Positive electrode comprising vinylidene fluoride and binder comprising perfluoroolefin copolymer for batteries circulating lithium ions

Abstract

The present invention relates to a positive electrode comprising vinylidene fluoride and a binder comprising a perfluoroolefin copolymer for batteries for recycling lithium ions. A lithium ion cycling battery includes a positive electrode comprising an electroactive positive electrode material and a polymer binder mixture. The polymeric binder mixture includes a polyvinylidene fluoride (PVDF) homopolymer and a copolymer comprising a vinylidene fluoride (VDF) monomer and at least one perfluoroolefin monomer. The positive electrode may be fabricated by depositing a precursor mixture on a substrate at a temperature of less than or equal to 30 degrees Celsius to form a precursor layer. The precursor mixture may include an electroactive positive electrode material, a polymeric binder mixture, and an organic solvent including gamma-valerolactone, dihydrolevoglucosenone, cyclopentanone, or a combination thereof. The organic solvent may be removed from the precursor layer to form the positive electrode on the substrate.

Description

Technical Field

[0001] The present disclosure relates to composite electrodes for battery packs for recycling lithium ions, and more particularly to a method of manufacturing composite electrodes using green solvents. Background Art

[0002] The information provided in this section is for a general introduction to the background of the present disclosure. The work of the currently named inventors described in this section, as well as aspects of the specification that may not have been determined to be prior art in other forms at the time of filing, are not expressly or implicitly admitted to be prior art of the present disclosure.

[0003] Lithium battery packs are widely used in various electronic devices and, due to their high energy and power density, are promising candidates for meeting the requirements of electric vehicles (including hybrid vehicles). Secondary lithium battery packs typically include a negative electrode, a positive electrode, and an electrolyte that provides a medium for lithium ion conduction between the negative and positive electrodes during discharge and charge of the battery pack. During manufacturing, the electrodes are typically deposited in the form of thin layers on a conductive metal current collector. The negative electrode layer and the positive electrode layer may have a composite structure that includes particles of an electrochemically active (electroactive) material embedded in a polymer binder. An example of a polymer binder that can be used to manufacture composite electrodes is polyvinylidene fluoride (PVDF).

[0004] Composite electrodes can be manufactured by depositing a slurry of electroactive material particles and a polymer binder in a solvent in the form of a continuous layer on a substrate and then removing the solvent. The polymer binder and solvent are typically selected to avoid undesirable chemical reactions with the electroactive material and to ensure good solubility of the polymer binder in the solvent. Summary of the Invention

[0005] According to one or more embodiments of the present disclosure, a battery pack for recycling lithium ions includes a positive electrode that includes a mixture of an electroactive material and a polymer binder. The polymer binder mixture includes a polyvinylidene fluoride (PVDF) homopolymer and a copolymer that includes vinylidene fluoride (VDF) monomers and at least one perfluoroolefin monomer. The copolymer has a structural formula of formula (1):

[0006]

[0007] Where:

[0008] m is greater than or equal to 3500 and less than or equal to 18000,

[0009] n is greater than or equal to 800 and less than or equal to 7500,

[0010] p is 1 or 0,

[0011] R1 is F or a perfluoroalkyl group,

[0012] R 2 is an alkylene group, and

[0013] X is an acidic functional group.

[0014] The copolymer may include poly(vinylidene fluoride - co - tetrafluoroethylene) (PVDF - TFE), poly(vinylidene fluoride - co - hexafluoropropylene) (PVDF - HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene (THV), or a combination thereof.

[0015] X may be selected from at least one acidic functional group including a carboxyl group (-C(=O)OH), a sulfo group (-S(=O) 2 -OH), a phosphonyl group (-P(=O)(-OH) 2 ), a nitro group (-NO 2 ), and a mercapto group (-SH).

[0016] The copolymer may have an ion - exchange capacity of greater than or equal to 0.05 milliequivalent H + per gram and less than or equal to 5 milliequivalents H + per gram.

[0017] The weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture may be greater than or equal to 1:1 and less than or equal to 3:1.

[0018] The PVDF homopolymer may have a molecular weight of greater than or equal to 500 kDa and less than or equal to 1500 kDa, and the copolymer may have a molecular weight of greater than or equal to 500 kDa and less than or equal to 1500 kDa.

[0019] The polymer binder mixture may account for greater than or equal to 0.5% and less than or equal to 5% by weight of the positive electrode.

[0020] The electroactive material may account for greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode.

[0021] The positive electrode may further comprise a carbon - based electrochemically inactive conductive material.

[0022] The battery pack may further include a negative electrode comprising an electroactive negative electrode material and an electrolyte permeating the positive electrode and the negative electrode. In this case, the electrolyte may comprise a non - aqueous polar aprotic organic solvent and a lithium salt in the non - aqueous polar aprotic organic solvent.

[0023] According to one or more embodiments of the present disclosure, a battery pack for recycling lithium ions includes a positive electrode comprising a mixture of an electroactive material and a polymer binder. The polymer binder mixture includes a polyvinylidene fluoride (PVDF) homopolymer and a copolymer, the copolymer including poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof.

[0024] The weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture can be greater than or equal to 1:1 and less than or equal to 3:1.

[0025] The PVDF homopolymer can have a molecular weight greater than or equal to 500 kDa and less than or equal to 1500 kDa, and wherein the copolymer can have a molecular weight greater than or equal to 500 kDa and less than or equal to 1500 kDa.

