A sodium ion solid-state electrolyte material with a dual-phase structure, a preparation method and applications thereof

Abstract

The present application relates to a kind of sodium ion solid electrolyte material of dual-phase structure and its preparation method and application, it simultaneously exists rhombic phase and monoclinic phase at 25 ℃~35 ℃, and it is atom level between two phases Binding;Its nominal composition Na 3+a Zr 2‑x‑y Sc x M y Si2PO 12 Wherein, M is other metal elements except Na, Zr and Sc, 0≤a≤0.5, 0.1≤x≤0.5, 0.3≤x+y≤1.2.The present application can promote the configuration entropy of sodium ion solid electrolyte material by introducing Sc and other metal elements except Na to replace part of Zr element in crystal lattice, make the rhombic phase of high ionic conductivity stable exist at room temperature and combine with monoclinic phase through superlattice structure, improve bulk conductivity at room temperature.In practical application, it can be used as positive electrode filler, reduce concentration polarization, improve the kinetic performance of thick electrode, significantly improve its rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a sodium-ion solid electrolyte material, particularly a two-phase structure sodium-ion solid electrolyte material, its preparation method, and its application. Background Technology

[0002] Uneven distribution, volatile prices, and supply security risks of key resources such as lithium and cobalt have become significant obstacles to the sustainable development of the industry. Sodium-ion batteries, as an emerging energy storage technology, have rapidly moved from the laboratory to the forefront of industrialization due to their unique resource and cost advantages, becoming a crucial piece in building a multi-layered energy storage system.

[0003] Sodium-ion batteries generally have lower theoretical specific capacity and voltage plateau than lithium-ion batteries, failing to meet the demand for long driving range. Therefore, increasing the areal loading of active material in the positive electrode through thick electrode design to reduce the proportion of inactive material, and using metallic sodium as the negative electrode, are effective ways to further improve battery energy density.

[0004] CN111106312A discloses the fabrication of a high-capacity self-supporting thick electrode and its application in sodium-ion batteries. The electrode has a thickness of 300 μm to 3000 μm and a capacity of 8 mg / cm³. 2 ~55mg / cm 2 This improves the mass ratio and energy density of active materials in the electrode. Furthermore, this electrode is self-supporting, eliminating the need for current collectors, binders, and additional conductive carbon, further enhancing the mass ratio and energy density of active materials. CN119481231A discloses a high-performance all-solid-state sodium-ion battery and its preparation method. This sodium-ion battery includes a Prussian white cathode, a metallic sodium anode, and a NASICON-type solid electrolyte. The stable three-dimensional open-frame structure of the Prussian white cathode, combined with the high room-temperature ionic conductivity of the NASICON-type solid electrolyte and the metallic sodium anode, effectively improves the ionic conductivity, electrochemical window, and capacity of the all-solid-state sodium-ion battery at room temperature.

[0005] However, thick electrode designs significantly increase ion / electron transport distances, reducing kinetic performance and leading to a substantial increase in concentration polarization at higher current densities, thus decreasing the rate performance of sodium-ion batteries. The high reactivity of the sodium anode causes it to form an unstable solid electrolyte interface film upon contact with the electrolyte, resulting in Na+... + Uneven deposition of Na dendrites leads to malignant growth of Na dendrites, which may even puncture the separator and cause a short circuit in the battery.

[0006] Therefore, how to improve the energy density of sodium-ion batteries while maintaining good kinetic performance, and thus improve the rate performance of sodium-ion batteries, is an urgent problem to be solved in the field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a dual-phase sodium-ion solid electrolyte material, its preparation method, and its applications. By introducing Sc and other non-Na metal elements to replace some Zr elements in the crystal lattice, the present invention effectively increases the configurational entropy of the sodium-ion solid electrolyte material. This allows the high-ionic-conductivity rhombic phase to exist stably at room temperature and combine with the highly structurally stable monoclinic phase through a superlattice structure. This atomic-level bonding significantly improves the bulk conductivity of the dual-phase sodium-ion solid electrolyte material at room temperature (25℃~35℃), which is beneficial for improving the kinetic performance of thick electrodes and avoiding concentration polarization. Therefore, while maintaining the high energy density of sodium-ion batteries, its rate performance is significantly improved.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a dual-phase sodium-ion solid electrolyte material, wherein the dual-phase sodium-ion solid electrolyte material simultaneously contains a rhombic phase and a monoclinic phase at 25℃~35℃, and the two phases are atomically bonded; the nominal composition of the dual-phase sodium-ion solid electrolyte material is Na. 3+a Zr 2-x-y Sc x M y Si2PO 12 Where M is a metallic element other than Na, Zr and Sc, 0≤a≤0.5, 0.1≤x≤0.5, 0.3≤x+y≤1.2.

