Negative pole piece and secondary battery

Abstract

The invention discloses a negative pole piece and a secondary battery, the negative pole piece comprises a current collector and a negative coating, and the negative coating is arranged on at least one surface of the current collector; the negative electrode coating comprises a negative electrode active material and a super-ion conductor, the mass fraction of the super-ion conductor in the negative electrode coating is 0.1-10%, and the super-ion conductor is selected from at least one of a lithium-containing oxide, a lithium-containing sulfide and a lithium-containing halide. According to the negative electrode plate in the embodiment of the invention, the negative electrode coating comprising the super-ion conductor is arranged on the current collector, and the super-ion conductor can serve as a bridge for lithium ion transmission between solid and liquid phases and between solid and solid phases, so that the lithium ion transmission rate of the novel negative electrode plate is improved, and the problem that the rate capability is reduced due to the improvement of energy density is solved; and thus, high energy density and high magnification are both realized.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 202411158461.1, filed on August 22, 2024, and entitled “Negative Electrode Plate and Secondary Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of negative electrode materials for lithium-ion batteries, and in particular to negative electrode sheets and secondary batteries. Background Art

[0004] With the rapid development of electric passenger vehicles, commercial energy storage, communication energy storage and other industries, the market demand for batteries with high energy density, long life and high rate characteristics is increasing. Electrodes are one of the key factors that determine the quality of the above characteristics. However, the technical means to improve the energy density and rate performance of lithium-ion batteries are often contradictory. For example, increasing the electrode coating surface density and improving the compaction density can improve the energy density of the battery, but at the same time, due to the longer ion transmission distance, increased pole piece tortuosity and poor electrolyte infiltration, the ion transmission rate is often reduced, and the rate performance is significantly reduced. In serious cases, lithium deposition is prone to occur on the pole piece surface, resulting in accelerated cycle life decay.

[0005] The existing improvement methods mainly include electrode material modification, adding through-holes to the pole pieces, and research and development of new materials. However, electrode material modification often brings about problems such as increased side reactions, rapid life decay, and increased material costs. Although there are many ways to increase through-holes in pole pieces, they have their own defects. The use of double-layer coating and laser drilling will increase equipment costs, and the use of pore-forming agents has many restrictions. New electrode materials are currently difficult to be compatible with the lithium-ion battery manufacturing system, and large-scale application is difficult.

[0006] Therefore, it is necessary to develop a new type of electrode that can ensure the ion transfer rate of the electrode while improving the battery energy density, so as to obtain a lithium-ion battery with both high energy density and high rate. Summary of the invention

[0007] The purpose of the present application is to provide a negative electrode plate and a secondary battery. By introducing a superionic conductor into the enriched coating on the surface of the current collector, the energy density of the battery can be increased while the ion transmission rate of the electrode can be guaranteed, thereby obtaining a lithium-ion battery with both high energy density and high rate.

[0008] In a first aspect, the present application provides a negative electrode sheet, comprising a current collector and a negative electrode coating disposed on at least one surface of the current collector, wherein the negative electrode coating comprises a negative electrode active material and a superionic conductor;

[0009] In the negative electrode coating:

[0010] The superionic conductors are evenly distributed;

[0011] Or, along the direction away from the current collector, the mass fraction of the superionic conductor gradually decreases or decreases in a gradient;

[0012] Alternatively, the mass fraction of the superionic conductor increases gradually or in a gradient along a direction away from the current collector.

[0013] In a second aspect, the present application provides a negative electrode sheet, comprising a current collector and a negative electrode coating, wherein the negative electrode coating is disposed on at least one surface of the current collector;

[0014] The negative electrode coating comprises a negative electrode active material and a superionic conductor, the mass fraction of the superionic conductor in the negative electrode coating is 0.1%-10%, and the superionic conductor is selected from at least one of lithium-containing oxides, lithium-containing sulfides and lithium-containing halides.

[0015] In an optional embodiment, the superionic conductor is uniformly distributed or gradually distributed in the negative electrode coating.

[0016] In an optional embodiment, the negative electrode coating disposed on one surface of the current collector includes two or more sub-coating layers disposed in sequence, and any two adjacent sub-coating layers among the two or more sub-coating layers are respectively recorded as the first sub-coating layer and the second sub-coating layer;

[0017] The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, and Delta_A is greater than 0, less than 0 or equal to 0;

[0018] Preferably, the absolute value of Delta_A is in the range of 1%-5%.

[0019] In an optional embodiment, the negative electrode coating disposed on one surface of the current collector includes three or more sub-coating layers disposed in sequence, and any three adjacent sub-coating layers among the three or more sub-coating layers are respectively recorded as the first sub-coating layer, the second sub-coating layer and the third sub-coating layer;

[0020] The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, the difference between the mass fraction of the superionic conductor in the third sub-coating layer and the mass fraction of the superionic conductor in the second sub-coating layer is Delta B, and Delta_A=Delta_B;

[0021] Preferably, the absolute value of Delta_A is in the range of 1%-3%.

