Rate type lithium ion battery electrolyte giving consideration to long circulation and lithium ion battery containing same

Abstract

The invention provides a multiplying power type lithium ion battery electrolyte considering long circulation and a lithium ion battery containing the same, the electrolyte comprises a non-aqueous organic solvent, a lithium salt, a first additive and a second additive, the first additive comprises vinylene carbonate, and the second additive comprises 1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3-pentanediol monoisobutyrate and 1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3-pentanediol monoisobutyrate. The invention relates to a combination of 2, 3-diallyl-5-methyl urea isocyanate and a thiophene compound. The electrolyte can form a stable solid electrolyte interface film on the surfaces of a positive electrode material and a negative electrode material of the lithium ion battery, so that the stability of the positive electrode material and the negative electrode material in the circulating process is effectively protected, the interface impedance of the positive electrode can be remarkably reduced, and the rate capability of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a lithium-ion battery electrolyte and a lithium-ion battery comprising the same, and more particularly to a rate-type lithium-ion battery electrolyte that takes into account long cycling and a lithium-ion battery comprising the same. Background Art

[0002] Lithium-ion batteries have achieved great commercial success in the portable energy and new energy vehicle markets. The lithium battery electrolyte is the carrier of ion transport in the battery and plays a crucial role in improving the comprehensive performance of lithium batteries. While improving the rate performance of lithium batteries, taking into account other performances is the current research direction.

[0003] In traditional cognition, the ionic conductivity decreases with the increase of the electrolyte concentration, which in turn leads to an increase in the impedance of lithium ions during transport in the electrolyte and at the interface, and the rate performance is considered to be poor. With the in-depth study of high-rate electrolytes, it has been found that a specific additive combination can form a special SEI film in the electrolyte. In traditional electrolytes, the SEI film mainly comes from the decomposition of solvents; in high-rate electrolytes, the SEI film formed mainly comes from the decomposition of electrolytic salts and the film-forming reaction of additives. The formed SEI film has a lower impedance, which can improve the conduction of lithium ions at the interface and thus improve the rate performance. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lithium-ion battery electrolyte and a lithium-ion battery comprising the same. The lithium-ion battery electrolyte of the present invention can form a stable solid electrolyte interface film on the surfaces of the positive and negative electrode materials of the lithium-ion battery, effectively protecting the stability of the positive and negative electrode materials during cycling, and can significantly reduce the interface impedance of the positive electrode and improve the rate performance of the battery.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] On the one hand, the present invention provides a lithium-ion battery electrolyte, which comprises a non-aqueous organic solvent, a lithium salt, a first additive, and a second additive. The first additive comprises vinylene carbonate, and the second additive comprises a combination of 1,3-diallyl-5-methylisocyanurate and a thiophene compound.

[0007] In the present invention, the lithium-ion battery electrolyte can enable the lithium-ion battery to improve the cycling stability and cycle life at room temperature and high temperature, and has long cycling performance. The long cycling means that at 25 °C, the capacity retention rate of the lithium-ion battery after cycling for more than 1000 weeks is ≥ 80%; at 45 °C, the capacity retention rate of the lithium-ion battery after cycling for more than 500 weeks is ≥ 80%.

[0008] In the present invention, through the design of the electrolyte components of the rate type that takes into account long cycle life, through the combined action of each component, and further through the use of the second additive, the lithium-ion battery prepared with it can take into account the long cycle performance while effectively improving the rate performance of the lithium-ion battery. Among the first additives, vinylene carbonate, as a negative electrode film-forming additive, can preferentially protect the non-aqueous organic solvent, undergo a reduction reaction at the negative electrode interface, and polymerize to form a high-quality SEI film, which can effectively improve the battery life; in the second additive, 1,3-diallyl-5-methyl isocyanuric acid and thiophene compounds have a synergistic effect, achieving the effects of protecting the positive and negative electrodes, reducing impedance, and improving rate performance. Among them, 1,3-diallyl-5-methyl isocyanuric acid can be used as a film-forming additive, and each of the three N atoms in the C-N six-membered ring has a lone pair of electrons, which synergistically with the carbonyl group, can effectively improve the complexation ability of N with the high-valent metal atoms of the positive electrode, thereby significantly reducing the interface impedance of the positive electrode, being beneficial to the migration of lithium ions at the positive electrode interface, and significantly improving the rate performance of the battery; the thiophene compound can preferentially undergo an oxidation reaction to form a sulfur-containing compound, which can effectively improve the ionic conductivity, reduce the interface impedance, and effectively improve the compatibility between the electrode and the electrolyte interface. The rate type electrolyte that takes into account long cycle life can form a stable solid electrolyte interface film on the surfaces of the positive and negative electrode materials of the lithium-ion battery, and the film-forming impedance is lower, which can effectively reduce the damage to the positive electrode material and capacity attenuation during the cycle process, as well as the problems such as excessive decomposition of the electrolyte and continuous thickening of the SEI film caused by the deposition of metal ions on the negative electrode surface, thereby improving the stability of the positive and negative electrode materials during the cycle process, the energy density of the lithium-ion battery, and effectively improving the rate performance of the lithium-ion battery while taking into account long cycle life.

