Precise coating forming method for lithium ion battery pole piece

Abstract

The invention provides a precise coating forming method for a lithium ion battery pole piece, and belongs to the field of lithium batteries. The method comprises the following steps: firstly preparing LiFePO4 sol, forming split-phase gel by utilizing phase separation generated in the sol-gel process, mixing to prepare pole piece slurry with uniformly dispersed particles, and finally, controlling a gasket structure and coating parameters in extrusion coating to prepare a uniform, well-combined and porous coating so as to finish the precise coating forming of the lithium ion battery pole piece. According to the invention, the problems of poor uniformity, porosity, cycle performance and the like of the coating in the coating of the existing lithium ion battery pole piece are solved, and the method can be used for preparing the high-performance lithium ion battery pole piece.

Description

TECHNICAL FIELD

[0001] The present application relates to a coating forming method, in particular to a precise coating forming method for lithium ion battery pole piece, and belongs to the fields of lithium battery, new energy, new material, advanced manufacturing and surface engineering. BACKGROUND

[0002] In recent years, the lithium ion battery industry has developed rapidly. On the one hand, the demand for lithium ion batteries in consumer electronics and new energy vehicles and other industries is growing rapidly. On the other hand, the manufacturing precision, consistency and life of the battery are increasingly required. The pole piece is the electrochemical reaction carrier of the lithium ion battery, and the positive and negative electrode paste is uniformly coated on the surface of the pole piece to form a coating. The coating process directly affects the active material load and coating precision, and is the core process of the pole piece and the entire battery manufacturing.

[0003] CN119400808A discloses a pole piece coating method. A multi-layer step-by-step coating method is adopted, a relatively thin first film layer is coated first, and then a relatively thick second film layer is coated, a short drying process is performed between each coating, effectively reducing the generation of bubbles and wrinkles. At the same time, segmented drying is adopted, the first film layer is preliminarily dried at low temperature and low wind speed, and then the second film layer is rapidly dried at high temperature and high wind speed, improving drying efficiency and quality, which can significantly improve the uniformity and thickness precision of coating, reduce coating defects, improve the consistency and stability of lithium batteries. In addition, it also improves the drying efficiency, shortens the production cycle and reduces the energy consumption. CN119056684A discloses a battery aluminum foil coating device and coating method, current collector and battery, by means of the aluminum foil is sequentially passed through the unwinding mechanism, the double-sided coating assembly, the first side coating assembly, the second side coating assembly and the winding mechanism to complete the double-sided coating, thereby combining the aluminum foil carbon layer coating process and the electrode slurry coating process, greatly reducing the production cost, shortening the production cycle and reducing resource waste; compared with using two devices to coat the carbon layer slurry on the first side and the second side of the aluminum foil respectively, the coating function is integrated through the design of the double-sided coating assembly, greatly saving the floor space of the coating device, allowing the use of different systems of carbon layer slurry and electrode slurry, and reducing the requirement for material compatibility. CN118825201A discloses an electrode pole piece coating slurry, a preparation method and use of an electrode pole piece, and a coating die. The preparation method of the electrode pole piece coating slurry comprises the following steps: mixing ion conductor particles, functional particles, a first binder and a first solvent to obtain a first mixed solution, and sanding and dispersing the mixed solution to obtain a coating slurry; the relationship between the thickness S of the coating and the solid content A of the coating slurry and the viscosity B of the coating slurry satisfies: S=A*B. The present application adjusts the relationship between the solid content and the viscosity of the coating slurry, and cooperates with the method of mixing first and then sanding, to obtain a coating slurry system with good dispersion effect and small particles that are not easy to aggregate, and then a uniform coating structure with thin thickness and controlled coating thickness is obtained through double-layer coating.

[0004] Although the existing coating method has many advantages, the uniformity, porosity and cycle performance of the coating after the coating of the lithium ion battery pole piece are still not good. Therefore, it is urgent to develop a new lithium ion battery pole piece precision coating forming method. SUMMARY

[0005] The present application aims at a lithium ion battery pole piece precision coating forming method, which proposes to prepare LiFePO4 sol first, use phase separation to form a phase-separated gel during sol-gel process, prepare a pole piece slurry with uniform particle dispersion, and finally control the gasket structure and coating parameters in extrusion coating to prepare a uniform, well-bonded and porous coating to complete the lithium ion battery pole piece precision coating forming.

