Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a negative pole piece and an electrolyte, the electrolyte comprises a fluorinated compound, the fluorinated compound comprises at least one of a compound shown as a formula I or a compound shown as a formula II, R1 is selected from fluorine atoms or C1-C5 alkyl groups at least partially substituted by fluorine, R2 and R3 are independently selected from C1-C5 alkyl groups, and R2 and R3 are independently selected from C1-C5 alkyl groups. R2 and R3 can be connected into a ring through a single bond; r4 is selected from C1 to C5 alkyl groups which are not substituted or substituted by fluorine; the negative electrode piece comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode current collector comprises a chromium element, based on the mass of the negative electrode current collector, the mass content of the chromium element is x, and x is larger than or equal to 0.001% and smaller than or equal to 0.5%. Through the arrangement, the high-temperature storage performance and the self-discharge performance of the secondary battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have significant advantages such as high energy density, miniaturization, and light weight, and are widely used in mobile phones, laptop computers, tablet computers, drones, electric vehicles, power tools, power storage systems, etc. Generally, a lithium-ion battery consists of a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte is responsible for maintaining the ion transport between the positive electrode sheet and the negative electrode sheet, and also for maintaining a stable interface to enable the lithium-ion battery to work stably. At present, users have also put forward higher and higher requirements for the performance of secondary batteries, such as self-discharge performance and high-temperature storage performance.

[0003] Therefore, there is an urgent need to provide a secondary battery with better self-discharge performance and high-temperature storage performance to meet the increasing usage requirements of people. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to improve the self-discharge performance and high-temperature storage performance of the secondary battery.

[0005] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] In the first aspect of the present application, a secondary battery is provided. The secondary battery includes a negative electrode sheet and an electrolyte. The electrolyte includes a fluorinated compound, and the fluorinated compound includes at least one of a compound of Formula I or a compound of Formula II.

[0007]

[0008] Wherein, R1 is selected from a fluorine atom or a C1-C5 alkyl group that is at least partially substituted with fluorine, R2 and R3 are each independently selected from C1-C5 alkyl groups, and R2 and R3 can be connected by a single bond to form a ring; R4 is selected from an unsubstituted or fluorine-substituted C1-C5 alkyl group; the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode current collector includes chromium element, and based on the mass of the negative electrode current collector, the mass content of chromium element is x, 0.001% ≤ x ≤ 0.5%. Through the above settings, the fluorinated compound in the electrolyte has good high-temperature stability, which is beneficial to improving the high-temperature storage performance of the secondary battery. The chromium element in the current collector is beneficial to reducing the reaction between the current collector and the acid, thereby reducing the risk of self-discharge of the secondary battery. The fluorinated compound in the electrolyte and the chromium element in the negative electrode current collector act synergistically to improve the high-temperature storage performance and self-discharge performance of the secondary battery.

[0009] In some embodiments of the present application, the compound of formula I includes at least one of the following compounds:

[0010]

[0011]

[0012] In some embodiments of the present application, the compound of formula II includes at least one of the following compounds:

[0013]

[0014] By selecting the compound of formula I or the compound of formula II within the above range, the compound of formula I and the compound of formula II have good high-temperature stability. Applying the electrolyte containing the compound of formula I or the compound of formula II to the secondary battery is beneficial to improving the high-temperature storage performance of the secondary battery, and acts synergistically with the negative electrode current collector containing chromium element, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0015] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the fluorinated compound is W I , 10% ≤ W I ≤ 90%; preferably, 20% ≤ W I ≤ 70%. By regulating the mass percentage content of the fluorinated compound within the above range, it is beneficial to improving the high-temperature storage performance of the secondary battery, and acts synergistically with the negative electrode current collector containing chromium element, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0016] In some embodiments of the present application, 0.01 ≤ W I / (1000x) ≤ 25; preferably, 0.01 ≤ W I / (1000x) ≤ 5. By regulating W I When the value of / (1000x) is within the above range, the electrolyte containing the fluorinated compound and the negative electrode current collector containing chromium element within the content range of the present application act synergistically, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0017] In some embodiments of the present application, the electrolyte includes a first component, and the first component includes at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, vinylene carbonate or ethylene vinylene carbonate. In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the first component is W III , 0.5% ≤ W III ≤ 15%; preferably, 1% ≤ W III ≤ 8%. Through the above settings, it is beneficial to form a dense solid electrolyte interface (SEI) film on the negative electrode surface, reducing the contact between the active material and the electrolyte, enabling the secondary battery to have a longer cycle life and improving the cycle stability of the secondary battery; thus, while taking into account the self-discharge performance of the secondary battery, the high-temperature storage performance of the secondary battery is further improved.

[0018] In some embodiments of the present application, 0.001% ≤ x ≤ 0.1%; preferably, 0.001% ≤ x ≤ 0.05%. By controlling x within the above range, it is beneficial to further exert the synergistic effect between the fluorinated compound and the chromium element in the negative electrode current collector, thereby, while taking into account the self-discharge performance of the secondary battery, further improving the high-temperature storage performance of the secondary battery.

