Secondary battery electrolyte, electrolyte additive, and secondary battery
By using thiophosphine additives in the electrolyte of secondary batteries to form a stable interfacial film, the problem of electrolyte decomposition under high pressure is solved, thereby improving the high-voltage resistance and cycle performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BYD CO LTD
- Filing Date
- 2022-06-30
- Publication Date
- 2026-06-05
AI Technical Summary
Existing secondary battery electrolytes have poor stability under high pressure and are prone to oxidation and decomposition, leading to rapid electrolyte consumption, battery expansion, and rapid performance degradation. In particular, high-nickel ternary cathode materials are prone to oxygen evolution at high potentials, resulting in poor battery interface stability and increased impedance.
A secondary battery electrolyte additive, including a first film-forming additive thiophosphine with the structural formula shown in formula (I), is used to form a stable interface film on the electrode surface, inhibit the oxidative decomposition of the electrolyte, and form an SEI film on the negative electrode and a CEI film on the positive electrode, thereby improving the high voltage resistance and cycle performance of the battery.
By forming a stable interfacial film on the electrode surface, side reactions of the electrolyte are suppressed, interfacial impedance is reduced, battery life is extended, and the cycle performance and safety performance of the battery are improved.
Smart Images
Figure CN117374387B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of secondary battery technology, specifically to a secondary battery electrolyte, electrolyte additive, and secondary battery. Background Technology
[0002] With the rapid development of the new energy industry, increasingly higher demands are being placed on the energy density of rechargeable batteries. One way to improve the energy density of rechargeable batteries is to increase the operating voltage. However, existing electrolyte solvents undergo oxidative decomposition at higher operating voltages, leading to rapid electrolyte consumption. The byproducts generated by the reaction also accelerate the dissolution of metals in the cathode material and structural collapse, damaging the interfacial film on the electrode surface and increasing the impedance of the electrode surface, ultimately leading to battery swelling and rapid performance degradation. In addition, high-voltage cathode materials, such as high-nickel ternary cathode materials, are prone to oxygen evolution at high potentials, which further accelerates the oxidative decomposition and gas production of the electrolyte, resulting in poorer battery interface stability, increased impedance, and reduced battery performance. Therefore, it is necessary to develop a new type of high-voltage resistant electrolyte to improve the electrochemical and safety performance of batteries. Summary of the Invention
[0003] In view of this, this application provides a secondary battery electrolyte in which additives can form a stable interface film on the surface of the positive and negative electrodes of the battery, thereby stabilizing the electrode electrolyte interface, inhibiting the contact reaction between the electrolyte and the positive and negative electrode materials, preventing the oxidative decomposition of the solvent electrolyte, improving the high voltage resistance of the lithium secondary battery, and enabling the battery to have excellent cycle performance and safety performance.
[0004] A first aspect of this application provides a secondary battery electrolyte, comprising an electrolyte salt, an organic solvent, and an electrolyte additive, wherein the electrolyte additive includes a first film-forming additive with the structural formula shown in formula (I):
[0005]
[0006] Wherein, R1 is selected from sulfur atoms or oxygen atoms; R2 is selected from hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms; R3 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms.
[0007] In the secondary battery electrolyte of this application, the first film-forming additive has a high reduction potential and can react before the electrolyte solvent to form a stable interfacial film on the positive and negative electrode surfaces, thereby stabilizing the electrode / electrolyte interface, suppressing side reactions in the electrolyte, and greatly reducing interfacial impedance, improving the cycle performance of the battery, and extending the battery's service life.
[0008] Optionally, at least one of R2 and R3 is a substituted or unsubstituted alkenyl group or a substituted or unsubstituted alkynyl group.
[0009] Optionally, in R2 and R3, the substituted or unsubstituted alkyl group, the substituted or unsubstituted alkenyl group, and the substituted or unsubstituted alkynyl group have 1-10 carbon atoms; the substituted or unsubstituted aryl group has 6-30 carbon atoms.
[0010] Optionally, R2 is selected from hydrogen atom, methyl, trifluoromethyl, phenyl, bis(2-chloroethyl)amino, dimethylamino, and chlorine atom; and R3 is selected from methyl, trifluoromethyl, phenyl, bis(2-chloroethyl)amino, dimethylamino, and chlorine atom.
[0011] Optionally, the first film-forming additive has a mass percentage content of 1%-10% in the secondary battery electrolyte.
[0012] Optionally, the electrolyte additive further includes a second film-forming additive, which includes one or more of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfite, and methylene disulfonate.
[0013] Optionally, the mass ratio of the first film-forming additive to the second film-forming additive is 1:(0.5 to 30).
[0014] Optionally, the electrolyte additive further includes a third film-forming additive, which includes propylene sulfite.
[0015] Optionally, the mass ratio of the first film-forming additive to the third film-forming additive is 1:(0.02-50).
[0016] Optionally, the electrolyte additive has a mass percentage content of 1%-10% in the secondary battery electrolyte.
[0017] Optionally, the organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents.
