Negative plate, battery, battery pack and electric equipment

Abstract

The invention provides a negative electrode plate, a battery, a battery pack and electric equipment, the negative electrode plate comprises a negative electrode current collector and a negative electrode coating located on at least one side surface of the negative electrode current collector, the negative electrode coating comprises non-coated graphite, and the OI value of the non-coated graphite in the negative electrode coating is 0.06-2. The battery impedance can be reduced, and the cycle life of the battery can be prolonged.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a negative electrode sheet, a battery, a battery pack and electrical equipment. Background Art

[0002] The negative electrode is a crucial component of batteries and a key factor influencing performance, including cycle life. Graphite is often used as the negative electrode active material in related technologies. However, due to factors such as volume expansion, poor ability to intercalate and deintercalate active ions such as lithium ions, and side reactions during battery charge and discharge, the resulting high battery impedance and poor cycle life performance are issues that urgently need to be addressed. Summary of the Invention

[0003] The present invention provides a negative electrode sheet, a battery, a battery pack and an electrical device, which can reduce battery impedance and improve battery cycle life and other performance, effectively overcoming the defects of the prior art.

[0004] In one aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode coating located on at least one side of the negative electrode current collector, wherein the negative electrode coating comprises non-coated graphite, and the OI value of the non-coated graphite in the negative electrode coating is 0.06 to 2.

[0005] According to one embodiment of the present invention, the OI value of the non-coated graphite in the negative electrode coating is 0.06 to 1.5.

[0006] According to one embodiment of the present invention, the specific surface area of ​​the non-coated graphite is 0.4 m 2 / g~2.2m 2 / g.

[0007] According to one embodiment of the present invention, the negative electrode coating comprises a conductive agent and a negative electrode active material, the negative electrode active material comprises the non-coated graphite, and the mass ratio of the conductive agent to the negative electrode active material is 0-1%.

[0008] According to one embodiment of the present invention, the surface density of the negative electrode coating is 80 to 600 g / m 2 .

[0009] According to one embodiment of the present invention, the resistivity of the negative electrode sheet is less than or equal to 0.53Ω*cm.

[0010] Another aspect of the present invention provides a battery comprising the above-mentioned negative electrode sheet.

[0011] According to one embodiment of the present invention, the battery includes an electrolyte, and the electrolyte includes a film-forming additive.

[0012] According to one embodiment of the present invention, the film-forming additive includes vinylene carbonate; and / or the ratio of the mass of the film-forming additive to the total mass of the electrolyte is 9% to 11%.

[0013] According to one embodiment of the present invention, the battery satisfies M≥18, M=1000000×(c×(0.12-c)(c-0.08) / (a×d)-0.0000545e), wherein a is the specific surface area of ​​the non-coated graphite, in m 2 / g; c is the mass percentage of the film-forming additive in the electrolyte; d is the OI value of the non-coated graphite in the negative electrode coating; e is the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the negative electrode active material.

[0014] According to one embodiment of the present invention, M is ≥50.

[0015] Another aspect of the present invention provides a battery pack comprising the above-mentioned battery.

[0016] Another aspect of the present invention provides an electrical device comprising the above-mentioned battery or the above-mentioned battery pack.

[0017] The implementation of the present invention has at least the following beneficial effects: the negative electrode coating includes non-coated graphite, and the OI value of the non-coated graphite in the negative electrode coating is controlled to be 0.06-2, which can improve the ion transmission capacity of the negative electrode sheet, reduce the liquid phase diffusion impedance and resistivity of the negative electrode sheet, thereby reducing the battery impedance, and can also take into account the improvement of battery cycle life and other performance. Specifically, it can be manifested in that the capacity retention rate of the battery after 1000 cycles at a rate of 1 / 3C is significantly improved, the number of cycle diving inflection points is reduced, and at the same time, the degree of change in the active specific surface area of ​​the negative electrode before and after the battery cycle is reduced, further demonstrating that the battery has good cycle life and rate performance. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0019] An embodiment of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode coating located on at least one side of the negative electrode current collector, wherein the negative electrode coating comprises non-coated graphite, and the OI value d of the non-coated graphite in the negative electrode coating is 0.06 to 2 (i.e., 0.06≤d≤2).

[0020] In the embodiment of the present invention, the non-coated graphite refers to graphite without carbon or other coating materials on its surface, which may specifically include non-coated natural graphite and / or non-coated artificial graphite.

