Particle size distribution variations in iron disulfide cathodes
A cathode, electrochemical cell and process for making either is disclosed. The cathode includes iron disulfide which exhibits multiple peaks representing distinct maxima of mean diameters for the volume-based particle size distribution. All of the maxima are less than 20 microns. A combination of natural pyrite ore and synthetic iron disulfide may be mixed to achieve the desired distribution, or a combination of natural pyrite ores may be processed in different manners to achieve the desired characteristics.
1. A cathode for a lithium iron disulfide electrochemical cell having a plurality of maxima of mean diameters in a volume-based particle size distribution of all iron disulfide particles present in the cathode material and a mean diameter of the volume-based particle size distribution that is greater than 100 nanometers and less than 20 microns, wherein a first maximum of the plurality of maxima is between 10 μm and 15 μm and a second maximum of the plurality of maxima is between 100 nm and 1 μm, and further wherein the iron disulfide particles include a naturally occurring iron disulfide source which accounts for the first maximum and a synthetic iron disulfide source which accounts for the second maximum, the naturally occurring iron disulfide source and the synthetic iron disulfide source provided at a ration of at least 2:1 on a volume basis.
2. The cathode according to claim 1 , wherein the plurality of maxima includes at least three maxima.
3. The cathode according to claim 1 , wherein the cathode material is coated onto a solid metal foil.
4. The cathode according to claim 3 , wherein a thickness of the coated cathode material is between 5 and 30 times greater than the first maximum.
5. The cathode according to claim 3 , wherein each maximum comprising the plurality of maxima, when considered on an individual basis, is less than one half of a thickness of the coated cathode material.
6. The cathode according to claim 3 , wherein each maximum comprising the plurality of maxima, when considered on an individual basis, is less than one third of a thickness of the coated cathode material.
7. A cathode for a lithium iron disulfide electrochemical cell wherein two separate sources of pyrite are combined to have a plurality of maxima of mean diameters in a volume-based particle size distribution of all iron disulfide particles present in the cathode material and wherein one of said maxima is between 100 nanometers and 1 μm and one of said maxima is between 10 μm and 15 μm, wherein the first source of pyrite accounts for the maximum between 10 μm and 15 μm and the second source of pyrite accounts for the maximum between 100 nanometers and 1 μm, and further wherein the first source and the second source are provided at a ratio of at least 2:1 on a volume basis.
8. A cathode for a lithium iron disulfide electrochemical cell wherein two separate sources of pyrite are combined to have a plurality of maxima of mean diameters in a volume-based particle size distribution of all iron disulfide particles present in the cathode material and wherein a first maximum of the plurality of maxima is greater than 20 μm and a second maximum of the plurality of maxima is between 100 nm and 1 μm, wherein the first source accounts for the first maximum and the second source accounts for the second maximum, and further wherein the first source and the second source are provided at a ratio of at least 2:1 on a volume basis.
9. The cathode according to claim 8 , wherein the first maximum is greater than 40 μm.
10. The cathode according to claim 8 , wherein the first maximum is greater than 50 μm.