A battery

Abstract

The present invention provides an electrolyte and a battery containing the electrolyte. The battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator; the electrolyte includes an electrolyte salt, an organic solvent, and a functional additive, the functional additive including a first additive, the first additive including a fluoropropane sultone compound; the negative electrode sheet contains a metallic Ni element; when the battery satisfies 50≥1000A‑B≥2, the electrolyte additive can well match the negative electrode, effectively improve the stability of the interface protective film on the positive and negative electrode surfaces, and can improve the content of lithium alkyl sulfonate and lithium fluoride in the SEI film on the negative electrode surface during the formation and charge and discharge processes of the battery, thereby improving the stability of the negative electrode SEI film, reducing the negative impact of the metallic Ni element in the negative electrode sheet on the battery, and further improving the battery's cycle performance and storage performance at high temperature and high voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and specifically relates to a battery, and in particular to a battery with good electrochemical performance under high temperature and high voltage. Background Art

[0002] Lithium-ion batteries are high-energy-density, highly efficient, and environmentally friendly batteries. Due to their numerous advantages, they have become the preferred power source for modern electronic devices and small power systems. The basic components of a lithium-ion battery include a positive electrode, a negative electrode, an electrolyte, and a separator. During charging, lithium ions are released from the negative electrode, passing through the electrolyte and entering the positive electrode. Simultaneously, electrons flow from the positive electrode back to the negative electrode through an external circuit.

[0003] The electrolyte acts as a medium for ion transport in lithium-ion batteries and is crucial to their performance and safety. The electrolyte is composed of electrolyte salts, organic solvents, and other additives. The electrolyte salts provide ions, while the organic solvents dissolve the electrolyte salts in the battery. To enhance battery performance, electrolyte additives are used to improve battery life, safety, and temperature characteristics.

[0004] The negative electrode is the carrier of lithium ions and electrons during the battery's charging process, storing and releasing energy. Negative electrode materials include graphite and silicon-based anodes. Graphite is the most widely used of these materials. However, after charging, graphite has a low potential and is prone to side reactions with the electrolyte. If the resulting interfacial film has a high impedance, the charge and discharge rates are low and lithium deposition is likely to occur. The layered structure of graphite can deform by approximately 10% during lithium ion insertion and deintercalation, affecting the battery's cycle life. Summary of the Invention

[0005] Research has found that introducing metallic Ni into the negative electrode material can significantly improve the conductivity of the negative electrode active material, thereby improving the large current discharge capacity; however, when divalent or trivalent metallic Ni elements (such as metallic Ni salts or metallic nickel oxide) are added to the negative electrode material, not only will the battery performance not be improved, but it will also destroy the interfacial protective film formed by the electrolyte additives on the surface of the positive and negative electrodes, thereby deteriorating the electrochemical performance of the battery.

[0006] To avoid deterioration of battery performance at high temperature and high voltage and to reduce the impact of metallic Ni in the negative electrode sheet on battery performance, the present invention provides a battery. The electrolyte of the battery contains a fluoropropane sultone compound, which can be introduced into the battery as an electrolyte additive. The addition of the fluoropropane sultone compound can effectively reduce the impact of metallic Ni in the negative electrode sheet on deterioration of battery performance, improve the adverse effect of metallic Ni in the negative electrode sheet on the interface film, and significantly enhance the stability of the positive and negative electrode interfaces and the electrolyte at high temperature and high voltage, thereby significantly improving the electrochemical performance of the battery at high temperature and high voltage.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator; the electrolyte comprises an electrolyte salt, an organic solvent, and a functional additive, the functional additive comprises a first additive, and the first additive comprises a fluoropropane sultone compound; the negative electrode sheet contains a metallic Ni element;

[0009] The battery meets the following requirements:

[0010] 50≥1000A-B≥2;

[0011] Wherein, A is the percentage of the mass of the fluoropropane sultone compound in the electrolyte to the total mass of the electrolyte; B is the percentage of the mass of the metal Ni element in the negative electrode sheet to the total mass of the negative electrode active material layer in the negative electrode sheet, in ppm.

[0012] In the present invention, unless otherwise specified, the metallic Ni element refers to Ni 2+ and / or Ni 3+ .

