Nasicon solid state electrolyte and low temperature synthesis method thereof, solid state battery

Abstract

The application discloses a method for synthesizing NASICON solid electrolyte at low temperature, which comprises the following steps: uniformly stirring Na x M2(PO4)3 in a lithium source solution, performing low-temperature reaction, and cooling to obtain NASICON solid electrolyte Li x M2(PO4)3. + In a lithium-rich aqueous solution, low-temperature Li + ion exchange is performed, so that the prepared solid electrolyte inherits the original stable structure and excellent ionic conductivity of the precursor material, and the phase structure and ionic conductivity of the M2(PO4)3 material are controlled from the source. x The coordination environment of Li + is optimized and adjusted through a low-temperature ion exchange environment, the migration energy barrier is reduced, the migration path is widened, and the Li x M2(PO4)3 solid electrolyte with excellent performance is prepared. The application also discloses the solid electrolyte prepared by the method and a battery comprising the solid electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to solid electrolytes for lithium-ion batteries, and more particularly to a method for synthesizing the superionic conductor NASICON solid electrolyte at low temperature. Background Technology

[0002] Lithium-ion batteries are the primary power source for new energy vehicles; however, their safety has always been constrained by the dangers posed by the flammable, reactive, and volatile liquid electrolyte and the battery itself under extreme conditions, including the risk of combustion and explosion. The application of highly stable solid electrolytes is a crucial approach to addressing these safety issues.

[0003] As a core component of lithium-ion solid-state batteries, solid electrolytes need to possess the following characteristics: high ionic conductivity, low ion diffusion resistance, a wide electrochemical window, good thermodynamic stability, sufficient mechanical flexibility, and excellent chemical compatibility. Superionic conductor (NASICON) solid electrolytes have attracted widespread attention due to their high ionic conductivity, excellent chemical and thermodynamic stability, good cathode compatibility, and extremely low raw material and manufacturing costs, especially Na+. x M2(PO4)3 solid electrolytes hold great potential for solid sodium-ion battery applications due to their stable phase structure and high ionic conductivity. However, in the lithium-ion battery field, the transport channel size of NASICON-type solid electrolytes is unsuitable for lithium-ion migration, primarily because Li... x In the traditional high-temperature calcination synthesis process of M2(PO4)3 material, Li + Occupying low-energy hexahedral positions, the ion channels during migration are very narrow and the migration energy barrier is large, resulting in poor ionic conductivity of the material.

[0004] To improve NASCION type Li x The application of M2(PO4)3 solid electrolyte in lithium-ion all-solid-state batteries has many shortcomings, and most of them use heteroelement doping to optimize Li x Methods such as M2(PO4)3, grain boundary phase engineering at the interface between negative electrode materials and electrolytes, and application of composite cathodes at the interface between positive electrode materials and electrolytes are employed. However, existing methods for Li... x The inherent defects of the high-temperature synthesis process of M2(PO4)3 solid electrolyte are difficult to avoid and almost impossible to demonstrate the advantages of NASICON solid electrolyte. Patent document CN109742449A discloses a method for preparing a NASICON-type solid electrolyte. This method involves uniformly mixing raw materials and then conducting a solid-phase reaction at room temperature to obtain a precursor. The metal salt generated in situ in the precursor is then used as a flux, and the precursor is melted at high temperature to finally prepare the NASICON-type solid electrolyte material Li. 1+x Ax B 2-x (PO4)3, where A = Al, In; B = Zr, Hf. The NASICON-type solid electrolyte obtained by this preparation method does not address the Li content at the source of synthesis. + The diffusion behavior needs to be controlled, but the synthesis process inevitably involves high-temperature, long-term calcination, and the equipment involved is complex, energy-intensive, and the process is complicated, making it unsuitable for large-scale production. Patent document CN110165292A discloses a modified NASICON-type solid electrolyte sheet and its preparation method, wherein the general chemical formula of the NASICON-type solid electrolyte sheet is Li. 1+x Al(Ti / Ge)2-x(PO4)3 was prepared by ball milling a mixture of lithium, titanium or germanium, aluminum, and phosphorus sources according to a specific molar ratio. The mixture was dried and sintered to obtain a solid electrolyte powder. This powder was then mixed with a low-boiling-point lithium salt, pressed into tablets, and sintered again to obtain a modified NASICON-type solid electrolyte sheet. However, this method did not address the inherent high lithium-ion migration barrier and narrow migration path of the material itself, and the room-temperature conductivity was not significantly improved. Summary of the Invention

[0005] In view of the defects and shortcomings of the existing technology, the purpose of this invention is to provide a method for low-temperature synthesis of NASICON solid electrolyte.

