Negative pole piece and preparation method thereof, battery and power utilization device

Abstract

The invention discloses a negative pole piece and a preparation method thereof, a battery and an electric device. The negative pole piece comprises a current collector and a film layer arranged on the surface of at least one side of the current collector, the film layer comprises an additive, the additive has lithium intercalation capacity, and the voltage of lithium intercalation reaction of the additive and Li < + > is higher than that of reduction reaction of Na < + > on the negative pole piece. Therefore, in the stage that active ions are subjected to reduction reaction on the negative pole piece, lithium ion impurities are subjected to reduction reaction on the surface of the negative pole piece prior to sodium ions and embedded into the additive, and the condition that lithium forms a lithium-containing interface film on the surface of the negative pole piece to hinder transmission of the sodium ions is inhibited.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a negative electrode plate and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Secondary batteries are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Sodium-ion batteries, a type of secondary battery, primarily rely on the movement of sodium ions between positive and negative electrodes to operate. With the development of today's society, people's demands for batteries are becoming increasingly demanding.

[0003] Public content

[0004] In view of the technical problems existing in the background technology, the present application provides a negative electrode plate, aiming to improve the high-rate cycle performance of the battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode plate, the negative electrode plate comprising a current collector and a film layer provided on at least one side surface of the current collector, the film layer comprising an additive, the additive having a lithium insertion capacity, the additive and the Li + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which a reduction reaction occurs on the negative electrode plate.

[0006] The negative electrode plate of the first aspect of the present application has at least the following beneficial effects: by introducing the additive into the negative electrode plate, lithium ion impurities can undergo reduction reaction on the surface of the negative electrode plate in preference to sodium ions and be embedded in the additive during the stage when the active ions undergo reduction reaction on the negative electrode plate, thereby inhibiting the formation of a lithium-containing interface film on the surface of the negative electrode plate and hindering the transmission of sodium ions, that is, it is beneficial to the reduction of sodium ions on the negative electrode plate and reduces the influence of lithium ions, thereby improving the transmission efficiency of sodium ions and improving the high-rate cycle performance of the battery.

[0007] In some embodiments of the present application, the film layer further includes a negative electrode active material, and the additive is + The voltage at which the lithium insertion reaction occurs is higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium intercalation occurs can inhibit the formation of a lithium-containing interface film on the surface of the negative electrode, thereby hindering the transmission of sodium ions.

[0008] In some embodiments of the present application, the mass ratio of the negative electrode active material to the additive is (80-99.5): (20-0.5). This not only effectively inhibits the formation of a lithium-containing interface film on the surface of the negative electrode by lithium ion impurities, improving the transmission efficiency of sodium ions, but also ensures a balanced energy density of the negative electrode and the battery.

[0009] In some embodiments of the present application, the mass ratio of the negative electrode active material to the additive is (95-99):(5-1).

[0010] In some embodiments of the present application, the lithium insertion capacity of the additive is ≥50 mAh / g, which is beneficial for further achieving both higher energy density and better high-rate cycle performance for the negative electrode sheet and the battery.

[0011] In some embodiments of the present application, a battery is assembled using a sodium metal sheet and the negative electrode sheet as electrode sheets, and the additive is mixed with Li + The voltage at which the lithium insertion reaction occurs is ≥0.8V. This further facilitates the lithium ion impurities to undergo a reduction reaction on the surface of the negative electrode before the sodium ions and be inserted into the additive, thereby avoiding or reducing the formation of a lithium-containing interface film on the negative electrode surface by the lithium ions, thereby improving the sodium ion transmission efficiency and the high-rate cycle performance of the battery.

[0012] In some embodiments of the present application, a battery is assembled using a sodium metal sheet and the negative electrode sheet as electrode sheets, and the additive is mixed with Li + The voltage at which the lithium insertion reaction occurs is ≥1 V. This is beneficial to further improve the sodium ion transmission efficiency and improve the high-rate cycle performance of the battery.

[0013] In some embodiments of the present application, the additive and Li + The voltage at which the lithium insertion reaction occurs is greater than the operating voltage of the sodium battery, which further helps prevent lithium ion impurities from being removed after being inserted into the additive.

[0014] In some embodiments of the present application, the additive includes one or more of TiO2, Fe2O3, ZnO, CuO, Sn, and SnO2. This can further enhance the additive's ability to capture lithium, thereby preventing lithium ion impurities that may be present in a sodium ion battery system from forming an interface film on the surface of the negative electrode, thereby affecting the transport of sodium ions.

[0015] In some embodiments of the present application, the negative electrode active material includes one or more of hard carbon, soft carbon, artificial graphite, and natural graphite.

[0016] In some embodiments of the present application, the film layer includes a negative electrode active material layer, and the additive is dispersed throughout the negative electrode active material layer, or the additive is dispersed on a side of the active material layer away from the negative electrode current collector.

