NOVELTY - An electrolyte (26) comprises lithium salt and silicone-containing compound (I).    USE - Electrolyte is used for rechargeable lithium battery (claimed) for electric vehicles and power storage systems.    ADVANTAGE - The electrolyte efficiently improves high-temperature lifetime characteristics and high-temperature stability of the lithium secondary battery.    DETAILED DESCRIPTION - An electrolyte comprises lithium salt and silicone-containing compound of formula (I).    X=N or P;    R,R1=H, hydroxy, cyano, -ORx, -C(=O)Ra, -C(=O)ORa, -OC(=O)Ra, -OC(=O)(ORa), -NRbRc, or 1-6C alkyl, 1-6C alkoxy, 2-6C alkenyl, 2-6C alkynyl, 3-12C cycloalkyl, 6-20C aryl, 6-20C aryloxy, or 6-20C heteroaryl (all optionally substituted);    Rx=1-6C alkyl or 6-20C aryl;    R2-R4=cyano, -ORy, -C(=O)Ra, -C(=O)ORa, -OC(=O)Ra, -OC(=O)(ORa), -NRbRc, or 1-12C alkyl, 1-12C alkoxy, 2-12C alkenyl, 2-12C alkynyl, 3-20C cycloalkyl, 6-12C aryl, 6-12C aryloxy or 6-12C heteroaryl (all optionally substituted);    Ry=1-12C alkyl or 6-12C aryl;    Ra=H, or 1-10C alkyl, 6-12C aryl or 6-12C heteroaryl (all optionally substituted by halo);    Rb,Rc=H, -Si(Rd)3, or 1-10C alkyl, 2-10C alkenyl, 3-12C cycloalkyl, 6-12C aryl or 6-12C heteroaryl (all optionally substituted by halo);and    Rd=1-10C alkyl.    When R is CF3, all of R2-R4 are same, or at least one of R2-R4 is cyano, -ORy, -C(=O)Ra, -C(=O)ORa, -OC(=O)Ra, -OC(=O)(ORa), -NRbRc, or 1-12C alkyl, 1-12C alkoxy, 2-12C alkenyl, 2-12C alkynyl, 3-20C cycloalkyl, 6-12C aryl, 6-12C aryloxy or 6-12C heteroaryl (all optionally substituted), or R2-R4 is cyano, -ORy, -C(=O)Ra, -C(=O)ORa, -OC(=O)Ra, -OC(=O)(ORa), -NRbRc, or primary 1-12C alkyl, secondary 1-12C alkyl, 1-12C alkoxy, 2-12C alkenyl, 2-12C alkynyl, 3-20C cycloalkyl, 6-12C aryl, 6-12C aryloxy or 6-12C heteroaryl (all optionally substituted). An INDEPENDENT CLAIM is included for rechargeable lithium battery, which has electrolyte, a cathode containing cathode active material capable of intercalating and deintercalating lithium, and anode (38) containing anode active material capable of intercalating and deintercalating lithium.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic cross-sectional view of thin film formed on a surface of an anode of a lithium secondary battery.    Electrolyte (26)    Thin film (28)    Anode active material layer (30)    Anode current collector (32)    Anode (38)