NOVELTY - A non-aqueous electrolyte contains 1,3-dithietane-1,1,3,3-tetra- oxide compound (I).    USE - Non-aqueous electrolyte for a lithium secondary battery (claimed) that is utilized as a power supply for small portable apparatus such as notebook personal computer, mobile personal computer, mobile telephone, headphone stereo cassette tape recorder, video movie, liquid crystal TV, handy cleaner, electronic organizer, calculator and radio, and for large sized apparatus such as game machine, timepiece, electric tool and camera, and as utilized as a backup power supply, motor, motor vehicle, electric vehicle, motorbike, electric motorcycle, bicycle and electric-power-assisted bicycle.    ADVANTAGE - The electrolyte improves charging/discharging performance, energy density, durability, and storing characteristics and low-temperature discharge characteristics of the battery.    DETAILED DESCRIPTION - A non-aqueous electrolyte contains 1,3-dithietane-1,1,3,3-tetra- oxide compound of formula (I).    M=alkali metal;    Y1=transition element or group 13, 14 or 15 element;    b=1-3;    m=1-4;    n=0-8;    q=0 or 1;    R1=1-10C alkylene, 1-10C halogenated alkylene, 6-20C arylene or 6-20C halogenated arylene group optionally containing substituent or heteroatom;    R2=halo, 1-10C alkyl, 1-10C halogenoalkyl, 6-20C aryl, 6-20C halogenated aryl group optionally containing substituent or heteroatom, or -Q3R3;    nR2=ring;    Q1-Q3=O, S or NR4;    R3,R4=H, 1-10C alkyl, 1-10C halogenoalkyl, 6-20C aryl or 6-20C halogenated aryl;and    R3+R4=ring.    An INDEPENDENT CLAIM is also included for a lithium secondary battery comprising a positive electrode and a negative electrode containing negative electrode active material comprising metallic lithium, lithium containing alloy, and/or doped and dedoped lithium oxide.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a lithium secondary battery.    Positive electrode (1)    Negative electrode (2)    Positive electrode can (3)    Sealing board (4)    Separator (5)    Gasket (6)    Spacer board (7, 8)