A pyrochlore type llnof solid electrolyte and a preparation method and application thereof

Abstract

The application discloses a pyrochlore type LLNOF solid electrolyte and a preparation method and application thereof, and belongs to the technical field of lithium ion battery solid electrolytes. 2‑ x La (1+x) / 3 Nb2O6F, the space group of the electrolyte is Fd-3m, each element occupies a specific lattice site, is a pure phase material without LiNbO3 impurity phase, has the advantage of high room temperature ionic conductivity, and can significantly improve the electrochemical performance of a lithium ion battery when the electrolyte is used as raw material in the preparation of the lithium ion battery. The application can inhibit lithium evaporation to the greatest extent in the sintering process, avoid the conversion of the Fd-3m metastable phase, and prepare multiple electrolyte sheets in a single process, so that the preparation efficiency is high, the amount of mother powder is small, and the application has universality.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology for lithium-ion batteries, specifically relating to a pyrochlore-type LLNOF solid electrolyte, its preparation method, and its application. Background Technology

[0002] Solid-state lithium-ion batteries represent a crucial development direction. Solid-state electrolytes, as the core component of solid-state lithium-ion batteries, directly determine battery performance and commercial value through their ionic conductivity, manufacturing cost, and phase purity. Currently, the mainstream oxide-based solid-state electrolyte is represented by garnet-type LLZO (lithium lanthanum zirconium oxide) materials. However, this material suffers from low room-temperature ionic conductivity, failing to meet the practical application requirements of lithium-ion batteries. Meanwhile, sulfide-based solid-state electrolytes, with their higher ionic conductivity, are costly, limiting their large-scale commercial application.

[0003] Research has revealed the existence of three-dimensional large-aperture tunnels within crystal structures with the Fd-3m space group, making it an important research direction for novel oxide solid electrolytes. However, the Fd-3m structure is a metastable phase, which is prone to the problem of large-scale lithium ion evaporation during high-temperature sintering. This causes local Fd-3m structures to transform into more stable R3c structures (such as LiNbO3 impurities), making it difficult to obtain electrolyte materials with a pure Fd-3m structure.

[0004] In addition, existing high-temperature sintering processes for solid electrolytes mostly adopt the conventional method of covering electrolyte discs with master powder in an alumina crucible. This method has problems such as a limited number of electrolyte discs that can be sintered in a single time, a large amount of master powder used, and low preparation efficiency. At the same time, it cannot effectively suppress lithium evaporation, which further aggravates the generation of impurity phases.

[0005] Therefore, developing a high ionic conductivity Fd-3m phase oxide solid electrolyte, and designing a preparation process that can effectively suppress lithium evaporation, improve preparation efficiency, and reduce costs, has become an urgent technical problem to be solved in the field of solid electrolytes. Summary of the Invention

[0006] To address the problems of low ionic conductivity, easy high-temperature crystallization and impurity phase formation in existing oxide lithium-ion solid electrolytes, severe lithium evaporation during sintering, low preparation efficiency, and large amount of masterbatch consumption, the first objective of this invention is to provide a pyrochlore-type LLNOF solid electrolyte. This electrolyte has a pure phase Fd-3m space group structure, no LiNbO3 impurity phase, high ionic conductivity at room temperature, and high density.

[0007] The second objective of this invention is to provide a method for preparing pyrochlore-type LLNOF solid electrolyte, which can effectively suppress lithium evaporation, avoid the generation of impurity phases, and produce a large quantity in a single batch with a small amount of masterbatch.

[0008] The third objective of this invention is to provide an application of pyrochlore-type LLNOF solid electrolyte, which, when used as a raw material in the preparation of lithium-ion batteries, can significantly improve the electrochemical performance of lithium-ion batteries.

