Method for preparing SEI-like film component additive, electrolyte, lithium ion battery, battery module, battery pack, and electric device

Abstract

Provided are a preparation method of a SEI film (solid electrolyte interphase) component additive, and an electrolyte containing the SEI film component additive prepared by the method. Compared with a conventional electrolyte (an electrolyte without the SEI film component additive), the obtained electrolyte can prevent the loss of effective components caused by the dissolution of a negative electrode SEI film in the electrolyte during storage and use, and can timely supplement the effective components to the SEI film that has been lost or damaged, so that the damaged SEI film is quickly and timely supplemented, and thus the adverse conditions such as electrolyte decomposition, increased side reactions, large gas production, and loss of active lithium caused by the damage of the SEI film are significantly improved, thereby significantly improving the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and more particularly to a method for preparing an SEI-like membrane (solid electrolyte interphase) component additive, as well as an electrolyte containing the SEI-like membrane component additive prepared by this method, a lithium-ion battery, a battery module, a battery pack, and an electrical device containing the same. Background Technology

[0002] With the rapid development of the new energy field, lithium-ion batteries are widely used in various large-scale power devices, energy storage systems and various consumer products due to their excellent electrochemical performance, no memory effect and low environmental pollution, especially in the field of new energy vehicles such as pure electric vehicles and hybrid electric vehicles.

[0003] During the initial charging of a lithium-ion battery, the electrolyte solvent and lithium salt form an SEI (solid electrolyte interphase) film on the negative electrode surface. This film is crucial for the electrochemical performance of lithium ions. However, during battery storage or use, the effective components of the SEI film are not stable. When the SEI film structure is damaged, it compromises the stability at the interface between the negative electrode active material and the electrolyte, exacerbating internal side reactions and negatively impacting the battery's cycle performance and safety. Furthermore, the formation of the SEI film consumes electrolyte and a large amount of lithium ions, reducing charge / discharge efficiency and accelerating capacity decay. The large amount of gas generated during SEI film formation also affects battery safety.

[0004] Therefore, if a method for preparing SEI-like film component additives could be developed, and these additives could be added to the electrolyte to replenish or restore the damaged SEI film when its structure is compromised or consumed, this would be highly significant for improving battery performance. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and aims to provide a method for preparing an SEI-like membrane component additive, as well as an electrolyte containing the SEI-like membrane component additive prepared by the method, a lithium-ion battery containing the additive, a battery module, a battery pack, and an electrical device.

[0006] The first aspect of this application provides a method for preparing an SEI membrane component additive, which includes the following steps:

[0007] In an inert gas atmosphere, a lithium naphthalene organic solution is reacted with a mixed solvent to obtain a mixture containing an SEI-like film component additive, wherein...

[0008] The mass ratio of lithium naphthalene to the mixed solvent in the lithium naphthalene organic solution is 2-8:1, and the mixed solvent includes an organic solvent used in battery electrolytes.

[0009] The mixture was dried in a vacuum to obtain an SEI-like membrane component additive.

[0010] In any embodiment, the mixed solvent includes one or more of cyclic esters, linear esters, cyclic sulfones, and linear sulfones.

[0011] In any embodiment, the mixed solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0012] In any embodiment, based on the mass of the mixed solvent, the amount of ethylene carbonate is 20%-30%, the amount of methyl ethyl carbonate is 30%-40%, the amount of dimethyl carbonate is 30%-50%, and the total is 100%.

[0013] In any embodiment, the reaction temperature W1 and the reaction time S1 of the lithium naphthalene organic solution and the mixed solvent satisfy: 23.59 K·min ≤ ln(W1+273.15)×lnS1 ≤ 30.16 K·min; preferably, the reaction is carried out under thorough stirring conditions.

[0014] In any embodiment, the reaction temperature W1 of the lithium naphthalene organic solution and the mixed solvent is 45-60°C, and the reaction time S1 is 60-180 minutes.

[0015] In any embodiment, the naphthalene-lithium organic solution is prepared by the following method:

[0016] In an inert gas atmosphere, lithium metal is added to an organic solvent containing naphthalene to react with the lithium metal, wherein the molar ratio of naphthalene to the added lithium metal is 1-3:1. During the reaction, the reaction temperature W2 and the reaction time S2 of the naphthalene and lithium metal satisfy: 23.59 K·min ≤ ln(W2+273.15)×lnS2 ≤ 30.16 K·min; preferably, the reaction is carried out under thorough stirring.

[0017] In any embodiment, the reaction temperature W2 of the naphthalene and the lithium metal is 45-60°C, and the reaction time S2 is 60-180 minutes.

[0018] In any embodiment, in the organic solution containing naphthalene, the molar ratio of the organic solvent to the naphthalene is 1-5:1, and the organic solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol methyl ethyl ether, and ethylene glycol methyl propyl ether.

[0019] In any embodiment, the mixture is dried in a vacuum at a temperature of 60-80°C; optionally, the resulting SEI-like membrane component additive is a solid.

[0020] A second aspect of this application provides an electrolyte comprising an SEI-like membrane component additive prepared according to the method of the first aspect of this application.

[0021] In any embodiment, the amount of the SEI-like membrane component additive added is 0.05-0.3% of the mass percentage of the electrolyte.

[0022] In any embodiment, the electrolyte contains a lithium-donating substance, and the mass ratio of the amount of the SEI-like membrane component additive to the lithium-donating substance is 0.5-5:100; optionally, the lithium-donating substance is one or more of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0023] The electrolyte contains other additives, the other additives accounting for 0.5%-3% of the mass of the electrolyte; optionally, the other additives are selected from one or more of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and vinyl sulfate.

[0024] A third aspect of this application provides a lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte according to a second aspect of this application, wherein the negative electrode comprises a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising one or more of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon-carbon composite, lithium-tin alloy, and lithium-aluminum alloy.

[0025] In any embodiment, let m1 be the mass percentage of the SEI-like membrane component additive relative to the electrolyte, and m1 be the mass of the negative electrode active material on the single-sided negative electrode current collector (unit: g / 77mm). 2 If m1 is m2, then the ratio of m1 to m2 is 1.1-2.8 (g / 77mm). 2 ) -1 .

[0026] In any embodiment, when the cathode material belongs to the lithium iron phosphate system, the charging cut-off voltage of the lithium-ion battery can reach 3.65-3.8V; when the cathode material belongs to the nickel-cobalt-manganese ternary system, the charging cut-off voltage of the lithium-ion battery can reach 4.0-4.8V.

[0027] This application provides a fourth aspect of a battery module, including the lithium-ion battery described in the third aspect of this application. The battery module can be manufactured using methods known in the prior art for manufacturing battery modules.

[0028] This application provides a battery pack, including one or more of the lithium-ion battery of the third aspect of this application or the battery module of the fourth aspect of this application. The battery pack can be manufactured using methods known in the prior art for manufacturing battery packs.

