Sodium ion battery and electric device

Abstract

The present application relates to a sodium ion battery and an electrical device, the sodium ion battery comprising a negative pole piece, the negative pole piece comprising a negative active material, the negative active material comprising hard carbon wherein 0.6 [mu] g / m < = (Dv99 + Dv50) / (2 * B) < = 5 [mu] g / m; dv99 and Dv50 respectively represent the corresponding particle sizes when the cumulative volume distribution percentage of the negative electrode active material reaches 99% and 50%; b represents the specific surface area of the negative pole piece.

Description

[0001] Related applications

[0002] This application is a divisional application of Chinese patent application filed on September 14, 2022, with application number CN2022800942424 and entitled "Negative electrode sheet, sodium-ion battery, power supply device and application", the entire text of which is incorporated herein by reference. Technical Field

[0003] This application relates to the field of sodium-ion battery technology, and further to a sodium-ion battery and an electrical device, as well as a negative electrode sheet and its application. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] As the new energy industry chain develops and expands, people's requirements for new energy batteries are also increasing, especially the safety of new energy batteries, which is increasingly regarded as a primary design consideration. The traditional mindset of prioritizing energy and driving range is gradually shifting towards prioritizing high safety. Generally, the most important indicator for evaluating the safety of a battery is its high-temperature resistance. The higher the temperature a battery can withstand, the less likely it is to cause the fire to spread to surrounding batteries in the event of combustion, thus greatly improving the safety of the battery pack.

[0006] Sodium-ion batteries utilize the insertion and extraction of sodium ions between the positive and negative electrodes to achieve charging and discharging. Compared to lithium in lithium-ion batteries, sodium resources are more widely distributed, abundant, and significantly cheaper. Therefore, sodium-ion batteries are considered a next-generation electrochemical system with the potential to replace lithium-ion batteries. The safety of sodium-ion batteries is currently a key research focus; however, improving safety often results in power loss.

[0007] Therefore, there is an urgent need to develop sodium-ion batteries that simultaneously meet the requirements of high safety and high power. Summary of the Invention

[0008] In view of the above problems, this application provides a sodium-ion battery containing a negative electrode sheet, wherein the negative electrode sheet can meet the combined requirements of high safety and high power, and is suitable for sodium-ion batteries. An electrical device including the negative electrode sheet is also provided.

[0009] In a first aspect, this application provides a sodium-ion battery, the sodium-ion battery including a negative electrode sheet, the negative electrode sheet including a negative electrode active material, the negative electrode active material including hard carbon;

[0010] The negative electrode also satisfies the following condition: 0.6 μg / m ≤ (D v 99+D v50) / (2×B) ≤ 5 μg / m; where, D v 99 represents the particle size corresponding to a cumulative volume distribution percentage of 99% for the negative electrode active material, in μm; D v 50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material, in μm; B represents the specific surface area of ​​the negative electrode sheet, in m². 2 / g.

[0011] It is generally believed that the main factors affecting battery safety include the negative electrode, positive electrode, and electrolyte. Through extensive experimental research, the inventors of this application have discovered that the particle size of the negative electrode active material affects battery safety, particularly finding that large-diameter particles have a significant impact on battery safety. Further research revealed that larger particle sizes in the negative electrode active material result in higher thermal decomposition initiation temperatures and higher temperature tolerance. Furthermore, larger particle sizes lead to smaller specific surface areas, slower reaction rates, and ultimately, safer batteries, but at the cost of power loss. By controlling the particle size of the negative electrode active material and the specific surface area of ​​the negative electrode sheet within a certain range, the battery can achieve both a high initial reaction temperature and minimize adverse effects on the reaction rate.

[0012] In this application, the negative electrode active material includes hard carbon, which has a high pyrolysis carbonization temperature, thus improving heat resistance and reducing heat generation. Furthermore, hard carbon has a large interlayer spacing and high porosity, allowing for the embedding of more active ions and exhibiting significantly low structural expansion, which is beneficial for improving the battery's charge-discharge cycle performance and battery life. Based on this, by comprehensively controlling the particle size of the negative electrode active material and the specific surface area of ​​the negative electrode sheet, a combination of high safety and high power is achieved. Further, (D v 99+D v 50) / 2 can characterize large particle size. This characteristic, together with the specific surface area B of the negative electrode, is used to define the electrode thermal stability coefficient (D) of the negative electrode. v 99+D v By adjusting the thermal stability coefficient of the negative electrode to a suitable range, the battery can be endowed with high safety and high power characteristics, and excellent high temperature resistance.

[0013] In some embodiments of this application, the negative electrode active material satisfies the following condition: 5 μm ≤ (D v 99+D v 50) / 2 ≤ 18 μm;

[0014] Optionally, the negative electrode active material satisfies the following condition: 6 μm ≤ (Dv 99+D v 50) / 2 ≤ 15 μm;

[0015] Optionally, the negative electrode active material satisfies the following condition: 7 μm ≤ (D v 99+D v 50) / 2 ≤ 12 μm;

[0016] Optionally, the negative electrode active material satisfies the following condition: 8 μm ≤ (D v 99+D v 50) / 2 ≤ 10 μm.

[0017] By reasonably controlling the large particles in the negative electrode active material within a suitable range, it is easier to combine precise control of the specific surface area of ​​the negative electrode active material, thereby better realizing the advantages of high battery safety and high power.

[0018] In some embodiments of this application, the negative electrode sheet satisfies the following condition: 0.7 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 5 μg / m;

[0019] Optionally, the negative electrode sheet satisfies the following condition: 0.8 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 4.2μg / m.

[0020] In some embodiments of this application, the negative electrode sheet satisfies the following condition: 0.7 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 4.5 μg / m.

[0021] By further controlling the thermal stability coefficient of the electrode within the above range, it is beneficial to better balance the impact of large particle size on battery safety and the impact of the specific surface area of ​​the negative electrode active material on battery power, thereby better balancing high battery safety and high power.

[0022] In some embodiments of this application, the negative electrode active material also satisfies the following condition: (x·D v 10) ≤D v 50 ≤ (y·D v 99); where x = 2.6 and y = 0.4;

[0023] Alternatively, x = 4 and y = 0.3.

[0024] In some embodiments of this application, the negative electrode active material also satisfies the following condition: (x·D v 10) ≤D v 50 ≤ (y·D v 99); where x = 3 and y = 0.3.

[0025] By rationally controlling the D of the negative electrode active material v 50 relative to D v 10. D v The 99 ratio of x to y ensures that both small and large particles in the negative electrode active material have appropriate particle size and content, better avoids battery power loss caused by large particles, and maintains as high a power as possible while improving battery safety.

[0026] In some embodiments of this application, the negative electrode sheet satisfies the following condition: 30 mAh·m -2 ≤ C / B≤ 140 mAh·m -2 Wherein, C is the specific capacity of the negative electrode sheet;

[0027] Optionally, 40 mAh·m -2 ≤ C / B ≤ 125 mAh·m -2 .

[0028] The inventors of this application have discovered that the C / B ratio of the negative electrode sheet can, to a certain extent, reflect the reactivity of the negative electrode active material within the negative electrode sheet. By synergistically controlling the specific capacity and specific surface area of ​​the negative electrode sheet, it is beneficial to better control the reaction rate during battery thermal runaway, thereby further improving battery safety. Controlling the specific capacity of the negative electrode sheet to an appropriate level ensures a suitable amount of active sodium ion insertion, resulting in a moderate reaction rate. Furthermore, controlling the specific surface area of ​​the negative electrode sheet within a suitable range ensures appropriate ion insertion / extraction pathways and polarization of the battery active materials, thus guaranteeing optimal battery power performance.

[0029] In some embodiments of this application, the specific capacity C of the negative electrode sheet satisfies the following condition: 300 mAh / g ≤ C ≤ 350 mAh / g.

[0030] Optionally, the specific capacity C of the negative electrode sheet satisfies the following condition: 310 mAh / g ≤ C ≤ 340 mAh / g.

[0031] By controlling the specific capacity of the negative electrode sheet, the amount of active sodium ion intercalation can be appropriately controlled, resulting in a moderate reaction rate during battery thermal runaway and improved battery safety.

[0032] In some embodiments of this application, B is selected from 2.5 m.2 / g ~10 m 2 / g;

[0033] Optionally, B is selected from 3 m 2 / g ~7 m 2 / g.

[0034] By controlling the specific surface area of ​​the negative electrode sheet within a suitable range, the ion insertion / extraction pathways and polarization of the battery active materials are moderate, which is more conducive to the performance of the battery power.

[0035] In some embodiments of this application, the position T of the first exothermic reaction peak in the differential scanning calorimetry analysis of the negative electrode sheet satisfies 150 °C ≤ T ≤ 180 °C; wherein, the test conditions for differential scanning calorimetry analysis include: nitrogen atmosphere, heating rate of 10 °C / min;

[0036] Optionally, 170 °C ≤ T ≤ 180 °C.

[0037] By controlling the position T of the first exothermic reaction peak in the differential scanning calorimetry (DSC) analysis of the negative electrode to a suitable range, it is more beneficial to further improve battery safety.

