Halogen-free polymer binders for cathodes

Abstract

The present invention relates to a halogen-free polymer binder for a cathode according to formula (I) wherein R1 is (CH2) x-R3 wherein x is from 1 to 20 and R3 is H or CN; r2 is a C1-C10 alkyl group or a C2-C10 alkenyl group; and n is from 50 to 5000. The invention also relates to a cathode comprising the halogen-free polymer binder and a process for preparing the halogen-free polymer binder. (I)

Description

Technical Field

[0001] This invention relates to a halogen-free polymer binder for use in cathodes. The invention also relates to a cathode comprising the halogen-free polymer binder and a method for preparing the halogen-free polymer binder. Background Technology

[0002] Recently, the battery industry has begun to shift away from fluorinated binders used in electrodes, particularly cathodes, due to a number of significant problems and drawbacks. Environmentally, the production and disposal of fluorinated materials such as polyvinylidene fluoride (PVDF) leads to the release of persistent organic pollutants that are difficult to degrade and cause long-term ecological damage. These processes are also associated with significant greenhouse gas releases, exacerbating climate change. Health and safety concerns are also critical, as the manufacture and handling of these materials expose operators to hazardous chemicals, and battery combustion releases highly toxic gases, such as hydrogen fluoride, posing serious risks to humans and the environment.

[0003] In terms of performance, the use of fluorinated binders such as PVDF in electrode production necessitates the use of toxic organic solvents, such as N-methyl-2-pyrrolidone (NMP), which complicates the production and recycling processes. NMP is not only harmful to human health but also environmentally damaging, making battery recycling more challenging and less sustainable. Furthermore, increasing global regulatory pressure makes reliance on fluorinated materials increasingly intolerable, as governments and law enforcement agencies impose stricter restrictions on the use of hazardous substances in industrial processes. All these factors have prompted the industry to seek safer and more sustainable technologies to replace fluorinated binders. Summary of the Invention

[0004] The object of this invention is to overcome one or more of the aforementioned disadvantages. One object of this invention is to provide a halogen-free polymer binder for electrodes in battery packs, particularly for cathodes. Another object is to provide an binder for electrodes that, because it is free of halogens, particularly fluorides, has a lower environmental impact. An object is to provide a method for preparing such a binder that uses as few harmful solvents as possible, or even none at all, thus having a lower environmental footprint.

[0005] Another object of the present invention is to provide an electrode, particularly a cathode, comprising the halogen-free polymer binder, wherein the cathode has at least similar performance to, or even better than, existing cathodes comprising halogen-containing binders such as PVDF. The performance includes mechanical properties, ease of handling when assembling the cathode in a battery pack, and electrochemical performance of the cathode in a battery pack.

[0006] In other words, the present invention aims to provide a method and an adhesive that is free of halogen atoms, thereby exhibiting higher durability, while a cathode containing the adhesive has performance equivalent to that of halogen-containing cathodes known in the art.

[0007] A first aspect of the present invention discloses a halogen-free polymer adhesive for a cathode, as described in the appended claims.

[0008] Halogen-free polymer adhesives are shown in formula (I):

[0009] (I),

[0010] in

[0011] R1 is (CH2) x -R3, where x is from 1 to 20, and R3 is H or CN;

[0012] R2 is C1-C 10 Alkyl or C2-C 10 alkenyl groups; and

[0013] n is between 50 and 5000.

[0014] A first particularly preferred example of a halogen-free polymer adhesive is an adhesive in which x is 6, R3 is CN, and R2 is (CH2)2. A second particularly preferred example of a halogen-free polymer adhesive is an adhesive in which x is 10, R3 is H, and R2 is (CH2)2.

[0015] A second aspect of the invention discloses a cathode for a battery pack, as described in the appended claims. The cathode comprises a halogen-free polymer binder according to the first aspect of the invention.

[0016] Advantageously, the cathode comprises 75% to 95% by weight, preferably 80% to 95% by weight, more preferably 85% to 92% by weight, for example 90% by weight, based on the total weight of the cathode.