[0029] A sixth aspect of this application provides an electrical device comprising one or more of the following: a lithium-ion battery as described in the third aspect of this application, a battery module as described in the fourth aspect of this application, or a battery pack as described in the fifth aspect of this application. The lithium-ion battery, the battery module, or the battery pack serves as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be manufactured using methods known in the prior art for manufacturing electrical devices.

[0030] [Beneficial Effects]

[0031] The preparation method of the SEI-like film component additive described in this application is simple to operate and easy to apply industrially. By adding the SEI-like film component additive prepared according to the method of this application to a conventional electrolyte, on the one hand, the dissolution of the SEI film by the electrolyte during the storage or use of lithium-ion batteries can be slowed down or avoided, reducing the consumption of the SEI film and thus maintaining the stability of the SEI film-electrolyte interface. This prevents the battery's cycle performance and safety performance from deteriorating due to continuous electrolyte consumption. On the other hand, when the SEI film is inevitably consumed due to abnormal conditions such as high temperature or high pressure, the SEI-like film component additive described in this application can quickly form a new SEI film, replenishing the damaged SEI film in a timely manner, thereby maintaining the battery's cycle performance and safety performance at the same level as when the SEI film was never damaged.

[0032] The battery module, battery pack, and power device of this application include the lithium-ion battery provided in this application, and therefore have at least the same advantages as the lithium-ion battery. Attached Figure Description

[0033] Figure 1 The A and C diagrams respectively correspond to the physical state diagrams of the organic solution containing naphthalene, the lithium naphthalene organic solution, and the mixture containing the SEI-like membrane component additive in the preparation process of the SEI-like membrane component additive involved in Example 1 of this application.

[0034] Figure 2 This is a graph showing the cycling performance of batteries corresponding to the electrolytes of Examples 1-1 and Comparative Example 1 at 3.65V and 60°C. Figure 2 A) and storage performance at 60℃ (Figure A) Figure 2 .B).

[0035] Figure 3 This is a graph showing the 60°C cycle performance of the batteries corresponding to the electrolytes of Examples 1-1 and Comparative Example 1 of this application at 3.8V. Figure 3 A) and storage performance at 60℃ (Figure A) Figure 3 .B).

[0036] Figure 4 This is a graph showing the cycling performance of a battery using a nickel-cobalt-manganese ternary layered material as the positive electrode active material according to an embodiment of this application at 4.8V and 60°C. Figure 4 A) and storage performance at 60℃ (Figure A) Figure 4 .B).

[0037] Figure 5 This is a schematic diagram of a lithium-ion battery according to one embodiment of this application.

[0038] Figure 6 yes Figure 5 An exploded view of a lithium-ion battery according to an embodiment of this application is shown.

[0039] Figure 7 This is a schematic diagram of a battery module according to one embodiment of this application.

[0040] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0041] Figure 9 yes Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0042] Figure 10 This is a schematic diagram of an electrical device according to one embodiment of this application.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1 battery pack

[0045] 2 upper box

[0046] 3 lower cabinets

[0047] 4 battery modules

[0048] 5 Lithium-ion batteries

[0049] 51 housing

[0050] 52 Electrode Assembly

[0051] 53 Top Cover Assembly Detailed Implementation

[0052] The following detailed description, with reference to the accompanying drawings, specifically discloses the preparation method of the SEI membrane component additive of this application, as well as the electrolyte containing the SEI membrane component additive obtained by this method, the lithium-ion battery containing the additive, the battery module, the battery pack, and the power supply device. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0053] For the sake of brevity, this application specifically discloses several numerical ranges, which can be combined to form corresponding implementation schemes. Any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value, or with other lower or upper limits, to form an unspecified range.

[0054] Unless otherwise stated, the terms used in this application have the common meanings understood by those skilled in the art. In this application, unless otherwise stated, "above" and "below" include the stated number; for example, "above one of a and b" means at least one of a and b, such as a, b, or a and b. Similarly, "above one" means including at least one. In the description herein, unless otherwise stated, the term "or" is inclusive, that is, the phrase "A or (or) B" means "A, B, or both A and B".

[0055] In this application, "SEI-like membrane component additive" refers to the product generated by the reaction of a lithium naphthalene organic solution with the mixed solvent described herein. Since this product, when added to the electrolyte, can slow down or prevent SEI membrane damage, thereby significantly improving the cycle performance and safety performance of the battery, and because this reaction product functions similarly to SEI membrane components, it is figuratively referred to as "SEI-like membrane component additive" for ease of description. It should be noted that the reaction between the lithium naphthalene organic solution and the mixed solvent is relatively complex, and the product may contain multiple components. However, this application does not intend to investigate the specific components contained in the SEI-like membrane component additive or the content of each component, but rather aims to study the preparation method of the SEI-like membrane component additive and the cycle performance and safety performance of batteries using electrolytes containing the SEI-like membrane component additive prepared by the method of this application.

[0056] During the initial charging of a lithium-ion battery, the electrolyte and lithium salt undergo a reduction reaction on the negative electrode surface. The reduction products deposit on the negative electrode surface, forming an organic-inorganic composite product, namely the SEI film. This film is crucial for the electrochemical performance of lithium-ion batteries. However, the inventors discovered during actual research that during the storage or use of lithium-ion batteries, the effective components of the formed SEI film inevitably dissolve into the electrolyte, leading to damage to the SEI film structure and a significant increase in the direct contact area between the effective components and the electrolyte. This greatly impairs the stability of the SEI film-electrolyte interface, exacerbates the occurrence of internal side reactions (mainly the deposition of electrolyte decomposition byproducts on the negative electrode surface and electrolyte gas generation), and ultimately deteriorates the battery's cycle performance and safety performance.

[0057] In particular, when the battery is under high temperature or high pressure, such as during long-term high-temperature storage or continuous high-voltage charging, the SEI film dissolves more in the electrolyte, and the loss or damage of the SEI film's own components is more severe, resulting in a more significant adverse impact on the battery's cycle performance and safety performance.

[0058] In particular, after the battery has undergone multiple high-temperature cycles, the repeated expansion-contraction-expansion of the negative electrode material will exacerbate the continuous dissolution or even shedding of the effective components of the SEI film, further deteriorating the battery's cycle performance and safety performance.

[0059] The inventors also discovered that if the effective components of the SEI film are generated solely through a reaction within the electrolyte, the amount of effective components generated by the reaction is small and the reaction rate is slow, which cannot replenish the lost SEI film in a timely and sufficient manner. Furthermore, the reaction requires the consumption of electrolyte and a large amount of lithium ions, generating a large amount of gas, which leads to accelerated capacity decay of the battery and damages the battery's safety performance.

[0060] Based on this, after extensive experimentation, the inventors developed a method for preparing SEI-like film component additives, and an electrolyte containing the SEI-like film component additives prepared by this method. Using the electrolyte of this application can significantly improve the problem of effective component loss from the SEI film in lithium-ion batteries, thereby significantly improving the battery's cycle performance and safety performance.

