Coated lithium iron phosphate battery electrode and method

Abstract

The invention provides a lithium iron phosphate battery and a manufacturing method thereof. A lithium iron phosphate battery includes a lithium iron phosphate (LFP) cathode, a lithium anode, and a liquid electrolyte. A lithium iron phosphate (LFP) cathode has a coating adhered thereto. The coating includes greater than 70% by weight of a first material and less than 30% by weight of a second material. The first material has an average particle size (D50) of 10 microns ([mu] m) and the second material has an average particle size (D50) of 1 [mu] m. The liquid electrolyte transports positively charged ions between the lithium anode and the LFP cathode. The liquid electrolyte includes LiPF6 of 1.0 M to 1.5 M and LiFSI of 0 M to 0.5 M.

Description

Technical Field

[0001] This disclosure relates to lithium iron phosphate batteries, and more specifically, to a coated lithium iron phosphate cathode within a lithium iron phosphate battery. Background Art

[0002] Lithium-ion battery cells, such as prismatic cell cells, typically comprise multiple electrode stacks. Each electrode stack includes at least one negative electrode or anode, typically made of graphite, and at least one positive electrode or cathode, typically made of lithium cobalt oxide. A separator is located between the anode and cathode and prevents direct contact between them. An electrolyte facilitates ion movement between the anode and cathode. Lithium-ion battery cells using lithium cobalt oxide offer advantages such as high energy density, light weight, and low self-discharge rate. However, lithium-ion battery cells using lithium cobalt oxide are also sensitive to high temperatures, posing a risk of thermal runaway, and have a limited lifespan.

[0003] While existing methods and systems attempt to minimize the drawbacks of lithium-ion batteries using lithium cobalt oxide cathodes and can achieve their specific purposes, new and improved lithium-ion battery cells are still needed. Therefore, there is a need for lithium-ion battery cells that maximize energy capacity. Summary of the Invention

[0004] According to several aspects of this disclosure, a lithium iron phosphate (LFP) battery is provided. The LFP battery includes a lithium iron phosphate (LFP) cathode, a lithium anode, and a liquid electrolyte. The LFP cathode has a coating adhered thereto. The coating comprises more than 70% by weight of a first material and less than 30% by weight of a second material. The average particle size (D50) of the first material is 10 micrometers (μm), and the average particle size (D50) of the second material is 1 μm. The liquid electrolyte transports positively charged ions between the lithium anode and the LFP cathode. The liquid electrolyte comprises 1.0 M to 1.5 M of LiPF6 and 0 M to 0.5 M of LiFSI.

[0005] According to another aspect of this disclosure, the lithium iron phosphate battery includes a lithium iron phosphate cathode with a thickness of 80 to 120 μm.

[0006] According to another aspect of this disclosure, the lithium iron phosphate battery includes a load greater than 4.0 mAh / cm³. 2 Lithium iron phosphate cathode.

[0007] According to another aspect of this disclosure, the lithium iron phosphate battery includes a lithium iron phosphate cathode with a porosity in the range of 25%-30%.

[0008] According to another aspect of this disclosure, a lithium iron phosphate battery includes a first material, the first material being lithium iron phosphate powder.

[0009] According to another aspect of this disclosure, the lithium iron phosphate battery includes a second material, which is lithium iron phosphate powder.

[0010] According to another aspect of this disclosure, the lithium iron phosphate battery includes a lithium anode with a thickness of 5 to 60 μm.

[0011] According to another aspect of this disclosure, the lithium iron phosphate battery includes a liquid electrolyte with a viscosity in the range of 0.3 to 1.3 centipoise.

[0012] According to another aspect of this disclosure, a lithium iron phosphate battery includes a liquid electrolyte having 10% to 50% by weight of cyclic carbonate.

[0013] According to another aspect of this disclosure, the lithium iron phosphate battery has a liquid electrolyte comprising a cyclic carbonate, the cyclic carbonate comprising at least one of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, or 3,3,3-trifluoropropylene carbonate.

