Method for manufacturing lithium iron manganese phosphate composite cathode particles

Abstract

This invention provides a method for producing lithium iron manganese phosphate composite cathode particles. [Solution] The method includes the steps of: introducing lithium ion conductor particles, LMFP particles, a carbon source, and a dispersant into a ball mill and mixing to form a mixed slurry, wherein the carbon source is an organic compound capable of forming conductive carbon in a reducing atmosphere; air-drying or vacuum-drying the mixed slurry to obtain a mixed powder; introducing the mixed powder into a sintering furnace and performing oxygen-free sintering to obtain composite cathode particles, wherein in an oxygen-free environment, a conductive layer is formed covering the outer surface of the LMFP particles with the carbon remaining after dehydrating the carbon source of the mixed powder, other sintering residues, and lithium ion conductor particles to form composite cathode particles; and the distribution morphology of the lithium ion conductor particles in the LMFP particles is continuous distribution morphology, discontinuous distribution morphology, or island particle morphology.

Description

[Technical Field]

[0001] This invention relates to a positive electrode material for batteries, and more specifically, to a method for producing lithium iron manganese phosphate composite positive electrode particles. [Background technology]

[0002] A battery consists of a positive electrode and a negative electrode, with the cathode being the positive electrode inside the battery. The positive electrode of a typical all-solid-state or semi-solid-state battery mainly comprises a positive electrode substrate and a positive electrode slurry layer, the positive electrode slurry layer containing positive electrode slurry and positive electrode particles. The positive electrode particles need to be conductive or conductive in order to allow free electrons to move within the positive electrode slurry and to prevent excessive energy loss due to internal resistance. As the material for the positive electrode particles, LMFP (lithium manganese iron phosphate) may be selected, as it has better operating voltage performance than lithium iron phosphate (LFP), releases energy at a higher energy density, is inexpensive, and is hydrophobic. [Overview of the project] [Problems that the invention aims to solve]

[0003] However, LMFPs have poor multiplier charge / discharge performance, low lithium guiding ability, and low conductivity, and their structure deteriorates quickly when used in batteries for extended periods. While many technologies already exist to improve the guiding ability of positive electrode particles to lithium ions, their conductivity is still insufficient for practical use.

[0004] Therefore, as a result of diligent research, the inventors have found that the above objective can be achieved by having a positive electrode of an all-solid-state battery with higher capacity and conductivity.

[0005] This invention was made through diligent research by the inventors in view of the above-mentioned problems, and its purpose is to provide a method for producing lithium iron manganese phosphate composite cathode particles. [Means for solving the problem]

[0006] To solve the above problems, a method for manufacturing lithium iron manganese phosphate composite cathode particles according to one aspect of the present invention improves overall performance by coating the outside of the LMFP particles with a carbon layer and a plurality of lithium ion conductor particles. The cost of LMFP is lower than that of ternary oxides, its charge and discharge performance is applicable to a specific range, and its use as a cathode material can suppress the manufacturing cost of batteries. The carbon layer can compensate for the disadvantage of low conductivity of LMFP, and by coating the outer surface of the LMFP with a plurality of lithium ion conductor particles, the overall lithium ion guiding ability is improved, and at the same time, the overall conductivity and lithium ion guiding ability are improved, resulting in an even better battery effect.

[0007] Other features of the present invention will be made clearer by description in this specification and the accompanying drawings. [Brief explanation of the drawing]

[0008] [Figure 1] This flowchart shows a method for producing lithium iron manganese phosphate composite cathode particles according to one embodiment of the present invention. [Figure 2] This is a flowchart of step A of the present invention. [Figure 3] This is a flowchart showing steps B to E of the present invention. [Figure 4] This is an example demonstrating a method for producing lithium iron manganese phosphate composite cathode particles according to the present invention. [Figure 5] A schematic diagram and a magnified view of a part showing composite cathode particles according to one embodiment of the present invention. [Figure 6] This is a schematic cross-sectional view showing composite cathode particles according to one embodiment of the present invention. [Figure 7] This is a schematic diagram showing composite cathode particles coated with a carbon material according to one embodiment of the present invention. [Figure 8] This is a schematic diagram showing lithium-ion composite conductive particles according to one embodiment of the present invention. [Figure 9]It is a cross-sectional view schematically showing composite positive electrode particles according to another embodiment of the present invention.

