Electrolyte additive, electrolyte, and battery

Abstract

The present application discloses an electrolyte additive, an electrolyte, and a battery. The electrolyte additive comprises a first additive and a second additive, wherein the first additive comprises a compound represented by formula 1, and the second additive comprises a compound represented by formula 2. The first additive and the second additive in the electrolyte additive of the present application are therefore capable of working together and forming a stable SEI film with low impedance on a negative electrode, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

Description

Electrolyte additive, electrolyte and battery

[0001] Priority information

[0002] The present application claims priority to and the benefit of the filing date of the patent application No. 202411242252.5 filed with the China National Intellectual Property Office on September 5, 2024, and incorporates herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and specifically relates to an electrolyte additive, an electrolyte and a battery. BACKGROUND

[0004] In recent years, the rapid development and wide application of various portable electronic devices, new energy electric vehicles and energy storage systems have made the demand for secondary batteries with high energy density, long cycle life, safe use and good rate characteristics increasingly urgent. Considering that the automobile needs to travel under complex road conditions and environmental conditions, or some electronic devices need to be used in poor environmental conditions, the battery as the power supply of the electric vehicle or electronic device needs to adapt to these complex conditions. In addition to considering these conditions, the service life of the battery and the charge-discharge cycle performance of the battery also need to be considered. Especially when the electric vehicle or electronic device is in a low-temperature environment or a high-temperature environment, the battery needs to have excellent low-temperature charge-discharge performance and high-temperature cycle performance.

[0005] Under low-temperature conditions, the internal ion conductivity of the battery is reduced, and the ion transmission is blocked, resulting in a significant decrease in the power output of the battery; at the same time, under low-temperature conditions, the chemical reaction kinetics of the electrode material is also inhibited, further limiting the discharge performance of the battery. Under high-temperature conditions, the side reactions inside the battery will be intensified, such as electrolyte decomposition, chemical deactivation of the electrode material, etc., accelerating the aging of each component of the battery and shortening the service life of the battery.

[0006] Therefore, based on the above deficiencies, it is necessary to develop an electrolyte that can improve the discharge performance of the secondary battery at low temperature and the cycle performance at high temperature. SUMMARY

[0007] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to propose an electrolyte additive, an electrolyte and a battery, and the addition of the electrolyte additive to the secondary battery can improve the discharge performance of the secondary battery at low temperature and the cycle performance at high temperature.

[0008] In a first aspect of the present application, an electrolyte additive is proposed. According to an embodiment of the present application, the electrolyte comprises: a first additive, the first additive comprising a compound represented by Formula 1:

[0009] wherein R1 comprises -S(O2)- or -C(O)-, R2, R3 each independently comprises and at least one of R1, R2 and R3 contains a sulfur atom;

[0010] a second additive, the second additive comprising a compound represented by Formula 2:

[0011] wherein R4 comprises a five-membered aromatic ring, a six-membered aromatic ring, R5 and R6 each independently comprises halogen, C1-C4 alkyl or C1-C4 fluoroalkyl.

[0012] Thus, the first additive and the second additive in the electrolyte additive of the present application can jointly play a role, and can form a stable and low-impedance SEI film on the negative electrode, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0013] According to the embodiments of the present application, the mass ratio of the first additive and the second additive is 1:(0.1-6). Thus, when the mass ratio of the first additive and the second additive is within the above range, the role can be better played, and a stable and low-impedance SEI film can be formed on the surface of the negative electrode, thereby effectively improving the low-temperature discharge performance and high-temperature cycle stability of the battery. According to the embodiments of the present application, the mass ratio of the first additive and the second additive is 1:(0.5-2).

[0014] According to the embodiments of the present application, the first additive comprises at least one of the following substances:

[0015] Thus, the first additive of the above type can improve the stability of the SEI film, inhibit the dissolution of transition metals on the surface of the positive electrode and the reaction at the interface between the positive electrode and the negative electrode, and improve the high-temperature cycle performance of the battery.

[0016] According to the embodiments of the present application, the second additive comprises at least one of the following substances:

[0017] Thus, the second additive of the above type can further enhance the stability of the SEI film, optimize the high-temperature performance of the battery, reduce the internal resistance of the battery, and enhance the low-temperature performance of the battery.

[0018] In the second aspect of the present application, an electrolyte is provided. According to the embodiments of the present application, the electrolyte comprises the electrolyte additive of the first aspect. Thus, when the electrolyte is added to a secondary battery, the low-temperature discharge performance and high-temperature cycle performance of the battery can be improved.