[0014] According to another aspect of this disclosure, the lithium iron phosphate battery has a liquid electrolyte comprising 10% to 90% by weight of at least one of acyclic acetate, propionate, or butyrate.

[0015] According to another aspect of this disclosure, the lithium iron phosphate battery has a liquid electrolyte, said liquid electrolyte comprising at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, or ethyl butyrate.

[0016] According to several aspects of this disclosure, a method for producing lithium iron phosphate (LFP) batteries is provided. The method includes: determining a coating formulation for a lithium iron phosphate (LFP) cathode; mixing a slurry; coating the LFP cathode with the slurry; drying the LFP cathode and the slurry to form a coating; and calendering the LFP cathode and the coating. The coating formulation comprises more than 70% by weight of a first material and less than 30% by weight of a second material. The average particle size (D50) of the first material is 10 μm, and the average particle size (D50) of the second material is 1 μm. The slurry comprises a coating form and at least one of a binder or a carbon suspension, and the solid content of the slurry is 55% or higher.

[0017] According to another aspect of this disclosure, the method includes a lithium iron phosphate cathode having a thickness of 80-120 μm.

[0018] According to another aspect of this disclosure, the method includes having a loading capacity greater than 4.0 mAh / cm³. 2 Lithium iron phosphate cathode.

[0019] According to another aspect of this disclosure, the method includes a lithium iron phosphate cathode having a porosity of 25% to 30%.

[0020] According to another aspect of this disclosure, the method includes a first material, which is lithium iron phosphate powder.

[0021] According to another aspect of this disclosure, the method includes a second material, which is lithium iron phosphate powder.

[0022] According to several aspects of this disclosure, a method for producing lithium iron phosphate (LFP) batteries is provided. The method includes: determining a coating formulation for a lithium iron phosphate (LFP) cathode; dry mixing a first material, a second material, and conductive carbon to form a dry mixture; wet mixing a polymer comprising polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) to form a first wet mixture; wet mixing PVDF, multi-walled carbon nanotubes (MWCNTs), and N-methyl-2-pyrrolidone (NMP) to form a second wet mixture; wet mixing the first wet mixture with the second wet mixture to form a third wet mixture; mixing the dry mixture with the third wet mixture to form a slurry, wherein the slurry has a solid content of 55% or higher; coating the lithium iron phosphate (LFP) cathode with the slurry; drying the lithium iron phosphate (LFP) cathode; and calendering the lithium iron phosphate (LFP) cathode. The coating formulation comprises more than 70% by weight of the first material and less than 30% by weight of the second material. The average particle size (D50) of the first material is 10 μm, and the average particle size (D50) of the second material is 1 μm. The solid content of the slurry is 55% or higher.

[0023] According to another aspect of this disclosure, the method includes adding N-methyl-2-pyrrolidone (NMP) to the slurry.

[0024] Other applicable areas of this disclosure will become apparent from the detailed description provided below. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0025] The above-described features and advantages, as well as other features and advantages, of the currently disclosed systems and methods will become apparent when taken in conjunction with the accompanying drawings and the detailed description including the claims and examples. Attached Figure Description

[0026] This disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0027] Figure 1This is a perspective view illustrating an example of a vehicle including a battery pack having multiple battery cells according to the present disclosure.

[0028] Figure 2 The diagram illustrates the settings according to this disclosure. Figure 1 The diagram shows a perspective view of a battery cell within a battery pack, wherein the battery cell includes at least one electrode stack having a lithium iron phosphate cathode, the cathode having a coating comprising a first material and a second material.

[0029] Figure 3 This is a flowchart illustrating a method for producing lithium iron phosphate batteries according to the present disclosure, the method comprising as follows: Figure 2 The coated lithium iron phosphate cathode is shown. Detailed Implementation

[0030] Reference will now be made in detail to several examples 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 following description is merely exemplary in nature and is not intended to limit the disclosure, its application, or its uses.

[0031] Compared to lithium-ion battery cells currently using nickel-cobalt-manganese (NCM) cathodes, lithium iron phosphate (LFP) cathodes exhibit higher thermal stability but lower specific capacity. For example, most current LFP cathodes have a loading of 3.25 mAh / cm². 2 The LFP battery cell and method disclosed in this paper have an increase in capacity to 4 mAh / cm³. 2 The load.

