Electrolyte and lithium ion battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to an electrolyte, which comprises a non-aqueous organic solvent, a composite lithium salt and a first additive, the first additive comprises a peroxide additive, the weight content of the non-aqueous organic solvent is 60% to 85%, the weight content of the composite lithium salt is 10% to 25%, and the weight content of the peroxide additive is 0.001 to 0.01 wt%. The electrolyte has excellent kinetic performance and excellent cycle performance, and also has high-voltage stability and high-temperature stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to an electrolyte and a lithium ion battery. BACKGROUND

[0002] Fast-charging lithium ion is a major direction in the application field, especially in the 3C digital field, and the market share is continuously increasing. Compared with ordinary lithium ion batteries, fast-charging lithium ion batteries not only use smaller particle size graphite negative electrodes, but also change the structure of the battery to a structure with a centrally-placed tab and multiple tabs, greatly improving the charge and discharge rate of the battery, which also brings safety problems, especially the deterioration of thermal abuse performance. The specific surface area of the smaller particle size graphite negative electrode increases, and the electrolyte side reaction increases; compared with the conventional structure, the polarization is reduced in the centrally-placed tab structure, and under the same charging system conditions, the voltage of the battery cell with the centrally-placed structure is higher. As one of the important factors affecting the safety performance of the battery cell, the electrolyte also needs to improve the safety performance of the battery cell while ensuring the fast-charging performance.

[0003] Solid or semi-solid electrolyte is considered an important way to solve the safety performance of the battery cell, and the principle is to improve the safety performance of the battery cell by reducing the amount of flammable organic solvent. However, reducing the amount of organic solvent will greatly weaken the kinetic performance of the battery cell at room temperature, which does not match the fast-charging demand of the current consumer market. Currently, there are few reports on electrolyte additives that take into account both fast-charging performance and safety performance. SUMMARY

[0004] One of the purposes of the present application is to provide an electrolyte with excellent kinetic performance and excellent cycle performance, and also with high-voltage stability and high-temperature stability, in view of the deficiencies of the prior art.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] An electrolyte, comprising a non-aqueous organic solvent, a composite lithium salt and a first additive, the first additive comprising a peroxide additive, the weight content of the non-aqueous organic solvent being 60% to 85%, the weight content of the composite lithium salt being 10% to 25%, and the weight content of the peroxide additive being 0.001 to 0.01 wt%.

[0007] Preferably, the first additive further comprises a silane additive, and the weight content of the silane additive is 0.1 to 3.0%.

[0008] Preferably, the composite lithium salt comprises lithium difluoro(oxalato)borate with a weight content of 1% to 5%.

[0009] Preferably, the complex lithium salt further comprises lithium hexafluorophosphate and lithium difluorophosphate, the weight content of lithium hexafluorophosphate is 12% to 18%, and the weight content of lithium difluorophosphate is 1% to 5%.

[0010] Preferably, the complex lithium salt further comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium tetrafluoroborate, lithium bis-oxalato-borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, LiN(SO2C2F5)2, lithium tris(trifluoromethylsulfonyl)methide, or lithium bis(trifluoromethylsulfonyl)imide, lithium difluoro-oxalato-phosphate, and lithium tetrafluoro-oxalato-phosphate.

[0011] Preferably, the peroxide additive comprises one or more of:

[0012]

[0013] Preferably, the silane additive comprises one or more of:

[0014]

[0015] Preferably, the electrolyte further comprises a second additive with a weight content of 5% to 15%, the second additive comprising any one or a combination of at least two of 1,3-propane sultone, fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propene sultone, 1,4-butane sultone, pentafluoroalkyloxy cyclotriphosphazene, cyclohexylbenzene, biphenyl, ethyl 4,4,4-trifluorobutyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol bispropionitrile ether, 1,3,6-hexanetricarbonitrile, hexanedinitrile, butanedinitrile, fluorobenzene, boron trifluoride tetrahydrofuran, and methanedisulfonate methylene.

