The present invention further adds a silicon-containing additive to the electrolyte, which can inhibit HF generated by lithium hexafluorophosphate in the electrolyte, remove moisture and acidic substances in the electrolyte, reduce the damage of HF to the negative electrode interface, and improve the cycle performance of the lithium-ion battery.

[0032] In some embodiments, based on the total mass of the electrolyte, the mass fraction of the silicon-containing additive is 0.01%-2%, for example, it can be 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.6%, 1.8%, 2%, or any value within the range formed by any two of the above values, and more preferably 0.05%-1%. When the mass fraction of the silicon-containing additive is too small (<0.01%), the silicon-containing additive cannot effectively inhibit HF; when the mass fraction of the silicon-containing additive is too large (>2%), the silicon-containing additive will generate a large amount of trimethylfluorosilane (TMSF) and other decomposed products, resulting in serious gas generation in the battery and deteriorating the low-temperature performance of the battery.

[0033] It should be noted that carbonate additives, sulfur-based additives, lithium salt additives, and silicon-containing additives in the electrolyte can all be tested by gas chromatography (GC) or gas chromatography-mass spectrometry (GCMS).

[0034] In some embodiments, the amorphous carbon material includes soft carbon and / or hard carbon, as well as other amorphous carbon materials similar to soft carbon and hard carbon. Preferably, the amorphous carbon material is soft carbon.

[0035] In some embodiments, the negative electrode active material is measured by a Raman spectrometer, and the peak intensity I within the range of 1300 cm -1 ~1400 cm -1 and the peak intensity I within the range of 1550 cm d ~1650 cm -1 satisfy the following: 0.1 ≤ I -1 / I g ≤ 0.8. For example, the ratio of I d / I g can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any value within the range composed of any two of the above values. d / I g The ratio can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any value within the range composed of any two of the above values.

[0036] In the present invention, the specific Raman test method for measuring the negative electrode active material by a Raman spectrometer is as follows: An in-situ micro laser confocal Raman spectrometer, model HORIBA·HR800, is used, which is equipped with four lasers with wavelengths of 325 nm, 532 nm, 633 nm, and 785 nm respectively. The Raman shift range is 100 cm -1 -4000 cm -1 The peak position of the D peak is: 1300 cm -1 ~1400 cm -1 The peak position of the G peak is 1550 cm -1 ~1650 cm -1 The diffraction intensity of the D peak is represented by I d and the diffraction intensity of the G peak is represented by I g .

[0037] I d measured by the Raman spectrometer represents the degree of defects in the negative electrode active material, Ig represents the degree of graphitization of the negative electrode active material, and the Raman test I d / I g When the value is small (<0.1), it represents a low degree of defects, less or no surface-coated amorphous carbon content, and thus a large polarization of the negative electrode active material during low-temperature charge and discharge, resulting in poor low-temperature performance of the battery; while I d / I gWhen the value is large (>0.8), it represents a high degree of defects in the negative electrode active material and a relatively large amount of amorphous carbon on the surface coating, which will lead to a decrease in the capacity, tap density, and initial efficiency of the negative electrode material. At the same time, too many defects on the surface of the graphite matrix will also make the negative electrode interface unstable, intensify the side reactions of the electrolyte in a high-temperature environment, and deteriorate the high-temperature performance of the battery. The present invention adjusts the I d / I g ratio of the negative electrode active material within the above range, which can improve the low-temperature performance of the negative electrode active material. When combined with carbonate additives and sulfur-based additives, it can also improve the high-temperature performance of the battery, enabling the battery to take into account both high and low-temperature performances.

[0038] In some embodiments, a Raman spectrometer is used to perform area scanning on the negative electrode active material to obtain the I d / I g peak intensity numerical distribution. The I d and I g satisfy: 0.3 ≤ I d / I g ≤ 0.6, and the numerical distribution of ≥ 90%. Performing area scanning with a Raman spectrometer means taking many points on the surface of the negative electrode active material for testing and statistically analyzing many Raman test data. These data generally show a normal distribution and can be used to evaluate the coating uniformity of the graphite matrix. The more concentrated the Raman data distribution, the more uniform the coating on the surface of the graphite matrix. When the numerical distribution of 0.3 ≤ I d / I g ≤ 0.6 is ≥ 90%, the amorphous carbon material coated on the surface of the graphite matrix in the negative electrode active material of the present invention is relatively uniform, which can improve the isotropy of the graphite matrix, reduce the lithium ion insertion impedance, and improve the low-temperature charging performance of the graphite matrix. When combined with carbonate additives and sulfur-based additives, it can enable the battery to take into account both high and low-temperature performances.