[0026] Wherein the copolymer can include at least one acidic functional group selected from carboxyl (-C(=O)OH), sulfo (-S(=O) 2 -OH), phosphonyl (-P(=O)(-OH) 2 ), nitro (-NO 2 ), and mercapto (-SH).

[0027] The polymer binder mixture can account for greater than or equal to 0.5% and less than or equal to 5% by weight of the positive electrode, and wherein the electroactive material can account for greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode.

[0028] According to one or more embodiments of the present disclosure, a method of manufacturing a positive electrode for a battery pack for recycling lithium ions includes depositing a precursor mixture on a substrate at a temperature less than or equal to 30 degrees Celsius to form a precursor layer. The precursor mixture includes an electroactive positive electrode material, a polymer binder mixture, and an organic solvent, the organic solvent including γ-valerolactone, dihydrolevoglucosenone, cyclopentanone, or a combination thereof. The organic solvent is removed from the precursor layer to form the positive electrode. The polymer binder mixture includes a polyvinylidene fluoride (PVDF) homopolymer and a copolymer having formula (1):

[0029]

[0030] Wherein:

[0031] m is greater than or equal to 3500 and less than or equal to 18000,

[0032] n is greater than or equal to 800 and less than or equal to 7500,

[0033] p is 1 or 0,

[0034] R 1 is F or a perfluoroalkyl group,

[0035] R 2 is an alkylene group, and

[0036] X is an acidic functional group.

[0037] The copolymer may include poly(vinylidene fluoride - co - tetrafluoroethylene) (PVDF - TFE), poly(vinylidene fluoride - co - hexafluoropropylene) (PVDF - HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof.

[0038] The weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture may be greater than or equal to 1:1 and less than or equal to 3:1.

[0039] The precursor mixture may have a solids content greater than or equal to 50% and less than or equal to 85%.

[0040] The method may further include preparing a polymer binder solution comprising the polymer binder mixture and the organic solvent. The polymer binder solution may have a solids content greater than or equal to 4% and less than or equal to 8%. Then, the electroactive positive electrode material may be introduced into the polymer binder solution to form the precursor mixture.

[0041] The present invention discloses the following solutions:

[0042] Solution 1. A battery pack for cycling lithium ions, the battery pack comprising:

[0043] A positive electrode comprising an electroactive material and a polymer binder mixture, the polymer binder mixture comprising a polyvinylidene fluoride (PVDF) homopolymer and a copolymer comprising a vinylidene fluoride (VDF) monomer and at least one perfluoroolefin monomer, the copolymer having the structural formula of formula (1):

[0044]

[0045] Wherein:

[0046] m is greater than or equal to 3500 and less than or equal to 18000,

[0047] n is greater than or equal to 800 and less than or equal to 7500,

[0048] p is 1 or 0,

[0049] R 1 is F or a perfluoroalkyl group,

[0050] R 2 is an alkylene group, and

[0051] X is an acidic functional group.

[0052] Embodiment 2. The battery pack according to Embodiment 1, wherein the copolymer comprises poly(vinylidene fluoride - co - tetrafluoroethylene) (PVDF - TFE), poly(vinylidene fluoride - co - hexafluoropropylene) (PVDF - HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof.

[0053] Embodiment 3. The battery pack according to Embodiment 1, wherein X is selected from at least one acidic functional group including carboxyl (-C(=O)OH), sulfo (-S(=O) 2 -OH), phosphonyl (-P(=O)(-OH) 2 ), nitro (-NO 2 ), and mercapto (-SH).

[0054] Embodiment 4. The battery pack according to Embodiment 1, wherein the copolymer has an ion - exchange capacity of greater than or equal to 0.05 milliequivalent H + per gram and less than or equal to 5 milliequivalents H + per gram.

[0055] Embodiment 5. The battery pack according to Embodiment 1, wherein the weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture is greater than or equal to 1:1 and less than or equal to 3:1.

[0056] Embodiment 6. The battery pack according to Embodiment 1, wherein the PVDF homopolymer has a molecular weight of greater than or equal to 500 kDa and less than or equal to 1500 kDa, and wherein the copolymer has a molecular weight of greater than or equal to 500 kDa and less than or equal to 1500 kDa.

[0057] Embodiment 7. The battery pack according to Embodiment 1, wherein the polymer binder mixture accounts for greater than or equal to 0.5% and less than or equal to 5% by weight of the positive electrode.

[0058] Embodiment 8. The battery pack according to Embodiment 1, wherein the electroactive material accounts for greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode.

[0059] Embodiment 9. The battery pack according to Embodiment 1, wherein the positive electrode further comprises a carbon - based electrochemically inactive conductive material.

[0060] Embodiment 10. The battery pack according to Embodiment 1 further includes:

[0061] a negative electrode comprising an electroactive negative electrode material; and

[0062] an electrolyte permeating the positive electrode and the negative electrode, the electrolyte comprising a non-aqueous polar aprotic organic solvent and a lithium salt in the non-aqueous polar aprotic organic solvent.

[0063] Embodiment 11. A battery pack for cycling lithium ions, the battery pack comprising:

[0064] a positive electrode comprising a mixture of an electroactive material and a polymer binder, the polymer binder mixture comprising a polyvinylidene fluoride (PVDF) homopolymer and a copolymer, the copolymer comprising poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof.

