Today, mining vehicle manufacturers are developing new, game-changing BEVS (Battery powered Electric Vehicles) powered by lithium-ion batteries as an alternative to diesel power. Given the high energy density of Li-ion batteries, they’re currently the most common and convenient battery for new BEV applications. The quiet, low heat, and zero-emission of Li-ion battery quickly improves underground work environments and eliminates health hazards to workers. Not to mention they’re responsive, have fewer moving parts, and require less maintenance.
The Lithium-ion battery industry has expanded rapidly in the last 10 years. Because of this, we also see many accidents of lithium-ion battery explosions and issues associated with fighting big battery fires. According to OSHA/CPSC, 25,000 overheating or fire incidents involving more than 400 types of lithium battery-powered consumer products occurred over a five-year period.
As the concern of safety becomes more obvious, some lithium-ion battery cells are claimed to be explosion-proof and fire resistant. It can be confusing and misleading if we don’t understand the different chemistries and types of lithium batteries. This article will uncover the myth of their differences and provide a deep analysis from the aspects of safety, lifespan, and commercial maturity, so you will understand why we think Prismatic LFP LifePO4 Lithium battery is the winning chemistry for modern underground mine equipment.
In a Li-ion battery, lithium ions travel back and forth between the anode and cathode during charge and discharge (negative electrode being anode, positive electrode being cathode). The ions move in an electrolyte and across a separator that sits between the two electrodes (Figure 1). The sequence involves reduction/oxidation (redox) reactions specific to the particular chemistry of the cathode, and the chemical energy of these reactions is harnessed to store and discharge electrical energy from the positive and negative terminals of the battery.
Anode materials include:
Graphite (the most common type)
LTO (Lithium Titanate Oxide)
Cathode materials include:
LCO-Lithium Cobalt Oxide
NMC-Lithium Nickel Manganese Cobalt Oxide
LFP- Lithium Iron Phosphate
The choice of the cathode material will affect greatly the end battery properties such as safety, energy, life cycle, and cost.
The electrolytes include:
Liquid organic solvents
Below, we made a comparison between the most common cathode materials that could be used in mine BEVs.
LCO-Lithium Cobalt Oxide
NMC-Lithium Nickel Manganese Cobalt Oxide
LFP- Lithium Iron Phosphate （LiFePO4）
LTO- Lithium Titanate LTO is anode, which can be combined with any cathode.
From the prospects of safety, life span, and cost, LFP battery is not doubt the winner among them all. It does have relatively low energy density. However, in the industrial application, the weight and space are not equally as demanding as, say, a passenger car. In reality, low energy density can turn to an advantage, it will require less counter weight in applications where counterweight is required.
Safety is always the #1 priority in the mine industry. One accident happens, it can cost businesses millions of dollars. The primary hazard from Li-ion batteries is a catastrophic event called thermal runaway in which the battery quickly and sometimes violently releases its stored electrochemical energy. We’ve seen several severe incidents of car and airplane explosions due to li-ion battery thermal runaways. This is why the mining industry must use the battery that has the highest thermal stability and tested explosion proof; both the battery pack and the cell itself.
The key advantage of LFP as a cathode material lies in its chemical stability and the ability to withstand relatively high temperatures. The molecular structure absorbs and releases lithium ions without a large change in volume, and it’s resistant to the growth of defects from daily charge and discharge cycles. The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and heat up like lithium cobalt oxide nor form strong oxidizing substances.
In China, for lithium-ion battery to be able used in mine equipment in coal mining, it has to be approved by Mining Products Safety Approval and Certification Center (MA Center) in Beijing, a stress test of the li-ion battery cell and modules needs to be done. There are 23 test items for lithium-ion batteries. Some of the extreme stress tests that can be related to real life battery abuse includes: nail penetration, baking with flame, external short circuit and over-charge.
During the some of the toughest tests, the LFP cell was smoking, no fire or burning occurred. In the baking with flame and external short circuit tests, LFP cell remains explosion-proof and fire-free. In the overcharge stress test, high charging voltage that was several times higher than the rated discharge voltage was used, and it was found that there was still no explosion on the LFP battery. The safety of overcharge is extremely important, as it is one of the most common thermal runaways.
LFP batteries can be used safely in ambient temperatures up to 55°C (131°F). Even if it catches fire, it shoulders like coal, and needs oxygen to burn. On the other hand, the popular NCM battery burns violently like gunpowder, and requires no oxygen to be set aflame. There are also differences in putting out the fire when your battery is burning. For LFP, normally water or foam can kill the fire. However. for NCM, it can get very complicated.
Frey New Energy shared some details of the nail penetration test they conducted to a 3.2V100Ah Cell. After the battery was fully charged, a steel nail was directly penetrating the center of the cell. With a speed of 40mm/S, the nail remained inside the cell. There was no fire or explosion.
Mine trucks and equipment are durable, built to last. They consume high power compared to passenger EVs. They need an equally durable and reliable power pack to match the nature of the equipment. That’s why it is wise to choose a battery pack that lasts long term and require few replacements in a very long period of time.
Current expectations on the lifetime for a battery in heavy‐duty vehicles is 6 years. However, for future generation batteries, the expectation is that they would last the lifetime of the vehicle. A defining factor in determining battery life is the particular cell chemistry used in the battery pack.