[0013] According to an embodiment of the present invention, the battery satisfies: 30≥1000A-B≥3. Exemplarily, 1000A-B is 2, 3, 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28 or 30.

[0014] According to the embodiment of the present invention, under high temperature and high voltage, the stability of the film formed on the surface of the positive and negative electrodes deteriorates, and a large amount of interface films formed on the surface of the positive and negative electrodes will decompose, resulting in a significant deterioration in the battery performance at high temperature and high voltage. In particular, when the negative electrode sheet contains metallic Ni elements, the cycle performance and storage performance of the battery at high temperature and high voltage will be aggravated and deteriorated. After research, the inventors of the present application found that when fluoropropane sultone compounds are introduced into the electrolyte, the fluoropropane sultone compounds have excellent positive and negative electrode protection properties, which can form films on the positive and negative electrodes. Specifically, fluoropropane sultone compounds can react on the surface of the negative electrode to form a stable SEI film. The SEI film is rich in lithium alkyl sulfonate and lithium fluoride compounds, which can effectively prevent the negative electrode surface from reacting with the electrolyte, and can significantly reduce the influence of metallic Ni elements in the negative electrode sheet on the battery performance, thereby improving the battery cycle performance. The SEI film also has good high temperature stability, and can also improve the high temperature and high voltage performance of the battery at the same time, and inhibit battery gas production. Fluoropropane sultone can also form a film on the positive electrode, generating a stable CEI film. This film can also inhibit electrolyte decomposition and improve the battery's high-temperature cycling and storage performance. Further research found that when the battery meets 50≥1000A-B≥2, the electrolyte additive can well match the negative electrode, effectively improving the stability of the interface protective film between the positive and negative electrode surfaces. It can also improve the content of lithium alkyl sulfonate and lithium fluoride in the SEI film on the negative electrode surface during the battery formation and charge and discharge processes, improve the stability of the negative electrode SEI film, reduce the negative impact of the metallic Ni element in the negative electrode sheet on the battery, and further improve the battery's cycling and storage performance at high temperatures and high voltages.

[0015] According to an embodiment of the present invention, the mass of the first additive accounts for a percentage of 0.1wt% to 5wt% of the total mass of the electrolyte, preferably 0.5wt% to 4wt%, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%.

[0016] According to an embodiment of the present invention, the mass percentage of the metallic Ni element in the negative electrode sheet to the total mass of the negative electrode active material layer in the negative electrode sheet is 0.1ppm to 40ppm, preferably 1ppm to 20ppm, for example, 0.2ppm, 0.3ppm, 0.5ppm, 0.8ppm, 1ppm, 2ppm, 5ppm, 8ppm, 10ppm, 12ppm, 15ppm, 18ppm, 20ppm, 25ppm, 30ppm, 35ppm or 40ppm.

[0017] According to an embodiment of the present invention, the first additive includes at least one of the compounds shown in Formula I:

[0018]

[0019] In Formula I, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted alkyl; if substituted, the substituent is fluorine or alkyl; at least one of R1, R2, and R3 contains a fluorine atom.

[0020] According to an embodiment of the present invention, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted C 1-20 Alkyl; if substituted, the substituent is fluorine or C 1-20 Alkyl group; at least one of R1, R2, and R3 contains a fluorine atom.

[0021] According to an embodiment of the present invention, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted C 1-12 Alkyl; if substituted, the substituent is fluorine or C 1-12 Alkyl group; at least one of R1, R2, and R3 contains a fluorine atom.

[0022] According to an embodiment of the present invention, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted C 1-6 Alkyl; if substituted, the substituent is fluorine or C 1-6 Alkyl group; at least one of R1, R2, and R3 contains a fluorine atom.

[0023] According to an embodiment of the present invention, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted C 1-3 Alkyl; if substituted, the substituent is fluorine or C 1-3 Alkyl group; at least one of R1, R2, and R3 contains a fluorine atom.

[0024] According to an embodiment of the present invention, the first additive includes at least one of the following compounds A1 to A6:

[0025]

[0026]

[0027] According to an embodiment of the present invention, the first additive can be purchased from commercial sources or prepared by methods known in the art.

[0028] According to an embodiment of the present invention, the functional additive further includes a second additive, and the second additive includes one or more of a dinitrile compound, a trinitrile compound, and a tetranitrile compound.