[0065] Embodiment 12. The battery pack according to Embodiment 11, wherein the weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture is greater than or equal to 1:1 and less than or equal to 3:1.

[0066] Embodiment 13. The battery pack according to Embodiment 11, wherein the PVDF homopolymer has a molecular weight greater than or equal to 500 kDa and less than or equal to 1500 kDa, and wherein the copolymer has a molecular weight greater than or equal to 500 kDa and less than or equal to 1500 kDa.

[0067] Embodiment 14. The battery pack according to Embodiment 11, wherein the copolymer comprises at least one acidic functional group selected from carboxyl (-C(=O)OH), sulfo (-S(=O) 2 -OH), phosphonyl (-P(=O)(-OH) 2 ), nitro (-NO 2 ), and mercapto (-SH).

[0068] Embodiment 15. The battery pack according to Embodiment 11, wherein the polymer binder mixture accounts for greater than or equal to 0.5% and less than or equal to 5% by weight of the positive electrode, and wherein the electroactive material accounts for greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode.

[0069] Embodiment 16. A method of manufacturing a positive electrode for a battery pack for cycling lithium ions, the method comprising:

[0070] Deposit a precursor mixture on a substrate at a temperature less than or equal to 30 degrees Celsius to form a precursor layer, the precursor mixture comprising an electroactive positive electrode material, a polymer binder mixture, and an organic solvent, the organic solvent including γ-valerolactone, dihydrolevoglucosenone, cyclopentanone, or a combination thereof, the polymer binder mixture including a polyvinylidene fluoride (PVDF) homopolymer and a copolymer having formula (1):

[0071]

[0072] Wherein:

[0073] m is greater than or equal to 3500 and less than or equal to 18000,

[0074] n is greater than or equal to 800 and less than or equal to 7500,

[0075] p is 1 or 0,

[0076] R 1 is F or a perfluoroalkyl group,

[0077] R 2 is an alkylene group, and

[0078] X is an acidic functional group; then

[0079] Remove the organic solvent from the precursor layer to form the positive electrode.

[0080] Aspect 17. The method according to aspect 16, wherein the copolymer comprises poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene (THV), or a combination thereof.

[0081] Aspect 18. The method according to aspect 16, wherein the weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture is greater than or equal to 1:1 and less than or equal to 3:1.

[0082] Aspect 19. The method according to aspect 16, wherein the precursor mixture has a solids content greater than or equal to 50% and less than or equal to 85%.

[0083] Aspect 20. The method according to aspect 16, further comprising:

[0084] Prepare a polymer binder solution comprising the polymer binder mixture and the organic solvent, the polymer binder solution having a solids content greater than or equal to 4% and less than or equal to 8%; then

[0085] The electroactive positive electrode material is introduced into the polymer binder solution to form the precursor mixture.

[0086] Further applicable fields of the present disclosure will be apparent from the detailed description, claims, and drawings. The detailed description and specific examples are intended only to illustrate and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] The present disclosure will be more fully understood from the detailed description and the drawings, in which:

[0088] Figure 1 is a schematic perspective view of a motor vehicle powered by a battery pack including a plurality of battery pack modules.

[0089] Figure 2 is Figure 1 a schematic cross-sectional view of a part of one of the battery pack modules, the battery pack module including a plurality of electrochemical cells or battery packs that cycle lithium ions.

[0090] Figure 3 is a schematic cross-sectional view of a battery pack that cycles lithium ions, the battery pack including a positive electrode, a negative electrode, a porous separator, and an electrolyte that permeates the positive electrode, the negative electrode, and the porous separator.

[0091] In the drawings, reference numerals may be reused to identify like and / or identical elements. DETAILED DESCRIPTION

[0092] Compared with petrochemical solvents such as N-methyl-2-pyrrolidone (NMP), the polymer binder mixture of the present disclosure can be used to manufacture a PVDF binder-containing positive electrode using a relatively harmless organic solvent (such as γ-valerolactone, GVL) at ambient temperature. The polymer binder mixture contains a PVDF homopolymer and a copolymer formulated to improve the ambient temperature solubility of the PVDF homopolymer in an organic solvent (such as in GVL). The copolymer includes a copolymer made from vinylidene fluoride (VDF) monomers and at least one perfluoroolefin monomer.

[0093] Figure 1 Depicts a motor vehicle 2 powered by an electric motor 4 that obtains electrical power from a battery pack 6 including one or more battery pack modules 8. The battery pack modules 8 can be electrically coupled together in a series and / or parallel arrangement to meet the required capacity and power requirements of the electric motor 4. The vehicle 2 can be a pure electric vehicle and can be powered entirely by the electric motor 4, or the vehicle 2 can be a hybrid vehicle and can be powered by the electric motor 4 and an internal combustion engine (not shown).