According the table, LTO has the best life span. However, due to its high cost and low energy density, it has not been widely used and hasn’t reach commercial maturity in mine industry. The cycle life of Lifepo4 is over 3,000 with 80% depth of discharge, while NCM only reaches 800. When the LFP battery is used with 50% depth of discharge, the cycle life can reach 4,000 times, and when 20% depth of discharge, it can reach even 6,000 times. In the mine industry, the cycle life can be up to 3,000 times. If the machines run 365 days a year, then it has a life span of 8.2 years. Most lithium-ion manufacturers give warranty on material handling, a very standard warranty of 5 years or 10,000 hours uptime. some are giving energy Amp hour of 2,000 x nominal capacity, for example, if a
battery is rated 200ah, then it gives warranty of 200×2000 =400KWH total power output for the entire life span. That means 2,000 times with of the battery capacity is 100% used. This is 4 times longer than a traditional lead-acid battery. LFP chemistry is winner again in the life span.
The electric passenger cars take 67% of global EV li-ion battery market, with a small fraction of 16% for commercial vehicles. The mine equipment takes a small part among the 16%. Small quantity, customized mine equipment is built in small batches, unlike passenger EVs. Massive production of one battery model to fit thousands of vehicles? That doesn’t work for mine equipment. Lithium batteries for mine equipment needs to be custom built. In the battery pack building process, it’s critical to choose the most ideal cell for the best efficiency, and we’ve concluded that the LFP chemistry is most ideal. There are many different shapes of LFP battery cells; the most common prismatic and cylindrical. It’s important to choose the right shape to make the lithium battery pack. Below is a comparison of advantages of drawbacks.
The prismatic battery has a large capacity from 3.2V50Ah to 3.2V200Ah. The cylindrical cell has a small capacity from 3.2V1.5Ah to 3.2V6Ah. Among the most common type of cylindrical cells is the 18650. The term 18650 comes from the IEC naming scheme for round cells based on their physical dimensions. The first two digits are its diameter in millimeters, while the last 3 digits are for its height in 1/10th millimeters.
But the question remains: why it is important to use large capacity cells?
We can explain this better with the “barrel theory”. Just like the capacity of a barrel is determined by the shortest wooden bars, the performance of the whole battery pack is determined not by the best performing cell, but by the worst. In the lithium battery pack assembling process, it is always an important step to choose the most consistent level cells. The consistency of the battery pack is also related to the number of cells. The more cells, the worse the consistency and the worse the performance of the battery pack will be.
For example, to make an 80V500Ah lithium battery pack, using a lithium iron phosphate LFP 3.2V100Ah prismatic battery cell will only require 125 battery cells. Use 25 of 3.2V100Ah to make 80V100Ah, and then serial connect 5 of the 80V100Ah to make 80V500Ah. If you use LFP cylindrical battery 32650-6Ah batteries, you’re looking at 2,075 battery cells. If you want to maintenance the battery pack by checking each battery cell’s performance or repair the pack by replacing bad cells, it would impossible for identifying the bad cylinder cells. It would be easy on the prismatic cells. Some battery suppliers even designed a battery kit system that you can check the voltage of each cell easily without taking apart the whole pack.
Making a battery with large prismatic cells has simplified assembling technology and convenient processing.
Large lithium battery packs can be assembled together through bus bar or laser welding process. This process is simple and convenient. However, if a cylindrical battery cell is used, the method is spot-welding, complicated, and much more difficult manufacturing. Recently, there have been cylindrical batteries using aluminum wire welding technology, which is costly with mediocre results.
The one advantage of cylindrical cell is that when the battery pack is assembled, the gap between two cells is large, and the heat dissipation is improved. A cylindrical battery coupled with the cell bracket has a stable structure, large cell gap, and better heat dissipation. However, this can also be the case when using prismatic cells. The cell bracket be designed with a gap between each cell too.
Prismatic LFP cells are widely used in energy storage, nowadays more and more EV makers. Companies like Tesla have started adapting their LFP cells, due to the excellent safety features, lack of toxic metal chemicals and low raw material cost. However, we have to keep in mind that the power consumption is very different between passenger EV and industrial EV. Passenger EVs pursuit long distances with small power consumption in short periods of time. Heavy-duty mine machines pursuit very high-power consumption in short periods of time. Should mining BEVs use the same standard on the battery as it is for passenger EVs and energy storage? Or it should be reviewed with the actual application of itself?
“Industrial heavy-duty machines need high c-rate and reinforced internal cell construction that brings more challenges on manufacturers who are used to making the lithium battery cells for the passenger EV industry. To achieve this heavy-duty feature matching tough mine vehicles, the production procedure needs to have a complete reset, and the material sourcing of electrodes, separators, even the terminal posts will need to have a completely new standard. For example, the aluminum film and copper film used for the separators all need to be thicker.” Said by production engineer of Zhenghai Hu, VP of Engineer at Frey New Energy.
Overall, there are thousands of lithium battery manufactures in China, and the global EV marketing’s booming lead is Tesla. However, this global mine industry is the one that demands a far safer and cleaner energy; more so than any other industries. Luckily, there are some manufacturers that know the special requirements of the mining industry. There is a clear path and solution of the mining industry’s lithium battery needs; it’s up to you to take it.