Electrolyte additive, battery electrolyte and application thereof

Abstract

The present application relates to the field of battery technology, and in particular to an electrolyte additive, a battery electrolyte, and its application. The provided electrolyte additive includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas I to II: The free radical scavengers of the provided structural formulas I to II are stable carriers of nitrogen free radicals or oxygen free radicals. Therefore, when used in the electrolyte, they can consume harmful groups such as CH3· free radicals, acyl free radicals, and CH3O· free radicals generated during the charging and discharging process of the secondary battery, and can effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively inhibiting the gas production phenomenon of the secondary battery during charging and discharging, significantly reducing the gas production, reducing the volume expansion of the secondary battery, and effectively improving the stability and safety of the secondary battery during charging and discharging.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to an electrolyte additive, a battery electrolyte and applications thereof. Background Art

[0002] During the first charge (i.e., formation) of a lithium-ion battery, a solid electrolyte membrane (SEI membrane) will form at the interface between the positive and negative electrodes and the electrolyte. Although the formation of this irreversible SEI membrane will consume the Li released from the electrolyte and the positive electrode material, + , resulting in irreversible capacity loss and a decrease in the first coulombic efficiency, but the organic solvent insolubility of the SEI film also plays a good protective role for the positive and negative electrode materials, avoiding damage to the electrode materials due to the co-embedding of solvent molecules, thereby greatly improving the cycle performance and service life of lithium-ion batteries. In addition to the large amount of gas generated during the formation stage of the SEI film, lithium-ion batteries will inevitably produce a certain amount of gas during actual use. The gas generated inside the battery and the accumulated pressure will cause problems such as battery volume expansion and increased impedance. Under abnormal conditions such as overcharging, over-discharging, and high temperature, the battery gas production will also increase significantly. The gas produced is both toxic and explosive, and is an important cause of battery safety problems. Therefore, solving the technical problem of large gas production of lithium-ion batteries during the formation and use stages is of great significance to improving battery safety performance.

[0003] To solve the gas production problem of the above-mentioned lithium-ion batteries, the methods currently used include using acid anhydride compounds, cyclic esters such as γ-butyrolactone, polynitrile compounds, etc. as additives and adding them to the electrolyte to form positive and negative electrode protective films to inhibit gas production. However, these measures often have problems such as poor ion conductivity of the protective film, increased impedance, and instability of the positive and negative electrode protective films.

[0004] In addition, in order to improve the low coulomb efficiency problem caused by irreversible loss of the negative electrode, researchers have developed lithium replenishment technology, including positive electrode lithium replenishment technology and negative electrode lithium replenishment technology. Among them, the positive electrode lithium replenishment technology is to add a small amount of high-capacity material (i.e. positive electrode lithium replenishment additive) during the positive electrode slurry process. During the charging process, Li + Lithium is extracted from high-capacity materials to replenish the irreversible capacity lost during the initial charge and discharge. Currently, materials used as positive electrode lithium supplement additives primarily include lithium-rich compounds, nanocomposites based on conversion reactions, and binary lithium compounds. However, research and practical applications have shown that the use of existing lithium supplement additives also leads to increased gas production during the formation phase of lithium-ion batteries. This can cause gassing within the sealed battery system, leading to battery volume expansion and safety issues.

[0005] Therefore, there is no good solution to effectively improve the problem of lithium-ion gas production without affecting other battery properties. Summary of the Invention

[0006] The purpose of the present application is to provide an electrolyte additive, a battery electrolyte and their application, aiming to solve the problem in the prior art that secondary batteries produce a large amount of gas during use, which affects battery performance.

[0007] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0008] In a first aspect, the present application provides an electrolyte additive, wherein the electrolyte additive includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas I to II:

[0009]

[0010] Wherein, in structural formula I, R1 and R2 are selected from the same or different hydrogen atoms or C1-C10 alkyl groups; in structural formula II, X1-X4 are selected from the same or different C1-C15 alkyl groups or C1-C15 substituted alkyl groups, and Y1 and Y2 are selected from the same or different C, N, O, S, B, Si atoms or their derivative groups.