[0094] As Figure 2As shown, each battery pack module 8 includes one or more electrochemical cells or battery packs 10 that cycle lithium ions. In practice, the battery packs 10 in the battery pack module 8 are typically assembled as stacked layers, which include a negative electrode layer 12, a negative electrode current collector 13, a positive electrode layer 14, a positive electrode current collector 15, and a separator layer 16. Each battery pack 10 is defined by a negative electrode layer 12 and a positive electrode layer 14 that are spaced apart from each other by the separator layer 16. In practice, the separator layer 16 can be permeated with an electrolyte that provides a medium for lithium ion conduction between the negative electrode layer 12 and the positive electrode layer 14, or the separator layer 16 itself can serve as the electrolyte. The negative electrode layer 12 is disposed on the negative electrode current collector 13 and is in electrical communication with the negative electrode current collector 13, while the positive electrode layer 14 is disposed on the positive electrode current collector 15 and is in electrical communication with the positive electrode current collector 15. As Figure 2 shown, for efficiency, these layers can be stacked such that some of the negative electrode current collectors 13 and some of the positive electrode current collectors 15 are double-sided and include a negative electrode layer 12 or a positive electrode layer 14, respectively, on both of their sides. In such an arrangement, adjacent negative electrode layers 12 and positive electrode layers 14 share a single negative electrode current collector 13 or a single positive electrode current collector 15, respectively.

[0095] Figure 3 An electrochemical cell or battery pack 20 that cycles lithium ions is depicted. The battery pack 20 can generate an electric current during discharge, which can be used to supply power to a load device (such as an electric motor 4), and can be charged by connecting to a power source. Similar to Figure 1 and 2 the battery pack 10 depicted in, in one aspect, the battery pack 20 can be used to supply power to the electric motor 4 of a motor vehicle 2. Additionally or alternatively, the battery pack 20 can be used in other transportation applications (such as motorcycles, boats, tractors, buses, motorcycles, mobile homes, campers, tanks, and airplanes), and can be used to power a wide variety of other stationary and / or portable electronic devices, components, and devices used in industrial and other applications, including industrial, residential, and commercial buildings, consumer goods, industrial equipment and machinery, agricultural or farm equipment, and heavy machinery (as non-limiting examples).

[0096] The battery pack 20 includes a negative electrode 22, a positive electrode 24, a separator 26, and an electrolyte 28. The electrolyte 28 provides a medium for lithium-ion conduction between the negative electrode 22 and the positive electrode 24. The negative electrode 22 is disposed on the main surface of a negative electrode current collector 30, while the positive electrode 24 is disposed on the main surface of a positive electrode current collector 32. In practice, the negative electrode current collector 30 and the positive electrode current collector 32 are electrically coupled to a power source or a load 34 (such as an electric motor 4) via an external circuit 36. The negative electrode 22 and the positive electrode 24 are formulated such that when the battery pack 20 is at least partially charged, an electrochemical potential difference is established between the negative electrode 22 and the positive electrode 24. During discharge of the battery pack 20, the electrochemical potential established between the negative electrode 22 and the positive electrode 24 drives spontaneous reduction and oxidation (redox) reactions within the battery pack 20 and releases lithium ions and electrons from the negative electrode 22. The released lithium ions travel from the negative electrode 22 through the separator 26 and the electrolyte 28 to the positive electrode 24, while the electrons travel from the negative electrode 22 to the positive electrode 24 via the external circuit 36, which generates an electric current. After the negative electrode 22 has been partially or completely depleted of lithium, the battery pack 20 can be charged by connecting the negative electrode 22 and the positive electrode 24 to a power source 34, which drives non-spontaneous redox reactions within the battery pack 20 and releases lithium ions and electrons from the positive electrode 24. The repeated discharge and charge of the battery pack 20 may be referred to herein as a "cycle", and a complete charge event followed by a complete discharge event is considered a complete cycle.

[0097] The positive electrode 24 is formulated to store and release lithium ions during discharge and charge of the battery pack 20. The positive electrode 24 may be in the form of a continuous porous layer disposed on the main surface of the positive electrode current collector 32. The positive electrode 24 includes an electrochemically active (electroactive) material, a polymer binder mixture, and an optional conductive material. In an aspect, the electroactive material of the positive electrode 24 may be a particulate material, and the particles of the electroactive material of the positive electrode 24 may be mixed with the polymer binder mixture and the optional conductive material. The positive electrode 24 may have a porosity greater than or equal to 20% and less than or equal to 50%. The positive electrode 24 may have a thickness greater than or equal to 30 micrometers (μm), optionally greater than or equal to 50 μm, optionally greater than or equal to 70 μm, or optionally greater than or equal to 100 μm and less than or equal to 500 μm.

