Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a negative plate and an electrolyte, the negative plate comprises a negative current collector and a negative active material layer located on the surface of one side or two sides of the negative current collector, the negative active material layer comprises a negative active material, and the negative active material comprises a substrate and a coating layer on the surface of the substrate. The matrix comprises one or more of artificial graphite, natural graphite, mesocarbon microbead graphite and hard carbon, and the coating layer comprises a soft carbon material; the electrolyte comprises lithium hexafluorophosphate and a silicon additive, the silicon additive comprises a compound with a general formula of ((R2) 3Si) n-R1, n is a positive integer of 1-4, R1 is selected from # imgabs0 # imgabs1 # * represents a connecting end, and R2 and R3 are respectively and independently selected from hydrogen and C1-C5 alkyl. At-40 DEG C to 0 DEG C, the battery provided by the invention has relatively good low-temperature charging performance.

Description

Technical Field

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

[0002] Since lithium-ion batteries have advantages such as high specific energy, long cycle life, no pollution, and high working voltage compared with traditional batteries, they have currently been widely used in many fields such as portable electronic devices, energy storage, and automotive power. However, lithium-ion batteries are greatly affected by temperature. Especially at low temperatures, there will be phenomena such as a significant increase in internal resistance, capacity attenuation, and even difficulty in charging. Summary of the Invention

[0003] Currently, the main way to solve the problems of increased internal resistance, capacity attenuation, and even difficulty in charging of lithium-ion batteries at low temperatures is to heat the battery through an additional heating system to make it return to normal performance. However, this method greatly increases the cost of the entire battery system.

[0004] It has been found through research that at low temperatures, the viscosity of the electrolyte increases, the internal resistance of the battery cell becomes larger, the polarization of the battery increases, the kinetics of lithium-ion migration significantly decreases, and lithium deposition is likely to occur, resulting in an accelerated decline in the capacity of the battery.

[0005] To solve the problems of increased internal resistance, capacity attenuation, and even difficulty in charging of lithium-ion batteries at low temperatures, the present invention provides a battery. At -40°C to 0°C, the battery of the present invention has good low-temperature charging performance.

[0006] To achieve the above object, the present invention provides a battery, the battery includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes a matrix and a coating layer on the surface of the matrix. The matrix includes one or more of artificial graphite, natural graphite, mesocarbon microbead graphite, and hard carbon. The coating layer includes a soft carbon material;

[0007] The electrolyte includes lithium hexafluorophosphate and a silicon-based additive. The silicon-based additive includes a compound with the general formula ((R2)3Si) n -R1, where n is a positive integer from 1 to 4, and R1 is selected from *-NR3*, *-O-*, * represents a connecting end, and R2 and R3 are each independently selected from hydrogen and C1-C5 alkyl groups.

[0008] Through the above technical solutions, the present invention has at least the following advantages compared with the prior art:

[0009] The negative electrode active material of the present invention includes a coating layer of soft carbon material, which can increase the lithium ion intercalation active sites, effectively improve the migration rate of lithium ions at low temperatures, reduce the internal resistance of the battery, thereby improving the low-temperature charging performance of the battery, especially improving the low-temperature charging performance of the battery at -40°C to 0°C; however, too many active sites will increase the side reactions of the electrolyte and reduce the cycle performance of the battery. Therefore, by cooperating with an electrolyte including a silicon-based additive at the same time, it can cover more active sites on the surface of the negative electrode active material, prevent the continuous decomposition of the electrolyte, reduce the loss of active lithium, reduce the attenuation of the battery capacity, improve the cycle stability of the battery, and the silicon-based additive can also reduce the desolvation energy of lithium ions, improve the rate of lithium ions transferring to the interface, improve the kinetic performance of the battery, reduce the internal resistance of the battery, and inhibit the hydrolysis of lithium hexafluorophosphate and remove HF in the electrolyte, inhibit the damage of HF to the SEI film, avoid the continuous recombination and repair of SEI, and improve the cycle stability of the battery.

[0010] Other features and advantages of the present invention will be described in detail in the following specific implementation section.

[0011] In the ranges disclosed herein, the endpoints and any values 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 and individual point values of each range, 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. Brief Description of the Drawings

[0012] Figure 1 The Raman spectrum of the negative electrode active material in the present invention is shown.

[0013] Figure 2 The XRD spectrum of the negative electrode sheet in the present invention is shown. Specific Embodiments

[0014] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention. In this article, unless otherwise specified, the data ranges include the endpoints.

[0015] It should be noted that the numerical representations such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent the difference in order.

[0016] The present invention provides a battery, which includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a matrix and a coating layer on the surface of the matrix. The matrix includes one or more of artificial graphite, natural graphite, mesocarbon microbead graphite, and hard carbon, and the coating layer includes a soft carbon material;

[0017] The electrolyte includes lithium hexafluorophosphate and a silicon-based additive. The silicon-based additive includes a compound with the general formula ((R2)3Si) n -R1, where n is a positive integer from 1 to 4, and R1 is selected from *-NR3*, *—O—*, * represents a connecting end, and R2 and R3 are each independently selected from hydrogen and C1-C5 alkyl groups.

[0018] n can be a positive integer from 1 to 4. For example, 1, 2, 3, or 4.

[0019] R2 and R3 can be the same or different, and are each independently selected from hydrogen and C1-C5 alkyl groups.

[0020] The C1-C5 alkyl group is, for example, selected from methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl.

[0021] * represents a connecting end, which refers to the position where R1 is connected to Si in (R2)3Si.

