Electrolytes for stable cycling of high capacity lithium based batteries
Electrolytes are described with additives that provide good shelf life with improved cycling stability properties. The electrolytes can provide appropriate high voltage stability for high capacity positive electrode active materials. The core electrolyte generally can comprise from about 1.1M to about 2.5M lithium electrolyte salt and a solvent that consists essentially of fluoroethylene carbonate and/or ethylene carbonate, dimethyl carbonate and optionally no more than about 40 volume percent methyl ethyl carbonate, and wherein the lithium electrolyte salt is selected from the group consisting of LiPF 6 , LiBF 4 and combinations thereof. Desirable stabilizing additives include, for example, dimethyl methylphosphonate, thiophene or thiophene derivatives, and/or LiF with an anion complexing agent.
1. An electrolyte composition comprising a solvent, from about 1.1M to about 2.5M lithium electrolyte salt, and from about 0.02 to about 0.5 weight percent thiophene or thiophene derivatives, wherein the solvent consists essentially of fluoroethylene carbonate, dimethyl carbonate and optionally methyl ethyl carbonate, wherein the solvent comprises no more than about 20 weight percent fluoroethylene carbonate relative to a total electrolyte weight, and wherein the lithium electrolyte salt is selected from the group consisting of LiPF 6 , LiBF 4 and combinations thereof.
2. The electrolyte composition of claim 1 further comprising from about 1 to about 5 weight percent LiBOB, LiDFOB or combinations thereof.
3. The electrolyte composition of claim 1 wherein the solvent comprises methyl ethyl carbonate in an amount of no more than about 20 weight percent relative to a total electrolyte weight.
4. The electrolyte composition of claim 1 wherein the solvent comprises methyl ethyl carbonate in an amount of no more than about 30 weight percent relative to a total electrolyte weight.
5. The electrolyte composition of claim 1 wherein the solvent consists essentially of fluoroethylene carbonate and dimethyl carbonate at a weight ratio from about 1:1 to about 1:4.
6. The electrolyte composition of claim 1 wherein the electrolyte composition comprises from about 1.15M to about 1.6M lithium electrolyte salt.
7. A lithium ion battery comprising a positive electrode, a negative electrode, a separator separating the positive electrode and negative electrode and the electrolyte composition of claim 1 , wherein the positive electrode comprises an active material comprising a lithium rich metal oxide approximately represented by the formula Li 1+b Ni α Mn β Co γ A δ O 2−z F z , where b ranges from about 0.01 to about 0.3, α ranges from about 0 to about 0.4, β ranges from about 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from 0 to about 0.15 and z ranges from 0 to about 0.2 with the proviso that both α and γ are not zero, and where A is a metal element different from Ni, Mn, or Co.
8. The lithium ion battery of claim 7 wherein the inorganic stabilization coating comprises metal oxide, metal halide or a combination thereof with an average thickness from about 0.5 nm to about 12 nm.
9. The lithium ion battery of claim 7 , wherein the solvent comprises methyl ethyl carbonate in an amount of no more than about 20 weight percent relative to a total electrolyte weight.
10. The lithium ion battery of claim 7 wherein the negative electrode comprises graphitic carbon.
11. The lithium ion battery of claim 7 wherein the positive electrode active material has a specific capacity of at least about 140 mAh/g at a 1C rate discharged from 4.35V to 2V and wherein the lithium ion battery has a capacity at a 500th cycle that is at least about 97.5% of a 5th cycle capacity when cycled at a discharge rate of 1C from 4.35V to 2.5V.
12. The lithium ion battery of claim 7 wherein the solvent consists essentially of fluoroethylene carbonate and dimethyl carbonate at a weight ratio from about 1:1 to about 1:4.