Lepidocrocite-type Layered Titanate Structures: New Lithium and Sodium Ion Intercalation Anode Materials

Abstract

The electrochemical characteristics of lepidocrocite-type titanates derived from K 0.8 Ti 1.73 Li 0.27 O 4 are presented for the first time. By exchanging sodium ions for potassium, the practical specific capacity of the titanate in both sodium and lithium half cells is considerably enhanced. Although the gross structural features of the titanate framework are maintained during the ion exchange process, the symmetry changes because sodium occupies different sites from potassium. The smaller size of the sodium ion compared to potassium and the change in site symmetry allow more alkali metal cations to be inserted reversibly into the structure during discharge in sodium and lithium cells than in the parent compound. Insertion of lithium cations takes place at an average of about 0.8V vs. Li + /Li while sodium intercalation occurs at 0.5V vs. Na + /Na, with sloping voltage profiles exhibited for both cell configurations, implying singlephase processes. Ex situ synchrotron X-ray diffraction measurements show that a lithiated 2 lepidocrocite is formed during discharge in lithium cells, which undergoes further lithium insertion with almost no volume change. In sodium cells, insertion of sodium initially causes an overall expansion of about 12% in the b lattice parameter but reversible uptake of solvent minimizes changes upon further cycling. In the case of the sodium cells, both the practical capacity and the cyclability are improved when a more compliant binder (polyacrylic acid) that can accommodate volume changes associated with insertion processes is used in place of the more common polyvinylidene fluoride. The ability to tune the electrochemical properties of lepidocrocite titanate structures by varying compositions and utilizing ion exchange processes make them especially versatile anode materials for both lithium and sodium ion battery configurations.

Rechargeable potassium-ion batteries with honeycomb-layered tellurates as high voltage cathodes and fast potassium-ion conductors

“…K-based compounds have also found their niche application in energy storage as host frameworks for reversible reinsertion of Li and Na electrodes. Such compounds include lepidocrocite K 0.8 Li 0.27 Ti 1.73 O 4 14 , K 2 Ti 6 O 13 15 , KFeF 3 16 , K A SO 4 F ( A  = Fe, Co) 17 , KVPO 4 F 18 , fedotovite K 2 Cu 3 O(SO 4 ) 3 19 , K 2 [(VO) 2 (HPO 4 ) 2 (C 2 O 4 )] 20 , KV 3 O 8 21 , K 1.33 Fe 11 O 17 22 , K 2 D 2 (SO 4 ) 3 ( D  = Cu, Fe) 19 , K x V 2 O 5 21 , Prussian analogues 23 , amongst others. Indeed, a great variety of K-based minerals and compounds have been documented, and most have yet to have their electrochemical properties studied.…”

N-doped Na2Ti6O13@TiO2 core–shell nanobelts with exposed {1 0 1} anatase facets and enhanced visible light photocatalytic performance

“…Due to their stoichiometrydependent structure and physicochemical properties, alkali metal titanates have been intensively explored in such applications as photocatalyst [9][10][11], lithium and sodium ion battery [12,13], gas and humidity sensing, and antibacterial agent [14,15]. As photocatalysts, these structures are suitable both for the accommodation of catalytic active phase (e.g., metal oxides) to raise the separation efficiency of photo-excited charge carriers and for the transfer of these carriers to adsorbed reactants at the surface [16].…”

Electrochemical Properties of Electrodes Derived from NaTi3O6OH·2H2O in Sodium and Lithium Cells

“…intercalation of sodium displaced interlayer water, as has also been observed in lepidocrocite-structured titanate anodes during cycling in sodium cells. 8 Further evidence for this is the greatly reduced intensity of the (-112) reflection observed in the recharged electrode; in this, the XRD pattern more closely resembles that of anh-NNT rather than pristine NNT itself, except that the interlayer spacing is somewhat greater.…”