ИСТИНА |
Войти в систему Регистрация |
|
ИСТИНА ИНХС РАН |
||
Complex phosphates LiFe1-yMnyPO4 became an object of a great interest as cathode materials for Li-ion batteries. Partial substitution of Fe by Mn in LiFePO4 allows to increase specific energy density of the cathode material because of higher electrochemical potential Mn2+/Mn3+, keeping proper stability and low degradation rate during galvanostatic cycling. Two-phase mechanism of Li+ deintercalation-intercalation is typical for LiFePO4, but for Mn-substituted olivines extraction and insertion of Li+ occurs via single phase in broad ranges of composition [1], [2]. Phase transformations in LixFe1-yMnyPO4 were studied in a number of works with in situ and ex situ diffraction methods, but X-ray diffraction data provides only one-sided notion about the processes which occur during Li+ (de)intercalation in these compounds. The aim of the present work is detailed study of phase transformations in LixFe1-yMnyPO4 (0≤x≤1, 0≤y≤0.5) by means of in situ X-ray powder diffraction (XRPD) and potentiostatic intermittent titration technique (PITT). Single-phase samples of LiFe1-yMnyPO4 (0≤y≤0.5) were obtained by hydrothermal method. Phase transformations during Li+ extraction/insertion in LixFe1-yMnyPO4 (0≤x≤1, 0≤y≤0.5) were studied using in situ XRD and – independently – by corresponding treatment of PITT data, described in [3]. Using this method, we calculated contribution of single-phase mechanism (parameter f, where f = 0 means complete two-phase reaction, and f = 1 regards to ideal solid solution) into total process of Li+ (de)intercalation. Results obtained by these two methods are in a good agreement with each other (Fig. 1). Three different types of phase transformations may be observed for the compositions LiFePO4, LiFe0.9Mn0.1PO4 and LiFe0.5Mn0.5PO4; also different behavior may be seen for LiFe0.5Mn0.5PO4 during charge and discharge. Explanation for the observed phenomena is proposed basing on crystal chemistry parameters of lithiated and delithiated phases. The work was supported with the RFBR grants (14-03-31473, 14-29-04064).