Preparation of Amorphous Solid Electrolytes by Mechanical Milling

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1.Amorphous materials with various compositions in the oxysulfide system Li_2S-SiS_2-LixMOy (LixMOy=Li_4SiO_4, Li_3PO_4) were obtained by mechanical milling (MM) of crystalline starting materials in a dry N_2 atmosphere at room temperature. The pelletized samples 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 amorphous materials was almost unity and the potential window as solid electrolytes was wider than 10V.2.Several spectroscopic measurements like MAS NMR and XPS revealed that the local structure of the amorphous oxysulfide powders prepared by MM was very close to thata of the corresponding melt quenched glass. Furthermore, the formation of continuous amorphous phase with the inrease of milling tive incresed conductivity grastically from 10^<-10> to 10^<-4> Scm^<-1> at room temperature.3.The amorphous Li_2S-P_2S_5 sample prepared by MM exhibited high conductivity of 9x10^<-5> S cm^<-1> at room temperature. After the sample was heated up to the crystallization temperature, the conductivity decreased with a smaller slope in the cooling process. The conductivity of the heated sample was 6x10^<-4> S cm^<-1> at room temperature. It was revealed that the conductivity improvement with forming the. 80Li_2S・20P_2S_5 glass-ceramics was brought about by the softening of glassy powders and the formation of highly conductive Li_7PS_6 crystal.4.Electrochemical cells were constructed using amorphous matterials in the system Li_2S-SiS_2-Li_4SiO_4 obtained by MM as an electrolyte, LiCoO_2 as a positive electrode and indium as a negative electrode. The charge-discharge capacity decreased gradually from 90 to 70 mAhcm^<-2> till about the 10th cycle and became stable after the 10th cycle.