Cathode electrode for a secondary battery

Abstract

Cathode electrode for a secondary battery (150), comprising: a cathode current collector (152); and a cathode (156) arranged on a surface of the cathode current collector (152), the cathode (156) comprising: an active material containing at least one lithium iron phosphate and one lithium manganese iron phosphate, a binder comprising polytetrafluoroethylene, styrene-butadiene rubber and at least one polyacrylic acid and one polyacrylic acid-polyacrylonitrile copolymer, and a conductive filler, wherein the cathode electrode has an area capacitance in the range of 3 milliampere-hours per square centimeter to 10 milliampere-hours per square centimeter; wherein the active material is present in the cathode (156) in a range of 82 wt.% to 97.5 wt.% of the total weight of the cathode (156), and the binder is present in the cathode (156) in a range of 1.5 wt.% to 7 wt.%.-% of the total weight of the cathode (156) is present and the conductive filler is present in the cathode (156) in a range of 0.5 wt.% to 10 wt.% of the total weight of the cathode (156), wherein the total weight is 100 wt.%; wherein the at least one of polyacrylic acid and a polyacrylic acid-polyacrylonitrile copolymer is present in the range of 0.4 wt.% to 1.5 wt.% of the total weight of the cathode (156), the styrene-butadiene rubber is present in the range of 2 wt.% to 4 wt.% of the total weight of the cathode (156), and the polytetrafluoroethylene is present in the range of 0.3 wt.% to 1 wt.% of the total weight of the cathode (156).

Description

background

[0001] Electric and hybrid electric vehicle technology is made possible by the development and use of rechargeable secondary batteries that power the vehicle's drivetrain. Secondary batteries include lithium-ion batteries, which generally consist of a cathode, an anode, a separator, and an electrolyte. The cathode is the source of the lithium ions and determines the battery's capacity and average voltage. The anode stores the lithium ions absorbed by the cathode and releases them when energy is needed. The separator prevents the cathode and anode from touching and short-circuiting the battery, and the electrolyte forms a medium between the cathode and anode through which the lithium ions move. The energy density, or...The surface capacity of the secondary battery can be increased by adding more active cathode and anode material and by increasing the density of the cathode and anode.

[0002] Cathode and anode electrodes can be formed by coating current collectors with active cathode material or active anode material, respectively. These coatings often contain the active materials, a binder, additives, and a solvent. However, at least in the case of cathodes, it has been found that simply adding more active cathode material and producing a thicker cathode coating to increase energy density is complicated by the formation of cracks during the coating drying process as the coating thickness increases. These cracks compromise the integrity of the thicker coating layers and can accelerate parasitic reactions with the electrolyte.

[0003] Although current lithium cathode chemistries fulfill their purpose, there is therefore a need for new and improved cathode chemistries that offer improved crack resistance when the area capacity of the cathode material coatings is increased. Description

[0004] According to various aspects, the present description relates to a cathode electrode for a secondary battery. The cathode comprises a cathode current collector and a cathode arranged on a surface of the cathode current collector. The cathode comprises an active material containing at least one lithium iron phosphate and one lithium manganese iron phosphate, a binder comprising polytetrafluoroethylene, styrene-butadiene rubber, and at least one polyacrylic acid and one polyacrylic acid-polyacrylonitrile copolymer, and a conductive filler, wherein the cathode electrode has an areal capacitance in the range of 3 milliampere-hours per square centimeter to 10 milliampere-hours per square centimeter.

[0005] In embodiments of the foregoing, the active material is present in the cathode in a range of 82 wt.% to 97.5 wt.% of the total weight of the cathode, the binder is present in the cathode in a range of 1.5 wt.% to 7 wt.% of the total weight of the cathode, and the conductive filler is present in the cathode in a range of 0.5 wt.% to 10 wt.% of the total weight of the cathode, the total weight being 100 wt.%.

[0006] In embodiments of the foregoing, the at least one of polyacrylic acid and a polyacrylic acid-polyacrylonitrile copolymer is present in the range of 0.4 wt.% to 1.5 wt.% of the total weight of the cathode, the styrene-butadiene rubber is present in the range of 2 wt.% to 4 wt.% of the total weight of the cathode, and the polytetrafluoroethylene is present in the range of 0.3 wt.% to 1 wt.% of the total weight of the cathode.

[0007] In embodiments of the above, the thickness of the cathode current collector is in the range of 5 micrometers to 50 micrometers and the thickness of the cathode is in the range of 100 micrometers to 500 micrometers.

[0008] In embodiments of the foregoing, the conductive filler comprises at least one of the following: metal wires, metal oxides, carbon nanotubes, carbon black, graphite flakes, graphite nanoparticles and graphite nanoplatelets.

[0009] In embodiments of the foregoing, the polytetrafluoroethylene is fibrillated.

[0010] In embodiments of the foregoing, the cathode current collector is coated with a layer of carbon particles, and the surface area of ​​the cathode current collector is in the range of 10 square meters per gram to 20 square meters per gram.

[0011] In other embodiments, the carbon particles have an average particle size in the range of 20 nanometers to 2000 nanometers and a specific surface area in the range of 25 square meters per gram to 2000 square meters per gram.

[0012] In further embodiments, the layer of carbon particles has a thickness in the range of 100 nanometers to 5 micrometers. Alternatively or additionally to the presence of the layer of carbon particles, the surface of the cathode current collector is etched.

