xlsx = pd.ExcelWriter(output_path)
df.to_excel(xlsx, 'Sheet 1')
sheet = xlsx.book.worksheets[0]
for col in sheet.columns[1:sheet.max_column]:
    for cell in col[1:sheet.max_row]:
        cell.number_format = '0.00%'
cell.value /= 100
xlsx.save()
Написание процентов в Excel с помощью Pandas