Secondary battery and electric device

Abstract

This application discloses a secondary battery and an electrical device, belonging to the field of battery technology. By controlling the mass ratio of the first lithium supplementer and the second lithium supplementer, the mass ratio of cyclic carbonate to chain carbonate in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator to satisfy: 0.17≤W≤11.18, this application significantly improves the gas generation problem of the secondary battery, effectively improves the cycle life of the secondary battery, and reduces the DCR.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a secondary battery and an electrical device. Background Technology

[0002] The emergence of portable electronic devices and electric vehicles has created a significant demand for high-energy-density rechargeable batteries. Furthermore, the energy storage industry, characterized by high growth potential and high certainty, is developing rapidly. With the increasing installed capacity, the market is demanding greater range from rechargeable batteries.

[0003] During the first cycle, the positive electrode active material used in secondary batteries irreversibly consumes a large number of active lithium ions due to the formation of the SEI film, which in turn leads to a decrease in cycle life.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a secondary battery and power device that effectively reduces the impedance of the secondary battery and improves its cycle performance.

[0006] To achieve the above objectives, a first aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector; the positive active material layer includes a lithium replenishing agent; the lithium replenishing agent includes a first lithium replenishing agent and a second lithium replenishing agent, the first lithium replenishing agent comprising Li5FeO4, and the second lithium replenishing agent comprising Li a M b O d Wherein, 1.5≤a≤6, 0≤b≤4, 1≤d≤6, and M includes at least one of Mg, Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, Sn, Si, B, and C;

[0007] The diaphragm includes a polyolefin membrane and a ceramic layer disposed on at least one surface of the polyolefin membrane;

[0008] The electrolyte includes cyclic carbonates, chain carbonates, and sulfur-containing additives;

[0009] The secondary battery satisfies:

[0010] Where Xμm is the thickness of the ceramic layer;

[0011] Y% is the mass percentage of the sulfur-containing additive in the electrolyte;

[0012] N is the mass ratio of the first lithium supplementer and the second lithium supplementer in the positive electrode active material layer;

[0013] Z is the ratio of the mass of cyclic carbonates to the mass of chain carbonates in the electrolyte.

[0014] As an embodiment of this application, the secondary battery satisfies: 0.35≤W≤6.12.

[0015] As an implementation scheme of this application, at least one of the following (Ⅰ) to (Ⅳ) is satisfied:

[0016] (Ⅰ) 1≤X≤5;

[0017] (II) 0.1≤Y≤5;

[0018] (Ⅲ) 1≤N≤5;

[0019] (Ⅳ) 0.2≤Z≤0.7.

[0020] As an embodiment of this application, the sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, vinyl sulfate, methylene disulfonate, vinyl sulfite, and 1,4-butanesulfonate lactone.

[0021] As an embodiment of this application, the electrolyte further includes a first additive, which includes at least one of tris(trimethylsilane) phosphate and lithium difluorobis(oxalato) phosphate, and the mass percentage of the first additive in the electrolyte is 0.5% to 5%.

[0022] As an embodiment of this application, the mass ratio of the sulfur-containing additive to the first additive is 1:(2-10).

[0023] As an implementation scheme of this application, the following condition must be met: 3≤N / Z≤20.

[0024] As an implementation scheme of this application, the following condition must be met: 0.5≤Y / Z≤10.

[0025] As an embodiment of this application, the cyclic carbonate includes at least one of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, and ethylene ethylene carbonate.

[0026] As an embodiment of this application, the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0027] As an embodiment of this application, the cyclic carbonate includes propylene carbonate and ethylene carbonate; the mass ratio of propylene carbonate to ethylene carbonate in the electrolyte is (0.5-5):(0.5-5).

[0028] As an embodiment of this application, the cyclic carbonate in the organic solvent has a mass percentage content of 9-42%.

[0029] As an embodiment of this application, the chain carbonate in the organic solvent has a mass percentage content of 58-91%.

