The secondary-battery rally drove the KOSDAQ up 8.1 percent to 920.57, while the KOSPI slipped 0.2 percent to 8,394.65 as key chipmakers Samsung Electronics and SK hynix fell.
Foreign investors turned net buyers on the main board, while institutional and retail buying fueled the KOSDAQ surge.
The same divide was seen across Asia, with battery and small-cap stocks bid up while chip heavyweights lagged from Seoul to Tokyo as the KOSPI dropped 16.56 points.
Samsung Electronics fell 4.9 percent to 323,000 won (about US$209), down 16,500 won. SK hynix lost 1.7 percent to 2,628,000 won (about $1,701), down 45,000 won.
SK square, SK hynix's holding company, dropped 4.7 percent to 1,640,000 won (about $1,061). The chip drop pulled the KOSPI 200, the index of the market's largest names, down 1.0 percent to 1,352.54.
The KOSDAQ told the other story. Battery and lithium names ran hard, with the lithium theme up more than 15 percent and the secondary-battery cell basket up about 14 percent.
LG Energy Solution jumped 19.9 percent to 397,500 won (about $257). The size of the move showed how far the battery bid spread across both boards.
Foreign investors bought a net 26.5 billion won of KOSPI shares, while institutions added 503.8 billion won. Individuals sold a net 526.5 billion won.
The won weakened, with the dollar trading at around 1,545.60 won.
Across the region, the rotation looked milder. Japan's Nikkei 225 edged up 0.2 percent, while China's Shanghai Composite added 0.8 percent to 4,054.99.
In Tokyo, the split echoed Seoul's. SoftBank Group fell 5.3 percent and Advantest slipped 1.5 percent, while Tokyo Electron rose 2.4 percent.
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