Electrolyte, lithium ion battery and vehicle

Abstract

The invention provides an electrolyte, a lithium ion battery and a vehicle, and belongs to the technical field of secondary batteries. The electrolyte comprises a lithium salt, an additive and a non-aqueous solvent, the additive comprises a carbonate additive, a heteroatom-containing additive and a sulfate additive, and heteroatoms in the heteroatom-containing additive are selected from P, Si, B and F; the sulfate additives comprise methylene methanedisulfonate and other sulfate additives, and the other sulfate additives are selected from one or more of ethylene sulfite, butane sultone, allyl sultone, ethylene disulfate and vinyl ethylidene sulfate; the non-aqueous solvent comprises the following components in percentage by mass: 20-50% of a carbonic ester solvent and 50-80% of a carboxylic ester solvent, wherein the mass of the carbonic ester solvent is 100%. According to the electrolyte provided by the invention, through reasonable matching of the components, the lithium ion battery can have good fast charging capacity and high and low temperature performance at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and specifically relates to an electrolyte, a lithium-ion battery, and a vehicle. Background Art

[0002] With the rapid development of the new energy field, the consumption of new energy vehicles has gradually increased, and the market has also put forward higher requirements for new energy vehicles. Based on the needs of different groups of people, each automobile manufacturer has launched new energy vehicles optimized for different performances, such as the improvement of the cruising range, the improvement of safety performance, the improvement of the 100-meter acceleration, the improvement of intelligence, etc.

[0003] However, compared with traditional fuel vehicles, new energy vehicles have the disadvantage of slow charging, which leads to the problem that users not only have to plan the charging situation of the vehicle in advance, but also have to face the problem of frequent charging during long-distance driving, resulting in low travel efficiency. This greatly limits the development of new energy vehicles.

[0004] To solve this problem, researchers have made various improvements to automotive power batteries to improve their fast charging performance. There are many factors affecting the fast charging performance of batteries. Among them, the structural design of the battery, the positive and negative electrode materials, and the electrolyte are the key factors affecting the fast charging performance of the battery, and the influence of the electrolyte on the fast charging performance is particularly prominent. During the rapid charging process of the battery, lithium ions quickly escape from the positive electrode and enter the electrolyte, then pass through the separator and enter the negative electrode for lithium intercalation. A large number of lithium ions need to migrate quickly, which requires the electrolyte to have high kinetic performance and smaller mass transfer resistance during the mass transfer process. Therefore, the electrolyte is required to have good wettability, lower viscosity, and lower lithium ion transport resistance.

[0005] Currently, some studies have tried to improve the fast charging performance of lithium-ion batteries by adding carboxylic ester solvents to the electrolyte to replace part of the carbonate solvents, thereby reducing the viscosity of the electrolyte and increasing the lithium ion transport rate. However, the compatibility of carboxylic ester solvents with graphite anodes is poor, which will lead to the deterioration of the high-temperature storage and cycling performance of the battery. Therefore, the addition amount needs to be controlled at a low level, and the improvement of the fast charging performance of the battery is limited. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an electrolyte, a lithium-ion battery, and a vehicle. Through reasonable combination of components, this electrolyte can endow lithium-ion batteries with good fast charging ability and high and low temperature performance at the same time.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides an electrolyte, which comprises a lithium salt, an additive, and a non-aqueous solvent;

[0009] The additive includes carbonate additives, heteroatom-containing additives, and sulfate additives. The heteroatom in the heteroatom-containing additive is selected from P, Si, B, and F;

[0010] The sulfate additives include methylene methanedisulfonate and other sulfate additives. The other sulfate additives are selected from one or more of vinylene sulfite, butane sultone, propene sultone, bis(vinyl sulfate), and ethylene ethylenesulfite;

[0011] Based on the mass of the non-aqueous solvent being 100%, the non-aqueous solvent includes: 20 - 50% of carbonate solvent and 50 - 80% of carboxylate solvent.

[0012] In some embodiments of the present invention, based on the mass of the electrolyte being 100%, the electrolyte includes 6 - 20% of lithium salt, 2 - 20% of additive, and the balance of non-aqueous solvent.

[0013] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0014] In some embodiments of the present invention, based on the mass of the additive being 100%, the additive includes: 35 - 94% of carbonate additives, 3 - 35% of heteroatom-containing additives, and 3 - 30% of sulfate additives.

