Lithium manganese iron phosphate battery and preparation method thereof

Abstract

According to the lithium manganese iron phosphate battery and the preparation method thereof provided by the invention, the positive electrode active material is optimized, and a combination of lithium manganese iron phosphate and a ternary material or manganese-doped lithium manganese iron phosphate is adopted as the positive electrode active material, so that the proportion of the lithium manganese iron phosphate and ternary material combined positive electrode active material is optimized; according to the present invention, the doping ratio of the manganese material is optimized so as to obtain the lithium manganese iron phosphate battery with characteristics of excellent energy density, excellent cycle stability, excellent safety and other excellent performances, the positive and negative electrode slurry preparation method adopts the semi-dry process, and the slurry produced by the process has characteristics of excellent viscosity, excellent fineness, excellent solid content consistency and excellent stability, and the proportion of the active substance, the conductive agent and the binder of the positive and negative electrode paste is optimized, so that the consistency and the stability of the paste are improved, and the energy density and the cycle performance of the battery are effectively improved.

Description

[Technical field]

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium manganese iron phosphate battery and a preparation method thereof. [Background technology]

[0002] At present, the positive electrode materials of power lithium batteries present a situation where lithium iron phosphate and ternary materials compete with each other. Thanks to the improvement of energy density by battery technology and the increase in economic demand after the price of lithium carbonate has risen, lithium iron phosphate batteries have risen all the way in recent years with their absolute advantages in safety and cost, surpassing ternary positive electrode materials. However, the actual energy density of lithium iron phosphate batteries is close to the upper limit of theoretical energy density, and the future of gradually improving the endurance requirements of new energy vehicles has restricted the further improvement of the installed share penetration rate of lithium iron phosphate positive electrode materials.

[0003] As an upgraded product of lithium iron phosphate, lithium manganese iron phosphate has significantly improved energy density and low-temperature performance compared to lithium iron phosphate, and has strong potential to replace medium- and low-nickel ternary batteries with high costs and poor safety. Lithium manganese iron phosphate takes into account the safety and low cost of lithium iron phosphate, while increasing energy density by 10-20%, and is expected to replace power lithium iron. Lithium manganese iron phosphate increases voltage and thus energy density by dissolving manganese, but it will damage cycle and rate performance, among which the manganese-iron ratio is the key to balanced performance. In addition, from the perspective of matching, lithium manganese iron phosphate can be mixed with high-nickel ternary batteries to obtain products that have both safety and high energy density, and form a series of endurance solutions.

[0004] In view of this, it is necessary to provide a new type of lithium manganese iron phosphate battery and a preparation method thereof to overcome the above-mentioned defects. [Summary of the invention]

[0005] The purpose of the present invention is to provide a lithium manganese iron phosphate battery and a preparation method thereof, so as to improve the energy density and cycle performance of the battery.

[0006] In order to achieve the above-mentioned purpose, in the first aspect, the present invention provides a lithium iron manganese phosphate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and a steel shell, wherein the positive electrode sheet, the separator and the negative electrode sheet are wound and accommodated in the steel shell; the positive electrode sheet comprises a positive electrode collector and a positive electrode slurry coated on the positive electrode collector, the positive electrode slurry comprises a positive electrode active material, the positive electrode active material is a combination of lithium iron manganese phosphate and a ternary material or lithium iron manganese phosphate doped with manganese, the structural formula of lithium iron manganese phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material and 811 nickel-cobalt-manganese ternary material.

[0007] In a preferred embodiment, when the ternary material adopts 811 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 811 nickel-cobalt-manganese ternary material is 7:3.

[0008] In a preferred embodiment, when the ternary material adopts 523 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 523 nickel-cobalt-manganese ternary material is 5:5.

[0009] In a preferred embodiment, when the ternary material adopts 622 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 622 nickel-cobalt-manganese ternary material is 5:5.

[0010] In a preferred embodiment, in the lithium manganese iron phosphate manganese-doped positive electrode active material, the weight of manganese doped accounts for 10-30% of the positive electrode active material.

