A method for injecting an electrolyte of a pouch-type battery cell, comprising: separating an injection hole cap, which covers an electrolyte injection hole formed in a battery case of a battery cell, according to user manipulation; connecting an injection cylinder of an electrolyte injecting device which includes the injection cylinder, a vacuum unit, and an electrolyte unit to the electrolyte injection hole; decompressing the inside of the battery case to a vacuum state by using the electrolyte injecting device; injecting an electrolyte into the battery case by using the electrolyte injecting device; separating the electrolyte injecting device from the electrolyte injection hole; and mounting the injection hole cap to the electrolyte injection hole according to user manipulation to cover the electrolyte injection hole, wherein anti-slip grooves for preventing a slip during the user manipulation are formed at an outer circumference of the injection hole cap, wherein the anti-slip grooves are formed to have a predetermined length along a length direction of the injection hole cap, which is perpendicular to a rotation direction according to the user manipulation, to preventing a slip during the user manipulation, wherein the user manipulation is performed by turning the injection hole cap for releasing or mounting the screwing, wherein the anti-slip grooves are spaced apart from each other by a predetermined distance, wherein the injection hole cap is screwed to the electrolyte injection hole, wherein the electrolyte injection hole has an inner hollow for injecting the electrolyte into the battery case and protrudes out of the battery case, wherein the electrolyte injecting device further includes a mount cylinder, the mount cylinder is mounted to a lower side of the injection cylinder and supports the injection cylinder when the electrolyte injection hole of the injection cylinder is mounted, and the mount cylinder is closely adhered to a surface of the battery case when the electrolyte injecting device is mounted, and the injection cylinder is provided to be capable of sliding in a vertical direction of the mount cylinder. separating an injection hole cap, which covers an electrolyte injection hole formed in a battery case of a battery cell, according to user manipulation; connecting an injection cylinder of an electrolyte injecting device which includes the injection cylinder, a vacuum unit, and an electrolyte unit to the electrolyte injection hole; decompressing the inside of the battery case to a vacuum state by using the electrolyte injecting device; injecting an electrolyte into the battery case by using the electrolyte injecting device; separating the electrolyte injecting device from the electrolyte injection hole; and mounting the injection hole cap to the electrolyte injection hole according to user manipulation to cover the electrolyte injection hole, wherein anti-slip grooves for preventing a slip during the user manipulation are formed at an outer circumference of the injection hole cap, wherein the anti-slip grooves are formed to have a predetermined length along a length direction of the injection hole cap, which is perpendicular to a rotation direction according to the user manipulation, to preventing a slip during the user manipulation, wherein the user manipulation is performed by turning the injection hole cap for releasing or mounting the screwing, wherein the anti-slip grooves are spaced apart from each other by a predetermined distance, wherein the injection hole cap is screwed to the electrolyte injection hole, wherein the electrolyte injection hole has an inner hollow for injecting the electrolyte into the battery case and protrudes out of the battery case, wherein the electrolyte injecting device further includes a mount cylinder, the mount cylinder is mounted to a lower side of the injection cylinder and supports the injection cylinder when the electrolyte injection hole of the injection cylinder is mounted, and the mount cylinder is closely adhered to a surface of the battery case when the electrolyte injecting device is mounted, and the injection cylinder is provided to be capable of sliding in a vertical direction of the mount cylinder.