Lithium-ion battery

Abstract

The present invention relates to the technical field of lithium ion batteries, and provides a lithium ion battery, wherein the lithium ion battery comprises a battery cell and an electrolyte, wherein the battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet arranged in a stacked manner, wherein the positive electrode sheet body comprises a first surface and a second surface opposite to each other in a thickness direction, wherein a plurality of protrusions exist on the first surface of the positive electrode sheet, and a recessed portion corresponding to the protrusions exists on the second surface, wherein the electrolyte comprises A wt% of a sulfur-containing additive, wherein the sulfur-containing additive comprises at least one of sulfonate, sulfate and sulfite, and wherein the lithium ion battery satisfies 0.3≤H / T≤6 and 2≤H / A≤100; wherein H is the height of the protrusion, in μm; and T is the thickness of the separator, in μm. The lithium ion battery has both good electrochemical performance and safety performance, can inhibit the generation of negative electrode lithium dendrites, and improve the self-discharge performance of the lithium ion battery.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in various portable electronic devices due to their high energy density and long cycle life. In today's fast-paced society, consumers have higher and higher requirements for battery charging efficiency and battery life. Battery engineers have developed various battery material technologies and electrode post-processing technologies to improve the kinetic performance and energy density of lithium-ion batteries, such as using nano-scale positive and negative electrode materials, ultra-thin diaphragms, developing high-kinetic electrolytes, embossing, punching and wiring of electrodes, etc.

[0003] The pole piece embossing technology can improve the dynamics and liquid storage performance of lithium-ion batteries to a certain extent, and improve the cycle life of lithium-ion batteries. However, after the positive electrode is embossed, the stress at the protrusion of the positive electrode is too large, which compresses the diaphragm, and some of the protrusions will pierce the diaphragm, making the diaphragm in the corresponding area relatively thinner, which will shorten the distance between the positive and negative electrodes, resulting in excessive self-discharge of the lithium-ion battery; and the negative electrode area corresponding to the protruding position is prone to lithium precipitation and lithium dendrites, resulting in short circuits, which cannot meet the requirements of commercial applications. Therefore, if you want to use pole piece embossing technology to obtain high-performance lithium-ion batteries, you need to solve these problems caused by pole piece embossing technology. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a lithium ion battery which has both good electrochemical performance and safety performance, can inhibit the formation of negative electrode lithium dendrites, and improve the self-discharge performance of the lithium ion battery.

[0005] In order to achieve the above-mentioned object, the present invention provides a lithium ion battery, the lithium ion battery comprising a battery cell and an electrolyte, the battery cell comprising a stacked positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet body having a first surface and a second surface opposite to each other in a thickness direction, a plurality of protrusions on the first surface of the positive electrode sheet, and depressions corresponding to the protrusions on the second surface, the electrolyte comprising A wt% of a sulfur-containing additive, the sulfur-containing additive comprising at least one of a sulfonate, a sulfate and a sulfite, the lithium ion battery satisfying 0.3≤H / T≤6 and 2≤H / A≤100; wherein H is the height of the protrusion, in μm; and T is the thickness of the separator, in μm.

[0006] The present invention adopts the above technical scheme to have the following beneficial effects: the positive electrode sheet of the lithium ion battery of the present invention comprises a plurality of protrusions and corresponding recessed portions, and combined with an appropriate amount of sulfur-containing additive added to the electrolyte, under the condition of satisfying a certain relationship, the lithium ion battery has both good electrochemical performance and safety performance, high energy density, can inhibit the formation of negative electrode lithium dendrites, and improves the self-discharge performance of the lithium ion battery.

[0007] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Shown is a schematic diagram of a battery cell in the present invention.

[0009] Figure 2 Shown is a schematic diagram of a positive electrode sheet in the present invention.

[0010] Figure 3 Shown is a schematic diagram of a positive electrode sheet in the present invention.

[0011] Figure 4 Shown is a partial cross-sectional schematic diagram of a positive electrode sheet in the present invention.

