LiFePO4 Cold Weather Charging, Heating and Sodium Ion Alternatives

LiFePO4 cold weather charging: why it is not allowed below 0 °C

During charging, lithium ions must insert into the graphite of the anode. In the cold this process slows down and part of the lithium deposits on the anode surface as metal. This plating irreversibly reduces capacity, accelerates ageing and raises the risk of an internal short circuit. That is why a lithium battery BMS blocks or sharply limits charging below 0 °C.

Discharge in frost is possible, but less energy is available: at -20 °C LFP delivers about 65 % of its capacity, and below -20 °C modules go into protective shutdown. Lead-acid batteries deliver about 40 % at -20 °C and about 25 % at -40 °C. The main problem on site is not discharge but recovery: if the grid fails at night in frost, an unheated lithium battery will not recharge before the next outage.

Heaters and insulation: how much energy climate control takes

The standard solution for outdoor LFP is an insulated enclosure and a heated battery compartment. The heater keeps cells in the allowed charging range, insulation reduces heat loss, and the EMS shifts charging to warmer hours and limits current in the cold. In liquid-cooled cabinets and containers the same system heats the cells in winter and evens out their temperature.

Heating has a cost in energy and reliability. By our estimate for an outdoor telecom cabinet, compartment heating for lead-acid and LFP uses about 900 kWh per year, and climate control takes about 15 % of daily energy at -20 °C and up to 25 % at -40 °C. This energy must be included in the autonomy calculation, because during a grid outage the heater runs from the same battery. The heater also becomes a point of failure: if it breaks, the site can no longer charge.

Sodium ion battery cold temperature performance: an alternative to heating

Sodium NFPP does not need heating to charge in frost. The 48 V modules charge from -20 °C, discharge at -40...+60 °C and retain 93 % of capacity at -20 °C and 80 % at -40 °C (cell manufacturer data). Almost no energy goes to cabinet climate control, so all stored energy goes to the load.

Sodium cell cycle life in the cold is lower than the rated value at +25 °C, so for a cold site it is calculated for the real temperature. Below are the manufacturer figures for the 160 Ah cell; we use the lower bound of each range. A separate test at -20 °C and 1C showed at least 8,000 cycles with remaining capacity above 80 %. More about the chemistry on the sodium NFPP page.

Battery storage for a cold climate: what to put in the specification

Datasheet figures are usually given at +25 °C. For a cold site that is not enough: the specification should require data for your actual temperature range. A minimum list:

• charging and discharge windows in degrees, separately for the cell and for the system in its enclosure;
• available capacity at the minimum site temperature;
• cycle life by temperature with test conditions: rate, depth of discharge, remaining capacity;
• heater power, its control logic and its power source during a grid outage;
• the BMS and EMS algorithm for limiting charge current in the cold;
• a manufacturer test report with -40 °C performance for the specific delivery.

Russia, Kazakhstan and Central Asia: example solutions

Most sites in Russia, Kazakhstan and northern Uzbekistan see -30 °C and below, while in summer cabinets in the sun heat up above +45 °C. The choice is therefore made for both ends of the range. Typical solutions in the OS Power range:

For base stations in outdoor cabinets without reliable heating, sodium 48 V modules; see base stations in frost. For generators at remote sites, the northern version heats the coolant, oil, fuel system and starter batteries; see generation for frost.

Limitations to take into account

A system operating range depends not only on chemistry but also on the cabinet or container design: for the sodium cell it is wider than for the assembled 115 kWh cabinet or 2.4 MWh container. Cycle life in frost is lower than rated, so the calculation uses the site temperature month by month. Performance at -40 °C is confirmed for each delivery by a manufacturer test report. Operating ranges of all systems and winter preparation measures are collected on the storage in frost page.