Secondary battery, preparation method therefor, and electrical device

Abstract

A secondary battery, a preparation method therefor, and an electrical device. The secondary battery comprises an electrode sheet. The electrode sheet comprises a current collector, an active material layer, and a base coating. The active material layer is located on at least one surface of the current collector. The base coating is located between the current collector and the active material layer. The base coating contains an additive, and anions of the additive comprise at least one of nitrate ions and nitrite ions. In the electrode sheet, the base coating is arranged between the current collector and the active material layer. The anions in the base coating comprise nitrate ions and nitrite ions, enabling the additive to gradually dissolve and diffuse into an electrolyte. In this way, the nitrate and nitrite undergo a reduction reaction, and the reduction product thereof becomes part of an SEI film to enable repair of the SEI film, thereby achieving thin, stable, and compact SEI films and significantly improving the cycle life of the battery.

Description

A secondary battery, a preparation method thereof and a power utilization device

[0001] The present application claims priority to the Chinese patent application No. 202410686340.8, filed on May 29, 2024 in the China Patent Office, and entitled "A secondary battery, a preparation method thereof and a power utilization device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a secondary battery, a preparation method thereof and a power utilization device. BACKGROUND

[0003] The statements herein are provided only to enhance understanding of the present application and are not necessarily intended to constitute the prior art.

[0004] In recent years, secondary batteries have made great progress, especially the rapid development of pure electric new energy vehicles powered by lithium-ion batteries as a representative of secondary batteries. With the continuous development of new energy vehicles, users also have higher requirements for the cycle life of lithium-ion batteries. At present, in the secondary batteries represented by lithium-ion batteries, the cycle life needs to be improved in actual use requirements.

[0005] SUMMARY

[0006] The purpose of the embodiments of the present application is to provide a secondary battery, a preparation method thereof and a power utilization device, which include but are not limited to solving the problem of unsatisfactory cycle performance of secondary batteries.

[0007] The technical solution adopted by the embodiments of the present application is:

[0008] In a first aspect, a secondary battery is provided, comprising a pole piece, the pole piece comprising:

[0009] a current collector;

[0010] an active material layer located on at least one surface of the current collector; and

[0011] a primer layer located between the current collector and the active material layer, the primer layer containing an additive, the anion of the additive comprising at least one of nitrate ions and nitrite ions.

[0012] The secondary battery provided by the embodiments of the present application sets a primer layer between the current collector and the active material layer of the pole piece, and the primer layer further comprises an additive containing nitrate ions and nitrite ions, and the additive can gradually dissolve and diffuse into the electrolyte. Thus, the nitrate and nitrite contained in the nitrate undergoes a reduction reaction, and the reduction product becomes part of the SEI film, thereby repairing the SEI film, obtaining a high-toughness and stable dense SEI film, reducing the direct current impedance of the battery, and comprehensively improving the cycle performance of the secondary battery.

[0013] In one embodiment, the molecular formula of the additive is A(NO x ) y wherein 2≤x≤3 and 1≤y≤3; A comprises at least one of Li, Na, K, Cs, Mg, Ca, and Al.

[0014] The additive containing nitrate or nitrite can enter the lithium ion solvation structure, thereby repairing the SEI film, and the reduction product of the additive, such as Li3N, can also accelerate the deposition or stripping of lithium ions, thereby effectively improving the cycle performance of the battery.

[0015] In one embodiment, the mass percentage of the additive in the primer layer is 5% to 30%.

[0016] Controlling the mass percentage of the additive in the primer layer within the above range enables the additive to be released into the electrolyte, thereby repairing the SEI film and improving the cycle life of the battery.

[0017] In one embodiment, the thickness of the primer layer is 0.07 μm to 3.1 μm.

[0018] Controlling the thickness of the primer layer within the above range not only enables the additive contained in the primer layer to function, but also enables the pole piece to contain an appropriate amount of active material layer, thereby enabling the secondary battery to have a high energy density.

[0019] In one embodiment, the coating weight of the primer layer is 0.1 mg / cm 2 to 4 mg / cm 2 .

[0020] Controlling the coating weight of the primer layer within the above range not only enables the additive contained in the primer layer to function and repair the SEI film, but also enables the active material contained in the pole piece to have appropriate kinetics and cohesion, thereby enabling the secondary battery to have a good energy density.

[0021] In an embodiment, the undercoat layer further comprises an electrically conductive agent and a binder, the electrically conductive agent comprises one or more of carbon black, graphite, ketjen black, carbon nanotube, graphene and carbon fiber, and the binder comprises one or more of styrene-butadiene rubber, olefin resin and acrylic resin.

[0022] The presence of the electrically conductive agent in the undercoat layer can endow the undercoat layer with excellent electrically conductive capacity, thereby forming a well-constructed electrically conductive channel between the active material layer and the current collector.

[0023] The presence of the binder in the undercoat layer enables the undercoat layer to be firmly attached between the current collector and the active material layer, thereby effectively preventing the undercoat layer from falling off and favorably improving the integrity of the electrode sheet.

[0024] In an embodiment, the electrode sheet is a positive electrode sheet, and the undercoat layer is a positive electrode undercoat layer, and the mass content of the electrically conductive agent contained in the positive electrode undercoat layer is 40% to 60%.

[0025] In an embodiment, the electrode sheet is a positive electrode sheet, and the undercoat layer is a positive electrode undercoat layer, and the mass content of the binder contained in the positive electrode undercoat layer is 20% to 60%.

[0026] The electrode sheet can be a positive electrode sheet, that is, the positive electrode sheet is provided with a positive electrode undercoat layer containing an additive, which can slowly diffuse into the electrolyte, thereby not only achieving protection of the positive electrode sheet but also repairing the SEI film, thereby improving the cycle life of the battery.

[0027] Controlling the parameters of the positive electrode undercoat layer, such as the mass content of the positive electrode electrically conductive agent and the mass content of the positive electrode binder, enables the additive contained in the positive electrode undercoat layer to diffuse into the electrolyte, thereby repairing the SEI film, and at the same time, the positive electrode active material contained in the positive electrode sheet has appropriate kinetics and cohesion, thereby achieving both improved cycle performance and energy density of the secondary battery.

[0028] In an embodiment, the electrode sheet is a negative electrode sheet, and the undercoat layer is a negative electrode undercoat layer, and the mass content of the electrically conductive agent contained in the negative electrode undercoat layer is 60% to 70%.

[0029] In an embodiment, the electrode sheet is a negative electrode sheet, and the undercoat layer is a negative electrode undercoat layer, and the mass content of the binder contained in the negative electrode undercoat layer is 7% to 40%.

[0030] In an embodiment, the electrode sheet is a negative electrode sheet, and the undercoat layer is a negative electrode undercoat layer, and the negative electrode undercoat layer further comprises a thickening agent, and the mass proportion of the thickening agent in the negative electrode undercoat layer is 2% to 5%.

[0031] The electrode can also be a negative electrode, which has a negative electrode undercoat containing additives. Because the negative electrode contains more electron donors, it is more conducive to the reduction of nitrate and nitrite contained in the additives, thereby promoting the repair of the SEI film and improving the cycle capacity of the battery.

