Lithium-ion batteries and electronic devices

Abstract

The present invention relates to the field of battery technology, and in particular to a lithium-ion battery and an electronic device including the lithium-ion battery. The lithium-ion battery includes a negative electrode sheet and an electrolyte; the negative electrode sheet has a first surface and a second surface opposite to each other in the thickness direction, the first surface has a plurality of protrusions, the second surface has a plurality of concave portions, the protrusions and the concave portions correspond, and the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet is S; the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on at least one side of the negative electrode current collector, the negative electrode active material layer includes a silicon-based material; the electrolyte includes ethyl 2,2-difluoroacetate with a content of F1 and 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether with a content of F2, 1.9≤(F1+F2) / S≤984. The lithium-ion battery of the present invention has the characteristics of long high-temperature cycle life and high safety.

Description

Technical Field

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

[0002] Silicon-based negative electrode materials are considered an important development direction for lithium-ion battery negative electrode materials due to their high specific capacity. However, silicon-based negative electrode materials have the problem of large volume expansion during charging and discharging, which leads to a decrease in the structural stability of the electrode and the detachment and incompleteness of the active substances on the electrode surface, resulting in a decrease in the cycle stability and safety performance of the battery, which is particularly significant in high-temperature environments. Summary of the Invention

[0003] The present invention aims to overcome the above-mentioned problems existing in the prior art and provides a lithium-ion battery and an electronic device including the lithium-ion battery. By regulating the relationship between the content of ethyl 2,2-difluoroacetate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in the electrolyte and the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet, the high-temperature cycle performance and safety of the lithium-ion battery of the present invention (hereinafter referred to as the battery) are optimized.

[0004] The inventors of the present invention have discovered that by embossing the surface of a silicon-based negative electrode sheet, a plurality of convex portions are formed on one side of the negative electrode sheet and a plurality of concave portions are formed on the other side of the negative electrode sheet. This can pre-compress the negative electrode active material and reduce its volume change during the charge and discharge process, thereby reducing the crushing of the negative electrode active material and the damage to the electrode structure, helping to improve the structural stability of the negative electrode sheet, avoiding the shedding of the negative electrode active material due to volume expansion during the charge and discharge process, ensuring the integrity of the electrode structure, and improving the cycle stability of the battery. However, the inventors of the present invention have discovered that although the embossing process can alleviate the volume expansion of the silicon-based negative electrode, the advantages of the embossing process, such as the increased contact area between the electrolyte and the negative electrode active material and the increased reactive sites, also exist. The problem of more intense side reactions under high temperature conditions exacerbates the consumption of the electrolyte and the generation of harmful gases, increases the internal pressure of the battery, deteriorates the high temperature performance, and increases the risk of thermal runaway.

[0005] To overcome the problem of poor high-temperature performance and increased risk of thermal runaway caused by embossing the silicon-based negative electrode, which increases the contact area between the electrolyte and the negative electrode sheet, the inventors of the present invention have discovered through extensive research that introducing ethyl 2,2-difluoroacetate (DFEA) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2), which have good chemical stability and flame retardancy, into the electrolyte can help improve the stability of the electrolyte and the stability of the electrode-electrolyte interface. Furthermore, by regulating the relationship between the DFEA and D2 contents in the electrolyte and the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet, the electrolyte is adapted to the embossed negative electrode sheet, thereby achieving improved high-temperature performance, cycle life, and safety of the battery.

[0006] Based on this, the inventors of the present invention propose the following solutions:

[0007] In a first aspect, the present invention provides a lithium-ion battery, comprising a negative electrode sheet and an electrolyte; the negative electrode sheet having a first surface and a second surface opposite to each other in a thickness direction, the first surface having a plurality of convex portions, the second surface having a plurality of concave portions, the convex portions corresponding to the concave portions, and the ratio of the sum of the orthographic projection areas of the convex portions on the first surface to the area of the negative electrode sheet being S, with a unit of 1; the negative electrode sheet comprising a negative electrode current collector and a surface located on at least one side of the negative electrode current collector. A negative electrode active material layer is provided on the surface; the negative electrode active material layer includes a silicon-based material; the electrolyte includes ethyl 2,2-difluoroacetate and 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, based on the total weight of the electrolyte, the content of ethyl 2,2-difluoroacetate is F1, and the content of 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is F2; F1, F2 and S satisfy 1.9≤(F1+F2) / S≤984.

[0008] A second aspect of the present invention provides an electronic device, comprising the lithium-ion battery according to the first aspect of the present invention.

[0009] Compared with the prior art, the present invention has at least the following effects:

[0010] (1) In the present invention, by introducing DFEA and D2 into the electrolyte, their chemical stability and flame retardancy can be brought into play, the chemical stability of the electrolyte and the electrode-electrolyte interface can be improved, and a stable SEI film can be formed on the surface of the silicon-based material, thereby improving the high-temperature performance of the battery.

[0011] (2) In the present invention, by regulating the relationship between the content of DFEA and D2 in the electrolyte and the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet, the compatibility of the electrolyte and the embossed negative electrode sheet is improved, and the aggravation of the side reaction caused by the excessive contact area between the electrolyte and the negative electrode sheet is avoided, thereby further improving the cycle stability and safety of the battery under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 FIG. 1 is a schematic structural diagram of the convex portion and the concave portion along the thickness direction of the negative electrode sheet in one embodiment of the present invention.

[0013] Figure 2 FIG. 1 is a schematic top view of the convex portion of the negative electrode sheet on the first surface in one embodiment of the present invention.

[0014] In the picture:

[0015] 1. First surface; 2. Negative electrode current collector; 3. Second surface; 4. Protrusion. DETAILED DESCRIPTION

[0016] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0017] A first aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode sheet and an electrolyte; the negative electrode sheet having a first surface and a second surface opposite to each other in a thickness direction, the first surface having a plurality of convex portions, the second surface having a plurality of concave portions, the convex portions corresponding to the concave portions, the ratio of the sum of the orthographic projection areas of the plurality of convex portions on the first surface to the area of the negative electrode sheet being S, with a unit of 1; the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; the negative electrode active material layer comprising a silicon-based material; the electrolyte comprising ethyl 2,2-difluoroacetate and 1,1,2,2,-tetrafluoroethylene 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, based on the total weight of the electrolyte, the content of the ethyl 2,2-difluoroacetate is F1, and the content of the 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is F2; F1, F2 and S satisfy 1.9≤(F1+F2) / S≤984, for example, 1.9, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 910, 920, 930, 940, 950, 960, 970, 975, 980, 982 or 984.

[0018] In one embodiment, 16.67≤(F1+F2) / S≤200.