[0010] For example, a can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, etc.; x can be 0.1, 0.2, 0.3, 0.4 or 0.5, etc.; x+y can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or 1.2, etc.

[0011] The general formula for this type of electrolyte is Na. 1+x M2Si x P 3-x O 12 M is a transition metal element represented by Zr. Under normal circumstances, when the M site is dominated by Zr, x=2, and the stoichiometry of Na is between 3 and 3.4, it is a monoclinic phase at room temperature. When the temperature is raised to above 150℃, it will transform into a rhombic phase with high ionic conductivity. This process is reversible. After cooling to room temperature, it will transform back into a monoclinic phase with high structural stability.

[0012] This invention effectively increases the configurational entropy of sodium-ion solid electrolyte materials by introducing Sc and other non-Na metal elements to replace part of the Zr element in the crystal lattice at the M site. This allows the high-ionic-conductivity rhombic phase to exist stably at room temperature and combine with the high-structural-stability monoclinic phase through a superlattice structure. Thus, a two-phase sodium-ion solid electrolyte material simultaneously contains both rhombic and monoclinic phases at 25℃~35℃, with atomic-level bonding between the two phases. On one hand, both crystal phases form a framework structure with shared angles, which can increase the intraphase Na... + Transmission rate; on the other hand, since the cell parameters a of the two crystal phases are close, atomic-level bonding is achieved between the two phases, which can greatly reduce interphase Na + The conduction energy barrier is reduced, resulting in a significant increase in ionic conductivity. High bulk conductivity is beneficial for improving the kinetic performance of thick electrodes and avoiding concentration polarization, thereby significantly improving the rate performance of sodium-ion batteries while maintaining their high energy density.

[0013] Preferably, the Na 3+a Zr 2-x-y Sc x M y Si2PO 12 M in the M includes at least three of Mg, Ca, Al, In, Sn, Hf, La, Nd, Ce, Y, Zn, or Nb. Typical but non-limiting combinations include combinations of Mg, Ca, and Al; combinations of In, Sn, and Hf; combinations of La, Nd, and Ce; combinations of Y, Zn, and Nb; combinations of Mg, Ca, Al, and In; combinations of Sn, Hf, La, and Nd; combinations of Ce, Y, Zn, and Nb; combinations of Mg, Ca, Al, In, Sn, and Hf; and combinations of La, Nd, Ce, Y, Zn, and Nb. Preferably, there are 4 to 6 types.

[0014] This invention introduces 4 to 6 additional M elements besides Sc to replace some of the Zr elements in the crystal lattice. Due to the different atomic radii and interactions with O, the configuration entropy of the sodium ion solid electrolyte material can be further increased, the Na-O bonds can be twisted, and the proportion of rhombic phase can be increased, which is beneficial to further improve the bulk conductivity of the two-phase sodium ion solid electrolyte material.

[0015] Preferably, the proportion of the rhomboid phase is 10% to 60%, for example, it can be 10%, 20%, 30%, 40%, 45%, 50%, 55% or 60%, etc., preferably 30% to 60%.

[0016] The biphase sodium-ion solid electrolyte material provided by this invention has the advantage of improving bulk conductivity when the proportions of the rhombic phase and the monoclinic phase are similar.

[0017] Preferably, the bulk conductivity of the biphase sodium-ion solid electrolyte material at 25℃~35℃ is 3mS / cm~8mS / cm, for example, it can be 3mS / cm, 4mS / cm, 5mS / cm, 6mS / cm, 7mS / cm or 8mS / cm, etc.

[0018] The dual-phase sodium-ion solid electrolyte material provided by this invention simultaneously exhibits two phase structures at room temperature: a rhombic phase with high ionic conductivity and a monoclinic phase with high structural stability. On one hand, both crystalline phases form a framework structure with shared angles, which can improve the intraphase Na... + Transmission rate; on the other hand, since the cell parameters a of the two crystal phases are close, atomic-level bonding is achieved between the two phases, which can reduce interphase Na + The conduction energy barrier is reduced, and the ionic conductivity is significantly improved.

[0019] Preferably, the dual-phase sodium-ion solid electrolyte material is used at 25℃~35℃ vs. Na / Na + The oxidation potential is 4.5V~5.0V, for example, it can be 4.5V, 4.6V, 4.7V, 4.8V, 4.9V or 5.0V, etc.

