Answer: Lima beans are far too starchy to be compatible with keto eating.
Beans in general are not very keto friendly, and lima beans are no exception. A half cup of cooked lima beans contains 13 g of net carbs. While they're a good source of protein, the carb count is far too high for a side dish.
If you need a bean to satisfy your bean craving, black soy beans are a popular keto-friendly bean. They're high in protein, rich in antioxidants, and only contain 1 g of net carbs per half-cup serving.