Electrolyte additive, electrolyte and battery

Abstract

Disclosed in the present application are an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a compound as represented by formula 1 and a compound as represented by formula 2: (I), wherein R1 and R2 are each independently selected from any one of a substituted or unsubstituted C1-C6 alkyl, a substituted or unsubstituted C2-C6 alkenyl, and a substituted or unsubstituted C2-C7 alkynyl. By adding the electrolyte additive to a secondary battery, the high-temperature cycle and rate capability of the battery can be improved, thereby reducing the dissolution of transition metals.

Description

Electrolyte additive, electrolyte and battery

[0001] Priority information

[0002] The present application claims priority to and the benefit of Chinese Patent Application No. 202410817652.8, filed on June 24, 2024, and is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and specifically relates to an electrolyte additive, an electrolyte and a battery. BACKGROUND

[0004] At present, secondary batteries are widely used in consumer electronic products, new energy power vehicles and other power battery products due to their environmental friendliness, low cost, high working voltage and other characteristics. Energy density and fast charging time have become the primary consideration for users. In order to further improve the energy density and solve the problem of insufficient capacity, the battery design is developing towards higher voltage. The voltage of the mass-produced high-voltage power battery products has reached 4.35V. When the voltage continues to increase to 4.5V or even higher, it is close to the decomposition potential of conventional carbonate solvents. The electrolyte is easy to decompose and produce gas, and the positive electrode material has structure instability and oxygen mismatching problem at this voltage, which leads to the dissolution of transition metals, deposition at the negative electrode, and thus deteriorates the high-temperature cycle performance.

[0005] Based on the above shortcomings, it is necessary to develop an electrolyte that significantly improves the cycle performance of secondary batteries at high temperature and inhibits the dissolution of transition metals. SUMMARY

[0006] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to propose an electrolyte additive, an electrolyte and a battery. The addition of the electrolyte additive to the secondary battery can improve the cycle performance of the secondary battery at high temperature and inhibit the dissolution of transition metals.

[0007] The first aspect of the present application proposes an electrolyte additive, which comprises a compound represented by Formula 1 and a compound represented by Formula 2:

[0008] wherein R1 and R2 are each independently selected from any one of a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, and a substituted or unsubstituted C2-C7 alkynyl group.

[0009] In the additive of the present application, the compound represented by Formula 1 can be formed by a strong interaction between PF6 - anions to form a compound represented by Formula 1-PF6 -The cluster has a lowest oxidation potential so that the compound shown in formula 1 can be preferentially oxidized on the positive side, reducing the transition metal dissolution of the positive active material; meanwhile, the lowest unoccupied molecular orbital (LUMO) energy level and the highest electron affinity of the compound shown in formula 1 give it preferential reducibility on the negative side, enabling it to form a film prior to the solvent on the negative side, but the film is thin, the quality is poor, and gas is easily produced by further reaction and decomposition at high temperature, and the SEI is easily broken during the cycle; therefore, the compound shown in formula 2 is added to the electrolyte additive, the compound shown in formula 2 is ring-opened to form a sulfur-containing oligomer on the negative electrode, the film-forming component of the sulfur-containing oligomer is the same as that of the compound shown in formula 1, the content of the sulfur-containing oligomer on the negative electrode interface and the stability of the SEI are improved, meanwhile, the compound shown in formula 2 also forms an SEI component rich in P-O, LiF and other groups on the negative electrode, further reducing the impedance of the negative electrode film, and by using the compound shown in formula 1 and the compound shown in formula 2 in combination, a high-stability and low-impedance SEI can be formed, the high-temperature cycle and rate performance of the battery are improved, and the transition metal dissolution is reduced.

[0010] In some embodiments, the mass ratio of the compound shown in formula 1 to the compound shown in formula 2 is 1:(0.05-20). In this way, the ratio of the two is appropriate, and the high-temperature cycle and rate performance of the battery can be improved, and the transition metal dissolution is reduced.