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples and can be arbitrarily changed without departing from the gist of the present invention.

[0010] First, referring to FIGS. 1 to 9, an embodiment of a method for manufacturing lithium manganese iron phosphate composite positive electrode particles according to the present invention will be described.

[0011] The method for manufacturing lithium manganese iron phosphate composite positive electrode particles according to the present invention is used for the positive electrode 100 of a semi-solid or all-solid battery. The positive electrode 100 mainly includes a positive electrode substrate 105 (see FIG. 4), and a positive electrode slurry layer 102 is coated on the positive electrode substrate 105. The positive electrode slurry layer 102 includes a positive electrode slurry 103 having a binder and a plurality of the composite positive electrode particles 200. The weight percentage of the total weight of the plurality of composite positive electrode particles 200 in the positive electrode slurry layer 102 is in the range of 88 wt% to 98 wt%.

[0012] As shown in FIGS. 1 to 3, the method of the present invention is used to manufacture a plurality of the composite positive electrode particles 200 and includes the following steps. <Step A>: A plurality of lithium ion conductor particles 10, a plurality of LMFP (lithium manganese iron phosphate) particles 12, a carbon source 14, and a dispersant 16 are put into a ball mill 300 and mixed to form a mixed slurry 20.

[0013] The lithium ion conductor particles 10 have a lithium ion conduction ability (ionic conductivity is 10 -5 cm 2Oxides or phosphates having a / s super (), or oxides having a garnet or perovskite structure. The oxides or phosphates having the lithium ion conduction ability are, for example, lithium aluminum titanium phosphate (LATP) having a NASICON (sodium (Na) super ionic conductor) structure, lithium aluminium germanium phosphate (LAGP), or phosphates such as lithium phosphate (Li3PO4) having lithium conduction ability. The oxides having a garnet or perovskite structure are, for example, lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , lithium lanthanum zirconium oxide, LLZO) or lithium lanthanum titanium oxide (lithium lanthanum titanium oxide, LLTO). The lithium ion conductor particles 10 may be a combination of the above components in any ratio.

[0014] The D50 particle diameter (mass-median-diameter, MMD, mass median diameter of the particle size distribution) of the LMFP particles 12 is less than 1 μm, and its form is a single crystal material or a polymer of fine crystal particles. The LMFP particles 12 are composed of lithium manganese iron phosphate (LiMn x Fe 1-x PO4, where x is in the range between 0.1 and 0.8), or lithium manganese iron phosphate doped with at least one metal element.

[0015] In step A, before introducing the plurality of lithium ion conductor particles into the ball mill, the outer surface of each lithium ion conductor particle 10 is coated with a boric acid layer 5 to form lithium ion composite conductor particles 106. The formation method involves grinding the plurality of lithium ion conductor particles 10 until the mass median particle diameter of the particle size distribution is less than 200 nm, then introducing them into a solution containing boric acid and mixing thoroughly, drying and grinding, or drying, sintering, and grinding, and then coating the surface of each lithium ion conductor particle 10 with the boric acid layer 5. The purpose of coating the outer surface of the lithium ion conductor particles 10 with the boric acid layer 5 is that in the manufacturing process of the composite positive electrode particles 200, in an oxygen-free sintering environment, the lithium ion conductor particles 10 become deficient in lithium due to oxygen deficiency, and their conductivity decreases. By coating the outer surface of the lithium ion conductor particles 10 with the boric acid layer 5 to form a protective layer, the lithium ion conductor particles 10 are prevented from being destroyed during the process. The size of the lithium-ion composite conductive particles 106 is 200 nm or less.

[0016] The carbon source 14 is an organic compound capable of forming conductive carbon in a reducing atmosphere. The organic compound is selected from carbohydrates (e.g., monosaccharides, disaccharides, oligosaccharides, polysaccharides), water-soluble fibers, or amino acid polymers. Preferably, the organic compound is a compound containing carbon and elements such as nitrogen, fluorine, phosphorus, and sulfur, and the overall electronic conductivity of the composite cathode particles 200 is increased by reducing it and then doping the carbon with these elements.