[0032] Furthermore, the LFP battery cell and method disclosed herein include an electrolyte system with low viscosity and high conductivity. The LFP battery cell can provide a specific capacity of approximately 130 mAh / g at a 3C rate, while the reference electrolyte provides only approximately 100 mAh / g.

[0033] Reference Figure 1The illustration shows a perspective view of a vehicle 10 having a battery pack 12 according to the present disclosure. The battery pack 12 is shown together with the exemplary vehicle 10. The vehicle 10 is an electric vehicle or a hybrid vehicle having wheels 11 driven by an electric motor / inverter 13. The electric motor / inverter 13 receives power from the battery pack 12. Although the vehicle 10 is illustrated as a passenger road vehicle, it should be understood that the battery pack 12 can be used with a variety of other types of vehicles. For example, the battery pack 12 can be used in marine vehicles (e.g., boats) or air vehicles (e.g., drones or passenger aircraft). Furthermore, the battery pack 12 can be used as a stationary power source separate from and independent of the vehicle. The battery pack 12 includes a housing 14 for supporting a plurality of battery cells 18. In the example, the battery pack 12 may have fifty or more battery cells 18.

[0034] Now refer to Figure 2 According to one aspect of this disclosure, the perspective view illustrates a setting... Figure 1 The battery pack 12 shown contains lithium iron phosphate (LFP) batteries 20. Each LFP battery 20 has a housing 22 or casing and at least one electrode stack 24, which includes a lithium iron phosphate (LFP) cathode 26, a lithium anode 28, a liquid electrolyte 30, and a separator 31. Each LFP battery 20 may have dozens or hundreds of electrode stacks 24. Each electrode stack 24 is connected to current collectors 32, 34. The electrode stacks are placed in the housing 22, and the housing 22 is filled with a suitable electrolyte 30. The current collectors 32, 34 are, for example, thin metal plates or foils disposed on either side of the electrode stacks 24 and / or the housing 22, and typically have a thickness of 0.4 mm to 1 mm. The current collectors 32, 34 may be made of copper or aluminum. The current collectors 32, 34 are connected to the electrode stacks 24 to transfer current to an external circuit (not shown).

[0035] Still refer to Figure 2 The LFP cathode 26 is formed from lithium iron phosphate (LiFePO4 or "LFP"). Unlike many cathode materials, LFP is a polyanionic compound composed of multiple negatively charged elements. Compared to the 2D plates made of nickel, manganese, and cobalt often used in many lithium batteries, LFP atoms are arranged in a crystalline structure, forming a 3D network of lithium ions. Phosphate is advantageous because it is a non-toxic material compared to cobalt oxide or manganese oxide, and LFP batteries are able to provide a constant voltage with longer charge cycles. In a specific example, the thickness of the LFP cathode 26 is 80 to 120 micrometers (μm). Cathode load is the volume fraction of cathode active material within the electrode mixture. Higher cathode loads typically result in increased energy density, which is the energy stored per unit volume or mass within a battery cell. In a specific example, the LFP cathode 26 has a capacity greater than 4.0 mAh / cm³. 2The loading. Porosity refers to the voids or pores present within the cathode. Porous cathodes (and electrodes) have high porosity, which facilitates the efficient transport of ions (such as lithium ions) and other electroactive materials. Low porosity can address the issue of high electrode density and improve battery energy density. In a specific example, the LFP cathode 26 has a porosity in the range of 25% to 30% and a loading of 2 g / cm³ (g / cc or g / cm³). 3 Electrode density in the range of 2.4 g / cc to 2.4 g / cc.

[0036] The LFP cathode 26 has a coating 36 comprising lithium particles adhered thereto, and the coating 36 may be disposed on multiple sides of the LFP cathode 26 (e.g., a first side opposite a second side). The coating 36 comprises a first material and a second material, each having a different particle size distribution. It has been found that using materials having only small particle sizes (e.g., ~1 μm) or only large particle sizes (e.g., ~10 μm) can lead to delamination and / or other problems. In some cases, the coating 36 may also be disposed on only one side of the LFP cathode 26.