[0012] Description of Reference Numerals

[0013] 1 is a positive electrode sheet; 2 is a separator; 3 is a negative electrode sheet; 11 is a first surface; 12 is a positive electrode current collector; 13 is a second surface; 14 is a protruding portion; and 15 is a recessed portion. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0015] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0016] The present invention provides a lithium ion battery, comprising a battery cell and an electrolyte, wherein the battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet arranged in a stacked manner, wherein the positive electrode sheet body comprises a first surface and a second surface opposite to each other in a thickness direction, wherein a plurality of protrusions are present on the first surface of the positive electrode sheet, and recesses corresponding to the protrusions are present on the second surface, wherein the electrolyte comprises A wt % of a sulfur-containing additive, wherein the sulfur-containing additive comprises at least one of a sulfonate, a sulfate and a sulfite, and wherein the lithium ion battery satisfies 0.3≤H / T≤6 (for example, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6) and 2≤H / A≤100 (for example, 2, 5, 10, 15, 20, 25, 30, 40, 60, 80, 100); wherein H is the height of the protrusion, in μm; and T is the thickness of the separator, in μm.

[0017] The study found that when the relationship between the protrusion height and the diaphragm thickness is controlled to meet 0.3≤H / T≤6, the generation of negative electrode lithium dendrites can be suppressed, the risk of lithium dendrites in the negative electrode area corresponding to the protrusion piercing the diaphragm and causing a short circuit can be reduced, and the self-discharge performance of the lithium-ion battery can be improved. When the height of the protrusion of the positive electrode sheet is small and the thickness of the diaphragm is thick, the electrolyte becomes less in the later stage of the cycle, the dynamic performance of the lithium-ion battery becomes worse, and lithium precipitation is more likely to occur; when the height of the protrusion is large and the thickness of the diaphragm is small, the stress of the protrusion is greater, resulting in a too fast self-discharge rate, and the lithium dendrites in the negative electrode area corresponding to the protrusion are more likely to pierce the diaphragm, resulting in a short circuit or a too fast self-discharge rate. When an appropriate amount of sulfur-containing additive is further added to the electrolyte to satisfy the H / A range, the sulfur-containing additive has a good film-forming ability at both the positive and negative electrodes, and can form a relatively flexible CEI film on the protruding portion of the positive electrode sheet, reducing the stress of the protruding portion of the positive electrode sheet on the diaphragm and reducing the self-discharge effect of the tip of the protruding portion; after the sulfur-containing additive is formed at the negative electrode, an organic-inorganic composite SEI film with good elasticity and lithium ion conductivity is formed, such as various alkyl lithium sulfates, alkyl lithium sulfonates, lithium sulfate, lithium sulfite, etc., so that the negative electrode still has good kinetic properties after film formation. In addition, the sulfur-containing additive can control the uniform release of lithium ions to a certain extent after film formation at the positive electrode, avoiding local concentrated release of lithium ions, thereby inhibiting the formation of lithium dendrites, thereby reducing the risk of battery short circuit and improving the battery cycle performance. If H / A does not meet this range, for example, when the height of the protrusion is small and the amount of sulfur-containing additive added is high, H / A is less than 2. In the later stage of the cycle, due to lack of electrolyte and too thick surface films of the positive and negative electrodes, the lithium-ion battery is prone to lithium precipitation and the cycle performance deteriorates. When the height of the protrusion is high and the content of the sulfur-containing additive is low, H / A is greater than 100. There are many cracks on the protrusion of the positive electrode sheet, and a CEI film of sufficient thickness and uniformity cannot be formed. The stress of the protrusion on the diaphragm is still large, the self-discharge rate of the lithium-ion battery is still fast, and the risk of lithium dendrites piercing the diaphragm and causing a short circuit cannot be effectively suppressed.

[0018] In the present invention, the positive electrode sheet can be prepared by embossing to obtain a positive electrode sheet containing multiple protrusions and corresponding protrusions. It can be understood that the corresponding arrangement of the recessed portion and the protruding portion can be understood as that the projection of the protruding portion in the thickness direction of the electrode sheet and the projection of the recessed portion in the thickness direction of the electrode sheet at least partially overlap, the former can fully cover the latter, or the latter fully covers the former, or the two partially overlap. In some embodiments, the projection area of ​​the protruding portion in the thickness direction of the electrode sheet is 80% to 120% (for example, 80%, 90%, 100%, 110%, 120%) of the projection area of ​​the recessed portion in the thickness direction of the electrode sheet.

[0019] In the present invention, H is the height of the protrusion, measured along the thickness direction of the positive electrode sheet (e.g. Figure 4The maximum height difference on the first surface is the distance between the highest point of the protrusion and the plane area of ​​the first surface of the pole piece, for example, Figure 4 H shown in ; T is the thickness of the separator, which can be measured by the size of the separator in the thickness direction of the positive electrode sheet.

