Electrolyte additive suitable for manganese-based positive electrode, electrolyte and battery

Abstract

The invention discloses a battery electrolyte additive suitable for a manganese-based positive electrode, the battery electrolyte additive comprises a compound with electron donating ability and a compound with coordination ability, and the compound with electron donating ability is a nitrile compound or a phosphate compound; the compound with the coordination capability is a heterocyclic compound or a fluorophosphate compound or a fluorocarbonate compound. According to the invention, a certain amount of a compound with an electron donating center or coordination capability is introduced into a battery electrolyte system containing a manganese-based positive electrode as an additive; the method can effectively relieve the problems of ginger-Taylor effect, manganese dissolution and the like of a manganese base in a battery with a manganese-based positive electrode in a charge-discharge cycle process, and limits structure collapse caused by repeated volume change, so that the service life of the battery is remarkably prolonged, and the charge-discharge capacity and the cycle performance of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium (sodium) battery electrolytes, and more particularly relates to a battery electrolyte additive suitable for manganese-based positive electrodes, and an electrolyte and a battery prepared therefrom. Background Art

[0002] Manganese-based oxide cathodes, due to their advantages such as high capacity, high energy density, and low cost contributed by the simultaneous redox reaction of anions and cations, have become highly competitive cathode materials for the development of high-energy-density secondary batteries, and hold broad development prospects in areas such as new energy vehicles and consumer electronics. However, due to issues such as oxygen defects, the Jan-Taylor effect, and manganese dissolution during cycling, manganese-based cathodes suffer from severe capacity decay and short cycle life. This poses a challenge to achieving both high energy density and cycling stability.

[0003] Electrolyte engineering can improve battery cycle stability and energy density by optimizing electrolyte composition and interfacial chemical behavior, inhibiting manganese dissolution, structural degradation, and side reactions. It is one of the effective means to solve the key scientific problems of manganese-based cathodes (such as lithium-rich manganese-based and spinel LiMn2O4). However, due to the irreversible reaction of PF6- in traditional ethylene carbonate (EC) / lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes, unstable CEI interface, and slow Li+ kinetic behavior, the performance of high-voltage lithium-rich manganese-based materials will continue to deteriorate.

[0004] Therefore, developing a new battery electrolyte suitable for manganese-based cathodes is of great significance. By suppressing the Jan-Taylor effect and manganese dissolution during the charge-discharge cycle, the capacity and cycle life of secondary batteries can be increased, improving the economic benefits of the batteries and ultimately achieving mass production. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide an electrolyte additive suitable for manganese-based positive electrodes.

[0006] To achieve the above object, the present invention provides the following technical solutions: An additive for battery electrolyte, Including compounds with electron-donating ability and compounds with coordination ability, The compound having electron-donating ability is a nitrile compound or a phosphate compound; The compound with coordination ability is a heterocyclic compound, a fluorophosphate compound, or a fluorocarbonate compound.

[0007] The volume ratio of the compound having electron donating ability to the compound having coordination ability is 0.3-1:0.3-1; Preferably, the volume ratio of the compound having electron donating ability to the compound having coordination ability is 1:1.

[0008] As a further improvement of the present invention, The phosphate compound is tris(trimethylsilyl)phosphate or thiotrifluoroethylphosphate or triethyl phosphate; The nitrile compound is hexanetrinitrile or succinonitrile or 1,2,3-tricyanopropane.

[0009] As a further improvement of the present invention, The heterocyclic compound is quinoline or porphyrin or a quinoline derivative or a porphyrin derivative; The quinoline derivative is 6-fluoro-2-methylquinoline.

[0010] As a further improvement of the present invention, The fluorophosphate compound is perfluorobutyl phosphate.

[0011] As a further improvement of the present invention, The fluorinated carbonate compound is fluorinated ethylene carbonate or difluorinated ethylene carbonate.

[0012] As another object of the present invention, a battery electrolyte is provided, characterized in that: Including the above-mentioned additives, electrolyte salts, and ester solvents.

[0013] As a further improvement of the present invention, The content of the additive in the electrolyte is 15.0~20.5 vol.% or 0.05~0.15 mol / L.

