Functional current collector and preparation method thereof

Abstract

The invention discloses a functional current collector. The functional current collector comprises a substrate layer; the surface of the substrate layer is covered with the lithium manganese iron phosphate coating; the lithium manganese iron phosphate layer comprises the following components in parts by weight: 62-68 parts of lithium manganese iron phosphate; 28-34 parts by weight of a conductive agent; and 2-4 parts by weight of a water-based binder. According to the invention, the surface of the aluminum foil is coated with the aqueous lithium manganese iron phosphate priming coat, the aqueous lithium manganese iron phosphate priming coat replaces a carbon-coated layer of a traditional carbon-coated aluminum foil through proportion adjustment, and deionized water is adopted as a solvent, so that the cost of raw materials is effectively reduced, NMP recovery system equipment can be omitted, and the cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a functional current collector and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have rapidly occupied the global new energy market due to their high energy density, good cycle stability, environmental friendliness and other advantages, and are currently applied in various fields from small 3C products to electric vehicles, ships and other large fields. Lithium iron phosphate battery (LiFePO4 battery) is a lithium ion battery with lithium iron phosphate (LiFePO4) as the positive electrode material. Lithium iron phosphate battery has the advantages of high safety, super-long cycle life, low cost and environmental protection. However, lithium iron phosphate battery currently still has the disadvantages of low energy density, poor low-temperature performance, low voltage platform and slow charge-discharge rate. In the prior art, a core-shell material of lithium manganese iron phosphate is proposed, but lithium manganese iron phosphate also has defects, such as poor cycle performance, low conductivity and easy to produce side reactions. Therefore, in order to further expand the advantages of lithium batteries and reduce the use cost of batteries, optimization design is needed from various aspects such as battery materials and structure. SUMMARY

[0003] In order to solve the problems of low platform voltage, poor low-temperature performance and low decomposition temperature of lithium iron phosphate battery, the present application proposes a functional current collector and a preparation method thereof. The above-mentioned purpose can be achieved by the following technical scheme:

[0004] A functional current collector comprises:

[0005] a substrate layer;

[0006] a lithium manganese iron phosphate coating layer covering the surface of the substrate layer; the lithium manganese iron phosphate layer comprises the following components by weight:

[0007] lithium manganese iron phosphate 62-68 parts by weight;

[0008] conductive agent 28-34 parts by weight;

[0009] aqueous binder 2-4 parts by weight.

[0010] Optionally, the aqueous binder is at least one of polyacrylonitrile, polyacrylic acid and aqueous polyurethane;

[0011] Preferably, the aqueous binder is polyacrylonitrile; the degree of polymerization of the polyacrylonitrile is 500-3000;

[0012] Preferably, the degree of polymerization of the polyacrylonitrile is 2000-3000.

[0013] Optionally, the lithium manganese iron phosphate layer further comprises 5-10 parts by weight of metal particles, the metal particles being at least one of magnesium, titanium, zinc, and aluminum;

[0014] Preferably, the lithium manganese iron phosphate, the conductive agent, and the metal particles have a particle size D50 of less than 1 μm.

[0015] Preferably, the lithium manganese iron phosphate and the conductive agent have a D50 of 0.5-1 μm.

[0016] Preferably, the metal particles have a D50 of 50-200 nm and a D90 of 80-300 nm.

[0017] Optionally, the conductive agent comprises conductive carbon black and conductive graphite.

[0018] Optionally, the lithium manganese iron phosphate coating has a thickness of 5-10 μm and an areal density of 11-11.3 g / m2. 2 and a water content of 200-230 ppm.

[0019] Optionally, the lithium manganese iron phosphate has a chemical formula of LiMn 1-x Fe x PO4, wherein 0.4 < x < 0.7.

[0020] Preferably, the substrate layer is an aluminum foil.

[0021] The above method for preparing the functional current collector comprises the following steps:

[0022] Step 1) mixing raw materials comprising lithium manganese iron phosphate, a conductive agent, and an aqueous binder with water to obtain a lithium manganese iron phosphate slurry; the slurry has a solid content of 44%-48%;

[0023] Step 2) coating the lithium manganese iron phosphate slurry on the surface of the substrate layer, and then drying to obtain the functional current collector.

