An electrolyte for a lithium ion secondary battery and a lithium ion secondary battery

Abstract

The present application provides a kind of electrolyte for lithium ion secondary battery and lithium ion secondary battery using the electrolyte.The electrolyte provided by the present application contains: organic solvent, electrolyte lithium salt and additive, the additive contains compound A, the compound A is as shown in the following structural formula a.By using the additive provided by the present application, the cycle performance of lithium ion secondary battery under high energy density and charge rate can be improved.[Compound A]

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to an electrolyte for lithium-ion secondary batteries and a lithium-ion secondary battery using the electrolyte. Background Technology

[0002] With the increasing demand for cathode materials in lithium-ion secondary batteries, battery voltage needs to be continuously increased, the specific capacity of battery materials needs to be gradually increased, and the battery is required to have good cycle performance.

[0003] However, after long-term cycling during battery use, the cell material expands due to its own volume effect, which damages the particle structure of the positive and negative electrode materials, causing serious cracks. This damages the existing solid electrolyte interphase (SEI, CEI) membrane structure, allowing the solvent in the electrolyte to enter the material and reform the solid electrolyte interphase (SEI, CEI) membrane, further damaging the particle structure of the positive and negative electrode materials, ultimately causing serious capacity decay and other problems.

[0004] In addition, the electrical performance of lithium-ion secondary batteries will deteriorate severely when used in multiple cycles or at high temperatures, and the cycle life cannot be guaranteed.

[0005] For example, CN 112201842A discloses a high-rate electrolyte for lithium iron phosphate power batteries, characterized in that it includes lithium salt and organic solvent; the organic solvent includes 90wt% to 95wt% non-aqueous organic solvent and 5wt% to 10wt% functional additives; the non-aqueous organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; the functional additives include vinylene carbonate, 1,3-propanesulfonate lactone, fluoroethylene carbonate and acetonitrile; the electrolyte is suitable for lithium iron phosphate power batteries with a rate of not less than 6C. Summary of the Invention

[0006] The purpose of this invention is to improve the cycle performance and charging rate of lithium-ion secondary batteries at high energy density, making them more economical and efficient.

[0007] In the manufacturing process of lithium-ion secondary batteries, electrolyte additives are usually added to the electrolyte, which can effectively improve the various performance characteristics of lithium-ion secondary batteries.

[0008] This invention provides a lithium-ion secondary battery electrolyte with a well-stabilized CEI / SEI membrane. The electrolyte comprises an organic solvent, an electrolyte lithium salt, and an additive. The additive contains compound A, which has the following structural formula a:

[0009] [Compound A]

[0010]

[0011] In the above structural formula a, R1 and R2 are independently selected from one of the following groups: halogen atom, halogen-substituted or unsubstituted C1-C20 alkane group, halogen-substituted or unsubstituted C3-C20 cycloalkyl group, halogen-substituted or unsubstituted phenyl group, halogen-substituted or unsubstituted C1-C20 olefin group, unsubstituted biphenyl group, halogen-substituted or unsubstituted C6-C26 phenylalkyl group, halogen-substituted or unsubstituted C6-C26 fused-ring aromatic group, and empty bond.

[0012] Preferably, the content of compound A is 0.5% to 10%, more preferably 3-5%, based on the total amount of the organic solvent.

[0013] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently halogen atoms, the halogen atom is F, Cl or Br, preferably F; the halogen in "substituted by halogen" is F, Cl or Br, preferably F.

[0014] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently a C1-C20 alkane group substituted with a halogen or not substituted, the alkane group is methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, dimethylbutyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methyl The following compounds are used: pentyl, 3-methylpentyl, 1,1,2-trimethylpropyl, 3,3-dimethylbutyl, n-heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, isoheptyl, cycloheptyl, n-octyl, cyclooctyl, nonyl, decyl, undecayl, dodecayl, tridecayl, tetradecayl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecayl, eicosyl, preferably methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, and isobutyl.

[0015] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently a C3-C20 cycloalkyl group that is substituted with a halogen or not substituted, the cycloalkyl group is cyclohexane, cyclopentane, or cycloheptane.