[0006] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0007] A method for low-temperature synthesis of NASICON solid electrolytes includes the following steps: [The text abruptly ends here, so the translation stops.] x M2(PO4)3 was stirred uniformly in a lithium source solution and reacted at a low temperature of 60–100°C. After cooling, the NASICON solid electrolyte Li was obtained. x M2(PO4)3; where M is at least one of Zr, Ti, and Al, and 1≤x≤1.5.

[0008] In a further preferred embodiment, the lithium source is one or more of lithium hydroxide, lithium chloride, and lithium acetate.

[0009] In a further preferred embodiment, Na is prepared by the following method. x M2(PO4)3 precursor: Sodium source, M source and phosphorus source with phosphate group are mixed evenly according to chemical ratio and sintered to obtain the precursor.

[0010] Furthermore, the sodium source is at least one of sodium acetate and its hydrate, sodium carbonate and its hydrate, and sodium hydroxide.

[0011] Furthermore, the source of M is at least one of the following: acetate and its hydrate, carbonate and its hydrate, and oxide of M.

[0012] Furthermore, the phosphorus source is at least one of phenylphosphoric acid, orthophosphoric acid, and ammonium dihydrogen phosphate.

[0013] Furthermore, the molar ratio of sodium in the sodium source, M in the M source, and phosphorus in the phosphorus source is 1 to 1.5:2:3.

[0014] Furthermore, the sintering is a two-stage sintering: first, the temperature is raised to 450-600℃ at a rate of 5-7℃ / min and sintered for 7-15 hours; then, the temperature is raised to 900-1400℃ at a rate of 6-9℃ / min and sintered for 8-15 hours.

[0015] In a further preferred embodiment, Na x The molar ratio of Na in M2(PO4)3 to lithium in the lithium source solution is 1:3 to 5.

[0016] In a further preferred embodiment, the steps of washing, filtering, and drying are also included.

[0017] Furthermore, based on the same inventive concept, the present invention also provides a NASICON solid electrolyte Li prepared by the above method. x M2(PO4)3.

[0018] The present invention also provides a solid-state battery comprising the NASICON solid electrolyte Li obtained by the above method. x M2(PO4)3.

[0019] Compared with the prior art, the present invention has the following significant advantages:

[0020] (1) In this invention, Na is first synthesized. x M2(PO4)3 precursor, benefiting from Na x M2(PO4)3 solid electrolyte has a stable three-dimensional structure and high ionic conductivity, making it a precursor material for low-temperature ion exchange products.

[0021] (2) Li was carried out at low temperature in a lithium-rich aqueous solution. + / Na + Ion exchange allows for the preparation of NASICON-type Li x M2(PO4)3 solid electrolyte inherits the stable structure and excellent ionic conductivity of the precursor material, thus controlling the Li content from the synthesis source. x Phase structure and ionic conductivity of M2(PO4)3 material;

[0022] (3) Li can be processed under low-temperature ion exchange conditions.+ The coordination environment was optimized to lower the migration energy barrier and broaden the migration path, resulting in the preparation of Li with excellent performance. x M2(PO4)3 solid electrolyte;

[0023] (4) The method of the present invention has mild reaction conditions, uniform phase, small particle size and uniform distribution, good dispersibility, simple process and low energy consumption. Attached Figure Description

[0024] Figure 1 The image shows the SEM image of LiZr2(PO4)3 prepared in Example 1. Detailed Implementation

