A battery

Abstract

The application provides a battery. The battery comprises 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, and the negative electrode current collector comprises a copper foil, the tensile strength of the copper foil is greater than or equal to 400 MPa; the electrolyte comprises an organic solvent, an electrolyte salt and an additive, and the additive comprises a phosphonitrile ester compound. The application reduces the volume expansion of the silicon negative electrode by using a high-strength copper foil with low elongation for the negative electrode, improves the negative electrode interface, and improves the high-temperature cycle stability of the battery by using a phosphonitrile ester compound for the electrolyte to improve the positive electrode interface. Meanwhile, the phosphonitrile ester compound can reduce the harm of burr copper, slightly corrode the copper foil, and obviously passivate the burr copper, thereby reducing the puncture of the separator and significantly improving the self-discharge performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a silicon-based battery. BACKGROUND

[0002] With the rapid development of the fields of portable devices, electric vehicles, renewable energy storage systems and the like, the demand for batteries with higher energy density and longer cycle life is growing in modern society, and the demand for high-performance batteries is increasingly urgent. The traditional lithium-ion battery uses graphite as the negative electrode material, although the graphite has high electrochemical stability and low potential, but its energy density is relatively low. In contrast, silicon has a higher theoretical capacity, and is therefore considered an ideal choice for the next generation of negative electrode materials. However, the silicon negative electrode faces problems such as high volume expansion rate and poor cycle performance. SUMMARY

[0003] It has been found that when a copper foil with a tensile strength of ≥400 MPa 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, which is mainly because the elongation of the copper foil with a tensile strength of ≥400 MPa 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 the copper foil with a tensile strength of ≥400 MPa is prone to generate more burrs, the existence of the burrs causes deterioration of the self-discharge performance of the battery, and also easily pierces the separator to cause short circuit of the battery, affecting the safety performance of the battery. In order to solve the problem of volume expansion of the silicon negative electrode while avoiding deterioration of the self-discharge performance of the battery, the application provides a battery, specifically, the application solves the problem of large volume expansion of the silicon negative electrode by introducing a copper foil with a tensile strength of ≥400 MPa; at the same time, the composition of the electrolyte is optimized to improve the cycle performance of the battery under high temperature and high pressure, and reduce the self-discharge phenomenon of the battery caused by the copper foil with a tensile strength of ≥400 MPa.

[0004] The application aims to achieve 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, and the negative electrode current collector comprises a copper foil, the tensile strength of the copper foil being ≥400 MPa; the electrolyte comprises an organic solvent, an electrolyte salt and an additive, and the additive comprises a phosphonate nitrile compound.

[0006] According to an embodiment of the application, the tensile strength of the copper foil is, for example, 400-800 MPa, such as 400 MPa, 500 MPa, 600 MPa, 700 MPa or 800 MPa.

[0007] The research finds that the copper foil with the tensile strength ≥400 MPa is a high-strength copper foil, and the use of the high-strength copper foil can obviously 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 the tensile strength ≥400 MPa is prone to generate more burrs, the existence of the burrs causes the deterioration of the self-discharge performance of the battery, and the burrs also easily pierce the diaphragm to cause the short circuit of the battery, thereby affecting the safety performance of the battery.

[0008] According to the embodiment of the present application, 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%.

[0009] The research finds that the elongation of the copper foil with the tensile strength ≥400 MPa is relatively low, only 3-5%, and such elongation can better inhibit the volume expansion of the silicon negative electrode and improve the cycle performance of the battery. When the elongation of the copper foil is greater than 5%, the copper foil cannot effectively inhibit the volume expansion of the silicon negative electrode after being applied to the battery, and cannot improve the cycle performance of the battery. When the elongation of the copper foil is less than 3%, the elongation cannot match the tensile strength of the copper foil, and the existing process cannot obtain the copper foil with such low elongation.