[0037] Coating 36 comprises more than 70 wt.% of a first material. The first material is lithium iron phosphate powder with an average particle size (D50) of 10 μm. Coating 36 also comprises less than 30 wt.% of a second material. The second material is lithium iron phosphate powder with a D50 of 1 μm. The combination of the first and second materials with different particle size distributions is advantageous for forming coating 36 from a slurry with a high solid content (e.g., >55% solids), which is a key factor in electrode manufacturing. Furthermore, the designed cathode 26 is capable of withstanding multiple rolling processes, thereby addressing the issues of high electrode density and low porosity.

[0038] like Figure 2 As shown, the LFP battery 20 includes a lithium anode 28. The lithium anode 28 includes an ultra-thin (e.g., 5–60 micrometers (μm)) lithium anode. Positive charge / current flows from an external circuit into the LFP battery 20 through the lithium anode 28.

[0039] Reference Figure 2Electrolyte 30 comprises a liquid solution of an organic solvent and a lithium salt. Liquid electrolyte 30 is a conductive medium for ion transfer between the LFP cathode 26 and the lithium anode 28. Electrolyte 30 facilitates the movement of lithium ions during charge and discharge cycles. The electrolyte is of low viscosity (e.g., 0.3–1.3 centipoise (cP)). Using a low-viscosity liquid electrolyte is advantageous because it generally allows for faster molecular motion and collisions, which favors higher reaction rates and provides higher conductivity. In a specific example, electrolyte 30 comprises 1.0–1.5 mol (M) of lithium hexafluorophosphate (LiPF6) as a salt and 0–0.5 M of lithium bis(fluorosulfonyl)imide (LiFSI). Electrolyte 30 comprises a cyclic carbonate (e.g., 10 wt.%–50 wt.%) as a solid electrolyte intermediate phase (SEI). For example, the electrolyte can be ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, or 3,3,3-trifluoropropylene carbonate, and the cyclic carbonate has one of the following chemical structures:

[0040]

[0041] Wherein R1 and R2 may include hydrogen atoms, alkyl groups, methoxy groups, vinyl groups, propargyl groups, alkynyl groups, benzyl groups, hydroxyl groups, alkoxy groups, alkenyloxy groups, alkynyloxy groups, aryloxy groups, heterocyclic alkoxy groups, silyl groups, silanoxy groups, oxy groups, carboxyl groups, ester groups, ether groups, cyano groups, cyanoalkyl groups, fluorine atoms, including those of formula C. n H x F y or CH2C n H x F y or CH2OC n H x F y or CF2OC n H x F y The fluorinated alkyl group and / or fluorinated alkoxy group, wherein group n is 1-5, group m is 1-6, group x is 0-11, and group y is 1-11.

[0042] Additionally, electrolyte 30 may include acyclic acetates, propionates, and / or butyrates (e.g., 10-90 wt.%). Some examples may include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and / or ethyl butyrate, comprising one of the following chemical structures:

[0043]

[0044] Where R1 and R2 are respectively hydrogen atoms, alkyl groups, methoxy groups, vinyl groups, propargyl groups, alkynyl groups, benzyl groups, hydroxyl groups, alkoxy groups, alkenyloxy groups, alkynyloxy groups, aryloxy groups, heterocyclic oxy groups, heterocyclic alkoxy groups, silyl groups, silanoxy groups, oxy groups, carboxyl groups, ester groups, ether groups, cyano groups, cyanoalkyl groups, fluorine atoms, including C n H x F y or CH2C n H x F y or CH2OC n H x F y or CF2OC n H x F y The fluorinated alkyl group and / or fluorinated alkoxy group, wherein group n is 1-5, group m is 1-6, group x is 0-11, and group y is 1-11.

