Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and relates to the technical field of batteries. The invention provides a secondary battery. The secondary battery comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte, the positive current collector contains an N element, and the N element comprises at least one of Zn, Ni, Cr, Ca and Ti; the secondary battery satisfies the following relationships: 1 < = (X + 50) / (P + 10 * Q) < = 25, 25 < = X < = 500, 3 < = P < = 50, 0.01 < = Q < = 5; wherein P is the weight percentage of the compound with the structure as shown in the structural formula A in the electrolyte; q is the weight percentage of the compound with the structure as shown in the structural formula B in the electrolyte; x is the content of the N element in the positive electrode current collector, and the unit is ppm. The elements of the positive current collector in the secondary battery have strong relevance with the first solvent A and the additive B, and under the selection, the performance of the secondary battery is better.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery and an electrical device using the same. Background Art

[0002] Lithium cobalt oxide (LiCoO2) is an attractive cathode material. Its reversible capacity can increase to 185 mAh / g and 220 mAh / g at 4.5 V and 4.6 V, respectively. However, high voltage brings serious problems, such as the oxidative decomposition of traditional carbonate electrolytes, oxygen release from the lithium cobalt oxide material, resulting in the degradation of CEI. Cyclic carbonate solvents undergo dehydrogenation reactions at high potentials, and C-H bonds are broken, which triggers the formation and accumulation of HF. In addition to corroding the cathode material and causing the dissolution of TM ions in the material itself, the corrosion problem of the cathode current collector at high voltages cannot be ignored. This is because there are inevitably some microscopic defect regions in the current collector during the manufacturing process. At these defect sites, the locally concentrated F - or HF species are prone to further corrode the current collector, continuously fluorinate the native Al2O3 layer at the defect sites to form AlF3 and LiF, which will make the defect region of the current collector brittle, generate microcracks and pits of Al dissolution in the later stage of cycling, affect the adhesion to the current collector, and cause continuous attenuation of the cycling capacity.

[0003] Therefore, how to further reduce the side reactions between the high-voltage cathode and the electrolyte and reduce the degree of corrosion, and how to make the cathode current collector more corrosion-resistant through reasonable design are technical problems that need to be solved urgently by those skilled in the art. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a secondary battery and an electrical device using the same.

[0005] To achieve the above purpose, in the first aspect of the present application, the technical solution adopted is: a secondary battery, including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte;

[0006] The positive current collector contains N elements, and the N elements include at least one of Zn, Ni, Cr, Ca, and Ti;

[0007] The electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent includes a first solvent and a second solvent; the first solvent is a halogenated carboxylic acid ester, and the halogenated carboxylic acid ester is a compound represented by structural formula A; the second solvent is at least one of a carbonate compound, a non-halogenated carboxylic acid ester compound, an ether compound, and a nitrile compound; the additive includes a compound represented by structural formula B;

[0008]

[0009] Among them, in formula A, R1 and R2 are each independently selected from a halogen atom, an alkyl group having 1 to 10 carbon atoms, and a halogenated alkyl group having 1 to 10 carbon atoms; and formula A contains at least 1 halogen atom; among them, in formula B, R3, R4, R5, R6, and R7 are each independently selected from an H atom, a halogen atom, a halogenated or non-halogenated alkyl group or olefin group having a carbon atom number

[0010] ≤ 3, or one or more of them; and formula B contains at least 1 halogen atom;

[0011] The secondary battery satisfies the following relationship: 1 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 25 ≤ X ≤ 500, 3 ≤ P ≤ 50, 0.01 ≤ Q ≤ 5;

[0012] Among them, P is the weight percentage of the compound represented by structural formula A in the electrolyte;

[0013] Q is the weight percentage of the compound represented by structural formula B in the electrolyte;

[0014] X is the content of N element in the positive electrode current collector, and the unit is ppm.

[0015] As an embodiment of the present application, the halogen atom is at least one of fluorine, chlorine, bromine, and iodine.

