High-voltage electrolyte and lithium ion battery

Abstract

The application relates to a high-voltage electrolyte and a lithium ion battery, and particularly relates to the field of lithium ion batteries. The high-voltage electrolyte comprises carbonates, fluorinated carbonates, vinylene carbonate, sodium bisfluorosulfonylimide, lithium salt additives and nitrile additives; the molar ratio of the vinylene carbonate and the sodium bisfluorosulfonylimide is 1:(2-4). The high-voltage electrolyte provided by the application improves the stability of the electrolyte under a voltage of greater than or equal to 4.6V by optimizing the electrolyte formula, utilizing the synergistic effect between the vinylene carbonate and the sodium bisfluorosulfonylimide, and simultaneously reducing the interface impedance and side reactions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically to a high-voltage electrolyte and a lithium-ion battery. Background Technology

[0002] Current research on high-voltage lithium-ion battery electrolytes mainly focuses on improving their oxidation stability at voltages above 4.5V.

[0003] In the prior art, carbonate-based electrolytes (such as ethylene carbonate / dimethyl carbonate) are widely used due to their low cost and high ionic conductivity. However, they are prone to solvent decomposition at high voltages (>4.3V), which leads to electrode interface degradation and the generation of gaseous byproducts (such as CO2 and C2H4), seriously affecting battery cycle life and safety.

[0004] To improve high-pressure stability, existing technologies propose using fluorinated solvents (such as fluoroethylene carbonate, FEC). Although FEC can suppress solvent oxidation by forming a dense SEI film, its low-temperature performance is significantly reduced, and excessive use will increase interfacial impedance.

[0005] Another solution is to add lithium salt additives (such as lithium bis(oxalato)borate, LiBOB). LiBOB can improve the high voltage tolerance of the electrolyte to above 4.5V, but its solubility in carbonate-based solvents is very limited and it cannot be used as the main salt.

[0006] In addition, some research has been conducted on nitrile compounds as electrolyte additives. For example, existing technologies use 1,3,6-hexanetrionitrile (HTCN) as an additive to improve the oxidation stability of the electrolyte, and adiponitrile as an additive to improve the stability of the high-voltage cathode interface. However, the optimal concentration range is narrow, and exceeding this range can easily lead to a sharp increase in the viscosity of the electrolyte, affecting the performance of conductivity and other properties.

[0007] In summary, current high-voltage electrolytes still suffer from drawbacks such as high interfacial impedance, susceptibility to deterioration, and poor stability. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of the present invention is to provide a high-voltage electrolyte and a lithium-ion battery to solve the defects of the current high-voltage electrolyte (≥4.7V) that still have high interfacial impedance, easy deterioration and poor stability.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a high-voltage electrolyte, the high-voltage electrolyte comprising:

[0011] Carbonates, fluorocarbonates, vinylene carbonate, sodium difluorosulfonamide, lithium salt additives, and nitrile additives;

[0012] The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:(2-4).

[0013] The high-voltage electrolyte provided by this invention improves the stability of the electrolyte at a voltage of ≥4.6V by optimizing the electrolyte formulation and utilizing the synergistic effect between vinylene carbonate and sodium difluorosulfonyl imide, while reducing interfacial impedance and side reactions.

[0014] As a preferred embodiment of the present invention, the volume ratio of carbonate to fluorocarbonate in the high-voltage electrolyte is 7:(3-5).

[0015] As a preferred embodiment of the present invention, the mass concentration of the vinylene carbonate is 0.5-1.5%.

[0016] As a preferred embodiment of the present invention, the mass concentration of lithium salt additive in the high-voltage electrolyte is 5-10%.

[0017] As a preferred embodiment of the present invention, the mass concentration of nitrile additives in the high-voltage electrolyte is 1-10%.

[0018] As a preferred embodiment of the present invention, the carbonate includes one or a combination of at least two of ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate.

[0019] Preferably, the fluorocarbonate includes one or a combination of at least two of the following: fluoroethylene carbonate, ethyl 2,2,2-trifluorobutyrate, difluoroethylene carbonate, or ethyl trifluoromethyl carbonate.

