Patent Application
20090117461
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None
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Ukrainian Patent Application # a 2006 04674, priority date of Apr. 27, 2006
PCT Application PCT/UA2006/000055, Int. filing date of Oct. 11, 2006
The present invention relates to electrodes for technologies of the lithium primary and secondary batteries and supercapacitors, and specifically to electrodes for such chemical power sources that use non-aqueous electrolytes.
Lithium and lithium-ion batteries are widely used in the various applications where energy storage and off grid power are required. Use of for such power sources continues to expand. The increasing number of variety of devices that use such power sources have also extended the requirements for operating temperature range, power, discharge energy, and discharge rate for primary batteries and the charge/discharge rate for secondary batteries and super capacitors.
Compounds such as MnO2, FeS2, TiS2, MoO3, CFx and others are widely used as cathode materials for primary lithium batteries, wherein Li-metal or Li—Al alloy is the active anode material. As a rule, these are used in primary batteries. Oxide compounds such as LiCoO2, LiNiO2, LiCo1-xNixO2, the spinel form of LiMn2O4 and others are usually used as active cathode materials for secondary lithium batteries. Graphite or other materials that can be intercalated with lithium are often used as the active anode materials for Li-ion batteries.
The electrode compositions contain the active materials, conductive additives and binder. Conductive additives enhance electron conductivity of the electrode materials. The binder is responsible for the mechanical durability of the coating materials, and for its flexibility and adhesion to a current collector. Graphite, carbon black, and other materials based on carbon are used as the conductive additives. Polymer materials such as PVDF, Teflon® and others are used for binders. The binders generate the structure that provides the link between the powder particles of active material and the electrically conductive additives.
Technologies for electrode production for lithium and lithium-ion batteries can be divided into two groups:
1. The first group includes the binders that do not dissolve in the organic solvents. In this case lamination of a rubber-like mass on the current collector is used. The lamination is followed by the thermal treatment. Under thermal treatment a partial melt of the binder occurs. The result is cohesion between particles of the active materials and conductive materials. The current collector can be in the form of a foil or a grid.
2. The second group of the technologies for electrode fabrication uses binders that are soluble in organic solvents. Initially, a slurry is formed. This slurry includes a solution of the binder in the organic solvent, powders of active components and conductive additives. The slurry is coated onto the current collector, followed by drying and calendaring (compacting). The current collector can be in the form of foil or grid.
More detailed descriptions regarding these two approaches are provided below.
For the first group of electrodes, a tetrafluoroethylene resin (hereinafter referred to as PTFE) in the form of powder or aqueous suspension is used. The particular property of this type of the suspension is the high level of PTFE fibrillation. The electrode mass produced by this method way is quite rigid. Therefore this mass is applied to a current collector by lamination. This method for electrode production was historically used in the batteries with alkaline electrolyte. At present, this technology is mainly utilized for production of coin-cells, as well as prismatic and cylindrical batteries based on MnO2 Water, ethyl alcohol or isopropanol is a dispersion medium used in this technology. Various thickeners and stabilizers are also used for preparing the electrode mass.
The authors of U.S. Pat. No. 5,543,249 used surface active materials from the polyglycol group for stabilization of the PTFE -based suspension. The high level of PTFE fibrillation makes it difficult to obtain a homogeneous cathode mass and thus additional homogenization is necessary.
For regulation of fiber formation, the authors of U.S. Pat. No. 5,707,763 propose a combined binder, wherein particles consist of a nucleus of fibrillating PTFE and a shell of the non-fibrillating polymer. A disadvantage of this technology is the difficulty in producing a thin coating due to poor adhesion of the PTFE. Another disadvantage is the incompatibility of some of the active cathode materials with water and stabilizers.
Polyvinylidene fluoride (PVDF) homopolymer or polyvinylidene fluoride hexafluoropropylene (PVDF/HFP) copolymer are used in the second group of electrode production technologies. These polymers are dissolved into such solvents as N-methyl-2-pyrrolidone, acetone, dimethylformamide, or dimethylacetoamide. The mixture of active materials and conductive additives is introduced into a polymer solution and a slurry is prepared by mixing and homogenization. Then the slurry is applied by extrusion to the current collector that is in the form of a foil or grid. Thereafter, the coating is dried and compressed prior to final electrode production for lithium or lithium ion batteries.
