Lithium ion conductive solid electrolyte and method for manufacturing the same
A solid electrolyte suitable for use in all solid type lithium ion secondary battery is made by sintering a form, particularly a greensheet, comprising at least lithium ion conductive inorganic substance powder. The solid electrolyte has porosity of 20 vol % or over.
1. A method for manufacturing a lithium ion conductive solid electrolyte comprising:
preparing a slurry comprising lithium ion conductive glass or glass-ceramic powder as a main component and comprising also at least an organic binder and water used as a solvent,
forming the slurry to a greensheet,
isotropically pressing the greensheet so as to make the greensheet dense, and
sintering the greensheet with variation in thickness of the greensheet being within a range from +10% to −10% relative to mean value of distribution of thickness of the greensheet,
wherein the solid electrolyte has porosity of 10 vol % or less, and the solid electrolyte has thickness of 200 μm or below wherein the glass or glass-ceramic powder comprises lithium, silicon, phosphorus and titanium, and average particle diameter of the glass or glass-ceramic powder is 20 μm or below.
2. A method as defined in claim 1 further comprising a step of superposing a plurality of the greensheets and pressing the superposed greensheets before sintering.
3. A method as defined in claim 1 wherein the lithium ion conductive glass-ceramic powder comprises crystalline of
L 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 where 0≦x≦1 and 0≦y≦1.
4. A method as defined in claim 3 wherein the crystalline is free of a pore or a crystal grain boundary which obstructs ion conduction.