[0013] In embodiments of the foregoing, the cathode electrode has a pressure density in the range of 1 gram per cubic centimeter to 3.0 grams per cubic centimeter.

[0014] In embodiments of the foregoing, the cathode electrode has a porosity in the range of 0.2 vol.% to 0.6 vol.% of the total volume of the cathode.

[0015] In embodiments of the foregoing, the cathode electrode has a charging efficiency and a specific capacitance, and the charging efficiency is greater than 98 percent, and the specific capacitance of the cathode electrode is in the range of 150 milliampere-hours per gram to 165 milliampere-hours per gram.

[0016] In embodiments of the foregoing, the binder contains polyacrylic acid, and at least a portion of the polyacrylic acid is lithium-substituted. Alternatively or additionally, the binder contains polyacrylic acid, wherein at least a portion of the polyacrylic acid is substituted by sodium.

[0017] According to various additional aspects, the present disclosure relates to a vehicle battery. The battery comprises a battery cell. The battery cell comprises a cathode arranged on the surface of a cathode current collector, an anode arranged on an anode current collector, a separator arranged between the anode and the cathode, and an electrolyte contacting the anode and the cathode. The cathode comprises an active material comprising at least one of lithium iron phosphate and lithium manganese iron phosphate, wherein the active material is present in the cathode in a range of 89 wt.% to 97.5 wt.% of the total weight of the cathode, and a binder comprising polyvinylidene fluoride and polytetrafluoroethylene, wherein the binder is present in a range of 2.1 wt.% to 6 wt.% of the total weight of the cathode.-% of the total weight of the cathode is present, and a conductive filler, wherein the conductive filler is present in a range of 0.5 wt.% to 5 wt.% of the total weight of the cathode.

[0018] In embodiments of the foregoing, the active material is present in the cathode in a range of 82 wt.% to 97.5 wt.% of the total weight of the cathode, the binder is present in the cathode in a range of 1.5 wt.% to 7 wt.% of the total weight of the cathode, and the conductive filler is present in the cathode in a range of 0.5 wt.% to 10 wt.% of the total weight of the cathode, the total weight being 100 wt.%.

[0019] In embodiments of the foregoing, the battery cell further comprises a cover which takes the form of either a pouch or a prismatic housing.

[0020] According to various additional aspects, the present disclosure relates to a method for manufacturing a cathode electrode for a secondary battery. The method comprises forming a slurry by mixing at least one polyacrylic acid and a copolymer of polyacrylic acid with polyacrylonitrile, an emulsion of styrene-butadiene rubber in water and a dispersion of polytetrafluoroethylene in water, an active material comprising at least one lithium iron phosphate and one lithium manganese iron phosphate, and a conductive filler to form a slurry. The method also comprises coating the slurry onto a cathode current collector and drying the coating to form a cathode.

[0021] In the above embodiments, the slurry has a solids content, and the method further comprises adjusting the solids content by adding water to the slurry prior to coating the slurry. Brief description of the drawings

[0022] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. Figure 1 shows a vehicle and a powertrain with a secondary battery according to the embodiments of the present disclosure. Fig. Figure 2A shows a battery according to the embodiments of the present disclosure. Fig. Figure 2B shows an exploded view of a pouch or prism battery cell according to the embodiments of the present disclosure. Fig.Figure 3 shows a general chemical structure for polyacrylic acid-polyacrylonitrile copolymers according to the embodiments of the present disclosure. Fig. Figure 4 illustrates a method for manufacturing a cathode electrode according to embodiments of the present disclosure. Fig. Figure 5 is a cross-sectional view of a cathode current collector comprising an olivine-like active cathode material and a triple binder according to the embodiments of the present disclosure. Fig. Figure 6 shows a diagram of a first charge and discharge cycle of a lithium iron phosphate electrode half-coin cell with 4 milliampere hours per square centimeter at 25 degrees Celsius, where the voltage (volts) on the y-axis is shown as a function of the area capacity (milliampere hours per square centimeter) shown on the x-axis. Fig.Figure 7 shows a diagram of the different discharge rates of a lithium iron phosphate electrode with an area capacitance of 4 milliampere hours per square centimeter at 25 degrees Celsius, where the voltage (volts) shown on the y-axis is shown as a function of the area capacitance (milliampere hours per square centimeter) shown on the x-axis. Fig. Figure 8 shows a diagram of the discharge capacity of a lithium iron phosphate electrode with an area capacity of 4 milliampere hours per square centimeter at 25 degrees Celsius, where the ratio of the discharge capacity to C / 3 (percentage) - shown on the y-axis - is shown as a function of the number of cycles - shown on the x-axis. Detailed description

[0023] The following description is merely exemplary and is not intended to limit the present disclosure, application, or use. Furthermore, there is no intention to be bound by any express or implied theory set forth in the preceding introduction, summary, or detailed description below. It should be understood that in the drawings, corresponding reference numerals denote identical or corresponding parts and features.

[0024] The following section refers in detail to several examples of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and the description to indicate identical or similar parts or steps. The drawings are simplified and not to scale.

[0025] References to "first," "second," "third," "fourth," etc., in the description and claims to designate elements are arbitrary and intended to facilitate understanding of the description. These references are not necessarily consistent between embodiments or between the description and the claims. In this sense, these references are not intended to limit the elements in any way. The elements are distinguishable by their arrangement, description, connections, and function.

