Negative electrode active material, negative electrode pole piece, sodium ion battery and electric device

Abstract

The embodiment of the invention discloses a negative electrode active material, a negative electrode plate, a sodium ion battery and an electric device, the negative electrode active material comprises hard carbon, the true density rho of the hard carbon is greater than or equal to 1.3 g / cm < 3 > and less than or equal to 1.8 g / cm < 3 >; and the interplanar spacing d of the embedded sodium storage material is more than or equal to 0.24 nm and less than or equal to 0.8 nm. The negative electrode active material can effectively reduce the thermal runaway risk of the sodium ion battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a negative electrode active material, a negative electrode plate, a sodium ion battery and an electrical device. Background Art

[0002] Compared with lithium-ion batteries, sodium resources are abundant and the cost is low. At the same time, sodium-ion batteries and lithium-ion batteries have the same "rocking chair" working principle, similar physical and chemical properties, and are compatible with existing lithium battery process equipment, thus becoming a secondary battery with great development potential.

[0003] Hard carbon is widely used as the negative electrode of sodium-ion batteries due to its high sodium storage capacity and low operating voltage. However, sodium-ion batteries also face problems such as short circuit and thermal runaway during actual use. When short circuit and thermal runaway problems occur, a large amount of metallic sodium will be formed when hard carbon stores sodium, and the thermal reaction temperature of hard carbon is low. It is also very easy to have thermal runaway at lower temperatures, which quickly aggravates the thermal runaway of the battery. In severe cases, it causes the sodium-ion battery to catch fire and explode. Therefore, how to improve the thermal runaway problem of sodium-ion batteries has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide a negative electrode active material, a negative electrode plate, a sodium ion battery and an electrical device, wherein the negative electrode active material can effectively reduce the thermal runaway risk of the sodium ion battery.

[0005] In a first aspect, a negative electrode active material is provided, comprising: hard carbon, wherein the true density ρ of the hard carbon satisfies: 1.3 g / cm 3 ≤ρ≤1.8g / cm 3 ; An embedded sodium storage material, wherein the interplanar spacing d of the embedded sodium storage material satisfies: 0.24nm≤d≤0.8nm.

[0006] In the embodiment of the present application, the negative electrode active material includes a true density of 1.3 g / cm 3 -1.8g / cm 3Hard carbon within the range and embedded sodium storage materials with a crystal plane spacing within the range of 0.24-0.8nm, wherein the hard carbon with a true density within the above range can provide a higher capacity for the sodium ion battery, and the embedded sodium storage material can affect the sodium storage mechanism of the negative electrode active material, reduce the deposition of sodium ions in the hard carbon to form metallic sodium, thereby reducing the risk of thermal runaway of sodium ions. The negative electrode active material provided by the embodiment of the present application can make the sodium ion battery have a higher capacity while reducing the risk of thermal runaway and heat spread of the sodium ion battery, thereby improving the safety of the sodium ion battery. In addition, the embedded sodium storage material with a crystal plane spacing within the above range can slip between layers in the microstructure, which helps to increase the powder compaction density of the negative electrode sheet when used in the sodium ion battery, thereby helping to improve the energy density of the sodium ion battery.

[0007] In one embodiment, the embedded sodium storage material includes at least one of a carbon-based embedded sodium storage material, a sulfur-based embedded sodium storage material, and a titanium-based embedded sodium storage material.

[0008] In one embodiment, the crystal plane spacing d of the carbon-based embedded sodium storage material satisfies: 0.335nm≤d≤0.4nm; the crystal plane spacing d of the sulfur-based embedded sodium storage material satisfies: 0.5nm≤d≤0.8nm; the crystal plane spacing d of the titanium-based embedded sodium storage material satisfies: 0.24nm≤d≤0.30nm.

[0009] In one embodiment, the carbon-based embedded sodium storage material includes at least one of soft carbon and modified graphite.

[0010] In one possible implementation, ID / IG of the soft carbon satisfies: 0.9≤ID / IG≤1.6; optionally, 0.9≤ID / IG≤1.5.

[0011] In the embodiments of the present application, by selecting a soft carbon whose ID / IG satisfies the above range, the soft carbon can have a higher degree of disorder, so that in addition to storing sodium based on an embedding mechanism, the soft carbon's ability to store sodium based on an adsorption mechanism is also enhanced, thereby further reducing the formation of metallic sodium, regulating the sodium storage mechanism of the negative electrode active material, and improving the safety performance of sodium ion batteries.

[0012] In one embodiment, the titanium-based embedded sodium storage material includes TiO2, Na2Ti3O7, Li4Ti5O 12 , or at least one of Na3Ti2(PO4)2.

[0013] In one embodiment, the sulfur-based embedded sodium storage material includes at least one of MoS2 and WS2.

[0014] In the embodiments of the present application, titanium-based embedded sodium storage materials and sulfur-based embedded sodium storage materials themselves usually have a higher capacity. The selection of titanium-based and sulfur-based embedded sodium storage materials helps to further improve the capacity and energy density of sodium-ion batteries.

[0015] In one embodiment, the mass content m1 of the hard carbon in the negative electrode active material satisfies: 90%≤m1; optionally, 95%≤m1≤99.5%.

[0016] In one embodiment, the mass content m2 of the embedded sodium storage material in the negative electrode active material satisfies: m2≤10%; optionally, 0.5%≤m2≤5%.

[0017] In the embodiments of the present application, by regulating the mass content of hard carbon and embedded sodium storage material in the negative electrode active material, the capacity and sodium storage mechanism of the negative electrode active material can be effectively regulated, and the formation of metallic sodium can be reduced. As a result, when the negative electrode active material is used in a sodium ion battery, the sodium ion battery can have both high capacity and good safety.

[0018] In one embodiment, the gram capacity W1 of the hard carbon satisfies: W1≤400 mAh / g; optionally, 280 mAh / g≤W1≤350 mAh / g.

