ELECTROACTIVE MATERIALS FOR METAL-ION BATTERIES

Abstract

This invention relates to particulate electroactive materials consisting of a plurality of composite particles, wherein the composite particles comprise a plurality of silicon nanoparticles dispersed within a conductive carbon matrix. The particulate material comprises 40 to 65 wt % silicon, at least 6 wt % and less than 20% oxygen, and has a weight ratio of the total amount of oxygen and nitrogen to silicon in the range of from 0.1 to 0.45 and a weight ratio of carbon to silicon in the range of from 0.1 to 1. The particulate electroactive materials are useful as an active component of an anode in a metal ion battery.

Claims

1. A method for preparing a particulate material consisting of a plurality of composite particles that comprise a plurality of silicon nanoparticles dispersed within a conductive pyrolytic carbon matrix, the method comprising the steps of: (a) milling a silicon starting material in the presence of a non-aqueous solvent to obtain a dispersion of silicon-containing nanoparticles having a D.sub.50 particle diameter in the range of 30 to 500 nm in the solvent; (b) contacting the dispersion of silicon nanoparticles in the solvent with a pyrolytic carbon precursor selected from one or more compounds comprising at least one oxygen or nitrogen atom; (c) removing the solvent to provide silicon nanoparticles coated with the pyrolytic carbon precursor; (d) optionally heating the coated silicon nanoparticles to a temperature of from 200 to 400° C. for a period of from 5 minutes to 10 hours before step (e); and (e) pyrolysing the coated silicon nanoparticles at a pyrolysis temperature in the range of from 600 to 1200° C. to form said plurality of composite particles that comprise a plurality of silicon nanoparticles dispersed within a conductive pyrolytic carbon matrix.

2. A method according to any of claim 1, wherein the pyrolytic carbon precursor is selected from one or more aromatic or aliphatic carbon-containing compounds comprising at least one oxygen or nitrogen atom.

3. A method according to claim 2, wherein the pyrolytic carbon precursor is selected from carbon-containing compounds comprising one or more electrophilic functional groups, preferably wherein the electrophilic functional groups comprise a carbonyl moiety, more preferably wherein the electrophilic functional groups are ester or amide groups.

4. A method according to claim 3, wherein the pyrolytic carbon precursor is a polymer or oligomer comprising a carbon-containing backbone and pendant electrophilic functional groups.

5. A method according to claim 4, wherein the pyrolytic carbon precursor is polyvinylpyrrolidone (PVP) or a copolymer of vinylpyrrolidone with one or more other ethylenically unsaturated monomers.

6. A method according to any of claims 3 to 5, wherein step (d) comprises crosslinking the silicon nanoparticles and the pyrolytic precursor by a reaction between nucleophilic functional groups on the surface of the silicon nanoparticles and the electrophilic functional groups of the pyrolytic carbon precursor.

7. A method according to claim 6, wherein step (d) comprises crosslinking the silicon nanoparticles and the pyrolytic carbon precursor under conditions such that the temperature increase in the reaction mixture is controlled to no more than 5° C./min and the maximum temperature of the crosslinking reaction is maintained below 270° C. for the duration of the crosslinking reaction.

8. A method according to claim 7, wherein the maximum temperature of the crosslinking reaction is maintained below 250° C., or below 240° C., or below 230° C., or below 220° C., or below 210° C., or below 200° C. for the duration of the crosslinking reaction.

9. A method according to any one of claims 6 to 8, wherein step (d) comprises mixing or agitating the coated silicon nanoparticles so as to ensure a homogenous reaction temperature during the crosslinking step.

10. A method according to any of claims 6 to 9, wherein step (d) is carried out in the presence of oxygen gas, optionally in the presence of air.

11. A method according to any of claims 6 to 10, wherein step (d) further comprises maintaining the coated silicon nanoparticles at a temperature in the range of from 100 to 400° C. for a period of time after completion of the crosslinking reaction.

12. A method according to any preceding claim, wherein the silicon-containing starting material is selected from metallurgical grade silicon.

13. A method according to any preceding claim, wherein the silicon starting material has a purity of at least 95 wt %, at least 98 wt % or at least 99 wt %.

14. A method according to any preceding claim, wherein the silicon starting material comprises no more than 4 wt % oxygen, no more than 2 wt % oxygen, no more than 1 wt % oxygen, or no more than 0.5 wt % oxygen.

15. A method according to any preceding claim, wherein the silicon-containing starting material consists of silicon microparticles having a D.sub.50 particle size in the range of from 1 to 100 μm, or in the range of from 2 to 50 μm, or in the range of from 2 to 20 μm, or in the range of from 2 to 10 μm.