[0021] According to the inventor's research, if coated graphite is used (i.e., the graphite surface is coated with a coating layer (such as carbon-coated graphite)), the resistivity and active specific surface area of ​​the negative electrode sheet will increase, thereby increasing the battery impedance and reducing the battery cycle life. The reason for this is that when there is a coating layer on the graphite surface, the impedance of the graphite will increase to a certain extent, and the active sites where side reactions occur between the graphite and the electrolyte will increase. The increase in impedance and active sites will affect the charge and discharge efficiency of the battery, leading to more side reactions, thereby exacerbating the consumption of compounds (such as VC and other film-forming additives) in the electrolyte that maintain the solid electrolyte interface film (SEI film) components formed on the surface of the electrode, making the SEI film less stable and affecting its protective effect on the graphite in the negative electrode sheet. For example, when the SEI film is damaged, active ions (such as active lithium ions) are continuously consumed, and the side reactions between the electrolyte and non-coated graphite will also increase, thereby affecting the cycle life and other performance of the battery.

[0022] In the embodiment of the present invention, non-coated graphite is used, which has a lower impedance and can ensure the charge and discharge efficiency of the battery. At the same time, the non-coated graphite has fewer active sites, which can reduce the active specific area of ​​the negative electrode sheet, reduce the side reactions between the non-coated graphite and other materials in the negative electrode sheet and the electrolyte, and reduce the consumption of compounds used to maintain the SEI components in the electrolyte, thereby maintaining the stability of the SEI film, reducing the consumption of active ions, and reducing the side reactions between the electrolyte and non-coated graphite, thereby improving the cycle life and other performance of the battery.

[0023] At the same time, under the above-mentioned structural system of the negative electrode sheet, the non-coated graphite in the negative electrode coating has a good directional arrangement state, which is conducive to the negative electrode sheet having a higher energy density, and can optimize the transmission path of active ions such as lithium ions in the negative electrode sheet, reducing the internal resistance of the negative electrode sheet. At the same time, the directional arrangement of the negative electrode structure can also reduce expansion, avoiding the non-coated graphite from shrinking and expanding to a large extent during the charge and discharge cycle of the battery, and the resulting cracking between the graphite layers, which in turn leads to battery performance degradation, cycle diving and other problems, thereby improving the battery's cycle life and other performance.

[0024] Therefore, the embodiments of the present invention can reduce battery impedance, improve battery rate performance (fast charging performance), and also improve battery cycle life and other performance.

[0025] In an embodiment of the present invention, non-coated graphite is used as the negative electrode active material of the negative electrode coating, that is, the negative electrode coating includes a negative electrode active material, and the negative electrode active material in the negative electrode coating includes non-coated graphite, which can specifically be non-coated graphite (that is, all the negative electrode active materials in the negative electrode coating are non-coated graphite).

[0026] For example, the OI value of the non-coated graphite in the negative electrode coating may be 0.06, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 2, or a range consisting of any two thereof.

[0027] In some preferred embodiments, the OI value d of the non-coated graphite in the negative electrode coating is 0.06 to 1.5. This is conducive to the non-coated graphite in the negative electrode coating having a better oriented arrangement state, optimizing the transmission path of active ions such as lithium ions in the negative electrode sheet, further reducing the liquid phase diffusion impedance and resistivity of the negative electrode sheet, and being more conducive to its capacity, thereby reducing the battery impedance and taking into account the improvement of battery cycle life and other performance.

[0028] In some embodiments, the specific surface area a of the non-coated graphite can be 0.4 m 2 / g~2.2m 2 / g (i.e. the unit is m 2 / g, 0.4≤a≤2.2), for example, 0.4m 2 / g, 0.6m 2 / g, 0.8m 2 / g、1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g, 2m 2 / g, 2.2m 2 / g or a range consisting of any two of them is beneficial to further reduce the impedance of the negative electrode sheet and improve the battery's rate performance and cycle life.

[0029] In the embodiments of the present invention, the non-coated graphite used can be purchased commercially or prepared by conventional methods in the art, and its specific surface area and other characteristics can be controlled by conventional methods in the art. For example, artificial graphite can generally be sintered from raw materials (aggregates) such as petroleum coke and needle coke. In specific implementation, the sintering temperature and sintering time and other conditions can be controlled to form a graphite material (non-coated graphite) with preset specific surface area and other characteristics.

[0030] In addition, the above-mentioned negative electrode coating may or may not include a conductive agent, and the ratio e of the mass of the conductive agent to the mass of the negative electrode active material may specifically be 0 to 1% (i.e., 0≤e≤1%), for example, 0 (i.e., the negative electrode coating does not contain a conductive agent), 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1% or a range consisting of any two of them.

