ELECTRODES FOR METAL-ION BATTERIES

Abstract

An electrode for a metal-ion battery is provided wherein the active layer of the electrode comprises a plurality of porous particles comprising an electroactive material selected from silicon, 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.sub.50 particles size of the carbon particles to the D.sub.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.

Claims

1. An electrode for 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 an electroactive material selected from silicon, germanium, tin, aluminium and mixtures thereof, wherein the porous particles have a D.sub.50 particle diameter in the range of 0.5 to 18 μm, and an intra-particle porosity in the range of from 30 to 90%; and (ii) a plurality of carbon particles selected from one or more of graphite, soft carbon and hard carbon and having a D.sub.50 particle diameter in the range of from 1 to 50 μm wherein the active layer comprises at least 50% by weight of the carbon particles (ii), and wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is in the range of from 1.5 to 30.

2. An electrode according to claim 1, wherein the porous particles (i) comprise 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.

3. An electrode according to claim 2, wherein the porous particles (i) comprise 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 % silicon or tin.

4. An electrode according to claim 3, wherein the porous particles (i) comprise 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 % silicon.

5. An electrode according to claim 4, wherein the porous particles (i) comprise at least 60 wt % silicon or tin and up to 40 wt % aluminium and/or germanium, preferably at least 70 wt % silicon or tin and up to 30 wt % aluminium and/or germanium, more preferably at least 75 wt % silicon or tin and up to 25 wt % aluminium and/or germanium, more preferably at least 80 wt % silicon or tin and up to 20 wt % aluminium and/or germanium, more preferably at least 85 wt % silicon or tin and up to 15 wt % aluminium and/or germanium, more preferably at least 90 wt % silicon or tin and up to 10 wt % aluminium and/or germanium, and most preferably at least 95 wt % silicon or tin and up to 5 wt % aluminium and/or germanium.

6. An electrode according to claim 5, wherein the porous particles (i) comprise at least 0.01 wt % aluminium and/or germanium, at least 0.1 wt % aluminium and/or germanium, at least 0.5 wt % aluminium and/or germanium, at least 1 wt % aluminium, at least 2 wt % aluminium and/or germanium, or at least 3 wt % aluminium and/or germanium.

7. An electrode according to any one of the preceding claims, wherein 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.

8. An electrode according to claim 7, wherein the porous particles (i) comprise a minor amount of one or more of nickel, silver or copper.

9. An electrode according to any one of the preceding claims, wherein the D.sub.50 particle diameter of the porous particles (i) is at least 0.8 μm, at least 1 μm, at least 1.5 μm, at least 2 μm, at least 2.5 μm, or at least 3 μm.

10. An electrode according to any one of the preceding claims, wherein the D.sub.50 particle diameter of the porous particles (i) is no more than 15 μm, no more than 12 μm, no more than 10 μm, no more than 8 μm, no more than 7 μm, no more than 6.5 μm, no more than 6 μm, no more than 5.5 μm, no more than 5 μm, no more than 4.5 μm, no more than 4 μm, or no more than 3.5 μm.

11. An electrode according to any one of the preceding claims, wherein the porous particles (i) have a particle size distribution span of 5 or less, 4 or less, 3 or less, 2 or less or 1.5 or less.

12. An electrode according to any one of the preceding claims, wherein the average aspect ratio of the porous particles (i) is 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.

13. An electrode according to any one of the preceding claims, wherein the porous particles (i) 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.

14. An electrode according to any preceding claim, wherein the intra-particle porosity of the porous particles (i) is in the range of from 35 to 90%.

15. An electrode according to claim 14, wherein the intra-particle porosity of the porous particles (i) is in the range of from 40 to 90%.

16. An electrode according to claim 15, wherein the porous particles (i) have an intra-particle porosity of at least 45%, at least 50%, at least 60%, or at least 70%.

17. An electrode according to any one of the preceding claims, wherein the porous particles (i) have an intra-particle porosity of no more than 89%, preferably no more than 88%, more preferably no more than 87%, more preferably no more than 86%, and most preferably no more than 85%.

18. An electrode according to claim 17, wherein the porous particles (i) have an intra-particle porosity of no more than 80%, no more than 75%, no more than 70%, no more than 65%, no more than 60%, no more than 55% or no more than 50%.

