A novel garnet-type solid electrolyte, its preparation method and application

Abstract

The present invention discloses a novel garnet-type solid electrolyte, the solid electrolyte Na 1‑x+y Ca 2‑x La x Mg 2 V 3‑ y Zr y O 12 , wherein, 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1. Applying the solid electrolyte of the present invention in a battery can improve the ionic conductivity of the electrolyte, thereby facilitating the improvement of the battery capacity. The present invention also provides a preparation method of the solid electrolyte, which can successfully dope La and Zr in NaCa 2 Mg 2 V 3 O 12 solid electrolyte simultaneously to obtain a solid electrolyte with a cubic phase structure. The solid electrolyte provided by the present invention can be used in sodium ion batteries.

Description

Technical Field

[0001] The present invention relates to the field of electrolytes for sodium-ion batteries, and particularly to a novel garnet-type solid electrolyte, its preparation method and application. Background Art

[0002] With the rapid consumption of fossil fuels, the greenhouse effect and environmental problems caused by the large-scale emission of carbon dioxide are becoming increasingly serious. Against the backdrop of the era of low-carbon energy, electrified transportation and intelligent devices, lithium batteries and sodium batteries, as green and clean secondary energy storage devices, have received extensive attention both internationally and domestically. In addition, China's energy structure has long been characterized by rich coal, scarce gas and lack of oil, and energy security and environmental sustainable development face huge challenges. The "Electric China" built by lithium batteries and sodium batteries will greatly improve China's energy structure, ensure energy security and achieve environmental sustainable development.

[0003] Since the commercialization of lithium-ion batteries in 1991, after more than 30 years of development, great success has been achieved, especially in the "3C" (i.e., Communication, Computer, Consumer electronics) market; lithium-ion batteries are also the best choice for power batteries of electric vehicles and have currently been applied to electric vehicles. With the large-scale application of electric vehicles, the demand for lithium will inevitably increase, while the reserves of lithium resources are limited and unevenly distributed in the earth's crust (about 70% of lithium is concentrated in South America). The current price of lithium carbonate is also around 150,000 yuan per ton. Therefore, it is difficult for lithium-ion batteries to simultaneously support the development of the two major industries of electric vehicles and grid energy storage.

[0004] Due to the advantages of rich resources and low cost of sodium element, sodium-ion batteries have received extensive attention from researchers. Relevant research institutions at home and abroad have included them in their R & D plans with a view to realizing industrialization. Similar to the very mature commercial lithium-ion batteries, current sodium-ion batteries all use organic liquid electrolytes, which have safety hazards such as flammability and explosiveness. Therefore, solid-state sodium batteries with the advantages of low cost and high safety have become an important development direction in the future large-scale energy storage field. The solid electrolytes in existing sodium solid-state batteries include NaCa 2 Mg 2 V 3 O 12 , although having good heat resistance, but when under high voltage conditions, the interface with the electrode is often unstable and prone to serious capacity attenuation. Research scholars believe that this may be due to the release of lattice oxygen in the electrolyte; secondly, this solid electrolyte has a low ionic conductivity. Therefore, how to solve the solid electrolyte NaCa 2 Mg 2 V 3O 12 The technical problems of capacity decay and ionic conductivity of Summary of the Invention

[0005] In view of the problems in the prior art, the present invention discloses a novel garnet-type solid electrolyte, its preparation method and application. By doping La into the NaCa 2 Mg 2 V 3 O 12 solid electrolyte with a cubic phase structure, the release of lattice oxygen in the solid electrolyte is reduced and Na vacancies are formed in the unit cell, promoting the migration of Na ions through transition, thereby improving the ionic conductivity of the battery while reducing the capacity decay of the battery; on this basis, further doping of Zr regulates the number of sodium vacancies in the unit cell, which is more conducive to improving the ionic conductivity of the battery.