[0017] Advantageously, the cathode comprises 1% to 15% by weight, preferably 2% to 12% by weight, and more preferably 5% to 10% by weight of a conductive compound based on the total weight of the cathode.

[0018] Advantageously, the cathode comprises 1% to 15% by weight, preferably 2% to 12% by weight, and more preferably 5% to 10% by weight of the halogen-free polymer binder according to the first aspect of the invention, based on the total weight of the cathode.

[0019] Advantageously, the cathode comprises 75% to 95% by weight of active material, 1% to 15% by weight of conductive compound, and 1% to 15% by weight of halogen-free polymer binder according to the first aspect of the invention, based on the total weight of the cathode.

[0020] Advantageously, in the cathode, the total weight percentage of the active material, the conductive compound, and the halogen-free polymer binder of the present invention is 100%, that is, the cathode advantageously consists of the active material, the conductive compound, and the halogen-free polymer binder of the present invention. Those skilled in the art will understand that when the sum of these three components is 100%, the cathode will contain more than 1% by weight of the conductive compound and more than 1% by weight of the binder of the present invention to achieve 100%, for example, 75% by weight of the active material and 12.5% ​​by weight each of the conductive compound and the binder of the present invention, or 90% by weight of the active material, 3% by weight of the conductive compound, and 7% by weight of the binder of the present invention.

[0021] Advantageously, the cathode has a porosity of at least 20%, preferably at least 25%, more preferably at least 30%, for example at least 40%, wherein the porosity is expressed as the ratio of the cathode density to the cathode theoretical density, wherein the cathode theoretical density is calculated from the composition of the cathode and the density of each compound in the cathode.

[0022] Advantageously, the active material comprises one or more of lithium nickel cobalt manganese oxide (NMC), LiFePO4, and V2O5, or is substantially composed of them. Preferred examples of NMC include LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811) and LiNi 0.6 Mn 0.2 Co 0.2 O2 (NMC622).

[0023] Advantageously, the conductive compound contains carbon. Carbon can exist in forms known in the art, such as carbon nanotubes or carbon black.

[0024] A non-limiting example of the cathode of the present invention is a cathode comprising 85% to 95% by weight of NMC, 2% to 10% by weight of a carbon black-containing conductive compound, and 2% to 10% by weight of a halogen-free polymer binder as described in the first aspect of the present invention, based on the total weight of the cathode.

[0025] Advantageously, the cathode consists of NMC, a carbon black-containing conductive compound, and the halogen-free binder of the present invention, i.e., the cathode contains no other components (additives), and the total weight percentage of these three components is advantageously 100%. A particularly preferred example of such a cathode is a cathode consisting of 90% by weight NMC, 5% by weight carbon black-containing conductive compound, and 5% by weight the halogen-free binder of the present invention.

[0026] Another non-limiting example of the cathode of the present invention is a cathode comprising 75% to 85% by weight of LiFePO4 (LFP), 5% to 15% by weight of a carbon black-containing conductive compound, and 5% to 15% by weight of a halogen-free polymer binder as described in the first aspect of the present invention, based on the total weight of the cathode.

[0027] Advantageously, the cathode consists of LFP, a carbon black-containing conductive compound, and the halogen-free binder of the present invention, i.e., the cathode contains no other components (additives), and the total weight percentage of these three components is advantageously 100%. A particularly preferred example of such a cathode is a cathode consisting of 80% by weight LFP, 10% by weight carbon black-containing conductive compound, and 10% by weight the halogen-free binder of the present invention.

[0028] A third aspect of the present invention discloses a method for preparing a halogen-free polymer adhesive, as described in the appended claims. The halogen-free polymer adhesive is the halogen-free polymer adhesive according to the first aspect of the present invention.

[0029] The method includes reacting an amino derivative based on H2N-R1 with... The reaction, wherein R1 is as described above, and R2 and n are as described above.

[0030] The reaction is carried out in the presence of dimethylformamide.

[0031] The reaction is carried out at a temperature T1 of 15°C to 80°C, more preferably 20°C to 60°C, such as room temperature or 50°C.

[0032] This reaction leads to the formation of an intermediate polymer. Advantageously, the intermediate polymer does not contain closed rings in its molecular structure, particularly imide rings.

