battery

Abstract

A battery, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer comprises a silicon-based negative electrode material. The negative electrode current collector comprises a copper foil. The tensile strength of the copper foil is ≥400 MPa. The electrolyte comprises an organic solvent, an electrolyte salt, and an additive. The additive comprises a phosphate nitrile compound. By using low-elongation high-strength copper foil for the negative electrode, volume expansion of a silicon negative electrode can be reduced and a negative electrode interface can be improved. The phosphate nitrile compound is used as the electrolyte to improve a positive electrode interface, thereby improving the high-temperature cycling stability of the battery. The phosphate nitrile compound can reduce the harm to burr copper, slightly corrode copper foil, and can significantly passivate burr copper, thereby reducing puncturing of a diaphragm, and improving self-discharge performance of the battery.

Description

A battery Technical Field

[0001] The present disclosure belongs to the field of battery technology, and particularly relates to a silicon-based battery. Background Art

[0002] With the rapid development of portable devices, electric vehicles, renewable energy storage systems, and other fields, modern society's demand for batteries with higher energy density and longer cycle life is growing, and the need for high-performance batteries is becoming increasingly urgent. Traditional lithium-ion batteries use graphite as the anode material. Although graphite has high electrochemical stability and low potential, its energy density is relatively low. In contrast, silicon has a higher theoretical capacity and is therefore considered an ideal candidate for the next generation of anode materials. However, silicon anodes face problems such as high volume expansion and poor cycling performance. Summary of the Invention

[0003] The study found that when copper foil with a tensile strength of ≥400MPa is selected as the negative electrode current collector, it can adapt to the silicon negative electrode and solve the problem of large volume expansion of the silicon negative electrode. This is mainly because the elongation of copper foil with a tensile strength of ≥400MPa is relatively low, which can better inhibit the volume expansion of the silicon negative electrode and improve the cycle performance of the battery. However, the cross-section of copper foil with a tensile strength of ≥400MPa is prone to produce more burrs. The presence of burrs deteriorates the self-discharge performance of the battery. At the same time, it is easy to pierce the diaphragm and cause a short circuit in the battery, affecting the safety performance of the battery. In order to solve the volume expansion of the silicon negative electrode while avoiding the deterioration of the self-discharge performance of the battery, the present disclosure provides a battery. Specifically, the present disclosure solves the problem of large volume expansion of the silicon negative electrode by introducing copper foil with a tensile strength of ≥400MPa; at the same time, by optimizing the composition of the electrolyte, the cycle performance of the battery under high temperature and high pressure is improved, and the self-discharge phenomenon of the battery caused by copper foil with a tensile strength of ≥400MPa is reduced.

[0004] The purpose of this disclosure is achieved through the following technical solutions:

[0005] A battery comprising a positive electrode, a negative electrode and an electrolyte; the negative electrode comprises a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer comprises a silicon-based negative electrode material, the negative electrode current collector comprises copper foil, and the tensile strength of the copper foil is ≥400 MPa; the electrolyte comprises an organic solvent, an electrolyte salt and an additive, and the additive comprises a phosphate nitrile compound.

[0006] Beneficial effects of the present disclosure:

[0007] The silicon negative electrode described in the present disclosure uses a low-elongation copper foil as the negative electrode current collector, which can inhibit the volume expansion of the silicon negative electrode material, reduce SEI rupture and interfacial decomposition of the electrolyte, and improve the cycle performance of the battery. At the same time, the phosphate nitrile compound included in the electrolyte can form a film on the surface of the positive electrode, and through the cyanide group and the transition metal in the positive electrode active material, it can coordinate to reduce the oxidative decomposition of the electrolyte at the interface by the positive electrode, thereby further improving the high-temperature cycle performance of the battery. The cross-section of the copper foil with low elongation is prone to produce more burrs, and the burrs can easily pierce the diaphragm, causing a micro-short circuit between the positive and negative electrodes, and deteriorating the self-discharge performance of the battery. The phosphate nitrile compound can slightly corrode the copper foil and can significantly passivate the burr copper, thereby reducing the puncture of the diaphragm and significantly improving the self-discharge performance of the battery.

