Battery Chemistry and Battery Self-Swapping
The battery chemistry used in all Sandvik’s BEV loaders and trucks is Lithium Iron Phosphate (LiFePO4 or also abbreviated to LFP). This chemistry was chosen because it is the safest option on the market for an underground environment. Our strong belief is that none of the advantages of other battery chemistries outweigh safety.
The following accelerated rate calorimetry chart illustrates the relative safety/volatility of available chemistries. Here a battery cell is placed into a chamber and heated at a slow rate, with measurement of the input energy and energy being emitted from the system, inside the calorimeter. The result demonstrates a sense of when these materials start to release their energy, at what temperature and how abuse-tolerant they are. Once the thermal runaway point has been reached, the amount of energy produced is measured (rate of combustion), which in turn demonstrates the volatility and how difficult it is to control the result of over-temperature or fire in batteries.
Source: Sandia National Laboratories, DOE Vehicle Technologies Peer Review
The graph demonstrates that:
- Lithium-cobalt-oxide (LiCoO2) is the most dangerous chemistry on the list, which starts to breakdown at relatively low temperatures (even below 200°C) and produces the most aggressive reaction. This is the most common chemistry, often found in laptops and cell phones. It has a good energy density but low cycle life to support consumerism.
- Nickel-cobalt on aluminium (NCA) is a chemical compound that adds nickel and aluminium with the aim to try and increase the abuse-tolerance by breaking down at slightly higher temperatures, making it harder to reach thermal runaway temperature and allow a more aggressive fast-charge and increased rates of discharge. This chemistry is used by Tesla. It has a high energy content but very high rate of energy release.
- Nickel-manganese-cobalt (NMC 111) has equal parts of the elements on the cathode. This blend aims to push the abuse-tolerance even higher by raising the temperature of thermal runaway even higher and at the same time, decreasing the rate of energy production. This chemistry is somewhat easier to contain when violent.
- Lithium-iron-phosphate (LFP) is the chemistry that Artisan/Sandvik uses for all BEV loaders and trucks. This is by far the safest chemistry on the list. The energy production is so low that the curve can only be visualised on the zoomed-in version of the graph. Thermal runaway occurs at around 225-230°C, higher than the other chemistries on the list. The real benefit is the normalised rate of approximately 1.6 compared to the next closest chemistry, NMC, at 180. In other words, LFP has more than 100 times the difference in rate of energy production, compared to the next closest chemistry. With this reaction, anything that can happen to the LFP battery chemistry, happens within the enclosure of the battery. Even if cells do go into thermal runaway, they do not generate enough heat to go on fire, instead the electrolyte boils, pushes out gas and vents.
A nail penetration test demonstrates the energetic/explosive release and fire with a nickel-manganese-cobalt (NMC) cell. With the lithium-iron-phosphate (LFP) cell, there is no fire, no explosion, only venting. When LFP chemistry reaches thermal runaway, it does not turn into a flame. The plastic wrapper melts on the cell, there is some swelling and gases are emitted.
In summary, we use Lithium Iron Phosphate (LiFePO4) as our battery chemistry because it is a safe option for underground mining.
Sandvik’s Generation 3 Battery Electric Vehicles are designed with a self-swapping battery system that enables a safe and quick battery swap option. There have been zero safety incidents with self-swapping to date. This system provides the following advantages over the traditional battery swap systems existing on the market:
- No major infrastructure
- No cranes and suspended loads
- No concrete floor
- No special or additional ventilation required
- No external fire suppression systems needed with LFP chemistry
- Can use old re-muck bays or passing bays
- Flexible and charging locations can be moved quickly as the mine develops
The self-swap is a fast and easy process achieved by the operator and includes:
- Disconnect battery (automated on 18-tonne loader)
- Drop battery cage
- Tram on auxiliary battery
- Pick-up next battery cage
- Connect battery (automated on 18-tonne loader)
Self-swapping mechanism on the 18-tonne battery electric loader: