Secondary batteries

Abstract

This application proposes a secondary battery comprising a positive electrode and an electrolyte; the positive electrode comprises a ternary positive electrode material; the electrolyte comprises a first additive and a second additive; the first additive comprises a compound of Formula I; the second additive comprises a lithium salt having an oxalic acid group. This application uses a ternary positive electrode material and an electrolyte that can significantly improve the cycle performance and high-temperature storage performance of the secondary battery, especially maintaining good performance under high voltage conditions.

Description

Technical Field

[0001] This application relates to the field of materials preparation, and more specifically, to secondary batteries. Background Technology

[0002] In recent years, secondary batteries have achieved great success in the field of high-energy batteries, but consumers still expect batteries with higher overall performance to emerge, which depends on the research and development of new electrode materials and electrolyte systems.

[0003] Factors such as the dissolution of cathode metal ions, the occurrence of electrolyte side reactions, and the degradation of the electrode-electrolyte interface can hinder the improvement of the storage performance and cycle life of secondary batteries. Under high-temperature conditions, the decomposition of lithium salts intensifies, and the decomposition products, which are Lewis acids, catalyze the decomposition of carbonate-based solvents in the electrolyte to form gases such as ethylene, carbon dioxide, and carbon monoxide, leading to gas generation in secondary batteries. In addition, another decomposition product of lithium salts, HF, corrodes the cathode material, exacerbating the dissolution of transition ions. Transition metal ions can also catalyze the decomposition of solvents, further exacerbating the gas generation phenomenon.

[0004] To address the aforementioned issue of high-temperature gas generation in batteries, additives are typically used to regulate the formation of a stable SEI film at the electrode-electrolyte interface. However, current additive-regulated SEI films tend to be thick or have poor ion conduction properties, resulting in high impedance in the secondary battery and consequently poor cycle performance. Therefore, providing a high-performance electrolyte additive to improve the storage performance and cycle life of secondary batteries is of great significance. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in related technologies. To this end, this application proposes a secondary battery. The secondary battery of this application uses a ternary cathode material, and the electrolyte can significantly improve the battery's cycle performance and high-temperature storage performance, especially maintaining good performance under high-voltage conditions.

[0006] This application discloses a secondary battery. According to an embodiment of this application, the secondary battery includes a positive electrode and an electrolyte;

[0007] The positive electrode sheet includes a ternary positive electrode material;

[0008] The electrolyte includes a first additive and a second additive;

[0009] The first additive comprises the compound shown in Formula I:

[0010] R1, R2 and R3 are each independently selected from any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl and R5-substituted benzyl.

[0011] R4 and R5 are each independently selected from H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl or C2-C4 fluoroalkenyl.

[0012] The second additive includes a lithium salt having an oxalic acid group.

[0013] The secondary battery of this application uses a ternary cathode material, and the electrolyte contains a first additive and a second additive. The first additive is a silicon-based fluorophosphate compound, which has the property of preferential oxidation-reduction and inhibiting solvent reduction during battery charging and discharging. This is beneficial for constructing a stable SEI / CEI interface film, improving the flexibility, smoothness, thermal stability and lithium-ion conduction performance of the interface film, preventing direct contact between transition metal ions and the electrolyte, reducing the dissolution of transition metal ions in the electrolyte, inhibiting the catalysis of transition metal ions on the electrolyte, and improving the capacity retention rate of the battery under high temperature / long cycle conditions. It can also prevent the reduction and deposition of transition metal ions on the negative electrode surface, and has a significant effect on reducing battery impedance and improving low-temperature discharge and cycle performance.

[0014] Although silicon-based fluorophosphates have many advantages, they are sensitive to HF components and easily react with HF to form fluorosilane gas, leading to SEI film damage. Especially at high temperatures of 60°C, not only does the battery produce gas, but electrolyte oxidation deposits also hinder lithium-ion migration, causing a surge in interfacial impedance and severe battery capacity decay.

[0015] The second additive includes a lithium salt with oxalic acid groups, which forms a continuous interfacial film at the electrode-electrolyte interface through ring-opening of the oxalic acid groups; simultaneously, Li is introduced into the film composition. + This can simultaneously enhance the stability of the electrode-electrolyte interface film and improve lithium-ion conduction at the electrode-electrolyte interface. However, the interface film formed by the ring-opening of the oxalic acid group is prone to decomposition under high temperature or high pressure conditions, forming CO2, which then forms pores in the SEI and CEI, causing the electrolyte to come into direct contact with the electrode, leading to side reactions in the electrolyte and causing gas production in the battery under high temperature and high pressure.