[0019] In the present invention, the embossing treatment can be obtained by conventional techniques in the field, such as by rolling an embossing roller on the surface of the negative electrode sheet; the sum of the orthographic projection areas of the protrusions on the first surface has the conventional meaning in the field, which refers to the sum of the areas of the projection surfaces formed by the protrusions on the first surface when the parallel projection line is perpendicular to the first surface on the negative electrode sheet, and correspondingly, the orthographic projection area formed by the concave portion is also present on the second surface. The correspondence between the protrusions and the concave portion means that the orthographic projection of the protrusions on the first surface and the orthographic projection of the concave portion on the second surface at least partially overlap, the former can fully cover the latter, or the latter can fully cover the former, or the two partially overlap. In some embodiments, the orthographic projection area of the protrusions on the first surface accounts for 80%-120% of the orthographic projection area of the concave portion on the second surface, for example, 80%, 90%, 100%, 110% or 120%.

[0020] like Figure 1 FIG2 is a schematic diagram showing the structure of the convex and concave portions along the thickness direction of the negative electrode sheet in one embodiment of the present invention, wherein 1 is the first surface, 2 is the negative electrode current collector, and 3 is the second surface. It can be seen from the figure that the negative electrode current collector has a first surface and a second surface on both sides, the first surface has convex portions, and the second surface has concave portions; Figure 2 The figure shows a top view of the convex portion on the first surface of the negative electrode sheet in one embodiment of the present invention, where 1 is the first surface and 4 is the convex portion. It can be seen from the figure that there are several convex portions distributed on the first surface, and the positive projection of the convex portion on the first surface is a circle.

[0021] In the present invention, when the area of the negative electrode sheet is determined, the larger the sum of the orthogonal projection areas of the protrusions on the first surface, the larger the contact area between the electrolyte and the negative electrode active material. This not only accelerates the consumption of the electrolyte, but also an excessively large sum of the orthogonal projection areas of the protrusions will lead to a decrease in the chemical stability of the electrolyte on the surface of the negative electrode sheet. When (F1+F2) / S is less than 1.9, the ratio of the sum of the orthogonal projection areas of the protrusions on the first surface to the area of the negative electrode sheet is too large, and the content of DFEA and D2 is relatively low. The improved stability of the electrolyte is insufficient to improve the aggravated side reactions caused by the excessive contact area, thereby deteriorating the high-temperature cycle performance. When (F1+F2) / S is greater than 984, the ratio of the sum of the orthogonal projection areas of the protrusions on the first surface to the area of the negative electrode sheet is too small, which is not conducive to suppressing the volume expansion of the silicon-carbon material. The DFEA and D2 content is relatively high, and the viscosity of the electrolyte increases, thereby affecting the wettability of the electrolyte to the separator and electrode. An unstable SEI film is easily formed under high temperature conditions, resulting in a reduced high-temperature cycle life of the battery.

[0022] In the present invention, when calculating (F1+F2) / S, F1, F2 and S are only substituted into the numerical calculation, and the unit does not participate in the calculation. For example, when F1=6%, F2=3%, and S=0.24, (F1+F2) / S=(6+3) / 0.24=37.5.

[0023] In the present invention, S is 0.03-0.6, with the unit being 1, for example, 0.03, 0.04, 0.05, 0.075, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.24, 0.28, 0.32, 0.36, 0.4, 0.45, 0.5, 0.52, 0.54, 0.56, 0.58 or 0.6.

[0024] In one embodiment, S is 0.1-0.4, with a unit of 1.

[0025] In the present invention, S can be measured using a combination of a scanning electron microscope and image analysis software. For example, a scanning electron microscope is used to image the first surface of the negative electrode sheet having a plurality of protrusions. Ten regions of equal area are selected from the obtained SEM image at different magnifications. The ratio of the sum of the areas of the orthographic projections of the protrusions in each region to the area of the region is measured and calculated, and the average value is finally taken to obtain S. The above test results can also be obtained by other conventional testing methods in the art.

[0026] In the present invention, F1 is 1-20, and the unit is %, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0027] In one embodiment, F1 is 2-13, and the unit is %.

[0028] In the present invention, F2 is 0.1-10, and the unit is %, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0029] In one embodiment, F2 is 2-7, and the unit is %.

[0030] In the present invention, embossing the surface of the silicon-based negative electrode sheet to form raised portions increases the specific surface area of the silicon-based negative electrode active material, improving the contact area with the electrolyte. This helps the electrolyte cover the surface of the negative electrode active material more evenly, improving wettability. However, the increased contact area and the resulting increase in reactive sites exacerbate side reactions at high temperatures. Introducing DFEA and D2, which have high chemical stability and are non-flammable, into the electrolyte improves the electrolyte's oxidative stability and flame retardancy, and forms a stable SEI film on the surface of the silicon-based negative electrode sheet, mitigating side reactions at high temperatures and improving the battery's high-temperature cycle life and safety. Among them, DFEA has high ionic conductivity and can make the SEI film on the surface of silicon-based materials have good thermal stability. D2, as a co-solvent of the electrolyte, not only prevents the electrolyte from being excessively oxidized on the surface of the negative electrode, but also further improves the stability of the SEI film on the surface of the positive electrode, prevents the electrolyte from oxidative decomposition, but also alleviates the viscosity increase caused by the addition of DFEA. DFEA will also make up for the low conductivity caused by the addition of D2. Therefore, the performance of DFEA and D2 is complementary. The stable solid electrolyte interphase (SEI) formed on the surface of the silicon-based negative electrode can mask the reaction active sites on the surface of the negative electrode, inhibit the decomposition of the electrolyte, reduce side reactions, and improve the high-temperature cycle stability and safety of the battery.

[0031] In the present invention, the negative electrode sheet is embossed to form a plurality of convex portions and a plurality of concave portions on both sides of the surface of the negative electrode sheet, and the concave portions and the convex portions have corresponding positional relationships and the same projection shapes. The shapes of the convex portions and the concave portions and their numbers per unit area are not limited, and the "several" means that the number of the convex portions or the concave portions is greater than or equal to 2.

[0032] In the present invention, the height of the protrusion is 3μm-40μm, for example, 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 25μm, 30μm, 35μm or 40μm; the diameter of the positive projection of the protrusion on the surface of the negative electrode sheet is 0.1mm-16mm, for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 3mm, 5mm, 7mm, 9mm, 10mm, 12mm, 14mm or 16mm.

[0033] In the present invention, the height of the protrusion refers to the maximum vertical distance from any point on the protrusion to the first surface of the negative electrode sheet. The diameter of the orthographic projection of the protrusion on the surface of the negative electrode sheet refers to: when the orthographic projection of the protrusion on the surface of the negative electrode sheet is a regular circle, the diameter of the protrusion is the diameter of the circle; when the orthographic projection of the protrusion on the surface of the negative electrode sheet is an irregular circle, the diameter of the protrusion is the equivalent diameter of a regular circle with the same area as the irregular circle.