[0022] In an optional embodiment, the mass fraction of the superionic conductor in the negative electrode coating is 0.1%-10%.

[0023] In an optional embodiment, the negative electrode coating includes more than two sub-coating layers, and in any two adjacent sub-coating layers, the mass fraction of the superionic conductor in the sub-coating layer close to the current collector is greater than the mass fraction of the superionic conductor in the sub-coating layer far from the current collector;

[0024] Alternatively, the negative electrode coating includes more than two sub-coating layers, and in any two adjacent sub-coating layers, the mass fraction of the superionic conductor in the sub-coating layer close to the current collector is less than the mass fraction of the superionic conductor in the sub-coating layer far from the current collector.

[0025] In an optional embodiment, the thickness of the negative electrode coating is 1 μm-200 μm.

[0026] In an optional embodiment, the superionic conductor is selected from at least one of a lithium-containing oxide, a lithium-containing sulfide, and a lithium-containing halide.

[0027] Preferably, the lithium-containing oxide is selected from at least one of lithium lanthanum titanate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium silicon sulfide, lithium boron sulfide, lithium germanium sulfide boron, lithium yttrium hexachloride, lithium yttrium hexabromide and lithium zirconium hexachloride.

[0028] In an optional embodiment, the average particle size of the superionic conductor is 0.05 μm to 10 μm.

[0029] In an optional embodiment, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, silicon-based materials and tin-based materials.

[0030] In an optional embodiment, the negative electrode coating further includes a conductive agent;

[0031] Preferably, the conductive agent is selected from at least one of superconducting carbon, carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers;

[0032] Preferably, the mass fraction of the conductive agent in the negative electrode coating is 0.1%-10%.

[0033] In an optional embodiment, the negative electrode coating further includes a binder;

[0034] Preferably, the adhesive is selected from at least one of styrene-butadiene rubber, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan;

[0035] Preferably, the mass fraction of the binder in the negative electrode coating is 0.1%-5%.

[0036] In an optional embodiment, the negative electrode coating further includes a dispersant;

[0037] Preferably, the dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and polyvinyl pyrrolidone;

[0038] Preferably, the mass fraction of the dispersant in the negative electrode coating is 0.1%-5%.

[0039] In a second aspect, the present application provides a secondary battery, comprising the negative electrode sheet described in any one of the aforementioned embodiments.

[0040] This application has the following beneficial effects:

[0041] The negative electrode plate in the embodiment of the present application is provided with a negative electrode coating including a superionic conductor on the current collector. The presence of the superionic conductor can act as a "bridge" for the transmission of lithium ions between the solid-liquid phase and the solid-solid phase, thereby improving the lithium ion transmission rate of the new negative electrode plate, solving the problem of decreased rate performance due to increased energy density, and thereby achieving both high energy density and high rate. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0043] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the description and claims of this application and any variations thereof are intended to cover non-exclusive inclusions.

[0044] 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.

[0045] Reference to "embodiments" in this application 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 in this application may be combined with other embodiments.

[0046] In the embodiments of the present application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0047] In the description of the embodiments of the present application, the term "plurality" refers to more than two (including two). The term "and / or" in the present application is only a description of the association relationship of the associated objects, indicating that three relationships may exist. For example, A and / or B can represent: only A exists, A and B exist at the same time, and only B exists. In addition, the character " / " in the present application generally indicates that the associated objects before and after are in an "or" relationship.

[0048] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "thickness", "up", "down", "front", "back", "top", "bottom", "inside", and "outside" are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply 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.

[0049] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "connection" and "fixed" 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, and 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.

[0050] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0051] 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.

[0052] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device in an embodiment of the present application.

[0053] The interior of the vehicle is provided with a battery, which can be arranged at the bottom, head or tail of the vehicle. The battery can be used for power supply of the vehicle, for example, the battery can be used as an operating power source of the vehicle.

[0054] The vehicle may further include a controller and a motor, wherein the controller is used to control the battery to supply power to the motor, for example, to meet the power requirements for starting, navigating, and driving the vehicle.

[0055] In some embodiments of the present application, the battery can be used not only as an operating power source for the vehicle, but also as a driving power source for the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0056] In the present application, battery cells may include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries or magnesium-ion batteries, etc., and the embodiments of the present application do not limit this. Battery cells may be cylindrical, flat, rectangular or other shapes, etc., and the embodiments of the present application do not limit this. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells, and the embodiments of the present application do not limit this.

