EP2460213A1

EP2460213A1 - Coating method for producing electrodes for electrical energy stores

Info

Publication number: EP2460213A1
Application number: EP10721496A
Authority: EP
Inventors: Bernd Bartkowiak; Armin Modlinger; Peter Pilgram; Markus Rudek; Claudia Veit
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2009-07-25
Filing date: 2010-05-25
Publication date: 2012-06-06
Also published as: KR20120038973A; JP2013500556A; CN102498594A; US20120208081A1; WO2011012343A1; DE102009034799A1

Abstract

The present invention relates to a method for coating a carrier during the production of an electrode for electrical energy stores, in particular for lithium ion cells, using a specific solvent and/or dispersant, characterized in that the solvent and/or dispersant is or comprises N-ethylpyrrolidone.

Description

Coating process for the production of electrodes for electrical energy storage

The present invention relates to a method for coating a carrier in the manufacture of an electrode for electrical energy storage, in particular for lithium ion cells, using a special solvent and / or dispersant.

In the production of electrodes, in particular for lithium-ion batteries, the prior art discloses wet-chemical methods for active materials,

Conductive additives and binder-containing coating compositions or dispersions coated on conductive films. Both water and organic solvent based systems are used to prepare these dispersions. In water-based systems, the binder is dispersed, the binding occurs at points between the particles.

The organic solvent-based systems behave differently, in which the binder dissolves completely in the solvent and the binder envelops the particles. For the coating process, a complete solution of the binder in the entire dispersion must be ensured. As a particularly suitable organic solvent for the production of electrodes, N-methylpyrrolidone (NMP) has been proven.

Usually, by measuring the viscosity of the dispersion or solution, the quality of the coating composition is checked. It should be noted that the viscosity of the coating composition may change over several hours, so that the composition is not used directly after preparation. Another problem with NMP is also that this is toxic

(teratogenic) is classified. From occupational safety, security and

For environmental reasons there is therefore a need to replace this NMP. Another need is solvent based systems for making these

To provide dispersions that require less solvent or dispersant than is the case with NMP. It was an object of the present invention, in the production of electrodes for electrical energy storage, in particular for lithium-ion cells, wherein in a coating process active materials, binders and additives are applied to a support to find a way that allows the Application of the active materials and additives with a lower dispersant or

To achieve the amount of solvent, that is to enable higher solids contents in the so-called Elektrodenslurry. At the same time, the dispersion or solvent should comply with safety and environmental regulations and, in addition, a good or

have improved storage stability with respect to NMP.

This object is surprisingly achieved by the use of N-ethylpyrrolidone (NEP) instead of N-methylpyrrolidone (NMP) as a solvent and / or dispersant in the coating composition used in the wet-chemical process step in electrode production ,

The invention thus relates to a process for coating a support in the production of an electrode for electrical energy storage, comprising the steps of: a) providing a composition comprising at least one solvent and / or dispersant and additionally at least one polymeric binder, b) coating the support with the composition, characterized in that the solvent and / or dispersant is or comprises N-ethyl-pyrrolidone.

The coating method according to the invention thus sees in its widest

Possibility that a carrier is coated with a composition containing at least N-ethyl-pyrrolidone and a polymeric binder. Typically, in addition to the N-ethylpyrrolidone as solvent and / or dispersant and the polymeric binder, the coating composition also contains at least one so-called active material and a conductivity additive. The coated with the coating composition carrier is then under

Production of an electrode further processed, the electrode can be used in turn for the production of an electrical energy storage. The Preparation of the electrode usually also includes the step of drying the coated support. In particular, the solution and / or

Dispersant to form a solid, conductive and after completion of the electrical energy storage "active" layer removed. The support itself is usually conductive, as e.g. in the common lithium-ion cells is the case. The following are more detailed explanations of the individual used

Components and various aspects of the invention made.

The purpose of the polymeric binder is to provide good adhesion, both within the layer and to the support. Particular preference is given to using polyvinylidene fluoride homopolymers (PVDF). PVDF is often used because of its electrochemical stability and because the swelling of PVDF in the electrolyte of the later finished electrical energy storage is low. However, suitable binders for the use according to the invention are also different PVDF copolymers, Teflon, polyamides, polynitriles, and others. Preferred polymers

