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CN-122025641-A - Negative plate with directional gradient pore structure, composite pore-forming agent for preparing negative plate, preparation method of composite pore-forming agent and lithium ion battery

CN122025641ACN 122025641 ACN122025641 ACN 122025641ACN-122025641-A

Abstract

The invention discloses a negative plate with a directional gradient pore structure, a composite pore-forming agent for preparing the negative plate, a preparation method and a lithium ion battery, wherein the composite pore-forming agent is provided with a core-shell coating structure and a surface functional modification layer, the core-shell coating structure comprises a core and a shell coated on the outer surface of the core, the core is a thermal decomposition type pore-forming material which can be thermally decomposed and release gas in a temperature range of 80-120 ℃, the shell is a thermal dissolution type polymer coating layer, and the surface functional modification layer is a charged polymer layer and uniformly coated on the outer surface of the shell, so that the surface charge characteristic of the composite pore-forming agent is endowed. According to the invention, by designing the composite pore-forming agent combining core-shell coating and surface functionalization modification and matching with electric field auxiliary gradient sedimentation and sectional heating pore-forming technology, the directional gradient regulation and control of the pore structure in the thickness direction of the pole piece is realized in a single pore-forming agent system.

Inventors

  • HE SHAOHUI

Assignees

  • 孝感楚能新能源创新科技有限公司

Dates

Publication Date
20260512
Application Date
20260326

Claims (10)