16. A method according to any preceding claim, wherein the solvent is selected from alcohols and ketones, preferably wherein the solvent is isopropyl alcohol.

17. A method according to any preceding claim, wherein the dispersion of silicon nanoparticles is contacted with the pyrolytic carbon precursor in situ during the milling of silicon, such that steps (a) and (b) are carried out simultaneously.

18. A method according to any of claims 1 to 16, wherein steps (a) and (b) are carried out sequentially.

19. A method according to any preceding claim, wherein the solvent is removed in step (c) by rotary evaporation or by spray drying.

20. A method according to any preceding claim, wherein step (e) comprises heating the coated silicon nanoparticle to a pyrolysis temperature in the range of from 700 to 1150° C., or in the range of from 800 to 1100° C., or in the range of from 900 to 1050° C.

21. A method according to any preceding claim, wherein step (e) is carried out in an inert atmosphere, preferably under argon or nitrogen, more preferably under nitrogen.

22. A method according to any preceding claim, further comprising the step of: (f) reducing the size of the composite particles from step (e).

23. A method according to any preceding claim, further comprising the step of: (g) sieving the composite particles from step (e) or step (f).

24. A method according to any preceding claim, further comprising the step of: (h) coating the composite particles from step (e), (f) or (g) with a carbon coating.

25. A method according to claim 24, wherein the carbon coating is obtained by a chemical vapour deposition (CVD) method.

26. A method according to any preceding claim, wherein the particulate material comprises 40 to 65 wt % silicon, or 43 to 65 wt % silicon, or 45 to 65 wt % silicon, or 48 to 62 wt % silicon, or from 50 to 60 wt % silicon, or from 52 to 58 wt % silicon.

27. A method according to any preceding claim, wherein the weight ratio of the total amount of oxygen and nitrogen to silicon in the particulate material is in the range of from 0.1 to 0.45, or from 0.1 to 0.42, or from 0.1 to 0.4, or from 0.1 to 0.38, or from 0.1 to 0.35.

28. A method according to any preceding claim, wherein the weight ratio of the total amount of oxygen and nitrogen to silicon in the particulate material is at least 0.2, more preferably at least 0.24, more preferably at least 0.28, more preferably at least 0.3, more preferably at least 0.32, more preferably at least 0.34.

29. A method according to any preceding claim, wherein the particulate material comprises at least 80 wt % in total of silicon, carbon, oxygen and nitrogen, at least 85 wt % in total of silicon, carbon, oxygen and nitrogen, at least 90 wt % in total of silicon, carbon, oxygen and nitrogen, or at least 95 wt % in total of silicon, carbon, oxygen and nitrogen, at least 98 wt % in total in total of silicon, carbon, oxygen and nitrogen, or at least 99 wt % in total of silicon, carbon, oxygen and nitrogen.

30. A method according to any preceding claim, wherein the weight ratio of carbon to silicon in the particulate material is in the range of 0.1 to 1.

31. A method according to claim 30, wherein the weight ratio of carbon to silicon in the particulate material is at least 0.15, at least 0.2, at least 0.25, or at least 0.3.

32. A method according to claim 30 or claim 31, wherein the weight ratio of carbon to silicon in the particulate material is no more than 0.8, no more than 0.7, no more than 0.6, no more than 0.55, no more than 0.5, or no more than 0.45.

33. A method according to any preceding claim, wherein the weight ratio of carbon to the total amount of oxygen and nitrogen in the particulate material is at least 0.7, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95.

34. A method according to any preceding claim, comprising at least 8 wt % oxygen, or at least 10 wt % oxygen, or at least 12 wt % oxygen, or at least 15 wt % oxygen.

35. A method according to any preceding claim, wherein the particulate material comprises 2 to 6 wt % nitrogen, more preferably from 2.5 to 5 wt % nitrogen, more preferably from 3 to 4.5 wt % nitrogen, and most preferably from 3.5 to 4.5 wt % nitrogen.

36. A method according to any preceding claim, wherein the particulate material comprises at least 10 wt % carbon, at least 15 wt % carbon, or at least 18 wt % carbon.

37. A method according to any preceding claim, wherein the particulate material comprises no more than 35 wt % carbon, no more than 30 wt % carbon, no more than 28 wt % carbon, or no more than 25 wt % carbon.

