Preparation method of high-compaction thick-electrode lithium iron phosphate battery

Abstract

The preparation method comprises the following steps: firstly, preparing a graphdiyne / porous aluminum oxide composite material, then adding the graphdiyne / porous aluminum oxide composite material into a negative electrode CMC (Carboxymethyl Cellulose) glue solution, uniformly dispersing, finally adding graphite and SBR (Styrene Butadiene Rubber), and uniformly stirring to prepare the high-compaction thick-electrode lithium iron phosphate battery. The porous alumina can improve the liquid absorption speed and liquid absorption amount of the pole piece, reduce the polarization internal resistance of the battery and prolong the cycle life of the battery. The ultrathin graphdiyne is coated on the surface of the porous aluminum oxide, so that the conductivity and the lubricity of the graphite material are improved, and the specific volume and the compaction of graphite are improved. According to the high-compaction thick-electrode lithium iron phosphate battery prepared by the technical scheme, the liquid absorption amount is improved by 2-3%, the direct-current internal resistance is reduced by 2-3%, and the cycle performance is improved by more than one time.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a preparation method of a high-compaction thick electrode lithium iron phosphate battery. Background Art

[0002] The lithium iron phosphate energy storage battery with safe and environmental protection characteristics has a very broad development prospect. Improving the energy density of the lithium iron phosphate battery can reduce the number of battery combinations, improve the space utilization rate, reduce the floor area, and lower the cost; similarly, improving the cycle life of the lithium iron phosphate battery can reduce the number of battery replacements or maintenance times, and can further reduce the cost, so as to meet the application requirements of high safety and low cost of the energy storage lithium battery. In order to improve the energy density of the lithium iron phosphate battery, people usually adopt the high-compaction thick electrode structure design. The high-compaction thick electrode can increase the proportion of active substances, thereby improving the energy density of the lithium iron phosphate battery. However, due to the tight filling of the internal material structure of the high-compaction thick electrode, it is difficult for the electrode to absorb the electrolyte, and the amount of electrolyte retained is insufficient, affecting the performance of the battery. Especially in the case of large current charge and discharge, the contact between the electrolyte and the interface is poor, the ion transport rate is low, and the concentration polarization inside the battery is large, affecting the rate and cycle performance of the battery.

[0003] Patents such as CN202411202615.2 and CN202410877746.4 respectively adopt the schemes of adding composite conductive agents or porous carbon to improve the liquid absorption and liquid retention effects. However, both the composite conductive agent and the porous carbon will increase the area of the negative electrode SEI film, accelerate the continuous dissolution and regeneration of lithium ions during battery storage and charge and discharge processes, and reduce the initial efficiency and calendar life of the lithium iron phosphate battery. How to improve the liquid absorption capacity of the high-compaction thick electrode without affecting the battery calendar life has become the key to the design of high specific energy and long cycle lithium iron phosphate batteries. Summary of the Invention

[0004] In view of the above problems, the present invention provides a preparation method of a high-compaction thick electrode lithium iron phosphate battery, which realizes improving the liquid absorption capacity of the high-compaction thick electrode lithium iron phosphate battery, and improving the rate performance and cycle life of the energy density lithium iron phosphate battery by increasing the lithium ion transport rate inside the battery.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: The preparation method of the high-compaction thick electrode lithium iron phosphate battery of the present invention includes the following steps: 1) First, prepare the graphdiyne / porous alumina composite material. Grind the porous alumina with a material diameter of 100 nm - 200 nm and a material pore diameter of 10 nm - 20 nm in a certain mass ratio with the ultra-thin graphdiyne with a thickness of 50 nm - 100 nm in a certain mass ratio, and then add the obtained uniform mixture into a certain amount of anhydrous ethanol solution and ultrasonically oscillate for 20 min - 30 min; 2) Stir the mixture at 70 °C - 80 °C until it becomes pasty. Finally, dry and grind the paste in an oven at 100 °C and then pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material. 3) Then add the graphdiyne / porous alumina composite material to the negative electrode CMC glue solution and disperse it evenly. Finally, add graphite and SBR and stir evenly to prepare a high-compaction thick electrode lithium iron phosphate battery.

[0006] According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, the graphdiyne / porous alumina composite material obtained in step 2) has no sealed blind holes and is an integrated structure stacked in a nano state. The average diameter of the stacked pores is 300 nm - 400 nm, and the average diameter of the mesopores is 100 nm - 200 nm. According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, the porous alumina and ultrathin graphdiyne are put into an agate mortar and ground for 20 min - 30 min.

[0007] According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, the stacking pore diameter of the raw material ultrathin graphdiyne is 200 nm - 300 nm.

[0008] According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, in step 1), the raw material porous alumina and ultrathin graphdiyne are mixed at a mass ratio of 5:3. The average diameter of the porous alumina is 160 nm, the average pore diameter is 20 nm, and the thickness of the graphdiyne is 50 - 100 nm.

