Composite powder for use in an anode of a lithium ion battery, method of preparing such a composite powder and method for analysing such a composite powder

1. A composite powder for use in an anode of a lithium ion battery, wherein particles of the composite powder comprise silicon-based domains in a matrix, and wherein the matrix comprises carbon or a precursor material that can be converted into carbon by thermal treatment, and wherein the individual silicon-based domains are either:

free silicon-based domains that are not or not completely embedded in the matrix, or

fully embedded silicon-based domains that are completely surrounded by the matrix,

wherein the percentage of free silicon-based domains is lower than or equal to 4 weight % of the total amount of Si in metallic or oxidized state in the composite powder, and

wherein the silicon-based domains have a weight based size distribution with a d 50 of 200 nm or less and a d 90 of 1000 nm or less, and wherein the composite powder also comprises graphite, wherein the graphite is not embedded in the matrix.

2. The composite powder according to claim 1 , wherein the percentage of free silicon-based domains is lower than 3 weight % of the total amount of Si in metallic or oxidised state in the composite powder.

3. The composite powder according to claim 1 , wherein the percentage of free silicon-based domains is the percentage as determined by placing a sample of the composite powder in an alkaline solution for a specified time, determining the volume of hydrogen that has evolved after the specified time, calculating the amount of silicon needed for evolving this amount of hydrogen based on a production of two moles of hydrogen for every mole of silicon reacted and dividing this by the total amount of Si in metallic or oxidised state present in the sample.

4. The composite powder according to claim 1 , wherein the powder contains less than 3 weight % of oxygen.

5. The composite powder according to claim 1 , wherein the powder contains between 2 weight % and 25 weight % of Si.

6. The composite powder according to claim 1 , wherein the matrix comprises pitch or thermally decomposed pitch.

7. The composite powder according to claim 1 , wherein the silicon-based domains are silicon-based particles.

8. The composite powder according to claim 1 , wherein the powder has an average particle diameter d 50 of between 1 and 20 microns.

9. The composite powder according to claim 1 , wherein at least 97% of the surface area of the silicon-based domains is covered by the matrix.

10. The composite powder according to claim 1 , wherein the silicon-based domains have a weight-based size distribution with a d 50 of 100 nm or less and a d 90 of 1000 nm or less.

11. The composite powder according to claim 1 , wherein a ratio between an average size of the composite powder and a d 50 of the silicon-based domains is 10 or more.