Battery

Abstract

Battery, characterized in that the battery comprises a positive electrode plate, a negative electrode plate and an electrolyte solution, wherein the negative electrode plate comprises a negative electrode current collector comprising a copper foil and a negative electrode active material layer on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material comprising a silicon-based active material, wherein the electrolyte solution contains lithium bis((trifluoromethyl)sulfonyl)imide, wherein for the battery B − 10 A − C / 10 + 3 ≥ 0 holds, where A is the grain size of the copper foil in µm, B is the mass content of lithium bis((trifluoromethyl)sulfonyl)imide in the electrolyte solution in wt.%, and C is the mass content of the silicon-based active material in the negative electrode active material in wt%, with C ≤ 50.

Description

Technical area

[0001] The present invention relates to the technical field of batteries and, in particular, to a battery. State of the art

[0002] With the constant advancement of science and technology, conventional lithium-ion batteries can no longer meet the stringent requirements of modern devices due to their limited energy density and cycle life, and there is an ever-increasing demand for high-performance batteries. Therefore, the development of next-generation high-performance lithium-ion batteries is now a focus of research.

[0003] Against this backdrop, lithium-ion batteries with a silicon negative electrode are emerging. Because silicon is a low-cost element with abundant supply, it is considered an ideal material for the negative electrode. Although it can provide higher energy density, many challenges arise in the development of lithium-ion batteries with a silicon negative electrode. The biggest problem lies in the volume effect of silicon, i.e., the volume of silicon changes significantly during the charging / discharging of the batteries. This makes the film at the interface very easy to destroy, leading to problems such as electrode breakage, accelerated consumption of the electrolyte solution, deteriorated cycling, and rapid capacity loss.In addition, the electrolyte solution can also react with the negative electrode containing silicon, so that the dynamic properties of the batteries with a negative electrode containing silicon are impaired and thus the battery has poor cycling performance. Disclosure of the invention

[0004] The object of the present invention is to overcome the above-mentioned problems in the prior art and to provide a battery that significantly mitigates the problem associated with the expansion of the negative electrode with silicon and has better cycling performance at room temperature.

[0005] To achieve this object, the present invention provides a battery comprising a positive electrode plate, a negative electrode plate, and an electrolyte solution. The negative electrode plate has a negative electrode current collector comprising a copper foil and a negative electrode active material layer on the surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material comprising a silicon-based active material. The electrolyte solution contains lithium bis((trifluoromethyl)sulfonyl)imide. The battery is B−10A−C / 10+3≥0, where A is the grain size of the copper foil in µm, B is the mass content of lithium bis((trifluoromethyl)sulfonyl)imide in the electrolyte solution in wt.%, and C is the mass content of the silicon-based active material in the negative electrode active material in wt%, with C ≤ 50.

[0006] Preferably, the electrolyte solution also contains a fluorophosphate.

[0007] The technical solutions used here have the following beneficial effects:

[0008] Through the interaction of the inventive development regarding the copper foil and the additive for the electrolyte solution, the problems caused by the expansion of the negative electrode with silicon can be significantly mitigated, thus avoiding problems such as the destruction of the film at the interface and thus the breakage of the electrode, the accelerated consumption of the electrolyte solution, deteriorated cycling, and the rapid drop in capacity. Furthermore, the electrochemical properties of the negative electrode with silicon can be improved, wear at the interface can be reduced, and the cycle life of the battery can be increased. Furthermore, the overall properties of the battery with a negative electrode made of silicon can be positively influenced, its dynamic properties can be enhanced, and its cycling performance at room temperature can be improved.

[0009] In addition, the battery according to the invention can also mitigate the deposition of lithium and extend the service life of the battery.

[0010] In the case where the battery also contains the fluorophosphate, the high temperature properties of the battery can be further improved while taking into account the cycling performance of the battery at room temperature.

[0011] The endpoints of a range or values ​​disclosed herein are not intended to be limited to the exact range or values, but should be understood to include the range or values ​​also including values ​​that are close to the range or values. With respect to value ranges, by combining endpoints of different ranges, an endpoint of a range with a stand-alone value point, and stand-alone value points, one or more new value ranges can be obtained, which are considered to be specifically disclosed herein. Unless specifically stated, the value ranges herein include the endpoints. Detailed embodiments

[0012] The following describes specific embodiments of the present invention in more detail. It should be understood that the detailed embodiments serve only to describe and explain the invention, without limiting it.

[0013] Unless otherwise specified, all technical and scientific terms used in the invention shall have the same meaning as commonly understood by a person skilled in the art in the field to which the invention belongs.