[0034] In the present invention, the depth of the recess is 3μm-40μm, for example, 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 25μm, 30μm, 35μm or 40μm; the diameter of the recess is 0.1mm-16mm, for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 3mm, 5mm, 7mm, 9mm, 10mm, 12mm, 14mm or 16mm.

[0035] In the present invention, the diameter of the recess refers to: when the orthographic projection of the recess on the surface of the negative electrode sheet is a regular circle, the diameter of the recess is the diameter of the circle; when the orthographic projection of the recess on the surface of the negative electrode sheet is an irregular circle, the diameter of the recess is the equivalent diameter of a regular circle with the same area as the irregular circle. The depth of the recess refers to the maximum vertical distance from any point within the recess to the second surface of the negative electrode sheet.

[0036] In the present invention, the diameter of the concave portion and the diameter of the orthographic projection of the convex portion on the surface of the negative electrode sheet can be obtained by combining a 3D microscope with image analysis software, selecting 10 convex portions and concave portions on the 3D microscope image, measuring them separately and calculating their respective average values; the depth of the concave portion and the height of the convex portion can be measured using a micrometer, selecting 10 concave portions and convex portions on the negative electrode sheet, measuring them separately and calculating their respective average values. The above test results can also be obtained by other conventional testing methods in the field.

[0037] In the present invention, the contents of DFEA and D2 can be obtained by conventional testing methods in the art, such as by gas chromatography or gas chromatography-mass spectrometry.

[0038] In the present invention, the silicon-based material includes a silicon-carbon material, and the mass content of silicon in the negative electrode active material layer is C Si , C Si3%-40%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%.

[0039] In one embodiment, C Si It is 5%-20%.

[0040] In the present invention, when C Si When the content of silicon in the negative electrode active material layer is less than 3%, the contribution to energy density is low, resulting in insignificant improvement in battery energy density. Si When it is greater than 40%, due to the excessively high content of silicon in the negative electrode active material layer, the volume expansion of the battery is aggravated during the charge and discharge process, resulting in instability of the SEI film under high temperature conditions, and at the same time, the side reactions of the electrolyte are aggravated and decomposed, resulting in an increased risk of thermal runaway of the battery and deterioration of the safety performance and cycle life at high temperatures.

[0041] In the present invention, the mass content of silicon in the negative electrode active material layer can be measured by conventional testing methods in the art, for example, by an ICP spectrometer. The testing method is as follows: 0.1 g of the negative electrode active material layer is scraped as a sample, 10 mL of hydrochloric acid is added, and the sample is digested on a 350°C hot plate for 10 min. After cooling, the volume is fixed to 100 mL, and then diluted 10 times. Part of the solution is taken and analyzed by an ICP spectrometer.

[0042] In the present invention, the median particle size Dv50 of the silicon-based material is 5μm-15μm, for example, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, or 15μm.

[0043] In the present invention, the median particle size Dv50 of the silicon-carbon material is 5μm-15μm, for example, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, or 15μm.

[0044] In the present invention, regulating the particle size distribution of the silicon-carbon material within a certain range can inhibit volume expansion and the occurrence of side reactions in the electrolyte, thereby optimizing the high-temperature cycle life and safety performance of the battery; when Dv50>15μm, the particle size of the silicon-based material is too large, resulting in increased volume expansion during the charge and discharge process, and when Dv50<5μm, the particle size of the silicon-based material is too small, the specific surface area of the silicon-carbon material increases, and the contact area with the electrolyte increases, resulting in increased side reactions and poor high-temperature cycle performance.

[0045] In the present invention, the median particle size Dv50 of the silicon-carbon material can be obtained by conventional testing methods in the art, for example, using a laser particle size analyzer and measuring by laser diffraction: the silicon-carbon material is peeled off from the current collector with NMP and dispersed in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content 0.02wt%-0.03wt%) to form a mixture, and the mixture is ultrasonicated for 2 minutes, and then placed in a Malvern particle size tester for testing.

[0046] In the present invention, the compaction density of the negative electrode active material layer is 1.5 g / cm 3 -1.9g / cm 3 , for example 1.5 g / cm 3 , 1.52g / cm 3 、1.54g / cm 3 , 1.56g / cm 3 、1.58g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 , 1.8g / cm 3 , 1.82g / cm 3 、1.84g / cm 3 , 1.86g / cm 3 , 1.88g / cm 3 or 1.9 g / cm 3 .

[0047] In the present invention, when the compaction density of the negative electrode active material layer is greater than 1.9 g / cm 3 When the compaction density is too high, it is difficult for the electrolyte to achieve good infiltration of the negative electrode sheet, the internal resistance increases, the specific capacity of the silicon-carbon material is not fully utilized, and the high-temperature cycle capacity of the battery decays faster; when the compaction density of the negative electrode active material layer is less than 1.5g / cm 3At this time, the compaction density is too low, resulting in a decrease in the energy density of the negative electrode and an increase in the porosity, which is not conducive to electronic conductivity and an increase in discharge polarization, which in turn causes the battery to decay rapidly during high-temperature cycling and a decrease in high-temperature cycling performance.

[0048] In the present invention, the compacted density of the negative electrode active material layer can be obtained using conventional testing methods in the art. For example, several unit area negative electrode sheets (area is denoted as S) are taken, and the mass of the unit area of the negative electrode sheet is measured using an analytical balance (denoted as m1). The thickness of the negative electrode sheet (denoted as d1) and the thickness of the current collector (denoted as d0) are measured using a micrometer or a 3D microscope. After scraping off the negative electrode active material layer with an acetone solution, the mass of the negative electrode current collector is weighed (denoted as m0). The compacted density of the negative electrode active material layer is calculated using the following formula:

[0049] The compaction density of the negative electrode active material layer = [S / (m1−m0)] / (d1−d0).

[0050] In the present invention, the electrolyte further comprises a fluorinated benzene compound, wherein the fluorinated benzene compound is obtained by replacing the hydrogen atoms on the benzene ring with fluorine atoms, and the chemical formula is C6H 6-n F n , n is an integer of 1-6, for example, 1, 2, 3, 4, 5 or 6.

[0051] In the present invention, the fluorobenzene compound includes at least one of fluorobenzene, o-difluorobenzene (1,2-difluorobenzene), m-difluorobenzene (1,3-difluorobenzene), p-difluorobenzene (1,4-difluorobenzene), 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, and perfluorobenzene.

[0052] In one embodiment, the fluorobenzene includes at least one of m-difluorobenzene, o-difluorobenzene, p-difluorobenzene and fluorobenzene.

[0053] In the present invention, based on the total weight of the electrolyte, the content of the fluorobenzene is F3, F3 is 2-20, and the unit is %, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18% or 20%.