[0039] In some embodiments, based on the total mass of the negative electrode active material, the mass ratio of the coating layer is 1% - 5%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range composed of the above two point values. When the mass ratio of the coating layer is too small (<1%), the amount of amorphous carbon coated on the surface of the graphite matrix will be less, and the polarization of the negative electrode active material during low-temperature charge and discharge will be large, resulting in poor low-temperature performance and unable to improve the low-temperature performance of the negative electrode active material. When the mass ratio of the coating layer is too large (>5%), the amount of amorphous carbon on the surface coating is relatively large, leading to a decrease in the capacity, tap density, and initial efficiency of the negative electrode material, making the negative electrode interface unstable and deteriorating the high-temperature performance of the battery. The present invention adjusts the content of amorphous carbon coated on the surface of the graphite matrix, improves the low-temperature performance of the negative electrode active material, and combines with carbonate additives and sulfur-based additives to improve the high-temperature performance, enabling the battery to take into account both high and low-temperature performances.

[0040] In some embodiments, the negative electrode active material satisfies at least one of the following conditions:

[0041] (i) Dv50 is 5 μm to 15 μm;

[0042] (ii) Dv90 / Dv10 is 2.3 - 2.5;

[0043] (iii) Dn10 ≥ 1.0 μm;

[0044] (iv) The specific surface area is 0.5 m 2 / g - 1.5 m 2 / g;

[0045] (v) The specific capacity is 320 mAh / g - 355 mAh / g.

[0046] (i) Among them, the Dv50 of the negative electrode active material is 5 μm to 15 μm, and for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any value within the range composed of any two of the above values. When the Dv50 particle size of the negative electrode active material is too small (<5 μm), there are many surface defects in the negative electrode active material, which will increase the side reaction between the negative electrode active material and the electrolyte, resulting in poor high-temperature performance of the battery; when the Dv50 particle size of the negative electrode active material is too large (>15 μm), the lithium-ion diffusion path is relatively long, resulting in a slow embedding speed of lithium ions on the negative electrode surface, large polarization at low temperature, and deterioration of the low-temperature charging performance of the battery.

[0047] In the present invention, Dv10, Dv50, and Dv90 are respectively the particle sizes corresponding to the cumulative volume distribution reaching 10%, 50%, and 90% after the particles are arranged in ascending order of particle size. The particle size of the negative electrode active material is tested by the laser particle size method, and the model of the instrument used is Mastersizer 3000.

[0048] (ii) Among them, the Dv90 / Dv10 of the negative electrode active material is 2.3 - 2.5, and for example, it can be 2.3, 2.32, 2.34, 2.35, 2.36, 2.38, 2.4, 2.42, 2.44, 2.45, 2.46, 2.48, 2.5 or any value within the range composed of any two of the above values. When the Dv90 / Dv10 of the negative electrode active material is within the above range, the particle size distribution uniformity of the negative electrode active material is better, which can improve the diffusion of lithium ions, reduce polarization, and enhance the long-cycle performance of the battery.

[0049] (iii), Dn10 ≥ 1.0 μm, where Dn10 represents the minimum particle size of the negative electrode active material, equivalent to Dv00, indicating that the minimum particle size in the negative electrode active material particles is greater than or equal to 1 μm. When Dn10 ≥ 1.0 μm, reducing the fine powder and micropowder with smaller particle sizes in the negative electrode active material can reduce the shedding and pulverization phenomena of the negative electrode active material during charge and discharge, as well as reduce the polarization phenomenon of the battery during charge and discharge, improving the cycle stability of the battery.

[0050] (iv), the specific surface area of the negative electrode active material is 0.5 m 2 / g - 1.5 m 2 / g, for example, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g or any point value within the range formed by the above two values. When the specific surface area of the negative electrode active material is within the above range, it can help form a stable SEI film, thereby improving the cycle performance of the battery.

[0051] The specific surface area of the negative electrode active material is tested using a Micromeritics TriStar II 3020Plus high-throughput specific surface area and pore size analyzer in the United States.

[0052] (v) The specific capacity of the negative electrode active material is 320 mAh / g - 355 mAh / g, which can increase the volumetric energy density of the battery, improve the cycle stability and rate performance of the battery.

[0053] In some embodiments, in the XRD pattern of the negative electrode sheet, the intensity of the diffraction peak of the (004) crystal plane where the diffraction angle 2θ is located at 54 ± 1° is D004, and the intensity of the diffraction peak of the (110) crystal plane where the diffraction angle 2θ is located at 78 ± 1° is D110. The ratio of D004 to D110 satisfies: 1.0 ≤ D004 / D110 ≤ 10.0; the ratio of D004 / D110 can be, for example, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, or any value within the range formed by any two of the above values. The ratio of D004 / D110 represents the ratio of the intensity of the graphite crystal plane parallel to the negative electrode current collector to the intensity of the graphite crystal plane perpendicular to the negative electrode current collector. When D004 / D110 is larger, it means that the intensity of the crystal plane parallel to the negative electrode current collector is high, the graphite is less isotropic, and the polarization during charging in the negative electrode sheet is large, which is not conducive to improving the low-temperature charging ability; while when D004 / D110 is smaller, it means that the intensity of the graphite crystal plane perpendicular to the current collector is high, the graphite is isotropic, which will reduce the peeling force between the negative electrode active material and the negative electrode current collector, and there is a risk of the negative electrode active material falling off the negative electrode current collector in the negative electrode sheet, which is not conducive to the long cycle performance of the lithium-ion battery. When the ratio of D004 / D110 is within the above range, it can not only reduce the polarization of the negative electrode sheet and improve the low-temperature charging performance of the battery, but also reduce the risk of powder falling off and peeling of the negative electrode sheet, and improve the long cycle performance of the battery.

