Secondary battery and electric device comprising same

Abstract

A secondary battery and an electric device comprising same. The secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, with the negative electrode film layer comprising an additive that can undergo a nucleophilic reaction with a cyclic carbonate compound. The secondary battery has high storage performance.

Description

Secondary battery and electric device including the same

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202310675468.X, filed on June 7, 2023, entitled “Secondary Battery and Electrical Device Including the Secondary Battery,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device including the secondary battery. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have made great progress, higher performance requirements have also been placed on them.

[0005] Therefore, how to make secondary batteries have better storage performance has become an urgent problem to be solved in this field.

[0006] Summary of the Invention

[0007] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a secondary battery having high storage performance and an electric device including the secondary battery.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, including a negative electrode plate, the negative electrode plate including a negative electrode collector and a negative electrode film layer arranged on at least one surface of the negative electrode collector, the negative electrode film layer including an additive capable of undergoing nucleophilic reaction with a cyclic carbonate compound.

[0009] Therefore, the secondary battery of the present application improves the storage performance of the secondary battery by making the negative electrode film layer include an additive capable of undergoing a nucleophilic reaction with the cyclic carbonate compound.

[0010] In any embodiment, the additive includes at least one of a sulfur-containing substance, a selenium-containing substance, a composite of a sulfur-containing substance and a carbon-based material, a composite of a selenium-containing substance and a carbon-based material, a sulfur-containing substance with a carbon coating, and a selenium-containing substance with a carbon coating; 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 a nanocarbon-based material and graphene, and optionally, the nanocarbon-based material includes carbon nanotubes. The sulfur-containing substance and the selenium-containing substance undergo a reduction reaction during battery charging and discharging, undergo a nucleophilic reaction with cyclic carbonate compounds, and participate in the formation of an SEI film. In addition, by being compounded with carbon nanotubes or having a carbon coating, the conductivity and fast charging performance of the battery can be improved.

[0011] In any embodiment, the additive accounts for less than or equal to 10% by mass of the total mass of the negative electrode film layer, and can be optionally 0.5%-5%. This allows the battery to achieve high storage performance while also achieving excellent conductivity and fast charging performance.

[0012] In any embodiment, the particle size Dv50 of the additive is 50 nm to 500 nm, optionally 100 nm to 200 nm. By controlling the particle size within the above range, a larger specific surface area can be obtained, thereby increasing the reaction activity.

[0013] 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 5% or more, and more preferably 5% to 25% by weight of the negative electrode active material. Optionally, the silicon-based material includes at least one of elemental silicon, a silicon-carbon composite material, and a silicon-oxygen compound. Adding a silicon-based material to the negative electrode film layer can increase the energy density of the battery.

[0014] 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 is arranged 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 include additives.

[0015] In any embodiment, in the first negative electrode film layer, the mass proportion of the additive is greater than 0% and less than or equal to 10%, and can be optionally 0.5%-5%. In the second negative electrode film layer, the mass proportion of the additive is 0%-5%, and can be optionally 0.1%-2%.

[0016] In any embodiment, both the first negative electrode film layer and the second negative electrode film layer include additives, and the materials of the additives in the first negative electrode film layer and the second negative electrode film layer are the same or different.

[0017] In any embodiment, both the first negative electrode film layer and the second negative electrode film layer include additives; in the first negative electrode film layer, the mass proportion of the additive is recorded as A1, and in the second negative electrode film layer, the mass proportion of the additive is recorded as A2; the secondary battery satisfies: A1 / A2>1; optionally, 2≤A1 / A2≤10.

[0018] 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 include a silicon-based material; optionally, both the first negative electrode active material and the second negative electrode active material include a silicon-based material, and the mass proportion of the silicon-based material in the first negative electrode active material is greater than the mass proportion of the silicon-based material in the second negative electrode active material.

[0019] In any embodiment, the mass proportion of the silicon-based material in the first negative electrode active material is greater than or equal to 5%, and can be optionally 5%-25%.

[0020] In any embodiment, the first negative electrode active material and / or the second negative electrode active material further comprises a carbon material; optionally, the carbon material comprises graphite, and more optionally, high-density graphite with a powder pressure of more than 1.8 g / cm 3 .

[0021] The present application uses the above-mentioned double-layer negative electrode film configuration to enable the secondary battery to obtain more excellent storage performance and conductivity.