[0054] In one embodiment, F3 is 5-13, and the unit is %.

[0055] In the present invention, F1, F2 and F3 satisfy 0.16≤(F1+F2) / F3≤15, for example, 0.16, 0.18, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 4, 5, 6, 8, 10, 12, 14 or 15.

[0056] In one embodiment, 0.68≤(F1+F2) / F3≤3.54.

[0057] In the present invention, the calculation of (F1+F2) / F3 only takes the numerical part for operation. For example, when F1=4%, F2=1.8%, and F3=6%, (F1+F2) / F3=(4+1.8) / 6=0.97.

[0058] In the present invention, the addition of DFEA and D2 to the electrolyte increases the viscosity of the electrolyte, thereby affecting the wettability of the electrolyte to the electrode material. The introduction of fluorobenzene compounds can reduce the surface energy between the electrolyte and the positive electrode active material layer and the negative electrode active material layer, thereby improving the spreading ability of the electrolyte on the electrode material and improving the wettability. At the same time, thanks to the high chemical stability of fluorobenzene compounds, the oxidative stability and thermal stability of the electrolyte are also improved, reducing the decomposition of the electrolyte under high temperature conditions, thereby improving the high-temperature cycle life and safety performance of the battery while improving the wettability of the electrolyte. However, fluorobenzene compounds have high acidity. When the content of fluorobenzene compounds is too high, side reactions will also occur during high-temperature cycling, affecting the safety and stability of the battery. By adjusting (F1+F2) / F3 within a certain range, the addition amounts of DFEA, D2 and fluorobenzene compounds in the electrolyte can be matched. The three complement each other, which can improve the wettability of the electrolyte, reduce side reactions occurring in the negative electrode, and improve the high-temperature safety performance of the battery.

[0059] In the present invention, the content of the fluorobenzene compound can be obtained by conventional testing methods in the art, such as gas chromatography or gas chromatography-mass spectrometry.

[0060] In the present invention, the electrolyte further includes diethylene sulfate (DTD). Based on the total weight of the electrolyte, the content of diethylene sulfate is F4, 0.1≤F4≤1, and the unit is %, for example, 0.1%, 0.01%, 0.05%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0061] In the present invention, the electrolyte also includes lithium difluorophosphate. Based on the total weight of the electrolyte, the content of the lithium difluorophosphate is F5, 0.1≤F5≤1.5, and the unit is %, for example, 0.1%, 0.05%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.2%, 1.3%, 1.4% or 1.5%.

[0062] In one embodiment, 0.1≤F5≤0.6, the unit is %.

[0063] In the present invention, since the addition of large amounts of DFEA and D2 increases impedance, the addition of DTD and / or lithium difluorophosphate can reduce battery impedance, minimize heat accumulation, and further enhance high-temperature safety. This is because DTD weakens the interaction between lithium ions and solvent molecules in the electrolyte, facilitating lithium ion desolvation, improving contact between the electrolyte and the electrode interface, enhancing electron transport, reducing polarization, and lowering the impedance of the SEI film. However, when F4 exceeds 1%, electrolyte acidity increases, affecting electrolyte quality. Therefore, the DTD content in the electrolyte needs to be maintained within a reasonable range. Meanwhile, lithium difluorophosphate forms a low-impedance solid electrolyte interface (SEI) film rich in LiF and PO compounds on the surface of the negative electrode, while also forming a stable interface film (CEI) on the surface of the positive electrode, effectively inhibiting oxidative decomposition of the electrolyte and protecting the integrity of the electrode structure. However, due to its poor solubility, when F5 exceeds 1.5%, lithium difluorophosphate precipitates at low temperatures, causing internal battery unevenness.

[0064] In the present invention, the electrolyte further includes lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Based on the total weight of the electrolyte, the content of the lithium bis(trifluoromethylsulfonyl)imide is F6, 1≤F6≤12, and the unit is %, for example, 1%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%.

[0065] In one embodiment, 2≤F6≤9, the unit is %.

[0066] In the present invention, LiTFSI has better thermal stability and a decomposition temperature above 200°C. During the charge and discharge process of the battery, LiTFSI helps form a stable solid electrolyte interface (SEI) film on the electrode surface, preventing further decomposition of the electrolyte, thereby improving the cycle stability of the battery at high temperatures. Adding LiTFSI to the electrolyte to replace part of lithium hexafluorophosphate can improve the stability of the electrolyte and improve the high-temperature performance of the battery. However, when F6>12%, it will cause the electrolyte viscosity to increase and corrode the aluminum foil.

[0067] In the present invention, the electrolyte further comprises tripropargyl phosphate (TPP, structural formula ), based on the total weight of the electrolyte, the content of the tripropargyl phosphate is F7, 0.1≤F7≤0.5, in %, for example, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%.

[0068] In the present invention, the introduction of TPP into the electrolyte can inhibit the dissolution of cobalt from the positive electrode and its deposition at the negative electrode, thereby preventing the aggravation of side reactions at the negative electrode. This is because TPP contains three carbon-carbon triple bond unsaturated functional groups, which can form a dense and protective CEI film on the surface of the positive electrode. This CEI film effectively inhibits the dissolution of cobalt from the positive electrode and its migration to the negative electrode, preventing the aggravation of side reactions at the negative electrode and improving the safety and stability of the battery. However, TPP has a large molecular weight, high melting point, and low dielectric constant, which will increase the freezing point of the electrolyte and enhance interionic forces. However, when F7 is greater than 0.5%, it will inhibit the dissociation of lithium salts.

[0069] In the present invention, the contents of TPP and LiTFSI can be obtained by conventional testing methods in the art, such as gas chromatography or gas chromatography-mass spectrometry.

[0070] In the present invention, the electrolyte further comprises an organic solvent, a lithium salt and other additives.

[0071] In the present invention, the organic solvent includes at least one of fluorine-substituted or unsubstituted carbonates and fluorine-substituted or unsubstituted carboxylates, the carbonates including at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl butyrate (EB), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The carboxylates include at least one of ethyl acetate (EA), propyl acetate, n-butyl acetate, isobutyl acetate, methyl propionate (MP), propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl n-butyrate.

[0072] In the present invention, the other additives include at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), tetravinylsilane (TVS), tris(trimethylsilyl)borate (TMSB), hexamethyldisilazane (HMDS), triphenyl phosphite (TPPi), benzonitrile, p-toluonitrile, 3,5-difluorobenzonitrile, adiponitrile (AND), succinonitrile (SN), glutaronitrile, suberonitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrinitrile (HTCN), 1,2,6-hexanetrinitrile and 1,2,3-tris(2-cyanoethoxy)propane.

[0073] In the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI) and lithium difluorobis(oxalatophosphate).

