Negative active material, negative pole piece, battery and electric device

Abstract

The embodiment of the invention provides a negative active material, a negative pole piece, a battery and an electric device, and relates to the field of batteries. The negative electrode active material comprises negative electrode active material particles and a coating layer coating the surfaces of the negative electrode active material particles, and the coating layer contains vinylene carbonate. The negative pole piece comprises a negative pole current collector and a negative pole active material layer arranged on at least one side surface of the negative pole current collector, and the negative pole active material layer comprises the negative pole active material. The negative electrode active material, the negative electrode pole piece, the battery and the electric device can improve the first coulombic efficiency of the battery and improve the cycle performance.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a negative electrode active material, a negative electrode sheet, a battery and an electrical device. Background Art

[0002] In lithium-ion batteries, vinylene carbonate (VC) is the most commonly used anode film-forming additive, which is reduced at the negative electrode to form a SEI film with polyvinyl carbonate as the main component. The SEI film has the advantages of good mechanical stability and resistance to HF corrosion. However, when the battery is used at a high voltage, vinylene carbonate (VC) will also undergo oxidative decomposition at the cathode to form an interface film with a large thickness and high impedance, resulting in a decrease in cathode capacity, a decrease in the first coulomb efficiency, and a deterioration in cycle performance. Summary of the invention

[0003] In view of the above problems, the present application provides a negative electrode active material, a negative electrode plate, a battery and an electrical device, which can enhance the initial coulombic efficiency of the battery and improve the cycle performance.

[0004] In a first aspect, the present application provides a negative electrode active material, comprising negative electrode active material particles and a coating layer coated on the surface of the negative electrode active material particles, wherein the coating layer contains polyvinylene carbonate.

[0005] In the technical solution of the embodiment of the present application, polyvinyl carbonate is coated on the surface of the negative electrode active material particles to form a negative electrode active material, which is applied to the negative electrode plate of the battery. On the one hand, it can play the role of anode film formation, and on the other hand, it can reduce the problems of oxidation and decomposition of anode film-forming additives (such as vinyl carbonate) added to the electrolyte on the cathode surface, as well as the increase in interface impedance. Therefore, it can improve the first coulombic efficiency of the battery and improve the cycle performance.

[0006] In some embodiments, the mass ratio of the polyvinyl carbonate to the negative electrode active material particles is 0.5:100 to 5:100, and can be 1:100 to 2:100. By coating the surface of the negative electrode active material particles with a certain mass ratio of polyvinyl carbonate, not only can the effect of the coating material on the function of the negative electrode active material particles be reduced, but polyvinyl carbonate can also play a role in the anode, reducing the effect on the cathode.

[0007] In some embodiments, the coating layer further contains 1,3-propane sultone, and optionally, the mass ratio of the polyvinylene carbonate to the 1,3-propane sultone is 1:0.1 to 1:1. By using 1,3-propane sultone and polyvinylene carbonate together, the first coulombic efficiency of the battery can be effectively improved and the cycle performance can be improved.

[0008] In some embodiments, the coating layer further contains vinyl sulfate, and optionally, the mass ratio of the polyvinylene carbonate to the vinyl sulfate is 1:0.1 to 1:1. The combination of vinyl sulfate and polyvinylene carbonate can effectively improve the first coulombic efficiency of the battery and improve the cycle performance.

[0009] In some embodiments, the particle size of the negative electrode active material particles is 2-8 μm; and the thickness of the coating layer is 1-5 nm.

[0010] In a second aspect, the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material of the above embodiment.

[0011] In a third aspect, the present application provides a battery comprising the negative electrode plate of the above embodiment.

[0012] In some embodiments, an electrolyte is also included, wherein the content of the negative electrode film-forming additive in the electrolyte is less than 0.2%, and optionally, the negative electrode film-forming additive includes vinylene carbonate. The negative electrode plate of the battery contains polyvinylene carbonate, and the polyvinylene carbonate is coated on the surface of the negative electrode active material particles, so that the electrolyte contains only a very small amount of or even no negative electrode film-forming additive (such as vinylene carbonate), reducing the side reactions caused by the addition of vinylene carbonate (oxidative decomposition at the positive electrode to generate a thicker interface film, CO2 and other gases), thereby improving the first coulomb efficiency of the battery and improving the cycle performance.

