Sodium ion battery and electronic device

Abstract

The invention provides a sodium ion battery and electronic equipment, the sodium ion battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one side of the positive current collector; the positive electrode active material layer comprises a positive electrode active material and a thermal expansion microcapsule, and the mass percentage of the thermal expansion microcapsule relative to the mass of the positive electrode active material is less than or equal to 3%. The sodium ion battery provided by the invention has relatively high safety, and also can relatively well consider the electrochemical performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a sodium ion battery and an electronic device. Background Art

[0002] With the widespread adoption of renewable energy and the growing demand for energy storage worldwide, sodium-ion batteries (SIBs), due to their abundant sodium resources and low cost, have become a promising option for large-scale energy storage. However, SIBs still face numerous challenges in terms of safety and electrochemical performance. Thermal runaway is a major safety risk in SIBs. For example, when the internal temperature of a battery rises sharply due to factors such as overcharging, short circuiting, or high external temperatures, it can trigger a series of exothermic reactions, leading to serious accidents such as battery fires and explosions. Summary of the Invention

[0003] Based on this, the present application provides a sodium ion battery and an electronic device, which can alleviate or prevent the occurrence of thermal runaway problems in sodium ion batteries and improve safety.

[0004] A first aspect of the present application provides a sodium ion battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector;

[0005] The positive electrode active material layer includes a positive electrode active material and thermally expandable microcapsules, and a mass percentage of the thermally expandable microcapsules relative to the mass of the positive electrode active material is less than or equal to 3%.

[0006] In some embodiments of the present application, one or more of the following conditions are met:

[0007] (1) The mass percentage of the thermally expandable microcapsules relative to the mass percentage of the positive electrode active material is 0.5% to 3%, and can be optionally 0.5% to 2.5%;

[0008] (2) The average particle size D0 of the thermally expandable microcapsules and the particle size D50 of the positive electrode active material satisfy the following relationship: 1 / 12≤D0 / D50≤10.

[0009] In some embodiments of the present application, one or more of the following conditions are met:

[0010] (1) The average particle size D0 of the thermally expandable microcapsules is 1 μm to 30 μm, and can be optionally 5 μm to 18 μm;

[0011] (2) The density of the thermally expandable microcapsules is 0.3 g / cm 3 ~0.8g / cm 3 .

[0012] In some embodiments of the present application, one or more of the following conditions are met:

[0013] (1) The particle size D50 of the positive electrode active material is 3 μm to 12 μm; optionally 5 μm to 8 μm;

[0014] (2) The specific surface area of ​​the positive electrode active material is 1.3 m 2 / g~3.0m 2 / g.

[0015] In some embodiments of the present application, the positive electrode active material includes a sodium ion positive electrode material and a fast ion conductor layer covering at least a portion of the surface of the sodium ion positive electrode material;

[0016] Optionally, the thickness of the fast ion conductor layer is 10 nm to 50 nm;

[0017] Optionally, the fast ion conductor layer comprises Na3Zr2Si2PO 12 ;

[0018] Optionally, the sodium ion diffusion coefficient of the positive electrode active material is greater than or equal to 1×10 -10 cm 2 / s.

[0019] In some embodiments of the present application, the thermally expandable microcapsule comprises a capsule core and a capsule wall surrounding the capsule core, the material of the capsule core comprises liquid hydrocarbon, and the material of the capsule wall comprises a thermoplastic polymer;

[0020] Optionally, the capsule wall has a thickness of 2 μm to 15 μm.

[0021] In some embodiments of the present application, the boiling point of the liquid hydrocarbon is 105°C to 125°C, and the softening point of the thermoplastic polymer is 100°C to 240°C.

[0022] In some embodiments of the present application, one or more of the following conditions are met:

[0023] (1) The liquid hydrocarbon includes one or more of n-octane, 2-methyloctane and methylcycloheptane;

[0024] (2) The thermoplastic polymer includes an acrylonitrile-based polymer;

[0025] Optionally, the acrylonitrile-based polymer comprises structural units derived from a first monomer and structural units derived from a second monomer;

[0026] The first monomer includes acrylonitrile, and the second monomer includes one or more of acrylonitrile, butadiene, styrene, and methyl methacrylate;

[0027] Further optionally, the acrylonitrile-based polymer includes one or more of polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, and acrylonitrile-methyl methacrylate copolymer.

