LITHIUM ION BATTERY ELECTRODE WITH UNIFORMLY DISPERSED ELECTRODE BINDER AND CONDUCTIVE ADDITIVE

Abstract

The present disclosure relates generally to an electrode produced with a non-toxic solvent, resulting in a homogeneous mixture with uniform distributions of a conductive additive and a binder. Electrodes produced according to the present disclosure feature narrow binder particle size distribution, which distinguishes such electrodes from typical electrodes produced via a N-Methyl-Pyrrolidone (NMP) process. The resulting microstructure promotes the flow of current through the electrode and has an improved cycling stability due, in part, to the binder's and the conductive additive's ability to bind with the active material particles used in the fabrication of the electrode.

Claims

1-15. (canceled)

16. A positive electrode for a secondary battery, comprising: a current collector having at least one lateral surface, wherein the at least one lateral surface is coated with an electrode slurry, wherein the electrode slurry comprises: a positive active material; substantially uniformly dispersed particles of conductive additive, wherein the conductive additive comprises carbon; and substantially uniformly dispersed particles of polyvinylidene fluoride (PVDF) binder.

17. The positive electrode of claim 16, wherein the thickness of the coating on the at least one lateral surface of the electrode is between 50 and 500 microns.

18. The positive electrode of claim 17, wherein the current collector comprises a second lateral surface, wherein the second lateral surface is coated with the electrode slurry, wherein the thickness of the coating on the second lateral surface is between 50 and 500 microns such that the combined thickness of the coatings on the at least one and the second lateral surfaces is between 100 and 1000 microns.

19. The positive electrode of claim 18, wherein the combined thickness of the coatings on the at least one and the second lateral surfaces is between 200 and 300 microns.

20. The positive electrode of claim 16, wherein the dispersed particles of polyvinylidene fluoride binder comprise 1 to 10 percent by weight of the positive electrode.

21. The positive electrode of claim 20, wherein the dispersed particles of polyvinylidene fluoride binder comprise 2 to 5 percent by weight of the positive electrode.

22. The positive electrode of claim 16, wherein the dispersed particles of conductive additive comprise 1 to 10 percent by weight of the positive electrode.

23. The positive electrode of claim 22, wherein the dispersed particles of conductive additive comprise 3 to 5 percent by weight of the positive electrode.

24. The positive electrode of claim 16, wherein the average particle size of the dispersed particles of polyvinylidene fluoride binder is between 150 and 450 nm.

25. The positive electrode of claim 24, wherein the average particle size of the dispersed particles of polyvinylidene fluoride binder is between 200 and 300 nm.

26. The positive electrode of claim 16, wherein there is an average distance of 500 nm or less between adjacent dispersed particles of conductive additive.

27. The positive electrode of claim 26, wherein there is an average distance of 300 nm or less between adjacent dispersed particles of conductive additive.

28. The positive electrode of claim 27, wherein there is an average distance of 200 nm or less between adjacent dispersed particles of conductive additive.

29. The positive electrode of claim 16, wherein there is an average distance of 500 nm or less between adjacent dispersed particles of polyvinylidene fluoride binder.

30. The positive electrode of claim 29, wherein there is an average distance of 300 nm or less between adjacent dispersed particles of polyvinylidene fluoride binder.

31. The positive electrode of claim 30, wherein there is an average distance of 200 nm or less between adjacent dispersed particles of polyvinylidene fluoride binder.

32. The positive electrode of claim 16, wherein the positive active material comprises lithium, manganese, nickel, cobalt, aluminum, or a combination thereof.

33. The positive electrode of claim 32, wherein the positive active material is selected from a group consisting of: LiCoO.sub.2, LiFePO.sub.4, LiMn.sub.2O.sub.4, LiNiO.sub.2, Li.sub.2FePO.sub.4F, LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2, and Li(Li.sub.aNi.sub.xMn.sub.yCo.sub.z).

34. The positive electrode of claim 16, wherein the conductive additive is selected from the group consisting of carbon black, acetylene black, and graphite, or combinations thereof.