[0018] Secondly, this application provides an electrolyte additive, the electrolyte additive comprising a first film-forming additive with the structural formula shown in formula (I):
[0019]
[0020] Wherein, R1 is selected from sulfur atoms; R2 is selected from hydrogen atoms, substituted or unsubstituted alkyl groups; and R3 is selected from alkyl groups, haloalkyl groups, substituted amino groups, and halogen atoms.
[0021] Thirdly, this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes the secondary battery electrolyte as described in the first aspect of this application.
[0022] Optionally, the positive electrode includes a current collector and a positive electrode active material layer disposed on the surface of the current collector, wherein the positive electrode active material layer includes a high-nickel ternary positive electrode material.
[0023] Optionally, the negative electrode includes a current collector and a negative electrode active material layer disposed on the surface of the current collector, wherein the negative electrode active material layer includes one or more of silicon, silicon suboxide, and silicon-carbon composite materials. Attached Figure Description
[0024] Figure 1 This is a crosslinking structure diagram of a polymer film provided in an embodiment of this application;
[0025] Figure 2 This is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application;
[0026] Figure 3 The graph shows the battery cyclic voltammetry test results for Example 1 and Comparative Example 1 of this application. Detailed Implementation
[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0028] Current rechargeable battery electrolyte systems exhibit poor stability under high voltage, are prone to oxidation and decomposition, and generate gas, leading to adverse consequences such as rapid electrolyte consumption, battery swelling, and capacity decay. This application provides a rechargeable battery electrolyte in which additives can improve the electrolyte's stability under high voltage, suppress side reactions of the electrolyte solvent, and have minimal impact on the battery cell system, without significantly increasing electrolyte viscosity, thus showing promising application prospects.
[0029] The electrolyte additive provided in this application includes a first film-forming additive, thiophosphine, the structural formula of which is shown in formula (I):
[0030] Wherein, R1 is selected from sulfur or oxygen atoms; R2 is selected from hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms, with R2 attached to a carbon atom other than P or S. R3 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms.
[0031] In this embodiment, the cyclic structure of the first film-forming additive, thiophosphine, allows the synergistic electron-donating effect of polysulfide atoms to lower the LUMO energy of the lowest unoccupied molecular orbital, resulting in a higher reduction potential. This reduction potential is higher than that of solvents in existing secondary battery electrolytes, such as carbonate solvents. Therefore, during battery charging and discharging, the first film-forming additive can undergo an electrochemical reaction and polymerize before the electrolyte solvent to form a polymer film, thereby improving the interface composition between the negative electrode and the electrolyte and stabilizing the electrode / electrolyte interface. The substituent R1 in thiophosphine is selected from sulfur or oxygen atoms. S and O atoms have stronger electronegativity, making it easier for the first film-forming additive to preferentially reduce and form a film before the solvent during battery formation.
[0032] In this application, the first film-forming additive, thiophosphine, can form a polymer film with a cross-linked network structure during the electrochemical reaction. Specifically, the thiophosphine's thiocations can link the polymer chains in the polymer film through the -SPS- groups. (See also...) Figure 1 , Figure 1 This is a cross-linked structure diagram of a polymer membrane provided in an embodiment of this application. In this diagram, disulfide bonds in the polymer membrane can link the polymer polymer chains to form a polymer membrane with a cross-linked network structure. This polymer membrane has good elasticity and toughness, which can suppress the interfacial membrane damage caused by changes in the structure of the positive and negative electrode materials and reduce the consumption of electrolyte caused by the regeneration of the interfacial membrane. Moreover, thiophosphine can also be reduced to generate inorganic substances with high ionic conductivity such as Li2O, Li2S, and phosphate salts, thereby reducing the interfacial impedance of the polymer membrane and ensuring the battery capacity.
[0033] In this embodiment, the substituents in thiophosphine can increase the electron cloud density of thiophosphine, resulting in a higher overall electron cloud density and an increase in free electrons in the structure. This is beneficial for further increasing the reduction potential of the first film-forming additive, making it easier for thiophosphine to be preferentially oxidized by the solvent, forming a CEI film at the positive electrode and an SEI film at the negative electrode. In some embodiments of this application, when the substituent is selected from alkyl groups, the alkyl group can be any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, cyclopropyl, or cyclobutyl; when the substituent is selected from alkenyl groups... The alkenyl group can be any one of vinyl, propenyl, and butenyl; when the substituent group is selected from alkynyl, the alkynyl group can be any one of ethynyl and propynyl; when the substituent group is selected from cycloalkyl, the cycloalkyl group can be any one of cyclobutyl, cyclopentyl, cyclohexyl, or cycloheptyl; when the substituent group is selected from aryl, the aryl group can be any one of phenyl, naphthyl, or anthracene; when the substituent group is selected from halogen atoms, the halogen atom can be any one of fluorine, chlorine, bromine, or iodine atoms; in some embodiments of this application, when the substituent group is selected from substituted alkyl, substituted alkenyl, substituted alkynyl, substituted amino, substituted cycloalkyl, or substituted aryl, the substituent group can be one or more of halogen, alkyl, haloalkyl, alkenyl, carboxyl, amino, and silyl.
