Ž . Materials and Design 22 2001 617623 Chemical synthesis and characterization of lithium ž / orthosilicate Li SiO 4 4 C.-C. Chang, C.C. Wang, P.N. Kumta  Department of Materials Science and Engineering, Carnegie Mellon Uni  ersity, Pittsburgh, PA, 15213, USA Abstract A solution based wet chemistry approach has been developed for synthesizing Li SiO powders at moderate temperatures of 4 4 500°C. LiOH  H O and LiNO have been used as starting materials for synthesizing this material in the present study. The phase 2 3 evolution behavior, surface area and morphology of the as-prepared and heat treated powders generated from both LiOH  HO 2 and LiNO have been studied and compared in this work. The feasibility of synthesizing a Li SiO  LiNi Co O based 3 4 4 0.75 0.25 2 electrolyte  electrode composite material using this chemical approach is also discussed and demonstrated.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Chemical synthesis; Li SiO; Characterisation 4 1. Introduction Ž .  Lithium orthosilicate Li SiO , Lisicon Li Zn 4 4 14 Ž .  GeO and their solid solution derivative systems 4 4 such as Li SiO  Li PO , Li SiO  Li ASO , 4 4 3 4 14 4 3 4 Li SiO  Li GeO , Li SiO Li AsO  Li PO , 4 4 4 4 4 4 3 4 3 4 Li SiO  Zn SiO and Li GeO  Li ZnGeO  Li PO 4 4 2 4 4 4 2 4 3 4 are known as an important class of fast Li-ion conduct-   ing materials 1  12 . These materials usually accommo- date Li vacancies which allow fast Li-ion conduction. Ž . Lithium orthosilicate Li SiO is commonly synthe- 4 4 sized using traditional solid state methods. These processes typically require heat treating the precursors Ž . at high temperatures usually  1000°C for a pro- Ž .   longed period 1  2 days 1  5,7,9,10 . High tempera- ture solid state methods lead to a myriad of problems including contamination, volatilization and lack of con- trol on the microstructure and composition. Chemical methods offer an opportunity for not only synthesizing a material at low temperatures but also the possibility to control its morphology and microstructure. A num- ber of chemical approaches have been developed by us  Corresponding author.   and others 13  16 for synthesizing electrochemically Ž . active materials such as LiMO M  Ni, M Co . 2 0.75 0.25 Keeping in line with our overall theme, a solution based wet chemistry approach is utilized for synthesiz- ing Li SiO powders. 4 4 In the present study, a low temperature chemical approach is investigated for synthesizing Li SiO . This 4 4 was attempted to not only decrease the concentration of thermally induced point defects caused by high tem- perature methods which potentially lead to the subse- quent loss of ionic conductivity, but also increase the possibility of synthesizing novel electrolyte  electrode Ž composite materials e.g. LiMO , M  Co, Ni, 2 Co Ni without causing decomposition of the parent x 1x Ž .   oxide, LiMO M  Ni, M Co 17,18 . The impor- 2 0.75 0.25 tance of synthesizing the electrolyte  electrode compos- ite materials arises from the fact that the performance Ž . power output of the solid state batteries is mainly determined by the Li-ion conductivity of the electrolyte and the efficiency of Li-ion transport from the elec- trode material to the electrolyte. The efficiency of Li-ion transport from the far end of the electrode material to the electrolyte actually determines the critical thickness of the electrode under certain Ž . chargedischarge rates C-rate . Developments of such 0261-306901$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. Ž . PII: S 0 2 6 1 - 3 0 6 9 01 00024-3