[0011] In some embodiments, the compound shown in formula 1 comprises:

[0012] In this way, the compound of the above structural formula as a component of the electrolyte additive can further reduce the transition metal dissolution.

[0013] The second aspect of the present application proposes an electrolyte comprising the electrolyte additive of the first aspect.

[0014] In some embodiments, the mass fraction of the compound shown in formula 1 is 0.03%-3%, optionally 0.03%-2%, based on the total mass of the electrolyte. In this way, when the electrolyte is added to a secondary battery, the transition metal dissolution can be further reduced.

[0015] In some embodiments, the mass fraction of the compound shown in formula 2 is 0.05%-2.5%, optionally 0.05%-2%, based on the total mass of the electrolyte. In this way, when the electrolyte is added to a secondary battery, the compound shown in formula 2 can participate in film formation together with the compound shown in formula 1, forming a high-stability and low-impedance SEI, and improving the high-temperature cycle and rate performance of the battery.

[0016] The third aspect of the present application proposes a battery comprising the electrolyte of the second aspect. In this way, the battery has excellent high-temperature cycle performance and rate performance, and the transition metal dissolution is small.

[0017] In some embodiments, the battery comprises a positive electrode active material, the positive electrode active material comprises at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese phosphate, lithium nickel manganese phosphate, lithium-rich manganese-based positive electrode material; optionally, the lithium nickel cobalt manganese phosphate comprises LiNi x M 1-x O2, wherein M comprises Co and Mn, and 0.8≤x≤0.92. Thus, the transition metal in the above positive electrode active material is more likely to be dissolved out at high temperature, and matching the additive containing formula 1 and formula 2 with the above positive electrode active material can further reduce the dissolution of transition metal and improve the high-temperature cycle performance of the battery.

[0018] In some embodiments, the positive electrode active material comprises Na X1 M1O2, Na X2 M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3and Na2M4(SO4)2·2H2O, wherein 0

[0019] Additional aspects and advantages of the application will be made apparent from the following description. DETAILED DESCRIPTION

[0020] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as a limitation of the present application.

[0021] The amount of electrolyte additive is only a small part of the electrolyte in the secondary battery, but the appropriate amount of additive can form SEI (Solid Electrolyte Interface) on the surface of the negative electrode active material and CEI (Cathode Electrolyte Interface) on the surface of the positive electrode active material. SEI and CEI are respectively formed on the surface of the negative electrode active material and the positive electrode active material, which reduces the problem of side reactions after the active material directly contacts with the electrolyte.

[0022] To further improve battery energy density and solve the problem of insufficient capacity, battery design is developing towards higher voltages. Currently, the voltage of mass-produced high-voltage power batteries has reached 4.35V. When the voltage is further increased to 4.5V or even higher, it is close to the decomposition potential of conventional carbonate solvents. The electrolyte is prone to decomposition and gas production. Moreover, the positive electrode material has structural instability and oxygen mismatch problems at this voltage, which leads to the dissolution of transition metals and their deposition on the negative electrode, thereby deteriorating the high-temperature cycle performance.

[0023] In view of this, the first aspect of this application provides an electrolyte additive, said electrolyte additive comprising the compound shown in Formula 1 and the compound shown in Formula 2:

[0024] R1 and R2 are each independently selected from any one of substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C2-C6 alkenyl groups, and substituted or unsubstituted C2-C7 alkynyl groups.