[0011] In a preferred embodiment, the positive electrode slurry further includes a positive electrode conductor and a positive electrode binder. The positive electrode conductor includes one or more of carbon nanotubes, conductive carbon black and graphene. The positive electrode binder is PVDF.

[0012] In a preferred embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode slurry coated on the negative electrode current collector, the negative electrode slurry includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, the negative electrode active material includes one or more of graphite, silicon carbon, and amorphous carbon, the negative electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black and graphene, and the negative electrode binder is one or more of CMC and SBR.

[0013] In a second aspect, the present invention further provides a method for preparing a lithium manganese iron phosphate battery, comprising the following steps:

[0014] Step S10, preparing a positive electrode sheet: mixing a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder PVDF powder, and stirring them evenly; adding part of the solvent NMP to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the positive electrode conductive agent to obtain a moist and viscous muddy slurry; after kneading, slowly adding the solvent NMP to adjust the slurry viscosity and solid content to form a black moist and viscous liquid to prepare a positive electrode slurry of a PVDF / NMP oily system, coating the positive electrode slurry on the positive electrode collector, and roller-forming to obtain a positive electrode sheet; the positive electrode active material is a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese, the structural formula of lithium manganese iron phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material, and 811 nickel-cobalt-manganese ternary material;

[0015] Step S20, preparing a negative electrode sheet: mixing graphite, a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder CMC, and stirring evenly; adding an appropriate amount of solvent to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the negative electrode conductive agent to obtain a wet and viscous soft mud slurry; after kneading, slowly adding solvent and negative electrode binder SBR to adjust the slurry viscosity and solid content to form a light gray wet and viscous liquid to prepare a negative electrode slurry of a graphite / CMC / SBR aqueous system, coating the negative electrode slurry on the negative electrode collector, and roller-forming to obtain a negative electrode sheet;

[0016] Step S30, cutting the formed positive electrode sheet and negative electrode sheet into positive electrode rolls and negative electrode rolls, welding the pole ears on the positive electrode rolls and negative electrode rolls, adding a separator between the positive electrode sheet and the negative electrode sheet, winding them, and assembling them into a steel shell;

[0017] Step S40, baking the assembled battery cells, injecting electrolyte into the steel shell and sealing the steel shell to obtain a finished battery, and then chemically dividing the finished battery into different capacities.

[0018] In a preferred embodiment, in step S10, the weight ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (70-90): (2-5): (2-5).

[0019] In a preferred embodiment, in step S20, the weight ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (70-90): (2-5): (2-5).

[0020] Compared with the prior art, the lithium manganese iron phosphate battery and the preparation method thereof provided by the present invention optimize the positive electrode active material, adopt a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese as the positive electrode active material, optimize the ratio of the positive electrode active material of the combination of lithium manganese iron phosphate and a ternary material, and optimize the doping ratio of the manganese material, so as to obtain a lithium manganese iron phosphate battery with excellent performance such as energy density, cycle stability, and safety. The preparation method of the positive and negative electrode slurry adopts a semi-dry process. The slurry produced by this process has excellent consistency and stability in viscosity, fineness and solid content, and the ratio of the active material, conductive agent and binder in the positive and negative electrode slurry is optimized, thereby improving the consistency and stability of the slurry and effectively improving the energy density and cycle performance of the battery.

Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 The present invention provides a flow chart of a method for preparing a lithium manganese iron phosphate battery. [Specific implementation method]

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0024] The present invention provides a lithium manganese iron phosphate battery, which effectively improves the energy density and cycle performance of the battery by optimizing the positive electrode active material and using a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese as the positive electrode active material.

[0025] The lithium manganese iron phosphate battery provided by the present invention comprises a positive electrode sheet, a negative electrode sheet, a separator and a steel shell, wherein the positive electrode sheet, the separator and the negative electrode sheet are wound and accommodated in the steel shell; the positive electrode sheet comprises a positive electrode collector and a positive electrode slurry coated on the positive electrode collector, the positive electrode slurry comprises a positive electrode active material, the positive electrode active material is a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese, the structural formula of lithium manganese iron phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material and 811 nickel-cobalt-manganese ternary material.