[0019] According to an embodiment of the present application, the mass percentage of the first additive is 0.1% to 3% based on the total mass of the electrolyte. In this way, by setting the mass percentage of the first additive in the above range, a relatively stable SEI film can be formed on the surface of the negative electrode. In this way, the impedance of the SEI film caused by excessive mass of the first additive can be reduced, and the low-temperature discharge performance of the battery can not be excessively reduced.

[0020] According to an embodiment of the present application, the mass percentage of the second additive is 0.1% to 3% based on the total mass of the electrolyte. In this way, by setting the mass percentage of the second additive in the above range, the stability of the SEI film can be further enhanced, the ion conductivity of the SEI film can be improved, the internal resistance of the battery can be reduced, the low-temperature discharge performance of the battery can be improved, and the influence of excessive mass of the second additive on the high-temperature performance of the battery can be avoided.

[0021] According to a third aspect of the present application, a battery is provided. According to an embodiment of the present application, the battery comprises a negative electrode sheet and the electrolyte of the second aspect. In this way, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0022] According to an embodiment of the present application, the ratio of the total mass of the electrolyte to the discharge capacity of the battery is 2 g / Ah to 5 g / Ah. In this way, by setting the ratio in the above range, the electrolyte can be effectively ensured to be fully soaked into the gap of the positive electrode sheet and the negative electrode sheet, and the gap between the positive electrode and the negative electrode can be controlled to reduce the internal resistance.

[0023] According to an embodiment of the present application, the specific surface area of the negative electrode sheet is 0.6 m 2 / g to 2.5 m 2 / g. In this way, by setting the specific surface area of the negative electrode sheet in the above range, a SEI film with high stability and low impedance can be formed, and the low-temperature discharge performance and high-temperature cycle stability of the battery can be improved.

[0024] According to an embodiment of the present application, the battery satisfies the following formula: the value of N x (M1+M2) / B is (0.16 to 20); wherein M1 is the mass percentage of the first additive; M2 is the mass percentage of the second additive; N is the ratio of the total mass of the electrolyte to the discharge capacity of the battery; and B is the specific surface area of the negative electrode sheet. In this way, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0025] According to an embodiment of the present application, the value of N x (M1+M2) / B is (1 to 15). In this way, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0026] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and / or can be learned by practice of the application. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described below with the intent to enable those skilled in the art to make and use them. It will be apparent, however, to those skilled in the art that the embodiments described below are merely examples and are not intended to limit the application.

[0028] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a common embodiment, or an embodiment that is independent of all other embodiments. One of ordinary skill in the art will readily recognize from the disclosure herein, that the embodiments described herein can be combined with embodiments not expressly described, but with modification expected of persons of ordinary skill in the art.

[0029] For the sake of brevity, only some of the numerous technical features of the application are specifically disclosed herein. However, it will be apparent to those skilled in the art from the disclosure herein that the application can be practiced without such specific details. Various representative features and techniques are grouped together in sections and / or paragraphs for the purpose of streamlining the disclosure and enhancing the legibility of the specification. Accordingly, the disclosure of features herein does not imply that a specific feature is necessary or indispensable to the practice of the application. Thus, the application should not be construed as being limited to the particular combinations of features disclosed, but rather, the application should be understood to include all features that are possible under the scope of the claims.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the meaning and definition of the terms used herein are therefore specified herein only if necessary for the understanding of the application. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of," and variations thereof. Unless otherwise noted, the terms "including" and "comprising" are open-ended and do not exclude the presence of additional features.

[0031] In this document, the terms "comprises" or "comprising" are used in the sense of "including" or "including, but not limited to", that is, in the sense of open-ended language that does not exclude additional features.

[0032] Terminology

[0033] The term "alkyl" refers to a saturated hydrocarbon containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. Phrases containing this term, such as "C1-C6alkyl," "C1-C6alkyl," "C1-C6alkyl," and the like, refer to a straight or branched hydrocarbon chain containing only carbon and hydrogen atoms, having the indicated number of carbon atoms, and which is attached completely through carbon atoms. 1-4"Alkyl" refers to an alkyl group containing 1 to 4 carbon atoms. Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1 -propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1 -butyl (n-Bu, n-butyl, -CH2CH2CH2CH3).

[0034] The term "five-membered ring" or "six-membered ring" refers to a cyclic structure formed by the connection of five carbon atoms or six carbon atoms, which can be connected by single bonds, or by alternating single and double bonds. For example, it can be cyclopentane, cyclohexane, cyclopentene, cyclohexene, benzene ring, etc.