[0006] The lithium ion battery pole piece precision coating forming method of the application comprises the following steps in sequence: (1) LiFePO4 sol preparation: take FeCl3·H2O, LiOH, H3PO4, polyethylene oxide and N-methyl formamide according to the molar ratio of 1:1:1: (1~3×10 -3 ):2, first take FeCl3·H2O and add it into deionized water to prepare a 1~2 mol / L solution and stir for 30 min, then add LiOH and continue stirring for 30 min, and then add H3PO4 and polyethylene oxide and stir for 2~4 h to prepare LiFePO4 sol; (2) Preparation of binder and conductive agent mixed slurry: take acetylene black, PVDF and NMP according to the weight ratio of (2~3):(2~3):45; mix the three and perform 1~2 h planetary ball milling to prepare the binder and conductive agent mixed slurry; (3) Pole piece slurry preparation: place the LiFePO4 sol in an ice water bath and stir for 30 min, drop N-methyl formamide to promote the gelation of the LiFePO4 sol, and phase separation occurs during the gelation process, the polyethylene oxide is adsorbed on the surface of the LiFePO4 oligomer through hydrogen bonding to form a polyethylene oxide-rich gel phase, and the hydrophobic group of the polyethylene oxide leads to the formation of a water-soluble solvent-rich phase, and after continuous stirring for 2~4 h, a continuous phase-separated structure LiFePO4 gel composed of a polyethylene oxide-rich gel phase and a water-soluble solvent-rich phase is formed; mix the prepared binder and conductive agent mixed slurry and the continuous phase-separated structure LiFePO4 gel according to the weight ratio of 1:(1.5~3), and perform 1~2 h planetary ball milling to prepare a uniformly dispersed pole piece slurry; (4) Pole piece precision coating forming: use the prepared pole piece slurry to perform slot extrusion coating on an aluminum foil, add a gasket between the upper die and the lower die of the coating machine, the characteristic parameters of the inner edge of the gasket are converging width L1=exit width L4*(1%~2%), converging length L2=converging width L1*(1.5~2.5), exit length L3=converging length L2*(8~10), gasket thickness T=exit width L4*(0.1~0.15%), and gasket surface roughness Ra0.2; after drying and rolling, the pole piece precision coating forming is completed, the thickness deviation of the pole piece is ≦4 μm, the porosity is 30~40%, and the capacity retention rate after 100 cycles at 0.1C rate is 85%~95%.

[0007] Further, in the steps of the lithium ion battery pole piece precision coating forming method of the application: During the preparation of LiFePO4 sol, the stirring rate is 100~150 r / min, and all the chemical reagents used are analytical pure; The rotation speed of the planetary ball mill is 250-400 r / min during preparation of the mixed slurry of the binder and the conductive agent; The dropping speed of N-methyl formamide is 1 mL / min, and the rotation speed of the planetary ball mill is 250-400 r / min during preparation of the pole piece slurry; The coating parameters during precise coating and forming of the pole piece are as follows: a coating gap of 90-110 μm, a foil movement speed of 0.3-0.4 m / s, an inlet flow speed of 0.05-0.1 m / s, and a drying temperature of 90-100 ℃.

[0008] The present application has the following advantages: (1) The present application utilizes phase separation of LiFePO4 sol to form a phase-separated gel during gelation, and the porosity of the pole piece after coating is high and the dispersion uniformity of the active material is good. (2) The porosity of the coating after coating in the present application is high, and the electrolyte can better infiltrate the pole piece, providing a path for lithium ion intercalation and deintercalation, and the effective lithium ion conductivity is also greater, and the battery energy density is high. (3) The coating porosity of the present application is high, which can relieve volume expansion and improve the cycle performance and life of the pole piece. (4) On the basis of preparing a uniformly dispersed slurry containing phase-separated gel, the present application adds a gasket and then performs precise coating, and the thickness uniformity of the coating is good. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 The present application has the following advantages: (1) The present application utilizes phase separation of LiFePO4 sol to form a phase-separated gel during gelation, and the porosity of the pole piece after coating is high and the dispersion uniformity of the active material is good. (2) The porosity of the coating after coating in the present application is high, and the electrolyte can better infiltrate the pole piece, providing a path for lithium ion intercalation and deintercalation, and the effective lithium ion conductivity is also greater, and the battery energy density is high. (3) The coating porosity of the present application is high, which can relieve volume expansion and improve the cycle performance and life of the pole piece. (4) On the basis of preparing a uniformly dispersed slurry containing phase-separated gel, the present application adds a gasket and then performs precise coating, and the thickness uniformity of the coating is good. DETAILED DESCRIPTION

[0010] Example 1: Precise coating and forming of the pole piece of the lithium ion battery are performed according to the following steps.