[0045] like Figure 2 As shown, the separator 31 is typically a thin, porous membrane or layer of material located between the anode 28 and the cathode 26, preventing contact between the anode 28 and the cathode 26 and thus preventing a short circuit. The separator 31 allows lithium ions to pass through and complete the circuit. Porous and chemically stable composite materials (e.g., composites made from polyethylene (PE), polypropylene (PP), or other natural materials) can be used as the separator 31. Furthermore, inorganic nanoparticles (e.g., TiO2, SiO2, Al2O3, AlO(OH) and ZrO2) can also be used to produce coating composites for the separator 31. Preferably, a thinner, more porous, and more conductive separator 31 can reduce resistance and improve the performance of the battery 20. The separator 31 is also selected to withstand high temperatures and manage thermal runaway, thereby preventing uncontrollable temperature increases due to exothermic reactions. Furthermore, the separator 31 has a high melting point and low shrinkage rate to avoid contact between the anode 28 and the cathode 26. The separator 31 has sufficient mechanical strength to resist puncture, tearing, or deformation during the manufacture and operation of the battery 20. The separator 31 is chemically inert and compatible with the electrolyte 30, cathode 26, anode 28, and other battery cell components. Furthermore, the separator 31 has a low affinity for water or other impurities that could contaminate the electrolyte 30 or cause corrosion of the cathode 26 or anode 28.

[0046] Reference Figure 3 According to this disclosure, a method 100 for bonding a foil stack 24 of electrode stacks 18 within a battery cell 18 is proposed.

[0047] The method begins at box 102. Box 102 depicts determining the coating formation of the lithium iron phosphate (LFP) cathode 26. Determining the coating formation may include using, for example, a computer processor to determine the content of a first material and a second material. Determining the first material may include determining a weight percentage of the first material such that the weight percentage of the first material is greater than 70 wt.%, and the average particle size of the first material is 10 μm. Determining the second material may include determining a weight percentage of the second material such that the weight percentage of the second material is less than 30 wt.%, and the average particle size of the second material is 1 μm. Method 100 may then proceed to box 104.

[0048] Box 104 depicts dry mixing of a first material, a second material, and conductive carbon to form a dry mixture. A stirrer configured for dry powder mixing can be used to mix the first material, the second material, and the conductive carbon. Dry mixing may include using a stirrer to at least substantially mix the first material, the second material, and the conductive carbon until the dry mixture is substantially homogeneous. Method 100 can then proceed to box 106.

[0049] Box 106 depicts the wet mixing of a polymer containing polyvinylidene fluoride (PVDF) (e.g., 1%-8%) in N-methyl-2-pyrrolidone (NMP) to form a first wet mixture. The mixing of the PVDF-containing polymer in N-methyl-2-pyrrolidone (NMP) can be carried out using a wet mixer (e.g., a tank with a grate mixer) until a first wet mixture with a general consistency is formed. In one example, the NMP includes TUBALL. TM BATT 0.4% NMP suspension (available from OCSiAl, Gahanna, Ohio) and 2% PVDF. Then method 100 can be moved to box 108.

[0050] Box 108 depicts the wet mixing of polyvinylidene fluoride (PVDF), multi-walled carbon nanotubes (MWCNTs), and N-methyl-2-pyrrolidone (NMP) to form a second wet mixture. The mixing of PVDF, MWCNTs, and NMP can be carried out using a wet mixer (e.g., a can with a grate mixer) until a second wet mixture with a generally consistent consistency is formed. Method 100 can then proceed to box 110.

[0051] Box 110 depicts the wet mixing of a first wet mixture with a second wet mixture to form a third wet mixture. The wet mixing of the first wet mixture with the second wet mixture can be achieved by adding the first wet mixture to the second wet mixture using, for example, a wet mixer (e.g., a tank with a screw mixer) to form a third wet mixture with a substantially consistent texture and viscosity. Method 100 can then proceed to box 112.

[0052] Box 112 describes mixing a dry mixture with a third wet mixture to form a slurry, wherein the slurry has a solids content of 50% or higher, or preferably 55% or higher. A reference solids content range can be 50% to 70%. The dry mixture and the third wet mixture can be mixed using, for example, a tank with a grate mixer, until a slurry with a consistent texture and little or no solid clusters is formed. The third wet mixture may include at least one of a binder or a carbon suspension. Method 100 then proceeds to box 114.

