Positive electrode for improving safety of acupuncture test of lithium ion battery and preparation method of positive electrode

Abstract

The invention discloses a positive electrode for improving the safety of a lithium ion battery acupuncture test and a preparation method of the positive electrode. The positive electrode comprises the following components in percentage by mass: 35-50% of NMP (N-Methyl Pyrrolidone); 20%-80% of a lithium manganese iron phosphate material; 20%-50% of a ternary material; 20%-40% of a lithium manganate material; 0.8%-1.2% of a conductive agent; and 2%-2.5% of PVDF. According to the positive electrode for improving the safety of the acupuncture test of the lithium ion battery and the preparation method of the positive electrode, the positive electrode plate of the lithium ion battery is prepared through the working procedures of material doping, pulping, coating, rolling and the like, the positive electrode plate, the negative electrode and the diaphragm are assembled into a battery cell, the lithium ion battery is prepared, the electrical performance of the battery is qualified, and fire and explosion are avoided when the battery is subjected to acupuncture, heavy object impact and other tests; and the battery is ensured to be good in stability and high in safety in actual use.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode for improving the safety of lithium ion battery needle puncture test and a preparation method thereof. Background Art

[0002] The puncture test and heavy object impact test of lithium-ion batteries are a test method to evaluate the safety performance of batteries when subjected to external pressure. This test is crucial to ensure the safety of batteries in transportation, use, and accidental drops. The puncture test simulates the reaction of the battery when it is punctured and subjected to external high temperature by triggering thermal runaway. Test standards such as GB 38031~2020 specify specific test methods and acceptance criteria. The heavy object impact test usually simulates the reaction of the battery when it is directly impacted by a heavy object. Test standards such as ISO 6469~1 AMD:2022, UN R100 and GB 31241~2022 specify specific test methods and acceptance criteria. The puncture test and heavy object impact test will directly reflect safety issues such as battery deformation, rupture, leakage, and whether thermal runaway will be triggered.

[0003] In the prior art, lithium-ion batteries have the characteristics of high specific capacity, better low temperature resistance and higher operating voltage, which can ensure the performance and cycle life of lithium-ion batteries. However, the pass rate of lithium-ion batteries for needle puncture safety tests is low. Lithium iron phosphate / lithium manganese iron phosphate batteries with high safety performance, long cycle life and low cost have a high pass rate for needle puncture safety tests, but they have the defects of low specific capacity, sensitivity to low temperature and relatively low operating voltage. Summary of the invention

[0004] The purpose of the present invention is to provide a positive electrode and a preparation method thereof for improving the safety of a lithium ion battery needle puncture test. Through material doping, pulping, coating, rolling and other processes, a lithium ion battery positive electrode sheet is prepared, and it is assembled with a negative electrode and a separator into a battery cell to prepare a lithium ion battery. The battery has qualified electrical performance and does not catch fire or explode when subjected to needle puncture, heavy object impact and other tests, thereby ensuring that the battery has good stability and high safety when actually used.

[0005] To achieve the above object, the present invention provides a positive electrode for improving the safety of lithium-ion battery puncture test, comprising the following components by mass fraction: NMP 35%~50%; Lithium manganese iron phosphate material 20%~80%; Ternary materials 20%~50%; Lithium manganate material 20%~40%; Conductive agent 0.8%~1.2%; PVDF 2%~2.5%.

[0006] Preferably, the lithium manganese iron phosphate material includes Mn and Fe, and the mass ratio of Mn to Fe in the lithium manganese iron phosphate material is Mn:Fe=6:4.

[0007] Preferably, the ternary material includes Ni, Co and Mn, and the mass ratio of the ternary material is one of Ni:Co:Mn=5:2:3, Ni:Co:Mn=8:1:1 or Ni:Co:Mn=9:0.5:0.5.

[0008] Preferably, the mass ratio of the ternary material, the lithium manganese oxide material and the lithium iron manganese phosphate material is 48:24:28, and the mass ratio of the ternary material is Ni:Co:Mn=5:2:3.

[0009] Preferably, the mass ratio of the ternary material, the lithium manganate material and the lithium iron manganese phosphate material is 25:35~40:35~40, and the mass ratio of the ternary material is Ni:Co:Mn=8:1:1.

[0010] Preferably, the mass ratio of the ternary material, the lithium manganate material and the lithium iron manganese phosphate material is 20:35:45, and the mass ratio of the ternary material is Ni:Co:Mn=9:0.5:0.5.

[0011] Preferably, the conductive agent is one or both of carbon nanotubes (CNTs) and conductive carbon black.

