Method of using cyclic pressure to increase the pressed density of electrodes for use in electrochemical cells
View Patent ↗The traditional method of building a CF x /current collector/SVO assembly is by the application of a static pressing force. However, the density of the electrode and, particularly the CF x component, can be increase by using a cyclic pressing protocol. That is where the active materials are formed into a blank or contacted to a current collector by the use of at least two pressing events separated by a period when the pressure is removed. Not only does this cyclic pressing protocol increase the density of the CF x material, it also provides an electrode that is relatively flat, and not cupped. Conventional pressing techniques often result in badly cupped electrodes, especially when disparate active materials are contacting opposite sides of the current collector. Cupping consequently reduces the effective volumetric energy density of the electrode or necessitates the addition of a process step of flattening of the cathode, if at all possible. According to the new cyclic pressing protocol, the physical density of the cathode is increased and electrode cupping is effectively eliminated.
1. An electrochemical cell, which comprises:
a) an anode;
b) a cathode comprising a fluorinated carbon selected from CF x with x equal to about 1.1 and C 2 F as a first cathode active material having a relatively high energy density but a relatively low rate capability contacted to a first major side of a cathode current collector and a second cathode active material having a relatively low energy density but a relatively high rate capability contacted to a second, opposite major side of the cathode current collector, wherein the fluorinated carbon contacted to the cathode current collector is characterized as having been subjected to a cyclic pressure at a frequency of about 0.1 Hz to about 1 Hz to thereby provide the fluorinated carbon having a compacted density of about 1.7 grams/cc to about 1.8 grams/cc;
c) a separator intermediate the anode and cathode in electrical association with each other; and
d) an electrolyte activating the anode and cathode.
2. The electrochemical cell of claim 1 wherein the second cathode active material is selected from the group consisting of SVO, CSVO, V 2 O 5 , MnO 2 , LiCoO 2 , LiNiO 2 , LiMnO 2 , CuO 2 , TiS 2 , Cu 2 S, FeS, FeS 2 , copper vanadium oxide, and mixtures thereof.
3. The electrochemical cell of claim 1 wherein the anode is lithium, the first cathode active material is CF x , and the second cathode active material is SVO.
4. The electrochemical cell of claim 1 wherein the cathode current collector is of titanium having a layer of graphite/carbon contacted thereto.
5. The electrochemical cell of claim 1 wherein the cathode current collector has a thickness from about 0.001 inches to about 0.01 inches.
6. The electrochemical cell of claim 1 wherein the anode is of lithium in the form of at least one plate comprising an anode current collector electrically connected to a casing as its terminal and the cathode is connected to a cathode terminal insulated from the casing.
7. An electrochemical cell, which comprises:
a) an anode;
b) a cathode comprising a fluorinated carbon selected from CF x with x equal to about 1.1 and C 2 F contacted to a cathode current collector characterized as the fluorinated carbon and the current collector having been subjected to a cyclic pressure at a frequency of about 0.1 Hz to about 1 Hz to thereby provide the fluorinated carbon having a compacted density of about 1.7 grams/cc to about 1.8 grams/cc;
c) a separator intermediate the anode and cathode in electrical association with each other; and
d) an electrolyte activating the anode and cathode.
8. The electrochemical cell of claim 7 wherein the cathode current collector is of titanium having a layer of graphite/carbon contacted thereto.
9. The electrochemical cell of claim 7 wherein the cathode current collector has a thickness from about 0.001 inches to about 0.01 inches.
10. An electrochemical cell, which comprises:
a) an anode;
b) a cathode comprising a fluorinated carbon having a fluorine content ranging from 0.5 to about 1.1 contacted to a cathode current collector characterized as the fluorinated carbon and the current collector having been subjected to a cyclic pressure at a frequency of about 0.1 Hz to about 1 Hz to thereby provide the fluorinated carbon having a compacted density of about 1.7 grams/cc to about 1.8 grams/cc;
c) a separator intermediate the anode and cathode in electrical association with each other; and
d) an electrolyte activating the anode and cathode.
11. The electrochemical cell of claim 10 wherein the cathode current collector is of titanium having a layer of graphite/carbon contacted thereto.
12. The electrochemical cell of claim 10 wherein the cathode current collector has a thickness from about 0.001 inches to about 0.01 inches.