[0019] In some embodiments of the present application, the negative electrode current collector is a copper foil.

[0020] In some embodiments of the present application, the electrolyte further includes a second component, and the second component includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate or lithium difluorophosphate. In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the second component is W IV , 0.01% ≤ W IV ≤ 5%; preferably, 0.1% ≤ W IV ≤ 1%. Through the above settings, it is beneficial to form a dense solid electrolyte interface (SEI) film on the negative electrode surface, reducing the occurrence of side reactions, and at the same time the second component has good thermal stability, thereby, while taking into account the self-discharge performance of the secondary battery, further improving the high-temperature storage performance of the secondary battery.

[0021] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. Thus, the electronic device of the present application has good use performance.

[0022] Advantages of the present application:

[0023] The present application provides a secondary battery and an electronic device. The secondary battery includes a negative electrode tab and an electrolyte. The electrolyte includes a fluorinated compound, and the fluorinated compound includes at least one of a compound of Formula I or a compound of Formula II. Wherein, R1 is selected from a fluorine atom or a C1-C5 alkyl group at least partially substituted by fluorine, R2 and R3 are each independently selected from a C1-C5 alkyl group, and R2 and R3 can be connected into a ring through a single bond; R4 is selected from an unsubstituted or fluorine-substituted C1-C5 alkyl group; the negative electrode tab includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, and the negative electrode current collector includes chromium element. Based on the mass of the negative electrode current collector, the mass content of chromium element is x, and 0.001% ≤ x ≤ 0.5%. Through the above arrangement, the fluorinated compound in the electrolyte has good high-temperature stability, which is beneficial to improving the high-temperature storage performance of the secondary battery. The chromium element in the current collector is beneficial to reducing the reaction between the current collector and acid, thereby reducing the risk of self-discharge of the secondary battery. The fluorinated compound in the electrolyte and the chromium element in the negative electrode current collector act synergistically to improve the high-temperature storage performance and self-discharge performance of the secondary battery.

[0024] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Detailed embodiments

[0025] Next, the technical solutions in the present application will be described clearly and completely in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0026] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0027] The first aspect of the present application provides a secondary battery. The secondary battery includes a negative electrode tab and an electrolyte. The electrolyte includes a fluorinated compound, and the fluorinated compound includes at least one of a compound of Formula I or a compound of Formula II.

[0028]

[0029] Among them, R1 is selected from a fluorine atom or a C1-C5 alkyl group that is at least partially substituted by fluorine, R2 and R3 are each independently selected from C1-C5 alkyl groups, and R2 and R3 can be connected by a single bond to form a ring; R4 is selected from an unsubstituted or fluorine-substituted C1-C5 alkyl group; the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode current collector includes chromium element, and based on the mass of the negative electrode current collector, the mass content of chromium element is x, 0.001% ≤ x ≤ 0.5%; preferably, 0.001% ≤ x ≤ 0.1%; more preferably, 0.001% ≤ x ≤ 0.05%. For example, the value of x can be 0.001%, 0.003%, 0.005%, 0.008%, 0.01%, 0.012%, 0.015%, 0.018%, 0.02%, 0.022%, 0.025%, 0.028%, 0.03%, 0.032%, 0.035%, 0.038%, 0.04%, 0.042%, 0.045%, 0.048%, 0.05%, 0.052%, 0.055%, 0.058%, 0.06%, 0.062%, 0.065%, 0.068%, 0.07%, 0.072%, 0.075%, 0.078%, 0.08%, 0.082%, 0.085%, 0.088%, 0.09%, 0.092%, 0.095%, 0.098%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5% or a range composed of any two of these values.

[0030] The inventors' research found that fluorinated compounds have good high-temperature stability. When added to the electrolyte, the stability of the electrolyte is enhanced, which is beneficial to improving the high-temperature performance of secondary batteries, especially the high-temperature storage performance. However, due to the hydrolysis property of its own structure, fluorinated compounds are prone to react with the residual moisture in the electrode assembly to generate hydrofluoric acid after liquid injection. At this time, it will accelerate the dissolution of metal ions in the current collector and is likely to deposit into dendrites during the formation stage of secondary batteries, posing a risk of accelerating the self-discharge of secondary batteries. When the negative current collector of a secondary battery contains chromium, chromium itself has relatively stable chemical properties. Chromium reacts with oxygen to form a stable chromium oxide film. The dense oxide film reduces the contact between hydrofluoric acid and other metal ions in the negative current collector, thereby reducing the reaction between the negative current collector and acid, and thus reducing the risk of self-discharge of secondary batteries and improving the self-discharge performance of secondary batteries. However, when the chromium content in the negative current collector is too high, such as greater than the upper limit value of this application, it will affect the electronic conductivity of the negative current collector. Therefore, the electrolyte containing fluorinated compounds in this application and the negative current collector containing chromium within the content range of this application act synergistically, thereby improving the high-temperature storage performance and self-discharge performance of secondary batteries.