[0054] In some embodiments, the tap density range of the negative electrode sheet is 1.2 g / cm 3 -1.65 g / cm 3 , for example, it can be 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 or any value within the range formed by any two of the above values. In the negative electrode active material of the present invention, after the graphite is coated with the amorphous material, the graphite shows anisotropy, the ion transport of the graphite has directionality, there are some defect sites on the surface after the graphite is coated with the amorphous material, and ions can be deintercalated in any direction of the graphite, which can improve the lithium ion transport. When the tap density of the negative electrode sheet is further limited within the above range, the tap density is relatively low, the porosity of the negative electrode sheet is relatively high, which can relieve the expansion of the negative electrode active material in all directions, and the electrolyte infiltration is good, and the ion transport efficiency is high, which can further improve the cycle performance of the battery.

[0055] In some embodiments, the negative electrode sheet includes a negative electrode binder, and the negative electrode binder can be selected from the binders commonly used in the art. For example, the negative electrode binder in the negative electrode sheet includes one or more of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, and polyvinylidene fluoride.

[0056] In order to further improve the high and low temperature performance of the battery, in some embodiments, the negative electrode binder includes a lithiated acrylic acid copolymer (lithiated PAA). An acrylic acid copolymer refers to a copolymer formed by polymerizing different monomers and containing acrylic acid groups. The lithiated acrylic acid copolymer can be prepared by neutralizing the carboxyl groups of the acrylic acid copolymer with lithium hydroxide or lithium carbonate, replacing the hydrogen on the carboxyl group with lithium, thereby forming a lithiated acrylic acid copolymer. Preferably, the monomers of the lithiated acrylic acid copolymer include at least two of acrylic acid, acrylonitrile, acrylamide, vinyl alcohol, and vinylidene fluoride. Further selecting the lithiated acrylic acid copolymer as the negative electrode binder can effectively enhance the bonding effect between the negative electrode binder and the negative electrode active material, improve the structural stability of the electrode, and enhance the lithium ion transport kinetics, thereby improving the high and low temperature performance of the battery.

[0057] In some embodiments, the lithium content of the lithiated acrylic acid copolymer is 1.5% - 4.0%, for example, it can be 1.5%, 2%, 2.5%, 3%, 4.5%, 4.0%, or any value within the range composed of any two of the above values. The lithium content can be obtained by testing the electrode sheet using inductively coupled plasma (ICP) technology. Specifically, first, obtain the mass content of lithium element in the negative electrode active material layer on the surface of the negative electrode sheet, and then calculate the mass content of lithium element in the lithiated acrylic acid copolymer through the proportion of the lithiated acrylic acid copolymer in the negative electrode active material layer. The lithium content in the lithiated acrylic acid copolymer is related to the electrical performance of the battery. If the lithium content is too low, it cannot improve the lithium ion transport, and the improvement of the low temperature performance of the battery is not obvious; if the lithium content is too high, it will accelerate the side reaction between the electrolyte and the negative electrode lithium, deteriorating the high temperature performance.

[0058] In some embodiments, the lithiated acrylic acid copolymer includes acrylonitrile groups, and the content of acrylonitrile groups is 10% - 45%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any value within the range composed of any two of the above values. The infrared characteristic peak of the acrylonitrile group is at 2000cm -1 -2500cm -1Within a certain range, the characteristic absorption peak of the cyano group (-CN) in the lithiated acrylic copolymer is measured by infrared spectroscopy (IR), the absorption value ratio of the sample is calculated, and combined with the standard working curve, the mass content of the acrylonitrile group can be determined. As a functional monomer of the lithiated acrylic copolymer, if the content of acrylonitrile is too high, it will affect the adhesion, and if the content is too low, it will weaken the kinetics of the binder. When the content of the acrylonitrile group is within the above range, it can improve the kinetic performance of the battery, improve the ion conduction performance, and thus is beneficial to improving the cycle performance of the battery.

[0059] In some embodiments, the glass transition temperature (Tg) of the lithiated acrylic copolymer is 60°C - 100°C. For example, it can be 60°C, 70°C, 80°C, 90°C, 100°C or any value within the range composed of any two of the above values. The lithiated acrylic copolymer has a relatively high Tg temperature, which is manifested as a relatively large hardness and can play a supporting role in the negative electrode sheet. There are certain pores between the negative electrode active materials, which is beneficial to the transmission of lithium ions in the electrode sheet and further improves the low-temperature performance of the battery.

