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

Abstract

The embodiment of the application discloses a negative electrode active material, a negative electrode sheet, a sodium ion battery and an electric device, and the negative electrode active material comprises: hard carbon, the true density p of the hard carbon satisfies: 1.3 g / cm 3 ≤ p ≤ 1.8 g / cm 3 ; and an embedded sodium storage material, the interplanar spacing d of the embedded sodium storage material satisfies: 0.24 nm ≤ d ≤ 0.8 nm. The negative electrode active material can effectively reduce the risk of thermal runaway of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, and more particularly, to a negative electrode active material, a negative electrode sheet, a sodium-ion battery and an electric device. BACKGROUND

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

[0003] Hard carbon is widely used in the negative electrode of sodium-ion batteries due to its high sodium storage specific capacity and low working voltage. However, sodium-ion batteries also face problems such as short circuit and thermal runaway in actual use. When short circuit or thermal runaway occurs, a large amount of metal-like sodium is formed during sodium storage of hard carbon, and the thermal reaction temperature of hard carbon is relatively low, so thermal runaway is also prone to occur at a relatively low temperature, thereby rapidly exacerbating the thermal runaway of the battery, and in severe cases, causing the sodium-ion battery to catch fire or explode. Therefore, how to improve the thermal runaway problem of sodium-ion batteries has become a technical problem to be solved. SUMMARY

[0004] The present application is made in view of the above technical problems, and aims to provide a negative electrode active material, a negative electrode sheet, a sodium-ion battery and an electric device, which can effectively reduce the risk of thermal runaway of the sodium-ion battery.

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

[0006] In the embodiments of the present application, the negative electrode active material comprises hard carbon with a true density of 1.3 g / cm 3 - 1.8 g / cm 3The hard carbon with the true density in the range and the interplanar spacing of the crystal face in the range of 0.24-0.8 nm is an intercalation type sodium storage material, wherein the hard carbon with the true density in the range can provide a higher capacity for the sodium ion battery, and the intercalation type 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 metal-like sodium, and thus reduce the risk of thermal runaway of sodium ions. By using the negative electrode active material provided in the embodiments of the present application, the sodium ion battery can have a higher capacity while reducing the risk of thermal runaway and thermal spread of the sodium ion battery, and improving the safety of the sodium ion battery. In addition, the intercalation type sodium storage material with the interplanar spacing of the crystal face in the range can slide between layers in the microstructure, which is helpful 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.

[0007] In an implementation manner, the intercalation type sodium storage material includes at least one of a carbon-based intercalation type sodium storage material, a sulfur-based intercalation type sodium storage material, and a titanium-based intercalation type sodium storage material.

[0008] In an implementation manner, the interplanar spacing d of the carbon-based intercalation type sodium storage material satisfies: 0.335 nm≤d≤0.4 nm; the interplanar spacing d of the sulfur-based intercalation type sodium storage material satisfies: 0.5 nm≤d≤0.8 nm; and the interplanar spacing d of the titanium-based intercalation type sodium storage material satisfies: 0.24 nm≤d≤0.30 nm.

[0009] In an implementation manner, the carbon-based intercalation type sodium storage material includes at least one of soft carbon and modified graphite.

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

[0011] In the embodiments of the present application, by selecting the soft carbon with the ID / IG satisfying the above range, the soft carbon can have a higher degree of disorder, the ability of the soft carbon to store sodium based on the adsorption mechanism is also enhanced in addition to the sodium storage based on the intercalation mechanism, the formation of metal-like sodium is further reduced, the sodium storage mechanism of the negative electrode active material is adjusted, and the safety performance of the sodium ion battery is improved.

[0012] In an implementation manner, the titanium-based intercalation type sodium storage material includes at least one of TiO2, Na2Ti3O7, Li4Ti5O 12 , and Na3Ti2(PO4)2.

[0013] In an implementation manner, the sulfur-based intercalation type sodium storage material includes at least one of MoS2 and WS2.

[0014] In the embodiments of the present application, the titanium-based intercalation type sodium storage material and the sulfur-based intercalation type sodium storage material generally have high capacity. By selecting the titanium-based and sulfur-based intercalation type sodium storage material, the capacity and energy density of the sodium ion battery can be further improved.

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

[0016] In an implementation manner, 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%.

[0017] In the embodiments of the present application, by adjusting the mass content of the hard carbon and the intercalation type sodium storage material in the negative electrode active material, the capacity and sodium storage mechanism of the negative electrode active material can be effectively adjusted, and the formation of metal-like sodium can be reduced. Therefore, when the negative electrode active material is applied to a sodium ion battery, the sodium ion battery can have high capacity and good safety.

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

[0019] In an implementation manner, the gram capacity W2 of the intercalation type sodium storage material satisfies: W2≤295mAh / g; optionally, 90mAh / g≤W2≤290mAh / g.

