Lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and provides a lithium ion battery, which comprises a battery cell and an electrolyte, and the battery cell comprises a positive electrode sheet, a diaphragm and a negative electrode sheet which are arranged in a stack, the positive electrode sheet body has a first surface and a second surface which are opposite to each other along the thickness direction, a plurality of protruding parts exist on the first surface of the positive electrode sheet, and corresponding recessed parts exist on the second surface, the electrolyte contains A wt% of a sulfur-containing additive, the sulfur-containing additive comprises at least one of a sulfonate, a sulfate and a sulfite, 0.3≤H / T≤6 and 0.1≤A≤6, wherein H is the height of the protruding part, the unit is μm, T is the thickness of the diaphragm, the unit is μm, 1≤D≤8, and / or 0.3≤Z=H / D≤80, 0.02≤A / Z≤4. The battery has good electrochemical performance and safety performance, can inhibit the generation of lithium dendrites of the negative electrode, and can improve the self-discharge performance and relieve the gas generation in high-temperature storage.

Description

[0001] This invention is a divisional application based on the invention with application number 202411708051.X, application date November 27, 2024, and invention title "Lithium-ion Battery". Technical Field

[0002] This invention relates to the technical field of lithium-ion batteries, and specifically to a lithium-ion battery. Background Technology

[0003] 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 increasingly higher demands 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 nanoscale positive and negative electrode materials, ultra-thin separators, developing high-kinetic electrolytes, and embossing, perforating, and wire bonding of the electrodes.

[0004] Electrode embossing technology can improve the kinetics and electrolyte performance of lithium-ion batteries to some extent, thus enhancing their cycle life. However, after embossing the positive electrode, the excessive stress at the protruding areas can compress the separator, and some protrusions can even pierce the separator, causing the separator in the corresponding area to become relatively thinner. This reduces the distance between the positive and negative electrodes, leading to excessive self-discharge in the lithium-ion battery. Furthermore, the negative electrode area corresponding to the protruding areas is prone to lithium deposition, forming lithium dendrites and causing short circuits, failing to meet the requirements for commercial applications. Therefore, to obtain high-performance lithium-ion batteries using electrode embossing technology, it is urgent to solve these problems caused by the electrode embossing technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a lithium-ion battery that combines good electrochemical performance and safety performance, can suppress the formation of lithium dendrites on the negative electrode, and at the same time improve the self-discharge performance of the lithium-ion battery and alleviate gas generation during high-temperature storage.

[0006] To achieve the above objectives, the present invention provides a lithium-ion battery comprising a cell and an electrolyte. The cell includes a positive electrode, a separator, and a negative electrode stacked together. The positive electrode body has a first surface and a second surface facing away from each other along the thickness direction. The first surface of the positive electrode has a plurality of protrusions, and the second surface has corresponding recesses. The electrolyte contains A wt% of a sulfur-containing additive, which includes at least one of sulfonates, sulfates, and sulfites. The lithium-ion battery satisfies 0.3 ≤ H / T ≤ 6 and 0.1 ≤ A ≤ 6; where H is the height of the protrusion in μm; T is the thickness of the separator in μm; the lithium-ion battery satisfies 0.1 ≤ D ≤ 16, where D is the maximum length of the protrusion projected along the thickness direction of the positive electrode in mm; and / or, 0.3 ≤ Z = H / D ≤ 80; the lithium-ion battery satisfies 0.02 ≤ A / Z ≤ 4.

[0007] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0008] The positive electrode of the lithium-ion battery of the present invention includes multiple protrusions and corresponding recesses. Combined with an appropriate amount of sulfur-containing additives added to the electrolyte, under certain conditions, the lithium-ion battery can achieve both good electrochemical performance and safety performance, high energy density, suppress the formation of lithium dendrites on the negative electrode, improve the self-discharge performance of the lithium-ion battery, and alleviate gas generation during high-temperature storage.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0010] Figure 1 The diagram shown is a schematic diagram of a battery cell according to the present invention.