[0010] According to the embodiment of the present application, the thickness of the copper foil is 3-8 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm. When the thickness of the copper foil is 3-8 μm, the copper foil with the tensile strength ≥400 MPa and the elongation of 3-5% can be obtained, the volume expansion of the silicon negative electrode can be better inhibited, and the cycle performance of the battery can be improved. More importantly, when the thickness of the copper foil is 3-8 μm, a high energy density can also be obtained. When the thickness of the copper foil is greater than 8 μm, the cycle performance of the battery is less affected, and mainly the energy density of the battery is deteriorated. When the thickness of the copper foil is less than 3 μm, the tensile strength and the elongation of the copper foil are affected, the effect of inhibiting the volume expansion of the silicon negative electrode is weakened, the improvement of the cycle performance of the battery is not obvious, and the strength of the negative electrode obtained is insufficient, and the preparation of the battery cannot be realized.

[0011] According to the embodiment of the present application, the copper foil can be obtained by being purchased through a commercial channel or being prepared by a method known in the art.

[0012] According to the embodiment of the present application, the phosphate nitrile compound comprises 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 comprises an alkyl group, an alkenyl group or an alkynyl group.

[0013] According to the embodiment of the present application, the phosphate nitrile compound is selected from at least one of the compounds with the structural formula shown in formula (1):

[0014]

[0015] In formula (1), R1, R2, R3 are the same or different, and are independently selected from unsubstituted or optionally substituted alkyl, alkenyl or alkynyl with one, two or more Ra; each Ra is the same or different, and is independently selected from halogen or alkyl.

[0016] According to an embodiment of the present application, in formula (1), R1, R2, R3 are the same or different, and are independently selected from unsubstituted or optionally substituted 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.

[0017] According to an embodiment of the present application, in formula (1), R1, R2, R3 are the same or different, and are independently selected from unsubstituted or optionally substituted 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.

[0018] According to an embodiment of the present application, in formula (1), R1, R2, R3 are the same or different, and are independently selected from unsubstituted or optionally substituted 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.

[0019] According to an embodiment of the present application, the phosphonitrilic compound includes at least one of compounds having structures shown in formula (2) to formula (7):

[0020]

[0021] According to an embodiment of the present application, the phosphonitrilic compound can be obtained by purchasing through commercial channels, or can be prepared by using methods known in the art.

[0022] According to an embodiment of the present application, the mass of the phosphonitrile 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%. Research has found that when the mass of the phosphonitrile compound accounts for 0.1wt%-5wt% of the total mass of the electrolyte, the phosphonitrile compound can form a protective layer on the surface of the positive electrode, improving the high-temperature and high-voltage performance of the battery; more importantly, the phosphonitrile compound at this content can match the copper foil, better inhibit the volume expansion of the silicon negative electrode, and improve the cycle performance of the battery; further, the phosphonitrile compound at this content can also slightly corrode the copper foil (as the phosphonitrile compound is easy to decompose into various short-chain mononitriles with high coordination and high polarity, these short-chain mononitriles are easy to decompose to form acid corrosion of the copper foil, and can also form strong coordination with copper ions to accelerate the corrosion of the copper foil), soften burrs, thereby significantly reducing the self-discharge phenomenon of the battery. Moreover, the phosphonitrile compound can reduce the self-discharge phenomenon of the battery caused by high-strength copper foil with an elongation rate of 3-5%, while the high-strength copper foil can significantly improve the stability of the negative electrode of the silicon-containing negative electrode battery, the phosphonitrile compound can improve the stability of the positive electrode of the silicon-containing negative electrode battery, and the two can synergistically improve the overall stability of the silicon-containing negative electrode battery, achieving better high-temperature cycle performance and low self-discharge phenomenon. When the mass of the phosphonitrile compound accounts for less than 0.1wt% of the total mass of the electrolyte, the addition amount of the phosphonitrile compound is too small to form a sufficient interface protection 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, which cannot effectively improve the cycle performance of the battery and improve the self-discharge phenomenon of the battery; when the mass of the phosphonitrile compound accounts for more than 5wt% of the total mass of the electrolyte, the addition amount of the phosphonitrile compound is too large, which will seriously corrode the copper foil, causing copper to be precipitated on the surface of the negative electrode, thereby worsening the self-discharge phenomenon of the battery, and the interface protection film formed on the surface of the positive electrode is too thick, causing the cycle performance of the battery at high temperature and high voltage to deteriorate.

