A lithium iron phosphate / lithium vanadium phosphate superstructure solid solution and its autocatalytic preparation method and application

Abstract

The present invention relates to the technical field of lithium battery power materials, and more specifically to a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, its preparation method, and application. The lithium iron phosphate / lithium vanadium phosphate superstructure solid solution provided by the present invention is xLiFePO4·(1-x)Li3V2(PO4)3, where 0.5<x<0.95. The lithium iron phosphate / lithium vanadium phosphate superstructure solid solution provided by the present invention has the advantages of high charge and discharge rates, high power density, good cycle stability, and high energy efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery power materials, and in particular to a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution and an autocatalytic preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have become the mainstream of power tools due to their high energy, high power, environmental protection and ability to be recycled multiple times.

[0003] Lithium iron phosphate material is currently the main lithium battery power material, with the advantages of good safety, long service life and low cost. However, the electrochemical performance of traditional lithium iron phosphate materials still needs to be improved. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution and its autocatalytic preparation method and application. The lithium iron phosphate / lithium vanadium phosphate superstructure solid solution provided by the present invention has the advantages of high charge and discharge rate, high power density, good cycle stability and high energy efficiency.

[0005] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0006] The present invention provides a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, wherein the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is xLiFePO4·(1-x)Li3V2(PO4)3; wherein 0.5<x<0.95.

[0007] Preferably, the particle size of the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is less than 200 mesh.

[0008] The present invention provides an autocatalytic preparation method of a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, comprising the following steps:

[0009] Mixing lithium carbonate, iron phosphate, a vanadium source and an autocatalytic guide to obtain a mixture; the vanadium source includes nano-vanadium trioxide; the autocatalytic guide is one or more of vanadium acetylacetonate, vanadyl acetylacetonate and vanadium acylhydrazone;

[0010] The mixed material is sintered to obtain a preliminary material;

[0011] The preliminary material is sieved, and the undersize material is taken to obtain the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution.

[0012] Preferably, the sintering temperature is 700-900° C., and the holding time is 9-11 hours.

[0013] Preferably, the sieve particle size is 200 mesh.

[0014] Preferably, the molar ratio of the iron in the iron phosphate to the vanadium in the vanadium source is (0.5-0.95):(1-0.1); and the molar ratio of the lithium in the lithium carbonate to the iron in the iron phosphate is 1:1.

[0015] Preferably, the mass of the autocatalytic guide agent is 0.5-3% of the total mass of the lithium carbonate, iron phosphate and vanadium source.

[0016] Preferably, the mixing method is stirring; and the mixing time is 2 to 3 hours.

[0017] The present invention also provides the use of the above-mentioned lithium iron phosphate / lithium vanadium phosphate superstructure solid solution or the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution prepared by the preparation method described in the above technical solution in lithium battery power materials.

[0018] The present invention provides a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, wherein the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is xLiFePO4·(1-x)Li3V2(PO4)3; wherein 0.5<x<0.95. The lithium iron phosphate / lithium vanadium phosphate superstructure solid solution of the present invention contains lithium vanadium phosphate (Li3V2(PO4)3); the introduction of lithium vanadium phosphate (Li3V2(PO4)3) can increase the charge and discharge rate, increase the power density, improve the cycle stability, enhance the energy efficiency, and improve the electrochemical performance of the material.

[0019] The present invention also provides a method for preparing the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution described above, comprising the following steps: mixing lithium carbonate, iron phosphate, a vanadium source, and an autocatalytic guide to obtain a mixture; the vanadium source comprising nano-vanadium trioxide; the autocatalytic guide being one or more of vanadium acetylacetonate, vanadium oxyacetylacetonate, and vanadium acylhydrazone; sintering the mixture to obtain a preliminary material; sieving the preliminary material and removing the sieve residue to obtain the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution. In the present invention, first, the autocatalytic guide (vanadium acetylacetonate, vanadium oxyacetylacetonate, and vanadium acylhydrazone) guides the nano-vanadium trioxide (reactant and autocatalyst) as crystal nuclei to promote rapid crystallization of lithium iron phosphate, thereby shortening the synthesis cycle. Second, the nano-vanadium trioxide can also serve as both a raw material and a catalyst, acting as a new crystal nucleus to catalyze its own reaction with lithium iron phosphate to form the fast ion lithium vanadium phosphate (Li3V2(PO4)3). The introduction of fast ions (Li3V2(PO4)3) can increase charge and discharge rates, increase power density, improve cycle stability, enhance energy efficiency, and enhance the electrochemical performance of the material. Thirdly, nano-vanadium trioxide also promotes the reaction between lithium iron phosphate and lithium vanadium phosphate, accelerating the material synthesis time and ultimately preparing the target product, xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution prepared in Example 1;

