NOVELTY - A composite solid electrolyte composition comprises binder containing core-shell-type particles containing inorganic solid electrolyte and dispersion medium. The core-shell-type particles have a core portion and a shell portion. The difference between glass transition temperature of high-molecular compound contained in core portion with respect to glass transition temperature of high-molecular compound contained in shell portion is 50 degrees C or more.    USE - Composite solid electrolyte composition is used in manufacture of battery electrode sheet used for manufacturing all-solid-state secondary battery (all claimed) e.g. lithium-ion secondary battery. Uses include but are not limited to notebook personal computer, mobile telephone, portable printer, liquid crystal television, electric shaver, transceiver, portable tape recorder, electric vehicle, lighting fixture, solar cell, etc.    ADVANTAGE - The composite solid electrolyte composition has excellent ionic conductivity and binding property, and provides all-solid-state secondary battery with high battery performance and suppressed interfacial resistance between solid particles and electrical power collector.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) battery electrode sheet, which is obtained by forming the composite solid electrolyte composition into a film on a metal foil;    (2) all-solid-state secondary battery (10), which consists of a positive electrode active material layer (4), a negative electrode active material layer (2), and an inorganic solid electrolyte layer (3). The positive electrode active material layer, negative electrode active material layer, or inorganic solid electrolyte layer contains the solid electrolyte composition;    (3) manufacture of battery electrode sheet; and    (4) manufacture of all-solid-state secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of all-solid-state secondary battery.    Negative electrode active material layer (2)    Inorganic solid electrolyte layer (3)    Positive electrode active material layer (4)    Positive electrode electrical power collector (5)    All-solid-state secondary battery (10)