Home – Home – Jornals – Chemistry for Sustainable Development 2024 number 5

In recent years, new classes of lithium-excess cathode and anode materials with disordered rock-salt structure (DRX), in which any channels for Li⁺ ion diffusion are absent, have attracted increased interest. In DRX cathode materials of Li _y (Me₁Me₂)_{2- y} O₂ composition, Li⁺ and transition metal ions (Me) are equally likely to occupy the same octahedral positions in the lattice, and the diffusion of Li⁺ ions occurs by hopping from one octahedron to another through an intermediate tetrahedron (o-t-o diffusion). The presence of fluorine in oxyfluorides DRX-F (Li_{1+ x} (MeMn³⁺)_{1- x} O_{2- y} F _y , where Me = Ti⁴⁺, Nb⁵⁺) affects the local ordering of Mn³⁺ ions, the stability of the redox couple O^2-/O^- and its contribution into specific capacity. On the other hand, high-entropy oxides (HEO), which are single-phase oxide systems containing five and more cations, were synthesised by mixing five oxides CoO, CuO, MgO, NiO and ZnO in equimolar ratios, followed by thermal treatment at 1000 °C. Stabilisation of single-phase solid solutions Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2O and Li _x (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_{2- x} O_{2- x} F _x (0 ≤ x ≤ 1) with a rock-salt crystal structure turned out to be possible due to the large contribution of the entropy of mixing to the Gibbs free energy. Another group of anode materials are high-entropy oxides with a spinel structure (HES), for example (Cr_0.2Fe_0.2Mn_0.2Co_0.2Ni_0.2)₃O₄ obtained by solid-state synthesis at T = 500-1000 °C in air. After ball grinding, the particle size is reduced to 20 nm. The initial specific capacity during cycling in the 0.01-3.0 V range is 1333.6 mA×h/g and decreases to 329.9 mA×h/g after 20 cycles. A comparative investigation of synthesis conditions, crystal structure, morphology and electrochemical characteristics has been carried out for the four classes of high-entropy oxides: 1) Li _y (MeMn³⁺)_{2- y} O₂, где Me = Ti⁴⁺, Nb⁵⁺; 2) Li_{1+ x} (MeMn³⁺)_{1- z} O_{2- y} F _y , где Me = Ti⁴⁺, Nb⁵⁺; 3) Li _x (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)_{2- x} O_{1- x} F _x ; 4) (Cr,Fe,Mn,Co,Ni)₃O₄.