[0061] [Preparation method of SEI membrane component additives]

[0062] This application provides a method for preparing an SEI membrane component additive, which includes the following steps:

[0063] In an inert gas atmosphere, a lithium naphthalene organic solution is reacted with a mixed solvent to obtain a mixture containing an SEI-like film component additive, wherein...

[0064] The mass ratio of lithium naphthalene to the mixed solvent in the lithium naphthalene organic solution is 2-8:1, and the mixed solvent includes an organic solvent used in battery electrolytes.

[0065] The mixture was dried in a vacuum to obtain an SEI-like membrane component additive.

[0066] The preparation method described in this application is simple to operate and easy to apply on an industrial scale.

[0067] It should be noted that lithium naphthalene organic solution is a strong reducing solution. Surprisingly, after extensive experimentation, the inventors discovered that the reaction product of the lithium naphthalene organic solution and the mixed solvent described herein, when added to the electrolyte, can effectively alleviate or prevent SEI film damage, thereby reducing electrolyte and active lithium consumption, and thus significantly improving battery cycle performance and safety performance. For ease of description, the product generated after the reaction of the lithium naphthalene organic solution and the mixed solvent described herein is referred to as an "SEI film component additive."

[0068] Furthermore, in existing technologies, the common method for preparing an SEI film is to pre-add a film-forming component, such as ethylene carbonate, to the electrolyte. This component then undergoes a reduction reaction at the negative electrode after the SEI film is damaged, generating a new SEI film. While this method can replenish the damaged SEI film, the reaction between the film-forming component and the negative electrode still consumes electrolyte and a large amount of lithium ions, and generates a significant amount of gas, leading to accelerated capacity decay and compromised battery safety. In contrast, the method described in this application pre-fabricates a SEI film-like component additive externally to the battery, effectively solving these problems.

[0069] It should be noted that, in order to avoid the influence of oxygen in the air, the method for preparing SEI membrane component additives described above in this application needs to be operated in a glove box filled with an inert gas atmosphere (H2O content less than 100ppm, O2 content less than 100ppm), wherein the inert gas is nitrogen, argon, or helium, preferably nitrogen or argon.

[0070] The following describes different implementation methods according to the commonly used preparation process of SEI membrane component additives of this application:

[0071] Preparation of organic solvents containing naphthalene

[0072] In some embodiments, to prepare an organic solution containing naphthalene, an organic solvent is added to a reaction vessel, followed by the addition of solid naphthalene. The mixture is stirred at room temperature until the naphthalene is completely dissolved, yielding a white, transparent naphthalene-containing solution, as shown in the image. Figure 1 As shown in A.

[0073] In some embodiments, optionally, the molar ratio of the organic solvent to the naphthalene is 1-5:1, and the organic solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol methyl ethyl ether, and ethylene glycol methyl propyl ether.

[0074] Preparation of lithium naphthalene organic solution

[0075] In some embodiments, optionally, to prepare a satisfactory naphthalene-lithium organic solution, lithium metal is added to an organic solution containing naphthalene in an inert gas atmosphere, causing the naphthalene to react with the lithium metal. The molar ratio of naphthalene to the added lithium metal is 1-3:1. During the reaction, the reaction temperature W2 and reaction time S2 satisfy: 23.59 K·min ≤ ln(W2 + 273.15) × lnS2 ≤ 30.16 K·min; preferably, the reaction is carried out under thorough stirring. The resulting naphthalene-lithium organic solution is a deep black solution with extremely strong reducing properties, and its form is as follows... Figure 1 As shown in .B.

[0076] In some embodiments, the reaction temperature W2 is optionally 45-60°C, and the reaction time S2 is 60-180 minutes.

[0077] In some embodiments, the stirring conditions are optionally controlled at a rotation speed of 200-500 r / min.

[0078] Reaction of lithium naphthalene organic solution with mixed solvent

[0079] In some embodiments, optionally, a lithium naphthalene organic solution is reacted with a mixed solvent to obtain a mixture containing an SEI-like film component additive, wherein...

[0080] The mass ratio of naphthalene lithium to the mixed solvent in the naphthalene lithium organic solution is 2-8:1, and the mixed solvent includes an organic solvent used in battery electrolytes; the resulting mixture containing SEI-like membrane component additives is a slightly yellow turbid liquid, and its morphology is as follows. Figure 1 As shown in .C.

[0081] This application does not limit the specific types of components in the mixed solvent, and can reasonably combine them according to the specific components of the organic solvent used in the electrolyte of the corresponding lithium-ion battery. For example, the mixed solvent can be selected from one or more of cyclic esters, linear esters, cyclic sulfones, and linear sulfones, specifically from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0082] In some embodiments, the mixed solvent may optionally be a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0083] In some embodiments, optionally, based on the mass of the mixed solvent, the amount of ethylene carbonate is 20-30%, the amount of ethyl methyl carbonate is 30-40%, the amount of dimethyl carbonate is 30-50%, and the total is 100%.

[0084] In some embodiments, optionally, the reaction temperature W1 and reaction time S1 of the lithium naphthalene organic solution and the mixed solvent satisfy 23.59 K·min ≤ ln(W1+273.15)×lnS1 ≤ 30.16 K·min; preferably, the reaction is carried out under thorough stirring conditions.

[0085] In some embodiments, optionally, the reaction temperature W1 of the lithium naphthalene organic solution and the mixed solvent is 45-60°C, and the reaction time S1 is 60-180 minutes.

[0086] In some embodiments, the stirring conditions may optionally be a controlled rotation speed of 200-500 r / min.

[0087] The reaction temperature and time were controlled so that 23.59 K·min ≤ ln(W1+273.15)×lnS1 ≤ 30.16 K·min in order to ensure that the mixed solvent was fully reduced by lithium naphthalene.

[0088] Vacuum drying yields SEI-like film component additives

[0089] The reaction product obtained by reacting a lithium naphthalene organic solution with a mixed solvent is dried under vacuum at 60-80°C to obtain the SEI film component additive product of this application; optionally, the obtained SEI film component additive is a solid. Adding this product to any commercial lithium-ion battery electrolyte can achieve the technical effects of improving the negative electrode expansion rate, improving high-temperature storage and high-temperature cycling performance.

[0090] The method for preparing SEI-like film component additives provided in this application is simple to operate and the raw materials are readily available. After the prepared SEI-like film component additives are added to the electrolyte, they can significantly improve the expansion growth rate of the negative electrode, the high-temperature cycle performance and the high-temperature storage performance of the battery.

[0091] Electrolyte

[0092] A second aspect of this application provides an electrolyte comprising an SEI-like membrane component additive prepared according to the method of the first aspect of this application.

[0093] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte of this application contains an SEI film-like component additive prepared according to the method described herein. Compared to conventional electrolytes without the SEI film-like component additive, the electrolyte of this application can prevent the loss of effective components caused by the dissolution of the negative electrode SEI film in the electrolyte during battery storage and use. Simultaneously, the electrolyte can promptly replenish the effective components of the lost or damaged SEI film, thereby quickly and timely replenishing the damaged areas of the SEI film. This significantly improves adverse conditions such as electrolyte decomposition, increased side reactions, high gas production, and loss of active lithium caused by SEI film damage, thus significantly improving the battery's cycle performance and safety performance.