[0022] It has been found through research that graphite-based materials have anisotropic characteristics, with relatively high impedance and polarization during low-temperature charging. In the present invention, by coating the surface of the carbon-based material with a soft carbon material, the lithium-ion insertion active sites of the carbon-based material can be increased, and the isotropy of the carbon-based material can be improved, thereby significantly reducing the lithium-ion insertion impedance, reducing polarization, effectively increasing the migration rate of lithium ions at low temperatures, and enhancing the low-temperature charging performance of the battery. In particular, it can improve the low-temperature charging performance of the battery at -40°C to 0°C. However, due to the relatively poor thermal stability of the lithium salt LiPF6 in the electrolyte, LiPF6 decomposes to produce hydrofluoric acid (HF), and HF continuously damages the SEI film. The recombination and repair of the SEI film consume active lithium. For the negative electrode active material coated with a soft carbon material on the surface, due to the relatively many defects in the amorphous carbon material (such as the soft carbon material), the electron cloud distribution is uneven. Therefore, there are relatively many reactive sites on the surface of the negative electrode active material. The relatively many reactive sites will increase the side reactions of the electrolyte and consume more active lithium, resulting in faster capacity decay of the battery. The silicon-based additive in the electrolyte of the present invention can also react on the surface of the negative electrode active material to form a Si-containing organic compound (for example, Li2SiO4) to cover the surface of the reactive sites of the negative electrode active material, thereby preventing the continuous decomposition of the electrolyte. Moreover, the above-mentioned Si-containing organic compound generated can also adsorb lithium ions in the electrolyte, reducing the desolvation energy during the transfer of lithium ions from the solvent to the SEI film, thereby increasing the rate of lithium ions transferred to the interface and improving the kinetic performance of the battery. In addition, it can be seen from the structure of the silicon-based additive that the silicon-based additive includes Si-O bonds and / or Si-N bonds. Both Si-O bonds and Si-N bonds can react with water to inhibit the hydrolysis of LiPF6. At the same time, the Si-O bond can also react with HF generated by the hydrolysis of LiPF6 to form a Si-F bond, thereby effectively removing HF in the electrolyte, effectively inhibiting the damage of HF to the SEI film, reducing the consumption of active lithium, preventing the rapid thickening of the negative electrode interface film caused by the continuous recombination and repair of the SEI, and improving the cycle stability of the battery.

[0023] In the present invention, through the synergistic effect of the negative electrode active material in the negative electrode sheet and the silicon-based additive in the electrolyte, the migration rate of lithium ions at low temperatures can be effectively increased, the phenomenon of lithium deposition during low-temperature charging of the battery can be improved, and at the same time, the loss of active lithium can be reduced, effectively inhibiting the capacity decay of the battery, thereby solving the problem of difficult low-temperature charging of the battery. Compared with the prior art, the low-temperature charging performance and cycle stability performance of the battery can already be improved. To further improve the effect, one or more technical features can be further optimized.

[0024] In one example, n is 2 or 3.

[0025] In one example, R2 is selected from C1-C3 alkyl groups.

[0026] In one example, R1 is selected from *—NR3—*, *-O-*, * represents a connecting end, and R3 is selected from hydrogen and C1-C3 alkyl groups.

[0027] According to a specific embodiment, n is 2 or 3, and R1 is selected from *-NR3-*, *—O—*, * represents a connecting end, and R2 and R3 are each independently selected from hydrogen and C1-C3 alkyl groups.

[0028] According to a specific embodiment, n is 2 or 3, and R1 is selected from *-NR3*, *—O—*, * represents a connecting end, R2 is methyl, and R3 is selected from hydrogen, methyl, and ethyl.

[0029] In one example, the silicon-based additive includes one or more of the following structures:

[0030]

[0031]

[0032] In one example, the silicon-based additive includes a silicon-oxygen additive and a silicon-nitrogen additive. The structure of the silicon-oxygen additive includes Si-O bonds, and the structure of the silicon-nitrogen additive includes Si-N bonds.

[0033] In one example, the weight ratio of the silicon-oxygen additive to the silicon-carbon additive is (1-2):1. Controlling the weight ratio of the silicon-oxygen additive to the silicon-carbon additive within the above range enables both Si-O bonds and Si-N bonds to react with water, inhibiting the hydrolysis of LiPF6. In addition, the Si-O bonds can also react with HF generated by the hydrolysis of LiPF6 to form Si-F bonds. Through the dual action of Si-O bonds and Si-N bonds, HF in the electrolyte can be more effectively removed, preventing the SEI from continuously recombining and repairing, resulting in a rapid thickening of the negative electrode interface film. On the one hand, it can effectively slow down the consumption of the electrolyte, and on the other hand, it can inhibit the rapid increase in the internal resistance of the battery, improve the cycle stability of the battery, and enhance the cycle life of the battery.

[0034] In one example, the weight ratio of the silicon-oxygen additive to the silicon-carbon additive is (1.2-1.5):1.

[0035] In one example, the weight percentage of lithium hexafluorophosphate in the electrolyte is 3% - 20% (for example, 3%, 5%, 8%, 10%, 13%, 15%, 18% or 20%). Controlling the weight percentage of lithium hexafluorophosphate in the electrolyte within the above range can, while ensuring a sufficient number of migratable ions, further reduce the viscosity of the electrolyte at low temperatures, increase the migration rate of lithium ions, improve the kinetic performance of the battery, solve the problem of lithium precipitation in the battery at low temperatures, and enhance the cycle stability of the battery.

[0036] In one example, the weight percentage of lithium hexafluorophosphate in the electrolyte is 5% - 15%.

[0037] In one example, the weight percentage of the silicon-based additive in the electrolyte is 0.1% - 5% (for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%).

[0038] In one example, the weight percentage of the silicon-based additive in the electrolyte is 0.2% - 2%.

[0039] In one example, the battery satisfies the following relationship: 1.5 ≤ L / a ≤ 200 (for example, 1.5, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200), where L is the weight percentage of lithium hexafluorophosphate in the electrolyte, in %, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

[0040] When L / a < 1.5, the content of the silicon-based additive in the electrolyte is too high, the kinetics of the battery seriously decline, and the excessive silicon-based additive will produce a large amount of by-products resulting in gas generation, increasing the expansion rate of the battery. At the same time, the generated gas makes the contact between the positive and negative electrodes and the separator not tight, increasing the risk of lithium precipitation in the battery at low temperatures. When L / a > 200, the viscosity of the electrolyte is relatively high at low temperatures, which will reduce the migration rate of lithium ions, and the content of the silicon-based additive is too low to effectively inhibit HF, leading to a rapid decay of the battery capacity. Controlling the battery to satisfy the above relationship can ensure that the amount of the silicon-based additive is sufficient to inhibit the hydrolysis of LiPF6 and remove HF in the electrolyte, and avoid the content of the silicon-based additive in the electrolyte being too high, ensuring a high matching degree between the silicon-based additive and lithium hexafluorophosphate, and further improving the low-temperature charging performance and cycle stability of the battery.

[0041] In one example, the battery satisfies the following relationship: 5 ≤ L / a ≤ 75, where L is the weight percentage of lithium hexafluorophosphate in the electrolyte, in %, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

[0042] According to a specific embodiment, L is 3 - 20, a is 0.1 - 5, and the battery satisfies the following relationship: 1.5 ≤ L / a ≤ 200, where L is the weight percentage of lithium hexafluorophosphate in the electrolyte, in %, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

[0043] According to a specific embodiment, L is 5 - 15, a is 0.2 - 2, and the battery satisfies the following relationship: 5 ≤ L / a ≤ 75, where L is the weight percentage of lithium hexafluorophosphate in the electrolyte, in %, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

[0044] In one example, the electrolyte further includes a linear solvent, and the linear solvent includes linear carbonates and linear carboxylates.

