Process for manufacturing lithium iron manganese phosphate composite positive electrode particles

Abstract

The invention discloses a manufacturing process for manufacturing a lithium manganese iron phosphate composite positive electrode particle, which is applied to a positive electrode of a solid-state or solid-state-like battery. The preparation process comprises the following steps: taking a plurality of lithium ion conductor particles, a plurality of LMFP particles, a carbon source and a dispersing agent, and simultaneously putting the materials into a ball mill for mixing to form mixture slurry; the carbon source is an organic compound capable of forming conductive carbon in a reducing atmosphere; then carrying out natural or vacuum drying on the mixture slurry to obtain mixture powder; and then putting the mixture powder into a sintering furnace for anaerobic sintering to obtain the composite positive electrode particles, in an oxygen-free environment, the carbon source in the mixture powder is dehydrated, and the residual carbon element, the residue after sintering and the plurality of lithium ion conductor particles jointly form a conductive layer which coats the outer surfaces of the LMFP particles, so that the composite positive electrode particles are formed; the distribution of the lithium ion conductor particles on the LMFP particles may be a continuous distribution or an island-like particle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery cathode material, and particularly relates to a process for manufacturing lithium manganese iron phosphate composite cathode particles. BACKGROUND

[0002] A battery is composed of a positive electrode and a negative electrode, and the cathode of the battery is the positive electrode inside the battery, which mainly includes a positive electrode substrate and a positive electrode slurry layer coated on the positive electrode substrate. The positive electrode slurry layer contains positive electrode slurry containing a binder and a plurality of positive electrode particles. The positive electrode particles are mainly used for the positive electrode of ordinary solid-state or quasi-solid-state batteries and must have conductive or conductive properties to enable free electrons to migrate in the positive electrode slurry without consuming too much energy due to internal resistance, thereby achieving effective conduction. Therefore, when manufacturing positive electrode particles, a specific conductive material must be used to adjust the conductivity of the positive electrode particles.

[0003] Traditionally, the material of the positive electrode particles can be LMFP (lithium manganese iron phosphate), which is an improvement on the traditional lithium iron phosphate (LFP). By adding manganese elements, LMFP outperforms traditional lithium iron phosphate in terms of working voltage and can release higher energy density. LMFP has the advantages of low price and hydrophobicity, and is therefore a quite common positive electrode material.

[0004] However, LMFP has poor rate charge and discharge performance, poor lithium and electric conduction capacity, and its structure is prone to aging during long-term use of the battery, resulting in a short battery life. In the prior art, although there are many technologies for improving the lithium ion guiding capacity of the positive electrode particles, the electric conduction capacity of lithium batteries in actual use is still insufficient. Therefore, the inventors hope to propose a completely new design to make the positive electrode of today's solid-state battery have higher electric capacity and conductivity to further improve the performance of the battery. SUMMARY

[0005] Therefore, the purpose of the present application is to solve the problems in the prior art. The present application proposes a process for manufacturing lithium manganese iron phosphate (LMFP) composite cathode particles, which comprehensively improves the performance by coating a carbon layer and a plurality of lithium ion conductor particles on the surface of LMFP. LMFP is cheaper than ternary oxides, although its charge and discharge performance is not as good as that of ternary oxides, but its performance can meet the needs of specific application scenarios, so using LMFP as a positive electrode material can effectively reduce the production cost of the battery.

[0006] Among them, coating a carbon layer on the outer surface of the LMFP particles can compensate for the poor conductivity of LMFP; in addition, the present application further coats a plurality of lithium ion conductor particles on the outer surface of LMFP to improve the overall lithium ion guiding capacity, thereby simultaneously improving the conductivity and lithium ion guiding capacity, and ultimately achieving more excellent battery performance.

[0007] To achieve the above object, the present application provides a process for manufacturing lithium manganese iron phosphate composite cathode particles, which is applied to the cathode of a solid-state or quasi-solid-state battery, and specifically comprises the following steps: Step A: Take a plurality of lithium ion conductor particles, a plurality of LMFP particles, a carbon source, and a dispersing agent, and simultaneously place the above materials into a ball mill for mixing to form a mixture slurry. The lithium ion conductor particles refer to oxides or phosphates with lithium ion conduction capability (i.e., ion conductivity greater than 10 -5 cm 2 / s), and oxides with garnet or perovskite structure; the carbon source is an organic compound that can form conductive carbon under a reducing atmosphere.

