Electroactive Materials for Metal-Ion Batteries

Abstract

A particulate material is provided consisting of a plurality of porous particles comprising an electroactive material selected from silicon, germanium or a mixture thereof (especially a silicon-aluminium alloy), wherein the porous particles have a D.sub.50 particle diameter in the range of 0.5 to 7 m, an intra-particle porosity between 50 and 90%, and a pore diameter distribution having at least one peak in the range of 30 to 400 nm as determined by mercury porosimetry. Also provided are electrodes (especially anodes) and electrode compositions comprising the particulate material, a rechargeable metal-ion battery (especially a Li-ion battery) comprising the particulate material, and a process for the preparation of the particulate material. It is suggested that the claimed particulate material can be repeatedly lithiated without fracturing, allows easy access to the electrolyte and can be easily dispersed in an electrode slurry.

Claims

1. A particulate material consisting of a plurality of porous particles comprising an electroactive material selected from silicon, germanium or a mixture thereof, wherein the porous particles have a D.sub.50 particle diameter in the range of 0.5 to 7 m, an intra-particle porosity in the range of from 50 to 90%, and a pore diameter distribution having at least one peak in the range of from 30 nm to less than 400 nm as determined by mercury porosimetry.

2. A particulate material according to claim 1, wherein the wherein the porous particles have a D.sub.50 particle diameter in the range of 1 to 7 m.

3. A particulate material according to claim 1 or claim 2, wherein the particulate material comprises at least 60 wt %, preferably at least 70 wt %, more preferably at least 75 wt %, more preferably at least 80 wt %, and most preferably at least 85 wt % of the electroactive material.

4. A particulate material according to any one of the preceding claims, wherein the electroactive material comprises at least 90 wt %, preferably at least 95 wt %, more preferably at least 98 wt %, more preferably at least 99 wt % silicon.

5. A particulate material according to any one of the preceding claims, wherein the particulate material comprises a minor amount of one or more additional elements selected from aluminium, antimony, copper, magnesium, zinc, manganese, chromium, cobalt, molybdenum, nickel, beryllium, zirconium, iron, sodium, strontium, phosphorus, tin, ruthenium, gold, silver, and oxides thereof.

6. A particulate material according to claim 5, wherein the particulate material comprises a minor amount of one or more of aluminium, nickel, silver or copper, preferably aluminium.

7. A particulate material according to claim 6, wherein the particulate material comprises at least 60 wt % silicon and up to 40 wt % aluminium, preferably at least 70 wt % silicon and up to 30 wt % aluminium, more preferably at least 75 wt % silicon and up to 25 wt % aluminium, more preferably at least 80 wt % silicon and up to 20 wt % aluminium, more preferably at least 85 wt % silicon and up to 15 wt % aluminium, more preferably at least 90 wt % silicon and up to 10 wt % aluminium, and most preferably at least 95 wt % silicon and up to 5 wt % aluminium.

8. A particulate material according to claim 6 or claim 7, wherein the particulate material comprises at least 0.01 wt % aluminium, at least 0.1 wt % aluminium, at least 0.5 wt % aluminium, at least 1 wt % aluminium, at least 2 wt % aluminium, or at least 3 wt % aluminium.

9. A particulate material according to any one of the preceding claims, wherein the porous particles have a D.sub.50 particle diameter of at least 1.5 m, at least 2 m, at least 2.5 m, or at least 3 m.

10. A particulate material according to any one of the preceding claims, wherein the porous particles have a D.sub.50 particle diameter of no more than 6 m, no more than 5 m, no more than 4.5 m, no more than 4 m, or no more than 3.5 m.

11. A particulate material according to any one of the preceding claims, wherein the porous particles have a D.sub.10 particle diameter of at least 500 nm, and preferably at least 800 nm.

12. A particulate material according to any one of the preceding claims, wherein the porous particles have a D.sub.90 particle diameter of no more than 12 m, preferably no more than 10 m, and more preferably no more than 8 m.

13. A particulate material according to any one of the preceding claims, wherein the porous particles have a D.sub.99 particle diameter of no more than 20 m, more preferably no more than 15 m, and most preferably no more than 12 m.

14. A particulate material according to any one of the preceding claims, wherein the porous particles have a particle size distribution span of 5 or less, preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less.