[0016] The second object of the present application is to provide a lithium ion battery with excellent kinetic performance and excellent cycle performance, and also with high voltage stability and high temperature stability.

[0017] In order to achieve the above object, the present application adopts the following technical solutions:

[0018] A lithium ion battery comprises the electrolyte described above.

[0019] Preferably, the lithium ion battery further comprises a positive electrode sheet, a separator, a negative electrode sheet, and a shell, the separator is used to separate the positive electrode sheet and the negative electrode sheet, and the shell is used to encapsulate the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte described above.

[0020] Preferably, the positive electrode sheet comprises a positive current collector and a positive active coating layer arranged on at least one surface of the positive current collector, the positive active coating layer comprises LiNix Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c O2, wherein M and N are each independently selected from any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, and 0≤y≤1, 0≤x<1, 0≤z≤1, x+y+z≤1, 0≤a≤1, 0≤b≤1, 0≤c≤1, a+b+c≤1.

[0021] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer arranged on at least one surface of the negative electrode current collector, and the negative electrode active coating layer comprises one or more of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, tin, tin oxide, tin dioxide, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

[0022] Preferably, the working voltage of the lithium ion battery is 4.40-4.53 V.

[0023] Compared with the prior art, the lithium ion battery of the application has excellent kinetic performance and excellent cycle performance, and also has high-voltage stability and high-temperature stability. DETAILED DESCRIPTION

[0024] The application will be further described in detail below in combination with specific embodiments and comparative examples, but the embodiments of the application are not limited thereto.

[0025] The electrolyte has excellent kinetic performance and excellent cycle performance, and also has high-voltage stability and high-temperature stability. The lithium ion battery of the application has excellent kinetic performance and excellent cycle performance, and also has high-voltage stability and high-temperature stability.

[0026] The electrolyte comprises a non-aqueous organic solvent, a composite lithium salt and a first additive, the first additive comprises a peroxide additive, the weight content of the non-aqueous organic solvent is 60%-85%, the weight content of the composite lithium salt is 10%-25%, and the weight content of the peroxide additive is 0.001-0.01 wt%.

[0027] The combined lithium salt in the electrolyte of the present application not only provides excellent kinetic performance, but also provides excellent cycle performance, high ionic conductivity, wide electrochemical stability window, good thermal stability performance, safety, low toxicity, and can better ensure that the lithium battery has the advantages of high voltage and high specific energy; the additive (Formula I) with an organic peroxide structure: ① The organic peroxide structure can be thermally decomposed at high temperature (≥ 90℃), rapidly initiating free radical polymerization of substances containing unsaturated C-C bonds in the electrolyte, rapidly reducing the content of unsaturated organic liquids, thereby improving the thermal abuse safety of the battery. ② Wide temperature stability. Within the operating temperature range of the battery cell (≤ 60℃), the peroxide structure does not participate in the electrode reaction, and has small impedance, which does not affect the fast charging performance of the battery. ③ As a free radical initiator, the additive has the characteristics of trace high efficiency, and the addition amount is 0.001-0.01% of the total mass, which is about 1% of the current amount of electrolyte additives. ④ The peroxide structure has high voltage stability. It can also maintain structural stability in a wide temperature range (-30-60℃) at high voltage (≥ 4.48V). Organic silane (Formula II): The silane additive has the advantages of high thermal stability, low flammability, non-toxicity, high conductivity, and high decomposition voltage. The silane additive containing unsaturated bonds can form a film on the surface of the negative electrode or the positive electrode, greatly improving the cycle performance of the battery. Under high voltage and high temperature conditions, the silane structure can react with HF, consume the acid produced by the decomposition of lithium salt, thereby protecting the electrode and improving safety performance.