[0015] In some embodiments of the present invention, the carbonate additive is vinylene carbonate.

[0016] In some embodiments of the present invention, the heteroatom-containing additive is selected from one to three of tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, hexamethyldisilazane, trimethyl phosphate, lithium bis(fluoroxalato) phosphate, lithium bis(fluoroxalato) borate, lithium tetrafluoroborate, and lithium bis(oxalato) borate, and the heteroatom in the heteroatom-containing additive is two or three of P, Si, B, and F.

[0017] In some embodiments of the present invention, when the heteroatom-containing additive contains two components, the mass content of each component in the heteroatom-containing additive is 15 - 85%.

[0018] In some embodiments of the present invention, when the heteroatom-containing additive contains three components, the mass content of each component in the heteroatom-containing additive is 10 - 50%.

[0019] In some embodiments of the present invention, based on the mass of the sulfate additives being 100%, the sulfate additives include 10 - 55% of methylene methanedisulfonate and 45 - 90% of other sulfate additives.

[0020] In some embodiments of the present invention, the carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, and methyl propyl carbonate.

[0021] In some embodiments of the present invention, the carboxylate solvent includes one or more of ethyl acetate, methyl propionate, propyl acetate, ethyl propionate, methyl acetate, propyl propionate, and methyl formate.

[0022] In a second aspect, the present invention provides a lithium-ion battery comprising the electrolyte as described in the first aspect.

[0023] In a third aspect, the present invention provides a vehicle comprising the lithium-ion battery as described in the second aspect.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The electrolyte provided by the present invention, by introducing a high content of carboxylate solvent in combination with the carbonate solvent, effectively reduces the freezing point and viscosity of the electrolyte, improves the ion transport rate of the electrolyte, and simultaneously improves the low-temperature performance of the lithium-ion battery; combined with carbonate additives, heteroatom-containing additives, and sulfate additives, the problem of poor compatibility between the carboxylate solvent and the graphite negative electrode is improved. Each component cooperates synergistically, so that the obtained electrolyte has good fast-charging performance and high and low-temperature performance at the same time. Detailed Embodiments

[0026] In order to more clearly understand the above objects, features, and advantages of the present invention, the solution of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0027] In the following description, many specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit this application.

[0029] It should be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0030] In a first aspect, an embodiment of the present invention provides an electrolyte, the electrolyte comprising a lithium salt, an additive and a non-aqueous solvent;

[0031] The additive includes a carbonate additive, a heteroatom-containing additive and a sulfate additive, and the heteroatom in the heteroatom-containing additive is selected from P, Si, B, F;

[0032] The sulfate additive includes methylene methanedisulfonate and other sulfate additives, and the other sulfate additives are selected from one or more of vinylene sulfite, butane sultone, propylene sultone, bis(vinylsulfate) ethylene and ethylene ethyl sulfite;

[0033] Based on the mass of the non-aqueous solvent being 100%, the non-aqueous solvent includes: 20-50% of a carbonate solvent (for example, it can be 20%, 22%, 23%, 25%, 26%, 28%, 30%, 32%, 33%, 35%, 36%, 38%, 40%, 42%, 43%, 45%, 48% or 50%, etc.) and 50-80% of a carboxylate solvent (for example, it can be 50%, 52%, 55%, 56%, 58%, 60%, 62%, 63%, 65%, 66%, 68%, 70%, 72%, 73%, 75%, 76%, 78% or 80%, etc.).

[0034] The electrolyte provided by the embodiment of the present invention, by introducing a high content of carboxylate solvent in combination with the carbonate solvent, effectively reduces the freezing point and viscosity of the electrolyte, enabling the electrolyte to have a higher ion transport speed when charging under high rate conditions; at the same time, the introduction of the carboxylate improves the dissociation degree of the lithium salt at the same concentration, significantly enhancing the ion-conducting ability of the electrolyte, thereby significantly improving the fast charging ability of the lithium-ion battery. In addition, the reduction of the freezing point and viscosity of the electrolyte can also enable the electrolyte to have better fluidity at low temperatures, thereby improving the low-temperature performance of the lithium-ion battery.