[0045] In one example, the weight percentage of the linear carbonate in the electrolyte is 10% - 90% (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%).

[0046] In one example, the weight percentage of the linear carbonate in the electrolyte is 50% - 70%.

[0047] In one example, the weight percentage of the linear carboxylate in the electrolyte is 5% - 70% (for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%).

[0048] In one example, the weight percentage of the linear carboxylate in the electrolyte is 20% - 50%.

[0049] In one example, the weight ratio of the linear carbonate to the linear carboxylate is 0.14 - 8 (for example, 0.14, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7 or 8). Controlling the weight ratio of the linear carbonate to the linear carboxylate within the above range can further reduce the viscosity of the electrolyte at low temperatures, increase the migration rate of lithium ions, and at the same time reduce the desolvation energy of lithium ions, which is beneficial to the desolvation of lithium ions and improves the kinetic performance of the battery, thereby further improving the cycle stability of the battery.

[0050] In one example, the weight ratio of the linear carbonate to the linear carboxylate is 1 - 3.5.

[0051] According to a specific embodiment, the weight percentage of the linear carbonate in the electrolyte is 10%-90%, the weight percentage of the linear carboxylate in the electrolyte is 5%-70%, and the weight ratio of the linear carbonate to the linear carboxylate is 0.14-8.

[0052] According to a specific embodiment, the weight percentage of the linear carbonate in the electrolyte is 50%-70%, the weight percentage of the linear carboxylate in the electrolyte is 20%-50%, and the weight ratio of the linear carbonate to the linear carboxylate is 1-3.5.

[0053] In one example, the linear carbonate includes ethyl methyl carbonate (EMC) and / or dimethyl carbonate (DMC).

[0054] In one example, the linear carboxylate includes one or more of ethyl acetate (EA), propyl propionate (PP), and propyl acetate (EP).

[0055] The electrolyte may further include a non-linear solvent (e.g., ethylene carbonate and / or propylene carbonate) and / or a non-silicon-containing additive (e.g., one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), and lithium difluorooxalate borate (LiODFB)). When the sum of the weight contents of the linear solvent, lithium hexafluorophosphate, and the silicon-based additive in the electrolyte is less than 100%, it can be supplemented with a non-linear solvent and / or a non-silicon-containing additive.

[0056] In one example, the soft carbon material includes one or more of petroleum coke, needle coke, pitch-based carbon material, carbon fiber, coke, and carbon microspheres.

[0057] In one example, the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.1-1.5 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, or 1.5). Controlling the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material within the above range can make the number of active sites on the surface of the negative electrode active material more appropriate, which can not only ensure enough active potentials to improve the migration rate of lithium ions, but also ensure that the number of active potentials is not excessive, avoiding increasing the side reactions of the electrolyte, so that the battery has both the effects of improving low-temperature charging performance and reducing the swelling rate.

[0058] The Raman spectrum of the negative electrode active material can be obtained by conventional methods in the art. For example, the ambient temperature is 20°C - 25°C, the temperature fluctuation range during use does not exceed ±2°C, and the relative humidity ≤ 60%; turn on the laser before testing, and perform the preheating and stabilization time according to the instrument manual; select the Raman shift range covering (100 - 3200) cm -1 of the certified reference material, perform linear calibration in the spectral range according to GB / T 36063, and make a standard curve; calibrate the Raman shifts of the D peak, G peak, and 2D peak of the sample through the calibration curve obtained by measuring the reference material, and calibrate the intensity ratios IG / I2D of the G peak and 2D peak and ID / IG of the D peak and G peak of the sample through the calibration factor obtained by measuring the Raman relative intensity reference material; the instrument calibration method refers to GB / T 33252 and GB / T 36063. As Figure 1 shown, the D peak represents the peak located at 1300 cm -1 -1400 cm -1 and the G peak represents the peak located at 1500 cm -1 -1600 cm -1 .

[0059] In one example, the battery satisfies the following relationship: 0.13 ≤ a / X ≤ 20 (for example, 0.13, 0.5, 1, 3, 5, 8, 10, 13, 15, 18, or 20), where X is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, and a is the weight percentage of the silicon-based additive in the electrolyte, with the unit of %. Controlling the battery to satisfy the above relationship can enable the silicon-based additive to cover excessive active sites on the surface of the negative electrode active material, thereby further reducing the side reactions of the electrolyte, avoiding the loss of active lithium while increasing the transmission rate of lithium ions, and making the battery have the effects of higher cycle stability and lower expansion rate.

[0060] In one example, the battery satisfies the following relationship: 0.25 ≤ a / X ≤ 10, where X is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, and a is the weight percentage of the silicon-based additive in the electrolyte, with the unit of %.

[0061] According to a specific embodiment, a is 0.1 - 5, X is 0.1 - 1.5, and the battery satisfies the following relationship: 0.13 ≤ a / X ≤ 20, where X is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, and a is the weight percentage of the silicon-based additive in the electrolyte, with the unit of %.

[0062] According to a specific embodiment, a is 0.2 - 2, X is 0.1 - 1.5, and the battery satisfies the following relationship: 0.25 ≤ a / X ≤ 10, where X is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, and a is the weight percentage of the silicon-based additive in the electrolyte, with the unit of %.

[0063] In one example, the median particle size Dv50 of the negative electrode active material is 5 μm - 15 μm (for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm).

[0064] In one example, the particle size distribution of the negative electrode active material is Dv90 / Dv10 = 2.3 - 3.5 (for example, 2.3, 2.5, 2.8, 3, 3.3, or 3.5), and Dn10 ≥ 1 μm.

[0065] In the present invention, Dv50 is the particle size of the negative electrode active material corresponding to the cumulative particle size distribution percentage reaching 50% in the volume distribution curve of the negative electrode active material. Dv90 is the particle size of the negative electrode active material corresponding to the cumulative particle size distribution percentage reaching 90% in the volume distribution curve of the negative electrode active material. Dv10 is the particle size of the negative electrode active material corresponding to the cumulative particle size distribution percentage reaching 10% in the volume distribution curve of the negative electrode active material. Dn10 is the particle size of the negative electrode active material corresponding to the cumulative particle size distribution percentage reaching 10% in the number distribution curve of the negative electrode active material. Dv50, Dv90, Dv10, and Dn10 can be obtained by conventional testing methods in the art, such as a particle size laser analyzer.