[0016] By using the first and second additives in combination, the F element in the fluorosilane gas generated by the first additive, the H element in the carbonate solvent, and the O element in the oxalic acid-rich interfacial film formed by the second additive can interact through hydrogen bonds, stabilizing the oxalic acid-rich interfacial film and the fluorosilane. Simultaneously, the hydrogen-bonded structure formed by these three elements further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interfacial film, further enhancing the stability of the electrode-electrolyte interface. Particularly on the positive electrode side, the weak interaction between F and O can capture reactive oxygen species released during the phase transition of the NCM ternary cathode, reducing the adverse effects of reactive oxygen species on the electrolyte and further optimizing the suppression of gas generation. In summary, the combined use of these two additives can suppress high-temperature gas generation and improve capacity retention during high-temperature storage without affecting battery impedance.

[0017] According to embodiments of this application, the first additive comprises at least one compound having the structure shown in Formulas 1 to 17:

[0018] According to embodiments of this application, the second additive includes at least one of lithium bis(oxalato)borate, lithium bis(fluoro)oxalato)borate, lithium bis(fluoro)bis(oxalato)phosphate, lithium bis(fluoro)oxalato)phosphate, and lithium tri(oxalato)phosphate.

[0019] According to an embodiment of this application, the mass ratio of the first additive to the second additive is (0.05~20):1.

[0020] According to an embodiment of this application, the mass ratio of the first additive to the second additive is (0.5-10):1.

[0021] According to an embodiment of this application, the mass percentage of the first additive is 0.05% to 5.0% based on the total mass of the electrolyte.

[0022] According to an embodiment of this application, the mass percentage of the first additive is 0.5% to 2.5% based on the total mass of the electrolyte.

[0023] According to an embodiment of this application, the mass percentage of the second additive is 0.3% to 2.5% based on the total mass of the electrolyte.

[0024] According to embodiments of this application, the secondary battery further includes a non-aqueous organic solvent, which includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl-(2,2,2-trifluoroethyl) carbonate.

[0025] According to an embodiment of this application, the electrolyte further comprises: lithium salt;

[0026] The lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4;

[0027] And / or, based on the total mass of the electrolyte, the lithium salt accounts for 6% to 25% of the total mass.

[0028] According to embodiments of this application, the ternary cathode material includes LiNi. a Co b M c O2, M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr and Cu, a+b+c=1, 0.3≤a<1.

[0029] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0030] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers, and ranges defined in this way can include endpoints a and b. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0035] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] This application discloses a secondary battery. According to an embodiment of this application, the secondary battery includes a positive electrode and an electrolyte;

[0037] The positive electrode sheet includes a ternary positive electrode material;

[0038] The electrolyte includes a first additive and a second additive;

[0039] The first additive comprises the compound shown in Formula I:

[0040] R1, R2 and R3 are each independently selected from any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl and R5-substituted benzyl.

[0041] R4 and R5 are each independently selected from H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl or C2-C4 fluoroalkenyl.

[0042] The second additive includes a lithium salt having an oxalic acid group.

[0043] The secondary battery of this application uses a ternary cathode material, and the electrolyte contains a first additive and a second additive. The first additive is a silicon-based fluorophosphate compound, which has the properties of preferential oxidation-reduction and inhibiting solvent reduction during battery charging and discharging. The silicon-based structure forms a stable SEI / CEI interface film, improving the flexibility and smoothness of the interface film. The fluorophosphate structure combines with lithium salt to form fluorinated lithium phosphate, participating in the film formation process and providing LiF, Li3PO3, and Li... x PO y F z Various lithium salt inorganic components are added to improve the thermal stability and lithium-ion conductivity of the SEI / CEI film. For the positive electrode CEI film, Li... x PO y F z Coating the surface of the positive electrode material prevents direct contact between transition metal ions and the electrolyte, reducing the solubility of transition metal ions in the electrolyte. The P=O, PO, and PF bonds can also complex the transition metals, reducing their chemical / electrochemical activity, inhibiting their catalytic effect on the electrolyte, and improving the battery's capacity retention under high-temperature / long-cycle conditions. For the negative electrode SEI film, fluorinated lithium phosphate can prevent the reduction and deposition of transition metal ions on the negative electrode surface, significantly reducing battery impedance and improving low-temperature discharge and cycle performance. Although silicon-based fluorophosphate compounds have many advantages, they are sensitive to HF components and readily react with HF to form fluorosilane gas, leading to SEI film damage, especially at 60°C. This not only results in battery gas production but also causes electrolyte oxidation deposits to hinder lithium-ion migration, causing a surge in interfacial impedance and severe battery capacity decay.

