Sodium-ion composite solid electrolyte, preparation method, and sodium-ion battery

Abstract

A preparation method for a sodium-ion composite solid electrolyte and a sodium-ion battery. The sodium-ion composite solid electrolyte comprises a polymer matrix, a sodium salt, and an inorganic active filler. The chemical general formula of the inorganic active filler is: Na5MSi4O12, wherein M is one or more of La, Al, Sm, Eu, Gd, Sc, and Y; and the particle size of the inorganic active filler is 80-600 nm, the mass ratio of the polymer matrix to the sodium salt is (0.25-50):1, and the inorganic active filler accounts for 0.1-80 wt.% of the total mass of the polymer matrix, the sodium salt, and the inorganic active filler. The sodium-ion composite solid electrolyte has good ionic conductivity and mechanical properties, greatly simplifies the production process, and also facilitates implementation of stable cycling of the sodium-ion battery.

Description

A sodium-ion composite solid electrolyte, its preparation method, and a sodium-ion battery Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion composite solid electrolyte, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have garnered significant attention in recent years due to their abundant and inexpensive resources and their similar operating principle to lithium-ion batteries. However, sodium-ion batteries based on organic liquid electrolytes suffer from serious safety issues, such as electrolyte leakage, poor thermal stability, and flammability / explosion. In contrast, solid-state sodium batteries based on solid-state electrolytes exhibit advantages such as high safety, a wide operating temperature range, and ease of direct stacking. Furthermore, using metallic sodium directly as the negative electrode can further improve the battery's energy density.

[0003] Currently, the most widely studied sodium-ion solid electrolytes mainly include inorganic solid electrolytes, polymer solid electrolytes, and composite solid electrolytes. Inorganic solid electrolytes typically possess high ionic conductivity, high ion transference number, good thermal stability, and a wide electrochemical stability window; however, their high hardness results in poor processability and poor interfacial contact with the electrode. In contrast, polymer electrolytes exhibit good viscoelasticity and flexibility, are easily processable and inexpensive, and readily form tight interfacial contacts with electrode materials; however, their ionic conductivity and ion transference number are relatively low, making them difficult to meet the requirements of battery operation. By combining inorganic and polymer solid electrolytes, composite solid electrolytes can, under certain conditions, combine the advantages of both.

[0004] Composite solid-state electrolytes are generally electrolytes obtained by combining inorganic fillers and polymer solid-state electrolytes. Inorganic fillers can be divided into inert fillers and active fillers. Inert fillers do not transport ions and mainly include Al2O3, SiO2, and ZrO2. Compared with inert fillers, active materials can participate in the ion conduction process and improve ionic conductivity. Currently, the main types of fillers are oxide solid-state electrolytes (such as NASICON-type electrolytes) and sulfide solid-state electrolytes. The main preparation method for oxide solid-state electrolytes is the traditional solid-state sintering method, which has a complex production process and usually requires secondary high-temperature sintering, resulting in high production costs. Sulfide solid-state electrolytes, on the other hand, face significant difficulties in preparation due to their poor air stability. To further promote the practical application of sodium-ion solid-state batteries, it is crucial to develop and prepare novel sodium-ion composite solid-state electrolyte materials that combine good processability and high ionic conductivity. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a sodium-ion composite solid electrolyte, its preparation method, and a sodium-ion battery.

[0006] In a first aspect, embodiments of the present invention disclose a sodium ion composite solid electrolyte, comprising a polymer matrix, a sodium salt, and an inorganic active filler, wherein the general chemical formula of the inorganic active filler is: Na₅MSi₄O₂. 12 M is one or more of La, Al, Sm, Eu, Gd, Sc, and Y; the particle size of the inorganic active filler is 80–600 nm; the mass ratio of the polymer matrix to the sodium salt is (0.25–50):1; and the inorganic active filler accounts for 0.1–80 wt.% of the total mass of the polymer matrix, sodium salt, and inorganic active filler.

[0007] Using the above technical solution, this invention proposes an inorganic active filler with the general chemical formula: Na₅MSi₄O₂ 12 The sodium ion composite solid electrolyte has high ionic conductivity, good electrochemical stability and high mechanical strength, which solves the problem of lack of high-performance sodium ion composite solid electrolytes and is conducive to simplifying the preparation process.

[0008] According to another specific embodiment of the present invention, the particle size of the inorganic active filler is 100-400 nm, the mass ratio of the polymer matrix to the sodium salt is (0.5-20):1, and the inorganic active filler accounts for 6-40 wt.% of the total mass of the polymer matrix, sodium salt, and inorganic active filler.