15. A particulate material according to any one of the preceding claims, wherein the porous particles have an intra-particle porosity of at least 60%, preferably at least 65%, more preferably at least 70%, more preferably at least 75%, and most preferably at least 78%.

16. A particulate material according to any one of the preceding claims, wherein the porous particles have an intra-particle porosity of no more than 87%, preferably no more than 86% and more preferably no more than 85%.

17. A particulate material according to any one of the preceding claims, wherein the particulate material has a pore diameter distribution having at least one peak at a pore size less than 350 nm, preferably less than 300 nm, more preferably less than 250 nm, and most preferably less than 200 nm, as determined by mercury porosimetry.

18. A particulate material according to any one of the preceding claims, wherein the particulate material has a pore diameter distribution having at least one peak at a pore size of more than 50 nm, preferably more than 60 nm, and more preferably more than 80 nm, as determined by mercury porosimetry.

19. A particulate material according to any one of the preceding claims, wherein the porous particles are spheroidal particles having an average sphericity S.sub.av of at least 0.70, preferably at least 0.85, more preferably at least 0.90, preferably at least 0.92, more preferably at least 0.93, more preferably at least 0.94, more preferably at least 0.95, more preferably at least 0.96, more preferably at least 0.97, more preferably at least 0.98 and most preferably at least 0.99.

20. A particulate material according to any one of the preceding claims, wherein the porous particles have an average aspect ratio of less than 3:1, preferably no more than 2.5:1, more preferably no more than 2:1, preferably no more than 1.8:1, more preferably no more than 1.6:1, more preferably no more than 1.4:1 and most preferably no more than 1.2:1.

21. A particulate material according to any one of the preceding claims, having a BET surface area of less than 300 m.sup.2/g, preferably less than 250 m.sup.2/g, more preferably less than 200 m.sup.2/g, more preferably less than 150 m.sup.2/g, and most preferably less than 120 m.sup.2/g.

22. A particulate material according to any one of the preceding claims, having a BET surface area of at least 10 m.sup.2/g, at least 15 m.sup.2/g, at least 20 m.sup.2/g, or at least 50 m.sup.2/g.

23. A particulate material according to any one of the preceding claims, wherein the porous particles comprise a network of interconnected irregular elongate structural elements, preferably wherein the particles comprise structural elements having an aspect ratio of at least 2:1 and more preferably at least 5:1.

24. A particulate material according to claim 23, wherein the porous particles comprise structural elements having a smallest dimension less than 300 nm, preferably less than 200 nm, more preferably less than 150 nm, and a largest dimension at least twice, and preferably at least five times the smallest dimension.

25. A particulate material according to claim 23 or claim 24, wherein the porous particles comprise structural elements having a smallest dimension of at least 10 nm, preferably at least 20 nm, preferably at least 30 nm.

26. A process for the preparation of a particulate material consisting of a plurality of porous particles comprising an electroactive material, the process comprising the steps of: (a) providing a plurality of alloy particles, wherein the alloy particles are obtained by cooling a molten alloy comprising: (i) from 11 to 30 wt % of an electroactive material component selected from silicon, germanium and mixtures thereof, and (ii) a matrix metal component, wherein said alloy particles have a D.sub.50 particle diameter in the range of 0.5 to 7 m, and wherein said alloy particles comprise discrete electroactive material containing structures dispersed in the matrix metal component; (b) leaching the alloy particles from step (a) to remove at least a portion of the matrix metal component and to at least partially expose the electroactive material containing structures; wherein the porous particles comprise no more than 40% by weight of the matrix metal component.

27. A process according to claim 26, wherein the alloy particles in step (a) have a D.sub.50 particle diameter in the range of 1 to 7 m.

28. A process according to claim 26 or claim 27, wherein the alloy particles have a D.sub.50 particle diameter of at least 1.5 m, preferably at least 2 m, more preferably at least 2.5 m, and most preferably at least 3 m.

29. A process according to any one of claims 26 to 28, wherein the alloy particles have a D.sub.50 particle diameter of no more than 6 m, preferably no more than 5 m, more preferably no more than 4.5 m, more preferably no more than 4 m, and most preferably no more than 3.5 m.

30. A process according to any one of claims 26 to 29, wherein the alloy particles have a D.sub.10 particle diameter of at least 500 nm, preferably at least 800 nm.