[0020] In the embodiments of the present application, by selecting the hard carbon and the intercalation type sodium storage material with high gram capacity, the sodium ion battery can have high capacity while reducing the risk of thermal runaway and thermal spread.

[0021] In an implementation manner, 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.

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

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

[0024] In a fourth aspect, an electric device is provided, which comprises the sodium ion battery in any possible implementation manner of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of the drawings.

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

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

[0028] Figure 3 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 A charge curve diagram of Comparative Example 1 of the present application.

[0031] Figure 6 A charge curve diagram of Example 1 of the present application. DETAILED DESCRIPTION

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

[0033] The ranges disclosed herein are intended to be "open" ranges, meaning that the upper and lower limits of the range are not included. The ranges of values are intended to encompass any and all sub-ranges of the same, i.e., every range of values between the upper and lower limits of the broader range. For example, a range of "60% to 120%" is intended to encompass any and all sub-ranges between (and including) the minimum of 60% and the maximum of 120%, e.g., 65 to 85%, 70 to 100%, 60 to 70, 90 to 120%, 65.1 to 65.9%, 62 to 66, and so forth. In other words, a range of "60-120" is intended to include any and all sub-ranges between (and including) the minimum of 60 and the maximum of 120, e.g., 60-61, 60-65.1, 60-65.9, 60-66, 61-85, 65.1-65.9, 65.1-66, 80-100, 85-120, 90-120, 90-100, 90.1-100, 90.1-100.9, 90.1-100.9, 90.1-100.99, 90.1-100.999, 90.1-100.9999, and so forth. Further, a range of "2 to 8" is intended to include any and all sub-ranges between (and including) the minimum of 2 and the maximum of 8, e.g., 2 to 3, 2 to 4, 2 to 5, 2 to 6, 2 to 7, 2 to 8, 3 to 4, 3 to 5, 3 to 6, 3 to 7, 3 to 8, 4 to 5, 4 to 6, 4 to 7, 4 to 8, 5 to 6, 5 to 7, 5 to 8, 6 to 7, 6 to 8, and 7 to 8. In other words, a range of "2-8" is intended to include any and all sub-ranges between (and including) the minimum of 2 and the maximum of 8, e.g., 2-3, 2-4, 2-5, 2-6, 2-7, 2-8, 3-4, 3-5, 3-6, 3-7, 3-8, 4-5, 4-6, 4-7, 4-8, 5-6, 5-7, 5-8, 6-7, 6-8, and 7-8. It will be further understood that the endpoints of the ranges are significant, and that the specific values recited will be understood to be meant in a literal sense and to be qualified by the term "comprising" or "comprising."

[0034] In the description of the present application, it is necessary to explain that, unless otherwise specified, the meaning of "a plurality of" is more than two; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer" and the like is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0035] If not specifically stated, all the steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0036] If not specifically stated, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

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

[0039] If mentioned, "hard carbon" refers to disordered carbon materials that cannot form a regular graphite structure at temperatures above 3000℃. Its precursors are generally polymers with multiple heteroatoms, such as sugars, cellulose, and phenolic resins.

[0040] If mentioned, "true density" refers to the actual mass of a solid substance per unit volume in an absolutely dense state, that is, the density after removing internal pores or voids between particles.

[0041] As mentioned, "intercalated sodium storage materials" refer to materials in which sodium ions can be intercalated and form compounds with them, such as soft carbon, graphite, and titanium-based materials. Intercalated sodium storage materials typically have a layered structure, allowing sodium ions to intercalate between the layers and form ionic compounds, i.e., sodium ion compounds.

[0042] If 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" represents intensity.

[0044] If mentioned, "titanium-based intercalated sodium storage materials" refers to TiO2 and other titanium-based oxides, such as Li4Ti5O 12 Na4Ti5O 12 wait.

[0045] If mentioned, "sulfur-based intercalated sodium storage materials" refers to sulfides such as molybdenum disulfide and titanium disulfide.

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

[0047] If mentioned, the "plateau region" refers to a region in the charge-discharge curve where the battery capacity changes but the potential changes slowly or almost unchanged, near a certain potential; the "ramp region" refers to a region in the charge-discharge curve where the electrode potential changes rapidly with capacity. For example, in a sodium-ion battery, at 0.15V (vs. Na... + There is a plateau region at the low potential of / Na, and the potential is higher than 0.15V (vs. Na).+ / Na) is a slope region.

[0048] Generally, 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 reversibly intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a 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, and mainly plays a role of preventing short circuit of the positive and negative electrodes, while allowing the active ions to pass through. In some embodiments, the above-mentioned battery cell is also referred to as a secondary battery.

[0049] During the charging process of the sodium-ion battery, sodium ions are deintercalated from the positive active material, move and intercalate into the negative material; and during the discharging process, sodium ions are deintercalated from the negative material, move and intercalate into the positive active material.

