Perovskites lithium conduction

The structure is named after the mineral perovskite, calcium titanate, that contains Ti " " in the octahedrally coordinated positions and in the large, 12-coordinate site in the centre of the unit cell. Lithium conductivity has been reported in closely related compounds that replace Ca with various combinations of Li" ", La and cation vacancies that maintain an overall divalent charge per formula unit. The... 

The presence of lithium on the large interstitial site in lithium lanthanum titanate perovskites gives rise to exceptional ionic mobility. The lithium conductivity in this system can be as high as 10 S cm at room temperature, i.e. several orders of magnitude higher than many other fast lithium ion conductors. However, it must be noted that this is the value of conductivity within a crystallite and the presence of grain... 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

Barium titanate is one example of a ferroelectric material. Other oxides with the perovskite structure are also ferroelectric (e.g., lead titanate and lithium niobate). One important set of such compounds, used in many transducer applications, is the mixed oxides PZT (PbZri-Ji/Ds). These, like barium titanate, have small ions in Oe cages which are easily displaced. Other ferroelectric solids include hydrogen-bonded solids, such as KH2PO4 and Rochelle salt (NaKC4H406.4H20), salts with anions which possess dipole moments, such as NaNOz, and copolymers of poly vinylidene fluoride. It has even been proposed that ferroelectric mechanisms are involved in some biological processes such as brain memory and voltagedependent ion channels concerned with impulse conduction in nerve and muscle cells. 

In several cationic conductors, for example sodium-ion conductors based upon Na2S04 and perovskite-type lithium-ion conductors, rare-earth elements are important constituents, which directly or indirectly aid the ionic conduction in such solids. Somewhat unexpectedly, rare-earth elements in oxidation state (III), despite their large size and high charge, themselves may be the mobile component in solid electrolytes such as P-alumina, LaNb309 and Sc2(W04)3 oxides. 

Lithium can be inserted into the material up to at least 0.08 Li" " per formula unit. This level of intercalation is insufficient for the number of lithium and lanthanum cations to exceed unity and so the A sites of the perovskite structure still contain some vacancies at this stoichiometry. Whilst this intercalation process is reversible, experiments using this electrolyte in conjunction with a graphite electrode show that an irreversible oxidation process occurs. The reduction of Ti" " narrows the band gap and leads to electronic conductivity of 0.01 S cm at room temperature. This reactivity and electronic conduction would lead to a rapid discharge via short circuit of a stored battery and so makes these materials unsuitable for use as an lithium electrolyte in these applications. 

Kawai H, Kuwano J (1994) Lithium ion conductivity of A-site deficient perovskite... 

Harada Y, Hirakoso Y, Kawai H et al (1999) Order-disorder of the A-slte ions and lithium ion conductivity in the perovskite solid solution Lao 67- cLi3 tTi03 (x = 0.11). Solid State Ionics 121 245-251... 

Inaguma Y, Katsumata T, Itoh M et al (2002) Crystal structure of a lithium ion-conducting perovskite La2/3 xLi3xTi03 (x = 0.05). J Solid State Chem 166 67-72... 

La2/3Ti03 is a perovskite-type oxide in which one third of the A-site cations is deficient. When lithium is partially substituted for La in A sites of this oxide, lithium ions become mobile [46]. The lithium ion conductivity of Lao.51Lio.34TiO2.94 is about 10 S cm at room temperature [47]. This value belongs to the highest among lithium ion conductors that are chemically stable in an atmospheric environment. As La and Li ions are randomly distributed in the A-site position in the perovskite-type structure and, therefore, A-site vacancies are also distributed randomly, it is considered that the lithium ions can easily move through the vacancies. The relationship between the conductivity and content of lithium ions obeys so-called percolation theory [48]. 

Lithium ion conduction has been observed in similar perovskite-type oxides of light rare earths such as Pr, Nd, and Sm the conductivity decreases with... 

Relatively high lithium ion conductivity was observed in perovskite-type SrV03 in which lithium ions were electrochemically inserted [50]. This material is an electronic conductor and has been studied as a candidate for a high-performance cathode material for lithium ion batteries. The lithium ion conductivity in this oxide is estimated to be about 10 S cm at room temperature. 

Ti,Nb)-0, and La-deficient La2-02 layers (Fig. 6.7(a)). Two-dimensional lithium cation conduction has also been reported in the orthorhombic layered perovskite-type compound Lao.62Lio.i6Ti03 [55], in which the Li cation exists and migrates only near the La-deficient La2-02 layer. This work has thus revealed that oxide ion diffusion in an ionic conductor with a double perovskite structure is two dimensional. 

Bohnke O, Bohnke C, Fourquet JL (1996) Mechanism of ionic conduction and electrochemical intercalation of Uthium into the perovskite lanthanum lithium titanate. Solid State Ionics 91(1-2) 21-31,http //dx.doi.org/10.1016/S0167-2738(96)00434-l... 

---