[0022] In any embodiment, the secondary battery includes a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector, the positive electrode film including a lithium replenisher; optionally, the lithium replenisher includes at least one of lithium sulfide, lithium selenide, lithium oxide, and lithium nitride. By including the lithium replenisher in the positive electrode film, active lithium can be replenished, thereby enabling the secondary battery to have high energy density and fast charging performance.

[0023] In any embodiment, the secondary battery includes an electrolyte comprising a cyclic carbonate compound; optionally, the cyclic carbonate compound comprises at least one of ethylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, vinylene carbonate, and butylene carbonate. The cyclic carbonate compound thus undergoes a nucleophilic reaction with an additive in the negative electrode film layer, participating in the formation of an SEI film and improving the storage performance of the secondary battery.

[0024] In any embodiment, the negative electrode film layer includes both high-valent sulfur and low-valent sulfur, and / or the negative electrode film layer includes both high-valent selenium and low-valent selenium. Optionally, the high-valent sulfur includes at least one of +4-valent sulfur and +6-valent sulfur. Optionally, the S2p peak of the high-valent sulfur is 168.5 eV-171 eV. Optionally, the low-valent sulfur includes -2-valent sulfur to -1 / 6-valent sulfur. Optionally, the S2p peak of the low-valent sulfur is 161 eV-166.5 eV. Optionally, the high-valent selenium includes at least one of +4-valent selenium and +6-valent selenium. Optionally, the Se3d peak of the high-valent selenium is 58.9 eV-61.2 eV. Optionally, the low-valent selenium includes -2-valent selenium. Optionally, the Se3d peak of the low-valent selenium is 54 eV-55.1 eV.

[0025] A second aspect of the present application provides an electrical device comprising the secondary battery according to the first aspect of the present application.

[0026] Effects of the Invention

[0027] According to the present application, a secondary battery having excellent storage performance and an electric device including the lithium ion battery can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a schematic diagram showing the structure of a negative electrode sheet in a secondary battery of the present application.

[0029] Explanation of reference numerals: 1 negative electrode current collector; 2 negative electrode film layer; 21 first negative electrode film layer; 22 second negative electrode film layer DETAILED DESCRIPTION

[0030] The secondary battery of the present application and the electrical device including the secondary battery are described in detail below with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] As used herein, "ranges" are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, i.e., any lower limit may be combined with any upper limit to form a range.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0034] A secondary battery is a battery that can be recharged after discharge to activate the active materials and continue to be used, such as a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (such as lithium ions) are embedded in and released from the positive and negative electrodes. The electrolyte between the positive and negative electrodes primarily serves to conduct active ions.

[0035] One embodiment of the present application provides a secondary battery, comprising a negative electrode plate, wherein 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, wherein the negative electrode film layer comprises an additive capable of undergoing a nucleophilic reaction with a cyclic carbonate compound.

[0036] The applicant unexpectedly discovered that when an additive capable of undergoing a nucleophilic reaction with a cyclic carbonate compound is added to the negative electrode film layer, the additive reacts with the cyclic carbonate compound in the electrolyte of the secondary battery, inducing its ring opening to form a highly elastic PEO-like polymer, which participates in SEI formation and strengthens film formation, reducing the irreversible capacity loss caused by the frequent repair of SEI rupture and the consumption of active lithium; at the same time, a conductive network with high ionic conductivity is formed, which is conducive to the migration of active ions (such as lithium ions, etc.) in the secondary battery, reduces charge transfer impedance and electrochemical polarization, reduces polarization capacity loss, and thus improves the storage performance of the battery.

[0037] As for the additive, as long as it can react with the cyclic carbonate compound to undergo nucleophilic reaction, there is no particular limitation. In some embodiments, as the additive, a sulfur-containing substance and / or a selenium-containing substance is included, for example, including at least one of elemental sulfur, lithium sulfide, sodium sulfide, a selenium-containing element, lithium selenide, sodium selenide, cobalt selenide, and nickel selenide. These additives undergo a reduction reaction during the charge and discharge process of the battery and further react with the cyclic carbonate electrolyte solvent. For example, lithium sulfide reacts with ethylene carbonate to generate a poly (ethylene oxide) (PEO)-type polymer, which participates in the formation of the SEI film. The specific reaction is as follows.