[0034] In some embodiments of this application, at least one of R2 and R3 is a substituted or unsubstituted alkenyl or substituted or unsubstituted alkynyl group. When the substituted group contains unsaturated double or triple bonds, the first film-forming additive is more likely to polymerize to form an organic polymer during electrochemical or chemical reaction. This organic polymer can improve the elasticity and structural strength of the interfacial film, which is beneficial to alleviate the volume expansion effect of the electrode material during battery charging and discharging and improve the stability of the electrode structure.
[0035] In some embodiments of this application, the substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, and substituted or unsubstituted alkynyl groups in R2 and R3 have 1-10 carbon atoms. The specific number of carbon atoms in the substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, and substituted or unsubstituted alkynyl groups can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments of this application, the substituted or unsubstituted aryl group has 6-30 carbon atoms, and the specific number of carbon atoms in the substituted or unsubstituted aryl group can be, but is not limited to, 6, 7, 8, 9, 10, 13, 17, 20, or 30. Controlling the number of carbon atoms in R2 and R3 is beneficial for adjusting the molecular weight of the additive, thereby better controlling the electrolyte viscosity, ensuring that the electrolyte can fully wet the electrode material, and promoting lithium-ion transport.
[0036] In some embodiments of this application, R2 and R3 are independently selected from methyl, trifluoromethyl, phenyl, bis(2-chloroethyl)amino, dimethylamino, and chlorine atoms, and R2 may also be selected from hydrogen atoms.
[0037] In some specific embodiments of this application, the first film-forming additive may be any one or more compounds as shown in Table 1:
[0038] Table 1. Structural formulas and names of first film-forming additives in some embodiments of this application.
[0039]
[0040]
[0041] The first film-forming additive provided in this application has a thiophosphine structure. Compounds with this structure have a high reduction potential, which can preferentially reduce the electrolyte solvent at the negative electrode to form an SEI film and oxidize it at the positive electrode to form a CEI film. This prevents the consumption of solvent and the damage to the interfacial film caused by the dissolution of metal ions at the positive electrode, and inhibits the oxidative decomposition of the solvent. Furthermore, since the additive forms coordination complexes only through strongly electronegative atoms, it has good compatibility with existing electrolyte systems, is miscible, does not affect the physicochemical properties of the parent electrolyte, has little impact on the cell system, and can be applied to different electrolyte systems, thus having universal applicability.
[0042] The electrolyte additives of this application can be prepared by various methods, and the specific preparation method is not limited. In some embodiments, the synthesis route of the first film-forming additive (D) numbered 4 is as follows:
[0043]
[0044] In some embodiments, the synthesis route of the first film-forming additive (E) numbered 5 is as follows:
[0045]
[0046] In some embodiments, the synthesis route of the first film-forming additive (G) numbered 6 is as follows:
[0047]
[0048] In some embodiments, the synthesis route of the first film-forming additive (F) numbered 7 is as follows:
[0049]
[0050] In some embodiments, the synthesis route of the first film-forming additive (H) numbered 8 is as follows:
[0051]
[0052] In the above synthetic route, the reaction temperature is 100℃~200℃, and the catalyst for the reaction includes one or more of palladium, rhodium, and platinum.
[0053] In some embodiments of this application, the mass percentage of the first film-forming additive in the secondary battery electrolyte is 0.1%-10%. In some embodiments, the mass percentage of the first film-forming additive in the secondary battery electrolyte is 0.1%-5%. The specific mass percentage of the first film-forming additive in the secondary battery electrolyte may be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, 5%, 8%, or 10%. The first film-forming additive within the above-mentioned mass percentage range is beneficial for forming a complete and appropriately thick interfacial film on the surface of the positive and negative electrode sheets, thereby effectively improving the high-voltage resistance of the electrolyte. Furthermore, the interfacial film has low impedance, and the electrolyte viscosity is moderate, which is beneficial for the battery performance.
[0054] In some embodiments of this application, the secondary battery electrolyte further includes a second film-forming additive. The second film-forming additive can be used as a negative electrode film-forming additive. In some embodiments, the second film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate (VEC), ethylene sulfite (ES), and methane disulfonate (MMDS). In some embodiments of this application, the mass percentage of the second film-forming additive in the secondary battery electrolyte is 0.1%-10%. The first film-forming additive provided in this application can be used as a positive electrode film-forming additive to inhibit the dissolution of positive electrode metals. Using the first and second film-forming additives in combination is more conducive to forming a stable interface film on the positive and negative electrode surfaces of the battery. In some embodiments of this application, the mass ratio of the first film-forming additive to the second film-forming additive is 1:(0.5-30). The specific mass ratio of the first film-forming additive to the second film-forming additive can be, but is not limited to, 1:0.5, 1:1, 1:3, 1:5, 1:10, 1:15, 1:20, or 1:30.
