Dual binder and dual solvent paste coating process for manufacturing olivine LFP / LMFP electrodes

Abstract

A positive electrode of a secondary battery, a vehicle battery including the same, and a method of forming a positive electrode of a secondary battery. The positive electrode comprises a positive electrode arranged on the surface of a positive current collector, wherein the positive electrode comprises an active material, an adhesive and a conductive filler; the active material comprises at least one of lithium iron phosphate and lithium manganese iron phosphate; the adhesive comprises polyvinylidene fluoride and polytetrafluoroethylene.

Description

Technical Field

[0001] This disclosure relates to a battery, and more particularly to a positive electrode of a secondary battery and a method for forming the electrode. Background Technology

[0002] Electric and hybrid electric vehicle technologies are realized through the development and deployment of rechargeable secondary batteries that power the vehicle's powertrain. Secondary batteries, including lithium-ion batteries, typically consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode provides the source of lithium ions and determines the battery's capacity and average voltage. The negative electrode stores and releases the lithium ions received from the positive electrode when energy is needed. The separator prevents the positive and negative electrodes from coming into contact and prevents short circuits. The electrolyte provides a medium between the positive and negative electrodes through which lithium ions move. The energy density or areal capacity of secondary batteries can be increased by adding more active materials to the positive and negative electrodes and by increasing the density of the positive and negative electrodes.

[0003] Positive and negative electrodes can be formed by coating the current collector with active positive and active negative electrode materials, respectively. The coating typically includes active materials, binders, additives, and solvents. However, at least for the positive electrode, it has been found that simply adding more active positive electrode material and creating a thicker positive electrode coating to increase energy density can be complicated by cracking that occurs during the drying process as the coating thickness increases. These cracks reduce the integrity of the thicker coating and may accelerate parasitic reactions with the electrolyte.

[0004] Therefore, while existing lithium cathode chemistry has achieved its intended purpose, new and improved cathode chemistry is needed to provide improved crack resistance as the areal capacity of cathode material coatings increases. Summary of the Invention

[0005] According to various aspects, this disclosure relates to a method for forming a positive electrode of a secondary battery. The method includes mixing a polyvinylidene fluoride solution dissolved in N-methyl-2-pyrrolidone, a first dispersion of polytetrafluoroethylene dissolved in water, further N-methyl-2-pyrrolidone, an active material, and a conductive filler together to form a slurry. The method further includes coating the slurry onto a positive electrode current collector and drying the coating to form the positive electrode.

[0006] In the above embodiments, the positive electrode includes an active material, polyvinylidene fluoride, polytetrafluoroethylene, and a conductive filler. The active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate, and the active material is present in the cathode at a weight of 89% to 97.5% of the total weight of the positive electrode. The polyvinylidene fluoride and polytetrafluoroethylene are present in total at a weight of 2.1% to 6% of the total weight of the positive electrode. The conductive filler includes at least one of metal wire, metal oxide, carbon nanotube, carbon black, graphite flakes, graphite nanoparticles, and graphite nanosheets, and the conductive filler is present at a weight of 0.5% to 5% of the total weight of the positive electrode.

[0007] In any of the above embodiments, the method further includes mixing using a planetary mixer.

[0008] Furthermore, in any of the above embodiments, water is present in the slurry in the range of 0.1% to 3% by weight of the total slurry weight.

[0009] Furthermore, in any of the above embodiments, the slurry is coated onto the positive current collector by die coating.

[0010] In any of the above embodiments, the method further includes mixing a first dispersion of polytetrafluoroethylene dissolved in water with N-methyl-2-pyrrolidone to form a second dispersion, adding a polyvinylidene fluoride solution dissolved in N-methyl-2-pyrrolidone to the second dispersion to form a third dispersion, adding a portion of conductive filler to the third dispersion, wherein the portion of conductive filler is a dry conductive filler, adding the remaining conductive filler to the third dispersion to form a fourth dispersion, wherein the remaining conductive filler is in the form of an aqueous slurry, and adding an active material to the fourth dispersion after mixing the dry conductive filler and the wet conductive filler. In other embodiments, the first dispersion of polytetrafluoroethylene dissolved in water comprises polytetrafluoroethylene present in the range of 10% to 60% by weight. Additionally, in any embodiment herein, the polyvinylidene fluoride solution comprising polyvinylidene fluoride present in the range of 5% to 12% by weight of the total weight of the solution. In yet another embodiment, N-methyl-2-pyrrolidone is added to the fourth dispersion and the solids content of the fourth dispersion is adjusted to be in the range of 40% to 70% of the total weight of the fourth dispersion. In yet another embodiment, the method further includes applying a vacuum to the third and fourth dispersions.

[0011] Alternatively, the method includes mixing an active material, a partially conductive filler (wherein the partially conductive filler is a dry conductive filler), and polyvinylidene fluoride powder to form a dry mixture; kneading the dry mixture with polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone and additional N-methyl-2-pyrrolidone in solution to form a dough; mixing N-methyl-2-pyrrolidone with a first dispersion of polytetrafluoroethylene dissolved in water; adding the mixture to water containing the dough to form a second dispersion; and mixing the second dispersion with the remaining conductive filler to form a third dispersion, wherein the remaining conductive filler is in the form of an aqueous slurry. In a further embodiment, the first dispersion of polytetrafluoroethylene dissolved in water comprises polytetrafluoroethylene present in the range of 10% to 60% by weight. Additionally, in an embodiment, the solution containing polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone contains polyvinylidene fluoride present in the range of 5% to 12% by weight of the total solution weight. In some further embodiments, the method includes adding N-methyl-2-pyrrolidone to a third dispersion and adjusting the solids content of the third dispersion to a range of 40% to 70% of the total weight of the third dispersion. Furthermore, in still other embodiments, the method includes applying a vacuum to the third dispersion.

[0012] According to various additional aspects, this disclosure relates to a positive electrode of a secondary battery. The positive electrode comprises a positive electrode disposed on the surface of a positive current collector. The positive electrode includes an active material, said active material comprising at least one of lithium iron phosphate and lithium manganese iron phosphate. The active material is present in the positive electrode in the range of 89% to 97.5% by weight of the total weight of the positive electrode. The positive electrode also includes a binder, said binder comprising polyvinylidene fluoride and polytetrafluoroethylene. The binder is present in the range of 2.1% to 6% by weight of the total weight of the positive electrode. The positive electrode further comprises a conductive filler. The conductive filler is present in the range of 0.5% to 5% by weight of the total weight of the positive electrode.

