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Amorphous B 2 O 3 thin films fabricated by pulsed laser deposition were investigated as lithium storage electrode materials for the first time. A high reversible capacity of 1100 mAh g −1 could be obtained. By using ex-situ X-ray photoelectron spectroscopy and Raman spectroscopy, a new mechanism of lithium insertion/extraction into/from an amorphous structure was revealed. Large reversible capacity and good rate performance of B 2 O 3 electrode made it potential application as lithium storage material for rechargeable ion batteries Boron oxide (B 2 O 3 ) has been found to be one of the most difficultly crystallized compounds. 1 Due to its poor conductivity, B 2 O 3 exhibited the poor electrochemical activity with the low reversible capacity about 12 mAh/g. 2 It never draws much attention as lithium storage materials. In contrary, many groups treat it as an addition agent in electrode materials to improve their electrochemical performance, For example, Courtney et al. 3 indicated that B 2 O 3 in SnO composite glasses did not react with lithium and could slow down the aggregation of Sn, which led to an improvement of the reversibility of this material. Ding et al. 4 suggested doping B 2 O 3 in SnO 2 could provide an amorphous oxide matrix and buffer the volume changes during the reactions. In the previous research, 5 it can be found that many electrochemically inactive materials could show considerable electrochemical activity when they were fabricated into nanostructured thin films. This stimulates us to investigate initially the electrochemical behavior of the amorphous B 2 O 3 thin film. In this letter, the physical and electrochemical properties of B 2 O 3 thin film electrode prepared by pulsed laser deposition (PLD) are reported. ExperimentalAmorphous B 2 O 3 thin films were prepared by PLD, where the details have been described elsewhere. 5 Experimental conditions for depositing thin films are described as follows: A 355 nm laser beam from a Q-switched Nd: yttrium aluminum garnet laser (Spectra Physics GCR-150) with a pulsed repetition rate of 10 Hz and a pulsed width of 5 ns was focused onto the surface of the target. The laser intensity was about 2 J cm −2 . The distance between the target and the substrate was 4 cm. Amorphous B 2 O 3 targets were obtained by cold pressing B 2 O 3 powder (99.98%, Aldrich). The films were deposited on a stainless steel substrate at room temperature. The thickness of the asdeposited films is about 110 nm for the depositing time of 50 minutes. Its weight was directly obtained by subtracting the original substrate weight from total weight of the substrate and deposited thin film onto its surface, which were examined by electrobalance (BP 211D, Sartorius). XPS measurements were performed on a PerkinElmer PHI 6000CESCA system with monochromatic Al Ka (1486.6 eV) irradiation. Raman spectra were achieved on a LABRAM-1B confocal Raman spectrometer with 647.1nm radiation from an Ar-Kr laser.For the electrochemical measurements, the cells were constructed by using the as-deposited B 2...