[0031] In some embodiments of the present application, R1 is selected from a fluorine atom, difluoromethyl, trifluoromethyl, tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, or nonafluorobutyl; R2 is selected from methyl, ethyl, propyl, or butyl; R3 is selected from methyl, ethyl, propyl, or butyl; R4 is selected from methyl, ethyl, propyl, butyl, pentyl, fluoroethyl, difluoroethyl, or trifluoroethyl. Fluorinated compounds containing groups within the above ranges have good high-temperature stability. Applying the electrolyte including fluorinated compounds to secondary batteries enhances the stability of the electrolyte, which is beneficial to improving the high-temperature performance of secondary batteries, especially the high-temperature storage performance, and acts synergistically with the negative current collector containing chromium, thereby improving the high-temperature storage performance and self-discharge performance of secondary batteries.

[0032] In some embodiments of the present application, the compound of formula I includes at least one of the following compounds:

[0033]

[0034]

[0035]

[0036] By selecting the compound of formula I within the above ranges, the compound of formula I has good high-temperature stability. Applying the electrolyte including the compound of formula I to secondary batteries enhances the stability of the electrolyte, which is beneficial to improving the high-temperature performance of secondary batteries, especially the high-temperature storage performance, and acts synergistically with the negative current collector containing chromium, thereby improving the high-temperature storage performance and self-discharge performance of secondary batteries.

[0037] In some embodiments of the present application, the compound of Formula II includes at least one of the following compounds:

[0038]

[0039] By selecting the compound of Formula II within the above range, the compound of Formula II has good high-temperature stability. When the electrolyte including the compound of Formula II is applied to a secondary battery, the stability of the electrolyte is enhanced, which is beneficial to improving the high-temperature performance of the secondary battery, especially the high-temperature storage performance, and synergistically acts with the negative electrode current collector containing chromium element, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0040] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the fluorinated compound is W I , 10% ≤ W I ≤ 90%; preferably, 20% ≤ W I ≤ 70%. For example, the value of W I can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90% or a range composed of any two of these values. The fluorinated compound has good high-temperature stability. By regulating the mass percentage content of the fluorinated compound within the above range, the fluorinated compound can better exert its own characteristics, and the dissociation of the lithium salt in the electrolyte is moderate, so that the solubility of the lithium salt is moderate. At this time, the lithium ions have good transport ability, and the secondary battery has good charge-discharge rate performance. When the electrolyte including the fluorinated compound is applied to a secondary battery, the stability of the electrolyte is enhanced, which is beneficial to improving the high-temperature performance of the secondary battery, especially the high-temperature storage performance, and synergistically acts with the negative electrode current collector containing chromium element, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0041] In some embodiments of the present application, 0.01 ≤ W I / (1000x) ≤ 25; preferably, 0.01 ≤ W I / (1000x) ≤ 5. For example, W IThe value of / (1000x) can be 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or a range composed of any two of these numerical values. The addition of the fluorinated compound improves the stability of the electrolyte itself and the high-temperature storage performance of the secondary battery; meanwhile, the chromium element in the current collector is beneficial to reducing hydrofluoric acid generated by the hydrolysis of the negative current collector and the fluorinated compound, reducing the risk of self-discharge of the secondary battery. By regulating W I When the value of / (1000x) is within the above range, the electrolyte containing the fluorinated compound and the negative current collector containing chromium element within the content range of the present application act synergistically, thereby improving the high-temperature storage performance and self-discharge performance of the secondary battery.

[0042] In some embodiments of the present application, the electrolyte includes a first component, and the first component includes at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, vinylene carbonate or ethylene vinylene carbonate. By selecting an electrolyte including the first component of the above types, it is beneficial to form a dense solid electrolyte interface (SEI) film on the surface of the negative electrode, reducing the contact between the active material and the electrolyte, enabling the secondary battery to have a longer cycle life and improving the cycle stability of the secondary battery; thus, while taking into account the self-discharge performance of the secondary battery, the high-temperature storage performance of the secondary battery is further improved.

[0043] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the first component is W III , 0.5% ≤ W III ≤ 15%; preferably, 1% ≤ W III ≤ 8%. For example, the value of W III can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range composed of any two of these numerical values. By regulating the mass percentage content of the first component within the above range, it is beneficial to form a dense solid electrolyte interface (SEI) film on the surface of the negative electrode, reducing the contact between the active material and the electrolyte, enabling the secondary battery to have a longer cycle life and improving the cycle stability of the secondary battery; thus, while taking into account the self-discharge performance of the secondary battery, the high-temperature storage performance of the secondary battery is further improved.