[0009] According to another specific embodiment of the present invention, the general chemical formula of the inorganic active filler is: Na5R 1-x La x Si4O 12 R is one of Sm, Eu, Gd, and Y, and x is in the range of 0.05 ≤ x ≤ 0.3.

[0010] According to another specific embodiment of the present invention, the thickness of the sodium ion composite solid electrolyte is 50-150 μm.

[0011] According to another specific embodiment of the present invention, the polymer matrix is ​​one or more of polyacrylonitrile, poly(vinylidene fluoride-co-hexafluoropropylene), polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate and polyacrylamide, and the sodium salt is one or more of NaClO4, NaTFSI, NaPF6, NaCF3SO3 and NaFSI.

[0012] Secondly, embodiments of the present invention disclose a method for preparing a sodium ion composite solid electrolyte, used to prepare a sodium ion composite solid electrolyte as described in any embodiment of the first aspect, comprising the following steps:

[0013] Preparation of powder A: Weigh Na2CO3, SiO2 and M metal oxide, mix them by wet ball milling, and dry to obtain powder A;

[0014] Preparation of inorganic active filler: Powder A is sintered once, and the product after the first sintering is dry ball milled to obtain inorganic active filler;

[0015] Suspension preparation: The polymer matrix and sodium salt are dissolved in a solvent, and inorganic active filler is added and stirred to obtain a suspension;

[0016] Preparation of sodium ion composite solid electrolyte: The suspension was cast into a mold and vacuum dried to obtain sodium ion composite solid electrolyte;

[0017] Among them, the metal oxide M is one or more of La2O3, Al2O3, Sm2O3, Eu2O3, Gd2O3, Sc2O3, and Y2O3.

[0018] By adopting the above technical solution and introducing a novel inorganic active filler, on the one hand, the crystallinity of the polymer matrix can be reduced, forming a rapid ion migration channel near the particles to promote sodium ion migration; on the other hand, it can directly participate in the sodium ion transport process, synergistically enhancing the sodium ion migration rate. The preparation method of this invention is simple, including secondary ball milling, primary sintering, and the composite of the inorganic active filler and the polymer matrix. The inorganic active filler can be prepared with only one sintering step, which can reduce the production cost of sodium ion composite solid electrolytes and is beneficial for large-scale manufacturing.

[0019] According to another specific embodiment of the present invention, in the preparation of powder A, Na2CO3, SiO2 and M metal oxide are weighed in a molar ratio of 5:8:1.

[0020] According to another specific embodiment of the present invention, the ball milling time of wet ball milling is 12 to 16 hours; the total ball milling time of dry ball milling is 10 to 20 hours; the temperature of the first sintering is 800 to 950°C and the sintering time is 8 to 15 hours; and the vacuum drying time is 12 to 24 hours.

[0021] According to another specific embodiment of the present invention, during the preparation of the suspension, the polymer concentration in the solvent is 0.1 to 0.5 g / mL; and the dissolution temperature is 30 to 60°C.

[0022] Thirdly, embodiments of the present invention also disclose a sodium-ion battery, comprising a sodium-ion composite solid electrolyte as described in any embodiment of the first aspect, or a sodium-ion composite solid electrolyte obtained by a preparation method as described in any embodiment of the second aspect.

[0023] By adopting the above technical solution, the sodium-ion composite solid electrolyte provided by the present invention has good practicality. It can provide the ionic conductivity required for sodium-ion battery operation, and can maintain good interfacial contact and stability with the electrodes, which helps to achieve stable cycling of sodium-ion batteries. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the sodium ion composite solid electrolyte of the present invention;

[0025] Figure 2 shows the constant current charge-discharge curve of the sodium-ion battery in Application Example 1 of the present invention;

[0026] Figure 3 shows the cycle performance of the sodium-ion battery in Application Example 1 of the present invention. 1. Polymer matrix, 2. Sodium salt, 3. Inorganic active filler Detailed Implementation

[0027] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0028] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] Through careful study of existing sodium-ion composite solid electrolytes and their preparation methods, the inventors discovered that existing inorganic active fillers typically employ oxide solid electrolyte fillers (such as NASICON-type electrolytes) and sulfide solid electrolytes. The main preparation method for oxide solid electrolyte materials in existing technologies is the traditional solid-state sintering method, which is complex and usually requires a second high-temperature sintering process to prepare the inorganic active filler, resulting in high production costs. Sulfide solid electrolytes have poor air stability and are difficult to handle in air, significantly increasing the difficulty of the preparation process. The inventors aim to develop and prepare a novel sodium-ion composite solid electrolyte that combines good processability and high ionic conductivity, achieving a sodium-ion composite solid electrolyte that requires only one sintering step in its preparation while maintaining high room-temperature ionic conductivity.

