NL2007153C2 - Electrode assembly for a lithium ion battery, process for the production of such electrode assembly, and lithium ion battery comprising such electrode assemblies. - Google Patents

Electrode assembly for a lithium ion battery, process for the production of such electrode assembly, and lithium ion battery comprising such electrode assemblies. Download PDF

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Publication number
NL2007153C2
NL2007153C2 NL2007153A NL2007153A NL2007153C2 NL 2007153 C2 NL2007153 C2 NL 2007153C2 NL 2007153 A NL2007153 A NL 2007153A NL 2007153 A NL2007153 A NL 2007153A NL 2007153 C2 NL2007153 C2 NL 2007153C2
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Prior art keywords
layer
pore
lithium ion
range
electrode
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NL2007153A
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Dutch (nl)
Inventor
Fokko Marten Mulder
Marnix Wagemaker
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Univ Delft Tech
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Priority to NL2007153A priority Critical patent/NL2007153C2/en
Priority to PCT/NL2012/050521 priority patent/WO2013012334A1/en
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Publication of NL2007153C2 publication Critical patent/NL2007153C2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Description

Electrode assembly for a lithium ion battery, process for the production of such electrode assembly, and lithium ion battery comprising such electrode assemblies
FIELD OF THE INVENTION
The invention relates to an electrode assembly for a lithium ion battery, to a process for the production of such electrode assembly, and to a lithium ion battery comprising such electrode assemblies as anode and cathode, respectively.
5
BACKGROUND OF THE INVENTION
Lithium ion batteries and high capacity lithium ion batteries are known in the art. WO2011056847, for instance, describes a high capacity silicon based anode active materials for lithium ion batteries. These materials are suggested to be effective in 10 combination with high capacity lithium rich cathode active materials. Supplemental lithium is suggested to improve the cycling performance and reduce irreversible capacity loss for at least certain silicon based active materials. In particular silicon based active materials can be formed in composites with electrically conductive coatings, such as pyrolytic carbon coatings or metal coatings, and composites can also be formed with other electrically conductive 15 carbon components, such as carbon nano fibers and carbon nanoparticles. Additional alloys with silicon are explored in this document.
Further, W02009131700 describes combinations of materials in which high energy density active materials for negative electrodes of lithium ion batteries. In general, metal alloy/intermetallic compositions can provide the high energy density. These materials 20 can have moderate volume changes upon cycling in a lithium ion battery. The volume changes can be accommodated with less degradation upon cycling through the combination with highly porous electrically conductive materials, such as highly porous carbon and/or foamed current collectors. Whether or not combined with a highly porous electrically conductive material, metal alloy/intermetallic compositions with an average particle size of 25 no more than a micron can be advantageously used in the negative electrodes to improve cycling properties.
Hence, especially W02009131700 describes a lithium ion battery comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode and an electrolyte comprising lithium ions, wherein the negative electrode 2 comprises a foamed current collector impregnated with an active material comprising a metal alloy/intermetallic material and wherein the negative electrode lacks a foil current collector or a grid current collector separate from the foamed current collector. Further, this document describes a powder comprising amorphous metal alloy/intermetallic particles wherein the 5 particles have an average particle size of no more than about 1 micron. In addition, W02009131700 describes a method for forming a metal alloy/intermetallic composition having a reduced degree of crystallinity, the method comprising milling amorphous elemental powders to form the alloy/ intermetallic composition.
10 SUMMARY OF THE INVENTION
Lithium ion batteries consist of an anode, cathode and in between an electrolyte. The electrodes contain the active materials in which Li can be stored in order to store energy. In practice the design of the battery is such that a large amount of inactive materials is necessary, reducing the weight percentage of the amount of active electrode 15 materials, and with it the energy density of the battery. The physically limited diffusion of lithium ions and electrons through the electrodes are the reason why currently only small amounts of active material can be used on the metal current collector foils. The basic problem is how to increase the amount of active material on the current collector foils, leading to a high energy density battery by the reduction of inactive materials.
