Preparation method of composite manganese series 5Ah cylindrical battery with high energy density and high safety

Abstract

The invention relates to the technical field of cylindrical batteries, and discloses a preparation method of a high-energy-density and high-safety composite manganese series 5Ah cylindrical battery, which comprises the following steps: step 1, tabletting, drying and slitting to obtain a positive plate; step 2, tabletting, drying and slitting to obtain a negative plate; step 3, winding to obtain a winding core; step 4, then carrying out steel shell slot rolling, electrolyte injection, cap sealing and sleeve film cleaning to complete battery cell assembly; and step 5, after the battery cell is assembled, carrying out first standing, formation, second standing and capacity grading to obtain a final product. According to the cylindrical battery prepared by the invention, the lithium intercalation capacity of the negative electrode is greatly improved after silicon carbon with high specific capacity is mixed in graphite, the space is saved, the surface density of the positive electrode can be remarkably improved, and the composite manganese cell can achieve relatively high energy density under the condition that the positive electrode is not mixed with nickel cobalt lithium manganate, and the energy density is 10-20% higher than that of a lithium iron phosphate cell.

Description

Technical Field

[0001] This invention relates to the field of cylindrical battery technology, specifically to a method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery. Background Technology

[0002] Currently, lithium iron phosphate cells have become the mainstream product due to their advantages such as high safety, long lifespan, and low cost, but they also face the bottleneck of low energy density.

[0003] To improve the energy density of the battery cell, lithium iron phosphate (LFP), doped with manganese, is used as the active material in the cathode. The high voltage plateau of LFP effectively increases the cell's energy density, but it also suffers from poor conductivity, low compaction, a dual plateau, and manganese dissolution. To mitigate these drawbacks, it needs to be blended with lithium manganese oxide or ternary lithium-ion batteries. Blending with ternary lithium-ion batteries can further improve the cell's energy density, but the instability of ternary materials significantly compromises the cell's safety performance. Blending with lithium manganese oxide, with its relatively low specific capacity, limits the improvement in energy density. Therefore, adjustments need to be made to the cell design to ensure that energy density is increased while maintaining safety.

[0004] Silicon-carbon anode materials have a high specific capacity (reversible lithium intercalation capacity ≥1800mAh / g), but they also have the disadvantage of large volume expansion. Therefore, by mixing a small amount of silicon-carbon with graphite, the lithium intercalation capacity of the anode can be greatly improved, the density of the anode coating can be effectively reduced, the internal space of the cell can be saved, and the expansion can be controlled within a certain range. This leaves more space for the positive electrode to increase the proportion of active material, thereby achieving the goal of improving the energy density of the cell. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery, in order to solve the problems mentioned in the background art.

[0006] To address the above problems, this invention provides a method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery, comprising the following steps: Step 1: Mix the active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone in a certain proportion and stir to prepare a positive electrode slurry; coat the prepared positive electrode slurry onto a carbon-coated aluminum foil current collector, and then press, dry, and slit to obtain a positive electrode sheet; Step 2: Mix artificial graphite, silicon carbide material, conductive carbon black, aqueous conductive paste, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water in a certain proportion and stir to prepare a negative electrode paste; coat the prepared negative electrode paste onto a copper foil current collector; and obtain a negative electrode sheet by pressing, drying, and slitting. Step 3: Cut the positive and negative electrode sheets, weld the tabs at the gaps, and attach protective tape to the tabs to make the positive and negative electrode sheets. Stack the negative electrode sheet, ceramic diaphragm, positive electrode sheet, and ceramic diaphragm in sequence and wind them to make the core. Step 4: Place the core in the steel shell, the negative electrode tab passes through the lower insulating sheet and is welded to the bottom of the cylindrical steel shell, and the positive electrode tab passes through the upper insulating sheet and is welded to the cap. Then, perform steel shell grooving, electrolyte injection, cap sealing, and cleaning of the diaphragm to complete the cell assembly. Step 5: After assembling the battery cells, the final product is obtained after resting for 1, forming, resting for 2, and capacity testing.