[0055] In some embodiments of this application, the secondary battery electrolyte further includes a third film-forming additive. The third film-forming additive can be used as a positive electrode film-forming additive; in some embodiments, the third film-forming additive includes propylene sulfite (PS). In some embodiments of this application, the mass percentage of the third film-forming additive in the secondary battery electrolyte is 0.1%-10%. The third film-forming additive can suppress the problem of high-temperature gas generation in the electrolyte, improving the stability of the battery under high-temperature storage or cycling conditions. The combination of the first and third film-forming additives can further improve the density and stability of the interfacial film. In some embodiments of this application, the mass ratio of the first film-forming additive to the third film-forming additive is 1:(0.02-50). The specific mass ratio of the first film-forming additive to the third film-forming additive can be, but is not limited to, 1:0.02, 1:0.05, 1:0.1, 1:1, 1:1, 1:5, 1:10, or 1:50.
[0056] In this embodiment of the application, the mass percentage of the electrolyte additive in the secondary battery electrolyte is less than or equal to 10%. In some embodiments, the mass percentage of the electrolyte additive in the secondary battery electrolyte is less than or equal to 5%. The specific mass percentage of the electrolyte additive in the secondary battery electrolyte may be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 5%, 8%, or 10%.
[0057] In this application, the organic solvent in the secondary battery electrolyte includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents. The carbonate solvents can be cyclic and / or chain-like, while the carboxylic acid ester solvents can be linear and / or branched. In some embodiments of this application, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, and ethyl butyrate, but is not limited thereto.
[0058] In some embodiments of this application, the organic solvent includes cyclic carbonates and chain carbonates. Cyclic carbonates have a higher dielectric constant but higher viscosity, while chain carbonates have lower viscosity. The combination of cyclic and chain carbonates can improve the overall ionic conductivity of the electrolyte, and cyclic carbonates can also participate in the formation of a solid electrolyte interphase (SEI) membrane at the negative electrode, thereby effectively suppressing side reactions at the negative electrode. In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate. In some embodiments, the chain carbonate includes one or more of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). In some embodiments of this application, the organic solvent includes ethylene carbonate (EC) and diethyl carbonate (DEC), wherein the volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) is 1:(1-2.5). In some embodiments, the volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) in the organic solvent is 1:(2-2.5).
[0059] In the embodiments of this application, depending on the different secondary battery systems, the electrolyte salt in the secondary battery electrolyte can be lithium salt, sodium salt, potassium salt, etc. In some embodiments of this application, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluoroxanthione)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium di(oxalateborate)borate (LiBOB), lithium di(fluorooxalateborate)borate (LiDFOB), lithium trifluoromethanesulfonate (LiCF3SO3), lithium perfluorobutylsulfonate (LiC4F9SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and lithium bis(perfluoroethylsulfonyl)imide (Li(C2F5SO2)2N). In some embodiments of this application, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluorosulfonyl)imide. Lithium bis(fluorosulfonyl)imide and lithium bis(trifluorosulfonyl)imide have lower fluorine content, resulting in less hydrofluoric acid production, which is beneficial for improving the high-temperature performance of the electrolyte. Simultaneously, the lithium salt can form a film on the negative electrode, further enhancing the stability of the SEI film. In this application, there are no special requirements for the electrolyte salt content in the secondary battery electrolyte; the content can be based on conventional usage in the art. In some embodiments of this application, the concentration of the electrolyte salt in the secondary battery electrolyte is 0.1 mol / L-5 mol / L, and further, the concentration of the electrolyte salt in the secondary battery electrolyte is 1 mol / L-1.5 mol / L.
[0060] This application also provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes the secondary battery electrolyte provided in this application. Please refer to... Figure 2 , Figure 2 This is a schematic diagram of a secondary battery provided in one embodiment of this application. The secondary battery includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40. During charging, lithium ions are released from the positive electrode 10, pass through the electrolyte 40, and are deposited on the negative electrode 20; during discharging, lithium ions are released from the negative electrode 20, pass through the electrolyte 40, and are embedded in the positive electrode 10. In this embodiment, the secondary battery can be a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, an aluminum secondary battery, etc.
[0061] In this application, the negative electrode of the secondary battery can be any negative electrode known in the art. In the embodiments of this application, the negative electrode may include one or more of the following: carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, and aluminum negative electrode. Specifically, the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, etc.; the silicon-based negative electrode may include silicon, silicon-carbon, silicon-oxygen, silicon metal compounds, etc.; the tin-based negative electrode may include tin, tin-carbon, tin-oxygen, tin metal compounds; and the lithium negative electrode may include metallic lithium or lithium alloys. The lithium alloy may specifically be at least one of the following: lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. In some embodiments of this application, the current collector of the negative electrode is copper foil, and the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon, silicon suboxide, aluminum, tin, and antimony; the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene-butadiene latex (SBR); the conductive agent includes one or more of acetylene black, Ketjen carbon black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene. In this application, the negative electrode can be prepared using any method known in the art.