[0098] The electroactive material of the positive electrode 24 can store and release lithium ions by undergoing a reversible redox reaction with lithium at an electrochemical potential higher than that of the electrochemical active material of the negative electrode 22, so that there is an electrochemical potential difference between the negative electrode 22 and the positive electrode 24. The electroactive material of the positive electrode 24 may include a material capable of lithium intercalation and deintercalation or a material capable of undergoing a conversion reaction with lithium. In aspects where the electroactive material of the positive electrode 24 contains an intercalation host material capable of reversible insertion or intercalation of lithium ions, the electroactive material of the positive electrode 24 may contain a lithium transition metal oxide. For example, the electroactive material of the positive electrode 24 may include a layered lithium transition metal oxide represented by the formula LiMeO 2 and / or Li 2 MeO 3 a layered lithium-rich transition metal oxide represented by the formula Li 1+x Me 1-x O 2 (where 0 < x ≤ 0.33), an olivine-type lithium transition metal oxide represented by the formula LiMePO 4 , a monoclinic lithium transition metal oxide represented by the formula Li 3 Me 2 (PO 4 ) 3 , a spinel-type lithium transition metal oxide represented by the formula LiMe 2 O 4 , a lithiophilite represented by one or both of the following formulas LiMeSO 4 F or LiMePO 4 F, or a combination thereof, where Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or a combination thereof). Specific examples of the lithium transition metal oxide include LiNi 1-x-y Co x Mn y O 2 (NMC), where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1; LiNi 1-x-y-z Co x Mn y Al z O 2 (NCMA), where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1; LiNi 1-x-y Co x Al y O 2 (NCA), where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1; LiNi x Mn 1-x O 2 (LNMO), where 0 ≤ x ≤ 1; lithium manganese oxide (LMO) (e.g., Li(1+x) Mn 2 O 4 , where 0.1 ≤ x ≤ 1); lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ); lithium cobalt oxide (LiCoO 2 )(LCO); lithium iron phosphate (LiFePO 4 ); lithium vanadium phosphate (LiVPO 4 ); lithium manganese iron phosphate (LiMn 1-x Fe x PO 4 , where 0 ≤ x ≤ 1); lithium-rich manganese layered oxide (LMR); and combinations thereof. The electroactive material of the positive electrode 24 can account for greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode 24, or optionally less than or equal to 90%.

[0099] The polymer binder mixture is electrochemically inactive and is included in the positive electrode 24 to provide structural integrity to the positive electrode 24 and / or assist the positive electrode 24 in adhering to the main surface of the positive electrode current collector 32. The polymer binder mixture includes polyvinylidene fluoride (PVDF) homopolymers and copolymers. The weight ratio of PVDF homopolymer to copolymer in the polymer binder mixture (PVDF homopolymer:copolymer) can be greater than or equal to 1:1 and less than or equal to 3:1. The polymer binder mixture can account for greater than or equal to 0.5%, optionally greater than or equal to 1%, or optionally greater than or equal to 2% and less than or equal to 10%, or optionally less than or equal to 5% by weight of the positive electrode 24.

[0100] The PVDF homopolymer can have the formula -(CH 2 CF 2 ) n -, where n represents the number of repeating monomers in the PVDF homopolymer. The PVDF homopolymer can have a molecular weight greater than or equal to 500 kilodaltons (kD) and less than or equal to 1500 kD. The PVDF homopolymer can account for greater than or equal to 0.25% and less than or equal to 3.75% by weight of the positive electrode 24. A specific example of the PVDF homopolymer is 5130 manufactured by Solvay.

[0101] The copolymer is included in the polymer binder mixture to help promote the dissolution of the PVDF homopolymer used during the manufacture of the positive electrode 24 in an organic solvent. The copolymer includes vinylidene fluoride (VDF) monomers and at least one perfluoroolefin monomer. Examples of perfluoroolefin monomers include tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). The TFE monomer has the formula -(C 2 F 4) - And the HFP monomer has the formula -CF 2 CF(CF 3 ) -. The copolymer may account for greater than or equal to 0.1% and less than or equal to 2.5% by weight of the positive electrode 24. The copolymer may have a molecular weight greater than or equal to 500 kilodaltons (kD) and less than 1500 kD.

[0102] In an embodiment, the copolymer may be an acid-functional polymer and may contain at least one acidic functional group. Examples of acidic functional groups include carboxyl (-C(=O)OH), sulfo (-S(=O) 2 -OH), phosphonyl (-P(=O)(-OH) 2 ), nitro (-NO 2 ), mercapto (-SH), and combinations thereof. In this case, the ion exchange capacity (IEC) of the copolymer, which represents the number of basic groups that can be neutralized by the copolymer, may be greater than or equal to 0.05 milliequivalents of H + per gram (meq H + / g) and less than or equal to 5 meq H + / g.

[0103] The copolymer may have a structural formula of formula (1):

[0104]

[0105] where 3500 ≤ m ≤ 18000, 800 ≤ n ≤ 7500, p is 1 or 0, R 1 is F or perfluoroalkyl, R 2 is alkylene, and X is an acidic functional group. Examples of perfluoroalkyl include trifluoromethyl (-CF 3 ) and pentafluoroethyl (-C 2 F 5 ). Examples of alkylene include methylene (-CH 2 -), ethylene (-CH 2 -CH 2 -), trimethylene (-CH 2 -CH 2 -CH 2 -), tetramethylene, pentamethylene, hexamethylene, vinylene (-HC=CH-), propenylene (-H 2 C=C=CH-), propylene (-CH(CH 3 )CH 2 -), phenylene (-C 6 H 4 -), tetrafluorophenylene, and cyclohexadiene.

[0106] In an embodiment, the copolymer may include poly(vinylidene fluoride - co - tetrafluoroethylene) (PVDF - TFE), poly(vinylidene fluoride - co - hexafluoropropylene) (PVDF - HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof. A specific commercially available PVDF - TFE copolymer is NEOFLON VT475 manufactured by Daikin Industries, Ltd.