[0009] To achieve the above-mentioned technical objectives, this invention provides a method for preparing a pyrochlore-type LLNOF solid electrolyte, wherein the electrolyte has the chemical formula Li. 2-x La (1+x) / 3 For Nb₂O₆F, the value of x ranges from 0 to 1, and the process includes the following steps:

[0010] S1 Take Li 0.5 La 0.5 Nb2O6 precursor, LaF3 and LiF were formulated according to the chemical formula of the electrolyte, a binder was added and wet ball milling was performed. After drying, a mixture powder was obtained. A portion of the mixture powder was pressed to obtain electrolyte tablets, and the remainder was used as master powder.

[0011] S2. High-temperature resistant sheets and electrolyte sheets are alternately layered in a sintering container. At the same time, master powder is filled into the gaps between the high-temperature resistant sheets and electrolyte sheets and the top gap of the sintering container. After sealing, oxidation sintering and inert sintering are performed in sequence to obtain pyrochlore-type LLNOF solid electrolyte. The top of the sintering container has a top cover that can be moved up and down.

[0012] The space group of the crystal structure of the electrolyte is Fd-3m.

[0013] The key to obtaining a high-density, pure Fd-3m phase LLNOF electrolyte in the preparation method of this invention lies in the synergistic effect of a special powder-spreading method, the addition of dual fluorine sources, and the sintering process. Specifically, firstly, a homogeneous Li... 0.5 La 0.5The Nb₂O₆ precursor provides a stable nucleation matrix for the final Fd-3m crystal phase, thus avoiding localized compositional differences caused by varying reactivity when oxide raw materials are directly mixed with the fluorine source. Secondly, the simultaneous introduction of LaF₃ and LiF as dual fluorine sources adjusts the stoichiometric ratio of La / Li to F, optimizing the atomic occupancy ratio in the lattice to improve ionic conductivity. Furthermore, the introduction of an appropriate amount of LaF₃ balances the concentrations of La and Li during sintering, preventing excessively high local lithium concentrations that could lead to the formation of the LiNbO₃ phase, thereby stabilizing the metastable structure of pyrochlore. Finally, this invention employs a powder-laying method that alternately stacks high-temperature resistant sheets and electrolyte sheets, filling the pores of the sintering container with masterbatch powder. Simultaneously, the downward movement of the top cover provides axial confinement and pre-compression for the internal electrolyte and high-temperature resistant sheets. This powder-laying method reduces lithium vapor escape during sintering, creating a locally balanced atmosphere containing lithium vapor inside the crucible, suppressing lithium loss from the electrolyte material, and promoting the acquisition of a pure-phase solid electrolyte. Furthermore, the high-temperature resistant sheet not only fills space but also prevents excessive contact between the mother powder and the electrolyte sheet surface, avoiding mass transfer of the LiF liquid phase at high temperatures. This ensures the sintered solid electrolyte sheet remains flat, reducing the risk of bending and cracking, and guaranteeing high material density. Finally, since the pyrochlore phase is a metastable structure, excessively high local lithium salt concentrations during primary sintering can lead to impurities. This invention, by first using lower-temperature oxidation sintering to remove the binder introduced from the raw materials, followed by high-temperature inert atmosphere sintering, effectively avoids impurities caused by excessively high local lithium salt concentrations or over-oxidation, thus ensuring the formation of a pure Fd-3m crystal phase.

[0014] The electrolyte of this invention has a crystal structure space group of Fd-3m, in which Li and La jointly occupy the 16d site of the lattice, Nb occupies the 16c site, O occupies the 48f site, and F occupies the 8b site. For lithium-ion conductors, the diffusion path and coordination environment of lithium ions directly affect ionic conductivity. The pyrochlore-type LLNOF electrolyte of this invention has a large-pore 3D tunnel, allowing lithium atoms to diffuse in multiple dimensions, thus exhibiting high ionic conductivity. Furthermore, although the presence of La hinders lithium conduction to some extent, La's role as a structural support for the large pores cannot be replaced by other elements.

[0015] Furthermore, the top cover is a threaded cap, and the sintering container is a cylindrical alumina crucible.