[0062] In some embodiments of this application, the negative electrode active material includes one or more of silicon, silicon suboxide, and silicon-carbon composite materials. In the secondary battery electrolyte of this application, the first film-forming additive can form an SEI film with a cross-linked network structure on the negative electrode surface, and the SEI film contains inorganic components with high ionic conductivity, thereby reducing the interfacial impedance of the polymer film. This SEI film has outstanding elastic properties, which can adapt to the volume expansion and contraction of silicon materials during electrochemical processes without rupture. This SEI film, which contains both organic and inorganic components, can effectively suppress side reactions between the electrolyte and the silicon negative electrode surface, while greatly reducing interfacial impedance and improving the high-temperature cycle performance of the battery.
[0063] In this application, the positive electrode of the secondary battery includes a positive electrode active material capable of reversibly inserting / deintercalating metal ions (lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). The positive electrode of the secondary battery in this application can be any positive electrode known in the art. Taking a lithium secondary battery as an example, the positive electrode active material can be, but is not limited to, lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), and LiNi... 0.33 Co 0.33 Mn 0.33 O2 (NCM111), LiNi 0.4 Co 0.2 Mn 0.4 O2(NCM424), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2 (NCM811).
[0064] In some embodiments of this application, the positive electrode active material includes a high-nickel ternary material, which includes a ternary nickel-cobalt-manganese material, specifically LiNi. 0.33 Co 0.33 Mn 0.33 O2(NCM111), LiNi 0.4 Co 0.2 Mn 0.4 O2 (NCM424), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.075 Mn 0.075High-nickel ternary materials possess high specific capacity, significantly improving battery energy density. However, at 4.5V, they form a large number of tetravalent nickel ions. These tetravalent nickel ions are highly oxidizing, oxidizing the electrolyte solvent and consuming active lithium and the electrolyte. Oxidation byproducts, such as water and other proton products, further degrade electrolyte performance. The first film-forming additive in this application preferentially oxidizes the solvent to form a stable CEI film on the cathode surface, thereby inhibiting the contact between the highly oxidizing tetravalent nickel ions and the solvent, reducing the oxidation of the electrolyte by the high-nickel cathode material, thus slowing electrolyte consumption and extending battery life.
[0065] In the embodiments of this application, the separator of the secondary battery can be any separator known to those skilled in the art. For example, the separator can be one or more of polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt or ultrafine glass fiber paper.
[0066] The secondary battery provided in this application has good cycle performance and safety performance even at high temperatures because it uses a secondary battery electrolyte with a specific composition.
[0067] In the embodiments of this application, the battery can be fabricated using either a lamination process or a winding process. In some embodiments of this application, the battery is fabricated using a lamination process.
[0068] This application also provides a power vehicle that includes the secondary battery provided in this application, the secondary battery supplying power to the power vehicle.
[0069] The technical solution of this application will be further described below with reference to several embodiments.
[0070] Example 1
[0071] 1) Preparation of secondary battery electrolyte
[0072] An organic solvent was prepared by mixing 60g of ethylene carbonate (EC) and 140g of diethyl carbonate (DEC). Then, 30g of lithium hexafluorophosphate (LiPF6) was dissolved in this solvent to achieve a lithium salt concentration of 1 mol / L. Next, a first film-forming additive (A) (2-methyl-1,3,2-dithiophosphine-2-thionone) and a second film-forming additive (fluoroethylene carbonate, FEC) were added to the solution to obtain the secondary battery electrolyte. The mass percentage of FEC in the secondary battery electrolyte was 3%, and the mass percentage of the first film-forming additive (A) was 0.05%.
[0073] The structural formula of the first film-forming additive (A) is as follows:
[0074]
[0075] 2) Preparation of lithium secondary batteries
[0076] 100 parts of graphite material, 1 part of conductive agent super-p, 1.5 parts of thickener sodium carboxymethyl cellulose (CMC), and 2.5 parts of binder styrene-butadiene rubber (SBR) were mixed into a uniform paste, which was then uniformly coated onto copper foil used as the negative electrode current collector. The paste was dried under vacuum at 80°C for 24 hours to obtain the negative electrode sheet.
[0077] 100 parts of LiNi 0.5 Co 0.2 Mn 0.3 O2 (type 523), 2 parts carbon nanotubes (CNT), 1 part conductive agent super-p, and 2 parts polyvinylidene fluoride (PVDF) are mixed into a uniform paste, which is then uniformly coated onto an aluminum foil used as the positive electrode current collector. The paste is dried under vacuum at 80°C for 24 hours to obtain the positive electrode sheet.
[0078] The positive electrode sheet, negative electrode sheet and separator prepared above are wound into a cell, filled with the above-mentioned secondary battery electrolyte, and then processed through formation and other processes to produce a soft-pack lithium secondary battery S1.
[0079] Formation process: The simulated battery is first charged to 1.5V with a current of 40mA (0.05C) and held at 1.5V for 10 hours to fully wet the battery electrode plates. After constant voltage is achieved, the battery is initially charged with a smaller current of 8mA (C / 100) for 10 hours to form a stable and dense SEI film, then charged to 4.35V with a current of 40mA (0.05C), and then discharged to 3.0V.