[0017] The second aspect of the present application provides a method for preparing the negative electrode sheet of the first aspect of the present application, comprising:

[0018] The additive is applied to at least one side of the negative electrode current collector in the form of a slurry to form a film layer.

[0019] Wherein, the additive has lithium insertion capacity, and the additive and Li + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which the reduction reaction occurs on the negative electrode.

[0020] The method for preparing a negative electrode plate in the second aspect of the present application has at least the following beneficial effects: the method is not only simple in process, but also the additive introduced into the negative electrode plate can, during the stage when the active ions undergo reduction reaction on the negative electrode plate, cause lithium ion impurities to undergo reduction reaction on the surface of the negative electrode plate in preference to sodium ions and be embedded in the additive, thereby inhibiting the formation of a lithium-containing interface film on the surface of the negative electrode plate and hindering the transmission of sodium ions, that is, facilitating the reduction of sodium ions on the negative electrode plate and reducing the influence of lithium ions, thereby improving the transmission efficiency of sodium ions and improving the high-rate cycle performance of the battery.

[0021] In some embodiments of the present application, the method for preparing a negative electrode sheet may include: mixing a negative electrode active material with the additive to prepare a slurry; applying the slurry to at least one side of the negative electrode current collector to form the film layer, wherein the additive and Li + The voltage at which the lithium insertion reaction occurs is higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium insertion reaction occurs.

[0022] The third aspect of the present application provides a battery, comprising: the negative electrode plate of the first aspect of the present application, and / or the negative electrode plate prepared by the method of the second aspect of the present application.

[0023] In some embodiments of the present application, the battery is a sodium secondary battery.

[0024] The fourth aspect of the present application provides an electrical device, which includes: the battery described in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0026] Figure 1 It is a schematic structural diagram of a battery according to one embodiment of the present application.

[0027] Figure 2 It is a schematic structural diagram of a battery module according to one embodiment of the present application.

[0028] Figure 3 It is a schematic structural diagram of a battery pack according to one embodiment of the present application.

[0029] Figure 4 yes Figure 3 Exploded diagram of .

[0030] Figure 5 It is a schematic diagram of an embodiment of an electrical device using a battery as a power source of the present application.

[0031] Figure 6 This is the specific capacity-voltage curve collected during the charge and discharge process of the half-cell prepared in Example 1 of the present application.

[0032] Description of reference numerals:

[0033] 1: Battery; 2: Battery module; 3: Battery pack; 4: Upper case; 5: Lower case. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0035] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0036] " Scope " disclosed in the present application is limited in the form of lower limit and / or upper limit, and given range is limited by selecting a lower limit and / or an upper limit, and the selected lower limit and / or the rear upper limit define the boundary of special range. The scope limited in this way can be to include end value, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form the scope of not clearly recording, and any lower limit can be combined with other lower limits to form the scope of not clearly recording, and any upper limit can be combined with any other upper limit to form the scope of not clearly recording. In addition, each separately disclosed point or single numerical value itself can be combined with any other point or single numerical value as lower limit or upper limit or form the scope of not clearly recording with other lower limit or upper limit combination.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0039] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed sequentially, or may include steps S2 and S1 performed sequentially. For example, the method may further include step S3, which means that step S3 may be added to the method in any order, for example, the method may include steps S1, S2, and S3, or may include steps S1, S3, and S2, or may include steps S3, S1, and S2, etc.

[0040] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0041] In this application, the terms "plurality" and "multiple" refer to two or more.

[0042] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0043] At present, sodium-ion batteries used as secondary batteries mainly rely on the movement of sodium ions between the positive and negative electrodes to work. In sodium-ion batteries, due to reasons or methods such as battery raw materials, production line residues, or doping introduced to improve battery performance, there will be more or less a small amount of lithium ions in the sodium battery. For example, lithium ions may be introduced by the positive electrode plate or the electrolyte. Taking the electrolyte as an example, its electrolyte material sodium hexafluorophosphate may contain a small amount of lithium hexafluorophosphate impurities. Commonly used sodium-ion battery negative electrode plates are more sensitive to trace lithium ion impurities in the sodium-ion battery system. Lithium ions easily form a lithium-containing interface film on the surface of the negative electrode plate, while sodium ions find it difficult to penetrate the interface film. The interface film will hinder the transmission of sodium ions, resulting in too slow reaction kinetics of the negative electrode plate. Sodium metal is easily precipitated during high-rate charge and discharge, leading to battery failure.