[0013] In a fourth aspect, the present application provides an electrical device, which includes the battery of the above embodiment, and the battery is used to provide electrical energy.

[0014] In a fifth aspect, the present application provides a method for preparing the negative electrode active material of the above embodiment, which comprises the following steps:

[0015] Mixing polyvinylene carbonate and an organic solvent uniformly to form a first slurry;

[0016] Adding negative electrode active material particles to the first slurry and stirring evenly to form a second slurry;

[0017] The second slurry is dried by a spray drying method to obtain a negative electrode active material.

[0018] In some embodiments, the organic solvent includes N,N-dimethylformamide and tetrahydrofuran. Optionally, the volume ratio of N,N-dimethylformamide to tetrahydrofuran is 1:1 to 5:1.

[0019] In some embodiments, the stirring temperature is 100-200°C.

[0020] In some embodiments, 1,3-propane sultone and / or vinyl sulfate are further added when forming the first slurry.

[0021] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0023] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0024] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0025] Figure 3 A schematic diagram of the structure of a battery cell provided in some embodiments of the present application;

[0026] Figure 4 This is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application.

[0027] Icons: 1000-vehicle; 100-battery; 10-casing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-casing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 24-current collecting member; 25-insulating protection member; 200-controller; 300-motor. DETAILED DESCRIPTION

[0028] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0030] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0033] In the description of the embodiments of the present application, the orientation or position relationship indicated by the technical terms "thickness", "up", "down", "inside", "outside", etc. is based on the orientation or position relationship shown in the accompanying drawings, and is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0034] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "fixation" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0035] At present, in lithium-ion batteries, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are the most commonly used anode film-forming additives, which are reduced at the anode to form a SEI film with polyvinylene carbonate as the main component, which has the advantages of good mechanical stability and resistance to HF corrosion. In addition, increasing the operating voltage of the battery is one of the effective ways to increase the energy density. However, when the battery is used at a high voltage, VC and FEC will be oxidized and decomposed at the cathode to form an interface film with a large thickness and high impedance, resulting in a decrease in the cathode capacity and a deterioration in the battery's cycle performance.

[0036] In order to improve the problem of oxidative decomposition of VC and FEC at the cathode, the prior art proposes a technical solution in which ethylene phosphate and its derivatives are used as additives in the electrolyte. Although the additives used in this method can reduce the amount of anode film-forming additives (VC, FEC), they cannot be completely replaced, so the problem of oxidative decomposition of the anode film-forming additives on the cathode surface may still occur; on the other hand, the mechanical stability of the anode SEI film is largely derived from VC, so if the VC content is too low, it will lead to repeated damage and repair of the anode SEI film.

[0037] In order to effectively improve the problem of oxidative decomposition of conventional anode film-forming additives at the cathode, a negative electrode active material formed by directly coating polyvinyl carbonate on the surface of the negative electrode active material particles can be designed, which can play the role of anode film-forming and can also reduce or even eliminate the addition of anode film-forming additives, so as to effectively improve the problem of oxidative decomposition of anode film-forming additives at the cathode, thereby improving the battery's first coulombic efficiency and improving the cycle performance.

[0038] The battery cells disclosed in the embodiments of the present application can be used, but not limited to, in electrical devices such as vehicles, ships or aircraft. A power supply system comprising the battery cells and batteries disclosed in the present application can be used to form the electrical device, which is conducive to alleviating and automatically adjusting the deterioration of the expansion force of the battery cell, replenishing the consumption of the electrolyte, and improving the stability of the battery performance and the battery life.

[0039] The embodiment of the present application provides an electric device using a battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0040] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0041] Please refer to Figure 1 , Figure 1 The schematic diagram of the structure of the vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 is provided with a battery 100 inside, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000.

[0042] The vehicle 1000 may further include a controller 200 and a motor 300 , wherein the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1000 .

[0043] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0044] Figure 2 This is a schematic diagram of the exploded structure of the battery 100 provided in some embodiments of the present application. Figure 2 The battery 100 includes a housing 10 and a battery cell 20 , and the battery cell 20 is accommodated in the housing 10 .

[0045] The box body 10 is used to provide a storage space 11 for the battery cell 20. In some embodiments, the box body 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 cover each other to define the storage space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, a sealant, etc.