20 It is recognized as a problem and much effort has been devoted to increase the intrinsic conductivity in the materials by e.g. nanostructuring and carbon coating. This has led to the present state of the art. Using the nanostructured and carbon coated materials we now address the conductivity on larger length scales because the rechargeability of the electrodes appears to be limited to a few microns of active material.
25 Hence, it is an aspect of the invention to provide an alternative electrode (or electrode assembly), which preferably further at least partly obviate one or more of above-described drawbacks, and which preferably allows quicker charging and/or higher capacities. It is yet a further aspect of the invention to provide a lithium ion battery comprising such alternative electrode (or electrode assembly).
30 Surprisingly, it has been found that a major step can be made when providing micro porosity. By making the electrodes porous on a scale of microns, with a pore volume fraction of for instance 10 - 20% it is possible to have fast conduction and rechargeabillity up to layer thicknesses of hundreds of microns. For the same energy storage capacity then a largely reduced amount of copper and/or aluminum foils as well as electrolyte and separator 3 layers may be required, which reduces the weight. In all it can be estimated that in this way a 2 times higher energy density of the battery can be realized than present state of the art batteries. Alternatively, the same methods can be applied to obtain electrodes that (discharge faster than the current state of the art. In that case the invention makes the prior art 5 choice of more active material on the current collector superfluous but rather provides the porous electrode for faster (dis-)charging.
Hence, to this end, the invention provides an electrode assembly for a lithium ion battery, the assembly comprising a lithium storage electrode layer on a current collector, 10 wherein the lithium storage electrode layer is a porous layer having a porosity in the range of 5-35 %, with pores having pore widths in the range of 0.5-100 pm, especially 1-10 pm, and having a porous layer thickness in the range of 5-500 pm, especially 10-200 pm.
Using such electrode assembly in a lithium ion battery, the above indicated advantages of the invention, i.e. faster charging and/or higher energy density (capacity) may 15 be obtained.
Herein, the term “electrode assembly” is used to indicate that the electrode or electrode assembly comprises the active layer, herein indicated as lithium storage electrode layer (which is a porous layer), and a current collector, on which the active layer is arranged (see also below). Often the term “electrode” is used for the active layer only, although the 20 electrode also comprises a current collector. Therefore, for the sake of understanding, herein the term “electrode assembly” is further applied. Herein, the term “lithium storage electrode layer” may also refer to a plurality of layers (i.e. a multi-layer structure). Such multi-layer structure may in an embodiment comprise layers with different compositions, such as different types of active material.
25 A specific feature of the electrode assembly is its porous layer. Porosity or void fraction is a measure of the void spaces in the layer and is a fraction of the volume of voids over the total volume as a percentage between 0-100%. As indicated above, especially, the porosity is in the range of 5-35 %, more preferably in the range of 10-30 %. For instance with SEM measurements and/or gas measurements, the porosity may be determined. 30 Alternatively or additionally, the chemical composition, the thickness and the weight can be used to evaluate the porosity.
The pore widths are preferably in the range of 0.5-100 pm, such as 0.5-80 pm, especially 0.5-50 pm, more especially at least 1 pm, even more especially in the range of 1-50 pm, such as at least 30 pm, like in the range of 1-30 pm, such as 1-10 pm. Preferably, at 4 least 50%, more especially at least 80%, yet even more especially at least 90% of the pores have such pore dimensions. Due to the presence of those pores, the lithium storage electrode layer has its above indicated porosity. Width may for instance also refer to diameter of substantially circular cross-sections of pores. Not all pores may substantially have circular 5 cross-sections, hence the pore width is chosen. Preferably, the pores show interconnectivity, which may be beneficial for good access of the liquid electrolyte in the battery.
Instead of pore width, the effective diameter may be chosen, which is preferably also in the range of 0.5-100 pm, such as 0.5-80 pm, especially 0.5-50 pm, more especially at least 1 pm, even more especially in the range of 1-50 pm, such as at least 30 10 pm, like in the range of 1-30 pm, such as 1-10 pm. The effective diameter can be evaluated by calculating the circumferential length of the cross-section of the pore, using the length as circumferential length of a (virtual) circle, and based thereon calculating the diameter of that circle. In this way, the effective diameter can be estimated of the pore.