[0035] The term "aromatic ring" can be used alone or as part of "aralkyl", "aralkoxy" or "aryloxyalkyl", and refers to monocyclic, bicyclic and tricyclic carbocyclic ring systems containing 6-14 members in total, wherein at least one ring system is aromatic, wherein each ring system contains 3-7 membered rings, and has one or more attachment points to the rest of the molecule. The term "aryl" can be used interchangeably with the term "aromatic ring", such as aromatic ring can include phenyl, naphthyl and anthryl.

[0036] The term "C1-C4 fluoroalkyl" refers to an alkyl group containing 1 to 4 carbon atoms, in which one or more hydrogen atoms are replaced by fluorine atoms. For example, it can be -CF3, -C(F2)C(F3), -C(F2)C(F2)C(F3), etc.

[0037] The term "halogen" or "halogen atom" refers to F, Cl, Br and I.

[0038] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0039] Electrolyte additive

[0040] The present application proposes an electrolyte additive. According to an embodiment of the present application, the electrolyte additive comprises: a first additive and a second additive.

[0041] The first additive comprises a compound represented by formula 1:

[0042] R1 comprises -S(O2)- or -C(O)-, R2, R3 respectively independently comprises at least one of R1, R2 and R3 contains a sulfur atom, and at least one of R1, R2 and R3 contains a sulfur atom.

[0043] It should be noted that the dashed line represents the position to be connected, and when the dashed line is located in the ring, it means that it can be connected to any position on the ring.

[0044] The second additive includes a compound shown in Formula 2:

[0045] R4 includes a five-membered aromatic ring or a six-membered aromatic ring, and R5 and R6 each independently includes halogen, C1-C4 alkyl or C1-C4 fluoroalkyl.

[0046] The electrolyte additive proposed in the present application includes a compound shown in Formula 1 and a compound shown in Formula 2, and the two compounds can jointly play a role. Among them, the compound shown in Formula 1 can preferentially occur electrochemical reaction on the positive and negative electrode surface during the first charging and cycling of the battery, because its reduction potential is higher than that of the organic solvent in the electrolyte. This reaction not only forms a protective film on the positive electrode, but also changes the SEI film composition of the negative electrode from carbonate lithium salt (ROCO2Li) to sulfate lithium salt (ROSO3Li). This change effectively improves the stability of the SEI film and prevents the dissolution of transition metals on the positive electrode surface and the adverse reaction at the positive and negative electrode interface. However, the SEI film mainly composed of sulfate lithium salt (ROSO3Li) has high impedance, which will reduce the discharge performance of the battery at low temperature. When the compound of Formula 2 is added, because it contains S=O double bond and fluoroalkyl, the local electron cloud density of the aromatic ring is reduced, thereby reducing the energy barrier of the electrochemical reaction, so that the compound of Formula 2 can react with the compound of Formula 1 containing three ring structures with close potential energy, thereby simultaneously occurring electrochemical reaction. This process regulates the SEI film constructed by the compound of Formula 1 and introduces N elements and more S elements into the SEI film, thereby enhancing the stability of the SEI film and further optimizing the high-temperature performance of the battery. In addition, the strong electron-withdrawing property of the fluoroalkyl also improves the ion conductivity of the SEI film, significantly reduces the internal resistance of the battery, and enhances the low-temperature performance of the battery. Therefore, the electrolyte additive of the present application can improve the stability of the SEI film of the battery, improve the low-temperature discharge performance and high-temperature cycle stability performance of the battery.

[0047] In some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:(0.1-6). For example, the mass ratio of the first additive to the second additive can be 1:0.5, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2, or the like, or can be a range consisting of any of the above values. In this way, by controlling the mass ratio of the first additive to the second additive within the above range, the effects of the first additive and the second additive can be fully exerted, the stability and ion conductivity of the SEI film can be improved, the internal resistance of the battery can be reduced, and the low-temperature discharge performance and high-temperature cycle stability of the battery can be improved. In some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:(0.5-2).

[0048] In some embodiments of the present application, the first additive comprises at least one of the following substances:

[0049] In this way, by using at least one of the above substances as the first additive, the SEI film component of the negative electrode can be changed from a carbonate lithium salt (ROCO2Li) to a sulfonate lithium salt (ROSO3Li) while the positive electrode participates in film formation, the stability of the SEI film can be improved, and the effects of the first additive and the second additive can be exerted together to further improve the stability of the SEI film, the low-temperature discharge performance of the battery, and the high-temperature cycle stability of the battery.