[0044] In some embodiments of the present application, the negative electrode current collector is a copper foil. When a copper foil is selected as the negative electrode current collector, the negative electrode current collector has good electrical conductivity, low production cost, simple operation steps, and is also beneficial to taking into account the energy density of the secondary battery.

[0045] The present application does not particularly limit the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0046] In some embodiments of the present application, the electrolyte further includes a second component, and the second component includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, or lithium difluorophosphate. By selecting an electrolyte including the second component of the above types, it is beneficial to form a dense solid electrolyte interface (SEI) film on the surface of the negative electrode, reducing the occurrence of side reactions. At the same time, the second component has good thermal stability. Thus, while taking into account the self-discharge performance of the secondary battery, the high-temperature storage performance of the secondary battery is further improved.

[0047] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage content of the second component is W IV , 0.01% ≤ W IV ≤ 5%; preferably, 0.1% ≤ W IV ≤ 1%. For example, the value of W IV can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5% or a range composed of any two of these values. By controlling the mass percentage content of the second component within the above range, it is beneficial to form a dense solid electrolyte interface (SEI) film on the surface of the negative electrode, reducing the occurrence of side reactions. At the same time, the second component has good thermal stability. Thus, while taking into account the self-discharge performance of the secondary battery, the high-temperature storage performance of the secondary battery is further improved.

[0048] In the present application, the electrolyte further includes a lithium salt and a non-aqueous solvent. The present application does not particularly limit the lithium salt, as long as the object of the present application can be achieved. For example, the lithium salt can include but is not limited to at least one of LiPF6, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, or lithium tetrafluoroborate. The present application does not particularly limit the content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the lithium salt is 8% to 15%.

[0049] The non-aqueous solvent of the present application is not particularly limited as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0050] The above carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC). The fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte as long as the object of the present application can be achieved. Exemplarily, based on the mass of the electrolyte, the mass percentage content of the non-aqueous solvent is 0% to 82%.

[0051] In some embodiments of the present application, the electrolyte may include a fluorinated compound, a lithium salt, and a non-aqueous solvent. The mass percentage contents of the fluorinated compound and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 0% to 82%. The secondary battery including the above electrolyte has good self-discharge performance and high-temperature storage performance.

[0052] In some embodiments of the present application, the electrolyte may include a fluorinated compound, a first component, a lithium salt, and a non-aqueous solvent. The mass percentage contents of the fluorinated compound, the first component, and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 0% to 81.5%. The secondary battery including the above electrolyte has good self-discharge performance and high-temperature storage performance.

[0053] In some embodiments of the present application, the electrolyte may include a fluorinated compound, a second component, a lithium salt, and a non-aqueous solvent. The mass percentage contents of the fluorinated compound, the second component, and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 0% to 81.99%. The secondary battery including the above electrolyte has good self-discharge performance and high-temperature storage performance.

[0054] In some embodiments of the present application, the electrolyte may include a fluorinated compound, a first component, a second component, a lithium salt, and a non-aqueous solvent. The mass percentage contents of the fluorinated compound, the first component, the second component, and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 0% to 81.49%. The secondary battery including the above electrolyte has good self-discharge performance and high-temperature storage performance.

[0055] The present application has no particular limitation on the preparation method of the negative electrode current collector as long as the purpose of the present application can be achieved. For example, the preparation method of the negative electrode current collector includes but is not limited to the following steps: preparing an electrolyte containing copper ions, preparing a copper foil by electrolysis, immersing the obtained copper foil into a chromium plating solution containing chromic acid for electroplating to form a chromium-containing coating, and then obtaining a negative electrode current collector including chromium element.

[0056] The present application has no particular limitation on the electrolyte containing copper ions as long as the purpose of the present application can be achieved, such as a copper sulfate electrolyte. The present application has no particular limitation on the concentration of chromic acid in the chromium plating solution as long as the purpose of the present application can be achieved. For example, the concentration of chromic acid can be 1 g / L to 10 g / L. The present application has no particular limitation on the electroplating process as long as the purpose of the present application can be achieved. For example, the current density during electroplating can be 2 A / dm 2 to 8 A / dm 2 ; the electroplating duration can be 1 s to 30 s; the electroplating temperature can be 30 °C to 40 °C.

[0057] In the present application, the mass percentage content of chromium element in the negative electrode current collector can be regulated by regulating the concentration of chromic acid in the chromium plating solution containing chromic acid, the current density during electroplating, the electroplating duration, or the electroplating temperature.

[0058] The negative electrode current collector Cu(Cr) involved in the present application is essentially a copper foil containing chromium element, but the actual Cu(Cr) that can be used as the negative electrode current collector is not limited to only containing Cu element and Cr element.

