NOVELTY - A rechargeable electrochemical cell comprises positive electrode having electroactive material having recharged potential; negative electrode; charge-carrying electrolyte containing charge carrying medium and electrolyte salt; and cyclable redox chemical shuttle containing either aromatic compound substituted with tertiary alkyl group and halogenated alkoxy group, dissolved in or dissolvable in electrolyte and having oxidation potential above recharged potential of electroactive material, or alkoxy-substituted fluoronaphthalene compound dissolved in or dissolvable in electrolyte.    USE - As rechargeable electrochemical cell such as rechargeable lithium-ion cell in electronic device (claimed) such as flashlights, radios and CD players; in lithium ion batteries, in power tools and plug-in hybrid electric vehicles; in a variety of devices including portable computers, tablet displays, personal digital assistants, mobile telephones, motorized devices (e.g. personal or household appliances and vehicles), instruments, illumination devices (e.g. flashlights) and heating devices; and in a battery pack.    ADVANTAGE - The redox chemical shuttle provides overcharge protection in a lithium ion cell for at least 10 charge/discharge cycles at C/10 rate and a charging voltage sufficient to oxidize the shuttle to its radical cation and an overcharge current flow equivalent to 100% of the cell capacity during each cycle. The rechargeable lithium-ion cells exhibit excellent charge-discharge cycle life, little or no memory effect, and high specific and volumetric energy. The cell exhibits ability to tolerate recharging to potentials above the manufacturer's recommended end of charge potential without degradation in cycle life; does not exhibit the danger of overheating, or adverse thermal event for cells recharged to potentials above the recommended end of charge potential; and does not exhibit difficulties in making large cells having sufficient tolerance to electrical and mechanical abuse for consumer applications. The shuttles are robust, high performance, chemical redox shuttles that operate at high voltage and can provide overcharge protection for lithium-ion electrochemical cells and batteries. The availability of the shuttles enables low cost mass market applications for rechargeable lithium ion batteries and accelerates applications in power tools and plug-in hybrid electric vehicles as well. The electrochemical cell and lithium-ion batteries incorporating these cells, exhibits desirable performance characteristics such as high initial capacities, high average voltages, and good capacity retention after repeated charge-discharge cycling. The cells do not evolve substantial amounts of heat during elevated temperature use, thereby improving battery safety since they are protected from overcharge.    DETAILED DESCRIPTION - A rechargeable electrochemical cell comprises a positive electrode having at least one electroactive material having a recharged potential; a negative electrode; a charge-carrying electrolyte containing a charge carrying medium and an electrolyte salt; and either a cyclable redox chemical shuttle (S1) containing an aromatic compound substituted with at least one tertiary alkyl group and at least one halogenated alkoxy group, dissolved in or dissolvable in the electrolyte and having an oxidation potential above the recharged potential of at least one of the electroactive materials of the positive electrode principal electroactive material, or a cyclable redox chemical shuttle (S2) containing an alkoxy-substituted fluoronaphthalene compound dissolved in or dissolvable in the electrolyte and having an oxidation potential above the recharged potential of at least one of the electroactive materials of the positive electrode. INDEPENDENT CLAIMS are included for the following:    (1) making rechargeable electrochemical cell involving providing a cell containing a positive electrode having at least one electroactive material having a recharged potential, and a negative electrode; and adding a charge-carrying electrolyte comprising a charge carrying medium and an electrolyte salt to the cell, and a cyclable redox chemical shuttle selected from an aromatic compound substituted with at least one tertiary alkyl group and at least one halogenated alkoxy group and/or alkoxy-substituted fluoronaphthalene compound, where the shuttle is dissolved in or dissolvable in the electrolyte and the shuttle has an oxidation potential above the recharged potential of at least one of the electroactive materials of the positive electrode;    (2) an electrolyte solution comprising a charge-carrying medium, an electrolyte salt, and a cyclable redox chemical shuttle selected from an aromatic compound substituted with at least one tertiary alkyl group and at least one halogenated alkoxy group and/or alkoxy-substituted fluoronaphthalene compound, where the redox chemical shuttle has a reversible oxidation potential of 3.7 V to about 4.8 V versus Li/Li+; and    (3) an electronic device comprising the electrochemical cell.