[0024] Optionally, the raw materials further comprise 1-3 parts by weight of an additive; the additive comprises a dispersant PVP and a wetting agent isopropyl alcohol.

[0025] Preferably, the slurry has a viscosity of 400-600 mPa.s.

[0026] A lithium battery positive electrode comprises the above functional current collector; a lithium iron phosphate positive electrode material layer is provided on the lithium manganese iron phosphate coating of the functional current collector.

[0027] The application further provides use of the above functional current collector and lithium battery positive electrode in the preparation of lithium batteries.

[0028] The technical solution of the application has the following advantages:

[0029] This invention involves coating an aluminum foil surface with an aqueous lithium manganese iron phosphate (LMFP) base layer. By adjusting the ratio, this base layer replaces the carbon coating layer of traditional carbon-coated aluminum foil. Using deionized water as the solvent effectively reduces raw material costs and eliminates the need for an NMP recovery system, significantly lowering overall costs. LFP and lithium iron phosphate share the same olivine structure and similar lattice parameters, reducing interfacial stress and promoting lithium-ion diffusion. Batteries made using the functional current collector of this invention achieve a plateau voltage of approximately 3.6V after charge-discharge, significantly improving energy density. Furthermore, it improves the low-temperature performance of LFP batteries, effectively solving problems such as low plateau voltage, poor low-temperature performance, and low decomposition temperature. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0031] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0034] This invention proposes a functional current collector, comprising:

[0035] basal layer;

[0036] A lithium manganese iron phosphate coating, wherein the lithium manganese iron phosphate layer covers the surface of the substrate layer; the lithium manganese iron phosphate layer comprises the following components in parts by weight:

[0037] 62-68 parts by weight of lithium manganese iron phosphate;

[0038] 28-34 parts by weight of conductive agent;

[0039] 2-4 parts by weight of water-based adhesive.

[0040] Optionally, the waterborne adhesive is at least one of polyacrylonitrile, polyacrylic acid, and waterborne polyurethane; preferably, the waterborne adhesive is polyacrylonitrile; the degree of polymerization of the polyacrylonitrile is 500-3000; more preferably, the degree of polymerization of the polyacrylonitrile is 2000-3000. At this degree of polymerization, it exhibits high mechanical strength, good toughness, and excellent thermal stability.

[0041] Optionally, the lithium manganese iron phosphate layer further comprises 5-10 parts by weight of metal particles, wherein the metal particles are at least one of magnesium, titanium, zinc, and aluminum; the particle size D50 of the lithium manganese iron phosphate, conductive agent, and metal particles is less than 1 μm. The functions of the metal particles are: first, to suppress lattice distortion: for example, Mg... 2 Doping with Mg can reduce the volume change caused by Li+ insertion / extraction during charging and discharging (approximately 6-7% volume difference during the LiFePO4 / FePO4 phase transition), thus improving structural stability. Secondly, it reduces side reactions: for example, Mg... 2 Doping can reduce the electrolyte's effect on Fe. 2 It reduces the erosion of +, decreases the dissolution of Fe during the cycle, and extends the cycle life.

[0042] Optionally, the conductive agent includes conductive carbon black and conductive graphite. The thickness of the lithium manganese iron phosphate coating is 5-10 μm, and the areal density of the lithium manganese iron phosphate coating is 11-11.3 g / m³. 2 The water content is 200-230 ppm. The thickness of the lithium manganese iron phosphate coating is about 5-10 μm. When the thickness of this base coating is less than 5 μm, it is difficult to achieve a voltage increase because there is an interface bonding layer between the lithium manganese iron phosphate and lithium iron phosphate. After rolling, this bonding layer will show a distinct wavy shape. If the lithium manganese iron phosphate coating is too thin, some of the low-lying lithium iron phosphate coating will come into contact with the current collector after rolling, affecting the overall plateau voltage. When the lithium manganese iron phosphate coating is greater than 5 μm, the contact between the lithium iron phosphate and the current collector after rolling is eliminated, effectively improving the overall battery plateau voltage. In the rolling process, compared with pure metal foil, composite aluminum foil has a higher elongation, but the elongation of its 1 μm metal layer is not large. Under high elongation, aluminum layer cracking may occur, and some of this cracking plays a role in the PTC mechanism, causing local short circuits and improving battery safety. The lower the water content of the lithium manganese iron phosphate coating, the better the battery cycle life.