[0016] As a preferred embodiment, in S1, the Li 0.5 La 0.5 The preparation process of Nb2O6 precursor is as follows: lithium source, lanthanum oxide and niobium oxide are mixed in stoichiometric ratio, and then ball-milled and calcined.

[0017] As a preferred embodiment, the lithium source includes lithium carbonate, the lanthanum oxide includes lanthanum oxide, and the niobium oxide includes niobium pentoxide.

[0018] As a preferred embodiment, the ball milling conditions are as follows: using alcohol as the milling medium, a rotation speed of 200-300 rpm, and a time of 5-10 hours; the alcohol is a C1-C4 monohydric alcohol or a dihydric alcohol. These preferred milling conditions can further ensure more uniform dispersion of the lithium source, lanthanum oxide, and niobium oxide.

[0019] As a preferred embodiment, the roasting is divided into two stages: the first stage roasting temperature is 500~550℃ and the time is 2~4h; the second stage roasting temperature is 1100~1300℃ and the time is 2~4h.

[0020] As a preferred embodiment, in S1, the adhesive includes at least one of PVA, CMC, and SBR.

[0021] As a preferred embodiment, the wet ball milling uses a mixture of alcohol and water as the milling medium, with a rotation speed of 200-300 rpm and a milling time of 5-10 hours. The alcohol is a C1-C4 monohydric alcohol or dihydric alcohol. This invention uses a mixture of alcohol and water as the milling medium in the wet ball milling process, which can better disperse the powder material after the addition of the binder, thereby ensuring the uniformity of material dispersion. A further preferred embodiment is a mixture of isopropanol and water.

[0022] As a preferred embodiment, in S1, the particle size of the mixed powder is controlled to be less than or equal to 0.074 mm.

[0023] As a preferred embodiment, the mass ratio of the mixed powder used for the electrolyte sheet to the mixed powder used for the master powder is (2~4):1. By controlling the mass ratio of the master powder to the mixed powder, the voids in the sintering container can be filled while ensuring that more electrolyte sheets are sintered at once, thereby avoiding the formation of impurity phases. A further preferred mass ratio is (2~3):1.

[0024] As a preferred embodiment, in S2, the high-temperature resistant sheet is selected from alumina, magnesium oxide, and zirconium oxide. Using the preferred high-temperature resistant sheet material of this invention not only serves as a space filler and provides support, but also prevents excessive contact between the precursor powder and the electrolyte sheet surface, thus avoiding bending of the electrolyte sheet during sintering due to the liquid-phase mass transfer effect of LiF at high temperatures. Since alumina is readily available and less expensive, and does not introduce other impurity elements, it is further preferred.

[0025] As a preferred embodiment, in step S2, a masterbatch powder layer is first laid at the bottom of the sintering container, followed by the sequential layering of high-temperature resistant sheets and electrolyte sheets. Finally, masterbatch powder is used to fill the gaps between the high-temperature resistant sheets and electrolyte sheets, as well as the top voids within the sintering container. The compression amount is controlled to be 0.1~3mm by controlling the downward movement of the top cover. The compression amount is defined as the distance the lower surface of the top cover begins to axially displace downwards from the point where it contacts the precursor masterbatch powder in the top voids. Experiments have shown that this further powder-laying method can maximize the filling of voids in the sintering container and ensure the uniformity of the reaction, thereby minimizing lithium-ion evaporation at high temperatures and preventing the Fd-3m structure from transforming into the more stable R3c structure.

[0026] In this invention, the sintering container is preferably a cylindrical alumina crucible with a threaded cap. Since the electrolyte sheets are generally circular, using a cylindrical crucible perfectly avoids the large-scale volatilization of lithium for metastable pyrochlore-type materials and prevents the electrolyte sheets from bending and deforming due to molten LiF at high temperatures.