[0020] The biphase sodium-ion solid electrolyte material provided by this invention has a high oxidation potential (vs. Na / Na). + This can be matched with high specific energy cathode materials, which is beneficial to improving the dynamic performance of the cathode (thick electrode) and thus improving the energy density of sodium-ion batteries.

[0021] Furthermore, the dual-phase sodium-ion solid electrolyte material provided by this invention exhibits good processing performance due to the corresponding decrease in its shear modulus caused by the distortion of the Na-OM lattice.

[0022] In a second aspect, the present invention provides a method for preparing a biphase sodium-ion solid electrolyte material as described in the first aspect, comprising the following steps: mixing Na2CO3, SiO2, NH4H2PO4 and oxides or carbonates of Zr, Sc, and M in stoichiometric ratios, then adding 3% to 10% excess Na2CO3 in stoichiometric ratios, and then sequentially performing a first ball milling and a first calcination to obtain a master powder; and sequentially performing a second ball milling and a second calcination on the master powder to obtain the biphase sodium-ion solid electrolyte material.

[0023] In this invention, Sc and M ions work together. Sc, due to its larger ionic radius, can improve the symmetry of the crystal structure, which is conducive to the formation of the rhombic phase. The introduction of multiple M ions can increase the configurational entropy and twist the Na-O bonds of the sodium-ion solid electrolyte material, and reduce the ion transport activation energy. The combined effect of these two ions allows the high-conductivity rhombic phase to exist stably at room temperature and combine with the highly structurally stable monoclinic phase through a superlattice structure. This atomic-level bonding can significantly improve the bulk conductivity of the two-phase sodium-ion solid electrolyte material at room temperature, which is beneficial for improving the kinetic performance of thick electrodes and avoiding concentration polarization. Thus, while maintaining the high energy density of sodium-ion batteries, its rate performance is significantly improved.

[0024] Preferably, the rotational speeds of the first ball mill and the second ball mill are independently 600 rpm to 1000 rpm, for example, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm.

[0025] Preferably, the time for the first ball milling and the second ball milling is independently 6h to 12h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0026] Preferably, the temperature of the first calcination is 1000℃~1300℃, for example, it can be 1000℃, 1050℃, 1200℃, 1250℃ or 1300℃.

[0027] Preferably, the first calcination time is 3h to 8h, for example, it can be 3h, 4h, 5h, 6h, 7h or 8h.

[0028] Preferably, the second calcination temperature is 1000℃~1250℃, for example, it can be 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or 1250℃.

[0029] Preferably, the second calcination time is 6h to 18h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 14h, 16h or 18h.

[0030] Thirdly, the present invention provides a thick electrode comprising a biphase sodium-ion solid electrolyte material as described in the first aspect.

[0031] This invention adds a dual-phase sodium-ion solid electrolyte material to a thick electrode. The high bulk conductivity of the dual-phase sodium-ion solid electrolyte material helps improve the kinetic performance of the thick electrode and avoids concentration polarization, thereby significantly improving the rate performance of the sodium-ion battery while maintaining its high energy density.

[0032] Preferably, the thick electrode further includes a positive electrode active material, a conductive agent, and a binder.

[0033] Preferably, the positive electrode active material includes NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 ternary cathode material and / or NaNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 ternary cathode material.

[0034] Preferably, the conductive agent comprises multi-walled carbon nanotubes and / or carbon black.

[0035] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, polyacrylic acid, or polytetrafluoroethylene. Typical but non-limiting combinations include combinations of polyvinylidene fluoride and polyacrylic acid, combinations of polyacrylic acid and polytetrafluoroethylene, combinations of polyvinylidene fluoride and polytetrafluoroethylene, and combinations of polyvinylidene fluoride, polyacrylic acid, and polytetrafluoroethylene.

[0036] Preferably, the mass ratio of the positive electrode active material, conductive agent, binder and biphase sodium ion solid electrolyte material is (80~95):(1~5):(1~5):(1~10), for example, it can be 90:2:3:5, 80:5:5:10, 85:5:5:5, 90:1:1:8, 90:3:3:4 or 95:1:1:3, etc.

[0037] Preferably, the thick electrode is prepared by a wet method or a dry method.

[0038] For example, the wet preparation includes the following steps:

[0039] (1) Dissolve the binder in N-methylpyrrolidone, and at the same time, dry mix the positive electrode active material, the biphase sodium ion solid electrolyte material and the conductive agent according to the mass ratio to obtain a mixture. After the binder is fully dissolved, add it to the above mixture and stir for 1h~8h to obtain the electrode slurry.

[0040] (2) The electrode paste is coated on both sides of the current collector foil, dried and rolled to obtain a thick electrode.