[0057] In a battery, there can be one or more battery cells. If there are multiple battery cells, the multiple battery cells can be connected in series, in parallel, or in a mixed connection. A mixed connection means that multiple battery cells are connected in series and in parallel. Multiple battery cells can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells is accommodated in a box; of course, multiple battery cells can be first connected in series, in parallel, or in a mixed connection to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in a box. The battery cell can be cylindrical, flat, rectangular, or in other shapes. In some embodiments, the battery may also include a busbar, and multiple battery cells can be electrically connected through the busbar to achieve the series connection, parallel connection, or mixed connection of multiple battery cells.

[0058] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The battery cell mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode collector. The current collector not coated with the positive electrode active material layer protrudes from the side of the current collector coated with the positive electrode active material layer. The part of the current collector not coated with the positive electrode active material layer serves as the positive electrode tab. Taking lithium-ion batteries as an example, the material of the positive electrode collector can be aluminum, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc. The negative electrode sheet includes a negative electrode collector and a negative electrode coating. The negative electrode coating is coated on the surface of the negative electrode collector. The current collector not coated with the negative electrode coating protrudes from the side of the current collector coated with the negative electrode coating. The part of the current collector not coated with the negative electrode coating serves as the negative electrode tab. The material of the negative electrode collector can be copper, and the negative electrode active material can be carbon or silicon, etc. In order to ensure that a large current can pass without melting, the number of positive electrode tabs is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the diaphragm can be PP (polypropylene) or PE (polyethylene).

[0059] For battery cells, energy density and rate performance are both important indicators, but the technical means to improve the energy density and rate performance of lithium-ion batteries are often contradictory. Existing improvement methods such as electrode material modification, adding through holes to pole pieces, and research and development of new materials also have problems such as increased costs, poor compatibility, and difficulty in large-scale application to varying degrees.

[0060] In view of the above problems, the embodiment of the present application provides a negative electrode sheet, comprising a current collector and a negative electrode coating disposed on at least one surface of the current collector, wherein the negative electrode coating comprises a negative electrode active material and a superionic conductor;

[0061] In the negative electrode coating:

[0062] The superionic conductors are evenly distributed;

[0063] Or, along the direction away from the current collector, the mass fraction of the superionic conductor gradually decreases or decreases in a gradient;

[0064] Alternatively, the mass fraction of the superionic conductor increases gradually or in a gradient along a direction away from the current collector.

[0065] The negative electrode sheet in the embodiment of the present application is provided with a negative electrode coating including a superionic conductor on the current collector. Compared with the solid electrolyte membrane (i.e., SEI membrane) formed by the surface of graphite alone to transmit lithium ions, the ionic conductivity of the superionic conductor at room temperature is as high as 10 -4 S / cm, which is 10 times greater than the SEI membrane ion conductivity on the graphite surface-6 S / cm, which is filled between graphite particles or attached to the surface of graphite particles, can act as a "bridge" for lithium ion transmission between solid-liquid phase and solid-solid phase, improve the lithium ion transmission rate of the new negative electrode plate, solve the problem of decreased rate performance caused by increased energy density, and thus achieve both high energy density and high rate.

[0066] It should be noted that, in the negative electrode coating in the embodiment of the present application, the superionic conductor can be relatively evenly distributed, or it can increase or decrease in the direction away from the current collector, wherein the increase and decrease can be gradually increasing or gradually decreasing, that is, when the distance from any position in the negative electrode coating to the surface of the current collector is taken as the x-axis, and the superionic conductor concentration is taken as the y-axis to draw a graph of y versus x, a continuous, uninterrupted curve or straight line is obtained; it can also be a gradient increase or gradient decrease, that is, when the distance from any position in the negative electrode coating to the surface of the current collector is taken as the x-axis, and the superionic conductor concentration is taken as the y-axis to draw a graph of y versus x, a discontinuous, discontinuous curve or straight line is obtained; in the direction perpendicular to the surface of the current collector coated with the negative electrode coating, the greater the distance from the surface of the current collector coated with the negative electrode coating, the farther away from the current collector, that is, when the mass fraction of the superionic conductor gradually increases in the direction away from the current collector, the greater the distance from the surface of the current collector coated with the negative electrode coating, the greater the concentration of superionic conductor in the negative electrode coating. In some embodiments, under the same conditions: compared with the gradient change, the gradual change of the superionic conductor concentration in the negative electrode coating is more in line with the distribution law of the liquid lithium ion concentration in the electrode, that is, the distribution law of the electrolyte in the electrode, which is conducive to achieving both high energy density and high rate; compared with the decrease, the increase of the superionic conductor concentration in the negative electrode coating is more consistent with the distribution state of the electrolyte in the electrode, which is more conducive to achieving both high energy density and high rate; compared with the uniform distribution, the gradual or gradient change of the superionic conductor concentration in the negative electrode coating is more conducive to achieving both high energy density and high rate.