[0011] Figure 2 The diagram shown is a schematic diagram of a positive electrode sheet according to the present invention.

[0012] Figure 3 The diagram shown is a schematic diagram of a positive electrode sheet according to the present invention.

[0013] Figure 4 The figure shown is a partial cross-sectional schematic diagram of a positive electrode sheet according to the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] 1 is the positive electrode; 2 is the separator; 3 is the negative electrode; 11 is the first surface; 12 is the positive current collector; 13 is the second surface; 14 is the protrusion; 15 is the recess. Detailed Implementation

[0016] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0018] This invention provides a lithium-ion battery comprising a cell and an electrolyte. The cell includes a positive electrode, a separator, and a negative electrode stacked together. The positive electrode body has a first surface and a second surface facing away from each other along its thickness direction. The first surface of the positive electrode has multiple protrusions, and the second surface has corresponding recesses. The electrolyte contains Awt% of a sulfur-containing additive, which includes at least one of sulfonates, sulfates, and sulfites. The lithium-ion battery satisfies 0.3 ≤ H / T ≤ 6 (e.g., 0.3, 0.5, 1, 1). 5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6) and 0.1≤A≤6 (e.g., 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6); where H is the height of the protrusion in μm; T is the thickness of the separator in μm; the lithium-ion battery satisfies 0.1≤D≤16, where D is the maximum length of the protrusion in the projection along the thickness direction of the positive electrode sheet in mm; and / or, 0.3≤Z=H / D≤80; the lithium-ion battery satisfies 0.02≤A / Z≤4.

[0019] Studies have found that controlling the relationship between the protrusion height and the separator thickness to satisfy 0.9≤H / T≤6 can suppress the formation of lithium dendrites on the negative electrode, reduce the risk of short circuits caused by lithium dendrites piercing the separator in the negative electrode region corresponding to the protrusion, and improve the self-discharge performance of lithium-ion batteries. When the protrusion height of the positive electrode is small and the separator thickness is thick, the electrolyte content decreases in the later stages of cycling, the kinetic performance of the lithium-ion battery deteriorates, and lithium plating is more likely to occur. When the protrusion height is large and the separator thickness is small, the stress on the protrusion is greater, resulting in a faster self-discharge rate. The lithium dendrites in the negative electrode region corresponding to the protrusion are also more likely to pierce the separator, leading to short circuits or excessively fast self-discharge rates. When a suitable amount of sulfur-containing additive is added to the electrolyte, the sulfur-containing additive has a good film-forming ability at both the positive and negative electrodes. It can form a relatively flexible CEI film at the protrusion of the positive electrode, reducing the stress of the positive electrode protrusion on the separator and reducing the self-discharge effect at the tip of the protrusion. After the sulfur-containing additive forms a film at the negative electrode, it forms an organic-inorganic composite SEI film with good elasticity and lithium-ion conduction ability, such as containing various alkyl lithium sulfates, alkyl lithium sulfonates, lithium sulfate, lithium sulfite, etc., so that it still has good kinetic performance after the film is formed at the negative electrode. In addition, the sulfur-containing additive can control the uniform release of lithium ions to a certain extent after the film is formed at the positive electrode, avoiding local concentrated release of lithium ions, thereby inhibiting the formation of lithium dendrites, reducing the risk of battery short circuit, and improving the cycle performance of the battery.

[0020] In this invention, the positive electrode sheet can be prepared by embossing to obtain a positive electrode sheet containing multiple protrusions and corresponding protrusions. It is understood that the corresponding arrangement of the protrusions and recesses means that the projection of the protrusions in the electrode sheet thickness direction at least partially overlaps with the projection of the recesses in the electrode sheet thickness direction; the former may completely cover the latter, or the latter may completely cover the former, or both may partially overlap. In some embodiments, the projected area of ​​the protrusions in the electrode sheet thickness direction is 80% to 120% (e.g., 80%, 90%, 100%, 110%, 120%) of the projected area of ​​the recesses in the electrode sheet thickness direction.

