Alleviating oxygen evolution from Li-excess oxide materials through theory-guided surface protection

Abstract

Li-excess cathodes comprise one of the most promising avenues for increasing the energy density of current Li-ion technology. However, the first-cycle surface oxygen release in these materials causes cation densification and structural reconstruction of the surface region, leading to encumbered ionic transport and increased impedance. In this work, we use the first principles Density Functional Theory to systematically screen for optimal cation dopants to improve oxygen-retention at the surface. The initial dopant set includes all transition metal, post-transition metal, and metalloid elements. Our screening identifies Os, Sb, Ru, Ir, or Ta as high-ranking dopants considering the combined criteria, and rationalization based on the electronic structure of the top candidates are presented. To validate the theoretical screening, a Ta-doped Li1.3Nb0.3Mn0.4O2 cathode was synthesized and shown to present initial improved electrochemical performance as well as significantly reduced oxygen evolution, as compared with the pristine, un-doped, system.

Enhancing surface oxygen retention through theory-guided doping selection in Li1−xNiO2 for next-generation lithium-ion batteries

“…Similar oxygen retention due to electron hybridization was also reported in Osdoped Li 2 MnO 3 structures. 42 To summarize, we rationalize the effectiveness of W, Sb, Ta, and Ti to enhance surface oxygen retention of Li 1Àx NiO 2 , which is attributed to their stronger local bonding interactions with oxygen, as compared to the pristine Ni-O pair. Conversely, Al and Mg were not found to improve oxygen retention, while B was expected to deteriorate the surface oxygen loss in Li 1Àx NiO 2 .…”

“…Interestingly, Ta was recently theoretically predicted and experimentally validated to alleviate oxygen evolution from Li-excess, Mn-rich layered cathode materials. 42 In addition, Ti has been found to improve the oxygen stability at the surface of Ti-doped LiNi 0.8 Mn 0.1 Co 0.1 O 2 and improve its electrochemical performance. 34 Finally, we attempt to elucidate the chemical and structural features that give rise to these dopants' effectiveness (or lack thereof) towards mitigating surface oxygen loss.…”

“…40 However, under-coordinated surface regions are likely to facilitate oxygen kinetics, promote oxygen loss and result in the formation of surface densied phases. 41 Recently, Shin et al 42 applied a high-throughput computational screening to guide the selection of the promising cation dopant to alleviate surface oxygen loss in Li-rich, Mn-rich cathode and identied Os, Sb, Ru, Ir and Ta as the top candidates. 42 Ta was experimentally validated to improve electrochemical performance and oxygen retention.…”

“…41 Recently, Shin et al 42 applied a high-throughput computational screening to guide the selection of the promising cation dopant to alleviate surface oxygen loss in Li-rich, Mn-rich cathode and identied Os, Sb, Ru, Ir and Ta as the top candidates. 42 Ta was experimentally validated to improve electrochemical performance and oxygen retention. Following a similar procedure, in this work we systematically evaluate the effectiveness of doping elements to enhance surface oxygen retention of Li 1Àx NiO 2 , which shares many structural and electrochemical properties with Ni-rich NCA and NCM materials.…”

Cation-disordered rocksalt transition metal oxides and oxyfluorides for high energy lithium-ion cathodes

“…A downside of the high potentials at which Ni redox processes occur is the incomplete oxidation of Ni 2+ As a consequence of the strong overlap between Ni and Li-O-Li electronic bands, more O 2 and CO 2 gas is released upon electrochemical cycling of Ni redox-based DRX materials compared to, e.g., Mn redox based DRXs, 20,66,134 which can lead to transition metal densification at the surface and to a large polarization of the discharge curve. 87 Bulk fluorination 87 and surface modification 144,145 are two effective strategies to mitigate irreversible gas loss and to reduce polarization on discharge.…”