[0027] Furthermore, the width of the high-temperature resistant sheet is greater than the width of the electrolyte sheet. In a further preferred configuration, excessive contact between the masterbatch powder and the electrolyte sheet surface can be minimized, avoiding mass transfer of the LiF liquid phase at high temperatures, thus keeping the sintered solid electrolyte sheet flat and reducing the risk of bending and cracking. When both the high-temperature resistant sheet and the electrolyte sheet are circular, the diameter of the high-temperature resistant sheet is greater than the diameter of the electrolyte sheet. Even further, the difference between the diameter of the high-temperature resistant sheet and the diameter of the electrolyte sheet is 3-5 mm.

[0028] As a preferred embodiment, in step S2, the oxidation sintering temperature is 550~650℃, the time is 1~2 hours, and the atmosphere is an air atmosphere or an oxygen atmosphere. Within the preferred temperature and time range of this invention, the binder in the raw materials can be completely removed without adversely affecting the phase of the final LLNOF solid electrolyte. More preferably, the oxidation sintering temperature is 600~650℃.

[0029] As a preferred embodiment, in step S2, the inert sintering refers to sintering under an inert atmosphere at a temperature of 1000-1100℃ for 6-8 hours. In this invention, the inert atmosphere includes commonly used atmospheres such as argon. The main purpose of inert sintering in this invention is to protect the material from excessive oxidation and the formation of impurity phases during crystal formation. Temperature control is crucial during inert sintering. If the sintering temperature is too low, LiNbO3 impurity phases will form. High temperatures can be used to allow LiF to melt, enabling better liquid-phase mass transfer. However, if the temperature is too high, some lithium will volatilize, causing localized uneven La / Li concentrations.

[0030] When the lithium source is lithium carbonate, the lanthanum oxide is lanthanum oxide, and the niobium oxide is niobium pentoxide, the raw materials are prepared according to the following chemical equation:

[0031] 0.25La2O3 + 0.25Li2CO3 + Nb2O5 → Li 0.5 La 0.5 Nb2O6;

[0032] Li 0.5 La 0.5 Nb2O6+(1.5-x)×LiF+(2x-1) / 6×LaF3→Li 2-x La (1+x) / 3 Nb2O6F;

[0033] The value of x ranges from 0 to 1.

[0034] The reason why the molar ratio of LaF3 to LiF is controlled according to the above-mentioned stoichiometric ratio is that pyrochlore crystals are metastable structures. Especially for structures with high lithium concentrations, large-sized trivalent ions are required to fill the lattice at a uniform concentration to prevent structural collapse and the generation of impurity phases. Therefore, by adding an appropriate amount of LaF3 to balance the Li / La concentration, local concentration imbalances are avoided.

[0035] More preferably, x is 0.7~0.8; even more preferably, x is 0.75, and the resulting electrolyte has the chemical formula Li. 1.25 La 0.58 Nb2O6F.

[0036] This invention also provides a pyrochlore-type LLNOF solid electrolyte, obtained by the above preparation method. The solid electrolyte of this invention has a pure-phase Fd-3m space group structure and has advantages such as high room-temperature ionic conductivity and high density.

[0037] Finally, this invention also provides an application of pyrochlore-type LLNOF solid electrolyte, which can be used as a raw material in the preparation of lithium-ion batteries to significantly improve the electrochemical performance of lithium-ion batteries, especially the cycle stability and capacity retention under high current, while the stable voltage window is as high as 5.05V, and it can be adapted to commercial high-voltage cathode materials.

[0038] Compared with the prior art, the present invention has at least the following beneficial effects:

[0039] (1) The LLNOF solid electrolyte prepared in this invention has a pure-phase Fd-3m space group structure, without LiNbO3 impurity phase, and its room temperature ionic conductivity reaches 7.44 × 10⁻⁶. -3With a S / cm ratio far exceeding that of traditional LLZO oxide electrolytes and approaching that of sulfide electrolytes, it exhibits excellent ion conductivity. When used as a raw material in the preparation of lithium-ion batteries, it can significantly improve the electrochemical performance of lithium-ion batteries. Under high current, it retains more than 80% of its capacity after 600 cycles, and has a stable voltage window as high as 5.05V, making it compatible with commercial high-voltage cathode materials.