[0031] In the related art, it is usually necessary to introduce a conductive agent into the negative electrode coating to meet the conductivity requirements of the negative electrode sheet. According to further research by the inventors, under the negative electrode sheet structure system of the embodiment of the present invention (using non-coated graphite, and making the OI value of the non-coated graphite in the negative electrode coating within the range of 0.06 to 2), when the negative electrode coating does not contain a conductive agent, the liquid phase diffusion impedance and resistivity of the negative electrode sheet can be further reduced, thereby reducing the battery impedance and significantly improving the battery cycle life and other performance. The reason for this is that under the above-mentioned negative electrode sheet structure system, based on the conductivity of the non-coated graphite and its directional regular arrangement in the negative electrode coating, the negative electrode sheet can be further reduced. , which can maintain a high conductivity of the negative electrode coating, and is conducive to the electrolyte infiltration of the negative electrode sheet, thereby improving the ion diffusion capacity of the negative electrode sheet. At the same time, the negative electrode coating does not contain a conductive agent (other conductive materials except for the non-coated graphite), that is, the negative electrode coating removes small particle components such as the conductive agent, thereby reducing its side reaction with the electrolyte. Therefore, while the electrolyte infiltrates the negative electrode sheet and reduces the liquid phase diffusion impedance of the negative electrode sheet, it can also take into account the suppression of the side reaction between the negative electrode sheet and the electrolyte, as well as the resulting expansion of the negative electrode sheet, deterioration of battery performance, and cycle diving. Problems, thereby reducing battery impedance and taking into account improving the battery's rate performance and cycle life.

[0032] Specifically, the resistivity of the above-mentioned negative electrode sheet may be less than or equal to 0.53Ω*cm (Ω·cm), specifically 0.25Ω*cm to 0.53Ω*cm, for example, 0.25Ω*cm, 0.26Ω*cm, 0.28Ω*cm, 0.3Ω*cm, 0.32Ω*cm, 0.35Ω*cm, 0.38Ω*cm, 0.4Ω*cm, 0.42Ω*cm, 0.45Ω*cm, 0.48Ω*cm, 0.5Ω*cm, 0.53Ω*cm or a range consisting of any two thereof.

[0033] In the embodiment of the present invention, the conductive agent can be a conventional conductive material in the art, for example, the conductive agent includes one or more of carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber.

[0034] Generally, the negative electrode coating further includes a binder. For example, the negative electrode coating is composed of a negative electrode active material and a binder.

[0035] In an embodiment of the present invention, the above-mentioned adhesive can be a conventional adhesive material in the field. For example, the adhesive can include one or more of styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0036] Specifically, based on the total mass of the negative electrode coating, the mass fraction of the negative electrode active material (that is, the ratio of the mass of the negative electrode active material to the total mass of the negative electrode coating) can be 80% to 99.5%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two thereof, and the mass fraction of the binder can be 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, 20% or a range consisting of any two thereof.

[0037] In addition, the negative electrode coating may further include a dispersant, which may include a carboxymethyl cellulose salt, specifically sodium carboxymethyl cellulose (CMC). The negative electrode coating is composed of, for example, a negative electrode active material, a binder, and a dispersant.

[0038] In the embodiment of the present invention, the performance of the negative electrode sheet under high surface density and compaction density is improved, and the cycle life and other performance of the battery are improved. The surface density of the negative electrode coating can be specifically 80 to 600 g / m 2 , for example 80g / m 2 , 100g / m 2 , 130g / m 2 , 150g / m 2 , 180g / m 2 , 200g / m 2 , 230g / m 2 , 250g / m 2 , 280g / m 2 , 300g / m 2 、350g / m 2 , 400g / m 2 , 450g / m 2 , 500g / m 2 , 550g / m 2 , 600g / m 2 or a range consisting of any two of them.

[0039] In an embodiment of the present invention, a negative electrode coating (negative electrode active material layer) may be provided on one surface of the negative electrode current collector, or a negative electrode coating may be provided on both surfaces of opposite sides in the thickness direction of the negative electrode current collector. When negative electrode coatings are provided on both surfaces of opposite sides of the negative electrode current collector, the negative electrode coating on one surface may be a negative electrode coating including non-coated graphite, and the OI value of the non-coated graphite may be 0.06 to 2, or the negative electrode coatings on both surfaces of opposite sides of the negative electrode current collector may be negative electrode coatings including non-coated graphite, and the OI value of the non-coated graphite may be 0.06 to 2.

[0040] The embodiment of the present invention may adopt a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0041] In an embodiment of the present invention, the OI value of the negative electrode active material in the negative electrode coating can be regulated by magnetic field induction or other methods. In an embodiment of the present invention, a conventional magnetic field application method can be used to apply a magnetic field and control conditions such as magnetic field strength to regulate the OI value of the negative electrode active material in the negative electrode coating. For example, in the process of preparing a negative electrode sheet by coating, a conventional coating device in the art, such as a continuous coating device, can be used to apply a negative electrode slurry for forming a negative electrode coating to a predetermined surface of a negative electrode current collector to form a negative electrode current collector coated with a wet film. At the same time, a magnetic field generating device is installed at the outlet of the coating device. The magnetic field generating device applies a magnetic field to the negative electrode current collector coated with the wet film to maintain a uniform and stable magnetic field. That is, the magnetic field generating device generates a magnetic field to form a magnetic field region, and the negative electrode current collector coated with the wet film passes through the magnetic field region. The time it takes for the negative electrode current collector coated with the wet film to pass through the magnetic field region is the magnetic field induction time. After the magnetic field induction is completed, the negative electrode current collector coated with the wet film is dried (baked) and roller-pressed to produce a negative electrode sheet.

