MICROPOROUS ELECTRODE OR SEPARATOR FOR USE IN A NON-AQUEOUS BATTERY, AND METHOD OF MANUFACTURING

Abstract: The invention relates to an element, in particular an electrode, to be used in an electrochemical cell, which element comprises at least a microporous sheet, consisting of inorganic, optionally electroconductive, particles, a polymer having a high molecular weight and a hydrocarbon-containing compound. The element can be used as an electrode in an electrochemical cell, such as a capacitor, or alternatively as a cathode, an anode and a separator in a battery built up of one or more layers of a current collector, an anode, a separator, a cathode, a current collector and an electrolyte, in particular a rechargeable Li-ion battery.

Description: MICROPOROUS ELECTRODE OR SEPARATION FOR USE IN A NON-AQUEOUS BATTERY, AND METHOD OF MANUFACTURING The invention relates to an element, in particular an electrode, for use in an electrochemical cell, which element comprises at least a microporous sheet consisting of inorganic, optionally electroconductive, particles, a polymer with a high molecular weight and a hydrocarbon-containing compound. The present invention further relates to a method of manufacturing such an element, as well as to the application of such an element as a cathode, an anode and a separator, respectively. The present invention additionally relates to an electrochemical cell, as well as to a battery which is successively composed of one or more layers of a current collector, an anode, a separator, a cathode and a current collector. The element as mentioned in the opening paragraph is known per se from United States patent specification 5,143,805. The element disclosed therein, in particular a cathode-electrode, comprises a microporous sheet, which is a self-supporting foil composed of an essentially homogeneous composition of approximately 70-98 wt.% electrochemically active and electroconductive particulate material, approximately 2-30 wt.% polyethene having a weight-averaged molecular weight of 150,000 to approximately 5 million, and 0 to approximately 5 wt.% of an organic softening agent for the polyethene, and a current collector which is composed of a conductive material, said collector being in close contact with at least one side of the microporous sheet. A drawback of such an electrode is the small quantity of inorganic particles in the polymer. The small quantity of inorganic particles reduces the activity of the electrode ultimately obtained. But increasing the quantity of inorganic particles leads, in practice, to a reduction of the integrity of the microporous sheet, and causes said microporous sheet to be susceptible to crack formation and disintegration. For this reason, it is an object of the invention to provide an element, in particular an electrode, wherein a substantially larger quantity of inorganic particles can be processed. Another object of the invention is to provide an element, in particular an electrode, which in spite of the high content of inorganic particles is not susceptible to crack- formation and disintegration. The element as mentioned in the opening paragraph is characterized in accordance with the invention, in that, if the microporous sheet is used for an anode and a separator, said microporous sheet comprises 80-99.9 wt.% inorganic, optionally electroconductive, particles, OJ-20.0 wt.% polyolefin compound with a high molecular weight, and 0-20.0 wt.% polymer, which polymer swells upon contacting electrolyte, and, if said microporous sheet is used for a cathode containing a quantity of polyolefin compound with a high molecular weight of OJ-1.9 wt.%, then said microporous sheet comprises 80-99.9 wt.% inorganic, optionally electroconductive, particles and 0-20 wt.% polymer, which polymer swells upon contacting electrolyte, and, if said microporous sheet is used for a cathode containing a quantity of polyolefin compound with a high molecular weight of 1.9- 20 wt.%, then said microporous sheet comprises 80-98 wt.% inorganic, optionally electroconductive, particles and OJ-20 wt.% polymer, which polymer swells upon contacting electrolyte. It will be obvious that the term cathode as used herein refers to a positive electrode, and the term anode refers to a negative electrode. For the polyolefin compound having a high molecular weight, use is preferably made of Ultra High Molecular Weight Polyethene (UHMWP) or Ultra High Molecular Weight Polypropene (UHMWPP) having a weight-averaged molecular weight in the range from 1-10 million. By using said polyolefin compounds very thin self-supporting sheets can be formed, which can be used as an electrode or as a separator. This polyolefin compound, which is used in the present invention, may additionally be composed of a mixture of polyethene having a high molecular weight and polyethene having a low molecular weight. It is alternatively possible, however, to use a mixture of polyethene with a high molecular weight and polypropene with a high molecular weight. Such a mixture exhibits a high resistance to high temperatures and a low shrinkage. To obtain a flexible, electroconductive electrode having a high temperature stability, it is desirable for the polyolefin compound to be linked. Linking can be brought about by using ionizing radiation, electron radiation or K-radiation. The quantity of polymer, which polymer exhibits swelling after contact with electrolyte, preferably ranges from 0J to 5 wt.