R-无法格式化日期列

我有这个数据帧:

            date  NO2
2 01/11/16 00:00 56.8
3 01/11/16 00:15 52.3
4 01/11/16 00:30 49.6
5 01/11/16 00:45 55.5
6 01/11/16 01:00   48
7 01/11/16 01:15   45

我想介绍日期格式,例如:

2016-01-11 00:00

# Convert chr to POSIXct, format for openair.
DF$date <- as.POSIXct(DF$date)
# Make sure that date values are POSIXct, format.
str(anonSpeciesDF)

'data.frame':   14497 obs. of  2 variables:
 $ date: POSIXct, format: "1-11-16 00:00:00" ...
 $ NO2 : Factor w/ 1093 levels "[\xb5g/m3]","10",..: 635 590 553 622 537 507 493 463 446 438 ...

# Format the date
DF$date <- format(DF$date, format='%Y-%m-%d %H:%M')
> View(DF)

结果:

           date  NO2
2 1-11-16 00:00 56.8
3 1-11-16 00:15 52.3
4 1-11-16 00:30 49.6
5 1-11-16 00:45 55.5
6 1-11-16 01:00   48
7 1-11-16 01:15   45