It had not been possible to establish the exact cause of death of the three, police investigators said in a statement.
There was no suspicion of a crime and no indication that the deaths were caused by exposure to any hazardous substance, and the case would now be closed, the police added.
"We've looked at various elements, and also specifically for substances we know have existed at Northvolt, and we've not been able to conclude that they have been exposed to anything in such a way as to cause death," lead investigator Johan Stabbfors told Reuters.
The police launched its investigation into the deaths on June 27 after a third man died at home shortly after working his shift at the Northvolt Ett factory in Skellefteå, northern Sweden.
The first death was at the start of the year, and the second only a month later.
Both of these people also died at home.
The ages of the deceased ranged from 19 to 60 and all had had reasonably good health prior to their deaths, the police previously told Reuters.
A fourth Northvolt worker died in August.
However, the police said this had been determined to be a drowning accident.
Northvolt said the findings confirmed its own investigation that the deaths were not connected to the workplace.
"We hope that this can lead to closure for colleagues and for the families," a company spokesperson said in an emailed statement.
"The safety of our employees is most important for us," the person added, noting that Northvolt's work safety statistics are in line with the Swedish average and that it aimed to improve.
Mikael Stenmark, Northvolt's chief labour union safety representative, told Reuters the police findings were a relief but that he would continue to seek improvements in the work environment.
Northvolt, which makes battery cells for electric vehicles, last month filed for Chapter 11 bankruptcy protection in the United States, dealing a blow to Europe's hopes of building a home-grown EV industry supply chain.
The company has said it needs to raise up to $US1.2 billion ($A1.9 billion) to restore its business while undergoing restructuring.