[0038] In addition, in some embodiments, a carbon-based material is used as a substrate, and a sulfur-containing substance and / or a selenium-containing substance is loaded on the carbon-based material to form a composite. The carbon-based material includes a nano-carbon-based material, graphene, etc. In some embodiments, the nano-carbon-based material is a carbon nanotube. In addition, carbon can also be used as a coating material. In some embodiments, nanoporous carbon is used as a coating material to coat the surface of the above-mentioned sulfur-containing substance and / or selenium-containing substance to form a sulfur-containing substance with a carbon coating layer and a selenium-containing substance with a carbon coating layer. This can improve the conductivity and fast charging performance of the battery while improving the battery storage performance. In addition, the amount of negative electrode conductive agent used can also be reduced.

[0039] In some embodiments, the mass proportion of the additive is less than or equal to 10% based on the total mass of the negative electrode film layer. In some embodiments, the mass proportion of the additive is 0.5%-5% based on the total mass of the negative electrode film layer. By making the content of the additive within the above range, the storage performance, conductivity and fast charging performance of the battery can be further improved. In some embodiments, the particle size Dv50 of the above additive is 50nm-500nm, and in some embodiments, the particle size Dv50 of the above additive is 100nm-200nm. By controlling the particle size within the above range, a larger specific surface area can be obtained and the reaction activity can be increased.

[0040] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon material. The carbon material can be at least one of graphite (including artificial graphite, natural graphite), soft carbon, and hard carbon. In some embodiments, the carbon material is graphite. The negative electrode active material also includes a silicon-based material. In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material is greater than or equal to 5%. In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material is 5%-25%. In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material is 5%-20%. As the silicon-based material, for example, it includes at least one of silicon element, silicon-carbon composite material, and silicon oxide compound. In some embodiments, the silicon-based material includes a silicon oxide compound with the chemical formula SiOx, where 0<x<2, in some embodiments, 0.5≤x≤1.5, and in some embodiments, x=1. The silicon oxide compound has high capacity performance and cycle life.

[0041] By including silicon-based materials as negative electrode active materials in the negative electrode film layer, the energy density of the secondary battery can be greatly improved. However, on the other hand, silicon-based negative electrode materials undergo huge volume changes during the embedding and de-embedding process of active ions, such as lithium ions. The electrode material is likely to generate internal stress due to the volume effect, causing the surface SEI to rupture. Frequent repair of SEI consumes a large amount of active lithium. In addition, it is easy to cause the electrode material to break, thereby losing electrical contact with the current collector. The above results in poor storage performance of the silicon-based negative electrode. However, the negative electrode film layer of the secondary battery of the present application contains the above-mentioned additive. As mentioned above, the additive can form a highly elastic polymer with the cyclic carbonate compound in the electrolyte to participate in SEI film formation, thereby effectively alleviating the volume expansion of the silicon-based material during charging at the negative electrode-electrolyte interface, thereby improving the battery capacity and the stability of the interface between the negative electrode and the electrolyte. It can be seen that through this embodiment, the secondary battery of the present application has high storage performance while also having high energy density.

[0042] In the present application, in some embodiments, the above-mentioned 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 above-mentioned second negative electrode film layer is arranged between the above-mentioned negative electrode current collector and the above-mentioned first negative electrode film layer, and the above-mentioned first negative electrode film layer and / or the above-mentioned second negative electrode film layer include the above-mentioned additive.

[0043] In some embodiments, the mass proportion of the above-mentioned additives in the above-mentioned first negative electrode film layer is greater than 0% and less than or equal to 10%. In some embodiments, the mass proportion of the above-mentioned additives in the above-mentioned first negative electrode film layer is 0.5%-5%; and / or, the mass proportion of the above-mentioned additives in the above-mentioned second negative electrode film layer is 0%-5%. In some embodiments, the mass proportion of the above-mentioned additives in the above-mentioned second negative electrode film layer is 0.1%-2%. When both the first negative electrode film layer and the second negative electrode film layer include additives, the additives in the two layers may be the same or different. When the mass proportion of the additives in the first negative electrode film layer is denoted as A1 and the mass proportion of the additives in the second negative electrode film layer is denoted as A2, A1 / A2>1; in some embodiments, 2≤A1 / A2≤10.