[0020] In some embodiments, 0.1≤A≤6 (for example, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6). The addition of an appropriate amount of sulfur-containing additives can further alleviate the lithium deposition at the negative electrode and improve the self-discharge performance of the battery; if the amount added is too much, in the later stage of the cycle, due to the lack of electrolyte and the thick surface film of the positive and negative electrodes, the lithium-ion battery is prone to lithium deposition and the cycle performance deteriorates; if the amount added is too low, the sulfur-containing additive cannot form a CEI film of sufficient thickness and uniformity, the stress of the protrusion on the diaphragm is still large, the self-discharge rate of the lithium-ion battery is still fast, and the risk of lithium dendrites piercing the diaphragm and causing a short circuit cannot be effectively suppressed.

[0021] In some embodiments, 3≤H≤40, for example, 3, 5, 10, 15, 20, 25, 30, 35, 40.

[0022] In some embodiments, 5≤T≤12, such as 5, 6, 7, 8, 9, 10, 11, 12, that is, the thickness of the diaphragm is 5μm-12μm, such as 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm. The diaphragm may include a base film and an optional coating located on at least one side of the base film, and the coating may be an inorganic particle layer, a rubber layer or a combination thereof. Its composition is conventional in the art, and those skilled in the art can select it as needed.

[0023] In the present invention, the sulfur-containing additive comprises at least one of sulfonate, sulfate and sulfite. In some embodiments, the sulfur-containing additive is a cyclic sulfur-containing compound.

[0024] In some embodiments, the sulfur-containing additive includes at least one of the compounds shown in Formula 1-1 to Formula 1-14;

[0025]

[0026] Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formula 1-5 Formula 1-6

[0027]

[0028] Formula 1-7 Formula 1-8 Formula 1-9 Formula 1-10

[0029]

[0030] Formula 1-11 Formula 1-12 Formula 1-13 Formula 1-14.

[0031] Sulfur-containing additives have good film-forming ability, but in the later stages of the cycle, the impedance will increase too much, which will lead to the intensification of lithium precipitation. Severe lithium precipitation will cause the electrolyte to decompose and produce gas, and the cycle will become worse. Studies have found that adding fluorosulfonamide solvents to the electrolyte can repair the SEI film during the cycle, and the impedance of the SEI film formed is lower than that of the SEI film formed by sulfur-containing additives, thereby improving the cycle performance; and in the later stages of the cycle, when other additives are almost consumed, they can remove F and reduce and decompose at the negative electrode, repair the cracked SEI film, and generate a stable SEI film with low impedance and rich in LiF, thereby inhibiting the formation of lithium dendrites at the negative electrode and the attenuation of the capacity retention rate, and extending the cycle life of lithium-ion batteries.

[0032] In some embodiments, the electrolyte further comprises a fluorosulfonamide solvent. The content of the fluorosulfonamide solvent in the electrolyte can be recorded as S wt%.

[0033] In some embodiments, 5≤S≤25, for example, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25.

[0034] In some embodiments, 6≤S+A≤28, such as 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28. Since both the sulfur-containing additive and the fluorosulfonamide solvent have good film-forming ability, controlling their total content within an appropriate range can enable the lithium-ion battery to have a good cycle life and the ability to inhibit the self-discharge of the lithium-ion battery. However, when the addition amount of the two is too high, since both have strong film-forming properties, the electrolyte will be consumed too quickly, thereby deteriorating the cycle life of the lithium-ion battery.

[0035] In some embodiments, 3≤S / A≤20, such as 3, 4, 6, 8, 10, 12, 14, 16, 18, 20. When S is too small and A is too large, the impedance of the electrolyte and the formed SEI film is large, which deteriorates the kinetic performance of the lithium-ion battery; when S is too large and A is too small, the amount of sulfur-containing additive added cannot form a good CEI film at the positive electrode, and the battery short circuit problem cannot be effectively suppressed, and the suppression effect on high-temperature gas production is limited, resulting in poor thermal safety performance of the lithium-ion battery.

[0036] In some embodiments, the lithium ion battery satisfies at least one of the following relationships (a)-(c): (a) 5≤S≤25; (b) 6≤S+A≤28; (c) 3≤S / A≤20.