[0050] It should be understood that the "intercalation" process described in the present application refers to the process of sodium ions intercalating into the positive active material and the negative material due to electrochemical reaction, and the "deintercalation" process described in the present application refers to the process of sodium ions deintercalating from the positive active material and the negative material due to electrochemical reaction.

[0051] With the in-depth research and application of sodium-ion batteries, new requirements are put forward for the capacity and safety performance of sodium-ion batteries. For example, in some application scenarios (such as electric vehicles and other electric devices), once the battery short-circuits, the temperature inside the battery will quickly rise and then thermal runaway will occur, which is not conducive to the user of the electric device to respond. Moreover, for sodium-ion batteries, hard carbon is usually used as the negative active material. At present, the process of sodium storage in hard carbon in sodium-ion batteries is generally considered to exist three mechanisms: (1) adsorption mechanism of sodium ions in the edge defects of graphite-like layers and in the surface open pores; (2) intercalation mechanism of sodium ions in the interlayer of graphite-like layers; and (3) pore-filling mechanism of sodium ions in the closed pores and some open pores of hard carbon to form metal-like sodium. Among them, the pore-filling mechanism is considered to be the main mechanism for hard carbon to contribute to the platform region capacity, that is, the higher the capacity of the sodium-ion battery, the more metal-like sodium is formed during the charge and discharge process of the battery. Based on this, in the aforementioned application scenarios, once the battery short-circuits, the sodium-ion battery using hard carbon as the negative active material is more prone to thermal runaway of the negative electrode due to the lower thermal reaction temperature of hard carbon itself than that of graphite and the existence of a large amount of metal-like sodium, and in severe cases, the heat spreads to the positive electrode, triggering thermal runaway of the entire sodium-ion battery, which seriously affects the safety of the sodium-ion battery.

[0052] In view of this, this application provides a negative electrode active material, a negative electrode sheet, a sodium-ion battery, and an electrical device. In addition to hard carbon, the negative electrode active material also includes an intercalated sodium storage material, which can regulate the sodium storage mechanism of the negative electrode active material; and by controlling the true density of the hard carbon and the intercalation spacing of the intercalated sodium storage material, the possibility of thermal runaway in the sodium-ion battery is reduced while enabling the sodium-ion battery to have a high capacity.

[0053] First, embodiments of this application provide a negative electrode active material, including hard carbon and an intercalated sodium storage material. The true density ρ of the hard carbon satisfies: 1.3 g / cm³. 3 ≤ρ≤1.8g / cm 3 The interplanar spacing d of the embedded sodium storage material satisfies: 0.24nm≤d≤0.4nm.

[0054] Specifically, ρ can be 1.3 g / cm³. 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 any combination of the above two 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 any combination of the above two values.

[0055] Intercalation-type sodium storage materials primarily store sodium through an intercalation mechanism, allowing sodium ions to be embedded and form ionic bonds, resulting in sodium ion compounds. Hard carbon, which primarily stores sodium through a pore-filling mechanism, generates more metalloid sodium during cycling, with sodium ions fixed by metallic bonds. The ionic bonds in sodium ion compounds are stronger than the metallic bonds in metalloid sodium. Therefore, compared to hard carbon, intercalation-type sodium storage materials require the battery to reach a higher temperature before thermal runaway occurs in the event of a short circuit, exhibiting better safety. Based on this, for negative electrode active materials, introducing intercalation-type sodium storage materials can effectively reduce the contribution of the pore-filling mechanism to the capacity of sodium-ion batteries and increase the contribution of the intercalation mechanism, thereby reducing the formation of metalloid sodium and lowering the possibility of thermal runaway and thermal propagation in sodium-ion batteries. Furthermore, the embodiments of this application, by controlling the true density of hard carbon within the aforementioned range, enable the negative electrode active material to have a high specific capacity, thus improving the safety of sodium-ion batteries while also providing them with higher capacity. In addition, by selecting intercalation-type sodium storage materials with interplanar spacing within the above range, their microstructure capable of interlayer slippage helps to increase the powder compaction density of the negative electrode sheet, thereby improving the energy density of ammonium ion batteries.

[0056] In one embodiment, the mass content m1 of hard carbon in the negative electrode active material satisfies: 90% ≤ m1; optionally, 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 a value within the range obtained by any combination of the above two values.

[0058] Hard carbon has a high reversible capacity, and it can be selected as the main material in the negative electrode active material. Controlling its mass content within a high range helps to improve the specific 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 a value within the range obtained by any combination of the above two values.

[0061] Intercalated 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 small range, the safety performance of the negative electrode active material can be improved, while reducing the impact of intercalated sodium storage materials on the capacity of the negative electrode active material, thus helping to improve the capacity of the negative electrode active material.