[0028] In some embodiments of the present application, the positive electrode active material layer further includes a binder and a conductive agent, and the mass ratio of the positive electrode active material, the thermally expandable microcapsules, the conductive agent and the binder is k:f:p:q, and k+f+p+q=100, wherein k is 95~99, f is 0.5~3, p is 0.5~2.5, and q is 1~3.

[0029] The second aspect of the present application provides an electrical device comprising the sodium ion battery of the first aspect of the present application.

[0030] The sodium-ion battery provided in this application incorporates thermally expandable microcapsules within the positive electrode sheet. These microcapsules exhibit a rapid thermal response, promptly initiating a thermal shutdown mechanism when the battery reaches a high temperature (e.g., just after reaching the thermal runaway threshold). These microcapsules rapidly expand and form a thermal barrier, preventing heat propagation, thereby effectively preventing battery overheating and improving safety. Furthermore, by controlling the mass ratio of the thermally expandable microcapsules to the positive electrode active material within an appropriate range, the thermally expandable microcapsules achieve good compatibility with the positive electrode active material, making them less likely to affect the structure of the positive electrode active material. Furthermore, the microcapsules are less likely to aggregate during the battery's charge and discharge processes and are less likely to chemically react with other components in the positive electrode active material layer. This improves battery safety while also providing a good balance between electrochemical performance and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the heat-absorbing microcapsule in Example 1.

[0032] Reference numerals: 11 capsule core; 12 capsule wall. DETAILED DESCRIPTION

[0033] To facilitate understanding of the present application, the present application will be described in more detail below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0034] For simplicity, this application only explicitly discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value may serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that, unless otherwise stated, the term "and / or" used herein includes any and all combinations of one or more related listed items, "above" and "below" are inclusive of the number, and the meaning of "multiple" in "one or more" is more than two.

[0036] As used herein, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is deemed to be continuous and includes the two numerical endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. "Numerical interval" allows for a broad range of numerical interval types including percentage intervals, ratio intervals, and ratio intervals.

[0037] In this document, if a method flow involves multiple steps, unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be performed in an order other than the order described. Moreover, any step can include multiple sub-steps or multiple stages, and these sub-steps or stages do not necessarily need to be completed at the same time, but can be performed at different times, and their execution order does not necessarily need to be sequential, but can be performed in rotation, alternation, or simultaneously with other steps or parts of sub-steps or stages of other steps.

[0038] The above disclosure of the present application is not intended to describe every disclosed embodiment or every implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0039] At present, in order to improve battery safety, traditional battery thermal management systems mainly rely on external devices such as heat sinks and fans. These methods not only increase the complexity and cost of the battery system, but also have a slow response speed when dealing with sudden thermal runaway situations, and cannot fundamentally solve the thermal safety problems inside the battery.

[0040] Based on this, some studies have attempted to introduce thermosensitive materials into sodium-ion positive electrode materials to achieve thermal shutdown function. However, the inventors found that the thermosensitive materials used in these studies have deficiencies in terms of compatibility with sodium-ion positive electrode materials, precise control of thermal shutdown temperature, and impact on battery electrochemical performance. For example, some thermosensitive materials will agglomerate or react chemically with other components during the battery charging and discharging process, resulting in a decrease in the battery's electrochemical performance; some thermal shutdown materials have a wide thermal response temperature range, and are unable to activate the thermal shutdown mechanism in time when the battery temperature just reaches the thermal runaway threshold, and the response speed is slow. In order to solve the aforementioned technical problems, the inventors proposed the following technical solution of this application.

[0041] In a first aspect, the present application provides a sodium ion battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector;

[0042] The positive electrode active material layer includes a positive electrode active material and thermally expandable microcapsules, and a mass percentage of the thermally expandable microcapsules relative to the mass of the positive electrode active material is less than or equal to 3%.

[0043] As an example, in the positive electrode active material layer, the percentage of the mass of the thermally expandable microcapsules relative to the mass of the positive electrode active material can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3% or any range thereof.