19. An electrode according to any one of the preceding claims, wherein the porous particles (i) have 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.

20. An electrode according to any one of the preceding claims, wherein the porous particles (i) have a pore diameter distribution having at least one peak at a pore size of more than 50 nm, more preferably more than 60 nm, and most preferably more than 80 nm, as determined by mercury porosimetry.

21. An electrode according to any one of the preceding claims, wherein the porous particles (i) 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.

22. An electrode according to claim 21, wherein the porous particles (i) 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.

23. An electrode according to any one of the preceding claims, wherein the porous particles (i) have 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.

24. An electrode according to any one of the preceding claims, wherein the porous particles (i) have 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.

25. An electrode according to any one of the preceding claims, wherein the carbon particles (ii) are graphite particles, preferably mesophase graphite particles.

26. An electrode according to any one of the preceding claims, wherein the D.sub.50 particle diameter of the carbon particles (ii) is at least 2 μm, at least 5 μm, at least 7 μm, at least 8 μm, at least 10 μm, at least 12 μm, or at least 15 μm.

27. An electrode according to any one of the preceding claims, wherein the D.sub.50 particle diameter of the carbon particles (ii) is no more than 45 μm, no more than 40 μm, no more than 35 μm, no more than 30 μm, or no more than 25 μm.

28. An electrode according to any one of the preceding claims, wherein the carbon particles (ii) 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, and most preferably at least 0.95.

29. An electrode according to any one of the preceding claims, wherein the carbon particles (ii) have 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.

30. An electrode according to any one of the preceding claims, wherein the active layer comprises from 60 to 95 wt %, preferably from 70 to 95 wt %, and most preferably from 80 to 95 wt % of the carbon particles (ii).

31. An electrode according to any one of the preceding claims, wherein the active layer comprises from 1 to 30 wt % of the porous particles (i).

32. An electrode according to claim 31, wherein the active layer comprises at least 2 wt %, preferably at least 5 wt % and most preferably at least 8 wt % of the porous particles (i).

33. An electrode according to claim 31 or claim 32, wherein the active layer comprises no more than 25 wt %, preferably no more than 20 wt %, more preferably no more than 15 wt % of the porous particles (i).

34. An electrode according to any one of the preceding claims, wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is at least 2, at least 2.5, at least 3, at least 3.5, or at least 4.

35. An electrode according to any one of the preceding claims wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is no more than 25, no more than 20, no more than 15, or no more than 10.

36. An electrode according to any one of the preceding claims, wherein the active layer has an inter-particle porosity of no more than 30%, preferably no more than 25%, and more preferably no more than 20%.

37. An electrode according to any one of the preceding claims, wherein the active layer has an inter-particle porosity of at least 2%, preferably at least 5%, more preferably at least 10%.

38. An electrode according to any one of the preceding claims, wherein the active layer has a density in the range of from 1 to 2 g/cm.sup.3.

39. An electrode according to any one of the preceding claims, 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%, preferably from 2% to 20%, more preferably from 5% to 20% and most preferably from 5% to 15%.

40. An electrode according to any one of the preceding claims, wherein the percent average cross-sectional area of the active layer occupied by the carbon particles (ii) is in the range of from 40% to 85%, preferably from 45% to 85%, more preferably from 45% to 80% and most preferably from 45% to 75%.

41. An electrode according to any one of the preceding claims, wherein the percent average cross-sectional area of the active layer occupied by the intra-particle pores of the active layer is in the range of from 2% to 30%, preferably from 2% to 25%, more preferably from 5% to 25%, more preferably from 10 to 25% and most preferably from 10 to 20%.

42. An electrode according to any one of the preceding claims, wherein the active layer comprises 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 active layer.

43. An electrode according to any one of the preceding claims, wherein the active layer comprises 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 active layer.

44. An electrode according to any one of the preceding claims, wherein the active layer has a thickness in the range of from 15 μm to 2 mm, preferably 15 μm to 1 mm, preferably 15 μm to 500 μm, preferably 15 μm to 200 μm, preferably 20 μm to 100 μm, preferably 20 μm to 60 μm.