[0025] This invention relates to Li x Li during the synthesis of M2(PO4)3 solid electrolyte + Source control is achieved by adjusting the coordination environment and transmission path, utilizing Na x M2(PO4)3 material, with its excellent electrical conductivity and stable structural framework, serves as a precursor material. During low-temperature reactions, it maintains its original large-framework structure while alkali metal ions undergo "Li" oxidation. + Na + The phenomenon of "out", Na + Ions migrate out from higher coordination sites, Li + It occupies the adjacent low-coordinate site. The migration process is structurally very stable, while simultaneously reducing Li. + By reducing the migration energy barrier and broadening the migration path, a novel NASCION-type Li₂ with excellent ionic conductivity was synthesized. x M2(PO4)3 solid electrolyte material.

[0026] Li at low temperature + / Na + Exchange preparation of NASCION type Li x M2(PO4)3 solid electrolyte material, on the one hand, Na x In M2(PO4)3 materials, the framework ion [M2(PO4)3] - The generated ion channels and Na + Na has a high degree of radius matching, stable three-dimensional structure, and excellent ionic conductivity, therefore Na was chosen. x M2(PO4)3 material is used as a precursor material; on the other hand, the low-temperature ion exchange process is mild, and Li + and Na + The entry and exit processes do not interfere with each other, which can maximize the stability of the material frame structure and change Li +By optimizing the coordination environment of Li, lowering its migration energy barrier, and improving the diffusion migration path, the structure of the synthesized material is stabilized, achieving better ionic conductivity. This invention regulates Li from the synthesis source. x The lithium-ion diffusion environment in M2(PO4)3 materials can effectively maintain the structural framework of the superionic conductor NASICON-type solid electrolyte, allowing Li... x M2(PO4)3 solid electrolyte demonstrates the advantages of NASCION solid electrolyte in lithium-ion solid batteries.

[0027] Specifically, this invention provides a method for low-temperature synthesis of NASICON solid electrolyte, comprising the following steps: [The text abruptly ends here, so the translation stops.] x The M2(PO4)3 precursor was uniformly stirred in a lithium source solution, reacted at a low temperature, and then cooled to obtain the NASICON solid electrolyte Li. x M2(PO4)3; where M is at least one of Zr, Ti, and Al, and 1≤x≤1.5.

[0028] In some preferred embodiments, Na is prepared by the following method. x M2(PO4)3 precursor: Sodium source, M source and phosphorus source with phosphate group are mixed evenly according to chemical ratio and sintered to obtain the precursor.

[0029] In some embodiments, the sodium source is at least one of sodium acetate and its hydrate, sodium carbonate and its hydrate, and sodium hydroxide.

[0030] In some embodiments, the source of M is at least one of the following: acetate and its hydrate, carbonate and its hydrate, and oxide of M.

[0031] In some embodiments, the phosphorus source is at least one of phenylphosphoric acid, orthophosphoric acid, and ammonium dihydrogen phosphate.

[0032] In some embodiments, the molar ratio of sodium in the sodium source, M in the M source, and phosphorus in the phosphorus source is 1 to 1.5:2:3.

[0033] In some embodiments, the sintering is a two-stage sintering: first, the temperature is raised to 450-600°C at a rate of 5-7°C / min and sintered for 7-15 hours; then, the temperature is raised to 900-1400°C at a rate of 6-9°C / min and sintered for 8-15 hours.

[0034] A suitable two-stage sintering process can synthesize Na with a good three-dimensional structure after the raw materials are uniformly mixed in the molten state. x For M2(PO4)3 precursors, a suitable heating rate can maintain the stability of the material structure, while an appropriate sintering mechanism and duration can improve the material's crystallinity.

[0035] In some preferred embodiments, the lithium source is at least one selected from lithium hydroxide, lithium chloride, and lithium acetate. These lithium sources are effectively soluble in deionized water, creating a stable lithium content. + Ionic solution environment promotes Li + / Na + Ion exchange.

[0036] In some preferred embodiments, Na x In the M2(PO4)3 precursor, the molar ratio of Na to Li in the lithium source solution is 1:3–5. This range of molar ratios provides a lithium-rich environment, preventing insufficient lithium-ion concentration and exchange motive force. If the lithium-ion concentration is too high, the intense diffusion motion during the exchange process can easily generate lattice defects.