[0011] (1) Preparation of LiFePO4 sol: FeCl3·H2O, LiOH, H3PO4, polyethylene oxide and N-methyl formamide are weighed according to a molar ratio of 1:1:1: (1×10 -3 ):2, and the used chemical reagents are all analytical pure; FeCl3·H2O is first added into deionized water to prepare a 1.2 mol / L solution and stirred for 30 min, then LiOH is added and stirred for another 30 min, the stirring speed is 110 r / min, and then H3PO4 and polyethylene oxide are added and stirred for 2 h to prepare the LiFePO4 sol; (2) Preparation of the mixed slurry of the binder and the conductive agent: acetylene black, PVDF and NMP are weighed according to a weight ratio of 2:2.5:45; the three are mixed and subjected to 1 h planetary ball milling, the rotation speed of the planetary ball mill is 260 r / min, and the mixed slurry of the binder and the conductive agent is prepared. (3) Pole piece slurry preparation: the LiFePO4 sol is placed in an ice water bath and stirred for 30 min, N-methyl formamide is added at a rate of 1 mL / min to promote gelation of the LiFePO4 sol, phase separation occurs during gelation, polyethylene oxide is adsorbed on the surface of the LiFePO4 oligomer through hydrogen bonding to form a polyethylene oxide-rich gel phase, and the hydrophobic group of polyethylene oxide leads to the formation of a water-solvent-rich phase, and after continuous stirring for 2-4 h, a continuous phase-separated structure LiFePO4 gel composed of a polyethylene oxide-rich gel phase and a water-solvent-rich phase is formed; the prepared binder and conductive agent mixed slurry and the continuous phase-separated structure LiFePO4 gel are mixed in a weight ratio of 1:1.5, and planetary ball milling is performed for 1 h at a planetary ball mill speed of 250 r / min; a uniformly dispersed pole piece slurry is prepared; (4) Pole piece precision coating forming: the prepared pole piece slurry is used for slit extrusion coating on an aluminum foil, the coating gap is 90 μm, the foil movement speed is 0.3 m / s, the inlet flow rate is 0.06 m / s, a gasket is added between the upper die and the lower die of the coating machine, the gasket structure is as shown in Figure 1 , the characteristic parameters of the inner edge of the gasket are outlet width L4=610 mm, convergence width L1=outlet width L4*1%=6.1 mm, convergence length L2=convergence width L1*1.5=9.15 mm, outlet length L3=convergence length L2*9=82.35 mm, thickness T of the gasket= outlet width L4*0.1%=0.61 mm, and surface roughness Ra of the gasket 0.2; after drying at 95°C and rolling, the pole piece precision coating forming is completed, the thickness deviation of the pole piece is 3.2 μm, the porosity is 32%, and the capacity retention rate after 100 cycles at 0.1C rate is 86%.

[0012] Example 2: The lithium ion battery pole piece precision coating forming is carried out according to the following steps.

[0013] (1) LiFePO4 sol preparation: FeCl3·H2O, LiOH, H3PO4, polyethylene oxide, and N-methyl formamide are weighed according to a molar ratio of 1:1:1: (2.8×10 -3 ):2; all the chemical reagents used are analytical pure; FeCl3·H2O is first added to deionized water to prepare a 2 mol / L solution and stirred for 30 min, then LiOH is added and stirred for another 30 min at a stirring rate of 150 r / min, and then H3PO4 and polyethylene oxide are added and stirred for 3 h to prepare a LiFePO4 sol; (2) Binder and conductive agent mixed slurry preparation: acetylene black, PVDF, and NMP are weighed according to a weight ratio of 3:2.4:45; the three are mixed and subjected to 2 h planetary ball milling at a planetary ball mill speed of 380 r / min to prepare a binder and conductive agent mixed slurry. (3) Preparation of electrode slurry: LiFePO4 sol was placed in an ice water bath and stirred for 30 min. N-methyl formamide was added at a rate of 1 mL / min to promote gelation of the LiFePO4 sol. Phase separation occurred during gelation, and polyethylene oxide was adsorbed on the surface of LiFePO4 oligomers by hydrogen bonding to form a polyethylene oxide-rich gel phase. The hydrophobic groups of polyethylene oxide caused the formation of a water-solvent-rich phase. After continuous stirring for 3 h, a LiFePO4 gel with a continuous phase structure composed of a polyethylene oxide-rich gel phase and a water-solvent-rich phase was formed. The prepared binder and conductive agent mixture slurry and the continuous phase structure LiFePO4 gel were mixed at a weight ratio of 1:2.5, and planetary ball milling was performed for 2 h at a speed of 400 r / min. A uniformly dispersed electrode slurry was prepared; (4) Precise coating and forming of the electrode: The prepared electrode slurry was subjected to slot extrusion coating on an aluminum foil at a coating gap of 110 μm, a foil movement speed of 0.5 m / s, and an inlet flow rate of 0.08 m / s. A gasket was added between the upper die and the lower die of the coating machine, and the structure of the gasket is shown in Figure 1 The characteristic parameters of the inner edge of the gasket are as follows: an outlet width L4 = 330 mm, a convergence width L1 = the outlet width L4 * 1.5% = 4.95 mm, a convergence length L2 = the convergence width L1 * 2 = 9.9 mm, an outlet length L3 = the convergence length L2 * 8 = 79.2 mm, a thickness T = the outlet width L4 * 0.15% = 0.495 mm, and a gasket surface roughness Ra 0.2. After drying at 100°C and rolling, the precise coating and forming of the electrode were completed. The thickness deviation of the electrode was 2.8 μm, the porosity was 36%, and the capacity retention rate after 100 cycles at a rate of 0.1 C was 91%.

