A polymeric sol electrolyte including a sol-forming polymer and an electrolytic solution consisting of a lithium salt and an organic solvent. Use of the polymeric sol electrolyte allows problems such as swelling or leakage to be overcome, compared to the case of using a liquid-type electrolytic solution. Also, the polymeric sol electrolyte has better ionic conductivity than a polymeric gel electrolyte. In addition, when the lithium battery according to the present invention is overcharged at 4.2 V or higher, an electrochemically polymerizable material existing in the polymeric sol electrolyte is subjected to polymerization to prevent heat runaway, which simplifies a separate protection circuit, leading to a reduction in manufacturing cost.