[0007] In step 1, the active material includes lithium manganese iron phosphate and lithium manganese oxide, which are mixed in a mass ratio of 20-50:50-80. The lithium manganese iron phosphate has a manganese iron element molar ratio of 6-7:3-4, and a reversible specific capacity of >148mAh / g at 0.1C within a voltage range of 2.5-4.35V. The lithium manganese oxide has a reversible specific capacity of >110mAh / g at 0.1C within a voltage range of 3.0-4.35V.

[0008] In step 1, the mass ratio of the active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone is 95-96: 0.8-1.2: 0.3-0.8: 2.5-3: 45-50.

[0009] In step 1, the positive electrode slurry is coated onto the carbon-coated aluminum foil current collector using a double-sided gap coating method, with a single-sided surface density of 250–280 g / m³. 2 The coating width is 300-1000mm, the longitudinal coating length of a single piece is 1200-1600mm, and the gap length is 7-15mm. Among them, the carbon-coated aluminum foil is a double-sided carbon-coated aluminum foil with a thickness of 10-15μm; The thickness of the positive electrode sheet after compression is 230-250μm, the width of the positive electrode sheet after slitting is 60-65mm, and the moisture content of the electrode roll after baking is ≤200ppm.

[0010] In step 2, the artificial graphite has a 0.1C reversible specific capacity ≥ 340 mAh / g, a particle size of 2-30 μm, a Dv50 of 10-20 μm, and a specific surface area of ​​1.0-2.0 m². 2 / g; The silicon-carbon material has a 0.1C reversible specific capacity ≥1800mAh / g.

[0011] In step 2, the mass ratio of the artificial graphite, silicon carbide material, conductive carbon black, aqueous conductive slurry, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water is 80-85: 12-15: 0.8-1.2: 0.1-0.3: 1.2-1.8: 1.2-1.8: 0.3-0.8: 75-80.

[0012] In step 2, the negative electrode slurry is coated onto the negative electrode copper foil current collector. The copper foil thickness is 5-8 μm, and the coating is applied using a double-sided gap coating method, with a single-sided surface density of 50-80 g / m². 2 The coating width is 300-1000mm, the longitudinal coating length of a single piece is 1280-1680mm, and the gap length is 20-40mm. The thickness of the negative electrode sheet after compression is 70-100μm, the width of the negative electrode sheet after slitting is 62-67mm, and the moisture content of the electrode roll after baking is ≤200ppm.

[0013] In step 3, when cutting the positive electrode sheet, the gap must be at 1 / 3-1 / 2 of the electrode sheet length. One positive electrode tab is provided and welded to the gap. The positive electrode tab is made of aluminum strip with a width of 3-6mm and a thickness of 0.1-0.2mm. The negative electrode sheet is cut in the middle of the gap position. Two negative electrode tabs are provided. The gap positions at both ends of the cut electrode sheet are welded together. The negative electrode tabs are made of either nickel strip or copper-nickel composite strip, with a width of 3-5mm and a thickness of 0.05-0.15mm. The base membrane of the ceramic diaphragm is made of either polyethylene or polypropylene, with a porosity of 35-50%. It is coated with alumina and / or boehmite on both sides and / or one side. The diaphragm thickness is 7-20 μm, the length is 1350-1800 mm, and the width is 65-70 mm.

