Electrolyte additive, electrolyte and battery

Abstract

Electrolyte additive, comprehensive: a compound represented by formula 1; and a compound represented by formula 2, wherein R1 and R2 are each independently selected from any one of substituted or unsubstituted C1- to C6-alkyl, substituted or unsubstituted C2- to C6-alkenyl or substituted or unsubstituted C2- to C7-alkynyl.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS

[0001] This application claims the priority and benefits of patent application no. 202410817652.8, filed with the Chinese Patent Office on June 24, 2024, which is incorporated in full by reference into this document. AREA

[0002] The present disclosure relates to the field of batteries and in particular to an electrolyte additive, an electrolyte and a battery. BACKGROUND

[0003] Currently, secondary batteries are widely used in consumer electronics, new energy vehicles, and other power battery products due to their environmental friendliness, low cost, and high operating voltage. Energy density and fast charging time are paramount for users. To further improve energy density and address the issue of insufficient capacity, battery design is shifting its focus towards higher voltages. Currently, the voltage of mass-produced high-voltage power batteries has reached 4.35 V. If the voltage is increased further to 4.5 V or even higher, this voltage approaches the degradation potential of conventional carbonate solvents, making the electrolyte susceptible to degradation and gas formation.Furthermore, the material of the positive electrodes exhibits structural instability and problems regarding an oxygen imbalance at this voltage, which leads to transition metals dissolving and being deposited on the negative electrode, thus degrading the high-temperature cycling performance.

[0004] Due to the aforementioned deficiencies, it is necessary to develop an electrolyte that significantly improves the cycling performance of secondary batteries at high temperatures and prevents the dissolution of transition metals. SUMMARY

[0005] The present disclosure aims to solve, at least to some extent, one of the technical problems in the prior art. In this context, one purpose of the present disclosure is to provide an electrolyte additive, an electrolyte, and a battery. By adding the electrolyte additive to a secondary battery, the cycling performance of the secondary battery at high temperatures can be improved, and the dissolution of transition metals can be prevented.

[0006] In a first aspect, the present disclosure provides an electrolyte additive. The electrolyte additive comprises a compound represented by formula 1 and a compound represented by formula 2: R1 and R2 are each independently selected from any one of substituted or unsubstituted C1- to C6-alkyl, substituted or unsubstituted C2- to C6-alkenyl or substituted or unsubstituted C2- to C7-alkynyl.

[0007] In the additive according to the present disclosure, the compound represented by formula 1, a group of the compound represented by formula 1, and PF6 can be - through strong interaction with PF6 --anions are formed. The lowest oxidation potential of the group allows the compound represented by formula 1 to be preferentially oxidized on the positive electrode side, thereby reducing the dissolution of transition metals from the active material for positive electrodes. Simultaneously, the lowest unoccupied molecular orbital (LUMO) energy level and the highest electron affinity of the compound represented by formula 1 lead to preferential reducibility on the negative electrode side, and they can form a film on the negative electrode in front of the solvent. However, the film is thin and of poor quality and prone to further reaction and degradation at high temperatures, generating gas, making the SEI film susceptible to cracking during the cycle. Based on this, the compound represented by formula 2 is added to the electrolyte additive.The compound represented by formula 2 opens the ring to form sulfur-containing oligomers on the negative electrode. This sulfur-containing oligomer, which is a film-forming component, is the same as the compound represented by formula 1, thereby increasing the concentration of sulfur-containing oligomers at the negative electrode interface and the stability of the SEI. Simultaneously, the compound represented by formula 2 also forms an SEI component rich in groups such as PO₄²⁻ and LiF on the negative electrode, further reducing the film-forming impedance at the negative electrode.By combining the compound represented by formula 1 and the compound represented by formula 2, a SEI with high stability and low impedance can be formed, thereby improving the high-temperature cycling performance and rate performance of the battery and reducing the dissolution of transition metals.

[0008] In some embodiments, the mass ratio of the compound represented by formula 1 to the compound represented by formula 2 is 1:(0.05 to 20). Therefore, the appropriate ratio of the two can improve the high-temperature cycling performance and rate performance of the battery and reduce the dissolution of transition metals.

[0009] In some embodiments, the compound represented by formula 1 comprises:

[0010] For this reason, the compound, which has the above structural formula, is used as a component of the electrolyte additive that can further reduce the dissolution of transition metals.

[0011] In a second aspect, the present revelation provides an electrolyte that includes the electrolyte additive according to the first aspect.

[0012] In some embodiments, the mass fraction of the compound represented by formula 1, based on a total mass of the electrolyte, is in the range of 0.03% to 3% and optionally from 0.03% to 2%. Therefore, by adding this electrolyte to the secondary battery, the dissolution of the transition metals can be further reduced.

[0013] In some embodiments, the mass fraction of the compound represented by formula 2, based on a total mass of the electrolyte, is in the range of 0.05% to 2.5% and optionally from 0.05% to 2%. Therefore, by adding this electrolyte to the secondary battery, the compound represented by formula 2 can participate in film formation together with the compound represented by formula 1 to form a very stable, low-impedance SEI, thereby improving the high-temperature cycling performance and the rate performance of the battery.

[0014] In a third aspect, the present disclosure provides a battery comprising the electrolyte according to the second aspect. As a result, the battery exhibits excellent high-temperature cycling performance and rate performance with low transition metal dissolution.

[0015] In some embodiments, the battery includes an active material for positive electrodes. The active material for positive electrodes comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, or a lithium-rich, manganese-based positive electrode material. Optionally, the lithium nickel cobalt manganese oxide comprises at least one of the compounds specified by LiNi x M 1-xO2 are represented, where M comprises Co and Mn and 0.8 ≤ x ≤ 0.92. For this reason, the transition metals in the aforementioned active material for positive electrodes are more readily dissolved at high temperature. By adapting the additive containing the compound represented by Formula 1 and the compound represented by Formula 2 to the aforementioned active material for positive electrodes, the dissolution of the transition metals can be further reduced in a targeted manner, and the high-temperature cycling performance of the battery can be further improved.