  1. 1. The composite pore-forming agent for preparing the negative plate with the directional gradient pore structure is characterized by comprising a core-shell coating structure and a surface functional modification layer, wherein the core-shell coating structure comprises a core and a shell coated on the outer surface of the core, the core is a thermal decomposition type pore-forming material, and the thermal decomposition type pore-forming material can be subjected to thermal decomposition and release gas in a temperature range of 80-120 ℃; The shell is a thermal dissolution type polymer coating layer, the thermal dissolution type polymer coating layer can be dissolved or softened and removed within the temperature range of 50-70 ℃, the dissolution temperature of the shell is lower than the decomposition temperature of the inner core, so that the shell is eliminated before the inner core in the segmented heating process, pores with different dimensions are sequentially formed in layers with different thicknesses of the negative electrode plate, the surface functional modification layer is a charged polymer layer and uniformly coats the outer surface of the shell, and the surface charge characteristic of the composite pore-forming agent is endowed.
  2. 2. The composite pore-forming agent for preparing a negative plate with a directional gradient pore structure according to claim 1, wherein the thermal decomposition type pore-forming material is at least one selected from ammonium carbonate, ammonium bicarbonate and azodicarbonamide; The thermal dissolution type polymer coating layer is made of polymethyl methacrylate, the surface functional modification layer is a polydopamine layer, and the polydopamine layer is negatively charged under neutral and weakly alkaline conditions.
  3. 3. The composite pore-forming agent for preparing the negative plate with the directional gradient pore structure according to claim 2, wherein the thickness of the polymethyl methacrylate shell is such that the dissolution temperature window is 55-65 ℃, the decomposition temperature window of the ammonium carbonate core is 90-110 ℃, the temperature difference between the two is not lower than 25 ℃, the particle size of the composite pore-forming agent is 1-50 mu m, and the absolute value of the surface potential of the polydopamine modified layer is not lower than 20mV.
  4. 4. A method for preparing the composite pore-forming agent for preparing a negative electrode sheet having a directional gradient pore structure as claimed in any one of claims 1 to 3, comprising the steps of: (1) Dispersing thermal decomposition type pore-forming material powder in an organic solvent, adding a dispersing agent accounting for 0.05-0.2wt% of the pore-forming material, stirring to form a uniform suspension, then dripping a polymerization monomer into the suspension, initiating free radical polymerization reaction at 60-80 ℃ to enable the polymerization monomer to polymerize in situ on the surfaces of the pore-forming material particles to form a polymer coating layer, and filtering and washing after the reaction is completed to obtain a precursor with a core-shell structure; (2) Dispersing the core-shell structure precursor obtained in the step (1) in Tris buffer solution containing dopamine hydrochloride, regulating the pH value of the system to 8.0-9.0, continuously stirring at room temperature to perform dopamine oxidation self-polymerization reaction for 8-36 hours, depositing dopamine on the surface of the polymer coating layer to form a polydopamine modified layer, and filtering, washing and drying to obtain the composite pore-forming agent.
  5. 5. The preparation method of the porous material according to claim 4, wherein in the step (1), the thermal decomposition type pore-forming material is ammonium carbonate, the organic solvent is absolute ethyl alcohol, the dispersing agent is sodium dodecyl sulfonate, the adding amount of the dispersing agent is 0.1wt% of the mass of the pore-forming material, the polymerization monomer is methyl methacrylate, the temperature of the free radical polymerization reaction is 70 ℃, and the reaction time is 2-6 hours; In the step (2), the pH value of the dopamine oxidation self-polymerization reaction is 8.5, the reaction time is 20-28 hours, and the concentration of the dopamine hydrochloride is 1-5 mg/mL.
  6. 6. A method for preparing a negative electrode sheet with a directional gradient pore structure, characterized in that the composite pore-forming agent of any one of claims 1 to 3 is adopted, comprising the following steps: (a) Dispersing a negative electrode active material, a conductive agent, a binder and the composite pore-forming agent in a solvent according to a preset proportion, and carrying out vacuum stirring and defoaming treatment to obtain uniform negative electrode slurry; (b) The negative electrode slurry is coated on the surface of a current collector, a direct current electric field is applied along the direction perpendicular to the plane of the current collector in the coating process or in a wet film state after the coating is finished, the direction of the electric field points to one side of the current collector from the surface of a pole piece, and the composite pore-forming agent with charges on the surface directionally migrates towards the direction close to the current collector under the driving of the electric field force, so that gradient distribution of gradually increasing concentration of the pore-forming agent along the thickness direction of the pole piece from a surface layer to a bottom layer is formed in the wet film; (c) The pole piece treated in the step (b) is subjected to sectional heating treatment, the first stage is dried under the condition of 50-70 ℃ to dissolve or soften and remove a polymer shell of the composite pore-forming agent, and a relatively large pore channel is formed on the surface layer of the pole piece after the shell is eliminated; (d) And cold pressing the pole piece after the pore forming treatment is finished, and locking the gradient pore structure in the compacting process to obtain the negative pole piece with the directional gradient pore structure.
  7. 7. The preparation method of claim 6, wherein in the step (a), the negative electrode active material is artificial graphite and/or natural graphite, the conductive agent is conductive carbon black, the binder is a composite binder system of sodium carboxymethyl cellulose and styrene-butadiene rubber, and the solvent is deionized water, wherein the addition amount of the composite pore-forming agent is 1-10wt% of the mass of the negative electrode active material; in the step (b), the field intensity of the direct current electric field is 50-100V/cm, the current collector is copper foil, and the application time of the electric field is within 1-30 minutes after coating is completed.
  8. 8. The method according to claim 6 or 7, wherein in the step (C), the drying temperature in the first stage is 60 ℃, the drying time is 0.5 to 2 hours, the porosity of the macroporous channels formed on the surface layer of the pole piece is 30 to 40%, and the heating temperature in the second stage is 100 ℃, the heating time is 0.5 to 3 hours, and the porosity of the microporous structure formed near the bottom layer region of the current collector is 8 to 15%.
  9. 9. The negative electrode plate with the directional gradient pore structure is characterized by being obtained by the preparation method of any one of claims 6 to 8, wherein the negative electrode plate is continuously gradient distributed with decreasing porosity from a surface layer far away from a current collector to a bottom layer close to the current collector along the thickness direction, the porosity of a surface layer area is 30-40%, and the porosity of a bottom layer area is 8-15%.
  10. 10. A lithium ion battery comprising the negative electrode sheet with the oriented gradient pore structure of claim 9.