[0025] The electrolyte additive proposed in this application, the compound shown in Formula 1, can react with PF6 - The strong interaction between anions forms the compound represented by Formula 1, -PF6. - The cluster possesses the lowest oxidation potential, allowing the compound shown in Formula 1 to preferentially oxidize on the positive electrode side, reducing the dissolution of transition metals from the positive electrode active material. Simultaneously, the lowest unoccupied molecular orbital (LUMO) level and highest electron affinity of the compound shown in Formula 1 grant it preferential reduction on the negative electrode side, enabling it to form a film on the negative electrode before the solvent. However, the film is thin and of poor quality, easily undergoing further reaction and decomposition at high temperatures, and the SEI is prone to rupture during cycling. Based on this, the compound shown in Formula 2 (CAS No.: 26) was added as an electrolyte additive. The compound shown in Formula 2 (81338-34-9) forms a sulfur-containing oligomer at the negative electrode through ring opening. The sulfur-containing oligomer in the film-forming component is the same as that in Formula 1, which improves the content of sulfur-containing oligomers at the negative electrode interface and the stability of the SEI. At the same time, the compound shown in Formula 2 also forms an SEI component rich in PO, LiF and other groups at the negative electrode, further reducing the film-forming resistance of the negative electrode. By using the compound shown in Formula 1 and the compound shown in Formula 2 in combination, a highly stable and low-resistance SEI can be formed, which improves the high-temperature cycling and rate performance of the battery and reduces the dissolution of transition metals.

[0026] In addition, the compound shown in formula 2 is reduced to form inorganic matter rich in F and Li on the negative electrode surface, reduces the impedance of the battery, improves the rate performance of the battery, the free radicals generated by P-O breakage diffuse to the positive electrode surface and are oxidized, participate in the formation of CEI together with the compound shown in formula 1, can stabilize the positive electrode active material, avoid direct contact between the electrolyte and the positive electrode, and P-O-M (M = Ni, Co, Mn) complexation occurs on the positive electrode surface, reduces the dissolution of transition metals, and improves the cycle; the -N- contains a lone pair of electrons, which can form a complex with H + form a complex, and can inhibit the PF5 reaction characteristics in the LiPF6-based electrolyte system, and reduce the decomposition of LiPF6.

[0027] As an example, when R1 and R2 are each independently selected from substituted or unsubstituted C1-C6 alkyl, the number of carbon atoms of the alkyl group can be 1, 2, 3, 4, 5, 6, etc.; when R1 and R2 are each independently selected from substituted or unsubstituted C2-C6 alkenyl, the number of carbon atoms of the alkenyl group can be 2, 3, 4, 5, 6, etc.; when R1 and R2 are each independently selected from substituted or unsubstituted C2-C7 alkynyl, the number of carbon atoms of the alkynyl group can be 2, 3, 4, 5, 6, 7, etc.

[0028] It can be understood that when the number of carbon atoms of R1 and R2 is two or more, two or more carbon atoms can participate in ring formation, or only one carbon atom can participate in ring formation, and the other carbon atoms are connected as a branched chain to the carbon atom participating in ring formation.

[0029] In some embodiments of the present application, the mass ratio of the compound shown in formula 1 to the compound shown in formula 2 is 1:(0.05-20). For example, the mass ratio of the compound shown in formula 1 to the compound shown in formula 2 can be 1:0.05, 1:0.5, 1:1, 1:5, 1:10, 1:15, 1:20, etc. Therefore, by controlling the mass ratio of the compound shown in formula 1 to the compound shown in formula 2 within the above range, the synergistic effect of the compound shown in formula 1 and the compound shown in formula 2 can be fully exerted, the thin film formed by too much compound shown in formula 1 can be reduced, the quality can be improved, the low impedance of the negative electrode film can be ensured, and the cycle performance and rate performance of the battery can be ensured; and the insufficient inhibition of transition metal dissolution caused by too little compound shown in formula 1 can also be reduced.

[0030] In some embodiments of the present application, the compound shown in formula 1 includes:

[0031] The CAS number of the compound shown in 1-1 (methyl methylene disulfonate, English name MMDS) is 99591-74-9, the CAS number of the compound shown in 1-2 is 99591-73-8, and the CAS number of the compound shown in 1-3 is 769973-24-2.

[0032] Therefore, the compound shown in formula 1 can be formed by the strong interaction between PF6 - anions to form a compound shown in formula 1-PF6 - cluster, which has the lowest oxidation potential so that the compound shown in formula 1 can be preferentially oxidized on the positive side, reducing the transition metal dissolution of the positive active material; at the same time, the lowest unoccupied molecular orbital (LUMO) energy level and the highest electron affinity of the compound shown in formula 1 give it preferential reducibility on the negative side, which can be filmed in the negative electrode prior to the solvent, which can ensure excellent cycle performance of the battery at high temperature.