[0006] The present invention is achieved through the following technical solutions:

[0007] A novel garnet-type solid electrolyte provided by the present invention, the solid electrolyte is Na 1-x+y Ca 2- x La x Mg 2 V 3-y Zr y O 12 , where 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1.

[0008] With the above design of the present invention, doping La into the cubic-phase NaCa 2 Mg 2 V 3 O 12 solid electrolyte, the doping of La replaces part of Ca 3+ , while changing the distribution of Na 2+ in the structure, La and O form La-O bonds with higher bond energy, which is conducive to the more stable existence of O in the lattice, and is conducive to reducing the capacity decay of the sodium-ion battery; and Na vacancies are formed in the unit cell, which is conducive to the transition of Na + on the vacancies, thereby realizing the migration of sodium ions and improving the ionic conductivity of the solid electrolyte. On this basis, we can further dope Zr in the unit cell. Zr + partially replaces V 4+ for substitution doping at the site, on the one hand, to adjust La 5+ sites for substitution doping, on the one hand, to adjust the number of sodium vacancies in the unit cell, which is more conducive to improving the ionic conductivity of the battery. 3+The excessive sodium vacancies caused by substitution may lead to the inability of the electrolyte to maintain the variation of its differential capacitance with voltage. On the other hand, the doping of La and Zr will change the unit cell structure to a certain extent, and the increase in the unit cell volume is beneficial to the transition of Na ions in the unit cell, which can improve the electrochemical performance of the solid electrolyte. The Zr-O bond can further enhance the stability of the unit cell structure after doping.

[0009] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 has a cubic phase structure. In the cubic phase structure, the transition distance between Na and Na is short, which is beneficial to the migration of Na + and is beneficial to improving the ionic conductivity.

[0010] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 In the X-ray powder diffraction pattern represented by the diffraction angle 2θ, there are characteristic diffraction peaks at 17°±1.1°, 20°±1.1°, 32°±1.1°, 33°±1.1°, 36°±1.1°, 39°±1.1°, 44°±1.1°, 50°±1.1°.

[0011] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 The unit cell parameters of the range of a the range of b the range of c

[0012] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12The Na element therein is derived from a sodium source, the Ca element is derived from a calcium source, the La element is derived from a lanthanum source, the Mg element is derived from a magnesium source, the Zr element is derived from a zirconium source, and the V element is derived from a vanadium source.

[0013] As a further solution, the sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium perchlorate, and sodium bis(trifluoromethanesulfonyl)imide.

[0014] As a further solution, the calcium source includes one or more of calcium oxide, calcium carbonate, and calcium hydroxide.

[0015] As a further solution, the lanthanum source includes one or more of lanthanum oxide, lanthanum nitrate, lanthanum chloride, and lanthanum fluoride.

[0016] As a further solution, the magnesium source includes one or more of magnesium oxide and basic magnesium carbonate.

[0017] As a further solution, the zirconium source includes one or more of zirconium oxide, zirconium nitrate, and zirconium acetate.

[0018] As a further solution, the vanadium source includes one or more of vanadium pentoxide, ammonium metavanadate, and vanadium trichloride.

[0019] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , wherein, 0 < y < 1, 0 < x < 1, y < x, and x + y < 1. The co-doping of La and Zr is more beneficial to the increase of the unit cell volume and is beneficial to improving the ionic conductivity and capacity of the battery.

[0020] As a further solution, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , wherein, 0 < y < 1, 0 < x < 1, y < x, and x + y = 0.1 - 0.3. When x + y = 0.1 - 0.3, the range of Na atoms in the solid electrolyte is 0.7 - 0.9, and there are appropriate sodium vacancies in the unit cell, which is more beneficial to promoting the transition of sodium ions, thereby improving the ionic conductivity and capacity of the battery.

