Method for solid phase synthesis of lithium pyrophosphate and use thereof

Abstract

The application relates to the technical field of lithium ion battery material preparation, and particularly discloses a solid-phase synthesis method and application of lithium pyrophosphate, which takes Li3PO4 and P2O5 as raw materials and obtains lithium pyrophosphate through wet grinding. The high-purity lithium ion fast conductor Li4P2O7 product is obtained through one-step synthesis by the solid-phase method, and the method has many advantages such as cheap and easily-obtained raw materials, simple process, easy scale production, no waste liquid and waste residue, high product yield and high purity, etc. The application has a wide application prospect in the subfields of lithium ion battery solid-state electrolyte, lithium supplement, positive electrode material coating modifier, etc., and has extremely high economic value and social value.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material preparation technology, specifically relating to a solid-phase synthesis method and application of lithium pyrophosphate. Background Technology

[0002] Lithium pyrophosphate (Li4P2O7) is a water-soluble white powder with a weakly alkaline aqueous solution (pH 9-10). It is a high-performance fast ion conductor with very high lithium-ion conductivity and a high lithium-ion diffusion coefficient. Due to its excellent electrochemical properties, it is considered a very promising new lithium salt product with broad application potential in lithium-ion solid electrolytes, conductive agents for cathode materials, lithium supplementation agents for cathode materials, pre-lithiation agents for anode materials, and interface agents for solid electrolytes.

[0003] In 2009, Ceder's research group at MIT developed LiFePO4 material with a Li4P2O7 layer coated on the particle surface using a two-step solid-state method. This method involved asymmetric stoichiometry of lithium, iron, and phosphorus sources in the solid-state reaction of LiFePO4, followed by low-temperature pre-calcination and high-temperature sintering. The material exhibited exceptional performance, maintaining excellent electrochemical properties even at ultra-high charge-discharge rates of 200°C. This research was published in *Nature* that year, attracting widespread attention from the industry. Later that year, Clemson University verified this, confirming that LiFePO4 material with these properties could indeed be synthesized using Li4P2O7 coating. This research was published in *Applied Physics Letters*.

[0004] A previous paper titled "Solid electrolyte composite Li4P2O7–Li3PO4 for lithium ion battery" described the process of uniformly mixing NH4H2PO4 and Li2CO3 and sintering them at 600, 800, and 900 °C to obtain Li4P2O7–Li3PO4 composites with different contents. The Li4P2O7 content reached 93.56% at 800 °C. However, this method generates many byproducts, requires high-temperature sintering, has high energy consumption and low efficiency, and the purity of the obtained Li4P2O7 still needs improvement. Currently, there are few reports on the synthesis of pure-phase Li4P2O7 materials using solid-state methods. Therefore, it is necessary to provide an improved method for the solid-state synthesis of lithium pyrophosphate to lay the foundation for its large-scale application in lithium batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a solid-phase synthesis method and application of lithium pyrophosphate. Using Li3PO4 and P2O5 as raw materials, Li4P2O7 is synthesized in one step via a solid-phase method. This method has numerous advantages, including readily available and inexpensive raw materials, simple process, easy large-scale production, no waste liquid or residue generated, and high product yield and purity. Therefore, the present invention has extremely high economic and social value.

[0006] To achieve the above objectives, the present invention provides a solid-phase synthesis method for lithium pyrophosphate, which uses Li3PO4 and P2O5 as reactants and obtains lithium pyrophosphate by wet grinding.

[0007] The reaction equation is as follows:

[0008] The reaction 4Li3PO4 + P2O5 = 3Li4P2O7, as shown in the chemical equation, produces a single phase with no byproducts. Furthermore, this reaction is exothermic; Li3PO4 and P2O5 are fully contacted under wet grinding conditions, and the reaction can be sustained by the heat generated during grinding and their own combustion, eliminating the need for additional heating. Therefore, it significantly saves energy, is simple to operate, and is suitable for industrial production.

[0009] Furthermore, the wet milling process uses anhydrous alcoholic organic solvents as the dispersion medium. Li3PO4 and P2O5 are insoluble in the dispersion medium, but can be in full contact to ensure the reaction occurs and improve the synthesis efficiency.

[0010] Furthermore, the anhydrous alcohol dispersion medium includes, but is not limited to, one or more of methanol, ethanol, and ethylene glycol.

[0011] Furthermore, the ratio of the total mass of Li3PO4 and P2O5 to the mass of the anhydrous alcohol is 1:5 to 2:1, for example, 1:5, 1:3, 1:2, 1:1, 2:1, etc.

[0012] Furthermore, the molar ratio of Li3PO4 to P2O5 is 4 ± 0.05:1, preferably 4:1.

[0013] Furthermore, the wet grinding time is 1 to 15 hours, preferably 1 to 10 hours, and more preferably 5 to 8 hours.