[0021] Figure 2 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution prepared in Example 2:

[0022] Figure 3 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution prepared in Example 3. DETAILED DESCRIPTION

[0023] The present invention provides a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, wherein the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is xLiFePO4·(1-x)Li3V2(PO4)3; wherein 0.5<x<0.95.

[0024] In the present invention, the particle size of the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is preferably less than 200 mesh.

[0025] The present invention also provides a method for preparing the above-mentioned lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, comprising the following steps:

[0026] Mixing lithium carbonate, iron phosphate, a vanadium source and an autocatalytic guide to obtain a mixture; the vanadium source includes nano-vanadium trioxide; the autocatalytic guide is one or more of vanadium acetylacetonate, vanadyl acetylacetonate and vanadium acylhydrazone;

[0027] The mixed material is sintered to obtain a preliminary material;

[0028] The preliminary material is sieved, and the undersize material is taken to obtain the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution.

[0029] The present invention mixes lithium carbonate, iron phosphate and a vanadium source to obtain a mixed material.

[0030] In the present invention, the vanadium source includes nano-vanadium trioxide; the autocatalytic guide is preferably one or more of vanadium acetylacetonate, vanadium oxyacetylacetonate and vanadium acylhydrazone, more preferably vanadium acetylacetonate or vanadium acylhydrazone.

[0031] In the present invention, the molar ratio of the iron in the ferric phosphate to the vanadium in the vanadium source is preferably (0.5-0.95):(1-0.1), more preferably 0.8:0.4; the molar ratio of the lithium in the lithium carbonate to the iron in the ferric phosphate is preferably 1:1. In the present invention, the mass of the autocatalytic guide is preferably 0.5-3% of the total mass of the lithium carbonate, ferric phosphate, and vanadium source, more preferably 1-2%.

[0032] In the present invention, the mixing method is preferably stirring, the stirring speed is preferably 200 to 600 rpm, more preferably 450 rpm, and the stirring time is preferably 2 to 3 hours, more preferably 2.5 hours.

[0033] After obtaining the mixed material, the present invention sintered the mixed material to obtain a preliminary material.

[0034] In the present invention, the sintering temperature is preferably 700-900°C, more preferably 750-850°C, and the holding time is preferably 9-11 hours, more preferably 10 hours. In the present invention, the heating rate to the sintering temperature is preferably 2-15°C / min, more preferably 8°C / min.

[0035] In the present invention, after the sintering, cooling is further included, and the cooling is preferably cooled to room temperature.

[0036] After obtaining the preliminary material, the present invention sieves the preliminary material and takes the undersize to obtain the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution.

[0037] In the present invention, the particle size of the sieve is preferably 200 mesh.

[0038] The present invention also provides the use of the above-mentioned lithium iron phosphate / lithium vanadium phosphate superstructure solid solution or the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution prepared by the preparation method described in the above technical solution in lithium battery power materials.

[0039] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] Lithium carbonate and ferric phosphate were used as raw materials, nano-vanadium trioxide was used as the raw material and catalyst, and vanadium acetylacetonate was used as the catalyst directing agent. The molar ratio of iron in the ferric phosphate, lithium in the lithium carbonate, and vanadium in the nano-vanadium trioxide was 0.8:0.8:0.4, with the vanadium acetylacetonate accounting for 1% of the total mass of the lithium carbonate, ferric phosphate, and nano-vanadium trioxide. The mixture was stirred at 450 rpm for 3 hours. The mixture was then sintered in a calciner at 800°C (at a heating rate of 8°C / min) for 9 hours to obtain a preliminary product. The preliminary product was passed through a 200-mesh standard sieve, and the undersize fraction was removed to obtain a xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution, where x = 0.8.

[0042] Figure 1 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 solid solution prepared in Example 1. Figure 1 It can be seen that the material was successfully prepared with regular shape and uniform particle size.