[0026] The present disclosure relates to an olivine-like cathode with an areal capacity of more than 3.2 milliampere-hours per square centimeter. The olivine-like cathode contains at least one lithium iron phosphate or lithium manganese iron phosphate in a double binder, and a process for forming such cathodes using a water-based slurry in the coating process for cathode production. The olivine-like cathode has a crystal structure similar to the mineral olivine. The cathodes are incorporated into battery cells and secondary batteries, such as prismatic or pouch batteries. The batteries can then be used in electric or hybrid electric vehicles.

[0027] As used herein, the term "vehicle" is not limited to motor vehicles. While the technology presented here is primarily described in the context of electric and hybrid electric vehicles, it is not limited to these. The concepts can be used in a wide variety of applications, such as in conjunction with components used in motorcycles, mopeds, locomotives, aircraft, watercraft, and other vehicles, as well as in other battery-powered applications, such as portable power plants used to supply electricity to remote construction sites. These can be powered, for example, by solar or wind power plants, power grids, and fuel-based generators such as gasoline, propane, kerosene, or diesel generators, as well as Stirling engines.

[0028] Fig.Figure 1 illustrates a vehicle 100 with a drive system 120. The drive system 120 generally comprises an electric motor 124 and a secondary battery 126 for powering the electric motor 124. In many embodiments, the drive system 120 further comprises an inverter 128 for converting direct current (DC), as supplied by the battery 126, into alternating current (AC), as used by the electric motor 124. The inverter 128 may be contained in a power electronics module 130, which includes, for example, transistors and diodes to switch the current from DC to AC and vice versa.

[0029] A controller 132 is connected to the inverter 128 and programmed to control and manage the operation of the electric motor 124 and the associated hardware, including the inverter 128. The electric motor 124 is connected to a gearbox (drive unit) 136 and a drive train 138, which transmits mechanical power and rotation to the wheels 140 of the vehicle 100. The controller 132 comprises one or more processors and a tangible, non-volatile memory 134.

[0030] Referring again to the electric motor 124, the electric motor 124 is powered by the battery 126 and comprises a stator 142 and a rotor 144, which is arranged with the stator 142. The stator 142 is the stationary part of the electric motor 124. The stator 142 provides a rotating magnetic field with which the stationary magnetic field of the rotor 144 attempts to align, thereby setting the rotor 144 into a rotational motion, which can be described as "motor operation." In other applications, the rotating field of the rotor 144 (caused by the physical rotation) generates an electric current in the stator 142—this mode of operation is called "generation," and the electric motor 124 used in this way is called a generator. In vehicle applications, motor operation provides the motion of the vehicle 100.In generation mode, some of the energy recovered by braking when the vehicle comes to a stop is stored back in the vehicle battery 126.

[0031] It will be directed to the Fig. 2A and Fig. Reference is made to 2B, which is an example of a secondary battery 126 for supplying an electric or hybrid electric vehicle 100, as in Fig. The electric vehicle shown is number 100. As mentioned above, secondary batteries are understood to be rechargeable batteries that can be discharged when a load is applied and recharged when an external power source is applied. In the Fig. 2A and Fig.Figure 2B shows the secondary battery 126 connected to a load 148, such as the electric motor 124. Other consumers 148 include various systems in the vehicle, such as air conditioning and infotainment systems. The secondary battery 126 comprises one or more battery cells 150 connected to each other. The battery cells 150 can be, for example, bag-shaped or prismatic, as described below. Alternatively, the battery cells 150 can also be cylindrical. During discharge, when a load is applied to the battery 126, Li + Ions move from the anode 158 to the cathode 156 through the separator 160 via the electrolyte 162. Equivalent electrons e- move through the circuit 146 from the cathode 156 to the anode 158 and deliver energy to the load 124. During the charging process, when an external voltage is applied, Li +Ions from the cathode 156 to the anode 158 via the electrolyte 162 through the separator 160 and can be deposited in the anode 158.

[0032] Each battery cell contains 150 cells, like those in Fig.The battery cell 150 shown in Figure 2B generally comprises a cathode current collector 152, a cathode 156 arranged on the cathode current collector 152, an anode current collector 154, an anode 158 arranged on the anode current collector 154, a separator 160 arranged between the cathode 156 and the anode 158, and an electrolyte 162. While the illustrated battery cells 150 comprise an anode 158 (and anode current collector 154) and a cathode (and a cathode current collector 152), the battery cell 150 can alternatively comprise two or more cathodes 156 (and cathode current collectors 152) and one or more anodes 158 (and anode current collectors 154). In further alternative embodiments, the battery cell 150 can contain one or more cathodes 156 (and cathode current collectors 152) and two or more anodes 158 (and anode current collectors 154).In each of the above embodiments, one or more separators 160 are inserted between the cathodes 156 and anodes 158 to prevent the cathodes 156 and the anodes 158 from coming into contact.

[0033] The battery cell 150 from Fig.2B can be used in a pouch-type battery cell or in a prismatic battery cell. In both embodiments, which have multiple cathodes 156 and multiple anodes 158, separators 160 are provided between the cathodes 156 and anodes 158. In some embodiments, a ribbon-shaped separator 160 can be folded in a Z-shape around each cathode 156 (and cathode current collector 152) and around each anode 158 (and anode current collector 154). In a pouch cell, the tabs 164 are welded to the cathode current collectors 152 and the anode current collectors 154, and the cover 166 is in the form of a flexible foil pouch made of aluminum or another material. In contrast, prismatic cells contain terminals to which the cathode current collectors 152 and anode current collectors 154 are connected, and the cover 166 consists of a relatively rigid housing, typically in the form of a cuboid.The tabs 164 or terminals connected to the cathode current collectors 152 originate from several battery cells 150 that are interconnected, for example by a busbar 168 or another electrical connection. Similarly, the tabs 164 or terminals connected to the anode current collectors 154 of several battery cells 150 are interconnected, for example by a busbar 169 or another electrical connection (see ). Fig. 2A).