Special coating machines are used for this technology. These machines exhibit higher productivity in comparison with lamination technology and maintain uniform thickness for electrodes with coating width of up to 20 centimeters with practically no limits with regard to thickness.
In spite of the fact that fluorine polymers of PVDF-group have better adhesion capability, the problems with adhesion and flexibility still occur as in the first and second technologies described so far. Moreover, there is a risk of PVDF/HFP-copolymers swelling in the electrolyte of the batteries that can lead to change in the electrode microstructure.
Attempts to solve these problems are mainly connected with binder modification and plasticizer utilization (U.S. Pat. No. 6,265,107; U.S. Pat. No. 6,001,507; U.S. Pat. No. 5,961,671). PVDF-based electrode production (the second technology) is the most advanced in comparison with the PVDF-based cathode mass lamination technology. Therefore, the appearance of a new polymer-solvent system with the object of adapting the materials used for lamination technology to extrusion technology is quite natural.
A search for new polymer-solvent systems for MnO2-cathodes was described in US Patent Application #20040091773. The authors proposed linear triblock styrene-ethylene-butylene copolymer cross-linked by melamine formaldehyde resin, EPDM-caoutchouc-riblock fluorocarbon polymers, hydro-nitryle caoutchouc, PVDF copolymers, thermoplastic polyurethanes and olefins, as binders. Normal and branched hydrocarbons, cyclic paraffinic solvents and aromatic hydrocarbons were used as solvents. The authors underlined the compatibility of this cathode production technology with traditional methods for the lithium-ion system based on PVDF. The traditional methods consist of preparing a cathode composition slurry based on binder-solvent solution and coating it on a current collector followed by drying. Although the authors covered a wide class of polymers and solvents, they did not notice their compatibility with MnO2. Correspondingly, electrochemical properties of cathodes and batteries were not disclosed. As a results, the practical value of this invention was not disclosed, and not confirmed.
Other binder-solvent systems have been proposed. These utilize similar technology to that based on PVDF. For example, application of latex binder based on a carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer (U.S. Pat. No. 6,399,246), and acrylonitrile-butadiene rubber with carboxymethylcellulose (U.S. Pat. No. 6,183,907) were described for non-aqueous electrolyte systems. Water was the dispersion medium in both cases. As pH of latex emulsion is about 8-10, it is not always acceptable for some active cathode materials due to chemical decomposition if the active materials and the resulting decrease in the electrochemical activity of the electrodes.
The goal of the present invention is to develop highly efficient electrodes for Li-ion batteries and Li-primary batteries with non-aqueous electrolyte based on new technology using PVDF for production of the electrodes. Specifically, the goal is to develop electrodes with improved mechanical and electrochemical properties. Among these electrodes are cathodes based on such materials as LiCoO2, LiNiO2, LiCo1-xNxO2, LiMn2O4 for Li-ion batteries. The additional objecti
that are based on such active materials as MnO2, FeS2, TiS2, MoO3, or CFx. Lamination technology is traditionally used for these types of electrodes.
An objective of the present invention is to develop electrodes with high efficiency, as well as a wide operating temperature range, high power, high discharge energy, high discharge rate for primary batteries, and a high charge/discharge rate for secondary batteries and super capacitors.
This objective of the present invention is achieved by using two types of the binders in the electrode mass composition that includes the active material and electrically conductive additive.
One of these binders is soluble in organic solvent during preparation of the electro-active composition slurry. The other binder is a powder that is insoluble in organic solvent. This binder is mixed with the dry powder that constitutes the active electrode mass and dry conductive additives.
The electrode is comprised of the following components:
The method of the present invention for electrode production of electrodes for primary and secondary lithium batteries is comprised of the following steps:
These process steps are described in more detail below.
Preparation of the mixture of solid phase components of the electrochemically active composition includes mixing the active material powders and conductive additives with the electron conducting powder and the PTFE binder powder using a ball mill.
Preparation of the binder solution includes dissolving the selected PVDF polymer into an appropriate solvent selected from the group of N-methyl-2-pyrrolidone, acetone, dimethylformamide, dimethylacetoamide (mainly dimethylacetoamide) with intermediate heating up to 60° C. using paddle type disperser.
The blend of solid phase components is introduced into the solution of soluble binder by 10% to 15% portions of the total amount of dry components using low-speed mixer with anchor or Z-type paddles.