[0031] In a first aspect, referring to Figure 1, an embodiment of the present invention discloses a sodium ion composite solid electrolyte, comprising a polymer matrix 1, a sodium salt 2, and an inorganic active filler 3, wherein the general chemical formula of the inorganic active filler 3 is: Na5MSi4O 12 M is one or more of La, Al, Sm, Eu, Gd, Sc, and Y; the particle size of the inorganic active filler 3 is 80-600 nm (including the endpoint value); the mass ratio of polymer matrix 1 to sodium salt 2 is (0.25-50):1; and the inorganic active filler 3 accounts for 0.1-80 wt.% (including the endpoint value) of the total mass of polymer matrix 1, sodium salt 2, and inorganic active filler 3.

[0032] Referring again to Figure 1, sodium salt 2 is uniformly dissolved in polymer matrix 1, and inorganic active filler 3 is uniformly dispersed in polymer matrix 1. The sodium ion composite solid electrolyte of this invention combines the characteristics of oxide solid electrolytes and polymer solid electrolytes, achieving both high ionic conductivity and retaining the flexibility and adhesion of the polymer. It possesses excellent processing characteristics, facilitating close contact between the electrolyte and the electrode.

[0033] Furthermore, this invention is the first to propose an inorganic active filler 3 with the general chemical formula: Na5MSi4O 12 The sodium-ion composite solid electrolyte exhibits high ionic conductivity, good electrochemical stability, and high mechanical strength, solving the problem of the lack of high-performance sodium-ion composite solid electrolytes and simplifying the preparation process. By controlling the particle size and mass ratio of the inorganic active filler 3, and the mass ratio of the polymer matrix 1 to the sodium salt 2, the mechanical properties of the sodium-ion composite solid electrolyte of this invention are also improved, making it easier to form a film.

[0034] Furthermore, the particle size of the inorganic active filler 3 is 100–400 nm (including endpoint values), the mass ratio of the polymer matrix 1 to the sodium salt 2 is (0.5–20):1, and the inorganic active filler 3 accounts for 6–40 wt.% (including endpoint values) of the total mass of the polymer matrix 1, sodium salt 2, and inorganic active filler 3. The inorganic active filler 3 and the polymer matrix 1 facilitate the formation of a continuous ion transport path. A smaller particle size, such as 300 nm, in the inorganic active filler 3 results in uniformly dispersed nanoparticles that increase the ion-conducting interface, which is beneficial for improving the ion conductivity of the composite solid electrolyte. When the mass ratio of the inorganic active filler is too low, the amorphous region of the polymer matrix 1 is small, and ion transport remains limited. When the mass ratio of the inorganic active filler reaches a critical value, on the one hand, it effectively inhibits the crystallization of the polymer matrix and increases the movement of local chain segments; on the other hand, both the polymer matrix / inorganic active filler interface and the ion-conducting active filler can guide sodium ion migration, constructing a continuous and rapid ion transport path. When an excessive amount of inorganic active filler 3 is added to the composite solid electrolyte, the interfacial ion channels are disturbed, which may also hinder the movement of polymer matrix 1 chain segments and reduce ion transport in the polymer matrix 1 region, resulting in a decrease in ionic conductivity. In addition, an excessive amount of inorganic active filler 3 may cause agglomeration, hindering the movement of polymer matrix 1 chain segments and reducing ion transport in the polymer matrix 1 region. The range of the mass ratio of polymer matrix 1 to sodium salt 2 will also affect the ionic conductivity of the sodium ion composite solid electrolyte. Therefore, a better ionic conductivity can only be obtained when all three conditions mentioned above are met simultaneously, that is, when the particle size of the inorganic active filler 3, the mass ratio of the polymer matrix 1 and the sodium salt 2, and the range of the inorganic active filler 3 in the total mass of the polymer matrix 1, the sodium salt 2 and the inorganic active filler 3 are satisfied.

[0035] Through experimental research, the inventors also discovered that when M in the inorganic active filler is a mixture of R and La, specifically, the general chemical formula of the inorganic active filler is: Na₅R 1-x La x Si4O 12 Where R is one of Sm, Eu, Gd, and Y, and x is in the range of 0.05≤x≤0.3, the ionic conductivity of the sodium ion composite solid electrolyte of the present invention can be further improved.

[0036] The thickness of the sodium ion composite solid electrolyte of this invention is 50–150 μm. This minimizes the electrolyte film thickness while ensuring good film-forming properties and mechanical strength.