[0046] The first part 12 and the second part 13 can be in various shapes, such as a cuboid, a cylinder, etc. The first part 12 can be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thereby forming a box body 10 with a receiving space 11. Of course, if Figure 2 As shown, the first part 12 may be a hollow structure with one side open, and the second part 13 may be a plate-like structure. The second part 13 covers the open side of the first part 12 to form a box body 10 with an accommodating space 11.

[0047] In the battery 100, there can be one or more battery cells 20. If there are more than one battery cell 20, the battery cells 20 can be connected in series, in parallel or in a mixed connection. A mixed connection means that the battery cells 20 are connected in series and in parallel. The battery cells 20 can be directly connected in series, in parallel or in a mixed connection, and then the whole formed by the battery cells 20 can be accommodated in the box 10; of course, the battery cells 20 can be connected in series, in parallel or in a mixed connection to form a battery module, and then the battery modules can be connected in series, in parallel or in a mixed connection to form a whole, and then accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular or in other shapes. Figure 2 The example shows that the battery cell 20 is in a square shape.

[0048] In some embodiments, the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the multiple battery cells 20 .

[0049] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application. Figure 4 This is a schematic diagram of the exploded structure of a battery cell 20 provided in some embodiments of the present application. Figure 3 and Figure 4 The battery cell 20 may include a housing 21 , an end cap assembly 22 and an electrode assembly 23 . The housing 21 has an opening 211 , the electrode assembly 23 is accommodated in the housing 21 , and the end cap assembly 22 is used to cover the opening 211 .

[0050] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a rectangular parallelepiped structure, the housing 21 can be a rectangular parallelepiped structure. Figure 3 and Figure 4 The case where the housing 21 and the electrode assembly 23 are square is exemplarily shown.

[0051] The shell 21 may also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0052] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a closed installation space (not shown), and the installation space is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 is a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0053] It should be noted that the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive pole ear and the negative pole ear of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, and the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive pole ear of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative pole piece of the electrode assembly 23.

[0054] In some embodiments, Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the periphery of the electrode assembly 23, and the insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is a tape bonded to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is arranged around the periphery of the multiple electrode assemblies 23, and the multiple electrode assemblies 23 are formed into an integral structure to keep the electrode assembly 23 structurally stable.

[0055] According to some embodiments of the present application, the present application provides a negative electrode active material, including negative electrode active material particles and a coating layer coated on the surface of the negative electrode active material particles, wherein the coating layer contains polyvinylene carbonate.

[0056] In some embodiments, the morphology of the negative electrode active material is characterized by: a rough coating layer exists on the surface of the negative electrode active material particles, and the coating layer may be a full coating or a partial coating.

[0057] In some embodiments, the negative electrode active material particles may be various negative electrode active materials suitable for lithium ion batteries in the art. As an example, the negative electrode active material particles may include but are not limited to carbon materials (graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, graphene, etc.), titanium oxide-based materials (lithium titanate, titanium dioxide, etc.), alloyed negative electrode materials (silicon-based materials, tin-based materials, germanium-based materials, etc.), conversion-type negative electrode materials (transition metal oxides, phosphides, sulfides, nitrides, etc.). For example, the negative electrode active material particles include common lithium ion battery negative electrode active materials such as graphite, silicon, and silicon oxide.

[0058] By coating polyvinyl carbonate on the surface of negative electrode active material particles to form negative electrode active material, it is applied to the negative electrode plate of the battery. On the one hand, it can play the role of anode film-forming, and on the other hand, it can reduce the oxidation and decomposition of anode film-forming additives (such as vinyl carbonate) added to the electrolyte on the cathode surface, as well as the increase in interface impedance. The problem, thereby improving the battery's first coulombic efficiency and cycle performance.

[0059] According to some embodiments of the present application, the mass ratio of polyvinylene carbonate to the negative electrode active material particles is 0.5:100 to 5:100, and can be 1:100 to 2:100. Exemplarily, the mass ratio of polyvinylene carbonate to the negative electrode active material particles is 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, or an intermediate value between any two of the above values.

[0060] According to some embodiments of the present application, the coating layer further contains 1,3-propane sultone (PS). Optionally, the mass ratio of polyvinylene carbonate to 1,3-propane sultone is 1:0.1 to 1:1.

