IPA: /ˌɛlɛktroʊˈkɛmɪkəl/
KK: /ɪˌlɛk.trəʊˈkɛm.ɪ.kəl/
Relating to a chemical reaction that is caused by electricity or produces electricity.
The electrochemical process in the battery allows it to store and release energy.
Electrochemical is formed from "electro-" (from Greek "ēlektron", meaning amber or electricity) and "chemical" (from Greek "khēmia", meaning the art of transmuting metals). The word refers to the chemical processes that involve electricity.
Think of 'electricity' ('electro-') and 'the art of transmuting' ('khēmia') to remember that 'electrochemical' relates to chemical processes involving electricity.