[0009] According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, in step 1), the raw material porous alumina and ultrathin graphdiyne are put into an agate mortar and ground thoroughly for 30 min, and then the obtained uniform mixture is added to an anhydrous ethanol solution with the same weight as the mixture and ultrasonically oscillated for 30 min.

[0010] According to the preparation method of the high-compaction thick electrode lithium iron phosphate battery, in step 2), stir the mixture at 80 °C until it becomes pasty. Finally, dry and grind the paste in an oven at 100 °C and then pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material.

[0011] Reduce the use cost of the lithium iron phosphate battery and realize the application of the lithium iron phosphate battery with safety and environmental protection characteristics.

[0012] The advantages and effects of the present invention are: 1) The porous alumina is of nano size. Its nano-stacked integrated structure can be compressed, which will not affect the compaction density of the thick electrode, and can provide an electrolyte transmission channel for the high-compaction thick electrode, improve the liquid absorption efficiency and liquid absorption effect of the high-compaction thick electrode, increase the lithium ion transmission rate, and improve the cycle life of the lithium iron phosphate battery.

[0013] 2) Porous alumina has no closed blind holes, the average diameter of the stacked pores is 300nm-400nm, and the average diameter of the mesopores is 100nm-200nm. Lithium ions can be freely solvated and desolvated in the stacked pores and mesopores of porous alumina. When the battery is charging and discharging, lithium ions preferentially pass through mesopores with larger diameters. When the electrolyte is insufficient, the electrolyte in the mesopores of porous alumina can be effectively supplemented, thereby increasing the cycle life of the lithium iron phosphate battery.

[0014] 3) Porous alumina can improve the battery's ability to absorb and retain liquid, reduce the amount of carbon black added, and alleviate the problem of self-consumption of electricity caused by the large SEI film area caused by carbon black. Porous alumina is not conductive and does not participate in the formation of SEI film. The formation of more SEI film will not accelerate the uninterrupted dissolution and regeneration of lithium ions, thereby reducing the battery's initial efficiency and calendar life.

[0015] 4) Graphyne has excellent planar two-dimensional properties and an atomic-level porous structure. Ultra-thin Graphyne is coated on the surface of porous alumina, which improves the conductivity and lubricity of graphite materials, and improves the specific volume and compaction of graphite. The Graphyne stacking pore size is 200nm-300nm, which provides a channel for the electrolyte to enter the porous alumina mesopores without blocking the porous alumina mesopores, making the porous alumina mesopores have better liquid absorption and retention effects, effectively reducing the internal polarization of the battery.

[0016] 5) The high-density thick-electrode lithium iron phosphate battery prepared by this technical solution has a 2%-3% higher liquid absorption capacity, a 2%-3% lower DC internal resistance DCR, and a more than 1-fold increase in cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1C charge-discharge cycle comparison curve of 46120-28Ah-3.2V lithium iron phosphate battery prepared by the traditional process method and the method of the present invention in the embodiment. DETAILED DESCRIPTION

[0018] The specific contents of the present invention are further described below: The present invention uses graphyne / porous alumina as raw materials to prepare negative electrode materials for lithium iron phosphate batteries.

[0019] The specific preparation process of the present invention comprises the following steps: Firstly, a graphyne / porous alumina composite material is prepared, wherein a certain mass ratio of porous alumina with a material diameter of 100nm-200nm and a material pore size of 10nm-20nm and a certain mass ratio of ultra-thin graphyne with a thickness of 50nm-100nm are put into an agate mortar and fully ground for 20min-30min, and then the obtained uniform mixture is added into a certain amount of anhydrous ethanol solution and ultrasonically vibrated for 20min-30min; Stir the mixture at 70 °C - 80 °C until it becomes pasty. Finally, dry the paste in an oven at 100 °C, grind it, and pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material. The graphdiyne / porous alumina composite material has no closed blind holes and is a nano-packed integrated structure. The average diameter of the packed pores is 300 nm - 400 nm, and the average diameter of the mesopores is 100 nm - 200 nm; Then add the graphdiyne / porous alumina composite material to the negative electrode CMC colloidal solution and disperse it evenly. Finally, add graphite and SBR and stir evenly to prepare a high-compaction thick electrode lithium iron phosphate battery.

[0020] The porous alumina used in the present invention can improve the liquid absorption speed and liquid absorption capacity of the electrode sheet. Lithium ions can freely perform solvation and desolvation in the packed pores and mesopores of the porous alumina. During the charge and discharge of the battery, lithium ions preferentially pass through the mesopores with a larger diameter. When the electrolyte is insufficient, the electrolyte in the mesopores of the porous alumina can be effectively supplemented, improving the cycle life of the lithium iron phosphate battery. Graphdiyne has excellent planar two-dimensional characteristics and an atomic-level porous structure. The ultra-thin graphdiyne is coated on the surface of the porous alumina, improving the conductivity and lubricity of the graphite material, increasing the specific volume and compaction of the graphite. Moreover, the stacked pore diameter of the graphdiyne is 200 nm - 300 nm, providing a channel for the electrolyte to enter the mesopores of the porous alumina and not blocking the mesopores of the porous alumina, making the mesopores of the porous alumina have a better liquid absorption and liquid retention effect. The lithium iron phosphate battery with a high-compaction thick electrode prepared by this technical solution has a 2% - 3% increase in liquid absorption capacity, a 2% - 3% reduction in the direct current internal resistance DCR, and a more than doubled cycle performance.

