Negative electrode active material, negative electrode sheet, sodium ion battery and electrical apparatus

Abstract

A negative electrode active material, a negative electrode sheet, a sodium ion battery, and an electrical apparatus. The negative electrode active material comprises: hard carbon, the true density ρ of the hard carbon satisfying 1.3 g / cm3≤ρ≤1.8 g / cm3; and an intercalation-type sodium storage material, the crystal plane spacing d of the intercalation-type sodium storage material satisfying 0.24 nm≤d≤0.8 nm. The negative electrode active material can effectively reduce the risk of thermal runaway of sodium ion batteries.

Description

Negative electrode active material, negative electrode sheet, sodium ion battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202311462058.3, filed on November 3, 2023, entitled “Negative Electrode Active Material, Negative Electrode Sheet, Sodium Ion Battery, and Electric Device.” The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

[0003] 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

[0004] 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.

[0005] 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 is formed when hard carbon stores sodium, and the thermal reaction temperature of hard carbon is low. It is very easy to cause thermal runaway at lower temperatures, which quickly aggravates the thermal runaway of the battery. In severe cases, it can cause 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.

[0006] Summary of the Invention

[0007] 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.

[0008] 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.

[0009] 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 lattice 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 lattice 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 applied to the sodium ion battery, thereby helping to improve the energy density of the sodium ion battery.

[0010] 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.

[0011] In one embodiment, 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.

[0012] In one embodiment, the carbon-based embedded sodium storage material includes at least one of soft carbon and modified graphite.

[0013] In one embodiment, the ID / IG of the soft carbon satisfies: 0.9≤ID / IG≤1.6; optionally, 0.9≤ID / IG≤1.5.

[0014] In the embodiments of the present application, by selecting soft carbon whose ID / IG satisfies the above-mentioned range, the soft carbon can have a higher degree of disorder, so that in addition to storing sodium based on the embedding mechanism, the soft carbon's ability to store sodium based on the adsorption mechanism is also enhanced, further reducing the formation of metallic sodium, regulating the sodium storage mechanism of the negative electrode active material, and improving the safety performance of the sodium ion battery.

[0015] In one embodiment, the titanium-based embedded sodium storage material includes TiO2, Na2Ti3O7, Li4Ti5O 12 , at least one of Na3Ti2(PO4)2.

[0016] In one embodiment, the sulfur-based embedded sodium storage material includes at least one of MoS2 and WS2.

[0017] In the embodiments of the present application, titanium-based embedded sodium storage materials and sulfur-based embedded sodium storage materials themselves usually have a relatively high 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.

[0018] 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%.

[0019] 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%.

[0020] 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.

[0021] In one embodiment, the gram capacity W1 of the hard carbon satisfies: W1≤400 mAh / g; optionally, 280 mAh / g≤W1≤350 mAh / g.

[0022] 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.

[0023] 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.

[0024] In one embodiment, 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.

[0025] In a second aspect, a negative electrode plate is provided, wherein the negative electrode plate includes the negative electrode active material in any possible implementation of the first aspect.

[0026] In a third aspect, a sodium ion battery is provided, comprising the negative electrode sheet according to any possible implementation of the second aspect.

[0027] In a fourth aspect, an electrical device is provided, wherein the electrical device includes the sodium ion battery in any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. 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 creative work.

[0029] FIG1 is a schematic diagram of a sodium ion battery cell according to an embodiment of the present application.

[0030] FIG2 is a schematic diagram of a sodium ion battery module according to an embodiment of the present application.

[0031] FIG3 is a schematic diagram of a sodium ion battery according to an embodiment of the present application.

[0032] FIG4 is another schematic diagram of a sodium ion battery according to an embodiment of the present application.

[0033] FIG5 is a charging curve diagram of Comparative Example 1 of the present application.

[0034] FIG6 is a charging curve diagram of Example 1 of the present application. DETAILED DESCRIPTION

[0035] Below, the embodiments of the negative electrode active material, negative electrode sheet, sodium ion battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. 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 description 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.

[0036] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0037] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] 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.

[0041] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0042] 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.

[0043] 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.

[0044] As mentioned, "intercalation-type sodium storage materials" refer to materials into which sodium ions can be intercalated to form compounds, such as soft carbon, graphite, and titanium-based materials. Intercalation-type sodium storage materials typically have a layered structure, and sodium ions can be intercalated between the layers to form ionic compounds, i.e., sodium ion compounds.