[0040] (2) The electrolyte raw materials of the present invention are inexpensive and have stronger commercial application value compared with sulfide electrolytes.

[0041] (3) The preparation method of the present invention uses a dual fluorine source combined with a closed sintering container and a layered laying method, which can minimize the evaporation of lithium ions during the high-temperature sintering process, effectively avoid the transformation of the Fd-3m metastable phase to the R3c phase, and ensure the purity of the electrolyte.

[0042] (4) The present invention uses a dual fluorine source, which can not only prevent structural imbalance caused by uneven local La / Li concentration during sintering, but also solves the problem of high cost caused by the need to compensate for lithium loss by excessive addition of LiF in the prior art.

[0043] (5) The sintering process of the present invention can prepare multiple electrolyte discs in a single batch, which significantly increases the number of discs prepared compared with conventional sintering methods, and significantly improves the preparation efficiency; moreover, the crucible space is maximized, which greatly reduces the amount of precursor powder used and further reduces the preparation cost. At the same time, this sintering process can be extended to the preparation of other pure phase lithium-ion solid electrolytes, such as garnet-type LLZO.

[0044] (6) The preparation process of the present invention is simple and the parameters are easy to control, making it suitable for large-scale industrial production. Attached Figure Description

[0045] Figure 1 The XRD patterns are those of the electrolyte sheets prepared in Example 1 and Comparative Example 1 of this invention.

[0046] Figure 2 The image shows the XRD pattern of the electrolyte sheet prepared in Comparative Example 2 of this invention.

[0047] Figure 3 The image shows the Fd-3m space group crystal structure model of the LLNOF electrolyte prepared in Example 1 of this invention, where the yellow area represents the diffusion path region of lithium ions.

[0048] Figure 4 The table shows the room temperature ionic conductivity spectrum of the LLNOF electrolyte sheet prepared in Example 1 of this invention, where (a) is the AC impedance spectrum at different temperatures and (b) is the ion activation energy calculated from the AC impedance spectrum.

[0049] Figure 5 This refers to the voltage window of the LLNOF electrolyte sheet prepared in Example 1 of the present invention.

[0050] Figure 6 The images show the SEM images of the electrolyte sheets prepared in Example 1 and Comparative Example 1 of this invention, where (a) is the SEM image of the electrolyte sheet prepared in Example 1 and (b) is the SEM image of the electrolyte sheet prepared in Comparative Example 1.

[0051] Figure 7 This is a schematic diagram of the layered arrangement of electrolyte discs and alumina discs inside a cylindrical alumina crucible in Embodiment 1 of the present invention, wherein 1-cylindrical alumina crucible, 2-electrolyte precursor powder, 3-threaded screw cap seal, 4-alumina disc, and 5-electrolyte disc. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to specific experimental procedures. This embodiment is only used to explain the present invention and is not intended to limit the scope of protection of the present invention.

[0053] Example 1

[0054] A method for preparing a pure-phase Fd-3m pyrochlore-type LLNOF solid electrolyte comprises the following steps:

[0055] S1 Li 0.5 La 0.5 Preparation of Nb2O6 precursor

[0056] Li₂CO₃, La₂O₃, and Nb₂O₅ powders were weighed in a molar ratio of 0.00125:0.00125:0.005 and placed in a 100 mL zirconia ball mill jar. Isopropanol was added as the milling medium at a solid-liquid mass ratio of 0.1:1. Zirconia milling balls were added, and the mixture was milled at 250 rpm for 10 hours on a planetary ball mill. After milling, the mixture was poured into an evaporating dish and dried in a 60°C forced-air drying oven until constant weight to obtain a mixed powder. The mixed powder was placed in an alumina crucible and placed in a muffle furnace. The temperature was increased to 550°C at 5°C / min under air atmosphere and held for 4 hours. Then, the temperature was increased to 1200°C at 5°C / min and held for 4 hours. After cooling with the furnace, Li₂CO₃, La₂O₃, and Nb₂O₅ powders were obtained. 0.5 La 0.5 Nb2O6 (LLNO) precursor powder.