[0014] In step 4, the electrolyte is prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 20-25:10-15:35-40 as an organic solvent, dissolving 1.0-1.2 mol of lithium hexafluorophosphate in the mixed organic solvent, adding vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and lithium bis(oxalato)borate as additives, and adding ethoxypentafluorocyclotriphosphazene flame retardant. The additives account for 5% of the mass of the electrolyte, and the mass ratio of vinylene carbonate, fluorovinyl carbonate, 1,3-propanesulfonate lactone, and lithium bis(oxalato)borate is 1:1:1:1. The flame retardant ethoxypentafluorocyclotriphosphazene accounts for 8-15% of the mass of the electrolyte; The amount of electrolyte injected is 12-15g; The steel shell is made of nickel-plated stainless steel with a thickness of 0.2-0.5mm. The assembled battery cell has a height of 70-72mm and a diameter of 26.0-6.5mm.

[0015] In step 5, the settling process includes two processes: settling 1 and settling 2. Standing temperature 1: 30-45℃, time: 12-48h; Standing temperature 2: 15-45℃, time: 0-7 days; The formation process is a step-charging process, which requires the charging current to gradually increase. First, charge with a current of 0.1C, then charge with currents of 0.25C and 0.5C, and finally end with a constant voltage charging of 0.25C. The constant voltage charging voltage is set to 4.2V and the cutoff current is set to 0.02C. The capacity grading process is the process of completing a full discharge, specifically: first, discharge at 1C to 2.7V, then discharge at 0.3C to 2.7V, then charge at 0.5C with constant current and constant voltage to 4.2V, then discharge at 0.5C with constant current to 2.7V, and finally charge the cell at 0.5C to 40-50% SOC.

[0016] Compared with the prior art, the beneficial effects of the present invention are: In the cylindrical battery prepared by this invention, the lithium intercalation capacity of the negative electrode is significantly improved by doping high-specific-capacity silicon-carbon into graphite. The space saved can significantly increase the areal density of the positive electrode. The composite manganese-based cell can achieve a high energy density without doping lithium nickel cobalt manganese oxide in the positive electrode, which is 10%-20% higher than that of lithium iron phosphate cells. At the same time, it has a safety advantage over cells with lithium nickel cobalt manganese oxide doped in the positive electrode. In addition, the use of ceramic film improves the cell's resistance to thermal runaway. The use of flame-retardant electrolyte reduces the risk of combustion and explosion of the cell and further improves the cell's safety performance. Through this differentiated positive and negative electrode combination, the composite manganese-based cell has both high energy density and high safety. Attached Figure Description

[0017] Figure 1 These are images of a battery cell needle penetration test according to Embodiment 1 of the present invention; Figure 2 These are images of the battery cell needle penetration test in Comparative Example 1 of this invention; Figure 3 The image shows a battery cell needle penetration test result from Comparative Example 2 of this invention. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1