[0067] In a second aspect, the present application provides a negative electrode sheet, comprising a current collector and a negative electrode coating, wherein the negative electrode coating is disposed on at least one surface of the current collector;

[0068] The negative electrode coating comprises a negative electrode active material and a superionic conductor, the mass fraction of the superionic conductor in the negative electrode coating is 0.1%-10%, and the superionic conductor is selected from at least one of lithium-containing oxides, lithium-containing sulfides and lithium-containing halides.

[0069] The negative electrode plate in the embodiment of the present application is provided with a negative electrode coating including a superionic conductor on the current collector. The presence of the superionic conductor can act as a "bridge" for the transmission of lithium ions between the solid and liquid phases, thereby improving the lithium ion transmission rate of the new negative electrode plate, solving the problem of decreased rate performance due to increased energy density, and thereby achieving both high energy density and high rate.

[0070] In an optional embodiment, the superionic conductor is uniformly distributed or gradually distributed in the negative electrode coating.

[0071] Under the same conditions: compared with uniform distribution, the gradual distribution of superionic conductor concentration in the negative electrode coating is more conducive to achieving both high energy density and high rate; compared with decreasing concentration, the increasing concentration of superionic conductor in the negative electrode coating is more conducive to achieving both high energy density and high rate.

[0072] In an optional embodiment, the negative electrode coating disposed on one surface of the current collector includes two or more sub-coating layers disposed in sequence, and any two adjacent sub-coating layers among the two or more sub-coating layers are respectively recorded as the first sub-coating layer and the second sub-coating layer;

[0073] The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, and Delta_A is greater than 0, less than 0 or equal to 0;

[0074] Preferably, the absolute value of Delta_A is in the range of 1%-5%.

[0075] When Delta_A=0, the superionic conductor is evenly distributed in the negative electrode coating; when Delta_A is greater than 0, the mass fraction of the superionic conductor in the sub-coating increases with the increase of the distance between the sub-coating and the current collector surface; when Delta_A is less than 0, the mass fraction of the superionic conductor in the sub-coating decreases with the decrease of the distance between the sub-coating and the current collector surface. It should be noted that the superionic conductor is evenly distributed in each sub-coating.

[0076] In an optional embodiment, the negative electrode coating disposed on one surface of the current collector includes three or more sub-coating layers disposed in sequence, and any three adjacent sub-coating layers among the three or more sub-coating layers are respectively recorded as the first sub-coating layer, the second sub-coating layer and the third sub-coating layer;

[0077] The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, the difference between the mass fraction of the superionic conductor in the third sub-coating layer and the mass fraction of the superionic conductor in the second sub-coating layer is Delta B, preferably Delta_A=Delta_B;

[0078] Preferably, the absolute value of Delta_A is in the range of 1%-3%.

[0079] In the embodiment of the present application, the mass fraction of the superionic conductor in each sub-coating layer shows an increasing or decreasing trend in sequence, preferably increasing or decreasing in an arithmetic progression. Compared with the increase and decrease of the mass fraction, the increase in the mass fraction has a distribution law that is more consistent with the liquid phase lithium ion concentration of the electrode, which can meet the "bridge" of the liquid and solid phase transmission requirements of each coating, and realize the improvement of the overall ionic conductivity. More preferably, Delta_A is 2%.

[0080] In an optional embodiment, the mass fraction of the superionic conductor in the negative electrode coating is 0.1%-10%, which is the best effect of achieving both high energy density and high rate.

[0081] If the mass fraction of superionic conductor is too low, it will be unfavorable to improve the rate performance of negative electrode. However, if the mass fraction of superionic conductor is too high, the proportion of active material in negative electrode coating will be reduced, which will lead to the problem of reduced capacity and affect energy density.

[0082] Specifically, the mass fraction of the superionic conductor in the negative electrode coating can be 0.1%, 0.2%, 0.5%, 1%, 2%, 4%, 7%, 10% or any value between 0.1% and 10%.

[0083] Preferably, the mass fraction of the superionic conductor in the negative electrode coating is 2%-10%.

[0084] Preferably, when the negative electrode contains two sub-coating layers, the difference Delta_A between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer can be 1%, 2%, 3%, 4%, 5% or any value between 1% and 5%. The mass fraction of the superionic conductor in the sub-coating layer increases with the increase of the distance between the sub-coating layer and the surface of the collector, showing an increasing distribution. Preferably, when Delta_A is 2%, the improvement in ionic conductivity is more obvious and most obvious.

