Process for preparing electroactive materials for metal-ion batteries

Abstract

The disclosure relates to a process for preparing particulate materials having high electrochemical capacities that are suitable for use as anode active materials in rechargeable metal-ion batteries. In one aspect, the disclosure provides a process for preparing a particulate material comprising a plurality of composite particles. The process includes providing particulate porous carbon frameworks comprising micro pores and/or mesopores, wherein the porous carbon frameworks have a D.sub.50 particle diameter of at least 20 m; depositing an electroactive material selected from silicon and alloys thereof into the micropores and/or mesopores of the porous carbon frameworks using a chemical vapour infiltration process in a fluidised bed reactor, to provide intermediate particles; and comminuting the intermediate particles to provide said composite particles.

Claims

1. A process for preparing composite particles, the process comprising: (a) providing particulate porous carbon frameworks comprising micropores and/or mesopores, wherein the porous carbon frameworks have a D.sub.50 particle diameter of at least 20 m; (b) depositing an electroactive material selected from silicon, tin, aluminium, germanium and alloys thereof into the micropores and/or mesopores of the porous carbon frameworks using a chemical vapour infiltration process while the porous carbon frameworks are fluidized, to provide intermediate particles; and (c) comminuting the intermediate particles to provide said composite particles.

2. The process according to claim 1, further comprising transferring the intermediate particles into a comminuting device prior to step (c).

3. The process according to claim 1, wherein the electroactive material is silicon.

4. The process according to claim 1, wherein the intermediate particles and the composite particles comprise a plurality of nanoscale domains of an elemental form of the electroactive material located within the micropores and/or mesopores of the porous carbon frameworks.

5. The process according to claim 1, wherein the chemical vapour infiltration process is performed at a temperature in the range from 200 to 1,250 C.

6. The process according to claim 1, further comprising a step of cooling the intermediate particles to a temperature of below 100 C. before comminuting the intermediate particles.

7. The process according to claim 1, further comprising a step of passivating the intermediate particles before comminuting the intermediate particles.

8. The process according to claim 1, wherein the comminuting is performed by a jet mill.

9. The process according to claim 1, wherein the step of comminuting the intermediate particles is performed in an inert gas or in an environment where the oxygen concentration is less than 10 vol % oxygen.

10. The process according to claim 1, wherein the micropores and/or mesopores of the porous carbon frameworks have a total pore volume as measured by gas adsorption of P.sub.1 cm.sup.3/g, wherein the value of P.sub.1 is in the range from 0.4 to 2.5.

11. The process according to claim 1, wherein the porous carbon frameworks have a D.sub.50 particle diameter in the range from 60 to 150 m.

12. The process according to claim 1, wherein the porous carbon frameworks have D.sub.50 particle diameter of at least 30 m.

13. The process according to claim 1, wherein the porous carbon frameworks have a D.sub.50 particle diameter of no more than 1000 m.

14. The process according to claim 1, wherein the porous carbon frameworks have a Do particle diameter of at least 5 m and a D.sub.90 particle diameter of no more than 1,500 m.

15. The process according to claim 1, wherein the porous carbon frameworks have a BET surface area of at least 750 m.sup.2/g and no more than 4,000 m.sup.2/g.

16. The process according to claim 1, wherein the porous carbon frameworks have a PD.sub.50 pore diameter as measured by gas adsorption of no more than 5 nm.

17. The process according to claim 1, wherein the composite particles have a D.sub.50 particle diameter in the range from 0.5 to 20 m.

18. The process according to claim 1, wherein the composite particles have a Do particle diameter of at least 0.2 m and a D.sub.90 particle diameter of no more than 80 m.

19. The process according to claim 1, wherein the composite particles have a particle size distribution span of no more than 5.

20. The process according to claim 1, wherein the electroactive material is silicon, wherein the pore volume of the composite particles is expressed as P.sub.1 cm.sup.3/g, and wherein the weight ratio, for the composite particles, of silicon to the porous carbon framework in the composite particles is in the range from [0.5P.sub.1 to 2.2P.sub.1]:1.

21. The process according to claim 1, wherein the electroactive material is silicon, and wherein the composite particles comprise 30 to 80 wt % silicon.