[0008] In summary, the present disclosure reduces the volume expansion of the silicon negative electrode and improves the negative electrode interface by using low-elongation copper foil with a tensile strength of 400 MPa or higher for the negative electrode. Furthermore, the electrolyte uses a phosphate nitrile compound to improve the positive electrode interface, thereby improving the battery's high-temperature cycling stability. Furthermore, the phosphate nitrile compound can reduce the damage caused by burred copper, slightly corrode the copper foil, and significantly passivate the burred copper, thereby reducing diaphragm penetration and significantly improving the battery's self-discharge performance. DETAILED DESCRIPTION

[0009] The present disclosure will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present disclosure and should not be construed as limiting the scope of protection of the present disclosure. All technologies implemented based on the above content of the present disclosure are included within the scope of protection intended by the present disclosure.

[0010] The present disclosure provides a battery. The battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer includes a silicon-based negative electrode material. The negative electrode current collector includes copper foil having a tensile strength of 400 MPa or greater. The electrolyte includes an organic solvent, an electrolyte salt, and an additive. The additive includes a phosphate nitrile compound.

[0011] The study found that copper foil with a tensile strength of ≥400MPa is a high-strength copper foil. The use of high-strength copper foil can significantly inhibit the volume expansion of the silicon negative electrode and improve the cycle performance of the battery. However, the cross-section of the copper foil with a tensile strength of ≥400MPa is prone to produce more burrs. The presence of burrs deteriorates the self-discharge performance of the battery. At the same time, it is easy to pierce the diaphragm and cause a short circuit in the battery, affecting the safety performance of the battery. The phosphate nitrile compound in the electrolyte of the present invention can slightly corrode the copper foil, passivate the burrs on the cross-section of the copper foil, reduce the possibility of the diaphragm being pierced, and improve the self-discharge of the battery. At the same time, the phosphate nitrile compound can also form a film on the surface of the positive electrode, and coordinate with the transition metal in the positive active material through the cyanide group, reducing the oxidative decomposition of the electrolyte on the positive electrode interface, thereby further improving the high-temperature cycle performance of the battery.

[0012] In one example, the tensile strength of the copper foil is, for example, 400 MPa-800 MPa, such as 400 MPa, 500 MPa, 600 MPa, 700 MPa, or 800 MPa.

[0013] In one example, the elongation of the copper foil is 3%-5%, for example, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%.

[0014] Research has found that copper foil with a tensile strength of 400 MPa or higher has a relatively low elongation of only 3%-5%. This elongation can effectively suppress the volume expansion of the silicon anode and improve the battery's cycling performance. When the elongation of the copper foil exceeds 5%, the elongation is too high, and its application in the battery limits the effect of suppressing the volume expansion of the silicon anode, and further fails to improve the battery's cycling performance. When the elongation of the copper foil is less than 3%, the elongation is too low to match the tensile strength of the copper foil, and existing processes cannot produce copper foil with such a low elongation.

[0015] In one embodiment, the copper foil has a thickness of 3 μm to 8 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm. When the copper foil has a thickness of 3 μm to 8 μm, a copper foil with a tensile strength of ≥400 MPa and an elongation of 3% to 5% can be obtained, which can effectively suppress the volume expansion of the silicon negative electrode and improve the cycle performance of the battery. More importantly, when the copper foil has a thickness of 3 μm to 8 μm, a high energy density can also be obtained. When the copper foil has a thickness greater than 8 μm, the effect on the cycle performance of the battery is relatively small, but the energy density of the battery is mainly deteriorated. When the copper foil has a thickness less than 3 μm, the tensile strength and elongation of the copper foil are affected, the effect of suppressing the volume expansion of the silicon negative electrode is weakened, the improvement in the cycle performance of the battery is not obvious, and the obtained negative electrode strength is insufficient, making it impossible to prepare the battery.

[0016] In one embodiment, the copper foil can be purchased from commercial sources or prepared by methods known in the art.

