Composition for battery electrodes

Abstract

This invention relates to compositions for battery electrodes. The invention further relates to compositions for battery electrodes wherein at least one solvent is a composition comprising N-methylpyrrolidone (NMP) in a mass ratio of 80% to 95%.

Description

[0001] This application is a divisional application of patent application No. 202180007234.7, filed on June 9, 2021, entitled "Composition for Battery Electrode".

[0002] The present invention relates to compositions for battery electrodes, wherein at least one solvent is a composition comprising between 80% and 95% by weight of N-methylpyrrolidone (NMP).

[0003] Compositions used in the manufacture of battery electrodes (cathode and anode) are known. They consist of: solvents, active materials, electronic conductors (e.g., carbon-based electronic conductors (carbon black, graphene, carbon nanotubes, graphite, or carbon fibers alone or in combination)), polymeric binders, or even other additives such as one or more polymeric or non-polymeric dispersants.

[0004] NMP was found among the solvents used due to its suitable properties (ability to dissolve polymeric adhesives, and a very high auto-ignition temperature (270°C), allowing the composition to be applied and dried in the presence of air).

[0005] The solvent is typically recycled through distillation or double distillation to achieve the highest possible NMP purity. This operation aims to limit NMP consumption throughout the manufacturing process, but it incurs industrial costs. Electrode manufacturing processes known to date require at least 99% NMP purity by weight. When recycling is not desired for cost reasons, the solvent is typically burned off, a process known as aberration.

[0006] To obtain a purity of at least 99% or even greater by mass during the recycling operation, distillation techniques, such as those described in EP2479167, are used.

[0007] In the process for manufacturing battery electrodes, a composition is deposited onto a current collector (current collector). For the main components, this composition consists of a solvent, an electronic conductor, an active filler, and a polymer. The solvent is then evaporated to obtain the electrode. The recovery of this solvent does not allow for the attainment of the purity possible in known distillation processes, such as EP2479167. The solvent recovered during the electrode manufacturing process may contain up to almost 20% compounds other than the pure solvent.

[0008] To date, industrial electrode manufacturing processes have required solvent purification or the use of "fresh" solvents.

[0009] The applicant has observed that, in the case of N-methylpyrrolidone, the reuse of this solvent, derived from an evaporation process in air during the electrode manufacturing steps, is not only possible without purification, but also presents several advantages:

[0010] - Better dispersion

[0011] -The formulation becomes more stable over time.

[0012] The electrodes produced have better quality: more precisely, they have a better distribution of carbon-based components within the electrode. Therefore, conductivity is improved.

[0013] The impure NMP has an NMP content between 80% and 99%, and preferably between 95% and 99%, a water content of less than or equal to 0.1%, and a compound derived from a preceding process in which NMP was used, typically containing compounds of the species γ-butyrolactam (2-pyrrolidone) or γ-butyrolactone.

[0014] The presence of γ-butyrolactam or γ-butyrolactone species in the impurities can act as dispersants or become grafted onto electronic conductors, thus promoting their distribution in the electrode. The applicant cannot explain and considers this effect to be unforeseen.

[0015] Therefore, by retaining certain compounds obtained from the previous electrode manufacturing process, such NMP can not only be used to manufacture battery electrode compositions, but the resulting compositions are of higher quality.

[0016] The electrode, and more particularly the cathode formulation, based on such an NMP solvent and applied to the current collector is dried in air at a temperature below the boiling point of NMP, typically below 220°C, under partial pressure. Under the same electrode manufacturing process conditions, using the NMP composition of the present invention allows for a reduction in electrode resistance, a critical parameter for battery applications. Furthermore, using the composition of the present invention simplifies the electrode formulation by reducing, for example, the amount of polymer and / or binder used for dispersion. Summary of the Invention:

[0017] This invention relates to a composition comprising:

[0018] - At least one solvent comprising N-methylpyrrolidone in a mass content between 80% and 98.99%, including limits, water in a mass content of less than 1%, and at least one compound having at least one γ-butyrolactam or γ-butyrolactone ring, excluding NMP, wherein each of these compounds is present individually or in combination in a mass proportion ranging from 0.01% to 19%, including limits, and the sum of these compounds does not exceed 19%, wherein the solvent is present in a mass proportion greater than or equal to 50%.