[0014] Preferably, the content of the additive in the electrolyte is 5-10 vol.% or 0.1-0.15 mol / L.

[0015] Under this dosage condition, it is more conducive to suppressing the Jan-Teller effect and manganese dissolution problem of the manganese-based positive electrode. As a further improvement of the present invention, The ester solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, vinylene carbonate, methyl propyl carbonate, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propyl acetate.

[0016] As a further improvement of the present invention, The electrolyte salt is at least one of a lithium salt or a sodium salt; The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide); Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalatoborate; The sodium salt is at least one of sodium hexafluorophosphate and sodium perchlorate; More preferably, the electrolyte salt is lithium hexafluorophosphate or sodium hexafluorophosphate.

[0017] Anion (PF6 - ) has a larger ionic radius and lower charge density, and is more easily dissociated in polar solvents (such as carbonates), releasing more free cations. It can inhibit manganese dissolution and side reactions by forming a more stable CEI interface chemical behavior, thereby improving the cycle stability and energy density of the battery.

[0018] The content of the electrolyte salt in the electrolyte solution is 0.5 to 5 mol / L.

[0019] Preferably, the content of the electrolyte salt in the electrolyte is 0.3 to 2 mol / L.

[0020] More preferably, the content of the electrolyte salt in the electrolyte is 0.8-1.2 mol / L.

[0021] As another object of the present invention, a battery is provided. include The above-mentioned electrolyte, manganese-based positive electrode, negative electrode, and separator; The manganese-based positive electrode is prepared from one or more of lithium manganese oxide, lithium-rich manganese-based, manganese-based Prussian blue analogs, lithium iron manganese phosphate, perovskite-type manganese oxide, spinel-type manganese oxide, and manganese dioxide.

[0022] Since the manufacture of batteries is an existing technology, this application provides a method for manufacturing a battery: Step 1: Preparation of positive electrode sheets: positive electrode materials, conductive additives, binders, and solvents are stirred to obtain positive electrode slurry, which is then evenly coated on aluminum foil (positive electrode aluminum current collector), dried, and then sliced ​​to obtain positive electrode sheets; The positive electrode material here is a manganese-based material, which is one or more of lithium manganese oxide, lithium-rich manganese-based, manganese-based Prussian blue analogues, lithium iron manganese phosphate, perovskite-type manganese oxide, spinel-type manganese oxide, and manganese dioxide.

[0023] Step 2: Preparation of negative electrode sheet, Directly select lithium metal sheet or sodium metal sheet as the negative electrode; or A negative electrode material, a conductive additive, a binder, and a solvent are stirred and mixed to obtain a negative electrode slurry, wherein the negative electrode material is graphite or hard carbon. The negative electrode slurry is then evenly coated on a copper foil, dried, and sliced ​​to obtain a negative electrode sheet. It should be noted here that when preparing lithium batteries, the negative electrode material is graphite; when preparing sodium batteries, the negative electrode material is hard carbon.

[0024] Step 3: Take the diaphragm, add the electrolyte dropwise onto the diaphragm, and assemble the button half-cell and the soft-pack battery according to the requirements for assembling button secondary batteries and soft-pack batteries.

[0025] As a common prior art, the conductive additives and binders used in the preparation of positive (negative) electrodes from positive (negative) materials are relatively mature technologies. Acetylene black and polyvinylidene fluoride binders are generally used, and N-methylpyrrolidone is used as the solvent. The mass ratio of positive (negative) material, acetylene black, and polyvinylidene fluoride binder is generally 8:1:1. Separators are typically made of ceramic filter paper or glass fiber, with lithium batteries typically using ceramic filter paper and sodium batteries using glass fiber filter paper.

[0026] Electron-donating compounds preferentially reduce on the negative electrode surface, forming an organic-rich SEI film, improving interfacial conductivity and inhibiting lithium dendrite growth. Phosphate-based organic compounds offer advantages over other organic compounds, including excellent thermal stability, antioxidant properties, flame retardancy, and the ability to suppress thermal runaway.

