Preparation Method of Electrolyte for Lithium-Ion Fast Charging Battery

Abstract

The present invention discloses an electrolyte for a lithium-ion fast-charging battery, which comprises a solvent, a lithium salt and an additive; the additive comprises at least one of benzonitrile compounds having the structure shown in Formula I, wherein n is an integer from 0 to 3; the present invention uses fluoroethylene carbonate, an organic substance containing a fluorine element additive, as a fast-charging film-forming additive for the lithium-ion electrolyte. This additive has a lower oxidation potential and can form a dense and stable interfacial film on the surface of the positive electrode during the first charging process, optimizing the surface of the positive electrode, inhibiting the generation of HF, reducing the oxidative decomposition of substances on the electrode surface and the electrolyte, and effectively ensuring the cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of fast - charging electrolytes, in particular to an electrolyte for a lithium - ion fast - charging battery and a preparation method thereof. Background Art

[0002] Currently, lithium - ion batteries have been widely used in tools such as mobile phones and electric vehicles. However, the battery life of these tools is generally short, and users need to charge frequently. If the charging time is long, it will not only reduce the user experience but also make it difficult for users to accept these new - energy products. Therefore, the length of the charging time is crucial for the popularization of new - energy tools.

[0003] When the charging rate of a lithium - ion battery is too fast, the temperature rise inside the battery will be much greater than that of a slow - charging battery. When the temperature of the lithium - ion battery is too high, polarization will occur, leading to problems such as lithium deposition and increased internal resistance. This not only reduces the battery capacity and cycle life but also generates excessive heat, affecting the charging efficiency and safety. As an important component of a lithium - ion battery, the electrolyte runs through the entire battery and plays a decisive role in the battery performance. Currently, most of the electrolytes used are lithium hexafluorophosphate (LiPF6) dissolved in a carbonate - based solvent system. This system cannot effectively guarantee its own performance and service life in a fast - charging environment. Due to insufficient power performance, it will exacerbate the decomposition of the electrolyte solvent during fast charging, leading to a series of side reactions, such as the decomposition of the lithium - layered transition metal oxide cathode material, causing irreversible damage to the battery. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an electrolyte for a lithium - ion fast - charging battery and a preparation method thereof.

[0005] The purpose of the present invention is achieved through the following technical solutions: An electrolyte for a lithium - ion fast - charging battery includes a solvent, a lithium salt, and an additive; the additive includes at least one of the phthalonitrile compounds having the structure shown in Formula I,

[0006]

[0007] where n is an integer from 0 to 3; if the carbon chain is too long, the viscosity will be too large, which is not conducive to ion transport. Therefore, it is better when the number of methyl groups is from 0 to 3.

[0008] The phthalonitrile compound is 5 - methyl - 1,3 - phthalodinitrile;

[0009] The solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate;

[0010] The lithium salt is lithium hexafluorophosphate;

[0011] The additive further includes a film-forming additive; the film-forming additive includes one or both of fluoroethylene carbonate and vinylene carbonate;

[0012] The additive further includes other additives; the other additives include one or more of 1,3-propane sultone, biphenyl, lithium difluorooxalate borate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide;

[0013] The present invention also provides a method for preparing an electrolyte for a lithium-ion fast-charging battery, including the following steps: preparing a solvent; adding a lithium salt at a temperature of 10-15°C; adding an optional additive; adding a benzonitrile compound having the structure shown in Formula I, and the addition amount accounts for 2-5% of the total mass of the electrolyte;

[0014] The step of preparing the solvent is: adding 20-25 parts of ethylene carbonate, then adding 65-70 parts of dimethyl carbonate, stirring for 25-35 min until the ethylene carbonate is completely dissolved, and then adding 8-15 parts of ethyl methyl carbonate, stirring for 25-35 min until uniformly mixed, and obtaining the solvent after purification and impurity removal;

[0015] The step of adding the lithium salt is: adding lithium hexafluorophosphate in an amount of 1-1.5 mol / L, and adding lithium hexafluorophosphate to the solvent at a rate of 5-15 g / min, while continuously stirring the solvent during the process;

[0016] A further technical solution is that the step of adding the additive is: adding 2-4 parts of fluoroethylene carbonate and 3-5 parts of vinylene carbonate, stirring for 25-35 min; the other additives added also include one or more of 0.5-1.5 parts of 1,3-propane sultone, 1-2 parts of biphenyl, 0.5-1 part of lithium difluorooxalate borate, 0.5-1 part of lithium difluorophosphate, and 0.5-1 part of lithium bis(fluorosulfonyl)imide.