[0021] Taking specific numbers as examples: Prepare a 46120 - 28Ah - 3.2V lithium iron phosphate battery. Design the surface density of the lithium iron phosphate positive electrode sheet to be 400 g / m 2 , the compaction density is 2.7 g / cc, and the surface density of the negative electrode sheet is 180 g / m 2 , the compaction density is 1.7 g / cc. Two schemes are used for comparison and verification of the negative electrode.

[0022] Scheme 1: Using the traditional process method, add 0.5% by mass of carbon nanotubes (LB126B - 23 of Jiangsu Tiannai Technology Co., Ltd.) and 0.5% by mass of acetylene black (HEXING Li - 2060 of Jiaozuo Hexing Chemical Industry Co., Ltd.) to the negative electrode CMC colloidal solution successively and disperse them evenly. Finally, add graphite and SBR and stir evenly to prepare a high-compaction thick electrode lithium iron phosphate battery.

[0023] Scheme 2: Using the inventive method, first prepare the graphdiyne / porous alumina composite material. Mix porous alumina (ATOP50, Suzhou Jinyi New Material Technology Co., Ltd.) and ultrathin graphdiyne (XFY07, Jiangsu Xianfeng Nano Material Technology Co., Ltd.) in a mass ratio of 5:3. The average diameter of the porous alumina is 160 nm, the average pore diameter is 20 nm, and the thickness of the graphdiyne is 50 - 100 nm. Put the two into an agate mortar and grind them thoroughly for 30 min. Then add the obtained uniform mixture to an anhydrous ethanol solution with the same weight as the mixture and ultrasonically oscillate for 30 min. Stir the mixture at 80 °C until it becomes pasty. Finally, dry the paste in an oven at 100 °C, grind it, and pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material. Then add the graphdiyne / porous alumina composite material to graphite and SBR and stir evenly to prepare a high-compaction thick electrode lithium iron phosphate battery.

[0024] The liquid absorption and DC internal resistance of the lithium iron phosphate batteries prepared by the two schemes are statistically as follows: The 1C charge-discharge cycle performance of the 46120-28Ah-3.2V lithium iron phosphate batteries prepared by the two schemes is as shown in the Figure 1 appendix. The liquid absorption of the high-compaction thick electrode lithium iron phosphate battery prepared by this technical scheme is increased by 2% - 3%, the DC internal resistance DCR is reduced by 2% - 3%, and the 1C charge-discharge cycle performance is increased by more than one time.

Claims

1. A preparation method of a high-compaction thick electrode lithium iron phosphate battery, characterized in that: Including the following steps: 1) First, prepare the graphdiyne / porous alumina composite material. Thoroughly grind porous alumina with a material diameter of 100 nm - 200 nm and a material pore diameter of 10 nm - 20 nm in a certain mass ratio with ultrathin graphdiyne with a thickness of 50 nm - 100 nm in a certain mass ratio. Then add the obtained uniform mixture into a certain amount of absolute ethanol solution and ultrasonically oscillate for 20 min - 30 min. 2) Stir the mixture at 70°C - 80°C until it becomes paste-like. Finally, dry the paste in an oven at 100°C, grind it, and pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material. 3) Then add the graphdiyne / porous alumina composite material into the negative electrode CMC colloidal solution and disperse it evenly. Finally, add graphite and SBR and stir evenly to prepare a high-compaction thick electrode lithium iron phosphate battery.

2. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, characterized in that: The graphdiyne / porous alumina composite material obtained in step 2) has no closed blind holes and is an integrated structure stacked in the nano state, with an average stacking pore diameter of 300 nm - 400 nm and an average mesopore diameter of 100 nm - 200 nm.

3. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, wherein: Put the porous alumina and ultrathin graphdiyne into an agate mortar and grind for 20 min - 30 min.

4. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, characterized in that: The stacking pore diameter of the raw material ultrathin graphdiyne is 200 nm - 300 nm.

5. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, characterized in that: In step 1), the raw material porous alumina and ultrathin graphdiyne are mixed in a mass ratio of 5:3, where the average diameter of the porous alumina is 160 nm, the average pore diameter is 20 nm, and the thickness of the graphdiyne is 50 - 100 nm.

6. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, characterized in that: In step 1), put the raw material porous alumina and ultrathin graphdiyne into an agate mortar and grind thoroughly for 30 min. Then add the obtained uniform mixture into an absolute ethanol solution with the same weight as the mixture and ultrasonically oscillate for 30 min.

7. The preparation method of the high-compaction thick electrode lithium iron phosphate battery according to claim 1, characterized in that: In step 2), stir the mixture at 80°C until it becomes paste-like. Finally, dry the paste in an oven at 100°C, grind it, and pass it through a 300-mesh sieve to obtain the graphdiyne / porous alumina composite material.

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