[0009] Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the first additive is 0.5% - 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, etc.

[0010] In the present invention, if the mass percentage content of the first additive is too small, a dense and stable solid electrolyte interface film cannot be formed, and the cycle life of the lithium-ion battery is greatly reduced; if the mass percentage content of the first additive is too large, the formed solid electrolyte interface film is too thick, resulting in an increase in the impedance of the lithium-ion battery and a decline in performance.

[0011] Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the second additive is 1% - 20%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16% or 18%, etc.

[0012] In the present invention, if the mass percentage content of the second additive is too small, the improvement effect on the rate performance of the lithium-ion battery is not significant; if the mass percentage content of the second additive is too large, the comprehensive performance of the prepared lithium-ion battery is greatly reduced, and a capacity drop phenomenon occurs during testing.

[0013] Preferably, the mass ratio of the 1,3-diallyl-5-methyl isocyanuric acid and the thiophene compound is 3-5:1 (such as 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1 or 4.8:1, etc.), and more preferably 4:1.

[0014] In the present invention, the structure of the 1,3-diallyl-5-methyl isocyanuric acid is as follows:

[0015]

[0016] Preferably, the thiophene compound includes 1-thia-2,4-cyclopentadiene.

[0017] Preferably, the non-aqueous organic solvent includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl acetate or tetrahydrofuran.

[0018] Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the non-aqueous organic solvent is 50%-98%, such as 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, etc.

[0019] Preferably, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium perchlorate or lithium bis(oxalato)borate.

[0020] Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the lithium salt is 0.5%-20%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16% or 18%, etc.

[0021] In a second aspect, the present invention provides a lithium-ion battery, which includes a battery housing, an electrode assembly and the lithium-ion battery electrolyte as described in the first aspect. The electrode assembly includes a positive electrode, a negative electrode and a separator or a solid electrolyte disposed between the positive electrode and the negative electrode.

[0022] Preferably, the electrode assembly and the lithium-ion battery electrolyte are sealed in the battery housing.

[0023] Preferably, the positive electrode includes a positive electrode active material.

[0024] Preferably, the positive electrode active material includes LiNi x Co y Mn z L (1-x-y-z) O2, LiCo x’ L (1-x’) O2, LiNi x” L y’ Mn (2-x”-y’) O4 and Li z’ MPO4, any one or a combination of at least two thereof.

[0025] Wherein, L is one or a combination of at least two of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe; M is one or a combination of at least two of Fe, Mn or Co, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ x + y + z ≤ 1, 0 ≤ x' ≤ 1, 0.3 ≤ x'' ≤ 0.6, 0.01 ≤ y' ≤ 0.2, 0.5 ≤ z' ≤ 1.

[0026] In the present invention, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0027] y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0028] z can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0029] x + y + z can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0030] x' can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc.

[0031] x'' can be 0.33, 0.36, 0.39, 0.42, 0.45, 0.48, 0.51, 0.53, 0.56 or 0.59, etc.

[0032] y' can be 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16 or 0.18, etc.

[0033] z' can be 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, etc.

[0034] Preferably, the negative electrode includes a negative electrode active material.

[0035] Preferably, the negative electrode active material includes a silicon-based negative electrode active material and / or a carbon-based negative electrode active material.

[0036] Preferably, the material of the separator is any one or a combination of at least two of polypropylene, polyethylene, glass fiber, vinylon or nylon.