[0044] The second additive includes a lithium salt with oxalic acid groups, which forms a continuous interfacial film at the electrode-electrolyte interface through ring-opening of the oxalic acid groups; simultaneously, Li is introduced into the film composition. + This can simultaneously enhance the stability of the electrode-electrolyte interface film and improve lithium-ion conduction at the electrode-electrolyte interface. However, the interface film formed by the ring-opening of the oxalic acid group is prone to decomposition under high temperature or high pressure conditions, forming CO2, which then forms pores in the SEI and CEI, causing the electrolyte to come into direct contact with the electrode, leading to side reactions in the electrolyte and causing gas production in the battery under high temperature and high pressure.

[0045] By using the first and second additives in combination, the F element in the fluorosilane gas generated by the first additive, the H element in the carbonate solvent, and the O element in the oxalic acid-rich interfacial film formed by the second additive can interact through hydrogen bonds, thereby stabilizing the oxalic acid-rich interfacial film and the fluorosilane. Simultaneously, the hydrogen-bonded structure formed by these three elements further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interfacial film, further enhancing the stability of the electrode-electrolyte interface.

[0046] During battery charging and discharging, NCM ternary cathode materials are prone to phase transitions and the release of active oxygen due to their structural instability. This release of active oxygen not only exacerbates electrolyte decomposition, leading to increased gas production, but also negatively impacts the battery's thermal stability. The fluorine (F) element in the fluorosilane gas of the first additive and the oxygen (O) element in the oxalic acid-rich interfacial film of the second additive exhibit a weak interaction, capturing the active oxygen released during the NCM ternary cathode phase transition, reducing the adverse effects of active oxygen on the electrolyte, and further optimizing the suppression of gas production.

[0047] In summary, the combined use of the first and second additives can suppress high-temperature gas generation and improve capacity retention during high-temperature storage without affecting battery impedance.

[0048] According to embodiments of this application, the first additive comprises at least one compound having the structure shown in Formulas 1 to 17:

[0049] (CAS No.: 2708941-25-5) (CAS No.: 4419-25-9) (CAS No.: 13683-39-1) (CAS No.: 4414-27-1) (CAS No.: 4414-26-0) (CAS No.: 4480-02-8) (CAS No.: 2577172-95-1) (CAS No.: 13683-40-4) (CAS No.: 2577172-93-9) (CAS No.: 6231-57-8) (CAS No.: 1386-54-9) (CAS No.: 2708941-26-6) (CAS No.: 6231-59-0)

[0050] Preparation method of the above compounds:

[0051] Compounds 14-17 were prepared according to the preparation method of Example 14 in patent CN114728992A, specifically, the dichlorophenylsilane in the reference document was replaced with the raw materials shown below.

[0052] Formula 14 The raw material is trivinylchlorosilane (1871-21-2).

[0053] Formula 15 The raw material is dimethylethynyl butylchlorosilane (2069196-19-4).

[0054] Formula 16 The raw material is dimethyl(trifluoropropylene)chlorosilane (89705-02-2).

[0055] Formula 17 The raw material is tris(pentafluoroethyl)chlorosilane (1620665-21-5).

[0056] During battery charging and discharging, the aforementioned first additive exhibits preferential oxidation-reduction properties and inhibits solvent reduction, which is beneficial for constructing a stable SEI / CEI interface film. This enhances the flexibility, smoothness, thermal stability, and lithium-ion conductivity of the interface film, prevents direct contact between transition metal ions and the electrolyte, reduces the dissolution of transition metal ions in the electrolyte, inhibits the catalytic effect of transition metal ions on the electrolyte, and improves the battery's capacity retention under high-temperature / long-cycle conditions. It also prevents the reduction and deposition of transition metal ions on the negative electrode surface, significantly reducing battery impedance and improving low-temperature discharge and cycle performance. Furthermore, the first additive, second additive, and carbonate solvent interact through hydrogen bonds, stabilizing the oxalate-rich interface film and fluorosilane. Simultaneously, the hydrogen-bonded structure formed by these three components further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interface film, further enhancing the stability of the electrode-electrolyte interface. In particular, the first and second additives mentioned above capture the active oxygen released during the phase transition of the NCM ternary cathode through weak mutual interaction, reducing the side effects of active oxygen on the electrolyte and further optimizing the effect of inhibiting gas production.

