{"id":284982,"date":"2026-08-16T17:54:24","date_gmt":"2026-08-16T15:54:24","guid":{"rendered":"https:\/\/www.heiwit.com\/batterie-sodio-basse-temperature\/"},"modified":"2026-08-16T17:54:24","modified_gmt":"2026-08-16T15:54:24","slug":"sodium-batteries-low-temperature","status":"publish","type":"post","link":"https:\/\/www.heiwit.com\/en\/batterie-sodio-basse-temperature\/","title":{"rendered":"Sodium batteries at low temperatures: why they still deliver 95% at \u221220 \u00b0C"},"content":{"rendered":"

There is a defect in home batteries that catalogues rarely mention: in the cold they perform less well. This is not a marginal detail, because the time when they perform less coincides with the time when they are needed most. In January, photovoltaic production is a fraction of what it produces in July, days are short, evening energy consumption is high \u2014 and it is precisely then that the storage system delivers only a fraction of the capacity you paid for.<\/p>\n

On this point the difference between the chemistries is clear and measurable. This article reports the qualification data for polyanionic NFPP cells<\/a> at low temperatures and explains where the gap comes from.<\/p>\n

The data<\/h2>\n

The test protocol is simple: the cell is charged to 3.5 V at 0.5P power, left to rest for ten minutes, and then discharged at the test temperature. A measurement is taken of how much of the nominal capacity it is actually able to deliver.<\/p>\n

\n\n\n\n\n\n\n
Temperature<\/th>\nLead-acid<\/th>\nLFP<\/th>\nNMC\/NCA<\/th>\nPolyanionic cellulose (PAC)<\/th>\n<\/tr>\n<\/thead>\n
-20 \u00b0C<\/td>\n< 60%<\/td>\n< 70%<\/td>\n> 70%<\/td>\n> 90%<\/strong><\/td>\n<\/tr>\n
-40 \u00b0C<\/td>\n0%<\/td>\n0%<\/td>\n0%<\/td>\n> 85%<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

In the direct test at \u221220 \u00b0C, the value measured on the NFPP cell is 95,04%<\/strong> of the nominal capacity. The reference LFP cell, in the same test, stops at 67,8%<\/strong>.<\/p>\n

The \u221240 \u00b0C row deserves careful reading, because the zero is not a rounding off: lead-acid, lithium iron phosphate and nickel-manganese-cobalt at that temperature are not simply inefficient, they are unusable<\/strong>. The sodium polyanionic chemistry remains above 85%.<\/p>\n

Why sodium gets off more lightly<\/h2>\n

There are two reasons, and they act on different parts of the cell.<\/p>\n

Desolvation at the interface<\/h3>\n

An ion moving within the electrolyte does not travel naked: it is surrounded by a shell of solvent molecules that attach themselves around it. To enter the electrode, it must get rid of them, and this costs energy. This is the process known as desolvation<\/strong>, and it is the main bottleneck at low temperatures: when the cell is cold, the energy available to make that transition is reduced and the reaction slows down.<\/p>\n

The sodium ion is larger than the lithium one, and for this very reason it retains its solvent shell less firmly<\/strong>the charge density on its surface is lower. Paradoxically, being bulkier \u2014 which is why sodium stores less energy per kilogram \u2014 is also why it detaches from the solvent more easily in the cold.<\/p>\n

Diffusion pathways in the cathode<\/h3>\n

The second reason relates to the structure of the active material. In lithium iron phosphate, which has an olivine structure, the ions move along one-dimensional channels<\/strong>a single possible path, and if that path becomes obstructed \u2014 due to a defect in the lattice or the slowdown induced by temperature \u2014 there are no alternatives.<\/p>\n

The NFPP polyanionic framework instead offers a network of three-dimensional diffusion pathways<\/strong>. The ion has multiple pathways to reach its site, and the slowdown caused by the cold weighs much less on the overall result.<\/p>\n

What changes to the system<\/h2>\n

The number on its own says little. It's worth translating.<\/p>\n

Let's take a 10 kWh battery storage system in an unheated technical room \u2014 a garage, a cellar, an outdoor meter cupboard \u2014 on a January morning in Northern Italy, at \u22125 \u00b0C. An LFP battery delivers a reduced fraction of its nominal capacity; the owner sees a \u201c10 kWh\u201d battery that delivers noticeably less, and they see this precisely during the days of the highest energy bills. The phenomenon is reversible \u2014 when mild temperatures return, the capacity comes back \u2014 but in the meantime, the storage system has operated below expectations for the entire cold season.<\/p>\n

With a cell that retains over 90% at \u221220 \u00b0C, the loss at \u22125 \u00b0C is negligible. The battery performs just as well in winter as it does in summer.<\/p>\n

The distinction becomes decisive in three situations:<\/p>\n