[0020] A method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery includes the following steps: Step 1: Lithium manganese oxide, lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone are mixed in a ratio of 67:28.7:1:0.5:2.8:49 and stirred to prepare a positive electrode slurry. The lithium manganese iron phosphate has a reversible specific capacity of 150.8 mAh / g at 0.1C within a voltage range of 2.5-4.35V; the lithium manganese oxide has a reversible specific capacity of 118 mAh / g at 0.1C within a voltage range of 3.0-4.35V. The prepared positive electrode slurry is coated onto a carbon-coated aluminum foil current collector using a double-sided gap coating method, with a single-sided areal density of 269 g / m². 2 The coating has a transverse width of 634 mm, a longitudinal coating length of 1380 mm per sheet, and a gap length of 10 mm. The positive electrode sheet is then rolled to 240 μm and then cut into positive electrode sheets with a width of 62.5 mm. After cutting, the sheets are placed in an oven at 90°C for vacuum baking until the moisture content of the electrode roll is ≤200 ppm. Step 2: Mix artificial graphite, silicon carbide material, conductive carbon black, aqueous conductive slurry, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water in a ratio of 81:14.3:1:0.2:1.5:1.5:0.5:77 and stir to prepare a negative electrode slurry; wherein the artificial graphite has a 0.1C reversible specific capacity of 355 mAh / g, a particle size of 10 μm, a Dv50 of 15 μm, and a specific surface area of ​​1.5 m². 2 / g; the reversible specific capacity of silicon-carbon material at 0.1C is 1826mAh / g; the prepared negative electrode slurry is coated onto a 6μm copper foil current collector; the coating is a double-sided gap coating with a single-sided areal density of 60g / m². 2 The coating width is 648mm, the longitudinal coating length of a single sheet is 1457mm, and the gap length is 30mm. Then the negative electrode sheet is rolled to 80μm, and then it is cut into negative electrode sheets with a width of 64mm. After cutting, it is placed in an oven at 100℃ for vacuum baking until the moisture content of the electrode roll is ≤200ppm. Step 3: Cut the positive and negative electrode sheets. When cutting the positive electrode sheet, ensure the gap is at 1 / 3 of the electrode sheet length. Provide one positive electrode tab, welded to the gap. The positive electrode tab is made of aluminum strip, 5mm wide and 0.15mm thick. Cut the negative electrode sheet in the middle of the gap. Provide two negative electrode tabs, welded to the gaps at both ends of the cut electrode sheet. The negative electrode tab is made of copper-nickel composite strip, 4mm wide and 0.08mm thick. Stack the negative electrode sheet, ceramic separator, positive electrode sheet, and ceramic separator in sequence and wind them to form a core. The ceramic separator base film is made of polyethylene with a porosity of 40%, coated with alumina on both sides, 10μm thick, 1550mm long, and 68mm wide. Step 4: Place the core in the steel shell, weld the negative electrode tab through the lower insulating sheet to the bottom of the cylindrical steel shell, and weld the positive electrode tab through the upper insulating sheet to the cap. Then, perform steel shell grooving, electrolyte injection, cap sealing, and cleaning of the diaphragm to complete the cell assembly. The electrolyte injection volume is 14g, the steel shell is stainless steel plated with nickel, and the height of the assembled cell is 71±0.2mm. Step 5: After assembling the battery cells, they undergo a settling period of 1 hour at 45°C for 48 hours. After settling period 1, the cells are cooled to room temperature for formation. The formation process involves a stepped charging process, requiring the charging current to gradually increase: first, a 0.1C current charge, then 0.25C, then 0.5C, and finally a 0.25C constant voltage charge. The constant voltage charging voltage is set to 4.2V, and the cutoff current is set to 0.02C. The formed cells then undergo a settling period of 2 hours at 25°C for 72 hours. After settling period 2, the cells are then subjected to capacity testing. This process involves completing a full discharge cycle: first, a 1C discharge to 2.7V, then a 0.3C discharge to 2.7V, then a 0.5C constant current and constant voltage charge to 4.2V, then a 0.5C constant current discharge to 2.7V, and finally a 0.5C charge to 50% SOC. After capacity testing, the final product is obtained.

[0021] Comparative Example 1 A method for preparing a highly safe 5Ah lithium-ion cylindrical battery includes the following steps: Step 1. Mix lithium iron phosphate cathode material, carbon nanotube conductive paste, polyvinylidene fluoride, and N-methylpyrrolidone in a ratio of 97.2:0.8:28:48 and stir to prepare a cathode paste; the lithium iron phosphate used has a reversible specific capacity of >158mAh / g at 0.1C within a voltage range of 2-3.65V. Coat the prepared cathode paste onto the cathode current collector aluminum foil using a double-sided gap coating method, with a single-sided areal density of 213g / m². 2The coating has a transverse width of 634 mm, a longitudinal coating length of 1380 mm per sheet, and a gap length of 10 mm. The positive electrode sheet is then rolled to 183 μm and then slit into 62.5 mm wide electrode rolls. After slitting, the rolls are placed in an oven at 90 °C for vacuum baking until the moisture content is ≤200 ppm.