For effective batteries, the porous layer thickness will be at least 5 pm, such as 15 5-500 pm, preferably at least 10 pm, such as 10-200 pm.
Hence, in a specific embodiment, the invention provides an electrode assembly as indicated above, wherein the porosity is in the range of 10-30%, wherein the pores have widths in the range of 1-100 pm, especially 1-30 pm, even more especially 1-10 pm, and having a porous layer thickness in the range of 10-200 pm.
20 In general, the lithium storage electrode layer further comprises carbon (especially carbon black) (herein also indicated as conductive carbon), for electronic conductivity reasons, and optionally some remaining binder (see below), and optionally some remaining pore former material (see below). Carbon will in general be present in the lithium storage electrode layer in the range of about 5-20 wt.%, such as 5-15 wt.%. The active 25 material will in general be present in the lithium storage electrode layer in the range of 60-95 wt.%, such as 75-95 wt.%, like at least 85 wt.%. Remaining binder may be present in an amount of about 5-20 wt.%, such as 10-15 wt.%. Remaining pore former material will in general be in the amount of 1 wt.% or less, such as 0.5 wt.% or less, like 0.1 wt.% or less. In an embodiment, the remaining amount of pore former material is in the range of 100 ppm -30 0.05 wt.%. These amounts are relative to the total weight of the lithium storage electrode layer. The presence (or absence) of the pore former material may be detected with X-ray scattering (assuming crystalline pore former material) and/or elemental analysis (EDX, as is often possible with SEM apparatus). When carbon is the active material, as in an anode embodiment, this material may then be present in the lithium storage electrode layer in the 5 range 85-95 wt.%. When the electrode is assembled in the battery configuration the liquid electrolyte will penetrate into the porous electrode.
The electrode assembly can be used as cathode or as anode, based on the active materials used. For use as cathode, the lithium storage electrode layer may comprise 5 for instance LiFePCL, Li[Ni,Mn,Co]204, such as LiMn204 or LiNio.5Mn1.5O4, or Li[Ni,Mn,Co]i02, such as LiCo02, or other high potential materials. Especially, the lithium storage electrode layer may comprise at least 75 wt.% of one of those materials. In another embodiment, the lithium storage electrode layer may comprise at least 75 wt.% of one of those materials. In a specific embodiment, the invention provides the electrode assembly as 10 indicated above, especially for use as cathode, wherein the lithium storage electrode layer comprises > 75 wt.% of a material selected from the group consisting of LiFePCL, LiMn204, LiNio.5Mn1.5O4, LiCo02, and Li[Ni,Mn,Co]i02. In an embodiment, the lithium storage electrode layer may also refer to a layer comprising different types of active materials.
For use as anode, the lithium storage electrode layer may comprise for 15 instance L^TisO^, Ti02, Si and C, or other high potential materials, may be applied. Hence, the lithium storage electrode layer may in an embodiment comprise at least 75 wt.% of one of those materials. In another embodiment, the lithium storage electrode layer may comprise at least 75 wt.% of one or more of those materials. Therefore, in a specific embodiment, the invention provides the electrode assembly as described above, (however) for use as anode, 20 wherein the lithium storage electrode layer comprises > 75 wt.% of one of those material selected from the group consisting of Li4Ti50i2, TiC>2, Si and C. Hence, whereas the cathode in general starts as lithium based lithium storage electrode layer, the anode may originally be provided as lithium based and as non-lithium based lithium storage electrode layer (for instance based on Si or on C).
25 In a specific embodiment, the porous layer thickness is at least 80 pm, more especially at least 100 pm, such as 100-500 pm, like 100-200 pm, such as especially 120-200 pm. Hence, in an embodiment, lithium storage electrode layer has a porous layer thickness of at least 100 pm. These relative thick layers may especially be of interest for use in high capacity batteries. When using the electrode assemblies of the invention in a battery (see also 30 below), the layer thicknesses and porosities and (mean) pore widths will in general be similar for both the cathode and anode, such as values for those respective features differing not more than 20%, preferably not more than 10%, of each other.