[0032] Controlling the parameters of the negative electrode undercoat, such as the mass content of the negative electrode conductive agent, the mass content of the negative electrode binder, and the mass content of other additives such as thickeners, allows the additives contained in the negative electrode undercoat to participate in the repair of the SEI film through the reduction of nitrate and nitrite. It can also ensure that the negative electrode active material contained in the negative electrode sheet has good kinetics and cohesiveness, thereby effectively improving the cycle performance and kinetics of the battery.

[0033] In one embodiment, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and at least a portion of the surface of the negative electrode active material layer is covered with an SEI film, the SEI film comprising Li3N and LiNaO. b At least one of the following, wherein 1≤a≤3 and 1≤b≤7.

[0034] The additives can be reduced during battery charging and discharging, thereby participating in the construction and repair of the SEI film and generating nitrogen-rich components such as Li3N and LiN in the SEI film. a O b This effectively improves the stability of the SEI film while maintaining its density, reduces the DC resistance of the secondary battery, and comprehensively improves the cycle performance of the secondary battery.

[0035] In a second aspect, an electrical device is provided, including the secondary battery described in the first aspect of this application.

[0036] By using the secondary battery provided in the embodiments of this application, such an electrical device has good cycle performance, high energy density, and can work more stably and for a longer period of time.

[0037] Thirdly, a method for preparing a secondary battery is provided, comprising the following steps:

[0038] Electrodes, separators, and electrolytes are provided and assembled to obtain the secondary battery described in the first aspect of this application;

[0039] The electrode is as defined in the first aspect of this application.

[0040] The secondary battery prepared by the method provided in this application contains additives that can participate in the modification of the SEI film and reduce the DC impedance of the battery, thereby giving the secondary battery excellent cycle performance.

[0041] In one embodiment, the method for preparing the pole piece comprises the following steps:

[0042] configuring the primer slurry containing the additive;

[0043] coating the primer slurry on at least one surface of the current collector to form the primer layer;

[0044] preparing the active material layer on the surface of the primer layer away from the current collector.

[0045] According to the method for preparing the pole piece provided in the embodiments of the present application, the pole piece prepared has good adhesion between the current collector and the primer layer, and between the primer layer and the active material layer, and the quality of the pole piece is good.

[0046] In one embodiment, the pole piece is a positive pole piece, and the solid content of the primer slurry is 10% to 20%.

[0047] Controlling the solid content of the primer slurry of the positive pole piece within a proper range makes the positive pole piece have good adhesion.

[0048] In one embodiment, the pole piece is a positive pole piece, and the viscosity of the primer slurry is 100 mPa·s to 1000 mPa·s.

[0049] Controlling the viscosity of the primer slurry of the positive pole piece within the above range is beneficial to the coating processing and drying of the slurry, and comprehensively improves the processing performance and use performance of the slurry.

[0050] In one embodiment, the pole piece is a negative pole piece, and the solid content of the primer slurry is 5% to 15%.

[0051] Controlling the solid content of the primer slurry of the negative pole piece within a proper range makes the negative pole piece have good adhesion.

[0052] In one embodiment, the pole piece is a negative pole piece, and the viscosity of the primer slurry is 100 mPa·s to 2000 mPa·s.

[0053] Controlling the viscosity of the primer slurry of the negative pole piece within the above range is beneficial to the coating processing and drying of the slurry, and comprehensively improves the processing performance and use performance of the slurry. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or exemplary technical descriptions will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0055] Fig. 1 is a schematic diagram of an embodiment of a pole piece according to the present application;

[0056] Fig. 2 is a schematic diagram of an embodiment of a positive pole piece according to the present application;

[0057] Fig. 3 is a schematic diagram of an embodiment of a negative pole piece according to the present application;

[0058] Fig. 4 is a schematic diagram of a secondary battery according to some embodiments of the present application;

[0059] Fig. 5 is a schematic diagram of an exploded structure of a secondary battery according to some embodiments of the present application;

[0060] Fig. 6 is a schematic diagram of a structure of a battery module according to some embodiments of the present application;

[0061] Fig. 7 is a schematic diagram of an exploded structure of a battery pack according to some embodiments of the present application;

[0062] Fig. 8 is a schematic diagram of an embodiment of an electric device comprising a secondary battery according to the present application as a power supply.

[0063] In the drawings:

[0064] 100, pole piece, 110, current collector, 120, base coating layer, 130, active material layer;

[0065] 200, positive pole piece, 210, positive current collector, 220, positive base coating layer, 230, positive active material layer;

[0066] 300, negative pole piece, 310, negative current collector, 320, negative base coating layer, 330, negative active material layer;

[0067] 3, secondary battery, 31, shell, 32, electrode assembly, 33, cover plate;

[0068] 4, battery module;

[0069] 5, battery pack, 51, box, 52, lower box. DETAILED DESCRIPTION

[0070] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0071] It should be noted that "at least one" refers to one or more, and "multiple" refers to two or more. "At least one of the following" or the like refers to any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0072] It should be understood that the size of the sequence number of the above-mentioned processes in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0073] It should be understood that the weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass in the specification of the embodiments of the present application can be μg, mg, g, kg, and other mass units commonly known in the chemical industry.

[0074] With the rapid popularization of lithium batteries, especially in electric vehicles, the requirements for lithium batteries, including cycle performance and energy density, are also increasing. During the first charging process of the battery, the electrolyte undergoes a reduction reaction on the surface of the negative electrode, producing a large amount of organic or inorganic products, which are deposited on the surface of the negative electrode to form a dense passivation film. This passivation film is called "solid electrolyte interface" (SEI film) for short.

[0075] However, as the cycle process continues, the SEI film will break and continue to form a new SEI film on the surface of the negative electrode. That is, during the cycle process, the SEI film will continuously break and recombine, increasing the consumption of active ions and reducing the cycle life of the battery. At the same time, the continuous breaking and recombination of the SEI film will cause its thickness to continuously thicken, prolonging the ion transport path and reducing the ion transport rate, resulting in an increase in interface impedance and deterioration of cycle performance.

[0076] Based on this, some embodiments of the present application provide a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising:

[0077] a current collector;

[0078] an active material layer on at least one surface of the current collector; and

[0079] The undercoat layer is located between the current collector and the active material layer, and contains an additive, an anion of which includes at least one of nitrate ions and nitrite ions.

[0080] The additive contained in the undercoat layer can gradually dissolve and diffuse into the electrolyte, and the additive is preferentially reduced into a film during the charging and discharging of the battery, at which time the nitrate anions and nitrite anions are reduced into nitrogen-containing substances Li3N, LiN a O b That is, nitrogen-containing components such as Li3N, LiN a O b are generated in the SEI film, so that a thin and stable dense SEI film is obtained; since the additive is located in the undercoat layer and has a low solubility in the electrolyte, the additive that has dissolved in the electrolyte will be consumed in the construction and repair of the SEI film on the electrode surface, at which time the additive stored in the undercoat layer will be continuously dissolved in the electrolyte to replenish the consumption during the film formation or repair, so that the additive is continuously released from the undercoat layer into the electrolyte to replenish the consumption of the additive during the battery cycle, thereby effectively prolonging the cycle life of the battery and improving the performance of the battery.

