Provided are a secondary battery including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode include first solid electrolyte particles, the solid electrolyte layer includes second solid electrolyte particles, and a particle diameter of the second solid electrolyte particles is greater than a particle diameter of the first solid electrolyte particles.
In the secondary battery, the electrode may increase the amount of movement of lithium ions by increasing a contact area between the solid electrolyte particles and electrode active material, and the solid electrolyte layer may minimize the reduction of ionic conductivity by decreasing interfacial resistance due to the contact between the electrode and the solid electrolyte layer. Thus, stability and performance of the secondary battery may be improved.