[0013] In the above embodiments, the conductive filler includes at least one of the following: metal wire, metal oxide, carbon nanotube, carbon black, graphite flakes, graphite nanoparticles, and graphite nanosheets.

[0014] In any of the above embodiments, polytetrafluoroethylene is fibrillated.

[0015] Furthermore, in any of the above embodiments, a layer of carbon particles is coated on the positive current collector, and the surface area of ​​the positive current collector is in the range of 25 m² / g to 2000 m² / g.

[0016] According to various additional aspects, this disclosure relates to vehicle batteries. The vehicle battery includes a positive electrode disposed on the surface of a positive current collector, a negative electrode disposed on a negative current collector, a separator located between the negative and positive electrodes, and an electrolyte in contact with the negative and positive electrodes. The positive electrode includes an active material, said active material including at least one of lithium iron phosphate and lithium manganese iron phosphate. The active material is present in the positive electrode in the range of 89% to 97.5% by weight of the total weight of the positive electrode. The positive electrode also includes a binder, said binder including polyvinylidene fluoride and polytetrafluoroethylene. The binder is present in the range of 2.1% to 6% by weight of the total weight of the positive electrode. The positive electrode also contains a conductive filler. The conductive filler is present in the range of 0.5% to 5% by weight of the total weight of the positive electrode. Attached Figure Description

[0017] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0018] Figure 1 The illustration shows a vehicle and a powertrain including a secondary battery according to an embodiment of this disclosure.

[0019] Figure 2A The illustration shows a battery according to an embodiment of the present disclosure.

[0020] Figure 2B The illustration shows a pouch-shaped or prismatic battery cell according to an embodiment of the present disclosure.

[0021] Figure 3 The illustration shows a method for forming a positive electrode according to an embodiment of the present disclosure.

[0022] Figure 4 The illustration shows a method for forming a positive electrode according to an embodiment of the present disclosure.

[0023] Figure 5 The illustration shows a method for forming a positive electrode according to an embodiment of the present disclosure.

[0024] Figure 6 This is a micrograph of an active material having an adhesive (including polytetrafluoroethylene fibers) illustrated at a scale of 1 micrometer according to an embodiment of the present disclosure.

[0025] Figure 7 The figure shows the first charge-discharge cycle curve of a 4 mA / cm² lithium iron phosphate electrode half-button battery at 25 degrees Celsius, where the voltage (volts) plotted on the y-axis is a function of the area capacity (mAh / cm²) plotted on the x-axis.

[0026] Figure 8The figure shows the discharge rates of a lithium iron phosphate electrode with an areal capacity of 4 mAh / cm² at 25 degrees Celsius, where the voltage (volts) plotted on the y-axis is a function of the areal capacity (mAh / cm²) plotted on the x-axis.

[0027] Figure 9 The figure shows a graph of the cycle number versus discharge capacity ratio of a lithium iron phosphate electrode with 4 mA / cm² at 25°C according to an embodiment of the present disclosure, where the y-axis represents the discharge capacity ratio and the x-axis represents the cycle number. Detailed Implementation

[0028] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or its uses. Furthermore, it is not intended to be bound by any express or implied theory presented in the foregoing background, summary of the invention, or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals denote similar or corresponding parts and features.

[0029] Reference will now be made in detail to several embodiments of this disclosure illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and description to denote the same or similar parts or steps. The drawings are simplified and not drawn to scale.

[0030] References to designated elements such as "first," "second," "third," "fourth," etc., in the specification and claims are arbitrary and intended to aid in understanding this disclosure. These references are not necessarily consistent between embodiments or between the specification and claims. In this sense, these references are not intended to limit the elements in any way. These elements can be distinguished by their configuration, description, connection, and function.

[0031] This disclosure relates to olivine-type cathodes with an areal density equal to or greater than 3.2 mAh / cm², and a method for forming such cathodes using a dual-solvent slurry during the coating process of preparing the cathode. The olivine-type cathode includes at least one of lithium iron phosphate or lithium manganese iron phosphate in a dual binder. The olivine-type cathode has a crystal structure similar to the mineral olivine. The cathode is incorporated into battery cells and secondary batteries, such as prismatic or pouch cells. These batteries can then be used in electric vehicles or hybrid electric vehicles.

[0032] As used herein, the term "vehicle" is not limited to automobiles. While this document primarily describes the technology in conjunction with electric vehicles and hybrid electric vehicles, the technology is not limited to electric vehicles and hybrid electric vehicles. These concepts can be used in a variety of applications, such as in combination with components for motorcycles, mopeds, locomotives, aircraft, ships and other vehicles, as well as other applications using batteries, such as portable power stations (e.g., portable power stations for powering remote work sites, emergency backup power), and permanent power stations associated with buildings and equipment, all of which can be powered by, for example, solar or wind power systems, power lines, and fuel-based generators (e.g., gasoline, propane, kerosene or diesel generators) as well as standard engines.

[0033] Figure 1 The illustration shows a vehicle 100 including a propulsion system 120. The propulsion system 120 typically includes an electric motor 124 and a secondary battery 126 for powering the electric motor 124. Furthermore, in many embodiments, the propulsion system 120 includes an inverter 128 for converting power from DC (direct current) supplied by the battery 126 to AC (alternating current) used by the electric motor 124. The inverter 128 may be included in a power electronics module 130, which includes, for example, transistors and diodes, for switching power from DC to AC and vice versa.

[0034] The controller 132 is connected to the inverter 128 and programmed to control and manage the operation of the electric motor 124 and related hardware including the inverter 128. The electric motor 124 is connected to the transmission (drive unit) 136 and the drivetrain 138, which transmits mechanical power and rotation to the wheels 140 of the vehicle 100. The controller 132 includes one or more processors and tangible, non-transitory memory 134.

[0035] Referring again to motor 124, the motor 124, powered by battery 126, includes a stator 142 and a rotor 144 arranged together with the stator 142. The stator 142 is the stationary part of the motor 124. The stator 142 provides a rotating magnetic field, and the stationary magnetic field of the rotor 144 attempts to align with this rotating magnetic field, thereby causing the rotor 144 to rotate in a so-called "electric" mode. In other applications, the rotating field of the rotor 144 (caused by physical rotation) generates current in the stator 142—this mode of operation is called "generating electricity," and the motor 124 used in this manner is called a generator. In traction motor vehicle applications, the driving mode provides motion to the vehicle 100. When the vehicle is stationary, the generating mode takes some energy recovered from braking and stores it back into the vehicle battery 126.