[0023] According to an embodiment of the present application, the percentage of the mass of the silicon-based negative electrode material in the total mass of the negative electrode active material layer is 2wt% to 30wt%, for example, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt% or 30wt%. Research has found that when the percentage of the mass of the silicon-based negative electrode material in the total mass of the negative electrode active material layer is 2wt% to 30wt%, the volume expansion of the silicon-based negative electrode material is moderate, and through the matching of the phosphonitrile ester compound and the copper foil, the volume expansion of the silicon negative electrode can be better inhibited, and the cycle performance of the battery can be improved. When the percentage of the mass of the silicon-based negative electrode material in the total mass of the negative electrode active material layer is less than 2wt%, the energy density of the battery is greatly affected.

[0024] According to an embodiment of the present application, the silicon-based negative electrode material includes at least one of nano-silicon (Si), a silicon-oxygen negative electrode material (SiOx(0

[0025] According to an embodiment of the present application, the silicon-carbon negative electrode material includes particles formed by mixing silicon or partially oxidized silicon with amorphous or crystalline carbon;

[0026] and / or particles formed by filling (including partial filling or complete filling) silicon or partially oxidized silicon in the pores of porous amorphous carbon or porous crystalline carbon.

[0027] According to an embodiment of the present application, the silicon-carbon negative electrode material has high initial efficiency, higher energy density than ordinary graphite negative electrode materials, but its expansion is significantly larger than ordinary graphite.

[0028] According to an embodiment of the present application, the negative electrode active material further includes a carbon-based negative electrode material.

[0029] According to an embodiment of the present application, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0030] According to an embodiment of the present application, the battery satisfies the following relationship formula (i) and / or formula (ii):

[0031] 5-0.05A≥B formula (i)

[0032] 5≥C≥2.6-0.5×B formula (ii)

[0033] Wherein, A is the percentage of the mass of the silicon-based negative electrode material in the total mass of the negative electrode active material layer, and the unit is wt%; B is the elongation of the high-strength copper foil, and the unit is %; C is the percentage of the mass of the phosphonitrile ester compound in the total mass of the electrolyte, and the unit is wt%.

[0034] According to the embodiment of the present application, when the battery satisfies the relationship formula 5-0.05A≥B shown in formula (i), it indicates that by adjusting the relationship between the mass ratio of the silicon-based negative electrode material and the elongation of the high-strength copper foil in the battery, 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; when 5-0.05A

[0035] According to the embodiment of the present application, when the battery satisfies the relationship formula 5≥C≥2.6-0.5×B shown in formula (ii), it indicates that by adjusting the relationship between the mass ratio of the phosphonitrile ester compound and the elongation of the high-strength copper foil in the battery, the electrolyte and the copper foil can be better matched. On the one hand, the phosphonitrile ester 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 at high temperature and high voltage; on the other hand, the phosphonitrile ester compound can soften the burrs on the surface of the copper foil, reduce the self-discharge phenomenon of the battery, and realize the improvement of the cycle performance of the battery and the improvement of the self-discharge phenomenon of the battery; when C

[0036] According to the embodiment of the present application, A satisfies: 2%≤A%≤30%.

[0037] According to the embodiment of the present application, B satisfies: 3%≤B%≤5%.

[0038] According to the embodiment of the present application, C satisfies: 0.1%≤C%≤5%.

[0039] According to the embodiment of the present application, the area density E of the negative electrode is 3mg / cm 2 -15mg / cm 2 , for example, 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 / cm2 12 mg / cm 2 13 mg / cm 2 14 mg / cm 2 or 15 mg / cm 2 When the surface density of the negative electrode is 3 mg / cm 2 - 15 mg / cm 2 , a battery with low expansion performance, low self-discharge phenomenon and high energy density can be obtained; 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 obtained battery is greater, which requires a higher strength copper foil to suppress the problem of battery expansion, resulting in more obvious burr phenomenon of the copper foil, exacerbating the self-discharge phenomenon of the battery.