An alternative method of introducing the solution of the soluble binder into the blend of the solid phase components is with continuous mixing using low-speed mixer anchor or Z-type paddles.
The product of the combination of the solid phase of the component blend and the solution of the soluble binder is subjected to homogenization using a high-shear mixer with speed changing from 1500 up to 8000 rpm during 30-45 minutes with cooling.
The homogenized slurry of the electrochemically active composition is subjected to degassing by vacuum while continuously mixing using a low-speed mixer anchor or Z-type paddles. The amount of solid phase components in the slurry is 30-60% by mass.
The slurry viscosity ranges from 5000 up to 12000 cp at 23° C., measured by Brookfield DV III, 20 rpm, spindle #31.
The slurry of electrochemically active composition is applied to the current collector by extrusion.
The electrochemically active composition is dried immediately after coating onto the current collector by gradually increasing the temperature from 80° C. up to 120° C. Solvent vapors are removed by purging with hot air.
After drying the electrochemically active composition that is coated onto the metal current collector, it is compressed by calendaring, gradually decreasing the thickness. As a result, the total reduction in thickness is approximately 20-25%. As compared with initial electrode mass density, the electrode mass density increases by 30-45%. The porosity of the electrode mass is 20-40%.
The cut-to-cell dimensions electrode is dried at 125° C.-170° C. in air with continuous gas re-cycling a system that removes residual moisture and organic solvent vapor.
The cut-to-cell dimensions electrode is then dried at 125° C.-170° C. under inert gas that is re-circulated through a system that removes residual moisture and organic solvent vapor.
The cut-to-cell dimensions electrodes is then dried at 125° C. to 170° C. under vacuum.
The method of electrode production according present invention provides the following advantages:
Moreover, this technical solution according to the present invention allows production of thin flexible electrodes with coating on one or both sides of the current collector made of foil or grid (preferably aluminum). Made in this way cathodes can be utilized at prismatic or spiral wound cells without cracking of the coating.
The flexibility of coating allows spiral winding around a 3 mm rod without any cracking or peeling from the current collector. It is possible to produce coatings with electrode mass density ranging from 1 mg/cm2 to 45 mg/cm2.
The stated advances are achieved by use of:
Thus, the electrode composition slurry that is produced according to the present invention and the range of the electrode temperature treatment for the drying are fully acceptable for processing by conventional and commonly used coating machines.
The lithium primary and lithium-ion secondary batteries contains anodes with a negative tab; cathode with a positive tab, separator and electrolyte. The electrolyte contains the dissociated lithium salt and aprotonic non-aqueous organic solvent. In this case of primary lithium cells, Li-metal or Li—Al alloy with Al content (of up to 5%, for example) can be used as an active anode material. In the case the lithium-ion system, graphite, carbon based material, or other materials that are capable of intercalating/de-intercalating the Li ion can be utilized as an anode. MnO2, CFx, FeS2, LiMn2O4, LiCoO2, LiNiO2, LiCo1-xNixO2 and other materials used in lithium or lithium-ion system can be used as active cathode materials.
Selgar polypropylene films or others providing similar properties can be used as the separator. One or several aprotic solvents such as 1,2-dimethoxy ethane, propylene carbonate, ethylene carbonate, DMC, DEC, 1,3-dioxolane, tetrahydrofuran, γ-butyrolacton and others can be used as the non-aqueous liquid component of the electrolyte. LiPF6, LiAsF6, LiClO4, LiN(CF3CF2SO2)2 or LiN(CF3SO2)2, or others can be used as a lithium salt.
Details of the construction and practice of the present invention are further illustrated in the drawings below, and by their associated legends and descriptions.
The invention can be practiced by the steps described below.
Step 1. Preparation of a powder-like blend of the electrode components including active electrode material, conductive additive in the form of graphitized carbon black with specific surface area from 40 up to 70 m2/g and 50% (material has a particle size up to 3 micron or the mix of carbon black and graphite in the ratio from 2:1 up to 1:1 by mass), PTFE powder with the particle sizes from 0.2 up to 4 μm. As a proportion of the total mass:
Mixing of solid phase cathode materials is carried out using a ball mixer or the other suitable mixers designed for dry component mixing.