[0066] In one example, the median particle size Dv50 of the negative electrode active material is 5 μm - 15 μm, the particle size distribution of the negative electrode active material is Dv90 / Dv10 = 2.3 - 3.5, and Dn10 ≥ 1 μm. Controlling the particle size distribution of the graphite to satisfy the above ranges simultaneously can reduce the lithium ion transmission distance, increase the lithium ion transmission rate, and improve the charge and discharge performance of the battery at low temperatures.

[0067] In one example, 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 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g or 1.5 m 2 / g). Controlling the specific surface area of the negative electrode active material within the above range can avoid excessive contact area between the negative electrode active material and the electrolyte, reduce the interfacial side reactions between the negative electrode active material and the electrolyte, thereby reducing the loss of active lithium and improving the capacity retention rate of the battery.

[0068] In one example, the specific capacity of the negative electrode active material is 320 mAh / g - 355 mAh / g (for example, 320 mAh / g, 325 mAh / g, 330 mAh / g, 335 mAh / g, 340 mAh / g, 345 mAh / g, 350 mAh / g or 355 mAh / g).

[0069] In one example, in the XRD pattern of the negative electrode sheet, the ratio D004 / D110 of the diffraction peak intensity D004 of the 004 crystal plane to the diffraction peak intensity D110 of the 110 crystal plane is 1 - 5.5 (for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or 5.5).

[0070] The XRD pattern of the negative electrode sheet can be obtained by conventional methods in the art. For example, the specification parameters are set as follows: the output power of the X-ray tube is 1.8 Kw (Cu target), the output voltage / current max of the X-ray tube is 50 kV / 55 mA, the goniometer system: the angle range is -110° to 168°, the angle reproducibility is + / -0.0001°, the minimum controllable step size is 0.0001°, the PIXCel detector system: the pixel size is 55 microns, the dynamic range is 3×10 10 cps, 97% linear range is 6.5×10 9 cps, the maximum static scan range is 3.3°, 97% linear range: 6.5×10 9 cps, the multi-functional test data processing and analysis software: Highscore Plus 5.0, the shutter technology in the radiation safety interlock device: pneumatic shutter, radiation of the Ministry of Ecology and Environment: <1 uSV / hr / cm 2 (at a distance of 10 cm).

[0071] As Figure 2 shown, the diffraction peak of the 004 crystal plane is located at 50° - 60°, and the diffraction peak of the 110 crystal plane is located at 70° - 80°.

[0072] In one example, the negative electrode active material layer further includes a negative electrode binder, and the negative electrode binder includes lithiated polyacrylic acid (lithiated PAA) and / or styrene-butadiene rubber.

[0073] In one example, the weight percentage of the negative electrode binder in the negative electrode active material layer is 1.2% - 5% (for example, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%).

[0074] In one example, the weight percentage of the negative electrode binder in the negative electrode active material layer is 1.5% - 2.5%.

[0075] In one example, the negative electrode binder includes lithiated polyacrylic acid. Lithiated polyacrylic acid can form a locally high concentration of lithium ion distribution near the negative electrode active material. Utilizing the concentration gradient can accelerate the transport of lithium ions, thereby improving the low-temperature charge and discharge performance of the battery.

[0076] In one example, the lithiated polyacrylic acid includes lithium element.

[0077] In one example, the weight percentage of the lithium element in the lithiated polyacrylic acid is 1% - 6% (for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%). Controlling the weight percentage of the lithium element in the lithiated polyacrylic acid within the above range can enable the lithiated polyacrylic acid to provide sufficient lithium element, thereby forming a locally high concentration of lithium ion distribution near the negative electrode active material and accelerating the lithium ion transport, so as to achieve the effect of improving the low-temperature charge and discharge performance of the battery.

[0078] In one example, the weight percentage of the lithium element in the lithiated polyacrylic acid is 1.8% - 3.8%.

[0079] In one example, the lithiated polyacrylic acid has an infrared characteristic peak at 2000 ppm - 2500 ppm (for example, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm or 2500 ppm).

[0080] In one example, the glass transition temperature of the lithiated polyacrylic acid is 80°C - 150°C (for example, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C).

[0081] In one example, the median particle size Dv50 of the styrene-butadiene rubber is 150 nm - 600 nm.

[0082] In one example, the styrene-butadiene rubber has an infrared characteristic peak at 1680 ppm - 1720 ppm (for example, 1680 ppm, 1690 ppm, 1700 ppm, 1710 ppm or 1720 ppm).

[0083] In one example, the glass transition temperature of the styrene-butadiene rubber is -40°C to 40°C (for example, -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, or 40°C). Controlling the glass transition temperature of the styrene-butadiene rubber within the above range is beneficial for processing, maintaining the stability of the electrode sheet structure without powder shedding, and taking into account the flexibility of the electrode sheet.

[0084] In one example, the styrene-butadiene rubber includes an ester-modified styrene-butadiene rubber. The ester-modified styrene-butadiene rubber includes an ester group, has a relatively high affinity for the electrolyte, and a strong liquid absorption capacity, which can improve the transport of lithium ions at low temperatures, thereby enhancing the low-temperature charge-discharge performance of the battery.

[0085] In one example, the negative electrode sheet has a weight loss peak at 400°C - 600°C (for example, 400°C, 430°C, 450°C, 480°C, 500°C, 530°C, 550°C, 580°C, or 600°C). In the thermogravimetric test spectrum of the negative electrode sheet, there is a weight loss peak at 400°C - 600°C.

[0086] In one example, the negative electrode active material layer further includes a negative electrode conductive agent.

[0087] In one example, the negative electrode conductive agent includes at least one of electrocarbon black (SP), Ketjen black, acetylene black, graphite conductive agents (KS-6, KS-15, S-O, SEG-6), carbon fiber (VGCG), carbon nanotube (CNT), and graphene.

[0088] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 87% - 99.5% (for example, 87%, 90%, 93%, 95%, 98%, or 99.5%), the weight content of the negative electrode binder is 0.4% - 8% (for example, 0.4%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%), and the weight content of the negative electrode conductive agent is 0.1% - 5% (for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%).

[0089] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 94% - 97.5%, the weight content of the negative electrode binder is 1% - 4%, and the weight content of the negative electrode conductive agent is 0.5% - 2%.

[0090] In one example, the battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on one or both surfaces of the positive electrode current collector, and the positive electrode active material layer includes a lithium iron phosphate material (LFP).

[0091] In one example, the lithium iron phosphate material includes an olivine structure.

[0092] In one example, the median particle size Dv50 of the lithium iron phosphate material is 1 μm - 5 μm (for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm). Controlling the median particle size of the lithium iron phosphate material within the above range can shorten the transmission distance of lithium ions, improve the transmission rate of lithium ions, and further enhance the low-temperature charge and discharge performance of the battery.