[0044] To solve the above problems, this application introduces a Li-ion battery into the negative electrode. + The negative electrode plate includes a current collector and a film layer arranged on at least one side of the current collector. The film layer includes an additive having a lithium insertion capacity. The additive reacts with Li + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which the reduction reaction occurs on the negative electrode. The additive can undergo lithium insertion reaction with lithium at a higher redox voltage during the charge and discharge cycle, which is beneficial to the Na + Lithium ions are consumed before the reduction reaction occurs on the negative electrode plate and the formation of a lithium-containing interface film on the surface of the negative electrode plate is inhibited, thereby reducing the impact of lithium ion impurities on the kinetic performance of the sodium ion battery, improving the transmission efficiency of sodium ions, and improving the high-rate cycle performance of the battery.

[0045] The negative electrode sheet disclosed in the embodiment of the present application is suitable for a secondary battery, and the battery disclosed in the embodiment of the present application can be used in an electrical device that uses the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0046] The first aspect of the present application provides a negative electrode plate, the negative electrode plate comprising a current collector and a film layer arranged on at least one side of the current collector, the film layer comprising an additive, the additive having a lithium insertion capacity, the additive and the Li + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which the reduction reaction occurs on the negative electrode.

[0047] Among them, in order to solve the problem that lithium ion impurities in the sodium ion battery system easily form a lithium-containing interface film on the surface of the negative electrode, hindering the transmission of sodium ions, a lithium-ion-containing interfacial film with lithium intercalation capacity can be introduced into the negative electrode. + The voltage at which lithium insertion occurs is higher than that of Na + The voltage additive of the reduction reaction on the negative electrode is used to solve the problem. In this design, lithium ions can be reduced on the surface of the negative electrode before sodium ions and embedded in the additive. As a result, lithium ions can be consumed, avoiding or reducing the formation of lithium-containing interface films on the negative electrode surface. Furthermore, the adverse effects of the presence of lithium ion impurities on sodium ion transmission can be reduced, the sodium ion transmission efficiency can be improved, and the high-rate cycle performance of the battery can be improved. It should be noted that the additive and Li + Lithium insertion reaction refers to the reaction between the additive and Li + The redox reaction occurs during which Li + is reduced; the lithium insertion reaction and Na + The reduction reaction that occurs on the negative electrode is the active ion (including Na + ) is carried out during the stage of reduction reaction on the negative electrode plate. For the full battery, the stage of reduction reaction of active ions on the negative electrode plate corresponds to the charging process; for the half battery, the stage of reduction reaction of active ions on the negative electrode plate corresponds to the discharging process.

[0048] The negative electrode plate of the first aspect of the present application has at least the following beneficial effects: by introducing the additive into the negative electrode plate, lithium ion impurities can undergo reduction reaction on the surface of the negative electrode plate in preference to sodium ions and be embedded in the additive during the stage when the active ions undergo reduction reaction on the negative electrode plate, thereby inhibiting the formation of a lithium-containing interface film on the surface of the negative electrode plate and hindering the transmission of sodium ions, that is, it is beneficial to the reduction of sodium ions on the negative electrode plate and reduces the influence of lithium ions, thereby improving the transmission efficiency of sodium ions and improving the high-rate cycle performance of the battery.

[0049] In this application, the presence of additives, additives and Li + The voltage at which lithium insertion reaction occurs, Na + The voltage at which the reduction reaction occurs on the negative electrode plate can be measured using conventional methods and instruments in the field. For example, the composition of the negative electrode plate can be analyzed by one or more methods including but not limited to X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), EDS spectrum analysis, inductively coupled plasma emission spectroscopy (ICP) testing, and then the half-electrical characterization of the potential of each component can be obtained.

[0050] Furthermore, the negative electrode sheet of the first aspect of the present application may optionally meet one or more of the following conditions on the basis of meeting the above conditions.

[0051] In some embodiments, the current collector of the negative electrode plate may also generally include a current collector body and an undercoat layer. The undercoat layer may be disposed on at least one side of the current collector body. The undercoat layer substantially contains no negative electrode active material and may include a small amount of carbon material. However, the carbon material coating is thin and cannot function as a negative electrode active material. In this embodiment, the negative electrode plate may be a plate without a negative electrode active material layer. For negative electrode plates without a negative electrode active material layer, when the current collector of the negative electrode plate does not include an undercoat layer, the film layer may be disposed on at least one side of the current collector. When the current collector of the negative electrode plate includes an undercoat layer, the film layer may be disposed on the surface of the undercoat layer on the side away from the current collector.

[0052] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode plate. The type of the binder is not particularly limited and can be flexibly selected by those skilled in the art based on actual needs.

[0053] In some embodiments of the present application, the film layer may further include negative electrode active materials, additives and Li + The voltage at which lithium insertion occurs can be higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium insertion reaction occurs.

[0054] Wherein, the negative electrode active material and Na + Sodium insertion reaction refers to the negative electrode active material and Na + The redox reaction occurs during which Na + Be restored.

