Secondary battery and electric device including the same

Abstract

The invention provides a secondary battery and a power device including the same. The secondary battery comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises an additive capable of performing nucleophilic reaction with a cyclic carbonate compound. The secondary battery of the present application has high storage performance.

Description

[0001] This application is a divisional application based on the invention with application number 202310675468.X, application date June 7, 2023, applicant CATL, and invention title "Secondary Battery and Electrical Device Including the Secondary Battery". Technical Field

[0002] This application relates to the field of battery technology, and more particularly to a secondary battery and an electrical device including the secondary battery. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher performance requirements have been placed on them.

[0004] Therefore, how to improve the storage performance of secondary batteries has become an urgent problem to be solved in this field. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device including the secondary battery, the secondary battery having high storage performance.

[0006] To achieve the above objectives, a first aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including an additive capable of nucleophilic reaction with cyclic carbonate compounds.

[0007] Therefore, the secondary battery of this application improves the storage performance of the secondary battery by including additives in the negative electrode film layer that can undergo nucleophilic reactions with cyclic carbonate compounds.

[0008] In any embodiment, the additive includes at least one of the following: sulfur-containing substances, selenium-containing substances, composites of sulfur-containing substances and carbon-based materials, composites of selenium-containing substances and carbon-based materials, sulfur-containing substances with a carbon coating layer, and selenium-containing substances with a carbon coating layer. Optionally, the sulfur-containing substance includes at least one of elemental sulfur, lithium sulfide, and sodium sulfide. Optionally, the selenium-containing substance includes at least one of elemental selenium, lithium selenide, sodium selenide, cobalt selenide, and nickel selenide. Optionally, the carbon-based material includes nano-carbon-based materials and graphene; optionally, the nano-carbon-based material includes carbon nanotubes. The sulfur-containing and selenium-containing substances undergo a reduction reaction during battery charging and discharging, and undergo a nucleophilic reaction with cyclic carbonate compounds to participate in the formation of an SEI film. Furthermore, by combining with carbon nanotubes or having a carbon coating layer, the conductivity and fast-charging performance of the battery can be improved.

[0009] In any embodiment, based on the total mass of the negative electrode film, the mass percentage of the additive is less than or equal to 10%, and can be selected as 0.5%-5%. Therefore, while achieving high storage performance, the battery can also achieve excellent conductivity and fast charging performance.

[0010] In any embodiment, the particle size Dv50 of the additive is 50nm-500nm, optionally 100nm-200nm. By controlling the particle size within the above range, a larger specific surface area can be obtained, thereby increasing the reactivity.

[0011] In any embodiment, the negative electrode film layer includes a negative electrode active material, which includes a silicon-based material; optionally, the silicon-based material accounts for more than or equal to 5% by mass in the negative electrode active material, more preferably 5%-25%; optionally, the silicon-based material includes at least one of elemental silicon, silicon-carbon composite material, and silicon oxide compound. Adding a silicon-based material to the negative electrode film layer can improve the energy density of the battery.

[0012] In any embodiment, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer being disposed between the negative electrode current collector and the first negative electrode film layer, and the first negative electrode film layer and / or the second negative electrode film layer including the additive.

[0013] In any embodiment, in the first negative electrode film layer, the mass percentage of the additive is greater than 0% and less than or equal to 10%, which can be selected as 0.5%-5%, and in the second negative electrode film layer, the mass percentage of the additive is 0%-5%, which can be selected as 0.1%-2%.

[0014] In any embodiment, both the first negative electrode film layer and the second negative electrode film layer include the additive, and the additive materials in the first negative electrode film layer and the second negative electrode film layer may be the same or different.

[0015] In any embodiment, both the first negative electrode film layer and the second negative electrode film layer include the additive; in the first negative electrode film layer, the mass percentage of the additive is denoted as A1, and in the second negative electrode film layer, the mass percentage of the additive is denoted as A2; the secondary battery satisfies: A1 / A2>1; optionally, 2≤A1 / A2≤10.