[0017] In this case, as shown in Figure 9, the carbon source 14 further comprises conductive carbon 141 that can be sufficiently dispersed in the dispersant 16, and the conductive carbon 141 is composed of at least one of graphite, graphene, nano-sized amorphous carbon, or carbon nanotubes with a length of 1 μm or less. When carbon nanotubes are used as a component of the carbon source 14, their weight percentage relative to the total weight of the carbon source 14 does not exceed 10 wt%.

[0018] The ratio of the total weight of the carbon source 14 to the total weight of the plurality of lithium ion conductor particles 10 is in the range between 10:1 and 1:10. The dispersant 16 is selected from at least one of water, alcohol, or isopropanol.

[0019] The weight ratio of the total weight of the plurality of lithium ion conductor particles 10 to the total weight of the plurality of LMFP particles 12 is 2:100 or less, and the weight ratio of the total weight of the carbon source 14 to the total weight of the plurality of LMFP particles 12 is 1:100 or less. In the mixed slurry 20, the weight percentage of "the total weight of the plurality of lithium ion conductor particles 10, the plurality of LMFP particles 12, and the carbon source 14" in the mixed slurry 20 is 35 wt% or less.

[0020] Each of the lithium ion conductor particles 10 is formed of at least one of LLZO, Ga-LLZO (Ga-doped LLZO, gallium-doped lithium lanthanum zirconium oxide), Cu-LLZO (Cu-doped LLZO, copper-doped lithium lanthanum zirconium oxide), Ta-LLZO (Ta-doped LLZO, tantalum-doped lithium lanthanum zirconium oxide), Sr-LLZO (Sr-doped LLZO, strontium-doped lithium lanthanum zirconium oxide), and Al-LLZO (Al-doped LLZO, aluminum-doped lithium lanthanum zirconium oxide).

[0021] Preferably, each of the lithium ion conductor particles 10 is Cu a ,X b -LLZO. The Cu a ,X b-LLZO is a lithium lanthanum zirconium oxide doped with copper and element 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. The technique of doping LLZO with copper is very difficult, but it further stabilizes the overall structure, makes the lithium ion channels smoother, improves the sintering rate, and results in very low manufacturing costs. In addition, when the LLZO material is exposed to air, it reduces the formation of lithium carbonate (Li2CO3), i.e., it increases the overall surface stability of the material during sintering.

[0022] If the lithium ion conductor particles 10 are composed of LAGP or LATP, then the LAGP or LATP is 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 x is in the range of 0.1 to 0.8, y is in the range of 0 to 0.2, and z is in the range of 0 to 0.2. A is Ge (germanium) or Ti (titanium). M is Sc 3+ (Scandium), Y 3+ (Yttrium), Ga 3+ (Gallium), In 3+ (Indium), La 3+ (Lanthanum) is a trivalent element, and N is Zr 4+ (Zirconium), Si 4+ (Silicon), Sn 4+ It is a tetravalent element such as tin.

[0023] The ball mill 300 is a wet ball mill, and the wet ball mill is a blade ball mill or a ball mill containing zirconium beads. In step A, the rotational speed of the ball mill 300 is in the range of 200 rpm to 1000 rpm, the grinding time is in the range of 2 hours to 10 hours, and grinding and stirring are performed at room temperature.

[0024] Step B: The mixed slurry 20 is air-dried or vacuum-dried to obtain the mixed powder 30.

[0025] <Step C>: The mixed powder 30 is placed in a sintering furnace 400 and subjected to oxygen-free sintering to obtain a plurality of composite cathode particles 200. In an oxygen-free environment, the carbon source 14 of the mixed powder 30 is dehydrated, leaving behind carbon and other sintering residues, which then coat the outer surface of each LMFP particle 12 (see Figure 5).

[0026] If the carbon source 14 is a carbohydrate, dehydrating the carbohydrate leaves only carbon. If the carbon source 14 is a water-soluble fiber, dehydrating the water-soluble fiber leaves only the carbon skeleton and residues of partial functional groups (e.g., sulfur, nitrogen, halogen, etc.), and the form of the carbon skeleton is determined by the structure of the original water-soluble fiber. If the carbon source 14 is an amino acid polymer, dehydrating the amino acid polymer forms a carbon skeleton having element-doped linear or branched chains. If the carbon source 14 contains conductive carbon 141 (including graphite, graphene, amorphous carbon, or carbon nanotubes), the structure of the conductive carbon 141 is not altered by the sintering heat treatment described above.