[0050] In some embodiments of the present application, the second additive comprises at least one of the following substances:

[0051] In this way, by using at least one of the above substances as the second additive, the S=O double bond and the fluoroalkyl group in the second additive can promote the electrochemical reaction of the second additive with the first additive, the effects of the second additive and the first additive can be exerted together to further improve the stability of the SEI film, the ion conductivity of the SEI film can be improved by the fluoroalkyl group, the internal resistance of the battery can be reduced, and the low-temperature performance of the battery can be improved.

[0052] Electrolyte

[0053] The present application provides an electrolyte. According to an embodiment of the present application, the electrolyte comprises the electrolyte additive described above. The electrolyte has all the features and advantages of the electrolyte additive described above, which will not be repeated here. In general, the electrolyte can improve the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0054] In some embodiments of the present application, the first additive accounts for 0.1% to 3% by mass based on the total mass of the electrolyte, i.e., 0.1% to 3% of the first additive is included in each gram of the electrolyte, for example, 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, or the like, or a range consisting of any of the foregoing values. In this way, the first additive accounts for a mass percentage within the above range, which is conducive to the first additive and the second additive being able to jointly fully play their roles, improving the stability and ionic conductivity of the SEI film, reducing the impedance of the SEI film and the internal resistance of the battery, and improving the low-temperature discharge performance and high-temperature cycle stability performance of the battery.

[0055] In some embodiments of the present application, the second additive accounts for 0.1% to 3% by mass based on the total mass of the electrolyte, i.e., 0.1% to 3% of the second additive is included in each gram of the electrolyte, for example, 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, or the like, or a range consisting of any of the foregoing values. In this way, the second additive accounts for a mass percentage within the above range, which is conducive to the first additive and the second additive being able to jointly fully play their roles, improving the stability and ionic conductivity of the SEI film, reducing the impedance of the SEI film and the internal resistance of the battery, and improving the low-temperature discharge performance and high-temperature cycle stability performance of the battery.

[0056] In some embodiments of the present application, the electrolyte further includes a solvent, and the solvent includes at least one of vinyl carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butyrolactone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2-difluoroethyl methyl carbonate.

[0057] In some embodiments of the present application, the solvent includes at least one of vinyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0058] In some embodiments of the present application, the solvent accounts for 65-87% by mass based on the total mass of the electrolyte. For example, 65%, 67%, 70%, 72%, 75%, 80%, 85%, 87%, etc., or a range consisting of any of the aforementioned values.

[0059] In some embodiments of the present application, the electrolyte can further include other additives selected from at least one of vinylene carbonate (VC), vinyl ethylene carbonate, vinyl sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sulfite, 1,3-propylene sulfite, 1,4-butane sulfite, 2,4-butane sulfite, succinic anhydride, maleic anhydride, 2-methyl maleic anhydride, methyl carbonic acid-2-propargyl ester, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, p-phenylene diisocyanate, 2,4-toluene diisocyanate, N-phenyl bis(trifluoromethane sulfonate) imide, bisvinyl sulfate, methyl sulfonic acid phenyl ester, bisvinyl sulfate, bispropylene sulfite, p-phenylenediamine difluorosulfonate, triallyl phosphate, tripropargyl phosphate, 2,4-butane sulfite, isocyanatoethyl methacrylate, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tris(vinyldimethylsilyl) phosphate, 4,4'-bi-1,3-dioxolan-2,2'-dione, propyl diprop-2-ynyl phosphate, ethyl diprop-2-ynyl phosphate, tetramethyl methylene diphosphate, isocyanatoethyl methacrylate, 2-fluoropyridine.

[0060] In some embodiments of the present application, the electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(trifluoromethane sulfonate) imide.

[0061] In some embodiments of the present application, the lithium salt accounts for 5-20% by mass based on the total mass of the electrolyte, for example, 5%, 10%, 15%, 20%, etc., or a range consisting of any of the aforementioned values.

[0062] Battery

[0063] The present application provides a battery. According to embodiments of the present application, the battery includes a negative electrode sheet and the above-mentioned electrolyte. The battery has all the features and advantages of the aforementioned electrolyte, which will not be repeated here. In general, the battery has excellent low-temperature discharge performance and high-temperature cycle stability.

[0064] In some embodiments of the present application, the ratio of the total mass of the electrolyte to the discharge capacity of the battery is 2 g / Ah to 5 g / Ah, for example, can be 2 g / Ah, 2.5 g / Ah, 3 g / Ah, 3.5 g / Ah, 4 g / Ah, 4.5 g / Ah, 5 g / Ah, or can be a range consisting of any of the above values. Among them, the ratio of the total mass of the electrolyte to the discharge capacity of the battery determines the total mass of the electrolyte added to the battery, which can affect the amount of compounds of formula 1 and formula 2 retained in the battery. When the ratio is within the above range, it can effectively ensure that the electrolyte is fully soaked into the interstices of the positive and negative electrode sheets, while controlling the gap between the positive and negative electrodes and reducing the internal resistance.