[0016] In some embodiments, the active material for positive electrodes comprises at least one of Na x1 M1O2, Na X2M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3 or Na2M4(SO4)2·2H2O, wobei: 0 <x1≤1; M1 mindestens eines von Ni, Co, Mn, Fe oder Cu umfasst; 0<x2<6; M2 mindestens eines von Ni, Fe oder Mn umfasst; M3 mindestens eines von Fe oder Mn umfasst; und M4 mindestens eines von Fe, Co, Mn oder Cu umfasst. Deshalb werden in dem Aktivmaterial für positive Elektroden der vorstehend genannten Natrium-Sekundärbatterie die Übergangsmetalle, insbesondere elementares Mn, leicht aufgelöst. Durch das Anpassen des Elektrolytadditivs an das vorstehend genannte Aktivmaterial für positive Elektroden kann die Auflösung der Übergangsmetalle weiter reduziert werden, und die Hochtemperatur-Zyklisierungsleistung der Batterie kann weiter verbessert werden.

[0017] Additional aspects and benefits of the present disclosure are partly provided in the following description, or will partly become apparent from the following description, or can be learned from the implementation of the present disclosure. DETAILED DESCRIPTION

[0018] The embodiments of the present disclosure are described in detail below and are intended to explain the present disclosure and not to be interpreted as restricting the present disclosure.

[0019] The amount of electrolyte additives only accounts for a small portion of the electrolyte in the secondary battery; however, a suitable amount of these additives can form SEI (Solid Electrolyte Interphase) on the surface of the active material for the negative electrodes and CEI (Cathode Electrolyte Interphase) on the surface of the active material for the positive electrodes. SEI and CEI form films on the surfaces of the active materials for the negative and positive electrodes, respectively, thereby reducing the problem of side reactions that occur after direct contact between the active materials and the electrolyte.

[0020] To further improve battery energy density and address the issue of insufficient capacity, battery design is shifting its focus towards higher voltages. Currently, the voltage of mass-produced high-voltage power batteries has reached 4.35 V. Increasing the voltage to 4.5 V or even higher places it close to the degradation potential of conventional carbonate solvents, making the electrolyte susceptible to degradation and gassing. Furthermore, at this voltage, the positive electrode material exhibits structural instability and oxygen imbalance, leading to the dissolution and deposition of transition metals on the negative electrode and thus degrading high-temperature cycling performance.

[0021] In light of the foregoing, the present disclosure provides, in a first aspect, an electrolyte additive. The electrolyte additive comprises a compound represented by formula 1 and a compound represented by formula 2:

[0022] R1 and R2 are each independently selected from any one of substituted or unsubstituted C1- to C6-alkyl, substituted or unsubstituted C2- to C6-alkenyl or substituted or unsubstituted C2- to C7-alkynyl.

[0023] In the electrolyte additive according to the present disclosure, the compound represented by formula 1, a group of the compound represented by formula 1, and PF6 can be - through strong interaction with PF6 --anions are formed. The lowest oxidation potential of the group allows the compound represented by Formula 1 to be preferentially oxidized on the positive electrode side, thereby reducing the dissolution of transition metals from the active material for positive electrodes. Simultaneously, the lowest unoccupied molecular orbital (LUMO) energy level and the highest electron affinity of the compound represented by Formula 1 lead to preferential reducibility on the negative electrode side, and they can form a film on the negative electrode in front of the solvent. However, the film is thin and of poor quality and prone to further reaction and degradation at high temperatures, generating gas, making the SEI film susceptible to cracking during the cycle. Based on this, the compound represented by Formula 2 (CAS No. 2681338-34-9) is added to the electrolyte additive.The compound represented by formula 2 opens the ring to form sulfur-containing oligomers on the negative electrode. This sulfur-containing oligomer, which is a film-forming component, is the same as the compound represented by formula 1, thereby increasing the concentration of sulfur-containing oligomers at the negative electrode interface and the stability of the SEI. Simultaneously, the compound represented by formula 2 also forms an SEI component rich in groups such as PO₄²⁻ and LiF on the negative electrode, further reducing the film-forming impedance at the negative electrode.By combining the compound represented by formula 1 and the compound represented by formula 2, a SEI with high stability and low impedance can be formed, thereby improving the high-temperature cycling performance and rate performance of the battery and reducing the dissolution of transition metals.

[0024] Additionally, after the compound represented by formula 2 is reduced, an inorganic substance rich in F and Li is formed on the surface of the negative electrode, reducing the battery's impedance and improving its rate performance. The free radicals generated by the cleavage of PO diffuse to the surface of the positive electrode, where they are oxidized and contribute to the formation of CEI along with the compound represented by formula 1. This stabilizes the active material for the positive electrodes and prevents direct contact between the electrolyte and the positive electrode. Furthermore, a complex of POM (M = Ni, Co, Mn) forms on the surface of the positive electrode, reducing the dissolution of transition metals and improving the cycle.The compound represented by formula 2 has a single electron pair that is compatible with H. + in the electrolyte, which can form and prevent the PF5 reaction properties in the LiPF6-based electrolyte system, thereby reducing the degradation of LiPF6.

[0025] For example, if R1 and R2 are each independently selected from substituted or unsubstituted C1 to C6 alkyl, the number of carbon atoms of the alkyl can be 1, 2, 3, 4, 5, 6, etc.; if R1 and R2 are each independently selected from substituted or unsubstituted C2 to C6 alkenyl, the number of carbon atoms of the alkenyl can be 2, 3, 4, 5, 6, etc.; and if R1 and R2 are each independently selected from substituted or unsubstituted C2 to C7 alkynyl, the number of carbon atoms of the alkynyl can be 2, 3, 4, 5, 6, 7, etc.