[0033] In some embodiments of the present application, the electrolyte additive further comprises other functional additives, which can also participate in the formation of SEI and CEI, protect the interface, and further improve the cycle performance of the battery at high temperature, such as 1,3-propane sultone (CAS number: 1120-71-4) (PS), ethylene sulfate (CAS number: 1072-53-3) (DTD), ethylene sulfite (CAS number: 3741-38-6) (ES), 1,3-propylene sultone (CAS number: 21806-61-1) (PST), vinylene carbonate (CAS number: 872-36-6) (VC), fluoroethylene carbonate (CAS number: 114435-02-8) (FEC), lithium difluorophosphate (CAS number: 409071-16-5) (LiODFB), lithium difluorophosphate (CAS number: 678966-16-0) (LiODFP), lithium difluorophosphate (CAS number: 24389-25-1) (LiPO2F2); in some embodiments of the present application, the electrolyte additive further comprises other functional additives, such as tris(trimethylsilyl)borate (CAS number: 4325-85-3) (TMSB), tris(trimethylsilyl)phosphate (CAS number: 10497-05-9) (TMSP), etc. Other additives are commonly used in the art, and those skilled in the art can select other functional additives according to the actual type and amount.

[0034] The second aspect of the present application proposes an electrolyte comprising the electrolyte additive of the first aspect.

[0035] In some embodiments of the present application, the mass fraction of the compound of Formula 1 is 0.03% to 3% based on the total mass of the electrolyte. For example, the mass fraction of the compound of Formula 1 can be 0.03%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 3%, etc. based on the total mass of the electrolyte. Thus, the electrolyte containing the compound of Formula 1 in the above amount is added to the secondary battery, which is further conducive to the preferential oxidation of the compound of Formula 1 at the positive electrode side, reduces the dissolution of transition metals from the positive electrode active material, and is conducive to the full play of the synergistic effect of the compound of Formula 1 and the compound of Formula 2, improves the stability and the content of the sulfur-containing oligomer at the negative electrode interface and the stability of the SEI, and can form a SEI with high stability and low impedance, thereby improving the high-temperature cycle and rate performance of the battery and reducing the dissolution of transition metals.

[0036] In some embodiments of the present application, the mass fraction of the compound of Formula 2 is 0.05% to 2.5% based on the total mass of the electrolyte. For example, the mass fraction of the compound of Formula 2 can be 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, etc. based on the total mass of the electrolyte. Thus, the electrolyte containing the compound of Formula 2 in the above amount is added to the secondary battery, the compound of Formula 2 is ring-opened to form a film at the negative electrode, forming a sulfur-containing oligomer, the film-forming component is the same as that of the compound of Formula 1, which improves the stability and the content of the sulfur-containing oligomer at the negative electrode interface and the stability of the SEI. In addition, the compound of Formula 2 also forms a SEI component rich in P-O, LiF, etc. at the negative electrode, further reducing the impedance of the film formed at the negative electrode. By using the compound of Formula 1 in combination with the compound of Formula 2, a SEI with high stability and low impedance can be formed. In addition, the inorganic substance rich in F and Li is formed on the surface of the negative electrode after the reduction of the compound of Formula 2, which reduces the impedance of the battery and improves the rate performance of the battery. The free radicals generated by the breaking of P-O diffuse to the surface of the positive electrode and are oxidized, which, together with the compound of Formula 1, forms a CEI that can stabilize the positive electrode active material, avoids direct contact between the electrolyte and the positive electrode, and improves the high-temperature cycle and rate performance of the battery and reduces the dissolution of transition metals. In some other embodiments of the present application, the mass fraction of the compound of Formula 2 is 0.05% to 2% based on the total mass of the electrolyte.