For instance the pore widths, for instance when averaged over the number of pore widths measured (for instance with SEM), may be about 25 pm for the cathode and 30 6 um for the anode (or vice versa). As reference the value for the layer with the larger value may be taken. In the above example, and assuming a 20% tolerance, the anode may have mean pore widths of 30 pm, and thus the cathode may have mean pore widths in the range of 24-36 pm.
5 The current collector in general comprises a foil. This foil may be used as support for the lithium storage electrode layer. The current collector may for instance comprise a Cu (copper) foil or an A1 (aluminum) foil. In an embodiment, the current collector comprises a multi-layer foil. In a specific embodiment, the current collector comprises a foil selected from the group consisting of a Cu foil and an A1 foil, and preferably, the foil has a 10 foil thickness in the range of 1-40 pm, such as in the range of 5-30 pm, such as in the range of 5-25 pm. Optionally, the current collector is a non massive layer, for instance comprising holes. In an embodiment, the current collector has a gauze shape. In an embodiment, the lithium storage electrode layer will substantially adopt such shape. This may depend upon the dimensions of the holes in the gauze. Optionally, such foil may be coated with carbon, for 15 instance with a layer of a few micron (this may add to the total thickness as indicated above. Such carbon layer may facilitate layer formation of the lithium storage electrode layer and better contact with the current collector.
In yet a further aspect (see also above), the invention provides a lithium ion battery comprising a cathode and an anode, wherein the cathode and anode comprise 20 electrode assemblies as described herein. Such battery may be charged quickly and/or may have a high capacity. In a specific embodiment, the invention provides such lithium ion battery, wherein the lithium storage electrode layers of the electrode assembly have porous layer thicknesses of at least 80 pm, especially at least 100 pm, and wherein the lithium ion battery has a capacity of at least 2.5 mAh/cm2, especially at least 3 mAh/cm2. Prior art high 25 performance lithium ion batteries may not have capacities over about 2.5 mAh/cm2, especially not larger than about 1 mAh/cm2.
The invention provides in a further aspect a process for the production of an electrode assembly.
For producing the cathodes the process may for instance involve the mixing of 30 10 -40 wt.% micronsized NaHCCb crystals (or an equally suitable other material) into the slurry that is used to produce a cathode. Such slurry may for instance include in the order of about of 80 wt.% LiFePC>4 active material, 10 wt.% PVDF (polyvinylidene fluoride) binder, and 10 wt.% conducting carbon altogether dissolved in a suitable organic solvent such as NMP (N-methylpyrrolidone). The NaHCC>3 (or equivalent) should not (substantially) 7 dissolve in the NMP (or other solvent) because these crystallites are present to produce after removing them the porous structure. After casting the electrode, evaporation of the solvent, pressing for a compacted layer, and drying in an oven, the NaHCC>3 is washed away in water upon which CO2 gas evolves and NaOH is dissolved and washed away through the pores.
5 The gas evolution is expected to especially contribute to the formation of connected pores. After thorough drying in a vacuum oven the electrode is ready for use in a battery with a liquid electrolyte. For producing the anodes a similar method may be applied with LLtTisO^ (LTO), or other materials, such as carbon. An alternative material for NaHCCh may for instance be other carbonate salts, like NH4CO3 that can be removed by thermal treatment, 10 NaCl that can be dissolved in water. In general salts that do not dissolve in NMP, and that show no H for Li exchange with the electrode materials. The advantage of NaHCCL is that it forms CO2 gas at room temperature, while the other materials do not. The emerging gas may help to form the pores and connect them.
Therefore, the mixture may in an embodiment comprise 5-40 parts pore 15 former material, 6-90 parts active material, 1-15 parts binder, and 1-20 parts conductive carbon.