[0017] In one example, the phosphate nitrile compound includes a phosphate group (P(=O)O3-) and a cyano group (-CN), and the phosphate group and the cyano group are connected by a hydrocarbon group, and the hydrocarbon group includes one or more of an alkyl group, an alkenyl group and an alkynyl group.

[0018] In one embodiment, the phosphate nitrile compound includes a phosphate group (P(=O)O3-) and a cyano group (-CN), and the phosphate group and the cyano group are connected through a hydrocarbon group, and the hydrocarbon group includes an alkyl group, an alkenyl group, or an alkynyl group.

[0019] In one embodiment, the phosphate nitrile compound includes at least one compound having the structural formula shown in formula (1).

[0020] In one embodiment, the phosphate nitrile compound is selected from at least one compound having the structural formula shown in formula (1):

[0021] In formula (1), R1, R2, and R3 are the same or different and are independently selected from alkyl, alkenyl, or alkynyl groups which are unsubstituted or optionally substituted with one, two, or more Ra; each Ra is the same or different and is independently selected from halogen or alkyl.

[0022] In one embodiment, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-12 Alkyl, C 2-12 Alkenyl or C 2-12 Alkynyl; each Ra is the same or different and is independently selected from halogen or C 1-12 alkyl.

[0023] In one embodiment, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-6 Alkyl, C 2-6 Alkenyl or C 2-6 Alkynyl; each Ra is the same or different and is independently selected from halogen or C 1-6 alkyl.

[0024] In one embodiment, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-3 Alkyl, C 2-3 Alkenyl or C 2-3 Alkynyl; each Ra is the same or different and is independently selected from halogen or C1-3 alkyl.

[0025] In one embodiment, the phosphate nitrile compound includes at least one of the compounds represented by formula (2) to formula (7):

[0026] In one embodiment, the phosphate nitrile compound can be purchased from commercial sources or prepared using methods known in the art.

[0027] In one embodiment, the mass of the phosphate nitrile compound accounts for 0.1wt%-5wt% of the total mass of the electrolyte, for example, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%. The study found that when the mass of the phosphate nitrile compound accounts for 0.1wt%-5wt% of the total mass of the electrolyte, the phosphate nitrile compound can form a protective layer on the surface of the positive electrode, thereby improving the high temperature and high pressure performance of the battery; more importantly, the phosphate nitrile compound at this content can match with the copper foil, can better inhibit the volume expansion of the silicon negative electrode, and improve the cycle performance of the battery. Furthermore, the phosphate nitrile compound at this content can also slightly corrode the copper foil (because the phosphate nitrile compound is easily decomposed into various short-chain mononitriles with high coordination and high polarity, these short-chain mononitriles are easily decomposed to form acid to corrode the copper foil, and can also form strong coordination with copper ions, accelerating the corrosion of the copper foil), softening burrs, thereby significantly reducing the self-discharge phenomenon of the battery cell. Moreover, the phosphate nitrile compound can reduce the self-discharge phenomenon of the battery cell caused by the high-strength copper foil with an elongation of 3%-5%, and the high-strength copper foil can significantly improve the stability of the negative electrode of the silicon-containing negative electrode battery, and the phosphate nitrile compound can improve the stability of the positive electrode of the silicon-containing negative electrode battery. The two can work together to greatly improve the overall stability of the silicon-containing negative electrode battery, achieving better high-temperature cycle performance and low self-discharge. When the mass of the phosphate nitrile compound is less than 0.1wt% of the total mass of the electrolyte, due to the small amount of phosphate nitrile compound added, it is not enough to form a sufficient interface protective film on the positive electrode surface, and the softening effect on the burrs on the copper foil surface is limited, which has limited effect on improving the cycle performance of the battery and improving the self-discharge phenomenon of the battery; when the mass of the phosphate nitrile compound is greater than 5wt% of the total mass of the electrolyte, due to the excessive amount of phosphate nitrile compound added, the copper foil will be severely corroded, resulting in copper precipitation on the negative electrode surface, thereby worsening the self-discharge phenomenon of the battery. At the same time, the interface protective film formed on the positive electrode surface is too thick, causing the cycle performance of the battery under high temperature and high voltage to deteriorate.