[0038] In some embodiments of this application, the negative electrode active material further includes one or more of soft carbon, graphite, and alloyed negative electrode;

[0039] Optionally, hard carbon accounts for ≥ 50% by mass in the negative electrode active material;

[0040] Optionally, hard carbon accounts for ≥90% by mass in the negative electrode active material.

[0041] Based on hard carbon as a negative electrode active material, introducing one or more other types of active materials, such as soft carbon, graphite, and alloyed negative electrodes, can leverage the advantages of these materials to give the battery better overall performance. For example, soft carbon has a low and stable charge / discharge potential plateau, large charge / discharge capacity, high efficiency, and good cycle performance. Graphite, for instance, has advantages such as good conductivity, high initial efficiency, and wide availability. Alloyed negative electrodes, on the other hand, offer advantages such as good power performance and high energy density.

[0042] In some embodiments, a sodium-ion battery is provided, which includes a positive electrode, a negative electrode as described in the first aspect of this application, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode.

[0043] The sodium-ion battery prepared using the negative electrode sheet in the first aspect of this application has the combined advantages of high safety and high power.

[0044] In some embodiments of this application, the electrolyte comprises an electrolyte sodium salt, which includes one or more sodium salts selected from sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium difluorosulfonamide, sodium bis(trifluoromethanesulfonamide), sodium trifluoromethanesulfonate, and sodium difluorophosphate.

[0045] Optionally, the electrolyte sodium salt includes one or more sodium salts selected from sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, and sodium trifluoromethanesulfonate.

[0046] In some embodiments of this application, the electrolyte further comprises an organic solvent, which includes one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), ethers such as dimethyl glycol ether (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MTHF), methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether.

[0047] Optionally, the organic solvent includes one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran. Sodium salts exhibit high solvability and conductivity in the solvent, which is beneficial for film formation and improving battery power.

[0048] In some embodiments of this application, the electrolyte further comprises additives, including one or more of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propane sulpholactone (PS), 1,3-propenyl-sulfonate lactone (PST), succinic anhydride (SA), lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiDFOP), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate (TMSB), ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0049] Optionally, the additives include one or more of the following: fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, 1,3-propane sulpholactone, 1,3-propenyl-sulfonate lactone, succinic anhydride, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate. By selecting suitable additives, it is possible to help the battery quickly form a solid electrolyte interphase (SEI) film, increase the thickness and stability of the SEI film, and improve battery safety.

[0050] In some embodiments of this application, the negative electrode sheet satisfies the following condition: 0.5°C ≤ T×M ≤ 6°C; wherein, T and M are the position of the first exothermic reaction peak and the first stage weight loss rate of the negative electrode sheet, respectively, and the test conditions for differential scanning calorimetry analysis include: nitrogen atmosphere, heating rate of 10 °C / min;

[0051] Optionally, 0.65 °C ≤ T×M ≤ 5.2 °C;

[0052] Optionally, 0.75 °C ≤ T×M ≤ 4.5 °C.

[0053] The inventors of this application hypothesize that T×M can, to some extent, reflect the tolerance of the negative electrode to high temperatures. The particle size of the negative electrode active material affects the starting temperature of the exothermic reaction; the larger the particles, the higher the temperature at which the reaction begins, and the safer the corresponding battery system. However, larger particles are detrimental to battery power. Therefore, balancing safety and power is crucial for the fabrication of batteries with high overall performance. By shifting the position (T) of the first exothermic reaction peak in the differential scanning calorimetry (DSC) analysis of the negative electrode to a higher temperature, the decomposition reaction temperature (corresponding to M) of the solid electrolyte interphase (SEI) film can be increased, which is beneficial for increasing the thickness of the SEI film, thereby further improving safety.

[0054] In some embodiments of this application, the first-stage weight loss rate M of the negative electrode sheet in differential scanning calorimetry meets the following condition: 0.25% ≤ M ≤ 3.5%; wherein, the test conditions for differential scanning calorimetry include: nitrogen atmosphere, heating rate of 10 °C / min;

[0055] Optionally, 0.5% ≤ M ≤ 2.5%;

[0056] Optionally, 0.65% ≤ M ≤ 2.0%.

[0057] By controlling the first-stage weight loss rate M of the differential scanning calorimetry analysis of the negative electrode sheet within a suitable range, the stability of the SEI interface can be improved, which is beneficial to improving battery safety and can also achieve better ion transport and charge / discharge performance.

[0058] In some embodiments of this application, the positive electrode sheet includes a positive electrode active material, which includes a positive electrode active material containing sodium ions, and the positive electrode active material containing sodium ions includes one or more of Prussian blue compounds, sodium transition metal oxides, and polyanionic compounds.

[0059] The appropriate positive electrode active material can be flexibly selected, thus making sodium-ion batteries more selective and applicable to a wider range of fields.

[0060] Secondly, this application provides an electrical device that includes the sodium-ion battery described in the first aspect of this application.

[0061] The electrical device obtained by using the sodium-ion battery provided in the first aspect of this application not only has high safety but also high power, which can meet consumers' comprehensive needs for high safety and high performance.

[0062] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0063] To better describe and illustrate embodiments or examples of the applications disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the embodiments or examples currently described, or the best mode of conduct of these applications as currently understood. Furthermore, throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0064] Figure 1 This is a differential scanning calorimetry (DSC) test result of the exothermic curve and thermogravimetric curve of the negative electrode sheet in one embodiment of this application, where Mass (%) represents the weight loss rate and DTG (% / min) represents the exothermic rate.

[0065] Figure 2 This is a schematic diagram of a sodium-ion battery according to an embodiment of this application;

[0066] Figure 3 yes Figure 2 An exploded view of a sodium-ion battery according to an embodiment of this application is shown.

[0067] Figure 4 This is a schematic diagram of an electrical device using a sodium-ion battery as a power source according to an embodiment of this application.

[0068] Explanation of reference numerals in the attached figures:

[0069] 5. Sodium-ion battery; 51. Casing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0070] The embodiments of the sodium-ion battery and power-consuming device of this application are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0071] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0073] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0074] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0075] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". Further, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0076] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0077] In this application, the terms "multiple", "various", "several", "multiple times", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0078] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0079] In this document, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the technical solution that enables the implementation of this application.

[0080] In this document, terms such as "preferred," "better," "more suitable," and "ideal" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0081] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0082] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0083] In this application, the term "room temperature" generally refers to 4 °C to 35 °C, and preferably 20 °C ± 5 °C. In some embodiments of this application, room temperature refers to 20 °C to 30 °C.

[0084] In this application, if the unit of a data range is only followed by the right endpoint, it indicates that the units of the left and right endpoints are the same. For example, 3~5 h or 3-5 h both indicate that the units of the left endpoint "3" and the right endpoint "5" are both h (hours).

[0085] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Furthermore, the weights mentioned in the embodiments of this application can be units known in the chemical industry, such as μg, mg, g, and kg.

[0086] It is generally believed that the main factors affecting battery safety include the negative electrode, positive electrode, and electrolyte. Through extensive experimental research, the inventors of this application have discovered that the particle size of the negative electrode active material affects battery safety, particularly finding that large-diameter particles have a significant impact on battery safety. Further research revealed that larger particle sizes in the negative electrode active material result in higher thermal decomposition initiation temperatures and higher temperature tolerance. Furthermore, larger particle sizes also lead to smaller specific surface areas, slower reaction rates, and ultimately, safer batteries, but at the cost of power loss. Therefore, balancing battery safety and power requirements is crucial for developing batteries with excellent overall performance.

[0087] The particle size, specific surface area, and other parameters of the negative electrode material vary significantly across different battery types. This leads to substantial differences in parameters between different battery types when designing for different particle size, specific surface area, and related parameters, necessitating specialized design for each battery type. For instance, materials or parameters suitable for lithium-ion batteries may not be suitable for sodium-ion batteries. For example, the negative electrode active material in traditional sodium-ion batteries typically uses hard carbon, D... v The 50 is relatively small, about a few micrometers (e.g., 5~6μm), and has a correspondingly larger specific surface area; while lithium-ion batteries more commonly use graphite anodes in traditional technologies, D v 50 is typically in the range of tens to hundreds of micrometers, indicating a relatively small specific surface area.

[0088] In some aspects of this application, a sodium-ion battery and an electrical device are provided, as well as a negative electrode and an application.

[0089] In some aspects of this application, a sodium-ion battery including the negative electrode sheet, an electrical device thereof, and the use of the negative electrode sheet in the preparation of a sodium-ion battery are provided.

[0090] In view of the common technical problems mentioned above, in a first aspect, this application provides a sodium-ion battery, which includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, and the negative electrode active material including hard carbon.

[0091] The negative electrode also satisfies the following condition: 0.6 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 5 μg / m; where, D v 99 represents the particle size corresponding to a cumulative volume distribution percentage of 99% for the negative electrode active material, in μm; D v 50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material, in μm; B represents the specific surface area of ​​the negative electrode sheet, in m². 2 / g.