[0008] Step B: The mixture slurry is naturally or vacuum dried to obtain a mixture powder.

[0009] Step C: The mixture powder is placed into a sintering furnace for oxygen-free sintering to obtain a plurality of composite cathode particles. In an oxygen-free environment, the carbon source in the mixture powder is dehydrated, and the remaining carbon elements and the residue after sintering form a conductive layer together with the plurality of lithium ion conductor particles to coat the outer surface of the LMFP particles, thereby forming the composite cathode particles. The distribution of the lithium ion conductor particles on the surface of the LMFP particles can be continuous or form island-shaped particles.

[0010] The outer surface of the lithium ion conductor particles can be further coated with a borate layer to form lithium ion composite conductor particles. The manufacturing method is as follows: a plurality of lithium ion conductor particles with a median particle size distribution of less than 200 nm are placed into a solution containing boric acid, mixed thoroughly, dried, and ground, or dried, sintered, and then ground, so that the surface of the lithium ion conductor particles is coated with a layer of borate.

[0011] In addition, the carbon source can also include at least one of graphite, graphene, nanoscale amorphous carbon, or nanocarbon tubes with a length of not more than 1 micrometer.

[0012] The present application also includes: Step D: The plurality of composite cathode particles are sieved to remove impurities to obtain a pure composite cathode particle powder.

[0013] Step E: The composite cathode particle powder and a slurry containing carbon material are mixed in a mixer to form a plurality of composite cathode particles coated with carbon material; wherein the carbon material is a plurality of nanocarbon tubes for improving electronic conductivity.

[0014] The ion conductivity is greater than 10 -5 cm 2Oxides or phosphates of Li, Na, K, Ag, Cu, Fe, Mn, Co, Ni, Cr, V, Ti, Zr, Hf, Mo, W, Re, Pd, Pt, Ru, Os, Ir, Rh, and / or Sn include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP) having a NASICON structure, or a phosphate having lithium ion conductivity such as lithium phosphate. The oxides having a garnet or perovskite structure include lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO). The LMFP particles have a median particle size of less than 1 micron and are in the form of single crystal material or aggregates of crystalline grains. The LMFP particles are selected from lithium manganese iron phosphate (LiMnxFe 1-x PO4, x is between 0.1 and 0.8), or lithium manganese iron phosphate doped with at least one metal element.

[0015] The organic compound is selected from a carbohydrate, a monosaccharide, a disaccharide, an oligosaccharide, a polysaccharide, a water-soluble fiber, or an amino acid polymer. When the carbon source is a carbohydrate, the carbohydrate leaves only carbon elements after dehydration; when the carbon source is a water-soluble fiber, the water-soluble fiber leaves a carbon skeleton and part of the functional group residues after dehydration, and the morphology of the carbon skeleton is affected by the structure of the original water-soluble fiber; when the carbon source is an amino acid polymer, the amino acid polymer forms a linear or branched carbon skeleton containing a doping element after dehydration.

[0016] The features and advantages of the present application will be further understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A flowchart showing the present application.

[0018] Figure 2 A flowchart showing Step A of the present application.

[0019] Figure 3 A flowchart showing Steps B to E of the present application.

[0020] Figure 4 A use example of the present application.

[0021] Figure 5 A structure diagram and an enlarged schematic diagram of the composite positive electrode particle of the present application.

[0022] Figure 6 A cross-sectional schematic diagram of the composite positive electrode particle of the present application.

[0023] Figure 7 A structure diagram of the composite positive electrode particle coated with carbon material of the present application.

[0024] Figure 8 A structure diagram of the lithium ion composite conductor particle of the present application.

[0025] Figure 9A cross-sectional view of a composite cathode particle of the present application is shown, wherein the conductive layer contains conductive carbon.

