NOVELTY - The electrochemical energy storage device comprises a cathode, an anode, a porous separator disposed between the two electrodes, and a lithium-containing electrolyte in physical contact with the two electrodes. The cathode comprises chemically functionalized nano graphene platelets or exfoliated graphite having a functional group that reversibly reacts with a lithium atom or ion. The nano graphene platelets or exfoliated graphite have a functional group including e.g. carboxylic acid groups, oxo groups, hydroxyl groups, and/or amine groups.    USE - The electrochemical energy storage device such as lithium super-battery is useful in hybrid electric vehicles such as an electric car to provide bursts of power needed for rapid acceleration.    ADVANTAGE - The electrochemical energy storage device exhibits excellent power density, high energy density, long and stable cycle life and wide operating temperature range by directly bonding with desired functional groups capable of rapidly and reversibly reacting with lithium ions or atoms.    DETAILED DESCRIPTION - The electrochemical energy storage device comprises a cathode, an anode, a porous separator disposed between the two electrodes, and a lithium-containing electrolyte in physical contact with the two electrodes. The cathode comprises chemically functionalized nano graphene platelets or exfoliated graphite having a functional group that reversibly reacts with a lithium atom or ion. The nano graphene platelets or exfoliated graphite have a functional group including carboxylic acid groups, oxo groups, hydroxyl groups, amine groups, an oxygen-containing group attached to a carbon atom at a graphene platelet, and/or oxo or ester group with a hydrocarbon radical. The anode comprises an electrode active material capable of absorbing or desorbing lithium. The electrode active material includes lithium metal, a lithium metal alloy, a mixture of lithium metal or lithium alloy with a lithium intercalation compound, a lithiated compound, lithiated titanium dioxide, lithium titanate, lithium manganate, a lithium transition metal oxide and/or lithium titanate (Li4Ti5O12). The electrode active material is in a fine powder form having a dimension less than 100 nm. The nano graphene platelets or exfoliated graphite have an oxygen content of 10-20 wt.% based on the total graphene platelet weight. The electrolyte comprises a lithium salt-doped ionic liquid. The nano graphene platelets comprise single-layer graphene, a few-layer graphene platelet formed of 3-7 graphene planes, or curved graphene platelets. One of the two electrodes further comprises a nano material including a carbon nano-tube, carbon nano-fiber, activated carbon, carbon black, nano-wire, metal oxide nanowire or fiber, and/or conductive polymer nano-fiber. The device provides an energy density of greater than 500 Wh/kg and power density of greater than 15 Kw/kg. The cathode has a thickness of greater than 100 mu m.