[0037] Preferably, the material of the solid electrolyte is any one or a combination of at least two of polypropylene, polyethylene, glass fiber, vinylon or nylon.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] In the present invention, through the design of the electrolyte components, through the combined action of each component, and further through the use of the second additive, the lithium-ion battery prepared therefrom can take into account the long cycle performance while effectively improving the rate performance of the lithium-ion battery.

[0040] In the first additive of the present invention, vinylene carbonate, as a negative electrode film-forming additive, can preferentially protect non-aqueous organic solvents, undergo a reduction reaction at the negative electrode interface, and polymerize to form a high-quality SEI film, which can effectively improve the battery life; in the second additive, 1,3-diallyl-5-methyl isocyanuric acid and thiophene compounds have a synergistic effect, achieving the functions of protecting the positive and negative electrodes, reducing impedance, and improving rate performance. Among them, 1,3-diallyl-5-methyl isocyanuric acid can be used as a film-forming additive, and each of the three N atoms in the C-N six-membered ring has a lone pair of electrons, which cooperate with the carbonyl group to effectively improve the complexation ability of N with the high-valent metal atoms of the positive electrode, thereby significantly reducing the interfacial impedance of the positive electrode, being beneficial to the migration of lithium ions at the positive electrode interface, significantly improving the rate performance of the battery, and the complexation of N atoms with high-valent metal atoms can effectively reduce the oxidation activity of the positive electrode material to the electrolyte. Moreover, the two cooperate with each other to improve the Lewis basicity of the carbonyl group, react preferentially with the by-product PF5 generated by the decomposition of lithium salt in the electrolyte system, thereby inhibiting the reaction between PF5 and organic solvents, effectively preventing the consumption of solvents in the electrolyte system during cycling, and thus improving the high-temperature storage and cycling performance of lithium-ion batteries; the thiophene compound can preferentially undergo an oxidation reaction to form a sulfur-containing compound, which can effectively improve the ionic conductivity, reduce the interfacial impedance, effectively improve the compatibility between the electrode and the electrolyte interface, and improve the battery cycling and rate performance. The rate-type electrolyte that takes into account long cycling can form a stable solid electrolyte interface film on the surfaces of the positive and negative electrode materials of the lithium-ion battery, and the film-forming impedance is lower, which can effectively reduce problems such as damage to the positive electrode material and capacity attenuation during cycling, as well as excessive decomposition of the electrolyte and continuous thickening of the SEI film caused by the deposition of metal ions on the negative electrode surface. Furthermore, it improves the stability of the positive and negative electrode materials during cycling, the energy density of the lithium-ion battery, and effectively improves the rate performance of the lithium-ion battery while taking into account long cycling. Detailed implementation manners

[0041] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0042] Example 1

[0043] This embodiment provides a rate-type electrolyte that takes into account long cycle life and its preparation method. The rate-type electrolyte that takes into account long cycle life includes the following components by mass percentage: lithium salt (lithium hexafluorophosphate) 13.75%, non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate with a mass ratio of 3:5:2) 79.75%, first additive (vinylene carbonate) 0.5%, and second additive (a mixture of 1,3-diallyl-5-methyl isocyanuric acid (CAS: 5320-26-3, Zhongneng Wancheng Co., Ltd.) and 1-thia-2,4-cyclopentadiene with a mass ratio of 4:1) 6%.

[0044] The preparation method of the rate-type electrolyte that takes into account long cycle life is as follows:

[0045] The preparation is carried out in a glove box. According to the formula amount, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed evenly, then lithium hexafluorophosphate after sufficient drying is added, a mixture of 1,3-diallyl-5-methyl isocyanuric acid and 1-thia-2,4-cyclopentadiene with a mass ratio of 4:1 is added, and then vinylene carbonate is added to obtain the rate-type electrolyte that takes into account long cycle life.

[0046] Example 2

[0047] This embodiment provides a rate-type electrolyte that takes into account long cycle life and its preparation method. The difference from Example 1 is only that the mass percentage of the second additive (a mixture of 1,3-diallyl-5-methyl isocyanuric acid and 1-thia-2,4-cyclopentadiene with a mass ratio of 4:1) is adjusted to 1.2%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate with a mass ratio of 3:5:2) is adjusted to 84.55%, and the others are the same as in Example 1.

