Electrolytic capacitor containing a liquid electrolyte
An electrolytic capacitor that contains an anodically oxidized porous anode, cathode, and an electrolyte that contains an alkali metal salt and ionically conductive polymer is provided. The alkali metal salt forms a complex with the ionically conductive polymer and thereby improves its ionic conductivity, particularly at higher temperatures. The electrolyte also contains an organic solvent that reduces the viscosity of the electrolyte and helps lower the potential barrier to metal ion transport within the electrolyte to improve conductivity. By selectively controlling the relative amount of each of these components, the present inventors have discovered that a highly ionically conductive electrolyte may be formed that is also in the form of a viscous liquid. The liquid nature of the electrolyte enables it to more readily enter the pores of the anode via capillary forces and improve specific capacitance. Further, although a liquid, its viscous nature may inhibit the likelihood of leakage.
1. An electrolytic capacitor comprising:
an anode comprising an anodically oxidized porous body, the porous body containing tantalum, niobium, or an electrically conductive oxide thereof;
a cathode comprising a metal substrate; and
a liquid electrolyte disposed between the cathode and the anode, wherein the electrolyte comprises a lithium salt selected from the group consisting of LiBr, Lil, LiSCN, LiClO 4 , LiBF 4 , LiAsF 6 , LiPF 6 , LiCF 3 SO 3 , LiAlCl 4 , LiC(CF 3 SO 2 ) 3 , LiPF 3 (CF 3 ) 3 , LiPF 3 (C 2 F 5 ) 3 , LiBF 4 , LiBF 3 CF 3 , LiBF 3 (C 2 F 5 ), LiBF 3 (C 3 F 7 ), LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ), bis[trifluoromethane-sulfonyl]imidolithium (LiTFSI), and mixtures thereof, an ionically conductive polymer, and an organic solvent, wherein the liquid electrolyte has a viscosity of from about 10 to about 400 Poise, as determined at a temperature of 25° C. and a shear rate of 1 sec −1 .
2. The electrolytic capacitor of claim 1 , wherein the ionically conductive polymer includes polyethylene oxide.
3. The electrolytic capacitor of claim 1 , wherein the organic solvent includes a cyclic carbonic acid ester.
4. The electrolytic capacitor of claim 3 , wherein the cyclic carbonic acid ester includes ethylene carbonate, propylene carbonate, butylene carbonate, or a mixture thereof.
5. The electrolytic capacitor of claim 1 , wherein organic solvents constitute from about 50 wt. % to about 99 wt. % of the electrolyte.
6. The electrolytic capacitor of claim 1 , wherein organic solvents constitute from about 70 wt. % to about 95 wt. % of the electrolyte.
7. The electrolytic capacitor of claim 1 , wherein ionically conductive polymers constitute from about 0.1 wt. % to about 20 wt. % of the electrolyte.
8. The electrolytic capacitor of claim 1 , wherein ionically conductive polymers constitute from about 0.5 wt. % to about 15 wt. % of the electrolyte.
9. The electrolytic capacitor of claim 1 , wherein lithium salts constitute from about 0.5 wt. % to about 25 wt. % of the electrolyte.
10. The electrolytic capacitor of claim 1 , wherein lithium salts constitute from about 1 wt. % to about 20 wt. % of the electrolyte.
11. The electrolytic capacitor of claim 1 , wherein the electrolyte further comprises an additional polymer, which has a glass transition temperature of from about 10° C. to about 80° C.
12. The electrolytic capacitor of claim 11 , wherein the additional polymer includes polyethylene carbonate, polypropylene carbonate, polybutadiene carbonate, polyvinylidene carbonate, or a combination thereof.
13. The electrolytic capacitor of claim 1 , wherein the liquid electrolyte has a viscosity of from about 30 to about 200 poise, as determined at a temperature of 25° C. and a shear rate of 1 sec −1 .
14. The electrolytic capacitor of claim 1 , wherein the metal substrate comprises titanium.
15. The electrolytic capacitor of claim 1 , wherein an electrochemically-active material is disposed on the metal substrate.
16. The electrolytic capacitor of claim 15 , wherein the electrochemically-active material includes a conductive polymer.
17. The electrolytic capacitor of claim 1 , wherein the ionically conductive polymer includes one or more monomers that contain a hetero atom with a lone pair of electrons available for metal ions of the alkali metal salt to coordinate to and move therebetween.
18. The electrolytic capacitor of claim 1 , wherein the ionically conductive polymer includes polyethylene oxide, poly(bis(methoxy-ethoxy-ethoxide))-phosphazene, a triol-type polyethylene oxide crosslinked with difunctional urethane, poly((oligo)oxyethylene)methacrylate-co-alkali metal methacrylate, polyacrylonitrile, polymethylmethacrylate, polymethylacrylonitrile, polysiloxanes, polyvinylidene fluoride or chloride, poly(chlorotrifluoro-ethylene), poly(ethylene-chlorotrifluoroethylene), poly(fluorinated ethylene-propylene), or a combination thereof.