[0026] Further, when the ternary material adopts 811 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 811 nickel-cobalt-manganese ternary material is 7:3. When the ternary material adopts 523 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 523 nickel-cobalt-manganese ternary material is 5:5. When the ternary material adopts 622 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 622 nickel-cobalt-manganese ternary material is 5:5.

[0027] It can be understood that 523, 622, and 811 are the proportions of nickel, cobalt, and manganese in the ternary material. The composition of the ternary material of 523 nickel-cobalt-manganese is 50% nickel, 20% cobalt, and 30% manganese; the composition of the ternary material of 622 nickel-cobalt-manganese is 60% nickel, 20% cobalt, and 20% manganese; the composition of the ternary material of 811 nickel-cobalt-manganese is 80% nickel, 10% cobalt, and 10% manganese.

[0028] Furthermore, in the lithium manganese iron phosphate manganese-doped positive electrode active material, the weight of the manganese-doped manganese accounts for 10-30% of the positive electrode active material.

[0029] The positive electrode slurry further includes a positive electrode conductor and a positive electrode binder. The positive electrode conductor includes one or more of carbon nanotubes, conductive carbon black and graphene. The positive electrode binder is PVDF.

[0030] The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry coated on the negative electrode current collector, the negative electrode slurry includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, the negative electrode active material includes one or more of graphite, silicon carbon, and amorphous carbon, the negative electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, and graphene, and the negative electrode binder is one or more of CMC and SBR.

[0031] See also Figure 1 , which is a flow chart of the method for preparing a lithium manganese iron phosphate battery provided by the present invention. The method for preparing a lithium manganese iron phosphate battery provided by the present invention comprises the following steps:

[0032] Step S10, preparing a positive electrode sheet: mixing a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder PVDF powder, and stirring them evenly; adding part of the solvent NMP to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the positive electrode conductive agent to obtain a moist and viscous muddy slurry; after kneading, slowly adding the solvent NMP to adjust the slurry viscosity and solid content to form a black moist and viscous liquid to prepare a positive electrode slurry of a PVDF / NMP oily system, coating the positive electrode slurry on the positive electrode collector, and roller-forming to obtain a positive electrode sheet; the positive electrode active material is a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese, the structural formula of lithium manganese iron phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material, and 811 nickel-cobalt-manganese ternary material;

[0033] Step S20, preparing a negative electrode sheet: mixing graphite, a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder CMC, and stirring evenly; adding an appropriate amount of solvent to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the negative electrode conductive agent to obtain a wet and viscous soft mud slurry; after kneading, slowly adding solvent and negative electrode binder SBR to adjust the slurry viscosity and solid content to form a light gray wet and viscous liquid to prepare a negative electrode slurry of a graphite / CMC / SBR aqueous system, coating the negative electrode slurry on the negative electrode collector, and roller-forming to obtain a negative electrode sheet;

[0034] Step S30, cutting the formed positive electrode sheet and negative electrode sheet into positive electrode rolls and negative electrode rolls, welding the pole ears on the positive electrode rolls and negative electrode rolls, adding a separator between the positive electrode sheet and the negative electrode sheet, winding them, and assembling them into a steel shell;

[0035] Step S40, baking the assembled battery cells, injecting electrolyte into the steel shell and sealing the steel shell to obtain a finished battery, and then chemically dividing the finished battery into different capacities.

[0036] Specifically, in step S10, the weight ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (70-90): (2-5): (2-5). In step S20, the weight ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (70-90): (2-5): (2-5). The positive electrode current collector may be an aluminum foil, and the negative electrode current collector may be a copper foil. The prepared battery may be a cylindrical battery.

[0037] The lithium manganese iron phosphate battery and the preparation method thereof provided by the present invention are tested through several embodiments.