[0012] To achieve the above object, the present invention also provides a method for preparing a positive electrode for improving the safety of a lithium ion battery puncture test, comprising the following steps: Step 1: Add NMP and PVDF according to mass fraction and stir evenly to obtain a base liquid; Step 2: Add conductive agent according to mass fraction and stir evenly; Step 3: Evenly mix the ternary material, the lithium manganate material and the lithium iron manganese phosphate material according to the mass ratio to obtain an active material; Step 4: Add the conductive agent obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, stir evenly, and obtain a positive electrode slurry; Step 5: coating: the positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate through a coating device; Step 6: Rolling: Drying, automatic deviation correction by a tension device, and then rolling up to obtain the positive electrode sheet.

[0013] Preferably, the stirring adopts a vacuum stirring tank with a vacuum degree of -0.090±0.005Mpa, and the vacuum stirring tank is first stirred at a speed of 10rpm for 10min, and then the speed is increased and stirred for 30~120min after the barrel is lowered and the material is scraped.

[0014] Therefore, the present invention adopts the above-mentioned positive electrode for improving the safety of lithium-ion battery needle puncture test and the preparation method thereof, and the beneficial effects are as follows: (1) The present invention uses lithium manganese iron phosphate, which has an olivine crystal structure. During the charging process, even if all lithium ions are released, the structure will not collapse, thereby ensuring the safety performance of the battery.

[0015] (2) The present invention prepares a lithium-ion battery positive electrode sheet through processes such as material doping, pulping, coating, and rolling, and assembles it into a battery cell with a negative electrode and a separator to prepare a lithium-ion battery having PO4 tetrahedrons connected by strong PO covalent bonds, making it difficult for O atoms to escape from the structure, further enhancing its stability and safety.

[0016] (3) The lithium-ion battery prepared by the present invention has qualified electrical performance and does not catch fire or explode in tests such as needle puncture and heavy object impact, thereby ensuring that the battery has good stability and high safety when actually used.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The diagram is a diagram showing the effects of a positive electrode for improving the safety of a lithium-ion battery acupuncture test and an embodiment of a preparation method thereof before and after acupuncture testing of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further illustrated by the following examples.

[0020] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0021] Embodiment 1 A method for preparing a positive electrode for improving the safety of a lithium-ion battery needle puncture test comprises the following steps: Step 1. Material doping: add 40% NMP and 2.5% PVDF according to the mass fraction, set the revolution speed of the vacuum stirring tank to 10rpm, the time to 10min, increase the revolution speed to 35rpm, the dispersion speed to 3500rpm, the time to 30min, lower the barrel to scrape the material, the revolution speed is 35rpm, the dispersion speed is 3500rpm, the time is 80min, the vacuum degree is -0.090±0.005Mpa, stir evenly, and obtain the base liquid.

[0022] Step 2, material doping: add 1.1% carbon nanotubes CNTs, set the vacuum stirring tank revolution speed to 10rpm, time to 10min, lower the barrel to scrape the material, lift the revolution speed to 40rpm, the dispersion speed to 4000rpm, time to 50min, the vacuum degree to -0.090±0.005Mpa, and stir evenly.

[0023] Step 3: Material doping: Evenly mix the ternary material (Ni:Co:Mn=5:2:3), lithium manganese oxide material and lithium iron manganese phosphate material (Mn:Fe=6:4) in a mass ratio of 48:24:28 to obtain an active material.

[0024] Step 4, slurry preparation: add the carbon nanotubes CNTs obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, set the orbital speed of the vacuum stirring tank to 10 rpm, the time to 10 min, lower the barrel to scrape the material, raise the orbital speed to 40 rpm, the dispersion speed to 4000 rpm, the time to 120 min, the vacuum degree to -0.090 ± 0.005 MPa, stir evenly, and obtain the positive electrode slurry.

[0025] Step 5: Coating: The positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate (Al foil) through a coating device. The coated positive electrode surface density is 19.55 mg / cm².

[0026] Step 6: Rolling: Drying, tension control by tension device, automatic deviation correction and then rolling to obtain the positive electrode sheet.

[0027] Embodiment 2 A method for preparing a positive electrode for improving the safety of a lithium-ion battery needle puncture test comprises the following steps: Step 1. Material doping: add 40% NMP and 2% PVDF according to the mass fraction, set the revolution speed of the vacuum stirring tank to 10rpm and the time to 10min, increase the revolution speed to 35rpm, the dispersion speed to 3500rpm, the time to 30min, lower the barrel to scrape the material, the revolution speed is 35rpm, the dispersion speed is 3500rpm, the time is 80min, the vacuum degree is -0.090±0.005Mpa, stir evenly to obtain the base liquid.