[0026] wherein, borate layer 5; lithium ion conductor particle 10; LMFP particle 12; carbon source 14; dispersant 16; mixture slurry 20; mixture powder 30; nanotube 40; short chain nanotube 42; long chain nanotube 44; nanoscale amorphous carbon 45; cathode 100; cathode substrate 101; cathode slurry layer 102; cathode slurry 103; cathode substrate 105; LMFP particle 121; conductive carbon 141; composite cathode particle 200; conductive layer 221; composite cathode particle powder 250; carbon-containing material slurry 255; carbon-coated composite cathode particle 280; wet ball mill 300; mixer 350; sintering furnace 400. DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings and specific examples.

[0028] Referring to Figures 1 to 9 , a process for manufacturing lithium manganese iron phosphate (LMFP) composite cathode particles of the present application is shown, which is applied to a cathode 100 of a solid-state or quasi-solid-state battery. The cathode 100 mainly includes: a cathode substrate 105 (such as Figure 4 ); a cathode slurry layer 102 coated on the cathode substrate 101, wherein the cathode slurry layer 102 contains a cathode slurry 103 containing a binder and a plurality of composite cathode particles 200. The total weight of the plurality of composite cathode particles 200 accounts for 88 wt% to 98 wt% of the weight percentage of the cathode slurry layer 102.

[0029] As shown in Figures 1 to 3 , the method of the present application is used to manufacture a plurality of composite cathode particles 200, which specifically includes the following steps: Step A: Take a plurality of lithium ion conductor particles 10, a plurality of LMFP particles 12, a carbon source 14, and a dispersant 16, and simultaneously place the above-mentioned materials into a wet ball mill 300 for mixing to form a mixture slurry 20.

[0030] The lithium ion conductor particle 10 refers to: (i) an oxide or a phosphate having lithium ion conduction capability (ionic conductivity greater than 10 -5 cm 2 / s), including but not limited to lithium titanium aluminum phosphate (LATP) and lithium germanium aluminum phosphate (LAGP) having a NASICON structure, or a phosphate having lithium ion conduction capability, such as lithium phosphate; (ii) Oxides having a garnet or perovskite structure, including but not limited to lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO).

[0031] The lithium-ion conductor particles 10 can be any combination of the above components in any proportion.

[0032] The LMFP particles 12 have a size D50 (median particle size distribution) of less than 1 micrometer and are in the form of single crystal material or microcrystalline aggregates. LMFP particles 12 can be lithium manganese iron phosphate (LiMn) x Fe 1-x Lithium iron manganese phosphate (PO4, x between 0.1 and 0.8) or doped with at least one metal element.

[0033] The outer surface of the lithium-ion conductor particles 10 can be further coated with a borate layer 5 to form lithium-ion composite conductor particles 106. The manufacturing method is as follows: multiple lithium-ion conductor particles 10 with a median particle size distribution of less than 200 nm are placed in a boric acid solution, thoroughly mixed, dried, and ground, or dried, sintered, and then ground, so that the surface of the lithium-ion conductor particles 10 is coated with a borate layer 5. The purpose of coating with the borate layer 5 is that during oxygen-free sintering in the manufacturing process of the composite cathode particles 200, the lithium-ion conductor particles 10 may experience lithium deficiency due to oxygen deficiency, leading to a decrease in conductivity. Therefore, a protective layer is needed to prevent the lithium-ion conductor particles 10 from being damaged. The size of the lithium-ion composite conductor particles 106 is no greater than 200 nm.

[0034] The carbon source 14 is an organic compound that can form conductive carbon under a reducing atmosphere. This organic compound is selected from carbohydrates (such as monosaccharides, disaccharides, oligosaccharides, and 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, because these elements can be incorporated into the carbon after reduction, thereby improving the overall electronic conductivity of the composite cathode particles 200.

[0035] like Figure 9 As shown, carbon source 14 may further include conductive carbon 141 that can be sufficiently dispersed in dispersant 16. Conductive carbon 141 is selected from at least one of graphite, graphene, nanoscale amorphous carbon, or carbon nanotubes with a length not exceeding 1 micrometer. If carbon nanotubes are used as part of carbon source 14, their proportion shall not exceed 10% of the total weight of carbon source 14.

[0036] The ratio of the total weight of carbon source 14 to the total weight of lithium-ion conductor particles 10 is between 10:1 and 1:10.