[0042] The direction of the magnetic field is substantially perpendicular to the surface of the negative electrode current collector coated with the wet film (ie, the direction of the magnetic field is substantially parallel to the thickness direction of the negative electrode current collector).

[0043] In an embodiment of the present invention, when a negative electrode coating is formed on both the front and back surfaces of the negative electrode current collector, the negative electrode slurry can be first coated on one side of the negative electrode current collector, and then induced by a magnetic field and dried. Then, the negative electrode slurry is coated on the other side of the negative electrode current collector, and then induced by a magnetic field and dried. Then, the negative electrode sheet is obtained by rolling, cutting, and other processes.

[0044] During the preparation process of the above-mentioned negative electrode sheet, magnetic induction technology is used to orient the negative electrode active material particles (non-coated graphite particles) so that the OI value of the negative electrode active material in the negative electrode coating is 0.06-2, thereby optimizing the arrangement structure of the negative electrode active material particles in the negative electrode coating, reducing the resistivity and liquid phase diffusion impedance of the negative electrode sheet, thereby reducing the battery impedance, and suppressing problems such as the expansion of the negative electrode sheet, while also improving the battery's cycle life and other performance.

[0045] Specifically, during the preparation of the above-mentioned negative electrode sheet, the magnetic field strength of the applied magnetic field can be 0.5T to 2T, for example, 0.5T, 0.8T, 1T, 1.3T, 1.5T, 1.8T, 2T or a range consisting of any two of them, and the magnetic field induction time is, for example, about 12s, but is not limited thereto.

[0046] In the embodiment of the present invention, the coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using a coating method, and are not described in detail. Specifically, the rolling pressure can be 1 to 20 T.

[0047] In an embodiment of the present invention, the negative electrode slurry can be prepared by conventional methods in the art. For example, the components used to form the negative electrode coating, such as the negative electrode active material, the conductive agent, and the binder, can be dispersed in a first solvent. The first solvent includes, for example, deionized water and / or N-methylpyrrolidone (NMP) to prepare the negative electrode slurry, which is then coated on the surface of the negative electrode current collector. After magnetic field induction, drying, rolling and other processes, the negative electrode coating is formed to obtain the negative electrode sheet.

[0048] In a specific implementation, the negative electrode slurry can be prepared at a temperature of 20 to 45° C., for example, at room temperature (25° C.).

[0049] An embodiment of the present invention further provides a battery, comprising the above-mentioned negative electrode sheet. The battery has advantages corresponding to the above-mentioned negative electrode sheet, which will not be described in detail.

[0050] The battery of the embodiment of the present invention may be a lithium-ion battery (such as a lithium-ion power battery), a solar cell, or other new energy storage batteries.

[0051] Generally, a battery consists of an electrolyte, a cell, and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing, and the cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, meaning that the cell is composed of a stacked positive electrode sheet, a separator, and a negative electrode sheet.

[0052] Specifically, the positive electrode sheet includes a positive electrode collector and a positive electrode coating located on at least one side surface of the positive electrode collector. Specifically, the positive electrode coating can be provided on one side surface of the positive electrode collector, or the positive electrode coating can be provided on both sides of the positive electrode collector in the thickness direction.

[0053] Specifically, the positive electrode coating (positive electrode active material layer) may include a positive electrode active material, a conductive agent and a binder, all of which may be conventional materials in the art. For example, the positive electrode active material may include a lithium-containing positive electrode active material for a lithium-ion battery, such as one or more of lithium iron phosphate, lithium cobalt oxide, and a positive electrode ternary material. The positive electrode ternary material may include, for example, a nickel-cobalt-manganese ternary material and / or a nickel-cobalt-aluminum ternary material; the conductive agent may include one or more of carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, and polyurethane.

[0054] Based on the total mass of the positive electrode coating, the mass fraction of the positive electrode active material (that is, the ratio of the mass of the positive electrode active material to the total mass of the positive electrode coating) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two thereof, the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof, and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0055] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0056] In an embodiment of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the components used to form the positive electrode coating, such as the positive electrode active material, the conductive agent, and the binder, can be dispersed in a second solvent, and the second solvent includes, for example, N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying, rolling and other processes, the positive electrode sheet is obtained.

[0057] In the embodiment of the present invention, the electrolyte may be a non-aqueous electrolyte.

[0058] In some embodiments, the electrolyte includes a film-forming additive, which may specifically include vinylene carbonate (VC). By introducing the film-forming additive into the electrolyte, it is advantageous to adapt to the above-mentioned negative electrode system, form a stable SEI film on the surface of the negative electrode, and further inhibit problems such as side reactions between non-coated graphite and the electrolyte, thereby further reducing the battery impedance and improving the battery's cycle life and other performance.