[0035] However, the compatibility between carboxylic ester solvents and graphite anodes is poor. The introduction of a large amount of carboxylic ester solvents will lead to the deterioration of the high-temperature storage and cycling performance of lithium-ion batteries. In addition, for ultrafast charging electrolytes, it is required that the electrolyte can rapidly conduct ions on the negative electrode side while matching the fast-charging type graphite anode and can quickly diffuse in the electrode / electrolyte interface layer. However, the ultra-fast charging of the battery cell will exacerbate the side reactions of the electrolyte, resulting in the failure of the battery cell due to increased temperature, lithium plating short circuit, and ultimately shortening the service life of the battery cell.

[0036] In order to enable the battery cell to have both fast charging ability and high-temperature performance, a composite additive of a carbonate additive, a heteroatom-containing additive, and a sulfate additive is further introduced into the electrolyte provided in the embodiments of the present invention.

[0037] Among them, carbonate additives (such as vinylene carbonate) can preferentially reduce at the negative electrode to form a porous polymer SEI film. However, the present invention finds that the higher the content of vinylene carbonate in the electrolyte, the greater the impedance of the SEI film formed on the negative electrode, which is not conducive to the high-rate fast charging performance of the battery cell. Moreover, due to its high reaction activity, it is very easy to gain and lose electrons and react during the charge and discharge process of the battery cell, resulting in a sharp thickening of the SEI film during the use of the battery cell, affecting the later wetting of the battery cell and thus shortening the service life of the battery cell.

[0038] The heteroatom-containing additive can react with the electrolyte to form an inorganic SEI layer with high ionic conductivity, and jointly form a highly stable and low-impedance composite SEI layer with vinylene carbonate, reducing the impedance of the lithium-ion transmission interface, thereby improving the fast charging performance of the battery cell.

[0039] The S atom in the sulfate additive has a stronger electronegativity than the C atom, and can preferentially decompose at the intercalation potential of solvated lithium ions to form a stable protective film, so as to inhibit the large amount of decomposition of other additives in the electrolyte (such as vinylene carbonate) and the degradation of the electrode material (such as the dissolution of transition metal ions resulting in the attenuation of the battery cell capacity), thereby further improving the film-forming quality of the electrode / electrolyte interface layer and enhancing the long-term performance of the battery cell. In the embodiments of the present invention, methylene methanedisulfonate is selected to cooperate with the other sulfate additives. Among them, methylene methanedisulfonate can reduce the impedance of the lithium-ion battery and improve the thermal stability of the SEI film at high temperature, thereby enhancing the high-temperature performance of the battery cell. However, its improvement of the high-rate charge and discharge performance is not significant. The compounding of methylene methanedisulfonate with the other sulfate additives helps to balance the fast charging performance and high-temperature performance of the battery cell.

[0040] In the embodiments of the present invention, through the synergistic cooperation of carbonate additives, heteroatom-containing additives, and sulfate additives, a multi-component, stable, inorganic- and organic-rich porous interface layer can be formed on the electrode surface, improving the lithium-ion transport rate. While ensuring the high-rate fast charging performance of the battery cell, it also has good high and low temperature performance, and improves the service life of the battery cell.

[0041] In some embodiments of the present invention, based on the mass of the electrolyte being 100%, the electrolyte includes 6-20% (such as 6%, 7%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18% or 20%, preferably 12.5-20%) of a lithium salt, 2-20% (such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18% or 20%) of an additive, and the balance being a non-aqueous solvent. However, the present invention is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0042] In the embodiments of the present invention, maintaining the proportions of the lithium salt, additive, and solvent within the above ranges helps to obtain an electrolyte with good comprehensive performance. If the content of the lithium salt is too low, it will result in a low ionic conductivity of the electrolyte, an increase in the impedance of the battery cell, and is not conducive to improving the fast charging performance of the battery cell. If the content of the lithium salt is too high, it will lead to a large viscosity of the electrolyte and a decrease in the ion transport rate, which is also not conducive to improving the fast charging performance of the battery cell. If the content of the additive is too low, its corresponding function is difficult to exert; if the addition amount is too high, it will cause a large amount of decomposition and consumption during the charge and discharge process of the battery, affecting the normal exertion of its function, and additives usually have a high cost, and when the addition amount is large, it will lead to a significant increase in the cost of the electrolyte.

[0043] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF 6 )、lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide (LiFSI).