[0014] During research, the inventor discovered that increasing the mechanical properties of the copper foil can suppress the expansion of the silicon negative electrode to a certain extent, and adding lithium bis((trifluoromethyl)sulfonyl)imide to the electrolyte solution can improve film formation and thus the dynamic properties of the battery. However, suppressing the expansion of the silicon negative electrode and improving the cycling performance of the battery cannot be considered simultaneously, and the problem of lithium deposition cannot be solved. The expansion of the silicon negative electrode can be suppressed to a certain extent, for example, if the grain size of the copper foil is set relatively small, so that it has good mechanical properties.However, it leads to poor dynamic properties at the interface between the electrolyte solution and the negative electrode, poor film formation of the electrolyte solution, and easy lithium deposition. Although the addition of LiTFSI improves film formation to some extent, the resulting film at the interface has a poor suppression effect on silicon expansion, so the film is easily broken, resulting in poor battery cycling stability. Lithium deposition and sometimes unsatisfactory cycling performance also occur when the grains of the copper foil are controlled during the addition of LiTFSI.After adjusting several parameters, it was found that suppressing the expansion of the silicon negative electrode and improving the battery's cycling performance can be simultaneously achieved when the grain size of the copper foil, the content of lithium bis((trifluoromethyl)sulfonyl)imide in the electrolyte solution, and the content of silicon element in the negative electrode satisfy a certain relationship. Specifically, the invention proposes the following solution.

[0015] The present invention provides a battery comprising a positive electrode plate, a negative electrode plate, and an electrolyte solution. The negative electrode plate has a negative electrode current collector comprising a copper foil and a negative electrode active material layer on the surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material comprising a silicon-based active material. The electrolyte solution contains lithium bis((trifluoromethyl)sulfonyl)imide (LiTFSI). The battery is B−10A−C / 10+3≥0, where A is the grain size of the copper foil in µm, B is the mass content of lithium bis((trifluoromethyl)sulfonyl)imide in the electrolyte solution in wt.%, and C is the mass content of the silicon-based active material in the negative electrode active material in wt%, with C ≤ 50.

[0016] In some embodiments, 0 ≤ B-10A-C / 10+3 ≤ 13, such as 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13.

[0017] The inventor discovered that a large grain size of the copper foil can mitigate or even suppress lithium deposition in the battery, but results in poor cycling performance of the battery at room temperature. In some embodiments, A ≤ 0.75, such as 0.75, 0.7, 0.65, 0.6, 0.55, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25. When the grain size is within this range, the battery exhibits good cycling performance at room temperature. A smaller grain size of the copper foil results in a smaller crystal boundary, thus a smaller crack in the metallic material and a lower possibility of displacement and deformation of the small grains.As a result, the copper foil material has better mechanical properties and can easily suppress the expansion of the negative electrode with silicon, so that the problems such as the destruction of the film at the interface and thus the breakage of the electrode, the accelerated consumption of the electrolyte solution, the deteriorated cycles, and the rapid decrease of the capacity are avoided.

[0018] In some embodiments, 0.4 ≤ A ≤ 0.7 applies. According to the invention, the grain size is measured according to the method in GB / T6394-2017 Determination of the average grain size of metals, which may be an average grain size.

[0019] During experiments, the inventor discovered that, assuming the relationship is satisfied, both too high and too low LiTFSI content worsen lithium deposition. While the dynamic properties increase with the LiTFSI content, too high a content significantly deteriorates due to the viscosity of the electrolyte solution, resulting in poor dynamic properties. In some embodiments, 0.5 ≤ B ≤ 15 holds, such as 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15. When the LiTFSI content is within this range, the battery's cycle performance can be significantly improved while simultaneously suppressing lithium deposition.The reason may be that at a certain concentration of LiTFSI in the electrolyte solution, the interface between the negative electrode and silicon contains a higher content of lithium ions, thus preventing lithium deposition during cycling at room temperature, which is caused by the poor dynamics of the negative electrode and silicon, and achieving excellent film formation. Thus, the formed film has a high content of inorganic substances and a certain toughness, suppressing the expansion of the negative electrode and silicon.

[0020] In some embodiments, 2 ≤ B ≤ 12. The energy density of the battery increases with the silicon content, but too high a silicon content leads to a significant deterioration of the battery's properties. In some embodiments, 2 ≤ C ≤ 50, such as 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50. If this relationship is satisfied and the Si content is within this range, the battery's cycling performance can be further improved with the reduction of the silicon content, and lithium deposition can be mitigated or even suppressed.

[0021] In some embodiments, 2 ≤ C ≤ 30. The inventor found during experiments that when the relationship is satisfied and the values ​​of A, B, and C are each within the preferred range, the battery can achieve good cycling performance and significant suppression of lithium deposition, but cannot achieve satisfactory cycling performance at high temperatures. This may be because at high temperatures, the stability of the positive electrode interface is significantly reduced, and therefore, better and sufficient protection for the positive electrode interface is needed. Research shows that by adding fluorophosphate to the electrolyte solution, good protection for the positive electrode interface can be formed, which further improves the cycling performance at high temperatures without affecting the cycling performance of the battery at room temperature.Furthermore, it was found that this substance has a lesser influence on the impedance of the negative electrode with silicon and does not cause obvious deterioration in cycling at room temperature. This substance can also significantly improve the stability of the positive electrode interface, which is low due to the high content of lithium salt at the positive electrode, to improve the stability of the electrolyte solution at the positive electrode. In some embodiments, the electrolyte solution also includes a fluorophosphate, the type of which is not particularly limited, including at least a compound of tris(2,2,2-trifluoroethyl)phosphate and tris(2,2,2-trifluoroethyl)phosphite, but is not limited thereto. In some embodiments, the content of fluorophosphate in the electrolyte solution is 0.1-6 wt%, such as 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%.