[0027] The role of the compound with coordination ability is that it tends to oxidatively decompose on the surface of the positive electrode to form a CEI film rich in inorganic components, enhance the interface stability, and inhibit the dissolution of transition metals.

[0028] The combined effect of the two can optimize the composition of the interface film (organic-inorganic composite structure), balance ionic conductivity and chemical stability, and reduce interface impedance.

[0029] The conjugated structure and heteroatom electronic effect of heterocyclic compounds such as quinoline or porphyrin or quinoline derivatives or porphyrin derivatives can capture active free radicals (such as O2 - PF5 inhibits oxidative decomposition of the electrolyte at high voltages and side reactions with the electrodes; fluorinated carbonates facilitate the formation of the SEI film. Coordinating electrolyte additives tend to oxidatively decompose on the cathode surface, forming an inorganic-rich CEI film that enhances interfacial stability and inhibits transition metal dissolution.

[0030] The nitrile compound has electron-donating ability and coordination ability, but its core attribute is more inclined to electron-donating type electrolyte, the molecular structure of the nitrile compound contains cyano group (-CN), and the nitrogen atom has lone pair of electrons, which can exhibit electron-donating ability in an electrochemical system. Hexanetristitride, butanedinitrile, 1,2,3-tricyanopropane and the like, due to multiple cyano groups (-CN), the nitrogen atom has high electronegativity and carries lone pair of electrons, which has electron-donating ability.

[0031] Compared with the prior art, the beneficial effects of the present application are that: by introducing a certain amount of a compound having an electron-donating center or having coordination ability as an additive in the electrolyte system of a battery containing a manganese-based positive electrode, the problems of Jahn-Teller effect and manganese dissolution of manganese-based in the battery during the charge and discharge cycle can be effectively alleviated by the method of interface chemical regulation, the structure collapse caused by repeated volume changes is limited, thereby the battery life is significantly prolonged, and the charge and discharge capacity and the cycle performance of the battery are improved.

[0032] The application method related by the present application is simple and low in cost, and can provide a new idea for efficient application of manganese-based positive electrode secondary batteries. DETAILED DESCRIPTION Example 1

[0033] Preparation of electrolyte: 0.5 mL of DEC (diethyl carbonate), 0.5 mL of EC (ethylene carbonate), 1 mmol of LiPF6 (lithium hexafluorophosphate), 75 uL of hexanetristitride and 75 uL of 6-fluoro-2-methylquinoline were weighed respectively; the weighed LiPF6, DEC and EC were stirred and mixed uniformly at room temperature, and then the hexanetristitride and 6-fluoro-2-methylquinoline were stirred and mixed uniformly, to obtain the lithium ion battery electrolyte.

[0034] Preparation of battery: Step 1: preparation of positive electrode sheet: 0.8 g of lithium manganate positive electrode material, 0.1 g of acetylene black and 0.1 g of polyvinylidene fluoride (PVDF) binder were uniformly mixed, 4 mL of N-methylpyrrolidone was added as a solvent, and the positive electrode slurry was obtained by stirring; the positive electrode slurry was uniformly coated on the positive electrode aluminum current collector, dried in an oven at 120 DEG C for 12 hours, and then sliced by a slicer with a pore size of 9 mm to obtain the positive electrode sheet; Step 2: preparation of negative electrode sheet, directly taking lithium metal sheet as negative electrode sheet; Step 3: taking ceramic filter paper as a separator, contacting one side of the separator with the positive electrode sheet, dropping 120 ul of electrolyte, and then assembling into a button cell. Example 2

[0035] The electrolyte additives hexanetricarbonitrile and 6-fluoro-2-methylquinoline, the specific steps for preparing the electrolyte and the positive electrode sheet are roughly the same as in Example 1, except that the components used in the electrolyte and their amounts are: 0.5mL DEC, 0.5mL EC, 1mmol LiPF6, 50uL of hexanetricarbonitrile and 50uL of 6-fluoro-2-methylquinoline.