[0093] In one example, the positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode binder.

[0094] In one example, the positive electrode conductive agent includes at least one of acetylene black, conductive carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, and conductive carbon fibers.

[0095] In one example, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylic acid, polyimide, and polyacrylic acid-acrylonitrile copolymer.

[0096] In one example, based on the total weight of the positive electrode active material layer, the weight content of the lithium iron phosphate material is 80% - 99.8% (for example, 80%, 83%, 85%, 88%, 90%, 93%, 95%, 98%, or 99.8%), the weight content of the positive electrode conductive agent is 0.1% - 10% (for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%), and the weight content of the positive electrode binder is 0.1% - 10% (for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%).

[0097] In one example, based on the total weight of the positive electrode active material layer, the weight content of the lithium iron phosphate material is 90% - 99%, the weight content of the positive electrode conductive agent is 0.5% - 5%, and the weight content of the positive electrode binder is 0.5% - 5%.

[0098] In one example, the battery further includes a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. The separator can be a conventional separator in the art.

[0099] In one example, the battery is a lithium-ion battery.

[0100] In one example, the battery is a lithium-ion secondary battery.

[0101] The present invention will be described in detail below with reference to embodiments. The embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts fall within the scope of protection of the present invention.

[0102] The following embodiments are used to illustrate the battery of the present invention.

[0103] Embodiment 1

[0104] (1) Negative electrode sheet

[0105] The negative electrode active material (artificial graphite coated with soft carbon material), negative electrode binder (lithiated polyacrylic acid: styrene-butadiene rubber modified by esters (weight ratio) = 2:1), sodium carboxymethyl cellulose, and acetylene black are put into a vacuum mixer according to a mass ratio of 96:2:1:1, and deionized water is added. Under the action of the vacuum mixer, they are fully mixed to finally form a uniform and good-fluidity negative electrode slurry with a solid content of 45 wt%. The above negative electrode slurry is uniformly coated on both sides of the negative electrode current collector (copper foil) with a thickness of 6 μm, dried, rolled, and die-cut to obtain a negative electrode sheet. Among them, the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.3. In the XRD spectrum of the negative electrode sheet, the ratio D004 / D110 of the diffraction peak intensity D004 of the 004 crystal plane to the diffraction peak intensity D110 of the 110 crystal plane is 7.5. The weight percentage of lithium element in lithiated polyacrylic acid is 3%. Lithiated polyacrylic acid has an infrared characteristic peak at 2000 ppm - 2500 ppm. The median particle size Dv50 of styrene-butadiene rubber is 300 nm. The negative electrode sheet has a weight loss peak at 400 °C - 600 °C.

[0106] (2) Electrolyte

[0107] In an argon glove box with a water content of <0.1 ppm and an oxygen content of <0.1 ppm, linear carbonates (ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), EMC:DMC (mass ratio) = 3:2), linear carboxylic esters (ethyl acetate (EA)), and ethylene carbonate (EC) are mixed evenly. Among them, based on the total mass of the electrolyte, the mass of the linear carbonate is 30%, the mass of the linear carboxylic ester is 20%, and the mass of ethylene carbonate is 33.3%. Lithium hexafluorophosphate (LiPF6) that has been fully dried is added thereto and stirred until dissolved. The added mass of LiPF6 is 12.5% of the total mass of the electrolyte. Silicon-based additives shown by formula (I-2) (tris(trimethylsilyl) phosphate (TMSP)) and formula (I-6) (ethylhexamethyldisilazane (EHMDS)) are added. The added mass of the silicon-based additives is 0.4% of the total mass of the electrolyte (wherein, the weight ratio of formula (I-2) to formula (I-6) is 1.4). A non-silicon-based additive (2.3% VC + 0.5% FEC + 0.5% DTD + 0.5% LiODFB) based on 3.8% of the total mass of the electrolyte is added, and it is stirred evenly. After passing the physical property test, the electrolyte is obtained.

[0108] (3) Positive electrode sheet

[0109] LFP (LFP has an olivine structure and a median particle size Dv50 of 1.5 μm), polyvinylidene fluoride, and acetylene black are put into a vacuum mixer according to a mass ratio of 96.5:1.5:2.0, and N-methylpyrrolidone (NMP) is added. Under the action of the vacuum mixer, they are fully mixed until a uniform and highly fluid positive electrode paste is formed, wherein the solid content is 55 wt%. The above positive electrode paste is evenly coated on an aluminum foil with a thickness of 13 μm, dried, rolled, slit, and punched to obtain a positive electrode sheet.

[0110] (4) Battery

[0111] The positive electrode sheet obtained in step (3), the negative electrode sheet obtained in step (1), and the separator (polyethylene film) are combined by winding to obtain a bare battery cell; the bare battery cell is placed in an outer packaging foil, and the electrolyte prepared in step (2) is injected into the dried and qualified battery cell. Through processes such as vacuum standing, vacuum packaging, aging, formation, secondary sealing, aging, and sorting, the battery is obtained. Among them, a / X = 0.4 / 0.3 = 1.33, L / a = 12.5 / 0.4 = 31.25.

[0112] Example 2

[0113] (1) Negative electrode sheet

[0114] The negative electrode active material (mesophase carbon microbead graphite coated with soft carbon material), negative electrode binder (lithiated polyacrylic acid: styrene-butadiene rubber modified with esters (weight ratio) = 2:1), sodium carboxymethyl cellulose, and acetylene black are put into a vacuum mixer according to a mass ratio of 93:5:1:1, deionized water is added, and they are fully mixed under the action of the vacuum mixer to finally form a uniform and good-fluidity negative electrode slurry with a solid content of 45 wt%. The above negative electrode slurry is uniformly coated on both side surfaces of a negative electrode current collector (copper foil) with a thickness of 6 μm, dried, roll-pressed, and die-cut to obtain a negative electrode sheet. Among them, the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.56. In the XRD spectrum of the negative electrode sheet, the ratio D004 / D110 of the diffraction peak intensity D004 of the 004 crystal plane to the diffraction peak intensity D110 of the 110 crystal plane is 2.3. The weight proportion of lithium element in lithiated polyacrylic acid is 6%. Lithiated polyacrylic acid has an infrared characteristic peak at 2000 ppm - 2500 ppm. The median particle size Dv50 of styrene-butadiene rubber is 581 nm. The negative electrode sheet has a weight loss peak at 400 °C - 600 °C.