[0021] In this invention, H is the height of the protrusion, which is along the thickness direction of the positive electrode sheet (e.g., as shown in the figure). Figure 4 The maximum height difference on the first surface (in the direction shown by z) is the distance from the highest point of the protrusion to the planar area of ​​the first surface of the electrode, for example... Figure 4 In the figure, H and T represent the thickness of the separator, which can be measured in terms of the separator's dimensions in the direction of the positive electrode thickness.

[0022] In some embodiments, 3≤H≤40, such as 3, 5, 10, 15, 20, 25, 30, 35, 40.

[0023] In some embodiments, 5 ≤ T ≤ 12, such as 5, 6, 7, 8, 9, 10, 11, or 12, that is, the thickness of the diaphragm is 5 μm-12 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm. The diaphragm may comprise a base film and optionally a coating located on at least one side of the base film. This coating may be an inorganic particle layer, an adhesive layer, or a combination thereof. Its composition is conventional in the art, and those skilled in the art can select it as needed.

[0024] In some embodiments, the battery cell is a wound battery cell, such as... Figure 1 As shown, the wound cell is obtained by winding a positive electrode 1, a separator 2, and a negative electrode 3 that are stacked together.

[0025] In this invention, the shape of the protrusions and recesses is not particularly limited. Their projection along the thickness direction of the electrode sheet can be circular, triangular, square, rhomboid, rectangular, elliptical, trapezoidal, hexagonal, etc. The distribution method is not particularly limited; it can be an array distribution, for example, an array distribution along the length or width direction of the positive electrode sheet, or an array distribution along a direction with a certain angle of inclination to the length direction of the positive electrode sheet. It can be distributed on the entire positive electrode sheet or in a local area of ​​the positive electrode sheet, for example... Figure 2 and Figure 3 As shown, the length direction of the positive electrode is the x-direction, the width direction is the y-direction, and the protrusions are arranged in an array along the a-direction with a certain tilt angle to the x-direction.

[0026] In some embodiments, the total area of ​​the projected protrusions along the thickness direction of the positive electrode sheet accounts for 2%-85% of the total area of ​​the positive electrode sheet, for example, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, preferably 20-70%. A gap exists between two adjacent protrusions, for example... Figure 4 As shown in the figure, W can be measured as the shortest distance between the projections of the two protrusions on the first surface of the positive electrode along the thickness direction of the positive electrode. Those skilled in the art can determine the size of W based on the proportion of the total area of ​​the projections of the protrusions.

[0027] In some embodiments, along the thickness direction of the positive electrode (e.g. Figure 4 In the z-direction, the projection of the protrusion is circular.

[0028] In some embodiments, the maximum length of the protrusion in the projection along the thickness direction of the positive electrode sheet is D mm, where 0.1 ≤ D ≤ 16, and can be, for example, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, or 16. When the projection of the protrusion is circular, D is the diameter of the projected circle. The maximum length of the protrusion is, for example,... Figure 4 As shown in D.

[0029] In some embodiments, the lithium-ion battery satisfies 1≤D≤8.

[0030] In some embodiments, 0.1 ≤ D ≤ 16, and / or 3 ≤ H ≤ 30. H and D within this range are beneficial for lithium-ion batteries to have good liquid retention properties.

[0031] In some embodiments, 0.3 ≤ Z = H / D ≤ 80, such as 0.3, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 40, 60, and 80. When Z is too large, the protrusion is sharper, and the positive electrode sheet in that area is more prone to microcracks. The more numerous and deeper the microcracks, the more they exacerbate the dissolution of metal ions from the positive electrode material and degrade gas generation during high-temperature storage. At the same time, they promote the formation of lithium dendrites, making it easier for them to puncture the separator. When Z is within this range, the generation of microcracks in the lithium-ion battery can be mitigated, thereby alleviating gas generation during high-temperature storage. This also allows the lithium-ion battery to have both good liquid retention and safety performance.