[0036] Now for reference Figure 2A and Figure 2B , Figure 2A and Figure 2B The illustration shows a device for use with electric vehicles or hybrid electric vehicles 100 (e.g. Figure 1 An embodiment of a secondary battery 126 powered by an electric vehicle 100 (illustrated in the diagram). As described above, a secondary battery is understood as a rechargeable battery that can discharge when a load is applied and recharge when an external power source is applied. (See reference...) Figure 2A and Figure 2B In the diagram, battery 126 is illustrated as being connected to a load 148, such as electric motor 124. However, other loads 148 include various systems in the vehicle, such as climate control systems and infotainment systems. Battery 126 includes one or more battery cells 150 assembled together. Battery cells 150 can be, for example, pouch-type or prismatic type, as discussed further below. Alternatively, battery cells 150 can be cylindrical. During discharge, when a load is applied to battery 126, Li + Ions move from the negative electrode 158 to the positive electrode 156 through the electrolyte 162 and membrane 160. Equivalent electrons (e - The energy is transferred from the positive terminal 156 to the negative terminal 158 via circuit 146, supplying energy to the load 124. During charging, when an external voltage is applied, Li... + Ions move from the positive electrode 156 to the negative electrode 158 through the electrolyte 162 and the membrane 160, and can be embedded in the negative electrode 158.

[0037] 150 per battery cell (e.g.) Figure 2B The illustrated battery cell typically includes a positive current collector 152, a positive electrode 156 disposed on the positive current collector 152, a negative current collector 154, a negative electrode 158 disposed on the negative current collector 154, a separator 160 disposed between the positive electrode 156 and the negative electrode 158, and an electrolyte 162. While the illustrated battery cell 150 includes one negative electrode 158 (and one negative current collector 154) and one positive electrode (and one positive current collector 152), the battery cell 150 may optionally include two or more positive electrodes 156 (and positive current collectors 152) and one or more negative electrodes 158 (and negative current collectors 154). In yet another alternative embodiment, the battery cell 150 may include one or more positive electrodes 156 (and positive current collectors 152) and two or more negative electrodes 158 (and negative current collectors 154). In any of the above designs, one or more diaphragms 160 are staggered between the positive electrode 156 and the negative electrode 158 to prevent the positive electrode 156 and the negative electrode 158 from coming into contact.

[0038] Figure 2BThe battery cell 150 shown can be used as a pouch cell or a prismatic cell. In any design with multiple positive electrodes 156 and multiple negative electrodes 158, a separator 160 is disposed between the positive electrodes 156 and the negative electrodes 158. In an embodiment, the strip separator 160 may be folded in a Z-shape around each positive electrode 156 (and positive current collector 152) and each negative electrode 158 (and negative current collector 154). In a pouch cell, tabs 164 are welded to the positive current collector 152 and the negative current collector 154, and the cover 166 is in the form of a flexible film pouch formed of aluminum or other materials. On the other hand, a prismatic cell includes terminals connected to the positive current collector 152 and the negative current collector 154, and the cover 166 is formed of a relatively rigid shell, typically in the form of a cuboid. Tabs 164 or terminals from multiple battery cells 150 connected to the positive current collector 152 are connected together, for example, via a busbar 168 or other electrical connection. Similarly, tabs 164 or terminals from multiple battery cells 150 connected to the negative current collector 154 are connected together, for example, via bus 169 or other electrical connectors (see...). Figure 2A ).

[0039] In the various types of battery cells 150 described above, the positive current collector 152 and the negative current collector 154 are formed of conductive material. In an embodiment, the positive current collector 152 comprises aluminum. Alternatively or additionally, the positive current collector 152 may comprise copper-clad aluminum and stainless steel. The negative current collector 154 may comprise one or more of copper, nickel, stainless steel, and titanium. Current collectors 152 and 154 are illustrated in the form of foil; however, it should be understood that other forms, such as a mesh, may be presented. In an embodiment, the foil positive current collector 152 and the foil negative current collector 154 are impermeable. The positive current collector 152 has a thickness ranging from 5 micrometers to 50 micrometers, including all values ​​and ranges therein (e.g., in the range of 5 micrometers to 25 micrometers). The negative current collector 154 has a thickness ranging from 4 micrometers to 50 micrometers, including all values ​​and ranges therein (e.g., in the range of 4 micrometers to 25 micrometers).

[0040] The surface area of ​​the positive electrode current collector 152 can be increased by adding a coating or etching. Therefore, in one embodiment, the positive electrode current collector 152 includes a carbon particle layer 153 disposed on the surface of the positive electrode current collector 152 in contact with the positive electrode 156. In one embodiment, the carbon particles have an average particle size in the range of 20 nm to 2000 nm (inclusive of all values ​​and ranges therein) and a surface area in the range of 25 m² / g to 2000 m² / g (inclusive of all values ​​and ranges therein). The thickness of the carbon particle layer 153 on the positive electrode current collector 152 is in the range of 100 nm to 5 μm (inclusive of all values ​​and ranges therein) (e.g., 300 nm to 1 μm). In an alternative or further embodiment, the surface of the positive electrode current collector 152 on which the positive electrode is disposed is etched to increase the surface roughness of the positive electrode current collector 152. In one embodiment, the application of the carbon particle layer 153 or the etching of the positive electrode current collector 152 increases the surface area to a range of 10 m² / g to 20 m² / g (inclusive of all values ​​and ranges therein) (e.g., 15 m² / g).

[0041] The positive electrode 156 includes an active material that provides lithium ions (Li ions). + The active material can be a source and can undergo reversible insertion or intercalation of lithium ions, thereby determining, for example, the battery capacity and average voltage. In embodiments, the active material includes at least one of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP). In embodiments, the active material is present in the range of 89 wt% to 97.5 wt% of the total weight of the positive electrode 156, including all values ​​and ranges therein (e.g., in the range of 94 wt% to 96 wt% of the total weight of the positive electrode 156). In embodiments, the active material is provided in powder form.