38. A particulate material consisting of a plurality of composite particles, wherein the composite particles comprise a plurality of silicon nanoparticles dispersed within a conductive carbon matrix, wherein: the silicon nanoparticles comprise a nanoparticle core and a nanoparticle surface, wherein the nanoparticle surface comprises a compound of oxygen or a compound of nitrogen or a mixture thereof disposed between the nanoparticle core and the conductive carbon matrix; the particulate material comprises 40 to 65 wt % silicon; the particulate material comprises at least 6 wt % and less than 20 wt % oxygen; the weight ratio of the total amount of oxygen and nitrogen to silicon in the particulate material is in the range of from 0.1 to 0.45; and the weight ratio of carbon to silicon in the particulate material is in the range of from 0.1 to 1.

39. A particulate material consisting of a plurality of composite particles, wherein the composite particles comprise a plurality of silicon nanoparticles dispersed within a conductive carbon matrix, wherein: the silicon nanoparticles comprise a nanoparticle core and a nanoparticle surface, wherein a plurality of bridging oxygen atoms and/or a plurality or bridging nitrogen atoms are disposed between the nanoparticle surface and at least a portion of the conductive carbon matrix such that the conductive carbon matrix is chemically bonded to the nanoparticle surface; and the particulate material comprises 40 to 65 wt % silicon; the particulate material comprises at least 6 wt % and less than 20 wt % oxygen; the weight ratio of the total amount of oxygen and nitrogen in the particulate material to silicon in the particulate material is in the range of from 0.1 to 0.45; and the weight ratio of carbon to silicon in the particulate material is in the range of from 0.1 to 1.

40. A particulate material according to claim 38 or claim 39, comprising 43 to 65 wt % silicon, or 45 to 65 wt % silicon, or 48 to 62 wt % silicon, or 50 to 60 wt % silicon, or 52 to 58 wt % silicon.

41. A particulate material according to any of claims 38 to 40, wherein the weight ratio of the total amount of oxygen and nitrogen to silicon in the particulate material is no more than 0.42, or no more than 0.4, or no more than 0.38, or no more than 0.35.

42. A particulate material according to any of claims 38 to 41, wherein the weight ratio of the total amount of oxygen and nitrogen to silicon in the particulate material is at least 0.2, more preferably at least 0.24, more preferably at least 0.28, more preferably at least 0.3, more preferably at least 0.32, more preferably at least 0.34.

43. A particulate material according to any of claims 38 to 42, comprising at least 80 wt % in total of silicon, carbon, oxygen and nitrogen, at least 85 wt % in total of silicon, oxygen, nitrogen and carbon, or at least 90 wt % in total of silicon, oxygen, nitrogen and carbon, or at least 95 wt % in total of silicon, oxygen, nitrogen and carbon, at least 98 wt % in total of silicon, oxygen, nitrogen and carbon, or at least 99 wt % in total of silicon, oxygen, nitrogen and carbon.

44. A particulate material according to any of claims 38 to 43, wherein the weight ratio of carbon to silicon is at least 0.15, at least 0.2, at least 0.25, or at least 0.3.

45. A particulate material according to any of claims 38 to 44, wherein the weight ratio of carbon to silicon is no more than 0.8, no more than 0.7, no more than 0.6, no more than 0.55, no more than 0.5, no more than 0.45.

46. A particulate material according to any of claims 38 to 45, wherein the weight ratio of carbon to the total amount of oxygen and nitrogen in the particulate material is at least 0.7, or at least 0.8, or at least 0.85, or at least 0.9, or at least 0.95.

47. A particulate material according to any of claims 38 to 46, comprising at least 8 wt % oxygen, or at least 10 wt % oxygen, or at least 12 wt % oxygen, or at least 15 wt % oxygen.

48. A particulate material according to any of claims 38 to 47, comprising from 2 to 6 wt % nitrogen, more preferably from 2.5 to 5 wt % nitrogen, more preferably from 3 to 4.5 wt % nitrogen, and most preferably from 3.5 to 4.5 wt % nitrogen.

49. A particulate material according to any of claims 38 to 48, comprising at least 10 wt % carbon, at least 15 wt % carbon, or at least 18 wt % carbon.

50. A particulate material according to any of claims 38 to 49, comprising no more than 35 wt % carbon, no more than 30 wt % carbon, no more than 28 wt % carbon, or no more than 25 wt % carbon.

51. A particulate material according to any of claims 38 to 50, wherein the conductive carbon matrix is obtainable by the pyrolysis of a pyrolytic carbon precursor selected from one or more aromatic or aliphatic carbon-containing compounds comprising at least one oxygen or nitrogen atom.

52. A particulate material according to any of claims 38 to 51, wherein the composite particles have a D.sub.50 particle diameter in the range of 1 to 25 μm.