Hence, in a further aspect, the invention also provides a process for the production of an electrode assembly, for instance as described herein, comprising: - providing a current collector (such as a foil as indicated above); 20 - applying a layer of a mixture of an active lithium storage material, binder, conducting carbon, a pore former material having dimensions in the range of 1-100 pm to at least part of the current collector, and optionally one or more of a liquid and a plasticizer; - removing the pore former material.
With such process, the electrode assemblies as described above may be 25 produced. The mixture may for instance be a slurry or a suspension. As active lithium storage material, a material selected from the group comprising LiFePCL, Li[Ni,Mn,Co]2C>4, such as LiMn2Ü4 or LiNio.5Mn1.5O4, or Li[Ni,Mn,Co]i02, such as LiCo02 for the cathode may be applied, and for the anode a material selected from the group comprising Li4Ti50i2, Ti02, Si and C may be applied (see also above).
30 The binder may comprise one or more of PVDF (polyvinylidene fluoride), CMC (carboxymethyl cellulose), and PTFE (polytetrafluoroethylene), although other materials may be applied as well. The binder may be a solid material, but may also be a liquid material. When using a slurry or suspension, the binder may be a liquid material during processing and/or a liquid is part of the mixture (and may be used to provide the liquid 8 properties of the slurry or suspension). The liquid is especially chosen that the pore former material does not (substantially) solve therein. In an embodiment, the liquid comprises one or more of NMP (N-methylpyrrolidone), acetone, and (dissolved) THF (tetrahydrofuran), but also other liquids may be applied. The binder may especially be solved in a solvent. In this 5 way a liquid is obtained which may be used to form for instance the liquid material, such as a slurry or suspension, with the other herein indicated ingredients.
As pore former material (or pore forming material) any suitable material may be applied, but preferably a pore former material that may easily be solvable in water or ethanol, especially in water. Further, preferably materials are used that may also form, upon 10 salvation or reaction with a solvent a gas, as gas formation may contribute to pore formation. In an embodiment, the pore former material comprises one or more of NaHCCh, NaCl, MgCfe, and NH4CO,. Preferably, the pore former material is a crystalline material. Hence, in an embodiment the pore former material may be removed by dissolving the pore former material in a solvent for the pore former material. The pore former material is preferably not 15 (well) solvable in the liquid (such as one of the indicated solvents).
Carbon may be provided per se, or may be present as coating on the active material. For instance carbon coated LLfTisO^ is commercially available. However, even when using carbon coated LLfTisO^, or other carbon coated materials, the addition of carbon may be desired, in order to further improve conductivity.
20 The mixture may be applied by casting the mixture to the current collector. In an embodiment, the mixture is melted to the current collector.
In an embodiment, wherein after applying the layer with mixture to the current collector (and removal of solvent, for instance by evaporation) and prior to removing the pore former material, the process comprises applying pressure to the thus formed layer. In an 25 embodiment, pressure may be applied after drying, and in another embodiment, pressure may be applied during drying.
In yet another embodiment, which may be combined with the previous one, wherein after removing the pore former from the layer and prior to drying the layer, the process comprises applying pressure to the thus formed layer. In an embodiment, pressure 30 may be applied after drying, and in another embodiment, pressure may be applied during drying.
Hence, in a further embodiment, the invention further provides a process comprising: - providing a current collector; 9 - applying a layer of a mixture of a lithium storage material, a binder, conducting carbon, a liquid, and a pore former material having dimensions in the range of 1-100 pm to at least part of the current collector; - optionally drying the layer (in this way, solvent - if any - may be removed); 5 - applying pressure to the layer; - removing the pore former material; and - drying the layer (again).
In a preferred embodiment, the lithium storage material comprises LiFeP04 or Li4TisOi2, the binder comprises one or more of PYDF, CMC, and PTFE, the liquid comprises 10 one or more of NMP, acetone, and THF, and the pore former material comprises one or more ofNaHCOs, NaCl, MgCl2, and NH4CO3.