[0042] The molecular formula of lithium iron phosphate is: LiFePO4. It should be understood that additional trace elements (such as carbon) may be present at up to 5.0 wt% of the total weight of lithium iron phosphate. Additionally, the average primary particle size of lithium iron phosphate observed by scanning electron microscopy is in the range of 0.1 micrometer to 100 micrometers, including all values and ranges therein (such as 1.0 to 30 micrometers), and the specific surface area measured using Brunauer - Emmett - Teller (BET) surface area analysis is in the range of 3 square meters per gram to 50 square meters per gram, including all values and ranges therein (such as 14.7 square meters per gram). Further, the tapped density of lithium iron phosphate is in the range of 0.3 grams per cubic centimeter to 2 grams per cubic centimeter, including all values and ranges therein (such as 2.02 grams per cubic centimeter). The tapped density is understood as the bulk density after mechanically tapping a graduated measuring cylinder or container containing a powder sample. The moisture content of lithium iron phosphate is less than 500 parts per million (e.g., in the range of 350 to 450 parts per million). Additionally, in an embodiment, lithium iron phosphate has a discharge capacity of 164 mAh / g at C / 5 (discharge over 5 hours) and 162.4 mAh / g at C / 2 (discharge over 2 hours), and a first - cycle Coulombic efficiency greater than 99%.

[0043] The molecular formula of lithium manganese iron phosphate is: LiMn x Fe (1-x) PO4, where 0 < x ≤ 1. In an embodiment, lithium manganese iron phosphate comprises one or more of the following components: LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.75 Fe 0.25 PO4 and LiMn 0.8 Fe 0.2 PO4. Alternatively or additionally, the lithium manganese iron phosphate composition may be doped with magnesium or aluminum. Thus, in addition to or as an alternative to the above - mentioned composition, the lithium manganese iron phosphate composition may further comprise one or more of the following compositions: LiMn 0.7 Mg 0.05 Fe 0.25 PO4 and LiMn 0.7 Mg 0.05 Fe 0.25PO4. It should be understood that trace elements may be present at a maximum of 2% by weight of the total weight of lithium manganese iron phosphate. The average primary particle size of lithium manganese iron phosphate is in the range of 10 nm to 1000 nm, including all values ​​and ranges therein (e.g., 20 nm to 300 nm), and the specific surface area is in the range of 5 m² / g to 50 m² / g, including all values ​​and ranges therein (e.g., 8 m² / g to 25 m² / g). In addition, the tap density of lithium manganese iron phosphate is in the range of 0.3 g / cm³ to 2.0 g / cm³, including all values ​​and ranges therein (e.g., 0.6 g / cm³ to 0.8 g / cm³). The moisture content of lithium manganese iron phosphate is less than 500 parts per million (e.g., in the range of 350 to 450 parts per million). In addition, in the implementation scheme, lithium manganese iron phosphate has a discharge capacity of 145 mAh / g at C / 5 (discharge for more than 5 hours) and a discharge capacity of 140 mAh / g at C / 2 (discharge for more than 2 hours), as well as a first-cycle coulombic efficiency of more than 96%.

[0044] In addition to the active material, the positive electrode 156 also includes a binder. The binder is present in the range of 2.1 wt% to 6 wt% of the total weight of the positive electrode 156, including all values ​​and ranges therein. The binder includes polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In an embodiment, PVDF is present in the range of 2 wt% to 5.9 wt% of the total weight of the positive electrode 156, including all values ​​and ranges therein (e.g., 2 wt% to 4 wt% of the total weight of the positive electrode 156). The average molecular weight (Mw) of PVDF is in the range of 300,000 to 2,000,000, including all values ​​and ranges therein. In an embodiment, a PVDF solution is provided by mixing PVDF powder with N-methyl-2-pyrrolidone at a temperature in the range of 50°C to 80°C (including all values ​​and ranges therein). PVDF is provided in the range of 5% to 12% by weight of the total weight of the solution, including all values ​​and ranges therein.

[0045] Polytetrafluoroethylene (PTFE) is present in the range of 0.1 wt% to 2 wt% of the total weight of the positive electrode 156, including all values ​​and ranges therein (e.g., 0.3 wt% to 0.6 wt% of the total weight of the positive electrode 156). The average molecular weight (Mw) of PTFE is in the range of 5,000,000 g / mol to 10,000,000 g / mol, including all values ​​and ranges therein. PTFE is provided as a dispersion in water. In an embodiment, PTFE is provided in the dispersion in the range of 10 wt% to 70 wt% of the total weight of the PTFE-water dispersion, including all values ​​and ranges therein (e.g., 60 wt%).

[0046] In addition, the positive electrode 156 also includes a conductive filler. The conductive filler includes one or more of, for example, metal wires, metal oxides, carbon nanotubes, carbon black (e.g., SUPER P carbon black available from IMERYS in Paris, France), graphite flakes, graphite nanoparticles, and graphite nanosheets. The carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The conductive filler is present in an amount ranging from 0.5 wt% to 5 wt% of the total weight of the positive electrode, including all values ​​and ranges therein. In an embodiment, carbon black is present in an amount ranging from 0.5 wt% to 3 wt% of the total weight of the positive electrode, including all values ​​and ranges therein (e.g., 2.0 wt%), graphite flakes are present in an amount ranging from 0 wt% to 1 wt% of the total weight of the positive electrode, including all values ​​and ranges therein, and single-walled carbon nanotubes are present in an amount ranging from 0 wt% to 1 wt% of the total weight of the positive electrode, including all values ​​and ranges therein.