[0040] According to an embodiment of the present application, the compaction density F of the negative electrode is 1.4 g / cm 3 - 1.9 g / cm 3 , for example, 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 or 1.9 g / cm 3 When the compaction density of the negative electrode is 1.4 g / cm 3 - 1.9 g / cm 3 , a battery with low expansion performance, low self-discharge phenomenon and high energy density can be obtained; when the compaction density of the negative electrode is 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, resulting in a smaller expansion buffer space for the silicon-carbon negative electrode material, and the expansion of the obtained battery is greater, which requires a higher strength copper foil to suppress the problem of battery expansion, resulting in more obvious burr phenomenon of the copper foil, exacerbating the self-discharge phenomenon of the battery.

[0041] According to an embodiment of the present application, the negative electrode active material layer further comprises a conductive agent and a binder.

[0042] According to an embodiment of the present application, the mass percentage content of each component in the negative electrode active material layer is: 80-99.8 wt% of negative electrode active material, 0.1-10 wt% of conductive agent, 0.1-10 wt% of binder.

[0043] Preferably, the mass percentage content of each component in the negative electrode active material layer is: 90-99.6 wt% of negative electrode active material, 0.2-5 wt% of conductive agent, 0.2-5 wt% of binder.

[0044] According to an embodiment of the present application, the electrolyte salt comprises 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.

[0045] According to an embodiment of the present application, the electrolyte lithium salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalate borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, or lithium bis(trifluoromethylsulfonyl)imide.

[0046] According to an embodiment of the present application, the organic solvent is selected from fluorinated or non-fluorinated carbonates and / or carboxylic acid esters, the carbonates being selected from one or more of the following solvents: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate; the carboxylic acid esters being selected from one or more of the following solvents: ethyl acetate (EA), propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), methyl butyrate, ethyl n-butyrate. Carbonates and carboxylic acid esters have high oxidation resistance and good lithium salt dissociation capacity, and can be used as excellent solvents for electrolyte.

[0047] According to an embodiment of the present application, the battery is a lithium ion battery.

[0048] According to an embodiment of the present application, the battery is a lithium ion secondary battery.

[0049] According to an embodiment of the present application, the electrolyte is a non-aqueous electrolyte.

[0050] According to an embodiment of the present application, the positive electrode comprises 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 comprising a positive electrode active material, a conductive agent, and a binder.

[0051] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% of positive electrode active material, 0.1-10 wt% of conductive agent, and 0.1-10 wt% of binder.

[0052] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt% of positive electrode active material, 0.2-5 wt% of conductive agent, and 0.2-5 wt% of binder.

[0053] According to an embodiment of the present application, the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder.

[0054] According to an embodiment of the present application, the binder comprises at least one of sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene, polyethylene oxide.

[0055] According to an embodiment of the present application, the positive electrode active material comprises one or more of transition metal lithium oxide, lithium iron phosphate, 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, Zr.

[0056] According to an embodiment of the present application, the battery further comprises a separator film.

[0057] The beneficial effects of the present application are as follows:

[0058] The present application provides a battery. The battery comprises 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, and the negative electrode current collector comprises a copper foil with a tensile strength of ≥400 MPa; the electrolyte comprises an organic solvent, an electrolyte salt and an additive, and the additive comprises a phosphonitrile ester compound. The silicon negative electrode uses a copper foil with low elongation as the negative electrode current collector, which can inhibit the volume expansion of the silicon negative electrode, reduce the interface decomposition of the SEI and the electrolyte, and improve the cycle performance of the battery. At the same time, the phosphonitrile ester compound included in the electrolyte can form a film on the surface of the positive electrode and coordinate with the transition metal in the positive electrode active material through the cyano group, thereby reducing the oxidative decomposition of the electrolyte at the positive electrode interface, and further improving the high-temperature cycle performance of the battery. The cross section of the copper foil with low elongation is prone to generate more burrs, and the burrs are easy to pierce the separator film, causing micro-short circuit between the positive and negative electrodes, which deteriorates the self-discharge performance of the battery. The phosphonitrile ester compound can slightly corrode the copper foil, and the burr copper can be obviously passivated, thereby reducing the piercing of the separator film and significantly improving the self-discharge performance of the battery.