22. The process according to claim 1, wherein the composite particles comprise no more than 15 wt % oxygen.

23. A particulate material comprising composite particles obtainable by the process according to claim 1.

Description

EXAMPLE

(1) Silicon-carbon composite materials were synthesized in a vertical bubble-fluidised bed reactor comprising an 83 mm internal diameter stainless steel cylindrical vessel. The reactor was dosed with 126 g of a pre-mixed mixture of porous carbon particle with BET surface area of 1777 m.sup.2/g, total pore volume of 0.78 cm.sup.3/g, PD.sub.10=0.97 nm, PD.sub.50=1.15 nm, PD.sub.90=2.23 nm and .sub.a=61%. An inert gas (nitrogen) at a low flow rate was injected into the reactor to remove any oxygen. The reactor was then heated to a reaction temperature between 420 and 440 C. and 1.25% v/v monosilane gas diluted in nitrogen was supplied to the bottom of the reactor at a flow rate sufficient to fluidize the carbon framework particles, for a duration of 32.3 hours (Sample 1) or 37 hours (Sample 2). Once reaction time was complete, the reactor atmosphere was switched to pure nitrogen whilst maintaining fluidisation, this purge lasted 30 minutes. After this the furnace was ramped to ambient temperature over several hours. On reaching ambient temperature, the furnace atmosphere was switched to air gradually over a period of hours.

(2) The product was added to the feed tray of a MC DecJet 30 mill and the grinding took place in an inert atmosphere. The ring pressure was set at 650 kPa and the Venturi pressure was set at 700 kPa. The product was micronized and then collected in a suitable container. The material characteristics of the two composite materials are given in Table 1.

(3) TABLE-US-00001 TABLE 1 BET Si C O Si:C Particle size distribution Sample (m.sup.2/g) wt % wt % wt % ratio D.sub.10 D.sub.50 D.sub.90 Sample 1 173 45.0 38.6 14.3 1.17 1.2 4.2 15.6 Sample 2 100 51.9 35.4 12.3 1.47 1.1 3.2 8.1

(4) Preparation of Negative Electrodes

(5) Negative electrode coatings (anodes) were prepared from each of the materials of Sample 1 and 2. A dispersion of carbon black SuperP (conductive carbon) in CMC binder was mixed in a Thinky mixer. The SiC composite 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 SiC composite material:CMC/SBR: carbon black of 70%:16%:14%. The slurry was further mixed for 30 min in the Thinky mixer, then was coated onto a 10 m thick copper substrate (current collector) and dried at 50 C. for 10 minutes, followed by further drying at 110 C. for 12 hours to thereby form a negative electrode.

(6) Cell Manufacture and Cycling

(7) Full Cell Manufacture

(8) Full coin cells were made using circular negative electrodes of 0.8 cm radius cut from the coatings made with Samples 1 and 2 (as described above), a porous polyethylene separator and a nickel manganese cobalt (NMC532) positive electrode. The positive and negative electrodes were designed to form a balanced pair, such that the capacity ratio of the positive to negative electrodes was 0.9. An electrolyte comprising 1 M LiPF 5 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.

(9) The 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 4.3 V. When the cut off was reached, a constant voltage of 4.3 V is applied until a cut off current of C/100 is reached. The cell was then rested for 10 minutes in the lithiated state. The anode is then delithiated at a constant current of C/25 with a cut off voltage of 2.75 V. The cell was then rested for 10 minutes. After this initial cycle, a constant current of C/2 was applied to lithiate the anode with a 4.3 V cut off voltage, followed by a 4.3 V constant voltage with a cut off current of C/40 with rest time of 5 minutes. The anode was then delithiated at a constant current of C/2 with a 2.75V cut off. This was then repeated for the desired number of cycles.

(10) The charge (lithiation) and discharge (delithiation) capacities for each cycle are calculated per unit mass of the silicon-carbon composite material and the capacity retention value is calculated for each discharge capacity as a percentage of the discharge capacity on the second cycle. The first cycle loss (FCL) is (1(1.sup.st delithiation capacity/1.sup.st lithiation capacity))100%. The key values are averaged over 3 coin cells for each material and are listed in Table 2.

(11) TABLE-US-00002 TABLE 2 Capacity Composite Average 1st Average Average Retention @500 Material in Lithiation 1st De- First cycle cycles/% Negative capacity Lithiation loss, FCL (with variation Electrode (mAh/g) (mAh/g) % between cells) Sample 1 1967 5 1327 8 32.5 0.6 65 3 Sample 2 2064 8 1470 10 28.8 0.2 58 4