[0021] The present invention also provides a preparation method of the solid electrolyte, including the following steps:

[0022] S1: According to the solid electrolyte Na1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , wherein 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1. Sodium source, calcium source, lanthanum source, magnesium source, zirconium source and vanadium source are weighed respectively according to the stoichiometric ratio of each element in the solid electrolyte;

[0023] S2: After adding a dispersant to the raw materials weighed in S1 and dispersing them, perform the first ball milling, and dry the mixture to obtain a mixed powder;

[0024] S3: Heat the mixed powder obtained in S2;

[0025] S4: Perform the second ball milling on the mixed powder after heating in S3 to obtain a secondary powder;

[0026] S5: Calcinate the mixed powder after dispersion in S4 to carry out a solid-phase reaction;

[0027] S6: Naturally cool after the solid-phase reaction is completed to obtain the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 .

[0028] In the preparation method of the present invention, during the first ball milling process, the sodium source, calcium source, lanthanum source, magnesium source, zirconium source and vanadium source can be fully and evenly dispersed, which is beneficial to promoting the preliminary reaction between substances during the heating process, thereby initially generating a cubic solid electrolyte doped with La and Zr; the second ball milling is beneficial to promoting the full exposure of substances that have not reacted during the heating process, which is beneficial to promoting the full solid-phase reaction of substances during the next sintering process, and then forming a stable cubic solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 for preparation.

[0029] As a further scheme, the dispersant in S1 includes ethanol; the ball milling medium for the first ball milling in S2 includes anhydrous ethanol or propanol; the ball milling medium for the second ball milling in S4 includes anhydrous ethanol or propanol.

[0030] As a further solution, by mass, the additive mass of the sodium source in S1 is 3%-8% more than the added amount mass of the theoretical sodium source calculated by stoichiometry in S1. The sodium source is liable to volatilize and be lost during the sintering process.

[0031] As a further solution, the conditions of both S1 and S2 are in an inert gas; the drying temperature in S2 is 100°C - 200°C, and the drying time is 5 - 8 h; the speed of the first ball milling in S2 is 300 rpm - 450 rpm, and the time of the first ball milling is 5 h - 10 h; the speed of the second ball milling in S4 is 300 rpm - 450 rpm, and the time of the first ball milling is 5 h - 10 h; the heating temperature in S3 is 350°C - 400°C, and the heating time is 15 h - 30 h; the calcination temperature in S5 is 700°C - 800°C, and the calcination reaction time is 10 h - 20 h; in S6, it is naturally cooled to 25°C - 27°C.

[0032] As an even further solution, the heating rate of the heating temperature in S3 is 2.5°C / min - 3.5°C / min; the heating rate of the calcination temperature in S5 is 2.5°C / min - 3.5°C / min; the inert gas includes one of nitrogen and argon.

[0033] The present invention also provides the application of the solid electrolyte in a battery.

[0034] The features and beneficial effects of the present invention are as follows:

[0035] (1) The present invention provides a solid electrolyte with a cubic phase structure of Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1. Applying the solid electrolyte of the present invention in a battery can improve the ionic conductivity of the electrolyte, thereby being beneficial to improving the capacity of the battery.

[0036] (2) The present invention also provides a preparation method of the solid electrolyte, which can successfully dope La and Zr into the NaCa 2 Mg 2 V 3 O 12 solid electrolyte simultaneously, so as to obtain a solid electrolyte with a cubic phase structure.

[0037] (3) The solid electrolyte provided by the present invention can be used in a sodium-ion battery. Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 For the undoped NaCa in the present invention 2 Mg 2 V 3 O 12 Schematic diagram of the crystal structure of the solid electrolytic powder.

[0040] Figure 2 For the Na provided in the embodiments of the present invention 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 Series X-ray diffraction (XRD) pattern of the solid electrolyte powder. Specific embodiments

[0041] To facilitate the understanding of a novel garnet-type solid electrolyte of the present invention, the following will provide a more comprehensive description of the functionalized conductive carbon layer aluminum current collector of the present invention, and examples of the present invention are given, but the scope of the present invention is not limited thereby.

