Electrodes for metal-ion batteries
An electrode for a metal-ion battery is provided wherein the active layer of the electrode comprises a plurality of low porosity particles comprising an electroactive material selected from silicon, silicon oxide germanium, tin, aluminium and mixtures thereof and a plurality of carbon particles selected from one or more of graphite, soft carbon and hard carbon. The ratio of the D 50 particles size of the carbon particles to the D 50 particle diameter of the porous particles is in the range of from 1.5 to 30. Also provided are rechargeable metal-ion batteries comprising said electrode and compositions of porous particles and carbon particles which may be used to prepare the active layer of said electrode.
1. An electrode for a metal-ion battery, the electrode comprising an active layer in electrical contact with a current collector, wherein the active layer comprises:
(i) a plurality of porous particles comprising a carbon matrix in which electroactive material-containing primary particles are dispersed, wherein the electroactive material is selected from silicon, silicon oxide of the formula SiO x wherein 0<x≤1.5, germanium, tin, aluminium and mixtures thereof, wherein the porous particles comprise no more than 80 wt % of the electroactive material, wherein the porous particles have a D 50 particle diameter in the range of 0.5 to 20 μm, a D 90 particle diameter of no more than 40 and an intra-particle porosity of less than 30%; and
(ii) a plurality of carbon particles selected from one or more of graphite, soft carbon and hard carbon and having a D 50 particle diameter in the range of from 1 to 100 μm
wherein the active layer comprises at least 50% by weight of the carbon particles (ii), and
wherein the ratio of the D 50 particle diameter of the carbon particles (ii) to the D 50 particle diameter of the porous particles (i) is in the range of from 1.5 to 30, and
wherein the active layer in a dry, uncharged state has a density in the range of from 0.6 to 1.8 g/cm 3 .
2. An electrode according to claim 1 wherein the porous particles (i) comprise at least 40 wt %, of the electroactive material.
3. An electrode according to claim 1 , wherein at least one of:
(a) the porous particles (i) comprise at least 0.01 wt % aluminium and/or germanium, and
(b) the porous particles (i) comprise a minor amount of one or more additional elements selected from antimony, copper, magnesium, zinc, manganese, chromium, cobalt, molybdenum, nickel, beryllium, zirconium, iron, sodium, strontium, phosphorus, tin, ruthenium, gold, silver, and oxides thereof.
4. An electrode according to claim 1 , wherein the D 50 particle diameter of the carbon particles (ii) is no more than 40 μm.
5. An electrode according to claim 1 , wherein the porous particles (i) have a particle size distribution span (D 90 -D 10 )/D 50 of 5 or less.
6. An electrode according to claim 1 , wherein the average aspect ratio of the porous particles (i) is less than 3:1.
7. An electrode according to claim 1 , wherein the porous particles (i) are spheroidal particles having an average sphericity S av of at least 0.70.
8. An electrode according to claim 1 , wherein the porous particles (i) have a pore diameter distribution having at least one peak at a pore size less than 500 nm.
9. An electrode according to claim 1 , wherein the porous particles (i) have a BET surface area of less than 300 m 2 /g.
10. An electrode according to claim 1 , wherein the electroactive material-containing primary particles have a smallest dimension which is less than 150 nm.
11. An electrode according to claim 1 , wherein the carbon particles (ii) have an average aspect ratio of less than 3:1.
12. An electrode according to claim 1 , wherein the active layer comprises from 1 to 30 wt % of the porous particles (i).
13. An electrode according to claim 1 , wherein the active layer has an inter-particle porosity of no more than 30%.
14. An electrode according to claim 1 , wherein the percent average cross-sectional area of the active layer occupied by the porous particles (i) is in the range of from 1% to 25%.
15. An electrode according to claim 1 , wherein the active layer comprises a binder in an amount of from 0.5 to 20 wt %, based on the total weight of the active layer.
16. An electrode according to claim 1 , wherein the active layer comprises one or more conductive additives in a total amount of from 0.5 to 20 wt %, based on the total weight of the active layer.
17. An electrode according to claim 1 , wherein the active layer has a thickness in the range of from 15 μm to 200 μm.
18. An electrode according to claim 1 , wherein the intra-particle porosity of the porous particles (i) is at least 3%.
19. An electrode according to claim 1 , wherein the electroactive material in the porous particles (i) is amorphous or nanocrystalline having a crystallite size of less than 60 nm.