[0014] Furthermore, the wet grinding process is performed using a sand mill. The grinding media used are zirconia beads, and the total mass ratio of the grinding media to Li3PO4 and P2O5 is 2:1. The sand mill speed is 800 rpm.

[0015] Furthermore, after the wet grinding is completed, the coarse material is filtered out using a 500-5000 mesh vibrating screen to obtain a slurry. After solid-liquid separation (preferably centrifugal separation), the obtained wet material is separated from the dispersion medium by vacuum evaporation. The vacuum evaporation temperature is 0-90℃, preferably 30-70℃, the pressure is -0.01 to -0.1 MPa, and the time is 1-24 h.

[0016] In some specific implementations, such as Figure 1 As shown, Li3PO4 and P2O5 are used as raw materials and mixed according to a metric ratio. Then, a certain amount of anhydrous alcohol is added as a dispersion medium. After the raw materials and anhydrous alcohol are mixed evenly by a mixer, the mixture is fed into a sand mill by an automatic feeder and ground for several hours. Without an external heating source, lithium pyrophosphate (Li4P2O7) with fast ion conductor characteristics is generated by the self-exothermic reaction and frictional heat generated during the sand milling process of Li3PO4 and P2O5. The coarse material is filtered out by a vibrating screen of a certain mesh to obtain a slurry. After solid-liquid separation, the obtained wet material is dried by low-temperature vacuum evaporation for several hours to obtain lithium pyrophosphate product. At the same time, anhydrous alcohol is recovered by condensation and reused in the mixing process to achieve zero emissions.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0018] 1) This invention uses Li3PO4 and P2O5 as raw materials, and can obtain Li4P2O7 product by simply grinding at room temperature. The yield and purity of the synthesized Li4P2O7 product can reach more than 97%.

[0019] 2) The reaction between Li3PO4 and P2O5 is an exothermic reaction. Production can be achieved at room temperature (without heating) under the reaction conditions of sand milling, resulting in low energy consumption per unit of production capacity.

[0020] 4) This invention is a one-step solid-phase reaction, which is simple in process and easy to mass-produce.

[0021] 5) This invention has broad application prospects in sub-fields such as solid electrolytes for lithium-ion batteries, lithium replenishing agents, and cathode material coating modifiers; it also has potential application value in multiple fields such as petrochemicals, fine chemicals, and pharmaceuticals. Attached Figure Description

[0022] Figure 1 A flowchart of the solid-phase synthesis method for lithium pyrophosphate provided by the present invention;

[0023] Figure 2 This is a photograph of the lithium pyrophosphate prepared according to the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Example 1

[0026] 464 kg of Li3PO4 (99% purity) and 142 kg of P2O5 (99% purity) were weighed as raw materials (molar ratio of 4:1). 606 kg of anhydrous ethanol was added as a dispersion medium. The raw materials and ethanol were mixed evenly using a mixer, and then the mixture was fed into a sand mill via an automatic feeder for thorough grinding for 8 hours. The grinding media was zirconium oxide beads, and the mill speed was 800 rpm. The coarse material was then filtered out using a 500-mesh vibrating screen to obtain a qualified slurry. The slurry was then centrifuged to obtain wet Li4P2O7. The wet material was then evaporated under reduced pressure at 60℃ and -0.06 MPa for 10 hours to obtain 594 kg of dried lithium pyrophosphate product (see actual image). Figure 2 (As shown); simultaneously, anhydrous ethanol is recovered by condensation and reused in the mixing process, achieving zero emissions. The obtained product was confirmed as Li4P2O7 by inductively coupled plasma optical emission spectrometry (ICP), X-ray fluorescence spectroscopy (XRF), and zinc sulfate titration pyrophosphate precipitation method (same as in Examples 2-3, not repeated). ICP test results showed that the purity of the lithium pyrophosphate product was 99.42%, and the impurity content test results are shown in Table 1.

[0027] Table 1. Results of lithium pyrophosphate content test obtained in Example 1

[0028]

[0029] Example 2

[0030] 464 kg of Li3PO4 (99% purity) and 142 kg of P2O5 (99% purity) were weighed as raw materials (molar ratio of 4:1). 606 kg of anhydrous methanol was added as a dispersion medium. The raw materials and methanol were mixed evenly using a mixer, and then the mixture was fed into a sand mill for 5 hours of thorough grinding using zirconium oxide beads as the grinding media at a speed of 800 rpm. The coarse material was then filtered out using a 1000-mesh vibrating screen to obtain a qualified slurry. The slurry was then centrifuged to obtain wet Li4P2O7 material. This wet material was then evaporated under reduced pressure at 90℃ and -0.06 MPa for 6 hours to obtain 590 kg of dried lithium pyrophosphate product. Simultaneously, anhydrous methanol was recovered by condensation and reused in the mixing process, achieving zero emissions. Inductively coupled plasma atomic emission spectrometry (ICP) analysis showed that the purity of the lithium pyrophosphate product was 98.36%.