[0033] The intermediate polymer undergoes imide ring closure, thereby forming a halogen-free polymer binder. The imide ring closure step can be carried out by heating the intermediate polymer to a temperature T2 of 100°C to 250°C, preferably 125°C to 200°C, more preferably 150°C to 180°C. Alternatively, the imide ring closure step can be carried out at T1 in the presence of a catalyst. In other words, imide ring closure using a catalyst can be carried out without heating the intermediate polymer to T2.

[0034] Advantageously, when the imide ring is closed by heating the intermediate polymer to T2, the heating step includes heating to an intermediate temperature T3, wherein T3 is higher than T1 and lower than T2. ​​Advantageously, T3 is equal to or higher than T1 + 5°C, preferably equal to or higher than T1 + 10°C, more preferably equal to or higher than T1 + 20°C. Advantageously, T3 is equal to or lower than T2 - 5°C, preferably equal to or lower than T2 - 10°C, more preferably equal to or lower than T2 - 20°C.

[0035] Advantageously, T3 is 30°C to 80°C, preferably 40°C to 70°C, and more preferably 50°C to 60°C.

[0036] According to the first implementation scheme, x is 6, R3 is CN, R2 is (CH2)2, T1 is 40°C to 60°C, and T2 is 150°C to 180°C.

[0037] According to the second implementation scheme, x is 10, R3 is H, R2 is (CH2)2, T1 is 15°C to 30°C, T3 is 50°C to 60°C, and T2 is 150°C to 180°C.

[0038] Advantageously, when the imide ring is closed in the presence of a catalyst, the catalyst comprises carbonyl diimidazole, or is essentially composed of carbonyl diimidazole.

[0039] This disclosure also relates to the use of the halogen-free polymer binder according to the first aspect in a slurry for preparing the cathode according to the second aspect. Attached Figure Description

[0040] The invention will now be described in more detail with reference to the accompanying drawings, wherein like reference numerals in the drawings denote like features, and wherein:

[0041] - Figure 1 The first halogen-free polymer adhesive of the present invention is shown to have an H-NMR spectrum.

[0042] - Figure 2 The Fourier transform infrared (FTIR) spectrum of the first halogen-free polymer adhesive is shown;

[0043] - Figure 3 The TGA analysis of the first adhesive is shown;

[0044] - Figure 4 The DSC analysis of the first adhesive is shown;

[0045] - Figure 5 The LSV analysis of the first adhesive is shown;

[0046] - Figure 6The H-NMR spectrum of the second halogen-free polymer adhesive of the present invention is shown;

[0047] - Figure 7 The FTIR spectrum of the second adhesive is shown;

[0048] - Figure 8 The TGA analysis of the second adhesive is shown;

[0049] - Figure 9 The DSC analysis of the second adhesive is shown;

[0050] - Figure 10 The LSV analysis of the second adhesive is shown;

[0051] - Figure 11 The porosity of the two cathodes of the present invention and the reference cathode is shown;

[0052] - Figure 12 The discharge capacity and coulombic efficiency of a first type of battery cell are shown, the first type of battery cell comprising a cathode obtained with a first type of binder;

[0053] - Figure 13 The voltage changes with the specific capacity of the first type of battery cell;

[0054] - Figure 14 The discharge capacity and coulombic efficiency of the second type of battery cell are shown, the second type of battery cell comprising a cathode obtained with the second type of binder;

[0055] - Figure 15 The voltage is displayed as the specific capacity of the second type of battery cell changes. Detailed Implementation

[0056] Halogen-free polymer adhesives are shown in formula (I):

[0057] (I),

[0058] in

[0059] R1 is (CH2) x -R3, where x is 1 to 20, preferably 2 to 15, more preferably 4 to 10, and where R3 is H or CN;

[0060] R2 is C1-C 10 Alkyl or C2-C 10 Alkenyl group.

[0061] Advantageously, n is 50 to 5000, preferably 75 to 4500, and more preferably 100 to 4000.

[0062] Advantageously, the halogen-free polymer adhesive has a molecular weight of 200 to 1500 kDa, preferably 250 to 1400 kDa, more preferably 300 to 1300 kDa, and most preferably 350 to 1200 kDa.