[0062] In the embodiments of this application, by adjusting the proportion of hard carbon and intercalated sodium storage materials in the negative electrode active material, the sodium storage mechanism of the negative electrode active material can be controlled, thereby controlling the contribution of different mechanisms to the capacity of sodium-ion batteries, reducing the generation of metalloid sodium, and reducing the possibility of thermal runaway of sodium-ion batteries.

[0063] It should be understood that the ratio of hard carbon and embedded sodium storage materials 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 the following: carbon-based embedded sodium storage material, titanium-based embedded sodium storage material, and sulfur-based embedded sodium storage material.

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

[0066] It should be understood that the interplanar spacing d of the carbon-based intercalated sodium storage material satisfies: 0.335 nm ≤ d ≤ 0.4 nm. This can be the interplanar spacing d of a certain family of crystal planes (e.g., the (002) crystal plane) of the carbon-based intercalated sodium storage material being in the range of 0.335 nm to 0.4 nm, or it can be the interplanar spacing of other crystal planes of the carbon-based intercalated sodium storage material within the aforementioned range. Similarly, the interplanar spacing d of the (002) crystal plane of the sulfur-based intercalated sodium storage material can be in the range of 0.5 nm to 0.8 nm, or it can be the interplanar spacing of other crystal planes of the sulfur-based intercalated sodium storage material within the aforementioned range. Similarly, the interplanar spacing d of the (110) crystal plane of the titanium-based intercalated sodium storage material can be in the range of 0.24 nm to 0.3 nm, or it can be the interplanar spacing of other crystal planes of the titanium-based intercalated sodium storage material within the aforementioned range.

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

[0068] 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 it to change its physicochemical properties from those before treatment. For example, graphite can be treated with substances such as surfactants. Modified graphite may include expanded graphite, graphite oxide, etc.

[0069] In one embodiment, the ID / IG ratio of the embedded sodium storage material satisfies: 0.9 ≤ ID / IG ≤ 1.6; alternatively, 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 any combination of the above two values.

[0071] In the embodiments of this application, by selecting soft carbon with an ID / IG ratio that meets the above-mentioned range, the soft carbon can have a higher capacity, thereby helping to improve the capacity of sodium-ion batteries.

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

[0073] More specifically, TiO2 can be anatase, rutile, brookite, or TiO2-B; layered Na2Ti3O7 can also be used.

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

[0075] In one embodiment, the specific capacity W1 of the hard carbon satisfies: W1≤400mAh / g; optionally 290mAh / g≤W1≤340mAh / 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 a value within the range obtained by any combination of the above two values.

[0077] In one embodiment, the specific capacity W2 of the embedded sodium storage material satisfies: W2≤295mAh / g; optionally, 90mAh / g≤W2≤290mAh / 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 a value within the range obtained by any combination of the above two values.

[0079] In one embodiment, the ratio of the discharge capacity Q2 corresponding to the plateau region (potential below 0.15V) of the discharge curve of the negative electrode active material to the discharge capacity Q1 corresponding to the ramp region (potential above 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 a value within the range obtained by any combination of the above two values.

[0081] Next, we will provide a detailed introduction to the electrode materials, positive electrode, negative electrode, separator, and electrolyte in sodium-ion batteries.

[0082] [Negative electrode plate]

[0083] A negative electrode typically includes a negative current collector, or includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

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

[0085] Optionally, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can 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 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 spheres (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 also 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.

[0088] Optionally, the negative electrode film layer further includes an adhesive, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0089] The above-mentioned negative electrode sheet can be prepared according to conventional methods in the art. For example, the components used to prepare the negative electrode sheet, such as 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 coated on a negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0090] The negative electrode sheet provided in this application includes the negative electrode active material described in the foregoing embodiments. Therefore, when applied to 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 subjected to XRD or TEM analysis to determine its composition, thus enabling the detection of the negative electrode active material described in the foregoing embodiments. Furthermore, after cycling the sodium-ion battery, by disassembling the cycled sodium-ion battery and obtaining the negative electrode active material on the surface of the cycled negative electrode sheet, and performing XRD or TEM analysis, the interplanar spacing of the intercalated sodium storage material can be detected. The change in the interplanar spacing of the intercalated sodium storage material after cycling indicates that sodium ions have successfully intercalated into the interlayer of the intercalated sodium storage material, reducing the formation of metalloid sodium and regulating the sodium storage mechanism of the negative electrode active material.

[0091] [Positive electrode plate]

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

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

[0094] Optionally, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can 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 positive electrode active materials known in the art for sodium-ion batteries. As mentioned above, the positive electrode active material may include one or more of polyanionic compounds, transition metal oxides, and Prussian blue compounds. As an example, polyanionic compounds may be compounds having sodium ions, transition metal ions, and tetrahedral anionic units, such as sodium iron phosphate (NaFePO4) and sodium vanadium phosphate (Na3V2(PO4)3). Transition metal oxides may be transition metal oxides having sodium ions, such as sodium copper iron manganate and sodium iron nickel manganate. Prussian blue compounds may be compounds having sodium ions, transition metal ions, and cyanide ions. However, this 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 further includes an adhesive, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0097] Optionally, the positive electrode film layer also 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.