[0016] As an embodiment of the present application, the structural formula A includes at least one of the following compounds:

[0017]

[0018] As an embodiment of the present application, the structural formula B includes at least one of the following compounds:

[0019]

[0020] As an embodiment of the present application, the secondary battery satisfies the following relationship: 5 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 50 ≤ X ≤ 200, 5 ≤ P ≤ 30, 0.1 ≤ Q ≤ 2.

[0021] As an embodiment of the present application, the positive electrode current collector further contains aluminum element; after the secondary battery is discharged, the content of aluminum element in the electrolyte is E, and the unit is ppm, satisfying 80 ≤ E ≤ 210.

[0022] As an embodiment of the present application, the N element contains Zn and / or Ni, and based on the total content of the N element, the mass percentage content of the Zn element and / or Ni element is F, satisfying F ≥ 60%.

[0023] As an embodiment of the present application, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluoro(oxalato)phosphate (LiODFP), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate (LiTDI).

[0024] As an embodiment of the present application, the additive further includes at least one of 1,3-propane sultone (PS), lithium difluorophosphate (LiDFP), lithium difluoro(oxalato)phosphate (LiODFP), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate (LiTDI), sulfate ester compounds, and nitrile compounds.

[0025] As an embodiment of the present application, as an additive, the nitrile compounds include at least one of succinonitrile, glutarodinitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, glycerol trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile; and the sulfate ester compounds include at least one of vinylene sulfate and fluorinated vinylene sulfate.

[0026] As an embodiment of the present application, the carbonate compounds of the second solvent include at least one of ethylene carbonate, fluorinated ethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, vinylene carbonate, fluorinated vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and diphenyl carbonate; the non-halogenated carboxylic ester compounds of the second solvent include at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the ether compounds of the second solvent include at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and the nitrile compounds of the second solvent include at least one of succinonitrile, glutarodinitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, glycerol trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0027] As an embodiment of the present application, in terms of the mass percentage of the electrolyte, the mass percentage of the lithium salt is 8-25%, the mass percentage of the additive is 0.01-15%, and the mass percentage of the second solvent is 10-85%.

[0028] As an embodiment of the present application, the negative electrode sheet includes a negative electrode material, and the negative electrode material includes at least one of lithium metal, graphite, silicon-oxygen composite material, and silicon-carbon composite material.

[0029] The third aspect of the present application provides an electrical device including the secondary battery.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: By introducing the compounds shown in Structural Formulas A and B into the electrolyte, the present invention has strong-correlated electrochemical properties with the characteristic elements of the current collector in the positive electrode film. The first solvent A has a lower HOMO value, which can improve the oxidation resistance of the electrolyte body, reduce the decomposition of the solvent and lithium salt on the positive electrode side, and further reduce the enrichment of by-products at the defects of the current collector. The additive B has a higher HOMO, and after halogenation, it can reduce the electron cloud density of the pyridyl group in the molecular structure, lower the desolvation energy barrier, form a film on the positive electrode material prior to the solvent, regulate the dehydrogenation process of the carbonate solvent, and reduce the local concentration of F - or HF species on the current collector, and can reduce the corrosion effect on the current collector.