[0030] A second aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0031] The beneficial effects of this invention are as follows: By controlling the mass ratio of the first lithium replenisher and the second lithium replenisher, the mass ratio of cyclic carbonates to chain carbonates in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator, this application satisfies the following conditions: 0.17 ≤ W ≤ 11.18. The combined use of the first and second lithium replenishers effectively increases the release of lithium sources, fully replenishes the lithium consumed in the SEI film formation reaction of the negative electrode, and promotes the insertion and extraction of lithium ions in the positive electrode active material. The addition of the second lithium replenisher improves the stability of the first lithium replenisher in the positive electrode active material layer, catalytically removes byproducts (such as active oxygen) generated by the first lithium replenisher, and inhibits side reactions in the electrolyte. The ceramic layer on the surface of the separator helps stabilize the separator structure, improves thermal stability, and blocks and reduces the amount of lithium replenisher. The gases produced by decomposition (including singlet oxygen) reach the electrolyte, thereby indirectly reducing the gas production from the oxidative decomposition of the electrolyte. Furthermore, the addition of sulfur-containing additives effectively forms an inorganic interface layer rich in Li₂SO₃, ROSO₂Li, etc., at the negative electrode, improving the stability of the SEI film, reducing interfacial side reactions, and effectively suppressing high-temperature gas production. By designing the mass ratio of cyclic carbonates to chain carbonates, the gas production of the secondary battery is effectively improved under high conductivity conditions. The combined effect of parameters such as the mass ratio of the first and second lithium supplementers, the mass ratio of cyclic carbonates to chain carbonates in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator significantly improves the gas production problem of the secondary battery, effectively increases the cycle life of the secondary battery, and reduces the DCR. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0034] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0035] The inventors of this application have discovered that for secondary batteries (especially lithium-ion batteries), the electrolyte-anode interface (SEI film) is essential, playing a crucial role in stable cycle performance. Essentially, the SEI film is electrically insulating but ionicly conductive, thus preventing direct contact between the negative electrode and the electrolyte and preventing excessive electrolyte decomposition. However, the formation of the SEI film results in a large irreversible capacity in the first cycle, and lithium loss reduces the battery's energy density and cycle life.

[0036] To compensate for lithium loss during the film formation process in secondary batteries, cathode lithium replenishment is a commonly used method. This method involves mixing a high-lithium-content, low-reversible-capacity cathode active material with a traditional cathode active material in a specific ratio and using this mixture as a novel cathode active material in battery assembly. The principle is based on the irreversible nature of lithium-containing compounds (lithium replenishers) after lithium loss; they can only provide lithium ions to the system and do not participate in subsequent reactions. However, most existing cathode lithium replenishment technologies generate gas due to the decomposition of the lithium replenisher, especially sacrificial lithium replenishers that undergo anion redox reactions. These sacrificial lithium replenishers produce a significant amount of oxygen during the first charging cycle, which severely impacts battery safety and cycle performance.

[0037] Therefore, based on the above-mentioned problems, this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector; the positive active material layer includes a lithium replenishing agent; the lithium replenishing agent includes a first lithium replenishing agent and a second lithium replenishing agent, the first lithium replenishing agent including Li5FeO4, and the second lithium replenishing agent including Li a M b O dWherein, 1.5≤a≤6, 0≤b≤4, 1≤d≤6, and M includes at least one of Mg, Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, Sn, Si, B, and C;

[0038] The diaphragm includes a polyolefin membrane and a ceramic layer disposed on at least one surface of the polyolefin membrane;

[0039] The electrolyte includes cyclic carbonates, chain carbonates, and sulfur-containing additives;

[0040] The secondary battery satisfies: For example, it can be 0.17, 0.18, 0.2, 0.3, 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.18 or a range of any two of these values;

[0041] Where Xμm is the thickness of the ceramic layer;

[0042] Y% is the mass percentage of the sulfur-containing additive in the electrolyte;

[0043] N is the mass ratio of the first lithium supplementer and the second lithium supplementer in the positive electrode active material layer;

[0044] Z is the ratio of the mass of cyclic carbonates to the mass of chain carbonates in the electrolyte.

[0045] The inventors of this application have discovered that the mass ratio of the first lithium supplementer and the second lithium supplementer in the positive electrode active material layer of the secondary battery, the mass ratio of cyclic carbonate to chain carbonate in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator can affect the performance of the secondary battery.

