Lithium secondary cell with high charge and discharge rate capability
View Patent ↗A high capacity, high charge rate lithium secondary cell includes a high capacity lithium-containing positive electrode in electronic contact with a positive electrode current collector, said current collector in electrical connection with an external circuit, a high capacity negative electrode in electronic contact with a negative electrode current collector, said current collector in electrical connection with an external circuit, a separator positioned between and in ionic contact with the cathode and the anode, and an electrolyte in ionic contact with the positive and negative electrodes, wherein the total area specific impedance for the cell and the relative area specific impedances for the positive and negative electrodes are such that, during charging at greater than or equal to 4C, the negative electrode potential is above the potential of metallic lithium. The current capacity per unit area of the positive and negative electrodes each are at least 3 mA-h/cm 2 , the total area specific impedance for the cell is less than about 20 Ω-cm 2 , and the positive electrode has an area specific impedance r 1 and the negative electrode has an area specific impedance r 2 , and wherein the ratio of r 1 to r 2 is at least about 10.
1. A secondary lithium battery, comprising:
a positive electrode comprising a layer on a positive electrode current collector, said layer comprising particulate conductive additive and a lithium transition metal phosphate having an olivine structure and having a thickness of about 50 μm to about 125 μm, and said positive electrode having a specific surface area of greater than 10 m 2 /g and a total pore volume between about 40% and about 60% by volume;
a negative electrode comprising a layer on a negative electrode current collector, said layer comprising conductive additive and carbon and having a thickness of about 20 μm to about 75 μm, the carbon having an average particle size of less than about 25 μm, and said negative electrode having a total pore volume between about 25 and 40% by volume;
a microporous electronically insulating high rate separator disposed between and in ionic contact with the cathode and the anode; and
an electrolyte in ionic contact with the anode and the cathode,
wherein the cell has a total area specific impedance, and the positive and negative electrodes each have an area specific impedance and the area specific impedance of the positive electrode is greater than the area specific impedance of the negative electrode,
wherein during charging at greater than or equal to 4C, the negative electrode potential is above the potential of metallic lithium.
2. The secondary lithium battery of claim 1 , wherein the area specific impedance of the total cell is localized predominantly at the positive electrode.
3. The lithium secondary battery of claim 1 , wherein the current capacity per unit area of the positive and negative electrodes each are at least 1.0 mA-h/cm2.
4. The lithium secondary battery of claim 1 , wherein the current capacity per unit area of the positive and negative electrodes each are at least 1.5 mA-h/cm2.
5. The lithium secondary battery of claim 1 , wherein the transition metal of the lithium transition metal phosphate comprises one or more of vanadium, chromium, manganese, iron, cobalt and nickel.
6. The lithium secondary battery of claim 1 , wherein the lithium transition metal phosphate is of the formula (Li 1−x Z x )MPO 4 , where M is one or more of vanadium, chromium, manganese, iron, cobalt and nickel, and Z is one or more of titanium, zirconium, niobium, aluminum, or magnesium, and x ranges from about 0.005 to about 0.05.
7. The lithium secondary battery of claim 6 , wherein Z is selected from the group consisting of zirconium and niobium.
8. The lithium secondary battery of claim 1 , wherein the positive electrode has a specific surface area of greater than about 15 m 2 /g.
9. The lithium secondary battery of claim 1 , wherein the positive electrode has a specific surface area of greater than about 20 m 2 /g.
10. The lithium secondary battery of claim 1 , wherein the positive electrode has a specific surface area of greater than about 30 m 2 /g.
11. The lithium secondary battery of claim 1 , wherein the carbon of the negative electrode is graphitic.
12. The lithium secondary battery of claim 11 , wherein the graphitic carbon of the negative electrode has an average particle size of less than about 10 μm.
13. The lithium secondary battery of claim 11 , wherein the graphitic carbon of the negative electrode has an average particle size of less than about 6 μm.
14. The lithium secondary battery of claim 1 , wherein the negative electrode has an area specific impedance, r 2 , of less than or equal to about 3.0 Ω-cm 2 .
15. The lithium secondary battery of claim 1 , wherein the negative electrode has an area specific impedance, r 2 , of less than or equal to about 2.5 Ω-cm 2 .
16. The lithium secondary battery of claim 1 , wherein the negative electrode has an area specific impedance, r 2 , of less than or equal to about 2.0 Ω-cm 2 .
17. The lithium secondary battery of claim 1 , wherein the negative electrode has an area specific impedance, r 2 , of less than or equal to about 1.5 Ω-cm 2 .
18. The lithium secondary battery of claim 1 , wherein the positive electrode has a charge and discharge capacity measured at a C-rate of 10C that is greater than 90% of the nominal capacity measured at a C-rate of 1/10C.
19. The lithium secondary battery of claim 1 , wherein the total area specific impedance for the cell is less than about 14 Ω-cm 2 and wherein the positive electrode has an area specific impedance r 1 and the negative electrode has an area specific impedance r 2 , wherein the ratio of r 1 to r 2 is at least about 6.
20. The lithium secondary battery of claim 1 , wherein the total area specific impedance for the cell is less than about 12 Ω-cm 2 and wherein the positive electrode has an area specific impedance r 1 and the negative electrode has an area specific impedance r 2 , wherein the ratio of r 1 to r 2 is at least about 5.
21. The lithium secondary battery of claim 1 , wherein the total area specific impedance for the cell and the relative area specific impedances for the positive and negative electrodes are such that the cell is capable of achieving at least about 80% state of charge within about 25 minutes, and wherein the cell is capable of multiple charge/discharge cycles with a capacity loss of less than about 0.2% per cycle.
22. The lithium secondary battery of claim 1 , wherein the lithium transition metal phosphate comprises a doped lithium transition metal phosphate.
23. The lithium secondary battery of claim 22 , wherein the doped lithium transition metal phosphate comprises a dopant selected from the group consisting of metals, metalloids and halogens.
24. The lithium secondary battery of claim 22 , wherein the doped lithium transition metal phosphate is doped one or more of the Li, M or O-sites.
25. The lithium secondary battery of claim 11 , wherein the graphitic carbon of the negative electrode has an average particle size of less than about 15 μm.
26. The lithium secondary battery of claim 11 , wherein the graphitic carbon is selected from the group consisting of natural graphite, spheroidal natural graphite, mesocarbon microbeads and carbon fibers, such as mesophase carbon fibers.