[0031] Example 3

[0032] 464 kg of Li3PO4 (99% purity) and 142 kg of P2O5 (99% purity) were weighed as raw materials (molar ratio of 4:1). 1212 kg of anhydrous ethylene glycol was added as a dispersion medium. The raw materials and ethylene glycol were mixed evenly using a mixer, and then the mixture was fed into a sand mill for 10 hours using an automatic feeder. The sand mill media was zirconia beads, and the mill speed was 800 rpm. Coarse materials were then filtered out using a 500-mesh vibrating screen to obtain a qualified slurry. The slurry was then centrifuged to obtain wet Li4P2O7 material. The wet material was then evaporated under reduced pressure at 70℃ and -0.1 MPa for 7 hours to obtain 592 kg of dried lithium pyrophosphate product. Simultaneously, anhydrous ethylene glycol was recovered by condensation and reused in the mixing process, achieving zero emissions. Inductively coupled plasma atomic emission spectrometry (ICP) analysis showed that the purity of the lithium pyrophosphate product was 97.55%.

[0033] Table 2. Yield and purity test results for each embodiment.

[0034] Example Product yield (%) Product purity (%) Example 1 98.02 99.42 Example 2 97.36 98.36 Example 3 97.69 97.55

[0035] In summary, this invention innovatively uses Li3PO4 and P2O5 as raw materials in a stoichiometric ratio of 4:1, adds a certain amount of anhydrous alcohol (anhydrous ethanol is the best) as a dispersion medium, mixes the raw materials and anhydrous alcohol in a certain proportion using a mixer, and then feeds the mixture into a sand mill or high-energy ball mill for thorough grinding for several hours using an automatic feeder. After filtering out coarse materials through a vibrating screen of a certain mesh size, a slurry with qualified particle size is obtained. The slurry is then dried by low-temperature vacuum evaporation for several hours to obtain lithium pyrophosphate product. At the same time, the anhydrous alcohol is recovered by condensation and reused in the mixing process, achieving zero emissions.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid-phase synthesis method for lithium pyrophosphate, characterized in that, Lithium pyrophosphate is obtained by wet milling using Li3PO4 and P2O5 as reactants. The dispersion medium used in the wet milling is an anhydrous alcoholic organic solvent, which is one or more of methanol, ethanol, and ethylene glycol. The mass ratio of the total mass of Li3PO4 and P2O5 to the mass of the anhydrous alcohol is 1:5 to 2:1, and the molar ratio of Li3PO4 to P2O5 is 4 ± 0.05:

1.

2. The solid-phase synthesis method of lithium pyrophosphate according to claim 1, characterized in that, The wet grinding time is 1~15 hours.

3. The solid-phase synthesis method of lithium pyrophosphate according to claim 1, characterized in that, After the wet grinding is completed, the coarse material is filtered out by a 500-5000 mesh vibrating screen to obtain a slurry. After solid-liquid separation, the obtained wet material is separated from the dispersion medium by vacuum evaporation. The vacuum evaporation is carried out at a temperature of 0~90℃, a pressure of -0.01~-0.1Mpa, and a time of 1~24h.

4. The solid-phase synthesis method of lithium pyrophosphate according to any one of claims 1-3, characterized in that, include: Using Li3PO4 and P2O5 as raw materials, they are mixed according to a stoichiometric ratio. Then, anhydrous alcohol is added as a dispersion medium. After the raw materials and anhydrous alcohol are mixed evenly by a mixer, they are fed into a sand mill and ground thoroughly for 1 to 15 hours to generate lithium pyrophosphate Li4P2O7 with fast ion conductor characteristics. The coarse material is filtered out by a 500 to 5000 mesh vibrating screen to obtain a slurry. After solid-liquid separation, the obtained wet material is dried by low-temperature vacuum evaporation for 1 to 24 hours to obtain lithium pyrophosphate product. At the same time, anhydrous alcohol is recovered by condensation and reused in the wet grinding process.

5. A lithium pyrophosphate, characterized in that, The lithium pyrophosphate is synthesized using the synthesis method described in any one of claims 1-4, and the purity of the lithium pyrophosphate is ≥97%.

6. The application of lithium pyrophosphate synthesized by the method according to any one of claims 1-4, characterized in that, The lithium pyrophosphate is used in the preparation of lithium-ion solid electrolytes, lithium iron phosphate material coating modifiers, ternary material coating modifiers, positive and negative electrode material conductive agents, positive electrode material lithium replenishing agents, negative electrode material pre-lithiation agents, positive or negative electrode material inorganic conductive adhesives and / or solid electrolyte interface agents.

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