[0059] In the present application, the "negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be located on one surface of the negative electrode current collector along its thickness direction, or can be located on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved. The negative electrode material layer includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 or at least one of Li-Al alloy. There is no special limitation on the thickness of the negative electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. The negative electrode material layer may further include a binder, a conductive agent, and a thickener. There is no special limitation on the type of the binder in the negative electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the binder can include, but is not limited to, at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. There is no special limitation on the type of the conductive agent in the negative electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, metal material, or conductive polymer. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fiber can include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fiber. Specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. There is no special limitation on the type of the thickener in the negative electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the thickener can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. There is no special limitation on the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer in the present application, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0060] In the present application, the secondary battery includes a positive electrode plate, and there is no particular limitation on the positive electrode plate in the present application as long as the object of the present application can be achieved. For example, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer located on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or can be located on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector or a partial area of the surface of the positive electrode current collector. There is no particular limitation in the present application as long as the object of the present application can be achieved. There is no particular limitation on the positive electrode current collector in the present application as long as the object of the present application can be achieved. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc. The positive electrode material layer of the present application includes a positive electrode active material, and there is no particular limitation on the type of the positive electrode active material in the present application as long as the object of the present application can be achieved. For example, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate or lithium titanate, etc. In the present application, the positive electrode active material can also include a non-metallic element. For example, the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode material layer as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode material layer is 30 μm to 120 μm. In the present application, the positive electrode material layer can also include a conductive agent and a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the positive electrode material layer in the present application as long as the object of the present application can be achieved. For example, the positive electrode binder can be the same as the type of the negative electrode binder in the above-mentioned negative electrode material layer. There is no particular limitation on the type of the conductive agent in the positive electrode material layer in the present application as long as the object of the present application can be achieved. For example, the conductive agent can be the same as the type of the conductive agent in the above-mentioned negative electrode material layer. There is no particular limitation on the mass ratio of the positive electrode active material, the conductive agent and the positive electrode binder in the positive electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0061] In the present application, the secondary battery further includes a separator. There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film.

[0062] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0063] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0064] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles in the present application. For example, the inorganic particles may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. There is no particular limitation on the binder in the present application. For example, the binder may be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0065] In the present application, there is no particular limitation on the thickness of the separator, as long as the object of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0066] The secondary battery further includes a housing for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application has no particular limitation on the housing, and it can be a housing well-known in the art as long as it can achieve the purpose of this application. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal, and this application does not limit the type of metal. Any known metal hard shell housing in the art can be used as long as it can achieve the purpose of this application. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0067] There is no particular limitation on the secondary battery of this application, and it can include any device that undergoes an electrochemical reaction. In one embodiment of this application, the secondary battery can include, but is not limited to: lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0068] The preparation process of the secondary battery of this application is well-known to those skilled in the art, and this application has no particular limitation. For example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly. Then, place the electrode assembly into the housing, inject the electrolyte into the housing and seal it to obtain the secondary battery. Or, stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fix the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly. Place the electrode assembly into the housing, inject the electrolyte into the housing and seal it to obtain the secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0069] The second aspect of this application provides an electronic device, which includes the secondary battery in any of the above embodiments. Thus, the electronic device of this application has good performance in use.

[0070] This application has no particular limitation on the type of the electronic device, and it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device can include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, hand-held cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0071] Example

[0072] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0073] Testing methods and equipment:

[0074] Test for mass percentage content of chromium element:

[0075] The lithium-ion battery in the test example or electrolyte is discharged to 2.5V at 0.5C and then disassembled. The negative electrode plate is taken out, soaked in dimethyl carbonate (DMC) for 4h and then dried naturally. The negative electrode material layer on the negative electrode plate is scraped off to obtain the tested negative electrode current collector. An inductively coupled plasma optical emission spectrometer (ICP-OES, model: AVIO-200) is used to measure the chromium element content in the negative electrode current collector, and the mass percentage content of chromium element is measured by combining the calibration curve method.

[0076] Test for voltage drop (K value) of lithium-ion battery per unit time:

[0077] The lithium-ion battery is placed in a constant temperature environment of 25°C and left to stand for 30 min to make the lithium-ion battery reach a constant temperature state of 25°C. It is charged at a constant current of 0.5C to 3.95V, charged at a constant voltage of 3.95V until the current is 0.025C, left to stand for 1h, and the open-circuit voltage of the battery is measured and recorded as OCV1. The lithium-ion battery is placed in a constant temperature environment of 25°C and left to stand for 48h, and the open-circuit voltage after standing is measured and recorded as OCV2.

[0078] K (mV / h) = (OCV1 - OCV2) / 48h.

[0079] High-temperature storage performance test:

[0080] The lithium-ion battery is placed in a constant temperature environment of 25°C and left to stand for 30 min to make the lithium-ion battery reach a constant temperature state of 25°C. It is charged at a constant current of 0.5C to 4.5V, charged at a constant voltage of 4.5V until the current is 0.025C, and the thickness of the lithium-ion battery at this time is recorded as the initial thickness H0. The lithium-ion battery is transferred to a constant temperature oven at 60°C for storage for 30 days. During this period, the thickness of the lithium-ion battery is measured and recorded every 6 days, and the measured thickness recorded after 30 days is the storage thickness H1.