[0065] In some embodiments of the present application, the specific surface area of the negative electrode sheet is 0.6 m 2 / g to 2.5 m 2 / g. For example, it can be 0.6 m 2 / g, 0.8 m 2 / g, 1 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g, 2 m 2 / g, 2.2 m 2 / g, 2.5 m 2 / g, etc., or can be a range consisting of any of the above values. Among them, the negative electrode active material is on the surface of the negative electrode sheet, and the active site is on the surface of the negative electrode active material. Compounds of formula 1 and formula 2 can be reduced at the active site on the surface of the negative electrode active material. The larger the specific surface area of the negative electrode sheet, the more active sites, so more compounds of formula 1 and formula 2 are needed to form a good SEI film. By controlling the specific surface area of the negative electrode active material within the above range, the present application can form an SEI film with low impedance and high stability, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0066] In some embodiments of this application, the battery satisfies the following formula: the value of N×(M1+M2) / B is (0.16~20); where M1 is the mass percentage of the first additive; M2 is the mass percentage of the second additive; N is the ratio of the total mass of the electrolyte to the discharge capacity of the battery; and B is the specific surface area of ​​the negative electrode. For example, N×(M1+M2) / B can be 0.16, 1, 2, 4, 6, 8, 10, 12, 15, 17, or 20, or a range of any of the above values. N determines the total mass of the electrolyte added to the battery and the number of molecules of the compounds shown in Formula 1 and Formula 2 in the battery; B significantly influences the number of molecules required for the formation of the SEI film by the compounds shown in Formula 1 and Formula 2. When they satisfy the above formula relationship, the number of molecules of the compounds shown in Formula 1 and Formula 2 in the battery is just enough to form a good SEI film without excess. Therefore, the battery can have excellent low-temperature discharge performance and high-temperature cycling performance.

[0067] In some embodiments of this application, the value of N×(M1+M2) / B can be (1~15), (2~15), (4~15), etc. This enables the battery to possess excellent low-temperature discharge performance and high-temperature cycle performance.

[0068] In some embodiments of this application, the battery includes a positive electrode active material. The specific type of the positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a battery can be used. Those skilled in the art can select according to actual needs.

[0069] When the battery is a lithium-ion battery, the positive electrode active material includes lithium iron phosphate material, nickel-cobalt-manganese ternary material, or lithium cobalt oxide material.

[0070] In some embodiments of this application, the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4 and Li2Mn 1-x At least one of O4, M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, 0≤a<0.2, 0≤x<1.

[0071] For example, 0≤a≤0.19, 0.05≤a≤0.15, 0.08≤a≤0.13, 0.1≤a≤0.12; 0≤x≤0.9, 0.1≤x≤0.8, 0.2≤x≤0.7, 0.3≤x≤0.6, 0.4≤x≤0.5, etc.

[0072] It can be understood that Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2 and LiFe 1-x M x PO4, the selection of M in each chemical formula is independent of each other and does not affect each other, and can be the same or different. Similarly, in the above list of positive active materials, the selection of a and x is also opposite to each other and does not affect each other, and can be the same or different.

[0073] When the battery is a sodium ion battery, the positive active material can include at least one of the following materials:

[0074] Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, Cu, and 0

[0075] Polyanionic compounds: NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, referred to as NVP), Na4Fe3(PO4)2(P2O7), NaM’PO4F (M’ includes at least one of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1).

[0076] Prussian blue compounds: Na a Me b Me’ c (CN)6, wherein Me and Me’ each independently includes at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0

[0077] In some embodiments, the battery includes a positive active material, and the positive active material includes Na X1 M1O2, Na X2at least one of M2[M3(CN)6], NaFeP04, Na3V2(P04)3, Na2M4P207, Na2Fe2(S04)3, Na2M4(S04)2-2H20, wherein 0 < xi < 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu.

[0078] Generally, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and functions to prevent short circuiting between the positive and negative electrodes while allowing ions to pass through.

[0079] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including the positive active material described above.

[0080] In some embodiments of the present application, the positive current collector can include a metal foil or a composite positive current collector. For example, the metal foil can be an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (e.g., a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0081] In some embodiments of the present application, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] In some embodiments of the present application, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic resin.

[0083] In some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and drying, cold-pressing, and the like.

[0084] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0085] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0086] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art. As an example, the negative electrode active material can include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, nanocarbon, elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, elemental tin, tin oxide compounds, tin-carbon composites, tin alloys, and at least one of lithium titanate.