35. The positive electrode of claim 16, wherein the positive active material is adhered strongly to the current collector.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0042] The available invention will be more easy to understand with support of the belonging figures, where

[0043] FIG. 1. shows a principle drawing for manufacturing of slurry for battery electrodes according to the available invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] In the following text, the available invention will be described with support from the belonging FIGURE

[0045] It shall be understood that according to the invention, the foil that normally is used as cathodes and anodes also may comprise materials similar to fabrics or more generally, any conductive conductor which is compatible with the methods according to the available invention.

[0046] First, there will be a description of a general implementation of the invention, followed by examples of the methods that will be shown.

[0047] As indicated introductorily there exists a desire to change the process of manufacturing the slurry for coating of battery electrodes for lithium batteries.

[0048] Lithium ion batteries normally consist of three active elements, namely anode, cathode plus an electrolyte. As indicated above, it is the purpose of the available invention to find an alternative to the disadvantageous use of solvents for coating of the electrode foils.

[0049] The slurry that is applied to the electrode foils must have the correct body and viscosity so that the active layer that is applied to the electrodes will have a correct dry film thickness and homogeneity.

[0050] In order to be able to form a paste or thinly liquid slurry from binder, such as PVDF and powder in the form of active materials, the mixture has to be added a liquid. By using a liquid which is entered as a component in the finished battery it is not necessary that the liquid is removed completely. This component will still be added at a later stage in the process. According to the execution of the available invention, a method for manufacturing of the slurry for coating of battery electrodes is provided, where the slurry, meaning active components and a binder will be diluted with a diluting agent, where the diluting agent is a component of the electrolyte which shall be used in the same lithium battery

[0051] In general the process for manufacturing of slurry according to the available patent can be described with support from FIG. 1. Active materials A which will be constituent parts in the final slurry, will be mixed with a binder B in a first homogenization step 1. in order to obtain correct viscosity and consistency of the slurry a solvent C is added. It is in accordance with the available invention that the solvent C represents a component of the final lithium ion battery cell.

[0052] After the homogenization step the slurry has obtained the desired body/viscosity and the electrode material D can be coated 2 with the slurry. The coating process may be in the form of extruding, rolling or tape casting, or other suitable coating processes known from the industry.

[0053] Step 3 in the process comprises evaporation of the thinner which was added to the homogenization process 1. The applied slurry will consequently change from being viscous slurry to become a more solid material.

[0054] In parallel with step 3 there may be an active recycling step 4 which recycles the thinner that evaporates.

[0055] The following step 5 that is the step following step 3 and 4 is a step where the electrode material with the applied coating is rolled.

[0056] The following step 6 comprises baking of the rolled electrode, this baking will among other things secure that the binder adheres sufficiently to the active electrode materials and to the electrode foil.

[0057] The final step 7 comprises further finishing of the lithium ion batteries.

[0058] It shall be understood that manufacturing according to the steps 1 to 7 may be run consecutively and continuously, so that when step 1 is finished and a batch from step 1 moves onto step 2, then new materials can be added a homogenization of step 1, same is valid for the following steps, so that a manufacturing process can run continuously.

Implementation According to the Available Invention

[0059] In the following the available invention will be described with an example.

[0060] In this example in accordance with the available invention, the materials that will be used in the manufacturing of a lithium ion battery cell will comprise the following.

[0061] The anode, that is the positive electrode, consists of a copper foil; this copper foil shall be coated with an active material, generally in the form of a graffiti powder (LiC.sub.6). Also other active materials such as titanat (Li.sub.4Ti.sub.5O.sub.12), Si(Li.sub.4,4Si) or Ge(Li.sub.4,4Ge) can be used as active anode material. The graffiti powder shall be applied to the copper foil, in order for such a coating process to be successful and give a homogeneous surface then the graffiti powder must be mixed with 1 PVDF, PVDF and the graffiti powder must consequently be given a viscosity which is suitable for coating and thus the mixture will be added an organic carbonate, such as ethylene carbonate (EC) C. This blending step corresponds to the homogenization step 1 according to the general process description. The mixture may be heated to a temperature above the melting point of the thinner, i.e. the ingredient that was blended in order to give the right viscosity. The temperature may well be above the melting point of the thinner and close to the transition temperature of the binder.