[0081] High-temperature storage thickness expansion rate (%) = (H1 - H0) / H0 × 100%.

[0082] Example 1-1

[0083] <Preparation of negative electrode current collector>

[0084] Put the raw material copper wire into a tank filled with sulfuric acid at a concentration of 20 g / L, introduce oxygen, control the temperature at 30 °C, and carry out an oxidation reaction to obtain a copper sulfate electrolyte solution; after filtering the prepared copper sulfate electrolyte solution, send it into an electrolytic cell, control the rotation speed of the cathode drum at 3 m / min, and the current density at 7000 A / m 2 , and the electrolysis temperature at 50 °C to deposit a copper foil.

[0085] Immerse the prepared copper foil into a chromium plating solution with chromic acid as the main component and sulfuric acid added. The concentration of chromic acid is 1.0 g / L, control the current density at 0.5 A / dm 2 , and the electroplating duration is 5 s to obtain a chromium-containing copper foil, that is, a negative electrode current collector with a mass percentage content x of chromium element of 0.03% based on the mass of the negative electrode current collector.

[0086] <Preparation of negative electrode plate>

[0087] Mix the negative electrode active material artificial graphite, binder styrene-butadiene rubber, and conductive agent acetylene black according to a mass ratio of 97.4:1.4:1.2, add deionized water as a solvent, and formulate it into a slurry with a solid content of 45 wt%. After stirring evenly with a vacuum mixer, a negative electrode slurry is obtained. Coat the negative electrode slurry evenly on one surface of a negative electrode current collector with a thickness of 6 μm, and dry it at 120 °C to obtain a negative electrode plate with a single-sided coated negative electrode material layer. The coating weight of the negative electrode material layer is 142 mg / 1540 mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode plate with a double-sided coated negative electrode material layer. After drying at 120 °C, it is cold-pressed and then cut into pieces to obtain a negative electrode plate with a specification of 78 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer is 54.5 μm.

[0088] <Preparation of positive electrode plate>

[0089] Mix the positive electrode active material lithium cobaltate, conductive agent (Super P), and binder polyvinylidene fluoride (PVDF) according to a mass ratio of 97:1.4:1.6, add N-methylpyrrolidone (NMP) as a solvent, and formulate it into a slurry with a solid content of 75 wt%. And stir it with a vacuum mixer until the system becomes a uniform positive electrode slurry. Coat the positive electrode slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dry it at 85 °C to obtain a positive electrode plate with a single-sided coated positive electrode material layer. Then, repeat the above steps on the other surface of the positive electrode plate to obtain a positive electrode plate with a double-sided coated positive electrode material layer. After coating, cold-press and cut the positive electrode plate into a specification of 74 mm × 867 mm for use. Among them, the coating weight of the positive electrode material layer is 267.8 mg / 1540 mm 2, the thickness of the positive electrode material layer after cold pressing is 42 μm.

[0090] <Preparation of electrolyte>

[0091] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate are mixed in a mass ratio of 1:1 to obtain a basic solvent. Then, a fluorinated compound of formula I-1 and lithium salt lithium hexafluorophosphate (LiPF6) are added to the basic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content W I of the fluorinated compound of formula I-1 is 50%, and the mass percentage content of the lithium salt LiPF6 is 8%, and the balance is the basic solvent.

[0092] <Separator>

[0093] A polyethylene (PE) film with a thickness of 7 μm is used.

[0094] <Preparation of lithium-ion battery>

[0095] The tab is welded to the positive electrode tab and the negative electrode tab prepared above. The positive electrode tab, separator, and negative electrode tab after welding the tab are stacked in sequence, with the separator in the middle of the positive electrode tab and the negative electrode tab to play an isolation role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging shell, dried in a vacuum oven at 85 °C for 12 h to remove moisture, injected with the above-prepared electrolyte, and subjected to vacuum packaging, standing, formation (constant current charging at 0.02C to 3.5V, and then constant current charging at 0.1C to 3.9V), shaping, capacity testing and other processes to obtain a lithium-ion battery.

[0096] Examples 1-2 to 1-25

[0097] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1. Among them, when the mass percentage content of chromium element in the negative current collector changes, the electroplating duration is adjusted so that the value of x is as shown in Table 1; when the mass percentage content W I of the fluorinated compound changes, the mass percentage content of the basic solvent changes accordingly, the proportion of each component in the basic solvent remains unchanged, and the mass percentage content of the lithium salt LiPF6 remains unchanged.

[0098] Example 2-1

[0099] Except for preparing the electrolyte according to the following steps, the rest are the same as Example 1-1.

