The big challenges presented when charging lithium with an alternator include the alternator overheating and the alternator rectifier diodes failing because of over voltage after disconnect by a BMS. Victron Energy has posted a good video on their website blog about how to avoid these exact problems. The only way to make sure the system is safe is by using the correct lithium battery charging solution. The PKYS online store sells a number of alternators and lithium ion batteries.