NOVELTY - Electrolyte comprises lithium salt(s); linear carbonate-based solvent; ammonium cation(s); phosphoric acid-based solvent(s); and oxalatoborate-based additive(s).    USE - Electrolyte for rechargeable lithium battery (claimed) i.e. lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries including cylindrical, prismatic, or coin-type batteries.    ADVANTAGE - By reducing or eliminating decomposition of the battery electrolyte solutions at high temperatures, the rechargeable lithium batteries have improved thermal stability, flame retardancy, and electrochemical characteristics, such as high rate and cycle-life properties. The electrolyte solution does not use cyclic carbonate-based solvent, and thus gas generation and collapse of the passivation film at high temperatures are prevented, resulting in improved high rate and cycle-life characteristics at room temperature. The phosphoric acid-based solvent selectively reacts with radicals, to prevent combustion of the electrolyte solution. Thus, combustion decomposition reaction of the electrolyte solution caused by heat generated inside the battery is suppressed. The additive including oxalatoborate is reductively decomposed at greater than or equal to 0.7 V, and is oxidatively decomposed at greater than or equal to 5 V during charging. Thus, stable negative electrode coating is formed by removing the reductively decomposed ionic solution, minimizing the thermo-decomposition between the fully charged negative electrode and the electrolyte solution, and maximizing the thermal stability and flame retardancy of the battery.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) rechargeable lithium battery (100) comprising positive electrode (114); negative electrode (112); separator (113); and electrolyte comprising lithium salt(s), linear carbonate-based solvent, ammonium cation(s), and phosphoric acid-based solvent(s), and oxalatoborate-based additive or oxalatoborate-based polymer; and    (2) making rechargeable lithium battery comprising providing electrode component comprising positive electrode, negative electrode, and separator; impregnating the electrode component with an electrolyte to form a battery; and performing charge of battery to decompose the oxalatoborate-based additive of the electrolyte and form a coating on the negative electrode.    DESCRIPTION OF DRAWING(S) - The drawing is a perspective, cross-sectional view of rechargeable lithium battery.    Rechargeable lithium battery (100)    Negative electrode (112)    Separator (113)    Positive electrode (114)    Battery case (120)