[0011] In a second aspect, the present application provides an electrolyte for a secondary battery, the electrolyte comprising a metal salt electrolyte, an organic solvent and an electrolyte additive, wherein the electrolyte additive is selected from electrolyte additives.

[0012] In a third aspect, the present application provides a method for preparing an electrolyte for a secondary battery, comprising the following steps:

[0013] Providing a metal salt electrolyte, an organic solvent, and an electrolyte additive according to the electrolyte of the secondary battery;

[0014] performing a first mixing process on the organic solvent and the electrolyte additive to obtain an electrolyte additive solution;

[0015] The metal salt electrolyte and the electrolyte additive solution are subjected to a second mixing process to obtain an electrolyte for a secondary battery.

[0016] In a fourth aspect, the present application provides a secondary battery, which includes a negative electrode collector, a negative electrode material, an electrolyte, a separator, a positive electrode material, and a positive electrode collector, wherein the electrolyte is an electrolyte of a secondary battery or an electrolyte prepared by a method for preparing an electrolyte of a secondary battery.

[0017] The electrolyte additive provided in the first aspect of the present application includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas I to II. The free radical scavengers of the provided structural formulas I to II are stable carriers of nitrogen free radicals or oxygen free radicals. Therefore, when used in the electrolyte, they can consume harmful groups such as CH3· free radicals, acyl radicals, CH3O· free radicals generated during the charging and discharging process of the secondary battery, and can effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively inhibiting the gas production phenomenon of the secondary battery during charging and discharging, significantly reducing the gas production, reducing the volume expansion of the secondary battery, and thus effectively improving the stability and safety of the charging and discharging of the secondary battery.

[0018] The electrolyte of the secondary battery provided in the second aspect of the present application includes an electrolyte additive, which is a free radical scavenger that can combine with harmful groups such as CH3·free radicals, acyl free radicals, CH3O·free radicals, and further effectively inhibit the generation of active oxygen. In the process of assembling a battery for use, it effectively solves the problem that the secondary battery is prone to gas generation during charging and discharging, thereby affecting the battery properties.

[0019] The third aspect of the present application provides a method for preparing an electrolyte for a secondary battery. The method can obtain the electrolyte through a two-step mixing process. The preparation method is simple and is conducive to wide use.

[0020] The secondary battery provided in the fourth aspect of the present application has an electrolyte assembled with an electrolyte that includes an electrolyte additive. Therefore, the obtained secondary battery does not expand or produce gas during circulation, or the expansion and gas production are small, and its cycle performance is high, thereby having high safety performance and a long service life. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0022] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0023] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0024] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0025] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0026] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0027] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referred to. For example, a first XX could also be referred to as a second XX, and similarly, a second XX could also be referred to as a first XX, without departing from the scope of the embodiments of this application. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0028] In a first aspect, an embodiment of the present application provides an electrolyte additive, wherein the electrolyte additive includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas I to II:

[0029]

[0030] Wherein, in structural formula I, R1 and R2 are selected from the same or different hydrogen atoms or C1-C10 alkyl groups; in structural formula II, X1-X4 are selected from the same or different C1-C15 alkyl groups or C1-C15 substituted alkyl groups, and Y1 and Y2 are selected from the same or different C, N, O, S, B, Si atoms or their derivative groups.

[0031] The electrolyte additive provided in the first aspect of the embodiment of the present application includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas I to II. The free radical scavengers of the provided structural formulas I to II are stable carriers of nitrogen free radicals or oxygen free radicals. Therefore, when used in the electrolyte, they can consume harmful groups such as CH3· free radicals, acyl radicals, CH3O· free radicals generated during the charging and discharging process of the secondary battery, and can effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively inhibiting the gas production phenomenon of the secondary battery during charging and discharging, significantly reducing the gas production, reducing the volume expansion of the secondary battery, and thus effectively improving the stability and safety of the charging and discharging of the secondary battery.