[0034] In the various types of battery cells 150 mentioned above, the cathode current collector 152 and the anode current collector 154 are formed from conductive materials. In some embodiments, the cathode current collector 152 includes aluminum. Alternatively or additionally, the cathode current collector 152 can also include copper-clad aluminum and stainless steel. The anode current collector 154 can contain one or more of the following elements: copper, nickel, stainless steel, and titanium. The current collectors 152 and 154 are shown in the form of a foil; however, it should be noted that other forms are also possible, such as grids. In embodiments, a foil-like cathode current collector 152 and a foil-like anode current collector 154 are gas-impermeable. The cathode current collector 152 has a thickness in the range of 5 micrometers to 50 micrometers, including all values ​​and ranges contained therein, e.g.in the range of 5 micrometers to 25 micrometers. The anode current collector 154 has a thickness in the range of 4 micrometers to 50 micrometers, including all values ​​and ranges contained therein, e.g. in the range of 4 micrometers to 25 micrometers or 13 micrometers.

[0035] The surface area of ​​the cathode current collector 152 can be increased by adding a coating or by etching. Accordingly, in certain embodiments, the cathode current collector 152 includes a layer 153 of carbon particles arranged on the surface(s) of the cathode current collector 152 that contacts the cathode 156. In embodiments, the carbon particles have an average particle size in the range of 20 nanometers to 2000 nanometers, including all values ​​and ranges therein, as observed by scanning electron microscopy, and a surface area in the range of 25 square meters per gram to 2000 square meters per gram, including all values ​​and ranges therein, as determined using specific surface analysis based on Brunauer, Emmett, and Teller theory.The thickness of the carbon particle layer 153 on the cathode current collector 152 is in the range of 100 nanometers to 5 micrometers, including all values ​​and ranges within this range, such as 300 nanometers to 1 micrometer. In alternative or further embodiments, the surface of the cathode current collector 152, on which the cathode is arranged, is etched to increase the surface roughness of the cathode current collector 152. In some embodiments, the application of the carbon particle layer 153 or the etching of the cathode current collector 152 increases the surface area to a range of 10 square meters per gram to 2000 square meters per gram, including all values ​​and ranges within this range, such as 60 square meters per gram.

[0036] The cathode 156 contains an active material that serves as a source of lithium ions (Li). +) and can cause reversible incorporation or intercalation of lithium ions, which, for example, determines the capacity and average voltage of a battery. In certain cases, the active material comprises at least one lithium iron phosphate (LFP) and one lithium manganese iron phosphate (LMFP). In embodiments, the active material is present in the range of 82 wt.% to 97.5 wt.% of the total weight of the cathode 156, including all values ​​and ranges therein, such as in the range of 91 wt.% to 96 wt.% of the total weight of the cathode 156. The total weight of the cathode is 100 wt.%. In some embodiments, the active material is provided as a powder.

[0037] Lithium iron phosphate has the following formula: LiFePO4. It should be noted that additional trace elements such as carbon may be present in amounts up to 5.0 wt% of the total weight of the lithium iron phosphate. Furthermore, lithium iron phosphate has an average primary particle size ranging from 0.1 micrometers to 100 micrometers, including all values ​​and ranges within this range, such as 1.0 to 30 micrometers, and a specific surface area ranging from 3 square meters per gram to 50 square meters per gram, including all values ​​and ranges within this range, such as 14.7 square meters per gram. Additionally, lithium iron phosphate has a tapped density ranging from 0.3 grams per cubic centimeter to 2 grams per cubic centimeter, including all values ​​and ranges within this range, such as 2.02 grams per cubic centimeter.Tapped density refers to the bulk density after mechanically tapping a graduated cylinder or vessel containing the powder sample. The moisture content of the lithium iron phosphate is less than 500 parts per million, e.g., in the range of 350 parts per million to 450 parts per million. Furthermore, in certain embodiments, the lithium iron phosphate exhibits a discharge capacity of 164 milliampere-hours per gram at C / 5 (discharge over 5 hours) and 162.4 milliampere-hours per gram at C / 2 (discharge over 2 hours), as well as a coulombic efficiency of more than 99 percent in the first cycle.

[0038] Lithium manganese iron phosphate has the following formula: LiMn x Fe (1-x )PO4, where 0 < x ≤ 1. In embodiments, the lithium manganese iron phosphate comprises one or more of the following compositions: LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.75 Fe 0.25PO4, and LiMn 0.8 Fe 0.2 PO4. Alternatively or additionally, the lithium manganese iron phosphate compositions can be doped with magnesium or aluminum. Thus, the lithium manganese iron phosphate compositions can contain one or more of the following compositions in addition to or as an alternative to the compositions mentioned above: LiMn 0.7 Mg 0.05 Fe 0.25 PO4 and LiMn 0.7 Mg 0.05 Fe 0.25PO4. It should be noted that trace elements may be present in the lithium manganese iron phosphate up to 2 wt% of the total amount of the lithium manganese iron phosphate. The lithium manganese iron phosphate has an average primary particle size in the range of 10 nanometers to 1000 nanometers, including all values ​​and ranges within this range, e.g., from 20 nanometers to 300 nanometers, and a specific surface area in the range of 5 square meters per gram to 50 square meters per gram, including all values ​​and ranges within this range, e.g., from 8 square meters per gram to 25 square meters per gram. Furthermore, the lithium manganese iron phosphate has a tapped density in the range of 0.3 grams per cubic centimeter to 2.0 grams per cubic centimeter, including all values ​​and ranges within this range. B. 0.6 grams per cubic centimeter to 0.8 grams per cubic centimeter.The moisture content of the lithium manganese iron phosphate is less than 500 parts per million, for example, in the range of 350 parts per million to 450 parts per million. Furthermore, in certain embodiments, the lithium manganese iron phosphate exhibits a discharge capacity of 145 milliampere-hours per gram at C / 5 (discharge over 5 hours) and 140 milliampere-hours per gram at C / 2 (discharge over 2 hours), as well as a first-cycle coulombic efficiency of more than 96 percent.