[0057] S2 Secondary Ball Milling and Sieving

[0058] According to Li 1.25 La 0.58The stoichiometric ratio of Nb₂O₆F is determined by weighing 0.0004 mol of LaF₃ powder and 0.00375 mol of LiF powder, and mixing them with the corresponding molar amounts of Li. 0.5 La 0.5 Nb2O6 precursor powder was mixed, and PVA binder (2 wt% of total powder mass) was added. The mixture was placed in a 500 mL zirconia ball mill jar. A mixture of isopropanol and water (1:1 volume ratio) was weighed out as the ball milling medium at a solid-liquid mass ratio of 0.1:1. The mixture was ball milled at 250 rpm for 10 h. After ball milling, the slurry was dried at 60 °C to constant weight. The resulting mixed powder was passed through a 200-mesh standard sieve to remove coarse particles.

[0059] S3 tableting

[0060] The sieved powder was placed in a cylindrical mold with a diameter of 16 mm, and a pressure of 100 MPa was applied on the powder tablet press for 2 minutes to press it into a round electrolyte tablet. After demolding, the tablet was collected for later use, and a round electrolyte tablet with a single mass of 0.3 g was obtained.

[0061] S4 High Temperature Sintering

[0062] A cylindrical alumina crucible with an inner diameter of 20 mm and a threaded cap was selected. A layer of 0.5 g of LLNO precursor powder was evenly spread at the bottom of the crucible. Then, 19 mm diameter alumina discs and the 16 mm electrolyte discs prepared above were alternately stacked, for a total of 12 alumina discs and 11 electrolyte discs. Finally, the gaps between the discs and the top of the crucible were filled with precursor powder, so that the powder filled all the space inside the crucible. The crucible cap was screwed downward to control the compression amount to 1 mm. The compression amount is the distance that the lower surface of the cap begins to move axially downward from the point where it contacts the precursor powder in the top gap. The mass ratio of the mixed powder used for all electrolyte discs to the mixed powder used for all precursor powders was 3.3:1.

[0063] The crucible was placed in a quartz tube furnace. First, the temperature was increased to 600℃ at 3℃ / min under air atmosphere and held for 2 hours to allow complete decomposition and venting of PVA. Then, high-purity argon gas was introduced into the quartz tube to replace the air, and the argon atmosphere was maintained. The temperature was increased to 1000℃ at 3℃ / min and held for 6 hours. The furnace was then cooled to room temperature to obtain pure-phase Fd-3m type LLNOF (chemical formula Li). 1.25 La 0.58 Nb₂O₆F solid electrolyte sheet, with a room temperature ionic conductivity of 7.44 × 10⁻⁶. -3 The capacitance per 600 cycles at a current density of 5C resulted in a capacity retention of 89.22%.

[0064] Example 2

[0065] Compared with Example 1, the only difference in this example is that the number of alumina discs in S4 is changed to 10 and the number of electrolyte discs is changed to 9. Correspondingly, the mass ratio of the mixed powder of all electrolyte discs to the mixed powder of all master powders is 2.7:1. At the same time, the oxygen calcination temperature is replaced with 550°C and the inert calcination temperature is replaced with 1050°C. All other steps and conditions are the same.

[0066] The obtained pure phase Fd-3m type LLNOF (chemical formula Li) 1.25 La 0.58 The Nb₂O₆F solid electrolyte sheet achieves a room temperature ionic conductivity of 3.43 × 10⁻⁶. -3 S / cm.

[0067] Example 3

[0068] Compared with Example 1, the only difference in this example is that the oxidation calcination conditions of S1 are replaced with heating to 500°C at 5°C / min in an air atmosphere, holding for 4 hours, and then heating to 1300°C at 5°C / min and holding for 4 hours. All other steps and conditions are the same.