[0037] In some preferred embodiments, the low-temperature range is 60–100°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, etc. A reaction temperature of 60–100°C allows ion exchange to proceed smoothly while maintaining a stable precursor structure.

[0038] In some preferred embodiments, the process also includes washing, filtering, and drying steps.

[0039] Furthermore, the present invention also provides a NASICON solid electrolyte Li prepared by the above method. x M2(PO4)3.

[0040] The present invention also provides a solid-state battery comprising the NASICON solid electrolyte Li obtained by the above method. x M2(PO4)3.

[0041] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0043] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0044] Example 1

[0045] (1) Weigh out Na2CO3, ZrO2 and NH4H2PO4 materials with a molar ratio of 0.5:2:3, grind and mix for 30 min, then place the mixture in a muffle furnace, calcining in an air atmosphere, raise the temperature to 450℃ at a rate of 5℃ / min and sinter for 10 h, then raise the temperature to 1200℃ at a rate of 8℃ / min and sinter for 12 h, and then slowly cool with the furnace to obtain NaZr2(PO4)3.

[0046] (2) Dissolve an appropriate amount of NaZr2(PO4)3 and LiOH in 50 mL of deionized water (the molar ratio of Na to Li is 1:4). Place the mixture in a beaker in a water bath and stir magnetically. The reaction temperature is 100℃ and the reaction time is 3 h.

[0047] (3) After the material is cooled in a water bath, it is filtered twice and then centrifuged three times at a speed of 6000 r / min and a centrifugation time of 8 min each time. Then it is placed in a forced-air drying oven to dry at a temperature of 80°C for 24 h to obtain NASICON solid electrolyte LiZr2(PO4)3.

[0048] The NaZr2(PO4)3 obtained in step (1) and the NASICON solid electrolyte LiZr2(PO4)3 obtained in step (3) were subjected to ICP-OES tests, and the results are shown in Table 1.

[0049] Table 1

[0050]

[0051] As can be seen from Table 1, the ion exchange rate reaches over 90% after the low-temperature reaction, leaving a very small amount of Na doping.

[0052] Figure 1 The image shows the SEM image of the NASICON solid electrolyte LiZr2(PO4)3 prepared in Example 1. The electrolyte obtained after low-temperature reaction has a uniform morphology and homogeneous phase.

[0053] Example 2

[0054] (1) Weigh out NaOH, TiO2, (CH3COO)3Al and phenylphosphoric acid in a molar ratio of 1.3:0.3:1.7:3, grind and mix for 30 min, then place the mixture in a muffle furnace. The calcination atmosphere is air. The temperature is increased to 600℃ at a rate of 7℃ / min and sintered for 7 h. Then, the temperature is increased to 1400℃ at a rate of 9℃ / min and sintered for 8 h. Finally, the furnace is slowly cooled to obtain Na. 1.3 Ti 1.7 Al 0.3 (PO4)3.

[0055] (2) Add an appropriate amount of Na1.3 Ti 1.7 Al 0.3 (PO4)3 and LiOH were dissolved in 50 mL of deionized water (Na:Li molar ratio of 1:3). The mixture was placed in a beaker in a water bath and magnetically stirred. The reaction temperature was 80 °C and the reaction time was 2 h.

[0056] (3) The material after low-temperature water bath was filtered twice and then centrifuged three times at a speed of 6000 r / min for 8 min each time; subsequently, it was dried in a forced-air drying oven at 80°C for 24 h to obtain NASICON solid electrolyte Li. 1.3 Ti 1.7 Al 0.3 (PO4)3.

[0057] Example 3

[0058] (1) Weigh CH3COONa, TiO2 and orthophosphoric acid in a molar ratio of 1.5:2:3, grind and mix for 30 min, then place the mixture in a muffle furnace. The calcination atmosphere is air. The temperature is increased to 500℃ at a rate of 6℃ / min and sintered for 7 h. Then the temperature is increased to 1200℃ at a rate of 6℃ / min and sintered for 15 h. After slow cooling in the furnace, Na is obtained. 1.5 Ti2(PO4)3.