[0026] It is understood that if R1 and R2 have more than two carbon atoms, more than two carbon atoms may be partially or completely involved in ring formation; or only one carbon atom may be involved in ring formation and the other carbon atoms are connected as branches to the carbon atoms involved in ring formation.

[0027] In some embodiments of the present disclosure, the mass ratio of the compound represented by formula 1 to the compound represented by formula 2 is 1:(0.05 to 20). For example, the mass ratio of the compound represented by formula 1 to the compound represented by formula 2 may be 1:0.05, 1:0.5, 1:1, 1:5, 1:10, 1:15, 1:20, etc. In this way, by controlling the mass ratio of the compound represented by formula 1 to the compound represented by formula 2 within the aforementioned range, the synergistic effect of the compound represented by formula 1 and the compound represented by formula 2 is fully exploited.This addresses the problem of thin and poor-quality films caused by excessive compounds represented by Formula 1, resulting in a low film-forming impedance of the negative electrode, thus ensuring the cycling performance and rate performance of the battery; and it can also reduce the inadequate prevention of transition metal dissolution caused by an insufficient amount of the compound represented by Formula 1.

[0028] In some embodiments of the present disclosure, the compound represented by formula 1 comprises:

[0029] The CAS number of the compound represented by 1-1 (methylene methyl disulfonate, German term MMDS) is 99591-74-9, the CAS number of the compound represented by 1-2 is 99591-73-8 and the CAS number represented by 1-3 is 769973-24-2.

[0030] For this reason, the compound represented by formula 1 can be a group of the compound represented by formula 1, and PF6 - through strong interaction with PF6 - -anions are formed. The lowest oxidation potential of the group allows the compound represented by formula 1 to be preferentially oxidized on the positive electrode side, thereby reducing the dissolution of transition metals from the active material for the positive electrodes. Simultaneously, the lowest unoccupied molecular orbital (LUMO) energy level and the highest electron affinity of the compound represented by formula 1 lead to preferential reducibility on the negative electrode side, and they can form a film on the negative electrode in front of the solvent, which can ensure that the battery exhibits excellent high-temperature cycling performance.

[0031] In some embodiments of the present disclosure, the electrolyte additive further comprises additional functional additives that may also be involved in the formation of SEI and CEI. In this way, the interface is protected and the cycling performance of the battery at high temperatures is further improved. For example, the additional functional additives include 1,3-propanesultone (CAS No. 1120-71-4) (PS), ethylene sulfate (CAS No. 1072-53-3) (DTD), ethylene sulfite (CAS No. 3741-38-6) (ES), 1,3-propanesultone (CAS No. 21806-61-1) (PST), vinylene carbonate (CAS No. 872-36-6) (VC), fluoroethylene carbonate (CAS No. 114435-02-8) (FEC), lithium difluoro(oxalate)borate (CAS No. 409071-16-5) (LiODFB), lithium difluorobis(oxalate)phosphate (CAS No. 678966-16-0) (LiODFP), and lithium difluorophosphate. (CAS No. 24389-25-1) (LiPO2F2).In some embodiments of the present disclosure, the electrolyte additive also comprises additional functional additives for removing water and acid, such as tris(trimethylsilyl)borate (CAS No. 4325-85-3) (TMSB), tris(trimethylsilyl)phosphate (CAS No. 10497-05-9) (TMSP), etc. The additional functional additives are all commonly used additives in the prior art, and the person skilled in the art can select the type and amount of the additional functional additives according to the actual conditions.

[0032] In a second aspect, the present revelation provides an electrolyte that includes the electrolyte additive according to the first aspect.

[0033] In some embodiments of the present disclosure, the mass fraction of the compound represented by Formula 1 is in the range of 0.03% to 3% based on the total mass of the electrolyte. For example, the mass fraction of the compound represented by Formula 1, based on the total mass of the electrolyte, may be 0.03%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 3%, etc. Therefore, by adding the electrolyte containing the compound represented by Formula 1 in the aforementioned proportions to the secondary battery, the preferred oxidation of the compound represented by Formula 1 on the positive electrolyte side is further simplified, and the dissolution of the transition metals of the active material for positive electrodes is reduced.Furthermore, it is advantageous that the compound represented by Formula 1 and the compound represented by Formula 2 exhibit a synergistic effect, increasing the content of sulfur-containing oligomers at the interface of the negative electrode and the stability of the SEI, thereby forming a highly stable, low-impedance SEI, improving the high-temperature cycling performance and the battery's rate performance, and reducing the dissolution of transition metals. In other embodiments of the present disclosure, the mass fraction of the compound represented by Formula 1, based on the total mass of the electrolyte, is in the range of 0.03% to 2%.

[0034] In some embodiments of the present disclosure, the mass fraction of the compound represented by formula 2, based on the total mass of the electrolyte, is in the range of 0.05% to 2.5%. For example, the mass fraction of the compound represented by formula 2, based on the total mass of the electrolyte, can be 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, etc. Therefore, by adding the electrolyte containing the compound represented by formula 2 in the aforementioned proportion to the secondary battery, the compound represented by formula 2 opens the ring to form a film and sulfur-containing oligomers at the negative electrode. The film-forming component is the same as the compound represented by formula 1, thereby increasing the content of sulfur-containing oligomers at the interface of the negative electrode and the stability of SEI.Additionally, the compound represented by formula 2 also forms a SEI component rich in groups such as PO₄²⁻ and LiF on the negative electrode, further reducing the film-forming impedance on the negative electrode. The combination of the compound represented by formula 1 and the compound represented by formula 2 allows the formation of a highly stable, low-impedance SEI. Furthermore, after the reduction of the compound represented by formula 2, an inorganic substance rich in F and Li is formed on the surface of the negative electrode, reducing the battery's impedance and improving its rate performance.The free radicals generated by the cleavage of PO diffuse to the surface of the positive electrode, where they are oxidized and contribute to the formation of CEI together with the compound represented by Formula 1. This stabilizes the active material for positive electrodes and prevents direct contact between the electrolyte and the positive electrode. Furthermore, complex formation of POM (M = Ni, Co, Mn) occurs on the surface of the positive electrode, improving the high-temperature cycling performance and the battery's rate performance, and reducing transition metal dissolution. In other embodiments of the present disclosure, the mass fraction of the compound represented by Formula 2, based on the total mass of the electrolyte, ranges from 0.05% to 2%.