[0016] In any embodiment, the first negative electrode film layer includes a first negative electrode active material, the second negative electrode film layer includes a second negative electrode active material, and the first negative electrode active material and / or the second negative electrode active material includes the silicon-based material; optionally, both the first negative electrode active material and the second negative electrode active material include the silicon-based material, and the mass percentage of the silicon-based material in the first negative electrode active material is greater than the mass percentage of the silicon-based material in the second negative electrode active material.

[0017] In any embodiment, the silicon-based material accounts for more than or equal to 5% of the mass of the first negative electrode active material, and can be selected as 5%-25%.

[0018] In any embodiment, the first negative electrode active material and / or the second negative electrode active material further include a carbon material; optionally, the carbon material includes graphite, and more preferably, the powder is pressed at 1.8 g / cm³. 3 The above high-pressure solid graphite.

[0019] This application achieves superior storage performance and conductivity in the secondary battery through the aforementioned double-layer negative electrode film configuration.

[0020] In any embodiment, the secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a lithium replenishing agent; optionally, the lithium replenishing agent includes at least one of lithium sulfide, lithium selenide, lithium oxide, and lithium nitride. By including a lithium replenishing agent in the positive electrode film layer, active lithium can be replenished, enabling the secondary battery to have high energy density and fast charging performance.

[0021] In any embodiment, the secondary battery includes an electrolyte comprising a cyclic carbonate compound; optionally, the cyclic carbonate compound includes at least one selected from ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, and butenyl carbonate. This allows it to undergo a nucleophilic reaction with additives in the negative electrode film, participating in the formation of the SEI film and improving the storage performance of the secondary battery.

[0022] In any embodiment, the negative electrode film layer simultaneously comprises high-valence sulfur and low-valence sulfur, and / or simultaneously comprises high-valence selenium and low-valence selenium; optionally, the high-valence sulfur comprises at least one of +4-valence sulfur and +6-valence sulfur; optionally, the S2p peak of the high-valence sulfur is 168.5 eV-171 eV; optionally, the low-valence sulfur comprises -2-valence sulfur to -1 / 6-valence sulfur, optionally, the S2p peak of the low-valence sulfur is 161 eV-166.5 eV. Optionally, the high-valence selenium comprises at least one of +4-valence selenium and +6-valence selenium; optionally, the Se3d peak of the high-valence selenium is 58.9 eV-61.2 eV; optionally, the low-valence selenium comprises -2-valence selenium; optionally, the Se3d peak of the low-valence selenium is 54 eV-55.1 eV.

[0023] A second aspect of this application provides an electrical device that includes the secondary battery of the first aspect of this application.

[0024] The effects of the invention According to this application, a secondary battery with excellent storage performance and an electrical device incorporating the lithium-ion battery can be provided. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the negative electrode plate in the secondary battery of this application.

[0026] Explanation of reference numerals in the attached figures: 1. Negative electrode current collector; 2. Negative electrode film layer; 21. First negative electrode film layer; 22. Second negative electrode film layer Detailed Implementation The secondary battery and the electrical device including the secondary battery of this application will be described in detail below with appropriate reference to the accompanying drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0029] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0030] A rechargeable battery is a battery that can be recharged after discharge to reactivate its active materials and continue to be used; examples include lithium-ion batteries. Typically, a rechargeable battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The electrolyte, located between the positive and negative electrodes, primarily serves to conduct these active ions.

[0031] One embodiment of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including an additive capable of nucleophilic reaction with cyclic carbonate compounds.

[0032] The applicant unexpectedly discovered that when an additive capable of nucleophilic reaction with cyclic carbonate compounds is added to the negative electrode film layer, the additive reacts with the cyclic carbonate compounds in the electrolyte of the secondary battery, inducing ring-opening and forming a highly elastic PEO-like polymer. This polymer participates in the formation of the SEI to strengthen the film, reducing irreversible capacity loss caused by the frequent repair of SEI rupture and consumption of active lithium. At the same time, it forms a conductive network with high ionic conductivity, which is beneficial to the migration of active ions (such as lithium ions) in the secondary battery, reduces charge transfer impedance and electrochemical polarization, reduces polarization capacity loss, and thus improves the battery's storage performance.