[0059] (2) Add an appropriate amount of Na 1.5 Ti2(PO4)3 and LiOH were dissolved in 50 mL of deionized water (Na:Li molar ratio of 1:4). The mixture was placed in a beaker in a water bath and magnetically stirred. The reaction temperature was 60 °C and the reaction time was 4 h.

[0060] (3) The material after low-temperature water bath was filtered twice and then centrifuged three times at a speed of 6000 r / min for 8 min each time; subsequently, it was dried in a forced-air drying oven at 80°C for 24 h to obtain NASICON solid electrolyte Li. 1.5 Ti2(PO4)3.

[0061] Comparative Example 1

[0062] LiZr2(PO4)3 was prepared by high-temperature sintering.

[0063] Li₂CO₃, ZrO₂, and NH₄H₂PO₄ were ground in ethanol at a molar ratio of 0.5:2:3 for 12 h, and then dried at 100 °C for 24 h. The mixture was heated at 250 °C for 1 hour, then heated at 650 °C for 3 h to remove gas, and then calcined at 900 °C for 6 h followed by slow cooling in the furnace to obtain LiZr₂(PO₄)₃.

[0064] The NASICON solid electrolytes prepared in Examples 1-3 and the LiZr2(PO4)3 obtained by high-temperature sintering in Comparative Example 1 were assembled into coin cells according to the following method: A certain amount of ground solid electrolyte powder was weighed, placed in a compaction mold, and pressed into a disc with a diameter of 12 mm and a thickness of 2 mm. In a glove box under an inert protective atmosphere, CR2032 coin cells were assembled using LiFePO4 as the positive electrode material and lithium metal sheet as the negative electrode material.

[0065] After the assembled battery was left to stand for 12 hours, its electrochemical performance was tested, and the results are shown in Table 2.

[0066] Table 2

[0067]

[0068] As can be seen from Table 2, the NASICON solid electrolyte Li synthesized at low temperature according to the present invention... x Batteries assembled from M2(PO4)3 exhibit good cycle performance, high capacity, and excellent rate performance.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for low-temperature synthesis of NASICON solid electrolyte, characterized in that, Includes the following steps: (1) Preparation of Na x M2(PO4)3 precursor: Sodium source, M source and phosphorus source with phosphate group are mixed evenly according to chemical ratio and sintered to obtain the precursor; the sintering is a two-stage sintering process, specifically: first, the temperature is raised to 450~600℃ at a rate of 5~7℃ / min and sintered for 7~15h; then the temperature is raised to 900~1400℃ at a rate of 6~9℃ / min and sintered for 8~15h. (2) The Na prepared in step (1) x The M2(PO4)3 precursor was uniformly stirred in a lithium source solution with deionized water as solvent, and Li was carried out at a low temperature of 60~100℃. + / Na + After the ion exchange reaction, the mixture is cooled, washed, filtered, and dried to obtain the NASICON solid electrolyte Li. x M2(PO4)3; where M is at least one of Zr, Ti, and Al, 1≤x≤1.5; Na x The molar ratio of Na in M2(PO4)3 to lithium in the lithium source solution is 1:3~5.

2. The method for low-temperature synthesis of NASICON solid electrolyte as described in claim 1, characterized in that, The lithium source is one or more of lithium hydroxide, lithium chloride, and lithium acetate.

3. The method for low-temperature synthesis of NASICON solid electrolyte as described in claim 1, characterized in that, The sodium source is at least one of sodium acetate and its hydrate, sodium carbonate and its hydrate, and sodium hydroxide; the M source is at least one of the acetate and its hydrate, carbonate and its hydrate, and oxide of M; the phosphorus source is at least one of phenylphosphoric acid, orthophosphoric acid, and ammonium dihydrogen phosphate.

4. The method for low-temperature synthesis of NASICON solid electrolyte as described in claim 3, characterized in that, The molar ratio of sodium in the sodium source, M in the M source, and phosphorus in the phosphorus source is 1~1.5:2:3.

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