[0043] Optionally, the lithium iron manganese phosphate has the chemical formula LiMn. 1-x Fe x PO4, of which 0.4 <x<0.7;

[0044] Preferably, the base layer is made of aluminum foil.

[0045] The above-mentioned method for preparing the functional current collector includes the following steps:

[0046] Step 1) Mix the raw materials containing lithium manganese iron phosphate, conductive agent and water-based binder evenly with water to obtain lithium manganese iron phosphate slurry; the solid content of the slurry is 44%-48%;

[0047] Step 2) Coat the substrate surface with lithium manganese iron phosphate slurry and then dry it to obtain the functional current collector.

[0048] Optionally, the raw material may further contain 1 to 3 parts by weight of additives; the additives include dispersant PVP and wetting agent isopropanol;

[0049] Preferably, the viscosity of the slurry is 400-600 mPa·s.

[0050] Example 1:

[0051] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (degree of polymerization 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 1.

[0052] Table 1

[0053] Material Proportion Lithium iron manganese phosphate 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0054] The chemical formula of lithium iron manganese phosphate is LiMn 0.5 Fe 0.5 PO4; Slurry solids content: 45.2%, single-sided surface density: 11.3 g / m³ 2 The single-sided coating thickness is 6.9 μm, the viscosity is 437 mPa.s, and the particle size D50 is 0.93 μm.

[0055] The slurry was uniformly coated onto 12μm aluminum foil using a gravure coating machine with a corresponding areal density of 12g / m². 2 Aqueous lithium manganese iron phosphate base-coated aluminum foil was prepared by coating at a speed of 50 m / min and an oven temperature of 110 ℃. The moisture content of the coating after drying was 217 ppm.

[0056] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. The positive electrode slurry contained the following components by weight: 96.6 parts LiFePO4, 2.5 parts polyvinylidene fluoride, 3 parts NMP4, 1.2 parts conductive agent SP, 1 part conductive agent CNT, and 0.7 parts conductive agent KS-6-. The negative electrode slurry consisted of 94.9 parts styrene-butadiene rubber, 2.2 parts sodium carboxymethyl cellulose, 1.3 parts deionized water, and 1.6% conductive agent SP. These components were uniformly coated onto the functional current collector and the surface of copper foil (8μm), respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and encapsulated to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate base coating.

[0057] The battery was measured to have a full-charge DCR of 0.83 mΩ, a battery plateau voltage of 3.58 V, an energy density of 209.1 Wh / kg, a discharge capacity of 16.67 Ah at -20℃, and a cycle life of 1611 cycles.

[0058] Example 2:

[0059] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (degree of polymerization 1000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 2.

[0060] Table 2

[0061] Material Proportion Lithium iron manganese phosphate 68％ Super-P 20％ KS-6 8％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0062] The chemical formula of lithium iron manganese phosphate is LiMn 0.6 Fe 0.4 PO4; Slurry solids content: 47.1%, single-sided surface density: 11 g / m³ 2 The single-sided coating thickness was 6.3 μm, the viscosity was 488.2 mPa·s, and the particle size D50 was 0.96 μm. This slurry was uniformly coated onto a 12 μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil. The moisture content of the base coating was 218 ppm.

[0063] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0064] The battery was measured to have a full-charge DCR of 1.03 mΩ, a battery plateau voltage of 3.53 V, an energy density of 202.7 Wh / kg, a discharge capacity of 16.43 Ah at -20℃, and a cycle life of 1623 cycles.

[0065] Example 3:

[0066] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 3000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 3.

[0067] Table 3

[0068] Material Proportion Lithium iron manganese phosphate 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0069] The chemical formula of lithium iron manganese phosphate is LiMn 0.3 Fe 0.7 PO4, slurry solids content: 45.2%, single-sided surface density: 11 g / m³ 2 The single-sided coating thickness is 5.0 μm, the viscosity is 401 mPa·s, and the particle size D50 is 0.77 μm.

[0070] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil with a base coating moisture content of 333ppm.

[0071] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0072] The battery was measured to have a full-charge DCR of 0.79 mΩ, a battery plateau voltage of 3.48 V, an energy density of 198.8 Wh / kg, a discharge capacity of 15.67 Ah at -20℃, and a cycle life of 1585 cycles.