[0032] In some embodiments, the electrolyte additive includes a free radical scavenger, wherein the free radical scavenger has a structural formula as shown in Formula I:

[0033]

[0034] Wherein, R1 and R2 are selected from the same or different hydrogen atoms or C1-C10 alkyl groups. The provided free radical scavenger of structural formula I contains nitrogen free radicals and has three benzene rings as a main chain structure. Under the action of the main chain structure containing three benzene rings, the nitrogen free radicals can exist stably, ensuring that when used in the electrolyte, they can consume harmful radicals such as CH3· free radicals, acyl free radicals, and CH3O· free radicals generated during the charging and discharging process of the secondary battery. It can also effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively suppressing the gas production of the secondary battery during charging and discharging, and significantly reducing the amount of gas produced.

[0035] In some embodiments, in Structural Formula I, R1 and R2 are selected from the same or different C1-C5 alkyl groups. In some specific implementations, R1 and R2 are selected from at least one of the same or different methyl, ethyl, and propyl groups.

[0036] In some embodiments, the electrolyte additive includes a free radical scavenger, wherein the free radical scavenger has a structural formula as shown in Formula II:

[0037]

[0038] Wherein, in structural formula II, X1 to X4 are selected from the same or different C1 to C15 alkyl groups or C1 to C15 substituted alkyl groups, and Y1 and Y2 are selected from the same or different C, N, O, S, B, Si, or any one of their derivative groups. The provided free radical scavenger of structural formula II contains oxygen free radicals, and structural formula II contains a heterocyclic structure. Under the action of the heterocyclic structure, the oxygen free radicals are stably present, ensuring that they can be used in the electrolyte to consume harmful groups such as CH3· free radicals, acyl free radicals, and CH3O· free radicals generated during the charging and discharging process of the secondary battery, and can effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively inhibiting the gas production of the secondary battery during charging and discharging, and significantly reducing the amount of gas produced.

[0039] In some embodiments, structural formula II comprises at least one of the following structural formulas III-II:

[0040]

[0041] Here, R3 is selected from any one of a hydrogen atom, a C1-C5 alkyl group, a hydroxyl group, a carboxyl group, and a benzene ring.

[0042] In some embodiments, in Formula II, X1-X4 are selected from the same or different C1-C10 alkyl groups. In some specific embodiments, X1-X4 are selected from at least one of the same or different methyl, ethyl, and propyl groups.

[0043] In some embodiments, X1-X4 are selected from the same or different C1-C10 substituted alkyl groups. In some specific embodiments, the substituents of the substituted alkyl groups include any one of C1-C15 alkenyl groups, carbonyl groups, and ether groups.

[0044] In some embodiments, the free radical scavenger comprises at least one of the following structural formulas III1 to III5:

[0045]

[0046] The provided electrolyte additive includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas III1 to III5. Since the free radical scavenger stably carries nitrogen free radicals or oxygen free radicals, it can be used in the electrolyte to consume harmful groups such as CH3· free radicals, acyl free radicals, and CH3O· free radicals generated during the charging and discharging process of the secondary battery, and can effectively inhibit the generation of active oxygen in the positive electrode additive in the secondary battery, thereby effectively inhibiting the gas production phenomenon of the secondary battery during charging and discharging, significantly reducing the gas production and reducing the volume expansion of the secondary battery, thereby effectively improving the stability and safety of the charging and discharging of the secondary battery.

[0047] In a second aspect, an embodiment of the present application provides an electrolyte for a secondary battery, the electrolyte comprising a metal salt electrolyte, an organic solvent, and an electrolyte additive, wherein the electrolyte additive is selected from electrolyte additives.

[0048] The electrolyte of the secondary battery provided in the second aspect of the embodiment of the present application includes an electrolyte additive, which is a free radical scavenger that can combine with harmful groups such as CH3·free radicals, acyl free radicals, CH3O·free radicals, and further effectively inhibit the generation of active oxygen. In the process of assembling a battery for use, it effectively solves the problem that the secondary battery is prone to gas generation during charging and discharging, thereby affecting the battery properties.

[0049] In some embodiments, the electrolyte additive comprises 0.1% to 15% by weight, based on the total mass of the electrolyte being 100%. If the electrolyte additive is present in too much content, it cannot be completely dissolved in the electrolyte and may reduce the mobility of lithium, sodium, and potassium ions, thereby reducing the performance of lithium, sodium, and potassium ion batteries. If the content is too little, it may not have the desired effect. In some specific embodiments, the electrolyte additive comprises 1% to 10% by weight, based on the total mass of the electrolyte being 100%.