[0087] In some embodiments of the present application, the negative electrode active material layer can further include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0088] In some embodiments of the present application, the negative electrode active material layer can further include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments of the present application, the negative electrode active material layer can further include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0090] In some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after drying, cold pressing and the like, a negative electrode sheet is obtained.

[0091] The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be selected.

[0092] In some embodiments of the present application, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyolefin film, aromatic polyamide film, polytetrafluoroethylene film, and polyether sulfone film.

[0093] The solutions of the present application will be explained below in connection with examples. Those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or according to the product manual are used. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be obtained commercially.

[0094] Example 1

[0095] 1. Preparation of electrolyte

[0096] Under an inert atmosphere (moisture <0.1 ppm, oxygen <1 ppm), ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC: EMC = 3:7, and after uniform mixing, lithium bisfluorosulfonylimide (LiFSI) and lithium hexafluorophosphate (LiPF6) were added, the mass ratio of LiFSI in the electrolyte was 2wt%, and the mass ratio of LiPF6 in the electrolyte was 10wt%. Then compound 1-1 and compound 2-1 were added, based on the total mass of the electrolyte, the mass ratio M1 of compound 1-1 (first additive) was 0.5wt%, and the mass ratio M2 of compound 2-1 (second additive) was 0.5wt%.

[0097] 2. Preparation of positive electrode sheet

[0098] The positive electrode active material Ni 0.6 Co 0.1 Mn 0.3The positive electrode active material (LiFePO4), conductive agent (acetylene black) and binder poly(vinylidene fluoride) were dispersed in N-methyl pyrrolidone (NMP) solvent in a mass ratio of 96:2:2, mixed thoroughly under stirring to form a uniform positive electrode slurry (solid content in the positive electrode slurry was 60wt%), the positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and then dried, rolled and cut to obtain the positive electrode sheet.

[0099] 3. Preparation of the negative electrode sheet

[0100] The negative electrode active material (graphite), conductive agent (acetylene black), binder (sodium carboxymethyl cellulose) and butadiene-styrene rubber (SBR) were dispersed in deionized water in a mass ratio of 95:2:2:1, mixed thoroughly under stirring to form a uniform negative electrode slurry (solid content in the negative electrode slurry was 50wt%), the negative electrode slurry was uniformly coated on the negative electrode current collector copper foil, and then dried, rolled and cut to obtain the negative electrode sheet, the specific surface area Bm of the graphite was 1.2m2 / g. 2 2 / g.

[0101] 4. Preparation of the battery

[0102] The above positive electrode sheet, separator and above negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, then wound to obtain a bare cell, and the bare cell was placed in an outer packaging shell, dried, and then injected with the electrolyte prepared in step 1, and the total mass of the electrolyte was 7g. After vacuum packaging, standing, formation and shaping, the preparation of the battery was completed, and the rated capacity of the battery was 2Ah, and the ratio N g / Ah of the total mass of the electrolyte to the discharge capacity of the battery was 3.5g / Ah. Specifically, the capacity obtained by discharging the battery at a current of 1C after being fully charged at a current of 1C was 2Ah.

[0103] The battery preparation methods of Examples 2-40 and Comparative Examples 1-6 were the same as those of Example 1, except that the additive compositions in the electrolyte were different, as shown in Table 1.

[0104] Table 1

[0105] Example 41

[0106] 1. Preparation of the electrolyte

[0107] ​Ethylene carbonate (EC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC: EMC = 3:7 under an inert atmosphere (moisture <0.1 ppm, oxygen <1 ppm), and sodium salt was added after uniform mixing. The sodium salt included NaPF6, and the substance concentration of sodium in the electrolyte was 1 mol / L. Then, compound 1-1 and compound 2-1 were added. Based on the total mass of the electrolyte, the mass ratio M1 of compound 1-1 (first additive) was 0.5 wt%, and the mass ratio M2 of compound 2-1 (second additive) was 0.5 wt%.

[0108] 2. Preparation of positive electrode sheet

[0109] The positive electrode active material Na(Ni 0.33 Fe 0.33 Mn 0.33 )O2, the conductive agent carbon black, the conductive agent carbon nanotube, the binder polyvinylidene fluoride, and the binder maleic acid were dispersed in the solvent N-methylpyrrolidone in a mass ratio of 95:2.5:0.5:1.8:0.2 to obtain a positive electrode active material layer slurry. The positive electrode active material layer slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying, rolling, baking, slitting, and spot welding of the tabs, a positive electrode sheet was obtained.

