Electrolyte for stable cycling of rechargeable alkali metal and alkali ion batteries

A battery, comprising:

• an electrolyte comprising
• an active salt,
• a solvent comprising an ether, a carbonate, a sulfone, an aliphatic ester, a lactone, a sulfoxide, water, a flame retardant compound, a nitrile, or any combination thereof, wherein the active salt is soluble in the solvent, and
• a fluorinated orthoformate, wherein the active salt has a solubility in the fluorinated orthoformate at least 10 times less than a solubility of the active salt in the solvent, the active salt has a concentration in the electrolyte within a range of 0.1 to 3 M, and a molar concentration of the active salt in the electrolyte is at least 20% less than a molar concentration of the active salt in the solvent in the absence of the fluorinated orthoformate;
• an anode comprising an alkali metal, carbon, silicon, a carbon/silicon composite, tin, or antimony, or an anode current collector in the absence of an anode;
• and
• a cathode,
• wherein the battery has a coulombic efficiency≥95%.