[0037] Dispersant 16 is selected from at least one of water, alcohol or isopropanol.

[0038] The weight ratio of the total weight of lithium-ion conductor particles 10 to the total weight of LMFP particles 12 is no greater than 2:100. The weight ratio of the total weight of carbon source 14 to the total weight of LMFP particles 12 is no greater than 1:100.

[0039] In the mixture slurry 20, the total weight of lithium-ion conductor particles 10, LMFP particles 12 and carbon source 14 accounts for no more than 35 wt% of the total mixture slurry 20.

[0040] When the lithium-ion conductor particle 10 is selected from LLZO, the LLZO is selected from LLZO (Li7La3Zr2O). 12 The LLZO is selected from at least one of the following: lithium lanthanum zirconium oxide (LLZO), Ga-LLZO (gallium-doped lithium lanthanum zirconium oxide), Cu-LLZO (copper-doped lithium lanthanum zirconium oxide), Ta-LLZO (tantalum-doped lithium lanthanum zirconium oxide), Sr-LLZO (strontium-doped lithium lanthanum zirconium oxide), and Al-LLZO (aluminum-doped lithium lanthanum zirconium oxide). Preferably, the LLZO is Cu,Xb-LLZO, i.e., lithium lanthanum zirconium oxide doped with copper and element X, wherein X is selected from Ga (gallium), Ta (tantalum), Sr (strontium), Ba (barium), and Al (aluminum), and a>0 and b>0. Preferably, a+b=0.25~0.8, and a>0.1. Although the technology of doping copper into LLZO is difficult, it can make the overall particle structure more stable, the lithium ion channel smoother, and improve the oxygen sintering speed, thereby reducing manufacturing costs; at the same time, it can reduce the formation of lithium carbonate (Li2CO3) when LLZO is exposed to air, and improve the surface stability of the overall structure during sintering.

[0041] When the lithium-ion conductor particle 10 is selected from LAGP or LATP, LAGP or LATP is selected 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, where x = 0.1–0.8, y = 0–0.2, z = 0–0.2. A represents Ge (germanium) or Ti (titanium); M represents a trivalent element such as Sc. 3+ (Scandium), Y 3+ (Yttrium), Ga 3+ (GaN), In 3+ (Indium), La 3+ (Lanium), etc., where N is a tetravalent element such as Zr. 4+ (Zirconium), Si 4+ (Silicon), Sn 4+ (Tin), etc.

[0042] The wet ball mill 300 is selected from a blade wet ball mill or a wet ball mill with zirconium beads. During the ball milling, the rotation speed of the wet ball mill 300 is 200 rpm to 1000 rpm, the ball milling time is 2 hours to 10 hours, and the grinding and stirring are performed at room temperature.

[0043] Step B: The mixture slurry 20 is naturally or vacuum dried to obtain a mixture powder 30.

[0044] Step C: The mixture powder 30 is placed in a sintering furnace 400 for oxygen-free sintering to obtain the composite positive electrode particles 200 of the present application. In an oxygen-free environment, the carbon source 14 in the mixture powder 30 is dehydrated, and the remaining carbon elements and the residues after sintering are coated on the outer surface of the LMFP particles 12 (such as Figure 5 ).

[0045] When the carbon source 14 is a carbohydrate, only carbon elements remain after the carbohydrate is dehydrated; When the carbon source 14 is a water-soluble fiber, carbon skeletons and part of the functional groups (such as sulfur, nitrogen, halogen, etc.) residues remain after the water-soluble fiber is dehydrated, and the morphology of the carbon skeleton is affected by the structure of the original water-soluble fiber; When the carbon source 14 is an amino acid polymer, a straight-chain or branched-chain carbon skeleton containing a doping element is formed after the amino acid polymer is dehydrated; When the carbon source 14 contains conductive carbon 141 (graphite, graphene, amorphous carbon, or nanometer carbon tube), the structure of the conductive carbon 141 will not change due to heat treatment.

[0046] The plurality of lithium ion conductor particles 10 and the carbon source 14 form a conductive layer 221 as a whole, which is coated on the outer surface of the LMFP particles 12, thereby forming the composite positive electrode particles 200 of the present application. The thickness of the conductive layer 221 is not greater than 200 nm. The distribution of the lithium ion conductor particles 10 on the LMFP particles 12 can be continuous distribution or form island-like particles.