[0042] Example 1

[0043] (1) According to the general formula: Na 0.8 Ca 1.8 La 0.2 Mg 2 V 3 O 12 Weigh 5 g of sodium carbonate, 21.23 g of calcium carbonate, 3.84 g of lanthanum oxide, 9.44 g of magnesium oxide, and 32.19 g of vanadium pentoxide according to the stoichiometric ratios required for each element;

[0044] (2) Add the weighed raw materials to ethanol as a dispersant, grind and mix them evenly, and then perform ball milling. The speed of ball milling is 400 rpm, and the time of ball milling is 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is then loaded into a corundum crucible;

[0045] (3) Place the corundum crucible containing the raw materials into a muffle furnace, heat it to 350 °C, and pre-burn it for 20 h to obtain a pre-burned block;

[0046] (4) The obtained pre-sintered bulk is subjected to secondary ball milling at a speed of 400 rpm for 7 h to obtain secondary powder.

[0047] (5) The obtained secondary powder is heated to 750 °C and calcined for 15 h to carry out solid-phase reaction.

[0048] (6) After the reaction is completed, it is naturally cooled to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.8 Ca 1.8 La 0.2 Mg 2 V 3 O 12 , and the unit cell parameters are

[0049] Example 2

[0050] (1) According to the general formula: Na 0.6 Ca 1.6 La 0.4 Mg 2 V 3 O 12 , weigh 3.75 g of sodium carbonate, 18.86 g of calcium carbonate, 7.68 g of lanthanum oxide, 9.44 g of magnesium oxide and 32.19 g of vanadium pentoxide according to the stoichiometric ratio of each element required;

[0051] (2) Add the weighed raw materials to dispersant ethanol, grind and mix them evenly, and then carry out ball milling at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is loaded into a corundum crucible;

[0052] (3) Put the corundum crucible filled with raw materials into a muffle furnace, heat it to 350 °C and pre-sinter for 20 h to obtain a pre-sintered bulk;

[0053] (4) The obtained pre-sintered bulk is subjected to secondary ball milling at a speed of 400 rpm for 7 h to obtain secondary powder;

[0054] (5) The obtained secondary powder is heated to 750 °C and calcined for 15 h to carry out solid-phase reaction;

[0055] (6) After the reaction is completed, it is naturally cooled to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.6 Ca 1.6 La 0.4 Mg 2 V 3 O 12 , and the unit cell parameters are

[0056] Example 3

[0057] (1) Weigh 2.51 g of sodium carbonate, 16.51 g of calcium carbonate, 11.53 g of lanthanum oxide, 9.44 g of magnesium oxide, and 32.19 g of vanadium pentoxide according to the stoichiometric ratios of the elements in the general formula: Na 0.4 Ca 1.4 La 0.6 Mg 2 V 3 O 12 ;

[0058] (2) Add the weighed raw materials to ethanol as a dispersant, grind and mix them evenly, and then perform ball milling at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is then loaded into a corundum crucible;

[0059] (3) Place the corundum crucible containing the raw materials in a muffle furnace, heat it to 350 °C, and pre-burn it for 20 h to obtain a pre-burned block;

[0060] (4) Perform secondary ball milling on the obtained pre-burned block at a speed of 400 rpm for 7 h to obtain a secondary powder;

[0061] (5) Heat the obtained secondary powder to 750 °C and calcine it for 15 h to carry out a solid-phase reaction;

[0062] (6) After the reaction is completed, it is naturally cooled to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.4 Ca 1.4 La 0.6 Mg 2 V 3 O 12 , and the unit cell parameters are

[0063] Example 4

[0064] (1) According to the general formula: Na 0.7 Ca 1.6 La 0.4 Mg 2 V 2.9 Zr 0.1 O 12Weigh 4.23 g of sodium carbonate, 18.86 g of calcium carbonate, 7.68 g of lanthanum oxide, 9.44 g of magnesium oxide, 31.12 g of vanadium pentoxide, and 2.74 g of zirconium oxide according to the stoichiometric ratios required for each element in the formula; (2) Add the weighed raw materials to the dispersant ethanol, grind and mix them evenly, then perform ball milling at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is then loaded into a corundum crucible;