[0017] The present invention has the following advantages:

[0018] 1. The present invention uses the organic compound fluoroethylene carbonate containing a fluorine element additive as a fast-charging film-forming additive for a lithium-ion electrolyte. This additive has a lower oxidation potential and can form a dense and stable interfacial film on the surface of the positive electrode during the first charging process, optimizing the surface of the positive electrode, inhibiting the generation of HF, reducing the oxidative decomposition of substances on the electrode surface and the electrolyte, and effectively ensuring the cycle performance of the battery.

[0019] 2. The present invention uses benzenedicarbonitrile as a fast - charging additive for lithium - ion electrolytes because the nitrile group in this additive can effectively improve the conductivity of carbonate - based electrolytes, and the phenyl group can enhance the stability of the electrolyte and slow down the decomposition of the electrolyte. Through comparison, it is found that when the nitrile group is in the meta - position on the benzene ring, the ion transport speed in the electrolyte is faster, which is beneficial to improving the fast - charging performance and cycling performance of the battery.

[0020] 3. At the same time, an alkyl group is also substituted at the meta - position of the benzene ring. Compared with no alkyl substitution, it is more conducive to the ion transport speed in the electrolyte and is beneficial to improving the fast - charging performance and cycling performance of the battery.

[0021] 4. The present invention preferably uses 5 - methyl - 1,3 - benzenedicarbonitrile as a fast - charging additive for lithium - ion electrolytes.

[0022] 5. Preferably, the solvent of the present invention is selected from one or more of ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate. Among them, ethylene carbonate has an extremely high dielectric constant, which can bring extremely high conductivity and is beneficial to high - rate discharge. The melting point of ethyl methyl carbonate is about - 55°C, which has excellent low - temperature performance and can be used as a temperature regulator. Dimethyl carbonate has a relatively high dielectric constant and a low viscosity, which can also bring high conductivity, but its boiling point is about 90°C, and it is easy to evaporate and gasify at high temperatures, resulting in swelling, so dimethyl carbonate is not considered for use in soft - pack batteries. Diethyl carbonate has slightly poor conductivity, but it can bring better temperature adaptability, so it is used as a regulating solvent in soft - pack batteries.

[0023] 6. Preferably, 1,3 - propane sultone can be added to the additive to improve the storage performance of the battery; biphenyl can be added to improve the over - charge performance of the battery; lithium difluorooxalate borate can be added to improve the cycling performance of the battery; lithium difluorophosphate can be added to meet the low - temperature discharge performance of the battery; lithium bis(fluorosulfonyl)imide can be added to meet the 15C ultra - high rate of the battery. Description of the Drawings

[0024] Figure 1 Shows the influence results of different electrolyte ratios on the internal resistance of the battery.

[0025] Figure 2 Shows the influence results of different electrolyte ratios on the battery capacity.

[0026] Figure 3 Shows the influence results of different electrolyte ratios on the cycling performance of the battery.

[0027] Figure 4 Shows the influence results of different electrolyte ratios on the fast - charging performance of the battery. Detailed Embodiments

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0030] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0031] It should be noted that like reference numerals and letters denote like items in the following accompanying drawings. Therefore, once an item is defined in one accompanying drawing, it does not need to be further defined and explained in subsequent accompanying drawings.

[0032] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship when the product of this invention is normally placed, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive distinction and cannot be understood as indicating or implying relative importance.

[0033] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] Example 1: A lithium-ion fast-charging battery electrolyte, comprising a solvent, a lithium salt, and an additive; the additive comprises at least one of the benzonitrile compounds having the structure shown in Formula I,

[0035]

[0036] wherein n is an integer from 0 to 3;

[0037] The benzonitrile compound is 5-methyl-1,3-benzenediacetonitrile;

[0038] The solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate;

[0039] The lithium salt is lithium hexafluorophosphate;

[0040] The additive further comprises a film-forming additive; the film-forming additive comprises fluorinated ethylene carbonate and vinylene carbonate;

[0041] The additive further comprises other additives; the other additives comprise one or more of 1,3-propane sultone, biphenyl, lithium difluorooxalate borate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide.