[0047] In step C, the sintering temperature is 400°C to 700°C, and the sintering time is 1 hour to 10 hours. The oxygen-free sintering can be vacuum sintering, atmosphere protection sintering (such as nitrogen and argon atmosphere protection sintering), etc.

[0048] Step D: The plurality of composite positive electrode particles 200 are screened to remove impurities to obtain a pure composite positive electrode particle powder 250.

[0049] Optionally, step E: the composite cathode particle powder 250 is mixed with the carbon-containing slurry 255 in a mixer 350 to form a plurality of carbon-coated composite cathode particles 280. The solvent in the carbon-containing slurry 255 can be water, ethanol, isopropanol, NMP (N-methyl pyrrolidone), and the carbon material accounts for no more than 5% of the total weight of the carbon-containing slurry 255. The carbon-containing slurry 255 can contain a dispersant (including SCS (sodium cumene sulfonate), mustard acid), which accounts for no more than 1% of the total weight of the carbon-containing slurry 255. The carbon material is a plurality of carbon nanotubes 40 (CNT) and a plurality of nanoscale amorphous carbon 45. The stirring speed of the mixer 350 is 50 rpm to 1000 rpm, and the stirring time is 1 hour to 3 hours. The mixer 350 is a direct current stirrer or a vacuum emulsifying mixer.

[0050] The plurality of carbon nanotubes 40 includes a plurality of short-chain carbon nanotubes 42 and a plurality of long-chain carbon nanotubes 44. The length of the short-chain carbon nanotubes 42 is between 0.2 microns and 1 micron; the length of the long-chain carbon nanotubes 44 is between 1 micron and 3 microns. The weight ratio of the short-chain carbon nanotubes 42 to the long-chain carbon nanotubes 44 is between 10:1 and 2:1. The weight ratio of the total weight of the carbon material in the slurry to the total weight of the composite cathode particle powder is no more than 1:100. 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 between 1:1 and 1:10. The size of the nanoscale amorphous carbon 45 is between 10 nm and 40 nm.

[0051] Carbon nanotubes 40 of different lengths can form different levels of bridging on the composite cathode particles 200: short-chain carbon nanotubes 42 bridge the lithium ion conductor particles 10 and their corresponding LMFP particles 12; long-chain carbon nanotubes 44 coat the entire composite cathode particles 200 to enhance the overall structural strength. When the carbon nanotubes 40 are attached to the composite cathode particles 200, a form similar to woolen thread is formed (as shown in Figure 7 ).

[0052] The carbon nanotubes are used to increase the electrical conductance, i.e. to form a conductive bridge around the composite cathode particles 200, so that the electrons can be conducted on the composite cathode particles 200. Since the carbon nanotubes have very high electrical conductivity, lithium ions can be conducted between different composite cathode particles 200 through the carbon nanotubes, thereby improving the electrical conductivity of the entire cathode 100. The nanoscale amorphous carbon, such as Super P, is also a conductive agent, and is the same as the carbon nanotubes. Since the nanoscale amorphous carbon is in the form of particles, while the carbon nanotubes are in the form of strips, the carbon nanotubes are longitudinally and transversely arranged, and gaps are formed between the carbon nanotubes. These gaps cannot conduct current, so adding nanoscale amorphous carbon in the gaps can make the charge cross-connect and conduct to the next carbon nanotube through the nanoscale amorphous carbon, thereby further improving the current transmission efficiency.

[0053] The present application has the following technical effects: The present application improves the overall performance by coating a carbon layer and a plurality of lithium ion conductor particles on the surface of the LMFP. The LMFP is less expensive than the ternary oxide, and although its charge and discharge performance is not as good as that of the ternary oxide, its performance can meet the requirements of specific application scenarios. Therefore, using LMFP as the cathode material can reduce the production cost of the battery. Coating a carbon layer on the outer surface of the LMFP particles can compensate for the poor electrical conductivity of the LMFP, and coating a plurality of lithium ion conductor particles on the outer surface of the LMFP can improve the overall lithium ion conductivity, thereby improving the electrical conductivity and the lithium ion conductivity at the same time, and achieving better battery performance.