[0055] In some embodiments, the membrane layer may include a negative electrode active material layer. In a sodium battery, a lithium-ion battery having lithium insertion capacity and Li + The voltage at which lithium insertion occurs is higher than the voltage at which the negative electrode active material and Na + The additive with a voltage that causes a sodium intercalation reaction can cause lithium ion impurities to undergo a reduction reaction on the surface of the negative electrode sheet before sodium ions during the stage of active ion intercalation into the negative electrode sheet and be intercalated into the additive. This can consume lithium ions, avoid or reduce the formation of a lithium-containing interface film on the negative electrode surface by lithium ions, and further reduce the adverse effects of the presence of lithium ion impurities on sodium ion transport, improve the efficiency of sodium intercalation and deintercalation of the negative electrode active material, and reduce the risk and amount of sodium metal precipitation during high-rate cycling of the battery. As a result, the precipitation of sodium metal during high-rate cycling of the battery can be suppressed, and the capacity retention rate of the battery during high-rate cycling can be improved.

[0056] In some embodiments of the present application, the mass ratio of the negative electrode active material to the additive may be (80-99.5):(20-0.5).

[0057] For example, the mass ratio of the negative electrode active material to the additive can be 80 / 20, 82 / 18, 85 / 15, 88 / 12, 90 / 10, 92 / 8, 95 / 5, 98 / 2, 99.5 / 0.5, etc. The mass ratio of the negative electrode active material to the additive can be measured by combining conventional methods such as XRD, ICP testing, and thermogravimetric analysis. Increasing the content of the negative electrode active material is beneficial to further suppressing the negative impact of lithium ion impurities that may exist in the sodium ion battery system on the sodium ion transport performance, while reducing the content of the additive is beneficial to balancing the energy density of the negative electrode sheet and the battery. Controlling the mass ratio of the negative electrode active material to the additive to meet the given range can not only effectively inhibit lithium ion impurities from forming a lithium-containing interface film on the surface of the negative electrode plate, improve the transmission efficiency of sodium ions, but also take into account the energy density of the negative electrode plate and the battery. For example, taking the negative electrode plate in which the film layer is the negative electrode active material layer as an example, it can not only effectively inhibit lithium ion impurities from forming a lithium-containing interface film on the surface of the negative electrode plate, thereby helping to improve the efficiency of sodium deintercalation of the negative electrode active material and inhibit the precipitation of sodium metal during high-rate cycling of the battery, but also reduce the risk of a significant decrease in the energy density of the negative electrode plate and the battery caused by the use of additives, which is beneficial to simultaneously take into account higher energy density and better high-rate cycling performance.

[0058] In some embodiments of the present application, the mass ratio of the negative electrode active material to the additive may be (95-99):(5-1), thereby facilitating a balance between higher energy density and better high-rate cycle performance.

[0059] In some embodiments of the present application, the lithium insertion capacity of the additive may be ≥50mAh / g. Exemplarily, the lithium insertion capacity of the additive may be 50mAh / g, 60mAh / g, 70mAh / g, 80mAh / g, 100mAh / g, 150mAh / g, 200mAh / g, 250mAh / g, 300mAh / g, 350mAh / g, and the like. The lithium insertion capacity of the additive can be tested by conventional methods in the art. When the lithium insertion capacity of the additive is high, more lithium can be consumed at a lower additive dosage, which is beneficial to further enable the negative electrode sheet and the battery to simultaneously take into account higher energy density and better high-rate cycle performance. Furthermore, the irreversible lithium insertion capacity of the additive can be ≥50 mAh / g, optionally ≥100 mAh / g, for example, 50 mAh / g, 80 mAh / g, 100 mAh / g, 110 mAh / g, 120 mAh / g, 150 mAh / g, etc. Increasing the irreversible lithium insertion capacity of the additive is also beneficial for preventing at least part of the lithium ions from being embedded in the additive and then being released, thereby further reducing the adverse effects of possible lithium ion impurities on the rate performance and cycle performance of the sodium ion battery system.

[0060] In some embodiments of the present application, a sodium metal sheet and a negative electrode sheet are used as electrode sheets to assemble a battery, and the additive is mixed with Li + The voltage at which the lithium storage reaction occurs can be ≥0.8V.