[0074] In the present invention, the negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 80%-98.5%, for example, 80%, 80.5%, 81%, 81.5%, 82%, 82.5%, 83%, 83.5%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 96.5%, 97%, 97.5%, 98%, or 98.5%. The content of the negative electrode conductive agent is 0.1%-10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The content of the negative electrode binder is 0.1%-10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0075] In one embodiment, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 89%-99.5%, the content of the negative electrode conductive agent is 0.1%-5%, and the content of the negative electrode binder is 0.1%-5%.

[0076] In the present invention, the negative electrode active material includes the silicon-based material.

[0077] In the present invention, the lithium ion 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 at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0078] In the present invention, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 80% - 99.8%, for example, 80%, 80.5%, 81%, 81.5%, 82%, 82.5%, 83%, 83.5%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.4% or 99.8%. The content of the positive electrode conductive agent is 0.1% - 10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%. The content of the positive electrode binder is 0.1% - 10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0079] In one embodiment, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 90% - 99.6%, the content of the positive electrode conductive agent is 0.2% - 5%, and the content of the positive electrode binder is 0.2% - 5%.

[0080] In the present invention, the positive electrode active material includes lithium cobaltate or a ternary material of chemical formula LiNi x Co y Mn z M a O2, 0.3 ≤ x ≤ 0.99, 0 < y ≤ 0.35, 0 < z ≤ 0.35, 0 ≤ b ≤ 0.05, and M is selected from at least one of Al, Zr, B, Y, Sr, W, Ti, and Nb. <00002​​​​​​​​z M a The mass content of the ternary material in the lithium cobalt oxide is 0-15%.

[0083] In the present invention, the introduction of the ternary material into the positive electrode active material can improve stability while maintaining high specific energy. The introduction of Ni can increase the separation of Co 3d and O 2p energy bands, reduce the instability of O at high voltage, and further improve the stability of the positive electrode active material. However, due to the presence of Ni 3+ The thermal stability of Ni is poor, and excessive introduction of Ni will lead to poor high-temperature performance and structural stability.

[0084] In the present invention, the positive electrode conductive agent and the negative electrode conductive agent are each independently selected from at least one of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers and graphene.

[0085] In the present invention, the positive electrode binder and the negative electrode binder are each independently selected from at least one of polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyethylene oxide, sodium carboxymethyl cellulose and polyvinylidene fluoride.

[0086] In the present invention, the lithium-ion battery further comprises a separator, and the separator comprises one of polyethylene (PE), polypropylene (PP), and a composite separator of PP and PE.

[0087] In the present invention, the positive electrode current collector and the negative electrode current collector are both conventionally selected by those skilled in the art.

[0088] The present invention also provides an electronic device comprising the lithium ion secondary battery. The present invention is not particularly limited to the electronic device, and it can be any electronic device known in the prior art. The electronic device includes, for example, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, an unmanned aerial vehicle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery or a lithium ion capacitor, etc.

[0089] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0090] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. Based on the examples of the present invention, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0091] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0092] The following examples are used to illustrate the lithium-ion battery of the present invention.

[0093] Example 1:

[0094] Preparation of positive electrode sheet: The positive electrode active material, conductive carbon black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 96.1:2.4:1.5, and stirred thoroughly to form a uniform positive electrode active material slurry. The positive electrode active material slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, rolling and cutting. The positive electrode active material is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.33 Co 0.33 Mn 0.33 The mass fraction of O2 in LiCoO2 is 8%.

[0095] Preparation of negative electrode sheet: weigh artificial graphite and silicon carbon (mass content of silicon element in negative electrode active material layer C Si =12%), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were dispersed in an appropriate amount of deionized water in a mass ratio of 85.5:11.7:0.5:1.0:1.3 and thoroughly stirred to form a uniform negative electrode active material slurry. The negative electrode active material slurry was then coated onto a negative electrode current collector copper foil, dried, and rolled using an embossing roller to obtain negative electrode embossing. The negative electrode sheet was then cut to obtain a negative electrode sheet. The orthographic projection of the protrusion on the surface of the negative electrode sheet had a diameter of 2 mm and a height of 30 μm, while the diameter of the recessed portion was 2 mm and a depth of 30 μm. The ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.135.

[0096] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / EP were mixed in a mass ratio of 1:1:1, and then 13% of fully dried lithium hexafluorophosphate (LiPF6) and 6.8% of fully dried LiTFSI were added based on the total weight of the electrolyte. After dissolution, 9.7% DFEA, 4% D2, 7% p-difluorobenzene, 0.7% DTD, 0.2% lithium difluorophosphate, and 0.2% TPP were added based on the total weight of the electrolyte. The mixture was stirred evenly and the desired non-aqueous electrolyte was obtained after passing the moisture and free acid tests.

[0097] Assembly of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet and separator (porous polymer film) are placed in order, with the separator between the positive and negative electrode sheets. The tabs are then welded and wound to obtain a core, which is then placed in an aluminum-plastic film packaging bag. The process then involves liquid injection, formation, secondary sealing, and sorting to prepare a lithium-ion battery. Finally, the battery's electrical performance is tested.

[0098] Example 2:

[0099] Preparation of positive electrode sheet: The positive electrode active material, conductive carbon black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 96.1:2.4:1.5, and stirred thoroughly to form a uniform positive electrode active material slurry. The positive electrode active material slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, rolling and cutting. The positive electrode active material is LiCoO2 and LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.2 Mn 0.3 The mass fraction of O2 in LiCoO2 is 8%.

[0100] Preparation of negative electrode sheet: weigh artificial graphite and silicon carbon (mass content of silicon element in negative electrode active material layer C Si =12%), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were dispersed in an appropriate amount of deionized water in a mass ratio of 85.5:11.7:0.5:1.0:1.3, and thoroughly stirred to form a uniform negative electrode active material slurry. The negative electrode active material slurry was then coated onto a negative electrode current collector copper foil, dried, and rolled using an embossing roller to obtain negative electrode embossing. The negative electrode sheet was then cut to obtain a negative electrode sheet. The orthographic projection of the protrusion on the surface of the negative electrode sheet had a diameter of 1 mm and a height of 3 μm, while the diameter of the recessed portion was 1 mm and a depth of 3 μm. The ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.21.

[0101] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / EP were mixed in a mass ratio of 1:1:1, and then 13% of fully dried lithium hexafluorophosphate (LiPF6) and 2% of fully dried LiTFSI were added based on the total weight of the electrolyte. After dissolution, 11.5% DFEA, 6.2% D2, 5% o-difluorobenzene, 0.65% DTD, 0.25% lithium difluorophosphate, and 0.27% TPP were added based on the total weight of the electrolyte. The mixture was stirred evenly and the desired non-aqueous electrolyte was obtained after passing the moisture and free acid tests.