45. An electrode composition comprising: (i) a plurality of porous particles comprising an electroactive material selected from silicon, germanium, tin and mixtures thereof, wherein the porous particles have a D.sub.50 particle diameter in the range of 0.5 to 18 μm, and an intra-particle porosity in the range of from 30 to 90%, (ii) a plurality of carbon particles selected from graphite, soft carbon and hard carbon and having a D.sub.50 particle diameter in the range of from 1 to 50 μm; and wherein the electrode composition comprises at least 50% by weight of the carbon particles, based on the solids content of the electrode composition, and wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is in the range of from 1.5 to 30.

46. An electrode composition according to claim 45, wherein the porous particles (i) are as defined in any one of claims 2 to 24.

47. An electrode composition according to claim 45 or claim 46, wherein the carbon particles (ii) are as defined in any one of claims 25 to 29.

48. An electrode composition according to any one of claims 45 to 47, comprising from 60 to 95 wt %, preferably from 70 to 95 wt %, and most preferably from 80 to 95 wt % of the carbon particles (ii), based on the solids content of the electrode composition.

49. An electrode composition according to any one of claims 45 to 48, comprising at least 1 wt %, at least 5 wt %, or at least 8 wt % of the porous particles (i), based on the solids content of the electrode composition.

50. An electrode composition according to any one of claims 45 to 49, comprising no more than 30 wt %, no more than 25 wt %, no more than 20 wt %, or no more than 15 wt % of the porous particles (i), based on the solids content of the electrode composition.

51. An electrode according to any one of claims 45 to 50, wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is at least 2, at least 2.5, at least 3, at least 3.5, or at least 4.

52. An electrode according to any one of claims 45 to 51, wherein the ratio of the D.sub.50 particle diameter of the carbon particles (ii) to the D.sub.50 particle diameter of the porous particles (i) is no more than 25, no more than 20, no more than 15, or no more than 10.

53. An electrode composition according to any one of claims 45 to 52, 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 solids content of the electrode composition.

54. An electrode composition according to any one of claims 45 to 53, 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 solids content of the electrode composition.

55. An electrode composition according to any one of claims 45 to 54, in the form of a slurry further comprising a solvent.

56. A method of preparing an electrode, the method comprising: (i) preparing a slurry comprising an electrode composition as defined in claim 55; (ii) casting the slurry onto the surface of a current collector; and (iii) removing the solvent to form an active layer in electrical contact with the current collector.

57. A method of preparing an electrode, the method comprising: (i) preparing a slurry comprising an electrode composition as defined in claim 55; (ii) casting the slurry onto a template; (iii) removing the solvent to form a freestanding film or mat comprising the electrode composition; and (iv) attaching the freestanding film or mat from step (iii) to a current collector to form an active layer in electrical contact with the current collector.

58. A method according to claim 56 or claim 57, further comprising the step of densifying the active layer to obtain an active layer density in the range of from 1 to 2 g/cm.sup.3.

59. A rechargeable metal-ion battery comprising: (i) an anode, wherein the anode comprises an electrode as described in any one of claims 1 to 44; (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.

60. Use of an electrode composition as defined in any one of claims 45 to 55 as an anode active material.

Description

[0169] The invention is demonstrated by the following examples and the accompanying figures, in which:

[0170] FIG. 1 is a plot of the Volumetric Energy Density in mAh/cm.sup.3 vs the Graphite:Silicon D.sub.50 particle diameter ratio for each of the half cells of Examples 7a to 7e and Comparative Examples 8a and 8b.

[0171] FIG. 2 is a plot of the Expansion in anode thickness (as a % increase of the initial thickness before lithiation) vs the Graphite:Silicon D.sub.50 particle diameter ratio for each of the half cells of Examples 7a to 7e and Comparative Examples 8a and 8b.

EXAMPLES

General Procedure for Leaching of Alloy Particles

[0172] Gas atomised 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 up to 50° C. 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

[0173] 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 ca. 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 10.2 μm, a D.sub.10 particle diameter of 5.2 μm, and a D.sub.90 particle diameter of 18.4 μm. The alloy particles contained iron and other metallic impurities in a total amount of less than 0.5 wt %.