[0073] In summary, the above examples show that the proportion of conductive agent in the undercoat directly affects the battery's DCR, and the thickness of the undercoat affects its overall plateau voltage. Different moisture control methods also affect the battery's cycle performance.

[0074] Example 4

[0075] Lithium iron manganese phosphate was mixed with metallic magnesium at a weight ratio of 92:8. The metallic magnesium was in nanoscale particles with a D50 of 57 nm and a D90 of 89 nm. The chemical formula of lithium iron manganese phosphate is LiMn. 0.5 Fe 0.5 PO4.

[0076] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 4.

[0077] Table 4

[0078] Material Proportion Lithium iron manganese phosphate + metal magnesium 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0079] Solid content of slurry: 46.2%, surface density on one side: 11 g / m³ 2 The single-sided coating thickness is 6.0 μm, the viscosity is 401 mPa·s, and the particle size D50 is 0.77 μm.

[0080] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil. The moisture content of the base coating was 333ppm.

[0081] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0082] The battery was measured to have a full-charge DCR of 0.79 mΩ, a battery plateau voltage of 3.51 V, an energy density of 200.8 Wh / kg, a discharge capacity of 16.55 Ah at -20℃, and a cycle life of 1831 cycles.

[0083] Example 5

[0084] Lithium iron manganese phosphate was mixed with metallic zinc at a weight ratio of 95:5. The zinc was in nanoscale particles with a D50 of 108 nm and a D90 of 176 nm. The chemical formula of lithium iron manganese phosphate is LiMn. 0.5 Fe 0.5 PO4.

[0085] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. Additive formulations are shown in Table 5.

[0086] Table 5

[0087] Material Proportion Lithium iron manganese phosphate + metal zinc 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0088] Slurry solids content: 46%, single-sided surface density: 11 g / m³ 2 The single-sided coating thickness is 6.0 μm, the viscosity is 399 mPa.s, and the particle size D50 is 0.76 μm.

[0089] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil with a base coating moisture content of 333ppm.

[0090] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0091] The battery was measured to have a full-charge DCR of 0.82 mΩ, a battery plateau voltage of 3.52 V, an energy density of 200.3 Wh / kg, a discharge capacity of 16.45 Ah at -20 °C, and a cycle life of 1797 cycles.

[0092] Example 6

[0093] Lithium iron manganese phosphate was mixed with metallic titanium at a weight ratio of 95:5. The titanium was in nanoscale particles with a D50 of 165 nm and a D90 of 288 nm. The chemical formula of lithium iron manganese phosphate is LiMn. 0.5 Fe 0.5 PO4.

[0094] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 6.

[0095] Table 6

[0096] Material Proportion Lithium iron manganese phosphate + metal titanium 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0097] Solid content of slurry: 46.4%, surface density on one side: 11 g / m³ 2 The single-sided coating thickness is 6.0 μm, the viscosity is 412 mPa.s, and the particle size D50 is 0.73 μm.

[0098] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil. The moisture content of the base coating was 333ppm.

[0099] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0100] The battery was measured to have a full-charge DCR of 0.84 mΩ, a battery plateau voltage of 3.51 V, an energy density of 200 Wh / kg, a discharge capacity of 16.41 Ah at -20℃, and a cycle life of 1807 cycles.

[0101] Example 7

[0102] Lithium iron manganese phosphate was mixed with metallic aluminum at a weight ratio of 95:5. The metallic aluminum was in nanoscale particles with a D50 of 175 nm and a D90 of 263 nm. The chemical formula of lithium iron manganese phosphate is LiMn. 0.5 Fe 0.5 PO4.

[0103] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 7.

[0104] Table 7

[0105]

[0106]

[0107] Solid content of slurry: 46.7%, surface density on one side: 11.3 g / m³ 2 The single-sided coating thickness is 6.0 μm, the viscosity is 421 mPa.s, and the particle size D50 is 0.78 μm.

[0108] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil. The moisture content of the base coating was 333ppm.

[0109] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0110] The battery was measured to have a full-charge DCR of 0.82 mΩ, a plateau voltage of 3.53 V, an energy density of 200.4 Wh / kg, a discharge capacity of 16.48 Ah at -20℃, and a cycle life of 1892 cycles.