[0081] The reduction and decomposition products of the nitrate ions and nitrite ions on the surface of the negative electrode (such as Li3N) can act as excellent lithium ion conductors, which can accelerate the deposition / stripping behavior of lithium ions, so that not only the charging and discharging efficiency of the battery is improved, but also the formation of lithium dendrites is inhibited, thereby further protecting the negative electrode of the battery to improve the cycle life of the battery.

[0082] In addition, the additive is arranged in the undercoat layer, which can also reduce the influence of the additive on the conductive network and the adhesive network of the active material contained in the active material layer, so that the active material layer and the electrode sheet have high structural stability, thereby helping to prolong the service life of the battery.

[0083] Therefore, the electrode sheet provided by the embodiments of the present application sets the undercoat layer between the current collector and the active material layer, and the undercoat layer further contains an additive containing nitrate ions and nitrite ions, so that the additive can gradually dissolve and diffuse into the electrolyte, thereby participating in the construction and / or repair of the SEI film to obtain a high-toughness and dense SEI film, reduce the direct current impedance of the battery, and comprehensively improve the cycle life of the battery.

[0084] It can be understood that the following methods can be used for testing:

[0085] The surface layer powder of the electrode sheet is scraped off, and the obtained undercoat powder is detected. The nitrate / nitrite can be detected by infrared spectroscopy, and the cations in the undercoat layer can be detected by ICP.

[0086] As an example, the current collector has two surfaces opposite in the thickness direction thereof, and the active material layer is provided on either one or both of the two opposite surfaces of the current collector. That is, the undercoat layer can be provided on either one or both of the two opposite surfaces of the current collector.

[0087] Referring to FIG. 1, provided is a structure of a pole piece 100 according to some embodiments of the present application.

[0088] According to some embodiments of the present application, referring to FIG. 1, provided is a pole piece 100, which includes a current collector 110, an undercoat layer 120, and an active material layer 130. The undercoat layer 120 is coated on a surface of the current collector 110, the active material layer 130 is coated on a surface of the undercoat layer 120, and the undercoat layer 120 is located between the current collector 110 and the active material layer 130.

[0089] Further, the pole piece 100 can be a positive pole piece, the current collector 110 can be a positive current collector, the undercoat layer 120 can be a positive undercoat layer, and the active material layer 130 can be a positive active material layer. The pole piece 100 can also be a negative pole piece, the current collector 110 can be a negative current collector, the undercoat layer 120 can be a negative undercoat layer, and the active material layer 130 can be a negative active material layer.

[0090] In one embodiment, the molecular formula of the additive is A(NO x ) y wherein 2≤x≤3 and 1≤y≤3; A includes at least one of Li, Na, K, Cs, Mg, Ca, and Al.

[0091] When x is 2, the valence of the nitrogen atom is +3, at this time, NO2- - is a nitrite structure, wherein the nitrogen atom adopts sp 2 hybridization to form two σ bonds, one π bond, and one lone pair of electrons.

[0092] When x is 3, the valence of the nitrogen atom is +5, at this time, NO3- is a nitrate structure, wherein the nitrogen atom forms bonds with sp 2 hybridized orbitals, and there are three σ bonds in the ion, and the ion is a planar triangle.

[0093] When x takes a value in the range of 2

[0094] When the A element is Li element, such as LiNO3, LiNO2, it means that the additive is a lithium-containing substance, at this time the additive can also provide additional active ions, reducing the consumption of active lithium when forming SEI.

[0095] For example, the additive can be at least one of LiNO3, LiNO2, NaNO3, NaNO2, CsNO3, CsNO2, Mg(NO3)2, Mg(NO2)2, Ca(NO3)2, Ca(NO2)2, Al(NO3)3, Al(NO2)3.

[0096] The additive containing nitrate and nitrite can enter the lithium ion solvation structure, thereby achieving the construction and / or repair of the SEI film, helping to form a stable and dense SEI film rich in nitrogen element, so that the battery has high coulomb efficiency and cycle stability, and the reduction product of the additive such as Li3N can also accelerate the deposition or stripping of lithium ions, further improving the cycle performance of the battery. At the same time, the cations in the additive will chemically react with other components in the electrode material or electrolyte during the charging and discharging of the battery, participating in the formation process of the SEI film. These reactions will produce some compounds that are beneficial to the stability of the SEI film and the lithium ion conductivity, thereby improving the performance of the battery; in addition, selecting appropriate metal cations can further inhibit the generation of lithium dendrites by shielding effect or participating in the formation of the SEI film.

[0097] In one embodiment, the mass percentage of the additive in the primer layer is 5% to 30%. For example, the mass percentage of the additive in the primer layer can be 5%, 10%, 15%, 20%, 25%, 30%, etc. typical but non-limiting values.

[0098] In one embodiment, the mass percentage of the additive in the primer layer is 10% to 20%. For example, the mass percentage of the additive in the primer layer can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 18%, 20%, etc. typical but non-limiting values.

[0099] Controlling the mass percentage of the additive in the primer layer within the above range not only can continuously release appropriate additives in the electrolyte, help to build and repair a stable and dense SEI film, reduce the direct current impedance of the battery, and comprehensively improve the cycle performance of the secondary battery; but also conducive to the adhesion performance of the primer layer, so that the primer layer, the current collector and the active material layer are in close contact, and a pole piece with high structural stability is obtained.

[0100] In one embodiment, the thickness of the primer layer is 0.07 μm to 3.1 μm. Exemplarily, the thickness of the primer layer can be 0.07 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 3 μm, 3.1 μm, and the like typical but non-limiting values.

[0101] Controlling the thickness of the primer layer within the above range can avoid the negative impact of the primer layer that is too thick on the content of the active material layer of the electrode sheet, and is less likely to affect the energy density of the battery.

[0102] It should be noted that the thickness of the primer layer in the electrode sheet refers to the thickness of the corresponding primer layer in the electrode sheet after cold pressing and compaction and used for assembling the battery.

[0103] In one embodiment, the coating weight of the primer layer is 0.1 mg / cm 2 ~ 4 mg / cm 2 . Exemplarily, the coating weight of the primer layer can be 0.1 mg / cm 2 , 0.2 mg / cm 2 , 0.3 mg / cm 2 , 0.5 mg / cm 2 , 0.8 mg / cm 2 , 1 mg / cm 2 , 1.1 mg / cm 2 , 1.5 mg / cm 2 , 2 g / cm 2 , 2.5 mg / cm 2 , 3 mg / cm 2 , 3.5 mg / cm 2 , 4 mg / cm 2 , and the like typical but non-limiting values.

[0104] Controlling the coating weight of the primer layer within the above range means that the primer layer has an appropriate thickness, so that the active material contained in the electrode sheet can fully exert its kinetics and cohesion, and impart the battery with good energy density; and can also reduce the possibility of the corner of the electrode sheet in the inner circle of the roll core being delaminated in the hot pressing process.