53. A particulate material according to claim 52, wherein the composite particles have a D.sub.50 particle diameter of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm.

54. A particulate material according to claim 52 or claim 53, wherein the composite particles have a D.sub.50 particle diameter of no more than 20 μm, no more than 18 μm, no more than 15 μm, no more than 12 μm, or no more than 10 μm.

55. A particulate material according to any of claims 38 to 54, wherein the composite particles have a D.sub.10 particle diameter of at least 0.5 μm, at least 1 μm, or at least 2 μm.

56. A particulate material according to any of claims 38 to 55, wherein the composite particles have a D.sub.90 particle diameter of no more than 40 μm, no more than 30 μm, no more than 25 μm, no more than 20 μm.

57. A particulate material according to any of claims 38 to 56, wherein the composite particles have a particle size distribution span of 5 or less, 4 or less, 3 or less, 2 or less, or 1.5 or less.

58. A particulate material according to any of claims 38 to 57, wherein the silicon nanoparticles have a D.sub.50 particle diameter in the range of 30 to 500 nm.

59. A particulate material according to claim 58, wherein the silicon nanoparticles have a D.sub.50 particle diameter of at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 75 nm, or at least 80 nm.

60. A particulate material according to claim 58 or claim 59, wherein the silicon nanoparticles have a D.sub.50 particle diameter of no more than 300 nm, or no more than 250 nm, or no more than 200 nm, or no more than 150 nm, or no more than 120 nm.

61. A particulate material according to any of claims 38 to 60, wherein the silicon nanoparticles have a D.sub.10 particle diameter of at least 10 nm, or at least 20 nm, or at least 40 nm, or at least 60 nm.

62. A particulate material according to any of claims 38 to 61, wherein the silicon nanoparticles have a D.sub.90 particle diameter of no more than 500 nm, no more than 400 nm, no more than 300 nm, or no more than 200 nm.

63. A particulate material according to any of claims 38 to 62, wherein the silicon nanoparticles have a particle size distribution span of 5 or less, 4 or less, 3 or less, 2 or less, or 1.5 or less.

64. A particulate material according to any of claims 38 to 63, comprising from 0.1 to 8 wt % of one or more elements selected from aluminium, iron, copper, gallium, magnesium, calcium, titanium and zirconium.

65. A particulate material according to any of claims 38 to 64, wherein the composite particles have an intra-particle porosity of no more than 30%, no more than 20%, no more than 10%, no more than 5%, or no more than 2%, as determined by mercury porosimetry.

66. A particulate material according to any of claims 38 to 65, wherein the composite particles have a BET surface area of no more than 100 m.sup.2/g, no more than 80 m.sup.2/g, no more than 60 m.sup.2/g, no more than 40 m.sup.2/g, no more than 30 m.sup.2/g, no more than 25 m.sup.2/g, no more than 20 m.sup.2/g, or no more than 15 m.sup.2/g.

67. A particulate material according to any of claims 38 to 66, wherein the composite particles have a BET surface area of at least 0.1 m.sup.2/g, at least 1 m.sup.2/g, at least 2 m.sup.2/g, or at least 5 m.sup.2/g.

68. A particulate material according to any of claims 38 to 67, having specific capacity on lithiation of 1200 to 2340 mAh/g.

69. A particulate material according to any of claims 38 to 68, wherein the silicon nanoparticles are characterised by a Si (111) crystal lattice spacing of at least 10 nm, at least 12 nm, at least 14 nm or at least 16 nm; and/or a Si (111) crystal lattice spacing of no more than 100 nm, no more than 50 nm, or no more than 35 nm, wherein the Si (111) crystal lattice spacing is measured by X-Ray Diffraction (XRD) techniques.

70. A particulate material consisting of a plurality of composite particles, wherein the particulate material is obtainable according to the method of any of claims 1 to 37.

71. A composition comprising a particulate material as defined in any of claims 38 to 70 and at least one other component.

72. A composition according to claim 71, which is an electrode composition comprising a particulate material as defined in any of claims 38 to 70, and at least one other component selected from: (i) a binder; (ii) a conductive additive; and (iii) an additional particulate electroactive material.

73. An electrode composition according to claim 72, wherein the particulate material constitutes from 0.5 to 80 wt %, from 1 to 70 wt %, from 1 to 60 wt %, from 2 to 50 wt %, from 2 to 40 wt %, from 2 to 30 wt %, or from 5 to 15 wt % of the total dry weight of the electrode composition.

74. An electrode composition according to claim 72 or claim 73, comprising at least one additional particulate electroactive material.