[0085] Preferably, when the negative electrode contains three sub-coating layers, the difference Delta_A between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer can be 1%, 2%, 3% or any value between 1% and 3%. Preferably, the difference Delta B between the mass fraction of the superionic conductor in the third sub-coating layer and the mass fraction of the superionic conductor in the second sub-coating layer is Delta_A=Delta_A. The mass fraction of the superionic conductor in the sub-coating layer increases with the increase of the distance between the sub-coating layer and the surface of the collector, presenting an increasing distribution. At this time, it is more in line with the distribution law of liquid lithium ion concentration in the electrode sheet, the ionic conductivity is more significantly improved, and the performance of the secondary battery used is better. Preferably, when Delta B=Delta_A=2%, the ionic conductivity is further improved, and the performance of the secondary battery used is optimal.

[0086] In an optional embodiment, the thickness of the negative electrode coating is 1 μm-200 μm, specifically 1 μm, 2 μm, 5 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, 200 μm or any value between 1 μm and 200 μm. If the negative electrode coating is too thin, the active material will be reduced, resulting in reduced capacity; but if the negative electrode coating is too thick, the lithium ion transmission path will further increase, and the active material close to the current collector will be difficult to use, which will also reduce the rate capability and energy density.

[0087] In an optional embodiment, the negative electrode coating includes more than two sub-coating layers, and in any two adjacent sub-coating layers, the mass fraction of the superionic conductor in the sub-coating layer close to the current collector is greater than the mass fraction of the superionic conductor in the sub-coating layer far from the current collector;

[0088] Alternatively, the negative electrode coating includes more than two sub-coating layers, and in any two adjacent sub-coating layers, the mass fraction of the superionic conductor in the sub-coating layer close to the current collector is less than the mass fraction of the superionic conductor in the sub-coating layer far from the current collector.

[0089] By setting up multiple sub-coating layers, the mass fraction of superionic conductors in the negative electrode coating can be gradually decreased or increased. Specifically, the superionic conductors are evenly distributed inside each sub-coating layer, and the concentration of superionic conductors gradually increases or decreases between each sub-coating layer. This method is conducive to regulating the concentration of superionic conductors at different positions of the negative electrode coating.

[0090] In an optional embodiment, the superionic conductor is selected from at least one of a lithium-containing oxide, a lithium-containing sulfide, and a lithium-containing halide.

[0091] Preferably, the lithium-containing oxide is selected from at least one of lithium lanthanum titanate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium silicon sulfide, lithium boron sulfide, lithium germanium sulfide boron, lithium yttrium hexachloride, lithium yttrium hexabromide and lithium zirconium hexachloride. These lithium-containing oxides have high ionic conductivity at room temperature and high chemical stability.

[0092] In an optional embodiment, the average particle size of the superionic conductor is 0.05 μm to 10 μm, specifically 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm or any value between 0.05 μm and 10 μm.

[0093] An average particle size of the superionic conductor that is too large or too small is not conducive to the uniform dispersion of the superionic conductor in the negative electrode slurry.

[0094] In an optional embodiment, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, silicon-based materials and tin-based materials.

[0095] In an optional embodiment, the negative electrode coating further includes a conductive agent;

[0096] Preferably, the conductive agent is selected from at least one of superconducting carbon, carbon black (such as SuperP, acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers;

[0097] Preferably, the mass fraction of the conductive agent in the negative electrode coating is 0.1%-10%.

[0098] In an optional embodiment, the negative electrode coating further includes a binder;

[0099] Preferably, the adhesive is selected from at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS);

[0100] Preferably, the mass fraction of the binder in the negative electrode coating is 0.1%-5%.

[0101] In an optional embodiment, the negative electrode coating further includes a dispersant;

[0102] Preferably, the dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and polyvinyl pyrrolidone;

[0103] Preferably, the mass fraction of the dispersant in the negative electrode coating is 0.1%-5%.

[0104] The embodiment of the present application further provides a secondary battery, comprising the negative electrode plate described above.

[0105] The battery in the present application specifically includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0106] The positive electrode plate of the present application includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector. The positive electrode active material in the positive electrode active material layer can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate and compounds obtained by adding other transition metals or non-transition metals to the above compounds.

[0107] For example, the positive electrode current collector may be made of a metal foil or a porous metal plate, for example, a foil or a porous plate made of a metal such as aluminum, copper, nickel, titanium or iron, or an alloy thereof, such as Al (aluminum) foil.

[0108] The negative electrode plate of the present application includes a negative electrode current collector and a negative electrode coating arranged on at least one surface of the negative electrode current collector.

[0109] As an example, the negative electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the negative electrode coating is laminated on any one or both of the two opposite surfaces of the negative electrode current collector.

[0110] The negative electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of conducting and collecting current. In some embodiments, the negative electrode current collector may be made of copper foil.

[0111] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

[0112] In some embodiments, the electrolyte salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium tetrafluorooxalophosphate (LiTFOP).

[0113] In some embodiments, the solvent may be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC) and diethyl sulfone (ESE).

