This is a mistake. It should be 'ON behalf of the team'. If you are the spokesperson for the team, and you are representing the whole team's sentiments by saying 'thank you', the correct phrase is 'on behalf of the team'. 'In' is wrong. This much I know. Beyond that, I'm on shaky ground. So I'm going to confess to ignorance here and say that I hadn't heard of 'in behalf of'. I've just seen a dictionary entry saying that 'in behalf of' means for 'the benefit of ', but I have never in my entire life heard or seen this expression. I suspect that it is a legal term to do with property and bequests and so on, rather than a general English term. Has anyone else heard of 'in behalf of'? It's a new one on me.

It *should* be "I thank you on behalf of the team". Maybe the speaker is not a native English speaker, or just said it awkwardly. It happens.

to express thanks from everyone in 'the team', not just from the individual writer of the text