[0019] - An electronic conductor in at least one solid form, comprising a proportion of less than or equal to 50%, excluding 0. Detailed implementation method:

[0020] The compositions of the present invention comprise less than 50% by weight, preferably less than 35% by weight, more preferably less than 25% by weight, more preferably less than 10% by weight, and even more preferably less than 5% by weight of a solid electronic conductor.

[0021] The term "electronic conductor in solid form" refers to carbon black, graphene, single-walled or multi-walled carbon nanotubes, graphite, and carbon fibers, either alone or in combination. Preferably, the electronic conductor includes carbon nanotubes.

[0022] The compositions of the present invention further include at least one compound having at least one pyrrolidone ring (γ-butyrolactam), excluding NMP, and / or γ-butyrolactone, wherein each compound is present alone or in combination in a proportion ranging from 0.01% to 19%, and the sum of the compounds does not exceed 19%.

[0023] The term "compound having at least one pyrrolidone ring (γ-butyrolactam) or γ-butyrolactone" can refer to any compound having a molecular weight of less than 15,000 g / mol, preferably less than 10,000 g / mol, and wherein the presence of the γ-butyrolactone or γ-butyrolactam ring is characterized (mass spectrometry, NMR or infrared spectroscopy).

[0024] The structures of γ-butyrolactone and γ-butyrolactam may contain substituents including C, H, N or O.

[0025] Among these compounds, the most prominent are γ-butyrolactone, succinimides such as N-methylsuccinimide and N-hydroxysuccinimide, formylpyrrolidone, 5-hydroxy-N-methylpyrrolidone, 2-pyrrolidone, or N-hydroxymethylpyrrolidone. They may also be oligomers with γ-butyrolactam and / or γ-butyrolactone rings in forms that are more or less complex or difficult to characterize in terms of their properties or concentrations.

[0026] It is believed that all impurities derived from γ-butyrolactam or γ-butyrolactone structures present in the solvent evaporated during the electrode manufacturing process may be present in the compositions of the present invention. Lighter compounds whose structures do not include γ-butyrolactam or γ-butyrolactone structures may also be found.

[0027] Preferably, these compounds are present in amounts between 0.01% and 19% by mass, more preferably between 0.1% and 10% by mass, and even more preferably between 0.5% and 5%, including the limits.

[0028] The solvent composition was obtained by recovering NMP vapor at temperatures above 120°C in the presence of air.

[0029] The solvent composition can also be obtained by intentionally adding γ-butyrolactam and / or γ-butyrolactone derivatives to NMP with a purity greater than 99%, although this is not the primary objective of the present invention, which uses NMP without the need for purification and thus contains these γ-butyrolactone and / or γ-butyrolactam compounds.

[0030] The compositions of the present invention may further include active fillers. The term "active filler" means: a lithium-ionized transition metal oxide, such as LiMO2, wherein M is of the LiMPO4 type, Li2MPO3F type, or Li2MSiO4 type, LiMn2O4 type, or S8 type, which are Co, Ni, Mn, Fe, or combinations thereof; artificial or natural graphite or silicon or silicon modified with carbides, nitrides, or oxides.

[0031] The compositions of the present invention may further comprise one or more polymers selected from the following: poly(vinylidene fluoride) (PVDF) polymer, poly(vinylpyrrolidone), poly(phenylacetylene), poly(m-phenylenevinylene), polypyrrole, poly(p-phenylenebenzodiene). The following are preferred: poly(vinyl alcohol), poly(vinyl alcohol), carboxymethyl cellulose, and mixtures thereof, as well as polyacrylonitrile and copolymers thereof. Preferably, they are poly(vinylidene fluoride) (PVDF) and poly(N-vinylpyrrolidone).