[0033] The additive is not particularly limited as long as it can undergo a nucleophilic reaction with cyclic carbonate compounds. In some embodiments, the additive includes sulfur-containing and / or selenium-containing substances, such as at least one selected from elemental sulfur, lithium sulfide, sodium sulfide, elemental selenium, lithium selenide, sodium selenide, cobalt selenide, and nickel selenide. These additives undergo a reduction reaction during the charge and discharge of the battery, further reacting with the cyclic carbonate electrolyte solvent. For example, lithium sulfide reacts with ethylene carbonate to generate poly(ethylene oxide) (PEO)-like polymers, which participate in the formation of the SEI film. The specific reaction is shown below.

[0034]

[0035] In some embodiments, a composite is formed by loading sulfur-containing and / or selenium-containing substances onto a carbon-based material as a substrate. This carbon-based material includes nano-carbon materials, graphene, etc., and preferably, carbon nanotubes. Alternatively, carbon, preferably nanoporous carbon, can be used as a coating material to coat the surface of the sulfur-containing and / or selenium-containing substances, forming sulfur-containing substances with carbon coating layers and selenium-containing substances with carbon coating layers. This improves battery storage performance, conductivity, and fast-charging performance, while also reducing the amount of negative electrode conductive agent required.

[0036] In some embodiments, the additive accounts for less than or equal to 10% of the total mass of the negative electrode film, optionally ranging from 0.5% to 5%. By keeping the additive content within the above range, the battery's storage performance, conductivity, and fast-charging performance can be further improved. In some embodiments, the particle size Dv50 of the additive is 50nm-500nm, optionally ranging from 100nm-200nm. By controlling the particle size within the above range, a larger specific surface area can be obtained, increasing the reactivity.

[0037] In some embodiments, the negative electrode film layer includes a negative electrode active material, which includes a carbon material. The carbon material can be at least one of graphite (including artificial graphite and natural graphite), soft carbon, and hard carbon, preferably graphite. The negative electrode active material also includes a silicon-based material. Optionally, the silicon-based material accounts for more than or equal to 5% of the mass of the negative electrode active material, preferably 5%-25%, and more preferably 5%-20%. As the silicon-based material, for example, it includes at least one of elemental silicon, silicon-carbon composite materials, and silicon oxide compounds. Preferably, it includes a silicon oxide compound with the chemical formula SiOx, where 0 < x < 2, preferably 0.5 ≤ x ≤ 1.5, and more preferably x = 1. This silicon oxide compound exhibits high capacity performance and cycle life.

[0038] By incorporating silicon-based materials as the negative electrode active material in the negative electrode film layer, the energy density of the secondary battery can be significantly improved. However, on the other hand, silicon-based negative electrode materials undergo significant volume changes during the insertion and extraction of active ions, such as lithium ions. The electrode material is likely to experience internal stress due to the volume effect, leading to surface SEI cracking. Frequent SEI repair consumes a large amount of active lithium. Furthermore, it is prone to electrode material breakage, resulting in loss of electrical contact with the current collector. All of these factors contribute to the poor storage performance of silicon-based negative electrodes. However, the negative electrode film layer of the secondary battery of this application contains the aforementioned additives. As described above, these additives can form highly elastic polymers with cyclic carbonate compounds in the electrolyte, participating in SEI film formation. This effectively alleviates the volume expansion of the silicon-based material during charging at the negative electrode-electrolyte interface, improving battery capacity and the stability of the negative electrode-electrolyte interface. Therefore, through this embodiment, the secondary battery of this application possesses both high storage performance and high energy density.

[0039] In this application, preferably, the negative electrode film layer is configured as a double-layer structure, that is, it includes a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer is disposed between the negative electrode current collector and the first negative electrode film layer, and the first negative electrode film layer and / or the second negative electrode film layer includes the additives.