[0102] Assembly of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet and separator (porous polymer film) are placed in order, with the separator between the positive and negative electrode sheets. The tabs are then welded and wound to obtain a core, which is then placed in an aluminum-plastic film packaging bag. The process then involves liquid injection, formation, secondary sealing, and sorting to prepare a lithium-ion battery. Finally, the battery's electrical performance is tested.

[0103] Example 3:

[0104] Preparation of positive electrode sheet: The positive electrode active material, conductive carbon black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 96.1:2.4:1.5, and stirred thoroughly to form a uniform positive electrode active material slurry. The positive electrode active material slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, rolling and cutting. The positive electrode active material is LiCoO2 and LiNi 0.5 Co 0.2 Mn 0.27 Al 0.03 O2, LiNi 0.5 Co 0.2 Mn 0.27 Al 0.03 The mass fraction of O2 in LiCoO2 is 8%.

[0105] Preparation of negative electrode sheet: weigh artificial graphite and silicon carbon (mass content of silicon element in negative electrode active material layer C Si =12%), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a mass ratio of 85.5:11.7:0.5:1.0:1.3 were dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode active material slurry. The negative electrode active material slurry was then coated on a negative electrode current collector copper foil, dried, and rolled using an embossing roller to obtain negative electrode embossing. The negative electrode sheet was then cut to obtain a negative electrode sheet. The orthographic projection of the protrusion on the surface of the negative electrode sheet had a diameter of 16 mm and a height of 25 μm, while the diameter of the recessed portion had a depth of 16 mm and a depth of 25 μm. The ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.4.

[0106] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / EP were mixed in a mass ratio of 1:1:1, and then 13% fully dried lithium hexafluorophosphate (LiPF6) and 9% fully dried LiTFSI were added based on the total weight of the electrolyte. After dissolution, 2% DFEA, 7% D2, 13% fluorobenzene, 0.72% DTD, 0.32% lithium difluorophosphate, and 0.25% TPP were added based on the total weight of the electrolyte. The mixture was stirred evenly and the desired non-aqueous electrolyte was obtained after passing the moisture and free acid tests.

[0107] Assembly of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet and separator (porous polymer film) are placed in order, with the separator between the positive and negative electrode sheets. The tabs are then welded and wound to obtain a core, which is then placed in an aluminum-plastic film packaging bag. The process then involves liquid injection, formation, secondary sealing, and sorting to prepare a lithium-ion battery. Finally, the battery's electrical performance is tested.

[0108] Example 4:

[0109] Preparation of positive electrode sheet: The positive electrode active material, conductive carbon black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone in a mass ratio of 96.1:2.4:1.5, and are fully stirred to form a uniform positive electrode active material slurry. The positive electrode active material slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, rolling and cutting; wherein the positive electrode active material is LiCoO2.

[0110] Preparation of negative electrode sheet: weigh artificial graphite and silicon carbon (mass content of silicon element in negative electrode active material layer C Si =12%), conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a mass ratio of 85.5:11.7:0.5:1.0:1.3 were dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode active material slurry. The negative electrode active material slurry was then coated on a negative electrode current collector copper foil, dried, and rolled using an embossing roller to obtain negative electrode embossing. The negative electrode sheet was then cut to obtain a negative electrode sheet. The orthographic projection of the protrusion on the surface of the negative electrode sheet had a diameter of 10 mm and a height of 40 μm, and the diameter of the recess had a depth of 10 mm and a depth of 40 μm. The ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.1.

[0111] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / EP were mixed in a mass ratio of 1:1:1, and then 13% of fully dried lithium hexafluorophosphate (LiPF6) and 5.2% of fully dried LiTFSI were added based on the total weight of the electrolyte. After dissolution, 13% DFEA, 2% D2, 7.8% m-difluorobenzene, 0.59% DTD, 0.34% lithium difluorophosphate, and 0.18% TPP were added based on the total weight of the electrolyte. The mixture was stirred evenly and the desired non-aqueous electrolyte was obtained after passing the moisture and free acid tests.

[0112] Assembly of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet and separator (porous polymer film) are placed in order, with the separator between the positive and negative electrode sheets. The tabs are then welded and wound to obtain a core, which is then placed in an aluminum-plastic film packaging bag. The process then involves liquid injection, formation, secondary sealing, and sorting to prepare a lithium-ion battery. Finally, the battery's electrical performance is tested.

[0113] Example 5 group:

[0114] This set of examples is used to verify the value of "(F1+F2) / S", that is, the impact of regulating the relationship between F1, F2 and S.

[0115] Based on Example 1, the difference is that the sizes of S, F1 and F2 are changed by adjusting the diameter of the protrusion, the amount of DFEA and D2 added to the electrolyte, as follows:

[0116] In Example 5a, during the preparation of the negative electrode sheet, the diameter of the orthographic projection of the convex portion obtained on the negative electrode sheet on the surface of the negative electrode sheet is 0.1 mm, and the height is 30 μm. The diameter of the concave portion is 0.1 mm, and the depth is 30 μm. At this time, the ratio of the sum of the orthographic projection areas of the convex portion on the first surface to the area of the negative electrode sheet is 0.03; during the preparation of the electrolyte, 19.8% DFEA and 9.7% D2 were added based on the total weight of the electrolyte.

[0117] In Example 5b, during the preparation of the negative electrode sheet, the diameter of the orthographic projection of the convex portion obtained on the negative electrode sheet on the surface of the negative electrode sheet is 12.5 mm, and the height is 30 μm. The diameter of the concave portion is 12.5 mm, and the depth is 30 μm. At this time, the ratio of the sum of the orthographic projection areas of the convex portion on the first surface to the area of the negative electrode sheet is 0.6. During the preparation of the electrolyte, 1.05% DFEA and 0.1% D2 were added based on the total weight of the electrolyte.

[0118] In Example 5c, during the preparation of the negative electrode sheet, the diameter of the orthographic projection of the convex portion obtained on the negative electrode sheet on the surface of the negative electrode sheet was 0.8 mm, and the height was 30 μm. The diameter of the concave portion was 0.8 mm, and the depth was 30 μm. At this time, the ratio of the sum of the orthographic projection areas of the convex portion on the first surface to the area of the negative electrode sheet was 0.28. During the preparation of the electrolyte, 3.5% DFEA and 2.2% D2 were added based on the total weight of the electrolyte.

[0119] In Example 5d, during the preparation of the negative electrode sheet, the diameter of the orthographic projection of the convex portion obtained on the negative electrode sheet on the surface of the negative electrode sheet is 16 mm, and the height is 25 μm. The diameter of the concave portion is 16 mm, and the depth is 25 μm. At this time, the ratio of the sum of the orthographic projection areas of the convex portion on the first surface to the area of the negative electrode sheet is 0.3. During the preparation of the electrolyte, 3% DFEA and 2% D2 are added based on the total weight of the electrolyte.