[0047] The positive electrode has a thickness ranging from 80 micrometers to 500 micrometers, including all values ​​and ranges therein (e.g., 110 micrometers). When coated on one side of the positive current collector 152, the positive electrode comprising the positive current collector 152 and the positive electrode 156 has a thickness ranging from 85 micrometers to 550 micrometers, including all values ​​and ranges therein, and when coated on both sides, the positive electrode comprising the positive current collector 152 and the positive electrode 156 has a thickness ranging from 165 micrometers to 1050 micrometers, including all values ​​and ranges therein for both sides of the positive electrode (e.g., in the range of 205 micrometers to 500 micrometers). In the embodiment, when the positive electrode 156 is coated on one side, the positive electrode has a capacity load in the range of 3 mAh / cm² to 6 mAh / cm² at a discharge rate of 0.1C (i.e., 10 hours of discharge) at room temperature (i.e., 21°C to 25°C), including all values ​​and ranges therein (e.g., 3.2 mAh / cm² to 4 mAh / cm²). Furthermore, the positive electrode has a compaction density in the range of 2 ± 0.7 g / cm³, or 1.5 g / cm³ to 2.5 g / cm³, including all values ​​and ranges therein. Compaction density can be understood as the density of the positive electrode after compaction using a calendering process. After compaction using a calendering process, the porosity of the positive electrode 156 is in the range of 20 vol% to 45 vol% of the total volume of the positive electrode 156. Furthermore, in the semi-button cell, the positive electrode has a first charge efficiency greater than 98% (including all values ​​and ranges from 98% to 104%), a high specific capacity in the range of 150 mAh / g to 165 mAh / g (including all values ​​and ranges therein, such as 161 mAh / g), and a discharge rate of greater than 91% at 2C / 0.33C and greater than 80% at 4C / 0.33C.

[0048] The negative electrode 158 comprises a material capable of undergoing reversible insertion or intercalation of lithium ions at a lower electrochemical potential than that of the positive electrode 156 material, such that an electrochemical potential difference exists between the negative electrode 158 and the positive electrode 156. The negative electrode material may include metallic lithium; lithium alloys (e.g., lithium-silicon alloys, lithium-aluminum alloys, lithium-indium alloys, lithium titanate, and lithium-tin alloys); carbon-based materials (e.g., graphite, activated carbon, carbon black, and graphene); silicon; silicon-based alloys; silicon oxide; silicon-based composites; tin oxide; aluminum; indium; zinc; germanium; and titanium oxide; and any combination thereof. In an embodiment, the negative electrode 158 has a thickness ranging from 50 micrometers to 150 micrometers, including all values ​​and ranges therein. In an embodiment, the negative electrode 158 is applied to the negative electrode current collector 154 using a deposition process (e.g., a slurry-based process, a hot roll forming process, extrusion, or additive manufacturing) to form a coating on the negative electrode current collector 154. The combined negative electrode 158 and negative current collector 154 provide the negative electrode, as further mentioned herein.

[0049] The separator 160 is a porous material formed of an electrically insulating material that prevents the positive electrode 156 and the negative electrode 158 from contacting and prevents potential short circuits. The separator 160 is sandwiched or at least partially surrounded between the positive electrode 156 and the negative electrode 158, allowing lithium ions and electrolyte 162 to pass through the pores of the separator 160. The separator 160 may comprise one or more of composite materials, polymeric materials, and nonwoven materials. In embodiments, the separator comprises at least one of polyethylene, polypropylene, polyamide, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride. Additionally, the separator 160 may be filled, i.e., include fillers dispersed therein, wherein the fillers include materials such as glass fibers. In additional or alternative embodiments, the separator 160 may comprise at least one of a thermally stable porous polymer coating and a ceramic coating such as an alumina coating. The coating is disposed on one or more surfaces of a porous polymer membrane selected from at least polyethylene and polypropylene. The separator 160 may comprise one or more layers, wherein each layer is formed of one or more of the aforementioned materials. The diaphragm 160 can be in the form of a membrane or a mesh, such as a woven mesh or a cut membrane. In an embodiment, the membrane 160 has a thickness ranging from 4 micrometers to 25 micrometers, including all values ​​and ranges therein.

[0050] Electrolyte 162 provides a medium for lithium ion passage between positive electrode 156 and negative electrode 158, through which lithium ions and electrolyte move. The medium can be liquid, gel, or solid and is capable of conducting lithium ions between positive electrode 156 and negative electrode 158. Electrolyte 162 permeates the pores of porous membrane 160 and wets or otherwise contacts the surfaces of positive electrode 156, negative electrode 158, and membrane 160. In embodiments, electrolyte 162 comprises one or more lithium salts dissolved in a non-aqueous organic solvent. The lithium salt may include one or more of the following: lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalate)borate (LiB(C2O4)2) (LiBOB), lithium difluorooxalateborate (LiB) Lithium salts, including lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethane)sulfonylimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiSFI), lithium bis(trifluoromethanesulfonyl)imide (Li(G3)) (TFSI), and lithium bis(trifluoromethanesulfonyl)nitrogen hybrid (LiTFSA), can be present in electrolyte 162 at concentrations ranging from 1M to 4M (moles of salt per liter of solvent), including all values ​​and ranges therein (e.g., 2M or 3M).

[0051] Non-aqueous aprotic organic solvents include a variety of alkyl carbonates, such as cyclic carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), fluoroethylene carbonate (FEC)), linear carbonates (e.g., dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC)), aliphatic carboxylic acid esters (e.g., methyl formate, methyl acetate, methyl propionate), γ-lactones (e.g., γ-butyrolactone, γ-valerolactone), chain ethers (e.g., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (e.g., tetrahydrofuran, 2-methyltetrahydrofuran), and 1,3-dioxolane.

[0052] In addition, electrolyte 162 may include a variety of additives, such as, but not limited to, ethylene carbonate, ethylene ethylene carbonate, propanesulfonate, 1,3,2-dioxane-2,2-dioxide (DTD), LiPF2O2, and combinations thereof. Other additives may include diluents (e.g., bis(2,2,2-trifluoroethyl) ether (BTFE)) that do not coordinate with lithium ions but can reduce the viscosity of electrolyte 162, and flame retardants (e.g., triethyl phosphate).

[0053] The aforementioned positive electrode 156 is formed by forming a slurry and coating the slurry onto the positive electrode current collector 152. For example... Figure 3 As shown, a method for forming a positive electrode coating typically includes mixing a binder, active material, and conductive filler at frame 302 to form a slurry, wherein the binder comprises a polytetrafluoroethylene dispersion dissolved in water with an N-methyl-2-pyrrolidone dispersion medium and polyvinylidene ethylene dissolved in an N-methyl-2-pyrrolidone solution. At frame 304, the slurry is coated onto the positive electrode current collector 152 using a coating process such as molding, roller coating, dip coating, etc., to form a positive electrode 156. At frame 306, the coating is dried, and any dispersion medium and solvent that have not yet evaporated from the slurry are removed from the coating. In one embodiment, the process begins with mixing the binder, forming a dispersion, incorporating powder material into the dispersion, and adjusting the solids content to obtain the desired slurry consistency for coating to form the positive electrode. In an alternative embodiment, the process begins with dry mixing of powder, adding the binder and forming a dispersion, and then adjusting the solids content to obtain the desired slurry consistency for coating to form the positive electrode. In any of the above processes, once the slurry is formed, a coating is applied to the positive current collector to form the positive electrode and the dispersion medium / solvent is removed. Furthermore, the process uses two solvents, i.e., a dual-solvent system. Without being bound by any particular theory, these two solvents allow for adjustment of the evaporation rate during the positive electrode coating drying process, which is understood to suppress surface cracking in the positive electrode 156.