[0038] Embodiment 1:

[0039] Preparation of positive electrode sheet: 29.59g of lithium manganese iron phosphate and 12.68g of 811 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0040] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0041] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0042] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0043] Embodiment 2:

[0044] Preparation of positive electrode sheet: 21.135g of lithium manganese iron phosphate and 21.135g of 811 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at 30r / min for 180min to wet the powder particles first, and then stirred at high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0045] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0046] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0047] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0048] Embodiment 3:

[0049] Preparation of positive electrode sheet: 12.68g of lithium manganese iron phosphate and 29.59g of 811 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0050] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0051] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0052] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0053] Embodiment 4:

[0054] Preparation of positive electrode sheet: 38.02g of lithium manganese iron phosphate and 4.227g of 523 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0055] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min to obtain negative electrode slurry. Apply the slurry on copper foil, roll-press and form to obtain negative electrode sheet.

[0056] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0057] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0058] Embodiment 5:

[0059] Preparation of positive electrode sheet: 21.135g of lithium manganese iron phosphate and 21.135g of 523 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0060] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min to obtain negative electrode slurry. Apply the slurry on copper foil, roll-press and form to obtain negative electrode sheet.

[0061] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0062] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0063] Embodiment 6:

[0064] Preparation of positive electrode sheet: 12.68g of lithium manganese iron phosphate and 29.59g of 523 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0065] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min to obtain negative electrode slurry. Apply the slurry on copper foil, roll-press and form to obtain negative electrode sheet.

[0066] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0067] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0068] Embodiment 7:

[0069] Preparation of positive electrode sheet: 29.59g of lithium manganese iron phosphate and 12.68g of 622 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0070] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min to obtain negative electrode slurry. Apply the slurry on copper foil, roll-press and form to obtain negative electrode sheet.

[0071] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0072] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0073] Embodiment 8:

[0074] Preparation of positive electrode sheet: 21.135g of lithium manganese iron phosphate and 21.135g of 622 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0075] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0076] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0077] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0078] Embodiment 9:

[0079] Preparation of positive electrode sheet: 12.68g of lithium manganese iron phosphate and 29.59g of 622 ternary material, 0.89g of SP, and 1.07g of PVDF dry powder were stirred at a speed of 20r / min for 30min to mix the dry powders evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and they were slowly stirred at 20r / min for 60min, and then stirred at a high speed of 30r / min for 180min to wet the powder particles first, and then stirred at a high speed to break and disperse the particle agglomerates, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain a positive electrode sheet.

[0080] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0081] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0082] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0083] Embodiment 10:

[0084] Preparation of positive electrode sheet: 38.04g of lithium manganese iron phosphate was doped with 4.23g of manganese powder as active material, 0.89g of SP, and 1.07g of PVDF dry powder, stirred at 20r / min for 30min, and the dry powder was mixed evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and stirred slowly at 20r / min for 60min, and then stirred at 30r / min for 180min, firstly the powder particles were wetted, and then the particle agglomerates were broken and dispersed by high-speed stirring, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain positive electrode sheet.

[0085] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0086] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0087] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0088] Embodiment 11:

[0089] Preparation of positive electrode sheet: 33.816g of lithium manganese iron phosphate was doped with 8.454g of manganese powder as active material, 0.89g of SP, and 1.07g of PVDF dry powder, stirred at 20r / min for 30min, and the dry powder was mixed evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and stirred slowly at 20r / min for 60min, and then stirred at 30r / min for 180min, firstly the powder particles were wetted, and then the particle agglomerates were broken and dispersed by high-speed stirring, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain positive electrode sheet.

[0090] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0091] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0092] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0093] Embodiment 12:

[0094] Preparation of positive electrode sheet: 38.04g of lithium manganese iron phosphate was doped with 12.68g of manganese powder as active material, 0.89g of SP, and 1.07g of PVDF dry powder, stirred at 20r / min for 30min, and the dry powder was mixed evenly; 23.88g of NMP solvent and 8.94g of CNT slurry were added, and stirred slowly at 20r / min for 60min, and then stirred at 30r / min for 180min, firstly the powder particles were wetted, and then the particle agglomerates were broken and dispersed by high-speed stirring, and the viscosity was adjusted after sufficient mixing to obtain positive electrode slurry. The positive electrode slurry was coated on aluminum foil and roll-formed to obtain positive electrode sheet.