[0022] In some embodiments, the electrolyte solution also includes a second additive that includes at least one of a nitrile compound, a sulfur-containing compound, and a fluorine compound other than fluorophosphate, but is not limited thereto.

[0023] In some embodiments, the nitrile compound includes at least one of, but is not limited to, 1,3,6-hexanetricarbonitrile (HTCN), hexanedinitrile (AND), butanenitrile (SN), 1,4-dicyano-2-butylene, ethylene glycol bis(propionitrile) ether (DENE), and tris(3-cyanopropyl) phosphate (PCN). In some embodiments, the proportion of the nitrile compound based on the total mass of the electrolyte solution is 2-8 wt%, such as 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, which increases the stability of the interface through coordination to the positive electrode and further improves the battery performance at high voltage.

[0024] In some embodiments, the sulfur-containing compound comprises at least one of 1,3-propanesultone (PS), 1-propylene-1,3-sultone (PST), 5-methyloxathiolane-2,2-dioxide, 2,4-butanesultone, and 1,4-butanesultone. In some embodiments, the proportion of the sulfur-containing compound based on the total mass of the electrolyte solution is 0.5-5 wt%, such as 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 5 wt%. The sulfur-containing additive can form a film at the interface of the negative electrode with high stability at high temperatures to reduce gas evolution and significantly increase high-temperature shelf life and high-temperature cycling performance.

[0025] In some embodiments, the fluorine compound, unlike fluorophosphate, comprises at least one compound selected from the group consisting of fluorocarbonates, fluorocarboxylic acids, and fluoroethers. For example, it may comprise at least one compound selected from the group consisting of fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC), fluorodiethyl carbonate (FDEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 2,2,2-trifluoroethyl acetate (FEA), 2,2-difluoroethyl acetate, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE). The fluorine compound not only exhibits good oxidation resistance and a strong stabilizing effect on the positive electrode, but can also form a film on the negative electrode and reduce the side reaction at the negative electrode. The film formed by the fluorine compound exhibits good toughness and can reduce SEI cracking caused by silicon expansion.In combination with the smaller copper grains, it can further suppress the expansion of the silicon to increase the stability and cycle performance of the battery and mitigate or even suppress the deposition of lithium in the battery.

[0026] In some embodiments, the content of the second additive in the electrolyte solution is 2-40 wt%, such as 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%.

[0027] In some embodiments, the electrolyte solution also includes an electrolyte salt.

[0028] In some embodiments, the electrolyte salt comprises at least one of lithium salt, sodium salt, potassium salt, aluminum salt, zinc salt and magnesium salt, more preferably lithium salt.

[0029] In some embodiments, the lithium salt comprises at least one salt of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium oxalatodifluoroborate (LiDFOB), lithium bisoxalatodifluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluorasenate, lithium bis(pentafluoroethylsulfonyl)imide, and lithium tris(trifluoromethylsulfonyl)methide.

[0030] In some embodiments, the content of the electrolyte salt in the electrolyte solution is 7-30 wt%, such as 7 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%.

[0031] In some embodiments, the electrolyte solution also comprises an organic solvent. The organic solvent comprises carbonic acid esters and / or carboxylic acid esters. For example, in some embodiments, the carbonic acid ester comprises at least one compound selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and ethyl methyl carbonate. In some embodiments, the carboxylic acid ester comprises at least one compound selected from propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl n-butyrate.

[0032] In some embodiments, the content of the organic solvent in the electrolyte solution is 30-80 wt%, such as 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%.

[0033] In some embodiments, the thickness of the copper foil is 4 µm - 12 µm, such as 4 µm, 6 µm, 8 µm, 10 µm, 12 µm.

[0034] In some embodiments, the silicon-based active material comprises at least one of nano-silicon (Si), silicon alloys, silicon-oxygen materials for the negative electrode (SiO x , where 0 < x < 2), and silicon-carbon materials for the negative electrode (such as Si / C), preferably silicon-carbon materials for the negative electrode. This can be a conventional silicon-based active substance, commercially available or homemade.