[0041] For example, the dry preparation includes the following steps:

[0042] (1) Mix the positive electrode active material, the two-phase structure sodium ion solid electrolyte material, the conductive agent and the binder in proportion, and use a planetary ball mill. After adding a small amount of ethanol, the mixture is ball-milled at a speed of 200 rpm to 500 rpm for 2 h to 8 h.

[0043] (2) The dough-like material after ball milling is hot rolled and pressed at a temperature of 45℃~75℃, rolled and pressed to a certain thickness, such as 75μm~500μm.

[0044] (3) The electrode after hot rolling is hot-pressed onto the surface of the current collector foil to obtain a thick electrode.

[0045] Preferably, the areal loading of the positive electrode active material in the thick electrode is 10 mg / cm³. 2 ~50mg / cm 2 For example, it could be 10 mg / cm³ 2 20mg / cm 2 30mg / cm 2 40mg / cm 2 Or 50mg / cm 2 wait.

[0046] Fourthly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a thick electrode as described in the third aspect.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] This invention effectively increases the configurational entropy of sodium-ion solid electrolyte materials by introducing Sc and other non-Na metal elements to replace part of the Zr element in the crystal lattice at the M site. This allows the high-ionic-conductivity rhombic phase to exist stably at room temperature and combine with the high-structural-stability monoclinic phase through a superlattice structure. Thus, a two-phase sodium-ion solid electrolyte material simultaneously contains both rhombic and monoclinic phases at 25℃~35℃, with atomic-level bonding between the two phases. On one hand, both crystal phases form a framework structure with shared corners, which can improve the Na... + Transmission rate; on the other hand, since the cell parameters a of the two crystal phases are close, atomic-level bonding is achieved between the two phases, which can greatly reduce Na... + The interphase transport energy barrier is reduced, resulting in a significant increase in ionic conductivity. High bulk conductivity is beneficial for improving the kinetic performance of thick electrodes and avoiding concentration polarization, thereby significantly improving the rate performance of sodium-ion batteries while maintaining their high energy density. Attached Figure Description

[0050] Figure 1 These are cryo-transmission electron microscope images of the biphase sodium-ion solid electrolyte material in Example 1;

[0051] A - Monoclinic phase, B - Rhomboid phase, C - Two-phase transition zone.

[0052] Figure 2 The differential scanning calorimeter test curves are those of the two-phase sodium ion solid electrolyte material in Example 1.

[0053] Figure 3 This is a refined XRD pattern of the biphase sodium-ion solid electrolyte material in Example 1.

[0054] Figure 4 This is the refined XRD pattern of the single-phase sodium-ion solid electrolyte material in Comparative Example 3. Detailed Implementation

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0056] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] Unless otherwise specified, the term "at least two combinations" in this invention refers to a quantity greater than or equal to 2. For example, "any one or at least two combinations" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention.

[0058] In this invention, unless otherwise specified, the feature or solution corresponding to "and / or" covers any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a set consisting of A, B, and combinations of A and B. "Including A and / or B" can be understood, depending on the context of the statement, as including A, including B, or simultaneously including both A and B. In this invention, "optional" means that the corresponding feature, component, step, or solution is not essential, i.e., selected from either "present" or "absent" parallel solutions. If multiple "optional" limitations appear in a technical solution, unless otherwise specified and without technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0059] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A may consist only of a1, a2, and a3, or it may include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements."

[0060] All embodiments and optional embodiments of the present invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of the present invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment or implementation of the present invention. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this invention can be combined with other embodiments without technical conflict.

[0061] In this invention, the ordinal numbers “first,” “second,” “third,” and “fourth” used in expressions such as “first aspect,” “second aspect,” “third aspect,” and “fourth aspect” 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. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0062] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0063] Example 1

[0064] This embodiment provides a two-phase sodium-ion solid electrolyte material with a nominal composition of Na. 3.3 ZrSc 0. 2Mg 0.1 Ca 0.1 Sn 0.3 Nb 0.3 Si2PO 12 It exhibits both rhombic and monoclinic phases at temperatures ranging from 25℃ to 35℃, with the two phases bonded at the atomic level, and the rhombic phase accounting for 51%.

[0065] The biphase sodium ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). Its bulk conductivity at room temperature was 7.8 mS / cm.

[0066] This biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.8V.

[0067] The preparation method of the two-phase structure sodium ion solid electrolyte material provided in this embodiment includes the following steps:

[0068] (1) Mix Na2CO3, SiO2, NH4H2PO4, ZrO2, Sc2O3, MgO, CaCO3, SnO2 and Nb2O5 according to the stoichiometric ratio, and add an additional 5% excess (stoichiometric ratio) of Na2CO3. Then, perform a first ball mill and a first calcination to obtain the mother powder. The first ball milling speed is 800 rpm and the first ball milling time is 8 h. The first calcination temperature is 1050℃ and the first calcination time is 6 h.