[0037] In some embodiments of the present application, the mass percentage of the other functional additive is 0.1%-3% based on the total mass of the electrolyte. For example, the mass percentage of the other functional additive can be 0.1%, 0.5%, 1.0%, 1.5%, 2%, 2.5%, 3%, etc. based on the total mass of the electrolyte. Thus, by adding the other functional additive in the electrolyte in the above amount, the additive can complement each other to form a stable interface film. When the electrolyte is added to a secondary battery, the high-temperature cycle and rate performance of the battery can be further improved, and the transition metal dissolution can be reduced.

[0038] In some embodiments of the present application, 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, and methyl propionate.

[0039] In some embodiments of the present application, the electrolyte further comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0040] The third aspect of the present application provides a battery. According to an embodiment of the present application, the battery comprises the electrolyte of the second aspect.

[0041] Thus, the battery containing the electrolyte can form a high-stability and low-impedance SEI by using the compound of formula 1 and the compound of formula 2 in combination during the formation and cycle of the battery, improve the high-temperature cycle and rate performance of the battery, and reduce the transition metal dissolution.

[0042] In some embodiments of the present application, when 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 iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium-rich manganese-based positive electrode material. When the positive electrode active material of the battery comprises at least one of the above-mentioned substances, in combination with the electrolyte containing the above-mentioned additive, a high-stability and low-impedance SEI can be formed, the high-temperature cycle and rate performance of the battery can be improved, and the transition metal dissolution can be reduced.

[0043] In some other embodiments of the present application, the lithium nickel cobalt manganese oxide comprises LiNi x M 1-xat least one of O2, wherein M comprises 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 limiting the content of nickel 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 radius of Li and Ni, too much Ni can cause lithium-nickel mixing, leading to crystal transformation. In the long-term cycle process, micro-cracks can be formed, new interfaces are continuously exposed, and reactions with electrolyte occur, causing performance degradation. In addition, when Mn is contained, the manganese element is prone to Jahn-Teller effect dissolution, complexing with electrolyte to cause side reactions, and even depositing at the negative electrode, causing the cycle performance of the battery to decay. The above high-nickel content positive electrode active material, matched with the electrolyte additive of the present application, can form a CEI with strong stability and low impedance on the surface of the positive electrode active material, reducing the generation of cracks in the above positive electrode active material, thereby improving the high-temperature cycle and rate performance of the battery and reducing the dissolution of transition metals, especially manganese elements.

[0044] In some embodiments of the present application, when the battery is a sodium ion battery, the positive electrode active material can include at least one of the following materials:

[0045] Na x MO2, wherein M comprises at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, Cu, and 0

[0046] Polyanionic compounds: NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, referred to as NVP), Na4Fe3(PO4)2(P2O7), NaM’PO4F (M’ comprises at least one of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1).

[0047] Prussian blue compounds: Na a Me b Me’ c (CN)6, wherein Me and Me’ each independently comprises at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0

[0048] In some embodiments of the present application, the positive electrode active material comprises Na X1 M1O2, Na X2at least one of M2[M3(CN)6], NaFeP04, Na3V2(P04)3, Na2M4P207, Na2Fe2(S04)3, and Na2M4(S04)2-2H20, where 0 < xi < 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2< 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu. Thus, the above positive electrode active material has a high operating voltage, and the electrolyte additive of the present application can better improve the high-temperature cycle performance and rate performance of the battery, and the transition metal, especially the manganese element, has less dissolution.

[0049] Generally, the battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are reversibly intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and mainly functions to prevent short circuiting between the positive electrode and the negative electrode while allowing ions to pass through.

[0050] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector, and the positive electrode active material layer includes the above positive electrode active material.

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

[0052] In some embodiments of the present application, the positive electrode active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0053] In some embodiments of the present application, the positive electrode active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0054] In some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0055] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0056] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can 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 can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0057] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art. For example, the negative electrode active material can include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, nanocarbon, elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, elemental tin, tin oxide compounds, tin-carbon composites, tin alloys, and at least one of lithium titanate.

[0058] In some embodiments of the present application, the negative electrode active material layer can further include a binder. The binder can 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).