[0065] (3) Place the corundum crucible containing the raw materials into a muffle furnace, heat it to 350 °C, and pre-burn for 20 h to obtain a pre-burned block;

[0066] (4) Perform secondary ball milling on the obtained pre-burned block at a speed of 400 rpm for 7 h to obtain secondary powder;

[0067] (5) Heat the obtained secondary powder to 750 °C and calcine for 15 h to carry out solid-phase reaction;

[0068] (6) After the reaction, naturally cool to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.7 Ca 1.6 La 0.4 Mg 2 V 2.9 Zr 0.1 O 12 , and the unit cell parameters are

[0069] Example 5

[0070] (1) According to the general formula: Na 0.8 Ca 1.6 La 0.4 Mg 2 V 2.8 Zr 0.2 O 12 Weigh 4.74 g of sodium carbonate, 18.86 g of calcium carbonate, 7.68 g of lanthanum oxide, 9.44 g of magnesium oxide, 30.044 g of vanadium pentoxide, and 5.48 g of zirconium oxide according to the stoichiometric ratios required for each element;

[0071] (2) Add the weighed raw materials to the dispersant ethanol, grind and mix them evenly, then perform ball milling at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is then loaded into a corundum crucible;

[0072] (3) Place the corundum crucible containing the raw materials into a muffle furnace, heat it to 350 °C, and pre-burn for 20 h to obtain a pre-burned block;

[0073] (4) The obtained pre-sintered compact is subjected to secondary ball milling at a speed of 400 rpm for 7 h to obtain secondary powder.

[0074] (5) The obtained secondary powder is heated to 750 °C and calcined for 15 h to carry out solid-phase reaction.

[0075] (6) After the reaction is completed, it is naturally cooled to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.8 Ca 1.6 La 0.4 Mg 2 V 2.8 Zr 0.2 O 12 and the unit cell parameters are

[0076] Example 6

[0077] (1) According to the general formula: Na 0.9 Ca 1.6 La 0.4 Mg 2 V 2.7 Zr 0.3 O 12 weigh 4.23 g of sodium carbonate, 18.86 g of calcium carbonate, 7.68 g of lanthanum oxide, 9.44 g of magnesium oxide, 28.97 g of vanadium pentoxide and 8.22 g of zirconium oxide according to the stoichiometric ratio of each element required in it;

[0078] (2) The weighed raw materials are added with dispersant ethanol, ground and mixed evenly, and then ball milled at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining mixed powder, which is loaded into a corundum crucible;

[0079] (3) The corundum crucible containing the raw materials is placed in a muffle furnace, heated to 350 °C and pre-sintered for 20 h to obtain a pre-sintered compact;

[0080] (4) The obtained pre-sintered compact is subjected to secondary ball milling at a speed of 400 rpm for 7 h to obtain secondary powder;

[0081] (5) The obtained secondary powder is heated to 750 °C and calcined for 15 h to carry out solid-phase reaction;

[0082] (6) After the reaction is completed, it is naturally cooled to 26 °C to obtain a new garnet-type solid electrolyte material with the composition of Na 0.9 Ca 1.6 La 0.4 Mg 2 V 2.7 Zr 0.3O 12 A novel garnet-type solid electrolyte material with unit cell parameters of

[0083] Comparative Example 1

[0084] (1) Weigh 5 g of sodium carbonate, 18.87 g of calcium carbonate, 7.55 g of magnesium oxide, and 25.75 g of vanadium pentoxide according to the stoichiometric ratios of the elements in the general formula: NaCa 2 Mg 2 V 3 O 12 ;