[0069] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein the rotation speed of the second ball mill was 800 rpm and the time of the second ball mill was 8 h; the temperature of the second calcination was 1150℃ and the time of the second calcination was 12 h.

[0070] Figure 1 This is a cryo-transmission electron microscope image of the biphase sodium-ion solid electrolyte material in this embodiment. It can be seen that it simultaneously contains a monoclinic phase and a rhombic phase.

[0071] Figure 2 The differential scanning calorimeter test curves of the two-phase sodium ion solid electrolyte material in this embodiment show that there are no obvious endothermic peaks within the test temperature range, indicating that its surface two-phase structure is stable and the phase transition process disappears at high temperatures.

[0072] Example 2

[0073] This embodiment provides a two-phase sodium-ion solid electrolyte material with a nominal composition of Na. 3.3 ZrSc 0. 2Ca 0.1 In 0.1 Sn 0.3 Nb 0.3 Si2PO 12 It exhibits both rhombic and monoclinic phases at temperatures ranging from 25℃ to 35℃, with the two phases bonded at the atomic level, and the rhombic phase accounting for 45%.

[0074] The biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). The bulk conductivity at room temperature was 6.2 mS / cm.

[0075] This biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.76V.

[0076] The preparation method of the two-phase structure sodium ion solid electrolyte material provided in this embodiment includes the following steps:

[0077] (1) Na2CO3, SiO2, NH4H2PO4, ZrO2, Sc2O3, CaO, In2O3, SnO2 and Nb2O5 are mixed in stoichiometric ratio, and an additional 8% excess (stoichiometric ratio) of Na2CO3 is added. The mixture is then subjected to a first ball mill and a first calcination to obtain a mother powder. The first ball milling speed is 600 rpm and the first ball milling time is 12 h. The first calcination temperature is 1100℃ and the first calcination time is 3 h.

[0078] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein, the rotation speed of the second ball mill was 600 rpm and the time of the second ball mill was 12 h; the temperature of the second calcination was 1150℃ and the time of the second calcination was 16 h.

[0079] Example 3

[0080] This embodiment provides a two-phase sodium-ion solid electrolyte material with a nominal composition of Na. 3.3 ZrSc 0. 2Mg 0.1 Ca 0.1 Sn 0.1 Hf 0.2 Nb 0.3 Si2PO 12 It exhibits both rhombic and monoclinic phases at temperatures ranging from 25℃ to 35℃, with the two phases bonded at the atomic level. The rhombic phase accounts for 47% of the total.

[0081] The biphase sodium ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). The bulk conductivity at room temperature was 5.8 mS / cm.

[0082] This biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.8V.

[0083] The preparation method of the two-phase structure sodium ion solid electrolyte material provided in this embodiment includes the following steps:

[0084] (1) Na2CO3, SiO2, NH4H2PO4, ZrO2, Sc2O3, MgO, CaCO3, SnO2, HfO2 and Nb2O5 are mixed in stoichiometric ratio, and an additional 3% excess (stoichiometric ratio) of Na2CO3 is added. The mixture is then subjected to a first ball mill and a first calcination to obtain a mother powder. The first ball milling speed is 1000 rpm and the first ball milling time is 6 h. The first calcination temperature is 1200℃ and the first calcination time is 8 h.

[0085] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein the rotation speed of the second ball mill was 1000 rpm and the time of the second ball mill was 6 h; the temperature of the second calcination was 1100℃ and the time of the second calcination was 6 h.

[0086] Comparative Example 1

[0087] This comparative example provides a two-phase sodium-ion solid electrolyte material with a nominal composition of Na. 3.4 Zr 1.6 Sc 0.4 Si2PO 12 It exists simultaneously as a monoclinic phase and a rhombic phase at 25℃~35℃, and the two phases are atomically bonded, with the rhombic phase accounting for about 42%.

[0088] The biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). The bulk conductivity at room temperature was 2.1 mS / cm.

[0089] This biphase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.8V.

[0090] The preparation method of the two-phase structure sodium-ion solid electrolyte material provided in this comparative example includes the following steps:

[0091] (1) Mix Na2CO3, SiO2, NH4H2PO4, ZrO2 and Sc2O3 according to the stoichiometric ratio, and add an additional 5% excess (stoichiometric ratio) of Na2CO3. Then, perform a first ball mill and a first calcination to obtain the mother powder. The first ball milling speed is 800 rpm and the first ball milling time is 8 h. The first calcination temperature is 1050℃ and the first calcination time is 6 h.