[0094] Specifically, when the battery is under high temperature or high pressure, the high temperature or high pressure will increase the solubility of the effective components of the SEI film in the electrolyte, thereby aggravating the loss of the effective components of the SEI film. However, correspondingly, the high temperature or high pressure will also promote the components in the electrolyte to re-form a new SEI film at a faster rate. Therefore, when the electrolyte of this application contains SEI film-like component additives, these SEI film-like component additives will be replenished in time to form a new SEI film.

[0095] Furthermore, because the effective components of the SEI-like film additives are very similar to those in the actual SEI film, the effective components of the SEI film in the electrolyte containing the SEI-like film additives in this application can be basically saturated or even supersaturated. Thus, even under harsh conditions such as high temperature or high pressure, the dissolution rate of the SEI film in the battery of this application is slower and less prone to rupture.

[0096] In particular, after the battery has undergone multiple high-temperature cycles and high-voltage charging, the repeated expansion-contraction-expansion of the negative electrode material will exacerbate the continuous dissolution or even detachment of the effective components of the SEI film. However, the electrolyte of this application contains SEI film-like additives, which can inhibit the expansion of the negative electrode material to a certain extent and effectively prevent the SEI film from continuously dissolving or even detaching due to the expansion of the negative electrode, thereby improving the cycle performance and safety performance of the battery.

[0097] Numerous experiments have shown that the SEI-like membrane component additives in the electrolyte of this application do not affect the function of other components in the electrolyte.

[0098] It should be noted that directly pre-coating the SEI-like film component additive onto the negative electrode surface also helps maintain the interfacial stability between the electrolyte and the negative electrode surface. However, from the perspective of better battery negative electrode performance, if it is simply coated onto the negative electrode surface, the SEI-like film component additive may not be able to penetrate / disperse evenly within the negative electrode film layer. Therefore, this application preferably adds the SEI-like film component additive to the electrolyte. By adding an appropriate amount of the SEI-like film component additive to the electrolyte, this application can, on the one hand, promptly replenish or restore the damaged SEI film, thereby improving the battery's cycle performance and safety performance; on the other hand, the SEI-like film component additive will be evenly dispersed in the electrolyte, which helps to form a uniform and dense SEI film on the negative electrode surface.

[0099] In some embodiments, optionally, the amount of the SEI-like membrane component additive added is 0.05%-0.3% of the mass of the electrolyte.

[0100] Extensive experiments have revealed that the content of SEI-like film component additives in the electrolyte is crucial to battery performance. When the content of SEI-like film component additives in the electrolyte is below 0.05%, the effect on improving the battery's high-temperature cycle performance and high-temperature storage performance is minimal. This is because, on the one hand, when the content of SEI-like film component additives is too low, the effective components of the SEI film in the electrolyte cannot reach saturation, thus failing to substantially inhibit the dissolution of the SEI film on the negative electrode. On the other hand, when the content of SEI-like film component additives is too low, even if the damaged SEI film is replenished, the amount replenished will not match the amount lost, resulting in a poor replenishment effect on the effective components of the SEI film.

[0101] Conversely, when the content of SEI-like film component additives in the electrolyte is higher than 0.3%, because the SEI-like film component additives contain substances with large molecular weights such as polycarbonate with high viscosity, when their addition amount is large, it will not only make the conductivity in the electrolyte worse, but also increase the resistance of the SEI-like film component additives to form the negative electrode SEI film, thus adversely affecting the battery cycle performance.

[0102] In some embodiments, optionally, the electrolyte contains a lithium-donating substance, and the mass ratio of the amount of the SEI-like membrane component additive to the mass of the lithium-donating substance is 0.5-5:100.

[0103] In some embodiments, the lithium-supplying material may optionally be selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; more preferably, the lithium-supplying material is one or more of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0104] It should be noted that the SEI-like film component additives in the electrolyte of this application, when combined with appropriate amounts of other substances in the electrolyte, such as lithium-donating materials, have a better effect on improving the performance of the negative electrode SEI film and thus the battery performance. For example, the negative electrode SEI film is a composite organic-inorganic network, which enables the SEI film to have suitable ionic conductivity, suitable mechanical strength, suitable flexibility, and density.

[0105] Therefore, adding the above-mentioned lithium-donating material to the electrolyte of this application is beneficial in two ways: firstly, it increases the number of active lithium ions in the electrolyte, thereby improving the cycle performance of the battery; secondly, as an inorganic lithium-donating material, it helps to form a new SEI film by interacting with SEI-like film component additives when the SEI film is damaged, thus improving battery performance.

[0106] The SEI-like film additives in the electrolyte of this application are mainly organic components, contributing to the flexibility and density of the SEI film. The lithium-donating material in the electrolyte primarily contributes to the ionic conductivity, mechanical strength, and stiffness of the SEI film. Therefore, when the mass ratio of the SEI-like film additives to the lithium-donating material is less than 0.5:100, the relative content of organic components in the newly formed SEI film is too low, resulting in poor flexibility and high stiffness. If the negative electrode experiences significant expansion, the SEI film is easily detached or damaged, adversely affecting the battery's high-temperature storage and cycle performance. Conversely, when the mass ratio of the SEI-like film additives to the lithium-donating material is greater than 5:100, the newly formed SEI film contains too much organic component and too little inorganic component, resulting in a denser SEI film. This reduces the number of lithium ions that can pass through per unit pore cross-section, leading to high lithium-ion transport resistance and poor high-temperature cycle performance.

[0107] In addition, when there is too much organic content in the newly formed SEI film, it will increase the thermoplasticity of the entire SEI film and reduce the overall thermal stability of the SEI film, thereby accelerating the dissolution or damage of the SEI film, triggering side reactions inside the battery, and further deteriorating the high-temperature cycling and storage performance of the battery.

[0108] In some embodiments, the electrolyte may optionally include other additives selected from one or more of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and vinyl sulfate, wherein the mass of the other additives accounts for 0.5%-3% of the mass of the electrolyte.

[0109] The introduced additives can further participate in film formation on the negative electrode surface, and also participate in the repair of the negative electrode SEI film during cycling. Through extensive experiments, the inventors discovered that using SEI-like film component additives in conjunction with the aforementioned additives achieves superior cycling performance, but their dosage needs to be controlled within a certain range. If no other additives are used, the film-forming effect of the SEI-like film component additives is somewhat insufficient. However, using too many other additives will not only affect the extent to which the SEI-like film component additives participate in film formation, but will also make the SEI film too thick, leading to a longer lithium-ion transport path and affecting the battery's cycle performance.

[0110] In some embodiments, the electrolyte may optionally include additives other than those described above. For example, it may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0111] [Lithium-ion battery]

[0112] In one embodiment of this application, a lithium-ion battery is provided, the battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte containing SEI-like film component additives.