[0035] Excessively large silicon particle sizes cause very high stresses that even small copper grains cannot withstand. This causes silicon to detach from the copper foil or pierce through the copper foil during expansion, resulting in corrosion of the copper foil, destruction of the copper crystal structure, and thus impairment of the dynamic properties of the electrolyte solution. Excessively small silicon particle sizes result in an excessively large specific surface area and excessive side reactions, so that the additive in the electrolyte solution cannot form a sufficient protective film, and the film is easily broken during expansion.If the relationships according to the invention are met, a protective film with good properties can still be formed even with a large or small silicon particle size, preventing film breakage, maintaining good dynamic properties of the electrolyte solution and thus good cycling performance of the battery, and suppressing lithium deposition. In some embodiments, the particle size of the silicon-based active material Dv50 is 3 µm - 15 µm, such as 3 µm, 5 µm, 7 µm, 9 µm, 11 µm, 13 µm, 15 µm. Within this range, the cycling performance of the battery at room temperature can be further improved.

[0036] In some embodiments, the active material for the negative electrode also comprises a carbon-based active material.

[0037] In some embodiments, the carbon-based active material comprises at least one of graphite (such as artificial or natural graphite), hard carbon, and soft carbon.

[0038] In some embodiments, the particle size of the carbon-based active material Dv50 is 4 µm - 20 µm, such as 4 µm, 6 µm, 8 µm, 10 µm, 12 µm, 14 µm, 16 µm, 18 µm, 20 µm. When the particle size of the carbon-based active material is within this range, in combination with the relationship between A, B, and C, the cycling performance of the product can be further increased. The reason is probably that the carbon-based active material with a particle size in this range is favorable for the incorporation of silicon, so that sufficient space is created for the expansion of silicon, the damage to the battery caused by the expansion of silicon is mitigated, the destruction of the copper foil is avoided, etc. This in turn achieves better stability of the negative electrode and improved dynamic properties.

[0039] In some embodiments, the negative electrode active material layer comprises 80-99.8 wt% negative electrode active material, 0.1-10 wt% of an electrically conductive agent, and 0.1-10 wt% binder.

[0040] In some embodiments, the negative electrode active material layer comprises 90-99.6 wt% negative electrode active material, 0.2-5 wt% of an electrically conductive agent, and 0.2-5 wt% binder.

[0041] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer on the surface of the positive electrode current collector.

[0042] In some embodiments, the positive electrode active material layer comprises a positive electrode active material, an electrically conductive agent, and a binder.

[0043] In some embodiments, the positive electrode active material layer comprises 80-99.8 wt% positive electrode active material, 0.1-10 wt% of an electrically conductive agent, and 0.1-10 wt% binder.

[0044] In some embodiments, the positive electrode active material layer comprises 90-99.6 wt% positive electrode active material, 0.2-5 wt% of an electrically conductive agent, and 0.2-5 wt% binder.

[0045] In some embodiments, the active material for the positive electrode comprises a lithium transition metal oxide.

[0046] In some embodiments, the lithium transition metal oxide has a chemical formula of Li 1+x Ni y Co z M mO2, where -0.1 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ m ≤ 1, and M contains at least one element selected from the group consisting of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Mo, Zr, Y, La, B, W, and Nb. Using lithium transition metal oxide as the positive electrode active material reduces the side reaction at the interface and realizes reversible charge / discharge with high dynamics. When used in conjunction with fluorophosphate, this can further enhance the stability at the interface and improve high-temperature cycling performance.

[0047] The type of binder and electrically conductive agent used in the positive electrode active material layer may be the same as or different from the type of binder and electrically conductive agent used in the negative electrode active material layer.

[0048] In some embodiments, the electrically conductive agent is at least one agent selected from electrically conductive carbon black, acetylene black, Ketjen black, electrically conductive graphite, electrically conductive carbon fiber, carbon nanotubes, and metal powder.

[0049] In some embodiments, the binder is at least one agent selected from sodium carboxymethylcellulose, styrene-butadiene polymer, polytetrafluoroethylene, and polyethylene oxide.

[0050] In some embodiments, the battery also includes a separator known in the art, such as polyethylene, polypropylene, and the like.

[0051] In some embodiments, the battery is a lithium secondary battery.

[0052] In some embodiments, the battery is a wound battery, that is, the battery is obtained by laminating and winding the positive electrode plate, the negative electrode plate, and the separator in the order of the positive electrode plate, the separator, and the negative electrode plate. The wound battery has a straight portion and a curved portion.

[0053] In some embodiments, the battery is a pouch battery and more preferably also includes an aluminum-plastic foil outside the battery. Thus, the pouch battery includes a cell and an aluminum-plastic foil surrounding the cell. The cell includes the positive electrode plate, the separator, and the negative electrode plate laminated together. The cell may be a wound cell and wound using a conventional method in the field. The cell may be inserted into the aluminum foil (such as aluminum-plastic foil) of the outer packaging. The electrolyte solution is filled into the aluminum foil of the outer packaging, vacuum-packed, allowed to stand, formed, shaped, and sorted to obtain the lithium secondary battery.