[0061] Exemplarily, the battery can be a button battery. When assembling the battery, a sodium metal sheet can be used as a counter electrode and a reference electrode. The electrolyte used can be obtained by the following method: Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in equal volumes to obtain an organic solvent, and the electrolyte NaClO4 is used to prepare an electrolyte with a concentration of 1 mol / L. A small amount of LiPF6 is added to the electrolyte (e.g., based on the total mass of the electrolyte containing lithium impurities, the mass proportion of LiPF6 can be 1%) to obtain a sodium ion battery electrolyte containing trace lithium impurities. A porous polyethylene film is used as an isolation membrane. The above-mentioned negative electrode sheet, isolation membrane, and sodium metal sheet are stacked in order so that the isolation membrane is located between the negative electrode sheet and the sodium metal sheet to act as an isolation membrane. The above-prepared electrolyte is added to complete the preparation of the button battery. Additives and Li + The voltage at which the lithium insertion reaction occurs can be obtained by performing a charge and discharge cycle test on the battery. +The voltage at which the lithium insertion reaction occurs can be ≥0.8V, ≥0.9V, ≥1V, ≥1.1V, ≥1.2V, etc. This further facilitates the lithium ion impurities to undergo a reduction reaction on the surface of the negative electrode sheet before sodium ions and to be inserted into the additive, thereby avoiding or reducing the formation of a lithium-containing interface film on the surface of the negative electrode by lithium ions, thereby improving the sodium ion transmission efficiency and enhancing the high-rate cycle performance of the battery. For example, taking the negative electrode sheet in which the film layer is the negative electrode active material layer as an example, satisfying the given conditions is conducive to improving the efficiency of sodium insertion and deintercalation of the negative electrode active material, and reducing the risk and amount of sodium metal precipitation during high-rate cycling of the battery.

[0062] In some embodiments of the present application, a sodium metal sheet and a negative electrode sheet are used as electrode sheets to assemble a battery, and the additive is mixed with Li + The voltage at which the lithium insertion reaction occurs can be ≥1V. This is beneficial for further improving the sodium ion transmission efficiency and improving the high-rate cycling performance of the battery. For example, taking the negative electrode sheet in which the membrane layer is the negative electrode active material layer as an example, meeting the given conditions is beneficial for further improving the efficiency of sodium insertion and deintercalation of the negative electrode active material and reducing the risk and amount of sodium metal precipitation during high-rate cycling of the battery.

[0063] In some embodiments of the present application, the additive and Li + The voltage at which the lithium insertion reaction occurs can be greater than the operating voltage of the sodium battery. This configuration further helps prevent lithium ion impurities from being removed after being inserted into the additive, thereby further reducing the adverse effects of possible lithium ion impurities on the rate performance and cycle performance of the sodium ion battery system.

[0064] In some embodiments of the present application, the additive may include one or more of TiO2, Fe2O3, ZnO, CuO, Sn, and SnO2. TiO2, Fe2O3, ZnO, CuO, Sn, and SnO2 have relatively strong lithium capture capabilities. Using one or more of these as additives is beneficial for further inhibiting the formation of an interfacial film on the surface of the negative electrode sheet that may be present in the sodium ion battery system, thereby affecting the transmission of sodium ions and improving the high-rate cycle performance of the battery. For example, taking the negative electrode sheet in which the film layer is the negative electrode active material layer as an example, meeting the given conditions is beneficial for further improving the efficiency of sodium deintercalation of the negative electrode active material and inhibiting the precipitation of sodium metal during high-rate cycling of the battery.

[0065] In some embodiments of the present application, the specific type of the negative electrode active material in the film layer is not limited. Active materials known in the art for use in sodium ion battery negative electrodes can be used, and those skilled in the art can select them according to actual needs. As an example, the negative electrode active material can include but is not limited to carbon materials, including but not limited to at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials, all of which can be obtained through commercial channels.

[0066] For example, the negative electrode active material may include one or more of hard carbon, soft carbon, artificial graphite, and natural graphite.

[0067] In some embodiments of the present application, the film layer may include a negative electrode active material layer, and the additive may be dispersed throughout the negative electrode active material layer, or the additive may be dispersed on the side of the active material layer away from the negative electrode current collector. In actual operation, the additive may be mixed with the negative electrode active material and then coated on the negative electrode current collector in the form of a slurry to form an active material layer, so that the additive and the negative electrode active material are uniformly dispersed in the negative electrode active material layer and distributed throughout the active material layer; or a portion of the negative electrode active material may be prepared into a slurry and coated on the surface of the negative electrode current collector to form a first coating layer, and then the additive is mixed with the remaining portion of the negative electrode active material and then coated on the surface of the first coating layer in the form of a slurry, so that the additive is dispersed on the side of the negative electrode active material layer away from the current collector. Both methods are beneficial for consuming lithium ions before sodium is embedded in the negative electrode plate and inhibiting the formation of a lithium-containing interface film on the surface of the negative electrode plate, thereby improving the efficiency of sodium deintercalation of the negative electrode active material and inhibiting the precipitation of sodium metal during high-rate cycling of the battery.