[0063] R1 can be linear or branched, i.e., (CH2). x - The chain can be linear or branched. Advantageously, R1, i.e. (CH2), x - The chain is a straight chain.

[0064] R2 can be linear or branched. Advantageously, R2 is based on (CH2). y C1-C 10 Alkyl, wherein y is 1 to 10, preferably 1 to 4, more preferably 1 or 2, i.e. CH2 or (CH2)2.

[0065] An example of a halogen-free polymer adhesive is an adhesive as shown in formula (II), where x is 6, R3 is CN, and R2 is (CH2)2:

[0066] (II).

[0067] Another example of a halogen-free polymer adhesive is an adhesive as shown in formula (III), where x is 10, R3 is H, and R2 is (CH2)2:

[0068] (III).

[0069] According to the first and preferred embodiments of this disclosure, the halogen-free binder according to formula (I) is obtained by reacting an amino derivative according to H2N-R1 with... The reaction is used to prepare the product, wherein R1 and x are as described above, and R2 and n are as described above.

[0070] The reaction was carried out in the presence of dimethylformamide (DMF) as a solvent and at a temperature T1 ranging from 15°C to 80°C.

[0071] This reaction leads to the formation of an intermediate polymer with the structure of formula (IV):

[0072] (IV), where R1 and R2 are as described above, meaning that the structure does not contain a ring structure, such as an imide ring.

[0073] For example, when x is 6, R3 is CN and R2 is (CH2)2, the intermediate polymer has the structure shown in formula (V):

[0074] (V).

[0075] For example, when x is 10, R3 is H and R2 is (CH2)2, the intermediate polymer has the structure shown in formula (VI):

[0076] (VI).

[0077] The intermediate polymer then undergoes an imide ring closure step, wherein the -OH and -NH- groups of the intermediate polymer react to close the ring and obtain the halogen-free polymer adhesive shown in formula (I). Water is formed as a byproduct.

[0078] According to a first embodiment of the imide ring closure step, the imide ring is closed by heating the intermediate polymer to a temperature above T1, preferably to a temperature of 100°C to 250°C, for example, 150°C to 180°C.

[0079] According to a second embodiment of the imide ring closure step, the closure of the imide ring is carried out at T1 in the presence of a catalyst, such as, but not limited to, carbonyl diimidazole.

[0080] Advantageously, the halogen-free polymer adhesive materials of the present invention have high heat resistance, i.e., they can withstand temperatures of at least 300°C, preferably at least 350°C, more preferably at least 400°C, as determined by thermogravimetric analysis (TGA) performed at 10°C / min with Ar flow at 60 mL / min.

[0081] Advantageously, the halogen-free polymeric adhesive material of the present invention has a glass transition temperature in the range of 25°C to 100°C, preferably 30°C to 80°C, more preferably 40°C to 60°C, for example 42°C to 55°C, which is determined by differential scanning calorimetry (DSC) in an Ar atmosphere at a heating / cooling rate of 10°C / min for two cycles from -80°C to greater than 200°C, wherein the result is obtained in the second cycle to ensure that the thermal history of the polymer has been eliminated, thereby ensuring a reliable and reproducible glass transition temperature value.

[0082] The cathode of the present invention comprises, or is composed of, the halogen-free polymer binder of the present invention, as well as an active compound and a conductive material.

[0083] The active material can be any cathode active material known in the art. It should be understood that the cathode can comprise two or more active materials. Non-limiting examples of suitable active materials include lithium nickel cobalt manganese oxide (NMC) such as LiNi. 0.8 Mn 0.1 Co 0.1 O2 (NMC811) and LiNi 0.6 Mn 0.2 Co 0.2O2(NMC622), LiFePO4, LiMn x Fe 1-x PO4(LMFP), LiMn 1.5 Ni 0.5 O (LMNO) and V2O5.

[0084] The conductive compound can be any conductive compound known in the art. Advantageously, the conductive compound contains carbon, or is substantially composed of carbon. Non-limiting examples of suitable conductive materials include carbon-containing compounds such as carbon black (e.g., C-65), carbon nanotubes (CNTs), graphene, and vapor-grown carbon fibers (VGCF).

