Water-stable lithium ion conducting solid electrolyte of iron and aluminum doped NASICON-type LiTi2(PO4)3

Abstract

High lithium ion conductivity solid electrolytes of Li 1+x Fe x Ti 2-x (PO 4) 3 and Li 1.4 Fe x Al 0.4-x Ti 1.6 (PO 4) 3 (x=0-0.4) with the NASICON-type structure were synthesized using a precursor prepared by the sol-gel method. The highest electrical conductivity was obtained for the Li 1.4 Fe 0.25 Al 0.15 Ti 1.6 (PO 4) 3 (LFATP) composition sintered at 1040 °C for 7 h in air. The total, grain boundary, and bulk conductivities of the pellet were stable after storage for one month and were 1.01×10-3 , 2.17×10-3 and 1.81×10-3 S cm-1 at 25 °C, respectively. The contribution of electron (or hole) conductivity to the total conductivity was negligibly small. LFATP was unstable in water, but stable in saturated LiOH and LiCl aqueous solution.

High lithium ion conductivity solid electrolyte of chromium and aluminum co-doped NASICON-type LiTi2(PO4)3

“…The total conductivity decrease by aging is mainly due to a decrease in the grain boundary conductivity. The bulk conductivity for Li 1.4 Al 0.3 Cr 0.1 Ti 1.6 (PO 4 ) 3 was the same as that for Li 1.4 Al 0.1.5 Fe 0.25 Ti 1.6 (PO 4 ) 3 [17]. The total conductivity of Li 1.4 Al 0.4 Ti 1.6 (PO 3 ) 3 was enhanced 1.8 times by the substitution of Cr 3+ for Al 3+ , although the bulk conductivity was increased by only 10%.…”

“…The relative density was increased by the substitution of Cr with Al up to x = 0.3 and then decreased by further substitution. The highest relative density of 92% was observed for Li 1.4 Al 0.3 Cr 0.1 (PO 4 ) 3 , which is comparable with Li 1.4 Al 0.15 Fe 0.25 Ti 1.6 (PO 4 ) 3 [17] and slightly lower than that for Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 [9]. The compositional dependence of the electrical conductivity indicated a maximum at x = 0.3.…”

“…The precursor of Li 1+ x + y Al x Cr y Ti 2 − x − y (PO 4 ) 3 was prepared by the sol-gel method using citric acid, as reported previously [17]. A stoichiometric amount of Ti(OC 4 H 9 ) 4 (Aldrich) was dissolved in ethylene glycol and added to 0.2 M aqueous solution of citric acid, and then stirred continuously with a magnetic stirrer at 120°C for 12 h to obtain a homogeneous solution.…”

“…A sintered pellet prepared using the glass ceramic powder had a lower conductivity of 1.48 × 10 −4 at 25°C [16]. We have previously reported [17] an enhancement in conductivity by the substitution of Fe 3+ for Al 3+ in Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 , from 5.8 × 10 −4 to 1.1 × 10 −3 S cm −1 at 25°C in Li 1.4 Fe 0.25 Al 0.15 Ti 1.6 (PO 4)3 . The effective ionic radius of Fe 3+ (0.0645 nm) is higher than that of Al 3+ (0.0535 nm) [18]; the average ionic radius of Al 3+ and Fe 3+ in 0.25 Fe and 0.15 Al is 0.0603 nm, which is close to the ionic radius of Ti 4+ (0.0605 nm).…”

Lithium Ion Conducting Solid Electrolytes for Aqueous Lithium-air Batteries

“…Our target conductivity is higher than 10 ¹3 S cm ¹1 at room temperature and the thickness of the electrolyte should be less than 200 µm. In the following chapters, we discuss the electrical conductivity and stability in aqueous solution for the Li 1+x A x Ti 2¹x¹y Ge y (PO 4 ) 3 (A = Al, Fe) system prepared from a sol-gel precursor, 15,16 and thin film preparation of Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 by tape-casting method is also introduced. The effect of Ge substitution for Ti on the electrical conductivity was studied for the entire Li 1.4 Al 0.4 Ti 1.6¹x Ge x (PO 4 ) 3 system (x = 0-1.6).…”