METHOD FOR PRODUCING POSITIVE LMFP ELECTRODE COMPOSITE PARTICLES

Abstract

A process for the production of positive LMFP electrode composite particles, comprising the following steps: introducing a variety of lithium-ion conductor particles and LMFP particles, a carbon source, and a first dispersion agent into a ball mill to combine everything into a mixed slurry, wherein each of the lithium-ion conductor particles consists of a first oxide or phosphate capable of conducting lithium ions, or of a second oxide having a garnet or perovskite structure; subsequent drying of the mixed slurry to obtain a variety of powder mixtures; and subsequent introduction of the powder mixtures into a sintering furnace to carry out oxygen-free sintering, with the aim of the carbon source undergoing a dehydration reaction to generate carbons and other residues and to form a conductive layer with which the outer surface of each of the LMFP particles is coated.

Description

AREA OF INVENTION

[0001] The invention relates to a positive electrode material for a battery and in particular to a method for producing positive LMFP electrode composite particles. BACKGROUND OF THE INVENTION

[0002] A typical battery comprises a positive and a negative electrode. The cathode of the battery comprises the positive electrode located inside the battery. This positive electrode of a solid-state or semi-solid-state battery includes a positive electrode substrate and a positive electrode mass layer. The positive electrode mass layer further comprises a positive electrode mass and a multitude of positive electrode particles. The positive electrode particles must be either conductive or electrically conductive to allow free electrons to migrate through the positive electrode mass without dissipating too much energy due to internal resistance. The material of the positive electrode particles can be LMFP (lithium manganese iron phosphate), which offers better operating voltage performance than LFP (lithium iron phosphate), releases a higher energy density, and is also cost-effective and hydrophobic.

[0003] However, LMFP exhibits a poor charge and discharge rate, as well as lower lithium-ion conductivity and electrical conductivity. Furthermore, it is prone to degradation with prolonged battery use. Although there are many ways to increase the lithium-ion conductivity of positive electrode particles, the electrical conductivity remains insufficient for practical applications. SUMMARY OF THE INVENTION

[0004] To overcome the aforementioned shortcomings of the current state of the art, the object of the invention is to provide a method for producing positive LMFP electrode composite particles in which a conductive layer is applied to an LMFP particle to increase its overall performance. The cost of LMFP is lower than that of ternary oxide. Furthermore, the charging and discharging performance of LMFP can be utilized in certain applications. The conductive layer on the outer surface of the LMFP particle compensates for the lower conductivity of LMFP. The LMFP particle is also coated with lithium-ion conductive particles to improve the overall lithium-ion conductivity and electrical conductivity, resulting in better battery performance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a step sequence diagram illustrating the process of the invention. Fig. Figure 2 shows a step sequence diagram illustrating the sequence of step A of the invention. Fig. Figure 3 shows a step sequence diagram illustrating the process of step B of the invention. Fig. Figure 4 shows a schematic view of an application of the invention. Fig. Figure 5 shows a schematic view of an overall structure and a partial structure of the positive electrode composite particle of the invention. Fig. Figure 6 shows a cross-sectional view illustrating the structure of the positive electrode composite particle of the invention. Fig. Figure 7 shows a schematic view illustrating the carbon-coated positive electrode composite particle of the invention. Fig. Figure 8 shows a schematic view of the lithium ion composite conductor particle of the invention. Fig. Figure 9 shows another cross-sectional view illustrating the structure of the positive electrode composite particle of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0005] With regard to the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8 to Fig. Section 9 of the invention provides a method for producing positive LMFP electrode composite particles 200. The positive electrode composite particles 200 are used in a positive (+) electrode 100 of a solid-state or semi-solid-state battery. The positive electrode 100 comprises a positive electrode substrate 105 and a positive electrode mass layer 102, which is applied to the positive electrode substrate 105 (as shown in Figure 9). Fig. (4 shown). The positive electrode mass layer 102 comprises the positive electrode composite particles 200 and a positive electrode mass 103 including a binder. The weight fraction of the positive electrode composite particle 200 in the positive electrode mass layer 102 is 88 wt.% to 98 wt.%.