[0098] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, additives, conductive agents, binders and any other components, in a solvent (e.g., NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0099] [Electrolytes]

[0100] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0101] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution 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-like 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-dioxane, etc.

[0104] Optionally, the electrolyte may also include electrolyte additives. For example, electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0105] [Isolation Component]

[0106] In some embodiments, the sodium-ion battery also includes a separator. This application does not impose any particular limitation on the type of separator; for example, the separator can be a separator membrane. The separator membrane can be any known porous structure separator membrane with good chemical and mechanical stability.

[0107] 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.

[0108] In some embodiments, the above-mentioned positive electrode, negative electrode and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

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

[0110] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] Sodium-ion batteries

[0112] This application also provides a sodium-ion battery, which includes the negative electrode sheet in any of the foregoing embodiments.

[0113] This application does not impose any particular limitation on the shape of the sodium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a sodium-ion battery 100 with a square structure.

[0114] Figure 2 This is a sample sodium-ion battery module 200. (See reference...) Figure 2 In the battery module 200, multiple sodium-ion batteries 100 can be arranged sequentially along the length of the battery module 200. Of course, they can also be arranged in any other manner. Furthermore, the multiple sodium-ion batteries 100 can be secured using fasteners.

[0115] Alternatively, in one embodiment, the battery module 200 may further include a housing with a receiving space in which a plurality of sodium-ion batteries 100 are received.

[0116] Optionally, in one embodiment, the battery module 200 can also be assembled into a battery pack. The number of battery modules 200 contained in the battery pack can be one or more, and the specific number can 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 This is a sample battery pack 300. (See reference...) Figure 3 and Figure 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 box 301 and a lower box 302, with the upper box 301 covering the lower box 302 to form a closed space for accommodating the battery modules 200. The multiple battery modules 200 may be arranged in any manner within the battery box.

[0118] It should be understood that in some embodiments, the battery pack 300 described above is also referred to as a battery. The sodium-ion batteries 100 can be first assembled into battery module 200, and the battery pack 300 is composed of battery module 200. Alternatively, the battery pack 300 can be directly assembled from sodium-ion batteries 100, omitting the intermediate form of battery module 200.

[0119] In addition, this 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 this application. The sodium-ion battery 100, battery module 200, or battery pack 300 can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

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

[0121] This is an example of an electrical device. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack 300 or a battery module 200 can be used.

[0122] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a sodium-ion battery (100) as their power source.

[0123] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, 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, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly 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 onto the positive electrode current collector aluminum foil, and after drying and rolling, a positive electrode sheet is obtained.

[0128] (2) Preparation of negative electrode sheet

[0129] The negative electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of NMP at a mass ratio of 8:1:1 to form a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector copper foil. After drying and rolling, the resulting negative electrode sheet has a powder compaction density controlled at 0.92 g / cm³. 3 about.

[0130] Among the negative electrode active materials, the intercalated sodium storage material is soft carbon, with a crystal interplanar spacing d = 0.35 nm, an ID / IG ratio of 1.2 in the Raman characteristic peaks of soft carbon, a specific capacity W2 = 260 mAh / g, and a mass content m2 = 2.5% of soft carbon in the negative electrode active material; the true density ρ of hard carbon is 1.5 g / cm³. 3 The mass content of hard carbon in the negative electrode active material is m1 = 97.5%, and the specific capacity of hard carbon is W1 = 310 mAh / g. Following the published procedure for "Testing the Capacity Ratio Corresponding to the Plateau Region and the Slope Region," the discharge curve of the negative electrode active material shows Q2 / Q1 = 3.033.

[0131] (3) Assembly of sodium-ion batteries

[0132] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After stacking, an electrode assembly is formed. The electrode assembly is then placed in a packaging shell, and a 1 mol / L NaPF6 electrolyte is added. After encapsulation, formation, and settling processes, a sodium-ion battery is obtained.

[0133] Example 2

[0134] Compared with Example 1, in Example 2, ρ = 1.3 g / cm³ 3 , W1=350mAh / g, Q2 / Q1=3.236.

[0135] Example 3

[0136] Compared with Example 1, in Example 3, ρ = 1.8 g / cm³ 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, and 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, and 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 was selected as the embedded sodium storage material, with d = 0.335 nm, ID / IG = 0.9, W2 = 70 mAh / g, and 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] Example 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] Example 13

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

[0157] Example 14

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

[0159] Comparative Example 1

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

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

[0162]

[0163] 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 specific capacity of hard carbon, “intercalated sodium storage material” indicates the type of intercalated sodium storage material in the negative electrode active material, “d” represents the interplanar spacing of the intercalated sodium storage material, “ID / IG” represents the ratio of the signal intensity of the D peak and the G peak in the Raman spectrum of the intercalated sodium storage material, “W2” represents the specific capacity of the intercalated sodium storage material, “m2” represents the mass content of the intercalated sodium storage material in the negative electrode active material, and “Q2 / Q1” represents the ratio of the discharge capacity corresponding to the plateau region and the slope region in the discharge curve of the negative electrode active material.