[0036] Preparation of the battery: Step 1: Preparation of positive electrode: 0.8 g of lithium manganate positive electrode material, 0.1 g of acetylene black, and 0.1 g of polyvinylidene fluoride (PVDF) binder were mixed evenly, and 4 mL of N-methylpyrrolidone solvent was added and stirred to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on the positive electrode aluminum current collector, dried in an oven at 120°C for 12 hours, and then sliced ​​with a microtome with an aperture of 9 mm to obtain a positive electrode sheet; Step 2: Preparation of negative electrode sheet: directly take lithium metal sheet as negative electrode sheet; Step 3: Use ceramic filter paper as a diaphragm, place the diaphragm in contact with one side of the positive electrode, add 120ul of electrolyte, and then assemble into a button battery. Example 3

[0037] The electrolyte additives tris(trimethylsilyl) phosphate and 6-fluoro-2-methylquinoline. The specific steps for preparing the electrolyte are roughly the same as those in Example 1, except that the components used in the electrolyte and their amounts are: 0.5mL DEC, 0.5mL EC, 1mmol LiPF6, 75uL 6-fluoro-2-methylquinoline and 75uL tris(trimethylsilyl) phosphate.

[0038] The positive electrode material of this embodiment is a layered lithium-rich manganese-based (Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2); Preparation of the battery: Step 1: Preparation of positive electrode: 0.8 g of lithium-rich manganese-based cathode material, 0.1 g of acetylene black, and 0.1 g of polyvinylidene fluoride (PVDF) binder were mixed uniformly in an argon-filled glove box, and 4 mL of N-methylpyrrolidone (NMP) solvent was added and stirred to obtain a cathode slurry. The cathode slurry was evenly coated on the cathode aluminum current collector, dried in a vacuum oven at 120°C for 12 hours, and then sliced ​​using a 9 mm aperture microtome to obtain a cathode electrode sheet. Step 2: Preparation of negative electrode sheet: directly take lithium metal sheet as negative electrode sheet; Step 3: Take ceramic filter paper as a separator, drop 120ul electrolyte on the side of the separator in contact with the positive electrode sheet, and then assemble into a button cell. Example 4

[0039] The additive of the battery electrolyte is sulfide trifluoroethyl phosphate and perfluorobutyl phosphate, and the specific steps are basically the same as those of Example 3, except that the components and their amounts used in the electrolyte are as follows: 0.25ml EC, 0.75ml DMC (dimethyl carbonate), 1mmol LiPF6, 50ul sulfide trifluoroethyl phosphate and 50ul perfluorobutyl phosphate.

[0040] The positive electrode material of this example is selected as a layered lithium-rich manganese-based (Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2); Preparation of the battery: Step 1: Preparation of the positive electrode sheet: Mix 0.8g lithium-rich manganese-based positive electrode material, 0.1g acetylene black and 0.1g polyvinylidene fluoride (PVDF) binder evenly in an argon-filled glove box, add 4ml N-methyl pyrrolidone (NMP) solvent, stir and obtain a positive electrode slurry; coat the positive electrode slurry evenly on a positive electrode aluminum current collector, dry in a vacuum oven at 120℃ for 12 hours, and then slice through a slicer with a pore size of 9mm to obtain a positive electrode sheet; Step 2: Preparation of the negative electrode sheet, directly take a lithium metal sheet as the negative electrode sheet; Step 3: Take ceramic filter paper as a separator, drop 120ul electrolyte on the side of the separator in contact with the positive electrode sheet, and then assemble into a button cell. Example 5

[0041] The additive of the electrolyte is sulfide trifluoroethyl phosphate and fluoroethylene carbonate, and the specific steps are basically the same as those of Example 1, except that the components and their amounts used in the electrolyte are as follows: 0.5ml EC, 0.5ml DEC, 1mmol LiPF6, 50ul sulfide trifluoroethyl phosphate and 50ul fluoroethylene carbonate.