[0028] Preferably, the peroxide additive is mainly selected from one or more of the following compounds:

[0029]

[0030]

[0031] Preferably, the peroxide additive is dibenzoyl peroxide (BPO), and the dibenzoyl peroxide (BPO) is additive a, and its chemical formula is as follows:

[0032]

[0033] Preferably, the silane additive is mainly selected from one or more of the following compounds:

[0034]

[0035] Preferably, the silane additive is preferably tetra-vinylsilane (TVSI), and the tetra-vinylsilane (TVSI) is additive b, and its chemical formula is as follows:

[0036]

[0037] In some embodiments, the non-aqueous organic solvent includes any one or a combination of at least two of ethylene carbonate and / or propylene carbonate, and diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, butyl butyrate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, dipropyl carbonate, dibutyl carbonate. Commonly used electrolyte solvents such as ethylene carbonate and polycarbonate are unsaturated carbonates, which contain unsaturated bonds and can be catalytically polymerized by peroxide to achieve the effect of reducing organic liquid at high temperature. Commonly used carboxylic acid ester solvents such as EP and PP do not contain unsaturated bonds and cannot be catalytically polymerized by peroxide, and are still liquid at high temperature. The range of unsaturated carbonates is set to ensure the safety performance in the subsequent process.

[0038] In some embodiments, the composite lithium salt includes 1% to 5% of lithium difluoro(oxalato)borate by weight. LiODFB participates in the film-forming reaction of the positive and negative electrodes, greatly improving the high-temperature and high-pressure resistance of the electrolyte. The weight content of lithium difluoro(oxalato)borate is 1%, 2%, 3%, 4%, or 5%.

[0039] In some embodiments, the composite lithium salt further includes 12% to 18% of lithium hexafluorophosphate by weight and 1% to 5% of lithium difluorophosphate by weight. Preferably, the weight content of lithium hexafluorophosphate is 12% to 18%, 12% to 15%, 15% to 16%, or 16% to 18%; specifically, the weight content of lithium hexafluorophosphate is 12%, 13%, 14%, 15%, 16%, 17%, or 18%. The weight content of lithium difluorophosphate is 1%, 2%, 3%, 4%, or 5%. Specifically, when lithium difluorophosphate (LiDFP) is used as an additive, it can greatly improve the kinetic performance of the battery and ensure the fast-charging performance.

[0040] In some embodiments, the composite lithium salt further includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, LiN(SO2C2F5)2, lithium tris(trifluoromethylsulfonyl)methide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluoro(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0041] In some embodiments, the electrolyte further comprises a second additive in a weight content of 5-15%, the second additive comprising a combination of any one or more of 1,3-propane sultone, fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propene sultone, 1,4-butane sultone, pentafluoroalkoxy cyclotriphosphazene, cyclohexylbenzene, biphenyl, ethyl 4,4,4-trifluorobutyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol bispropionitrile ether, 1,3,6-hexanetricarbonitrile, hexanedinitrile, butanedinitrile, fluorobenzene, boron trifluoride tetrahydrofuran, and methane disulfonate methylene. The weight content of the second additive is 2%, 3%, 4%, 5%, 6%, 10%, 12%, 13%, 15%.

[0042] The second object of the present application is to provide a lithium ion battery with excellent kinetic performance and superior cycle performance, and also with high voltage stability and high temperature stability.

[0043] To achieve the above object, the present application adopts the following technical solutions:

[0044] A lithium ion battery comprising the electrolyte described above.

[0045] In some embodiments, the lithium ion battery further comprises a positive electrode sheet, a separator, a negative electrode sheet, and a shell, the separator being configured to separate the positive electrode sheet and the negative electrode sheet, and the shell being configured to encapsulate the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte described above.

[0046] In some embodiments, the positive electrode sheet comprises a positive current collector and a positive active coating layer disposed on at least one surface of the positive current collector, the positive active coating layer comprising LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c O2, wherein M and N are each independently selected from any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≤y≤1, 0≤x<1, 0≤z≤1, x+y+z≤1, 0≤a≤1, 0≤b≤1, 0≤c≤1, a+b+c≤1.