[0057] According to embodiments of this application, the second additive includes at least one selected from lithium dioxalatoborate, lithium difluorooxalatoborate, lithium difluorodioxalatophosphate, lithium tetrafluorooxalatophosphate, and lithium trioxalatophosphate. Using the above-mentioned second additive, a continuous interfacial film is formed at the electrode-electrolyte interface through ring-opening of the oxalic acid group; simultaneously, Li is introduced into the film composition. + This process simultaneously enhances the stability of the electrode-electrolyte interface film and improves lithium-ion conduction at the electrode-electrolyte interface. Furthermore, the second additive, the first additive, and the carbonate solvent interact through hydrogen bonds, stabilizing the oxalic acid-rich interface film and the fluorosilane. Simultaneously, the hydrogen-bonded structure formed by these three components further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interface film, further enhancing interface stability. In particular, the second and first additives, through weak interactions, capture reactive oxygen species released during the NCM ternary cathode phase transition, reducing their negative impact on the electrolyte and further optimizing the suppression of gas generation.

[0058] According to embodiments of this application, the mass ratio of the first additive to the second additive is (0.05–20):1, for example, it can be 0.05:1, 0.1:1, 0.5:1, 1:1, 2:1, 4:1, 5:1, 6:1, 8:1, 10:1, 12:1, 14:1, 15:1, 16:1, 18:1, 20:1, preferably (0.5–10):1. When the mass ratio of the first additive to the second additive meets the above conditions, their synergistic effect can be enhanced, thereby improving overall performance, ensuring the maximization of the interaction between the additives, significantly improving the cycle performance and high-temperature storage performance of the battery, especially maintaining good performance under high voltage conditions, while reducing unnecessary side reactions or waste and lowering costs.

[0059] According to embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.05% to 5.0%, for example, it can be 0.05%, 0.1%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%, preferably 0.5% to 2.5%. Thus, the amount of the first additive meets the above conditions, further facilitating the construction of a stable SEI / CEI interface film, improving the flexibility, smoothness, thermal stability, and lithium-ion conductivity of the interface film, preventing direct contact between transition metal ions and the electrolyte, reducing the dissolution of transition metal ions in the electrolyte, inhibiting the catalytic effect of transition metal ions on the electrolyte, improving the capacity retention rate of the battery under high temperature / long cycle conditions, and preventing the reduction and deposition of transition metal ions on the negative electrode surface. This has a significant effect on reducing battery impedance, improving low-temperature discharge, and cycle performance. Furthermore, it can better interact with the second additive and carbonate solvent through hydrogen bonds, further stabilizing the interface film rich in oxalic acid groups and the fluorosilane. Simultaneously, it helps to further form a network-structured electrode-electrolyte interface film, further improving the stability of the electrode-electrolyte interface. In particular, the first and second additives mentioned above, through weak mutual interactions, capture the reactive oxygen species released during the phase transition of the NCM ternary cathode, reducing the side effects of reactive oxygen species on the electrolyte and further optimizing the effect of inhibiting gas production.

[0060] According to embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.3% to 2.5%, for example, 0.3%, 0.5%, 1.0%, 1.5%, 2.0%, or 2.5%. Using a second additive that meets the above conditions further forms a continuous interfacial film at the electrode-electrolyte interface, simultaneously enhancing the stability of the electrode-electrolyte interfacial film and improving lithium-ion conduction at the electrode-electrolyte interface. Furthermore, the second additive meeting the above conditions can further stabilize the oxalic acid-rich interfacial film and the fluorosilane with the first additive and the carbonate solvent. Simultaneously, the hydrogen-bonded structure formed by these three components further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interfacial film, further improving the stability of the electrode-electrolyte interface. In particular, the second additive and the first additive meeting the above conditions further better capture the reactive oxygen species released during the NCM ternary cathode phase transition, reducing the side effects of reactive oxygen species on the electrolyte and further optimizing the suppression of gas generation.