[0019] In one embodiment, the gram capacity W2 of the embedded sodium storage material satisfies: W2≤295mAh / g; optionally, 90mAh / g≤W2≤290mAh / g.

[0020] In the embodiments of the present application, by selecting a combination of hard carbon and embedded sodium storage materials with higher gram capacity, the sodium ion battery can have a higher capacity while reducing the risk of thermal runaway and heat spread of the sodium ion battery.

[0021] In one embodiment, the ratio of the charge and discharge capacity Q2 corresponding to the platform region of the charge and discharge curve of the negative electrode active material to the charge and discharge capacity Q1 corresponding to the slope region satisfies: Q2 / Q1≤3.3; optionally, 0.05≤Q2 / Q1≤3.

[0022] In a second aspect, a negative electrode plate is provided, wherein the negative electrode plate comprises the negative electrode active material in any possible implementation of the first aspect.

[0023] In a third aspect, a sodium ion battery is provided, wherein the sodium ion battery comprises the negative electrode plate in any possible implementation of the second aspect.

[0024] In a fourth aspect, an electrical device is provided, wherein the electrical device comprises a sodium ion battery according to any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0026] Figure 1 This is a schematic diagram of a sodium ion battery cell according to an embodiment of the present application.

[0027] Figure 2 This is a schematic diagram of a sodium ion battery module according to an embodiment of the present application.

[0028] Figure 3 This is a schematic diagram of a sodium ion battery according to an embodiment of the present application.

[0029] Figure 4 Another schematic diagram of a sodium ion battery according to an embodiment of the present application.

[0030] Figure 5 This is a charging curve diagram of comparative example 1 of the present application.

[0031] Figure 6 This is a charging curve diagram of Example 1 of the present application. DETAILED DESCRIPTION

[0032] Hereinafter, the embodiments of the negative electrode active material, negative electrode sheet, sodium ion battery and electric device of the present application are specifically disclosed with appropriate reference to the drawings in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0033] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0039] As mentioned, "hard carbon" refers to disordered carbon materials that cannot form a regular graphite structure at high temperatures above 3000°C. Its precursors are generally polymers with multiple heteroatoms, such as sugar, cellulose, phenolic resin, etc.

[0040] As mentioned, "true density" refers to the actual mass of a solid substance per unit volume when the material is absolutely dense, that is, the density after removing the internal pores or spaces between particles.

[0041] As mentioned, "intercalation type sodium storage material" refers to a material in which sodium ions can be intercalated to form a compound with it, such as soft carbon, graphite, titanium-based materials, etc. Intercalation type sodium storage materials usually have a layered structure, and sodium ions can be intercalated between its layers to form an ionic compound with it, that is, to form a sodium ion compound.

[0042] Where mentioned, "interplanar spacing" refers to the distance between two adjacent crystal planes in a family of parallel crystal planes.

[0043] If mentioned, “ID / IG” refers to the intensity ratio of the D peak to the G peak in the Raman spectrum, and “I” stands for intensity.

[0044] Where mentioned, “titanium-based intercalation sodium storage materials” refers to TiO2 and other titanium-based oxides, such as Li4Ti5O 12 、Na4Ti5O 12 wait.

[0045] Where mentioned, "sulfur-based embedded sodium storage materials" refer to sulfides such as molybdenum disulfide and titanium disulfide.

[0046] As mentioned, "charge and discharge curve" refers to a graph showing the relationship between the electrode potential and the battery capacity during the charging or discharging process of a battery when a certain material is used as an electrode active material, or a graph showing the relationship between the electrode potential (voltage) and the battery specific capacity.

[0047] As mentioned, the "plateau region" refers to the region near a certain potential in the charge-discharge curve where the battery capacity changes but the potential changes slowly or almost does not change; the "slope region" refers to the region in the charge-discharge curve where the electrode potential changes rapidly with the capacity. For example, in a sodium-ion battery, at 0.15V (vs. Na + / Na) has a platform area at the low potential, and at the potential higher than 0.15V (vs.Na+ / Na) has a slope region.

[0048] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery.

[0049] During the charging process of sodium-ion batteries, sodium ions are released from the positive electrode active material, moved and embedded in the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, moved and embedded in the positive electrode active material.

[0050] It should be understood that the "embedding" process described in this application refers to the process in which sodium ions are embedded in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the "extraction" and "de-intercalation" processes described in this application refer to the process in which sodium ions are extracted from the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0051] With the in-depth research and application of sodium-ion batteries, new requirements have been put forward for the capacity and safety performance of sodium-ion batteries. For example, in some application scenarios (such as electric vehicles and other electrical devices), once a short circuit occurs in the battery, the internal temperature of the battery will rise rapidly and then thermal runaway will occur, which is not conducive to the user of the electrical device to respond to it. In addition, for sodium-ion batteries, hard carbon is usually used as the negative electrode active material. At present, the process of sodium storage in hard carbon in sodium-ion batteries is generally considered to have three mechanisms: (1) the adsorption mechanism of sodium ions at the edge defects of graphite-like layers and in the open pores on the surface; (2) the embedding mechanism of sodium ions in and out of the graphite-like layers; and (3) the pore filling mechanism of sodium ions depositing in the closed pores and some open pores of hard carbon to form metallic sodium. Among them, the pore filling mechanism is considered to be the main mechanism for hard carbon to contribute to the capacity of the platform region, that is, the higher the capacity of the sodium-ion battery, the more metallic sodium is formed during the charge and discharge process of the battery. Based on this, in the aforementioned application scenario, once a short circuit occurs in the battery, the sodium-ion battery with hard carbon as the negative electrode active material is more prone to thermal runaway at the negative electrode due to the fact that the thermal reaction temperature of hard carbon itself is lower than that of graphite and there is a large amount of metallic sodium. In severe cases, the heat spreads to the positive electrode, causing thermal runaway of the entire sodium-ion battery, seriously affecting the safety of the sodium-ion battery.