Step 2. Preparation of the solution of high-molecular weight PVDF or PVDF/HFP in dimethyl acetoamide in the following proportions of the total mass:
PVDF or PVDF/HFP is dissolved using a paddle type mixer-emulsifier with moderate heating up to 60° C.
Step 3. The solid phase component blend is mixed with a dimethylacetoamide solution of PVDF or PVDF/HFP carried out by one of two methods:
The mass ratio between solid phase component blend and dimethylacetoamide solution of PVDF or PVDF/HFP is as follows:
Step 4. Homogenization of slurry using three types of mixing:
Homogenization is carried out for 30-45 minutes with continuous cooling.
Step 5. The homogenized slurry is degassed by applying moderate vacuum (10-50 mmHg) while constant agitating using a low-speed mixer with anchor or Z-type paddles (ROSS Model VMC-100 VACUUM MIXER or equivalent).
Step 6. The electrode active material, in the form of a slurry, is coated2 on one or both sides of the current collector in the form of a foil or grid (preferable aluminum) by extrusion using extruder heads with variable slurry distribution through slots with fixed gaps. The coated foil or grid (preferable aluminum) moves through two drying zones and is dried by heated air blow at 80° C. and 120° C., respectively. The tape advances at a speed of about 0.5 to 1.0 meters per minute.
Step 7. The electrode tape is then subjected to a calendaring process that gradually reduces the coating thickness by up to 20-25%.
Step 8. The electrodes are shaped to conform to the design of the battery in which they will be used.
Step 9. Final drying of the electrodes is accomplished by one of three methods:
Described below are examples illustrating the use and application of the present invention. These application examples and results are for illustration purposes only, and in no way limit the intended scope of applications of the invention.
This Example is connected with cathode based on MnO2 as the active material. Cathode was produced by the method according invention.
Content of electrochemically active composition slurry are as follows:
A blend of solid-phase components of MnO2, carbon black, graphite and PTFE was prepared by mixing for 5-6 hours using a ball-mixer.
An N,N-Dimethylacetamide solution of PVDF was made by using Lab mixer with a DL-attachment at 250 rpm for 3 hours with moderate heating up to 60° C.
A slurry of the electrochemically active composition was prepared in three stages using a VACUUM MIXER as follows:
The resulting slurry was applied to both sides of a 35 micron thick aluminum grid using a COATING MACHINE. The speed of the tape was 1 meter per minute. The tape then passed passing through dryers at 80° C. and 120° C.
The resulting cathodes were utilized in prismatic battery assembly consisting of 10 cathodes and 11 Li-anodes. The overall battery dimension was 34 mm×60 mm×3.8 mm. The weight was 16 g. Cathode mass density was 2.7 g/cm3 to 2.8 g/cm3. The electrolyte was PC, DME, TGF and 0.5 M LiClO4 The battery was discharged with a 50 mA current. MnO2 specific capacity was determined to be 270 mAh/g, The specific energy was 730 mWh/g. Discharge characteristics of the battery are shown in
The results shown here confirm the high discharge capacity of the electrode and high energy of the cells based on the electrodes that were produced according to the present invention. The resulting cells have excellent properties at operating temperature ranging from minus 40 up to plus 65° C. and a battery storage temperature ranging from minus 40° C. up to plus 70° C.
This Example is a cathode based on MnO2 as the active material. The cathode was produced by the method of the present invention.
The electrochemically active slurry composition was composed as follows:
Blending of the solid-phase components of MnO2, graphitized carbon black, and PTFE was prepared by mixing for 5-6 hours using a ball-mixer.
An N,N-Dimethylacetamide solution of PVDF was produced by using a Lab mixer with DL-attachment at 250 rpm for 3 hours with moderate heating up to 60° C.
A slurry of the electrochemically active composition was prepared in three stages using a VACUUM MIXER:
The slurry was applied to both sides of a 35 micron thick current collector composed of an aluminum grid using COATING MACHINE. The tape was advanced at a speed of 1 meter per minute and it passed sequentially through drying zones at 80° C. and 120° C.
The resulting cathodes were utilized to assemble a prismatic electrochemical cell consisting of 1 cathode and 2 Li-anodes. The electrolyte was composed of PC, DME, TGF, and 0.5 M LiClO4. The cells were discharged at room temperature at current densities ranging from 0.15 mA/cm2 up to 12 mA/cm2. This corresponded to the charge currents from 0.05 up to 4.0 C. Discharge characteristics are shown in
Results from testing of the lithium primary cells with cathodes produced according to the present invention confirm the high efficiency of the discharge process over a wide operating range of discharge currents up to 12 mA/cm2.