[0035] In some embodiments of the present disclosure, the mass fraction of the additional functional additives, based on the total mass of the electrolyte, is in the range of 0.1% to 3%. For example, the mass fraction of the additional functional additives, based on the total mass of the electrolyte, can be 0.1%, 0.5%, 1.0%, 1.5%, 2%, 2.5%, 3%, etc. Therefore, the addition of the additional functional additives to the electrolyte in the aforementioned amounts can complement the additive to form a stable interface film. By adding the electrolyte to the secondary battery, the high-temperature cycling performance and the rate performance of the battery can be further improved, and the dissolution of transition metals can be reduced.

[0036] In some embodiments of the present disclosure, the electrolyte further comprises a solvent, and the solvent is at least two of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate or methyl propionate.

[0037] In some embodiments of the present disclosure, the electrolyte further comprises a lithium salt and the lithium salt comprises at least one of lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide.

[0038] In a third aspect, the present disclosure provides a battery. According to one embodiment of the present disclosure, the battery comprises the electrolyte according to the second aspect.

[0039] For this reason, during the formation and cycling process of the battery, a highly stable and low-impedance SEI can be formed by combining the compound represented by formula 1 and the compound represented by formula 2, thereby improving the high-temperature cycling performance and rate performance of the battery and reducing the dissolution of transition metals.

[0040] In some embodiments of the present disclosure, if the battery is a lithium-ion battery, the battery comprises a positive electrode active material, and the positive electrode active material comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, or a lithium-rich, manganese-based positive electrode material. If the positive electrode active material of the battery contains at least one of the aforementioned substances in combination with the electrolyte containing the aforementioned additive, a highly stable, low-impedance SEI can be formed, thereby improving the high-temperature cycling performance and rate performance of the battery and reducing transition metal dissolution.

[0041] In some other embodiments of the present disclosure, the lithium nickel cobalt manganese oxide comprises at least one of the compounds specified by LiNi x M 1-xO2 are represented, where M includes Co and Mn, and 0.8 ≤ x ≤ 0.92. For example, x can be 0.8, 0.85, 0.88, 0.9, 0.92, etc. Specifically, by restricting the nickel content within the above range, the energy density can be further improved, and the problem of insufficient battery capacity can be solved. Due to the similar radii of Li and Ni, excessive Ni can cause lithium-nickel disorder with Li, leading to crystal transformation. During a long cycle, microcracks form, continuously exposing new interfaces that react with the electrolyte, resulting in degraded performance. Additionally, if Mn is present, elemental manganese is readily dissolved by the Jan-Taylor effect, forming a complex with the electrolyte and initiating further side reactions. It can even deposit on the negative electrode, further degrading the battery's cycling performance.The aforementioned active material for positive electrodes with a high nickel content is identical to the electrolyte additive of the present disclosure. In this way, a CEI with high stability and low impedance can be formed on the surface of the active material for positive electrodes, and the generation of cracks in the aforementioned active material for positive electrodes can be reduced, thereby improving the high-temperature cycling performance and the rate performance of the battery and reducing the dissolution of transition metals, in particular elemental manganese.

[0042] In other embodiments of the present disclosure, if the battery is a sodium-ion battery, the active material for positive electrodes may comprise at least one of the following materials: Na xMO2, where M comprises at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr or Cu and 0 <x≤1; polyanionische Verbindungen: beinhalten mindestens eines von NaFePO4, Na3V2(PO4)3 (Natriumvanadiumphosphat, abgekürzt als NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' umfasst mindestens eines von V, Fe, Mn oder Ni) oder Na3(VO y )2(PO4)2F 3-2y (0≤y≤1); Prussian blue connections: Na a Me b Me' c (CN)6, wherein Me and Me' each independently contain at least one of Ni, Cu, Fe, Mn, Co or Zn, 0 <a≤2, 0<b<1 und 0<c<1.

[0043] In some embodiments of the present disclosure, the active material for positive electrodes comprises at least one of Na X1 M1O2, Na X2M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3 or Na2M4(SO4)2·2H2O, wobei: 0 <x1≤1; M1 mindestens eines von Ni, Co, Mn, Fe oder Cu umfasst; 0<x2<6; M2 mindestens eines von Ni, Fe oder Mn umfasst; M3 mindestens eines von Fe oder Mn umfasst; und M4 mindestens eines von Fe, Co, Mn oder Cu umfasst. Aus diesem Grund weist das vorstehend genannte Aktivmaterial für positive Elektroden eine hohe Betriebsspannung auf und stimmt es mit dem Elektrolytadditiv der Ausführungsformen der vorliegenden Offenbarung überein. Auf diese Weise können die Hochtemperatur-Zyklisierungsleistung und die Ratenleistung der Batterie verbessert werden und wird die Auflösung der Übergangsmetalle, insbesondere Mangan, reduziert.

[0044] A typical battery consists of a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charging and discharging process, active ions are intercalated and deintercalated between the positive and negative electrode plates. The electrolyte conducts ions between the positive and negative electrode plates. The separator is located between the positive and negative electrode plates to primarily prevent short circuits between them while allowing ions to pass through.

[0045] The positive electrode plate comprises a current collector with a positive electrode and a layer of active material for positive electrodes, which is arranged on at least one side surface of the current collector with positive electrodes. The layer of active material for positive electrodes comprises the active material for positive electrodes.