[0092] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein the rotation speed of the second ball mill was 800 rpm and the time of the second ball mill was 8 h; the temperature of the second calcination was 1150℃ and the time of the second calcination was 12 h.

[0093] Comparative Example 2

[0094] This comparative example provides a single-phase sodium-ion solid electrolyte material with a nominal composition of Na. 3.2 Zr 1.2 Mg 0.5 Nb 0.3 Si2PO 12 Only monoclinic phases exist; rhomboid phases do not exist.

[0095] The single-phase sodium ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). Its bulk conductivity at room temperature was 1.8 mS / cm.

[0096] This single-phase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.8V.

[0097] The preparation method of the single-phase sodium-ion solid electrolyte material provided in this comparative example includes the following steps:

[0098] (1) Mix Na2CO3, SiO2, NH4H2PO4, ZrO2, MgO and Nb2O5 according to the stoichiometric ratio, and add an additional 5% excess (stoichiometric ratio) of Na2CO3. Then, perform the first ball milling and the first calcination in sequence to obtain the mother powder. The first ball milling speed is 800 rpm and the first ball milling time is 8 h. The first calcination temperature is 1050℃ and the first calcination time is 6 h.

[0099] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein the rotation speed of the second ball mill was 800 rpm and the time of the second ball mill was 8 h; the temperature of the second calcination was 1150℃ and the time of the second calcination was 12 h.

[0100] Comparative Example 3

[0101] This comparative example provides a single-phase sodium-ion solid electrolyte material with a nominal composition of Na3Zr2Si2PO4. 12 Only monoclinic phases exist; rhomboid phases do not exist.

[0102] The single-phase sodium ion solid electrolyte material was pressed into an electrolyte sheet, and its ionic conductivity was tested at 25°C using a symmetrical blocking electrode (stainless steel sheet). Its bulk conductivity at room temperature was 0.7 mS / cm.

[0103] This single-phase sodium-ion solid electrolyte material was pressed into an electrolyte sheet, and a Na anode / electrolyte sheet / stainless steel sheet battery was assembled. Electrochemical window testing was performed to measure its oxidation potential (vs. Na / Na). + The voltage is 4.8V.

[0104] The preparation method of the single-phase sodium-ion solid electrolyte material provided in this comparative example includes the following steps:

[0105] (1) Mix Na2CO3, SiO2, NH4H2PO4 and ZrO2 according to the stoichiometric ratio, and add an additional 5% excess (stoichiometric ratio) of Na2CO3. Then, perform the first ball milling and the first calcination in sequence to obtain the mother powder. The first ball milling speed is 800 rpm and the first ball milling time is 8 h. The first calcination temperature is 1050℃ and the first calcination time is 6 h.

[0106] (2) The mother powder was subjected to a second ball mill and a second calcination in sequence to obtain a two-phase sodium ion solid electrolyte material; wherein the rotation speed of the second ball mill was 800 rpm and the time of the second ball mill was 8 h; the temperature of the second calcination was 1150℃ and the time of the second calcination was 12 h.

[0107] The biphase (single-phase) sodium-ion solid electrolyte materials in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to X-ray diffraction (XRD) analysis at 25°C and then refined to analyze their phase structure and the proportion of each phase.

[0108] Figure 3 This is a refined XRD pattern of the two-phase sodium-ion solid electrolyte material in Example 1. Figure 4 This is the refined XRD pattern of the single-phase sodium-ion solid electrolyte material in Comparative Example 3. From... Figure 3 It can be seen that the biphase sodium-ion solid electrolyte material in Example 1 simultaneously contains a rhombic phase and a monoclinic phase, with a ratio close to 1:1. From Figure 4 It can be seen that the single-phase sodium ion solid electrolyte material in Comparative Example 3 only has a monoclinic phase and no rhombic phase.

[0109] The dual-phase sodium-ion solid electrolyte materials provided in Examples 1-3 exhibit high bulk conductivity and high oxidation potential. On one hand, the high bulk conductivity is beneficial for improving the kinetic performance of the thick electrode and avoiding concentration polarization, thereby significantly improving the rate performance of the sodium-ion battery while maintaining its high energy density. On the other hand, the high oxidation potential is beneficial for matching high-specific-energy cathode materials, improving the kinetic performance of the cathode (thick electrode), and thus increasing the energy density of the sodium-ion battery.

