катодные материалы

Synthesis of electrode material based on Li₂MnSiO₄/С using widely used, environmentally safe and inexpensive Li, Si and Mn-containing precursors was considered. Mechanochemical activation was used for improving the flow of thesolid-state synthetic process and providing the necessary reactivity to obtain the target product with a high content of the main lithium-accumulating compound.Structural and morphological features of the composite were investigated by X-ray diffraction, laser diffraction granulometry.

Various strategies for the synthesis of promising electrode materials for lithium-ion battery (LIB) based on iron(II)-lithium orthosilicate (Li₂FeSiO₄) using widely distributed, environmentally friendly and inexpensive starting materials are considered. The materials obtained are multicomponent electroactive composites that include, in addition to the main lithium accumulating component, also auxiliary structure-forming and electrically conductive components based on the products of the pyrolytic decomposition of organic compounds.

Behavior of PH/P1 lithiated iron phosphate (Phostech Lithium Inc, Canada) used as positive electrode material for Li-ion battery with LiPF₆-based electrolyte was investigated. Specific capacity of the material reached 130 mA·h/g at a rate of 0.5С and 20°C, 105 mA·h/g (1С) and 95 mA·h/g (2.1C). Cell capacity increased by 20% during first 50 cycles and minor capacity fade at a rate of 0.04% per cycle is observed after 300 cycle when cycled at 2C rate versus carbon negative electrode (CMS, PRC).

The complex oxides Li_{1 + x}Ni_{1 / 3}Co_{1 / 3}Mn_{1 / 3}O₂ were obtained by solid state method. The conclusion about influence of lithium concentration on Ni²⁺ and Ni³⁺ ions ratio in Li_{1 + x}Ni_{1 / 3}Co_{1 / 3}Mn_{1 / 3}O₂ is made. Monotonous decrease of g-factor value identified by EPR method testifies the intensification of local exchange interactions with temperature descent. That is in agreement with magnetic susceptibility data indicating the antiferromagnetic ordering at T=4 K.

The review summarizes literature data on the thermal decomposition of ferrous oxalate with the formation of Fe, FeO, Fe₂O₃, Fe₃O₄, Fe₃C, and other products. Historical evolution of views on the ways and mechanisms of oxalate thermolysis is traced. The current state of the art is analyzed from the perspective of FeC₂O₄·2Н₂O0 compound for the synthesis of lithium iron phosphate LiFePO₄, which is a promising cathode material for lithium-ion batteries.

The methods for the synthesis of lithium iron phosphate LiFePO₄ with olivine structure have been developed. New materials based on lithium iron phosphate, including doped with metals, the «LiFePO₄ + carbon» composites obtained by pyrolysis of organic compounds have been synthesized. Crystallographic characterization of the synthesized materials was carried out; their electrochemical characteristics of the extraction and intercalation of lithium have been identified. A correlation between the crystallographic and electrochemical characteristics of the materials was found. It was confirmed that an effective way to improve the electrical conductivity of LiFePO₄ is to create a carbon shell of the products of pyrolysis of organic compounds on the material's particles surface. A correlation of electrical conductivity and temperature of synthesis of the material was determined. The sequence of chemical interaction between precursors for the synthesis of LiFePO₄ is defined; the mechanism of solid-phase interaction is described.

A series of solid phases (mixed lithium-iron-manganese phosphates) of the common formula LiMn_yFe_1-yPO₄ (0 ≤ y ≤ 1) with a carbon coating on the particle surface was synthesized by mechanochemical activation with carbothermal reduction. The synthesized mixed phosphates were examined as promising cathode materials for lithium-ion batteries. The positive effect of replacement of a rather small fraction of iron by manganese is shown, which improves the electrochemical performance at the rates C/10–10C. The highest discharging capacity (above 160 mA·h/g at the C/10 rate, about 100 mA·h/g at the 10C rate) and cycling stability (the capacity decrease rate less than 0.05 mA·h/g per cycle at the 10 C rate) were established for the weakly doped cathode material LiMn_0.05Fe_0.95PO₄.

The review generalizes the literary data on physical-chemical and electrochemical properties of lithium-iron phosphate connected with perspectives of LiFePO₄ use as a cathode material for lithium-ion batteries and published up to 2009 inclusive.

The methods of increasing performances of cathode materials based on lithium-manganese spinel are discussed in this review. Next questions are examined: the reasons of LiMn₂O₄ degradation and the basic variants of problem solving including the doping of spinel matrix by metal cations; the substitution of oxygen in system Li–Mn–O by another anions; the creation of protective shell on the surface of particles; the preparation of different composites. The possibility of working substitution's spinel matrixes in 5 V domain are demonstrated. The synthetic methods of stable and power-consuming lithium-manganese spinel are examined.