Method for removing foreign material from carbonaceous material dispersion

A method for removing foreign materials from a carbonaceous material dispersion in which carbonaceous material particles are dispersed in a dispersing medium, the method comprising:

• (i) applying the dispersion to a primary filter a specified number of times in circulation, the primary filter comprising at least one filter device, comprising repeatedly applying the dispersion to the primary filter a number of times after it has been passed through the primary filter once, until the specified number of times is reached;
• and
• (ii) applying the dispersion treated by the primary filter to a secondary filter a single time, the secondary filter comprising at least two filter devices arranged in series;
• wherein each respective filter device satisfies the following conditions:
• (a) a variation of a cumulative undersize distribution Q [%] with respect to a reference particle diameter, and a variation of non-volatile content, before and after being applied to each respective filter element, are not more than 0.1%, respectively;
• and
• (b) a removal rate of particles with a threshold particle diameter being not less than 20%;
• wherein the reference particle diameter is set as a particle diameter of the carbonaceous material particles having a cumulative frequency of 99.8% or more, and the threshold particle diameter is set as a value of at least 5 μm greater than the reference particle diameter;
• and
• wherein the carbonaceous material is one or more selected from the group consisting of graphite, carbon black, carbon nanotubes, carbon nanofiber, carbon fiber, fullerene, and natural graphite.