[0061] According to embodiments of this application, the secondary battery further includes a non-aqueous organic solvent, which includes at least one selected from ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl-(2,2,2-trifluoroethyl) carbonate. Thus, the aforementioned carbonate solvent can interact with the first and second additives via hydrogen bonds, stabilizing the oxalate-rich interfacial film and the fluorosilane. Simultaneously, the hydrogen-bonded structure formed by these three components further reacts at the electrode-electrolyte interface, forming a network-structured electrode-electrolyte interfacial film, further enhancing the stability of the electrode-electrolyte interface.

[0062] As an example, the non-aqueous organic solvent may also include non-carbonate compounds, such as at least one selected from γ-butyrolactone, sulfolane, fluoroethylene carbonate, dimethyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2-difluoroethyl acetate.

[0063] As an example, based on the total mass of the electrolyte, the mass percentage of the non-aqueous organic solvent is 65.5% to 93.2%.

[0064] According to embodiments of this application, the electrolyte additive further comprises: a lithium salt; the lithium salt includes at least one selected from LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4.

[0065] According to embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the lithium salt is 6% to 25%, for example, 6%, 10%, 12%, 15%, 18%, 20%, 22%, or 25%. Thus, the lithium salt meets the above conditions, resulting in efficient migration and stable transport of ions in the electrolyte, thereby improving the battery's charge / discharge efficiency and power density. Furthermore, it helps maintain the chemical stability of the electrolyte, reducing side reactions during high-voltage charging, such as electrolyte decomposition and gas generation, which helps extend the battery's cycle life and improve its safety.

[0066] According to embodiments of this application, the ternary cathode material includes LiNi. a Co b M c O2, M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr, and Cu, a+b+c=1, 0.3≤a<1. During battery charging and discharging, NCM ternary cathode materials are prone to phase transitions and the release of active oxygen due to their structural instability. This release of active oxygen not only exacerbates electrolyte decomposition, leading to increased battery gas production, but also negatively impacts the battery's thermal stability. The F element in the fluorosilane gas of the first additive and the O element in the oxalic acid-rich interfacial film of the second additive exhibit a weak interaction, capturing the active oxygen released during the NCM ternary cathode phase transition, reducing the side effects of active oxygen on the electrolyte, and further optimizing the suppression of gas production. This significantly improves the battery's cycle performance and high-temperature storage performance, especially maintaining good performance under high-voltage conditions.

[0067] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes the positive active material.

[0068] According to embodiments of this application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite positive electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0069] According to embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] According to embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0071] According to embodiments of this application, the positive electrode sheet can be prepared in the following manner: the components used to prepare the positive electrode sheet, such as positive active material, conductive agent, and binder, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on a positive current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0072] According to an embodiment of this application, the battery further includes a negative electrode and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0073] According to an embodiment of this application, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a binder.

[0074] According to embodiments of this application, the adhesive may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0075] According to embodiments of this application, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate.

[0076] According to embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] According to embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] According to an embodiment of this application, the negative electrode sheet includes a negative electrode current collector, and the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector.

[0079] According to embodiments of this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, aluminum or copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0080] According to embodiments of this application, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0081] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0082] According to embodiments of this application, the material of the separator may include one or more of polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone. Further, the separator may include one or both of polyethylene and polypropylene. Moreover, the separator may be obtained by sequentially stacking multiple layers of materials; for example, the separator may include sequentially stacked polypropylene layers, polyethylene layers, and polypropylene layers.

[0083] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0084] Example 1

[0085] 1. Preparation of positive electrode sheet

[0086] LiNi, the positive electrode active material 0.6 Co 0.1 Mn 0.3 O2, conductive carbon black, and polyvinylidene fluoride (PVDF) binder are added to N-methylpyrrolidone (NMP) in a mass ratio of 97:1.8:1.2 to prepare a positive electrode slurry (the solid content of the positive electrode slurry is 72wt%). The positive electrode slurry is coated on the upper and lower surfaces of aluminum foil, dried, and then cold-pressed. After trimming, cutting, and slitting, the positive electrode sheet is made.