[0174] The porous particles obtained after the leaching process had a D.sub.50 particle diameter of 10.4 μm, a D.sub.10 particle diameter of 4.7 μm, and a D.sub.90 particle diameter of 20 μm. The residual aluminium content of the porous particles was 4.7 wt % based on the total weight of the porous particles and the BET value was 114 m.sup.2/g.

[0175] From mercury porosimetry measurements on a powder sample of the porous particles, a peak in the intra-particle pore distribution is observed at a pore diameter of 236 nm and the porosity is estimated at 85%.

Example 2—Process to Form Electrode with Active Layer Comprising PAA Binder

[0176] A 15 wt % Na-PAA polymer solution was prepared by dissolving 450,000 molecular weight PAA in water and adding NaOH to the PAA in a molar ratio of PAA:NaOH=1.43:1 so that 70% of the COOH groups of the PAA are neutralised. 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 of Example 1 and spheroidal MCMB graphite (D50=16.5 μm, BET=2 m.sup.2/g). The Na-PAA solution was then mixed in to prepare a slurry with a solids content of 40 wt % and a weight ratio of the porous silicon particles:MCMB graphite:Na-PAA:conductive carbon of 10:75.5:6.5:8. The slurry was then 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.

Comparative Example 3

[0177] An electrode was made as in Example 2 except that non-porous Silgrain™ silicon powder (from Elkem) was used instead of the porous particles. The silicon powder had a D.sub.90 particle diameter of 4.1 μm, a D.sub.10 particle diameter of 2.1 μm, and a D.sub.90 particle diameter of 7.4 μm. The BET value was 2 m.sup.2/g and the particles had a silicon purity of 99.8 wt %.

Example 4—Production and Test of Half Cells

[0178] Coin half cells were made using circular electrodes of 0.8 cm radius from Example 2 or Comparative Example 3, with a Tonen® porous polyethylene separator, a lithium foil as the counter electrode and an electrolyte comprising 1M LiPF.sub.6 in a 3:7 solution of EC/FEC containing 3 wt % vinylene carbonate. These half cells were used to measure the initial charge and discharge capacity and first cycle loss 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 first or second charge, the electrode was removed from the cell in a glove box and washed with DMC 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 volumetric energy density of the electrode, in mAh/cm.sup.3, was calculated from the initial charge capacity and the volume of the active layer in the lithiated state after the second charge.

[0179] 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. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Volumetric First Initial active Increase in energy Electrode Cycle layer thickness active layer density of tested in half Loss (before 1.sup.st thickness at end electrode cell (%) charge) of 2.sup.nd charge (mAh/cm.sup.3) Example 2 15% 41.1 μm 32% 457 Comparative 9% 46.4 μm 67% 446 Example 3

[0180] The values in the table are averages from three test cells of each type. The expansion of the active layer in the half cell comprising the non-porous silicon powder is significantly more than for the electrode of example 3, leading to a reduced volumetric energy density even though the active layer of the comparative electrode has a higher initial density and a lower first cycle loss.

Example 5—Production and Test of Full Cells

[0181] Coin cells were made as in Example 4 except that the lithium counter electrode was replaced by an LCO cathode with a coat weight of 3.7 g/cm.sup.3. Cell cycling tests were performed using CC-CV cycling between 4.2 and 3.0 V at a rate of C/5 with a 10 minute rest between cycles. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Electrode Specific Capacity on tested in full first discharge Capacity retention cell (mAh/g) after ten cycles Example 2 495 98% Comparative 518 89% Example 3

[0182] The capacity retention of the full cell of Example 5 comprising the electrode of Example 2 is significantly better than that for the full cell comprising the electrode of Comparative Example 1 comprising a non-porous silicon even though the comparative cell has a higher initial specific capacity.

Examples 6a, 6b and 6c—Process to Form Electrode with Active Layer Comprising CMC/SBR Binder

[0183] Electrodes were prepared as in Example 2 except that Na-PAA was replaced by a 50:50 mixture of CMC:SBR in solution to prepare an active layer with the weight ratio of porous silicon particles:MCMB graphite:CMC:SBR:conductive carbon of 10:80:2.5:2.5:5. The active layers of the electrodes had the following densities: [0184] Example 6a—uncalendered, 1.15 g/cc [0185] Example 6b—calendered to a coat weight of 1.22 g/cc [0186] Example 6c—calendered to a coat weight of 1.4 g/cc

[0187] Half cells were made as in Example 4 but using the electrodes 6a, 6b and 6c. The volumetric energy density of the active layers in the lithiated state was measured as shown in Table 3.

