Temperature is a key parameter in the safe operation of lithium-ion batteries (LIBs). In this paper, we present a novel optical fiber temperature sensor design and fabrication process that can operate within LIBs. The optical fiber is coated with two materials, a temperature sensitive layer and a protective layer. The temperature sensitive coating is polymethylmethacrylate (PMMA), which is highly sensitive to the organic electrolyte solution within LIBs; thus requiring a second protective layer. The chemically resistant protective coating is a fluorinated polymer AL-2233, which is a Teflon-like polymer able to resist organic solvents. The presented results demonstrate the performance of the temperature sensor within a temperature range from 24 to 32º C, as well as its resistance to organic solvents.