[0032] 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, or 4. When A / Z is too small, the sulfur-containing additive is insufficient to effectively fill or cover the surface of the microcracks on the protrusions, thus failing to effectively alleviate problems such as gas generation during high-temperature storage and the formation of lithium dendrites. When the relationship between A and Z satisfies this range, adding a sulfur-containing additive to the electrolyte can oxidize the positive electrode, fill or cover the surface of these microcracks, thereby inhibiting the dissolution of metal ions caused by cracks, alleviating gas generation during high-temperature storage, and further reducing lithium metal deposition on the negative electrode, while also considering the cycle performance of the lithium-ion battery.

[0033] In some embodiments, 2 ≤ H / A ≤ 100, for example, 2, 5, 10, 15, 20, 25, 30, 40, 60, 80, 100. When the protrusion height is small and the amount of sulfur-containing additive is high, in the later stages of cycling, due to electrolyte shortage and excessively thick positive and negative electrode surface films, lithium-ion batteries are prone to lithium plating, resulting in deteriorated cycle performance. When the protrusion height is high and the content of sulfur-containing additive is low, there are more cracks in the protrusion of the positive electrode sheet, making it impossible to form a sufficiently thick and uniform CEI film. The stress of the protrusion on the separator is still relatively high, the self-discharge rate of the lithium-ion battery is still relatively fast, and it is also impossible to effectively suppress the risk of short circuit caused by lithium dendrites piercing the separator.

[0034] In this invention, the sulfur-containing additive includes at least one selected from sulfonates, sulfates, and sulfites. In some embodiments, the sulfur-containing additive is a cyclic sulfur-containing compound.

[0035] In some embodiments, the sulfur-containing additive includes at least one of the compounds shown in Formula 1-1 to Formula 1-14;

[0036]

[0037]

[0038] Sulfur-containing additives possess excellent film-forming capabilities, but they can lead to excessive impedance growth in the later stages of cycling, which in turn exacerbates lithium plating. Severe lithium plating can cause electrolyte decomposition and gas generation, resulting in poor cycle performance. Studies have found that adding fluorosulfonamide solvents to the electrolyte can repair the SEI film during cycling. The SEI film formed by this solvent has a lower impedance than that formed by sulfur-containing additives, thus improving cycle performance. Furthermore, in the later stages of cycling, when other additives are almost depleted, this solvent can decompose and remove F at the negative electrode, repairing the cracked SEI film and generating a stable SEI film with lower impedance and rich in LiF. This inhibits the formation of lithium dendrites at the negative electrode and the decay of capacity retention, thereby extending the cycle life of lithium-ion batteries.

[0039] In some embodiments, the electrolyte further comprises a fluorosulfonamide solvent. The content of the fluorosulfonamide solvent in the electrolyte can be expressed as 5 wt%.

[0040] In some embodiments, 5≤S≤25, such as 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25.

[0041] In some embodiments, 6 ≤ S + A ≤ 28, such as 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28. Since both sulfur-containing additives and fluorosulfonamide solvents have good film-forming abilities, controlling their total content within an appropriate range can enable lithium-ion batteries to have better cycle life and suppress self-discharge. However, when the addition amount of either is too high, due to their strong film-forming properties, the electrolyte consumption rate will be too fast, thereby degrading the cycle life of the lithium-ion battery.

[0042] 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 relatively 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 additives added cannot form a good CEI film at the positive electrode, so it cannot effectively suppress the battery short circuit problem, and the effect of suppressing high-temperature gas generation is limited, resulting in poor thermal safety performance of the lithium-ion battery.

[0043] In some embodiments, the lithium-ion battery satisfies at least one of the following relationships (a)-(c):

[0044] (a) 5 ≤ S ≤ 25;

[0045] (b) 6 ≤ S + A ≤ 28;

[0046] (c)3≤S / A≤20.

[0047] In some embodiments, the fluorosulfonamide solvent comprises a compound represented by Formula 2.