[0044] In some embodiments, the first negative electrode film layer comprises a first negative electrode active material, the second negative electrode film layer comprises a second negative electrode active material, and the first negative electrode active material and / or the second negative electrode active material comprise the silicon-based material. In some embodiments, both the first and second negative electrode active materials comprise the silicon-based material, and the weight percentage of the silicon-based material in the first negative electrode active material is greater than the weight percentage of the silicon-based material in the second negative electrode active material. The silicon-based material comprises greater than or equal to 5% by weight of the first negative electrode active material. In some embodiments, the silicon-based material comprises 5% to 25% by weight of the first negative electrode active material. In some embodiments, the silicon-based material comprises 5% to 20% by weight of the first negative electrode active material. 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 further comprises a carbon material, and the carbon material comprises at least one of graphite, soft carbon, and hard carbon. In some embodiments, the carbon material comprises graphite. In addition, the second negative electrode active material includes a carbon material, which is the same as or different from the carbon material in the negative electrode film layer. In some embodiments, the carbon material includes a powder pressure of 1.8 g / cm 3 The above high-density graphite materials.

[0045] The negative electrode sheet comprising the first and second negative electrode film layers can be prepared, for example, as follows.

[0046] By double-layer coating technology, firstly, the two sides of the current collector 1 are coated with a powder pressure of 1.8 g / cm 3 The above-mentioned high-density graphite and / or additive slurry forms the second negative electrode film layer 22, and a composite slurry containing graphite, silicon-based materials, additives, etc. is then coated on this basis to form the first negative electrode film layer 21, forming a double-layer negative electrode film layer 2, thereby obtaining a negative electrode sheet, as shown in Figure 1. Through 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, and a high-density negative electrode sheet with high fast charging performance can be obtained.

[0047] In some embodiments, the negative electrode film layer includes both high-valent sulfur and low-valent sulfur, and / or the negative electrode film layer includes both high-valent selenium and low-valent selenium. In some embodiments, the high-valent sulfur includes at least one of +4-valent sulfur and +6-valent sulfur, with an S2p spectrum peak of 168.5eV-171eV; the low-valent sulfur includes -2-valent sulfur to -1 / 6-valent sulfur, with an S2p spectrum peak of 161eV-166.5eV. In some embodiments, the high-valent selenium includes at least one of +4-valent selenium and +6-valent selenium, and the Se3d spectrum peak of the high-valent selenium is 58.9eV-61.2eV; in some embodiments, the low-valent selenium includes -2-valent selenium, with an Se3d spectrum peak of 54eV-55.1eV. The above-mentioned high-valent sulfur and high-valent selenium are produced due to oxidation after losing electrons to form alkyl sulfates and alkyl selenates that participate in SEI film formation. The production of low-valent sulfur and low-valent selenium is due to reduction after gaining electrons to form PEO polymers that participate in SEI film formation.

[0048] In the secondary battery of the present application, as an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode film layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0049] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0050] In some embodiments, the negative electrode film layer may further include a binder. For 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).

[0051] In some embodiments, the negative electrode film layer may further include a conductive agent. For 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.

[0052] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0053] In some embodiments, the negative electrode sheet can be prepared by the following method: the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material (carbon material and / or silicon-based material), the above-mentioned additives, conductive agent, binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet is obtained.

[0054] The secondary battery of the present application includes a positive electrode sheet.

[0055] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a lithium replenisher, 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 plate, including the lithium replenisher in the positive electrode film layer replenishes active lithium, thereby enabling the secondary battery to have high energy density and fast charging performance.

[0056] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0057] In some embodiments, the positive electrode active material in the positive electrode film layer may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0058] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0059] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, the lithium supplement and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0061] In the secondary battery of the present application, the electrolyte includes a cyclic carbonate compound. In some embodiments, the cyclic carbonate compound includes at least one of ethylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, vinylene carbonate, and butylene carbonate. These compounds can undergo a nucleophilic reaction with the additive in the negative electrode film layer, participating in the formation of the SEI film and improving the storage performance of the secondary battery.

[0062] 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 the lithium salt are not subject to specific restrictions and can be selected according to actual needs. For example, the electrolyte salt can be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate. For the solvent, in addition to the above-mentioned cyclic carbonate compounds, it can also be selected from at least one of ethyl methyl 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, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0063] The secondary battery of the present application also includes a separator. The present application has no particular restrictions on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0064] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0065] The secondary battery of the present application can be prepared by conventional methods, for example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining a battery cell, placing the battery cell in an outer package, injecting an electrolyte, and obtaining an electrode assembly. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0066] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0067] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0068] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0069] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device 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 is not limited thereto.

