Yes, no, maybe...
Halon is effective in extinguishing a Lithium Ion battery fire. A typical use case is an undeclared lithium ion battery shorting, catching fire, then igniting everything else in the cargo hold container. Halon will extinguish this type of fire.
But, if there are many batteries or cells close together (such as in bulk shipments), the remaining heat from one cell due to thermal runaway will probably ignite adjacent cells, even if the flame has been extinguished. Halon is not effective in preventing this from happening.
But, along with halon, there are Fire Containment Covers and Fire Resistant Containers (FCC/FRC) demonstrating containment of a 1,500 cell Lithium Ion fire for a full 6 hours. Many operators are already using FCCs and FRCs on highest risk cargo.