Electrolyte additive, electrolyte and battery

Abstract

The invention discloses an electrolyte additive, an electrolyte and a battery, the electrolyte additive comprises a first additive and a second additive, the first additive comprises a compound shown in a formula 1, and the second additive comprises a compound shown in a formula 2. The first additive and the second additive in the electrolyte additive can play a role together, a stable and low-impedance SEI film can be formed on a negative electrode, and the low-temperature discharge performance and the high-temperature cycle stability performance of the battery are improved. # imgabs0 #

Description

Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to an electrolyte additive, an electrolyte and a battery. Background Art

[0002] In recent years, with the rapid development and widespread application of various portable electronic devices, new energy electric vehicles and energy storage systems, the demand for secondary batteries with high energy density, long cycle life, safe use and good rate characteristics has become increasingly urgent. Considering that cars need to travel under complex road conditions and environmental conditions, or some electronic devices need to be used in poor environmental conditions, the batteries used as power sources for electric vehicles or electronic devices need to adapt to these complex conditions. In addition to considering these conditions, the battery's service life and the battery's charge and discharge cycle performance must also be considered. Especially when electric vehicles or electronic devices are in low or high temperature environments, the battery needs to have excellent low-temperature charge and discharge performance and high-temperature cycle performance.

[0003] In low temperature environments, the ionic conductivity inside the battery decreases, ion transmission is blocked, and the battery power output drops significantly. At the same time, the chemical reaction kinetics of the electrode material will be inhibited under low temperature conditions, further limiting the battery's discharge performance. In high temperature environments, the side reactions inside the battery will intensify, such as electrolyte decomposition and chemical inactivation of electrode materials, which will accelerate the aging of the battery components and shorten the battery life.

[0004] Therefore, based on the above-mentioned shortcomings, it is necessary to develop an electrolyte that improves the discharge performance of secondary batteries at low temperatures and the cycle performance at high temperatures. Summary of the invention

[0005] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present application is to provide an electrolyte additive, an electrolyte and a battery, which can improve the discharge performance of the secondary battery at low temperatures and the cycle performance at high temperatures by adding the electrolyte additive to the secondary battery.

[0006] In a first aspect of the present application, an electrolyte additive is provided. According to an embodiment of the present application, the electrolyte includes: a first additive, wherein the first additive includes a compound shown in Formula 1:

[0007]

[0008]

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

[0010] The second additive comprises a compound represented by Formula 2:

[0011]

[0012] Wherein, R4 includes a five-membered aromatic ring or a six-membered aromatic ring, and R5 and R6 independently include halogen, C1-C4 alkyl or C1-C4 fluoroalkyl.

[0013] Therefore, the first additive and the second additive in the electrolyte additive of the present application can work together to form a stable and low-impedance SEI film at the negative electrode, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0014] According to an embodiment of the present application, the mass ratio of the first additive to the second additive is 1:(0.1-6). Thus, when the mass ratio of the first additive to the second additive is within the above range, it can play a better role and form a stable and low-impedance SEI film on the surface of the negative electrode, effectively improving the low-temperature discharge performance and high-temperature cycle stability of the battery. According to an embodiment of the present application, the mass ratio of the first additive to the second additive is 1:(0.5-2).

[0015] According to an embodiment of the present application, the first additive includes at least one of the following substances:

[0016]

[0017]

[0018] Therefore, the first additive of the above type can improve the stability of the SEI film, inhibit the dissolution of transition metals on the positive electrode surface and the positive and negative electrode interface reaction, and improve the high-temperature cycle performance of the battery.

[0019] According to an embodiment of the present application, the second additive includes at least one of the following substances:

[0020]

[0021] Therefore, the second additive of the above type can further enhance the stability of the SEI film, optimize the high temperature performance of the battery, and at the same time reduce the internal resistance of the battery and enhance the low temperature performance of the battery.

[0022] In the second aspect of the present application, an electrolyte is provided. According to an embodiment of the present application, the electrolyte includes the electrolyte additive described in the first aspect. Thus, adding the electrolyte to a secondary battery can improve the low-temperature discharge performance and high-temperature cycle performance of the battery.