[0068] In a battery, the negative electrode active material layer generally also includes a conductive agent and a binder. The conductive agent can be used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the binder to the negative electrode current collector. This application does not specifically limit the types of conductive agents and binders, and they can be selected according to actual needs. As an example, the conductive agent can include but is not limited to at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. As an example, the binder can include but is not limited to at least one of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin and carboxymethyl cellulose (CMC). In addition, the negative electrode active material layer may optionally include a thickener, such as carboxymethyl cellulose (CMC). However, this application is not limited to this, and this application can also use other materials that can be used as thickeners for sodium ion battery negative electrode sheets.

[0069] In some embodiments, the negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0070] The second aspect of the present application provides a method for preparing the negative electrode sheet of the first aspect of the present application, comprising: applying an additive in the form of a slurry to at least one side of the negative electrode current collector to form a film layer, wherein the additive has a lithium insertion capacity, and the additive is + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which the reduction reaction occurs on the negative electrode.

[0071] The method for preparing a negative electrode sheet according to the second aspect of the present application has at least the following beneficial effects: the method is not only simple in process, but also the additive introduced into the negative electrode sheet can cause lithium ion impurities to undergo a reduction reaction on the surface of the negative electrode sheet before sodium ions during the stage of the reduction reaction of active ions on the negative electrode sheet and embed into the additive, thereby inhibiting the formation of a lithium-containing interface film on the surface of the negative electrode sheet and hindering the transmission of sodium ions. In other words, it is beneficial to the reduction of sodium ions on the negative electrode sheet and reduces the influence of lithium ions. This is beneficial to improving the transmission efficiency of sodium ions and improving the high-rate cycle performance of the battery. It should be noted that the characteristics and effects described for the battery according to the first aspect of the present application are also applicable to the method for preparing a negative electrode sheet and will not be repeated here.

[0072] In some embodiments, the negative electrode plate may be a plate without a negative electrode active material layer. In this case, the additive may be applied in the form of a slurry to at least one side of the current collector of the negative electrode plate to form a film layer; or the additive may be applied in the form of a slurry to the side of the base coating of the current collector of the negative electrode plate away from the negative electrode current collector to form a film layer.

[0073] In some embodiments of the present application, the method for preparing a negative electrode sheet may include: mixing a negative electrode active material with the additive to prepare a slurry; applying the slurry to at least one side of the negative electrode current collector to form the film layer, wherein the additive and Li + The voltage at which the lithium insertion reaction occurs is higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium insertion occurs. Exemplary:

[0074] In some embodiments, the negative electrode active slurry prepared by mixing the negative electrode active slurry with the additive may be directly coated on the surface of the negative electrode current collector, so that the additive is dispersed throughout the negative electrode active material layer.

[0075] In some embodiments, the negative electrode active material can be divided into two parts, one part is made into a first negative electrode active slurry and coated on the surface of the negative electrode current collector to form a first coating layer, and the remaining part of the negative electrode active slurry is mixed with an additive to prepare a second negative electrode active slurry, and the second negative electrode active slurry is coated on the surface of the first coating layer so that the additive is dispersed on the side of the negative electrode active material layer away from the current collector.

[0076] In some embodiments, when preparing the negative electrode active slurry, a conductive agent and a binder are generally also included. The types and relative amounts of the negative electrode active materials and additives, as well as the types of the conductive agent and binder, have been described in the previous section and will not be repeated here. In addition, when preparing the negative electrode active slurry, a thickener may optionally be added. The selection of the thickener has also been described in the previous section and will not be repeated here. In addition, when preparing the negative electrode active material, the relative amounts of the conductive agent, binder, and optional thickener can be selected according to conventional methods in the art. The types of the negative electrode current collector have also been described in the previous section and will not be repeated here.

[0077] The third aspect of the present application provides a battery, comprising: the negative electrode plate of the first aspect of the present application, and / or the negative electrode plate prepared by the method of the second aspect of the present application.

[0078] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0079] It can be understood that the battery proposed in this application can be a sodium secondary battery.

[0080] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions move back and forth between the positive and negative electrodes (e.g., embedding and de-embedding). The separator is placed between the positive and negative electrodes to isolate them. The electrolyte conducts ions between the positive and negative electrodes.

[0081] [Positive electrode]

[0082] In a battery, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0083] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may include at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0084] The positive electrode active material layer may also optionally include at least one of a binder, a conductive agent, and other optional auxiliary agents. As an example, the conductive agent may include, but is not limited to, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0085] These materials are all commercially available.

[0086] [Electrolyte]

[0087] The electrolyte solution may include an electrolyte salt and a solvent.

[0088] As an example, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0089] As an example, the solvent may include at least one 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), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0090] In some embodiments, the electrolyte may further include electrolyte additives. For example, the electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and other additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0091] [Isolation film]

[0092] As the above-mentioned isolation membrane, the present application has no special restrictions and any known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can include a single-layer or multi-layer film containing at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0093] The embodiment of the present application has no particular limitation on the shape of the battery, which can be cylindrical, square or any other shape. Figure 1 The battery 1 is a square structure as an example.