[0006] Referring to the Fig. 1, Fig. 2 to Fig. 3 The method of the invention comprises the following steps: Step A: Introducing a variety of lithium ion conductor particles 10, a variety of LMFP particles 12, a carbon source 14 and a first dispersing agent 16 into a ball mill 300 for mixing to obtain a mixed slurry 20.

[0007] Each of the lithium-ion conductor particles 10 is formed by a first oxide or phosphate, which can conduct lithium ions, or by a second oxide with a garnet or perovskite structure. The lithium-ion conductivity of the first oxide or phosphate is higher than 10. -5 S / cm (Siemens per centimeter). The first oxide or phosphate with lithium ion conductivity can be either LATP (lithium aluminum titanium phosphate) with a NASICON structure (sodium (Na) superion conductor), LAGP (lithium aluminum germanium phosphate), or lithiophosphate (Li3PO4). The second oxide with the garnet or perovskite structure can be LLZO (Li7La3Zr2O). 12 The lithium ion conductor particle 10 can be made from lithium lanthanum zirconium oxide or LLTO (lithium lanthanum titanium oxide). It can also be formed by combining the above-mentioned materials in any desired ratio.

[0008] The D50 value (mass median diameter, MMD) of each LMFP particle 12 is less than 1 µm. Each LMFP particle 12 is a polymer of monocrystalline materials or microcrystalline particles. Each LMFP particle 12 consists of LMFP (lithium manganese iron phosphate, LiMn₂). x Fe 1-x PO4, 0.1 ≤ x ≤ 0.8) or LMFP doped with at least one metal.

[0009] In step A, before the lithium-ion conductor particles 10 are introduced into the ball mill 300, a borate layer 5 is applied to an outer surface of each lithium-ion conductor particle 10 to form a plurality of lithium-ion composite conductor particles 106. The borate layer 5 is formed by milling the lithium-ion conductor particles 10 so that the D50 value of each lithium-ion conductor particle 10 is less than 200 nm. The lithium-ion conductor particles 10 are then mixed with a boric acid-containing solution to form a melange, which is dried and milled or dried, sintered, and milled, thereby coating all outer surfaces of each lithium-ion conductor particle 10 with the borate layer 5. Each lithium-ion composite conductor particle 106 has a size of less than or equal to 200 nm.

[0010] The positive electrode composite particles 200 are manufactured using an oxygen-free sintering process. During this oxygen-free sintering, the conductivity of the lithium-ion conductor particles 10 decreases due to the lithium deficiency caused by the lack of oxygen. Therefore, the borate layer 5 is applied to the outer surface of the lithium-ion conductor particles 10 to serve as a protective layer and thus prevent damage to the structure of the lithium-ion conductor particles 10.

[0011] The carbon source 14 consists of an organic compound capable of forming a conductive carbon structure under a reduction atmosphere. The organic compound is selected from carbohydrates (such as monosaccharides, disaccharides, oligosaccharides, or polysaccharides), water-soluble fibers, or amino acid polymers. Preferably, the organic compound is a compound containing carbon, nitrogen, fluorine, phosphorus, and sulfur, wherein the nitrogen, fluorine, phosphorus, and sulfur are doped into the carbon by a reduction reaction, thereby increasing the electrical conductivity of the positive electrode composite particle 200.

[0012] Referring to Fig. 9. Carbon source 14 also contains a variety of conductive carbons 141, which can be dispersed within the first dispersion medium 16. The conductive carbons 124 are formed by at least one of the following components: graphite, graphenes, amorphous carbons on the nanoscale, and carbon nanotubes with a length of less than or equal to 1 µm. If carbon source 14 contains carbon nanotubes, the weight percentage of carbon nanotubes in carbon source 14 is less than or equal to 10 wt.%.

[0013] The ratio of the weight of the carbon source 14 to the total weight of the lithium ion conductor particles 10 is 10:1 to 1:10. The first dispersion agent 16 consists of at least one of the following substances: water, ethanol and isopropyl alcohol.