[0022] Step 2. Artificial graphite, conductive carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water are mixed in a ratio of 96.5:0.5:1.6:1.4:86.2 and stirred to prepare a negative electrode slurry. The 0.1C reversible specific capacity of the graphite used is 355 mAh / g. The prepared negative electrode slurry is coated onto a 6 μm copper foil current collector using a double-sided gap coating method, with a single-sided areal density of 97.3 g / m². 2 The coating width is 648 mm, the longitudinal coating length of a single sheet is 1468 mm, and the gap length is 30 mm. Then, the negative electrode sheet is rolled to 121 μm and then cut into electrode rolls with a width of 64 mm. After cutting, it is placed in an oven at 100℃ for vacuum baking until the moisture content of the electrode roll is ≤200 ppm.

[0023] Step 3. Cut the positive and negative electrode sheets. When cutting the positive electrode sheet, ensure the gap is at 1 / 3 of the total length of the electrode sheet. Provide one positive electrode tab, welded to the gap position. The tab should be made of aluminum strip, 5mm wide and 0.15mm thick. Cut the negative electrode sheet in the middle of the gap position. Provide two negative electrode tabs, welded to the gap positions at both ends of the cut electrode sheet. The tab should be made of copper-nickel composite strip, 4mm wide and 0.08mm thick. Stack the negative electrode sheet, separator, and positive electrode sheet in sequence, and wind them to form a core. The separator used is a 9+3 ceramic membrane.

[0024] Step 4. Place the core in the steel shell. The negative electrode tab passes through the lower insulating sheet and is welded to the bottom of the cylindrical steel shell. The positive electrode tab passes through the upper insulating sheet and is welded to the cap. Then, perform steel shell grooving, electrolyte injection, cap sealing, and cleaning of the diaphragm to complete the cell assembly. The electrolyte injection volume is 12.5g, the steel shell is nickel-plated stainless steel, and the assembled cell height is 71±0.2mm.

[0025] Step 5. After assembly, the cells undergo a settling period of 1 hour at 45°C for 72 hours. After settling period 1, the cells are cooled to room temperature for formation. They are first charged at 0.1C for 1 hour, then at 0.25C for 72 minutes, then at 0.5C for 130 minutes, and finally charged at 0.1C with constant current and constant voltage to 4.15V, with a cutoff current of 0.01C. The formed cells then undergo a settling period of 2 hours at 25°C for 72 hours. After settling period 2, the cells are subjected to capacity testing. During capacity testing, they are first discharged at 0.5C to 2V, then charged at 1C with constant current and constant voltage to 3.65V, then discharged at 0.5C with constant current to 2V, and finally charged at 0.5C with constant current and constant voltage to 50% SOC.

[0026] Comparative Example 2 A method for preparing a high-energy-density 5Ah lithium-ion cylindrical battery includes the following steps: Step 1. Mix lithium manganese oxide, lithium manganese iron phosphate, ternary cathode material, conductive carbon black, carbon nanotube conductive slurry, polyvinylidene fluoride, and N-methylpyrrolidone in a ratio of 43.2:28.8:24:1:0.8:2.2:42 and stir to prepare a cathode slurry. The lithium manganese oxide used has a 0.1C reversible specific capacity of 118 mAh / g in the 3.0-4.35V voltage range; the lithium manganese iron phosphate used has a 0.1C reversible specific capacity of 150.8 mAh / g in the 2.5-4.35V voltage range; and the ternary material used has a 0.1C reversible specific capacity of 210 mAh / g in the 3-4.3V voltage range. Coat the prepared cathode slurry onto the cathode current collector aluminum foil using a double-sided gap coating method, with a single-sided areal density of 234 g / m². 2 The coating has a transverse width of 634 mm, a longitudinal coating length of 1380 mm per sheet, and a gap length of 10 mm. The positive electrode sheet is then rolled to 185 μm and then slit into 62.5 mm wide electrode rolls. After slitting, the rolls are placed in an oven at 90 °C for vacuum baking until the moisture content is ≤200 ppm.