[0046] This application controls the mass ratio of the first and second lithium replenishing agents, the mass ratio of cyclic carbonates to chain carbonates in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator to satisfy the following conditions: 0.17 ≤ W ≤ 11.18. The combined use of the first and second lithium replenishing agents effectively increases the release of lithium source, fully replenishes the lithium consumed in the SEI film formation reaction of the negative electrode, and promotes the insertion and extraction of lithium ions in the positive electrode active material. The addition of the second lithium replenishing agent improves the stability of the first lithium replenishing agent in the positive electrode active material layer, catalytically removes byproducts (such as active oxygen) generated by the first lithium replenishing agent, and inhibits side reactions in the electrolyte. The ceramic layer on the separator surface helps stabilize the separator structure, improves thermal stability, and blocks and reduces the gases generated by the decomposition of the lithium replenishing agent. The presence of gas (including singlet oxygen) in the electrolyte indirectly reduces the oxidative decomposition and gas generation of the electrolyte. Furthermore, the addition of sulfur-containing additives effectively forms an inorganic interface layer rich in Li₂SO₃, ROSO₂Li, etc., at the negative electrode, improving the stability of the SEI film, reducing interfacial side reactions, and effectively suppressing high-temperature gas generation. By designing the mass ratio of cyclic carbonates to chain carbonates, the gas generation of the secondary battery is effectively improved under high conductivity conditions. The combined effect of parameters such as the mass ratio of the first and second lithium supplementers, the mass ratio of cyclic carbonates to chain carbonates in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator significantly improves the gas generation problem of the secondary battery, effectively increases the cycle life of the secondary battery, and reduces the DCR.

[0047] In some embodiments, the secondary battery satisfies: 0.35≤W≤6.12. In particular, when W is within this range, it effectively improves the impact of irreversible capacity loss in the first cycle on the lifespan, more effectively improves the gas generation problem of the secondary battery, can further reduce the battery impedance, and improve the cycle performance of the secondary battery.

[0048] In some implementations, 1≤X≤5, for example, it can be a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two of these values. By controlling X within this range, the wetting effect of the electrolyte can be effectively improved, the diffusion path of lithium ions can be shortened, the gas generated by the decomposition of lithium replenishing agent can be more effectively blocked and reduced from reaching the electrolyte, the oxidation decomposition of the electrolyte can be effectively reduced, and the cycle performance of the secondary battery can be further improved and the impedance reduced.

[0049] In one embodiment, the ceramic coating comprises ceramic particles, the ceramic particles comprising at least one of SiO2, TiO2, ZrO2, Al2O3, MgO, SiC, and boehmite.

[0050] In one embodiment, the ceramic coating further includes an adhesive.

[0051] In one embodiment, the adhesive comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber.

[0052] In one embodiment, the ceramic particles constitute 50% to 99% of the ceramic coating by mass, for example, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or any combination of two of these values.

[0053] In one embodiment, the binder has a mass percentage content of 1 to 50% in the ceramic coating, for example, it can be 1%, 5%, 10%, 20%, 30%, 40%, 50%, or any two of these values.

[0054] In some embodiments, the polyolefin film includes at least one of polyethylene and polypropylene.

[0055] In some embodiments, the thickness of the polyolefin film is 4 to 10 μm, for example, it can be a range of 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any two of these values.

[0056] In some embodiments, 0.1≤Y≤5, for example, it can be a range of 0.1, 0.2, 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two of these values. By controlling Y within this range, the stability of the SEI film can be effectively improved, interfacial side reactions can be reduced, and the stability of the electrolyte can be improved, enabling it to maintain good cycle performance under high voltage, reducing the initial internal resistance of the secondary battery and the increase in internal resistance during cycling, thus effectively improving the cycle performance of the secondary battery.

[0057] In some embodiments, 1≤N≤5, for example, it can be a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two of these values. By controlling N within this range, the stability of the electrolyte can be effectively improved, the wetting effect of the electrolyte on the separator and the positive electrode can be improved, the gas production of the secondary battery can be effectively improved, and the cycle performance of the secondary battery can be effectively improved.

[0058] In some embodiments, 0.2≤Z≤0.7, for example, can be a range of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or any two of these values. By controlling Z within this range, the processing performance of the positive electrode slurry containing lithium replenishing agent can be effectively improved, the gelation phenomenon can be avoided, the release of lithium source can be more effectively increased, the lithium consumption of the negative electrode SEI film formation reaction can be fully replenished, the insertion and extraction process of lithium ions in the positive electrode active material can be promoted, the by-products (such as active oxygen) generated by the first lithium replenishing agent can be more effectively removed by catalytic reaction, the side reactions of the electrolyte can be suppressed, and the cycle performance of the secondary battery can be further improved and the impedance can be reduced.