[0042] In this example, the organic compound fluorinated ethylene carbonate containing a fluorine element additive is used as a fast-charging film-forming additive for the lithium-ion electrolyte. This additive has a lower oxidation potential and can form a dense and stable interfacial film on the surface of the positive electrode during the first charging process, optimizing the surface of the positive electrode, inhibiting the generation of HF, reducing the oxidative decomposition of the substances on the electrode surface and the electrolyte, and effectively ensuring the cycle performance of the battery.

[0043] In this example, benzenediacetonitrile is used as a fast-charging additive for the lithium-ion electrolyte because the nitrile group in this additive can effectively improve the conductivity of carbonate-based electrolytes, and the phenyl group can improve the stability of the electrolyte and slow down the decomposition of the electrolyte; through comparison, it is found that when the nitrile group is in the meta position on the benzene ring, the ion transport speed in the electrolyte is faster, which is beneficial to improving the fast-charging performance and cycle performance of the battery;

[0044] In this example, an alkyl group is also substituted at the meta position of the benzene ring, which is more beneficial to the ion transport speed in the electrolyte and is beneficial to improving the fast-charging performance and cycle performance of the battery compared with no alkyl substitution;

[0045] In this example, 5-methyl-1,3-benzenediacetonitrile is preferably used as a fast-charging additive for the lithium-ion electrolyte;

[0046] In this embodiment, the solvent is selected from one or more of ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate. Among them, ethylene carbonate has an extremely high dielectric constant, which can bring extremely high conductivity and is beneficial to high-rate discharge. The melting point of ethyl methyl carbonate is about -55°C, and it has excellent low-temperature performance and can be used as a temperature regulator. Dimethyl carbonate has a relatively high dielectric constant and a low viscosity, which can also bring high conductivity. However, its boiling point is about 90°C, and it is easy to evaporate and gasify at high temperatures, resulting in bloating. Therefore, dimethyl carbonate is not considered for use in soft-pack batteries. The conductivity of diethyl carbonate is slightly poor, but it can bring better temperature adaptability. Therefore, it is used as a regulating solvent in soft-pack batteries.

[0047] In this embodiment, 1,3-propane sultone can also be added to the additive to improve the storage performance of the battery; biphenyl can also be added to the additive to improve the overcharge performance of the battery; lithium difluorooxalate borate can also be added to the additive to improve the cycle performance of the battery; lithium difluorophosphate can also be added to the additive to meet the low-temperature discharge performance of the battery; lithium bis(fluorosulfonyl)imide can also be added to the additive to meet the 15C ultra-high rate

[0048] Example 2: A method for preparing a fast-charging electrolyte includes the following steps: preparing a solvent; adding a lithium salt at a temperature of 10-15°C; adding a film-forming additive; adding a phthalonitrile compound with the structure shown in Formula I, and the addition amount accounts for 2-5% of the total mass;

[0049] The step of preparing the solvent is as follows: add 20-25 parts of ethylene carbonate, then add 65-70 parts of dimethyl carbonate, stir for 25-35 minutes until the ethylene carbonate is completely dissolved, then add 8-15 parts of ethyl methyl carbonate, and stir for 25-35 minutes until evenly mixed. After purification and impurity removal, the solvent is obtained;

[0050] The step of adding the lithium salt is as follows: add lithium hexafluorophosphate in an amount of 1-1.5 mol / L, and add lithium hexafluorophosphate to the solvent at a rate of 5-15 g / min, and keep the solvent stirring continuously throughout the process;

[0051] The step of adding the additive is as follows: add 2-4 parts of fluorinated ethylene carbonate and 3-5 parts of vinylene carbonate, and stir for 25-35 minutes;

[0052] Other additives added also include one or more of 0.5-1.5 parts of 1,3-propane sultone, 1-2 parts of biphenyl, 0.5-1 part of lithium difluorooxalate borate, 0.5-1 part of lithium difluorophosphate, and 0.5-1 part of lithium bis(fluorosulfonyl)imide.