[0014] The ratio of the total weight of the lithium-ion conductor particles 10 to the total weight of the LMFP particles 12 is less than or equal to 0.02 (i.e., the ratio is not greater than 2:100). The ratio of the weight of the carbon source 14 to the weight of the LMFP particles 12 is less than or equal to 0.01 (i.e., the ratio is not greater than 1:100). The weight fraction of the lithium-ion conductor particles 10, the LMFP particles 12, and the carbon source 14 in the mixed slurry 20 is less than or equal to 35 wt.%.

[0015] Preferably, each of the lithium-ion conductor particles 10 is formed by at least one of the following components: LLZO (Li7La3Zr2O 12 ), Ga-LLZO (gallium-doped LLZO), Cu-LLZO (copper-doped LLZO), Ta-LLZO (tantalum-doped LLZO), Sr-LLZO (strontium-doped LLZO) and Al-LLZO (aluminium-doped LLZO).

[0016] Preferably, each of the lithium ion conductor particles 10 is encased by Cu a ,X b -LLZO is formed, which represents LLZO doped with copper (Cu) and a metal X, where X is selected from gallium (Ga), tantalum (Ta), strontium (Sr), barium (Ba), and aluminum (Al), and a > 0 and b > 0. Preferably, a + b = 0.25 ~ 0.8 and a > 0.1. Copper doping in the LLZO proves to be technically difficult, but Cu a ,X b -LLZO can stabilize the overall structure, smooth the channels for lithium ions, and increase the sintering rate, thereby also reducing costs. Furthermore, it also reduces the production of lithium carbonate (Li2CO3) upon contact with air, which increases surface stability during sintering.

[0017] If each of the lithium ion conductor particles 10 is formed by LAGP or LATP, the LAGP or LATP is produced from Li 1+x Al x A 2-x (PO4)3 or Li 1+x+y Al x A 2-x-y-z M y Nz (PO4)3 selected where 0.1 ≤ x ≤ 0.8, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, A is germanium (Ge) or titanium (Ti), M is a trivalent cation (such as scandium cation (Sc)). 3+ ), Yttrium cation (Y 3+ ), Gallium cation (Ga 3+ ), Indium cation (In 3+ ) or lanthanum cation (La 3+ )) is and N is a tetravalent cation (like zirconium cation (Zr) 4+ ), silicon cation (Si 4+ ) or tin cation (Sn 4+ )) is.

[0018] The ball mill 300 is a wet ball mill, specifically a paddle ball mill or a ball mill using zirconium balls. In step A, the rotational speed of the ball mill 300 is 200 to 1,000 rpm. The grinding time of the ball mill 300 is two to ten hours. The grinding temperature of the ball mill 300 is room temperature.

[0019] Step B: Carrying out natural drying or vacuum drying of the mixed slurry 20 to obtain a variety of powder mixtures 30.

[0020] Step C: Placement of the powder mixtures 30 in a sintering furnace 400 to perform oxygen-free sintering of the powder mixtures 30. During oxygen-free sintering, the carbon source 14 in the powder mixtures 30 carries out a dehydration reaction to produce carbons and other residues after oxygen-free sintering. The carbons and residues remaining after oxygen-free sintering are applied to the outer surface of each of the LMFP particles 12 (as shown in Fig. 5 shown).

[0021] In oxygen-free sintering, carbon remains after a dehydration reaction of the carbohydrates if the carbon source consists of carbohydrates. If the carbon source consists of water-soluble fibers, carbon skeletons and functional groups (such as sulfur, nitrogen, or halogens) remain after a dehydration reaction of the water-soluble fibers. The structure of the carbon skeletons is determined by the structure of the original water-soluble fibers. If the carbon source consists of amino acid polymers, carbon skeletons with straight chains or side chains containing dopants remain after a dehydration reaction of the amino acid polymers.If the carbon source 14 contains the conductive carbons 141 (which consist of graphite, graphene, nanoscale amorphous carbons or carbon nanotubes), the structure of each of the conductive carbons 141 is not altered and remains in its original form after oxygen-free sintering.

[0022] In oxygen-free sintering, the outer surface of each of the LMFP particles 12 is coated with a conductive layer 221, which is formed from the lithium-ion conductor particles 10 and the carbon source 14 (i.e., the carbons and other residues resulting from the dehydration reaction of the carbon source 14) to form the positive electrode composite particles 200. The thickness of the conductive layer 221 is less than or equal to 200 nm. The lithium-ion conductor particles 10 on each of the LMFP particles 121 form a continuous layered structure, a discontinuously distributed structure, or an island-like structure.