[0050] In some embodiments, the metal salt electrolyte includes any one of a lithium salt electrolyte, a sodium salt electrolyte, and a potassium salt electrolyte. Different metal salt electrolytes are selected according to different batteries to be obtained.

[0051] In some embodiments, the concentration of the metal salt electrolyte is 0.1 to 10 mol L -1 ; Further, the concentration is 1 mol L -1 .

[0052] In some specific embodiments, a lithium salt electrolyte is selected to obtain a lithium secondary battery, wherein the lithium salt electrolyte includes but is not limited to one or more of lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6) and lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bis(difluorosulfonyl imide) (LiFSI) and lithium bis(trifluoromethylsulfonyl imide) (LiTFSI).

[0053] In some specific embodiments, a sodium salt electrolyte is selected to obtain a sodium secondary battery, wherein the sodium salt electrolyte includes but is not limited to one or more of sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethylsulfonyl)imide [NaN(CF3SO2)2] and its derivatives, sodium perfluoroalkyl phosphate [NaPF3(C2F5)3], sodium tetrafluorooxalatophosphate [NaPF4(C2O4)], sodium bisoxalatoborate [NaB(C2O4)2], sodium tris(catechol)phosphate (NTBP), sulfonated polysulfonamide sodium salt, sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium nitrate (NaNO3), sodium carbonate (NaCO3), and sodium chloride (NaCl).

[0054] In some specific embodiments, a potassium salt electrolyte is selected to obtain a potassium secondary battery, wherein the potassium salt electrolyte includes but is not limited to one or more of potassium trifluoromethanesulfonate (KCF3SO3), potassium bis(trifluoromethylsulfonyl)imide [KN(CF3SO2)2] and its derivatives, perfluoroalkyl potassium phosphate [KPF3(C2F5)3], potassium tetrafluorooxalatephosphate [KPF4(C2O4)], potassium bisoxalatoborate [KB(C2O4)2], potassium tris(catechol)phosphate, sulfonated polysulfonamide potassium salt, potassium hexafluorophosphate (KPF6), potassium perchlorate (KClO4), potassium tetrafluoroborate (KBF4), potassium hexafluoroarsenate (KAsF6), potassium nitrate (KNO3), potassium carbonate (KCO3), and potassium chloride (KCl).

[0055] In some embodiments, the organic solvent includes at least one of an ester organic solvent, a sulfone organic solvent, an ether organic solvent, a nitrile organic solvent, or an ionic liquid organic solvent.

[0056] In some specific embodiments, the organic solvent includes but is not limited to propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), N,N-dimethylacetamide (DMA), fluoroethylene carbonate (FEC), methyl propionate (MP), ethyl propionate (EP), ethyl acetate (EA), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), triethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DME), ethylene sulfite (ES), propylene sulfite (PS), dimethyl sulfite (DMS), sulfite Diethyl ester (DES), crown ether (12-crown-4), 1-ethyl-3-methylimidazole-hexafluorophosphate, 1-ethyl-3-methylimidazole-tetrafluoroborate, 1-ethyl-3-methylimidazole-bis(trifluoromethylsulfonyl)imide, 1-propyl-3-methylimidazole-hexafluorophosphate, 1-propyl-3-methylimidazole-tetrafluoroborate, 1-propyl-3-methylimidazole-bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylimidazole-hexafluorophosphate, 1 -butyl-1-methylimidazole-tetrafluoroborate, 1-butyl-1-methylimidazole-bis(trifluoromethylsulfonyl)imide salt, N-butyl-N-methylpyrrolidine-bis(trifluoromethylsulfonyl)imide salt, 1-butyl-1-methylpyrrolidine-bis(trifluoromethylsulfonyl)imide salt, N-methyl-N-propylpyrrolidine-bis(trifluoromethylsulfonyl)imide salt, N-methylpropylpiperidine-bis(trifluoromethylsulfonyl)imide salt, N-methylbutylpiperidine-bis(trifluoromethylsulfonyl)imide salt.

