Solder sleeves provide solderability to copper, tinned, and most silver wires/shields. If you are soldering to nickel plated wire/shields you will have to get one to support that since soldering to nickel is more difficult and of higher temperatures. Since there is no filter currently in Digi-Key to filter this, it is best to sift through datasheets after all other filtering is completed.
Regular tin/copper solder sleeve example datasheet:
“These controlled soldering devices are designed to splice tin-plated or bare copper stranded wires rated for at least +85°C”
https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=B-155-90XX&DocType=Customer+Drawing&DocLang=English
Nickel plated solder sleeve example datasheet:
“These controlled soldering devices are designed for termination of a nickel plated copper shield of a cable having an insulation rated for at least +200°C continuous.”
https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=B-023-0X&DocType=Customer+Drawing&DocLang=English
Digi-Key’s Solder Sleeve Selection:
Solder Sleeves