[0037] The polymer matrix 1 of this invention is one or more of polyacrylonitrile (PAN), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and polyacrylamide (PAM), and the sodium salt 2 is one or more of sodium perchlorate (NaClO4), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (NaCF3SO3), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0038] Secondly, embodiments of the present invention disclose a method for preparing a sodium ion composite solid electrolyte, comprising the following steps:

[0039] Preparation of powder A: Weigh Na2CO3, SiO2 and M metal oxide, mix them by wet ball milling, and dry to obtain powder A;

[0040] Preparation of inorganic active filler: Powder A is sintered once, and the product after the first sintering is dry ball milled to obtain inorganic active filler;

[0041] Suspension preparation: The polymer matrix and sodium salt are dissolved in a solvent, and inorganic active filler is added and stirred to obtain a suspension;

[0042] Preparation of sodium ion composite solid electrolyte: The suspension was cast into a mold and vacuum dried to obtain sodium ion composite solid electrolyte;

[0043] Among them, the metal oxide M is one or more of La2O3, Al2O3, Sm2O3, Eu2O3, Gd2O3, Sc2O3, and Y2O3.

[0044] By adopting the above technical solution, a novel inorganic active filler is introduced. The inorganic active filler can be prepared by only one sintering. Moreover, the inorganic active filler does not form a dense structure during the first sintering. At this time, ball milling is more likely to obtain nanoparticles, which greatly simplifies the production process, reduces the production cost of sodium ion composite solid electrolyte, and is conducive to large-scale manufacturing.

[0045] In the preparation of powder A, Na₂CO₃, SiO₂, and M metal oxide are weighed in a molar ratio of 5:8:1. Therefore, a sodium-ion solid electrolyte with stable properties and high room-temperature ionic conductivity can be obtained without adding more sodium salt and with only a lower primary sintering temperature.

[0046] The wet ball milling time is 12–16 hours (including endpoints); the dry ball milling uses a stepped milling method, with each milling cycle lasting 2 hours, for a total milling time of 10–20 hours (including endpoints); the primary sintering temperature is 800–950℃ (including endpoints), and the sintering time is 8–15 hours (including endpoints); the vacuum drying time is 12–24 hours (including endpoints). Furthermore, the vacuum drying temperature is 50–80℃. The inorganic active filler of this invention does not require secondary sintering during preparation, exhibiting a lower sintering temperature and shorter sintering time. The entire preparation cycle is short and simple, significantly reducing the preparation cost of the composite solid electrolyte.

[0047] During the preparation of the suspension, the polymer concentration in the solvent is 0.1–0.5 g / mL (inclusive); the dissolution temperature is 30–60 °C (inclusive). Good dispersibility of the inorganic active filler 3 in the polymer matrix 1 is a prerequisite for obtaining any good structure or performance. The aforementioned polymer concentration and dissolution temperature facilitate uniform dispersion of the inorganic active filler 3, resulting in a composite solid electrolyte with good overall performance. The type of solvent is determined based on the degree of solubility in the polymer matrix.

[0048] Thirdly, embodiments of the present invention also disclose a sodium-ion battery, comprising the aforementioned sodium-ion composite solid electrolyte. The sodium-ion composite solid electrolyte provided by the present invention has good practicality, providing the ionic conductivity required for sodium-ion battery operation while maintaining good interfacial contact and stability with the electrodes, thereby ensuring stable cycling of the sodium-ion battery.

[0049] Sodium-ion batteries also include a positive electrode and a negative electrode, with the aforementioned sodium-ion composite solid electrolyte located between the positive and negative electrodes. The positive electrode comprises positive electrode active material particles, conductive additives, and a binder. The negative electrode can be elemental sodium or a sodium alloy, or it can also comprise negative electrode active material particles, conductive additives, and a binder. Positive electrode active material particles refer to sodium-intercalated compounds capable of reversibly inserting and extracting sodium ions, such as polyanionic materials, layered metal oxide materials, and Prussian blue materials. Negative electrode active material particles refer to sodium-intercalated materials capable of reversibly inserting and extracting sodium ions, such as carbon materials, metal oxides, and transition metal sulfides. Conductive additives are generally selected from Super P (SP), Ketjen Black (KB), acetylene black (AB), carbon nanotubes (CNT), and graphene. Binders are generally selected from polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and sodium alginate (SA).

[0050] Furthermore, the mass ratio of positive electrode active material particles, conductive additives and binders is (0.7~0.9):(0.05~0.2):(0.05~0.1); the mass ratio of negative electrode active material particles, conductive additives and binders is (0.7~0.9):(0.05~0.2):(0.05~0.1), for example 0.7:0.2:0.1.