75. An electrode composition according to claim 74, wherein the at least one additional particulate electroactive material is selected from graphite, hard carbon, silicon, germanium, gallium, aluminium and lead.

76. An electrode composition according to any of claims 72 to 75, comprising a binder, optionally in an amount of from 0.5 to 20 wt %, 1 to 15 wt %, or 2 to 10 wt %, based on the total dry weight of the electrode composition.

77. An electrode composition according to any of claims 72 to 76, comprising one or more conductive additives, optionally in a total amount of from 0.5 to 20 wt %, 1 to 15 wt %, or 2 to 10 wt %, based on the total dry weight of the electrode composition.

78. An electrode comprising a particulate material as defined in any of claims 38 to 70 in electrical contact with a current collector.

79. An electrode according to claim 78, wherein the particulate material is in the form of an electrode composition as defined in any of claims 72 to 77.

80. A rechargeable metal-ion battery comprising: (i) an anode, wherein the anode comprises an electrode as described in claim 78 or claim 79; (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.

81. Use of a particulate material as defined in any of claims 38 to 70 as an anode active material.

82. Use according to claim 81, wherein the particulate material is in the form of an electrode composition as defined in any of claims 72 to 77.

Description

EXAMPLES

Example 1—Preparation of Particulate Silicon-Carbon Materials

[0176] The particulate silicon-carbon materials of samples 1 to 12 and control sample (CS1) were prepared using the silicon raw materials and the carbon sources in the amounts specified in Table 1.

[0177] The specified carbon source was dissolved in the specified solvent (approximately 40 mL) in a glass beaker. The particulate raw silicon material was added and the mixture was stirred to form a slurry. The resulting slurry was transferred to a Retsch ball mill cup containing 1 mm zirconium oxide grinding beads. The beaker was rinsed out with additional solvent (2×15 mL) and the washings were added to the Retsch ball mill cup. The lid was placed on the ball mill cup, which was weighed. A second ball mill cup was weighed and its weight was adjusted until it was the same as that of the first ball mill cup; this second cup acts as a counter-balance to the first during planetary ball milling. Both cups were secured to a Retsch PM200 planetary ball mill and the mixture was milled at 500 rpm for 30 minute intervals, rested for 15 minutes, reversing the direction of the mill and repeating these steps until a total active milling time for each sample as set out in Table 1 had been reached.

TABLE-US-00001 TABLE 1 Particulate Raw Silicon Active Sample BET/ Carbon Mass Si/ Mass C/ Milling Number D.sub.50 m.sup.2/g Purity Source g g Solvent time/mins 1  2.5 μm 6.62 99.9% 2,3-DHN.sup.1 5 10 IPA.sup.4 180 2  2.5 μm 6.62 99.9% DAN.sup.2 5 5 IPA 180 3  2.5 μm 6.62 99.9% 2,3-DHN 5 10 IPA 180 4  2.5 μm 6.62 99.9% 2,3-DHN 10 10 acetone 120 5  2.5 μm 6.62 99.9% 2,3-DHN 10 10 IPA 90 6 5.16 μm 1.99   99% 2,3-DHN 5 10 IPA 180 7 5.16 μm 1.99   99% 2,3-DHN 5 5 Acetone 120 8 5.16 μm 1.99   99% 2,3-DHN 10 10 IPA 180 9 5.16 μm 1.99   99% DAB.sup.3 5 5 IPA 180 10 5.16 μm 1.99   99% Naphthalene 5 5 IPA 180 11 5.16 μm 1.99   99% DAN 5 5 IPA 180 12 5.16 μm 1.99   99% 2,3-DHN 5 5 IPA 180 13   6 μm nd.sup.5 98.4% 2,3-DHN 5 5 IPA 180 14   6 μm nd.sup.  98.4% 2,3-DHN 5 5 Acetone 180 CS1 5.16 μm 1.99   99% — 5 5 IPA 180 .sup.12,3-dihydronaphthalene; .sup.22,3-diaminonaphthalene; .sup.31,2-diaminobenzene; .sup.4iso-propyl alcohol; .sup.5not determined

[0178] The milling cups were allowed to cool down. The milled materials were filtered through a 53 μm mesh and washed with additional solvent (about 150 mL) until the filtrate was pale. The solvent was removed from the filtrate under reduced pressure using a Buchi rotary evaporator. The resulting residue was further dried overnight in an oven at 75° C.