Binders may be selected from the group comprising polyvinylidene fluoride homopolymers (PVDF); Polyvinylidene fluoride copolymers (PVDF copolymers), e.g. PVDF hexafluoropropylene (PVDF-HFP), PVDF tetrafluoroethylene (PVDF-TFE) and PVDF chlorotetrafluoroethylene (PVDF-CTFE); Blends of PVDF and PVDF copolymer (s); Polytetrafluoroethylene (PTFE); Polyvinyl chloride (PVC); Polyvinyl fluoride (PVF); Polychlorotrifluoroethylene (PCTFE); Polychlorotrifluoroethylene-ethylene (ECTFE); Polytetrafluoroethylene-ethylene (ETFE); Polytetrafluoroethylene-hexafluoropropene (FEP); Polymethyl methacrylate (PMMA); Polyethylene oxide (PEO); Polypropylene oxide (PPO);

Polypropylene (PP); Polyethylene (PE); Polyimide (PI); and styrene butadiene rubber (SBR). It may also be possible to use mixtures of binders, for. B.

Blends of PVDF homopolymer and copolymer in any proportions, or the binders may be crosslinkable.

As mentioned above, a coating composition contains the here

described in addition to the solvent and / or dispersant and the polymeric binder at least one so-called active material. The term "active material" is understood here by a person skilled in the art generally to mean a material which contains the reversible input and output - A -

Elimination of electrically charged particles allows. In the finished and

functional electric energy storage can then during storage or. Auslagerungsvorganges the electrically charged particles depending on the structure of the memory, a charging or discharging flow. In the case of a lithium ion cell, the electrically charged particles are lithium ions. The

Storage and retrieval operations take place during loading and unloading, respectively at the cathode and at the anode. For the production of anode and cathode respectively different active materials are used. In the method according to the invention, the coating composition therefore typically additionally contains an active material enabling the reversible incorporation and removal of electrically charged particles, which is preferably selected from the group comprising

Graphite; amorphous carbons, e.g. Hard carbon, soft carbon; Lithium storage metals and alloys (eg nanocrystalline or amorphous silicon and silicon-carbon composites; tin, aluminum, antimony); Li ₄ Ti ₅ Oi ₂ or mixtures of these materials; Lithium metal oxides of the type LiM _× O ₂ (eg LiCoO ₂ ; LiNiO ₂ ; LiNh- _x Co _x O ₂ ; Li N io, 85Co ₀ , i Alo ₁ OsO ₂ ; Lii _{+ x} (Ni _y Co ₂ -y _y yn _y ) i _-x θ2, 0 <x <0.17, 0 <y <0.5); LiMn ₂ O ₄ spinel doped or undoped; and lithium metal phosphates LiMPO ₄ (eg LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiVPO ₄ ) doped or undoped; as well as conversion materials such as iron (III) fluoride (FeF ₃ ) or mixtures of these materials. The active material is dispersed in the composition. Soft carbon is not understood to mean graphitic carbons that convert into graphite at high temperatures of up to 3200 ^° C. Hard carbon is not understood to mean graphitic carbons that do not convert to graphite at the temperatures realized in the prior art, such as the Handbook of Battery Materials, JO Besenhard, Wiley VCH, pages 233f, 388f, 402f. Suitable dopants for the lithium metal phosphates are, for example, magnesium or niobium.

Usually, a coating composition of the type described herein further contains at least one conductivity additive.

This has the task of improving the electrical conductivity of the coating and thus the electrochemical reaction, ie the storage and retrieval of the electrically charged particles. Particular preference is given to carbon blacks or carbon blacks conductive materials used. Carbon blacks are carbonaceous finely divided solids with mostly spherical primary particles between 10 and 300 nm in size, determined by TEM evaluation according to ASTM D 3849, which grow together into chain-like and partly lumpy aggregates. As a conductive

However, materials for the application according to the invention are also suitable for small-particle graphites with d50 between 1 μm and 8 μm, preferably with d50 between 2 μm and 6 μm, determined by means of laser light diffraction. Optionally, mixtures of conductive materials may also be used, e.g. B. mixtures of carbon blacks and graphites in any proportions. Furthermore, carbon fibers can be used as conductivity additives.

The support itself is not critical to the coating process described herein and the use of NEP according to the invention as a solvent and / or dispersant per se. Typically, however, it is electrically conductive. In particular, in the common lithium-ion cells, which are considered preferred here, the support is usually a conductive foil made of aluminum (positive electrode) or copper (negative electrode). The negative electrode may also be made of aluminum. Other conductive metals which have suitable redox potentials are also suitable in principle, but are generally not used for cost reasons.

According to the invention, the carrier thus consists of a conductive sheet-like

Material or comprises such a material, e.g. in the context of a compound material. Preferably, the support consists of either aluminum or copper or films of these metals. There are also laminates comprising such films as a carrier conceivable. The supports may also be porous supports, woven, nonwoven or expanded metal of the corresponding metals, or polymeric films coated with these metals, apertured films, porous supports, woven or nonwoven fabrics.