[0057] In some embodiments, taking the total mass of the electrolyte as 100%, the mass percentage of the metal salt electrolyte is 10% to 30%, and the mass percentage of the organic solvent is 55% to 75%.

[0058] In a third aspect, a method for preparing an electrolyte for a secondary battery comprises the following steps:

[0059] S01 provides a metal salt electrolyte, an organic solvent and an electrolyte additive according to the secondary battery electrolyte;

[0060] S02. The organic solvent and the electrolyte additive are first mixed to obtain an electrolyte additive solution;

[0061] S03. Perform a second mixing process on the metal salt electrolyte and the electrolyte additive solution to obtain an electrolyte for a secondary battery.

[0062] The third aspect of the embodiment of the present application provides a method for preparing an electrolyte for a secondary battery. The method can obtain the electrolyte through a two-step mixing process. The preparation method is simple and is conducive to wide use.

[0063] In step S01, a metal salt electrolyte, an organic solvent and an electrolyte additive are provided according to the electrolyte of the secondary battery. The types of the provided metal salt electrolyte, organic solvent and electrolyte additive are as described above and will not be described again here to save space.

[0064] In step S02, the organic solvent and the electrolyte additive are subjected to a first mixing process to obtain an electrolyte additive solution. The first mixing process includes but is not limited to stirring, etc., in order to completely and evenly dissolve the electrolyte additive.

[0065] In step S03, the metal salt electrolyte and the electrolyte additive solution are subjected to a second mixing treatment to obtain an electrolyte for a secondary battery; the second mixing treatment includes but is not limited to stirring and the like, the purpose of which is to mix the components evenly so that the components of the obtained electrolyte are evenly mixed.

[0066] In a fourth aspect, the present application provides a secondary battery, which includes a negative electrode collector, a negative electrode material, an electrolyte, a separator, a positive electrode material, and a positive electrode collector, wherein the electrolyte is an electrolyte of a secondary battery or an electrolyte prepared by a method for preparing an electrolyte of a secondary battery.

[0067] The secondary battery provided in the fourth aspect of the embodiment of the present application has an electrolyte assembled in the secondary battery including an electrolyte additive. Therefore, the obtained secondary battery does not expand or produce gas during circulation, or the expansion and gas production are small, and its cycle performance is high, thereby having high safety performance and a long service life.

[0068] In some embodiments, the negative electrode current collector includes but is not limited to at least one of aluminum, copper, titanium, stainless steel, and nickel foil.

[0069] In some embodiments, the negative electrode material includes, but is not limited to, one or more of NASICON-type materials, conversion-type and alloying-type materials, organic materials, and carbon-based materials.

[0070] In some embodiments, the separator includes, but is not limited to, at least one of an insulating porous polymer film and an inorganic porous film. Further, the separator includes, but is not limited to, one or more of a porous polypropylene film, a porous polyethylene film, a porous composite polymer film, glass fiber paper, and a porous ceramic separator.

[0071] In some embodiments, the cathode material includes, but is not limited to, a material containing a transition metal salt.

[0072] In some embodiments, the cathode material includes a gassing lithium supplement additive.

[0073] In some embodiments, the lithium supplementing additive contains oxygen.

[0074] In some embodiments, the positive electrode current collector includes but is not limited to at least one of aluminum foil, carbon-coated aluminum foil, iron foil, tin foil, zinc foil, nickel foil, titanium foil, and manganese foil.

[0075] The following describes the details in conjunction with specific embodiments.

[0076] Electrolyte Example:

[0077] Example A1 to Example A5

[0078] Examples A1 to A5 provide electrolytes, each containing components as shown in Table 1 below. Specifically, the electrolyte of Example A1 contains an electrolyte additive of molecular formula III1, the electrolyte of Example A2 contains an electrolyte additive of molecular formula III2, and so on. The concentrations of the components in the electrolytes are shown in Table 1.

[0079] The electrolytes of each embodiment were prepared as follows:

[0080] According to the types and contents of the components contained in Examples A1 to A5, the basic components ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a mass ratio of EC:EMC:PC = 1.5:8:0.5, and then lithium salts were added to a concentration of 1.0 mol / L lithium hexafluorophosphate (LiPF6), stirred until completely dissolved, and then a compound accounting for 1% of the total mass of the electrolyte was added, and the electrolytes of each embodiment were obtained by thorough mixing and dissolution.

