Preparation of High Lithium Ion Conducting Glass-Ceramics by Mechanical Milling

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1. Amorphous materials with various compositions in the systems Li_2S-P_2S_5, Li_2S-P_2S_5-SiS_2, and Li_2S-P_2S_5-GeS_2 were prepared by mechanical milling (MM) of crystalline starting materials in a dry N_2 atmosphere at room temperature. The pelletized samples of these glassy materials exhibited high conductivities in the order of 10^<-4> Scm^<-1> at 25℃. It was found that the transport number of lithium ions of the glassy materials was almost unity and the potential window as solid electrolytes was wider than 10 V.2. Highly conductive glass-ceramics were obtained by the heat treatment under a variety of conditions of the above glassy materials prepared by MM. The glass-ceramics obtained after heating at around 230℃ showed the X-ray diffraction patterns very similar to those of highly conductive thio-LISICON II phases in Li_<4-x>Ge_<1-x>P_xS_4, suggesting that the thio-LISICON II analogue is formed in the glass-ceramics derived from the mechanically milled glassy powder in these systems.3. The highly conductive glass-ceramics were also obtained by the MM of starting materials of elements. Glassy Li_2S-P_2S_5 samples were successfully prepared by the MM of Li_2S, P, and S. The properties and structure of the glassy samples are very similar those of the samples prepared using Li_2S and P_2S_5. The glass-ceramics obtained by the heating of such an element-derived sulfide glasses exhibited similar properties to the glass-ceramics from P_2S_5-derived glasses.4. Electrochemical cells were constructed using glass-ceramics in the system Li_2S-P_2S_5 obtained by MM and heat treatment as an electrolyte, LiCoO_2, as a positive electrode and indium as a negative electrode. The all-solid-state cell exhibited excellent cycling performances with the reversible charge-discharge capacities of about 100mAhg^<-1> even after 200 cycles.