[0094] In some embodiments, the battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0095] In some embodiments, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0096] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the housing. The number of electrode assemblies in a battery can include one or more, which can be adjusted according to needs.

[0097] In some embodiments, the outer packaging of the battery may include a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0098] The outer packaging of the battery may also include a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0099] In some embodiments, the battery may be either a single battery cell or a battery module or battery pack assembled from battery cells. The battery module or battery pack may contain multiple batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0100] Figure 2 2 is an example of a battery module. Figure 2 In the battery module 2, the multiple batteries 1 can be arranged in sequence along the length direction of the battery module 2. Of course, they can also be arranged in any other manner. Further, the multiple batteries 1 can be fixed by fasteners.

[0101] The battery module 2 may further include a housing having a housing space, wherein the housing space accommodates a plurality of batteries 1. In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0102] Figure 3 and 4 The battery pack 3 is used as an example. Figure 3 and 4 The battery pack 3 may include a battery box and multiple battery modules 2 disposed in the battery box. The battery box includes an upper box body 4 and a lower box body 5. The upper box body 4 can cover the lower box body 5 and form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in the battery box in any manner.

[0103] The fourth aspect of the present application provides an electrical device, which includes: the battery of the third aspect of the present application.

[0104] Specifically, the battery can serve as a power source or an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0105] Figure 5 This is an example of an electrical device. This device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Another example of an electrical device may include a mobile phone, a tablet computer, or a laptop computer. These devices are typically required to be lightweight and thin, and may use batteries as a power source.

[0106] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0107] Example 1

[0108] (1) Preparation of batteries

[0109] (1) Negative electrode

[0110] Hard carbon powder, TiO2 powder, sodium carboxymethyl cellulose and conductive carbon black are weighed in a mass ratio of 95:5:5:5 respectively, deionized water is added according to a solid-liquid ratio of 1:1, and the mixture is ground and mixed evenly. The resulting slurry is then coated on the surface of aluminum foil and dried. The dried electrode is rolled and cut to obtain the negative electrode.

[0111] (2) Preparation of positive electrode sheet

[0112] The positive electrode active material Na3V2(PO4)3, conductive agent Super P, and polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 9:0.5:0.5. The resulting slurry is evenly coated on the surface of the positive electrode current collector aluminum foil. After drying, cold pressing, and cutting, the positive electrode sheet is obtained.

[0113] (3) Preparation of electrolyte: Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in equal volumes to obtain an organic solvent. NaClO4 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. LiPF6 is then added to obtain a sodium ion battery electrolyte containing trace lithium impurities. The mass percentage of LiPF6 in the electrolyte containing lithium impurities is 1%.

[0114] (4) Isolation membrane: A porous polyethylene membrane is used as the isolation membrane.

[0115] (5) Preparation of half-cell

[0116] A sodium metal sheet is used as the counter electrode and reference electrode. The above-mentioned negative electrode sheet, isolation membrane, and sodium metal sheet are stacked in order, so that the isolation membrane is placed between the negative electrode sheet and the sodium metal sheet to play an isolating role. The above-prepared electrolyte is added to complete the preparation of the button battery.

[0117] (6) Preparation of full battery

[0118] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation layer. The prepared electrolyte is added to complete the preparation of the full battery.

[0119] Examples 2 to 9 and Comparative Examples 1 to 3

[0120] The differences between Examples 2 to 9 and Comparative Examples 1 to 3 and the Examples are shown in Table 1.

[0121] (2) Test method

[0122] (1) Reversible specific capacity of half-cell

[0123] At 25° C., the prepared half-cell was discharged at a constant current density of 10 mA / g to 0.005 V, and then charged at a constant current density of 10 mA / g to 2 V, to obtain the reversible specific capacity C0 of the half-cell.

[0124] 2. Test of the voltage of lithium insertion reaction between additives and lithium ions

[0125] At 25°C, the prepared half-cell was first discharged at a constant current density of 16 mA / g to 0.005 V, and then charged at a constant current of 16 mA / g to 2 V. The charge-discharge capacity versus voltage curves during the discharge and charge processes were collected, and the voltage at which lithium and additives undergo lithium insertion reaction was determined based on the curve changes.

[0126] 3. Full battery cycle 100 cycles capacity retention test

[0127] At 25°C, the full battery prepared in Reference Example 1 was charged to 3.5V at a current density of 300mA / g (based on the amount of negative electrode active material). After standing for 1h, it was discharged to 1.5V at a current density of 300mA / g. The discharge capacity at this time was recorded as the initial capacity. The subsequent steps were repeated to perform charge and discharge cycles, and the discharge specific capacity after 100 cycles was recorded. The cycle capacity retention rate was calculated based on the initial capacity.