31. A process according to any one of claims 26 to 30, wherein the alloy particles have a D.sub.90 particle diameter of no more than 12 m, preferably no more than 10 m, and more preferably no more than 8 m.

32. A process according to any one of claims 26 to 31, wherein the alloy particles have a D.sub.99 particle diameter of no more than 20 m, more preferably no more than 15 m, and most preferably no more than 12 m.

33. A process according to any one of claims 26 to 32, wherein the alloy particles have a particle size distribution span of 5 or less, preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less.

34. A process according to any one of claims 26 to 33, wherein the alloy particles have an average sphericity S.sub.av of at least 0.70, preferably at least 0.85, more preferably at least 0.90, preferably at least 0.92, more preferably at least 0.93, more preferably at least 0.94, more preferably at least 0.95, more preferably at least 0.96, more preferably at least 0.97, more preferably at least 0.98, and most preferably at least 0.99.

35. A process according to any one of claims 26 to 34, wherein the alloy particles have an average aspect ratio of less than 3:1, preferably no more than 2.5:1, more preferably no more than 2:1, preferably no more than 1.8:1, more preferably no more than 1.6:1, more preferably no more than 1.4:1 and most preferably no more than 1.2:1.

36. A process according to any one of claims 26 to 35, wherein the electroactive material component of the alloy particles comprises at least 90 wt %, preferably at least 95 wt %, more preferably at least 98 wt %, more preferably at least 99 wt % silicon.

37. A process according to any one of claims 26 to 36, wherein the alloy particles comprise at least 11.2 wt %, preferably at least 11.5 wt %, more preferably at least 11.8 wt %, more preferably at least 12 wt %, more preferably at least 12.2 wt % of the electroactive material component.

38. A process according to any one of claims 26 to 37, wherein the alloy particles comprise less than 27 wt %, preferably less than 24 wt %, more preferably less than 18 wt % of the electroactive material component.

39. A process according to any one of claims 26 to 38, wherein the matrix metal component of the alloy particles is selected from aluminium, antimony, copper, magnesium zinc, manganese, chromium, cobalt, molybdenum, nickel, beryllium, zirconium, iron, tin, ruthenium, silver, gold and combinations thereof.

40. A process according to claim 39, wherein the matrix metal component of the alloy particles comprises at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt %, more preferably at least 90 wt %, and most preferably at least 95 wt % of one or more of aluminium, nickel, silver or copper, preferably of aluminium.

41. A process according to claim 40, wherein the electroactive material component of the alloy particles comprises at least 90 wt %, more preferably at least 95 wt %, preferably at least 98 wt %, more preferably at least 99 wt % silicon and the matrix metal component of the alloy particles comprises at least 90 wt %, more preferably at least 95 wt % aluminium.

42. A process according to any one of claims 26 to 41, wherein the particulate material comprises no more than 30 wt %, more preferably no more than 25 wt %, more preferably no more than 20 wt %, more preferably no more than 15 wt %, more preferably no more than 10 wt %, and most preferably no more than 5 wt % of the matrix metal component, relative to the total weight of the particulate material.

43. A process according to any one of claims 26 to 42, wherein the particulate material comprises residual matrix metal component in an amount of at least 0.01 wt %, at least 0.1 wt %, at least 0.5 wt %, at least 1 wt %, at least 2 wt %, or at least 3 wt % relative to the total weight of the particulate material.

44. A process according to any one of claims 26 to 43 wherein the alloy particles in step (a) are obtained by cooling a molten alloy from the liquid state to the solid state at a cooling rate of at least 510.sup.4 K/s, or at least 110.sup.5 K/s.

45. A particulate material consisting of a plurality of porous particles comprising an electroactive material, wherein the particulate material is obtainable by a process as defined in any one of claims 26 to 44.

46. A particulate material according to claim 45, wherein the particulate material is as defined in any one of claims 1 to 25.

47. A composition comprising a particulate material as defined in any one of claims 1 to 25, 45 and 46, and at least one other component.

48. A composition according to claim 47, which is an electrode composition comprising a particulate material as defined in any one of claims 1 to 25, 45 and 46, and at least one other component selected from: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material.

49. An electrode composition according to claim 48, comprising at least one additional particulate electroactive material.

50. An electrode composition according to claim 49, wherein the at least one additional particulate electroactive material is selected from graphite, hard carbon, silicon, germanium, gallium, aluminium and lead.

