Is there a lightning cable power splitter / double charger? A small example use case will make this clearer. I have a really long lightning cable that I use to charge my iPhone on my bedside table at night (there's no wall socket close). I'm thinking of buying AirPods and naturally I would like to charge them with a cable also on my bedside table next to my iPhone. However, I have no interest in using another USB wall adapter or buying/using another really long cable.

So, is there any small lightning cable power splitter for charging two devices from one cable? What I mean is a small adapter where on one side there is a female lightning port (to connect to the already existing cable) and on the other side the cable splits into two small cables each with a male lightning connector.

I imagine this would be quite easy to do by manually splicing the cables. Since I'm only going to use this for charging (not syncing), it is just a question of splicing two male lightning connectors together by putting power and ground in parallel. But I'd be willing to pay a few bucks for something fabricated. Does anyone know of any product like this?

Note: This is NOT a power/headphone lightning splitter for iPhone7+. I've searched the internet with all the search terms I can think of and all I can find are those splitters.
No, this is not possible to make.

Your question implies that you think of the Lightning cable as solely providing power in the form of two wires with +/- electricity. This is not the case.

In addition to simply power supply, the cable also contains wires that are used for communication between the charger and the device. When you plug your phone or other device into the charger, they start negotiating right away what kind of supply is needed. The charger acts differently according to the needs of the device plugged in.

This is the reason why you cannot have both a phone and AirPods (for example) spliced into the same charger cable - as the negotiation process would go hay-wire with multiple devices communicating on a protocol that is designed strictly for one-to-one communication.

I would recommend instead getting a charger with multiple USB outputs. These can be bought quite cheaply - for example IKEA has a cheap charger with 3 USB outputs for plugging in Lightning cables. 

In order to keep the Lightning cables short, you would have to extend the use of the 110/230V cable and place the actual charger nearer your devices.