[0092] In the context of this application, the volumetric cumulative distribution particle size D can be used. v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, referring to the particle size corresponding to the cumulative volume distribution percentage of the material reaching N%, and the particle size is less than or equal to D. v N's volume percentage is N%. D v N can be obtained from the volumetric cumulative distribution curve of the material particles. Unless otherwise specified, the volumetric cumulative distribution curve is accumulated from zero on the smaller particle size side. Let D... v 99. D v 90. D v50. D v For example, D in 10 v 99 refers to the particle size corresponding to a cumulative volume distribution percentage of 99% for a material; D v 90 refers to the particle size corresponding to a cumulative volumetric distribution percentage of 90% for a material; D v 50 refers to the particle size corresponding to a cumulative volumetric distribution percentage of 50% for the material; D v 10 refers to the particle size corresponding to a cumulative volumetric distribution percentage of 10% for the material. (The last part, "D," appears to be a typo and can be left as is.) v For example, 50 means that the particle size of 50% of the material volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. With D v For example, 90 indicates that 90% of the material's volume consists of particles with a diameter less than or equal to D. v 90, and particles accounting for 10% of the material volume have a particle size greater than D. v 90. With D v For example, 10 indicates that particles accounting for 10% of the material volume have a particle size less than or equal to D. v 10, and the particle size of particles accounting for 90% of the material volume is greater than D. v 10. Those skilled in the art will understand D v 99. D v 90. D v 50. D v The meaning of 10 can be determined using instruments and methods known in the field. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd., UK, by referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0093] In the context of this application, (D v 99+D v 50) / 2 can be used to characterize the large particle size in a material, and can be denoted as the "average particle size of large particles". By controlling D v 99 and D v The average value of 50 reflects the particle size level of large particles in the material. A higher value indicates larger particle sizes. According to the inventors' research, larger particle sizes in the negative electrode active material result in higher battery thermal runaway initiation temperatures and better battery safety.

[0094] The negative electrode sheet in the first aspect of this application 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.

[0095] In the context of this application, unless otherwise specified, the specific surface area B of the negative electrode sheet refers to the specific surface area of ​​the aforementioned negative electrode film layer (i.e., without considering the contribution of the negative electrode current collector). Further, the specific surface area B of the negative electrode sheet refers to the ratio of the sum of the outer surface area of ​​the negative electrode film layer and the inner surface area of ​​the internal pores to the weight of the negative electrode film layer, and the unit can be m². 2 / g. The definition of the specific surface area B of the negative electrode sheet can be found in the standard GB / T 19587-2004.

[0096] In this application, the specific surface area B of the negative electrode can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a TriStar II specific surface area and porosity analyzer from Micromeritics, Inc., USA. The test procedure can refer to GB / T 19587-2004. In some embodiments, the specific surface area of ​​the negative electrode sheet can be tested as follows: Select the sample to be tested, which can be a directly prepared negative electrode sheet or a negative electrode sheet disassembled from a battery (in this case, it needs to be cleaned with anhydrous ethanol to remove the electrolyte and dried in a vacuum drying oven at 60°C for 1-2 hours); then use nitrogen or argon as the adsorption gas, and plot the adsorption-desorption curve with a relative pressure P / P0 of 0-0.99 using a specific surface area and porosity analyzer, and calculate the specific surface area of ​​the negative electrode sheet using the BET method, where P represents the equilibrium adsorption pressure and P0 represents the saturated vapor pressure. When the test sample is a negative electrode active material, the negative electrode active material powder can be prepared using the following method: The specific surface area of ​​the active material can be tested as follows: Dry the negative electrode active material in a vacuum drying oven at 200°C for 2 hours; then use the above-mentioned gas adsorption test method to test the specific surface area of ​​the negative electrode active material. In this application, the larger the specific surface area of ​​the negative electrode sheet, the slower the battery thermal runaway reaction rate and the better the battery safety.

[0097] In some embodiments, the particle size and specific surface area of ​​the negative electrode active material can be obtained by the following control or screening methods (but not limited to these methods): Method 1: Prepare materials with different specific surface areas by selecting different negative electrode material precursors such as wheat straw, coconut shell, and asphalt; Method 2: Obtain negative electrode materials with different particle sizes by setting different pulverization times, rotation speeds, and filter screens during the negative electrode material synthesis process.

[0098] In the context of this application, (D) v 99+D v50) / (2×B) is defined as the thermal stability coefficient of the electrode, denoted as S. This parameter can reflect the thermal stability of the electrode. When this value is controlled within a reasonable range (0.6 μg / m~5 μg / m), the electrode can withstand high temperatures and the degree of thermal runaway of the electrode is small.

[0099] By controlling the particle size of the negative electrode active material and the specific surface area of ​​the negative electrode sheet within a certain range, the battery can achieve both a high initial reaction temperature and minimize adverse effects on the reaction rate. In this application, by comprehensively controlling the particle size of the negative electrode active material and the specific surface area of ​​the negative electrode sheet, a combination of high safety and high power is achieved. Furthermore, (D) is defined. v 99+D v 50) / 2 characterizes the large particle size, and this characteristic, together with the specific surface area B of the negative electrode, is used to define the electrode thermal stability coefficient (D) of the negative electrode. v 99+D v By adjusting the thermal stability coefficient of the electrode to a suitable range, the battery can be endowed with high safety and high power characteristics, resulting in excellent high temperature resistance.

[0100] Furthermore, the negative electrode active material includes hard carbon. Hard carbon has a high pyrolysis carbonization temperature, which is beneficial for improving the heat resistance temperature and reducing heat generation. In addition, the internal interlayer spacing of hard carbon is large and the porosity is high, which allows for the embedding of more metal ions. The structure has significantly low expansion, which is beneficial for improving the charge-discharge cycle performance and battery life.

[0101] In this application, the larger the particle size of the negative electrode active material, the higher the thermal runaway initiation temperature of the battery, and the better the battery safety; the larger the specific surface area of ​​the negative electrode sheet, the slower the thermal runaway reaction rate of the battery, and the better the battery safety. However, if (D v 99+D v If (50) / 2 is too large, it will result in lower battery power and energy density. When (D v 99+D v When (50) / (2×B) is less than 0.6 μg / m, the particle size is too small to increase the material reaction temperature, or the specific surface area is too large, which can easily lead to an excessively fast thermal runaway rate; when (D) v 99+D v When (50) / (2×B) is greater than 5 μg / m, the particle size is too large, resulting in too few normal active sites in the battery, which will deteriorate the battery's charge and discharge performance.

[0102] In some embodiments, the negative electrode active material satisfies the following condition: 5 μm ≤ (D v 99+D v 50) / 2 ≤18 μm.

[0103] In some embodiments, the negative electrode active material satisfies the following condition: 6 μm ≤ (D v 99+D v 50) / 2 ≤15 μm.

[0104] In some embodiments, the negative electrode active material satisfies the following condition: 7 μm ≤ (D v 99+D v 50) / 2 ≤12 μm.

[0105] In some embodiments, the negative electrode active material satisfies the following condition: 8 μm ≤ (D v 99+D v 50) / 2 ≤10 μm.

[0106] In some embodiments, the negative electrode active material (D v 99+D v 50) / 2 can also be selected from any one of the following sizes or any two intervals: 5 μm, 5.2 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.5 μm, 7.6 μm, 7.8 μm, 8 μm, 8.2 μm, .4 μm, 8.5 μm, 8.6 μm, .8 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 17.7 μm, etc.

[0107] By reasonably controlling the large particles in the negative electrode active material within a suitable range, it is easier to combine precise control of the specific surface area of ​​the negative electrode active material, thereby better realizing the advantages of high battery safety and high power.

[0108] In some embodiments, the negative electrode sheet satisfies the following condition: 0.7 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 5 μg / m.

[0109] In some embodiments, the negative electrode sheet satisfies the following condition: 0.7 μg / m ≤ (D v 99+D v50) / (2×B) ≤ 4.5 μg / m.

[0110] In some embodiments, the negative electrode sheet satisfies the following condition: 0.8 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 4.2 μg / m.

[0111] In some embodiments, the negative electrode sheet (D) v 99+D v 50) / (2×B) can also be selected from any one or any two of the following intervals: 0.6 μg / m, 0.7 μg / m, 0.8 μg / m, 0.9 μg / m, 1 μg / m, 1.2 μg / m, 1.4 μg / m, 1.5 μg / m, 1.6 μg / m, 1.8 μg / m, 2 μg / m, 2.2 μg / m, 2.5 μg / m, 2.6 μg / m, 2.8 μg / m, 3 μg / m, 3.5 μg / m, 4 μg / m, 4.5 μg / m, 5 μg / m, 5.5 μg / m, 6 μg / m, etc.

[0112] By further controlling the thermal stability coefficient (D) of the electrode v 99+D v Within a suitable range, 50) / (2×B) is beneficial to better balance the impact of large particle size on battery safety and the impact of the specific surface area of ​​the negative electrode on battery power, thereby better balancing high battery safety and high power.

[0113] In some embodiments of this application, the negative electrode active material also satisfies the following condition: (x·D v 10) ≤D v 50 ≤ (y·D v 99); where x = 2.6 and y = 0.4;

[0114] Alternatively, x = 3 and y = 0.3.

[0115] In some embodiments of this application, the negative electrode active material also satisfies the following condition: (x·D v 10) ≤D v 50 ≤ (y·D v 99); where x = 4 and y = 0.3.