[0023] According to an embodiment of the present application, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1% to 3%. Thus, by making the mass proportion of the first additive within the above range, a relatively stable SEI film can be formed on the surface of the negative electrode. This can reduce the increase in SEI film impedance caused by the excessive mass of the first additive, and will not significantly reduce the low-temperature discharge performance of the battery.

[0024] According to an embodiment of the present application, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1% to 3%. Thus, by making the mass proportion of the second additive within the above range, the stability of the SEI film can be further enhanced, the ionic conductivity of the SEI film can be improved, the internal resistance of the battery can be reduced, and the low-temperature discharge performance of the battery can be improved, while avoiding the influence of the high-temperature performance of the battery caused by the excessive mass of the second additive.

[0025] In 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 described in the second aspect. Thus, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0026] 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 2g / Ah to 5g / Ah. Therefore, the ratio within the above range can effectively ensure that the electrolyte fully infiltrates into the gap between the positive electrode sheet and the negative electrode sheet, and can also control the gap between the positive and negative electrodes and reduce the internal resistance.

[0027] According to the embodiment of the present application, the specific surface area of ​​the negative electrode plate is 0.6 m 2 / g~2.5m 2 Thus, by making the specific surface area of ​​the negative electrode sheet within the above range, a highly stable and low-impedance SEI film can be formed, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0028] According to the embodiment of the present application, the battery satisfies the following formula: the value of N×(M1+M2) / B is (0.16-20); wherein M1 is the mass proportion of the first additive; M2 is the mass proportion of the second additive; N is the ratio of the total mass of the electrolyte of the electrolyte to the discharge capacity of the battery; and B is the specific surface area of ​​the negative electrode sheet. Thus, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0029] According to an embodiment of the present application, the value of N×(M1+M2) / B is (1 to 15). Thus, the battery has excellent low-temperature discharge performance and high-temperature cycle performance.

[0030] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application are described in detail below, which are intended to be used to explain the present application but should not be construed as limiting the present application.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] For simplicity, only some numerical ranges are specifically disclosed herein. However, 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, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the description and claims of this application and any variations thereof are intended to cover non-exclusive inclusions.

[0035] In this document, the terms "include" or "comprising" are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0036] Explanation of terms

[0037] 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 "C 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).

[0038] The term "five-membered ring" or "six-membered ring" refers to a ring structure formed by five or six carbon atoms connected together, and the carbon atoms can be connected by single bonds or alternating single and double bonds. For example, it can be cyclopentane, cyclohexane, cyclopentene, cyclohexene, benzene ring, etc.

[0039] The term "aromatic ring" may be used alone or as a large part of "aralkyl", "aralkyloxy" or "aryloxyalkyl" to refer to monocyclic, bicyclic and tricyclic carbon ring systems containing 6-14 ring members, wherein at least one ring system is aromatic, wherein each ring system contains 3-7 ring members and has one or more points of attachment to the rest of the molecule. The term "aryl" may be used interchangeably with the term "aromatic ring", for example, aromatic rings may include phenyl, naphthyl and anthracenyl.

[0040] The term "C1-C4 fluoroalkyl" refers to an alkyl group containing 1 to 4 carbon atoms, wherein one or more hydrogen atoms are replaced by fluorine atoms, such as -CF3, -C(F2)C(F3), -C(F2)C(F2)C(F3), etc.

[0041] The term "halogen" or "halogen atom" refers to F, Cl, Br and I.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Electrolyte Additives

[0044] The present application provides an electrolyte additive. According to an embodiment of the present application, the electrolyte additive includes: a first additive and a second additive.

[0045] Wherein, the first additive includes a compound shown in Formula 1:

[0046]

[0047] R1 includes -S(O2)- or -C(O)-, and R2 and R3 each independently include 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.

[0048] It should be noted that the dotted line indicates the position to be connected, and when half of the dotted line is within the ring, it means that it can be connected to any position on the ring.

[0049] Wherein, the second additive includes a compound shown in Formula 2:

[0050]

[0051] R4 includes a five-membered aromatic ring or a six-membered aromatic ring, and R5 and R6 each independently include a halogen, a C1-C4 alkyl group or a C1-C4 fluoroalkyl group.