[0054] Figure 4 An embodiment of method 400 for forming a slurry to produce a positive electrode 156 is illustrated. At block 402, an N-methyl-2-pyrrolidone 401 dispersion medium is mixed with a first dispersion of polytetrafluoroethylene 403 dissolved in water to form a second dispersion. As described above, polytetrafluoroethylene is provided in the first dispersion dissolved in water at a rate ranging from 10% to 70% by weight of the total weight of the first dispersion, including all values ​​and ranges therein (e.g., 60% by weight). In an embodiment, mixing is performed at a rate ranging from 20 rpm to 500 rpm (inclusive) during a first mixing time period ranging from 10 minutes to 20 minutes (inclusive of all values ​​and ranges therein, e.g., 15 minutes).

[0055] At frame 404, a polyvinylidene fluoride solution 405 is incorporated into the second dispersion to form a third dispersion, wherein the polyvinylidene fluoride solution 405 comprises polyvinylidene fluoride provided in N-methyl-2-pyrrolidone at a weight percentage ranging from 5% to 12% of the total weight percentage of the above solution. Mixing is carried out at a speed ranging from 20 rpm to 1000 rpm during a first mixing time period ranging from 20 minutes to 40 minutes (inclusive, e.g., 30 minutes).

[0056] At frame 406, one or more dry conductive fillers 407 are incorporated into a third dispersion containing two binders. The dry conductive filler forms part of the conductive filler added to the coating. Alternatively, the dry conductive filler is the only filler added to the third dispersion. In an embodiment, the conductive filler comprises carbon black and graphite flakes. However, any of the aforementioned conductive fillers or additional conductive fillers may be added at this time. During a first mixing time period ranging from 20 to 40 minutes (inclusive, e.g., 30 minutes), the dispersion including the dry conductive filler is mixed at a speed ranging from 30 rpm to 2000 rpm (inclusive).

[0057] At box 408, one or more wet conductive fillers 409 (i.e., conductive fillers provided in the form of an aqueous slurry) are mixed into the third dispersion to form a fourth dispersion. In an embodiment, the wet conductive filler forms the remainder of the conductive filler added to the third dispersion. Alternatively, the wet conductive filler is the only filler added to the third dispersion. In an embodiment, carbon nanotubes from the slurry are added to the third dispersion. However, any of the aforementioned conductive fillers or other conductive fillers present in the dispersion or solution may be added at this time. During a first mixing time period ranging from 20 minutes to 40 minutes (inclusive, such as 30 minutes), the fourth dispersion containing the wet conductive filler is mixed at a speed ranging from 30 rpm to 2000 rpm (inclusive). Although box 408 is shown after box 406, it should be understood that in alternative embodiments, box 408 may be performed before or simultaneously with box 406.

[0058] At box 410, active material 411 is added to the fourth dispersion. The active material can be added as a dry powder or as a wet powder in a dispersion or solution. During a first mixing time period ranging from 40 minutes to 80 minutes (inclusive, e.g., 60 minutes), the fourth dispersion containing the active material is mixed under vacuum at a speed ranging from 30 rpm to 3000 rpm (inclusive). Although box 410 is shown after boxes 406 and 408, box 410 can be performed simultaneously with or before boxes 406 or 408.

[0059] At box 412, during a first mixing time period ranging from 5 to 30 minutes (inclusive, e.g., 15 minutes), N-methyl-2-pyrrolidone 413 is added to the fourth dispersion and mixed under vacuum at a speed ranging from 30 rpm to 2000 rpm (inclusive). The content of N-methyl-2-pyrrolidone is adjusted to obtain a solids content ranging from 40% to 70% by weight of the total slurry weight, inclusive, e.g., a solids content ranging from 45% to 65% by weight of the total slurry weight.

[0060] At box 414, mixing continues to form a slurry. Water is present in the slurry at a rate ranging from 0.05% to 5% of the total slurry weight, including all values ​​and ranges therein (e.g., 0.1% to 3% of the total slurry weight). During a first mixing period of 20 to 40 minutes (inclusive, e.g., 30 minutes), the dispersion is mixed under vacuum at a rate ranging from 20 rpm to 500 rpm (inclusive).

[0061] At box 416, the slurry is used to coat the positive current collector 152, as described above. The slurry coating is applied to the positive current collector 152 using a coating process such as die coating. Alternatively, other slurry coating processes, such as spraying or roller coating, may be used. At box 418, any remaining N-methyl-2-pyrrolidone is recovered from the slurry and coating, such that the N-methyl-2-pyrrolidone content in the coating is less than 0.1% by weight, including all values ​​and ranges therein (e.g., 0% to 0.1%). The water content of the coating is reduced to less than 500 parts per million, including all values ​​and ranges in the range of 0 to 500 parts per million.

[0062] Figure 5 Another embodiment of the method 500 for forming the positive electrode 156 is illustrated. At box 502, dry components comprising active material 501 and one or more dry conductive fillers 503, 505 are dry-mixed together to form a dry mixture. In one embodiment, the dry conductive filler comprises carbon black and graphite flakes. During a first mixing time period ranging from 20 minutes to 40 minutes (inclusive, e.g., 30 minutes), the dry powder is mixed at a speed ranging from 20 rpm to 500 rpm (inclusive).

[0063] At box 504, the polyvinylidene fluoride solution prepared as described above and dissolved in N-methyl-2-pyrrolidone 507 is added to the dry mixture along with additional N-methyl-2-pyrrolidone 509 to form a dough. During a first mixing time period of 20 to 40 minutes (inclusive, e.g., 30 minutes), the mixture is kneaded at a speed of 40 to 1000 rpm (inclusive).