[0107] The optional conductive material is electrochemically inactive and may be included in the positive electrode 24 to provide the positive electrode 24 with sufficient conductivity to support the penetration of electrons therethrough. Examples of the conductive material include carbon - based materials, metals (e.g., nickel), and / or conductive polymers. Examples of carbon - based conductive materials include carbon black (CB) (e.g., acetylene black), graphite, graphene (e.g., graphene nanosheets, GNP), graphene oxide, carbon nanotubes (CNT), and / or carbon fibers (e.g., carbon nanofibers). Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and / or polypyrrole. When included in the positive electrode 24, the optional conductive material may account for greater than 0% by weight, optionally greater than or equal to about 1%, or optionally greater than or equal to about 5% and less than or equal to about 10% of the positive electrode 24.

[0108] The negative electrode 22 is configured to store and release lithium ions to facilitate charging and discharging of the battery pack 20, respectively. The negative electrode 22 may be in the form of a continuous material layer disposed on the major surface of the negative electrode current collector 30. The negative electrode 22 includes an electrochemically active (electroactive) material (electroactive negative electrode material) that can store and release lithium ions through reversible redox reactions with lithium during charging and discharging of the battery pack 20. Examples of electroactive negative electrode materials include lithium, lithium - based materials (e.g., alloys of lithium and silicon, aluminum, indium, and / or tin), carbon - based materials (e.g., graphite, activated carbon, carbon black, hard carbon, soft carbon, and / or graphene), silicon, silicon - based materials (e.g., alloys of silicon and lithium, tin, iron, aluminum, and / or cobalt), silicon oxides, tin oxides, aluminum, indium, zinc, germanium, titanium oxides, lithium titanate, and combinations thereof.

[0109] In an embodiment, the electroactive material of the negative electrode 22 may be a granular material, and the particles of the electroactive material of the negative electrode 22 may be mixed with a polymer binder, a copolymer, and an optional conductive material. The same polymer binder, copolymer, and conductive material as described above for the positive electrode 24 may be included in the negative electrode 22 in substantially the same amounts.

[0110] The separator 26 is configured to physically and electrically isolate the negative electrode 22 and the positive electrode 24 from each other while allowing lithium ions to pass through. The separator 26 has an open microporous structure and may comprise organic and / or inorganic materials. For example, the separator 26 may comprise a polymer. Examples of polymers for the separator 26 may include polyolefins (e.g., polyethylene (PE) and / or polypropylene (PP)), polyamides (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and / or poly(vinyl chloride) (PVC), and combinations thereof.

[0111] The electrolyte 28 is ion-conductive and provides a medium for the conduction of lithium ions between the negative electrode 22 and the positive electrode 24. The electrolyte 28 comprises an organic solvent and a lithium salt in the organic solvent.

[0112] The organic solvent may include non-aqueous polar aprotic organic solvents. Non-limiting examples of non-aqueous polar aprotic organic solvents include cyclic carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC)); 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); lactones (e.g., γ-butyrolactone, γ-valerolactone, and / or δ-valerolactone); nitriles (e.g., succinonitrile, glutaronitrile, and / or adiponitrile); sulfones (e.g., tetramethylene sulfone, ethyl methyl sulfone, vinyl sulfone, phenyl sulfone, 4-fluorophenyl sulfone, benzyl sulfone, and / or sulfolane); aliphatic ethers (e.g., triethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, 1,3-dimethoxypropane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and / or ethoxymethoxyethane); cyclic ethers (e.g., 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane); phosphate esters (e.g., triethyl phosphate and / or trimethyl phosphate); and combinations thereof.

[0113] The lithium salt is soluble in the organic solvent and provides a channel for lithium ions to pass through the electrolyte 28. The lithium salt may include inorganic lithium salts, organic lithium salts, or combinations thereof. Examples of lithium salts include lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium perchlorate (LiClO 4 ), lithium tetrachloroaluminate (LiAlCl 4 ), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium trifluoromethanesulfonate (LiCF 3 SO3 ) Lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 )) 2 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 )) (LiSFI), lithium tetraphenylborate (LiB(C 2 )(LiSFI), lithium bis(oxalato)borate (LiB(C 6 H 5 )) 4 ), lithium difluoro(oxalato)borate (LiBF 2 (C 4 ))(LiDFOB), and combinations thereof. 2 )(LiBOB), lithium difluoro(oxalato)borate (LiBF 2 (C 2 O 4 ))(LiDFOB), and combinations thereof.

[0114] The negative electrode current collector 30 and the positive electrode current collector 32 are conductive and provide electrical connections between the external circuit 36 and the negative electrode 22 and the positive electrode 24, respectively. In aspects, the negative electrode current collector 30 and the positive electrode current collector 32 can be made of metal and can be in the form of a non-porous metal foil, a perforated metal foil, a porous metal mesh, or a combination thereof. The negative electrode current collector 30 can be made of copper, nickel, or an alloy thereof, stainless steel, or other suitable conductive materials. The positive electrode current collector 32 can be made of aluminum (Al) or other suitable conductive materials.

[0115] Method

[0116] The positive electrode 24 can be manufactured by depositing a precursor mixture on a substrate to form a precursor layer and then drying the precursor layer to form the positive electrode 24 on the substrate. The precursor mixture can be deposited on the substrate via any suitable method. In an embodiment, the slot die coating method or the semi-dry extrusion method can be used to deposit the precursor mixture on the substrate. In an embodiment, the substrate can be made of metal. For example, the substrate can be made of substantially the same material as the positive electrode current collector 32. In other embodiments, the substrate can include a release film, and the positive electrode 24 can be transferred from the substrate to the positive electrode current collector 32 before assembling the battery pack 20.