[0095] Preparation of negative electrode sheet: Add 24.4g graphite, 0.347g 1.7% CMC glue, 0.4g graphene, stir at 20r / min for 120min, mix evenly; add 1.042g NMP solvent, stir at 30r / min for 120min, high-speed stirring to break and disperse the particle agglomerates, finally add 1.131g SBR, stir at 15r / min for 30min, mix well and adjust the viscosity to obtain negative electrode slurry. Apply the slurry on copper foil, roll-form, and obtain negative electrode sheet.

[0096] The formed positive and negative electrode sheets are cut into positive electrode rolls and negative electrode rolls, the pole ears are welded on the electrode rolls, and a separator is added between the positive and negative electrode sheets for winding and assembly into a steel shell.

[0097] The assembled battery cells are baked, electrolyte is injected, and the batteries are sealed. The finished batteries are then divided into different capacities.

[0098] The following is a performance test of the batteries prepared in Examples 1 to 7.

[0099] The normal temperature cycle life of the battery (referred to as cycle performance): After the capacity-fractionated battery has been left to stand for 24 hours, the battery is fully charged at a rate of 0.5C within the voltage range of 2.5 to 4.3V, and then discharged to 2.0V at a rate of 0.5C; then the battery is placed at room temperature, fully charged at a rate of 1C within the voltage range of 2.5 to 4.3V, and then discharged to 2.0V at a rate of 1C; repeat the above cycle.

[0100] As shown in the following Table 1, Table 1 is a comparison table of the cycle performance of the lithium manganese iron phosphate batteries prepared in various embodiments.

[0101] Table 1

[0102]

[0103]

[0104] As can be seen from Table 1, from Examples 1-12, the capacity retention rate of the lithium manganese iron phosphate cylindrical battery of the present invention can reach more than 80% after 600 cycles, and it has excellent performance.

[0105] By comparison of Examples 1-3, it can be seen that when lithium iron manganese phosphate and 811 ternary materials are mixed in a ratio of 7:3, the gram-to-weight capacity is not as good as that of batteries mixed in a ratio of 5:5 and 3:7, but the battery mixed in this ratio has the best cycle performance, and is 10 points higher than the gram-to-weight capacity of pure lithium iron phosphate batteries; the battery in which lithium iron manganese phosphate and 811 ternary materials are mixed in a ratio of 3:7 has the highest gram-to-weight capacity, but the cycle performance does not meet the experimental requirements; the battery in which lithium iron manganese phosphate and 811 ternary materials are mixed in a ratio of 5:5 has a gram-to-weight capacity and a cycle performance that are stuck in the middle; overall, when lithium iron manganese phosphate and 811 ternary materials are mixed in a ratio of 7:3, the gram-to-weight capacity and cycle performance are the best, and it is most suitable for industrialization.

[0106] By comparison of Examples 4-6, it can be seen that when lithium iron manganese phosphate and 523 ternary materials are mixed in a ratio of 5:5, although the gram-to-weight capacity is not as good as the battery mixed in a ratio of 3:7, the comprehensive performance of this ratio is the best; the battery in which lithium iron manganese phosphate and 523 ternary materials are mixed in a ratio of 3:7 has the highest gram-to-weight capacity, but the cycle performance does not meet the experimental requirements; the battery in which lithium iron manganese phosphate and 523 ternary materials are mixed in a ratio of 1:9 has better cycle performance than 5-6, but the gram-to-weight capacity of the battery is too low and is not suitable; comprehensively speaking, when lithium iron manganese phosphate and 523 ternary materials are mixed in a ratio of 5:5, their comprehensive performance is the best.

