Synthesis and Electrochemical Properties of &ITI&IT(4)over-bar-Type Li1+2&ITx&ITZn1-&ITx&ITPS4 Solid Electrolyte

I(4)over-bar-type LiZnPS4 solid electrolyte was synthesized starting from Li2S, P2S5, and ZnS, and its room temperature ionic conductivity, sigma(25 degrees C), was similar to 10(-8) S/cm. To improve sigma(25 degrees C), compositions of Li1+2xZn1-xPS4 (x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.8, 0.9) were synthesized from mixtures of LiZnPS4 and amorphous Li3PS4 (a-LPS). The samples with x <= 0.8 were confirmed by means of XRD and Raman spectroscopy to have the I(4)over-bar structure. The maximum sigma(25 degrees C) was 5.7 x 10(-4) S/cm at x = 0.625. NMR measurement revealed that Li1+2xZn1-xPS4 (x <= 0.625) is almost a single phase material and not a simple mixture of LiZnPS4 and a-LPS, confirming that its crystal structure is responsible for the improved ionic conductivity. Li2.25Zn0.325PS4 (x = 0.625) was reactive to graphite and indium anodes but stable against a Li4Ti5O12 anode and a 4 V class cathode. We fabricated an all-solid-state battery in the form of graphitela-LPS vertical bar Li2.25Zn0.375PS4 vertical bar Li2O-ZrO2 coated Li(Ni, Mn, Co)O-2 and examined its performance. It showed a first-cycle discharge capacity of similar to 144 mAh/g(-Nmc) with a capacity retention of 83% after 100 cycles.