[0059] In summary, the application reduces the volume expansion of the silicon negative electrode by using a copper foil with a tensile strength of ≥400 MPa and a low elongation rate as the negative electrode, improves the negative electrode interface, uses a phosphonitrile compound as the electrolyte to improve the positive electrode interface, and realizes the improvement of the high-temperature cycle stability of the battery. At the same time, the phosphonitrile compound can reduce the harm of burr copper, slightly corrode the copper foil, and can obviously passivate the burr copper, thereby reducing the puncture of the separator and significantly improving the self-discharge performance of the battery. DETAILED DESCRIPTION

[0060] The application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is covered within the scope of protection intended by the application.

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

[0062] The copper foils used in the following examples and comparative examples are obtained by commercial purchase, and the tensile strength and elongation rate of the copper foils are tested by GB-228-87 testing method, with 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 are prepared by the following method:

[0064] 1) Preparation of positive electrode sheet

[0065] The positive electrode active material lithium cobaltate (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-methyl pyrrolidone (NMP) is added, and stirring is carried out under the action of a vacuum stirrer until the mixed system becomes a homogeneous and flowable positive electrode active paste; the positive electrode active paste is uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, then rolled and cut to obtain the required positive electrode sheet.

[0066] 2) Preparation of negative electrode sheet

[0067] The negative active material artificial graphite, silicon-carbon negative material, carboxymethyl cellulose sodium (CMC-Na), butyl rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) are mixed according to the mass ratio (94.5-A):A:2.5:1.5:1:0.5, deionized water is added, and a negative active slurry is obtained under the action of a vacuum stirrer; the negative active slurry is uniformly coated on both surfaces of a copper foil with an elongation rate of B; the coated copper foil is air-dried at room temperature, then transferred to a 80℃ oven for drying for 10h, and then cold-pressed and cut to obtain a negative sheet with a surface density of Emg / cm 2 and a compacted density of Fg / cm 3 . The specific parameters of A and B are shown 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 are mixed uniformly according to the mass ratio of 20:10:20:50. Then 14wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte is quickly added, and after dissolution, C wt% of phosphonate nitrile compound, 2wt% of HTCN (1,3,6-hexanetricarbonitrile) and 3wt% of PS (1,3-propane sulfone lactone) based on the total mass of the electrolyte are added, and the specific amounts are shown in Table 1. After stirring uniformly, the required electrolyte is obtained after passing the water and free acid detection.

[0070] 4) Preparation of lithium ion battery

[0071] The positive sheet of step 1), the negative sheet of step 2) and the separator are stacked in the order of positive sheet, separator and negative sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, the electrolyte of step 3) is injected into the outer packaging, and after vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium ion battery is obtained. The battery of the present application has a charge-discharge range of 3.0-4.5V.

[0072] The lithium ion batteries obtained in the examples and comparative examples are respectively tested for 45℃ cycle performance and storage self-discharge K value, and the test results are shown in Table 2.

[0073] 1) 45℃ cycle performance test

[0074] The battery of Table 1 is charged and discharged at 45℃ in the range of charge-discharge cut-off voltage at 1C rate, the discharge capacity of the first week is counted as x mAh, the discharge capacity of the Nth week is counted as y mAh; the capacity of the Nth week divided by the capacity of the first week, the cycle capacity retention rate R of the Nth week = y / x, record the cycle number corresponding to the cycle capacity retention rate R of 80%.

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

[0076] The prepared lithium ion battery is charged at 25℃ to the cut-off voltage 4.5V at 1C rate, the cut-off current is 0.025C, and the voltage U of the lithium ion battery is tested after standing for 10h. Calculate the self-discharge K value of the lithium ion battery: K=(U-4.5)*1000 / 10.