[0016] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently a C1-C20 olefin group that is substituted with a halogen or not substituted, the olefin group is vinyl, n-propenyl, isopropenyl, or butenyl.

[0017] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently a C6-C26 phenylalkyl group substituted with or unsubstituted with halogen, the phenylalkyl group is tolyl, ethylbenzene, or isopropylbenzene; when R1 and R2 are each independently a C6-C26 fused-ring aromatic group substituted with or unsubstituted with halogen, the fused-ring aromatic group is a compound containing a naphthyl group, preferably naphthyl.

[0018] Preferably, the additive contains compound A, a sulfonate compound, a fluorocarbonate, and a nitrile compound; the sulfonate compound is 1,3-propanesulfonate lactone; the fluorocarbonate is fluoroethylene carbonate; and the nitrile compound is one or more of succinic anionyl, adiponitrile, and 1,3,6-hexanetrionitrile.

[0019] Preferably, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran; the electrolyte lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonyl, lithium difluoro(trifluoromethanesulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, and lithium difluoroimidesulfonate; in the electrolyte, the concentration of the electrolyte lithium salt is 0.5M-1.5M, preferably 0.8M-1.3M.

[0020] The present invention also provides a lithium-ion secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte provided by the present invention.

[0021] The present invention has the following beneficial effects:

[0022] The lithium-ion secondary battery electrolyte provided by this invention contains an additive denoted as compound A. With a very small amount of compound A added, and in the presence of the organic solvent in the electrolyte, the cyclic structure of compound A is preferentially reduced at the negative electrode, and the resulting ring-opening sulfonate structure binds to Li at the negative electrode. + Compound A forms a conductive network of lithium alkane sulfonate, while the remaining cyclic portion participates in the formation of lithium alkoxy groups. Specifically, with the participation of the organic solvent in the electrolyte, Compound A enters the interior of the negative electrode material to form a CEI film, and simultaneously, with the participation of the organic solvent in the electrolyte, it enters the interior of the positive electrode material to form an SEI film. Both films are relatively dense and do not easily generate gas. Furthermore, due to the symmetrical structure of the delocalized large π-bonds of the benzene ring, the entire molecular structure is planar, enabling more uniform film formation. Compound A can form stable interfacial protective films at both the positive and negative electrodes.

[0023] In addition, compound A containing sulfur forms lithium alkyl sulfonate with a conductive network after reduction, which forms a CEI film inside the negative electrode material. This film is relatively stable, can protect and improve battery performance, and can further enhance ionic conductivity, thus ensuring the kinetic performance of lithium-ion secondary batteries at high energy densities. Detailed Implementation

[0024] This invention provides a lithium-ion secondary battery electrolyte with a well-stabilized CEI / SEI membrane, comprising: an organic solvent, an electrolyte lithium salt, and an additive, wherein the additive is designated as compound A and has the following structural formula a:

[0025] [Compound A]

[0026]

[0027] In the above structural formula a, R1 and R2 are independently selected from one of the following groups: halogen atom, halogen-substituted or unsubstituted C1-C20 alkane group, halogen-substituted or unsubstituted C3-C20 cycloalkyl group, halogen-substituted or unsubstituted phenyl group, halogen-substituted or unsubstituted C1-C20 olefin group, unsubstituted biphenyl group, halogen-substituted or unsubstituted C6-C26 phenylalkyl group, halogen-substituted or unsubstituted C6-C26 fused-ring aromatic group, and empty bond.

[0028] Preferably, the content of compound A is 0.5% to 10% based on the total weight of the organic solvent, and more preferably 3-5%. Excessive content of compound A will lead to excessive internal impedance of the battery and deteriorate electrical performance; insufficient content will result in inadequate protection of the interface and cause battery capacity decay.

[0029] Preferably, in the structural formula a of compound A, when R1 and R2 are each independently halogen atoms, the halogen atom is F, Cl or Br, preferably F.

[0030] Preferably, in the structural formula a of compound A, when R1 and R2 are substituted by halogens, the halogen in "substituted by halogens" is F, Cl or Br, preferably F.

