Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals

Abstract

Nanostructured lithium metal orthosilicate materials hold a lot of promise as next generation cathodes but their full potential realization is hampered by complex crystal and electrochemical behavior. In this work Li2FeSiO4 crystals are synthesized using organic-assisted precipitation method. By varying the annealing temperature different structures are obtained, namely the monoclinic phase at 400°C, the orthorhombic phase at 900°C, and a mixed phase at 700°C. The three Li2FeSiO4 crystal phases exhibit totally different charge/discharge profiles upon delithiation/lithiation. Thus the 400°C monoclinic nanocrystals exhibit initially one Li extraction via typical solid solution reaction, while the 900°C orthorhombic crystals are characterized by unacceptably high cell polarization. In the meantime the mixed phase Li2FeSiO4 crystals reveal a mixed cycling profile. We have found that the monoclinic nanocrystals undergo phase transition to orthorhombic structure resulting in significant progressive deterioration of the material's Li storage capability. By contrast, we discovered when the monoclinic nanocrystals are cycled initially at higher rate (C/20) and subsequently subjected to low rate (C/50) cycling the material's intercalation performance is stabilized. The discovered rate-dependent electrochemically-induced phase transition and stabilization of lithium metal silicate structure provides a novel and potentially rewarding avenue towards the development of high capacity Li-ion cathodes.

Insight into cations substitution on structural and electrochemical properties of nanostructured Li2FeSiO4/C cathodes

“…Figure B shows the refined crystal structures, in which Ti incorporation effectively decreases the Li–Li hoping distance between the adjacent LiO 4 tetrahedron that favors facile Li‐ion movement in the sample. Many of the previous studies report that the monoclinic structure of LFSO/C has been changed to a stable orthorhombic phase with better electrochemical properties after a few charge‐discharge cycles . This work reports a direct preparation of the stable orthorhombic structure ( Pmn 2 1 ) for bare and doped LFSO/C samples to obtain the best electrochemical performance with better cycling.…”

“…The absence of the peak located at 2 θ = 31.6°, corresponding to the (112) plan of the monoclinic phase and the low‐intensity ratio of the peaks at 2 θ = 33.22/33.70° corresponding to (210)/(020) planes in the XRD pattern demonstrated that the prepared samples assume orthorhombic structure with the Pmn 2 1 space group. It is very difficult to differentiate the orthorhombic phase with the Pmn 2 1 space group from the monoclinic phase with P 2 1 / n (coexisting with minor differences).…”

“…Many of the previous studies report that the monoclinic structure of LFSO/C has been changed to a stable orthorhombic phase with better electrochemical properties after a few charge-discharge cycles. 17,19 This work reports a direct preparation of the stable orthorhombic structure (Pmn2 1 ) for bare and doped LFSO/C samples to obtain the best electrochemical performance with better cycling. The Ti 4+ ion-doped LFSO/C sample shows better crystallinity in comparison with all other samples, which reflects in the electrical performance of the sample.…”

Eggshell-Membrane-Derived Carbon Coated on Li2FeSiO4 Cathode Material for Li-Ion Batteries

“…Therefore, quality has been recognized by the Raman spectrum and nitrogen adsorption and desorption experiment for the as-prepared LFS@ESM, as shown in Figure 2c. From the Raman spectrum, two peaks are pointed out one is for order graphite (G) peak at 1586 cm −1 and another one is for disorder (D) peak at 1340 cm −1 , which were aroused due to E2g zone-center and A1g zone-edge mode vibration [40]. The degree of graphitization of LFS@ESM depends on the ratio of integrated intensity of D and G-band (ID/IG) is equal to 0.94, the value less than one indicates that higher graphitized carbon (better quality).…”

Investigation of carbon phase evolutions in titanium nitride-carbon nanocomposites prepared in supercritical benzene with respect to their lithium storage capacity

“…Therefore, there are great interests in upgrading anode performance by doping TiN into anode matrix. Anchoring of TiN nanoparticles to graphene layers not only promotes the electrical conductivity along caxis, but also suppresses the agglomeration of graphene sheets, resulting in the formation of a exible porous texture [7][8][9][10].…”