[0045] Where mentioned, "interplanar spacing" refers to the distance between two adjacent crystal planes in a family of parallel crystal planes.

[0046] Where 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.

[0047] Where mentioned, “titanium-based intercalation sodium storage materials” refers to TiO2 and other titanium-based oxides, such as Li4Ti5O 12 、Na4Ti5O 12 wait.

[0048] Where mentioned, "sulfur-based embedded sodium storage materials" refer to sulfides such as molybdenum disulfide and titanium disulfide.

[0049] As mentioned, the "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.

[0050] 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 sodium-ion batteries, 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 area.

[0051] 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 in and released from the positive and negative electrode sheets. The electrolyte conducts ions between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets, primarily to prevent a short circuit between the positive and negative electrodes while allowing active ions to pass through. In some embodiments, the battery cell is also referred to as a secondary battery.

[0052] During the charging process of sodium-ion batteries, sodium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0053] It should be understood that the "intercalation" 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 electrochemical reactions, and the "extraction" and "deintercalation" processes described in this application refer to the process in which sodium ions are removed from the positive electrode active material and the negative electrode material due to electrochemical reactions.

[0054] 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 the graphite-like layer and the open pores on the surface; (2) the embedding mechanism of sodium ions in the interlayer of the graphite-like layer and the desorption mechanism; 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 platform capacity. 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 because 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.

[0055] In light of this, the present application provides a negative electrode active material, a negative electrode plate, a sodium-ion battery, and an electrical device. In addition to hard carbon, the negative electrode active material also includes an intercalation-type sodium storage material, which can adjust the sodium storage mechanism of the negative electrode active material. By controlling the true density of the hard carbon and the interplanar spacing of the intercalation-type sodium storage material, the sodium-ion battery can achieve a higher capacity while reducing the likelihood of thermal runaway.

[0056] First, the 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 interplanar spacing d of the embedded sodium storage material satisfies: 0.24nm≤d≤0.4nm.

[0057] 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.

[0058] 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. However, hard carbon, which 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 metallic bonds. The strength of the ionic bonds in the sodium ion compound is stronger than the metallic 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 increase 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 embodiments 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, thereby improving the safety of the sodium ion battery while making the sodium ion battery have a higher capacity. In addition, by selecting an embedded sodium storage material with a crystal plane spacing within the above range, its microstructure capable of interlayer slip can help increase the powder compaction density of the negative electrode sheet, thereby improving the energy density of the ammonium ion battery.

[0059] 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%.

[0060] 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.

[0061] 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.

[0062] In one embodiment, the mass content m2 of the intercalation type sodium storage material in the negative electrode active material satisfies: m2≤10%; optionally, 0.5%≤m2≤5%.

[0063] 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.

[0064] Embedded sodium storage materials have good safety, but their reversible capacity is not as good as 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.

[0065] 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.

[0066] 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.

[0067] In one embodiment, the intercalation type sodium storage material includes at least one of a carbon-based intercalation type sodium storage material, a titanium-based intercalation type sodium storage material, and a sulfur-based intercalation type sodium storage material.

[0068] In one embodiment, the interplanar spacing d of the carbon-based intercalation sodium storage material satisfies the following: 0.335 nm ≤ d ≤ 0.4 nm. In another embodiment, the interplanar spacing d of the sulfur-based intercalation sodium storage material satisfies the following: 0.5 nm ≤ d ≤ 0.8 nm. In yet another embodiment, the interplanar spacing d of the titanium-based intercalation sodium storage material satisfies the following: 0.24 nm ≤ d ≤ 0.30 nm.

[0069] It should be understood that the interplanar spacing d of the carbon-based embedded sodium storage material satisfies: 0.335nm≤d≤0.4nm. The interplanar spacing d of a certain family of crystal planes (e.g., (002) crystal plane) of the carbon-based embedded sodium storage material may be within 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 within the aforementioned range. Similarly, the interplanar spacing d of the (002) crystal plane of the sulfur-based embedded sodium storage material may be within 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 within the aforementioned range. The interplanar spacing d of the (110) crystal plane of the titanium-based embedded sodium storage material may be within 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 within the aforementioned range.

[0070] The (002) crystal planes mentioned above refer 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 planes mentioned above refer to a family of crystal planes that are parallel to or coincident with the plane with coordinate (110).