[0042] The positive electrode material of this example is selected as manganese iron lithium phosphate; Preparation of the battery: Step 1: Preparation of the positive electrode sheet: 0.8 g of lithium manganese iron phosphate positive electrode material, 0.1 g of acetylene black, and 0.1 g of polyvinylidene fluoride (PVDF) binder were mixed uniformly in an argon-filled glove box, and 4 mL of N-methylpyrrolidone (NMP) solvent was added and stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode aluminum current collector, dried in a vacuum oven at 120°C for 12 hours, and then sliced ​​using a 9 mm aperture microtome to obtain a positive electrode sheet. Step 2: Preparation of negative electrode sheet: directly take lithium metal sheet as negative electrode sheet; Step 3: Use ceramic filter paper as a diaphragm, place the diaphragm in contact with one side of the positive electrode, add 150uL of electrolyte, and then assemble into a button battery. Example 6

[0043] The additives of the battery electrolyte are fluoroethylene carbonate and triethyl phosphate. The specific steps are roughly the same as those in Example 1, except that the components used in the electrolyte and their amounts are: 0.25mL EC, 0.75mL DMC (dimethyl carbonate), 1mmol NaPF6, 30uL fluoroethylene carbonate and 30uL triethyl phosphate.

[0044] The positive electrode material of this embodiment is manganese-based Prussian blue; Step 1: Preparation of positive electrode: 0.8 g of manganese-based Prussian blue cathode material, 0.1 g of acetylene black, and 0.1 g of polyvinylidene fluoride (PVDF) binder were mixed uniformly in an argon-filled glove box, and 4 mL of N-methylpyrrolidone (NMP) solvent was added and stirred to obtain a cathode slurry. The cathode slurry was evenly coated on the cathode aluminum current collector, dried in a vacuum oven at 120°C for 12 hours, and then sliced ​​using a 9 mm aperture microtome to obtain a cathode electrode sheet. Step 2: Preparation of negative electrode sheet: directly take lithium metal sheet as negative electrode sheet; Step 3: Use glass fiber as a separator, place the separator in contact with one side of the positive electrode, add 150uL of electrolyte, and then assemble it into a button battery.

[0045] Comparative Example 1: Acetonitrile was used as the battery electrolyte additive, and the specific steps were substantially the same as those in Example 1, except that the components and amounts of the electrolyte used were: 0.5 mL DEC, 0.5 mL EC, 1 mmol LiBF4, and 150 uL acetonitrile; the battery was also prepared in the same manner as in Example 1.

[0046] Comparative Example 2: The battery electrolyte additive used porphyrin, and the specific steps were roughly the same as in Example 4, except that the components and amounts used in the electrolyte were: 0.75 mL DMC, 0.25 mL EC, 1 mmol LiBF4, and 100 uL porphyrin. The battery was also prepared in the same way as in Example 4.

[0047] Comparative Example 3: Hexanetricarbonitrile was used as the electrolyte additive. The specific steps were similar to those in Example 5, except that the components and amounts used in the electrolyte were: 0.5 mL DEC, 0.5 mL EC, 1 mmol LiBF4, and 100 μL hexanetricarbonitrile. The battery was also prepared in the same manner as in Example 5.

[0048] Comparative Example 4: No electrolyte additives were added to the battery electrolyte. The specific steps were essentially the same as in Example 6, except that the components and amounts used in the electrolyte were: 0.7 mL DEC, 0.3 mL EC, 1 mmol NaPF6, and 100 μL fluoroethylene carbonate. The battery was also prepared in the same manner as in Example 6.

[0049] Comparative Example 5: The battery electrolyte additive uses hexanetricarbonitrile, and the specific steps are roughly the same as those in Example 1, except that the components and amounts used in the electrolyte are: 0.5mL DEC, 0.5mL EC, 1mmol LiPF6, and 150uL hexanetricarbonitrile; the preparation of the battery is also the same as in Example 1.

[0050] Comparative Example 6: The battery electrolyte additive uses 6-fluoro-2-methylquinoline, and the specific steps are roughly the same as those in Example 1, except that the components used in the electrolyte and their amounts are: 0.5mL DEC, 0.5mL EC, 1mmol LiPF6, and 150uL 6-fluoro-2-methylquinoline; the preparation of the battery is also the same as in Example 1.

