Coating method of electrode material

Abstract

The invention discloses a coating method of an electrode material, which comprises the following steps: (1) olefin-substituted imidazole and halogenated hydrocarbon are mixed for an addition reaction to form a quaternary ammonium salt type ionic liquid monomer, and the halogenated hydrocarbon is one or a mixture of several of 3-bis (bromomethyl) benzene, 1, 3-bis (bromoethyl) benzene, 1, 2-dichloroethane and benzyl bromide; (2) thermally initiating the quaternary ammonium salt type ionic liquid monomer, and carrying out polymerization reaction to form a diazolium type polymeric ionic liquid; and (3) mixing the diazolium type polymeric ionic liquid and the electrode material, and calcining to form a carbon coating layer outside the electrode material. The coating material is prepared firstly, and during coating, the electrode material is directly mixed with the coating material, so that element doping is reduced, the capacity and the cycling stability are improved, the types of the electrode materials are not limited, and the application range is wide.

Description

A method for coating electrode materials Technical Field

[0001] This invention relates to a method for preparing electrode materials, and more particularly to a method for coating electrode materials. Background Technology

[0002] Olivine-type lithium iron phosphate (LiFePO4, LFP) has become one of the core cathode materials for power batteries and energy storage systems due to its excellent thermal stability, long cycle life, and high safety. However, LFP has low intrinsic electronic conductivity and limited lithium-ion diffusion rate, resulting in a significantly lower energy density than ternary materials, which limits its application in high-end electric vehicles.

[0003] To overcome the conductivity bottleneck, carbon coating technology has been widely adopted. However, traditional carbon sources such as sucrose and glucose are prone to violent decomposition during high-temperature carbonization, producing a large number of gaseous byproducts that cause pores, fractures, or uneven coverage in the carbon layer, which in turn leads to problems such as discontinuous conductive network, increased iron dissolution, and poor process stability.

[0004] CN 105633369 A discloses a method for preparing carbon-coated lithium iron phosphate material. First, lithium iron phosphate is reacted with a coupling agent to obtain surface-modified lithium iron phosphate. Then, an ionic liquid monomer containing imidazole and boron or phosphorus is added, causing it to polymerize on the surface-modified lithium iron phosphate to form a polymer layer. Finally, high-temperature calcination is performed, and the polymer layer decomposes to form a carbon-coated layer. Silicon or titanium contained in the coupling agent enters the lithium iron phosphate lattice during the high-temperature decomposition process, becoming dopant ions to improve the cycle performance and rate performance of the prepared cathode material. This method requires prior modification of the cathode material with a coupling agent, has a long process route, and cannot be extended to other cathode materials. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a coating method for electrode materials to shorten the process route, improve the electronic conductivity of the electrode materials, and increase cycle life.

[0006] Technical solution: The present invention provides a method for coating an electrode material, comprising the following steps:

[0007] (1) Mixed olefin-substituted imidazoles and haloalkanes undergo an addition reaction to form a quaternary ammonium salt type ionic liquid monomer, wherein the haloalkanes are one or a mixture of several of 3-di(bromomethyl)benzene, 1,3-di(bromoethyl)benzene, 1,2-dichloroethane, benzyl bromide, and benzyl chloride;

[0008] (2) Thermally initiated quaternary ammonium salt ionic liquid monomers undergo polymerization to form diazonium-type polymeric ionic liquids;

[0009] (3) Mix diazonium-type polymeric ionic liquid and electrode material, calcine to form a carbon coating layer on the outside of the electrode material.

[0010] By employing symmetrically structured haloalkanes, quaternary ammonium salt-type ionic liquid monomers are formed, enabling the creation of nanopores during polymerization. During calcination, the diazonium-type polymeric ionic liquid undergoes pyrolysis to form a carbon layer. Simultaneously, its nanopores regulate the morphology of the electrode material, ensuring its electronic conductivity and improving cycle life. The diazonium-type polymeric ionic liquid is mixed with the electrode material in polymer form, preventing electrode material particles from acting as foreign matter and hindering uniform monomer diffusion in the early stages of polymerization, thus avoiding defects in the resulting polymer network structure.

[0011] Preferably, in step (1), the molar ratio of the olefin-substituted imidazole to the haloalkane is 1.8~2.4:1.

