Non-aqueous electrolyte and lithium ion battery thereof

Abstract

The application discloses a nonaqueous electrolyte and a lithium ion battery thereof. The nonaqueous electrolyte comprises a lithium salt, an organic solvent and an additive. The additive comprises a compound A containing a six-membered ring and / or a cyclic anhydride compound B. The content of the compound A is 0.5% to 5% of the total weight of the electrolyte, and the content of the cyclic anhydride compound B is 0.2% to 0.8% of the total weight of the electrolyte. The structural formula of the compound A is shown in the following formula (1), and the structural formula of the cyclic anhydride compound B is shown in the following formula (2) or formula (3).

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a non-aqueous electrolyte and a lithium ion battery thereof. Background Art

[0002] Lithium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of lithium ions between the positive and negative electrodes to work. + Insertion and deinsertion back and forth between the two electrodes: During charging, Li + It is deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge.

[0003] However, as the limiting voltage of the positive electrode material continues to increase, the gram capacity of the battery material gradually increases, while the high-temperature performance of the battery deteriorates seriously, and long cycle life cannot be guaranteed. Especially under high voltage (>4.5V) and long-term cycle charge and discharge, the volume of the material will expand and cause serious cracks. The solvent in the electrolyte enters the interior of the positive electrode material, destroying the structure, and ultimately causing serious capacity attenuation and thickness expansion problems.

[0004] Therefore, there is an urgent need for a non-aqueous electrolyte that can improve the cycle performance of lithium-ion batteries at high energy density, increase capacity retention, and have a low thickness expansion rate. Summary of the Invention

[0005] The present invention aims to provide a non-aqueous electrolyte and a lithium ion battery thereof, which can improve the cycle performance of the lithium ion battery under high energy density, improve the capacity retention rate, and have a low thickness expansion rate.

[0006] The present invention discloses a non-aqueous electrolyte, which includes a lithium salt, an organic solvent and an additive. The additive includes a compound A containing a 6-membered ring and / or a cyclic acid anhydride compound B. The content of the compound A is 0.5% to 5% of the total weight of the electrolyte, and the content of the cyclic acid anhydride compound B is 0.2% to 0.8% of the total weight of the electrolyte. The structural formula of the compound A is the following formula (1), and the structural formula of the cyclic acid anhydride compound B is the following formula (2) or formula (3):

[0007]

[0008] Wherein, in formula (1), R1, R2, R3, and R4 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups substituted or unsubstituted by halogen, or biphenyl groups, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 fused ring aromatic groups substituted or unsubstituted by halogen, and empty bonds; wherein the number of carbon atoms connected to -CN and O atoms is C1-C12;

[0009] In formula (2) and formula (3), R5, R6, R7, and R8 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups or unsubstituted biphenyl groups substituted or unsubstituted by halogen, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 condensed ring aromatic groups substituted or unsubstituted by halogen, and empty bonds.

[0010] Optionally, the additive is compound A, and the content of compound A is 1% of the total weight of the electrolyte.

[0011] Optionally, the additive package is a cyclic acid anhydride compound B, and the content of the cyclic acid anhydride compound B is 0.5% of the total weight of the electrolyte.

[0012] Optionally, the additive includes compound A and cyclic acid anhydride compound B; the content of compound A is 1% of the total weight of the electrolyte, and the content of cyclic acid anhydride compound B is 0.5% of the total weight of the electrolyte.

[0013] Optionally, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0014] Optionally, the organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate, and the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate is 1:1:2:6.

[0015] The present invention also discloses a lithium ion battery comprising the non-aqueous electrolyte as described above.

[0016] Optionally, the lithium-ion battery also includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active slurry layer located on the positive electrode current collector, the positive electrode active slurry layer includes a positive electrode active material, and the positive electrode active material is one or more selected from lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium ferrous phosphate, and lithium manganese oxide.