[0051] In this invention, the preparation method of the positive electrode is as follows: the positive electrode active material particles, conductive additives and binders are weighed according to the above mass ratio, a solvent is added to make uniform dispersion and mixing, and then the obtained slurry is coated on the surface of aluminum foil, dried and cut into electrode sheets of a certain size for later use.

[0052] In this invention, the method for preparing sodium metal or sodium alloy anodes is as follows: sodium metal is cut into sheets, or alloy powder is pressed into sheets for use. The specific method for preparing sodium-embedded anodes is as follows: anode active material particles, conductive additives, and binders are weighed according to the above mass ratio, a solvent is added to uniformly disperse and mix, and then the resulting slurry is coated onto the surface of aluminum or copper foil, dried, and cut into electrode sheets of a certain size for later use. The solvent is generally selected from deionized water or N-methylpyrrolidone (NMP) depending on the type of binder.

[0053] In this invention, the area of ​​the sodium-ion composite solid electrolyte membrane is greater than the negative electrode area and greater than or equal to the positive electrode area to ensure that the positive electrode capacity is fully utilized. Furthermore, to ensure good electrochemical performance of the sodium-ion battery, the aforementioned sodium-ion composite solid electrolyte is adhered to the surface of at least one of the positive and negative electrodes of the sodium-ion battery. This adhesion can, for example, refer to the sodium-ion composite solid electrolyte suspension being directly cast onto the surface of the positive or negative electrode and then dried, or it can be achieved by attaching the sodium-ion composite solid electrolyte to the surface of the positive or negative electrode using ion-conductive adhesive. The adhesion of the composite solid electrolyte to the surface of the positive or negative electrode helps reduce the interfacial resistance between the electrolyte and the electrode, ensuring the normal operation of the sodium-ion battery.

[0054] This invention provides a method for preparing a sodium-ion battery, comprising the following steps:

[0055] S1 prepares a viscous slurry by uniformly mixing positive or negative electrode active material particles, conductive additives, and binders in a solvent;

[0056] S2. The above slurry is uniformly coated on aluminum foil or copper foil. After the solvent evaporates, the coated foil is placed in a vacuum oven to dry the electrode completely. The electrode is then cut into fixed sizes for later use.

[0057] S3. Place the electrode obtained in step S2 into a polytetrafluoroethylene mold, and cast the suspension obtained in the above method for preparing sodium ion composite solid electrolyte onto the electrode surface, and dry it completely under vacuum.

[0058] S4 removes the oxide layer on the surface of the sodium metal, rolls it, and then cuts it into sodium metal discs of a fixed diameter.

[0059] S5 assembles the battery in an argon-filled glove box, following the order of positive electrode, composite solid electrolyte, and negative electrode.

[0060] Example 1

[0061] PAN-NaClO4-Na5SmSi4O 12 The preparation of sodium ion composite solid electrolyte membrane is as follows:

[0062] (1) Preparation of powder A: Anhydrous Na2CO3, SiO2 and Sm2O3 were weighed according to a molar ratio of 5:8:1 and then wet ball milled. Anhydrous ethanol was used as a dispersant. The total mass ratio of anhydrous Na2CO3, SiO2 and Sm2O3 to anhydrous ethanol was 1:2. The ball-to-material ratio was 15:1. The ball milling speed was 600 rpm and the ball milling time was 15 hours. Powder A was obtained after ball milling.

[0063] (2) Preparation of inorganic active filler: Powder A was dried at 120℃ for 12 hours and then sintered once at a heating rate of 5℃ / min. -1 The sintering temperature was 800℃ and the sintering time was 8 hours. After natural cooling to room temperature, dry ball milling was carried out with a ball-to-material mass ratio of 15:1 and a ball milling speed of 600 rpm. Step ball milling was adopted, with each ball milling session lasting 2 hours and a total of 7 cycles, for a total ball milling time of 14 hours, resulting in a particle size of approximately 300 nm.

[0064] (3) Preparation of suspension: PAN and NaClO4 were weighed at a mass ratio of 0.85:1, and N,N-dimethylformamide (DMF) was added as solvent. The polymer concentration in the solvent was 0.1 g / mL. After stirring at 60°C until completely dissolved, 20 wt.% Na5SmSi4O3 was weighed. 12 Add and stir for 24 hours until well mixed;

[0065] (4) Preparation of sodium ion composite solid electrolyte: The above suspension was cast onto the surface of a polytetrafluoroethylene mold and completely dried under vacuum at 60°C for 24 hours to obtain a PAN-NaClO4-Na5SmSi4O4 composite solid electrolyte with a thickness of approximately 90μm. 12 Sodium ion composite solid electrolyte membrane.