[0052] The electrolyte additive proposed in this application includes a compound shown in Formula 1 and a compound shown in Formula 2, and these two compounds can work together. Among them, the compound shown in Formula 1 can preferentially react electrochemically on the surface of the positive and negative electrodes 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, prevents the dissolution of transition metals on the positive electrode surface and adverse reactions at the positive and negative electrode interfaces. However, the SEI film dominated by sulfate lithium salt (ROSO3Li) has a higher impedance, which reduces the discharge performance of the battery at low temperatures. When the compound of formula 2 is added, because it contains S=O double bonds and fluoroalkyl groups, 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 be close to the reaction potential of the compound of formula 1 containing three ring structures, thereby simultaneously generating an 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 group also improves the ionic 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, and improve the low temperature discharge performance and high temperature cycle stability of the battery.

[0053] 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 may be 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, etc., or may be a range consisting of any of the above numerical values. Thus, 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 ionic 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).

[0054] In some embodiments of the present application, the first additive includes at least one of the following substances:

[0055]

[0056] Therefore, the first additive adopts at least one of the above-mentioned substances, which can change the negative electrode SEI film component from carbonate lithium salt (ROCO2Li) to sulfate lithium salt (ROSO3Li) while participating in the film formation at the positive electrode, thereby improving the stability of the SEI film. At the same time, it can also work together with the second additive to further improve the stability of the SEI film and improve the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0057] In some embodiments of the present application, the second additive includes at least one of the following substances:

[0058]

[0059] Therefore, the second additive adopts at least one of the above-mentioned substances, wherein the S=O double bond and the fluoroalkyl group can promote the electrochemical reaction between the second additive and the first additive, and work together to further enhance the stability of SEI. At the same time, the fluoroalkyl group can improve the ionic conductivity of the SEI film, reduce the internal resistance of the battery, and enhance the low-temperature performance of the battery.

[0060] Electrolyte

[0061] The present application proposes an electrolyte. According to an embodiment of the present application, the electrolyte includes: the above-mentioned electrolyte additive. The electrolyte has all the characteristics and advantages of the above-mentioned electrolyte additive, 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.

[0062] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1% to 3%, that is, each gram of the electrolyte includes 0.1% to 3% of the first additive, for example, it can be 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, etc., or it can be a range composed of any of the above values. Therefore, the mass proportion of the first additive is within the above range, which is conducive to the first additive and the second additive to fully play their role together, which can effectively improve the stability and ionic conductivity of the SEI film, reduce the impedance of the SEI film and the internal resistance of the battery, and improve the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0063] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1% to 3%, that is, each gram of the electrolyte includes 0.1% to 3% of the second additive, for example, it can be 0.1%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, etc., or it can be a range composed of any of the above values. Therefore, the mass proportion of the second additive is within the above range, which is conducive to the first additive and the second additive to fully play their role together, improve the stability and ionic conductivity of the SEI film, reduce the impedance of the SEI film and the internal resistance of the battery, and improve the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0064] In some embodiments of the present application, the electrolyte also includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butane sultone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, ethyl methyl 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.

[0065] In other embodiments of the present application, the solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0066] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the solvent is 65%-87%, for example, 65%, 67%, 70%, 72%, 75%, 80%, 85%, 87%, etc., or can be a range consisting of any of the above values.

[0067] In some embodiments of the present application, the electrolyte may further include other additives, and the other additives are selected from vinylene carbonate (VC), vinyl ethylene carbonate, vinyl sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, succinic anhydride, maleic anhydride, 2-methyl maleic anhydride, methyl carbonate-2-propynyl ester, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, p-phenylene diisocyanate, 2,4-toluene diisocyanate, N-phenylbis (trifluoromethane At least one of imide, vinyl bisulphate, phenyl methanesulfonate, vinyl bisulphate, bis-spiro propylene sulphate, hydroquinone difluorosulfonate, triallyl phosphate, tripropargyl phosphate, 2,4-butane sultone, isocyanoethyl methacrylate, tris(trimethylsilyl)borate, tris(trimethylsilane)phosphate, tris(vinyldimethylsilyl)phosphate, 4,4'-bi-1,3-dioxolane-2,2'-dione, propyl diprop-2-ynyl phosphate, ethyl diprop-2-ynyl phosphate, tetramethylmethylene diphosphate, isocyanoethyl methacrylate, and 2-fluoropyridine.

