trying to increase current output of a generator
Please realize that:

Power = Voltage x Current

So the actual value of the current does not matter !

Hmm, OK, but I still want more current !

Well then, do you have enough voltage ? You mention 30 V, what is the voltage of the battery you're trying to charge ? As long as it is lower than 30V we're OK.
You can use an electronic device called a DCDC converter to convert that 30V and too low
current into a lower voltage and a proportionally higher current !
This is such a device: DCDC Downconverter module

I would advise to also use some kind of charge control unit since Lithium based batteries are a bit picky concerning charging and especially overcharging.

Probably there are also modules that can do both (lower voltage and increase current, charge control) in one but these are a bit harder to find.

So: keep the motor as-is but use some electronics to connect the generator to the batteries

Hope this helps.