[0053] Example 2: A method for preparing a fast-charging electrolyte includes the following steps: preparing a solvent; adding a lithium salt at a temperature of 10-15 °C; adding a film-forming additive; adding a benzonitrile compound having the structure shown in Formula I, and the addition amount accounts for 2-5% of the total mass;

[0054] The step of preparing the solvent is as follows: adding 20-25 parts of ethylene carbonate, then adding 65-70 parts of dimethyl carbonate, stirring for 25-35 min until all the ethylene carbonate is dissolved, then adding 8-15 parts of ethyl methyl carbonate, and stirring for 25-35 min until evenly mixed, and obtaining the solvent after purification and impurity removal;

[0055] The step of adding the lithium salt is as follows: adding lithium hexafluorophosphate in an amount of 1-1.5 mol / L, and adding lithium hexafluorophosphate to the solvent at a rate of 5-15 g / min, and continuously stirring the solvent throughout the process;

[0056] The step of adding the additive is as follows: adding 2-4 parts of fluoroethylene carbonate and 3-5 parts of vinylene carbonate, and stirring for 25-35 min;

[0057] Other additives added also include one or more of 0.5-1.5 parts of 1,3-propane sultone, 1-2 parts of biphenyl, 0.5-1 part of lithium difluorooxalate borate, 0.5-1 part of lithium difluorophosphate, and 0.5-1 part of lithium bis(fluorosulfonyl)imide;

[0058] Example 3: A method for preparing a fast-charging electrolyte includes the following steps: preparing a solvent; adding a lithium salt at a temperature of 10 °C; adding a film-forming additive; adding a benzonitrile compound having the structure shown in Formula I, and the addition amount accounts for 2% of the total mass;

[0059] The step of preparing the solvent is as follows: adding 20 parts of ethylene carbonate, then adding 65 parts of dimethyl carbonate, stirring for 25 min until all the ethylene carbonate is dissolved, then adding 8 parts of ethyl methyl carbonate, and stirring for 25 min until evenly mixed, and obtaining the solvent after purification and impurity removal;

[0060] The step of adding the lithium salt is as follows: adding lithium hexafluorophosphate in an amount of 1 mol / L, and adding lithium hexafluorophosphate to the solvent at a rate of 5 g / min, and continuously stirring the solvent throughout the process;

[0061] The step of adding the additive is as follows: adding 2 parts of fluoroethylene carbonate and 3 parts of vinylene carbonate, and stirring for 25 min;

[0062] Other additives added also include one or more of 0.5 part of 1,3-propane sultone, 1 part of biphenyl, 0.5 part of lithium difluorooxalate borate, 0.5 part of lithium difluorophosphate, and 0.5 part of lithium bis(fluorosulfonyl)imide;

[0063] Example 4: A preparation method of a fast-charging electrolyte includes the following steps: preparing a solvent; adding a lithium salt at a temperature of 15°C; adding a film-forming additive; adding a benzonitrile compound having the structure shown in Formula I, and the addition amount accounts for 5% of the total mass;

[0064] The step of preparing the solvent is as follows: adding 25 parts of ethylene carbonate, then adding 70 parts of dimethyl carbonate, stirring for 35 min until all the ethylene carbonate is dissolved, adding 15 parts of ethyl methyl carbonate, and stirring for 35 min until evenly mixed, and obtaining the solvent after purification and impurity removal;

[0065] The step of adding the lithium salt is as follows: adding lithium hexafluorophosphate in an amount of 1.5 mol / L, and adding lithium hexafluorophosphate to the solvent at a rate of 15 g / min, and continuously stirring the solvent throughout the process;

[0066] The step of adding the additive is as follows: adding 4 parts of fluoroethylene carbonate and 5 parts of vinylene carbonate and stirring for 35 min;

[0067] Other additives added also include one or more of 1.5 parts of 1,3-propane sultone, 2 parts of biphenyl, 1 part of lithium difluorooxalate borate, 1 part of lithium difluorophosphate, and 1 part of lithium bis(fluorosulfonyl)imide;

[0068] Example 5: A steel shell battery, with a positive electrode of lithium nickel cobalt manganate (Ni:Co:Mn = 5:2:3), a negative electrode of artificial graphite, a capacity of 2000 mAh, a rate of 1C, an injection volume of 5.6 ± 0.15 g, and the following 5 sets of schemes are adopted. 10 batteries are made for each scheme to test the battery performance.