[0020] As a preferred embodiment of the present invention, the lithium salt additive includes one or a combination of at least two of LiPF6, LiDFOB, LiBF4, LiPO2F2 or LiFSI.

[0021] As a preferred embodiment of the present invention, the nitrile additives include one or a combination of at least two of the following: acetonitrile, propionitrile, acrylonitrile, valerate, glutaronitrile, adiponitrile, 1,3,5-pentanetricarbonyl nitrile, fluoroacetonitrile, chloroacetonitrile, n-butyronitrile, isobutyronitrile, benzonitrile, p-fluorobenzonitrile, isophthalonitrile, terephthalonitrile, 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, 2-methyl-3-butenonitrile, lauryl nitrile, myristonitrile, stearyl nitrile, or oleonitrile.

[0022] As a preferred embodiment of the present invention, the nitrile additive includes one or a combination of at least two of the following: 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, or 2-methyl-3-butenonitrile.

[0023] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising: the high-voltage electrolyte as described in the first aspect.

[0024] Compared with existing technical solutions, the present invention has the following beneficial effects:

[0025] (1) Significantly improved high-voltage stability: The synergistic effect of nitrile additives and fluorinated solvents effectively inhibits the oxidative decomposition of electrolyte at voltages above 4.7V, solves the problem of solvent instability under high-voltage conditions in the prior art, reduces the generation of by-products at the electrode interface (such as acidic substances and gases), significantly improves the reliability of long-term battery cycling, and while improving high-voltage stability, the introduction of nitrile additives does not have a negative impact on electrolyte conductivity and negative electrode compatibility, overcoming the defect of poor low-temperature performance of traditional fluorinated solvents.

[0026] (2) The organic layer formed by vinylene carbonate and the inorganic layer formed by sodium difluorosulfonyl imide form a gradient structure of "organic buffer layer-inorganic barrier layer" at the electrode interface: the vinylene carbonate film on the negative electrode side provides flexibility to adapt to volume changes, and the sodium difluorosulfonyl imide derivative film on the positive electrode side provides high-pressure antioxidant properties. The two together suppress interfacial side reactions, so that the electrolyte remains stable under high voltage above 4.6V.

[0027] (3) Reduced interfacial impedance: The optimized electrolyte can form a stable and dense interfacial film on the positive and negative electrode surfaces, reducing charge transport resistance and thus improving the rate performance and cycle efficiency of the battery.

[0028] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims. Detailed Implementation

[0029] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0030] While additives are currently used to improve the performance of lithium-ion battery electrolytes, their addition can lead to performance degradation, such as decreased stability, increased interfacial impedance, and side reactions during use. Therefore, this invention optimizes the electrolyte formulation to improve the performance of high-voltage electrolytes, as detailed below:

[0031] I. This embodiment provides a high-voltage electrolyte, which includes:

[0032] Carbonates, fluorocarbonates, vinylene carbonate, sodium difluorosulfonamide, lithium salt additives, and nitrile additives;

[0033] The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:(2-4).

[0034] The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:(2-4), for example, it can be 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8 or 1:4, but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0035] The volume ratio of carbonate to fluorocarbonate in the high-voltage electrolyte is 7:(3-5), for example, it can be 7:3, 7:3.2, 7:3.4, 7:3.6, 7:3.8, 7:4, 7:4.2, 7:4.4, 7:4.6, 7:4.8 or 7:5, but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0036] The mass concentration of the vinylene carbonate is 0.5-1.5%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0037] The mass concentration of lithium salt additive in the high-voltage electrolyte is 5-10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0038] The mass concentration of the nitrile additive in the high-voltage electrolyte is 1-10%, for example, it can be 1%, 1.9%, 2.8%, 3.7%, 4.6%, 5.5%, 6.4%, 7.3%, 8.2%, 9.1% or 10%, but is not limited to the listed values. Other unlisted values ​​within this range are also acceptable.

[0039] The carbonate includes one or a combination of at least two of ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate.