[0179] The oven-dried material was washed with 5×20 mL portions of acetone to remove any of the unbound carbon source. The acetone washed material was then subject to pyrolysis in an alumina crucible in a furnace using the pyrolysis protocols specified in Table 2. The materials were sealed in the alumina crucible under a flow of argon (1 L/min) and the furnace was programmed to heat to an initial temperature (T1) as specified in Table 2 at a rate of 5° C./minute. The crucible was maintained at this initial temperature for a first hold time (t1) as specified in Table 2 before ramping the temperature at a rate of 5° C./min to a final temperature (T2) as specified in Table 2 and holding the crucible at this temperature for a second hold time (t2) as specified in Table 2 before cooling to room temperature.

[0180] The pyrolysed material was removed from the crucible and micronized using a hand held micronizer for periods of 10 seconds up to a total micronization time of between 30 seconds and a minute. The micronized material was then dry milled using a Retsch PM200 planetary ball mill using the conditions specified in Table 2. The material was placed in the ball mill cup in the amount specified in Table 2 together with the required quantity of milling beads, milled at 500 rpm for 2 minutes, rested for 1 minute, changing the direction of the mill and repeating until the total active milling time as specified in Table 2 had been achieved.

TABLE-US-00002 TABLE 2 Dry Milling Protocol Pyrolysis Protocol 10 13 Active Sample T1/ t1/ T2/ T2/ mm mm Sample milling Number ° C. h ° C. h beads beads mass/g time/mins 1 300 1 1000 2 4 4 16 220 2 150 1 1000 2 8 8 15 120 3 300 1 1000 2 4 4 16 220 4 300 1 1000 2 4 4 5 180 5 300 1 1000 2 4 4 9 120 6 300 1 1000 2 4 4 14 75 7 300 1 1000 2 4 4 16 150 8 300 1 1000 2 4 4 12 150 9 150 1 1000 2 4 4 15 220 10 150 1 1000 2 4 4 10 150 11 300 1 1000 2 4 4 14 150 12 300 1 1000 2 4 4 14 150 13 300 1 1000 1 4 4 16 120 14 300 1 1000 1 4 4 11 120 CS1 150 1 1000 2 4 4 14 120

[0181] The particulate material was then subjected to particle size analysis using a Malvern Mastersizer 3000 instrument and elemental analysis using both ICP/MS and LECO techniques. The BET surface area value of the resulting particulate material was also determined using a Micromeritics Tristar II 3020 instrument and the results for samples 1 to 12 and comparative sample 1 are presented in Table 3.

TABLE-US-00003 TABLE 3 Elemental Elemental Sample Composition (LECO) Ratio Particle Size/μm BET/ Number Si % C % O % C/Si O/Si D.sub.10 D.sub.50 D.sub.90 m.sup.2/g 1 49.5 35.8 14.2 0.72 0.29 1 5 20 18 2 49 29.1 9.2 0.59 0.19 1 4 22 48 3 49.5 35.8 14.2 0.72 0.29 1 5 20 18 4 63.4 25.1 11.3 0.40 0.18 1 5 30 28 5 64.1 25.2 10.5 0.39 0.16 1 6 22 15 6 58.4 26.8 14.6 0.46 0.25 1 5 20 15 7 52.3 33.1 14.3 0.63 0.27 1 5 15 20 8 58.4 28 13.5 0.48 0.23 1 6 30 26 9 65.9 18.6 10.2 0.28 0.15 1 6 29 28 10 51.5 32.7 9.7 0.63 0.19 0.89 5.39 22.6 15 11 84 7.5 8.5 0.09 0.10 1 9 100 102 12 83.1 6.7 10.1 0.08 0.12 nd nd nd 134 CS1 80.8 8.4 10.8 0.10 0.13 1.25 11.2 56.5 73

Example 2—Preparation of Electrodes

[0182] Anodes having the composition specified in Table 4 were prepared from the materials of Examples 1 to 12 and control sample 1 (CS1) using the following method. Test coin cells were made with negative electrodes comprising the silicon-carbon particulate material prepared as described above. A dispersion of Carbon Super P (conductive carbon) and natural graphite (D.sub.50=2.85 μm) in CMC binder was mixed in a Thinky™ mixer. The silicon carbon particulate material was added to the mixture and mixed for 30 min in the Thinky™ mixer. SBR binder was then added to give a CMC:SBR ratio of 1:1, yielding a slurry with a weight ratio of particulate silicon-carbon:graphite:CMC/SBR:conductive carbon as set out in Table 4. The slurry was further mixed by magnetic stirring for one hour, then was coated onto a 10 μm 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. The active layer was calendared at 2T prior to cell manufacture.