[0116] By rationally controlling the D of the negative electrode active material v 50 relative to D v 10. D vA 99 ratio for x and y ensures that both small and large particles in the negative electrode active material have appropriate particle size and content, better avoiding energy density loss caused by large particles. This improves battery safety while maintaining a high energy density. When x is large, the small particle size is too small, resulting in a larger specific surface area, which may reduce the material's temperature tolerance. When x is small, the small particle size is close to the average particle size, potentially leading to insufficient filling of interparticle pores and a lower electrode energy density. When y is large, the large particles are too small and may not effectively fill pores, resulting in a lower measurable electrode density. When y is small, the large particles are too large, leading to a longer ion shuttle path and potentially reducing battery power.

[0117] In some embodiments of this application, the negative electrode sheet satisfies the following condition: 30 mAh·m -2 ≤ C / B≤ 140 mAh·m -2 Where C is the specific capacity of the negative electrode sheet.

[0118] In some implementations, 40 mAh·m -2 ≤ C / B ≤ 125 mAh·m -2 .

[0119] In some embodiments, the C / B ratio of the negative electrode may also be selected from any one or two of the following ranges: 30 mAh·m -2 35 mAh·m -2 40 mAh·m -2 45 mAh·m -2 50 mAh·m -2 55 mAh·m -2 60 mAh·m -2 65 mAh·m -2 70 mAh·m -2 75 mAh·m -2 80 mAh·m -2 85 mAh·m -2 90 mAh·m -2 95mAh·m -2 100 mAh·m -2 105 mAh·m -2 110 mAh·m -2 115 mAh·m -2 120 mAh·m -2 125mAh·m -2 130 mAh·m -2 135 mAh·m -2 140 mAh·m-2 wait.

[0120] The inventors of this application have discovered that the C / B ratio of the negative electrode can reflect its reactivity to a certain extent. By synergistically controlling the specific capacity and specific surface area of ​​the negative electrode, it is beneficial to better control the reaction rate during battery thermal runaway, thereby further improving battery safety. Controlling the specific capacity of the negative electrode to an appropriate level ensures a suitable amount of active sodium ion insertion, resulting in a moderate reaction rate. Furthermore, controlling the specific surface area of ​​the negative electrode within a suitable range ensures appropriate ion insertion / extraction pathways and polarization of the battery's active materials, thus guaranteeing optimal battery power performance.

[0121] When C / B is low (e.g., less than 30 mAh·m), -2 When the specific capacity of the negative electrode active material is low, the battery capacity is low; or when the specific surface area of ​​the negative electrode sheet is large, the reaction rate during thermal runaway is high, and the battery safety is relatively low. When the C / B ratio is high (e.g., greater than 140 mAh·m⁻¹), the battery capacity is low. -2 When the specific capacity of the negative electrode active material is too high, the amount of active ion insertion is too high. Once it gets out of control, the degree of aggression is too high. Alternatively, if the specific surface area of ​​the electrode is very small and the material particle size is large, the ion insertion and extraction path of the battery active material is too long, the polarization is too large, and the battery power performance is relatively poor.

[0122] In some embodiments of this application, the specific capacity C of the negative electrode sheet satisfies 300 mAh / g ≤ C ≤ 350 mAh / g.

[0123] In some embodiments, the specific capacity C of the negative electrode sheet satisfies 310 mAh / g ≤ C ≤ 340 mAh / g.

[0124] In some embodiments, the specific capacity C of the negative electrode sheet may also be selected from any one or any two of the following ranges: 300 mAh / g, 305 mAh / g, 310 mAh / g, 315 mAh / g, 320 mAh / g, 325 mAh / g, 330 mAh / g, 335 mAh / g, 340 mAh / g, 345 mAh / g, 350 mAh / g, etc.

[0125] In this application, the specific capacity of the negative electrode sheet can be measured according to the WI-ATC-2014 specific capacity test details. Electrode processing before testing: The negative electrode sheet can be a directly prepared negative electrode sheet, or a negative electrode sheet disassembled from a battery (in this case, it needs to be cleaned with anhydrous ethanol to remove the electrolyte, and then dried in a vacuum drying oven at 60 °C for 2 hours). Then, multiple small discs are punched using a punching machine, and the average weight W1 of each small disc is taken. The active material on the small discs is then cleaned and dried, and the average weight W2 of the substrate is taken. The weight of the active material is (W1-W2). When the negative electrode slurry is coated on both sides, the weight of the negative electrode active material on one side of the substrate of each small disc is (W1-W2) / 2. The specific capacity is calculated based on the capacity C0 of the small disc: C0 / (W1-W2), in mAh / g. In some embodiments, C0 can be tested as follows: Take a small disc prepared by a die-casting machine, wipe off the active material layer on one side of the substrate with alcohol, inject electrolyte, and fabricate a coin cell. Then charge and discharge it with a 0.1C current between 0V and 2V. The capacity after being fully charged to 2V and then fully discharged to 0V is C0 (in mAh).

[0126] By controlling the specific capacity of the negative electrode sheet, the amount of active sodium ion intercalation can be appropriately controlled, resulting in a moderate reaction rate during battery thermal runaway and improved battery safety.

[0127] In some embodiments of this application, the specific surface area B of the negative electrode sheet is selected from 2.5 m². 2 / g ~10 m 2 / g.

[0128] In some embodiments, the specific surface area B of the negative electrode is selected from 3 m². 2 / g ~7 m 2 / g.

[0129] In some embodiments, the specific surface area B of the negative electrode sheet may also be selected from any one or two of the following ranges: 2.5 m² 2 / g、3 m 2 / g, 3.5 m 2 / g、4 m 2 / g, 4.5 m 2 / g、5 m 2 / g, 5.5 m 2 / g、6 m 2 / g, 6.5m 2 / g、7 m 2 / g, 7.5 m 2 / g、8 m 2 / g, 8.5 m 2 / g、9 m 2 / g, 9.5 m2 / g、10 m 2 / g etc.

[0130] By controlling the specific surface area of ​​the negative electrode sheet and the particle size of the negative electrode active material within a suitable range, the ion insertion / extraction pathway and polarization of the battery active material are moderate, which is more conducive to the performance of the battery power.

[0131] In some embodiments of this application, the position T of the first exothermic reaction peak of the negative electrode sheet in differential scanning calorimetry satisfies 150 °C ≤ T ≤ 180 °C; further, the test conditions for differential scanning calorimetry include: nitrogen atmosphere, heating rate of 5 °C / min ~ 10 °C / min.

[0132] This application relates to differential scanning calorimetry (DSC). Unless otherwise specified, test conditions may include a nitrogen atmosphere and a heating rate of 5 °C / min to 10 °C / min. Non-limiting examples of heating rates include 5 °C / min, 7.5 °C / min, 10 °C / min, etc.

[0133] In some implementations, T satisfies 170 °C ≤ T ≤ 180 °C.

[0134] In some embodiments, T may also be selected from any one or any two of the following: 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, etc.

[0135] Controlling the position T of the first exothermic reaction peak in the differential scanning calorimetry (DSC) analysis of the negative electrode sheet within a suitable range is beneficial to further improve battery safety. If T is too low, it will not improve battery safety, while a higher T presents technical difficulties and requires replacing the organic polymer binder in the traditional electrode powder with a more heat-resistant material, while also increasing the pyrolysis temperature of the negative electrode active material.

[0136] The negative electrode active material of the negative electrode sheet provided in the first aspect of this application includes at least hard carbon.

[0137] In some embodiments, hard carbon accounts for ≥ 50% by mass in the negative electrode active material.

[0138] In some embodiments, hard carbon accounts for ≥90% by mass in the negative electrode active material.

[0139] In some embodiments, the mass percentage of hard carbon in the negative electrode active material may also be selected from any one of the following percentages or any two of the following ranges: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0140] Hard carbon has a high pyrolysis carbonization temperature, and the higher the hard carbon content, the better it is at improving heat resistance and reducing heat generation. In addition, the large interlayer spacing and high porosity of hard carbon structure allow for the embedding of more metal ions, resulting in significantly low structural expansion, which is beneficial for improving the charge-discharge cycle performance and battery life.

[0141] In some embodiments of this application, the negative electrode active material further includes one or more of soft carbon, graphite, and alloyed negative electrodes.

[0142] Based on hard carbon as a negative electrode active material, introducing one or more other types of active materials, such as soft carbon, graphite, and alloyed negative electrodes, can leverage the advantages of these materials to give the battery better overall performance. For example, soft carbon has a low and stable charge / discharge potential plateau, large charge / discharge capacity, high efficiency, and good cycle performance. Graphite, for instance, has advantages such as good conductivity, high initial efficiency, and wide availability. Alloyed negative electrodes offer advantages such as high power and high energy density.

[0143] Negative electrode sheet

[0144] The negative electrode sheet in the first aspect of this application 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. The definition of the negative electrode active material is as described above.

[0145] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0146] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil, aluminum foil, iron foil, or nickel foil may 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 may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc., aluminum, aluminum alloy) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0147] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0148] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0149] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0150] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0151] In some embodiments of this application, a sodium-ion battery is provided, which includes a positive electrode, a negative electrode as described in the first aspect of this application, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode.