[0028] In one example, the percentage of the mass of the silicon-based anode material in the total mass of the anode active material layer is 2 wt% to 30 wt%, such as 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt% or 30 wt%. It is found that when the percentage of the mass of the silicon-based anode material in the total mass of the anode active material layer is 2 wt% to 30 wt%, the volume expansion of the silicon-based anode material is moderate, and through the matching of the phosphonitrile compound and the copper foil, the volume expansion of the silicon anode can be better inhibited, and the cycle performance of the battery can be improved. When the percentage of the mass of the silicon-based anode material in the total mass of the anode active material layer is less than 2 wt%, it has a greater impact on the energy density of the battery.

[0029] In one example, the silicon-based anode material includes at least one of nano-silicon (Si), silicon-oxide anode material (SiOx(0 < x < 2)), and silicon-carbon anode material.

[0030] In one example, the silicon-carbon anode material includes particles formed by mixing silicon or partially oxidized silicon with amorphous or crystalline carbon, and / or particles formed by filling silicon or partially oxidized silicon (including partial filling or complete filling) in the pores of porous amorphous carbon or porous crystalline carbon.

[0031] In one example, the silicon-carbon anode material has a high initial efficiency and a higher energy density compared to ordinary graphite anode materials, but its expansion is also significantly larger than that of ordinary graphite.

[0032] In one example, the anode active material layer includes anode active substances, and the anode active substances include silicon-based anode materials.

[0033] In one example, the anode active substances further include carbon-based anode materials.

[0034] In one example, the carbon-based anode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0035] In one example, the battery satisfies the relational expressions shown in the following formula (i) and / or formula (ii): 5 - 0.05×A ≥ B Formula (i) 5 ≥ C ≥ 2.6 - 0.5×B Formula (ii)

[0036] Wherein, A is the percentage of the mass of the silicon-based anode material in the total mass of the anode active material layer, with the unit of wt%; B is the elongation of the high-strength copper foil, with the unit of %; C is the percentage of the mass of the phosphonitrile compound in the total mass of the electrolyte, with the unit of wt%.

[0037] In one example, when the battery satisfies the relational expression 5 - 0.05×A ≥ B shown in formula (i), it indicates that by adjusting the relationship between the mass proportion of the silicon-based anode material in the battery and the elongation rate of the high-strength copper foil, the silicon anode and the high-strength copper foil can be better matched, enabling the high-strength copper foil to better inhibit the volume expansion of the silicon anode; when 5 - 0.05×A < B, it indicates that the elongation rate of the high-strength copper foil is too high to inhibit the volume expansion of the silicon anode, resulting in the deterioration of the battery cycle performance.

[0038] In one example, when the battery satisfies the relational expression 5 ≥ C ≥ 2.6 - 0.5×B shown in formula (ii), it indicates that by adjusting the relationship between the mass proportion of the phosphonitrile compound in the battery and the elongation rate of the high-strength copper foil, the electrolyte and the copper foil can be better matched. On the one hand, the phosphonitrile compound can form a sufficient interfacial protective film on the surface of the positive electrode, which is beneficial to the improvement of the battery cycle performance under high temperature and high voltage; on the other hand, the phosphonitrile compound can soften the burrs on the surface of the copper foil, reduce the self-discharge phenomenon of the battery, and achieve the improvement of the battery cycle performance and the improvement of the battery self-discharge phenomenon; when C < 2.6 - 0.5×B, due to the过少 addition amount of the phosphonitrile compound, it is insufficient to form a sufficient interfacial protective film on the surface of the positive electrode, and the softening effect on the burrs on the surface of the copper foil is not good, and it is impossible to effectively improve the battery cycle performance and improve the battery self-discharge phenomenon; when C > 5, due to the过多 addition amount of the phosphonitrile compound, it will seriously corrode the copper foil, cause copper to precipitate on the surface of the negative electrode, thus deteriorating the self-discharge phenomenon of the battery, and at the same time, the interfacial protective film formed on the surface of the positive electrode is too thick, resulting in the deterioration of the battery cycle performance under high temperature and high voltage.

[0039] In one example, A satisfies: 2% ≤ A% ≤ 30%.