[0052] In view of this, the present application provides a negative electrode active material, a negative electrode plate, a sodium ion battery and an electric device. In addition to hard carbon, the negative electrode active material also includes an embedded sodium storage material, which can adjust the sodium storage mechanism of the negative electrode active material; and by controlling the true density of the hard carbon and the interplanar spacing of the embedded sodium storage material, the possibility of thermal runaway of the sodium ion battery is reduced, while the sodium ion battery has a higher capacity.

[0053] First, an embodiment of the present application provides a negative electrode active material, including hard carbon and an embedded sodium storage material. The true density ρ of the hard carbon satisfies: 1.3 g / cm 3 ≤ρ≤1.8g / cm 3 ; The crystal plane spacing d of the embedded sodium storage material satisfies: 0.24nm≤d≤0.4nm.

[0054] Specifically, ρ can be 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , or its value is within the range obtained by combining any two of the above values; d can be 0.24nm, 0.245nm, 0.25nm, 0.255nm, 0.26nm, 0.265nm, 0.27nm, 0.275nm, 0.28nm, 0.285nm, 0.29nm, 0.295nm, 0.3nm, 0.305nm, 0.31nm, 0.315nm, 0.32nm, 0.325nm, 0.33nm, 0.335nm, 0.34nm, 0.345nm, 0.35nm, 0.355nm, 0.36nm, 0.365nm, 0.37nm, 0.375nm, 0.38nm, 0.385nm, 0.39nm, 0.395nm, 0.4nm, or its value is within the range obtained by combining any two of the above values.

[0055] The embedded sodium storage material stores sodium based on the embedding mechanism, which enables sodium ions to be embedded therein, forming ionic bonds with sodium ions to form sodium ion compounds. The hard carbon that mainly stores sodium based on the pore filling mechanism produces more metallic sodium during the cycle, and the sodium ions are fixed in the form of metal bonds. The strength of the ionic bonds in the sodium ion compound is stronger than the metal bonds in the metallic sodium. Therefore, compared with hard carbon, the embedded sodium storage material has good safety when the battery is short-circuited. The battery needs to be raised to a higher temperature before thermal runaway occurs. Based on this, for the negative active material, the introduction of the embedded sodium storage material can effectively reduce the contribution of the pore filling mechanism to the capacity of the sodium ion battery, and enhance the contribution of the embedding mechanism to the capacity, thereby reducing the formation of metallic sodium and reducing the possibility of thermal runaway and heat spread in the sodium ion battery. In addition, the embodiment of the present application can make the negative active material have a higher gram capacity by controlling the true density of the hard carbon within the above range, so that the sodium ion battery has a higher capacity while improving the safety of the sodium ion battery. In addition, by selecting an embedded sodium storage material with a crystal plane spacing within the above range, its microstructure capable of interlayer slip helps to increase the powder compaction density of the negative electrode sheet, thereby improving the energy density of the ammonium ion battery.

[0056] In one embodiment, the mass content m1 of the hard carbon in the negative electrode active material satisfies: 90%≤m1; alternatively, 95%≤m1≤99.5%.

[0057] Specifically, m1 can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, or its value is within the range obtained by combining any two of the above values.

[0058] Hard carbon has a high reversible capacity. It can be selected as the main material in the negative electrode active material. Controlling its mass content within a higher range will help improve the gram capacity of the negative electrode active material.

[0059] In one embodiment, the mass content m2 of the embedded sodium storage material in the negative electrode active material satisfies: m2≤10%; optionally, 0.5%≤m2≤5%.

[0060] Specifically, m2 can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or its value is within the range obtained by combining any two of the above values.

[0061] Embedded sodium storage materials have good safety, but their reversible capacity is not as good as that of hard carbon. By controlling their content within a smaller range, the safety performance of negative electrode active materials can be improved while reducing the impact of embedded sodium storage materials on the capacity of negative electrode active materials, thereby helping to increase the capacity of negative electrode active materials.

[0062] In the embodiments of the present application, by regulating the proportion of hard carbon and embedded sodium storage materials in the negative electrode active material, the sodium storage mechanism of the negative electrode active material can be regulated, thereby controlling the contribution of different mechanisms to the capacity of the sodium ion battery, reducing the generation of metallic sodium, and reducing the possibility of thermal runaway of the sodium ion battery.

[0063] It should be understood that the ratio of hard carbon and embedded sodium storage material can be adjusted according to different battery models and application scenarios.

[0064] In one embodiment, the embedded sodium storage material includes at least one of a carbon-based embedded sodium storage material, a titanium-based embedded sodium storage material, and a sulfur-based embedded sodium storage material.

[0065] In one embodiment, the interplanar spacing d of the carbon-based embedded sodium storage material satisfies: 0.335nm≤d≤0.4nm. In another embodiment, the interplanar spacing d of the sulfur-based embedded sodium storage material satisfies: 0.5nm≤d≤0.8nm. In yet another embodiment, the interplanar spacing d of the titanium-based embedded sodium storage material satisfies: 0.24nm≤d≤0.30nm.

[0066] It should be understood that the interplanar spacing d of the carbon-based embedded sodium storage material satisfies: 0.335nm≤d≤0.4nm, and the interplanar spacing d of a family of crystal planes (for example, (002) crystal plane) of the carbon-based embedded sodium storage material may be in the range of 0.335nm to 0.4nm, or the interplanar spacing of other crystal planes of the carbon-based embedded sodium storage material may be in the aforementioned range. Similarly, the interplanar spacing d of the (002) crystal plane of the sulfur-based embedded sodium storage material may be in the range of 0.5nm to 0.8nm, or the interplanar spacing of other crystal planes of the sulfur-based embedded sodium storage material may be in the aforementioned range. The interplanar spacing d of the (110) crystal plane of the titanium-based embedded sodium storage material may be in the range of 0.24nm to 0.3nm, or the interplanar spacing of other crystal planes of the titanium-based embedded sodium storage material may be in the aforementioned range.