[0027] In step C, during sintering, the outer surface of each LMFP particle 12 is covered with a conductive layer 221 formed from the lithium ion conductor particles 10 and the carbon source 14, thereby forming the composite positive electrode particle 200 according to the present invention. The thickness of the conductive layer 221 is 200 nm or less. The distribution morphology of the lithium ion conductor particles 10 in each LMFP particle 12 may be a continuous distribution morphology, a discontinuous distribution morphology, or an island particle morphology.

[0028] In step C, the sintering temperature is in the range of 400°C to 700°C, and the sintering time is in the range of 1 hour to 10 hours. The oxygen-free sintering may be vacuum sintering or atmospheric sintering such as nitrogen-argon atmosphere sintering.

[0029] Step D: The multiple composite cathode particles 200 are sieved to remove impurities and a pure composite cathode particle powder 250 is obtained.

[0030] The present invention further includes the following steps. <Step E>: The composite cathode particle powder 250 and the first slurry 255 containing the carbon material are placed in a mixer 350 and mixed to form composite cathode particles 280 that coat multiple carbon materials. The solvent in the slurry 255 may be water, ethanol, isopropanol, or NMP (N-Methyl-2-pyrrolidone), and the weight percentage of the carbon material in the first slurry 255 is 5 wt% or less. The first slurry 255 may also contain a dispersant (SCS (sodium o-cumenesulfonate), sinapinic acid), and the weight percentage of the dispersant in the first slurry 255 is 1 wt% or less. The carbon material consists of multiple carbon nanotubes 40 (CNT) and multiple nanoscale amorphous carbon 45. The stirring rotation speed of the mixer 350 is in the range of 50 rpm to 1000 rpm, and the stirring time is in the range of 1 hour to 3 hours. The mixer 350 is a DC type agitator or a vacuum emulsifying agitator.

[0031] The plurality of carbon nanotubes 40 according to the present invention comprises a plurality of short-chain carbon nanotubes 42 and a plurality of long-chain carbon nanotubes 44, wherein the length of each short-chain carbon nanotube 42 is in the range of 0.2 μm to 1 μm, and the length of each long-chain carbon nanotube 44 is in the range of 1 μm to 3 μm. The weight ratio of the plurality of short-chain carbon nanotubes 42 and the plurality of long-chain carbon nanotubes 44 is in the range of 10:1 to 2:1, and the weight ratio of the total weight of the carbon material in the slurry 255 to the total weight of the composite cathode particle powder is 1:100 or less. The weight ratio of the total weight of the plurality of carbon nanotubes 40 to the total weight of the plurality of nanoscale amorphous carbon 45 is in the range of 1:1 to 1:10. The size of the nanoscale amorphous carbon 45 is in the range of 10 nm to 40 nm.

[0032] The carbon nanotubes 40 of different lengths form crosslinks of different numbers on the composite cathode particles 200. The short-chain carbon nanotubes 42 crosslink each of the lithium-ion conductor particles 10 and their corresponding LMFP particles 12, while the long-chain carbon nanotubes 44 are used to coat the entire composite cathode particles 200 to increase the overall structural strength. When the carbon nanotubes 40 adhere to the composite cathode particles 200, a ball-like structure is formed (see Figure 7).

[0033] The carbon nanotubes 40 are used to form conductive crosslinks around each of the composite cathode particles 200, enabling electron conduction on each of the composite cathode particles 200. The carbon nanotubes have extremely high conductivity, and the carbon nanotubes 40 enable lithium ions to conduct between different composite cathode particles 200, thereby increasing the conductivity of the cathode 100.

[0034] The nanoscale amorphous carbon 45 is, for example, a super P conductive agent. Both the nanoscale amorphous carbon 45 and the carbon nanotubes 40 are conductive agents. The nanoscale amorphous carbon 45 is in particle form, and the carbon nanotubes 40 are in elongated form. The nanoscale amorphous carbon 45 fills the gaps between multiple carbon nanotubes 40 that intersect vertically and horizontally, and the nanoscale amorphous carbon 45 is crosslinked, allowing charge to be conducted to other carbon nanotubes 40, further increasing the efficiency of current transmission.