[0060] In some embodiments, the negative electrode binder further includes acrylate-modified styrene-butadiene rubber. Acrylates include polyacrylate, polymethacrylate, poly(styrene-acrylate), etc. In the acrylate-modified styrene-butadiene rubber, the infrared characteristic peak of the carbonyl functional group is in the range of 1680 cm -1 -1720 cm -1 range. The acrylate-modified styrene-butadiene rubber contains an ester group, has a better affinity for the electrolyte, a strong liquid absorption capacity, can improve the lithium ion transmission performance at low temperature, and improve the low-temperature charge and discharge performance of the battery.

[0061] In some embodiments, the Dv50 of the acrylate-modified styrene-butadiene rubber is 150 nm - 600 nm. For example, it can be 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm or any value within the range composed of any two of the above values. The compaction density of the negative electrode sheet is relatively low and the porosity is relatively large, which may cause problems such as powder falling off and active material shedding of the negative electrode sheet. Further adjusting the Dv50 of the acrylate-modified styrene-butadiene rubber within a smaller range, the specific surface area is larger, the contact points with the negative electrode active material are more, which can improve the bonding strength of the negative electrode binder, reduce the situation of negative electrode powder falling off, improve the stability of the negative electrode, and improve the cycle performance of the battery.

[0062] In some embodiments, the glass transition temperature of the acrylate-modified styrene-butadiene rubber is -40°C to 40°C, for example, it can be -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, or any value within the range composed of any two of the above values. The TG of the acrylate-modified styrene-butadiene rubber is relatively low, maintaining good elasticity and adhesiveness under low-temperature conditions, reducing the brittleness of the negative electrode sheet, and improving the stability of the negative electrode sheet.

[0063] In some embodiments, in the negative electrode binder, the mass ratio of the lithiated acrylic acid copolymer to the acrylate-modified styrene-butadiene rubber is 3:1 to 1:1. For example, it can be 3:1, 2.8:1, 2.5:1, 2.2:1, 2:1, 1.8:1, 1.6:1, 1.5:1, 1.4:1, 1.2:1, 1:1, or any value within the range composed of any two of the above values. The mass ratio of the lithiated acrylic acid copolymer to the acrylate-modified styrene-butadiene rubber can be understood as the ratio of the addition amounts of two different types of negative electrode binders in the negative electrode binder. Generally, it can be obtained by calculation when adding the binder of the negative electrode active material layer. The lithiated acrylic acid copolymer has good kinetic performance and relatively strong adhesiveness, which is good for the low-temperature transmission of lithium ions and has a relatively high content; however, the Tg of the lithiated acrylic acid copolymer is relatively high, which will cause the negative electrode sheet to be relatively brittle and prone to powder falling during the preparation of wound batteries. To improve this situation, the above two binders are used together. The Tg of the acrylate-modified styrene-butadiene rubber is relatively low and it is relatively soft, which can improve the flexibility of the negative electrode sheet and reduce the powder falling of the negative electrode sheet; controlling the ratio of the two binders within the above range can enable the battery to have better low-temperature performance.

[0064] In some embodiments, based on the total mass of the negative electrode sheet, the total mass ratio of the lithiated acrylic acid copolymer and the acrylate-modified styrene-butadiene rubber is 1.5% - 5%. For example, it can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range composed of any two of the above values. When the total mass of the two negative electrode binders is within the above range, the bonding effect between the negative electrode binder and the negative electrode active material can be effectively enhanced, the structural stability of the electrode can be improved, the lithium ion transmission kinetics can be enhanced, and the high and low temperature performance of the battery can be improved.

[0065] In some embodiments, the total mass ratio of the two anode binders can be obtained by thermogravimetric testing. For example, the temperature of the weight loss peak of the two binders in the anode sheet is 400-600°C. The sample is placed in a thermogravimetric analyzer and heated under a specified temperature program, and the change in the sample mass with temperature or time is recorded to obtain a thermogravimetric curve (TGA curve). According to the original sample dosage and the weight loss at each temperature interval, the weight loss percentage at each temperature interval can be calculated. The weight loss percentage can be calculated by the following formula: weight loss percentage = (weight loss / initial mass) × 100%. The group can test the total mass ratio of the two anode binders and the individual mass ratios of the two anode binders.

[0066] In some embodiments, the electrolyte includes an organic solvent, the organic solvent includes a linear solvent, and the linear solvent includes a linear carboxylic acid ester and a chain carbonate. Preferably, the mass ratio of the linear carboxylic acid ester to the chain carbonate is 0 to 2.5, for example, it can be 0, 0.01, 0.1, 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5 or any value in the range composed of any two of the above values. Preferably, based on the total mass of the electrolyte, the mass ratio of the linear carboxylic acid ester is 0%-90%, for example, it can be 0%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any value in the range composed of any two of the above values, and more preferably 0-50%. Preferably, based on the total mass of the electrolyte, the mass ratio of the chain carbonate is 10%-90%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any value in the range composed of any two of the above values, and more preferably 10-70%. The linear carboxylic acid ester and the chain carbonate have a lower viscosity, which reduces the viscosity of the electrolyte at low temperatures, improves the kinetics of the electrolyte, increases the conductivity of the electrolyte, reduces the solvation energy, increases the desolvation rate, reduces the interfacial transfer impedance of lithium ions, and improves the low-temperature performance of the battery.

