ELECTRODE SURFACE ROUGHNESS CONTROL FOR SPRAY COATING PROCESS FOR LITHIUM ION BATTERY
A method and apparatus for fabricating energy storage devices and device components is provided. It has been found that spraying of slurries comprising electro-active materials onto a flexible substrate and subsequently exposing the substrate to an increasing temperature gradient leads to the deposition of a dry or mostly dry film having reduced surface roughness. The increasing temperature gradient may result from a plurality of heated rollers over which the substrate traverses wherein each heated roller is heated to a temperature greater than the previous heated roller leading to the deposition of a dry or mostly dry film having a relatively smooth surface with low porosity. Deposition of a dry or mostly dry film eliminates the need for large and costly drying mechanism thus reducing both the cost and footprint of the apparatus.
1 . A method for forming an electrode structure, comprising:
spraying an electro-active material over a flexible conductive substrate;
transferring the flexible conductive substrate having the electro-active material deposited thereon over a first heated roller having a first temperature; and then
transferring the flexible conductive substrate having the electro-active material deposited thereon over a second heated roller having a second temperature, wherein the second temperature is greater than the first temperature and the electro-active material comprises a cathodically active material.
2 . The method of claim 1 , further comprising transferring the flexible conductive substrate having the electro-active material deposited thereon over a third heated roller having a third temperature after transferring the flexible conductive substrate over the second heated roller, wherein the third temperature is greater than the second temperature.
3 . The method of claim 2 , wherein the first temperature is between about 60 degrees Celsius and about 90 degrees Celsius and the second temperature is between about 90 degrees Celsius and about 100 degrees Celsius or between about 120 degrees Celsius and about 130 degrees Celsius.
4 . The method of claim 3 , wherein the third temperature is between about 120 degrees Celsius and about 130 degrees Celsius.
5 . The method of claim 4 , wherein the transferring the flexible conductive substrate having the electro-active material deposited thereon over a first heated roller and the spraying an electro-active material over a flexible conductive substrate occur simultaneously.
6 . The method of claim 5 , wherein the spraying an electro-active material over a flexible conductive substrate is performed using a hydraulic spray technique, an atomizing spray technique, an electrospray technique, a pneumatic spray technique, a plasma spray technique, and a flame spray technique.
7 . The method of claim 6 , wherein the electro-active material is part of a slurry mixture further comprising a binding agent and a solvent.
8 . The method of claim 7 , wherein the slurry mixture has a solids content of from about 50 wt. % to about 70 wt. % based on the total weight of the slurry mixture.
9 . The method of claim 8 , wherein the slurry mixture has a solids content of from about 65 wt. % to about 70 wt. % based on the total weight of the slurry mixture.
10 . The method of claim 8 , wherein the slurry mixture is delivered toward the flexible conductive substrate at a flow rate from about 0.1 ml/minute and about 10 ml/minute.
11 . The method of claim 10 , wherein the slurry mixture is delivered toward the flexible conductive substrate at a flow rate from about 0.5 ml/minute and about 4 ml/minute.
12 . The method of claim 11 , wherein the substrate travels at a rate from about 10 meters/minute to about 20 meters/minute.
13 . The method of claim 12 , wherein the flexible conductive substrate comprises aluminum.
14 . The method of claim 13 , wherein the cathodically active material is selected from the group consisting of: lithium cobalt dioxide (LiCoO 2 ), lithium manganese dioxide (LiMnO 2 ), titanium disulfide (TiS 2 ), LiNixCo 1-2x MnO 2 , LiMn 2 O 4 , LiFePO 4 , LiFe 1-x MgPO 4 , LiMoPO 4 , LiCoPO 4 , Li 3 V 2 (PO 4 ) 3 , LiVOPO 4 , LiMP 2 O 7 , LiFe 1.5 P 2 O 7 , LiVPO 4 F, LiAlPO 4 F, Li 5 V(PO 4 ) 2 F 2 , Li 5 Cr(PO 4 ) 2 F 2 , Li 2 CoPO 4 F, Li 2 NiPO 4 F, Na 5 V 2 (PO 4 ) 2 F 3 , Li 2 FeSiO 4 , Li 2 MnSiO 4 , Li 2 VOSiO 4 , LiNiO 2 , and combinations thereof.
15 . The method of claim 14 , wherein the slurry mixture further comprises:
a binding agent selected from the group consisting of: styrene butadiene rubber (SBR), carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF) and combinations thereof; and
a solvent.