[0054] The technical solutions according to the invention are described clearly and comprehensively below using the exemplary embodiments of the invention. Of course, the described exemplary embodiment does not represent all of the exemplary embodiments of the invention, but only a portion. Based on the exemplary embodiment in the present invention, the other exemplary embodiments that can be derived by a person skilled in the art without inventive step are intended to fall within the scope of the invention.

[0055] Unless otherwise stated, the materials and agents used in the following embodiments are commercially available.

[0056] The invention is described in more detail below in connection with the specific embodiments, which serve to better understand the invention without limiting it. Examples of Group 1

[0057] In the group of examples, the lithium secondary battery is described, which corresponds to different values ​​of A, B, C and k. 1) Preparation of a positive electrode plate

[0058] As the positive electrode active material, lithium cobalt oxide, polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added and stirred with a vacuum stirrer until a homogeneous, flowable positive electrode slurry was formed in the mixture. The positive electrode slurry was evenly coated on two surfaces of the aluminum foil. The coated aluminum foil was dried, rolled, and then cut to obtain the desired positive electrode plate. 2) Manufacturing a negative electrode plate

[0059] As the negative electrode active material, artificial graphite (with a Dv50 of 12 µm), a silicon-carbon material (with a Dv50 of 9 µm), sodium carboxymethylcellulose (CMC-Na), styrene-butadiene polymer, electrically conductive carbon black (SP), and single-walled carbon nanotubes (SWCNT) were mixed in a mass ratio of (94.5 - C):C:2.5:1.5:1:0.5. The specific contents of the negative electrode containing silicon and carbon are shown in Table 1. Deionized water was added and stirred with a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on two surfaces of the 6 µm copper foil. The coated copper foil was dried at room temperature, then transferred to an 80°C oven for 10 hours, cold-pressed, and cut to obtain the negative electrode plate. A represents the grain size of the copper foil in µm.The specific values ​​are shown in Table 1. 3) Preparation of an electrolyte solution

[0060] In an argon-filled glove box (H2O < 0.1 ppm and O2 < 0.1 ppm), EC / PC / DEC / PP were homogeneously mixed in a mass ratio of 15:15:20:50. Subsequently, 14 wt% of a completely dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte solution was quickly added. After separation, 8 wt% of LiTFSI based on the total mass of the electrolyte solution was added. The specific amounts used are shown in Table 1. Subsequently, 2 wt% of HTCN, 1 wt% of AND, and 12 wt% of FEC were added, each based on the total mass of the electrolyte solution. The mixture was homogeneously mixed, and the desired electrolyte solution was obtained when it passed the moisture and free acid tests.

[0061] Where k = B-10A-C / 10+3. The specific values ​​are shown in Table 1. 4) Manufacturing a lithium secondary battery

[0062] The positive electrode plate prepared in step 1), the negative electrode plate prepared in step 2), and the separator were laminated and wound in the order of the positive electrode plate, separator, and negative electrode plate to obtain a cell. The cell was placed in the aluminum foil of the outer package. The electrolyte solution from step 3 was poured into the outer package, vacuum-packed, allowed to stand, formed, molded, and sorted to obtain a lithium secondary battery.

[0063] The charge / discharge range of the lithium secondary battery was 3.0 - 4.5 V. Comparative examples of Group 1

[0064] The procedure was the same as in the examples of Group 1, with A, B, C, and k being different from those in the examples of Group 1. The specific values ​​are shown in Table 1. Comparative examples of Group 2

[0065] The procedure was carried out as in Example 1-1, using a different lithium salt instead of LiTFSI with the same weight. The type and content of the lithium salt are shown in Table 1. Table 1 number A B C k Type of lithium salt Example 1-1 0,4 7 10 5 B wt.% LiTFSI +14 wt.% LiPF6 Example 1-2 0,5 * * 4 * Examples 1-3 0, 6 * * 3 * Examples 1-4 0,7 * * 2 * Examples 1-5 0, 8 * * 1 * Examples 1-6 * 2 * 0 B wt.% LiTFSI +14 wt.% LiPF6 Examples 1-7 * 5 * 3 Examples 1-8 * 10 * 8 Examples 1-9 * 12 * 10 Example 1-10 * 14 * 12 B wt.% LiTFSI +14 wt.% LiPF6 Example 1-11 * * 2 5,8 * Example 1-12 * * 6 5,4 * Example 1-13 * * 25 3,5 * Example 1-14 * * 45 1,5 * Comparison example 1-1 0,7 3 * -2 * Comparison example 1-2 * 1 * -1 * Comparison example 1-3 * 0,2 * 1,8 B wt.% LiTFSI +14 wt.% LiPF6 Comparison example 1-4 * * 55 0,5 * Comparison example 2-1 * 0 * -2 21 wt% LiPF6 Comparison example 2-2 * 0 * -2 7 wt% LiFSI +14 wt% LiPF6

[0066] Note: * in Table 1 means it is the same as Example 1-1. Examples of Group 2

[0067] The procedure was as in Example 1-1 except that the electrolyte solution also contained a fluorophosphate whose type and composition are shown in Table 2.