[0037] In some embodiments, the fluorosulfonamide solvent comprises a compound represented by Formula 2, Formula 2, wherein R1 and R2 are independently substituted or unsubstituted C1-C2 alkyl groups, or R1, R2 and the N connected thereto form a ring, and if substituted, the substituent is F.

[0038] In the present invention, the C1-C2 alkyl group may be a methyl group or an ethyl group; R1, R2 and the N connected thereto form a ring, that is, R1 and R2 are connected, and together with the N connected thereto they form a ring, and the ring may be a five-membered ring or a six-membered ring.

[0039] In some embodiments, the fluorosulfonamide solvent includes at least one of the compounds shown in Formula 2-1 to Formula 2-10:

[0040]

[0041] Formula 2-1 Formula 2-2 Formula 2-3 Formula 2-4 Formula 2-5

[0042]

[0043] Formula 2-6 Formula 2-7 Formula 2-8 Formula 2-9 Formula 2-10.

[0044] In some embodiments, the electrolyte further comprises lithium salt, other functional additives and other solvents.

[0045] In some embodiments, the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethylsulfonate, lithium difluorobis(oxalatophosphate), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium, lithium bis(difluorophosphoryloxy)difluoroborate, lithium tetra(difluorophosphoryloxy)borate, and lithium bis(trifluoromethylsulfonyl)imide.

[0046] In some embodiments, the lithium salt accounts for 12 wt%-28 wt% of the total mass of the electrolyte, for example, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, or 28 wt%.

[0047] In some embodiments, the other functional additives include at least one of vinylene carbonate (VC), vinyl carbonate, vinyl sulfate, succinonitrile (SN), glutaronitrile, adiponitrile (ADN), pimelonitrile, suberonitrile, hemponitrile, 1,3,6-hexanetrinitrile (HTCN), ethylene glycol bis(propionitrile) ether (DENE), glycerol trinitrile (TCP), tetravinylsilane (TVS), tris(trimethylsilyl)borate (TMSB), hexamethyldisilazane (HMDS), 1,2-bis(2-cyanoethoxy)ethane, fluorobenzene (FB), triphenyl phosphite (TPPi) and pentafluoroethoxycyclotriphosphazene (PFPN).

[0048] In some embodiments, the amount of the other functional additives added is 0.1 wt%-8 wt% of the total mass of the electrolyte, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%.

[0049] In some embodiments, the other solvent comprises carbonates and / or carboxylates.

[0050] In some embodiments, the carbonate includes at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0051] In some embodiments, the carboxylic acid ester includes at least one of ethyl acetate (EA), propyl acetate (PA), n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate and ethyl n-butyrate.

[0052] In some embodiments, the other solvents account for 30 wt%-80 wt% of the total mass of the electrolyte, for example, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, or 80 wt%.

[0053] In some embodiments, the battery cell is a wound battery cell, such as Figure 1 As shown, the wound battery cell is obtained by winding a stacked positive electrode sheet 1, a separator 2 and a negative electrode sheet 3.

[0054] In the present invention, there is no particular restriction on the shape of the protrusions and recesses, and their projections along the thickness direction of the electrode sheet can be circular, triangular, square, rhombus, rectangular, elliptical, trapezoidal, hexagonal, etc. There is no particular restriction on the distribution method, and they can be arrayed, such as along the length direction or width direction of the positive electrode sheet, or along the direction with a certain inclination angle to the length direction of the positive electrode sheet, and can be distributed on the entire positive electrode sheet, or in a local area of ​​the positive electrode sheet, such as Figure 2 and Figure 3 As shown, the length direction of the positive electrode sheet is the direction indicated by x, the width direction is the direction indicated by y, and the protrusions are distributed in an array along the direction indicated by a with a certain inclination angle to the direction indicated by x.

[0055] In some embodiments, along the thickness direction of the positive electrode sheet, the total area of ​​the projection of the protrusion accounts for 2%-85% of the total area of ​​the positive electrode sheet, such as 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, preferably 20-70%. There is a gap between two adjacent protrusions, such as Figure 4 As shown in W, W can be measured by the shortest distance between the projections of the two protrusions on the first surface of the positive electrode sheet along the thickness direction of the positive electrode sheet. Those skilled in the art can determine the size of W based on the total area ratio of the projections of the protrusions.