[0040] In one example, B satisfies: 3% ≤ B% ≤ 5%.

[0041] In one example, C satisfies: 0.1% ≤ C% ≤ 5%.

[0042] In one example, the areal density E of the negative electrode is 3mg / cm 2 -15mg / cm [[ID=|18]] 2 For example, it is 3mg / cm 2 、4mg / cm 2 、5mg / cm 2 、6mg / cm 2 、7mg / cm 2 、8mg / cm 2 、{9mg / cm 2 、10mg / cm 2 、11mg / cm 2 、12mg / cm 2 、13mg / cm2 , 14mg / cm 2 or 15 mg / cm 2 When the surface density of the negative electrode is 3 mg / cm 2 -15mg / cm 2 When the surface density of the negative electrode is greater than 15 mg / cm 2 Although the energy density of the battery can be further improved, the expansion of the battery is greater, which requires a higher strength copper foil to suppress the battery expansion problem, resulting in more obvious burrs on the copper foil and aggravating the self-discharge of the battery.

[0043] The negative electrode active material layer may be located on one or both sides of the negative electrode current collector. The surface density of the negative electrode is the single-sided surface density. For example, when the negative electrode active material layer is located on one side of the negative electrode current collector, the surface density of the negative electrode is the surface density of that side (the side with the negative electrode active material layer); when the negative electrode active material layer is located on both sides of the negative electrode active current collector, the surface density of the negative electrode active material layer on both sides is equal, and the surface density of the negative electrode is the surface density of the negative electrode active material layer on either side.

[0044] In one embodiment, the compaction density F of the negative electrode is 1.4 g / cm 3 -1.9g / cm 3 , for example 1.4 g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or 1.9 g / cm 3 When the compaction density of the negative electrode is 1.4 g / cm 3 -1.9g / cm 3 When the negative electrode has a compact density greater than 1.9 g / cm 3 Although the energy density of the battery can be further improved, the higher the compaction density, the lower the porosity of the negative electrode, which makes the expansion buffer space of the silicon-carbon negative electrode material smaller and the expansion of the obtained battery greater. This requires higher strength copper foil to suppress the battery expansion problem, resulting in more obvious burrs on the copper foil and aggravated self-discharge of the battery.

[0045] In one example, the negative electrode active material layer further includes a negative electrode conductor and a negative electrode binder.

[0046] In one example, the mass percentage of each component in the negative electrode active material layer is: 80 wt% to 99.8 wt% (for example, 80 wt%, 83 wt%, 85 wt%, 88 wt%, 90 wt%, 93 wt%, 95 wt%, 98 wt% or 99.8 wt%) of the negative electrode active material, 0.1 wt% to 10 wt% (for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%) of the negative electrode conductor, and 0.1 wt% to 10 wt% (for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%) of the negative electrode binder.

[0047] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90 wt% to 99.6 wt% of the negative electrode active material, 0.2 wt% to 5 wt% of the negative electrode conductor, and 0.2 wt% to 5 wt% of the negative electrode binder.

[0048] In one example, the electrolyte salt includes at least one of electrolyte lithium salt, electrolyte sodium salt, electrolyte potassium salt, electrolyte aluminum salt, electrolyte zinc salt, electrolyte magnesium salt, and the like.

[0049] In one example, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bisfluorosulfonyl imide (LiTFSI), lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium or lithium bis(trifluoromethylsulfonyl)imide.

[0050] In one embodiment, the organic solvent is selected from fluorinated or non-fluorinated carbonates and / or carboxylates, wherein the carbonate is selected from one or more of the following solvents: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate (DEC), and ethyl methyl carbonate; and the carboxylates are selected from one or more of the following solvents: ethyl acetate (EA), propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), methyl butyrate, and ethyl butyrate. Carbonates and carboxylates have high oxidation resistance and good lithium salt dissociation ability, and can serve as excellent solvents for electrolytes.

[0051] In one example, the battery is a lithium-ion battery.

[0052] In one example, the battery is a lithium-ion secondary battery.

[0053] In one example, the electrolyte is a non-aqueous electrolyte.