[0031] In the positive current collector, the selection of different elements has different improvement degrees on the corrosion resistance and ductility of the current collector. Specifically, the corrosion-resistant elements include Zn, Ni, and Cr. Zn can form a protective layer or a metal phase to improve corrosion resistance; Ni, as a stabilizer, is beneficial to the formation of intergranular compounds with high melting points and inhibits the tendency of pitting corrosion; Cr is beneficial to the formation of an oxide film to inhibit corrosion. In addition, the ductility elements include Ca and Ti, both of which can refine grains and improve mechanical ductility. Through a large amount of experimental data of researchers, it is found that when the N element contains both corrosion-resistant elements and ductility elements, and when the total amount of the corrosion-resistant elements Zn and Ni accounts for more than 60% of the total amount of the N element, there is an excellent improvement effect on the performance of the battery cell. However, when the total content of the N element is too high, it will instead lead to an increase in the impedance of the current collector and affect electron transport; when the total content of the N element is low, the ductility and corrosion resistance of the current collector are limited. Therefore, there is a strong correlation between the elements of the positive current collector and the first solvent A and the additive B. It is manifested as follows: First, the number of exposed highly active corrosion sites is different, resulting in different required reaction equivalents of the first solvent A and the additive B; second, the ductility is different, resulting in stress in the spatial distribution of the active material, which causes the rupture and repair of the film, and also makes the required reaction equivalents of the first solvent A and the additive B different. By correlating and defining the relationship between the key components in the electrolyte and the characteristic element N content of the positive electrode film current collector, the above-mentioned appropriate ratio and dosage of the first solvent A and the additive B can avoid the continuous oxidation of the electrolyte itself under high voltage and reduce the PF 6- decomposition rate, avoiding the rapid accumulation of locally concentrated F - or HF species at the defect sites, reducing the generation of microcracks and pits of Al dissolution in the later stage of cycling, ensuring the adhesion between the material and the current collector, and effectively improving the cycling performance of the high-voltage silicon-carbon system. Detailed implementation manners

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0033] In the present application, among the technical features described in an open-ended manner, a closed technical solution composed of the listed features is included, and an open technical solution including the listed features is also included.

[0034] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0036] Unless otherwise specified, the component raw materials or instruments used in each embodiment and comparative example of the present invention are all commercially available raw materials or instruments, and the component raw materials used in each parallel experiment are of the same kind.

[0037] In the first aspect of the present application, the technical solution adopted by the present application is: a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0038] The positive current collector contains N elements, and the N elements include at least one of Zn, Ni, Cr, Ca, and Ti;

[0039] The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes a first solvent and a second solvent; the first solvent is a halogenated carboxylic acid ester, and the halogenated carboxylic acid ester is a compound represented by structural formula A; the second solvent is at least one of a carbonate compound, a non-halogenated carboxylic acid ester compound, an ether compound, and a nitrile compound; the additive includes a compound represented by structural formula B;

[0040]

[0041] Wherein, in formula A, R1 and R2 are each independently selected from a halogen atom, an alkyl group having 1 to 10 carbon atoms, and a halogenated alkyl group having 1 to 10 carbon atoms; and formula A contains at least 1 halogen atom;

[0042] Wherein, in formula B, R3, R4, R5, R6, and R7 are each independently selected from an H atom, a halogen atom, a halogenated or non-halogenated alkyl or alkenyl group having a carbon atom number ≤ 3, and one or more of them; and formula B contains at least 1 halogen atom;

[0043] The secondary battery satisfies the following relationship: 1 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 25 ≤ X ≤ 500, 3 ≤ P ≤ 50, 0.01 ≤ Q ≤ 5;

[0044] Wherein, P is the weight percentage of the compound shown by structural formula A in the electrolyte;

[0045] Q is the weight percentage of the compound shown by structural formula B in the electrolyte;

[0046] X is the content of N element in the positive electrode current collector, and the unit is ppm.

[0047] In some embodiments, the halogen atom is at least one of fluorine, chlorine, bromine, and iodine.

[0048] In some embodiments, the structural formula A includes at least one of the following compounds:

[0049]

[0050] The inventors of the present application have found through research that after the halogenation of compound A, the number of H substituents decreases, the molecular boiling point increases, and the self-thermal decomposition of the electrolyte at high temperatures is reduced. In addition, compound A has a lower HOMO value, which can improve the oxidation resistance of the electrolyte body, reduce the decomposition of the solvent and lithium salt on the positive electrode side, and reduce the enrichment of by-products at the defects of the current collector.

[0051] In some embodiments, the structural formula B includes at least one of the following compounds:

[0052]

[0053] The inventors of the present application have found through research that compound B has a relatively high HOMO, and after halogenation, it can reduce the electron cloud density of the pyridyl group in the molecular structure, reduce the desolvation energy barrier, preferentially form a film on the positive electrode material to protect it, regulate the dehydrogenation process of the carbonate solvent, reduce the locally concentrated F- or HF species on the current collector, and can reduce the corrosion effect on the current collector.