[0039] In addition to the active materials, the cathode 156 also contains a binder. The binder is present in the range of 1.5 to 7 wt.% of the total weight of the cathode 156, including all values ​​and ranges therein, such as 2.5 to 2.7 wt. The total weight of the cathode is 100 wt.%. The binder comprises polyacrylic acid polymer or a copolymer thereof, styrene-butadiene rubber, and polytetrafluoroethylene. In embodiments, the polyacrylic acid polymer is present in the range of 0.4 wt.% to 1.5 wt.% of the total weight of the cathode 156, including all values ​​and ranges therein, such as 0.75 wt.% to 1.25 wt.% of the total weight of the cathode 156. The average molecular weight (Mw) of the polyacrylic acid polymer is in the range of 2,000,000 to 5,000,000 wt.%, including all values ​​and ranges therein. Polyacrylic acid can generally be represented by the formula -(CH2-CHCO2H)-.In embodiments, the carboxyl group hydrogen of polyacrylic acid (COOH) can be partially or completely replaced by Li. + via reaction with lithium-containing compounds, such as LiOH, to form lithium-substituted polyacrylic acid, PAALi x H (1-x) , to form, where 0 ≤x ≤ 1. In alternative or additional embodiments, the carboxyl group hydrogen of polyacrylic acid (COOH) can be partially or completely replaced by Na + by reaction with sodium-containing compounds, such as NaOH, to form sodium-substituted polyacrylic acid, PAANa x H (1-x) , to form, where 0 ≤ x ≤ 1. In further alternative or additional embodiments, the polyacrylic acid is copolymerized with polyacrylonitrile, resulting in a polyacrylic acid-polyacrylonitrile copolymer, wherein the general structure of the repeating units of the copolymer is given in Fig.Figure 3 shows the ratio n of m to in the range of 1:1 to 10:1.

[0040] The styrene-butadiene rubber is present in the range of 2 wt.% to 4 wt.% of the total weight of the cathode, including all values ​​and ranges within this range. The average molecular weight Mw of the styrene-butadiene rubber is in the range of 20,000 to 1,000,000, including all values ​​and ranges within this range. In embodiments, the styrene-butadiene rubber is provided as an emulsion in water, and the styrene-butadiene rubber is present in the emulsion in the range of 35 wt.% to 55 wt.% of the total weight of the emulsion, including all values ​​and ranges within this range, such as 40 wt.% of the total weight of the emulsion. In further embodiments, the emulsion contains a surfactant, such as carboxymethylcellulose (CMC) or other surfactants, in an amount of 0.3 wt.% to 1 wt.% of the total weight of the emulsion, including all values ​​and ranges therein.

[0041] The polytetrafluoroethylene is present in the range of 0.3 wt% to 1 wt% of the total weight of the cathode 156, including all values ​​and ranges therein, such as the range of 0.3 wt% to 0.5 wt% of the total weight of the cathode 156. The total weight of the cathode is 100 wt%. The average molecular weight (Mw) of the polytetrafluoroethylene is in the range of 5,000,000 grams per mole to 10,000,000 grams per mole, including all values ​​and ranges in between. The polytetrafluoroethylene is provided as a dispersion in water. In embodiments, the polytetrafluoroethylene is provided in the dispersion in the range of 10 wt% to 70 wt% of the total weight of the polytetrafluoroethylene-water dispersion, including all values ​​and ranges therein, such as 60 wt%.After application, the polytetrafluoroethylene is fibrillated and forms a fibrous web over the active materials, with the fibers in certain embodiments generally being aligned in a specific direction along the length of the fibers.

[0042] Furthermore, the cathode 156 also contains one or more conductive fillers. The conductive filler comprises, for example, one or more metal wires, metal oxides, carbon nanotubes, carbon black such as SUPER P-carbon black available from (IMERYS, Paris, France), graphite flakes, graphite nanoparticles, and graphite nanoplatelets. The carbon nanotubes include at least one single-walled carbon nanotube and one multi-walled carbon nanotube. The conductive filler is present in a range of 0.5 wt.% to 10 wt.% of the total weight of the cathode, including all values ​​and ranges therein. In embodiments, carbon black is present in a range of 0.5 wt.% to 3 wt.% of the total weight of the cathode, including all values ​​and ranges therein, such as 2.0 wt.% of the total weight of the cathode, and graphite flakes are present in a range of 0 wt.% to 1 wt.% of the total weight of the cathode.Conductive fillers are present in a range of 0% to 1% of the total weight of the cathode, including all values ​​and ranges within it, such as 0.5 wt% of the total weight of the cathode. Single-walled carbon nanotubes are present in a range of 0 wt% to 1 wt% of the total weight of the cathode, including all values ​​and ranges within it. The conductive fillers can be in either dry or wet form. In dry form, the conductive fillers are in the form of powders, flakes, nanotubes, etc. In wet form, the conductive fillers are in a dispersion or solution. The dispersion or solution may be aqueous in certain cases.

