SEOUL, Jan 11 (Reuters) - South Korea"s LG Chem Ltd (051910.KS) said on Tuesday it plans to invest about 500 billion won ($418.52 million) by 2025 to build a cathode material production plant for batteries in Gumi, South Korea. The plant will help LG Chem secure cathode material production capacity of 60,000 tonnes per year, and is expected to be one of the largest cathode material plants in the world when completed, LG Chem said in a statement. ($1 = 1,194.6800 won)