An electrochemical method for manufacturing a lithium phosphate (Li3PO4) thin film includes preparing an electroplating solution and forming the lithium phosphate thin film on a conductive substrate under suitable conditions. The electroplating bath includes about 10−2 M to about 10−1 M lithium ion and about 10−2 M to about 1 M monohydrogen phosphate ion (HPO42−) or dihydrogen phosphate ion (H2PO4−).