[0056] In some embodiments, along the thickness direction of the positive electrode sheet (e.g. Figure 4 In the z direction), the projection of the protrusion is a circle.

[0057] In some embodiments, in the projection along the thickness direction of the positive electrode sheet, the maximum length of the protrusion is D mm, 0.1≤D≤16, for example, it can be 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16. When the projection of the protrusion is a circle, D is the diameter of the projection circle. The maximum length of the protrusion is, for example, Figure 4 As shown in D.

[0058] In some embodiments, the lithium ion battery satisfies 1≤D≤8.

[0059] In some embodiments, 0.1≤D≤16, and / or, 3≤H≤30. H and D within this range are beneficial for the lithium ion battery to have good liquid retention performance.

[0060] In some embodiments, 0.3≤Z=H / D≤80, for example, it can be 0.3, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 40, 60, 80. When Z is too large, the sharper the protrusion, the easier it is for the positive electrode sheet in this area to produce microcracks, and the more and deeper the microcracks are, these microcracks will aggravate the dissolution of metal ions in the positive electrode material and deteriorate the high-temperature storage gas production, and at the same time promote the formation of lithium dendrites and make it easier to pierce the diaphragm. When Z is within this range, the lithium-ion battery can alleviate the generation of microcracks, thereby alleviating the high-temperature storage gas production, and at the same time make the lithium-ion battery have both good liquid retention performance and safety performance.

[0061] In some embodiments, the lithium-ion battery satisfies 0.02≤A / Z≤4, for example, it can be 0.02, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4. When A / Z is too small, the sulfur-containing additive is not sufficient to effectively fill or cover the microcrack surface of the protrusion, and thus cannot effectively alleviate the problems of high-temperature storage gas production and lithium dendrite formation. When the relationship between A and Z satisfies this range, adding a sulfur-containing additive to the electrolyte can be oxidized at the positive electrode, fill or cover the surface of these microcracks, thereby inhibiting the dissolution of metal ions caused by the cracks, alleviating high-temperature storage gas production, and can further reduce the negative electrode lithium metal deposition, taking into account the cycle performance of the lithium-ion battery.

[0062] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on one side or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0063] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 90-99.2 wt % of positive electrode active material, 0.4-5 wt % of conductive agent, and 0.4-5 wt % of binder.

[0064] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 90-99.2 wt % of the negative electrode active material, 0.3-5 wt % of the conductive agent, and 0.5-5 wt % of the binder.

[0065] In some embodiments, the conductive agent includes but is not limited to at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0066] In some embodiments, the binder includes butadiene styrene rubber latex, polytetrafluoroethylene latex, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxylated chitosan or more.

[0067] In some embodiments, the positive electrode active material is selected from at least one of transition metal lithium oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium-rich lithium manganese oxide; the chemical formula of the transition metal lithium oxide is Li (1+x) Ni y Co z M (1-y-z) O2, where -0.1≤x≤1 (e.g., -0.1, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1); 0≤y≤1 (e.g., 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1), 0≤z≤1 (e.g., 0, 0.1, 0.2, 0.3 , 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1), and 0≤y+z≤1 (for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1); wherein M is at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0068] In some embodiments, the positive electrode current collector may be a positive electrode current collector conventionally used in the art, such as aluminum foil or a composite current collector.

[0069] In some embodiments, the negative electrode sheet includes a negative electrode active material layer.

[0070] In some embodiments, the negative electrode active material layer comprises a negative electrode active material.

[0071] Since fluorosulfonamide solvents can repair SEI during the battery cycle, and the SEI impedance they form is relatively small, when used with silicon-based electrodes, they can not only improve energy density, but their good kinetics and film-forming ability can also continuously repair the rupture of the SEI film after the silicon-based material expands, reduce the impedance of the SEI film, and thus inhibit the expansion of the silicon-based negative electrode and the intensification of side reactions, avoid the early inactivation of silicon particles, and extend the cycle life of silicon particles. The concave part of the positive electrode can be used as a space to store electrolyte, continuously provide electrolyte, and improve the cycle life of the silicon negative electrode; the pre-deformation of the positive electrode can make the positive electrode have a better ability to withstand deformation, and the gap formed by the protrusion also provides sufficient space for the expansion of the silicon negative electrode.

[0072] In some embodiments, the negative electrode active material includes silicon.

