Metal fluoride passivation coatings prepared by atomic layer deposition for Li-ion batteries
The fabrication of robust interfaces between transition metal oxides and non-aqueous electrolytes is one of the great challenges of lithium ion batteries. Atomic layer deposition (ALD) of aluminum tungsten fluoride (AlW x F y ) improves the electrochemical stability of LiCoO 2 . AlW x F y thin films were deposited by combining trimethylaluminum and tungsten hexafluoride. in-situ quartz crystal microbalance and transmission electron microscopy studies show that the films grow in a layer-by-layer fashion and are amorphous nature. Ultrathin AlW x F y coatings (<10 Å) on LiCoO 2 significantly enhance stability relative to bare LiCoO 2 when cycled to 4.4 V. The coated LiCoO2 exhibited superior rate capability (up to 400 mA/g) and discharge capacities at a current of 400 mA/g were 51% and 92% of the first cycle capacities for the bare and AlW x F y coated materials. These results open new possibilities for designing ultrathin and electrochemically robust coatings of metal fluorides via ALD to enhance the stability of Li-ion electrodes.
1. A method of preparing a metal fluoride passivation coating on a cathode comprising:
performing a atomic layer deposition cycles of TMA at a first deposition temperature between 50° C. and 300° C.; and
performing b atomic layer deposition cycles of WF 6 at a second deposition temperature between 50° C. and 300° C., and
forming a layer consisting of AlW x F y C z on the cathode such that the layer excludes oxygen, where x>0, y>0, and z≥0.
2. The method of claim 1 , wherein the ratio of a:b is selected from the group consisting of 3:1, 2:1, 1:1, and 4:2.
3. The method of claim 1 , wherein the first deposition temperature and the second deposition temperature are about 200° C.
4. The method of claim 1 , wherein the cathode comprises LiCoO 2 .
5. The method of claim 1 , wherein z>0.
6. The method of claim 1 , wherein the AlW x F y C z layer has a thickness of less than about 1 nm.
7. The method of claim 1 , wherein the a cycles each comprise: a 1 second TMA dose followed by a 5 second gas purge.
8. The method of claim 1 , wherein the b cycle depositions each comprise: a 1 second WF 6 dose followed by a 5 second gas purge.
9. The method of claim 1 , wherein the metal fluoride passivation coating comprises particles of WC z , wherein z≥0, disposed in a matrix of AlF 3 .