[0105] In one embodiment, the primer layer further comprises a conductive agent and a binder, the conductive agent comprises one or more of carbon black, graphite, Ketjen black, carbon nanotube, graphene and carbon fiber, and the binder comprises one or more of styrene butadiene rubber, olefin resin and acrylic resin.

[0106] The presence of the conductive agent in the undercoat layer can impart excellent conductive capacity to the undercoat layer, thereby forming a well-constructed conductive channel between the active material layer and the current collector. In addition, the additive in the undercoat layer can recrystallize based on the small particle size of the conductive agent, thereby making the particle size of the additive smaller and more easily dissolved in the electrolyte.

[0107] The presence of the binder in the undercoat layer enables the undercoat layer to be firmly attached between the current collector and the active material layer, thereby effectively preventing the undercoat layer from peeling off and favorably improving the integrity of the electrode sheet.

[0108] [Positive electrode sheet]

[0109] The electrode sheet provided by the embodiments of the present application is a positive electrode sheet, the current collector in the electrode sheet is a positive current collector, the active material layer in the electrode sheet is a positive active material layer, and the undercoat layer in the electrode sheet is a positive undercoat layer.

[0110] The electrode sheet can be a positive electrode sheet, i.e., the positive electrode sheet is provided with an undercoat layer containing an additive that can slowly diffuse into the electrolyte, thereby enabling a reduction reaction to occur at the surface of the negative electrode and the electrolyte, forming a stable, dense and thin SEI film, which can protect the negative electrode sheet while significantly improving the life of the battery; the undercoat layer contains nitrite anions, which can enable oxidation and reduction at the surface of the positive electrode sheet, thereby protecting the positive electrode sheet. In addition, in general, the solvent used in the positive active material layer is an organic solvent such as N-methyl pyrrolidone, which has a low solubility for the additive, thereby reducing the diffusion of the additive to the positive active material layer and making it difficult to affect the conductive network and adhesive network of the positive active material layer.

[0111] As an example, the positive current collector has two opposite surfaces in the thickness direction thereof, and the positive active material layer is disposed on either one or both of the opposite surfaces of the positive current collector. That is, the positive undercoat layer can be disposed on either one or both of the opposite surfaces of the positive current collector.

[0112] Referring to FIG. 2, the present application provides a positive electrode sheet 200, which includes a positive current collector 210, a positive undercoat layer 220 and a positive active material layer 230. The positive undercoat layer 220 is coated on one surface of the positive current collector 210, the positive active material layer 230 is coated on the surface of the positive undercoat layer 220, and the positive undercoat layer 220 is located between the positive current collector 210 and the positive active material layer 230.

[0113] In one embodiment, the mass content of the conductive agent contained in the positive electrode undercoat layer is 40% to 60%. Illustratively, the mass content of the conductive agent can be 40%, 42%, 45%, 47%, 50%, 52%, 55%, 58%, 60%, and the like typical but non-limiting values. Illustratively, the conductive agent can be one or more of carbon black, graphite, ketjen black, carbon nanotube, graphene, and carbon fiber.

[0114] The main role of the conductive agent in the positive electrode undercoat layer is to provide a channel for electron movement, thereby reducing the internal resistance of the electrode and accelerating the movement rate of electrons. Therefore, controlling the content of the conductive agent in the positive electrode undercoat layer helps to build a good electron channel between the positive electrode active layer and the positive electrode current collector, thereby improving the charge and discharge efficiency of the positive electrode plate.

[0115] In one embodiment, the mass content of the binder contained in the positive electrode undercoat layer is 20% to 60%. Illustratively, the mass content of the binder can be 20%, 25%, 30%, 35%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 58%, 60%, and the like typical but non-limiting values. Illustratively, the binder includes one or more of olefin-based resin and acrylic resin.

[0116] By controlling the content of the binder within the above range, the embodiments of the present application can enhance the adhesion between the positive electrode undercoat layer and the positive electrode current collector, as well as the adhesion between the positive electrode undercoat layer and the positive electrode active material layer, which is conducive to improving the structural stability of the positive electrode plate, preventing the positive electrode undercoat layer from peeling and cracking, and thereby improving the cycle life of the battery.

[0117] In one embodiment, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can include a polymer matrix material and a metal layer formed on at least one surface of the polymer matrix material. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer matrix material (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In one embodiment, the positive electrode active material layer contains a positive electrode active material, which can employ a positive electrode active material for a lithium ion battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, at least one of lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also can be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and a modified compound thereof, etc. Examples of the lithium-containing phosphate of an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4(also can be abbreviated as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, etc.

[0119] In one embodiment, the positive electrode active material layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0120] In one embodiment, the positive electrode active material layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In one embodiment, the positive electrode tab can be prepared by:

[0122] The components described above for preparing the positive electrode primer coating, such as the additives, the conductive agent, the binder, are dispersed in an aqueous solvent to form a positive electrode primer coating slurry, wherein the anion of the additive includes at least one of nitrate ions and nitrite ions;

[0123] The positive electrode primer coating slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode primer coating;

[0124] The components described above for preparing the positive electrode active material layer, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as N-methyl pyrrolidone) to form a positive electrode active material slurry, which is coated on the surface of the positive electrode primer coating, with the positive electrode primer coating located between the positive electrode current collector and the positive electrode active material layer. After drying, cold pressing, and other processes, the positive electrode tab is obtained.

[0125] According to the method for preparing the tab and the tab prepared according to the embodiments of the present application, the positive electrode current collector and the primer coating, and the primer coating and the active material layer have good adhesion, and the quality of the tab is good.

[0126] In one embodiment, the solid content of the positive electrode primer coating slurry is 10% to 20%. As an example, the solid content of the positive electrode primer coating slurry can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, and the like typical but non-limiting values.

[0127] The solid content of the positive electrode primer coating slurry can be tested using methods and equipment known in the art. As an example: take a copper foil and weigh it in a loss on drying tester, record as M0, and clear zero. Take the positive electrode primer coating slurry, coat a small amount on the copper foil, and then put it into the moisture tester and weigh it, record as M1. Close the equipment and start drying. After the end, record the weighing data as M2, and calculate the solid content, which is (M2-M0) / (M1-M0).

[0128] Controlling the solid content of the positive electrode primer coating slurry within a suitable range means that the positive electrode primer coating slurry has appropriate viscosity, thereby not only making the positive electrode tab have good adhesion, but also being beneficial to the processing and coating of the positive electrode primer coating slurry.

[0129] In an embodiment, the viscosity of the positive electrode primer coating slurry is 100 mPa s to 1000 mPa s. The viscosity of the positive electrode primer coating slurry at 25°C at a stirring speed of 30 rpm can be selected from 100 mPa s, 200 mPa s, 400 mPa s, 600 mPa s, 800 mPa s, 1000 mPa s, or any value therebetween.