[0080] Example 2
[0081] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 2 are the same as those in Example 1, except that the mass percentage of the first film-forming additive (A) in Example 2 is 2.5%.
[0082] The soft-pack lithium secondary battery prepared in Example 2 is named S2.
[0083] Example 3
[0084] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 3 are the same as those in Example 1, except that the mass percentage of the first film-forming additive (A) in Example 3 is 5%.
[0085] The soft-pack lithium secondary battery prepared in Example 3 is named S3.
[0086] Example 4
[0087] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 4 are the same as those in Example 1, except that the mass percentage of the first film-forming additive (A) in Example 4 is 8%.
[0088] The soft-pack lithium secondary battery prepared in Example 4 is named S4.
[0089] Example 5
[0090] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 5 are the same as those in Example 1, except that the mass percentage of the first film-forming additive (A) in Example 5 is 15%.
[0091] The soft-pack lithium secondary battery prepared in Example 5 is named S5.
[0092] Example 6
[0093] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 6 are the same as in Example 3, except that the electrolyte additive in Example 6 is a first film-forming additive (B) (1,3,2-dithiophosphine-2-phenyl-2-sulfide), and the structural formula of the first film-forming additive (B) is as follows:
[0094]
[0095] The soft-pack lithium secondary battery prepared in Example 6 is named S6.
[0096] Example 7
[0097] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 7 are the same as in Example 3, except that the electrolyte additive in Example 7 is a first film-forming additive (C) (2-[bis(2-chloroethyl)amino]-1,3,2-dithiophosphine 2-oxide), and the structural formula of the first film-forming additive (C) is as follows:
[0098]
[0099] The soft-pack lithium secondary battery prepared in Example 7 is named S7.
[0100] Example 8
[0101] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 8 are the same as in Example 3, except that the electrolyte additive in Example 8 is a first film-forming additive (D) (2-(trifluoromethyl)-1,3,2-dithiophosphine 2-sulfide), and the structural formula of the first film-forming additive (D) is as follows:
[0102]
[0103] The soft-pack lithium secondary battery prepared in Example 8 is named S8.
[0104] Example 9
[0105] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 9 are the same as in Example 3, except that the electrolyte additive in Example 9 is a first film-forming additive (E) (2-(dimethylamino)-1,3,2-dithiophosphine 2-sulfide), and the structural formula of the first film-forming additive (E) is as follows:
[0106]
[0107] The soft-pack lithium secondary battery prepared in Example 9 is named S9.
[0108] Example 10
[0109] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 10 are the same as in Example 3, except that the electrolyte additive in Example 10 is a first film-forming additive (F) (2-(bis(2-chloroethyl)amino)-1,3,2-dithiophosphine 2-sulfide), and the structural formula of the first film-forming additive (F) is as follows:
[0110]
[0111] The soft-pack lithium secondary battery prepared in Example 10 is named S10.
[0112] Example 11
[0113] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 11 are the same as in Example 3, except that the electrolyte additive in Example 11 is a first film-forming additive (G) (2-chloro-1,3,2-dithiophosphine 2-sulfide), and the structural formula of the first film-forming additive (G) is as follows:
[0114]
[0115] The soft-pack lithium secondary battery prepared in Example 11 is named S11.
[0116] Example 12
[0117] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 12 are the same as in Example 3, except that the electrolyte additive in Example 12 is a first film-forming additive (H) (2,4-dimethyl-1,3,2-dithiophosphine-2-sulfide), and the structural formula of the first film-forming additive (H) is as follows:
[0118]
[0119] The soft-pack lithium secondary battery prepared in Example 12 is named S12.
[0120] Example 13
[0121] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 13 are the same as in Example 3, except that the electrolyte additive in Example 13 is a first film-forming additive (I) (2-(prop-1-enyl)-1,3,2-dithiophosphine-2-sulfide), and the structural formula of the first film-forming additive (I) is as follows:
[0122]
[0123] The soft-pack lithium secondary battery prepared in Example 13 is named S13.
[0124] Example 14
[0125] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 14 are the same as those in Example 3, except that the secondary battery electrolyte in Example 14 does not contain FEC.
[0126] The soft-pack lithium secondary battery prepared in Example 14 is named S14.
[0127] Example 15
[0128] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 15 are the same as those in Example 3, except that the mass percentage of FEC in the secondary battery electrolyte of Example 15 is 0.1%.
[0129] The soft-pack lithium secondary battery prepared in Example 15 is named S15.
[0130] Example 16
[0131] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 16 are the same as those in Example 3. The difference is that the electrolyte additives in the secondary battery electrolyte of Example 16 include a first film-forming additive (A) and a third film-forming additive propylene sulfite (PS). The mass percentage of the first film-forming additive (A) is 5%, and the mass percentage of propylene sulfite is 3%.
[0132] The soft-pack lithium secondary battery prepared in Example 16 is named S16.