[0113] In this application, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0114] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0115] In the lithium-ion battery of this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), but this application is not limited to these materials.

[0116] In the negative electrode sheet of this application, the negative electrode film layer typically comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water. As an example, the conductive agent can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments, the coating of the negative electrode material can optionally employ methods commonly used in the art for coating negative electrode materials. As an example, the negative electrode material can be dissolved in deionized water in a certain proportion with a conductive agent, binder, etc., and mixed evenly to obtain a negative electrode slurry. This slurry is then uniformly coated onto the negative electrode current collector in one or more applications. During multiple charge-discharge cycles of the battery, the negative electrode sheet expands due to the repeated insertion and extraction of lithium ions, thereby damaging the negative electrode structure and adversely affecting the battery's cycle performance and safety performance.

[0118] In some embodiments, optionally, the expansion growth rate of the negative electrode sheet is 2%-10%. Optionally, the negative electrode material on the negative electrode sheet includes one or more of natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon-carbon composite, lithium-tin (Li-Sn) alloy, and lithium-aluminum (Li-Al) alloy.

[0119] In some embodiments, the Li-Sn alloy may optionally be a Li-Sn-O alloy.

[0120] In some embodiments, the negative electrode material on the negative electrode sheet may optionally include one or more of silicon, Sn, SnO, SnO2, and lithium metal.

[0121] For lithium-ion batteries, after multiple charge-discharge cycles, although metal and alloy anode materials, as well as silicon-rich anode materials, are beneficial for improving the battery's fast-charging performance, they also result in a relatively large expansion rate of the anode. Surprisingly, the inventors discovered through experiments that when this type of anode is used in conjunction with an electrolyte containing an SEI film component additive as described in this application, the expansion rate of the anode is significantly improved.

[0122] In some embodiments, optionally, the amount of the SEI-like membrane component additive added is set as m1, which is the mass percentage of the electrolyte, and the mass of the negative electrode active material on the single-sided negative electrode current collector is set as g / 77mm. 2 If m1 is m2, then the ratio of m1 to m2 is 1.1-2.8 (g / 77mm). 2 ) -1 The inventors discovered through extensive experimentation that when the above ratio is 1.1-2.8 (g / 77mm), 2 ) -1 At the same time, the combination of the content of SEI film-like additives in the electrolyte of the same battery and the coating amount of the negative electrode material is reasonable. The combination of the two has a synergistic effect, which is conducive to giving full play to the high-temperature storage performance and high-temperature cycle performance of lithium-ion batteries.

[0123] When the above ratio is too small, the coating amount of the negative electrode material on the negative electrode sheet is relatively large, while the corresponding content of SEI-like film component additives in the electrolyte is relatively small. When the coating amount of the negative electrode material on the negative electrode sheet is too large, more SEI-like film component additives are needed to replenish the SEI film components in time. If the content of SEI-like film component additives in the electrolyte is too small, it will affect the efficiency and quality of film formation on the negative electrode, thus affecting the performance of the battery's electrochemical properties. Conversely, when the above ratio is too large, there is a large amount of SEI-like film component additives, while the coating amount of the negative electrode material on the corresponding negative electrode sheet is small. In this case, the excessive SEI-like film component in the electrolyte will deteriorate the conductivity of the electrolyte, thereby deteriorating the battery performance.

[0124] In this application, the positive electrode includes a positive current collector and a positive electrode material disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0125] In the lithium-ion battery of this application, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), 1,3-propanesulfonate lactone (PS), polyethylene (PE), etc.), but this application is not limited to these materials.

[0126] In this application, non-limiting examples of cathode materials include conventional cathode active materials that can be used in secondary batteries, such as lithium iron phosphate system or nickel cobalt manganese ternary system cathode materials.

[0127] In some embodiments, optionally, when the cathode material belongs to the lithium iron phosphate system, the charging cut-off voltage of the lithium-ion battery can reach 3.65-3.8V; when the cathode material belongs to the nickel-cobalt-manganese ternary system, the charging cut-off voltage of the lithium-ion battery can reach 4.0-4.8V.

[0128] Surprisingly, batteries containing the SEI film component additives described in this application can effectively improve electrolyte side reactions under high voltage, and enhance cycle capacity retention and high-temperature storage performance under high temperature and high pressure. For batteries, increasing the charge / discharge voltage is beneficial for maximizing the capacity of the positive electrode active material and increasing the battery's energy density. However, excessively high charge / discharge voltages often lead to electrolyte decomposition side reactions, deteriorating battery cycle performance and safety. Through extensive experimental research, the inventors discovered that batteries made with electrolytes containing the SEI film component additives described in this application still exhibit good cycle performance and safety even at higher voltages. Taking lithium iron phosphate as an example, the charging cutoff voltage of conventional lithium iron phosphate batteries is generally 3.6-3.65V. Battery performance deteriorates at higher voltages, but the lithium-ion battery described in this application exhibits good high-temperature cycle performance and high-temperature storage performance even at 3.8V (performance diagram referenced). Figure 3 .AB).

[0129] For ternary systems, such as ternary layered materials, the typical upper voltage limit for these materials is 4.0V-4.3V. Increasing this upper voltage limit can significantly improve the capacity and operating voltage of the cathode material, thereby substantially increasing the energy density of the lithium-ion battery. However, simply raising the upper voltage limit, due to the narrow electrochemical window of the electrolyte, will drastically degrade the battery's high-temperature storage and cycling performance. Nevertheless, by using SEI-like film component additives, the corresponding lithium-ion battery exhibits good high-temperature cycling and storage performance even at 4.8V (performance diagram referenced). Figure 4 .AB).

[0130] Optionally, the positive electrode material further includes a conductive agent. However, there is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used in the positive electrode material can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] The positive electrode sheet in this application can be prepared according to methods known in the art. The coating of the positive electrode material can be carried out using a method similar to that used for coating the negative electrode material. As an example, the positive electrode active material, conductive agent, and binder of this application can be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated onto a positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet is obtained.

[0132] [Isolation membrane]

[0133] Lithium-ion batteries using electrolytes, and some lithium-ion batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0134] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0135] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0136] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0137] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is an example of a square-structured lithium-ion battery 5.

[0138] In some implementations, refer to Figure 6 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 via a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific needs.

[0139] [Battery Module]

[0140] In some implementations, lithium-ion batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0141] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7 In battery module 4, multiple lithium-ion batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries 5 can be fixed in place using fasteners.

[0142] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple lithium-ion batteries 5 are housed.

[0143] [Battery Pack]

[0144] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0145] Figure 8 and Figure 9This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0146] [Electrical appliances]

[0147] In addition, this application also provides an electrical device, which includes one or more of the lithium-ion battery, battery module, or battery pack provided in this application. The lithium-ion battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0148] As the electrical device, a lithium-ion battery, battery module, or battery pack can be selected according to its usage requirements.