[0031] In the structural formula a of compound A, when R1 and R2 are alkane groups with 1 to 20 carbon atoms that are halogenated or unsubstituted, there is no specific restriction on the specific type of alkane group. They can be selected according to actual needs. For example, chain groups or cyclic groups are both acceptable. Chain groups include straight-chain groups and branched-chain groups. In addition, cyclic groups may or may not contain substituents. For example, the alkane group can be categorized as follows: methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, dimethylbutyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl, 1,1,2-trimethylpropyl, 3,3-dimethylbutyl, n-heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, isoheptyl, cycloheptyl, n-octyl, cyclooctyl, nonyl, decyl, undecyl, dodecayl, tridecayl, tetradecayl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl. Preferably, the alkane group is methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, or isobutyl.

[0032] In the structural formula a of compound A, when R1 and R2 are independently C3-C20 cycloalkyl groups that are halogenated or unsubstituted, examples of cycloalkyl groups include cyclohexane, cyclopentane, and cycloheptane.

[0033] In the structural formula a of compound A, when R1 and R2 are independently C1-C20 olefin groups that are halogenated or unsubstituted, examples of such olefin groups include: vinyl, n-propenyl, isopropenyl, and butenyl.

[0034] In the structural formula a of compound A, when R1 and R2 are independently C6-C26 phenylalkyl groups that are halogenated or unsubstituted, examples of such phenylalkyl groups include tolyl, ethylbenzene, and isopropylbenzene.

[0035] When R1 and R2 are each independently a C6-C26 fused-ring aromatic group that is halogenated or unsubstituted, examples of the fused-ring aromatic group include compounds containing a naphthyl group. Preferably, the fused-ring aromatic group is a naphthyl group.

[0036] This invention does not impose any particular restrictions on organic solvents and electrolyte lithium salts; commonly used substances and their amounts in the art can be used.

[0037] For example, the electrolyte lithium salt may be selected from at least one of organic lithium salts and inorganic lithium salts. Preferably, the electrolyte lithium salt is selected from at least one of compounds containing fluorine and lithium. More preferably, the electrolyte lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonyl, lithium difluoro(trifluoromethanesulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, and lithium difluoroimidesulfonate.

[0038] Preferably, the concentration of the lithium salt in the electrolyte is 0.5M-1.5M. If the lithium salt concentration is too low, the electrolyte conductivity is low, which will affect the rate capability and cycle performance of the entire battery system; if the lithium salt concentration is too high, the electrolyte viscosity is too high, which will also affect the rate capability of the entire battery system. More preferably, the lithium salt concentration is 0.8M-1.3M.

[0039] Preferably, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0040] Preferably, the content of the organic solvent is 50%-90% based on the total weight of the electrolyte.

[0041] In this invention, the additive may contain other commonly used additives in the electrolyte field besides compound A, such as sulfonate compounds, fluorocarbonates, and nitrile compounds. This invention does not impose any particular limitation on the content of these other commonly used additives; the content can be as commonly used in the field, for example, based on the total weight of the organic solvent, the content of these other commonly used compounds is 10% to 20%. Specifically, the sulfonate compound may be 1,3-propanesulfonate lactone; the fluorocarbonate may be fluoroethylene carbonate; and the nitrile compound may be one or more of succinic anionyl, adiponitrile, and 1,3,6-hexanetrionitrile.

[0042] The present invention also provides a lithium-ion secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte provided by the present invention.

[0043] In the aforementioned lithium-ion secondary battery, the positive electrode includes a positive electrode current collector and a positive electrode slurry layer located on the positive electrode current collector. The positive electrode slurry layer includes a positive electrode active material, a positive electrode binder, and a positive electrode solvent. The negative electrode includes a negative electrode current collector and a negative electrode slurry layer located on the negative electrode current collector. The negative electrode slurry layer includes a negative electrode active material, a negative electrode binder, and a negative electrode solvent. There are no specific limitations on the specific types and contents of the positive electrode active material, positive electrode binder, positive electrode solvent, negative electrode active material, negative electrode binder, and negative electrode solvent; substances and their contents known in the art can be selected according to requirements.