Description

Negative plate with directional gradient pore structure, composite pore-forming agent for preparing negative plate, preparation method of composite pore-forming agent and lithium ion battery Technical Field The invention relates to the technical field of lithium batteries, in particular to a negative plate with a directional gradient pore structure, a composite pore-forming agent for preparing the negative plate, a preparation method and a lithium ion battery. Background With the wide popularization of mobile electronic equipment and electric automobiles, lithium ion batteries are currently the most dominant energy storage devices by virtue of their high energy density, long cycle life and the like. To further increase the energy density of the battery, the use of thick electrode designs is one of the important technical directions. However, the traditional thick electrode has a series of problems in terms of dynamic performance due to the increase of the thickness of the coating, namely the obvious extension of an ion diffusion path and the increase of tortuosity, electrolyte is difficult to infiltrate into the thick coating, particularly electrode polarization is aggravated due to untimely lithium ion transmission under the condition of high-current charge and discharge, and voltage shock is caused by uneven local lithium ion concentration distribution, so that the rate performance and the cycle life of the battery are seriously restricted. In addition, in a low-temperature environment, the viscosity of the electrolyte is increased, the diffusion coefficient of lithium ions is greatly reduced, and the dynamics problem is further aggravated. The introduction of a controlled pore structure in the negative electrode coating is one of the effective ways to ameliorate the above problems. The reasonable pore structure can shorten the diffusion path of lithium ions, reduce tortuosity, promote electrolyte infiltration and relieve mechanical stress caused by volume expansion of the active material in the charge and discharge process to a certain extent. The pore-forming techniques that have been reported so far mainly include the use of sacrificial template methods (e.g., polymer microspheres, carbonate particles, etc., that are removed by dissolution or decomposition during post-treatment to leave voids), freeze-drying methods, laser drilling methods, etc. However, the prior pore-forming technology has the defects that firstly, the process is complex, the preparation difficulty is high, the cost is high, the pore-forming technology is difficult to be compatible with the prior roll-to-roll coating production line, secondly, the pore size is difficult to accurately regulate and control, the volume ratio of active materials in the pole piece is directly reduced to lose energy density due to overlarge pore diameter, the effect of improving ion transmission is limited due to overlarge pore diameter, thirdly, the pore structure formed in the pole piece by the traditional pore-forming method is generally uniformly distributed, the difference of the different thickness layers of the pole piece on the pore structure is not considered, and ideally, the surface layer of the pole piece has higher porosity to facilitate rapid infiltration of electrolyte and introduction of lithium ions, and the bottom layer has lower porosity to ensure the volume ratio and the energy density of the enough active materials. In order to realize the gradient pore structure, one intuitive idea is to mix and use a plurality of pore formers with different decomposition temperatures. However, in actual operation, unstable phenomena such as layered sedimentation and agglomeration are very easy to occur in the slurry stirring and coating process due to the differences of density, particle size, surface properties and solubility among different pore formers, and predictable directional pore gradient cannot be formed. The traditional single pore-forming agent (such as ammonium bicarbonate, polymethyl methacrylate microspheres and the like) is randomly distributed in the slurry, so that ordered gradient arrangement along the thickness direction of the pole piece cannot be realized. Therefore, how to design a technical scheme which has simple process and good controllability and can directionally construct a gradient pore structure in the negative electrode plate is a key problem to be solved in the field. Disclosure of Invention The invention aims to overcome the defects of the background technology, and provides a negative plate with a directional gradient pore structure, a composite pore-forming agent for preparing the negative plate, a preparation method of the composite pore-forming agent and a lithium ion battery comprising the negative plate. According to the invention, by designing the composite pore-forming agent combining core-shell coating and surface functionalization modification and matching with electric field auxiliary gradient sedimentati