[0073] In some embodiments, the content of silicon element in the negative electrode active material is B wt%, and 5 ≤ B ≤ 50 is satisfied, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50. If the amount of silicon doping is too small, the improvement of the energy density of the negative electrode sheet is relatively limited; if the amount of silicon doping is too high, the distribution of silicon particles is relatively dense, which easily leads to a relatively high local self-discharge rate and local lithium deposition, and the cycle expansion of the battery is too large.

[0074] In some embodiments, 0.5 ≤ B / A ≤ 20, such as 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.

[0075] In some embodiments, the lithium-ion battery satisfies 5 ≤ B ≤ 50, and / or, 0.5 ≤ B / A ≤ 20.

[0076] In some embodiments, the silicon element exists in the form of a silicon-based material, and the silicon-based material may include at least one of nano-silicon, silicon oxide material (SiO x , 0 < x < 2) and silicon-carbon material.

[0077] In some embodiments, the negative electrode active material further includes a carbon-based material, and the carbon-based material may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

[0078] In some embodiments, 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.

[0079] In some embodiments, the negative electrode active material layer further includes a conductive agent and a binder. The types of the conductive agent and the binder can refer to the types described in the part of the positive electrode active material layer.

[0080] In some embodiments, the negative electrode active material layer contains 80 - 99.8 wt% of the negative electrode active material, 0.1 - 10 wt% of the conductive agent, and 0.1 - 10 wt% of the binder.

[0081] In some embodiments, the negative electrode active material layer contains 90 - 99.6 wt% of the negative electrode active material, 0.2 - 5 wt% of the conductive agent, and 0.2 - 5 wt% of the binder.

[0082] The negative electrode current collector can be a negative electrode current collector commonly used in the art, such as copper foil or composite current collector, etc.

[0083] In some embodiments, the lithium-ion battery may further include a housing that wraps the battery cell, and the material of the housing may be, for example, an aluminum-plastic film.

[0084] If there is no special explanation, other options of the lithium-ion battery are conventional options in the art. The assembly method of the lithium-ion battery can be carried out in a conventional manner in the art.

[0085] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0086] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0087] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0088] Example 1

[0089] (1) Preparation of negative electrode

[0090] The negative electrode active material (composed of 85wt% graphite + 15wt% silicon-carbon material), styrene-butadiene rubber (SBR), lithium polyacrylate, conductive carbon black (SP) and carbon nanotubes (CNTs) were mixed evenly at a mass ratio of 96.5:1.5:0.5:1.0:0.5, and then appropriate amounts of deionized water were added step by step to obtain negative electrode slurry under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of the copper foil by a coating machine; the coated copper foil was dried, and then rolled, slit and other processes were performed to obtain the desired negative electrode sheet. The silicon content in the negative electrode active material is about 9wt%, that is, B is 9.

[0091] (2) Preparation of positive electrode

[0092] Commercial lithium cobalt oxide (LiCoO2) material, polyvinylidene fluoride (PVDF), SP and carbon nanotubes (CNTs) are dry-mixed in a mass ratio of 96.0:2.0:1.5:0.5. Subsequently, under the action of a vacuum mixer, an appropriate amount of N-methylpyrrolidone (NMP) is gradually added to mix into a uniform slurry. Subsequently, a coating machine is used to evenly coat the positive electrode active slurry on both surfaces of the aluminum foil; the coated positive electrode current collector is dried, and then the desired positive electrode sheet is obtained through roller pressing, slitting, embossing and other processes. The distribution of the protrusion 14 on the positive electrode sheet is as follows: Figure 3 as shown; Figure 4As shown, the embossing makes a plurality of protrusions 14 exist on the first surface 11 of the positive electrode sheet, and a depression 15 corresponding to the protrusions exists on the second surface 13. The positive electrode current collector 12 is an aluminum foil. The projection of the protrusion 14 along the thickness direction z of the positive electrode sheet is circular. The height of the protrusion is 20 μm, that is, H is 20, and its diameter is 2 mm, that is, D is 2, Z = H / D = 10. Along the thickness direction of the positive electrode sheet, the total area of ​​the projection of the protrusion accounts for 45% of the total area of ​​the positive electrode sheet.