[0120] In Example 5e, during the preparation of the negative electrode sheet, the diameter of the orthographic projection of the convex portion obtained on the negative electrode sheet on the surface of the negative electrode sheet is 10 mm, and the height is 40 μm. The diameter of the concave portion is 10 mm, and the depth is 40 μm. At this time, the ratio of the sum of the orthographic projection areas of the convex portion on the first surface to the area of the negative electrode sheet is 0.1. During the preparation of the electrolyte, 13% DFEA and 7% D2 were added based on the total weight of the electrolyte.

[0121] The calculation results of "(F1+F2) / S" are shown in Table 1.

[0122] Example 6 group:

[0123] This set of embodiments is used to verify the formula "(F1+F2) / F3" and regulate the impact of the relationship between F1, F2 and F3.

[0124] Based on Example 1, the difference is that the sizes of F1, F2 and F3 are changed by adjusting the amount of DFEA, D2 and fluorobenzene compounds added to the electrolyte, as follows:

[0125] In Example 6a, during the preparation of the electrolyte, 19.6% DFEA, 9.7% D2, and 2% p-difluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0126] In Example 6b, during the preparation of the electrolyte, 2% DFEA, 0.97% D2, and 19.8% p-difluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0127] In Example 6c, during the preparation of the electrolyte, 3.5% DFEA, 2.1% D2, and 8.2% p-difluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0128] In Example 6d, during the preparation of the electrolyte, 3.5% DFEA, 2.1% D2, and 0% p-difluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0129] In Example 6e, during the preparation of the electrolyte, 9.7% DFEA, 4% D2, and 7% pentafluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0130] In Example 6f, during the preparation of the electrolyte, 9.7% DFEA, 4% D2, and 7% perfluorobenzene were added based on the total weight of the electrolyte, and the rest were the same as in Example 1.

[0131] The calculation results of "(F1+F2) / F3" are shown in Table 1.

[0132] Example 7 group:

[0133] This group of examples is used to verify the effect of the amount of DTD added to the electrolyte.

[0134] Based on Example 1, the difference is that the addition amount of DTD in the electrolyte is adjusted as follows:

[0135] In Example 7a, during the preparation of the electrolyte, the content of DTD was 0% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0136] In Example 7b, during the preparation of the electrolyte, the content of DTD was 1% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0137] In Example 7c, during the preparation of the electrolyte, DTD was replaced with PST. Based on the total weight of the electrolyte, the content of PST was 0.7%. The rest was consistent with Example 1.

[0138] Example 8 group:

[0139] This group of examples is used to verify the effect of the amount of lithium difluorophosphate added to the electrolyte.

[0140] Based on Example 1, the difference is that the addition amount of lithium difluorophosphate in the electrolyte is adjusted, as follows:

[0141] In Example 8a, during the preparation of the electrolyte, the content of lithium difluorophosphate was 0% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0142] In Example 8b, during the preparation of the electrolyte, the content of lithium difluorophosphate was 1.5% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0143] In Example 8c, during the preparation of the electrolyte, lithium difluorophosphate was replaced with lithium difluorooxalate (LiODFB). Based on the total weight of the electrolyte, the content of LiODFB was 0.2%. The rest was consistent with Example 1.

[0144] Example 9 group:

[0145] This group of examples is used to verify the effect of the amount of LiTFSI added to the electrolyte.

[0146] Based on Example 1, the difference is that the addition amount of LiTFSI in the electrolyte is adjusted as follows:

[0147] In Example 9a, during the preparation of the electrolyte, the content of LiTFSI was 1.1% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0148] In Example 9b, during the preparation of the electrolyte, the content of LiTFSI was 11.8% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0149] In Example 9c, during the preparation of the electrolyte, no LiTFSI was added, and only lithium hexafluorophosphate was added. Based on the total weight of the electrolyte, the total content of lithium hexafluorophosphate was 19.8%. The rest was consistent with Example 1.

[0150] Example 10 group:

[0151] This group of examples is used to verify the effect of the amount of TPP added to the electrolyte.

[0152] Based on Example 1, the difference is that the addition amount of TPP in the electrolyte is adjusted as follows:

[0153] In Example 10a, during the preparation of the electrolyte, the content of TPP was 0% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0154] In Example 10b, during the preparation of the electrolyte, the content of TPP was 0.49% based on the total weight of the electrolyte, and the rest was consistent with Example 1.

[0155] Example 11 group:

[0156] This group of examples is used to verify the mass content of silicon element C in the negative electrode active material layer. Si The impact caused.

[0157] Based on Example 1, the difference is that the C Si The implementation is as follows:

[0158] In Example 11a, during the preparation of the negative electrode sheet, the mass content of silicon in the negative electrode active material layer was controlled to be 3.2%, and the rest was consistent with Example 1.

[0159] In Example 11b, during the preparation of the negative electrode sheet, the mass content of silicon in the negative electrode active material layer was controlled to be 5%, and the rest was consistent with Example 1.

[0160] In Example 11c, during the preparation of the negative electrode sheet, the mass content of silicon in the negative electrode active material layer was controlled to be 20.4%, and the rest was consistent with Example 1.

[0161] In Example 11d, during the preparation of the negative electrode sheet, the mass content of silicon in the negative electrode active material layer was controlled to be 39.7%, and the rest was consistent with Example 1.

[0162] Comparative Example 1:

[0163] Based on Example 1, the difference is that DFEA is not added during the preparation of the electrolyte, that is, F1=0, and the rest is consistent with Example 1.

[0164] Comparative Example 2:

[0165] Based on Example 1, the difference is that D2 is not added during the preparation of the electrolyte, that is, F2=0, and the rest is consistent with Example 1.

[0166] Comparative Example 3:

[0167] Based on Example 1, the difference is that DFEA and D2 are not added during the preparation of the electrolyte, that is, F1=0, F2=0, and the rest are consistent with Example 1.

[0168] Comparative Example 4:

[0169] This group is used to verify the effect of regulating "(F1+F2) / S" by adjusting the ratio S of the sum of the orthographic projection area of DFEA, D2 and the convex portion on the first surface to the area of the negative electrode sheet, as follows:

[0170] Comparative Example 4a: During the preparation of the negative electrode sheet, the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.5; during the preparation of the electrolyte, 1.5% DFEA and 0.85% D2 were added based on the total weight of the electrolyte.

[0171] Comparative Example 4b: During the preparation of the negative electrode sheet, the ratio of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet was 0.027; during the preparation of the electrolyte, 30% DFEA and 10.5% D2 were added based on the total weight of the electrolyte.

[0172] In all embodiments, the orthographic projection area of the convex portion on the first surface accounts for 80%-120% of the orthographic projection area of the concave portion on the second surface.