[0054] In one example, the positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder.

[0055] In one example, the mass percentage of each component in the positive electrode active material layer is: 80wt% to 99.8wt% (for example, 80wt%, 83wt%, 85wt%, 88wt%, 90wt%, 93wt%, 95wt%, 98wt% or 99.8wt%) of the positive electrode active material, 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%) of the positive electrode conductor, and 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%) of the positive electrode binder.

[0056] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90 wt% to 99.6 wt% of positive electrode active material, 0.2 wt% to 5 wt% of positive electrode conductor, and 0.2 wt% to 5 wt% of positive electrode binder.

[0057] In one example, the negative electrode conductive agent and the positive electrode conductive agent each independently include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0058] In one example, the negative electrode binder and the positive electrode binder each independently include at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber (also known as styrene-butadiene latex), polytetrafluoroethylene, polyethylene oxide, and polyvinylidene fluoride (PVDF).

[0059] In one embodiment, the positive electrode active material includes one or more of transition metal lithium oxide, lithium iron phosphate, and lithium manganate; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z)O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0060] In one example, the battery further includes a separator.

[0061] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0062] The copper foil used in the following examples and comparative examples was purchased from commercial sources, and the tensile strength and elongation of the copper foil were tested using the GB-228-87 test method with the test parameters being a gauge length of 50 mm and a tensile speed of 10 mm / min.

[0063] The lithium-ion batteries of the following examples and comparative examples were prepared using the following method:

[0064] 1) Preparation of positive electrode sheet

[0065] The positive electrode active materials lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode active slurry with uniform fluidity; the positive electrode active slurry is evenly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, and then rolled and cut to obtain the desired positive electrode sheet.

[0066] 2) Negative electrode preparation

[0067] The negative electrode active material artificial graphite, silicon carbon negative electrode material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of (94.5-A):A:2.5:1.5:1:0.5, and deionized water was added to obtain a negative electrode active slurry under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of a copper foil with an elongation of B; the coated copper foil was dried at room temperature and then transferred to an 80°C oven for drying for 10 hours, and then cold pressed and cut to obtain a copper foil with a surface density of E mg / cm 2 , compacted density is Fg / cm 3 The specific parameters of A and B are described in Table 1.

[0068] 3) Preparation of electrolyte

[0069] In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), EC / FEC / PC / DEC / PP were mixed in a mass ratio of 20:10:20:50. Then, 14 wt% of fully dried lithium hexafluorophosphate (LiPF6) (based on the total weight of the electrolyte) was quickly added. After dissolution, 3 wt% of a phosphate nitrile compound (based on the total weight of the electrolyte), 2 wt% of HTCN (1,3,6-hexanetricarbonitrile) (based on the total weight of the electrolyte), and 3 wt% of PS (1,3-propane sultone) (based on the total weight of the electrolyte) were added. The specific addition amounts are listed in Table 1. After stirring thoroughly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0070] 4) Preparation of lithium-ion batteries

[0071] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum packaging, standing, forming, shaping, and sorting, a lithium-ion battery is obtained. The battery disclosed herein has a charge and discharge range of 3V-4.5V (for example, 3V, 3.3V, 3.5V, 3.8V, 4V, 4.3V, or 4.5V).

[0072] The lithium-ion batteries obtained in the examples and comparative examples were subjected to 45°C cycle performance and storage self-discharge K value tests, respectively. The test results are shown in Table 2.

[0073] 1) 45℃ cycle performance test

[0074] The battery in Table 1 was charged and discharged at a rate of 1C at 45°C within the charge and discharge cut-off voltage range (wherein the charge cut-off voltage was 4.5V and the discharge cut-off voltage was 3V). The discharge capacity in the first week of the test was calculated as x mAh, and the discharge capacity in the Nth week was calculated as y mAh. The capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R = y / x in the Nth week. The number of cycles corresponding to the cycle capacity retention rate R of 80% was recorded.