[0028] Step 2. Material doping: add 0.8% conductive carbon black, set the vacuum stirring tank's revolution speed to 10rpm, the time to 10min, lower the barrel to scrape the material, raise the revolution speed to 40rpm, the dispersion speed to 4000rpm, the time to 50min, the vacuum degree to -0.090±0.005Mpa, and stir evenly.

[0029] Step 3: Material doping: Evenly mix the ternary material (Ni:Co:Mn=8:1:1), lithium manganese oxide material and lithium iron manganese phosphate material (Mn:Fe=6:4) in a mass ratio of 25:35:40 to obtain an active material.

[0030] Step 4, slurry preparation: add the conductive carbon black obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, set the orbital speed of the vacuum stirring tank to 10 rpm, the time to 10 min, lower the barrel to scrape the material, raise the orbital speed to 40 rpm, the dispersion speed to 4000 rpm, the time to 120 min, the vacuum degree to -0.090 ± 0.005 MPa, stir evenly, and obtain the positive electrode slurry.

[0031] Step 5: Coating: The positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate (Al foil) through a coating device. The coated positive electrode surface density is 19.55 mg / cm².

[0032] Step 6: Rolling: Drying, tension control by tension device, automatic deviation correction and then rolling to obtain the positive electrode sheet.

[0033] Embodiment 3 A method for preparing a positive electrode for improving the safety of a lithium-ion battery needle puncture test comprises the following steps: Step 1. Material doping: add 40% NMP and 2% PVDF according to the mass fraction, set the revolution speed of the vacuum stirring tank to 10rpm and the time to 10min, increase the revolution speed to 35rpm, the dispersion speed to 3500rpm, the time to 30min, lower the barrel to scrape the material, the revolution speed is 35rpm, the dispersion speed is 3500rpm, the time is 80min, the vacuum degree is -0.090±0.005Mpa, stir evenly to obtain the base liquid.

[0034] Step 2, material doping: add 1.1% carbon nanotubes CNTs, set the vacuum stirring tank revolution speed to 10rpm, time to 10min, lower the barrel to scrape the material, lift the revolution speed to 40rpm, the dispersion speed to 4000rpm, time to 50min, the vacuum degree to -0.090±0.005Mpa, and stir evenly.

[0035] Step 3: Material doping: Evenly mix the ternary material (Ni:Co:Mn=8:1:1), lithium manganese oxide material and lithium iron manganese phosphate material (Mn:Fe=6:4) in a mass ratio of 25:40:35 to obtain an active material.

[0036] Step 4, slurry preparation: add the carbon nanotubes CNTs obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, set the orbital speed of the vacuum stirring tank to 10 rpm, the time to 10 min, lower the barrel to scrape the material, raise the orbital speed to 40 rpm, the dispersion speed to 4000 rpm, the time to 120 min, the vacuum degree to -0.090 ± 0.005 MPa, stir evenly, and obtain the positive electrode slurry.

[0037] Step 5: Coating: The positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate (Al foil) through a coating device. The coated positive electrode surface density is 19.55 mg / cm².

[0038] Step 6: Rolling: Drying, tension control by tension device, automatic deviation correction and then rolling to obtain the positive electrode sheet.

[0039] Embodiment 4 A method for preparing a positive electrode for improving the safety of a lithium-ion battery needle puncture test comprises the following steps: Step 1. Material doping: add 40% NMP and 2.5% PVDF according to the mass fraction, set the revolution speed of the vacuum stirring tank to 10rpm, the time to 10min, increase the revolution speed to 35rpm, the dispersion speed to 3500rpm, the time to 30min, lower the barrel to scrape the material, the revolution speed is 35rpm, the dispersion speed is 3500rpm, the time is 80min, the vacuum degree is -0.090±0.005Mpa, stir evenly, and obtain the base liquid.

[0040] Step 2. Material doping: add 0.8% conductive carbon black, set the vacuum stirring tank's revolution speed to 10rpm, the time to 10min, lower the barrel to scrape the material, raise the revolution speed to 40rpm, the dispersion speed to 4000rpm, the time to 50min, the vacuum degree to -0.090±0.005Mpa, and stir evenly.

[0041] Step 3. Material doping: Mix the ternary material (Ni:Co:Mn=9:0.5:0.5), lithium manganese oxide material and lithium iron manganese phosphate material (Mn:Fe=6:4) in a mass ratio of 20:35:45 to obtain an active material.

