Electrodes and lithium ion cells with high capacity anode materials
High capacity silicon based anode active materials are described for lithium ion batteries. These materials are shown to be effective in combination with high capacity lithium rich cathode active materials. Supplemental lithium is shown to improve the cycling performance and reduce irreversible capacity loss for at least certain silicon based active materials. In particular silicon based active materials can be formed in composites with electrically conductive coatings, such as pyrolytic carbon coatings or metal coatings, and composites can also be formed with other electrically conductive carbon components, such as carbon nanofibers and carbon nanoparticles. Additional alloys with silicon are explored.
1. A lithium ion battery comprising a positive electrode comprising a lithium metal oxide, a negative electrode comprising a silicon-based active material, a separator between the positive electrode and the negative electrode, and supplemental lithium distinct from lithium associated with the lithium metal oxide and supplemental to cycling lithium supplied by the lithium metal oxide, the supplemental lithium being in an amount corresponding to about 2.5% to about 50% of the negative electrode capacity, wherein the supplemental lithium is in the form of lithium metal and/or alloy configured for spontaneous reaction with the negative electrode.
2. The lithium ion battery of claim 1 having an amount of supplemental lithium corresponding to at least about 10% of the negative electrode capacity.
3. The lithium ion battery of claim 1 wherein the negative electrode comprises nanostructured silicon.
4. The lithium ion battery of claim 1 wherein the silicon-based active material comprises a silicon-carbon composite.
5. The lithium ion battery of claim 1 wherein the negative electrode has a specific discharge capacity of at least about 750 mAh/g at a rate of C/3.
6. The lithium ion battery of claim 1 wherein the lithium metal oxide is represented by Li 1+x M 1−y O 2−z F z where M is one or more metal elements, x is from 0.01 to 0.33, y is from x−0.2 to x+0.2 with the proviso that y≥0, and z is from 0 to 0.2.
7. The lithium ion battery of claim 1 wherein the lithium metal oxide comprises lithium cobalt oxide.
8. The lithium ion battery of claim 1 wherein the lithium metal oxide comprises lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.
9. The lithium ion battery of claim 1 having a first cycle negative electrode irreversible capacity loss of no more than about 20% of the initial charge capacity.
10. The lithium ion battery of claim 1 wherein the silicon-based active material comprises nano-porous silicon.