[0107] By comparison of Examples 7-9, it can be seen that when lithium iron manganese phosphate and 622 ternary materials are mixed in a ratio of 5:5, although the gram-to-weight capacity is not as good as that of the battery mixed in a ratio of 3:7, the comprehensive performance of this ratio is the best; the battery in which lithium iron manganese phosphate and 622 ternary materials are mixed in a ratio of 3:7 has the highest gram-to-weight capacity, but the cycle performance does not meet the experimental requirements; the battery in which lithium iron manganese phosphate and 622 ternary materials are mixed in a ratio of 7:3 has a better cycle than 5-6, but the gram-to-weight capacity of the battery is too low and does not meet the requirements; comprehensively speaking, the comprehensive performance of lithium iron manganese phosphate and 622 ternary materials is best when they are mixed in a ratio of 5:5.

[0108] From the comparison of Examples 10-12, it can be seen that the lithium manganese iron phosphate doped with 10-30% manganese powder and the lithium manganese iron phosphate doped with 30% manganese powder is better than the other two in terms of gram capacity and cycle performance. Overall, the comprehensive performance of lithium manganese iron phosphate doped with manganese is the best when it is mixed with manganese in a ratio of 7:3.

[0109] Therefore, by comparing Examples 1-12, it can be concluded that the 811 ternary material is the most suitable for mixing lithium manganese iron phosphate. Compared with 523 ternary material and 622 ternary material, the battery prepared by mixing 811 ternary material with lithium manganese iron phosphate has the best effect, the most comprehensive performance meets the requirements, and is most suitable for industrialization. The cycle performance of lithium manganese iron phosphate doped with 30% manganese powder is the best in all tests, and has good application prospects.

[0110] According to the lithium manganese iron phosphate cylindrical battery of the present application, a dry mixing process, also known as a "kneading" process, is used. The basic process is to mix the active material, the conductive agent and the binder dry powder - add an appropriate amount of solvent to moisten - add the solvent to disperse and crush at high speed - dilute to adjust the viscosity. When the slurry is stirred at ultra-high viscosity, the large shear force can more fully disperse the conductive agent with fine particles that are easy to agglomerate, and it is also more conducive to the dissolution and stability of the binder. The slurry produced by this process has excellent consistency and stability in viscosity, fineness and solid content, and the resistivity of the produced pole piece is low, and the capacity retention rate of the produced battery cell is higher.

[0111] According to the lithium iron manganese phosphate cylindrical battery of the present application, by mixing ternary materials and slurry with excellent conductive network, the ratio of positive and negative electrode slurry active materials, conductive agent and binder is optimized, the adhesion and conductivity of positive and negative electrode materials are improved, and the energy density and cycle performance of the battery are significantly improved. By optimizing the positive electrode active material lithium iron manganese phosphate material, optimizing the content of lithium and manganese elements in lithium iron manganese phosphate, and optimizing the doping ratio of manganese material, a lithium iron manganese phosphate battery with excellent performance such as energy density, cycle stability, safety, etc. is obtained.

[0112] In summary, the lithium manganese iron phosphate battery and the preparation method thereof provided by the present invention optimize the positive electrode active material, adopt a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese as the positive electrode active material, optimize the ratio of the positive electrode active material of the combination of lithium manganese iron phosphate and a ternary material, and optimize the doping ratio of the manganese material, so as to obtain a lithium manganese iron phosphate battery with excellent performance such as energy density, cycle stability, and safety. The preparation method of the positive and negative electrode slurry adopts a semi-dry process. The slurry produced by this process has excellent viscosity, fineness and solid content consistency and stability performance. The ratio of the active material, conductive agent and binder in the positive and negative electrode slurry is optimized, which improves the consistency and stability of the slurry, and effectively improves the energy density and cycle performance of the battery.

[0113] The above description is only an implementation mode of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A lithium manganese iron phosphate battery, characterized in that: It includes a positive electrode sheet, a negative electrode sheet, a separator and a steel shell, wherein the positive electrode sheet, the separator and the negative electrode sheet are wound and accommodated in the steel shell; the positive electrode sheet includes a positive electrode collector and a positive electrode slurry coated on the positive electrode collector, the positive electrode slurry includes a positive electrode active material, the positive electrode active material is a combination of lithium iron manganese phosphate and a ternary material or lithium iron manganese phosphate doped with manganese, the structural formula of lithium iron manganese phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material and 811 nickel-cobalt-manganese ternary material.

