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CN-122025554-A - High-compaction-density lithium iron phosphate positive plate and preparation method thereof

CN122025554ACN 122025554 ACN122025554 ACN 122025554ACN-122025554-A

Abstract

The invention discloses a high-compaction density lithium iron phosphate positive plate and a preparation method thereof, relating to the technical field of lithium battery positive electrode preparation, comprising a positive current collector and a positive active layer on the surface thereof, the active layer contains a lithium iron phosphate active material system, a conductive network system, a crosslinking curing type bonding system and a channel lining type inorganic nano component. The preparation method comprises the steps of depositing channel lining type inorganic nano components on the surfaces of removable core material particles to form core-shell pore-forming units, mixing the core-shell pore-forming units with each system, pulping, coating, drying, rolling, performing low-temperature vacuum heat treatment to remove the removable core material and crosslink and solidify a crosslinked and solidified bonding system to form a macro Kong Tongdao, wherein the pore wall is provided with a pore wall lining layer formed by the channel lining type inorganic nano components. The positive plate is suitable for thick electrode scenes, can obviously improve the infiltration uniformity of electrolyte, effectively reduce dry cores and gas stagnation, shorten standing time, and maintain compaction density and peeling strength.

Inventors

  • WANG ZHIHAI
  • ZHANG ZHENGFEI
  • YANG XIAOYAN

Assignees

  • 湖南兆科动力新能源有限公司
  • 贵州兆科能源有限公司

Dates

Publication Date
20260512
Application Date
20260403

Claims (10)

  1. 1. The high-compaction-density lithium iron phosphate positive plate is characterized by comprising the following components: The positive electrode active layer comprises a positive electrode current collector and a positive electrode active layer on the surface of the positive electrode current collector, wherein the compaction density after removing a removable core material is not lower than 2.65 grams per cubic centimeter, the active layer comprises a lithium iron phosphate active material system component A, a conductive network system component B, a crosslinking curing type bonding system component C and a channel lining type electrophilic liquid inorganic nano component E, the component E comprises boehmite nano particles or boehmite nano fibers, and the component C comprises sodium carboxymethyl cellulose, styrene-butadiene rubber emulsion, polyacrylic acid and a water-dispersible type polycarbodiimide crosslinking agent or a water-dispersible type polyepoxy crosslinking agent; Wherein, a through macro Kong Tongdao is formed in the active layer, the wall of the macro pore passage is provided with a pore wall lining layer composed of a component E, the macro pore passage is formed after the removable core material in the core-shell pore-forming unit D@E is removed, and the shell layer of the core-shell pore-forming unit D@E contains the component E.
  2. 2. The high-compaction-density lithium iron phosphate positive electrode sheet according to claim 1, wherein: Based on the positive electrode active layer with the removable core material removed, the content of the component B is 1.2 to 2.8 mass percent, the content of the component C is 1.0 to 2.2 mass percent, the content of the component E is 0.05 to 0.60 mass percent, the balance is the component A, and the aperture of the macro-pore channel is larger than 5 microns.
  3. 3. The high-compaction-density lithium iron phosphate positive electrode sheet according to claim 2, wherein: the component A comprises secondary particle type lithium iron phosphate A1 and fine particle size lithium iron phosphate A2; The median particle diameter D50 of A1 is 6 to 12 micrometers, the tap density is not less than 1.3 grams per cubic centimeter, the carbon coating content is 0.8 to 2.0 mass percent, the median particle diameter D50 of A2 is 0.6 to 1.8 micrometers, and the content of A2 in the total amount of A1 and A2 is 5 to 25 mass percent.
  4. 4. A high-compaction-density lithium iron phosphate positive electrode sheet according to claim 3, wherein: The component B comprises conductive carbon black B1 and conductive carbon nano-tubes B2, wherein the mass ratio of the conductive carbon nano-tubes B1 to B2 is 6 to 12 to 1, the diameter of the conductive carbon nano-tubes is 6 to 15 nanometers, the length of the conductive carbon nano-tubes is 5 to 20 micrometers, and the conductive carbon black is medium-ratio surface conductive carbon black with the nitrogen adsorption specific surface area of 40 to 90 square meters per gram and the DBP oil absorption value of 120 to 220 milliliters per hundred grams, or high-ratio surface conductive carbon black with the nitrogen adsorption specific surface area of 600 to 1600 square meters per gram and the DBP oil absorption value of 350 to 520 milliliters per hundred grams.
  5. 5. The high-compaction-density lithium iron phosphate positive electrode sheet according to claim 4, wherein: The total content of component C is 1.0 to 2.2 mass%, the content of the crosslinking agent in the final dry film is 0.05 to 0.25 mass%, and component E further includes nano silica having a particle size of 10 to 40 nm.
  6. 6. The preparation method of the lithium iron phosphate positive plate with high compaction density is characterized by comprising the following steps: Preparing an inorganic dispersion comprising boehmite and polyacrylic acid and depositing the inorganic dispersion on the surface of the removable core particles to obtain core-shell pore-forming units D@E; Mixing the lithium iron phosphate active material system component A, the conductive network system component B, the crosslinking curing type bonding system component C and the core-shell pore-forming unit D@E to prepare positive electrode slurry, coating the positive electrode slurry on a positive electrode current collector, drying and rolling, and carrying out vacuum heat treatment on the rolled precursor pole piece to remove a removable core material and crosslink and cure the bonding system, thereby obtaining the positive electrode piece with the inorganic nano lining layer on the wall of the macro-pore passage.
  7. 7. The method of manufacturing according to claim 6, wherein: The inorganic dispersion has a pH of 7.0 to 9.0, a boehmite solid content of 5 to 12 mass%, a polyacrylic acid concentration of 0.2 to 0.6 mass%, and the inorganic dispersion is subjected to high-speed shearing dispersion for 20 to 40 minutes and ultrasonic dispersion for 10 to 20 minutes.
  8. 8. The method of manufacturing according to claim 7, wherein: The removable core material is adamantane or a cognate high-melting point adamantane derivative, the removable core material comprises a first core particle D1 with a median particle diameter D50 of 12 to 20 micrometers and a second core particle D2 with a median particle diameter D50 of 2 to 5 micrometers, the mass ratio of D1 to D2 is 4 to 1 to 8 to 1, and the addition amount of the removable core material is 0.8 to 3.5 mass percent relative to the total solid of the component A, the component B, the component C and the component E in the positive electrode active layer after the removal of the removable core material, and the mass fraction of the shell layer of the core-shell pore-forming unit D@E is 6 to 20 mass percent relative to the removable core material and the thickness of the shell layer is 80 to 350 nanometers.
  9. 9. The method of manufacturing according to claim 8, wherein: The solid content of the positive electrode slurry is 58 to 68 mass percent, the core-shell pore-forming unit D@E adds and vacuum defoams 10 to 20 minutes in a low shear mixing mode after the slurry is uniform, and the compaction density of the precursor pole piece containing the removable core material reaches 2.75 to 2.90 grams per cubic centimeter by rolling.
  10. 10. The method of manufacturing according to claim 9, wherein: the vacuum heat treatment is carried out under the conditions of 20 to 500 Pa vacuum degree, 105 to 150 ℃ temperature and 0.5 to 6 hours heat preservation.

