%0 Journal Article
%A Dongchang Chen
%A Jinpeng Wu
%A Joseph K Papp
%A Bryan D McCloskey
%A Wanli Yang
%A Guoying Chen
%B Small
%D 2020
%G eng
%N 22
%P 2000656
%R 10.1002/smll.202000656
%T Role of Redox‐Inactive Transition‐Metals in the Behavior of Cation‐Disordered Rocksalt Cathodes
%V 16
%8 05/2020
%! Small
%X <p><span>Owing to the capacity boost from oxygen redox activities, Li‐rich cation‐disordered rocksalts (LRCDRS) represent a new class of promising high‐energy Li‐ion battery cathode materials. Redox‐inactive transition‐metal (TM) cations, typically&nbsp;</span><em>d</em><sup><sub><span>0</span></sub></sup><span>&nbsp;TM, are essential in the formation of rocksalt phases, however, their role in electrochemical performance and cathode stability is largely unknown. In the present study, the effect of two&nbsp;</span><em>d</em><sup><span>0</span></sup><span>&nbsp;TM (Nb</span><sup><span>5+</span></sup><span>&nbsp;and Ti</span><sup><span>4+</span></sup><span>) is systematically compared on the redox chemistry of Mn‐based model LRCDRS cathodes, namely Li</span><sub><span>1.3</span></sub><span>Nb</span><sub><span>0.3</span></sub><span>Mn</span><sub><span>0.4</span></sub><span>O</span><sub><span>2</span></sub><span>&nbsp;(LNMO), Li</span><sub><span>1.25</span></sub><span>Nb</span><sub><span>0.15</span></sub><span>Ti</span><sub><span>0.2</span></sub><span>Mn</span><sub><span>0.4</span></sub><span>O</span><sub><span>2</span></sub><span>&nbsp;(LNTMO), and Li</span><sub><span>1.2</span></sub><span>Ti</span><sub><span>0.4</span></sub><span>Mn</span><sub><span>0.4</span></sub><span>O</span><sub><span>2</span></sub><span>&nbsp;(LTMO). Although electrochemically inactive,&nbsp;</span><em>d</em><sup><span>0</span></sup><span>&nbsp;TM serves as a modulator for oxygen redox, with Nb</span><sup><span>5+</span></sup><span>&nbsp;significantly enhancing initial charge storage contribution from oxygen redox. Further studies using differential electrochemical mass spectroscopy and resonant inelastic X‐ray scattering reveal that Ti</span><sup><span>4+</span></sup><span>&nbsp;is better in stabilizing the oxidized oxygen anions (O</span><sup><em><span>n</span></em><span>−</span></sup><span>, 0 &lt;&nbsp;</span><em>n</em><span>&nbsp;&lt; 2), leading to a more reversible O redox process with less oxygen gas release. As a result, much improved chemical, structural and cycling stabilities are achieved on LTMO. Detailed evaluation on the effect of&nbsp;</span><em>d</em><sup><span>0</span></sup><span>&nbsp;TM on degradation mechanism further suggests that proper design of redox‐inactive TM cations provides an important avenue to balanced capacity and stability in this newer class of cathode materials.</span></p>