[0017] The non-aqueous electrolyte of the present invention contains 0.5% to 5% of compound A and / or 0.2% to 0.8% of cyclic anhydride compound B. The cyano functional group (-CN) contained in compound A can effectively stabilize the positive electrode / electrolyte interface properties, inhibiting the dissolution of transition metal ions and the further oxidative decomposition of electrolyte components. The unsaturated double bonds therein can also form polymers at the positive electrode, providing protection for the positive electrode. The pyran compound contained therein has an electronic structure similar to that of benzene, and the oxygen atom in the ring has extremely strong alkalinity, which can be combined with the F in the lithium salt LiPF6 to form a salt, thereby stabilizing the electrolyte. Cyclic anhydride compound B is an anhydride-type compound that can bind trace water in the electrolyte, preventing excessive HF from being generated in the late stages of lithium-ion battery cycling and corroding the positive and negative electrode interface films. Furthermore, the anhydride can form a relatively dense CEI film on the positive electrode surface, synergistically acting with additive A to protect the positive electrode interface film. When compound A and cyclic anhydride compound B are added separately, they can improve the cycling performance of lithium-ion batteries at high energy density, increase capacity retention, and reduce thickness expansion. The combined use of the two is even more effective than using either alone. DETAILED DESCRIPTION

[0018] It should be understood that the terms used herein, the specific structures and functional details disclosed are only for describing specific embodiments and are representative. However, the present invention can be implemented in many alternative forms and should not be construed as being limited to only the embodiments described herein.

[0019] The following optional embodiments describe the present invention in detail.

[0020] As one embodiment of the present invention, a non-aqueous electrolyte is disclosed. The non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive. The additive includes a compound A containing a 6-membered ring and / or a cyclic acid anhydride compound B. The content of the compound A is 0.5% to 5% of the total weight of the electrolyte, and the content of the cyclic acid anhydride compound B is 0.2% to 0.8% of the total weight of the electrolyte. The structural formula of the compound A is the following formula (1), and the structural formula of the cyclic acid anhydride compound B is the following formula (2) or formula (3):

[0021]

[0022] Wherein, in formula (1), R1, R2, R3, and R4 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups substituted or unsubstituted by halogen, or unsubstituted biphenyl groups, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 condensed aromatic groups substituted or unsubstituted by halogen, and empty bonds; wherein the number of carbon atoms connected to -CN and the O atom is C1-C12.

[0023] In formula (2) and formula (3), R5, R6, R7, and R8 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups or unsubstituted biphenyl groups substituted or unsubstituted by halogen, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 condensed ring aromatic groups substituted or unsubstituted by halogen, and empty bonds.

[0024] The non-aqueous electrolyte of the present invention contains 0.5% to 5% of compound A and / or 0.2% to 0.8% of cyclic anhydride compound B. The cyano functional group (-CN) contained in compound A can effectively stabilize the positive electrode / electrolyte interface properties, inhibiting the dissolution of transition metal ions and the further oxidative decomposition of electrolyte components. The unsaturated double bonds therein can also form polymers at the positive electrode, providing protection for the positive electrode. The pyran compound contained therein has an electronic structure similar to that of benzene, and the oxygen atom in the ring has extremely strong alkalinity, which can be combined with the F in the lithium salt LiPF6 to form a salt, thereby stabilizing the electrolyte. Cyclic anhydride compound B is an anhydride-type compound that can bind trace water in the electrolyte, preventing excessive HF from being generated in the late stages of lithium-ion battery cycling and corroding the positive and negative electrode interface films. Furthermore, the anhydride can form a relatively dense CEI film on the positive electrode surface, synergistically acting with additive A to protect the positive electrode interface film. When compound A and cyclic anhydride compound B are added separately, they can improve the cycling performance of lithium-ion batteries at high energy density, increase capacity retention, and reduce thickness expansion. The combined use of the two is even more effective than using either alone.

[0025] Specifically, compound A may account for 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% of the total weight of the electrolyte. Preferably, the additive is compound A, and the content of compound A is 1% of the total weight of the electrolyte.

[0026] Specifically, the cyclic anhydride compound B can account for 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% of the total weight of the electrolyte. Preferably, the additive package is the cyclic anhydride compound B, and the content of the cyclic anhydride compound B is 0.5% of the total weight of the electrolyte.

[0027] Specifically, the additive includes compound A and cyclic anhydride compound B; the content of compound A is 1% of the total weight of the electrolyte, and the content of cyclic anhydride compound B is 0.5% of the total weight of the electrolyte.

[0028] Specifically, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran. Preferably, the organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate, and the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate is 1:1:2:6.

[0029] Specifically, the electrolyte lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonyl, lithium difluoro(trifluoromethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bisfluoroimide sulfonate. Preferably, the concentration of the electrolyte lithium salt is 0.5M-1.5M. Specifically, the electrolyte further includes a sulfonate compound, a fluorocarbon acid ester, and a nitrile compound.

[0030] The application also discloses a lithium ion battery comprising the non-aqueous electrolyte as described above. Specifically, the lithium ion battery further comprises a positive electrode sheet, a negative electrode sheet, and a lithium battery separator. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active paste layer on the positive electrode current collector, wherein the positive electrode active paste layer comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active paste layer on the negative electrode current collector, wherein the negative electrode active paste layer comprises a negative electrode active material. The specific types of the positive electrode active material, the positive electrode binder, and the negative electrode active material are not specifically limited and can be selected according to requirements.

[0031] Preferably, the positive electrode active material is selected from one or more of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material, lithium iron phosphate (LiFePO4), and lithium manganate (LiMn2O4).

[0032] Preferably, the negative electrode active material is graphite and / or silicon, such as natural graphite, artificial graphite, mesophase carbon microbeads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O12-Li4Ti5O12, Li-Al alloy, etc. 12 , Li-Al alloy.

[0033] The following is further explained in detail through specific examples.

[0034] Preparation of solution

[0035] The preparation steps of the electrolyte are as follows: ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) / propyl propionate (PP) are mixed in a mass ratio of 1 / 1 / 2 / 6 as an organic solvent. After adding additives PS and FEC to the organic solvent and mixing evenly, LiPF6 is added to obtain a mixed solution with a LiPF6 concentration of 1.1 mol / L, thereby obtaining the comparative example 2 scheme, and compound A and cyclic acid anhydride compound B are added to the mixed solution to prepare the electrolytes of Examples 1-5 and Comparative Example 1, as shown in Table 1. PS is 1,3-propane sultone, FEC is fluoroethylene carbonate, SN is succinonitrile, ADN is adiponitrile, and HTCN is 1,3,6-hexanetrinitrile. The structural formula of compound A is as follows:

[0036]

[0037] The structure of the cyclic anhydride compound B is as follows:

[0038]

[0039] The experimental scheme of the electrolyte is shown in Table 1 below:

[0040] Table 1

[0041]

[0042]

[0043] In Table 1, the ratios of EC, PC, DEC, and PP are by mass, and the contents of PS, FEC, SN, ADN, HTCN, compound A, and cyclic anhydride compound B are by weight percentages of the total electrolyte.

[0044] Battery production

[0045] To prepare the positive electrode sheet, the positive electrode active material LCO, the conductive agent CNT, and the binder polyvinylidene fluoride were thoroughly mixed in N-methylpyrrolidone at a ratio of 97:1.5:1.5 by weight to form a uniform positive electrode slurry. This slurry was applied to the positive electrode current collector Al foil, dried, and cold-pressed to produce the positive electrode sheet.

[0046] To prepare the negative electrode sheet, graphite (the negative electrode active material), acetylene black (the conductive agent), styrene-butadiene rubber (the binder), and sodium carboxymethyl cellulose (the thickener) are thoroughly mixed in a suitable amount of deionized water at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. This slurry is then applied to the negative electrode current collector (Cu foil), dried, and cold-pressed to produce the negative electrode sheet.

[0047] Lithium-ion battery production: Stack the positive electrode sheet, separator, and negative electrode sheet in order, placing the separator between the positive and negative electrodes to provide isolation. The sheets are then wound into bare cells. The bare cells are placed in an outer packaging bag. The electrolytes listed in Table 1 are injected into the dried cells. After vacuum packaging, resting, formation, and shaping, the lithium-ion battery is completed.