The term “substantially” herein will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where 15 applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of’.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for 20 describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
It should be noted that the above-mentioned embodiments illustrate rather than 25 limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not 30 exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
10
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 5 Figs.la-Id schematically depicts some aspects of the invention. These drawings are not necessarily on scale;
Fig. 2 schematically depicts a SEM figure of the macroporous lithium storage electrode layer (here a LiFeP04-based layer).
10 DETAILED DESCRIPTION OF THE EMBODIMENTS
Fig. la schematically depicts an electrode assembly 100 (“assembly 100”) for a lithium ion battery, the assembly 100 comprising a lithium storage electrode layer 110 on a current collector 120, such as a Cu foil, wherein the lithium storage electrode layer 110 is a porous layer 10 having a porosity in the range of 5-35 %, comprising pores 11 having pore 15 widths d (see below) in the range of 1-100 pm, and having a porous layer thickness hi in the range of 5-500 pm. The current collector 120 has a height h2; the total height of the electrode assembly 100 is indicated with h.
Fig. lb very schematically depicts a lithium ion battery 200, with anode 101 and cathode 102. Both the anode 101 and the cathode 102 are electrode assemblies 100 as 20 described herein, but with different properties, such as for instance the lithium storage electrode layer 110 of the cathode 102 being based on LiFePCL as Li storage material, and the lithium storage electrode layer 110 of the anode 101 being based on C. During charging of the lithium ion battery 200, Li ions will enter the anode (for instance via the electrolyte in the pores of the lithium storage electrode layer 110 of the anode 101). Reference 201 25 indicates a separator (which is soaked in the liquid electrolyte). Note that only the most relevant elements for the invention have been depicted.
Figs, lc-ld schematically depict in more detail the lithium storage electrode layer 110. As can be seen, pores 11 can also be interconnected. Especially when the pore former material has a volume fraction of at least 7 wt.%, interconnection may be achieved. 30 Interconnection of the pores 11 is preferred.
Fig. 2 is a SEM picture of the lithium storage electrode layer 110 based on LiFePCL. In this example, the presence of pore former after removal was below the detection limit of the elemental analysis unit of the SEM.
11
EXAMPLES
Example 1: production of electrodes
For producing the cathodes: The method involves the mixing of 10 - 40% micronsized NaHC'CE crystals (or an equally suitable other material) into the normal slurry 5 that is used to produce a cathode. Such slurry involves of the order of 80 wt% LiFePCE active material, 10 wt% PVDF binder, and 10wt.% conducting carbon altogether dissolved in a suitable organic solvent such as NMP. The NaFICCE (or equivalent) should not dissolve in the NMP (or other solvent) because these crystallites are present to produce after removing them the porous structure. After casting, evaporation of the solvent, pressing for a 10 compacted layer, and drying in an oven, the NaFICCE is washed away in water upon which CO2 gas evolves and the NaOH is dissolved and washed away through the pores. The gas evolution is expected to contribute to the formation of good porosity. After thorough drying in a vacuum oven the electrode is ready for use in a battery with a liquid electrolyte.
For producing the anodes: a similar method has been used with LftTisO^ 15 (LTO).
Example 2: measurements
Lithium ion batteries with electrode assemblies as described herein ware made and compared to similar systems, but without porosity of the lithium storage electrode layer 20 of the anode and cathode.
Charge rate Capacity untreated electrode Capacity NaHCCE treated electrode C/20 (20h) 98% 98% C/10 (lOh) 9l% 97% C/5 (5h) 85% 95% C/2 (2h) 65% 95% 1C (lh) 35% 94% 2C (30min) 0% 92% 5C (12min) 0% 82% 10C (6min) 0% 70% 20C (3min) 0% 55%
Comparison of the capacity (C) of an untreated and treated electrode for increasing charge rate. 100% capacity means 170 mAh/g, the theoretical capacity of 12
LiFePC>4. The thickness and weight of both films is approximately 100 micron and 20 mg/cm2 carbon coated LiFeP04. C/20 indicates the capacity when charging 20 h. The percentages are relative to an ideal material. As can be seen, the micro porous lithium storage electrode layers provide a superior capacity, especially at the preferred shorter charging 5 times.