[0068] In some embodiments of the present application, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0069] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the lithium salt is 5%-20%, for example, it can be 5%, 10%, 15%, 20%, etc., or it can be a range composed of any of the above values.

[0070] Battery

[0071] The present application proposes a battery. According to an embodiment of the present application, the battery includes a negative electrode plate and the above-mentioned electrolyte. The battery has all the characteristics and advantages of the above-mentioned electrolyte, which will not be repeated here. In general, the battery has excellent low-temperature discharge performance and high-temperature cycle stability.

[0072] In some embodiments of the present application, the ratio of the total mass of the electrolyte to the discharge capacity of the battery is 2g / Ah to 5g / Ah, for example, 2g / Ah, 2.5g / Ah, 3g / Ah, 3.5g / Ah, 4g / Ah, 4.5g / Ah, 5g / Ah, etc., or can be a range composed 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 retention of the compound of formula 1 and the compound of formula 2 in the battery. When the ratio is within the above range, it can effectively ensure that the electrolyte is fully infiltrated into the gap between the positive electrode sheet and the negative electrode sheet, while controlling the gap between the positive and negative electrodes and reducing the internal resistance.

[0073] In some embodiments of the present application, the specific surface area of ​​the negative electrode plate is 0.6 m 2 / g~2.5m 2 / g. For example, it can be 0.6m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g, 2.5m 2 / g, etc., or can be a range composed of any of the above numerical values. Among them, the surface of the negative electrode sheet has a negative electrode active material, and the surface of the negative electrode active material has active sites. The compound shown in Formula 1 and the compound shown in Formula 2 can be reduced at the active sites on the surface of the negative electrode active material. When the specific surface area of ​​the negative electrode sheet is larger, the more active sites there are, so more compounds shown in Formula 1 and compounds shown in Formula 2 are needed to form a good SEI film. The present application controls the specific surface area of ​​the negative electrode active material within the above range to form a SEI film with low impedance and high stability, thereby improving the low-temperature discharge performance and high-temperature cycle stability of the battery.

[0074] In some embodiments of the present application, the battery satisfies the following formula: the value of N×(M1+M2) / B is (0.16-20); wherein M1 is the mass ratio of the first additive; M2 is the mass ratio 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 plate. For example, N×(M1+M2) / B can be 0.16, 1, 2, 4, 6, 8, 10, 12, 15, 17 or 20, or can be a range composed of any of the above values. Among them, N determines the total mass of the electrolyte added to the battery, determines the number of molecules of the compound shown in Formula 1 and the compound shown in Formula 2 in the battery; B greatly affects the number of molecules required for the compound shown in Formula 1 and the compound shown in Formula 2 to form the SEI film. When the above formula relationship is satisfied between them, the number of molecules of the compound shown in Formula 1 and the compound shown in Formula 2 in the battery can just form a good SEI film without excess. As a result, the battery can have excellent low-temperature discharge performance and high-temperature cycle performance.

[0075] In some embodiments of the present application, the value of N×(M1+M2) / B may be (1-15), (2-15), (4-15), etc. Thus, the battery can have excellent low-temperature discharge performance and high-temperature cycle performance.

[0076] In some embodiments of the present application, the battery includes a positive electrode active material. The specific type of the positive electrode active material is not limited. Active materials known in the art that can be used for battery positive electrodes can be used. Those skilled in the art can select according to actual needs.

[0077] 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.

[0078] In some embodiments of the present application, the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, 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.

[0079] 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.

[0080] Understandable, Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2 and LiFe 1-x M x In PO4, the selection of M in each chemical formula is independent of each other and does not affect each other. They can be the same or different. Similarly, in the above-mentioned list of positive electrode active materials, the selection of a and x is also opposite to each other and does not affect each other. They can be the same or different.