[0110] Compared to Example 1, Comparative Example 1, which only contained Sc as a substituent, also achieved a two-phase structure, but this only increased the crystal symmetry; the Na-O bonds were not sufficiently twisted, resulting in a minimal improvement in the bulk conductivity of its two-phase sodium-ion solid electrolyte material. In contrast, Comparative Example 2, which did not contain Sc, contained three metal ions with different valence states, allowing for some degree of Na-O bond twisting, but the insufficient crystal symmetry made it difficult to achieve better performance.

[0111] Application Examples 1 to 9 and Comparative Application Examples 1 to 3

[0112] Application Examples 1 to 9 and Comparative Application Examples 1 to 3 provide a sodium-ion battery, the preparation method of which includes the following steps:

[0113] (1) The two-phase sodium-ion solid electrolyte materials in Examples 1 to 3 and the single-phase sodium-ion solid electrolyte material in Comparative Example 3 were respectively mixed with NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 ternary cathode material and multi-walled carbon nanotubes were dry-mixed to obtain a mixture; polyvinylidene fluoride was dissolved in N-methylpyrrolidone, and after complete dissolution, it was added to the above mixture. After stirring for 4 hours, an electrode slurry was obtained. NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The mass ratio of O2 ternary cathode material, multi-walled carbon nanotubes, polyvinylidene fluoride, and biphase (single-phase) sodium-ion solid electrolyte material is 90:2:3:5.

[0114] (2) The electrode paste is coated on both sides of the current collector foil, dried, and rolled to obtain a thick electrode, wherein the areal loading of the positive electrode active material is approximately 10.5, 35.4, or 47.2 mg / cm³, respectively. 2 .

[0115] In Application Examples 1 to 3, the biphase sodium-ion solid electrolyte material of Example 1 was used, but the areal loading of the positive electrode active material was different; in Application Examples 4 to 6, the biphase sodium-ion solid electrolyte material of Example 2 was used, but the areal loading of the positive electrode active material was different; in Application Examples 7 to 9, the biphase sodium-ion solid electrolyte material of Example 3 was used, but the areal loading of the positive electrode active material was different; in Comparative Application Examples 1 to 3, the single-phase sodium-ion solid electrolyte material of Comparative Example 3 was used, but the areal loading of the positive electrode active material was different.

[0116] (4) In a glove box where the moisture and oxygen content are both less than 1 ppm, the thick electrode is used as the positive electrode and metallic sodium is used as the negative electrode. The sodium-ion battery is assembled using commercially available membranes and electrolytes.

[0117] Compare and contrast application examples 4 to 6.

[0118] Comparative Application Examples 4 to 6 provide a sodium-ion battery that is identical to Application Examples 1 to 3 except that it does not contain a two-phase sodium-ion solid electrolyte material.

[0119] The sodium-ion batteries from Application Examples 1 to 9 and Comparative Application Examples 1 to 6 were activated at room temperature by charging and discharging at a rate of 0.05C for one week. At room temperature, they were then charged and discharged at a rate of 0.1C for one week between 2V and 4.2V, and their capacity was calibrated. After 5 cycles, the charging rate was fixed at 0.1C, and the discharge rate was increased to 0.2C, 0.5C, and 1C, respectively, and 5-week charge-discharge tests were performed for each. Finally, the discharge rate was reduced to 0.1C, and another 5-week charge-discharge test was performed. To eliminate the specific capacity anomaly caused by fluctuations in the coulombic efficiency of the counter electrode (sodium metal) under high areal loading, the specific capacity (in mAh / g) at the second week of each discharge rate was recorded as the reversible capacity, and its rate performance was evaluated.

[0120] The test results are shown in Table 1.

[0121]

[0122] As can be seen from Table 1, the sodium-ion battery provided in Application Example 1 exhibits high energy density and excellent rate performance. For electrodes with comparable areal loading of the positive electrode active material, when the areal loading is low, such as 10.5 mg / cm³, the energy density is significantly higher. 2 (Application Examples 1, 4, and 7 and Comparative Application Examples 1 and 4) There was no obvious concentration polarization in the thick electrode. Even at a discharge rate of 1.0C, the sodium-ion batteries all exhibited considerable reversible capacity due to the good performance of the sodium electrolyte.

[0123] However, as the surface load increases, especially when the surface load reaches 40 mg / cm³, 2 In the above examples (Application Examples 3, 6, and 9 versus Comparative Application Examples 3 and 6), the reversible capacity of the comparative applications all showed a significant decrease. Even at a discharge rate of 0.1C, their reversible capacity was significantly lower than that of thick electrodes with low areal load (sodium-ion batteries). In contrast, Application Examples 1 to 9, due to the introduction of a two-phase sodium-ion solid electrolyte material with high bulk conductivity, still exhibited a higher reversible capacity even at a discharge rate of 1.0C.