[0111] Comparative Example 1

[0112] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent, water-based polyacrylonitrile (polymerization degree 2000) is used as the binder, and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. The additive formulations are shown in Table 8.

[0113] Table 8

[0114] Material Proportion Lithium iron manganese phosphate 62％ Super-P 23％ KS-6 11％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0115] The chemical formula of lithium iron manganese phosphate is LiMn 0.5 Fe 0.5 PO4. Slurry solids content: 17%, single-sided surface density: 1 g / m³ 2 The single-sided coating thickness is 0.8 μm, the viscosity is 227 mPa.s, and the particle size D50 is 0.67 μm.

[0116] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil. The moisture content of the base coating was 233ppm.

[0117] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0118] The battery was measured to have a full-charge DCR of 0.73 mΩ, a battery plateau voltage of 3.22 V, an energy density of 173.3 Wh / kg, a discharge capacity of 15.61 Ah at -20℃, and a cycle life of 877 cycles.

[0119] Comparative Example 2

[0120] Materials for preparing aqueous lithium manganese iron phosphate: Deionized water is used as the solvent; water-based polyacrylonitrile (polymerization degree 2000) is used as the binder; and a conductive agent consisting of a conductive carbon black + conductive graphite binary system is used. Additive formulations are shown in Table 9.

[0121] Table 9

[0122] Material Proportion Lithium iron manganese phosphate 83％ Super-P 8％ KS-6 5％ PVP 0.5％ Isopropyl alcohol 0.5％ Polyacrylonitrile 3％

[0123] The chemical formula of lithium iron manganese phosphate is LiMn 0.5 Fe 0.5 PO4. Slurry solids content: 50.3%, single-sided surface density: 13 g / m³ 2 The coating thickness on one side is 6.8 μm; the viscosity is 477 mPa·s; and the particle size D50 is 0.83 μm.

[0124] The slurry was uniformly coated onto a 12μm aluminum foil to prepare an aqueous lithium manganese iron phosphate base-coated aluminum foil with a base coating moisture content of 333ppm.

[0125] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0126] The battery was measured to have a full-charge DCR of 0.77mΩ, a battery plateau voltage of 3.6V, an energy density of 210.6Wh / kg, a discharge capacity of 16.16Ah at -20℃, and a cycle life of 1233 cycles.

[0127] Comparative Example 3

[0128] Materials for carbon coating preparation: Deionized water was used as the solvent, PAA as the binder, and a conductive agent consisting of a binary system of conductive carbon black and conductive graphite. Additive formulations are shown in Table 10.

[0129] Table 10

[0130] Material Proportion Super-P 23％ KS-6 11％ PVP 1.5％ Isopropyl alcohol 1.5％ PAA 63％

[0131] The chemical formula of lithium iron manganese phosphate is LiMn 0.5 Fe 0.5 PO4. Slurry solids content: 7.3%, single-sided surface density: 0.5 g / m³ 2 The coating thickness is 1 μm, the viscosity is 227 mPa·s, and the particle size D50 is 0.67 μm.

[0132] The slurry was uniformly coated onto a 12μm aluminum foil to prepare carbon-coated aluminum foil.

[0133] The battery fabrication process then commenced. This battery used LiFePO4 as the positive electrode material and artificial graphite + hard carbon as the negative electrode material, employing a 25μm polypropylene (PP) separator and carbonate-based LiPF6 electrolyte. Polyvinylidene fluoride (PVDF) was used as the positive electrode binder, styrene-butadiene rubber (SBR) as the negative electrode binder, NMP as the positive electrode solvent, deionized water as the negative electrode solvent, and conductive agents including conductive carbon black (Super-P) and conductive graphite (KS-6). Positive and negative electrode slurries were prepared according to the method described in Example 1, and uniformly coated onto the surfaces of aluminum and copper foils, respectively. After drying, rolling, cutting, and drying, the required electrode sheets were fabricated. The electrode sheets were then stacked, assembled, baked, injected with electrolyte, and packaged to produce a 20Ah soft-pack stacked aqueous lithium iron phosphate battery with a manganese iron phosphate substrate.