[0110] 3. Preparation of negative electrode sheet

[0111] The negative electrode active material hard carbon, the conductive agent carbon black, the binder SBR, and the binder CMC were dispersed in deionized water in a mass ratio of 95:1.5:2:1.5, and after uniform stirring, a negative electrode active material layer slurry was obtained. The negative electrode active material layer slurry was uniformly coated on the surface of the negative electrode current collector copper foil, and after drying, rolling, baking, slitting, and spot welding of the tabs, a negative electrode sheet was obtained.

[0112] 4. Isolation film

[0113] A polyethylene film was used as the isolation film.

[0114] 5. Preparation of sodium ion battery

[0115] The positive electrode sheet, the isolation film, and the negative electrode sheet were stacked in order, with the isolation film between the positive electrode sheet and the negative electrode sheet to separate the positive electrode and the negative electrode. A bare cell was obtained by winding, and the tabs were welded. The bare cell was placed in an outer package, and the electrolyte prepared above was injected into the dried cell. After packaging, standing, formation, shaping, and the like, the preparation of the sodium ion battery was completed.

[0116] The preparation method of the sodium ion battery of Comparative Examples 7-8 was the same as that of Example 41, except that the additive composition in the electrolyte was different, as shown in Table 2.

[0117] Table 2

[0118] Performance test

[0119] The low-temperature discharge performance and high-temperature cycle performance of the batteries obtained from Examples 1-40 and Comparative Examples 1-6 were characterized, and the characterization results are shown in Table 3.

[0120] 1. Low-temperature discharge performance test

[0121] At 25°C, the battery was charged at 1C constant current to 4.4V, charged at constant voltage 4.4V to the cutoff current 0.05C, and then discharged at 0.5C constant current to 2.75V, and the discharge capacity was recorded as C1. At -20°C, the battery was rested for 4 hours, and then discharged at 0.5C constant current, and the discharge capacity was recorded as C2, and the -20°C low-temperature discharge capacity retention rate = C2 / C1*100%.

[0122] 2. High-temperature cycle performance test

[0123] At 45°C, the battery was charged at 1C constant current to 4.4V, and then charged at constant voltage to the cutoff current 0.05C, and then discharged at 1C constant current to 2.75V, and the discharge capacity was recorded as C3, and the charge-discharge was repeated until the capacity decayed to 80% C3, and the cycle number was recorded.

[0124] The low-temperature discharge performance and high-temperature cycle performance of the batteries obtained from Examples 41 and Comparative Examples 1-2 were characterized, and the characterization results are shown in Table 4.

[0125] 1. Low-temperature discharge performance test

[0126] At 25°C, the battery was charged at 1C constant current to 4.0V, charged at constant voltage 4.0V to the cutoff current 0.05C, and then discharged at 0.5C constant current to 1.50V, and the discharge capacity was recorded as C1. At -20°C, the battery was rested for 4 hours, and then discharged at 0.5C constant current, and the discharge capacity was recorded as C2, and the -20°C low-temperature discharge capacity retention rate = C2 / C1*100%.

[0127] 2. High-temperature cycle performance test

[0128] At 45°C, the battery was charged at 1C constant current to 4.0V, and then charged at constant voltage to the cutoff current 0.05C, and then discharged at 1C constant current to 1.50V, and the discharge capacity was recorded as C3, and the charge-discharge was repeated until the capacity decayed to 80% C3, and the cycle number was recorded.

[0129] Table 3

[0130] Table 4

[0131] As can be seen from Table 3, in the embodiments 1-40 of the present application, the first additive and the second additive can jointly play a role, and can be added to the secondary battery to improve the low-temperature discharge performance and the high-temperature cycle performance of the battery.

[0132] Compared with the embodiment 2, the low-temperature discharge performance and the high-temperature cycle performance of the battery obtained in the comparative examples 1-6 are obviously poorer, because the first additive and the second additive are not added at the same time, which shows that the electrolyte additives proposed in the present application can jointly play a role, and can be added to the secondary battery to improve the low-temperature discharge performance and the high-temperature cycle performance of the battery.

[0133] The low-temperature discharge performance of the battery in the other embodiments of the embodiments 1-6 is obviously better than that of the embodiment 6, because the first additive is added in a larger amount (3%) in the embodiment 6 than in the other embodiments, and the possible reason is that the use of excessive first additive can increase the impedance of the SEI film, thereby reducing the low-temperature discharge performance of the battery; the high-temperature cycle performance of the battery in the other embodiments of the embodiments 1-6 is obviously better than that of the embodiment 1, because the first additive is added in a smaller amount (0.1%) in the embodiment 1 than in the other embodiments, and the possible reason is that the use of too little first additive can reduce the stability of the SEI film, thereby affecting the high-temperature cycle performance of the battery.