[0071] In one embodiment, the carbon-based intercalated sodium storage material includes at least one of soft carbon and modified graphite. Modified graphite refers to a product obtained by modifying graphite. Modifying graphite means treating the graphite to change its physical and chemical properties compared to before the treatment. For example, the graphite can be treated with a substance such as a surfactant. Modified graphite can include expanded graphite, oxidized graphite, and the like.

[0072] In one embodiment, the ID / IG of the intercalation type sodium storage material satisfies: 0.9≤ID / IG≤1.6; optionally, 0.9≤ID / IG≤1.5.

[0073] 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.

[0074] 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.

[0075] In one embodiment, the titanium-based embedded sodium storage material includes TiO2, Na2Ti3O7, Li4Ti5O 12 , at least one of Na3Ti2(PO4)2.

[0076] More specifically, TiO2 may use anatase, rutile, brookite, or TiO2-B; and layered Na2Ti3O7 may be used.

[0077] In one embodiment, the sulfur-based intercalation type sodium storage material includes at least one of MoS2 and WS2.

[0078] In one embodiment, the gram capacity W1 of the hard carbon satisfies: W1≤400 mAh / g; optionally 290 mAh / g≤W1≤340 mAh / g.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] In one embodiment, the ratio of the discharge capacity Q2 corresponding to the plateau region (potential lower than 0.15 V) of the discharge curve of the negative electrode active material to the discharge capacity Q1 corresponding to the slope region (potential higher than 0.15 V) satisfies: Q2 / Q1≤3.3; optionally, 0.05≤Q2 / Q1≤3.

[0083] 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.

[0084] Next, the electrode materials, positive electrode sheets, negative electrode sheets, separators and electrolytes in sodium ion batteries are introduced in detail.

[0085] [Negative electrode]

[0086] 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.

[0087] 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 can be provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0088] Alternatively, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. 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 base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] Optionally, the negative electrode active material may also include negative electrode active materials known in the art for sodium ion batteries. For example, the negative electrode active material may also include at least one of the following materials: natural graphite, artificial graphite, and mesophase microcarbon beads (MCMBs). These negative electrode active materials may be used alone or in combination of two or more.

[0090] 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.

[0091] Optionally, the negative electrode film layer further 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.

[0092] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the components for preparing the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, can be dispersed in a solvent to form a negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet can be obtained after drying, cold pressing, and other processes.

[0093] The negative electrode sheet provided in the present application includes the negative electrode active material of the aforementioned embodiment. Thus, when used in a sodium ion battery, the negative electrode active material on the surface of the negative electrode sheet can be obtained by disassembling the sodium ion battery and performing XRD or TEM analysis on it to determine the components of the negative electrode active material, thereby detecting the negative electrode active material of the aforementioned embodiment. In addition, after the sodium ion battery is cycled, the negative electrode active material on the surface of the negative electrode sheet after cycling can be obtained by disassembling the cycled sodium ion battery and performing XRD or TEM analysis on it to detect the interplanar spacing of the embedded sodium storage material. After cycling, 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 regulating the sodium storage mechanism of the negative electrode active material.

[0094] [Positive electrode]

[0095] 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.

[0096] 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 provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0097] 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 made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] Alternatively, the positive electrode active material may include a positive electrode active material for sodium ion batteries known in the art. As mentioned 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, the 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), etc. The transition metal oxide may be a transition metal oxide having sodium ions, such as sodium copper iron manganate, sodium iron nickel manganate, etc. 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 two or more materials may be used in combination.

[0099] Optionally, the positive electrode film layer also includes an adhesive, 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.

[0100] Optionally, the positive electrode film layer further includes a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0101] In some embodiments, the positive electrode sheet can be prepared by the following method: 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.

[0102] [Electrolytes]

[0103] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0104] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0105] Optionally, the electrolyte salt includes NaPF6, NaClO4, NaSO3CF3 and Na(CH3)C6H4SO3, etc.

[0106] Optionally, the solvent includes a carbonate or ether solvent. 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.

[0107] 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, and additives that improve battery high or low temperature performance.

[0108] [Isolator]

[0109] In some embodiments, the sodium-ion battery further includes a separator. This application does not specifically limit the type of separator; for example, the separator may be a separator membrane. The separator membrane may be any known porous separator membrane with good chemical and mechanical stability.

[0110] Optionally, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0111] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly through a winding process or a lamination process.

[0112] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0113] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0114] [Sodium-ion battery]

[0115] The present application also provides a sodium ion battery, which includes the negative electrode plate in any of the aforementioned embodiments.