[0164] The performance test results of the sodium-ion batteries in the above embodiments and comparative examples are detailed in Table 2.

[0165] Table 2. Battery performance test results for different embodiments and comparative examples.

[0166] Energy density (Wh / kg) Rate of thermal propagation (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 Example 11 112 ＞0.15 Example 12 140 ＞0.15 Example 13 128 ＞0.15 Example 14 130 ＞0.15 Comparative Example 1 120 ≤0.15

[0167] In Table 2, "energy density" represents the energy density of sodium ions in each embodiment and comparative example, and "thermal spread rate" represents the thermal spread rate measured when the negative electrode is removed after disassembling the sodium ion battery and subjected to a thermal spread test.

[0168] Based on the comparative analysis of the examples and comparative examples, it can be seen that in the sodium-ion batteries of Examples 1-14, the negative electrode active material contains materials with a true density of 1.3 g / cm³. 3 -1.8g / cm 3In the comparison of hard carbon and intercalated sodium storage materials, the thermal runaway rate of sodium-ion batteries in the thermal runaway test was greater than 0.15 m / s. However, in Comparative Example 1, the negative electrode active material lacked an intercalated sodium storage material capable of regulating the sodium storage mechanism, and the thermal runaway rate in the thermal runaway test was less than or equal to 0.15 m / s. This demonstrates that by combining hard carbon with a suitable true density and intercalated sodium storage material with a suitable interplanar spacing, the sodium storage mechanism of hard carbon can be regulated, reducing the formation of metalloid sodium. This effectively reduces the risk of thermal runaway and thermal runaway in sodium-ion batteries, while simultaneously enabling sodium-ion batteries to possess both high capacity and energy density.

[0169] A comparison of the data from Examples 1-3 shows that the higher the true density of hard carbon, the lower its specific capacity. A possible mechanism is that the structure of hard carbon with 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 specific capacity. Therefore, by selecting hard carbon with a true density within a suitable range, the negative electrode active material provided in this application can reduce the risks of thermal runaway and thermal propagation in sodium-ion batteries while also possessing a high capacity.

[0170] Comparison of data from Examples 1 and 4-5 shows that the specific capacity of intercalated sodium storage materials is related to the interplanar spacing. Within a certain range, intercalated sodium storage materials with larger interplanar spacing have higher specific capacity. A possible mechanism is that intercalated 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 intercalated sodium cannot be completely extracted, which is detrimental to the coulombic efficiency of sodium-ion batteries. Therefore, selecting intercalated sodium storage materials with an appropriate interplanar spacing can also help improve the specific capacity of the negative electrode active material. Furthermore, intercalated sodium storage materials with interplanar spacing within the aforementioned range can exhibit interlayer slip in their microstructure, which helps increase the powder compaction density of the negative electrode sheet when applied in sodium-ion batteries, thereby improving the energy density of the sodium-ion battery. Therefore, by introducing intercalated sodium storage materials into the negative electrode active material, the sodium storage mechanism of the negative electrode active material can be controlled, improving the safety performance of sodium-ion batteries. Selecting intercalated sodium storage materials with an appropriate interplanar spacing also helps improve the specific capacity of the negative electrode active material and enhances the energy density of sodium-ion batteries.

[0171] A comparison of data from Examples 6-10 shows that the specific capacity of carbon-based intercalation sodium storage materials is also related to the ID / IG ratio. A higher ID / IG value indicates a greater proportion of the D peak in the Raman spectrum of the carbon-based material, and a higher proportion of amorphous carbon. On one hand, more amorphous carbon results in more sodium storage sites, thus increasing the specific capacity of the carbon-based material and contributing to higher energy density in sodium-ion batteries. On the other hand, more amorphous carbon enhances the ability of carbon-based materials to store sodium not only through intercalation but also through adsorption, further reducing the formation of metalloid sodium and regulating the sodium storage mechanism of the negative electrode active material. Therefore, by selecting carbon-based materials with an ID / IG ratio within a suitable range, the safety performance of sodium-ion batteries can be improved.