[0048] Example 3

[0049] This embodiment provides a rate-type electrolyte that takes into account long cycle life and its preparation method. The difference from Example 1 is only that the mass percentage of the second additive (a mixture of 1,3-diallyl-5-methyl isocyanuric acid and 1-thia-2,4-cyclopentadiene with a mass ratio of 4:1) is adjusted to 2.4%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate with a mass ratio of 3:5:2) is adjusted to 83.35%, and the others are the same as in Example 1.

[0050] Example 4

[0051] The present embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 4:1) is adjusted to 4.8%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3:5:2) is adjusted to 80.95%. The rest is the same as in the embodiment 1.

[0052] Example 5

[0053] The present embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 4:1) is adjusted to 12%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3:5:2) is adjusted to 73.75%. The rest is the same as in the embodiment 1.

[0054] Example 6

[0055] The present embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 4:1) is adjusted to 18%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3:5:2) is adjusted to 67.75%. The rest is the same as in the embodiment 1.

[0056] Example 7

[0057] This embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive is kept unchanged, and the mass ratio of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in the second additive is adjusted to 3:1. The rest is the same as the embodiment 1.

[0058] Example 8

[0059] This embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive is kept unchanged, and the mass ratio of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in the second additive is adjusted to 5:1. The rest is the same as the embodiment 1.

[0060] Example 9

[0061] The present embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The rate-type electrolyte that takes into account a long cycle includes the following components, measured by mass percentage: 0.5% of a lithium salt (lithium difluorooxalate borate), 78.5% of a non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3:5:2), 1% of a first additive (vinylene carbonate), and 20% of a second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 3:1).

[0062] The preparation method of the rate-type electrolyte taking into account long cycle is as follows:

[0063] The preparation is carried out in a glove box. After ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are evenly mixed according to the formula, fully dried lithium difluorooxalate borate is added, and a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 3:1 is added, and then vinylene carbonate is added to obtain the rate-type electrolyte that takes into account long circulation.

[0064] Example 10

[0065] The present embodiment provides a rate-type electrolyte that takes into account long cycle and a preparation method thereof. The rate-type electrolyte that takes into account long cycle includes the following components, measured by mass percentage: 20% of lithium salt (lithium tetrafluoroborate), 69% of non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 3:5:2), 10% of a first additive (vinylene carbonate), and 1% of a second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 5:1).

[0066] The preparation method of the rate-type electrolyte taking into account long cycle is as follows:

[0067] The preparation is carried out in a glove box. After ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are evenly mixed according to the formula, fully dried lithium tetrafluoroborate is added, and a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 5:1 is added, and then vinylene carbonate is added to obtain the rate-type electrolyte that takes into account long circulation.

[0068] Embodiment 11

[0069] The present embodiment provides a rate-type electrolyte that takes into account long cycle and a preparation method thereof. The rate-type electrolyte that takes into account long cycle includes the following components, measured in mass percentage: 20% of lithium salt (lithium tetrafluoroborate), 69% of non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 3:5:2), 5% of a first additive (vinylene carbonate), and 6% of a second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 5:1).

[0070] The preparation method of the rate-type electrolyte taking into account long cycle is as follows:

[0071] The preparation is carried out in a glove box. After ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are evenly mixed according to the formula, fully dried lithium tetrafluoroborate is added, and a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 5:1 is added, and then vinylene carbonate is added to obtain the rate-type electrolyte that takes into account long circulation.

[0072] Example 12

[0073] The present embodiment provides a rate-type electrolyte that takes into account a long cycle and a preparation method thereof. The only difference between the present embodiment and the embodiment 1 is that the mass percentage of the second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 4:1) is adjusted to 24%, and the mass percentage of the non-aqueous organic solvent (ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 3:5:2) is adjusted to 61.75%. The rest is the same as in the embodiment 1.

[0074] Comparative Example 1

[0075] This comparative example provides an electrolyte and a preparation method thereof, which is different from Example 1 only in that the second additive is not added, the mass percentage of the first additive (vinylene carbonate) is adjusted to 6.5%, and the rest is the same as Example 1.

[0076] Comparative Example 2

[0077] This comparative example provides an electrolyte and a preparation method thereof, which differs from Example 1 only in that the first additive is not added, the mass percentage of the second additive (a mixture of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene in a mass ratio of 4:1) is adjusted to 6.5%, and the rest is the same as Example 1.