[0029] According to an embodiment of the present invention, the nitrile compound is selected from at least one of a dinitrile compound represented by formula II-1, a trinitrile compound represented by formula II-2, and a tetranitrile compound represented by formula II-3:

[0030] NC-R 21 -CN Formula II-1

[0031]

[0032] Among them, R 21 is a group having 1 to 10 carbon atoms and having at least 2 substitution positions; R 22 is a group having 1 to 10 carbon atoms and at least 3 substitution positions (such as a phosphorus-containing group having 1 to 10 carbon atoms and 3 substitution positions); R 23 It is a group having 1 to 10 carbon atoms and having at least 4 substitution sites.

[0033] According to an embodiment of the present invention, the group having 1 to 10 carbon atoms is selected from substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 1-10 Alkoxy, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 1-10 Alkyl-OC 1-10 Alkyl, substituted or unsubstituted C 1-10 Alkyl-C(O)-C 1-10 Alkyl, substituted or unsubstituted C 4-10 Heteroaryl, substituted or unsubstituted C 4-10 Heterocyclic group, substituted or unsubstituted C 6-10 Aryl, substituted by halogen, substituted or unsubstituted C 1-10 alkyl.

[0034] According to an embodiment of the present invention, the phosphorus-containing group having 1 to 10 carbon atoms and having 3 substitution positions is selected from the phosphate group shown in formula III-1 or the phosphite group shown in formula III-2;

[0035]

[0036] Among them, * is the connecting bond; R 31 、R 32 and R 33 The same or different, independently selected from C 1-10 Alkyl; such as selected from C 1-6 Alkyl; such as C 1-3 Alkyl groups such as methyl, ethyl or propyl.

[0037] According to an embodiment of the present invention, the dinitrile compound represented by formula II-1 is selected from at least one of the following compounds: glutaronitrile, succinonitrile (SN), adiponitrile (ADN), sebaconinitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranimethylenemalononitrile, butylene dicarbonitrile, ethylene glycol bis(propionitrile) ether (DENE) and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazine dicarbonitrile.

[0038] According to an embodiment of the present invention, the trinitrile compound represented by formula II-2 is selected from at least one of the following compounds: 1,3,6-hexanetrinitrile (HTCN), 1,3,5-cyclohexanetrinitrile, 1,3,5-benzenetricyanide, 1,2,3-propanetricarbonitrile, glycerol trinitrile, and tris(3-cyanopropyl)phosphate (PCN).

[0039] According to an embodiment of the present invention, the tetranitrile compound represented by formula II-3 is selected from at least one of the following compounds: 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene.

[0040] According to an embodiment of the present invention, the mass percentage of the second additive to the total mass of the electrolyte is 0.1 to 8 wt%, preferably 2 to 6 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 7 wt% or 8 wt%.

[0041] According to an embodiment of the present invention, the second additive can undergo a coordination reaction with the positive electrode, thereby improving the battery interface stability and further improving the cycle performance and storage performance of the battery at high temperature and high voltage.

[0042] According to an embodiment of the present invention, the functional additive further includes a third additive, and the third additive includes a fluorinated compound.

[0043] According to an embodiment of the present invention, the fluorinated compound includes but is not limited to fluorinated carbonates, fluorinated carboxylates, fluorinated ethers, and the like, specifically fluoroethylene carbonate (FEC), trifluoroethyl methyl carbonate (FEMC), fluorodiethyl carbonate (FDEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), ethyl 2,2,2-trifluoroacetate (FEA), ethyl 2,2-difluoroacetate, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE).

[0044] According to an embodiment of the present invention, the fluorinated compound itself has good oxidation resistance and strong stability to the positive electrode, and can also form a film on the negative electrode, further reducing the negative electrode interface side reaction.

[0045] According to an embodiment of the present invention, the fluorinated compound additive can be purchased from commercial sources or prepared using methods known in the art.

[0046] According to an embodiment of the present invention, the mass of the third additive accounts for 5wt% to 15wt% of the total mass of the electrolyte, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0047] According to an embodiment of the present invention, the battery satisfies: C<5A;

[0048] Wherein, A is the percentage of the mass of the fluoropropane sultone compound in the electrolyte to the total mass of the electrolyte; C is the percentage of the mass of the second additive in the electrolyte to the total mass of the electrolyte.

