Improving the Electrochemical Performance of Li 2 RuO 3 through Chemical Substitution: A Case Study of ( x )LiCoO 2 ‐(1‐ x )Li 2 RuO 3 Solid Solution ( x ≤0.4)

The present work reports an enhancement in the electrochemical properties of Li 2 RuO 3 by Co +3 substitution. We explore the Li 1.33‐ x /3 Ru 0.66‐2 x /3 Co x O 2 series (in the solid solution notation ( x )LiCoO 2 ‐(1‐ x )Li 2 RuO 3 ) for x ≤0.4 by partial substitution of Co +3 for both Ru +4 and Li + in the metal layer; in this way, creation of oxygen non‐stoichiometry is avoided. Powder XRD reveals that an increase in the cobalt content in the series leads to a structural transformation from monoclinic to rhombohedral phase, owing to increased cation disorder in the metal layer. Cyclic voltammetric scans shows clear evidence for decreased oxygen evolution for Co‐substituted samples. The x =0.3 member delivers an initial discharge capacity of about 232 mAh g −1 and, after the 100 th cycle, 85 % capacity retention is observed. Furthermore, the rate capability is also significantly improved by Co substitution. Li + removal during the first charge is more than expected by counting on cation oxidation alone, demonstrating the participation of anion redox. Interestingly, the x =0.2 and 0.3 members of the series Li 1.33‐ x /3 Ru 0.66‐2 x /3 Co x O 2 show better Li reversibility upon long‐term cycling, endorsing the beneficial effect of Co +3 in stabilizing the layered structure during electrochemical cycling.