Research On Modification And Application Of Sulfide Electrolyte Materials

With high lithium ion conductivity, perfect compatibility with metallic Li, wide electrochemical window（> 6V vs.Li/Li⁺）,sulfide solid electrolyte has a distinct advantage in the inorganic solid electrolyte. Thus, sulfide solid electrolyte has excellent prospect in the application of new generation lithium-ion battery. Although sulfide solid electrolyte has various advantages, there are still some problems to be solved in the practical application. Lithium ion conductivity of some binary sulfide solid electrolyte is not high enough. Lithium ion conductivity is high enough of ternary sulfide solid electrolyte, but it is not compatible with metallic Li. In order to solve these problems, doping method and compounding preparation have been used to improve ionic conductivity, as well as the compatibility with metallic Li. The main research work is as follows:（1） 75Li₂S·25P₂S₅ solid state electrolyte is prepared by optimized mechanical milling technique and subsequent heat-treatment process. The ball-to-powder weight ratio is 45/1. The rotating speed and milling time were 500 rpm and 12 hours（h）, respectively. The amorphous powders are heated at 270 ℃ for 4 h to obtain the 75Li₂S·25P₂S₅ glassceramics. The 75Li₂S·25P₂S₅ electrolyte is composed mainly of kind of spherical particles with a particle size ranging from less than one to several micrometers. The prepared 75Li₂S·25P₂S₅ electrolyte presents the highest conductivity of 3.67 × 10^-4 Scm^-1 at room temperature.（2） For the high-energy battery using Li metal as a negative electrode, the electrolyte is one of the most critical factors that significantly affects the cell performance. Herein, new 75Li₂S·（25-x）P₂S₅·x P₂O₅（mol%） solid state electrolytes are prepared by optimized mechanical milling technique and subsequent heat-treatment process. The electrolyte substituted with 1 mol% P₂O₅ presents the highest conductivity of 8× 10^-4S cm^-1 at room temperature, which increases up to 56% compared to that of the pristine sample. The enhanced conductivity could be attributed to the introducing of O atoms. Compared to the P-S bond, P-O bond has stronger binding, resulting in the weaker force to lithium ion,conducive to the rapid migration of lithium ions. The as-prepared 75Li₂S·24P₂S₅·1P₂O₅ electrolyte exhibits good electrochemical stability and compatibility with the metallic lithium electrode. The all-solid-state cell with a structure of Li CoO₂/75Li₂S·24P₂S₅·1P₂O₅/Li shows a discharge capacity of 109 m Ah g-1 at 0.1 C and high capacity retention 85.2% after 30 cycles at 25 ℃, which are better than these of the cell use the 75Li₂S·25P₂S₅ as electrolyte.（3）（1-ω%）LPOS-ω%（t-LGPS）（ω=3, 5, 7, 10） are prepared by mixing the glass precursor of sulfide solid electrolyte 75Li₂S·24P₂S₅·1P₂O₅（LPOS） and Li₁₀ Ge P₂S₁₂（LGPS） precursor in different proportions and sintering the mixture at 270 ℃ for 4.5 hours. The prepared 95%LPOS-5%（t-LGPS） presents the highest conductivity of 1.0 × 10^-3Scm^-1 at room temperature. The prepared novel solid electrolyte was characterized systematically by XRD, EIS and SEM, et al., furthermore, the probable mechanism of the conductivity enhanced has been discussed. The all-solid-state cell with a structure of Li CoO₂/95%LPOS-5%（t-LGPS）/Li shows a discharge capacity of 115.7mAhg^-1 at 0.1 C and high capacity retention 80.38% after 20 cycles at 25 ℃, which are better than these of the cell use the LPOS as electrolyte.