[0051] Comparative Example 7: The battery electrolyte additive used was tris(trimethylsilyl) phosphate, and the specific steps were substantially the same as those in Example 3, except that the components and amounts of the electrolyte used were: 0.5 mL DEC, 0.5 mL EC, 1 mmol LiPF6, and 150 μL 6-fluoro-2-methylquinoline; the battery was also prepared in the same manner as in Example 3.

[0052] Comparative Example 8: The battery electrolyte additive used was tris(trimethylsilyl) phosphate. The specific steps were substantially the same as those in Example 3, except that the components and amounts of the electrolyte used were: 0.5 mL DEC, 0.5 mL EC, 1 mmol LiPF6, and 150 μL tris(trimethylsilyl) phosphate. The battery was also prepared in the same manner as in Example 3.

[0053] Ingredients: Name Factory Diethyl carbonate (DEC) MaddaChemicals Ethylene carbonate (EC) MaddaChemicals <![CDATA[六氟磷酸锂(LiPF6)]]> MaddaChemicals <![CDATA[六氟磷酸钠(NaPF6)]]> MaddaChemicals <![CDATA[四氟硼酸锂(LiBF4)]]> MaddaChemicals Hexanetristitnitrile Macklin 6-Fluoro-2-methylquinoline Macklin Tris(trimethylsilyl) phosphate Macklin Thiotrifluoroethyl phosphate Macklin Perfluorobutyl phosphate Macklin Fluoroethylene carbonate Macklin Triethyl phosphate Macklin Acetonitrile Macklin Porphyrin Macklin Lithium manganese oxide cathode material Kureha Lithium manganese iron phosphate cathode material Kureha Manganese-based prussian blue cathode material Kureha Lithium-rich manganese-based cathode material Songhushenjian Technology (Dongguan) Co., Ltd. (Fast Dog Scientific Research) Acetylene black Kureha Polyvinylidene fluoride (PVDF) binder Kureha N-Methylpyrrolidone Macklin Positive aluminum current collector Shenzhen Kexing Ceramic filter paper Jinghong New Energy Glass fiber Whatman Cycling performance test: At 25°C, the lithium (sodium) ion battery electrolyte prepared using the above scheme was used to prepare lithium-ion batteries. The electrode material was activated by charging and discharging for three cycles at a rate of 0.1 C. Then, the battery was charged and discharged for three cycles at a rate of 0.33 C. The battery was fully charged and discharged for a full cycle test, and the battery life and corresponding capacity retention rate were recorded.

[0054] Examples 1-6 and Comparative Examples 1-8 were tested respectively, and Examples 1-6 and Comparative Examples 1-8 were tested without adding electrolyte additives.