[0044] The sodium-ion battery provided in this application incorporates thermally expandable microcapsules within the positive electrode sheet. These microcapsules exhibit a rapid thermal response, promptly initiating a thermal shutdown mechanism when the battery reaches a high temperature (e.g., just after reaching the thermal runaway threshold). These microcapsules rapidly expand and form a thermal barrier, preventing heat propagation, thereby effectively preventing battery overheating and improving safety. Furthermore, by controlling the mass ratio of the thermally expandable microcapsules to the positive electrode active material within an appropriate range, the thermally expandable microcapsules achieve good compatibility with the positive electrode active material, making them less likely to affect the structure of the positive electrode active material. Furthermore, the microcapsules are less likely to aggregate during the battery's charge and discharge processes and are less likely to chemically react with other components in the positive electrode active material layer. This improves battery safety while also providing a good balance between electrochemical performance and performance.

[0045] In some embodiments, the mass percentage of the thermally expandable microcapsules relative to the mass of the positive electrode active material is 0.5% to 3%, and optionally 0.5% to 2.5%. This allows for better compatibility between the thermally expandable microcapsules and the positive electrode active material, making them less likely to affect the structure of the positive electrode active material, less likely to aggregate during battery charge and discharge, and less likely to chemically react with other components in the positive electrode active material layer. This improves battery safety while also providing better electrochemical performance.

[0046] In some embodiments, the average particle size D0 of the thermally expandable microcapsules and the particle size D50 of the positive electrode active material satisfy the following relationship: 1 / 12 ≤ D0 / D50 ≤ 10. For example, D0 / D50 can be 1 / 12, 1 / 10, 1 / 8, 1 / 6, 1 / 4, 1 / 2, 1 / 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any range thereof. Thus, the thermally expandable microcapsules and the positive electrode active material have an appropriate particle size combination. This appropriate particle size combination facilitates more uniform dispersion of the positive electrode slurry, achieves better compatibility between the thermally expandable microcapsules and the positive electrode active material, and is less likely to agglomerate during battery charge and discharge, and is less likely to chemically react with other components in the positive electrode active material layer. This improves battery safety while also better balancing electrochemical performance.

[0047] In some embodiments, the average particle size D0 of the thermally expandable microcapsules is 1 μm to 30 μm, and can optionally be 5 μm to 18 μm. For example, the average particle size D0 of the thermally expandable microcapsules can be 1 μm, 4 μm, 8 μm, 13 μm, 16 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 30 μm, or within a range consisting of any of the above values. This facilitates a more uniform dispersion of the thermally expandable microcapsules in the positive electrode active material layer, making them less likely to agglomerate during battery charging and discharging, and less likely to affect the structure of the positive electrode active material, thereby improving battery safety while better balancing electrochemical performance.

[0048] In some embodiments, the density of the thermally expandable microcapsules is 0.3 g / cm 3 ~0.8g / cm 3 For example, the density of thermally expandable microcapsules can be 0.3 g / cm 3 , 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 Or within the range of any of the above values. This helps to better balance the safety and electrochemical performance of the battery.

[0049] In some embodiments, the particle size D50 of the positive electrode active material is 3 μm to 12 μm, or optionally 5 μm to 8 μm. For example, the particle size D50 of the positive electrode active material can be 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 12 μm, or any range thereof. This helps to better balance battery safety and electrochemical performance.

[0050] In some embodiments, the specific surface area of ​​the positive electrode active material is 1.3 m 2 / g~3.0m 2 / g. For example, the specific surface area of ​​the positive electrode active material can be 1.3m 2 / g,1.5m 2 / g,1.7m 2 / g,1.9m 2 / g, 2.1m 2 / g,2.3m 2 / g,2.5m 2 / g,2.7m 2 / g,2.9m 2 / g,3.0m 2 / g or within the range of any of the above values. This helps to better balance the safety and electrochemical performance of the battery.

[0051] In some embodiments, the positive electrode active material includes a sodium ion positive electrode material and a fast ion conductor layer coated on at least a portion of the surface of the sodium ion positive electrode material. The thermally expandable microcapsules mixed with the positive electrode active material may affect the ion conductivity of the positive electrode active material. Therefore, providing the fast ion conductor layer on at least a portion of the surface of the sodium ion positive electrode material can improve the ion conductivity of the positive electrode active material, thereby achieving a better balance between safety and electrochemical performance of the battery.