[0067] In some embodiments, the linear carboxylic acid ester includes one or more of propyl propionate (PP), ethyl propionate (EP), ethyl acetate (EA), methyl acetate (MA), and methyl propionate (MP).

[0068] In some embodiments, the chain carbonate includes one or more of ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0069] In some embodiments, the electrolyte further includes cyclic carbonates; based on the total mass of the electrolyte, the mass percentage of the cyclic carbonates is 5%-50%, for example, it can be 5%, 10%, 20%, 30%, 40%, 50% or any value within the range composed of any two of the above values. Adding cyclic carbonates to the electrolyte can make the interface formed on the negative electrode of the electrolyte more stable, reduce the gas generation due to electrolyte decomposition, reduce the swelling of the battery, and improve the cycle performance of the battery.

[0070] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0071] In some embodiments, the solvent is selected from at least one of the combinations of cyclic carbonate + linear carbonate, cyclic carbonate + linear carboxylate, and cyclic carbonate + linear carbonate + linear carboxylate.

[0072] In some embodiments, the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate (LiFePO4). The olivine structure of lithium iron phosphate provides a stable lithium ion transmission channel, which helps to reduce the diffusion impedance of lithium ions and improve the low-temperature performance and rate performance of the battery.

[0073] In some embodiments, the lithium iron phosphate includes a carbon coating layer; based on the total mass of the lithium iron phosphate, the content of carbon element is 1.0%-1.5%, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any value within the range composed of any two of the above values. If the content of carbon element is too high and the carbon coating layer is too thick, it will affect the capacity of lithium iron phosphate and the energy density of the battery; if the content of carbon element is too low, the conductivity of lithium iron phosphate will be poor, the internal resistance will be large, and the low-temperature performance of the battery will be affected.

[0074] In some embodiments, based on the total mass of the lithium iron phosphate, the content of lithium element is 1-10%, the content of iron element is 25-40%, and the content of phosphorus element is 10-20%. When the lithium element, iron element, and phosphorus element are within the above ranges,

[0075] In lithium iron phosphate, the carbon element, lithium element, iron element, and phosphorus element can be obtained by testing the positive electrode sheet through inductively coupled plasma (ICP) technology.

[0076] In some embodiments, the lithium ion battery can be a power lithium ion battery, a consumer lithium ion battery, or an energy storage lithium ion battery.

[0077] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer includes the above-mentioned negative electrode active material, the above-mentioned negative electrode binder, and a negative electrode conductive agent. The negative electrode current collector is one or more of copper foil, chromium foil, nickel foil, and titanium foil. The type of the negative electrode conductive agent is not specifically limited, and a conventional conductive agent in the art can be selected. The types of the negative electrode conductive agent include, but are not limited to, at least one of acetylene black, conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0078] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector. The positive electrode active layer includes lithium iron phosphate, a positive electrode conductive agent, and a positive electrode binder. The positive electrode conductive agent is not specifically limited. For example, a conventional conductive agent in the art can be selected, including but not limited to one or more of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene. The positive electrode binder is not specifically limited. For example, a conventional binder in the art can be selected, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide.

[0079] In some embodiments, the type of the separator is not specifically limited. For example, a conventional lithium-ion battery separator in the art can be selected, including but not limited to woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, rolled membranes, polyethylene microporous membranes, polypropylene microporous membranes, etc. A glue coating layer is provided on the surface of the separator, and the glue coating layer includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid resin, methyl polyacrylate, acrylate-butadiene copolymer, polyacrylonitrile, ethylene-acrylic acid copolymer, ethyl polyacrylate, or sodium carboxymethyl cellulose.

[0080] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0081] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0082] The present invention will be described in detail below with reference to specific embodiments, and these embodiments are for understanding rather than limiting the present invention.

[0083] Example 1-1:

[0084] (1) Preparation of the positive electrode sheet:

[0085] Lithium iron phosphate (LiFePO4, with a carbon content of 1.25%; a lithium content of 6%, an iron content of 35%, and a phosphorus content of 15%), conductive carbon (Super-P), and polyvinylidene fluoride (PVDF) are mixed in a solvent of N-methylpyrrolidone in a mass ratio of approximately 96.5:1.5:2, and stirred evenly to obtain a positive electrode paste. The paste is coated on an aluminum foil with a thickness of approximately 12 μm, dried, cold-pressed, and then cut into pieces and the tabs are welded to obtain a positive electrode sheet.

[0086] (2) Preparation of the negative electrode sheet:

[0087] Graphite (graphite coated with soft carbon, with the mass ratio of the coating layer being 3%), binder (lithiated PAA + acrylate-modified SBR = 1:0.5, with a total mass ratio of 2%), sodium carboxymethyl cellulose, and acetylene black are mixed in deionized water in a mass ratio of 96.2:1.8:1:1, and stirred evenly to obtain a negative electrode paste. The paste is coated on a copper foil with a thickness of approximately 6 μm, dried, cold-pressed (the compaction density is 1.55 g / cm 3 ), and then cut into pieces and the tabs are welded to obtain a negative electrode sheet.