[0149] Figure 10 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density lithium-ion batteries, a battery pack or battery module can be used.

[0150] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0151] Example

[0152] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products commonly used in the art and available commercially. Unless otherwise specified, the content of each component in the embodiments of this application is based on the mass of the component excluding crystallization water.

[0153] The sources of raw materials involved in the embodiments of this application are as follows:

[0154] Lithium iron phosphate (LiFePO4, Tianjin Guoan Mengguli New Material Technology Co., Ltd.)

[0155] Nickel-cobalt-manganese ternary (LiMO2, M is a Ni-Co-Mn solid solution, with a mass ratio of 8:1:1)

[0156] Artificial graphite (Guangdong Kaijin New Energy Technology Co., Ltd.)

[0157] Separator membrane (polypropylene membrane, CATL)

[0158] N-Methylpyrrolidone (NMP, CAS: 872-50-4, purity ≥99%, Shanghai Maclean Biotechnology Co., Ltd.)

[0159] Polyvinylidene fluoride (CAS: 24937-79-9, molecular weight between 800,000 and 1,500,000, Shanghai Maclean Biotechnology Co., Ltd.)

[0160] Acetylene black (Guangdong Kaijin New Energy Technology Co., Ltd.)

[0161] Conductive agent carbon black (Guangdong Kaijin New Energy Technology Co., Ltd.)

[0162] Acrylates (CAS: 25067-02-1, purity ≥99%, Shanghai Maclean Biotechnology Co., Ltd.)

[0163] Ethylene carbonate (EC, purity ≥99.5%, CAS: 96-49-1, Shanghai Maclean Biotechnology Co., Ltd.)

[0164] Dimethyl carbonate (DMC, purity ≥99.5%, CAS: 616-38-6, Shanghai Maclean Biotechnology Co., Ltd.)

[0165] Ethyl methyl carbonate (EMC, purity ≥99.5%, CAS: 623-53-0, Shanghai Maclean Biotechnology Co., Ltd.)

[0166] Ethylene glycol dimethyl ether (CAS: 110-71-4, purity ≥99%, Shanghai Maclean Biotechnology Co., Ltd.)

[0167] Naphthalene solid (CAS: 91-20-3, purity ≥99%, Shanghai Maclean Biotechnology Co., Ltd.)

[0168] Lithium metal flakes (CAS: 7439-93-2, Shanghai Maclean Biotechnology Co., Ltd.)

[0169] Potassium bromide (KBr, CAS: 7758-02-3, purity ≥98%, Shanghai Maclean Biotechnology Co., Ltd.)

[0170] Lithium hexafluorophosphate (LiPF6, CAS: 21324-40-3, Guangzhou Tinci Advanced Materials Co., Ltd.)

[0171] Lithium difluorophosphate (LiPO2F2, CAS: 24389-25-1, Guangzhou Tinci Advanced Materials Technology Co., Ltd.) and lithium tetrafluoroborate (LiBF4, CAS: 14283-07-9, Guangzhou Tinci Advanced Materials Technology Co., Ltd.)

[0172] Example 1-1

[0173] Preparation of electrolytes containing SEI-like membrane component additives

[0174] The entire preparation process was carried out in a glove box filled with an inert atmosphere (filled with argon, with H2O less than 100 ppm and O2 less than 100 ppm):

[0175] Take a beaker and add 1 mol of pure ethylene glycol dimethyl ether solvent to it; then add 1 mol of solid naphthalene (100% pure naphthalene C) to the solvent. 10 (Based on H8), the mixture was stirred at 50°C and 500 r / min for 3 hours to obtain an organic solution containing naphthalene;

[0176] Add 1 mol of solid lithium metal (calculated as Li) to the above organic solution containing naphthalene, and stir at 500 r / min for 2 h at 50 °C to completely dissolve the lithium sheet, thus obtaining a naphthalene-lithium organic solution.

[0177] At 25°C, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC:EMC:DMC = 30:30:40 to obtain a mixed solvent.

[0178] At 50°C, according to the mass ratio of lithium naphthalene organic solution to mixed solvent = 10:1, 20g of mixed solvent was slowly poured into 200g of lithium naphthalene organic solution, and the reaction was carried out at 300r / min for 3 hours to obtain a mixture containing SEI-like membrane component additives.

[0179] The mixture was dried in a vacuum at 60°C for 2 hours to obtain 10g of SEI membrane component additive solid.

[0180] Preparation of electrolytes containing SEI-like membrane component additives

[0181] At 25°C, 300g of ethylene carbonate (EC), 300g of ethyl methyl carbonate (EMC), and 400g of dimethyl carbonate (DMC) were mixed to obtain a mixed solvent.

[0182] Take 91.65g of the above mixed solvent, and add 0.1g of SEI membrane component additive, 2g of fluoroethylene carbonate and 6.25g of lithium hexafluorophosphate (calculated as LiPF6) to it. After stirring and dissolving, the electrolyte shown in Example 1-1 is obtained.

[0183] Preparation of the positive electrode sheet

[0184] The positive electrode active material lithium iron phosphate (calculated as LiFePO4), binder polyvinylidene fluoride, conductive agent acetylene black, and N-methylpyrrolidone (NMP) were mixed in a weight ratio of 48:1:1:50 and stirred evenly with a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 12 μm, coating one side only. After drying, cold pressing, and slitting, the positive electrode sheet of Example 1-1 was obtained.

[0185] Preparation of the negative electrode sheet

[0186] Artificial graphite (anode material), carbon black (conductive agent), acrylate (binder), and deionized water were mixed evenly in a weight ratio of 48:1:1:50 and stirred uniformly using a vacuum mixer to obtain a cathode slurry. The cathode slurry was then uniformly coated onto a copper foil with a thickness of 8 μm, coating one side to achieve a coating weight of 0.008 g / 77 mm. 2 After drying, cold pressing, and slitting, the negative electrode sheet of Example 1-1 is obtained.

[0187]

Isolation Film

[0188] Polypropylene film is used as the separator.

[0189] [Preparation of Lithium-ion Batteries]

[0190] The positive electrode, separator, and negative electrode of Example 1-1 are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. 12g of the electrolyte containing the SEI-like film additive is then injected, and the casing is sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0191] Examples 1-2 to 1-7

[0192] Except that the percentage of the amount of SEI membrane component additives added to the electrolyte is 0.15%, 0.2%, 0.25%, 0.3%, 0.05%, and 0.35%, respectively, the other steps in Examples 1-2 to 1-7 are the same as in Example 1-1.

[0193] Examples 2-1 to 2-10

[0194] Except that the lithium-supplying material is changed to LiPF6 and LiPO2F2 (the molar ratio of LiPF6 to LiPO2F2 is 1:1), the other additives are changed from fluoroethylene carbonate to vinylethylene carbonate, and the mass ratio of the amount of SEI-like membrane component additives to the lithium-supplying material is changed to 0.5:100, 0.8:100, 1.6:100, 2.4:100, 3.2:100, 4.0:100, 4.8:100, 5:100, 0.1:100, and 6:100, the other steps in Examples 2-1 to 2-10 are the same as those in Examples 1-3.