[0061] According to some embodiments of the present application, the coating layer further contains diethylene sulfate (DTD). Optionally, the mass ratio of polyvinyl carbonate to diethylene sulfate is 1:0.1 to 1:1.

[0062] According to some embodiments of the present application, the particle size of the negative electrode active material particles is 2 to 8 μm; the thickness of the coating layer is 1 to 5 nm. Exemplarily, the particle size of the negative electrode active material particles is 2 μm, 3 μm, 4 μm, 6 μm, 8 μm, or an intermediate value between any two of the above values; the thickness of the coating layer is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or an intermediate value between any two of the above values.

[0063] According to some embodiments of the present application, the present application also provides a negative electrode plate, which includes a negative electrode collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode collector, and the negative electrode active material layer contains the negative electrode active material of any of the above schemes.

[0064] The negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0065] In some embodiments, the negative electrode active material of any of the above schemes can be used alone, or in combination with the uncoated negative electrode active material particles of the above embodiments, or in combination with the negative electrode active material formed by other coating modifications of the negative electrode active material particles of the above embodiments. Exemplarily, the mass proportion of the negative electrode active material of any of the above schemes in the negative electrode active material layer is 90% to 100%.

[0066] In some embodiments, the negative electrode current collector can be any material suitable for use as a negative electrode current collector for lithium-ion batteries in the art, and the negative electrode current collector can be a metal foil or a composite current collector. Optionally, the negative electrode current collector includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0067] In some embodiments, the negative electrode active material layer may further include a binder. The binder includes, butadiene styrene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and at least one of carboxymethyl chitosan (CMCS). Exemplarily, the binder includes butadiene styrene rubber, polyacrylic acid, and the like.

[0068] In some embodiments, the negative electrode active material layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon fibers. Exemplarily, the conductive agent includes Super P, carbon nanotubes, carbon fibers, graphene, and the like.

[0069] In some embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0070] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0071] According to some embodiments of the present application, the present application also provides a battery, which includes the negative electrode plate of any of the above schemes.

[0072] The battery in the present application includes any form of a single cell, a battery module and a battery pack. The battery includes a secondary battery, which can be a metal ion battery, wherein the metal ion battery is a battery system that releases capacity through a redox reaction between metal ions and metal elements. In some embodiments, the metal ion battery is a lithium ion battery, and in some other embodiments, the metal ion battery is a sodium ion battery or a battery of other metal ions.

[0073] According to some embodiments of the present application, the content of the negative electrode film-forming additive in the electrolyte is less than 0.2%. Optionally, the negative electrode film-forming additive includes vinylene carbonate (VC).

[0074] In some embodiments, the negative electrode film-forming additive further includes fluoroethylene carbonate (FEC).

[0075] By coating the surface of the negative electrode active material particles with polyvinyl carbonate, the amount of negative electrode film-forming additives added can be reduced, or even no negative electrode film-forming additives are used at all.

[0076] In order to enable a clearer understanding of the technical solution of the present application, the embodiments of the present application are mainly described using lithium-ion batteries. Other types of batteries can be appropriately adjusted according to the battery type and will not be described in detail.

[0077] The lithium-ion battery provided in the present application includes an electrode assembly and an electrolyte, and the electrode assembly includes a positive electrode plate, a negative electrode plate of any of the above solutions, and a separator.

[0078] [Positive electrode]

[0079] According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.

[0080] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0081] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0082] In some embodiments, the binder includes an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.

[0083] In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0084] [Isolation film]

[0085] The present application has no particular limitation on the material and shape of the isolation membrane, which may be any material disclosed in the prior art.

[0086] In some embodiments, the isolation film includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application. For example, the isolation film may include a substrate layer and a surface treatment layer.

[0087] The substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0088] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).

[0089] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0090] [Electrolyte]

[0091] The electrolyte conducts ions between the positive electrode and the negative electrode.

[0092] The electrolyte of the present application may be an electrolyte known in the prior art.

[0093] In some embodiments, the electrolyte includes an organic solvent, a lithium salt and an optional additive. The organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and it can be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl propionate, propyl propionate, or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium di(oxalatoborate) LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate, succinonitrile, glutaronitrile, 1,3 propane sultone, and adiponitrile.