[0044] Preferably, the positive electrode active material is selected from one or more of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials, lithium iron phosphate (LiFePO4), and lithium manganese oxide (LiMn2O4).

[0045] Preferably, the negative electrode active material is graphite and / or silicon, such as natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Both Li-Al alloys can be used as negative electrode active materials.

[0046] The present application is described below with reference to the embodiments. These embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0047] Example

[0048] Example 1

[0049] Electrolyte preparation:

[0050] The electrolyte preparation steps are as follows: Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a mass ratio of EC / PC / DEC / PP = 1 / 1 / 2 / 6 to serve as an organic solvent. Additives 1,3-propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and nitrile compounds succinate (SN), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN) are added to this organic solvent. After thorough mixing, LiPF6 is added to obtain a mixed solution with a LiPF6 concentration of 1.1 mol / L. Compound A, as shown in the formula below, is added to the mixed solution to prepare electrolyte L1, as shown in Table 1. Except for LiPF6, the units of measurement for each component in Table 1 are "parts by mass".

[0051]

[0052] Examples 2-9

[0053] Except for adjusting the amount of LiPF6 or compound A as shown in Table 1, the electrolytes L2-L9 of Examples 2-9 were prepared in the same manner as in Example 1.

[0054] Examples 10-14

[0055] Except for altering the structure of compound A as shown in Table 1, the electrolytes L10-L14 of Examples 10-14 were prepared in the same manner as in Example 1.

[0056] [Compound A]

[0057]

[0058] Comparative Example 1

[0059] Except that compound A was not added as shown in Table 1, the electrolyte LL1 of Comparative Example 1 was prepared in the same manner as in Example 1.

[0060] Table 1

[0061]

[0062] Battery manufacturing

[0063] The production of the positive electrode:

[0064] The positive electrode active material LCO, conductive agent CNT, and binder polyvinylidene fluoride were thoroughly mixed in N-methylpyrrolidone solvent at a weight ratio of 97:1.5:1.5 to form a uniform positive electrode slurry. This slurry was then coated onto the positive electrode current collector Al foil, dried, and cold-pressed to obtain the positive electrode.

[0065] Making the negative electrode:

[0066] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in an appropriate amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. This slurry was then coated onto a Cu foil negative electrode current collector, dried, and cold-pressed to obtain the negative electrode.

[0067] Manufacturing of lithium-ion secondary batteries:

[0068] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound onto the bare battery cell. The bare battery cell is placed in an outer packaging bag, and the electrolyte listed in Table 1 is injected into the dried battery. After vacuum sealing, settling, formation, and shaping processes, the lithium-ion secondary battery is prepared, yielding the battery.

[0069] Battery performance testing

[0070] (1) High-temperature cycle test of the battery

[0071] Test method: Place the battery in an environment of 45±2℃ and perform standard charge-discharge cycles at a cycle rate of 1C and a charging voltage of 3.0-4.5V. Calculate the capacity retention rate of the battery after the cycles. The calculation formula is as follows:

[0072] Capacity retention rate after nth cycle (%) = (Discharge capacity after nth cycle) / (Discharge capacity after first cycle) * 100%

[0073] (2) High-temperature storage test of battery

[0074] Test method: Charge the fully charged cells to 4.5V at room temperature with a current of 0.5C. Place the fully charged battery in an environment of 85 degrees Celsius for 6 hours and measure the thermal expansion rate. After returning to room temperature, discharge the battery to 3.0V with a current of 0.5C and record the discharge capacity.

[0075] (3) 3C rate charging performance test

[0076] First, after the battery has undergone capacity testing, let it stand for 10 minutes. Then, discharge it at 0.2C to 3V, let it stand for 10 minutes, and then fully charge it at 3C. Cut off the charge at 0.05C and let it stand for 10 minutes. Test the voltage, internal resistance, and thickness of the fully charged state at 25±5℃. Then, discharge it at a rate of 0.5C and record the discharge capacity. Calculate the capacity retention rate by dividing the discharge capacity by the charge capacity.

