Lithium-iron disulfide cell design
View Patent ↗The invention relates to primary electrochemical cells, in addition to methods for manufacturing and discharging the same, having a jellyroll electrode assembly that includes a positive electrode with a coating comprising iron disulfide deposited on a current collector situated on the outermost circumference of the jellyroll, a lithium-based negative electrode and a polymeric separator. More particularly, the invention relates to a cell design which optimizes cell capacity and substantially eliminates premature voltage drop-off on intermittent service testing by eliminating the edge effect through, for example, deliberately relieving stack pressure and/or extending the distance lithium ions proximate to the terminal end of the positive electrode must travel to undergo an electrochemical reaction in that region.
1. A method for making a cathode outer wrap battery which does not experience premature voltage drop-off upon intermittent discharge of the battery, the method comprising:
continuously coating a cathode mixture comprising iron disulfide onto both sides of a solid foil current collector and subsequently creating a plurality of zones of reduced electrochemical activity on at least one side of the current collector;
cutting the coated cathode into individual strips to create a plurality of individual cathodes so that the zone of reduced electrochemical activity is positioned at a terminal end of each individual cathode;
providing a separator and an anode consisting essentially of lithium or a lithium alloy wherein the anode does not include a current collector;
spirally winding the anode, the individual cathode strip and the separator into a electrode assembly so that less than 50% of an outermost surface of the electrode assembly, excluding the separator and optional non active components, is covered by the anode and the zone of reduced electrochemical activity is situated along the outermost surface of the electrode assembly; and
disposing the electrode assembly in a conductive container, introducing a non-aqueous electrolyte to the container and closing the container.
2. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by creating a mass free zone prior to disposing the electrode assembly in the container.
3. The method according to claim 2 , wherein the mass free zone is created by providing a sacrificial substrate to the current collector prior to coating the cathode mixture and then removing the sacrificial substrate subsequent to coating the cathode mixture.
4. The method according to claim 2 , wherein the mass free zone is created by physically removing the cathode coating as the cathode is cut into individual strips.
5. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by discharging the cathode in the zone prior to disposing the electrode assembly in the container.
6. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by insulating the cathode mixture from the ionic conductivity within the zone prior to disposing the electrode assembly in the container.
7. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by reducing an amount of active cathode material in the zone prior to disposing the electrode assembly in the container.
8. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by reducing the thickness of the cathode coating.
9. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created utilizing an initiator to induce a change within the cathode.
10. The method according to claim 9 , wherein the initiator is selected from radiation, electromagnetic radiation or a light source.
11. The method according to claim 9 , wherein the cathode mixture includes a chemical which reacts with or to the initiator.
12. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by providing a spacer having a thickness that is: i) greater than a combined thickness of the anode, the cathode and the separator, or ii) at least twice the thickness of the cathode, inclusive of the coating on both sides and the current collector between the anode and the individual cathode strip proximate to the terminal end.
13. The method according to claim 1 , wherein the zone of reduced electrochemical activity is created by relieving electrode stack pressure at the terminal end as the cell discharged.
14. The method according to claim 1 , wherein the anode is provided in an amount to create an interfacial, theoretical anode-to-cathode input capacity ratio that is less than 1.0.