[0054] As an embodiment of the present application, the secondary battery satisfies the following relationship: 5 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 50 ≤ X ≤ 200, 5 ≤ P ≤ 30, 0.1 ≤ Q ≤ 2.

[0055] As an embodiment of the present application, the positive electrode current collector further contains aluminum element; after the secondary battery is discharged, the content of aluminum element in the electrolyte is E, and the unit is ppm, satisfying 80 ≤ E ≤ 210.

[0056] As an embodiment of the present application, the N element contains Zn and / or Ni, and based on the total content of the N element, the mass percentage content of the Zn element and / or Ni element is F, satisfying F≥60%.

[0057] As an embodiment of the present application, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluoro(oxalato)phosphate (LiODFP), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI).

[0058] As an embodiment of the present application, the additive further includes at least one of 1,3-propane sultone (PS), lithium difluorophosphate (LiDFP), lithium difluoro(oxalato)phosphate (LiODFP), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI), sulfate ester compounds, and nitrile compounds.

[0059] As an embodiment of the present application, the nitrile compounds include at least one of succinonitrile, glutarodinitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, glycerol trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile. The sulfate ester compounds include at least one of vinylene sulfate and fluorinated vinylene sulfate.

[0060] In some embodiments, the carbonate compounds of the second solvent include at least one of ethylene carbonate, fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, vinylene carbonate, fluorovinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate; the non-halogenated carboxylate compounds of the second solvent include at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate; the ether compounds of the second solvent include at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the nitrile compounds of the second solvent include at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, glycerol trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile.

[0061] In some embodiments, based on the mass percentage of the electrolyte, the mass percentage of the lithium salt is 8-25%, the mass percentage of the additive is 0.01-15%, and the mass percentage of the second solvent is 10-85%.

[0062] Exemplarily, in the positive electrode sheet, the content X of N element is 25, 28, 30, 35, 38, 40, 45, 48, 50, 55, 58, 60, 65, 68, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 190, 200, 220, 250, 280, 300, 320, 350, 380, 400, 420, 450, 480, 500 or the range composed of any two of these values.

[0063] Exemplarily, in the electrolyte, the weight percentage P of the compound shown in Structural Formula A is 3, 5, 8, 10, 15, 18, 20, 25, 28, 30, 35, 38, 40, 45, 48, 50 or the range composed of any two of these values.

[0064] Exemplarily, in the electrolyte, the weight percentage Q of the compound shown in Structural Formula B is 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.5, 1.8, 2, 2.2, 2.4, 2.5, 2.8, 3, 3.2, 3.4, 3.5, 3.8, 4, 4.2, 4.4, 4.5, 4.8, 5 or the range composed of any two of these values.

