Flame-made Lithium Transition Metal Orthosilicates

Abstract

Vanadium substitution is an interesting approach to manipulate the properties of the poor electronic and ionic conducting lithium transition metal orthosilicates. Especially, if incorporated on the Si-site it could alter the highly insulating character of the SiO 4 framework. This study addresses the feasibility and limitations of V substitution in Li 2 MnSiO 4 . Nominal compositions of Li 2 Mn 1-x V x SiO 4 (0 ≤ x ≤ 0.2) and Li 2 MnSi 1-x V x O 4 (0 ≤ x ≤ 0.3) were synthesized by a sol-gel method, and the structural evolution was analyzed by X-ray diffraction and transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS). While the solid solubility of V on tetrahedral Mn-sites was shown to be limited, substantial amounts of V entered the structure when intended to substitute Si. Elemental mapping by TEM showed that V was highly inhomogeneously distributed and high energy resolution EELS demonstrated that the majority of V was present in a tetravalent state. The nominal compositions Li 2 MnSi 1-x V x O 4 (0 ≤ x ≤ 0.3) showed superior electrochemical performance, with reduced charge transfer resistance and an increased Li-ion diffusion coefficient. Furthermore, cyclic voltammetry revealed increased redox activity which can be attributed to V within the concentration series. The best performance was achieved with 25 mol % V substitution. V substitution beyond 25 mol % caused deterioration of the properties.

Tuning anisotropic ion transport in mesocrystalline lithium orthosilicate nanostructures with preferentially exposed facets

“…Theoretically, half of the capacity (~165 mAhg −1 ) should be observed at the first charge plateau of~3.1V, corresponding to the oxidation of Fe 2+ to Fe 3+ , and another half capacity should be observed for the second charge plateau of~4.6V (Fe 3+ to Fe 4+ ) 13,47,[49][50][51][52][53] . However, the initial charge capacity at the 3.1 V plateau is less than 165 mA hg -1 (~70 mA hg −1 in this work), which has also been observed in previous work 17,18,20,21,24,27,47,50,51,[53][54][55][56][57][58][59][60][61] . This commonly observed non-ideal voltage behavior has been thoroughly investigated with theoretical calculations and experimental characterization 13,50,52,62 .…”

A Critical Review on Electrochemical Properties and Significance of Orthosilicate‐Based Cathode Materials for Rechargeable Li/Na/Mg Batteries and Hybrid Supercapacitors

“…Transitional metal oxide cathodes offer excellent electrochemical efficiency over the various cathode materials due to their numerous valence states, which promote further electron storage sites. The electronegativity is an enormous force that influences the electrochemical potential of a cathode, and it describes the propensity of an atom or a functional group to attract electrons to itself [19] . The Gibbs free energy and the electrochemical potential of a cathode material depend on ionic radius, valence state, and the local cation interaction in the compounds [20] .…”

“…Similarly, during the first Li extraction, the ferrous to ferric transition reveals that the lattice oxygen participates in the charge transfer process, causing structural instability and the creation of Li−Fe mixing [53] . The Li 2 FeSiO 4 cell was disassembled after 300 cycles, and the isolated Li 2 FeSiO 4 electrode was cleaned with DEC solvents [19] . According to the post‐structural analysis, the amorphization and structural degradation of Li 2 FeSiO 4 produced substantial capacity fading.…”

“…The electronegativity is an enormous force that influences the electrochemical potential of a cathode, and it describes the propensity of an atom or a functional group to attract electrons to itself. [19] The Gibbs free energy and the electrochemical potential of a cathode material depend on ionic radius, valence state, and the local cation interaction in the compounds. [20] The cathode materials with polyanionic groups such as phosphates, sulphates and silicates have higher electrochemical properties compared to metal oxides.…”

“…Based on the immense criteria for the selection of cost-effective high-capacity cathode materials, polyanion cathode materials have been considered as potential candidates for high-energy rechargeable batteries. [19] Numerous investigations have been conducted in recent years with Li 2 /Na 2 XSiO 4 (X = Fe, Mn, Co, Ni) and MgXSiO 4 (X = Fe, Mn, Co, Ni) based cathode materials for lithium/sodium/magnesium rechargeable batteries. The M 2 XSiO 4 (M = Li and Na) affords the extraction of two lithium/ sodium ions per formula unit with a high theoretical capacity of 333 mAh g À 1 .…”