[0032] The compositions of the present invention may also include one or more free radical generating agents, such as peroxides, redox pairs, azo compounds or alkoxyamines, in a content of less than 5% by mass and preferably less than 1% relative to the NMP content.

[0033] The present invention also relates to a process (method) for obtaining electrodes, comprising the following steps:

[0034] - The composition of the present invention, comprising at least one active filler and at least one polymer, is deposited onto the current collector.

[0035] - Evaporate the solvent

[0036] - Optional rolling.

[0037] The present invention also relates to a process for obtaining electrodes, wherein the solvent recovered by evaporation includes the solvent of the present invention.

[0038] The metal current collector is selected in a non-limiting manner from the following metals: Al, Cu, Ni, and has a thickness between 8 and 35 μm. The metal collector may also be coated with an undercoat deposited on the electronic conductor with a thickness between 0.5 and 5 μm.

[0039] Calendering involves pressing an electrode between two counter-rotating rollers, wherein the gap between the rollers is less than the thickness of the electrode.

[0040] The electrode can be a cathode or an anode. Preferably, it is a cathode.

[0041] For the cathode, the active material is selected from lithium-ion transition metal oxides, such as LiMO2, wherein M is of the LiMPO4 type, Li2MPO3F type, Li2MSiO4 type, LiMn2O4 type, or S8 type, which are Co, Ni, Mn, Fe, or combinations thereof.

[0042] For the anode, the active material is selected from artificial or natural graphite or silicon or silicon modified with carbides, nitrides or oxides.

[0043] The present invention also relates to batteries using cathodes and / or anodes obtained using the process according to the present invention.

[0044] The present invention also relates to the use of the compositions of the invention in, for example, the fields of inks and coatings, or in petroleum refining.

[0045] The electrode (cathode or anode) can be prepared in the following non-limiting manner:

[0046] - Solids content between 20% and 90% by mass, the remainder being solvent (composition comprising N-methylpyrrolidone in a mass content between 80% and 98.99%, including limits; water in a mass content of less than 1%; and at least one compound having at least one γ-butyrolactam or γ-butyrolactone ring, excluding NMP, these compounds being present individually or in combination in a mass proportion ranging from 0.01% to 19%, including limits, the sum of these compounds not exceeding 19%).

[0047] - One or more electronic conductors in proportions between 0.1% and 5% of the total formulation used to manufacture the electrodes.

[0048] - Polymer or non-polymer additives (binders, dispersants) in proportions between 0.3% and 5% of the total formulation used to manufacture electrodes.

[0049] This invention includes the following aspects / implementations / features in any order and / or in any combination:

[0050] 1. A composition comprising:

[0051] - At least one solvent comprising: N-methylpyrrolidone in a mass content between 80% and 98.99%, including limits; water in a mass content of less than 1%; and at least one compound having at least one γ-butyrolactam or γ-butyrolactone ring, excluding NMP, wherein each of these compounds is present individually or in combination in a mass proportion ranging from 0.01% to 19%, including limits, and the sum of these compounds does not exceed 19%, wherein the solvent is present in a mass proportion greater than or equal to 50%.

[0052] - An electronic conductor in at least one solid form, comprising a proportion of less than or equal to 50%, excluding 0.

[0053] 2. The composition of any of the foregoing or subsequent embodiments / features / aspects further includes an active filler and at least one polymer.

[0054] 3. Any composition of the foregoing or subsequent embodiments / features / aspects, further comprising a free radical generating agent.

[0055] 4. A process for obtaining electrodes, comprising the following steps:

[0056] - Deposit any of the foregoing or subsequent embodiments / features / aspects of the composition onto the current collector;

[0057] - Evaporate the solvent;

[0058] - Optional rolling.