[0067] The (002) crystal plane refers to a family of crystal planes that are parallel to or coincident with the plane with coordinate (002) when the crystal is placed in a spatial rectangular coordinate system. Similarly, the (110) crystal plane refers to a family of crystal planes that are parallel to or coincident with the plane with coordinate (110).

[0068] In one embodiment, the carbon-based embedded sodium storage material includes at least one of soft carbon and modified graphite. Modified graphite refers to a product obtained by modifying graphite, and modifying graphite means treating graphite so that the physical and chemical properties of graphite are different from those before treatment. For example, graphite can be treated with substances such as surfactants. Modified graphite can include expanded graphite, oxidized graphite, etc.

[0069] In one embodiment, ID / IG of the embedded sodium storage material satisfies: 0.9≤ID / IG≤1.6; optionally, 0.9≤ID / IG≤1.5.

[0070] Specifically, ID / IG can be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or a value within the range obtained by combining any two of the above values.

[0071] In the embodiments of the present application, by selecting soft carbon whose ID / IG satisfies the above range, the soft carbon can have a higher capacity, thereby helping to improve the capacity of the sodium ion battery.

[0072] In one embodiment, the titanium-based embedded sodium storage material includes TiO2, Na2Ti3O7, Li4Ti5O 12 , or at least one of Na3Ti2(PO4)2.

[0073] More specifically, TiO2 may use anatase, rutile, brookite, or TiO2-B; and layered Na2Ti3O7 may be used.

[0074] In one embodiment, the sulfur-based embedded sodium storage material includes at least one of MoS2 and WS2.

[0075] In one embodiment, the gram capacity W1 of the hard carbon satisfies: W1≤400 mAh / g; optionally 290 mAh / g≤W1≤340 mAh / g.

[0076] Specifically, W1 can be 290mAh / g, 300mAh / g, 310mAh / g, 320mAh / g, 330mAh / g, 340mAh / g, 350mAh / g, 360mAh / g, 370mAh / g, 380mAh / g, 390mAh / g, 400mAh / g, or its value is within the range obtained by combining any two of the above values.

[0077] In one embodiment, the gram capacity W2 of the embedded sodium storage material satisfies: W2≤295 mAh / g; optionally, 90 mAh / g≤W2≤290 mAh / g.

[0078] Specifically, W2 can be 90mAh / g, 100mAh / g, 110mAh / g, 120mAh / g, 130mAh / g, 140mAh / g, 150mAh / g, 160mAh / g, 170mAh / g, 180mAh / g, 190mAh / g, 200mAh / g, 210mAh / g, 220mAh / g, 230mAh / g, 240mAh / g, 250mAh / g, 260mAh / g, 270mAh / g, 280mAh / g, 290mAh / g, 295mAh / g, or its value is within the range obtained by combining any two of the above values.

[0079] In one embodiment, the ratio of the discharge capacity Q2 corresponding to the platform region (potential lower than 0.15V) of the discharge curve of the negative electrode active material to the discharge capacity Q1 corresponding to the slope region (potential higher than 0.15V) satisfies: Q2 / Q1≤3.3; optionally, 0.05≤Q2 / Q1≤3.

[0080] Specifically, Q2 / Q1 can be 0.1, 0.2, 0.5, 0.7, 1.0, 1.2, 1.3, 1.5, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.1, 3.2, or its value is within the range obtained by combining any two of the above values.

[0081] Next, the electrode materials, positive electrode sheets, negative electrode sheets, separators and electrolytes in sodium-ion batteries are introduced in detail.

[0082] [Negative electrode]

[0083] The negative electrode sheet generally includes a negative electrode current collector, or includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0084] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer may be disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0085] Alternatively, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] Optionally, the negative electrode active material may also include a negative electrode active material for sodium ion batteries known in the art. For example, the negative electrode active material may also include at least one of the following materials: natural graphite, artificial graphite, mesophase microcarbon beads (MCMB). These negative electrode active materials may be used alone or in combination of two or more materials.

[0087] Optionally, the negative electrode film layer further includes a conductive agent, and the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0088] Optionally, the negative electrode film layer also includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0089] The above-mentioned negative electrode sheet can be prepared according to conventional methods in the art. For example, the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, can be dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0090] For the negative electrode plate provided in the present application, it includes the negative electrode active material in the aforementioned embodiment. Therefore, when applied to a sodium ion battery, the negative electrode active material on the surface of the negative electrode plate can be obtained by disassembling the sodium ion battery and performing XRD or TEM detection on it to determine the components of its negative electrode active material, and the negative electrode active material in the aforementioned embodiment can be detected. In addition, after the sodium ion battery is cycled, the negative electrode active material on the surface of the negative electrode plate after the cycle is obtained by disassembling the sodium ion battery after the cycle and performing XRD or TEM detection on it, the interplanar spacing of the embedded sodium storage material can be detected. After the cycle, the interplanar spacing of the embedded sodium storage material changes, indicating that the sodium ions are successfully embedded in the interlayer of the embedded sodium storage material, reducing the formation of metallic sodium and adjusting the sodium storage mechanism of the negative electrode active material.