[0048]

[0049] R1 and R2 are either substituted or unsubstituted C1-C2 alkyl groups, or R1, R2 and the N group connected thereto form a ring. If substituted, the substituent is F.

[0050] In this invention, the alkyl groups of C1-C2 can be methyl or ethyl; R1, R2 and the N connected thereto form a ring, that is, R1 and R2 are connected together and the N connected to them together constitute a ring, which can be a five-membered ring or a six-membered ring.

[0051] In some embodiments, the fluorosulfonamide solvent comprises at least one of the compounds shown in Formulas 2-1 to 2-10:

[0052]

[0053] In some embodiments, the electrolyte further comprises lithium salts, other functional additives, and other solvents.

[0054] In some embodiments, the lithium salt comprises at least one selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium difluorobis(oxalate phosphate), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate borate), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium bis(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, lithium bis(difluorophosphoryloxy)difluoroborate, lithium tetra(difluorophosphoryloxy)borate, and lithium bis(trifluoromethanesulfonyl)imide.

[0055] In some embodiments, the lithium salt accounts for 12wt%-28wt% of the total mass of the electrolyte, for example, it can be 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 22wt%, 24wt%, 26wt%, or 28wt%.

[0056] In some embodiments, the other functional additives include at least one selected from vinylene carbonate (VC), vinyl ethylene carbonate, vinyl sulfate, succinate (SN), glutaronitrile, adiponitrile (ADN), heptanonitrile, octanoic acid nitrile, sebaconitrile, 1,3,6-hexanetrionitrile (HTCN), ethylene glycol bis(propionitrile) ether (DENE), glyceryl trinitrile (TCP), tetravinylsilane (TVS), tri(trimethylsilyl)borate (TMSB), hexamethyldisilazane (HMDS), 1,2-bis(2-cyanoethoxy)ethane, fluorobenzene (FB), triphenyl phosphite (TPPi), and pentafluoroethoxycyclotriphosphazene (PFPN).

[0057] In some embodiments, the amount of the other functional additives added accounts for 0.1wt%-8wt% of the total mass of the electrolyte, for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%.

[0058] In some embodiments, the other solvents include carbonates and / or carboxylic esters.

[0059] 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 methyl ethyl carbonate (EMC).

[0060] In some embodiments, the carboxylic acid ester includes at least one of ethyl acetate (EA), propyl acetate (PA), n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate, and n-ethyl butyrate.

[0061] In some embodiments, the other solvent accounts for 30wt%-80wt% of the total mass of the electrolyte, for example, it can be 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, or 80wt%.

[0062] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector, wherein the positive active material layer includes a positive 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% positive electrode active material, 0.4-5 wt% conductive agent, and 0.4-5 wt% binder.

[0064] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 90-99.2 wt% negative electrode active material, 0.3-5 wt% conductive agent, and 0.5-5 wt% 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 adhesive includes, but is not limited to, one or more of styrene-butadiene rubber latex, polytetrafluoroethylene latex, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxylated chitosan.

[0067] In some embodiments, the positive electrode active material is selected from at least one of transition metal lithium oxides, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium-rich 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 (e.g., 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, Zr.

[0068] In some embodiments, the positive current collector can be a positive current collector conventionally used in the art, such as an 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 contains a negative electrode active material.

[0071] Because fluorosulfonamide solvents can repair the SEI during battery cycling and form a relatively low SEI impedance, when paired with a silicon-based electrode, they not only improve energy density, but their superior kinetics and film-forming ability can also continuously repair the SEI film rupture caused by the expansion of the silicon-based material, reducing the SEI film impedance. This suppresses the expansion of the silicon-based anode and the aggravation of side reactions, preventing premature deactivation of silicon particles and extending the cycle life of the silicon particles. The recessed portion of the positive electrode can serve as a space for storing electrolyte, continuously supplying electrolyte and improving the cycle life of the silicon anode; the pre-deformation of the positive electrode can give it better resistance to deformation, while the gaps formed by the protrusions provide sufficient space for the expansion of the silicon anode.