The coating composition used in the invention usually contains from 30 to 80% by weight, preferably from 40 to 70% by weight, of N-ethylpyrrolidone and, preferably, from 0.5 to 8% by weight of polymeric binder %, preferably 1.0 to 5.0% by weight, and / or of active material of 20 to 70% by weight, preferably 30 to 60% by weight, and / or conductivity additive of 0 to 5 Wt .-%, preferably 0.2 to 3 wt .-%, each based on the composition.

The composition provided should have a viscosity in the range from 1000 to 7000 mPas, preferably 2000 to 5000 mPas, at a shear rate of 112 s ^-1 , measured at 20 ^° C. The determination of the viscosity values in the context of the present invention is carried out with the aid of a Rheometers (Model RS 600) from Thermo Haake GmbH, Karlsruhe, Germany, with a plate / plate measuring device with a diameter of 35 mm The viscosities are recorded at shear rates of 1 to 500 s ^-1 . The measured values are recorded with the software RheoWin.

According to the coating method according to the invention, the electrodes to be produced may be anodes or cathodes. In the production of such electrodes, the compositions used typically contain, in addition to a solvent and / or dispersant, here: NEP, and a binder also a so-called active material as described above. Such compositions are also referred to as "electrode slurry", "anode slurry" or "cathode slurry", in the latter case depending on which type of electrode is produced therewith.

In one embodiment of the invention, the electrode to be produced is an anode. In this case, the composition, ie the "anode slurry", contains an active material, which is preferably selected from the group comprising graphite; amorphous carbons, e.g. Hard carbon, soft carbon; Lithium storage metals and

alloys (eg nanocrystalline and amorphous silicon and silicon-carbon composites; tin, aluminum, antimony); and Li ₄ Ti ₅ Oi ₂ or mixtures of these

Materials.

In one embodiment of the invention, the electrode to be produced is a cathode. In this case, the composition, ie the "cathode slurry" contains

Active material, which is preferably selected from the group comprising

Lithium metal oxides of the type LiM _× O 2 (for example LiCoO 2; LiNiO 2; LiNii _-x Co _× θ 2;

LiNio, 85Co ₀ , iAlo, o5θ ₂ ; LiI ₊ X (NIyCOi- _2Y Mn ₇ ) I-XO ₂ ), 0 <x <0.17, 0 <y <0.5; LiMn ₂ O ₄ spinel doped or undoped; and lithium metal phosphates LiMPO ₄ (eg LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiVPO ₄ ) doped or undoped; as well as conversion materials such as iron (III) fluoride (FeF ₃ ) or mixtures of these materials

The present invention also provides a coated carrier prepared by the method described above, if such a carrier for the

Production of an electrode for electrical energy storage is suitable. Correspondingly prepared electrodes are also included in the present invention.

The present invention further provides a composition comprising as solvent and / or dispersant at least N-ethyl-pyrrolidone, and additionally at least one polymeric binder, an active material enabling the introduction and removal of electrically charged particles, and, optionally,

at least one conductivity additive. A preferred composition of this type contains a proportion of N-ethyl-pyrrolidone of from 30 to 80% by weight, preferably 40 to 70% by weight, a proportion of polymeric binder of from 0.5 to 8% by weight, preferably 1 , 0 to 5.0 wt .-%, a content of active material from 20 to 70 wt .-%, preferably 30 to 60 wt .-%, and optionally a proportion of conductivity additive from 0 to 5 wt .-%, preferably 0 , 2 to 3 wt .-%, each based on the composition.

The use of N-ethyl-pyrrolidone in the manufacture of electrodes for electrical energy storage and the use of N-ethyl-pyrrolidone for the preparation of a composition used for the coating of a support in the manufacture of an electrode for electrical energy storage, also falls under the present Invention.

N-ethyl-pyrrolidone is very similar to N-methyl-pyrrolidone in many of its chemical and physical properties. However, it has a higher boiling and

Flashpoint on (NMP: bp 202 ⁰ C, FP 91 ⁰ C, NEP: bp 208-210 ⁰ C, FP 93 ⁰ C), which has a certain advantage in terms of labor and storage security.

In addition, it is particularly important to the invention that the use of N-ethyl-pyrrolidone as solvent and / or dispersion medium makes it possible to use active materials and optionally to apply additives with a lower amount of dispersant on a support, ie to achieve higher solids contents in the composition than is possible with N-methyl-pyrrolidone as a dispersant.