[0040] For example, the combination of carbonates may be selected as: a combination of ethylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and ethyl methyl carbonate, a combination of ethylene carbonate and ethyl methyl carbonate, etc.

[0041] The fluorocarbonate includes one or a combination of at least two of the following: fluoroethylene carbonate, ethyl 2,2,2-trifluorobutyrate, difluoroethylene carbonate, or ethyl trifluoromethyl carbonate.

[0042] In this invention, the combination of fluorocarbonates can be selected as: a combination of fluoroethylene carbonate and difluoroethylene carbonate, a combination of difluoroethylene carbonate and ethyl trifluoromethyl carbonate, a combination of fluoroethylene carbonate and ethyl trifluoromethyl carbonate, etc.

[0043] The lithium salt additives include one or a combination of at least two of LiPF6, LiDFOB, LiBF4, LiPO2F2 or LiFSI.

[0044] In this invention, the combination of lithium salt additives can be selected as: a combination of LiPF6 and LiDFOB, a combination of LiDFOB and LiBF4, a combination of LiBF4 and LiPO2F2, or a combination of LiPO2F2 and LiFSI.

[0045] The nitrile additives include one or a combination of at least two of the following: acetonitrile, propionitrile, acrylonitrile, valerate, glutaronitrile, adiponitrile, 1,3,5-pentanetricarbonyl nitrile, fluoroacetonitrile, chloroacetonitrile, n-butyronitrile, isobutyronitrile, benzonitrile, p-fluorobenzonitrile, isophthalonitrile, terephthalonitrile, 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, 2-methyl-3-butenonitrile, lauryl nitrile, myristonitrile, stearyl nitrile, or oleonitrile.

[0046] In this invention, the combination of nitrile additives can be selected from: a combination of acetonitrile and propionitrile, a combination of propionitrile and acrylonitrile, a combination of acrylonitrile and valeronitrile, a combination of valeronitrile and glutaronitrile, a combination of glutaronitrile and adiponitrile, a combination of adiponitrile and fluoroacetonitrile, a combination of fluoroacetonitrile and chloroacetonitrile, a combination of chloroacetonitrile and n-butyronitrile, a combination of n-butyronitrile and isobutyronitrile, a combination of isobutyronitrile and benzonitrile, a combination of p-fluorobenzonitrile and isophthalonitrile, a combination of terephthalonitrile and 1,2-diacetonitrile ethane, a combination of 1,5-dicyanopentane and 3-methoxypropionitrile, a combination of 2-methyl-3-butenonitrile and lauryl nitrile, a combination of myristonitrile and stearonitrile, a combination of oleonitrile and 1,5-dicyanopentane, etc. Preferably, the nitrile additives include one or a combination of at least two of 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, or 2-methyl-3-butenonitrile.

[0047] II. This embodiment provides a lithium-ion battery, which includes: a high-voltage electrolyte.

[0048] In this invention, the lithium-ion battery also includes other related materials, such as positive electrode materials, negative electrode materials, separators, etc., which can be designed based on existing technologies in the field.

[0049] III. To illustrate the electrochemical performance of the high-voltage electrolyte provided by this invention, the following examples are used for explanation:

[0050] Example 1

[0051] This embodiment provides a high-voltage electrolyte, as detailed below:

[0052] Carbonate (dimethyl carbonate), fluorocarbonate (difluoroethylene carbonate), vinylene carbonate, sodium difluorosulfonamide, lithium salt additive (LiPF6 and LiDFOB in a molar ratio of 10:1) and nitrile additive (1,5-dicyanopentane).

[0053] The volume ratio of carbonate to fluorocarbonate is 7:3;

[0054] The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:3; the mass concentration of the vinylene carbonate is 1%.

[0055] The mass concentration of the lithium salt additive is 8%;

[0056] The mass concentration of the nitrile additive is 3%.