[0043] The cathode 156 has a thickness in the range of 80 micrometers to 500 micrometers, including all values ​​and ranges within this range, such as 110 micrometers. The cathode electrode, which comprises both the cathode current collector 152 and the cathode 156, has a thickness in the range of 85 micrometers to 550 micrometers when coated on one side of the cathode current collector 152, including all values ​​and ranges within this range, and when coated on both sides, it has a thickness in the range of 165 micrometers to 1050 micrometers, including all values ​​and ranges within this range for a double-sided cathode electrode, for example, in the range of 205 micrometers to 500 micrometers.In embodiments, the cathode electrode, when coated on one side with cathode 156, has an areal capacitance or charge capacity in the range of 3 milliampere-hours per square centimeter to 10 milliampere-hours per square centimeter, including all values ​​and ranges therein, such as 3.5 milliampere-hours per square centimeter to 4 milliampere-hours per square centimeter at a discharge rate of 0.1C (i.e., a 10-hour discharge) at room temperature, i.e., 21°C to 25°C. In certain embodiments, the deviation of the areal capacitance is ±0.3 percent. Furthermore, the cathode electrode has a density in the range of 1 gram per cubic centimeter to 3.0 grams per cubic centimeter, including all values ​​and ranges therein, such as 2 grams per cubic centimeter to 2.5 grams per cubic centimeter. In certain embodiments, the deviation of the density is ±0.3 percent.The compression density can be understood as the density of the cathode electrode after compaction by a calendering process. The porosity of the cathode 156 ranges from 20 vol% to 60 vol% of the total volume of the cathode 156, including all values ​​and ranges within this range, such as 25 vol% to 35 vol% of the total volume of the cathode, after compaction using a calendering process. Furthermore, the cathode electrode in half-coin cells exhibits a first charge efficiency of more than 98 percent, including all values ​​and ranges from 98 percent to 104 percent, a high specific capacity in the range of 150 milliampere-hours per gram to 165 milliampere-hours per gram, including all values ​​and ranges within this range, such as 158 milliampere-hours per gram, and a discharge rate ratio of 2C / 0.33C of more than 90 percent (where 2C is a half-hour discharge rate and 0.33C is a three-hour discharge rate).

[0044] The anode 158 comprises materials capable of reversible incorporation or intercalation of lithium ions at a lower electrochemical potential than the cathode material 156, such that an electrochemical potential difference exists between the anode 158 and the cathode 156. The anode material may include one or more of the following materials: lithium metal; lithium alloys such as lithium silicon alloy, lithium aluminum alloy, lithium indium alloy, lithium titanate, and lithium tin alloy; carbon-based materials such as graphite, activated carbon, carbon black, and graphene; silicon; silicon-based alloys; silicon oxide; silicon-based composite materials; tin oxide; aluminum; indium; zinc; germanium; and titanium oxide; as well as any combination thereof. In embodiments, the anode 158 has a thickness in the range of 50 micrometers to 150 micrometers, including all values ​​and ranges within this range.In embodiments, the anode 158 is applied to the anode current collector 154, forming a coating on the anode current collector 154 using a deposition process, such as a slurry-based process, a hot rolling process, extrusion, or additive manufacturing. The combined anode 158 and anode current collector 154 form an anode electrode, which will be discussed further here.

[0045] The separator 160 is a porous material consisting of an electrically insulating material that prevents the cathode 156 and the anode 158 from coming into contact and potentially shortening the circuit. The separator 160 is sandwiched between the cathode 156 and the anode 158, or at least partially enclosed, so that the lithium ions and the electrolyte 162 can pass through the pores of the separator 160. The separator 160 can consist of one or more composite materials, a polymeric material, and a nonwoven fabric. In certain embodiments, the separator contains at least one of the following materials: polyethylene, polypropylene, polyamide, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride. Furthermore, the separator 160 can be filled, i.e., contain fillers dispersed within it, the filler comprising a material such as glass fiber.In additional or alternative embodiments, the separator 160 can comprise at least one thermally stable porous polymer coating and a ceramic coating, such as an aluminum oxide coating. The coating is arranged on one or more surfaces of a porous polymer film, the polymer film being selected from at least one of the materials polyethylene and polypropylene. The separator 160 can contain one or more layers, each layer being formed from one or more of the aforementioned materials. The separator 160 can be in the form of a film or a mesh, e.g., a woven mesh or a slotted film. In embodiments, the separator 160 has a thickness in the range of 4 micrometers to 25 micrometers, including all values ​​and ranges contained therein.

[0046] The electrolyte 162 provides a medium between the cathode 156 and the anode 158 through which the lithium ions and the electrolyte migrate. The medium can be a liquid, a gel, or a solid and is capable of conducting the lithium ions between the cathode 156 and the anode 158. The electrolyte 162 penetrates the pores of the porous separator 160 and wets or otherwise contacts the surfaces of the cathode 156 and the anode 158, as well as the separator 160. In embodiments, the electrolyte 162 contains one or more lithium salts dissolved in a non-aqueous organic solvent.The lithium salts may contain 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(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethane)sulfonylimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiSFI), lithium (triethylene glycol dimethyl-1 ether) bis(trifluoromethanesulfonyl)imide (Li(G3)(TFSI)). and lithium to (trifluoromethanesulfonyl)azanide (LiTFSA). The lithium salt can be present in electrolyte 162 at a concentration (moles of salt per liter of solvent) in the range of 1 M to 4 M, including all values ​​and ranges within it, such as 2 M or 3 M.