[0130] The viscosity of the positive electrode primer coating slurry can be tested using methods and equipment known in the art. As an example, the viscosity of the primer coating slurry is measured using a rotary viscometer. A suitable rotor is selected, the viscometer rotor is fixed, the primer coating slurry is placed below the viscometer rotor, and the slurry just submerges the scale line of the rotor. The instrument model is Shanghai Fangrui NDJ-5S, the rotor is 62#, the rotation speed is 30 rpm, and the viscosity range of the slurry that can be measured is 0-1000 mPa s. The rotor is 63#, the rotation speed is 30 rpm, and the viscosity range of the slurry that can be measured is 0-2000 mPa s. The test temperature is 25°C, and the test time is 5 minutes. The data is read when the reading is stable.

[0131] Controlling the viscosity of the positive electrode primer coating slurry within the above range is beneficial for the coating and drying of the slurry, and improves the processing performance and use performance of the slurry.

[0132] [Negative electrode tab]

[0133] The electrode tab provided by the embodiments of the present application is a negative electrode tab, the current collector in the electrode tab is a negative electrode current collector, the active material layer in the electrode tab is a negative electrode active material layer, and the primer coating layer in the electrode tab is a negative electrode primer coating layer.

[0134] The electrode tab can also be a negative electrode tab, i.e., the negative electrode tab is provided with a primer coating layer containing an additive. Since the negative electrode tab contains more electrons, it is more conducive to the reduction of nitrate and nitrite, thereby promoting the repair of the SEI film and forming a component rich in nitrogen elements in the SEI film to obtain a stable, dense, and thin SEI film, thereby effectively improving the cycle performance of the battery. In addition, the additive in the primer coating layer is closer to the current collector, and the primer coating layer has a high content of conductive carbon, so it is easier to reduce the electron to produce an SEI film rich in nitrogen elements.

[0135] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. That is, the negative electrode primer coating layer can be arranged on any one or both of the two opposite surfaces of the negative electrode current collector.

[0136] Referring to FIG. 3, the application provides a negative electrode sheet 300, which comprises a negative electrode current collector 310, a negative electrode primer layer 320, and a negative electrode active material layer 330. The negative electrode primer layer 320 is coated on one surface of the negative electrode current collector 310, and the negative electrode active material layer 330 is coated on the surface of the negative electrode primer layer 320, with the negative electrode primer layer 320 being located between the negative electrode current collector 310 and the negative electrode active material layer 330.

[0137] In one embodiment, the mass content of the conductive agent contained in the negative electrode primer layer is 60% to 70%. Exemplarily, the mass content of the conductive agent can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, etc. typical but non-limiting values. Exemplarily, the conductive agent can be one or more of carbon black, graphite, ketjen black, carbon nanotube, graphene, and carbon fiber.

[0138] The embodiments of the application control the content of the conductive agent within the above range, so that the negative electrode primer layer has a higher conductive capacity, which is conducive to building a good electronic channel between the negative electrode active layer and the negative electrode current collector, reducing the internal resistance of the negative electrode sheet, and increasing the moving rate of electrons.

[0139] In one embodiment, the mass content of the binder contained in the negative electrode primer layer is 7% to 40%. Exemplarily, the mass content of the binder can be 7%, 10%, 15%, 20%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. typical but non-limiting values. Exemplarily, the binder can be at least one of styrene butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, and polyvinyl alcohol.

[0140] The embodiments of the application control the content of the binder within the above range, which can enhance the adhesion between the negative electrode primer layer and the negative electrode current collector, and the adhesion between the negative electrode primer layer and the negative electrode active material layer, prevent the negative electrode primer layer from peeling and cracking, and thus improve the cycle life of the battery.

[0141] In one embodiment, the negative electrode primer layer further comprises a thickening agent, and the mass content of the thickening agent in the negative electrode primer layer is 2% to 5%. Exemplarily, the mass content of the thickening agent can be 2%, 3%, 4%, 5%, etc. typical but non-limiting values.

[0142] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] In some embodiments, the negative active material contained in the negative active material layer can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0144] In some embodiments, the negative active material layer can further optionally include a binder. As an example, the binder can 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).

[0145] In some embodiments, the negative active material layer can further optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0146] In some embodiments, the negative active material layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0147] In some embodiments, the negative electrode sheet can be prepared by:

[0148] The components for preparing the negative base coating layer described above, such as the additive, the conductive agent, the binder, and the thickening agent, are dispersed in an aqueous solvent to form a negative base coating slurry, wherein the anion of the additive includes at least one of nitrate ion and nitrite ion.

[0149] coating the negative electrode base coating slurry on at least one surface of the negative electrode current collector to form a negative electrode base coating layer;

[0150] The components for preparing the negative electrode active material layer, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in the aqueous solvent to form a positive electrode active slurry, which is coated on the surface of the negative electrode base coating layer, so that the negative electrode base coating layer is located between the negative electrode current collector and the negative electrode active material layer. After drying, cold pressing and other processes, the negative electrode sheet is obtained.

[0151] In one embodiment, the solid content of the negative electrode base coating slurry is 5% to 15%. Exemplarily, the solid content of the negative electrode base coating slurry can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% and the like typical but non-limiting values.

[0152] The solid content of the negative electrode base coating slurry can be tested by using the methods and devices known in the art. As an example, a copper foil is weighed in a loss on drying tester, denoted as M0, and the device is reset. The negative electrode base coating slurry is taken and coated on the copper foil in a small amount, and then placed in a moisture tester for weighing, denoted as M1. The device is closed and drying is started. After completion, the weighing data is recorded as M2, and the solid content is calculated as (M2-M0) / (M1-M0).

[0153] Controlling the solid content of the negative electrode base coating slurry within a suitable range means that the negative electrode base coating slurry has a proper viscosity, so that the negative electrode sheet has good adhesion, and the processing and coating of the negative electrode base coating slurry are facilitated.

[0154] In one embodiment, the viscosity of the negative electrode base coating slurry is 100 mPa·s to 2000 mPa·s. The viscosity of the negative electrode base coating slurry at 25°C under a stirring speed of 30 rpm can be selected as 100 mPa·s, 200 mPa·s, 400 mPa·s, 600 mPa·s, 800 mPa·s, 1000 mPa·s, 1200 mPa·s, 1500 mPa·s, 1800 mPa·s, 2000 mPa·s or any value therebetween.

[0155] The viscosity of the negative electrode base coating slurry can be tested by using the methods and devices known in the art. As an example, the rotary viscometer is used to measure the viscosity of the base coating slurry. A suitable rotor is selected, and the viscometer rotor is fixed. The base coating slurry is placed below the viscometer rotor, and the slurry just submerges the scale line of the rotor. The instrument model is Shanghai Fangrui NDJ-5S, the rotor is 62#, the rotation speed is 30 rpm, the viscosity range of the slurry that can be measured is 0-1000 mPa·s, the rotor is 63#, the rotation speed is 30 rpm, the viscosity range of the slurry that can be measured is 0-2000 mPa·s, the test temperature is 25°C, and the test time is 5 minutes. The data is read when the reading is stable.

[0156] The viscosity of the negative electrode primer slurry is controlled within the above range, which is beneficial to the coating and drying of the slurry, and improves the processing performance and use performance of the slurry.