[0081] Comparative Example A1

[0082] This comparative example A1 provides an electrolyte, the components of which are shown in the following Table 1. Specifically, the electrolyte of comparative example A1 is prepared as follows:

[0083] According to the types and contents of components contained in Comparative Example A1, the basic components ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a mass ratio of EC:EMC:PC=1.5:8:0.5, and then lithium salt was added to a concentration of 1.0 mol / L lithium hexafluorophosphate (LiPF6), and the mixture was fully mixed and dissolved to obtain the electrolyte of Comparative Example A1.

[0084] Table 1 Electrolyte compositions of various embodiments and comparative examples

[0085]

[0086] 3. Lithium-ion battery example:

[0087] Examples B1 to B6 and Comparative Example B1

[0088] Examples B1 to B6 and Comparative Example B1 each provide a lithium-ion battery. Each lithium-ion battery is assembled into a lithium-ion battery according to the following method:

[0089] 1) Positive electrode:

[0090] In Examples B1 to B6, the positive electrode sheet of Comparative Example B1 was prepared by uniformly mixing the positive electrode active material LiFePO4, the conductive agent SuperP, the binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) to form a positive electrode slurry, wherein the mass ratio of LiFePO4:SuperP:PVDF was 95:2:3. The positive electrode slurry was coated onto a current collector aluminum foil and subjected to a drying, roller pressing, and secondary drying process to produce the positive electrode sheet. The positive electrode sheet of Example B6 contained a lithium-supplementing additive Li5FeO4, with the mass ratio of Li5FeO4:LiFePO4:SuperP:PVDF being 2:93:2:3.

[0091] 2) Negative Electrode Sheet: Graphite (the negative electrode active material), Super P (the conductive agent), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) (the binder) are mixed in deionized water to create a negative electrode slurry. The mass ratio of graphite: Super P: CMC: SBR is 95:2:0.5:2.5. The negative electrode slurry is coated onto the current collector copper foil and then dried, rolled, and dried again to create the negative electrode sheet.

[0092] 3) Diaphragm: Use polyethylene (PE) diaphragm

[0093] 4) Electrolyte:

[0094] The electrolytes provided in Examples A1 to A5 and Comparative Example A1 were used as the electrolytes for the secondary batteries, respectively. Specifically, the electrolyte provided in Example A1 was used as the electrolyte for the secondary battery in Example B1, and the electrolyte provided in Example A2 was used as the electrolyte for the secondary battery in Example B2. Similarly, the electrolyte provided in Comparative Example A1 was used as the electrolyte for the secondary battery in Comparative Example B1, and the electrolyte provided in Comparative Example A2 was used as the electrolyte for the secondary battery in Comparative Example B2. In particular, the electrolyte for the secondary battery in Example B6 was the electrolyte provided in Example A1.

[0095] 5) Assembly of secondary batteries:

[0096] The positive electrode sheet, negative electrode sheet, electrolyte and separator are assembled into a lithium-ion soft-pack battery according to the lithium-ion battery assembly requirements.

[0097] 6) Lithium-ion battery performance test:

[0098] The lithium-ion batteries of each embodiment assembled in Section 5) were subjected to the following performance tests:

[0099] Room temperature cycle test: The battery is placed at 25°C and charged and discharged at a current of 1C in the charge and discharge voltage range of 3.0-4.4V. The initial thickness is recorded as T0 and the initial capacity is recorded as Q0. The thickness after 300 cycles is recorded as T1 and the capacity is recorded as Q1. The thickness change rate and capacity retention rate of the battery after 300 cycles at room temperature are calculated using the following formula:

[0100] Thickness change rate after 300 cycles at room temperature (%) = (T1-T0) / T0×100%;

[0101] Capacity retention rate after 300 cycles at room temperature (%) = Q1 / Q0×100%.