[0133] Example 17
[0134] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Example 17 are the same as those in Example 3. The difference is that the electrolyte additives in the secondary battery electrolyte of Example 17 include a first film-forming additive (A) and a third film-forming additive propylene sulfite (PS). The mass percentage of the first film-forming additive (A) is 5%, and the mass percentage of propylene sulfite is 0.05%.
[0135] The soft-pack lithium secondary battery prepared in Example 17 is named S17.
[0136] To highlight the beneficial effects of this application, the following comparative examples are provided.
[0137] Comparative Example 1
[0138] 1) Preparation of secondary battery electrolyte
[0139] 60g of ethylene carbonate (EC) and 140g of diethyl carbonate (DEC) were mixed to obtain an organic solvent. Then, 30g of lithium hexafluorophosphate (LiPF6) was dissolved in the solvent to make the lithium salt concentration 1mol / L, thus obtaining the secondary battery electrolyte.
[0140] 2) Preparation of lithium secondary batteries
[0141] Positive and negative electrode sheets were prepared using the same method as in Example 1. The prepared positive and negative electrode sheets and separator were wound into a battery cell, filled with the above-mentioned secondary battery electrolyte, and then processed through formation and other processes to produce a soft-pack lithium secondary battery DS1.
[0142] Comparative Example 2
[0143] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Comparative Example 2 are the same as those in Comparative Example 1. The difference is that the secondary battery electrolyte in Comparative Example 2 also contains the electrolyte additive FEC. The mass percentage of FEC in the secondary battery electrolyte is 3%. The soft-pack lithium secondary battery prepared in Comparative Example 2 is named DS2.
[0144] Comparative Example 3
[0145] The preparation methods of the secondary battery electrolyte and lithium secondary battery in Comparative Example 3 are the same as those in Comparative Example 1. The difference is that the secondary battery electrolyte in Comparative Example 3 also contains electrolyte additive PS. The mass percentage of PS in the secondary battery electrolyte is 3%. The soft-pack lithium secondary battery prepared in Comparative Example 3 is named DS3.
[0146] The composition of the secondary battery electrolyte in each embodiment and comparative example is shown in Table 2.
[0147] Table 2 Electrolyte composition in Examples 1-17 and Comparative Examples 1-3
[0148]
[0149]
[0150] Effect Example
[0151] To strongly support the beneficial effects of the technical solutions in the embodiments of this application, the following tests are provided:
[0152] 1) Additive Reduction Potential Test: Cyclic voltammetry tests were performed on the secondary battery electrolytes in Examples 1, 6-14, and Comparative Examples 1-3, respectively. The scan rate was 0.2 mV / s, and the scan range was 0.005–3 V. The testing equipment was a domestically produced Chenhua CHI600C electrochemical workstation. The test results are shown in Table 3, where vs.Li+ / Li represents the cathode film formation potential value with lithium metal as the reference electrode, in volts (V). Additionally, the cyclic voltammetry test results for Example 1 (first film-forming additive (A)) and Comparative Example 1 are as follows: Figure 3 As shown, Figure 3 The graph shows the battery cyclic voltammetry test results for Example 1 and Comparative Example 1 of this application.
[0153] Table 3. Cyclic voltammetry test results of the electrolytes for each embodiment and comparative example of the secondary battery.
[0154]
[0155]
[0156] Depend on Figure 3 As can be seen from Table 3, the secondary battery electrolyte containing the first film-forming additive in this application has a higher film-forming potential than the electrolyte system without additives in the comparative example. This indicates that the first film-forming additive in the embodiment can preferentially reduce the electrolyte solvent, thereby effectively protecting the electrolyte.
[0157] 2) After disassembling the pouch cells of Examples 1-17 and Comparative Examples 1-3, the amount of nickel dissolved in the cells was tested. The test conditions were as follows: after disassembling the cells, the positive and negative electrode separators and aluminum-plastic films were repeatedly rinsed with 5 mL of dichloromethane. The washing solution was then sent to an inductively coupled plasma spectrometer (ICP) for testing. The instrument used was an inductively coupled plasma spectrometer manufactured by Thermo Fisher Scientific. Ten sets of cells were set up for each example and comparative example. The average value of the test results was taken. Please refer to Table 4 for the test results.
[0158] Table 4. Nickel leaching test results of pouch cells from Examples 1-17 and Comparative Examples 1-3.
[0159]
[0160]
[0161] As shown in Table 4, the secondary battery in this embodiment has a low nickel leaching amount, indicating that the first film-forming additive in the electrolyte can effectively suppress the leaching of metal ions from the cathode material. In Example 1, the amount of the first film-forming additive was low, resulting in a thinner interfacial film and a weaker leaching suppression effect.