[0064] At frame 506, a mixture 513 of polytetrafluoroethylene first dispersion 511 dissolved in water and N-methyl-2-pyrrolidone 515 is added to the dough to form a second dispersion. During a first mixing time period ranging from 40 to 80 minutes (inclusive, e.g., 60 minutes), the second dispersion is mixed at a speed ranging from 30 rpm to 3000 rpm (inclusive).

[0065] At box 508, wet conductive filler 517 (i.e., conductive filler dispersed in a dispersion medium or solvent) is added to the second dispersion to form a third dispersion. In an embodiment, carbon nanotubes in the slurry are added to the second dispersion. However, any of the aforementioned conductive fillers or other conductive fillers present in the dispersion or solution may be added at this time. During a first mixing time period ranging from 20 to 40 minutes (inclusive, e.g., 30 minutes), the third dispersion containing the wet conductive filler is mixed at a speed ranging from 30 rpm to 3000 rpm (inclusive). Although box 508 is illustrated after box 506, it should be understood that in alternative embodiments, box 508 may be performed before or simultaneously with box 506.

[0066] At box 510, during a first mixing period of 20 to 40 minutes (inclusive, e.g., 30 minutes), N-methyl-2-pyrrolidone 519 is mixed under vacuum at a speed in the range of 30 rpm to 2000 rpm (inclusive). The content of N-methyl-2-pyrrolidone is adjusted to obtain a solids content in the range of 40% to 70% by weight of the total slurry weight, inclusive (e.g., 45% to 65% by weight of the total dispersion weight).

[0067] At box 512, mixing continues to form a slurry. Water is present in the slurry at a rate ranging from 0.05% to 5% of the total slurry weight, including all values ​​and ranges therein (e.g., 0.1% to 3% of the total slurry weight). During a first mixing period of 20 to 40 minutes (inclusive, e.g., 30 minutes), the dispersion is mixed under vacuum at a rate ranging from 20 rpm to 500 rpm (inclusive).

[0068] At box 514, the slurry is used to coat the positive current collector 152, as described above. The slurry coating is applied to the positive current collector 152 using a coating process such as die coating. Alternatively, other slurry coating processes, such as spraying or roller coating, may be used. At box 516, any remaining N-methyl-2-pyrrolidone is recovered from the slurry and coating, such that the N-methyl-2-pyrrolidone content in the coating is less than 0.1% by weight, including all values ​​and ranges therein (e.g., 0% by weight to 0.1% by weight). The water content of the coating is reduced to less than 500 parts per million, including all values ​​and ranges in the range of 0 to 500 parts per million.

[0069] Above Figures 3 to 5 In the described method, the mixer is capable of exhibiting speeds up to 10,000 rpm, including all values ​​and ranges from 10 rpm to 10,000 rpm. In this implementation, the mixer is a planetary mixer. Alternatively, other mixers may be used.

[0070] Figure 6 An embodiment of the resulting positive electrode is illustrated, showing a micrograph at a 1-micrometer scale of the active material 602 and binder 604 forming the positive electrode 156 on the positive current collector 152. As shown, the active material 602 and polyvinylidene fluoride maintain a relatively granular shape. However, the polytetrafluoroethylene in the binder 604 fibrillates and forms fibers that are generally axially oriented in a given direction. In this embodiment, the orientation of the polytetrafluoroethylene fibers is caused by the coating process and forms a web on the active material 602.

[0071] Example

[0072] Using 94 wt% lithium iron phosphate, 2 wt% carbon black, 0.5 wt% graphite flakes, 0.1 wt% carbon nanotubes, 3 wt% polyvinylidene fluoride, and 0.4 wt% polytetrafluoroethylene, according to... Figure 4 The method shown constructs the positive electrode, where the weight percentage is the weight percentage of the total weight of the positive electrode. The solids content of the slurry is adjusted to 50% by weight of the total slurry weight. When applied to rods of various diameters of 8 mm, 10 mm, and 18 mm, the positive electrode was observed to exhibit flexibility without cracking.

[0073] A positive electrode coating is applied to three aluminum electrodes, which are used to provide three half-button cells. The positive electrode of the half-button cell has an areal density of 4 mA / cm². Figure 7 The graph illustrates the relationship between areal capacity (mAh / cm²) (on the x-axis) and measured voltage (volts) (on the y-axis). Under constant current mode, charging was performed from 2.2V to 3.65V at a rate of C / 20 (20 hours), followed by constant voltage charging mode with a cutoff current of C / 100 and a discharge rate of C / 20 to 2.2V. The graph shows that the performance of the three and a half coin cells is relatively consistent. The average first-charge coulombic efficiency of the three and a half coin cells was measured at 25°C. Table 1 below illustrates the charge capacity (mAh / g), discharge capacity (mAh / g), coulombic efficiency (%), and average coulombic efficiency (%).

[0074] Table 1. Charge, Discharge and Coulombic Efficiency

[0075]

[0076] The electrode discharge rate was tested using one and a half coin cells at 25 degrees Celsius. Figure 8 The diagram illustrates the effect of discharge rate on voltage (volts) as a function of areal capacity (mAh / cm²). The tested discharge rates were C / 3 (3 hours), 1C (1 hour discharge time), 2C (1 / 2 hour discharge time), and 4C (15 minutes discharge time). At a 2C discharge rate, the battery retained 91% of its capacity, and at a 4C discharge rate, it retained 80% of its capacity.

[0077] Figure 9 The figure illustrates the discharge capacity of three and a half coin cells as a function of cycle number, expressed as a percentage of the actual discharge rate to the C / 3 discharge rate. As shown in the figure, the discharge capacity decreases with increasing discharge rate; however, it recovers when the discharge rate returns to C / 5. The tested discharge rates included two tests at C / 20 (discharge over 20 hours), C / 10 (discharge over 10 hours), C / 5 (discharge over 5 hours), C / 3 (discharge over 3 hours), 1C (discharge over 1 hour), 2C (discharge over half an hour), and 4C (discharge over 15 minutes). All three and a half coin cells exhibited a similar trend.