[0052] In some embodiments, the thickness of the fast ion conductor layer is 10 nm to 50 nm. For example, the thickness of the fast ion conductor layer can be 10 nm, 12 nm, 23 nm, 34 nm, 46 nm, 50 nm, or any range thereof. This improves ion conductivity while also enhancing mechanical properties of the positive electrode active material and reducing interfacial impedance.

[0053] In some embodiments, the fast ion conductor layer comprises Na3Zr2Si2PO 12 .

[0054] In some embodiments, the sodium ion diffusion coefficient of the positive electrode active material is greater than or equal to 1×10 -10 cm 2 / s.

[0055] As a non-limiting example, the fast ion conductor layer can be coated on the sodium ion positive electrode material by the following method: using the material of the fast ion conductor layer as a target material, the sodium ion positive electrode material is subjected to magnetron sputtering (power such as 60 W, pressure such as 1.0 Pa) in an argon atmosphere, so that the fast ion conductor layer can be deposited and coated on the surface of the sodium ion positive electrode material.

[0056] In some embodiments, the sodium ion positive electrode material includes at least one of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and one or more other conventionally known materials that can be used as sodium ion battery positive electrode materials may also be used.

[0057] In some embodiments, the transition metal in the sodium transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0058] In some embodiments, the polyanionic compound may be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence.

[0059] In some embodiments, the polyanionic compound may also be a compound having sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0060] In some embodiments, the polyanionic compound is, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0061] In some embodiments, the Prussian blue compound may be a compound having sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0062] In some embodiments, see Figure 1 The thermally expandable microcapsules include a capsule 11 and a capsule wall 12 surrounding the capsule core 11. The capsule core 11 is made of a liquid hydrocarbon, and the capsule wall 12 is made of a thermoplastic polymer. When the battery temperature reaches the thermal runaway threshold, the thermoplastic polymer in the capsule wall softens, while the liquid hydrocarbon in the capsule core vaporizes. This increases the internal pressure of the thermally expandable microcapsules, causing them to expand and form a thermal barrier, preventing heat from spreading.

[0063] In some embodiments, the capsule wall has a thickness of 2 μm to 15 μm. For example, the capsule wall thickness can be 2 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, or any range thereof. Thus, the thermally expandable microcapsules have high mechanical strength and good solvent resistance, and can effectively serve as a heat blocker in the positive electrode active material layer.

[0064] In some embodiments, the boiling point of the liquid hydrocarbon is 105°C to 125°C, and the softening point of the thermoplastic polymer is 100°C to 240°C. The thermoplastic polymer has a suitable softening point, allowing it to soften quickly during thermal runaway, facilitating the rapid expansion and enlargement of the thermally expandable microcapsules, thereby facilitating rapid thermal isolation. Furthermore, the combination of hydrocarbons with these boiling points narrows the thermal response temperature range, enabling the thermal shutdown mechanism to be activated promptly as soon as the battery temperature reaches the thermal runaway threshold, thereby achieving a faster thermal response.

[0065] In some embodiments, the liquid hydrocarbon comprises one or more of n-octane, 2-methyloctane, isobutane, isopentane, and methylcycloheptane.

[0066] In some embodiments, the thermoplastic polymer includes an acrylonitrile-based polymer. The acrylonitrile-based polymer can achieve a faster thermal response and has a higher mechanical strength, which is conducive to the thermal expansion microcapsules playing an effective and stable heat blocking role in the positive electrode active material layer.

[0067] It is understood that the "acrylonitrile-based polymer" mentioned in this application refers to a polymer formed by homopolymerization or copolymerization with other monomers using acrylonitrile as the main monomer.

[0068] In some embodiments, the acrylonitrile-based polymer includes structural units derived from a first monomer and structural units derived from a second monomer; the first monomer includes acrylonitrile, and the second monomer includes one or more of acrylonitrile, butadiene, styrene, and methyl methacrylate.

[0069] In some embodiments, the acrylonitrile-based polymer includes one or more of polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, and acrylonitrile-methyl methacrylate copolymer.