[0114] In some embodiments, the electrolyte may further include additives.

[0115] The separator is disposed between the positive electrode sheet and the negative electrode sheet to play a role of isolation. The lithium-ion battery of the present application has no particular restrictions on the type of separator, and any known porous structure separator for lithium-ion batteries can be selected. For example, the separator can be one or more of a glass fiber film, a non-woven fabric film, and a multilayer composite film containing one or more of them.

[0116] The electrochemical device can be prepared according to conventional methods in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain an electrode assembly, or the electrode assembly can be obtained by winding; the electrode assembly is placed in a packaging shell, and the electrolyte is injected and sealed to obtain the electrochemical device.

[0117] The electrochemical device of the present application may include any device that generates an electrochemical reaction, and specific examples thereof include all kinds of primary batteries or secondary batteries.

[0118] The secondary batteries in the present application include but are not limited to ternary lithium-ion batteries, lithium cobalt oxide lithium-ion batteries, lithium iron phosphate lithium-ion batteries, lithium manganese oxide lithium-ion batteries and manganese iron phosphate lithium-ion batteries.

[0119] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0120] The coating thickness in the following examples and comparative examples refers to the single-sided thickness, and the description of the slurry involved is as follows:

[0121] Slurry A: Graphite, superionic conductor, conductive agent, adhesive, and dispersant are mixed with water in a mass ratio of 95%:1%:1%:1.8%:1.2% to obtain negative electrode slurry A; wherein the superionic conductor is lithium aluminum titanium phosphate with a particle size of 1um; the conductive agent is carbon black, the adhesive is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0122] Slurry B: Graphite, a conductive agent, a binder, and a dispersant are mixed with water in a mass ratio of 96%:1%:1.8%:1.2% to obtain negative electrode slurry B; wherein the conductive agent is carbon black, the binder is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0123] Slurry C: Graphite, superionic conductor, conductive agent, adhesive, and dispersant are mixed with water in a mass ratio of 95.5%:0.5%:1%:1.8%:1.2% to obtain negative electrode slurry C; wherein the superionic conductor is lithium aluminum titanium phosphate with a particle size of 1um; the conductive agent is carbon black, the adhesive is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0124] Slurry D: Graphite, superionic conductor, conductive agent, adhesive, and dispersant are mixed with water in a mass ratio of 95.9%:0.1%:1%:1.8%:1.2% to obtain negative electrode slurry D; wherein the superionic conductor is lithium aluminum titanium phosphate with a particle size of 1um; the conductive agent is carbon black, the adhesive is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0125] Slurry E: Graphite, superionic conductor, conductive agent, adhesive, and dispersant are mixed with water in a mass ratio of 86%:10%:1%:1.8%:1.2% to obtain negative electrode slurry E; wherein the superionic conductor is lithium aluminum titanium phosphate with a particle size of 1um; the conductive agent is carbon black, the adhesive is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0126] Slurry F: Graphite, superionic conductor, conductive agent, adhesive, and dispersant are mixed with water in a mass ratio of 94.6%:1.4%:1%:1.8%:1.2% to obtain negative electrode slurry E; wherein the superionic conductor is lithium aluminum titanium phosphate with a particle size of 1um; the conductive agent is carbon black, the adhesive is styrene-butadiene rubber, and the dispersant is sodium carboxymethyl cellulose;

[0127] Example 1

[0128] This embodiment provides a composite negative electrode sheet, and the preparation method is as follows:

[0129] The negative electrode slurry A is coated on both sides of the current collector, dried, cold pressed and cut to obtain the negative electrode sheet; wherein the dry thickness of the negative electrode single-side coating is 0.12 mm.

[0130] Example 2

[0131] This embodiment provides a composite negative electrode sheet, and the preparation method is as follows:

[0132] Apply negative electrode slurry A on both sides of the current collector and dry it;

[0133] Applying negative electrode slurry B on the surface of slurry A to form a coating;

[0134] The electrode sheet coated with slurry B was dried, cold pressed and cut to obtain a negative electrode sheet, wherein the dry thickness of the coating formed by slurry A and slurry B was 0.06 mm and 0.06 mm respectively.

[0135] Example 3

[0136] This embodiment provides a composite negative electrode sheet, which is different from Embodiment 2 only in that slurry B is first coated on both sides of the current collector, and then slurry A is coated on the coating formed by slurry B, wherein the dry thickness of the coating formed by slurry A and slurry B is 0.06 mm and 0.06 mm, respectively.

[0137] Example 4

[0138] This embodiment provides a composite negative electrode sheet, which differs from Embodiment 2 only in that:

[0139] First, slurry B is coated on both sides of the current collector, and then slurry C is coated on the coating formed by slurry B, and then slurry A is coated on the coating formed by slurry C, wherein the dry thicknesses of the coatings formed by slurry A, slurry B and slurry C are 0.04 mm, 0.04 mm and 0.04 mm, respectively.