[0012] Preferably, in step (1), the olefin-substituted imidazole is one or a mixture of several of 1-vinylimidazolium, 1-allylimidazolium, and 1-butenylimidazolium.

[0013] Preferably, in step (1), the addition reaction is carried out at a temperature of 60-80°C for 12-24 hours. Extending the reaction time makes the generated quaternary ammonium salt ionic liquid monomer structure more uniform, reduces residual haloalkanes, and ensures the integrity of the diazonium-type polymeric ionic liquid structure formed subsequently.

[0014] Preferably, in step (1), the reaction medium is ethanol. After the addition reaction is completed, the reaction medium is removed, the residue is precipitated in ethyl acetate, the solid is separated, and a quaternary ammonium salt type ionic liquid monomer is obtained. The quaternary ammonium salt type ionic liquid monomer is dried for 12-24 hours.

[0015] Preferably, in order to reduce the resistivity of the formed electrode material and increase its capacity, in step (2), a crosslinking agent and a dispersant are added to carry out a polymerization reaction, wherein the mass ratio of the quaternary ammonium salt ionic liquid monomer, the crosslinking agent and the dispersant is 1:1.0~1.5:1.2~1.8.

[0016] Preferably, the crosslinking agent is one or a mixture of divinylbenzene, vinyltoluene, chlorostyrene, and dicyclopentadiene acrylate; and the dispersant is one or a mixture of polyvinylpyrrolidone, polyacrylic acid, and polyethylene glycol.

[0017] Preferably, in step (2), the polymerization reaction is carried out at a temperature of 60-80°C for 24-48 hours. Extending the reaction time reduces the amount of unreacted monomers and small oligomer molecules in the system, thus avoiding a decrease in the mechanical properties and thermal stability of the final polymer network. The polymerization product is a solid and can be obtained by centrifugation or filtration.

[0018] Preferably, in step (2), after the polymerization reaction is completed, the temperature is lowered to room temperature, the product is separated and washed with ethanol, and dried to obtain a diazonium-type polymeric ionic liquid; the drying time is 12~24.

[0019] Preferably, in step (3), the electrode material is lithium manganese iron phosphate and / or lithium iron phosphate, and the mass ratio of the diazonium-type polymeric ionic liquid to the iron element in the electrode material is (0.05~0.075):1.

[0020] Preferably, both the addition reaction and the polymerization reaction are carried out under nitrogen protection to protect the double bonds in the molecule.

[0021] Preferably, in step (3), the mixing step is as follows: mixing lithium source, phosphorus source, iron source and / or manganese source, water and diazonium-type polymeric ionic liquid to form a mixture, adjusting the pH of the mixture to generate lithium iron phosphate or lithium manganese iron phosphate, and obtaining a reaction mixture; heating the reaction mixture to 60~100 ℃, keeping it at that temperature for 2~6 h, aging it for 10~20 min, and then grinding and drying it.

[0022] Preferably, in step (3), the pH of the mixture is adjusted to pH = 5-8. This maintains a suitable PO4 level. 3- Concentration, making Fe 2+ Li + PO4 3- The reaction is complete, forming a uniform precipitate.

[0023] Preferably, the lithium source is one or a mixture of lithium carbonate, lithium phosphate, and lithium hydroxide; the phosphorus source is one or a mixture of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate; the iron source is one or a mixture of ferrous sulfate heptahydrate, ferric phosphate, ferrous oxalate, and iron oxide; and the molar ratio of the lithium source, phosphorus source, and iron source is 1.0~1.05:1.0~1.2:1.

[0024] Preferably, the manganese source is one or more of manganese carbonate, manganese oxalate, and manganese sulfate monohydrate, and the molar ratio of the lithium source, phosphorus source, iron source, and manganese source is Li:P:(Fe+Mn) = 1.0 ~ 1.05:1.0 ~ 1.2:1.

[0025] Preferably, the mixture is stirred at a speed of 60-150 rpm.

[0026] Preferably, the drying is a two-fluid spray drying, with a nozzle size of 0.5~5 mm; a spray gun pressure of 0.3~0.8 MPa; an inlet air temperature of 110~250 ℃; and an outlet air temperature of 70~150 ℃.

