HIGH PROFILE
the early movers in the lithium iron phosphate ( LFP ) -based battery space , and Huff is keen to point out the safety benefits that come with using such battery chemistry .
“ Our approach to battery safety , which is part of the standardised Sandvik approach for safety with ISO and other standardisation bodies , is to look , first , at reducing the severity of a potential incident or eliminating the hazard ,” Huff said . “ For us that means reducing the severity of a thermal runaway , which is primarily a chemistry choice .” Thermal runaway is categorised as a chain reaction within a battery cell that occurs when the temperature inside a battery reaches the point that causes a chemical reaction to take place inside the battery . This chemical reaction produces heat , which drives the temperature higher , causing further chemical reactions to take place and further heat generation . Excessive heat generation at an accelerated rate can cause batteries to melt or be damaged beyond repair , or , in extreme circumstances , ignite and start fires .
With the potential to cause such an incident , thermal runaway preventions are often the first thing battery companies mention in safety briefings .
When plotting the main commercial battery chemistries against the heat-release-rate ( HRR ) on a graph , it is easy to see Huff ’ s point ( see graph below ). The rate of temperature rise ( left ) indicates the severity of a thermal event , with the higher the HRR , the harder it is to contain an incident , Sandvik says .
Taking all this into account , the LFP rate of temperature rise is over 100 times lower than other batteries with chemistries such as nickelmanganese-cobalt ( NMC ), lithium-cobalt oxide
( LCO ) and lithium-nickel-cobalt-aluminium ( NCA ), making containment more achievable , according to the company .
In thermal runaway tests , LFP-based cells have emitted a flammable gaseous electrolyte but do not self-ignite during standardised safety tests , Sandvik clarified .
Tests on batteries looking at the release of harmful emissions have also highlighted the safety benefits of using LFP-based batteries . A US CDC nail penetration test showed minimal emissions of the likes of carbon monoxide , nitrous oxides and hydrogen fluoride , compared with much higher levels emitted from NMC- and lithium-ion-manganese-oxide ( LMO ) -based batteries .
Passive and intrinsic safety
The battery chemistry choice fits into the ‘ severity reduction ’ basket in terms of safety controls , but it is not where Sandvik ’ s battery system safety approach ends .
“ We then move to reducing the likelihood of the hazard occurring through design controls ,” Huff said . “ This is where the engineering comes in , with the best design controls often deemed to
In Sandvik ’ s battery system design , a battery cell ( far left ) is placed into a battery module ( second from left ), which is then incorporated into a battery pack ( second from right ). This pack is then enclosed in a cage ( far right )
be passive and intrinsic – where you don ’ t have to do anything in the case an event arises .”
Sandvik has more than a handful of such controls in its locker , starting at the cell .
The cells in Sandvik ’ s battery systems are equipped with high-reliability vents that prevent pressure build-up in case of thermal runaway . This eliminates the risk of a case rupture / burst , according to the company . They also come equipped with a laser-welded aluminium housing that offers thermal conduction and mechanical safety with mylar and polycarbonate insulation .
A shutdown separator coating , meanwhile , is designed to melt if the temperature inside the cell reaches 110-130 ° C , blocking the ion flow , interrupting the current and preventing further temperature increases . An additional porous ceramic separator coating melts at 160-175 ° C , bonding with a polypropylene electrode separator to help block dendrites and provide structural support to prevent shrinkage and maintain the separation of electrodes .
Huff expands on this : “ Dendrite growth is an effect of overcurrent , overcharging , charging at cold temperatures and a side effect of ageing . Excessive growth can result in an electrical short as well , which can then lead to thermal runaway .”
These cells are placed into a battery module , which operates at low voltage for safe servicing , comes with isolating foam potting to block moisture and prevent isolation faults , offers thermal conduction to draw heat away from a hot cell and distribute it across the entire module to moderate temperature rises , and offers environmental and mechanical damage protection , according to Sandvik .
These modules are then incorporated into a battery pack , which comes with mechanical protections such as a 6-mm plate steel enclosure ; a non-conductive coolant to manage temperature during charging ; and gore vents and drains to prevent pressure build-up , allowing vented gases to expel air in the enclosure and fluids to drain rather than collect , all while limiting ingress of dust and contaminants .
32 International Mining | OCTOBER 2022