[0081] When the battery is a sodium ion battery, the positive electrode active material may include at least one of the following materials:

[0082] Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0<x≤1.

[0083] 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 At least one of (0≤y≤1).

[0084] Prussian blue compounds: Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0<a≤2, 0<b<1, and 0<c<1.

[0085] In some embodiments, the battery includes a positive electrode active material including Na X1 M1O2、Na X2At least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 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.

[0086] Under normal circumstances, the battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting 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, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0087] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes the above-mentioned positive electrode active material.

[0088] In some embodiments of the present application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be an aluminum foil. The composite positive electrode current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. For example, the composite negative electrode current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. substrates).

[0089] In some embodiments of the present application, the positive electrode active material layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments of the present application, the positive electrode active material layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0091] In some embodiments of the present application, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0092] 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, wherein the negative electrode active material layer includes a negative electrode active material.

[0093] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0094] In some embodiments of the present application, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nanocarbon, elemental silicon, silicon oxide, silicon carbon composite, silicon alloy, elemental tin, tin oxide, tin carbon composite, tin alloy, lithium titanate.

[0095] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may 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).

[0096] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments of the present application, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0098] In some embodiments of the present application, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0099] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0100] In some embodiments of the present application, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

[0101] The scheme of the present application will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are indicated in the embodiments, the technology or conditions described in the literature in this area or the product specification are carried out. The reagents used or the instruments that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0102] Example 1

[0103] 1. Preparation of Electrolyte

[0104] In an inert atmosphere (water <0.1ppm, oxygen <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:EMC=3:7, and after mixing evenly, bis(fluorosulfonyl)imide lithium salt (LiFSI) and lithium hexafluorophosphate (LiPF6) were added, and the mass proportion of LiFSI in the electrolyte was 2wt%, and the mass proportion of LiPF6 in the electrolyte was 10wt%. Compound 1-1 and compound 2-1 were then added, and based on the total mass of the electrolyte, the mass proportion M1 of compound 1-1 (first additive) was 0.5wt%, and the mass proportion M2 of compound 2-1 (second additive) was 0.5wt%.

[0105] 2. Preparation of positive electrode

[0106] The positive electrode active material (nickel-cobalt-manganese ternary material), conductive agent (acetylene black) and binder poly(vinylidene fluoride) are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 96:2:2, and are fully stirred and mixed to form a uniform positive electrode slurry (the solid content in the positive electrode slurry is 60wt%). The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, rolling and slitting, the positive electrode sheet is obtained.

[0107] 3. Preparation of negative electrode sheet

[0108] The negative electrode active material (graphite), conductive agent (acetylene black), binder (sodium carboxymethyl cellulose) and styrene-butadiene rubber (SBR) are dispersed in an appropriate amount of deionized water at a mass ratio of 95:2:2:1, and fully stirred to form a uniform negative electrode slurry (solid content in the negative electrode slurry is 50wt%). The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and after drying, rolling and slitting, a negative electrode sheet is obtained. The specific surface area Bm of graphite is 2 / g is 1.2m 2 / g.

[0109] 4. Preparation of Cells

[0110] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell, and the bare cell is placed in an outer packaging shell, and after drying, the electrolyte prepared in step 1 is injected, and the total mass of the electrolyte is 7g. After vacuum packaging, standing, forming, shaping and other processes, the preparation of the battery is completed, and its rated capacity is 2Ah, and the ratio of the total mass of the electrolyte to the discharge capacity of the battery is Ng / Ah of 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 is 2Ah.

[0111] The battery preparation methods of Examples 2-40 and Comparative Examples 1-6 are the same as that of Example 1, except that the composition of additives in the electrolyte is different, as shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] Embodiment 41

[0116] 1. Preparation of Electrolyte

[0117] Under an inert atmosphere (water <0.1ppm, oxygen <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of EC:EMC=3:7, and after mixing evenly, sodium salt is added, the sodium salt includes NaPF6, and the molar concentration of sodium in the electrolyte is 1mol / L. Compound 1-1 and compound 2-1 are then added, and based on the total mass of the electrolyte, the mass proportion M1 of compound 1-1 (first additive) is 0.5wt%, and the mass proportion M2 of compound 2-1 (second additive) is 0.5wt%.