FIG. 1 graphically depicts the viscosity behavior η of FIG

Electrode slurries with a solids content of 50% at 20 ⁰ C depending on the shear rate \. The solids content is composed of 91.5% by weight of graphite (d50 = 16.8 μm, BET surface area 2.5 m ² / g), 8% PVDF (Solvay Solef 1013) and 0.5%.

Carbon Black (Timcal, Super P).

FIG. 2 graphically shows the viscosity behavior η of 9.1% by weight PVDF homopolymer solutions (PVDF homopolymer: MeIt Flow Index, MFI 1, 5-3.5 g / 10 min) in NEP or NMP at 20 ⁰ C depending on the shear rate \.

FIG. 3 shows different binder systems: a) aqueous-based system, b) solvent-based system.

In the manufacture of a Elektrodenslurries invention consisting of NMP or NEP, PVDF, graphite and Leitruß was found that a NEP-based dispersion with increasing shear rate shows a greater reduction in viscosity than an NMP-based dispersion (Figure 1). Decisive for typical

Coating methods are shear rates of about 112 s ^-1 . Since NEP-based electrode slurries are of lower viscosity at these shear rates, higher solids contents can be achieved in this case and thus a reduction of the

Dispersant quantity can be achieved. To prepare such Elektrodenslurries the binder PVDF is often pre-dissolved in the solvent in question. at

Use of NEP as a solvent shows a significantly improved

Storage stability compared to NMP as a solvent. As a measure of the storage stability, the degree of increase in the viscosity of the solution in question is used with increasing storage time. The lower the increase in viscosity over time, the greater the storage stability (FIG. 2). Examples

The NMP or NEP was initially introduced into a 150 ml beaker, and the PVDF was added therein in portions in 15 minutes while stirring with a toothed disk (dissolver stirrer type R1303, IKA), diameter 42 mm, speed 750 rpm. At a PVDF content of 9.1% by weight (12.5 g in 125.0 g of solvent), the addition was stopped and stirred for a further 1.5 h (750 rpm). Subsequently, the viscosity was in

Dependence of the time determined.

Table: Comparison of solubility of PVDF in NEP and NMP, respectively

Rheometer: HAAKE RheoStress® RS600 viscosity in mPas at shear rates of

20 1 / s 73 1 / s 1 12 1 / s

PVDF in NMP after preparation, measurement 1 600.4 597.1 592.3 PVDF in NMP after preparation, measurement 2 601, 5 600.5 596.1 PVDF in NMP after 16 h, measurement 1 650.0 644.7 637 , 6 PVDF in NMP after 16 h, measurement 2 651, 2 647.4 641, 1 PVDF in NMP after 5 days, measurement 2 671, 2 661, 8 652.8 PVDF in NMP after 27 days 695.9 689.8 680.6

PVDF in NEP after preparation, measurement 1 573.5 570.1 564.7 PVDF in NEP after preparation, measurement 2 574.6 568.3 563.1 PVDF in NEP after 16 h, measurement 1 579.1 577.8 573 , 3 PVDF in NEP after 16 h, measurement 2 582.7 579.2 573.0 PVDF in NEP after 5 days, measurement 2 583.0 580.2 575.3 PVDF in NEP after 27 days 584.6 578.6 572.1

It was found in the solutions with NMP that the viscosity increased much more over time than was the case with the NEP solutions.

In addition, it was found that the NEP solution already after about 16 h has a constant viscosity, while in the NMP solution, the viscosity increased even after 5 days even further.

Claims

claims:

A method of coating a carrier in the manufacture of an electrode for electrical energy storage, comprising the steps of: a) providing a

Composition comprising at least one solvent and / or dispersant and additionally at least one polymeric binder, b) coating the carrier with the composition,

characterized,

the solvent and / or dispersant is or comprises N-ethyl-pyrrolidone.

2. The method of claim 1, wherein the polymeric binder is selected from the group comprising polyvinylidene fluoride homopolymers (PVDF);

Polyvinylidene fluoride copolymers (PVDF copolymers), e.g. PVDF hexafluoropropene (PVDF-HFP), PVDF tetrafluoroethylene (PVDF-TFE) and PVDF chlorotetrafluoroethylene (PVDF-CTFE); Blends of PVDF and PVDF copolymer (s); Polytetrafluoroethylene (PTFE); Polyvinyl chloride (PVC);

Polyvinyl fluoride (PVF); Polychlorotrifluoroethylene (PCTFE);

Polychlorotrifluoroethylene-ethylene (ECTFE); Polytetrafluoroethylene-ethylene

(ETFE); Polytetrafluoroethylene-hexafluoropropene (FEP); Polymethyl methacrylate (PMMA); Polyethylene oxide (PEO); Polypropylene oxide (PPO); Polypropylene (PP); Polyethylene (PE); Polyimide (PI); and styrene butadiene rubber (SBR).