[0055] Capacity retention rate Example 1 (add electrolyte additive) 72.67% (300 cycles under the condition of 4.2 V cut-off voltage and 0.33 C rate) Example 1 (without adding electrolyte additive) 47.36% (300 cycles under the condition of 4.2 V cut-off voltage and 0.33 C rate) Example 2 (add electrolyte additive) 76.81% (300 cycles under the condition of 4.2 V cut-off voltage and 0.33 C rate) Example 2 (without adding electrolyte additive) 51.17% (300 cycles under the condition of 4.2 V cut-off voltage and 0.33 C rate) Example 3 (add electrolyte additive) 83% (300 cycles under the condition of 4.8 V cut-off voltage and 0.33 C rate) Example 3 (without adding electrolyte additive) 35.51% (300 cycles under the condition of 4.8 V cut-off voltage and 0.33 C rate) Example 4 (add electrolyte additive) 72.16% (300 cycles under the condition of 4.8 V cut-off voltage and 0.33 C rate) Example 4 (without adding electrolyte additive) 35.16% (300 cycles under the condition of 4.8 V cut-off voltage and 0.33 C rate) Example 5 (add electrolyte additive) 72.84% (300 cycles under the condition of 4.1 V cut-off voltage and 0.33 C rate) Example 5 (without adding electrolyte additive) 29.34% (300 cycles under the condition of 4.1 V cut-off voltage and 0.33 C rate) Example 6 (add electrolyte additive) 75.41% (300 cycles under the condition of 4.0 V cut-off voltage and 0.33 C rate) Example 6 (without adding electrolyte additive) 31.89% (300 cycles under the condition of 4.0 V cut-off voltage and 0.33 C rate) Comparative Example 1 (add electrolyte additive) 52% (300 cycles under the condition of 4.2 V cut-off voltage and 0.33 C rate) Comparative Example 1 (without adding electrolyte additive) 35.1% (300 cycles at a cutoff voltage of 4.2 V and a rate of 0.33 C) Comparative Example 2 (addition of electrolyte additives) 47% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C) Comparative Example 2 (no electrolyte additives added) 29.38% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C) Comparative Example 3 (addition of electrolyte additives) 39% (300 cycles at a cutoff voltage of 4.1 V and a rate of 0.33 C) Comparative Example 3 (no electrolyte additives added) 19.3% (300 cycles at a cutoff voltage of 4.1 V and a rate of 0.33 C) Comparative Example 4 (addition of electrolyte additives) 45.53% (300 cycles at a cutoff voltage of 4.0 V and a rate of 0.33 C) Comparative Example 4 (no electrolyte additives added) 29.37% (300 cycles at a cutoff voltage of 4.0 V and a rate of 0.33 C) Comparative Example 5 (addition of electrolyte additives) 41.33% (300 cycles at a cutoff voltage of 4.2 V and a rate of 0.33 C) Comparative Example 5 (no electrolyte additives added) 28.71% (300 cycles at a cutoff voltage of 4.2 V and a rate of 0.33 C) Comparative Example 6 (addition of electrolyte additives) 43.43% (300 cycles at a cutoff voltage of 4.2 V and a rate of 0.33 C) Comparative Example 6 (no electrolyte additives added) 26.79% (300 cycles at a cutoff voltage of 4.2 V and a rate of 0.33 C) Comparative Example 7 (addition of electrolyte additives) 33.91% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C) Comparative Example 7 (no electrolyte additives added) 27.95% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C) Comparative Example 8 (addition of electrolyte additives) 62.07% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C) Comparative Example 8 (no electrolyte additives added) 35.64% (300 cycles at a cutoff voltage of 4.8 V and a rate of 0.33 C)

[0056] In the tests of Examples 1 to 6, cycle performance tests were conducted with and without the addition of electrolyte additives, respectively. It can be clearly seen that the capacity retention rate of the battery with the addition of electrolyte additives is significantly higher than that of the battery without the addition of electrolyte additives.

[0057] Comparative Examples 1 to 4 are common electrolyte additives. It can be seen that when used alone, their capacity retention rates are significantly lower than when the compound with electron-donating ability and the compound with coordination ability are used in combination in the examples.

[0058] Comparative Examples 5 to 8 respectively used the electrolyte additives used in the examples alone, that is, the compounds with electron donating ability or the compounds with coordination ability were used alone. Comparative Examples 5 and 6 correspond to Example 1, and Comparative Examples 7 and 8 correspond to Example 3. The capacity retention rates of Comparative Examples 5 and 6 are lower than those of Example 1, and the capacity retention rates of Comparative Examples 7 and 8 are lower than those of Example 3.