[0087] 2. Preparation of negative electrode sheet

[0088] A negative electrode slurry (with a solid content of 51 wt%) is prepared by mixing graphite with conductive carbon black (a conductive agent), carboxymethyl cellulose (CMC) (a thickener), and styrene-butadiene rubber (SBR) (a binder) in deionized water at a mass ratio of 95.8:1.2:1.5:1.5. The negative electrode slurry is coated on the upper and lower surfaces of copper foil and dried. Then, it is cold-pressed, trimmed, cut into sheets, and slit to form a negative electrode sheet.

[0089] 3. Preparation of electrolyte

[0090] In an argon-filled glove box, the first additive (the compound shown in Formula 1), the second additive (lithium bis(oxalato)borate), and the third additive (lithium difluorophosphate) were added to an organic solvent (the organic solvent included ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, with a volume ratio of 3:5:2). After mixing thoroughly, LiPF6 was slowly added. After the lithium salt was completely dissolved, an electrolyte with a lithium salt concentration of 12 w / w% was obtained. Based on the total mass of the electrolyte, the mass percentage of the first additive was 1%, the mass percentage of the second additive was 1%, and the mass percentage of the third additive was 0.5%.

[0091] 4. Separating membrane

[0092] A 16μm polyethylene film was used as the separator.

[0093] 5. Lithium-ion battery manufacturing

[0094] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and tested for capacity to complete the preparation of the lithium-ion battery.

[0095] The differences between Examples 2-41 and Comparative Examples 1-8 and Example 1 are shown in Table 1. Among them,

[0096] The difference between Example 18 and Example 1 is that the first additive is replaced with the compounds shown in Formula 1 and Formula 2 in a mass ratio of 0.5:0.5.

[0097] The difference between Example 19 and Example 1 is that the second additive is replaced with lithium difluorooxalate borate and lithium trioxalate phosphate in a mass ratio of 0.5:0.5.

[0098] The difference between Comparative Example 5 and Example 1 is that the second additive is replaced with lithium difluorosulfonylimide.

[0099] The difference between Comparative Example 6 and Example 1 is that the first additive is replaced with the compound shown in Formula 18. CAS number 754-05-2).

[0100] Test Case

[0101] The performance of the batteries prepared in Examples 1-41 and Comparative Examples 1-8 was tested, as follows:

[0102] 1) Capacity retention test after 30 days of storage at 60℃

[0103] The battery was charged at 25℃ with a constant current of 1.0C to 4.4V, and then charged at a constant voltage of 4.4V until the cutoff current was 0.05C. It was then discharged at a constant current of 0.5C, and the discharge capacity was recorded as C2. The battery was removed, and its initial thickness was measured using a thickness meter and recorded as T1. At 25℃, the battery was charged at a constant current of 1.0C to 4.4V, and then charged at a constant voltage of 4.4V until the cutoff current was 0.05C. The battery was then transferred to 60℃ and stored for 15 days, and its thickness after 15 days was measured using a thickness meter and recorded as T2. The battery was then discharged at a constant current of 1.0C, and the discharge capacity was recorded as C3. The capacity retention rate after 15 days of storage at 60℃ was calculated as C3 / C2 * 100%, and the battery expansion rate was calculated as 100% * (T2 - T1) / T1.

[0104] 2) Initial DCR Test

[0105] After capacity grading, the battery was charged to 4.4V at 1C at room temperature, left to stand for 5 minutes, then discharged at 1C for 30 minutes, left to stand for 1 hour, and then discharged at 2C for 10 seconds. The DCIR of the battery at 50% SOC was calculated.

[0106] The results are shown in Table 1.

[0107]

[0108]

[0109]

[0110]

[0111] The results are shown in Table 1. It can be seen that the batteries prepared in Examples 1-41 generally outperformed those in Comparative Examples 1-8. This indicates that the combination of silicon-based fluorophosphate compounds and lithium salts with oxalic acid groups stabilizes the oxalic acid-rich interfacial film and fluorosilanes. Simultaneously, a network-structured electrode-electrolyte interfacial film is formed, further enhancing the stability of the electrode-electrolyte interface. Furthermore, the F element in the fluorosilane gas from the silicon-based fluorophosphate compounds interacts weakly with the O element in the oxalic acid-rich interfacial film of the lithium salts, capturing the active oxygen released during the NCM ternary cathode phase transition, reducing the adverse effects of active oxygen on the electrolyte, and further optimizing the suppression of gas production. Therefore, the overall battery internal resistance is reduced, and high-temperature storage performance and cycle performance are improved.