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

[0073] In some embodiments, the silicon content in the negative electrode active material is B wt%, and satisfies 5 ≤ ​​B ≤ 50, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50. Too little silicon doping results in limited improvement in the energy density of the negative electrode; too much silicon doping leads to a denser distribution of silicon particles, which can easily cause higher local self-discharge rates and localized lithium plating, and excessive cycle expansion of the battery.

[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, silicon elements exist in the form of silicon-based materials, and the silicon-based materials may include at least one of nano-silicon, silicon-oxygen materials (SiO x , where 0 < x < 2), and silicon-carbon materials.

[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 9,0-99.6 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 a copper foil or a 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 can be, for example, an aluminum-plastic film.

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

[0085] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0086] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0087] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the 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 uniformly in a mass ratio of 96.5:1.5:0.5:1.0:0.5. Then, appropriate amounts of deionized water were added stepwise, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode active slurry was then uniformly coated onto both surfaces of a copper foil using a coating machine. The coated copper foil was dried, and then processed through rolling and slitting to obtain the desired negative electrode sheet. The silicon content in the negative electrode active material is approximately 9wt%, i.e., the boron content is 9%.

[0091] (2) Preparation of positive electrode

[0092] Commercially available lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), polystyrene (SP), and carbon nanotubes (CNTs) were dry-mixed at a mass ratio of 96.0:2.0:1.5:0.5. Then, under vacuum stirring, an appropriate amount of N-methylpyrrolidone (NMP) was gradually added to form a homogeneous slurry. Subsequently, the positive electrode active slurry was uniformly coated onto both surfaces of an aluminum foil using a coating machine. The coated positive electrode current collector was dried, and then processed through rolling, slitting, and embossing to obtain the desired positive electrode sheet. The distribution of the protrusions 14 on the positive electrode sheet is as follows: Figure 3 As shown; Figure 4 As shown, the embossing creates multiple protrusions 14 on the first surface 11 of the positive electrode sheet, and corresponding recesses 15 on the second surface 13. The positive current collector 12 is aluminum foil. The projection of the protrusions 14 along the thickness direction z of the positive electrode sheet is circular, with a height of 20 μm (H = 20) and a diameter of 2 mm (D = 2), where Z = H / D = 10. Along the thickness direction of the positive electrode sheet, the total area of ​​the projected protrusions accounts for 45% of the total area of ​​the positive electrode sheet.

[0093] (3) Preparation of electrolyte

[0094] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the required mass of each component was calculated based on the total mass of the electrolyte. Ethylene carbonate (EC) at 10% of the total electrolyte mass, fluoroethylene carbonate (FEC) at 10% of the total electrolyte mass, n-propyl propionate (PP) at 40% of the total electrolyte mass, and N,N-dimethylaminosulfonyl fluoride (Formula 2-1) were mixed thoroughly. Then, LiPF6 at 15 wt% of the total electrolyte mass and LiTFSI at 5 wt% of the total electrolyte mass were quickly added and dissolved. After dissolution, HTCN at 2.0 wt%, VC at 1.0 wt%, and 1,3-propanesulfonyl lactone (Formula 1-1) at 2 wt% of the total electrolyte mass were added. After thorough stirring, the electrolyte was tested for moisture, free acid, and color, and found to be within acceptable limits to obtain the desired electrolyte. That is, the electrolyte has an A content of 2 and a S content of 15. 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 3 prepared in the above steps, the commercially available separator 2 (thickness 8μm, i.e., T=8), and the positive electrode 1 prepared in the above steps are stacked in a certain manner, so that the separator 2 completely separates the positive electrode 1 and the negative electrode 3, while ensuring that the negative electrode active material layer completely covers the positive electrode active material layer. Then, a core with a certain thickness and width is formed by winding. Subsequently, it is packaged with aluminum-plastic film and injected with the electrolyte prepared in the above steps. After vacuum sealing, aging, formation, shaping, and sorting processes, a soft-pack lithium-ion battery with specific 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 carried out according to the method described in Example 1, except that the height H of the protrusion and the thickness T of the diaphragm are different, as shown in Table 1.