[0069] The obtained pure phase Fd-3m type LLNOF (chemical formula Li) 1.25 La 0.58 The Nb₂O₆F solid electrolyte sheet achieves a room temperature ionic conductivity of 2.18 × 10⁻⁶. -3 S / cm.

[0070] Example 4

[0071] Compared with Example 1, the only difference in this example is that the compression amount in S4 is replaced with 1.5mm, while the other steps and conditions are the same.

[0072] The obtained pure phase Fd-3m type LLNOF (chemical formula Li) 1.25 La 0.58 The Nb₂O₆F solid electrolyte sheet achieves a room temperature ionic conductivity of 6.89 × 10⁻⁶. -3 S / cm.

[0073] Example 5

[0074] Compared with Example 1, the only difference in this example is that the diameter of the alumina is replaced with 16mm, while the rest of the steps and conditions are the same.

[0075] The obtained pure phase Fd-3m type LLNOF (chemical formula Li) 1.25 La 0.58 The Nb₂O₆F solid electrolyte sheet achieves a room temperature ionic conductivity of 7.04 × 10⁻⁶. -3 S / cm.

[0076] Comparative Example 1

[0077] The only difference between this comparative example and Example 1 is that a common rectangular alumina crucible is used, and its top cover cannot be moved downwards. A single electrolyte disc is placed in the crucible, and the electrolyte disc is completely covered with precursor powder. It is sintered at 600°C in air for 2 hours to remove PVA, and then at 1000°C in argon atmosphere for 6 hours. The remaining steps are completely the same as in Example 1.

[0078] Testing revealed that the electrolyte sheet prepared in Comparative Example 1 contained a LiNbO3 impurity phase (R3c space group), indicating it was a non-pure phase material. In contrast, the electrolyte sheet prepared in Example 1 was a pure-phase Fd-3m type LLNOF, exhibiting a room-temperature ionic conductivity of 7.44 × 10⁻⁶. -3 S / cm.

[0079] Comparative Example 2

[0080] The only difference between this comparative example and Example 1 is that: Li₂CO₃, La₂O₃, and Nb₂O₅ powders were weighed in a molar ratio of 0.00125:0.00145:0.005 to prepare Li₂CO₃, La₂O₃, and Nb₂O₅ powders. 0.5 La 0.58 For the Nb2O6 precursor, only 0.00375 mol of LiF powder was added in the second step, without adding LaF3, and the remaining steps and conditions were the same.

[0081] Testing revealed that the electrolyte sheet prepared in Comparative Example 2 contained a LiNbO3 impurity phase (R3c space group), indicating it was a non-pure phase material.

[0082] Figure 1 The XRD patterns of electrolyte sheets from Example 1 and Comparative Example 1 are shown. It can be seen that Example 1 is a pure phase without impurity phase peaks and has a high peak intensity; while in Comparative Example 1, obvious LiNbO3 impurity phase peaks are observed and the peak intensity is low, indicating that the crystallinity is not high.

[0083] Figure 2 The obvious LiNbO3 impurity phase peaks observed in Comparative Example 2 are shown.

[0084] Figure 4 (a) shows the AC impedance spectral curves of the electrolyte sheet prepared in Example 1 at different temperatures. All curves have the same characteristics and low impedance values. The ionic conductivity at different temperatures was calculated by fitting the AC impedance spectral curves and using the Arrhenius formula. Figure 4 (b) in the figure is the ion activation energy obtained by linear fitting of the ion conductivity value, which is 0.12 eV, matching the high ion conductivity result.

[0085] Figure 5The voltage window curve of Example 1 is shown, with an oxidation potential of 5.05 V, indicating that it is suitable for existing high-voltage cathode materials, such as ternary and lithium-rich manganese-based cathode materials.

[0086] Figure 6 Image (a) shows a cross-sectional SEM image of the electrolyte sheet prepared in Example 1, revealing small particle size and small interparticle pores, resulting in high density; while Figure 6 (b) shows that the electrolyte sheet prepared in Comparative Example 1 has a larger particle size and larger interparticle pores, resulting in a lower density. This is because the mother powder covering method causes a large amount of lithium vapor to escape and form large pores.