[0053] Box 114 depicts coating a lithium iron phosphate (LFP) cathode 26 with a slurry. Coating the lithium iron phosphate (LFP) cathode 26 may include using various deposition techniques, such as chemical vapor deposition. Coating the lithium iron phosphate (LFP) cathode 26 may include coating one or more sides of the cathode 26. The method then moves to box 116.

[0054] Box 116 depicts a dried lithium iron phosphate (LFP) cathode 26. Drying the cathode 26 may include using a dryer until the slurry and the resulting coating 36 are at least substantially dry. Method 100 then moves to box 118.

[0055] Box 118 depicts a calendered lithium iron phosphate (LFP) cathode 26. The calendered cathode 26 may include passing the cathode 26 and coating 36 between rolls at elevated temperatures to compact and homogenize the cathode 26 and coating 36. The calendered cathode 26 reduces electrode porosity, increasing the electrode density and volumetric energy density of the LFP cell 20.

[0056] In some cases, as shown in box 120, method 100 may include adding N-methyl-2-pyrrolidone (NMP) to the slurry prior to coating the LFP cathode 26. Adding NMP can adjust the total solids content of the slurry.

[0057] The LFP battery 20 disclosed herein is advantageous and beneficial compared to existing LFP batteries or other lithium batteries. Compared to current NCM (nickel-cobalt-manganese) cathodes, the LFP cathode 26 exhibits good thermal stability but has a lower specific capacity. The LFP cathode 26 disclosed herein addresses these issues by including a coating 36 with multiple particle size distributions on the LFP cathode 26 and combining it with a lithium anode 28 and reduced electrolyte viscosity. This combination provides a high loading capacity (e.g., 4 mAh / cm³). 2 Low porosity (e.g., 25%–30%) and high density (e.g., 1.8–2.4 g / cm³) 3 This increases energy density and exhibits good thermal behavior.

[0058] This description is merely illustrative in nature and is in no way intended to limit this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in many forms. Therefore, while this disclosure includes specific examples, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, description, and appended claims.

Claims

1. A lithium iron phosphate battery, comprising: A lithium iron phosphate (LFP) cathode having a coating adhered to the lithium iron phosphate cathode, wherein the coating comprises more than 70% by weight of a first material and less than 30% by weight of a second material, wherein the average particle size (D50) of the first material is 10 μm and the average particle size (D50) of the second material is 1 μm; Lithium anode; and A liquid electrolyte that transports positively charged ions between the lithium anode and the LFP cathode, wherein the liquid electrolyte comprises 1.0 M to 1.5 M LiPF6 and 0 M to 0.5 M LiFSI.

2. The lithium iron phosphate battery according to claim 1, wherein the thickness of the lithium iron phosphate cathode is 80-120 μm.

3. The lithium iron phosphate battery according to claim 1, wherein the lithium iron phosphate cathode has a loading greater than 4.0 mAh / cm². 2 .

4. The lithium iron phosphate battery according to claim 1, wherein the porosity of the lithium iron phosphate cathode is in the range of 25% to 30%.

5. The lithium iron phosphate battery according to claim 1, wherein the first material is lithium iron phosphate powder.

6. The lithium iron phosphate battery according to claim 1, wherein the second material is lithium iron phosphate powder.

7. The lithium iron phosphate battery according to claim 1, wherein the thickness of the lithium anode is 5-60 μm.

8. The lithium iron phosphate battery according to claim 1, wherein the viscosity of the liquid electrolyte is in the range of 0.3 to 1.3 centipoise.

9. The lithium iron phosphate battery according to claim 1, wherein the liquid electrolyte comprises 10% to 50% by weight of cyclic carbonate.

10. The lithium iron phosphate battery according to claim 9, wherein the cyclic carbonate comprises at least one selected from ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, or 3,3,3-trifluoropropylene carbonate.

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