Effects of Cr doping on the electrochemical properties of Li2FeSiO4 cathode material for lithium-ion batteries

Formation of oxygen vacancies in Li2FeSiO4: first-principles calculations

The formation of oxygen vacancies could affect various properties of oxides. Herein we have investigated the formation energies of an oxygen vacancy (V_O) with the relevant charge states in bulk Pnma-Li₂FeSiO₄ using first-principles calculations. The formation energies of the V_O are essentially dependent on the atomic chemical potentials that represent the experimental conditions. The calculated formation energies of an oxygen vacancy in different charge states indicate that it would be energetically favorable to fully ionize the oxygen vacancy in Li₂FeSiO₄. The presence of V_O is accompanied by a distinct redistribution of the electronic charge densities only around the Fe and Si ions next to the O-vacancy site, which shows a very local influence on the host material arising from V_O. This local characteristic is also confirmed by the calculated partial densities of states (PDOS). We also studied the influence of substitutional (Mn_Fe and Co_Fe) and cation vacancy defects (i.e., V_Fe and V_Li) in the vicinity of an O-vacancy on the formation of an O-vacancy, respectively. We find that the calculated interaction energies between these defects and the oxygen vacancy are all negative, which implies that the formation of an oxygen vacancy becomes easier when the above defects are introduced. Compared to the substitutional defects, the interaction energies between the vacancy defects and the oxygen vacancy are significantly larger. Among them, the interaction energy between V_Fe and V_O is the largest.

The Core-Shell Heterostructure CNT@Li2FeSiO4@C as a Highly Stable Cathode Material for Lithium-Ion Batteries

The reasonable design of nanostructure is the key to solving the inherent defects and realizing a high performance of Li₂FeSiO₄ cathode materials. In this work, a novel heterostructure CNT@Li₂FeSiO₄@C has been designed and synthesized and used as a cathode material for lithium-ion battery. It is revealed that the product has a uniform core-shell structure, and the thickness of the Li₂FeSiO₄ layer and the outer carbon layer is about 19 nm and 2 nm, respectively. The rational design effectively accelerates the diffusion of lithium ions, improves the electric conductivity, and relieves the volume change during the charging/discharging process. With the advantages of its specific structure, CNT@Li₂FeSiO₄@C has successfully overcome the inherent shortcomings of Li₂FeSiO₄ and shown good reversible capacity and cycle properties.

New materials for Li-ion batteries: synthesis and spectroscopic characterization of Li2(FeMnCo)SiO4 cathode materials

Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanion compounds with high theoretical capacity such as the lithium metal orthosilicates, Li2MSiO4 is of great importance. In particular, mixed silicates represent an advancement with practical applications. Here we present results on a rapid solid state synthesis of mixed Li2(FeMnCo)SiO4 samples in a wide compositional range. The solid solution in the P21/n space group was found to be stable for high iron concentration or for a cobalt content up to about 0.3 atom per formula unit. Other compositions led to a mixture of polymorphs, namely Pmn21 and Pbn21. All the samples contained a variable amount of Fe(3+) ions that was quantified by Mössbauer spectroscopy and confirmed by the TN values of the paramagnetic to antiferromagnetic transition. Preliminary characterization by cyclic voltammetry revealed the effect of Fe(3+) on the electrochemical response. Further work is required to determine the impact of these electrode materials on lithium batteries.

Advances in high-capacity Li2MSiO4 (M = Mn, Fe, Co, Ni, …) cathode materials for lithium-ion batteries

This review highlights the high-capacity Li₂MSiO₄ (M = Mn, Fe, Co, Ni, …) cathode materials for lithium-ion batteries.

The first investigation of the synthetic mechanism and lithium intercalation chemistry of Li9Fe3(P2O7)3(PO4)2/C as cathode material for lithium ion batteries

Li₉Fe₃(P₂O₇)₃(PO₄)₂ with mixed-polyanion groups is introduced as a novel cathode material for Li-ion batteries.

How to synthesize pure Li2−xFeSi1−xPxO4/C (x = 0.03–0.15) easily from low-cost Fe3+ as cathode materials for Li-ion batteries

Self-catalysis helps to synthesize pure Li_2−xFeSi_1−xP_xO₄/C (0.03–0.15) easily by using the low cost compounds Fe(NO₃)₃·9H₂O and NH₄H₂PO₄.

Systematic investigation on Cadmium-incorporation in Li₂FeSiO₄/C cathode material for lithium-ion batteries

Cadmium-incorporated Li₂FeSiO₄/C composites have been successfully synthesized by a solid-state reaction assisted with refluxing. The effect and mechanism of Cd-modification on the electrochemical performance of Li₂FeSiO₄/C were investigated in detail by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectra, transmission electron microscopy, positron annihilation lifetime spectroscopy and Doppler broadening spectrum, and electrochemical measurements. The results show that Cd not only exists in an amorphous state of CdO on the surface of LFS particles, but also enters into the crystal lattice of LFS. Positron annihilation lifetime spectroscopy and Doppler broadening spectrum analyses verify that Cd-incorporation increases the defect concentration and the electronic conductivity of LFS, thus improve the Li⁺-ion diffusion process. Furthermore, our electrochemical measurements verify that an appropriate amount of Cd-incorporation can achieve a satisfied electrochemical performance for LFS/C cathode material.

Polymorphism and magnetic properties of Li2MSiO4 (M = Fe, Mn) cathode materials

Transition metal-based lithium orthosilicates (Li₂MSiO₄, M = Fe, Ni, Co, Mn) are gaining a wide interest as cathode materials for lithium-ion batteries. These materials present a very complex polymorphism that could affect their physical properties. In this work, we synthesized the Li₂FeSiO₄ and Li₂MnSiO₄ compounds by a sol-gel method at different temperatures. The samples were investigated by XRPD, TEM, ⁷Li MAS NMR, and magnetization measurements, in order to characterize the relationships between crystal structure and magnetic properties. High-quality ⁷Li MAS NMR spectra were used to determine the silicate structure, which can otherwise be hard to study due to possible mixtures of different polymorphs. The magnetization study revealed that the Néel temperature does not depend on the polymorph structure for both iron and manganese lithium orthosilicates.

Progression of the silicate cathode materials used in lithium ion batteries

Poly anionic silicate materials, which demonstrate a high theoretical capacity, high security, environmental friendliness and low-cost, are considered one of the most promising candidates for use as cathode materials in the next generation of lithium-ion batteries. This paper summarizes the structure and performance characteristics of these materials. The effects of different synthesis methods and calcination temperature on the properties of these materials are reviewed. Materials that demonstrate low conductivity, poor stability, cationic disorder or other drawbacks, and the use of various modification techniques, such as carbon-coating or compositing, elemental doping and combination with mesoporous materials, are evaluated as well. In addition, further research topics and the possibility of using these kinds of cathode materials in lithium-ion batteries are discussed.