TABLE-US-00003 TABLE 3 Electrode tested Volumetric energy density of in half-cell Coating weight (g/cc) active layer (mAh/cm.sup.3) Example 6a 1.15 354 Example 6b 1.22 576 Example 6c 1.4 599

[0188] Optimum volumetric energy density was obtained for the electrode of Example 5c.

Examples 7a to 7e and Comparative Examples 8a and 8b

[0189] Example electrodes 7a to 7e and Comparative Example electrodes 8a to 8b were prepared as in previous examples but with different electrode formulations as detailed in the table below. The binder was a 1:1 mix of CMC and SBR. The electrodes comprised porous silicon particles obtained according to Example 1 except that different size classifications were used such that:

(i) Example 7a and Comparative Examples 8a to 8b comprised porous silicon particles with a D.sub.50 particle diameter of 10 μm, a D.sub.10 particle diameter of 4.3 μm, a D.sub.98 particle diameter of 19.4 μm and a BET value of 117 m.sup.2/g; [0190] (ii) Examples 7b to 7e comprised porous silicon particles with a D.sub.50 particle diameter of 4.4 μm, a D.sub.10 particle diameter of 0.7 μm, a D.sub.98 particle diameter of 32.2 μm and a BET value of 125 m.sup.2/g.

[0191] The graphite particles used in the electrodes formulations were MCMB graphite powders with different particle size distributions purchased from Shanshan Technology, China (see table for D.sub.50 particle diameters used in each electrode). The active layers of the electrodes had a coating weight 1.04 g/cm.sup.3. The dimensions of the silicon and carbon particles and the formulation of the electrode active layer are as shown in Table 4.

TABLE-US-00004 TABLE 4 Porous Graphite Electrode formulation Electrode coat Si size Size D.sub.50 Graphite:Si wt % ratio of: density Electrode D.sub.50 (μm) (μm) D.sub.50 size ratio Si:Graphite:Binder:Carbon (g/cm.sup.3) C. Ex 8a 10 11.5 1.15 5:87.5:2.5:5 1.076 C. Ex 8b 10 12.1 1.21 5:87.5:2.5:5 1.01 Ex 7a 10 16.4 1.64 5:87.5:2.5:5 0.956 Ex 7b 4.4 11.5 2.6 5:87.5:2.5:5 1.086 Ex 7c 4.4 12.1 2.8 5:87.5:2.5:5 1.043 Ex 7d 4.4 16.4 3.7 5:87.5:2.5:5 1.01 Ex 7e 4.4 21.4 4.9 5:87.5:2.5:5 0.98

[0192] Half cells were made and tested as described in Example 3 except that the electrodes of Examples 7a to 7e and Comparative Examples 8a to 8b were respectively used as an anode in each cell. The test results of the half cells containing electrodes of Examples 7a to 7e and Comparative Examples 8a to 8b are summarised in Table 5.

TABLE-US-00005 TABLE 5 First Volumetric Energy Energy Density of Increase in active Anode Cycle energy density Density of Density of 1st. anode at end layer thickness at of half Loss of active layer 1st. Lithiation Delithiation of 2.sup.nd charge end of 2.sup.nd charge cell (%) (mAh/cm.sup.3) (mAh/g) (mAh/g) (g/cm.sup.3) (%) C. Ex 8a 12.5 297 472 413 0.68 60 C. Ex 8b 11.7 318 478 422 0.72 42 Ex 7a 10.4 317 483 433 0.71 41 Ex 7b 13.8 349 478.1 412.4 0.79 38 Ex 7c 13.4 338 463.2 401.3 0.79 33 Ex 7d 12.9 334 469.1 408.9 0.77 35 Ex 7e 12.7 373 498 434.5 0.81 24

[0193] It has been found that the cells with a higher graphite:silicon D.sub.50 particle diameter ratio have a higher volumetric energy density and a smaller expansion in electrode thickness.