[0088] Among them, the preparation method of lithiated PAA includes: successively adding 60 parts (parts by mass, the same below) of acrylic acid, 25 parts of acrylonitrile, 10 parts of acrylamide, and 5 parts of butyl acrylate into a reaction kettle for soap-free emulsion polymerization, and then neutralizing with an aqueous LiOH solution to obtain a lithiated PAA aqueous adhesive.

[0089] The preparation method of acrylate-modified SBR includes: successively adding 40 parts (parts by mass, the same below) of styrene, 60 parts of butadiene, 0.4 part of acrylic acid, 20 parts of butyl acrylate, 200 parts of water, 4.5 parts of sodium stearate, and 0.5 part of molecular weight regulator dodecyl mercaptan into a reaction kettle, introducing nitrogen for protection, stirring at 300 rpm, and heating to 65°C. After continuing to stir for 20 minutes, 0.31 part of potassium persulfate is added, and the temperature is kept at 60°C for condensation, and stirring is continued at 300 rpm for 7 h. After the reaction is completed, the pH value is adjusted with ammonia water, and the gel in it is filtered through a 200-mesh screen to obtain an acrylate-modified styrene-butadiene rubber latex binder.

[0090] (3) Preparation of the electrolyte

[0091] In a glove box filled with argon (with a water content < 10 ppm and an oxygen content < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate are mixed evenly in a mass ratio of 30:40:30. Lithium hexafluorophosphate that has been fully dried based on 12.5% of the total mass of the electrolyte is quickly added to the mixed solution; 3% VC, 0.5% FEC, and 0.5% DTD based on the total mass of the electrolyte are added, and stirred evenly to obtain the electrolyte.

[0092] (4) Preparation of Lithium-ion Batteries

[0093] Stack the above-prepared positive electrode sheet, separator, and negative electrode sheet through a Z-type laminator to obtain an un-injected bare battery cell; place the bare battery cell in an outer packaging foil, inject the above-prepared electrolyte into the dried bare battery cell, and obtain the required lithium-ion battery through processes such as vacuum packaging, standing, formation, secondary sealing, and sorting.

[0094] Testing the Battery

[0095] (1) -20°C 0.2C / 0.3C Cycle Test

[0096] Place the batteries obtained in the examples and comparative examples in an environment of (-20±2)°C, leave them for 120 min. When the battery body reaches (-10±2)°C, charge the battery at 0.2C until 3.65V with a cut-off of 0.05C, leave it for 30 min, discharge it at 0.3C until 2.2V, leave it for 30 min. Record the highest discharge capacity of the first 3 cycles as the initial capacity Q. When the cycle reaches the required number of times, record the last discharge capacity Q1 of the battery.

[0097] The calculation formula used is as follows: Capacity Retention Rate (%) = Q1 / Q × 100%.

[0098] (2) -30°C 0.2C / 0.2C Cycle 50 Times Dissection Test

[0099] Place the battery in an environment of -30±2°C, leave it for 120 min, discharge it at a constant current of 0.5C until 2.2V, leave it for 30 min, charge it at a constant current and voltage of 0.2C until 3.65V with a cut-off current of 0.05C, leave it for 30 min, discharge it at a constant current of 0.2C until 2.2V, leave it for 30 min, which is one cycle. Cycle 50 times according to the above steps, dissect it when it is fully charged and taken off the bench, and observe whether there is lithium deposition on the negative electrode sheet;

[0100] (3) 45°C 1C / 1C Cycle Test

[0101] Place the battery in an environment of 45±2°C, leave it for 180 min, discharge it at a constant current of 1C until 2.5V, leave it for 30 min, charge it at a constant current and voltage of 1C until 3.65V with a cut-off current of 0.05C, leave it for 30 min, discharge it at a constant current of 1C until 2.5V, record the discharge capacity C0, leave it for 30 min, charge it at a constant current and voltage of 1.0C0 until 3.65V with a cut-off current of 0.05C0, leave it for 30 min, discharge it at a constant current of 1.0C until 2.5V. When the cycle reaches n number of cycles, record the last discharge capacity Cn. The calculation formula for the capacity retention rate of the nth cycle is: Capacity Retention Rate (%) = Cn / C0 × 100%

[0102] (4) Store at 60°C for 30 days

[0103] At 25°C, leave the battery to stand for 30 min, then charge it at a constant current of 0.5C rate until 3.65V, then charge it at a constant voltage of 3.65V until 0.05C, and leave it to stand for 5 min. Measure the thickness h1 before storage. Then, after storing at 60°C for 30 days, measure the thickness h2 of the battery after storage. Calculate it through the following formula: Thickness expansion rate = [(Thickness h2 after storage - Thickness h1 before storage) / Thickness h1 before storage] × 100%.