[0059] After further research, the mass percentage of the film-forming additive in the electrolyte (i.e., the ratio of the mass of the film-forming additive to the total mass of the electrolyte) c can be 9% to 11% (i.e., 9%≤c≤11%), for example, 9%, 9.5%, 10%, 10.5%, 11% or a range composed of any two of them, further reducing the battery impedance and improving the battery's cycle life and other performance.

[0060] In addition, the electrolyte also includes an organic solvent and an electrolyte salt. The organic solvent includes, for example, ethylene carbonate and / or diethyl carbonate. The electrolyte salt may include a lithium salt. The lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0061] In the embodiment of the present invention, the battery satisfies M≥18, M=1000000×(c×(0.12-c)(c-0.08) / (a×d)-0.0000545e); wherein a is the specific surface area of ​​the non-coated graphite, in m 2 / g; d is the OI value of the non-coated graphite in the negative electrode coating; e is the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the negative electrode active material; c is the mass percentage of the film-forming additive in the electrolyte.

[0062] According to the inventors' research, the larger the specific surface area of ​​negative electrode active materials such as graphite in the negative electrode sheet, the more conducive it is to reducing the impedance of the negative electrode sheet and improving the rate performance of the battery. However, when the specific surface area of ​​the negative electrode active material is large, it will also lead to more reaction sites between it and the electrolyte, which will increase the side reactions between the negative electrode active material and materials such as the electrolyte, affecting the cycle life of the battery. At the same time, the content of the conductive agent in the negative electrode sheet is also a means of regulating the conductivity of the negative electrode sheet. When the content of the conductive agent in the negative electrode sheet is high, it is beneficial to improve the conductivity of the negative electrode sheet and improve the rate performance of the battery. However, the increase in the conductivity of the negative electrode sheet will also increase the side reactions between the materials in the negative electrode sheet and the electrolyte, affecting the cycle life of the battery. The lower the OI value of the graphite in the negative electrode coating, the more conducive it is to the conductivity of the negative electrode sheet in the vertical direction, which can reduce the impedance of the negative electrode sheet. In addition, the film-forming additive in the electrolyte is conducive to the formation of the SEI film on the surface of the negative electrode sheet and maintains the stability of the SEI film. Based on this, the inventors found through long-term research that by adopting non-coated graphite and synergistically regulating the specific surface area a of the non-coated graphite, the mass percentage c of the film-forming additive in the electrolyte, the OI value d of the non-coated graphite in the negative electrode coating, and the mass ratio e of the conductive agent to the negative electrode active material in the negative electrode coating, by satisfying M≥18, it is beneficial to reduce the internal resistance of the battery, improve the battery rate performance, and further improve the cycle life and other performance of the battery. For example, the cycle capacity retention rate of the battery cycled at a rate of 1 / 3C is improved, and the number of battery cycle diving inflection points is significantly increased. Especially when M≥50, the cycle life and other performance of the battery can be more significantly improved.

[0063] Illustratively, M is, for example, greater than or equal to 18.2, greater than or equal to 20, greater than or equal to 30, greater than or equal to 35, greater than or equal to 40, greater than or equal to 45, greater than or equal to 50, greater than or equal to 55, greater than or equal to 60, greater than or equal to 65, greater than or equal to 70, greater than or equal to 75, greater than or equal to 80, greater than or equal to 85, greater than or equal to 90, greater than or equal to 95, greater than or equal to 100, greater than or equal to 130, greater than or equal to 150, greater than or equal to 180, greater than or equal to 200, greater than or equal to 300, greater than or equal to 400, greater than or equal to 500, greater than or equal to 600, or a range consisting of any two values ​​therebetween.

[0064] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The embodiment of the present invention can adopt conventional separators in the art, for example, the separator includes a polypropylene film, but is not limited thereto.

[0065] In the embodiment of the present invention, the battery cell may be encapsulated with conventional shell materials in the art. The shell may include, for example, soft packaging materials such as aluminum-plastic film (ie, the battery is a soft packaging battery), but is not limited thereto.

[0066] In the embodiment of the present invention, the positive electrode sheets, separators, negative electrode sheets and other components can be assembled into a battery by conventional methods in the field. Specifically, the battery can be assembled in an inert gas atmosphere such as argon (Ar). For example, the positive electrode sheets, separators, and negative electrode sheets can be stacked in an alternating manner to produce a stacked battery cell (dry battery cell); the battery cell is then placed in a shell and injected with an electrolyte. After packaging and other processes, the battery is obtained.

[0067] An embodiment of the present invention further provides a battery pack including the above-mentioned battery. The battery has advantages corresponding to those of the negative electrode sheet, which will not be described in detail.