[0140] Example 5

[0141] This embodiment provides a composite negative electrode sheet, which differs from Embodiment 2 only in that:

[0142] First, slurry B is coated on both sides of the current collector, and then slurry D is coated on the coating formed by slurry B, and then slurry C is coated on the coating formed by slurry D, and then slurry A is coated on the coating formed by slurry C, wherein the dry thickness of the coatings formed by slurry A, slurry B, slurry C and slurry D are 0.03 mm, 0.03 mm, 0.03 mm and 0.03 mm, respectively.

[0143] Example 6

[0144] This embodiment provides a composite negative electrode sheet, which differs from Embodiment 2 only in that:

[0145] First, slurry B is coated on both sides of the current collector, and then slurry D is coated on the coating formed by slurry B, and then slurry C is coated on the coating formed by slurry D, wherein the dry thicknesses of the coatings formed by slurry B, slurry C and slurry D are 0.04 mm, 0.04 mm and 0.04 mm, respectively.

[0146] Example 7

[0147] This embodiment provides a composite negative electrode sheet, which differs from Embodiment 2 only in that:

[0148] First, slurry B is coated on both sides of the current collector, and then slurry D is coated on the coating formed by slurry B, and then slurry C is coated on the coating formed by slurry D, and then slurry A is coated on the coating formed by slurry C, and then slurry E is coated on the coating formed by slurry A, wherein the dry thickness of the coatings formed by slurry A, slurry B, slurry C, slurry D and slurry E are 0.015 mm, 0.03 mm, 0.03 mm, 0.3 mm and 0.015 mm, respectively.

[0149] Example 8

[0150] This embodiment provides a composite negative electrode sheet, and the preparation method is as follows:

[0151] First, slurry B is coated on both sides of the current collector, and then slurry D is coated on the coating formed by slurry B, and then slurry F is coated on the coating formed by slurry D, wherein the dry thickness of the coatings formed by slurry B, slurry D and slurry F are 0.04 mm, 0.04 mm and 0.04 mm respectively.

[0152] Comparative Example

[0153] A composite negative electrode sheet, the preparation method is as follows:

[0154] The slurry B was coated on both sides of the current collector, dried, cold pressed and cut to obtain the negative electrode sheet, wherein the dry thickness of the negative electrode coating was 0.12 mm.

[0155] The negative electrode plate and the positive electrode plate of lithium iron phosphate, electrolyte, separator, aluminum-plastic film, etc. are assembled into a soft-pack lithium-ion battery, and the performance of the assembled soft-pack lithium-ion battery is tested, specifically including:

[0156] DC internal resistance DCR test: adjust to 50% SOC state at 25℃, leave for 1h, record OCV1, discharge at 3C for 10s, record OCV2, and then calculate DCR according to (OCV1-OCV2) / 3C×1000.

[0157] Potential test: Charge to 3.65V at 1C constant current and constant voltage at 25℃, cut off the current at 0.05C, and monitor the negative electrode potential to lithium.

[0158] Rate discharge performance test: charge to 3.65V at 1C constant current and constant voltage at 25℃, cut off the current at 0.05C, leave for 30min, discharge to 2.2V at nC constant current, record the discharge capacity retention rate, n=1, 3, 5, the discharge capacity retention rate is: nC discharge capacity / 1C discharge capacity×100%.

[0159] Cycle life test: Charge at 1C constant current and constant voltage to 3.65V at 25℃, cut off at 0.05C, leave for 30min, discharge at 1C constant current, cut off at 2.0V, leave for 30min after discharge, and repeat the charge and discharge steps.

[0160] The above test results are shown in Table 1.

[0161] Table 1

[0162]

[0163]