[0047] The non-aqueous aprotic organic solvent contains one or more of various alkyl carbonates, such as cyclic carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC)), linear carbonates (e.g., dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)), aliphatic carboxylic acid esters (e.g., methyl formate, methyl acetate, methyl propionate), g-lactones (e.g., g-butyrolactone, g-valerolactone), chain ethers (e.g., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (e.g., tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane).

[0048] Furthermore, electrolyte 162 may contain a number of additives, such as vinyl carbonate, vinyl ethylene carbonate, propanesulfonate, 1,3,2-dioxathiolane-2,2-dioxide (DTD), LiPF₂O₂, and combinations thereof. Other additives may be diluents that do not coordinate with lithium ions but can reduce the viscosity of electrolyte 162, such as bis(2,2,2-trifluoroethyl) ether (BTFE), and flame retardants, such as triethyl phosphate.

[0049] In embodiments, a method 400 for forming a cathode electrode in Fig. 4 shown, with reference to Fig. 2B and further reference to Fig.Figure 5 shows a cathode electrode 500. In block 402, an aqueous slurry is formed, containing the active material, the binder, and the conductive fillers in an aqueous dispersion medium. The solids content of the slurry is in the range of 40 wt.% to 70 wt.% in embodiments, including all values ​​and ranges contained therein. As mentioned above, the cathode current collector 152 may, in certain embodiments, have been previously coated or etched with a layer 153 of carbon particles. During the formation of the slurry in block 402, each component (i.e., active material, binder, and conductive filler(s)) may be added individually or in groups.In one embodiment, for example, dry conductive fillers can be mixed together, then the wet conductive fillers can be added to the dry conductive fillers, the active material can be added to the conductive fillers, then the binders are added, and water can be added to adjust the solids content; or the steps can be rearranged. The slurry in block 402 can be mixed using a planetary mixer. In addition, or alternatively, other mixers can be used. The mixer can have rotational speeds up to 10,000 revolutions per minute, including all values ​​and ranges from 10 revolutions per minute to 10,000 revolutions per minute.

[0050] In block 404, the slurry is then applied to the cathode current collector 152. In some embodiments, the coating is applied by nozzle coating. In the Fig. In the embodiment shown in Figure 5, a cathode 156 is coated on both sides of the cathode current collector 152. Alternatively or additionally, the coating can also be applied by other methods such as roller coating, dip coating, or dip coating. In block 406, the cathode 156 dries on the cathode current collector 152, and the water can be removed by evaporation. In some embodiments, the coated cathode current collector 152, including the coating, can be placed in an oven. The amount of water is reduced to 500 parts per million or less, for example, to 0 parts per million to 500 parts per million. Example

[0051] A cathode electrode was used after the Fig.The cathode was constructed according to the methods described in Figure 4 using 93.4 wt% lithium iron phosphate, 2 wt% carbon black, 0.5 wt% graphite flakes, 0.1 wt% single-walled carbon nanotubes, 1 wt% polyacrylic acid, 2.5 wt% styrene-butadiene rubber, and 0.4 wt% polytetrafluoroethylene, where wt% represents the wt% of the total weight of the cathode. The mass loading of the cathode was 26.7 milligrams per square centimeter. The cathode was observed to exhibit flexibility without cracking when applied to rods of various diameters of 8 mm, 10 mm, and 18 mm.

[0052] The cathode coating was applied to three aluminum electrodes, which were used to manufacture three half-coin cells. The cathode electrode of the half-coin cells had an area capacitance of 4 milliampere-hours per square centimeter. Fig.Figure 6 shows the capacity per unit area, milliampere-hours per square centimeter (on the x-axis), as a function of the measured voltage, volts (on the y-axis). Charging was performed from 2.2 volts to 3.65 volts at a charging rate of C / 20 (or 20 hours) in constant current mode to reach 3.65 V. Then, the charging was switched to constant voltage mode, with a cutoff current of C / 100, and a discharge rate of C / 20 (or 20 hours) to 2.2 V. As can be seen in the graph, the three half-cells exhibited relatively uniform performance. The average coulombic efficiency of the first charge of the three half-cells was determined at 25 degrees Celsius. Table 1 shows the milliampere-hours per gram (mAh / g) during charging, the milliampere-hours per gram (mAh / g) during discharging, the coulombic efficiency in percent (%), and the average coulombic efficiency in percent (%). Table 1. Charging, discharging and coulombic efficiency Cell No. Charge (mAh / g) Discharge (mAh / g) Coulomb efficiency % Average Coulomb efficiency % 1 157,7 158,3 100,4 100,4 2 157,8 158,4 100,4 3 157,9 158,6 100,5

[0053] The discharge rates of the electrodes were tested at 25 degrees Celsius using one of the half-coin cells. Fig. Figure 7 shows the effect of the discharge rate on the voltage (volts) as a function of the capacity per unit area (milliampere-hours per square centimeter). The discharge rates tested were C / 3 (3 hours), 1C (1 hour discharge time), 2C (1 / 2 hour discharge time), and 4C (15 minutes discharge time). At a discharge rate of 2C, the battery retains 90 percent of its capacity, and at a discharge rate of 4C, the battery retains 65 percent of its capacity.

