In addtionion to 表示‘除……以外’
"In addition to" can add a sentence after it;
如：Everyone went there in addtionion to Tom.
除了Tom，其他每个人都去了。
例：In addition to what I just described above for you, you can look at other materials.
而
as well as 表示‘…和…’。
As well as is a phrase, followed by noun.
如：Jack runs fast as well as Sam.
Jack跑得和Sam一样快。
例：She is very good at the spelling as well as Math.