[0059] In some embodiments of the present application, the negative electrode active material layer can further include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments of the present application, the negative electrode active material layer can further include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0061] In some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0062] The type of the separation film is not particularly limited in the present application, and any known porous structure separation film with good chemical stability and mechanical stability can be selected.

[0063] In some embodiments of the present application, the material of the separation film can include at least one of glass fiber, non-woven fabric, polyolefin film, aromatic polyamide film, polytetrafluoroethylene film, and polyether sulfone film.

[0064] In some embodiments of the present application, the thickness of the separation film can be 8 μm-12 μm, for example, 8 μm, 10 μm, 11 μm, 12 μm, etc.

[0065] It should be noted that the features and advantages described above for the electrolyte also apply to the battery, which will not be described here again.

[0066] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also easily obtained by those skilled in the art.

[0067] Example 1

[0068] 1. Preparation of the positive electrode sheet

[0069] The positive electrode active material NCM811, the binder polyvinylidene fluoride (PVDF) and the conductive agent acetylene black were mixed in a weight ratio of 96.5:2:1.5, N-methyl pyrrolidone (NMP) was added, and stirring was carried out under the action of a vacuum stirrer until the mixed system became a homogeneous positive electrode slurry; the positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 7 μm; after the above-mentioned coated aluminum foil was baked in an oven, it was dried in an oven at 120°C for 8 h, and then it was rolled to control the positive electrode sheet compaction density to be 3.5 g / cm 3 , and the positive electrode sheet was obtained by slitting.

[0070] 2. Preparation of the negative electrode sheet

[0071] The negative active material graphite, thickening agent sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, conductive agent single-walled carbon nanotube (SWCNT) are mixed according to the weight ratio of 95.9:1:2:1:0.1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a copper foil with a thickness of 6 μm; after drying and rolling, the compaction density of the negative electrode sheet is controlled to be 1.5 g / cm 3 , and a negative electrode sheet is obtained by die cutting.

[0072] 3. Preparation of electrolyte

[0073] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), the solvent EC:EMC:DEC is mixed uniformly according to the mass ratio of 3:5:2, and fully dried 14.5% LiPF6 and additives are quickly added to the mixed solution. After being mixed and stirred uniformly, an electrolyte is obtained (see Table 1 for specific selection and amount).

[0074] 4. Isolation film

[0075] An 8 μm thick coated polyethylene separation film is selected.

[0076] 5. Preparation of lithium ion battery

[0077] The prepared positive electrode sheet, the separation film, and the negative electrode sheet are wound to obtain a bare cell without liquid injection; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, standing, formation, shaping, sorting, and other processes, a required secondary battery is obtained.

[0078] The preparation method of the secondary batteries of Examples 2-25, 31-38 and Comparative Examples 1-3 is the same as that of Example 1, except that the additive composition in the electrolyte is different, as shown in Table 1.

[0079] Among them, Example 38 is different from Example 1 in the preparation of the positive electrode sheet, and the other preparation methods are the same as those of Example 1. Specifically, the positive electrode sheet of Example 38 is prepared as follows:

[0080] Example 38

[0081] Preparation of the positive electrode sheet:

[0082] The positive active material lithium manganese iron phosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a weight ratio of 96.5:2:1.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 7 μm; the coated aluminum foil is baked in an oven, and then dried in an oven at 120°C for 8 h, followed by rolling, to control the positive electrode sheet compaction density to be 2.3 g / cm 3 , and slitting to obtain the positive electrode sheet.

[0083] Table 1

[0084] Example 26

[0085] 1. Preparation of a positive electrode sheet

[0086] The positive active material Na[Ni 0.33 Fe 0.33 Mn 0.33 ]O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a weight ratio of 96.5:2:1.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 7 μm; the coated aluminum foil is baked in an oven, and then dried in an oven at 120°C for 8 h, followed by rolling, to control the positive electrode sheet compaction density to be 3.5 g / cm 3 , and slitting to obtain the positive electrode sheet.