[0091] [Positive electrode]

[0092] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0093] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer can be disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0094] Alternatively, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] Optionally, the positive electrode active material may include a positive electrode active material for sodium ion batteries known in the art. As described above, the positive electrode active material may include one or more of a polyanionic compound, a transition metal oxide, and a Prussian blue compound. As an example, a polyanionic compound may be a class of compounds having sodium ions, transition metal ions, and tetrahedral anion units, such as sodium iron phosphate (NaFePO4), sodium vanadium phosphate (Na3V2(PO4)3), and the like. The transition metal oxide may be a transition metal oxide having sodium ions, such as sodium copper iron manganate, sodium iron nickel manganate, and the like. The Prussian blue compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions. However, the present application is not limited to these materials, and other materials that can be used as positive electrode active materials for sodium ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more materials.

[0096] Optionally, the positive electrode film layer also includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0097] Optionally, the positive electrode film layer further includes a conductive agent, and the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0098] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, additives, conductive agent, binder and any other components are dispersed in a solvent (such as NMP) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0099] [Electrolytes]

[0100] The electrolyte plays the role of 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 liquid, gel or all-solid.

[0101] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0102] Optionally, the electrolyte salt includes NaPF6, NaClO4, NaSO3CF3 and Na(CH3)C6H4SO3, etc.

[0103] Optionally, the solvent includes carbonate or ether solvents. Carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC) and chain dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc.; ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, etc.

[0104] Optionally, 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 may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0105] [Isolator]

[0106] In some embodiments, the sodium ion battery further includes a separator. The present application has no particular restrictions on the type of separator, for example, the separator may be a separator membrane. The separator membrane may be any known porous structure separator membrane with good chemical stability and mechanical stability.

[0107] Optionally, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0109] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0110] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] [Sodium-ion battery]

[0112] The present application also provides a sodium ion battery, which includes the negative electrode plate in any of the aforementioned embodiments.

[0113] The present application has no particular restrictions on the shape of the sodium ion battery, which can be cylindrical, square or any other shape. For example, Figure 1 A sodium ion battery 100 having a square structure is shown as an example.

[0114] Figure 2 2 is a battery module 200 of a sodium ion battery as an example. Figure 2 In the battery module 200, the plurality of sodium ion batteries 100 may be arranged in sequence along the length direction of the battery module 200. Of course, they may also be arranged in any other manner. Further, the plurality of sodium ion batteries 100 may be fixed by fasteners.

[0115] Optionally, in one embodiment, the battery module 200 may further include a housing having a housing space, and the plurality of sodium ion batteries 100 are accommodated in the housing space.

[0116] Optionally, in one embodiment, the battery modules 200 may also be assembled into a battery pack. The battery pack may contain one or more battery modules 200, and the specific number may be selected by those skilled in the art according to the application scenario and capacity of the battery pack.

[0117] Figure 3 and Figure 4 300 is an example of a battery pack. Figure 3 and Figure 4 The battery pack 300 may include a battery box and a plurality of battery modules 200 disposed in the battery box. The battery box includes an upper box body 301 and a lower box body 302. The upper box body 301 can cover the lower box body 302 and form a closed space for accommodating the battery modules 200. The plurality of battery modules 200 may be arranged in the battery box in any manner.

[0118] It should be understood that in other embodiments, the battery pack 300 is also referred to as a battery. The sodium ion battery 100 may first be formed into a battery module 200, and the battery pack 300 is composed of the battery module 200. The battery pack 300 may also be directly formed of the sodium ion battery 100, omitting the intermediate form of the battery module 200.

[0119] In addition, the present application also provides an electrical device, which includes at least one of the sodium ion battery 100, battery module 200, or battery pack 300 provided in the present application. The sodium ion battery 100, battery module 200, or battery pack 300 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0120] As an electrical device, the number of sodium ion batteries 100, battery modules 200, or battery packs 300 can be selected according to its usage requirements.

[0121] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack 300 or a battery module 200 may be used.

[0122] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a sodium ion battery 100 may be used as a power source.

[0123] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0124] [Examples and Comparative Examples]

[0125] Example 1

[0126] (1) Preparation of positive electrode sheet

[0127] The positive electrode active material sodium vanadium phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are fully and evenly mixed in a proper amount of NMP at a mass ratio of 8:1:1 to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying and rolling.

[0128] (2) Preparation of negative electrode sheet

[0129] The negative electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were fully stirred in an appropriate amount of NMP at a mass ratio of 8:1:1 to form a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained after drying and rolling. The powder compaction density of the negative electrode sheet was controlled at 0.92 g / cm 3 about.

[0130] Among them, in the negative electrode active material, the embedded sodium storage material is soft carbon, the crystal plane spacing of soft carbon is d = 0.35nm, the Raman characteristic peak of soft carbon is ID / IG = 1.2, the gram capacity of soft carbon is W2 = 260mAh / g, the mass content of soft carbon in the negative electrode active material is m2 = 2.5%; the true density of hard carbon is ρ = 1.5g / cm 3 The mass content of hard carbon in the negative electrode active material is m1 = 97.5%, and the gram capacity of hard carbon is W1 = 310 mAh / g. According to the test steps disclosed in the "Test method for the capacity ratio corresponding to the platform area and the slope area", the discharge curve of the negative electrode active material is measured, and Q2 / Q1 = 3.033.

[0131] (3) Assembly of sodium ion batteries

[0132] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet. After the stacking process, an electrode assembly is formed. The electrode assembly is loaded into a packaging shell, and a NaPF6 electrolyte with a concentration of 1 mol / L is added. After packaging, formation, standing and other processes, a sodium ion battery is obtained.

[0133] Example 2

[0134] Compared with Example 1, in Example 2, ρ = 1.3 g / cm 3 , W1=350mAh / g, Q2 / Q1=3.236.

[0135] Example 3

[0136] Compared with Example 1, in Example 3, ρ = 1.8 g / cm 3 , W1=280mAh / g, Q2 / Q1=3.00.

[0137] Example 4

[0138] Compared with Example 1, in Example 4, d=0.335nm, ID / IG=1.1, W2=90mAh / g, Q2 / Q1=3.197.