[0068] In Examples 2-5, 2 wt% tris(2,2,2-trifluoroethyl)phosphate was used instead of 2 wt% LiTFSI, i.e. in the electrolyte solution, the content of LiTFSI was 5 wt% and the content of tris(2,2,2-trifluoroethyl)phosphate was 2 wt%. Table 2 number Type and content of fluorophosphate Example 1-1 - Example 2-1 2% by weight tris(2,2,2-trifluoroethyl) phosphate Example 2-2 0.5% by weight tris (2,2,2-trifluoroethyl) phosphate Example 2-3 5% by weight tris(2,2,2-trifluoroethyl) phosphate Example 2-4 2% by weight tris(2,2,2-trifluoroethyl) phosphite Example 2-5 2 wt% tris(2,2,2-trifluoroethyl)phosphate (instead of part of LiTFSI)

[0069] Note: - means absence in Table 2. Examples of Group 3

[0070] The procedure was carried out as in Example 1-1 with nitrile compounds of different types and contents in the electrolyte solution, which are specifically shown in Table 3. Table 3 number Type and content of nitrile compounds Example 1-1 2 wt% HTCN and 1 wt% ADN Example 3-1 1 wt% HTCN and 1 wt% ADN Example 3-2 4 wt% HTCN and 4 wt% ADN Example 3-3 3 wt% HTCN and 2 wt% ADN Example 3-4 2 wt% HTCN and 3 wt% ADN Examples of Group 4

[0071] The procedure was as in Example 1-1 except that the electrolyte solution also contained a sulfur-containing compound, the type and composition of which are shown in Table 4.

[0072] In Examples 4-5, 3 wt% of 1,3-propanesultone was used instead of 3 wt% of LiTFSI, i.e., in the electrolyte solution, the content of LiTFSI was 4 wt% and the content of 1,3-propanesultone was 3 wt%. Table 4 number Type and content of sulfur-containing compounds Example 1-1 - Example 4-1 3 wt.% 1,3-propane sultone Example 4-2 0.5 wt% 1,3-propane sultone Example 4-3 5 wt.% 1,3-propane sultone Example 4-4 3 wt.% 2,4-butane sultone Example 4-5 3 wt% 1,3-propanesultone (instead of part of LiTFSI)

[0073] Note: - means absence in Table 4. Examples of Group 5

[0074] The procedure was carried out as in Example 1-1 with a fluorine compound other than fluorophosphate, which has a different chemical compound and a different content in the electrolyte solution, which are concretely shown in Table 5. Table 5 number Type and content of fluorine compound other than fluorophosphate Example 1-1 12 wt% FEC Example 5-1 5 wt% FEC Example 5-2 18 wt% FEC Example 5-3 12 wt% DFEC Examples of Group 6

[0075] The procedure was the same as in Example 1-1 except that the particle sizes of the artificial graphite and the silicon-carbon material in the negative electrode active material were different, which are concretely shown in Table 6. Table 6 number Particle size of artificial graphite Dv50 / um Particle size of the silicon-carbon material Dv50 / um Example 1-1 12 9 Example 6-1 4 * Example 6-2 20 * Example 6-3 * 3 Example 6-4 * 15

[0076] Note: * in Table 6 means it is the same as Example 1-1. Example 7

[0077] The process was carried out as in Example 1-1 using a silicon-oxygen material (with Dv50 of 9 µm) instead of the silicon-carbon material with the same mass. Example of tests

[0078] The lithium secondary batteries of the examples and the comparative examples were each subjected to the performance tests, the results of which are summarized in Table 7 and Table 8. 1) Cycle performance test at 25°C

[0079] The batteries prepared in Examples and Comparative Examples were subjected to charge / discharge cycles within the range of the cut-off voltage at a discharge rate of 1C at 25°C. The discharge capacity in the first cycle of the test was recorded as x1 mAh, and the discharge capacity in the Nth cycle was recorded as y1 mAh. The capacity in the Nth cycle was divided by the capacity in the first cycle to obtain a cyclic retention rate of capacity in the Nth cycle, R = y1 / x1. The number of cycles at which the cyclic retention rate of capacity R was 80% was recorded. 2) Cycle performance test at 45°C

[0080] The batteries prepared in Examples and Comparative Examples were subjected to charge / discharge cycles within the range of the cut-off voltage at a discharge rate of 1C at 45°C. The discharge capacity in the first cycle of the test was recorded as x2 mAh, and the discharge capacity in the Nth cycle was recorded as y2 mAh. The capacity in the Nth cycle was divided by the capacity in the first cycle to obtain a cyclic retention rate of capacity in the Nth cycle, R = y2 / x2. The number of cycles at which the cyclic retention rate of capacity R was 80% was recorded. 3) Test for lithium deposition

[0081] At 25°C, the batteries prepared in Examples and Comparative Examples were fully charged and then disassembled to isolate the positive electrode, the negative electrode, and the separator from each other, thereby observing the deposition of lithium on the surface of the negative electrode.