Claims

1. A method for precision coating and forming of lithium-ion battery electrode sheets, characterized in that... The steps are as follows: (1) Preparation of LiFePO4 sol: molar ratio 1:1:1:(1~3×10 -3 ):2 Weigh out FeCl3·H2O, LiOH, H3PO4, polyethylene oxide, and N-methylformamide; first, add the weighed FeCl3·H2O to deionized water to prepare a 1~2 mol / L solution and stir for 30 min, then add LiOH and continue stirring for 30 min, then add H3PO4 and polyethylene oxide and stir for 2~4 h to prepare LiFePO4 sol; (2) Preparation of binder and conductive agent mixed slurry: weigh acetylene black, PVDF and NMP according to the weight ratio (2~3): (2~3): 45; mix the three and perform planetary ball milling for 1~2 hours to prepare binder and conductive agent mixed slurry; (3) Preparation of electrode slurry: Place LiFePO4 sol in an ice-water bath and stir for 30 min. Add N-methylformamide dropwise to promote the gelation of LiFePO4 sol. During the gelation process, phase separation occurs. Polyethylene oxide is adsorbed on the surface of LiFePO4 oligomer through hydrogen bonds to form a polyethylene oxide-rich gel phase. The hydrophobic groups of polyethylene oxide lead to the formation of a water-rich solvent phase. After stirring for 2-4 h, a continuous phase-separated LiFePO4 gel composed of a polyethylene oxide-rich gel phase and a water-rich solvent phase is formed. Mix the prepared binder and conductive agent mixture slurry and the continuous phase-separated LiFePO4 gel at a weight ratio of 1:(1.5-3) and prepare a uniformly dispersed electrode slurry after planetary ball milling for 1-2 h. (4) Precision coating and forming of electrode sheets: The prepared electrode slurry is applied to aluminum foil by slit extrusion coating. A gasket is added between the upper and lower dies of the coating machine. The characteristic parameters of the inner edge of the gasket are convergence width L1 = exit width L4 * (1%~2%), convergence length L2 = convergence width L1 * (1.5~2.5), exit length L3 = convergence length L2 * (8~10), gasket thickness T = exit width L4 * (0.1~0.15%), and gasket surface roughness Ra0.

2. After drying and rolling, the precision coating and forming of the electrode sheet is completed. The thickness deviation of the electrode sheet is ≦4μm, the porosity is 30~40%, and the capacity retention rate after 100 cycles at 0.1C is 85%~95%.

2. The method for precision coating and forming of lithium-ion battery electrodes according to claim 1, further characterized in that: (1) When preparing LiFePO4 sol, the stirring rate was 100~150 r / min, and all chemical reagents used were of analytical grade; (2) The planetary ball mill speed is 250~400 r / min when preparing the slurry of binder and conductive agent mixture; (3) When preparing the electrode slurry, the rate of N-methylformyl addition is 1 mL / min, and the rotation speed of the planetary ball mill is 250~400 r / min; (4) The coating parameters for the precision coating of the electrode are: coating gap 90~110μm, foil movement speed 0.3~0.4m / s, inlet flow velocity 0.05~0.1m / s, and drying temperature 90~100℃.

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