[0134] The low-temperature discharge performance of the battery in the other embodiments of the embodiments 7-11 is obviously better than that of the embodiment 7, because the second additive is added in a smaller amount (0.1%) in the embodiment 7 than in the other embodiments, and the possible reason is that the use of too little second additive can jointly play a smaller role with the first additive, and can have a smaller effect on reducing the internal resistance of the battery, thereby having a weaker effect on improving the low-temperature cycle performance of the battery; the high-temperature cycle performance of the battery in the other embodiments of the embodiments 7-11 is obviously better than that of the embodiment 11, because the second additive is added in a larger amount (3%) in the embodiment 11 than in the other embodiments, and the possible reason is that the use of excessive second additive can affect the film formation of the second additive, thereby reducing the effect between the two.

[0135] Compared with the embodiment 2, when any one of the ratio of the total mass of the electrolyte to the discharge capacity of the battery (N), the specific surface area of the negative electrode plate (B), or N x (M1+M2) / B is changed in the embodiments 28-40, the low-temperature discharge performance and the high-temperature cycle performance of the battery are affected. Therefore, the three need to satisfy a certain relationship, i.e., N is 2 g / Ah~5 g / Ah, B is 0.6 m 2 / g~2.5 m 2 / g, and 0.16≤N x (M1+M2) / B≤20, so as to help improve the high-temperature cycle performance and the low-temperature discharge performance of the battery.

[0136] As can be seen from Table 4, the low-temperature discharge performance and high-temperature cycle performance of the sodium ion battery can also be improved by using the first additive and the second additive of the application in Example 41 compared with Comparative Examples 7 and 8, which indicates that the electrolyte additive of the application is also suitable for sodium ion batteries.

[0137] In addition, the applicant also verified whether the electrolyte additive of the application can improve the low-temperature discharge performance and high-temperature cycle performance of lithium batteries prepared by using different positive active materials (such as lithium cobalt oxide, lithium nickel manganese oxide, etc.) or sodium batteries prepared by using different positive active materials (such as NaFePO4, Na3V2(PO4)3, etc.). It was found that the electrolyte additive of the application can be suitable for lithium batteries / sodium batteries with different positive active materials, and can improve the high-temperature cycle performance and low-temperature discharge performance of lithium batteries / sodium batteries prepared by using different positive active materials.

[0138] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0139] Although the embodiments of the application have been shown and described above, it should be understood that the above-described embodiments are exemplary and should not be construed as limiting the application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the application.

Claims

1. An electrolyte additive characterized in that, comprises: a first additive comprising a compound of Formula 1: wherein R1comprises -S(O2)- or -C(O)-, R2, R3each independently comprises and at least one of R1, R2 and R3 contains a sulfur atom; a second additive comprising a compound of Formula 2: wherein R4 comprises a five-membered aromatic ring or a six-membered aromatic ring, and R5 and R6 each independently comprises a halogen, a C1-C4 alkyl group or a C1-C4 fluoroalkyl group.

2. The electrolyte additive according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.1-6), optionally 1:(0.5-2).

3. The electrolyte additive according to claim 1 or 2, characterized in that, The first additive includes at least one of the following: and / or, the second additive comprises at least one of the following:

4. An electrolyte, characterized by The electrolyte comprises the electrolyte additive according to any one of claims 1-3.

5. The electrolyte according to claim 4, characterized in that The mass percentage of the first additive is 0.1%-3% based on the total mass of the electrolyte. And / or, the mass percentage of the second additive is 0.1%-3% based on the total mass of the electrolyte.

6. A battery, characterized by The battery comprises the negative electrode sheet and the electrolyte according to any one of claims 4-5.

7. The battery of claim 6, wherein, The ratio of the total mass of the electrolyte to the discharge capacity of the battery is 2 g / Ah-5 g / Ah.

8. The battery according to claim 6 or 7, characterized in that The specific surface area of the negative electrode sheet is 0.6 m 2 / g ~ 2.5 m 2 / g.

9. The battery according to any one of claims 6 to 8, characterized in that The battery satisfies: The value of N×(M1+M2) / B is (0.16-20); wherein, M1 is the mass percentage of the first additive; M2 is the mass percentage of the second additive; N is the ratio of the total mass of the electrolyte to the discharge capacity of the battery; B is the specific surface area of the negative electrode sheet.

10. The battery of claim 9, wherein, The value of N×(M1+M2) / B is (1-15).

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