[0054] The above detailed description is for a specific embodiment of the present application, but this embodiment is not intended to limit the patent scope of the present application. Any equivalent implementation or modification made without departing from the spirit of the present application should be included in the patent scope of the present application.

Claims

1. A process for manufacturing lithium iron manganese phosphate composite cathode particles, characterized by, The application is applied to a positive electrode of a solid-state or quasi-solid-state battery; the preparation process comprises the following steps: Step A: take a plurality of lithium ion conductor particles, a plurality of LMFP particles, a carbon source and a dispersant, and simultaneously place the above materials into a ball mill for mixing to form a mixture slurry; the LMFP is lithium iron manganese phosphate; The lithium ion conductor particles refer to oxides or phosphates having lithium ion conductivity, wherein the lithium ion conductivity refers to an ion conductivity of more than 10 -5 cm 2 / s, or oxides having a garnet or perovskite structure; The carbon source is an organic compound that can form conductive carbon in a reducing atmosphere; Step B: naturally or vacuum dry the mixture slurry to obtain a mixture powder; Step C: place the mixture powder into a sintering furnace for oxygen-free sintering to obtain the composite positive electrode particles; in an oxygen-free environment, the carbon source in the mixture powder is dehydrated, and the remaining carbon elements and the residue after sintering form a conductive layer together with the plurality of lithium ion conductor particles to coat the outer surface of the LMFP particles, thereby forming the composite positive electrode particles; the distribution of the lithium ion conductor particles on the LMFP particles is continuous distribution or island-shaped particles.

2. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that, Wherein, Ion conductivity greater than 10 -5 cm 2 oxides or phosphates having an ion conductivity greater than 10 cm / s, including phosphotitanate-aluminate-lithium having a NASICON structure, phosphogermanate-aluminate-lithium, or phosphates having lithium ion conductivity; where phosphotitanate-aluminate-lithium is LATP and phosphogermanate-aluminate-lithium is LAGP.

3. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, characterized in that, Wherein, The oxide with a garnet or perovskite structure includes lithium lanthanum zirconium oxide, i.e. LLZO, or lithium lanthanum titanium oxide, i.e. LLTO.

4. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, wherein, Wherein, The plurality of LMFP particles have a median particle size distribution of less than 1 micron, and the morphology is single crystal material or an aggregate of microcrystalline grains.

5. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, wherein, Wherein, The LMFP particles are selected from lithium manganese iron phosphate, i.e. LiMn x Fe 1-x PO4, x is between 0.1 and 0.8, or lithium manganese iron phosphate doped with at least one metallic element.

6. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, wherein, Wherein, A layer of borate is coated on the outer surface of the lithium ion conductor particles to form lithium ion composite conductor particles.

7. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, wherein, Wherein, The manufacturing method of the lithium ion composite conductor particles is: first, grind the plurality of lithium ion conductor particles to a median particle size distribution of less than 200 nm, and then put them into a solution containing boric acid; after sufficient mixing, dry and grind, or dry and then sinter and grind again, so that a layer of borate is coated on the surface of the lithium ion conductor particles.

8. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 1, wherein, Wherein, The organic compound is selected from at least one of a carbohydrate, a monosaccharide, a disaccharide, an oligosaccharide, a polysaccharide, a water-soluble fiber, and an amino acid polymer; When the carbon source is a carbohydrate, only carbon elements are left after dehydration of the carbohydrate; when the carbon source is a water-soluble fiber, a carbon skeleton and a residue containing part of the functional groups are left after dehydration of the water-soluble fiber, and the morphology of the carbon skeleton is affected by the structure of the original water-soluble fiber; when the carbon source is an amino acid polymer, a straight-chain or branched carbon skeleton containing a doping element is formed after dehydration of the amino acid polymer.

9. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Wherein, The organic compound is a compound containing carbon and nitrogen, fluorine, phosphorus, and sulfur elements; after reduction, these elements can be doped into carbon, thereby improving the overall electronic conductivity of the composite positive electrode particles.

10. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Wherein, The carbon source further comprises at least one of graphite, graphene, nanoscale amorphous carbon, or a nanocarbon tube with a length of not more than 1 micron.

11. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Wherein, The ratio of the total weight of the carbon source to the total weight of the lithium ion conductor particles is between 10:1 and 1:

10.

12. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Wherein, The ratio of the total weight of the lithium ion conductor particles to the total weight of all LMFP particles is not more than 2:100; the ratio of the total weight of the carbon source to the total weight of all LMFP particles is not more than 1:100; in the mixture slurry, the total weight of the "lithium ion conductor particles, all LMFP particles and carbon source" accounts for not more than 35 wt% of the overall mixture slurry.

13. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Wherein, The lithium ion conductor particles are made of at least one of lithium lanthanum zirconium oxide, Ga-doped lithium lanthanum zirconium oxide, Cu-doped lithium lanthanum zirconium oxide, Ta-doped lithium lanthanum zirconium oxide, Sr-doped lithium lanthanum zirconium oxide, and Al-doped lithium lanthanum zirconium oxide.

14. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, The lithium ion conductor particles consist of Cu a X b - LLZO, i.e. lithium lanthanum zirconium oxide doped with copper and the element X, X being selected from the group consisting of gallium, tantalum, strontium, barium, aluminum, and a > 0, b > 0.

15. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 14, characterized in that, In the formula, a+b = 0.25 ~ 0.8, and a > 0.1, so that the overall particle structure is more stable, the lithium ion channel is smoother, and the aerobic sintering speed is improved.

16. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, When the lithium ion conductor particles are composed of LAGP or LATP, the LAGP or LATP is selected from Li 1+x Al x A 2-x (PO4)3or Li 1+x+y Al x A 2-x-y-z M y N z (PO4)3, wherein x is between 0.1 and 0.8, y is between 0 and 0.2, and z is between 0 and 0.2; A is Ge or Ti; M is a trivalent element, and N is a tetravalent element.

17. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, The ball mill is a wet ball mill; The wet ball mill is selected from a blade type wet ball mill or a wet ball mill containing zirconium beads; during ball milling, the rotation speed of the wet ball mill is 200 rpm ~ 1000 rpm, the ball milling time is 2 hours ~ 10 hours, and the grinding and stirring are carried out at room temperature.

18. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, The thickness of the conductive layer is not more than 200 nanometers.

19. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, In step C, the sintering temperature is 400℃ ~ 700℃, and the sintering time is 1 hour ~ 10 hours; the oxygen-free sintering can be vacuum sintering or nitrogen argon atmosphere protection sintering.

20. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Further comprising step D: screening the plurality of composite positive electrode particles to remove impurities to obtain a pure composite positive electrode particle powder.

21. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, Further comprising step E: mixing the composite positive electrode particle powder and a slurry containing carbon material in a mixer to form a plurality of composite positive electrode particles coated with carbon material; wherein the carbon material is a plurality of nanometer carbon tubes; the nanometer carbon tubes are used to improve the electronic conductivity.

22. The process for manufacturing lithium iron manganese phosphate composite cathode particles according to claim 21, wherein, In the formula, The carbon material further comprises a plurality of nanometer-sized amorphous carbon with a particle size range of 10 nm to 40 nm.

23. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 21 wherein, In the formula, In step E, the stirring rotation speed of the mixer is 50 rpm to 1000 rpm, and the stirring time is 1 hour to 3 hours; the mixer uses a direct current stirrer or a vacuum emulsifying stirrer.

24. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, The carbon material accounts for not more than 5% of the total weight of the slurry; the solvent in the carbon-containing slurry is selected from water, ethanol, isopropyl alcohol, or N-methyl pyrrolidone; the slurry contains a dispersing agent selected from sodium isopropylbenzene sulfonate SCS or mustard acid, and the amount of the dispersing agent accounts for not more than 1% of the total weight of the slurry.

25. The process for manufacturing lithium iron manganese phosphate composite cathode particles as claimed in claim 1 wherein, In the formula, The plurality of nanometer carbon tubes include a plurality of short-chain nanometer carbon tubes and a plurality of long-chain nanometer carbon tubes; each short-chain nanometer carbon tube has a length of 0.2-1 microns, and each long-chain nanometer carbon tube has a length of 1-3 microns.

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