[0087] 2. Preparation of a negative electrode sheet

[0088] The negative active material graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber, the conductive agent acetylene black, and the conductive agent single-walled carbon nanotube (SWCNT) are mixed in a weight ratio of 95.9:1:2:1:0.1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a copper foil with a thickness of 6 μm; after drying and rolling, the negative electrode sheet compaction density is controlled to be 1.5 g / cm 3 , and die cutting to obtain the negative electrode sheet.

[0089] 3. Preparation of an electrolyte

[0090] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), the solvent EC:EMC:DEC is mixed uniformly in a mass ratio of 3:5:2, fully dried 14.5% NaPF6 and additives (see Table 3 for specific selection and amount) are quickly added to the mixed solution, the mixture is thoroughly mixed and uniformly stirred to obtain the electrolyte.

[0091] 4. Separation membrane

[0092] 8 μm thick coated polyethylene separation membrane was selected.

[0093] 5. Sodium-ion battery preparation

[0094] The prepared positive electrode sheet, the separation membrane, and the negative electrode sheet were wound to obtain a bare cell without liquid injection. The bare cell was placed in an outer packaging foil, and the prepared electrolyte was injected into the dried bare cell. Through vacuum packaging, standing, formation, shaping, sorting, and other processes, the required secondary battery was obtained.

[0095] The secondary battery preparation method of Examples 27-30 was the same as that of Example 26, except that the additive composition in the electrolyte was different, as shown in Table 2.

[0096] Table 2

[0097] The high-temperature cycle performance and rate performance of the secondary batteries obtained in Examples 1-25, Examples 31-38, and Comparative Examples 1-3, and the transition metal dissolution were characterized, and the characterization results are shown in Table 3.

[0098] (1) 3C constant current injection ratio test: the obtained battery was placed in a 25°C environment, and the battery was discharged at 1C constant current to the cut-off voltage 2.75V, recorded as the initial capacity Q1, and then charged at 3C constant current to the upper limit voltage 4.2V, recorded as the 3C charge capacity Q2, and then discharged at 1C constant current to the cut-off voltage 2.75V, and then recorded the results as shown in Table 3. The calculation formula used is as follows:

[0099] 3C constant current injection ratio = Q2 / Q1 x 100%

[0100] (2) 45°C high-temperature cycle test: the battery was placed in a (45±2) °C environment, and after standing for 3 hours, it was charged at 1C constant current to the upper limit voltage 4.2V, and the cut-off current was 0.05C. After the battery was fully charged, it was left to stand for 5 min, and then discharged at 1C constant current to the cut-off voltage 2.75V. The highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q3. When the cycle reached 500 times, the last discharge capacity Q4 of the battery was recorded. The calculation formula is as follows:

[0101] Capacity retention rate (%) = Q4 / Q3 x 100%

[0102] (3) Transition metal test: the battery was discharged to the cut-off voltage 2.5V after 45°C cycle 500T, and was disassembled in a glove box to obtain a negative electrode sheet. The negative electrode powder was dried and tested for ICP (Ni / Co / Mn elements).

[0103] Table 3

[0104] As can be seen from Table 3, in Examples 1-25 and Examples 31-38, the combination of the compound represented by Formula 1 and the compound represented by Formula 2 can form a highly stable and low-resistance SEI, improve the high-temperature cycle and rate performance of the battery, and reduce transition metal dissolution.

[0105] Compared with Example 3, no compound represented by Formula 1 and compound represented by Formula 2 are added in Comparative Examples 1-3, and the high-temperature cycle performance and rate performance of the obtained battery are obviously lower, and the transition metal dissolution is obviously increased. It can be seen that the electrolyte additive proposed in the present application, the compound represented by Formula 1 and the compound represented by Formula 2 synergistically act, and when added to the secondary battery, the high-temperature cycle and rate performance of the battery can be improved, and the transition metal dissolution can be reduced.