Claims (13)

1. Een elektrode-eenheid voor een lithiumion-batterij, waarbij de elektrode-eenheid een lithiumopslag elektrodelaag op een stroomgeleider omvat, waarbij 5 de lithiumopslag elektrodelaag een poreuze laag is met een porositeit van 5- 35%, met poriën met poriebreedtes in het bereik van 0.5-50 pm, en welke een poreuzelaagdikte in het bereik van 5-500 pm heeft.An electrode unit for a lithium ion battery, wherein the electrode unit comprises a lithium storage electrode layer on a current conductor, wherein the lithium storage electrode layer is a porous layer with a porosity of 5 to 35%, with pores with pore widths in the range from 0.5-50 µm, and which has a porous layer thickness in the range of 5-500 µm. 2. De elektrode-eenheid volgens conclusie 1, waarbij de porositeit in het bereik is 10 van 10-30%, waarbij de poriën poriebreedtes in het bereik van 1-30 pm hebben, en welke een poreuzelaagdikte in het bereik van 10-200 pm heeft.The electrode unit according to claim 1, wherein the porosity is in the range of 10-30%, wherein the pores have pore widths in the range of 1-30 µm, and which have a porous layer thickness in the range of 10-200 µm has. 3. De elektrode-eenheid volgens een van de conclusies 1-2, voor toepassing als kathode, waarbij de lithiumopslag elektrodelaag 75 gew.% of meer omvat van 15 een materiaal gekozen uit de groep bestaande uit LiFePCL, LiMn2C>4, LiNio.5Mn1.5O4, LiCo02, and Li[Ni,Mn,Co]i02.3. The electrode unit according to any of claims 1-2, for use as a cathode, wherein the lithium storage electrode layer comprises 75 wt% or more of a material selected from the group consisting of LiFePCL, LiMn2C> 4, LiNio.5Mn1 .5O4, LiCoO2, and Li [Ni, Mn, Co] iO2. 4. De elektrode-eenheid volgens een van de conclusies 1-2, voor toepassing als anode, waarbij de lithiumopslag elektrodelaag 75 gew.% of meer omvat van 20 een materiaal gekozen uit de groep bestaande uit Li4Ti50i2, Ti02, Si and C.The electrode unit according to any of claims 1-2, for use as an anode, wherein the lithium storage electrode layer comprises 75 wt% or more of a material selected from the group consisting of Li 4 Ti 50 12, TiO 2, Si and C. 5. De elektrode-eenheid volgens een van voorgaande conclusies, waarbij de lithiumopslag elektrodelaag een poreuzelaagdikte van tenminste 100 pm heeft.The electrode unit according to any of the preceding claims, wherein the lithium storage electrode layer has a porous layer thickness of at least 100 µm. 6. De elektrode-eenheid volgens een van voorgaande conclusies, waarbij de stroomgeleider een folie omvat gekozen uit de groep bestaande uit een Cu folie en een Al folie, en waarbij de folie een dikte heeft in het bereik van 1-30 pm.The electrode unit according to any of the preceding claims, wherein the current conductor comprises a film selected from the group consisting of a Cu film and an Al film, and wherein the film has a thickness in the range of 1-30 µm. 7. Een lithiumion-batterij omvattende een kathode en een anode, waarbij de 30 kathode en de anode elektrode-eenheden volgens een van de conclusies 1-6 omvatten.7. A lithium ion battery comprising a cathode and an anode, wherein the cathode and the anode comprise electrode units according to any of claims 1-6. 8. De lithiumion-batterij volgens conclusie 7, waarbij de lithiumopslag elektrodelagen van de elektrode-eenheden poreuzelaagdiktes in het bereik van tenminste 100 pm hebben, en waarbij de lithiumion-batterij een capaciteit heeft van tenminste 3 mAh/cm2. 5The lithium ion battery according to claim 7, wherein the lithium storage electrode layers of the electrode units have porous layer thicknesses in the range of at least 100 µm, and wherein the lithium ion battery has a capacity of at least 3 mAh / cm 2. 