[0070] As the above-mentioned electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0071] Example

[0072] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0073] Example 1

[0074] (1) Preparation of negative electrode sheet

[0075] The negative electrode active material (artificial graphite and silicon oxide, the mass ratio of the two is 90%:10%), the additive elemental sulfur (particle size Dv50 = 200nm), the conductive agent Super P, carbon nanotubes (CNTs), the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 94.5%:2%:1%:0.5%:1%:1% to form a negative electrode slurry.

[0076] 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.

[0077] (2) Preparation of positive electrode sheet

[0078] LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent Super P, and binder polyvinylidene fluoride are mixed in a weight ratio of 96%:2%:2%. An appropriate amount of solvent NMP is added and 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. After drying and cold pressing, the positive electrode sheet is obtained.

[0079] (3) Electrolyte

[0080] In an argon atmosphere glove box (H2O <0.01ppm, O2 <0.01ppm), solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 4:6, LiPF6 lithium salt was added thereto to dissolve it, and stirred evenly. The final concentration of LiPF6 lithium salt was 12.5%, which was used as the electrolyte.

[0081] (4) Isolation film

[0082] Polyethylene film is used as the isolation film.

[0083] (5) Lithium-ion batteries

[0084] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets, and wound to form a battery cell. The battery cell was placed in a battery outer packaging, and then injected with electrolyte, packaged, allowed to stand, formed, shaped, and capacity tested to produce a lithium-ion battery having a thickness of 4.2 mm, a width of 42 mm, and a length of 49.5 mm.

[0085] Examples 2-14

[0086] The preparation method is similar to that of Example 1, except that different types or contents of additives are used. See Table 1 for details.

[0087] Example 15

[0088] The preparation method is similar to that of Example 1, except that the preparation method of the negative electrode sheet is as follows:

[0089] The first negative electrode active material (artificial graphite and silicon oxide, the mass ratio of the two is 80%:20%), a composite material of elemental sulfur and carbon nanotubes (particle size Dv50 = 200nm), a conductive agent Super P, carbon nanotubes (CNTs), a binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 94.5%:2%:1%:0.5%:1%:1% to form a first slurry.

[0090] The second negative electrode active material (artificial graphite and silicon oxide, the mass ratio of the two is 95%:5%), nanoporous carbon-coated elemental selenium (particle size Dv50 = 200nm), conductive agent Super P, carbon nanotubes (CNTs), binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96%: 0.5%: 1%: 0.5%: 1%: 1% to form a second slurry.

[0091] The first and second slurries are extruded simultaneously through a dual-chamber coating device. The second slurry is coated on both surfaces of the negative electrode current collector copper foil, and the first slurry is coated on the second slurry. After drying and cold pressing, the negative electrode sheet is obtained.

[0092] Comparative Example 1

[0093] The preparation method is similar to that of Example 1, except that: the preparation method of the negative electrode sheet is as follows: the negative electrode active material (artificial graphite and silicon oxide, the mass ratio of the two is 90%:10%), the conductive agent Super P, carbon nanotubes (CNTs), the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96.5%:1%:0.5%:1%:1% to form a negative electrode slurry.

[0094] 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.

[0095] Comparative Example 2

[0096] The preparation method is similar to that of Example 15, except that the preparation method of the negative electrode sheet is as follows:

[0097] The first active material (artificial graphite and silicon oxide, the mass ratio of the two is 80%:20%), the conductive agent Super P, carbon nanotubes (CNTs), the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96.5%:1%:0.5%:1%:1% to form a first slurry.

[0098] The second active material (artificial graphite and silicon oxide, the mass ratio of the two is 95%:5%), the conductive agent Super P, carbon nanotubes (CNTs), the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of solvent deionized water in a weight ratio of 96.5%:1%:0.5%:1%:1% to form a second slurry.

[0099] The first and second slurries are extruded simultaneously through a dual-chamber coating machine. The second slurry is coated on both surfaces of the negative electrode current collector copper foil, and the first slurry is coated on the second slurry. After drying and cold pressing, the negative electrode sheet is obtained.

[0100] The secondary batteries of the above-mentioned examples and comparative examples were subjected to the following tests, and the results are shown in Table 1 below.