[0100] <Preparation of electrolyte>

[0101] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate were mixed in a mass ratio of 1:1 to obtain a base solvent. Then, a fluorinated compound of formula I-1, a first component of fluorinated ethylene carbonate, and a lithium salt of lithium hexafluorophosphate (LiPF6) were added to the base solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content W of the fluorinated compound of formula I-1 I was 50%, the mass percentage content W of the first component of fluorinated ethylene carbonate III was 5%, and the mass percentage content of the lithium salt LiPF6 was 8%. The balance was the base solvent.

[0102] Examples 2-2 to 2-8

[0103] Except for adjusting the relevant preparation parameters according to Table 2, the rest was the same as in Example 2-1. Among them, when the mass percentage content W of the first component III changed, the mass percentage content of the base solvent changed accordingly, the proportions of the components in the base solvent remained unchanged, and the mass percentage contents of other substances except the base solvent remained unchanged.

[0104] Example 2-9

[0105] Except for preparing the electrolyte according to the following steps, the rest was the same as in Example 1-1.

[0106] <Preparation of electrolyte>

[0107] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate were mixed in a mass ratio of 1:1 to obtain a base solvent. Then, a fluorinated compound of formula I-1, a second component of lithium tetrafluoroborate, and a lithium salt of lithium hexafluorophosphate (LiPF6) were added to the base solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content W of the fluorinated compound of formula I-1 I was 50%, the mass percentage content W of the second component of lithium tetrafluoroborate IV was 0.50%, and the mass percentage content of the lithium salt LiPF6 was 8%. The balance was the base solvent.

[0108] Examples 2-10 to 2-16

[0109] Except for adjusting the relevant preparation parameters according to Table 2, the rest was the same as in Example 2-8. Among them, when the mass percentage content W of the second component IV changed, the mass percentage content of the base solvent changed accordingly, the proportions of the components in the base solvent remained unchanged, and the mass percentage contents of other substances except the base solvent remained unchanged.

[0110] Example 2-17

[0111] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0112] <Preparation of electrolyte>

[0113] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate are mixed in a mass ratio of 1:1 to obtain a basic solvent. Then, a fluorinated compound of Formula I-1, a first component of fluorinated ethylene carbonate, a second component of lithium tetrafluoroborate, and a lithium salt of lithium hexafluorophosphate (LiPF6) are added to the basic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content W of the fluorinated compound of Formula I-1 I is 50%, the mass percentage content W of the first component of fluorinated ethylene carbonate III is 5%, the mass percentage content W of the second component of lithium tetrafluoroborate IV is 0.50%, the mass percentage content of the lithium salt LiPF6 is 8%, and the balance is the basic solvent.

[0114] Example 2-18

[0115] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-17. Among them, when the mass percentage content W of the first component III and the mass percentage content W of the second component IV change, the mass percentage content of the basic solvent changes accordingly, the proportion of each component in the basic solvent remains unchanged, and the mass percentage content of other substances except the basic solvent remains unchanged.

[0116] Comparative Example 1

[0117] Except for using a conventional copper foil with a thickness of 6 μm as the negative electrode current collector in <Preparation of negative electrode sheet>, that is, no chromium element is added to the negative electrode current collector, the rest is the same as in Example 1-1.

[0118] Comparative Example 2

[0119] Except for preparing the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0120] <Preparation of electrolyte>

[0121] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate are mixed in a mass ratio of 1:1 to obtain a basic solvent. Then, a lithium salt of lithium hexafluorophosphate (LiPF6) is added to the basic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content of the lithium salt LiPF6 is 8%, and the balance is the basic solvent.

[0122] Comparative Example 3

[0123] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, when the mass percentage of chromium element in the negative electrode current collector changes, the electroplating duration is adjusted so that the value of x is as shown in Table 1.

[0124] Comparative Example 4

[0125] Except that the <preparation of the negative electrode sheet> is the same as in Comparative Example 1 and the <preparation of the electrolyte> is the same as in Comparative Example 2, the rest is the same as in Example 1-1.

[0126] The negative electrode current collector Cu(Cr) involved in the examples and comparative examples is essentially a copper foil containing chromium element, but the actual Cu(Cr) that can be used as the negative electrode current collector is not limited to only containing Cu element and Cr element.

[0127] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 and Table 2.

[0128] Table 1

[0129]

[0130] Note: " / " in Table 1 indicates no relevant preparation parameters.

[0131] It can be seen from Example 1-1 to Example 1-25 and Comparative Example 1 to Comparative Example 4 that through the synergistic effect of the electrolyte containing fluorinated compounds and the negative electrode current collector containing chromium element within the content range of the present application, the K value of the lithium-ion battery is small, indicating that the self-discharge performance of the lithium-ion battery is improved, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance. In Comparative Example 1, the negative electrode current collector does not contain chromium element; in Comparative Example 2, the electrolyte does not include fluorinated compounds; in Comparative Example 3, the mass percentage of chromium element in the negative electrode current collector is not within the range of the present application; in Comparative Example 4, the negative electrode current collector does not contain chromium element and the electrolyte does not include fluorinated compounds; at this time, the K value of the lithium-ion battery in Comparative Example 1 to 4 is large; and / or, the thickness expansion rate during high-temperature storage is large, indicating that the lithium-ion batteries in the comparative examples cannot balance the self-discharge performance and high-temperature storage performance. While the K value of the lithium-ion batteries in Example 1-1 to Example 1-25 is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion batteries have good self-discharge performance and high-temperature storage performance.