5 9. Een proces voor de productie van een elektrode-eenheid volgens een van de conclusies 1-6, omvattende: a. het verschaffen van een stroomgeleider; b. het toepassen van een laag van een mengsel van een actief lithiumion 10 opslagmateriaal, een bindmiddel, geleidend koolstof, een porievormmateriaal met dimensies in het bereik van 0.5-50 pm, in het bijzonder 1-50 pm, aan tenminste een deel van de stroomgeleider, en optioneel een of meer van een vloeistof en een plasticizer; c. het verwij deren van het porievormmateriaal. 15A process for producing an electrode unit according to any of claims 1-6, comprising: a. Providing a current conductor; b. applying a layer of a mixture of an active lithium ion storage material, a binder, conductive carbon, a pore-forming material with dimensions in the range of 0.5-50 µm, in particular 1-50 µm, to at least a part of the current conductor, and optionally one or more of a liquid and a plasticizer; c. removing the pore-forming material. 15 10. Het proces volgens conclusie 9, waarbij na het toepassen van de laag met het mengsel op de stroomgeleider en voor het verwijderen van het porievormmateriaal, het proces het toepassen van druk aan de aldus gevormde laag omvat. 20The process of claim 9, wherein after applying the layer with the mixture to the flow conductor and removing the pore-forming material, the process comprises applying pressure to the layer thus formed. 20 11. Het proces volgens een van de conclusies 9-10 omvattende: a. het verschaffen van een stroomgeleider b. het toepassen van een laag van een mengsel van een actief lithiumion opslagmateriaal, een bindmiddel, geleidend koolstof, een 25 porievormmateriaal met dimensies in het bereik van 0.5-50 pm, aan tenminste een deel van de stroomgeleider, en optioneel een of meer van een vloeistof en een plasticizer; c. het drogen van de laag; d. het toepassen van druk op de laag; 30 e. het verwijderen van het porievormmateriaal; en f. het drogen van de laag.The process of any one of claims 9-10 comprising: a. Providing a current conductor b. applying a layer of a mixture of an active lithium ion storage material, a binder, conductive carbon, a pore-forming material with dimensions in the range of 0.5-50 µm, to at least a part of the current conductor, and optionally one or more of a liquid and a plasticizer; c. drying the layer; d. applying pressure to the layer; 30 e. removing the pore-forming material; and f. drying the layer. 12. Het proces volgens een van de conclusies 9-11, waarbij het porievormmateriaal wordt verwijderd door het oplossen ervan in een oplosmiddel voor het porievormmateriaal.The process according to any of claims 9-11, wherein the pore-forming material is removed by dissolving it in a solvent for the pore-forming material. 13. Het proces volgens een van de conclusies 9-12, waarbij het actief lithiumion opslagmateriaal LiFePC>4 of LitTisO^, omvat, waarbij de binder een of meer gekozen uit de groep bestaande uit PYDF, CMC en PTFE omvat, waarbij de vloeistof een of meer van NMP, aceton en THF omvat, en waarbij het porievormmaterial een of meer materiaal gekozen uit de groep bestaande uit 10 NaHCC>3, NaCl, MgCf, and NH4CO3 omvat.The process according to any of claims 9-12, wherein the active lithium ion storage material comprises LiFePC> 4 or LitTisO 4, wherein the binder comprises one or more selected from the group consisting of PYDF, CMC and PTFE, the liquid comprising a or more of NMP, acetone and THF, and wherein the pore shape material comprises one or more material selected from the group consisting of NaHCC> 3, NaCl, MgCf, and NH 4 CO 3.
NL2007153A 2011-07-21 2011-07-21 Electrode assembly for a lithium ion battery, process for the production of such electrode assembly, and lithium ion battery comprising such electrode assemblies. NL2007153C2 (en)

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