[0023] In step C, the sintering temperature of the sintering furnace 400 ranges from 400°C to 700°C. The sintering time in the sintering furnace 400 is one to ten hours. Oxygen-free sintering is either vacuum sintering or sintering under a protective atmosphere (for example, sintering under a protective atmosphere of argon (Ar) and nitrogen (N2)).

[0024] Step D: Performing a sieving process of the positive electrode composite particles 200 to remove impurities and obtain a variety of positive electrode composite particle powders 250.

[0025] The invention further comprises the following step: Step E: The composite particle powders of the positive electrode 250 and a first slurry 255 containing a carbon material are introduced into a mixer 350 for mixing to form a plurality of carbon-coated composite particles of the positive electrode 280. A solvent in the first slurry 255 is selected from water, ethanol, isopropyl alcohol, and NMP (N-methyl-2-pyrrolidone). The weight percentage of the carbon material in the first slurry 255 is less than or equal to 5 wt%. The first slurry 255 may further contain a second dispersing agent, wherein the second dispersing agent is selected from SCS (sodium O-cumenesulfonate) and sinapic acid. The weight percentage of the second dispersing agent in the first slurry 255 is less than or equal to 1 wt%.The carbon material comprises a variety of first carbon nanotubes 40 and a variety of amorphous carbons at the nanoscale 45. The rotational speed of the mixer 350 is 50 rpm to 1,000 rpm. The mixing time of the mixer 350 is one to three hours. The mixer 350 can be a DC stirrer or a vacuum emulsifying mixer.

[0026] The first carbon nanotubes 40 comprise a variety of short-chain carbon nanotubes 42 and a variety of long-chain carbon nanotubes 44. The length of each of the short-chain carbon nanotubes 42 is 0.2 µm to 1 µm. The length of each of the long-chain carbon nanotubes 44 is 1 µm to 3 µm. The weight ratio of the short-chain carbon nanotubes 42 to the weight of the long-chain carbon nanotubes 44 is 10:1 to 2:1. The ratio of the total weight of the carbon material of the first suspension 255 to the weight of the positive composite electrode particle powder 250 is less than or equal to 0.01 (that is, the ratio is not greater than 1:100). The ratio of the weight of the first carbon nanotubes 40 to the weight of the nanoscale amorphous carbons 45 is 1:1 to 1:10. The size of each of the nanoscale amorphous carbons 45 is 10 nm to 40 nm.

[0027] Different lengths of the first carbon nanotubes 40 form different strain planes on the positive electrode composite particle 200. The short-chain carbon nanotubes 42 are connected between the lithium-ion conductor particles 10 and the LMFP particle 12. The long-chain carbon nanotubes 44 cover the positive electrode composite particle 200 to increase its structural strength. The positive electrode composite particle 200 covered by the first carbon nanotubes 40 forms a hairball-like structure (as shown in Fig. 7 shown).

[0028] The first carbon nanotubes 40 serve to form conductive bridges around the positive electrode composite particle 200, thus conducting the electrons on the positive electrode composite particle 200. The first carbon nanotubes 40 have extremely high electrical conductivity, allowing lithium ions to pass through the first carbon nanotubes 40 and conduct between different positive electrode composite particles 200, thereby increasing the electrical conductivity of the entire positive electrode 100.

[0029] Preferably, the nanoscale amorphous carbons 45 are amorphous carbons of a super-P auxiliary. The first carbon nanotubes 40 and the nanoscale amorphous carbons 45 are used as a further auxiliary. The nanoscale amorphous carbons 45 have the form of particles, the first carbon nanotubes 40 have the form of long strips, and the nanoscale amorphous carbons 45 are filled into the gaps formed in the intervening first carbon nanotubes 40 in order to transfer the electrical charge between the first carbon nanotubes 40 by means of the overpotential of the nanoscale amorphous carbons 45, thereby further increasing the transmission efficiency of the electrical current.