[0173] Test Example 1:

[0174] Determination of median particle size of silicon-carbon materials:

[0175] Use a laser particle size analyzer and laser diffraction to measure: Use NMP to peel off the negative electrode active material from the current collector and disperse it in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content 0.02wt%-0.03wt%) to form a mixture. Ultrasonicate the mixture for 2 minutes and then place it in a Malvern particle size tester for testing.

[0176] In the above embodiments, the median particle size of the silicon-carbon material is in the range of 5-15 μm.

[0177] Test Example 2:

[0178] Determination of the compaction density of the negative electrode active material layer:

[0179] Take several negative electrode sheets per unit area (area is denoted as S), weigh the mass of the negative electrode sheets per unit area (denoted as m1) using an analytical balance, and then measure the thickness of the negative electrode sheets (denoted as d1) and the thickness of the current collector (denoted as d0) using a micrometer or a 3D microscope. Then, scrape off the negative electrode active material layer with acetone solution and weigh the mass of the negative electrode current collector (denoted as m0). Calculate the compaction density of the negative electrode active material layer using the following formula:

[0180] The compaction density of the negative electrode active material layer = [S / (m1−m0)] / (d1−d0).

[0181] In the above embodiments, the compaction density of the negative electrode active material layer is 1.5-1.9 g / cm 3 within the range.

[0182] Test Example 3:

[0183] Battery performance test:

[0184] (1) Cycle performance test: Place the lithium-ion battery in a 45°C environment and let it stand for 2 hours. When the battery temperature is 45±2°C, charge it to the upper limit voltage (4.53V) at a constant current of 1C, let it stand for 5 minutes and measure the thickness as H0. Then discharge it to 3.0V at a constant current of 0.5C and let it stand for 5 minutes. This is one charge and discharge cycle. The charge and discharge cycles are 500 times. The highest discharge capacity of the first three cycles is recorded as the initial capacity Q0, the discharge capacity of the 500th cycle is Q1, and the thickness after the battery is fully charged is H1. Calculate the battery capacity retention rate = Q1 / Q0×100%; thickness change rate = H1 / H0×100%;

[0185] (2) EIS impedance test: discharge at 0.2C to 3.0V at 25℃±5℃; let it stand for 10 minutes; adjust SOC: charge at 0.7C constant current to 50% SOC of capacity, let it stand for 10 minutes; test the internal resistance in the half-charge state, and then perform AC impedance test, fit the test data, and output the data battery impedance R (unit: mΩ).

[0186] (3) 130℃ thermal shock test: The above lithium-ion battery is subjected to a 130℃ thermal shock test. The test process is as follows: first, the battery is charged to the upper limit voltage at a constant current and constant voltage of 0.7C, and the cut-off current is 0.05C. The initial state of the battery, including voltage, internal resistance, thickness, etc., is tested; then the above battery is placed in a convection or circulating hot air box, and heated at an initial temperature of 25±3℃, with a heating rate of 5±2℃. The temperature is raised to 130±2℃ and maintained for 60 minutes. The test ends after that. The passing standard of the 130℃ thermal shock test is: the battery cell does not catch fire and does not explode. Among them, 15 / 15 means: 15 out of 15 tests passed; 14 / 15 means: 14 out of 15 tests passed; and so on.

[0187] The test results of the battery performance are shown in Table 3.

[0188] Table 1:

[0189]

[0190] Table 2:

[0191]

[0192] It can be seen from Table 2 that the lithium ion battery prepared by the present invention has good high temperature cycle performance and safety compared with the comparative example.

[0193] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery includes a negative electrode sheet and an electrolyte; the negative electrode sheet has a first surface and a second surface opposite to each other in a thickness direction; the first surface has a plurality of protrusions, and the second surface has a plurality of concave portions, the protrusions corresponding to the concave portions, and a ratio S of the sum of the orthographic projection areas of the protrusions on the first surface to the area of the negative electrode sheet, where S is 0.1-0.4, with a unit of 1; the height of the protrusions is 3 μm-40 μm, and the diameter of the orthographic projection of the protrusions on the surface of the negative electrode sheet is 0.1 mm-16 mm; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; the negative electrode active material layer comprises a silicon-based material; The electrolyte comprises ethyl 2,2-difluoroacetate and 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, wherein based on the total weight of the electrolyte, the content of ethyl 2,2-difluoroacetate is F1, and the content of 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is F2; F1, F2 and S satisfy 16.67≤(F1+F2) / S≤200; F1 is 2-13, unit is %; and F2 is 2-7, unit is % The electrolyte also includes a fluorobenzene compound; based on the total weight of the electrolyte, the content of the fluorobenzene compound is F3, F3 is 2-20, and the unit is %; F1, F2 and the content F3 of the fluorobenzene compound satisfy 0.16≤(F1+F2) / F3≤15.

2. The lithium-ion battery according to claim 1, wherein The silicon-based material includes a silicon-carbon material; And / or, the mass content of silicon in the negative electrode active material layer is C Si , C Si 3%-40%; and / or, the median particle size Dv50 of the silicon-based material is 5 μm-15 μm; And / or, the compaction density of the negative electrode active material layer is 1.5 g / cm 3 -1.9g / cm 3 .

3. The lithium ion battery according to claim 1, wherein The electrolyte satisfies the following requirements: the fluorinated benzene compound includes at least one of fluorobenzene, o-difluorobenzene, m-difluorobenzene, p-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, and perfluorobenzene.

4. The lithium ion battery according to claim 1 or 3, wherein The fluorobenzene compound includes at least one of m-difluorobenzene, o-difluorobenzene, p-difluorobenzene and fluorobenzene; And / or, F3 is 5-13, unit is %; and / or, 0.68≤(F1+F2) / F3≤3.

54.

5. The lithium ion battery according to claim 1, wherein The electrolyte further includes vinyl sulfate. Based on the total weight of the electrolyte, the content of the vinyl sulfate is F4, 0.1≤F4≤1, and the unit is %; And / or, the electrolyte further includes lithium difluorophosphate, and the content of the lithium difluorophosphate is F5, 0.1≤F5≤1.5, based on the total weight of the electrolyte, in %.

6. The lithium ion battery according to claim 1, wherein The electrolyte further includes lithium bis(trifluoromethylsulfonyl)imide. Based on the total weight of the electrolyte, the content of lithium bis(trifluoromethylsulfonyl)imide is F6, 1≤F6≤12, and the unit is %.

7. The lithium-ion battery according to claim 1, wherein The electrolyte further includes tripropargyl phosphate, and the content of the tripropargyl phosphate is F7, 0.1≤F7≤0.5, based on the total weight of the electrolyte, in %.

8. An electronic device, characterized in that: The electronic device comprises the lithium-ion battery according to any one of claims 1 to 7.

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