[0042] Step 4, slurry preparation: add the conductive carbon black obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, set the orbital speed of the vacuum stirring tank to 10 rpm, the time to 10 min, lower the barrel to scrape the material, raise the orbital speed to 40 rpm, the dispersion speed to 4000 rpm, the time to 120 min, the vacuum degree to -0.090 ± 0.005 MPa, stir evenly, and obtain the positive electrode slurry.

[0043] Step 5: Coating: The positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate (Al foil) through a coating device. The coated positive electrode surface density is 19.55 mg / cm².

[0044] Step 6: Rolling: Drying, tension control by tension device, automatic deviation correction and then rolling to obtain the positive electrode sheet.

[0045] Embodiment 5 The preparation of a negative electrode sheet for a lithium-ion battery comprises the following steps: S1. Add CMC and deionized water, set the revolution speed of the vacuum stirring tank to 10 rpm, the time to 10 min, increase the revolution speed to 35 rpm, the dispersion speed to 3500 rpm, the time to 30 min, lower the barrel to scrape the material, the revolution speed to 35 rpm, the dispersion speed to 3500 rpm, the time to 80 min, the vacuum degree to -0.090 ± 0.005 MPa, stir evenly to obtain the base liquid.

[0046] S2. Add conductive agent, set the revolution speed of the vacuum stirring tank to 30rpm, the time to 10min, lower the barrel to scrape the material, raise the revolution speed to 35rpm, the dispersion speed to 3500rpm, the time to 50min, the vacuum degree to -0.090±0.005Mpa, and stir evenly.

[0047] S3, slurry preparation: add the active material and the conductive agent obtained in S2 to the base liquid obtained in S1, set the orbital speed of the vacuum stirring tank to 10 rpm, the time to 10 min, lower the barrel to scrape the material, raise the orbital speed to 35 rpm, the dispersion speed to 3500 rpm, the time to 120 min, the vacuum degree to -0.090±0.005 MPa, and stir evenly; then add SBR, the orbital speed is 35 rpm, the dispersion speed is 2500 rpm, the time is 30 min, the vacuum degree is -0.090±0.005 MPa, and stir evenly to obtain the negative electrode slurry.

[0048] S4, coating: The negative electrode slurry obtained in S2 is pumped into the intermediate material tank through a liquid supply pump, and then the negative electrode slurry is evenly coated on the surface of the substrate (Cu foil) through a coating device. The coated negative electrode surface density is 9.16 mg / cm² and the NP ratio is 1.06.

[0049] S5, rolling: drying, tension control by tension device, automatic deviation correction and then rolling up to obtain negative electrode sheet.

[0050] Experimental Testing The positive electrode sheets prepared in Examples 1 to 4 were assembled into cells with the separator and the negative electrode sheet prepared in Example 5 to prepare lithium ion batteries, namely lithium ion battery I, lithium ion battery II, lithium ion battery III, and lithium ion battery IV. The above four lithium ion batteries were used to conduct acupuncture safety tests with commercially available lithium iron manganese phosphate batteries and commercially available ternary lithium ion batteries.

[0051] The test method is as follows: a) Needle material: steel; b) Needle diameter: 5mm; c) Needle tip shape: conical, angle 45°; d) Needle puncture speed: 25 mm / s; e) Acupuncture position and direction: The needle is perpendicular to the direction of the electrode; f) Needle penetration stop conditions: internal heating until thermal runaway; or the needle penetration depth reaches 90% of the triggered battery cell.

[0052] In addition, in order to avoid the test results being affected by the exhaust from the puncture holes, the puncture holes in the battery pack are sealed. Figure 1 As shown, (a) is a sealed lithium-ion battery II, (b) is a sealed ternary lithium-ion battery, (c) is a rendering of the sealed lithium-ion battery II after testing, and (d) is a rendering of the sealed ternary lithium-ion battery after testing. The specific test results are shown in Table 1.

[0053] Table 1. Battery puncture test results

[0054] The positive electrode sheets prepared in Examples 1 to 4 were assembled into cells with the separator and the negative electrode sheet prepared in Example 5 to prepare lithium ion batteries, namely lithium ion battery I, lithium ion battery II, lithium ion battery III, and lithium ion battery IV. The above four lithium ion batteries were used to conduct a heavy object impact safety test with commercially available lithium iron manganese phosphate batteries and commercially available ternary lithium ion batteries.

[0055] The test method is as follows: After the battery is fully charged according to the prescribed test method, place the battery on the platform surface and place a metal rod with a diameter of 15.8mm±0.2mm horizontally on the upper surface of the geometric center of the battery. Use a weight with a mass of 9.1kg±0.1kg to hit the battery surface with the metal rod in a free fall state from a height of 610mm±25mm and observe for 6h.