[0139] Example 5

[0140] Compared with Example 1, in Example 5, d=0.4 nm, ID / IG=1.2, W2=285 mAh / g, and Q2 / Q1=3.024.

[0141] Example 6

[0142] Compared with Example 1, in Example 6, ID / IG=0.9, W2=220 mAh / g, and Q2 / Q1=3.071.

[0143] Example 7

[0144] Compared with Example 1, in Example 7, ID / IG=1.2, W2=260 mAh / g, Q2 / Q1=3.033.

[0145] Example 8

[0146] Compared with Example 1, in Example 8, ID / IG=1.6, W2=293 mAh / g, and Q2 / Q1=3.00.

[0147] Example 9

[0148] Compared with Example 1, in Example 9, graphite is selected as the embedded sodium storage material, d = 0.335nm, ID / IG = 0.9, W2 = 70mAh / g, Q2 / Q1 = 3.219.

[0149] Example 10

[0150] Compared with Example 1, in Example 10, d=0.38, ID / IG=1.3, W2=295 mAh / g, and Q2 / Q1=3.0.

[0151] Embodiment 11

[0152] Compared with Example 1, in Example 11, m1=95%, m2=5%, and Q2 / Q1=2.795.

[0153] Example 12

[0154] Compared with Example 1, in Example 12, m1=99.5%, m2=0.5%, and Q2 / Q1=3.239.

[0155] Embodiment 13

[0156] Compared with Example 1, in Example 13, sodium titanate is selected as the embedded sodium storage material, d=0.371nm, W2=240mAh / g, Q2 / Q1=3.04.

[0157] Embodiment 14

[0158] Compared with Example 1, in Example 14, molybdenum disulfide is selected as the embedded sodium storage material, d=0.68nm, W2=240mAh / g, Q2 / Q1=3.04.

[0159] Comparative Example 1

[0160] Compared with Example 1, in Comparative Example 1, only hard carbon is used as the negative electrode active material.

[0161] Table 1 Product parameters of the embodiments and comparative examples

[0162] In Table 1, "ρ" represents the true density of hard carbon in the negative electrode active material, "m1" represents the mass content of hard carbon in the negative electrode active material, "W1" represents the gram capacity of hard carbon, "intercalation type sodium storage material" represents the type of intercalation type sodium storage material in the negative electrode active material, "d" represents the interplanar spacing of the intercalation type sodium storage material, "ID / IG" represents the ratio of the signal intensities of the D peak and the G peak in the Raman spectrum of the intercalation type sodium storage material, "W2" represents the gram capacity of the intercalation type sodium storage material, "m2" represents the mass content of the intercalation type sodium storage material in the negative electrode active material, and "Q2 / Q1" represents the ratio of the discharge capacity corresponding to the platform area and the slope area in the discharge curve of the negative electrode active material.

[0163] The performance test results of the sodium ion batteries of the above embodiments and comparative examples are shown in Table 2.

[0164] Table 2 Battery performance test results of different embodiments and comparative examples Energy density (Wh / kg) Heat spread rate (m / s) Example 1 126 ＞0.15 Example 2 130 ＞0.15 Example 3 121 ＞0.15 Example 4 121 ＞0.15 Example 5 132 ＞0.15 Example 6 122 ＞0.15 Example 7 129 ＞0.15 Example 8 131 ＞0.15 Example 9 119 ＞0.15 Example 10 132 ＞0.15 Embodiment 11 112 ＞0.15 Example 12 140 ＞0.15 Embodiment 13 128 ＞0.15 Embodiment 14 130 ＞0.15 Comparative Example 1 120 ≤0.15

[0165] In Table 2, “Energy Density” indicates the energy density of sodium ions in each embodiment and comparative example, and “Heat propagation rate” indicates the heat propagation rate measured when the negative electrode sheet is taken out after disassembling the sodium ion battery and subjected to a heat propagation test.

[0166] According to the comparative analysis of the embodiments and the comparative examples, in the sodium ion batteries of the embodiments 1-14, the negative electrode active material includes a 3 -1.8g / cm 3The heat spread rate of the sodium ion battery in the heat spread test is greater than 0.15m / s for the hard carbon and embedded sodium storage material between them. In Comparative Example 1, there is no embedded sodium storage material that can adjust the sodium storage mechanism in the negative electrode active material, and the heat spread rate is less than or equal to 0.15m / s in the heat spread test. Therefore, it is shown that by matching hard carbon with a true density in a suitable range and embedded sodium storage materials with a crystal plane spacing in a suitable range, the sodium storage mechanism of the hard carbon can be adjusted, and the formation of metallic sodium can be reduced, thereby effectively reducing the risk of thermal runaway and heat spread of the sodium ion battery, and at the same time, the sodium ion battery has both higher capacity and energy density.

[0167] According to the data comparison of Examples 1-3, the greater the true density of the hard carbon, the lower the gram capacity. The possible mechanism is: the hard carbon structure with a larger true density is closer to graphite, and the sodium storage capacity of graphite is lower. The closer the structure is to graphite, the weaker the sodium storage capacity of the material, and the lower the gram capacity. Therefore, by selecting hard carbon with a true density within a suitable range, the negative active material provided in the embodiment of the present application can reduce the risk of thermal runaway and heat spread of sodium ion batteries while having a higher capacity.