[0040] In some embodiments, the mass percentage of the additive in the first negative electrode film layer is greater than 0% and less than or equal to 10%, optionally 0.5%-5%; and / or, the mass percentage of the additive in the second negative electrode film layer is 0%-5%, optionally 0.1%-2%. When both the first and second negative electrode film layers include additives, the additives in the two layers can be the same or different. When the mass percentage of the additive in the first negative electrode film layer is denoted as A1 and the mass percentage of the additive in the second negative electrode film layer is denoted as A2, A1 / A2 > 1; preferably, 2 ≤ A1 / A2 ≤ 10.

[0041] In some embodiments, the first negative electrode film layer includes a first negative electrode active material, the second negative electrode film layer includes a second negative electrode active material, and the first negative electrode active material and / or the second negative electrode active material includes the silicon-based material. Optionally, both the first and second negative electrode active materials include the silicon-based material, and the mass percentage of the silicon-based material in the first negative electrode active material is greater than the mass percentage of the silicon-based material in the second negative electrode active material. The mass percentage of the silicon-based material in the first negative electrode active material is greater than or equal to 5%, preferably 5%-25%, and more preferably 5%-20%. The type of silicon-based material is the same as described above. In addition to the silicon-based material, the first negative electrode active material also includes a carbon material, which includes at least one of graphite, soft carbon, and hard carbon. Preferably, the carbon material includes graphite. Furthermore, the second negative electrode active material includes a carbon material, which may be the same as or different from the carbon material in the negative electrode film layer. Preferably, the carbon material includes a powder with a compressibility of 1.8 g / cm³. 3 The above high-pressure solid graphite materials.

[0042] The negative electrode sheet containing the first and second negative electrode film layers described above can be prepared, for example, as follows.

[0043] Using a double-layer coating technique, a powder with a powder density of 1.8 g / cm³ is first coated on both sides of the current collector 1. 3 The above-mentioned high-pressure compacted graphite and / or additive slurry forms the second negative electrode film layer 22. Then, a composite slurry containing graphite, silicon-based materials, additives, etc., is coated onto this layer to form the first negative electrode film layer 21, thus forming a double-layer negative electrode film layer 2, thereby obtaining the negative electrode sheet, such as... Figure 1 As shown. By using this composite slurry and double-layer coating method, the advantages of graphite and silicon-based materials are fully utilized. Through different distributions in the direction perpendicular to the current collector, the fast-charging performance of the negative electrode sheet can be improved, resulting in a negative electrode sheet with high fast-charging performance and high compaction.

[0044] In some embodiments, the negative electrode film layer simultaneously includes high-valence sulfur and low-valence sulfur, and / or simultaneously includes high-valence selenium and low-valence selenium. Optionally, the high-valence sulfur includes at least one of +4-valent sulfur and +6-valent sulfur, with an S2p peak of 168.5 eV-171 eV; the low-valence sulfur includes sulfur from -2-valent to -1 / 6-valent sulfur, with an S2p peak of 161 eV-166.5 eV. Optionally, the high-valence selenium includes at least one of +4-valent selenium and +6-valent selenium, with a Se3d peak of 58.9 eV-61.2 eV; optionally, the low-valence selenium includes -2-valent selenium, with a Se3d peak of 54 eV-55.1 eV. The formation of high-valence sulfur and high-valence selenium is due to the oxidation of alkyl sulfates and alkyl selenates after losing electrons, which participate in SEI film formation. The formation of low-valence sulfur and low-valence selenium is due to the reduction of PEO polymers after gaining electrons, which participate in SEI film formation.

[0045] In the secondary battery of this application, as an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0046] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0047] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from 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).

[0048] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0049] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0050] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active materials (carbon materials and / or silicon-based materials), the above-mentioned additives, conductive agents, binders and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0051] The secondary battery in this application includes a positive electrode.

[0052] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a lithium replenishing agent, which includes at least one of lithium sulfide, lithium selenide, lithium oxide, and lithium nitride. Since active lithium is consumed during the formation of lithium polysulfide / lithium polyselenide from sulfur-containing / selenium-containing substances in the negative electrode, including a lithium replenishing agent in the positive electrode film layer replenishes active lithium, enabling the secondary battery to have high energy density and fast-charging performance.