[0043] Example 2

[0044] Lithium carbonate and ferric phosphate were used as raw materials, nano-vanadium trioxide was used as the raw material and catalyst, and vanadium acetylacetonate was used as the catalyst directing agent. The molar ratio of iron in the ferric phosphate, lithium in the lithium carbonate, and vanadium in the nano-vanadium trioxide was 0.7:0.7:0.4, with vanadium acetylacetonate accounting for 2% of the total mass of the lithium carbonate, ferric phosphate, and nano-vanadium trioxide. The mixture was stirred at 450 rpm for 3 hours. The mixture was then sintered in a calciner at 800°C (at a heating rate of 8°C / min) for 9 hours to obtain a preliminary product. The preliminary product was then passed through a 200-mesh standard sieve, and the undersize fraction was removed to obtain a superstructured solid solution of xLiFePO4·(1-x)Li3V2(PO4)3, where x = 0.7.

[0045] Figure 2 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution prepared in Example 2. Figure 2 It can be seen that the material was successfully prepared, with a relatively regular shape and uniform particle size, but with a small amount of agglomeration.

[0046] Example 3

[0047] Lithium carbonate, iron phosphate, and nano-vanadium trioxide were used as raw materials, and acylhydrazone vanadium was used as a catalyst-directing agent. The molar ratio of iron in the iron phosphate, lithium in the lithium carbonate, and vanadium in the nano-vanadium trioxide was 0.6:0.6:0.4, with acylhydrazone accounting for 2% of the total mass of the lithium carbonate, iron phosphate, and nano-vanadium trioxide. The mixture was stirred at 400 rpm for 2 hours. The mixture was sintered in a calcination furnace at 750°C (at a heating rate of 8°C / min) for 9 hours to obtain a preliminary product. The preliminary product was passed through a 200-mesh standard sieve, and the undersize fraction was removed to obtain a xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution, where x = 0.6.

[0048] Figure 3 This is the SEM image of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solution prepared in Example 3. Figure 3 It can be seen that the material was successfully prepared, but the shape and particle size were quite different.

[0049] The present invention also tested the electrochemical properties (charge and discharge rate, power density, cycle stability, and energy efficiency) of the xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solutions prepared in Examples 1 to 3. The testing method was as follows: the electrochemical performance tests were conducted using 2032 button cells. The mass ratio of the prepared active material xLiFePO4·(1-x)Li3V2(PO4)3, conductive agent (acetylene black), and binder (PVDF) was 8:1:1. The electrolyte consisted of 1 mol / L LiPF6, EC+DEC (volume ratio 1:1). The test environment temperature was constant at 25°C. The test results are shown in Table 1.

[0050] Table 1 Electrochemical properties of xLiFePO4·(1-x)Li3V2(PO4)3 superstructure solid solutions of Examples 1 to 3

[0051]

[0052] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for the autocatalytic preparation of a lithium iron phosphate / lithium vanadium phosphate superstructure solid solution, characterized in that: It consists of the following steps: Mixing lithium carbonate, iron phosphate, a vanadium source and an autocatalytic guide agent to obtain a mixture; the vanadium source comprises nano-vanadium trioxide; and the autocatalytic guide agent is vanadium acetylacetonate; The mixed material is sintered to obtain a preliminary material; Sieving the preliminary material and taking the sieve underfill to obtain the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution; The lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is xLiFePO4·(1-x)Li3V2(PO4)3, wherein 0.5<x<0.

95.

2. The autocatalytic preparation method according to claim 1, wherein The particle size of the lithium iron phosphate / lithium vanadium phosphate superstructure solid solution is less than 200 meshes.

3. The autocatalytic preparation method according to claim 1, wherein The sintering temperature is 700-900° C., and the holding time is 9-11 hours.

4. The autocatalytic preparation method according to claim 1, wherein The particle size of the sieve is 200 meshes.

5. The autocatalytic preparation method according to claim 1, wherein The molar ratio of the iron in the iron phosphate to the vanadium in the vanadium source is (0.5-0.95):(1-0.1); the molar ratio of the lithium in the lithium carbonate to the iron in the iron phosphate is 1:

1.

6. The autocatalytic preparation method according to claim 1, wherein The mixing method is stirring; the mixing time is 2 to 3 hours.

7. The autocatalytic preparation method according to claim 1, wherein: The mass of the autocatalytic guide agent is 0.5-3% of the total mass of the lithium carbonate, the iron phosphate and the vanadium source.

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