[0078] Comparative Example 3

[0079] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that the second additive (a mixture of 1,3 - diallyl - 5 - methyl isocyanuric acid and 1 - thia - 2,4 - cyclopentadiene with a mass ratio of 4:1) is replaced with the same mass of 1,3 - diallyl - 5 - methyl isocyanuric acid, and the others are the same as in Example 1.

[0080] Comparative Example 4

[0081] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that the second additive (a mixture of 1,3 - diallyl - 5 - methyl isocyanuric acid and 1 - thia - 2,4 - cyclopentadiene with a mass ratio of 4:1) is replaced with the same amount of 1 - thia - 2,4 - cyclopentadiene, and the others are the same as in Example 1.

[0082] Comparative Example 5

[0083] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that 1,3 - diallyl - 5 - methyl isocyanuric acid is replaced with the same amount of vinylene sulfate, and the others are the same as in Example 1.

[0084] Comparative Example 6

[0085] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that the first additive is not added, 1 - thia - 2,4 - cyclopentadiene is not added, the mass percentage of 1,3 - diallyl - 5 - methyl isocyanuric acid is 6.5%, and the mass percentage of the non - aqueous organic solvent is adjusted to 79.75%, and the others are the same as in Example 1.

[0086] Comparative Example 7

[0087] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that the first additive is not added, 1,3 - diallyl - 5 - methyl isocyanuric acid is not added, the mass percentage of 1 - thia - 2,4 - cyclopentadiene is 6.5%, and the mass percentage of the non - aqueous organic solvent is adjusted to 79.75%, and the others are the same as in Example 1.

[0088] Comparative Example 8

[0089] This comparative example provides an electrolyte and a preparation method thereof. The difference from Example 1 is only that the second additive is not added, the mass percentage of the first additive is 0.5%, and the mass percentage of the non - aqueous organic solvent is adjusted to 85.75%, and the others are the same as in Example 1.

[0090] Comparative Example 9

[0091] This comparative example provides an electrolyte and its preparation method. The difference from Example 1 is only that the first additive and the second additive are not added, and the mass percentage of the non-aqueous organic solvent is adjusted to 86.25%, and the others are the same as in Example 1.

[0092] Comparative Example 10

[0093] This comparative example provides an electrolyte and its preparation method. The difference from Example 1 is only that 1,3-diallyl-5-methyl isocyanuric acid in the second additive is replaced with an equal amount of triallyl isocyanurate.

[0094] The rate-type electrolyte that takes into account long cycle life provided in the example and the electrolyte provided in the comparative example are made into lithium-ion batteries, and the following performance tests are carried out.

[0095] The preparation method of the lithium-ion battery is as follows:

[0096] The positive electrode uses a binder PVDF S5130, a composite conductive agent Super P / KS6 (mass ratio of Super P:KS6 = 2:1), a 523 nickel-cobalt-manganese ternary positive electrode material, and a solvent NMP. Among them, the mass ratio of the 523 nickel-cobalt-manganese ternary positive electrode material, the binder, and the composite conductive agent is 96:1.5:2.5. The positive electrode slurry is prepared by a wet pulping process, and the viscosity of the positive electrode slurry is adjusted to 10000 - 13000 mPa·s.

[0097] The artificial graphite negative electrode material (model: Shanshan P15), the conductive carbon black (Super P) conductive agent, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binder (model: Zeon BM-451B) are mixed according to a mass ratio of 95.9:0.4:1.5:2.1, and the solvent is H2O. The negative electrode slurry is prepared by a wet pulping process, and the viscosity of the negative electrode slurry is adjusted to 1500 - 3000 mPa·s.

[0098] Separator: Polypropylene separator, with a thickness of 26 μm.

[0099] Preparation of lithium-ion battery: The positive electrode slurry is coated on the aluminum foil and then dried to obtain the positive electrode sheet. The negative electrode slurry is coated on the copper foil and then dried to obtain the negative electrode sheet. The positive electrode sheet and the negative electrode sheet are respectively slit, rolled, cut, baked, tab welded, and tape pasted. Then the prepared positive and negative electrode sheets and the separator are wound together, and then placed in an aluminum-plastic shell to make a dry battery cell. The electrolyte is injected into the dry battery cell. After the injection is completed, the battery is sealed to obtain the lithium-ion soft-pack battery (LiNi0.5Co0.2Mn0.3O2 / artificial graphite).