[0065] The first solvent A has a lower HOMO value, which can improve the oxidation resistance of the electrolyte bulk, reduce the decomposition of the solvent and lithium salt on the positive electrode side, and further reduce the enrichment of by-products at the defects of the current collector. The additive B has a relatively high HOMO, and after halogenation, it can reduce the electron cloud density of the pyridyl group in the molecular structure, lower the desolvation energy barrier, form a film on the positive electrode material prior to the solvent, regulate the dehydrogenation process of the carbonate solvent, and reduce the local concentration of F on the current collector - or HF species, which can reduce the corrosion effect on the current collector. In the positive electrode current collector, the selection of different elements has different improvement ranges for the corrosion resistance and ductility of the current collector. Specifically, the corrosion-resistant elements include Zn, Ni, and Cr. Zn can form a protective layer or a metal phase to improve corrosion resistance; Ni, as a stabilizer, is beneficial to the formation of intergranular compounds with high melting points and inhibits the tendency of pitting corrosion; Cr is beneficial to the formation of an oxide film to inhibit corrosion. In addition, the ductile elements include Ca and Ti, both of which can refine the grains and improve the mechanical ductility. Through a large number of experimental data of researchers, it is found that when the N element contains both corrosion-resistant elements and ductile elements, and when the total amount of the corrosion-resistant elements Zn and Ni accounts for more than 60% of the total amount of the N element, there is an excellent improvement effect on the performance of the battery cell. However, when the total content of the N element is too high, it will instead lead to an increase in the impedance of the current collector and affect electron transport; when the total content of the N element is low, the ductility and corrosion resistance of the current collector are limited. Therefore, there is a strong correlation between the elements of the positive electrode current collector and the first solvent A and the additive B. It is manifested as follows: First, the number of exposed highly active corrosion sites is different, resulting in different required reaction equivalents of the first solvent A and the additive B; second, the ductility is different, resulting in stress in the spatial distribution of the active substances, leading to the rupture and repair of the film, which also makes the required reaction equivalents of the first solvent A and the additive B different. When the total content of the N element is too high, it will instead lead to an increase in the impedance of the current collector and affect electron transport; when the total content of the N element is low, the ductility and corrosion resistance of the current collector are limited. By correlating and defining the relationship between the key components in the electrolyte and the characteristic element N content of the positive electrode film current collector, the above-mentioned appropriate ratio and dosage of the first solvent A and the additive B can avoid the continuous oxidation of the electrolyte itself under high voltage and reduce the decomposition rate of PF6 - to avoid the rapid accumulation of locally concentrated F - or HF species at the defect sites, reduce the generation of microcracks and pits of Al dissolution in the later stage of cycling, ensure the adhesion between the material and the current collector, and improve the capacity stability of the cycle.

[0066] In some embodiments, the positive electrode tab includes an aluminum foil current collector and a positive electrode film. The positive electrode film includes a positive electrode active material lithium cobalt oxide LiCoO₂, a conductive agent, and a binder; the conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers. The binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0067] The negative electrode tab includes a copper foil current collector and a negative electrode film. The negative electrode film includes a negative electrode active material graphite and a silicon oxide active material SiOx (or a silicon carbide active material SiC), a conductive agent, a thickener sodium carboxymethyl cellulose (CMC), and a binder polyacrylic acid PAA. The conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In the secondary battery of the present invention, due to the applicability of the electrolyte, the active materials on the positive and negative electrode tabs can be selected and matched with different types according to needs, and good electrochemical activity and safety stability can be achieved.

[0069] The third aspect of the present application provides an electrical device including the secondary battery described above.

[0070] In the specific embodiments of the present invention, the sources of the organic solvent and the additive can be commercially purchased or self-made. Specifically, the preparation methods are all conventional synthesis methods, which are not listed one by one here.

[0071] In the specific embodiments of the present invention, the positive electrode current collector deposits a target element on the surface of the aluminum foil by electrochemically depositing, and finally obtains a thin film with different characteristic elements. The present invention purchases the corresponding current collector from a manufacturer that can customize the modification of the aluminum foil, and it is purchased from Henan Mingtai Aluminum Co., Ltd.

[0072] Example 1

[0073] Electrolyte preparation: In a glove box filled with argon, first, EC, PC, PP, and the first solvent A are mixed in a mass ratio of 8:10:70.2:11.8 to obtain a mixed solution. Secondly, 13% of lithium salt LiPF₆, 12% of the second solvent fluoroethylene carbonate (FEC), 2% of the additive 1,3-propane sultone (PS), 2% of the additive 1,3,6-hexanetricarbonitrile (HTCN), and 3% of the additive B are sequentially and slowly added to the mixed solution. Finally, after stirring evenly, the electrolyte of Example 1 is obtained, that is, the first solvent A accounts for 8% of the total weight of the electrolyte, and the additive B accounts for 3% of the total weight of the electrolyte.

[0074] Preparation of secondary battery:

[0075] 1. Preparation of positive electrode sheet: It includes positive electrode active material lithium cobalt oxide LiCoO2, conductive agent Super P, and binder polyvinylidene fluoride PVDF. After mixing each substance according to the weight ratio of LiCoO2:Super P:PVDF = 98.5:0.5:1, it is added to N-methylpyrrolidone (NMP), and mixed evenly to prepare the positive electrode slurry of the lithium-ion battery cell; the positive electrode slurry is coated on the current collector aluminum foil, dried at 85°C, then cold-pressed, and then trimmed and slit. After that, it is dried in a vacuum at 85°C for 4 hours, and the tab is welded to prepare the positive electrode sheet.