[0048] High temperature cycle testing of batteries

[0049] Test method: Place the battery in an environment of 45±2 degrees, follow the standard charge and discharge cycle, cycle rate 1C, charging voltage 3.0-4.5V, and calculate the capacity retention rate of the battery after the cycle.

[0050] The calculation formula is as follows:

[0051] The n-th cycle capacity retention rate (%)=(n-th cycle discharge capacity) / (first cycle discharge capacity)*100%.

[0052] High-temperature storage test of the battery: Test method: Charge the divided battery cell to 4.5V at room temperature with a current of 0.5C, place the fully charged battery in an environment of 85 degrees for 6 hours, measure the thickness expansion rate, and after returning to room temperature, discharge it to 3.0V with a current of 0.5C and record the discharge capacity.

[0053] The battery test results are shown in Table 2:

[0054] Table 2

[0055]

[0056] As can be seen from Examples 1-5, Comparative Examples 1 and 2 in Table 2, Example 3, in which Compound A alone is added, exhibits the best high-temperature cycling and safety performance, i.e., the best effect is achieved when Compound A is added at a concentration of 1%. As can be seen from Examples 7-8 and Comparative Example 3, Example 7 exhibits the best performance, i.e., the best effect is achieved when the cyclic anhydride Compound B is added at a concentration of 0.5%.

[0057] Furthermore, in order to verify the combined effect of additive A and cyclic anhydride compound B, the following experimental scheme was designed:

[0058]

[0059] The test results are as follows:

[0060]

[0061] By comparing Examples 3, 7, and 10, it can be found that the effect of using compound A and cyclic acid anhydride compound B in combination is better than using a single additive, that is, the combination of the two can jointly improve the electrical performance of the battery.

[0062] The above is a further detailed description of the present invention in conjunction with specific optional embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises a compound A containing a 6-membered ring or the additive comprises a compound A containing a 6-membered ring and a cyclic acid anhydride compound B; the content of the compound A is 0.5% to 5% of the total weight of the electrolyte, and the content of the cyclic acid anhydride compound B is 0.2% to 0.8% of the total weight of the electrolyte; the structural formula of the compound A is the following formula (1), and the structural formula of the cyclic acid anhydride compound B is the following formula (2) or formula (3): Wherein, in formula (1), R1, R2, R3, and R4 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups substituted or unsubstituted by halogen, or biphenyl groups, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 fused ring aromatic groups substituted or unsubstituted by halogen, and empty bonds; wherein the number of carbon atoms connected to -CN and O atoms is C1-C12; In formula (2) and formula (3), R5, R6, R7, and R8 are independently selected from C1-C20 alkyl groups substituted or unsubstituted by halogen, C3-C20 cycloalkyl groups substituted or unsubstituted by halogen, phenyl groups substituted or unsubstituted by halogen, C1-C20 olefin groups or unsubstituted biphenyl groups substituted or unsubstituted by halogen, C6-C26 phenylalkyl groups substituted or unsubstituted by halogen, C6-C26 condensed ring aromatic groups substituted or unsubstituted by halogen, and empty bonds.

2. The non-aqueous electrolyte according to claim 1, wherein The additive is compound A, and the content of compound A is 1% of the total weight of the electrolyte.

3. The non-aqueous electrolyte according to claim 1, wherein The additive package is a cyclic acid anhydride compound B, and the content of the cyclic acid anhydride compound B is 0.5% of the total weight of the electrolyte.

4. The non-aqueous electrolyte according to claim 1, wherein The additives include compound A and cyclic acid anhydride compound B; the content of compound A is 1% of the total weight of the electrolyte, and the content of cyclic acid anhydride compound B is 0.5% of the total weight of the electrolyte.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that The organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

6. The non-aqueous electrolyte according to claim 5, wherein The organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate, and the mass ratio of the ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate is 1:1:2:

6.

7. A lithium-ion battery, characterized in that: Comprising the non-aqueous electrolyte according to any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, wherein The lithium-ion battery also includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active slurry layer located on the positive electrode current collector. The positive electrode active slurry layer includes a positive electrode active material, and the positive electrode active material is one or more selected from lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium ferrous phosphate, and lithium manganese oxide.

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