[0070] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent. The mass ratio of the positive electrode active material, the thermally expandable microcapsules, the conductive agent, and the binder is k:f:p:q, and k+f+p+q=100, where k is 95-99, f is 0.5-3, p is 0.5-2.5, and q is 1-3. This helps to better balance battery safety and electrochemical performance.

[0071] It is understood that the binder and conductive agent used in this application are conventional binders and conductive agents that can be used in positive electrode sheets. For example, the binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); and the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] In a second aspect, the present application provides a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector;

[0073] The positive electrode active material layer includes a positive electrode active material and thermally expandable microcapsules, and a mass percentage of the thermally expandable microcapsules relative to the mass of the positive electrode active material is less than or equal to 3%.

[0074] In some embodiments, the positive electrode plate is the positive electrode plate in the sodium ion battery of the first aspect of the present application.

[0075] The positive electrode plate of the second aspect of the present application plays the same or similar role as that in the sodium ion battery of the first aspect, and will not be described in detail here.

[0076] In a third aspect, the present application provides an electrical device comprising the sodium ion battery of the first aspect of the present application.

[0077] Example

[0078] The following are specific examples, which describe the present disclosure in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0079] In the following embodiments, the thermally expandable microcapsules all use Matsumoto microspheres, model of which is Matsumoto microspheres F-65. The wall material of the Matsumoto microspheres is acrylonitrile-methyl methacrylate copolymer, the core material is isobutane, and the wall thickness is 2 μm.

[0080] Example 1

[0081] (1) Preparation of positive electrode

[0082] Sodium vanadium phosphate was used as the positive electrode active material. Carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were added as the conductive agent, with the mass ratio of the positive electrode active material, carbon black, carbon nanotubes, and binder being 96:1.2:0.8:2. Matsumoto microspheres were then added, accounting for 2.5% of the total mass of the positive electrode active material, along with N-methylpyrrolidone (NMP) as the solvent. Thorough mixing was performed in a stirring apparatus to ensure uniform dispersion of the components, resulting in a positive electrode slurry with excellent fluidity and stability. The prepared positive electrode slurry was evenly coated on both sides of an aluminum foil current collector. After drying and roller pressing, the positive electrode sheet was formed.

[0083] Among them, the particle size D50 of the positive electrode active material is 7 μm and the specific surface area is 9.55 m 2 / g; the average particle size D0 of Matsumoto microspheres is 8μm and the density is 1200kg / m 3 , D0 / D50=8 / 7.

[0084] (2) Preparation of negative electrode sheet

[0085] Hard carbon is used as the negative electrode active material, where the D50 of the hard carbon is 9 μm and the specific surface area is 4.2 m 2 The negative electrode active material, thickener carboxymethyl cellulose (CMC), conductive agent carbon black, and binder styrene-butadiene rubber (SBR) were dissolved in deionized water at a mass ratio of 95:1.5:1:2.5. The mixture was stirred and dispersed in a vacuum blender to form a uniform, bubble-free slurry, which was then evenly coated on both sides of a copper foil to form a negative electrode sheet.

[0086] (3) Packaging and formation

[0087] The positive electrode sheets, separators, and negative electrode sheets are stacked to form a battery cell. The cells have tabs on the same side. The tabs are welded to the current collector using an ultrasonic welder and then encapsulated with aluminum-plastic film. After the cells are baked, the aforementioned non-aqueous electrolyte is injected into the cells and, after chemical composition, a sodium-ion battery is prepared. The non-aqueous electrolyte comprises the following: a solvent comprising EC (ethylene carbonate), PC (propylene carbonate), EMC (ethyl methyl carbonate), and EP (ethyl phosphate) in a mass ratio of 5:25:30:40; sodium salts comprising NaPF6 and NaFSI, each with a molar concentration of 0.5 mol / L; and additives comprising DTD (ethylene sulfate) and FEC (fluoroethylene carbonate), each accounting for 0.5% and 1% by mass of the electrolyte, respectively.

[0088] Example 2

[0089] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the amount of Matsumoto microspheres added accounts for 0.5% of the total mass of the positive electrode active material.

[0090] Example 3

[0091] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the amount of Matsumoto microspheres added accounts for 3% of the total mass of the positive electrode active material.