[0076] 2. Preparation of negative electrode sheet: It includes negative electrode active material graphite and silicon-carbon material, conductive agent carbon nanotube (CNT), thickening agent sodium carboxymethyl cellulose (CMC), and binder polyacrylic acid (PAA), where the median particle size u of the SiOx material is 4.8 μm. The mixture of graphite and silicon-carbon material according to the weight ratio of 85:15 is used as the negative electrode active material. After mixing the negative electrode active material:CNT:CMC:PAA = 97:0.8:1.2:1 according to the weight ratio, it is added to deionized water and mixed evenly to prepare the negative electrode slurry; the negative electrode slurry is coated on the current collector copper foil, dried at 85°C, then cold-pressed, and then trimmed and slit. After that, it is dried in a vacuum at 85°C for 12 hours, and the tab is welded to obtain the negative electrode sheet.

[0077] 3. Preparation of soft-pack battery cell: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets, and wound to obtain a bare battery cell; the designed capacity of the battery cell is 6.0 Ah, and the voltage range is 3.0 - 4.55 V. The bare battery cell is placed in an aluminum-plastic film outer package for encapsulation, and then the battery cell is placed in a vacuum oven at 85°C for baking for 48 hours. The electrolyte is injected into the baked battery cell, and then it is encapsulated, left standing, formed, shaped, and sorted. Then, it is secondarily encapsulated, and the liquid retention coefficient is 1.1 g / Ah to complete the preparation of the lithium-ion secondary soft-pack battery.

[0078] Comparative Examples 1-12 and Examples 2-29 are used to illustrate the lithium-ion batteries disclosed in the present invention, including most of the operation steps in Example 1. For example, for electrolyte preparation: deduct 13% LiPF6 from the total weight of 100%, additives: 2% PS, 2% HTCN, second solvent: 12% FEC and a specific content of additive B to obtain the remaining weight M. Calculate the percentage of A in the remaining weight M based on the total weight of the electrolyte of the first solvent A. For example, in Example 16, the content of A is 3% and the content of B is 5%, then M = 100% - 13% LiPF6 - 2% PS - 2% HTCN - 12% FEC - 5% additive B = 66%. Since A accounts for 3% of the total electrolyte content, A accounts for 4.5% of M, that is, the solvents in M are EC:PC:PP:first solvent A = 8:10:77.5:4.5. In the present invention, the proportions of EC and PC in the remaining weight M are fixed at 8% and 10% respectively; while the proportion of PP in M is M - 8% EC - 10% PC - first solvent A. For the same content types except for the first solvent A and additive B, the corresponding content changes of PP are not listed and elaborated in Tables 1 and 2.

[0079] The other differences are as follows: The types and contents of the first solvent halogenated carboxylic acid ester A, the key additive B, and the types and contents of the key characteristic elements N of the positive electrode film current collector are different. The specific values are shown in Tables 1 and 2. Among them, " / " means that the substance is not contained. In the column of the types and contents of the characteristic elements N of the positive electrode film current collector, the types and contents are in a one-to-one correspondence relationship. For example, in Example 16, the type is: Zn+Ni+Ca, and the content is: 100+50+50 = 200, that is, the Zn content is 100, the Ni content is 50, and the Ca content is 50, with a total content of 200. Other examples are not elaborated one by one.

[0080] The following performance tests are carried out on each secondary soft-pack battery:

[0081] (1) 45°C high-temperature cycle test: In an environment of 45°C, charge the divided-capacity battery at a constant current and constant voltage of 0.7C to 4.55V, with a cut-off current of 0.05C, and then discharge it at a constant current of 0.5C to 3.0V. Cycle in this way, and calculate the capacity retention rate of the 400th cycle after 400 charge-discharge cycles. The calculation formula is as follows:

[0082] Capacity retention rate of the 400th cycle (%) = (Discharge capacity of the 400th cycle / Discharge capacity of the first cycle) × 100%;

[0083] Thickness growth rate of the 400th cycle (%) = (Thickness in the fully charged state of the 400th cycle / Thickness in the fully charged state of the first cycle) × 100%.