[0116] The present application has no particular limitation on the shape of the sodium ion battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a sodium ion battery 100 having a square structure as an example.

[0117] Figure 2 illustrates an example sodium-ion battery module 200. Referring to Figure 2 , within battery module 200, multiple sodium-ion batteries 100 may be arranged sequentially along the length of battery module 200. Alternatively, they may be arranged in any other manner. Furthermore, the multiple sodium-ion batteries 100 may be secured together using fasteners.

[0118] Optionally, in one embodiment, the battery module 200 may further include a housing having a receiving space, and the plurality of sodium ion batteries 100 are received in the receiving space.

[0119] Optionally, in one embodiment, the battery modules 200 may be assembled into a battery pack. The battery pack may contain one or more battery modules 200. The specific number may be selected by those skilled in the art based on the application scenario and capacity of the battery pack.

[0120] Figures 3 and 4 illustrate an example battery pack 300. Referring to Figures 3 and 4, the battery pack 300 may include a battery box and multiple battery modules 200 disposed within the battery box. The battery box includes an upper case 301 and a lower case 302. The upper case 301 can be placed over the lower case 302 to form an enclosed space for accommodating the battery modules 200. The multiple battery modules 200 can be arranged in any manner within the battery box.

[0121] It should be understood that in other embodiments, the battery pack 300 is also referred to as a battery. The sodium-ion batteries 100 can be first assembled into the battery modules 200, and the battery pack 300 can be composed of the battery modules 200. Alternatively, the battery pack 300 can be directly assembled from the sodium-ion batteries 100, omitting the intermediate battery module 200.

[0122] 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, but is not limited to, 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.

[0123] 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.

[0124] 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. 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.

[0125] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a sodium ion battery 100 as a power source.

[0126] 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.

[0127] [Examples and Comparative Examples]

[0128] Example 1

[0129] (1) Preparation of positive electrode sheet

[0130] The positive electrode active material sodium vanadium phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are fully stirred in an appropriate amount of NMP at a mass ratio of 8:1:1 to form a positive electrode slurry. 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.

[0131] (2) Preparation of negative electrode sheet

[0132] The negative electrode active material, conductive agent acetylene black, and 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. After drying and rolling, the negative electrode sheet was obtained. The powder compaction density of the negative electrode sheet was controlled at 0.92g / cm 3 about.

[0133] Among them, the embedded sodium storage material in the negative electrode active material is soft carbon, the interplanar spacing of soft carbon is d = 0.35nm, the Raman characteristic peak of soft carbon has 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, m1, was 97.5%, and the gram capacity of the hard carbon, W1, was 310 mAh / g. Following the published procedures in the "Test Method for Capacity Ratio Corresponding to Plateau and Slope Regions," the discharge curve of the negative electrode active material showed a Q2 / Q1 ratio of 3.033.

[0134] (3) Assembly of sodium ion batteries

[0135] The positive electrode sheet, separator and negative electrode sheet are stacked in order so that the separator is located between the positive electrode sheet and the negative electrode sheet. After the lamination process, an electrode assembly is formed. The electrode assembly is placed in 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.

[0136] Example 2

[0137] Compared with Example 1, in Example 2, ρ = 1.3 g / cm 3 , W1=350mAh / g, Q2 / Q1=3.236.

[0138] Example 3

[0139] Compared with Example 1, in Example 3, ρ = 1.8 g / cm 3 , W1=280mAh / g, Q2 / Q1=3.00.

[0140] Example 4

[0141] Compared with Example 1, in Example 4, d=0.335 nm, ID / IG=1.1, W2=90 mAh / g, and Q2 / Q1=3.197.

[0142] Example 5

[0143] Compared with Example 1, in Example 5, d=0.4 nm, ID / IG=1.2, W2=285 mAh / g, and Q2 / Q1=3.024.

[0144] Example 6

[0145] Compared with Example 1, in Example 6, ID / IG=0.9, W2=220 mAh / g, and Q2 / Q1=3.071.

[0146] Example 7

[0147] Compared with Example 1, in Example 7, ID / IG=1.2, W2=260 mAh / g, and Q2 / Q1=3.033.

[0148] Example 8

[0149] Compared with Example 1, in Example 8, ID / IG=1.6, W2=293 mAh / g, and Q2 / Q1=3.00.

[0150] Example 9

[0151] Compared with Example 1, in Example 9, graphite is selected as the embedded sodium storage material, d = 0.335 nm, ID / IG = 0.9, W2 = 70 mAh / g, Q2 / Q1 = 3.219.