[0085] Advantageously, the cathode comprises a cathode current collector. The cathode current collector can be any current collector known in the art for cathodes, such as aluminum foil, which optionally comprises a carbon-containing coating. When the cathode comprises a cathode current collector, the cathode advantageously comprises a layer containing an active material, a conductive compound, and the aforementioned binder, which contacts and is advantageously adhered to or attached to the cathode current collector.

[0086] A non-limiting example of the cathode of the present invention is a cathode comprising a cathode current collector and a layer comprising 85% to 95% by weight of NMC, 2% to 10% by weight of a carbon black-containing conductive compound, and 2% to 10% by weight of the halogen-free polymer binder of the present invention, based on the total weight of the layer. Advantageously, the layer consists of NMC, the carbon black-containing conductive compound, and the halogen-free binder of the present invention, i.e., the sum of their weight percentages in the layer is 100%.

[0087] Another non-limiting example of the cathode of the present invention is a cathode comprising a cathode current collector and a layer comprising 75% to 85% by weight of LiFePO4, 5% to 15% by weight of a carbon black-containing conductive compound, and 5% to 15% by weight of the halogen-free polymer binder of the present invention, based on the total weight of the layer. Advantageously, the layer consists of LiFePO4, the carbon black-containing conductive compound, and the halogen-free binder of the present invention, i.e., the sum of their weight percentages in the layer is 100%.

[0088] The cathode according to the present invention can be prepared by methods known in the art. A preferred method includes preparing a slurry containing the above-described halogen-free polymer binder, active material and conductive compound of the present invention in a solvent, and casting the slurry onto a cathode current collector.

[0089] Advantageously, the slurry contains 25% to 75% by weight of solids based on the total weight of the slurry, preferably 30% to 70% by weight, more preferably 35% to 65% by weight, and most preferably 40% to 60% by weight, for example 45% to 55% by weight.

[0090] Advantageously, the slurry contains 75% to 95% by weight of active material, 1% to 10% by weight of conductive compound and 1% to 10% by weight of halogen-free polymer binder.

[0091] Advantageously, the solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetonitrile, methyl-tetrahydrofuran, cyclohexanone, DMF and propylene carbonate (PC).

[0092] Advantageously, the cathode has an adhesion strength to the cathode current collector of at least 20 N / m, preferably at least 25 N / m, more preferably at least 30 N / m, and most preferably at least 40 N / m, as measured according to the test standard ISO-8510-1.

[0093] Example

[0094] Example 1

[0095] HO-(CH2)6-NH2 was reacted with di-tert-butyl dicarbonate in the presence of tetrahydrofuran at room temperature for 15 hours. After solvent removal, the reaction product was placed in diethyl ether and washed with aqueous solutions of acetic acid and sodium bicarbonate. The solvent was removed under vacuum. The resulting reaction product was then reacted with methanesulfonyl chloride / triethylamine in the presence of dichloromethane (DCM) at room temperature for 3 hours. The resulting mixture was then washed with aqueous solution of sodium bicarbonate. After removing dichloromethane, the resulting product was reacted with KCN in the presence of DMF as a solvent at 80°C for 18 hours. The reaction product was then placed in a mixture of ethyl acetate and water and washed with water and brine. The organic matter was collected and the solvent was removed under vacuum. The resulting reaction product was then reacted with HCl in 1,4-dioxane at a temperature from 0°C to room temperature for 5 hours. The reaction was quenched with sodium bicarbonate, the product was extracted in dichloromethane, and treated with sodium hydroxide to give the product H2N-(CH2)6-CN (“amino derivative”).

[0096] Then, the amino derivative with The reaction was carried out at 50 °C in the presence of DMF for 24 hours, where n is from 100 to 4000. The resulting reaction product is shown in formula (V), and the reaction was continued at 170 °C in the presence of DMF for 16 hours. Figure 1 and Figure 2 The 1H nuclear magnetic resonance (H-NMR) spectrum and Fourier transform infrared (FTIR) spectrum of the obtained halogen-free polymer adhesive are shown respectively.

