electric vehicles (HEVs), next-generation lithium-ion batteries (LIBs) that utilize high-energy cathode materials are crucially needed. [1][2][3] Among various types of cathode materials, Li-and Mn-rich layered oxides (LMLOs) are regarded as one of the most promising cathode candidates owing to their high capacity (≥250 mAh g −1 ) and low cost. [4][5][6][7] The high capacity of LMLOs is widely believed to originate predominantly from the reversible cationic and anionic redox activities, [8][9][10] which remarkably overcome the capacity limitations of conventional cathode materials (<200 mAh g −1 ) like olivine LiFePO 4 (space group: Pnma), [11,12] spinel LiMn 2 O 4 (Fd3m), [13,14] and layered Li[Ni,Co,Mn]O 2 (NCM, square brackets represent transition metal ions located on octahedral positions, R3m) [15][16][17][18] because of the sole transition metal (TM) redox activity in these cathodes. Nevertheless, LMLOs always undergo a severe voltage decay upon cycling, [19,20] which seriously hinders the practical application of LMLOs. Over the last two decades, a series of attempts have been made to reveal the underlying structural degradation mechanism and mitigate the voltage decay during extended cycling.Lithium-and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g −1 ) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and oxygen release induced chemo-mechanical breakdown. Herein, a Co-free single-crystalline LMLO, that is, Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 (LLNMO-SC), is prepared via a Li + /Na + ionexchange reaction. In situ synchrotron-based X-ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro-strain are observed in LLNMO-SC compared to its polycrystalline counterpart (LLNMO-PC) during the charge-discharge process. Specifically, the as-synthesized LLNMO-SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li-ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long-term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO-SC decreases by only ≈0.2 V after 100 cycles at 28 mA g −1 between 2.0 and 4.8 V, which is much lower than that of LLNMO-PC (≈0.5 V). Such a single-crystalline strategy offers a promising solution to constructing stable high-energy lithium-ion batteries (LIBs).
The hybrid improper ferroelectricity Ca3Mn2O7 (CMO) has been a subject of remarkable interest due to potential multiferroicity. In this paper we synthesized CMO and Ca2.94Na0.06Mn2O7 (CNMO) ceramics and investigated their structural and magnetic properties. It is found that Na doping effectively weakens the structural distortion as decreasing the orthorhombic distortion and Jahn-Teller distortion. Although both samples undergo an antiferromagnetic transition at temperature around 111 K, the exchange bias and coercive fields increase in CNMO. Such increased exchange bias field could be explained within a model of size-variable nanoscale ferromagnetic clusters embedded in an antiferromagnetic matrix.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.