[0059] In some embodiments, the second lithium supplement includes at least one of Li2NiO2, Li6CoO4, Li2O, Li2C2O4, Li2C3O5, Li2C4O4, and Li2C4O6.

[0060] In some embodiments, the second lithium supplement includes at least one of Li2NiO2, Li6CoO4, Li2O, and Li2C2O4.

[0061] In some embodiments, the surfaces of the first lithium supplement and the second lithium supplement mentioned in this application may include a coating layer, which may include at least one of poly(3,4-ethylenedioxythiophene), polypyrrole, polyacrylic acid, AlF3, V2O5, Al2O3, ZrO2, TiO2, ZnO, Co3O4, SiO2, AlPO4, FePO4, Co3(PO4)2, Ni3(PO4)2, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, graphene, and carbon nanotubes.

[0062] The content and mass ratio of the first lithium replenisher and the second lithium replenisher can be obtained by testing the following method: scrape the positive electrode active material layer from the positive electrode sheet, dissolve it with NMP, filter it through a microporous membrane to separate the lithium replenisher and the positive electrode active material, and then characterize the lithium replenisher by ICP to obtain the content of the first lithium replenisher and the second lithium replenisher, thereby obtaining their mass ratio.

[0063] The test method for the M element in the second lithium supplement is as follows: cut the positive electrode sheet into small circular pieces with a diameter of 12±2mm, take 20 small circular pieces for ICP test, and refer to EPA 6010D-2018 Inductively Coupled Plasma Atomic Emission Spectrometry.

[0064] The content of each component in the electrolyte can be obtained by GC-MS testing.

[0065] In some embodiments, the sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methylene disulfonate (MMDS), vinyl sulfite (ES), and 1,4-butanesulfonate lactone.

[0066] In some embodiments, the electrolyte further includes a first additive, which includes at least one of tris(trimethylsilane)phosphate (TMSP) and lithium difluorobis(oxalato)phosphate (LiDFOP). The first additive is present in the electrolyte at a mass percentage of 0.5% to 5%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of these values. By adding such a first additive to the electrolyte, the electrochemical and thermal stability of the electrolyte can be effectively improved, the decomposition and volatilization of the electrolyte can be reduced, the formation of the SEI film can be promoted, and the cycle performance of the secondary battery can be further improved.

[0067] In some embodiments, the mass ratio of the sulfur-containing additive to the first additive is 1:(2 to 10), for example, it can be 1:2, 1:4, 1:6, 1:10 or any two of these values. By controlling the mass ratio of the sulfur-containing additive to the first additive within this range, it is possible to promote the formation of a denser and more stable SEI film and further improve battery gas production, thereby further improving cycle performance and reducing impedance.

[0068] In some implementations, the following condition is met: 3≤N / Z≤20. For example, it can be a range of 3, 5, 6, 8, 10, 12, 15, 16, 18, 20 or any two of these values. In particular, controlling the N / Z ratio within this range can more effectively remove byproducts generated by the lithium replenishment agent, improve gas generation, further enhance cycle performance, and reduce impedance.

[0069] In some implementations, the following condition is satisfied: 0.5≤Y / Z≤10, for example, it can be a range of 0.5, 0.8, 1, 2, 4, 5, 6, 8, 10 or any two of these values. By controlling Y / Z within this range, a more stable and dense SEI film can be formed, reducing interfacial side reactions, effectively suppressing high-temperature gas generation, effectively improving the cycle life of the secondary battery, and reducing DCR.

[0070] In some embodiments, the cyclic carbonate includes at least one of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, ethyleneene carbonate, and ethylene ethylene carbonate.

[0071] In some embodiments, the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0072] In some embodiments, the cyclic carbonate includes propylene carbonate and ethylene carbonate; the mass ratio of propylene carbonate to ethylene carbonate in the electrolyte is (0.5-5):(0.5-5).

[0073] In some embodiments, the cyclic carbonate is present in the organic solvent at a mass percentage of 9-42%.

[0074] In some embodiments, the chain carbonate has a mass percentage of 58-91% in the organic solvent.