[0082] The results of the above tests are shown in Table 7. Table 7 number Number of cycles at 25°C Number of cycles at 45°C Deposition of lithium Example 1-1 952 679 No Example 1-2 943 673 No Examples 1-3 930 662 No Examples 1-4 912 651 No Examples 1-5 618 455 No Examples 1-6 917 659 No Examples 1-7 929 664 No Examples 1-8 941 672 No Examples 1-9 913 655 No Example 1-10 853 599 No Example 1-11 1072 803 No Example 1-12 1022 771 No Example 1-13 829 605 No Example 1-14 751 576 No Comparison example 1-1 733 558 Yes Comparison example 1-2 758 569 Yes Comparison example 1-3 658 588 Yes Comparison example 1-4 582 417 Yes Comparison example 2-1 825 438 No Comparison example 2-2 599 402 Yes Example 2-1 954 714 No Example 2-2 952 702 No Example 2-3 953 712 No Example 2-4 952 708 No Example 2-5 953 706 No Example 3-1 949 657 No Example 3-2 912 633 No Example 3-3 957 709 No Example 3-4 959 703 No Example 4-1 922 713 No Example 4-2 947 692 No Example 4-3 901 703 No Example 4-4 925 705 No Example 4-5 933 701 No Example 5-1 862 663 No Example 5-2 955 667 No Example 5-3 841 674 No Example 6-1 869 602 No Example 6-2 931 687 No Example 6-3 947 671 No Example 6-4 941 681 No Example 7 887 642 No

[0083] From Table 7, it can be seen that a battery with a Si content less than or equal to 50 wt% has good cycling performance, and lithium deposition can be significantly suppressed or mitigated when the condition B-10A-C / 10+3 ≥ 0 is satisfied. By further comparing the data in the examples of Group 1, it can be seen that the battery has significantly better cycling performance when 0.4 ≤ A ≤ 0.7; that the improvement of the battery's cycling performance is promoted while simultaneously suppressing lithium deposition; and that the cycling performance of the battery is gradually improved with the decrease of the silicon content when 2 ≤ C ≤ 50, but this occurs at the expense of the energy density induced by the Si material, so the Si content should be controlled within an appropriate range.

[0084] From the examples of Group 2 and Group 4, it can be seen that the use of the fluorophosphate or the sulfur-containing compound significantly increases the cycling performance at 45°C, while maintaining the cycling performance at 25°C. Furthermore, it can be seen from Table 7 and Table 8 that the use of the fluorophosphate or the sulfur-containing compound instead of a portion of LiTFSI leads to significantly increased cycling performances at 45°C and 60°C compared to the case where only LiTFSI is added, while still maintaining the cycling performance at 25°C.

[0085] From the data of Group 3 and Group 5 examples, it can be seen that adding an appropriate amount of the nitrile compounds and the fluorine compound other than fluorophosphate is beneficial for improving the cycle performance of the battery.

[0086] From the data of the examples in Group 6, it can be seen that the selection of graphite and silicon-carbon material with appropriate particle sizes is beneficial for increasing the cycle performance of the battery.

[0087] From the data of Example 7, it is clear that a battery with better performance can be obtained by using a silicon-carbon material as the active material for the negative electrode of the battery compared to using a silicon-oxygen material.

[0088] It should be noted that the terms "comprising," "containing," or any variation thereof, are intended to mean inclusively including, such that a set of processes, procedures, items, or equipment that includes certain elements also includes other unlisted elements or elements inherent in such processes, procedures, items, or equipment. Unless further limited, an element limited by the phrase "comprises a" does not preclude the possibility that one or more other similar elements are included in the processes, procedures, items, or equipment containing that element.It should also be noted that the scope of the methods and devices in the application's embodiments is not intended to be limited to performing the functions in the order shown or specified, but may also include performing the functions in question substantially simultaneously or in an opposite order. For example, the described method may be performed in an order different from the described order, and various steps may also be added, removed, or combined. Furthermore, the features described with reference to some examples may be combined in another example.

[0089] Only the preferred embodiments of the present invention have been explained above, but the invention is not intended to be limited thereto. All modifications and equivalent substitutions that fall within the spirit and principle of the invention are intended to be included within the scope of the invention.