Description

High-compaction-density lithium iron phosphate positive plate and preparation method thereof Technical Field The invention relates to the technical field of lithium battery positive electrode preparation, in particular to a high-compaction-density lithium iron phosphate positive electrode sheet and a preparation method thereof. Background Lithium iron phosphate batteries are widely used in electric vehicles and energy storage systems due to safety and life advantages. Along with the improvement of the requirements of whole vehicle endurance, system integration efficiency and energy storage electricity cost, a large-capacity square or soft package battery core (for example, a hundred ampere time level to three hundred ampere time levels) tends to adopt a positive plate with higher surface density so as to improve the volume energy density. In engineering, the improvement of the loading of active substances in unit volume is generally realized by improving the compaction density of the lithium iron phosphate positive plate and matching with a thick coating (larger coating thickness and surface capacity), and meanwhile, the beat and consistency of the procedures of coating drying, rolling to fix thickness, slitting lamination/winding and the like are considered in the roll-to-roll manufacturing. Under the application scene, electrolyte injection and infiltration belong to key processes after assembly, and the time and uniformity of the process directly influence the formation efficiency, internal resistance distribution and batch consistency. In the prior art, the compaction density is improved by means of grain composition, secondary grain densification, carbon cladding, rolling and the like, and infiltration is promoted by adopting processes of vacuum liquid injection, temperature rising and standing or liquid injection for multiple times, and the like, and the technology also attempts to adjust the pore structure at the electrode structure level so as to improve ion transmission. However, when the positive electrode sheet satisfies both high compacted density and thick electrode conditions, the electrode porosity decreases, the pore size distribution migrates toward the pores and the tortuosity increases, and the rolling may also form a relatively dense region of the surface layer, resulting in a decrease in the permeation rate of the electrolyte in the thickness direction and accompanying gas retention, and the progress of the infiltration front in the electrode is hindered, which is prone to insufficient infiltration near the current collector side or local region. The insufficient infiltration can affect the formation and uniformity of the interfacial film in the formation stage, so that the local ion/electron transmission impedance is higher, and further the current distribution is uneven, the polarization is increased and the temperature rise is different, which is manifested by the reduction of capacity utilization rate, the discrete increase of direct current internal resistance and the early cycle attenuation risk, and in large-area electrodes and large electric cores, the non-uniformity is more difficult to be completely covered by the process margin, and the standing or the process control is required to be prolonged, so that the manufacturing beat, the product occupation and the cost pressure are brought. In addition, the actual product often controls the electrolyte ratio to improve the energy density, the available electrolyte reservoir capacity of the electrode is limited, and when the capillary driving force is insufficient or the connectivity of the pore canal is reduced, even if the outer layer is imbibed, the inner part can still be in a low saturated state for a long time, so that the difference between impedance and heating is amplified along with time. Therefore, the technical problem to be solved in the prior art is that in the lithium iron phosphate positive plate with high compaction density and thick coating, the infiltration speed and the infiltration uniformity of the electrolyte in the thickness direction are difficult to be compatible, and local dry core and gas retention are easy to occur. Disclosure of Invention (One) solving the technical problems Aiming at the defects of the prior art, the invention provides a high-compaction-density lithium iron phosphate positive plate and a preparation method thereof, wherein during the preparation, channel lining type inorganic nano components are deposited on the surface of removable core material particles to form a core shell pore-forming unit, the core shell pore-forming unit is mixed with each system for pulping, coating, drying and rolling, then low-temperature vacuum heat treatment is carried out to remove the removable core material and crosslink and solidify a crosslinking and solidifying type bonding system, a macro Kong Tongdao is formed, the pore wall is provided with a pore wall lining layer formed by the channel lining type