% and is preferably chosen from the group formed by polystyrene, polyethene oxide, polypropene oxide, polyacrylate, polycarbonate and copolymers thereof. The element in accordance with the invention can suitably be used as a cathode. If said element is used as a cathode, use is preferably made of inorganic particles, such as particles selected from the group consisting of 3d-transition metal oxides, such as LiMn 2 O 4 , LiCoO , LiNiO 2 , to which, optionally, electroconductive particles, such as carbon and/or metal, are added. The relevant element can also suitably be used as an anode. If the relevant element is used as an anode, preferably, carbon and/or graphite are used for the inorganic, electroconductive particles. The relevant element can also suitably be used as a separator. If the relevant element is used as a separator, use is preferably made of inorganic, non-electrical particles, which particles are preferably selected from ceramic materials and/or oxides. For the ceramic material use is preferably made of Li( 1+X )Al x Ti( - X )(PO 4 ) 3 and/or Li 3x La( /3 - X )TiO 3 . For the oxides, use can suitably be made of Al 2 O 3 and/or SiO 2 . The present invention further relates to an electrochemical cell, at least comprising an electrode and an electrolyte, said electrochemical cell being characterized in that the electrode is an element as described above. Such electrochemical cell may comprise a capacitor, such as an electric double-layer capacitor (EDLC). As it is desirable to build small capacitors with a high capacitance, the application of the element according to the invention as an electrode is very advantageous as it reduces the size of the capacitor while the relative capacitance is enhanced. The use of polytetrafluoroethylene (PTFE) as a binder in an electrode for an electric double layer capacitor is known from the United States patent specification US-A- 6,038,123. However, the electrode sheet formed using said binder has a relatively high thickness of about 0.65 mm. By using a polyolefin compound with high molecular weight according to the present invention in the electrode element, a smaller thickness thereof can be obtained. Moreover, the present invention relates to a battery composed of one or more layers of a current collector, an anode, a separator, a cathode and a current collector, the battery in accordance with the invention being characterized in that at least one of the components: cathode, anode and separator, is the above-described cathode, anode and separator. The present invention further relates to a method of manufacturing an element as described hereinabove, said method being characterized in that the starting materials, namely inorganic, optionally electroconductive, particles, polyolefin compound and polymer are mixed with a solvent, whereafter the resultant mixture is supplied to an extruder so as to form a foil, after which the solvent is removed from the foil to obtain a microporous sheet. Said element can be used as an electrode. In accordance with the method of the invention, an anode, a cathode and a separator can be manufactured in this manner. If a separator is manufactured, ceramic particles are used, as described hereinabove. The element thus obtained can for example be used to manufacture lithium-ion batteries. The manufacturing process may be carried out in a number of different ways. The anode and the cathode can be laminated with current collectors by heating under pressure. This may be carried out in the dry state or in the presence of a solvent, which is subsequently removed from the system. In this way, composite sheets of, successively, a current collector/an anode/a separator/a cathode/a current collector are manufactured. It is alternatively possible to jointly subject the anode and the cathode as well as the separator to a co-extrusion treatment. The resultant, composite element can be subsequently provided with current collectors and arranged to manufacture a battery. It is also possible to subject either the anode or the cathode with the separator to a co-extrusion treatment. The resultant composite sheet material can be subsequently provided with current collectors and arranged to manufacture a battery. In accordance with yet another method, both the anode and the cathode are provided, during the manufacture thereof, with a current collector. These self-supporting sheet materials may be subsequently combined with a conventional separator to manufacture a battery. The systems described hereinabove may be finally provided with an organic ion-conducting liquid to obtain the final batteries. The present invention will be explained by means of a number of examples, which examples should not be construed as limiting the scope of the present invention. Manufacture of an anode A mixture of 5.3 g meso-carbon micro-grains, 5 g decalin and 0.05 g UHMWPE having a molecular weight above 1 million were prepared. The mixture was dissolved in an inert solvent and a film was prepared. After the excess solvent was removed, the film was subjected to a rolling operation to obtain a microporous sheet. Manufacture of a cathode The cathode was manufactured in a similar way as the anode, with the exception that first a mixture of 5 g LiCoO 2 , 5 g decalin, 0.05 g UHMWPE with a molecular weight above 1 million and 0.3 g soox was prepared. Said mixture was subsequently dissolved in an inert solvent and treated in a similar way as the anode. After removing the solvent, dry microporous sheets were obtained. Experiments have shown that the modulus of the sheets increases as the polymer content increases. Manufacture of a separator A separator was manufactured using 1 g UHMWPE having a molecular weight above 1 million and 9 g Lio. 55 Lao. 35 TiO 3 particles having a particle size of approximately 1 Tm. Both starting materials were dissolved in decalin whereafter a porous polymer film was formed. The conductivity at room temperature of such a film comprising 1 mol% LiPF 6 in propene carbonate solution was found to be 1.2 mS/cm. Manufacture of a battery Using a copper current collector for the anode and an aluminium current collector for the cathode, a battery was manufactured consisting of alternate anode, cathode and separator layers. The battery was subsequently immersed in 1 mol LiPF in a EC:DEC 1 :1 solution. Subsequently, the battery was provided in an aluminium-laminated synthetic resin holder. The battery could be charged without any external pressure being necessary.