[0172] A comparison of data from Examples 1 and 11-12 shows that when the intercalated sodium storage material is soft carbon, the specific capacity of soft carbon is lower than that of hard carbon. Therefore, the higher the mass content of the intercalated sodium storage material in the negative electrode active material, the lower the energy density of the sodium-ion battery. Specifically, the energy density of Example 11 is lower than that of Example 12. However, as the mass content of the intercalated sodium storage material increases, the value of Q2 / Q1 decreases significantly. That is, the Q2 / Q1 of Example 11 is lower than that of Example 12. This indicates that increasing the mass content of the intercalated sodium storage material increases the capacity of the ramp region, reduces the contribution of the plateau region corresponding to the pore-filling mechanism to the capacity of the sodium-ion battery, and effectively regulates the sodium storage mechanism of the negative electrode active material. Furthermore, when the specific capacity of the intercalated sodium storage material is higher than that of hard carbon, increasing the mass content of the intercalated sodium storage material can help improve the energy density of the sodium-ion battery.

[0173] According to the data from Examples 13-14, the embedded material can also be a titanium-based embedded sodium storage material or a sulfur-based embedded sodium storage material.

[0174] Figure 5 The charging curve is shown for the negative electrode active material in Comparative Example 1. Figure 6 This is a charging curve for the negative electrode active material in Example 1. It should be understood that the ratio of the specific capacity corresponding to the plateau region and the ramp region can represent the ratio of the capacities corresponding to the plateau region and the ramp region, Q2 / Q1. Here, the charging curves of Example 1 and Comparative Example 1 are used as examples; the discharge curves also have corresponding plateau and ramp regions.

[0175] according to Figure 5 and Figure 6 The data can be measured, with 0.15V as the boundary. Figure 5 The Q2 / Q1 ratio is approximately 3.5. Figure 6The Q2 / Q1 ratio is approximately 3.01. In other words, compared to Comparative Example 1, the plateau region in Example 1 is smaller, Q2 / Q1 is less than 3.3, and no thermal propagation occurs during the thermal propagation test, while in Comparative Example 1, Q2 / Q1 is greater than 3.3, and thermal propagation occurs during the thermal propagation test. This demonstrates that in Example 1, by introducing an intercalated sodium storage material into the anode material with hard carbon as the main material, the sodium storage mechanism of the anode active material was successfully controlled, reducing the contribution of the plateau region capacity to the total capacity during the entire charge-discharge process, thereby reducing the risk of thermal runaway and thermal propagation in the sodium-ion battery.

[0176] Next, the testing methods for the physical parameters and performance parameters involved in the embodiments of this application will be introduced.

[0177] 1. True density test method

[0178] The true density of a material can be tested using methods known in the art. For example, instruments such as the AccuPyc 1340, the Antonpah DMA4200M, and the ZS-102 tap density meter can be used to test the true density of a material. A specific example of testing true density is given below.

[0179] Sample requirements: Powder (preferably 10ml); Blocks: dimensions smaller than the following: diameter 15mm, height 35mm, total volume not less than 6mL. True density refers to the actual mass of a solid substance per unit volume in an absolutely dense state, i.e., the density after removing internal pores or voids between particles.

[0180] The material to be tested is placed in a true density analyzer, using helium as the medium. The measuring chamber is gradually pressurized, causing the helium to expand and enter 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 volumes of the measuring and expansion chambers are calibrated using a standard sphere, and the volume of the material is then determined to calculate the true density. Applying Archimedes' principle—the gas expansion and displacement method—and utilizing Bohr's law (PV = nRT) for small-molecule inert gases under certain conditions, the true volume of the material to be tested is accurately determined by measuring the reduction in gas volume in the sample testing chamber caused by the insertion of the sample. Thus, its true density is obtained: True density = mass / true volume.

[0181] It should be understood that the above fixed values ​​are manually set based on testing experience and can be adjusted as needed. After pressurizing to this fixed value, further pressurization will result in the volume of helium in the expansion chamber no longer changing or changing only slightly; for example, the volume change rate is less than or equal to 1%.

[0182] 2. Test method for interplanar spacing

[0183] The interplanar spacing of materials can be detected using methods such as X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HTEM). Taking X-ray diffraction as an example, an appropriate amount of the sample to be tested can be placed on the sample stage, and the sample can be detected using an X-ray diffractometer with copper as the anode target to obtain the XRD diffraction peak pattern of the sample. Then, the lattice constant corresponding to the sample, such as the interplanar spacing, can be calculated according to Bragg's formula.

[0184] 3. Methods for determining ID / IG in Raman spectroscopy

[0185] Take an appropriate amount of the sample to be tested, and detect the sample using a Raman spectrometer to obtain the Raman scattering spectrum of the sample. The abscissa of the spectrum is Raman shift (unit: cm). -1 The vertical axis represents intensity. The D peak typically appears at 1300 cm⁻¹. -1 The G peak typically appears at 1580 cm⁻¹. -1 The maximum intensity of peak D represents ID, and the maximum intensity of peak G represents IG. Calculate the ID / IG ratio for the sample being tested.