[0047] In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer disposed on at least one surface of the negative electrode current collector, the negative electrode active coating layer comprising one or more of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

[0048] In some embodiments, the working voltage of the lithium ion battery is 4.40-4.53 V. The temperature range of the thermal abuse performance test of the lithium ion battery is 120-140℃. The lithium ion battery of the present application has a high charging and discharging working voltage, and the temperature range of the thermal abuse of the battery is 120-140℃, and the battery has good heat resistance, so the battery has high safety performance.

[0049] Comparative Example 1

[0050] 1) Preparation of the positive electrode

[0051] The positive electrode active material LCO, conductive carbon black Super-P and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.9:1.6:1.0, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated on the positive electrode foil, and the corresponding position was laser cleaned; then the nickel tab was ultrasonically welded on the cleaned position of the positive electrode foil.

[0052] 2) Preparation of the negative electrode

[0053] The negative electrode active material artificial graphite, conductive carbon black Super-P, the binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.3:0.3:1.3:1.1, and then dispersed in ionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode foil, and the corresponding position was laser cleaned; then the copper tab was ultrasonically welded on the cleaned position of the negative electrode foil.

[0054] 3) Preparation of the electrolyte

[0055] Vinyl carbonate (EC), propyl propionate (PP), propylene carbonate (PC), diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:PP:DEC = 1:1:3:5, 0.5wt% VC, 4.0wt% PS, 1.0wt% SN, 1.0wt% ADN, 2.0wt% HTCN, 7.0wt% FEC were added respectively, and then 14.0wt% lithium hexafluorophosphate (LiPF6) was added, and after fully mixing and dissolving, it was ready for use.

[0056] 4) Preparation of the lithium ion battery

[0057] The positive and negative electrode sheets with middle tab prepared by the above method were wound together with the separator, and were packaged to prepare a lithium ion battery with middle tab. The battery was vacuum baked at 80℃ for 48h to obtain an electrode core to be injected with electrolyte. The electrolyte prepared above was injected into the electrode core in a glove box with a dew point controlled below -40℃, and was vacuum packaged and left for 24h, followed by conventional formation and capacity distribution. The average capacity of the prepared electrode core was 5148mAh, and the average volume energy density was 755wh / L.

[0058] Examples 1-7

[0059] Different from Comparative Example 1 was the preparation of the electrolyte:

[0060] The electrolyte of Examples 1-7 further contained at least one of the additives a, b and lithium salts LiODFB and LiDFP. The specific compositions of the additives a, b and lithium salts LiBF4 and LiBOB in each example are shown in Table 1. The rest was the same as Comparative Example 1, which will not be repeated here.

[0061] The lithium ion batteries prepared in Comparative Example 1 and Examples 1-7 were subjected to performance tests, and the test results are shown in Table 1.

[0062] High temperature cycle performance test: the batteries prepared in Comparative Example 1 and Examples 1-7 were placed in an oven at a constant temperature of 45℃, 3C constant current constant voltage charged to 4.25V, the cutoff current was 2C, 2C constant current constant voltage charged to 4.3V, the cutoff current was 1.2C, 1.2C constant current constant voltage charged to 4.48V, the cutoff current was 0.05C, and left for 5min; 1C constant current discharged to 3.0V, and left for 5min. This cycle was repeated for 600 weeks, and the discharge capacity of each week was recorded. The capacity retention rate of high temperature cycle was calculated according to the following formula: n-week capacity retention rate = discharge capacity of the nth week / discharge capacity of the first week * 100%.

[0063] Thermal abuse test: the batteries prepared in Comparative Example 1 and Examples 1-7 were taken, 3C constant current constant voltage charged to 4.25V, the cutoff current was 2C, 2C constant current constant voltage charged to 4.3V, the cutoff current was 1.2C, 1.2C constant current constant voltage charged to 4.48V, the cutoff current was 0.02C, and left for 2-4h at room temperature. The battery was hung in a test box, and the temperature was raised to 130℃ or 135℃ at a temperature rise rate of 5±2℃ / min, and was kept at a constant temperature for 60min. The surface temperature, voltage and ambient temperature of the battery were monitored.