[0085] (2) Add the weighed raw materials to ethanol as a dispersant, grind and mix them evenly, and then perform ball milling at a speed of 400 rpm for 7 h. The mixture is dried in a vacuum drying oven at 120 °C for 2 h to evaporate the ethanol solvent, obtaining a mixed powder, which is then loaded into a corundum crucible;

[0086] (3) Place the corundum crucible containing the raw materials into a muffle furnace, heat it to 350 °C, and pre-burn for 20 h to obtain a pre-burned block;

[0087] (4) Perform secondary ball milling on the obtained pre-burned block at a speed of 400 rpm for 7 h to obtain a secondary powder;

[0088] (5) Heat the obtained secondary powder to 750 °C and calcine for 15 h to carry out a solid-phase reaction;

[0089] (6) After the reaction, naturally cool to 26 °C to obtain a novel garnet-type solid electrolyte material with the composition of NaCa 2 Mg 2 V 3 O 12 with unit cell parameters of α = β = γ = 90°,

[0090] Assemble the prepared solid electrolyte material into a sodium|solid electrolyte|sodium battery system. Preparation of the full cell: Disperse NVP (sodium vanadium phosphate), acetylene black, and polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) according to a mass ratio of 8:1:1, and evenly coat the prepared slurry on aluminum foil to finally make a positive electrode plate; then roll and cut a sodium block into a thin sheet with a diameter of 10 mm and place it on one side of a ceramic sheet as the negative electrode. Subsequently, assemble the positive electrode shell, nickel foam, positive electrode plate, the solid electrolyte of the present invention, sodium metal sheet, nickel foam, and negative electrode shell into a C2032 battery shell in the order from bottom to top, and finally use a button-type encapsulation machine to encapsulate the battery under a pressure of 3 MPa to obtain a sodium metal battery.

[0091] We also measured the ionic conductivity of the obtained battery. The method includes: from the bulk resistance R in the electrolyte AC impedance spectrum, the area A of the electrolyte film facing the contact electrode, and the thickness d of the electrolyte film, the ionic conductivity σ of the electrolyte film can be obtained through the following formula:

[0092] In addition, the cycle capacities of Examples 1 - 6 and Comparative Example 1 of the present invention at 0.1C for 100 cycles were tested, and the test results of the cycle capacities are shown in Table 1.

[0093] Analysis of verification results

[0094] Table 1 Results of ionic conductivity of Examples and Comparative Examples of the present invention

[0095]

[0096] We successfully co-doped La and Zr into NaCa 2 Mg 2 V 3 O 12 as shown, in the X-ray powder diffraction pattern represented by the diffraction angle 2θ of the solid electrolyte Na Figure 2 Ca 1-x+y La 2-x Mg x V 2 Zr 3-y Zr y O 12 there are characteristic diffraction peaks at 17°±1.1°, 20°±1.1°, 32°±1.1°, 33°±1.1°, 36°±1.1°, 39°±1.1°, 44°±1.1°, 50°±1.1°.