TABLE-US-00004 TABLE 4 Anode Composition Sample wt % Si/C wt % wt % Carbon wt % Number product Graphite Super P binder 1 10 81 5 4 2 10 81 5 4 3 15 76 5 4 4 10 81 5 4 5 10 81 5 4 6 10 81 5 4 7 10 81 5 4 8 10 81 5 4 9 10 81 5 4 10 10 81 5 4 11 10 81 5 4 12 10 81 5 4 CS1 10 81 5 4

Example 3—Cell Manufacture and Cycling

Half Cell Manufacture

[0183] Coin half cells were made using circular electrodes of 0.8 cm radius cut from the electrode of example 2 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.

[0184] These half cells were used to measure the initial volumetric energy density (VED1), first cycle loss (FCL) and first delithiation capacity (DC1) of the active layer. The relevant values are listed in Table 5. 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/25 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/100.

Full Cell Manufacture

[0185] Full coin cells were made using circular negative electrodes of 0.8 cm radius cut from this electrode with a porous polyethylene separator and a lithium cobalt oxide positive electrode. The positive and negative electrodes were designed to form a balanced pair, such that the projected capacity ratio of the electrodes was around 1:1. An electrolyte comprising 1 M LiPF.sub.6 in a 7:3 solution of EMC/FEC (ethylene methyl carbonate/fluoroethylene carbonate) containing 3 wt % vinylene carbonate was then added to the cell before sealing.

[0186] The full coin cells were cycled as follows: A constant current was applied at a rate of C/25, to lithiate the anode, with a cut off voltage of 4.2 V. When the cut off was reached, a constant voltage of 4.2 V is applied until a cut off current of C/100 is reached. The cell was then rested for 1 hour in the lithiated state. The anode is then delithiated at a constant current of C/25 with a cut off voltage of 3.0 V. The cell was then rested for 1 hour. After this initial cycle, a constant current of C/2 was applied to lithiate the anode with a 4.2 V cut off voltage, followed by a 4.2 V constant voltage with a cut off current of C/40. The anode was then delithiated at a constant current of C/2 with a 3.0 V cut off. The cell was then rested for 5 minutes. This was then repeated for the desired number of cycles. The charge and discharge capacity at 100 cycles (DC100) and the capacity retention (CR100) was determined for each sample; the values are also listed in Table 5.

TABLE-US-00005 TABLE 5 Cell Cycling Properties Sample VED1 FCL DC1 DC100 CR100 Number (mAh/g) (%) (mAh/g) (mAh/g) (%) 1 429 21.2 403 322 0.80 2 468 29.4 386 302 0.78 3 479 27 406 310 0.76 4 441 23.4 432 309 0.72 5 465 24 449 308 0.69 6 303 26 355 284 0.80 7 497 30 312 265 0.85 8 505 24 390 286 0.73 9 358 26 402 273 0.68 10 481 32 296 nd nd 11 416 nd nd nd nd 12 265 nd nd nd nd CS1 360 25 437 265 0.61

[0187] FIG. 1 is a plot of capacity retention (y-axis) vs carbon:silicon ratio. It is observed that good capacity retention is observed when the carbon:silicon ratio is greater than 0.10. At a carbon:silicon ratio of 0.1 or below, the capacity retention is relatively poor. Ideally the carbon to silicon ratio in the particulate material is of the order of 0.4 to 0.65.

Example 4—Preparation of Particulate Silicon-Carbon Material

[0188] Isopropyl alcohol (IPA) was transferred into a Netzsch high-energy agitated bead mill containing 200 micron zirconium oxide grinding beads. The bead mill was then set to recirculate the IPA and silicon was slowly added to the solvent to create a silicon slurry of approx. 27% w/w. The slurry was then milled to a D.sub.90<800 nm while maintaining a slurry temperature less than 50° C. The particle size measurement was performed on a Malvern Mastersizer 3000. The resultant milled slurry was then discharged into a suitable container and the solid content was measured on a loss-on-drying (LOD) moisture analyser (typically ˜30% w/w). This slurry is referred to as ‘pre-milled’ silicon slurry.

[0189] The ‘pre-milled’ silicon slurry was then adjusted to 20% w/w solid content with IPA and charged into a Netzsch bead mill containing 50 micron zirconium oxide grinding beads. This slurry was then milled to a D.sub.98<188 nm while maintaining a slurry temperature less than 50° C. The particle size measurement was performed on a Malvern Mastersizer 3000. The resultant milled slurry was then discharged into a suitable container and the solid content was measured on a LOD moisture analyser (typically 27-30% w/w). This slurry is referred to as ‘nano-milled’ silicon slurry.