51. An electrode composition according to claim 50, wherein the at least one additional particulate electroactive material is graphite.

52. An electrode composition according to any one of claims 49 to 51, wherein the at least one additional particulate electroactive material is in the form of spheroidal particles having an average sphericity of at least 0.70, preferably at least 0.85, more preferably at least 0.90, more preferably at least 0.92, more preferably at least 0.93, more preferably at least 0.94, and most preferably at least 0.95.

53. An electrode composition according to any one of claims 49 to 52, wherein the at least one additional particulate electroactive material has an average aspect ratio of less than 3:1, preferably no more than 2.5:1, more preferably no more than 2:1, more preferably no more than 1.8:1, more preferably no more than 1.6:1, more preferably no more than 1.4:1 and most preferably no more than 1.2:1.

54. An electrode composition according to any one of claims 49 to 53, wherein the at least one additional particulate electroactive material has a D.sub.50 particle diameter in the range of from 10 to 50 m, preferably from 10 to 40 m, more preferably from 10 to 30 m, more preferably from 10 to 25 m, and most preferably from 15 to 25 m.

55. An electrode composition according to any one of claims 49 to 54, wherein the at least one additional particulate electroactive material has a D.sub.10 particle diameter of at least 5 m, preferably at least 6 m, more preferably at least 7 m, more preferably at least 8 m, more preferably at least 9 m, and still more preferably at least 10 m.

56. An electrode composition according to any one of claims 49 to 55, wherein the at least one additional particulate electroactive material has a D.sub.90 particle diameter of no more than 100 m, preferably no more than 80 m, more preferably no more than 60 m, more preferably no more than 50 m, and most preferably no more than 40 m.

57. An electrode composition according to any one of claims 49 to 56, wherein the ratio of the at least one additional particulate electroactive material to the particulate material of the invention is in the range of from 50:50 to 99:1 by weight, preferably from 60:40 to 98:2 by weight, more preferably 70:30 to 97:3 by weight, more preferably 80:20 to 96:4 by weight, and most preferably 85:15 to 95:5 by weight.

58. An electrode composition according to any one of claims 49 to 57, wherein the at least one additional particulate electroactive material and the particulate material of the invention together constitute at least 50 wt %, preferably at least 60% by weight of, more preferably at least 70 wt %, and most preferably at least 80 wt %, for example at least 85 wt %, at least 90 wt %, or at least 95 wt % of the total weight of the electrode composition.

59. An electrode composition according to any one of claims 48 to 58, comprising a binder, preferably in an amount of from 0.5 to 20 wt %, more preferably 1 to 15 wt % and most preferably 2 to 10 wt %, based on the total weight of the electrode composition.

60. An electrode composition according to any one of claims 48 to 59, comprising one or more conductive additives, preferably in a total amount of from 0.5 to 20 wt %, more preferably 1 to 15 wt % and most preferably 2 to 10 wt %, based on the total weight of the electrode composition.

61. An electrode comprising a particulate material as defined in any one of claims 1 to 25, 45 and 46 in electrical contact with a current collector.

62. An electrode according to claim 61, wherein the particulate material is in the form of an electrode composition as defined in any one of claims 48 to 60.

63. A rechargeable metal-ion battery comprising: (i) an anode, wherein the anode comprises an electrode as described in claim 61 or claim 62; (ii) a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions; and (iii) an electrolyte between the anode and the cathode.

64. Use of a particulate material as defined in any one of claims 1 to 25, 45 and 46 as an anode active material.

65. Use according to claim 64, wherein the particulate material is in the form of an electrode composition as defined in any one of claims 48 to 60.

Description

[0119] The invention will now be described by way of examples and the accompanying figures, in which:

[0120] FIG. 1 shows the pore diameter distribution of the particulate material obtained according to Example 1, as determined by mercury porosimetry.

[0121] FIG. 2 is a scanning electron micrograph image of a porous particle having diameter of ca. 4.5 m and obtained according to Example 1.

[0122] FIG. 3 is a close up of the particle of FIG. 2 showing the surface morphology.

[0123] FIG. 4 shows the overlaid pore diameter distributions of the particulate materials obtained according to Examples 1 and 2, as determined by mercury porosimetry.

[0124] FIG. 5 is a scanning electron micrograph image of a porous particle having diameter of ca. 3.5 m and obtained according to Example 2.