[0152] The sodium-ion battery prepared using the negative electrode sheet described in the first aspect of this application possesses the combined advantages of high safety and high power. Typically, a sodium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charging and discharging process, active ions (Na+)... + The electrolyte moves back and forth between the positive and negative electrodes, inserting and removing itself. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0153] It should be understood that, unless otherwise specified, the sodium-ion battery of the first aspect is a secondary battery.

[0154] electrolytes

[0155] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0156] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes a sodium salt of electrolyte and a solvent.

[0157] In some embodiments, the electrolyte sodium salt may be selected from one or more of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, etc.

[0158] In some embodiments, the electrolyte sodium salt includes one or more sodium salts selected from sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, and sodium trifluoromethanesulfonate.

[0159] In some embodiments of this application, the electrolyte further comprises an organic solvent.

[0160] In some embodiments of this application, the organic solvent may include one or more of the following: ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyl tert-butyl ether, etc.

[0161] In some embodiments of this application, the organic solvent may include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), ether solvents (such as dimethyl glycol ether (DME)), tetrahydrofuran (THF), and 2-methyltetrahydrofuran (2-MTHF).

[0162] In some embodiments of this application, the organic solvent may include one or more of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyl tert-butyl ether, etc.

[0163] Sodium salts have high solvability and high conductivity in solvents, which is beneficial for film formation and improving battery power.

[0164] In some embodiments of this application, the electrolyte also includes additives.

[0165] In some embodiments of this application, the additive includes one or more of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonyl lactone (PS), 1,3-propenyl-sulfonyl lactone (PST), succinic anhydride (SA), lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiDFOP), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate (TMSB), ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0166] In some embodiments of this application, the additive includes one or more of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propane sulfonyl lactone (PS), 1,3-propenyl sulfonyl lactone (PST), succinic anhydride (SA), lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiDFOP), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate ester (TMSB).

[0167] By selecting appropriate additives, batteries can quickly form a solid electrolyte interphase (SEI) film, increasing the thickness and stability of the SEI film and improving battery safety.

[0168] In some embodiments, the current during battery formation can be reduced, for example, formation can be performed at a current of 0.05C or 0.1C. Furthermore, the formation temperature can be set at 25°C, thereby obtaining a thicker SEI film. In some embodiments, the negative electrode sheet satisfies the following condition: 0.5 °C ≤ T×M ≤ 6 °C; where T and M are the position of the first exothermic reaction peak and the first stage weight loss rate of the negative electrode sheet, respectively, by differential scanning calorimetry (DSC); furthermore, the test is performed under a nitrogen atmosphere, with a heating rate of 5 °C / min ~ 10 °C / min.

[0169] In some implementations, the negative electrode sheet satisfies the following condition: 0.65 °C ≤ T×M ≤ 5.2 °C.

[0170] In some implementations, the negative electrode sheet satisfies the following condition: 0.75 °C ≤ T×M ≤ 4.5 °C.

[0171] In some embodiments, the T×M of the negative electrode can also be selected from any one or any two of the following ranges: 0.5 °C, 0.52 °C, 0.54 °C, 0.55 °C, 0.56 °C, 0.58 °C, 0.60 °C, 0.65 °C, 0.70 °C, 0.75 °C, 0.80 °C, 0.85 °C, 0.90 °C, 0.95 °C, 1 °C, 1.5 °C, 2 °C, 2.5 °C, 3 °C, 3.5 °C, 4 °C, 4.5 °C, 5 °C, 5.5 °C, 6 °C, etc.

[0172] In this application, the first exothermic reaction S position (T) and the first segment weight loss rate (M) of the negative electrode sheet can be obtained from the DSC spectrum of the negative electrode sheet. M can reflect the amount of decomposition at the solid electrolyte interface (SEI). The DSC test of the negative electrode sheet can refer to the general rules of thermal analysis method in JYT014—1996. Unless otherwise specified, the following test method can be used: dry the electrode sheet in a vacuum drying oven at 60 °C for 6 h, take a sample weight W3, program the temperature to 600 °C under a nitrogen atmosphere, and measure the weight loss rate and DCS exothermic peak of the sample.

[0173] In some implementations, the gas atmosphere is nitrogen, argon, or a combination thereof.

[0174] In some implementations, the heating rate can be 5 °C / min to 10 °C / min, with non-limiting examples such as 5 °C / min, 10 °C / min, etc.

[0175] As mentioned above, this application relates to differential scanning calorimetry. Unless otherwise specified, the test conditions may include: a nitrogen atmosphere and a heating rate of 5 °C / min to 10 °C / min. Non-limiting examples of heating rates include 5 °C / min, 7.5 °C / min, 10 °C / min, etc.

[0176] The inventors of this application hypothesize that T×M can, to some extent, reflect the tolerance of the negative electrode to high temperatures. The particle size of the negative electrode active material affects the starting temperature of the exothermic reaction; the larger the particles, the higher the temperature at which the reaction begins, and the safer the corresponding battery system. However, larger particles can be detrimental to battery power. Therefore, balancing safety and battery power is crucial for the fabrication of batteries with high overall performance. By shifting the position (T) of the first exothermic reaction peak in the differential scanning calorimetry (DSC) analysis of the negative electrode to a higher temperature, the decomposition reaction temperature (corresponding to M) of the solid electrolyte interphase (SEI) film can be increased, which is beneficial for increasing the thickness of the SEI film, thereby further improving safety.

[0177] In some embodiments of this application, the first-stage weight loss rate M of the negative electrode sheet in differential scanning calorimetry satisfies the following condition: 0.25% ≤ M ≤ 3.5%; further, the test conditions for differential scanning calorimetry include: nitrogen atmosphere, and a heating step of 5 °C / min ~ 10 °C / min (e.g., 10 °C / min).

[0178] In some implementations, 0.5% ≤ M ≤ 2.5%.

[0179] In some implementations, 0.65% ≤ M ≤ 2%.

[0180] In some implementations, M may also be selected from any of the following percentages or any two of the following ranges: 0.28%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, 3.3%, etc.

[0181] By controlling the first-stage weight loss rate M of the differential scanning calorimetry (DSC) analysis of the negative electrode sheet within a suitable range, the stability of the SEI interface can be improved, which is beneficial to enhancing battery safety and achieving better ion transport and charge / discharge performance. A lower M indicates a thinner SEI, which is less conducive to battery interface stability and lowers battery safety; however, an excessively thick SEI indicates poor ion transport and deteriorates charge / discharge performance.

[0182] Positive electrode sheet

[0183] 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.

[0184] In some embodiments, the positive electrode comprises a positive electrode active material containing sodium ions. In some of these embodiments, the sodium-ion-containing positive electrode active material comprises one or more of Prussian blue compounds, sodium transition oxides, and polyanionic compounds. The ability to flexibly select suitable positive electrode active materials allows for greater selectivity and wider applicability of sodium-ion batteries.

[0185] The positive electrode active material may include, but is not limited to, one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to the materials listed above, and other known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0186] In some embodiments, the transition metal in the sodium transition metal oxide may be one or more selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of a sodium transition metal oxide is Na. x ZO2, where Z can be one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0187] In some embodiments, the sodium transition metal oxide can be Na. 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It can be one or more of the following: Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba. <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2。

[0188] In some embodiments, the sodium transition metal oxide can be Na. 0.67 Mn 0.7 Ni q M 2 0.3-z O2, where M 2 It can be one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, and Ba, 0 <q≤0.1。

[0189] In some embodiments, the sodium transition metal oxide can be Na. a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0190] In some embodiments, the polyanionic compound can be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal here can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; n represents (YO4).n- The price state.

[0191] In some embodiments, the polyanionic compound may also be a compound containing sodium ions, transition metal ions, or tetrahedral (YO4) ions. )n- A class of compounds containing anionic units and halide anions. The transition metal here can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; and n represents (YO4). n- The valence state; halogens can be one or more of F, Cl and Br.

[0192] In some embodiments, the polyanionic compound may also be a tetrahedral compound (YO4) containing sodium ions. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, n represents the valence state of (YO4)n-; Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents (ZO4)n-. y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0193] In some embodiments, the polyanionic compound may be NaFePO4, Na3V2(PO4)3, NaM'PO4F, and Na3(VO4)2(PO4)3. y )2(PO4)2F 3- 2 y One or more of (0≤y≤1); wherein, M' in NaM'PO4F can be one or more of V, Fe, Mn and Ni.

[0194] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). — A class of compounds. The transition metal here can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of Prussian blue compounds is Na. a Me b Me' c (CN)6, wherein Me and Me' can each independently be one or more of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0195] In some embodiments, the positive electrode active material layer may further include a conductive agent to improve the conductivity of the positive electrode. This application does not impose any particular limitation on the type of conductive agent, which can be selected according to actual needs. As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0196] In some embodiments, the positive electrode film layer may optionally include an adhesive. As a non-limiting example, this adhesive is used to firmly bond the positive electrode active material and an optional conductive agent to the positive electrode current collector. This application does not particularly limit the type of adhesive, which can be selected according to actual needs. As a non-limiting example, the adhesive may be one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0197] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0198] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0199] In some embodiments, the positive current collector can be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, carbon-coated metal foil, and porous metal plate can each be independently selected from one or more of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil with a polymer base film.