[0084] (2) Test for Al content in the electrolyte: In an environment of 25 °C, after the lithium-ion battery is discharged, it is centrifuged. The liquid obtained after centrifugation is monitored for elements by inductively coupled plasma (ICP) to obtain the weight percentage of Al metal ions in the electrolyte.

[0085] (3) Judgment of the corrosion degree of the positive current collector surface: In an environment of 25 °C, after the lithium-ion battery is discharged, the battery is disassembled. Take the aluminum current collector and the electrode sheet in the exposed tab area of the positive electrode membrane. The electrode sheet can be carefully wiped with NMP to obtain the exposed current collector area. Place the above-mentioned exposed tab area and the exposed central area of the electrode sheet that meet the requirements in a scanning electron microscope (SEM) for observation. Within a magnification of 100, if the number of corrosion holes observed in the image is ≤ 10, it is defined as slight corrosion; if 10 < the number of corrosion holes ≤ 50, it is defined as medium corrosion; if 50 < the number of corrosion holes, it is defined as severe corrosion.

[0086] The test results are shown in Table 3.

[0087] Table 1

[0088]

[0089]

[0090] Table 2

[0091]

[0092] Table 3

[0093]

[0094] From the comparison results of Tables 1 and 2, it can be seen from Examples 1-29 and Comparative Examples 1-12 that for the weight percentages of the compounds (the first solvent) with the structure shown in Formula A in different types of electrolytes, the weight percentages of the compounds (key additives) with the structure shown in different types of Formula B, and the content of the characteristic element N of the positive electrode membrane current collector of different types satisfy the formula 1 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 25 ≤ X ≤ 500, 3 ≤ P ≤ 50, 0.01 ≤ Q ≤ 5. The corrosion degree of the battery positive current collector obtained is low, the dissolution of aluminum ions is small, the high-temperature cycle capacity retention rate is high, and the swelling rate is low. This shows that the first solvent A participates in the solvation process and affects the internal and external arrangement of the key additive B in the solvation sheath, thereby affecting its electrochemical oxidation film-forming effect. And the key characteristic element affects the electron transport and defect degree of the current collector. Collaborating with the film-forming effect of the above-mentioned first solvent A and additive B, the electrolyte minimizes continuous oxidation on the positive electrode side, reduces the decomposition rate of PF6-, and avoids the rapid accumulation of locally concentrated F- or HF species at the defect sites.

[0095] As can be seen from Examples 1-27, when different types of the first solvent A, different types of the key additive B, and different types of the characteristic element X of the positive electrode film current collector further satisfy the formula 5 ≤ (X + 50) / (P + 10*Q) ≤ 25, and 50 ≤ X ≤ 200, 5 ≤ P ≤ 30, 0.1 ≤ Q ≤ 2, the corrosion degree of the positive electrode current collector of the lithium-ion battery is lower and the high-temperature cycle performance is better. This shows that when the first solvent A, the key additive B, and the characteristic element X of the positive electrode film current collector are within the preferred ranges of this application and satisfy the formula 5 ≤ (X + 50) / (P + 10*Q) ≤ 25, the strong correlation characteristics of the three can be more manifested, and thus the performance of the battery cell is better.

[0096] As can be seen from Examples 27-29, when other additives such as succinonitrile (SN) and vinylene carbonate (VC) are further introduced into the electrolyte, the performance of the battery cell is further improved. It is speculated that the above additives synergistically participate in the formation of the electrode interface film, reduce the local enrichment of F- and HF, and avoid the rapid progress of the corrosion reaction.

[0097] As can be seen from Comparative Examples 8-10, even if different types of the first solvent A, different types of the key additive B, and different types of the characteristic element X of the positive electrode film current collector in different types of electrolytes satisfy the formula 1 ≤ (X + 50) / (P + 10*Q) ≤ 25, but the contents of A, B, and X do not meet their range limitations, the battery cell does not have excellent performance.