[0044] In some embodiments of the present invention, based on the mass of the additive being 100%, the additive includes: 35-94% of a carbonate additive (such as 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92% or 94%, etc.), 3-35% of a heteroatom-containing additive (such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18%, 20%, 22%, 25%, 28%, 30%, 32% or 35%, etc.) and 3-30% of a sulfate additive (such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 15%, 16%, 18%, 20%, 22%, 25%, 28% or 30%, etc.). However, the present invention is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0045] In the embodiments of the present invention, keeping the proportions of the carbonate additive, the heteroatom-containing additive and the sulfate additive within the above ranges helps the electrolyte to obtain better fast charging performance and high-temperature performance. Among them, if the content of the carbonate additive is too small, the content of the organic components of the interfacial SEI film is insufficient, which will affect the interfacial passivation effect and lead to a decrease in the stability of the interfacial SEI film; if the content of the carbonate additive is too large, the impedance of the SEI film formed on the negative electrode of the battery cell will be relatively large, which is not conducive to the improvement of the fast charging performance of the battery cell. If the content of the heteroatom-containing additive is too small, its improvement effect on the SEI film formation effect is weak, and its improvement effect on the fast charging performance of the battery cell is weak; if the content of the heteroatom-containing additive is too large, the thickness of the SEI film at the interface will be relatively large, offsetting the exertion of its function and possibly having a negative impact on the ion transport at the interface. If the content of the sulfate additive is too small, its improvement effect on the SEI film formation effect is weak, and its improvement effect on the long-term performance of the battery cell is weak; if the content of the sulfate additive is too large, it is easy to cause a decrease in the stability of the interfacial SEI film, affecting the cycle life of the battery.

[0046] In some embodiments of the present invention, the carbonate additive is vinylene carbonate.

[0047] Among the carbonate additives, vinylene carbonate has a good film-forming efficiency upon decomposition, the best passivation effect, and a relatively low cost.

[0048] In some embodiments of the present invention, the heteroatom-containing additive is selected from one to three of tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, hexamethyldisilazane, trimethyl phosphate, lithium difluoro(oxalato)phosphate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, and lithium bis(oxalato)borate, and the heteroatoms in the heteroatom-containing additive are two or three of P, Si, B, and F.

[0049] In the embodiments of the present invention, an additive containing two or three heteroatoms is selected, and the additives containing different heteroatoms are combined according to the principle of complementary action to improve the comprehensive performance of the battery cell. For example, the P-containing additive can form phosphorus radicals in the electrolyte to remove hydrogen and hydroxide radicals generated by side reactions of the electrolyte, which is beneficial to improving the safety performance of the battery cell. However, the P-containing group will deteriorate the DC impedance of the battery cell. Therefore, a F-containing additive (such as a difluorooxalate additive) is generally used in combination to generate inorganic components mainly composed of LiF, Li 2 CO 3 to balance the resistance risk of the battery cell. However, the above inorganic component Li 2 CO 3 is not easily stable under higher acidic conditions. Therefore, based on this, a Si-containing additive (such as a trimethylsilyl group (TMS)) can be added to the electrolyte to coordinate with a strong Lewis acid (such as PF 5 to eliminate hydrofluoric acid (HF), thereby improving the stability of the SEI film. Moreover, in different electrolyte systems, TMS can undergo redox reactions at the anode and cathode respectively to optimize the CEI / SEI structure on the electrode surface to improve the transport rate of Li ions in the battery cell system. In addition, the B-containing additive has the following multiple action mechanisms: 1) It can enhance the stability of the electrolyte, improve the thermal stability of the electrolyte at high temperatures to improve the safety performance; 2) It can inhibit side reactions of the electrolyte to improve the long-term service life; 3) It can broaden the electrochemical stability window of the electrolyte so that the electrolyte remains stable under high voltage; 4) An appropriate amount of boric acid is beneficial to improving the conductivity of the electrolyte and the charge and discharge performance of the battery cell. However, the B-containing additive (such as BF 4 -)In a ternary system, the electrode surface design can be optimized at the positive and negative electrodes to improve the interface structure and stabilize the high-voltage performance. However, in the lithium iron system, there will be a problem of deteriorating the negative electrode interface impedance, which is not conducive to the fast charging performance. Therefore, for cells with safety requirements, an additive combination containing F and P, or an additive combination containing F and B can be used; for cells with fast charging performance, an additive combination containing F and Si, or an additive combination containing B and F, or an additive combination containing B, F, and Si can be used; for the design of high-voltage cells with guaranteed safety and no risk, an additive combination containing Si and B, or an additive combination containing P and B can be considered. The practical cases described in the embodiments of the present invention are not limited to the additive combinations introduced above. In summary, the heteroatom-containing additives need to be combined according to the intrinsic characteristics of the groups carried in each additive and the actual usage requirements of the cell to better meet the usage objectives of the cell. The main reason for not using more heteroatom combinations in the embodiments of the present invention is to avoid the lack of expected effects due to the repeated actions of multiple atoms.