[0100] (1) Rate discharge capacity retention rate: At room temperature, the lithium-ion battery (LiNi 0.5Co 0.2 Mn 0.3 O2 / artificial graphite), charge at a constant current and constant voltage of 1C (cut-off current is 0.05C) to 100% state of charge (SOC), discharge at a constant current of 2C and 3C rates, record the discharge capacity, and calculate the retention rate of the discharge capacity at different rates;

[0101] Retention rate of discharge capacity at 2C rate (%) = (Discharge capacity at 2C / Initial discharge capacity at 1C) × 100%.

[0102] Retention rate of discharge capacity at 3C rate (%) = (Discharge capacity at 3C / Initial discharge capacity at 1C) × 100%.

[0103] (2) Normal and high-temperature cycle performance: Charge at a constant current of 1C to 4.4V at a constant current and constant voltage (cut-off current is 0.05C), discharge at a constant current to 2.75V, and perform such charge and discharge cycles; Use a Neware test cabinet, place the lithium-ion battery in an environment of 25°C and 45°C. After such charge / discharge cycles, calculate the retention rate of the capacity after the corresponding number of cycles to evaluate its normal and high-temperature cycle performance;

[0104] The calculation formula for the retention rate of the capacity of the lithium-ion battery after cycling is as follows:

[0105] Retention rate of capacity = (Discharge capacity after cycling / First discharge capacity) × 100%. The test results are shown in Table 1 and Table 2.

[0106] Table 1

[0107]

[0108]

[0109] Table 2

[0110]

[0111]

[0112] According to the test results in Table 1 and Table 2, the retention rate of the discharge capacity at 2C rate of the lithium-ion battery prepared with the rate-type electrolyte considering long cycle life provided in Examples 1-11 is 88.02% - 93.66%, the retention rate of the discharge capacity at 3C rate is 89.18% - 92.97%, the retention rate of the capacity after 1000 cycles at 25°C is 80.80% - 89.80%, and the retention rate of the capacity after 600 cycles at 45°C is 80.10% - 85.20%.

[0113] The lithium-ion battery prepared by using the rate-type electrolyte with long cycle provided in Examples 1-6 has a 2C rate discharge capacity retention rate of 92.59% to 93.66%, a 3C rate discharge capacity retention rate of 92.12% to 92.97%, a capacity retention rate of 87.30% to 89.80% after 1000 cycles at 25°C, and a capacity retention rate of 82.70% to 85.20% after 600 cycles at 45°C.

[0114] Compared with Example 1, it can be seen that if the mass ratio of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene is reduced (Example 7), the density of the solid electrolyte interface film formed on the positive and negative electrode surfaces of the lithium ion battery decreases, resulting in a decrease in rate performance and cycle discharge capacity retention rate; if the mass ratio of 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene is increased (Example 8), the impedance of the manufactured lithium ion battery will increase, thereby affecting the rate and cycle discharge capacity retention rate.

[0115] Compared with Example 1, it can be seen that if the mass percentage of the second additive is too large (Example 12), the rate and cycle capacity retention rate of the obtained lithium ion battery decrease, which proves that when the mass percentage of the second additive is within a specific range, the lithium ion battery made of the rate-type electrolyte that takes into account long cycle performance is better.

[0116] Compared with Example 1, if the second additive is not added (Comparative Example 1) or the first additive is not added (Comparative Example 2), the rate and cycle capacity retention rate of the prepared lithium ion battery decrease; this proves that the second additive and the first additive are combined to obtain a lithium ion battery with a rate-type electrolyte that takes into account long cycles, and the performance is better.

[0117] Compared with Example 1, if 1-thia-2,4-cyclopentadiene is not added (Comparative Example 3) or 1,3-dipropylene-5-methylisocyanurate is not added (Comparative Example 4), the rate and cycle capacity retention rate of the prepared lithium ion battery decrease; it is proved that 1,3-dipropylene-5-methylisocyanurate and 1-thia-2,4-cyclopentadiene are combined as the second additive, and the lithium ion battery made of the rate-type electrolyte with long cycle performance is better.

[0118] Compared with Example 1, if 1,3-dipropylene-5-methyl isocyanurate is replaced with the same mass of vinyl sulfate (Comparative Example 5), the cycle performance of the prepared lithium ion battery decreases; the reason is that although vinyl sulfate can improve the rate performance of lithium ion batteries, it is easy to produce gas, which has a greater impact on long-cycle performance.

