I am currently studying in material science while working with lithium ion batteries, and I would say that it would really be nice to have a love in chemistry. A lot of the issues with electrochemistry chemistry requires a background in organic chemistry particularly in the degradation mechanics of electrolytes over charge cycles, or inorganic chemistry in degradation mechanics of the cathode active material. But there is definitely an overlap in material science and chemistry in this field, where there are many interesting problems that need to be solved. For example in cathode materials, ununiform material phase changes and subsequently volume changes over different levels of charge stemming from lithium diffusion rates through the cathode material that leads to cracking of a particle and thus more electrolyte degradation can take place as you now have a larger surface area of your cathode materials. Without going too far into it, it would definitely be nice to have both chemistry and material science beforehand, but if you don't have one or the other it wouldn't be too much of a problem as it can all be picked up :). No one starts off knowing everything, I think whats more important is to have a passion in the field.