[0068] Generally, a battery pack includes multiple batteries as described above, which are connected as single cells to form a battery pack. These batteries can be electrically connected using conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without particular limitation.

[0069] An embodiment of the present invention further provides an electrical device, comprising the above-mentioned battery or the above-mentioned battery pack. The electrical device has advantages corresponding to those of the negative electrode sheet, which will not be described in detail.

[0070] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc.

[0071] In an embodiment of the present invention, after obtaining the negative electrode sheet, the negative electrode coating of the negative electrode sheet can be subjected to X-ray diffraction (XRD) analysis to measure the OI value of the non-coated graphite in the negative electrode coating. Specifically, the OI value represents the degree of orientation of the non-coated graphite particles in the negative electrode coating. A smaller OI value indicates a higher perpendicularity of the non-coated graphite particles in the negative electrode coating. In the XRD analysis results, I1 is the peak area of ​​the (110) peak of the non-coated graphite, and I2 is the peak area of ​​the (004) peak of the non-coated graphite. Therefore, the OI value of the graphite in the negative electrode coating = I2 / I1.

[0072] In the embodiments of the present invention, the areal density of the negative electrode coating refers to the double-sided areal density. The areal density testing process of the negative electrode coating may include: taking a negative electrode sheet sample (specifically, the negative electrode sheet may be cut using a 1.5 cm diameter cutter to obtain a negative electrode sheet sample with a diameter of 1.5 cm), measuring the total mass m1 of the negative electrode sheet sample and the surface area S of a single side of the negative electrode sheet sample in the thickness direction; then scraping off the electrode coating on the negative electrode sheet sample and measuring the mass m2 of the negative electrode current collector obtained. The areal density of the negative electrode coating = (m1-m2) / S. The total mass m1 of the negative electrode sheet sample and the mass m2 of the negative electrode current collector may be weighed using an electronic scale.

[0073] In the embodiment of the present invention, the specific surface area of ​​the non-coated graphite in the negative electrode coating can be measured by conventional methods in the art, specifically by Best BSD-660 (fully automatic high-throughput specific surface area and pore size analyzer).

[0074] In an embodiment of the present invention, after obtaining the negative electrode sheet, the cross section of the negative electrode coating (the cross section is substantially parallel to the thickness direction of the negative electrode sheet (also the thickness direction of the negative electrode coating)) can be subjected to electron microscopy analysis such as a scanning electron microscope (SEM) on the cross section. Based on the size, morphology, and shape characteristics of the negative electrode active material (non-coated graphite) and the conductive agent (for example, relative to graphite, carbon black (conductive agent) is spherical and its size is much smaller than graphite), it is determined whether the negative electrode coating contains a conductive agent and the content of the conductive agent is determined. Alternatively, the negative electrode coating can be scraped off the negative electrode sheet and then ground into powder to obtain a negative electrode powder sample. The negative electrode powder sample is then analyzed using an electron microscope such as an SEM. Based on the size, morphology, and shape characteristics of the negative electrode active material and the conductive agent (for example, relative to graphite, carbon black (conductive agent) is spherical and its size is much smaller than graphite), it is determined whether the conductive agent is contained in the negative electrode coating.

[0075] In specific implementation, the negative electrode sheet can be cut with a cutter of 1.5 cm in diameter to obtain a negative electrode sheet sample of 1.5 cm in diameter, and then the cross section is subjected to SEM analysis with a magnification of 500 times and a test area of ​​100 square micrometers (μm 2 The ratio of the conductive agent area in the region of 100 μm to the negative electrode active material area is the test result, which is the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the negative electrode active material e; wherein the conductive agent area is an area of ​​100 μm 2 The total area of ​​the conductive agent particles in the region of 100 μm is the area of ​​the negative electrode active material. 2 The total area of ​​the negative electrode active material particles within the region.

[0076] In specific implementation, the battery can be disassembled to remove the negative electrode sheet, and then the negative electrode sheet can be washed with an organic solvent such as dimethyl carbonate (DMC) to remove components such as electrolyte salt on the negative electrode sheet. After the negative electrode sheet is dried, the negative electrode sheet is subjected to the above-mentioned XRD, SEM and other analyses to measure the OI value of the negative electrode active material in the negative electrode coating and the content of the conductive agent and other characteristics.

[0077] The present invention is further described below through specific examples. In the following examples, when the negative electrode coating contains a conductive agent, the conductive agent used is carbon black.

