Safety shutdown separators
View Patent ↗The present invention pertains to electrochemical cells which comprise (a) an anode; (b) a cathode; (c) a solid porous separator, such as a polyolefin, xerogel, or inorganic oxide separator; and (d) a nonaqueous electrolyte, wherein the separator comprises a porous membrane having a microporous coating comprising polymer particles which have not coalesced to form a continuous film. This microporous coating on the separator acts as a safety shutdown layer that rapidly increases the internal resistivity and shuts the cell down upon heating to an elevated temperature, such as 110° C. Also provided are methods for increasing the safety of an electrochemical cell by utilizing such separators with a safety shutdown layer.
1. An electrochemical cell comprising:
(i) an anode;
(ii) a cathode;
(iii) a solid porous separator; and
(iv) a nonaqueous electrolyte, wherein said separator and said electrolyte are interposed between said anode and said cathode;
and wherein said separator comprises an inorganic oxide separator layer having a microporous coating on one side of said separator layer, wherein said microporous coating comprises styrenated acrylic polymer particles having a diameter of between 100 and 150 nm.
2. The cell of claim 1 , wherein the internal resistivity of said cell increases to a level sufficient to safely terminate the current producing operation of said cell at a temperature in the presence of said electrolyte.
3. The cell of claim 2 , wherein said temperature is 150° C.
4. The cell of claim 2 , wherein said temperature is 130° C.
5. The cell of claim 2 , wherein said temperature is 110° C.
6. The cell of claim 2 , wherein said temperature is 100° C.
7. The cell of claim 1 , wherein said microporous coating comprises said polymer particles and a colloidal metal oxide.
8. The cell of claim 7 , wherein said metal oxide is a xerogel particle.
9. The cell of claim 7 , wherein said metal oxide is an aluminum oxide.
10. The cell of claim 7 , wherein said metal oxide is a zirconium oxide.
11. The cell of claim 7 , wherein said metal oxide is silica.
12. The cell of claim 7 , wherein said non-coalesced polymer particles comprise styrenated acrylic polymer particles.
13. The cell of claim 1 , wherein said microporous coating has a thickness from 0.1 to 5.0 microns.
14. The cell of claim 1 , wherein said microporous coating has a thickness from 0.5 to 2 microns.
15. An electrochemical cell comprising:
(i) an anode;
(ii) a cathode;
(iii) a solid porous separator; and
(iv) a nonaqueous electrolyte, wherein said separator and said electrolyte are interposed between said anode and said cathode;
and wherein said separator comprises an inorganic oxide separator layer having a microporous coating on one side of said separator layer, wherein said microporous coating comprises styrenated acrylic polymer particles having a diameter of between 100 and 150 nm wherein said separator shuts down by increasing the Gurley air porosity of said separator to above 60 minutes/100 cm 3 at a temperature at least 40° C. below the temperature at which said separator shuts down when heated in air with none of said electrolyte present.