[0112] As can be seen from Examples 2, 24-26, 28-29, and 31-33, when the mass percentage of the first additive is 0.05% to 5.0%, it is beneficial for constructing a stable SEI / CEI interface film, improving the capacity retention rate of the battery under high temperature / long cycle conditions, and preventing the reduction and deposition of transition metal ions on the negative electrode surface. This significantly reduces battery impedance and improves low-temperature discharge and cycle performance. Furthermore, it can further stabilize the interface film rich in oxalic acid groups and fluorosilanes. Simultaneously, it helps to further form a network structure electrode-electrolyte interface film, further improving the stability of the electrode-electrolyte interface. In particular, it is beneficial for better capturing the active oxygen released during the phase transition of the NCM ternary cathode, reducing the side effects of active oxygen on the electrolyte, and further optimizing the suppression of gas generation. Therefore, it further improves the battery's cycle performance and high-temperature storage performance. The effect is even better at 0.5% to 2.5%.

[0113] As can be seen from Examples 2, 27, 30, and 34-39, when the mass percentage of the second additive is 0.3% to 2.5%, it is beneficial to form a continuous interfacial film at the electrode-electrolyte interface, while simultaneously enhancing the stability of the electrode-electrolyte interfacial film and improving lithium-ion conduction at the electrode-electrolyte interface. Furthermore, it stabilizes the interfacial film rich in oxalic acid groups and enhances the effect of fluorosilanes. Simultaneously, it better forms a network structure electrode-electrolyte interfacial film, further improving the stability of the electrode-electrolyte interface. In particular, it is beneficial to better capture the active oxygen released during the phase transition of the NCM ternary cathode, reducing the adverse effects of active oxygen on the electrolyte and further optimizing the suppression of gas generation. Therefore, it further improves the battery's cycle performance and high-temperature storage performance.

[0114] As can be seen from Examples 24-39, when the mass ratio of the first additive to the second additive is (0.05-20):1, their synergistic effect can be enhanced, thereby improving the overall performance, ensuring the maximization of the interaction between the additives, and significantly improving the cycle performance and high-temperature storage performance of the battery. Preferably, the ratio is (0.5-10):1. In Examples 27 and 38, the low proportion of the second additive and in Example 33, the high proportion of the first additive resulted in slightly lower cell performance.

[0115] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A secondary battery, characterized in that, Includes the positive electrode and the electrolyte; The positive electrode sheet includes a ternary positive electrode material; The electrolyte includes a first additive and a second additive, wherein the mass ratio of the first additive to the second additive is (0.05~20):1; The first additive comprises the compound shown in Formula I: Formula I; R1, R2 and R3 are each independently selected from any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl and R5-substituted benzyl. R4 and R5 are each independently selected from H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl or C2-C4 fluoroalkenyl. The second additive includes a lithium salt having an oxalic acid group; Based on the total mass of the electrolyte, the first additive accounts for 0.05% to 5.0% of the mass; based on the total mass of the electrolyte, the second additive accounts for 0.3% to 2.5% of the mass.

2. The secondary battery according to claim 1, characterized in that, The first additive includes at least one of the compounds having the structures shown in Formulas 1 to 17: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9 Formula 10 Formula 11 Formula 12 Formula 13 Formula 14 Formula 15 Formula 16 Formula 17.

3. The secondary battery according to claim 1, characterized in that, The second additive includes at least one of lithium bis(oxalate)borate, lithium bis(fluorooxalate)borate, lithium bis(fluoro)bis(oxalate)phosphate, lithium bis(fluoro)oxalate phosphate, and lithium tri(oxalate)phosphate.

4. The secondary battery according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is (0.5~10):

1.

5. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.5% to 2.5%.

6. The secondary battery according to claim 1, characterized in that, It also includes non-aqueous organic solvents, which include at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl-(2,2,2-trifluoroethyl) carbonate.

7. The secondary battery according to claim 1, characterized in that, Further includes: Lithium salts; The lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiN(SO2F)2, LiN(SO2CF3)2, and LiPO2F2; And / or, based on the total mass of the electrolyte, the lithium salt accounts for 6% to 25% of the mass.

8. The secondary battery according to claim 1, characterized in that, The ternary cathode material includes LiNi. a Co b M c O2, M includes at least one of Mn, Al, Ti, V, Fe, Zn, V, Zr, Ce, Cr and Cu, a+b+c=1, 0.3≤a<1.

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