[0157] [Electrolyte]

[0158] During the charging and discharging of the secondary battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting the active ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the embodiments of the present application, and can be selected according to actual needs.

[0159] The electrolyte includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited, and can be selected according to actual needs.

[0160] As an example, the electrolyte salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0161] As an example, the solvent can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0162] In one embodiment, the electrolyte can also optionally include an electrolyte additive. As an example, the electrolyte additive can include a negative electrode film-forming additive, can also include a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, an additive capable of improving low-temperature power performance of the battery, etc.

[0163] [Separator]

[0164] In one embodiment, the secondary battery further includes a separator.

[0165] The kind of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0166] In one embodiment, the material of the separator can include 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0167] In one embodiment, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly by a winding process or a stacking process.

[0168] [Secondary battery]

[0169] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can be used continuously after the active material is activated by charging after the battery is discharged. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (e.g., lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, and mainly functions to conduct the active ions.

[0170] One embodiment of the present application provides a secondary battery including the electrode sheet described in one embodiment of the present application.

[0171] In one embodiment, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0172] In one embodiment, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0173] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, FIG. 4 is a secondary battery 3 of a square structure as an example.

[0174] In one embodiment, referring to FIG. 5, FIG. 5 is a schematic diagram of an exploded structure of the secondary battery 3 according to some embodiments of the present application. The secondary battery 3 can include a housing 31 and a cover plate 33. The housing 31 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 31 has an opening communicating with the receiving cavity, and the cover plate 33 is used to cover the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 32 through a winding process and / or a stacking process. The electrode assembly 32 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 32. The number of electrode assemblies 32 contained in the secondary battery 3 can be one or more, which can be adjusted according to actual needs. Among them, the negative electrode sheet includes the negative electrode sheet of the above-mentioned embodiments.

[0175] In one embodiment, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0176] Referring to FIG. 6, FIG. 6 is a schematic diagram of a battery module 4 according to an embodiment of the present application. In the battery module 4, a plurality of secondary batteries 3 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of secondary batteries 3 can be fixed by fasteners.

[0177] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 3 are received in the receiving space.

[0178] In one embodiment, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0179] Referring to FIG. 7, FIG. 7 is a schematic diagram of an exploded structure of a battery pack 5 according to an embodiment of the present application. The battery pack 5 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 51 and a lower box body 52, and the upper box body 51 is used to cover the lower box body 52 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0180] In addition, the fourth aspect of the present application also provides an electric device including the secondary battery according to the embodiments of the present application. The secondary battery according to the embodiments of the present application can be used as a power supply of the electric device, or can be used as an energy storage unit of the electric device. Therefore, the standby or endurance time of the electric device according to the embodiments of the present application is long, and the safety performance is good.

[0181] Some embodiments of the present application provide a power consumption device using a battery as a power source. The power consumption device can be, but is not limited to, a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be, but is not limited to, a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be, but is not limited to, a pure electric vehicle, a hybrid electric vehicle, or a range extended electric vehicle. The spacecraft includes an airplane, a rocket, a space shuttle, a spacecraft, and the like. The electric toy includes a fixed or mobile electric toy, such as a game machine, an electric automobile toy, an electric ship toy, an electric airplane toy, and the like. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, an electric planer, and the like.

[0182] As the power consumption device, a battery monomer, a battery module, or a battery pack can be selected according to the use requirement thereof.

[0183] Referring to FIG. 8, FIG. 8 is a schematic diagram of a power consumption device provided by an embodiment of the present application. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirement of high power and high energy density of the power consumption device, a battery pack or a battery module can be used.

[0184] Embodiment

[0185] Hereinafter, an embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiment, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0186] Embodiment 1

[0187] The present embodiment provides a secondary battery.

[0188] [Preparation of the positive electrode tab]

[0189] The positive electrode tab includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode primer layer. The positive electrode active material layer is located on both sides of the positive electrode current collector. The positive electrode primer layer is located between the positive electrode current collector and the positive electrode active material layer. The positive electrode primer layer contains an additive, and the additive is lithium nitrate. The thickness of the positive electrode primer layer is 0.61 μm, and the coating weight of the positive electrode primer layer is 0.8 mg / cm 2 .

[0190] The positive electrode tab is prepared by the following preparation method:

[0191] The additive lithium nitrate, the conductive agent carbon black, and the binder polyacrylate are mixed and dispersed in a water solvent according to a mass ratio of 5:50:45 to form a positive electrode bottom coating slurry with a solid content of 15%; the positive electrode bottom coating slurry is coated on two surfaces of a positive electrode current collector aluminum foil to form a positive electrode bottom coating layer.

[0192] The positive electrode active material lithium iron phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are stirred and mixed uniformly in an N-methyl pyrrolidone solvent according to a weight ratio of 97:1:2 to obtain a positive electrode active slurry; the positive electrode active slurry is then uniformly coated on the positive electrode bottom coating layer according to a surface density of 13.7 mg / cm 2

[0193] [Preparation of a negative electrode sheet]

[0194] The negative electrode active material artificial graphite, the binder styrene butadiene rubber, the conductive agent carbon black, and the thickening agent sodium hydroxymethyl cellulose are mixed according to a mass ratio of 95.2:2.3:1.3:1.2, and then dissolved in deionized water to obtain a negative electrode slurry, which is coated on a copper foil surface, dried, and then cold-pressed to obtain a negative electrode sheet.

[0195] [Separator film]

[0196] The separator film is a polyethylene porous film with a size of 45 mm x 55 mm.

[0197] [Electrolyte]

[0198] Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are mixed uniformly according to a volume ratio of 3:7, and then LiPF6 is uniformly dissolved in the mixed solvent to obtain an electrolyte, in which the concentration of lithium salt is 12.5%.

[0199] [Preparation of a secondary battery]

[0200] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, with the separator film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain a bare cell; the bare cell is welded with a tab, and then put into an aluminum shell and baked at 80°C to remove water; electrolyte is injected into the aluminum shell, and then sealed to obtain a non-charged battery. The non-charged battery is sequentially subjected to processes of standing, hot and cold pressing, formation, shaping, and capacity testing, to obtain a lithium ion battery product of Example 1.

[0201] Examples 2-11

[0202] ​Examples 2-11 provide a secondary battery, wherein the main difference between the secondary battery and Example 1 is that the positive electrode sheet is different, such as at least one of the mass fraction of the additive in the positive electrode undercoat layer, the thickness of the positive electrode undercoat layer, the coating weight of the positive electrode undercoat slurry, and the type of the additive is different. For details, see Table 1. The preparation method of the secondary battery in Examples 2-11 is the same as that of the secondary battery in Example 1.

[0203] Table 1

[0204] It should be noted that the thickness of the undercoat layer in the positive electrode sheet mentioned above is determined by the following method: taking the positive electrode sheet, measuring the thickness of the undercoat layer of the positive electrode sheet, i.e. the thickness of the positive electrode undercoat layer, by cross-section polishing-scanning electron microscopy (CP-SEM).