[0195] Examples 3-1 to 3-8

[0196] Except that the lithium-supplying material is changed to LiPF6, LiPO2F2, and LiBF4 (the molar ratio of LiPF6, LiPO2F2, and LiBF4 is 1:1:1), the other additives are changed from fluoroethylene carbonate to ethylene sulfate, and the percentage of the mass of the other additives in the electrolyte is changed to 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 0%, and 5%, respectively, the other steps in Examples 3-1 to 3-8 are the same as those in Examples 1-3.

[0197] Examples 4-1 to 4-6

[0198] Except in the step of [Preparation of Negative Electrode Sheet], the coating quality is reduced from 0.008g / 77mm. 2 Change to 0.01g / 77mm 2 0.01g / 77mm 2 0.008g / 77mm 2 0.008g / 77mm 2 0.008g / 77mm 2 0.008g / 77mm 2 Except that the SEI membrane component additives are present in the electrolyte at mass percentages of 0.01%, 0.01%, 0.012%, 0.016%, 0.0224%, and 0.024%, respectively, the other steps in Examples 4-1 to 4-6 are the same as in Example 1-1.

[0199] Comparative Example 1

[0200] The electrolyte contains 30 parts by mass of ethylene carbonate (EC), 30 parts by mass of ethyl methyl carbonate and 40 parts by mass of dimethyl carbonate (DMC), and the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte is 0.5 mol / L.

[0201] The other steps are the same as in Example 1-1.

[0202] [Relevant parameters and battery performance tests]

[0203] 1. Negative electrode expansion growth rate test

[0204] At 60°C, the lithium-ion battery corresponding to Example 1-1 was charged at a constant current of 1C to 3.65V, and then charged at a constant voltage to a current of 0.05C. The battery was then disassembled, and the negative electrode portion was removed separately. The thickness h1 of the negative electrode was measured using calipers. For another lithium-ion battery from the same batch, after 300 consecutive charge-discharge cycles (cycle conditions: charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, rested for 5 minutes, and then discharged at a constant current of 1C to 2.5V), this battery was continued to be charged at 1C to 3.65V and charged at a constant voltage to a current of 0.05C. The battery was then disassembled, and the negative electrode portion was removed separately. The thickness h2 of the negative electrode was measured using calipers. The negative electrode expansion growth rate was calculated as [(h2-h1) / h1]×100%. The testing process for the comparative example and other examples was the same. The negative electrode expansion growth rate data are shown in Table 1.

[0205] 2. 60℃ Cyclic Performance Test

[0206] (1) Cyclic performance test of lithium-ion battery at 60℃ under full charge voltage of 3.65V

[0207] Taking Example 1-1 as an example, the battery capacity retention rate test process is as follows: At 60°C, the battery corresponding to Example 1-1 is charged to 3.65V with a constant current of 1C, then charged to 0.05C with a constant voltage of 3.65V, left to rest for 5 minutes, and then discharged to 2.5V with a constant current of 1C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and counting is started simultaneously. The discharge capacity Cn of the battery after the nth cycle is recorded. Then, the battery capacity retention rate Pn after each cycle is Pn = Cn / C0 * 100%, and P1, P2...P... 300 The 100 points are plotted on the y-axis, and the corresponding number of iterations is plotted on the x-axis, as shown in the attached figure. Figure 2 The graph shown in Example 1-1 is a curve of battery capacity retention versus cycle number.

[0208] During this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 300th cycle to n=300. The battery capacity retention rate data for Example 1-1 in Table 1 are data obtained after 300 cycles under the above test conditions, i.e., P. 300 The values ​​were as follows. The testing procedures for the comparative example and other embodiments were the same as above. The data on capacity retention at 60°C were obtained in Table 1.

[0209] (2) Cyclic performance test of lithium-ion battery at 60℃ under full charge voltage of 3.8V

[0210] Taking Example 1-1 as an example, except that the full charge voltage is changed from 3.65V to 3.8V, the other test procedures are the same as those in (1), and the results of this application are obtained. Figure 3 Figure A.

[0211] 3. Storage performance test at 60℃

[0212] (1) Storage performance test of lithium-ion battery at 60℃ under full charge voltage of 3.65V

[0213] Taking Example 1-1 as an example, the battery high-temperature reversible capacity retention rate test process is as follows: At 25°C, the battery corresponding to Example 1-1 is charged to 3.65V with a constant current of 0.5C, and then charged to a current of 0.05C with a constant voltage of 3.65V. After resting for 5 minutes, it is discharged to 2.5V with a constant current of 0.5C. The discharge capacity at this time is recorded as the initial capacity C0.

[0214] The battery was then charged at a constant current of 0.5C to 3.65V, and then charged at a constant voltage of 3.65V to a current of 0.05C. The battery was then placed in a 60°C constant temperature chamber and stored for 60 days. Afterward, the battery was placed in an ambient temperature environment of 25°C. Once the lithium-ion battery temperature had completely cooled to 25°C, it was discharged at a constant current of 0.5C to 2.5V (fully discharged), then charged at a constant current of 0.5C to 3.65V, and finally discharged at a constant current of 0.5V to 2.5V. The discharge capacity at this point is C1. Therefore, the high-temperature reversible capacity retention rate of the battery after 60 days of storage is M = C1 / C0 × 100%. The testing process for the comparative example and other embodiments was the same, and the data on the reversible capacity retention rate at 60°C storage in Table 1 were obtained.

[0215] (2) Storage performance test of lithium-ion battery at 60℃ under full charge voltage of 3.8V

[0216] Taking Example 1-1 as an example, except that the full charge voltage is changed from 3.65V to 3.8V, the other test procedures are the same as those in (1), and the results of this application are obtained. Figure 3 Figure B.

[0217] Note: When the positive electrode active material of the lithium-ion battery in this application is a nickel-cobalt-manganese ternary layered material, this application mainly focuses on its 60°C cycle performance test and 60°C cycle performance test at a full charge voltage of 4.8V. The measured data can be found in [reference needed]. Figure 4 Figures A and B.

[0218] Table 1: Relevant parameters and performance of lithium-ion batteries in the examples and comparative examples

[0219]

[0220]

[0221]

[0222] Table 2: Relevant parameters and performance of lithium-ion batteries in the examples

[0223]

[0224] As shown in Table 1, the high-temperature cycle retention rate and high-temperature storage capacity retention rate of the lithium-ion batteries in all the above embodiments are significantly higher than those in Comparative Example 1. At the same time, the negative electrode expansion growth rate of all embodiments is also lower than that of Comparative Example 1.