[0093] (3) Preparation of electrolyte

[0094] In a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), the required mass of each component is calculated according to the total mass of the electrolyte, and 10% of the total mass of the electrolyte is ethylene carbonate (EC), 10% of fluoroethylene carbonate (FEC), 40% of n-propyl propionate (PP), and 15% of N,N-dimethylaminosulfonyl fluoride (Formula 2-1) are mixed evenly. Then, 15wt% of LiPF6 and 5wt% of LiTFSI based on the total mass of the electrolyte are quickly added thereto, and after dissolution, 2.0wt% of HTCN, 1.0wt% of VC, and 2.0wt% of 1,3-propane sultone (Formula 1-1) based on the total mass of the electrolyte are added. After stirring evenly, the required electrolyte is obtained after passing the tests of moisture, free acid, color, etc. That is, A is 2 and S is 15 in this electrolyte. H / A is 10, S+A is 17, S / A is 7.5, A / Z is 0.2, and B / A is 4.5.

[0095] (4) Preparation of lithium-ion batteries

[0096] like Figure 1 As shown, the negative electrode sheet 3 prepared in the above steps, the commercial separator 2 (thickness of 8 μm, that is, T is 8), and the positive electrode sheet 1 prepared in the above steps are stacked in a certain way, so that the separator 2 completely separates the positive electrode sheet 1 and the negative electrode sheet 3, and at the same time, the negative electrode active material layer completely covers the positive electrode active material layer, and then a winding core with a certain thickness and width is made by winding. Subsequently, an aluminum-plastic film is used for packaging and the electrolyte prepared in the above steps is injected. After vacuum packaging, aging, formation, shaping, sorting and other processes, a soft-pack lithium-ion battery with certain specifications is obtained. The prepared lithium-ion voltage test window is 3.0-4.53V. H / T is 2.5.

[0097] Example 2 and Comparative Example 1

[0098] The operation is performed according to the method described in Example 1, except that the height H of the protrusion is different from the thickness T of the diaphragm, as shown in Table 1.

[0099] Table 1

[0100]

[0101] Note: “*” indicates the same as Example 1.

[0102] Example 3 Group

[0103] The method described in Example 1 is followed, except that the height H of the protrusion is different from the diameter D of the protrusion, as shown in Table 2.

[0104] Table 2

[0105]

[0106] Note: “*” indicates the same as Example 1.

[0107] Example 4 and Comparative Example 2

[0108] The operation was carried out according to the method described in Example 1, except that the height H of the protrusion and the content A of the sulfur-containing additive were different, as shown in Table 3.

[0109] Table 3

[0110]

[0111] Note: “*” indicates the same as Example 1, and “ / ” indicates non-existence.

[0112] Example 5 Group

[0113] The operation was carried out according to the method described in Example 1, except that the content S of the fluorosulfonamide solvent was different, as shown below.

[0114] Example 5-1: S is 0, that is, no fluorosulfonamide solvent is added, S+A is 2, and S / A is 0.

[0115] Example 5-2: S is 2, S+A is 4, S / A is 1.

[0116] Example 5-3: S is 8, S+A is 10, and S / A is 4.

[0117] Example 5-4: S is 22, S+A is 24, and S / A is 11.

[0118] Example 5-5: S is 28, S+A is 30, and S / A is 14.

[0119] Example 6 Group

[0120] The operation was carried out according to the method described in Example 1, except that the silicon content B in the negative electrode active material was different, as shown below.

[0121] Example 6-1: B is 5, B / A is 2.5.

[0122] Example 6-2: B is 20, B / A is 10.

[0123] Example 6-3: B is 30, B / A is 15.

[0124] Example 6-4: B is 40, B / A is 20.

[0125] Example 7 Group

[0126] The operation was carried out according to the method described in Example 1, except that the types of the sulfur-containing additive and the fluorosulfonamide solvent were different, as shown in Table 4.

[0127] Table 4

[0128]

[0129] Note: * indicates the same as Example 1.

[0130] Test Case

[0131] The performance tests of the lithium-ion batteries prepared in the examples and comparative examples were carried out using the following specific test methods. The test results are shown in Tables 5-1 and 5-2.

[0132] (1) Cyclic performance test: In a constant temperature box at 25°C, charge to the upper limit voltage at an initial rate of 3C, and then charge at a constant voltage until the current drops to 0.05C. This is a charging process. After the charging process is completed, let it stand for 10 minutes, and then discharge it to 3.0V at a rate of 0.7C. One charge and discharge process is a cycle. The maximum discharge capacity of the first three cycles is taken as the initial capacity. The percentage of the discharge capacity of a certain cycle in the cycle process to the initial discharge capacity is the capacity retention rate of the cycle to that time.