[0046] In some embodiments of the present disclosure, the positive electrode current collector may comprise a metal foil or a composite positive electrode current collector. For example, the metal foil may be an aluminum foil. The composite positive electrode current collector may comprise a polymer material base layer and a metal layer formed on at least one side face of the polymer material base layer. 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.).

[0047] In some embodiments of the present disclosure, the layer of active material for positive electrodes may optionally further comprise a conductive element. For example, the conductive element may comprise at least one of superconducting carbon, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphite, or carbon nanofibers.

[0048] In some embodiments of the present disclosure, the active material layer for positive electrodes may optionally further include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorine-containing acrylate resin.

[0049] In some embodiments of the present disclosure, the positive electrode plate can be produced by the following process: dispersing the components for producing the positive electrode plate, such as the active material for positive electrodes, the conductive agent, and the binder, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; applying the positive electrode slurry to the positive electrode collector; and obtaining the positive electrode plate after drying, cold pressing, and other processes.

[0050] The negative electrode plate comprises a current collector with a negative electrode and a layer of active material for negative electrodes, which is arranged on at least one side face of the current collector with negative electrodes. The layer of active material for negative electrodes comprises the active material for negative electrodes.

[0051] In some embodiments of the present disclosure, the current collector with a negative electrode may include a metal foil or a composite current collector. For example, a copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0052] In some embodiments of the present disclosure, the active material for negative electrodes can be an active material for negative electrodes for batteries known in the art. For example, the active material for negative electrodes can comprise at least one of the following materials: natural graphite, synthetic graphite, soft carbon, hard carbon, mesophase carbon microspheres, nanocarbon, elemental silicon, silicon oxides, silicon-carbon composites, silicon alloys, elemental tin, tin oxides, tin-carbon composites, tin alloys, or lithium titanate.

[0053] In some embodiments of the present disclosure, the layer of active material for negative electrodes may further comprise a binder. The binder may comprise 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), or carboxymethyl chitosan (CMCS).

[0054] In some embodiments of the present disclosure, the layer of active material for negative electrodes may further comprise a conductive element. The conductive element may comprise at least one of superconducting carbon, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, or carbon nanofibers.

[0055] In some embodiments of the present disclosure, the layer of active material for negative electrodes may optionally further include other additives, such as a thickening agent (e.g. sodium carboxymethylcellulose (CMC-Na)).

[0056] In some embodiments of the present disclosure, the negative electrode plate can be produced by the following method: Dispersing the components for producing the negative electrode plates, such as the active material for negative electrodes, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; applying the negative electrode slurry to the current collector with the negative electrode and obtaining the negative electrode plate after drying, cold pressing, and other processes.

[0057] The present disclosure is not particularly limited to the type of separator and any separator with a porous structure that exhibits good chemical and mechanical stability can be selected.

[0058] In some embodiments of the present disclosure, the separator material may be at least one of glass fiber, nonwoven fabric, polyolefin, aromatic polyamide film, polytetrafluoroethylene film or polyethersulfone film.

[0059] In some embodiments of the present disclosure, the thickness of the separator can be in the range of 8 µm to 12 µm, for example 8 µm, 10 µm, 11 µm, 12 µm, etc.

[0060] It goes without saying that the characteristics and advantages described above for the electrolyte also apply to the battery and are not repeated here.

[0061] The embodiments of the present disclosure are described in detail below. It is understood that the embodiments described below are exemplary and are used only to illustrate the present disclosure, and are not to be understood as limiting the present disclosure. Furthermore, unless otherwise stated, all reagents used in the following examples are commercially available or can be prepared according to the methods in this document or known methods. The reaction conditions not listed are also readily available to the person skilled in the art. Example 11. Production of a positive electrode plate

[0062] An active material for positive electrodes, NCM811, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene carbon black were mixed in a weight ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) was added. The mixture was stirred using a vacuum mixer until it became a positive electrode slurry with homogeneous fluidity. The positive electrode slurry was uniformly applied to a 7 µm thick aluminum foil. The coated aluminum foil was oven-baked and then oven-dried at 120 °C for 8 hours. The compressible density of the positive electrode plate was determined to be 3.5 g / cm³ after rolling. 3 The electrode was adjusted and the positive electrode plate was obtained by cutting. 2. Production of a negative electrode plate

[0063] An active material for negative electrodes (graphite), a thickening agent (sodium carboxymethylcellulose, CMC-Na), a binder (styrene-butadiene rubber), a conductive agent (acetylene carbon black), and a conductive agent (single-walled carbon nanotube, SWCNT) were mixed in a weight ratio of 95.9:1:2:1:0.1, and deionized water was added using a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly applied to a 6 µm thick copper foil; and after drying and rolling, the compressible density of the negative electrode plate was reduced to 1.5 g / cm³. 3 controlled. The negative electrode plate was obtained by punching. 3. Preparation of an electrolyte

[0064] In a glovebox filled with argon gas (humidity <10 ppm, oxygen <1 ppm), the solvents EC:EMC:DEC were mixed uniformly according to a mass ratio of 3:5:2. Fully dried 14.5% LiPF6 and an additive were rapidly added to the mixed solution, thoroughly mixed, and stirred uniformly to obtain the electrolyte (specific selection and dosage are shown in Table 1). 4. Separator

[0065] A coated polyethylene separator with a thickness of 8 µm was selected. 5. Manufacturing a lithium-ion battery

[0066] The positive electrode plate, separator, and negative electrode plate, manufactured as described above, were wound to obtain a raw battery cell without liquid injection. This raw battery cell was placed in an outer packaging film, and the prepared electrolyte was injected into the dried raw battery cell. After vacuum packaging, resting, forming, molding, sorting, and other processes, the required secondary battery was obtained.