[0099] Table 1

[0100] Group H D Z T H / T H / A A / Z Example 1 20 2 10 8 2.50 10 0.20 Example 2-1 5 * 2.5 * 0.63 2.5 0.8 Example 2-2 15 * 7.5 * 1.88 7.5 0.27 Example 2-3 25 * 12.5 * 3.13 12.5 0.16 Examples 2-4 35 * 17.5 * 4.38 17.5 0.11 Examples 2-5 45 * 22.5 * 5.63 22.5 0.09 Examples 2-6 * * * 6 3.33 * * Examples 2-7 * * * 10 2.00 * * Examples 2-8 * * * 13 1.54 * * Comparative Example 1-1 2 * 1 * 0.25 1 2 Comparative Examples 1-2 40 * 20 5 8.00 20 0.1

[0101] Note: "*" indicates that it is the same as in Example 1.

[0102] Example 3 Group

[0103] The operation is carried out according to the method described in Example 1, except that the height H of the protrusion and the diameter D of the protrusion are different, as shown in Table 2.

[0104] Table 2

[0105] Group H D Z H / T H / A A / Z Example 1 20 2 10 2.50 10 0.20 Example 3-1 * 0.2 100 * * 0.02 Example 3-2 * 0.5 40 * * 0.05 Example 3-3 * 1 20 * * 0.1 Examples 3-4 * 5 4 * * 0.5 Examples 3-5 * 10 2 * * 1 Examples 3-6 3 15 0.2 0.38 1.5 10

[0106] Note: "*" indicates that it is the same as in Example 1.

[0107] Example 4 and Comparative Example 2

[0108] The procedure is performed 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 are different, as shown in Table 3.

[0109] Table 3

[0110]

[0111]

[0112] Note: "*" indicates that it is the same as in Example 1, and " / " indicates that it does not exist.

[0113] Example 5 group

[0114] The operation is carried out according to the method described in Example 1, except that the content S of the fluorosulfonamide solvent is different, as detailed below.

[0115] Example 5-1: S is 0, that is, no fluorosulfonamide solvent is added, S+A is 2, and S / A is 0.

[0116] Example 5-2: S is 2, S+A is 4, S / A is 1.

[0117] Example 5-3: S is 8, S+A is 10, and S / A is 4.

[0118] Example 5-4: S is 22, S+A is 24, S / A is 11.

[0119] Example 5-5: S is 28, S+A is 30, and S / A is 14.

[0120] Example 6 group

[0121] The operation is carried out according to the method described in Example 1, except that the silicon element content B in the negative electrode active material is different, as detailed below.

[0122] Example 6-1: B is 5, B / A is 2.5.

[0123] Example 6-2: B is 20, B / A is 10.

[0124] Example 6-3: B is 30, B / A is 15.

[0125] Example 6-4: B is 40, B / A is 20.

[0126] Example 7 group

[0127] The operation is carried out according to the method described in Example 1, except that the types of sulfur-containing additives and fluorosulfonamide solvents are different, as shown in Table 4.

[0128] Table 4

[0129] Group Sulfur-containing additives Fluorosulfonamide solvents Example 1 The compound shown in Formula 1-1 The compound shown in Formula 2-1 Example 7-1 The compounds shown in Formula 1-2 * Example 7-2 Compounds shown in Formula 1-3 * Example 7-3 Compounds shown in Formulas 1-6 * Example 7-4 Compounds shown in Formulas 1-9 * Example 7-5 * The compound shown in Formula 2-2 Examples 7-6 * The compounds shown in Formula 2-3 Example 7-7 * The compounds shown in Formula 2-8 Examples 7-8 * The compound shown in Formula 2-10

[0130] Note: * indicates that it is the same as in Example 1.

[0131] Test case

[0132] The specific test methods for the performance testing of the lithium-ion batteries prepared in the examples and comparative examples are as follows, and the test results are shown in Tables 5-1 and 5-2.