[0066] Example 2

[0067] PEO-NaTFSI-Na5SmSi4O 12 The preparation of sodium ion composite solid electrolyte membrane is as follows:

[0068] (1) Preparation of powder A: Anhydrous Na2CO3, SiO2 and Sm2O3 were weighed according to a molar ratio of 5:8:1 and then wet ball milled. Anhydrous ethanol was used as a dispersant. The total mass ratio of anhydrous Na2CO3, SiO2 and Sm2O3 to anhydrous ethanol was 1:2. The ball-to-material ratio was 15:1. The ball milling speed was 600 rpm and the ball milling time was 15 hours. Powder A was obtained after ball milling.

[0069] (2) Preparation of inorganic active filler: Powder A was dried at 120℃ for 12 hours and then sintered once at a heating rate of 5℃ / min. -1 The sintering temperature was 800℃ and the sintering time was 8 hours. After natural cooling to room temperature, dry ball milling was carried out with a ball-to-material mass ratio of 15:1 and a ball milling speed of 600 rpm. Stepped ball milling was adopted, with each ball milling session lasting 2 hours and a total of 7 cycles, for a total ball milling time of 14 hours, resulting in a particle size of approximately 300 nm.

[0070] (3) Preparation of suspension: PEO and NaTFSI were weighed at a mass ratio of 1.75:1, and deionized water was added as solvent. The polymer concentration in the solvent was 0.15 g / mL. After stirring at 60 °C until completely dissolved, 5 wt.% Na5SmSi4O was weighed. 12 Add and stir for 24 hours until well mixed;

[0071] (4) Preparation of sodium ion composite solid electrolyte: The above suspension was cast onto the surface of a polytetrafluoroethylene mold and completely dried under vacuum at 60°C for 24 hours to obtain a PEO-NaTFSI-Na5SmSi4O with a thickness of approximately 100μm. 12 Sodium ion composite solid electrolyte membrane.

[0072] Example 3

[0073] PEO-NaTFSI-Na5Sm 0.95 La 0.05 Si4O 12 The preparation of sodium ion composite solid electrolyte membrane is as follows:

[0074] (1) Preparation of powder A: Anhydrous Na2CO3, SiO2, Sm2O3 and La2O3 were weighed according to the molar ratio of 5:8:0.95:0.05 and then wet ball milled. Anhydrous ethanol was used as the dispersant. The total mass ratio of anhydrous Na2CO3, SiO2, Sm2O3 and La2O3 to anhydrous ethanol was 1:2. The ball-to-material ratio was 15:1. The ball milling speed was 600 rpm and the ball milling time was 15 hours. Powder A was obtained after ball milling.

[0075] (2) Preparation of inorganic active filler: Powder A was dried at 120℃ for 12 hours and then sintered once at a heating rate of 5℃ / min. -1 The sintering temperature was 800℃ and the sintering time was 8 hours. After natural cooling to room temperature, dry ball milling was carried out with a ball-to-material mass ratio of 15:1 and a ball milling speed of 600 rpm. Step ball milling was adopted, with each ball milling session lasting 2 hours and a total of 8 cycles, for a total ball milling time of 16 hours, resulting in a particle size of approximately 300 nm.

[0076] (3) Preparation of suspension: PEO and NaTFSI were weighed at a mass ratio of 1.75:1, and deionized water was added as solvent. The polymer concentration in the solvent was 0.15 g / mL. After stirring at 60°C until completely dissolved, 5 wt.% Na5Sm was weighed. 0.95 La 0.05 Si4O 12 Add and stir for 24 hours until well mixed;

[0077] (4) Preparation of sodium ion composite solid electrolyte: The above suspension was cast onto the surface of a polytetrafluoroethylene mold and completely dried under vacuum at 60°C for 24 hours to obtain a PEO-NaTFSI-Na5Sm composite solid electrolyte with a thickness of approximately 100 μm. 0.95 La 0.05 Si4O 12 Sodium ion composite solid electrolyte membrane.

[0078] Example 4

[0079] The difference from Example 2 is that the total dry ball milling time in step (2) is 10 hours, the particle size of inorganic active filler 3 is about 600 nm, and a PEO-NaTFSI-Na5SmSi4O with a thickness of about 100 μm is obtained. 12 Sodium ion composite solid electrolyte membrane.