[0117] The precursor mixture comprises an electroactive positive electrode material, a polymer binder mixture, and an optional conductive material in an organic solvent. The electroactive positive electrode material, the polymer binder mixture, and the optional conductive material may be present in the precursor mixture in substantially the same proportions as in the positive electrode 24. The electroactive positive electrode material, the polymer binder mixture, and the optional conductive material contained in the precursor mixture may have substantially the same composition as the electroactive positive electrode material, the polymer binder mixture, and the optional conductive material contained in the positive electrode 24. In particular, the polymer binder mixture contained in the precursor mixture comprises PVDF homopolymer and copolymer. The precursor mixture may have a solids content of greater than or equal to 50%, optionally greater than or equal to 75% and less than or equal to 85%.

[0118] The organic solvent used to prepare the precursor mixture may include γ-valerolactone (also known as gamma-valerolactone or GVL), dihydrolevoglucosenone (also known as Cyrene), cyclopentanone, or a combination thereof. The organic solvent may be considered a "green" solvent, meaning that it is relatively harmless or environmentally friendly compared to petrochemical solvents such as N-methyl-2-pyrrolidone (NMP). In particular, GVL has relatively low acute toxicity to aquatic organisms and is readily biodegradable. The organic solvent may account for greater than or equal to 15% and less than or equal to 50% by weight of the precursor mixture.

[0119] The copolymer in the polymer binder mixture is formulated to facilitate the dissolution of the PVDF homopolymer in the organic solvent at ambient temperature, such as at a temperature of less than or equal to 30 degrees Celsius (°C), or optionally less than or equal to 25 °C. The PVDF homopolymer is relatively insoluble in GVL, and when mixed with GVL at ambient temperature, the GVL and PVDF homopolymer mixture tends to gel and precipitate in the form of the PVDF homopolymer. In the absence of the copolymer, in order to effectively dissolve the PVDF homopolymer in GVL, the GVL and PVDF homopolymer mixture must be heated to a temperature of greater than or equal to 60 °C, which introduces complexity and cost to the positive electrode manufacturing method. The inventors of the present disclosure have found that combining the copolymer with the PVDF homopolymer in the precursor mixture for forming the positive electrode 24 ensures complete dissolution of the PVDF homopolymer in the organic solvent (e.g., GVL) at ambient temperature. Without being bound by theory, it is believed that the copolymer prevents the PVDF homopolymer chains from aligning and / or physically associating with each other in GVL, thereby preventing gelling of the precursor mixture and precipitation of the PVDF homopolymer therefrom.

[0120] The precursor mixture can be prepared by mixing an electroactive negative electrode material, a polymer binder mixture (PVDF homopolymer and copolymer), an organic solvent, and optionally a conductive material at ambient temperature. In an embodiment, the precursor mixture can be prepared by preparing a polymer binder solution and then mixing the electroactive positive electrode material and optionally the conductive material in the polymer binder solution to form the precursor mixture. The polymer binder solution can have a solids content greater than or equal to 4% and less than or equal to 8%. After introducing the electroactive positive electrode material and optionally the conductive material into the polymer binder solution, the electroactive positive electrode material, optionally the conductive material, and the polymer binder solution can be mixed together at ambient temperature, for example, using a planetary mixer or an extruder, to form the precursor mixture. In an embodiment where the positive electrode 24 includes an optional conductive material, the precursor mixture can be prepared by preparing a polymer binder solution, introducing the conductive material into the polymer binder solution, and then introducing the electroactive positive electrode material into the polymer binder solution to form the precursor mixture.

[0121] After forming the positive electrode 24 on the substrate, the positive electrode 24 can be assembled into the battery pack 20, and the negative electrode 22, the positive electrode 24, and the separator 26 can be infiltrated with the electrolyte 28. Then, the negative electrode current collector 30 and the positive electrode current collector 32 can be electrically coupled to the power source 34 to cause lithium ions to be released from the positive electrode 24 and incorporated into the negative electrode 22.

[0122] The foregoing description is merely exemplary and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Thus, while the disclosure includes specific examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be performed in a different order (or concurrently) without altering the principles of the disclosure. Additionally, although the embodiments are described above as having certain features, any one or more of the features described with respect to any one embodiment of the disclosure can be implemented in and / or combined with any other embodiment, even if not explicitly described in that combination. In other words, the embodiments are not mutually exclusive, and permutations of one or more embodiments are still within the scope of the disclosure. Any method steps, processes, and operations described herein should not be construed as necessarily requiring them to be performed in the order discussed or illustrated, unless specifically identified as an order of performance. It should also be understood that additional or alternative steps may be employed unless otherwise stated.

[0123] As used herein, the phrase "at least one of A, B, and C" shall be construed to mean the logic (A or B or C) using non-exclusive logical OR, and shall not be construed to mean "at least one of A, at least one of B, and at least one of C". As used herein, the term "and / or" includes any combination of one or more of the associated listed terms.