[0067] The manufacturing processes of the secondary batteries in Examples 2 to 25, Examples 31 to 38 and Comparative Examples 1 to 3 differ from those in Example 1 in that the composition of the additive in the electrolyte was different, as shown in Table 1.

[0068] In Example 38, with the exception that the manufacturing process of the positive electrode plate differed from that of Example 1, the manufacturing processes used were different from those of Example 1. Specifically, the positive electrode plate from Example 38 was manufactured as follows. Example 38 Production of the positive electrode:

[0069] The active material for the positive electrodes, lithium manganese iron phosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene carbon black were mixed in a weight ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) was added. The mixture was stirred using a vacuum mixer until it became a positive electrode slurry with homogeneous fluidity. The positive electrode slurry was uniformly applied to a 7 µm thick aluminum foil. The coated aluminum foil was baked in an oven and then dried in an oven at 120 °C for 8 hours. The compressible density of the positive electrode plate was determined to be 2.3 g / cm³ after rolling. 3 The electrode was adjusted and the positive electrode plate was obtained by cutting. [Table 1] Active material for positive electrodes A compound represented by formula 1 Additional amount of the compound represented by formula 1, / % Additional amount of the compound represented by formula 2, / % Mass ratio of the compound represented by formula 1 to the compound represented by formula 2 Additional functional additives Example 1 NCM811 1-1 0,05 0,5 1:10 \ Example 2 NCM811 1-1 0,1 0,5 1:5 \ Example 3 NCM811 1-1 0,5 0,5 1:1 \ Example 4 NCM811 1-1 1 0,5 1:0,5 \ Example 5 NCM811 1-1 2 0,5 1:0,25 \ Example 6 NCM811 1-1 0,03 0,5 1:16,7 \ Example 7 NCM811 1-1 3 0,5 1:0,17 \ Example 8 NCM811 1-1 0,5 0,05 1:0,1 \ Example 9 NCM811 1-1 0,5 0,1 1:0,2 \ Example 10 NCM811 1-1 0,5 1 1:2 \ Example 11 NCM811 1-1 0,5 2 1:4 \ Example 12 NCM811 1-1 0,5 2,5 1:5 \ Example 13 NCM811 1-1 2 0,1 1:0,05 \ Example 14 NCM811 1-1 0,1 2 1:20 \ Example 15 NCM811 1-2 0,5 0,5 1:1 \ Example 16 NCM811 1-3 0,5 0,5 1:1 \ Example 17 NCM811 1-1 0,5 0,5 1:1 PS: 1%, DTD: 1%, VC: 0.5% Example 18 NCM811 1-1 0,5 0,5 1:1 PS: 1%, DTD: 1%, TMSP: 0.3% Example 19 NCM811 1-1 0,5 0,5 1:1 PST: 0.5%,TMSB: 0.3%,LiODFP: 0.3% Example 20 NCM811 1-1 0,5 0,5 1:1 PS: 1%, ES: 0.3%, LiODFB: 0.3% Example 21 NCM811 1-1 0,5 0,5 1:1 PST: 0.5%,TMSB: 0.3%,LiPO2F2: 0.3% Example 22 NCM811 1-1 0,5 0,5 1:1 PS: 1%, FEC: 1%, VC: 1% Example 23 NCM811 1-1 0,5 0,5 1:1 VC: 0.1% Example 24 NCM811 1-1 0,5 0,02 1:0,04 \ Example 25 NCM811 1-1 0,5 12 1:24 \ Example 31 NCM811 1-1 0,02 0,1 1:5 \ Example 32 NCM811 1-1 5 0,5 1:0,1 \ Example 33 NCM811 1-1 0,05 0,02 1:0,4 \ Example 34 NCM811 1-1 1 12 1:12 \ Example 35 NCM811 1-1 2 0,05 1:0,025 \ Example 36 NCM811 1-1 0,05 2 1:40 \ Example 37 NCM811 1-1+1-2 0,25(1-1)+0,25(1-2) 0,5 1:1 \ Example 38 Lithium manganese iron phosphate 1-1 0,5 0,5 1:1 \ Comparative example 1 \ \ \ \ \ Comparative example 2 1-1 1 \ \ \ Comparative example 3 \ \ 1 \ \ Example 261. Production of the positive electrode plate

[0070] The active material for positive electrodes Na[Ni 0,33 Fe 0,33 Mn 0,33 [O2], the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene carbon black were mixed in a weight ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) was added. The mixture was stirred using a vacuum mixer until it became a positive electrode slurry with homogeneous fluidity. The positive electrode slurry was uniformly applied to a 7 µm thick aluminum foil. The coated aluminum foil was baked in an oven and then dried in an oven at 120 °C for 8 hours. The compressible density of the positive electrode plate was determined to be 3.5 g / cm³ after rolling. 3 The electrode was adjusted and the positive electrode plate was obtained by cutting. 2. Production of the negative electrode plate

[0071] The active material for the negative electrode, graphite, the thickening agent sodium carboxymethylcellulose (CMC-Na), the binder styrene-butadiene rubber, the conductive agent carbon black, and the conductive single-walled carbon nanotube (SWCNT) were mixed according to a weight ratio of 95.9:1:2:1:0.1, and deionized water was added using a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was applied uniformly to a 6 µm thick copper foil; and after drying and rolling, the compressible density of the negative electrode plate was reduced to 1.5 g / cm³. 3 controlled. The negative electrode plate was obtained by punching. 3. Preparation of the electrolyte

[0072] In a glovebox filled with argon gas (humidity <10 ppm, oxygen <1 ppm), the solvents EC:EMC:DEC were mixed uniformly according to a mass ratio of 3:5:2. Completely dried 14.5% NaPF6 and the additive (specific selection and dosage are shown in Table 2) were rapidly added to the mixed solution, thoroughly mixed, and stirred uniformly to obtain the electrolyte. 4. Separator

[0073] A coated polyethylene separator with a thickness of 8 µm was selected. 5. Manufacturing a sodium-ion battery

[0074] The positive electrode plate, separator, and negative electrode plate, manufactured as described above, were wound to obtain a raw battery cell without liquid injection. This raw battery cell was placed in an outer packaging film, and the prepared electrolyte was injected into the dried raw battery cell. After vacuum packaging, resting, forming, molding, sorting, and other processes, the required secondary battery was obtained.