[0075] In some embodiments, the electrolyte further includes a lithium salt, at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorophosphate, and lithium tetrafluorophosphate.

[0076] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 to 2 M, for example, it can be 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.8 M, 2 M or any two of these values.

[0077] In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0078] In some embodiments, the concentration of lithium hexafluorophosphate in the electrolyte is 0.4 to 1.8 M, for example, it can be 0.4 M, 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.8 M or any two of these values.

[0079] In some embodiments, the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 to 1.6 M, for example, it can be 0.1 M, 0.2 M, 0.4 M, 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.6 M, or any two of these values.

[0080] This application uses a combination of lithium hexafluorophosphate and lithium difluorosulfonylimide as a lithium salt, which can improve the lithium ion transference number and antioxidant performance, as well as have good aluminum foil passivation ability. It has good compatibility with the electrolyte additive system and separator of this application, improves stability, repairs the electrode / electrolyte interface, improves ionic conductivity, and promotes the conduction of lithium ions in the bulk phase.

[0081] In some embodiments, the positive electrode active material may be a known positive electrode active material for secondary batteries. As a non-limiting example, the positive electrode active material may include lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials or substances, and other conventional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Non-limiting examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0082] In some embodiments, the positive electrode active material includes a lithium phosphate, wherein the lithium phosphate comprises a general chemical formula of Li. e Fe 1-f M f Compounds of PO4, wherein 0.8≤e≤1.2, 0≤f≤0.9, and M is selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, and Ti.

[0083] This application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector; the positive active material layer includes a lithium replenishing agent and a positive active material; the lithium replenishing agent includes a first lithium replenishing agent and a second lithium replenishing agent, the first lithium replenishing agent including Li5FeO4, and the second lithium replenishing agent including Li a M b O d Wherein, 1.5≤a≤6, 0≤b≤2, 1≤d≤6, and M includes at least one of Mg, Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, Sn, Si, B, and C; the positive electrode active material includes lithium phosphate.

[0084] The diaphragm includes a polyolefin membrane and a ceramic layer disposed on at least one surface of the polyolefin membrane;

[0085] The electrolyte includes cyclic carbonates, chain carbonates, and sulfur-containing additives;

[0086] The secondary battery satisfies: For example, it can be 0.17, 0.18, 0.2, 0.3, 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.18 or a range of any two of these values;

[0087] Where Xμm is the thickness of the ceramic layer;

[0088] Y% is the mass percentage of the sulfur-containing additive in the electrolyte;

[0089] N is the mass ratio of the first lithium supplementer and the second lithium supplementer in the positive electrode active material layer;

[0090] Z represents the mass ratio of cyclic carbonates to chain carbonates in the electrolyte.

[0091] Especially when the positive electrode active material contains lithium phosphate, the mass ratio of the first lithium supplementer and the second lithium supplementer, the mass ratio of cyclic carbonate to chain carbonate in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator can meet the above conditions, which can make the secondary battery system more compatible, the overall performance of the secondary battery better, and further improve the cycle performance of the secondary battery and reduce impedance.

[0092] In some embodiments, there are no particular limitations on the type of positive current collector, which may be any material known to be suitable for use as a positive current collector.

[0093] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0094] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0095] In some embodiments, the positive electrode active material layer also includes a conductive agent and a positive electrode binder.

[0096] In some embodiments, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0097] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0098] In some embodiments, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0099] In some embodiments, the negative electrode active material layer further includes a conductive agent and a negative electrode binder.

[0100] In some embodiments, the types of conductive agents mentioned in this application are not limited, and known conductive agents can be used.

[0101] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0102] In some embodiments, the type of adhesive mentioned in this application is not limited, and known adhesives may be used.

[0103] In some embodiments, the positive electrode binder and negative electrode binder mentioned each independently include at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0104] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0105] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0107] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0108] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0109] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0110] The present application is further illustrated below with specific embodiments:

[0111] Example 1

[0112] A method for preparing a secondary battery includes the following steps:

[0113] (1) Electrolyte preparation: At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), EC, PC, EMC, and DMC were mixed evenly at a mass ratio of 2:1:6:4. Molecular sieves were used to remove water, resulting in a mixed solvent. A mixed lithium salt (0.8 M LiPF6 / 0.2 M LiFSI) was added to the mixed solvent in batches, and the mixture was continuously stirred and cooled with dry ice to ensure that the electrolyte temperature did not rise by more than 2 °C. Finally, a colorless and transparent liquid was obtained. Then, tris(trimethylsilane) phosphate and methylene methane disulfonate were added to obtain the electrolyte, wherein the mass percentage of tris(trimethylsilane) phosphate was 2% and the mass percentage of methylene methane disulfonate was 0.3%.

