Crystallographic Habit Tuning of Li2MnSiO4 Nanoplates for High-Capacity Lithium Battery Cathodes

Li₂MnSiO₄ has attracted significant attention as a cathode material for lithium ion batteries because of its high theoretical capacity (330 mA h g^-1 with two Li⁺ ions per formula unit), low cost, and environmentally friendly nature. However, its intrinsically poor Li diffusion, low electronic conductivity, and structural instability preclude its use in practical applications. Herein, elongated hexagonal prism-shaped Li₂MnSiO₄ nanoplates with preferentially exposed {001} and {210} facets have been successfully synthesized via a solvothermal method. Density functional theory calculations and experimental characterization reveal that the formation mechanism involves the decomposition of solid precursors to nanosheets, self-assembly into nanoplates, and Ostwald ripening. Hydroxyl-containing solvents such as ethylene glycol and diethylene glycol play a crucial role as capping agents in tuning the preferential growth. Li₂MnSiO₄@C nanoplates demonstrate a near theoretical discharge capacity of 326.7 mA h g^-1 at 0.05 C (1 C = 160 mA h g^-1), superior rate capability, and good cycling stability. The enhanced electrochemical performance is ascribed to the electrochemically active {001} and {210} exposed facets, which provide short and fast Li⁺ diffusion pathways along the [001] and [100] axes, a conformal carbon nanocoating, and a nanoscaled platelike structure, which offers a large electrode/electrolyte contact interface for Li⁺ extraction/insertion processes.

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.

Depolarization effects of Li2FeSiO4 nanocrystals wrapped in different conductive carbon networks as cathodes for high performance lithium-ion batteries

We report composite electrodes with Li₂FeSiO₄ nanocrystals wrapped in three different types of conductive carbon, Acetylene Black, carbon nanotubes and Ketjen Black, to demonstrate depolarization effects on the electrochemical performance of Li-ion batteries.

Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals

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.

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.

Formation, structure and electrochemical performance of nano-sized Li2FeSiO4/C synthesized with the co-incorporation of citric acid and glucose followed by a two-step annealing

Nano-sized Li₂FeSiO₄/C composites are synthesized using a simple recipeviathe co-incorporation of citric acid and glucose with various molar ratios followed by a two-step annealing.