[0097] NaCa 2 Mg 2 V 3 O 12 The solid electrolyte has a cubic structure (as Figure 1 shown), where Na + 、Ca 2+ 、Mg 2+ and V 5+ 4 kinds of ions are respectively surrounded by different numbers of O 2- ions. Among them, Ca 2+ is surrounded by 8 O 2- ions to form an eight-coordinate CaO 8 dodecahedral structure; Mg 2+ is located at the center of the octahedron and forms a MgO 2- octahedral structure with 6 O 6 ions; V5+ coordinates with 4 O 2- ions to form a VO 4 tetrahedral structure. Among them, CaO 8 dodecahedron, MgO 6 octahedron and VO 4 tetrahedra are connected by sharing edges. In the present invention, in NaCa 2 Mg 2 V 3 O 12 solid electrolyte, La is successfully doped. On the one hand, La 3+ partially replaces the position of Ca in the structure 2 + in the structure, and the distribution of Na + in the unit cell changes due to the structural change, forming sodium vacancies in the unit cell, promoting the migration of Na + on the vacancies, thereby realizing the migration of sodium ions and improving the ionic conductivity of the solid electrolyte; on the other hand, La and O form La-O bonds with higher bond energy, which is beneficial to the more stable existence of O in the lattice, and is beneficial to reducing the capacity decay of the sodium-ion battery; on this basis, we can further dope Zr. Zr 4+ partially replaces the V 5+ site. On the one hand, it can be used to adjust the excessive sodium vacancies generated due to La doping. On the other hand, because the doping of La and Zr will change the unit cell structure to increase to a certain extent, the Zr-O bond can further improve the stability of the unit cell structure after doping, so as to promote the migration of sodium ions in the unit cell on the basis of the stable unit cell structure, thereby realizing the improvement of the ionic conductivity of the sodium-ion battery and reducing the battery capacity decay. As can be seen from Table 1, the ionic conductivities and capacities of the batteries in Examples 1-6 are better than those in Comparative Example 1. It can be seen that the solid electrolyte obtained by doping La or co-doping La and Zr in the NaCa 2 Mg 2 V 3 O 12 solid electrolyte structure is beneficial to the improvement of the ionic conductivity and capacity of the battery.

[0098] We first studied the optimization of the unit cell parameters by doping with La alone and co-doping with La and Zr. The doping of both La and Zr can affect the change of the unit cell parameters, and further affect the change of the unit cell volume. From Table 1, we can see that the co-doping of La and Zr has a more significant improvement on the unit cell parameters than the doping of La alone, when comparing Examples 4 - 6 with Examples 1 - 4. We believe that a certain increase in the unit cell volume is beneficial to improving the ionic conductivity, probably because the increase in the unit cell volume makes it easier for sodium ions to transition in the unit cell. On this basis, the Zr - O bond can further enhance the structural stability of the unit cell after doping, thus making the transition channels of sodium ions more stable. We further optimized the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 < y < 1, 0 < x < 1, y < x, and x + y < 1.

[0099] On this basis, we also studied the sodium vacancies in the unit cell. The sodium vacancies in the unit cell are beneficial for the transition of sodium ions to achieve the transfer of sodium ions. If there are too many sodium vacancies in the unit cell, it may cause the electrolyte to lose its differential capacitance change with voltage, thus affecting the electrical performance of the battery. While when there are too few sodium vacancies in the unit cell, it will limit the transfer of sodium ions. As found by comparing Examples 1 - 3 in Table 1, the ionic conductivity and capacity of the battery in Example 2 are the best, which can also be verified by comparing Examples 4 - 6. We further optimized the solid electrolyte Na 1-x+ y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 < y < 1, 0 < x < 1, y < x, and x + y = 0.1 - 0.3.

[0100] In summary, the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 used in the battery is beneficial to improving the ionic conductivity and capacity of the sodium - ion battery.

[0101] It should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A novel garnet-type solid electrolyte, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3- y Zr y O 12 , where 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1.

2. The novel garnet-type solid electrolyte according to claim 1, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 has a cubic phase structure.

3. The novel garnet-type solid electrolyte according to claim 1, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 In the X-ray powder diffraction pattern expressed by the diffraction angle 2θ, there are characteristic diffraction peaks at 17° ± 1.1°, 20° ± 1.1°, 32° ± 1.1°, 33° ± 1.1°, 36° ± 1.1°, 39° ± 1.1°, 44° ± 1.1°, and 50° ± 1.1°.

4. The novel garnet-type solid electrolyte according to claim 1, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 has a unit cell parameter a in the range b in the range c in the range α = 90° ± 2°, β = 90° ± 2°, γ = 90° ± 2°.

5. The novel garnet-type solid electrolyte according to claim 1, characterized in that The Na element in the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 is sourced from a sodium source for the Na element, a calcium source for the Ca element, a lanthanum source for the La element, a magnesium source for the Mg element, a zirconium source for the Zr element, and a vanadium source for the V element.