[0053] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0054] In some embodiments, the positive electrode active material in the positive electrode film layer may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0055] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0056] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder, lithium supplementer and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0058] In the secondary battery of this application, the electrolyte includes cyclic carbonate compounds. Preferably, the cyclic carbonate compounds include at least one selected from ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, and butenyl carbonate. These compounds can undergo nucleophilic reactions with additives in the negative electrode film layer to participate in the formation of the SEI film and improve the storage performance of the secondary battery.

[0059] In some embodiments, the electrolyte includes an organic solvent and an electrolyte salt dispersed in the organic solvent. The specific types and compositions of the organic solvent and lithium salt are not specifically limited and can be selected according to actual needs. For example, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. For the solvent, in addition to the above-mentioned cyclic carbonate compounds, it can also be selected from at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0060] The secondary battery of this application also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0061] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0062] The secondary battery of this application can be prepared using conventional methods. For example, a positive electrode, a separator, and a negative electrode are sequentially wound or stacked, with the separator acting as a separator between the positive and negative electrodes to obtain a battery cell. The battery cell is then placed in an outer packaging, and electrolyte is injected to obtain an electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging can be a soft package, such as a pouch. The material of the soft package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0063] 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.

[0064] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0065] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0066] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0067] For the aforementioned electrical devices, secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0068] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0069] Example 1 (1) Preparation of negative electrode sheet The negative electrode active material (artificial graphite and silicon suboxide in a mass ratio of 90%:10%), additive elemental sulfur (particle size Dv50=200nm), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 94.5%:2%:1%:0.5%:1%:1% to form a negative electrode slurry.

[0070] The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet is obtained.

[0071] (2) Preparation of positive electrode sheet LiNi 0.8 Co 0.1 Mn0.1 O2 (NCM811), conductive agent Super P, and binder polyvinylidene fluoride are mixed in a weight ratio of 96%:2%:2%, and an appropriate amount of solvent NMP is added. The mixture is stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0072] (3) Electrolyte In an argon atmosphere glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 4:6. Lithium LiPF6 salt was then added to dissolve the mixture and stirred until uniform. The final concentration of lithium LiPF6 salt was 12.5%, which was used as the electrolyte.

[0073] (4) Separating membrane Polyethylene film is used as the separation membrane.

[0074] (5) Lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and then wound to form a battery cell. The battery cell is placed in a battery outer packaging, followed by electrolyte injection, encapsulation, settling, formation, shaping, and capacity testing to produce a lithium-ion battery with a thickness of 4.2 mm, a width of 42 mm, and a length of 49.5 mm.

[0075] Example 2-14 The preparation method is similar to that in Example 1, except that different types or amounts of additives are used, as detailed in Table 1.

[0076] Example 15 The preparation method is similar to that in Example 1, except that the negative electrode sheet is prepared as follows: The first negative electrode active material (artificial graphite and silicon suboxide in a mass ratio of 80%:20%), a composite material of elemental sulfur and carbon nanotubes (particle size Dv50=200nm), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 94.5%:2%:1%:0.5%:1%:1% to form the first slurry.

[0077] The second negative electrode active material (artificial graphite and silicon suboxide in a mass ratio of 95%:5%), elemental selenium coated with nanoporous carbon (particle size Dv50=200nm), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96%:0.5%:1%:0.5%:1%:1% to form the second slurry.

[0078] The first and second slurries are simultaneously extruded using a dual-cavity coating device. The second slurry is coated on both surfaces of the negative electrode current collector copper foil, while the first slurry is coated on the second slurry. After drying and cold pressing, the negative electrode sheet is obtained.

[0079] Comparative Example 1 Similar to the preparation method in Example 1, the difference is that the negative electrode sheet is prepared as follows: the negative electrode active material (artificial graphite and silicon suboxide in a mass ratio of 90%:10%), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.5%:1%:0.5%:1%:1% to form a negative electrode slurry.

[0080] The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet is obtained.

[0081] Comparative Example 2 The preparation method is similar to that of Example 15, except that the preparation method of the negative electrode sheet is as follows: The first active material (artificial graphite and silicon suboxide in a mass ratio of 80%:20%), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.5%:1%:0.5%:1%:1% to form the first slurry.