[0077] The battery performance test results are shown in Table 2 below.

[0078] Table 2

[0079]

[0080] As can be seen from Tables 1 and 2, the batteries formulated with the electrolytes prepared in Examples 1-14 of this invention exhibit better high-temperature cycle performance, battery thickness expansion rate, and 3C charging rate than those in Comparative Example 1 where compound A was not added. In particular, the only difference between Example 1 and Comparative Example 1 is that compound A was not added to the electrolyte in Comparative Example 1. This demonstrates that the addition of compound A to the electrolyte of this invention improves the battery's cycle performance and charging rate.

[0081] In addition, the batteries prepared with electrolytes prepared in Examples 1 and 4-7 have better high-temperature cycle performance, battery thickness expansion rate, and 3C charging rate than the batteries prepared in Examples 8-9 where the content of compound A in the electrolyte is not in the preferred range of 0.5% to 10%.

[0082] The batteries prepared with electrolytes prepared in Examples 1 and 4-5 have better high-temperature cycle performance, battery thickness expansion rate, and 3C charging rate than those in Examples 6-7 where the content of compound A in the electrolyte is not in the preferred range of 3-5%, because the content of compound A in the electrolyte is in the preferred range of 3-5%.

[0083] In addition, the batteries prepared with electrolytes prepared in Examples 12-14 have better high-temperature cycle performance, battery thickness expansion rate, and 3C charging rate than the batteries prepared in Examples 1 and 10-11 where the substituents of compound A in the electrolyte do not contain F.

Claims

1. An electrolyte for lithium-ion secondary batteries, characterized in that, Contains: an organic solvent, an electrolyte lithium salt, and an additive, wherein the additive contains compound A, which has the following structural formula a: a In the above structural formula a, R1 and R2 are each independently selected from halogen atoms and halogen-substituted C1-C20 alkane groups; Based on the total weight of the organic solvent, the content of compound A is 0.5% to 10%.

2. The electrolyte according to claim 1, characterized in that, Based on the total weight of the organic solvent, the content of compound A is 3-5%.

3. The electrolyte according to claim 1, characterized in that, In the structural formula a of compound A, when R1 and R2 are each independently halogen atoms, the halogen atom is F, Cl or Br; The halogen in "replaced by halogen" is F, Cl, or Br.

4. The electrolyte according to claim 1, characterized in that, In the structural formula a of compound A, when R1 and R2 are each independently halogen atoms, the halogen atom is F; The halogen in "replaced by halogen" is F.

5. The electrolyte according to claim 1, characterized in that, In the structural formula a of compound A, when R1 and R2 are independently C1-C20 alkane groups substituted with or unsubstituted with halogens, the alkane group is methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, dimethylbutyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-ethylpropyl, ethylpropyl, methylbutyl, ethylbutyl, methylbutyl, ethylbutyl, isohexyl, 2-hexyl, ethylbutyl ... - Hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl, 1,1,2-trimethylpropyl, 3,3-dimethylbutyl, n-heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, isoheptyl, cycloheptyl, n-octyl, cyclooctyl, nonyl, decyl, undecayl, dodecayl, tridecayl, tetradecayl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecayl, eicosyl.

6. The electrolyte according to claim 1, characterized in that, The additive contains compound A, sulfonate compounds, fluorocarbonates, and nitrile compounds; The sulfonate compound is 1,3-propanesulfonic acid lactone; the fluorocarbonate is fluoroethylene carbonate; and the nitrile compound is one or more of succinic acid, adiponitrile, and 1,3,6-hexanetrionitrile.

7. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran. The electrolyte lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonyl, lithium difluoro(trifluoromethanesulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, and lithium difluoroimidesulfonate; in the electrolyte, the concentration of the electrolyte lithium salt is 0.5M-1.5M.

8. The electrolyte according to claim 7, characterized in that, The concentration of the electrolyte lithium salt is 0.8M-1.3M.

9. A lithium-ion secondary battery, characterized in that, The battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte described in any one of claims 1-8.

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