[0075] The manufacturing processes of the secondary batteries from Examples 27 to 30 differ from those from Example 26 in that the composition of the additive in the electrolyte was different, as shown in Table 2. [Table 2] A compound represented by formula 1 Additional amount of the compound represented by formula 1, / % Additional amount of the compound represented by formula 2, / % Mass ratio of the compound represented by formula 1 to the compound represented by formula 2 Additional functional additives Example 26 1-1 0,5 0,5 1:1 \ Example 27 1-1 0,03 0,5 1:16,7 \ Example 28 1-1 3 0,5 1:0,17 \ Example 29 1-1 0,5 0,05 1:0,1 \ Example 30 1-1 0,5 2,5 1: 5 \

[0076] The high-temperature cycling performance, rate performance, and transition metal dissolution of the secondary batteries obtained in Examples 1 to 25, Examples 31 to 38, and Comparative Examples 1 to 3 were characterized. The characterization results are shown in Table 3. (1) Testing the charge ratio at a constant current of 3C: The battery was placed in an environment of 25°C and discharged at a constant current of 1C to a cutoff voltage of 2.75V, at which time the initial capacity Q1 was recorded and the battery was left to rest for 10 minutes. The battery was then charged at a constant current of 3C to an upper limit voltage of 4.2V, at which time the 3C charge capacity Q2 was recorded and the battery was left to rest for 10 minutes. Finally, the battery was discharged at a constant current of 1C to a cutoff voltage of 2.75V and left to rest for 10 minutes. The results were recorded as shown in Table 3. The calculation formula used was: Charging ratio at a constant current of 3 C=Q2 / Q1×100%. (2) 45°C High-Temperature Cycle Test: The battery was placed in an environment of (45±2)°C, allowed to rest for 3 hours, and then charged to the upper limit voltage of 4.2 V at a constant current of 1 C and a constant voltage with a cutoff current of 0.05 C. After full charging, the battery was allowed to rest for 5 minutes and then discharged to the cutoff voltage of 2.75 V at a constant current of 1 C. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q3. When the cycle reached 500 cycles, the final discharge capacity of the battery was recorded as Q4. The calculation formula was: Capacity retention rate(%)=Q4 / Q3×100%. (3) Transition metal test: After cycling for 500 T at 45 °C, the battery was discharged to a cut-off voltage of 2.5 V and placed in a glove box for disassembly to obtain the negative electrode plate. The negative electrode powder was dried and tested for ICP (Ni / Co / Mn cells). [Table 3] Charging ratio at a constant current of 3 C (%) Total content of Ni / Co / Mn in the negative electrode plate (ppm) Capacity retention rate after 500 T cycles at 45 °C (%) Example 1 84,22 % 152 80,41 % Example 2 85,14 % 134 82,67 % Example 3 89,73 % 96 91,56 % Example 4 86,65 % 109 89,77 % Example 5 82,23 % 105 85,35 % Example 6 83,48 % 162 79,11 % Example 7 79,37 % 170 77,89 % Example 8 84,52 % 102 82,77 % Example 9 86,66 % 104 85,83 % Example 10 85,34 % 103 90,21 % Example 11 83,41 % 102 86,55 % Example 12 81,37 % 104 84,73 % Example 13 83,05 % 109 85,55 % Example 14 84,62 % 127 85,98 % Example 15 89,59 % 95 91,61 % Example 16 89,66 % 96 91,64 % Example 17 89,21 % 97 90,97 % Example 18 88,95 % 96 91,02 % Example 19 89,53 % 97 91,13 % Example 20 89,64 % 97 90,98 % Example 21 90,03 % 96 91,05 % Example 22 87,77 % 98 91,63 % Example 23 88,21 % 97 90,12 % Example 24 77,53 % 169 77,46 % Example 25 76,99 % 173 75,79 % Example 31 78,84 % 171 77,67 % Example 32 77,69 % 172 77,52 % Example 33 78,52 % 173 77,85 % Example 34 78,39 % 170 77,71 % Example 35 77,63 % 171 77,60 % Example 36 77,70 % 168 77,68 % Example 37 89,79 % 97 91,47 % Example 38 89,66 % 95 91,63 % Comparison example 1 72,44 % 195 70,58 % Comparison example 2 76,52 % 176 74,66 % Comparison example 3 74,38 % 189 72,29 %

[0077] As can be seen from Table 3, in Examples 1 to 25 and Examples 31 to 38 of the present disclosure, the compound represented by Formula 1 and the compound represented by Formula 2 are used in combination. In this way, a SEI with high stability and low impedance can be formed, the high-temperature cycling performance and the rate performance of the battery can be improved, and the dissolution of the transition metals can be reduced.

[0078] In comparison with Example 3, in Comparative Examples 1 to 3, the compound represented by Formula 1 and the compound represented by Formula 2 are not added simultaneously. The high-temperature cycling performance and the rate performance of the resulting battery are significantly lower, and the dissolution of the transition metals is significantly increased. It can be seen that in the electrolyte additive according to the present disclosure, the compound represented by Formula 1 and the compound represented by Formula 2 have a synergistic effect. After adding the electrolyte additive to the secondary battery, the high-temperature cycling performance and the rate performance of the battery can be improved, and the dissolution of the transition metals can be reduced.