[0057] Example 2

[0058] This embodiment provides a high-voltage electrolyte, as detailed below:

[0059] Carbonate (dimethyl carbonate), fluorocarbonate (fluoroethylene carbonate and ethyl trifluoromethyl carbonate in a volume ratio of 1:1), vinylene carbonate, sodium difluorosulfonyl imide, lithium salt additive (LiPF6 and LiBF4 in a molar ratio of 20:1) and nitrile additive (glutaronitrile).

[0060] The volume ratio of carbonate to fluorocarbonate is 7:4.7;

[0061] The molar ratio of vinylene carbonate to sodium difluorosulfonamide is 1:2; the mass concentration of the vinylene carbonate is 1.5%.

[0062] The mass concentration of the lithium salt additive is 5%;

[0063] The mass concentration of the nitrile additive is 4%.

[0064] Example 3

[0065] This embodiment provides a high-voltage electrolyte, as detailed below:

[0066] Carbonates (ethyl methyl carbonate), fluorocarbonates (fluoroethylene carbonate and ethyl 2,2,2-trifluorobutyrate in a volume ratio of 2:1), vinylene carbonate, sodium difluorosulfonyl imide, lithium salt additive (LiPF6), and nitrile additives (1,3,5-pentanetricarbonyl).

[0067] The volume ratio of carbonate to fluorocarbonate is 7:3;

[0068] The molar ratio of vinylene carbonate to sodium difluorosulfonamide is 1:4; the mass concentration of the vinylene carbonate is 0.5%.

[0069] The mass concentration of the lithium salt additive is 10%;

[0070] The mass concentration of the nitrile additive is 2%.

[0071] Example 4

[0072] This embodiment provides a high-voltage electrolyte, as detailed below:

[0073] Carbonates (ethylene carbonate), fluorocarbonates (difluoroethylene carbonate), vinylene carbonate, sodium difluorosulfonamide, lithium salt additives (LiFSI), and nitrile additives (2-methyl-3-butenonitrile).

[0074] The volume ratio of carbonate to fluorocarbonate is 7:4;

[0075] The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:3; the mass concentration of the vinylene carbonate is 1.5%.

[0076] The mass concentration of the lithium salt additive is 8%;

[0077] The mass concentration of nitrile additives is 5%.

[0078] Example 5

[0079] The only difference from Example 1 is that the volume ratio of carbonate to fluorocarbonate in the high-voltage electrolyte is 3:7.

[0080] Example 6

[0081] The only difference from Example 1 is that the mass concentration of the nitrile additive in the high-voltage electrolyte is 0.5%.

[0082] Example 7

[0083] The only difference from Example 1 is that the mass concentration of the nitrile additive in the high-voltage electrolyte is 15%.

[0084] Example 8

[0085] The only difference from Example 1 is that the mass concentration of vinylene carbonate in the high-voltage electrolyte is 0.1%.

[0086] Example 9

[0087] The only difference from Example 1 is that the mass concentration of vinylene carbonate in the high-voltage electrolyte is 2%.

[0088] Example 10

[0089] The only difference from Example 2 is that the glutaronitrile in the high-voltage electrolyte is replaced with an equal amount of 3-methoxypropionitrile.

[0090] Example 11

[0091] The only difference from Example 3 is that the 1,3,5-pentanetricarbonitrile in the high-voltage electrolyte is replaced with an equal amount of 1,2-diacetonitrile ethane.

[0092] Comparative Example 1

[0093] The only difference from Example 1 is that the carbonate is replaced with an equal amount of fluorocarbonate.

[0094] Comparative Example 2

[0095] The only difference from Example 1 is that the fluorocarbonate is replaced with an equal amount of carbonate.

[0096] Comparative Example 3

[0097] The only difference from Example 1 is that the high-voltage electrolyte does not contain vinylene carbonate.

[0098] Comparative Example 4

[0099] The only difference from Example 1 is that the high-voltage electrolyte does not contain sodium difluorosulfonamide.

[0100] Comparative Example 5

[0101] The only difference from Example 1 is that the molar ratio of vinylene carbonate and sodium difluorosulfonyl imide is 1:1.