[0152] Example 10

[0153] Compared with Example 1, in Example 10, d=0.38, ID / IG=1.3, W2=295 mAh / g, and Q2 / Q1=3.0.

[0154] Example 11

[0155] Compared with Example 1, in Example 11, m1=95%, m2=5%, and Q2 / Q1=2.795.

[0156] Example 12

[0157] Compared with Example 1, in Example 12, m1=99.5%, m2=0.5%, and Q2 / Q1=3.239.

[0158] Example 13

[0159] Compared with Example 1, in Example 13, sodium titanate is selected as the embedded sodium storage material, d = 0.371 nm, W2 = 240 mAh / g, Q2 / Q1 = 3.04.

[0160] Example 14

[0161] Compared with Example 1, in Example 14, molybdenum disulfide is selected as the embedded sodium storage material, d = 0.68 nm, W2 = 240 mAh / g, Q2 / Q1 = 3.04.

[0162] Comparative Example 1

[0163] Compared with Example 1, in Comparative Example 1, only hard carbon was used as the negative electrode active material.

[0164] Table 1 Product parameters of the embodiments and comparative examples

[0165] 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.

[0166] The performance test results of the sodium ion batteries of the above embodiments and comparative examples are detailed in Table 2.

[0167] Table 2 Battery performance test results of different embodiments and comparative examples

[0168] 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 removed after disassembling the sodium ion battery and performing a heat propagation test on it.

[0169] According to the comparative analysis of the examples and the comparative examples, the sodium ion batteries in Examples 1-14 include the negative electrode active material having a true density of 1.3 g / cm 3 -1.8g / cm 3 The heat spread rate of the sodium-ion battery in the heat spread test was greater than 0.15 m / s for the hard carbon and intercalation type sodium storage material with a true density within a suitable range. In contrast, in Comparative Example 1, where there was no intercalation type sodium storage material capable of regulating the sodium storage mechanism in the negative electrode active material, the heat spread rate was less than or equal to 0.15 m / s in the heat spread test. This indicates that by combining hard carbon with a true density within a suitable range and intercalation type sodium storage material with a lattice spacing within a suitable range, the sodium storage mechanism of the hard carbon can be adjusted, reducing the formation of metallic sodium, thereby effectively reducing the risk of thermal runaway and heat spread in the sodium-ion battery, while enabling the sodium-ion battery to have both higher capacity and energy density.

[0170] According to the data comparison of Examples 1-3, the higher the true density of hard carbon, the lower the gram capacity. The possible mechanism is that the structure of hard carbon with a higher true density is closer to graphite, and graphite has a lower sodium storage capacity. 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 electrode active material provided in the embodiments of the present application can have a higher capacity while reducing the risk of thermal runaway and heat spread in sodium-ion batteries.

[0171] Comparing the data from Examples 1, 4, and 5, it can be seen that the gram capacity of intercalation-type sodium storage materials is related to the interplanar spacing. Within a certain range, intercalation-type sodium storage materials with larger interplanar spacing have higher gram capacities. A possible mechanism is that intercalation-type sodium storage materials store sodium through an intercalation mechanism; the larger the interplanar spacing, the greater the sodium storage capacity. However, beyond a certain range, the embedded sodium cannot be completely released, which is detrimental to the Coulombic efficiency of sodium-ion batteries. Therefore, selecting an intercalation-type sodium storage material with an interplanar spacing within an appropriate range can also help increase the gram capacity of the negative electrode active material. Furthermore, intercalation-type sodium storage materials with interplanar spacing within this range allow for interlayer slip in their microstructure, which, when used in sodium-ion batteries, helps 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 intercalation-type sodium storage material into the negative electrode active material, the sodium storage mechanism of the negative electrode active material can be modulated, improving the safety performance of the sodium-ion battery. Selecting an intercalation-type sodium storage material with an appropriate interplanar spacing can also help increase the gram capacity of the negative electrode active material and enhance the energy density of the sodium-ion battery.

[0172] 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 the sodium-ion battery. On the other hand. The more amorphous carbon there is, the more the carbon-based material can store sodium based on the adsorption mechanism in addition to the embedding mechanism, further reducing the formation of metallic sodium and regulating 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 the sodium-ion battery can be improved.

[0173] 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, the Q2 / Q1 of Example 11 is smaller 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 contributes less 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.

[0174] 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.