[0059] 5. The process of any of the foregoing or subsequent embodiments / features / aspects, wherein the solvent recovered by evaporation includes the solvent of any of the foregoing or subsequent embodiments / features / aspects.

[0060] 6. An electrode, which is obtained according to the process of any of the foregoing or subsequent embodiments / features / aspects.

[0061] 7. A battery, which is obtained having one or two electrodes of any of the foregoing or subsequent embodiments / features / aspects.

[0062] This invention may include any combination of the different features or embodiments described in the preceding and / or following statements and / or paragraphs. Any combination of the features disclosed herein is to be considered part of this invention and there is no limitation on the combinable features.

[0063] Example 1:

[0064] Preparation of a dispersion (reference) of C100HP carbon nanotubes in electronic-grade NMP solvent.

[0065] C100HP CNTs are commercial grade CNTs from Arkema containing <20 ppm of metallic impurities. This grade of purified CNTs is recommended for use in the cathodes of Li-ion batteries. These carbon nanotubes are multi-walled (between 10 and 15 walls) and have a specific surface area between 180 and 240 cm². 2 Between / g.

[0066] Preparation of dispersions:

[0067] 100g of powdered flocculation was processed using a deflocculation centrifuge equipped with a 55mm paddle. C100HP is premixed with 400g of NMP (electronic grade, purity >99.8%, by mass).

[0068] Gradually add 25g of PVP K 30 (BASF) over one hour while stirring at 1000-1600rpm.

[0069] Add a further 70g of NMP after 30 minutes, and then add a further 65g of NMP after 30 minutes.

[0070] The pre-dispersion, in an amount of 660g containing 15% CNT and 3.8% PVP, was prepared for the grinding step in a Brandt horizontal ball mill (HBM) with a mill chamber volume of 250ml.

[0071] The mill is filled with 180 ml of ceramic beads with a diameter of 0.4-0.7 mm and a gap size of 0.1-0.15 mm.

[0072] Apply a base coat to the grinding circuit using a separate 230g of NMP for 5 minutes.

[0073] While increasing the rotor speed to 3000 rpm and the pump to 35% of its capacity, the pre-dispersion was gradually added over a period of 15-20 minutes.

[0074] Solids content and absorbance were measured to monitor the evolution of the dispersion (Table 1).

[0075] [Table 1]

[0076]

[0077]

[0078] For each absorbance measurement, the dispersion taken from the mill was diluted to 50 ppm CNT. It was measured at a wavelength of 355 nm using a DR / 2000 spectrometer (Hach).

[0079] Example 2: Recovery of NMP and CNT dispersions based on this solvent (Invention)

[0080] Typical cathode formulations for Li batteries were prepared using the NMP solvent of Example 1 at an "electronic" grade. For 960 g of NMC 622 (LiNi) produced by Umicore... 0.6 Mn 0.2 Co 0.2 O2), add 20g of Arkema-produced HSV 1810PVDF. The dry premix was dispersed in 1950 ml of NMP using a disc mixer for 30 minutes. Then, 50 g of the CNT dispersion from Example 1 was added. This solvent dosage is excessive relative to the formulation used in cathode production because the purpose of this example is to establish a model of solvent recovery in the presence of typical cathode components.

[0081] The dispersion was placed in a 5L Lab Rotovap rotary evaporator. The evaporator was heated to 145°C and the condensate container was kept at 110°C. The condenser vacuum valve was kept open to maintain contact between the NMP condensate and air.

[0082] During the 24-hour period, 900g of the solvent, which has a distinctly yellow color, was recovered in the container.

[0083] The presence of the recovered NMP in water was analyzed using the Karl Fischer method, yielding a value of 650 ppm. The NMP purity was 94.6% obtained by mass spectrometry. Therefore, approximately 5% of the recovered NMP can be attributed to non-volatile NMP oxidation products.

[0084] Using the recovered NMP sample, CNT dispersions were prepared under the same conditions as described in Example 1.