[0200] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0201] 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, optional conductive agent, optional binder and any other components, in a solvent (e.g., N-methylpyrrolidone) 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.

[0202] Separating membrane

[0203] In some embodiments, the sodium-ion battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0204] For different battery systems, such as sodium-ion batteries and lithium-ion batteries, the different diameters of sodium and lithium ions lead to different requirements for the structure of the separator. Sodium ions have a larger diameter than lithium ions, thus requiring a more specific thickness. While achieving the separation function, it is also necessary to ensure that the large-diameter sodium ions can pass through, so as to ensure battery safety while maintaining a good battery rate.

[0205] In some embodiments, the material of the separator in the sodium-ion battery of this application can be any material suitable for separators in electrochemical energy storage devices, including, but not limited to, one or more of glass fiber, nonwoven 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.

[0206] In some embodiments, at least one surface of the separator includes an insulating material coating, optionally a ceramic coating.

[0207] In some embodiments, the base material of the separator includes one or more of polyethylene and polypropylene.

[0208] In some embodiments, the thickness of the separator is 5 μm to 15 μm. In some embodiments, the thickness of the separator is 7 μm to 13 μm. Examples of separator thickness include any one or two of the following ranges: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0209] In some embodiments, the shrinkage rate of the separator in the TD direction after heating at 90°C for 1 hour is ≤4%. In some embodiments, the shrinkage rate of the separator in the TD direction after heating at 90°C for 1 hour is selected from 0.5% to 3.5%.

[0210] In this application, the TD direction shrinkage rate refers to the width direction shrinkage rate, which corresponds to the lateral shrinkage rate.

[0211] In this application, the shrinkage rate of the separator can be tested using the following method: Cut a 10 cm × 10 cm separator and place it flat on a smooth glass surface. Then, cut an area of ​​at least 15 cm × 15 cm from A4 paper, cover the separator in the center, and use tape to stick the four corners of the A4 paper to the glass. Then, place it in an oven and heat for 1 hour, and then take it out and measure the size of the separator at this time.

[0212] The smaller the shrinkage rate, the more stable the separator is when the battery is baked at high temperature, and the less likely it is to deform and shrink, thus more effectively avoiding the failure of the positive and negative electrode isolation function and short circuit.

[0213] In some embodiments, the areal density of the separator is selected from 2 g / m³. 2 ~ 6 g / m 2 In some embodiments, the areal density of the separator is selected from 3 g / m³. 2 ~ 5 g / m 2 In some embodiments, the areal density of the separator may also be selected from any one or two of the following ranges: 2 g / m³ 2 2.5 g / m 2 3 g / m 2 3.5 g / m 2 4 g / m 2 4.5 g / m 2 5 g / m 2 5.5 g / m 2 6 g / m 2 wait.

[0214] In this application, the areal density of the separator can be determined using instruments and methods known in the art. For example, the mass of a separator with a certain area can be weighed using a Sartorius electronic balance, and the areal density of the separator can be calculated by dividing the mass of the separator by the area of ​​the separator.

[0215] The higher the areal density, the less likely the separator will be punctured, but the weight of the separator will increase; the lower the areal density, the looser the separator will be, and the easier it will be punctured by the sharp corners of hard carbon to cause a short circuit.

[0216] In some embodiments of this application, the separator membrane satisfies one or more of the following characteristics:

[0217] (tm1): At least one surface of the isolation membrane includes an insulating material coating, optionally, the insulating material coating is a ceramic coating;

[0218] (tm2) The base material of the separator includes one or more of polyethylene and polypropylene;

[0219] (tm3) The thickness of the isolation membrane is 5 μm to 15 μm, and optionally, the thickness of the isolation membrane is 7 μm to 13 μm;

[0220] (tm4) The TD shrinkage rate of the separator after heating at 90 °C for 1 h is ≤4%, optionally, the TD shrinkage rate of the separator after heating at 90 °C for 1 h is selected from 0.5% to 3.5%; and

[0221] (tm5) The areal density of the separator is selected from 2 g / m³. 2 ~ 6 g / m 2 Optionally, the areal density of the separator is selected from 3 g / m³. 2 ~ 5 g / m 2 .

[0222] In another aspect of this application, a negative electrode sheet as described in the first aspect of this application is also provided.

[0223] Another aspect of this application provides the application of the negative electrode sheet described in the first aspect of this application in the preparation of sodium-ion batteries.

[0224] The negative electrode sheet in the first aspect of this application can be used to prepare sodium-ion batteries, thereby obtaining the combined advantages of high safety and high energy density.

[0225] Assembly of sodium-ion batteries

[0226] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0227] In some embodiments, the sodium-ion battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0228] In some implementations, the outer packaging of a sodium-ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a sodium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0229] 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 2 This is an example of a square-structured sodium-ion battery.

[0230] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The sodium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to actual needs.

[0231] In some embodiments, the positive electrode, separator, and negative electrode are stacked in sequence to obtain a battery cell, with the separator positioned between the positive and negative electrode to provide isolation. Alternatively, the battery cell can be obtained by winding. The battery cell is then placed in a packaging shell (which can be a soft pack, a square aluminum shell, a square steel shell, a cylindrical aluminum shell, or a cylindrical steel shell), electrolyte is injected, and the shell is sealed to obtain a sodium-ion battery.

[0232] Secondly, this application provides an electrical device that includes the sodium-ion battery described in the first aspect of this application.

[0233] The electrical device obtained by using the sodium-ion battery provided in the first aspect of this application not only has high safety but also high energy density, which can meet consumers' comprehensive needs for high safety and high performance.

[0234] The sodium-ion battery 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, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices may include, for example, mobile phones and laptops; electric vehicles may include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0235] As the electrical device, a sodium-ion battery can be selected according to its usage requirements.

[0236] Figure 4 Here is an example of an electrical device 6. This electrical 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 sodium-ion batteries for this electrical device, a battery pack or battery module can be used.

[0237] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use sodium-ion batteries as their power source.

[0238] The following describes some 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 detailed technical or conditional specifications are not specified in the embodiments, they are performed according to the description above, or according to the technical or conditional specifications described in the literature in the art, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially, or can be synthesized from commercially available products using conventional methods.

[0239] In the following examples, room temperature refers to 20 °C ~ 30 °C, which can be 25 °C.

[0240] Unless otherwise specified, the specifications and models of the following raw materials are as follows:

[0241] The following embodiments and comparative examples can be prepared with reference to the parameters in Tables 1, 2 and 3 below.

[0242] 1. Preparation of negative electrode sheet

[0243] Preparation of negative electrode 1

[0244] The negative electrode active material (hard carbon), conductive agent (Super P), thickener (sodium carboxymethyl cellulose (CMC), and binder (styrene-butadiene rubber latex (SBR)) were mixed in a mass ratio of 97:0.7:1.8:0.5, added to deionized water as a solvent, and stirred evenly under vacuum to obtain a negative electrode slurry. The solid content of this negative electrode slurry was 56% by weight.

[0245] The particle size control and screening method of the negative electrode active material is as follows: using phenolic resin generated by the reaction of resorcinol and formaldehyde as a precursor, using polyacrylonitrile (PAN) as a carbon source for coating, adjusting the specific surface area and closed pore amount of the material through carbon coating, setting the pyrolysis temperature under nitrogen atmosphere to 1300 °C, and obtaining the target size material after pyrolysis through primary screening and fine screening.

[0246] The aforementioned negative electrode slurry was uniformly coated onto both sides of the negative electrode current collector copper foil using an extrusion coating machine or a transfer coating machine, and dried at 85 °C. Then, it was cold-pressed, trimmed, cut, and slit to obtain a negative electrode sheet with a size of 91 mm × 5680 mm.

[0247] Preparation of negative electrode sheets 2-17: The method is basically the same as that used for negative electrode sheet 1. The difference between negative electrode sheets 2-10, 13, and 14 and negative electrode sheet 1 lies in the size of the negative electrode active material, which is determined using the cumulative volume distribution particle size D shown in Table 1. v 99. D v 50. D v The negative electrode active material is 10. The difference between negative electrode sheets 11-12 and 15-17 and negative electrode sheet 1 is that the type and size of the negative electrode active material are different. See Table 1.

[0248] 2. Preparation of sodium-ion batteries (Examples 1-16 and Comparative Examples 1-4)

[0249] For Examples 1-16 and Comparative Examples 1-4, the methods for obtaining the negative electrode sheet and electrolyte are shown in Table 3. The preparation and assembly methods for the remaining structural components use the same parameters, as shown below.

[0250] 2.1. Selection of Negative Electrode

[0251] Select the negative electrode sheet for each embodiment and comparative example according to Table 3.

[0252] 2.2. Preparation of the positive electrode sheet

[0253] The positive electrode active material Na2MnFe(CN)6, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 96:2.5:1.5 and added to the solvent N-methylpyrrolidone (NMP). The mixture was stirred evenly under vacuum to obtain a slurry for the positive electrode active material layer. The solid content of the slurry was 60% by weight.