[0175] Figure 5 shows a charge curve corresponding to the negative electrode active material in Comparative Example 1. Figure 6 shows a charge curve corresponding to the negative electrode active material in Example 1. It should be understood that the ratio of the specific capacities corresponding to the plateau region and the slope region can represent the ratio of the capacities corresponding to the plateau region and the slope region, Q2 / Q1. The charge curves of Example 1 and Comparative Example 1 are used as examples here; discharge curves also have corresponding plateau and slope regions.

[0176] According to the data in Figures 5 and 6, it can be measured that, with 0.15V as the boundary, Q2 / Q1 in Figure 5 is approximately 3.5, and Q2 / Q1 in Figure 6 is approximately 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.

[0177] Next, the testing methods of the physical parameters and performance parameters involved in the embodiments of the present application are introduced.

[0178] 1. True density test method

[0179] The true density of a material can be tested using methods known in the art. For example, the true density of a material can be tested using an instrument such as the AccuPyc 1340, the Anton Paar DMA 4200M, or the ZS-102 tap density meter. A specific example of testing true density is provided below.

[0180] Sample requirements: Powder (10ml minimum); Blocks: Dimensions must be less than the following: 15mm in diameter, 35mm in height, and a total volume of at least 6mL. True density refers to the actual mass per unit volume of a solid material in an absolutely dense state, i.e., after removing internal pores or spaces between particles.

[0181] The material to be tested is placed in a true density tester, using helium as the medium. The measuring chamber is gradually pressurized, causing the helium to expand into the expansion chamber. The equilibrium pressure of the two processes is automatically recorded by the instrument. Based on the law of conservation of mass, the volume of the measuring chamber and the expansion chamber are calibrated using a standard ball. The volume of the material is then determined and the true density is calculated. Applying the Archimedean principle - the gas expansion displacement method, and utilizing Bohr's law (PV = nRT) for inert gases with small molecular diameters under certain conditions, the true volume of the material to be tested is accurately determined by measuring the decrease in gas volume in the sample test chamber caused by the sample being placed in the test chamber, thereby obtaining its true density: true density = mass / true volume.

[0182] It should be understood that the above fixed value is a numerical value set artificially based on test experience and can be adjusted as needed. After pressurization reaches this fixed value, the volume of helium in the expansion chamber does not change or changes slightly with further pressurization, for example, the volume change rate is less than or equal to 1%.

[0183] 2. Test method of interplanar spacing

[0184] Methods such as X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HTEM) can be used to measure the interplanar spacing of a material. For example, using X-ray diffraction, a suitable amount of the sample to be tested can be placed on a sample stage and examined using an X-ray diffractometer using a copper anode target. The XRD diffraction peak spectrum of the sample can then be obtained. The Bragg formula can then be used to calculate the corresponding lattice constant, such as the interplanar spacing.

[0185] 3. Test method of ID / IG in Raman spectroscopy

[0186] 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 vertical axis is intensity. Among them, 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.

[0187] 4. Test method for capacity ratio between platform area and slope area

[0188] The negative electrode active material, conductive agent acetylene black, and 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. After drying and rolling, the negative electrode sheet was obtained. The powder compaction density of the negative electrode sheet was controlled at 0.92g / cm 3 A half-cell was assembled using a sodium sheet as the negative electrode and 1M NaPF6 electrolyte. Charge and discharge tests were performed at a current density of 0.05C between 0.005V and 2V. The capacity above 0.18V in the second cycle of discharge is the slope capacity, and below 0.18V is the plateau capacity.

[0189] 5. Test method for energy density of sodium ion batteries

[0190] Mass energy density (Wh / kg) = battery capacity (mAh) × voltage platform 3.0V / battery weight.

[0191] 6. Heat spread test method

[0192] The cycled sodium-ion battery is disassembled to obtain the cycled negative electrode sheet. 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 can be disassembled in a glove box, the negative electrode sheet can be taken out, and cut into 30cm×15cm strips. In an inert glove box, a heat gun (200℃) is used for forced ignition, and the burning rate and burning time are recorded. Thus, the heat spread can also be quantified by the burning rate and burning time. Heat spread rate: v=L / (t_P-t_b)

[0193] Where L is the distance between the two temperature sensing lines T-ignition and T-spread, t_P is the time when the temperature at the pole piece spread position reaches the highest, and t_b is the time when the temperature at the ignition position reaches the highest.

[0194] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described 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 encompasses all technical solutions 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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