[0092] Example 4

[0093] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the average particle size D0 of the Matsumoto microspheres is 5 μm, and D0 / D50=5 / 7.

[0094] Example 5

[0095] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the average particle size D0 of the Matsumoto microspheres is 30 μm, and D0 / D50=30 / 7.

[0096] Example 6

[0097] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the particle size D50 of the positive electrode active material is 3 μm, and D0 / D50=8 / 3.

[0098] Example 7

[0099] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the particle size D50 of the positive electrode active material is 12 μm, and D0 / D50=8 / 12.

[0100] Example 8

[0101] The preparation process is similar to that of Example 1, with the main difference being that in step (1), the positive electrode active material is sodium vanadium phosphate coated with a fast ion conductor layer, and the material of the fast ion conductor layer is Na3Zr2Si2PO 12 , with a thickness of 12nm.

[0102] Comparative Example 1

[0103] The preparation method is similar to that of Example 1, with the main difference being that in step (1), the Matsumoto microspheres are omitted.

[0104] Comparative Example 2

[0105] The preparation method is similar to that of Example 1, with the main difference being that in step (1), the amount of Matsumoto microspheres added accounts for 5% of the total mass of the positive electrode active material.

[0106] The sodium ion batteries prepared in Examples 1-8 and Comparative Examples 1-2 were subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0107] Among them, the test conditions or test standards for each performance test item are as follows:

[0108] (1) Room temperature ionic conductivity test

[0109] The powder material is pressed into sheet samples (such as discs) of different densities by hot pressing or cold pressing, at a pressure of, for example, 10 MPa, and the density is increased by sintering (such as 650°C).

[0110] Electrode preparation: Spray conductive powder (such as gold, platinum, carbon powder) on both sides of the sheet sample to form a blocking circuit to prevent electron conduction from interfering with the conductivity test.

[0111] Impedance test: Applicable to the measurement of resistance by AC impedance spectroscopy (EIS), the frequency range is usually 10 -2 Hz to 10 6 Hz, amplitude 2-30mV. Calculate conductivity: Use the formula σ = L / (R * S) (σ is conductivity, L is thickness, R is resistance, and S is area), combined with the density model, to extrapolate to the theoretical conductivity at 100% density.

[0112] (2) Thermal runaway test

[0113] At 25°C ± 3°C, charge the sodium ion battery to 3.4V at a constant current and constant voltage of 0.5C, with a cut-off current of 0.05C; and leave it for 30 minutes.

[0114] The battery is then placed in a heating device and the temperature is gradually increased at a pre-set rate of 5°C / min. Closely monitor the data fed back by the temperature sensor. When the battery temperature reaches a certain value, such as 120°C, maintain that temperature for a period of time, such as 30 minutes, to observe whether the battery exhibits thermal runaway symptoms, such as smoke, fire, or explosion. If not, continue heating at the original rate until thermal runaway occurs. Record the temperature at this point and the time when the relevant phenomenon occurs (i.e., the thermal trigger response time).

[0115] (3) Battery electrochemical performance test

[0116] At 25℃±3, charge the sodium ion battery at a constant current and constant voltage of 0.5C to 3.8V, with a cut-off current of 0.05C; let it sit for 30 minutes; discharge at a constant current of 1C to 1.5V at 25℃±3, and record the capacity D1 at this time; let it sit for 30 minutes; after cycling the above steps for 500 times, record the attenuated capacity D2; the capacity retention rate D=D2 / D1*100%.

[0117] It should be noted that the energy density of the batteries in the above embodiments and comparative examples is 120wh / kg, where energy density = platform voltage * current / battery weight; it can be understood that the platform voltage refers to a relatively stable voltage range in the voltage change curve over time during the battery's charge and discharge process, usually manifested as a "platform" form with small voltage fluctuations and long maintenance time (that is, the voltage corresponding to the stage where the voltage changes slightly but the capacity changes significantly).