[0124] In summary, this invention, by introducing Sc and other non-Na metal elements to replace part of the Zr element in the crystal lattice at the M site, can effectively increase the configuration entropy of sodium-ion solid electrolyte materials. This allows the high-ionic-conductivity rhombic phase to exist stably at room temperature and combine with the high-structural-stability monoclinic phase through a superlattice structure. Thus, the dual-phase sodium-ion solid electrolyte material simultaneously contains both rhombic and monoclinic phases at 25℃~35℃, with atomic-level bonding between the two phases. On one hand, both crystal phases form a framework structure with shared angles, which can increase the intraphase Na... + Transmission rate; on the other hand, since the cell parameters a of the two crystal phases are close, atomic-level bonding is achieved between the two phases, which can greatly reduce interphase Na + The conduction energy barrier is reduced, resulting in a significant increase in ionic conductivity. High bulk conductivity is beneficial for improving the kinetic performance of thick electrodes and avoiding concentration polarization, thereby significantly improving the rate performance of sodium-ion batteries while maintaining their high energy density.

[0125] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A two-phase sodium-ion solid electrolyte material, characterized in that, The dual-phase sodium-ion solid electrolyte material exhibits both a rhombic phase and a monoclinic phase at 25℃~35℃, with the two phases bonded at the atomic level. The nominal composition of the dual-phase sodium-ion solid electrolyte material is Na. 3+a Zr 2-x-y Sc x M y Si2PO 12 Where M is a metallic element other than Na, Zr and Sc, 0≤a≤0.5, 0.1≤x≤0.5, 0.3≤x+y≤1.

2.

2. The dual-phase sodium-ion solid electrolyte material according to claim 1, characterized in that, The Na 3+ a Zr 2-x-y Sc x M y Si2PO 12 M in the formula includes at least three of Mg, Ca, Al, In, Sn, Hf, La, Nd, Ce, Y, Zn or Nb, preferably four to six.

3. The dual-phase sodium-ion solid electrolyte material according to claim 1 or 2, characterized in that, The rhomboid phase accounts for 10% to 60%, preferably 30% to 60%.

4. The dual-phase sodium-ion solid electrolyte material according to any one of claims 1 to 3, characterized in that, The bulk conductivity of the biphase sodium ion solid electrolyte material at 25℃~35℃ is 3mS / cm~8mS / cm; Preferably, the dual-phase sodium-ion solid electrolyte material is used at 25℃~35℃ vs. Na / Na + Its oxidation potential is 4.5V~5.0V.

5. A method for preparing a biphase sodium-ion solid electrolyte material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The oxides or carbonates of Na2CO3, SiO2, NH4H2PO4 and Zr, Sc and M are mixed in stoichiometric ratio, and then 3% to 10% excess of Na2CO3 is added. The mixture is then subjected to a first ball milling and a first calcination to obtain the mother powder. The mother powder was subjected to a second ball milling and a second calcination to obtain the dual-phase sodium ion solid electrolyte material.

6. The preparation method according to claim 5, characterized in that, The rotational speeds of the first ball mill and the second ball mill are independently 600 rpm to 1000 rpm; Preferably, the time for the first ball milling and the second ball milling is independently 6h~12h; Preferably, the temperature of the first calcination is 1000℃~1300℃; Preferably, the first calcination time is 3h~8h; Preferably, the second calcination temperature is 1000℃~1250℃; Preferably, the second calcination time is 6h to 18h.

7. A thick electrode, characterized in that, The thick electrode comprises a biphase sodium-ion solid electrolyte material as described in any one of claims 1 to 4.

8. The thick electrode according to claim 7, characterized in that, The thick electrode also includes a positive electrode active material, a conductive agent, and a binder; Preferably, the positive electrode active material includes NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 ternary cathode material and / or NaNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 ternary cathode material; Preferably, the conductive agent comprises carbon nanotubes and / or carbon black; Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, polyacrylic acid, or polytetrafluoroethylene; Preferably, the mass ratio of the positive electrode active material, conductive agent, binder and biphase sodium ion solid electrolyte material is (80~95):(1~5):(1~5):(1~10).

9. A thick electrode as described in claim 7 or 8, characterized in that, The thick electrode is prepared by a wet method or a dry method; Preferably, the areal loading of the positive electrode active material in the thick electrode is 10 mg / cm³. 2 ~50mg / cm 2 .

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a thick electrode as described in any one of claims 7 to 9.

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