[0027] Preferably, the calcination is carried out in a nitrogen or argon atmosphere, with a heating rate of 2-5°C / min, a sintering temperature of 600-850°C, and a calcination time of 4-6 hours. More preferably, the calcination temperature is 700-850°C.

[0028] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: 1. Shortened process route: During coating, the electrode material is directly mixed with the coating material, eliminating the need to introduce coupling agents to modify the electrode material beforehand; 2. Reduced elemental doping, improved capacity and cycle stability: The quaternary ammonium salt ionic liquid monomer uses symmetrical structured haloalkanes and introduces dinitrogen atoms as raw materials to form a diazonium-type polymeric ionic liquid with strong σ-donors and relatively weak π-acceptors, forming a stable poly(N-heterocyclic carbene) structure. The poly(N-heterocyclic carbene) structure has stronger stability and activation effects on the metal center, providing uniformly dispersed anchoring points for the lithium iron phosphate precursor, avoiding particle agglomeration, and facilitating the adsorption of negatively charged phosphate ions. The nanopore confinement effect of the diazonium-type polymeric ionic liquid itself forces the generation of small-sized, monodisperse LFP crystals, which can shorten the lithium-ion cycle time. The diffusion path, with its flexible carbon layer formed by carbonization encapsulating LFP particles, can buffer the volumetric strain during cycling and significantly improve cycle life; 3. After the nitrogen-rich framework of the diazonium-type polymeric ionic liquid is pyrolyzed, a continuous nitrogen-doped carbon conductive layer is formed. The nitrogen atoms in its molecules are doped into the carbon-based network in the form of pyridine nitrogen (N-6) and graphitic nitrogen (NQ), forming a continuous nitrogen-doped carbon conductive layer. Nitrogen doping induces the delocalization of sp² hybrid orbitals of the carbon layer, improving the electronic conductivity of lithium iron phosphate materials; 4. The pyridine nitrogen in the diazonium-type polymeric ionic liquid forms a strong coordination bond with Fe atoms, anchoring iron ions in the crystal lattice, reducing the dissolution of iron ions, and effectively maintaining the integrity and stability of the crystal structure. The reduction stability of the diazonium cation can inhibit Fe²⁺ oxidation and reduce the generation of harmful byproducts; 5. No initiator is required, avoiding side reactions within the electrochemical window that could deteriorate the cycle life and coulombic efficiency of the battery. Attached Figure Description

[0029] Figure 1 is a SEM image of the lithium iron phosphate synthesized in Example 1;

[0030] Figure 2 is a SEM image of the lithium iron phosphate precursor synthesized in Example 1;

[0031] Figure 3 shows a SEM image of the lithium iron phosphate synthesized in Example 2;

[0032] Figure 4 shows the SEM image of the lithium iron phosphate synthesized in Comparative Example 1. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1: Preparation of Lithium Iron Phosphate Materials

[0035] (1) Synthesis of quaternary ammonium salt type ionic liquid monomer III: 1-vinylimidazolium I and 1,3-bis(bromomethyl)benzene II were dissolved in an appropriate amount of ethanol at a molar ratio of 2:1 to prepare an ionic mixture. The ionic mixture was transferred to a magnetically stirred container, evacuated, and filled with nitrogen. The solution was heated to 60℃ and kept at this temperature for 12 h to obtain mixed liquid A. The reaction equation is as follows:

[0036]

[0037] After the mixed liquid A was cooled to room temperature, the solvent was removed by rotary evaporation and precipitated in ethyl acetate. Then it was dried in an oven for 12 h to obtain ionic liquid monomer III.

[0038] (2) Synthesis of diazonium-type polymeric ionic liquid: Ionic liquid monomer III, divinylbenzene and polyvinylpyrrolidone were mixed and dissolved in anhydrous ethanol at a mass ratio of 1:1.0:1.2 to prepare mixed liquid B; mixed liquid B was transferred to a magnetically stirred container, evacuated and filled with nitrogen and heated to 60°C; and kept at this temperature for 24 h; after mixed liquid B cooled to room temperature, the product was separated and washed with ethanol, and dried in an oven for 12 h to obtain diazonium-type polymeric ionic liquid.