[0027] Step 2. Mix artificial graphite, conductive carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water in a ratio of 97:0.5:1.5:1:78 and stir to prepare a negative electrode slurry. The 0.1C reversible specific capacity of the graphite used is 355 mAh / g. Coat the prepared negative electrode slurry onto a 6 μm copper foil current collector using a double-sided gap coating method, with a single-sided areal density of 96.7 g / m². 2 The coating width is 648 mm, the longitudinal coating length of a single sheet is 1458 mm, and the gap length is 30 mm. Then, the negative electrode sheet is rolled to 121 μm and then cut into electrode rolls with a width of 64 mm. After cutting, it is placed in an oven at 100℃ for vacuum baking until the moisture content of the electrode roll is ≤200 ppm.

[0028] Step 3. Cut the positive and negative electrode sheets. When cutting the positive electrode sheet, ensure the gap is at 1 / 3 of the total length of the electrode sheet. Provide one positive electrode tab, welded to the gap position. The tab should be made of aluminum strip, 5mm wide and 0.15mm thick. Cut the negative electrode sheet in the middle of the gap position. Provide two negative electrode tabs, welded to the gap positions at both ends of the cut electrode sheet. The tab should be made of copper-nickel composite strip, 4mm wide and 0.08mm thick. Stack the negative electrode sheet, separator, and positive electrode sheet in sequence, and wind them to form a core. The separator used is a 9+3 ceramic membrane.

[0029] Step 4. Place the core in the steel shell. The negative electrode tab passes through the lower insulating sheet and is welded to the bottom of the cylindrical steel shell. The positive electrode tab passes through the upper insulating sheet and is welded to the cap. Then, perform steel shell grooving, electrolyte injection, cap sealing, and cleaning of the diaphragm to complete the cell assembly. The electrolyte injection volume is 13g, the steel shell is nickel-plated stainless steel, and the assembled cell height is 71±0.2mm.

[0030] Step 5. After assembly, the cells undergo a resting period of 1 hour at 45°C for 72 hours. After resting period 1, the cells are cooled to room temperature for formation. They are first charged at 0.1C and 0.25C for 1 hour each, then charged at 0.5C for 2 hours, and then charged at 0.25C with constant current and constant voltage to 4.2V, with the cutoff current set to 0.02C. The formed cells undergo a resting period of 2 hours at 25°C for 72 hours. After resting period 2, the cells are subjected to capacity testing. During capacity testing, they are discharged at 1C and 0.3C to 2.7V, then charged at 0.5C with constant current and constant voltage to 4.2V, then discharged at 0.5C with constant current to 2.7V, and finally charged at 0.5C with constant current and constant voltage to 50% SOC.

[0031] Experimental Example 1: The cell discharge performance of the cylindrical batteries prepared in Example 1 and Comparative Examples 1 and 2 was tested. The test results are shown in Table 1 below: Table 1. Cell discharge performance test data

[0032] Experimental Example 2: The cell safety performance of the cylindrical batteries prepared in Example 1 and Comparative Examples 1 and 2 was tested. The test results are shown in Table 2 below: Table 2 Cell safety performance test results Trial Project Comparative Example 1 Comparative Example 2 Example Overcharging Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Over-discharge Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. External short circuit Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. heating Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. extrusion Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. Two samples were tested, and neither caught fire nor exploded. acupuncture Four samples were tested, and none of them caught fire or exploded. All four tested caught fire and exploded. Five samples were tested, and none of them caught fire or exploded. Experimental Example 3: The cylindrical batteries prepared in Example 1 and Comparative Examples 1 and 2 were subjected to nail penetration tests. The test results are shown in the appendix. Figure 1-3 As shown, Figure 1 Images of the battery cell needle penetration test in Example 1; Figure 2 The image shows a battery cell needle penetration test result from Comparative Example 1. Figure 3 The image shows a battery cell needle penetration test result from Comparative Example 2.