[0056] It is required that during the impact test of cylindrical batteries, the longitudinal axis of the battery should be parallel to the surface of the weight, and the metal rod should be perpendicular to the longitudinal axis of the battery and as parallel to the impact surface as possible. The test results are shown in Table 2.

[0057] Table 2. Battery Heavy Object Impact Safety Test Results

[0058] In summary, the lithium-ion batteries prepared using the positive electrode sheets prepared in Examples 1 to 4 have qualified electrical performance and do not catch fire or explode in tests such as needle puncture and heavy object impact, ensuring that the batteries have good stability and high safety in actual use.

[0059] Therefore, the present invention adopts the above-mentioned positive electrode and preparation method for improving the safety of lithium-ion battery needle puncture test, and prepares the positive electrode sheet of lithium-ion battery through material doping, pulping, coating, rolling and other processes, and assembles it with the negative electrode and the separator into a battery cell to prepare a lithium-ion battery. The battery has qualified electrical performance and does not catch fire or explode during needle puncture, heavy object impact and other tests, ensuring that the battery has good stability and high safety when used in actual use.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A positive electrode for improving the safety of lithium-ion battery puncture test, characterized in that: Includes the following mass fraction components: NMP 35%~50%; Lithium manganese iron phosphate material 20%~80%; Ternary materials 20%~50%; Lithium manganate material 20%~40%; Conductive agent 0.8%~1.2%; PVDF 2%~2.5%.

2. A positive electrode for improving the safety of lithium-ion battery puncture test according to claim 1, characterized in that: The lithium manganese iron phosphate material includes Mn and Fe, and the mass ratio of Mn to Fe in the lithium manganese iron phosphate material is Mn:Fe=6:

4.

3. A positive electrode for improving the safety of lithium-ion battery puncture test according to claim 1, characterized in that: The ternary material includes Ni, Co and Mn, and the mass ratio of the ternary material is one of Ni:Co:Mn=5:2:3, Ni:Co:Mn=8:1:1 or Ni:Co:Mn=9:0.5:0.

5.

4. A positive electrode for improving the safety of lithium-ion battery puncture test according to claim 3, characterized in that: The mass ratio of the ternary material, the lithium manganate material and the lithium iron manganese phosphate material is 48:24:28, and the mass ratio of the ternary material is Ni:Co:Mn=5:2:

3.

5. The positive electrode for improving the safety of lithium-ion battery puncture test according to claim 3, characterized in that: The mass ratio of the ternary material, the lithium manganate material and the lithium iron manganese phosphate material is 25:35-40:35-40, and the mass ratio of the ternary material is Ni:Co:Mn=8:1:

1.

6. A positive electrode for improving the safety of lithium-ion battery puncture test according to claim 3, characterized in that: The mass ratio of the ternary material, the lithium manganate material and the lithium iron manganese phosphate material is 20:35:45, and the mass ratio of the ternary material is Ni:Co:Mn=9:0.5:0.

5.

7. A positive electrode for improving the safety of lithium-ion battery puncture test according to claim 1, characterized in that: The conductive agent is one or both of carbon nanotubes (CNTs) and conductive carbon black.

8. A method for preparing a positive electrode for improving the safety of a lithium ion battery puncture test according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Add NMP and PVDF according to mass fraction and stir evenly to obtain a base liquid; Step 2: Add conductive agent according to mass fraction and stir evenly; Step 3, uniformly mixing the ternary material, the lithium manganate material and the lithium iron manganese phosphate material according to the mass ratio to obtain an active material; Step 4: Add the conductive agent obtained in step 2 and the active material obtained in step 3 to the base liquid obtained in step 1, stir evenly, and obtain a positive electrode slurry; Step 5: coating: the positive electrode slurry obtained in step 4 is pumped into the intermediate material tank through a liquid supply pump, and then the positive electrode slurry is evenly coated on the surface of the substrate through a coating device; Step 6: Rolling: Drying, automatic deviation correction by a tension device, and then rolling up to obtain the positive electrode sheet.

9. A method for preparing a positive electrode for improving the safety of a lithium-ion battery needle penetration test according to claim 8, characterized in that: The stirring adopts a vacuum stirring tank with a vacuum degree of -0.090±0.005Mpa. The vacuum stirring tank is first stirred at a speed of 10rpm for 10min, and then the speed is increased to stir for 30~120min after the barrel is lowered and the material is scraped.

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