[0075] 2) Battery storage self-discharge K value test

[0076] The prepared lithium-ion battery was charged at a rate of 1C at 25°C to a cutoff voltage of 4.5V and a cutoff current of 0.025C. After standing for 10 hours, the voltage U of the lithium-ion battery was measured. The self-discharge K value of the lithium-ion battery was calculated as: K = (U-4.5) * 1000 / 10.

[0077] Table 1 Composition of the negative electrode and electrolyte of the battery of the embodiment and the comparative example

[0078] Where A is the percentage of the mass of the silicon-based negative electrode material to the total mass of the negative electrode active material layer, in wt%; B is the elongation of the copper foil, in %; C is the percentage of the mass of the phosphate nitrile compound to the total mass of the electrolyte, in wt%. E is the surface density of the negative electrode, in mg / cm 2 ; F is the compaction density of the negative electrode, in g / cm 3 .

[0079] Example 33

[0080] Other operations are the same as those in Example 4, except that the negative electrode material is nano-silicon.

[0081] Example 34

[0082] Other operations are the same as those in Example 4, except that the negative electrode material is a silicon oxide negative electrode material.

[0083] Table 2 Performance test results of batteries of Examples and Comparative Examples

[0084] The performance test results of the above examples and comparative examples demonstrate that the present disclosure utilizes low-elongation, high-strength copper foil for the negative electrode to reduce volume expansion of the silicon negative electrode, improve the negative electrode interface, and utilizes a phosphate nitrile compound in the electrolyte to improve the positive electrode interface, thereby enhancing the battery's high-temperature cycling stability. Furthermore, the phosphate nitrile compound can reduce the damage caused by burred copper, slightly corrode the copper foil, and significantly passivate the burred copper, thereby reducing diaphragm penetration and significantly improving the battery's self-discharge performance.

[0085] In particular, when the battery satisfies the relationship shown in formula (i) (5-0.05A≥B) and the relationship shown in formula (ii) (5≥C≥2.6-0.5×B), it shows that by adjusting the mass ratio of the silicon-based negative electrode material in the battery and the relationship of the elongation of the high-strength copper foil, the silicon negative electrode and the high-strength copper foil can be better matched, so that the high-strength copper foil can better inhibit the volume expansion of the silicon negative electrode; by adjusting the mass ratio of the phosphate nitrile compound in the battery and the relationship of the elongation of the high-strength copper foil, the electrolyte and the high-strength copper foil can be better matched. On the one hand, the phosphate nitrile compound can form a sufficient interface protection film on the surface of the positive electrode, which is beneficial to the improvement of the cycle performance of the battery under high temperature and high voltage; on the other hand, the phosphate nitrile compound can soften the burrs on the surface of the high-strength copper foil, reduce the self-discharge phenomenon of the battery, and achieve the improvement of the battery cycle performance and the improvement of the battery self-discharge phenomenon.

[0086] The above describes the embodiments of the present disclosure. However, the present disclosure is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

Claims

1. A battery, which includes a positive electrode, a negative electrode and an electrolyte; the negative electrode includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a silicon-based negative electrode material, the negative electrode current collector includes a copper foil, and the tensile strength of the copper foil is ≥400 MPa; the electrolyte includes an organic solvent, an electrolyte salt and an additive, and the additive includes a phosphonitrile compound.

2. The battery according to claim 1, wherein The thickness of the copper foil is 3 μm - 8 μm; and / or, the elongation of the copper foil is 3% - 5%; and / or, the tensile strength of the copper foil is 400 MPa - 800 MPa.

3. The battery according to claim 1 or 2, wherein The phosphonitrile compound includes a phosphonate group (P(=O)O3-) and a cyano group (-CN), and the phosphonate group and the cyano group are connected by a hydrocarbon group, and the hydrocarbon group includes one or more of an alkyl group, an alkenyl group and an alkynyl group; Preferably, the phosphonitrile compound includes a phosphonate group (P(=O)O3-) and a cyano group (-CN), and the phosphonate group and the cyano group are connected by a hydrocarbon group, and the hydrocarbon group includes an alkyl group, an alkenyl group or an alkynyl group.