[0102] Comparative Example 6

[0103] The only difference from Example 1 is that the molar ratio of vinylene carbonate and sodium difluorosulfonyl imide is 1:7.

[0104] Comparative Example 7

[0105] The only difference from Example 1 is that vinylene carbonate is replaced with an equal amount of 1,3-propanesulfonate lactone.

[0106] Comparative Example 8

[0107] The only difference from Example 1 is that the nitrile additive is replaced with an equal amount of acetamide.

[0108] Comparative Example 9

[0109] The only difference from Example 1 is that the nitrile additive is replaced with an equal amount of tri-n-propylphosphonic anhydride.

[0110] Comparative Example 10

[0111] The only difference from Example 1 is that the nitrile additive is replaced with an equal amount of N,N-dimethyltrifluoroacetamide.

[0112] Comparative Example 11

[0113] The only difference from Example 1 is that the fluorocarbonate is replaced with an equal amount of N,N-dimethyltrifluoroacetamide.

[0114] The high-voltage electrolytes obtained in the above embodiments and comparative examples were subjected to cyclic voltammetry and AC impedance tests. Graphite||NCM811 batteries were assembled using the obtained high-voltage electrolytes, with a cutoff voltage of 4.7V, and 1C and 5C charge-discharge cycle tests were performed. The results are detailed in Table 1 below.

[0115] Table 1

[0116]

[0117] As shown in Table 1, the solution provided by the present invention improves the stability of the electrolyte at a voltage of ≥4.7V by optimizing the electrolyte formulation and utilizing the synergistic effect between vinylene carbonate and sodium difluorosulfonyl imide, while reducing interfacial impedance and side reactions.

[0118] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0119] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0120] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A high-voltage electrolyte, characterized in that, The high-voltage electrolyte comprises: Carbonates, fluorocarbonates, vinylene carbonate, sodium difluorosulfonamide, lithium salt additives, and nitrile additives; The molar ratio of vinylene carbonate to sodium difluorosulfonyl imide is 1:(2-4).

2. The high-voltage electrolyte as described in claim 1, characterized in that, The volume ratio of carbonate to fluorocarbonate in the high-voltage electrolyte is 7:(3-5).

3. The high-voltage electrolyte as described in claim 1, characterized in that, The mass concentration of the vinylene carbonate is 0.5-1.5%.

4. The high-voltage electrolyte as described in claim 1, characterized in that, The mass concentration of lithium salt additive in the high-voltage electrolyte is 5-10%.

5. The high-voltage electrolyte as described in claim 1, characterized in that, The mass concentration of nitrile additives in the high-voltage electrolyte is 1-10%.

6. The high-voltage electrolyte as described in claim 1, characterized in that, The carbonate includes one or a combination of at least two of ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate. The fluorocarbonate includes one or a combination of at least two of the following: fluoroethylene carbonate, ethyl 2,2,2-trifluorobutyrate, difluoroethylene carbonate, or ethyl trifluoromethyl carbonate.

7. The high-voltage electrolyte as described in claim 1, characterized in that, The lithium salt additives include one or a combination of at least two of LiPF6, LiDFOB, LiBF4, LiPO2F2, or LiFSI.

8. The high-voltage electrolyte as described in claim 1, characterized in that, The nitrile additives include one or a combination of at least two of the following: acetonitrile, propionitrile, acrylonitrile, valerate, glutaronitrile, adiponitrile, 1,3,5-pentanetricarbonyl, fluoroacetonitrile, chloroacetonitrile, n-butyronitrile, isobutyronitrile, benzonitrile, p-fluorobenzonitrile, isophthalonitrile, terephthalonitrile, 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, 2-methyl-3-butenonitrile, lauryl nitrile, myristonitrile, stearyl nitrile, or oleonitrile.

9. The high-voltage electrolyte as described in claim 8, characterized in that, The nitrile additives include one or a combination of at least two of the following: 1,2-diacetonitrile ethane, 1,5-dicyanopentane, 3-methoxypropionitrile, or 2-methyl-3-butenonitrile.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes: the high-voltage electrolyte as described in any one of claims 1-9.

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