[0078] 1. Preparation of negative electrode sheet

[0079] (1) At room temperature, uncoated artificial graphite, SBR, and CMC were mixed in a mass ratio of 100:3.5:1.5, and deionized water was added and stirred to prepare a negative electrode slurry;

[0080] (2) A continuous coating device is used to coat the negative electrode slurry on one side of a copper foil (thickness of 6 μm) to obtain a negative electrode current collector coated with a wet film, and a magnetic field generating device is installed at the outlet position of the coating device. The magnetic field generating device generates a magnetic field to form a magnetic field region, and the magnetic field is kept uniform and stable, so that the negative electrode current collector coated with the wet film passes through the magnetic field region. The time for the negative electrode current collector coated with the wet film to pass through the magnetic field region is about 12 seconds; then, the negative electrode current collector coated with the wet film is dried; wherein, the magnetic field intensity is 1.2 T, and the magnetic field direction is perpendicular to the surface of the copper foil coated with the wet film;

[0081] (3) Then, the coating, magnetic field induction and drying processes of step (2) are repeated on the other side of the copper foil to form a coating layer on both the front and back surfaces of the copper foil, and then the copper foil is rolled with a pressure of about 6T and cut into a preset shape and size to obtain a negative electrode sheet with a negative electrode coating formed on both the front and back surfaces of the copper foil; wherein the surface density of the negative electrode coating (double-sided surface density is 204g / m 2 ), the compaction density of the negative electrode coating is 1.57g / cm 3 .

[0082] 2. Preparation of positive electrode

[0083] Lithium iron phosphate, carbon black, and PVDF were mixed in a mass ratio of 100:1:1.8, and NMP was added and stirred evenly to prepare a positive electrode slurry;

[0084] The positive electrode slurry is coated on both the front and back surfaces of the aluminum foil. After drying and rolling, a positive electrode coating is formed on both the front and back surfaces of the aluminum foil. The positive electrode sheet is cut into a preset shape and size (corresponding to the size and shape of the negative electrode sheet). The surface density (double-sided surface density) of the positive electrode coating of the positive electrode sheet is 448g / m 2 .

[0085] 3. Battery assembly

[0086] In a glove box, under an Ar gas atmosphere, the positive electrode sheets, separators (polypropylene films) and negative electrode sheets were alternately stacked to produce a stacked battery cell (dry battery cell); the dry battery cell was placed in an aluminum-plastic film and injected with electrolyte to assemble into a soft-pack battery (the battery design capacity is 1.8Ah); the composition of the electrolyte used is as follows: the organic solvents are ethylene carbonate and diethyl carbonate, the volume ratio of ethylene carbonate and diethyl carbonate is 1:1, the film-forming additive is VC, the ratio of the mass of VC to the total mass of the electrolyte (i.e., the VC content in the electrolyte) is 10%, and the LiPF6 concentration in the electrolyte is 1 mol / L.

[0087] Implementation 2 to Example 17, Comparative Examples 1 to Comparative Example 2: The differences from Example 1 are that the specific surface area a of the non-coated graphite, the OI value d of the non-coated graphite in the negative electrode coating, the VC content c in the electrolyte, the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the non-coated graphite (the conductive agent content e in Table 1), the M value satisfied by the battery (M = 1000000 × (c × (0.12-c) (c-0.08) / (a ​​× d) - 0.0000545e)), and the magnetic field strength involved in the preparation process of the negative electrode sheet are different. See Table 1 for details. Except for the differences shown in Table 1, the other conditions are the same as those in Example 1. Among them, the compacted density of the negative electrode coating in Examples 1 to 17, Comparative Example 1 and Comparative Example 2 is 1.57 g / cm 3 .

[0088] Among them, the difference between Comparative Example 1 and Example 1 is that during the preparation of the negative electrode sheet, the magnetic field is turned off (that is, the magnetic field strength is 0), that is, the magnetic field is not applied to the negative electrode current collector coated with the wet film, and the orientation of the non-coated graphite therein is not induced. Except for this difference and the differences shown in Table 1, the other conditions are the same as those in Example 1.

[0089] The following performance tests were performed on the negative electrode sheets or soft-pack batteries of each embodiment and comparative example, and the results are shown in Table 2.

[0090] (1) Liquid phase diffusion impedance test

[0091] The liquid-phase diffusion impedance is measured by electrochemical impedance spectroscopy (EIS). On the basis of the reference potential, a small-amplitude sinusoidal potential signal of a certain frequency is applied to the electrode. The impedance of the electrode system is measured as the frequency of the sinusoidal wave changes, and the spectrum is then analyzed and fitted to obtain the electrode process kinetic information and the electrode interface structure. Generally, the diffusion impedance value of lithium ions in the electrolyte can be obtained by fitting an equivalent circuit to characterize the impedance value inside the battery. The liquid-phase diffusion impedance test process is as follows: the negative electrode, diaphragm, and negative electrode stack are made into a symmetrical battery (the electrolyte used is the same as the electrolyte in the above-mentioned soft-pack battery). Using the electrochemical workstation HVS-9000, at a frequency of 0.02-200000HZ and a voltage of 5V, the AC impedance of the symmetrical battery is tested and analyzed as the liquid-phase diffusion impedance.