[0114] (2) Preparation of the positive electrode sheet: LiFePO4, lithium supplement, conductive agent SP, and binder PVDF were mixed in a mass ratio of 93:3:2:2. After adding NMP, the mixture was stirred under vacuum until the system became homogeneous to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil, dried in an oven, and then cold-pressed to obtain the positive electrode film. The compaction density of the positive electrode film was 2.45 g / cm³. 3 .

[0115] (3) Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:Super P:SBR=94:3:3 and evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0116] (4) Separator: A 7μm thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and PVDF binder were mixed evenly in an appropriate amount of deionized water at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 60%. The ceramic slurry was coated onto both surfaces of the substrate using a coating machine and dried to form a ceramic coating with a single-sided thickness of 3μm. The coating machine used a gravure roller with a line count of 150 LPI, a coating speed of 10 m / min, a drying temperature of 40℃, and a drying time of 2 hours. The resulting diaphragm was then obtained.

[0117] (5) Fabrication of secondary battery: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive electrode and negative electrode. After winding, hot pressing and shaping, the tabs are welded to obtain the bare cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery. After standing, formation and capacity testing, the secondary battery is completed.

[0118] The parameters of Example 1 are shown in Tables 1 and 2.

[0119] Examples 2-4

[0120] The difference between Examples 2-4 and Example 1 is that the value of Z is adjusted by adjusting the mass ratio of EC, PC, EMC, and DMC.

[0121] Example 5

[0122] Example 5 differs from Example 1 in that the type of the second lithium supplement is changed.

[0123] Examples 6-13, Comparative Examples 1-4

[0124] Examples 6-13 and Comparative Examples 1-4 differ from Example 1 in that the mass ratios of EC, PC, EMC, and DMC, the amount of sulfur-containing additives added, and the mass ratio of Li5FeO4 and Li2NiO2 are adjusted, thereby adjusting the values ​​of Y, N, and Z.

[0125] Examples 14-16

[0126] The difference between Examples 14-16 and Example 1 is that the mass ratio of Li5FeO4 and Li2NiO2 is adjusted, thereby adjusting the value of N.

[0127] Examples 17-19

[0128] The difference between Examples 17-19 and Example 1 is that the thickness of the ceramic layer is adjusted, thereby adjusting the value of X.

[0129] Examples 20-23

[0130] The difference between Examples 20-23 and Example 1 is that the amount of sulfur-containing additive (MMDS) added is adjusted, thereby adjusting the value of Y.

[0131] Examples 24-25

[0132] The difference between Examples 24 and 25 and Example 1 is that the mass ratio of EC, PC, EMC, and DMC, the amount of sulfur-containing additives added, the mass ratio of Li5FeO4 and Li2NiO2, and the thickness of the ceramic layer are adjusted, thereby adjusting the values ​​of X, Y, N, and Z.

[0133] Example 26

[0134] Example 26 differs from Example 1 in that the types of sulfur-containing additives and the first additive are changed.

[0135] Examples 27-31

[0136] The difference between Examples 27-31 and Example 1 is that the amount of the first additive is changed.

[0137] Example 32

[0138] The difference between Example 32 and Example 1 is that the type of organic solvent is changed.

[0139] Comparative Examples 5-6

[0140] The lithium supplement in Comparative Example 5 was a single Li5FeO4 (the total amount of lithium supplement remained unchanged).

[0141] Preparation of the positive electrode sheet in Comparative Example 5: LiFePO4, Li5FeO4, conductive agent SP, and binder PVDF were mixed in a mass ratio of 93:3:2:2. NMP was added, and the mixture was stirred under vacuum until the system became homogeneous, thus obtaining the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil, dried in an oven, and then cold-pressed to obtain the positive electrode film. The compacted density of the positive electrode film was 2.45 g / cm³. 3 .