[0254] The aforementioned positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to a 90 °C oven for further drying. It was then cut into circular pieces with a diameter of 88 mm × 5450 mm as positive electrode sheets, and subjected to cold pressing, edge trimming, cutting, and slitting to obtain positive electrode sheets with a thickness of 150 μm.

[0255] 2.3. Preparation of the separating membrane

[0256] Using a 7 μm thick polyethylene (PE) membrane as the base membrane for the separator, alumina, sodium carboxymethyl cellulose (CMC), and acrylate in a weight ratio of 93%:3%:4% were added to deionized water and stirred evenly under vacuum to obtain a slurry. The solid content of the slurry was 55% by weight. The obtained slurry was then uniformly sprayed onto both sides of the base membrane to a thickness of 2 μm on each side to obtain the separator.

[0257] 2.4. Preparation of Electrolyte

[0258] In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried sodium salt (NaPF6) was dissolved in the organic solvent ethylene carbonate (EC), followed by the addition of the additive ethylene carbonate (VC), and mixed thoroughly to obtain the electrolyte. The concentration of sodium salt was 1 mol / L. The types and amounts of sodium salt, organic solvent, and additives are shown in Table 3.

[0259] 2.5. Assembly of Sodium-ion Batteries

[0260] The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation. The resulting stack is then wound into a square bare cell, tabs are welded on, and the bare cell is installed in a square aluminum casing. The top cover is laser-welded. After vacuum baking at 80 °C to remove water, the previously prepared electrolyte is injected and the casing is sealed. Following this, the battery undergoes a series of processes including settling at 45 °C, formation (0.02C constant current charging to 3.3 V, then 0.1C constant current charging to 3.6 V), shaping, and capacity testing to obtain a finished hard-shell sodium-ion battery with a thickness of 28 mm, a width of 97.5 mm, and a length of 148 mm.

[0261] 3. Testing Methods

[0262] 3.1. Negative electrode plate

[0263] (1) Volumetric cumulative distribution particle size D of negative electrode active material v N(D) v 99. D v 50. D v 10) test

[0264] Sample pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add sodium dodecyl sulfate as a surfactant, add deionized water as a dispersant, and perform ultrasonic treatment (frequency 120 W, duration 5 min) to ensure that the sample is completely dispersed in the dispersant.

[0265] Test: Following GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, the particle size distribution (D) was determined using a laser particle size analyzer. v N. The LS-909 laser particle size analyzer (Omec) was used for testing. After the sample was poured into the injection tower, it circulated with the solution to the test optical path system. The scattered light emitted by the particles under laser beam irradiation was collected, and its energy distribution was measured. This yielded the particle size distribution characteristics (obscuration level: 8%~12%), ultimately obtaining the material's various density values ​​(D). v The value of N.

[0266] (2) Test of the specific surface area B of the negative electrode sheet

[0267] The nitrogen adsorption specific surface area was tested using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using the TriStar II specific surface area and porosity analyzer from Micromeritics, USA. The test procedure can refer to GB / T 19587-2004.

[0268] The detailed steps are as follows: Select the sample to be tested, which can be the negative electrode sheet directly prepared in the above steps, or the negative electrode sheet disassembled from the battery (in this case, it needs to be cleaned with anhydrous ethanol to remove the electrolyte, and then dried in a vacuum drying oven at 60 °C for 2 hours); then use nitrogen as the adsorption gas, and plot the adsorption-desorption curve with a relative pressure P / P0 of 0 to 0.99 (P is the equilibrium adsorption pressure, P0 is the saturated vapor pressure) using a specific surface area and porosity analyzer, and calculate the specific surface area of ​​the negative electrode sheet using the BET method.

[0269] (3) The thermal stability coefficient S of the negative electrode sheet

[0270] Using the formula S=(D v 99+D v The result is calculated as 50) / 2B. Where, (D v 99+Dv 50) / 2 was determined using the method at point (1), and B was obtained using the method at point (2).

[0271] (4) Differential scanning calorimetry (DSC) analysis

[0272] Referring to the general rules of thermal analysis methods in JYT014—1996, the following test method can be used: Dry the negative electrode sheet in a vacuum drying oven at 60°C for 6 hours, take a sample weight W3, and heat it to 600°C under a nitrogen atmosphere at a heating rate of 10°C / min. Measure the weight loss rate and DCS exothermic peak of the sample to obtain the position T of the first exothermic reaction peak and the first-stage weight loss rate M.

[0273] (5) Reaction rate factor P of the negative electrode

[0274] The formula P=C / B is used for calculation. C is measured according to the method in point (2) of section 1.6.3, and B is obtained using the method in point (2).

[0275] 3.2. Performance of negative electrode sheet and cell

[0276] (1) Specific capacity of the negative electrode

[0277] Specific Capacity: Refer to the WI-ATC-2014 specific capacity test details. Select the sample to be tested; it can be the negative electrode sheet directly prepared in the above steps, or it can be the negative electrode sheet disassembled from the battery (in this case, it needs to be cleaned with anhydrous ethanol to remove the electrolyte, and then dried in a vacuum drying oven at 60 °C for 2 hours). Then, use a punching machine to cut 15 small round pieces with a diameter of 16 mm. Randomly select 12 of these, weigh each small round piece, and record the average weight as W1. Then, clean and dry the active material on the small round pieces, weigh the substrate of each small round piece, and record the average weight as W2. The weight of the negative electrode active material on one side of the substrate on each small round piece is (W1-W2) / 2. Calculate the specific capacity C = 2 × C0 / (W1-W2) based on the capacity C0 of the small round piece, in mAh / g.

[0278] The C0 test method is as follows: Take the remaining three small discs from the above-mentioned punching process, wipe off the active material layer on one side of the substrate with alcohol, use a Na metal sheet as the counter electrode, inject electrolyte (refer to 2.4 of Example 2 above), and fabricate a coin cell. Then charge and discharge it with a 0.1C current between 0V and 2V. The capacity after being fully charged to 2V and then fully discharged to 0V is C0 (mAh).

[0279] (2) Temperature tolerance

[0280] The hot chamber test method was adopted. The heating test method for lithium-ion batteries was referenced in GB38031-2020.

[0281] At 1.22 °C ± 5 °C, the battery was discharged to 0% SOC at 0.33C, allowed to stand for 1 h, and then charged to 100% SOC (the upper limit of the battery's specified operating voltage) at a constant current and constant voltage of 0.33C. The sample was placed in a high-temperature chamber, and the temperature was increased from room temperature to 0°C at a rate of 5°C / min until the battery exploded or the voltage reached 0V. Observation was performed for 1 h.

[0282] SOC represents the state of charge of a battery, which reflects the remaining capacity of the battery. Numerically, it is defined as the ratio of the remaining capacity to the total battery capacity.

[0283] (4) Measurement of 60s pulse discharge power

[0284] The power performance of a battery is determined by measuring its 60-second pulse discharge power.

[0285] More specifically, the battery cell was placed in the Nebula Battery Charge-Discharge Test System at 25°C and charged at a constant current and constant voltage rate of 0.5C to the charging cutoff voltage of 3.75V. After resting for 5 minutes, it was discharged at a specific power to ensure that the battery voltage reached exactly 2V and the discharge stopped at 60s. The power at this time is the 60s pulse discharge power.

[0286] 4. Test Results and Analysis

[0287] The cumulative volume distribution particle size D of the negative electrode sheet v N(D) v 99. D v 50. D v 10) The test and analysis results of electrode specific surface area B, electrode thermal stability coefficient S, DSC analysis, electrode reaction rate factor P, electrode specific capacity C, and electrode reaction rate factor P can be found in Tables 1 and 2. Figure 1 The sodium-ion batteries prepared in each embodiment and comparative example were subjected to DSC analysis and hot box testing to withstand certain temperatures.

[0288] Figure 1 The figures show the exothermic and thermogravimetric curves of the negative electrode sheet obtained by differential scanning calorimetry (DSC) in Example 3. As can be seen from the figures, the first exothermic reaction peak T in the DSC spectrum is approximately 170°C, and the first-stage weight loss rate M in the DSC spectrum is approximately 1.2%.

[0289] Negative electrode plates 1-10 and 15-17 have suitable (D) v 99+D vThe sodium-ion batteries prepared using this electrode in Examples 1-16 all exhibit high tolerable temperatures in hot box tests and high 60s pulse discharge power, with the range of 50) / (2×B) being within the range of 0.6 μg / m to 5 μg / m. They also possess the advantages of high safety and high power.

[0290] For the negative electrode plates 11-14 in Comparative Examples 1-4, the corresponding (D) v 99+D v The 50) / (2×B) value is outside the range of 0.6 μg / m ~ 5 μg / m, and the temperature tolerance and 60s pulse discharge power of the hot box test are inferior to those of the aforementioned embodiments.

[0291] Table 1.

[0292]

[0293] Table 2.

[0294]

[0295] Where S=(D v 99+D v 50) / (2×B).

[0296] It should be noted that the position T of the first exothermic reaction peak of DSC for multiple negative electrode plates is recorded as 180°C in Table 2. This is a rounded result, and there are slight fluctuations between the actual values.

[0297] Table 3.