[0094] In some embodiments, the battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0095] In some embodiments, the outer packaging of the battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0096] According to some embodiments of the present application, the present application further provides an electrical device, which includes a battery according to any of the above schemes, and the battery is used to provide electrical energy to the electrical device.

[0097] According to some embodiments of the present application, the present application also provides a method for preparing a negative electrode active material according to any one of the above schemes, which comprises the following steps:

[0098] (1) stirring polyvinylene carbonate and an organic solvent to form a first slurry;

[0099] (2) adding negative electrode active material particles to the first slurry and stirring evenly to form a second slurry;

[0100] (3) Drying the second slurry by spray drying to obtain a negative electrode active material.

[0101] According to some embodiments of the present application, the mass ratio of polyvinylene carbonate to negative electrode active material particles is 1:100 to 5:100.

[0102] According to some embodiments of the present application, the organic solvent includes N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). Optionally, the volume ratio of N,N-dimethylformamide (DMF) to tetrahydrofuran (THF) is 1:1 to 5:1.

[0103] According to some embodiments of the present application, the temperature during stirring is 100-200°C.

[0104] According to some embodiments of the present application, when forming the first slurry, 1,3-propane sultone and / or vinyl sulfate are further added to form a composite coating layer on the surface of the negative electrode active material particles.

[0105] Next, one or more embodiments are described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0106] Example 1

[0107] Preparation of negative electrode sheet:

[0108] (1) Polyvinylene carbonate was added to a mixed solution of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) in a volume ratio of 3:1, and the mixture was stirred uniformly to form slurry A.

[0109] (2) Add negative electrode active material particles (graphite particles, Dv50 is 10 μm) to slurry A and stir evenly to form slurry B.

[0110] (3) The slurry B was dried by spray drying to obtain a negative electrode active material (graphite particles coated with polyvinyl carbonate). The mass ratio of the negative electrode active material particles to the polyvinyl carbonate coating was about 100:1.56.

[0111] (4) The above-mentioned negative electrode active material, conductive agent (Super p), binder (styrene-butadiene rubber), and auxiliary agent (sodium carboxymethyl cellulose) are dispersed in deionized water at a mass fraction of 97.5%:1%:1%:0.5%, and the viscosity is adjusted to 10000 mPa.s to form a negative electrode slurry.

[0112] (5) The negative electrode slurry is coated on a 6 μm negative electrode current collector copper foil, baked at 130° C. until all the water evaporates, and then cold pressed and cut to obtain negative electrode sheets.

[0113] Positive electrode sheet: NCM523 material is used as the positive electrode active material, and its mass fraction is 97%. The mass fractions of the conductive agent SuperP and the binder PVDF are 1.5% and 1.5% respectively. The positive electrode active material, the conductive agent and the binder are fully stirred and mixed in an N-methylpyrrolidone solvent system to obtain a positive electrode slurry; the above positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13μm, baked at 130°C until all the water is volatilized, and then cold pressed and cut to obtain a positive electrode sheet.

[0114] Electrolyte: Conventional formula electrolyte, the electrolyte composition is 1 mol LiPF6-EC / DMC (3 / 7).

[0115] Preparation of the battery: Then assemble the bare cell in the order of positive electrode sheet, separator, and negative electrode sheet, inject the electrolyte, and obtain a secondary battery.

[0116] Examples 2 to 8 and Comparative Examples 1 to 3

[0117] The negative electrode sheets and batteries of each embodiment and comparative example were prepared by the same method as in embodiment 1, and the differences are shown in Table 1.

[0118] Test Section

[0119] 1. First Coulomb efficiency test

[0120] The secondary batteries prepared above were subjected to the following tests:

[0121] Formation: The unformed secondary battery is first charged to 3.4V at 25℃ and 0.1C, and then charged to 3.8V at 0.33C. The charge capacity is counted as C0.

[0122] Capacity test: first discharge to 2.5V, the discharge capacity is counted as D0; then charge to 4.4V at 0.33C constant current, then charge to 0.05C at 4.4V constant voltage, the charge capacity is counted as C1; after 10 minutes of storage, discharge to 2.5V at 0.33C constant current, the discharge capacity is counted as D1. Calculate the first coulomb efficiency of the secondary battery according to the following formula:

[0123] First coulombic efficiency (%) = D1 / (C0+C1-D0).