[0128] 4. Sodium precipitation test

[0129] The full battery after 100 cycles was disassembled to observe whether there was any sodium precipitation on the surface of the negative electrode.

[0130] Relevant tests were carried out on Examples 1 to 9 and Comparative Examples 1 to 3. The test results are shown in Figure 6 and Table 1.

[0131] Table 1 Differences between Examples 1 to 9 and Comparative Examples 1 to 3 and related test results

[0132]

[0133] Results and Conclusions:

[0134] Combining Examples 1 to 9, Comparative Examples 1 to 3 and Table 1, it can be seen that after the additive is introduced into the negative electrode plate, the cycle capacity retention rate and sodium precipitation phenomenon of the battery are significantly improved, indicating that the introduction of additives that can undergo lithium intercalation reactions with lithium ions into the negative electrode plate is beneficial to reducing the impact of lithium ion impurities on the kinetic performance of sodium ion batteries and can improve high-rate cycle performance. In addition, according to the specific capacity-voltage curve test results during the charge and discharge process of the half-cells prepared in each embodiment and comparative example, it is shown that during the discharge process, the voltage at which the additive undergoes lithium intercalation reaction with lithium ions is higher than the voltage at which the negative electrode active material undergoes sodium intercalation reaction with sodium ions, which is further beneficial to improving the cycle capacity retention rate and sodium precipitation problem of the negative electrode plate under high-rate charge and discharge. Taking Example 1 as an example, Figure 6 The specific capacity-voltage curves of the half-cell prepared in Example 1 during the charge and discharge processes are shown. The figure shows a plateau in each of the charge and discharge curves. Taking the discharge curve as an example, the platform indicated by the arrow is the voltage plateau caused by the premature reaction between lithium ions and TiO2, indicating that lithium ions can be consumed before sodium ions are embedded in the negative electrode. Combining Examples 1-9 also shows that appropriately increasing the amount of additives in the negative electrode active material layer is beneficial for achieving both good cycle capacity retention and specific capacity. Optionally, the mass ratio of negative electrode active material to additive can be (80-99):(20-1), and further can be (95-99):(5-1).

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector and a film layer provided on at least one side of the current collector, wherein the film layer includes an additive having a lithium insertion capacity. + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which a reduction reaction occurs on the negative electrode plate.

2. The negative electrode sheet according to claim 1, characterized in that: The film layer also includes negative electrode active materials, the additives and Li + The voltage at which the lithium insertion reaction occurs is higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium insertion reaction occurs.

3. The negative electrode sheet according to claim 2, characterized in that: The mass ratio of the negative electrode active material to the additive is (80-99.5): (20-0.5).

4. The negative electrode sheet according to claim 2 or 3, characterized in that: The mass ratio of the negative electrode active material to the additive is (95-99):(5-1).

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The lithium insertion capacity of the additive is ≥50 mAh / g.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The battery is assembled with the sodium metal sheet and the negative electrode sheet as the electrode sheet, and the additive is mixed with Li + The voltage at which lithium insertion reaction occurs is ≥0.8V.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The battery is assembled with the sodium metal sheet and the negative electrode sheet as the electrode sheet, and the additive is mixed with Li + The voltage at which lithium insertion reaction occurs is ≥1V.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The negative electrode plate is used for sodium battery, and the additive is + The voltage at which the lithium insertion reaction occurs is greater than the operating voltage of the sodium battery.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The additives include one or more of TiO2, Fe2O3, ZnO, CuO, Sn, and SnO2.

10. The negative electrode sheet according to any one of claims 2 to 9, characterized in that: The negative electrode active material includes one or more of hard carbon, soft carbon, artificial graphite, and natural graphite.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that: The film layer includes a negative electrode active material layer, and the additive is dispersed throughout the negative electrode active material layer, or the additive is dispersed on a side of the active material layer away from the negative electrode current collector.

12. A method for preparing the negative electrode sheet according to any one of claims 1 to 11, characterized in that: include: The additive is applied to at least one side of the negative electrode current collector in the form of a slurry to form a film layer. Wherein, the additive has lithium insertion capacity, and the additive and Li + The voltage at which lithium insertion occurs is higher than that of Na + The voltage at which the reduction reaction occurs on the negative electrode.

13. The method according to claim 12, characterized in that include: mixing the negative electrode active material with the additive to prepare a slurry; Applying the slurry to at least one side of the negative electrode current collector to form the film layer, Wherein, the additive and Li + The voltage at which the lithium insertion reaction occurs is higher than the voltage at which the negative electrode active material and Na + The voltage at which sodium insertion reaction occurs.

14. A battery, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 11, and / or comprises the negative electrode sheet produced by the method according to any one of claims 12 to 13. The battery according to claim 14 , which is a sodium secondary battery.

16. An electrical device, characterized in that: include: The battery according to claim 14 or 15.

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