[0077] Table 1 composition of the battery negative electrode and electrolyte of the examples and comparative examples

[0078]

[0079]

[0080] Wherein, A is the mass percentage of the silicon-based negative electrode material in the total mass of the negative electrode active material layer, unit: wt%; B is the elongation of copper foil, unit: %; C is the mass percentage of phosphonate nitrile compound in the total mass of electrolyte, unit: wt%. E is the area density of the negative electrode, unit: mg / cm 2 ; F is the compacted density of the negative electrode, unit: g / cm 3 .

[0081] Example 33

[0082] Other operations are the same as Example 4, except that the negative electrode material is nano-silicon.

[0083] Example 34

[0084] Other operations are the same as Example 4, except that the negative electrode material is silicon-oxygen negative electrode material.

[0085] Table 2 performance test results of the batteries of the examples and comparative examples

[0086]

[0087]

[0088] From the performance test results of the above examples and comparative examples, it can be seen that the application reduces the volume expansion of the silicon negative electrode by using a high-strength copper foil with low elongation for the negative electrode, improves the negative electrode interface, and uses a phosphonitrile ester compound electrolyte to improve the positive electrode interface, thereby achieving the improvement of the high-temperature cycle stability of the battery. At the same time, the phosphonitrile ester compound can reduce the harm of burr copper, slightly corrode the copper foil, and can obviously passivate the burr copper, thereby reducing the puncture of the separator and significantly improving the self-discharge performance of the battery.

[0089] In particular, when the battery satisfies the relationship formula (5-0.05A≥B) shown in formula (i) and the relationship formula (5≥C≥2.6-0.5×B) shown in formula (ii), it indicates that by adjusting the relationship between the mass ratio of the silicon-based negative electrode material and the elongation of the high-strength copper foil in the battery, 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 relationship between the mass ratio of the phosphonitrile ester compound and the elongation of the high-strength copper foil in the battery, the electrolyte and the high-strength copper foil can be better matched, on the one hand, the phosphonitrile ester 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 at high temperature and high voltage; on the other hand, the phosphonitrile ester compound can soften the burr on the surface of the high-strength copper foil, reduce the self-discharge phenomenon of the battery, and achieve the improvement of the cycle performance of the battery and the self-discharge phenomenon of the battery.

[0090] The above describes the embodiments of the application. However, the application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A battery, the 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, 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 phosphonitrile compound; The battery satisfies the relational expressions shown in the following formula (i) and / or formula (ii): 5 - 0.05A ≥ B Formula (i) 5 ≥ C ≥ 2.6 - 0.5×B Formula (ii) in, A is the percentage of the mass 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 percentage of the mass of the phosphonitrile compound in the total mass of the electrolyte, with the unit of wt%; A satisfies: 2% ≤ A% ≤ 30%; B satisfies: 3% ≤ B% ≤ 5%; C satisfies: 0.1% ≤ C% ≤ 5%.

2. The battery according to claim 1, wherein, The thickness of the copper foil is 3 - 8 μm.

3. The battery according to claim 1, wherein, The phosphonitrile compound comprises 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 comprises an alkyl group, an alkenyl group or an alkynyl group.

4. The battery according to claim 3, wherein, The phosphonitrile compound is selected from at least one of the compounds 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.

5. The battery according to claim 4, wherein, In equation (1), R1, R2, and R3 may be the same or different, and are independently selected from C that is unsubstituted or arbitrarily substituted by one, two, or more Ra. 1-12 Alkyl, C 2-12 alkenyl or C 2-12 Alkyne group; each Ra may be the same or different, and each is independently selected from halogens or C. 1-12 alkyl.

6. The battery according to any one of claims 1-5, wherein, The silicon-based negative electrode material comprises at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiOx(0 < x < 2)) and silicon-carbon negative electrode material.

7. The battery according to claim 6, wherein, The silicon-carbon negative electrode material comprises 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.

8. The battery according to any one of claims 1-5, wherein, The areal density of the negative electrode is 3 mg / cm³. 2 -15mg / cm 2 ; And / or, the compaction density of the negative electrode is 1.4 g / cm³. 3 -1.9g / cm 3 .

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