[0115] (2) Electrolyte

[0116] In an argon glove box with a water content < 0.1 ppm and an oxygen content < 0.1 ppm, a linear carbonate (ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), EMC:DMC (mass ratio) = 0.37:1), a linear carboxylic acid ester (ethyl acetate (EA)), and ethylene carbonate (EC) are mixed evenly. Among them, based on the total mass of the electrolyte, the mass of the linear carbonate is 13.5%, the mass of the linear carboxylic acid ester is 36.5%, and the mass of ethylene carbonate is 24.2%. Sufficiently dried lithium hexafluorophosphate (LiPF6) is added thereto and stirred for dissolution. The added mass of LiPF6 is 18.4% of the total mass of the electrolyte. A silicon-based additive shown in formula (I-3) is added, and the added mass of the silicon-based additive is 3.6% of the total mass of the electrolyte (wherein, the weight ratio of formula (I-2) to formula (I-6) is 1.8). A non-silicon-based additive (2.3% VC + 0.5% FEC + 0.5% DTD + 0.5% LiODFB) based on 3.8% of the total mass of the electrolyte is added and stirred evenly. After passing the physical property test, an electrolyte is obtained.

[0117] (3) Positive electrode sheet

[0118] LFP (LFP has an olivine structure with a median particle size Dv50 of 4.8 μm), polyvinylidene fluoride, and acetylene black were put into a vacuum mixer according to a mass ratio of 96.5:1.5:2.0, and N-methylpyrrolidone (NMP) was added. Under the action of the vacuum mixer, they were fully mixed until a uniform and well-flowing positive electrode paste was formed, with a solid content of 55 wt%. The above positive electrode paste was evenly coated on an aluminum foil with a thickness of 13 μm, dried, roll-pressed, slit, and punched to obtain a positive electrode sheet.

[0119] (4) Battery

[0120] Refer to Example 1. Among them, a / X = 3.6 / 0.56 = 6.43, L / a = 18.4 / 3.6 = 5.11.

[0121] Example 3

[0122] Refer to Example 1. The difference is that the negative electrode active material was adjusted to hard carbon coated with soft carbon material. Then, the ratio of the intensity of the D peak to the intensity of the G peak X in the Raman spectrum of the negative electrode active material was 1.1, and D004 / D110 did not exist, a / X = 0.4 / 1.1 = 0.36.

[0123] Example 4 Group

[0124] This group of examples is used to illustrate the influence when the specific selection of the silicon-based additive is changed.

[0125] Example 4a

[0126] Refer to Example 1. The difference is that the silicon-based additive has the structure shown in formula (I-1).

[0127] Example 4b

[0128] Refer to Example 1. The difference is that the silicon-based additive has the structure shown in formula (I-4).

[0129] Example 4c

[0130] Refer to Example 1. The difference is that the silicon-based additive has the structure shown in formula (I-7).

[0131] Example 4d

[0132] Refer to Example 1. The difference is that the silicon-based additive has the structure shown in formula (I-9).

[0133] Example 5 Group

[0134] This group of examples is used to illustrate the influence when the weight ratio of the structure shown in formula (I-2) to the weight of the structure shown in formula (I-6) is changed.

[0135] Example 5a

[0136] It is carried out with reference to Example 1, except that the silicon-based additive has the structures shown in formula (I-2) and formula (I-6), and the weight ratio of the structure shown in formula (I-2) to the weight of the structure shown in formula (I-6) is 1.

[0137] Example 5b

[0138] It is carried out with reference to Example 1, except that the silicon-based additive has the structures shown in formula (I-2) and formula (I-6), and the weight ratio of the structure shown in formula (I-2) to the weight of the structure shown in formula (I-6) is 2.

[0139] Example 6 group

[0140] This group of examples is used to illustrate the effects produced when the weight percentage of the silicon-based additive in the electrolyte changes.

[0141] Example 6a

[0142] It is carried out with reference to Example 1, except that the weight percentage of the silicon-based additive in the electrolyte is 0.1%, then a / X = 0.1 / 0.3 = 0.33, and L / a = 12.5 / 0.1 = 125.

[0143] Example 6b

[0144] It is carried out with reference to Example 1, except that the weight percentage of the silicon-based additive in the electrolyte is 0.2%, then a / X = 0.2 / 0.3 = 0.67, and L / a = 12.5 / 0.2 = 62.5.

[0145] Example 6c

[0146] It is carried out with reference to Example 1, except that the weight percentage of the silicon-based additive in the electrolyte is 2%, then a / X = 2 / 0.3 = 6.67, and L / a = 12.5 / 2 = 6.25.

[0147] Example 5d

[0148] It is carried out with reference to Example 1, except that the weight percentage of the silicon-based additive in the electrolyte is 5%, then a / X = 5 / 0.3 = 16.67, and L / a = 12.5 / 5 = 2.5.

[0149] Example 7 group

[0150] This group of examples is used to illustrate the effects produced when L / a changes.

[0151] Example 7a

[0152] Performed in reference to Example 1, with the difference that the weight percentage of lithium hexafluorophosphate in the electrolyte is 7.5%, and the weight percentage of the silicon-based additive in the electrolyte is 5%. Then a / X = 5 / 0.3 = 16.67, and L / a = 7.5 / 5 = 1.5.

[0153] Example 7b

[0154] Performed in reference to Example 1, with the difference that the weight percentage of lithium hexafluorophosphate in the electrolyte is 15%, and the weight percentage of the silicon-based additive in the electrolyte is 0.4%. Then L / a = 15 / 0.4 = 37.5.

[0155] Example 7c

[0156] Performed in reference to Example 1, with the difference that the weight percentage of lithium hexafluorophosphate in the electrolyte is 20%, and the weight percentage of the silicon-based additive in the electrolyte is 0.1%. Then a / X = 0.1 / 0.3 = 0.33, and L / a = 20 / 0.1 = 200.

[0157] Example 7d

[0158] Performed in reference to Example 1, with the difference that the weight percentage of lithium hexafluorophosphate in the electrolyte is 10%, and the weight percentage of the silicon-based additive in the electrolyte is 2%. Then a / X = 2 / 0.3 = 6.67, and L / a = 10 / 2 = 5.

[0159] Example 7e

[0160] Performed in reference to Example 1, with the difference that the weight percentage of lithium hexafluorophosphate in the electrolyte is 7.5%, and the weight percentage of the silicon-based additive in the electrolyte is 0.1%. Then a / X = 0.1 / 0.3 = 0.33, and L / a = 7.5 / 0.1 = 75.

[0161] Example 8 group

[0162] This group of examples is used to illustrate the effects produced when the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is changed by adjusting the weight percentage of the soft carbon material in the negative electrode active material.