[0082] The second active material (artificial graphite and silicon suboxide in a mass ratio of 95%:5%), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.5%:1%:0.5%:1%:1% to form the second slurry.

[0083] The first and second slurries are simultaneously extruded using a dual-cavity coating device. The second slurry is coated on both surfaces of the negative electrode current collector copper foil, while the first slurry is coated on the second slurry. After drying and cold pressing, the negative electrode sheet is obtained.

[0084] The secondary batteries of the above embodiments and comparative examples were tested as follows, and the results are shown in Table 1 below.

[0085] Battery test Storage performance (capacity retention rate after 100 days of storage at 60℃) The battery capacity recovery rate test process is as follows: Before storage, at 25°C, the batteries of the examples and comparative examples were charged to 4.25V with a constant current of 1 / 3C, then charged to 0.05C with a constant voltage of 4.25V, rested for 30 minutes, and then discharged to 2.8V with 1 / 3C. The resulting capacity was recorded as the initial capacity C0. After storing at 60°C for 100 days, the battery temperature was cooled to room temperature, and the above steps were repeated. The measured capacity was recorded as Cr. The battery capacity recovery rate after 100 days of storage is then calculated as H = Cr / C0 * 100%.

[0086] The higher the value of H, the better the storage performance.

[0087] Conductivity (electrode and film resistance) The rolled diaphragm is cut into a rectangle of approximately 5cm × 10cm and placed between the two electrodes of the diaphragm resistance meter. The test pressure is set to 25MPa and the holding time is 25s on the MRMS software. The software automatically reads data such as diaphragm thickness, resistance, resistivity, and conductivity, and records the resistance data.

[0088] A lower resistance value indicates better conductivity. Fast charging performance (10%-80% SOC fast charging time) The 10%-80% SOC charging time test procedure is as follows: At 25°C, the batteries in the examples and comparative examples are charged from 10% SOC to 80% SOC in steps at 1.0C / 0.8C / 0.5C / 0.33C. The charging time at which lithium plating does not occur at the negative electrode is the fast charging time of the battery at this time.

[0089] The shorter the fast charging time, the better the battery's fast charging performance.

[0090] Table 1

[0091] As can be seen from the results in Table 1 above, the secondary batteries of Examples 1 to 15 all achieved excellent storage performance compared with Comparative Examples 1 and 2.

[0092] Furthermore, compared with Examples 1-4, the additives in Examples 5-7, by adopting the form of a composite with carbon nanotubes or having a carbon coating layer, not only have excellent battery storage performance, but also reduce resistance, improve the conductivity of the secondary battery, and obtain better fast charging performance.

[0093] In Examples 8-14, compared with Example 14, Examples 8-13 achieved excellent storage performance, conductivity, and fast charging performance by making the mass ratio of the additive less than or equal to 10% relative to the total mass of the negative electrode film. Furthermore, compared with Examples 12 and 13, Examples 8-11 achieved even better storage performance, conductivity, and fast charging performance by making the mass ratio of the additive 0.5%-5% relative to the total mass of the negative electrode film.

[0094] Furthermore, in Example 15, by making the negative electrode film layer a double-layer structure, the storage performance and fast charging performance of the secondary battery can be further improved.

[0095] In contrast, Comparative Examples 1 and 2, since they do not contain the specific additives described in this application, failed to improve storage performance and could not achieve the technical effects described in this application.

[0096] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising an additive capable of nucleophilic reaction with a cyclic carbonate compound.

2. The secondary battery according to claim 1, wherein, The additive includes at least one of the following: sulfur-containing substances, selenium-containing substances, complexes of sulfur-containing substances and carbon-based materials, complexes of selenium-containing substances and carbon-based materials, sulfur-containing substances with carbon coatings, or selenium-containing substances with carbon coatings. Optionally, the sulfur-containing substance includes at least one of elemental sulfur, lithium sulfide, or sodium sulfide; Optionally, the selenium-containing substance includes at least one of elemental selenium, lithium selenide, sodium selenide, cobalt selenide, or nickel selenide; Optionally, the carbon-based material includes nano-carbon-based materials and / or graphene; alternatively, the nano-carbon-based material includes carbon nanotubes.

