Silicon-silicon oxide-carbon composites for lithium battery electrodes and methods for forming the composites
Composite silicon based materials are described that are effective active materials for lithium ion batteries. The composite materials comprise processed, e.g., high energy mechanically milled, silicon suboxide and graphitic carbon in which at least a portion of the graphitic carbon is exfoliated into graphene sheets. The composite materials have a relatively large surface area, a high specific capacity against lithium, and good cycling with lithium metal oxide cathode materials. The composite materials can be effectively formed with a two step high energy mechanical milling process. In the first milling process, silicon suboxide can be milled to form processed silicon suboxide, which may or may not exhibit crystalline silicon x-ray diffraction. In the second milling step, the processed silicon suboxide is milled with graphitic carbon. Composite materials with a high specific capacity and good cycling can be obtained in particular with balancing of the processing conditions.
1. A composite material comprising processed silicon suboxide and graphitic carbon comprising graphene as determined by observation of graphene in electron micrographs and a decrease in graphite x-ray scattering, wherein the composite material has a D50 volume average particle size of no more than about 5 microns, a BET surface area from about 5 m 2 /g to 35 m 2 /g and a discharge capacity of at least 1100 mAh/g at a rate of C/20 discharged from 1.5V to 0.005V against lithium metal, wherein the composite material has from about 0.5 weight percent to about 18 weight percent graphitic carbon.
2. The composite material of claim 1 having an x-ray scattering diffractogram with visible peaks corresponding to crystalline silicon.
3. The composite material of claim 1 having an x-ray scattering diffractogram with no visible peaks corresponding to crystalline silicon.
4. The composite material of claim 1 wherein the composite material has from 1.0 weight percent to 15 weight percent graphitic carbon.
5. The composite material of claim 1 having a BET surface area from 14 m 2 /g to 33 m 2 /g and a D50 volume average secondary particle size of no more than 4 microns.
6. The composite material of claim 1 wherein the material has a 50th cycle discharge capacity that is at least 87% of the 5th cycle discharge capacity when cycled against lithium from 1.5V to 0.005V at a discharge rate of C/3.
7. The composite material of claim 1 wherein the processed silicon suboxide is formed through high energy mechanical milling of silicon suboxide prior to combination with graphitic carbon.
8. The composite material of claim 7 wherein the graphene sheets are formed by the high energy mechanical milling of the processed silicon suboxide with graphite powder.
9. The composite material of claim 8 wherein the high energy mechanical milling is performed with zirconium oxide milling medium.
10. The composite material of claim 8 wherein the material has a 50th cycle discharge capacity that is at least 87% of the 5th cycle discharge capacity when cycled against lithium from 1.5V to 0.005V at a discharge rate of C/3.
11. The composite material of claim 10 comprising from 2 weight percent to 10 weight percent graphitic carbon.
12. The composite material of claim 10 having a specific discharge capacity of at least 1400 mAh/g at a rate of C/20 discharged from 1.5V to 0.005V against lithium metal.
13. The composite material of claim 10 having a specific discharge capacity of at least 1250 mAh/g at a rate of C/3 discharged from 1.5V to 0.005V against lithium metal.
14. The composite material of claim 10 having a 50th cycle discharge capacity that is at least 90% of the 5th cycle discharge capacity when cycled against lithium from 1.5V to 0.005V at a discharge rate of C/3.
15. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator between the positive electrode comprising a lithium metal oxide and the negative electrode and an electrolyte comprising lithium ions,
wherein the negative electrode comprises a composite material comprising processed silicon suboxide and graphitic carbon comprising graphene as determined by observation of graphene in electron micrographs and a decrease in graphite x-ray scattering is in graphene sheets and having at a discharge rate of C/3 at the 50th cycle a positive electrode specific capacity of at least 150 mAh/g and a negative electrode specific capacity of at least 1000 mAh/g when discharged from 4.5V to 1V from the 7th cycle to the 50th cycle at a rate of C/3.
16. The lithium ion secondary battery of claim 15 having at a discharge rate of C/3 at the 50th cycle a positive electrode specific capacity of at least 170 mAh/g and a negative electrode specific capacity of at least 1150 mAh/g when discharged from 4.5V to 1V.
17. The lithium ion secondary battery of claim 15 wherein the battery exhibits a discharge capacity decrease of no more than 15 percent at the 50th discharge cycle relative to the 7th discharge cycle.
18. The lithium ion secondary battery of claim 15 wherein the composite material has a BET surface area from 5 m 2 /g to about 35 m 2 /g.
19. The lithium ion secondary battery of claim 15 wherein the composite material has from 0.5 weight percent to 10 weight percent graphitic carbon a D50 volume average secondary particle size of no more than 5 microns.
20. The lithium ion secondary battery of claim 15 wherein the positive electrode active material represented by the formula Li 1+b Ni α Mn β Co γ A δ O 2-z F z , where b ranges from 0.01 to 0.3, α ranges from 0 to about 0.4, β range from 0.2 to 0.65, γ ranges from 0 to 0.46, δ ranges from 0 to 0.15 and z ranges from 0 to 0.2 with the proviso that both α and γ are not zero, and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof.
21. The lithium ion secondary battery of claim 15 further comprising supplemental lithium distinct from the lithium supplied by the positive electrode active material.
22. The lithium ion secondary battery of claim 15 wherein an active material of the positive electrode comprises a stabilization coating.
23. The lithium ion secondary battery of claim 22 wherein the stabilization coating comprises a metal halide.