[0101] Battery Test

[0102] Storage performance (capacity retention after 100 days of storage at 60°C)

[0103] The battery capacity recovery rate test process is as follows: Before storage, at 25°C, the batteries of the embodiment and comparative example were charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, left for 30 minutes, and then discharged at 1 / 3C to 2.8V. The resulting capacity was recorded as the initial capacity C0. After storage 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 H = Cr / C0*100%.

[0104] The higher H is, the better the storage performance is.

[0105] Conductivity (electrode diaphragm resistance)

[0106] The rolled membrane was cut into a rectangular size of about 5 cm × 10 cm and placed between the two electrodes of the membrane resistance meter. The test pressure was set to 25 MPa and the holding time was set to 25 s on the MRMS software. The software automatically read the membrane thickness, resistance, resistivity, conductivity and other data and recorded the resistance data.

[0107] The smaller the resistance value, the better the conductivity.

[0108] Fast charging performance (10%-80% SOC fast charging time)

[0109] The 10%-80% SOC charging time test procedure is as follows: At 25°C, the batteries in the examples and comparative examples were charged from 10% SOC to 80% SOC at a step-by-step rate of 1.0C / 0.8C / 0.5C / 0.33C. The charging time until lithium plating does not occur at the negative electrode is the battery's fast charge time at that point. A shorter fast charge time indicates better fast charge performance.

[0110] Table 1

[0111] According to the results in Table 1, compared with Comparative Examples 1 and 2, the secondary batteries of Examples 1 to 15 all achieved excellent storage performance.

[0112] Moreover, compared with Examples 1 to 4, the additives in Examples 5 to 7, by being in the form of a composite with carbon nanotubes or having a carbon coating layer, not only have excellent storage performance of the battery, but also reduce resistance, improve the conductivity of the secondary battery, and obtain better fast charging performance.

[0113] In Examples 8 to 14, compared with Example 14, Examples 8 to 13 obtained excellent storage performance, conductivity and fast charging performance by making the mass proportion of the additive less than or equal to 10% relative to the total mass of the negative electrode film layer. Furthermore, compared with Examples 12 and 13, Examples 8 to 11 obtained even better storage performance, conductivity and fast charging performance by making the mass proportion of the additive 0.5%-5% relative to the total mass of the negative electrode film layer.

[0114] In addition, 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.

[0115] In contrast, since Comparative Examples 1 and 2 do not contain the specific additives of the present application, the storage performance cannot be improved and the technical effects of the present application cannot be achieved.

[0116] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

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

2. The secondary battery according to claim 1, wherein The additive comprises at least one of a sulfur-containing substance, a selenium-containing substance, a composite of a sulfur-containing substance and a carbon-based material, a composite of a selenium-containing substance and a carbon-based material, a sulfur-containing substance with a carbon coating layer, or a selenium-containing substance with a carbon coating layer; 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 selenium, lithium selenide, sodium selenide, cobalt selenide, or nickel selenide; Optionally, the carbon-based material includes nano-carbon-based material and / or graphene. Optionally, 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 layer, the mass proportion of the additive is less than or equal to 10%, and can be optionally 0.5%-5%.

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

5. The secondary battery according to any one of claims 1 to 4, wherein: The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. Optionally, the mass proportion of the silicon-based material in the negative electrode active material is greater than or equal to 5%, and optionally greater than or equal to 10%; Optionally, the silicon-based material includes at least one of silicon element, silicon-carbon composite material, and silicon-oxygen compound.

6. The secondary battery according to any one of claims 1 to 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 The film layer is arranged 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 includes the additive.

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

8. The secondary battery according to claim 6 or 7, wherein: The first negative electrode film layer and the second negative electrode film layer both include the additive; In the first negative electrode film layer, the mass proportion of the additive is recorded as A1, and in the second negative electrode film layer, the mass proportion of the additive is recorded 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 to 8, wherein The first negative electrode film layer and the second negative electrode film layer both include the additive, and the additive materials in the first negative electrode film layer and the second negative electrode film layer are the same or different.

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

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

13. The secondary battery according to any one of claims 1 to 12, wherein: The secondary battery includes an electrolyte, and the electrolyte includes a cyclic carbonate compound; Optionally, the cyclic carbonate compound includes at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate and butylene carbonate.

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

15. An electrical device comprising the secondary battery according to any one of claims 1 to 14.

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