[0119] Compared with Example 1, if the first additive is not added and 1-thia-2,4-cyclopentadiene is not added (Comparative Example 6), the rate performance and the retention rate of the cycle capacity of the fabricated lithium-ion battery will decrease.

[0120] Compared with Example 1, if the first additive is not added and 1,3-diallyl-5-methylisocyanuric acid is not added (Comparative Example 7), the rate performance and the retention rate of the cycle discharge capacity of the fabricated lithium-ion battery will decrease.

[0121] Compared with Example 1, if the second additive is not added and the mass percentage of the first additive is 0.5% (Comparative Example 8), the rate performance and the retention rate of the cycle discharge capacity of the fabricated lithium-ion battery will decrease.

[0122] Compared with Example 1, if neither the first additive nor the second additive is added (Comparative Example 9), the rate performance and the retention rate of the cycle discharge capacity of the fabricated lithium-ion battery will decrease.

[0123] Compared with Example 1, if 1,3-diallyl-5-methylisocyanuric acid is replaced with an equal amount of triallyl isocyanurate, the rate performance and the retention rate of the cycle discharge capacity of the lithium-ion battery will decrease.

[0124] The applicant declares that the present invention uses the above examples to illustrate the lithium-ion battery electrolyte of the present invention and the lithium-ion battery containing the same. However, the present invention is not limited to the above examples, that is, it does not mean that the present invention must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, a first additive and a second additive, wherein the first additive includes vinylene carbonate, and the second additive includes a combination of 1,3-dipropylene-5-methyl isocyanate urea and a thiophene compound.

2. The lithium ion battery electrolyte according to claim 1, characterized in that: Taking the total mass of the lithium-ion battery electrolyte as 100%, the mass percentage content of the first additive is 0.5%-10%.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that: Taking the total mass of the lithium-ion battery electrolyte as 100%, the mass percentage content of the second additive is 1%-20%.

4. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that: The mass ratio of the 1,3-dipropylene-5-methyl isocyanate urea to the thiophene compound is 3-5:

1.

5. The lithium ion battery electrolyte according to any one of claims 1 to 4, characterized in that: The thiophene compound includes 1-thia-2,4-cyclopentadiene and / or diethyl 2-(thienylmethyl)phosphonate.

6. The lithium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The non-aqueous organic solvent includes any one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl acetate or tetrahydrofuran, or a combination of at least two thereof; Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the non-aqueous organic solvent is 50%-98%.

7. The lithium ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The lithium salt includes any one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium perchlorate or lithium dioxalatoborate, or a combination of at least two thereof; Preferably, based on the total mass of the lithium-ion battery electrolyte being 100%, the mass percentage content of the lithium salt is 0.5%-20%.

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises a battery housing, a battery cell and a lithium-ion battery electrolyte as claimed in any one of claims 1 to 7, and the battery cell comprises a positive electrode, a negative electrode and a separator or a solid electrolyte arranged between the positive electrode and the negative electrode.

9. The lithium-ion battery according to claim 8, characterized in that: The battery core and lithium-ion battery electrolyte are sealed in a battery housing; Preferably, the positive electrode comprises a positive electrode active material; Preferably, the positive electrode active material comprises LiNi x Co y Mn z L (1-x-y-z) O2、LiCo x’ L (1-x’) O2、LiNi x” L y’ Mn (2-x”-y’) O4 and Li z’ Any one or a combination of at least two of MPO4. Wherein, L is one or a combination of at least two of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe; M is one or a combination of at least two of Fe, Mn or Co, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤x+y+z≤1, 0≤x'≤1, 0.3≤x”≤0.6, 0.01≤y'≤0.2, 0.5≤z'≤1.

10. The lithium ion battery according to claim 8 or 9, characterized in that: The negative electrode includes a negative electrode active material; Preferably, the negative electrode active material comprises a silicon-based negative electrode active material and / or a carbon-based negative electrode active material; Preferably, the material of the diaphragm is any one of polypropylene, polyethylene, glass fiber, vinylon or nylon, or a combination of at least two thereof; Preferably, the solid electrolyte is made of any one of polypropylene, polyethylene, glass fiber, vinylon or nylon, or a combination of at least two of them.

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