[0050] In some embodiments of the present invention, when the heteroatom-containing additive contains two components, the mass content of each component in the heteroatom-containing additive is 15-85%; for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, etc. However, the present invention is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] In some embodiments of the present invention, when the heteroatom-containing additive contains three components, the mass content of each component in the heteroatom-containing additive is 10-50%; for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc. However, the present invention is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0052] When the heteroatom-containing additive contains two or three components, controlling the content of each component within the above range is to avoid too much or too little of a certain component and ensure that each component plays its role fully.

[0053] In some embodiments of the present invention, based on the mass of the sulfate ester additive being 100%, the sulfate ester additive includes 10-55% of methylene methanedisulfonate (for example, it can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52% or 55%, etc.) and 45-90% of other sulfate ester additives (for example, it can be 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88% or 90%, etc.). However, the present invention is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0054] In the embodiments of the present invention, controlling the ratio of methylene methanedisulfonate and the other sulfate ester additives within the above range helps to fully exert the functions of both, and further improve the fast charging performance and high-temperature performance of the battery cell. If the proportion of methylene methanedisulfonate is too high, it is not conducive to the improvement of the fast charging performance of the battery cell; if the proportion of the other sulfate ester additives is too high, it is not conducive to the improvement of the high-temperature performance of the battery cell.

[0055] In some embodiments of the present invention, the carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate and methyl propyl carbonate.

[0056] In some embodiments of the present invention, the carboxylate solvent includes one or more of ethyl acetate, methyl propionate, propyl acetate, ethyl propionate, methyl acetate, propyl propionate and methyl formate.

[0057] In a second aspect, an embodiment of the present invention provides a lithium-ion battery, including the electrolyte as described in the first aspect.

[0058] In a third aspect, an embodiment of the present invention provides a vehicle, including the lithium-ion battery as described in the second aspect.

[0059] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0060] In the examples where specific techniques or conditions are not specified, they shall be carried out according to the conventional techniques or conditions in the art, or the techniques or conditions described in the literature, or the product specifications. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0061] Example 1

[0062] This example provides an electrolyte, and its components are as follows:

[0063]

[0064]

[0065] Example 2

[0066] This example provides an electrolyte, and its components are as follows:

[0067]

[0068] Example 3

[0069] This example provides an electrolyte, and its components are as follows:

[0070]

[0071] Example 4

[0072] This example provides an electrolyte, and its components are as follows:

[0073]

[0074]

[0075] Example 5

[0076] This example provides an electrolyte, and its components are as follows:

[0077]

[0078] Comparative Example 1

[0079] This comparative example provides an electrolyte. The difference from Example 1 is only that the mass contents of each additive in the electrolyte are: 3.55% of carbonate additives, 0.45% of heteroatom-containing additives, and 0% of sulfate additives.

[0080] Comparative Example 2

[0081] This comparative example provides an electrolyte. The difference from Example 1 is only that the mass contents of each additive in the electrolyte are: 3.55% of carbonate additives, 0% of heteroatom-containing additives, and 0.45% of sulfate additives.

[0082] Comparative Example 3

[0083] This comparative example provides an electrolyte, which is only different from that of Example 1 in that the mass contents of each additive in the electrolyte are: 0% of carbonate additives, 2% of heteroatom-containing additives, and 2% of sulfate additives.

[0084] Comparative Example 4

[0085] This comparative example provides an electrolyte, which is only different from that of Example 1 in that the sulfate additive is methylene methanedisulfonate.

[0086] Comparative Example 5

[0087] This comparative example provides an electrolyte, which is only different from that of Example 1 in that the sulfate additive is vinylene sulfite.