[0124] 2. 25℃ Cycle Test

[0125] At 25°C, the secondary battery after the capacity test is charged to 4.4V at a constant current of 0.33C, then charged at a constant voltage of 4.4V until the current is less than 0.05C, and then the secondary battery is discharged to 2.5V at a constant current of 0.33C to obtain the discharge capacity at 0.5C, which is counted as one cycle. Repeat the above charging and discharging steps until the capacity retention rate reaches 90% SOH, at which point the number of cycles represents the battery cycle performance.

[0126] The capacity retention rate calculation formula is: Capacity retention rate = discharge capacity in the last week / discharge capacity in the first week.

[0127] The test results are shown in Table 1:

[0128] Table 1 Battery composition and test results

[0129]

[0130]

[0131] Combining the results in Table 1, we can see that:

[0132] Compared with Comparative Examples 1 to 3, Examples 1 to 7 use negative electrode active material particles coated with polyvinyl carbonate as negative electrode active materials, and the content of negative electrode film-forming additives in the electrolyte is below 0.1%, which can improve the first coulombic efficiency of the battery and improve the cycle performance, and is suitable for situations where the battery voltage is higher.

[0133] According to Examples 1 to 4, the mass ratio of the polyvinylene carbonate in the negative electrode active material to the negative electrode active material particles is 1:100 to 5:100, and can be optionally 1.56:100 to 2.1:100, which can increase the first coulombic efficiency of the battery and improve the cycle performance.

[0134] According to Examples 5 and 6, the surface of the negative electrode active material particles is coated with polyvinylene carbonate and 1,3-propane sultone, and the surface of the negative electrode active material particles is coated with polyvinylene carbonate and vinyl sulfate, which can significantly improve the first coulombic efficiency of the battery and improve the cycle performance.

[0135] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A negative electrode active material, characterized in that: The invention comprises negative electrode active material particles and a coating layer coated on the surface of the negative electrode active material particles, wherein the coating layer contains polyvinylene carbonate.

2. The negative electrode active material according to claim 1, characterized in that The mass ratio of the polyvinylene carbonate to the negative electrode active material particles is 0.5:100 to 5:100, and can be optionally 1:100 to 2:

100.

3. The negative electrode active material according to claim 1 or 2, characterized in that: The coating layer further contains 1,3-propane sultone. Optionally, the mass ratio of the polyvinylene carbonate to the 1,3-propane sultone is 1:0.1 to 1:

1.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The coating layer further contains vinyl sulfate. Optionally, the mass ratio of the polyvinylene carbonate to the vinyl sulfate is 1:0.1 to 1:

1.

5. The negative electrode active material according to any one of claims 1 to 4, characterized in that: The particle size of the negative electrode active material particles is 2 to 8 μm; the thickness of the coating layer is 1 to 5 nm.

6. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 5.

7. A battery, characterized in that: It includes the negative electrode sheet as claimed in claim 6.

8. The battery according to claim 7, characterized in that The invention also comprises an electrolyte, wherein the content of the negative electrode film-forming additive in the electrolyte is less than 0.2%. Optionally, the negative electrode film-forming additive comprises vinylene carbonate.

9. An electrical device, characterized in that: It comprises the battery according to claim 7 or 8.

10. A method for preparing a negative electrode active material according to any one of claims 1 to 5, characterized in that: It includes the following steps: Mixing polyvinylene carbonate and an organic solvent uniformly to form a first slurry; Adding negative electrode active material particles to the first slurry and stirring evenly to form a second slurry; The second slurry is dried by a spray drying method to obtain a negative electrode active material.

11. The method for preparing the negative electrode active material according to claim 10, characterized in that: The organic solvent includes N,N-dimethylformamide and tetrahydrofuran. Optionally, the volume ratio of N,N-dimethylformamide to tetrahydrofuran is 1:1 to 5:

1.

12. The method for preparing a negative electrode active material according to claim 10 or 11, characterized in that: The temperature during the stirring is 100-200°C.

13. The method for preparing a negative electrode active material according to any one of claims 10 to 12, characterized in that: When forming the first slurry, 1,3-propane sultone and / or vinyl sulfate are also added.

Images