[0030] In describing the invention, it is obvious that it can be varied in many ways. Such variations are not to be considered a departure from the spirit and scope of the invention, and all modifications that would be obvious to a person skilled in the art are to fall within the scope of the following claims.

Claims

[1] A method for producing positive LMFP electrode composite particles; the positive electrode composite particles are used in a positive electrode of a solid-state or semi-solid-state battery; the method comprises the following steps: Step A: Introducing a variety of lithium-ion conductor particles, a variety of LMFP particles, a carbon source, and a first dispersant into a ball mill for mixing to form a mixed slurry; wherein each of the lithium-ion conductor particles consists of a first oxide or phosphate capable of conducting lithium ions, or of a second oxide having a garnet or perovskite structure; a lithium-ion conductivity of the first oxide or phosphate is greater than 10 -5 S / cm (Siemens per centimeter); and the carbon source consists of an organic compound capable of forming a conductive carbon structure under a reduction atmosphere; Step B: Performing natural drying or vacuum drying on the mixed slurry to obtain a variety of mixed powders; Step C: The powder mixture is introduced into a sintering furnace to carry out oxygen-free sintering of the powder mixture to form the positive composite electrode particles; wherein, during oxygen-free sintering, the carbon source in the powder mixture undergoes a dehydration reaction to generate carbons and other residues after oxygen-free sintering; the carbons and residues remaining after oxygen-free sintering form a conductive layer, and the conductive layer is applied to an outer surface of each of the LMFP particles; and the lithium-ion conductor particles on each of the LMFP particles form a continuous layered structure, a discontinuously distributed structure, or an island-like structure. [2] A method according to claim 1, wherein the first oxide or phosphate may be equipped with the lithium ion conductivity LATP (lithium aluminum titanium phosphate) with a NASICON structure (sodium (Na) superion conductor), LAGP (lithium aluminum germanium phosphate) or lithiophosphate (Li3PO4). [3] A method according to claim 1, wherein the second oxide has the garnet or perovskite structure LLZO (Li7La3Zr2O 12 , lithium lanthanum zirconium oxide) or LLTO (lithium lanthanum titanium oxide). [4] A method according to claim 1, wherein a D50 value (mass median diameter, MMD) of each of the LMFP particles is less than 1 µm; and each of the LMFP particles is a polymer of monocrystalline materials or microcrystalline particles; and a thickness of the conductive layer is less than or equal to 200 nm. [5] A method according to claim 1, wherein each of the LMFP particles is made of LMFP (lithium manganese iron phosphate, LiMn₂).x Fe 1-x PO4, 0.1 ≤ x ≤ 0.8) or is formed with LMFP doped with at least one metal. [6] A method according to claim 1, wherein in step A, before the lithium ion conductor particles are placed in the ball mill, an outer surface of each of the lithium ion conductor particles is coated with a borate layer to cause the lithium ion conductor particles to form a plurality of lithium ion composite conductor particles. [7] A method according to claim 6, wherein the borate layer is formed by grinding the lithium-ion conductor particles to cause the D50 value of each of the lithium-ion conductor particles to be less than 200 nm and then mixing the lithium-ion conductor particles with a boric acid-containing solution to form a mixture; and then drying and grinding the mixture or drying, sintering and grinding the mixture, thereby coating each of the outer surfaces of each of the lithium-ion conductor particles with the borate layer. [8] A method according to claim 1, wherein the organic compound is selected from monosaccharide, disaccharide, oligosaccharide and polysaccharide as water-soluble fiber and amino acid polymer; wherein, during the oxygen-free sintering of step C, if the carbon source is formed by carbohydrates, the carbons remain after a dehydration reaction of the carbohydrates; if the carbon source is formed by water-soluble fibers, carbon skeletons and functional groups remain after a dehydration reaction of the water-soluble fibers; the structure of the carbon skeletons is determined by the structure of the original water-soluble fibers; and if the carbon source is formed by amino acid polymers, carbon skeletons with straight chains or side chains containing dopants remain after a dehydration reaction of the amino acid polymers. [9] A method according to claim 1, wherein the organic compound is a compound containing carbon, nitrogen, fluorine, phosphorus and sulfur, wherein nitrogen, fluorine, phosphorus and sulfur are doped into the carbon by a reduction reaction. [10] A method according to claim 1, wherein the carbon source further comprises at least one of the following components: graphite, graphenes, amorphous carbons on the nanoscale and carbon nanotubes with a length of less than or equal to 1 µm. [11] A method according to claim 1, wherein the ratio of the weight of the carbon source to the total weight of the lithium-ion conductor particles is 10:1 to 1:10; the ratio of the total weight of the lithium-ion conductor particles to the total weight of the LMFP particles is less than or equal to 0.02; the ratio of the weight of the carbon source to the total weight of the LMFP particles is less than or equal to 0.01; and the weight fraction of the lithium-ion conductor particles, the LMFP particles and the carbon source in the mixed slurry is less than or equal to 35 wt.%. [12] A method according to claim 1, wherein each of the lithium ion conductor particles is formed from at least one of the following materials: LLZO (Li7La3Zr2O 12), Ga-LLZO (gallium-doped LLZO), Cu-LLZO (copper-doped LLZO), Ta-LLZO (tantalum-doped LLZO), Sr-LLZO (strontium-doped LLZO) and Al-LLZO (aluminium-doped LLZO). [13] A method according to claim 1, wherein each of the lithium ion conductor particles is made of Cu a ,X b -LLZO is formed, which is LLZO doped with copper (Cu) and a metal X, where X is selected from gallium (Ga), tantalum (Ta), strontium (Sr), barium (Ba) and aluminium (Al) and a+b=0.25~0.8 and a>0.