Claims

1. A method for preparing a pyrochlore-type LLNOF solid electrolyte, characterized in that: The electrolyte has the chemical formula Li 2-x La (1+x) / 3 For Nb₂O₆F, the value of x ranges from 0 to 1, and the process includes the following steps: S1 Take Li 0.5 La 0.5 Nb2O6 precursor, LaF3 and LiF were formulated according to the chemical formula of the electrolyte, a binder was added and wet ball milling was performed. After drying, a mixture powder was obtained. A portion of the mixture powder was pressed to obtain electrolyte tablets, and the remainder was used as master powder. S2 First, a master powder layer is laid at the bottom of the sintering container, then high-temperature resistant sheets and electrolyte sheets are layered and laid in sequence. Finally, master powder is used to fill the gaps between the high-temperature resistant sheets and electrolyte sheets and the top void in the sintering container. The compression amount is controlled to be 0.1~3mm by controlling the downward movement of the top cover. The compression amount is defined as the distance from which the lower surface of the top cover contacts the precursor master powder in the top void and begins to move axially downward. After sealing, oxidation sintering and inert sintering are performed in sequence to obtain pyrochlore-type LLNOF solid electrolyte. The top of the sintering container has a top cover that can move up and down. The space group of the crystal structure of the electrolyte is Fd-3m.

2. The method for preparing a pyrochlore-type LLNOF solid electrolyte according to claim 1, characterized in that: In S1, the Li 0.5 La 0.5 The preparation process of Nb2O6 precursor is as follows: lithium source, lanthanum oxide and niobium oxide are mixed in stoichiometric ratio, and then ball-milled and calcined.

3. The method for preparing a pyrochlore-type LLNOF solid electrolyte according to claim 2, characterized in that: The lithium source includes lithium carbonate, the lanthanum oxide includes lanthanum oxide, and the niobium oxide includes niobium pentoxide; The conditions for ball milling are as follows: alcohol is used as the ball milling medium, the rotation speed is 200~300 rpm, the time is 5~10 h, and the alcohol is a C1~C4 monool or diol. The roasting process is divided into two stages. The first stage of roasting is carried out at a temperature of 500~550℃ for 2~4 hours, and the second stage of roasting is carried out at a temperature of 1100~1300℃ for 2~4 hours.

4. The method for preparing a pyrochlore-type LLNOF solid electrolyte according to claim 1, characterized in that: In S1, The adhesive includes at least one of PVA, CMC and SBR; The wet ball milling uses a mixed solution of alcohol and water as the milling medium, with a rotation speed of 200~300 rpm and a milling time of 5~10 h. The alcohol is a C1~C4 monool or diol.

5. A method for preparing a pyrochlore-type LLNOF solid electrolyte according to any one of claims 1 to 4, characterized in that: In S1, The particle size of the mixed powder is controlled to be less than or equal to 0.074 mm; The mass ratio of the mixed powder used in the electrolyte tablets to the mixed powder used in the master powder is (2~4):

1.

6. The method for preparing a pyrochlore-type LLNOF solid electrolyte according to claim 5, characterized in that: In S2, the high-temperature resistant sheet is selected from one of alumina, magnesium oxide, and zirconium oxide.

7. The method for preparing a pyrochlore-type LLNOF solid electrolyte according to claim 1, characterized in that: In S2, the oxidation sintering temperature is 550~650℃, the time is 1~2h, and the atmosphere is an air atmosphere or an oxygen atmosphere. The inert sintering refers to sintering under an inert atmosphere at a temperature of 1000~1100℃ for 6~8 hours.

8. A pyrochlore-type LLNOF solid electrolyte, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 7.

9. An application of the pyrochlore-type LLNOF solid electrolyte as described in claim 8, characterized in that: It is used as a raw material in the preparation of lithium-ion batteries.

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