[0118] 2. Preparation of positive electrode

[0119] The positive electrode active material Na(Ni 0.33 Fe 0.33 Mn 0.33 )O2, conductive agent carbon black, conductive agent carbon nanotubes, binder polyvinylidene fluoride and binder maleic acid are dispersed in a 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 is evenly coated on the surface of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, rolling, baking, slitting and spot welding of the pole ears.

[0120] 3. Preparation of negative electrode sheet

[0121] The negative electrode active material hard carbon, conductive agent carbon black, binder SBR and binder CMC are dispersed in deionized water in a mass ratio of 95:1.5:2:1.5, and stirred evenly to obtain a negative electrode active material layer slurry; the negative electrode active material layer slurry is evenly coated on the surface of the negative electrode collector copper foil, and the negative electrode sheet is obtained after drying, rolling, baking, slitting and spot welding of the pole ears.

[0122] 4. Isolation film

[0123] A polyethylene film is used as the isolation film.

[0124] 5. Preparation of sodium ion batteries

[0125] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to isolate the positive and negative electrodes, and the bare battery cell is wound, and the pole ears are welded. The bare battery cell is placed in an outer package, and the prepared electrolyte is injected into the dried battery cell. The sodium ion battery cell is packaged, allowed to stand, formed, and shaped to complete the preparation of the sodium ion battery.

[0126] The preparation method of the sodium ion battery of Comparative Examples 7-8 is the same as that of Example 41, except that the composition of the additives in the electrolyte is different, as shown in Table 3.

[0127] Table 3

[0128]

[0129] Performance Testing

[0130] The low-temperature discharge performance and high-temperature cycle performance of the batteries obtained in Examples 1-40 and Comparative Examples 1-6 were characterized. The characterization results are shown in Table 4.

[0131] 1. Low temperature discharge performance test

[0132] At 25°C, charge to 4.4V at 1C constant current, charge to 0.05C at 4.4V constant voltage, and then discharge to 2.75V at 0.5C constant current. The discharge capacity is recorded as C1. At -20°C, leave for 4 hours, then discharge at 0.5C constant current. The discharge capacity is recorded as C2. -20°C low temperature discharge capacity retention rate = C2 / C1*100%.

[0133] 2. High temperature cycle performance test

[0134] At 45°C, charge the battery at 1C constant current to 4.4V, then charge at constant voltage to a cut-off current of 0.05C, and then discharge the battery at 1C constant current to 2.75V. The discharge capacity is recorded as C3. Repeat the charge and discharge until the capacity decays to 80% C3 and record the number of cycles.

[0135] The low-temperature discharge performance and high-temperature cycle performance of the batteries obtained in Example 41 and Comparative Examples 1-2 were characterized. The characterization results are shown in Table 5.

[0136] 1. Low temperature discharge performance test

[0137] At 25°C, charge to 4.0V at 1C constant current, charge to 0.05C at 4.0V constant voltage, and then discharge to 1.50V at 0.5C constant current. The discharge capacity is recorded as C1. At -20°C, leave for 4 hours, then discharge at 0.5C constant current. The discharge capacity is recorded as C2. The -20°C low temperature discharge capacity retention rate = C2 / C1*100%.

[0138] 2. High temperature cycle performance test

[0139] At 45°C, charge the battery at 1C constant current to 4.0V, then charge at constant voltage to a cut-off current of 0.05C, and then discharge the battery at 1C constant current to 1.50V. The discharge capacity is recorded as C3. Repeat the charge and discharge until the capacity decays to 80% C3 and record the number of cycles.

[0140] Table 4

[0141]

[0142]

[0143] Table 5

[0144] Low temperature discharge performance / % High temperature cycle performance / cycle Embodiment 41 74.2％ 1898 Comparative Example 7 70.2％ 1648 Comparative Example 8 71.9％ 1594

[0145] It can be seen from Table 4 that in Examples 1-40 of the present application, the first additive and the second additive can work together and are added to the secondary battery to improve the low-temperature discharge performance and high-temperature cycle performance of the battery.