[0142] The lithium supplement in Comparative Example 6 was a single Li2NiO2 (the total amount of lithium supplement remained unchanged).

[0143] Preparation of the positive electrode sheet in Comparative Example 6: LiFePO4, Li2NiO2, conductive agent SP, and binder PVDF were mixed in a mass ratio of 93:3:2:2. NMP was added, and the mixture was stirred under vacuum until the system became homogeneous, thus obtaining the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil, dried in an oven, and then cold-pressed to obtain the positive electrode film. The compacted density of the positive electrode film was 2.45 g / cm³. 3 .

[0144] Comparative Examples 7-8

[0145] The difference between Comparative Example 7 and Example 1 is that the organic solvent is different, and Comparative Example 7 does not contain cyclic carbonates.

[0146] Preparation of the electrolyte for Comparative Example 7: At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), EMC and DMC were mixed evenly at a mass ratio of 6:4. Molecular sieves were used to remove water, resulting in a mixed solvent. A mixed lithium salt (0.8 M LiPF6 / 0.2 M LiFSI) was added to the mixed solvent in batches, and the mixture was continuously stirred and cooled with dry ice to ensure that the electrolyte temperature did not rise by more than 2 °C. Finally, a colorless and transparent liquid was obtained. Then, tris(trimethylsilane) phosphate and methylene methane disulfonate were added to obtain the electrolyte, wherein the mass percentage of tris(trimethylsilane) phosphate was 2% and the mass percentage of methylene methane disulfonate was 0.3%.

[0147] The difference between Comparative Example 8 and Example 1 is that the organic solvent is different, and Comparative Example 8 does not contain chain carbonates.

[0148] Preparation of the electrolyte for Comparative Example 8: At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), EC and PC were mixed thoroughly at a mass ratio of 2:1. Molecular sieves were used to remove water, resulting in a mixed solvent. A mixed lithium salt (0.8 M LiPF6 / 0.2 M LiFSI) was added to the mixed solvent in batches, and the mixture was continuously stirred and cooled with dry ice to ensure that the electrolyte temperature did not rise by more than 2 °C. Finally, a colorless and transparent liquid was obtained. Then, tris(trimethylsilane) phosphate and methylene methane disulfonate were added to obtain the electrolyte, wherein the mass percentage of tris(trimethylsilane) phosphate was 2% and the mass percentage of methylene methane disulfonate was 0.3%.

[0149] Table 1 Parameter Table

[0150]

[0151] Table 2 Parameter Table

[0152]

[0153]

[0154]

[0155] Performance testing

[0156] 1. Room temperature DCR test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were charged to 3.65V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, they were pulsed at 10C constant current for 10 seconds. The SOC was then adjusted to 50% again using the above method, and charged for another 10 seconds. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current. After 500 cycles, the DCR was tested again. The DCR change rate was calculated as (DCR after 500 cycles - initial DCR) / initial DCR * 100%.

[0157] 2. Room Temperature Cycling Performance Test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were subjected to charge-discharge cycle tests within the range of 2.5~3.65V at a charge-discharge rate of 1C / 1C. The discharge specific capacity of the secondary battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle * 100%.

[0158] 3. High-temperature storage gas generation test: At 25±2℃, the secondary batteries obtained from each implementation case and comparative example were charged to 3.65V at 1C (CC-CV) with a cutoff current of 0.05C; the initial volume V0 was tested using the water displacement method; then the secondary batteries were placed in a 70℃ high and low temperature chamber and the volume V of the secondary batteries was tested after 60 days; the expansion rate of the secondary battery = (volume V after 60 days - initial volume V0) / initial volume * 100%.

[0159] Table 3 Performance Test Table

[0160]

[0161]

[0162] As can be seen from Table 1, this application significantly improves the gas generation problem of secondary batteries, effectively improves the cycle life of secondary batteries, and reduces DCR by controlling the mass ratio of the first lithium supplementer and the second lithium supplementer, the mass ratio of cyclic carbonate to chain carbonate in the electrolyte, the mass percentage content of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator to satisfy: 0.17≤W≤11.18.