[0225] A comprehensive comparison of Examples 1-1 to 1-7 shows that when the amount of the SEI-like film component additive accounts for 0.1%-0.3% of the electrolyte mass, the lithium-ion battery exhibits a high high-temperature cycle retention rate (not less than 94.8%) and a high high-temperature storage capacity (not less than 96.1%). Simultaneously, the negative electrode of this lithium-ion battery also shows a lower negative electrode expansion rate (not exceeding 14.1%). However, when the amount of the SEI-like film component additive is less than 0.1% (Examples 1-6) or greater than 0.3% (Examples 1-7) of the electrolyte mass, the improvement effect on the high-temperature cycle performance, high-temperature storage performance, and negative electrode expansion of the lithium-ion battery is not significant.

[0226] A comprehensive comparison of Examples 2-1 to 2-10 shows that when the mass ratio of the SEI-like film component additive to the lithium-donating material is within the range of 0.5-5:100, the lithium-ion battery exhibits a high high-temperature cycle retention rate (not less than 94%) and a high high-temperature storage capacity (not less than 95.3%). Simultaneously, the negative electrode of this lithium-ion battery also shows a lower negative electrode expansion rate (not exceeding 14.1%). However, when the mass ratio of the SEI-like film component additive to the lithium-donating material is lower than 0.5:100 (Examples 2-9) or higher than 5:100 (Examples 2-10), the improvement on the high-temperature cycle performance, high-temperature storage performance, and negative electrode expansion of the lithium-ion battery is not significant.

[0227] A comprehensive comparison of Examples 3-1 to 3-8 shows that when the electrolyte contains SEI-like film component additives, and the content of other additives in the electrolyte is in the range of 0.5%-3%, the high-temperature cycle retention rate of the lithium-ion battery is relatively high (not less than 95.1%), and the lithium-ion battery also has a relatively high high-temperature storage capacity (not less than 96.9%). However, when the content of other additives in the electrolyte is less than 0.5% (Example 3-7) or more than 3% (Example 3-8), the improvement on the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery is not significant.

[0228] A comprehensive comparison of Examples 4-1 to 1-6 shows that when the ratio of m1 to m2 is between 1.1 and 2.8 (g / 77mm), 2 ) -1 Within this range, the negative electrode expansion of lithium-ion batteries is significantly improved, the high-temperature cycle retention rate of lithium-ion batteries is high, and lithium-ion batteries also have a high high-temperature storage capacity. However, when this ratio is below 1.1 or above 2.8, the improvement in the negative electrode expansion growth rate, the high-temperature cycle performance, and the high-temperature storage performance of the battery is not significant.

Claims

1. A method for preparing an SEI-like membrane component additive, characterized in that, Includes the following steps: In an inert gas atmosphere, a lithium naphthalene organic solution is reacted with a mixed solvent to obtain a mixture containing an SEI-like film component additive, wherein... The mass ratio of lithium naphthalene to the mass of the mixed solvent in the lithium naphthalene organic solution is 2-8:1, and the mixed solvent is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate; The mixture was dried in a vacuum to obtain an SEI-like membrane component additive; The reaction temperature W1 between the lithium naphthalene organic solution and the mixed solvent is 45-60℃, and the reaction time S1 is 60-180 minutes.

2. The method according to claim 1, characterized in that, Based on the mass of the mixed solvent, the amount of ethylene carbonate is 20%-30%, the amount of ethyl methyl carbonate is 30%-40%, the amount of dimethyl carbonate is 30%-50%, and the total is 100%.

3. The method according to claim 2, characterized in that, The reaction was carried out under conditions of thorough stirring.

4. The method according to claim 1, characterized in that, The lithium naphthalene organic solution was prepared by the following method: In an inert gas atmosphere, lithium metal is added to an organic solution containing naphthalene, causing the naphthalene to react with the lithium metal, such that the molar ratio of naphthalene to the added lithium metal is 1-3:

1. During the reaction, the reaction temperature W2 and the reaction time S2 of the naphthalene and lithium metal satisfy the following: 23.59 K·min ≤ ln(W2+273.15)×lnS2 ≤ 30.16 K·min.

5. The method according to claim 4, characterized in that, The reaction between the naphthalene and the lithium metal is carried out under thorough stirring.

6. The method according to claim 4, characterized in that, The reaction temperature W2 is 45-60℃, and the reaction time S2 is 60-180 minutes.

7. The method according to claim 4, characterized in that, In the organic solution containing naphthalene, the molar ratio of the organic solvent to the naphthalene is 1-5:1, and the organic solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol methyl ethyl ether, and ethylene glycol methyl propyl ether.

8. The method according to claim 1, characterized in that, The mixture is dried in a vacuum at a temperature of 60-80°C.

9. The method according to claim 1, characterized in that, The obtained SEI-like film component additive is a solid.

10. An electrolyte, characterized in that, It includes an SEI-like membrane component additive prepared by any one of claims 1-9.

11. The electrolyte according to claim 10, characterized in that, The amount of the SEI-like membrane component additive added is 0.05%-0.3% of the mass percentage of the electrolyte.

12. The electrolyte according to claim 10, characterized in that, The electrolyte contains a lithium-donating substance, and the mass ratio of the amount of the SEI-like membrane component additive to the mass of the lithium-donating substance is 0.5-5:

100.

13. The electrolyte according to claim 12, characterized in that, The lithium-donating material is one or more of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

14. The electrolyte according to claim 10, characterized in that, The electrolyte contains other additives, and the mass of the other additives accounts for 0.5%-3% of the mass of the electrolyte.

15. The electrolyte according to claim 14, characterized in that, The other additives are selected from one or more of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and vinyl sulfate.

16. A lithium-ion battery, characterized in that, It includes a positive electrode, a separator, a negative electrode, and the electrolyte according to any one of claims 10-15, wherein, The negative electrode sheet includes a negative electrode film layer, which includes a negative electrode active material. The negative electrode active material includes one or more of the following: natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon-carbon composite, lithium-tin alloy, and lithium-aluminum alloy.

17. The lithium-ion battery according to claim 16, characterized in that, Let m1 be the mass percentage of the SEI-like membrane component additive in the electrolyte, and m2 be the mass of the negative electrode active material on the single-sided negative electrode current collector. Unit: g / 77mm 2 Therefore, the ratio of m1 to m2 is 1.1-2.8 (g / 77mm). 2 ) -1 .

18. The lithium-ion battery according to claim 16, characterized in that, When the cathode material belongs to the lithium iron phosphate system, the charging cut-off voltage of the lithium-ion battery can reach 3.65-3.8V; when the cathode material belongs to the nickel-cobalt-manganese ternary system, the charging cut-off voltage of the lithium-ion battery can reach 4.0-4.8V.

19. A battery module, characterized in that, The lithium-ion battery includes any one of claims 16-18.

20. A battery pack, characterized in that, Includes the lithium-ion battery according to any one of claims 16-18 or the battery module according to claim 19.

21. An electrical appliance, characterized in that, The device includes one or more of the lithium-ion battery according to any one of claims 16-18, the battery module according to claim 19, or the battery pack according to claim 20, wherein the lithium-ion battery, the battery module, or the battery pack is used as a power source for the electrical device or as an energy storage unit for the electrical device.

Images