Recent research has focused on improving the performance of solid-state sodium-ion batteries (SIBs) through the development of solid electrolytes (SSEs). While SIBs are cost-effective and have similar charge/discharge principles to lithium-ion batteries, their energy density is lower due to less development. SSEs offer higher energy density compared to liquid electrolytes, making them more suitable for energy storage systems. However, SSEs currently have low ionic conductivity and other issues, such as narrow electrochemical stability windows and poor electrode contact. This review discusses recent advancements in SSEs for SIBs, including inorganic electrolytes like Na-β-Al2O3, NASICON, and Na3PS4, polymer electrolytes based on PEO, PVDF-HFP, and PAN, and plastic crystal electrolytes composed mainly of succinonitrile. The review also addresses solutions for the key challenges in SSEs, such as low ionic conductivity, narrow electrochemical stability windows, and poor electrode contact. SIBs are promising alternatives to lithium-ion batteries due to the abundance of sodium and lower production costs. However, their capacity is limited due to shorter development time compared to lithium-ion batteries. Research has focused on improving capacity and cycle life, with new "anode-free" technologies being developed to increase energy density. These technologies remove the anode active material and form a sodium metal layer on the anode side current collector, significantly increasing energy density. However, new problems such as sodium dendrite formation and electrolyte-sodium metal reactions may arise. The electrolyte plays a crucial role in SIBs, influencing energy density and rate capability. Electrolyte systems can be divided into water-based, organic solvent-based, and solid-state systems. While water-based electrolytes provide stable cycling performance, they have a low electrochemical window, limiting energy density. Organic liquid electrolytes, such as carbonates and ethers, are increasingly used in SIBs. However, they have limitations in terms of electrochemical window and safety. Ionic liquids (ILs) are considered safer and more stable than carbonate and ether electrolytes, but their high cost and viscosity hinder their application. Solid-state electrolytes (SSEs) are considered a possible alternative to liquid electrolytes, offering good processability and safety. SSEs with polymer-based materials can have even lower costs. The number of publications on SSEs for SIBs has increased significantly since 2010. SSEs have characteristics such as electrochemical stability, mechanical strength, and increased energy density, making them attractive for SIBs.Recent research has focused on improving the performance of solid-state sodium-ion batteries (SIBs) through the development of solid electrolytes (SSEs). While SIBs are cost-effective and have similar charge/discharge principles to lithium-ion batteries, their energy density is lower due to less development. SSEs offer higher energy density compared to liquid electrolytes, making them more suitable for energy storage systems. However, SSEs currently have low ionic conductivity and other issues, such as narrow electrochemical stability windows and poor electrode contact. This review discusses recent advancements in SSEs for SIBs, including inorganic electrolytes like Na-β-Al2O3, NASICON, and Na3PS4, polymer electrolytes based on PEO, PVDF-HFP, and PAN, and plastic crystal electrolytes composed mainly of succinonitrile. The review also addresses solutions for the key challenges in SSEs, such as low ionic conductivity, narrow electrochemical stability windows, and poor electrode contact. SIBs are promising alternatives to lithium-ion batteries due to the abundance of sodium and lower production costs. However, their capacity is limited due to shorter development time compared to lithium-ion batteries. Research has focused on improving capacity and cycle life, with new "anode-free" technologies being developed to increase energy density. These technologies remove the anode active material and form a sodium metal layer on the anode side current collector, significantly increasing energy density. However, new problems such as sodium dendrite formation and electrolyte-sodium metal reactions may arise. The electrolyte plays a crucial role in SIBs, influencing energy density and rate capability. Electrolyte systems can be divided into water-based, organic solvent-based, and solid-state systems. While water-based electrolytes provide stable cycling performance, they have a low electrochemical window, limiting energy density. Organic liquid electrolytes, such as carbonates and ethers, are increasingly used in SIBs. However, they have limitations in terms of electrochemical window and safety. Ionic liquids (ILs) are considered safer and more stable than carbonate and ether electrolytes, but their high cost and viscosity hinder their application. Solid-state electrolytes (SSEs) are considered a possible alternative to liquid electrolytes, offering good processability and safety. SSEs with polymer-based materials can have even lower costs. The number of publications on SSEs for SIBs has increased significantly since 2010. SSEs have characteristics such as electrochemical stability, mechanical strength, and increased energy density, making them attractive for SIBs.