[0085] Solids content and absorbance were measured to monitor the evolution of the dispersion (Table 2).

[0086] [Table 2]

[0087]

[0088] For absorbance control, the recovered NMP was used for the reference cell. It was observed that the dispersion evolved more rapidly in the case of recovered NMP. The absorbance approached saturation after 90 minutes of milling, whereas in Example 1, it approached saturation after 120 minutes of milling. The absorbance values ​​were higher than in Example 1, reflecting better performance of the dispersion of the present invention.

[0089] Example 3: Electrical properties of CNT dispersions from Examples 1 and 2 in the cathode formulation

[0090] Preparation of cathode materials

[0091] Using a disc mixer at 400 rpm, 8% of a 12.5 g amount of "electronic" grade NMP was mixed. The HSV1810PVDF solution was mixed with the same amount of the CNT dispersion from Example 1. After 15 minutes of mixing, 98.5 g of NMC 622 and a further 10 g of NMP were gradually added to maintain good flowability of the dispersion. The target viscosity was between 3500 and 5000 cPs. Mixing was completed after 30 minutes at 1500 rpm.

[0092] The dispersion was then applied to the polyethylene terephthalate (PET) carrier to a thickness of 100 μm using a doctor blade, with a target coating thickness of 120 μm. The coating was then dried in a ventilated oven at 130°C for 30 minutes.

[0093] The solid content of the cathode preparation for this "model" is as follows:

[0094] NMC: 98.5%; PVDF 1%; CNT 0.5%

[0095] Coated PET sheets were cut to obtain 3×4 cm samples. The ends of each sample were coated with silver-containing conductive ink. Resistivity was measured using a Keithlley electrometer.

[0096] The same scheme was used to obtain the cathode model using the CNT dispersion from Example 2. The results of the electrical measurements are summarized in Table 3.

[0097] [Table 3]

[0098]

[0099] Under similar conditions, CNT dispersions prepared based on recycled NMP exhibit better electrical performance in NMC622 cathode formulations, with lower electrode resistivity, which is beneficial for proper battery operation.

Claims

1. A composition for use as a battery electrode, comprising: - At least one solvent comprising: N-methylpyrrolidone at a mass content between 80% and 98.99%, including limits; water at a mass content of less than 1%; and at least one compound containing at least one γ-butyrolactam, excluding NMP, wherein each compound is present individually or in combination at a mass ratio ranging from 0.01% to 19%, including limits, and the total amount of these compounds does not exceed 19%, wherein the solvent is present at a mass ratio greater than or equal to 50%. - An electronic conductor in at least one solid form with a proportion of less than or equal to 50%, excluding 0.

2. The composition for battery electrodes as described in claim 1 further comprises an active filler and at least one polymer.

3. The composition for a battery electrode as described in any one of claims 1 and 2 further comprises a free radical generator.

4. The composition for a battery electrode as described in claim 3, wherein the free radical generator is selected from peroxides, redox pairs, azo compounds, or alkoxyamines.

5. A process for obtaining electrodes, comprising the following steps: - Deposit the composition for battery electrodes as described in any one of claims 2 to 4 onto the current collector; - Evaporate the solvent.

6. The process as described in claim 5, comprising the following steps: - Deposit the composition for battery electrodes as described in any one of claims 2 to 4 onto the current collector; - Evaporate the solvent; - Calendering.

7. The process of claim 5, wherein the solvent recovered by evaporation comprises at least one solvent having the following composition: The mixture comprises N-methylpyrrolidone in a mass content between 80% and 98.99%, including the limit, water in a mass content of less than 1%, and at least one compound containing at least one γ-butyrolactam, excluding NMP, wherein each compound is present alone or in combination in a mass proportion ranging from 0.01% to 19%, including the limit, and the sum of the compounds does not exceed 19%.

8. An electrode, obtained by the process described in claim 5 or 6.

9. A battery having one or two electrodes as described in claim 8.

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