[0186] 4. Test method for the capacity ratio between the platform area and the slope area

[0187] The negative electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of NMP at a mass ratio of 8:1:1 to form a negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector copper foil. After drying and rolling, the resulting negative electrode sheet has a powder compaction density controlled at 0.92 g / cm³. 3 The two sides are shown in the figure. Using a sodium sheet as the negative electrode and 1M NaPF6 electrolyte, a half-cell was assembled. Charge and discharge tests were conducted at a current density of 0.05C in the range of 0.005-2V. The capacity above 0.18V in the second discharge cycle is the ramp capacity, and the capacity below 0.18V is the plateau capacity.

[0188] 5. Test method for energy density of sodium-ion batteries

[0189] Mass energy density (Wh / kg) = Battery capacity (mAh) × Voltage plateau 3.0V / Battery weight.

[0190] 6. Test method for heat spread

[0191] Disassembling a cycled sodium-ion battery yields the cycled negative electrode. Igniting this negative electrode allows for direct observation of heat spread. More specifically, the prepared cell can be charged to 4.0V, disassembled in a glove box, and the negative electrode removed and cut into 30cm × 15cm strips. Forced ignition is then performed using a heat gun (200℃) in an inert glove box, and the combustion rate and time are recorded. Thus, heat spread can also be quantified using combustion rate and time.

[0192] Thermal propagation rate: v = L / (t_P - t_b)

[0193] Where L is the distance between the two sensing lines T-ignition and T-propagation, t_P is the moment when the temperature at the electrode propagation position reaches its maximum, and t_b is the moment when the temperature at the ignition position reaches its maximum.

[0194] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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, wherein the true density ρ of the hard carbon satisfies: 1.3 g / cm³ 3 ≤ρ≤1.8 g / cm 3 ; An embedded sodium storage material, wherein the interplanar spacing d of the embedded sodium storage material satisfies: 0.24 nm ≤ d ≤ 0.8 nm.

2. The negative electrode active material according to claim 1, characterized in that, The embedded sodium storage material includes at least one of carbon-based embedded sodium storage material, sulfur-based embedded sodium storage material, and 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 intercalated sodium storage material satisfies: 0.335 nm ≤ d ≤ 0.4 nm; The interplanar spacing d of the sulfur-based intercalated sodium storage material satisfies: 0.5 nm ≤ d ≤ 0.8 nm; The interplanar spacing d of the titanium-based embedded sodium storage material satisfies: 0.24 nm ≤ d ≤ 0.30 nm.

4. The negative electrode active material according to claim 2, characterized in that, The carbon-based intercalated 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, The ID / IG ratio of the soft carbon satisfies: 0.9 ≤ ID / IG ≤ 1.

6.

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

5.

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

8. The negative electrode active material according to claim 2, characterized in that, The sulfur-based intercalated sodium storage material includes at least one of MoS2 and WS2.

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

10. The negative electrode active material according to claim 9, characterized in that, The mass content m1 of hard carbon in the negative electrode active material satisfies: 95%≤m1≤99.5%.

11. The negative electrode active material according to any one of claims 1-7, characterized in that, The mass content m2 of the embedded sodium storage material in the negative electrode active material satisfies: m2≤10%.

12. The negative electrode active material according to claim 11, characterized in that, The mass content m2 of the embedded sodium storage material in the negative electrode active material satisfies: 0.5% ≤ m2 ≤ 5%.

13. The negative electrode active material according to any one of claims 1-7, characterized in that, The specific capacity W1 of the hard carbon satisfies: W1≤400 mAh / g.

14. The negative electrode active material according to claim 13, characterized in that, The specific capacity W1 of the hard carbon satisfies: 280 mAh / g ≤ W1 ≤ 350 mAh / g.

15. The negative electrode active material according to any one of claims 1-7, characterized in that, The specific capacity W2 of the embedded sodium storage material satisfies: W2≤295 mAh / g.

16. The negative electrode active material according to claim 15, characterized in that, The specific capacity W2 of the embedded sodium storage material satisfies: 90 mAh / g ≤ W2 ≤ 260 mAh / g.

17. The negative electrode active material according to any one of claims 1-7, characterized in that, The ratio of the charge / discharge capacity Q2 corresponding to the plateau region and the charge / discharge capacity Q1 corresponding to the slope region of the charge / discharge curve of the negative electrode active material satisfies: Q2 / Q1≤3.

3.

18. The negative electrode active material according to claim 17, characterized in that, The ratio of the charge / discharge capacity Q2 corresponding to the plateau region and the charge / discharge capacity Q1 corresponding to the slope region of the charge / discharge curve of the negative electrode active material satisfies: 0.05≤Q2 / Q1≤3.

19. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode active material as described in any one of claims 1-18.

20. A sodium-ion battery, characterized in that, The sodium-ion battery includes the negative electrode as described in claim 19.

21. An electrical appliance, characterized in that, The electrical device includes the sodium-ion battery as described in claim 20.

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