[0134] The battery was measured to have a full-charge DCR of 0.88 mΩ, a battery plateau voltage of 3.17 V, an energy density of 178.3 Wh / kg, a discharge capacity of 14.31 Ah at -20 °C, and a cycle life of 883 cycles.

[0135] The above comparative examples show that the thinner the lithium manganese iron phosphate (LFP) undercoat, the lower the voltage plateau, tending towards the LFP voltage plateau, and the lower the energy density. Conversely, the higher the LFP content, the more stable the voltage plateau, and the better the low-temperature cycling performance of the battery with increasing LFP coating thickness and areal density. The test results are shown in Table 11.

[0136] Table 11

[0137]

[0138] By neutralizing the lithium iron phosphate (LFP) active material with a lithium manganese phosphate (MFP) undercoat, the LFP plateau voltage is around 3.4V, while the LFP plateau voltage is around 4.1V. After charge and discharge, it was found that the LFP battery plateau voltage with an aqueous MFP undercoat can reach around 3.6V, significantly improving energy density. LFP has poor low-temperature performance but good cycle life, while LFP shows some improvement at low temperatures. However, manganese leaching leads to a shorter cycle life, thus complementing each other. LFP has poor conductivity; by adjusting the undercoat ratio and increasing the amount of conductive agent, a good conductive network is constructed. Furthermore, the decomposition temperature of LFP is more than 100°C higher than that of LFP, and LFP directly contacts the foil, effectively slowing down the material decomposition rate. Additionally, the doping of magnesium and zinc metals improves its electronic conductivity, structural stability, and electrochemical performance, significantly enhancing the battery's cycle performance.

[0139] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A functional current collector, characterized in that, include: basal layer; A lithium manganese iron phosphate coating, wherein the lithium manganese iron phosphate layer covers the surface of the substrate layer; the lithium manganese iron phosphate layer comprises the following components in parts by weight: 62-68 parts by weight of lithium manganese iron phosphate; 28-34 parts by weight of conductive agent; 2 to 4 parts by weight of water-based adhesive.

2. The functional current collector according to claim 1, characterized in that, The water-based adhesive is at least one of polyacrylonitrile, polyacrylic acid, and water-based polyurethane; Preferably, the water-based adhesive is polyacrylonitrile; the degree of polymerization of the polyacrylonitrile is 500 to 3000. Preferably, the degree of polymerization of the polyacrylonitrile is 2000 to 3000.

3. The functional current collector according to claim 1, characterized in that, The lithium manganese iron phosphate layer also contains 5-10 parts by weight of metal particles, wherein the metal particles are at least one of magnesium, titanium, zinc and aluminum. Preferably, the particle size D50 of the lithium manganese iron phosphate, conductive agent, and metal particles is less than 1 μm.

4. The functional current collector according to claim 1, characterized in that, The conductive agent includes conductive carbon black and conductive graphite.

5. The functional current collector according to claim 1, characterized in that, The thickness of the lithium manganese iron phosphate coating is 5-10 μm; the areal density of the lithium manganese iron phosphate coating is 11-11.3 g / m³. 2 The water content is 200-230 ppm.

6. The functional current collector according to claim 1, characterized in that, The chemical formula of the lithium iron manganese phosphate is LiMn. 1- x Fe x PO4, of which 0.4 <x<0.7; Preferably, the base layer is made of aluminum foil.

7. A method for preparing the functional current collector according to any one of claims 1 to 6, comprising the following steps: Step 1) Mix the raw materials containing lithium manganese iron phosphate, conductive agent and water-based binder evenly with water to obtain lithium manganese iron phosphate slurry; the solid content of the slurry is 44% to 48%; Step 2) Coat the substrate surface with lithium manganese iron phosphate slurry and then dry it to obtain the functional current collector.

8. The preparation method according to claim 7, characterized in that, The raw materials also contain 1 to 3 parts by weight of additives; the additives include dispersant PVP and wetting agent isopropanol; Preferably, the viscosity of the slurry is 400–600 mPa·s.

9. A lithium battery positive electrode, characterized in that, The present invention includes the functional current collector as described in any one of claims 1 to 6; wherein the lithium manganese iron phosphate coating of the functional current collector is provided with a lithium iron phosphate cathode material layer.

10. The application of the functional current collector according to any one of claims 1 to 6 or the lithium battery positive electrode according to claim 9 in the preparation of lithium batteries.

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