Claims

[1] Battery, characterized by that the battery comprises a positive electrode plate, a negative electrode plate and an electrolyte solution, wherein the negative electrode plate comprises a negative electrode current collector comprising a copper foil and a negative electrode active material layer on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material comprising a silicon-based active material, wherein the electrolyte solution contains lithium bis((trifluoromethyl)sulfonyl)imide, wherein for the battery B−10A−C / 10+3≥0 applies, where A is the grain size of the copper foil in µm, B is the mass content of lithium bis((trifluoromethyl)sulfonyl)imide in the electrolyte solution in wt.%, and C is the mass content of the silicon-based active material in the negative electrode active material in wt%, with C ≤ 50. [2] Battery according to claim 1, characterized by that A ≤ 0.75, preferably 0.4 ≤ A ≤ 0.7; 0.5 ≤ B ≤ 15, preferably 2 ≤ B ≤ 12; 2 ≤ C ≤ 50, preferably 2 ≤ C ≤ 30; and 0 ≤ B-10A-C / 10+3 ≤ 13 apply. [3] Battery according to claim 2, characterized by that the electrolyte solution further comprises a fluorophosphate, wherein the fluorophosphate preferably comprises tris(2,2,2-trifluoroethyl)phosphate and / or tris(2,2,2-trifluoroethyl)phosphite, and wherein preferably the content of fluorophosphate in the electrolyte solution is 0.1 - 6 wt.%. [4] Battery according to one of claims 1-3, characterized bythat the electrolyte solution also comprises a second additive which contains at least one compound of a nitrile compound, a sulphur-containing compound, and a fluorine compound other than fluorophosphate, wherein preferably the nitrile compound comprises at least one compound of 1,3,6-hexanetricarbonitrile, hexanedinitrile, butandinitrile, 1,4-dicyano-2-butylene, ethylene glycol bis(propionitrile) ether, and tris(3-cyanopropyl)phosphate, wherein preferably the sulfur-containing compound comprises at least one compound of 1,3-propanesultone, 1-propylene-1,3-sultone, 5-methyloxathiolane-2,2-dioxide, 2,4-butanesultone and 1,4-butanesultone, wherein the fluorine compound, other than fluorophosphate, preferably comprises at least one compound of fluorocarbonates, fluorocarboxylic acid esters and fluoroethers, preferably at least one compound of fluoroethylene carbonate, methyl trifluoroethyl carbonate, fluorodiethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl acetate, 2,2-difluoroethyl acetate and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and wherein preferably the content of the second additive in the electrolyte solution is 2 - 40 wt.%. [5] Battery according to one of claims 1-4, characterized by that the electrolyte solution also contains an electrolyte salt, wherein the electrolyte salt preferably comprises at least one salt of lithium salt, sodium salt, potassium salt, aluminum salt, zinc salt and magnesium salt, preferably lithium salt, wherein more preferably the lithium salt comprises at least one salt of lithium hexafluorophosphate, lithium difluorophosphate, lithium oxalatodifluoroborate, lithium bisoxalatodifluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluorasenate, lithium bis(pentafluoroethylsulfonyl)imide and lithium tris(trifluoromethylsulfonyl)methide, and wherein preferably the content of electrolyte salt in the electrolyte solution is 7 - 30 wt.%. [6] Battery according to one of claims 1-4, characterized by that the electrolyte solution also contains an organic solvent, wherein preferably the organic solvent contains a carbonic acid ester and / or a carboxylic acid ester, more preferably, the carbonic acid ester comprises at least one compound of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, more preferably, the carboxylic acid ester comprises at least one compound selected from propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate, ethyl propionate, methyl butyrate and ethyl n-butyrate, and wherein preferably the content of the organic solvent in the electrolyte solution is 30 - 80 wt%. [7] Battery according to one of claims 1-6, characterized by that the thickness of the copper foil is 4 µm - 12 µm. [8] Battery according to one of claims 1-7, characterized by that the silicon-based active material comprises at least one material selected from the group consisting of nano-silicon, silicon alloys, silicon-oxygen materials for the negative electrode, and silicon-carbon materials for the negative electrode, preferably silicon-carbon materials for the negative electrode, wherein preferably the active material for the negative electrode also comprises a carbon-based active material, and more preferably, the carbon-based active material comprises at least one of graphite, hard carbon and soft carbon, wherein the particle size of the silicon-based active material Dv50 is preferably 3 µm - 15 µm, and wherein the particle size of the carbon-based active material Dv50 is preferably 4 µm - 20 µm. [9] Battery according to one of claims 1-8, characterized by that the positive electrode plate has a positive electrode current collector and a positive electrode active material layer on the surface of the positive electrode current collector, wherein preferably the positive electrode active material layer comprises a positive electrode active material, an electrically conductive agent and a binder, more preferably, the active material for the positive electrode comprises a lithium transition metal oxide, wherein more preferably the lithium transition metal oxide has a chemical formula of Li 1+x Ni y Co z M m O2, where -0.1 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ m ≤ 1, and M comprises at least one element from Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Mo, Zr, Y, La, B, W, Nb. [10] Battery according to one of claims 1-9, characterized by that the battery is a lithium secondary battery, preferably the battery is a wound battery, and preferably the battery is a pouch cell.