[0078] The cathode, battery cell, secondary battery, and manufacturing method described herein offer numerous advantages. These advantages include, for example, the ability to produce olivine-type cathodes (including one or both of lithium iron phosphate and lithium manganese iron phosphate) with an areal density of 3.2 mAh / cm² or greater. Furthermore, the use of a dual-solvent system during cathode formation suppresses surface cracking in the cathode coating. Additionally, in semi-coin cells, the cathode exhibits a first-charge efficiency greater than 98% (including all values ​​and ranges from 98% to 104%), a high specific capacity in the range of 150 mAh / g to 165 mAh / g (including all values ​​and ranges therein, e.g., 161 mAh / g), and a discharge rate greater than 91% at 2C / 0.33C and greater than 80% at 4C / 0.33C.

[0079] As used herein, the term "controller" and related terms (e.g., microcontroller, control module, module, controller, control unit, processor, and similar terms) refer to one or more combinations of application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), electronic circuits, central processing units (e.g., microprocessors), and related non-transient memory components (read-only, programmable read-only, random access, hard disk drives, etc.) in the form of memory and storage devices. Controller 132 may also consist of multiple controllers electrically connected to each other. Controller 132 may interconnect with additional systems and / or controllers of vehicle 100, thereby allowing controller 132 to access data such as the speed, acceleration, braking, and steering angle of vehicle 100.

[0080] The processor may be a custom or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among several processors associated with the controller 132, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, a combination thereof, or generally a device for executing instructions.

[0081] The tangible non-transitory memory 134 may include volatile and non-volatile memory such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operational variables when the processor is powered off. The tangible non-transitory memory 134 may be implemented using multiple storage devices, such as PROM (programmable read-only memory), EPROM (electrical PROM), EEPROM (electrically erasable PROM), flash memory, or other electrical, magnetic, optical, or combined storage devices capable of storing data used by the controller 132 to control various systems of the vehicle 100, some of which represent executable instructions.

[0082] The descriptions in this disclosure are merely exemplary in nature, and changes that do not depart from the spirit and scope of this disclosure are intended to fall within its scope. Such changes should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A method for forming a positive electrode of a secondary battery, comprising: A slurry is formed by mixing polyvinylidene fluoride solution dissolved in N-methyl-2-pyrrolidone, polytetrafluoroethylene first dispersion dissolved in water, another N-methyl-2-pyrrolidone, active material and conductive filler together. The slurry is coated onto the positive current collector; and The coating is dried to form a positive electrode.

2. The method according to claim 1, wherein the positive electrode comprises the active material, polyvinylidene fluoride, polytetrafluoroethylene, and the conductive filler, wherein the active material comprises at least one of lithium iron phosphate and lithium manganese iron phosphate and the active material is present in the positive electrode in an amount ranging from 89% to 97.5% by weight of the total weight of the positive electrode, the polyvinylidene fluoride and polytetrafluoroethylene are present in total in an amount ranging from 2.1% to 6% by weight of the total weight of the positive electrode, and the conductive filler comprises at least one of metal wire, metal oxide, carbon nanotube, carbon black, graphite flakes, graphite nanoparticles, and graphite nanosheets and the conductive filler is present in an amount ranging from 0.5% to 5% by weight of the total weight of the positive electrode.

3. The method according to claim 2, further comprising: The first dispersion of polytetrafluoroethylene dissolved in water is mixed with the N-methyl-2-pyrrolidone to form a second dispersion; The polyvinylidene fluoride solution dissolved in N-methyl-2-pyrrolidone is added to the second dispersion to form a third dispersion; A portion of the conductive filler is added to the third dispersion, wherein the conductive filler is a dry conductive filler; The remaining conductive filler is added to the third dispersion to form a fourth dispersion, wherein the remaining conductive filler is in the form of an aqueous slurry. as well as After the dry conductive filler and the wet conductive filler are mixed in, the active material is added to the fourth dispersion.

4. The method according to claim 3, further comprising: N-methyl-2-pyrrolidone is added to the fourth dispersion and the solids content of the fourth dispersion is adjusted to be in the range of 40% to 70% of the total weight of the fourth dispersion.

5. The method according to claim 2, further comprising: The active material, a portion of the conductive filler, and polyvinylidene fluoride powder are mixed to form a dry mixture, wherein the portion of the conductive filler is a dry conductive filler. The dry mixture is kneaded with a polyvinylidene fluoride solution dissolved in N-methyl-2-pyrrolidone and another N-methyl-2-pyrrolidone to form a dough; N-methyl-2-pyrrolidone was mixed with a first dispersion of polytetrafluoroethylene dissolved in water, and the mixture was added to water containing dough to form a second dispersion; and The second dispersion is mixed with the remaining conductive filler to form a third dispersion, wherein the remaining conductive filler is in the form of an aqueous slurry.

6. The method according to claim 5, further comprising: N-methyl-2-pyrrolidone is added to the third dispersion and the solids content of the third dispersion is adjusted to be in the range of 40% to 70% of the total weight of the third dispersion.

7. A positive electrode of a secondary battery, comprising: A positive electrode, disposed on the surface of a positive electrode current collector, the positive electrode comprising: The active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate, wherein the active material is present in the positive electrode in a range of 89% to 97.5% by weight of the total weight of the positive electrode. An adhesive comprising polyvinylidene fluoride and polytetrafluoroethylene, wherein the adhesive is present in an amount ranging from 2.1% to 6% by weight of the total weight of the positive electrode. The conductive filler is present in the range of 0.5% to 5% by weight of the total weight of the positive electrode.

8. The positive electrode according to claim 7, wherein the conductive filler comprises at least one of the following: metal wire, metal oxide, carbon nanotube, carbon black, graphite flakes, graphite nanoparticles, and graphite nanosheets.

9. The positive electrode according to claim 7, wherein the positive current collector is coated with a layer of carbon particles, and the surface area of ​​the positive current collector is in the range of 25 m² / g to 2000 m² / g.

10. A vehicle battery, comprising: A positive electrode, disposed on the surface of a positive electrode current collector, the positive electrode comprising... The active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate, wherein the active material is present in the positive electrode in a range of 89% to 97.5% by weight of the total weight of the positive electrode. An adhesive comprising polyvinylidene fluoride and polytetrafluoroethylene, wherein the adhesive is present in an amount ranging from 2.1% to 6% by weight of the total weight of the positive electrode. A conductive filler, wherein the conductive filler is present in the range of 0.5% to 5% by weight of the total weight of the positive electrode; a negative electrode, which is disposed on a negative electrode current collector; A diaphragm, located between the negative electrode and the positive electrode; and An electrolyte that contacts both the negative electrode and the positive electrode.

Images