[0039] (3) Lithium carbonate, phosphoric acid and ferrous sulfate heptahydrate are mixed in a molar ratio of Li:P:Fe=1.0:1.0:1.0, and diazonium-type polymeric ionic liquid is added. The mass ratio of iron element in ferrous sulfate heptahydrate to the mass of diazonium-type polymeric ionic liquid is 1:0.075. Water is added to prepare a mixture C. The mixture C is transferred to a magnetic stirring container. The pH of the mixture C is adjusted to 5 with phosphoric acid to obtain a reaction mixture. The reaction mixture is stirred and the stirring speed is controlled at 60 rpm. After heating to 60℃, it is kept at the temperature for 2 hours and then aged for 10 minutes to obtain a reaction slurry.

[0040] (4) Grind the reaction slurry and then perform two-fluid spray drying. The nozzle size is 0.5 mm, the spray gun pressure is 0.3 MPa, the inlet temperature is 110℃, and the outlet temperature is 70℃ to obtain the lithium iron phosphate precursor.

[0041] (5) Under a nitrogen atmosphere, the lithium iron phosphate precursor was heated to 800 °C at a rate of 2 °C / min and calcined for 4 h to obtain lithium iron phosphate material.

[0042] Figure 2 shows the SEM characterization of the lithium iron phosphate precursor obtained in step (4) of this embodiment; the precursor particles are rhomboid plates, which helps to improve the distribution uniformity of lithium iron phosphate materials.

[0043] Figure 1 shows the SEM characterization of the lithium iron phosphate material obtained in step (5) of this embodiment. The lithium iron phosphate is a dispersed and uniformly distributed spherical particle, which can avoid agglomeration.

[0044] Example 2 The preparation method of the lithium iron phosphate material in this example is similar to that in Example 1, except that the mass ratio of ferrous sulfate heptahydrate to diazonium-type polymeric ionic liquid in step (3) is 1:0.05, and the other steps are the same. As shown in Figure 3, the lithium iron phosphate material obtained in this example is a SEM characterization image. Similar to the example, the lithium iron phosphate is a dispersed, uniformly distributed spherical particle.

[0045] Example 3 The preparation method of lithium iron phosphate material in this example is the same as in Example 1, except that the pH of the mixture C in step (3) is adjusted to 8, and the other steps are the same.

[0046] Example 4 The preparation method of lithium iron phosphate material in this example is the same as in Example 1, except that in step (5), the temperature is raised to 600°C, and the other steps are the same.

[0047] Example 5 The preparation method of lithium iron phosphate material in this example is the same as that in Example 1, except that lithium iron phosphate is replaced with lithium manganese iron phosphate. Specifically: (3) Lithium carbonate, phosphoric acid, manganese oxalate and ferrous oxalate are mixed in a molar ratio of Fe+Mn:Li:P=1:1:1, wherein the molar ratio of Fe:Mn is 0.4. The pH of the mixture is adjusted to 5 with phosphoric acid. Other steps are the same.

[0048] Comparative Example 1 The preparation method of the lithium iron phosphate material provided in this embodiment is the same as that in Example 1, except that in step (2), divinylbenzene and polyvinylpyrrolidone are not added; and ionic liquid monomer is used directly as carbon source.

[0049] Comparative Example 2 The preparation method of the lithium iron phosphate material provided in this example is the same as that in Example 1, except that in step (3), sucrose is used instead of diazonium-type polymeric ionic liquid as carbon source, and the mass ratio of iron to sucrose is 1:0.05.

[0050] Comparative Example 3 The preparation method of the lithium iron phosphate material provided in this example is the same as that in Example 1, the only difference is that in step (1), benzyl bromide is used as raw material to prepare ionic liquid monomer, and the molar ratio of 1-vinylimidazolium to benzyl bromide is 1:1, which is referred to as monoazole type polymeric ionic liquid.

[0051] Materials Testing

[0052] The electrochemical performance of the lithium iron phosphate materials prepared in Examples 1-5 and Comparative Examples 1-3 was tested, and the results are shown in Table 1.

[0053] Test method: Lithium iron phosphate material, acetylene black, and PVDF were mixed with an appropriate amount of N-methylpyrrolidone in a ratio of 8:1:1 to prepare a slurry. The slurry was then coated, dried, and punched to obtain circular electrodes. Finally, the circular electrodes, separator, and lithium foil were assembled into coin cells in a glove box for testing. The coin cells were charged and discharged within a voltage range of 2–3.75V.

