I got some "wire glue" from I think KaiDomain awhile back. It's not a 2-component. Just got it "because".
Even 2-part epoxy would be a terrible idea. The electrical connection will inevitably be fairly high resistance. Look at the Arctic Silver for reference- the
thermal resistance is "low" for grease but still MUCH higher (orders of magnitude higher) than pure silver because the particles have limited contact with each other and the substrate, because there's a layer of binder coating each particle and two spheres will only touch over an almost infintesimally small portion of its total cross-section. I expect any electrical conductor will exhibit a similar penalty over the conductive material upon which it is based. Under current this will form heat right at the epoxy layer and epoxy doesn't take really high heat. Stresses from thermal expansion will be high. And in fact epoxy is not even a really stellar performer for metal-metal bonds, especially on tabs where there's a peeling force.
Do not solder lithium or NiMH cells. Especially lithium. It's dangerous and is VERY likely to damage these expensive cells whether you realize it or not. Given the differences in cell construction, it's hard to predict what would happen with soldering. The only thing we can be sure of is the mfgs don't allow for it.
What you need to do is build a capacitive spot welder. There are many descriptions of people doing this with a big stereo booster cap, a large SCR, and a couple of pieces of solid copper ground wire filed down to make electrodes. Such as
http://www.ledhacks.com/power/battery_tab_welder.htm
Get the nickel tab from
SunStone Engineering
:sweat:And I think that's why it's not working. I think there is such a thing but it's very expensive and I was hoping for a cheaper/simpler solution. 