[0098] As can be seen from Comparative Examples 11 and 12, even if different types of the first solvent A, different types of the key additive B, and different types of the characteristic element of the positive electrode film current collector in different types of electrolytes meet their respective range limitations, but when they do not satisfy the formula 1 ≤ (X + 50) / (P + 10*Q) ≤ 25, the performance of the battery cell is still lacking. The above shows that there is a strong correlation between the parameters A, B, and X, and the formula 1 ≤ (X + 50) / (P + 10*Q) ≤ 25 can comprehensively correlate various influencing factors to achieve a better cooperation and synergistic effect.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, characterized in that: Including positive electrode sheet, negative electrode sheet, separator and electrolyte; The positive electrode current collector contains N element, and the N element includes at least one of Zn, Ni, Cr, Ca, and Ti; The electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a first solvent and a second solvent; the first solvent is a halogenated carboxylate, and the halogenated carboxylate is a compound represented by structural formula A; the second solvent is at least one of a carbonate compound, a non-halogenated carboxylate compound, an ether compound and a nitrile compound; The additive includes a compound shown in structural formula B; Wherein, in formula A, R1 and R2 are each independently selected from one of a halogen atom, a C1-C10 alkyl group, and a C1-C10 halogenated alkyl group; and formula A contains at least one halogen atom; Wherein, in formula B, R3, R4, R5, R6, and R7 are each independently selected from H atoms, halogen atoms, halogenated or non-halogenated alkyl or olefin groups with ≤3 carbon atoms, One or more of; and formula B contains at least one halogen atom; The secondary battery satisfies the following relationship: 1≤(X+50) / (P+10*Q)≤25, and 25≤X≤500, 3≤P≤50, 0.01≤Q≤5; Wherein, P is the weight percentage of the compound represented by structural formula A in the electrolyte; Q is the weight percentage of the compound represented by structural formula B in the electrolyte; X is the content of N element in the positive electrode current collector, and the unit is ppm.

2. The secondary battery according to claim 1, wherein: The structural formula A comprises at least one of the compounds shown below:

3. The secondary battery according to claim 1, wherein: The structural formula B comprises at least one of the compounds shown below:

4. The secondary battery according to claim 1, wherein: The positive electrode current collector further comprises aluminum element; after the secondary battery is discharged, the content of aluminum element in the electrolyte is E, in ppm, satisfying 80≤E≤210.

5. The secondary battery according to claim 1, wherein: The N element contains Zn and / or Ni, and based on the total content of the N element, the mass percentage of the Zn element and / or the Ni element is F, satisfying F≥60%.

6. The secondary battery according to claim 1, wherein: The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, lithium bisfluorosulfonyl imide, and 4,5-dicyano-2-(trifluoromethyl)isoimidazole lithium.

7. The secondary battery according to claim 1, wherein: The additive also includes at least one of 1,3-propane sultone, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, lithium bisfluorosulfonyl imide, 4,5-dicyano-2-(trifluoromethyl)isoimidazole lithium, nitrile compounds, and sulfate compounds.

8. The secondary battery according to claim 1, wherein: The carbonate compound of the second solvent includes at least one of ethylene carbonate, fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, vinylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and diphenyl carbonate; the non-halogenated carboxylic acid ester compound of the second solvent includes methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, At least one of propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the ether compound of the second solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the nitrile compound of the second solvent includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, glyceroltrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile.

9. The secondary battery according to claim 1, wherein: Calculated by mass percentage of the electrolyte, the mass percentage of the lithium salt is 8-25%, the mass percentage of the additive is 0.01-15%, and the mass percentage of the second solvent is 10-85%.

10. The secondary battery according to claim 1, wherein: The negative electrode plate includes a negative electrode material, and the negative electrode material includes at least one of lithium metal, graphite, silicon-oxygen composite material and silicon-carbon composite material.

11. An electrical device, characterized in that: A secondary battery comprising any one of claims 1 to 8.

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