[0088] Performance Test

[0089] Preparation of Lithium-Ion Battery:

[0090] Positive electrode sheet: The positive electrode material LiFePO 4 , binder PVDF, and conductive agent acetylene black are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone solvent is added, and the mixture is stirred by a vacuum mixer until the system becomes a homogeneous transparent state to obtain a positive electrode slurry. Then, it is uniformly coated on a current collector aluminum foil (with a thickness of 12 μm), and the coating surface density is 328 g / m 2 . After air drying at room temperature, it is transferred to an oven at 120 °C for drying for 1 h, and then cold pressed (the compaction density is 2.5 g / cm 3 ) and slit to obtain a positive electrode sheet;

[0091] Negative electrode sheet: The negative electrode material graphite, thickening agent sodium carboxymethyl cellulose solution (93 wt%), and binder styrene-butadiene rubber emulsion (40 wt%) are mixed in a mass ratio of 96:2:2, deionized water is added, and the mixture is stirred by a vacuum mixer to obtain a negative electrode slurry. Then, it is uniformly coated on a current collector copper foil (with a thickness of 8 μm), and the coating surface density is 145 g / m 2 . After air drying at room temperature, it is transferred to an oven at 120 °C for drying for 1 h, and then cold pressed (the compaction density is 1.6 g / cm 3 ) and slit to obtain a negative electrode sheet;

[0092] Separator: Polypropylene separator film;

[0093] The positive electrode sheet, negative electrode sheet, and polypropylene separator film are wound, wrapped with an aluminum-plastic film, baked to remove water, then injected with a primary electrolyte and sealed. After standing, hot and cold pressing, pre-forming, injecting a secondary electrolyte, and re-forming, etc., the injection coefficient is 3.2 g / Ah to prepare a soft-pack lithium-ion battery;

[0094] One portion of the electrolyte and two portions of the electrolyte are both the electrolytes provided in the above embodiments or comparative examples, and the proportions of the one portion of the electrolyte and the two portions of the electrolyte are 80% and 20% of the total amount of the electrolyte, respectively.

[0095] 1. Conductivity of the electrolyte

[0096] The electrolyte is kept at a constant temperature of 25 °C in a constant temperature water bath for 30 min, and then the conductivity is measured with a conductivity meter.

[0097] 2. Low-temperature performance test of the lithium-ion battery

[0098] At 25 °C, the lithium-ion battery is first discharged at 1C to 2.0 V, then charged at a constant current of 1C to 3.75 V, and then charged at a constant voltage until the cut-off current is 0.05C. The charging capacity is denoted as C 1 ; then the lithium-ion battery is placed in a constant temperature furnace at -20 °C for 60 min and discharged at a constant current of 1C to 2.0 V. The discharge capacity is denoted as C 2 . Then the discharge capacity retention rate at low temperature of -20 °C = C 2 / C 1 × 100%.

[0099] 3. Lithium plating analysis test for 6C fast charging of the lithium-ion battery

[0100] At 25 °C, the lithium-ion battery is first discharged at 1C to 2.0 V, then charged at a constant current of 6C to 3.75 V, discharged at a constant current of 1C to 2.0 V. After 10 charge-discharge cycles, it is charged at a constant current of 1C to 3.75 V and charged at a constant voltage until the current is 0.05C, and then the battery cell is disassembled to observe the lithium plating situation at the negative electrode interface.

[0101] 4. High-temperature cycle performance test of the lithium-ion battery

[0102] At 45 °C, the lithium-ion battery is first discharged at 1C to 2.0 V and then subjected to a cycle test. The test process is to first charge at a constant current of 1C to 3.75 V, then charge at a constant voltage until the current is 0.05C, and then discharge at a constant current of 1C to 2.0 V. Such cycle charging and discharging are carried out, and the discharge capacity retention rate of the lithium-ion battery at 45 °C for 1C / 1C cycle 1000 times is calculated.

[0103] The results of the above performance tests are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] As can be seen from the performance data in Table 1, the electrolyte provided by the embodiments of the present invention has a high conductivity. For a lithium-ion battery using the electrolyte provided by the embodiments of the present invention, there is no obvious lithium deposition on the negative electrode during charging under the condition of a high rate of 6C. The discharge capacity retention rate at low temperature of -20°C reaches more than 37.9%, and the discharge capacity retention rate reaches more than 79.2% after 1000 cycles of 1C / 1C charge and discharge at high temperature of 45°C. This indicates that the electrolyte provided by the present invention can endow the lithium-ion battery with good fast charging performance and high and low temperature performance simultaneously.