[0104] Examples 1 - 3, and Comparative Examples 1 - 6 were carried out with reference to Example 1 - 1. The main differences are shown in Table 1. Among them, in Example 1, the content of carbonate additives was mainly adjusted; in Example 2, the content of sulfur - based additives was mainly adjusted; in Example 3, a lithium salt additive was additionally added and the content of the lithium salt additive was adjusted. In Comparative Example 1, no carbonate and sulfur - based additives were added; in Comparative Example 2, no sulfur - based additives were added; in Comparative Example 3, no carbonate additives were added; in Comparative Example 4, the content of carbonate additives was too high and exceeded the protection range; in Comparative Example 5, the content of sulfur - based additives was too high and exceeded the protection range; in Comparative Example 6, the mass ratio of carbonate additives and carbonate additives exceeded the protection range.

[0105] Table 1

[0106]

[0107] “ / ” indicates that the corresponding component was not added or the corresponding parameter was not tested.

[0108] As can be seen from Table 1, adding carbonate additives and sulfur - based additives to the electrolyte of the present invention can reduce the reactivity of the negative electrode active material, reduce side reactions of the electrolyte, reduce lithium plating of the battery, and improve the high - temperature and low - temperature performance of the battery. Further adding a lithium salt additive to the electrolyte of the present invention can better improve the high - temperature and low - temperature performance of the battery.

[0109] Examples 4 - 6 were carried out with reference to Example 3 - 1. The main differences are shown in Table 2. Among them, in Example 4, the type of carbonate additives was changed; in Example 5, the type of sulfur - based additives was changed; in Example 6, the type of lithium salt additives was changed.

[0110] Table 2

[0111]

[0112] As can be seen from Table 2, multiple types of carbonate additives, sulfur - based additives, and lithium salt additives can improve the high - temperature and low - temperature performance of the battery.

[0113] Example 7 was carried out with reference to Example 3-1, and the main differences are shown in Table 3. Among them, a silicon-containing additive was additionally added to the Example 7 group and the content of the silicon-containing additive was adjusted.

[0114] Table 3

[0115]

[0116] As can be seen from Table 3, further adding a silicon-containing additive to the electrolyte can better improve the cycling performance of the lithium-ion battery.

[0117] Example 8 was carried out with reference to Example 7-1, and the main differences are shown in Table 4. Among them, in Example 8, the mass ratio of the surface coating layer of the graphite matrix of the negative electrode active material was changed, and the Id / Ig ratio and the D004 / D110 ratio changed accordingly.

[0118] Table 4

[0119]

[0120]

[0121] As can be seen from Table 4, by adjusting the content of amorphous carbon coated on the surface of the graphite matrix in the present invention, the low-temperature performance of the negative electrode active material is improved, and the combination with carbonate additives and sulfur-based additives improves the high-temperature performance, enabling the battery to take into account both high and low temperature performances.

[0122] Example 9 to Example 11 were carried out with reference to Example 7-1, and the main differences are shown in Table 5. Among them, in Example 9, the mass ratio of lithiated PAA to acrylate-modified SBR was adjusted; in Example 10, the total mass ratio of the two binders of lithiated PAA and acrylate-modified SBR was adjusted; in Example 11, the Dv50 of acrylate-modified SBR.

[0123] Table 5

[0124]

[0125]

[0126] As can be seen from Table 5, by using the two binders together in the present invention, the bonding effect between the negative electrode binder and the negative electrode active material can be effectively enhanced, the lithium ion transport kinetics can be improved, and the high and low temperature performances of the battery can be improved.

[0127] Example 12 was carried out with reference to Example 7-1, and the main differences are shown in Table 6. Among them, a linear carboxylic acid ester was added to the electrolyte of the Example 12 group and the content of the linear carboxylic acid ester was adjusted.

[0128] Table 6

[0129]

[0130] As can be seen from Table 6, linear carboxylic acid esters and chain carbonates have relatively low viscosities, which improves the kinetics of the electrolyte and the low-temperature performance of the battery.

[0131] It should be noted that in this text, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising that element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0132] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The battery includes a negative electrode sheet and an electrolyte; The negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a graphite matrix and a coating layer, and the coating layer includes an amorphous carbon material; The electrolyte includes a carbonate additive and a sulfur-based additive; based on the total mass of the electrolyte, the mass ratio of the carbonate additive is 0.01%-8%, and the mass ratio of the sulfur-based additive is 0.01%-3%; The mass ratio of the carbonate additive to the sulfur-based additive is 0.3-300.

2. The lithium ion battery according to claim 1, characterized in that, The mass ratio of the carbonate additive to the sulfur-based additive is 5-25; Preferably, based on the total mass of the electrolyte, the mass ratio of the carbonate additive is 1%-5%; Preferably, based on the total mass of the electrolyte, the mass ratio of the sulfur-based additive is 0.2%-1.5%.