6. The novel garnet-type solid electrolyte according to claim 5, characterized in that the sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium perchlorate, and sodium bis(trifluoromethanesulfonyl)imide.

7. The novel garnet-type solid electrolyte according to claim 5, characterized in that the calcium source includes one or more of calcium oxide, calcium carbonate, and calcium hydroxide.

8. The novel garnet-type solid electrolyte according to claim 5, characterized in that the lanthanum source includes one or more of lanthanum oxide, lanthanum nitrate, lanthanum chloride, and lanthanum fluoride.

9. The novel garnet-type solid electrolyte according to claim 5, characterized in that the magnesium source includes one or more of magnesium oxide and basic magnesium carbonate.

10. The novel garnet-type solid electrolyte according to claim 5, characterized in that more preferably, the zirconium source includes one or more of zirconium oxide, zirconium nitrate, and zirconium acetate.

11. The novel garnet-type solid electrolyte according to claim 5, characterized in that the vanadium source includes one or more of vanadium pentoxide, ammonium metavanadate, and vanadium trichloride.

12. The novel garnet-type solid electrolyte according to claim 1, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 < y < 1, 0 < x < 1, y < x, and x + y < 1.

13. The novel garnet-type solid electrolyte according to claim 12, characterized in that The solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 < y < 1, 0 < x < 1, y < x, and x + y = 0.1 - 0.

3.

14. A method for preparing the solid electrolyte according to any one of claims 1-13.

15. The preparation method according to claim 14, characterized in that the preparation method includes: S1: According to the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 , where 0 ≤ y < 1, 0 < x < 1, y < x, and x + y < 1. Weigh the sodium source, calcium source, lanthanum source, magnesium source, zirconium source, and vanadium source respectively according to the stoichiometric ratio of each element in the solid electrolyte; S2: After adding a dispersant to the raw materials weighed in S1 and dispersing them, performing the first ball milling, and drying the mixture to obtain a mixed powder; S3: Heating the mixed powder obtained in S2; S4: Performing the second ball milling on the mixed powder heated in S3 to obtain a secondary powder; S5: Calcining the mixed powder dispersed in S4 to cause a solid-phase reaction; S6: After the solid-phase reaction is completed, it is naturally cooled to obtain the solid electrolyte Na 1-x+y Ca 2-x La x Mg 2 V 3-y Zr y O 12 。 16. The preparation method according to claim 15, characterized in that the dispersant in S1 includes ethanol; the ball milling medium for the first ball milling in S2 includes absolute ethanol or propanol; the ball milling medium for the second ball milling in S4 includes absolute ethanol or propanol.

17. The preparation method according to claim 15, characterized in that by mass, the additive mass of the sodium source in S1 is 3%-8% more than the addition amount of the theoretical sodium source calculated according to the stoichiometric ratio in S1.

18. The preparation method according to claim 15, characterized in that The conditions of S1 and S2 are both in an inert gas; the drying temperature in S2 is 100°C - 200°C, and the drying time is 5 - 8 h; the speed of the first ball milling in S2 is 300 rpm - 450 rpm, and the time of the first ball milling is 5 h - 10 h; the speed of the second ball milling in S4 is 300 rpm - 450 rpm, and the time of the first ball milling is 5 h - 10 h; the heating temperature in S3 is 350°C - 400°C, and the heating time is 15 h - 30 h; the calcination temperature in S5 is 700°C - 800°C, and the time of the calcination reaction is 10 h - 20 h; in S6, it is naturally cooled to 25°C - 27°C.

19. According to the preparation method described in claim 18, characterized in that, the heating rate of the heating temperature in S3 is 2.5°C / min - 3.5°C / min; the heating rate of the calcination temperature in S5 is 2.5°C / min - 3.5°C / min; the inert gas includes one of nitrogen and argon.

20. A battery, characterized in that, the battery includes the solid electrolyte described in any one of claims 1 - 13.

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