[0054] Table 1: Electrochemical performance test results of Examples 1-4 and Comparative Examples 1-2

[0055]

[0056] As can be seen from Table 1, the carbon-coated lithium iron phosphate materials based on diazonium-type polymeric ionic liquids prepared by the method of the present invention have improved electrochemical performance and exhibit excellent electrochemical properties.

[0057] In Comparative Example 1, the crosslinking agent and dispersant were omitted. After thermal initiation, the degree of polymerization of the diazonium-type polymeric ionic liquid decreased, indicating that increasing the degree of polymerization of the ionic liquid monomer is more beneficial to the electrochemical performance of the material. Figure 4 shows the characterization of lithium iron phosphate prepared in Comparative Example 1. The lithium iron phosphate particles are spherical, but agglomeration occurred. The reason is that the monomeric ionic liquid with a low degree of polymerization (almost no polymerization) as a coating material will decompose into small molecule gas and carbon fragments at high temperature. These fragments are randomly deposited on the surface of the precursor, easily forming dotted, discontinuous carbon layers, which cannot effectively isolate the particles. On the contrary, it may promote agglomeration, resulting in uneven distribution of lithium iron phosphate particles.

Claims

1. A method for coating an electrode material, characterized in that, The process includes the following steps: (1) mixing olefin-substituted imidazoles and halogenated hydrocarbons, and performing an addition reaction to form a quaternary ammonium salt type ionic liquid monomer, wherein the halogenated hydrocarbon is one or a mixture of several of 3-di(bromomethyl)benzene, 1,3-di(bromoethyl)benzene, 1,2-dichloroethane, benzyl bromide, and benzyl chloride; (2) thermally initiating the quaternary ammonium salt type ionic liquid monomer to perform a polymerization reaction to form a diazonium type polymeric ionic liquid; (3) mixing the diazonium type polymeric ionic liquid and electrode materials, and calcining to form a carbon coating layer on the outside of the electrode materials.

2. The coating method for electrode material according to claim 1, characterized in that, In step (1), the molar ratio of the olefin-substituted imidazole to the haloalkane is 1.8~2.4:1, and the olefin-substituted imidazole is one or a mixture of several of 1-vinylimidazolium, 1-allylimidazolium, and 1-butenylimidazolium.

3. The coating method for electrode material according to claim 1, characterized in that, In step (1), the temperature of the addition reaction is 60~80℃ and the duration is 12~24h.

4. The coating method for electrode material according to claim 1, characterized in that, In step (2), a crosslinking agent and a dispersant are added to carry out a polymerization reaction. The mass ratio of the quaternary ammonium salt ionic liquid monomer, the crosslinking agent, and the dispersant is 1:1.0~1.5:1.2~1.

8.

5. The coating method for electrode material according to claim 4, characterized in that, The crosslinking agent is one or a mixture of divinylbenzene, vinyltoluene, chlorostyrene, and dicyclopentadiene acrylate; the dispersant is one or a mixture of polyvinylpyrrolidone, polyacrylic acid, and polyethylene glycol.

6. The coating method for electrode material according to claim 1, characterized in that, In step (2), the polymerization reaction is carried out at a temperature of 60-80°C for a duration of 24-48 hours.

7. The coating method for electrode material according to claim 1, characterized in that, In step (3), the electrode material is lithium manganese iron phosphate and / or lithium iron phosphate, and the mass ratio of the diazonium-type polymeric ionic liquid to the iron element of the electrode material is (0.05~0.075):

1.

8. The coating method for electrode material according to claim 7, characterized in that, In step (3), the mixing step is as follows: mix lithium source, phosphorus source, iron source and / or manganese source, water and diazonium type polymeric ionic liquid to form a mixture, adjust the pH of the mixture to generate lithium iron phosphate or lithium manganese iron phosphate, and obtain a reaction mixture; heat the reaction mixture to 60~100℃, keep it at the temperature for 2~6 h, age it for 10~20 min, grind it, and dry it.

9. The coating method for electrode material according to claim 8, characterized in that, Adjust the pH of the mixture to pH 5-8.

10. The coating method for electrode material according to claim 1, characterized in that, The calcination is carried out in a nitrogen or argon atmosphere, with a heating rate of 2~5℃ / min, a sintering temperature of 600~850℃, and a time of 4~6h.

Images