To safely dispose of a lithium cell in the garbage stream.... simply discharge the battery in a safe manner... Use a reasonable load such as an automotive light bulb and perform the discharge outdoors on concrete/stone away from anything that might catch fire should the cell erupt. I just toss a clay flowerpot over top of the pack, just in case it decides to misbehave. Once the battery charge is reduced to 0V, there is no more stored energy and it can be safely disposed of in the garbage (but it can NEVER be SAFELY recharged again!). There are no nasty heavy metals to worry about, or major toxins. IF, for some reason, you MUST dispose of a rechargeable lithium cell/pack without discharging because it's in an unsafe condition to do so. You should cover the terminals with several layers of electrical tape or some such to avoid any accidental shorting out. This is usually required when turning in such cells/packs for recycling. The problem with this is that if you toss such a battery in the garbage and it somehow gets bent or pierced/cut in the garbage truck compactor, it could start a fire right then and there.
One thing that should be avoided is charging devices that use lithium batteries, while they are still turned on. I realize some of us just can't bear the thought of missing a txt or phone call, but the fact that a device is still turned on during charging, can cause the charger to miscalculate and overcharge the battery which can lead to swelling or worse.... vent with flame! Ditto, it's best to purchase the correct replacement cell and not a Chinese cheapy from Ebay, as they may not have the proper safety circuits or even be manufactured to the same safety standards as the original unit which was chosen by the engineer who designed that circuit.
One other thing regarding making batteries last in cell phones and the like. Don't run them down until the phone switches off and then charge them back up... This is very hard on a lithium battery. They much prefer shallow discharge/charge cycles and you would be better off charging the battery every day (just do it with the phone turned off, eh!), instead of once or twice a week when it dies.
Regards
Christian