[0298]

[0299] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0300] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. The above-described embodiments only illustrate several embodiments of this application, and their descriptions are relatively detailed, but they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this application without departing from the spirit of this application. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A sodium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising hard carbon; The negative electrode sheet also satisfies the following condition: 0.6 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 5 μg / m, wherein, D v 99 represents the particle size corresponding to the cumulative volume distribution percentage of 99% of the negative electrode active material, in units of μm; D v 50 represents the particle size corresponding to the cumulative volume distribution percentage of 50% of the negative electrode active material, in units of μm; B represents the specific surface area of the negative electrode sheet, in m2 / g. 2 / g.

2. The sodium-ion battery of claim 1, wherein, The negative active material satisfies the following condition: 5 μm ≤ (D v 99 + D v 50) / 2 ≤ 18 μm.

3. The sodium-ion battery of claim 2, wherein, The negative active material satisfies the following condition: 5 μm ≤ (D v 99 + D v 50) / 2 ≤ 15 μm.

4. The sodium-ion battery of claim 2, wherein, The negative active material satisfies the following condition: 6 μm ≤ (D v 99 + D v 50) / 2 ≤ 15 μm.

5. The sodium-ion battery of claim 2, wherein, The negative electrode active material satisfies the following condition: 5.5 μm ≤ (D v 99 + D v 50) / 2 ≤ 13.5 μm.

6. The sodium-ion battery of claim 2, wherein, The negative active material satisfies the following condition: 7 μm ≤ (D v 99 + D v 50) / 2 ≤ 12 μm.

7. The sodium-ion battery of any one of claims 1-6, wherein, The negative electrode sheet satisfies the following conditions: 0.7 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 4.5 μg / m.

8. The sodium-ion battery of claim 7, wherein, The negative electrode sheet satisfies the following condition: 0.8 μg / m ≤ (D v 99 + D v 50) / (2 x B) ≤ 4.2 μg / m.

9. The sodium-ion battery of claim 7, wherein, The negative electrode sheet satisfies the following conditions: 1 μg / m ≤ (D v 99+D v 50) / (2×B) ≤ 4 μg / m.

10. The sodium-ion battery of any one of claims 1-9, wherein, The negative active material also satisfies the following condition: (x · D v 10) ≤ D v 50 ≤ (y · D v 99); wherein x = 2.6, and y = 0.

4.

11. The sodium-ion battery of claim 10, wherein, The negative electrode active material also satisfies the following condition: (x · D v 10) ≤ D v 50 ≤ (y · D v 99); wherein x = 3, and y = 0.

3.

12. The sodium-ion battery of any one of claims 1-11, wherein, The negative electrode sheet also satisfies the following condition: 30 mAh·m -2 ≤ C / B ≤ 140 mAh·m -2 ; wherein C is the specific capacity of the negative electrode sheet.

13. The sodium-ion battery of claim 12, wherein, 40 mAh·m -2 ≤ C / B ≤125 mAh·m -2 .

14. The sodium-ion battery of any one of claims 1-13, wherein, a gram capacity C of the negative electrode sheet satisfies a condition of 300 mAh / g ≤ C ≤ 350 mAh / g.

15. The sodium-ion battery of claim 14, wherein, a gram capacity C of the negative electrode sheet satisfies a condition of 310 mAh / g ≤ C ≤ 340 mAh / g.

16. The sodium-ion battery of any one of claims 1-15, wherein, The B is selected from 2.5 m 2 / g ~10 m 2 / g.

17. The sodium-ion battery of claim 16, wherein, The B is selected from 3 m 2 / g ~7 m 2 / g.

18. The sodium-ion battery of any one of claims 1-17, wherein, a first exothermic reaction peak position T of a differential scanning calorimetry analysis of the negative electrode sheet satisfies a condition of 150 °C ≤ T ≤ 180 °C; wherein, a test condition of the differential scanning calorimetry analysis comprises a nitrogen atmosphere and a heating rate of 10 °C / min.

19. The sodium-ion battery of claim 18, wherein, 170 °C ≤ T ≤ 180 °C.

20. The sodium-ion battery of any one of claims 1-19, wherein, the negative electrode active material further comprises one or more of soft carbon, graphite, and alloying negative electrode; optionally, the negative electrode active material comprises hard carbon and graphite.

21. The sodium-ion battery of claim 20, wherein, a mass ratio of hard carbon in the negative electrode active material is ≥ 50%.

22. The sodium-ion battery of claim 20, wherein, a mass ratio of hard carbon in the negative electrode active material is greater than or equal to 65% and less than or equal to 100%.

23. The sodium-ion battery of claim 20, wherein, a mass ratio of hard carbon in the negative electrode active material is greater than or equal to 90% and less than or equal to 100%.

24. The sodium-ion battery of any one of claims 1-23, wherein, the sodium-ion battery is a secondary battery, the sodium-ion battery comprising a positive electrode sheet, the negative electrode sheet of any one of claims 1-23, a separator, and an electrolyte, the separator being disposed between the positive electrode sheet and the negative electrode sheet.

25. The sodium-ion battery of claim 24, satisfying one, two, or three of the following characteristics: the electrolyte comprises an electrolyte sodium salt, the electrolyte sodium salt comprising one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethylsulfonate, sodium bisfluorosulfonylimide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, and sodium difluorophosphate; the electrolyte further comprises an organic solvent, the organic solvent comprising one or more of vinyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, methyl acetate, ethyl propionate, fluoroethylenecarbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether; the electrolyte further comprises an additive, the additive comprising one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,3-propenyl-sulfonic acid inner ester, succinic anhydride, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyrosulfone, methyl ethyl sulfone, and diethyl sulfone.

26. The sodium-ion battery of claim 24 or 25, which satisfies one, two, or three of the following characteristics: the electrolyte sodium salt comprises one or more sodium salts of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, and sodium trifluoromethylsulfonate; the electrolyte further comprises an organic solvent, which comprises one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; the electrolyte further comprises an additive, which comprises one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,3-propenyl-sulfonic acid inner ester, succinic anhydride, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate.

27. The sodium-ion battery of any one of claims 24-26, wherein, the negative electrode tab satisfies the following condition: 0.5 °C ≤ TxM ≤ 6 °C; wherein, T and M are the first exothermic reaction peak position and the first stage weight loss rate of the negative electrode tab in differential scanning calorimetry analysis, respectively, and the test conditions of the differential scanning calorimetry analysis comprise: nitrogen atmosphere, and a heating rate of 10 °C / min.

28. The sodium-ion battery of any one of claims 24-27, wherein, the first stage weight loss rate M of the negative electrode tab in differential scanning calorimetry analysis satisfies the following condition: 0.25% ≤ M ≤ 3.5%; wherein, the test conditions of the differential scanning calorimetry analysis comprise: nitrogen atmosphere, and a heating rate of 10 °C / min.

29. The sodium-ion battery of any one of claims 24-28, wherein, the positive electrode tab comprises a sodium-ion-containing positive electrode active material, which comprises one or more of Prussian blue compounds, sodium transition metal oxides, and polyanion compounds.

30. The sodium-ion battery of claim 29, wherein, the transition metal in the sodium transition metal oxide comprises one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Optionally, the sodium transition metal oxide is Na x Z02, where Z includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 < x < 1 ; Optionally, the sodium transition metal oxide is Na 1-x Cu h Fe k Mn l M 1 m O 2-y wherein M 1 includes one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 < x < 0.33, 0 < h < 0.24, 0 < k < 0.32, 0 < l < 0.68, 0 < m < 0.1, h + k + l + m = 1, 0 < y < 0.2; Optionally, the sodium transition metal oxide is Na 0.67 Mn 0.7 Ni q M 2 0.3-z O2, wherein M 2 including one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, and Ba, 0 < q < 0.1; Optionally, the sodium transition metal oxide is Na a Li b Ni c Mn d Fe e O2, wherein 0.67 < a < 1, 0 < b < 0.2, 0 < c < 0.3, 0.67 < d + e < 0.8, b + c + d + e = 1.

31. The sodium-ion battery of claim 29, wherein, the polyanionic compound is a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4)n- anion unit, where the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents the valence state of (YO4)n- n- the polyanionic compound is a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4)n- anion unit, where the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents the valence state of (YO4)n- n- the polyanionic compound is a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4)n- anion unit, where the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents the valence state of (YO4)n- )n- the polyanionic compound is a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4)n- anion unit, where the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents the valence state of (YO4)n- n- the polyanionic compound is a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4)n- anion unit, where the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents the valence state of (YO4)n- or, The polyanionic compound is a tetrahedral (YO4) compound containing sodium ions. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds containing optional halide anions, where Y includes one or more of P, S, and Si, n represents the valence state of (YO4)n-; Z represents a transition metal, including one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents (ZO4)n-. y ) m+ The valence state of the halogen includes one or more of F, Cl, and Br; optionally, the polyanionic compounds are NaFePO4, Na3V2(PO4)3, NaM'PO4F, and Na3(VO y )2(PO4)2F 3- 2 y One or more of the following, 0≤y≤1, wherein M' in NaM'PO4F includes one or more of V, Fe, Mn and Ni.

32. An electrical device, comprising: comprising the sodium-ion battery of any one of claims 1-31.

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