[0132] The type of fluorinated compound usually affects the self-discharge performance and high-temperature storage performance of the lithium-ion battery. It can be seen from Example 1-1, Example 1-9 to Example 1-17 that when the fluorinated compound within the range of the present application is selected, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0133] W I The value of W usually affects the self-discharge performance and high-temperature storage performance of lithium-ion batteries. It can be seen from Examples 1-1, 1-18 to 1-25 that when the value of W I is within the scope of this application, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance. Among them, in Example 1-23, the value of W I is relatively large. At this time, the dissociation ability of the lithium salt in the electrolyte is poor, and the lithium-ion transport ability is limited, resulting in poor charge-discharge rate performance of the lithium-ion battery.

[0134] W I The value of W / (1000x) usually affects the self-discharge performance and high-temperature storage performance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-8, 1-18 to 1-25 that when the value of W I / (1000x) is within the scope of this application, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0135] Table 2

[0136]

[0137]

[0138] Note: " / " in Table 2 indicates no relevant preparation parameters. Among them, in Example 2-4, the first component being fluoroethylene carbonate + vinylene carbonate means that the first component is fluoroethylene carbonate and vinylene carbonate. W III being 3 + 2 means that, based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is 3%, and the mass percentage of vinylene carbonate is 2%. The other examples are understood analogously.

[0139] W III The value of W usually affects the self-discharge performance and high-temperature storage performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-8 that when the value of W III is within the scope of this application, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0140] The type of the first component usually affects the self-discharge performance and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1, 2-4 and 2-8 that when the first component within the scope of this application is selected, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0141] W IV The value of usually affects the self-discharge performance and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-9 to 2-16 that when the value of W IV is within the scope of this application, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0142] The type of the second component usually affects the self-discharge performance and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-12 to 2-14 that when the second component within the scope of this application is selected, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance.

[0143] Electrolytes with different combinations usually affect the self-discharge performance and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-18 that when the electrolyte within the combination scope of this application is selected, the K value of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good self-discharge performance and high-temperature storage performance. The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method or article.

[0144] Each embodiment in this specification is described in a related manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0145] The above are only the preferred embodiments of this application, and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery comprising a negative electrode plate and an electrolyte, wherein the electrolyte comprises a fluorinated compound, wherein the fluorinated compound comprises at least one of a compound of formula I or a compound of formula II, in, R1 is selected from a fluorine atom or a C1 to C5 alkyl group at least partially substituted by fluorine, R2 and R3 are each independently selected from a C1 to C5 alkyl group, and R2 and R3 can be connected to form a ring by a single bond; R4 is selected from an unsubstituted or fluorine-substituted C1 to C5 alkyl group; The negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode current collector includes a chromium element. Based on the mass of the negative electrode current collector, the mass content of the chromium element is x, and 0.001%≤x≤0.5%.

2. The secondary battery according to claim 1, wherein The compound of formula I includes at least one of the following compounds:

3. The secondary battery according to claim 1, wherein The compound of formula II includes at least one of the following compounds:

4. The secondary battery according to claim 1, wherein Based on the mass of the electrolyte, the mass percentage of the fluorinated compound is W I , 10% ≤ W I ≤90%; preferably, 20%≤W I ≤70%.

5. The secondary battery according to claim 4, wherein 0.01≤W I / (1000x)≤25; preferably, 0.01≤W I / (1000x)≤5.

6. The secondary battery according to claim 1, wherein The electrolyte includes a first component, and the first component includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, vinylene carbonate or vinylethylene carbonate.

7. The secondary battery according to claim 6, wherein Based on the mass of the electrolyte, the mass percentage of the first component is W III , 0.5% ≤ W III ≤15%; preferably, 1%≤W III ≤8%.

8. The secondary battery according to claim 1, wherein 0.001%≤x≤0.1%; preferably, 0.001%≤x≤0.05%.

9. The secondary battery according to claim 1, wherein The negative electrode current collector is copper foil.

10. The secondary battery according to claim 1, wherein The electrolyte also includes a second component, which includes at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate or lithium difluorophosphate.

11. The secondary battery according to claim 10, wherein Based on the mass of the electrolyte, the mass percentage of the second component is W IV , 0.01% ≤ W IV ≤5%; preferably, 0.1%≤W IV ≤1%. 12 . An electronic device comprising the secondary battery according to claim 1 .

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