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 LiCoO 2 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 battery comprising:
LiCoO 2 cathode core;
a metal fluoride passivation coating conformally coated on the cathode core;
the metal fluoride passivation coating consisting of AlW x F y C z excluding oxygen, the metal fluoride coating comprising W particles uniformly dispersed in an ALF 3 matrix; and
wherein x>0, y>0, and z> or equal to 0.
2. The battery of claim 1 , wherein the metal fluoride passivation coating has a thickness of less than 1 nm.
3. The battery of claim 1 , wherein the AlF 3 matrix is amorphous.
4. The battery of claim 3 , wherein the W particles have a size of ˜1 nm.
5. The battery of claim 1 , wherein z>0.
6. The battery of claim 5 , wherein the metal fluoride passivation coating also comprises particles of WC z disposed in the matrix of AlF 3 .
7. The battery of claim 1 , wherein the battery retains 99% of its initial capacity after 50 charge-discharge cycles.
8. The battery of claim 1 , wherein the LiCoO 2 cathode core comprises LiCoO 2 powder, carbon and polyvinylidenefluoride in N-methyl pyrrolidone.
9. The battery of claim 1 , further comprising a current collector, the LiCoO 2 cathode core disposed on the current collector.
10. The battery of claim 1 , further comprising an electrolyte, the electrolyte comprising a LiPF 6 solution in ethylene carbonate and ethylmethyl carbonate.