[0049] The study found that when the battery meets the condition of C<5A, the synergistic effect between the first additive and the second additive can be more fully realized, and the protective effect of the two additives on the positive and negative electrodes can be fully exerted (which is more conducive to the protection of the negative electrode by the first additive and the positive electrode by the second additive), thereby avoiding insufficient protection or deterioration of the positive and negative electrodes due to excessively high or low additive content.

[0050] According to an embodiment of the present invention, the electrolyte salt includes an electrolyte lithium salt.

[0051] According to an embodiment of the present invention, the electrolyte lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobisoxalatophosphate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4C2O4), lithium oxalatophosphate (LiPO2C2O4), lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonyl imide (LiTFSI) and lithium bisfluorosulfonyl imide (LiFSI).

[0052] According to an embodiment of the present invention, the mass percentage of the electrolyte salt to the total mass of the electrolyte is 10wt% to 15wt%, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0053] According to an embodiment of the present invention, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB) and γ-butyrolactone (GBL).

[0054] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material; the negative electrode active material contains metallic Ni. That is, the metallic Ni is introduced into the negative electrode sheet through the negative electrode active material.

[0055] According to an embodiment of the present invention, the negative electrode sheet containing the metallic Ni element can be a negative electrode sheet after formation or charge-discharge cycling (i.e., a negative electrode sheet obtained after disassembly from a battery), or it can be a prepared negative electrode sheet that has not been assembled into a battery.

[0056] According to an embodiment of the present invention, the surface density of the negative electrode sheet is 1-13 mg / cm 2 .

[0057] According to an embodiment of the present invention, the positive electrode sheet 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. The positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

[0058] According to an embodiment of the present invention, the negative electrode active material layer further includes a conductive agent and a binder.

[0059] According to an embodiment of the present invention, 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.

[0060] 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.

[0061] According to an embodiment of the present invention, the mass percentage 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, and 0.1-10 wt % of binder.

[0062] Preferably, the mass percentage 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, and 0.2-5 wt % of binder.

[0063] According to an embodiment of the present invention, the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, hard carbon, soft carbon, and silicon-based negative electrode materials.

[0064] According to an embodiment of the present invention, the positive electrode active material includes one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganate, lithium manganese iron phosphate, and lithium vanadium phosphate; 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.

[0065] According to an embodiment of the present invention, the charging cut-off voltage of the battery is ≥4.5V.

[0066] Beneficial effects of the present invention:

[0067] The present invention provides a battery. Under high temperature and high voltage, the stability of the film formed on the surface of the positive and negative electrodes deteriorates, and a large amount of interface films formed on the surface of the positive and negative electrodes will decompose, resulting in a significant deterioration in the battery performance under high temperature and high voltage. In particular, when the negative electrode sheet contains metallic Ni elements, the electrochemical performance of the battery under high temperature and high voltage will be aggravated and deteriorated. After research, the inventors of the present application found that when fluoropropane sultone compounds are introduced into the electrolyte, the fluoropropane sultone compounds have excellent positive and negative electrode protection properties and can form films on the positive and negative electrodes. Specifically, the fluoropropane sultone compounds can react on the surface of the negative electrode to form a stable SEI film. The SEI film is rich in lithium alkyl sulfonate and lithium fluoride compounds, which can effectively prevent the negative electrode surface from reacting with the electrolyte, significantly reduce the influence of metallic Ni elements in the negative electrode sheet on the battery performance, and improve the battery cycle performance. The SEI film also has good high-temperature stability, and can also improve the high-temperature and high-voltage performance of the battery and inhibit battery gas production. Fluoropropane sultone can also form a film on the positive electrode, generating a stable CEI film. This film can also inhibit electrolyte decomposition and improve the battery's high-temperature cycling and storage performance. Further research found that when the battery meets 50≥1000A-B≥2, the electrolyte additive can well match the negative electrode, effectively improving the stability of the interface protective film between the positive and negative electrode surfaces. It can also improve the content of lithium alkyl sulfonate and lithium fluoride in the SEI film on the negative electrode surface during the battery formation and charge and discharge processes, improve the stability of the negative electrode SEI film, reduce the negative impact of the metallic Ni element in the negative electrode sheet on the battery, and further improve the battery's cycling and storage performance at high temperatures and high voltages. DETAILED DESCRIPTION

[0068] The present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0069] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0070] The negative electrode active material used in the following examples is doped with a small amount of metallic nickel, which can degrade battery performance. By adjusting the doping level of metallic nickel in the negative electrode active material, negative electrode sheets with varying Ni content (0 ppm, 5.3 ppm, or 17.9 ppm) were obtained.