[0205] Example 12

[0206] The present embodiment provides a secondary battery.

[0207] [Preparation of the negative electrode sheet]

[0208] The negative electrode sheet comprises a negative electrode current collector, a negative electrode active material layer, and a negative electrode undercoat layer, the negative electrode active material layer being located on both sides of the negative electrode current collector; the negative electrode undercoat layer being located between the negative electrode current collector and the negative electrode active material layer, the negative electrode undercoat layer containing an additive, the additive comprising lithium nitrate; wherein the thickness of the negative electrode undercoat layer is 0.4 μm, and the coating weight of the negative electrode undercoat layer is 0.5 mg / cm 2 .

[0209] The negative electrode sheet is prepared by the following method:

[0210] The additive lithium nitrate, the conductive agent carbon black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose are mixed and dispersed in the water solvent in a mass ratio of 5:60:32:3 to form a negative electrode undercoat slurry with a solid content of 12.5%; the negative electrode undercoat slurry is coated on both surfaces of the negative electrode current collector copper foil to form a negative electrode undercoat layer.

[0211] The negative electrode active material artificial graphite, the binder (SBR styrene-butadiene rubber), the conductive agent (carbon black), and the thickening agent (sodium hydroxymethyl cellulose CMC) are mixed in a mass ratio of 95.2:2.3:1.3:1.2, and then dissolved in deionized water to obtain a negative electrode active slurry after stirring uniformly; the negative electrode active slurry is then uniformly coated on the negative electrode undercoat layer, and the negative electrode sheet is obtained after drying and cold pressing.

[0212] [Preparation of the positive electrode sheet]

[0213] The positive active material lithium iron phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1:2 in an N-methylpyrrolidone solvent to obtain a positive active slurry; then the positive active slurry is uniformly coated on both surfaces of the positive current collector aluminum foil by doctor blade coating at a surface density of 13.7 mg / cm 2 After drying at 140°C, cold pressing, and slitting, a positive electrode sheet is obtained.

[0214] [Separator]

[0215] The separator is a polyethylene porous film with a size of 45 mm x 55 mm.

[0216] [Electrolyte]

[0217] Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:7, and then LiPF6 is uniformly dissolved in the mixed solvent to obtain an electrolyte. In the electrolyte, the concentration of lithium salt is 12.5%.

[0218] [Preparation of secondary battery]

[0219] The positive electrode sheet of the example, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator. Then, a bare cell is obtained by winding. The bare cell is welded with tabs, and is placed in an aluminum shell and baked at 80°C to remove water. Then, the electrolyte is injected and sealed to obtain a non-charged battery. The non-charged battery is subjected to the processes of standing, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the lithium ion battery product of Example 12.

[0220] Examples 13-22

[0221] Examples 13-22 provide a secondary battery, wherein the main difference between the secondary battery and Example 12 is that the negative electrode sheet is different, such as at least one of the mass percentage of the additive in the negative electrode undercoat, the thickness of the negative electrode undercoat, the coating weight of the negative electrode undercoat slurry, and the type of additive. For details, see Table 2. The preparation method of the secondary battery in Examples 13-22 is the same as that of the secondary battery in Example 12.

[0222] Table 2

[0223] It should be noted that the thickness of the undercoat in the above-mentioned negative electrode sheet is determined by the following method: the negative electrode sheet is taken, and the thickness of the undercoat of the negative electrode sheet, i.e., the thickness of the negative electrode undercoat, is measured by cross-section polishing-scanning electron microscopy (CP-SEM).

[0224] Example 23

[0225] The present example provides a secondary battery, which is mainly different from the secondary battery of Example 3 in that the negative electrode sheet of the present example is the negative electrode sheet prepared in Example 14, and the other aspects are the same as the secondary battery of Example 3.

[0226] Example 24

[0227] The present example provides a secondary battery, which is mainly different from Example 9 in that the negative electrode sheet of the present example is the negative electrode sheet prepared in Example 20, and the other aspects are the same as the secondary battery of Example 9.

[0228] Example 25

[0229] The present example provides a secondary battery, which is mainly different from Example 10 in that the negative electrode sheet of the present example is the negative electrode sheet prepared in Example 21, and the other aspects are the same as the secondary battery of Example 10.

[0230] Example 26

[0231] The present example provides a secondary battery, which is mainly different from Example 11 in that the negative electrode sheet of the present example is the negative electrode sheet prepared in Example 22, and the other aspects are the same as the secondary battery of Example 11.

[0232] Comparative Example 1

[0233] The main difference between the preparation method of the secondary battery in Comparative Example 1 and the preparation method of the secondary battery in Example 1 is that only the conductive agent and the binder are added in the positive electrode base coating slurry, and no additive is added; the mass ratio of the conductive agent and the binder is 1:1; and the other aspects are the same. For details, see Table 1.

[0234] Comparative Example 2

[0235] The main difference between the preparation method of the secondary battery in Comparative Example 2 and the preparation method of the secondary battery in Example 1 is that no base coating layer is prepared in the positive electrode sheet, and the other aspects are the same. For details, see Table 1.

[0236] Comparative Example 3

[0237] The main difference between the preparation method of the secondary battery in Comparative Example 3 and the preparation method of the secondary battery in Example 3 is that the types of additives are different; and the other aspects are the same. For details, see Table 1.

[0238] Comparative Example 4

[0239] The main difference between the preparation method of the secondary battery in Comparative Example 4 and the preparation method of the secondary battery in Example 12 is that only the conductive agent, the binder and the thickening agent are added in the negative electrode base coating slurry, and no additive is added; the mass ratio of the conductive agent, the binder and the thickening agent is 65:32:3; and the other aspects are the same. For details, see Table 2.

[0240] Comparative Example 5

[0241] The difference between the preparation method of the secondary battery in Comparative Example 5 and the preparation method of the secondary battery in Example 14 mainly lies in the different types of additives; the others are the same. For details, see Table 2.

[0242] Comparative Example 6

[0243] The difference between the preparation method of the secondary battery in Comparative Example 6 and the preparation method of the secondary battery in Example 12 mainly lies in that the additive is located in the negative active material layer, and the negative electrode plate does not contain a primer layer; the others are the same.

[0244] The preparation method of the negative electrode plate is as follows:

[0245] The negative active material artificial graphite, the binder styrene-butadiene rubber, the conductive agent carbon black, the thickening agent sodium hydroxymethyl cellulose, and the additive lithium nitrate were mixed according to a mass ratio of 94.9:2.3:1.3:1.2:0.3, then dissolved in deionized water, stirred uniformly to obtain a negative electrode slurry, coated on the surface of a copper foil, and dried and cold-pressed to obtain a negative electrode plate.

[0246] Performance detection

[0247] (1) Battery capacity retention rate test

[0248] The battery capacity retention rate test process is as follows: at 25°C, the battery corresponding to Example 1 is charged at 1 / 3C constant current to 3.65V, then charged at 3.65V constant voltage to a current of 0.05C, and left for 5min, then discharged at 1 / 3C to 2.5V, and the obtained capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle is recorded at the same time, then the battery capacity retention rate Pn=Cn / C0*100% after each cycle is obtained, and the battery capacity retention rate is obtained.