[0124] The terms used herein are for the purpose of describing exemplary embodiments only and are not intended to be limiting. Unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" as used herein are also intended to include the plural forms. The terms "comprising", "including", and "having" are inclusive and thus specify the presence of the stated features, elements, compositions, steps, integers, operations, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. Although the open-ended terms "comprising", "including", and "having" are to be understood as non-limiting terms for describing and claiming the various embodiments herein, in some instances these terms may alternatively be understood as more restrictive and limiting terms, such as "consisting of" or "consisting essentially of". Thus, for any given embodiment that lists a composition, material, component, element, ingredient, feature, integer, operation, and / or method step, the present disclosure also expressly includes embodiments consisting of or consisting essentially of these listed compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps. In the case of "consisting of", the alternative embodiment does not include any additional compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps, while in the case of "consisting essentially of", such an embodiment does not include any additional compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps that materially affect the basic and novel features, but may include any compositions, materials, components, elements, ingredients, features, integers, operations, and / or method steps that do not materially affect the basic and novel features.

[0125] Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers, and / or sections, these steps, elements, components, regions, layers, and / or sections should not be limited by these terms unless otherwise specified. These terms are only used to distinguish one step, element, component, region, layer, or section from another. Unless the context clearly indicates, terms such as "first", "second", and other ordinal terms do not imply an order or sequence when used herein. Thus, the first step, element, component, region, layer, or section discussed below may be referred to as the second step, element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0126] Unless otherwise specified, the terms "composition" and "material" as used herein are used interchangeably to generally refer to a substance that contains at least a preferred chemical component, element, or compound but may also contain additional elements, compounds, or substances, including trace impurities. A "X-based" composition or material generally refers to a composition or material in which "X" is the single largest component by weight percentage (%) of the composition or material. This can include compositions or materials having greater than 50 wt% X, and can also include compositions or materials having less than 50 wt% X, as long as X is the single largest component based on the total weight of the composition or material. When a composition or material is referred to as "substantially free" of a substance, the composition or material may contain less than 5 wt%, optionally less than 3 wt%, optionally less than 1 wt%, or optionally less than 0.1 wt% of the substance by weight.

Claims

1. A battery pack for circulating lithium ions, the battery pack comprising: A positive electrode comprising an electroactive material and a polymer binder mixture, the polymer binder mixture comprising a polyvinylidene fluoride (PVDF) homopolymer and a copolymer comprising a vinylidene fluoride (VDF) monomer and at least one perfluoroolefin monomer, the copolymer having the structural formula (1): in: m is greater than or equal to 3500 and less than or equal to 18000, n is greater than or equal to 800 and less than or equal to 7500, p is 1 or 0, R 1 is F or a perfluoroalkyl group, R 2 is an alkylene group, and X is an acidic functional group.

2. The battery pack of claim 1, wherein the copolymer comprises poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a copolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), or a combination thereof.

3. The battery according to claim 1, wherein X is at least one acidic functional group selected from carboxyl (-C(=O)OH), sulfonyl (-S(=O)2-OH), phosphonyl (-P(=O)(-OH)2), nitro (-NO2) and mercapto (-SH).

4. The battery pack according to claim 1, wherein the copolymer has a H + per gram and less than or equal to 5 milliequivalents of H + Ion exchange capacity per gram. 5 . The battery pack according to claim 1 , wherein a weight ratio of the PVDF homopolymer to the copolymer in the polymer binder mixture is greater than or equal to 1:1 and less than or equal to 3:

1.

6. The battery of claim 1, wherein the PVDF homopolymer has a molecular weight greater than or equal to 500 kilodaltons and less than or equal to 1500 kilodaltons, and wherein the copolymer has a molecular weight greater than or equal to 500 kilodaltons and less than or equal to 1500 kilodaltons.

7. The battery pack of claim 1, wherein the polymer binder mixture constitutes greater than or equal to 0.5% and less than or equal to 5% by weight of the positive electrode, and wherein the electroactive material constitutes greater than or equal to 80% and less than or equal to 98% by weight of the positive electrode.

8. The battery pack according to claim 1, further comprising: a negative electrode comprising an electroactive negative electrode material; and an electrolyte that permeates the positive electrode and the negative electrode, the electrolyte comprising a non-aqueous polar aprotic organic solvent and a lithium salt in the non-aqueous polar aprotic organic solvent; and Wherein the positive electrode further comprises a carbon-based electrochemically inactive conductive material.

9. A method of making a positive electrode for a battery for cycling lithium ions, the method comprising: A precursor mixture is deposited on a substrate at a temperature of less than or equal to 30 degrees Celsius to form a precursor layer, the precursor mixture comprising an electroactive positive electrode material, a polymer binder mixture, and an organic solvent, the organic solvent comprising γ-valerolactone, dihydrolevulinone, cyclopentanone, or a combination thereof, the polymer binder mixture comprising a polyvinylidene fluoride (PVDF) homopolymer and a copolymer having formula (1): in: m is greater than or equal to 3500 and less than or equal to 18000, n is greater than or equal to 800 and less than or equal to 7500, p is 1 or 0, R 1 is F or a perfluoroalkyl group, R 2 is an alkylene group, and X is an acidic functional group; then The organic solvent is removed from the precursor layer to form the positive electrode.

10. The method according to claim 9, further comprising: preparing a polymer binder solution comprising the polymer binder mixture and the organic solvent, the polymer binder solution having a solid content greater than or equal to 4% and less than or equal to 8%; Then The electroactive positive electrode material is introduced into the polymer binder solution to form the precursor mixture, the precursor mixture having a solids content greater than or equal to 50% and less than or equal to 85%.

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