Layered lithium-rich (Li-rich) oxide cathodes with additional capacity contribution via oxygen redox are promising high energy density cathodes for next generation Li-ion batteries. However, the chemical states of the oxidized oxygen in charged materials are under fierce debate, including the O2- with stable electron holes, O-O dimer (O2)n- (n > 0), molecular O2, and oxygen π redox. Here, we show using electron paramagnetic resonance (EPR) spectroscopy that in the 4d Li-rich ruthenate compounds, Li2Ru0.75Sn0.25O3 and Li2Ru0.5Sn0.5O3, strong covalency between 4d transition metal and oxygen can inhibit the formation of trapped molecular O2 but not suppress the formation of O-O dimer. As the covalent bond of Ru-O weakens and the ionic bond Sn-O becomes dominant in Li2Ru0.25Sn0.75O3, (O2)- will detach from Sn4+, eventually leading to the formation of trapped molecular O2 during the deep oxygen redox. We propose two possible evolution paths of oxidized oxygen as (1) oxygen electron holes → Ru-(O2)m- (m > 1) → Ru-(O2)- or (2) oxygen electron holes → Sn-(O2)m- (m > 1) → Sn-(O2)- → O2, and the species to which they will evolve are related to which metal (O2)- bonds to and whether the ionicity dominates.