3. The lithium-ion battery according to claim 1, wherein, The carbonate additive includes at least one of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, trifluoromethyl carbonate, 1,2-difluoroethylene carbonate, and divinyl carbonate; And / or, the sulfur-based additive includes one or more of the following compounds:

4. The lithium ion battery according to claim 1, wherein, The electrolyte further includes a lithium salt additive; the total mass ratio of the carbonate additive and the lithium salt additive to the mass of the sulfur-based additive is 0.5-200, preferably 1.2-65; Preferably, based on the total mass of the electrolyte, the mass ratio of the lithium salt additive is 0.01%-1%, more preferably 0.1%-1%; Preferably, the lithium salt additive includes at least one of lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium tetrafluoroborate, and lithium tetrafluoro(oxalato)phosphate.

5. The lithium-ion battery according to claim 1, wherein, The electrolyte further includes a silicon-containing additive; Preferably, based on the total mass of the electrolyte, the mass ratio of the silicon-containing additive is 0.01%-2%, more preferably 0.05%-1%; Preferably, the silicon-containing additive includes at least one of trimethylfluorosilane, hexamethyldisilazane, heptamethyldisilazane, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate.

6. The lithium-ion battery according to claim 1, characterized in that, The amorphous carbon material includes soft carbon and / or hard carbon; Preferably, the negative electrode active material is measured by a Raman spectrometer, and the peak intensity I within the range of 1300 cm -1 ~1400 cm -1 and the peak intensity I d within the range of 1550 cm -1 ~1650 cm -1 satisfy the following intensity ratio: 0.1 ≤ I g / I d / I g ≤ 0.8; Preferably, I d and I g satisfy: 0.3 ≤ I d / I g ≤ 0.6, and the numerical distribution of ≥ 90%; Preferably, based on the total mass of the negative electrode active material, the mass ratio of the coating layer is 1%-5%.

7. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material satisfies at least one of the following conditions: (i) Dv50 is 5μm to 15μm; (ii) Dv90 / Dv10 is 2.3-2.5; (iii) Dn10≥1.0μm; (iv) The specific surface area is 0.5 m 2 / g - 1.5 m 2 / g; (v) The specific capacity is 320mAh / g-355mAh / g.

8. The lithium ion battery according to any one of claims 1-7, characterized in that, In the XRD pattern of the negative electrode sheet, the intensity of the diffraction peak of the (004) crystal plane where the diffraction angle 2θ is located at 54±1° is D004, and the intensity of the diffraction peak of the (110) crystal plane where the diffraction angle 2θ is located at 78±1° is D110. The ratio of D004 and D110 satisfies: 1.0≤D004 / D110≤10.0; Preferably, the compaction density of the negative electrode sheet ranges from 1.2 g / cm 3 - 1.65 g / cm 3 .

9. The lithium-ion battery according to any one of claims 1-7, characterized in that, The negative electrode sheet includes a negative electrode binder, and the negative electrode binder includes a lithiated acrylic copolymer; Preferably, the monomers of the lithiated acrylic acid copolymer include at least two monomers selected from acrylic acid, acrylonitrile, acrylamide, vinyl alcohol, and vinylidene fluoride; Preferably, the lithium content of the lithiated acrylic acid copolymer is 1.5% - 4.0%; Preferably, the lithiated acrylic acid copolymer includes acrylonitrile groups, and the content of acrylonitrile groups is 10% - 45%; Preferably, the glass transition temperature of the lithiated acrylic acid copolymer is 60°C - 100°C.

10. The lithium-ion battery according to claim 9, characterized in that, The negative electrode binder further includes acrylate-modified styrene-butadiene rubber; Preferably, the glass transition temperature of the acrylate-modified styrene-butadiene rubber is -40°C to 40°C; Preferably, the Dv50 of the acrylate-modified styrene-butadiene rubber is 150 nm - 600 nm.

11. The lithium ion battery according to claim 10, wherein, In the negative electrode binder, the mass ratio of the lithiated acrylic acid copolymer to the acrylate-modified styrene-butadiene rubber is 3:1 to 1:1; Preferably, based on the total mass of the negative electrode sheet, the total mass ratio of the lithiated acrylic acid copolymer and the acrylate-modified styrene-butadiene rubber is 1.5% - 5%.

12. The lithium ion battery according to any one of claims 1-7, characterized in that, The electrolyte includes an organic solvent, the organic solvent includes a linear solvent, and the linear solvent includes a linear carboxylic acid ester and a chain carbonate; Preferably, the mass ratio of the linear carboxylic acid ester to the chain carbonate is 0 to 2.5; Preferably, based on the total mass of the electrolyte, the mass ratio of the linear carboxylic acid ester is 0% - 90%, more preferably 0 - 50%; Preferably, based on the total mass of the electrolyte, the mass ratio of the chain carbonate is 10% - 90%, more preferably 10% - 70%.

13. The lithium-ion battery according to any one of claims 1-7, characterized in that, The battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate; Preferably, the lithium iron phosphate includes a carbon coating layer; based on the total mass of the lithium iron phosphate, the carbon element content is 1.0% - 1.5%; Preferably, based on the total mass of the lithium iron phosphate, the lithium element content is 1 - 10%, the iron element content is 25 - 40%, and the phosphorus element content is 10 - 20%.

Images