Promoting Reversibility of Multielectron Redox in Alkali-Rich Sulfide Cathodes through Cryomilling

Abstract

Conventional cathodes for Li-ion batteries (LIBs) are reaching their theoretical capacity limits. One way to meet the growing demands for high-capacity LIBs is by developing so-called Li-rich cathode materials that greatly benefit from additional capacities from anionic moieties in the structure. Li-rich materials are intrinsically subject to higher degrees of (de)­intercalation, leaving the particles more prone to fractures and thus rapid capacity fade. Alkali-rich LiNaFeS2 reversibly cycles with capacities exceeding 300 mAh g–1, but its capacity fades faster than an isostructural material Li2FeS2. Using synchrotron-based transmission X-ray microscopy (TXM), we demonstrate that the capacity fade of LiNaFeS2 stems from particle fractures in the first charge cycle. We improve the cycling performance of LiNaFeS2 by means of cryomilling, which enhances capacity retention at cycle 50 by 76%. Through crystallographic and morphological characterization techniques, we confirm that cryomilling not only decreases particle and crystallite size while increasing microstrain but also prevents particles from fracturing. Cryomilling is a powerful tool to engineer nanoscale battery materials, and TXM allows the direct observation of morphological changes of the particles, which can be leveraged to develop next-generation cathode materials for LIBs.

Mechanochemical synthesis of Li-rich (Li2Fe)SO cathode for Li-ion batteries

“…Noteworthy, optimizing the internal lattice strain, is feasible for (Li 2 Fe)SO by post-heat treatment strategy, was recently reported to have strong influence on the electrochemical performance for other cathode materials. 30 This observation also confirms the possibility of using post-milling heat treatment to control the internal structure and crystallinity of (Li 2 Fe)SO. Changing the material's crystallinity was reported to have a strong influence on the transport properties of Li + inside the material, with no general rule determining which has the higher ionic conductivity.…”

Effect of Metal d Band Position on Anion Redox in Alkali-Rich Sulfides

“…The discharge and charge profiles for both materials are compared in Figure b. The capacity of LiNaFeS 2 fades somewhat quickly, largely due to particle fracturing associated with the removal of large Na + . Though the capacity fades, the cycle 1 and cycle 2 charge curves are similar in shape, suggesting that the mechanism is largely unchanged.…”

Synthesis, electronic structure, and redox chemistry of Li2MnP2S6, a candidate high-voltage cathode material

“…Transition metal sulfides are an attractive class of materials for emerging battery cathodes, but a foremost challenge is increasing the energy density by identifying higher voltage materials. 12,[39][40][41] The equilibrium voltages of reported sulfide cathodes are mostly around ~2-2.5 V, and encompass a variety of physical and electronic mechanisms associated with cation and anion redox. 10 In this (and concurrently emerging 8 ) work, a class of thiophosphates (Li2FeP2S6, https://doi.org/10.26434/chemrxiv-2024-sd2kb ORCID: https://orcid.org/0000-0002-1670-9933 Content not peer-reviewed by ChemRxiv.…”