[0164] In the embodiments of the present application, a superionic conductor is introduced into the negative electrode plate to obtain a negative electrode plate with improved lithium ion transmission rate, and the resistance of the assembled lithium ion battery is significantly reduced, and the rate performance is improved. For example, as in the above-mentioned embodiments 1-8 and comparative example 1, in the lithium ion battery prepared by embodiments 1-8, during the 1C direct charging process, the lowest potential of the negative electrode is >0V, while the potential of the comparative example is lower than 0V, and lithium precipitation occurs. The increase in the negative electrode charging potential can increase the cycle life of the battery; for example, if the DC internal resistance of the battery is reduced from 16mΩ in the comparative example to 12mΩ in embodiment 1, the 3C discharge capacity retention rate is 4.5% higher than that of the comparative example, and the rate performance of the battery is significantly improved, indicating that the introduction of superionic conductors into the negative electrode plate in the present application can effectively increase the ion transmission rate and reduce the impedance; when the amount of superionic conductors is equal, preferably, the increasing method starting from the side close to the current collector is more effective, and the uniform dispersion method of the superionic conductor in embodiment 1 is changed to the decreasing method in embodiment 2. Compared with the incremental method of Example 3, the impedance of Example 3 is further reduced to 10mΩ; preferably, the incremental method increases the number of layers, which can reduce the amount of superionic conductors used. The amount of Example 5 is lower than that of Example 3, but the impedance is similar, and the 3C capacity retention rate and cycle life are basically the same; preferably, the content and number of layers of superionic conductors are increased at the same time, and the beneficial effect is further increased. The effect of Example 7 is greatly improved, the DC internal resistance is reduced by 46.9%, and the cycle life is increased by 3.6 times; compared with Example 4 and Example 8, under the same amount of superionic conductors, preferably, the superionic conductor of Example 4 starts from the current collector in the entire coating, and gradually increases with the increase of thickness x, which can more specifically improve the lithium ion transmission at different positions in the thickness direction of the pole piece, and the DC internal resistance is more significantly reduced, and the cycle life is longer. This technical solution has a simple structure, is easy to prepare, is compatible with the current process, and is conducive to its large-scale use in the market.

[0165] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a current collector and a negative electrode coating disposed on at least one surface of the current collector, wherein the negative electrode coating comprises a negative electrode active material and a super ion conductor; In the negative electrode coating: The superionic conductors are evenly distributed; Or, along the direction away from the current collector, the mass fraction of the superionic conductor gradually decreases or decreases in a gradient; Alternatively, the mass fraction of the superionic conductor increases gradually or in a gradient along a direction away from the current collector.

2. A negative electrode plate, characterized in that: It includes a current collector and a negative electrode coating, wherein the negative electrode coating is disposed on at least one surface of the current collector; The negative electrode coating comprises a negative electrode active material and a superionic conductor, the mass fraction of the superionic conductor in the negative electrode coating is 0.1%-10%, and the superionic conductor is selected from at least one of lithium-containing oxides, lithium-containing sulfides and lithium-containing halides.

3. The negative electrode sheet according to claim 2, characterized in that: The superionic conductor is uniformly distributed or gradually distributed in the negative electrode coating.

4. The negative electrode sheet according to claim 2, characterized in that: The negative electrode coating disposed on one surface of the current collector includes two or more sub-coating layers disposed in sequence, and any two adjacent sub-coating layers among the two or more sub-coating layers are respectively recorded as the first sub-coating layer and the second sub-coating layer; The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, and Delta_A is greater than 0, less than 0 or equal to 0; Preferably, the absolute value of Delta_A is in the range of 1%-5%.

5. The negative electrode sheet according to claim 2, characterized in that: The negative electrode coating disposed on one surface of the current collector includes three or more sub-coating layers disposed in sequence, wherein any three adjacent sub-coating layers among the three or more sub-coating layers are respectively recorded as the first sub-coating layer, the second sub-coating layer and the third sub-coating layer; The first sub-coating layer is closer to the current collector than the second sub-coating layer, the difference between the mass fraction of the superionic conductor in the second sub-coating layer and the mass fraction of the superionic conductor in the first sub-coating layer is Delta_A, the difference between the mass fraction of the superionic conductor in the third sub-coating layer and the mass fraction of the superionic conductor in the second sub-coating layer is Delta B, and Delta_A=Delta_B; Preferably, the absolute value of Delta_A is in the range of 1%-3%.

6. The negative electrode sheet according to claim 2, characterized in that: The thickness of the negative electrode coating is 1 μm-200 μm; and / or, the superionic conductor is at least one selected from lithium lanthanum titanate, lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium silicon sulfide, lithium boron sulfide, lithium germanium sulfide boron, lithium yttrium hexachloride, lithium yttrium hexabromide and lithium zirconium hexachloride; And / or, the average particle size of the superionic conductor is 0.05 μm to 10 μm; And / or, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, silicon-based materials and tin-based materials.

7. The negative electrode sheet according to claim 2, characterized in that: The negative electrode coating also includes a conductive agent; Preferably, the conductive agent is selected from at least one of superconducting carbon, carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; Preferably, the mass fraction of the conductive agent in the negative electrode coating is 0.1%-10%.

8. The negative electrode sheet according to claim 2, characterized in that: The negative electrode coating also includes a binder; Preferably, the adhesive is selected from at least one of styrene-butadiene rubber, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan; Preferably, the mass fraction of the binder in the negative electrode coating is 0.1%-5%.

9. The negative electrode sheet according to claim 2, characterized in that: The negative electrode coating also includes a dispersant; Preferably, the dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and polyvinyl pyrrolidone; Preferably, the mass fraction of the dispersant in the negative electrode coating is 0.1%-5%.

10. A secondary battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 9.

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