[0033] From Table 1, Table 2 and Figure 1-3 It can be seen that, with the same 5Ah cell, and with the comparative example cell having a slightly higher capacity, the energy of the comparative example cell is 2.7Wh lower than that of the example cell, and the energy density is 27.8Wh / kg lower, about 14%. The energy and energy density of the comparative example cell are the same as those of the example cell, but the comparative example cell fails the nail penetration test, while the example cell passes all safety tests.

[0034] In summary, the cylindrical battery prepared by this invention significantly improves the lithium intercalation capacity of the negative electrode by doping it with high-specific-capacity silicon-carbon. The space saved can significantly increase the areal density of the positive electrode. The composite manganese-based cell can achieve a high energy density, which is 10%-20% higher than that of lithium iron phosphate cells, without doping the positive electrode with lithium nickel cobalt manganese oxide. At the same time, it has a safety advantage over cells with lithium nickel cobalt manganese oxide doped in the positive electrode. In addition, the use of ceramic film improves the cell's resistance to thermal runaway. The use of flame-retardant electrolyte reduces the risk of combustion and explosion of the cell and further improves the cell's safety performance. Through this differentiated combination of positive and negative electrodes, the composite manganese-based cell has both high energy density and high safety.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery, characterized in that, Includes the following steps: Step 1: Mix the active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone in a certain proportion and stir to prepare a positive electrode slurry; coat the prepared positive electrode slurry onto a carbon-coated aluminum foil current collector, and then press, dry, and slit to obtain a positive electrode sheet; Step 2: Mix artificial graphite, silicon carbide material, conductive carbon black, aqueous conductive paste, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water in a certain proportion and stir to prepare a negative electrode paste; coat the prepared negative electrode paste onto a copper foil current collector; and obtain a negative electrode sheet by pressing, drying, and slitting. Step 3: Cut the positive and negative electrode sheets, weld the tabs at the gaps, and attach protective tape to the tabs to make the positive and negative electrode sheets. Stack the negative electrode sheet, ceramic diaphragm, positive electrode sheet, and ceramic diaphragm in sequence and wind them to make the core. Step 4: Place the core in the steel shell, the negative electrode tab passes through the lower insulating sheet and is welded to the bottom of the cylindrical steel shell, and the positive electrode tab passes through the upper insulating sheet and is welded to the cap. Then, perform steel shell grooving, electrolyte injection, cap sealing, and cleaning of the diaphragm to complete the cell assembly. Step 5: After assembling the battery cells, the final product is obtained after resting for 1, forming, resting for 2, and capacity testing.

2. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 1, the active material includes lithium manganese iron phosphate and lithium manganese oxide, which are mixed in a mass ratio of 20-50:50-80. The lithium manganese iron phosphate has a manganese iron element molar ratio of 6-7:3-4, and a reversible specific capacity of >148mAh / g at 0.1C within a voltage range of 2.5-4.35V. The lithium manganese oxide has a reversible specific capacity of >110mAh / g at 0.1C within a voltage range of 3.0-4.35V.

3. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 1, the mass ratio of the active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone is 95-96: 0.8-1.2：0.3-0.8：2.5-3：45-50。 4. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 1, the positive electrode slurry is coated onto the carbon-coated aluminum foil current collector using a double-sided gap coating method, with a single-sided areal density of 250–280 g / m³. 2 The coating width is 300-1000mm, the longitudinal coating length of a single piece is 1200-1600mm, and the gap length is 7-15mm. Among them, the carbon-coated aluminum foil is a double-sided carbon-coated aluminum foil with a thickness of 10-15μm; The thickness of the positive electrode sheet after compression is 230-250μm, the width of the positive electrode sheet after slitting is 60-65mm, and the moisture content of the electrode roll after baking is ≤200ppm.

5. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 2, the 0.1C reversible specific capacity of the artificial graphite is ≥340mAh / g, and the particle size of the artificial graphite is 2-30μm; Where Dv50 = 10-20 μm, and specific surface area is 1.0-2.0 m². 2 / g; The silicon-carbon material has a 0.1C reversible specific capacity ≥1800mAh / g.

6. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 2, the mass ratio of the artificial graphite, silicon carbide material, conductive carbon black, aqueous conductive slurry, sodium polyacrylate, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water is 80-85: 12-15: 0.8-1.2: 0.1-0.3: 1.2-1.8: 1.2-1.8: 0.3-0.8: 75-80.

7. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 2, the negative electrode slurry is coated onto the negative electrode copper foil current collector. The copper foil thickness is 5-8 μm, and the coating is applied using a double-sided gap coating method, with a single-sided areal density of 50-80 g / m². 2 The coating width is 300-1000mm, the longitudinal coating length of a single piece is 1280-1680mm, and the gap length is 20-40mm. The thickness of the negative electrode sheet after compression is 70-100μm, the width of the negative electrode sheet after slitting is 62-67mm, and the moisture content of the electrode roll after baking is ≤200ppm.

8. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 3, when cutting the positive electrode sheet, it is necessary to ensure that the gap is at 1 / 3-1 / 2 of the electrode sheet length. One positive electrode tab is provided and welded to the gap position. The positive electrode tab is made of aluminum strip with a width of 3-6mm and a thickness of 0.1-0.2mm. The negative electrode sheet is cut in the middle of the gap position. Two negative electrode tabs are provided. The gap positions at both ends of the cut electrode sheet are welded together. The negative electrode tabs are made of either nickel strip or copper-nickel composite strip, with a width of 3-5mm and a thickness of 0.05-0.15mm. The base membrane of the ceramic diaphragm is made of either polyethylene or polypropylene, with a porosity of 35-50%. It is coated with alumina and / or boehmite on both sides and / or one side. The diaphragm thickness is 7-20 μm, the length is 1350-1800 mm, and the width is 65-70 mm.

9. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 4, the electrolyte is prepared as follows: ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 20-25:10-15:35-40 as an organic solvent; 1.0-1.2 mol of lithium hexafluorophosphate is dissolved in the mixed organic solvent; vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and lithium bis(oxalato)borate are added as additives; and ethoxypentafluorocyclotriphosphazene flame retardant is added to the solution. The additives account for 5% of the mass of the electrolyte, and the mass ratio of vinylene carbonate, fluorovinyl carbonate, 1,3-propanesulfonate lactone, and lithium bis(oxalato)borate is 1:1:1:

1. The flame retardant ethoxypentafluorocyclotriphosphazene accounts for 8-15% of the mass of the electrolyte; The amount of electrolyte injected is 12-15g; The steel shell is made of nickel-plated stainless steel with a thickness of 0.2-0.5mm. The assembled battery cell has a height of 70-72mm and a diameter of 26.0-6.5mm.

10. The method for preparing a high-energy-density, high-safety composite manganese-based 5Ah cylindrical battery according to claim 1, characterized in that, In step 5, the settling process includes two processes: settling 1 and settling 2. Standing temperature 1: 30-45℃, time: 12-48h; Standing temperature 2: 15-45℃, time: 0-7 days; The formation process is a step-charging process, which requires the charging current to gradually increase. First, charge with a current of 0.1C, then charge with currents of 0.25C and 0.5C, and finally end with a constant voltage charging of 0.25C. The constant voltage charging voltage is set to 4.2V and the cutoff current is set to 0.02C. The capacity grading process is the process of completing a full discharge, specifically: first, discharge at 1C to 2.7V, then discharge at 0.3C to 2.7V, then charge at 0.5C with constant current and constant voltage to 4.2V, then discharge at 0.5C with constant current to 2.7V, and finally charge the cell at 0.5C to 40-50% SOC.

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