[0071] The batteries of Examples 1-9 and Comparative Examples 1-7 were prepared by the following steps:

[0072] 1) Preparation of positive electrode sheet

[0073] 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.

[0074] 2) Negative electrode preparation

[0075] The negative electrode active materials silicon carbon / artificial graphite (containing 5% silicon carbon and 95% artificial graphite), 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 94.5:2.5:1.5:1:0.5, deionized water was added, and a negative electrode active slurry was obtained under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of the copper foil; the coated copper foil was dried at room temperature, then transferred to an 80°C oven for drying for 10 hours, and then cold pressed and slit to obtain the negative electrode sheet.

[0076] 3) Preparation of electrolyte

[0077] In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), EC / PC / DEC / PP were mixed uniformly in a mass ratio of 10 / 20 / 20 / 50, and then fully dried lithium hexafluorophosphate (LiPF6) was quickly added thereto to a final concentration of 1 mol / L. After dissolution, 12 wt% of fluoroethylene carbonate based on the total mass of the electrolyte was added, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN) based on the total mass of the electrolyte was added, 2 wt% of adiponitrile (ADN) based on the total mass of the electrolyte was added, and the first additive (specific amount and selection are described in Table 1) was added. After stirring, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0078] 4) Battery Preparation

[0079] 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 form a battery cell. The battery cell is placed in an outer aluminum foil package, and the electrolyte from step 3) is injected into the outer packaging. The battery is vacuum packaged, allowed to stand, formed, shaped, and sorted to obtain a battery. The battery of the present invention has a charge and discharge range of 3.0-4.5V.

[0080] The batteries of Examples 10-14 were prepared by the following steps:

[0081] Other operations were the same as those in Example 5, with the only difference being that the first additive and the second additive of different mass proportions and types were added during the preparation of the electrolyte, as shown in Table 3.

[0082] The batteries obtained in the examples and comparative examples were subjected to a 60° C. storage performance test and a 45° C. cycle performance test, respectively.

[0083] 1) 60℃ storage performance test

[0084] Charge the batteries in Table 1 at 25°C at a rate of 1C to the cutoff voltage and a cutoff current of 0.025C. Let them rest for 5 minutes, and then measure the thickness of the lithium-ion battery (this is the thickness before storage). Place the fully charged cells / batteries at (60±2)°C in an open circuit for 35 days. After 35 days of storage, place them in an open circuit at room temperature for 2 hours, measure the thickness after storage, and calculate the thickness expansion rate of the lithium-ion battery:

[0085] Thickness expansion ratio = [(thickness after storage - thickness before storage) / thickness before storage] × 100%. The results are shown in Tables 2 and 4.

[0086] 2) 45℃ cycle performance test

[0087] The battery in Table 1 was charged and discharged at a rate of 1C within the charge and discharge cut-off voltage range at 45°C. The discharge capacity in the first week of the test was calculated as x2mAh, and the discharge capacity in the Nth cycle was calculated as y2mAh. The capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R2 = y2 / x2 in the Nth week. The number of battery cycles when the cycle capacity retention rate R2 was 70% was recorded. The results are shown in Tables 2 and 4.

[0088] 3) Scrape off the negative electrode active material layer from the negative electrode sheet. Take 5 mg of the negative electrode active material layer, add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid, and heat to 180°C until the solution is clear and transparent. After cooling, add water to make the volume 50 mL. Send the sample for testing. The metallic Ni content in the sample is measured using an ICP (Inductive Coupled Plasma Emission Spectrometer).