[0190] A 20% w/w polyvinylpyrrolidone (PVP) solution in IPA was prepared by dissolving PVP in IPA using an overhead stirrer. This was then measured for solid content using a LOD moisture analyser. This PVP solution was then combined with the ‘nano-milled’ silicon slurry at a solid weight ratio of 1 part silicon and 1.1 part PVP and mixed with an overhead stirrer until fully homogenized in a high pressure homogenizer. This homogenized Si:PVP slurry was then passed through a high pressure homogenizer under a pressure of approx. 1500 bar and collected in a suitable container. The solid content was then measured on a LOD moisture analyser (Sartorius MA37 at 100° C.) and adjusted to 20% w/w total solid content with IPA prior to spray drying.

[0191] Spray drying was performed on a ProCept 4M8Trix dryer with a Nitrogen closed loop. The homogenised Si/PVP/IPA slurry (410 g) was fed to the spray dryer at a rate of 10 g/min. The dried product was collected from the cyclone (71.2 g, 87% recovery) and found to have a D.sub.50=10.5 μm (Malvern Mastersizer/Aero) and a volatiles content of 7 wt %.

[0192] Further dried product was recovered from the drying chamber walls (10.9 g) but not combined with material from the cyclone.

[0193] The spray dried material (20 g batch size) was then charged into a 400 mL glass rotary furnace vessel and placed into a Carbolite HTR1100 rotary furnace. The material was then placed under a 0.2 ml/min flow of dry compressed air and rotated at approx. 0.75 rpm. This air flow and rotation was maintained throughout the process. The furnace was heated under controlled conditions to a maximum temperature of 270° C. at a rate of temperature increase of no more than 5° C./min and then held at this temperature for 4 hours in order to cross-link the PVP and the silicon. After cross-linking the material was left for approx. 2 hours to cool prior to discharging from the vessel. At this stage a ˜2 g sample was removed and the material composition was analysed using both ICP/MS and LECO techniques.

[0194] The cross-linked material was then placed in an alumina crucible and pyrolysed in a static Carbolite tube furnace under a flow nitrogen (0.6 L/min). The furnace was heated to 1170° C. at a rate of 5° C./min and then held at this temperature for 3 hours before cooling naturally (typically 10-15 hours).

[0195] The pyrolysed product is then sieved via a 38 micron mesh prior to use. The material is also fully characterized with respect to elemental composition (as per above) and surface area (BET), particle size and tap density. The BET is measured using a Micromeritics Tristar II 3020 instrument. The properties of the final product are provided below in Table 6.

Example 5—Preparation of Particulate Silicon-Carbon Material without Temperature Control

[0196] Example 5 was carried out in the manner described for Example 4, except that the cross-linking reaction was carried out in a static furnace and without controlling the maximum temperature of the cross-linking reaction. Due to the exothermic cross-linking reaction the internal temperature increased rapidly from 100° C. to well over 300° C. The properties of the final product are provided below in Table 6.

Example 6—Preparation of Carbon Coated Silicon-Carbon Composite Material Via CVD

[0197] 11.1 g of a silicon-carbon composite material prepared according to the method of Example 5 was charged to a tared quartz reaction vessel (400 ml/85 mm diam.) and heated to 900° C. under Argon (200 mL/min) in a Carbolite HTR1100 rotary furnace at 5° C./min. Oscillation was set at approx. 1/min. When the furnace had reached the target temperature, ethylene gas was admitted (20 mL/min) for 20 mins. The ethylene flow was then stopped and argon was allowed to flow for a further 5 mins, after which time the heating was stopped. The product was allowed to cool passively under argon while rotating until the internal temperature had dropped to 50° C. The reaction vessel was weighed and an approximate weight increase of 0.3 g (2.6%) was recorded. The product was collected (10.6 g) and the BET was found to have reduced from 5.0 to 3.4 m.sup.2/g. The properties of the final product are provided below in Table 6.

TABLE-US-00006 TABLE 6 Comparative Example 4 Example 5 Example 6 Surface Carbon 89.7% 86% 96.6% Characterisation Silicon 3.5% 4.63% 1.22% via XPS Silicon Oxides 1.6% 3.74% 0.82% Oxygen 4.6% 8.0% 1.8% Bulk Oxygen 15.38 16.4 16.4 Carbon 19.21 21.24 21.24 Silicon 56.22 55.09 55.09 Half cell First % 21.9 24.5 23.9 Cycle Loss Half Cell mAh/g 1647 1719 1691 Delithiation Capacity