[0162] 3) Battery expansion test: The specific test conditions were as follows: The soft-pack batteries of Examples 1-17 and Comparative Examples 1-3 were charged at 0.5C (400mA) with a cutoff voltage of 4.5V, followed by constant voltage charging at 4.5V with a cutoff current of 40mA. The fully charged batteries were stored in a 60℃ constant temperature oven for 5 days. Ten sets of batteries were set up for each example and comparative example, and the average value of the test results was taken. The thickness of the batteries before and after storage was measured using vernier calipers. The battery expansion rate (%) was calculated by subtracting the thickness before storage from the thickness after storage, and then dividing the difference by the thickness before storage to obtain the percentage. The expansion rate test results of Examples 1-17 and Comparative Examples 1-3 are shown in Table 5.
[0163] Table 5. Expansion rate test results of pouch cells in Examples 1-17 and Comparative Examples 1-3
[0164]
[0165] As can be seen from Table 5, the secondary battery in this embodiment has a lower expansion rate than the secondary battery in the comparative example. This indicates that the first film-forming additive can reduce the expansion rate of the secondary battery when it is fully charged and stored at high temperature, thereby improving the safety performance of the secondary battery at high temperature.
[0166] 4) High-voltage cycle performance tests were conducted on the pouch batteries of Examples 1-17 and Comparative Examples 1-3. The specific test conditions were as follows: the batteries were cycled 200 times at a current of 1C (800mA) between 2.75V and 4.5V, and the tests were carried out in a constant temperature chamber at 25℃. The capacity retention rate (%) was calculated by dividing the discharge capacity of the 300th cycle by the initial discharge capacity of the first cycle. The percentage obtained was the capacity retention rate. Ten sets of batteries were set up for each example and comparative example, and the test results were averaged. The test results of the high-voltage cycle performance of the pouch batteries of Examples 1-17 and Comparative Examples 1-3 are shown in Table 6.
[0167] Table 6 High-voltage cycle performance of pouch cells in Examples 1-17 and Comparative Examples 1-3
[0168] Battery number Capacity retention rate after 300 cycles (%) S1 42.42 S2 79.53 S3 84.15 S4 78.37 S5 41.48 S6 81.71 S7 80.32 S8 81.94 S9 81.17 S10 83.65 S11 82.12 S12 81.90 S13 84.74 S14 69.35 S15 79.85 S16 83.22 S17 72.13 DS1 31.24 DS2 39.19 DS3 40.23
[0169] As can be seen from the test results in Table 6, the secondary batteries of this application have a higher capacity retention rate compared to the comparative examples. Specifically, compared to Examples 1 and 5, the concentration of the first film-forming additive in Examples 2-4 is within a moderate range, thus resulting in a higher battery capacity retention rate. Example 14 uses a single-component film-forming additive, and its performance is slightly worse than the secondary batteries with combined electrolyte additives in other examples. In Example 15, the content of the second film-forming additive FEC is low, and the battery capacity retention rate is slightly worse than that of Example 3. In Example 17, the content of the third film-forming additive propylene sulfite is low, and the battery capacity retention rate is slightly worse than that of Example 16.
[0170] The above description represents the preferred embodiments of this application, but should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.
Claims
1. A secondary battery electrolyte, comprising an electrolyte salt, an organic solvent, and an electrolyte additive, characterized in that, The electrolyte additive includes a first film-forming additive with the structural formula shown in formula (I): Equation (I); Wherein, R1 is selected from sulfur atoms or oxygen atoms; R2 is selected from hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms; R3 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted amino groups, and halogen atoms.
2. The secondary battery electrolyte as described in claim 1, characterized in that, At least one of R2 and R3 is a substituted or unsubstituted alkenyl group or a substituted or unsubstituted alkynyl group.
3. The secondary battery electrolyte as described in claim 1, characterized in that, In R2 and R3, the substituted or unsubstituted alkyl group, the substituted or unsubstituted alkenyl group, and the substituted or unsubstituted alkynyl group have 1-10 carbon atoms; the substituted or unsubstituted aryl group has 6-30 carbon atoms.
4. The secondary battery electrolyte as described in claim 1, characterized in that, R2 is selected from hydrogen atom, methyl, trifluoromethyl, phenyl, bis(2-chloroethyl)amino, dimethylamino, and chlorine atom; R3 is selected from methyl, trifluoromethyl, phenyl, bis(2-chloroethyl)amino, dimethylamino, and chlorine atom.
5. The secondary battery electrolyte as described in claim 1, characterized in that, The first film-forming additive has a mass percentage content of 0.1%-10% in the secondary battery electrolyte.
6. The secondary battery electrolyte as described in claim 1, characterized in that, The electrolyte additive further includes a second film-forming additive, which includes one or more of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, ethylene sulfite, and methylene disulfonate.
7. The secondary battery electrolyte as described in claim 6, characterized in that, The mass ratio of the first film-forming additive to the second film-forming additive is 1:(0.5~30).
8. The secondary battery electrolyte as described in claim 1, characterized in that, The electrolyte additive also includes a third film-forming additive, which includes propylene sulfite.
9. The secondary battery electrolyte as described in claim 8, characterized in that, The mass ratio of the first film-forming additive to the third film-forming additive is 1:(0.02~50).
10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes the secondary battery electrolyte as described in any one of claims 1-9.