[0168] According to the data comparison of Examples 1, 4-5, it can be seen that the gram capacity of the embedded sodium storage material is related to the interplanar spacing. Within a certain range, the gram capacity of the embedded sodium storage material with a larger interplanar spacing is higher. The possible mechanism is: the embedded sodium storage material stores sodium through an embedding mechanism, and the larger the interplanar spacing, the larger the sodium storage amount. However, after exceeding a certain range, the embedded sodium cannot be completely removed, which is not conducive to the coulomb efficiency of the sodium ion battery. Therefore, by selecting an embedded sodium storage material with an interplanar spacing in a suitable range, it is also helpful to improve the gram capacity of the negative electrode active material. In addition, the embedded sodium storage material with an interplanar spacing in the above range can slip between layers in the microstructure, and when applied to a sodium ion battery, it helps to increase the powder compaction density of the negative electrode sheet, thereby helping to improve the energy density of the sodium ion battery. Therefore, by introducing an embedded sodium storage material into the negative electrode active material, the sodium storage mechanism of the negative electrode active material can be regulated to improve the safety performance of the sodium ion battery. By selecting an embedded sodium storage material with an interplanar spacing in a suitable range, it is also helpful to improve the gram capacity of the negative electrode active material and improve the energy density of the sodium ion battery.

[0169] According to the data comparison of Examples 6-10, for carbon-based embedded sodium storage materials, their gram capacity is also related to ID / IG. The larger the value of ID / IG, the greater the proportion of D peak in the Raman spectrum of the carbon-based material, and the more amorphous carbon components in the carbon-based material. On the one hand, the more amorphous carbon there is, the more sodium storage sites there are, and the gram capacity of the carbon-based material is improved, which helps to improve the energy density of sodium-ion batteries. On the other hand. The more amorphous carbon there is, the more the carbon-based material stores sodium based on the embedding mechanism, and its ability to store sodium based on the adsorption mechanism is also enhanced, further reducing the formation of metallic sodium and adjusting the sodium storage mechanism of the negative electrode active material. Therefore, by selecting a carbon-based material with ID / IG within a suitable range, the safety performance of sodium-ion batteries can be improved.

[0170] According to the data comparison of Examples 1 and 11-12, when the embedded sodium storage material is soft carbon, since the gram capacity of soft carbon itself is lower than that of hard carbon, the higher the mass content of the embedded sodium storage material in the negative electrode active material, the lower the energy density of the sodium ion battery, that is, the energy density of Example 11 is lower than that of Example 12. However, as the mass content of the embedded sodium storage material increases, the value of Q2 / Q1 becomes significantly smaller, that is, Q2 / Q1 of Example 11 is less than that of Example 12, indicating that increasing the mass content of the embedded sodium storage material increases the capacity of the slope area, and the platform area corresponding to the pore filling mechanism reduces the contribution to the capacity of the sodium ion battery, and the sodium storage mechanism of the negative electrode active material is effectively regulated. In addition, when the gram capacity of the embedded sodium storage material is higher than that of hard carbon, increasing the mass content of the embedded sodium storage material can help improve the energy density of the sodium ion battery.

[0171] According to the data of Examples 13-14, the embedded material can also be a titanium-based embedded sodium storage material or a sulfur-based embedded sodium storage material.

[0172] Figure 5 This is a charging curve diagram corresponding to the negative electrode active material in Comparative Example 1. Figure 6 is a charge curve corresponding to the negative electrode active material in Example 1. It should be understood that the ratio of the specific capacity corresponding to the platform area and the slope area can represent the ratio of the capacity corresponding to the platform area and the slope area Q2 / Q1. Here, the charge curves of Example 1 and Comparative Example 1 are used as examples, and the discharge curve also has corresponding platform areas and slope areas.

[0173] according to Figure 5 and Figure 6 The data in can be measured, with 0.15V as the limit, Figure 5 The Q2 / Q1 ratio is about 3.5. Figure 6Q2 / Q1 is about 3.01. That is to say, compared with Comparative Example 1, the platform area of ​​Example 1 is reduced, Q2 / Q1 is less than 3.3 and no heat spread occurs in the heat spread test, while Q2 / Q1 of Comparative Example 1 is greater than 3.3 and heat spread occurs in the heat spread test. This shows that in Example 1, by introducing an embedded sodium storage material into the negative electrode material with hard carbon as the main material, the sodium storage mechanism of the negative electrode active material is successfully regulated, reducing the contribution of the platform area capacity to the total capacity of the entire charge and discharge process, thereby reducing the risk of thermal runaway and heat spread of the sodium ion battery.

[0174] Next, the testing methods of the physical parameters and performance parameters involved in the embodiments of the present application are introduced.

[0175] 1. True density test method

[0176] The true density of the material can be tested by a method known in the art for testing true density. For example, the true density of the material can be tested by using instruments such as AccuPyc 1340, Austrian Anton Paar DMA4200M, and ZS-102 tap density meter. A specific example of testing true density is given below.

[0177] Sample requirements: Powder (10ml as much as possible); Block: size less than the following requirements: diameter 15mm, height 35mm, total volume should not be less than 6mL. True density refers to the actual mass of a solid substance per unit volume when the material is absolutely dense, that is, the density after removing the internal pores or gaps between particles.

[0178] Place the material to be tested in the true density tester, use helium as the medium, operate the measuring chamber to gradually pressurize so that the helium expands into the expansion chamber, and the equilibrium pressure of the two processes is automatically recorded by the instrument. According to the law of conservation of mass, the volume of the measuring chamber and the expansion chamber is calibrated by the standard ball, and then the volume of the material is determined to calculate the true density. Applying the Archimedean principle-gas expansion displacement method, using the Bohr law (PV=nRT) of inert gas with a small molecular diameter under certain conditions, the true volume of the material to be tested is accurately determined by measuring the reduction in the gas capacity of the sample test chamber caused by the sample being placed in the sample test chamber, thereby obtaining its true density, true density=mass / true volume.

[0179] It should be understood that the above fixed value is a value set artificially based on test experience and can be adjusted as needed. After pressurizing to the fixed value, if pressurizing is continued, the volume of helium in the expansion chamber does not change or changes slightly, for example, the volume change rate is less than or equal to 1%.

