Lecithin can't be used as the sole emulsifier in an oil in water lotion like product. Don't get me wrong - I love lecithin as an emollient and as a water absorber in a few of my mostly oil based products - but it isn't a full emulsifier on its own for a lotion. The short answer is this: If you want to use lecithin as an emulsifier in your products, you have to create your own emulsifier using the HLB system or hydrophilic-lipophilic system.
I really encourage you to click on this post (shorter, summary) or this one (longer, introduction to a series) to see what the HLB is all about before reading further...It's okay, I can wait.
How to do this? You would get the HLB value for your lecithin - 4, 7, or 9.7 (ask your supplier) - and combine it with an emulsifier that works out well mathematically. If you have an HLB value of 4, you would choose something much higher, say polysorbate 80 with an HLB value of 15, to combine with it. If you have an HLB value of 9.7, you'd choose something with a much lower number, like glycol distearate with an HLB value of 1. You'd figure out the HLB value of your oil phase - all the things that could be considered oil soluble in your product, such as your oils, butters, fatty acids, fatty alcohols, silicones, etc. - and then calculate how much of each emulsifier you'll need.
Here's a post on how to work on the figures for the HLB system. And click here to see the list of the emulsifiers and their values (scroll down to page 10).
If you're new to making lotions, please go buy an all in one emulsification system like Polawax, Incroquat BTMS-50, Ritamulse SCG, Ritamulse BTMS-225, and so on. Please don't start by creating your own emulsifiers! And please don't start off by making your own recipes! Use something tried and true that works well. (Click here for a post on that topic!)
Emulsifying systems - e-wax, Polawax, and Incroquat BTMS-50