[0106] The high-temperature cycle performance, rate performance, and transition metal dissolution rate of the batteries in other examples in Examples 1-6 are obviously better than those in Example 7, because the addition amount of the compound represented by Formula 1 in Example 7 (3%) is higher than that in other examples. The possible reason is that the use of excessive compound represented by Formula 1, and it is speculated that the possible reason is that the content of the compound represented by Formula 1 is too high, a part of which is thickly formed on the positive and negative electrodes, and the active lithium is continuously consumed during high-temperature cycle, resulting in low high-temperature cycle capacity retention rate. In addition, the thick interface film affects the lithium ion intercalation and deintercalation, affecting the rate, and another part of the compound represented by Formula 1 that is not consumed is prone to further reaction and decomposition to produce gas at high temperature, which does not have a good complex transition metal effect.

[0107] The high-temperature cycle performance and rate performance of the secondary batteries obtained in Examples 26-30 were characterized, and the characterization results are shown in Table 4.

[0108] (1) 2C constant current injection ratio test: the obtained battery was placed in a 25°C environment, and the battery was discharged at 1C constant current to the cut-off voltage 1.5V, recorded as the initial capacity Q1, and then charged at 2C constant current to the upper limit voltage 4.2V, recorded as the 2C charge capacity Q2, and then discharged at 1C constant current to the cut-off voltage 1.5V, and then recorded as the result in Table 4. The calculation formula used is as follows:

[0109] 2C constant current charge ratio = Q2 / Q1 x 100%

[0110] (2) 45℃ high temperature cycle test: 45℃ high temperature cycle test: the battery is placed in a (45±2)℃ environment, and after standing for 3 hours, it is charged to the upper limit voltage 4.2V at 1C constant current and constant voltage, the cutoff current is 0.05C, and after the battery is fully charged, it is standing for 5min, then discharged to the cutoff voltage 1.5V at 1C constant current, the highest discharge capacity of the first 3 cycles is recorded as the initial capacity Q3, when the cycle reaches 500 times, the last discharge capacity Q4 of the battery is recorded. The calculation formula is as follows:

[0111] Capacity retention rate (%) = Q4 / Q3 x 100%

[0112] (3) Transition metal test: after 45℃ cycle 500T, the battery is discharged to the cutoff voltage 1.5V, and then disassembled in a glove box to obtain a negative electrode sheet. The negative electrode powder is dried and tested for ICP (Mn element).

[0113] Table 4

[0114] As can be seen from Table 4, in Examples 26-30 of the present application, the combination of the compound represented by Formula 1 and the compound represented by Formula 2 can form a high-stability and low-impedance SEI, improve the high-temperature cycle and rate performance of the battery, and reduce the dissolution of transition metals. It can be seen that the electrolyte additive of the present application is also applicable to sodium ion batteries, which can improve the high-temperature cycle and rate performance of the battery and reduce the dissolution of transition metals.

[0115] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0116] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. An electrolyte additive, wherein, The electrolyte additive includes the compounds shown in Formula 1 and Formula 2: R1 and R2 are each independently selected from any one of substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C2-C6 alkenyl groups, and substituted or unsubstituted C2-C7 alkynyl groups.

2. The electrolyte additive according to claim 1, wherein, The mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 is 1:(0.05-20).

3. The electrolyte additive according to claim 1 or 2, wherein, The compounds shown in Formula 1 include:

4. An electrolyte, wherein, The electrolyte additive included in any one of claims 1-3.

5. The electrolyte according to claim 4, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound represented by Formula 1 is 0.03%-3%.

6. The electrolyte according to claim 4, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound represented by Formula 1 is 0.03% to 2%.

7. The electrolyte according to any one of claims 4-6, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula 2 is 0.05%-2.5%.

8. The electrolyte according to any one of claims 4-6, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula 2 is 0.05%-2%.

9. A battery, wherein, The electrolyte includes any one of claims 4-6.

10. The battery according to claim 9, wherein, The battery includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium-rich manganese-based positive electrode materials; optionally, the lithium nickel cobalt manganese oxide includes LiNi x M 1-x At least one of O2, wherein M includes Co and Mn, 0.8 ≤ x ≤ 0.92; or, The positive electrode active material includes Na X1 M1O2, Na X2 at least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, and Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu.

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