[0035] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention. [Explanation of symbols]

[0036] 5. Boric acid layer 10 Lithium-ion conductor particles 12 LMFP particles 14 Carbon sources 16 Dispersant 20 Mixed Slurry 30 Mixed powder 40 Carbon nanotubes 42 Short-chain carbon nanotubes 44 Long-chain carbon nanotubes 45 nanoscale amorphous carbon 100 positive electrode 102 Cathode slurry layer 103 Positive electrode slurry 105 Positive electrode substrate 106 Lithium-ion composite conductive particles 141 Conductive carbon 200 composite cathode particles 221 Conductive layer 250 Composite Cathode Particle Powder 255 Slurry No. 1 280 Composite cathode particles coated with carbon material 350 Mixer 300 Ball Mill 400 sintering furnaces

Claims

1. A method for producing lithium iron manganese phosphate composite cathode particles, in which the composite cathode particles are used as the cathode of a semi-solid or all-solid-state battery, Step A involves forming a mixed slurry by introducing multiple lithium-ion conductor particles, multiple LMFP particles, a carbon source, and a dispersant into a ball mill and mixing them, The lithium ion conductor particles have an ionic conductivity of 10 －５ cm ２ Step A refers to an oxide or phosphate having a lithium ion conductivity of more than 1 / s, or an oxide having a garnet or perovskite structure, wherein the carbon source is an organic compound that forms conductive carbon in a reducing atmosphere. Step B involves air-drying or vacuum-drying the mixed slurry to obtain a mixed powder. A method for producing lithium iron manganese phosphate composite cathode particles, comprising step C, which involves: introducing the mixed powder into a sintering furnace and performing oxygen-free sintering to obtain a plurality of the composite cathode particles; dehydrating the carbon source of the mixed powder in an oxygen-free environment; forming a conductive layer covering the outer surface of each LMFP particle with the carbon remaining after dehydration, other sintering residues, and the plurality of lithium ion conductor particles to form the composite cathode particles, wherein the distribution morphology of the lithium ion conductor particles in each LMFP particle exhibits a continuous distribution morphology, a discontinuous distribution morphology, or an island particle morphology.

2. The aforementioned ionic conductivity is 10 －５ cm ２ The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the oxide or phosphate having a ratio greater than / s is lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), or lithium phosphate, which have a NASICON (sodium (Na) super ionic conductor) structure.

3. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the oxide having a garnet or perovskite structure is lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO).

4. A method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the mass median particle diameter of the particle size distribution of the plurality of LMFP particles is less than 1 μm, the form is a single crystal material or a polymer of fine crystalline particles, and the thickness of the conductive layer is 200 nm or less.

5. The LMFP particles are lithium manganese iron phosphate (LiMn ｘ Fe １－ｘ PO ４ A method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that it is composed of lithium manganese iron phosphate doped with at least one metal element (where x is in the range of 0.1 to 0.8).

6. A method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that lithium ion composite conductive particles are formed by coating the outer surface of each lithium ion conductor particle with a boric acid layer.

7. A method for producing lithium iron manganese phosphate composite cathode particles according to claim 6, characterized in that, in step A, before introducing the plurality of lithium ion conductor particles into the ball mill, the plurality of lithium ion conductor particles are first ground until the mass median particle diameter of the particle size distribution is less than 200 nm, then introduced into a solution containing boric acid and thoroughly mixed, dried and ground, or dried, sintered and then ground, and the outer surface of each lithium ion conductor particle is coated with the boric acid layer.

8. The aforementioned organic compound is selected from carbohydrates, monosaccharides, disaccharides, oligosaccharides, polysaccharides, water-soluble fibers, or amino acid polymers. A method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that when the carbon source is a carbohydrate, dehydrating the carbohydrate leaves only carbon; when the carbon source is a water-soluble fiber, dehydrating the water-soluble fiber leaves a carbon skeleton and residues of partial functional groups, the morphology of the carbon skeleton is determined by the structure of the original water-soluble fiber; and when the carbon source is an amino acid polymer, dehydrating the amino acid polymer forms a carbon skeleton having element-doped linear or branched chains.

9. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the organic compound is a compound containing carbon, nitrogen, fluorine, phosphorus, and sulfur, and after reduction, these elements are doped into the carbon to increase the overall electronic conductivity of the composite cathode particles.

10. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the carbon source further comprises at least one of graphite, graphene, nano-sized amorphous carbon, or carbon nanotubes having a length of 1 μm or less.

11. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the ratio of the total weight of the carbon source to the total weight of the lithium ion conductor particles is in the range of 10:1 to 1:10, the weight ratio of the total weight of the lithium ion conductor particles to the total weight of the plurality of LMFP particles is 2:100 or less, the weight ratio of the total weight of the carbon source to the total weight of the plurality of LMFP particles is 1:100 or less, and the weight percentage of the mixed slurry in which "the total weight of the plurality of lithium ion conductor particles, the plurality of LMFP particles, and the carbon source" is 35% wt or less.

12. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that each of the lithium ion conductor particles is formed of at least one of LLZO, Ga-LLZO (Ga-dope LLZO, gallium-doped lithium lanthanum zirconium oxide), Cu-LLZO (Cu-dope LLZO, copper-doped lithium lanthanum zirconium oxide), Ta-LLZO (Ta-dope LLZO, tantalum-doped lithium lanthanum zirconium oxide), Sr-LLZO (Sr-dope LLZO, strontium-doped lithium lanthanum zirconium oxide), and Al-LLZO (Al-dope LLZO, aluminum-doped lithium lanthanum zirconium oxide).

13. Each of the lithium ion conductor particles is Cu ａ , X ｂ -LLZO, and the Cu ａ , X ｂ -LLZO is a lithium lanthanum zirconium oxide doped with copper and element X, X is selected from gallium (Ga), tantalum (Ta), strontium (Sr), barium (Ba), aluminum (Al), and is in the range of 0.25 to 0.8 where a + b = 0.25 to 0.8, and a > 0.1, the method for producing lithium iron manganese phosphate composite cathode particles according to claim 1.

14. If the lithium ion conductor particles are composed of LAGP or LATP, then the LAGP or LATP is Li １＋ｘ Al ｘ A ２－ｘ (PO ４ ) ３ or Li １＋ｘ＋ｙ Al ｘ A ２－ｘ－ｙ－ｚ M ｙ N ｚ (PO ４ ) ３ A method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that x is selected from the above, x is in the range of 0.1 to 0.8, y is in the range of 0 to 0.2, z is in the range of 0 to 0.2, A is Ge (germanium) or Ti (titanium), M is a trivalent element, and N is a tetravalent element.

15. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that the ball mill is a wet ball mill, which is selected from a blade wet ball mill or a wet ball mill containing zirconium beads, and in step A, the rotational speed of the wet ball mill is in the range of 200 rpm to 1000 rpm, the grinding time is in the range of 2 hours to 10 hours, and grinding and stirring are performed at room temperature.

16. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that in step C, the sintering temperature is in the range of 400°C to 700°C, the sintering time is in the range of 1 hour to 10 hours, and the oxygen-free sintering is vacuum sintering or atmosphere-protected sintering.

17. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 1, further comprising step D of performing a process to remove impurities by sieving a plurality of the composite cathode particles to obtain a pure composite cathode particle powder.

18. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 17, further comprising step E, in which a first slurry containing the composite cathode particle powder and carbon material is put into a mixer and mixed to form composite cathode particles coated with a plurality of carbon materials, wherein the carbon material comprises a plurality of carbon nanotubes and a plurality of nanoscale amorphous carbon.

19. The method for producing lithium iron manganese phosphate composite cathode particles according to claim 18, characterized in that, in step E, the stirring rotation speed of the mixer is in the range of 50 rpm to 1000 rpm, the stirring time is in the range of 1 hour to 3 hours, and the mixer is a DC type stirrer or a vacuum emulsifying stirrer.

20. The weight percentage of the carbon material in the first slurry is 5 wt% or less, the solvent of the first slurry is selected from water, ethanol, isopropanol, and NMP (N-methyl-2-pyrrolidone), and the first slurry further contains a dispersant, the dispersant being SCS (sodium o-cumenesulfonate) or sinapic acid. A method for producing lithium iron manganese phosphate composite cathode particles according to claim 18, characterized in that the dispersant is selected from (acid), the weight percentage of the dispersant in the slurry is 1 wt% or less, the plurality of carbon nanotubes include a plurality of short-chain carbon nanotubes and a plurality of long-chain carbon nanotubes, the length of each short-chain carbon nanotube is in the range of 0.2 μm to 1 μm, the length of each long-chain carbon nanotube is in the range of 1 μm to 3 μm, and the size of the nanoscale amorphous carbon is in the range of 10 nm to 40 nm.

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