[0163] Comparing Examples 1-23 with Examples 24 and 25, it can be seen that this application further improves the cycle life of the secondary battery and reduces the DCR by controlling the mass ratio of the first lithium replenisher and the second lithium replenisher, the mass ratio of cyclic carbonates to chain carbonates in the electrolyte, the mass percentage of sulfur-containing additives in the electrolyte, and the thickness of the ceramic layer in the separator to satisfy: 0.35≤W≤6.12.

[0164] Comparing Example 1 with Comparative Examples 5-6, it can be seen that by simultaneously adding the first lithium replenisher and the second lithium replenisher, this application significantly improves the cycle life of the secondary battery and reduces the DCR.

[0165] Comparing Example 1 with Comparative Examples 7-8, it can be seen that the present application significantly improves the cycle life of the secondary battery and reduces the DCR by simultaneously adding cyclic carbonate and chain carbonate.

[0166] Comparing Examples 1 and 32, it can be seen that the present application uses propylene carbonate and ethylene carbonate as cyclic carbonates, which further improves the cycle life of the secondary battery and reduces the DCR.

[0167] Comparing Examples 1, 6-9, it can be seen that by controlling 3≤N / Z≤20, the cycle life of the secondary battery is further improved and the DCR is reduced.

[0168] Comparing Examples 1, 10-13, it can be seen that by controlling 0.5≤Y / Z≤10, the cycle life of the secondary battery is further improved and the DCR is reduced.

[0169] Comparing Examples 1 and 27-31, it can be seen that by controlling the mass ratio of sulfur-containing additive to the first additive to be 1:(2-30), the cycle life of the secondary battery is further improved and the DCR is reduced.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, characterized in that, The system includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a lithium replenishing agent. The lithium replenishing agent includes a first lithium replenishing agent and a second lithium replenishing agent, wherein the first lithium replenishing agent includes Li5FeO4, and the second lithium replenishing agent includes Li a M b O d Wherein, 1.5≤a≤6, 0≤b≤4, 1≤d≤6, and M includes at least one of Mg, Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, Sn, Si, B, and C; The diaphragm includes a polyolefin membrane and a ceramic layer disposed on at least one surface of the polyolefin membrane; The electrolyte includes cyclic carbonates, chain carbonates, and sulfur-containing additives; The secondary battery satisfies: , 0.17≤W≤11.18; Where X μm is the thickness of the ceramic layer, 1≤X≤5; Y% is the mass percentage of the sulfur-containing additive in the electrolyte, where 0.1 ≤ Y ≤ 5; N is the mass ratio of the first lithium supplementer and the second lithium supplementer in the positive electrode active material layer, where 1 ≤ N ≤ 5; Z is the ratio of the mass of cyclic carbonate to the mass of chain carbonate in the electrolyte, where 0.2 ≤ Z ≤ 0.

7. The sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, vinyl sulfate, methylene disulfonate, vinyl sulfite, and 1,4-butanesulfonate lactone.

2. The secondary battery according to claim 1, characterized in that, The secondary battery satisfies the following conditions: 0.35 ≤ W ≤ 6.

12.

3. The secondary battery according to claim 1, characterized in that, The electrolyte further includes a first additive, which includes at least one of tris(trimethylsilane) phosphate and lithium difluorobis(oxalato) phosphate, and the first additive has a mass percentage of 0.5-5% in the electrolyte.

4. The secondary battery according to claim 3, characterized in that, The mass ratio of the sulfur-containing additive to the first additive is 1:(2~10).

5. The secondary battery according to claim 1, characterized in that, It satisfies: 3≤N / Z≤20.

6. The secondary battery according to claim 1, characterized in that, It satisfies: 0.5≤Y / Z≤10.

7. The secondary battery according to claim 1, characterized in that, The cyclic carbonate includes at least one of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate; and / or The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

8. The secondary battery according to claim 7, characterized in that, The cyclic carbonates include propylene carbonate and ethylene carbonate; the mass ratio of propylene carbonate to ethylene carbonate in the electrolyte is (0.5~5):(0.5~5).

9. The secondary battery according to claim 1, characterized in that, Based on the total mass of the cyclic carbonates and chain carbonates, the mass percentage of the cyclic carbonates is 9-42%; and / or Based on the total mass of the cyclic carbonate and the chain carbonate, the chain carbonate has a mass percentage content of 58-91%.

10. An electrical device, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 9, wherein the secondary battery serves as the power supply for the electrical device.

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