4. The battery according to any one of claims 1 to 3, wherein The phosphate nitrile compound includes at least one compound having the structural formula shown in formula (1): In formula (1), R1, R2, and R3 are the same or different, and are independently selected from an alkyl group, an alkenyl group or an alkynyl group which is unsubstituted or optionally substituted by one, two or more Ra; each Ra is the same or different, and is independently selected from a halogen or an alkyl group; Preferably, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-12 Alkyl, C 2-12 Alkenyl or C 2-12 Alkynyl; each Ra is the same or different and is independently selected from halogen or C 1-12 alkyl; Preferably, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-6 Alkyl, C 2-6 Alkenyl or C 2-6 Alkynyl; each Ra is the same or different and is independently selected from halogen or C 1-6 alkyl; Preferably, in formula (1), R1, R2, and R3 are the same or different and are independently selected from C 1-3 Alkyl, C 2-3 Alkenyl or C 2-3 Alkynyl; each Ra is the same or different and is independently selected from halogen or C 1-3 alkyl.

5. The battery according to any one of claims 1 to 4, wherein The phosphate nitrile compound includes at least one of the compounds having structures shown in formula (2) to formula (7):

6. The battery according to any one of claims 1 to 5, wherein: The mass of the phosphonitrile compound accounts for 0.1 wt% - 5 wt% of the total mass of the electrolyte.

7. The battery according to any one of claims 1 to 6, wherein: The mass percentage of the silicon-based negative electrode material in the total mass of the negative electrode active material layer is 2 wt% - 30 wt%.

8. The battery according to any one of claims 1 to 7, wherein: The negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based negative electrode material, and the silicon-based negative electrode material includes at least one of nano-silicon, silicon oxide negative electrode material (SiOx(0 < x < 2)) and silicon-carbon negative electrode material.

9. The battery according to claim 8, wherein The silicon-carbon negative electrode material includes particles formed by mixing silicon or partially oxidized silicon with amorphous or crystalline carbon, and / or particles formed by filling silicon or partially oxidized silicon into the pores of porous amorphous carbon or porous crystalline carbon.

10. The battery according to any one of claims 1 to 9, wherein The negative electrode active material further includes a carbon-based negative electrode material, and the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

11. The battery according to any one of claims 1 to 10, wherein The battery satisfies the relational expressions shown in the following formula (i) and / or formula (ii): 5 - 0.05×A ≥ B Formula (i) 5 ≥ C ≥ 2.6 - 0.5×B Formula (ii) Where, A is the mass percentage of the silicon-based negative electrode material in the total mass of the negative electrode active material layer, with the unit of wt%; B is the elongation of the high-strength copper foil, with the unit of %; C is the mass percentage of the phosphonitrile compound in the total mass of the electrolyte, with the unit of wt%; Preferably, A satisfies: 2% ≤ A% ≤ 30%; Preferably, B satisfies: 3% ≤ B% ≤ 5%; Preferably, C satisfies: 0.1% ≤ C% ≤ 5%.

12. The battery according to any one of claims 1 to 11, wherein The surface density of the negative electrode is 3 mg / cm 2 -15mg / cm 2 ; And / or, the compaction density of the negative electrode is 1.4 g / cm 3 -1.9g / cm 3 ; And / or, the negative electrode active material layer further includes a negative electrode conductor and a negative electrode binder, and the mass percentage of each component in the negative electrode active material layer is: 80wt% to 99.8wt% of the negative electrode active material, 0.1wt% to 10wt% of the negative electrode conductor, and 0.1wt% to 10wt% of the negative electrode binder.

13. The battery according to claim 12, wherein The positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a positive electrode conductor and a positive electrode binder. The mass percentage of each component in the positive electrode active material layer is: 80wt% to 99.8wt% of the positive electrode active material, 0.1wt% to 10wt% of the positive electrode conductor, and 0.1wt% to 10wt% of the positive electrode binder.

14. The battery according to claim 13, wherein The negative electrode conductive agent and the positive electrode conductive agent each independently include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder; And / or, the negative electrode binder and the positive electrode binder each independently include at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyethylene oxide and polyvinylidene fluoride.

15. The battery according to any one of claims 1 to 14, wherein The battery is a lithium-ion secondary battery.

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