[0249] In this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 1000th cycle corresponds to n=1000.

[0250] (2) DC impedance test of the battery after 1000 cycles

[0251] After the battery is cycled for 1000 times, the battery DC impedance test process is as follows: at 25°C, the battery is charged at 1 / 3C constant current to 3.65V, then charged at 3.65V constant voltage to a current of 0.05C, left for 5min, then discharged at 1 / 3C constant current for 90min, left for 120min, and then the voltage V1 is recorded. Then discharged at 4C for 30s, and the voltage V2 is recorded, then (V2-V1) / 4C, and the internal resistance DCR of the battery is obtained.

[0252] (3) Adhesion test of negative electrode sheet

[0253] Adhesion between negative active material layer and negative current collector: Referring to GB / T 2792-2014 “Test method for adhesive tape peeling strength”. Specifically, a sheet with double-sided coated negative active material layer was taken with a length of 100 mm and a width of 15 mm; the sheet was attached to a steel plate with 3M double-sided tape; one end of the tensile testing machine clamped the steel plate and the other end clamped the sheet, and the adhesion between the film surface and the substrate was tested by 180° pulling; the performance test results of the above examples and comparative examples are shown in Table 3.

[0254] (4) Shear strength test of positive electrode sheet

[0255] A freshly baked positive electrode sheet was taken, and a special die-cut double-sided tape (9 mm*9 mm) was attached, and the other side was attached to a stainless steel plate after sanding and wiping. The stainless steel plate and the area of the sheet not attached with double-sided tape were fixed on the tensile testing machine, the tensile testing machine was turned on, the parameters were set, and the test record was recorded. The maximum tensile force Fs (N) was taken, the stress area S was recorded, and the shear strength Q = Fs / S (MPa) was calculated.

[0256] (5) Thickness test of primer layer

[0257] The thickness of the primer layer of the negative electrode sheet, i.e. the thickness of the negative electrode primer layer, was measured by cross-section polishing-scanning electron microscopy (CP-SEM).

[0258] (6) Coating weight test

[0259] The surface powder of the sheet was scraped off, and then a punch was used to take a circle of the primer area and a tab area (a circle without primer layer), and their masses were m1 and m2, respectively. The coating mass of the single-sided primer layer was (m1-m2) / 2.

[0260] (7) Component test

[0261] The primer powder was scraped off from the surface of the substrate and washed with ethanol. Since nitrate is soluble in ethanol, the powder after washing is the total amount of components in the primer layer except for the additives. In other words, the mass of the powder before washing is m1, and the mass of the powder after washing is m2. The mass of the additives is m1-m2. The powder after washing was subjected to thermogravimetric test in a nitrogen atmosphere. Since the decomposition temperatures of the binder and the thickening agent are different, and the conductive agent does not decompose, the masses of the three components can be obtained.

[0262] Table 3

[0263] From the results of Examples 1 to 26 and Comparative Examples 1 to 6, it can be seen that the electrode tab and the secondary battery provided by the present application have a high capacity retention rate and a low direct current resistance, and can improve the cycle life of the battery in a comprehensive manner.

[0264] The above merely provides optional embodiments of the present application, but is not intended to limit the present application. The present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A secondary battery, characterized in that, Includes an electrode, said electrode comprising: current collector; An active material layer is located on at least one surface of the current collector; and A base coating layer, located between the current collector and the active material layer, contains an additive, wherein the anion of the additive includes at least one of nitrate ions and nitrite ions.

2. The secondary battery according to claim 1, characterized in that, The molecular formula of the additive is A(NO). x ) y , Where 2≤x≤3, 1≤y≤3; A includes at least one of Li, Na, K, Cs, Mg, Ca, and Al.

3. The secondary battery according to claim 1 or 2, characterized in that, The additive constitutes 5% to 30% of the mass of the base coating.

4. The secondary battery according to any one of claims 1-3, characterized in that, The thickness of the base coating is 0.07 μm to 3.1 μm.

5. The secondary battery according to any one of claims 1-3, characterized in that, The coating weight of the primer is 0.1 mg / cm³. 2 ~4mg / cm 2 .

6. The secondary battery according to any one of claims 1-5, characterized in that, The base coating also includes a conductive agent and a binder. The conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers. The binder includes one or more of styrene-butadiene rubber, olefin resins, and acrylic resins.

7. The secondary battery according to any one of claims 1-6, characterized in that, The electrode is a positive electrode, the base coating is a positive electrode base coating, and the conductive agent contained in the positive electrode base coating has a mass content of 40% to 60%.

8. The secondary battery according to any one of claims 1-6, characterized in that, The electrode sheet is a positive electrode sheet, the base coating is a positive electrode base coating, and the binder content in the positive electrode base coating is 20% to 60% by mass.

9. The secondary battery according to any one of claims 1-6, characterized in that, The electrode sheet is a negative electrode sheet, the bottom coating is a negative electrode bottom coating, and the mass content of the conductive agent contained in the negative electrode bottom coating is 60% to 70%.

10. The secondary battery according to any one of claims 1-6, characterized in that, The electrode sheet is a negative electrode sheet, the base coating is a negative electrode base coating, and the binder content in the negative electrode base coating is 7% to 40% by mass.

11. The secondary battery according to any one of claims 1-6, characterized in that, The electrode sheet is a negative electrode sheet, the base coating is a negative electrode base coating, and the negative electrode base coating also includes a thickener, the thickener accounting for 2% to 5% of the mass of the negative electrode base coating.

12. The secondary battery according to any one of claims 1-11, characterized in that, The electrode is a negative electrode, the active material layer is a negative active material layer, and at least a portion of the surface of the negative active material layer is covered with an SEI film, the SEI film comprising Li3N and LiN. a O b At least one of the following, wherein 1≤a≤3 and 1≤b≤7.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-12.

14. A method for preparing a secondary battery, characterized in that, Includes the following steps: The electrode, separator, and electrolyte are provided and assembled to obtain the secondary battery according to any one of claims 1-3; The electrode is defined in any one of claims 1-12.

15. The method for preparing a secondary battery according to claim 14, characterized in that, The method for preparing the electrode includes the following steps: Prepare a primer slurry containing the additives described above; The primer slurry is applied to at least one surface of the current collector to form the primer coating layer; The active material layer is prepared on the surface of the base coating that is opposite to the current collector.

16. The method for preparing a secondary battery according to claim 15, characterized in that, The electrode is a positive electrode, and the solid content of the primer slurry is 10% to 20%.

17. The method for preparing a secondary battery according to claim 15, characterized in that, The electrode is a positive electrode, and the viscosity of the base coating slurry is 100 mPa·s to 1000 mPa·s.

18. The method for preparing a secondary battery according to claim 15, characterized in that, The electrode is a negative electrode, and the solid content of the primer slurry is 5% to 15%.

19. The method for preparing a secondary battery according to claim 15, characterized in that, The electrode is a negative electrode, and the viscosity of the base coating slurry is 100 mPa·s to 2000 mPa·s.

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