[0080] Comparative Example 1

[0081] (1) Preparation of suspension: Weigh PEO and NaTFSI at a mass ratio of 1.75:1, add deionized water as solvent, the polymer concentration in the solvent is 0.15 g / mL, and stir at 60℃ until completely dissolved;

[0082] (2) Preparation of polymer solid electrolyte membrane: The above suspension was cast onto the surface of a polytetrafluoroethylene mold and dried completely under vacuum at 60°C for 24 hours to obtain a PEO-NaTFSI polymer solid electrolyte membrane with a thickness of about 100 μm.

[0083] Comparative Example 2

[0084] (1) Suspension preparation: PEO and NaTFSI were weighed at a mass ratio of 1.75:1, and deionized water was added as solvent. The polymer concentration in the solvent was 0.15 g / mL. After stirring at 60°C until completely dissolved, 5 wt.% of the purchased inorganic active filler Na3Zr2Si2PO4 with a particle size of approximately 300 nm was weighed. 12 Add and stir for 24 hours until well mixed;

[0085] (2) Preparation of sodium ion composite solid electrolyte: The above suspension was cast onto the surface of a polytetrafluoroethylene mold and completely dried under vacuum at 60°C for 24 hours to obtain a PEO-NaTFSI-Na3Zr2Si2PO with a thickness of approximately 100μm. 12 Sodium ion composite solid electrolyte membrane.

[0086] Application Example 1

[0087] Na4Fe(PO4)2P2O7 / PAN-NaClO4-Na5SmSi4O 12 Preparation of Na solid sodium battery.

[0088] (1) Na4Fe(PO4)2P2O7, Super P and CMC binder were uniformly mixed in deionized water at a mass ratio of 7:2:1 to prepare a viscous slurry;

[0089] (2) The above slurry is uniformly coated on aluminum foil. After the surface deionized water evaporates, the coated aluminum foil is transferred to a 60°C vacuum oven to dry the electrode completely. Then the electrode is cut into a circular piece with a diameter of 1 cm as the positive electrode.

[0090] (3) The above positive electrode is placed in a polytetrafluoroethylene mold, and the PAN-NaClO4-Na5SmSi4O in Example 1 is placed in the mold. 12 Step (3) The suspension is cast onto the surface of the positive electrode and completely dried under vacuum at 60°C;

[0091] (4) In a glove box filled with argon, the oxide layer on the surface of the sodium metal is removed, rolled into a thin sheet, and then cut into sodium metal discs with a diameter of 1.2 cm as negative electrodes.

[0092] (5) Attach the sodium metal disc to the side of the electrolyte membrane without the positive electrode, ensuring that the edge of the negative electrode extends beyond the edge of the positive electrode, and finally encapsulate it with a CR2032 button cell.

[0093] To further highlight the effects of the present invention, Table 1 summarizes the ionic conductivity of different embodiments and comparative examples. The ionic conductivity was measured by AC impedance spectroscopy, with a stainless steel sheet as the blocking electrode, a test frequency range of 1 Hz to 5 MHz, and an applied bias voltage of 20 mV. As shown in the table, the sodium-ion composite solid electrolyte of the various embodiments of the present invention, compared to the solid electrolyte in Comparative Example 1 without the addition of inorganic active filler and Comparative Example 2 using the existing inorganic active filler Na3Zr2Si2PO4, demonstrates superior performance. 12 The composite solid electrolyte of this invention significantly improves the ionic conductivity of the sodium ion composite solid electrolyte. Meanwhile, in Examples 2 and 4, the ionic conductivity of Example 4 is lower than that of Example 2 because the inorganic active filler particle size is approximately 600 nm. And because Example 3 satisfies the general chemical formula of the inorganic active filler: Na₅R 1-x La x Si4O 12 R is one of Sm, Eu, Gd, and Y, and x ranges from 0.05 to x ≤ 0.3. The ionic conductivity of Example 3 is further improved.

[0094] Table 1 Ionic conductivity of different embodiments and comparative examples

[0095] Figures 2 and 3 show the constant current charge-discharge curves and cycle performance of the sodium-ion battery in Application Example 1 of this invention under a constant temperature condition of 60°C, respectively. Here, "Voltage" represents voltage, "Specific Capacity" represents specific capacity, and "Cycle Number" represents the number of cycles. It can be seen that the PAN-NaClO4-Na5SmSi4O prepared using Example 1 of this invention... 12 Application Example 1 of Electrolyte Assembly: Sodium-ion battery, which can provide 98 mA hg during constant current charge-discharge testing at a rate of 0.5C. -1 The reversible specific capacity (calculated based on the mass of the positive electrode active material) of the sodium-ion battery of this invention can be stably cycled for more than 300 times, proving that the sodium-ion composite solid electrolyte provided by this invention has good practicality. It can provide the ionic conductivity required for the operation of sodium-ion batteries, and can maintain good interfacial contact and stability with the electrodes, thereby ensuring the stable cycling of sodium-ion batteries.

