Yan Sun,Wenning Yan,Li An,Bingbin Wu,Kaifu Zhong,Ruizhi Yang
A super solid electrolyte of Ba-substituted Li 10 GeP 2 S 12 is designed and fabricated to achieve high electrochemical stability. Among the Ba-substituted Li 10 GeP 2 S 12 solid electrolytes, the composition of Li 9.4 Ba 0.3 GeP 2 S 12 exhibits the highest ionic conductivity of 7.04 × 10 − 4 S cm − 1 with an activation energy of 28.27 kJ mol − 1 at 25 °C. The electrochemical window of Li 9.4 Ba 0.3 GeP 2 S 12 is between 0 and 6 V (vs. Li), which is higher than the typical 5 V window of Li 10 GeP 2 S 12 . As compared with Li 10 GeP 2 S 12 , Li 9.4 Ba 0.3 GeP 2 S 12 demonstrates a significantly reduced polarization and a better cycle stability though its ionic conductivity is slightly lower than that of the former. The electrochemical stability of Ba-substituted Li 10 GeP 2 S 12 can be attributed to the structural stability resulting from the stable interaction between Ba 2 + and S 2 − in the structure.
The development of a solid electrolyte with superb Li+ conductivity is the key to enabling safe and high-performance all-solid lithium ion batteries which are free of the safety issues associated with flammable organic liquid electrolyte. Systematic experimental work has been carried out as a follow up to our recent theoretical prediction that superb ionic conductivity could be achieved through the tuning of the lattice chemistry in the cubic argyrodite Li6PS5Cl. Remarkable enhancement of the ionic conductivity has been achieved through the combined effect of excess Li and substitution of S with Te. This leads to an alloy, Li6.25PTe0.125S5.125Cl0.75, having the superb Li+ conductivity of 4.5 mS cm−1 at 25 °C, together with a low activation energy of 0.16 eV to safeguard adequate ionic conductivity at low temperature. This current work conclusively affirms the theoretical outcome that the superb ionic conductivity is attributed to weakened bonding, an enlarged unit cell, and a softened lattice, making it easier for the long-distance diffusion of Li+. In addition, this new class of solid electrolyte based on cubic chalcogenide is electrochemically compatible with the Li anode over a large potential window up to 7 V, which is highly desirable for high performance solid lithium ion batteries.
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