1. [14] A method according to claim 1, wherein, if each of the lithium ion conductor particles is formed from LAGP (lithium aluminum germanium phosphate) or LATP (lithium aluminum titanium phosphate), the LAGP or LATP is formed from Li 1+x Al x A 2-x (PO4)3 or Li 1+x+y Al x A 2-x-y-z M y N z(PO4)3 is selected where 0.1 ≤ x ≤ 0.8, 0 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, A is germanium (Ge) or titanium (Ti), M is a trivalent cation and N is a tetravalent cation. [15] A method according to claim 1, wherein the ball mill is a wet ball mill, wherein the wet ball mill is a paddle ball mill or a ball mill with zirconium balls; in step A the rotational speed of the ball mill is 200 rpm to 1,000 rpm; a grinding time of the ball mill is two to ten hours; and a grinding temperature of the ball mill is at room temperature. [16] A method according to claim 1, wherein in step C the sintering temperature of the sintering furnace is 400°C to 700°C; the sintering time of the sintering furnace is one to ten hours; and the oxygen-free sintering is vacuum sintering or sintering under a protective atmosphere. [17] A method according to claim 1, further comprising the following step D: Step D: Performing a sieving process on the positive electrode composite particles to remove impurities and obtain a variety of positive electrode composite particle powders. [18] A method according to claim 17, further comprising the following step E: Step E: Introducing the positive composite electrode particle powder and a first slurry containing a carbon material into a mixer for mixing to form a plurality of carbon-coated positive composite electrode particles; wherein the carbon material contains a plurality of first carbon nanotubes and a plurality of nanoscale amorphous carbons. [19] A method according to claim 18, wherein in step E the rotational speed of the mixer is 50 rpm to 1,000 rpm; the mixing time of the mixer is one to three hours; and the mixer can be a direct current stirrer or a vacuum emulsifying mixer. [20] A method according to claim 18, wherein a weight percentage of the carbon material in the first slurry is less than or equal to 5 wt%; a solvent in the first slurry is selected from water, ethanol, isopropyl alcohol and NMP (N-methyl-2-pyrrolidone); the first slurry further comprises a second dispersion agent, wherein the second dispersion agent is selected from SCS (sodium O-cumenesulfonate) and sinapic acid; and a weight percentage of the second dispersion agent in the first slurry is less than or equal to 1 wt%; the first carbon nanotubes comprise a plurality of short-chain carbon nanotubes and a plurality of long-chain carbon nanotubes; a length of each of the short-chain carbon nanotubes is 0.2 µm to 1 µm; The length of each of the long-chain carbon nanotubes is 1 µm to 3 µm; and the size of each of the amorphous carbons on the nanoscale is 10 nm to 40 nm.

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