This Example describes fabrication of a cathode based on MnO2 as the active material. The cathode was produced by the method of the present invention.
The contents of electrochemically active composition slurry are as follows:
Blending of the solid-phase components MnO2, graphitized carbon black and PTFE was carried out by mixing for 5-6 hours using a ball mill.
An N,N-Dimethylacetamide solution of PVDF was prepared using the Lab mixer with DL-attachment at 250 rpm for 1 hour with moderate heating up to 60° C. The slurry of the electrochemically active composition was prepared using a Lab mixer with an L-high-shear attachment with 8000 rpm for three 10-minute steps followed by periodic cooling. The slurry was applied to both sides of a 50 micron thick aluminum foil using a Lab coating machine.
The resulting cathodes were utilized to assemble prismatic electrochemical cells consisting of 2 cathodes and 3 anodes, based on an Li—Al alloy. The electrolyte was PC, DME, TGF, and 0.5 M LiClO4. The cell was discharged at 1.31 mA/cm2 and 1.22 mA/cm2 currents at minus 40° C. to a voltage of 1.75 V. Discharge characteristics of the cell are shown in
Results from testing of the cells with cathodes produced according to the present invention show high efficiency of the cell at low temperatures of minus 40° C., even after prior battery storage at low temperature of minus 40° C. This type of the cell could be used for emergency purposes after long term storage at low temperatures.
This Example is a cathode based on CFx as the active material. The cathode was produced by the method of the present invention.
Content of electrochemically active composition slurry are as follows:
Blending of solid-phase components CFx, graphitized carbon black and PTFE was carried out by mixing for 5-6 hours using a ball-mill. A PVDF solution in N,N-Dimethylacetamide was prepared using a Lab mixer with DL-attachment at 250 rpm for 1 hour with moderate heating up to 60° C. the slurry of an electrochemically active composition was prepared using a Lab mixer with L-high-shear attachment at 8000 rpm in three stages. Each was carried out for 10 minutes with periodical cooling. The slurry was applied to both sides of a 20 micron thickness aluminum foil using a Lab coating machine.
The resulting cathodes were utilized for assembling an electrochemical cell of prismatic design consisting of 1 cathode and 2 Li-anodes. The electrolyte was PC, DME, TGF, and 0.5 M LiClO4. The cell was discharged at current densities of 6 mA/cm2 (discharge voltage 2.23 V) and 12 mA/cm2 (discharge voltage 2.10 V) at room temperature. Cell discharge characteristics are presented in
Results of testing confirmed the high efficiency of the cathode based on CFx that was produced according to the present invention. The cathode has a high discharge capacity at high discharge currents of up to 12 mA/cm without any voltage delay.
This Example is describes a cathode based on LiMn2O4-spinel as the active material. The cathode was produced by the method of the present invention.
The composition of the electrochemically active slurry was as follows:
Blending of the solid-phase component manganese spinel, graphitized carbon black and PTFE was carried out by mixing for 5-6 hours using a ball-mill. An N,N-Dimethylacetamide solution of PVDF was prepared using a Lab mixer with DL-attachment at 250 rpm for 1 hour with moderate heating up to 60° C. A slurry of electrochemically active composition was prepared using a Lab mixer with L-high-shear attachment at 8000 rpm in three stages, each with a duration of 10 minutes with periodic cooling. The resulting slurry was applied to both sides of a 20 micron thick aluminum foil using a Lab coating machine.
The resulting cathodes were utilized for assembling prismatic electrochemical cells consisting of 1 cathode and 2 Li-anodes. The electrolyte was EC, DMC, and 1.0 M LiClO4. The cells were discharged at current densities ranging from 0.24 up to 17.7 mA/cm2, corresponding to discharge currents of from 0.5 C to 36.5 C. Discharge characteristics are shown in
Results of testing of the batteries with cathodes based on LiMn2O4-spinel produced according to the present invention confirm the high level of the cathode efficiency even at a high rate of discharge (36.5 C).
While various embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 2006 04674 | Apr 2006 | UA | national |
| PCT/UA2006/000055 | Oct 2006 | UA | national |
