Electrode active material for the anode or the cathode of an electrochemical cell

Described is an electrode active material for an electrochemical cell, said electrode active material being a borate (BO 3 ) compound of formula : A a M b O d (BO 3 ) c wherein: - "A" is at least one alkali metal selected from Li, Na, K ; and 0‰¤ a ‰¤0.75; - "M" is M' x M" y , wherein M' is at least one redox active element, M" is at least one non-redox active element; and x + y = b , with 0.03 < b ‰¤ 0.45 ; - "BO 3 " is the borate anion; c ‰¥b+0.03 and c ‰¤0.75, with a + b + c = 1 ; - "O" is oxygen ; and -0.1 ‰¤ d ‰¤ 0.1 .