When the batteries are cold or hot, the computer can limit the power available. Driving the car will warm them some as they discharge. It takes the REx about 10-minutes to warm up enough to then be able to produce full power. Until that time, it's not going to rev very high which means that it can't produce maximum power. When the vehicle is cold-soaked is the best time to consider setting a departure time so the car can warm things up. Try that, and see if you then have full power available when you start up...you probably will.
If you have the all-season, or worse, the 20" tires, or, their tread is getting thin or they're old, they don't have all that much traction in the cold let alone on ice. Tires aren't like a good wine that get better with age...more like a loaf of bread...great when fresh, gets old quick. IMHO, the i3 begs for a good set of winter tires when the temperature drops. I have the OEM Bridgestones, but when I replace them, assuming I still have the car, I'll put some Nokian R3's on it. Tried them on my ICE, and they seem to be a great tire for the winter. They beat the Blizzaks in every comparison test I've been able to find. The difference in traction with a good winter tire is day and night over a summer tire, and also makes an all-season tire look lame when the conditions get cold or slippery in the winter.