[0107] Among them, compared with Example 1, the sulfate ester additive was not added to the electrolyte of Comparative Example 1, resulting in insufficient interfacial kinetic performance of the lithium-ion battery. During charging under the condition of a high rate of 6C, medium lithium deposition occurred on the negative electrode, the fast charging performance decreased significantly, and the capacity performance at low temperature decreased significantly.

[0108] Compared with Example 1, the heteroatom-containing additive was not added to the electrolyte of Comparative Example 2, resulting in insufficient stability of the interfacial SEI film of the lithium-ion battery. During charging under the condition of a high rate of 6C, medium lithium deposition occurred on the negative electrode, and both the fast charging and high temperature cycle performances decreased significantly.

[0109] Compared with Example 1, the carbonate ester additive was not added to the electrolyte of Comparative Example 3, resulting in insufficient stability of the interfacial SEI film of the lithium-ion battery. During charging under the condition of a high rate of 6C, medium lithium deposition occurred on the negative electrode, and both the fast charging and high temperature cycle performances decreased significantly.

[0110] Compared with Example 1, in the electrolyte of Comparative Example 4, only methylene methanedisulfonate was used as the sulfate ester additive, resulting in a decrease in the interfacial kinetic performance of the lithium-ion battery. During charging under the condition of a high rate of 6C, slight lithium deposition occurred on the negative electrode, and the fast charging performance decreased somewhat.

[0111] Compared with Example 1, in the electrolyte of Comparative Example 5, only vinylene sulfite was used as the sulfate ester additive, resulting in insufficient stability of the interfacial SEI film of the lithium-ion battery. During charging under the condition of a high rate of 6C, slight lithium deposition occurred on the negative electrode, the fast charging performance decreased somewhat, and the high temperature cycle performance decreased.

[0112] The above are only specific embodiments of the present disclosure, which enable those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a lithium salt, an additive and a non-aqueous solvent; The additives include carbonate additives, heteroatom-containing additives and sulfate additives, wherein the heteroatom in the heteroatom-containing additive is selected from P, Si, B and F; The sulfate ester additives include methylene methane disulfonate and other sulfate ester additives, wherein the other sulfate ester additives are selected from one or more of vinyl sulfite, butane sultone, propylene sultone, vinyl disulfate and vinyl ethylene sulfate; Taking the mass of the non-aqueous solvent as 100%, the non-aqueous solvent comprises: 20-50% of a carbonate solvent and 50-80% of a carboxylate solvent.

2. The electrolyte according to claim 1, characterized in that Taking the mass of the electrolyte as 100%, the electrolyte includes 6-20% of lithium salt, 2-20% of additives and the balance of non-aqueous solvent.

3. The electrolyte according to claim 1 or 2, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide.

4. The electrolyte according to claim 1 or 2, characterized in that Taking the mass of the additive as 100%, the additive comprises: 35-94% of carbonate additive, 3-35% of heteroatom-containing additive and 3-30% of sulfate additive.

5. The electrolyte according to claim 1, 2 or 4, characterized in that: The carbonate additive is vinylene carbonate; And / or, the heteroatom-containing additive is selected from one to three of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, hexamethyldisilazane, trimethyl phosphate, lithium difluorooxalate phosphate, lithium difluorooxalate borate, lithium tetrafluoroborate and lithium dioxalate borate, and the heteroatoms in the heteroatom-containing additive are two or three of P, Si, B and F.

6. The electrolyte according to claim 5, characterized in that When the heteroatom-containing additive comprises two components, the mass content of each component in the heteroatom-containing additive is 15-85%; When the heteroatom-containing additive comprises three components, the mass content of each component in the heteroatom-containing additive is 10-50%.

7. The electrolyte according to claim 1, 2 or 4, characterized in that: Taking the mass of the sulfate ester additive as 100%, the sulfate ester additive comprises 10-55% of methylene methane disulfonate and 45-90% of other sulfate ester additives.

8. The electrolyte according to claim 1 or 2, characterized in that: The carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate and methylpropyl carbonate; And / or, the carboxylate solvent includes one or more of ethyl acetate, methyl propionate, propyl acetate, ethyl propionate, methyl acetate, propyl propionate and methyl formate.

9. A lithium ion battery, characterized in that: Contains the electrolyte according to any one of claims 1 to 8.

10. A vehicle, characterized in that: Comprising the lithium ion battery as claimed in claim 9.

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