[0079] The high-temperature cycling performance, rate performance, and transition metal dissolution rate of the batteries in Examples 1 to 6 are significantly better than those in Example 7. This is because the additional amount of compound represented by Formula 1 is higher in Example 7 (3%) than in the other examples. The likely reason for this is the use of an excessive amount of compound represented by Formula 1. It is suspected that the concentration of compound represented by Formula 1 is too high, and that a section of the compound represented by Formula 1 forms a thicker film on the positive and negative electrodes. Active lithium is continuously consumed by this film formation during high-temperature cycling, resulting in a low capacity retention rate under high-temperature cycling.Additionally, the thicker interface film influences the intercalation and deintercalation of lithium ions, which affects the rate performance. The other part of the unconsumed compound, represented by formula 1, reacts further and degrades at high temperatures to produce gas, thus not forming an effective complex with transition metals.

[0080] The high-temperature cycling performance, rate performance, and transition metal dissolution of the secondary batteries obtained in Examples 26 to 30 were characterized. The characterization results are shown in Table 4. (1) Testing the charge ratio at a constant current of 2C: The battery was placed in an environment of 25°C and discharged at a constant current of 1C to a cutoff voltage of 1.5V, at which time the initial capacity Q1 was recorded and the battery was left to rest for 10 minutes. The battery was then charged at a constant current of 2C to an upper limit voltage of 4.2V, at which time the 2C charge capacity Q2 was recorded and the battery was left to rest for 10 minutes. Finally, the battery was discharged at a constant current of 1C to a cutoff voltage of 1.5V and left to rest for 10 minutes. The results were recorded as shown in Table 4. The formula used for the calculation was: Charging ratio at a constant current of 2 C=Q2 / Q1×100%. (2) 45°C High-Temperature Cycle Test: The battery was placed in an environment of (45±2)°C, allowed to rest for 3 hours, and then charged to the upper limit voltage of 4.2 V at a constant current of 1 C and a constant voltage with a cutoff current of 0.05 C. After full charging, the battery was allowed to rest for 5 minutes and then discharged to the cutoff voltage of 1.5 V at a constant current of 1 C. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q3. When the cycle reached 500 cycles, the final discharge capacity of the battery was recorded as Q4. The calculation formula was: Capacity retention rate(%)=Q4 / Q3×100%. (3) Transition metal test: After cycling for 500 T at 45 °C, the battery was discharged to a cut-off voltage of 1.5 V and placed in a glove box for disassembly to obtain the negative electrode plate. The negative electrode powder was dried and tested for ICP (manganese cell). [Table 4] Charging ratio at a constant current of 2 C (%) Total Mn content in the negative electrode plate (ppm) Capacity retention rate after 500 T cycles at 45 °C (%) Example 26 85,88 % 31 95,02 % Example 27 82,45 % 58 84,41 % Example 28 79,23 % 45 86,52 % Example 29 83,67 % 40 85,33 % Example 30 80,44 % 42 87,07 %

[0081] As can be seen from Table 4, in Examples 26 to 30 of the present disclosure, a highly stable, low-impedance SEI can be formed by combining the compound represented by Formula 1 and the compound represented by Formula 2, thereby improving the high-temperature cycling performance and rate performance of the battery and reducing the dissolution of transition metals. It can be seen that the electrolyte additives of the embodiments of the present disclosure are also applicable to sodium-ion batteries, which can improve the high-temperature cycling performance and rate performance of the battery and reduce the dissolution of transition metals.

[0082] In this description, the use of reference terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples" means that the specific features, structures, materials, or properties described with reference to the embodiment or example are included in at least one embodiment or example of the present disclosure. In this description, examples of the foregoing terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or properties described may be combined in any one or more embodiments or examples in a suitable manner.Furthermore, the person skilled in the art may combine different embodiments or examples and features of different embodiments or examples described in this description, provided that they do not contradict each other.

[0083] Although embodiments of the present disclosure are illustrated and described above, it is understood that the above embodiments are for illustrative purposes only and are not to be interpreted as limitations of the present disclosure. A person skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present disclosure.

Claims

[1] Electrolyte additive comprising: a compound represented by formula 1; and a compound represented by formula 2, wherein R1 and R2 are each independently selected from any one of substituted or unsubstituted C1- to C6-alkyl, substituted or unsubstituted C2- to C6-alkenyl or substituted or unsubstituted C2- to C7-alkynyl. [2] Electrolyte additive according to claim 1, wherein the mass ratio of the compound represented by formula 1 to the compound represented by formula 2 is 1:(0.05 to 20). [3] Electrolyte additive according to claim 1 or 2, wherein the compound represented by formula 1 comprises: [4] Electrolyte comprising the electrolyte additive according to any one of claims 1 to 3. [5] Electrolyte according to claim 4, wherein a mass fraction of the compound represented by formula 1 is in the range of 0.03% to 3% based on a total mass of the electrolyte. [6] Electrolyte according to claim 4, wherein a mass fraction of the compound represented by formula 1 is in the range of 0.03% to 2% based on a total mass of the electrolyte. [7] Electrolyte according to any one of claims 4 to 6, wherein a mass fraction of the compound represented by formula 2 is in the range of 0.05% to 2.5% based on a total mass of the electrolyte. [8] Electrolyte according to any one of claims 4 to 6, wherein a mass fraction of the compound represented by formula 2 is in the range of 0.05% to 2% based on a total mass of the electrolyte. [9] Battery comprising the electrolyte according to any one of claims 4 to 6. [10] Battery according to claim 9, comprising an active material for positive electrodes, wherein: the active material for positive electrodes comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide or a lithium-rich positive electrode material based on manganese, lithium nickel cobalt manganese oxide optionally at least one of the compounds that are connected by LiNi x M 1-x O2 are represented, comprising M Co and Mn and 0.8≤x≤0.92; or the active material for positive electrodes at least one of Na X1 M1O2, Na X2 M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3 or Na2M4(SO4)2·2H2O includes, where: 0