[0069] Scheme 1: 20% ethylene carbonate, 65% dimethyl carbonate, 10% ethyl methyl carbonate, 1.45 mol / L lithium hexafluorophosphate, 3% vinylene carbonate, 2% fluoroethylene carbonate.

[0070] Scheme 2: 20% ethylene carbonate, 65% dimethyl carbonate, 10% ethyl methyl carbonate, 1.45 mol / L lithium hexafluorophosphate, 1% vinylene carbonate, 1% fluoroethylene carbonate, 3% 5-methyl-1,3-benzenediacetonitrile.

[0071] Scheme 3: 20% ethylene carbonate, 65% dimethyl carbonate, 10% ethyl methyl carbonate, 1.45 mol / L lithium hexafluorophosphate, 1% vinylene carbonate, 2% fluoroethylene carbonate, 2% 5-methyl-1,3-benzenediacetonitrile.

[0072] Scheme 4: 20% ethylene carbonate, 65% dimethyl carbonate, 10% ethyl methyl carbonate, 1.45 mol / L lithium hexafluorophosphate, 1% vinylene carbonate, 2% fluoroethylene carbonate, 1% 1,3 - propane sultone, 1% 5 - methyl - 1,3 - benzenediacetonitrile.

[0073] Scheme 5: 20% ethylene carbonate, 65% dimethyl carbonate, 10% ethyl methyl carbonate, 1.45 mol / L lithium hexafluorophosphate, 1% vinylene carbonate, 1% fluoroethylene carbonate, 1% lithium difluoro(oxalato)borate, 2% 5 - methyl - 1,3 - benzenediacetonitrile.

[0074] According to the appendix Figure 1 Based on the results, it can be seen that after formation, the internal resistance of Scheme 1 is the largest. The reason is that the film formed by vinylene carbonate is relatively thick, increasing the impedance of the SEI film, which is manifested as an increase in the battery internal resistance. In Scheme 2, the content of vinylene carbonate decreases, and the internal resistance decreases significantly. In Scheme 4, due to the addition of 1,3 - propane sultone, the internal resistance is slightly higher than that of Scheme 2. The reason is that the film - forming characteristics of 1,3 - propane sultone are very similar to those of vinylene carbonate, and the SEI film is relatively thick. The internal resistance of Scheme 3 is slightly reduced compared to Scheme 2. The reason is that the resistance value of 5 - methyl - 1,3 - benzenediacetonitrile is relatively large, and as its content decreases, the resistance value also decreases. The internal resistance of Scheme 5 is the lowest. The reason is that due to the special film - forming component of lithium difluoro(oxalato)borate, the film formed by lithium difluoro(oxalato)borate is thinner, the rate performance is higher, and the internal resistance is relatively lower.

[0075] According to the appendix Figure 2 Based on the results, it can be seen that in terms of capacity, there is almost no difference among the five groups of schemes. The lithium salts used in this experiment are all 1.45 mol / L. Under the condition of sufficient lithium salts, the main influencing factor of capacity is the positive and negative electrode materials. Therefore, the capacity differences among the five groups of schemes are not significant.

[0076] According to the appendix Figure 3 Based on the results, it can be seen that for the 1C charge and 1C discharge cycle of 300 weeks, the performances of Scheme 2, Scheme 3, Scheme 4, and Scheme 5 all exceed that of Scheme 1, indicating that the scheme proposed in this patent to add 5 - methyl - 1,3 - benzenediacetonitrile has no impact on the battery cycle and meets the cycle requirements. At the same time, Scheme 5 has the best cycle performance, indicating that lithium difluoro(oxalato)borate significantly improves the cycle performance.

[0077] According to the appendix Figure 4 Based on the results, it can be seen that for each group of schemes, the same batteries are taken for fast - charge testing. Charge at 1C for 30 min and check the proportion of the capacity charged into the battery. In Scheme 2, about 75% of the total capacity is charged within 30 min, with the best effect. In Scheme 5, about 72% is charged. The capacity charged in Scheme 3 and Scheme 4 has little difference, both reaching about 63%. Scheme 1 does not meet the basic requirements of fast - charge without adding 5 - methyl - 1,3 - benzenediacetonitrile.

[0078] Experiments show that the electrolytes used in the above Schemes II, III, IV, and V can all be used as fast-charging electrolytes for lithium-ion batteries. When assembled into nickel-cobalt-manganese ternary and graphite batteries, they have good cycling performance and a high capacity retention rate.