[0097] Figure 3 The TGA analysis of the adhesive shows high heat resistance exceeding 400°C. Figure 4The DSC analysis of the adhesive shows that the glass transition temperature is 52°C. Figure 5 Linear sweep voltammetry (LSV) analysis of the polymer binder in propylene carbonate (PC) solution shows high oxidative stability.

[0098] Example 2

[0099] H2N-(CH2)9-CH3 as an amino derivative and The reaction was carried out at room temperature in the presence of DMF for 16 hours, where n is from 100 to 4000. The resulting reaction product is shown in formula (VI), and the reaction was continued at 50 °C in the presence of DMF for 8 hours, and then at 170 °C in the presence of DMF for 16 hours. Figure 6 and Figure 7 The H-NMR and FTIR spectra of the obtained halogen-free polymer adhesive are shown respectively.

[0100] Figure 8 The TGA analysis of the adhesive shows high heat resistance exceeding 400°C. Figure 9 The DSC analysis of the adhesive shows that the glass transition temperature is 44°C. Figure 10 The LSV analysis of the polymer binder in PC solution shows high oxidative stability.

[0101] Example 3

[0102] The halogen-free polymer binders obtained in Examples 1 and 2 were subsequently used to prepare cathodes. A first slurry with a solid content of 49-52% by weight was prepared using the binder of Example 1; a second slurry with a solid content of 46-49% by weight was prepared using the binder of Example 2. The solvent used for both slurries was NMP. The solid content of each slurry comprised 90% by weight of NMC622 as the active material, 5% by weight of carbon black (C-65) as the conductive compound, and 5% by weight of the corresponding halogen-free polymer binder. This resulted in slurries with a solid content of 3 to 4 mAh·cm⁻¹. -2 The loading of active materials.

[0103] The slurry is then cast onto a carbon-coated aluminum foil, which serves as the cathode current collector, using a doctor blade coating technique, thereby producing the cathode. In other words, the cathode consists of a cathode current collector and a layer composed of NMC622, C-65, and a halogen-free polymer binder.

[0104] The reference cathode was also prepared by casting a slurry using a doctor blade method. The slurry had a similar solid content and loading, wherein the solid content included 90% by weight of NMC622 as an active material, 5% by weight of carbon black (C-65) as a conductive compound, and 5% by weight of polyvinylidene fluoride (PVdF) as a binder.

[0105] The porosity of all three types of cathodes, and especially the porosity of the layer on the current collector, was measured by dividing the cathode density by the theoretical cathode density. Figure 11 It is evident that the cathode of the present invention has a porosity similar to that of the reference cathode.

[0106] Peel strength, expressed as adhesive strength, was also tested and determined according to ISO-8510-1. The cathode obtained with the adhesive of Example 1 had an adhesive strength of 58 N / m, the cathode obtained with the adhesive of Example 2 had an adhesive strength of 42 N / m, and the reference cathode obtained with PVdF had an adhesive strength of 41 N / m. In other words, the halogen-free cathode of the present invention has an adhesive strength at least as good as or even better than that of the fluoride-containing reference cathode.

[0107] Example 4

[0108] Three types of button batteries were assembled using the cathode of the present invention obtained in Example 3. Lithium metal was used as the anode, and the electrolyte was a liquid electrolyte containing 1M LiPF6 in a solvent mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[0109] Two types of button batteries were cycled at 25°C at different charge / discharge rates, namely C / 20, C / 10, C / 5, C / 2, and 1C, for at least 30 cycles without any problems. Figure 12 The discharge capacity and coulombic efficiency of two coin cells comprising the cathode described in Example 3, which was prepared using the binder of Example 1, are shown. Clearly, despite harsh test conditions, very high coulombic efficiencies approaching 100% are achieved, along with excellent rated capacity and high actual discharge capacity. This demonstrates that the halogen-free polymer binder provides excellent adhesion and allows for cell cyclability. It is also clearly shown that the results for the two coin cells are very similar, indicating that the cathode of the present invention and, consequently, the halogen-free polymer binder of the present invention, possess very stable and reproducible properties. Figure 13 The display voltage changes with the specific capacitance.