2. The lithium manganese iron phosphate battery according to claim 1, characterized in that: When the ternary material adopts 811 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 811 nickel-cobalt-manganese ternary material is 7:

3.

3. The lithium manganese iron phosphate battery according to claim 1, characterized in that: When the ternary material adopts 523 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 523 nickel-cobalt-manganese ternary material is 5:

5.

4. The lithium manganese iron phosphate battery according to claim 1, characterized in that: When the ternary material uses 622 nickel-cobalt-manganese ternary material, the weight ratio of lithium iron manganese phosphate to 622 nickel-cobalt-manganese ternary material is 5:

5.

5. The lithium manganese iron phosphate battery according to claim 1, characterized in that: In the lithium manganese iron phosphate manganese-doped positive electrode active material, the weight of the manganese-doped manganese accounts for 10-30% of the positive electrode active material.

6. The lithium manganese iron phosphate battery according to claim 1, characterized in that: The positive electrode slurry further includes a positive electrode conductor and a positive electrode binder. The positive electrode conductor includes one or more of carbon nanotubes, conductive carbon black and graphene. The positive electrode binder is PVDF.

7. The lithium manganese iron phosphate battery according to any one of claims 1 to 6, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode slurry coated on the negative electrode current collector, the negative electrode slurry includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, the negative electrode active material includes one or more of graphite, silicon carbon, and amorphous carbon, the negative electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, and graphene, and the negative electrode binder is one or more of CMC and SBR.

8. A method for preparing a lithium manganese iron phosphate battery, characterized in that: The steps include: Step S10, preparing a positive electrode sheet: mixing a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder PVDF powder, and stirring them evenly; adding part of the solvent NMP to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the positive electrode conductive agent to obtain a moist and viscous muddy slurry; after kneading, slowly adding the solvent NMP to adjust the slurry viscosity and solid content to form a black moist and viscous liquid to prepare a positive electrode slurry of a PVDF / NMP oily system, coating the positive electrode slurry on the positive electrode collector, and roller-forming to obtain a positive electrode sheet; the positive electrode active material is a combination of lithium manganese iron phosphate and a ternary material or lithium manganese iron phosphate doped with manganese, the structural formula of lithium manganese iron phosphate is LiMn6Fe4PO4, and the ternary material adopts one of 523 nickel-cobalt-manganese ternary material, 622 nickel-cobalt-manganese ternary material, and 811 nickel-cobalt-manganese ternary material; Step S20, preparing a negative electrode sheet: mixing graphite, a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder CMC, and stirring evenly; adding an appropriate amount of solvent to wet the powder particles, dispersing the particle agglomerates under the action of high-speed shear force, and evenly distributing the negative electrode conductive agent to obtain a wet and viscous soft mud slurry; after kneading, slowly adding solvent and negative electrode binder SBR to adjust the slurry viscosity and solid content to form a light gray wet and viscous liquid to prepare a negative electrode slurry of a graphite / CMC / SBR aqueous system, coating the negative electrode slurry on the negative electrode collector, and roller-forming to obtain a negative electrode sheet; Step S30, cutting the formed positive electrode sheet and negative electrode sheet into positive electrode rolls and negative electrode rolls, welding the pole ears on the positive electrode rolls and negative electrode rolls, adding a separator between the positive electrode sheet and the negative electrode sheet, winding them, and assembling them into a steel shell; Step S40, baking the assembled battery cells, injecting electrolyte into the steel shell and sealing the steel shell to obtain a finished battery, and then chemically dividing the finished battery into different capacities.

9. The method for preparing a lithium manganese iron phosphate battery according to claim 8, characterized in that: In step S10, the weight ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (70-90): (2-5): (2-5).

10. The method for preparing a lithium manganese iron phosphate battery according to claim 8, characterized in that: In step S20, the weight ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (70-90): (2-5): (2-5).

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