3. The method according to any one of the preceding claims, wherein the

Composition is a dispersion and additionally contains an active material enabling the insertion and removal of electrically charged particles, which is preferably selected from the group comprising graphite; amorphous

Carbons; Lithium storage metals and alloys, including

nanocrystalline or amorphous silicon and silicon-carbon composites, tin, aluminum, and antimony; Li ₄ Ti ₅ Oi ₂ or mixtures thereof;

Lithium metal oxides of the type LiM _x O2, including UCOO2; LiNiθ2; LiNi _-x Co _x θ2; LiNio, 85Co ₀ , iAlo, o5θ ₂ ; Lii _{+ x} (Ni _y Cθi _-2 _y Mn _y ) i _-x θ 2, 0 <x <0.17, 0 <y <0.5; doped or undoped LiMn ₂ O ₄ spinels; and doped or undoped lithium metal phosphates LiMPO ₄ , including LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiVPO ₄ ; as well as conversion materials such as iron (III) fluorohd (FeF ₃ ) or mixtures thereof.

4. The method according to any one of the preceding claims, wherein the

Composition additionally contains at least one conductivity additive, which is preferably selected from the group comprising small-sized graphite with d50 between 1 micron and 8 microns; Carbon blacks or carbon blacks with

Primary particles between 10 and 80 nm; and carbon fibers; or any mixtures thereof.

5. The method according to any one of the preceding claims, wherein the carrier a

conductive or sheet-like material including or consisting of aluminum, copper, laminates comprising films of these metals, porous supports, woven, nonwoven or expanded metal, respectively, of these metals and polymeric films coated with these metals, apertured films, porous supports, woven or nonwoven fabrics wherein the support preferably comprises or consists of aluminum or copper.

6. The method according to any one of the preceding claims, wherein the

A proportion of N-ethyl-pyrrolidone of 30 to 80 wt .-%, and, preferably, a content of polymeric binder of 0.5 to 8 wt .-%, and / or of active material of 20 to 70 wt. %, and / or contains conductivity additive from 0 to 5 wt .-%, each based on the composition.

7. The method according to any one of the preceding claims, wherein the

Composition has a viscosity in the range of 1,000 to 7,000 mPas at a shear rate of 112 s ^"1 , measured at 20 ⁰ C having.

A method according to any one of the preceding claims, wherein the electrode to be produced is an anode and contains an active material selected from the group comprising graphite; amorphous carbons; Lithium storage metals and alloys, including nanocrystalline or amorphous silicon as well Silicon-carbon composites, tin, aluminum, and antimony; and Li ₄ Ti ₅ Oi ₂ or mixtures thereof.

A method according to any one of the preceding claims, wherein the electrode to be produced is a cathode and contains an active material selected from the group LiM _x O 2 type lithium metal oxides, including LJCOO 2;

LiNiO ₂ ; LiNii _-x Co _x O ₂ ; LiNio, 85Co ₀ , iAlo, o5θ ₂ ; Lii _{+ x} (Ni _y Cθi _-2y Mn _y ) i _-x O ₂ , 0 <x <0.17, 0 <y <0.5; doped or undoped LiMn ₂ O ₄ spinels; and doped or undoped lithium metal phosphates LiMPO ₄ , including LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , LiVPO ₄ ; as well as conversion materials such as iron (III) fluoride (FeF ₃ ) or mixtures thereof.

10. Coated carrier produced by a method according to one of

previous claims.

11. Electrode prepared by a process which is a process step

Method according to one of claims 1 to 9.

12. Composition comprising at least one solvent and / or dispersant, at least one polymeric binder, an active material enabling the introduction and removal of electrically charged particles, and, optionally, at least one conductivity additive, characterized in that the solvent and / or dispersant N -Ethyl-pyrrolidone is.

13. The composition of claim 12, wherein the proportion of N-ethyl-pyrrolidone from 30 to 80 wt .-%, the proportion of polymeric binder from 0.5 to 8 wt .-%, the proportion of active material from 20 to 70 wt .-%, and optionally the proportion of conductivity addition of O to 5 wt .-% is, in each case based on the

Composition.

14. Use of N-ethyl-pyrrolidone in the manufacture of electrodes for electrical energy storage.

Use of N-ethyl-pyrrolidone for the preparation of a composition used for coating a support in the manufacture of an electrode for electrical energy storage.