[0163] Example 8a

[0164] Performed in reference to Example 1, with the difference that the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.12, D004 / D110 is 5.3, and a / X = 0.4 / 0.12 = 3.33.

[0165] Example 8b

[0166] Performed with reference to Example 1, except that the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.77, D004 / D110 is 1.2, and a / X = 0.4 / 0.77 = 0.52.

[0167] Example 9 group

[0168] This group of examples is used to illustrate the influence when a / X changes.

[0169] Example 9a

[0170] Performed with reference to Example 1, except that the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.63, D004 / D110 is 1.4, the weight percentage of the silicon-based additive in the electrolyte is 0.1%, then a / X = 0.1 / 0.63 = 0.16, and L / a = 12.5 / 0.1 = 125.

[0171] Example 9b

[0172] Performed with reference to Example 1, except that the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.63, D004 / D110 is 1.4, the weight percentage of the silicon-based additive in the electrolyte is 0.16%, then a / X = 0.16 / 0.63 = 0.25, and L / a = 12.5 / 0.16 = 78.1.

[0173] Example 9c

[0174] Performed with reference to Example 1, except that the weight percentage of the silicon-based additive in the electrolyte is 3%, then a / X = 3 / 0.3 = 10, and L / a = 12.5 / 3 = 4.17.

[0175] Example 9d

[0176] Performed with reference to Example 1, except that the ratio X of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.12, D004 / D110 is 5.3, the weight percentage of the silicon-based additive in the electrolyte is 2.3%, then a / X = 2.3 / 0.12 = 19.17, and L / a = 12.5 / 2.3 = 5.43.

[0177] Example 10 group

[0178] This group of examples is used to illustrate the influence when the weight percentage of lithium element in lithiated polyacrylic acid changes.

[0179] Example 10a

[0180] Performed with reference to Example 1, except that the weight percentage of lithium element in lithiated polyacrylic acid is 1%.

[0181] Example 10b

[0182] It is carried out with reference to Example 1, except that the weight percentage of lithium element in lithiated polyacrylic acid is 1.8%.

[0183] Example 10c

[0184] It is carried out with reference to Example 1, except that the weight percentage of lithium element in lithiated polyacrylic acid is 3.8%.

[0185] Example 10d

[0186] It is carried out with reference to Example 1, except that the weight percentage of lithium element in lithiated polyacrylic acid is 6%.

[0187] Example 10e

[0188] It is carried out with reference to Example 1, except that the weight percentage of lithium element in lithiated polyacrylic acid is 0%.

[0189] Example 11 group

[0190] This group of examples is used to illustrate the influence when the specific selection of the negative electrode binder is changed.

[0191] Example 11a

[0192] It is carried out with reference to Example 1, except that the ester-modified styrene-butadiene rubber in the negative electrode binder is adjusted to conventional styrene-butadiene rubber (styrene-butadiene rubber not modified with esters).

[0193] Example 11b

[0194] It is carried out with reference to Example 1, except that the negative electrode binder is adjusted to polyacrylic acid and styrene-butadiene rubber, where polyacrylic acid:styrene-butadiene rubber (weight ratio) = 2:1, and the negative electrode active material:negative electrode binder:sodium carboxymethylcellulose:acetylene black (mass ratio) is 96:2:1:1.

[0195] Example 12 group

[0196] This group of examples is used to illustrate the influence when the weight ratio of linear carbonate to linear carboxylate changes.

[0197] Example 12a

[0198] It is carried out with reference to Example 1, except that based on the total mass of the electrolyte, the mass of linear carbonate is 25% and the mass of linear carboxylate is 25%, and the weight ratio of linear carbonate to linear carboxylate is 1.

[0199] Example 12b

[0200] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 44.3%, the mass of the linear carboxylate is 5.7%, and the weight ratio of the linear carbonate to the linear carboxylate is 7.77.

[0201] Example 12c

[0202] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 38.5%, the mass of the linear carboxylate is 11.5%, and the weight ratio of the linear carbonate to the linear carboxylate is 3.35.

[0203] Example 12d

[0204] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 7%, the mass of the linear carboxylate is 43%, and the weight ratio of the linear carbonate to the linear carboxylate is 0.16.

[0205] Example 12e

[0206] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 50%, and the mass of the linear carboxylate is 0%.

[0207] Example 12f

[0208] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 0%, and the mass of the linear carboxylate is 50%.

[0209] Example 12g

[0210] Performed in reference to Example 1, except that, based on the total mass of the electrolyte, the mass of the linear carbonate is 10%, the mass of the linear carboxylate is 40%, and the weight ratio of the linear carbonate to the linear carboxylate is 0.25.

[0211] Example 12h

[0212] Among them, based on the total mass of the electrolyte, the mass of the linear carbonate is 70%, the mass of the linear carboxylate is 5%, the mass of ethylene carbonate is 8.3%, and the weight ratio of the linear carbonate to the linear carboxylate is 14.

[0213] Example 12i

[0214] Among them, based on the total mass of the electrolyte, the mass of the linear carbonate is 5%, the mass of the linear carboxylate is 70%, the mass of ethylene carbonate is 8.3%, and the weight ratio of the linear carbonate to the linear carboxylate is 0.07.

[0215] Comparative Example 1

[0216] It was carried out with reference to Example 1, except that the negative electrode active material was adjusted to artificial graphite.

[0217] Comparative Example 2

[0218] It was carried out with reference to Example 1, except that the silicon-based additive was not added to the electrolyte.

[0219] Test Example

[0220] The lithium-ion batteries obtained in the examples and comparative examples were tested according to the following method.

[0221] 1. Low-temperature cycling test

[0222] The specific test steps were as follows: (1) Place the battery in an environment of -10 ± 1 °C, let it stand for 180 min, discharge it at a constant current of 0.3C to 2.2V, let it stand for 30 min, charge it at a constant current and constant voltage of 0.2C to 3.65V, with a cut-off current of 0.05C, let it stand for 30 min, discharge it at a constant current of 0.3C to 2.2V, record the discharge capacity C0, and let it stand for 30 min; (2) Charge it at a constant current and constant voltage of 0.2C0 to 3.65V, with a cut-off current of 0.05C0, let it stand for 30 min, discharge it at a constant current of 0.3C0 to 2.2V, and this is the first cycle; (3) Repeat step (2) for 300 cycles. When the 300th cycle is reached, record the discharge capacity Cn of the 300th cycle. The calculation formula for the cycle capacity retention rate is: Capacity retention rate (%) = Cn / C0 × 100%.