[0059] For the manganese-based positive electrode lithium ion battery electrolyte system described in the present invention, the additive molecules of the present invention having electron-donating center ability and coordination ability introduced respectively can achieve effective coordination with manganese ions, inhibit the ion dissolution of manganese elements due to the Jan-Taylor effect and disproportionation reaction, and effectively inhibit the structural collapse and short cycle life faced by the manganese-based positive electrode. By introducing electron-donating groups similar to phosphorus-containing centers or fluorine elements, they are preferentially adsorbed on the electrode surface and participate in the formation of a dense, highly ion-conductive interface film, promoting the formation of a stable CEI interface and accelerating ion kinetic transport, thereby improving the electrochemical performance of the battery. In addition, porphyrin, quinoline, quinoline derivatives, and porphyrin derivatives have a strong ability to coordinate Mn ions, and can coordinate the manganese-based positive electrode at the interface to a certain extent, thereby reducing the lattice distortion caused by the Jan-Taylor effect, thereby stabilizing the structure of the manganese-based positive electrode and improving the stability of the battery. Among them, ester solvents can effectively dissolve lithium (sodium) salts such as lithium hexafluorophosphate, forming an electrolyte system containing lithium ions (Li+) and corresponding anions. During the battery's charge and discharge process, Li+ needs to migrate between the positive and negative electrodes through the electrolyte. The molecular structure of ester solvents can wrap Li+ through solvation, allowing it to move freely in the solution, thereby achieving charge conduction. Ester solvents can, to a certain extent, regulate electrode interface stability, broaden the operating temperature range, and affect the overall performance of the battery. In lithium-ion battery electrolytes, ester solvents are not only the dissolution medium for lithium salts, but also the core factor that determines the battery's interface stability, electrochemical performance, and safety. By rationally selecting the type and ratio of ester solvents, a balance can be achieved between the battery's energy density, cycle life, fast charging performance, and safety.

[0060] The beneficial effects of the present invention are as follows: by introducing a certain amount of a compound having an electron-donating center or a coordination ability as an additive into a battery electrolyte system containing a manganese-based positive electrode, the present invention can effectively alleviate the problems of the Jan-Taylor effect and manganese dissolution in the manganese-based battery during the charge and discharge cycle through the method of interface chemical regulation, limit the structural collapse caused by repeated volume changes, thereby significantly extending the battery life and improving the battery's charge and discharge capacity and battery cycle performance.

[0061] The application method of the present invention is relatively simple and has low cost, and can provide a new idea for the efficient application of manganese-based positive electrode secondary batteries.

[0062] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An additive for a battery electrolyte suitable for a manganese-based positive electrode, characterized in that: Including compounds with electron-donating ability and compounds with coordination ability, The compound having electron-donating ability is a nitrile compound or a phosphate compound; The compound with coordination ability is a heterocyclic compound, a fluorophosphate compound, or a fluorocarbonate compound.

2. The additive for battery electrolyte suitable for manganese-based positive electrode according to claim 1, characterized in that: The phosphate compound is tris(trimethylsilyl)phosphate or thiotrifluoroethylphosphate or triethyl phosphate; The nitrile compound is hexanetrinitrile or succinonitrile or 1,2,3-tricyanopropane.

3. The additive for battery electrolyte suitable for manganese-based positive electrode according to claim 1, characterized in that: The heterocyclic compound is quinoline or porphyrin or a quinoline derivative or a porphyrin derivative; The quinoline derivative is 6-fluoro-2-methylquinoline.

4. The additive for battery electrolyte suitable for manganese-based positive electrode according to claim 1, characterized in that: The fluorophosphate compound is perfluorobutyl phosphate.

5. The battery electrolyte additive according to claim 1, characterized in that: The fluorinated carbonate compound is fluorinated ethylene carbonate or difluorinated ethylene carbonate.

6. A battery electrolyte containing the additive according to any one of claims 1 to 5, characterized in that: The invention comprises the additives, electrolyte salt and ester solvent.

7. The battery electrolyte according to claim 6, characterized in that: The content of the additive in the electrolyte is 15.0~20.5 vol.% or 0.05~0.15 mol / L.

8. The battery electrolyte according to claim 6, characterized in that: The ester solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, vinylene carbonate, methyl propyl carbonate, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propyl acetate.

9. The battery electrolyte according to claim 6, characterized in that: The electrolyte salt is at least one of a lithium salt or a sodium salt; The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide); The sodium salt is at least one of sodium hexafluorophosphate and sodium perchlorate; The content of the electrolyte salt in the electrolyte is 0.5 to 5 mol / L.

10. A battery comprising the electrolyte according to any one of claims 6 to 9, characterized in that: include The electrolyte, manganese-based positive electrode, negative electrode, and separator; The manganese-based positive electrode is one or more of lithium manganese oxide, lithium-rich manganese-based, manganese-based Prussian blue analogs, lithium iron manganese phosphate, perovskite-type manganese oxide, spinel-type manganese oxide, and manganese dioxide.