[0125] FIG. 6 is a close up of the particle of FIG. 2 showing the surface morphology.

[0126] FIG. 7 is a scanning electron micrograph image of a porous particle obtained according to Example 3.

[0127] FIG. 8 shows the pore diameter distribution of the particulate material obtained according to Example 3 and Comparative Example 1, as determined by mercury porosimetry.

EXAMPLES

[0128] General Procedure for Leaching of Alloy Particles

[0129] Alloy particles (5 g) are slurried in deionised water (50 mL) and the slurry is added to a 1 L stirred reactor containing aqueous HCl (450 mL, 6 M). The reaction mixture is stirred at ambient temperature for 20 minutes. The reaction mixture is then poured into deionised water (1 L) and the solid product is isolated by Buchner filtration. The product is dried in an oven at 75 C. before analysis.

Example 1

[0130] Particles of a silicon-aluminium alloy (12.9 wt % silicon) were leached according to the general procedure set out above. The alloy particles were obtained by gas atomisation of the molten alloy with a cooling rate of >10.sup.5 K/s followed by classification of the gas atomised product to obtain alloy particles having a D.sub.50 particle diameter of 3.5 m, a D.sub.10 particle diameter of 1.8 m, and a D.sub.90 particle diameter of 6.1 m. The alloy particles contained iron and other metallic impurities in a total amount of less than 0.5 wt %.

[0131] The porous particles obtained after the leaching process had a D.sub.50 particle diameter of 3.4 m, a D.sub.10 particle diameter of 1.8 m, and a D.sub.90 particle diameter of 6.0 m. The particle size distribution span was 1.2. The residual aluminium content of the porous particles was 5.2 wt % based on the total weight of the porous particles.

[0132] The pore diameter distribution of the porous particles is shown in FIG. 1. An intra-particle peak is observed at a pore diameter of 123 nm and an inter-particle peak is observed at a pore diameter of 505 nm. The position of the inter-particle peak is in close agreement with the inter-particle pore diameter of 525 nm calculated from close-packed spheres of diameter 3.4 m. The BET value of the leached product was 190 m.sup.2/g. SEM images of a particle obtained according to Example 1 are provided in FIGS. 2 and 3.

Example 2

[0133] Particles of a silicon-aluminium alloy (11.9 wt % silicon) were leached according to the general procedure set out above. The alloy particles were obtained by gas atomisation of the molten alloy with a cooling rate of >10.sup.5 K/s followed by classification of the gas atomised product to obtain alloy particles having a D.sub.50 particle diameter of 5.1 m, a D.sub.10 particle diameter of 2.8 m, and a D.sub.90 particle diameter of 9.3 m. The alloy particles contained iron and other metallic impurities in a total amount of less than 0.5 wt %.

[0134] The porous particles obtained after the leaching process had a D.sub.50 particle diameter of 5.0 m, a D.sub.10 particle diameter of 2.6 m, and a D.sub.90 particle diameter of 9.7 m. The particle size distribution span was 1.4. The residual aluminium content of the porous particles was 12.3 wt % based on the total weight of the porous particles.

[0135] The pore diameter distribution of the porous particles is shown in FIG. 4. An intra-particle peak is observed at a pore diameter of 150 nm and an inter-particle peak is observed at a pore diameter of 880 nm. The position of the inter-particle peak is in good agreement with the inter-particle pore diameter of 773nm calculated from close-packed spheres of diameter 3.4 m. The BET value of the leached product was 131 m.sup.2/g. SEM images of a particle obtained according to Example 2 are provided in FIGS. 5 and 6.

Example 3

[0136] A powder of particles of an aluminium-silicon alloy (12.6 wt % silicon) were leached according to the general procedure set out above. The alloy particles were obtained by gas atomisation of the molten alloy with a cooling rate of >10.sup.5 K/s followed by classification of the gas atomised product to obtain alloy particles having a D.sub.50 particle diameter of 3.7 m, a D.sub.10 particle diameter of 1.8 m, and a D.sub.90 particle diameter of 7.3 m, and a BET value of 1.5 m.sup.2/g. The alloy particles contained 0.15 wt % iron and other metallic and carbon impurities in a total amount of less than 0.05 wt %.