[0102] High-temperature cycling test: At a high temperature of 45°C, charge and discharge cycles were performed with a current of 1C in the charge and discharge voltage range of 3.0-4.4V. The initial thickness was recorded as T2 and the initial capacity was recorded as Q2. The thickness after 300 cycles was recorded as T3 and the capacity was recorded as Q3. The thickness change rate and capacity retention rate of the battery after 300 cycles at high temperature (45°C) were calculated using the following formula:

[0103] Thickness change rate after 300 cycles at high temperature (45°C) = (T3-T2) / T2×100%;

[0104] High temperature (45°C) cycle 300 cycles capacity retention (%) = Q3 / Q2×100%.

[0105] The relevant performance test results are shown in Table 2 below:

[0106] Table 2

[0107]

[0108] From the test results in Table 2, it can be seen that the thickness change rate and capacity retention rate of Comparative Example B1 after 300 cycles at room temperature are 10.37% and 83.30%, respectively, and the thickness change rate and capacity retention rate after 300 cycles at high temperature (45°C) are 19.24% and 79.10%, respectively. The thickness change rate from room temperature to high temperature (45°C) increases by 8.87%. In Examples B1-B6, due to the presence of a small amount of the electrolyte additive compound of the present application, the thickness change rate after 300 cycles at room temperature is much smaller than that of Comparative Example B1. Therefore, their capacity retention rates are all above 90%, and even after 300 cycles at high temperature (45°C), the thickness change rate is significantly improved. , and the thickness change rate is also less than 10%; by comparing Example B1 with Example B6, it is found that even though Example B6 contains a lithium supplement that can produce gas, its thickness change rate at room temperature / high temperature for 300 cycles is basically the same as that of Example B1, and its capacity retention rate at room temperature / high temperature for 300 cycles is higher than that of Example B1 without a lithium supplement. This shows that the electrolyte additive compound of the present application can not only inhibit the gas production phenomenon in the positive electrode material, but also inhibit the generation of active oxygen of the lithium supplement in the positive electrode material, thereby reducing the gas production of the lithium secondary battery, reducing the volume expansion of the lithium secondary battery, and effectively improving the stability and safety of the lithium secondary battery during the charge and discharge process.

[0109] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. An electrolyte additive, characterized in that Applied to a secondary battery, the secondary battery contains a gas-generating lithium supplement additive Li5FeO4, and the electrolyte additive includes a free radical scavenger, wherein the free radical scavenger includes at least one of the following structural formulas III3 to III4:

2. An electrolyte for a secondary battery, characterized in that The electrolyte comprises a metal salt electrolyte, an organic solvent and an electrolyte additive, wherein the electrolyte additive is selected from the electrolyte additive according to claim 1.

3. The electrolyte of the secondary battery according to claim 2, characterized in that Taking the total mass of the electrolyte as 100%, the mass percentage of the electrolyte additive is 0.1% to 15%.

4. The electrolyte of the secondary battery according to claim 2, characterized in that The metal salt electrolyte includes any one of a lithium salt electrolyte, a sodium salt electrolyte, and a potassium salt electrolyte; and / or, The organic solvent includes at least one of an ester organic solvent, a sulfone organic solvent, an ether organic solvent, a nitrile organic solvent or an ionic liquid organic solvent.

5. A method for preparing an electrolyte for a secondary battery, characterized in that: The steps include: The electrolyte of the secondary battery according to any one of claims 2 to 4 provides a metal salt electrolyte, an organic solvent and an electrolyte additive; performing a first mixing process on the organic solvent and the electrolyte additive to obtain an electrolyte additive solution; The metal salt electrolyte and the electrolyte additive solution are subjected to a second mixing process to obtain an electrolyte for a secondary battery.

6. A secondary battery, characterized in that: The secondary battery includes a negative electrode collector, a negative electrode material, an electrolyte, a separator, a positive electrode material, and a positive electrode collector, wherein the electrolyte is the electrolyte of the secondary battery according to any one of claims 2 to 4 or the electrolyte prepared by the method for preparing the electrolyte of the secondary battery according to claim 5.

7. The secondary battery according to claim 6, characterized in that The positive electrode material includes a gas-generating lithium-supplementing additive.

8. The secondary battery according to claim 7, wherein: The lithium supplement additive contains oxygen element.

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