[0089] Table 1 Composition of electrolyte additives in the batteries of Examples 1-7 and Comparative Examples 1-7

[0090]

[0091]

[0092] Table 2 Performance test results of batteries of Examples 1-9 and Comparative Examples 1-7

[0093]

[0094] From the comparison of Comparative Examples 2-4 (or Comparative Examples 1 and 6), it can be seen that the metallic Ni element contained in the negative electrode sheet will deteriorate the high-temperature cycling performance and high-temperature storage performance of the battery at high voltage. From the comparison of Comparative Examples 3, Comparative Example 5, Comparative Example 7, Examples 1-5 and Examples 8-9 (such as Comparative Example 4, Comparative Example 6 and Examples 6-7), it can be seen that the fluoropropane sultone compound introduced into the electrolyte can enable the battery to form a stable interface film at the positive and negative electrodes earlier during the formation and charge-discharge processes, reduce side reactions between the electrolyte and the positive and negative electrode interfaces, improve the stability of the positive and negative electrodes at high voltage, reduce the consumption of electrolyte and damage to the positive and negative electrode structures during battery cycling, and improve the high-temperature cycling performance and high-temperature storage performance of the battery at high voltage. The introduction of fluoropropane sultone compounds can improve the deteriorating effect of the metallic Ni element contained in the negative electrode sheet on the high-temperature cycling performance and high-temperature storage performance of the battery at high voltage. In particular, by adjusting the content of the fluoropropane sultone compound in the electrolyte and its ratio to the metallic Ni element in the negative electrode sheet, that is, when the battery satisfies the following relationship: 50≥1000A-B≥2, the content of LiF and the like in the SEI film on the negative electrode surface of the battery during the formation and charge-discharge processes can be improved, thereby improving the stability of the negative electrode SEI film and further improving the high-temperature cycling performance and high-temperature storage performance of the battery at high voltage.

[0095] Furthermore, by comparing Comparative Example 5, Example 1, and Example 9, it can be seen that when the battery satisfies: C<5A, the synergistic effect between the first additive and the second additive can be more fully realized, and the protective effect of the two additives on the positive and negative electrodes can be fully exerted, thereby avoiding insufficient protection or deterioration of the positive and negative electrodes due to excessively high or low additive content.

[0096] Furthermore, by comparing Example 1 and Example 8, it can be seen that when the surface density of the negative electrode sheet is ≤13 mg / cm 2 When the electrolyte additives are added, it can better match the specific content of electrolyte additives and give full play to the effect of the electrolyte additives.

[0097] Table 3 Composition of electrolyte additives in the batteries of Examples 10-14

[0098]

[0099]

[0100] Table 4 Performance test results of the batteries of Examples 10-14

[0101]

[0102] It can be seen from the performance test results in Table 4 that the battery performance can be adjusted by adjusting the types of the first additive and the second additive in the electrolyte, but both can achieve the effect of improving the high-temperature cycle performance and high-temperature storage performance of the battery at high voltage.

[0103] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the electrolyte comprises an electrolyte salt, an organic solvent and a functional additive, the functional additive comprises a first additive, and the first additive comprises a fluoropropane sultone compound; the negative electrode sheet contains a metallic Ni element; The battery meets the following requirements: 50≥1000A-B≥2; Wherein, A is the percentage of the mass of the fluoropropane sultone compound in the electrolyte to the total mass of the electrolyte; B is the percentage of the mass of the metal Ni element in the negative electrode sheet to the total mass of the negative electrode active material layer in the negative electrode sheet, in ppm.

2. The battery according to claim 1, characterized in that The battery satisfies: 30≥1000A-B≥3.

3. The battery according to claim 1, characterized in that The mass of the first additive accounts for 0.1 to 5 wt % of the total mass of the electrolyte.

4. The battery according to claim 3, characterized in that The mass percentage of the first additive to the total mass of the electrolyte is 0.5 wt% to 4 wt%.

5. The battery according to claim 1, characterized in that The percentage of the mass of the metal Ni element in the negative electrode sheet to the total mass of the negative electrode active material layer in the negative electrode sheet is 0.1ppm to 40ppm.

6. The battery according to claim 5, characterized in that The percentage of the mass of the metal Ni element in the negative electrode sheet to the total mass of the negative electrode active material layer in the negative electrode sheet is 1 ppm to 20 ppm.

7. The battery according to any one of claims 1 to 6, characterized in that: The first additive includes at least one of the compounds shown in Formula I: In Formula I, R1, R2, and R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted alkyl; if substituted, the substituent is fluorine or alkyl; at least one of R1, R2, and R3 contains a fluorine atom.

