NOVELTY - A cyano compound contains fluoro and chloro cyano groups.    USE - A cyano compound for electrolyte formulation used for electrochemical and/or optoelectronic devices, such as batteries, capacitors, supercapacitors, electrochemical cells, photovoltaic cell, LED, electrochemical sensor or biosensor, and dye sensitized solar cell (all claimed).    ADVANTAGE - The cyano compound exhibits high thermal stability, low melting point, high stability against acids or bases, and good electrochemical properties.    DETAILED DESCRIPTION - A cyano compound of formula (I) contains fluoro and chloro cyano groups. Compound (I) is selected from compound of formula (Catn+) ((PF1(CN)5)-)n (Ib), compound of formula (Catn+) ((PF4(CN)2)-)n (Ic), compound of formula (Catn+) ((PF5(CN))-)n (Id), compound of formula (Catn+) ((PCl2(CN)4)-)n (Ie), compound of formula (Catn+) ((PCl3(CN)3)-)n (If), and compound of formula (Catn+) ((PCl4(CN)2)-)n (Ig).Catn+=inorganic cation CatINORGn+ or organic cation CatORGn+;n=1, 2, 3, or 4;CatINORGn+=group 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 cation, cation from lanthanides, cation from actinides, NH4+, H3O+, or H5O2+;    CatORGn+=CatORG-A+, CatORG-B+, CatORG-C+, CatORG-D+, CatORG-E+, guanidinium, or (H2(R18)N-R16-N(R19)H2)2+;    CatORG-A+=(WR2R3R4R5)+;W=N or P;R2, R3, R4, R5=H,    C1-20 alkyl, C1-20 perfluoroalkyl, C3-10 cycloalkyl, or C6-10 aryl, provided that at least one of the residues R2, R3, R4 and R5 is not H, R2 and R3 are hydrocarbon chains and form together with W a 5- to 7-membered saturated or unsaturated heterocyclic ring, and R4 and R5 are hydrocarbon chains and form together with W 5- to 7-membered saturated or unsaturated heterocyclic ring;    CatORG-B+=(XR6R7R8)+;X=N;R6, R7=hydrocarbon chain;    R6+R7+X=5- to 7-membered unsaturated heterocyclic ring in which X is connected by single bond and double bond to R6 and R7, respectively;R8=H, C1-20 alkyl, C2-8 alkenyl, C1-20 perfluoroalkyl, C3-10 cycloalkyl, or C6-10 aryl;CatORG-C+=(YR9R10R11)+;Y=S;R9, R10, R11=H, C1-20 alkyl,    C1-20perfluoroalkyl, C3-10 cycloalkyl, or C6-10 aryl;R9+R10+Y=5- to 7-membered saturated or unsaturated ring;CatORG-D+=(ZR12R13)+;Z=O or S;R12, R13=hydrocarbon chain, provided that in any hydrocarbon chain formed by R2 and R3, by R4 and R5, by R6 and R7, by R9 and R10, and by R12 and R13, 1 or 2 C atoms of hydrocarbon chain can be exchanged for 1 or 2 heteroatoms selected from O, N, and S and, in case of exchange for N, N is optionally substituted by C1-8 alkyl, C3-10 cycloalkyl,    C2-8 alkenyl, or C1-8 perfluoroalkyl;R12+R13+Z=5- to 7-membered heterocyclic ring in which Z is connected by single bond and double bond to R12 and R13, respectively;CatORG-E+=(cyclic) Cnx alkane or (cyclic) Cnx alkene bearing positive charge in which (cyclic) alkane and (cyclic) alkene are optionally substituted by 1 to nx substituents selected from C1-6 alkyl, Ph, N(R14)R15, and Si(CH3)3;nx=3, 5, 7, or 9, provided that (cyclic) alkene contains 1 double bond when nx is 3, 2 double bonds when nx is 5, 3 double bonds when nx is 7, and 4 double bonds when nx is 9;R14, R15=H or C1-6 alkyl, provided that residues R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, and R13 are optionally substituted by 1, 2, 3, 4, 5 or 6 substituents selected from C1-4 alkyl, C3-10 cycloalkyl, C2-8 alkenyl, Ph, benzyl, halo, CN, and    C1-4 alkoxy;R16=C2-8 alkylene, C3-8 cycloalkylene, phenylene, C(H)(Ph), or R17(-O-R17)n1;R17=CH2-CH2, CH2-CH2-CH2, CH2-C(H)(CH3)-CH2, CH2-CH2-C(H)(CH3), or CH2-CH2-CH2-CH2;R18, R19=H, C1-8 alkyl, C3-8 cycloalkyl, Ph, or benzyl; and    n1=1-20.    INDEPENDENT CLAIMS are included for:    (1) use of compound of formula (I) as component in electrolyte formulation in which electrolyte formulation containing compound (I) is used in electrochemical and/or optoelectronic devices, such as batteries, capacitors, supercapacitors, electrochemical cells, photovoltaic cell, LED, electrochemical sensor or biosensor, and dye sensitized solar cell; and    (2) electrolyte formulation containing compound (I).