[0110] Figure 14The discharge capacity and coulombic efficiency of three coin cells comprising the cathode described in Example 3, which was prepared using the binder of Example 1, are shown. Clearly, despite harsh test conditions, very high coulombic efficiencies approaching 100% are achieved, along with excellent rated capacity and high actual discharge capacity. This demonstrates that the halogen-free polymer binder provides excellent adhesion and allows for the cyclability of the battery cells. It is also clearly shown that the results for these coin cells are very similar, indicating that the cathode of the present invention and, consequently, the halogen-free polymer binder of the present invention, possess very stable properties. Figure 15 The display voltage changes with the specific capacitance.

Claims

1. A halogen-free polymer binder of formula (I) for use in a cathode: (I)， in R1 is (CH2) x -R3, where x is from 1 to 20, and R3 is H or CN; R2 is C1-C 10 Alkyl or C2-C 10 alkenyl groups; and n is between 50 and 5000.

2. The halogen-free polymer adhesive according to claim 1, wherein x is 6, R3 is CN, and R2 is (CH2)2.

3. The halogen-free polymer adhesive according to claim 1, wherein x is 10, R3 is H, and R2 is (CH2)2.

4. A cathode comprising a halogen-free polymer binder according to any one of the preceding claims.

5. The cathode of claim 4, comprising 75% to 95% by weight of active material, 1% to 15% by weight of conductive compound, and 1% to 15% by weight of halogen-free polymer binder based on the total weight of the cathode.

6. The cathode according to claim 4 or claim 5, having a porosity of at least 20%.

7. The cathode according to any one of claims 4-6, wherein the active material comprises one or more of lithium nickel cobalt manganese oxide (NMC), LiFePO4 and V2O5, wherein the lithium nickel cobalt manganese oxide is preferably NMC811 or NMC622.

8. The cathode according to any one of claims 4-7, wherein the conductive compound comprises carbon black.

9. The cathode according to any one of claims 4-8, comprising 85% to 95% by weight of NMC, 2% to 10% by weight of a carbon black-containing conductive compound, and 2% to 10% by weight of a halogen-free polymer binder according to any one of claims 1-3, based on the total weight of the cathode.

10. The cathode according to any one of claims 4-8, comprising 75% to 85% by weight of LiFePO4, 5% to 15% by weight of a carbon black-containing conductive compound, and 5% to 15% by weight of a halogen-free polymer binder according to any one of claims 1-3, based on the total weight of the cathode.

11. A method for preparing a halogen-free polymer adhesive according to any one of claims 1-3, comprising: - To make the amino derivatives according to H2N-R1 and An intermediate polymer is formed by reacting in the presence of dimethylformamide at a temperature T1 ranging from 15°C to 80°C. Where R1 is (CH2) x -R3, where x is from 1 to 20, and R3 is H or CN; R2 is C1-C 10 Alkyl or C2-C 10 Alkenyl groups; and n is 50 to 5000; and - The intermediate polymer undergoes imide ring closure, thereby forming a halogen-free polymer adhesive. The closure of the imide ring is carried out by heating the intermediate polymer to a temperature T2 of 100°C to 250°C, or at T1 in the presence of a catalyst.

12. The method of claim 11, wherein the imide ring is closed by heating the intermediate polymer to a temperature T2, wherein heating to T2 comprises heating to an intermediate temperature T3, wherein T3 is higher than T1 and lower than T2, preferably T3 is 30°C to 80°C, and then heating from T3 to T2.

13. The method of claim 11, wherein x is 6, R3 is CN, and R2 is (CH2)2, and wherein T1 is 40°C to 60°C, and T2 is 150°C to 180°C.

14. The method of claim 12, wherein x is 10, R3 is H, and R2 is (CH2)2, and wherein T1 is 15°C to 30°C, T3 is 50°C to 60°C, and T2 is 150°C to 180°C.

15. The method of claim 11, wherein the imide ring is closed at T1 in the presence of a catalyst, wherein the catalyst comprises carbonyl diimidazole.

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