8. The battery according to claim 7, characterized in that R1, R2, R3 are the same or different and are independently selected from hydrogen, fluorine, substituted or unsubstituted C 1-20 Alkyl; if substituted, the substituent is fluorine or C 1-20 Alkyl group; at least one of R1, R2, and R3 contains a fluorine atom.

9. The battery according to claim 8, characterized in that The first additive includes at least one of the following compounds A1 to A6:

10. The battery according to any one of claims 1 to 6, characterized in that: The functional additive further includes a second additive, which includes a nitrile compound; the nitrile compound is selected from at least one of the dinitrile compound shown in formula II-1, the trinitrile compound shown in formula II-2, and the tetranitrile compound shown in formula II-3: NC-R 21 -CN Formula II-1 Among them, R 21 is a group having 1 to 10 carbon atoms and having at least 2 substitution positions; R 22 is a group having 1 to 10 carbon atoms and having at least 3 substitution positions; R 23 It is a group having 1 to 10 carbon atoms and having at least 4 substitution sites.

11. The battery according to claim 10, characterized in that The group having 1 to 10 carbon atoms is selected from substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 1-10 Alkoxy, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 1-10 Alkyl-OC 1-10 Alkyl, substituted or unsubstituted C 1-10 Alkyl-C(O)-C 1-10 Alkyl, substituted or unsubstituted C 4-10 Heteroaryl, substituted or unsubstituted C 4-10 Heterocyclic group, substituted or unsubstituted C 6-10 Aryl, substituted by halogen, substituted or unsubstituted C 1-10 alkyl; And / or, the phosphorus-containing group having 1 to 10 carbon atoms and having 3 substitution positions is selected from the phosphate group shown in formula III-1 or the phosphite group shown in formula III-2; Among them, * is the connecting bond; R 31 、R 32 and R 33 The same or different, independently selected from C 1-10 alkyl.

12. The battery according to claim 10, characterized in that The mass percentage of the second additive to the total mass of the electrolyte is 0.1 to 8 wt %.

13. The battery according to claim 12, characterized in that The mass percentage of the second additive to the total mass of the electrolyte is 2 wt% to 6 wt%.

14. The battery according to claim 10, characterized in that The dinitrile compound represented by formula II-1 is at least one selected from the following compounds: glutaronitrile, succinonitrile (SN), adiponitrile (ADN), sebacononitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, fumaronitrile, ethylene glycol bis(propionitrile) ether (DENE) and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazine dicarbonitrile; and / or, the trinitrile compound represented by formula II-2 is selected from at least one of the following compounds: 1,3,6-hexanetrinitrile (HTCN), 1,3,5-cyclohexanetrinitrile, 1,3,5-benzenetricyanide, 1,2,3-propanetricarbonitrile, glycerol trinitrile, tris(3-cyanopropyl)phosphate (PCN); And / or, the tetranitrile compound represented by formula II-3 is selected from at least one of the following compounds: 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene.

15. The battery according to any one of claims 1 to 6, characterized in that: The functional additive further includes a third additive, wherein the third additive includes a fluorinated compound, and the fluorinated compound includes at least one of a fluorinated carbonate, a fluorinated carboxylate, or a fluorinated ether.

16. The battery according to claim 15, characterized in that The fluorinated compound includes at least one of fluoroethylene carbonate (FEC), trifluoroethyl methyl 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).

17. The battery according to claim 15, characterized in that The mass percentage of the third additive to the total mass of the electrolyte is 5 wt% to 15 wt%.

18. The battery according to claim 10, characterized in that The functional additive further includes a third additive, wherein the third additive includes a fluorinated compound, and the fluorinated compound includes at least one of a fluorinated carbonate, a fluorinated carboxylate, or a fluorinated ether.

19. The battery according to claim 18, characterized in that The fluorinated compound includes at least one of fluoroethylene carbonate (FEC), trifluoroethyl methyl 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).

20. The battery according to claim 18, characterized in that The mass percentage of the third additive to the total mass of the electrolyte is 5 wt% to 15 wt%.

21. The battery according to claim 10, characterized in that The battery meets the following requirements: C<5A; Wherein, A is the percentage of the mass of the fluoropropane sultone compound in the electrolyte to the total mass of the electrolyte; C is the percentage of the mass of the second additive in the electrolyte to the total mass of the electrolyte.

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