ИСТИНА

The electrochemical properties of lithium-ion batteries are primordially determined by cathode materials. Recently, Li(Ni,Mn)O2 materials have been intensively studied due to their high discharge potential (3.7 V), high discharge capacity (up to 200 mAh/g) and ecological safety [1,2]. In the last decade, the freeze-drying technique has been successfully used for the synthesis of Li(Ni,Mn)O2 materials [3]. It is based on the combination of low-temperature and high-temperature stages and allows multicomponent materials with high chemical homogeneity and controllable particle size to be obtained. In the present work, Li1.5Ni0.5Mn0.5O2+δ was synthesized by isothermal heat treatment (at 900°С) using the powders obtained after freeze-drying of co-precipitated transition metal hydroxides (P = 0.5 mbar, T = -30  +40°C). The as-obtained Li1.5Ni0.5Mn0.5O2+δ materials possess a high crystallinity and a narrow particle size distribution. An additional annealing at 500˚C allows a crystallite size to be decreased from 800 to 200 nm, but at the same time, Ni2+ content in Li+ positions enhances from 5.5 to 8 % according to the Rietveld refinement of XRD patterns. Apparently, the formation of intermediate spinel and ilmenite phases at 500°C makes difficult a subsequent crystallographic ordering of Li1.5Ni0.5Mn0.5O2+δ, and inhibits a particle growth of cathode materials. In addition, the electrochemical impedance measurements demonstrate the evidence of the decrease in the charge transfer resistance and the passivation film resistance. The specific discharge capacity of these materials exceeds 160 mAh/g. The calculated values of diffusion coefficient are 6.8∙10- 17 и 1∙10-17 cm2/s at a discharge potential of 3.67 V and a charge potential of 3.73 V, respectively. The reported study was supported by RFBR, research project No. 14-08-31644 mol_a and 12-08-01241а. [1] Fergus J.W. Recent developments in cathode materials for lithium ion batteries. // J. Power Sources. 2010. V. 195. P. 939-954. [2] Deng H., Belharouak Il., Sum Y.K., Amine Kh. LixNi0.25Mn0.75Oy (0.5 ≤ x ≤ 2.2 ≤ y ≤ 2.75) compounds for high-energy lithium-ion batteries. // J. Materials Chem. 2009. V. 19. P. 4510–4516.