[0092] (2) Resistivity test: Place the negative electrode sheet to be tested in a longitudinal resistivity tester (Yuanneng BER2500 electrode sheet resistivity tester). Input the test conditions as 25 MPa, copper foil thickness 6 μm, and holding time 30 s. Test 6 points on each negative electrode sheet, and take the average value as the resistivity of the negative electrode sheet.

[0093] (3) 1 / 3-1000 cycle capacity retention test: At an ambient temperature of 25°C, the soft-pack battery is first calibrated for rpt capacity and recorded as C0 (i.e., the soft-pack battery is charged and discharged at a rate of 1 / 3 of the design capacity (i.e., 1 / 3C) for 3 cycles, and the discharge capacity of the last cycle is recorded as C0). After standing for 30 minutes, the soft-pack battery is charged and discharged at 1 / 3C0. After 1000 cycles, the rpt capacity is recalibrated and recorded as C 1000 (The soft pack battery is charged and discharged at 1 / 3C0 for 3 cycles, and the discharge capacity of the last cycle is recorded as C 1000 ), then the capacity retention rate of the battery after 1000 cycles (i.e. 1 / 3-1000 cycle capacity retention rate) = C 1000 / C0.

[0094] (4) Cycle diving inflection point number: Under normal temperature conditions, the battery is charged to 3.8V at a rate of 1 / 3C, and then discharged to 2V at a rate of 1 / 3C. The charge and discharge cycle is performed according to this charge-discharge process to obtain the battery cycle curve (i.e., the curve of the change of capacity retention rate with the number of cycles). The cycle diving inflection point is the inflection point of the battery cycle curve, and the number of cycles corresponding to this inflection point is the cycle diving inflection point number, that is, when the battery cycles to this number of cycles, the capacity retention rate suddenly drops.

[0095] Table 1

[0096]

[0097] Table 2

[0098]

[0099] As can be seen from Table 2, compared with Comparative Examples 1 and 2, Examples 1 to 17 use non-coated graphite as the negative electrode active material of the negative electrode sheet, and the OI value of the non-coated graphite in the negative electrode coating is within the range of 0.06 to 2, which can maintain a low resistivity and liquid phase diffusion impedance of the negative electrode sheet, thereby making the battery have a low internal resistance, while taking into account the improvement of the battery's cycle life and other performance. Specifically, the battery has a high cycle capacity retention rate and a cycle diving inflection point number, so that the battery has both good cycle life and rate performance.

[0100] Specifically, compared to Examples 15 to 17, Examples 1 to 14, by further controlling M to ≥ 18, can further maintain a low resistivity of the negative electrode sheet and liquid phase diffusion impedance, thereby reducing the internal resistance of the battery and improving the cycle life of the battery. In particular, Examples 1, 4, 6 to 9, and 13 to 14, by further controlling M to ≥ 50, can maintain a low resistivity of the negative electrode sheet and liquid phase diffusion impedance while significantly improving the cycle life of the battery.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a negative electrode coating located on at least one side of the negative electrode current collector, wherein the negative electrode coating comprises non-coated graphite, and the OI value of the non-coated graphite in the negative electrode coating is 0.06-2.

2. The negative electrode sheet according to claim 1, characterized in that: The OI value of the non-coated graphite in the negative electrode coating is 0.06 to 1.

5.

3. The negative electrode sheet according to claim 1, characterized in that: The specific surface area of ​​the non-coated graphite is 0.4m 2 / g~2.2m 2 / g.

4. The negative electrode sheet according to claim 1, characterized in that: The negative electrode coating comprises a conductive agent and a negative electrode active material, the negative electrode active material comprises the non-coated graphite, and the mass ratio of the conductive agent to the negative electrode active material is 0-1%.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The surface density of the negative electrode coating is 80 to 600 g / m 2 .

6. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The resistivity of the negative electrode sheet is less than or equal to 0.53Ω*cm.

7. A battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 6.

8. The battery according to claim 7, characterized in that The battery includes an electrolyte including a film-forming additive.

9. The battery according to claim 8, characterized in that The film-forming additive includes vinylene carbonate; And / or, the ratio of the mass of the film-forming additive to the total mass of the electrolyte is 9% to 11%.

10. The battery according to claim 8 or 9, characterized in that The battery satisfies M≥18, M=1000000×(c×(0.12-c)(c-0.08) / (a×d)-0.0000545e), wherein a is the specific surface area of ​​the non-coated graphite, in m 2 / g; c is the mass percentage of the film-forming additive in the electrolyte; d is the OI value of the non-coated graphite in the negative electrode coating; e is the ratio of the mass of the conductive agent in the negative electrode coating to the mass of the negative electrode active material.

11. The battery according to claim 10, characterized in that The M≥50.

12. A battery pack, characterized in that: A battery comprising the battery according to any one of claims 7 to 11.

13. An electrical device, characterized in that: The invention comprises the battery according to any one of claims 7 to 11 or the battery pack according to claim 12.

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