3. The secondary battery according to claim 1 or 2, wherein, Based on the total mass of the negative electrode film, the mass percentage of the additive is less than or equal to 10%, and can be selected as 0.5%-5%.

4. The secondary battery according to any one of claims 1-3, wherein, The particle size Dv50 of the additive is 50nm-500nm, and can be selected as 100nm-200nm.

5. The secondary battery according to any one of claims 1-4, wherein, The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Optionally, the silicon-based material accounts for more than or equal to 5% of the mass of the negative electrode active material, and optionally more than or equal to 10%. Optionally, the silicon-based material includes at least one of elemental silicon, silicon-carbon composite materials, and silicon oxide compounds.

6. The secondary battery according to any one of claims 1-5, wherein, The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is disposed between the negative electrode current collector and the first negative electrode film layer. The first negative electrode film layer and / or the second negative electrode film layer include the additive.

7. The secondary battery according to claim 6, wherein, In the first negative electrode film layer, the mass percentage of the additive is greater than 0% and less than or equal to 10%, and can be selected as 0.5%-5%. In the second negative electrode film layer, the mass percentage of the additive is 0%-5%, and can be selected as 0.1%-2%.

8. The secondary battery according to claim 6 or 7, wherein, Both the first negative electrode film layer and the second negative electrode film layer include the additive; In the first negative electrode film layer, the mass percentage of the additive is denoted as A1, and in the second negative electrode film layer, the mass percentage of the additive is denoted as A2; the secondary battery satisfies: A1 / A2>1; optionally, 2≤A1 / A2≤10.

9. The secondary battery according to any one of claims 6-8, wherein, Both the first negative electrode film layer and the second negative electrode film layer include the additive, and the additives in the first negative electrode film layer and the second negative electrode film layer may be made of the same or different materials.

10. The secondary battery according to any one of claims 6-9, wherein, The first negative electrode film layer includes a first negative electrode active material, the second negative electrode film layer includes a second negative electrode active material, and the first negative electrode active material and / or the second negative electrode active material includes the silicon-based material; Optionally, both the first negative electrode active material and the second negative electrode active material include the silicon-based material, and the mass percentage of the silicon-based material in the first negative electrode active material is greater than the mass percentage of the silicon-based material in the second negative electrode active material.

11. The negative electrode sheet according to claim 10, wherein, The first negative electrode active material and / or the second negative electrode active material further include carbon materials; optionally, the carbon materials include graphite.

12. The secondary battery according to any one of claims 1-11, wherein, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a lithium replenishing agent; Optionally, the lithium supplement includes at least one of lithium sulfide, lithium selenide, lithium oxide, and lithium nitride.

13. The secondary battery according to any one of claims 1-12, wherein, The secondary battery includes an electrolyte, which includes cyclic carbonate compounds. Optionally, the cyclic carbonate compound includes at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, and butene carbonate.

14. The secondary battery according to any one of claims 1-13, wherein, The negative electrode film layer simultaneously includes high-valence sulfur and low-valence sulfur, and / or, the negative electrode film layer simultaneously includes high-valence selenium and low-valence selenium; Optionally, the high-valence sulfur includes at least one of +4-valent sulfur and +6-valent sulfur; Optionally, the S2p peak of the high-valence sulfur is 168.5-171 eV; Optionally, the low-valence sulfur includes sulfur with a valence of -2 to -1 / 6. Optionally, the S2p peak of the low-valence sulfur is 161-166.5 eV; Optionally, the high-valence selenium includes at least one of +4-valent selenium and +6-valent selenium; Optionally, the Se3d spectral peak of the high-valence selenium is 58.9-61.2 eV; Optionally, the low-valence selenium includes divalent selenium; Optionally, the Se3d spectral peak of the low-valence selenium is 54-55.1 eV.

15. An electrical device comprising a secondary battery as described in any one of claims 1-14.

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