[0137] The porous particles obtained after the leaching process had a D.sub.50 particle diameter of 4.4 m, a D.sub.10 particle diameter of 1.7 m, and a D.sub.90 particle diameter of 7.1 m. The elemental composition of the porous particles was 5.3 wt % Al, 0.7 wt % Fe, the remainder being silicon and native oxide. The BET value of the leached porous particles was 125 m.sup.2/g.

[0138] FIG. 7 shows an SEM image of a particle obtained according to Example 3.

Comparative Example 1

[0139] Comparative porous particles were made by selecting and leaching larger alloy particles made using a similar gas-atomisation process with a lower particle cooling rate. The porous particles obtained after the leaching process had a D.sub.50 particle diameter of 10.4 m, a D.sub.10 particle diameter of 4.7 m, and a D.sub.90 particle diameter of 20 m. The residual aluminium content of the porous particles was 4.7 wt % with other metallic impurities being less than 0.5 wt % and the remainder being silicon and native oxide. The BET value of the porous particles was 114 m.sup.2/g.

[0140] The pore diameter distribution of the porous particles of Example 3 and Comparative Example 1 is shown in FIG. 8. As can be seen from the graph, the peak in the intra-particle pore-size distribution of Example 3 is 153 nm, smaller than that of Comparative Example 2 at 236 nm. In each case, the second peak at a higher pore size represents that of the inter-particle pore size distribution which is dependent on particle size.

Example 4

Process to Form Electrode and Coin Cell Comprising the Porous Particles

[0141] Coin test cells were made with electrodes comprising the porous particles of Example 3 or Comparative Example 1 as follows. A dispersion of conductive carbons (a mixture of carbon black, carbon fibres and carbon nanotubes) in water was mixed in a Thinky mixer with the porous particles and spheroidal MCMB (MesoCarbon MicroBead) graphite (D.sub.50=16.5 m, BET=2 m.sup.2/g). A CMC/SBR binder solution (CMC:SBR ratio of 1:1) was then mixed in to prepare a slurry with a solids content of 40 wt % and a weight ratio of the porous particles:MCMB graphite:CMC/SBR:conductive carbon of 3:89.5:2.5:5. The slurry was then coated onto a 10 m thick copper substrate (current collector) and dried at 50 C. for 10 minutes, followed by further drying at 120-180 C. for 12 hours to thereby form an electrode comprising an active layer on the copper substrate. Coin half cells were then made using circular electrodes of 0.8 cm radius cut from this electrode with a porous polyethylene separator, a lithium foil as the counter electrode and an electrolyte comprising 1M LiPF.sub.6 in a 7:3 solution of EC/FEC (ethylene carbonate/fluoroethylene carbonate) containing 3 wt % vinylene carbonate.

[0142] These half cells were used to measure the initial charge and discharge capacity and first cycle efficiency of the active layer and the expansion in thickness of the active layer at the end of the second charge (in the lithiated state). For expansion measurements, at the end of the second charge, the electrode was removed from the cell in a glove box and washed with DMC (dimethyl carbonate) to remove any SEI layer formed on the active materials. The electrode thickness was measured before cell assembly and then after disassembly and washing. The thickness of the active layer was derived by subtracting the known thickness of the copper substrate. The half cells were tested by applying a constant current of C/25, (wherein C represents the specific capacity of the electrode in mAh, and 25 refers to 25 hours), to lithiate the electrode comprising the porous particles, with a cut off voltage of 10 mV. When the cut off is reached, a constant voltage of 10 mV is applied with a cut off current of C/100. The cell is then rested for 1 hour in the lithiated state. The electrode is then delithiated at a constant current of C/25 with a cut off voltage of 1V and the cell is then rested for 1 hour. A constant current of C/20 is then applied to lithiate the cell a second time with a 10 mV cut off voltage, followed by a 10 mV constant voltage with a cut off current of C/80.

[0143] The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Porous particles Gravimetric Gravimetric Electrode used Energy Density Energy First thickness in negative (mAh/g) Density (mAh/g) Cycle Expansion electrode 1st charge 1st discharge Efficiency (%) Example 3 491 416 85% 46% Comparative 482 404 84% 62% Example 1

[0144] The values in the table are averages from three test cells of each type. It has been found that whilst the energy densities and first cycle efficiencies of both cells are similar, the expansion in thickness of the negative electrode comprising 3 wt % Example 3 porous particles is much less than for the electrode comprising 3 wt % Comparative Example 1 porous particles.