Claims: CLAIMS: 1. An element, in particular an electrode, for use in an electrochemial cell, which element comprises at least a microporous sheet consisting of inorganic, optionally electroconductive, particles, a polymer with a high molecular weight and a hydrocarbon- containing compound, characterized in that, if the microporous sheet is used for an anode and a separator, said microporous sheet comprises 80-99.9 wt.% inorganic, possibly electroconductive, particles, OJ-20.0 wt.% polyolefin compound with a high molecular weight, and 0-20.0 wt.% polymer, which polymer swells upon contacting electrolyte, and, if said microporous sheet is used for a cathode containing a quantity of polyolefin compound with a high molecular weight of OJ-1.9 wt.%, then said microporous sheet comprises 80-99.9 wt.% inorganic, optionally electroconductive, particles and 0-20 wt.% polymer, which polymer swells upon contacting electrolyte, and, if said microporous sheet is used for a cathode containing a quantity of polyolefin compound with a high molecular weight of 1.9- 20 wt.%, then said microporous sheet comprises 80-98 wt.% inorganic, optionally electroconductive, particles and OJ-20 wt.% polymer, which polymer swells upon contacting electrolyte. 2. An element as claimed in claim 1, characterized in that UHMW-polyethene having a weight-averaged molecular weight in the range from 1 to 10 million is used for the polyolefin compound having a high molecular weight. 3. An element as claimed in claim 1, characterized in that UHMW-polypropene having a weight-averaged molecular weight in the range from 1 to 10 million is used for the polyolefin compound having a high molecular weight. 4. An element as claimed in claims 1-3, characterized in that the polyolefin compound having a high molecular weight is linked. 5. An element as claimed in claim 1-3, characterized in that the quantity of polymer ranges from 0J to 5 wt.%. 6. An element as claimed in claims 1-5, characterized in that the polymer which exhibits swelling after contact with electrolyte is selected from the group formed by polystyrene, polyethene oxide, polypropene oxide, polyacrylate, polycarbonate and copolymers thereof. 7. The use of an element as claimed in claims 1-6 as a cathode. 8. A cathode obtained in accordance with the application of claim 7, characterized in that the inorganic, electroconductive particles are selected from the group formed by LiMn 2 O 4 , LiCoO 2 , LiNiO 2 , to which electroconductive particles, such as carbon and/or metal, are optionally added. 9. The application of an element as claimed in claims 1 to 6 as an anode. 10. An anode obtained in accordance with the application of claim 9, characterized in that the inorganic particles are selected from carbon and/or graphite. 11. The application of an element as claimed in claims 1 - 6 as a separator. 12. A separator obtained in accordance with the application of claim 11 , characterized in that the inorganic particles are selected from ceramic materials and/or oxides. 13. A separator as claimed in claim 12, characterized in that Li (1+X) Al x Ti ( -X) (PO 4 ) 3 and/or Li 3x La (2/3 . x) TiO 3 is used as the ceramic material. 14. A separator as claimed in claim 12, characterized in that for the oxides use is made of Al 2 O 3 and/or SiO 2 . 15. An electrochemical cell, at least comprising an electrode and an electrolyte, characterized in that the electrode is an element according to one of the claims 1-6. 16. A battery composed of one or more layers of a current collector, an anode, a separator, a cathode and a current collector and an electrolyte, characterized in that at least one of the components: cathode, anode and separator, is a cathode as claimed in claim 8, an anode as claimed in claim 10, and a separator as claimed in claim 12. 17. A method of manufacturing an element as claimed in claims 1-6, characterized in that the starting materials are inorganic, optionally electroconductive, particles, a polyolefin compound and a polymer, which are mixed with a solvent, whereafter the mixture thus obtained is supplied to an extruder to form a foil, whereafter the solvent is removed from the foil to obtain the microporous sheet.

Inventors: FEIL HANS, HIKMET RIFAT A M, FEIL, HANS, HIKMET, RIFAT, A., M.
Applicants: FEIL HANS, HIKMET RIFAT A M, KONINKL PHILIPS ELECTRONICS NV, FEIL, HANS, HIKMET, RIFAT, A., M., KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H01M4
IPC codes: H01G9, H01M2, H01M4, H01M6, H01M10