[0146] Compared with Example 2, in Comparative Examples 1-6, the first additive and the second additive were not added at the same time, and the low-temperature discharge performance and high-temperature cycle performance of the obtained batteries were significantly poorer. It can be seen that the electrolyte additives, the first additive and the second additive proposed in the present application can work together and be added to the secondary battery to improve the low-temperature discharge performance and high-temperature cycle performance of the battery.

[0147] The low-temperature discharge performance of the batteries of other embodiments in Examples 1-6 is significantly better than that of Example 6. This is because the amount of the first additive added in Example 6 (3%) is higher than that in other embodiments. The possible reason is that the use of excessive first additive will increase the impedance of the SEI film, thereby reducing the low-temperature discharge performance of the battery; the high-temperature cycle performance of the batteries of other embodiments in Examples 1-6 is significantly better than that of Example 1. This is because the amount of the first additive added in Example 1 (0.1%) is lower than that in other embodiments. The possible reason is that the use of too little first additive will reduce the stability of the SEI film, thereby affecting the high-temperature cycle performance of the battery.

[0148] The low-temperature discharge performance of the batteries of other embodiments in Examples 7-11 is significantly better than that of Example 7. This is because the amount of the second additive added in Example 7 (0.1%) is lower than that in other embodiments. The possible reason is that too little of the second additive is used, and the effect of the second additive and the first additive together is small, and the effect of reducing the internal resistance of the battery is small, so the effect of improving the low-temperature cycle performance of the battery is weak; the high-temperature cycle performance of the batteries of other embodiments in Examples 7-11 is significantly better than that of Example 11. This is because the amount of the second additive added in Example 11 (3%) is higher than that in other embodiments. The possible reason is that the use of excessive second additive affects the film formation of the second additive and reduces the effect between the two.

[0149] Compared with Example 2, when changing 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 sheet (B), or any one of N×(M1+M2) / B, the low-temperature discharge performance and high-temperature cycle performance of the battery will be affected. Therefore, the three need to meet a certain relationship, that is, N is 2g / Ah to 5g / Ah, B is 0.6m 2 / g~2.5m 2 / g, 0.16≤N×(M1+M2) / B≤20, which helps to improve the high temperature cycle performance and low temperature discharge performance of the battery.

[0150] It can be seen from Table 5 that compared with comparative examples 7 and 8, Example 41 of the present application, by using the first additive and the second additive of the present application at the same time, can also improve the low-temperature discharge performance and high-temperature cycle performance of the sodium ion battery, indicating that the electrolyte additive of the present application is also suitable for sodium ion batteries.

[0151] In addition, the applicant also verified whether the electrolyte additive of the present application can improve the low-temperature discharge performance and high-temperature cycle performance of lithium batteries / sodium batteries with different positive electrode active materials (such as lithium cobalt oxide, lithium nickel manganese oxide, etc.) or sodium batteries with different positive electrode active materials (such as NaFePO4, Na3V2(PO4)3, etc.). The results show that the electrolyte additive of the present application can be applied to lithium batteries / sodium batteries with different positive electrode active materials, and can improve the high-temperature cycle performance and low-temperature discharge performance of lithium batteries / sodium batteries prepared with different positive electrode active materials.

[0152] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0153] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

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

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 2, characterized in that: The first additive includes at least one of the following substances: And / or, the second additive includes at least one of the following substances:

4. An electrolyte, characterized in that: The electrolyte additive comprises the electrolyte additive according to any one of claims 1 to 3.

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

6. A battery, characterized in that: The invention comprises a negative electrode sheet and the electrolyte according to any one of claims 4 to 5.

7. The battery according to claim 6, characterized in that The ratio of the total mass of the electrolyte to the discharge capacity of the battery is 2 g / Ah to 5 g / Ah.

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

9. The battery according to any one of claims 6 to 8, characterized in that: The battery meets the following requirements: The value of N×(M1+M2) / B is (0.16~20); 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 plate.

10. The battery according to claim 9, characterized in that The value of N×(M1+M2) / B is (1 to 15).

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