[0118] Table 1

[0119]

[0120] As shown in the table above, a comparison of Examples 1-8 with Comparative Example 1 demonstrates that the inclusion of thermally expandable microcapsules in the positive electrode active material layer allows for timely activation of the thermal shutdown mechanism when the battery reaches a relatively high temperature (e.g., just after reaching the thermal runaway inhibition temperature of 135°C), thereby improving safety performance. A comparison of Examples 1-8 with Comparative Example 2 demonstrates that controlling the mass percentage of thermally expandable microcapsules relative to the positive electrode active material within an appropriate range facilitates a balanced approach to safety and electrochemical performance.

[0121] Furthermore, by comparing Examples 1 and 4 to 7, it can be seen that by controlling the ratio between the average particle size D0 of the thermally expandable microcapsules and the particle size D50 of the positive electrode active material within an appropriate range, it is beneficial to better balance the electrochemical performance while improving the safety performance.

[0122] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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.

[0123] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A sodium ion battery, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector; The positive electrode active material layer includes a positive electrode active material and thermally expandable microcapsules, and a mass percentage of the thermally expandable microcapsules relative to the mass of the positive electrode active material is less than or equal to 3%.

2. The sodium ion battery according to claim 1, characterized in that One or more of the following conditions are met: (1) The mass percentage of the thermally expandable microcapsules relative to the mass percentage of the positive electrode active material is 0.5% to 3%, and can be optionally 0.5% to 2.5%; (2) The average particle size D0 of the thermally expandable microcapsules and the particle size D50 of the positive electrode active material satisfy the following relationship: 1 / 12≤D0 / D50≤10.

3. The sodium ion battery according to claim 1 or 2, characterized in that One or more of the following conditions are met: (1) The average particle size D0 of the thermally expandable microcapsules is 1 μm to 30 μm, and can be optionally 5 μm to 18 μm; (2) The density of the thermally expandable microcapsules is 0.3 g / cm 3 ~0.8g / cm 3 .

4. The sodium ion battery according to claim 1 or 2, characterized in that One or more of the following conditions are met: (1) The particle size D50 of the positive electrode active material is 3 μm to 12 μm; optionally 5 μm to 8 μm; (2) The specific surface area of ​​the positive electrode active material is 1.3 m 2 / g~3.0m 2 / g.

5. The sodium ion battery according to claim 1 or 2, characterized in that The positive electrode active material includes a sodium ion positive electrode material and a fast ion conductor layer covering at least a portion of the surface of the sodium ion positive electrode material; Optionally, the thickness of the fast ion conductor layer is 10 nm to 50 nm; Optionally, the fast ion conductor layer comprises Na3Zr2Si2PO 12 ; Optionally, the sodium ion diffusion coefficient of the positive electrode active material is greater than or equal to 1×10 -10 cm 2 / s.

6. The sodium ion battery according to claim 1 or 2, characterized in that The thermally expandable microcapsule comprises a capsule core and a capsule wall surrounding the capsule core, wherein the material of the capsule core comprises liquid hydrocarbon, and the material of the capsule wall comprises a thermoplastic polymer; Optionally, the capsule wall has a thickness of 2 μm to 15 μm.

7. The sodium ion battery according to claim 6, characterized in that The boiling point of the liquid hydrocarbon is 105°C to 125°C, and the softening point of the thermoplastic polymer is 100°C to 240°C.

8. The sodium ion battery according to claim 6, characterized in that One or more of the following conditions are met: (1) The liquid hydrocarbon includes one or more of n-octane, 2-methyloctane and methylcycloheptane; (2) The thermoplastic polymer includes an acrylonitrile-based polymer; Optionally, the acrylonitrile-based polymer comprises structural units derived from a first monomer and structural units derived from a second monomer; The first monomer includes acrylonitrile, and the second monomer includes one or more of acrylonitrile, butadiene, styrene, and methyl methacrylate; Further optionally, the acrylonitrile-based polymer includes one or more of polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, and acrylonitrile-methyl methacrylate copolymer.

9. The sodium ion battery according to claim 1 or 2, characterized in that The positive electrode active material layer further includes a binder and a conductive agent. The mass ratio of the positive electrode active material, the thermally expandable microcapsules, the conductive agent and the binder is k:f:p:q, and k+f+p+q=100, wherein k is 95-99, f is 0.5-3, p is 0.5-2.5, and q is 1-3.

10. An electronic device, characterized in that: A sodium ion battery comprising the sodium ion battery according to any one of claims 1 to 9.

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