[0223] 2. Lithium plating test

[0224] The specific test steps were as follows: (1) Place the battery in an environment of -10 ± 1 °C, let it stand for 180 min, discharge it at a constant current of 0.5C to 2.2V, let it stand for 30 min, charge it at a constant current and constant voltage of 0.2C to 3.65V, with a cut-off current of 0.05C, let it stand for 30 min, discharge it at a constant current of 0.5C to 2.2V, record the discharge capacity C0, and let it stand for 30 min; (2) Charge it at a constant current and constant voltage of 0.2C0 to 3.65V, with a cut-off current of 0.05C0, let it stand for 30 min, discharge it at a constant current of 0.5C0 to 2.2V, and this is the first cycle; (3) Repeat step (2) for 50 cycles. When the 50th cycle is reached, charge it at a constant current and constant voltage of 0.2C0 to 3.65V, with a cut-off current of 0.05C0, and dissect it after being fully charged. If there is lithium plating on the negative electrode sheet, the result is indicated as "lithium plating", and if there is no lithium plating on the negative electrode sheet, the result is indicated as "no lithium plating". When there is lithium plating on the negative electrode sheet, it indicates that lithium ions cannot be embedded in the negative electrode sheet in time during low-temperature charging, resulting in the battery being unable to be charged or having a poor charging effect.

[0225] 3. DCR test

[0226] Place the battery in an environment of 25 ± 1 °C, leave it standing for 60 min, discharge it at a constant current of 0.3C until 2.2V, leave it standing for 30 min, charge it at a constant current and constant voltage of 0.3C until 3.65V, with a cut-off current of 0.05C, leave it standing for 30 min, discharge it at a constant current of 0.3C until 2.2V, record the discharge capacity C0, leave it standing for 30 min, charge it at a constant current and constant voltage of 0.3C0 until 3.65V, with a cut-off current of 0.05C0, leave it standing for 30 min, put the battery cell into a -20 °C constant temperature oven, leave it standing for 4 h until thermal equilibrium; discharge it at a constant current of 0.1C0 until 50% SOC, leave it standing for 1 h, record the voltage V1, discharge it at a constant current of 0.5C0 for 30 s, record the voltage V2 after 30 s, and the formula for calculating DCR is: DCR = (V1 - V2) / 0.5C0.

[0227] Record the obtained results in Table 1.

[0228] Table 1

[0229]

[0230]

[0231] It can be seen from Table 1 that by comparing the comparative examples and the examples, it can be seen that the low-temperature cycle capacity retention rate of the battery in the examples is significantly improved, the lithium deposition situation is significantly improved, and the DCR is significantly reduced, indicating that through the synergistic effect of the negative active material in the negative electrode sheet and the silicon-based additive in the electrolyte, the low-temperature charging performance and cycle stability performance of the battery are improved.

[0232] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a matrix and a coating layer on the surface of the matrix. The matrix includes one or more of artificial graphite, natural graphite, mesocarbon microbead graphite, and hard carbon; the coating layer includes a soft carbon material; The electrolyte includes lithium hexafluorophosphate and a silicon-based additive, and the silicon-based additive includes a compound with the general formula ((R2)3Si) n -R1, where n is a positive integer from 1 to 4, and R1 is selected from *-NR3-*, *-O-*, * represents a connecting end, and R2 and R3 are each independently selected from hydrogen and C1-C5 alkyl groups.

2. The battery according to claim 1, wherein The silicon-based additive includes one or more of the following structures:

3. The battery according to claim 2, wherein, The weight percentage of lithium hexafluorophosphate in the electrolyte is 3%-20%, preferably 5%-15%; And / or, the weight percentage of the silicon-based additive in the electrolyte is 0.1%-5%, preferably 0.2%-2%; And / or, the battery satisfies the following relationship: 1.5 ≤ L / a ≤ 200, where L is the weight percentage of lithium hexafluorophosphate in the electrolyte, in %, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

4. The battery according to any one of claims 1 - 3, wherein, The ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material is 0.1-1.5; And / or, the battery satisfies the following relationship: 0.13 ≤ a / X ≤ 20, preferably 0.25 ≤ a / X ≤ 10; where X is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the negative electrode active material, and a is the weight percentage of the silicon-based additive in the electrolyte, in %.

5. The battery according to claim 4, wherein, The battery satisfies the following relationship: 5 ≤ L / a ≤ 75; And / or, the median particle size Dv50 of the negative electrode active material is 5 μm-15 μm; And / or, the particle size distribution of the negative electrode active material is Dv90 / Dv10 = 2.3-3.5, and Dn10 ≥ 1 μm; and / or, the specific surface area of the negative electrode active material is 0.5 m 2 / g - 1.5 m 2 / g; And / or, the specific capacity of the negative electrode active material is 320 mAh / g-355 mAh / g.

6. The battery according to claim 1, wherein, In the XRD spectrum of the negative electrode sheet, the ratio D004 / D110 of the diffraction peak intensity D004 of the 004 crystal plane to the diffraction peak intensity D110 of the 110 crystal plane is 1-5.

5.

7. The battery according to claim 1, wherein, The negative electrode active material layer further includes a negative electrode binder, and the negative electrode binder includes lithiated polyacrylic acid and / or styrene-butadiene rubber.

8. The battery according to claim 7, wherein, The weight percentage of the negative electrode binder in the negative electrode active material layer is 1.2%-5%, preferably 1.5%-2.5%; And / or, the lithiated polyacrylic acid includes lithium element, and the weight percentage of the lithium element in the lithiated polyacrylic acid is 1%-6%, preferably 1.8%-3.8%; And / or, the lithiated polyacrylic acid has an infrared characteristic peak at 2000 ppm-2500 ppm; And / or, the glass transition temperature of the lithiated polyacrylic acid is 80°C-150°C.

9. The battery according to claim 8, wherein, The median particle size Dv50 of the styrene-butadiene rubber is 150 nm-600 nm; And / or, the styrene-butadiene rubber has an infrared characteristic peak at 1680 ppm-1720 ppm; And / or, the glass transition temperature of the styrene-butadiene rubber is -40°C to 40°C; And / or, the styrene-butadiene rubber includes an ester-modified styrene-butadiene rubber; And / or, the negative electrode sheet has a weight loss peak at 400°C-600°C.

10. The battery according to claim 1, wherein, The electrolyte further includes a linear solvent, and the linear solvent includes a linear carbonate and a linear carboxylate. The weight percentage of the linear carbonate in the electrolyte is 10%-90%, and the weight percentage of the linear carboxylate in the electrolyte is 5%-70%. Preferably, the weight ratio of the linear carbonate to the linear carboxylate is 0.14-8.

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