[0180] 2. Testing method of interplanar spacing

[0181] The interplanar spacing of the material can be detected by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HTEM), etc. Taking X-ray diffraction as an example, a suitable amount of the sample to be tested can be placed on a sample table, and an X-ray diffractometer using copper as an anode target can be used to detect the sample to be tested, and the XRD diffraction peak spectrum of the sample to be tested can be obtained. Then, the lattice constant corresponding to the sample to be tested, for example, the interplanar spacing, can be calculated according to the Bragg formula.

[0182] 3. Testing method of ID / IG in Raman spectroscopy

[0183] Take an appropriate amount of the sample to be tested and test it with a Raman spectrometer to obtain the Raman scattering spectrum of the sample to be tested. The horizontal coordinate of the spectrum is Raman shift (unit: cm -1 ), the ordinate is intensity. The D peak usually appears at 1300cm -1 , G peak usually appears at 1580cm -1 The maximum intensity of the D peak represents ID, and the maximum intensity of the G peak represents IG, and the ID / IG of the sample to be tested is calculated.

[0184] 4. Test method for capacity ratio between platform area and slope area

[0185] The negative electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were fully stirred in an appropriate amount of NMP at a mass ratio of 8:1:1 to form a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained after drying and rolling. The powder compaction density of the negative electrode sheet was controlled at 0.92 g / cm 3 With sodium sheet as negative electrode and 1M NaPF6 electrolyte, a half-cell was assembled and the charge and discharge test was carried out at 0.005-2V at a current density of 0.05C. The capacity above 0.18V in the second cycle of discharge is the capacity in the slope area, and the capacity below 0.18V is the capacity in the platform area.

[0186] 5. Test method for energy density of sodium ion batteries

[0187] Mass energy density (Wh / kg) = battery capacity (mAh) × voltage platform 3.0V / battery weight.

[0188] 6. Heat spread test method

[0189] The cycled sodium-ion battery is disassembled to obtain the cycled negative electrode sheet, and the negative electrode sheet is ignited to directly observe the heat spread on the negative electrode sheet. More specifically, the prepared battery cell can be charged to 4.0V, the battery cell is disassembled in a glove box, the negative electrode sheet is taken out, and cut into 30cm×15cm strips. In an inert glove box, a heat gun (200°C) is used for forced ignition, and the combustion rate and combustion time are recorded. Thus, the heat spread can also be quantified by the combustion rate and combustion time. Heat spread rate: v = L / (t_P-t_b)

[0190] Among them, L is the distance between the two temperature sensing lines T-ignition and T-spread, t_P is the time corresponding to the highest temperature at the pole piece spread position, and t_b is the time corresponding to the highest temperature at the ignition position.

[0191] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode active material, characterized in that: include: Hard carbon, the true density ρ of the hard carbon satisfies: 1.3 g / cm 3 ≤ρ≤1.8g / cm 3 ; An embedded sodium storage material, wherein the interplanar spacing d of the embedded sodium storage material satisfies: 0.24nm≤d≤0.8nm.

2. The negative electrode active material according to claim 1, characterized in that The embedded sodium storage material includes at least one of a carbon-based embedded sodium storage material, a sulfur-based embedded sodium storage material, and a titanium-based embedded sodium storage material.

3. The negative electrode active material according to claim 2, characterized in that: The interplanar spacing d of the carbon-based embedded sodium storage material satisfies: 0.335nm≤d≤0.4nm; The interplanar spacing d of the sulfur-based embedded sodium storage material satisfies: 0.5nm≤d≤0.8nm; The interplanar spacing d of the titanium-based embedded sodium storage material satisfies: 0.24nm≤d≤0.30nm.

4. The negative electrode active material according to claim 2 or 3, characterized in that: The carbon-based embedded sodium storage material includes at least one of soft carbon and modified graphite.

5. The negative electrode active material according to claim 4, characterized in that ID / IG of the soft carbon satisfies: 0.9≤ID / IG≤1.6; optionally, 0.9≤ID / IG≤1.

5.

6. The negative electrode active material according to claim 2 or 3, characterized in that: The titanium-based embedded sodium storage material includes: TiO2, Na2Ti3O7, Li4Ti5O 12 , or at least one of Na3Ti2(PO4)2.

7. The negative electrode active material according to claim 2 or 3, characterized in that: The sulfur-based embedded sodium storage material includes at least one of MoS2 and WS2.

8. The negative electrode active material according to any one of claims 1 to 7, characterized in that The mass content m1 of the hard carbon in the negative electrode active material satisfies: 90%≤m1; optionally, 95%≤m1≤99.5%.

9. The negative electrode active material according to any one of claims 1 to 8, characterized in that The mass content m2 of the embedded sodium storage material in the negative electrode active material satisfies: m2≤10%; optionally, 0.5%≤m2≤5%.

10. The negative electrode active material according to any one of claims 1 to 9, characterized in that The gram capacity W1 of the hard carbon satisfies: W1≤400mAh / g; optionally, 280mAh / g≤W1≤350mAh / g.

11. The negative electrode active material according to any one of claims 1 to 10, characterized in that The gram capacity W2 of the embedded sodium storage material satisfies: W2≤295mAh / g; optionally, 90mAh / g≤W2≤260mAh / g.

12. The negative electrode active material according to any one of claims 1 to 11, characterized in that The ratio of the charge-discharge capacity Q2 corresponding to the platform region of the charge-discharge curve of the negative electrode active material to the charge-discharge capacity Q1 corresponding to the slope region satisfies: Q2 / Q1≤3.3; optionally, 0.05≤Q2 / Q1≤3.

13. A negative electrode plate, characterized in that: The negative electrode sheet comprises the negative electrode active material according to any one of claims 1 to 12.

14. A sodium ion battery, characterized in that: The sodium ion battery comprises the negative electrode sheet as claimed in claim 13.

15. An electrical device, characterized in that: The electrical device comprises the sodium ion battery as claimed in claim 14.

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