[0062] The cathode, i.e. the negative electrode consists of an aluminum foil this aluminum foil shall be coated by an active material in the form of a lithium metal oxide. The lithium metal oxide shall be coated on the copper foil, so that such a coating process shall be successful and give a homogeneous surface then the lithium metal oxide A must be mixed with 1 PVDF, PVDF and lithium metal oxide must consequently be given a viscosity suitable for coating therefore the mixture will be added ethylene carbonate (EC) C. This step of the mixing corresponds with the homogenization step 1 according to the general process description

[0063] The following steps for cathode and anode follow roughly the same process as described in FIG. 1.

Another Performance Specification According to the Available Invention

[0064] In the following the available invention will be described with another example.

[0065] In this example in accordance with the performance specification of the available invention the material used during the manufacturing of a lithium ion battery cell comprises the following.

[0066] The anode, that is the positive electrode consists of a copper foil, this copper foil shall typically be coated by an active material in the form of a graffiti powder, thus the process for the anode is according to the description above.

[0067] The cathode that is the negative electrode consists of an aluminum foil this aluminum foil shall be coated by an active material in the form of a metal oxide such like one of Lithium cobalt oxide (LiCoO.sub.2), a polyanion such like Lithium iron phosphate (LiFePO.sub.4) or a lithium manganese oxide (LiMn.sub.2O.sub.4). Further cathode materials are found in the not supplementary group, LiNiO.sub.2, Li.sub.2FePO.sub.4F, LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2, Li.sub.aNi.sub.xMn.sub.yCo.sub.z)O.sub.2. For simplicity the term metal oxide will be used in the following for these mentioned phosphates/oxides.

[0068] The metal oxide shall be coated on the copper foil, in order for such a coating process shall be successful and give a homogeneous surface, the metal oxide A must be mixed 1 with a binder B, for instance PVDF and the metal oxide must in addition be given a viscosity suitable for coating therefore the mixture is added an organic carbonate such as ethylene carbonate (EC) C or diethyl carbonate. This mixing step corresponds to the homogenization step 1 according to the general process description.

[0069] The following steps for cathode and anode will roughly follow the same process as described in FIG. 1.

[0070] It shall be understood that a number of binders and active raw materials can be combined, where the central issue is that the thinner shall be a component in the final battery.

[0071] In the following is a description of the electrolyte and the properties associated with the materials composing the parts of the electrolyte. The electrolyte in a normal battery normally consists of organic carbonates such as EC (ethylene carbonate), diethyl carbonate. EC which is the most common is a waxy material which melts at approximately 40° C. and is then a liquid with low viscosity. EC is not poisonous; it is without smell and is only flammable at higher temperatures (above 140° C.).

[0072] According to an aspect of the invention the desired viscosity of this slurry may be generated by mixing the binder B (such as PVDF), the powder A (active, materials) and molten EC C. The amount of EC is adjusted according to the desired viscosity of the mixture.

[0073] This mixture is homogenized 1 vigorously at a temperature above the melting point of EC and below the melting point of the binder (for example at approx. 180° C. for PVDF). The particles with the binder will then because of the vigorous mixture be dispersed between all the particles in the mixture. If the homogenization takes place at a temperature above the melting temperature of the binder B, the mixture will obtain a lower viscosity.

[0074] When the mixture is homogenized sufficiently 1, so that the binder particles B are dispersed evenly between all the particles in the mixture, the metal foil D can be coated with the mixture. This may be done by extrusion, rolling or tape-casting. The battery film will then have to be heated 3 in order to evaporate the EC till the EC concentration is equal to or less than the desired EC concentration of the finished battery cell.

[0075] The consequent rolling 5 of the battery film will press the particles together and will improve the binding between the particles.

[0076] The EC-vapor which is formed by drying of the battery film can be condensed, filtered and reused in the process. EC is a harmless liquid with few health and environmental impacts. [0077] A: Active materials, such as graffiti and lithium oxide [0078] B: Binder, for example PVDF [0079] C Thinner according to the available invention, an electrolyte component such as organic carbonates [0080] D: Leading foil, such as aluminum foil, copper foil, aluminum canvas and copper canvas among others [0081] 1: Homogenization [0082] 2: Coating, for instance by extruding, tape-casting, rolling or similar [0083] 3: Evaporation of solvents [0084] 4: Recycling of solvents [0085] 5: Rolling [0086] 6: Baking, to melt the binder [0087] 7: Further processing to build up the battery