[0079] Example 6: Influence of the structure of benzonitrile compounds on the fast-charging performance of batteries.

[0080] Comparative Example 1: The electrolyte and battery were prepared in the same manner as in Scheme II, except that the benzonitrile compound used was 1,3-benzenedicarbonitrile.

[0081] Comparative Example 2: The electrolyte and battery were prepared in the same manner as in Scheme II, except that the benzonitrile compound used was 3-methyl-1,2-benzenedicarbonitrile.

[0082] Comparative Example 3: The electrolyte and battery were prepared in the same manner as in Scheme II, except that the benzonitrile compound used was pentamethyl-1,3-dicyanobenzene.

[0083] Comparative Example 4: The electrolyte and battery were prepared in the same manner as in Scheme II, except that the benzonitrile compound used was 2,5-dicyanotoluene.

[0084] The battery performance of Comparative Examples 1-4 is shown in Table 1 below.

[0085] Table 1 Battery performance of Comparative Examples 1-4

[0086]

[0087] It can be seen from the results in Table 1 that in Comparative Examples 1-4, the ion transport ability in the electrolyte is not strong, which affects the capacity performance, cycling performance, and fast-charging performance of the battery. The fast-charging performance of Comparative Examples 1-4 cannot meet the basic requirements, and both the battery capacity and cycling performance cannot meet the requirements.

[0088] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion fast-charging battery electrolyte, characterized in that: it includes a solvent, a lithium salt, and an additive; the additive includes at least one of the benzonitrile compounds having the structure shown in Formula I below, where n is an integer from 0 to 3.

2. The lithium-ion fast-charging battery electrolyte according to claim 1, characterized in that: the benzonitrile compound is 5-methyl-1,3-benzenedicarbonitrile.

3. The lithium-ion fast-charging battery electrolyte according to claim 1, characterized in that: the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate.

4. The lithium-ion fast-charging battery electrolyte according to claim 1, characterized in that: the lithium salt is lithium hexafluorophosphate.

5. The lithium-ion fast-charging battery electrolyte according to claim 1, characterized in that: the additive further includes a film-forming additive; the film-forming additive includes one or two of fluoroethylene carbonate and vinylene carbonate.

6. The lithium-ion fast-charging battery electrolyte according to claim 5, characterized in that: the additive further includes other additives; the other additives include one or more of 1,3-propane sultone, biphenyl, lithium difluorooxalate borate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide.

7. A preparation method of the lithium-ion fast-charging battery electrolyte based on claim 6, characterized in that, it includes the following steps: preparing the solvent; adding the lithium salt at a temperature of 10 - 15 °C; adding the film-forming additive and other additives; adding the benzonitrile compound having the structure shown in Formula I, and the addition amount accounts for 2 - 5% of the total mass of the electrolyte.

8. The preparation method of the lithium-ion fast-charging battery electrolyte according to claim 7, characterized in that, the step of preparing the solvent is: adding 20 - 25 parts of ethylene carbonate, then adding 65 - 70 parts of dimethyl carbonate, stirring for 25 - 35 min until the ethylene carbonate is completely dissolved, then adding 8 - 15 parts of ethyl methyl carbonate, stirring for 25 - 35 min until evenly mixed, and obtaining the solvent after purification and impurity removal.

9. The preparation method of the lithium-ion fast-charging battery electrolyte according to claim 7, characterized in that, the step of adding the lithium salt is: adding lithium hexafluorophosphate in an amount of 1 - 1.5 mol / L, and adding lithium hexafluorophosphate to the solvent at a rate of 5 - 15 g / min, and keeping the solvent constantly stirred throughout the process.

10. The preparation method of the lithium-ion fast-charging battery electrolyte according to claim 7, characterized in that, the step of adding the film-forming additive is: adding 2 - 4 parts of fluoroethylene carbonate and 3 - 5 parts of vinylene carbonate and stirring for 25 - 35 min; the other additives added also include one or more of 0.5 - 1.5 parts of 1,3-propane sultone, 1 - 2 parts of biphenyl, 0.5 - 1 part of lithium difluorooxalate borate, 0.5 - 1 part of lithium difluorophosphate, and 0.5 - 1 part of lithium bis(fluorosulfonyl)imide.

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