Towards commercialization of fluorinated cation-disordered rock-salt Li-ion cathodes

Abstract

Cation-disordered rock-salt cathodes (DRX) are promising materials that could deliver high capacities (>250 mAh g−1) with Earth abundant elements and materials. However, their electrochemical performances, other than the capacity, should be improved to be competitive cathodes, and many strategies have been introduced to enhance DRXs. Fluorination has been shown to inhibit oxygen loss and increase power density. Nevertheless, fluorinated cation-disordered rock-salts still suffer from rapid material deterioration and low scalability which limit their practical applications. This mini-review highlights the key challenges for the commercialization of fluorinated cation-disordered rock-salts, discusses the underlying reasons behind material failure and proposes future development directions.

Realising higher capacity and stability for disordered rocksalt oxyfluoride cathode materials for Li ion batteries

“…5c and d that the capacity difference between charge and discharge was 52.7 mA h g −1 for LMTO@C which was reduced to 20.2 mA h g −1 for LMTOF@C, showing both higher capacity and reversibility for LMTOF@C than LMTO@C. The results suggest that fluorination suppresses O loss, while the oxidation state of lattice O is 2−, the oxidation state of F is 1−, so F substitution allows TM to have more d electrons by reduction. 55 In general, the charge compensation for the Li + ion extraction preferentially happens through d orbitals of TMs as they are closer to the Fermi level than O. 56 As a result, F reduces O loss without inhibiting significantly redox reactions that contribute to capacities.…”

Synthesis of Li1.20Mn0.432+Nb0.39O2 disordered rock-salt under reducing conditions for Li-ion batteries

“…[5][6][7] To modify the transition-metal oxidation state and to moderate oxygen redox, partial replacement of oxide by fluoride in this material is an important strategy. 1,8,9 This allows access to materials with a lower transition-metal oxidation state, such as Mn 2+ , to adjust electrochemical performance. Solid-state synthesis forms the most thermodynamically stable phases, whilst mechanochemical synthesis generates defects and amorphous species without heat treatment, 5,8 but its application is hindered in large-scale manufacturing purposes because of irreproducibility and impurities from the grinding media.…”

“…1,8,9 This allows access to materials with a lower transition-metal oxidation state, such as Mn 2+ , to adjust electrochemical performance. Solid-state synthesis forms the most thermodynamically stable phases, whilst mechanochemical synthesis generates defects and amorphous species without heat treatment, 5,8 but its application is hindered in large-scale manufacturing purposes because of irreproducibility and impurities from the grinding media. 10 In this paper, we report a different approach to access low oxidation states of transition-metal cations in lithium niobate DRS materials, with the use of a reductive gas atmosphere during synthesis.…”