[0054] The discharge capacity, expressed as a percentage of the actual discharge rate to the discharge rate as C / 3, for the three half-coin cells as a function of the number of cycles is in Fig.Figure 8 illustrates this. As shown in the figure, the discharge capacity decreases with increasing discharge rate; however, when the discharge rate is reduced to C / 5 (discharge over 5 hours), the discharge capacity returns. The tested discharge rates include 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 half-cells showed similar trends.

[0055] The cathodes, battery cells, secondary batteries, and manufacturing processes described here offer a number of advantages. These advantages include, for example, the ability to produce an olivine-type cathode (including lithium iron phosphate or lithium manganese iron phosphate, or both) with an areal capacity of 3.2 milliampere-hours per square centimeter or more. Furthermore, the use of the triple binder system in cathode manufacturing suppresses surface cracking in the cathode coating.Furthermore, the cathode electrode in half-coin cells exhibits a first charge efficiency of more than 98 percent, including all values ​​and ranges from 98 percent to 104 percent, a high specific capacity in the range of 150 milliampere-hours per gram to 165 milliampere-hours per gram, including all values ​​and ranges within this range such as 161 milliampere-hours per gram, and a discharge rate of more than 90 percent at 2C / 0.33C and more than 65 percent at 4C / 0.33C. An additional advantage is that the cathode electrode can be molded and coated with a water-based coating, thereby reducing the reliance on organic dispersions that might otherwise require collection and recycling.

[0056] The term "controller" as used herein, and related terms such as microcontroller, control module, module, control unit, control system, 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., microprocessor(s), and associated non-volatile memory component(s) in the form of storage and storage devices (read-only memory, programmable read-only memory, random-access memory, hard disk, etc.). The controller 132 may also consist of several controllers electrically interconnected. The controller 132 may be connected to additional systems and / or controls of the vehicle 100, enabling the controller 132 to access data such as the vehicle 100's speed, acceleration, braking, and steering angle.

[0057] A processor can be a custom or off-the-shelf processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among several processors connected to 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.

[0058] The tangible, non-volatile memory 134 can include volatile and non-volatile memory, such as read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM). KAM is persistent or non-volatile memory that can be used to store various operating variables while the processor is powered off. The tangible, non-volatile memory 134 can be implemented using a variety of memory devices such as PROMs (programmable read-only memory), EPROMs (electrical PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combined memory devices capable of storing data, some of which represents executable table instructions used by the controller 132 to control various systems of the vehicle 100.

[0059] The description of the present revelation is merely exemplary, and variations that do not deviate from the core of the present revelation are to fall within its scope. Such variations are not to be considered a deviation from the spirit and scope of the present description.

Claims

[1] Cathode electrode for a secondary battery, comprising: a cathode current collector; and a cathode arranged on a surface of the cathode current collector, the cathode comprising: an active material containing at least one of lithium iron phosphate and one of lithium manganese iron phosphate, a binder comprising polytetrafluoroethylene, styrene-butadiene rubber and at least one polyacrylic acid and a polyacrylic acid-polyacrylonitrile copolymer, and a conductive filler, the cathode electrode has an area capacitance in the range of 3 milliampere hours per square centimeter to 10 milliampere hours per square centimeter. [2] Cathode electrode according to claim 1, wherein the active material is present in the cathode in a range of 82 wt.% to 97.5 wt.% of the total weight of the cathode, the binder is present in the cathode in a range of 1.5 wt.% to 7 wt.% of the total weight of the cathode and the conductive filler is present in the cathode in a range of 0.5 wt.% to 10 wt.% of the total weight of the cathode, wherein the total weight is 100 wt.%. [3] Cathode electrode according to claim 2, wherein the at least one of polyacrylic acid and a polyacrylic acid-polyacrylonitrile copolymer is present in the range of 0.4 wt.% to 1.5 wt.% of the total weight of the cathode, the styrene-butadiene rubber is present in the range of 2 wt.% to 4 wt.% of the total weight of the cathode, and the polytetrafluoroethylene is present in the range of 0.3 wt.% to 1 wt.% of the total weight of the cathode. [4] Cathode electrode according to claim 2, wherein the thickness of the cathode current collector is in the range of 5 micrometers to 50 micrometers and the thickness of the cathode is in the range of 100 micrometers to 500 micrometers. [5] Cathode electrode according to claim 2, wherein the conductive filler contains at least one of the following: metal wires, metal oxides, carbon nanotubes, carbon black, graphite flakes, graphite nanoparticles and graphite nanoplatelets. [6] Cathode electrode according to claim 2, wherein the polytetrafluoroethylene is fibrillated. [7] Cathode electrode according to claim 2, wherein the cathode current collector is coated with a layer of carbon particles and the surface area of ​​the cathode current collector is in the range of 10 square meters per gram to 20 square meters per gram. [8] Cathode electrode according to claim 7, wherein the carbon particles have an average particle size in the range of 20 nanometers to 2000 nanometers and a specific surface area in the range of 25 square meters per gram to 2000 square meters per gram. [9] Cathode electrode according to claim 7, wherein the layer of carbon particles has a thickness in the range of 100 nanometers to 5 micrometers. [10] Cathode electrode according to claim 2, wherein a surface of the cathode current collector is etched.

Images