[0133] After 500 cycles, the discharge capacity was recorded and the capacity retention rate after 500 cycles was calculated.

[0134] (2) Lithium deposition: After the battery has been cycled for 500 T, it is fully charged and disassembled to observe the lithium deposition at the arc of the negative electrode. If only small dots or only slight gray lithium deposition appears, it is slight arc lithium deposition; if obvious silver lithium deposition is observed and the lithium deposition is connected into strips, it is more serious arc lithium deposition; if lithium deposition is obviously observed not only at the arc, but also around the arc, that is, lithium deposition spreads from the arc area to the periphery, it is severe arc lithium deposition; if there is only golden negative electrode powder at the arc of the negative electrode, and the corresponding diaphragm area is only white, it is judged that there is no lithium deposition.

[0135] (3) Self-discharge performance test: Measure the open circuit potential of the sorted lithium-ion batteries to obtain V1, let them stand for 24 hours, and measure the open circuit potential of the battery again to obtain V2. The difference between V1 and V2 is divided by the standing time to obtain the K value of the battery.

[0136] (4) 85℃ storage test for lithium-ion batteries: Charge the lithium-ion battery to full capacity and place it in a thermostat at 85℃. Measure the thickness of the battery every 4 hours until the battery thickness expands by more than 20% of the initial thickness. The difference between the battery thickness after storage and the initial thickness of the battery and the percentage of the initial thickness of the battery are expressed as the battery thickness expansion rate. The storage time exceeding 20% ​​is the battery's lifespan at 85℃ when fully charged.

[0137] Table 5-1

[0138]

[0139] Table 5-2

[0140]

[0141] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: The lithium ion battery comprises a battery cell and an electrolyte, wherein the battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet which are stacked, wherein the positive electrode sheet body comprises a first surface and a second surface which are opposite to each other in a thickness direction, wherein a plurality of protrusions are present on the first surface of the positive electrode sheet, and a recessed portion corresponding to the protrusions is present on the second surface, wherein the electrolyte comprises A wt % of a sulfur-containing additive, wherein the sulfur-containing additive comprises at least one of a sulfonate, a sulfate and a sulfite, and wherein the lithium ion battery satisfies 0.3≤H / T≤6, 2≤H / A≤60, and 0.1≤A≤6, 3≤H≤40, and 5≤T≤12; wherein H is the height of the protrusion, in μm; and T is the thickness of the separator, in μm; In the projection along the thickness direction of the positive electrode sheet, the maximum length of the protrusion is D mm, 1≤D≤8; 0.3≤Z=H / D≤80; 0.02≤A / Z≤4; The electrolyte further comprises a fluorosulfonamide solvent, wherein the content of the fluorosulfonamide solvent in the electrolyte is S wt %; the lithium-ion battery satisfies the following relationship: (a) 5≤S≤25; (b) 6≤S+A≤28; (c) 3≤S / A≤20; the fluorosulfonamide solvent comprises a compound shown in Formula 2, Formula 2, Wherein, R1 and R2 are each independently a substituted or unsubstituted C1-C2 alkyl group, or R1, R2 and the N connected thereto form a ring, and if substituted, the substituent is F; The negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises silicon, the content of silicon in the negative electrode active material is B wt %, and satisfies 5≤B≤50, 0.5≤B / A≤20.

2. The lithium-ion battery according to claim 1, characterized in that The sulfur-containing additive includes at least one of the compounds represented by Formula 1-1 to Formula 1-14; Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formula 1-5 Formula 1-6 Formula 1-7 Formula 1-8 Formula 1-9 Formula 1-10 Formula 1-11 Formula 1-12 Formula 1-13 Formula 1-14.

3. The lithium-ion battery according to claim 1, characterized in that The fluorosulfonamide solvent includes at least one of the compounds shown in Formula 2-1 to Formula 2-10: Formula 2-1 Formula 2-2 Formula 2-3 Formula 2-4 Formula 2-5 Formula 2-6 Formula 2-7 Formula 2-8 Formula 2-9 Formula 2-10.

4. The lithium-ion battery according to claim 1, characterized in that: 3≤H≤30。

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