[0133] (1) Cyclic performance test: In a constant temperature chamber at 25℃, the battery is charged in steps at an initial rate of 3C to the upper limit voltage, and then charged at a constant voltage until the current drops to 0.05C, which constitutes one charging process. After the charging process is completed, the battery is left to stand for 10 minutes, and then discharged at a rate of 0.7C to 3.0V. One charge-discharge process is one cycle. The maximum discharge capacity in the first three cycles is taken as the initial capacity. The percentage of the discharge capacity in a certain cycle to the initial discharge capacity is the capacity retention rate to that cycle.

[0134] After 500 cycles, the discharge capacity was recorded and the capacity retention rate after 500 cycles was calculated.

[0135] (2) Lithium plating: After the battery has been cycled for 500T, it is fully charged and disassembled to observe the lithium plating at the arc of the negative electrode. The presence of only small dots or only slight gray lithium plating indicates slight arc lithium plating; the presence of obvious silver lithium plating connected in strips indicates severe arc lithium plating; the presence of lithium plating not only at the arc but also around the arc indicates severe arc lithium plating; the presence of only golden yellow negative electrode powder at the arc of the negative electrode and only white in the corresponding separator area indicates no lithium plating.

[0136] (3) Self-discharge performance test: Measure the open circuit potential of the lithium-ion battery after sorting to obtain V1. After standing for 24 hours, measure the open circuit potential of the battery again to obtain V2. The K value of the battery is obtained by subtracting V2 from V1 and dividing by the standing time.

[0137] (4) Lithium-ion battery 85℃ storage test: The lithium-ion battery was fully charged and placed in a constant temperature chamber at 85℃. The thickness of the battery was measured every 4 hours until the battery thickness expanded by more than 20% of the initial thickness. The difference between the battery thickness after storage and the initial thickness was expressed as the percentage of the initial thickness. The storage time exceeding 20% ​​was defined as the battery's lifespan when fully charged and stored at 85℃.

[0138] Table 5-1

[0139]

[0140]

[0141] Table 5-2

[0142]

[0143]

[0144] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0145] 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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a cell and an electrolyte. The cell includes a positive electrode, a separator, and a negative electrode stacked together. The positive electrode body has a first surface and a second surface facing away from each other along the thickness direction. The first surface of the positive electrode has a plurality of protrusions, and the second surface has a recess corresponding to the protrusions. The electrolyte contains Awt% of sulfur-containing additives, and the sulfur-containing additives include at least one of sulfonates, sulfates, and sulfites. The lithium-ion battery satisfies 0.3≤H / T≤6 and 0.1≤A≤6. Where H is the height of the protrusion, in μm; and T is the thickness of the diaphragm, in μm. The lithium-ion battery satisfies 0.1≤D≤16, where D is the maximum length of the protrusion in the projection along the thickness direction of the positive electrode sheet, in mm; and / or, 0.3≤Z=H / D≤80; The lithium-ion battery satisfies 0.02≤A / Z≤4.

2. The lithium-ion battery according to claim 1, characterized in that, 3≤H≤40, preferably 3≤H≤30.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, 5≤T≤12。 4. The lithium-ion battery according to any one of claims 1-3, characterized in that, 0.3≤H / T≤4.

5.

5. The lithium-ion battery according to claim 1, characterized in that, 1≤A≤5。 6. The lithium-ion battery according to claim 1 or 5, characterized in that, 2≤H / A≤100.

7. The lithium-ion battery according to claim 1, characterized in that, The sulfur-containing additive includes at least one of the compounds shown in Formula 1-1 to Formula 1-14; 8. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery satisfies 1≤D≤8; And / or, 2≤Z=H / D≤20; And / or, 0.05≤A / Z≤2.

5.

9. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains silicon element, and the silicon element content in the negative electrode active material is B wt%, and satisfies 5≤B≤50; And / or, 0.5≤B / A≤20.

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