[0064] Table 1

[0065] As can be seen from the data in Table 1, the secondary battery prepared in the present application has better high temperature cycle performance and high temperature abuse performance than the secondary battery of Comparative Example 1.

[0066] 1) The 45℃ cycle performance of Example 1 with the addition of peroxide additive a alone has little change compared with Comparative Example 1. This shows that the peroxide additive has no obvious effect on the high-temperature cycle performance of fast-charging batteries.

[0067] 2) The 45℃ cycle performance of Example 2 with the addition of silane additive b alone has little change compared with Comparative Example 1. This shows that the silane additive has no obvious effect on the high-temperature cycle performance of fast-charging batteries.

[0068] 3) The 45℃ cycle performance of Example 4 with the addition of LiODFB alone has obvious improvement compared with Comparative Example 1. This shows that LiODFB can greatly improve the high-temperature cycle performance of batteries.

[0069] 4) The 45℃ cycle performance of Example 5 with the addition of LiDFP alone has little change compared with Comparative Example 1. This shows that LiDFP has no obvious effect on the high-temperature cycle performance of fast-charging batteries.

[0070] 5) Examples 4 and 5 with the addition of LiODFB or LiDFP alone cannot pass the 130℃ and 135℃ thermal abuse tests. This shows that LiODFB and LiDFP cannot improve the thermal abuse performance of batteries.

[0071] 6) Examples with the addition of peroxide additive a can pass the 130℃ and 135℃ thermal abuse tests. This shows that the peroxide additive has a significant improvement on the thermal abuse performance of batteries, and 135℃ is much higher than the current market standard (130℃).

[0072] 7) Examples with the addition of silane additive b alone can pass the 130℃ thermal abuse test, but cannot pass the 135℃ thermal abuse test compared with Comparative Example 1. This shows that silane can improve the thermal abuse performance of batteries to a certain extent.

[0073] When the addition of an embodiment including the following raw materials is set: 0.005wt% a, 0.5wt% b, 1wt% LiODFB, 0.5wt% LiDFP, the secondary battery prepared has both fast-charging high-temperature cycle performance and thermal abuse safety performance.

[0074] Based on the disclosure and teachings of the above specification, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. An electrolyte, characterized in that, The mixture includes a non-aqueous organic solvent, a composite lithium salt, and a first additive. The first additive includes a peroxide additive and a silane additive. The non-aqueous organic solvent has a weight content of 60% to 85%, the composite lithium salt has a weight content of 10% to 25%, the peroxide additive has a weight content of 0.001 to 0.01 wt%, and the silane additive has a weight content of 0.1% to 3.0%. The composite lithium salt includes lithium difluorooxalate borate at a weight content of 1% to 5%, lithium hexafluorophosphate at a weight content of 12% to 18%, and lithium difluorophosphate at a weight content of 1% to 5%.

2. The electrolyte according to claim 1, characterized in that, The composite lithium salt further includes any one or a combination of at least two of the following: lithium difluorosulfonylimide, lithium ditrifluoromethylsulfonylimide, lithium tetrafluoroborate, lithium dioxalate borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethylsulfonyl)imide, LiN(SO2C2F5)2, lithium tri(trifluoromethylsulfonyl)methyl or lithium di(trifluoromethylsulfonyl)imide, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

3. The electrolyte according to claim 1, characterized in that, The peroxide additives include one or more of the following:

4. The electrolyte according to claim 1, characterized in that, The silane additives include one or more of the following:

5. The electrolyte according to claim 1, characterized in that, The electrolyte further includes a second additive at a weight content of 5-15%, the second additive comprising any one or more combinations of 1,3-propanesulfonate lactone, fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, pentafluoroalkoxycyclotriphosphazene, cyclohexylbenzene, biphenyl, ethyl 4,4,4-trifluorobutyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, adiponitrile, succinic anion, fluorobenzene, boron trifluoride tetrahydrofuran, and methane disulfonate.

6. A lithium-ion battery, characterized in that, The electrolyte includes any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, characterized in that, The operating voltage of the lithium-ion battery is 4.40 to 4.53V.

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