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Battery warranty and temperature below -30C (-22F)

Discussion in 'Model S: Battery & Charging' started by Matias, Jun 22, 2014.

  1. green1

    green1 Active Member

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    The reason freezing is such a problem for water based systems is because water expands when it freezes, the expansion (and not the solidity of the water) is what usually causes the damage.
    Other liquids generally do not expand when frozen, so freezing is less likely to cause any damage. The bigger problem then becomes that you simply can't do anything until it thaws out. If that were the case, the warranty shouldn't be voided, you'd just be stuck until you thawed.
     
  2. siai47

    siai47 Member

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    The reason for concern at low temperatures is a process know as "lithium plating" that can occur in a cold battery when a re-charge is attempted. Around -30 c, and below, the lithium will "plate" the cathode of the cell and cause a non reversable loss of capacity in the cell. This is the primary reason for not allowing the battery to get this cold. I believe the Tesla BMS also tries to warm a cold battery pack before high charge currents are applied.
     
  3. stopcrazypp

    stopcrazypp Well-Known Member

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    #23 stopcrazypp, Jun 25, 2014
    Last edited: Jun 25, 2014
    This type of plating occurs when charging at 0C, which is well above -30C. The Tesla BMS will kick in to prevent this (it also disables regen), so the -30C limit does not have to do with this either.

    As for the extent of damage from electrolyte freezing, I'll have to do some more research and post some links.

    Most of the references to damage from freezing electrolyte come from "Characteristics and Behavior of 1M LiPF6 1EC:1DMC Electrolyte at Low Temperatures," unfortunately I wasn't able to find a direct link. The sources that reference this don't go into any detail, but say that damage doesn't occur if the battery is thawed to room temperature before use.

    I found another source from an article discussing batteries for the Mars Rover. It doesn't go into details of the actual damage, but basically the cell can be recovered after thawing. However the battery needs to be at medium SOC and there must be zero load on the battery while it is frozen (this was not possible in the Phoenix Rover).
    http://www.edn.com/electronics-blogs/powersource/4307792/Power-on-Mars-Part-3--Really-low-temperatures-for-a-lithium-ion-battery

    With the zero load and medium SOC requirement for recovery (which the Model S probably doesn't meet), I'm going to guess the damage from freezing has something to do with voltage drop and over-discharge.
     

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