[0096] In summary, the sodium-ion composite solid electrolyte of this invention introduces a novel oxide sodium ion conductor with high ionic conductivity as an inorganic active filler. On the one hand, the addition of the inorganic active filler 3 can reduce the crystallinity of the polymer matrix 1, forming a rapid ion transport channel near the particles; on the other hand, the inorganic active filler 3 of this invention can partially participate in sodium ion migration, playing a synergistic role in improving the ionic conductivity of the composite solid electrolyte. The sodium-ion composite solid electrolyte of this invention retains the flexibility and adhesion of the polymer matrix 1, ensuring good interfacial contact with the electrodes, which helps to achieve normal operation and stable cycling of sodium-ion batteries. Moreover, in the preparation process, no secondary sintering is required, and it has a lower sintering temperature and shorter sintering time, reducing the preparation cost of the composite solid electrolyte and facilitating large-scale production.

[0097] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A sodium ion composite solid electrolyte, characterized in that, It includes a polymer matrix, a sodium salt, and an inorganic active filler, wherein the general chemical formula of the inorganic active filler is: Na₅MSi₄O₂ 12 M is one or more of La, Al, Sm, Eu, Gd, Sc, and Y; the particle size of the inorganic active filler is 80-600 nm; the mass ratio of the polymer matrix to the sodium salt is (0.25-50):1; and the inorganic active filler accounts for 0.1-80 wt.% of the total mass of the polymer matrix, sodium salt, and inorganic active filler.

2. The sodium ion composite solid electrolyte as described in claim 1, characterized in that, The inorganic active filler has a particle size of 100–400 nm, the mass ratio of the polymer matrix to the sodium salt is (0.5–20):1, and the inorganic active filler accounts for 6–40 wt.% of the total mass of the polymer matrix, sodium salt, and inorganic active filler.

3. The sodium ion composite solid electrolyte as described in claim 2, characterized in that, The general chemical formula of the inorganic active filler is: Na5R 1-x La x Si4O 12 R is one of Sm, Eu, Gd, and Y, and x is in the range of 0.05 ≤ x ≤ 0.

3.

4. The sodium ion composite solid electrolyte as described in claim 1, characterized in that, The thickness of the sodium ion composite solid electrolyte is 50–150 μm.

5. The sodium ion composite solid electrolyte as described in claim 1, characterized in that, The polymer matrix is ​​one or more of polyacrylonitrile, poly(vinylidene fluoride-co-hexafluoropropylene), polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate and polyacrylamide, and the sodium salt is one or more of NaClO4, NaTFSI, NaPF6, NaCF3SO3 and NaFSI.

6. A method for preparing a sodium ion composite solid electrolyte, characterized in that, The method for preparing the sodium ion composite solid electrolyte as described in any one of claims 1-4 comprises the following steps: Preparation of powder A: Weigh Na2CO3, SiO2 and M metal oxide, mix them by wet ball milling, and dry to obtain powder A; Preparation of inorganic active filler: Powder A is sintered once, and the product after the first sintering is dry ball milled to obtain inorganic active filler; Suspension preparation: The polymer matrix and sodium salt are dissolved in a solvent, and the inorganic active filler is added and stirred to obtain a suspension; Preparation of sodium ion composite solid electrolyte: The suspension was cast into a mold and vacuum dried to obtain sodium ion composite solid electrolyte; Wherein, the M metal oxide is one or more of La2O3, Al2O3, Sm2O3, Eu2O3, Gd2O3, Sc2O3, and Y2O3.

7. The method for preparing the sodium ion composite solid electrolyte as described in claim 6, characterized in that, In the preparation of powder A, Na2CO3, SiO2 and M metal oxide are weighed in a molar ratio of 5:8:

1.

8. The method for preparing the sodium ion composite solid electrolyte as described in claim 6, characterized in that, The wet ball milling time is 12-16 hours; the dry ball milling time is 10-20 hours; the first sintering temperature is 800-950℃ and the sintering time is 8-15 hours; the vacuum drying time is 12-24 hours.

9. The method for preparing the sodium ion composite solid electrolyte as described in claim 6, characterized in that, During the preparation of the suspension, the polymer concentration in the solvent is 0.1–0.5 g / mL; the dissolution temperature is 30–60 °C.

10. A sodium-ion battery, characterized in that, It includes the sodium ion composite solid electrolyte as described in any one of claims 1 to 5, or the sodium ion composite solid electrolyte obtained by any one of the preparation methods described in claims 6 to 9.

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