Electrolyte and lithium-ion secondary battery

An electrolyte comprising:

• a non-aqueous solvent;
• a lithium salt (A);
• and
• at least one compound (B) selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2) and a compound having a constitutional unit represented by the following formula (3a) and a constitutional unit represented by the following formula (3b),
• wherein X represents a Li atom or a hydrogen atom;
• M represents a P atom or a B atom;
• n represents an integer of 0 when M represents a B atom, and n represents an integer of 0 or 1 when M represents a P atom;
• and R1 and R2 each independently represent a group selected from the group consisting of an OH group, an OLi group, an alkyl group having 1 to 10 carbon atoms, which may have a substituent, an alkoxy group having 1 to 10 carbon atoms, which may have a substituent, an aryl group having 6 to 10 carbon atoms, which may have a substituent, an aryloxy group having 6 to 10 carbon atoms, which may have a substituent, and an siloxy group having 3 to 10 carbon atoms,
• wherein X represents a Li atom or a hydrogen atom;
• and R3 represents a hydrocarbon group having 1 to 20 carbon atoms, which may have a substituent,
• wherein R4 represents a group selected from the group consisting of an OH group, an OLi group, an alkyl group having 1 to 10 carbon atoms, which may have a substituent, an alkoxy group having 1 to 10 carbon atoms, which may have a substituent, an aryl group having 6 to 10 carbon atoms, which may have a substituent, an aryloxy group having 6 to 10 carbon atoms, which may have a substituent, and an siloxy group having 3 to 10 carbon atoms;
• and X represents a Li atom or a hydrogen atom.